Double Anion Deep Eutectic Electrolyte with Fluoroacetonitrile Cosolvent for High Performance Lithium Metal Battery

Abstract Deep eutectic electrolytes (DEE) are considered as highly safe electrolytes for developing high‐energy density lithium metal batteries (LMBs). However, these electrolytes are limited by their high reactivity with lithium metal and low ionic conductivity. Herein, a novel and structurally simple DEE‐based double anion deep eutectic electrolyte (D‐DEEF) by using lithium difluoro(oxalato)borate (LiDFOB) as an additive and fluoroacetonitrile (FAN) as cosolvent is developed. The additive can form a stable interphase in situ to inhibit electrolyte decomposition, while the FAN can reduce viscosity and improve ionic conductivity. Li||LiFePO 4 full cells have a capacity retention rate of over 85% after 500 cycles at 1C, while Li||LiCoO 2 full cells have a capacity retention rate of 87% after 260 cycles at 4.4 V. This study might provide a new technological pathway for developing high‐safety LMBs.