BATTERY, ELECTRONIC DEVICE, AND VEHICLE

A secondary battery with high capacity and a high level of safety is provided. The battery includes a positive electrode including a positive electrode active material and a conductive material. The positive electrode active material contains cobalt, oxygen, magnesium, and nickel. A median diameter of the positive electrode active material is greater than or equal to 1 μm and less than or equal to 12 μm. In EDX line analysis in a depth direction on a region of the positive electrode active material having a plane other than a (001) plane, a distribution of the magnesium partly overlaps with a distribution of the nickel. The conductive material adheres to part of the plane other than the (001) plane of the positive electrode active material.