Secondary battery

A secondary battery comprising:

• an electrode body including a positive electrode plate and a negative electrode plate;
• a battery case containing the electrode body;
• a terminal attached to the battery case;
• a conductive member having an opening adjacent to the electrode body;
• a deformation plate that seals the opening, and a current collector;
• wherein
• the positive electrode plate or the negative electrode plate is electrically connected to the terminal via the current collector, the deformation plate, and the conductive member,
• the deformation plate has a thick portion, which has a larger thickness than a surrounding area, in a central part,
• the thick portion is weld-connected to the current collector to form a weld, the deformation plate has an annular first groove on its surface adjacent to the electrode body and an annular second groove on its surface adjacent to the terminal,
• in a radial direction of the deformation plate, at least part of the first groove is located outward of the second groove,
• in the radial direction of the deformation plate, a width of the second groove is larger than a width of the first groove,
• wherein a depth of the first groove is larger than a depth of the second groove,
• and the deformation plate deforms when an internal pressure of the battery case reaches a predetermined value or higher,
• and the deformation of the deformation plate causes electrical disconnection between the positive electrode plate or the negative electrode plate and the terminal.