The LiNi0.5− x Mn0.5− x Co2 x O2 (0 < x ≤ 0.1) series was first prepared at 800 °C by the spray dry method. The structural and electrochemical characteristics of these compounds were also studied. The Co substitution seems to promote the formation of LiNi0.5− x Mn0.5− x Co2 x O2. In addition, the Co introduction in LiNi0.5Mn0.5O2 can not only reduce the cell polarization, but increase the reversible capacity. The LiNi0.5− x Mn0.5− x Co2 x O2 series shows an excellent cyclability and rate ability. After 50 cycles, LiNi0.425Mn0.425Co0.15O2 shows a reversible capacity of about 110mAh g−1 at the rate of 1mA cm−2 (100mA g−1) in 3–4.6V at room temperature and more than 140mAh g−1 at the rate of 2mA cm−2 (200mA g−1) at 55 °C.