Optimized Solid Electrolyte Interphase and Solvation Structure of Potassium Ions in Carbonate Electrolytes for High‐Performance Potassium Metal Batteries

Abstract The introduction of electrolyte additives is one of the most potential strategies to improve the performance of potassium metal batteries (PMBs). However, designing an additive that can alter the K + solvation shell and essentially inhibit K dendrite remains a challenge. Herein, the amyl‐triphenyl‐phosphonium bromide was introduced as an additive to build a stable solid electrolyte interphase layer. The amyl‐TPP cations can form a cation shielding layer on the metal surface during the nucleation stage, preventing K + from gathering at the tip to form K dendrites. Besides, the cations can be preferentially reduced to form K x P y with fast K + transport kinetics. The Br − anions, as Lewis bases with strong electronegativity, can not only coordinate the Lewis acid pentafluoride to inhibit the formation of HF, but also change the K + solvation structure to reduce solvent molecules in the first solvation structure. Therefore, the symmetrical battery exhibits a low deposition overpotential of 123 mV at 0.1 mA cm −2 over 4200 h cycle life. The full battery, paried with a perylene‐tetracarboxylic dianhydride (PTCDA) cathode, possesses a cycle life of 250 cycles at 2 C and 81.9% capacity retention. This work offers a reasonable electrolyte design to obtain PMBs with long‐term stablity and safety.