1.  Field
Aspects of embodiments of the present invention relate to a rechargeable battery. 
2.  Description of the Related Art
Generally, unlike a primary battery which is not rechargeable, a rechargeable battery is capable of being charged and discharged.  A low-capacity rechargeable battery composed of a single battery cell may be used as a power source for various small portable electronic devices, e.g., cellular phones and camcorders.  A high-capacity rechargeable battery in which a plurality of battery cells are connected to each other in a pack structure may be used as a power source, such as for driving a motor of an electric vehicle or a hybrid electric vehicle. 
Rechargeable batteries may be manufactured in various shapes.  Generally, rechargeable batteries may be classified as a cylindrical-shaped battery or a prismatic-shaped battery, for example.  The rechargeable battery is formed such that an electrode assembly formed by disposing a separator as an insulator between positive and negative electrode plates, and an electrolyte are accommodated in a case.  A cap assembly having electrode terminals may then be provided on the case. 
When excess heat is generated, such as due to over-charge or when an electrolyte is decomposed, the internal pressure of a rechargeable battery may increase, resulting in fire or explosion.  Accordingly, there is a need for a rechargeable battery configured to improve safety.