Enabling High Performance Potassium Storage in Ceramic Structures by Dual Salt Electrolyte

A dual-salt electrolyte of KPF₆/KFSI in carbonate ester solvents have been developed for long-life and high-capacity SiOC ceramic anodes in K-ion batteries. The KPF₆/KFSI in ethylene carbonate (EC)/diethyl carbonate (DEC) exhibits higher ionic conductivity than single-salt KPF₆ solution. Here, it is shown that the capacity retention and Coulombic efficiency of polymer-derived SiOC ceramics can be remarkably improved by simply using KPF₆/KFSI dual salt dissolved in EC/DEC as the electrolyte over the KPF₆ salt dissolved in EC/DEC electrolyte. By investigating different SiOC electrode structures (powder and fiber), it is discovered that the degradation of SiOC half-cells in KPF₆-containing electrolyte originates from the failure of the electrode. The SEI layer formed on SiOC during cycling was systematically investigated by using a series of characterizations.