Lithium secondary battery including non-aqueous electrolyte solution

Abstract

The present invention relates to a lithium secondary battery which includes a non-aqueous electrolyte solution including lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorobiphenyl compound, a positive electrode including a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material, a negative electrode, and a separator. In the lithium secondary battery including a non-aqueous electrolyte solution for a lithium secondary battery of the present invention, since the non-aqueous electrolyte solution may form a robust solid electrolyte interface (SEI) on the negative electrode during initial charge and may prevent decomposition of the surface of the positive electrode and an oxidation reaction of the electrolyte solution during a high-temperature cycle, excellent low-temperature output characteristics as well as improved high-temperature storage characteristics and life characteristics may be achieved.

1 . A lithium secondary battery comprising:
 a non-aqueous electrolyte solution including lithium bis(fluorosulfonyl)imide (LiFSI) and a fluorobiphenyl compound;   a positive electrode including a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material;   a negative electrode; and   a separator.   
     
     
         2 . The lithium secondary battery of  claim 1 , wherein the non-aqueous electrolyte solution further comprises a lithium salt excluding the lithium bis(fluorosulfonyl)imide. 
     
     
         3 . The lithium secondary battery of  claim 2 , 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. 
     
     
         4 . The lithium secondary battery of  claim 1 , wherein the lithium bis(fluorosulfonyl)imide has a concentration of 0.01 mol/L to 2 mol/L in the non-aqueous electrolyte solution. 
     
     
         5 . The lithium secondary battery of  claim 2 , wherein the lithium salt 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. 
     
     
         6 . The lithium secondary battery of  claim 1 , wherein the lithium-nickel-manganese-cobalt-based oxide comprises an 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.   
     
     
         7 . The lithium secondary battery of  claim 1 , wherein the non-aqueous organic solvent comprises a nitrile-based solvent, linear carbonate, cyclic carbonate, ester, ether, ketone, or a combination thereof. 
     
     
         8 . The lithium secondary battery of  claim 7 , 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.   
     
     
         9 . The lithium secondary battery of  claim 7 , 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. 
     
     
         10 . The lithium secondary battery of  claim 1 , wherein the fluorobiphenyl compound is a compound represented by Formula 2: 
       
         
           
           
               
               
           
         
         wherein, in Formula 2, n is an integer of 1 to 5. 
       
     
     
         11 . The lithium secondary battery of  claim 1 , wherein the fluorobiphenyl compound is 2,3-difluorobiphenyl. 
     
     
         12 . The lithium secondary battery of  claim 1 , wherein an amount of the fluorobiphenyl compound is in a range of 0.5 wt % to 10 wt % based on a total weight of the non-aqueous electrolyte solution. 
     
     
         13 . The lithium secondary battery of  claim 1 , wherein the lithium bis(fluorosulfonyl)imide and the fluorobiphenyl compound are included in a weight ratio of 1:0.02 to 1:10. 
     
     
         14 . A lithium secondary battery comprising the non-aqueous electrolyte solution of  claim 1 .