Battery system

A battery system comprising a controller and a solid-state lithium secondary battery comprising a cathode, an anode and a solid electrolyte layer disposed between the cathode and the anode,

• wherein the cathode comprises a cathode layer;
• wherein the cathode layer comprises a cathode active material;
• wherein the anode comprises a facing part and a non-facing part;
• the facing part is a region facing the cathode;
• and the non-facing part is a region non-facing the cathode;
• wherein the controller estimates an end part cathode potential Ve2 from a voltage relaxation amount ΔV2;
• the end part cathode potential Ve2 is a local potential of an end part of the cathode;
• and the voltage relaxation amount ΔV2 is generated by diffusion of, into the non-facing part of the anode, lithium transferred to the facing part of the anode from the cathode of the solid-state lithium secondary battery in a charged state;
• and
• wherein the controller controls execution and inexecution of charging of the solid-state lithium secondary battery so that the end part cathode potential Ve2 is equal to or less than a potential Vlimit at which a change in crystal structure of the cathode active material occurs.