The effect of nickel and sulfur substitution for manganese and oxygen on the structure and electrochemical properties of the LiNi0.5Mn1.5O4−x S x is examined. The LiNi0.5Mn1.5O4−x S x (x =0 and 0.05) compounds are successfully synthesized at 500 and 800°C by co-precipitation using the metal carbonate (Ni0.5Mn1.5)CO3 as a precursor. The resulting powder with sulfur doping exhibits different morphology from a Ni-only doped spinel in terms of particle size and surface texture. The LiNi0.5Mn1.5O4−x S x (x =0 and 0.05) powders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge–discharge cycling. The nickel- and sulfur-doped spinel displays excellent capacity retention and rate capability in the 3-V region, compared with Ni-only doped spinel material.