Symposium S.EN12 : Materials for Safe and Sustainable Electrochemical Energy Storage

Efforts to convert sustainable solar energy into a storable form of chemical fuels have generated much interest. Among various technologies, photoelectrochemical (PEC) water splitting, which is capable of producing hydrogen fuel in an environmentally friendly manner, is being intensively studied. Because PEC water splitting has an operating principle similar to that of photovoltaic devices, a good photovoltaic material must be a good candidate for a photoelectrode of PEC solar water splitting. In this talk, I will present the recent research efforts of our laboratory to produce highly efficient and stable photoelectrodes, Cu(In,Ga)Se₂ (CIGS)-based heterojunction. First, I will discuss the application of functional overlayers acting as a protective layer and reduced graphene oxide as a catalyst binder to improve long-term stability of the photocathodes.[1], [2] Next, I will present the enhancement of PEC performance of CIGS photocathodes by introducing a greater degree of surface band bending with ZnS/CdS double buffer layers. Finally, we demonstrate a bias-free water splitting PEC cell consisting of the surface band-modified CIGS photocathode with the ZnS/CdS double buffer and a halide perovskite solar cell, and an IrOx anode, with a STH efficiency over 9 %.

[1] B. Koo, S. Nam, R. Haight, S. Kim, S. Oh, M. Cho, J. Oh, J. Lee, B. Ahn, B. Shin, "Tailoring Photoelectrochemical Performance and Stability of Cu(In,Ga)Se₂ Photocathode via TiO₂-Coupled buffer Layers", ACS Applied Materials & Interfaces 9, 5279 (2017).
[2] B. Koo, S. Byun, S. W. Nam, S. Y. Moon, S. Kim, J. Y. Park, B. T. Ahn, B. Shin, "Reduced Graphene Oxide as a Catalyst Binder: Greatly Enhanced Photoelectrochemical Stability of Cu(In,Ga)Se₂ Photocathode for Solar Water Splitting", Advanced Functional Materials 28, 16 (2018).

Lithium-sulfur (Li-S) batteries hold great potential given their theoretic energy density of 2600 Wh/kg, low cost, and S abundance. However, Li-S batteries are currently being retarded from commercialization due to several severe issues. On the S cathode side, S is highly insulating electrically and ionically. Thus, conductive materials are essential to maintain S cathodes accessible to electrons and ions. To date, many carbon materials such as carbon black, carbon nanotubes and graphene are widely used as conductive materials in various battery systems. Nevertheless, there lacks a comparative study on identifying their effects on the electrochemical properties of the S cathode. Knowing that optimizing the configuration and composition of the carbon conductive materials is the most inexpensive and simple way to improve the electrochemical performance of Li-S batteries, we recently conducted a fundamental study on the effects of a carbon black (Super P, SP) and a nitrogen-doped graphene nanosheets (NGS) on S cathodes. Experimental results showed that the S@SP (SSP) cathode and S@NGS (SNGS) cathode have different structures, interactions with the active materials and electrochemical impedance spectra, and thus exhibited different electrochemical properties and performance. For SSP, its initial specific capacity is as twice as that of SNGS but fade rapidly. In contrast, SNGS exhibits better capacity retention and rate cyclability. We also found that by simply mixing the SP and NGS mechanically, the S@SP@NGS (SSP/NGS) cathode shows both good capacity and cyclability. The fundamental mechanisms of these phenomena are discussed and a charge transfer model for these electrodes is proposed.

Polymer electrolyte-based Lithium metal batteries are attractive for safe energy storage with high-energy-density. However, various material challenges present inside, such as interfacial stability with electrodes and low ionic conductivity. In this talk I will present material characterizations and designs to understand and address some challenges inside. Specifically, a combination of stimulated Raman scattering microscopy and AFM measurements first illustrate how mechano-chemical coupling at the lithium/polymer electrolyte interface affect dendrite formation in polymer electrolyte. Second, interfacial designs are developed to suppress the oxidation of PEO electrolyte at the cathode side, and thus long-term cycling is achieved in 4V LCO or NMC-PEO-Li cells. The capacity retention reaches 85% after 200 cycles.

Li-ion batteries are the critical enabling technology for the portable devices, electric vehicles (EV), and renewable energy. However, the safety and energy density of current Li-ion batteries still need to be improved to satisfy the requirments for these applications. We systematically investigated the electrochemical performance of the nonflemable fluorinated orgnic electrolytes and solid state electyrolytes for high energy Li and Li-ion batteries. The Li dendrite formation in liquid electrolyte and solid state Li metal batteries was proposed and validiated. The critical issues of these safe electrolytes are also discussed.

Abstract: The thermodynamically instable nature of lithium metal in liquid electrolytes significantly plagues the implementation of the high-energy rechargeable lithium battery technology in electrical vehicles. Although many approaches have been proposed to rescue Li metal anodes, most of the work are performed in small-scale coincellsand tested in the conditions drastically different from the reality.A full knowledge of Li metal activities at the cell level is lacking but extremely critical for the success of developing next-generation rechargeable Li metal batteries. This talk will discuss the fundamental challenges of utilizing Li metal anode in at cell-level and demonstrate a prototypic 350 Wh/kg lithium metal pouch cell > 250 stable cycling.

Li metal anode materials are the most promising anodes for next-generation Li batteries. The poor interfacial stability in the battery has been the primary issue hindering their practical application. In this talk, I will present approaches developed in my group to design and architect the solid-electrolyte interphase (SEI), particularly using a chemically and electrochemically active organic makers. The maker coated on the Li surface can generate the SEI by preferentially chemically occupying the Li surface site and subsequently electrochemically self-decomposing at the interface. The maker-derived SEI presented desirable ionic conductivity, density, homogeneity, and mechanical strength. The SEI reinforced by the organic maker shows much better stability than the SEI reinforced by electrolyte additive strategy, which is the current state-of-art and commercially used solution to SEI stability issue. Our findings open a new way to design stable electrochemical interfaces for battery materials.

There are increasing demands for high-performance electrochemical-energy-storage devices, such as lithium ion batteries and fuel cells, for microelectronics, electrical vehicles, and other applications. Generally, such devices are operated through charge separation in one electrode, during which electrons and ions are transported respectively through the external circuit and the electrolyte and recombined in the other electrode, accomplished through the redox reactions occurred in the electrodes. Material design that lead to better charge separation, transport, and recombination, in this context, holds great promise towards better electrochemical-energy-storage devices. In this presentation, the design of electrode materials and electrolytes, which lead to better performance lithium-ion batteries, lead acid batteries, and fuel cells will be discussed.

Enabling long cyclability of high-voltage oxide cathodes is a persistent challenge for all-solidstate batteries, largely due to their poor interfacial stabilities against sulfide solid electrolytes. While protective oxide coating layers such as LiNbO3 (LNO) have been proposed, its precise working mechanisms are still not fully understood. Existing literature attributes reductions in interfacial impedance growth to the coating’s ability to prevent interfacial reactions. However, its true nature is more complex, with cathode interfacial reactions and electrolyte electrochemical decomposition occurring simultaneously, making it difficult to decouple each effect. Herein, we utilized various advanced characterization tools and first-principles calculations to probe the interfacial phenomenon between solid electrolyte and high-voltage cathode. We segregated the effects of spontaneous reaction between the electrode and electrolyte at the interface and quantified the intrinsic electrochemical decomposition of LPSCl during cell cycling. We will also discuss a few important aspects related to the mechanical compatibility of electrode and electrolyte in all solid state batteries.

Under the influences from both classical analytical electrochemistry pursuing ideal ionic behavior at infinitely diluted state and classical physical electrochemistry pursuing the most conductive ionics, the study of non-aqueous electrolytes have been confined within the narrow concentrations around 1 molarity. This confinement was only breached in recent years when investigators discovered that unexpected properties often arise from excessively concentrated electrolytes, benefitting mechanical, thermal, transport, interfacial structure as well as interphasial chemistries. The most extreme examples of the super-concentrated electrolytes include the high voltage (4 V) aqueous electrolytes and non-aqueous electrolytes that enables highly aggressive battery chemistries (Li-metal, high NMC, etc).
Aside from their various novelties in physical, transport and electrochemical/interphasial properties, super-concentrated electrolytes enhances the overall safety of batteries, primarily because solvent molecules therein were bound by new liquid structures that never exists previously.
In this talk, I will briefly summarize the current status of these battery chemistries.

Rising concerns on sustainability have brought great interest for ecofriendly energy storage solutions and motivated searching for sustainable electrode chemistry for lithium ion batteries (LIBs), most widely used portable power sources. Organic materials, which are derived from biomass or naturally abundant resources, are attractive electrode candidates for LIBs due to their minimal environmental footprint. The chemical tunability of organic materials can additionally allow a design flexibility required for electrodes in various types of rechargeable batteries. Especially, exploiting redox-active molecules in biological energy transduction, which have been optimized over many years of natural selection, is an appealing approach to green energy storage combined with the demonstrated efficiency. Biological energy transductions share many aspects with rechargeable battery operation in underlying redox mechanism with respect to unidirectional transportation of charged ions (H⁺ or Li⁺) and electrons to a redox-active center, resulting in reversible energy storage. This analogy suggests a potential feasibility for utilizing new redox center from biological reactions to energy storage in rechargeable batteries.

Nicotinamide adenine dinucleotide (NAD⁺) is one of the most well-known redox cofactors carrying electrons. The redox-active NAD⁺ motif is involved in over 80 % of all biotransformations and electron transfer reactions in natural systems by carrying charged ions and electrons from one reaction to another. The versatility of NAD⁺ motif may present promises in its electrochemical activity in other energy storage systems such as LIBs. Nevertheless, the exploration of its applicability as an electrode in conventional LIB setup is not trivial, since its charged state (NAD⁺) and the dissolved nature are not compatible with the electrode fabrication requirements, where active compounds are generally in neutral state and ready for process into solid electrode. While significant portion of the energy carrying molecules are in charged states and/or dissolved states in the biocells, a general fixation strategy would aid in expediting the exploration of these bio redox molecules.

Herein, we exploited the NAD⁺ motif, one of the most versatile redox centers in nature, to facilitate reversible electrochemical energy storage in LIB system for the first time. To exploit the redox reaction of NAD⁺ motif in LIBs, nicotinamide cofactor was modified into a simple structure bearing the redox-active part to produce nicotinamide analogue (mNAD⁺). The charged mNAD⁺ were crystallized using counter anions such as I^-, Br^-, and Cl^-, resulting in a neutral and solid-state powder. It is demonstrated that these NAD⁺-derivatives (mNAD-X, X= I^-, Br^-, and Cl^-) are capable of reversibly facilitating lithium coupled electron transfer in solid electrode form, exhibiting the intrinsic redox capability of NAD⁺. Combined experimental and theoretical calculations revealed that mNAD-X retains the intrinsic redox activity of natural NAD⁺ motif, accompanying lithium coupled electron transfer which is similar to the proton-coupled electron transfer mechanism in the biological systems. Furthermore, the operating voltage and capacity are tunable by altering the anchoring anion species without modifying the redox center itself. This work not only demonstrates the redox capability of NAD⁺, but also suggests that anchoring the charged molecules with anion incorporation is a viable new approach to exploit various charged biological cofactors in rechargeable battery systems.

Binary oxides with novel nanoarchitectures are increasingly explored for their application in energy storage devices. The nanoarchitecture of these oxides is usually varied via synthesis route, which usually requires complex technologies, expensive equipment, andharmful organic reagents or surfactants, which might further hinder their application. Hence, it is highly desirable to explore facile synthesis strategies, which are cost-effective, simple, and environmentally friendly to get “green” nanomaterials. Recently, bio-templatinghas emerged as a promising technique for the synthesis of Co₃O₄capacitors [[i]]. Nature offers us various and excellent bio-templates[[ii],[iii],[iv]] such as bamboo, pig bone, crab shells, lotus pollen grains, bacteria [[v]], leaf [[vi]], sorghum straw [[vii]], butterfly wing [[viii]], jute fibers [[ix]], and cotton [ix]. Such bio-templatesexhibit precise widths and lengths, complex exterior and interior surfaces, and uniform geometries, all of which have inspired researchers to produce multiscale hybrid inorganic materials that exhibit hierarchical morphologies.

In this work, we present a comparative study of the electrochemical performance of tubular MCo₂O₄ (M= Mn, Ni, Cr) microstructures prepared using cotton fiber as a biotemplate. The as-obtained templated MCo₂O₄(M= Mn, Ni, Cr) structures inherit the morphology and microstructure of cotton fiber. The electrochemical performance of the electrode made up of tubular MCo₂O₄(M= Mn, Ni, Cr) structure was evaluated in 3M KOH aqueous electrolytes. The large-surface-area of tubular MCo₂O₄(M= Mn, Ni, Cr) microstructures has a noticeable pseudocapacitive performance with a capacitance of 161 F/g, 190 F/g, and 231 F/g at 1 A/g current density and 378.13F/g , 407.16 F/g , and 403.39 F/g at 2 mV/s scan rate for MnCo₂O₄, NiCo₂O₄, and CrCo₂O₄ respectively. Also a Coulombic efficiency ~100%, and excellent cycling stability with capacitance retention of about 91%, 100%, and 92% for MnCo2O4, NiCo₂O₄, and CrCo₂O₄ respectively even after 5,000 cycles. These obtained tubular MCo₂O₄(M= Mn, Ni, Cr) microstructure display superior electrochemical performance in aqueous 3M KOH electrolyte with peak power density reaching 295.5 W/Kg, 296.3 W/Kg, and 293.5 W/Kg, and energy density 7.8Wh/kg, 9.3 Wh/Kg, and 11.1 Wh/Kg, for MnCo₂O₄, NiCo₂O₄, and CrCo₂O₄ respectively. The superior performance of tubular MCo₂O₄(M= Mn, Ni, Cr) microstructure electrode is attributed to their high surface area and adequate pore volume distribution, which allows effective redox reaction and diffusion of hydrated ions.





[i]. Yan, D., Zhang, H., Chen, L., Zhu, G., Li, S., Xu, H. and Yu, A., 2014. ACS applied materials & interfaces, 6(18), pp.15632-15637.

[ii]. Fan, T.X., Chow, S.K. and Zhang, D., 2009. Progress in Materials Science, 54(5), pp.542-659.

[iii]. Sotiropoulou, S., Sierra-Sastre, Y., Mark, S.S. and Batt, C.A., 2008. Chemistry of Materials, 20(3), pp.821-834.

[iv]. Zhou, H., Fan, T. and Zhang, D., 2011. ChemSusChem, 4(10), pp.1344-1387.

[v]. Shim, H.W., Lim, A.H., Kim, J.C., Jang, E., Seo, S.D., Lee, G.H., Kim, T.D. and Kim, D.W., 2013. Scientific reports, 3, p.2325.

[vi]. Han, L., Yang, D.P. and Liu, A., 2015. Biosensors and Bioelectronics, 63, pp.145-152.

[vii]. Song, P., Zhang, H., Han, D., Li, J., Yang, Z. and Wang, Q., 2014. Sensors and Actuators B: Chemical, 196, pp.140-146.

[viii]. Weatherspoon, M.R., Cai, Y., Crne, M., Srinivasarao, M. and Sandhage, K.H., 2008. Angewandte Chemie International Edition, 47(41), pp.7921-7923.

[ix] Yan, D., Li, S., Zhu, G., Wang, Z., Xu, H. and Yu, A., 2013. Materials Letters, 95, pp.164-167.

The preparation of transition metal oxides has attracted the interest of many research groups in recent years because of their unique properties and envisioned applications in electronics, optics, magnetic materials, and energy storage devices. Co₃O₄ belongs to a class of complex oxides known as spinels with the chemical formulas of AB₂O₄ in which A ions are generally divalent cations occupying tetrahedral sites, and B ions are trivalent cations in octahedral sites. Co₃O₄ has been explored for its good pseudocapacitance along with othere stablished materials, in which charge is stored using redox-based Faradic reactions. Many synthesis techniques such as solvothermal synthesis[[i]], sol-gel method [[ii]], electrospinning method [[iii]] and lithography technique [[iv]], a hydrothermal technique[[v],[vi]], have been explored for the synthesis of nanostructured materials. However, many of these strategies generally require complex technologies, expensive equipment, andharmful organic reagents or surfactants, which might further hinder their application. In the present work, we usedaone-stepfacile procedure for the synthesis of biomorphic Co₃O₄ using cotton fiber as a bio-template.
Template-assisted facile synthesis of tubular Co₃O₄ microstructures and its electrochemical performance was studied to understand its use as a potential electrode material for supercapacitors. Tubular porous Co₃O₄ microstructures were synthesized using cotton fibers as bio-template. The as-obtained templated Co₃O₄ structure inherits the morphology and microstructure of cotton fiber. The electrochemical performance of the electrode made up of tubular Co₃O₄ structure was evaluated in 3M KOH, NaOH, and LiOH aqueous electrolytes. The large-surface-area of tubular Co₃O₄ microstructure has a noticeable pseudocapacitive performance with a capacitance of 401 F/g at 1 A/g and 828 F/g at 2 mV/s, a Coulombic efficiency averaging ~100%, and excellent cycling stability with capacitance retention of about 80% after 5,000 cycles. Overall, the tubular Co₃O₄ microstructure displayed superior electrochemical performance in 3M KOH electrolyte with peak power density reaching 5,500 Wh/kg and energy density exceeding 22 Wh/kg. The superior performance of tubular Co₃O₄ microstructure electrode is attributed to its high surface area and adequate pore volume distribution, which allows effective redox reaction and diffusion of hydrated ions. The facile synthesis method can be adapted for preparing various metal oxide microstructures for possible applications in catalysis, electrochemical, sensors, and fuel cells applications.






[i]. Mai, L.Q., Yang, F., Zhao, Y.L., Xu, X., Xu, L. and Luo, Y.Z., 2011. Hierarchical MnMoO ₄/CoMoO₄heterostructured nanowires with enhanced supercapacitor performance. Nature communications, 2, p.381.

[ii]. Debecker, D.P. and Mutin, P.H., 2012. Non-hydrolytic sol–gel routes to heterogeneous catalysts. Chemical Society Reviews, 41(9), pp.3624-3650.

[iii]. Liu, H., Kameoka, J., Czaplewski, D.A. and Craighead, H.G., 2004. Polymeric nanowire chemical sensor. Nano letters, 4(4), pp.671-675.

[iv]. Cen, C., Thiel, S., Mannhart, J. and Levy, J., 2009. Oxide nanoelectronics on demand. Science, 323(5917), pp.1026-1030.

[v]. Adhikari, H., Ghimire, M., Ranaweera, C.K., Bhoyate, S., Gupta, R.K., Alam, J. and Mishra, S.R., 2017. Synthesis and electrochemical performance of hydrothermally synthesized Co₃O₄nanostructured particles in presence of urea. Journal of Alloys and Compounds, 708, pp.628-638.

[vi]. Zequine, C., Bhoyate, S., Siam, K., Kahol, P.K., Kostoglou, N., Mitterer, C., Hinder, S.J., Baker, M.A., Constantinides, G., Rebholz, C. and Gupta, G., 2018. Needle grass array of nanostructured nickel cobalt sulfide electrode for clean energy generation. Surface and Coatings Technology, 354, pp.306-312.

Nowadays the binary metal oxides are highly use as supercapacitor electrodes in energy storing devices. Particularly NiCo₂O₄ has shown promising electrocapacitive performance with high specific capacitance and energy density. The electrocapacitive performance of these oxides largely depends on their morphology and electrical properties governed by their energy band-gaps and defects. The morphological structure of NiCo₂O₄ can be altered via synthesis route while energy band-gap could be altered by doping. Also, doping can enhance crystal stability and bring in grain refinement, which can further enhance the much-needed surface area for high specific capacitance. In view of the above, this study evaluates the electrochemical performance of Ca-doped Ni_1-xCa_xCo₂O₄(0 ≤ x ≤ 0.8) compounds. The Ni_1-xCa_xCo₂O₄ samples were prepared via a facile and cost effective hydrothermal technique by varying Ca to Ni molar ratio. Physical, morphological, and electrochemical properties of Ni_1-xCa_xCo₂O₄ were observed on the variation of Ca. The increase of Ca concentration in Ni_1-xCa_xCo₂O₄ leads to the morphological transformation from nanoplates to urchin-like structure with an increase in the surface area reaching up to 73.2m2/g for x=0.2. The higher specific capacitance of 247.5F/g at a current density of 1 A/g, 934.4 F/g at 2 mV/s scan rate, the energy density of 14.8 Wh/kg and power density of 136.3 W/kg in 3M KOH electrolyte was observed for x = 0.6 sample. An increased retention capacity ∼255% measured at 5 A/g current density and Coulombic efficiency of 99%. The density functional theory (DFT) calculations of the electronic density of states identified Ni_1-xCa_xCo₂O₄ with optimal band-gap varies from 2.67 eV to 3.88 eV for x=0 to x=0.8. Such impressive electrocatalytic activity results in the high intrinsic electronic conductivity and can largely improve the interfacial electroactive sites as well as charge transfer rates. This work of doping NiCo₂O₄ by calcium is very nobel which will stipulates promising applications for electrodes in future supercapacitors.

Energy Storage Systems (ESS) will play a central role in reducing fossil fuel consumption and greenhouse gas emissions by providing solutions to store energy produced from renewable sources and to implement electrical vehicles.

Graphite is the traditional material employed in standard rechargeable batteries or hybrid electrochemical capacitors, but it shows restrictions because of its limited intrinsic capacity, moderate Li-ion intercalation and capacity rate. Also, Li and Co, all standard materials for hybrid capacitors and Li-ion batteries, are limited resources, and the European Union (EU) is dependent on external supply.

To solve these shortcomings, NOEL aims at developing new, low-cost and environmentally friendly layered semiconductor-carbon composites for their use as innovative electrodes in the next generation of batteries or supercapacitors. Specifically, NOEL will provide new carbon substrates and carbons decorated with layered sulfide nanoparticles and will test their performance as electrodes for supercapacitors and post-Li batteries (Na, Mg, or Ca), looking for improved performance, low price, high material availability being locally produced in EU, and environmentally friendly properties.

For that purpose, NOEL consists of 2 European universities (Zaragoza University, UNIZAR, in Spain, and Poznan University of Technology, PUT, in Poland), and 1 European research institution (National Institute of Chemistry, NIC, in Slovenia). The balancing expertise includes development and characterization of nanomaterials (UNIZAR), and manufacture and testing of batteries (NIC), or supercapacitors (PUT).

Iron (III) fluoride (FeF₃) is considered as a potential cathode for sodium-ion batteries (SIBs) due to its high capacity and low cost. However, the particle pulverization upon cycling generally results in rapid degradations in its structure and capacity. Here, we introduce a free-standing nanoconfined FeF₃ cathode and a novel electrolyte salt sodium-difluoro(oxalato)borate (NaDFOB) for SIBs. The assembled cells show high discharge capacity up to ~ 230 mAh g^-1 at the rate of 20 mA g^-1 (~200 mAh g^-1 at 100 mA g^-1) and capacity retention up to ~ 70% after 100 cycles, which represent the best results reported on FeF₃ in Na-ion electrolytes. The achieved high performance can be attributed to the synergic protection provided by the nanoconfined FeF₃ electrode and the NaDFOB electrolyte. Post-mortem analysis and quantum mechanics show that DFOB anion facilitated the formation of a thin cathode electrolyte interphase (CEI) at the surface of FeF₃-carbon nanofibers (CNFs) via oligomerization.

Despite much progress, developing a cost-effective and environmental-friendly method to upgradeearth-abundant coal into high value-added products is still a grand challenge. Here, we report a one-stepand facile approach to synthesize graphene based materials from coal under ambient conditionsviadirect CO2 laser scribing. The obtained laser scribed graphene from coal (C-LSG) has been well charac-terized, showing good electrical conductivity (12U/square), high electrochemical sensitivity and ionicstorage properties. These properties make C-LSG a multifunctional material for applications in Jouleheating, electrochemical dopamine sensing, and supercapacitors. Moreover, when electrochemicallydeposited with FeNi hydroxide, the hybridized FeNi/C-LSG shows impressive electrocatalysis perfor-mance toward oxygen evolution reaction. As such, this direct laser scribing of coal into graphene basedmaterials can not only potentially expands new business opportunities by adding coal into the value-chain of industries that usually do not use coal as the starting materials in their manufacturing pro-cesses but also brings down the cost of the graphene based materials, which would make theirdeployment in variousfield more economically attractive.

Since any electrochemical reactions occur at the interface between electrodes and electrolytes, an electrode with well-defined open pores and high surface area is preferred for an efficient electrochemical system, such as supercapacitors and batteries. Recently, it has been reported that a conducting polymer, polyaniline, can be crosslinked by phytic acid, to form a conducting hydrogel with hierarchical open-pores. Here, we present a facile fabrication method of a conducting porous electrode, by a doctor-blading technique of the polyaniline hydrogel paste and successive dehydration process. We carefully investigated the effect of compositions in preparation of PANI on its pore morphology and electrical property. It turns out that as initiator/crosslinker contents increase or monomer content decreases, the PANI conducting hydrogel has denser morphology with decreased pore size, resulting in higher electrical conductivity. Notably, hierarchical pores, ranging from tens of nanometers to tens of micrometers in size, are well developed, even in the dense porous PANI film. Due to its characteristic pore morphology and redox activity, the PANI film could serve as an efficient electrode for a pseudo-capacitor. In the 3-electrode configuration, the porous PANI electrode prepared at the optimized composition, in the pristine form without any conducting additive, exhibited ~690 F/cm³ of volumetric capacitance, which is much higher than those of the PANI based capacitors reported so far. Finally, we fabricated a practical capacitor with two symmetric PANI hydrogel electrodes, which shows 110 mF/cm³ of volumetric capacitance with improved cycle stability of 80 % retention rate for 5000 cycles.

Molten sodium batteries offer a promising technology for grid scale energy storage. The molten sodium anode minimizes dendrite formation, while the elevated operating temperature minimizes hazards associated with assembly of MWh capacities at room temperature. Typical molten sodium battery chemistries such as Na-S and Na-NiCl₂ (ZEBRA) operate near 300 and 200 °C, respectively. Driving operating temperatures down to 100 °C would decrease operating costs, minimize materials aging effects, and enable use of low temperature polymeric seals. Successful development of a molten sodium battery that operates near 100 °C, however, requires significant reengineering of the catholyte. Besides being molten at 100 °C, such a catholyte must possess (1) electrochemically reversibility, (2) chemical stability, (3) high ionic conductivity, and (4) minimal reactivity to molten sodium metal. Herein we describe the development of fully inorganic molten salt catholytes based on mixtures of NaI and group 13 halide salts that satisfy these requirements. The NaI enables use of the facile, energy-dense I^-/I₃^- redox couple, while targeted group 13 halide salts engender sufficiently low melting points over a wide range of NaI concentrations. These molten salts demonstrate good electrochemical I^-/I₃^- reversibility and at high I^- concentrations near 100 °C, without use of any organic solvent. We characterize the ionic conductivity and electrochemical kinetics of these salts for a variety of compositions and electrode materials. Full cell cycling using a molten sodium anode and a ceramic NaSICON separator demonstrates promising performance and indicates points for further electrolyte refinement. Together, these molten salts offer a pathway for safe, reliable, grid-scale energy storage.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Improved energy storage technologies have received intense attention since there is a fast-growing market for portable electronic devices such as the internet of things. Micro-supercapacitors possess a remarkable feature of high electrochemical performance and relatively small volume in which they can reach high power density and fast charge-discharge rates. In contrast to batteries, these next-generation energy storage devices are fast, efficient and environmentally friendly with longer life cycles without losing performance. We developed a novel integrated, flexible glassy carbon micro-supercapacitor technology with 30 interdigitated fingers as seen in figure 1. We compacted the complete electrical routing path and contact pads within the device's area, utilizing through-via bottom electrodes. The glassy carbon electrode achieved a surface area of 0.1655 and mass of 0.278 mg. The device showed a specific capacitance of 963.979 uf/cm² for a scan rate of 0.1 v/s, which is greater than the values reported for vertically aligned carbon nanotubes . In addition, it achieved an energy density of, and a power density of , higher than those reported from multilayer reduced graphene oxide [2].


Hsia, B.; Marschewski, J.; Wang, S.; In, J. Bn; Carraro, C.; Poulikakos, D.; Grigoropoulos, C. P.; Maboudian, R. Highly Flexible, All Solid-State MicroSupercapacitors from Vertically Aligned Carbon Nanotubes. Nanotechnology 2014, 25 (5), 55401.
J. J. Yoo, K. Balakrishnan, J. Huang, V. Meunier, B. G. Sumpter, A. Srivastava, M. Conway, A. L. Mohana Reddy, J. Yu, R. Vajtai, P. M. Ajayan, Nano Lett. 2011, 11, 1423.

Nowadays nickel cobaltite, NiCo₂O₄ with excellent electrochemical properties has become good source of energy storage electrode for electrochemical supercapacitor. NiCo₂O₄ has shown promising electrocapacitive performance with high specific capacitance and energy density. The electrocapacitive performance of these oxides highly depends on their morphology and electrical properties governed by their energy band-gaps and defects. The variation of morphological structure can be occur via synthesis route, on the other hand energy band-gap could be changed by doping. Also, doping can enhance crystal stability and bring in grain refinement, which can further enhance the much-needed surface area for high specific capacitance. This study evaluates the electrochemical performance of Al-doped Ni_1-xAl_xCo₂O₄ (0 ≤ x ≤ 0.8) compounds. These Ni_1-xAl_xCo₂O₄ samples were prepared via a hydrothermal technique by varying Al to Ni in molar ratio. Physical, morphological, and electrochemical properties of Ni_1-xAl_xCo₂O₄ were observed on the variation of Al. The characterization was performed by using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Quantachrome Instrument, and X-Ray Photoelectron Spectroscopy (XPS). XRD confirms the formation of phase pure Ni_1-xAl_xCo₂O₄ (0 ≤ x ≤ 0.8). The increase of Al concentration in Ni_1-xAl_xCo₂O₄ leads to the morphological transformation from urchin like spheres to nanoplates like structure with an increase in the surface area reaching up to 107.2 m²/g for x=0.4. XPS give the elemental composition of Al dope Ni_1-xAl_xCo₂O₄ (0 ≤ x ≤ 0.8). The electrochemical performace was observed using Cyclic Voltammetry (CV) , Galvanostatic Charge Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) measurement. The higher specific capacitance of 511.5 F/g at 2 mV/s scan rate, 267.9 F/g at a current density of 0.5 A/g, and the energy density of 12.4 Wh/kg in 3M KOH electrolyte was observed for x = 0.0 sample. The power density of 4660.4 W/kg was observed for x = 0.8 sample. The capacitance retention ∼97%, 108.52% and Coulombic efficiency of 100%, 99.24% for x=0.0 and x=0.8 respectively. All these results indicate Al dope NiCo₂O₄ composites electrode shows promishing electrocatalytic activity results in the high intrinsic electronic conductivity, can largely improve the interfacial electroactive sites, increase charge transfer rates and help to stabilize the structure of compound.

Transition metal oxides have been extensively studies as an electrode material for the energy storage devices including fuel cell, Li-ion batteries, and electrochemical capacitors. Nowadays, it has been found that ternary metal oxides with two different metal cations exhibit much higher electrochemical activities because of their complex chemical composition and effect of multiple metal ions [[1]]. NiCo₂O₄ urchin like Nano-flower are decorated by graphitic carbon nitride (g-C₃N₄). Graphitic carbon nitride is a graphene derivative, has been explored due to its interesting electronic feature, low price, and high environmental-friendly features [[2], [3]]. We have prepared first NiCo₂O₄ by hydrothermal method and decorated NiCo₂O₄ by g-C₃N₄ composite material by calcination of urea. The structural property of NiCo₂O₄ was confirmed by X-ray diffraction (XRD) and found phase pure crystalline structure. On the other hand, presence of g-C₃N₄ is confirmed by Scanning Electron Microscopy (SEM) which show the NiCo₂O₄ with g-C₃N₄ have thicker urchin Nano-flowers compare to NiCo₂O₄ without it. X-ray Photoelectron Spectroscopy (XPS) confirm the presence of graphitic carbon on NiCo₂O₄ composition. The obtained surface area by using Quanta-chrome surface area analyzer is 40.1 m²/gm for NiCo₂O₄ and 63.7 m²/gm for NiCo₂O₄ decorated with g-C₃N₄. Higher surface area could provide more channels for the access of hydrated electrolyte ions, so we can assume that g-C3N4 decorated NiCo₂O₄ have shown better electrochemical performance compare to NiCo₂O₄ alone. The electrochemical performance was observed using Cyclic Voltammetry (CV), Galvanostatic Charge Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) measurement. The higher specific capacitance of 601 F/g and 712 F/g at 2 mV/s scan rate, specific capacitance of 289 F/g and 394F/g at a current density of 0.5 A/g, and the energy density of 13 Wh/kg and 14.5 Wh/kg observed for NiCo₂O₄ and g-3N4 decorated NiCo₂O₄ respectively, when measure in 3M KOH electrolyte. Furthermore, the observed power density of 4740 W/kg and 5010 W/Kg, capacitance retention ∼97% and 99% and Coulombic efficiency of 97% and 99.5% for NiCo₂O₄ and g-3N4 decorated NiCo₂O₄ respectively. This project will be promising for future energy storing devices.



[1]. Cheng, F., Shen, J., Peng, B., Pan, Y., Tao, Z. and Chen, J., 2011. Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts. Nature chemistry, 3(1), p.79.

[2]. Wang, X., Maeda, K., Thomas, A., Takanabe, K., Xin, G., Carlsson, J.M., Domen, K. and Antonietti, M., 2009. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nature materials, 8(1), p.76.

[3]. Zhang, Y., Zhou, Z., Shen, Y., Zhou, Q., Wang, J., Liu, A., Liu, S. and Zhang, Y., 2016. Reversible assembly of graphitic carbon nitride 3D network for highly selective dyes absorption and regeneration. ACS nano, 10(9), pp.9036-9043

The investigation and development of flexible power sources has motivated the development of flexible, lightweight, binder and current-collector-free electrodes for Li-ion batteries (LIB). For the fabrication of conventional LIB electrode, binder and current collector are introduced to inhibit the collapse of the active materials and maintain the electrode conductivity, respectively. The usage of binders and current collectors contributes nothing but dead weight to the lithium storage, which decreases the energy density of LIBs. Free-standing carbon nanotube ‘buckypaper’ can be fabricated by using both single-walled carbon nanotubes and multi-walled carbon nanotubes (MWCNTs), and their composites with other active electrode materials and then can be used as working electrodes for LIBs. Compared with conventional electrode material in the bulky form, free-standing paper type electrodes have several advantages. First of all, with the removal of the binders and current collector, the dead weight of an electrode is decreased, leading to the increase of usable capacity and specific energy density for the overall battery design. Secondly, the ease of handling the ‘buckypaper’ makes them readily shaped into various forms required in a variety of flexible and lightweight electronic devices. Here, we are proposing the fabrication of free-standing, flexible and foldable MWCNTs/ lithium titanate oxide (Li₄Ti₅O₁₂, LTO) based composite ‘buckypaper’ by a facile, scalable, cost-effective and environmental friendly surface-engineered tape casting (SETC) method. The SETC technique has several advantages such as tunable length, thickness, density, composition and implementation in both batch and roll to roll process. The composite ‘buckypaper’ is demonstrated as anode material for LIB. Electrical conductivity was found to be 4.4×10² Scm^-1 at room temperature. The composite electrode shows the specific capacity of ~150 mAhg^-1 at 0.2 C rate which is mainly attributed to enhanced electric and ionic transfer during electrochemical reactions.

Acknowledgements
This project is part of the implementation plan for the United Arab Emirates Space Agency’s ST&I Roadmap and it falls under Level 1 ST&I area of "space power and energy storage" and level 2 "energy storage". The project is aimed at developing enabling technologies for promising mission and system concept; in particular, an in-house prototype of lithium-ion battery. The project can potentially result in a commercially viable lithium-ion battery technology for spacecrafts/satellites. This work is funded by the United Arab Emirates Space Agency, Space Missions’ Science and Technology Directorate, Reference M04-2016-001.

Supercapacitors have the potential to bridge the gap between traditional capacitors and secondary batteries, providing high power and energy densities that may be used for clean energy storage, hybrid vehicles, and other applications. Manganese oxides, including Mn₂O₃, are inexpensive, environmentally benign materials that have shown promising performances as supercapacitor electrodes. Inherent low conductivity limits application of Mn₂O₃ in bulk form; however, nanostructured oxides demonstrate enhanced charge-transfer capabilities that render them feasible electrode materials. Additionally, the increased specific surface areas of nanomaterials provide a route for further enhancement of electrode performance, as electrochemical capacitors store charge through surface interactions with the electrolyte. However, in the fabrication of electrodes from nanostructured manganese oxides, the active materials are mixed with binders and conductive agents before pasting onto a charge-collecting substrate. By eliminating additives, mass can be minimized, and the specific capacitance of assembled devices can be improved. Free-standing web electrodes have been reported in several materials systems but have primarily been carbon-fiber based. A similarly independent structure for manganese oxides may improve performance to allow for enhanced widespread use.

In this work, a free-standing Mn₂O₃ web electrode is fabricated directly onto a charge collector using a facile, two-step electrospinning and thermal treatment process. To fabricate freestanding web electrodes, polymer fibers containing manganese salts are electrospun directly onto foil charge collecting substrates. The fibers are calcined in air to remove the carrier polymer and convert the manganese salts to an oxide. X-ray diffraction is used to confirm the oxide phase produced during calcination so that comparison of electrochemical performance to literature values may be performed. The fabricated electrodes are imaged with scanning electron microscopy; fiber mat morphology and structure are qualitatively observed, while quantitative image analysis is used to calculate the active mass of oxide in the electrodes. The web electrodes are tested in an electrochemical system using cyclic voltammetry and galvanostatic charge-discharge to measure specific capacitance and capacity fading over many cycles. Contact angle measurements are performed to analyze electrode wettability and determine whether poor wettability and the accompanying reduced interfacial area present a barrier to optimized capacitance. After electrochemical cycling, the electrodes are again imaged with electron microscopy, and morphological changes are qualified with electron microscopy and comparison to the as-fabricated structures. Electrodes prepared using pre-calcination processing steps such as hot-pressing and chemical melting are examined alongside untreated fiber mats to determine the effects of multiple processing steps on final manganese oxide electrode morphology and performance.

EDLC supercapacitors have drawn wide-ranging consideration and significant scientific interest in recent years due to their rapid charging and discharging capabilities, high energy density, large capacity and better performance in terms of degradation. Supercapacitors are emerging as an alternative to batteries particularly for applications where rapid charging/discharging is needed. Another reason for their advent is their increased energy density that is approaching to the leading competitive technology of lithium ion battery. However the major drawback of lithium-ion cell is its electrochemistry that causes the rapid degradation in its performance in addition to its high failure rate that puts the user at high risk. On the other hand the energy storage mechanism of EDLC supercapacitors does not involve any electrochemical reaction therefore it offers more charging discharging cycles and more safe operation compared to Li-Ion batteries. However a key component of their performance is activated carbon whose electrical and morphological property plays a crucial role in governing the performance of supercapacitor. The newer techniques to synthesize activated carbonaceous material having a precise control on their morphological and electrical properties could be more useful for improvement in their capacity and energy density. In present investigations use of carbonaceous materials with different dimensions and aspect ratio obtained from soot generated by controlled burning of various oils derived from plant/animal sources such as coconut oil, mustard oil, olive oil, wax, kerosene etc are explored for their application in EDLC supercapacitor. A systematic study has been carried out to understand the dependence of soot’s composition and its properties on composition of oil and further optimizing the properties of as obtained soot by several measures including its activation to accomplish the improved performance. Although the present study is focused on supercapacitor application, the work may have broad technological scope because the soot synthesized in this work has potential to be used in various other applications also such as sensors, conductive additives for EMI shielding applications etc.

Novel methods to fabricate bendable and stretchable energy storage devices with improved performance for flexible and wearable electronics are of great current interest. Scalable manufacturing procedures are crucial for practical application in the fabrication of complete functional electronic devices.[1] Here we report a scalable hybrid fabrication process of 3D printing combined with laser engraving to construct highly flexible and stretchable supercapacitors. CAD-designed supercapacitors were manufactured with a customized commercial 3D-printer equipped with a 460 nm commercial laser.
In addition, we present our route to the development, formulation and preparation of the main components required for a fully 3D-printed flexible and stretchable supercapacitor. A range of functional 3D-printable inks were developed to enable printing of the current collectors, electroactive electrode materials, the electrolytes, as well as the flexible and stretchable housing. In addition to the development of such inks, we have combined printing with laser-scribing of the functional inks. Specifically, high areal capacitance is achieved with conductive current collectors obtained by simple laser-scribing reduction of graphene oxide (GO) flakes in a 3D-printed polyethylene oxide (PEO)/GO-based material.[2],[3] The resulting reduced GO-based 3D microstructures are transferred onto a commercial UV-curable silicon rubber to obtain flexible current collectors.[4] The flexible conductive collectors were coated with a 3D-printed PEO/polyaniline-based electroactive material.[5] These component are integrated with a polyvinyl alcohol/sulphuric acid-based gel electrolyte to obtain a flexible and stretchable supercapacitor.

References:
[1]. Han, Y. & Dai, L. Conducting Polymers for Flexible Supercapacitors. Macromol. Chem. Phys. 220, 1–14 (2019).
[2]. Zhu, Z. et al. 3D Printed Functional and Biological Materials on Moving Freeform Surfaces. Adv. Mater. 30, 1–8 (2018).
[3]. Mohammad, M. A. et al. Tunable graphene oxide reduction and graphene patterning at room temperature on arbitrary substrates. Carbon N. Y. 109, 173–181 (2016).
[4]. Park, S., Lee, H., Kim, Y. J. & Lee, P. S. Fully laser-patterned stretchable microsupercapacitors integrated with soft electronic circuit components. NPG Asia Mater. 10, 959–969 (2018).
[5]. Pan, L. et al. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proc. Natl. Acad. Sci. U. S. A. 109, 9287–9292 (2012).

Si anodes are one of the most promising anodes for the next generation high energy density lithium-ion batteries (LIBs) because of its high theoretical capacity, low operating potential and high abundance of Si. However, the large volume expansion and continuous electrolyte consumption during lithiation and delithiation leads to a poor cycling performance of Si anodes. It is critical to understand how the electrolyte is consumed, how to stabilize the interface and form a stable solid electrolyte interphase (SEI) in order to develop Si anodes with good cycling stability. Oxygen is almost inevitable in Si anodes where the surface of Si forms a native oxide layer when it exposes to air. In addition, the different preparation processes of Si anodes may also lead to different levels of oxygen content [1,2]. Thus, a better understanding about how the oxygen would affect the surface SEI formation, (ir)reversible capacity, and electrochemical cycling of Si anodes is needed.

In this study, we synthesized a series of model Si anodes with different oxygen levels by sputtering on Cu foils, to investigate SEI formation and electrochemical cycling in GEN-2 electrolyte with FEC additive in half-cells configuration with Li-metal counter electrode. The obtained Si anodes clearly showed different lithiation/delithiation behaviors and cycling performance with different oxygen level, where higher oxygen level leads to a longer plateau at around 0.6 V during the first lithiation and better cycling performance. Via comprehensive in situ and ex situ characterization techniques, such as XPS, AFM and EQCM, we revealed how oxygen affects the SEI formation and electrochemical performance of Si anodes.

[1] Xu, Y., Teeter, G., Burrell, A. and Zakutayev, A., et al The Journal of Physical Chemistry C 123, 13219 (2019)
[2] Xu, Y., Teeter, G., Burrell, A.K. and Zakutayev, A. et al ACS Applied Materials & Interfaces 10, 44 (2018)

Metal chalcogenides (MCs) are widely studied for low cost and high performance sodium ion batteries (SIBs).^[1-3] However, the thickness and morphology of solid electrolyte interface (SEI) formed on MC based electrodes still remain to be elucidated because the formation of SEI is highly sensitive to ambient conditions and electron beam in vacuum.^[4] Herein, two Sb-based MCs, Sb₂Te₃ and Sb₂Se₃, are selected to study the SEI formed on their pristine particles and composites assembled with functionalized CNTs through high energy ball milling. The ex-situ cryogenic electron microscope (cryo-EM) is employed to distinguish the morphologies and dimensions of the SEI layers formed on pristine Sb₂Te₃, Sb₂Se₃ and their composite electrodes. Uniform and thin SEI layers of ~19.1 and ~35.7 nm are observed for the Sb₂Te₃/CNT and Sb₂Se₃/CNT composite electrodes, respectively. In contrast, irregular SEI films with maximum thicknesses of ~67.3 and ~71.8 nm are revealed for the pristine Sb₂Te₃ and Sb₂Se₃ electrodes, respectively. The ex-situ electrochemical impedance spectroscopy (EIS) analysis corroborates the effect of thin and uniform SEI on reduced charge transfer resistances of 126.9 and 290 Ω for the Sb₂Te₃/CNT and Sb₂Se₃/CNT composite electrodes, respectively, which are much lower than 556.1 and 466.3 Ω of the pristine Sb₂Te₃ and Sb₂Se₃ counterparts, respectively. The significant increase in electrochemical kinetics of the composite electrodes results in outstanding high-rate capabilities. The sodium-ion full cells (SIFCs) are assembled by pairing the Sb₂Te₃/CNT and Sb₂Se₃/CNT composite anodes with a Na₃V₂(PO₄)₂F₃ cathode, which deliver high energy densities of ~229 and ~176 Wh kg^-1, respectively, at 0.5 C together with remarkable power densities of 5384 W kg^-1 at 40 C and 5760 W kg^-1 at 80 C. These findings may shed new insight into the important role played by the optimal SEI layers on the rationally designed composite electrodes in giving rise to high-rate capabilities.

Recently a rapid technological progress in various fields of industry and daily life has been driven by miniaturization of electronics. Components such as medical devices, logic and memory circuits, and various sensors have been drastically reduced to smaller dimensions with vastly improved performance. Limited performance of batteries is one of the most critical problems to be tackled for sustainable technological advances and to allow for further development of novel and future technologies.

Lithium-ion batteries (LIBs) exhibit excellent cycle performance and high energy capacity and thus are the best choice to power miniaturized devices. However, the current architecture used in LIBs’ electrodes limits the energy and power densities in electrodes. Furthermore, safety issues arising from flammable liquid electrolytes and lithium dendrite growth upon cycling still remain as the major challenges for implementation of LIBs in this area. Advanced architectures and materials are needed to design high performance LIBs with increased energy storage capacity per unit volume while maintaining a small footprint area.

A three-dimensional (3D) architecture design of the battery electrodes is believed to enhance the energy and power densities of conventional LIBs. In this regard, we report a unique 3D architecture anode designed for all-solid battery and fabricated by electrodeposition of ultrathin Ni₃Sn₄ intermetallic alloy onto a commercially available nickel foam current collector from an aqueous electrolyte. The X-ray diffraction results obtained from three-dimensional electrodes indicated that the main phase of electrodeposited alloys was Ni₃Sn₄. The designed three-dimensional electrode demonstrated a high discharge capacity of 843,75 mAh g^-1 during initial cycles and an improved cycle performance over 100 cycles. The high surface area of the electrode and short Li⁺-ions diffusion paths along with suppression of volume expansion provided by the proposed 3D structure and Ni inactive matrix play a key role in improving the performance of the electrode.

Acknowledgements

This work was supported by the CRP research grant “Three-Dimensional All Solid State Rechargeable Batteries” from Nazarbayev University.

References

[1] J.M. Tarascon, M. Armand, Issues and challenges facing rechargeable lithium batteries, Nature. 414 (2001) 359–67. https://doi.org/10.1038/35104644.
[2] M.T. McDowell, I. Ryu, S.W. Lee, C. Wang, W.D. Nix, Y. Cui, Studying the kinetics of crystalline silicon nanoparticle lithiation with in situ transmission electron microscopy, Adv. Mater. 24 (2012) 6034–6041. https://doi.org/10.1002/adma.201202744.

A TiN_xO_y (TiNO) material system has been synthesized in a thin film form using a pulsed laser deposition process with a wide range of x and y realized by varying the oxygen pressure from 5 to 50 mTorr. X-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy measurements have been carried out to confirm the phase purity, partial oxidation, and chemical bonding information. The XPS compositions of the TiNO film deposited in 5, 15, 25, and 50 mTorr oxygen pressures were found to be TiN_0.57O_0.76, TiN_0.44O_0.99, TiN_0.37O_1.19, and TiN_0.29O_1.25 after 15 seconds of Ar-ions surface etch which was performed to remove carbon as well physically adsorbed O 1s and N 1s signals. The XPS depth profile study has shown that O and N profiles act opposite, i.e., when the O goes down, N goes up; when O goes up, N goes down. The electrocatalytic activities of these films were performed in 1M KOH solution for oxygen evolution reaction. It was observed that the electrocatalytic activities of these films depend on the growth conditions. Films grown under low oxygen partial pressure (5 mTorr) showed an overpotential of 390 mV to achieve a current density of 10 mA/cm², whereas the TiNO film grown under high oxygen partial pressure of 50 mTorr displayed the lowest overpotential of 320 mV at 10 mA/cm². This range of overpotential observed in this study is among the lowest values reported for any oxynitride systems. In addition to low overpotentials, these TiNO based films showed a stable electrocatalytic performance over 24 hours of chronoamperometric testing. Thus, our results suggest that a very high level electrocatalytic activity can be accomplished in TiNO films for the oxygen evolution reaction in the water-splitting process by controlling the substitutional defects in the starting TiN material.

Cathodes based on layered LiMO₂ are the limiting components in the path toward Li-ion batteries with high energy density. Introducing an over-stoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. Yet the role and fate of the oxide ligands in such intriguing additional capacity remain unclear. This reactivity is hypothesized in Li₃Ru⁵⁺O₄, making it a valuable model system. A comprehensive analysis of the redox activity of both Ru and O under different electrochemical conditions was carried out, and the effect of Li/Ru ordering was evaluated. Li₃RuO₄ displays highly reversible Li intercalation to Li₄RuO₄ below 2.5 V vs. Li⁺/Li⁰, with conventional reactivity through the formal Ru⁵⁺-Ru⁴⁺ couple. In turn, it can also undergo anodic Li extraction at 3.9 V, which involves of O states to a much greater extent than Ru. Although the associated capacity is reversible, reintercalation subsequently unlocks a conventional pathway involving the formal Ru⁵⁺-Ru⁴⁺ couple despite operating above 2.5 V, leading to chemical hysteresis. This new pathway is both chemically and electrochemically reversible. This work exemplifies both the challenge of stabilizing highly depleted O states, and the ability of solids to access the same redox couple at two very different potential windows depending on the underlying structural changes. It highlights the importance of properly defining the covalency of oxides when defining charge compensation in view of the design of materials with high capacity for Li storage.

Li₂MnSiO₄ (LMS) offers a promising opportunity as a high capacity potential cathode for next generation lithium ion battery because of its high theoretical capacity 333 mAhg^-1 which is ascribed to the possible deintercalation/intercalation of two lithium ions per formula unit through the excursion of Mn^II/Mn^III and Mn^III/Mn^IV redox couples within the voltage range of used electrolyte (1 M LiPF₆ in EC: DC, 1:1 vol. %) However, the main drawbacks associated with LMS are its poor electronic conductivity (5x10^-16 Scm^-1), low Li-ion diffusion coefficient (10^-17-10^-18 cm²s^-1), unstable crystallographic structure, and poor cyclability, which hinder its possibility to be used as a commercial cathode material. Additionally, only a small difference in the formation energy of its polymorphisms, namely, orthorhombic Pmn2_1, Pmnb, and monoclinic P2₁/n, further challenges its pure phase synthesis, and the investigation of its electrochemical behaviour. In view of this, although various synthesis approaches have been adopted in the recent past to get reproduceable pure phase LMS yet still not facile, and the formation of some impure phases such as MnO, Li₂SiO₃, and Mn₂SiO₄ usually appear along with LMS phase. In most of the reported synthesis approaches, a little amount of carbon has been used, which suppresses the growth of impurity phases in the sample. In this study, carbon free pure phase orthorhombic Li₂MnSiO₄ cathode with space group Pmn2₁ has been prepared at low temperature (180 °C) via facile one-step hydrothermal approach. The pure phase formation has been confirmed by Rietveld refinement followed by other characterizations like TGA, FE-SEM, EDAX, XPS, HR-TEM, FTIR, Raman, and EPR at room temperature. Further, the electrochemical activity of such synthesized LMS as a prospective cathode for LIBs has been investigated thoroughly via galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). We believe our findings can be utilized in exploring the possible commercial utility of the Li₂MnSiO₄ as cathode material for Li-ion batteries.


References:


[1] Dominko, R.; Bele, M.; Kokalj, A.; Gaberscek, M.; Jamnik, J. Li₂MnSiO₄ as a Potential Li-Battery Cathode Material. J. Power Sources. 2007, 174(2), 457-461.
[2] Dominko, R.; Li₂MnSiO₄ (M = Fe and/or Mn) Cathode Materials. J. Power Sources 2008,184(2), 462-468.
[3] Bini, M.; Ferrari, S.; Ferrara, C.; Mozzati, M. C.; Capsoni, D.; Pell, A. J.; Pintacuda, G.; Canton, P.; Mustarelli, P. Polymorphism and Magnetic Properties of Li₂MnSiO₄ (M = Fe, Mn) Cathode Materials. Sci. Rep. 2013, 3, 1–7.
[4] Fleischmann, S.; Mancini, M.; Axmann, P.; Golla-Schindler, U.; Kaiser, U.; Wohlfahrt-Mehrens, M. Insights into the Impact of Impurities and Non-Stoichiometric Effects on the Electrochemical Performance Li₂MnSiO₄. Chem Sus Chem 2016, 9(20), 2982–2993.

YMnO₃ (and related compositions) is a multiferroic perovskite oxide, which is recently attracting attention as a visible light driven photocatalyst due to optical absorption that extends to ~900 nm. Similarly, quinary and senary non-stoichiometric double perovskite oxides such as BCNF (Absorption edge ~800 nm) have been used for gas sensing, solid-state ionics and thermochemical CO₂ reduction. Herein, we examined the potential of both non-stoichiometric YMnO₃ and BCNF-family of compounds, as narrow bandgap semiconductors for use in solar energy harvesting.

Both YMnO₃ and BCNF showed p-type conduction and a distinct photoresponse upto red wavelengths. Due to poor carrier transport in these materials, these perovskite oxides need to be nanostructured in order to ensure that the critical dimension is roughly comparable to the minority carrier diffusion length. While YMnO₃ was nanostructured through solvothermal processing, BCNF was nanostructured by forming composites with few-layer sheets of g-C₃N₄. For both types of nanostructured perovskites, scanning Kevin probe force microscopy (KPFM) and photoluminescence measurements indicated efficient charge separation following visible light illumination. In this poster, we will be presenting our preliminary results exploiting these materials in photocatalytic CO₂ reduction and photoelectrochemical water splitting.

Photoelectrochemical oxidation of water presents a pathway for sustainable production of hydrogen peroxide (H₂O₂). Two-electron water oxidation toward H₂O₂, however, competes with the popular four-electron process to form oxygen and one-electron water oxidation to form OH radical. To date, bismuth vanadate (BiVO₄) has been shown to exhibit promising selectivity toward H₂O₂, especially under illumination, but it suffers from high overpotential and notoriously poor stability. Herein, using density functional theory calculations, we predict that doping BiVO₄ with optimal concentrations of gadolinium (Gd) not only enhances its activity for H₂O₂ production but also improves its stability. Experimentally, we demonstrate that intermediate amounts of Gd doping (6–12%) reduce the onset potential of BiVO₄ for H₂O₂ production by ∼110 mV while achieving a Faradaic efficiency of ∼99.5% under illumination and prolonging the catalytic lifetime by more than a factor of 20 at 2.0 V vs RHE under illumination.

Nowadays, many applications of optoelectronics require materials with tailored properties. Chalcogenide metallic materials have become an important research field in order to get semiconductors. Specifically, CuS and CuIn₂ are a promising materials for device applications like in solar energy conversion, lighting, display technology, or biolabelling. However, is important to avoid the use of toxic heavy metals as cadmium or lead, one of the possible alternatives are copper sulfide and Copper indium disulfide.
Copper sulfide is a p-type semiconductor with a a bandgap in the range of 2.0-2.36 eV and a low resistivity with a value of 1x10^-4 Ωcm, has a covelite structure with a hexagonal arrangement. Copper indium disulfide (CuInS₂), a direct semiconductor with a bandgap in the bulk of 1.45 eV, it has a chalcopyrite type crystalline structure, this metal chalcogenide has a high absorption coefficient of 10⁵ cm^-1.
Here, we show preliminary results of the influence of the solvent in the formation of CuS and CuInS₂ nanoparticles by controlled precipitation, also we studied de influence of the metallic precursors and the source of the sulfur ions in the formation of the nanoparticles. The solvents used were ethanol, ethylene glycol and deionized water. The metal precursors were Cu(NO₃)₂ 2.5H₂O and CuCl₂H₂O for CuS nanoparticles, Cu(NO₃)₂ 2.5H₂O , CuCl₂ H₂O, In(C₂H₃O₂)₃ and InCl₃ for CuInS₂ nanoparticles. Sulfur ion sources were CH₃CSNH₂, NaS₂ 9H₂O and NaSH xH₂O at low temperature 80^○C and 1 hour stirring. It is important to note that the addition of the solution containing the sulfur ions to the solution containing the metal ions should be drop by drop, otherwise an abrupt reaction and rapid precipitation occurs, resulting in metal oxides and sulfur ions not react with copper ions.
First, a formulation was made to obtain CuS nanoparticles, using Cu(NO₃)₂ 2.5H₂O as a metal salt and a variation of the sulfur ion precursor was made CH₃CSNH₂, NaS₂ 9H₂O and NaSH xH₂O using water and ethanol as solvents, with the objective of obtaining CuS with covelite crystalline structure. The results obtained by an XRD analysis show that when using NaS₂ 9H₂O as a source of sulfur ions, the desired crystalline structure for CuS is obtained. Subsequently ethylene glycol was used as a solvent, to obtain CuS and CuInS₂, the characterization by DRX and EDAX in the nanoparticles of CuS and CuInS₂ showed contamination by oxides and in the case of CuInS₂ showed low content of atomic In%. Finally, deionized water was used as a solvent, in this case the optical properties, the crystalline structure and the morphology of the CuS and CuInS₂ nanoparticles are related to the results reported in the literature. The objective was achieved, the nanoparticles were analyzed structurally, morphologically and optically to study the effect of using different sources of metal ions and vary the solvent used in the obtention of CuS and CuInS₂ nanoparticles.

Recently, Sodium-ion batteries (NIBs) have emerged as an economical alternative to lithium-ion batteries (LIBs) for large scale energy storage applications and therefore the successful implementation of renewable energy technologies. Developing optimum negative electrodes is of crucial importance to improve the energy density and stability of NIBs. Hard carbons with tunable morphologies are preferred due to their low cost, operating voltage (high energy density) and high reversible capacities.

Here, in our research work, a series of hard carbon anode materials prepared via the Hydrothermal Carbonisation (HTC) followed by high-temperature carbonisation. Applying various carbonization temperatures, templating agents and dopants results in materials with different pore morphologies, functional groups and graphitisation degrees which were characterised by HRTEM, XPS, Raman, gas adsorption, SAXS/WAXS and Total Neutron Scattering. The influence of material morphology and microstructural change during the electrochemical cycling were investigated by in-situ Electrochemical Dilatometry. By tuning the degree of graphitic regions to disordered domains, capacity obtained from slope and plateau regions of the discharge curve adjusted and a capacity up to 300 mAh/g with a very good initial Coulombic efficiency of 83% was achieved. The degree of graphitisation, pore structure, particle size and defects were found to have a significant effect on on the storage mechanism and electrochemical performance of the batteries. Being able to design and modify the electrode structure and chemistry allowing us to move closer to electrochemically optimized, high performance and efficient Na-ion batteries.

Efficient water pumping and selective salt rejection is highly desirable for solar or thermally driven seawater desalination, but its realization has been challenging with the typical capillary pumping mechanism. Here we proposed and demonstrated a new liquid supply mechanism, ionic pumping effect, realized using a polyelectrolyte hydrogel foam (PHF) containing poly(sodium acrylate) [P(SA)] embedded in a microporous carbon foam (CF). The PHF simultaneously possesses high osmotic pressure for efficient liquid transport and strong salt-rejection effect. The PHF was able to sustain high water flux of ~ 24 liter per m² per hour (LMH), comparable to the evaporative flux under 15 suns, and a salt rejection ratio over 80%. Compared to the porous carbon foam without the polyelectrolyte hydrogel, i.e., with only the capillary pumping effect, the PHF yielded a 42.4% higher evaporative flux, at ~ 1.6 LMH with DI-water and ~ 1.3 LMH with simulated seawater due to the more efficient ionic liquid pumping. More importantly, thanks to the strong salt-rejection effect, the PHF showed a continuous and stable solar-driven desalination flux of ~ 1.3 LMH under one-sun over 288 hours consecutively using real seawater without salt clogging in the pore and sediment on the surface, which was not achieved before. The successful demonstration of both efficient ionic pumping and strong salt rejection effects makes the PHF an attractive platform for sustainable solar-driven desalination.

Rechargeable metal batteries that employ metals, including Li and Na, as anodes have been gained increasing attention in recent years due to their high energy density.¹ However, poor chemical stability of traditional liquid electrolytes in contact with the metal anode limit both the performance and safety of such cells.² Solid-state electrolytes are considered particularly promising because of their inherent safety characteristics and potential to prevent dendritic deposition of the metal,³ in which solid polymer electrolytes (SPEs) are considered attractive from a range of perspectives, including their light-weight characteristics, lower cost, excellent mechanical toughness, and compatibility with roll-to-roll manufacturing processes.⁴ In general, a successful SPE is required to have at least two characteristics. Firstly, it should have high bulk ionic conductivity and fast interfacial transport; and secondly it should remain mechanically stable and chemically inert during extended battery cycling.⁵
In present talk, I will present our recent progresses on the preparation of in-built SPEs. Firstly, we found that the ring-opening polymerization of molecular ethers (for example, 1,3-dioxolane) inside an electrochemical cell can produce SPEs with high ionic conductivity at room temperature. These SPEs retain conformal interfacial contact with all cell components and exhibit low interfacial resistances, uniform lithium deposition and high Li plating/striping efficiencies. Secondly, we will report how to further improve cathode-electrolyte interphases of in-built SPEs. In the presence of designed fluorinated nanofillers, the designed SPEs enable the stable cycling performance in high areal capacity and high voltage LiNi_0.6Mn_0.2Co_0.2O₂ cathodes. We found the fluorinated nanofillers can plays a dual role as a Lewis acid catalyst and in building fluoridized interphase to protect both the electrolyte and aluminum current collector from degradation reactions. Finally, we will report how to maintain long-term stability for in-built SPEs by designing plasticizer. The complex kinetics of in-built SPEs with plasticizer results in nonlinear phase behavior, including the appearance of a critical transition to an entangled, solid-like electrolyte state.

References:
1) Choi, J. W. & Aurbach, D. Promise and reality of post-lithium-ion batteries with high energy densities. Nat. Rev. Mater. 1, 16013 (2016).
2) Tikekar, M. D., Choudhury, S., Tu, Z. & Archer, L. A. Design principles for electrolytes and interfaces for stable lithium-metal batteries. Nat. Energy 1, 16114 (2016)
3) Manthiram, A., Yu, X. W. & Wang, S. F. Lithium battery chemistries enabled by solid-state electrolytes. Nat. Rev. Mater. 2, 16103 (2017).
4) Quartarone, E. & Mustarelli, P. Electrolytes for solid-state lithium rechargeable batteries: recent advances and perspectives. Chem. Soc. Rev. 40, 2525–2540 (2011)
5) Zhao, Q., Liu, X., Stalin, S., Khan, K. & Archer, L. A. Solid-state polymer electrolytes with in-built fast interfacial transport for secondary lithium batteries. Nature Energy 4, 365-373 (2019).

Li-ion batteries are complex systems whose long-term performance is still the subject of much research. Of particular interest is the degradation of electrode materials during long term cycling under a variety of cycling rates and operating temperatures. Electrode degradation in Li-ion batteries has been the focus of much study in recent years and mechanisms for degradation have been proposed. These proposed mechanisms have not been tied to performance of commercial cells during long term cycling under a variety of operating conditions. Determining and understanding systematic trends in degradation is crucial to further improvement of Li-ion battery performance and safety.
Previously, researchers at Sandia National Labs conducted a systematic study of commercially available battery cycling behavior. Dozens of commercial NCA (LiNI_xCo_xAl_1-x-yO₂) and NMC (LiNi_xMn_yCo_1-x-yO₂) cells were cycled to 80% capacity and end of life across a range of temperatures, discharge rates, and depth of discharge windows. To better understand the reasons for the observed degradation trends, postmortem analysis was carried out at pristine condition, 80% capacity, and end of life. As such, multiple cells were started at the same operating conditions but stopped at different points to be analyzed.
Postmortem analysis of the anode and cathode of each cell included X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), and Brunauer-Emmett-Teller Isotherms (BET). Each provided different insights into crucial changes in the electrodes of these batteries, including phase changes in the cathode, micro-cracking, SEI layer formation, and Li plating. Critically, DSC in combination with BET showed changes in reactions and reaction rates that contribute to thermal runaway and generally indicates changes in chemical properties of the electrode. Materials properties were correlated to whole cell electrochemical performance to understand the causes of performance fade and failure of the cell. The breadth of operating conditions and duration of cycling considered in this study fills a substantial gap in the literature, enabling optimization of Li-ion batteries for application beyond 80% capacity.

Na-ion batteries (NIBs) have been recently reconsidered for storing the electricity from renewable energy due to the abundant sodium resources and low cost. The progress of NIBs intensively relies on the application of appropriate cathode and anode materials, especially, the anode side has become the main bottleneck in enhancing the batteries’ performance. Among all available anode candidates, disordered carbon still shows the best overall performance in terms of capacity, cycling stability and cost. In this talk, I will present several superior low cost disordered carbon anodes made from pitch, focusing on the strategies adopted to surpress the graphitization degree of pitch-derived carbon at high carbonization temperature. Besides, pore structures of a porous biomass-devirved carbon are regulated to enhance the Na stroage perforamnce. Furthermore, two kinds of carbon anodes demonstrate a high Na storage capacity ≥400 mAh/g through controlled synthesis, which help unravel the Na storage mechanism in disoredered carbon. The understanding gained potentially provides reference for the design and development of high-performance disordered carbon materials for NIBs.

References
Li, Y. M.; Hu, Y.-S.*; et al., Journal of Materials Chemistry A 2016, 4, 96.
Li, Y. M.; Mu, L.; Hu, Y.-S.* et al. Energy Storage Materials 2016, 2, 139.
Zhao, C.; Wang, Q.; Lu, Y.X.*; …; Hu, Y.-S.* Science Bulletin 2018, 63, 1125.
Lu, Y.X.; …; Hu, Y.-S.* Advanced Energy Materials 2018, 8, 1800108.
Qi, Y.; Lu, Y.X.*; …; Hu, Y.-S.* Angew. Chem. Int. Ed. 2019, 58, 4361-4365.
Meng, Q.; Lu, Y.X.*; …; Hu, Y.-S.* ACS Energy Lett. 2019, 4, 2608-2612.
Li, Y.Q.; Lu, Y.X.*; …; Hu, Y.-S.* Advanced Energy Materials 2019, accepted.

Lithium-ion batteries have been manufactured for nearly three decades and represent an excellent example of the role steady improvements in design and science can have on end users and research opportunities. As more uses become viable the number of cells produced increases and puts a strain on the metals and mining industry to maintain the supplies of component metals, such as cobalt. Some reports have noted that for cobalt, almost 25% of the worlds yearly output is used in lithium ion batteries creating the need to vary the amount of metals used and identify new compositions made of more abundant materials. In addition to new supplies, the opportunity exists with previously manufactured lithium ion cells to recover and reuse the metals and components. As with the lead-acid battery industry, collection of end-of-life lithium ion cells (automotive, consumer, or medical) can act as a supply of reusable materials. In this talk we will discuss the role Direct Recycling has on these pathways and highlight methods to relithiate lithium-deficient samples and deal with the need for compositional changes as market needs change over time with advances in chemistry and technology.

The performance deterioration of a solid-state Li battery is the result of a combination of interfacial events. Characterization of these interfaces has been an ongoing challenge, and solid-state batteries are considered by some as a “black box”. Only during the past few years has been there exponential growth in the efforts to apply a variety of microscopic and spectroscopic techniques to characterizing solid-state batteries, but the interfacial phenomena are still far from being well understood. We will report the progress of establishing a structural-chemical-mechanical diagnostics toolset to investigate the interface evolutions in solid-state Li batteries. We will acquire detailed information of interfaces and dendrites evolutions including but not limited to (1) real-time visualization of Li dendrites growth within the whole thickness of electrolyte layer, (2) chemical composition, mechanical property, and evolution of electrolyte decomposition products, including intermediate and metastable ones, at both cathode and anode interfaces, and, (3) quantitative correlation between electrolyte decomposition, void formation, and cell performance. These in-depth understandings will allow us to effectively predict and optimize the physical and chemical changes of components within solid-state Li batteries during charge and discharge.
In addition to tool development, we have studied new cathode and electrolyte materials that form reversible cathode-electrolyte interfacial resistance evolution during cycling as the result of the reversible conversion between the superionic conductor Na₃PS₄ and the resistive oxidation products Na₄P₂S₈/Na₂P₂S₆. Structural and mechanical analyses further showed that a low- modulus cathode material like PTO (Young’s modulus = 4.2 ± 0.2 GPa) can effectively accommodate interfacial stress and maintain intimate interfacial contact with solid electrolytes. The reversible electrolyte decomposition, revealed by time-of-flight secondary ion mass spectrometry (ToF-SIMS), the consistently intimate interfacial contact, visualized by focused ion beam-scanning electron microscopy (FIB-SEM), and the soft nature of cathode material, characterized by nanoindentation, are all first-time reports in the field of solid-state batteries, and they have collectively led to a high specific energy (587 Wh kg-1) at the active-material level and an 89% capacity retention over 500 cycles, a record cycling stability among all-solid-state Na batteries.

The discovery of a large-capacity cathode material is a major task for developing batteries of high energy density, and an additional oxygen redox capacity has recently been regarded as a new impetus. From the electronic-structure point of view, lithium-rich layered oxides, typical oxygen-redox cathode materials, possess oxide ions with a nonbonding O 2p state along the Li-O-Li coordination axis, which provides the oxygen redox activity. After oxygen oxidation, either a π-type M t_2g-O 2p interaction (M: transition metal) or a O-O bond formation should stabilize oxidized oxide ions. However, the layered structure is generally unstable after extracting an excess amount of Li ions, leading to the capacity fade and potential decay upon cycling. Therefore, for achieving the stable additional oxygen-redox capacity, of particular importance is to implement oxide ions with nonbonding O 2p state into a stable host framework against excess Li-ion extraction. As layered to spinel transformation has been claimed as a origin of a voltage drop and the latter have a stable three-dimensional framework, it is attractive to explore for spinel oxides capable of the oxygen-redox reactions.
Here, we diagnose the oxygen-redox activity of spinel oxides with combined experimental and density functional theory (DFT) calculations. Li₄Mn₅O₁₂ and LiMg_0.5Mn_1.5O₄ is employed as a model material, as its spinel structure is expected to have oxide ions with nonbonding O 2p state owing to the existence of ionic Li⁺ or Mg²⁺ in the framework. The electronic structure change and phase stability during the oxygen-redox reaction is compared with that of a typical Li-rich layered oxide (Li₂MnO₃).

The worldwide development of Li-ion batteries has led to a revolution in the field of consumer electronics and completely transformed the way we access information. It is currently the leading technology for the technological transition towards electricity-powered transportation and large-scale energy storage capabilities. However, it is still unclear whether the cost of Li-ion batteries will meet this challenge, as they contain non-abundant elements such as lithium, nickel, cobalt, which price is bound to vary with market and political decisions. Developing Na-ion batteries as a cheaper alternative is therefore a promising route, as it would help diversifying technology for grid or local storage applications that do not require high energy density.

Recent work on a new anti-perovskite cathode Li₂FeOS^1,2 has shown that oxysulfides represent a promising family of material. Oxysulfides have long been overlooked in the literature due to their complex synthesis conditions and lower voltage compared to oxides. However, they can deliver high capacities using abundant elements. We prepared a new oxysulfide material with a crystallographic structure yet unexplored in cathode materials for Li and Na-ion batteries, by a simple mechanosynthesis method in dry air, and studied its electrochemical properties. Interestingly, the material becomes amorphous upon its initial oxidation but still delivers a reversible capacity of 160 mAh/g between 1.5 and 3 V vs Na⁺/Na and a good capacity retention upon cycling. To understand the evolution of the material during (de)sodiation, we combined several techniques (X-ray diffraction, X-ray absorption and X-ray photoemission spectroscopies) and obtained insight on the local structure evolution and oxidation/reduction of the different elements in the material. Finally, full Na-ion cells were assembled using hard carbon anodes, showing the possibility to prepare Na-ion batteries with abundant and cheap materials. Oxysulfides, and more generally multiple anion materials, give us an opportunity to control the energy storage properties of electrode materials without relying on non-abundant transition metals.

References :
1. Lai, K. T., Antonyshyn, I., Prots, Y. & Valldor, M. Anti-Perovskite Li-Battery Cathode Materials. J. Am. Chem. Soc. 139, 9645–9649 (2017).
2. Lai, K. T., Antonyshyn, I., Prots, Y. & Valldor, M. Extended Chemical Flexibility of Cubic Anti-Perovskite Lithium Battery Cathode Materials. Inorg. Chem. 57, 13296–13299 (2018).

An inability to routinely identify, quantify and control specific structural defects in photoelectrodes leads to inconsistencies in observed photoelectrocatalytic behavior that inhibit material development. Photophysical analysis of key electron transfer processes in hematite photoanodes, for example, have provided insight into fundamental behavior and properties but have not resolved the persistent variability photoelectrocatalytic performance values reported across the literature. We aim to address such issues by developing simple methodologies to routinely identify and quantify structural defects in photoelectrodes. We initiate this work with structure-property analyses on a series of hematite photoanodes prepared by annealing lepidocrocite films under varied conditions. Raman spectroscopy reveals the presence of a formally Raman inactive vibrational mode in Raman spectra for all hematite samples. The intensity of this feature is dependent on annealing conditions and protocols and is found to correlate with behavioral descriptors extracted from photoelectrochemical, Raman and UV-visible spectroscopic datasets. Specifically, the intensity of this Raman vibrational mode correlates to the measured photocurrent density, to the position of the semiconductor band edges, and to the location of intraband trap states. Observation of such a formally Raman inactive vibration signifies a lattice distortion, and the observed correlations reveal a systematic change in the magnitude of the distortion. Analysis of the full Raman spectrum, X-ray diffraction patterns, and the synthetic conditions lead us to conclude that the lattice distortion is caused by iron vacancies that are themselves induced by the trapping of protons within the crystal lattice. These results provide the foundation for a rapid diagnostic protocol to identify and quantify specific structural defects to guide the optimization of fabrication protocols for photoelectrodes.

Ta-doped LLZO (LLZTO) is of great interest due to its high ionic conductivity, electrochemical stability in contact with metallic lithium, and the fact that doping the Zr-sites with Ta does not block Li-ion conduction as is the case with other common dopants such as Al or Ga, which reside on the Li sublattice. As with most methods for synthesis of LLZO, LLZTO is primarily obtained via the solid-state reaction (SSR) method, incurring a high energy cost and producing bulk powders that require high energy milling after synthesis to promote higher reactivity towards sintering. Other methods such as sol-gel and combustion methods have also been employed seeking smaller particle sizes, but generally do not result in as good of performance as the SSR method. Herein, a novel non-aqueous polymer combustion method is used to produce LLZTO nanopowders, which enables somewhat better control over synthesis conditions and better reproducibility than conventional nitrate-based combustion methods. Compared to SSR LLZTO, which is generally sintered at temperatures between 1150-1250 °C, as-synthesized LLZTO nanopowders are easily consolidated via conventional pressureless sintering at 1100 °C. This lower sintering temperature is enabled in part by mitigating Li₂O volatility and in part by the relatively higher reactivity of nanosized LLZTO compared to coarse LLZTO powders obtained via SSR. LLZTO processed with this method exhibits relative densities up to 93.6 % with ionic conductivities as high as 0.67 mS cm^-1, which compares well with dense LLZTO ceramics processed at higher temperatures or via advanced consolidation processes such as hot pressing. This method can be easily extended to other doping schemes, and the ease with which nanosized LLZO can be obtained makes this polymer combustion method promising for producing active fillers for composite polymer electrolytes.

Safety issue remains a major obstacle towards large-scale applications of high-energy lithium-ion batteries. Embedding thermoresponsive polymer switching materials (TRPS) into batteries is a potential strategy to prevent thermal runaway, which is a major cause of battery failures. Here, we report thin, flexible, highly responsive polymer nanocomposites enabled by bio-inspired nanospiky metal (Ni) particles. These unique Ni particles were synthesized by a simple aqueous reaction at gram-scale with controlled surface morphology and composition to optimize electrical properties of the nanocomposites. The Ni particles provide TRPS films with a high room-temperature conductivity of up to 300 S cm^-1. Such TRPS composites films also have a high rate (< 1s) of resistance switching within a narrow temperature range, good reversibility upon on/off switching and a tunable T_s (75 to 170 oC) that can be achieved by tailing their compositions. The small size (~500 nm) of Ni particles enables ready fabrication of thin and flexible TPRS films with thickness approaching 5 µm or less. These features suggest the great potential of using this new type of responsive polymer composites for more effective battery thermal regulation without sacrificing cell performance.

Lithium sulfur (Li-S) batteries deliver great promise to support the next-generation energy storage when the sluggish redox kinetics and polysulfide shuttling can be well addressed. The rational design of sulfur electrode plays key roles in tacking these problems and fulfilling a high-efficiency sulfur electrochemistry. Herein, we demonstrate a synergetic defect and architecture engineering strategy to design highly disordered spinel Ni-Co oxide double-shelled microspheres (NCO-HS), which consists defective spinel NiCo₂O_4-x (x=0.9 if all nickel is Ni²⁺ and cobalt is Co^2.13+), as the multifunctional sulfur host material. The in-situ constructed cation and anion defects endow the NCO-HS with significantly enhanced electronic conductivity and superior polysulfide adsorbability. Meanwhile, the delicate nano-construction offers abundant active interfaces and reduced ion diffusion pathways for efficient Li-S chemistry. Attributed to these synegistic features, the sulfur composite electrode achieved excellent rate performance up to 5 C, remarkable cycling stability over 800 cycles and good areal capacity of 6.3 mAh cm^-2 under high sulfur loading. This proposed strategy based on synergy engineering is also promising to enlighten the material engineering in related energy storage and conversion fields.

Silicon is a viable alternative to graphitic carbon as an electrode in lithium-ion cells and can theoretically store >3,500 mAh/g. However, lifetime problems have been observed that severely limit its use in practical systems. The major issues appear to involve the stability of the electrolyte and the uncertainty associated with the formation of a stable solid electrolyte interphase (SEI) at the electrode. Recently, calendar-life studies have indicated that the SEI may not be stable even under conditions where the cell is supposedly static. Clearly, a more foundational understanding of the nature of the silicon/electrolyte interface is required if we are to solve these complex stability issues. A multi-lab consortium has been formed to address a critical barrier in implementing a new class of materials used in lithium-ion batteries that will allow for smaller, cheaper, and better performing batteries for electric-drive vehicles. This consortium, named the Silicon Electrolyte Interface Stabilization (SEISta) project, was formed to focus on overcoming the barrier to using such anode materials. Five national laboratories are involved: the National Renewable Energy Laboratory (NREL), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), Oak Ridge National Laboratory (ORNL), and Sandia National Laboratories (SNL). The SEISta project was specifically developed to tackle the foundational understanding of the formation and evolution of the solid-electrolyte interphase on silicon. This project will has a primary goal of understanding the reactivity of the silicon and lithiated silicon interface with the electrolyte in lithium-ion systems. The overall objective for SEISta is to understand the nature and evolution of the SEI on silicon anodes.
Several issues must be addressed to enable progress in this area. Materials Standardization is critical to this project and deployment of standardized samples and experimental procedures across the team is a foundation of the project. Full characterization of any new sample that is to be used for SEI studies to ensure reproducibility and full understanding of the material. The materials standardization and model compounds will enable the researchers to systematically investigate the formation of the solid-electrode interphase using a wide variety of the spectroscopy techniques—from different optical, microscopy, and electrochemistry—to determine how the SEI forms based on the nature of the silicon surface, and how it evolves over time. This presentation will detail recent advances that the SEISta team has made to the understanding of the SEI on silicon.

Lithium ion batteries are the dominating energy storage technology for various applications, especially in the field of portable electronics as well as for large scale applications like electric mobility, due to an outstanding mix of high energy density, high power density and long cycle life. However, a growing demand of rechargeable batteries for automotive and stationary applications raises also concerns about resources, growing costs, and sustainability aspects. Especially for stationary grid storage and large-scale applications, sustainability aspects and low installation and lifetime costs are mandatory requirements in order to compete with other energy storage technologies.[1] Driven by that motivation, a huge number of several alternative energy storage technologies rised up in the last decade. One prominent candidate are dual-ion batteries (DIBs), which gained increased attention as alternative energy storage recently. [2] DIBs are characterized by the simultaneous uptake of both, anions and cations from the electrolyte into the respective host materials during charge and their release during discharge. This working principle allows to use non-lithium as well as non-heavy metal containing positive electrode materials like graphite, organic cathodes or even metal organic frameworks for anion storage. [2-4] Due to the promising high working potential of graphite for anion intercalation of ≥4.5 V vs. Li|Li⁺ especially dual-graphite batteries (DGB) achieved an increased attention in the last years. However, the high working potential generates new issues and requirements like high oxidative stability of the electrolyte. Therefore, ionic liquids as well as highly concentrated electrolytes were studied and show promising results. [2,5] However, in terms of cost, safety and sustainability these cell chemistries need further improvement.
The presented work shows first approaches by introducing water-based electrolytes in DIBs as well as new electrode materials for anion insertion. In the first part, a water-based DIB using graphite as cathode material is presented. The impact of different anode materials on the electrochemical performance as well as structural changes during charge and discharge are systematically investigated by ex situ studies as well as in situ X-Ray diffraction and other techniques. In a second part, new organic/inorganic positive electrode materials for reversible anion insertion are presented and evaluated for application in DIB cells with regard to their electrochemical and structural properties.


References:
[1] D. Larcher; J.-M. Tarascon, Nat. Chem. 2015; 7; 19.
[2] T. Placke, A. Heckmann, R. Schmuch, P. Meister, K. Beltrop, M. Winter, Joule 2018, 2, 2528;
[3] M. Kolek, F. Otteny, P. Schmidt, C. Mück-Lichtenfeld, C. Einholz, J. Becking, E. Schleicher, M. Winter, P. Bieker, B. Esser, Energy Environ. Sci. 2017, 10, 2334.
[4] Aubrey, M. L.; Long, J. R., J. Am. Chem. Soc. 2015, 137 (42), 13594.
[5] A. Heckmann, J. Thienenkamp, K. Beltrop, M. Winter, G. Brunklaus, T. Placke, Electrochim. Acta 2018, 260, 514.

Liquid-phase Transmission Electron Microscopy (TEM) provides a unique platform to perform time-resolved analysis of materials and chemical processes in realistic experimental conditions at the atomic scale. However the resolution of liquid-phase TEM is strongly hindered by the thickness of liquid that must be traversed by the electron beam, which increases spatial and chromatic broadening. This effect negatively impacts imaging resolution and elemental analysis in liquid-phase conditions. We have developed a new technique to achieve atomic-scale resolution while keeping the sample in liquid condition. To do that we use a chip equipped with active electrodes to generate a gas bubble through electrochemical water splitting and we have shown that this leaves only a thin layer of liquid covering the sample. The thin-film liquid layer permits atomic-scale image resolution and elemental analysis through Electron Energy Loss Spectroscopy (EELS), which makes this technique very appealing for in situ/operando studies. Electrochemical analysis indicates that the remaining thin-film liquid layer exhibits good ion transport and electrical conductivity. We recently used this method to study the dissolution of platinum when it is subjected to an oxidizing electrochemical potential in an aqueous electrolyte, which allowed us to identify new ways to decelerate the degradation of platinum during oxygen evolution reaction (OER) conditions. We are also using this method to determine the active sites for hydrogen and oxygen evolution at the atomic scale in a variety of electrode surfaces, including polycrystalline platinum (Pt), monolayer molybdenum disulfide (MoS₂) and gold nanoprisms (Au). The approach here developed opens the opportunity to study and develop nanomaterials with enhanced performance in applications with worldwide impact, such as ion batteries, hydrogen fuel cells and reduction of CO₂ to biofuels. Moreover, the liquid thin-film is achieved without any damage to the sample in study, which makes this technique also suitable for sensitive samples, such as organic materials and biological samples.

The main challenge that hinders the use of Li-ion batteries in space applications is its low performance at ultra-low temperatures. This is due to the low ionic conductivity and freezing of the electrolyte which leads to the loss of battery’s capacity. Another challenge is the moisture absorption of the electrodes and polymer electrolyte. In this research, a protective packaged case is designed and fabricated using 3D printing technique to enhance the ionic conductivity and restrict moisture absorption from the surrounding. This pack is made of polyether–ether–ketone (PEEK) which can withstand temperature range from -100 to 260°C and hence improve the ionic conductivity and prevent freezing of the electrolyte. Furthermore, the full cell battery is coated with a protective layer made of polydopamine to decrease the moisture absorption and improve the performance and lifetime of the battery. The battery case is simulated using COMSOL software to study the thermal and mechanical effect under space environment. In addition, the full cell packaged battery will be tested in terms of mechanical, electrical, and electrochemical performance using battery test setup. Moreover, thermal and radiation tests will be conducted in the vacuum thermal chamber to analyze the battery’s performance in harsh space environment. Parameters such as weight, lifetime and capacity loss are taken into consideration.

Solid-state battery is one of the most discussed next generation energy storage devices in both industry and academia. While Li-ions battery has been popularised by the success in mobile electronics, Na-ions battery has higher potential in stationary energy storage system due to the cost and availability of raw materials. Among the solid-state electrolyte, NASICON (NA Super Ionic CONductor), Na_1+xZr₂Si_xP_2-xO₁₂, possesses high mechanical strength, large electrochemical stability, and good chemical and thermal stability makes it one of the potential materials to be utilised. However, the processing of NASICON involves long exposure at high temperature thermal treatment. In addition, the lower grain boundary ionic conductivity limits the total ionic conductivity to be around 0.64 mS cm^-1. In this study, sodium metasilicate, Na₂SiO₃, was added into the NASICON matrix and facilitated the sintering process. The addition of Na₂SiO₃ has effectively reduced the sintering duration and temperature. Furthermore, the diffusion of cation from Na₂SiO₃ into the bulk NASICON resulted in changes in the stoichiometry and improve the bulk ionic conductivity. More importantly, as Na₂SiO₃ melt pool penetrate through the grain boundary, it formed a Si-rich secondary phase that significantly improve the grain boundary ionic conductivity. The highest ionic conductivity measured at room temperature is when 5wt% of Na₂SiO₃ was added into the NASICON at 1.48 mS cm^-1. This study has shown facile addition of liquid-phase during sintering can effectively achieve high ionic conductivity.

Catastrophic battery failure due to internal short is extremely difficult to detect and mitigate. In order to enable next generation lithium-metal batteries, a “fail safe” mechanism for internal short will be highly desirable. We introduce a novel separator design and approach to mitigate the effects of an internal short circuit by limiting the self-discharge current to prevent cell temperature rise. A nano-composite Janus separator—with a fully electronically insulating side contacting the anode and a partially electronically conductive (PEC) coating with tunable conductivity contacting the cathode—is implemented to intercept dendrites, control internal short circuit resistance, and slowly drain cell capacity. Galvanostatic cycling experiments demonstrate Li-metal batteries with the Janus separator perform normally before shorting, which then results in a gradual increase of internal self-discharge over >25 cycles due to PEC mitigated shorting. Abuse charge testing of Li metal batteries containing the Janus separator shows a remarkable ability to reduce short circuit current and heat generated during internal shorting incidents. This new separator design can not only greatly improve battery safety, but also lower battery costs by relaxing manufacturing tolerance and accelerate the adoption of high-energy next-generation batteries.

The demand from portable electronics and electric vehicles call for high energy batteries beyond the current lithium ion batteries. Here I will present our recent progress on materials and interfacial design to enable much high energy density batteries, which include 1) High capacity Si anodes with success in commercialization; 2) Li metal anodes: host and interface design to over the lithium metal dendrite formation and interfacial instability; 4) Sulfur as an earth abundant material for high capacity cathodes; 4) Our pioneering development of cryogenic electron microscopy for understanding the battery materials and solid-electrolyte interphase down to atomic scale resolution.

Solid electrolyte interphase (SEI), which forms at the interface between the electrolyte and the electrode, can passivate the surface of graphite anodes and finally facilitate the intercalation of lithium ions into graphite electrodes. The concept of using SEI protects the electrode surface from the reductive electrolyte has been used for developing other Lithium-ion (Li-ion) anodes, such as intermetallic silicon (Si) anodes. Different from the intercalation chemistry in graphite anodes, Si anodes experience alloying/dealloying reactions during electrochemical process, leading to phase transformation, morphology and volumetric changes. It generates great complexity in understanding the formation and the structural/composition evolution of the SEI layer during electrochemical process. Considering the high theoretical capacity Si anodes can offer, the investigation of SEI behavior on Si anodes is critical for developing next-generation anode materials. This presentation, which is based on recent results from advanced electrochemical and spectroscopy characterization, systematically elaborates the chemical and physical properties of SEI chemistry, towards developing mitigation strategies for stabilizing SEI on Li-ion anodes.

Long cycle life, high rate properties, sustainable active materials, reduced manufacturing cost, and improved safety aspects of dual-carbon batteries (DCBs) make them promising alternatives for the state-of-the-art rechargeable battery technologies. The DCB chemistry exploits the redox-amphoteric host capability of graphite as both electrodes for Faradaic charge storage by intercalating active species such as alkaline cations (typically Li⁺) and fluorinated anions (e.g. PF₆^-) into anode and cathode respectively. Recently, as part of the quest for elevating discharge potentials of DCBs, intercalation properties of larger sized anions such as bis(trifluoromethanesulfonyl)imide (TFSI^-) into the graphitic carbon cathode have been investigated. However, rather low coulombic efficiency values obtained by using the LiTFSI salts in DCBs prove to be a greater challenge.
Co-intercalation of PF₆^- and TFSI^- anions as a result of the use of a mixed salt of LiPF₆ and LiTFSI was studied for the increased performance of a dual-carbon battery (DCB). Unlike the fluorine- or the imide-based anions (eg. PF₆^- and TFSI^-), the cluster formation between co-intercalated PF₆^- and TFSI^- in the positive electrode of a dual carbon battery resulted in achieving high discharge capacities with significant increased cycle properties. A reversible discharge capacity of 90 mAh/g-cathode over 350 cycles with no significant degradation is presented. The Coulombic efficiency of almost 100% is reached after the initial 10 cycles and suitable rate property is also observed. F-NMR analysis on graphitic carbon intercalated with PF₆^- and TFSI^- suggested the interaction between two anions resulting in the increased stability of the intercalated structure which is also supported by first principles calculations. Gas formation at high potential during charge step is also suppressed by using mixed salt of LiPF₆-LiTFSI.

In the expanding search for safe, sustainable, low-cost large scale energy storage solutions, molten sodium batteries have been recognized as an attractive candidate technology. The relatively high operating temperature (near 300°C) of traditional molten sodium-sulfur and sodium-nickel chloride batteries, however, has discouraged the widespread adoption of these battery chemistries. We are developing a new, lower temperature molten sodium battery that operates near 100°C, based on a sodium anode, a solid state separator, and a sodium iodide-based molten halide salt catholyte. This new lower temperature system opens the door to lower materials costs, improved material lifetimes, and simplified, less costly operation. The reduced operating temperature, however, introduces new material and electrochemical challenges to not only the key molten components of the battery, but also critical interfaces and functional materials associated with the solid state separator, the current collectors, and even the material packaging of the battery. Here, we will discuss creative engineering solutions to emergent low temperature-specific problems related to interfacial wetting, ionic conductivity, chemical compatibility, and charge transfer efficiency. We highlight new approaches to solid state separator development, manipulating not only ceramic or composite chemistry but also separator structure and interfacial chemistry to enhance low temperature ionic conductance. Meanwhile, efforts to tailor high surface area, low resistance current collectors show progress toward higher efficiency battery cycling. Addressing the specific solid state materials in this functionally molten battery system allows us to accelerate the development of this potentially safe and sustainable sodium-based energy storage option.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

The electrochemical performance of lithium-ion batteries has been substantially improved in the last decades. However, with the increasing demand of electrochemical energy storage technologies, other challenges such as scarcity of raw materials, toxicity, and recyclability ought to be considered. In this regard, redox active polymers are promising materials thanks to their abundance, low cost, low toxicity and environmentally friendly disposal.[1-3] In addition, their redox properties can be tailored to be used as negative electrodes storing cations (Li⁺, Na⁺, H⁺) as well as positive electrodes incorporating anions (PF₆⁻, TFSI⁻). However, redox active polymers also possess some limitations, such as dissolution into the electrolytes, poor conductivity and low operational voltage.[4] To overcome some of those limitations, we have investigated different redox active conducting polymers with enhanced conductivity and reduced solubility to be used as positive and negative electrodes.
As negative electrode, we have chosen a polyimide-polyether block copolymer that combines the versatile redox activity and electronic conductivity of aromatic imide groups with the ion conducting polyether. As positive electrode, we have studied a PEDOT-lignin biopolymer composite combining the PEDOT conducting backbone with redox active lignin to increase the capacity. These two materials have been paired to build an all-organic aqueous battery with long cycle life at high current densities.[5] Additionally, another positive electrode based on PEDOT with hydroquinone and pyridine pendant groups has been investigated as a proton trap material. In this system, the redox reaction occurs in the hydroquinone moieties and the protons are transferred to the pyridine sites preventing its diffusion to the electrolyte. This material is very versatile as it can be used in many different electrolytes (conventional liquid electrolytes and ionic liquids), regardless of the coordinating salt (lithium or sodium based).[6]
Overall, redox active polymers can be tailored with specific backbones and redox active moieties to feature the desired properties and to be used as negative and positive electrodes towards more sustainable and environmentally friendlier energy storage technologies.
[1] Liang, Y.; Tao, Z; Chen, J. Adv. Energy Mater. 2012, 2, 742−769.
[2] Muench S.; Wild A.; Friebe C.; Häupler B.; Janoschka T.; Schubert U. S. Chem. Rev. 2016, 116, 16, 9438−9484.
[3] Casado N.; Hernández G.; Sardon H.; Mecerreyes D. Prog. Polym. Sci. 2016, 52, 107−135.
[4] Mauger A.; Julien C.; Paolella A.; Armand M.; Zaghib K. Materials 2019, 12, 1770.
[5] Hernández G.; Casado N.; Zamarayeva A.M.; Duey J.K.; Armand M.; Arias A.C.; Mecerreyes D. ACS Appl. Energy Mater. 2018, 1, 7199−7205.
[6] Åkerlund L.; Emanuelsson R.; Hernández G.; Ruipérez F.; Casado N.; Brandell D.; Strømme M.; Mecerreyes D.; Sjodin M. ACS Appl. Energy Mater. 2019, 2, 4486−4495.

Lithium conducting garnets in the family of lithium lanthanum zirconate (nominally Li₇La₃Zr₂O₁₂, LLZO) are of great interest as oxide solid electrolytes for solid-state lithium-metal batteries. Various synthetic approaches have been investigated to date, including sol-gel, co-precipitation, thin film deposition, spray pyrolysis, combustion, and molten salt synthesis, not to mention the standard solid-state reaction (SSR) method. Most of the aforementioned methods can generate LLZO with expected good properties, but nearly all have drawbacks including cost, high processing temperatures, complexity, poor properties (in the case of vacuum deposition of thin films), or difficulty of producing fine powders for thin films of LLZO, which are necessary for practical solid-state batteries. Thus, despite the promising properties of LLZO in terms of electrochemical stability and ionic conductivity, processing of garnet powders into dense solid electrolytes in practically useful forms is still a challenge. Herein, submicron (200-500 nm) powders of doped LLZO of nominal composition Li_6.4La₃Zr_1.4Ta_0.6O₁₂ are demonstrated to form at an unprecedented low temperature of 400 °C using a basic molten salt synthetic approach, ameliorating two main challenges of processing temperature and particle size. However, a curious phenomenon is observed: the composition of individual LLZO particles can vary considerably from the nominal composition, producing a distribution in the ratio of Zr and Ta that is difficult to detect during routine characterization (requiring the high spatial resolution of analytical transmission electron microscopy) but may have deleterious consequences on performance. Indeed, LLZTO synthesized via SSR exhibits higher ionic conductivity despite comparable relative density and sintering conditions. Backscatter electron imaging and energy dispersive spectroscopy shows that this compositional inhomogeneity persists even after sintering at high temperatures, indicating that interdiffusion between Zr and Ta does not go to completion at relevant sintering times if a distribution in composition exists in the feedstock powder. Variation in composition between individual grains implicates subcritical doping in some percentage of grains in a dense ceramic as the source of poorer performance relative to SSR LLZTO. The thermodynamic and kinetic origins of compositional inhomogeneity are discussed in Ta-doped LLZO and addressed by use of novel elementally homogeneous precursors. Implications of compositional inhomogeneity on performance of garnet solid electrolytes via this and other common synthesis methods are discussed.

The facile transport of lithium ions in inorganic crystalline materials is a prerequisite for the many electrochemical processes in rechargeable batteries, the production of which is now being rapidly scaled up to electrify vehicles and even enable grid-scale energy storage. Achieving fast ion transport kinetics in electrode materials requires an optimized crystal structure with favorable short-range atomic arrangements, which are, in the meantime, extensively connected in the long range. In conventional electrode materials, wherein a single unit cell exactly repeats its chemistry and geometry into infinity, the two criteria conveniently become one. Such perfectly-ordered structures, though easy to characterize, lack flexibility and impose a narrowed selection in chemistry, causing significant strains on several metal resources, such as cobalt and nickel. In this talk, I will show how strategically introducing compositional and structural disorder into a simple rocksalt lattice can lead to the discovery of novel electrode materials with ultrahigh energy and power density as well as a reversible anion redox process. The design strategies might open up a vast chemical space for the search of new battery materials made from earth-abundant elements.

In this talk, we show how mechanically-induced metastability greatly widens the voltage window and modulates the dynamic interface decomposition of sulfide solid electrolyte at high voltage, going beyond our recent work [1,2, 3]. By comparing ab-initio simulation and XPS measurement, the thermodynamic pathway of decomposition is determined. Beyond this thermodynamic stability window, kinetic effects are also discussed. We show both experimentally and theoretically how the decomposition of LGPS at high voltage is largely prohibited by these effects via mechanical constraint. We further discuss the potential of this effect on the cathode-electrolyte interface design to enable high voltage solid state batteries beyond the commercial level.
1. A high-throughput search for functionally stable interfaces in sulfide solid-state lithium ion conductors, Advanced Energy Materials, 9, 1900817 (2019)
2. Strain-stabilized ceramic-sulfide electrolytes, Small, 15, 1901470 (2019)
3. The effects of mechanical constriction on the operation of sulfide based solid-state batteries, Journal of Materials Chemistry A: 7, 23604 - 23627 (2019)

Rechargeable lithium ion batteries (LiBs) are commonly used as power sources, and they became the dominant energy storage technology for various range of applications including portable electronic, electrical vehicles, and large-scale energy storage.
Used as negative electrode for most of commercial cells because of its low cost and good theoretical capacity (372 mAh.g^-1), graphite, suffers from important stability issues.
The passivating layer formed on graphite electrode, well-known as solid electrolyte interphase (SEI), occurring because of the decomposition of organic liquid electrolyte can lead to capacity fading, electrolyte consummation and low lifetime. Despite the presence of the “stable” SEI layer, lithium plating, dendrite formation and in some case thermal run away may occur depending on the charging conditions. This poor interface, especially sensitive to low temperature and high currents poses an important challenge for the development of electric vehicles (EVs).
For some years, with safety and performance in mind, titanates composites have been studied as anode material. The lithium titanate spinel Li₄Ti₅O₁₂ (LTO) has drawn attention of many research groups, due to its high operating voltage preventing lithium plating, its long cycle life and its ultra-low volume change during the lithium insertion. This material might have been perfect for hybrid electric vehicles requiring high rate cycling and fast charge even with low temperature. However, a low specific capacity (175mAh.g^-1) leading to a low energy density associated as well with a gassing phenomenon drastically hinder the deployment of this material.
Another family of material exhibiting Wadsley-Roth shear structures, mainly composed of mixed Ti and Nb was introduced during the 50s and has shown the ability to intercalate lithium ions [1]. Later, Goodenough et al. showed in 2011 that TiNb₂O₇ (TNO) can be used as negative electrode material in a full cell system [2], keeping LTO’s advantages (high working potential and safety ) but offering a theoretical capacity of 387.6 mAh.g^-1 that is comparable to the one of graphite.
Many groups report advanced ways to synthesize this material such as solvothermal synthesis [3] and spray drying [4] but only little consideration was given to the study of the lithiation and degradation mechanisms [5].
In this work, we report that TNO electrodes present important differences of performances at high rates following their cycling history. Indeed, we notice that, when previously cycled at low rate (C/10 or below), the material exhibits less than the half of the discharge capacity obtained when directly cycled at high rate.
To understand this phenomenon, many investigations have been carried, in particular using in situ and post-mortem X-ray diffraction. In situ and operando X-ray diffraction can be a powerful tool to characterize crystalline evolution upon cycling and pushing forward the understanding of lithiation reactions.
We used a cell fitted with thin beryllium windows, with a mix of TNO and black carbon, a lithium metal as counter electrode and using EC/PC/DMC (1/1/3v) +1M LiPF₆ electrolyte.
Different conditions of cycling where used and diffractograms obtained were compared for a same lithiation rate. Clear and important evolutions of peak positions, shapes and intensities can be followed all along the lithiation process and allowed us to refine the lattice parameter.
We have been able to follow the lithiation process in the materials at different cycling conditions. We also try to stabilize and improve the comportment of the material with different solutions such as carbon coating or doping and we will present the results of these studies.

[1]. Cava et al., J. Electrochem. Soc., 1983, 130, 12, 2345
[2]. Hal & Goodenough, Chem. Mater., 2011, 23, 3404
[3]. Ise, et al., Solid State Ion., 2018, 320, 7
[4]. Zhu, et al., Appl. Mater. Interfaces, 2017, 9, 47, 41258
[5]. Guo et al., Energy Environ. Sci., 2014, 7, 2220

Electrode performance is largely determined by the structure of active materials, and thus can be advanced by synthesis of phase-pure materials, and control of their stoichiometry, morphology, surface properties. However, synthesizing materials with desired structure and properties has been difficult due to the complexity associated with chemical reaction and involvement of metastable intermediates. Additional challenge comes from the fact that synthesis is often undertaken under non-equilibrium conditions, making it hard to predict the synthesis process by theoretical computations. Herein, we report development and application of in situ spectroscopy techniques for real-time studies of synthesis to capture intermediates, thereby elucidating how synthesis parameters affect the kinetic reaction pathways and, consequently, the structural properties of the final products both in the bulk and at particle surface. By coupling with electrochemical characterization of the synthesized materials, such studies elucidate how structure, composition and synthesis affect electrochemical performance and therefore provide a basis for synthesis of cathode materials by design. Specific examples will be given on developing LiNi_0.8Mn_0.1Co_0.1 (NMC811) and other high-Ni cathodes for Li-ion batteries.
ACKNOWLEDGMENT. This work was supported by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office, Contract No. DE-SC0012704.

Improving the extremely low temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of high-rate discharge are in short supply. Herein, we demonstrate the holistic design of dual-graphite batteries, which circumvent the sluggish ion desolvation process found in typical lithium-ion batteries during discharge. These batteries were enabled by a novel electrolyte, which simultaneously provided high electrochemical stability and ionic conductivity at low temperature. The dual-graphite cells, when compared to industry-type graphite || LiCoO₂ full-cells demonstrated an 11 times increased capacity retention at -60 ^oC for a 10 C discharge rate, indicative of the superior kinetics of the “dual-ion” storage mechanism. These trends are further supported by GITT and EIS measurements at reduced temperature. This work provides a new design strategy for extreme low-temperature batteries.

As one of the most important energy storage devices, lithium ion batteries (LIBs) have been widely used in portable electronic devices due to its high energy density and long cycle life. However, for commercial lithium ion batteries with graphite as anode material, a common drawback is the relatively low specific capacity (372mAh g^-1) and the problem of Li plating under high current density. To solve the problems, one of effective strategies is to develop anode materials with high theoretical capacity. Among them, SnO₂, with higher theoretical capacity, low toxicity and natural abundance, is widely studied as the promising alternative anode material for LIBs. However, SnO₂ is accompanied by pulverization and aggregation during charge and discharge process, resulting in its fast capacity fading and poor rate performance. Herein, we have designed and synthesized SnO₂ nanoparticle (≈10 nm) uniformly distributing in porous carbon nanosphere with a continuous N-doped carbon shell (denoted as SnO₂/po-C@NC) via a multistep method. Here, dopamine due to its excellent physicochemical property was adopted as a conductive carbon shell to provide a fast electronic transport framework and thus homogenize lithiation/delithiation, when used as anode material, This architecture demonstrate enhanced capacity and excellent rate performance, SnO₂/Po-C@NC can deliver a high reversible capacity 936.8 mAh g^-1 after 100 cycles at 100 mA g^-1，even at the high current density of 3.2 A g^-1，an average capacity of 460.0 mA h g^-1 can be achieved.

Among electrical energy storage (EES) systems, sodium-ion batteries (SIBs) are very promising and have been attracting an ever-growing research interest in the past decade, due to the low cost and natural abundance of sodium element. Compared to the success of cathodes in SIBs, one main challenge is seeking high-performance anodes. To this end, in this work we investigated copper(I) sulfide (Cu₂S) as a promising SIB anode through mixing with nitrogen-doped graphene nanosheets (NGS) via a facile high-energy ball milling route. The resultant Cu₂S@NGS composite could achieve a sustainable high capacity of 300 mAh g^-1 over 500 cycles and accomplish a high rate capability up to 10 C (1C = 337 mA/g). Compared to all studies reported so far, our Cu₂S@NGS composite electrodes demonstrated the highest electrode capacity. Our analyses revealed that the substitution of NGS for carbon black has produced multiple beneficial effects: (i) inhibiting polysulfide shuttling effect, (ii) suppressing the formation of SEI layer, (iii) offering high electron and ion conductivity, and (iv) enhancing mechanical integrity of electrodes. We also systematically investigated the effects of voltage windows and surface coatings on enhancing the stable electrochemical performance of Cu₂S@NGS composite electrodes. This work represents a great advance in seeking high-performance anodes in SIBs.

Silicon has been regarded as the most promising high energy density anode for Li-ion batteries. However, it suffers from large volume expansion upon full lithiation and fast capacity fade. Si of porous structure has been known to accommodate the volume change and improve the cycling stability and hence has attracted extensive attention. Here, we report the synthesis of porous Si microspheres by thermite reduction of SiO₂ microspheres (500nm to 10 micron) from self-assembly of 70 nm SiO2 colloidal particles. The porous Si microspheres have uniform mesopores and Si crystallites of ~20 nm. The fine primary particles can shorten the Li⁺ transport route and avoid the pulverization of Si. The obtained porous silicon delivers a reversible capacity of 1900 mAh g^-1 at 0.5C and 85% capacity can be retained after 100 cycles. In another effort, CNT@SiO₂ coaxial cables were synthesized using sol-gel method and then self-assembled into microspheres in microemulsion. Hierarchical porous CNT@Si@C microspheres obtained after thermite reduction reaction demonstrated excellent electrochemical performance. The anodes deliver 90% capacity retention over 100 cycles at the areal loading of ~3 mAh/cm2. These works represent significant steps in the development of Si anodes and provide guidance for battery material synthesis.

Si anode with high theoretical capacity has shown its promise as the next generation anode for high energy density lithium ion batteries. The large volume change of Si anode during cycling has been well accepted as the main reason that leads to its poor cycling stability. However, the high reactivity of lithiated Si, namely Li_xSi, is also responsible for the fast consumption of electrolyte and therefore, the quick capacity decay. To address this issue, we coated Si anode with Mg where the Mg can diffuse into the bulk Si anode and involve in the formation of ternary Li-Mg-Si Zintl phase upon lithiation. The ternary Zintl phase had been proved to be more stable toward electrolyte than Li_xSi. The formation of this new phase by Mg coating suppressed the decomposition of electrolyte, altered the solid electrolyte interphase, and resulted in a significantly improved cycling performance of Si anode. This work provides a new approach to tuning the compositions and properties of Si anodes.

Rechargeable aluminum-graphite dual-ion batteries (AGDIBs) have attracted the attention of electrochemists and material scientists in recent years due to their low cost and high-performance metrics, such as high power density (up to 175 kW kg⁻¹), energy efficiency (≈ 80-90%), long cycling life, and high energy density (up to 70 Wh kg⁻¹), suited for grid-level stationary storage of electricity [1]. The key feature of AGDIBs is the exploitation of the reversible oxidation of the graphite network with concomitant and highly efficient intercalation/de-intercalation of AlCl₄^- anionic species between graphene layers. In this talk, we discuss the utility of AGDIBs as a highly promising post-Li-ion technology for low-cost and/or large--scale storage of electricity [2,3]. In particular, we provide a balanced analysis of the overall cell-level energy density of AGDIBs. In view of its non-rocking chair operation mechanism, we show the achievable energy densities as a function of the composition of chloroaluminate ionic liquid (AlCl₃ content) and compare it with other battery electrochemistries suited for stationary storage of electricity (such as lead-acid or vanadium redox flow). Specific emphasis is given to the unbiased and correct reporting of their theoretical cell-level energy densities. Furthermore, we discuss also other issues associated with this technology, one being the incompatibility of most metallic current collectors with the corrosive AlCl_3-based ionic liquids. We then demonstrate a novel concept of flexible AGDIB using current collectors from earth-abundant elements and point to key challenges in the development and practical deployment of AGDIBs [4]. Finally, we also discuss an amternative dual-ion battery utilizing a highly concentrated electrolyte solution of 5 M potassium bis(fluorosulfonyl)imide in alkyl carbonates [5]. The resultant battery offers an energy density of 207 Wh kg⁻¹, owing to the high weight content of the electroactive species (65 wt%) in the electrolyte and a high operation voltage of 4.7 V.

References
[1] K.V. Kravchyk, M.V. Kovalenko. Adv. Energy Mater. 2019, 1901749.
[2] K. V. Kravchyk, S. Wang, L. Piveteau, and M.V. Kovalenko. Chem. Mater. 2017, 29, 4484-4492.
[3] S. Wang, K.V. Kravchyk, F. Krumeich, and M.V. Kovalenko. ACS Appl. Mater. Interfaces. 2017, 9, 28478-28485.
[4] S. Wang, K.V. Kravchyk, A.N. Filippin, U. Müller, A.N. Tiwari, S. Buecheler, M.I. Bodnarchuk, and M.V. Kovalenko. Adv. Sci. 2017, 1700712.
[5] K.V. Kravchyk, P. Bhauriyal, L. Piveteau, C.P. Guntlin, B. Pathak, M.V. Kovalenko
Nat. Commun. 2018, 9, 4469.

The growth of the lithium-ion battery market is being fueled by the expansion of its use in electric vehicles. To achieve long cycle life and high reliability, lithium-ion batteries have to be operated in the limited conditions as for voltage, current, and temperature. Above all, it is important for using lithium-ion batteries safety that understanding and improvement of the thermal stabilities of active materials with electrolyte under elevated temperature. In this study, the thermal stability of the graphite electrode used in Li-ion batteries was studied by in-situ X-ray diffraction (XRD) during elevating the temperature. The in-situ XRD measurements clarified that phase transitions from C₆Li to C₁₂Li and from C₁₂Li to graphite occured in the temperature range of 250-305 degree C and 305-320 degree C, respectively, which corresponds to the exothermic behaviors detected by differential scanning calorimetry. The de-lithiation behavior under anomalous elevated temperature might be passed with an intermediate state between C₆Li and C₁₂Li, which is not observed in electrochemical processes.

The search for electrochemical energy storage that provides good safety as well as high energy storage performance has reignited interested in materials that operate in aqueous electrolytes. In these electrolytes, protons are increasingly identified as the relevant intercalating species into the vacant sites of transition metal oxide electrodes. Using selective ion etching of a bismuth tungsten oxide, we synthesized a non-equilibrium tungsten oxide hydrate (W₂O₆*H₂O) that exhibits both high proton intercalation capacity (~ 55 mAh/g) and excellent kinetics enabling charge/discharge times of just 12 seconds. The capacity is significantly higher than what can be attained with tungsten oxide hydrates obtained via typical acid precipitation routes or the anhydrous tungsten oxide. Intriguingly, the performance is attained with thick electrodes consisting of large particles tens of microns in diameter. Utilizing a combined experimental and theoretical approach, this talk will discuss how the structure of the non-equilibrium hydrate influences its proton intercalation kinetics. Finally, we will discuss future opportunities in the use of selective-ion etching of transition metal oxides for the synthesis of non-equilibrium structures for energy storage.

Interfaces play a fundamental role in defining the performance of batteries, regardless of the type of battery configuration. However, the localized nature of interfaces requires high spatial resolution characterization techniques to fully understand their structure and properties. State-of-the-art atomic-resolution and/or in situ scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) are indispensable tools for characterizing the local structure and chemistry of materials but they are difficult to use to measure many properties that dictate the cycling performance of batteries. For example, it is challenging to directly observe the lithium distribution at lattice sites, to probe electrostatic potential drop at interfaces, to measure electronic and ionic conductivity of local features, and to detect interfacial dynamic evolution under in situ electrochemical cycling conditions. Further, current techniques are largely limited to electron-beam irradiation and samples that do not contain liquids. Here, we outline emerging electron microscopy techniques that allow us to overcome these limitations and highlight several recent studies that have been enabled by techniques such as 4D-STEM, monochromated EELS, cryo-STEM, and new integrated in situ stages. The limitations of these techniques and the pitfalls in data interpretations will be discussed. We provide a perspective as to how these methods can be paired to deliver new insights into the static and dynamic behavior of functional interfaces in batteries.

Acknowledgement
Research sponsored by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy Office of Science User Facility.

Global demand for high-performance energy storage systems has grown tremendously in recent years. The all-solid-state lithium-ion batteries (ASSLIBs) are promising for such storage solutions on account of the lithium metal anodes with high areal capacity and the solid-state electrolytes (SSEs) with critical safety.¹ However, the interfacial failure of the ASSLIBs posed a major hurdle towards the design of high-performance solid-state batteries.^2,3,4 Time-resolved in operando techniques (e.g. in situ microscopy, synchrotron X-ray tomography) are ideal for the direct and quantitative characterization of the interfacial deteriorations. However, the in situ analysis of solid-state batteries is still in its primary stage due to the difficulties in probing the buried interfacial layer. The specific causes of the high interfacial impedance and the lithium dendrite growth that deteriorates the battery in a few cycles remain nebulous.

To this end, we developed a multi-dimensional diagnostic platform that allows the direct probe of the chemical and spatial distribution on the interface while the cell operates. Parameters such as pressure and temperature, which have a strong influence on cell behavior, are also enabled by the platform. Moreover, the platform can be transferred between analytical instruments, including SEM, ToF-SIMS, and Raman, for a synergistic diagnose of the structural and chemical evolutions in solid-state Li batteries. A deeper understanding of interfaces and dendrites evolutions has been acquired by the testing platform, including (1) correlation between void formation and electrolyte decomposition, and (2) creeping mechanical properties of the lithium metal during the cell operations. These in-depth understandings will allow us to effectively optimize and enable further enhancements of solid-state Li batteries.

References
[1] T. Famprikis and C Masquelier et al, Nat. Mater. 18, (2019) 1278-1291
[2] K Park and J Goodenough et al, Chem. Mater. 28, (2016) 8051-8059
[3] S Wang and A Manthiram et al, J. Am. Chem. Soc. 140 (2018) 250-257
[4] Y Tian and G Ceder et al, Energy Environ. Sci. 10 (2017) 1150-1166

Li-ion batteries are the critical enabling technology for the portable devices, electric vehicles (EV), and renewable energy. However, the safety and energy density of current Li-ion batteries still need to be improved to satisfy the requirments for these applications. We systematically investigated the electrochemical performance of the nonflemable fluorinated orgnic electrolytes and solid state electyrolytes for high energy Li and Li-ion batteries. The Li dendrite formation in liquid electrolyte and solid state Li metal batteries was proposed and validiated. The critical issues of these safe electrolytes are also discussed.

Silicon is a viable alternative to graphitic carbon as an electrode in lithium-ion cells and can theoretically store >3,500 mAh/g. However, lifetime problems have been observed that severely limit its use in practical systems. The major issues appear to involve the stability of the electrolyte and the uncertainty associated with the formation of a stable solid electrolyte interphase (SEI) at the electrode. Recently, calendar-life studies have indicated that the SEI may not be stable even under conditions where the cell is supposedly static. Clearly, a more foundational understanding of the nature of the silicon/electrolyte interface is required if we are to solve these complex stability issues. A multi-lab consortium has been formed to address a critical barrier in implementing a new class of materials used in lithium-ion batteries that will allow for smaller, cheaper, and better performing batteries for electric-drive vehicles. This consortium, named the Silicon Electrolyte Interface Stabilization (SEISta) project, was formed to focus on overcoming the barrier to using such anode materials. Five national laboratories are involved: the National Renewable Energy Laboratory (NREL), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), Oak Ridge National Laboratory (ORNL), and Sandia National Laboratories (SNL). The SEISta project was specifically developed to tackle the foundational understanding of the formation and evolution of the solid-electrolyte interphase on silicon. This project will has a primary goal of understanding the reactivity of the silicon and lithiated silicon interface with the electrolyte in lithium-ion systems. The overall objective for SEISta is to understand the nature and evolution of the SEI on silicon anodes.
Several issues must be addressed to enable progress in this area. Materials Standardization is critical to this project and deployment of standardized samples and experimental procedures across the team is a foundation of the project. Full characterization of any new sample that is to be used for SEI studies to ensure reproducibility and full understanding of the material. The materials standardization and model compounds will enable the researchers to systematically investigate the formation of the solid-electrode interphase using a wide variety of the spectroscopy techniques—from different optical, microscopy, and electrochemistry—to determine how the SEI forms based on the nature of the silicon surface, and how it evolves over time. This presentation will detail recent advances that the SEISta team has made to the understanding of the SEI on silicon.

The demand from portable electronics and electric vehicles call for high energy batteries beyond the current lithium ion batteries. Here I will present our recent progress on materials and interfacial design to enable much high energy density batteries, which include 1) High capacity Si anodes with success in commercialization; 2) Li metal anodes: host and interface design to over the lithium metal dendrite formation and interfacial instability; 4) Sulfur as an earth abundant material for high capacity cathodes; 4) Our pioneering development of cryogenic electron microscopy for understanding the battery materials and solid-electrolyte interphase down to atomic scale resolution.