Understanding the Electrochemical–Mechanical Coupled Volume Variation of All-Solid-State Lithium Metal Batteries

Abstract Appropriate stack pressure improves the solid-to-solid interfacial stability and prolongs cyclability of the all-solid-state lithium metal batteries (ASSLBs). A low stack pressure is required for the commercialization of ASSLBs, and the key to reduce stack pressure is to regulate the volume variation of the components during charging/discharging. This study establishes a three-dimensional electrochemical–mechanical coupled model to investigate the underlying mechanism of the volume variation of ASSLBs comprised of LiNi0.8Co0.1Mn0.1O2 cathode, Li6PS5Cl solid electrolyte, and lithium metal anode, considering the electrochemical kinetics, Li diffusion, elastic–plastic deformation, and their interplays. Results reveal that lithium plating at the lithium anode surface significantly increases the volumetric strain (>60%) and dominates the overall volume expansion of ASSLBs during charging. Increasing the thickness of the lithium metal anode is beneficial to accommodate the Li deposition through the deformation of soft lithium, reduce the expansion in the thickness direction, and lower the external pressure. The carbon black-binder domain (CBD) with a lower Young's modulus can be used as a buffer layer to adjust the volume change in the cathode domain, which can also effectively alleviate the mechanical stress to reduce possible damage. Increasing the volume fraction of NCM particles can induce a larger volumetric strain of the cathode, resulting in an increase in the expansion of ASSLBs. The developed multiphysics model reveals the underlying electrochemical–mechanical coupled volume variation mechanism of the ASSLBs to provide guidance on the design and fabrication of next-generation ASSLBs under low pressure.