The effect of doping foreign metal ions into the LiMn2O4 spinel structure on the oxygen deficiency by high-temperature firing has been investigated. The degree of the oxygen deficiency in the Mg- and/or Al-doped spinel is very small even when fired at 1000°C, and then the oxygen deficiency nearly disappeared after low temperature annealing. Mg-doped Mn-spinels (Li1.05Mn1.94−x Mg x Ca0.01O4−z , 0≤ x ≤0.15) obtained at 1000°C contained a small oxygen deficiency amount when the x-value reached 0.03 or more. The annealing at 800°C then reduced the oxygen defect content in the Mg-doped spinels. The crystallinity of the spinels is improved by doping with a small amount of Ti. The storage performance of the coin-type cell at 60°C is improved about 1.6 times using both Mg- and Ti-doping, which would be due to the oxygen stoichiometric spinels with a low solubility by firing at high temperatures and/or by Ti-doping to increase the crystallinity.