POSITIVE ELECTRODE ACTIVE MATERIAL, POSITIVE ELECTRODE, ALL-SOLID-STATE BATTERY, AND METHOD OF PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL

A positive electrode active material (5) comprises an active material particle (1) and a coating film (2). The coating film (2) covers at least part of a surface of the active material particle (1). The coating film (2) includes a first compound or a second compound. The first compound includes a glass network forming element. The first compound does not include phosphorus. The first compound satisfies the relationship of "0.55≤CLi/CE≤1.03". The second compound includes phosphorus and the glass network forming element. The second compound satisfies the relationship of "0.20≤CP/CE≤8.72". Each of Cu, CE, and CP represents an element concentration measured by XPS. CLi represents an element concentration of lithium. CE represents an element concentration of the glass network forming element. CP represents an element concentration of phosphorus.