AlF3-modified anode-electrolyte interface for effective Na dendrites restriction in NASICON-based solid-state electrolyte

Abstract Inorganic Na+ conducting solid-state electrolyte (SSE) has received extensive attention in assembling large-scale sodium metal batteries. However, continuous Na dendrites propagation has prevailingly hampered its implementation due to premature cell failure and safety concerns. Herein, a coating layer of AlF3 was decorated between Na anode and NASICON SSE for the first time, which can in situ form a Na+ conducting buffer layer by a conversion reaction with Na during initial cycles. Profiting from the intimate modification of AlF3 interlayer, the Na/SSE interfacial contact is extremely ameliorated. Moreover, owing to the “overpotential triggering” mechanism of the reaction between AlF3 and Na, the locally agminated electron at the anode-electrolyte interface can be released by preferentially driving more Na+ to react with AlF3 instead of forming dendrites at large current density. According to DFT calculations, the critical dendrites length is also enlarged owing to the increased interfacial energy between AlF3-induced interlayer and Na. Therefore, the critical current density of Na/AlF3-NASICON/Na cells has multiplied three-fold to 1.2 ​mA ​cm−2 at 60 ​°C, and the cycling stability of Na metal SSE batteries is also dramatically ameliorated. The rational strategy of modifying AlF3 interlayer is believed to be helpful in resisting dendrites propagation among solid alkalis metal batteries.