Nonflammable cosolvent enables methyl acetate-based electrolyte for 4.6 V-class lithium-ion batteries operating at −60 °C

The operational demands of electronic devices in extreme environments present a significant challenge for lithium-ion batteries (LIBs) to function effectively at low temperatures. To address this challenge, methyl acetate (MA) has been considered as a potential electrolyte solvent. However, MA-based electrolytes show poor compatibility with graphite anodes and high flammability, which affects battery cycle life and brings safety risks. Herein, an advanced non-flammable MA-based diluted highly concentrated electrolyte (DHCE) is designed incorporating ethoxy (pentafluoro) cyclotriphosphazene (PFPN) as a multifunctional diluent. The MA-based DHCE forms an anion-dominated solvation structure with improved thermodynamic stability. Moreover, PFPN synergizes with anions to form a protective LiF-rich solid electrolyte interphase (SEI), which effectively prevents continuous solvent decomposition. More importantly, PFPN can quench the free radical reaction and stop the spread of flames. This electrolyte enables LiNi_0.65Co_0.15Mn_0.2O₂ (NCM65)/graphite full cell to maintain 94.6 % capacity retention after 300 cycles at 1 C and −20 °C. Moreover, it allows NCM65/graphite full cell to operate at a high voltage of 4.6 V and −60 °C. This work demonstrates the importance of co-solvents for electrolyte design and provides new routes for the development of LIBs operating in harsh conditions.