RU2612192C1 - Working electrolyte for double electric layer capacitor, method of its preparation and capacitor with this electrolyte - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: according to the invention, the following is included into the working electrolyte composition: 12-47 wt % of ionogens, an organic solvents mixture, wherein the main solvent acetonitrile occupies 30-78 wt %, and the co-solvent belongs to nitriles, or cyclic carbonates or lactones, or esters or cyclic esters 5-35 wt %, wherein the electrolyte further contains a gas-absorbing additive, 0.1-5 wt %. The method for working electrolyte preparation comprises ionogen dilution in a solvent at the room temperature under stirring speed of 60 rpm, addition of the main solvent while stirring the solution for 12-48 hours, after which the solvent with the dissolved ionogen is subjected to dewatering using a molecule sieve under continuous stirring, and then after gas-absorbing additive introduction, the mixture is heated to 50 °C.

EFFECT: creation of a capacitor with a double electric layer with low equivalent series resistance at a nominal voltage of 2,5 V with operating temperature range of minus 55 to 65 degrees, including those operating at peak loads without current operating voltage reduction at low temperatures.

7 cl, 9 tbl

Description

The working electrolyte for the capacitor, the method of its preparation and the capacitor with a double electric layer with such an electrolyte.

The invention relates to the field of electrical engineering, specifically to the production of capacitors with a double electric layer (hereinafter referred to as a capacitor with DES), in particular with a low equivalent series resistance to a nominal voltage of 2.5 V with a range of operating temperatures from minus 55 to 65 ° C, including for capacitors with DES operating at peak current loads with no decrease in operating voltage at low temperatures.

A capacitor with a DEL has such characteristics as capacitance, operating voltage, energy density, internal resistance. Currently, developments are underway to improve all these characteristics, as well as developments are underway to ensure the reliability of capacitors with DES in a wide range of operating temperatures and increase their service life. Reliable operation of the capacitor with DES on the entire range of operating temperatures provides a working electrolyte, or rather its composition. The service life of a capacitor with a DEL is affected by residual moisture both in the working electrolyte and in the capacitor with a DEL.

Known electrolyte for electronic devices, including capacitors with DES, described in patent US 7675737, class. H01G 9/00, publ. 2010-03-09, containing acetonitrile as the main solvent, at least two aprotic cosolvents, a mixture of conductive salts and ionic liquids. However, this electrolyte has a low conductivity at low temperatures.

The closest is a capacitor with DES, described in patent US 8804309, CL. H01G 9/00, H01M 6/04, publ. 2011-12-20, containing an electrolyte based on acetonitrile as the main solvent, with a minimum working temperature, but not more than 40%, otherwise the conductivity of the solution will decrease under normal conditions.

The ionogen must have good solubility in the solvents used and a sufficiently large electrochemical window to provide the required operating voltage of the capacitor. The ionogen concentration is selected in such a way as to ensure high values of electrolyte conductivity both under normal conditions and at low temperatures. The decisive factor will be the ratio of the electrolyte conductivity value under normal conditions to the electrolyte conductivity value at low temperature. Table 1 shows the electrolyte conductivity at various concentrations of 1-ethyl-3-methylimidazolium tetrafluoroborate in a mixture of acetonitrile and propionitrile.

Despite the fact that the maximum electrical conductivity under normal conditions is achieved at an ionogen concentration of 2 mol / L, at a temperature of minus 55 ° C, the maximum electrical conductivity is observed at a concentration of 1.5 mol / L, and the lowest value of the electrolyte conductivity ratio corresponds to the same concentration. Therefore, the optimal concentration of ionogen for this system is 1.5 mol / L.

The most preferred substance for use as an ionogen is at least one substance selected from quaternary alkylammonium salts or ionic liquids, or a mixture thereof. Of the quaternary alkylammonium salts, tetraethylammonium tetrafluoroborate is most preferred due to its high solubility in a mixture of solvents and low cost. Of the ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate is most preferred due to its high electrical conductivity.

As can be seen from Table 2, at the same concentration of salt and ionic liquid in the electrolyte, in the case of using salt, the electrical conductivity is lower. In the case of using a mixture of salt and ionic liquid, the electrical conductivity at lower temperature is higher than when using salt or ionic liquid separately. Thus, the use of a mixture of ionogens improves the low-temperature characteristics of the electrolyte and capacitor with DES.

Nitrobenzyl alcohol is most preferred as a getter additive because of its low toxicity compared to other nitroaromatic compounds, as well as the absence of the effect of a decrease in electrical conductivity when added to an electrolyte at low temperatures. The use of a getter additive is necessary in cases where a capacitor with a DEL made using a working electrolyte in accordance with the present invention is operated at peak current loads. An electrolyte of the following composition is proposed:

The ratios of these components were optimized, which made it possible to obtain optimal electrolyte parameters. The parameters of this electrolyte are shown in Table 4:

The parameters of the working electrolyte depend on the mode of its preparation, during which the mixing of the electrolyte components among themselves occurs.

First, the salt and / or ionic liquid is dissolved in one of the solvents, then another solvent is added. At a minimum, a solvent with a dissolved salt and / or ionic liquid is drained by a molecular sieve with continuous stirring, which is associated with a significant content of water in the salt and ionic liquid.

The final solution is stirred for a certain period of time.

The technological process of preparing a working electrolyte includes the following steps:

1) loading one of the solvents into the reactor at ambient temperature. It is preferable to load the solvent whose content in the mixture of solvents is less, namely propionitrile;

2) loading the salt and / or ionic liquid into the solvent and mixing until completely dissolved. The mixing speed is set at 60 revolutions of the mixer in 1 minute. In the event that a mixture of salt and ionic liquid is used, the ionic liquid is first charged, and then the salt;

3) loading nitrobenzyl alcohol. To accelerate dissolution, the mixture is heated to complete dissolution, while the temperature should not exceed + 50 ° C;

4) the mixture is cooled to ambient temperature with constant stirring;

5) loading the molecular sieve into the mixture and mixing until the water content in the mixture decreases to 20 ppm;

6) loading a second solvent (acetonitrile) and stirring the resulting solution for 12-48 hours. Mixing is preferred for 24-27 hours;

7) the movement of the finished electrolyte in a sealed container for storage.

A section of a capacitor with a DEL is made of electrodes based on highly porous carbon materials and a separator material located between them, and has the form of a layered or spirally wound structure formed by alternating electrodes and a separator. The section is dried in vacuum for a certain time at a temperature of at least 100 ° C. Then the section is impregnated with a working electrolyte, placed in a housing, closed by a sealing element and sealed under controlled humidity. When impregnated, alternating pressures above and below atmospheric is preferred.

In accordance with the cooking process described above, working electrolytes were made. Their composition and norms correspond to the above. The compositions and parameters of electrolytes are shown in Tables 6-9. Working electrolyte, Example 2, is intended for use in capacitors with DES operating at peak current loads.

Example 1

Example 2

As can be seen from the parameters of the electrolytes, an increase in the concentration of nitrobenzyl alcohol slightly reduces the electrical conductivity of the electrolyte, however, its parameters fully comply with the standards given above.

Example 3

In accordance with the above method, capacitors with DEL were made. For the manufacture of used working electrolyte, Example 2.

The parameters of the capacitors with DEL were measured, the measurement results are shown in Table 9.

As can be seen from the parameters shown in the table, capacitors with DES using the electrolyte in accordance with the present invention have a high voltage, while the operating voltage does not decrease with decreasing temperature.

Claims (7)

1. A working electrolyte for a capacitor with a double electric layer for a nominal voltage of 2.5 V and operating temperatures from minus 55 to 65 ° C, which includes: a mixture of ionogens in the form of a quaternary alkylammonium salt and an organic or inorganic acid with an ionic liquid; a mixture of organic solvents, where the main solvent is acetonitrile, and the co-solvent is nitriles, or cyclic carbonates, or lactones, or ethers, or cyclic ethers, the main solvent occupying 30-78 wt.%, characterized in that the ionogen in the electrolyte occupies 12- 47 wt.%, Co-solvent occupies 5-35 wt.%, And an additional getter additive occupies 0.1-5 wt.%. 2. The working electrolyte according to claim 1, characterized in that the optimal concentration for the ionogen is 38 wt.%. 3. The working electrolyte according to claim 1, characterized in that the tetraethylammonium tetrafluoroborate salt of the quaternary alkylammonium and inorganic acid is. 4. The working electrolyte according to claim 1, characterized in that the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate. 5. The working electrolyte according to claim 1, characterized in that the getter additive is nitrobenzyl alcohol. 6. A method of preparing a working electrolyte for DES for a nominal voltage of 2.5 V and operating temperatures from minus 55 to 65 ° C, which consists in the fact that ionogens, namely, first 1-ethyl-3-methylimidazolium tetrafluoroborate, then tetraethylammonium tetrafluoroborate, are dissolved in one of the solvents, namely propionitrile, at room temperature with a stirring speed of 60 rpm after loading a getter additive, namely nitrobenzyl alcohol, to accelerate the dissolution process, the mixture is heated to + 50 ° C, and the mixture is cooled carried out with constant stirring, after which the solvent with the dissolved ionogen is dried with a molecular sieve, then another solvent, namely acetonitrile, is added and the solution is stirred preferably for 12-48 hours, while the main solvent occupies 30-78 wt.%, differing in that the cosolvent occupies 5-35 wt.%, the ionogen occupies 12-47 wt.%, the getter additive occupies 0.1-5 wt.%. 7. A capacitor with a DES for a nominal voltage of 2.5 V and operating temperatures from minus 55 to 65 ° C is a section made on the basis of highly porous carbon materials and a separator material located between them, having the form of a layered or spiral wound structure formed by alternation electrodes and a separator, impregnated with a working electrolyte in alternating pressure mode and placed in a housing that is closed by a sealing element, characterized in that the section is dried in vacuum at a temperature round at least 100 ° C, the body is compacted under controlled humidity, and the working electrolyte has a composition according to Claim. 1 and prepared by the process of claim. 6.