Heat resistant lithium cell

Abstract

The present invention provides a cell that does not impair heat resistant safety and electrochemical characteristics such as a discharge characteristic, and enhances long-period reliability. In the cell of the present invention, a nonaqueous solvent has, among compounds represented by the following general formula (1), at least one solvent having a boiling point of 200° C. or higher, and has, among compounds represented by the following general formula (1), at least one solvent having a boiling point of lower than 200° C.; and the total volume ratio at 23° C. of the compounds represented by the following general formula (1) is 95 to 100 percent of the nonaqueous solvent, X—(O—C 2 H 4 ) n —O—Y  (1) (where X and Y are independently an alkyl group (number of carbons: 1-4), and n is 1-5).

What is claimed is:  
     
         1 . A lithium cell comprising: 
 a positive electrode;    a negative electrode;    a separator interposed between the positive electrode and the negative electrode; and    a nonaqueous electrolyte including a nonaqueous solvent and an electrolytic salt, wherein:    the nonaqueous solvent includes: among compounds represented by the following general formula (1), at least one compound having a boiling point of 200° C. or higher; and among compounds represented by the following general formula (1), at least one compound having a boiling point of lower than 200° C.; and    a total volume ratio at 23° C. of the compounds represented by the following general formula (1) is 95 to 100 percent of the nonaqueous solvent,    X—(O—C 2 H 4 ) n —O—Y  (1)    (where X and Y are independently an alkyl group (number of carbons: 1-4), and n is 1-5).    
     
     
         2 . The lithium cell according to  claim 1 , wherein: 
 the compound having a boiling point of lower than 200° C. includes 1,2-dimethoxyethane, the compound being among compounds represented by the above general formula (1); and    a volume ratio of the compound having a boiling point of lower than 200° C. is 50 to 60 percent of a total volume at 23° C. of the compounds represented by the above general formula (1).    
     
     
         3 . The lithium cell according to  claim 1 , wherein: 
 the compound having a boiling point of lower than 200° C. is a compound other than 1,2-dimethoxyethane, the compound being among compounds represented by the above general formula (1); and    a volume ratio of the compound having a boiling point of lower than 200° C. is 50 to 90 percent of a total volume at 23° C. of the compounds represented by the above general formula (1).    
     
     
         4 . The lithium cell according to  claim 1 , wherein the nonaqueous solvent includes cyclic ester carbonate and/or lactone, the cyclic ester carbonate and/or lactone being a subsidiary component and 5 volume percent or lower in total at 23° C.  
     
     
         5 . The lithium cell according to  claim 1 , wherein the electrolytic salt is lithium bis(trifluoromethanesulfonyl)imide and/or lithium bis(pentafluoroethanesulfonyl)imide.  
     
     
         6 . The lithium cell according to  claim 1 , wherein the nonaqueous electrolyte includes at least one compound selected from the group consisting of carboxylic acid, carboxylic acid ester, and carboxylic acid anhydride at 0.01 to 5 pts. mass in total per 100 pts. mass of the nonaqueous solvent, the carboxylic acid ester excluding lactone.