Regulated Electrolyte Solvation Enables Rapid Charge Transfer for Red Phosphorus Anodes toward High-Performance Potassium Batteries

Potassium–ion batteries (KIBs) with red phosphorus (RP) anodes offer competitive energy densities for energy storage systems. However, their practical deployment is hindered by the fundamental challenges stemming from the substantial volume change that cumulatively destabilizes the electrode–electrolyte interphase (EEI), triggering persistent parasitic reactions and sluggish ion transport. Here, we address these challenges through electrolyte engineering featuring anion–enriched solvation to regulate the EEI chemistry. By coherently tuning the solvent composition, anion species, and salt concentration, a highly electron-deficient anion–solvation structure is established, which facilitates nucleophilic attack by electrons at the phosphorus electrode surface, resulting in predominant anion decomposition and formation of a uniform, inorganic–rich interphase. Furthermore, rapid ion diffusion within the SEI enabled by the anion decomposition and improved charge transfer kinetics at the low–conductivity electrode interface are observed. With the anion–rich solvation-based electrolyte, the RP anode achieves stable cycling for 1500 cycles at a high current density of 1.0 A g –1, maintaining an average Coulombic efficiency of 99.7%. This study highlights the essence of electrolyte and interphase engineering in enabling stable cycling of electrodes with substantial volume expansion and an inherently low conductivity.