Secondary Battery

A secondary battery comprises an electrode assembly, a can, and an insulator. The electrode assembly includes a first electrode, a separator, and a second electrode alternately stacked and wound. The can has an accommodation part accommodating the electrode assembly therein, and the can comprises a first can and a second can having cylindrical shapes open in a direction facing each other. The insulator insulates an overlapping portion between the first can and the second can. The first can is electrically connected to the first electrode, and the second can is electrically connected to the second electrode. The insulator has a short-circuit induction through-part defined by a through-hole or a cutoff line, such that a short circuit occurs between the first can and the second can through the short-circuit induction through-part when it is deformed in shape as heat or a pressure is applied to contract or expand the insulator.