Enhanced performance of LiNi1/3Co1/3Mn1/3O2 cathodes at elevated temperatures using an imidazolium-based electrolyte with lithium difluoro(oxalate)borate

Abstract

Novel electrolytes containing 1,2-dimethyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide, an ionic liquid (DMEITFSI); carbonate solvents; and lithium difluoro(oxalate)borate (LiDFOB) were prepared, and the electrochemical performance in Li/LiNi1/3Co1/3Mn1/3O2 half cells was investigated. The ionic liquid electrolytes exhibited excellent physical and electrochemical properties, including high thermal stability, incombustibility and a wide electrochemical window. The addition of LiDFOB significantly improved the compatibility of the ionic liquid with Li/LiNi1/3Co1/3Mn1/3O2, which presented a discharge capacity of 138.5 mAh g-1 after 100 cycles at 1.0 C. Among the tested electrolytes, Li/LiNi1/3Co1/3Mn1/3O2 cells showed the best performance at high temperatures, delivering superior discharge capacities of 157.7 mAh g-1 after 50 cycles at a rate of 1.0 C and a temperature of 80 °C. The decomposition of LiDFOB resulted in the formation of a stable and protective film on the surface of the LiNi1/3Co1/3Mn1/3O2 cathode. Therefore, nonflammable DMEITFSI-based electrolytes are an excellent alternative for lithium-ion batteries at room and elevated temperatures.