The present invention relates to a lithium secondary battery including a positive electrode including a positive active material, the positive active material including a nickel-containing lithium transition metal compound; a negative electrode including a negative active material; and an electrolyte including a non-aqueous organic solvent, a lithium salt, and an additive comprising a compound represented by Chemical Formula 1, wherein the content of Ni is 60 mol % or more based on 100 mol % of the total transition metals in the lithium transition metal compound.

##STR00001## wherein, in Chemical Formula 1, A is a substituted or unsubstituted aliphatic chain or (C.sub.2H.sub.4OC.sub.2H.sub.4-)n, and n is an integer from 1 to 10.

A sulfonium salt is formed of a sulfonium cation selected from a group indicated by general formulas (1), (2), and (3) and a gallate anion represented by formula (a). A photoacid generator is characterized in that said sulfonium salt is contained therein. An energy-ray curable composition contains the acid generator and a cationic polymerizable compound. A cured product is formed by curing these substances.

##STR00001##

The present invention relates to a non-aqueous electrolyte solution additive, and a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery which comprise the same, wherein, specifically, since the non-aqueous electrolyte solution, which comprises a compound capable of maintaining a passive effect by increasing an effect of forming a solid electrolyte interface (SEI) on surfaces of a positive electrode and a negative electrode, is provided, high-temperature storage characteristics and life characteristics of the lithium secondary battery may be improved.