Secondary battery

A battery pack comprising:

• a battery case comprising a first case member and a second case member, which in combination define an enclosed space, the first case member comprising a first sealing portion, the second case member comprising a second sealing portion, wherein the first and second sealing portions adhere to each other for sealing the enclosed space and wherein the first and second sealing portions each comprise an inner resin layer;
• an electrode assembly contained in the enclosed space, the electrode assembly comprising a first electrode plate, a second electrode plate, and a separator disposed between the first and second electrode plates;
• an electrolyte contained in the enclosed space;
• and
• a pocket formed in at least one of the first and second sealing portions, wherein the pocket contains an ionic material and the pocket further comprises a recess formed in the first sealing portion, wherein the second sealing portion covers the recess of the first sealing portion, and
• wherein when the battery pack is overheated, the inner resin layer melts, and the ionic material contacts the inner resin layer and flows into the enclosed space through a channel formed between the pocket and the enclosed space, thereby contacting chemical entities contained in the enclosed space.