Gs Yuasa International Ltd.

Miki Yasutomi

Daisuke Endo

Toshiyuki Nukuda

Yoshihiro Katayama

A lithium secondary battery is produced by employing a charging method where a positive electrode upon charging has a maximum achieved potential of 4.3 V (vs. Li/Li) or lower. The lithium secondary battery contains an active material including a solid solution of a lithium transition metal composite oxide having an &#x3b1;-NaFeO-type crystal structure. The solid solution has a diffraction peak observed near 20 to 30&#xb0; in X-ray diffractometry using CuK&#x3b1; radiation for a monoclinic Li[LiMn]O-type before charge-discharge. The lithium secondary battery is charged to reach at least a region with substantially flat fluctuation of potential appearing in a positive electrode potential region exceeding 4.3 V (vs. Li/Li) and 4.8 V (vs. Li/Li) or lower. A dischargeable electric quantity in a potential region of 4.3 V (vs. Li/Li) or lower is 177 mAh/g or higher.

Method for producing active material for lithium secondary battery and method of using lithium secondary battery

The active material for a lithium secondary battery includes a solid solution of a lithium transition metal composite oxide having an &#x3b1;-NaFeOtype crystal structure, in which the composition ratio of Li, Co, Ni, and Mn contained in the solid solution satisfies LiCoNiMn(x+y&#x2266;1, 0&#x2266;y and 1&#x2212;x&#x2212;y=z); in an Li[LiMn]O(x)-LiNiMnO(y)-LiCoO(z) type ternary phase diagram, (x, y, z) is represented by values in a range present on or within a line of a heptagon (ABCDEFG) defined by the vertexes; point A(0.45, 0.55, 0), point B(0.63, 0.37, 0), point C(0.7, 0.25, 0.05), point D(0.67, 0.18, 0.15), point E(0.75, 0, 0.25), point F(0.55, 0, 0.45), and point G(0.45, 0.2, 0.35); and the intensity ratio between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is I/I&#x2267;1.56 and at the end of discharge is I/I&#x3e;1.

Active material for lithium secondary battery, lithium secondary battery, and method for producing the same

A process for producing a lithium secondary battery employs a charging method where a positive electrode upon charging has a maximum achieved potential of 4.3 V (vs. Li/Li+) or lower. The process includes charging the lithium secondary battery to reach at least a region with relatively flat fluctuation of potential appearing in a positive electrode potential region exceeding 4.3 V (vs. Li/Li) and 4.8V (vs. Li/Li) or lower. The lithium secondary battery includes an active material having a solid solution of a lithium transition metal composite oxide having an &#x3b1;-NaFeOtype crystal structure. The composition ratio of Li, Co, Ni, and Mn contained in the solid solution satisfies LiCoNiMn(x+y&#x2266;1, 0&#x2266;y and 1&#x2212;x&#x2212;y=z).

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Kyoto, Japan

Miki Yasutomi