Method for producing active material for lithium secondary battery and method of using lithium secondary battery
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 α-NaFeO 2 -type crystal structure. The solid solution has a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li 1/3 Mn 2/3 ]O 2 -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.
1. A method for producing a lithium secondary battery, comprising:
producing a hydroxide precursor by coprecipitation of a compound containing Co, Ni, and Mn in a solvent, wherein a hydroxide in the hydroxide precursor is expressed by M(OH) 2 where M is a transition metal,
mixing the hydroxide precursor and a lithium compound, and calcining the mixture, thereby producing a solid solution of a lithium transition metal composite oxide,
preparing the lithium secondary battery including a positive electrode having an active material comprising the solid solution of a lithium transition metal composite oxide having an α-NaFeO 2 crystal structure, said solid solution having a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before an initial charge-discharge process, and
charging the positive electrode of the lithium secondary battery in said 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 4.3 V (vs. Li/Li + ) but lower than 4.8 V (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
the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li + ) or lower, of 177 mAh/g or higher.
2. A method for producing a lithium secondary battery according to claim 1 , wherein the charging to reach at least the region with substantially flat fluctuation of potential appearing in the positive electrode potential region exceeding 4.3 V (vs. Li/Li + ) but lower than 4.8 V (vs. Li/Li + ) to a charging electric quantity, is the initial charge-discharge process.
3. A method for producing a lithium secondary battery according to claim 1 , wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before the initial charge-discharge process has an intensity of the diffraction peak about 7% or lower relative to the diffraction peak of a (003) plane.
4. A method for producing a lithium secondary battery according to claim 3 , wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before the initial charge-discharge process has the intensity of the diffraction peak about 4 to 7% of the intensity of the diffraction peak of the (003) plane.
5. A method for producing a lithium secondary battery according to claim 1 , wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, which is I (003) /I (104) ≧1.56 before the charge-discharge process and I (003) /I (104) >1 at an end of discharge.
6. A method for producing a lithium secondary battery according to claim 1 , wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, the intensity ratio at the end of discharge relative to before the initial charge-discharge step is 70% or higher.
7. A method for producing a lithium secondary battery according to claim 1 , wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li + ) or lower, of 200 mAh/g or higher.
8. A method of using a lithium secondary battery, comprising:
producing a hydroxide precursor by coprecipitation of a compound containing Co, Ni, and Mn in a solvent, wherein a hydroxide in the hydroxide precursor is expressed by M(OH) 2 where M is a transition metal,
mixing the hydroxide precursor and a lithium compound, and calcining the mixture, thereby producing a solid solution of a lithium transition metal composite oxide,
preparing the lithium secondary battery to contain an active material including the solid solution of a lithium transition metal composite oxide having an α-NaFeO 2 crystal structure, said solid solution having a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before an initial charge-discharge process,
charging initially a positive electrode of the lithium secondary battery in the 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 4.3 V (vs. Li/Li + ) but lower than 4.8 V (vs. Li/Li + ), and
in the actual usage after the initial charge-discharge process, charging the positive electrode with a maximum achieved potential of 4.3 V (vs. Li/Li + ) or lower, and discharging the positive electrode with a minimum achievable potential of 2.0 V(vs. Li/Li + ),
wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li + ) or lower, of 177 mAh/g or higher.
9. A method of using a lithium secondary battery according to claim 8 , wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before the initial charge-discharge process has an intensity of a diffraction peak about 7% or lower relative to the diffraction peak of a (003) plane.
10. A method of using a lithium secondary battery according to claim 8 , wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li 1/3 Mn 2/3 ]O 2 before the initial charge-discharge process has an intensity of a diffraction peak about 4 to 7% of the intensity of the diffraction peak of the (003) plane.
11. A method of using a lithium secondary battery according to claim 8 , wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, which is I (003) /I (104) ≧1.56 before the initial charge-discharge process and I (003) /I (104) >1 at an end of discharge.
12. A method of using a lithium secondary battery according to claim 8 , wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, and the intensity ratio at the end of discharge relative to before the initial charge-discharge process is 70% or higher.
13. A method of using a lithium secondary battery according to claim 8 , wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li + ) or lower, of 200 mAh/g or higher.
14. A method of using a lithium secondary battery according to claim 8 , wherein the charging to reach at least the region with substantially flat fluctuation of potential appearing in the positive electrode potential region exceeding 4.3 V (vs. Li/Li + ) but lower than 4.8 V (vs. Li/Li + ) to a charging electric quantity, is the initial charge-discharge process.