Interface Engineering in Solid‐State Sodium Batteries: Advances in Materials Design, Interfacial Strategies, and Multiscale Characterization

ABSTRACT Interfacial processes play a crucial role in the electrochemical performance, stability, and lifespan of solid‐state sodium batteries (SSSBs). Based on the significant impact of SSSBs, understanding and controlling these interfacial phenomena have become a critical objective in advancing SSSBs technologies. This review article aims to gain insights into material design principles, interfacial failure types, and multiscale electrochemical behaviors to provide a comprehensive overview of the interface engineering for various SSSBs components, including cathode materials, cathode–solid electrolyte interface, solid‐state electrolyte, solid electrolyte–anode interface, and anode materials. In addition, we explore recent advancements in in‐situ and operational characterization techniques across multiple scales enabling the elucidation of dynamic interfacial behavior. By integrating the design of materials and interface with advanced characterization techniques, this review elucidates key relevant challenges and strategies, and hence offers perspectives on future pathways for constructing high‐performance SSSBs.