| 摘要 |
PROBLEM TO BE SOLVED: To prevent the discharge characteristic from deteriorating as a result of reduced action of active oxygen contributing to the reaction to the nonaqueous electrolyte and resultantly the reaction between positive active material and the nonaqueous electrolyte is suppressed to enable prevention of discharging characteristic drop by lowering the average valence number of a transition metal on a positive active material surface where lithium-transition metal compound oxide is used, than the average valence number of the transition metal across the entire positive active material. SOLUTION: A positive active material using lithium-transition metal compound oxide is heat treated under an environment in which a reducing gas is mixed so as to reduce the positive active material surface and such a layer is provided, that the average valence number of the transition metal on the positive active material surface part. If this layer thickness is too large, the rate of the layer of low average valence number of the transition metal grows high, lithium ion dispersion rate becomes slow so as to cause a drop in the discharge capacity in the case of discharge with high discharge current. Therefore, the layer thickness is set to be less than 15% of the particle diameter of the positive active material. Hereat, the thickness of a layer of low average valence number of the transition metal is allowed to be thin, and if such a layer is exists is the positive active material surface, its effect can be exhibited well. |
