Lithium secondary battery including non-aqueous electrolyte solution

1. A lithium secondary battery comprising:

a non-aqueous electrolyte solution including lithium bis(fluorosulfonyl)imide (LiFSI), a lithium salt excluding the lithium bis(fluorosulfonyl)imide, and 2,3-difluorobiphenyl;

a positive electrode including a positive electrode active material consisting of a lithium-nickel-manganese-cobalt-based oxide represented by Formula 1:

Li 1+x (Ni a Co b Mn c )O 2   Formula 1]

wherein, in Formula 1, 0.55≤a≤0.65, 0.18≤b≤0.22, 0.18≤c≤0.22, −0.2≤x≤0.2, and x+a+b+c=1;

a negative electrode; and

a separator, and

wherein the lithium bis(fluorosulfonyl)imide has a concentration of 0.01 mol/L to 2 mol/L in the non-aqueous electrolyte solution, and

the 2,3-difluorobiphenyl is included in an amount ranging from 3 wt % to 5 wt % based on a total weight of the non-aqueous electrolyte solution.

2. The lithium secondary battery of claim 1 , wherein a mixing ratio of the lithium salt and the lithium bis(fluorosulfonyl)imide is in a range of 1:0.01 to 1:1 as a molar ratio.

3. The lithium secondary battery of claim 1 , wherein the lithium salt excluding the lithium bis (fluorosulfonyl)imide comprises one selected from the group consisting of LiPF 6 , LiAsF 6 , LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiBF 6 , LiSbF 6 , LiN(C 2 F 5 SO 2 ) 2 , LiAlO 4 , LiAlCl 4 , LiSO 3 CF 3 , and LiClO 4 , or a mixture of two or more thereof.

4. The lithium secondary battery of claim 1 , wherein the non-aqueous electrolyte solution contains a non-aqueous organic solvent, wherein the non-aqueous organic solvent comprises a nitrile-based solvent, linear carbonate, cyclic carbonate, ester, ether, ketone, or a combination thereof.

5. The lithium secondary battery of claim 4 , wherein the cyclic carbonate comprises one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), or a mixture of two or more thereof, and

the linear carbonate comprises one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), and ethylpropyl carbonate (EPC), or a mixture of two or more thereof.

6. The lithium secondary battery of claim 4 , wherein the nitrile-based solvent comprises at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

7. The lithium secondary battery of claim 1 , wherein the lithium bis(fluorosulfonyl)imide and the 2,3-difluorobiphenyl compound are included in a weight ratio of 1:0.02 to 1:10.

8. A lithium secondary battery comprising the non-aqueous electrolyte solution of claim 1 .