Patent ID: 8852797

Claim:
A lithium ion secondary battery comprising: an electrode assembly having a positive electrode plate, a negative electrode plate and a separator; a can containing the electrode assembly and an electrolyte; a cap assembly including a cap plate having a terminal through-hole, an insulation plate, a terminal plate, and an electrode terminal, the cap assembly coupled to an insulation case and the can; wherein an anti-rotation groove is on a first surface of the cap plate on a first side of the terminal through-hole and is recessed from the cap plate in a direction away from the electrode assembly, wherein the anti-rotation groove has a substantially square shape with a length corresponding to between about 10-40% of a length of the cap plate and a width corresponding to at least 40% of a width of the cap plate; wherein an insulation plate protrusion is on a second surface of the insulation plate facing the first surface and protrudes from the insulation plate in the first direction, the insulation plate protrusion coupled to the anti-rotation groove, wherein a seating groove is on the insulation plate; wherein a fixing groove is on the seating groove; wherein the terminal plate has an anti-rotation protrusion that is seated in the fixing groove in the seating groove of the insulation plate; and wherein a coupling tip spaced from the anti-rotation groove protrudes from the first surface of the cap plate on a second side of the terminal through-hole and is coupled to a coupling groove spaced from the insulation plate protrusion on the second surface of the insulation plate; and wherein at least a portion of the insulation plate protrusion and the anti-rotation protrusion of the terminal plate at least partially overlap each other in the first direction.