SECONDARY BATTERY

A secondary battery including: a case defining an open area a first side, the open area being configured to accommodate an electrode assembly; a cap plate seated on and coupled to the open area of the case and having a through-hole; a terminal plate configured to include a body and an insertion portion extending through the through-hole of the cap plate; and an insulating layer between the cap plate and the body of the terminal plate, wherein the cap plate includes a central portion and a peripheral portion provided on a periphery the central portion, the peripheral portion being configured to be coupled to the first side of the case, and wherein the peripheral portion has a greater thickness than the central portion.