Weakly Solvated Electrolyte Driven Anion Interface Chemistry for Potassium Batteries/Hybrid Capacitors

Potassium metal batteries/hybrid capacitors (PMBs/PHCs) have attracted attention due to the abundant reserves of potassium (K), but the unstable solid electrolyte interphase (SEI) formed by conventional ether electrolytes has led to low Coulombic efficiency (CE) and reduced cycle life of PMBs/PHCs. Herein, we discovered that the CE can be significantly enhanced to 98.1% by using a weakly solvated electrolyte of 1 M KFSI/1,2-diethoxyethane (DEE). The DEE electrolyte enable K//Prussian blue full cells to achieve an energy density of 80 Wh kg–1. Additionally, K//AC capacitors deliver a specific capacity of 60 mAh g–1 with stable cycling over the course of a year. By weakening the interactions between the solvent and K+, the DEE electrolyte promotes the formation of a stable anion-dominated SEI. The robust SEI regulates the deposition of K+ ions and inhibits the growth of K dendrites. This work provides a straightforward and efficient strategy for developing high-performance PMBs/PHCs.