POSITIVE-ELECTRODE ACTIVE MATERIAL FOR ALL-SOLID-STATE LITHIUM ION SECONDARY BATTERIES, AND ALL-SOLID-STATE LITHIUM ION SECONDARY BATTERY

An object is to provide a positive electrode active material having a high discharge capacity in an all-solid-state lithium ion secondary battery. [0002] The positive electrode active material for an all-solid-state lithium ion secondary battery includes a lithium-transition metal composite oxide including a secondary particle including a plurality of primary particles being aggregated and includes a coating layer coating a surface of the secondary particle, the lithium-transition metal composite oxide contains lithium and nickel and optionally contains cobalt and an element M being an additive element other than lithium, nickel, cobalt, and oxygen, the coating layer contains a compound containing at least lithium and tungsten, the surface of the secondary particle is coated with tungsten at a percentage of coverage of 30% or more and 95% or less, and the percentage of coverage is represented by P (%) and calculated using XPS analysis with (Formula 1) described below. P = W / W + Ni + Co + M × 100 %