Self-Regulating Interfacial-Boosted Electrolytes for Fast-Charging and Long-Life Aqueous Batteries.

Abstract

Aqueous batteries are promising for large-scale energy storage due to inherent safety and low cost; however, their long-term cycling stability is fundamentally limited by interfacial degradation. Although existing strategies such as "water-in-salt" and water-organic hybrid electrolytes can widen the electrochemical stability window (ESW), trace water electrolysis still occurs at the interface, leading to gradual pH drift, electrode dissolution, and eventual battery failure. Here, we propose a self-regulating interfacial-boosted electrolyte that effectively addresses these challenges. By introducing phosphate‑based components into wide‑ESW electrolytes, this design autonomously ensures pH stability via intrinsic buffering capability, spontaneously forms a protective cathode-electrolyte interphase in response to metal-ion dissolution, and reconfigures the ion solvation structure to widen the electrochemical stability window and lowers the interfacial impedance. Demonstrated in a Na₁.₈₅Mn[Fe(CN)₆]₀.₉₇·2H₂O//NaTi₂(PO₄)₃ full cell with an energy density of 81.7 Wh kg^-1, this electrolyte enables fast charging (75% capacity retention from 1 C to 80 C) and ultra-long cycling stability (71% capacity retention after 20 000 cycles at 80 C). The strategy offers an effective and generalizable pathway toward high-performance aqueous batteries.