New organic borate compounds and the nonaqueous electrolytes and lithium secondary batteries using the compounds

Abstract

The object of the present invention is to supply organic borates highly soluble even in a solvent of a low dielectric constant; nonaqueous electrolytes made from these organic borates and excellent in characteristics; lithium secondary batteries with improved high-temperature storage characteristics; electric appliances that can be free of protection circuits, and; various applications of the electric appliances. The present invention relates to: organic borate compounds represented by structural formula (1) where X denotes lithium or quaternary ammonium or quaternary phosphonium and R 1 , R 2 , R 3 , and R 4 each denote an independent halogen-atom displacement alkyl group whose carbon number ranges from 1 to 4, and organic borate compounds whose R 1 , R 2 , R 3 , and R 4 are represented by trifluoromethyl groups or pentafluoroethyl groups, in particular, can be easily dissolved to concentrations of at least 0.8 mol/dm −3 in solvent mixtures heavily laden with a fluorinated solvent and offer a maximum electroconductivity value at a low concentration of 0.4 mol/dm −3 ; lithium secondary batteries using the lithium borates pertaining to the invention; nonaqueous electrolytes that minimize decreases in the high-temperature recovery capacities of these lithium secondary batteries; electric appliances that can be free of protection circuits, and; various applications of the electric appliances.

What is claimed is  
     
         1 . An organic borate compound characterized in that it is represented by general structural formula (1)  
       
         
           
           
               
               
           
         
       
       where X denotes lithium or quaternary ammonium or quaternary phosphonium and R 1 , R 2 , R 3 , and R 4  each denote an independent halogen-atom displacement alkyl group whose carbon number ranges from 1 to 4.  
     
     
         2 . An organic borate compound as described in  claim 1  above, wherein the substances denoted as R 1 , R 2 , R 3 , and R 4  in general structural formula (1) above are trifluoromethyl groups or pentafluoroethyl groups.  
     
     
         3 . A nonaqueous electrolyte characterized in that it includes a solvent and the organic borate compound described in  claim 1  or  2  above.  
     
     
         4 . A nonaqueous electrolyte characterized in that in  claim 3  above, said solvent comprises at least one of three types of substances: a ring carbonate, a chain carbonate, and ether.  
     
     
         5 . A nonaqueous electrolyte characterized in that in  claim 3  above, said solvent comprises at least one of five types of substances: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and dimethoxyethane.  
     
     
         6 . A nonaqueous electrolyte characterized in that it includes a fluorinated solvent in  claim 3 ,  4 , or  5  above.  
     
     
         7 . A nonaqueous electrolyte characterized in that in  claim 6  above, the foregoing fluorinated solvent consists of at least one of three types of substances: perfluorobutyl methyl ether, perfluorobutyl ethyl ether, and methyl perfluoroalkyl ether.  
     
     
         8 . A nonaqueous electrolyte characterized in that it includes inorganic lithium salt in  claim 3 ,  4 ,  5 ,  6 , or  7  above.  
     
     
         9 . A nonaqueous electrolyte characterized in that in  claim 8  above, said inorganic lithium salt consists of at least one of six types of substances: LiPF 6 , LiBF 4 , LiCl, LiF, LiBr, and LiI.  
     
     
         10 . A lithium secondary battery having a negative electrode capable of occluding and releasing lithium, a positive electrode capable of occluding and releasing lithium, a separator, and a nonaqueous electrolyte, wherein said lithium secondary battery is characterized in that said nonaqueous electrolyte further includes the nonaqueous electrolyte set forth in  claim 3 ,  4 ,  5 ,  6 ,  7 ,  8 , or  9  above.  
     
     
         11 . An electric appliance characterized in that its power supply is the lithium secondary battery set forth in  claim 10  above.  
     
     
         12 . An electric appliance characterized in that it, in  claim 11  above, comprises a means for protecting said secondary battery from overcharge and overdischarge by detecting freely the temperature and pressure of the battery, a means of detecting the voltage or current of the battery, and a means for controlling the opening and closing of said power supply according to the detected voltage or current value.  
     
     
         13 . An electric automobile characterized in that it comprises the electric appliance set forth in  claim 11  or  12  above.  
     
     
         14 . Electric power storage equipment characterized in that it comprises the electric appliance set forth in  claim 11  or  12  above.