Lithium secondary battery of improved high-temperature cycle life characteristics

Abstract

Disclosed is a lithium secondary battery comprising a cathode including a lithium-containing transition metal oxide, and a non-aqueous electrolyte with addition of a compound of formula (1). Incorporation of the compound (1) into the electrolyte significantly improves the high-temperature performance and cycle life characteristics of the battery.

1 . A lithium secondary battery comprising:
 (a) a cathode active material including a lithium-containing transition metal oxide having reversible lithium intercalation/deintercalation capacity;   (b) a porous separator; and   (c) a non-aqueous electrolyte containing (i) a lithium salt, (ii) an electrolyte compound, and (iii) a compound of formula (1);   
       
         
           
           
               
               
           
         
         wherein R 1  is C 1 -C 5  lower alkyl, and R 2  is hydrogen or C 1 -C 5  lower alkyl. 
       
     
     
         2 . The lithium secondary battery according to  claim 1 , wherein R 1  is methyl. 
     
     
         3 . The lithium secondary battery according to  claim 1 , wherein R 2  is methyl. 
     
     
         4 . The lithium secondary battery according to  claim 1 , wherein the compound of formula (1) has solubility of 1% by weight or higher in the electrolyte. 
     
     
         5 . The lithium secondary battery according to  claim 4 , wherein the compound of formula (1) has solubility of 10% by weight or higher in the electrolyte. 
     
     
         6 . The lithium secondary battery according to  claim 1 , wherein a content of the compound (1) is in the range of 0.01 to 10% by weight, based on the total weight of the electrolyte. 
     
     
         7 . The lithium secondary battery according to  claim 1 , wherein the lithium-containing transition metal oxide is selected from the group consisting of LiCoO 2 , LiNiO 2 , LiCo  1/3 Mn 1/3 Ni 1/3 O 2 , LiCo 0.2 Mn 0.3 Ni 0.5 O 2 , LiCo 0.2 Mn 0.4 Ni 0.4 O 2 , LiMn 2 O 4  and LiNi 1-x Co x O 2  (0<X<1). 
     
     
         8 . The lithium secondary battery according to  claim 1 , wherein the carbon-based material is graphitized carbon having the lattice spacing (d 002 ) of less than 0.338 nm, as measured by X-ray diffraction, and a specific surface area of less than 10 m 2 /g, as measured by a BET method. 
     
     
         9 . The lithium secondary battery according to  claim 1 , wherein the lithium salt is selected from the group consisting of LiClO 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiPF 6 , LiBF 4 , LiAsF 6 , LiN(C 2 F 5 S0 2 ) 2  and LiN(CF 3 SO 2 ) 2 . 
     
     
         10 . The lithium secondary battery according to  claim 1 , wherein the electrolyte compound is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), gamma-butyro lactone (GBL), sulfolane, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), and any combination thereof. 
     
     
         11 . A battery module comprising the lithium secondary battery of  claim 1 , as a unit battery. 
     
     
         12 . The lithium secondary battery according to  claim 1 , wherein the lithium-containing transition metal oxide is at least one selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiCo x Mn y Ni z O 2  (0<x<0.4, 0<y<0.5, 0<z<0.7), LiMn 2 O 4  and LiNi 1-x Co x O 2  (0<X<1).