A secondary battery comprising: an electrode assembly in which a positive electrode, a separator (124, 125), and a negative electrode are alternately combined to be stacked; and a pouch accommodating the electrode assembly and an electrolyte solution therein, wherein the separator comprises: a first separator disposed between the positive electrode and the negative electrode and having a through-hole penetrated in a direction facing the positive electrode and the negative electrode; and a second separator covering the through-hole of the first separator and having an end connected to the pouch, the first separator is fixed to the positive electrode or the negative electrode, which face each other, and the second separator is slidably provided without being bonded to the positive electrode or the negative electrode, which face each other, wherein the end of the second separator is fixed to an inner surface of the pouch, and when the pouch is expanded due to the generation of the internal gas, the second separator moves in a lateral direction with respect to a direction in which the positive electrode, the separator, and the negative electrode are stacked so as to open the through-hole of the first separator so that a power supply is interrupted by the internal short circuit to interrupt the overcharging. an electrode assembly in which a positive electrode, a separator (124, 125), and a negative electrode are alternately combined to be stacked; and a pouch accommodating the electrode assembly and an electrolyte solution therein, wherein the separator comprises: a first separator disposed between the positive electrode and the negative electrode and having a through-hole penetrated in a direction facing the positive electrode and the negative electrode; and a second separator covering the through-hole of the first separator and having an end connected to the pouch, the first separator is fixed to the positive electrode or the negative electrode, which face each other, and the second separator is slidably provided without being bonded to the positive electrode or the negative electrode, which face each other, wherein the end of the second separator is fixed to an inner surface of the pouch, and when the pouch is expanded due to the generation of the internal gas, the second separator moves in a lateral direction with respect to a direction in which the positive electrode, the separator, and the negative electrode are stacked so as to open the through-hole of the first separator so that a power supply is interrupted by the internal short circuit to interrupt the overcharging. a first separator disposed between the positive electrode and the negative electrode and having a through-hole penetrated in a direction facing the positive electrode and the negative electrode; and a second separator covering the through-hole of the first separator and having an end connected to the pouch, the first separator is fixed to the positive electrode or the negative electrode, which face each other, and the second separator is slidably provided without being bonded to the positive electrode or the negative electrode, which face each other, wherein the end of the second separator is fixed to an inner surface of the pouch, and when the pouch is expanded due to the generation of the internal gas, the second separator moves in a lateral direction with respect to a direction in which the positive electrode, the separator, and the negative electrode are stacked so as to open the through-hole of the first separator so that a power supply is interrupted by the internal short circuit to interrupt the overcharging.