LITHIUM-SULFUR SECONDARY BATTERY COMPRISING ELECTROLYTE CONTAINING BORATE-BASED LITHIUM SALT

A lithium-sulfur secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte contains a borate-based lithium salt, and the borate-based lithium salt is lithium difluoro(oxalato)borate, lithium bis(oxalate)borate, or a combination thereof. The borate-based lithium salt is contained in the electrolyte in an amount exceeding 0 ppm and less than 1,000 ppm based on the total weight of the electrolyte. The cycle performance of the lithium-sulfur secondary battery is improved because the lithium-sulfur secondary battery contains specific borate-based lithium salt in the electrolyte.