Positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery
A positive electrode active material for nonaqueous electrolyte secondary batteries contains a lithium transition metal composite oxide that contains not less than 80% by mole of Ni relative to the total number of moles of metal elements other than Li; and Ti is present at least in the surfaces of particles of the composite oxide. With respect to this positive electrode active material, if particles having a volume-based particle diameter more than the 70% particle diameter (D70) are taken as first particles and particles having a volume-based particle diameter less than the 30% particle diameter (D30) are taken as second particles, the molar fraction (A2) of Ti relative to the total number of moles of metal elements in the surfaces of the second particles is higher than the molar fraction (A1) of Ti relative to the total number of moles of metal elements in the surfaces of 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
Ti being present on at least a particle surface of the composite oxide, wherein
when particles having a particle diameter on a volumetric basis larger than a 70% particle diameter (D70) are defined as first particles, and particles having a particle diameter on a volumetric basis smaller than a 30% particle diameter (D30) are defined as second particles,
a mole fraction of Ti based on a total number of moles of metal elements excluding Li on surfaces of the second particles is larger than a mole fraction of Ti based on a total number of moles of metal elements excluding Li on surfaces of the first particles, wherein the lithium-transition metal composite oxide is a composite oxide represented by the general formula Li a Ni b Co c Mn d Ti e O f , wherein 0.8≤a≤1.2, b≥0.82, c≤0.12, 0.03≤d≤0.12, 0.01≤e≤0.05, and 1≤f≤2, and may further contain at least one metal element selected from Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si.
2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the Ti is present in a state of lithium titanate on the particle surface of the lithium-transition metal composite oxide.
3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein a ratio (A2/A1) of the mole fraction of Ti on the surfaces of the second particles (A2) to the mole fraction of Ti on the surfaces of the first particles (A1), is 1.20 or more.
4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the second particles have a larger ratio than the first particles, of the mole fraction of Ti present on the particle surface to a mole fraction of Ti in an entirety of particles.
5. 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.