SECONDARY BATTERY

The present invention relates to a secondary battery, wherein the length of a second bending portion of a safety plate covering an extension portion of a cap-up can be adjusted to prevent deformation of the safety plate and improve the sealing force of the secondary battery, even when a crimping part having a flat upper structure in which the sealing force can deteriorate due to the low compression rate of an insulating gasket is used. For example, disclosed is a secondary battery comprising: a cylindrical can; an electrode assembly which, together with an electrolyte, is accommodated in the cylindrical can; a cap assembly coupled to an upper portion of the cylindrical can; and an insulating gasket interposed between the cap assembly and the cylindrical can. The cap assembly comprises: a cap-up; and a safety plate which is installed below the cap-up and has a second bending portion that surrounds an extension portion of an edge of the cap-up and covers a portion of the upper surface of the extension portion. A second length, which is the length of the second bending portion, has any one value between 50% to 54%, inclusive, of a first length, which is the length of the extension portion.