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Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid–solid interfaces remains limited compared to at solid–liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li 10 SnP 2 S 12 ) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries. Understanding electrochemical behaviour and stability at solid–solid interfaces remains challenging. Operando synchrotron X-ray computed microtomography loss reveals that reconfiguration of interfacial contact is critical to explain cell failure during solid-state battery cycling.

Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro‐chemo‐mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity‐induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms—mechanical, transport, and kinetic—that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes. The electrochemical and structural heterogeneities in the solid electrolyte interphase (SEI) influence the reaction kinetics of Na metal electrodes, resulting in current focusing and stress hotspots during electrodeposition. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.

Lithium (Li) metal‐based solid‐state batteries (SSBs) are considered promising candidates for next‐generation energy storage due to their superior energy density and enhanced safety compared to conventional Li‐ion systems. However, their practical application is limited by challenges such as void formation at the Li‐solid electrolyte (SE) interface, which disrupts ion transport and accelerates interfacial degradation. This work investigates how the coupled effects of electro‐dissolution kinetics and surface diffusion at the Li metal surface govern the evolution of interfacial morphology during stripping. This work examines the influence of three distinct surface diffusion modes, which are terrace diffusion, step diffusion, and interlayer diffusion, on maintaining interfacial stability. In addition, how the dominant surface diffusion mechanism can overcome the contact loss due to high reaction kinetics is explored. Furthermore, the roughness of the Li metal anode surface is quantified, and the influence of different diffusion mechanisms on the evolution of the dynamic solid–solid interface is examined. The critical role of temperature in enhancing Li surface diffusivity and expanding the regime of stable contact is highlighted. By identifying distinct regimes of interface stability, this study analyzes how non‐uniform electrochemical dynamics dictate void morphology evolution and interfacial contact. These insights offer guiding principles for engineering robust Li–SE interfaces in SSBs. Understanding void formation at the lithium(Li) metal–solid electrolyte (SE) interface is crucial to improving interfacial stability in solid‐state batteries(SSBs). In this work, the competing electrochemical interactions, including surface diffusion modes are studied in dictating interface evolution during electro‐dissolution. A distinct surface diffusion mode for stable contact is identified, and the role of temperature and overpotential is explored.

As solid‐state batteries (SSBs) with lithium (Li) metal anodes gain increasing traction as promising next‐generation energy storage systems, a fundamental understanding of coupled electro‐chemo‐mechanical interactions is essential to design stable solid‐solid interfaces. Notably, uneven electrodeposition at the Li metal/solid electrolyte (SE) interface arising from intrinsic electrochemical and mechanical heterogeneities remains a significant challenge. In this work, the thermodynamic origins of mechanics‐coupled reaction kinetics at the Li/SE interface are investigated and its implications on electrodeposition stability are unveiled. It is established that the mechanics‐driven energetic contribution to the free energy landscape of the Li deposition/dissolution redox reaction has a critical influence on the interface stability. The study presents the competing effects of mechanical and electrical overpotential on the reaction distribution, and demarcates the regimes under which stress interactions can be tailored to enable stable electrodeposition. It is revealed that different degrees of mechanics contribution to the forward (dissolution) and backward (deposition) reaction rates result in widely varying stability regimes, and the mechanics‐coupled kinetics scenario exhibited by the Li/SE interface is shown to depend strongly on the thermodynamic and mechanical properties of the SE. This work highlights the importance of discerning the underpinning nature of electro‐chemo‐mechanical coupling toward achieving stable solid/solid interfaces in SSBs. This work explores the thermodynamic foundations of mechanics‐coupled reaction kinetics and reveals its implications on electrodeposition stability in solid‐state batteries. Depending on the material properties of the solid electrolyte (SE), lithium (Li) metal/SE interfaces can exhibit distinct mechanics‐driven energetic contributions to the free energy landscape of the reaction, resulting in different scenarios of mechanics‐reaction kinetics coupling and electrodeposition stability regimes.

Sodium metal batteries (SMBs) have gained interest due to the high natural abundance and lower cost of sodium (Na) compared to lithium (Li), making them a promising alternative to conventional Li‐based battery systems. However, a key challenge toward the commercial viability of SMBs lies in mitigating uneven electrodeposition and dendrite growth, stemming from inherent interfacial instabilities during Na plating. This work explores how electrodeposition stability in SMBs is governed by thermal conditions, which directly affect ionic transport and interfacial reaction kinetics. A range of thermal environments are explored using a phase‐field modeling (PFM) framework, with a particular emphasis on the influence of temperature gradient‐induced thermodiffusion (Soret effect) on deposition dynamics. A quantitative analysis of dendrite growth under varying thermal conditions is conducted to identify regimes that promote stable plating behavior. It is found that operational temperature serves as a strong modulator of plating instability by simultaneously influencing reaction kinetics and ion transport, and thermodiffusion under imposed temperature gradients further redistributes ionic flux and alters deposition morphology. This work provides new insights into the role of thermal landscapes in dictating interface evolution during Na metal plating and offers design guidelines for leveraging thermal conditions to enhance deposition stability in Na metal electrodes. Unstable electrodeposition in sodium metal electrodes during plating gives rise to dendritic morphologies. A comprehensive analysis of how various thermal profiles, including uniform and non‐uniform temperature distributions and thermodiffusion can affect electrodeposition instability has been performed. Mechanistic interface instability descriptors have been introduced to quantify dendritic growth.

Dendrite growth arising from interfacial instability remains a major obstacle to the advancement and commercialization of metal anode-based batteries. Sodium metal batteries (SMBs), a promising alternative to lithium (Li)-based systems due to the broad availability and lower cost of sodium (Na), suffer from pronounced interfacial instabilities during plating. A principal modulating factor influencing the propensity for dendritic growth in metal anodes is the interfacial surface energy at the active metal-electrolyte interface. This work explores the role of surface energy-induced interfacial instability in SMBs employing liquid electrolytes. It is shown that higher interfacial energies promote a more uniform deposition front, thereby reducing the tendency for uneven electrodeposition. For low interfacial energies, the reduced energetic penalty for creating new surfaces promotes rapid tip growth and branching, leading to highly unstable deposition morphologies with pronounced dendritic features. Furthermore, a comparative analysis between Li and Na metal anodes reveals that intrinsic differences in the material properties significantly influence electrodeposition stability. Through a combination of qualitative visualization and quantitative analysis, this study provides a comprehensive understanding of the role of surface energy in dictating interface evolution in SMBs, offering insights for the rational design of stable metal anode systems.

Anode-free solid-state batteries contain no active material at the negative electrode in the as-manufactured state, yielding high energy densities for use in long-range electric vehicles. The mechanisms governing charge–discharge cycling of anode-free batteries are largely controlled by electro-chemo-mechanical phenomena at solid–solid interfaces, and there are important mechanistic differences when compared with conventional lithium-excess batteries. This Perspective provides an overview of the factors governing lithium nucleation, growth, stripping and cycling in anode-free solid-state batteries, including mechanical deformation of lithium, the chemical and mechanical properties of the current collector, microstructural effects, and stripping dynamics. Pathways for engineering interfaces to maximize performance and extend battery lifetime are discussed. We end with critical research questions to pursue, including understanding behaviour at low stack pressure, tailoring interphase growth, and engineering current collectors and interlayers. Anode-free batteries contain no active material at the negative electrode when manufactured, and this can enable them to have high energy density. This Perspective presents a critical overview of the mechanisms governing the behaviour of anode-free solid-state batteries and provides guidance to improve this type of battery.

The interlaboratory comparability and reproducibility of all-solid-state battery cell cycling performance are poorly understood due to the lack of standardized set-ups and assembly parameters. This study quantifies the extent of this variability by providing commercially sourced battery materials—LiNi 0.6 Mn 0.2 Co 0.2 O 2 for the positive electrode, Li 6 PS 5 Cl as the solid electrolyte and indium for the negative electrode—to 21 research groups. Each group was asked to use their own cell assembly protocol but follow a specific electrochemical protocol. The results show large variability in assembly and electrochemical performance, including differences in processing pressures, pressing durations and In-to-Li ratios. Despite this, an initial open circuit voltage of 2.5 and 2.7 V vs Li + /Li is a good predictor of successful cycling for cells using these electroactive materials. We suggest a set of parameters for reporting all-solid-state battery cycling results and advocate for reporting data in triplicate. More transparent protocol reporting and comprehensive battery cell data are needed. Twenty-one research groups joined forces to assess solid-state battery performance and found considerable differences in assembly protocols that cause variable results.

There is an urgent need for improved energy storage devices to enable advances in markets ranging from small-scale applications (such as portable electronic devices) to large-scale energy storage for transportation and electric-grid energy. Next-generation batteries must be characterized by high energy density, high power density, fast charging capabilities, operation over a wide temperature range and safety. To achieve such ambitious performance metrics, creative solutions that synergistically combine state-of-the-art material systems with advanced architectures must be developed. The development of 3D batteries is a promising solution for achieving these targets. However, considerable challenges remain related to integrating the various components of a battery into an architecture that is truly 3D. In this Review, we describe the status of 3D batteries, highlight key advances in terms of mechanistic insights and relevant performance descriptors, and suggest future steps for translating current concepts into commercially relevant solutions. In this Review, we provide an overview of the current state of the field of 3D batteries. We discuss critical performance metrics, the potential for scalability and commercialization, and suggest focused areas for future development.

Solid‐state lithium–sulfur (SSLS) batteries offer high theoretical energy density, yet their practical viability is hindered by poor sulfur utilization and limited rechargeability. At the core of this challenge lies the passivating nature of Li 2 S, which restricts ionic and electronic transport, suppresses interfacial activity, and severely impedes the reversibility of electrochemical reactions. In this study, we elucidate the mechanistic origins of these limitations by resolving how charge and discharge species form, grow, and spatially evolve within the cathode microstructure under varied current densities and electrode compositions. By resolving the species distribution at the particle scale and coupling it with Raman spectroscopy and X‐ray diffraction, we demonstrate how Li 2 S formation induces localized surface passivation that progressively limits electrochemical accessibility within the cathode microstructure. Sulfur utilization is found to be strongly governed by the interplay between sulfur loading, residual porosity, and interfacial architecture. High sulfur contents result in buried, electrochemically isolated domains due to poor solid electrolyte (SE) percolation, while low sulfur contents trigger SE degradation via parasitic reactions. The resulting sulfur‐porosity maps delineate the mechanistic boundaries between reversible and transport‐limited regimes, offering actionable design guidance for SSLS cathodes with enhanced sulfur utilization.