WO2006036078A1

WO2006036078A1 - Electrochemical capacitor

Info

Publication number: WO2006036078A1
Application number: PCT/RU2004/000327
Authority: WO
Inventors: Sergey Nikolaevich Razumov; Igor Nikolaevich Varakin; Ekaterina Alekseevna Kilganova; Aleksey Borisovich Stepanov
Original assignee: Sergey Nikolaevich Razumov; Igor Nikolaevich Varakin; Ekaterina Alekseevna Kilganova; Aleksey Borisovich Stepanov
Priority date: 2004-08-31
Filing date: 2004-08-31
Publication date: 2006-04-06

Abstract

The invention relates to electromechanical engineering and can be used for producing asymmetrical aqueous electrolyte electrochemical capacitors. The aim of said invention is to extend the length of the unattended operation of an electrochemical capacitor at a high temperature (equal to or greater than 50°C) under intensive continuous cycling conditions. The inventive electrochemical capacitor comprises a body, a polarisable electrode made of an activated carbon material, a non-polarisable electrode, a porous separator disposed between said electrodes and an electrolyte for filling separator and electrode pores, wherein a pressure applied to the capacitor on the large lateral side of the body thereof is equal to or greater than a capillary pressure in the separator pores.

Description

Electrochemical capacitor

Technical field

The invention relates to the field of electrical industry and can be used in the production of asymmetric electrochemical capacitors with an aqueous electrolyte.

The prior art.

Known electrochemical capacitor with a water (alkaline) electrolyte, consisting of a negative polarizable electrode made of activated carbon material, and a non-polarizable electrode [US Patent JSГ ° 5,986,876, class. HOlG 9/00, 1999). [one]

Known electrochemical capacitor containing a housing, a polarizable electrode made of activated carbon material, a non-polarizable electrode, a porous separator located between the electrodes, and an aqueous acid-based electrolyte filling the pores of the separator and electrodes. (Patent RU JVo 2140681, CL HOlG 9/00, 2000) [2]

A feature of the electrochemical capacitor is _chto during operation of these devices potential non-polarizable electrode remains substantially constant due to the flow on the electrode reversible electrochemical reaction: NiOOH + H ₂ _{^{O + e ~ <→ Ni (}} OH) ₂ + OH ^'(1) in the alkaline electrolyte PbO ₂ + 4H ⁺ + SO ₄ ^{2 '} + 2e ^" <→ PbSO ₄ + 2H ₂ O (2) in an acid electrolyte.

The disadvantage of these devices is the process of oxygen evolution at the positive electrode at the end of the charge, proceeding, for example, in the reactions 4OH ^" → 2H ₂ O + O ₂ + 4e ^~ (3) in an alkaline medium and 2H ₂ O ^" → 4H ⁺ + O ₂ + 4e ^~ (4) in an acidic medium.

This process is due to the fact that the electrochemical potentials corresponding to the reactions that take place according to equations (1) and (2) and are 0.45V and 1.68V (. Handbook of electrochemistry / Ed. By A.M. Sukhotin. - L .: Chemistry, 1981, p. 422) [3], significantly positive potentials corresponding to reactions (3) and (4) in the same electrolytes (0.401 and 1.229 V, respectively). The occurrence of reactions (3) and (4) at an elevated temperature or when the capacitors are charged with a very high current becomes especially noticeable.

The consequence of these processes is a significant decrease in the charge level of the positive electrode, leading to a decrease in the duration of the capacitors at elevated ambient temperatures or during intensive operation and inadequate cooling.

The life of the capacitor at elevated temperatures can be increased if the oxygen released does not leave the capacitor, but will be restored to the negative electrode of the capacitor by the reactions opposite to (3) or (4).

The less the currents of oxygen evolution and its reduction differ, the less the charge level of the positive electrode decreases as it cycles, and under conditions of quantitative oxygen transfer and electroreduction in the capacitor, the charge level of the positive electrode does not change at all.

The closest in technical essence to the proposed solution is an electrochemical capacitor containing a housing, a polarizable electrode made of activated carbon material, non-polarizable electrode, a porous separator located between the electrodes, and an electrolyte filling the pores of the separator and electrodes (US Patent No. 6,335,858, CL HOlG 9/04, 2000) [4]. In the known construction, the transfer of oxygen to the negative electrode is ensured by the fact that both electrodes and the separator have a porous structure and the degree of filling of the pores of the separator and both electrodes with electrolyte is in the range from 40 to 90% of the pore volume. The disadvantages of this invention are as follows.

Firstly, if the pores of the separator and the electrodes are partially filled with electrolyte, then its electrical resistance increases compared to the capacitor, in which the electrolyte is contained in excess. Since heat dissipation is proportional to resistance, the temperature of the capacitor will inevitably increase with its intensive cycling.

Secondly, the thermal conductivity of the separator and electrodes partially filled with electrolyte is less than their thermal conductivity when completely filled with electrolyte.

Therefore, at the same level of thermal power generated by the capacitor during its operation, the temperature will be higher inside the capacitor, the pores of which are partially filled with electrolyte. Disclosure of the invention.

The problem solved by the invention is to increase the duration of maintenance free operation of the electrochemical capacitor at elevated (50 ⁰ C or more) temperature, as well as in conditions of intensive continuous cycling. The technical result in the present invention is achieved by creating an electrochemical capacitor containing a housing, a polarizable electrode made of activated carbon material, a non-polarizable electrode, a porous separator located between the electrodes, and an electrolyte filling the pores of the separator and electrodes, in which, according to the invention, the pressure applied to the condenser from the wide side of the capacitor housing, equal to or more capillary pressure in the pores of the separator. The invention is also characterized in that the capillary pressure in the pores of the negative electrode is 0.2-1.5 capillary pressure in the pores of the separator, and the main pores of the separator are 3-30 microns in size.

The selected conditions can be justified as follows.

If the pressure on the electrode block is less than the capillary pressure in the pores of the separator, then the released oxygen penetrates between the positive electrode and the separator into the gas space of the capacitor without falling onto the negative electrode. If the capillary pressure in the pores of the negative electrode is significantly greater than in the pores of the separator, then oxygen cannot displace the electrolyte from the pores of the negative electrode and penetrates mainly into the gas space of the capacitor.

Finally, if the pore size of the separator is less than 3 μm, oxygen transfer to the negative electrode becomes possible only with very high pressure on the side wall of the capacitor, which is technologically unacceptable.

Subject to the above conditions, the operation of the capacitor is as follows. When the positive electrode starts to stand out oxygen, it partially displaces the electrolyte from the pores of the separator, and the flow of electrolyte is directed to the auxiliary electrode and then to its ends.

This nature of the electrolyte flow is due to the above ratio of the pore sizes of the separator and the auxiliary electrode. Oxygen, following the flow of electrolyte, penetrates the negative electrode.

In this case, the electrolyte is displaced from the large pores of the auxiliary electrode. This is due to the fact that, with the indicated ratio of the sizes of the prevailing pores of the auxiliary electrode and the separator, the capillary pressure of the electrolyte in the pores of the auxiliary electrode is comparable with the capillary pressure in the pores of the separator.

Partial filling of the auxiliary electrode with oxygen leads to the fact that the interface between the liquid and gas becomes many times larger than the geometric area of the auxiliary electrode.

In turn, this creates conditions under which a large diffusion flow of dissolved oxygen to the surface of the carbon material becomes possible.

Finally, due to the fact that the carbon material is activated, oxygen ionization occurs at a high rate on it.

Brief description of illustrative material The essence of the present invention can be illustrated by the following examples and graphs, where:

Chart 1 shows the change in the energy supplied to the module depending on the number of charge-discharge cycles; Figure 2 shows the change in the discharge energy of the capacitor depending on the number of charge-discharge cycles in the case of using a dosed electrolyte;

Figure 3 shows the change in the testing process of the characteristics of the module, in which oxygen transfer and reduction are provided in the capacitors.

The best versions of the proposed design. Example 1

The objects of the test were five prismatic capacitors with a capacity of 6000 farads. The negative electrode material was a fabric of activated carbon fibers with a specific surface of 1000 m / g. As a separator, a FPP10-CG brand separator was used with main pore sizes

2-3 microns and a capillary pressure of 45-120 kPa. The capillary pressure of the negative electrode material was 0.7 - 1 kPa.

The electrolyte was taken in excess.

Five capacitors connected in series were pressed against each other by wide sides with a force corresponding to a pressure of 120 kPa. During testing, the assembly was placed in a heating cabinet.

The air temperature was maintained at 50 ± 2 ⁰ C.

The tests were carried out with the following parameters of the charge-discharge cycle: a) a constant current charge of 150 A to a voltage of 6.5 (7.0) V on the module, b) a pause of 40 seconds, c) a discharge to a constant resistance to a voltage of 3.25 (3 5) V, the initial discharge current was 190 A; d) a pause of 40 seconds. On the chart. Figure 1 shows how the delivered energy of a module changes depending on the number of charge-discharge cycles. The temperature inside the condenser ranged from 64 - 67 ⁰ C.

A monotonous decrease in the energy supplied is noticeable, and after 4000 cycles, the energy supplied falls by more than 50%.

Example 1 shows that when using a capacitor with excess electrolyte and using a finely porous separator, the capacitor resource is only 4000 charge-discharge cycles.

Example 2. The same capacitors were used as in example 1, but part of the electrolyte was removed from them, having carried out an excess charge in an inverted state and with valves turned out.

By weighing, it was determined that, as a result of dosing, approximately 70% of the pore and separator volume was filled with electrolyte, i.e. the requirements specified in the prototype were met. The tests were carried out as in example 1.

Chart 2 shows how the discharge energy of the capacitor changes depending on the number of charge-discharge cycles in the case of using a dosed electrolyte. It can be seen that in a capacitor with a dosed electrolyte, the resource increases significantly.

However, the effect of dosing the electrolyte did not fully manifest itself, probably due to the fact that it is difficult to achieve partial removal of the electrolyte from the pores using a fine-porous separator due to the high capillary pressure of the electrolyte.

The measurements showed that there was an increase in the internal resistance of the capacitor by about 20% compared with example 1, and the temperature difference on the case and inside the capacitor increased, obviously, due to an increase in resistance and a decrease in thermal conductivity.

Example 3

The capacitors were the same in design as in Example 1. The PP-7B non-woven polypropylene material with a predominant pore diameter of about 12 μm and a capillary pressure of 1-2 kPa was used as the separator material.

Figure 3 shows how the characteristics of the module, in which oxygen transfer and reduction were provided in the capacitors, were changed during the testing process. It can be seen that as a result of the changes made, the resource of continuous operation of the condenser at elevated temperature increased at least 20 times and amounted to at least 80 thousand cycles.

Example 4. The capacitors were the same in design as in example 3. As the material of the negative electrode, a material made of carbon powder with a particle size of about 50 μm with a fluoroplastic binder was used. Its capillary pressure was 0.8 - 2 kPa. The tests were carried out as in example 1. The resource characteristics amounted to about thousands of charge-discharge cycles without a significant reduction in the energy supplied.

Thus, in the implementation of the present invention allows at least six times to increase the cyclic resource of the capacitor of an asymmetric design in comparison with the known analogues.

The above examples do not exhaust all the possibilities of implementing the invention.

The proposed design can be implemented using any capacitors, during operation of which oxygen evolution is possible on one of the electrodes: positive electrode capacitors containing Pb and PbO ₂ ; MnO ₂ ; ruthenium oxides etc.

The chemical composition of the electrolyte can also be different: aqueous solutions of alkalis, including KOH, NaOH, LiOH and their mixtures, solutions of alkali metal carbonates and their mixtures with alkali solutions, mineral acids, including H ₂ SO ₄ , etc.

Claims

Claim.

1. An electrochemical capacitor comprising a housing with wide lateral sides, a polarizable electrode made of activated carbon material, a non-polarizable electrode, a porous separator located between the electrodes, and an electrolyte filling the pores of the separator and electrodes, characterized in that the pressure applied to the capacitor with the wide side of the capacitor housing, equal to or more capillary pressure in the pores of the separator.

2. The electrochemical capacitor according to claim 1, characterized in that the capillary pressure in the pores of the negative electrode is 0.2-1.5 capillary pressure in the pores of the separator.

3. The electrochemical capacitor according to claim 1, 2, characterized in that the main pores of the separator are 3-30 microns in size.