A Safe Electrolyte\nEnriched with Flame-Retardant Solvents\nfor High-Voltage LiCoO<sub>2</sub>||Graphite Pouch Cells

Employing a flame-retardant solvent (FRS) in the electrolyte\nhas\nshown great potential for improving the safety of lithium-ion batteries\n(LIBs). Nevertheless, their poor compatibility with salts and commonly\nused solvents leads to the formation of a heterogeneous system, which\ndrastically limits their concentration in the electrolyte and consequently\ndeteriorates the safety performance. In this work, we employ a bridging\nsolvent diethyl carbonate to raise the solubility of a highly effective\nFRS, ethoxy pentafluorocyclotriphosphonitrile (PFPN), to a concentration\nas high as 75 vol % in the electrolyte. The target electrolyte forms\na stable N/P-rich cathode–electrolyte interface to protect\nthe electrode from oxygen evolution and transition-metal ion dissolution,\nthereby enabling the LiCoO<sub>2</sub> cathode to preserve 72% capacity\nretention over 500 cycles at 4.62 V. Moreover, this electrolyte can\neffectively delay occurrence time and improve the critical temperature\nof thermal runaway of 1 Ah LiCoO<sub>2</sub>||graphite pouch cells.\nOur work proposes a new direction for nonflammable electrolytes toward\nsafe and high-energy LIBs.