Power storage element and electric double layer capacitor

• US 7,626,804 B2
• Filed: 01/21/2005
• Issued: 12/01/2009
• Est. Priority Date: 03/10/2004
• Status: Expired due to Fees

• Current Assignee: Masaki Yoshio
• Original Assignee: Masaki Yoshio
• Inventors: Nakamura, Hitoshi, Yoshio, Masaki
• Primary Examiner(s): THOMAS, ERIC W
• Application Number:
  US10/592,047
• Publication Number:
  US 20070201185A1
• Time in Patent Office: 1,775 Days
• Field of Search: 361502-503, 29/250.3, 252/62.2
• US Class Current: 361/502
• CPC Class Codes: H01G 11/06 with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
• CPC Class Codes: H01G 11/32 Carbon-based
• CPC Class Codes: H01G 11/56 Solid electrolytes, e.g. gels; Additives therein
• CPC Class Codes: H01G 11/62 characterised by the solute, e.g. salts, anions or cations therein
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors

Abstract

To provide electric double layer capacitors which have large electrostatic capacitances. Graphite with a BET surface area of from 10 to 300 m²/g, wherein the graphite has an energy storing ability of 10 to 200 mAh at a voltage of 1 V or more based on the oxidation-reduction potential of lithium.

Claims

1. An electric double layer capacitor comprising a carbonaceous positive electrode comprising graphite and a carbonaceous negative electrode, immersed in an electrolytic solution obtained by making a solute dissolved in a nonaqueous solvent, wherein

the electrolytic solution includes no lithium ion, and

the graphite has a rhombohedral crystal-to-hexagonal crystal ratio (lb/la ratio) determined by X-ray diffractometry of 0.3 or more.

2. The electric double layer capacitor according to claim 1, wherein the carbonaceous negative electrode is a carbonaceous negative electrode comprising graphite.

3. The electric double layer capacitor according to claim 1, wherein the graphite has a BET surface area of from 10 to 300 m²/g.

4. The electric double layer capacitor according to claim 1, wherein the graphite has an l(1360)/l(1580) ratio determined by Raman spectroscopy within the range of from 0.02 to 0.30.

5. The electric double layer capacitor according to claim 1, wherein the solute is at least one electrolyte selected from the group consisting of a tetrafluoroborate salt of an quaternary ammonium and its derivatives, and a hexafluorophosphate salt of an quaternary ammonium and its derivatives.

6. The electric double layer capacitor according to claim 5, wherein the quaternary ammonium is the pyrrolidinium compound represented by the formula:

wherein R is each independently an alkyl group having from 1 to 10 carbon atoms or R and R form together an alkylene group having 3 to 8 carbon atoms.

7. An electric double layer capacitor, wherein at least one electrode comprises graphite of which changing rate in voltage turns smaller than a voltage changing curve based on a time constant through intake of ions in the electrolytic solution into the graphite in the course of charging at the time of charging with a constant current, and wherein charging/discharging is performed through adsorption and desorption of the ions, wherein

the electrolytic solution includes no lithium ion, and

the graphite has a rhombohedral crystal-to-hexagonal crystal ratio (lb/la ratio) determined by X-ray diffractometry of 0.3 or more.

8. The electric double layer capacitor according to claim 7, wherein both the positive electrode and the negative electrode comprise graphite of which changing rate in voltage turns smaller than a voltage changing curve based on a time constant through intake of ions in the electrolytic solution into the graphite in the course of charging at the time of charging with a constant current.

9. The electric double layer capacitor according to claim 7, wherein at least one electrode is composed of a carbon electrode comprising graphite-like microcrystalline carbon of which electrostatic capacitance has been developed through insertion of ions at a first charging, and the carbon therefore showing a voltage changing curve based on a time constant at a second and subsequent charging with a constant current.

10. An electric double layer capacitor, wherein at least one electrode is composed of an electrode made of graphite of which changing rate in voltage turns smaller than a voltage changing curve based on a time constant through intake of ions in the electrolytic solution into the graphite in the course of charging at the time of charging with a constant current, and the counter electrode comprises activated carbon, wherein

the electrolytic solution includes no lithium ion, and

the graphite has a rhombohedral crystal-to-hexagonal crystal ratio (lb/la ratio) determined by X-ray diffractometry of 0.3 or more.