Fluorinated Carbonate-Based Electrolyte for High-Voltage Li(Ni_0.5Mn_0.3Co_0.2)O₂/Graphite Lithium-Ion Battery

A stable electrolyte system at a charge voltage over 4.5 V is the key to successfully obtaining higher energy density by raising the charging cutoff voltage. We demonstrate a fluorinated electrolyte (1 M LiPF 6 fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) (FEC/FEMC = 1/9, v/v)) for a high-voltage LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite system. The stability of the fluorinated electrolyte for the LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) cathode was investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The charge-discharge performance of the fluorinated electrolyte was superior to the corresponding non-fluorinated electrolyte system at a charging cutoff voltage of 4.7 V.