Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery
This positive electrode active material used in a non-aqueous electrolyte secondary battery includes a lithium transition metal composite oxide containing Al and Ni in an amount of at least 80 mol % with respect to the total number of moles of metal elements excluding Li, wherein a primary particle of the lithium transition metal composite oxide has a surface modification layer containing at least Ca on the surface thereof.
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; and
a surface modification layer formed on a surface of a primary particle of the lithium transition metal composite oxide and including at least Ca and Al, wherein:
a thickness of the surface modification layer is 0.1 nm to 5 nm,
a content of Ca in a total number of mole of metal elements excluding Li in the surface modification layer is 3.1 mol % to 6.5 mol %, as analyzed compositionally by energy dispersive X-ray spectroscopy (TEM-EDX), and
a content of Al in a total number of mole of metal elements excluding Li and Ca in the surface modification layer is 7.6 mol % to 13.3 mol %, as analyzed compositionally by energy dispersive X-ray spectroscopy (TEM-EDX).
2 . The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , 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.
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 molar ratio of Al to Ni in the surface modification layer is more than a molar ratio of Al to Ni in the main body portion, as analyzed compositionally by energy dispersive X-ray spectroscopy (TEM-EDX).
4 . The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 3 , wherein a molar ratio of Al to Ni in the surface modification layer is twice a molar ratio of Al to Ni in the main body portion, as analyzed compositionally by energy dispersive X-ray spectroscopy (TEM-EDX).
5 . The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein a content 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.
6 . The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 , wherein no peak derived from CaO is present in an X-ray diffraction pattern obtained by X-ray diffraction measurement of the lithium transition metal composite oxide including the surface modification layer.
7 . 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.