A secondary battery comprising: an electrode assembly in which a positive electrode , a separator , 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 , 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. <EOS>