Li—Ni composite oxide particles and non-aqueous electrolyte secondary battery
Provided herein are positive electrode active substance particles comprising a lithium nickelate composite oxide which have a high energy density and are excellent in repeated charge/discharge cycle characteristics when charging at a high voltage, as well as a non-aqueous electrolyte secondary battery. The positive electrode active substance particles herein can each comprise a core particle X comprising a lithium nickelate composite oxide having a layer structure which is represented by the formula: Li 1+a Ni 1-b-c CO b M c O 2 , as defined herein; and a coating compound Y comprising at least one element selected from the group consisting of Al, Mg, Zr, Ti and Si and having an average film thickness of 0.2 to 5 nm, in which a crystal phase having a layered rock salt structure and comprising Ni 2+ ions is present in the form of a layer between the core particle X and the coating compound Y.
1. Positive electrode active substance particles each comprising:
a core particle X comprising a lithium nickelate composite oxide having a layer structure which is represented by the formula:
Li 1+a Ni 1−b−c CO b M c O 2
wherein M is at least one element selected from the group consisting of Mn, Al, B, Mg, Ti, Sn, Zn and Zr; a is a number of −0.1 to 0.2; b is a number of 0.05 to 0.5; and c is a number of 0.01 to 0.4; and
a coating compound Y comprising at least one element selected from the group consisting of Al, Mg, Zr, Ti and Si, wherein the coating compound Y is in the form of a thin film having an average film thickness of 0.2 to 5 nm,
in which a crystal phase having a layered rock salt structure and comprising Ni 2+ ions is present in the form of a layer between the core particle X and the coating compound Y, wherein the ratio of the crystal phase to the core particle X is in the range of 0.1 mol % to 3.0 mol %,
wherein the ratio of Ni 2+ /Ni 3+ in the core particle X is lower than the ratio of Ni 2+ /Ni 3+ in the positive electrode active substance particles, wherein the ratio of Ni 2+ /Ni 3+ is measured by Rietveld method.
2. The positive electrode active substance particles according to claim 1 , wherein an average valence of Ni in the positive electrode active substance particles is 2.80 to 3.10.
3. The positive electrode active substance particles according to claim 1 , wherein a content of lithium hydroxide LiOH in the positive electrode active substance particles is not more than 0.50% by weight, a content of lithium carbonate Li 2 CO 3 in the positive electrode active substance particles is not more than 0.65% by weight, and a weight ratio of the content of the lithium carbonate to the content of the lithium hydroxide is not less than 0.9.
4. The positive electrode active substance particles according to claim 1 , wherein the positive electrode active substance particles have a BET specific surface area of 0.05 to 0.70 m 2 /g, a median diameter D 50 of aggregated particles of 1 to 30 μm, and a 2% powder pH value of not more than 11.6.
5. A non-aqueous electrolyte secondary battery comprising a positive electrode active substance that at least partially comprises the positive electrode active substance particles as claimed in claim 1 .
6. The positive electrode active substance particles according to claim 1 , wherein the average film thickness of the coating compound Y is 0.2 to 2.0 nm.
7. The positive electrode active substance particles according to claim 1 , having a BET specific surface area of 0.05 to 0.5 m 2 /g.
8. The positive electrode active substance particles according to claim 1 , wherein the ratio of the crystal phase to the core particle X is 0.2 mol % to 2.5 mol %.