A cap assembly for a secondary battery , comprising: a cap plate comprising a main portion and a convex portion , wherein the main portion comprises a first surface and a second surface that are disposed opposite to each other in a thickness direction of the main portion and an electrode lead-out hole passing through the first surface and the second surface ; an electrode terminal connecting to the main portion and covering the electrode lead-out hole , wherein the electrode terminal comprises an extension portion that extends beyond a hole wall of the electrode lead-out hole in a radial direction of the electrode lead-out hole , the extension portion extends in a circumferential direction of the electrode lead-out hole to form a ring structure, and the extension portion is arranged on a side of the first surface away from the second surface ; a fixing component , wherein the electrode terminal is connected to the cap plate through the fixing component ; and a sealing ring which is at least partially disposed between the extension portion and the main portion to seal the electrode lead-out hole , wherein the convex portion is disposed on the second surface and around the electrode lead-out hole , a top surface of the convex portion extends out of the second surface , and the convex portion has a thickness of 0.01 mm to 2 mm, the thickness of the convex portion refers to a maximum vertical distance at which the convex portion protrudes from the second surface in the thickness direction; the fixing component is welded to the cap plate and forms a welding zone , and along the radial direction, the convex portion exceeds the welding zone or the convex portion is flush with an outermost boundary of the welding zone . a cap plate comprising a main portion and a convex portion , wherein the main portion comprises a first surface and a second surface that are disposed opposite to each other in a thickness direction of the main portion and an electrode lead-out hole passing through the first surface and the second surface ; an electrode terminal connecting to the main portion and covering the electrode lead-out hole , wherein the electrode terminal comprises an extension portion that extends beyond a hole wall of the electrode lead-out hole in a radial direction of the electrode lead-out hole , the extension portion extends in a circumferential direction of the electrode lead-out hole to form a ring structure, and the extension portion is arranged on a side of the first surface away from the second surface ; a fixing component , wherein the electrode terminal is connected to the cap plate through the fixing component ; and a sealing ring which is at least partially disposed between the extension portion and the main portion to seal the electrode lead-out hole , wherein the convex portion is disposed on the second surface and around the electrode lead-out hole , a top surface of the convex portion extends out of the second surface , and the convex portion has a thickness of 0.01 mm to 2 mm, the thickness of the convex portion refers to a maximum vertical distance at which the convex portion protrudes from the second surface in the thickness direction; the fixing component is welded to the cap plate and forms a welding zone , and along the radial direction, the convex portion exceeds the welding zone or the convex portion is flush with an outermost boundary of the welding zone . <EOS>