Secondary battery

A secondary battery comprising:

• an electrode stack formed by stacking a sheet-shaped electrode element;
• and
• an outer casing housing the electrode stack thereinside, wherein
• the outer casing includes a hollow-shaped laminated-film outer casing that covers at least both end faces and a pair of facing side faces of the electrode stack in a stacking direction, and an inner lid disposed at an opening part of the laminated-film outer casing,
• the inner lid has a protruding part extending from a peripheral portion thereof to an inside of the outer casing, and at least a portion of the electrode stack is present in an area surrounded by the protruding part,
• in the stacking direction, a maximum thickness of the inner lid is smaller than a maximum thickness of the electrode stack, and
• the peripheral portion of the inner lid and an end portion of the laminated-film outer casing are joined to each other to seal the electrode stack in the outer casing, the end portion of the laminated-film outer casing overlapping the peripheral portion of the inner lid;
• wherein the inner lid is partially exposed.