Low temperature lithium manganese cobalt oxide spinels, Li_4-xMn_5-2xCo_3xO₁₂ (0 ≤ x ≤ 1), for use as cathode materials in rechargeable lithium batteries

Low temperature synthesis of the lithium-rich cubic spinel Li₄Mn₅O₁₂ with an oxidation state very close to +4 is described. The effect of doping this compound with cobalt according to the solid solution mechanism Li_4-xMn_5-2xCo_3xO₁₂ up to the solid solution limit, LiMnCoO₄, has also been explored. The evolution of the structure and electrochemistry with increasing cobalt doping is described. With increasing x there is increasing population of the tetrahedral 8a site by transition metal ions reaching 25% occupancy by Co at LiMnCoO₄ with corresponding displacement of Li to 16d sites. The optimum performance was obtained for the composition Li_3.75Mn_4.5Co_0.75O₁₂ which yields a capacity of 150 mA g^-1 at a rate of 25 mA g^-1 (equivalent to C/6) with no perceptible capacity loss, in sharp contrast to the pure Mn materials.