Positive electrode active material particle

A lithium-ion secondary battery comprising:

• a positive electrode active material particle comprises lithium cobalt oxide,
• wherein the positive electrode active material particle comprises a crystal grain boundary and a crystal grain,
• wherein the crystal grain boundary and a periphery of the crystal grain boundary comprises a region where a concentration of at least one of fluorine, magnesium, silicon, and calcium is detected beyond a level of a lower detection limit, and
• wherein an inner portion of the crystal grain comprises a region where a concentration of at least one of fluorine, magnesium, silicon, and calcium is at the level of the lower detection limit.

A lithium-ion secondary battery comprising:

• a positive electrode active material particle comprises lithium cobalt oxide,
• wherein the lithium cobalt oxide comprises a layered rock-salt crystal structure,
• wherein the positive electrode active material particle comprises a crystal grain boundary and a crystal grain,
• wherein the crystal grain boundary and a periphery of the crystal grain boundary comprises a region where a concentration of silicon is detected beyond a level of a lower detection limit,
• wherein an inner portion of the crystal grain comprises a region where a concentration of at least one of fluorine, magnesium, silicon, and calcium is at the level of the lower detection limit,
• wherein a width of the crystal grain boundary and the periphery of the crystal grain boundary is greater than or equal to 1 nm and less than or equal to 10 nm, and
• wherein the positive electrode active material particle comprises a region in which a ratio of an atomic concentration of magnesium in the crystal grain boundary and the periphery of the crystal grain boundary to an atomic concentration of cobalt in the inner portion of the crystal grain is greater than or equal to 0.01 and less than or equal to 0.5.