| CPC H01M 4/366 (2013.01) [H01M 4/485 (2013.01); H01M 4/525 (2013.01); H01M 4/582 (2013.01); H01M 10/0525 (2013.01); H01M 2004/028 (2013.01)] | 13 Claims |

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1. A positive electrode active material comprising a particle comprising oxygen, cobalt, lithium, magnesium, titanium, nickel, aluminum, and fluorine,
wherein the particle comprises a superficial portion, an inner portion, a depression, and a projection on the superficial portion,
wherein the particle comprises a region where a titanium concentration in the depression is higher than a titanium concentration in the superficial portion,
wherein the particle comprises a region where a titanium concentration in the projection is higher than the titanium concentration in the superficial portion,
wherein the particle comprises a region where a magnesium concentration in the projection is higher than a magnesium concentration in the superficial portion,
wherein the particle comprises a region where a nickel concentration in the projection is higher than a nickel concentration in the superficial portion,
wherein the particle comprises a region where a fluorine concentration in the projection in the projection is higher than a fluorine concentration in the superficial portion, and
wherein the particle comprises a region where an aluminum concentration in the superficial portion is higher than an aluminum concentration in the projection.
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