CYLINDRICAL LITHIUM ION SECONDARY BATTERY

The present invention relates to a cylindrical lithium ion secondary battery which, when an upper end of a cylindrical can is clamped, can prevent deformation of a cap assembly so as to improve safety. For an example, a cylindrical lithium ion secondary battery is disclosed, the battery comprising: a cylindrical can; an electrode assembly received in the cylindrical can; and a cap assembly for sealing the cylindrical can, wherein: the cap assembly comprises a top plate having a notch formed thereon, a support plate disposed in close contact with a lower surface of the top plate and including a first through-hole formed through the center thereof, and a bottom plate electrically connected with the electrode assembly and connected to the lower surface of the top plate through the first through-hole; and the support plate has a strength greater than a strength of the top plate.