Double layer capacitors

Abstract

Activated carbons having improved volumetric capacitance and double layer capacitors including these activated carbons are described herein.

What is claimed is: 
     
         1 . A method for making an activated carbon for use in an electrochemical double layer capacitor comprising:
 heating a carbonaceous material to a temperature of from about 1600° F. to about 2200° F. for a time period sufficient to produce a volumetric surface are of about 400 m 2 /cc to about 800 m 2 /cc; and   contacting the carbonaceous material with an electrolyte.   
     
     
         2 . The method of  claim 1 , further comprising pulverizing the carbonaceous material. 
     
     
         3 . The method of  claim 1 , further comprising contacting the carbonaceous material with an activating gas. 
     
     
         4 . The method of  claim 1 , wherein the activating gas is comprises steam or carbon dioxide (CO 2 ). 
     
     
         5 . The method of  claim 1 , wherein the volumetric surface area is from about 500 m 2 /cc to about 700 m 2 /cc. 
     
     
         6 . The method of  claim 1 , wherein the carbonaceous material comprises a carbonaceous char derived from coconut shell, babassu nut shell, macadamia nut shell, dende nut shell, walnut shell, peach pit, cherry pit, olive pit, and combinations thereof. 
     
     
         7 . The method of  claim 1 , wherein the carbonaceous material comprises a carbonaceous char derived from nut shells, pits, coal, wood, petroleum, petroleum by-products, polymers, resins, and combinations thereof. 
     
     
         8 . The method of  claim 1 , wherein the electrolyte comprises an organic solvent or water. 
     
     
         9 . The method of  claim 1 , wherein the organic solvent is selected from the group consisting of propylene carbonate (PC), y-butyrolactone, acetonitrile (AN), dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane acetonitrile (ACN), or combinations thereof. 
     
     
         10 . The method of  claim 1 , wherein the electrolyte comprises an organic solvent and one or more alkali metal salt, amine salts, tetraalkylammonium salts,
 tetraalkylphosphonium salts, and combinations thereof.   
     
     
         11 . The method of  claim 1 , wherein the electrolyte comprises an aqueous electrolyte comprising a solution of water and an inorganic acid, sulfuric acid, tetrafluoroboric acid, an inorganic base, potassium hydroxide, sodium hydroxide, or inorganic salts, or combinations thereof. 
     
     
         12 . The method of  claim 1 , wherein the time period is from about 2 hours to about 10 hours. 
     
     
         13 . A method for making an activated carbon for use in an electrochemical double layer capacitors comprising:
 identifying an activation time for a carbon source that provides a maximum volumetric capacitance; and   activating carbon from the carbon source for the activation time identified to produce activated carbon.   
     
     
         14 . The method of  claim 13 , wherein the activation time is sufficient to produce an activated carbon having a volumetric surface area of about 400 m 2 /cc to about 800 m 2 /cc. 
     
     
         15 . The method of  claim 13 , wherein the activation time is sufficient to produce an activated carbon having a volumetric surface area of from about 500 m 2 /cc to about 700 m 2 /cc. 
     
     
         16 . The method of  claim 13 , wherein the carbon source is coconut shell, babassu nut shell, macadamia nut shell, dende nut shell, walnut shell peach pit, cherry pit, olive pit, and combinations thereof. 
     
     
         17 . The method of  claim 13 , wherein the carbon source is nut shells, pits, coal, wood, petroleum, petroleum by-products, polymers, resins, and combinations thereof.