Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
1999-01-29
2001-03-06
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S530000, C361S511000
Reexamination Certificate
active
06198623
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to capacitors which are capable of exhibiting high-energy capacitance and high current density discharge over extended time periods ranging from a few seconds to minutes. Such “supercapacitors” are particularly useful for delivering high levels of electrical current to utilization devices in a much shorter time than required by battery systems alone. The invention is directed in particular to a supercapacitor structure, and method of making the same, which incorporates activated carbon fabric electrode elements in a unitary, flexible structure which may be sized and shaped as desired to be most compatible with utilization devices while providing advantageously high energy capacities and current densities.
In large measure, available supercapacitors are of the double layer type in which a pair of electrodes, typically comprising particulate activated carbon, are separated by a microporous, electron-insulating, ion-conducting sheet element comprising a uniformly-dispersed electrolyte component. The structure of the typical supercapacitor further comprises electrically-conductive current collector elements in intimate contact with the respective electrodes. Common among the structural variants of such prior supercapacitor devices are means, such as compressive arrangements, which maintain the essential close physical contact between elements in order to ensure low internal electrical resistance. An example of a capacitor of this type may be seen in U.S. Pat. No. 3,536,936 where the considerable compacting pressure required to reduce to usable levels the internal electrical resistance of a carbon particle electrode composition, as well as such resistance at the electrode/collector interface, creates severe difficulties in the fabrication of the capacitor cell.
Attempts have been made to reduce the internal electrical resistance in supercapacitor electrodes by means other than directly-applied physical pressure, notably through some manner of unifying the particulate carbon electrode composition and conductive collectors. A process of high-temperature sintering of the elements to achieve this end is described in U.S. Pat. No. 5,115,378, yet, as is apparent there, the extensive processing steps and high energy consumption lead to economic undesirability of this approach. Further limiting the general acceptance of the process is the intractability of the resulting solid and unyielding preformed capacitor body which cannot be readily shaped to conform to spacial requirements of varying utilization devices.
Other approaches to minimizing the internal resistance of supercapacitor structures have, for example, attempted to combine pyrolyzed aerogel carbon foam electrodes with high-temperature soldering of conductive collector elements, as described in U.S. Pat. No. 5,260,855. Such approaches have realized limited success, however, due to the extensive processing and high energy and time consumption required, in addition to the lack of manipulability of the resulting devices.
Overcoming such limitations of prior supercapacitor structures and fabrication procedures, the present invention provides, in particular, means for readily preparing flexible, low resistance supercapacitor structures under economical ambient conditions. These simple fabrication procedures, such as direct interelement lamination operations, enable the expanded use of these devices in a wide variety of configurations and applications, including combinations with integrated rechargeable battery energy sources of compatible composition and structure.
SUMMARY OF THE INVENTION
The supercapacitor structures of the present invention comprise as electrode elements an activated carbon fabric which has been discovered to have exceptional strength and durability, yet which provides the low electrical resistance and electrolyte-retentive porosity essential to supercapacitor cell functionality. Utilizing such a carbon fabric material, supercapacitor devices have been constructed which exhibit low internal resistance and are capable of yielding high energy and high current density over considerable time periods. Through the use of this material, supercapacitor devices may be conveniently fabricated by thermal lamination of the electrode elements with conductive current collector elements and high-porosity separator films to form flexible and exceptionally sturdy cell structures which may be readily activated with commonly-employed electrolyte compositions to yield their distinguishingly remarkable capacitive performance.
In a preferred process of constructing a supercapacitor cell, electrode elements of desired dimension are cut from a sheet of activated carbon fabric and are thermally laminated to respective electrically-conductive current collector foils, e.g., copper and aluminum reticulated grids, to form negative and positive capacitor electrode member subassemblies. The foils are preferably precoated with a minimal layer of electrically-conductive thermoadhesive composition to promote a low-resistance laminate interface in the electrode member.
A separator membrane of microporous thermoplastic composition, such as a high density polyethylene, is interposed between the carbon fabric surfaces of the electrode member subassemblies to form an assembly which is-then heated under pressure to thereby effect lamination of the cell elements into a unitary flexible supercapacitor structure. The laminated structure may thereafter be activated by immersion or other contact with an electrolyte solution, e.g., 1 M LiPF
6
in 2 parts ethylene carbonate and 1 part dimethyl carbonate, which fills the pores of the separator membrane, as well as of the carbon fabric electrode elements, to ensure essential ionic conductivity within the cell structure.
The advantageous simplicity in fabricating supercapacitor cells according to the present invention contributes greatly to its desirable utility. The capability of directly laminating the cell elements into a unitary flexible cell structure, for example, promotes the economy of time and resources, in addition to eliminating the superfluous weight of electrolytically nonfunctional structural components, such as composite binder or adhesive layers, and heavy compression elements or strengthening members. The invention thus provides a single, unitary high-capacity device comprising an economical and reliable source of both high energy and high power to meet the wide range of demands presented by modern electronic systems.
REFERENCES:
patent: 4616290 (1986-10-01), Watanabe et al.
patent: 5635138 (1997-06-01), Amatucci et al.
patent: 5859761 (1999-01-01), Aoki et al.
patent: 5922492 (1999-07-01), Takita et al.
patent: 5972531 (1999-10-01), Kawakami
Dinkins Anthony
Hey David A.
Telcordia Technologies Inc.
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