Sealed battery cell and manufacturing method thereof

A sealed battery cell comprising:

• an anti-explosion mechanism disposed between an electrode group and a top cover, the electrode group including a positive electrode and a negative electrode that are laminated together;
• wherein
• the anti-explosion mechanism comprises a diaphragm, a connection plate comprising a lower surface and an upper surface that is welded to the diaphragm, and a connection lead welded to the lower surface of the connection plate;
• the connection plate includes a thinner portion having a flat upper surface across an entirety of the thinner portion, the flat upper surface being recessed below an upper surface of adjacent portions of the connection plate, the thinner portion being thinner than portions of the connection plate immediately adjacent thereto;
• a lower surface of the thinner portion is coplanar with the lower surface of the portions of the connection plate immediately adjacent to the thinner portion, and comprises a welded portion where the connection lead is welded directly to the lower surface of the thinner portion;
• and
• a thickness ratio between the thinner portion and a thickest portion of the connection plate is from 0.5 to 0.9.