A new electrolyte based on fluorinated 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane (F-EPE) solvent is studied in LiNi0.5Mn1.5O4/Li cells. The electrochemical stability of the electrolyte with 10% F-EPE is carried out by linear sweep voltammetry and electrochemical floating test. These results indicate that the electrolyte with F-EPE has an oxidation potential of more than 5.2 V vs. Li+/Li, which is higher than that without F-EPE and enlarges the oxidative window of electrolyte. A thin and uniform SEI layer is formed on the surface of LiNi0.5Mn1.5O4 cathode by using electrolyte with F-EPE, leads to an improvement in the electrochemical performance, validated by charge-discharge tests, EIS, SEM, TEM, and XPS analysis.