Nonpolar Cosolvent Driving LUMO Energy Evolution of Methyl Acetate Electrolyte to Afford Lithium-Ion Batteries Operating at-60 °C

The operation of lithium-ion batteries (LIBs) at low temperatures (<-20 degrees C) is hindered by the low conductivity and high viscosity of conventional carbonate electrolytes. Methyl acetate (MA) has proven to be a competitive low-temperature electrolyte solvent with low viscosity and low freezing point, but its interfacial stability is poor and remains elusive until now. Here, it is revealed thaat the reductive stability of MA-based electrolytes is fundamentally governed by the anion-prevailed solvation structure. Based on this framework, fluorobenzene is employed in the electrolyte to promote the entry of anions into the solvation shell via dipole-dipole interactions and the generation of free MA, thus enhancing the lowest unoccupied molecular orbital energy of MA. The designed electrolyte enables LiCoO2 (LCO)/graphite cells to exhibit excellent cycling performance at -20 degrees C (90% retention after 1000 cycles at 1 C) and to remain 91% of their room-temperature capacity at a super-low temperature of -60 degrees C at 0.05 C. Thanks to the plentiful free MA, this electrolyte has a high conductivity (2.61 mS cm(-1)) at -60 degrees C and allows LCO/graphite cell to charge at -60 degrees C. This study offers the possibility of practical applications for those solvents with poor reductive stability and provides new approaches to designing advanced electrolytes for low-temperature applications.

Automated summary

This study reveals that the reductive stability of methyl acetate-based electrolytes is determined by the solvation structure dominated by anions. By using fluorobenzene, the entry of anions into the solvation shell is promoted, generating free methyl acetate and enhancing its lowest unoccupied molecular orbital energy. The designed electrolyte enables LiCoO2/graphite cells to exhibit excellent cycling performance at low temperatures, offering new approaches to designing electrolytes for low-temperature applications.