CZ20002241A3 - Capacitor with double electric layer - Google Patents

Abstract

The double-layer capacitor contains two electrodes (5), one or both of which are polarizable, liquid electrolyte and separator (8). Degree of pore filling The separator and the two electrodes of the electrolyte fall within the range of 90 and 40% of the total pore space.

Description

Condenser with double electrical layer

Technical field

The invention relates to electrical engineering, in particular to the field of capacitor manufacturing, and may find application in the manufacture of high capacity double capacitor electrical capacitors (DEL). DEL capacitors will find use as standby power sources in systems requiring uninterrupted power supply, such as computing, communication equipment, numerically controlled machines, in continuous production processes; for electric starters starting diesel engines; for powering wheelchairs, golf carts, etc.

BACKGROUND OF THE INVENTION

Electricity accumulators containing double electric layer capacitors (DEL), such as those disclosed in U.S. Pat. Nos. 4,313,084 (1982) and 4,562,511 (1985), have long been known in the art. Said capacitors comprise two porous polarizable electrodes and a porous separator made of dielectric material and placed between them and conventional interleaves. The liquid electrolytic solution in which either aqueous or non-aqueous electrolytes are used is contained in the electrode and separator pores, as well as in the open spaces inside the capacitor housing. The electric charge is accumulated at the surface interface in the pores between the electrode material and the electrolyte. The materials used for the polarizable electrodes are various porous carbon materials. In order to increase the capacitance of the double-layer capacitor, said carbon materials are subjected to pre-activation with a view to increasing their specific surface area up to 300 - 3000 square meters / gram.

DEL capacitors have a much higher capacitance compared to conventional coil capacitors and electrolytic capacitors, i.e., capacitors. small number of farads per gram of active electrode materials. However, such capacitors suffer from having a somewhat low specific energy, not more than 3 W-hour / liter.

Another disadvantage inherent to DEL capacitors is the formation of gases during recharging, for example oxygen at the + ve electrode and / or hydrogen at the - ve electrode. This is due to the fact that, during recharging, there is potential on the individual electrodes for the development of said gases. The result is an increase in the gas pressure inside the condenser sleeve, which can lead to its compression and self-pressure damage if measures are not taken for special pressure valves. However, the functional reliability of such valves is often inadequate to provide for such pressure damage due to their possible clogging with dirt, etc. This is one of the disadvantages of DEL capacitors mentioned above that they have the basic disadvantage of the risk of pressure damage resulting in their special servicing and maintenance. To achieve a more reliable prevention of pressure damage during recharging, consideration could be given to reducing the final charging voltage in the interest of a "double fuse", hence the initial discharge voltage is limited so that it does not reach the dangerous limit. This results in a very large drop in the specific energy of the DEL capacitor which, as is well known, is directly proportional to the square of the specific energy of the DEL capacitor, which is known to be directly proportional to the square of the difference between the start and end values of the discharge voltage.

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A DEL capacitor (WO 97/07518 of February 27, 1997) is known from the prior art, having a polarizable electrode made of porous carbon material and a non-polarizable electrode made of nickel oxide. The electrolyte used is aqueous carbon or alkali metal hydroxide. Such a capacitor provides a much greater specific energy value as compared to a DEL capacitor having two polarizable electrodes (45 J / cm cubic or 12.5 Wh / lit) and a maximum voltage of 1.4 V. the problem of how to ensure its total pressure and the need for special service and maintenance. Measures for total capacitor pressures result in limited maximum charging voltage and specific energy values, as well as inadequately high charging current values and excessive charging time.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a complete pressurization service without requiring the operation of the capacitor.

Another object of the invention is to increase the capacitor specific energy and to reduce the charging time.

The aforementioned purposes are achieved by the invention as described herein, wherein the double-layer capacitor comprises two electrodes, one or both of which are polarizable, a liquid electrolyte and a separator, and the degree of filling of the void space of the separator and both electrodes falls within the range. 90 and 40%.

The principle of the present invention results in the fact that the gaseous oxide released on the DEL electrode positive electrode at the end of the charging and during recharging is basically absorbable on the negative electrode during the whole period. Its ionization reaction (electrical reduction) due to the very high polarization of the reaction (Ep> 1 V) and the fact that activated carbon is a very good catalyst for the process when it is used in cell fuel current sources ", VS Bagotski and AM Skunden, Moscow," Energhia "PH, 1981, pp. 80, 116 (in Russian). On the other hand, hydrogen gas that can be released at the negative electrode during recharging of the DEL capacitor can be essentially completely absorbed by the positive electrode during its ionization reaction (electrical oxidation) due to the very high polarization of the reaction (Ep However, in conventional 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 eliminated. Under such conditions, there are very many diffusion difficulties as well as the transfer of gas released during the charging and charging process from one electrode to the other. The mechanism of such transfer consists in dissolving said gases in the liquid electrolyte contained in the electrode pores where it is generated, in its diffused state in the dissolved state through the flooded pores of said electrode, separator and counter electrode, wherein the ionization reaction does not occur when said operations are complete. This is due to the very low solubility of hydrogen and oxygen in liquid electrolytes under normal conditions and hence very low corresponding to the diffusion coefficient value so that the resulting ionization ratio of said gases on opposite electrodes with virtually completely filled separator space and both electrodes is also very low. The ratio is similarly low in cases where one or both of the electrodes exhibit gaseous porosity, wherein the separator pores are filled completely. The very low gas transfer rate between the electrodes is much less during charging, while the pressure inside the capacitor housing rises until there is a risk of underpressure.

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The inventive idea underlining the present invention is that in the DEL capacitor there is a single gas pore system of the electrochemical group (ECGp) comprising porous electrodes and a porous separator. Thus, the oxygen and hydrogen gases that are released during the charging and charging of the capacitor are very quickly converted by said system to opposite electrodes, where both gases ionize to water or to single ions (H +, OH, and others). The fact is that the gas diffusion coefficients in the gas phase are four times greater than in the liquid phase. Such a gas pore system is realized due to the fact that the void space of both the porous electrodes and the porous separator has a degree of pore filling of between 90 and 40%. If the proportion of unfilled gas void space (gas porosity) in each of the porous bodies falls within the range of 10 and 60%, the desired system is ultimately established. Further limitation of the degree of filling of the ECGp with electrolyte is undesirable as the internal resistance of the capacitor would increase considerably.

The establishment of the gas porosity can be accomplished by a variety of technologies, one of which is possible when the electrolyte is contained only in the pores of the electrodes and the separator, i. if free electrolyte is not present in the capacitor. The final values of the degree of filling of the void space in the electrodes and the separator in the above range of 90 to 40% of the total space are achievable, firstly through a suitably measured range of electrolyte introduced into the capacitor and secondly by using electrodes and separator with finely cooperating porous structures. It is a fact that the distribution of liquid within a system of inter-porous porous bodies depends quantitatively on the size of the pore distribution curves (porograms) of said porous bodies. These quantitative dependencies are set forth in the following documents (Volfkovich Yu. M. the Journal "Elektrokhimia", 1978, v. 14, * 4, p. 546, vol. 14, * 6, p. 831; * 10, p. 1477 (in Russian); Volfkovich Yu. M. and Bagotzky VS Power Sources, 0 4 4 4 00 »· · · · 4 * 1 · ♦ 004 0 · 00 00» <4 ·

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1994, v. 48, pp.327, 339). For example, with an increase in the proportion of large pores in the separator compared to the electrodes, the degree of filling of the separator pores is reduced with respect to said electrodes. The control of adjusting the pore filling level values in each porous ECGp body can be accomplished first by weighing both the electrodes and the separator into a fully filled state (under vacuum) and then impregnating the separator and electrodes, assembling the capacitors and disassembling them; and second, by taking the electrode porograms and the separator, as well as weighing the whole ECGp before and after electrolyte impregnation.

To fulfill the above conditions, the electrolyte is contained only in the pores of the electrodes and the separator, the capacitor or group of capacitor elements is held between the housing cover and the internal resistance of the capacitors is increased.

Another way of performing the desired gas porosity is to add the dispersed water repellent to one or both of the electrodes and / or to the separator, for example polytetrafluoroethylene or polyethylene. The water repellant treatment of the negative electrode increases the extent of diffusion in the dissolved oxygen electrolyte within the pores directly to the internal electrode / electrolytic interface, resulting in a greater extent of its electrical reduction. Since the recharging of capacitors (with E <0) cannot be completely eliminated, hydrogen is prone to release on the negative electrode. The addition of the dispersed water repellent to the + ve electrode accelerates the process of transferring hydrogen to the inner surface and leads to a process of hydrogen electric oxidation at said electrode. Thus, the addition of water repellents to the porous electrode composition assists in solving the problem of forming completely pressurized capacitors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

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Giant. 1 shows an embodiment of a capacitor according to the present invention;

Giant. 2 shows an alternative embodiment of a capacitor according to the present invention;

Giant. 3 shows another embodiment of a capacitor according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

The double-film capacitor (Fig. 1) consists of two polarizable electrodes 5, made of "Viscumac" activated carbon with a specific surface area of 1200 square meters / g and a total thickness of 0.9 mm, porous separator 8, FPP-20 grade SA, made of perchlorvinyl with a total thickness of 120 microns, of power leads 3 made of steel; A 0.3 mm thick steel support housing 7; 0.3 mm thick housing side panel 6 of the housing; a non-conductive seal 7 made of atactic polypropylene; and an insulator 2 made of rigid PVC. The current-carrying protective layer 4 is made of a graphite film of 0.3 mm thick, impregnated with an acid-resistant polymer and adhered at several points to the metal electrode of the current-supply. Both electrodes are pads, each measuring 123x143 mm. A sulfuric acid solution with a density of 1.3 g / cm @ 3 is used as the electrolyte. The capacitor is pressurized, the pressure of this ECGp is 3 kg / cm2. The electrolyte is located only in the pores of this ECGp. The degrees of filling of the free space with electrolyte as measured by weighing are as follows: for electrodes 73%, for separator 81%.

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The following characteristics were obtained as a result of testing: maximum voltage 1V; specific energy 2 W-h / lit;

maximum gas overpressure measured inside the enclosure 0.02 atm.

Example 2

The double-film capacitor (Fig. 2) consists of the following elements:

The negative polarizable electrode 4, which is made of a 10-layer activated carbon fabric of the "Viscumac" type, with a specific surface area of 1200 square m / g. Positive (non-polarizable electrode 5 contains active nickel hydroxide (NiOH3) material) Grades FPP-20 SA polypropylene, from which a 60 micron thick separator 6 is made. The self-supporting sheet steel cover 1 and the self-supporting side panel 8 of the casing are used to pressurize the ECGp capacitor The non-conductive seal 7 is made of atactic polypropylene and the insulator 2 is made of rigid PVC 30% aqueous potassium hydroxide as electrolyte. The electrolyte filling levels were measured by weighing the following: for the negative electrode 63%, for the positive electrode 71%, for the separator 79%, the capacitor is assembled in vacuum, the overall dimensions of the complete assembly are 130x150x14 mm.

The following characteristics were obtained as a result of testing: maximum voltage 1.45 V; specific energy 16 W-h / lit; internal resistance 2.5 mOhm; charging time 20 min; maximum gas overpressure measured inside the enclosure of 0.01 atm.

Example 3

The capacitor with double electrical layer (Fig. 2) consists of the following elements.

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The negative polarizable electrode 7 is made by molding and sintering a composition comprising 20% polyethylene powder and 80% activated powdered carbon, grade AG-3, with a specific surface area of 1100 square m / g. The electrode 7 is 3 mm thick. The positive polarizable electrode 5 consists of a grid made of an alloy containing 95% lead and 5% antimony. Embedded within the lattice cells is a mixture containing 85% lead sulfate and 15% polytetrafluoroethylene. 60 microns thick, grade FPP-20 SA, is a perchlorvinyl separator 6 impregnated with 15% PTFE based lacquer. The current conductors 3 are made of sheet steel. The current conductor protective layer 4 is made of a graphite film impregnated with a 0.3 mm thick acid-resistant polymer, said film being attached at several points to the metal electrode of the power lead. Each electrode is a surface measuring 123x143 mm. The self-supporting housing 1 and the self-supporting side panel 9 of the housing are made of sheet steel and are used to pressurize the ECGp capacitor. The non-conductive seal 8 is made of atactic polypropylene and the insulator 2 is made of rigid PVC. As the electrolyte, aqueous sulfuric acid having a density of 1.05 g / cm @ 3 is used. The compression pressure of this ECGp is 10 kg / square centimeter. The degrees of electrolyte filling are measured by weighing and are as follows: for a negative electrode 63%, for a positive electrode 71%; for 79% separator. The capacitor is assembled under vacuum. The overall dimensions of the whole assembly are 130x150x17 mm.

The following characteristics were obtained as a result of testing: maximum voltage 2 V; the specific energy with a discharge current of 2.5 A is 51 W-h / lit; the number of available charge and discharge cycles is 6500; internal resistance 2 mOhm; charging time 15 min; the maximum gas excess pressure measured inside the enclosure is 0,01 atm.

As is evident from the present examples of the practical embodiment of the invention, the maximum gas overpressure measured is obtained.

99 • Inside the housing of all tested DEL capacitors in the range of 0.01 - 0.02 atm. These values are very low and are much lower than the breaking strength of the capacitor shells, thus not posing a risk of underpressure.

Industrial applicability

The invention described above solves the problem of performing complete pressurization of any type of DEL capacitor with both or one polarizable electrode. The practical solution to the problem of higher specific energy is achieved due to the increased maximum charging voltage on account of the non-hazardous underpressure of the capacitor. For the same reason, there is the possibility of a considerably large increase in the charging current and hence a corresponding limitation of the charging time, which is of primary importance for the large number of practical applications of the present capacitor.

Yet another positive result of the practical application of the technical solution proposed here is that the electrolyte is contained only in a portion of the free space of the electrodes and the separator, and also in the absence of free electrolyte, resulting in For the same reasons, the designed capacitor must operate normally in moving objects with a high acceleration range, such as motor vehicles, aircraft, space vehicles, etc.

Finally, capacitors made according to the present invention do not need any special operation.

Claims (6)

PATENT CLAIMS 1. A double electrode layer capacitor comprising a housing adapted to two electrodes, one or both of which are polarizable, a separator and a liquid electrolyte, both electrodes and a separator having a porous structure, wherein the degree of electrolyte filling of the separator and both electrodes falls within the range. 90 and 40% of the total pore volume. 2. The capacitor of claim 1 wherein the electrolyte is contained only in the pores of the electrodes and the separator, the degree of filling of the pores of the separator and both electrodes with the electrolyte being between 90 and 40% of the total pore volume. Condenser according to any one of the preceding claims, characterized in that the material of one or both of the electrodes is doped with a dispersed water repellent, for example polytetrafluoroethylene or polyethylene. Condenser according to any one of the preceding claims, characterized in that the separator material is doped with a dispersed water repellent, for example polytetrafluoroethylene or polyethylene. • 4 • 44 · 4 · 4 · 4 · 4 · 4 · 4 · 4 · 4 4 · · 4 · · 45 ·· ·· 4 « 4 4 94 4 4 4 4 • · · 9 4 4 4 4 4 9 4 9 4 4 A capacitor according to any one of the preceding claims, characterized in that its internal space is vacuumed. Condenser according to any one of the preceding claims, characterized in that it is pressurized. 15-JUN-2000 14:49 FROM GSHMOSCOW 2213187 9357187 TO «121810420224946724