High-energy all-solid-state batteries require thick composite cathodes, yet these architectures exhibit heterogeneous reaction distributions that limit performance. Here, we show that chemo-mechanical transport switching governs the spatiotemporal lithiation behaviour in such electrodes. By combining operando depth-resolved diffraction with microstructureresolved and multi-scale simulations, we link utilisation gradients to the dominant transport pathway and demonstrate that the reversal of reaction fronts between charge and discharge arises from dynamically evolving transport limitations. This switching originates from the coupled reconfiguration of electronic and ionic transport networks during cycling. Particle breathing and interfacial delamination disrupt electronic percolation, while stress-field interactions within the solid electrolyte introduce a mechanics-dependent limitation on ionic transport. This stress-limited ionic conduction, governed by the activation volume and elastic properties of the electrolyte, can reduce effective conductivity by orders of magnitude as cathode interparticle spacing decreases and stress fields begin to overlap at high activematerial loadings. Our findings establish a direct link between chemo-mechanical evolution and transport control in solid-state cathodes, and highlight the need for solid electrolytes with low pressure sensitivity and sufficient mechanical compliance to enable high-energy all-solid-state battery architectures.

For insertion-type lithium-ion batteries, the solid-state diffusion coefficient of Li+ in an active material is considered a key parameter within the research community. The capabilities and limits of related parameter extraction methods are usually well-established. However, there is a gap in understanding the influence of the applied measurement setup. In practice, many setups unintentionally violate the assumptions of the extraction method. We apply the galvanostatic intermittent titration technique (GITT) in virtual experiments using 3D microstructure-resolved simulations in varying model measurement setups. Diffusion coefficients are extracted by applying a state-of-the-art Bayesian optimization approach which is particularly suitable for non-uniquely solvable problems. The investigated parameters are within the typical literature range of LiNi0.8Mn0.1Co0.1O2 (NMC811). Because experimental boundary conditions are precisely known within the simulation setups, the influence of microstructural features on the extracted diffusion can be isolated and quantified. The investigation shows, that the applied monodisperse thin-electrode and single-particle setup are capable of extracting the actual diffusivity with up to 4% and 17% point-estimate deviation, respectively. Particle cracking proved to have the largest impact on extracted diffusion coefficients. Nevertheless, all predictions remained close to the correct order of magnitude, i.e. point estimates deviated at most by factors in the range of 10 +/- 0.88.

For many applications it is of interest to find the capacitance corresponding to a specific interface or bulk element from electrochemical impedance spectroscopy (EIS). Often a constant phase element (CPE) is used to model the data. While some formulas are commonly used in literature to find the capacitance of a CPE they lack the physical foundation for such a general usage. A CPE mathematically has an infinite capacitance, which in most cases is physically impossible. Here we investigate EIS elements that closely follow a CPE above a certain frequency. For these we can give finite lower bounds for the capacitance depending on that frequency. We additionally develop formulas to include experimental uncertainties in the calculation of a minimum capacitance for CPE-like EIS elements.

Lithium-Sulfur batteries (LSBs) are believed to have a high potential for aerospace applications due to their high gravimetric energy density. However, despite decades of research and advances, they still suffer from poor rate capability and low power output, eventually preventing their practical implementation. One particular aspect we want to shed light on is the influence of the porous cathode structure on the rate performance during discharge. Therefore, we present a scale-resolved simulation methodology that aims to provide structural insights into the electrochemical cell behavior that are experimentally hardly accessible even for modern operando methods. Our numerical operando approach employs high-performance computing (HPC) and is based on a coarse-grained continuum model. The latter is spatially discretized with a Discontinuous Galerkin (DG) method and advanced in time by an adaptive controller. The models and methods as well as HPC aspects of our toolbox will be critically discussed, finally showcasing the capabilities of our workflow to improve LSBs.

Ni-rich cathode materials suffer from structural instability when cycled to high cutoff voltages. A transformation from the layered crystal structure to other phases, such as rocksalt, deteriorates the particle surface at low states of lithiation. Inhomogeneous potential and concentration fields as they occur in electrodes can have a significant impact on the degradation. In this work, we demonstrate rocksalt growth on a realistic high-energy NMC811 electrode using 3D microstructure-resolved simulations. We unravel inhomogeneities through transport in the electrode with a stronger active material degradation near the separator. To study individual particles in the electrode, we apply a watershed algorithm to segment the structure into distinct particles. A high correlation between both particle size as well as particle position and rocksalt thickness is observed in our half-cell simulations. We further shed light on inhomogeneities that can arise on single-particle level due to inhomogeneous lithiation.

Lattice Boltzmann methods are usually derived under the assumption of isotropy. In this work, we present a derivation of a Lattice Boltzmann method for anisotropic fluid flow. Starting from an anisotropic equilibrium distribution, we show a full derivation of the resulting lattice Boltzmann method. We ensure that our method correctly reproduces macroscopic behavior via Chapman-Enskog analysis for a single-relaxation time collision operator. As a result, we are able to show that a properly discretized anisotropic Maxwell-Boltzmann equilibrium does macroscopically in fact lead to an anisotropic variation of the Navier-Stokes equations. All desired properties of lattice Boltzmann methods, such as locality of the collision operator, isotropic discrete position and velocity space, or mass and momentum conservation are retained. While it is explicitly shown in the context of fluid flow, the presented scheme is straight-forward to adopt to advection-diffusion problems.

Silicon is frequently used as active material in the negative electrode of Lithium-ion batteries as it provides substantial improvements in the energy density compared to conventional graphite electrodes. Due to large volume changes during cycling, the Si content in state-of-the-art Si/graphite composite electrodes is often rather low. As significantly higher Si contents are desirable, the effects of structural changes that influence ion and electron transport and, thus, battery performance and degradation have to be analyzed. An aspect which is often overlooked is the displacement of electrolyte into the void regions of the cells.In our work, we developed a homogenized electrochemical model of Li-ion batteries including single phase flow through the porous electrode media to account for electrolyte motion. The considered Darcy flow is generated by the change in active material volume during battery operation. In our studies, we keep track of the amount of displaced electrolyte and the Li concentration therein. Considering different material compositions and cell designs highlights that the ratio of anode and cathode thickness and permeability are the dominant parameters determining the Li concentration in the displaced electrolyte volume.The difference between inner and displaced electrolyte Li concentration results in a concentration gradient in outflow direction. While the accumulation or depletion of local Li concentration favors degradation during prolonged cycling, our simulations show that this effect can be mitigated by tuning the permeability.

Abstract Garnet Li 7 La 3 Zr 2 O 12 electrolyte is considered a key enabler of solid-state batteries with Li metal electrodes, but the grain boundaries impair its performance. To date, the understanding of grain boundary structures and its impact on performance remains elusive. Here, we show that element segregation at Li 7 La 3 Zr 2 O 12 grain boundaries critically governs Li transport and nucleation. During conventional sintering, Al, Ta, and La segregate at grain boundaries, locally depleting Li and creating space-charge layers that lower total ionic conductivity. Simultaneously, this segregation leads to higher electronic conductivity along grain boundaries, which promotes Li nucleation at grain boundary edges with increased risk of dendrite formation. The underlying mechanism of segregation is governed by both thermodynamic driving forces and diffusion kinetics. Building on this understanding, we develop a strategy to achieve segregation-free grain boundaries through a rapid sintering protocol that utilizes the onset of solid-state softening. This approach yields transparent, polycrystalline Li 7 La 3 Zr 2 O 12 with negligible grain boundary impedance and enhanced dendrite tolerance. By elucidating the structural origins and electrochemical consequences of grain boundary segregation, this work provides a guidance for the rational optimization of solid electrolytes.

The intricate internal stresses within porous electrode coatings (PEC) are induced by charging and discharging of lithium-ion batteries. The incorporation of silicon-based particles in the anode further exacerbates the volume change of active particles and the microstructure change of PECs during battery cycling. This highlights the urgent need for a mechanical model of the PEC in electrochemically and mechanically coupled cell simulations. The first step to develop such a model is a layer-resolved, homogenized mechanical characterization of the PEC. In cylindrical cells, the mechanical properties of the PEC are highly nonlinear due to its multiphase granular microstructure combined with its thin, rolled geometry inside the cell housing. Herein, microindentation is employed and analyzed to extract the one-dimensional mechanical response of a single PEC-layer. Three major challenges of microindentation, thermal drift, substrate effect, and tip size effect are overcome. Quantification of short-term elasticity as well as long-term viscoelasticity is done for a silicon-containing dry anode sample by the proposed workflow. The results demonstrate that microindentation is a suitable and effective measurement method for characterizing PECs, thereby facilitating the development of mechanical models for multidisciplinary cell simulations.

Garnet Li 7 La 3 Zr 2 O 12 (LLZO) electrolyte is considered a key enabler of solid-state batteries (SSBs) with Li metal anodes, but the formation of grain boundaries (GBs) impairs its performance. To date, the mechanistic understanding of GB structures and its impact on cell performance remains elusive. Here, we show that element segregation at LLZO GBs critically governs Li transport and nucleation behavior by forming an intricate GB structure comprising GB core and edges. During conventional sintering, Al, Ta, and La segregate at GBs, locally depleting Li and creating space-charge layers that lower total ionic conductivity. Simultaneously, this segregation leads to higher electronic conductivity along GBs, which promotes microscale Li nucleation at GB edges and increases the risk of dendrite formation. The underlying mechanism of segregation is contributed to the interplay between thermodynamic driving forces and diffusion kinetics along the Li-ion migration pathways during sintering. Building on this mechanistic understanding, we develop a universal strategy to achieve segregation-free GBs through a rapid yet precisely controlled sintering protocol that utilizes the onset of solid-state softening, identified by an inflection in the densification curve, and is applicable to various ceramic materials. This approach yields transparent, polycrystalline LLZO with negligible GB impedance and markedly enhanced dendrite tolerance. By elucidating the structural origins and electrochemical consequences of GB segregation, this work provides a blueprint for the rational development of next-generation electrolytes with superior performance in SSBs.

Lithium (Li) metal is considered the 'holy grail' of battery anodes and has attracted enormous interest due to its low density (0.59 g cm -3 ), high theoretical capacity (3860 mAh g -1 ) and lowest electrochemical potential (-3.07 V vs. standard hydrogen electrode - SHE). However, numerous issues during cycling have hindered its commercialization. Some notable problems include the formation of an unstable solid electrolyte interphase (SEI), excessive dendrite growth and subsequent short-circuiting during the Li stripping/plating process. One possible solution to alleviate these issues is through the use of 'hosted' Li metal anodes, where lithiophilic materials are used to guide Li metal stripping and plating. These solutions must not add significant weight to the system, as this negates the potential energy density benefit of the Li metal anode. This presentation will examine the use of lithiophilic group 14 nanowires (NWs) to control Li metal deposition within hosted Li metal anodes. We will highlight our three recently developed architectures shown in the figure: i) a NW decorated carbon paper (CP) Li metal host, 1 ii) a Lithiophilic interlayer that can induce ‘bottom-up Li infilling 2 and iii) a NW decorated Cu current collector for Li metal applications. 3 Detailed electrochemical testing, materials analysis, density functional theory (DFT) calculations and multi-physics modelling are used to shed light on the lithiophilic properties of the NWs and explain their ability to improve the modified Li metal anodes. The role of the current collector morphology and the elemental composition of the lithiophilic material (from Si, to SixGe 1-x and Ge) will also be examined. Full-cell compatibility of these hosted anodes with high capacity NMC and S cathodes is detailed, with significant capacity and cycle life enhancements relative to unmodified Li foil anodes. This work is aimed at the development of high energy density (ED) Li metal anodes to meet the rising ED demands of electric vehicle (EV) industry and other demanding applications. References: 1: Abdul Ahad, Syed; Bhattacharya, Shayon; Kilian, Seamus; Ottaviani, Michela; Ryan, Kevin M; Kennedy, Tadhg; Thompson, Damien; Geaney,* Hugh; Lithiophilic nanowire guided Li deposition in Li metal batteries. Small. 2023, 19,2, 2205142 2: Ahad, Syed Abdul; Drews, Janina; Danner, Timo; Latz, Arnulf; Geaney,* Hugh; Lithiophilic interlayer driven ‘bottom-up’ metal infilling in high current density Li-metal anodes. J. Mater. Chem. A 2024, 12, 20,12250-12261,2024 3: Abdul Ahad, Syed; Adegoke, Temilade Esther; Ryan, Kevin M; Geaney,* Hugh; Cu Current Collector with Binder‐Free Lithiophilic Nanowire Coating for High Energy Density Lithium Metal Batteries. Small. 2023, 19, 20, 2207902 Figure 1

Solid-state batteries are transformative solutions for electric vehicles, offering superior energy density and safety. Sulfide-based solid electrolytes like Li₆PS₅Cl (LPSCl) combine high ionic conductivity and mechanical adaptability, but challenges remain in scaling up high-performance separator tapes due to particle size distribution (PSD) and processing constraints. This study investigates the uni-axial densification of slurry-casted LPSCl tapes, focusing on PSD refinement and compaction pressure. Wet milling has been identified to effectively reduce PSD to submicron levels while preserving structural integrity and near-pristine conductivity. A critical pressure threshold (≈350 MPa) for tape-casted LPSCl slurries (2.5% hydrated poly(acrylonitrile-co-butadiene)) is identified, where ionic conductivity peaks due to particle fusion and the formation of conductive networks. However, open porosity (≈30%), particularly along the densification direction, and surface irregularities persist. These structural issues have significant implications for battery performance. For example, surface roughness and interfacial voids lead to localized current focusing, with current densities exceeding applied values by over 20 times. Percolating porosity accelerates dendritic failure modes, undermining stability and limiting cycling rates. This work underscores the need for optimized powder processing and densification techniques to enhance scalability and performance, advancing LPSCl-based separators for the practical adoption of solid-state batteries in electric vehicles and other high-energy applications.

Solid-state batteries present a promising technology to overcome the energy density limitations of lithium-ion batteries. However, achieving a high areal loading in cathodes without introducing significant transport limitations remains a key challenge, particularly in thick electrodes. In this work, we study the impact of a three-layer graded cathode design on the performance of a LiNi0.83Co0.11Mn0.06O2 (NCM83)/Li6PS5Cl (LPSCl) composite cathode using a combination of experiments and microstructure-resolved simulations. An increased LPSCl content at the separator and higher NCM83 content toward the current collector improve effective charge transport, resulting in better rate performance and reduced overpotentials at high current densities. This comprehensive experimental and theoretical study demonstrates that the optimization of cathode design has the potential to significantly enhance the performance of solid-state batteries.

The growing demand for advanced energy storage systems requires the development of next-generation battery technologies with superior energy density and cycle stability, with lithium-sulfur (Li-S) batteries representing a promising solution. Sulfur-containing polyacrylonitrile cathodes (SPAN) for Li-S batteries are a significant advancement for this next-generation battery chemistry, addressing the major issue of limited cycle life encountered in conventional carbon/sulfur composite cathodes. In the presented study, the influence of available ionic and electronic conduction pathways within the cathode on the electrochemical performance of SPAN-based Li-S batteries is studied in details. To this end, a series of SPAN cathodes with different microstructures is prepared by adapting the compression degree of calendering. Mechanical and morphological characterizations confirm a pronounced springback effect due to a characteristic elastic deformation behavior of SPAN. Electrochemical impedance spectroscopy (EIS) shows increased cathode impedance values with multiple overlapping processes in the high- to mid-frequency region in highly compressed SPAN cathodes. Moreover, while the (first) discharge capacity is unaffected, the subsequent charge capacity decreases substantially for highly compressed cathodes. The electrochemical experiments and electrochemical continuum simulations confirm that this phenomenon is mainly due to the disturbance of the electronic percolation pathways caused by the springback behavior during calendering.

Nickel-Manganese-Cobalt (NMC) oxides are widely used as cathode materials in lithium-ion batteries. While increasing the nickel content increases the available capacity in a given voltage window, it also reduces the structural stability of the material when cycled to high cutoff voltages. Oxygen release from the crystal structure as well as a layered-to-rocksalt phase transformation of the layered oxide material cause capacity loss and impedance rise. In this work, we propose a continuum approach to model oxygen release and the associated phase transformation using a 1+1D model informed by atomistic simulations to predict the thickness of reconstructed active material over time. An efficient interface model allows us to combine this approach with 3D microstructure-resolved simulations in order to study the effect of a resistive layer on a real cathode microstructure. This novel workflow enables us to investigate the effect of individual electrode properties on the phase transformation and guide future electrode design.

All‐solid‐state batteries offer enhanced safety and energy density compared to conventional systems, but their performance critically depends on the microstructure of the composite cathode. Sulfide‐based solid electrolytes (SEs) are promising Li‐ion conductors, yet they degrade upon contact with cathode active materials, necessitating passivating coatings that impair electronic conductivity. Herein, an electron‐conducting matrix of SE and 4 wt% conductive additive (C65) at the percolation threshold is introduced to minimize side reactions. The effect of coated active material fraction on ionic and electronic conductivities is investigated using electrochemical impedance spectroscopy, rate tests, 2D/3D imaging, and numerical simulations. The results highlight the critical role of the electronically conductive network, which percolates at low CAM loadings, collapses at 50 wt% as C65 adheres to coated CAM surfaces—depleting the bulk network—and recovers at higher loadings via percolation of C65‐coated particles, demonstrating the essential function of C65. At 70 wt%, a robust network yields 99.8 mAh g − 1 at C/10 and 84% retention at C/5; at 80 wt%, ionic conductivity diminishes despite improved electronic transport, reducing rate performance. These findings underscore the need to balance ionic and electronic pathways and provide new insights into the role of additives in composite cathodes.

This perspective rationalizes different design strategies and elucidates the most effective approaches for spatially controlling Li deposition for anode-free Li metal batteries.

Solid-state batteries are transformative solutions for electric vehicles, offering superior energy density and safety. Sulfide-based electrolytes like Li₆PS₅Cl (LPSCl) combine high ionic conductivity and mechanical adaptability, but challenges remain in scaling up high-performance separator tapes due to particle size distribution (PSD) and processing constraints. This study investigates the uni-axial densification of slurry-casted LPSCl tapes, focusing on PSD refinement and compaction pressure. Wet milling has been identified to effectively reduce PSD to submicron levels while preserving structural integrity and near-pristine conductivity. A critical pressure threshold (~350 MPa) for tape-casted LPSCl slurries (2.5% hydrated poly(acrylonitrile-co-butadiene)) was identified, where ionic conductivity peaks due to particle fusion and the formation of conductive networks. However, open porosity (~30%), particularly along the densification direction, and surface irregularities persist. These structural issues have significant implications for battery performance. For example, surface roughness and interfacial voids lead to localized current focusing, with current densities exceeding applied values by over 20 times. Percolating porosity accelerates dendritic failure modes, undermining stability and limiting cycling rates. This work underscores the need for optimized powder processing and densification techniques to enhance scalability and performance, advancing LPSCl-based separators for the practical adoption of solid-state batteries in electric vehicles and other high-energy applications.

Ni-rich cathode materials suffer from structural instability when cycled to high cutoff voltages. A transformation from the layered crystal structure to other phases, such as spinel and/or rocksalt, deteriorates the particle surface at low states of lithiation. Inhomogeneous potential and concentration fields as they occur in electrodes can have a significant impact on the degradation. In this work, we demonstrate rocksalt growth on a realistic high-energy NMC811 electrode using 3D microstructure-resolved simulations. We unravel inhomogeneities through transport in the electrode with a stronger active material degradation near the separator. To study individual particles in the electrode, we apply a watershed algorithm to segment the structure into distinct particles. A high correlation between both particle size as well as particle position and rocksalt thickness is observed in our half-cell simulations. We further shed light on inhomogeneities that can arise on the single-particle level due to inhomogeneous lithiation.

While nickel-based layered oxide cathodes offer promising energy and power densities in lithium-ion batteries, they suffer from instability when fully delithiated upon charge. Ex situ studies often report a structural degradation of the charged cathode materials, but the precise mechanism is still poorly understood on the atomic scale. In this work, we combine high-level ab initio calculations with molecular dynamics using machine-learning interatomic potentials to study structural degradation of fully delithiated LiNiO2 surfaces at the top of charge. We find a previously unreported, stable reconstruction of the (012) facet with more facile oxygen loss compared to the pristine surfaces. The oxygen vacancy formation energy closely corresponds to the experimental decomposition temperatures of charged cathodes. Furthermore, we use molecular dynamics simulations to sample Ni ion migration into alkali-layer sites that is a kinetically plausible initiation step for surface degradation toward thermodynamically stable products.