All-solid-state Batteries Research Articles

Surface modification of perforated separator for more robust and thinner all‐solid‐state electrolyte membrane

AbstractSolid electrolytes (SEs) play an essential role in the development of all‐solid‐state batteries (ASSBs) due to their exceptional ionic conductivity. However, conventional pelletized SEs with hundreds of micrometers result in highly reduced energy density and suffer from mechanical brittleness, which delay the commercialization of ASSBs. In this study, we present an innovative approach to fabricate SE membranes with perforated Al2O3 nanolayer‐coated polyethylene (PE) separator as a mechanical supporter. Al2O3‐coated separators exhibit better adhesion with LPSCl particles and better thermal stability. As a result, the SE membrane exhibits thickness of 35 μm while maintaining a superior mechanical tensile strength. Furthermore, when the SE membrane is applied to Li||LiNi0.7Co0.15Mn0.15O2 full‐cells, stable cycling performance over 250 cycles, which is comparable to thick LPSCl pellet cell, can be achieved even with higher conductance (>150 mS). Our results highlight the potential of thin and durable SE membranes in contributing to the commercialization of ASSBs.

Surface-enriched Co engineering promoting electronic conductivity for single-crystalline Ni-based layered oxide cathodes

Single-crystalline layered oxides are at the forefront of the development of high-energy lithium-ion battery (LiB) electrode materials, offering prolonged durability by circumventing the crack-related structural reconstruction and mechanical collapse seen in their polycrystalline counterparts. However, the sluggish carrier transport in large-crystalline particles impedes their rate capability. While most research has prioritized improving ion diffusion, the pivotal role of electron transport in electrochemical kinetics has been relatively overlooked. Herein, we enhance the kinetics of charge transfer and inhibit Mn dissolution from the bulk lattice by modulating the cobalt concentration on the surface of a single-crystalline Ni-based layered oxide cathode, LiNi0.5Co0.2Mn0.3O2. Liquid pouch-type full cells employing surface Co-concentrated cathodes exhibit exceptional high-temperature (55 °C) specific capacity (193.6 mAh g−1 at 0.2C), capacity retention (90.1 % after 2000 cycles at 1 C), and impressive rate performance at 12C. Moreover, by utilizing the varying composition-related kinetics in the composite cathode of sulfide-based all-solid-state batteries (ASSBs), we find that surface-enriched Co modification enhances the electronic percolation within the composite cathode, significantly contributing to the rate performance of ASSBs, beyond the effect of ion diffusion. This research underscores the significance of electronic properties in single-crystalline layered oxides for achieving high-power LiBs and ASSBs.

Direct Recycling of β‐Li3PS4‐Based All‐Solid‐State Li‐Ion Batteries: Interactions of Electrode Materials and Electrolyte in a Dissolution‐Based Separation Process

All‐solid‐state batteries (ASSB) are currently developed at high pace and show a strong potential for market introduction within the next years. Though their performance has improved considerably over the last years, investigation of their sustainability and the development of suitable recycling strategies have received less attention. However, their potential for efficient circular processes must be accessed comprehensively. In this article, the separation of the solid electrolyte β‐Li3PS4 from different lithium transition metal oxide electrode materials (LiCoO2, LiMn2O4, LiNi0.8Mn0.1Co0.1O2, LiFePO4, LiNi0.8Co0.15Al0.05O2, and Li4Ti5O12) are investigated via an approach based on the dissolution and subsequent precipitation of the thiophosphate using N‐methylformamide as solvent. A combination of X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, inductively coupled plasma mass spectrometry, iodometric titration, and X‐ray photoelectron spectroscopy as well as electrochemical impedance spectroscopy and electrochemical characterization is used to characterize the electrolyte and electrode materials before and after separation. Herein, it is found that the presence of electrode materials in the dissolution process can lead to significant chemical reactions. These interactions can (but most not) lead to strong alteration of the electrochemical characteristics of the individual compounds. Thus, it is shown that an efficient recovery of materials likely depends on the precise material combination within an ASSB.

Formation Processes of a Solid Electrolyte Interphase at a Silicon/Sulfide Electrolyte Interface in a Model All-Solid-State Li-Ion Battery.

Understanding the electrochemical reactions at the interface between a Si anode and a solid sulfide electrolyte is essential in improving the cycle stabilities of Si anodes in all-solid-state batteries (ASSBs). Highly dense Si films with very low roughnesses of <1 nm were fabricated at room temperature via cathodic arc plasma deposition, which led to the formation of a Si/sulfide electrolyte model interface. Li (de)alloying through the model interface hardly occurred during the first cycle, whereas it proceeded stably in subsequent cycles. Hard X-ray photoelectron spectroscopy and neutron reflectometry directly revealed that the reduction or oxidation of the interfacial component or Li3PS4 electrolyte occurred during the first cycle. Consequently, an interfacial layer with a thickness of 13 nm and primarily composed of Li2S, SiS2, and P2S5 glasses was formed during the first cycle. The interfacial layer acted as a Li-conductive, electron-insulating solid electrolyte interphase (SEI) that provided reversible (de)lithiation. Our model interface directly demonstrates the electrochemical reaction processes at the Si/Li3PS4 interface and provides insights into the structures and electrochemical properties of SEIs to activate the (de)lithiation of Si anodes using a sulfide electrolyte.

Impact of Polymer Interlayers on All-Solid-State Battery Performance Using a Physicochemical Modeling Approach

Recent studies presented the advantages of incorporating solid-polymer-electrolyte (SPE) interlayers in all-solid-state batteries (ASSB). Still, drawbacks regarding the cell performance are expected due to additional polymer-related overpotentials. The pseudo-two-dimensional (p2D) physicochemical model is extended to account for Li-ion transport in the SPE interlayer and in the ceramic LLZO solid electrolyte (SE), as well as for the charge transfer at the SPE∣LLZO interface using Butler-Volmer-like kinetics. The overpotential analysis for a reference parameterization disclosed a dominant overpotential contribution from the SPE∣LLZO charge transfer and a facilitation with increasing discharge C-rate. Variance-based global sensitivity analyses demonstrate that as the exchange current density between SPE and LLZO increases, polarization losses exhibit an exponential-like reduction. Additionally, the radius of the active material (AM) particles within the composite cathode exerts a significant and dominant influence on cell performance. With an optimization of the SPE∣LLZO exchange current density, the accessible capacity could be increased compared to the reference parameterization from 41% to 61% for a 2C discharge.

The Formation of Residual Lithium Compounds on Ni‐Rich NCM Oxides: Their Impact on the Electrochemical Performance of Sulfide‐Based ASSBs

AbstractResidual lithium compounds (RLCs) are known to form on the surface of nickel‐rich LiNi1‐x‐yCoxMnyO2 (NCM) oxides during synthesis and storage. In this study, the impact of RLCs on cathode performance in sulfide‐based all‐solid‐state batteries (ASSBs) is investigated by employing practically relevant approaches to generate (or remove) RLCs on (or from) NCM single crystal particles. It is revealed that Li2CO3 is the predominant component in samples exposed to air. Surprisingly, heat treatment at high temperatures does not remove RLCs but increases the overall RLC content, accompanied by the partial transformation of existing RLCs into Li2O. These samples exhibit compromised electrochemical performance due to asymmetric overpotential increase during cell discharge. However, it is possible to recover performance through controlled ambient air storage which enables the conversion of existing Li2O into Li2CO3 and formation of fresh Li2CO3 on the surface. Notably, the beneficial effects are not replicated with pure CO2 or moisturized air storage, emphasizing the significance of storage conditions and reaction pathways for Li2CO3 formation. This study demonstrates that removal of Li2O residuals through the formation of Li2CO3 under controlled ambient air exposure proves to be advantageous for sulfide‐based ASSBs, thereby offering valuable guidance for the development of optimized NCM‐based ASSB systems.

Amorphous Oxyhalide Matters for Achieving Lithium Superionic Conduction.

The recently surged halide-based solid electrolytes (SEs) are great candidates for high-performance all-solid-state batteries (ASSBs), due to their decent ionic conductivity, wide electrochemical stability window, and good compatibility with high-voltage oxide cathodes. In contrast to the crystalline phases in halide SEs, amorphous components are rarely understood but play an important role in Li-ion conduction. Here, we reveal that the presence of amorphous component is common in halide-based SEs that are prepared via mechanochemical method. The fast Li-ion migration is found to be associated with the local chemistry of the amorphous proportion. Taking Zr-based halide SEs as an example, the amorphization process can be regulated by incorporating O, resulting in the formation of corner-sharing Zr-O/Cl polyhedrons. This structural configuration has been confirmed through X-ray absorption spectroscopy, pair distribution function analyses, and Reverse Monte Carlo modeling. The unique structure significantly reduces the energy barriers for Li-ion transport. As a result, an enhanced ionic conductivity of (1.35 ± 0.07) × 10-3 S cm-1 at 25 °C can be achieved for amorphous Li3ZrCl4O1.5. In addition to the improved ionic conductivity, amorphization of Zr-based halide SEs via incorporation of O leads to good mechanical deformability and promising electrochemical performance. These findings provide deep insights into the rational design of desirable halide SEs for high-performance ASSBs.

Effects of Grain Boundaries and Surfaces on Electronic and Mechanical Properties of Solid Electrolytes

AbstractExtended defects, including exposed surfaces and grain boundaries (GBs), are critical to the properties of polycrystalline solid electrolytes in all‐solid‐state batteries (ASSBs). These defects can alter the mechanical and electronic properties of solid electrolytes, with direct manifestations in the performance of ASSBs. Here, by building a library of 590 surfaces and grain boundaries of 11 relevant solid electrolytes—including halides, oxides, and sulfides— their electronic, mechanical, and thermodynamic characteristics are linked to the functional properties of polycrystalline solid electrolytes. It is found that the energy required to mechanically “separate” grain boundaries can be significantly lower than in the bulk region of materials, which can trigger preferential cracking of solid electrolyte particles in the grain boundary regions. The brittleness of ceramic solid electrolytes, inferred from the predicted low fracture toughness at the grain boundaries, contributes to their cracking under local pressure imparted by lithium (sodium) penetration in the grain boundaries. Extended defects of solid electrolytes introduce new electronic interfacial states within bandgaps of solid electrolytes. These states alter and possibly increase locally the availability of free electrons and holes in solid electrolytes. Factoring effects arising from extended defects appear crucial to explain electrochemical and mechanical observations in ASSBs.

Multiphysics modeling of the influence of initial pressure on mechanical and electrochemical performance of all-solid-state batteries

All-solid-state batteries (ASSBs) are emerging as promising energy storage solutions owing to their enhanced safety and high energy density. However, the application of higher pressures is also required to improve electrochemical performance. This study employs a multiphysics approach by combining the discrete element method (DEM) and finite element method (FEM) to investigate the impact of the compression rate and initial pressure on electrochemical performance. To the best of the authors' knowledge, this is the first study to integrate the DEM and FEM methodologies for the prediction of electrochemical and mechanical responses, capitalizing on the advantages of both approaches. The DEM is used to investigate the compaction behaviors of solid electrolyte and electrode mixtures, yielding essential data on mechanical properties, which are subsequently incorporated into the FEM model. The FEM is utilized to systematically explore the electrochemical performance and mechanical responses. The findings highlight that elevated stress enhances geometric properties, including surface area and volume fraction, leading to improved electronic and ionic conductivity. Although higher compression ratios can enhance electrochemical performance, they also elevate stress levels, thereby increasing the potential for mechanical failure. Therefore, a well-balanced electrode design is crucial. This study provides valuable insights into the design of ASSBs.

Virtues of Cold Isostatic Pressing for Preparation of All-Solid-State-Batteries with Poly(Ethylene Oxide).

All-solid-state-batteries (ASSBs) necessitate the preparation of a solid electrolyte and an electrode couple with individually dense and compact structures with superior interfacial contact to minimize overall cell resistance. A conventional preparation method of solid polymer electrolyte (SPE) with polyethylene-oxide (PEO) generally consists in employing uni-axial hot press (HP) to densify SPE. However, while uni-axial press with moderate pressure effectively densifies PEO with Li salts, excessive pressure also unavoidably results in perpendicular elongation and deformation for polymer matrix. In this research, to overcome this limitation for the uni-axial press technique, a cold isostatic press (CIP) is applied to the fabrication of ASSB with PEO and LiFePO4 . CIP effectively and uniformly applies pressure as high as 500 MPa without deformation. Characterizations confirm that CIP treated SPE has enhanced mechanical puncture strength, increasing from 499.3±22.6 to 539.3±22.6 g, and ionic conductivity, increasing from 1.04×10-4 to 1.91×10-4 S cm-1 at 50 °C. ASSB treated by CIP demonstrates remarkably enhanced rate capability and cyclability compared with the cell processed by HP, which is further evidenced by improvement of the apparent Li ion diffusion constant based on Sand equation analysis. The improvement enabled by CIP treatment originates from the superior interface uniformity between electrodes and SPE and from the densification of the LiFePO4 and SPE composite electrode.

Interlayer Engineering and Prelithiation: Empowering Si Anodes for Low-Pressure-Operating All-Solid-State Batteries.

Silicon (Si) anodes, free from the dendritic growth concerns found in lithium (Li) metal anodes, offer a promising alternative for high-energy all-solid-state batteries (ASSBs). However, most advancements in Si anodes have been achieved under impractical high operating pressures, which can mask detrimental electrochemo-mechanical issues. Herein, we effectively address the challenges related to the low-pressure operation of Si anodes in ASSBs by introducing an silver (Ag) interlayer between the solid electrolyte layer (Li6PS5Cl) and anode and prelithiating the anodes. The Si composite electrodes, consisting of Si/polyvinylidene fluoride/carbon nanotubes, are optimized for suitable mechanical properties and electrical connectivity. Although the impact of the Ag interlayer is insignificant at an exceedingly high operating pressure of 70MPa, it substantially enhances the interfacial contacts under a practical low operating pressure of 15MPa. Thus, Ag-coated Si anodes outperform bare Si anodes (discharge capacity: 2430vs 1560mAhg-1). The robust interfacial contact is attributed to the deformable, adhesive properties and protective role of the in situ lithiated Ag interlayer, as evidenced by comprehensive ex situ analyses. Operando electrochemical pressiometry is used effectively to probe the strong interface for Ag-coated Si anodes. Furthermore, prelithiation through the thermal evaporation deposition of Li metal significantly improves the cycling performance.

Investigating the production of all-solid-state battery composite cathodes by numerical simulation of the stressing conditions in a high-intensity mixer

All-solid-state batteries (ASSB) are considered as attractive further development of conventional lithium-ion batteries, since they are expected to deliver higher energy and power densities. So far, ASSB with inorganic solid electrolytes have not been applied in large-scale due to difficulties in processing, insufficient overall ionic conductivities, and high interfacial resistances between active material and solid electrolyte. In this publication, the influence of stressing conditions on the scalable production of ASSB composite cathodes via a high-intensity mixer is investigated. The high-intensity mixer is supposed to circumvent the challenge of high interfacial resistances within an ASSB cathode consisting of submicron-sized active material LiFePO4, carbon black and solid electrolyte Li3InCl6. The mixing process is simulated employing the discrete-element-method, from which the stressing conditions acting on the particles are extracted and linked with microstructural observations and electrochemical data. These investigations show that the capacity of the ASSB increases with increasing specific energy input, which is, however, limited by a certain stress intensity determined by the rotational speed of the mixer. This examination of the influence of stressing conditions on the production and electrochemical performance of ASSB cathodes lays the foundation for further simulations and experimental investigations in the field of up-scaled ASSB cathode production.

State of Charge-Dependent Impedance Spectroscopy as a Helpful Tool to Identify Reasons for Fast Capacity Fading in All-Solid-State Batteries.

Thiophosphate-based all-solid-state batteries (ASSBs) are considered the most promising candidate for the next generation of energy storage systems. However, thiophosphate-based ASSBs suffer from fast capacity fading with nickel-rich cathode materials. In many reports, this capacity fading is attributed to an increase of the charge transfer resistance of the composite cathode caused by interface degradation and/or chemo-mechanical failure. The change in the charge transfer resistance is typically determined using impedance spectroscopy after charging the cells. In this work, we demonstrate that large differences in the long-term cycling performance also arise in cells, which exhibit a comparable charge transfer resistance at the cathode side. Our results confirm that the charge transfer resistance of the cathode is not necessarily responsible for capacity fading. Other processes, such as resistive processes on the anode side, can also play a major role. Since these processes usually depend on the state of charge, they may not appear in the impedance spectra of fully charged cells; i.e., analyzing the impedance spectra of charged cells alone is insufficient for the identification of major resistive processes. Thus, we recommend measuring the impedance at different potentials to get a complete understanding of the reasons for capacity fading in ASSBs.

A strategy involving the use of 3D self-supporting B·N co-doped carbon nanofiber composite solid polymer electrolytes to stabilize the interface between polymer electrolytes and lithium metal.

All-solid-state batteries (ASSBs) have gained significant attention in the field of energy storage owing to their enhanced safety features based on the nonflammable solid-state electrolyte (SSE). To achieve high energy density, lithium metal is commonly considered the best choice as an anode material. However, the compatibility issues at the interface between polymer electrolytes and lithium metal pose significant challenges to their practical implementation. In this work, we present a new strategy to protect the typical polymer electrolyte polyethylene oxide (PEO) from significant decomposition and puncture caused by lithium dendrites, which is achieved through the combination of PEO and B·N co-doped carbon nanofibers (B·N-CNF) to modify the surface of the lithium anode. The stable cycling performance of the symmetric battery can last over 900 h at a high current density of 1 mA cm-2. The ASSBs (LiFePO4 is used as the cathode and Li metal is employed as the anode) exhibit a high capacity close to 120 mA h g-1 at 2C and cycle for over 300 cycles at 0.2C stably. This work provides inspiration for the rational design of a modification layer on the Li anode, enabling the development of high-performance ASSBs based on polymer electrolytes.

Computational approach inspired advancements of solid-state electrolytes for lithium secondary batteries: from first-principles to machine learning.

The increasing demand for high-security, high-performance, and low-cost energy storage systems (EESs) driven by the adoption of renewable energy is gradually surpassing the capabilities of commercial lithium-ion batteries (LIBs). Solid-state electrolytes (SSEs), including inorganics, polymers, and composites, have emerged as promising candidates for next-generation all-solid-state batteries (ASSBs). ASSBs offer higher theoretical energy densities, improved safety, and extended cyclic stability, making them increasingly popular in academia and industry. However, the commercialization of ASSBs still faces significant challenges, such as unsatisfactory interfacial resistance and rapid dendrite growth. To overcome these problems, a thorough understanding of the complex chemical-electrochemical-mechanical interactions of SSE materials is essential. Recently, computational methods have played a vital role in revealing the fundamental mechanisms associated with SSEs and accelerating their development, ranging from atomistic first-principles calculations, molecular dynamic simulations, multiphysics modeling, to machine learning approaches. These methods enable the prediction of intrinsic properties and interfacial stability, investigation of material degradation, and exploration of topological design, among other factors. In this comprehensive review, we provide an overview of different numerical methods used in SSE research. We discuss the current state of knowledge in numerical auxiliary approaches, with a particular focus on machine learning-enabled methods, for the understanding of multiphysics-couplings of SSEs at various spatial and time scales. Additionally, we highlight insights and prospects for SSE advancements. This review serves as a valuable resource for researchers and industry professionals working with energy storage systems and computational modeling and offers perspectives on the future directions of SSE development.

In pursuit of all solid state batteries (ASSB): advances at the cathode–electrolyte interface for garnet-based ASSB

This review focuses on developments at the complex cathode–electrolyte interface (CEI) for garnet Li7La3Zr2O12 (LLZO)-based all solid state batteries.

3D current collector based on cellulose-carbon nanotube nanocomposites for all-solid-state batteries

We developed an eco-friendly conductive ink in water by dispersing nanocomposites using natural cellulose and SWCNTs (C-CNTs). The 3D hybrid current collector with the randomly entangled C-CNTs improved the electrochemical performance in an ASSB.

Revealing interfacial parasitic reactions of nitrile rubber binders in all-solid-state lithium batteries

The nitrile components in NBR lead to an irreversible side reaction during the initial charging process. However, the problematic chemical stability of NBR has been improved through coordination chemistry, resulting in enhanced battery performance.

Designing low-strain cathode materials for long-life all-solid-state batteries

This review provides valuable insights and suggestions for future research on designing low-strain cathode materials for long-life and high-energy-density all-solid-state batteries under low external pressure conditions.

Influence of oxygen distribution on the Li-ion conductivity in oxy-sulfide glasses - taking a closer look.

Lithium thiophosphates are a promising class of solid electrolyte (SE) materials for all-solid-state batteries (ASSBs) due to their high Li-ion conductivity. Yet, the practical application of lithium thiophosphates is hindered by their chemical instability, which remains a prevalent challenge in the field. Oxygen substitution has been discussed in the literature as a promising strategy to enhance stability. Nevertheless, the lack of understanding of the role of synthesis strategy on the resulting structure-property relationship makes it difficult to predict and control the material's behaviour, limiting our ability to fully utilize oxygen substitution as a viable solution. Here, we show that not only the total oxygen content but also the oxygen distribution within the material affects the ion conductivity. By carefully analysing the local structure of oxy-sulfide glasses, we find that few highly oxygenated structural units like [PO4]3- and [PO3S]3- are more detrimental to the ionic conductivity than a larger amount of less substituted units like [POS3]3-. Further, we demonstrate how the oxygen distribution is connected to the synthesis in high-energy ball milling by comparing two different sets of precursor materials. The results may explain the deviations in the past literature. The findings should be transferable to other Li-thiophosphate materials and enable more directed design of new materials.