Secondary Battery and Battery Module Including the Same

Disclosed is a secondary battery including: an electrode assembly including electrode sheets and a separator interposed between the electrode sheets; a pouch-like battery casing in which the electrode assembly is received; an electrode lead connected to the electrode assembly and protruding out from the battery casing; and a lead film covering the electrode lead and interposed between the electrode lead and the battery casing, wherein the lead film includes an outer layer covering the electrode lead and an inner layer disposed inside of the outer layer, and the inner layer includes a material having a higher air permeability as compared to the outer layer.