Fluorinated High-Voltage Electrolyte: Synergetic Effect of Solvents and Additives

High-voltage electrolytes (HVEs) for Li-ion battery refer to the electrolytes that are intrinsically stable towards oxidative decomposition on the cathode at high charging potential. To develop HVEs that are compatible with 5 V spinel LiNi_0.5Mn_1.5O₄ (LNMO), we focus on incorporating fluorinated solvents in the electrolyte formulation. In the meantime, we also take into account the stability of such electrolytes on the anode. A combination of cathode-compatible fluorinated solvents with anode-protecting additives is envisaged to be a promising solution for a successful HVE.

A new HVE containing fluorinated carbonates was evaluated against LNMO cathode and showed excellent oxidative stability. Several additives were found to form solid-electrolyte interphase (SEI) layers that effectively prevented significant decomposition of the HVE on the graphite anode. Cell performance was evaluated at both ambient and elevated temperatures. The fluorinated HVE exhibited much improved performance compared with conventional non-fluorinated carbonate-based electrolyte especially at high temperature. Cycling results and electrochemical impedance spectroscopy (EIS) data clearly demonstrated the synergetic effect of the fluorinated solvents and the SEI forming additives.