A lithium ion secondary battery is provided having a cap plate, an insulation plate, and a terminal plate, each shaped to prevent the terminal plate from rotating when assembling a cap assembly. The cap plate has an anti-rotation groove formed on a lower surface thereof and the insulation plate has an insulation plate protrusion formed on an upper surface thereof. When the anti-rotation groove is coupled to the insulation plate protrusion, the terminal plate may be prevented from rotating.