Tertiary polyamines as additives to lithium-ion cell electrolytes to provide lithium-ion cell having improved properties

Abstract

A secondary, lithium-ion electrochemical cell having improved properties and a method for providing a secondary, lithium-ion electrochemical cell having the same. Specifically, the invention relates to a method for reducing and/or preventing the exfoliation of the graphitic carbonaceous electrode of a lithium-ion cell, wherein the exfoliation is caused by the intercalation of electrolyte solvent along with lithium ion into the graphitic carbonaceous electrode. This method is accomplished by adding one or more chelating polyamines to the electrolyte solution of the lithium-ion cell. The novel method and the improved lithium-ion cell are claimed herein.

We claim:  
     
       1. A rechargeable, electrochemical cell comprising 
       a graphitic carbonaceous anode;  
       a cathode capable of reversibly intercalating lithium; and  
       an electrolyte solution comprising at least one polyamine chelating agent and a lithium salt, wherein said at least one polyamine chelating agent is present in said electrolyte in concentrations at least equal to or greater than the concentration of the lithium-ion therein.  
     
     
       2. The rechargeable, electrochemical cell of claim  1 , wherein said graphitic carbonaceous anode is composed of graphite. 
     
     
       3. The rechargeable, electrochemical cell of claim  1 , wherein said cathode has a potential versus lithium metal of 3.5 V or less. 
     
     
       4. The rechargeable, electrochemical cell of claim  1 , wherein said at least one polyamine chelating agent is selected from the group consisting of N, N, N′, N″, N″-pentamethyldiethylenetriamine, N, N, N′, N″, N″′, N″′-hexamethyltriethylenetetramine and N, N, N′, N′-tetramethylethylnediamine, and mixtures thereof. 
     
     
       5. The rechargeable, electrochemical cell of claim  1 , wherein said lithium salt is selected from the group consisting of lithium chloride, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium imide, and lithium methide. 
     
     
       6. The rechargeable, electrochemical cell of claim  1 , wherein said lithium salt is present in said electrolyte solution in concentrations ranging from 0.5M to 1.5M. 
     
     
       7. A rechargeable, electrochemical cell comprising 
       a graphitic carbonaceous anode;  
       a cathode capable of reversibly intercalating lithium; and  
       an electrolyte solution, wherein said electrolyte solution comprises at least one polyamine chelating agent; a lithium salt; and a polar solvent having a dielectric constant greater than about 20, wherein said at least one polyamine chelating agent is present in said electrolyte solution in concentrations at least equal to or greater than the concentration of the lithium-ion therein.  
     
     
       8. The rechargeable, electrochemical cell of claim  7 , wherein said graphitic carbonaceous anode is composed of graphite. 
     
     
       9. The rechargeable, electrochemical cell of claim  7 , wherein said cathode has a potential versus lithium metal of 3.5 V or less. 
     
     
       10. The rechargeable, electrochemical cell of claim  7 , wherein said at least one polyamine chelating agent is selected from the group consisting of N, N, N′, N″, N″-pentamethyldiethylenetriamine, N, N, N′, N″, N″′, N″′-hexamethyltriethylenetetramine and N, N, N′, N′-tetramethylethylenediamine, and mixtures thereof. 
     
     
       11. The rechargeable, electrochemical cell of claim  7 , wherein said lithium salt is selected from the group consisting of lithium chloride, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium pechlorate, lithium imide, and lithium methide. 
     
     
       12. The rechargeable, electrochemical cell of claim  7 , wherein said lithium salt is present in said electrolyte solution in concentrations ranging from 0.5M to 1.5M. 
     
     
       13. The rechargeable, electrochemical cell of claim  7 , wherein said polar solvent having a dielectric constant greater than about 20 is selected from the group consisting of ethylene carbonate, sulfolane, mixtures of propylene carbonate with ethylene carbonate, and mixtures thereof. 
     
     
       14. The rechargeable, electrochemical cell of claim  7 , wherein said electrolyte solution comprises PMDT, lithium hexafluorophosphate, propylene carbonate, and ethylene carbonate, wherein the molar ratio of N, N, N′, N″′, N″′-pentamethyldiethylenetriamine to lithium hexafluorophosphate is at least 1:1, and wherein the ratio by volume of propylene carbonate to ethylene carbonate is approximately 1:1. 
     
     
       15. The rechargeable, electrochemical cell of claim  7 , wherein said electrolyte solution further includes a non-polar organic solvent. 
     
     
       16. The rechargeable, electrochemical cell of claim  15 , wherein said non-polar organic solvent is selected from the group consisting of dioxolane, 1,2-dimethoxyethane, benzene, toluene, 1-methyl pyrrole, and mixtures thereof.