Lithium ion secondary battery and system using same

A lithium ion secondary battery comprising:

• a wound electrode assembly in which a long sheet-shaped positive electrode and a long sheet-shaped negative electrode are wound using a direction orthogonal to the length direction as a winding axis such that the negative electrode is positioned on the outer side of the positive electrode;
• a third electrode that is disposed outside the wound electrode assembly and that has an Li supply source capable of supplying lithium ion;
• and
• a porous insulating film that is disposed between the wound electrode assembly and the third electrode and that is formed from a material usable as a separator in a battery,
• wherein the insulating film has a bag shape,
• the wound electrode assembly is inserted into the bag-shaped insulating film,
• the third electrode has a portion facing, across the insulating film, an outer surface of the negative electrode that constitutes the outermost circumference of the negative electrode of the wound electrode assembly, and has a portion facing, across the insulating film, a wound electrode assembly open end face that communicates with the interior of the wound electrode assembly and is an end face of the wound electrode assembly along the direction of the winding axis,
• the wound electrode assembly is formed into a flat shape that has two flat faces between two open end faces in the direction of the winding axis,
• the insulating film is disposed in a state of intimate contact with the two flat faces and faces of the third electrode that face the flat faces, and
• the third electrode is formed into a strip-shaped sheet and is positioned on the outer periphery of the wound electrode assembly so as to face the two flat faces of the wound electrode assembly and so as to face the two open end faces of the wound electrode assembly.