Battery

Provided is a highly safe battery. The present invention is a battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution, the positive electrode active material including a first region including cobalt, magnesium, fluorine, and oxygen, and a second region including cobalt and oxygen, the first region being closer to the surface of the positive electrode active material than the second region, the negative electrode active material contains graphite, the electrolyte contains a mixed organic solvent, and when a needle punching test is performed under conditions where the battery is in a fully charged state, the diameter of a steel needle is 3 mm, and the needle punching rate is 5 mm/sec, the battery voltage becomes higher than a second voltage Vc after falling from a first voltage Vb to the second voltage Vc. 提供一种安全性高的电池。本发明是一种包括包含正极活性物质的正极、包含负极活性物质的负极以及电解液的电池，正极活性物质包括第一区域及第二区域，第一区域包含钴、镁