High-voltage electrolyte for supercapacitor and preparation method of high-voltage electrolyte

Abstract

The invention discloses a high-voltage electrolyte for a supercapacitor and a preparation method of the high-voltage electrolyte, and belongs to the field of supercapacitors. The high-voltage electrolyte comprises acetonitrile, fluoro-ether and double salt; the double salts are quaternary ammonium salt electrolyte salts and imide lithium salts. Through the design of a solvent system and a double-salt system, the voltage window, the cycle life and the safety of the supercapacitor electrolyte are remarkably improved. The method has good compatibility with commercial supercapacitors, and is expected to be widely applied in the field of supercapacitors.

Description

Technical Field

[0001] The present application relates to a high-voltage electrolyte for supercapacitors and a preparation method thereof, and belongs to the field of supercapacitors. Background Art

[0002] As a high-performance energy storage device, supercapacitors have attracted much attention due to their fast charging and discharging capabilities and high power density. However, traditional supercapacitor electrolytes have many limitations in terms of voltage window, safety and low-temperature performance. Existing electrolyte systems mostly focus on a single solvent or a single salt system, which is difficult to meet the requirements of high voltage, wide temperature range and high safety at the same time. For example, patent CN112331734A only involves a single solvent system, and the single salt system electrolyte mentioned has insufficient oxidation potential, and fails to give full play to the synergistic effect of the electrolyte. Traditional electrolytes cannot take into account the contradictions of high voltage, wide temperature range and high safety. Therefore, it is of great practical significance to develop a new high-voltage electrolyte to break through the bottleneck of existing technologies. Summary of the Invention

[0003] The present invention aims to provide a high-voltage electrolyte for supercapacitors and a preparation method thereof, which achieves a synergistic improvement in high-voltage stability, wide temperature range adaptability and high safety through innovative solvent system and dual salt system.

[0004] According to a first aspect of the present application, a high-voltage electrolyte for a supercapacitor is provided.

[0005] A high-voltage electrolyte for a supercapacitor, comprising acetonitrile, a fluoroether, and a double salt;

[0006] The double salt is a quaternary ammonium salt electrolyte salt and an imide lithium salt.

[0007] Optionally, the degree of fluorination of the fluoroether is ≥50%.

[0008] Optionally, the fluorinated ether is selected from at least one of perfluorinated ether and partially fluorinated ether.

[0009] Optionally, the perfluoroether is selected from at least one of perfluorodimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and perfluorinated bis(2,2,2-trifluoroethyl) ether (BTFE);

[0010] The partially fluorinated ether is selected from at least one of 2-fluorophenethyl ether, bis(2-fluoroethoxy)ethane, and methyl nonafluorobutyl ether (MFE).

[0011] Optionally, the volume ratio of acetonitrile to fluoroether is 1:0.2-5.

[0012] Preferably, the volume ratio of acetonitrile to fluoroether is 1:0.5-3.

[0013] Optionally, the quaternary ammonium electrolyte salt is selected from at least one of tetraethylammonium tetrafluoroborate (TEA-BF4) and spiro-1,1-dipyrrolidinium tetrafluoroborate (SBP-BF4);

[0014] The imide lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0015] Optionally, the total concentration of the double salt is 0.5-1.5M.

[0016] Optionally, the molar ratio of the quaternary ammonium electrolyte salt to the imide lithium salt is 5:1 to 1:5.

[0017] The present invention adopts a mixed solvent system of acetonitrile (ACN) and fluoroether, wherein the volume ratio of acetonitrile to fluoroether is accurately controlled at 1: 0.24 to 1: 5. It is verified by experiments that the ratio can balance the contradiction between high dielectric constant and high flash point. Perfluoroether (such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, perfluorinated bis (2,2,2-trifluoroethyl) ether, etc.) or partially fluoroether (such as bis (2-fluoroethoxy) ethane, methyl nonafluorobutyl ether, etc.) are preferably selected, and its degree of fluorination is positively correlated with the oxidation potential of electrolyte. The high solvation ability of acetonitrile (promoting ionic conductivity) and the interfacial film-forming effect (suppressing side reactions) of fluoroether synergistically promote the high-voltage stability of electrolyte.

[0018] This invention utilizes a double salt combination of conventional supercapacitor quaternary ammonium electrolyte salts (such as tetraethylammonium tetrafluoroborate and spiro-1,1-dipyrrolidinium tetrafluoroborate) and imide lithium salts (such as lithium bis(trifluoromethanesulfonyl imide) and lithium bis(fluorosulfonyl imide). The quaternary ammonium salt improves conductivity, while the imide salt broadens the voltage window. The molar ratio is controlled between 5:1 and 1:5, and the total salt concentration is preferably 0.5-1.5M.

[0019] According to a second aspect of the present application, a method for preparing a high-voltage electrolyte for a supercapacitor is provided.

[0020] The high-voltage electrolyte is prepared by mixing acetonitrile and fluoroether, stirring evenly, adding quaternary ammonium salt electrolyte salt and imide lithium salt, and stirring and dissolving until completely transparent to obtain the high-voltage electrolyte.

[0021] Specifically, acetonitrile and fluoroether are mixed in a set ratio at 25° C., stirred evenly, and then quaternary ammonium salt and imide lithium salt are added, and stirred at 500 rpm for 2 hours until completely transparent, thereby obtaining the high-voltage electrolyte.

[0022] Application of the above-mentioned high-voltage electrolyte in supercapacitors.

[0023] Optionally, the applicable temperature range of the electrolyte is -40 to 80°C.

[0024] The electrode material used in conjunction with the electrolyte has a specific surface area > 2000m 2 / g of activated carbon.

[0025] The beneficial effects of this application include:

[0026] The high-voltage electrolyte for supercapacitors and its preparation method provided in this application significantly improve the voltage window, cycle life, and safety of the supercapacitor electrolyte through the design of a solvent system and a dual salt system. They also exhibit good compatibility with commercial supercapacitors and are expected to be widely used in the supercapacitor field. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is a comparison diagram of the cyclic voltammetry curves of Comparative Example 1 and Example 1 under different voltage ranges.

[0028] Figure 2 The linear scans (0.1 mV s -1 )Comparison chart.

[0029] Figure 3 The constant current charge and discharge curves of Comparative Example 1 at different temperature ranges (-30, 30 and 80°C) are shown.

[0030] Figure 4 The constant current charge and discharge curves of Example 1 at different temperature ranges (-30, 30 and 80°C) are shown.

[0031] Figure 5 The constant current charge and discharge curves of Example 2 at different temperature ranges (-30, 30 and 80°C) are shown. DETAILED DESCRIPTION

[0032] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0033] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0034] Unless otherwise specified, conventional methods were used for testing, and instrument settings were those recommended by the manufacturer.

[0035] Comparative Example 1

[0036] At 25° C., tetraethylammonium tetrafluoroborate (TEA-BF 4 ) was added to acetonitrile solvent, with the concentration of TEA-BF 4 being 1 M. The mixture was stirred at 500 rpm for 2 hours until completely transparent, thereby obtaining a commercial electrolyte.

[0037] Example 1

[0038] The volume ratio of acetonitrile to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is 1:1.

[0039] The molar ratio of tetraethylammonium tetrafluoroborate (TEA-BF4) to LiTFSI is 3:1, and the total concentration is 1.0M.

[0040] Preparation process: At 25°C, acetonitrile and TTE were mixed in proportion, stirred evenly, and then TEA-BF4 and LiTFSI were added. The mixture was stirred at 500 rpm for 2 hours until completely transparent to obtain a high-voltage electrolyte.

[0041] Example 2

[0042] The volume ratio of acetonitrile to bis(2-fluoroethoxy)ethane is 1:1.

[0043] The molar ratio of tetraethylammonium tetrafluoroborate (TEA-BF4) to LiFSI is 3:1, and the total concentration is 1.5M.

[0044] Preparation process: At 25°C, acetonitrile and bis(2-fluoroethoxy)ethane were mixed in proportion, stirred evenly, and then TEA-BF4 and LiFSI were added. The mixture was stirred at 500 rpm for 2 hours until completely transparent to obtain a high-voltage electrolyte.

[0045] Examples 3 to 5

[0046] The operation was the same as in Example 1, except that the volume ratios of acetonitrile to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) were 1:2, 1:3, and 1:4, respectively, to obtain a high-voltage electrolyte.

[0047] Examples 6 to 8

[0048] The operation was the same as that in Example 1, except that the fluorinated ethers used were perfluorodimethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, and 2-fluorophenyl ethyl ether, respectively, to obtain a high-voltage electrolyte.

[0049] The electrical performance of the high-voltage electrolytes of Comparative Example 1 and Examples 1 and 2 was tested using the following method and process:

[0050] (1) Assembly of supercapacitors: Take a number of commercial activated carbon electrode sheets (cut into round pieces with sizes matching the button battery shell), place them in the order of positive electrode shell, electrode, diaphragm, electrode, gasket, and spring, add a certain amount of electrolyte, generally enough to fully soak the electrode and diaphragm; align the negative electrode shell and the positive electrode shell of the battery shell, use a dedicated button battery sealing device, and seal the battery shell tightly according to a certain pressure and method. After the packaging is completed, the assembled button supercapacitor can be left at room temperature for one day to allow the electrolyte to fully soak the electrode and diaphragm, and to allow the electrochemical system inside the capacitor to reach a relatively stable state.

[0051] (2) Electrochemical testing of supercapacitors: The assembled supercapacitors were placed on an electrochemical workstation and subjected to cyclic voltammetry and linear sweep tests. The scanning potential range of the cyclic voltammetry test was set to 0V to 2.7V (or 3V) with a scan rate of 1mV / s; the scanning potential range of the linear sweep test was set to 0V to 5V with a scan rate of 0.1mV / s to observe the electrochemical behavior of the capacitor at different rates. The supercapacitors were connected to a constant current charge and discharge tester with a charge and discharge current density of 0.2A / g and a cutoff voltage of 3, 3.1 or 3.2V.

[0052] Figure 1 The figure shows a comparison of the cyclic voltammetry curves of Comparative Example 1 and Example 1 at different voltage ranges. At the voltage windows of 2.7V and 3V, the curve of Example 1 is closer to an ideal rectangle and has a smaller polarization current, demonstrating that Example 1 has a wider and more stable voltage window.

[0053] Figure 2 The linear scans (0.1 mV s -1 The smaller polarization current of Example 1 and the larger reaction current of Comparative Example 1 indicate that the electrolyte has insufficient antioxidant capacity and a narrow electrolyte voltage window.

[0054] Figure 3 The constant current charge and discharge curves of comparative example 1 at different temperature ranges (-30, 30 and 80°C) show that the constant current charge and discharge curve of the comparative example is obviously polarized at 3V voltage and 30°C, and cannot be charged and discharged normally at 80°C.

[0055] Figure 4 The constant current charge and discharge curves of Example 1 at different temperature ranges (-30, 30 and 80°C) are shown. It can be seen that within the temperature range of -30 to 80°C, the supercapacitor has a stable charge and discharge curve at a voltage of 3V and can work normally.

[0056] Figure 5The constant current charge and discharge curves of Example 2 at different temperature ranges (-30, 30 and 80°C) show that within the temperature range of -30 to 80°C, the supercapacitor has a stable charge and discharge curve at a voltage of 3.2V and can work normally.

[0057] The result data of the voltage window, capacitance retention at -30°C / 80°C, and capacitance retention after 10,000 cycles of Comparative Example 1 and Examples 1-4 are shown in Table 1.

[0058] Table 1: Comparison of voltage window, capacitance retention at -30°C / 80°C, and capacity decay rate after 10,000 cycles.

[0059]

[0060] As can be seen in Table 1, the maximum operating voltage of the comparative example does not exceed 3V, and the supercapacitor cannot stably charge and discharge when the temperature rises to 80°C. However, the examples incorporating fluorinated ether and imide lithium salts significantly improve both the operating voltage window and high-temperature performance. Example 2 achieves a capacity retention rate of 97.2% after 10,000 cycles at a high voltage of 3.2V, far exceeding the performance of the comparative example.

[0061] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A high-voltage electrolyte for supercapacitors, characterized in that: The high-voltage electrolyte includes acetonitrile, fluoroether and double salt; The double salt is a quaternary ammonium salt electrolyte salt and an imide lithium salt.

2. The high-voltage electrolyte according to claim 1, characterized in that The degree of fluorination of the fluoroether is ≥50%.

3. The high-voltage electrolyte according to claim 2, characterized in that The fluorinated ether is selected from at least one of perfluorinated ether and partially fluorinated ether; Preferably, the perfluoroether is selected from at least one of perfluorodimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and perfluorinated bis(2,2,2-trifluoroethyl) ether; The partially fluorinated ether is selected from at least one of 2-fluorophenethyl ether, bis(2-fluoroethoxy)ethane, and methyl nonafluorobutyl ether.

4. The high-voltage electrolyte according to claim 1, characterized in that The volume ratio of acetonitrile to fluoroether is 1:0.2-5; Preferably, the volume ratio of acetonitrile to fluoroether is 1:0.5-3.

5. The high-voltage electrolyte according to claim 1, characterized in that The quaternary ammonium salt electrolyte salt is selected from at least one of tetraethylammonium tetrafluoroborate and spiro-1,1-dipyrrolidinium tetrafluoroborate; The imide lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

6. The high-voltage electrolyte according to claim 1, characterized in that The total concentration of the double salt is 0.5-1.5M.

7. The high-voltage electrolyte according to claim 1, characterized in that The molar ratio of the quaternary ammonium electrolyte salt to the imide lithium salt is 5:1 to 1:

5.

8. The method for preparing a high-voltage electrolyte according to any one of claims 1 to 7, characterized in that: Acetonitrile and fluoroether are mixed and stirred evenly, and then quaternary ammonium salt electrolyte salt and imide lithium salt are added and stirred and dissolved until completely transparent to obtain the high-voltage electrolyte.

9. Use of the high-voltage electrolyte according to any one of claims 1 to 7 in a supercapacitor.

10. The use according to claim 9, characterized in that The applicable temperature range of the electrolyte is -40 to 80°C.

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