Nonflammable dual-salt localized high-concentration electrolyte for graphite/LiNi0.8Co0.1Mn0.1O2 lithium-ion batteries: Li+ solvation structure and interphase

Abstract

Trimethyl phosphate (TMP) is the most promising safe solvent for lithium-ion battery (LIB) electrolyte because of the nonflammability, oxidation stability and low cost, but its application is hindered by the incompatibility with the graphite anode. Herein, a nonflammable localized high-concentration electrolyte with ordinary concentration (1 mol L−1) is developed for graphite/LiNi0.8Co0.1Mn0.1O2 (Gr/NCM811) LIBs with TMP/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) binary solvents. The origin of the capacity decay is elucidated with a comprehensive investigation of the Li+ solvation structure and electrode/electrolyte interface. On this basis, a dual-salt strategy of lithium hexafluorophosphate (LiPF6)/lithium difluoro(oxalato)borate (LiDFOB) is employed, and a stable cycling of the Gr/NCM811 full cell is achieved with upper voltages of both 4.3 V and 4.6 V. The optimization of the nonflammable TMP/TTE electrolyte demonstrates that Li+ solvation structure and interphase are respectively the thermodynamic and kinetic factors for the side reactions of the electrolyte occurring at the electrode: the Li+ solvation structure determines the reduction and oxidation tolerances of the electrolyte in thermodynamics, while the interface determines the decomposition rate in kinetics.