Patent ID: 8071231

Claim:
A plate-shaped secondary battery constructed in a structure in which an electrode assembly of a cathode/separator/anode structure is mounted in a battery case, and the battery case is sealed by thermal welding, wherein the secondary battery comprises at least one one-way exhaust valve, mounted at a sealed portion, formed at the outer circumference of an electrode assembly receiving part of the battery case, for allowing internal high-pressure gas to be exhausted out of a battery cell and preventing external gas from being introduced into the battery cell, and wherein the one-way exhaust valve comprises a first film attached to the sealed portion, a porous film constructed in a structure in which the outer circumference of the porous film, excluding an upper end opening of the one-way exhaust valve, is coupled to the first film, and the upper end of the porous film is lower than that of the first film, a variable film constructed in a structure in which the outer circumference of the variable film, excluding the upper end opening of the one-way exhaust valve, is coupled to the porous film, the lower end of the variable film is coupled to the porous film at a position where the lower end of the variable film is spaced apart from the lower end of the porous film by a predetermined width, and the upper end of the variable film is higher than that of the porous film, the variable film being made of a material more flexible than that of the porous film or having a thickness less than that of the porous film, and a second film constructed in a structure in which the second film is attached to the sealed portion at the opposite side of the first film, and the outer circumference of the second film, excluding the upper end opening of the one-way exhaust valve, is coupled to the lower end of the variable film; and wherein the upper end opening of the one-way exhaust valve is closed by the sealed portion by a predetermined width.