Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery
A positive electrode active material is constituted by lithium transition metal-containing composite oxide particles having a layered rock salt type crystal structure and are composed of secondary particles each formed of an aggregation of primary particles. The secondary particles have a d50 of 3.0 to 7.0 μm, a BET specific surface area of 1.8 to 5.5 m 2 /g, a pore peak diameter of 0.01 to 0.30 μm, and a log differential pore volume [dV/d(log D)] of 0.2 to 0.6 ml/g within a range of the pore peak diameter. In each of a plurality of primary particles having a primary particle size of 0.1 to 1.0 μm, a coefficient of variation of the concentration of an additive element M is 1.5 or less.
1. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material comprising
composite oxide particles constituted by lithium transition metal-containing composite oxide particles having a composition represented by general formula (A): Li 1+u Ni x Mn y Co z M t O 2 , where −0.05≤u≤0.5, x+y+z+t=1, 0.3≤x≤0.9, 0≤y≤0.5, 0≤z≤0.5, 0≤t≤0.1, and M is one or more additive elements selected from Mg, Al, Si, Ca, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, and a layered rock salt type crystal structure, and
the lithium transition metal-containing composite oxide particle being composed of secondary particles, the secondary particles each formed of an aggregation of primary particles,
wherein the secondary particle has an aggregated section, one or more communication holes communicating with an outer periphery section of the aggregated section, and two or more space sections present inside the aggregated section and communicating with the one or more communication holes, and
wherein the secondary particles has:
a 50% cumulative diameter d50 of 3.0 μm or more and 7.0 μm or less, the 50% cumulative diameter d50 being determined from a particle size distribution measured value;
a BET specific surface area of 1.8 m 2 /g or more and 5.5 m 2 /g or less;
a pore peak diameter of 0.01 μm or more and 0.30 μm or less in a pore portion obtained by a mercury intrusion method; and
a log differential pore volume [dV/d(log D)] of 0.2 ml/g or more and 0.6 ml/g or less within a range of the pore peak diameter of 0.01 μm or more and 0.30 μm or less, and
for each of a plurality of primary particles having a primary particle size within a range of 0.1 μm or more and 1.0 μm or less among the primary particles, when a concentration of the additive element M is measured at a plurality of locations by cross-sectional STEM or TEM-EDX analysis, and a coefficient of variation of the concentration of the additive element M, which is a value obtained by dividing a standard deviation of the concentration of the additive element M by an average concentration of the additive element M, is calculated, the coefficient of variation being 1.5 or less.
2. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the 50% cumulative diameter d50 of the secondary particles is 4.0 μm or more and 6.0 μm or less.
3. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein [(d90−d10)/d50], where d10 is a 10% cumulative diameter determined from a particle size distribution measured value, and d90 is a 90% cumulative diameter determined from the particle size distribution measured value, the [(d90−d10)/d50] being an index indicating spread of a particle size distribution of the secondary particles, is 1.0 or less.
4. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a value of d90/d10 of the secondary particles, where d10 is a 10% cumulative diameter determined from a particle size distribution measured value, and d90 is a 90% cumulative diameter determined from the particle size distribution measured value, is 1.0 or more and 2.0 or less.
5. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the additive element M is at least one selected from the group consisting of Mg, Al, Si, Ti, Zr, Nb, Mo, and W.
6. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the additive element M is W.
7. A lithium ion secondary battery comprising: a positive electrode; a negative electrode; a separator; and a non-aqueous electrolyte, or a positive electrode; a negative electrode; and a solid electrolyte, wherein the positive electrode active material for a lithium ion secondary battery according to claim 1 is used as a positive electrode active material used in the positive electrode.