Abstract: A positive electrode active material for an all-solid-state lithium ion secondary battery, containing: a lithium-metal composite oxide particle having a niobium solid solution layer and a center other than the niobium solid solution layer; and a coating layer coating at least a part of a surface of the lithium-metal composite oxide particle and formed of a compound containing lithium and niobium, an average thickness of the coating layer is 2 nm or more and 1 ?m or less, and an average thickness of the niobium solid solution layer is 0.5 nm or more and 20 nm or less.

Abstract: A main object of the present disclosure is to provide an all solid state battery with good capacity property. The present disclosure achieves the object by providing an all solid state battery comprising a cathode layer including a composite cathode active material, an anode layer, and a solid electrolyte layer formed between the cathode layer and the anode layer, and the composite cathode active material includes a cathode active material represented by LiaNixCoyAlzNbbO2 wherein 1.0?a?1.05, x+y+z+b=1, 0.8?x?0.83, 0.13?y?0.15, 0.03?z?0.04, 0<b?0.011; and a coating layer covering at least a part of a surface of the cathode active material and including an ion conductive oxide, and at least one of the cathode layer and the solid electrolyte layer includes a sulfide solid electrolyte.