Positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery
This positive electrode active material for a nonaqueous electrolyte secondary battery includes a lithium transition metal composite oxide that contains at least 80 mol % of Ni with respect to the total number of moles of metal elements excluding Li. B is present at least on the surfaces of the particles of the composite oxide. When particles having a particle diameter larger than a volume-based particle diameter of 70% (D70) are defined as first particles and particles having a particle diameter smaller than a volume-based particle diameter of 30% (D30) are defined as second particles, the molar fraction of B with respect to the total number of moles of metal elements excluding Li in the second particles is higher than the molar fraction of B with respect to the total number of moles of metal elements excluding Li in the first particles.
1 . A positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material including:
a lithium-transition metal composite oxide containing 80 mol % or more of Ni based on a total number of moles of metal elements excluding Li; and
B being present on at least a particle surface of the lithium-transition metal composite oxide, wherein
B is present in the state of a boron compound containing Li and B,
the lithium-transition metal composite oxide comprises first particles and second particles,
the first particles having a particle diameter on a volumetric basis larger than a 70% particle diameter (D70), and the second particles having a particle diameter on a volumetric basis smaller than a 30% particle diameter (D30), wherein the D70 is 9 μm to 19 μm, and the D30 is 3 μm to 13 μm,
a mole fraction of B based on a total number of moles of metal elements excluding Li in the second particles is larger than a mole fraction of B based on a total number of moles of metal elements excluding Li in the first particles, and
B is contained in a boron compound containing Li on surfaces of the first particles and second particles,
a thickness of the boron compound on the surfaces of the first particles and the second particles is 10 nm to 100 nm.
2 . The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the lithium-transition metal composite oxide is a composite oxide represented by the general formula Li a Ni b Co c M1 d M2 e B f O g , wherein 0.8≤a≤1.2, b≥0.80, 0≤c≤0.15, 0.01≤d≤0.12, 0≤e≤0.05, 0.001≤f≤0.020, 1≤g≤2, b+c+d+e+f=1, M1 represents at least one or more elements selected from the group consisting of Mn and Al, and M2 represents at least one or more elements selected from the group consisting of Groups 4 to 6 elements.
3 . A non-aqueous electrolyte secondary battery, comprising:
a positive electrode including the positive electrode active material according to claim 1 ;
a negative electrode; and
a non-aqueous electrolyte.