Abstract: Disclosed is a rechargeable lithium battery including a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and a gel polymer electrolyte, wherein the positive electrode includes a positive electrode active material including a lithium cobalt-based oxide; the gel polymer electrolyte includes a polymer and an electrolyte solution; the polymer has three or more functional groups but not include an ether group; the electrolyte includes a lithium salt and a solvent; and the lithium slat includes lithium difluoro(oxalato)borate and LiBF4.

Abstract: The present invention relates to: a cross-linking agent for a quasi-solid electrolyte, the agent being a polyester derivative comprising boron at the center thereof; a quasi-solid electrolyte using the cross-linking agent for a quasi-solid electrolyte; and a secondary battery using same.