A battery capable of improving cycle characteristics is provided. An anode active material layer is alloyed with an anode current collector at least in part of the interface with the anode current collector. The anode active material layer contains silicon and oxygen as an element. The average oxygen content in the anode active material layer is 40 atom % or less. When the average oxygen content on the current collector side is A and the average oxygen content on the surface side is B where the anode active material layer is divided into two in the thickness direction, the average oxygen content on the current collector side A is larger than the average oxygen content on the surface side B, and the difference therebetween, A-B is from 4 atom % to 30 atom %.