Secondary battery and assembling method thereof

Provided is a secondary battery, which can improve safety by reducing heat generated due to electric short between electrodes (111, 112) when a needle-shaped body, such as a nail, passes through the same. In order to reduce heat generated by short circuit current, the secondary battery includes a case (140) accommodating an electrode assembly (110) in its inner space; a cap plate (151) coupled to the case (140) and sealing the case (140); a collector plate (121) coupled to the electrode assembly (110); a collector terminal (122) coupled to the collector plate (121) and protruding to an upper portion of the cap plate (151); a fastening plate (155) positioned on the cap plate (151); and a terminal plate (123) formed on the fastening plate (155) and coupled to the collector terminal (122), wherein an insulating layer (156, 256, 356) is formed on at least one surface of the fastening plate (155).