Enhanced electrochemical cyclability of composite sodium metal anode with inorganic-rich solid electrolyte interphase

The practical application of sodium (Na) metal anode in rechargeable batteries is impeded by inferior electrochemical properties and safety hazards arising from uneven Na plating/stripping behaviors. The Na-ion diffusion within the solid electrolyte interphase (SEI) plays a pivotal role in influencing these behaviors and the electrochemical performance of the Na metal anode. In this study, we leveraged the spontaneous reaction between red phosphorus (P) and metallic Na to fabricate a Na/Na3P (NNP) composite foil using a straightforward folding and mechanical rolling method at room temperature. The in-situ formed Na3P phase fosters the formation of an inorganic-rich SEI layer with high ionic conductivity, effectively enhancing the Na-ion diffusion kinetics and curbing the formation of Na dendrites. Moreover, the Na3P present in the NNP composite can continually replenish the functional component and promptly repair the fracture of the SEI layer, thereby ensuring the stability of its structure and properties. Consequently, the NNP composite electrode significantly extends the Na plating/stripping cyclic lifespan compared to a bare Na anode. As a demonstration, the Na3V2(PO4)3||NNP full cell exhibits stable performance over 400 cycles with 96.7 % capacity retention at 5C. This work paves the way for designing stable SEI layers with fast ion diffusion capability for alkali metal anodes, and the findings are anticipated to propel the development of alkali metal batteries.