Performance Of Solid-state Batteries Research Articles

Editors’ Choice—Visualizing the Impact of the Composite Cathode Microstructure and Porosity on Solid-State Battery Performance

The kinetics of composite cathodes for solid-state batteries (SSBs) relies heavily on their microstructure. Spatial distribution of the different phases, porosity, interface areas, and tortuosity factors are important descriptors that need accurate quantification for models to predict the electrochemistry and mechanics of SSBs. In this study, high-resolution focused ion beam-scanning electron microscopy tomography was used to investigate the microstructure of cathodes composed of a nickel-rich cathode active material (NCM) and a thiophosphate-based inorganic solid electrolyte (ISE). The influence of the ISE particle size on the microstructure of the cathode was visualized by 3D reconstruction and charge transport simulation. By comparison of experimentally determined and simulated conductivities of composite cathodes with different ISE particle sizes, the electrode charge transport kinetics is evaluated. Porosity is shown to have a major influence on the cell kinetics and the evaluation of the active mass of electrochemically active particles reveals a higher fraction of connected NCM particles in electrode composites utilizing smaller ISE particles. The results highlight the importance of homogeneous and optimized microstructures for high performance SSBs, securing fast ion and electron transport.

Double-skeleton interpenetrating network-structured alkaline solid-state electrolyte enables flexible zinc-air batteries with enhanced power density and long-term cycle life

The alkaline solid-state electrolytes have received widespread attention for their good safety and electrochemical stability. However, they still suffer from low conductivity and poor mechanical properties. Herein, we report the synthesis of double-network featured hydroxide-conductive membranes fabricated by polyvinyl alcohol (PVA) and chitosan (CS) as the double-skeletons. Then, we implanted quaternary ammonium salt guar hydroxypropyltrimonium chloride (GG) as the OH− conductor for high-performance electrochemical devices. By virtue of the unique stripe-like structure shared from the double skeleton with a high degree of compatibility and stronger hydrogen bond interactions, the polyvinyl alcohol/chitosan-guar hydroxypropyltrimonium chloride (PCG) solid-state electrolytes achieved optimal thermal stability (> 300 °C), mechanical property (∼ 34.15 MPa), dimensional stability (at any bending angle), and high ionic conductivity (13 mS cm−1) and ion mobility number (tion ∼ 0.90) compared with chitosan-guar hydroxypropyltrimonium chloride (CG) and polyvinyl alcohol-guar hydroxypropyltrimonium chloride (PG) electrolyte membrane. As a proof-of-concept application, the “sandwich”-type zinc-air battery (ZAB) assembled using PCG membrane as the electrolyte realized a high open-circuit voltage (1.39 V) and an excellent power density (128 mW cm−2). Notably, in addition to its long-term cycle life (30 h, 2 mA cm−2) and stable discharge plateau (12 h, 5 mA cm−2), it could even enable a flexible ZAB (F-ZAB) to readily power light-emitting diodes (LED) at any bending angle. These merits afford the PCG membrane a promising electrolyte for improving the performance of solid-state batteries.

Incorporating Sodium-Conductive Polymeric Interfacial Adhesive with Inorganic Solid-State Electrolytes for Quasi-Solid-State Sodium Metal Batteries.

Inorganic solid-state electrolytes have attracted enormous attention due to their potential safety, increased energy density, and long cycle-life benefits. However, their application in solid-state batteries is limited by unstable electrode-electrolyte interface, poor point-to-point physical contact, and low utilization of metallic anodes. Herein, interfacial engineering based on sodium (Na)-conductive polymeric solid-state interfacial adhesive is studied to improve interface stability and optimize physical contacts, constructing a robust organic-rich solid electrolyte interphaselayer to prevent dendrite-induced crack propagation and security issues. The interfacial adhesive strategy significantly increases the room-temperature critical current density of inorganic Na-ion conductors from 0.8 to 3.2mAcm-2 and markedly enhances the cycling performance of solid-state batteries up to 500 cycles, respectively. Particularly, the Na3V2(PO4)3-based full solid-state batteries with high cathode loading of 10.16mgcm-2 also deliver an excellent cycling performance, further realizing the stable operation of solid-state laminated pouch cells. The research provides fundamental perspectives into the role of interfacial chemistry and takes the field a step closer to realizing practical solid-state batteries.

Quantifying Resistive and Diffusive Kinetic Limitations of Thiophosphate Composite Cathodes in All-Solid-State Batteries

Increasing the specific capacity and rate performance of thiophosphate composite cathodes is a major challenge in solid-state battery development. Understanding the charge transport kinetics and rate-limiting mechanisms within the cathode is key towards efficient optimization. Herein, we use quantitative analysis of chronoamperometric rate performance data to differentiate between resistive and diffusive rate limitations of NCM811—Li6PS5Cl cathodes with different morphology and composition. We substantiate our findings with separate measurements of the effective ionic conductivity and Li+ diffusion coefficients using impedance spectroscopy and GITT techniques, respectively. Increasing the active material to solid electrolyte ratio is found to increase diffusive limitations, which originate from the small contact area between the active material and solid electrolyte. The diffusive limitation is especially pronounced for single crystal NCM811 cathodes at over 84% AM. Employing fine particle catholyte significantly increases the contact area, alleviates the diffusive limitation, and increases rate performance. These results provide guidelines towards bringing the solid-state battery performance levels closer to practical targets.

Ionogel hybrid polymer electrolytes encompassing room-temperature ionic liquids for 4V-class Li-metal batteries operating at ambient temperature

ABSTRACT In this study, we prepare ionogels composed of bisphenol A ethoxylate dimethacrylate, poly(ethylene glycol) methyl ether methacrylate, lithium bis(trifluoromethanesulfonyl)imide, and 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide or 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ionic liquids via rapid, scalable, solvent-free UV-induced polymerization. The various hybrid polymer electrolyte formulations are thoroughly characterized using a comprehensive set of physico-chemical and electrochemical methods, including gel content, FTIR, rheology, DTMA, TGA, SEM, cycling voltammetry, impedance spectroscopy, and galvanostatic cycling in laboratory-scale Li-metal cells. We particularly focus on the influence of using two different ionic liquids as reaction medium on the properties of the resulting materials and their electrochemical behaviors. Our results indicate that viscosity affects the polymerization kinetics of the ionogels, which in turn might affect their thermal stability and galvanostatic cycling behavior. In the purpose of promoting overall performance of solid-state batteries, we also present the results of composite electrolytes obtained by introducing Li7La3Zr2O12 (LLZO) into ionogels and following in-situ UV-polymerisation. The addition of LLZO ceramic results in more porous solid networks, leading to enhanced charge/discharge stability at ambient temperature and higher C-rates featuring 4V-class NMC cathodes, enlightening the promising prospects of the developed materials to be successfully implemented as stable, durable, and efficient electrolytes in next-generation Li-metal cells.

A Machine-Learning-Based Approach to Analyse the Feature Importance and Predict the Electrode Mass Loading of a Solid-State Battery

Solid-state batteries are currently developing into one of the most promising battery types for both the electrification of transport and for energy storage applications due to their high energy density and safe operating behaviour. The performance of solid-state batteries is largely determined by the manufacturing process, particularly in the production of electrodes. However, efficiently analysing the effects of key manufacturing features and predicting the mass loading of electrodes in the early stages of battery manufacturing remain a major challenge. In this study, a machine-learning-based approach is proposed to effectively analyse the importance of manufacturing features and accurately predict the mass loading of electrodes. Specifically, the importance of four key features during the manufacturing process of solid-state batteries is first quantified and analysed using a machine-learning-based method to analyse the importance of features. Then, four effective machine-learning-based regression methods, including decision tree, boosted decision tree, support vector regression and Gaussian process regression, are used to predict the mass loading of the electrodes in the mixing and coating stages. The comparative results show that the developed machine-learning-based approach is able to provide a satisfactory prediction of the electrode mass loading of a solid-state battery with 0.995 R2 while successfully quantifying the importance of four key features in the early manufacturing stages. Due to the advantages of its data-driven nature, the developed machine-learning-based approach can efficiently assist engineers in monitoring/predicting the electrode mass loading of solid-state batteries and analysing/quantifying the importance of manufacturing features of interest. This could benefit the production of solid-state batteries for further energy storage applications.

Construction of a High-Performance Composite Solid Electrolyte Through In-Situ Polymerization within a Self-Supported Porous Garnet Framework

HighlightsA scalable tape-casting method produces self-supported porous Li6.4La3Zr1.4Ta0.6O12.Combining the in-situ polymerization approach, a composite solid electrolyte with superior electrochemical properties is fabricated.Solid-state Li|CSE|LiNi0.8Co0.1Mn0.1O2 cells show remarkable cyclability and rate capability.LiF-and B-rich interphase layers mitigate interfacial reactions, enhancing solid-state battery performance.

Understanding the role of aliovalent cation substitution on the li-ion diffusion mechanism in Li6+xP1-xSixS5Br argyrodites.

Due to their high ionic conductivity, lithium-ion conducting argyrodites show promise as solid electrolytes for solid-state batteries. Aliovalent substitution is an effective technique to enhance the transport properties of Li6PS5Br, where aliovalent Si substitution triples ionic conductivity. However, the origin of this experimentally observed increase is not fully understood. Our density functional theory (DFT) study reveals that Si4+ substitution increases Li diffusion by activating Li occupancy in the T4 sites. Redistribution of Li-ions within the lattice results in a more uniform distribution of Li around the T4 and neighboring T5 sites, flattening the energy landscape for diffusion. Since the T4 site is positioned in the intercage jump pathway, an increase in the intercage jump rate is found, which is directly related to the macroscopic diffusion and bulk conductivity. Analysis of neutron diffraction experiments confirms partial T4 site occupancy, in agreement with the computational findings. Understanding the aliovalent substitution effect on interstitials is crucial for improving solid electrolyte ionic conductivity and advancing solid-state battery performance.

Understanding the Effect of Mechanical Degradation on the Performance of Solid-State Batteries through Particle Simulations

All-solid-state batteries (ASSBs) have garnered significant interest as a promising alternative to conventional lithium-ion batteries, offering improved safety, higher energy density, longer lifespan, faster charging and wider operating temperature range. A key advantage of ASSBs is the use of solid electrolytes (SE), which eliminate the risks associated with flammable liquid electrolytes. However, the complex electrochemical behavior and multi-scale nature of ASSBs pose challenges in designing and optimizing their performance. This study employs Discrete Element Method (DEM) particle-based models to better understand degradation behavior of ASSBs by considering electrochemical reaction, mass and charge transfer, intercalation expansion and material deformationOur simulations were developed in MATLAB and were performed on a half-cell configuration comprising a SE-layer and an anode electrode. The anode electrode was composed of a particle mixture containing active material (AM) and SE. In our simulations, Si was employed as AM, which experiences substantial intercalation expansion during charge cycling 1. Our previously developed DEM model2,3 resolved elastic and plastic deformation of both AM and SE particles which become compressed due to the intercalation expansion. The simulation of intercalation was achieved by integrating the Newman electrochemical model,4 into the DEM mechanical model. Building on our earlier study5, where the Li concentration was resolved within each AM particle, this study is also accounting for the Li-ion potential within each SE particle. Interparticle conduction and diffusion were computed by determining the contact area of AM-AM and SE-SE contacts, which were affected by the compression of the electrode. The electrochemical reaction was calculated at the AM-SE interface using the Butler-Volmer equation, and in addition the influence of compressive stress on the reaction6 was included.Figure 1(a) depicts the Li concentration and Li-ion potential distribution within the half-cell during charging at different states of charge (SOC), while Figure 1(b) provides a 3D view of the distributions at a SOC of 50%. A considerable expansion of the Si anode is evident. The gradients of Li concentration and Li-ion potential signify significant mass and charge transfer resistance during the charging process. Comparing the distribution of the particles, the anode becomes more porous after the first cycle for the same value of SOC. This effect is attributed to the extensive expansion of the Si anode, leading to plastic compression of the SE layer, which becomes more compact after each cycle. The growing porosity diminishes the contact area between particles, ultimately resulting in the degradation of the half-cell's capacity. In addition to SE-layer compaction, this study aims to investigate several degradation mechanisms and their impact on the performance of ASSBs, including the development of shell voids resulting from AM-SE delamination, crack propagation through SE, and fragmentation of AM.The results of this study provide valuable insights into understanding the effect of mechanical degradation on the performance of ASSBs. By improving our understanding of these mechanisms, we can work towards enhancing the durability and lifespan of ASSBs, ultimately contributing to the development of next-generation energy storage systems. Acknowledgment This work was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices, Computational & Data Science” (Gp-A03, grant number 19H05815); and MEXT “Program for Promoting Researches on the Supercomputer Fugaku” (Fugaku battery & Fuel Cell Project), grant number JPMXP1020200301. References M. N. Obrovac and L. Christensen, Electrochem. Solid-State Lett., 7, A93 (2004).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, J. Electrochem. Soc., 168, 030538 (2021).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, Journal of Power Sources, 508, 230344 (2021).J. Newman and K. E. Thomas-Alyea, Electrochemical Systems, 3rd edition., p. 672, Wiley-Interscience, Hoboken, N.J, (2004).M. So, S. Yano, A. Permatasari, T. D. Pham, K. Park, and G. Inoue, Journal of Power Sources, 546, 231956 (2022).G. Bucci, T. Swamy, S. Bishop, B. W. Sheldon, Y.-M. Chiang, and W. C. Carter, J. Electrochem. Soc., 164, A645 (2017). Figure 1

A Novel, Efficient Approach to Simulate the 3D Resolved Spatial and Temporal Development of Space-Charge Layers in Solid Electrolytes

The role of space-charge layers (SCLs) on the overall battery performance of solid-state batteries is heavily discussed in the scientific community ranging from dominant to negligible [1]. Reasons for this are that direct measurements of SCLs in experiments are difficult and so far, simulation models that can efficiently resolve the transient development of the shape of SCLs while being thermodynamically consistent are missing. The different length scales of SCLs on the one hand and of the microstructure of a battery cell on the other hand make a spatial discretization of realistic microstructures with resolved SCLs infeasible. To date, this was circumvented by using phenomenological models that do not require a spatial discretization of the SCL, by applying thermodynamically consistent models to simplified one-dimensional geometries, or by performing simulations on the sub-continuum scale, e.g. DFT simulations or kinetic Monte Carlo simulations. As all models, the mentioned models have limitations. In this case, they are for example either thermodynamically not consistent or limited to small, not representative geometries.In this work [2], we propose a model that enables the prediction of the spatial and temporal development of SCLs within geometrically resolved microstructures while being thermodynamically consistent [3]. We exploit that effects in SCLs are predominantly one-dimensional. Furthermore, it can be shown, that SCLs develop orthogonal to the interface between the solid electrolyte and the electrode in the steady state. This allows to project the equations in the regions of the solid electrolyte where SCLs are expected in one dimension. In the remaining region of the solid electrolyte, the equations remain three-dimensional. A consistent coupling strategy between the three-dimensional and the one-dimensional region is derived and is irrevocably connected to the fulfilment of conservation properties. This modelling approach allows to drastically reduce the size of the numerical discretization required to resolve SCLs in space, as a fine discretization is only required in one direction embedded into a coarse three-dimensional discretization which represents the geometric microstructure. Thus, the required computational effort significantly reduces.The continuous equations are discretized in space using the finite element method. The obtained nonlinear system of equations is solved with the Newton-Raphson scheme using one monolithic system, i.e. the concurrent solution of the differently discretized regions to ensure robustness and efficiency of the solver. Tailoring an iterative solver by utilizing physical information of the system (similar to [4]), enables to apply the model to realistic microstructures with more than 10 million unknowns.With the proposed approach it is possible for the first time to quantify the influence of realistic microstructures on the transient and spatial formation process of SCLs. This work is the first to show that the formation process of SCLs at the interface between solid electrolyte and electrode is strongly influenced by the geometry of the microstructure (see Fig. 1): The dominating trend is a propagation of the SCL through the composite electrode, i.e. from the separator side to the current collector side of each electrode. Simultaneously, an inhomogeneity in the plane being orthogonal to the dominant direction is observed. This can be attributed to different conduction paths within this two-dimensional manifold due to the irregularity of the investigated microstructures and their geometric complexity. Furthermore, characteristic points in the microstructure can be identified where more charge is stored in the SCL during the transient development compared to the steady state. Again, this is attributed to the complex microstructures in interplay with the impedance of the bulk electrolyte and of the SCL. For these observations a modelling approach that resolves SCLs in realistic microstructures is mandatory.

Modeling and simulation of a composite solid-state battery: The effects of stack pressure on electrochemical and mechanical behavior

The high interfacial resistance of solid electrolyte/electrode interfaces impedes the development of solid-state batteries (SSBs). To mitigate this issue, it is necessary to apply external pressure to SSBs during cell fabrication and cycling. In this study, we investigated the influence of the stack pressure on the electrochemical and mechanical behavior of composite SSBs. A pseudo-3D physics-based model was developed using semi-empirical parameters to examine the impact of pressure on the physical, electrochemical, and mechanical properties of SSBs. Our findings revealed that increasing pressure leads to higher volume fractions of active materials and solid electrolytes, thereby enhancing the electrochemical performance of SSBs. However, pressure-induced changes also affect the electronic conductivity of solid electrolytes, necessitating careful optimization. Additionally, the effect of the C-rate on SSB performance was explored, highlighting the importance of optimizing the ionic and electronic conductivities for higher C-rates. Finally, the influence of Young's modulus of the solid electrolyte on the volume fraction, voltage profile, and mechanical behavior was investigated. This study provides valuable insights for optimizing SSB design and offers guidance for achieving the desired balance between electrochemical performance and mechanical stability.

Unraveling the Performance Decay of Micro-sized Silicon Anodes in Sulfide-based Solid-State Batteries

Solid-state batteries (SSBs) containing Si anodes have recently emerged as a promising solution to overcome challenges associated with Li anodes. However, the development of Si anodes is hindered by the requirement of high external pressure and the unclear understanding of failure mechanisms. Herein, with experiments and simulations under varying Si loads and external pressures, we report that the long diffusion path generates a large Li+ concentration gradient and a pronounced hydrostatic stress gradient, thereby restricting the Li storage capacity of Si via the stress-induced chemical potential. Additionally, the resultant uneven distribution of high Von Mises stress leads to easy cracking of Si anodes during delithiation, thus disturbing the electron/ion transport path, altering reaction sites, and deteriorating the cycle performance of SSBs. External pressure was also shown to have minimal benefits on Li+ diffusion, mainly by reducing the Von Mises stress to reduce the cracking degree for ensuring electron/ion transport, so as to realize the balance of Li+ concentration gradient and electrochemical potential, and avoid Li plating and interfacial side reactions. Our findings propose the failure mechanism of Si anodes in SSBs, emphasizes the importance of minimizing the Li+ concentration gradient under low external pressure, and provide valuable insights for the development of Si-containing SSBs.

Developing Single‐Ion Conductive Polymer Electrolytes for High‐Energy‐Density Solid State Batteries

AbstractSingle‐ion conductive polymer electrolytes (SICPEs) with a cationic transference number (tLi+) close to unity exhibit specific advantages in solid‐state batteries (SSBs), including mitigating the ion concentration gradient and derived problems, suppressing the growth of lithium dendrites, and improving the utilization of cathode materials and the rate performance of SSBs. However, the application of SICPEs remains major challenges, i.e., the ionic conductivity is inferior at room temperature. Therefore, the recent accomplishments in improving the ambient ionic conductivity to be compatible SICPEs with a high transference number are discussed in this review. In particular, some strategies of delocalizing charges in polyanions, designing a highly conductive polymer matrix, and utilizing synergistic effects in SICPEs are focused to shed light on the further development of solid polymer electrolytes for SSBs. Finally, multifunctional species of SICPEs are discussed in view of the mechanical contact and/or charge transfer problems at the solid–solid interface in SSBs.

(Invited) Multi-Scale Implications of Material Heterogeneity on Solid State Battery Performance

Solid state batteries are comprised of an ensemble of materials with varying structural, mechanical, chemical, and transport properties1,2. Orchestrating these materials to act synergistically and enable high power and high energy densities requires understanding how solid state electrodes and electrolytes can be engineered to enable: (1) efficient ion and electron transport and (2) maintain uniform contact between components during electrochemical cycling. Bulk processing approaching (e.g. coating, sintering, densification, etc.) do not lead to much control over material properties across various length scales (nano-to-meso). Material heterogenities exist within the cathode, solid electrolyte, and anode. In the cathode, the solid electrolyte and active material can be non-uniformly distributed leading to bottlenecks for transport and non-uniform active material utilization. In the solid electrolyte, active and passive heterogenities can influence how the ion moves between the anode and cathode and cause deleterious current focusing dynamics3,4. Finally, at the anode voiding and contact loss can occur in alkali metal anodes. This talk discusses our recent work combining operando synchrotron studies, electrochemical characterization, and advanced material characterization to unravel the implications of heterogenity on performance and degradation mechanism in solid state batteries.[1] Zaman, Wahid, and Kelsey B. Hatzell. "Processing and manufacturing of next generation lithium-based all solid-state batteries." Current Opinion in Solid State and Materials Science 26.4 (2022): 101003.[2] Ren, Yuxun, and Kelsey B. Hatzell. "Elasticity-oriented design of solid-state batteries: challenges and perspectives." Journal of Materials Chemistry A 9.24 (2021): 13804-13821.[3]Dixit, Marm B., et al. "Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics." Nature Materials 21.11 (2022): 1298-1305.[4]Ren, Yuxun, Nicholas Hortance, and Kelsey B. Hatzell. "Mitigating Chemo-Mechanical Failure in Li-S Solid State Batteries with Compliant Cathodes." Journal of The Electrochemical Society 169.6 (2022): 060503.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Mechanistic Analysis of Interface Stability in Solid-State Batteries

Solid-state batteries (SSBs) utilizing lithium metal anodes are promising next-generation energy storage systems, capable of offering enhanced energy density and power density when compared to conventional lithium-ion batteries. However, the morphological instability of the lithium anode continues to be a major challenge, resulting in filamentous lithium growth and internal short circuit across a wide range of inorganic solid electrolytes. In addition, the formation and growth of interfacial voids during stripping is a critical mechanism that limits the rate performance of SSBs. A coupled set of electrochemical-transport-mechanics processes governs the dynamic evolution and stability of the solid electrolyte/lithium interface. This interaction is affected by various factors including the mechanical properties and microstructure of the solid electrolyte and lithium metal, external pressure, operating temperature, and interfacial heterogeneities. In this presentation, the competing nature of interfacial mechanisms including electrodissolution, lithium mechanics and lithium diffusion kinetics on the origin of voids during stripping will be discussed. The coupled electrochemical-mechanical processes governing the evolution of lithium filaments, especially driven by microstructural heterogeneities such as grain boundaries will be delineated. An analysis pertaining to the dependence of such failure mechanisms on the external temperature, temperature and current density will be presented. Lastly, the role of underlying electrochemical interactions at the solid-solid interface on the onset of thermal instability in SSBs will be evaluated.

High Performance Ternary Solid Polymer Electrolytes Based on High Dielectric Poly(vinylidene fluoride) Copolymers for Solid State Lithium-Ion Batteries.

Renewable energy sources require efficient energy storage systems. Lithium-ion batteries stand out among those systems, but safety and cycling stability problems still need to be improved. This can be achieved by the implementation of solid polymer electrolytes (SPE) instead of the typically used separator/electrolyte system. Thus, ternary SPEs have been developed based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), P(VDF-TrFE-CFE) as host polymers, clinoptilolite (CPT) zeolite added to stabilize the battery cycling performance, and ionic liquids (ILs) (1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN])), 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PMPyr][TFSI]) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), incorporated to increase the ionic conductivity. The samples were processed by doctor blade with solvent evaporation at 160 °C. The nature of the polymer matrix and fillers affect the morphology and mechanical properties of the samples and play an important role in electrochemical parameters such as ionic conductivity value, electrochemical window stability, and lithium-transference number. The best ionic conductivity (4.2 × 10-5 S cm-1) and lithium transference number (0.59) were obtained for the PVDF-HFP-CPT-[PMPyr][TFSI] sample. Charge-discharge battery tests at C/10 showed excellent battery performance with values of 150 mAh g-1 after 50 cycles, regardless of the polymer matrix and IL used. In the rate performance tests, the best SPE was the one based on the P(VDF-TrFE-CFE) host polymer, with a discharge value at C-rate of 98.7 mAh g-1, as it promoted ionic dissociation. This study proves for the first time the suitability of P(VDF-TrFE-CFE) as SPE in lithium-ion batteries, showing the relevance of the proper selection of the polymer matrix, IL type, and lithium salt in the formulation of the ternary SPE, in order to optimize solid-state battery performance. In particular, the enhancement of the ionic conductivity provided by the IL and the effect of the high dielectric constant polymer P(VDF-TrFE-CFE) in improving battery cyclability in a wide range of discharge rates must be highlighted.

Influence of Solvent Evaporation Temperature on the Performance of Ternary Solid Polymer Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) Combining an Ionic Liquid and a Zeolite.

Solid polymer electrolytes (SPEs) will allow improving safety and durability in next-generation solid-state lithium-ion batteries (LIBs). Within the SPE class, ternary composites are a suitable approach as they provide high room-temperature ionic conductivity and excellent cycling and electrochemical stability. In this work, ternary SPEs based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a polymer host, clinoptilolite (CPT) zeolite, and 1-butyl-3-methylimidazolium thiocyanate ([Bmim][SCN])) ionic liquid (IL) as fillers were produced by solvent evaporation at different temperatures (room temperature, 80, 120, and 160 °C). Solvent evaporation temperature affects the morphology, degree of crystallinity, and mechanical properties of the samples as well as the ionic conductivity and lithium transference number. The highest ionic conductivity (1.2 × 10-4 S·cm-1) and lithium transference number (0.66) have been obtained for the SPE prepared at room temperature and 160 °C, respectively. Charge-discharge battery tests show the highest value of discharge capacity of 149 and 136 mAh·g-1 at C/10 and C/2 rates, respectively, for the SPE prepared at 160 °C. We conclude that the fine control of the solvent evaporation temperature during the preparation of the SPE allows us to optimize solid-state battery performance.

Unraveling Li growth kinetics in solid electrolytes due to electron beam charging.

Revealing the local structure of solid electrolytes (SEs) with electron microscopy is critical for the fundamental understanding of the performance of solid-state batteries (SSBs). However, the intrinsic structural information in the SSB can be misleading if the sample's interactions with the electron beams are not fully understood. In this work, we systematically investigate the effect of electron beams on Al-doped lithium lanthanum zirconium oxide (LLZO) under different imaging conditions. Li metal is observed to grow directly on the clean surface of LLZO. The Li metal growth kinetics and the morphology obtained are found to be heavily influenced by the temperature, accelerating voltage, and electron beam intensity. We prove that the lithium growth is due to the LLZO delithiation activated by a positive charging effect under electron beam emission. Our results deepen the understanding of the electron beam impact on SEs and provide guidance for battery material characterization using electron microscopy.

Influence of ionic liquid characteristics on the performance of ternary solid polymer electrolytes with poly(vinylidene fluoride-co-hexafluoropropylene) and zeolite

Solid polymer electrolytes (SPEs) are the necessary step towards solid-state lithium-ion batteries (LIBs). Their function as separator and electrolyte allows to increase the safety of energy storage devices by the elimination of the liquid components. In this work, three-component SPEs based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as host polymer, clinoptilolite zeolite, and different ionic liquids (ILs) (1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][NCN2]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM][NCN2]) were produced and characterized. The influence of the nature of the IL anion and cation on the morphology, degree of crystallinity, mechanical properties, ionic conductivity, and battery cycling performance were studied. It is demonstrated that the [SCN]- anion is the most suitable if SPE applications are envisaged. The ionic conductivity depends on the IL type. At room temperature, a maximum value of 1.3 × 10−5 S cm−1 was obtained for the SPE doped with [BMIM][NCN2]. Regarding battery performance, the best value of discharge capacity was observed for the SPE based on [BMIM][SCN], which for an initial discharge capacity of 135 mAh.g−1 yielded a capacity loss below 30% after 30 cycles at room temperature. Thus, it is concluded that proper selection of the IL (cation chain length and anion size) allows tailoring battery performance of solid-state batteries based on three-component SPEs.

Revealing the Influence of Surface Microstructure on Li Wettability and Interfacial Ionic Transportation for Garnet‐Type Electrolytes

AbstractPoor interfacial contacts of Li mental/solid‐state electrolytes (SSEs) cause high impedance and induce lithium dendrite growth, which hinders the practical viability of solid‐state batteries (SSBs). Optimizing the surface chemistry of SSEs has been widely adopted for improving the Li/SSE interfacial contact. Their surface's microstructure, another critical factor influencing the actual performance of SSBs, however, has seldom been paid attention to; and the corresponding mechanism remains unclear. Addressing this issue, the authors herein propose a “surface microstructure optimization” strategy that can significantly enhance the Li/SSE interfacial contact, and in the meantime, quantify the correlations between SSB's performance and SSE's surface roughness regarding the interfacial resistance, current focusing, critical current density (CCD), and lithium deposition. Based on these fundamental understandings, a low‐surface‐roughness SSE is developed, which shows extremely small interfacial impedance (1.7 Ω cm2) and ultra‐long stable cycling life (4500 h at 0.2 mA cm−2). This work not only comprehensively demonstrates the fundamental relationship between the surface microstructure of SSEs and their battery performance but also presents a new insight into the modulation of surface kinetics of ceramic SSEs toward achieving dendrite‐free SSBs.