Positive electrode active material for lithium ion secondary battery, manufacturing method thereof, and lithium ion secondary battery
A compound having a layered structure that is used for a positive electrode active material for a lithium ion secondary battery achieves both a high energy density and a high cyclability. The positive electrode active material for a lithium ion secondary battery contains a compound having a layered structure belonging to a space group R-3m, in which the compound having a layered structure is represented by a compositional formula: Li 1+a M1O 2+α wherein M1 represents a metal element or metal elements other than Li, and contains at least Ni, −0.03≤a≤0.10, and −0.1<α<0.1, a proportion of Ni in M1 is larger than 70 atom %, and a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%, and a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less.
1. A positive electrode active material for a lithium ion secondary battery, comprising:
a compound having a layered structure belonging to a space group R-3m,
wherein the compound having the layered structure is represented by a compositional formula:
Li 1+a Ni b Mn c Co d M2 e O 2+α , wherein
M2 represents a metal element other than Li, Ni, Mn, and Co, 0≤a≤0.10, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≤e<0.1, b+c+d+e=1, and −0.1<α<0.1,
a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%,
a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less, and
a content of residual lithium compound, which includes the residual amount of lithium hydroxide, in the positive electrode active material is from 0.1 mass % to 2.0 mass %.
2. The positive electrode active material for a lithium ion secondary battery according to claim 1 , further comprising:
a secondary particle formed by aggregation and bonding of a plurality of primary particles, wherein the primary particles have an average particle diameter of less than 1 μm, and the secondary particle has an average particle diameter of larger than 1 μm.
3. A manufacturing method of the positive electrode active material for a lithium ion secondary battery according to claim 1 , the method comprising:
a pulverizing and mixing step of pulverizing and mixing a raw material comprising a metal element other than Li with a lithium raw material comprising 80 mass % or more of lithium carbonate so as to make an average particle diameter of the raw material and the lithium raw material 0.3 μm or less;
a heat treatment step of heat-treating, at 650° C. or lower, a pulverized and mixed powder obtained through the pulverizing and mixing step; and
a firing step of firing, at 740° C. or higher and lower than 850° C., the heat-treated pulverized and mixed powder.
4. The manufacturing method of the positive electrode active material for a lithium ion secondary battery according to claim 3 , the method further comprising, between the pulverizing and mixing step and the heat treatment step, a granulating step of granulating the pulverized and mixed powder obtained through the pulverizing and mixing step to make aggregated particles having an average particle diameter of 1 μm or more.
5. The manufacturing method of the positive electrode active material for a lithium ion secondary battery according to claim 4 , wherein the granulating step is performed using a spray drying method.
6. A lithium ion secondary battery, comprising:
a positive electrode comprising a positive electrode active material;
a negative electrode; and
a separator,
wherein the positive electrode active material comprises a compound having a layered structure belonging to a space group R-3m,
wherein the compound having the layered structure is represented by a compositional formula:
Li 1+a Ni b Mn c Co d M2 e O 2+α , wherein
M2 represents a metal element other than Li, Ni, Mn, and Co, 0≤a≤0.10, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≤e<0.1, b+c+d+e=1, and −0.1<α<0.1,
a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%,
a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less, and
a content of residual lithium compound, which includes the residual amount of lithium hydroxide, in the positive electrode active material is from 0.1 mass % to 2.0 mass %.
7. The lithium ion secondary battery according to claim 6 , wherein the positive electrode active material further comprises:
a secondary particle formed by aggregation and bonding of a plurality of primary particles, wherein the primary particles have an average particle diameter of less than 1 μm, and the secondary particle has an average particle diameter of larger than 1 μm.
8. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the content of residual lithium hydroxide in the positive electrode active material is from 0.35 mass % to 1 mass %.
9. The lithium ion secondary battery according to claim 6 , wherein the content of residual lithium hydroxide in the positive electrode active material is from 0.35 mass % to 1 mass %.