Positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery
This positive electrode active material for nonaqueous electrolyte secondary batteries comprises a lithium-transition metal composite oxide and a surface modification layer. The lithium transition metal composite oxide contains at least Al and 80 mol % or more Ni with reference to the total number of moles of metal elements excluding Li, and the surface modification layer contains at least Sr and is formed on the surface of primary particles of the lithium-transition metal composite oxide.
1. A positive electrode active material for non-aqueous electrolyte secondary batteries, including:
a lithium transition metal composite oxide including at least 80 mol % or more of Ni to a total number of mole of metal elements excluding Li, and Al,
wherein the lithium transition metal composite oxide is represented by a formula: Li a Ni x Al y Co z M w O 2-b wherein in the formula, 0.95<a<1.05, 0.8≤x≤0.96, 0<y≤0.10, 0≤z≤0.15, 0≤w≤0.1, 0≤b<0.05, x+y+z+w=1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo and Zn; and
a surface modification layer formed on a surface of a primary particle of the lithium transition metal composite oxide and including at least Sr.
2. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein the surface modification layer further includes Al.
3. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein
the lithium transition metal composite oxide has a surface layer present on an inner side from a surface and a main body portion present on an inner side of the surface layer, and
a proportion of Al to a total number of mole of metal elements excluding Li in the surface modification layer is larger than a proportion of Al to the total number of mole of metal elements excluding Li in the main body portion.
4. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 3 , wherein a proportion of Al to a total number of mole of metal elements excluding Li in the surface layer is 1.3 times or more a proportion of Al to a total number of mole of metal elements excluding Li in the main body portion.
5. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein a proportion of Sr in the surface modification layer is 0.05 mol % to 0.25 mol % to a total number of mole of metal elements excluding Li in the surface modification layer.
6. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein a proportion of Ni to a total number of mole of metal elements excluding Li in the lithium transition metal composite oxide is 90 mol % or more.
7. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein an amount of Li remaining on a surface of the lithium transition metal composite oxide is 0.03 wt % to 0.08 wt %.
8. A non-aqueous electrolyte secondary battery, comprising:
a positive electrode including the positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 ;
a negative electrode; and
a non-aqueous electrolyte.
9. A positive electrode active material for non-aqueous electrolyte secondary batteries, including:
a lithium transition metal composite oxide including at least 80 mol % or more of Ni to a total number of mole of metal elements excluding Li, and Al; and
a surface modification layer formed on a surface of a primary particle of the lithium transition metal composite oxide and including at least Sr,
wherein Sr is not dissolved in the lithium transition metal composite oxide.
10. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 9 , wherein the lithium transition metal composite oxide is represented by a formula: Li a Ni x Al y Co z M w O 2-b wherein in the formula, 0.95<a<1.05, 0.8≤x≤0.96, 0<y≤0.10, 0≤z≤0.15, 0≤w≤0.1, 0≤b<0.05, x+y+z+w=1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo and Zn.