RU2296383C2 - Electrochemical capacitor - Google Patents

Abstract

FIELD: electrical engineering; electrochemical capacitors (those with double electrolytic layer).

SUBSTANCE: proposed electrochemical capacitor has alkali electrolyte, at least one polarized electrode incorporating at least one current collector and active material and made primarily of activated carbon, and at least one nonpolarized electrode whose current collector incorporates porous-structure part with its pores accommodating active material capable of reversible oxidation and reduction in alkali electrolyte wherein, according to invention, current collectors of polarized and nonpolarized electrodes are primarily made of iron and surfaces of both current electrodes are covered with electricity conducting layer resistant to electrochemical corrosion in alkali electrolyte medium.

EFFECT: enhanced power of electrochemical capacitor.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to the field of electrical engineering or, more specifically, to electrochemical capacitors (capacitors with a double electric layer).

The invention can be used to create devices that accumulate electrical energy, and is used, for example, in high-quality and emergency power supply systems;

to ensure a constant energy supply when using periodically acting energy sources;

in systems that accumulate regenerative braking energy in vehicles;

as traction batteries for electric vehicles, in devices for reliable starting of internal combustion engines.

At the modern level of technology, capacitors are already known that store energy in a double electric layer formed at the boundary of an electronic conductor and an electrolyte.

An electrochemical capacitor is known, including an alkaline electrolyte, a polarizable electrode made mainly of carbon material, and another electrode that is essentially non-polarizable and contains mainly nickel hydroxides as an active material. The porous structure of the non-polarizable hydroxide-nickel electrode current collector is created by introducing into the active material - nickel hydroxide - an electrically conductive additive based on carbon or nickel powder with a content of about 30 wt.% And 50 wt.%, Respectively (A.I. Belyakov, “Effect of morphology and Nickel Oxide Electrode Capacitor Capacitors and Similar Energy Storage Devices. December 11, 2001, Deerfield Beach, Florida. The 11th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices.

In a known design, an active mass with an electrically conductive additive is pressed onto a current-carrying base.

Hydroxide-nickel electrodes obtained in a known manner do not have the power and resource characteristics necessary for operation as part of an electrochemical capacitor.

For capacitors with known electrodes, a decrease in performance during life tests is observed due to oxidation of the conductive additive. The service life of the capacitors when holding at a constant voltage of 1.2 V at room temperature was no more than 2000 hours.

The closest to the claimed solution in terms of technical nature and the effect achieved is an electrochemical capacitor comprising an alkaline electrolyte, at least one polarizable electrode, consisting of a current collector and active material made mainly of activated carbon material, and at least one non-polarizable electrode, the collector of the current of which has a part with a porous structure, in the pores of which there is an active material capable of reversibly oxidizing and reducing in the medium electrolyte (US Patent No. 6181546 according to class H 01 L 9/00, 1999).

In the known capacitor, the non-polarizable electrode current collector is made of sintered nickel powder and nickel metallized polymer felt, and the polarizable electrode current collector is made of copper, silver or nickel coated with silver or gold.

Sintered and fiber hydroxide-nickel electrodes, with a certain optimization of their thickness and active material content, as well as the selection of appropriate additives, fully satisfy the requirements for a non-polarizable electrode of an electrochemical capacitor, namely they have high power characteristics in a wide temperature range (from -50 to + 60 ° C), a resource of more than 500,000 cycles and a service life of more than 10 years.

However, a disadvantage of the known design is the difficulty of implementing high power. An increase in capacitor power is directly related to a decrease in the thickness of the electrodes and an increase in their number in the capacitor.

The technology of sintered and fiber electrodes limits the manufacture of electrodes with a thickness of less than 200 microns, and also requires complex technological processes, the use of hydrogen furnaces and expensive reagents.

The objective of the invention is to increase the power of the electrochemical capacitor while maintaining its specific energy.

The technical result in the present invention is achieved by creating an electrochemical capacitor including an alkaline electrolyte, at least one polarizable electrode, consisting of a current collector and active material made mainly of activated carbon material, and at least one non-polarizable electrode, a current collector which has a part with a porous structure, in the pores of which there is an active material capable of reversibly oxidizing and reducing in an alkaline electrolyte environment, in torus, according to the invention, the current collector of the polarizable and non-polarizable electrode made mainly of iron, and the surface of both electrode current collector having a layer of electrically conductive material resistant to galvanic corrosion in an alkali electrolyte medium.

Metallic iron in an alkaline electrolyte is resistant to destruction due to passivation and the formation of a layer of oxide materials on the surface, which does not allow good contact with the active material of a polarizable activated carbon electrode and the active material of a non-polarizable electrode.

At the same time, metallic iron combines low cost and high electrical conductivity, therefore, it can act as a current collector of a non-polarizable electrode.

To ensure the necessary good contact of the active material with the current collector, the surface of the current collectors of polarizable and non-polarizable electrodes, including the pore surface of the non-polarizable electrode, has a layer of material resistant to electrochemical corrosion in an alkaline electrolyte environment. This layer has the necessary electrical contact with the iron collector and the active electrode material.

In this case, the layer may not be continuous and may not protect the iron collector from corrosion, since at the working potentials of the electrode, the iron is in a passive state.

The invention is also characterized in that the layer on the surface of the current collector of the non-polarizable electrode can be made of carbon and / or carbide and / or metal, for example platinum metal (ruthenium, rhodium, palladium, platinum, osmium, iridium), cobalt, nickel, also their alloys, carbides and their various combinations.

The proposed materials are resistant to corrosion in an alkaline electrolyte environment and have good contact with both the iron collector and the active electrode material.

According to the invention, the layer on the surface of the current collector of the polarizable electrode is made of carbon and / or metal, for example platinum metal (ruthenium, rhodium, palladium, platinum, osmium, iridium), cobalt, nickel, copper, silver, as well as their alloys, carbides and their various combinations.

The carbon coating of the current collector of a polarizable electrode can be applied to the collector by pyrolysis of hydrocarbons.

The metal may be galvanized or sprayed.

The invention is characterized in that the current collector of the polarizable electrode of the inventive capacitor can be made of copper, since it is found that copper is resistant to corrosion in a wide range of capacitor operating voltages.

In the present invention, the porous portion of the current collector of a non-polarizable electrode can be made of iron material with a high surface, such as powder or fibers.

To increase electrical conductivity, the powder and felt can be sintered in a reducing atmosphere.

To simplify the technology, the porous part of the current collector, made mainly of iron, can be made of a continuous material, the surface of which is machined, for example, using steel brushes or electrochemical, for example by electrochemical etching of an iron tape in an aqueous electrolyte.

The active material of the non-polarizable electrode in the present invention can be made on the basis of nickel hydroxides, or hydroxides and oxides of other metals: manganese, iron, copper, silver. These materials can be reversibly oxidized and reduced in an alkaline electrolyte environment with almost constant potential and act as an non-polarizable electrode.

When a capacitor is charged and discharged on a polarizable electrode of activated carbon material, a double electric layer is charged and discharged, which leads to a change in the electrode potential.

The processes reversibly occurring on an unpolarizable electrode of nickel hydroxides can be illustrated by the following equation:

These processes take place predominantly at a potential of about +0.43 V relative to the hydrogen reference electrode, therefore, the electrode is substantially non-polarizable.

The processes reversibly occurring on an non-polarizable electrode of copper oxides can be illustrated by the following equation:

These processes take place predominantly at a potential of about −0.3 V relative to the hydrogen reference electrode, therefore, the electrode is substantially non-polarizable.

The processes reversibly occurring on an unpolarizable silver oxide electrode can be illustrated by the following equation:

These processes take place predominantly at a potential of about +0.56 V relative to the hydrogen reference electrode, therefore, the electrode is substantially non-polarizable.

The processes reversibly occurring on an unpolarizable electrode of hydroxides and iron oxides can be illustrated by the following equations:

When the capacitor is operating, one of the reactions described by equations (2) or (3) can be used. These processes occur, respectively, at potentials of about -0.6 and +0.9 V relative to the hydrogen reference electrode; therefore, the electrode is substantially non-polarizable.

The processes reversibly occurring on an non-polarizable electrode containing manganese oxides can be illustrated by the following equation:

These processes take place in a narrow potential range of + 0.15- + 0.35 V relative to the hydrogen reference electrode, therefore, the electrode is substantially non-polarizable.

The invention is illustrated by the following description of the design and the drawing, which shows the proposed electrochemical capacitor.

The alkaline electrolyte electrochemical capacitor 1 comprises at least one polarizable electrode, consisting of a current collector 2 and active material 3, made mainly of activated carbon material, and at least one non-polarizable electrode, the current collector 2 of which has a part with a porous structure 4, in the pores of which the active material 5 is located, capable of reversibly oxidizing and reducing in an alkaline electrolyte environment.

The current collectors of polarized and non-polarizable electrodes are made mainly of iron. Each current collector of both electrodes has on its surface a layer 6 of a material resistant to electrochemical corrosion in an alkaline electrolyte environment. Moreover, the layers of each collector can be made of different materials, selected depending on the technological conditions.

The surface of the current collector of the polarizable electrode has a layer of material 6, which is in electrical contact with the current collector and the active material of carbon 3. The surface of the current collector of the non-polarizable electrode, including its porous part 4, has a layer of material 6, which has electrical contact with the current collector and active material 5 non-polarizable electrode, placed in the pores 4 of the current collector.

The essence of the invention is illustrated by the following examples.

Example 1. A polarizable electrode of a capacitor with dimensions of 75 × 70 mm and a thickness of 150 μm included a current collector 2 of iron foil (100 μm) with a coating 6 containing carbon and iron carbide, and the active material 3 in the form of a plate of carbon activated powder with a surface 1500 m ² / g and a binder.

The non-polarizable hydroxide-nickel electrode with a working surface of 75 × 70 mm and a thickness of 120 μm included an iron current collector 2, which had a porous part 4 with a thickness of up to 30 μm, obtained by machining the surface of an iron strip using steel brushes. The layer of material 6 on the pore surface of the collector of the non-polarizable electrode consisted of a mixture of iron carbide and carbon. The active material of the non-polarizable nickel hydroxide electrode 5 was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous solution of nickel and alkali salts.

The polarizable and non-polarizable electrodes were separated by a separator of porous polymeric material.

As electrolyte 1, a potassium hydroxide solution with a concentration of 6 mol / L was used. The total count of pairs of polarizable and non-polarizable electrodes in the capacitor was 40 pcs. The total capacitance of parallel-connected polarized electrodes was 2200 As, non-polarized - 4800 As. The capacitor volume was 0.19 liters. The operating voltage of the capacitor was 1.4 V.

Example 2. In contrast to example 1, the active material of a non-polarizable electrode of iron hydroxide 5 was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous solution of iron and alkali salts. The operating voltage of the capacitor was 0.4 V.

Example 3. Unlike example 1, the active material of a non-polarizable manganese oxide electrode 5 was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous solution of manganese salt and alkali. The operating voltage of the capacitor was 1.2 V.

Example 4. Unlike example 1, the active material of a non-polarizable copper oxide electrode 5 was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous solution of copper and alkali salts. The operating voltage of the capacitor was 0.7 V.

Example 5. Unlike example 1, the layer of material 6 on the surface of the pores 4 of the current collector of the non-polarizable electrode was made of nickel, and the active material 5 of the non-polarizable electrode of nickel hydroxide was synthesized in the pore space of the current collector by cathodic treatment of the current collector in an aqueous solution of nickel salt .

Example 6. In contrast to example 5, the layer of material 6 on the surface of the pores 4 of the collector current of the non-polarizable electrode was made of platinum.

Example 7. Unlike example 1, the layer of material 6 on the surface of the pores 4 of the non-polarizable electrode current collector was made of nickel, and the active material 5 of the non-polarizable electrode containing iron oxides was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous salt solution iron and alkali.

As electrolyte 1, a solution of potassium and barium hydroxides was used. The operating voltage of the capacitor was 1.8 V.

Example 8. In contrast to example 1, the active material of a non-polarizable silver oxide electrode 5 was synthesized in the pore space of the current collector by alternately impregnating the current collector in an aqueous solution of silver and alkali salts. The operating voltage of the capacitor was 1.6 V.

Example 9. Unlike example 1, the current collector 2 of the polarizable electrode is made of copper (50 μm), and the porous part 4 of the current collector of the non-polarizable electrode up to 50 μm thick was obtained by electrochemical etching of an iron tape in an aqueous electrolyte.

The total capacitance of parallel-connected polarized electrodes was 2200 As, non-polarized - 8500 As.

Example 10. Unlike example 9, the current collector 2 of the polarizable electrode is made of iron (100 μm) with a coating of 6 of silver.

Example 11. In contrast to example 9, the current collector 2 of the polarizable electrode is made of iron (100 μm) with a coating 6 containing nickel and carbon.

Example 12. In contrast to example 9, the current collector 2 of the polarizable electrode is made of iron (100 μm) with a coating 6 containing palladium.

Example 13. In contrast to example 1, the porous part of the current collector 4 with a thickness of up to 70 μm was obtained by baking iron powder to an iron tape in a reducing atmosphere.

The total capacitance of parallel-connected polarized electrodes was 2200 As, non-polarized - 12000 As.

The characteristics of capacitors with the active material of a non-polarizable electrode based on nickel hydroxides described in examples 1, 5, 6, 9-13 in comparison with the prototype are presented in the table.

Table
Capacitor Characteristics Example 1, 5, 6, Prototype 9-13 Operating voltage, V 1.4 1.4 Capacity, f 3200 3200 Internal resistance, mOhm 0.2 0.4 The number of electrode pairs 40 twenty The thickness of the polarizable electrode, microns 150 300 The thickness of the non-polarizable electrode, microns 120 300 The total capacity of non-polarizable electrodes. As 4800-12000 18000 The volume of the condenser, l 0.19 0.19 Stored energy, Wh / l 4.6 4.6 Maximum power, W / l 12.9 6.4 Service life at a temperature of 80 ° C and a voltage of 1.35 V More than 2 months More than 3 months Resource at a temperature of 40 ° C, cycles More than 200,000 More than 500,000

From the table it follows that the capacitors made in accordance with the invention have the same specific capacitance and energy compared to the capacitor described in the prototype, but surpass it in power characteristics.

Thanks to the iron collectors, the capacitors described in the examples are much cheaper than the capacitor described in the prototype.

Claims (3)

1. An electrochemical capacitor comprising an alkaline electrolyte, at least one polarizable electrode, consisting of a current collector and active material made of activated carbon material, and at least one non-polarizable electrode, the current collector of which has a porous structure, in the pores of which there is an active material capable of reversibly oxidizing and reducing in an alkaline electrolyte environment, characterized in that the current collectors of the polarizable and non-polarizable electrodes are iron or copper flax and the current collectors of both electrodes have a layer made of an electrically conductive material resistant to electrochemical corrosion in an alkaline electrolyte environment. 2. The electrochemical capacitor according to claim 1, characterized in that the layer material on the surface of the current collector of the non-polarizable electrode is made of carbon and / or metal, for example ruthenium, rhodium, palladium, platinum, osmium, iridium, cobalt, nickel, and also their alloys, carbides, oxides and their various combinations. 3. The electrochemical capacitor according to claim 1, characterized in that the layer material on the surface of the current collector of the polarizable electrode is made of carbon and / or metal, for example ruthenium, rhodium, palladium, platinum, osmium, iridium, cobalt, nickel, copper, silver, as well as their alloys, oxides, carbides and their various combinations.