A Safe Electrolyte Enriched with Flame-Retardant Solvents for High-Voltage LiCoO2||Graphite Pouch Cells

Employing a flame-retardant solvent (FRS) in the electrolyte has shown great potential for improving the safety of lithium-ion batteries (LIBs). Nevertheless, their poor compatibility with salts and commonly used solvents leads to the formation of a heterogeneous system, which drastically limits their concentration in the electrolyte and consequently deteriorates the safety performance. In this work, we employ a bridging solvent diethyl carbonate to raise the solubility of a highly effective FRS, ethoxy pentafluorocyclotriphosphonitrile (PFPN), to a concentration as high as 75 vol % in the electrolyte. The target electrolyte forms a stable N/P-rich cathode-electrolyte interface to protect the electrode from oxygen evolution and transition-metal ion dissolution, thereby enabling the LiCoO2 cathode to preserve 72% capacity retention over 500 cycles at 4.62 V. Moreover, this electrolyte can effectively delay occurrence time and improve the critical temperature of thermal runaway of 1 Ah LiCoO2||graphite pouch cells. Our work proposes a new direction for nonflammable electrolytes toward safe and high-energy LIBs.