In view of new applications for lithium and lithium ion batteries, i.e., electric vehicles and stationary storage, the interest in battery technology in Germany has been renewed and intensified. In this presentation, we will present various German R&D programs, which are embedded in the German federal government's high-tech strategy, which is aimed at creating lead markets, intensify cooperation between science and industry, and continue to improve the general conditions for innovation in a number of future markets, for example e-mobility and climate and energy. We will highlight scientific achievements, in particular those, which have been achieved at the MEET Battery Research Center in Muenster (Germany). Topics will comprehend lithium ion battery materials and cell systems, as well as lithium metal and recycling activities.

The lithium-ion battery industry needs new approaches to advance high capacity anode materials, particularly for large format batteries, for example, EV/PHEV automotive markets. FMCâ?Ts innovative material, Lectro® Max Powder (SLMP®) enables a new generation of lithium-ion batteries by providing an independent source for lithium (1-3), which opens up choices for both anode and cathode materials. Introducing lithium in a stabilized powder form with the anode host material, such as Si and Sn-based, leads to a higher energy battery with more efficient utilization of lithium. Using non-lithium providing cathodes like manganese, vanadium or other metal oxides and metal fluorides4 that are more overcharge tolerant and potentially have lower costs, leads to safer and cheaper batteries. When used in combination, these anode and cathode materials can potentially double the energy density of the current lithium-ion battery. This presentation will focus on the enabling aspect of Stabilized Lithium Metal Powder Technology that provides an independent source of lithium not only for lithium-ion batteries, but also for lithium-ion capacitors (LIC). This technology can, potentially, replace lithium metal electrode in the Lithium/Sulphur systems when used to fully lithiate high capacity carbonaceous, silicon or tin anode materials. Special emphasis in this presentation will be made on application techniques: from conventional slurry manufacturing process to innovative Lithium Metal Carrier Film (LMCF) technology.

New cathode materials with high energy densities, such as layer structured solid solutions between layered Li[Li1/3Mn2/3]O2 (i.e. Li2MnO3) and LiMO2 (M = Mn, Ni, and Co) are becoming appealing recently. Surface coating can significantly suppress cation dissolution during cycling, lower the impedance of the interface between cathode and electrolyte, as well as enhance the structural stability of the cathode material at high voltage. Therefore, surface coating has been proposed as an effective method to improve the battery performance. Here, we present the surface modification of Li1.2Ni0.17Co0.07Mn0.54O2 by an atomic layer deposition (ALD) method using Al2O3, TiO2 etc as coating layer. Atomic layer deposition is a well established method to apply conformal thin films on high-surface area tortuous networks and the thickness of ALD coatings is easily tailored at the atomic level. In this presentation, Synchrotron based X-ray diffraction (XRD), soft X-ray absorption (XAS) and Transmission electron microscope (TEM) techniques have been used to study the ALD coated and uncoated Li1.2Ni0.13Co0.07Mn0.6O2 cathode. ALD coated Li1.2Ni0.13Co0.07Mn0.6O2 cathode shows much improvement of the surface stablity under the air exposure without formation of Li2CO3 comparing to the uncoated sample and thermal stability during heating Structural changes of another type of interesting materials, the olivine structured LiFe1-xMnxPO4 were also studied by synchrotron based XAS and XRD. Mesoporous LiMn0.4Fe0.6PO4 was developed to achieve high energy density cathode materials for lithium ion batteries. The comparative in-situ X ray diffraction and x-ray absorption studies were conducted to understand the phase transition behaviours of this type of materials. The XRD and XAS studies of a whole series of mesoporous LiMnxFe1-xPO4 (with x=0, 0.2, 0.4, 0.6, and 0.8) will also be discussed. The work at Brookhaven National Lab. was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, under the Vehicle Technology Program, under Contract Number DEAC02-98CH10886, and by U.S. Department of Energy, through Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract Number DE-SC0001294, the work at Stony brook University was supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The work at Institute of Physics, CAS was supported by Nature Sciences Fundation of China (NSFC 50672122, 50730005).

Nanostructured electrochemically active materials may provide the key to improve performance of electrode materials for energy storage. However, the synthesis and the stability of nanomaterials are also significant challenges for practical applications. In this talk, we will discuss some recent advance we made in the in-situ characterization of nanostructured electrode materials and the fundamental failure mechanisms. Based on these understanding, we will discuss some new approaches to synthesize high capacity electrode materials for energy storage applications. The synthesis approaches involve systematic understanding and control of the surface chemistry in order to control the nucleation and growth, and manipulation of self-assembly of both molecular and nanoscale building blocks to produce multicomponent electrode materials with good conductivity, stability and high capacity. Examples include high capacity based SnO2 and Si anode materials for Li-ion batteries, and nanostructured materials for Na-ion batteries.

Conversion reaction electrodes in lithium batteries provide high specific capacity by utilizing all of the possible redox states of the transition metals. The reversible conversion reaction occurs via a 3-phase reaction at equilibrium and, although thermodynamically allowed, it is very often hindered by slow kinetics. A better understanding of the conversion reaction mechanism requires tracking the local phase nucleation and evolution with lithiation, which is extremely challenging due to the complexity of the reaction and involvement of multiple phases within the nanometer-sized domains. Electron energy-loss spectroscopy in the transmission electron microscope (TEM-EELS) was used to generate high-resolution (1 nm scale) compositional maps of the primary phases present in the electrode material at different states of lithiation[1, 2]. In-situ TEM-EELS, performed using a vacuum-compatible solid or liquid electrolyte in the TEM column, also provides an opportunity for real-time observation of the lithium reaction of single particles (mimicking an electrochemical cell). We will present some results on TEM-EELS studies of high-capacity cathode materials including FeF2, FeF3, and CuF2. The underlying mechanisms of the conversion reaction, along with results from first-principles calculations and kinetic Monte Carlo simulations will also be discussed. [1] F. Wang, J., Graetz, M.S. Moreno, C. Ma, L. Wu, V.V. Volkov, and Y. Zhu. "Chemical Distribution and Bonding State of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy-loss Spectroscopy�, ACS Nano, 5, 1190-1197 (2011).[2] F. Wang, R. Robert, N. Chernova, N. Pereira, F. Omenya, F. Badway, X. Hua, M. Ruotolo, R. Zhang, L.J. Wu, V. Volkov, D. Su, B. Key, M.S. Whittingham, C.P. Grey, G.G. Amatucci, Y. Zhu, and J. Graetz. Conversion Reaction Mechanisms in Lithium Ion Batteries: Study of the Binary Metal Fluoride Electrodes. J. Am. Chem. Soc. (ASAP). This work was supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. DOE, BES under award No. DE-SC0001294.

High-energy density Li batteries are highly desirable for portable devices and vehicles. Negative electrodes that would outperform the traditional Li-graphite electrode are particularly sought. This next generation of negative electrode materials will have to combine several features: low-cost metals and materials, eco-friendly preparation routes and high processability for incorporation into films, solid-state electrolytes or polymeric networks. The metal phosphide nanoparticles were only scarcely studied and are still considered exotic. Yet, they often employ cheap transition metals and undergo conversion mechanisms upon cycling. Thus, metal phosphides bring promising perspectives to the field by providing a new set of materials and electrochemical properties. Moreover, as nanoparticles, they are easy to incorporate into safer nanostructured electrodes such as all-solid-state batteries. In this context, our groups demonstrated the use of carbon-coated nickel phosphide nanoparticles (Ni2P) as negative electrode materials. The monodisperse Ni2P nanoparticles were obtained through an efficient and cost-effective colloidal route using a biomass-derived amine (oleylamine) as both solvent and reductant for concentrated Ni(+2) solution.[1] This cheap transition metal was associated with phosphorus to produce the phosphide phase using the ton-scale available industrial source of phosphorus, white phosphorus (P4), in a very soft process that was conducted in the same pot at low temperature (ca 120-220°C).[2] Interestingly, low amounts of tri-n-octylphosphine ligands (TOP) were shown to succeed in perfectly calibrating the nanoparticles diameter to 25 nm. A percolating graphitic-like carbon coating (3 nm thick) was then obtained without adding any other carbon source through a fast calcination under N2 and analyzed through XPS and TEM.[3] At only 400°C, surface nickel played a catalytic role in the formation of graphite-like carbon from the nanoparticles ligands set (TOP). Consequently, the formation of percolating carbon occurred without sintering of the 25 nm nanoparticles. Electrochemical properties of the resulting nanocomposite materials were found to largely outreach those of bulk Ni2P and non-coated nanoparticles, both in terms of gravimetric capacity and robustness over cycling. The carbon/nanoparticles synergetic effect was found to be adjustable by varying the initial ligands set, opening an avenue for the optimization of carbon-coated nanomaterials in innovative Li storage devices. [1] Carenco S, Boissière C, Nicole L, Sanchez C, Le Floch P, Mézailles N, Chem. Mater. 2010, 22, 1340 [2] Carenco S, Le Goff X, Shi J, Roiban L, Ersen O, Boissière C, Sanchez C, Mézailles N, Chem. Mater. 2011, 23, 2270. [3] Carenco S, Surcin C, Morcrette M, Larcher D, Mézailles N, Boissiere C, Sanchez C, Submitted paper.

We demonstrate synthesis of a novel SiCN functionalized MoS2 nanosheet composite for use as Li-ion battery anode for high power applications. The nanosheet composite was prepared by thermal decomposition of polyureasilazane on exfoliated MoS2 surfaces. The morphology and chemical structure as studied by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed a sidewall functionalization of exfoliated MoS2 sheets by the polymeric precursor. The composite is thermodynamically stable up to 1000 degree C (highlighted by thermo-gravimetric analysis). Batteries assembled using SiCN/MoS2 nanosheets as active anode material showed that lithium can be reversibly intercalated in the voltage range of 0-2.5 V with first cycle discharge capacity of 620 mAh/g at a current density of 100 mA/g.

Iron oxyfluoride (FeOF) nanocomposite has been considered as a high energy density cathode material with theoretical capacity in excess of 700 mAhg-1. Unlike the intercalation compounds, the rutile FeOF converts into intermediate structures during discharge and at the end of conversion, converts to metallic Fe with all the valence states of Fe used in the conversion reactions. At the present time, the intermediate phase changes occurring during charge and discharge processes are not known. In this study, the structural changes of FeOF/C during the first cycle at 60°C in a Li-ion battery were studied by combined high resolution transmission electron microscopy (HRTEM) imaging and selected area electron diffraction (SAED) techniques. The first-cycle voltage profile of FeOF/C shows 3 regions during the first discharge. In the first region from 3.5 to 2.2 V, lithium intercalates into FeOF/C with the diffraction pattern still revealing the rutile structure. However, in the second region (2.2-1.5V), the rutile structure converts into Fe, LiF and a Li-Fe-O-F cubic rocksalt intermediate phase. The third region corresponding to complete discharged to 0.8 V and complete conversion to metallic Feo plus LiF and Li2O. During the recharge process, diffraction patterns show reconversion to only metastable rocksalt type structure with decreasing Fe metallic content as revealed from the SAED intensity profiles. Upon annealing, the metastable rocksalt structure remains rocksalt up to 2.9 V and transforms back to the original FeOF rutile phase above 2.9 V. In this paper, the mechanisms for the metastable rocksalt to rutile transformation will be presented.

The solid electrolyte interface (SEI) layer formed on the electrode surface plays an important role in Lithium-ion battery performance. Previous mathematical models for SEI formation show the capacity for predicting SEI growth, but they generally consider the SEI growth in one dimension only and ignore the microstructural evolution inside of SEI layer. In this talk, a phase field model is proposed to simulate SEI formation that is able to capture microstructural evolution in the SEI layer and predict SEI growth simultaneously. Moreover, the diffuse interface between SEI and electrolyte makes it possible to handle complex interface morphology. In this model, SEI formation is treated as a phase transformation process where electrolyte is transformed into SEI due to various thermodynamic driving forces as well as electrochemical reactions. The SEI growth rate is determined by the motion of SEI/electrolyte interface. In the bulk region of SEI and electrolyte, ions are transported by diffusion and electrical migration, and at the SEI/electrolyte interface, a set of electrochemical reactions that correspond to SEI formation occur. The effect of ion concentration, temperature and electrical potential on the microstructure evolution and growth rate of SEI is investigated. Further development along this direction is also discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energyâ?Ts National Nuclear Security Administration under contract DE-AC04-94AL85000.

Transition metal fluorides were widely investigated as potential cathode materials due to their much higher energy density compared to the conventional intercalation compounds. It has been demonstrated that carbon - metal fluoride nanocomposites (C-FeF3, C-FeF2 and C-BiF2) may be utilized as cathodes for the next generation Li-ion batteries, with a high energy density and good cycling properties. In this study, we explore the conversion mechanisms in pristine NiF2 and NiO-doped NiF2. The conversion mechanisms of NiF2 and NiO-doped NiF2 during electrochemical cycling were investigated using a combination of ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and quasi in-situ X-ray absorption spectroscopy (XAS). It was observed that the conversion reactions in both cathode materials were partially reversible, however, they differ in their conversion rates. NiO-doped NiF2 exhibited enhanced electrochemical properties in terms of the conversion potential and the reversibility due to the presence of a NiO phase, which has slightly higher electronic conductivity than NiF2. It is suggested that the NiO doping reduced the nucleation sites for Ni nanoparticles, subsequently enhancing the kinetics of the conversion reaction involving the growth of Ni particles formed during lithiation. The XRD and SQUID data (HC and MS) indicate that the average dimension of the nanosized-Ni particles formed along with LiF in pristine NiF2 and NiO-doped NiF2 during the 1st lithiation was in the superparamagnetic regime.

This talk will present a review of on-going research in our group in the field of advanced electrode and electrolyte materials for next-generation energy storage systems. Our recent activity deals with the following interconnected topics : fine characterization of positive electrode/electrolyte interface, design of Si-based negatives, comprehension of reaction mechanism, design of high power electrodes and design of safe electrolytes for next-generation Li-ion batteries. In addition, some developments on electrodes for Na-ion batteries are being pursued. The longevity of the batteries depends on the side reactions at the interfaces that must be minimized. MAS NMR is developed to characterize interface species on electrode materials and their evolution upon battery aging and cycling [1]. Increasing the stored energy requires the implementation of electrodes with high capacity. Binding mechanism and internal electric connectivity of Si electrodes are key issues [2]. Recent advances deal with optimisation of CMC binding mechanism, use of a conductive network of bridged carbon nanotubes and nanofibers, and determination of end-of-life mechanism. Increasing the power is also a challenge for some applications. Composite electrode design and processing has a strong influence on electrode performance [3]. We will see what parameters limit the power of a thick composite electrode [4]. Safety problems of lithium ion batteries need intrinsic solutions. The concept of all-solid lithium using an ionic liquid confined in a mesoporous solid is described. It should enable the production of safer Li-ion batteries. Understanding the limitations of batteries while they are functioning is a key requirement, which will allow their optimization. Monitoring by diffraction and synchrotron X-ray absorption of a battery electrode in operation shows a non-homogeneity at all spatial scales used. We will show that some fractions of the electrode are delayed compared to the average electrode composition. Finally we describe on-going research on promising electrodes for future sodium batteries [5]. Literature [ ]. N. Dupré et al., JMC, 18, 4266, 2008. N. Dupré et al., EC, 10, 1897, 2008. N. Dupré et al., JPS, 189, 557, 2009. N. Dupré et al., JECS, 156, C180, 2009. N. Dupré et al., JPS, 195, 7415, 2010. N. Dupré et al., JPS, 196, 4791, 2011. [2]. B. Lestriez et al., EC, 9, 2801, 2007. D. Mazouzi et al., ESL, 12, A215, 2009. S. Desaever et al. ESL, 12, A76, 2009. Y. Oumellal et al., JMC, 21, 6201, 2011. [3]. D. Guy et al., AM, 16, 553, 2004. D. Guy et al., JECS, 153, A679, 2006. E. Ligneel et al., JECS, 154, A235, 2007. E. Ligneel et al., JPS, 174, 716, 2007. W. Porcher et al., JECS, 156, A133, 2009. W. Porcher et al., JPS, 195, 2835, 2010. [4]. C. Fongy et al., JECS, 157, A885 & A1347, 2010. C. Fongy et al., JPS, 196, 8494, 2011. [5]. P. Moreau et al., CM, 22, 4126, 2010.

High power, lightweight, long-lasting energy storage devices, such as Li-ion batteries, are critical for the development of zero-emission electrical vehicles, large scale smart grid, and energy efficient cargo ships and locomotives. The energy storage characteristics of Li-ion batteries are mostly determined by the specific capacities of their electrodes. Si has received particular attention due to its highest gravimetric capacity for Li. The challenge to achieve a stable performance of the Li alloying elements originates from the large volume changes occuring during the Li insertion/extraction processes. The ability of carbon to afford very high electrical conductivity and very high surface area with controlled pore size complement the capability of Si to efficiently store Li ions. This makes porous carbon-silicon (C-Si) nanocomposites attractive for high energy anode applications. Pre-existing pores provide the volume needed for Si expansion and allow for fast transport of Li ions, while C will allow the improved solid/electrolyte interface formation, structural integrity and high electrical conductivity. In the last two years our groups has explored different architecture of C-Si nanocomposite anodes, which included self-assembled spherical granules [1], C-coated Si nanoparticles [2], Si-in-C tubular nanostructures [3], three-dimensional (3-D) porous particles composed of curved 2-D C-Si layers [4], ultra-thick electrodes composed of Si-coated carbon nanotube (CNT) arrays [5], multi-functional CNT-Si-based nonwoven fabric and Si/C nanoparticles mixed with an alginate [6]. Capacities of up to 3000 mAh/g (normalized by the total mass of the composites) and stable performance for up to 1000 cycles has been demonstrated. This talk will provide an overview of our recent developments, it will also discuss advantages and disadvantages of different architectures of C-Si nanocomposites and will reveal critical parameters needed to design stable Si-containing anodes and full cells. References 1. A. Magasinski, P. Dixon, B. Hertzberg, A. Kvit, J. Ayala, and G. Yushin, Nature Materials, 2010, 9, 353-358 2. A. Magasinki, B. Zdyrko, I. Kovalenko, B. Hertzberg, I. Burtovyy, T. Fuller, I. Luzinov, and G. Yushin, ACS Appl. Mater. Interfaces, 2010, 2, 3004-3010. 3. B. Hertzberg, A. Alexeev, and G. Yushin, J. Am. Chem. Soc., 2010, 132, 8548-8549. 4. K. Evanoff, A. Magasinski, J. Yang, and G. Yushin, Advanced Energy Materials, 2011. 5. K. Evanoff, J. Khan, A.A. Balandin, A. Magasinski, W.J. Ready, T.F. Fuller, and G. Yushin, Advanced Materials, 2011, in review. 6. I. Kovalenko, B. Zdyrko, A. Magasinski, B. Hertzberg, Z. Milicev, R. Burtovyy, I. Luzinov, and G. Yushin, Science, 2011, 334 no. 6052, 75-79. Acknowledgement Different aspects of this work were supported by NASA and US AFOSR

Lithium metal exhibits an extremely high specific capacity (3860 mAh/g) and the lowest negative potential (-3.04 V vs. SHE) among the anode materials. It is an attractive anode material for high energy batteries. However, the development of rechargeable lithium batteries has been hindered by the growth of lithium dendrites during repeated charging-discharging cycles, which causes internal short-circuit of the batteries and may lead to serious safety hazards. Continuous growth of solid electrolyte interface (SEI) layer on lithium anode surface during cycling is another problem, which consumes the electrolyte, increases the internal resistance of the lithium battery, lowers the Coulombic efficiency of each cycle and shortens the battery life. The formation of irreversible mossy lithium in the anode will also reduce the capacity of the lithium metal battery. These problems have prevented the practical applications of lithium metal as an anode material in rechargeable batteries. During the past decades, the progress in this field was limited. In recent years, the urgent needs to double the energy density of batteries used for electric vehicles have driven the renewed efforts around the world to improve the stability of lithium metal anode so that it can be used in rechargeable lithium batteries. There are several ways to improve the stability of lithium metal anode, including using lithium alloy instead of lithium metal, adding electrolyte additives, modifying lithium surface, and so on. In this work, we systematically investigated the effects of electrolyte solvents, salts and additives on lithium metal morphology and repeated cycling efficiency. The morphology of lithium electrode formed in different electrolytes was characterized by optical microscopy and scanning electronic microscopy. The cycling efficiency was evaluated in coin cells. It has been found that all these factors have significant effects on the morphologies and cycling efficiencies of deposited lithium films. Smooth and uniform lithium metal films were obtained during the electrochemical deposition process if an optimized electrolyte (with appropriate solvents, salts and additives) was used. The detailed results of this investigation will be reported in this presentation.

The usage of lithium alloys as anodes can lead to the development of ultra-high-capacity lithium batteries having capacities (> 1200 Wh/kg) several times higher than that (~ 300 Wh/kg) provided by traditional Li-ion intercalation anodes. The Li-Mg system offers several unique advantages as negative electrode. Unlike intermetallic anodes, Li forms a stable solid solution phase with Mg over a wide compositional range. The insertion/removal of Li ion in Li(Mg) alloys does not cause large volume changes, thereby preserving the structural integrity of the electrode during charge/discharge cycles. This research attempts to investigate the feasibility of using Li(Mg) alloys as the negative electrode in Li-ion batteries. Homogeneous Li(Mg) alloys of compositions: Li-30 wt% Mg and Li-60 wt% Mg were synthesized. The alloy composition and homogeneity, as well as the phase transition during electrochemical discharge were evaluated using X-ray diffraction. The electrochemical charge/discharge characteristics of the Li(Mg) alloys were studied in a Teflon cell. During discharge of Li(Mg) anodes, a gradual phase transformation, from the bcc Li(Mg) β-phase to the hcp Mg(Li) α-phase, was found to occur. On the other hand, during charging, both alloying and plating were observed. The results of the charge/discharge cycling tests conducted on different anode microstructures at several current densities are presented.

Si anodes for Li-ion batteries are attractive due to their high specific capacity, but the volume expansion and fracture that occur during the Li-Si alloying process degrade performance. Si nanostructures have shown improved resistance to fracture, but the nature of volume change and fracture in these structures is not completely understood. In particular, the effects of silicon crystallinity and conductive coatings on volume expansion have not been fully characterized. Since lithiation of crystalline Si has been shown to result in anisotropic volume expansion [1], NWs with different crystallinity (amorphous, polycrystalline, and single crystalline) are expected to deform differently. In addition, Cu coating has previously been demonstrated to have a positive effect on the electrochemical performance of Si [2], but the mechanical compatibility of metal coatings with Si nanostructures undergoing large deformation is poorly understood. In this study, we use in-situ and ex-situ transmission electron microscopy techniques to probe volume changes in single crystalline, polycrystalline, and amorphous Cu-coated Si NWs. It was found that different crystallinity strongly affects the overall deformation of the NWs during lithiation: crystalline NWs primarily expand radially, while amorphous NWs expand both radially and axially. For NWs coated with Cu on one sidewall, the axial length changes are partially manifested through uniform bending of the composite structures with different degrees of curvature for NWs of different crystallinity. In most cases, the Cu remains intact after lithiation, but sometimes (especially during fast lithiation), volume expansion causes cracking of the Cu layer. In addition, fast lithiation was found to result in inhomogeneous volume expansion in single-crystalline NWs, which sometimes causes crack formation at the surface of the Si. Finally, in-situ TEM was employed to observe the lithiation/delithiation process in these Cu coated NWs in real time. In single-crystalline NWs, lithiation occurred by the movement of a phase front with little corresponding bending of the bilayer structure, while the structure bent immediately in a uniform manner upon delithiation. Overall, these observations give insight into the different atomic-scale processes that occur during lithiation/delithiation of Si, and will help in the design of better Si anodes. References [1] SW Lee et. al., Nano Lett. 11 (7) 2011. [2] VA Sethuraman et. al., J. Power Sources 196 (1) 2011.

The importance of the SEI layer in Li-ion batteries cannot be overstated. However, their formation kinetics and properties at the nanoscale are still not well understood. From EIS measurements, Jow et al inferred that SEI formation on graphite takes place in 2 stages, above and below 250 mV, but there is little other information about the evolution of the SEI film during formation. In this work we use TOF-SIMS to depth profile through SEI films grown on Cu substrates at voltages between 0 and 700 mV. (The use of Cu substrates allows us to isolate the SEI formation process without interference from any insertion process.) Our results show how the SEI film thickness, porosity profile, and composition vary with formation voltage, and we use this information to draw conclusions about the chemical processes that create the SEI films.

Graphitic carbon is the dominant anode material for Li-ion Batteries because of its long cycle life and ample availability. However, its low volumetric capacity severely limits increasing the energy density of lithium batteries. Sn and Sn based alloys are promising candidate anode due to their high capacity and safety characteristic. The first successful tin-based anode was a SnCoC compound introduced by SONY in 2005, showing an improved volumetric capacity than carbon. However, the high cost and relative scarcity of cobalt restricts its wide application. In this work the cobalt was substituted by iron, and a series of Sn-Fe alloy based nano-materials were synthesized via low cost approaches. Nanosized Sn-Fe alloy materials synthesized by mechanical reduction of SnO precursor maintained a capacity of more than 400 mAh/g for up to 200 cycles without obvious capacity decay, and achieved double the volumetric capacity of carbon. Solvothermally formed Sn-Fe has a higher capacity but the capacity fades more quickly; however after ball-milling with graphite the capacity is retained. This capacity retention is due to the formation of carbon coated nano-sized particles, in which the carbon had become amorphous. Our work indicates that mechanical milling is a powerful technique for synthesizing alloy-based nano-materials for lithium-ion batteries. This work is supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies (BATT) Program.

Li-ion batteries (LIBs) have been considered one of the most promising power sources for various types of electric vehicles and large-scale energy storage because of their high energy density, high power density, and environmental friendly features. With regard to commercial LIBs, graphites are commonly used as anode materials and carbonate-based organic compounds are used as electrolytes. In general, carbonate-based electrolytes result in a solid electrolyte interphase (SEI) formation on the surface of graphite electrodes when the discharged voltage is below 1.0 V, leading to low rate capability and moderate cycling performance. Nb-based compounds have attracted great attention because Nb5+/Nb4+ and Nb4+/Nb3+ redox couples are located between 1.0 and 3.0 V versus Li+/Li. LiV3O8 has been extensively investigated as a cathode material for LIBs in the last decades. Its analogs, LiNb3O8, however, to the best of our knowledge, has not been reported for the use as an electrode for LIBs. Here we report a novel anode material of LiNb3O8 with a high theoretical capacity of 389 mAh/g between 1.0 and 3.0 V assuming a two-electron transfer (Nb5+ to Nb3+). After the as-prepared LiNb3O8 is ball-milled with acetylene black, its initial reversible capacity can reach 212 mAh/g at a current rate of 0.05 C, which corresponds to 3.3 Li extraction from Li6.4Nb3O8 and the capacity can remain at 180 mAh/g after 50 cycles. Combined characterizations including discharge/charge Test, CV, XPS, it is confirmed that the partial two-electron transfer reaction from Nb5+ to Nb3+ is achieved in this material. Its average Li storage voltage is located at 1.65 V versus Li+/Li. These properties make it a promising anode material candidate for LIBs.

Si material has a superior theoretical specific capacity of 3759 mAh/g at Li15Si4 stage, and is regarded as a promising candidate to replace or combine with conventional graphite negative electrode materials for the next generation of high capacity lithium-ion batteries. The size effect of Si particle during cycling has been extensively investigated recently, and has been generally accepted that nanosized of Si particles is a key aspect to enable long-term and stable cycling. However, an important aspect that has not been well studied is the initial surface properties of the Si nanoparticle and its impacts on the initial cell performance. In this report, the correlation between electrochemistry properties and native oxide layer of commercial Si nanoparticles were studied. X-ray photoelectron spectroscopy and transmission electron microscopy experimental techniques were applied to identify the chemical state and morphology of native oxide layer. Elemental analysis and thermogravimetric analysis were used to estimate the oxide content for the Si samples. To reduce the oxide layer, Si nanoparticles were etched by hydrofluoric acid for different period of times. The reversible capacity of etched Si nanoparticles was enhanced significantly compared with that of as-received Si sample. This work has demonstrated that the oxide surface layer on Si is a significant factor to the performance variation of Si nanoparticles based electrode, and removal of this layer leads to improved initial Si electrode performance.

Silicon based anodes have attracted intensive attention worldwide in recent years since it has a theoretical capacity as high as 4200 mAh/g. However, its stability is still a significant concern due to the huge volume change (>300%) during lithiation/delithiation which may result in rapid electrode structure failure. In this work, silicon composite with a three-dimensional rigid structure is studied as a stable and high-capacity anode material for lithium ion batteries. With the employment of the structure supporting skeleton, micron sized silicon particles were broken down to nano-sized particle and well-bonded to the supporting material to form a Si/core shell structure during ball milling process. This structure significantly improved the stability of the composite anode. Furthermore, a conductive carbon was coated on the surface of Si/core shell structure and enhanced the electronic conductivity of the silicon based anode and reduced the cell impedance. Our results show that the composite with optimized composition has a high capacity of around 800 mAh/g (based on the whole electrode weight including binder, carbon black additive and the composite), good stability and high initial columbic efficiency of around 80%. The effect of preparation conditions on the performance of the electrode will also be reported

Metal-air batteries are attracting much attention due to their high capacity. There are some candidates as the metal electrode, Lithium, magnesium, calcium, aluminum, iron, zinc and others. Although lithium, magnesium, calcium, and aluminum show high energy density, they easily react with water and require the use of non-aqueous electrolyte. Water in atmospheric air should also be excluded with these metal electrodes. The last two, iron and zinc operate in aqueous solution. Dendritic deposition of metal has been one of the most difficult issues to use metal negative electrodes for rechargeable batteries. The dendritic deposition of lithium leads to the formation of dead lithium, which caused the fatal issue on safety of lithium metal rechargeable batteries. Many researches are being conducting fundamental research to suppress the dendritic deposition of lithium but still time is required to realize the practical application of lithium negative electrode. Zinc has the merits over some metal negative electrodes; use of aqueous electrolyte, high safety, high volumetric energy density, etc. And zinc has long history of R&D for application as a negative electrode of rechargeable batteries suppressing dendritic deposition and shape change during charging. Different kinds of additives have been investigated to suppress the capacity fade of zinc electrode. In this work, the effect of organic solvent like carbonates is focused. It is considered that high solubility of zinc species in the electrolyte causes the dendritic deposition of zinc. The addition of propylene carbonate (PC) drastically decreased the solubility of zinc species in the solution. The solubility depended on the concentration of PC. The addition of PC caused passivation of zinc surface during discharge and the discharge capacity decreased with the increase of PC concentration. The morphology zinc deposits is remarkably influenced and becomes flat. The surface morphology of charge/discharge cycles was improved remarkably by PC addition. The PC addition enhanced coulombic efficiency of charge and discharge. Soluble species of zinc was examined by Raman spectroscopy and XAFS. No change was observed on nearest atoms of Zn2+ and Zn-O distance was not changed by the addition of PC. This results suggests that the interaction between PC and Zn2+ is weak compared with that between water and Zn2+. XAFS measurements were carried out with the help of Profs. Uchimoto and Arai. This work was done as part of the Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project of the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Much attention has been focused on improving the capacitance of supercapacitors, and their performance at high current densities, by constructing complex heterostructures with increased surface areas. However, the rational synthesis and supercapacitor performance of hierarchical MnMoO4/CoMoO4heterostructured nanowires remains challenging and needs to be explored in depth. Herein, hierarchical MnMoO4/CoMoO4heterostructured nanowires were controllably synthesized using a facile micro-emulsion & refluxing method under mild conditions. Investigations of asymmetric supercapacitors based on hierarchical heterostructured nanowires show that the capacitance for hierarchical heterostructured nanowires is 187.1 F g â^' 1 at a current density of 1 A g â^' 1, significantly higher than that for the MnMoO4 backbone nanoweire (9.7 F/g). The hierarchical heterostructured nanowire electrode exhibited good reversibility with cycling efficiency of 98 % after 1000 cycles. The enhanced supercapacitor performance is related to the fact that the surface area was increased (The BET surface area of MnMoO4 is 3.17 m2/g,while hierarchical heterostructured nanowires can reach to 54.06 m2/g),self-aggregation of the hierarchical heterostructured nanowires was greatly reduced,and hierarchical heterostructured nanowires can provide more surface sites for redox reaction to enable OH- access to the heterostructures facilely. The hierarchical nanowire heterostructure will be a unique structure that has potential applications in energy storage and other electrochemical nano-devices. ACKNOWLEDGMENT This work was partially supported by National Basic Research Program of China (973-program) (2012CB933000) and the National Nature Science Foundation of China (51072153), Program for New Century Excellent Talents in University (NCET-10-0661). Thanks to Professor C.M. Lieber of Harvard University, Professor Q.J. Zhang of Wuhan University of Technology, Professor Z.L. Wang of Georgia Institute of Technology and Professor J. Liu of PacificNorthwest National Laboratory for strong support and stimulating discussion.

The ability to quickly store and deliver a significant amount of electrical energy at ultra-low temperatures is critical for the energy-efficient operation of high altitude aircraft and spacecraft, exploration of natural resources in Polar Regions and mountains, and astronomical observatories exposed to ultra-low temperatures. Commercial high-power electrochemical capacitors fail to operate at temperatures below â?"40 °C. According to conventional wisdom, mesoporous electrochemical capacitor electrodes with pores large enough to accommodate fully solvated ions are needed for sufficiently rapid ion transport at lower temperatures. Here we demonstrate that strictly microporous carbon electrodes with much higher volumetric capacitance can be efficiently used at temperatures as low as â?"70 °C. We further discuss the critical parameters, with respect to electrolyte properties and electrode porosity and microstructure, needed for achieving both rapid ion transport and efficient ion electroadsorption in porous carbons. As an example, we demonstrate the fabrication of an electrochemical capacitor with an outstanding performance at temperatures as low as â?"60 and â?"70 °C. At such low temperatures the capacitance of the synthesized electrodes is up to 123 F g-1 (76 F cm-3), which is 50-100 % higher than that of the most common commercial electrochemical capacitor electrode at room temperature. At â?"60 °C selected cells based on ~0.2 mm electrodes exhibited characteristic charge-discharge time constants of less than 9 s, which is faster than the majority of commercial devices at room temperature. The achieved combination of high energy and power densities at such ultra-low temperatures is unprecedented and extremely promising for the advancement of energy storage systems.

Supercapacitors in recent years have emerged as a viable device option for electrochemical energy storage with high energy-power density capabilities and long cycle life. Though supercapacitor electrodes based on activated carbon, carbon fabrics, carbon xerogels and carbon nanotubes electrodes have been studied, graphene nanosheets with two dimensional nanostructure appear most potent engineered carbon for supercapacitors owing to their high planer electrical conductivity and high specific surface area [1]. Graphene supercapacitors studies are mostly based on aqueous electrolytes containing inorganic anions or with anions within polymer gels which establish an electric double layer. In this work we have studied graphene based supercapacitors with ionic liquid based gel polymer electrolytes. The aim is to exploit the wide electrochemical potential window, excellent thermal stability and nonvolatile attributes of ionic liquid polymer gels [2] and fabricate stable and high energy density graphene supercapacitors. Though ionic liquid electrolytes are of much interest for rechargeable batteries and conducting polymer supercapacitors, their use in graphene based supercapacitors have only rarely been investigated. In the present paper, we report on the fabrication and characterization of graphene-based all solid-state supercapacitor using 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4) ionic liquid electrolyte. The electrolyte is used in the form of a gel polymer prepared by immobilizing [BMIm]BF4 ionic liquid in poly(vinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) which also serves as a separator. Highly uniform and coherent graphene electrode layer over graphite sheet substrates was formed using optimally loaded graphene powder in a PVdF-HFP binder. The supercapacitor cells were fabricated by sandwiching gel polymer electrolyte between the two identical graphene electrodes. Electrochemical functionalities of the solid-state graphene supercapacitors were evaluated using impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. Highly capacitive behavior of the cells was evidenced from steep rising behavior of the impedance curve at low frequencies. Detailed analysis of the supercapacitor performance has been carried out and electrical parameters associated with the electrolytes and electrode-electrolyte interfaces have been evaluated from the impedance data. The maximum value of capacitance was shown to be ~75 mF cm-2 corresponding to the single electrode specific capacitance of ~79 F g-1 of graphene. Sequential charge discharge cycling tests revealed nearly stable cyclic performance for over 5000 charge-discharge cycles with only an initial ~ 10% fading in the capacitance. References: [1] Y. Zhu, S. Murali , W. Cai, X. Li, J.W. Suk , J.R. Potts, R.S. Ruoff, Adv. Mater. 22 (2010) 3906 [2] M. Armand, F. Endres, D.R. MacFarlane, H. Ohno, B. Scrosati, Nat. Mater. 8 (2009) 621-629

A simple and scalable method has been developed to fabricate nanostructured MnO2-CNT-sponge hybrid electrodes. A novel supercapacitor, henceforth referred to as â?osponge supercapacitorâ?, has been fabricated using these hybrid electrodes with remarkable performance. Ultrahigh specific capacitance (based on the mass of MnO2) of 1230 F/g was achieved, which is close to the theoretical value of MnO2 (1370 F/g). Capacitors based on CNT-sponge substrates (without MnO2) can be operated even under an extremely high scan rate of 200 V/s, and they exhibit outstanding cycle performance with only 2% degradation after 100000 cycles under a scan rate of 10 V/s. The MnO2-CNT-sponge supercapacitors show only 4% of degradation after 10000 cycles at a charge-discharge specific current of 5 A/g. The maxima specific power and energy of the MnO2-CNT-sponge supercapacitors are high with values of 63 kW/kg and 31 Wh/kg, respectively. The attractive performances exhibited by these sponge supercapacitors make them promising candidates for future high-performance energy storage systems.

Here we report for a facile chemical route to synthesize three-dimensional (3D) porous nanostructures constructed by interconnected polymer nanofibers. SEM reveals the3D porous foam morphology of the PAni. The foam-like nanostructures are constructed by coral-like dendritic nanofiber with uniform diameter of 60~100 nm. Such a 3D interconnected PAni nanofiber structures can be more effective than wires and particles for electrochemical device applications due to both large open channels between the branches and nanoscale porosities within the structures. The 3D hierarchical structure renders PAni as high-performance nanostructured supercapacitor electrodes with specific capacitance of ~480 F/g and areal capacitance as high as ~2.3 F/cm2. Moreover, the charge transfer resistance of the 3D PAni nanostructure is remarkably small suggesting favourable ion transport within the 3D continuous nanostructured framework. We found that our 3D PAni based electrodes yield excellent rate performance with only ~7% capacitance loss when current density increases by a factor of 10 (e.g. ~450 F/g at 0.5 A/g decreased to ~420 A/g at 5 A/g), showing an exceptional rate capability for high power performance. In addition, 3D PAni based electrodes exhibited good cycling stability, ~91% capacitance retention over 5000 cycles and ~83% retention over 10000 cycles at a high current density of 5 A/g. *The first two authors contribute equally to this work.

Quantum dot sensitized solar cells (QD-SSCs) are a DSSC analogue in which the dye sensitizer is replaced by inorganic quantum dots, the rest being conceptually similar. The change of redox electrolyte system and counter electrode associated with most QD-SSCs alters the cell parameters but has no influence on the fundamental cell mechanisms. Recent results of QD based photo-electrochemical cells seem to indicate the replacement of the molecular dye by inorganic sensitizer involves new mechanisms that should be considered when applying DSSC theory to QD-SSCs studies. New results of photo electrochemical solar cells that consist of quantum dots (QDs) deposited directly onto FTO glass identify chemical potential within the QD layer as the source for the observed photovoltage. Charge extraction and transient photovoltage measurements of this cell quantify the lifetime and density of the photo generated electrons within the QDs layer. At open circuit voltage, the electron density approaches 1e19, which corresponds to one electron per dot. The electron lifetime varies from 10 milliseconds at low photovoltage to 0.1 milliseconds at open circuit. These results lead to new understanding of the photo electrochemical mechanisms in quantum dot sensitized solar cell. Under illumination, the QD sensitizer layer can charge up to levels that alter the relative energetics within the cell thus affecting both the generation and recombination mechanisms. The new insight, identifying a conceptual difference between QD and dye-sensitized solar cells, opens new paths for improvement and optimization of QDs based solar cell.

Light weight and highly efficient wearable energy storage is critical to the operation of electronic devices in the field of smart and electronic textiles. Previously reported fabric supercapacitors focused primarily on technologies which are not direclty applicable for full device integration (e.g., nonwoven or electrospun textiles) or use expensive carbon nanomaterials with limited energy and power density (e.g., carbon nanotubes). Supercapacitors, based on non-toxic and non-flammable materials are attractive for developing textile supercapacitors for wearable electronics. Such textile supercapacitors can be used to power wearable sensors and antennas or harvest energy from wearable solar panels or piezoelectric materials. We have previously shown [Energy and Envir. Sci.; DOI: 10.1039/c1ee02421c] that screen printing is an excellent technique for impregnating commonly worn textiles with capacitive carbon materials, and achieved electrodes made of cotton and activated carbon having ~0.5 F/cm^2 areal capacitance and 85 F/g gravimetric capacitances with low series resistance of 4 Ωcm^2, results that are comparable to conventional film carbon electrodes. This research demonstrates how using established textile technologies with conventional carbon materials enables the direct implementation of energy storage devices into textiles. In this study, we present the next step of our research by designing knitted carbon fiber electrodes for integration into 3D knitted garments. The entire device is comprised of active carbon material, dramatically increasing the capacitance per unit of volume and area. We use highly conductive carbon fiber yarns, and knit these electrodes into fabrics of both commonly worn and custom designed 3D knitted architectures. We hypothesize that textile structure has the potential to affect device performance depending on the tension (i.e., mechanical stress) of the yarn within the textile, and the hierarchical porosity of the knitted structure. We will present the electrochemical performance of these devices from cyclic voltammetry, galvanostatic cycling, and impedance spectroscopy tested in both 1M sodium sulfate and a solid proton conducting polymer electrolyte for â?ono leakâ? capacitors. Such analysis of the affect of textile structure on capacitance will also inform future research of energy storing fabrics of various capacitive materials. (â?oCarbon Coated Textiles for Flexible Energy Storage.â? K. Jost et al. Energy and Environmental Science. 2011. doi: 10.1039/c1ee02421c)

The alarming phenomenon of global warming has led to efforts to better manage energy use and the carbon cycle. Indeed, more efficient technologies for saving energy have become a national priority. Since the building sector accounts for 39% of total US primary energy consumption, fenestration can significantly contribute to lowering the energy use for heating, cooling, and lighting. In spite of the great research and engineering efforts in the fast growing area of smart windows, development of glazings able to provide efficient, durable, and inexpensive dynamic daylight control is in its infancy. Here we report a novel technology for switchable daylight-redirecting glazing with great potential to respond to the current market needs. Based on a unique class of polymer-based optical elements, these glazings change their geometry in response to an applied stimulus, thereby enabling solar tracking. We will discuss their fabrication at length, from simulation-driven designs to materials synthesis and device integration. These responsive glazings with dynamic daylight control are broadly applicable to vertical windows and skylights with significant energy-savings potential.

Latent heat storage opens many opportunities for advancement in thermal energy storage systems for concentrated solar thermal power plants. If the phase-change properties of the molten salts that are typically used as storage media could be leveraged, solar energy storage could be significantly improved. For example, utilizing latent heat storage over the current sensible heat storage systems can potentially result in a 30% reduction in amount of molten salt, 60% reduction in container size, and a 2-3% improvement in overall system efficiency. The main problem however is transferring the heat efficiently from the storage system. A method is presented that utilizes coatings and surface treatments to improve overall performance. Theoretical analysis and experimental data will be presented with particular attention to the effects of material composition and microstructure will be presented.

A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li2MnO3 precursor has been investigated. The technique, which is simple and versatile, can be used to prepare a variety of composite electrode structures, such as â?~layered-layeredâ?T xLi2MnO3.(1-x)LiMO2, â?~layeredâ?"spinelâ?T xLi2MnO3.(1-x)LiM2O4, â?~layered-rocksaltâ?T xLi2MnO3.(1-x)MO, in which M is typically Mn, Ni, and/or Co, and more complex types. Early indications are that electrodes prepared by this method may be effective in 1) countering the voltage decay that occurs on cycling â?~layered-layeredâ?T xLi2MnO3.(1-x)LiMO2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge (~12% first cycle capacity loss). The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions will be discussed.

Benefits accrue for electrochemical energy storage when one deliberately creates cation-deficient metal oxides as charge-storage hosts. The amazing aspect of cation-deficient insertion oxides is that two key metrics in energy storage can be improved by the absence of a metal in its lattice site, thereby affording a double enhancement in energy density because higher capacity ensues as well as an increase in the thermodynamic potential for the ion-insertion reaction thereby yielding higher cell voltage. As this class of defective materials is pushed into the nanoscale regime, rate capability also increases. Although the advantages of structural cation vacancies have been known since at least the mid-1980s, research efforts exploring the charge-storage behavior of cation-deficient metal oxides to date are limited but promising. We have incorporated cation vacancies into transition metal oxides to improve performance for lithium-ion capacity by using one of three protocols. In a processing approach, point defects can be induced in conventional oxides using traditional solid-state-ionics routes that treat the oxide under appropriate atmospheres with a driving force such as temperature, as seen for polycrystalline V₂O₅ [1]. In a synthetic approach, substitutional doping of a highly oxidized cation such as Mo(VI) into a low-capacity inverse spinel iron oxide framework can significantly increase cation-vacancy content and corresponding charge-storage capacity [2]. In a scaling approach, electrode materials that are expressed in high-surface-area morphologies, such as aerogels, are inherently more defective due to a greater fraction of surface sites where the formation of cation vacancies is favorable, as shown for poorly crystalline γ-Fe₂O₃ aerogel stable chargeâ?"discharge cycling and Li-ion capacities of 100 mA h g^-1. The challenges and limitations of these defective structures and their promise as battery materials will also be discussed. [1] K.E. Swider-Lyons, C.T. Love, and D.R. Rolison, Solid State Ionics152-153 (2002) 99â?"104. [2] B.P. Hahn, J.W. Long, A.N. Mansour, K.A. Pettigrew, M.S. Osofsky, and D.R. Rolison, Energy Environ. Sci.4 (2011) 1495â?"1502.

In recent days, there has been increasing demand for high energy density and high power density cathode materials for application in lithium ion battery for next generation of transportation and various electrical and electronic devices. So, researchers are focused their interest on Lithium metal silicate (Li2MSiO4) based cathodes due to their overwhelming advantages such as high theoretical capacity and thermal stability, moreover cost effective and eco-friendly. However, the possibility of practical application of Li2MSiO4 restricted due to the poor conductivity. If these materials are synthesized in nanoscale and coated by conductive polymer would increase the electrochemical performances at elevated temperature. Herein, we used a rapid supercritical fluid process to synthesize nanocrytalline Li2MSiO4 (M=Fe and Mn) cathodes. The as-synthesized cathodes were characterized by XRD, TEM, AFM, FTIR and their electrochemical property was investigated by galvanostatic discharge method. The as-synthesized materials showed 4-20 nm depending upon their morphology and exhibited single crystalline phase. Conductive polymer and other carbon sources were used for coating by wet ball milling method. Further, the electrochemical results showed the discharge capacity is almost near 2 Li+ ion capacity in nanocrytalline Li2MSiO4 cathode material. The process of synthesis and electrochemical property will be discussed.

The discovery that LiFePO₄ can serve as a high-rate and high-capacity (170 mAh/g) cathode despite its limited ionic and electronic conductivity has demonstrated that the larger class of oxoanion compounds should be considered as a promising class of energy storage materials. Investigations of the even higher charge capacity material LiFeBO₃ (220 mAh/g) have been carried out. Crystallographic studies on single crystals samples demonstrate that LiFeBO₃ has a higher degree of symmetry than previously believed, and the implications of this revised structure on Li-O bonding and Li⁺ mobility will be presented. These structural studies will be discussed in the context of a comprehensive investigation (electrochemical performance as well measurements of powder and neutron diffraction, NMR, XANES, EXAFS, SEM, STEM/EELS, and DFT theory) of the delithiation and degradation mechanisms of LiFeBO₃ that provide important insights into the suitability of this compound for battery applications. Nearly the full charge capacity of LiFeBO₃ is accessible in our preparations of this material, though thus far only at low rates of charge/discharge.

It has become generally accepted that the use of vanadium in the synthesis of LiFePO₄ either as a dopant or as a composite compound results into improved rate capabilities. However, there has been a controversy on whether vanadium can be substituted into LiFePO₄ and, if substituted, which site it will occupy, and/or whether it forms a separate phase. We have shown that up to at least 10 mol. % of vanadium can be incorporated at the iron site of the LiFePO₄ structure without any observable impurity using solid-state synthesis at 550 °C. When the synthesis temperature is increased to 700 °C, vanadium solubility decreases and a second phase Li₃V₂(PO₄)₃ is formed. Vanadium substitution improves the electrochemical performance of LiFePO₄ produced at 550 °C; however the best rate performance is demonstrated by the 700 °C products. Here we use x-ray diffraction (XRD) and absorption (XAS) techniques, as well as TEM studies to reveal why the vanadium substitution is beneficial. XRD and XAS indicate that 550 °C pure olivine-phase product is mainly delithiated by a two-phase mechanism. However, increased range of Li_x(Fe,V)PO₄ solid solution at the beginning and the end of the delithiation process results in smaller lattice mismatch, and, hence, better rate capability. TEM studies reveal fairly small particle size, 30-50 nm, in both cases. For 550 °C product, a uniform vanadium substitution is found, as expected for single phase solid solution. For the two-phase Li(Fe,V)PO₄/Li₃V₂(PO₄)₃ composite prepared at 700 °C, 20 nm size vanadium-rich inclusions attributed to the Li₃V₂(PO₄)₃ are observed. Magnetic studies of this composite suggest presence of Fe₂P, while TEM does not reveal Fe-rich particles. We are investigating whether Fe₂P forms a conductive coating, thus contributing to the rate capability improvement. This work was supported as part of NECCES (the Northeastern Center for Chemical Energy Storage), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001294.

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that present higher potentials. A key tool to do this relies in exploiting the inductive effect of polyanions. It is now well established that modifying the electronegativity of the polyanions provides as a important way to tune redox potentials in a wide variety of systems. Pursuing this approach, our group recently embarked in the study of replacing (PO4)3- in the well-known LiFePO4 by a more electronegative group (SO4)2- to prepare a novel family of electrode materials termed fluorosuphates and having the general formula AMSO4F (A=Li or Na, M=transition metal). This fluorosulphate family exhibits a rich crystal chemistry. Depending upon the synthesis conditions and the nature of the cation, they can either crystallize in the the tavorite, sillimanite, or triplite polymorphs. We will discuss how one can trigger from one structure to another, and the relationship between the structure and electrochemical performance. Besides a few of these new family members are very promising for applications in Li-ion batteries. LiFeSO4F in the tavorite (ref 1) phase exhibits a plateau at 3.6V vs Li+/Li, which is 150mV larger than LiFePO4, while the triplite polymorph displays a potential of 3.9V (ref 2) which is the largest ever observed in an iron-based material. The compound LiZnSO4F displays a high ionic conductivity and could find some applications as solid electrolyte (ref 3). These new phases not only offer promising performance in Li-ion batteries, but also frequently reveal new physics. Many of the compositions display highly anisotropic antiferromagnetic ground states at low temperatures, which we have characterized using susceptibility measurements and powder neutron diffraction. We will present the magnetic structures obtained for LiFeSO4F and the delithiated analog FeSO4F and discuss them in terms of ion anisotropy (ref 4). References 1. Recham, N.; Chotard, J. N.; Dupont, L.; Delacourt, C.; Walker, W.; Armand, M.; Tarascon, J.M., Nature Materials 2010, 9, (1), 68-74. 2. Barpanda, P.; Ati, M.; Melot, B. C.; Rousse, G.; Chotard, J. N.; Doublet, M.-L.; Sougrati, M. T.; Corr, S. A.; Jumas J. C.; Tarascon J. M. Nature Materials 2011, 10(10), 772-779. 3. Barpanda, P.; Chotard, J. N.; Delacourt, C.; Reynaud, M.; Filinchuk, Y.; Armand, M.; Deschamps, M.; Tarascon, J. M., Angewandte Chemie-International Edition 2011, 50, (11), 2526-2531. 4. Melot, B. C.; Rousse, G.; Chotard, J.; Ati, M.; Rodriguez-Carvajal, J.; Kemei, M.; Tarascon, J.M., Chemistry of Materials 2011, 23, (11), 2922-2930.

Transition-metal fluorosulfates are receiving much recent interest for their potential use as cathodes in Li-ion batteries. Several new phases of LiMSO4F (M= Fe, Mn, Zn) crystallizing in the tavorite, triplite and sillimanite structures have captured much fascination in these phases, but synthetic access to them is very limited and the underlying phase stability and ion transport in these materials is poorly understood. Here we report that simple, cost-effective routes to LiMSO4F (M= Fe, Mn, Zn) offers significant advantage over both exotic ionothermal methods and solid state synthesis by enabling greater control of the chemistry. We show new limits for the onset of triplite crystallization, and report new phases in the Li[Fe,Zn]SO4F system, enabling an understanding of the complex chemistry and thermodynamics underlying these exciting materials. The transition of LiFeSO4F from the tavorite structure to the triplite polymorph is triggered in the absence of any substituents, proving that tavorite is an intermediate in the reaction pathway. As a result of the structural changes between tavorite and triplite, Li+ transport paths are quite different, as revealed here by combined neutron/XRD diffraction studies of the triplites, and involve intra-site zig-zag paths owing to complete cation disorder that impacts the electrochemical behavior.

Cathodes with high energy density and safety are continually sought in order to improve the performance of Li ion batteries for electric vehicle and consumer electronics applications. To accelerate the discovery of such improved cathodes, the authors conducted a high-throughput computational search encompassing tens of thousands of potential cathode compositions and crystal structures.[1-4] One candidate from our search is Li₉V₃(P₂O₇)₃(PO₄)₂, a potential two-electron material that uses the V3+/5+ redox couple. Li₉V₃(P₂O₇)₃(PO₄)₂ provides higher voltage and potentially higher specific energy compared to LiFePO4. Our preliminary experimental results indicate that more than one electron can be reversibly cycled.[5] More detailed experimental results on Li₉V₃(P₂O₇)₃(PO₄)₂ were also recently reported independently by Kuang et al.[6-8] In this presentation, we report on the computed voltage profile, volume change, stability, safety, and diffusivity of Li₉V₃(P₂O₇)₃(PO₄)₂. We explain the voltage steps observed in the experimental voltage profile, and determine that the experimentally-observed capacity loss upon cycling in this material is likely neither the result of cathode decomposition to other phases nor due to formation of Li-Fe antisite defects. In addition, our computations reveal that the intrinsic diffusivity of Li₉V₃(P₂O₇)₃(PO₄)₂ is moderate, and that diffusion within Li layers is affected by the presence of Li vacancies in the channel. The results of our computational investigation also suggest that the full capacity of Li₉V₃(P₂O₇)₃(PO₄)₂ might be difficult to achieve reversibly at safe voltages. We suggest an alloying strategy that is predicted to improve the properties of the pure Li₉V₃(P₂O₇)₃(PO₄)₂ material. 1 Anubhav Jain, Geoffroy Hautier, Charles J. Moore, Shyue Ping Ong, Christopher C. Fischer, Tim Mueller, Kristin A. Persson, and Gerbrand Ceder, Computational Materials Science 50, 2295â?"2310 (2011). 2 Geoffroy Hautier, Anubhav Jain, Hailong Chen, Charles Moore, Shyue Ping Ong, and Gerbrand Ceder, Journal of Materials Chemistry 21, 17147-17153 (2011). 3 Geoffroy Hautier, Anubhav Jain, Shyue Ping Ong, Byoungwoo Kang, Charles Moore, Robert Doe, and Gerbrand Ceder, Chemistry of Materials 23, 3495-3508 (2011). 4 Jae Chul Kim, Charles J. Moore, Byoungwoo Kang, Geoffroy Hautier, Anubhav Jain, and Gerbrand Ceder, Journal of The Electrochemical Society 158, A309 (2011). 5 G. Ceder, A. Jain, G. Hautier, J. C. Kim, and B. W. Kang, U.S. Patent No. U.S. Patent Application No. 12/857,262 (2010). 6 Quan Kuang, Jiantie Xu, Yanming Zhao, Xiaolong Chen, and Liquan Chen, Electrochimica Acta 56, 2201-2205 (2011). 7 Jiantie Xu, Yanming Zhao, Quan Kuang, and Youzhong Dong, Electrochimica Acta 56, 6562-6567 (2011). 8 Quan Kuang, Zhiping Lin, Yanming Zhao, Xiaolong Chen, and Liquan Chen, Journal of Materials Chemistry 3, 2-7 (2011).

Hybrid lithium ion energy storage devices are attractive for combining high energy density with high power capability and long cycle life. These advantages have been demonstrated in both asymmetric (activated carbon / Li4Ti5O12 (LTO) device) and hybrid lithium ion device (activated carbon- Li4Ti5O12 / Li cathode) where the emphasis was on the anode and improved charging rates. For rapid discharge, several researchers have focused on the formation of hybrid cathodes by combining conductive organic polymers (COP), or other organic charge transfer materials with inorganic materials. However these concepts have suffered other drawbacks such as high self-discharge rates and an insertion-deinsertion mechanism of anions that is rate limiting. To improve upon this concept, we present a hybrid device in which a composite cathode contains a high power organic radical combined with a high energy capacity metal oxide cathode. Characterization of the polymer material and composite electrode along with cycle performance data will be presented.

The storage kinetics of electrode materials for lithium ion batteries critically depends on the chemical diffusivity of Li in these materials. The two major transport processes included in this chemical diffusivity of Li are the transport of Li⁺ ions and the electronic conductivity of the material. Promising materials such as LiFePO₄ or TiO₂ suffer from intrinsically low electronic conductivities, rendering the pure materials unusable as electrodes. Here, superimposing networks of electronically conductive second phases can help improving the electron transport in such electrodes. A critical point in designing such networks is that the Li⁺ transport must not be hindered. Furthermore, the second phase must not use too large volume fractions. Still, for efficient electronic wiring, percolation of the conductive phase is required. In extreme cases (spherical particles, equal particle size as active material), up to 30 vol.% are lost to the secondary phase. Nanostructuring the active material, such as introducing porosity for improved Li⁺ transport [1], sometimes even further reduces volumetric density of the electrode. This contribution presents some concepts to improve the Li transport properties in electrode material, while keeping volume demands for secondary phases low. We report on novel electronic/ionic mixed conducting networks of anatase TiO_2-δ nanoparticles formed by thermal treatment in hydrogen atmosphere [2]. A major effect of the hydrogen-thermal treatment is the reduction of stoichiometric TiO₂ nanoparticles in the surface-near region of the particle, giving rise to the formation of n-type charge carriers close to the surface. The treated anatase particles show double to almost triple capacities compared to stoichiometric anatase, and also rate capabilities are strongly enhanced. At the same time, there is no volume loss for a secondary electronically conductive phase. We compare to conductive network formation by mixed electronic/lithium conducting oxides [3]. [1] J.-Y. Shin, D. Samuelis, J. Maier, Adv. Func. Mater. 2011, 21, 3464. [2] J.-Y. Shin, J.H. Joo, D. Samuelis, J. Maier, Chem. Mater. 2011, submitted. [3] Y.-G. Guo, Y.-S. Hu, W. Sigle, J. Maier, Adv. Mater., 2007, 19, 2087.

The high cost and toxicity of cobalt have prompted the search for alternative cathode materials for lithium-ion batteries. In particular, the series Li[Ni_x Li_1/3-2x/3Mn_2/3-x/3]O₂(0 < x â?¤Â½) has been extensively studied due to their high capacities, ranging from 140 mAh g^-1 to 250 mAh g^-1. It is known that the Li content in these materials sensitively influences the capacity. Despite intensive investigations, the exact role played by Li is not fully understood. To address this issue, we have examined four compositions prepared by an EDTA synthesis route. We find that the composition with no excess lithium (the x = 0.5 sample Li[Ni_0.5Mn_0.5]O₂) shows no oxygen loss, while the composition with the highest excess lithium investigated here (the x = 0.2 sample Li[Li_0.2Ni_0.2Mn_0.6]O₂) exhibits the highest oxygen loss and consequently the highest capacity. Interestingly, however, the compositions with intermediate amounts of excess lithium (the x = 0.3 sample Li[Li_0.13Ni_0.3Mn_0.57]O₂) shows the lowest capacity and very little oxygen loss. The x = 0.4 sample Li[Li_0.067Ni_0.4Mn_0.533]O₂ also shows little oxygen loss and low capacity. To develop a better understanding of the role of Li on the electrochemical performance, the atomic structures of the aforementioned compounds were investigated. Using aberration-corrected HAADF/STEM imaging, diffraction STEM (D-STEM), and EDS analyses, we find that the amount of excess lithium causes significant changes in the phases formed. In the absence of excess lithium, the material is almost composed entirely of an R-3m phase. As the excess lithium content increases up to x=0.2, the composition distribution among particles becomes more heterogeneous. Particles of C2/m symmetry with little to no Ni, similar to Li₂MnO₃, and particles with little to no Li in the Li layer, similar to rock salt MO, form and increase in number with increasing excess lithium content, while the number of R-3m particles decreases. On the other hand, at x=0.2 (Li[Li_0.2Ni_0.2Mn_0.6]O₂), the material becomes homogenous with particles having a C2/m symmetry and a solid solution. However, unlike the compositions with a small amount of excess lithium, these particles of C2/m symmetry contain Ni. These results suggest that when the amount of excess lithium is not sufficient, the R-3m phase decreases and the material partitions into two new phases: one rich in Li but deficient in Ni and the other deficient in Li but rich in Ni. Without much Ni, the covalency of the metal-oxygen bond in the C2/m particles decreases, resulting in a decrease in oxygen loss from the lattice. When Ni is incorporated into the particles of C2/m symmetry, as in the x = 0.2 sample Li[Li_0.2Ni_0.2Mn_0.6]O₂, the metal-oxygen covalency increases, facilitating the release of oxygen from the lattice. Overall, the best electrochemical performance is found when the excess lithium content is sufficient to form homogenous particles containing Ni, with a solid solution C2/m structure.

Li-ion batteries have been the high performance technology of choice for an increasing number of applications, from small-scale portable electronics to automotive, and even grid-based technologies. In particular, the high voltage of dense cathode materials, and the emergence of new anodes with high capacity densities, have made the volumetric energy density of Li-ion hard to beat. To understand where Li-ion technology can end up we have used high-throughput first principles computations to evaluate the voltage, capacity, stability, and theoretical energy density of several thousands of potential intercalation cathode materials. These results have given us some insights into the chemistries where higher energy density can be found, and the trade-offs that will have to be made to achieve higher energy density. Na-ion systems are intriguing due to the high abundance and low cost of sodium, though the larger volume of the Na ion will need to be compensated with larger cathode or anode capacity to make the system volumetrically competitive with Li-ion. Initial results indicate that there is a much broader choice of excellent Na-intercalation cathode and anode materials than is the case for Li-ion. I will show some examples of novel and existing Na-intercalation materials which indicate that this may be a competitive technology. Divalent and trivalent intercalating ions such as Mg2+ and Al3+ offer the highest potential for significant gains in volumetric energy density but require new electrolyte and electrode designs. Using high-throughput first principles computations, significant success has been achieved in this area, making this a technology a likely contender to displace Li-ion. While Li-S and Li-air are promising technologies in terms of their specific (gravimetric) energy, they are unlikely to compete with optimized intercalation systems on a volumetric basis.

The spinel cathodes are excellent candidates for Li-ion batteries because of their structural stability and high rate capability. We used first-principles calculations and analyses on the high voltage Li(Ni0.5,Mn1.5)O4 spinel to uncover the preferred Li-vacancy arrangement coupled with the cation ordering which explains the origin of the voltage profile and phase sequence as a function of lithiation. A coupled cluster expansion model is used to describe the ionic ordering in ordered (P4332) and disordered (Fd_3m) structures. The developed model predicts the preferred ionic orderings and demonstrates the incommensurateness of the preferred Li/vacancy configuration with the Ni/Mn configuration in P4332.

In support of the development of liquid metal batteries for grid-level storage applications, the thermodynamic properties of calcium-antimony alloys were determined by emf measurements in a cell configured as Ca(s)â",CaF₂â",Ca-Sb over the temperature range, 550 < T < 830 °C. Activity coefficients of calcium and antimony, enthalpy, Gibbs free energy and entropy of mixing of Ca-Sb alloys were calculated for x_Ca < 55 at%. To explain how short-range ordering of liquid Ca-Sb alloys is reflected in the strong deviation from ideality in the thermodynamic properties, the regular association model, assuming the presence of a CaSb₂ associate, and the molecular interaction volume model were invoked.

LiNiO₂ is a potential material for rechargeable lithium ion batteries. Despite the enormous amount of effort directed towards this compound, the ground state properties (in particular the magnetic behaviour) and local structure of LiNiO₂ remain unclear[1][2]. The attempt to synthesise truly stoichiometric samples has been unsuccessful [2,3,4]. There is always an excess amount of nickel ions sitting at lithium sites, which gives the formula [Li_1-xNi_x]NiO₂ where x is usually greater than 0.02. In addition, this compound has been found to lose up to 5% oxygen under certain synthesis conditions [5]. However it is not clear what defects exist to accommodate the oxygen non-stoichiometry. To improve electrochemical properties, the solid solution of Li(Ni,Co,Mn)O₂ has been extensively studied. In this study, we attempt to investigate the influences of Co and Mn ions on defect formation. The corresponding defects in NaNiO₂ were also calculated for comparison. Density functional theory first principles methods were used to investigate the effects of Co and Mn ions on defect formation. All calculations were carried out with the DFT+U method incorporated in the VASP code [6]. The cation antisite is found to be the most likely defect in LiNiO₂ followed by a defect where one extra Ni ion replaces one Li ion and the Ni charge states change to ensure overall neutrality. This result is consistent with the experimental difficulties encountered in synthesising stoichiometric LiNiO₂. The oxygen vacancy is the least likely point defect and the defect formation energy is ~0.6 eV, much higher than that for the cation antisite defect. The concentration of oxygen vacancy defects is reduced by Co or Mn doping. With 50% Co and Mn, the defect formation energies of oxygen vacancy rise to 1.62 and 2.75 eV respectively. Upon oxygen loss, transition metal ions are reduced and hence the stabilities of electronic configurations of transition metal ions seem to be a key factor to reduce the tendency to lose oxygen. Conversely the cation antisite defect concentration is greater in LiNi_0.5Mn_0.5O₂. This is due to the similar ionic radii of Ni²⁺ and Li⁺ and also electrostatic attraction between Mn⁴⁺ and Li⁺. The detailed local geometries and electronic structures are discussed. [1]. A. Rougier, C. Delmas, and A.V. Chadwick, Solid State Communications, 1995, 94 123. [2]. A. Rougier, C. Delmas and G. Chouteay, J. Phys. Chem. Solids, 1996, 57 1101. [3]. R. Kanno, et al, J. Solid State Chemistry, 1994, 110 216. [4]. H. Arai, S. Okada, H. Ohtsuka, M. Ichimura and J. Yamaki, Solid State Ionics, 1995, 80 261. [5]. M. S. Idris, Synthesis and Characterization of Lithium Nickel Manganese Cobalt Oxide As Cathode Material , Dept of Materials Science and Engineering, University of Sheffield, PhD thesis (2011) [6]. G. Kresse, and J. Furthmuller, Phys. Rev. B, 1996, 54 11169.

The assessment of critical properties for next generation battery materials is a topic of great economic and design importance. To properly assist the development and synthesis of novel materials, theoretical tools have to be designed, that allows for the calculations of critical parameters, like Li mobility and capacity, voltage, potential-capacity profiles. A better microscopic basis for a better understanding of properties is called for. We propose a manifold of approaches to battery materials. First, using state-of-art molecular dynamics simulations we determine mechanisms and efficiency of Li translocation in cathode materials[ 1]. Second, we point out the necessity of properly assessing the electronic ground stare of Fe based phosphate materials, beyond standard DFT methods, to properly compute electronic transport [2]. Third [3], we show how potential-capacity profiles and electrodynamics response are entangled at the microscopic level, paving the way for ab anitio calculations of critical material properties. All in all, we present a consistent platform transferable to battery materials in general. [1] S. Leoni et al, J. Mat. Chem. 2011, 21, 16365 [2] L. Craco and S. Leoni, J. Appl. Phys, 2011. in press. & S. Leoni et al. DOI 10.1524/zpch.2012.0158 [3] L. Craco, S.Leoni, Appl. Phys, Lett. 2011 in press.

The experimental search for new Li-ion battery cathode materials is very time consuming as any new proposed compound needs to be synthesized, characterized and tested electrochemically. On the other hand ab initio computations can be used to compute accurately many important battery properties (e.g., stability, voltage, Li-ion diffusion). This opens up the possibility to perform large scale unbiased searches of new materials and evaluate battery properties for thousands of cathode materials even before their synthesis, enabling the experimentalist to focus on the most promising chemistries. In this talk, we report in on the carbonophosphates: a new class of materials identified through a computational high-throughput search. We will present computed results on the stability, voltage, and Li-ion diffusion in the compounds of formula Li3M(CO3)(PO4) (where M is a +2 metal) within the crystal structure of the sidorenkite mineral, and show that this family offers opportunities for two-electrons, high capacity (> 200 mAh/g) cathode materials active in a voltage window compatible with standard electrolyte. Motivated by this computational analysis, we will analyze our results on the synthesis, characterization and electrochemical test of several of those predicted new materials. Finally, we will discuss other opportunities for new cathode materials within the sidorenkite crystal structure and within other mixed polyanionic crystal structures.

There has been a resurgence of research interest in Na-ion battery chemistries in recent years because of its potential cost advantages, the greater abundance of sodium (though it has not been conclusively demonstrated that lithium reserves would be an issue for the foreseeable future) and the exciting possibility of novel intercalation structures, some of which may not exist in their Li equivalents. Using established first principles methods that have been highly successful in the study of Li-ion battery chemistry, we will elucidate the differences in three key battery properties â?" voltage, phase stability and diffusion barriers â?" of Na-ion and Li-ion based intercalation chemistries. The compounds investigated comprise a broad spectrum of known battery compounds in a variety of different crystal structures, including the layered oxides and sulfides, as well as the olivine, maricite and NASICON structures. We will relate the observed differences between the sodium and lithium versions of these compounds with structural features, and provide insights for the future development of Na-ion battery chemistry.

Understanding the interfacial kinetics is a challenge for lithium-ion battery (LIB) electrodes. Here we propose a modified Potentiostatic Intermittent Titration Technique (PITT) for electrochemical systems governed by diffusion as well as interfacial kinetics. PITT is one of the widely used methods for determining the diffusion coefficient in electrochemical materials, such as lithium diffusion in lithium-ion battery electrodes. The conventional PITT analysis neglects interfacial resistance and assumes the system is diffusion controlled. For real electrode systems, however, surface reaction, as well as diffusion, may be rate limiting. Here we analyze PITT measurements for material systems with finite surface reaction rates. For small amplitude potential steps, we derive analytic solutions for the measured transient current associated with PITT, taking into account the effects of finite surface reaction rates. Using the analytic solutions, the diffusion coefficient, surface reaction rate, and the exchange current density can be determined simultaneously. The modified PITT is applicable to LIB electrodes, as well as other electrochemical systems wherein the measurement of diffusion and kinetic parameters characterizing surface reaction resistance are of interest. An example of lithium diffusion in amorphous silicon thin-film electrodes is used to demonstrate the enhanced PITT approach. The results show that the diffusion coefficient of Li in Si can be underestimated without considering the interfacial kinetics. In addition, we applied this modified PITT to liquid Ga electrode for LIBs, which is a self-healing electrode because the cracks generated during charging can be self-healed by the solid-liquid transformation of metallic Ga. The quantitative results showed that Li diffusivity and interfacial kinetics in liquid Ga are approximately 1,000 times larger than that in solid Ga and are larger than that in Si electrode. Thus, liquid Ga can be practically used as a LIB electrode.

Materials research and engineering design optimization are both necessary to meet the USABC long-term goals for advanced batteries for electric vehicles. Presently lithium-ion batteries are preferred by most vehicle manufacturers (OEMs) to meet both power and energy density requirements. The robustness of electrochemical models of lithium-ion cells and the limiting mechanism(s) suggested under different operating conditions depend on the accuracy of (a) design adjustable parameters, (b) electrode properties, (c) transport properties of the electrolyte and (d) thermodynamic (open-circuit potential vs. composition) data of the electrodes. Electrochemical models may also be modified to include volume changes, stress, etc. for certain systems such as Li-Si alloy electrodes which will then require additional information. Furthermore, capacity fade can lead to changes in various properties and also complicate the measurements. Therefore, it is imperative to obtain model input data specific to each new chemistry as a function of temperature, concentration and other independent variables to ensure that any phenomenon that could affect battery performance and life is captured in the theoretical analysis. Electrode and cell manufacturers play a critical role by providing these data to the OEMs. Universities, national labs and vehicle manufacturers themselves also obtain these values from experiments. Hence, consistent experimental methodology is critical. Potential confounding factors, including interference from other components of the lithium-ion cell and the specific theory and assumptions used to obtain a parameter (e.g. diffusion coefficient values from the Galvanostatic Intermittent Titration Technique) could lead to orders of magnitude differences if care is not exerted. Simulation of responses under different techniques such as galvanostatic charge-discharge, cyclic voltammetry, impedance, etc. are sometimes used to estimate parameters by comparison with experimental results. All these important aspects will be discussed from the standpoint of an OEM in an effort to arrive at a consensus on optimal procedures that are needed to achieve high fidelity in model predictions. Acknowledgements: Andy Drews and Ted Miller are acknowledged for their support.

Recent studies have shown that several O3 type transition metal layered oxides reversibly intercalate sodium while their lithium counterparts do not. Examples include NaCrO2, NaVO2 and NaMnO2. In this work, we use first principles calculations to study several phase transformations that layered oxides may undergo when alkali ions are removed. In particular, we focus on the composition A0.5MO2 (A = Li, Na), (M = Ti, V, Cr, Mn, Fe, Co, Ni and Mo). In lithium compounds, we observe that all lithium compounds except for Li0.5MoO2 have spinel as their lowest energy structure among those considered, and we investigate the energetics of the pathway for the layered to spinel transformation. In lithium compounds, formation of the Atet-Mtet dumbbell structure has been shown to be critical in this transformation [1]. Dumbbell configurations in lithium compounds have similar energy to layered structure making the transformation to spinel rather facile. Sodium structures are, however, found to behave substantially different: Most sodium compounds show no tendency to transform into any form of spinel structure. Although several sodium compounds exhibit similar energetics for dumbbell formation, this intermediate structure will revert back to layered structure because spinel structures are energetically unfavorable. Instead, several sodium compounds are found to prefer P3 configurations at A0.5MO2 composition, allowing sodium to occupy a prismatic environment. References: [1] J. Reed, G. Ceder, A. Van der Ven, Electrochemical and Solid-State Letters 4 (2001) A78-A81

Li-S and Li-O2 batteries represent two promising technologies to meet the needs for high energy density storage systems. The presentation will compare and contrast the two, and focus on their improvement with emphasis on porous cathode materials comprised of two-phase nanophase systems deliberately designed to overcome some of the challenges presented by their inherent cell chemistries. These embody mesoporous carbon materials with high surface area, large pore volume, and good electrical conductivity to function as electrically conductive scaffolds. For Li-S cells, confinement of active mass including soluble reaction intermediates during cycling is vital. The diffusion of polysulfides which is mostly retarded by the nanostructure may still occur at a slow rate, which limits the long term cycling performance. We will discuss the merit of a variety of our recent approaches to solving these issues. In the case of Li-O2 cells, we will discuss our exploration of high surface area transition metal oxide catalysts where surface defects offer increased levels of catalytic activity and stability, and hierarchical porosity can aid in optimizing storage capacity and charging characteristics. Exploration of the underlying battery chemistry using a plethora of ex-situ and in-situ techniques will also be highlighted in the presentation.

Transport of molecular oxygen in the cathode of a non-aqueous Li-O₂ cell is of critical importance in determining the final discharge capacity of such a system. The ability to move oxygen from the surface of the cathode into the bulk is a good predictor for the final discharge capacity. The oxygen flux, being a function of both O₂ concentration and diffusion, will be affected by factors such as oxygen partial pressure, electrode tortuosity, electrolyte viscosity, dielectric constant, and molecular structure. Under discharge, the concentration of oxygen also varies throughout the cathode, and this can affect the deposition process for Li₂O₂ and Li₂O as well as the composition and location of the discharge products. Discharge behavior in this system will be discussed along with several possible approaches to solve the obvious transport limitations of this high energy chemistry.

Large scale deployment of electrical vehicles needs to have an energy storage system which has an energy density far exceed those of the state of the art Li-ion batteries. Li-air battery is one of the most promising systems which can satisfy this need. However, there are many barriers on the practical applications of these systems. The practical specific energy and cyclability of these batteries are strongly limited by the structure of electrode materials, stability of electrolytes, and gas separation membranes used in these batteries. A newly developed air electrode consisting of a hierarchical arrangement of functionalized graphene sheets has demonstrated a record capacity of 15,000 mAh/g in a Li-air battery. The effect of the oxygen/moisture separation membranes will be reported in this work. Fundamental mechanisms on the effect of nanostructured materials on the performance of these batteries will also be discussed.

Carbon nanotubes (CNTs) have a high-aspect-ratio structure with a length of more than 100 μm and a diameter of 1-50 nm. Since CNTs are good electronic conductors and have a high chemical stability, they are used in various electrochemical devices, such as capacitors. In this study, we synthesized vertically aligned CNTs directly on metal foils by using thermal CVD and applied them to an electrode of a lithium-Sulfur (Li-S) rechargeable battery, which is a promising candidate for the next-generation Li-ion battery. By means of the direct growth, CNTs were electrically connected to a current collector and the spaces between the CNTs were filled up with a liquid electrolyte. Therefore, at the CNT electrode, the electrons from the current collector and Li⁺ ions from the electrolyte could move quickly in the thickness direction. On the base of this, we suggested the fabrication of a high-power and high-energy battery, i.e., a CNT/S-Li battery. Sulfur has a large theoretical specific capacity of 1675 mAhg^-1. Moreover, it is abundant, inexpensive, and nontoxic. However, there are two main problems with the Li-S battery, namely, a poor cycle life and low availability of S active material. The former is due to active mass loss and generation of inactive Li-S compounds at the anode, which are caused by the high solubility of polysulfide formed during the discharge-charge process. On the other hand, the latter is caused by the insulating property of S. Usually, various carbon materials, such as acetylene black (AB), are mixed with S cathode as electrically conductive additives. Since CNTs are long carbonaceous objects with a length of over 100 μm, they exhibit lower resistance than AB and other carbon materials. It is expected that the performance of S cathode would be improved by using a high-conductivity CNT/S composite. CNTs were grown on a Ni foil (20 μm thick) at 700 °C using Fe as a catalyst and acetylene as a source gas. CNT/S composites were fabricated by impregnating the CNT electrode with molten S. The CNT/S composite (CNT:S = 1:1.16 by wt.) and a conventional cathode coated with mixture of S, AB, and a binder (45:45:10 by wt.) were prepared and combined with a Li-foil anode and a liquid electrolyte, i.e., 3 mol dm^-3 of lithium bis(trifluoromethanesulfonyl)imide / dimethoxy ethane + dioxolane (9:1 by vol.). At a rate of 0.1 C, the initial discharge capacities of the CNT/S composite and the S/AB cathode were 1283 and 1007 mAhg^-1, respectively. After 10 charge-discharge cycles, the capacity of the CNT/S composites was larger than that of the S/AB cathode. Moreover, at a rate of 1 C, the capacity of the CNT/S composites (809 mAhg-1) was much larger than that of the S/AB cathode (141 mAhg-1). Consequently, a rate capability test showed that the CNT/S composites could operate at a current density that is five times that of the S/AB cathode.

One of the major limitations cited in the commercialization of electric drive vehicles is the range anxiety. This problem originates from the available energy per unit weight (Wh/kg) of the battery and its relation to the drivable electric range per charge. The Lithium-Air battery has been identified as one of the promising candidates that can deliver as much as ten times the theoretical capacity of the present generation batteries (11 kWh/kg). The reactions taking place during discharge within a Li/O2 non-aqueous cell have been debated and several mechanisms have been proposed. The most widely accepted schematic is as follows: At the anode: Li <--> Li+ + e- Eo = 0 V (vs. Li/Li+) At the cathode: 2Li + O2 <--> Li2O2 Eo = 3.10 V (vs. Li/Li+) 4Li + O2 <--> 2Li2O Eo = 2.91 V (vs. Li/Li+) The technical barriers to be overcome at the air-carbon cathode include identification of suitable catalysts that will reduce the polarization between the charge and discharge and the elimination of capacity loss due to the formation of insulating oxides of lithium that block the pores of the air cathode. In this work we will analyze data from voltammetry and rotating ring disk electrode experiments using a mathematical model to estimate the reaction rates and transport coefficients for the individual reactions. Catalytic regenerative reactions that enhance the polarization curves in the potential region that generates the peroxide will be included in the reaction schematic.

Non-aqueous Li-air battery which utilizes metallic Li and abundant O2 in the air as anode and cathode, respectively, is very attractive owing to the potential very high energy density. Such batteries are considered as the chemistry beyond Li-ion to power the next generation of PHEV and EV. However, there remain many critical technical obstacles. Among them, the slow kinetic of recharging (oxidizing) Li oxides, which is the products of O2 reduction is a major one. The charging voltage, thus the â?oround-tripâ? efficiency relies on the oxidation over-potential. In this report, a unique mechanism facilitated by the electrolyte additives will be discussed. The discharge capacity of the air diffusion electrode in the non-aqueous electrolytes is significantly increased. The over-potential of Li2O2 re-oxidation is reduced. The unique chemistry and cell design open up a new avenue for the high energy density Li-air battery.

Rechargeable lithium-air batteries offer great promise for transportation and stationary applications due to their high specific energy and energy density compared to all other battery chemistries. Therefore such batteries could be developed for powering electric vehicles, enabling driving ranges comparable to gasoline powered automobiles. Although the theoretical discharge capacity of Li-Air cell is extremely high, the practical capacity is much lower and is always cathode limited. On charging, the cathode acts catalytically to evolve oxygen (the oxygen evolution reaction, OER) and on discharge acts to reduce oxygen (the oxygen reduction reaction, ORR). However, due to the slow kinetics and higher overpotential especially in OER together with clogging of Li2O2 in the pores of air electrode limit the re chargeability of Li-Air batteries. A key for rechargeable systems is the development of an air electrode with bifunctional catalyst on an electrochemically stable carbon matrix. The use of Graphene as a stable catalyst matrix for Air cathode has been studied in this work. A Li-Air cell constructed using an air cathode consists of nano Pt on graphene nanosheets (GNS) has showed promising improvement of 85% energy efficiency with average capacity of 1800 mAh/g and more than 30 cycles without significant loss of total energy efficiency. Replacement of Pt with nano structured Perovskite type bifunctional catalyst resulted more than 100 cycles with an average capacity of 2000 mAh/g and total energy efficiency about 75%. The electrochemical impedance spectroscopy data revealed increasing solution and charge transfer (polarization) resistance during cycling, which hinder the cycle life. The increased solution resistance can be attributed to the evaporation and decomposition of carbonate based electrolyte especially at high charge voltages. Further improvements of the bifunctional catalyst as well as the use of non- carbonate and ionic liquid based electrolytes on the electrochemical performance of Li-air systems are under investigation.

Rechargeable lithium air battery is emerging as a transformative energy storage technology. It is considered to be one of the most promising battery technologies that can provide the energy storage capacity as high as that of liquid fuels and enable driving ranges of electric vehicles comparable to gasoline powered vehicles. The reasons for the high energy density of Li-air battery are its â?ofreeâ? oxygen cathode (from ambient environment) and excellent electrochemical properties of lithium metal anode (theoretical capacity of 3860 mAh/g, the lowest electrochemical potential of -3.10V vs. SHE). However, the use of oxygen cathode and lithium metal anode also presents significant challenges for nonaqueous electrolytes. For a practical nonaqueous Li-air battery, the requirements of electrolytes, in addition to those for Li-ion battery, should at least include: 1) high stability in oxygen-rich electrochemical conditions, 2) compatibility with Li metal anode, and 3) high boiling point. Since Li-air battery is still at its very early development stage, currently it might be too difficult to find a perfect electrolyte that meets all the requirements. We believe that searching for a proper electrolyte should include several stages (i.e., to meet the requirements one by one) and the requirement of electrolyte stability in oxygen-rich electrochemical condition is the priority to meet at the first stage. Due to the high reactivity of oxygen reduction/oxidation intermediates (O, O2-, LiO2, etc.) in Li-air battery, traditional organic electrolytes are decomposed during discharge and charge. This leads to the formation of lithium carbonate and lithium alkyl carbonates, instead of the desirable Li2O2 as discharge product, only which can make Li-air battery sustainably rechargeable. Therefore, a stable electrolyte which can exclusively form Li2O2 is very important. In this work, we developed a protocol for fast screening of stable electrolytes for Li-air battery. The stability of nonaqueous electrolytes and the mechanisms behind this will be presented.

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li2S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO3 additive to the electrolyte was shown to improve the coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy

First principles computation methods play an important role in developing and optimizing new energy storage and conversion materials. In this talk, we focus on recent progress made in first principles computation investigation towards understanding, controlling and improving the intrinsic properties of high energy density electrode materials in lithium based electrochemical systems. In different materials chemistry families, we describe the crystal structures, the redox potentials, the ion mobilities, the possible phase transformation mechanisms and structural stability changes, and their relevance to the high-energy high-power low-cost electrochemical systems. We demonstrate that computational tools will be critically important to enable real-world materials development, to optimize or minimize traditional experimental synthesis or testing, and to predict materials performance under diverse conditions

The lithiation-delithiation processes of anode materials in lithium ion batteries were observed by in-situ electron microscopy. The lithiation-delithiation was strongly materials, size, and orientation dependent. Upon charging of SnO2 nanowires, we observed high density of dislocations in the reaction front, while in charging of ZnO nanowires, we observed discrete cracks in the reaction front. In charging Si nanowires, we found the volume expansion was highly anisotropic, resulting in a dumbbell-shaped cross-section and cracking, eventually splitting the single nanowire into sub-wires. Carbon coating not only increases rate performance but also alters the lithiation-induced strain of SnO2 nanowires. The radial expansion of the coated nanowires was completely suppressed. The lithiation process of individual Si nanoparticles was strongly size-dependent, i.e., there exists a critical particle size with a diameter of ~ 150 nm, below which the particles neither cracked nor fractured upon lithiation, above which the particles first formed cracks and then fractured. Upon lithiation insertion, crystalline Ge (c-Ge) underwent a two-step phase transformation process: first the c-Ge nanowire was converted to an amorphous LixGe alloy, which then crystallized to the crystalline Li15Ge4 phase. Nanopores were formed only during the delithiation process, similar to the formation porous metals during a de-alloying process. Upon each delithiation cycle, nanopores formed first at the end of the nanowires close to the lithium drain, which then extended along the nanowire to the other end, converting the Li15Ge4 nanowire to a porous sponge amorphous Ge nanowire. Intriguingly, the sponge nanowires with nanopores showed very fast lithiation/delithiation rate and excellent mechanical robustness due to the short lithium ion diffusion path and the formation of the strong ligands, respectively. These results nano porous Ge network structure is a perfect anode candidate for lithium ion batteries with high capacity, high rate performance and good mechanical stability. References: Science 330, 1515 (2010); 330, 1485 (2010); Nano Lett. Doi: 10.1021/nl200412p, 10.1021/nl2024118, 10.1021/nl201684d, 10.1021/nl202088h, ACS Nano, doi: 10.1021/nn200770p, 10.1021/nn202071y; PRL 106, 248302 (2011); Eng. Env. Sci. doi: 10.1039/c1ee01918j

Sulfur has a high theoretical specific capacity (1673 mAhg^{â^'1}), but suffers from capacity fading because of active material loss and parasitic side reactions due to the solubility of polysulfides in the electrolyte. To address this problem, we have prepared three different sulfur/carbon composites, namely a mixture of micron-sized sulfur particles and carbon black, a processed mixture of the same and graphene-wrapped sulfur particles, in an effort to trap the soluble polysulfides in the carbon matrix. To better understand these cathode materials, we have studied the reduction mechanism of elemental sulfur with in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) as a function of these three sulfur cathode architectures. To study these processes, we developed sealed pouch and coin cells with X-ray transparent polymer and silicon nitride windows, respectively, which allowed us to monitor the Liâ?"S conversion reactions in situ during electrochemical cycling. Diffraction showed that the reformation of crystalline sulfur at full charge is dependent on the sulfur/carbon morphology. Furthermore, crystalline Li₂S, which is reported in a number of ex situ XRD studies, does not form in situ in the three different morphologies studied. These results suggest that the soluble polysulfides are trapped in the carbon matrix. Combining XAS and XRD analytic techniques have allowed us to understand both amorphous and crystalline reaction intermediates and provide us with valuable mechanistic information for Liâ?"S batteries.

Electrodes for Li batteries are characteristically complex porous composite materials. The microstructure of these materials will affect the fundamental physics occurring at the electrode and sub-electrode level from intercalation to charge-transfer to SEI growth. Therefore, to some extent, they will dictate the macroscopic performance of the device â?"affecting the energy and power density as well as the battery lifetime. In spite of the importance, historically there has been only a limited understanding of the relationship between electrode microstructure and battery performance. Recent developments in x-ray microscopy techniques provide a platform to explore these materials with unprecedented detail. The non-destructive nature of the technique further allows the exploration of temporal changes to electrode microstructures that may be associated with state of charge, degradation, and device failure. Here, we present the successful application of laboratory- and synchrotron-based x-ray microscopy to the three-dimensional (3D) study of battery materials at multiple length scales. The authors find that the resolution requirement for tomographic study depends on a variety of factors, the most notable of which is the geometrical parameter that is under investigation. We explore the application of x-ray microscopy at the particle, electrode, and device length scales, including studies of the effects of charge cycling on microstructure and attempts to isolate constituent phases in composite electrodes. Combination of this tomographic data with relevant simulation has enabled us to draw direct links between the geometry of these electrodes and their performance at microscopic length scales. Furthermore, this has allowed us to explore the effects of local heterogeneity on mechanical and electrochemical performance.

We will present recent transmission X-ray microscopy (TXM) work on two Liâ?"ion battery materials. High resolution X-ray imaging allows for direct studies of morphology changes during operation. Additionally, using in situ 3D microscopy, volume and density changes can be tracked on the same particle over time. With its high specific capacity (1673 mAhg^{â^'1}), sulfur is an attractive Liâ?"ion battery cathode material. However, due to the solubility of the higher order polysulfides, Liâ?"S batteries suffer from capacity fading and loss of active material. We will present results from in situ TXM studies on the capability of various cathode preparation techniques to trap higher order polysulfide and the dependence of charge rate on this trapping. The theoretical capacity (4200 mAhg^{â^'1}) of silicon is more than ten times higher than existing commercial anode materials. Nevertheless, with a theoretical volume increase of around 400% due to Liâ?"ion insertion, the Si anode has been shown to crack and pulverize leading to capacity fading. With 3D in situ TXM studies, we will quantify this volume change in micron-size Si particles due to the insertion of Liâ?"ions.

In order to develop new electrode materials for the next generation of energy storage devices such as batteries and super capacitors with high power density, the in-depth understanding of the relationship between the structural changes and the electrochemical performance, especially the structure limitation for ultra high charge and discharge rate is quite critical. Therefore, the in situ time resolved spectroscopic techniques to monitor and study the structural changes during the fast delihiation and lithiation are quite important. Recently, a new in situ synchrotron x-ray diffraction technique to study crystalline structural changes of LiFePO4 during chemical delithiation has been developed and reported by our group, with excellent time resolving ability for dynamic studies. Here, we introduce another new in situ technique of quick X-ray absorption spectroscopy (XAS) to investigate the fast chemical and electrochemical delithiation of cathode materials for Lithium-ion batteries. X-ray absorption spectroscopy is a powerful technique which provides information of both electronic structure and local structure of the material. In standard XAS, data points are collected step by step after the monochromator is moved by a small angle. Normally, it will take more than 15 minutes to collect one spectrum. Quick EXAFS replace the stepwise scanning mode by a continued moving mode of the monochromator at constant velocity. The scanning time of one spectrum can be as short as one minute, and in some special case, even less than one second. This quick data collection technique provides a method to study the structural changes of ultra-fast reactions, such as battery charge and discharge at ultra high C-rates (e.g. 100C). In this presentation, LiFePO4 and LiFe0.2Mn0.8PO4 were tested examples. Fe and Mn K-edge XAS spectra were collected during in situ cycling at different C-rates (from 1C to 10C) to study the rate related structural changes and charge compensation mechanism. Chemical delithiation was also carried out in comparison with electrochemical delithiation to investigate the dynamic properties of these materials. This technique provides a new powerful tool to study both electrochemical and chemical reactions with excellent time-resolving power for dynamic studies. The work was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, under the program of Vehicle Technology Program, under Contract Number DEAC02-98CH10886. Xiaojian Wang is supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract Number DE-SC0001294. Work at Institute of Physics of CAS was supported by NSFC (50672122, 50730005), of China.

Commercialized electrode materials must demonstrate the ability to maintain their chemical structure over the course of hundreds of charge/discharge cycles and range of climate conditions. Although the olivine phosphates o-Li_xFe_1-yMn_yPO₄ are used in rechargeable battery systems, the thermodynamics and stability data for their delithiated forms is scarce and contradictory. o-FePO₄ is stable in air up to 620 °C, while o-MnPO₄ is reported to decompose above 210 °C with oxygen release. The stability of intermediate compositions is not known. In this work we have synthesized o-LiFe_1-yMn_yPO₄ using hydrothermal and solid state methods, resulting in particle sizes varying from micro- to nanometers. Chemical delithiation was performed using NO₂BF₄ or Br₂ in acetonitrile to obtain corresponding delithiated olivine phases. The structure and thermal stability of the products was then studied by in-situ synchrotron x-ray diffraction upon heating the samples up to 800 °C. The structural analysis was complemented by x-ray absorption and magnetic studies, and thermal stability investigated by TGA-MS and DSC techniques. The results indicate that with increase of Mn content to y = 0.8, the delithiated compounds become more hygroscopic and less crystalline. Iron substitution is shown to improve the thermal stability, for example o-Fe_0.6Mn_0.4PO₄ is stable up to 450 °C. The decomposition mechanism as a function of Mn content, particle size, synthesis method and reaction atmosphere will be discussed. This research is supported as part of the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award Number DE-SC0001294.

Transparent electronics is one direction for the development of future electronic devices. As a key component in electronic devices, batteries have not yet been demonstrated to be transparent. As battery electrode materials are not transparent and have to be thick enough to store energy, the traditional approach of using thin films for transparent devices is not suitable. Here we demonstrate a grid-structured electrode to solve this dilemma, which is fabricated by a microfluidics-assisted method. The microfluidics-assisted approach could design electrode with various shapes and structure. The feature dimension in the electrode is below the resolution limit of human eyes, and, thus, the electrode appears transparent. Moreover, by aligning multiple electrodes together, the amount of energy stored increases readily without sacrificing the transparency. This results in a battery with energy density of 10 Wh/L at a transparency of 60%. The device is also flexible, further broadening their potential applications. We also demonstrate that the transparent device configuration allows in situ Raman study of fundamental electrochemical reactions in batteries. Related paper: Yang, Y.; Jeong, S.; Hu, L. B.; Wu, H.; Lee, S. W.; Cui, Y. Transparent Lithium-ion Batteries. Proceedings of the National Academy of Sciences of the United States of America 108, 13013-13018 (2011).

We report the direct observation of microstructural changes of LixSi electrode with lithium insertion/deinsertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. HRTEM study using Si wafer is performed as well for the better understanding on preferred diffusion direction of Li insertion to Si. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion/deinsertion. Because lithiation-induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high-capacity Si anodes in lithium-ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials.

The development of new energy storage technologies remains a critical challenge to meeting growing global demands on electrical energy storage. Rechargeable batteries, in particular, stand to impact applications ranging from vehicle electrification to renewable energy harvesting to powering our ubiquitous energy-hungry portable electronics. It is becoming increasingly clear, however, that meeting these challenges in next generation energy storage systems will require developing materials that provide not only high energy densities, but that can be produced at low cost and demonstrate good cyclability, safety, and environmental friendliness. Iron oxides represent an underdeveloped class of electrochemically active materials with the potential to meet many of these requirements. We explore here the application of a diverse collection of iron oxides as electrodes for lithium ion batteries, investigating the influences of particle size, morphology, chemical composition and crystallographic phase on cycled electrochemical charge and discharge behaviors. Coupling tools such as in-situ x-ray diffraction during electrochemical cycling with computational modeling, we present fundamental insights into the promising utility of these materials in lithium ion batteries. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Novel carbon materials have been synthesized for their applications in electrochemical capacitors. Using KOH activation of microwave exfoliated graphite oxide (MEGO), a porous carbon (activated MEGO, or a-MEGO) with a BET surface area of up to 3100 m2/g, a high electrical conductivity, and a low oxygen and hydrogen content was obtained.[1] This sp2-bonded carbon apparently has a continuous 3D network of highly curved, atom-thick walls that form primarily 0.6- to 5-nm-width pores. Two-electrode supercapacitor cells constructed with a-MEGO yielded gravimetric capacitance of up to 200 F/g (normalized to carbon) and energy density of above 20 Wh/Kg (normalized to a typical supercapacitor device) with ionic liquid electrolytes. A parametric study of the loading of KOH to activate MEGO (to generate a-MEGO) and the temperature of activation was performed to study their effects on the BET surface area and supercapacitor performance.[2] In addition, mechanical pressure was applied to consolidate the carbon, leading to a higher mass density. After compression, the gravimetric capacitance remained about the same, but the volumetric capacitance was significantly improved, yielding a high volumetric energy density in the capacitor.[3] We also have learned that a-MEGO can act as an efficient scaffold for hosting other active materials used for electrochemical capacitors due to its unique pore distribution. For example, MnO2/a-MEGO composites have been synthesized by in situ deposition of nanometer-thick MnO2 through the 3D porous structure of a-MEGO.[4] The homogeneous MnO2 deposit, coupled with the high electrical conductance of a-MEGO has led to a pseudocapacitance close to the theoretical value for MnO2 in aqueous electrolytes such as 1M H2SO4. These results suggest that a-MEGO itself along with a-MEGO derived materials are likely to play important roles in future high-performance electrochemical capacitor devices. References: [1] Yanwu Zhu, Shanthi Murali, Meryl D. Stoller, K. J. Ganesh, Weiwei Cai, Paulo J. Ferreira, Adam Pirkle, Robert M. Wallace, Katie A. Cychosz, Matthias Thommes, Dong Su, Eric A. Stach, Rodney S. Ruoff, Science 332, 1537, 2011 [2] Shanthi Murali, Jeff Potts, Scott Stoller, Joono Park, Meryl Stoller, Lili Zhang, Yanwu Zhu and Rodney S. Ruoff, submitted. [3] Shanthi Murali, Neil Quarles, Yanwu Zhu, Rodney S. Ruoff, in preparation. [4] Xin Zhao, Lili Zhang, Shanti Murali, Qinghua Zhang, Yanwu Zhu, Rodney S. Ruoff, to be submitted.

Because lithium is the most electropositive and lightest metal element it is generally thought that batteries with the highest gravimetric energy theoretically possible are those based on lithium. Nonetheless, as the size of consumer devices has decreased, battery volumetric energy density has become more important than gravimetric energy density. In automotive applications, reducing battery cost has the highest importance, while volumetric and gravimetric energy densities are similar in importance. Battery chemistries based on alternative metals to lithium may reduce cost and/or provide significantly higher volumetric energy density than batteries based on lithium. This makes such chemistries extremely attractive, from the theoretical point of view. Progress in the development of battery technologies based on electropositive metals other than lithium (e.g. Na, Mg) will be discussed.

At the present time, lithium resources are confirmed to be unevenly distributed, located primarily in South America. The cost of lithium-based raw materials has roughly doubled from the first practical application in 1991 to now, and it may drastically increase when the demand for lithium increases as a result of commercialization of large-scale lithium-ion batteries in the future. However, sodium resources are inexhaustible and unlimited everywhere around the world. Furthermore, the electrochemical equivalent and standard potential of sodium are the most advantageous for aprotic battery applications after lithium. Graphitic carbon cannot form staged intercalation compounds with Na. The situation is different for non-graphitic carbon and it is suggested that the storage mechanisms for Na and Li are similar, although the capacity is smaller in the case of sodium. Despite the fact that â?~â?~sodium-ion batteriesâ?Tâ?T could be based on an electrochemistry similar to Li ion batteries, to date no workable system exists that allows satisfying operation at room temperature and we believe that porous hydrothermal carbon materials could be ideal candidates in this direction. Therefore, in this paper the performance of amorphous carbon hollow spheres as negative electrodes in Na+ ion cells was investigated. These hollow spheres were synthesized using hydrothermal carbonization of glucose in the presence of nanosized latexes templates. The first discharge/charge cycle delivered specific capacities of 537 and 223 mAhg-1 respectively at a current rate of 50 mAg-1 The large irreversible capacity arises from both electrolyte decomposition at the electrode/electrolyte surface and the irreversible insertion of sodium into potentially unique shell positions as demonstrated by features in the corresponding CV curves, which is interestingly analogous to previous literature discussions regarding lithium storage in disordered carbons. The reversible capacity of 200 mAhg-1 at a current density of 50 mAg-1 is significant, and only few reports achieved capacities more than 200 mAhg-1 for sodium anode materials typically obtained at much lower current densities than that reported here.The cycling stability during sodium insertion / extraction in the hollow carbon nanospheres was also investigated at a current density of 50 mAg-1 for the first ten cycles and then 100 mAhg-1 for subsequent cycles. After 100 cycles, a reversible capacity of ~ 160 mAhg-1 is stably maintained. The coulombic efficiency approaches ~ 94 % after several cycles, Remarkably the reversible capacities at various discharge/charge rates, are retained at 168, 142, 120, 100 and 75 mAhg-1 at current densities of 0.2 A/g, 0.5 A/g, 1A/g, 2 A/g and 5 A/g, respectively. Even at a very high current density of 10 A/g, a capacity of ~ 50 mAhg-1 is still maintained, demonstrating the excellent rate performance of the hollow carbon nanospheres based electrode.

Lithium ion batteries (LIBs) are getting to be the foremost representative power sources for clean vehicles such as hybrid vehicle (HV), plug-in hybrid vehicle (PHV) and electric vehicle (EV) due to its high energy density. However since a battery system with even higher energy density is required for the long-range PHV or EV applications, post lithium ion batteries (PLIB) such as Li-sulfur battery or Li-air battery have been getting more attention and studied in recent years. Rechargeable magnesium battery can also be a candidate for the PLIB due to the nature abundance of magnesium and intrinsic safe behavior when using as anode1. In addition, magnesium-metal electrode is expected to have high energy density and power density, due to its divalent electrons transformation2, 3. However, there is no much progress on cathode side since the innovation of Chevrel phase such as MgMo3S4 4. The difficult lies in the strong polarization character of the small and divalent Mg2+ and consequently the intercalation and diffusion of Mg 2+ ions is somewhat difficult and complex1. In this presentation, we will report our recent investigation on the reversibility of MnO2 as cathode for magnesium batteries. MnO2 as cathode has been applied in lithium ion batteries but has never been reported in real rechargeable magnesium battery system5. In our study, electrochemical cycling shows this material yielded a capacity over 200 mAh/g during both discharge (Mg2+ insertion) and charge ( Mg2+ extraction) process between 0.8 and 3.0 V vs Mg2+/Mg. The phase transformation of MnO2 during Mg2+ intercalation/deintercaltion was investigated by ex-situ XRD. The morphology change of MnO2 at different stage of charge (SOC) was followed by SEM. The reversible mechanism was further investigated using XPS, which suggests the red-ox process of Mn ion at charge and discharge process. The high capacity and reversible behavior of MnO2 indicate this material could be a candidate cathode for rechargeable magnesium batteries. References: 1. T.Ichitsubo et al J. Mater.Chem., 2011, 21, 11764 2. M. Matsui, J. Power Sources, 2011,196, 7048 3. H.S. Kim, et al , Nat Commun, 2011, 2, 427 4. D. Aurbach, et al, Nature, 2000,407, 724 5. Y. Kadoma, et al J. Phys.Chem. B, 2006, 110, 174

There is a growing interest for electrochemical storage systems with higher storage densities and better safety. A new type of secondary battery based on fluoride ion shuttle has the potential to meeting these demands. The reaction of highly electronegative fluorine with metal leads to the formation of metal fluorides which are accompanied by large change in free energy and thus high electromotoric force. By choosing appropriate metal/metal fluoride combinations, electrochemical cells can be built with theoretical gravimetric and volumetric energy densities which exceed the theoretical potential of current Li ion batteries by an order of magnitude. Though few reports are known about attempts to build a high temperature primary battery [1], the battery chemistry of fluoride ion cells was largely overlooked in the past years. The recent report by Potanin et al., [2] revised the interest in this field. Recently, a first proof-of concept was published [3] which shows the principle applicability of a secondary fluoride ion battery. The key success of fluoride ion battery is largely dependent on the fluoride ion transport media. It was known that the tysonite MF3 (M= La and Ce) and fluorite MF2 (M= Ca, Sr and Ba) type compounds are super fluoride ion conductors at high temperatures. However, when they are doped with aliovalent fluorides they conduct at ambient temperatures. We synthesized fast fluoride ion conductors in the La1-xBaxF3-x (x � 0.15) system by mechanical milling. The compounds were characterized by powder XRD and 19F MAS NMR spectroscopy. The fluoride ion conductivity was measured by electrochemical impedance spectroscopy. The highest conductivity is found for La0.9Ba0.1F2.9. Electrochemical cells were built with CuF2 as cathode, La0.9Ba0.1F2.9 as electrolyte and La as the anode. The cells show an initial discharge capacity of approx. 200 mAh/g at 130 °C with a current density of 5 μA/cm2. The analysis of the electrode confirms the fluoride transfer between the two electrodes. The complete structural and electrochemical characterization results will be described presented and discussed. 1. J. H. Kennedy and J. C. Hunter, J. Electrochem. Soc., 1976, 123(1), 10. 2. A. A. Potanin and N. I.Vedeneev, US patent, US 6379841 B1; European Patent, EP 1873850 A1 3.M. Anji Reddy and M. Fichtner, J. Mater. Chem. (2011) in press

High-performance battery materials are critical for the development of new alternative energy storage systems. While Liâ?"ion batteries are a mature technology for energy storage, disadvantages include cost, Li supply, safety, reliability and stability. Moreover, the electrolyte stability over time is additional major concern for long-term operation and advanced applications. Thus, the discovery, research and development of new transporting ions that can provide an alternative choice to Li batteries are essential for further advancement of energy storage materials. Sodium-based batteries are attractive due to the promise of low cost associated with the abundance of sodium, and enhanced stability of non-aqueous battery electrolytes due to the lower operating voltages. The research dedicated to room temperature sodium ion batteries is still in infancy. Growing body of knowledge related to materials that are suitable for application in Na-ion batteries suggests that tailoring nanoarchitecture of materials offers unprecedented opportunities in utilization of their functional properties. In addition, the nanostructured batteries will move existing battery technologies to higher energy and power densities. In our previous work we show that electrochemical synthesis is a method of choice for preparation of nanoscale architectures that require electronic conductivity, it eliminates the need for conductive carbon additives and binders typically used in electrodes that alter their long-term stability. In addition, the electronically interconnected porosity of the electrochemically prepared nanoscale organized electrodes allows excellent ion transport while the large surface area provides an electrochemically active surface that is not constrained by diffusion limitations. It is at the nanoscale that near theoretical capacity and high power electrodes can be achieved using simple self-organization processes. We have recently developed several Na-ion battery systems exclusively made by nanomaterials that operate in both non-aqueous ( 1M NaClO4 in PC) and aqueous electrolyte (0.5 M Na2SO4 in water). All nanomaterials are directly grown on current collectors without binders and additives. The Na-ion full-cell constructed by a amorphous titanium dioxide nanotube (TiO2NT) as anode and a bilayered V2O5 as cathode has cell capacity â^¼150 mAh/g (limited by the mass of the anode) and shows excellent rate capability. Same cell operating in aqueous electrolyte, at room temperature shows promising cell capacity â^¼50 mAh/g. Furthermore, we developed another aqueous Na-ion full-cell based entirely on MnO2 (low cost and environmentally benign nature) as both anode and cathode. Our results demonstrate feasibility of development of the aqueous, ambient temperature Na-ion rechargeable batteries by employment of electrodes with tailored nanoarchitectures.

Growing concerns over the environmental consequences of burning fossil fuels and their resource constrains, along with the increasing world energy consumption, have spurred great interests in renewable energy from sources such as wind and solar. However, the power from these intermittent sources is constantly varied, making quite challenging for its use and dispatch through the aging electrical grid. One effective way to smooth out the intermittency is to employ electrical energy storage (EES). As such EES has been widely considered as a key enabler of the future grid or smart grid that is expected to integrate a significant level of renewable, while providing electricity or â?ofuelâ? to hybrid and electrical vehicles. Among the potential technologies are electrochemical energy storage technologies or batteries that are capable of storing a large quantity of electricity and releasing it according to demands. There remain significant challenges however for the current technologies to meet the performance and cost matrices for broad market penetration. This paper offers an overview on varied technologies, in particular batteries, and discusses the status, challenges and research needs.

The Vanadium redox flow battery (VRB) was received widely attention due to its attractive features for large scale energy storage. In the vanadium redox flow battery, the function of a membrane/separator is to prevent cross mixing of the positive and negative electrolytes, while still allowing the transport of ions to complete the circuit during the passage of current. The ion exchange membranes as key materials of VRB should possess low vanadium ion crossover, high ionic conductivity, good chemical stability, and low cost. The membranes traditionally used in PEMFC are perfluoro sulfonic acid polymers such as Dupont Nafion®. Although they show both high proton conductivity and chemical stability, the extremely high cost and low ion selectivity of these membranes (high vanadium crossover) have limited their further commercialization. Hence alternative ion exchange membrane materials are being sought. Different kinds of membranes were proposed and fabricated for VRB applications, among which Non fluorinated polymer membranes were mostly investigated due to their low cost and high ion selectivity. However, these membranes suffer from their low chemical stability, which induced by the introduction of ion exchange groups. In this presentation, porous NF membranes were first proposed and applied in VRB application. The concept was based on the idea of tuning Vanadium/protons selectivity via size exclusion. The columbic efficiency and energy efficiency of VRB battery assembled with prepared membrane can be adjusted from 65% to 98% and from 51% to 78% respectively with controlled pore size distribution. The results indicated that: NF membranes show very good potential usage in VRB applications. References 1. Hongzhang Zhang, Huamin Zhang, Xianfeng Li * , Zhensheng Mai, Wenping Wei, Energy & Environmental Science, DOI:10.1039/C1EE02571F 2. Hongzhang Zhang, Huamin Zhang, Xianfeng Li*, Zhensheng Mai, Jianlu Zhang, Energy & Environmental Science 2011, 4 (5), 1676 â?" 1679

Safe, low-cost, high-energy-density and long-lasting rechargeable batteries are highly demanded to address pressing environmental needs for energy storage systems that can be coupled to renewable sources. The aim of this work is addressed to improve the actual performance increasing the density of active sites in the PAN-derived electrodes synthesized. Different functionalization treatments (e.g. thermal and chemical treatments) have been applied, in order to functionalize the activated electrodes. These activated electrodes contain a high amount of N- and O- groups that act as active sites which plays an important role in the positive reaction of the VFRB because they favor the adsorption of a larger amount of vanadium ions onto the electrode surface. As a result, the electron and oxygen transfer processes involved in reaction become accelerated at the surface of derived PAN-based electrodes. The structural and morphological characterization of the treated PAN-based electrodes was carried out by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization using electrochemical impedance spectroscopy and cyclic voltammetric techniques has been applied in order to evaluate the electrocatalytic activity towards the reaction VO2+/VO2+. The derived PAN- based electrodes shows a higher reversibility, higher current collection and lower oxidation potential peaks that the conventional electrodes used en VFRB. In addition, several experiments were carried out to measure the double-layer capacitance, in order to estimate the effective electroactive area and the percentage of active sites. Finally, a small-scale cell prototype of VRFB has been designed in order to verify these findings.

The hydrogen-halogen flow battery (HHFB) is being considered for affordable grid-scale and intermittent renewable electricity storage. It is also envisaged in the long term for use in the electrochemical acceleration of chemical weathering for CO2 capture and sequestration. In charge mode, hydrohalic acid is electrolyzed, forming hydrogen and elemental halogen. In discharge mode, these products are recombined to form hydrohalic acid. Its advantages include high round-trip efficiency and inexpensive reactants. The required storage energy and power characteristics for leveling intermittent wind and photovoltaic power sources will be presented. It will be shown that solid-electrode batteries typically store two orders of magnitude too little energy per unit of required power, thereby demonstrating the advantage of a flow battery. A quantitative model for the HHFB using chlorine and bromine as the halogen will be presented, taking into account the four major loss mechanisms: cathode and anode overpotentials, electrolyte ohmic loss, and neutral reactant mass transport loss. Best operating parameters for "base case" and for "dream case" engineering parameters will be identified. Optimization is predicted to enable operation at > 90% voltage efficiency at current densities >1 A/cm2 in both electrolytic and galvanic modes.

Porosity, both at nanoscale (e.g. single particles of active material) and micron-scale (e.g. composite electrodes), has significant impact on the performance of energy storage systems such as lithium-ion batteries. In this presentation, quantitative assessment of three-dimensional structures will be demonstrated using three examples related to energy storage materials: (1) Nanoporous nickel oxide plates 100-150 nm in width and 10-30 nm in thickness were synthesized by thermal decomposition of hydrothermally-prepared nickel hydroxide crystals. The pore and domain structures were characterized using STEM tomography and aberration-corrected TEM, respectively. The process of nickel hydroxide decomposition was also observed directly by in-situ TEM experiments. The porosity calculated from the measured decrease in volume upon decomposition and the theoretical volume change obtained from the unit cell volumes of Ni(OH)2 and NiO were found to be in good agreement with the pore volume measured from the tomograms. (2) Model mesoporous TiO2 thin films with pore sizes varying from 3 to 40 nm were synthesized by dip-coating of tin-doped indium oxide glass substrate using soft-templating methods. STEM tomography was used to characterize the three dimensional porous network and the orientation of pores with respect to the Li-insertion channels in TiO2. Also, the crystalline nano-domains and their orientation with respect to the pores were studied using TEM. (3) The distribution of pores, active material , and carbon-filled binder was studied in a LiNi1/3Mn1/3Co1/3O2 composite cathode using serial sectioning in a dual-beam FIB/SEM followed by three-dimensional reconstruction.

A major challenge related to integrating renewable energy sources with the electrical energy grid is the high frequency of short-term transients. Balancing these transients requires energy storage devices that operate on very short time scales for thousands of charge/discharge cycles. We recently demonstrated1 that open-framework materials with the Prussian Blue structure may be used as high performance battery electrodes. These electrodes operate at extremely high rates (up to 83C) for over 40,000 deep discharge cycles in high-safety aqueous alkali ion electrolytes. Their low cost, scalable syntheses and operation also make them desirable for use in batteries integrated with the electrical grid. We will discuss the physical properties and electrochemical performance of a variety of Prussian Blue analogue electrode materials. References: 1. Wessells, C. D., Huggins, R. A., and Cui, Y. Nature Communications, in press, 2011.