Multiscale Failure Mechanisms and Safety Assessment of Commercial Sodium‐Ion Batteries

Abstract Compared with coin cells, commercial Ah‐level sodium‐ion batteries (CSIBs) are more susceptible to boundary effects, stress variations, and interfacial reactions, which exacerbate battery degradation and safety concerns. While considerable efforts have been directed toward optimizing electrode materials, systematic reviews addressing the swelling behavior and thermal runaway (TR) in CSIBs remain scarce. This review systematically traces the development history of CSIBs and offers a detailed analysis of their failure mechanisms and safety challenges across multiple length scales, from the microscopic to the macroscopic level. Furthermore, it compiles recent advances and improvement strategies in a structured manner. Particular emphasis is placed on the underlying causes, evolution stages, and early warning indicators of TR. In addition, advanced diagnostic techniques, including fiber optic sensors, real‐time simulations, and battery management system optimization, are critically evaluated. This review highlights the importance of sustainable battery design and closed‐loop resource management, aiming to establish a scientifically robust safety framework that facilitates the industrial deployment of next‐generation sodium‐ion energy storage technologies.