Disclosed is a lithium ion battery. The lithium ion battery includes a positive electrode plate, a negative electrode plate and a separator. The positive electrode plate, the separator and the negative electrode plate are stacked successively and then wound from inside to outside. The positive electrode plate includes a positive electrode current collector. At least one functional surface of the positive electrode current collector is provided with a protective layer. A surface of the protective layer away from the positive electrode current collector is provided with a positive electrode active layer. A length of the protective layer is greater than a length of the positive electrode active layer in a winding direction of the positive electrode current collector. According to the present application, by increasing a protection area of the protective layer for a positive electrode current collector, safety performance of the lithium ion battery is improved.