Electrolytic solution for an electrochemical capacitor and an electrochemical capacitor using the same

Abstract

There is provided an electrolytic solution which may significantly improve performance deterioration with time of an electrochemical capacitor. There is provided an electrolytic solution, comprising an electrolyte salt (A) shown as the following formula (1). In the formula, “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “R 4 ” and “R 5 ” independently represent hydrogen atom or an alkyl group having a carbon number of 1 to 3, and “X − ” represent a counterpart anion.

1 : An electrolytic solution, comprising: 
 an electrolyte salt (A) shown as the following formula (1),                          where “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “R 4 ” and “R 5 ” independently represent hydrogen atom or an alkyl group having a carbon number of 1 to 3, and “X − ” represents a counterpart anion.    
     
     
         2 : An electrolytic solution according to  claim 1 , wherein in the formula (1), “R 1 ,” “R 2 ,” and “R 3 ” independently represent methyl group or ethyl group, and “R 4 ” and “R 5 ” independently represent hydrogen atom, methyl group or ethyl group.  
     
     
         3 : An electrolytic solution according to  claim 2 , wherein in the formula (1), “R 1 ” represents methyl group.  
     
     
         4 : An electrolytic solution according to  claim 1 , wherein the electrolytic salt (A) comprises at least one cation selected from the group consisting of 1,2,3-trimethyl imidazolium, 1-ethyl-2,3-dimethyl imidazolium and 1,2,3,4-tetramethyl imidazolium.  
     
     
         5 : An electrolytic solution according to  claim 4 , wherein the electrolytic salt (A) comprises a cation of 1-ethyl-2,3-dimethyl imidazolium.  
     
     
         6 : An electrolytic solution according to  claim 1 , wherein the counterpart anion “X − ” is selected from the group consisting of PF 6   − , BF 4   − , AsF 6   − , SbF 6   − , N(RfSO 3 ) 2 —, C(RfSO 3 ) 3   − , RfSO 3   −  (where “Rf” represents a fluoroalkyl group having a carbon number of 1 to 12), F − , ClO 4   − , AlF 4   − , AlCl 4   − , TaF 6   − , NbF 6   − , SiF 6   − , CN −  and F(HF) n   − , wherein “n” represents an integral number of 1 to 4.  
     
     
         7 : An electrolytic solution according to  claim 1 , wherein the electrolytic salt (A) is 1-ethyl-2,3-dimethyl imidazolium tetrafluoroborate.  
     
     
         8 : An electrolytic solution according to  claim 1 , further comprising at least one non-aqueous solvent selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, sulforan, methyl sulforan, acetonitrile, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.  
     
     
         9 : An electrolytic solution according to  claim 8 , wherein the electrolytic salt (A) is 1-ethyl-2,3-dimethyl imidazolium tetrafluoroborate.  
     
     
         10 : An electrolytic solution according to  claim 1 , further comprising a first imidazolium salt (B1) shown as the following formula (2), and a second imidazolium salt (B2) shown as the following formula (3),  
       
         
           
           
               
               
           
         
         where “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “R 4 ” and “R 5 ” independently represent hydrogen atom or an alkyl group having a carbon number of 1 to 3, “X” represents a counterpart anion, “Y 1 ” represents carboxyl group (—CO 2 H) or carboxyoxy group (—OCO 2 H), and “Y 2 ” represents carboxylate group (—CO 2   − ) or carboxylate oxy group (—OCO 2   − ).  
         
           
             
             
                 
                 
             
           
         
         where “R 1 ”, and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “X − ” represents a counterpart anion, “Y 1 ” represents carboxyl group (—CO 2 H) or carboxyoxy group (—OCO 2 H), and “Y 2 ” represents carboxylate group (—CO 2   − ) or carboxylate oxy group (—OCO 2   − ),  
         wherein the first imidazolium salt (B1) and the second imidazolium salt (B2) are totally included at an amount of 10 mole % or less in a total molar number of the electrolyte salt (A), the first imidazolium salt (B1) and the second imidazolium salt (B2).  
       
     
     
         11 : An electrolytic solution according to  claim 10 , wherein the first imidazolium salt (B1) and the second imidazolium salt (B2) are totally included at an amount of 2 mole % or less in a total molar number of the electrolyte salt (A), the first imidazolium salt (B1) and the second imidazolium salt (B2).  
     
     
         12 : An electrolytic solution according to  claim 10 , wherein the electrolyte salt is 1-ethyl-2,3-dimethyl imidazolium tetrafluoroborate.  
     
     
         13 : An electrochemical capacitor, comprising: 
 a polarizable electrode impregnated with an electrolytic solution, comprising:    an electrolyte salt shown as the following formula (1),                          where “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “R 4 ” and “R 5 ” independently represent hydrogen atom or an alkyl group having a carbon number of 1 to 3, and “X-” represents a counterpart anion.    
     
     
         14 : An electrochemical capacitor according to  claim 13 , wherein the electrolytic salt (A) comprises a cation of 1-ethyl-2,3-dimethyl imidazolium.  
     
     
         15 : An electrochemical capacitor according to  claim 13 , wherein the electrolytic salt (A) is 1-ethyl-2,3-dimethyl imidazolium tetrafluoroborate.  
     
     
         16 : An electrochemical capacitor according to  claim 13 , wherein the electrolytic solution further comprises a first imidazolium salt (B1) shown as the following formula (2), and a second imidazolium salt (B2) shown as the following formula (3),  
       
         
           
           
               
               
           
         
         where “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “R 4 ” and “R 5 ” independently represent hydrogen atom or an alkyl group having a carbon number of 1 to 3, “X − ” represents a counterpart anion, “Y” represents carboxyl group (—CO 2 H) or carboxyoxy group (—OCO 2 H), and “Y 2 ,” represents carboxylate group (—CO 2   − ) or carboxylate oxy group (—OCO 2   − ).  
         
           
             
             
                 
                 
             
           
         
         where “R 1 ,” “R 2 ,” and “R 3 ” independently represent an alkyl group having a carbon number of 1 to 3, “X − ” represents a counterpart anion, “Y 1 ” represents carboxyl group (—CO 2 H) or carboxyoxy group (—OCO 2 H), and “Y 2 ” represents carboxylate group (—CO 2   − ) or carboxylate oxy group (—OCO 2   − ),  
         wherein the first imidazolium salt (B1) and the second imidazolium salt (B2) are totally included at an amount of 10 mole % or less in a total molar number of the electrolyte salt (A), the first imidazolium salt (B1) and the second imidazolium salt (B2).