The present invention relates to a lithium rechargeable battery having outer covers, each having a rib formed on the inner surface thereof, coupled to both sides of a core pack, which makes it possible to prevent resin from flowing into the outer covers when resin molding parting is performed on an upper part of the core pack and thus to reduce defects occurring in the outer covers due to the flow of resin. A lithium rechargeable battery according to an embodiment of the invention includes a core pack having a bare cell and a protective circuit module which is arranged on the top side of the bare cell so as to be electrically connected to the bare cell through lead plates; outer covers covering two short lateral sides of the core pack on which the lead plates are provided; and a resin molding part formed at an upper part of the core pack, the upper part of the core pack includes a portion of each of the outer covers and the protective circuit module. In the lithium rechargeable battery, ribs are formed on the inner surfaces of the outer covers to isolate gaps formed between the outer covers and the two short lateral sides of the core pack due to the lead plates from the resin molding part.