SECONDARY BATTERY

The present invention relates to a secondary battery, and the technical problem to be solved is to provide a secondary battery having the reduced thickness, having no thickness deviation by regions due to high dimensional accuracy, and being capable of improving the strength of a cell bottom portion and cell side portions (a long side portion and a short side portion) and the cooling efficiency. To this end, disclosed is a secondary battery comprising: an electrode assembly; a case in which the electrode assembly is accommodated; and a cap assembly coupled to the case for sealing the case. The case comprises a bottom portion, a long side portion bent and extending from the bottom portion, a short side portion bent and extending from the long side portion, and a side bent portion provided between the long side portion and the short side portion, wherein the side bent portion has a radius of curvature increasing as it goes farther away from the bottom portion.