Mixed Lithium Salts Electrolyte Improves the High-Temperature Performance of Nickel-Rich Based Lithium-Ion Batteries

The long-term cycle performance of NCM811/Li batteries at high temperature was achieved by mixing LiDFOB and LiPF6 salts into the ethylene carbonate (EC) and ethyl methyl carbonate (EMC) solution (EC/EMC = 3:7 by volume). The differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) tests indicate 0.8 M LiPF6/0.2 M LiDFOB electrolyte system could improve thermal stability. The NCM811 cell with the mixed lithium salts electrolyte shows superior high temperature cycling performance, as demonstrated by the high capacity retention (89.00%) after 100 cycles at 0.5 C, which is much better than that of the 1.0 M LiPF6 electrolyte (51.34%). Inductively coupled plasma (ICP), Scanning electron microscopy (SEM) and other spectroscopic analyses reveal that adding LiDFOB salt could suppress Ni/Co/Mn dissolution into the electrolyte, due to the LiDFOB salt can be decomposed to produce a protective CEI layer on NCM811 surface. These results show that mixed lithium salts (LiDFOB and LiPF6) is an efficient solution to enhance the high temperature performance of nickel-rich based lithium-ion batteries.