Synergistic Effect of Fluorinated Solvents for Improving High Voltage Performance of LiNi0.5Mn1.5O4 Cathode

A "dual-fluorinated" electrolyte consisting of fluoroethylene carbonate (FEC), 1H,1H,5H-Perfluoropentyl-1,1,2,2-tetrafluoroethylether (F-EAE) was investigated for 5V-class LiNi0.5Mn1.5O4 (LNMO)-based batteries. It is found that the synergistic effect of two fluorinated solvents brings about high oxidation durability of exceeding 5 V (vs Li+/Li), and then excellent cycle performance with the capacity retention of ∼92% after 200 cycles at the cutoff voltage of 5 V, far beyond conventional carbonate-based electrolyte and another "mono-fluorinated" electrolyte merely with F-EAE. The SEM, TEM and XPS test reveal that a uniform and F/P-contained surface film exists in the cycled LNMO cathode in the "dual-fluorinated" electrolyte, possibly derived from the interactivity of two fluorinated solvents under the high voltage environment. It is further stressed that that the suitable interface modification on the cathode is another important factor for the long-term and stable cycling at 5 V operation besides the oxidation-resistivity of the electrolyte self.