A novel lithium difluoro(oxalate) borate and lithium hexafluoride phosphate dual-salt electrolyte for Li-excess layered cathode material

The electrochemical properties of a Li-excess Li1.18Ni0.15Co0.15Mn0.52O2 cathode material in a lithium difluoro (oxalate) borate (LiDFOB, 20 wt%) and lithium hexafluoride phosphate (LiPF6, 80 wt%) dual-salt electrolyte are investigated. The use of a dual-salt electrolyte significantly improves the material's electrochemical performance, especially at elevated temperature. The capacity retention of the electrode increases from 24% to 92% after charging-discharging at 55 °C for 100 cycles. Spectroscopic analysis demonstrates that LiDFOB salt suppressed Mn2+ dissolution into the electrolyte and improved the electrode's electrochemical kinetic properties. In addition, the thermal safety of the fully-charged electrode is improved by the dual-salt electrolyte, which results in high onset temperature and reduces thermal release.