Low-temperature-resistant working electrolyte for liquid capacitor and preparation method of low-temperature-resistant working electrolyte

Abstract

The invention discloses a low-temperature-resistant working electrolyte for a liquid capacitor and a preparation method of the low-temperature-resistant working electrolyte, and relates to the technical field of electrolytes for capacitors. The low-temperature-resistant working electrolyte is prepared from the following raw materials: ethylene glycol, an auxiliary solvent, a solute, ammonium hypophosphite, a synergist, a stabilizer, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imine, boron nitride nanosheets and 2, 2, 2-trifluoroethyl acrylate. According to the invention, while the auxiliary solvent with a specific proportion is added, the synergist capable of improving the conductivity, the cycle life, the low-temperature ion mobility and the low-temperature power density and the 2, 2, 2-trifluoroethyl acrylate capable of further improving the electrochemical performance stability at the low temperature are also introduced, so that the low-temperature electrochemical performance of the lithium ion battery is improved. And a specific preparation method capable of preventing agglomeration and improving the smoothness of an ion conduction path is combined. Therefore, the electrolyte is more excellent in chemical performance at low temperature and wider in application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes for capacitors, and in particular to a low-temperature resistant working electrolyte for liquid capacitors and a preparation method thereof. Background Art

[0002] Liquid capacitors are usually composed of electrodes, electrolytes, and isolation media. Their working principle is based on the basic characteristics of capacitance. When voltage is applied to the two electrodes, the electrodes will accumulate positive and negative charges respectively, and the ions in the electrolyte can move under the action of the electric field, assisting the storage and release of charges, thereby realizing the storage function of electrical energy. Common liquid capacitors are aluminum electrolytic capacitors and tantalum electrolytic capacitors. Aluminum electrolytic capacitors use aluminum foil as electrodes and paper or other porous materials soaked in electrolyte as isolation media. Due to their lower cost, higher rated withstand voltage, wider capacity range, mature production process, and wide range of material sources compared to tantalum electrolytic capacitors, aluminum electrolytic capacitors have broader application prospects in audio circuits, communication equipment, industrial control, automotive electronics, consumer electronics and other fields.

[0003] The electrolyte of an aluminum electrolytic capacitor is formulated from various chemical reagents based on the required conductivity and flash voltage. It serves as the capacitor's true negative electrode, and its primary solvents are typically ethylene glycol and deionized water. Its conductivity directly affects the capacitor's losses and equivalent series resistance; its flash voltage determines the maximum voltage the electrolyte can withstand; and its pH affects its corrosion resistance to the conductor pins. Therefore, the electrolyte has a crucial impact on the electrochemical performance of aluminum electrolytic capacitors. However, existing electrolytes still suffer from performance degradation at low temperatures, leading to poor electrochemical performance of the capacitor.

[0004] To solve this technical problem, patent document CN112768248B proposes a low-temperature resistant electrolyte for aluminum electrolytic capacitors, which includes the following components: ethylene glycol, propylene glycol, diethylene glycol, diethylene glycol monomethyl ether, dibutyl carbonate, 2-methylbutyl butyrate, solute, flash enhancer, waterproofing mixture, stabilizer, and hydrogen scavenger. The low-temperature resistant electrolyte for aluminum electrolytic capacitors described in this invention has low capacity loss at low temperatures and high flash voltage; by using ethylene glycol, propylene glycol, and diethylene glycol as main solvents and using diethylene glycol monomethyl ether, dibutyl carbonate, and 2-methylbutyl butyrate as auxiliary solvents to form the solvent system of the present invention, the ionization equilibrium of the dielectric is favored to move toward the ionization direction, the formation ability of the electrolyte is improved, the solvation effect of the electrolyte solvent is enhanced, and the activity of the electrolyte is increased, thereby improving the low-temperature resistance and reducing the capacity loss at low temperatures. However, these existing optimization methods mostly optimize the solvent system of the electrolyte without considering the impact of other components on the performance of the electrolyte. Therefore, the improvement of the electrochemical performance of the electrolyte at low temperatures is limited. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-temperature resistant working electrolyte for liquid capacitors and a preparation method thereof, and to solve the following technical problems: The existing low-temperature resistant working electrolyte still has poor electrochemical performance and stability at low temperatures.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A low-temperature resistant working electrolyte for liquid capacitors, comprising the following raw materials in parts by weight: 60-75 parts of ethylene glycol, 20-24 parts of an auxiliary solvent, 5-6.5 parts of a solute, 1.2-1.5 parts of ammonium hypophosphite, 2-5 parts of a synergist, 1-1.5 parts of a stabilizer, 0.8-1.5 parts of a regulator, 3-6 parts of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.1-0.2 parts of boron nitride nanosheets, and 2-3 parts of 2,2,2-trifluoroethyl acrylate; Preferably, the synergist is prepared from manganese dioxide powder and niobium nitrate solution; The stabilizer is any one of sorbitol and diammonium hydrogen phosphate; The regulator is any one of p-nitrophenol, p-nitrobenzyl alcohol and p-nitrobenzoic acid.

[0007] Preferably, the auxiliary solvent is obtained by mixing diethylene glycol and propylene glycol.

[0008] The mass ratio of diethylene glycol to propylene glycol is 5-6.5:15-17.5.

[0009] Preferably, the solute is any one or more of tetraethylammonium tetrafluoroborate, ammonium hydrogen azelaic acid, and formic acid.

[0010] Preferably, the preparation method of the synergist is as follows: Step A1: Under an argon atmosphere, treating manganese dioxide powder with a low-temperature plasma to obtain pretreated manganese dioxide; Step A2: adding the pretreated manganese dioxide to the niobium nitrate solution, heating to 80-100° C. under stirring, stirring for 7-10 hours, filtering, washing, and drying to obtain a synergist.

[0011] Preferably, the pressure during the low-temperature plasma treatment in step A1 is 30-80 Pa; the power during the low-temperature plasma treatment is 80-160 W; the treatment temperature during the low-temperature plasma treatment is 30-50° C.; and the treatment time during the low-temperature plasma treatment is 10-25 min.

[0012] Preferably, the concentration of the niobium nitrate solution in step A2 is 0.01-0.1 mol / L.

[0013] Preferably, the ratio of the pretreated manganese dioxide to the niobium nitrate solution in step A2 is 8.7-43.5 g:100 mL.

[0014] The preparation method of the low temperature resistant working electrolyte for liquid capacitors is as follows: Step B1: Add auxiliary solvent to ethylene glycol, stir evenly, then add solute, and continue stirring for 3-5 hours to obtain a composite solvent; Step B2: Add ammonium hypophosphite, a synergist, a stabilizer, a regulator, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, boron nitride nanosheets, and 2,2,2-trifluoroethyl acrylate to the composite solvent in sequence while stirring, and then continue stirring for 12-15 hours under ultrasonic assistance to obtain a low-temperature resistant working electrolyte.

[0015] Preferably, the ultrasonic power during the ultrasonic assistance in step B2 is 80-90 W; the ultrasonic frequency during the ultrasonic assistance is 30-45 kHz.

[0016] As a further embodiment of the present invention.

[0017] Beneficial effects of the present invention: The present invention provides a low-temperature resistant working electrolyte for liquid capacitors and a preparation method thereof. The present invention effectively improves the electrochemical properties of the electrolyte, such as low-temperature stability, electrical conductivity, and flash voltage, by the following method.

[0018] (1) The present invention effectively removes organic pollutants, oxide layers or other impurities on the surface of manganese dioxide powder by subjecting manganese dioxide powder to low-temperature plasma treatment. At the same time, it also forms a micro-nanoscale rough structure on the surface of manganese dioxide, introduces oxygen-containing functional groups on the surface of manganese dioxide, and improves the hydrophilicity of the surface of manganese dioxide, thereby improving the interfacial bonding force between manganese dioxide and the subsequently loaded niobium compound, so that niobium ions in the niobium nitrate solution can be more tightly and evenly bound to the surface of manganese dioxide. At the same time, the synergist prepared has better capabilities of improving conductivity, enhancing low-temperature stability, widening the electrochemical window, increasing specific capacity, improving cycle stability, inhibiting side reactions, optimizing interface performance and improving power density.

[0019] (2) The 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide added in the present invention has an extremely low freezing point and high electrical conductivity, which can significantly improve the low-temperature performance of the electrolyte. At the same time, its unique anion-cation structure can effectively inhibit the crystallization of the electrolyte at low temperatures and improve the stability of the electrolyte.

[0020] (3) The addition of 2,2,2-trifluoroethyl acrylate can introduce a strong electron-withdrawing group, trifluoromethyl, thereby reducing the viscosity of the electrolyte and improving the ion mobility; at the same time, the polymer network formed after polymerization can stabilize the electrolyte structure and inhibit the decomposition of the electrolyte at low temperatures.

[0021] (4) The ultrasonic-assisted treatment in the preparation process of the low-temperature resistant working electrolyte can effectively disperse nanomaterials such as boron nitride nanosheets to prevent their agglomeration, and can also reduce phase separation or precipitation in the electrolyte. By promoting uniform dispersion and sufficient mixing of the components, the ion conduction path in the electrolyte is more unobstructed and the interface impedance is reduced. At the same time, by accelerating the dissolution, dispersion and mixing processes, the time required for traditional stirring is reduced.

[0022] Therefore, the low-temperature resistant working electrolyte prepared by the present invention has more excellent low-temperature stability, electrical conductivity, and electrochemical properties such as more ideal flash voltage value. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] Example 1: The preparation method of the low-temperature resistant working electrolyte for liquid capacitors is as follows: S1: Under an argon atmosphere, the manganese dioxide powder was subjected to a low-temperature plasma treatment at a pressure of 30 Pa, a power of 80 W, a temperature of 30°C, and a duration of 10 min to obtain pretreated manganese dioxide; S2: 8.7 g of pretreated manganese dioxide was added to 100 mL of 0.01 mol / L niobium nitrate solution, heated to 80°C with stirring, and then stirred for 7 h. The synergist was obtained after filtration, washing, and drying. S3: 5 g of diethylene glycol and 15 g of propylene glycol were mixed to obtain an auxiliary solvent; S4: Add 20 g of auxiliary solvent to 60 g of ethylene glycol, stir evenly, then add 5 g of tetraethylammonium tetrafluoroborate, and continue stirring for 3 h to obtain a composite solvent; S5: 1.2 g of ammonium hypophosphite, 2 g of enhancer, 1 g of sorbitol, 0.8 g of p-nitrophenol, 3 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.1 g of boron nitride nanosheets, and 2 g of 2,2,2-trifluoroethyl acrylate were added to 85 g of the composite solvent while stirring, and then stirring was continued for 12 hours under ultrasonic assistance at a power of 80 W and a frequency of 30 kHz to obtain a low-temperature resistant working electrolyte.

[0025] Example 2: The preparation method of the low-temperature resistant working electrolyte for liquid capacitors is as follows: S1: Under an argon atmosphere, the manganese dioxide powder was subjected to a low-temperature plasma treatment at a pressure of 50 Pa, a power of 100 W, a temperature of 35°C, and a duration of 15 min to obtain pretreated manganese dioxide; S2: 15 g of pretreated manganese dioxide was added to 100 mL of 0.03 mol / L niobium nitrate solution, heated to 90°C with stirring, and then stirred for 8 h. The synergist was obtained after filtering, washing, and drying. S3: 5.5 g of diethylene glycol and 15.5 g of propylene glycol were mixed to obtain an auxiliary solvent; S4: Add 21 g of auxiliary solvent to 65 g of ethylene glycol, stir evenly, then add 5.5 g of ammonium hydrogen azelate, and continue stirring for 3.5 hours to obtain a composite solvent; S5: 1.3 g of ammonium hypophosphite, 3 g of enhancer, 1.2 g of diammonium hydrogen phosphate, 1.0 g of p-nitrobenzyl alcohol, 4 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.13 g of boron nitride nanosheets, and 2.3 g of 2,2,2-trifluoroethyl acrylate were added to 91.5 g of the composite solvent while stirring, and then stirring was continued for 13 hours under ultrasonic assistance at a power of 83 W and a frequency of 35 kHz to obtain a low-temperature resistant working electrolyte.

[0026] Example 3: The preparation method of the low-temperature resistant working electrolyte for liquid capacitors is as follows: S1: Under an argon atmosphere, the manganese dioxide powder was subjected to a low-temperature plasma treatment at a pressure of 45 Pa, a power of 110 W, a temperature of 40°C, and a duration of 20 min to obtain pretreated manganese dioxide; S2: 30 g of pretreated manganese dioxide was added to 100 mL of 0.07 mol / L niobium nitrate solution, heated to 90°C with stirring, and then stirred for 9 h. The synergist was obtained after filtering, washing, and drying. S3: 6 g of diethylene glycol and 17 g of propylene glycol were mixed to obtain an auxiliary solvent; S4: Add 23 g of auxiliary solvent to 70 g of ethylene glycol, stir evenly, then add 3 g of formic acid and 3 g of tetraethylammonium tetrafluoroborate, and continue stirring for 4 h to obtain a composite solvent; S5: 1.4 g of ammonium hypophosphite, 4 g of enhancer, 1.4 g of sorbitol, 1.2 g of p-nitrobenzoic acid, 5 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.17 g of boron nitride nanosheets, and 2.7 g of 2,2,2-trifluoroethyl acrylate were added to 99 g of the composite solvent while stirring, and then stirring was continued for 14 hours under ultrasonic assistance at a power of 85 W and a frequency of 40 kHz to obtain a low-temperature resistant working electrolyte.

[0027] Example 4: The preparation method of the low-temperature resistant working electrolyte for liquid capacitors is as follows: S1: Under an argon atmosphere, the manganese dioxide powder was subjected to a low-temperature plasma treatment at a pressure of 80 Pa, a power of 160 W, a temperature of 50°C, and a duration of 25 min to obtain pretreated manganese dioxide; S2: 43.5 g of pretreated manganese dioxide was added to 100 mL of 0.1 mol / L niobium nitrate solution, heated to 100°C with stirring, and then stirred for 10 h. The synergist was obtained after filtering, washing, and drying. S3: 6.5 g of diethylene glycol and 17.5 g of propylene glycol were mixed to obtain an auxiliary solvent; S4: Add 24 g of auxiliary solvent to 75 g of ethylene glycol, stir evenly, then add 4 g of tetraethylammonium tetrafluoroborate, 2 g of formic acid, and 0.5 g of ammonium hydrogen azelaic acid, and continue stirring for 5 h to obtain a composite solvent; S5: 1.5 g of ammonium hypophosphite, 5 g of enhancer, 1.5 g of diammonium hydrogen phosphate, 1.5 g of p-nitrobenzoic acid, 6 g of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.2 g of boron nitride nanosheets, and 3 g of 2,2,2-trifluoroethyl acrylate were added to 105.5 g of the composite solvent while stirring, and then stirring was continued for 15 hours under ultrasonic assistance at a power of 90 W and a frequency of 45 kHz to obtain a low-temperature resistant working electrolyte.

[0028] Comparative Example 1: Compared with Example 1, this comparative example only replaces the "pretreated manganese dioxide" added in the synergist preparation process with "manganese dioxide powder". The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, a low-temperature resistant working electrolyte is obtained.

[0029] Comparative Example 2: Compared with Example 1, this comparative example only replaces the "5g diethylene glycol and 15g propylene glycol" added during the preparation of the auxiliary solvent with "15g diethylene glycol and 5g propylene glycol". The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, a low-temperature resistant working electrolyte is obtained.

[0030] Comparative Example 3: Compared with Example 1, this comparative example only replaces the "1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide" added during the preparation of the low-temperature resistant working electrolyte with "2,2,2-trifluoroethyl acrylate". The remaining steps and parameters are the same, and this comparative example will not be repeated. Finally, a low-temperature resistant working electrolyte is obtained.

[0031] Comparative Example 4: Compared with Example 1, this comparative example only replaces the "2,2,2-trifluoroethyl acrylate" added in the preparation process of the low-temperature resistant working electrolyte with "1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide". The remaining steps and parameters are the same, and this comparative example will not be repeated. Finally, a low-temperature resistant working electrolyte is obtained.

[0032] Comparative Example 5: Compared with Example 1, this comparative example only does not perform ultrasonic assistance during the preparation of the low-temperature resistant working electrolyte. The remaining steps and parameters are the same and will not be repeated in this comparative example. Finally, a low-temperature resistant working electrolyte is obtained.

[0033] Performance testing: Determination of conductivity: 15 mL of electrolyte was placed in a CT-57101B measurement cell manufactured by DKK East Asia. The thermostat was adjusted to 30°C. After the electrolyte temperature reached 30°C, its conductivity was measured. The conductivity (mS·cm) of the low-temperature resistant working electrolytes prepared in Examples 1 to 4 and Comparative Examples 1 to 5 was measured using this method. -1 ), the measurement results are shown in Table 1; Determination of pH value: The electrolyte temperature was adjusted to 25°C, and the pH of the electrolyte was measured using a DST-5421C pH meter manufactured by DKK East Asia. The pH values ​​of the low-temperature-resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 were measured using this method. The results are shown in Table 1. Determination of flash point voltage: A high voltage chemical conversion etched aluminum foil was used as the anode and cathode, and a GP650-05R manufactured by Takasago was used as a DC stabilized power supply. The load constant current (current density: 10 mA / cm) at -60°C was read. 2) when a voltage drop (short circuit) is observed, which is taken as the flashover voltage. The flashover voltage (V) of the low-temperature-resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was measured using this method. The results are shown in Table 1. Determination of stability: The electrolyte was placed in a transparent glass bottle and placed in a thermostat at -60°C for 24 hours. The bottle was then tilted at -60°C and visually observed for evaluation according to the following criteria: Pass: Transparent, no precipitates, and fluidity when tilted; Good: Slightly turbid but no precipitates, and fluidity when tilted; Unacceptable: Overall solidification. The stability of the low-temperature-resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was measured using this method. The results are shown in Table 1. Determination of capacitance loss: The capacitance values ​​of the electrolytes were measured and recorded at 20°C and -60°C using the same method, and the capacitance loss at -60°C (relative to 20°C) was then calculated. The capacitance loss (%) of the low-temperature-resistant working electrolytes prepared in Examples 1-4 and Comparative Examples 1-5 was measured using this method. The results are shown in Table 1. Table 1: Performance test results of Examples 1-4 and Comparative Examples 1-5 Data Analysis: As can be seen from Table 1, the low-temperature resistant working electrolyte prepared by the present invention has more excellent low-temperature stability and electrical conductivity, as well as more ideal electrochemical properties such as flash voltage value and capacitance loss value.

[0034] This may be because the present invention effectively removes organic pollutants, oxide layers or other impurities on the surface of manganese dioxide powder by low-temperature plasma treatment of manganese dioxide powder, while also forming a micro-nanoscale rough structure on the surface of manganese dioxide, introducing oxygen-containing functional groups on the surface of manganese dioxide, and improving the hydrophilicity of the surface of manganese dioxide, thereby improving the interfacial binding force between manganese dioxide and the subsequent loaded niobium compound, so that the niobium ions in the niobium nitrate solution can be more tightly and evenly bound to the surface of manganese dioxide. At the same time, the synergist prepared also has better electrical conductivity, enhanced low-temperature stability, widened the electrochemical window, increased specific capacity, improved cycle stability, suppressed side reactions, optimized interface performance and increased power density. The specific proportion of auxiliary solvent added in the present invention can lower the freezing point of the solvent system, improve low-temperature viscosity, improve electrical conductivity, enhance thermal stability, optimize the solvation effect, inhibit crystallization and phase separation, improve wettability and produce a synergistic effect, thereby maximizing the electrochemical performance of the electrolyte at low temperatures. The 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide added in the present invention has an extremely low freezing point and high electrical conductivity, which can significantly improve the low-temperature performance of the electrolyte. At the same time, its unique anionic and cationic structure can effectively inhibit the crystallization of the electrolyte at low temperatures and improve the stability of the electrolyte. The addition of 2,2,2-trifluoroethyl acrylate can introduce a strong electron-withdrawing group trifluoromethyl, thereby reducing the viscosity of the electrolyte and improving the ion mobility; at the same time, the polymer network formed after its polymerization can stabilize the electrolyte structure and inhibit the decomposition of the electrolyte at low temperatures. The ultrasonic-assisted treatment performed in the preparation process of the low-temperature resistant working electrolyte of the present invention can effectively disperse nanomaterials such as boron nitride nanosheets and prevent them from agglomerating. At the same time, it can also reduce phase separation or precipitation in the electrolyte, and by promoting uniform dispersion and sufficient mixing of the components, the ion conduction path in the electrolyte is more unobstructed and the interface impedance is reduced. At the same time, by accelerating the dissolution, dispersion and mixing processes, the time required for traditional stirring is reduced. Therefore, the low-temperature resistant working electrolyte prepared by the present invention has more excellent low-temperature stability, electrical conductivity, and electrochemical properties such as more ideal flash voltage value.

[0035] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A low-temperature resistant working electrolyte for liquid capacitors, characterized in that: The invention comprises the following raw materials in parts by mass: 60-75 parts of ethylene glycol, 20-24 parts of auxiliary solvent, 5-6.5 parts of solute, 1.2-1.5 parts of ammonium hypophosphite, 2-5 parts of synergist, 1-1.5 parts of stabilizer, 0.8-1.5 parts of regulator, 3-6 parts of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 0.1-0.2 parts of boron nitride nanosheets and 2-3 parts of 2,2,2-trifluoroethyl acrylate.

2. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that: The synergist is prepared from manganese dioxide powder and niobium nitrate solution; The stabilizer is any one of sorbitol and diammonium hydrogen phosphate; The regulator is any one of p-nitrophenol, p-nitrobenzyl alcohol and p-nitrobenzoic acid.

3. The low-temperature resistant working electrolyte for liquid capacitors according to claim 2, characterized in that: The auxiliary solvent is obtained by mixing diethylene glycol and propylene glycol; The mass ratio of diethylene glycol to propylene glycol is 5-6.5:15-17.

5.

4. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that: The solute is any one or more of tetraethylammonium tetrafluoroborate, ammonium hydrogen azelaic acid, and formic acid.

5. The low-temperature resistant working electrolyte for liquid capacitors according to claim 1, characterized in that: The preparation method of the synergist is as follows: Step A1: Under an argon atmosphere, treating manganese dioxide powder with a low-temperature plasma to obtain pretreated manganese dioxide; Step A2: adding the pretreated manganese dioxide to the niobium nitrate solution, heating to 80-100° C. under stirring, stirring for 7-10 hours, filtering, washing, and drying to obtain a synergist.

6. The low-temperature resistant working electrolyte for liquid capacitors according to claim 5, characterized in that: The pressure during the low-temperature plasma treatment in step A1 is 30-80 Pa; the power during the low-temperature plasma treatment is 80-160 W; the treatment temperature during the low-temperature plasma treatment is 30-50° C.; and the treatment time during the low-temperature plasma treatment is 10-25 min.

7. The low-temperature resistant working electrolyte for liquid capacitors according to claim 5, characterized in that: The concentration of the niobium nitrate solution in step A2 is 0.01-0.1 mol / L.

8. The low-temperature resistant working electrolyte for liquid capacitors according to claim 5, characterized in that: The ratio of the pretreated manganese dioxide to the niobium nitrate solution in step A2 is 8.7-43.5 g:100 mL.

9. A method for preparing a low-temperature resistant working electrolyte for a liquid capacitor, characterized in that: The preparation method is as follows: Step B1: Add auxiliary solvent to ethylene glycol, stir evenly, then add solute, and continue stirring for 3-5 hours to obtain a composite solvent; Step B2: Add ammonium hypophosphite, a synergist, a stabilizer, a regulator, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, boron nitride nanosheets, and 2,2,2-trifluoroethyl acrylate to the composite solvent in sequence while stirring, and then continue stirring for 12-15 hours under ultrasonic assistance to obtain a low-temperature resistant working electrolyte.

10. The method for preparing a low-temperature resistant working electrolyte for a liquid capacitor according to claim 9, characterized in that: The ultrasonic power during the ultrasonic assistance in step B2 is 80-90W; the ultrasonic frequency during the ultrasonic assistance is 30-45kHz.

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