OXIDE-BASED POSITIVE ELECTRODE ACTIVE MATERIAL FOR ALL-SOLID-STATE LITHIUM ION BATTERIES, METHOD FOR PRODUCING PRECURSOR OF OXIDE-BASED POSITIVE ELECTRODE ACTIVE MATERIAL FOR ALL-SOLID-STATE LITHIUM ION BATTERIES, METHOD FOR PRODUCING OXIDE-BASED POSITIVE ELECTRODE ACTIVE MATERIAL FOR ALL-SOLID-STATE LITHIUM ION BATTERIES, AND ALL-SOLID-STATE LITHIUM ION BATTERY

Provided is an oxide-based positive electrode active material for all-solid-state lithium ion batteries, which can obtain improved battery characteristics upon use for an all-solid-state lithium ion battery. An oxide-based positive electrode active material for all-solid-state lithium ion batteries, the oxide-based positive electrode active material having a compositional formula represented by LiaNixCoyMn1-x-yO, with 0.98 ≤ a ≤ 1.05; 0.8 ≤ x ≤ 1.0; and 0 ≤ y ≤ 0.20, wherein the oxide-based positive electrode active material has an average particle diameter D50 of from 1.0 to 5.0 µm, a tap density of from 1.6 to 2.5 g/cc, and a circularity of from 0.85 to 0.95.