Water-resistant LiNi0.5Mn1.5O2 spinel cathode was prepared by surface coating with carbon, Al2O3 and Nb2O5 to use a water-based hybrid polymer (TRD202A, JSR, Japan) as a binder and to form the cathode film on an Al current collector. The surface composition and degree of the surface coverage of carbon, Al2O3 and Nb2O5 were characterized with field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The coated LiNi0.5Mn1.5O2 particles not only exhibited water-resistant property but also showed no decrease in discharge capacity and only a small degradation of discharge rate performance. In addition, the coated LiNi0.5Mn1.5O2 particles, that were exposed to water-based binder solution for one week, exhibited the same charge/discharge cycle performance as observed for the cathode of the pristine LiNi0.5Mn1.5O4 particles, suggesting that the coated particles are promising as cathode materials with a water-resistant property and therefore water can be used as solvent for preparing the cathode slurry solution in the place of e.g., carcinogenic N-methyl-2-pyrrolidone which is used actually.