Cathode active material, process for its production, cathode and lithium ion secondary battery
To provide a cathode active material with which a lithium ion secondary battery having favorable cycle characteristics and having a high energy density even when discharged at a high voltage can be obtained; a cathode comprising the cathode active material; and a lithium ion secondary battery having the cathode. A cathode active material comprising a composite oxide (A) containing Li and at least one transition metal element selected from the group consisting of Ni, Co and Mn, and the following particles (B) and the following fluorinated carbon material (C) present on the surface of the composite oxide (A): particles (B): particles containing an oxide of at least one metal element selected from the group consisting of Ti, Sn, Si, Al, Ce, Y, Zr, Co, W, V, Nb, Ta, La and Mg; and fluorinated carbon material (C): a fluorinated carbon material in the form of particles or fibers.
1. A cathode active material comprising a composite oxide (A) containing Li and at least one transition metal element selected from the group consisting of Ni, Co and Mn, and the following particles (B) and the following fluorinated carbon material (C) present on the surface of the composite oxide (A):
particles (B): particles containing an oxide of at least one metal element selected from the group consisting of Ti, Sn, Si, Al, Ce, Y, Zr, and Co; and
fluorinated carbon material (C): a fluorinated carbon material in the form of particles or fibers,
wherein the composite oxide (A) is represented by the following formula (I):
Li a Ni x Co y Mn z Me b O 2 (I)
wherein 0.95<a<1.1, 0<x<1, 0<y<1, 0<z<1, 0<b<0.3, 0.9<x+y+z+b<1.05, and Me is at least one element selected from the group consisting of Al, Mg, Fe, Cr, Mo, Cu, Zr, Ti, W, V, and Y.
2. The cathode active material according to claim 1 , wherein the mass of the particles (B) based on the mass of the composite oxide (A) is from 0.1 to 10%.
3. The cathode active material according to claim 1 , wherein the mass of the fluorinated carbon material (C) based on the mass of the composite oxide (A) is from 0.1 to 10%.
4. The cathode active material according to claim 1 , wherein the particles (B) are particles containing an oxide of at least one metal element selected from the group consisting of Ti, Sn, Al, Ce and Y.
5. The cathode active material according to claim 1 , wherein the average particles size (2) of the following secondary particles of the particles (B) is from 2 to 100 nm, provided that the average particle size (2) is a value calculated from the surface area and the true density of the particles in accordance with the following formula:
average particle size (2)=6/(ρ Sw )
wherein ρ (unit: g/cm 3 ) is the true density of particles as measured by a fixed volume expansion method, and Sw (unit: m 2 /g) is the specific surface area of particles as calculated by a Brunauer, Emmet, Teller method using a nitrogen gas as an adsorption gas.
6. The cathode active material according to claim 1 , wherein the fluorinated carbon material (C) is a material obtained by bringing a carbon material in the form of particles or fibers into contact with fluorine (F 2 ).
7. The cathode active material according to claim 1 , wherein the fluorinated carbon material (C) is fluorinated Ketjen black or fluorinated activated carbon.
8. A cathode comprising the cathode active material as defined in claim 1 .
9. A lithium ion secondary battery having the cathode as defined in claim 8 .