LiNi0.5−x Co2x Mn1.5−x O4 (0≤2x ≤0.2) was prepared by spray drying, then re-annealing in O2. Their structural and electrochemical properties were studied by ex-situ XRD, GITT, and charge–discharge testing. The substitution of cobalt for Ni and Mn in the LiNi0.5Mn1.5O4 resulted in significant structural and electrochemical variations, such as the change in structural transformation with lithium extraction, the increase in the lithium diffusion coefficient and the decrease in the area specific impedance. Moreover, the improved kinetic properties caused by the Co substitution for Ni and Mn result in an improved cyclic performance at a high rate and at elevated temperature as well as the rate capability.