Lithium-deficient thin films Li1-xNi0.5Mn0.5O2 were synthesized by sol-gel method using metal lithium, manganese and nickel acetate salts and acetylacetonate salts as started materials, respectively. The microstructures and electrochemical performance of Li1-xNi0.5Mn0.5O2 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic charge–discharge measurements. Lithium-deficient was due to the formation of spinel LiNi0.5Mn1.5O4 impurities. The lithium-deficient was more seriously for SB film due to contain crystal water in the acetate salts. The raw material had great influence on the morphology of the films. The SA film had better electrochemical properties than that of SB film. The first discharge capacity was about 51 μAh/cm2-μm. After 40 cycles, 76% of its discharge capacity can be retained. The metal acetylacetonate salts without crystal water are more suitable for the preparation of LiNi0.5Mn0.5O2 film by sol-gel method.