Positive electrode active material, method for manufacturing positive electrode active material, and secondary battery
A positive electrode active material having high capacity and excellent cycle performance is provided. The positive electrode active material has a small difference in a crystal structure between the charged state and the discharged state. For example, the crystal structure and volume of the positive electrode active material, which has a layered rock-salt crystal structure in the discharged state and a pseudo-spinel crystal structure in the charged state at a high voltage of approximately 4.6 V, are less likely to be changed by charge and discharge as compared with those of a known positive electrode active material.
1. A lithium ion secondary battery comprising:
a positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide which comprises magnesium and aluminum,
wherein:
a magnesium concentration in a surface portion of the positive electrode active material is higher than a magnesium concentration in an inner portion of the positive electrode active material;
the positive electrode active material has an O3 crystal structure when a charge depth of the positive electrode active material is 0.06 or less; and
a X-ray diffraction pattern of the positive electrode active material has at least a first diffraction peak at 2θ of 19.30±0.20° and a second diffraction peak at 2θ of 45.55±0.10° when the positive electrode is analyzed by powder X-ray diffraction by using CuKα1 ray, when a charge depth of the positive electrode active material is 0.8 or greater.
2. The lithium ion secondary battery according to claim 1 , wherein the lithium cobalt oxide further comprises fluorine.
3. The lithium ion secondary battery according to claim 1 , wherein in an EDX linear analysis of the positive electrode active material, a concentration peak of aluminum is located in a deeper region than a concentration peak of magnesium.
4. The lithium ion secondary battery according to claim 1 , in a crystal structure of the positive electrode active material, coordinate of cobalt is represented by (0, 0, 0.5) and coordinate of oxygen is represented by (0, 0, x), where x is defined as 0.20≤x≤0.25, when the positive electrode is analyzed by powder X-ray diffraction when a charge depth of the positive electrode active material is 0.8 or greater.
5. The lithium ion secondary battery according to claim 1 , wherein the surface portion of the positive electrode active material is a region from a surface of the positive electrode active material to a depth of approximately 10 nm.
6. The lithium ion secondary battery according to claim 1 , wherein a charge depth when all lithium ions that can be inserted into and extracted from a positive electrode active material are inserted is 0, and a charge depth when all lithium ions that can be inserted into and extracted from a positive electrode active material are extracted is 1.
7. The lithium ion secondary battery according to claim 1 ,
wherein the charge depth of 0.06 or less is a state where a battery comprising the positive electrode and a counter electrode of lithium is discharged until a voltage decreases to 3 V or lower, and
wherein the charge depth of 0.8 or greater is a state where a battery comprising the positive electrode and the counter electrode of lithium is charged until a voltage becomes 4.6 V or higher.
8. The lithium ion secondary battery according to claim 1 ,
wherein the charge depth of 0.8 or greater is a state where a battery comprising the positive electrode and a counter electrode of lithium is charged to greater than or equal to 219.2 mAh/g.
9. A lithium ion secondary battery comprising:
a positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide which comprises magnesium and aluminum,
wherein:
a magnesium concentration in a surface portion of the positive electrode active material is higher than a magnesium concentration in an inner portion of the positive electrode active material; and
a X-ray diffraction pattern of the positive electrode active material has at least a first diffraction peak at 2θ of 19.30±0.20° and a second diffraction peak at 2θ of 45.55±0.10° when the positive electrode is analyzed by powder X-ray diffraction by using CuKα1 ray, when a battery comprising the positive electrode and a counter electrode of lithium is charged at 4.6V.
10. The lithium ion secondary battery according to claim 9 , wherein the lithium cobalt oxide further comprises fluorine.
11. The lithium ion secondary battery according to claim 9 , wherein in an EDX linear analysis of the positive electrode active material, a concentration peak of aluminum is located in a deeper region than a concentration peak of magnesium.
12. The lithium ion secondary battery according to claim 9 , in a crystal structure of the positive electrode active material, coordinate of cobalt is represented by (0, 0, 0.5) and coordinate of oxygen is represented by (0, 0, x), where x is defined as 0.20≤x≤0.25, when the positive electrode is analyzed by powder X-ray diffraction when the battery with the positive electrode and the counter electrode of lithium is charged at 4.6V.
13. The lithium ion secondary battery according to claim 9 , wherein the surface portion of the positive electrode active material is a region from a surface of the positive electrode active material to a depth of approximately 10 nm.
14. The lithium ion secondary battery according to claim 9 ,
wherein the battery with the positive electrode and the counter electrode of lithium is charged by CCCV charge.
15. The lithium ion secondary battery according to claim 9 ,
wherein a unit cell volume of a crystal structure of the positive electrode active material is 94.39 Å 3 or greater when the battery comprising the positive electrode and the counter electrode of lithium is charged at 4.6V.
16. A lithium ion secondary battery comprising:
a positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide which comprises magnesium and aluminum,
wherein:
in an EDX linear analysis of the positive electrode active material, a concentration peak of aluminum is located in a deeper region than a concentration peak of magnesium,
the positive electrode active material has an O3 crystal structure when a charge depth of the positive electrode active material is 0.06 or less; and
a X-ray diffraction pattern of the positive electrode active material has at least a first diffraction peak at 2θ of 19.30±0.20° and a second diffraction peak at 2θ of 45.55±0.10° when the positive electrode is analyzed by powder X-ray diffraction by using CuKα1 ray, when a charge depth of the positive electrode active material is 0.8 or greater.
17. The lithium ion secondary battery according to claim 16 , wherein the lithium cobalt oxide further comprises fluorine.
18. The lithium ion secondary battery according to claim 16 ,
wherein the positive electrode active material comprises a first region comprising a crystal grain boundary and a second region not comprising a crystal grain boundary, and
wherein a concentration of magnesium in the crystal grain boundary or its vicinity in the first region is higher than a concentration of magnesium in the second region.
19. The lithium ion secondary battery according to claim 16 , in a crystal structure of the positive electrode active material, coordinate of cobalt is represented by (0, 0, 0.5) and coordinate of oxygen is represented by (0, 0, x), where x is defined as 0.20≤x≤0.25, when the positive electrode is analyzed by powder X-ray diffraction when a charge depth of the positive electrode active material is 0.8 or greater.
20. The lithium ion secondary battery according to claim 16 , wherein a charge depth when all lithium ions that can be inserted into and extracted from a positive electrode active material are inserted is 0, and a charge depth when all lithium ions that can be inserted into and extracted from a positive electrode active material are extracted is 1.
21. The lithium ion secondary battery according to claim 16 ,
wherein the charge depth of 0.06 or less is a state where a battery comprising the positive electrode and a counter electrode of lithium is discharged until a voltage decreases to 3 V or lower, and
wherein the charge depth of 0.8 or greater is a state where a battery comprising the positive electrode and the counter electrode of lithium is charged until a voltage becomes 4.6 V or higher.
22. The lithium ion secondary battery according to claim 16 ,
wherein the charge depth of 0.8 or greater is a state where a battery comprising the positive electrode and a counter electrode of lithium is charged to greater than or equal to 219.2 mAh/g.
23. The lithium ion secondary battery according to claim 16 ,
wherein the positive electrode comprises conductive additive, and
wherein the conductive additive includes carbon nanotube or graphene.
24. A lithium ion secondary battery comprising:
a positive electrode comprising a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide which comprises magnesium and aluminum,
in an EDX linear analysis of the positive electrode active material, a concentration peak of aluminum is located in a deeper region than a concentration peak of magnesium,
wherein a X-ray diffraction pattern of the positive electrode active material has at least a first diffraction peak at 2θ of 19.30±0.20° and a second diffraction peak at 2θ of 45.55±0.10° when the positive electrode is analyzed by powder X-ray diffraction by using CuKα1 ray, when a battery comprising the positive electrode and a counter electrode of lithium is charged at 4.6V.
25. The lithium ion secondary battery according to claim 24 , wherein the lithium cobalt oxide further comprises fluorine.
26. The lithium ion secondary battery according to claim 24 ,
wherein the positive electrode active material comprises a first region comprising a crystal grain boundary and a second region not comprising a crystal grain boundary, and
wherein a concentration of magnesium in the crystal grain boundary or its vicinity in the first region is higher than a concentration of magnesium in the second region.
27. The lithium ion secondary battery according to claim 24 , in a crystal structure of the positive electrode active material, coordinate of cobalt is represented by (0, 0, 0.5) and coordinate of oxygen is represented by (0, 0, x), where x is defined as 0.20≤x≤0.25, when the positive electrode is analyzed by powder X-ray diffraction when the battery with the positive electrode and the counter electrode of lithium is charged at 4.6V.
28. The lithium ion secondary battery according to claim 24 ,
wherein the battery with the positive electrode and the counter electrode of lithium is charged by CCCV charge.
29. The lithium ion secondary battery according to claim 24 ,
wherein the positive electrode comprises conductive additive, and
wherein the conductive additive includes carbon nanotube or graphene.
30. The lithium ion secondary battery according to claim 24 ,
wherein a unit cell volume of a crystal structure of the positive electrode active material is 94.39 Å 3 or greater when the battery comprising the positive electrode and the counter electrode of lithium is charged at 4.6V.