Sodium ion secondary battery and positive electrode active material particles

Positive electrode active material particles for a sodium ion secondary battery, each positive electrode active material particle comprising an oxide particle that absorbs and releases sodium ions and a covering layer covering the oxide particle,

• wherein the oxide particle comprises an oxide A containing Ni and Mn,
• the covering layer comprises at least one material B selected from the group consisting of a ceramic and a carbonaceous material, and
• the oxide A is a sodium-containing transition metal oxide represented by formula (1):
• NaxMeO2, where elements Me are transition metal elements including at least Ni, Mn, and Ti, and x is a ratio of Na to the elements Me and is from ⅔ to 1 in a fully discharged state.

A sodium ion secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a sodium-ion-conducting nonaqueous electrolyte,

• wherein the positive electrode comprises positive electrode active material particles, a conductive additive, and a binder,
• each positive electrode active material particle comprises an oxide particle that absorbs and releases sodium ions and a covering layer covering the oxide particle,
• the oxide particle comprises an oxide A containing Ni and Mn,
• the covering layer comprises at least one material B selected from the group consisting of a ceramic and a carbonaceous material,
• the binder comprises a fluorocarbon resin, and
• the oxide A is a sodium-containing transition metal oxide represented by formula (1):
• NaxMeO2, where elements Me are transition metal elements including at least Ni, Mn, and Ti, and x is a ratio of Na to the elements Me and is from ⅔ to 1 in a fully discharged state.

A sodium ion secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a sodium-ion-conducting nonaqueous electrolyte,

• wherein the positive electrode comprises positive electrode active material particles, a conductive additive, and a binder,
• each positive electrode active material particle comprises an oxide particle that absorbs and releases sodium ions and a covering layer covering the oxide particle,
• the oxide particle comprises an oxide A containing Ni and Mn,
• the covering layer comprises at least one material B selected from the group consisting of a ceramic and a carbonaceous material,
• the binder comprises a fluorocarbon resin, and
• the ceramic is at least one material selected from the group consisting of zirconia and alumina.