A dual-cationic ionic liquid, its preparation method and an electrolyte for a supercapacitor

Abstract

The present invention provides a dicationic ionic liquid, a preparation method thereof, and an electrolyte for a supercapacitor, relating to the technical field of supercapacitors. The present invention provides a dicationic ionic liquid having a structure shown in any one of Formula 1 to Formula 4. The present invention provides a cyclic amine-based dicationic ionic liquid with imidazole, pyrrolidine, pyridine or piperidine as the cation core group. Compared with the monocationic ionic liquid, the dicationic ionic liquid has better thermal stability and surface ion density, can significantly improve the electrochemical working window, and thus greatly improves the defect of low device energy density. Moreover, the dicationic ionic liquid has the same excellent impedance performance as the monocationic ionic liquid, and also has a high discharge specific capacity and excellent cycle performance. When the dicationic ionic liquid provided by the present invention is formulated into an electrolyte for assembling a supercapacitor, a stable working window of up to 3.2 V can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of supercapacitors, and particularly to a dicationic ionic liquid, a preparation method thereof, and a supercapacitor electrolyte. Background Art

[0002] Supercapacitors have the characteristics of high power density, ultra-long life, and fast charge and discharge, which enable them to have a wide range of application scenarios in short-term high-power occasions. Especially in the field of electric vehicles, they are often used in combination with power batteries, which can effectively alleviate the damage to the battery caused by large-current charge and discharge and extend the service life of the battery; in addition, supercapacitors are also widely used in fields such as portable electronic devices, power systems, rail transit, and smart grids.

[0003] The main problem faced by supercapacitors is their low energy density. As a key component of supercapacitors, the electrolyte directly determines the overall performance of the device. Since the energy density of a supercapacitor is proportional to the square of its working voltage, therefore, finding ways to increase its working window has become an important research direction for supercapacitors. Currently, the commercially available electrolyte is mainly an electrolyte formed by dissolving tetraethylammonium tetrafluoroborate (TEABF4) in propylene carbonate (PC) or acetonitrile (AN), and its window can only reach 2.7V. Therefore, exploring electrolytes that can achieve a high voltage window is an urgent problem to be solved at present. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a dicationic ionic liquid, a preparation method thereof, and a supercapacitor electrolyte. Using the dicationic ionic liquid provided by the present invention in a supercapacitor electrolyte can effectively increase the working window of the supercapacitor.

[0005] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a dicationic ionic liquid having any one of the structures shown in Formula 1 to Formula 4:

[0007]

[0008]

[0009] In Formula 1 to Formula 4, R is a straight-chain alkyl group with a carbon atom number less than or equal to 6, 1 ≤ a ≤ 16, and Y - is TFSI - 、BF4 - or PF6 - .

[0010] Preferably, the R is methyl, ethyl or butyl.

[0011] Preferably, 2 ≤ a ≤ 10.

[0012] Preferably, the dicationic ionic liquid is any one of the following compounds:

[0013]

[0014]

[0015] The present invention provides a preparation method of the dicationic ionic liquid described in the above technical solution, including the following steps:

[0016] Mix a cyclic amine compound with a dihaloalkane for a nucleophilic reaction to obtain a dicationic halide salt;

[0017] Mix the dicationic halide salt, an anion source and a solvent for an ion exchange reaction to obtain the dicationic ionic liquid; the anion source is a tetrafluoroborate, a hexafluorophosphate or a bis(trifluoromethylsulfonyl)imide salt;

[0018] The cyclic amine compound has a structure shown in any one of Formulas 5 to 8:

[0019]

[0020] The dihaloalkane has a structure shown in Formula 9:

[0021] In Formula 9, X is Cl, Br or I.

[0022] Preferably, the molar ratio of the dihaloalkane to the cyclic amine compound is (1.0 - 1.1):2; the temperature of the nucleophilic reaction is 40 - 70 °C, and the time is 8 - 16 h.

[0023] Preferably, when the anion source is a tetrafluoroborate, the solvent is acetonitrile; when the anion source is a hexafluorophosphate or a bis(trifluoromethylsulfonyl)imide salt, the solvent is water.

[0024] Preferably, the molar ratio of the dicationic halide salt to the anion source is 1:(2 - 2.1); the temperature of the ion exchange reaction is 20 - 70 °C, and the reaction time is 4 - 16 h.

[0025] The present invention provides a supercapacitor electrolyte, including an electrolyte and an organic solvent, wherein the electrolyte is the dicationic ionic liquid described in the above technical solution or the dicationic ionic liquid prepared by the preparation method described in the above technical solution.

[0026] Preferably, the concentration of the electrolyte in the electrolyte solution is 0.5 - 2.0 mol / L.

[0027] Preferably, the organic solvent includes an ester solvent and / or a nitrile solvent.

[0028] The present invention provides a dicationic ionic liquid having any of the structures shown in Formulas 1 to 4. The dicationic ionic liquid provided by the present invention is a cyclic amine-based dicationic ionic liquid with imidazole, pyrrolidine, pyridine or piperidine as the cation core group, and its anion is a relatively stable tetrafluoroborate, hexafluorophosphate, bis(trifluoromethylsulfonyl)imide anion. The dicationic ionic liquid has better thermal stability and surface ion density compared with the monocationic ionic liquid, can significantly improve the electrochemical working window, and thus greatly improve the defect of low device energy density; and the dicationic ionic liquid has the same excellent impedance performance as the monocationic ionic liquid, and at the same time has a high discharge specific capacity and excellent cycle performance.

[0029] The present invention provides a preparation method of the dicationic ionic liquid described in the above technical solution, which has a simple process, is easy to scale up production, and has an extremely high yield.

[0030] The present invention also provides a supercapacitor electrolyte, which includes an electrolyte and an organic solvent. The electrolyte is the dicationic ionic liquid described in the above technical solution or the dicationic ionic liquid prepared by the preparation method described in the above technical solution. The supercapacitor electrolyte provided by the present invention can make the supercapacitor have the characteristics of a high window and high stability. The results of the examples show that when a supercapacitor is assembled with the electrolyte provided by the present invention, a stable working window of up to 3.2 V can be achieved. When a constant current charge-discharge cycle test is carried out at a current density of 1 A / g, after 10,000 cycles, the capacity retention rate is 74.6 - 86.9%. Description of the Drawings

[0031] Figure 1 1H NMR spectrum of the bisimidazole tetrafluoroborate (C4Im·2BF4) with a bridging group of C4H8 prepared in Example 2; 1 1H NMR spectrum;

[0032] Figure 2 Cyclic voltammetry test chart of a supercapacitor assembled with an electrolyte prepared by dissolving the bisimidazole tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate;

[0033] Figure 3 Galvanostatic charge-discharge chart of a supercapacitor assembled with an electrolyte prepared by dissolving the bisimidazole tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate;

[0034] Figure 4 Cyclic stability test chart of a supercapacitor assembled with an electrolyte prepared by dissolving the bisimidazole tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate;

[0035] Figure 5 The cyclic voltammetry test chart of the supercapacitor assembled with the electrolyte prepared by dissolving the bis(imidazole) bis(trifluoromethylsulfonyl)imide salt (C2Im·2TFSI) obtained in Example 4 in acetonitrile;

[0036] Figure 6 The cyclic voltammetry test chart of the supercapacitor assembled with the electrolyte prepared by dissolving the bis(pyrrole) tetrafluoroborate (C6Py·2BF4) obtained in Example 11 in propylene carbonate. Detailed implementation mode

[0037] The present invention provides a dicationic ionic liquid having a structure shown in any one of Formulas 1 to 4:

[0038]

[0039] In Formulas 1 to 4, R is a straight-chain alkyl group with the number of carbon atoms less than or equal to 6, 1 ≤ a ≤ 16, and Y - is TFSI - (bis(trifluoromethylsulfonyl)imide ion), BF4 - or PF6 - . In the structure shown in Formula 3, R can be connected to any carbon atom substitution position on the pyridine ring.

[0040] In the present invention, the R is preferably methyl, ethyl or butyl, and a is preferably 2 ≤ a ≤ 10. Specifically, a can be 2, 4, 6 or 10; the dicationic ionic liquid preferably has any one of the following structures:

[0041]

[0042] The dicationic ionic liquid provided by the present invention is a cyclic amine-based dicationic ionic liquid with imidazole, pyrrolidine, pyridine or piperidine as the cation core group. The dicationic ionic liquid has better thermal stability and surface ion density compared with the monocationic ionic liquid, can significantly improve the electrochemical working window, and thus greatly improve the defect of low device energy density; and the dicationic ionic liquid has the same excellent impedance performance as the monocationic ionic liquid, and at the same time has a high discharge specific capacity and excellent cycle performance.

[0043] The present invention provides a preparation method of the dicationic ionic liquid described in the above technical solution, including the following steps:

[0044] Mix the cyclic amine compound with the dihaloalkane for a nucleophilic reaction to obtain a dicationic halide salt;

[0045] Mix the double cationic halo-salt, anion source and solvent to carry out an ion exchange reaction to obtain the double cationic ionic liquid; the anion source is tetrafluoroborate, hexafluorophosphate or bis(trifluoromethylsulfonyl)imide salt;

[0046] The cyclic amine compound has any one of the structures shown in Formula 5 to Formula 8:

[0047]

[0048] The dihaloalkane has the structure shown in Formula 9:

[0049] In Formula 9, X is Cl, Br or I.

[0050] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well-known to those skilled in the art or prepared by methods well-known to those skilled in the art.

[0051] In the present invention, the cyclic amine compound and the dihaloalkane are mixed to carry out a nucleophilic reaction to obtain a double cationic halo-salt. In the present invention, the cyclic amine compound has any one of the structures shown in Formula 5 to Formula 8, and R in the structures shown in Formula 5 to Formula 8 is consistent with R in the structures shown in Formula 1 to Formula 4; the dihaloalkane has the structure shown in Formula 9, and the value of a in the structure shown in Formula 9 is consistent with the value of a in the structures shown in Formula 1 to Formula 4. In the present invention, the molar ratio of the dihaloalkane to the cyclic amine compound is preferably (1.0 - 1.1):2; the temperature of the nucleophilic reaction is preferably 40 - 70 °C, more preferably 50 - 60 °C, and the time is preferably 8 - 16 h, more preferably 10 - 16 h. In the present invention, the nucleophilic reaction is preferably carried out under stirring, and the stirring rate is preferably 300 r / min. After the nucleophilic reaction, the present invention preferably washes the obtained nucleophilic reaction solution with ethyl acetate to remove the unreacted raw materials and dries it to obtain a double cationic halo-salt; the drying temperature is preferably 110 °C and the time is preferably 12 h. In the present invention, taking the cyclic amine compound having the structure shown in Formula 5 as an example, the reaction formula of the nucleophilic reaction is as follows:

[0052]

[0053] After obtaining the dicationic halide salt, the present invention mixes the dicationic halide salt, an anion source and a solvent to carry out an ion exchange reaction to obtain the dicationic ionic liquid. In the present invention, the anion source is a tetrafluoroborate, a hexafluorophosphate or a bis(trifluoromethylsulfonyl)imide salt; the tetrafluoroborate is preferably ammonium tetrafluoroborate or potassium tetrafluoroborate, the hexafluorophosphate is preferably potassium hexafluorophosphate or sodium hexafluorophosphate, and the bis(trifluoromethylsulfonyl)imide salt is preferably lithium bis(trifluoromethylsulfonyl)imide (LiTFSI); the molar ratio of the dicationic halide salt to the anion source is preferably 1:(2-2.1). In the present invention, when the anion source is a tetrafluoroborate, the solvent is preferably acetonitrile; when the anion source is a hexafluorophosphate or a bis(trifluoromethylsulfonyl)imide salt, the solvent is preferably water, and the water is preferably deionized water or distilled water; the present invention has no particular requirement for the amount of the solvent, as long as the reaction can proceed smoothly. In the present invention, the temperature of the ion exchange reaction is preferably 20-70°C, more preferably 25-60°C, and the reaction time is preferably 4-16 h, more preferably 10-12 h. In the present invention, the specific operation of the ion exchange reaction is preferably: adding the dicationic halide salt into the solvent and mixing to obtain a dicationic halide salt solution; then adding the anion source into the dicationic halide salt solution and carrying out the ion exchange reaction under stirring conditions. In the present invention, when the solvent is water, the anion source is preferably added dropwise into the dicationic halide salt solution in the form of an anion source aqueous solution; when the solvent is acetonitrile, the anion source is preferably directly added into the dicationic halide salt solution; the stirring rate is preferably 400 r / min; the time of the ion exchange reaction is calculated starting from the completion of the addition of the anion source. After the ion exchange reaction, the present invention preferably performs post-treatment on the obtained ion exchange reaction solution. In the present invention, when the solvent is water, the post-treatment method is preferably: filtering the ion exchange reaction solution, washing the obtained solid phase successively with deionized water and vacuum drying to obtain the dicationic ionic liquid; the number of times of washing with deionized water is preferably three times, and the temperature of the vacuum drying is preferably 110°C and the time is preferably 12 h. In the present invention, when the solvent is acetonitrile, the post-treatment method is preferably: filtering the ion exchange reaction solution, collecting the filtrate, and the filter cake is the by-product salt generated by the ion exchange reaction; evaporating the solvent from the filtrate and recrystallizing with absolute ethanol to obtain a precipitate; vacuum drying the precipitate to obtain the dicationic ionic liquid; the temperature of the vacuum drying is preferably 110°C and the time is preferably 12 h.

[0054] The preparation method of the dicationic ionic liquid provided by the present invention has a simple process, is easy to scale up production, and has an extremely high yield.

[0055] The present invention also provides a supercapacitor electrolyte, which includes an electrolyte and an organic solvent. The electrolyte is the dicationic ionic liquid described in the above technical solution or the dicationic ionic liquid prepared by the preparation method described in the above technical solution. In the present invention, the organic solvent preferably includes an ester solvent and / or a nitrile solvent. The ester solvent is preferably one or more of ethylene carbonate, propylene carbonate, and γ-butyrolactone, and the nitrile solvent is preferably acetonitrile. In the present invention, the concentration of the electrolyte in the electrolyte is preferably 0.5 to 2.0 mol / L, more preferably 1 to 1.5 mol / L. The present invention has no special requirements for the preparation method of the electrolyte, as long as the electrolyte and the organic solvent are uniformly mixed. The supercapacitor electrolyte provided by the present invention can endow the supercapacitor with the characteristics of a high window and high stability.

[0056] The following examples are used to illustrate in detail the dicationic ionic liquid, its preparation method, and the supercapacitor electrolyte provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] Add 13.8 g (0.108 mol) of 1,4-dichlorobutane and 16.4 g (0.20 mol) of N-methylimidazole into a round-bottom flask, and carry out a nucleophilic reaction at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; wash the reaction product with ethyl acetate, and place the washed product in a drying oven at 110 °C for drying for 12 h to obtain a bisimidazole chloride salt with a bridging group of C4H8 (denoted as C4Im·2Cl).

[0059] Take 14.55 g (0.05 mol) of the bisimidazole chloride salt C4Im·2Cl with a bridging group of C4H8 in a beaker and dissolve it in deionized water. During stirring, gradually add an aqueous solution containing 29.28 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) (0.102 mol). After the addition is completed, continue stirring and carry out an ion exchange reaction at room temperature for 12 h. After the reaction, filter and wash three times with deionized water, and dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain bisimidazole bis(trifluoromethylsulfonyl)imide salt (denoted as C4Im·2TFSI), with a yield of 92.4%. The structural formula is as follows:

[0060]

[0061] Example 2

[0062] According to the preparation method of Example 1, the bis(imidazolium) chloride C4Im·2Cl with a bridging group of C4H8 was obtained. 14.55 g (0.05 mol) of C4Im·2Cl was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 11.03 g (0.105 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask. The ion exchange reaction was carried out for 16 h under the conditions of a reaction temperature of 60 °C and a rotation speed of 400 r / min. After the reaction, the reaction solution was filtered to retain the filtrate. The solvent was evaporated and recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain the bis(imidazolium) tetrafluoroborate with a bridging group of C4H8 (denoted as C4Im·2BF4), with a yield of 85.4%. The structural formula is as follows:

[0063]

[0064] Figure 1 1H NMR spectrum of the bis(imidazolium) tetrafluoroborate (C4Im·2BF4) with a bridging group of C4H8 prepared in Example 2 1 1H NMR spectrum.

[0065] Example 3

[0066] According to the preparation method of Example 1, the bis(imidazolium) chloride C4Im·2Cl with a bridging group of C4H8 was obtained. 7.28 g (0.025 mol) of C4Im·2Cl was taken in a round-bottom flask and distilled water was added. Subsequently, 9.66 g (0.052 mol) of potassium hexafluorophosphate KPF6 dissolved in water was added to the round-bottom flask and mixed with the bis(imidazolium) chloride. The ion exchange reaction was carried out for 16 h under the conditions of a reaction temperature of 60 °C and a rotation speed of 400 r / min. After the reaction was completed, it was filtered and washed three times with deionized water. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain the bis(imidazolium) hexafluorophosphate with a bridging group of C4H8 (denoted as C4Im·2PF6), with a yield of 86.7%. The structural formula is as follows:

[0067]

[0068] Example 4

[0069] 4.95 g (0.05 mol) of 1,2-dichloroethane and 8.16 g (0.0995 mol) of N-methylimidazole were added to a round-bottom flask. The nucleophilic reaction was carried out for 16 h under the conditions of a reaction temperature of 60 °C and a rotation speed of 300 r / min. The product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain the bis(imidazolium) chloride with a bridging group of C2H4 (denoted as C2Im·2Cl).

[0070] Take 6.58 g (0.025 mol) of bis(imidazolium) chloride C2Im·2Cl with a bridging group of C2H4 in a beaker and dissolve it in deionized water. During stirring, gradually add an aqueous solution containing 14.71 g (0.051 mol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). After addition at room temperature, continue stirring for an ion exchange reaction for 12 h. After the reaction is completed, filter and wash three times with deionized water. Dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain bis(imidazolium) bis(trifluoromethanesulfonyl)imide salt (denoted as C2Im·2TFSI), with a yield of 90.1%. The structural formula is as follows:

[0071]

[0072] Example 5

[0073] Prepare bis(imidazolium) chloride C2Im·2Cl with a bridging group of C2H4 according to the method of Example 4. Take 6.58 g (0.025 mol) of C2Im·2Cl in a round-bottom flask and add acetonitrile solvent. Subsequently, weigh 5.38 g (0.051 mol) of ammonium tetrafluoroborate (NH4BF4) and add it to the round-bottom flask. Carry out an ion exchange reaction at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 16 h. After the reaction is completed, filter the reaction solution to retain the filtrate. Evaporate the solvent and recrystallize with absolute ethanol. Dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain bis(imidazolium) tetrafluoroborate with a bridging group of C2H4 (denoted as C2Im·2BF4), with a yield of 83.2%. The structural formula is as follows:

[0074]

[0075] Example 6

[0076] Add 15.5 g (0.1 mol) of 1,6-dichlorohexane and 16.56 g (0.205 mol) of N-methylimidazole to a round-bottom flask. Carry out a nucleophilic reaction at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h. Wash the product obtained from the reaction with ethyl acetate. Place the washed product in a drying oven and dry at 110 °C for 12 h to obtain bis(imidazolium) chloride with a bridging group of C6H 12 and denoted as C6Im·2Cl.

[0077] Take 6.34 g (0.02 mol) of bis(imidazolium) chloride with a bridging group of C6H 12The bis(imidazolium) chloride C6Im·2Cl was placed in a beaker and dissolved in deionized water. An aqueous solution containing 11.82 g (0.0412 mol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added dropwise during stirring. After the addition was complete, stirring was continued for 12 h for the ion exchange reaction. After the reaction was completed, the mixture was filtered and washed three times with deionized water. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain bis(imidazolium) bis(trifluoromethanesulfonyl)imide salt (denoted as C6Im·2TFSI), with a yield of 92.5%. The structural formula is as follows:

[0078]

[0079] Example 7

[0080] The bis(imidazolium) chloride C6Im·2Cl with a bridging group of C6H was prepared according to the method of Example 6. 6.34 g (0.02 mol) of C6Im·2Cl was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 4.33 g (0.0412 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask. The ion exchange reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 16 h; after the reaction was completed, the reaction solution was filtered to retain the filtrate. After evaporating the solvent, it was recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain the bis(imidazolium) tetrafluoroborate with a bridging group of C6H 12 (denoted as C6Im·2BF4), with a yield of 83.2%. The structural formula is as follows: 12 (denoted as C6Im·2BF4), with a yield of 83.2%. The structural formula is as follows:

[0081]

[0082] Example 8

[0083] 10.56 g (0.05 mol) of 1,10-dichlorodecane and 8.41 g (0.103 mol) of N-methylimidazole were added to a round-bottom flask. The nucleophilic reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven at 110 °C for 12 h to obtain the bis(imidazolium) chloride with a bridging group of C 10 H 20 (denoted as C 10 Im·2Cl).

[0084] 3.75 g (0.01 mol) of the bis(imidazolium) chloride with a bridging group of C 10 H 12 was taken 10Dissolve Im.2Cl in a beaker and add deionized water. During stirring, gradually add an aqueous solution containing 6.03 g (0.021 mol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). After the addition is complete, continue stirring for the ion exchange reaction for 12 h. After the reaction is complete, filter and wash three times with deionized water. Dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain bis(imidazole) bis(trifluoromethanesulfonyl)imide salt (C 10 Im.2TFSI), with a yield of 87.6%. The structural formula is as follows:

[0085]

[0086] Example 9

[0087] Add 6.35 g (0.05 mol) of 1,4-dichlorobutane and 8.52 g (0.104 mol) of N-methylpyrrolidine to a round-bottom flask, and carry out a nucleophilic reaction at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; wash the product obtained from the reaction with ethyl acetate, and place the washed product in a drying oven at 110 °C for 12 h to obtain a dipyrrolidine chloride salt with a bridging group of C4H8 (denoted as C4Py.2Cl).

[0088] Take 5.78 g (0.02 mol) of dipyrrolidine chloride salt C4Py.2Cl in a beaker and add deionized water to dissolve it. During stirring, gradually add an aqueous solution containing 12.05 g (0.042 mol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). After the addition is complete, continue stirring for the ion exchange reaction for 12 h. After the reaction is complete, filter and wash three times with deionized water. Dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain dipyrrolidine bis(trifluoromethanesulfonyl)imide salt (denoted as C4Py.2TFSI). The structural formula is as follows:

[0089]

[0090] Example 10

[0091] Prepare dipyrrolidine chloride salt C4Py.2Cl according to the method of Example 9. Take 5.78 g (0.02 mol) of C4Py.2Cl in a round-bottom flask and add acetonitrile solvent. Subsequently, weigh 4.33 g (0.0412 mol) of ammonium tetrafluoroborate (NH4BF4) and add it to the round-bottom flask. Carry out an ion exchange reaction at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 16 h; after the reaction is completed, filter the reaction solution to retain the filtrate, evaporate the solvent and recrystallize with absolute ethanol. Dry the obtained white precipitate in a vacuum drying oven at 110 °C for 12 h to obtain dipyrrolidine tetrafluoroborate (denoted as C4Py.2BF4). The structural formula is as follows:

[0092]

[0093] Example 11

[0094] 15.5 g (0.1 mol) of 1,4-dichlorohexane and 17.43 g (0.205 mol) of N-methylpyrrolidine were added to a round-bottom flask, and a nucleophilic reaction was carried out for 16 h at a reaction temperature of 60 °C and a rotation speed of 300 r / min; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain a dipyrrolidine chloride salt with a bridging group of C6H 12 and denoted as C6Py·2Cl.

[0095] 6.34 g (0.02 mol) of C6Py·2Cl was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 4.31 g (0.041 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask, and an ion exchange reaction was carried out for 16 h at a reaction temperature of 60 °C and a rotation speed of 400 r / min; after the reaction was completed, the reaction solution was filtered to retain the filtrate, the solvent was evaporated, and the residue was recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain dipyrrolidine tetrafluoroborate (denoted as C6Py·2BF4), and the structural formula is as follows:

[0096]

[0097] Example 12

[0098] 6.35 g (0.05 mol) of 1,4-dichlorobutane and 9.76 g (0.105 mol) of 2-methylpyridine were added to a round-bottom flask, and a nucleophilic reaction was carried out for 16 h at a reaction temperature of 60 °C and a rotation speed of 300 r / min; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain a dipyridine chloride salt with a bridging group of C4H8 (denoted as C4Pd·2Cl).

[0099] 6.26 g (0.02 mol) of C4Pd·2Cl was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 4.33 g (0.0412 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask, and an ion exchange reaction was carried out for 16 h at a reaction temperature of 60 °C and a rotation speed of 400 r / min; after the reaction was completed, the reaction solution was filtered to retain the filtrate, the solvent was evaporated, and the residue was recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain dipyridine tetrafluoroborate (denoted as C4Pd·2BF4), and the structural formula is as follows:

[0100]

[0101] Example 13

[0102] 6.35 g (0.05 mol) of 1,4-dichlorobutane and 10.39 g (0.105 mol) of 1-methylpiperidine were added to a round-bottom flask, and a nucleophilic reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain a dipiperidine chloride salt with a bridging group of C4H8 (denoted as C4Pi.2Cl).

[0103] 6.5 g (0.02 mol) of C4Pi.2Cl was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 4.33 g (0.0412 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask, and an ion exchange reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 12 h; after the reaction was completed, the reaction solution was filtered to retain the filtrate, the solvent was evaporated, and the residue was recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain dipiperidine tetrafluoroborate (denoted as C4Pi.2BF4), and the structural formula is as follows:

[0104]

[0105] Example 14

[0106] 13.8 g (0.108 mol) of 1,4-dichlorobutane and 19.2 g (0.20 mol) of N-ethylimidazole were added to a round-bottom flask, and a nucleophilic reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain a diimidazole chloride salt with a bridging group of C4H8 (denoted as C4EIm.2Cl).

[0107] 15.95 g (0.05 mol) of the diimidazole chloride salt C4EIm.2Cl with a bridging group of C4H8 was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 11.03 g (0.105 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask, and an ion exchange reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 16 h; after the reaction was completed, the reaction solution was filtered to retain the filtrate, the solvent was evaporated, and the residue was recrystallized with absolute ethanol. The obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain a diimidazole tetrafluoroborate with a bridging group of C4H8 (denoted as C4EIm.2BF4), and the structural formula is as follows:

[0108]

[0109] Example 15

[0110] 13.8 g (0.108 mol) of 1,4-dichlorobutane and 24.8 g (0.20 mol) of N-butylimidazole were added to a round-bottom flask, and a nucleophilic reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 300 r / min for 16 h; the product obtained from the reaction was washed with ethyl acetate, and the washed product was placed in a drying oven and dried at 110 °C for 12 h to obtain a bis(imidazolium) chloride salt with a bridging group of C4H8 (denoted as C4BIm.2Cl).

[0111] 18.75 g (0.05 mol) of the bis(imidazolium) chloride salt C4BIm.2Cl with a bridging group of C4H8 was taken in a round-bottom flask and acetonitrile solvent was added. Subsequently, 11.03 g (0.105 mol) of ammonium tetrafluoroborate (NH4BF4) was weighed and added to the round-bottom flask, and an ion exchange reaction was carried out at a reaction temperature of 60 °C and a rotation speed of 400 r / min for 16 h; after the reaction was completed, the reaction solution was filtered to retain the filtrate, the solvent was evaporated and recrystallized with absolute ethanol, and the obtained white precipitate was dried in a vacuum drying oven at 110 °C for 12 h to obtain a bis(imidazolium) tetrafluoroborate salt with a bridging group of C4H8 (denoted as C4BIm.2BF4), and the structural formula is as follows:

[0112]

[0113] Application Example

[0114] Application Comparative Example 1

[0115] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), an electrolyte solution with a concentration of 1 mol / L was prepared using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm.BF4) as the electrolyte and propylene carbonate (PC) as the solvent.

[0116] The button battery was assembled using the electrolyte solution described in Application Comparative Example 1, where the positive and negative electrode active materials were YP-50F activated carbon materials, the mass of the active material of a single electrode was 2 mg, and a glass fiber separator was selected as the battery separator.

[0117] The supercapacitor battery assembled with Comparative Example 1 was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 - 2.8 V; an AC impedance test was conducted under the condition of a signal source frequency of 0.0 - 100000 Hz, and the impedance was 34 ohm; the supercapacitor battery was subjected to a constant current charge-discharge test at a current density of 1 A / g, the voltage range was 0 - 2.8 V, and the specific capacitance was 24.74 F / g; the supercapacitor battery was subjected to a rate performance test, and the specific capacitance at a current density of 5 A / g was 33.6% of that at a current density of 1 A / g; finally, a constant current charge-discharge cycle test was conducted at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 53.5%.

[0118] Application Example 1

[0119] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), an electrolyte solution with a concentration of 1 mol / L was prepared by using propylene carbonate (PC) as a solvent and dissolving the bis(imidazolium) cation tetrafluoroborate (C4Im·2BF4) prepared in Example 2.

[0120] According to the method of Comparative Example 1 for Application, the electrolyte solution of Application Example 1 was assembled into a button battery, and the same method was used for electrochemical performance testing; the supercapacitor battery was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 - 3.2 V, Figure 2 It is the cyclic voltammetry test chart of the supercapacitor assembled by dissolving the bis(imidazolium) tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate to prepare the electrolyte solution; an AC impedance test was conducted under the condition of a signal source frequency of 0.01 - 100000 Hz, and the impedance was 38 ohm; the supercapacitor battery was subjected to a constant current charge-discharge test at a current density of 1 A / g, the voltage range was 0 - 3.2 V, and the specific capacitance was 26.9 F / g, Figure 3 It is the constant current charge-discharge chart of the supercapacitor assembled by dissolving the bis(imidazolium) tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate to prepare the electrolyte solution; the supercapacitor battery was subjected to a rate performance test, and the specific capacitance at a current density of 5 A / g was 74.7% of that at a current density of 1 A / g; finally, a constant current charge-discharge cycle test was conducted at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 86.6%, Figure 4 It is the cyclic stability test chart of the supercapacitor assembled by dissolving the bis(imidazolium) tetrafluoroborate (C4Im·2BF4) prepared in Example 2 in propylene carbonate to prepare the electrolyte solution.

[0121] Application Example 2

[0122] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using acetonitrile (AN) as the solvent, an electrolyte solution with a concentration of 1 mol / L was prepared from the bis(imidazolium) bis(trifluoromethylsulfonyl)imide salt (C2Im.2TFSI) prepared in Example 4.

[0123] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 2 was assembled into a button battery, and the same method was used for the electrochemical performance test; the supercapacitor battery was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 to 3.0 V. Figure 5 This is the cyclic voltammetry test chart for assembling a supercapacitor with an electrolyte solution prepared by dissolving the bis(imidazolium) bis(trifluoromethylsulfonyl)imide salt (C2Im.2TFSI) prepared in Example 4 in acetonitrile; an AC impedance test was carried out under the condition that the signal source frequency was 0.01 to 100000 Hz, and the impedance was 19 ohm; the supercapacitor battery was subjected to a constant current charge-discharge test at a current density of 1 A / g, the voltage range was 0 to 3.0 V, and the specific capacitance was 25.0 F / g; the supercapacitor battery was subjected to a rate test, and the specific capacitance at a current density of 5 A / g was 66.2% of that at a current density of 1 A / g; finally, a constant current charge-discharge cycle test was carried out at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 85.9%.

[0124] Application Example 3

[0125] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using propylene carbonate (PC) as the solvent, an electrolyte solution with a concentration of 1 mol / L was prepared from the bis(imidazolium) cation bis(trifluoromethylsulfonyl)imide salt (C4Im.2TFSI) prepared in Example 1.

[0126] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 1 was assembled into a button battery, and the same method was used for the electrochemical performance test; the supercapacitor battery was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 to 3.1 V; an AC impedance test was carried out under the condition that the signal source frequency was 0.01 to 100000 Hz, and the impedance was 39 ohm; the supercapacitor battery was subjected to a constant current charge-discharge test at a current density of 1 A / g, the voltage range was 0 to 3.1 V, and the specific capacitance was 24.9 F / g; the supercapacitor battery was subjected to a rate test, and the specific capacitance at a current density of 5 A / g was 68.2% of that at a current density of 1 A / g; finally, a constant current charge-discharge cycle test was carried out at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 86.9%.

[0127] Application Example 4

[0128] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), a 1 mol / L electrolyte solution was prepared using propylene carbonate (PC) as the solvent and the dipyrrolidine tetrafluoroborate (C6Py.2BF4) prepared in Example 11.

[0129] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 1 was assembled into a button cell, and the same method was used for electrochemical performance testing; the supercapacitor cell was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 - 3.2 V. Figure 6 Figure for cyclic voltammetry testing of a supercapacitor assembled with an electrolyte solution prepared by dissolving the dipyrrolidine tetrafluoroborate (C6Py.2BF4) prepared in Example 11 in propylene carbonate; AC impedance testing was carried out under the condition of a signal source frequency of 0.01 - 100000 Hz, and the impedance was 36 ohm; the supercapacitor cell was subjected to constant current charge and discharge testing at a current density of 1 A / g, the voltage range was 0 - 3.2 V, and the specific capacitance was 26.2 F / g; the supercapacitor cell was subjected to rate performance testing, and the specific capacitance at a current density of 5 A / g was 58.2% of that at a current density of 1 A / g; finally, constant current charge and discharge cycling testing was carried out at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 74.6%.

[0130] Application Example 5

[0131] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), a 1 mol / L electrolyte solution was prepared using propylene carbonate (PC) as the solvent and the dipyridinium tetrafluoroborate (C4Pd.2BF4) prepared in Example 12.

[0132] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 1 was assembled into a button cell, and the same method was used for electrochemical performance testing; the supercapacitor cell was subjected to cyclic voltammetry testing using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 - 3.0 V; AC impedance testing was carried out under the condition of a signal source frequency of 0.01 - 100000 Hz, and the impedance was 40 ohm; the supercapacitor cell was subjected to constant current charge and discharge testing at a current density of 1 A / g, the voltage range was 0 - 3.0 V, and the specific capacitance was 24.5 F / g; the supercapacitor cell was subjected to rate performance testing, and the specific capacitance at a current density of 5 A / g was 63.2% of that at a current density of 1 A / g; finally, constant current charge and discharge cycling testing was carried out at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 76.9%.

[0133] Application Example 6

[0134] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using propylene carbonate (PC) as the solvent, an electrolyte solution with a concentration of 1 mol / L was prepared from the dipiperidinium tetrafluoroborate (C4Pi·2BF4) prepared in Example 13.

[0135] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 1 was assembled into a button cell, and the same method was used for the electrochemical performance test; the supercapacitor cell was subjected to cyclic voltammetry test using an electrochemical workstation at a scan rate of 5 mV / s, and the measured voltage range was 0 - 3.0 V; an AC impedance test was carried out under the condition of a signal source frequency of 0.01 - 100000 Hz, and the impedance was 39 ohm; the supercapacitor cell was subjected to a constant current charge-discharge test at a current density of 1 A / g, the voltage range was 0 - 3.0 V, and the specific capacitance was 25.1 F / g; the supercapacitor cell was subjected to a rate performance test, and the specific capacitance at a current density of 5 A / g was 68.7% of that at a current density of 1 A / g; finally, a constant current charge-discharge cycle test was carried out at a current density of 1 A / g, and after 10000 cycles, the capacity retention rate was 73.1%.

[0136] Application Example 7

[0137] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using propylene carbonate (PC) or propylene carbonate (PC) as the solvent, the other bis-cationic ionic liquids prepared in the examples were respectively formulated into electrolyte solutions with a concentration of 1 mol / L.

[0138] According to the method of Application Comparative Example 1, the electrolyte solution of Application Example 7 was assembled into a button cell, and the same method was used for the electrochemical performance test; the measured voltage window, specific capacitance, and impedance are listed in Table 1 respectively.

[0139] Table 1 Electrochemical performance of supercapacitors assembled with electrolyte solutions prepared from bis-cationic ionic liquids prepared in Examples 1 - 15

[0140]

[0141]

[0142] It can be seen from the above examples that the bis-cationic ionic liquid provided by the present invention can significantly improve the electrochemical working window, and has the same excellent impedance performance as the mono-cationic ionic liquid. At the same time, it has a high discharge specific capacitance and excellent cycle performance. When the bis-cationic ionic liquid is formulated into an electrolyte solution for a supercapacitor, the supercapacitor can have the characteristics of a high window and high stability.

[0143] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of an electrolyte in a supercapacitor, wherein the electrolyte comprises an electrolyte and an organic solvent, and the electrolyte is a dicationic ionic liquid; The dicationic ionic liquid has the following structure:

2. The application according to claim 1, wherein The preparation method of the dicationic ionic liquid comprises the following steps: Mix a cyclic amine compound with a dihaloalkane for a nucleophilic reaction to obtain a dicationic halide salt; Mix the dicationic halide salt, an anion source and a solvent for an ion exchange reaction to obtain the dicationic ionic liquid; the anion source is a tetrafluoroborate; The cyclic amine compound is 2-methylpyridine, The dihaloalkane is 1,4-dichlorobutane.

3. The application according to claim 2, wherein The molar ratio of the dihaloalkane to the cyclic amine compound is (1.0 - 1.1):2; the temperature of the nucleophilic reaction is 40 - 70 °C, and the time is 8 - 16 h.

4. The application according to claim 2, wherein When the anion source is a tetrafluoroborate, the solvent is acetonitrile.

5. The application according to claim 2, wherein The molar ratio of the dicationic halide salt to the anion source is 1:(2 - 2.1); the temperature of the ion exchange reaction is 20 - 70 °C, and the reaction time is 4 - 16 h.

6. The application according to claim 1, characterized in that, The concentration of the electrolyte in the electrolyte is 0.5 - 2.0 mol / L.

7. The application according to claim 1, wherein The organic solvent comprises an ester solvent and / or a nitrile solvent.

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