RU2782246C1 - Electrolyte for a double-layer electrochemical capacitor and method for its preparation - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering, in particular to an electrolyte for a two-layer electrochemical capacitor and a method for its preparation. According to the invention, the composition of the electrolyte includes an ionogen in the form of a salt of a quaternary ammonium base and a mixture of organic solvents, where the main solvent is acetonitrile, and the co-solvent is selected from among ethers, while methyltriethylammonium tetrafluoroborate is used as a salt of a quaternary ammonium base, ethyl acetate is used as a co-solvent, and additionally as a component that lowers the melting point of the electrolyte, toluene, or ethoxyethane, or vinylene carbonate is introduced.

EFFECT: extending the boundaries of the temperature range of performance of a two-layer electrochemical capacitor with a voltage of 2.5 V to the range from minus 65°C to 65°C without a significant decrease in capacitive characteristics in the entire range of operating temperatures, including after passing through 10,000 charge-discharge cycles, and ensuring " cold start” with a current of at least 0.5 A/g at a temperature of minus 65°C is the technical result of the invention.

2 cl, 3 tbl, 3 ex

Description

The invention relates to the field of electrical engineering, in particular to an electrolyte for a two-layer electrochemical capacitor and a method for its preparation. The invention can be used in the production of double-layer capacitors used for energy storage and pulse output in hybrid energy storage systems paired with batteries, in hybrid vehicles and electric vehicles for recuperation of braking energy, and also as power sources when starting engines, turbines, including number in special climatic conditions, etc.

The specific energy intensity and power of double-layer capacitors are determined by the properties of the electrode material-electrolyte pair, and the operating temperature range depends on the properties of the electrolyte. The use of acetonitrile as a solvent in the composition of the electrolyte guarantees the performance of double-layer capacitors in the temperature range from minus 40°C to 65°C. However, for a number of applications, such as power supply in the conditions of the Far North and the Arctic, double-layer capacitors are required with an operating temperature range from minus 65 to 65°C, maintaining high capacitance and power characteristics over the entire temperature range.

An electrolyte for a two-layer electrochemical capacitor is known, described in US Pat. l.

The disadvantage of this electrolyte is the low electrical conductivity at low temperatures (less than 2 mS/cm at minus 60°C), which leads to a significant decrease in the specific capacitive characteristics of the capacitor. In addition, due to the presence of a low-boiling component, such as methyl formate, in the composition of the electrolyte, the electrolyte does not provide resource stability at temperatures above 25°C.

Known electrolyte for a double-layer electrochemical capacitor, described in US patent 8804309, containing acetonitrile as the main solvent and 1,3-dioxolane, methyl formate, propionitrile and butyronitrile as co-solvents, quaternary ammonium salts as ionogens.

The disadvantage of this electrolyte is the low electrical conductivity, because to prevent the crystallization of ionogens, they are introduced into the electrolyte at low concentrations - from 0.1 to 0.75 mol/l. In addition, due to the presence of a low-boiling component, such as methyl formate, and an electrochemically unstable component, such as 1,3-dioxolane, in the electrolyte composition, the proposed electrolyte does not provide resource stability at temperatures above 25°C.

Known electrolyte for a two-layer electrochemical capacitor, described in patent CN 102254691 A, designed for operation at ultra-low temperatures and representing a solution of quaternary ammonium salts in propylene carbonate or acetonitrile with nitriles or esters as low-temperature additives. However, the lowest temperature at which the properties of this electrolyte are characterized is -40°C.

The disadvantage of this electrolyte is the low resource stability at room and elevated temperatures, as well as an insufficiently wide electrochemical window.

Known electrolyte for a double-layer electrochemical capacitor, described in patent CN 105070528 A, providing stable operation at temperatures up to minus 60 degrees. It uses salts of quaternary ammonium bases as ionogens, and acetonitrile and other nitriles as polar aprotic solvents. In addition, the electrolyte contains low-temperature additives - alkyl nitrates.

The disadvantage of this electrolyte is the use of highly toxic compounds in its composition: nitromethane, nitroethane, 2-nitropropane (see "Federal Register of Potentially Hazardous Chemical and Biological Substances"). In addition, the patent does not provide data on the electrochemical window, capacitive characteristics and resource stability at various temperatures.

Known electrolyte for a two-layer electrochemical capacitor, described in patent CN 104681302 A, which contains a mixture of salts of quaternary ammonium bases, ionic liquids, acetonitrile as a polar aprotic solvent, as well as one or more low-temperature additives - diethyl carbonate, ethyl propionate, dimethyl sulfite, isobutyl formate , butyl acetate, hexyl acetate, butylvalerate. The electrolyte provides high resource stability at 70°C - after 10 thousand cycles of galvanostatic charge-discharge, the capacity decreases by no more than 10%. The lowest temperature at which a double-layer capacitor with this electrolyte is capable of charging and discharging is minus 65°C.

The disadvantage of this electrolyte is a significant decrease in the capacitance of a double-layer capacitor with decreasing temperature: for example, at a temperature of minus 65°C, only 43 to 49% of the capacitance of a double-layer capacitor is retained compared to its capacitance at 25°C.

Known electrolyte for a two-layer electrochemical capacitor, described in US patent 20210057170 A1, containing acetonitrile as a polar aprotic solvent, low-boiling solvents such as methyl formate and 1,3-dioxolane as low-temperature additives, and tetrafluoroborate 1,1'- as an ionogen spirobipyrollidinium. This electrolyte provides high capacitive characteristics of a double-layer capacitor in the temperature range from minus 100°C to 20°C.

The disadvantage of this electrolyte is the low concentration of the ionogen (not more than 0.5 M) and the high proportion of low-polarity co-solvent, due to which the electrical conductivity of the electrolyte is not high enough. In addition, due to the low boiling point of cosolvents, the operating conditions of the electrolyte are limited to temperatures not exceeding 20°C, and electrolytes containing 1,3-dioxolane have low resource stability due to the polymerization of this additive.

An electrolyte for a two-layer electrochemical capacitor is known, described in patent CN 109192536 A, in which an ionic liquid with 1-methyl-3-methylimidazolinium and N,N-methylpropylpiperidinium cations, propylene carbonate or acetonitrile as a polar aprotic solvent, as well as methyl acetate is used as an ionogen , methyl formate, pentane and anhydrous alcohol as a low temperature additive. The proposed electrolyte ensures the performance of a double-layer capacitor at temperatures from minus 90°C to 25°C.

The disadvantage of this electrolyte is the decrease in capacitive characteristics by more than 2 times with decreasing temperature. In addition, due to the presence of low-boiling components, such as methyl formate, pentane, etc., in the composition of the electrolyte, the proposed electrolyte does not provide resource stability at temperatures above 25°C.

The closest in technical essence and the achieved result is the electrolyte described in patent RU 2612192 C1, which ensures the operability of a two-layer electrochemical capacitor in the operating temperature range from minus 55°C to 65°C at a nominal voltage of 2.5 V. The composition of the electrolyte includes a mixture of ionogens in the form of a quaternary alkylammonium salt - tetraethylammonium tetrafluoroborate with an ionic liquid - 1-ethyl-3-methylimidazolium tetrafluoroborate, a mixture of organic solvents, where the main solvent is acetonitrile, and the co-solvent is selected from among nitriles, or cyclic carbonates, or lactones, or ethers, or cyclic ethers , and gas-absorbing additive, and the concentration of the ionogen in the electrolyte is 12-47 wt. %, the main solvent is 30-78 wt. %, co-solvent - 5-35 wt. %, and an additional gas-absorbing additive - 0.1-5 wt. %.

The disadvantage of the prototype is the insufficient lower limit of the temperature range of performance, which is minus 55°C. In addition, the co-solvent ethanenitrile, which is present in significant amounts in the electrolyte, is highly toxic (see Federal Register of Potentially Hazardous Chemical and Biological Substances).

Taking into account the fact that double-layer electrochemical capacitors must remain operational at temperatures down to minus 65°C and provide a “cold start” with a current of at least 0.5 A/g at these temperatures, it is necessary to expand the operating temperature range of the electrolyte for a double-layer electrochemical capacitor in the region low temperatures.

The objective of the invention is to expand the boundaries of the temperature range of performance of a two-layer electrochemical capacitor with a voltage of 2.5 V to the range from minus 65°C to 65°C without a significant reduction in capacitive characteristics over the entire operating temperature range, including after passing through 10,000 charge-discharge cycles , and providing a "cold start" with a current of at least 0.5 A/g at a temperature of minus 65°C.

The problem is solved by using an electrolyte, which includes an ionogen in the form of a salt of a quaternary ammonium base and a mixture of organic solvents, where the main solvent is acetonitrile, and the co-solvent is selected from among the ethers, while methyltriethylammonium tetrafluoroborate is used as a salt of a quaternary ammonium base, as a co-solvent - ethyl acetate, and additionally as a component that lowers the melting point of the electrolyte, toluene, or ethoxyethane, or vinylene carbonate is introduced in the following ratio of components in wt. %:

- methyltriethylammonium tetrafluoroborate - 23-30,

- acetonitrile - 44-49,

- ethyl acetate - 19-21,

- toluene, or ethoxyethane, or vinylene carbonate - 3-10.

The problem is also solved by the method of preparing an electrolyte, which consists in the fact that acetonitrile, ethyl acetate and a component that lowers the melting point of the electrolyte are mixed for 0.5 hours, then methyltriethylammonium tetrafluoroborate is dissolved in the resulting mixture by stirring for 3 hours, after which it is kept the resulting solution over molecular sieves for 72 hours, then the electrolyte is filtered and the residual moisture in the electrolyte is controlled by Fischer titration, and the residual moisture content should not be more than 0.002 wt. %.

The present invention is illustrated by the following examples.

Example 1

Electrolyte composition:

- methyltriethylammonium tetrafluoroborate,

- acetonitrile,

- ethyl acetate,

- vinyl carbonate.

The preparation process consists in mixing 420 g of acetonitrile (48.3 wt.%), 180 g of ethyl acetate (20.7 wt.%) and 26 g of vinylene carbonate (3.0 wt.%) for 0.5 hour without heating and dissolving in the resulting mixture, 244 g of methyltriethylammonium tetrafluoroborate (28.0 wt. %) by mixing the components for 3 hours without heating, keeping the resulting solution over 3 A molecular sieves for 72 hours, filtering the electrolyte, controlling the residual moisture content by Fischer titration. The residual moisture content is 0.0014 wt. %.

The electrolyte performance tests were carried out as part of a two-layer electrochemical capacitor for a nominal voltage of 2.5 V with electrodes made from an electrode tape GMCC-61255 (China), consisting of aluminum foil and a layer based on activated carbon deposited on it. The results obtained are shown in table 1.

Example 2

Electrolyte composition:

- methyltriethylammonium tetrafluoroborate,

- acetonitrile,

- ethyl acetate,

- toluene.

The preparation process consists in mixing 420.3 g of acetonitrile (46.7 wt.%), 177.3 g of ethyl acetate (19.7 wt.%) and 90.0 g of toluene (10.0 wt.%) for 0 .5 hours without heating and dissolving 212.4 g of methyltriethylammonium tetrafluoroborate (23.6 wt.%) in the resulting mixture of solvents by stirring the components for 3 hours without heating, keeping the resulting solution over 3 A molecular sieves for 72 hours, filtering the electrolyte , control of residual moisture content by titration according to Fischer. The residual moisture content is 0.0012 wt. %.

The electrolyte performance tests were carried out as part of a two-layer electrochemical capacitor for a nominal voltage of 2.5 V with electrodes made from an electrode tape GMCC-61255 (China), consisting of aluminum foil and a layer based on activated carbon deposited on it. The results obtained are shown in table 2.

Example 3

Electrolyte composition:

- methyltriethylammonium tetrafluoroborate,

- acetonitrile,

- ethyl acetate,

- ethoxyethane.

The preparation process consists in mixing 390 g of acetonitrile (44.8 wt.%), 166.5 g of ethyl acetate (19.1 wt.%)) and 61 g of ethoxyethane (7.0 wt.%) for 0.5 hours without heating and dissolving 254 g of methyltriethylammonium tetrafluoroborate (29.1 wt.%) in the resulting mixture of solvents by mixing the components for 3 hours without heating, keeping the resulting solution over 3 A molecular sieves for 72 hours, filtering the electrolyte, controlling the residual moisture content Fischer titration. The residual moisture content is 0.0015 wt. %.

The electrolyte performance tests were carried out as part of a two-layer electrochemical capacitor for a nominal voltage of 2.5 V with electrodes made from an electrode tape GMCC-61255 (China), consisting of aluminum foil and a layer based on activated carbon deposited on it. The results obtained are shown in table 3.

As can be seen from the examples, the developed electrolyte has the following advantages.

1. Provides an extended operating temperature range of a two-layer electrochemical capacitor for a nominal voltage of 2.5 V from minus 65°C to 65°C.

2. Provides high stability of the capacitive characteristics of a two-layer electrochemical capacitor in the entire range of operating temperatures, which manifests itself in a decrease in electrical capacitance by no more than 12-30% at a temperature of minus 65°C relative to the electrical capacitance at a temperature of 25°C.

3. Provides a high discharge current density of a two-layer electrochemical capacitor at a temperature of minus 65°C after long-term storage at temperatures below minus 65°C (the so-called "cold start").

4. Provides high resource stability of a two-layer electrochemical capacitor, which is manifested in the absence of a decrease in electrical capacity after 10 thousand charge-discharge cycles by more than 10-20% of the original one.

5. Reduces the cost of the electrolyte through the use of cheaper components.

6. Does not contain highly toxic components.

Thus, examples of implementation of the claimed invention prove the achievement of the technical result, which consists in expanding the boundaries of the temperature range of the performance of a two-layer electrochemical capacitor at a nominal voltage of 2.5 V to the range from minus 65 ° C to 65 ° C without a significant decrease in capacitive characteristics over the entire range of operating temperatures , including after passing through 10,000 charge-discharge cycles, as well as in the possibility of a "cold start" with currents not lower than 0.5 A/g.

The decrease in the content of methyltriethylammonium tetrafluoroborate in the composition of the electrolyte below 23 wt. % leads to a decrease in the electrical conductivity of the electrolyte and a decrease in the discharge current density. The increase in the content of methyltriethylammonium tetrafluoroborate above 30 wt. % leads to its crystallization at temperatures below minus 60°C. The decrease in the content of ethyl acetate in the composition of the electrolyte below 19 wt. %, as well as components that lower the melting point of the electrolyte below 3 wt. % leads to an increase in the lower limit of the temperature range of electrolyte operation. The increase in the content of ethyl acetate in the composition of the electrolyte above 21 wt. %, as well as components that lower the melting point of the electrolyte above 10 wt. % leads to a decrease in the specific electrical conductivity of the electrolyte and a decrease in the discharge current density.

Claims (6)

1. An electrolyte for a two-layer electrochemical capacitor with a voltage of 2.5 V, including an ionogen in the form of a salt of a quaternary ammonium base and a mixture of organic solvents, where the main solvent is acetonitrile, and the co-solvent is selected from among ethers, characterized in that the salt of a quaternary ammonium base is used methyltriethylammonium tetrafluoroborate, ethyl acetate as a co-solvent, and additionally, toluene, or ethoxyethane, or vinylene carbonate is introduced as a component that lowers the melting point of the electrolyte in the following ratio, wt. %: - methyltriethylammonium tetrafluoroborate - 23-30, - acetonitrile - 44-49, - ethyl acetate - 19-21, - toluene, or ethoxyethane, or vinylene carbonate - 3-10. 2. The method for preparing an electrolyte for a double-layer electrochemical capacitor according to paragraph 1, which consists in the fact that acetonitrile, ethyl acetate and a component that lowers the melting point of the electrolyte are mixed for 0.5 hours, then methyltriethylammonium tetrafluoroborate is dissolved in the resulting mixture by stirring for 3 hours , after which the resulting solution is kept over molecular sieves for 72 hours, then the electrolyte is filtered and the residual moisture in the electrolyte is controlled by Fischer titration, and the residual moisture content should not be more than 0.002 wt. %.