SECONDARY BATTERY

A secondary battery includes an electrode assembly including a wound structure of first electrode, a second electrode, and a separator disposed between the first electrode and the second electrode, the electrode assembly including a through-hole at a winding core of the wound structure, a case having an opening at one side thereof, the case accommodating the electrode assembly, a cap assembly that seals the opening of the case, and an insulating sheet between the cap assembly and the electrode assembly, the insulating sheet including a main sheet and a protrusion on the main sheet, and the protrusion being inserted into the through-hole of the electrode assembly.