Process for producing lithium secondary battery

1. A process for producing a lithium secondary battery, comprising:

preparing the lithium secondary battery including a positive electrode having an active material comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO 2 crystal structure;

wherein a composition ratio of Li, Co, Ni, and Mn contained in the solid solution satisfies Li 1+(1/3)x Co 1−x−y Ni (1//2)y Mn (2//3)x+(1/2)y wherein x+y≦1, 0≦y and 1−x−y=z;

in an Li[Li 1/3 Mn 2/3 ]O 2 (x)-LiNi 1/2 Mn 1/2 O 2 (y)-LiCoO 2 (z) ternary phase diagram, the active material is used where (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

an intensity ratio between diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is 2.25≧l (003) /l (104) ≧1.56, and

charging the positive electrode of the lithium secondary battery in an initial charge-discharge process after preparing the lithium secondary battery and before an actual usage, the positive electrode of the lithium secondary battery being charged in said initial charge-discharge process to reach at least a region with relatively flat fluctuation of potential appearing relative to a charging electric amount in a positive electrode potential region, and exceeding 4.3V (vs. Li/Li + ) but lower than 4.8V (vs. Li/Li + ) or lower,

wherein in charging the battery in the actual usage after said initial charge-discharge process, the positive electrode of the lithium secondary battery is always charged at a maximum achieved potential of 4.3V (vs. Li/Li + ) or lower.

2. The process for producing a lithium secondary battery according to claim 1 , wherein the lithium secondary battery has a dischargeable electric quantity of 177 mAh/g or higher in a potential region of 4.3V (vs. Li/Li + ) or lower.

3. The process for producing a lithium secondary battery according to claim 1 , wherein the active material, (x, y, z) is represented by values in a range present on or within a line of a tetragon (HIJK) defined by the vertexes; point H(0.6, 0.4, 0), point I (0.67, 0.13, 0.2), point J (0.7, 0, 0.3), and point K (0.55, 0.05, 0.4).

4. The process for producing a lithium secondary battery according to claim 3 , wherein the lithium secondary battery has a dischargeable electric quantity of 200 mAh/g or higher in a potential region of 4.3V (vs. Li/Li + ) or lower.

5. The process for producing a lithium secondary battery according to claim 1 , wherein the solid solution of the lithium transition metal composite oxide has a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before charge-discharge, and intensity of the diffraction peak is about 4 to 7% of intensity of the diffraction peak of (003) plane.

6. The process for producing a lithium secondary battery according to claim 1 , wherein in the solid solution of the lithium transition metal composite oxide, an intensity ratio between diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is I (003) /I (104) ≧1.56 and at the end of discharge it is I (003) /I (104) >1.

7. The process for producing a lithium secondary battery according to claim 1 , wherein the solid solution of the lithium transition metal composite oxide has valances of respective metal elements as Li + , Co 3+ , Ni 2+ , and Mn 4+ .

8. The process for producing a lithium secondary battery according to claim 1 , further comprising preparing the solid solution of the lithium transition metal composite oxide by a coprecipitation method.

9. The process for producing a lithium secondary battery according to claim 8 , wherein the process of preparing the solid solution of the lithium transition metal composite oxide, comprises:

coprecipitating a Co compound, a Mn compound, and a Ni compound in a solution to make a precursor; and

mixing and calcining the precursor and a Li compound.

10. A process for producing a lithium secondary battery, comprising:

preparing the lithium secondary battery including a positive electrode formed of an active material comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO 2 crystal structure;

wherein a composition ratio of Li, Co, Ni, and Mn contained in the solid solution satisfies Li 1+(1/3)x Co 1−x−y Ni (1//2)y Mn (2//3)x+(1/2)y wherein x+y≦1, 0≦y and 1−x−y=z; and

in an Li[Li 1/3 Mn 2/3 ]O 2 (x)-LiNi 1/2 Mn 1/2 O 2 (y)-LiCoO 2 (z) ternary phase diagram, the active material is used where (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 an intensity ratio between diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is 2.25≧l (003) /l (104) ≧1.56, and

charging the positive electrode of the lithium secondary battery in an initial charge-discharge process after preparing the lithium secondary battery and before an actual usage, the positive electrode of the lithium secondary battery being charged in said initial charge-discharge process to reach at least a region with relatively flat fluctuation of potential appearing relative to a charging electric amount in a positive electrode potential region, and exceeding 4.3V (vs. Li/Li + ) but lower than 4.8V (vs. Li/Li+),

wherein in charging the battery in the actual usage after said initial charge-discharge process, the positive electrode of the lithium secondary battery is always charged at a maximum achieved potential of 4.3V (vs. Li/Li + ) or lower, and a discharge capacity of the battery in charging the battery at said maximum achieved potential of 4.3V or lower is 177 mAh/g or higher.