Multi-solvent low-temperature high-voltage electrolyte for supercapacitor, method and application

Abstract

According to the multi-solvent low-temperature high-voltage electrolyte for the supercapacitor, the method and the application, EA (ethyl acetate) and EB (ethyl butyrate) are added into a common solvent AN (acetonitrile) to serve as organic cosolvents, and the viscosity and the melting point of the electrolyte can be effectively reduced by mixing high-voltage-resistant and low-temperature-resistant imidazole ionic liquid; meanwhile, the stability of the electrolyte at high voltage is improved, the ionic conductivity of the electrolyte at low temperature is remarkably improved, and it is guaranteed that a supercapacitor using the electrolyte has excellent rate capability and cycling stability at the low temperature of-60 DEG C and the high voltage of 3.5 V.

Description

Technical Field

[0001] The present invention belongs to the field of supercapacitor electrochemical technology, and specifically relates to a multi-solvent low-temperature high-voltage electrolyte for supercapacitors, a method and an application thereof. Background Art

[0002] Supercapacitors face challenges at low temperatures, including electrolyte freezing, sluggish ion transport between electrodes and electrolytes, and excessively high charge transfer resistance at the electrode-electrolyte interface, hindering their proper operation. Therefore, developing excellent low-temperature electrolytes to enable supercapacitors to operate at the lowest possible temperatures is crucial for the development of low-temperature electronic devices and equipment. Researchers have primarily focused on reducing the viscosity and melting point of electrolytes to prepare low-temperature electrolytes. Adding salt, similar to sprinkling salt to melt ice and snow, forms hydrated ions with free water molecules, reducing hydrogen bonding and thus lowering the freezing point of aqueous electrolytes. Furthermore, the addition of salt can enhance the electrolyte's ionic conductivity. Furthermore, the introduction of antifreeze additives, such as high-concentration inorganic salts, eutectic organic compounds, or ionic liquids, can lower the freezing point of the electrolyte, enabling low-temperature operation. However, aqueous electrolytes typically exhibit a relatively low operating voltage window (typically less than 1.2 V), and ionic liquids exhibit high viscosities, making them unsuitable for use as standalone electrolytes in environments below -20°C. Consequently, many researchers have shifted their research focus to optimizing organic electrolytes.

[0003] The combination of ionic liquids and organic solvents has gradually become the mainstream research direction of low-temperature electrolytes in recent years. Ester solvents such as methyl acetate (MA), methyl butyrate (MB), methyl formate (MF) and ethyl acetate (EA) with low melting point characteristics are often blended with solvents with low viscosity and high dielectric constants such as acetonitrile (AN) to prepare co-solvents. By changing the dipole-dipole interaction between solvents and the ion-dipole interaction between salts and solvents, the operating temperature of the electrolyte can be effectively reduced and the ion transport performance can be improved. The development of ternary and higher-polymer solvents has also gradually become a research trend in low-temperature electrolytes to increase the dielectric constant of the electrolyte and reduce its viscosity, thereby improving the low-temperature electrochemical performance of the electrolyte. Therefore, the introduction of ionic liquids and the compounding of low-melting-point, low-viscosity solvents to optimize organic electrolytes can be an effective way to improve the low-temperature electrochemical performance of electrolytes, which is of vital practical significance. Summary of the Invention

[0004] To address the problems in the prior art, the present invention provides a multi-solvent, low-temperature, high-voltage electrolyte for supercapacitors, a method, and applications thereof. The addition of EA (ethyl acetate) and EB (ethyl butyrate) as organic cosolvents to the commonly used solvent AN, along with a high-voltage and low-temperature resistant imidazole ionic liquid, effectively reduces the viscosity and melting point of the electrolyte while improving its stability at high voltages. This significantly enhances the electrolyte's ionic conductivity at low temperatures, ensuring that supercapacitors using this electrolyte exhibit excellent rate performance and cycling stability at -60°C and a high voltage of 3.5V. Furthermore, the electrolyte is simple and easy to prepare at low cost.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors, wherein the solvent in the electrolyte is a mixture of acetonitrile, ethyl acetate, and ethyl butyrate; and the ionic liquid is a high-pressure and low-temperature resistant imidazole ionic liquid.

[0006] Furthermore, the volume fraction of the acetonitrile is 30% to 60%, the volume fraction of the ethyl acetate is 20% to 35%, and the volume fraction of the ethyl butyrate is 20% to 35%.

[0007] The present invention also provides a method for preparing a multi-solvent low-temperature high-voltage electrolyte for supercapacitors, the specific steps of which are as follows:

[0008] Under a protective gas environment, the dehydrated acetonitrile, ethyl acetate, and ethyl butyrate are mixed and stirred to obtain a mixed liquid;

[0009] A high-voltage and low-temperature resistant imidazole ionic liquid is added to the mixed solution, and the mixture is mixed and stirred to obtain a multi-solvent low-temperature and high-voltage electrolyte.

[0010] Furthermore, in the step of mixing and stirring the dehydrated acetonitrile, ethyl acetate and ethyl butyrate under a protective gas environment to obtain a mixed solution:

[0011] Molecular sieves were added to acetonitrile, ethyl acetate and ethyl butyrate solvents respectively for dehydration, ensuring that the water content of the solvent after dehydration was less than 0.05% of the solvent mass;

[0012] Under a protective gas environment, the dehydrated acetonitrile, ethyl acetate and ethyl butyrate solvent are stirred at 200 r / min to 400 r / min for 20 min to 40 min.

[0013] Furthermore, in the step of adding a high-voltage and low-temperature resistant imidazole ionic liquid to the mixed solution, mixing and stirring to obtain a multi-solvent low-temperature and high-voltage electrolyte:

[0014] The high pressure and low temperature resistant imidazole ionic liquid is based on BF 4- With PF 6-The invention relates to an anionic high-pressure and low-temperature resistant imidazole ionic liquid, wherein the concentration of the high-pressure and low-temperature resistant imidazole ionic liquid is 0.5 mol / L to 1.5 mol / L.

[0015] Furthermore, the BF 4- With PF 6- The high-pressure and low-temperature resistant imidazolium ionic liquid as an anion is specifically: 1-butyl-3-methylimidazolium tetrafluoroborate or 1-hexyl-3-methylimidazolium hexafluorophosphate.

[0016] Furthermore, in the step of adding a high-voltage and low-temperature resistant imidazole ionic liquid to the mixed solution, mixing and stirring to obtain a multi-solvent low-temperature and high-voltage electrolyte:

[0017] The stirring speed is 200 r / min to 400 r / min, and the stirring time is 20 min to 40 min.

[0018] The present invention also provides a supercapacitor, wherein the solvent of the electrolyte of the supercapacitor is a mixed solution of acetonitrile, ethyl acetate and ethyl butyrate.

[0019] Furthermore, in the mixed solution, the volume fraction of the acetonitrile is 30% to 60%, the volume fraction of the ethyl acetate is 20% to 35%, and the volume fraction of the ethyl butyrate is 20% to 35%.

[0020] Furthermore, the ionic liquid of the electrolyte is a high-pressure and low-temperature resistant imidazole ionic liquid, and the concentration of the high-pressure and low-temperature resistant imidazole ionic liquid is 0.5 mol / L to 1.5 mol / L.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The present invention proposes a multi-solvent, low-temperature, high-voltage electrolyte for supercapacitors. The selected acetonitrile (AN), ethyl acetate (EA), and ethyl butyrate (EB) are all common commercially available solvents with relatively low cost. Acetonitrile itself has a certain degree of low-temperature adaptability. Ethyl acetate and ethyl butyrate, when mixed with acetonitrile as organic co-solvents, can improve the chemical environment of the electrolyte, reduce side reactions that may occur at high voltages, enhance the electrochemical stability of the electrolyte at high voltages, and optimize the electrolyte's low-temperature characteristics. Supercapacitors using the electrolyte of the present invention can operate stably at a high voltage of 3.5V in an extreme low-temperature environment of -60°C, meeting the demand for high-performance power supplies in modern electronic devices.

[0023] The present invention rationally blends the solvent volume fractions (30% to 60% acetonitrile, 20% to 5% ethyl acetate, and 20% to 35% ethyl butyrate). The resulting mixed solvent system effectively reduces the viscosity and melting point of the electrolyte. Even at extremely low temperatures of -60°C, the electrolyte maintains high ionic conductivity, significantly improving ion transport efficiency at low temperatures. This ensures the supercapacitor can function properly under these conditions, broadening its application temperature range and making it adaptable to more complex and harsh environments.

[0024] The solvent of the present invention is combined with BF 4- With PF 6- The high-voltage and low-temperature resistant imidazole ionic liquid with an anion further enhances the tolerance of the electrolyte under high voltage, so that the supercapacitor using this electrolyte can operate stably at a high voltage of 3.5V, with excellent rate performance and cycle stability, greatly improving the energy density and power density of the supercapacitor, and meeting the needs of modern electronic devices for high-performance power supplies.

[0025] The present invention provides a method for preparing a multi-solvent, low-temperature, high-voltage electrolyte for supercapacitors, which has numerous advantages, including simple operation, easy control, and low cost. The entire preparation process is carried out under a protective gas environment. Molecular sieves are added to the solvent for dehydration, and the solvent water content is strictly controlled to be below 0.05% of the solvent mass, thereby ensuring the quality and performance of the electrolyte. Subsequently, the dehydrated solvent is mixed and stirred, and a high-pressure and low-temperature resistant imidazole ionic liquid is added and stirred continuously. The entire process has clear steps, does not require complex equipment or harsh conditions, and is easily promoted and applied on a large scale in industrial production, thereby reducing preparation costs and improving production efficiency.

[0026] The present invention provides a supercapacitor that utilizes the multi-solvent, low-temperature, high-voltage electrolyte of the present invention. The supercapacitor can operate stably at a low temperature of -60°C and a high voltage of 3.5V, exhibiting excellent rate performance and cycle stability. This means that it can still charge and discharge rapidly in extremely low-temperature environments, meeting high power requirements, while also having a long service life and reducing replacement and maintenance costs. In addition, due to the low cost of the electrolyte, the overall cost of the supercapacitor is also reduced, making it more competitive in the market and capable of being widely used in various electronic devices with high temperature and voltage requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a low-temperature optical image of the electrolyte of an embodiment of the present invention at -60°C;

[0028] Figure 2 The differential scanning calorimetry (DSC) diagram of the electrolyte of the embodiment of the present invention is shown in FIG.

[0029] Figure 3 ion conductivity diagram of the electrolyte at different temperatures in a button-type supercapacitor according to an embodiment of the present invention;

[0030] Figure 4 This is the ionic conductivity diagram of the electrolyte in a button-type supercapacitor according to an embodiment of the present invention at -60°C;

[0031] Figure 5 This is a linear sweep voltammetry (LSV) curve of the electrolyte in a button-type supercapacitor according to an embodiment of the present invention;

[0032] Figure 6 This is a charge-discharge curve (GCD) diagram of the electrolyte of an embodiment of the present invention in a button-type supercapacitor at -60°C and 3.5V. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] The present invention provides a multi-solvent low-temperature high-voltage electrolyte for supercapacitors, which is prepared by the following steps:

[0035] S1: Add appropriate amount of molecular sieves to acetonitrile (AN), ethyl acetate (EA) and ethyl butyrate (EB) solvents for physical dehydration, ensuring that the water content of the solvent after dehydration is less than 0.05% of the solvent mass;

[0036] S2: The three dehydrated solvents obtained in step S1 are uniformly mixed and stirred using a magnetic stirrer in a glove box filled with argon to obtain a mixed solution;

[0037] S3: Will be BF 4- With PF 6- A high-pressure and low-temperature resistant imidazole ionic liquid is added to the mixed solution, and a low-temperature electrolyte is obtained after magnetic stirring for a period of time;

[0038] Preferably, BF 4- With PF 6-The high-pressure and low-temperature resistant imidazolium ionic liquids as anions are specifically: 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) or 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF6);

[0039] S4: The low-temperature electrolyte prepared in step S3 is used to assemble supercapacitors, including button-type, cylindrical, soft-pack, etc.

[0040] Specifically, in step S1, the volume fraction of AN is 30% to 60%, the volume fraction of EA is 20% to 35%, and the volume fraction of EB is 20% to 35%; the concentration of the high-pressure and low-temperature resistant imidazole ionic liquid is 0.5 mol / L to 1.5 mol / L.

[0041] Specifically, in step S2, the speed of the magnetic stirring treatment is 200 r / min to 400 r / min, and the time of the magnetic stirring is 20 min to 40 min.

[0042] Specifically, in step S3, the speed of the magnetic stirring treatment is 200 r / min to 400 r / min, and the time of the magnetic stirring is 20 min to 40 min.

[0043] Example 1

[0044] This embodiment provides a multi-solvent low-temperature, high-voltage electrolyte for supercapacitors, and the preparation method thereof is as follows:

[0045] (1) adding molecular sieves to the solvent for physical dehydration to control the water content of the solvent to 10 ppm; in a glove box filled with argon, uniformly mixing the physically dehydrated solvent;

[0046] In step (1), the purity of the solvent is 99.99 wt %;

[0047] In step (1), the solvent is a mixture of acetonitrile (AN), ethyl acetate (EA) and ethyl butyrate (EB) in a volume ratio of 2:1:1 (volume fractions of 50%, 25%, and 25%);

[0048] In step (1), the speed of magnetic stirring is 300 r / min, and the time of magnetic stirring is 30 min;

[0049] (2) adding the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate BMIMBF4 to the mixture and magnetically stirring for a certain period of time to obtain a low-temperature electrolyte based on BMIMBF4 / AN-EB-EA;

[0050] In step (2), the speed of magnetic stirring is 300 r / min, and the time of magnetic stirring is 30 min;

[0051] In step (2), the concentration of BMIMBF4 in the low-temperature electrolyte is 1 mol / L.

[0052] Example 2

[0053] This embodiment provides a multi-solvent low-temperature, high-voltage electrolyte for supercapacitors, and the preparation method thereof is as follows:

[0054] (1) adding molecular sieves to the solvent for physical dehydration to control the water content of the solvent to 10 ppm; in a glove box filled with argon, uniformly mixing the physically dehydrated solvent;

[0055] In step (1), the purity of the solvent is 99.99 wt %;

[0056] In step (1), the solvent is a mixture of acetonitrile (AN), ethyl acetate (EA) and ethyl butyrate (EB) in a volume ratio of 1:1:1 (volume fractions of 35%, 35%, and 35%);

[0057] In step (1), the speed of magnetic stirring is 200 r / min, and the time of magnetic stirring is 40 min;

[0058] (2) adding the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate BMIMBF4 to the mixture and magnetically stirring for a certain period of time to obtain a low-temperature electrolyte based on BMIMBF4 / AN-EB-EA;

[0059] In step (2), the speed of magnetic stirring is 200 r / min, and the time of magnetic stirring is 40 min;

[0060] In step (2), the concentration of BMIMBF4 in the low-temperature electrolyte is 0.5 mol / L.

[0061] Example 3

[0062] This embodiment provides a multi-solvent low-temperature, high-voltage electrolyte for supercapacitors, and the preparation method thereof is as follows:

[0063] (1) adding molecular sieves to the solvent for physical dehydration to control the water content of the solvent to 10 ppm; in a glove box filled with argon, uniformly mixing the physically dehydrated solvent;

[0064] In step (1), the purity of the solvent is 99.99 wt %;

[0065] In step (1), the solvent is a mixture of acetonitrile (AN), ethyl acetate (EA) and ethyl butyrate (EB) in a volume ratio of 3:1:1 (volume fractions of 60%, 20%, and 20%);

[0066] In step (1), the speed of magnetic stirring is 400 r / min, and the time of magnetic stirring is 20 min;

[0067] (2) adding the ionic liquid BMIMBF4 to the mixture and magnetically stirring for a certain period of time to obtain a low-temperature electrolyte based on BMIMBF4 / AN-EB-EA;

[0068] In step (2), the speed of magnetic stirring is 400 r / min, and the time of magnetic stirring is 20 min;

[0069] In step (2), the concentration of BMIMBF4 in the low-temperature electrolyte is 1.5 mol / L.

[0070] Example 4

[0071] This embodiment provides a multi-solvent low-temperature, high-voltage electrolyte for supercapacitors, and the preparation method thereof is as follows:

[0072] (1) adding molecular sieves to the solvent for physical dehydration to control the water content of the solvent to 10 ppm; in a glove box filled with argon, uniformly mixing the physically dehydrated solvent;

[0073] In step (1), the purity of the solvent is 99.99 wt %;

[0074] In step (1), the solvent is a mixture of acetonitrile (AN), ethyl acetate (EA) and ethyl butyrate (EB) in a volume ratio of 1:1:1 (volume fractions of 30%, 30%, and 30%);

[0075] In step (1), the speed of magnetic stirring is 200 r / min, and the time of magnetic stirring is 40 min;

[0076] (2) adding the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate HMIMPF6 to the mixture and magnetically stirring for a certain period of time to obtain a low-temperature electrolyte based on HMIMPF6 / AN-EB-EA;

[0077] In step (2), the speed of magnetic stirring is 200 r / min, and the time of magnetic stirring is 40 min;

[0078] In step (2), the concentration of HMIMPF6 in the low-temperature electrolyte is 1.2 mol / L.

[0079] Comparative Example

[0080] This embodiment provides an electrolyte for supercapacitors, and the preparation method thereof is as follows:

[0081] (1) adding molecular sieves to the solvent for physical dehydration to control the water content of the solvent to 10 ppm; in a glove box filled with argon, uniformly mixing the physically dehydrated solvent;

[0082] In step (1), the purity of the solvent is 99.99 wt %;

[0083] In step (1), the solvent is a mixture of acetonitrile (AN) and ethyl butyrate (EB) in a volume ratio of 1:1;

[0084] (2) adding the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate BMIMBF4 to the mixture and magnetically stirring for a certain period of time to obtain a low-temperature electrolyte based on BMIMBF4 / AN-EB;

[0085] In step (2), the speed of magnetic stirring is 300 r / min, and the time of magnetic stirring is 30 min;

[0086] In step (2), the concentration of BMIMBF4 in the low-temperature electrolyte is 1 mol / L.

[0087] Figure 1 The experiment of storing the low-temperature electrolyte prepared by Example 1, Comparative Example and 1M BMIMBF4 / AN at -60°C; Figure 1 It can be observed that the 1M BMIMBF4 / AN-EB-EA and 1MBMIMBF4 / AN-EB low-temperature electrolytes prepared in Example 1 and the comparative example remain liquid and have good fluidity when stored at -60°C, while the 1M BMIMBF4 / AN electrolyte solidifies at -60°C. It can be seen that the multi-solvent electrolyte prepared by introducing the low-melting-point solvents EB and EA has a low freezing point.

[0088] Figure 2 Differential scanning calorimetry (DSC) of different electrolytes is shown. The solidification temperature T of the DSC curve of pure AN g =-51.47℃, while the solidification temperature of 1M BMIMBF4 / AN electrolyte is T g =-60.41°C. With the addition of EA and EB solvents, the freezing points of the electrolytes of Example 1 and the comparative example (1M BMIMBF4 / AN-EB-EA, 1M BMIMBF4 / AN-EB) dropped to below -80°C, which may be due to the increase in entropy in the mixture system.

[0089] The electrolytes obtained in Example 1 and the comparative example and the 1M BMIMBF4 / AN electrolyte were placed in a high-low temperature alternating test chamber at temperatures of 20°C, 0°C, -20°C, -40°C, and -60°C, and their conductivity was measured at different temperatures. Figure 3 and Figure 4The conductivity of the three electrolytes at different temperatures was compared. At 20°C, all three exhibited high ionic conductivity. As the temperature decreased, the ionic conductivity decreased, but the ionic conductivity of 1M BMIMBF4 / AN remained high. However, the electrolyte prepared with pure acetonitrile solvent had severe side reactions at high voltage and poor stability. At -60°C, due to the crystallization of the 1M BMIMBF4 / AN electrolyte, the ionic conductivity dropped rapidly, with a significant drop at -40°C. The other two samples showed a slow downward trend overall, without showing a significant drop. Figure 4 It can be clearly seen that 1M BMIMBF4 / AN-EB-EA electrolyte has excellent ion migration ability at -60℃.

[0090] In the 1M BMIMBF4 / AN-EB-EA low-temperature electrolyte prepared in Example 1, Ag||SS batteries were assembled using silver sheets and stainless steel sheets. The test temperature was -20°C and linear sweep voltammetry (LSV) was used at a speed of 10 mV s -1 The electrochemical stability window of the supercapacitor was tested in the range of -1V to 6V at a scan rate of Figure 5 It can be seen that the voltage window (OVW) of 1M BMIMBF4 / AN is only 1.3 V; the voltage window (OVW) of 1M BMIMBF4 / AN-EB in the comparative example is 1.5 V; and the voltage window (OVW) of 1M BMIMBF4 / AN-EB-EA in Example 1 is 3.0 V. This proves that the synergistic effect of multiple solvents can broaden the voltage window of the electrolyte.

[0091] Figure 6 The GCD curves of the 1MBMIMBF4 / AN-EB-EA electrolyte prepared in Example 1 and the 1M commercial electrolyte at different current densities under the working conditions of -60°C and 3.5V were compared. It can be seen from the figure that under the conditions of -60°C and 3.5V, the GCD curve of the electrolyte prepared in Example 1 is an isosceles triangle, and the charge and discharge time is significantly longer than that of the 1M commercial electrolyte using the same electrode mass, indicating that it has good charge and discharge performance at different current densities, verifying its excellent rate performance at low temperature and outstanding electrochemical stability at high voltage.

[0092] In summary, the present invention provides a multi-solvent low-temperature, high-voltage electrolyte for supercapacitors. The solvents and ionic liquids used are low-cost and have been commercialized. The prepared low-temperature electrolyte has a large ionic conductivity and a small charge transfer impedance at -60°C, a large operating voltage window, electrochemical stability, and high rate performance, and can be used in high-voltage supercapacitors.

[0093] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A multi-solvent low-temperature and high-voltage electrolyte for supercapacitors, characterized in that: The solvent in the electrolyte is a mixture of acetonitrile, ethyl acetate and ethyl butyrate; and the ionic liquid is an imidazole ionic liquid that is resistant to high pressure and low temperature.

2. The multi-solvent low-temperature and high-voltage electrolyte for supercapacitors according to claim 1, characterized in that: The volume fraction of the acetonitrile is 30% to 60%, the volume fraction of the ethyl acetate is 20% to 35%, and the volume fraction of the ethyl butyrate is 20% to 35%.

3. A method for preparing a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors, characterized in that: The specific steps are as follows: Under a protective gas environment, the dehydrated acetonitrile, ethyl acetate, and ethyl butyrate are mixed and stirred to obtain a mixed liquid; A high-voltage and low-temperature resistant imidazole ionic liquid is added to the mixed solution, and the mixture is mixed and stirred to obtain a multi-solvent low-temperature and high-voltage electrolyte.

4. The method for preparing a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors according to claim 3, characterized in that: In the step of mixing and stirring the dehydrated acetonitrile, ethyl acetate and ethyl butyrate under a protective gas environment to obtain a mixed solution: Molecular sieves were added to acetonitrile, ethyl acetate and ethyl butyrate solvents respectively for dehydration, ensuring that the water content of the solvent after dehydration was less than 0.05% of the solvent mass; Under a protective gas environment, the dehydrated acetonitrile, ethyl acetate and ethyl butyrate solvent are stirred at 200 r / min to 400 r / min for 20 min to 40 min.

5. The method for preparing a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors according to claim 3, characterized in that: In the step of adding a high-voltage and low-temperature resistant imidazole ionic liquid to the mixed solution, mixing and stirring to obtain a multi-solvent low-temperature and high-voltage electrolyte: The high pressure and low temperature resistant imidazole ionic liquid is based on BF 4- With PF 6- The invention relates to an anionic high-pressure and low-temperature resistant imidazole ionic liquid, wherein the concentration of the high-pressure and low-temperature resistant imidazole ionic liquid is 0.5 mol / L to 1.5 mol / L.

6. The method for preparing a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors according to claim 5, characterized in that: The BF 4- With PF 6- The high-pressure and low-temperature resistant imidazolium ionic liquid as an anion is specifically: 1-butyl-3-methylimidazolium tetrafluoroborate or 1-hexyl-3-methylimidazolium hexafluorophosphate.

7. The method for preparing a multi-solvent low-temperature and high-voltage electrolyte for supercapacitors according to claim 3, characterized in that: In the step of adding a high-voltage and low-temperature resistant imidazole ionic liquid to the mixed solution, mixing and stirring to obtain a multi-solvent low-temperature and high-voltage electrolyte: The stirring speed is 200 r / min to 400 r / min, and the stirring time is 20 min to 40 min.

8. A supercapacitor, characterized in that: The solvent of the electrolyte of the supercapacitor is a mixed solution of acetonitrile, ethyl acetate and ethyl butyrate.

9. The supercapacitor according to claim 8, characterized in that: In the mixed liquid, the volume fraction of the acetonitrile is 30% to 60%, the volume fraction of the ethyl acetate is 20% to 35%, and the volume fraction of the ethyl butyrate is 20% to 35%.

10. The supercapacitor according to claim 8, characterized in that: The ionic liquid of the electrolyte is a high-pressure and low-temperature resistant imidazole ionic liquid, and the concentration of the high-pressure and low-temperature resistant imidazole ionic liquid is 0.5 mol / L to 1.5 mol / L.

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