Secondary battery and method of manufacturing secondary battery

A secondary battery comprising:

• an electrode assembly comprising a first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode;
• and
• a case to accommodate the electrode assembly, wherein the case comprises:
• a body comprising an accommodation part for accommodating the electrode assembly and an extension part extending from an open end of the accommodation part around a circumference of the open end of the accommodation part;
• a cover coupled with the extension part to seal the open end of the accommodation part, the cover and the open end of the accommodation part configured to form a flange part when coupled together;
• and
• a binding line on the flange part, the binding line comprising:
• a binding part that binds the extension part and the cover;
• and
• a venting part that is fracturable by a predetermined internal pressure of the accommodation part when sealed,
• wherein a portion of the flange part in which the venting part is disposed is more concave than a remaining portion of the flange part where the binding part is located.