SOLID-STATE SECONDARY BATTERY

A solid-state secondary battery with high safety is provided. The solid-state secondary battery includes a first film that has a function of releasing and accumulating a lithium ion and is over a negative electrode current collector layer, a second film that has a function of transporting a lithium ion and is over the first film, a third film that has a function of releasing and accumulating a lithium ion and is over the second film, and a positive electrode current collector layer over the third film. The total thickness of the first to third films is the same before and after charging.