Browse Prior Art Database

Electrochemical Double Layer Capacitor

IP.com Disclosure Number: IPCOM000075109D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Peekema, RM: AUTHOR

Abstract

Electrochemical double-layer capacitors utilize capacitance phenomena at the interface between an ionically conductive electrolyte and an electronically conductive high surface area nonfilm forming electrode. To complete the circuit another electrode of the same kind is placed in contact with the electrolyte and forms another capacitor at the interface between the electrolyte and the second electronic conductor.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 48% of the total text.

Page 1 of 3

Electrochemical Double Layer Capacitor

Electrochemical double-layer capacitors utilize capacitance phenomena at the interface between an ionically conductive electrolyte and an electronically conductive high surface area nonfilm forming electrode. To complete the circuit another electrode of the same kind is placed in contact with the electrolyte and forms another capacitor at the interface between the electrolyte and the second electronic conductor.

The usual electrode material is activated carbon which allows a very high surface area per unit volume and the usual electrolyte is a liquid which wets the carbon so as to provide an extensive double-layer interface with the carbon and a correspondingly high capacitance value. Since the activated carbon is porous, other means are needed to contain the electrolyte within the package and, where the capacitor has multiple cells in series, to prevent shorting out from cell-to-cell through the electrolyte. This liquid barrier, in addition to being impervious to the electrolyte, must be inert to the electrolyte so as not to form an insulating film with the same and must be a good electronic conductor. Certain noble metals, such as gold, serve well but would raise the cost of the device.

The separate barrier part is eliminated in the illustrated capacitor. Flat, disk- shaped electrode structures 10, 12 and electrolyte saturated porous separator 14 form the basic capacitor cell structure described above. However, in this case, the bodies 16 of the electrodes are of nonporous carbon and the active electrode surfaces are in the form of porous activated carbon layers 18. The assembly 10, 12, 14 is held together by ring 20 of insulator material. Electrical connection to adjacent cells or outside circuitry is made through metalized surfaces 22 serving as flat contact buttons. The cell is filled with electrolyte through port 24 by vacuum impregnation, the electrolyte saturating 14 and filling reservoir 26 which is formed by annular grooves in 10, 12. Port 20 is then closed with plug 28 and sealer 30.

Nonporous carbon layers 16 are approximately 0.040" thick coated on one side by a highly porous activated carbon layer, 18, approximately 0.005" thick, and coated on the other side with a thin layer 22, approximately 0.001" thick, of a highly conductive metal such as copper or silver.

The electrode elements 10, 12 may be fabricated in a number of different ways, and from various starting materials. For example:

1) Each of 10, 12 is molded as a nonporous body from carbon powder in a press using enough binder to ensure strength and impermeability, but not enough to ruin conductivity of the carbon particles. Contained in the powder are particles of a material inert to the chosen electrolyte, but which can be selectively leached out by another suitable solvent. (For example, silica pore-former powder could be leached out with HF, but would be unaffected by an aqueous sulfuric acid electrolyte.) This leachi...