SECONDARY BATTERY

The present invention relates to a secondary battery in which a first region and a second region of an insulation sheet are made of different materials, and thus thermal conduction between an electrode assembly and a cap plate can be blocked, light reflection that may occur during welding can be prevented, and the presence of checking foreign matter can be checked through vision inspection. Disclosed in an embodiment is a secondary battery comprising: an electrode assembly having a first electrode tab and a second electrode tab; a first terminal electrically connected to the first electrode tab of the electrode assembly; an insulation sheet having a first region covering the upper side of the electrode assembly and a second region covering both long sides of the electrode assembly; a case accommodating the electrode assembly, the first terminal, and the insulating sheet; and a cap plate sealing an top opening of the case, wherein in the insulation sheet, the first region consists of three layers and the second region is capable of transmitting light.