Electrolyte Chemistry Enables Simultaneous Stabilization of Potassium Metal and Alloying Anode for K‐Ion Batteries

: Alloying anodes are promising high-capacity electrode materials for K-ion batteries (KIBs). However, KIBs based on alloying anodes suffer from rapid capacity decay due to the instability of K metal and large volume expansion of alloying anodes. Herein, the effects of salts and solvents on the cycling stability of KIBs based on a typical alloying anode such as amorphous red phosphorus (RP) are investigated, and the potassium bis(fluorosulfonyl)imide (KFSI) salt-based carbonate electrolyte is versatile to achieve simultaneous stabilization of K metal and RP electrodes for highly stable KIBs. This salt-solvent complex with a moderate solvation energy can alleviate side reactions between K metal and the electrolyte and facilitate K+ ion diffusion/desolvation. Moreover, robust SEI layers that form on K metal and RP electrodes can suppress K dendrite growth and resist RP volume change. This strategy of electrolyte regulation can be applicable to other alloying anodes for high-performance KIBs.