Interfacial electrochemistry engineering via advanced electrolyte design for anode-free sodium metal batteries : innovations and prospects

Abstract

Anode-free sodium metal batteries (AFSMBs) represent promising alternatives to commercial lithium-ion batteries, offering high energy density, simplified configuration, and abundant sodium resources. However, their practical deployment is impeded by uncontrolled electrochemical dendrite growth and irreversible sodium loss. Recent advances integrating electrolyte formulation with solid electrolyte interphase (SEI) engineering have enabled more stable operation under demanding electrochemical conditions. Still, a systematic review correlating these developments from an electrochemical perspective remains lacking. This work fills that gap by providing a critical review and forward-looking perspective on electrolyte design for AFSMBs, emphasizing interfacial electrochemical kinetics/stability of sodium metal anodes. We first outline fundamental electrochemical challenges and the role of electrolyte kinetics and thermodynamics in governing AFSMB performances. Special focus is given to advanced liquid electrolytes tailored for extreme electrochemical conditions, such as low/high temperature and high-voltage operation. The discussion is then extended to semi-solid and all-solid-state systems, with a critical analysis of their interfacial electrochemistry. We examine how gel polymer electrolytes function as electrochemically stabilizing matrices, and how all-solid-state polymer electrolytes regulate ion transport kinetics and suppress dendrite growth via their electrochemical and interfacial characteristics. Finally, we present a research roadmap centered on achieving interfacial electrochemical stability and full cell integration.