Xiaolin Li, Pacific Northwest National Laboratory
Prashant Kumta, University of Pittsburgh
Xinping Qiu, Tsinghua University
Donghai Wang, The Pennsylvania State University
ACS Energy Letters | ACS Publications
Angstrom Thin Film Technologies LLC
Bio-Logic USA, LLC
Pacific Northwest National Laboratory
ET06.01: General Introduction, Reliability and Safety
Monday PM, November 26, 2018
Hynes, Level 3, Room Ballroom A
8:30 AM - *ET06.01.01
Materials for High Energy Li and Li-Ion Batteries
M. Stanley Whittingham1
State University of New York at Binghamton1Show Abstract
Over the last decade the energy density of lithium-based batteries has gradually increased, but commercially available cells have now topped out at around 200-250 Wh/kg at the cell level. I will describe several materials-centered approaches that will allow in excess of 300-350 Wh/kg and 700 Wh/l. First the carbon-based anode must be replaced by a higher capacity material, preferably lithium metal itself; we have found that tin-based anodes can achieve 50-100% greater capacity than carbons with coulombic efficiencies over 99.5%. Second on the cathode side, I will describe two options: two-electron systems using lithium, and high nickel NMCAs, both of which have theoretical energy densities of around 1 kWh/kg and have the capability of attaining 1 kWh/liter. The safety aspects will also be covered. This work is supported by US DOE, BES-EFRC and EERE-VTO-BMR.
9:00 AM - *ET06.01.02
Reliability of Li-Ion Batteries for Grid Application
Daiwon Choi1,Alasdair Crawford1,Vilayanur Viswanathan1,David Reed1,Vincent Sprenkle1
Pacific Northwest National Laboratory1Show Abstract
Li-ion batteries are expected to play a vital role in stabilizing the electrical grid as solar and wind generation capacity becomes increasingly integrated into the electric infrastructure. In this work, different commercial Li-ion batteries based on LiNi0.8Co0.15Al0.05O2 (NCA), LiNixMnyCozO2 (NMC) and LiFePO4 (LFP) cathode chemistries have been tested under the grid duty cycle protocols recently developed for frequency regulation (FR) and peak shaving (PS) with and without being subjected to electric vehicle (EV) drive cycles. The lifecycle comparison derived from capacity, round trip efficiency (RTE), resistance, charge/discharge energy and total utilized energy of the battery chemistries will be presented. Furthermore, degradation mechanisms of different battery chemistries will be discussed. The results can be used as a guideline for selection, deployment, operation and cost analyses of Li-ion batteries used for different applications.
10:00 AM - *ET06.01.03
Mechanisms and Ramification of Overcharge on Battery Materials
Joshua Lamb1,Loraine Torres-Castro1,Mohan Karulkar1,June Stanley1
Sandia National Laboratories1Show Abstract
Overcharge testing has long been used as a standard abuse test evaluation for lithium ion batteries, which have notably poor tolerance for overcharge and overvoltage conditions. While this has historically been strictly an abuse test, large potential gradients created by high rate charge and discharge operations in electric vehicle and stationary storage applications may lead to areas of localized overcharge or overpotential on the electrodes. This work looks at high capacity (10 AH) prismatic pouch cells, applying overcharge from 105 – 200% total State of Charge (SOC), up to and including energetic thermal runaway of cells. The mechanisms of overcharge failure are investigated using electrochemical techniques including EIS and differential capacity measurements to evaluate the degradation and failure mechanisms that occur during the overcharge condition. This is supported with materials evaluations to further evaluate the impact of overcharge on the constituent materials.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & 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.
10:30 AM - ET06.01.04
Multifunctional Lithium-Ion Exchanged Zeolite Coated Separator for Lithium-Ion Batteries
Jiagang Xu1,Xingcheng Xiao1,Sherman Zeng1,Mei Cai1,Mark Verbrugge1
General Motors1Show Abstract
The skyrocketing price of cobalt pushes battery manufacturers to look back into low cost manganese containing positive electrodes. However, manganese dissolution has been considered as a critical problem for the majority of manganese containing positive electrodes. Although many efforts have been devoted to stabilizing the crystal structure and exploring new electrolyte additives, less progress has been reported so far. In this work, we have developed a novel multifunctional separator, targeting the root cause of manganese dissolution. A lithium-ion exchanged zeolite has been coated on polymer separator as the ceramic coating, which provides multi-functions to mitigate the issues arose from sequential scenario associated with manganese dissolution, including: 1. Trapping trace water: the high surface area in zeolite traps the trace water in the electrolyte, mitigating the hydrolysis of lithium salt and HF generation. 2. HF scavenger: in case of the HF already existing in the electrolyte, Al2O3 in the zeolite can preferentially react with HF as the scavenger due to the high surface area, therefore protecting the oxides in positive electrodes 3. Trapping Mn ions: in the worst scenario of Mn dissolved into electrolyte, the Li ion in zeolite will have the ion exchange with Mn ions in the electrolyte and trap Mn ions in the separator to avoid its damage to the SEI layer on anode side. In addition, lithium-ion exchanged zeolite separator can improve the wettability and thermal stability of the plain separator on which zeolite is coated. Based on this technology, we have demonstrated that Lithium-ion exchanged zeolite separator leads to the enhanced cycle performance (high capacity and Coulombic efficiency) of graphite/ (LiNi0.5Mn0.3Co0.2O2+LiMn2O4) full cells at both room temperature and elevated temperature, comparing with the plain separator and commercial alumina coated separator. The coin cell with Li-zeolite coated separator exhibits an average Coulombic efficiency of 99.89% and achieves a capacity retention rate of 78.3% after 500 cycles at 25 °C. We find out that a lower amount of manganese is present on the cycled graphite electrode when Li-zeolite coated separator is used, suggesting less side reactions resulted from Mn.
10:45 AM - ET06.01.05
Novel Battery Separators Enabled by Ultrathin, Robust Solid Electrolytes
Shaofei Wang1,Andrew Westover2,Sergiy Kalnaus2,Andrew Kercher2,Nancy Dudney2,William West3,Wyatt Tenhaeff1
University of Rochester1,Oak Ridge National Laboratory2,NASA Jet Propulsion Laboratory3Show Abstract
Solid electrolytes with low area specific resistance must be developed to enable high energy density lithium metal batteries. In addition to high ionic conductivities and large electrochemical stability windows, solid electrolytes also require robust mechanical properties to allow for large-scale production and successful integration into conventional lithium battery cell designs. To achieve these features, a novel solid electrolyte separator design was developed, in which a 50 - 100 nm fully dense solid electrolyte layer was coated onto microporous Celgard separators. The supporting Celgard made the solid electrolyte more robust and flexible, which enabled integration into coin cells. Due to its thinness, the resistance of the solid electrolyte layer was 5 - 10 Ω-cm2. The solid electrolyte also showed low interfacial resistance with liquid electrolyte. The total resistance of solid electrolyte-Celgard membrane was determined to be 40 Ω-cm2 in alkyl carbonate electrolytes, which is much lower than Garnet and Ohara solid electrolytes. The solid electrolyte membrane also was also shown to inhibit the crossover between anode and cathode in Li-S cells. The Li-S cell enabled by the new solid electrolyte membranes showed high coulombic efficiency and stable cycling performance. The advent of the new robust solid electrolyte paves the way for the commercialization of high energy density lithium metal batteries.
This work was supported by the ARPA-E IONICS program, U.S. Department of Energy, award DE-AR0000775.
11:00 AM - ET06.01.06
Long-Term Calendar Degradation in Li-Ion Batteries
Aziz Abdellahi1,Berislav Blizanac1,Brian Sisk1
A123 Systems LLC1Show Abstract
With the increased penetration of electrified vehicles in the automotive market, requirements pertaining to battery durability are becoming increasingly stringent. To meet the requirements of the automotive industry, lithium-ion batteries must exhibit extensive life before reaching a terminal state of capacity loss and impedance growth. For battery designers and manufacturers, it is therefore of paramount importance to understand and predict long-term battery cell degradation based on a necessarily limited set of accelerated degradation tests.
Long-term calendar aging, defined as the temperature-induced cell degradation in the absence of current, is especially difficult to predict at relevant battery operating temperatures (25oC – 45oC). Unlike cycling tests, which can be rapidly conducted to the end-of-life by removing rest periods between cycles, calendar tests cannot be directly accelerated. To this end, a variety of empirical and physics-based models have been developed to predict the long-term storage behavior of battery packs based on a set of accelerated storage tests conducted at high temperatures. However, the validity of these calendar predictions has not, to the best of our knowledge, been extensively studied against actual long-term storage data surpassing the 4 year mark.
In this presentation, we present a set of long-term storage experiments performed over the course of 4-to-6 years on LiFePO4/graphite cells, at various states of charge and temperatures. Analysis of the storage data sheds light on the long-term degradation mechanism in the cell, and demonstrates a transition between a reaction-controlled to a diffusion-controlled growth of the anodic solid electrolyte interphase (SEI). The dependence of state of charge and temperature on the degradation rate is clarified, and the predictive performance of empirical calendar life models is assessed. This work provides a mechanistic analysis of the nature of long-term degradation mechanisms in Li-ion batteries and paves the way towards an improvement of the predictive ability of empirical calendar life models. The conclusions of this study can also serve to understand long-term calendar degradation in higher-voltage NMC/graphite batteries, in which both the anode and the cathode may experience calendar degradation at high states-of-charge.
11:15 AM - ET06.01.07
Adaptive Current-Collectors for Safe High-Energy Rechargeable Batteries
Sean Doris1,Adrien Pierre1,Elif Karatay1,Warren Jackson1,Robert Street1
Palo Alto Research Center1Show Abstract
High energy density rechargeable batteries are critical for the widespread adoption of EVs, however their high energy density leads to an inherent safety risk if an internal short circuit (ISC) forms and releases all the energy in the battery in seconds. When an ISC occurs – from dendrite formation, cell deformation/damage, or a manufacturing defect – the entire battery capacity rapidly discharges. This release of energy leads to extremely high temperatures near the short that can induce thermal runaway, cell rupture or venting, and fire. While the use of shutdown separators can help mitigate ISCs in smaller cells, they are often ineffective in the larger, high-energy batteries used in EVs and grid storage applications. Rather than relying on thermally-induced shutdown that may fail to shut down regions of the battery far from the ISC, it is preferable to directly detect and stop the internal current that flows during an ISC. In this presentation, I will introduce our work on adaptive current-collectors, which allow for direct control over the local current that flows between the current-collector and the active material by simple printed electronic circuits. I will show how the electrical properties of printed electronics can be tuned to meet the demanding requirements of adaptive current-collectors, including low resistance during normal operating currents and high resistance under abuse conditions. Our simulations indicate that adaptive current-collectors can reduce the current flowing through ISCs by more than 90%, converting this catastrophic failure mode into a graceful one. In addition to enabling safe high-energy rechargeable batteries, the development of adaptive current-collectors will give battery users finer control over current flow at the sub-cell level, which is expected to improve battery reliability and rate capability.
ET06.02: All Solid-State Battery
Monday PM, November 26, 2018
Hynes, Level 3, Room Ballroom A
1:30 PM - *ET06.02.01
All-Solid-State Lithium Metal Batteries Utilizing Polyrotaxanes as New Family of Solid Polymer Electrolytes
Martin Winter1,2,Laura Imholt1,Gunther Brunklaus1,Isidora Cekic-Laskovic1
Forschungszentrum Juelich GmbH1,University of Münster2Show Abstract
Lithium metal constitutes an attractive anode material mainly due to its high theoretical specific capacity of 3860 mAh g−1, ten times higher than graphite (372 mAh g−1). The use of lithium metal in rechargeable batteries with typical liquid organic solvent based electrolytes suffers so far from severe safety problems associated with the formation of high surface area metallic lithium (HSAL) upon repeated charge/discharge. Solid polymer electrolytes (SPEs) designed to be compatible with lithium metal are able to mechanically suppress HSAL formation and are considered as viable alternative. Solvent-free SPEs exhibit advantages in terms of mechanical stability, operational safety and simplicity of cell design. However, application of polymer electrolytes to all-solid-state lithium ion batteries (ASS-LIBs) and all-solid-state lithium ion batteries (ASS-LMBs), requires improvements in respect to lithium ion conductivity, especially at ambient temperature.
Although high ionic conductivities can be achieved by high chain mobility linked to low molecular weight polymers, they are mostly too soft and therefore cause deterioration in mechanical stability of the SPE. In order to use low molecular weight polymers for fast lithium ion transport with sufficient mechanical strength at the same time, one strategy is related to utilization of a hyperbranched co-polymer where one segment represents a stable, hard backbone while the second segment is derived from a soft polymer with high ionic conductivities. With this in line, a new generation of Li+-conducting SPEs obtained from supramolecular self-assembly of PEO, cyclodextrin (CD) and lithium salt was designed and thoroughly investigated for application in lithium metal batteries (LMBs) and LIBs. When mixing an aqueous solution of PEO together with an aqueous solution of CD, a precipitate forms where the CD is threaded onto a PEO chain. The channel-type structure formed by self-assembly of PEO and CD can be used as the backbone structure whereas the hydroxyl groups of CD rings can be modified. Here, we use the ability of CD being the initiator for ring-opening polymerization of cyclic carbonates. This strategy enables synthesis of grafted polycarbonate side chains with low molecular weight. The obtained inclusion complexes show impressive ionic conductivity up to 1 mS cm-1 at 60 °C, together with high oxidative stability and allow for application in LFP/Li cells at 40 °C for more than 200 charge/discharge cycles. Post mortem XPS and SEM studies confirm that the polymer/LiTFSI penetrates the cathode upon cycling, facilitating improved contacts. This new system provides a platform for further modifications of the polymer side-chains.
2:00 PM - ET06.02.02
First-Principles Modeling of Polymer Electrolyte/Lithium-Metal Interfaces for High Energy Batteries
Moyses Araujo1,Mahsa Ebadi1,Cleber Marchiori1,Daniel Brandell1
Uppsala University1Show Abstract
Lithium metal combines the lowest reduction potential in the electrochemical reactivity series with a high theoretical specific capacity, and using metallic Li as anode would therefore significantly improve the energy density of the Li-battery. There exist, however, some challenges in the application of the Li metal electrode, such as safety risks and low coulombic efficiency . In recent years, there has been a growing interest to find more stable electrolytes when in contact with the reactive Li electrode in Li-metal batteries. It has in this context been found that solid polymer electrolytes (SPEs), formed by doping a polymer with a lithium salt, are promising candidates, which can provide both high mechanical stability and better battery safety [2,3]. The major disadvantage of SPEs – their low inherent ion conductivity – can be resolved by a somewhat higher operational temperature.
We have, in a number of studies [4-6], modelled the Li metal/electrolyte interface using different simulation techniques. In this current study, we apply computational materials modelling to investigate the interface between the ion-conductive polymeric systems and Li metal surfaces by first principle calculations. To this end, Density Functional Theory (DFT) have been used to study several potential SPE host polymers such as poly(trimethylene carbonate) (PTMC), poly(vinyl alcohol) (PVA) and polycaprolactone (PCL), in order to get insights into their electronic structures and their stability when in contact with the Li metal surface. Using this knowledge, conclusions are drawn on which ion-conductive polymers are stable at the Li-metal surface, and which can adhere well to it.
 X. B. Cheng, R. Zhang, C.-Z. Zhao, F. Wei, J.-G. Zhang, Q. Zhang, Adv. Sci. 3 (2015) 1500213.
 J. Kalhoff, G. G. Eshetu, D. Bresser, S. Passerini, ChemSusChem 8 (2015), 2154.
 J. Mindemark, M. J. Lacey, T. Bowden, Daniel Brandell, Prog. Polym. Sci (2018), doi.org/10.1016/j.progpolymsci.2017.12.004
 M. Ebadi, D. Brandell, C.M. Araujo, J. Chem. Phys. 145 (2016) 204701.
 M. Ebadi, L.T. Costa, C.M. Araujo, D. Brandell, Electrochim. Acta. 234 (2017) 43.
 M. Ebadi, M. J. Lacey, D. Brandell, C. M. Araujo, J. Phys. Chem. C, 121 (2017) 23324.
2:15 PM - ET06.02.03
Stabilizing Polymer Electrolytes in High-Voltage Lithium Batteries
Snehashis Choudhury1,Lynden Archer1
Cornell University1Show Abstract
More than forty years after the first report of a rechargeable lithium battery, electrochemical cells that utilize metallic lithium anodes are again under active study for their potential to provide more energy dense storage in batteries. Electrolytes based on small-molecule ethers and their polymeric counterparts are known to form stable interfaces with alkali metal electrodes and for this reason are among the most promising choices for rechargeable lithium batteries. Uncontrolled anionic polymerization of the electrolyte at the low anode potentials and oxidative degradation at the working potentials of the most interesting cathode chemistries have led to a quite concession in the field that solid-state or flexible batteries based on polymer electrolytes can only be achieved in cells based on low- or moderate-voltage cathodes. In this work, we show that cationic chain transfer agents in an ether electrolyte provide a fundamental strategy for limiting polymer growth at the anode, enabling long term (at least 2000) cycles of high-efficiency operation of asymmetric lithium cells. Building on these ideas, we also report that cathode electrolyte interphases composed of anionic polymers and the superstructures they form spontaneously at high electrode potentials provide as fundamental a strategy for extending the high voltage stability of ether-based electrolytes to potentials well above conventionally accepted limits. Through computational chemistry, we discuss the mechanistic processes responsible for the extended high voltage stability and on this basis report Li||NCM cells based on a simple diglyme electrolyte that offer unprecedented stability in extended galvanostatic cycling studies.
3:30 PM - *ET06.02.04
Design Principles for Solid Electrolyte–Electrode Interfaces in All-Solid-State Li-Ion Batteries
University of Maryland-College Park1Show Abstract
All-solid-state Li-ion battery is a promising next-generation energy storage technology, providing intrinsic safety and higher energy density. Currently, high interfacial resistance and interfacial degradation at the solid electrolyte-electrode interfaces are the critical issues limiting the cycling and rate performance of all-solid-state battery. Fundamental understanding about the interfaces is yet lacking due to the difficulties of direct experimental characterizations. In this presentation, I will show how we use first principles computation to bring new understanding about these buried interfaces. Using our developed computation approach based on large materials database, we calculated the true electrochemical stability window of solid electrolytes and predicted interphase decomposition products, which are verified by in-situ experiments at solid electrolyte-electrode interfaces. I will discuss the critical role of decomposition interphase layers at electrolyte-electrode interface and their effects on the battery performance. From these insights, we are able to classify different interface types for different solid-electrolyte and cathode pairs and to estimate their impacts on battery performance. Moreover, specific interfacial engineering strategies are proposed to address potential issues at these interfaces in all-solid-state Li-ion batteries. I will present the predicted novel chemistry and strategies to stabilize lithium metal anode, which is greatly impeded by the lack of knowledge about lithium-stable materials chemistry. With first-principles calculations based on large materials database, we found that most oxides, sulfides, and halides, which were commonly studied as protection materials, are reduced by lithium metal due to the reduction of metal cations. New materials chemistry that are stable against Li metal are predicted, as promising candidates for lithium metal anode protection to achieve long-term stability. This series of computational studies provides novel insights and general design principles for interface engineering in all-solid-state Li-ion batteries.
4:00 PM - ET06.02.06
Effects of Polymer Coatings on Electrodeposited Lithium Metal
Jeffrey Lopez1,Allen Pei1,Yi Cui1,Zhenan Bao1
Stanford University1Show Abstract
The electrodeposition of lithium metal is a core process in next-generation, high energy density energy storage devices. However, the high reactivity of the lithium metal causes short cycling lifetimes, and there are safety issues due to the growth of dendrites. Recently, a number of approaches have been pursued to stabilize the lithium metal interface, including soft polymeric coatings that have shown the ability to enable high-rate and high-capacity lithium metal cycling, but a clear understanding of how to design and modify these coatings has not yet been established. In this work, we studied the effects of several polymers with systematically varied chemical and mechanical properties as coatings on the lithium metal anode. By examining the early stages of lithium metal deposition we determine that while global morphology depends on the coating quality and mechanics, the local morphology of the lithium particles is strongly influenced by the chemistry of the polymer coating. We have identified polymer dielectric constant and surface energy as two key descriptors of the lithium deposit size. Low surface energy polymers were found to promote larger deposits with smaller surface areas. This is consistent with a reduction of the coatings interaction with the lithium surface and thus an increase in the interfacial energy. On the other hand, high dielectric constant polymers were found to increase the exchange current and gave larger lithium deposits, suggesting improved Li+ ion solvation in the coating and decreased nucleation rate. We also note that the thickness of the polymer coating should be optimized for each individual polymer, and that polymer reactivity is an important parameter to be considered as it was found to strongly influence the Coulombic efficiency. Overall, this work offers new fundamental insights into lithium electrodeposition processes and provides direction for the design of new polymer coatings to better stabilize the lithium metal anode.
4:15 PM - ET06.02.07
Design and Architecture of a Stable Solid-Electrolyte Interphase for the Lithium Metal Battery Anode Using a Reactive Polymeric Composite
Yue Gao1,Tianhang Chen1,Qingquan Huang1,Thomas Mallouk1,Donghai Wang1
The Pennsylvania State University1Show Abstract
Rechargeable battery technology based on the lithium (Li) metal anode is plagued by the unstable solid-electrolyte interphase (SEI), which grows upon cycling and is associated with dendritic/mossy Li deposition. A key challenge in improving SEI stability lies in regulating its chemical composition and nanostructure. Here we report a new approach that enables the design of SEI layers with tunable structure and stable properties. This involves the use of a reactive polymeric composite, which can generate a stable SEI layer in situ by reacting with Li to occupy surface sites and then electrochemically decomposing to form nanoscale SEI components. Cryo-TEM shows that the resulting SEI layer is composed of organic polymeric Li salts, nanoparticles of inorganic Li salts, and two-dimensional nanosheet components. This conformal nanocomposite SEI layer exhibits excellent passivation, homogeneity, ionic conductivity, and mechanical strength and stabilizes the interface for dendrite-free Li deposition in a conventional carbonate electrolyte. 950-cycle life was achieved in a full cell paired with a LiNi0.5Co0.2Mn0.3O2 cathode. Moreover, under lean electrolyte conditions, the full cells also show significantly extended cycle lives, owing to the excellent stability of the polymeric nanocomposite SEI.
4:30 PM - ET06.02.08
Design and Characterization of a Solid Hybrid Electrolyte for Lithium-Ion Batteries
Florent Leclercq1,Cédric Lorthioir1,Laura Coustan1,Christel Laberty-Robert1
Laboratoire de Chimie de la Matière Condensée de Paris1Show Abstract
Despite the development of new technologies, such as lithium-sulfur or sodium-ion cells, lithium-ion devices remain the most used batteries: they are found in a majority of electronic devices and the demand for electric vehicles keeps growing. Their performance and characteristics vary according to the chosen electrode but their main advantages are their high energy density and their low self-discharge. However, lithium-ion batteries suffer safety risks which are mainly due to the use of liquid electrolytes. These electrolytes are based on a lithium salt dissolved in a mix of organic solvents and therefore are highly flammable. A safer alternative is to replace this liquid electrolyte by a solid one. Ceramic electrolytes are a first possibility but they are often complex to synthesize and too rigid. Thus, solid polymer electrolytes are good candidates regarding their flexibility but they have a rather low conductivity and poor mechanical properties.
This work focuses on the conception of a solid hybrid electrolyte. The organic part is composed of a mix of polyethylene oxide (PEO), known for its lithium conductivity, and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), known for its mechanical properties. The inorganic part is a silica network formed in situ via a sol gel reaction. This network is functionalized with an immobilized ionic liquid in order to increase the conductivity of the electrolyte. These components are dissolved in N,N-dimethylformamide altogether with a lithium salt, LiTFSI, and a first set of solid electrolyte is accomplished by solvent casting. Conductivity and lithium transference number are measured in temperature while the structure and the transport at different scales are analyzed by NMR, SAXS-WAXS, and Differential Scanning Calorimetry (DSC). Electrochemical performances at different rates are assessed in full cell using LiFePO4 as the cathode and metallic lithium as the anode. Then, the importance of microstructure is investigated by achieving a second set of solid electrolyte. A skeleton of PVDF-co-HFP and functionalized silica is electrospun, producing a mat of fibers of 100nm in diameter. The space between fibers is then filled by concentrated LiTFSI or PEO/LiTFSI salts. The structure as well as their performances will be discussed using the same techniques.
4:45 PM - ET06.02.09
Effects of Ionic Correlation on Transport in Solid Polymer and Concentrated Ionic Liquid-Based Electrolytes from Molecular Dynamics Simulations
Nicola Molinari1,2,Jonathan Mailoa2,Boris Kozinsky1,2
Harvard University1,Robert Bosch LLC2Show Abstract
Electrolytes have become key players in the design of modern high-energy solutions as they can be leveraged to enhance various important aspects of the device such as recharge time and efficiency, anode/cathode stability, and safety. However, conductivity and general transport properties of the cation/anion pair(s) dissolved in the electrolyte often pose a technological limit to the viability of the battery, and progress in fundamental insights into the origin of transport limitations are challenging yet extremely valuable. In our group, molecular modelling techniques are adopted in order to shine light on transport properties and correlation effects in electrolyte system.
Poly(ethylene) oxide (PEO) -based solid polymer electrolytes have a long history of research due to the easy processability and good transport properties, yet new observations that challenge our conventional understanding are still reported, especially at high salt concentrations relevant for technological applications. Our molecular dynamics simulation study of such regimes for one of the most prominent materials, PEO-Li-TFSI, reveals the central role of the anion in coordinating and hindering Li ion movements. In particular we observed significant competition between the anion and the polymer backbone to coordinate lithium atoms and surprising formation of asymmetric cation-anion clusters. In particular, the latter novel observation resonates well with recent experimental findings, where negatively-charged Li-anion clusters were speculated to exist to justify the surprising negative lithium transference number observed in this system for high salt concentrations.
Ionic liquids (ILs) -based electrolytes are attractive candidates as they generally exhibit better diffusion properties then polymer-based electrolytes, and several recent studies focus on assessing the performance of different mixtures. Given the highly-correlated nature of these systems, understanding the role of species correlation is non-trivial yet crucial for a rational design of future solutions. As a case study we investigated the promising NaFSI-C3C1PyrrFSI system at different Na concentrations and focus on highlighting the correlations in this system as well as how they effect the transference number for high NaFSI concentrations.
ET06.03: Poster Session I
Tuesday AM, November 27, 2018
Hynes, Level 1, Hall B
8:00 PM - ET06.03.01
Probing Electrode/Electrolyte Interface Using Oxide-Only Electrodes in Li-Ion Batteries
Pinar Karayaylali1,Magali Gauthier2,Livia Giordano1,Shuting Feng1,Filippo Maglia3,Simon Lux3,Peter Lamp3,Yang Shao-Horn1
Massachusetts Institute of Technology1,Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA Saclay2,BMW Group3Show Abstract
Understanding the surface reactivity between electrode and electrolyte is critical for cycle life of Li-ion batteries. The composition, properties and mechanisms behind electrolyte/electrolyte interface (EEI) on positive electrode are still unidentified for most lithium ion battery positive electrode materials [1,2]. Especially at high potentials, EEI layer on positive electrode becomes more critical since it approaches electrolyte instability limit for oxidation. The EEI layers on carbon-free, binder-free and thin film LiCoO2 electrodes were investigated by using X-ray photoelectron spectroscopy (XPS). The growth of oxygenated and carbonated species was observed together with salt decomposition starting at 4.1 VLi . By DFT calculations, we correlated the EEI composition to the thermodynamic tendency of the EC solvent for dissociative adsorption on the LixCoO2 surface, which can have a role in the salt decomposition on oxide surfaces . The salt decomposition products had been also observed by solution 19F-NMR measurements. Finally, we demonstrated that the addition of diphenyl carbonate to the electrolyte has a strong impact on EEI layer and salt decomposition on LiCoO2 surface. With this study, we also highlight the strength of using the carbon-free, binder-free electrodes to get fundamental insights in the reactivity of the positive electrode with the electrolyte.
 Xu, K. Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries. Chem. Rev. 2004, 104 (10), 4303–4418.
 Gauthier, M.; Carney, T. J.; Grimaud, A.; Giordano, L.; Pour, N.; Chang, H.-H.; Fenning, D. P.; Lux, S. F.; Paschos, O.; Bauer, C. Electrode–electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights. J. Phys. Chem. Lett. 2015, 6 (22), 4653–4672.
 Gauthier, M.; Karayaylali, P.; Giordano, L.; Feng, S.; Lux, S. F.; Maglia, F.; Lamp, P.; Shao-Horn, Y. Probing Surface Chemistry Changes Using LiCoO2-Only Electrodes in Li-Ion Batteries. J. Electrochem. Soc. 2018, 165 (7), A1377–A1387.
 Giordano, L.; Karayaylali, P.; Yu, Y.; Katayama, Y.; Maglia, F.; Lux, S.; Shao-Horn, Y. Chemical Reactivity Descriptor for the Oxide-Electrolyte Interface in Li-Ion Batteries. J. Phys. Chem. Lett. 2017, 8 (16), 3881–3887.
8:00 PM - ET06.03.03
Porous Single-Crystal NaTi2(PO4)3 via Liquid Transformation of TiO2 Nanosheets for Flexible Aqueous Na-Ion Battery
Yang Qi1,Chunyi Zhi1
City University of Hong Kong1Show Abstract
Recently, aqueous energy storage systems (AESSs), such as Na-ion battery & capacitor, have demonstrated their uniqueness compared with their non-aqueous counterparts due to the excellent safety performance in nature. Furthermore, the advantage of their low cost derived from the high abundance of sodium and the simplified assemble process in ambient endows AESSs the possibility of application in large-scale power grid. However, restricted by the narrow electrochemical window (~1.23 V) of water, the common used electrode materials in non-aqueous batteries/capacitors such as transition metal oxides/sulfides/selenides are directly excluded from the scope due to the high voltage platform, other than limited kinds of materials like NASICON-type NaTi2(PO4)3 with appropriate voltage platform. Nevertheless, conventional NaTi2(PO4)3 materials with irregular morphology and large size prepared by solid-state reaction still hinder the application of AESSs. Herein, a newly structured porous single-crystal NaTi2(PO4)3 with uniform sizes was fabricated via a well-designed novel liquid transformation of ultrathin TiO2 nanosheets, followed by coating a conductive carbon sheath. To best of our knowledge, this is the first report of the porous single-crystal structure of NaTi2(PO4)3 materials. Examined in a three-electrode cell, this NaTi2(PO4)3 electrode demonstrates an outstanding rate capability of 80-102 mA h g-1 at varied current densities of 0.5-3 A g-1 due to the synergistic effect between porous nanostructure and outstanding stability originated from single-crystal structure. The high-quality NaTi2(PO4)3 was also assembled with N-doped carbon to fabricate an aqueous Na-ion battery with robust flexibility. This work paves the way for designing advanced NASICON based materials for aqueous energy storage systems.
8:00 PM - ET06.03.04
Solid State Synthesis Revisited—Ni-Rich Cathode
Yanhao Dong1,Ju Li1
Massachusetts Institute of Technology1Show Abstract
Ni-rich cathode materials for lithium-ion batteries, commonly in the forms of LiNi1-x-yCoxMnyO2 (NCM) and LiNi1-x-yCoxAlyO2 (NCA), are of great interests in commercial applications due to their high reversible capacity and relative low cost compared to LiCoO2. Due to the well-known Ni/Li cation mixing problem, such a multicomponent (high-entropy) compound cannot be synthesized at elevated temperatures, the more so the higher Ni concentration. This temperature doctrine suppresses the inter-diffusion kinetics between transitional metal ions (Ni, Co, Mn, Al etc.) during material synthesis, hindering a homogeneous distribution and electrochemical properties, and limits the achievable particle size, impairing electrode packing and volumetric energy density. This is part of the reason why solid state synthesis of NCM/NCA materials was not successful. The conundrum is tentatively solved by introducing a specialized co-precipitation technique and self-agglomerated secondary particles (~10 micron) for NCM/NCA systems. Yet the secondary particles would still crack along grain boundaries during electrode pressing and electrochemical cycling. Therefore, micron-size single-crystalline NCM/NCA with good electrochemical properties is a great treasure. In our recent work, we revisited the solid state synthesis of such single-crystalline Ni-rich cathodes and obtained competing capacities with the state-of-the-art co-precipitation technique, thus re-opening the doors to process Ni-rich cathodes in the same synthesizing route as classical LiCoO2 and genius control of doping and coating at the primary-particle level.