Disclosed is a battery pack which includes: 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; 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.