CATHODE MATERIALS FOR LITHIUM SECONDARY BATTERIES

Abstract

The present invention provides a lithium secondary battery small in the volume variation caused by charge-discharge and excellent in cycle performance. The lithium secondary battery includes a cathode capable of storing and releasing lithium and an anode capable of storing and releasing lithium, the cathode including a lithium-nickel-manganese-cobalt compound oxide having a layered crystal structure and a lithium-manganese compound oxide having a layered crystal structure distributed in the lithium-nickel-manganese-cobalt compound oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a lithium secondary battery;

FIG. 2 is a chart of an X-ray diffraction measurement using the Cu Kα line;

FIG. 3 is a graph showing a relation between a diffraction intensity ratio and a volume variation rate; and

FIG. 4 is a schematic diagram showing a secondary battery system.

Claims

1. A lithium secondary battery comprising a cathode capable of storing and releasing lithium and an anode capable of storing and releasing lithium, the cathode comprising: a lithium-nickel-manganese-cobalt compound oxide having a layered crystal structure and a lithium-manganese compound oxide having a layered crystal structure distributed in the lithium-nickel-manganese-cobalt compound oxide.

2. The lithium secondary battery according to claim 1, wherein the lithium-manganese compound oxide is Li2MnO3.

3. The lithium secondary battery according to claim 1, wherein the lithium-nickel-manganese-cobalt compound oxide comprises primary particles agglomerating to form secondary particles and the lithium-manganese compound oxide is formed in the interface between the primary particles of the lithium-nickel-manganese-cobalt compound oxide.

4. The lithium secondary battery according to claim 1, wherein the lithium-manganese compound oxide is formed in the interior of the crystal of the lithium-nickel-manganese-cobalt compound oxide.

5. The lithium secondary battery according to claim 1, wherein the lithium-manganese compound oxide is an inactive material.

6. A lithium secondary battery comprising a cathode capable of storing and releasing lithium and an anode capable of storing and releasing lithium, the cathode comprising: a lithium-nickel-manganese-cobalt compound oxide having a layered crystal structure and Li2MnO3, wherein the ratio (q/p) between the (003) diffraction peak intensity (p) of the lithium-nickel-manganese-cobalt compound oxide at a diffraction angle of 2θ=18.3±1° in an X-ray diffraction measurement using the Cu Kα line and the (020) diffraction peak intensity (q) of Li2MnO3 at a diffraction angle of 2θ=21.1±1° in the X-ray diffraction measurement using the Cu Kα line falls in the range of 0.04≦q/p≦0.07.

7. The lithium secondary battery according to claim 6, wherein the lithium-nickel-manganese-cobalt compound oxide has a hexagonal crystal unit lattice, and the lattice parameter a, the lattice parameter c and the crystal lattice volume V of the hexagonal crystal, in a state of 3.0 V to 4.2 V with reference to lithium metal, fall in the ranges of 2.80 Å≦a≦2.86 Å, 14.1 Å≦c≦14.5 Å and 98.9 Å3≦V≦101.0 Å3, respectively.

8. The lithium secondary battery according to claim 1, wherein the lithium-nickel-manganese-cobalt compound oxide is represented by a composition formula LiaNixMnyCozO2 with the proviso that 0≦a≦1.2, 0.10≦x≦0.45, 0.45≦y≦0.80, 0.1≦z≦0.3, and x+y+z=1.

9. A lithium secondary battery comprising a pair of a cathode and an anode facing each other through the intermediary of a separator and a nonaqueous electrolyte, wherein the active material of the cathode is represented by the composition formula LiaNixMnyCozO2 with the proviso that 0<a≦1.2, 0.10≦x≦0.45, 0.45≦y≦0.80, 0.1≦z≦0.3, and x+y+z=1, and the active material comprises Li2MnO3.

10. The lithium secondary battery according to claim 9, wherein the output power density thereof is 2500 W/kg or more under the condition that the depth of charge thereof is 80%.

11. The lithium secondary battery according to claim 9, wherein the capacity retention rate thereof after 1000 cycles is 85% or more.

12. A lithium secondary battery comprising a cathode capable of storing and releasing lithium and an anode capable of storing and releasing lithium, the cathode comprising: a lithium-nickel-manganese-cobalt compound oxide having a layered crystal structure and a lithium-manganese compound oxide having a layered crystal structure, wherein:the cathode has the diffraction peak of the lithium-manganese compound oxide at the diffraction angle of 2θ=21.1±1° in the X-ray diffraction measurement using the Cu Kα line; andthe isolation rate of manganese in the lithium-manganese compound oxide in relation to cobalt of the lithium-nickel-manganese-cobalt compound oxide is 1% or less.

13. The lithium secondary battery according to claim 12, wherein the lithium-manganese compound oxide is Li2MnO3.