An Intrinsically Non‐flammable Electrolyte for High‐Performance Potassium Batteries

Potassium‐ion batteries are promising for low‐cost and large‐scale energy storage applications, but the major obstacle to their application is the lack of safe and effective electrolytes. A phosphate‐based fire retardant such as triethyl phosphate is now shown to work as a single solvent with potassium bis(fluorosulfonyl)imide at 0.9  m , in contrast to previous Li and Na systems where phosphates cannot work at low concentrations. This electrolyte is optimized at 2  m , where it exhibits the advantages of low cost, low viscosity, and high conductivity, as well as the formation of a uniform and robust salt‐derived solid‐electrolyte interphase layer, leading to non‐dendritic K‐metal plating/stripping with Coulombic efficiency of 99.6 % and a highly reversible graphite anode.