Button-type secondary battery

A button-type secondary battery, comprising:

• an electrode assembly;
• a lower can in which the electrode assembly is disposed and on which a first screw thread is defined on an outer circumferential surface of the lower can;
• an upper can which is configured to cover an opening of an upper end of the lower can and on which a second screw thread corresponding to the first screw thread is defined on an inner circumferential surface of the upper can;
• and
• an insulator interposed between the upper can and the lower can to prevent the upper can and the lower can from being electrically short-circuited with each other,
• wherein an electrode tab extending from an electrode of the electrode assembly is in contact with the upper can,
• wherein the first screw thread faces a flat surface of the upper can,
• wherein the second screw thread faces a flat surface of the lower can, and
• wherein the first screw thread has an upper surface and a lower surface, and neither the upper surface nor the lower surface is perpendicular to the outer circumferential surface of the lower can.