A double-layer hetero-polyionic liquid gel electrolyte and a preparation method and application thereof

Abstract

This invention relates to a bilayer heterogeneous polyionic liquid gel electrolyte, its preparation method, and its applications. The bilayer heterogeneous polyionic liquid gel is synthesized by dissolving the anionic monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate and the cationic monomer (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and then by free radical polymerization. A supercapacitor is constructed using the bilayer heterogeneous polyionic liquid gel as the electrolyte and double-layer materials (carbon nanotubes or activated carbon) as electrodes. Compared with existing technologies, this invention can effectively suppress charge rearrangement during the self-discharge process of supercapacitors, thereby prolonging the self-discharge time of supercapacitors. Furthermore, it can significantly increase the operating voltage, thereby improving the specific capacitance and energy density of supercapacitors. This provides a new strategy for solving the problem of rapid self-discharge in supercapacitors and has broader application value.

Description

Technical Field

[0001] This invention relates to the field of energy storage device technology, and in particular to a bilayer heterogeneous polyionic liquid gel electrolyte, its preparation method, and its application. Background Technology

[0002] Supercapacitors, as a novel and highly efficient energy storage device, have attracted much attention due to their high power density, rapid charge-discharge capability, and ultra-long cycle life. However, a fully charged supercapacitor is in a high-energy state, which spontaneously generates a driving force that causes charge rearrangement and redox reactions in the open-circuit state, leading to a decrease in the open-circuit voltage. This self-discharge phenomenon of supercapacitors severely restricts their widespread application. Researchers have attempted to suppress the self-discharge rate of supercapacitors by functionalizing electrode materials, separators, and electrolytes, but with limited success. Recently, studies have shown that constructing aqueous polyelectrolytes with heterostructures can effectively suppress the self-discharge phenomenon of supercapacitors; however, the voltage window of aqueous gel electrolytes is limited, resulting in lower specific capacitance and energy density of the supercapacitors.

[0003] Ionic liquids are a class of compounds composed of organic cations and organic or inorganic anions. Their unique structure endows them with properties distinct from small-molecule salts, including low vapor pressure, flame retardancy, high ionic conductivity, a wide electrochemical window, good solubility, and excellent thermal and chemical stability. Polyionic liquids not only retain these superior properties of ionic liquids but also possess advantages such as polymer processability and good mechanical stability. Supercapacitors based on polyionic liquid gel electrolytes also exhibit higher operating voltage, specific capacitance, and energy density.

[0004] Chinese patent CN112201482A discloses a supercapacitor with a heterojunction polymer gel electrolyte and its preparation method. The supercapacitor uses carbon nanotubes or their composite films as electrodes, and heterojunction films formed by polyvinyl alcohol / phosphoric acid / sodium poly(4-styrene sulfonate) and polyvinyl alcohol / phosphoric acid / polydienedimethylammonium chloride serve as both solid electrolyte and separator. The heterojunction solid electrolyte constructed by this patent can effectively suppress charge rearrangement in the electric double layer and pseudocapacitive supercapacitors, and significantly extend the self-discharge time of the supercapacitor. However, the supercapacitor constructed has a low operating voltage and specific capacitance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a bilayer heterogeneous polyionic liquid gel electrolyte, its preparation method, and its application. The bilayer heterogeneous polyionic liquid gel electrolyte is applied to supercapacitors to improve their electrochemical performance. At the same time, the introduction of the heterostructure can effectively suppress the self-discharge behavior of the supercapacitor. The supercapacitor with high energy density and long self-discharge time involved in this invention has great application value in the field of portable wearable energy storage devices.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A bilayer heterogeneous polyionic liquid gel electrolyte is composed of ionic gels with different Zeta potentials.

[0008] Furthermore, the bilayer heterogeneous polyionic liquid gel electrolyte is composed of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel.

[0009] This invention also provides a method for preparing a bilayer heterogeneous polyionic liquid gel electrolyte, the specific steps of which are as follows:

[0010] S1. Monomer synthesis: 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate and (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide were prepared by ion exchange method;

[0011] S2. Preparation of prepolymer solution: Dissolve the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate or (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide obtained in step S1 in a solvent, add crosslinking agent and initiator, and stir to obtain a prepolymer solution with uniform viscosity.

[0012] S3. Preparation of ion gels: The prepolymer liquid obtained in step S2 is polymerized by thermal initiation to obtain poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel respectively.

[0013] S4. Preparation of bilayer heterogeneous polyionic liquid gel electrolyte: The poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and the poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel obtained in step S3 are assembled together to obtain a bilayer heterogeneous polyionic liquid gel electrolyte.

[0014] Further, in step S1, the specific method for preparing the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate is as follows: equimolar amounts of 1-ethyl-3-methylimidazolium chloride and potassium salt of 3-sulfopropyl methacrylate are dissolved in acetonitrile solvent, and methoxyphenol is added as an inhibitor. The resulting mixture is stirred vigorously at room temperature; the generated potassium chloride is removed by centrifugation, and then acetonitrile is removed to obtain a viscous yellow oily product, 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate.

[0015] Furthermore, the concentration of the 1-ethyl-3-methylimidazolium chloride is 0.67–6.67 mol / L.

[0016] Furthermore, the concentration of the potassium 3-sulfopropyl methacrylate is 0.67–6.67 mol / L.

[0017] Furthermore, the concentration of the methoxyphenol is 0.17–0.67 mg / mL.

[0018] Furthermore, the stirring time is 6 to 12 hours.

[0019] Furthermore, the method for removing acetonitrile involves first removing part of the solvent acetonitrile through rotary evaporation, and then placing the crude solution in a vacuum drying oven for 6–12 hours at room temperature to completely remove the acetonitrile.

[0020] Further, in step S1, the specific method for preparing the monomer (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imine is as follows: equimolar amounts of methacryloyloxyethyltrimethylammonium chloride are mixed with an aqueous solution of lithium bis(trifluoromethanesulfonyl)imine and stirred at room temperature; after phase separation, the lower oily liquid is collected and vacuum dried to obtain the transparent oily product (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imine.

[0021] Furthermore, the concentration of the methacryloyloxyethyltrimethylammonium chloride is 0.2–5 mol / L.

[0022] Furthermore, the concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.2–5 mol / L.

[0023] Furthermore, the room temperature stirring time is 2–6 hours.

[0024] Furthermore, the lower oily liquid is first washed with deionized water and then dried.

[0025] Furthermore, the vacuum drying temperature is 60–80°C, and the time is 6–12 hours.

[0026] Further, in step S2, the ratio of the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate to the solvent is 1:(0.1~10).

[0027] Further, in step S2, the ratio of (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide to solvent is 1:(0.1-10).

[0028] Further, in step S2, the solvent is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0029] Further, in step S2, the crosslinking agent is polyethylene glycol diacrylate, and the concentration of polyethylene glycol diacrylate is 1-5 mol% of the monomer.

[0030] Further, in step S2, the initiator is azobisisobutyronitrile (AIBN), and the concentration of AIBN is 0.5–5 mol% of the monomer.

[0031] Furthermore, in step S2, the stirring time is 2 to 6 hours, and the temperature is room temperature.

[0032] Furthermore, in step S3, the prepolymer liquid is poured into a self-made mold and then polymerized by thermal initiation.

[0033] Furthermore, in step S3, the thermal initiation temperature is 70°C, and the time is 2–6 hours.

[0034] The present invention also provides an application of a bilayer heterogeneous polyionic liquid gel electrolyte, wherein the above-mentioned bilayer heterogeneous polyionic liquid gel electrolyte is applied to a supercapacitor.

[0035] In addition, the present invention also provides a supercapacitor, including electrode plates on both sides and a bilayer heterogeneous polyionic liquid gel electrolyte located between the two electrode plates.

[0036] Furthermore, the electrode plate is a carbon nanotube electrode or an activated carbon / carbon nanotube composite electrode, and the bilayer heterogeneous polyionic liquid gel electrolyte is a bilayer heterogeneous polyionic liquid gel electrolyte composed of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel.

[0037] Furthermore, the thickness of the bilayer heterogeneous polyionic liquid gel electrolyte is 200–600 μm.

[0038] Furthermore, the carbon nanotube electrode has a thickness of 10–200 μm, and the activated carbon / carbon nanotube composite electrode has a thickness of 10–400 μm.

[0039] This invention also provides a method for preparing a supercapacitor, the specific steps of which are as follows:

[0040] (1) An activated carbon / carbon nanotube composite electrode was obtained by coating activated carbon onto a carbon nanotube film using a blade coating method.

[0041] (2) 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is drop-coated on the surface of carbon nanotube electrode or activated carbon / carbon nanotube composite electrode. Two polyionic liquid gel electrolytes are respectively attached to the cut electrode materials. Then, the electrolyte side of the two electrodes is pressed together to obtain a supercapacitor based on bilayer heterogeneous polyionic liquid gel electrolyte.

[0042] Further, in step (1), the specific preparation method of the activated carbon / carbon nanotube composite electrode is as follows: activated carbon, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone, stirred to obtain a viscous electrode slurry, which is then coated onto a carbon nanotube film with a scraper and dried in a vacuum oven to obtain the activated carbon / carbon nanotube composite electrode.

[0043] Furthermore, the mass ratio of activated carbon, conductive carbon black, and polyvinylidene fluoride is 8:1:1.

[0044] Furthermore, the stirring time is 6–12 hours, and the temperature is room temperature.

[0045] Furthermore, the drying time is 6–12 hours, and the temperature is 60–80°C.

[0046] Furthermore, the thickness of the scraper is 100–400 μm.

[0047] Further, in step (2), the amount of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide used is 1–10 μL / cm² relative to the area of ​​the cutting electrode. 2 .

[0048] The principle of this invention is as follows:

[0049] This invention uses poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel with different Zeta potentials as bilayer heterogeneous polyionic liquid gel electrolytes. The introduction of the solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide gives the gel electrolyte a high ionic conductivity. Both poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide possess the same counterion ion 1-ethyl-3-methylimidazolium, and both poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide possess the same counterion ion bis(trifluoromethanesulfonyl)imide, which is beneficial for miscibility with monomers.

[0050] When a forward voltage is applied to charge the prepared supercapacitor (with the electrode on the lower potential side of the poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) gel electrolyte connected to the positive electrode), after the external power source is removed, the potential difference at the electrode-electrolyte interface is large, and the potential difference between the two electrolyte layers is low, insufficient to cause the counterions accumulated on the electrode surface to rearrange, thus effectively prolonging the self-discharge time of the supercapacitor. Conversely, when a reverse voltage is applied (with the electrode on the higher potential side of the poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) gel electrolyte connected to the positive electrode), there is a large potential difference between the two electrolyte layers, which accelerates the rearrangement of counterions on the electrode surface, thus increasing the self-discharge rate of the supercapacitor.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] (1) The bilayer heterogeneous polyionic liquid gel electrolyte prepared in this invention can effectively delay the self-discharge time of supercapacitors compared with traditional homogeneous electrolytes. Due to the different Zeta potentials of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel, after applying a positive voltage to charge the supercapacitor, a small potential difference is formed between the two electrolyte layers, thereby delaying the rearrangement of counterions accumulated on the electrode surface, and thus producing the effect of inhibiting self-discharge behavior.

[0053] (2) The present invention introduces poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate), poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide with high electrochemical windows, and the supercapacitor constructed has higher operating voltage and specific capacitance.

[0054] (3) The bilayer heterogeneous polyionic liquid gel electrolyte has excellent interfacial stability, which enables the constructed supercapacitor to have good flexibility and cyclic bending stability.

[0055] (4) The bilayer heterogeneous polyionic liquid gel electrolyte designed in this invention can effectively extend the self-discharge time of supercapacitors while significantly increasing their operating voltage, thereby improving the specific capacity and energy density of supercapacitors and having a wider range of application value. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of the bilayer heterogeneous polyionic liquid gel electrolyte involved in this invention;

[0057] Figure 2 Scanning electron microscope (SEM) images of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel;

[0058] Figure 3 Comparison of ionic conductivity of homogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionogel, homogeneous poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel, and poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) / poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel forming a bilayer heterostructure;

[0059] Figure 4 Comparison of Zeta potentials (ζ) between poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel;

[0060] Figure 5 This is a schematic diagram illustrating the principle of suppressing self-discharge in a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte, as described in this invention.

[0061] Figure 6 The self-discharge curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte with carbon nanotube membranes as electrodes after being charged by forward and reverse voltages, respectively.

[0062] Figure 7The self-discharge curves of supercapacitors based on polyionic liquid gel electrolytes constructed with carbon nanotube membranes as electrodes are shown. The electrolytes are homogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel, homogeneous poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel, and bilayer heterogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) / poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel.

[0063] Figure 8 Scanning electron microscope image of activated carbon / carbon nanotube composite electrode;

[0064] Figure 9 The self-discharge curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte constructed with activated carbon / carbon nanotube composite electrodes after being charged by forward and reverse voltages, respectively.

[0065] Figure 10 The self-discharge curves of supercapacitors based on polyionic liquid gel electrolytes constructed with activated carbon / carbon nanotube composite electrodes are shown. The electrolytes are homogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel, homogeneous poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel, and bilayer heterogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) / poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel.

[0066] Figure 11 The self-discharge curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte, constructed with activated carbon / carbon nanotube composite electrodes of different thicknesses, after being charged by a forward voltage.

[0067] Figure 12 Cyclic voltammetry diagrams of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte constructed with activated carbon / carbon nanotube composite electrodes at different bending angles.

[0068] Figure 13 Cyclic voltammetry diagrams of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte constructed with an activated carbon / carbon nanotube composite electrode under different bending cycles. Detailed Implementation

[0069] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0070] Example 1

[0071] The application of a bilayer heterogeneous polyionic liquid gel electrolyte involves the following specific steps:

[0072] (1) Dissolve 0.04 mol of 1-ethyl-3-methylimidazolium chloride and 0.04 mol of potassium 3-sulfopropyl methacrylate in 30 mL of acetonitrile, and add 10 mg of methoxyphenol as an inhibitor. The resulting mixture is stirred vigorously at room temperature for 6 h. Centrifuge to remove the generated potassium chloride, and remove the solvent acetonitrile by rotary evaporation. Place the crude solution in a vacuum drying oven for 6 h to completely evaporate the acetonitrile at room temperature, to obtain a viscous yellow oily product, 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate.

[0073] (2) 0.04 mol of methacryloyloxyethyltrimethylammonium chloride was mixed with 40 mL of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide aqueous solution and stirred at room temperature for 2 h. After phase separation, the lower oily liquid was collected and washed several times with deionized water. After vacuum drying at 60 °C for 6 h, a transparent oily product (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide was obtained.

[0074] (3) Dissolve 5 mmol of 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate or (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide in 3 mmol of solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, add 40 μL of crosslinking agent polyethylene glycol diacrylate and 4 mg of initiator azobisisobutyronitrile. After stirring at room temperature for 2 h, a prepolymer with uniform viscosity is obtained. Pour the prepolymer into a 200 μm thick mold and polymerize at 70 °C for 2 h to obtain poly(1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel, respectively.

[0075] (4) The two polyionic liquid gel electrolytes obtained in step (3) are respectively attached to carbon nanotube electrodes (10 μm thick) coated with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (5 μL). Then, the electrolyte side of the two electrodes is pressed together to obtain a supercapacitor based on bilayer heterogeneous polyionic liquid gel electrolyte.

[0076] Figure 1 This is a schematic diagram of the bilayer heterogeneous polyionic liquid gel electrolyte structure obtained by free radical polymerization.

[0077] Figure 2Scanning electron microscope (SEM) images of poly(1-ethyl-3-methylimidazolium (3-sulfopropyl)methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel after removing the solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide by ethanol immersion. The images show that the polyionic liquid gel has a wrinkled surface structure, which allows for the efficient absorption of the solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide within the polymer network, thereby improving the ionic conductivity of the polyionic liquid gel.

[0078] Figure 3 This is a comparison of the ionic conductivity of homogeneous and bilayer heterogeneous polyionic liquid gel electrolytes. The ionic conductivity of the bilayer heterogeneous polyionic liquid gel electrolyte is 0.179 mS / cm, while that of the homogeneous polyionic gel is 0.147 and 0.182 mS / cm, respectively, indicating that the ionic conductivity of the bilayer heterogeneous polyionic liquid gel electrolyte is comparable to that of the homogeneous polyionic liquid gel electrolyte.

[0079] Figure 4 This chart compares the Zeta potentials of two polyionomer gels. The poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionomer gel has a Zeta potential of -7.1 mV, while the poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionomer gel has a Zeta potential of -30.6 mV. Utilizing this potential difference, and combining it with the Poisson-Boltzmann equation, the principle of bilayer suppression of self-discharge in supercapacitors using polyionomer liquid gel electrolytes can be further summarized. Figure 5 When a positive voltage is applied to charge the capacitor, the potential difference at the electrode-electrolyte interface is large, while the potential difference between the two electrolyte layers is small. Therefore, after the external power source is removed, the insufficient potential difference between the two electrolyte layers causes the counterions accumulated on the electrode surface to rearrange, thereby suppressing the self-discharge behavior of the supercapacitor. Figure 6 The experimental results well demonstrate this point. For comparison, we compared the self-discharge process of the supercapacitor based on a bilayer heterostructure polyionic liquid gel electrolyte with other supercapacitors based on homogeneous polyionic liquid gel electrolytes, including homogeneous poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ionogel and homogeneous poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel. Figure 7 The results show that the introduction of bilayer heterostructure polyionic liquid electrolyte effectively suppressed the self-discharge process of supercapacitors.

[0080] Example 2

[0081] The preparation of a bilayer heterogeneous polyionic liquid gel electrolyte and its application in supercapacitors are described in the following steps:

[0082] (1) Dissolve 0.10 mol of 1-ethyl-3-methylimidazolium chloride and 0.10 mol of potassium 3-sulfopropyl methacrylate in 45 mL of acetonitrile, and add 15 mg of methoxyphenol as an inhibitor. The resulting mixture is stirred vigorously at room temperature for 12 h. Centrifuge to remove the generated potassium chloride, and remove the solvent acetonitrile by rotary evaporation. Place the crude solution in a vacuum drying oven for 12 h to completely evaporate the acetonitrile at room temperature, to obtain a viscous yellow oily product, 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate.

[0083] (2) 0.10 mol of methacryloyloxyethyltrimethylammonium chloride was mixed with 100 mL of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide aqueous solution and stirred at room temperature for 6 h. After phase separation, the lower oily liquid was collected and washed several times with deionized water. After vacuum drying at 80 °C for 12 h, a transparent oily product (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide was obtained.

[0084] (3) Dissolve 12 mmol of 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate or (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide in 8 mmol of solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, add 100 μL of crosslinking agent polyethylene glycol diacrylate and 10 mg of initiator azobisisobutyronitrile. After stirring at room temperature for 6 h, a prepolymer with uniform viscosity is obtained. Pour the prepolymer into a 300 μm thick mold and polymerize at 70 °C for 4 h to obtain poly(1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel, respectively.

[0085] (4) Dissolve activated carbon, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 8:1:1 and stir at room temperature for 12 h to obtain a viscous electrode slurry. Coat the slurry onto a carbon nanotube film with a scraper of 100, 250 and 400 μm thickness and dry it in a vacuum oven at 80 °C for 12 h to obtain an activated carbon / carbon nanotube composite electrode.

[0086] (5) The two polyionic liquid gel electrolytes obtained in step (3) are respectively attached to the activated carbon / carbon nanotube composite electrode coated with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (5 μL), and then the electrolyte side of the two electrodes is pressed together to obtain a supercapacitor based on bilayer heterogeneous polyionic liquid gel electrolyte.

[0087] To further improve the electrochemical performance of supercapacitors, activated carbon / carbon nanotube composite electrodes were used to construct supercapacitors. Figure 8 This is a scanning electron microscope image of the activated carbon / carbon nanotube composite electrode. It can be seen that the activated carbon is uniformly loaded in particulate form on the surface of the carbon nanotube film.

[0088] Figure 9 The image shows the self-discharge curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte constructed with activated carbon / carbon nanotube composite electrodes after being charged with forward and reverse voltages. Figure 10 The figure shows the self-discharge characteristics of supercapacitors constructed with activated carbon / carbon nanotube composite electrodes and based on bilayer heterogeneous polyionic liquid gel electrolytes and homogeneous polyionic liquid gel electrolytes. As can be seen from the figure, the self-discharge behavior of the supercapacitors based on activated carbon / carbon nanotube composite electrodes and bilayer heterogeneous polyionic liquid gel electrolytes is significantly suppressed. Figure 9 , Figure 10 ).

[0089] Figure 11 The figure shows the self-discharge curves of supercapacitors based on bilayer heterogeneous polyionic liquid gel electrolytes constructed with activated carbon / carbon nanotube composite electrodes of varying thicknesses under forward voltage. As can be seen from the figure, the self-discharge time of the supercapacitor decreases with increasing electrode thickness.

[0090] Example 3

[0091] The preparation of a bilayer heterogeneous polyionic liquid gel electrolyte and its application in supercapacitors are described in the following steps:

[0092] (1) 0.16 mol of 1-ethyl-3-methylimidazolium chloride and 0.16 mol of potassium 3-sulfopropyl methacrylate were dissolved in 60 mL of acetonitrile, and 20 mg of methoxyphenol was added as an inhibitor. The resulting mixture was stirred vigorously at room temperature for 12 h. The generated potassium chloride was removed by centrifugation, and the solvent acetonitrile was removed by rotary evaporation. The crude solution was placed in a vacuum drying oven for 12 h to completely evaporate the acetonitrile at room temperature, yielding a viscous yellow oily product, 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate.

[0093] (2) 0.16 mol of methacryloyloxyethyltrimethylammonium chloride was mixed with 160 mL of 1 mol / L lithium bis(trifluoromethanesulfonyl)imide aqueous solution and stirred at room temperature for 6 h. After phase separation, the lower oily liquid was collected and washed several times with deionized water. After vacuum drying at 70 °C for 12 h, a transparent oily product (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide was obtained.

[0094] (3) Dissolve 18 mmol of 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate or (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide in 18 mmol of solvent 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, add 200 μL of crosslinking agent polyethylene glycol diacrylate and 20 mg of initiator azobisisobutyronitrile. After stirring at room temperature for 6 h, a prepolymer with uniform viscosity is obtained. Pour the prepolymer into a 300 μm thick mold and polymerize at 70 °C for 6 h to obtain poly(1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate) ionogel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ionogel, respectively.

[0095] (4) Dissolve activated carbon, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone at a mass ratio of 8:1:1 and stir at room temperature for 12 hours to obtain a viscous electrode slurry. Coat the slurry onto a carbon nanotube film with a 250 μm thick doctor blade and dry it in a vacuum oven at 60 °C for 10 hours to obtain an activated carbon / carbon nanotube composite electrode.

[0096] (5) The two polyionic liquid gel electrolytes obtained in step (3) are respectively attached to the activated carbon / carbon nanotube composite electrode coated with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (3μL), and then the electrolyte side of the two electrodes is pressed together to obtain a supercapacitor based on bilayer heterogeneous polyionic liquid gel electrolyte.

[0097] Figure 12 Cyclic voltammetry curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte constructed with activated carbon / carbon nanotube composite electrodes at different bending angles are shown. It can be seen that the cyclic voltammetry curves almost overlap at different bending angles, indicating that the device possesses excellent flexibility and stable electrochemical performance.

[0098] Figure 13 Cyclic voltammetry curves of a supercapacitor based on a bilayer heterogeneous polyionic liquid gel electrolyte, constructed with activated carbon / carbon nanotube composite electrodes, under different bending cycles are shown. It can be seen that after 3000 bends at 180°, the cyclic voltammetry curves almost overlap, further demonstrating its good flexibility and mechanical stability.

[0099] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A bilayer heterogeneous polyionic liquid gel electrolyte, characterized in that, Composed of ionogels with different Zeta potentials; The bilayer heterogeneous polyionic liquid gel electrolyte is composed of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel. When in use, due to the different Zeta potentials of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel, a small potential difference is formed between the two electrolyte layers after a positive voltage is applied to the supercapacitor for charging. This delays the rearrangement of counterions that accumulate on the electrode surface, thereby inhibiting self-discharge behavior.

2. A method for preparing the bilayer heterogeneous polyionic liquid gel electrolyte as described in claim 1, characterized in that, The specific steps are as follows: S1. Monomer synthesis: 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate and (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide were prepared by ion exchange method; S2. Preparation of prepolymer solution: Dissolve the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate or (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide obtained in step S1 in a solvent, add a crosslinking agent and an initiator, and stir to obtain a prepolymer solution with uniform viscosity. S3. Preparation of ion gels: The prepolymer liquid obtained in step S2 is polymerized by thermal initiation to obtain poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel. S4. Preparation of bilayer heterogeneous polyionic liquid gel electrolyte: The poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and the poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel obtained in step S3 are assembled together to obtain a bilayer heterogeneous polyionic liquid gel electrolyte.

3. The method for preparing a bilayer heterogeneous polyionic liquid gel electrolyte according to claim 2, characterized in that, In step S1, the specific method for preparing the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate is as follows: equimolar amounts of 1-ethyl-3-methylimidazolium chloride and potassium salt of 3-sulfopropyl methacrylate are dissolved in acetonitrile solvent, and methoxyphenol is added as an inhibitor. The resulting mixture is stirred vigorously at room temperature; the generated potassium chloride is removed by centrifugation, and then acetonitrile is removed to obtain a viscous yellow oily product, 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate. The specific method for preparing the monomer (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imine is as follows: equimolar amounts of methacryloyloxyethyltrimethylammonium chloride are mixed with an aqueous solution of lithium bis(trifluoromethanesulfonyl)imine and stirred at room temperature; after phase separation, the lower oily liquid is collected and vacuum dried to obtain the transparent oily product (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imine; The concentration of 1-ethyl-3-methylimidazolium chloride is 0.67~6.67 mol / L. The concentration of the potassium 3-sulfopropyl methacrylate is 0.67~6.67 mol / L. The concentration of the methoxyphenol is 0.17~0.67 mg / mL. The stirring time is 6-12 hours. The method for removing acetonitrile involves first removing part of the solvent acetonitrile through rotary evaporation, and then placing the crude solution in a vacuum drying oven for 6-12 hours at room temperature to completely remove the acetonitrile. The concentration of the methylpropenoxyethyltrimethylammonium chloride is 0.2~5 mol / L. The concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.2~5 mol / L. The stirring time at room temperature is 2-6 hours. The lower oily liquid is first washed with deionized water and then dried. The vacuum drying temperature is 60~80℃. o C, the time is 6~12 hours.

4. The method for preparing a bilayer heterogeneous polyionic liquid gel electrolyte according to claim 2, characterized in that, In step S2, the molar ratio of the monomer 1-ethyl-3-methylimidazolium (3-sulfopropyl) methacrylate to the solvent is 1:(0.1~10). The molar ratio of (2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide to the solvent is 1:(0.1~10). The solvent is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; The crosslinking agent is polyethylene glycol diacrylate, and the amount of polyethylene glycol diacrylate added is 1-5 mol% of the monomer added. The initiator is azobisisobutyronitrile (AIBN), and the amount of AIBN added is 0.5-5 mol% of the monomer amount. The stirring time is 2-6 hours, and the temperature is room temperature; In step S3, the prepolymer liquid is poured into a self-made mold, and then polymerization is initiated by heat. The thermal initiation temperature is 70°C. o C, the time is 2~6 hours.

5. An application of a bilayer heterogeneous polyionic liquid gel electrolyte, characterized in that, The bilayer heterogeneous polyionic liquid gel electrolyte as described in claim 1 is applied to supercapacitors.

6. A supercapacitor, characterized in that, It includes electrode plates on both sides and a bilayer heterogeneous polyionic liquid gel electrolyte as described in claim 1, located between the two electrode plates.

7. A supercapacitor according to claim 6, characterized in that, The electrode plate is a carbon nanotube electrode or an activated carbon / carbon nanotube composite electrode. The bilayer heterogeneous polyionic liquid gel electrolyte is a bilayer heterogeneous polyionic liquid gel electrolyte composed of poly(1-ethyl-3-methylimidazolium(3-sulfopropyl)methacrylate) ion gel and poly((2-methacryloyloxyethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide) ion gel. The thickness of the bilayer heterogeneous polyionic liquid gel electrolyte is 200~600 μm. The carbon nanotube electrode has a thickness of 10~200 μm. The thickness of the activated carbon / carbon nanotube composite electrode is 10~400 μm.

8. A method for preparing a supercapacitor as described in claim 6, characterized in that, The specific steps are as follows: (1) Activated carbon / carbon nanotube composite electrode is obtained by coating activated carbon onto carbon nanotube film by a blade coating method; (2) 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide is dropped onto the surface of carbon nanotube electrode or activated carbon / carbon nanotube composite electrode. Two polyionic liquid gel electrolytes are respectively attached to the cut electrode materials. Then, the electrolyte side of the two electrodes is pressed together to obtain a supercapacitor based on bilayer heterogeneous polyionic liquid gel electrolyte.

9. A method for preparing a supercapacitor according to claim 8, characterized in that, In step (1), the specific preparation method of the activated carbon / carbon nanotube composite electrode is as follows: Dissolve activated carbon, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone, stir to obtain a viscous electrode slurry, coat it onto a carbon nanotube film with a scraper, and dry it in a vacuum oven to obtain the activated carbon / carbon nanotube composite electrode. The activated carbon, conductive carbon black, and polyvinylidene fluoride are in a mass ratio of 8:1:

1. The stirring time is 6-12 hours, and the temperature is room temperature. The drying time is 6-12 hours, and the temperature is 60-80 degrees Celsius. o C, The thickness of the scraper is 100~400 μm; In step (2), the amount of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide used is 1~10 μL / cm relative to the area of ​​the cutting electrode. 2 .

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