Cathode active material plate-like particle for lithium secondary battery
An object of the present invention is to realize more effective intercalation and deintercalation of lithium ions in a cathode active material. The preset invention provides a cathode active material plate-like particle for a lithium secondary battery, the particle having a layered rock salt structure, wherein lithium-intercalation/deintercalation-plane-oriented grains (primary crystal grains whose (003) plane is oriented so as to intersect a plate surface of the plate-like particle) are present in a dispersed state among numerous (003)-plane-oriented grains (primary crystal grains whose (003) plane is oriented in parallel with the plate surface of the plate-like particle).
1. A cathode active material plate-like particle for a lithium secondary battery, the particle being in a polycrystalline form composed of numerous primary crystal grains having a layered rock salt structure, comprising:
when t represents the thickness of the particle, d represents the size of the particle as measured in a direction orthogonal to the thickness direction which defines the thickness, and d/t represents an aspect ratio, the following relations: t≦30 μm and d/t≧2 are satisfied;
lithium-intercalation-deintercalation-plane-oriented grains, which are primary crystal grains whose (003) plane is oriented so as to intersect a plate surface of the plate-like particle, are present in a dispersed state among numerous (003)-plane-oriented grains, which are primary crystal grains whose (003) plane is oriented in parallel with the plate surface of the plate-like particle; and
the peak intensity ratio [003]/[104], which is the ratio of intensity of diffraction by the (003) plane to intensity of diffraction by the (104) plane, as obtained through X-ray diffractometry, is 10 to 100.
2. A cathode active material plate-like particle for a lithium secondary battery according to claim 1 , wherein, when the proportion of lithium-intercalation-deintercalation-plane-oriented grains at the plate surface of the plate-like particle is determined in 10 visual fields, each containing 100 to 200 primary crystal grains, by means of an electron backscatter diffractometer, the standard deviation of the thus-determined proportions is 15 or less.
3. A cathode active material plate-like particle for a lithium secondary battery according to claim 1 , wherein, when the proportion of lithium-intercalation-deintercalation-plane-oriented grains at a cross section orthogonal to the plate surface of the plate-like particle is determined in 10 visual :fields, each containing 100 to 200 primary crystal grains, by means of an electron backscatter diffractometer, the standard deviation of the thus-determined proportions is 15 or less.
4. A cathode active material plate-like particle for a lithium secondary battery according to claim 2 , wherein, when the proportion of lithium-intercalation-deintercalation-plane-oriented grains at a cross section orthogonal to the plate surface of the plate-like particle is determined in 10 visual fields, each containing 100 to 200 primary crystal grains, by means of an electron backscatter diffractometer, the standard deviation of the thus-determined proportions is 15 or less.
5. A cathode active material plate-like particle for a lithium secondary battery according to claim 1 , wherein the primary crystal grains have a grain size of t/100 or more and 5 μm or less.
6. A cathode active material plate-like particle for a lithium secondary battery according to claim 2 , wherein the primary crystal grains have a grain size of t/100 or more and 5 μm or less.
7. A cathode active material plate-like particle for a lithium secondary battery according to claim 3 , wherein the primary crystal grains have a grain size of t/100 or more and 5 μm or less.
8. A cathode active material plate-like particle for a lithium secondary battery according to claim 4 , wherein the primary crystal grains have a grain size of t/100 or more and 5 μm or less.
9. A cathode active material plate-like particle for a lithium secondary battery according to claim 1 , wherein the material has a composition represented by the following formula:
Li p (Ni x , Co y , M z )O 2
wherein M is at least one species selected from the group consisting of Al, Mn, and Mg; 0.9≦p≦1.3; 0.6<x≦0.95; 0.01<y≦0.3; 0≦z≦0.2; and x+y+z=1.
10. A cathode active material plate-like particle for a lithium secondary battery according to claim 2 , wherein the material has a composition represented by the following formula:
Li p (Ni x , Co y , M z )O 2
wherein M is at least one species selected from the group consisting of Al, Mn, and Mg; 0.9≦p≦1.3; 0.6<x≦0.95; 0.01<y≦0.3; 0≦z≦0.2; and x+y+z=1.
11. A cathode active material plate-like particle for a lithium secondary battery according to claim 3 , wherein the material has a composition represented by the following formula:
Li p (Ni x , Co y , M z )O 2
wherein M is at least one species selected from the group consisting of Al, Mn, and Mg; 0.9≦p≦1.3; 0.6<x≦0.95; 0.01<y≦0.3; 0≦z≦0.2; and x+y+z=1.
12. A cathode active material plate-like particle for a lithium secondary battery according to claim 4 , wherein the material has a composition represented by the following formula:
Li p (Ni x , Co y , M z )O 2
wherein M is at least one species selected from the group consisting of Al, Mn, and Mg; 0.9≦p≦1.3; 0.6<x≦0.95; 0.01<y≦0.3; 0≦z≦0.2; and x+y+z=1.
13. A cathode active material plate-like particle for a lithium secondary battery according to claim 10 , wherein M in the formula is Al.
14. A cathode active material plate-like particle for a lithium secondary battery according to claim 9 , wherein M in the formula is Al.