Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2000-08-16
2002-01-01
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S505000, C361S512000, C361S508000, C361S517000, C029S025030
Reexamination Certificate
active
06335858
ABSTRACT:
TECHNICAL FIELD
The invention relates to electrical engineering, in particular, to capacitor-making industry and can find application in producing high-capacity electric capacitors making use of double electric layer (DEL). Capacitors with DEL have found application as stand-by power sources in systems requiring uninterrupted power supply, such as computation engineering, communications equipment, numerically controlled machine tools, in uninterrupted cycle production processes; for electric-starter starting of diesel engines; for power supply of invalid carriages, golf carriages, etc.
BACKGROUND ART
Known in the art presently are electric energy accumulators appearing double electric layer (DEL) capacitors, e.g., those disclosed in U.S. Pat. No. 4,313,084 (1982) and 4,562,511 (1985). Said capacitors comprise each two porous polarizable electrodes and porous separator made of a dielectric material and placed therebetween, and current leads. A liquid electrolyte solution in the capacity of which either aqueous or non aqueous electrolytes are used (is contained in the pores of the electrodes and separator, as well in a certain free space inside the capacitor casing. Electric charge is accumulated on an interphase surface in the pores between the electrode material and the electrolyte. Used as the materials of polarizable electrodes are various routine porous carbon materials. To increase the capacitor capacitance with double electric layer said carbon materials are subjected to preactivation with a view to increasing their specific surface area up to 300-3000 sq.m/g.
DEL capacitors have much higher capacity compared with routine film-type and electrolytic capacitors, i.e., up to a few scores of Farads per gram of active electrode materials. However, such capacitors suffer from a rather specific energy, i.e., not more than 3 watt-hours/lit.
Another disadvantage inherent in DEL capacitors resides in evolving gases during recharging, e.g., oxygen on the positive electrode and/or hydrogen on the negative electrode. The fact is due to the fact that the potential of evolution of said gases on the respective electrodes is reached during recharging. The result is an increased pressure of the gases inside the capacitor casing which may lead to its depressurization and even blasting if no provision is made for a special pressure release valve. However, operating reliability of such valves is frequently inadequate to ensure against such depressurization or blasting due to their getting clogged with dirt, and so on. It is for said and other reasons that DEL capacitors suffer from a fundamental disadvantage, that is, a danger of their depressurization and even blasting which involves special service and maintenance thereof. To provide more reliable prevention of depressurization during recharging, one should considerably reduce the final charging voltage for the sake of “double insurance”, whence the initial discharge voltage is reduced, too so as not to approach a dangerous border-line. This in turn results in a considerable drop of the specific energy of the DEL capacitor which, as is commonly known, is directly proportional to the squared specific energy of the DEL capacitor which, as is commonly known, is directly proportional to the squared difference between the initial and final discharge voltage values.
Known in the present state of the art is a DEL capacitor (cf. WO 97/07518 of Feb. 27, 1997) having a polarizable electrode made of a porous carbon material, and a non-polarizable electrode made of nickel oxide. Used as electrolyte is an aqueous carbonate or hydroxide of an alkali metal. Such a capacitor gives much more specific energy value compared with a DEL capacitor having two polazable electrodes (up to 45 J/cu.cm or 12.5 W-h/lit), and a maximum voltage of 1.4 V. However, the capacitor described before yet suffers from substantial disadvantages, that is, the problem of how to provide its complete pressurization and need in special service and maintenance thereof. As a result of non-provision of a complete pressurization of the capacitor are reduced values of a maximum charging voltage and specific energy, as well as inadequately high charging current values and hence too long a charging time.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a completely pressurized service—and attendance-free capacitor.
It is another object of the invention to enhance the specific energy of the capacitor and to reduce the charging time.
The foregoing objects are accomplished due to the herein-disclosed invention whose essence resides in that in a dual electric layer capacitor comprising two electrodes of which either one or both are polarizable, a liquid electrolyte, and a separator, the degree of filling the void space of the separator and of both electrodes with electrolyte falls within 90 and 40%.
The essence of the present technical solution resides in that gaseous oxygen liberated on the positive electrode of a DEL capacitor at the end of charging and during recharging is basically absorbable completely on the negative electrode during its ionization reaction (electric reduction) due to very high polarization of said reaction (Ep>1 V) and due to the fact that the activated carbon is a very good catalyst for the process in question, whereby it is made use of in fuel cells (cf. “Chemical current sources” by V. S. Bagotski and A. M. Skunden, Moscow, “Energhia” PH, 1981, pp. 80, 116 (in Russian). On the other hand, gaseous hydrogen which can be liberated on the negative electrode during recharging a DEL capacitor, can substantially be absorbed completely on the positive electrode during its ionization reaction (electric oxidation) due to a very high polarization of said reaction (Ep>1 V). However, in routine DEL capacitors the pores of the separator and of both electrodes are filled with electrolyte virtually completely so that gas porosity in said porous bodies is virtually absent. Under such conditions very much trouble is encountered as regards diffusion as far as the transfer of the gases liberated during the charging and recharging procedures, from one electrode to the other is concerned. The point is that the mechanism of such a transfer consists in dissolving said gases in liquid electrolyte contained in the pores of the electrode, wherein it is generated, in its diffusing in a dissolved state over the flooded pores of said electrode, of the separator and of thee opposite electrode, the reaction of its ionization occurring not until said operations are completed. It is due to very low solubility of hydrogen and oxygen in liquid electrolytes under standard conditions and thereby very low corresponding value of the diffusion coefficient that the resultant ionization rate of said gases on the opposite electrodes with a virtually completely filled void space of the separator and of both electrodes is very low, too. Said rate is likewise as low even in cases where one or both electrodes feature certain gas porosity whereas the separator pores are footed completely. Very low rate of transfer of the gases between the electrodes is much less their generation rate during recharging, whereby the pressure inside the capacitor casing increases which is fraught with its depressurization and even with blasting.
An inventive concept underlying the present invention consists in that a single system of gas pores is established in a DEL capacitor throughout the entire electrochemical group (ECGp) thereof, comprising porous electrodes and a porous separator. Thus, oxygen and hydrogen gases which are liberated during capacitor charging and recharging are conveyed very rapidly along said system to the opposite electrodes whereon both gases undergo ionization to form water or respective ions (H+, OH, and others). The fact is that the diffusion coefficients of gases in the gaseous phase is four orders of magnitude higher than that in the liquid phase. Such a system of gas pores is provided due to the fact that the void space of both porous electrodes and the porous sep
Ashmarin Evgeny Alexandrovich
Dashko Oleg Grigorievich
Shmatko Pavel Andreevich
Vasechkin Vladimir Ivanovich
Volfkovich Jury Mironovich
Collard & Roe P.C.
Ha Nguyen T
Nauchno-Proizvodstvennoe Predpriyatie “EXIN”
Reichard Dean A.
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