Failure Mechanisms and Fault Evolution in All‐Solid‐State Batteries: From Materials to Cell‐Level Degradation

ABSTRACT All‐solid‐state batteries (ASSBs) are widely regarded as a promising next‐generation energy storage technology due to their potential advantages in intrinsic safety, energy density, and operating temperature window. However, growing evidence indicates that their performance degradation and failure cannot be attributed to a single material or an isolated interface issue, but rather arise from the coupled evolution of intrinsic material instabilities, constrained solid–solid interfacial contact, and strong chemo–electro–mechanical interactions. This review systematically summarizes the failure mechanisms and fault evolution of ASSBs from the material level to the cell level. First, the chemical stability and mechanical properties of solid electrolytes and electrode materials are examined, with particular emphasis on thermodynamic instability, interfacial decomposition, and structural embrittlement under high‐voltage cathodes or lithium‐metal anodes. Subsequently, the formation and evolution of real contact area at solid–solid interfaces are discussed, elucidating the intrinsic links between volume‐change‐induced stress concentration, contact loss, and the nonlinear growth of interfacial resistance. Furthermore, the mutual reinforcement between interfacial chemical reactions and mechanical damage is analyzed, along with how these processes are amplified at the electrode scale and ultimately evolve into capacity fading and safety risks at the cell level. By integrating experimental observations, operando/three‐dimensional characterization, and multiscale modeling, this work establishes a unified framework connecting materials, interfaces, and cell‐level degradation, providing theoretical guidance for interfacial engineering, structural optimization, and lifetime prediction of ASSBs.