The present disclosure provides a lithium secondary battery comprising a non-aqueous liquid electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a trimethylsilyl phosphate (TMSPa) additive, a positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material, a negative electrode and a separator.The non-aqueous liquid electrolyte for a lithium secondary battery of the present disclosure is capable of forming a solid SEI membrane in the negative electrode when initially charging a lithium secondary battery comprising the same, is capable of improving an output property of the lithium secondary battery, and is also capable of enhancing an output property and a capacity property after high temperature storage.