Electrolytic Solution for Secondary Battery and Lithium Secondary Battery Including the Same

1 . An electrolytic solution for a secondary battery, comprising:

a lithium salt;

a non-aqueous organic solvent; and

a mixture of two or more bis(sulfonyl)imide lithium salts represented by the following Chemical Formula 1 as an additive:

wherein

R 1 and R 2 are each independently fluoro or fluoro C1-C10 alkyl; and

R 1 and R 2 may be linked to each other by fluoro C2-C10 alkylene to form a ring.

2 . The electrolytic solution of claim 1 , wherein

Chemical Formula 1 is a bis(sulfonyl)imide lithium salt represented by the following Chemical Formula 2 or 3:

wherein

A is —(CR 15 R 16 ) n —;

R 11 to R 16 are each independently fluoro or perfluoro C1-C5 alkyl; and

n is an integer of 0 to 3.

3 . The electrolytic solution of claim 1 , wherein

the bis(sulfonyl)imide lithium salt represented by Chemical Formula 1 is selected from the following compounds:

4 . The electrolytic solution of claim 1 , wherein

the additive is present at a concentration of 0.1 to 0.5 M.

5 . The electrolytic solution of claim 1 , wherein

the additive is a mixture of lithium bis(fluorosulfonyl)imide and one or more compounds selected from bis(sulfonyl)imide lithium salts represented by the following Chemical Formula 4:

wherein

R 3 and R 4 are each independently perfluoro C1-C10 alkyl; and

R 3 and R 4 may be linked to each other by perfluoro C2-C10 alkylene to form a ring.

6 . The electrolytic solution of claim 5 , wherein

the bis(sulfonyl)imide lithium salt represented by Chemical Formula 4 is contained in an amount of 0.1 to 1.5 moles with respect to 1 mole of the lithium bis(fluorosulfonyl)imide.

7 . The electrolytic solution of claim 1 , further comprising a fluoro-substituted cyclic carbonate compound.

8 . The electrolytic solution of claim 7 , wherein

the fluoro-substituted cyclic carbonate compound is contained in an amount of 0.1 to 5 wt % with respect to a total weight of the electrolytic solution.

9 . The electrolytic solution of claim 1 , wherein

the lithium salt is one or two or more selected from the group consisting of LiPF 6 , LiBF 4 , LiClO 4 , LiSbF 6 , LiAsF 6 , LiN(SO 3 C 2 F 5 ) 2 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC 6 H 5 SO 3 , LiSCN, LiAlO 2 , LiAlCl 4 , LiCl, LiI, and LiB(C 2 O 4 ) 2 .

10 . The electrolytic solution of claim 9 , wherein

the lithium salt is present at a concentration of 0.3 to 1.0 M.

11 . A lithium secondary battery comprising:

a cathode comprising a nickel-cobalt-manganese-based cathode active material containing the following Chemical Formula 11, the following Chemical Formula 12, or a mixture thereof;

an anode;

a separator interposed between the cathode and the anode; and

the electrolytic solution for a secondary battery of claim 1 :

Li x (Ni a Co b Mn c )O 2    [Chemical Formula 11]

wherein 0.5<x<1.3, 0.8≤a<1.2, 0<b<1, 0<c<1, and a+b+c=1,

Li x (Ni a Co b Mn c )O 4    [Chemical Formula 12]

wherein 0.5<x<1.3, 0.8≤a<2, 0<b<2, 0<c<2, and a+b+c=2.

12 . The lithium secondary battery of claim 11 , wherein

the cathode active material is Li x (Ni a Co b Mn c )O 2 in which 0.95≤x≤1.10, 0.8≤a<0.9, and a+b+c=1.