Electrolyte for lithium secondary battery and lithium secondary battery comprising same

Disclosed is an electrolyte solution for a lithium secondary battery capable of improving the lifetime of a lithium secondary battery, by including a certain amount of magnesium chloride (MgCl) in the electrolyte to form a stable electrode protective layer that prevents the consumption of salts and additives in the electrolyte solution, and a lithium secondary battery comprising the same. The electrolyte solution for the lithium secondary battery comprises a first solvent comprising a heterocyclic compound containing at least one of an oxygen atom and a sulfur atom; a second solvent comprising at least one of an ether-based compound, an ester-based compound, an amide-based compound, and a carbonate-based compound; a lithium salt; magnesium chloride; and lithium nitrate.