We report a new approach to improve the cyclic stability of lithium nickel manganese oxide (LiNi0.5Mn1.5O4) cathode, in which the cathode/electrolyte interface is modified by using prop-1-ene-1, 3-sultone (PES) as an electrolyte additive. The interfacial properties of LiNi0.5Mn1.5O4 cathode in PES-containing electrolyte have been investigated by scanning electron spectroscopy (SEM), transmission electron microscopy (TEM), thermal gravimetry (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammometry (CV), chronoamperometry (CA), and constant current charge/discharge test. It is found that the application of PES improves significantly the cyclic stability of LiNi0.5Mn1.5O4. After 400 cycles at 1C rate (1C=147mAg−1), the capacity retention of LiNi0.5Mn1.5O4 is 90% for the cell using 1.0 wt% PES, while only 49% for the cell without the additive. The characterizations from SEM, TEM, TG, XRD, and XPS confirm that the LiNi0.5Mn1.5O4/electrolyte interface is modified and a protective solid electrolyte interface film is formed on LiNi0.5Mn1.5O4 particles, which prevents LiNi0.5Mn1.5O4 from destruction and suppresses the electrolyte decomposition.