Transparent supramolecular ionic gel, preparation method and application of transparent supramolecular ionic gel as electrolyte of electrochromic device

Abstract

The invention relates to the technical field of ionic gel electrolyte, in particular to transparent supramolecular ionic gel, a preparation method and application of the transparent supramolecular ionic gel as electrolyte of an electrochromic device. The transparent supramolecular ionic gel contains a gelator and an ionic liquid; the gel factor is selected from at least one of saccharide gel factors, stearic acid gel factors, surfactant gel factors and cholesterol gel factors, and the molecular weight of the gel factor does not exceed 1000; the ionic liquid is selected from at least one of imidazole ionic liquid, quaternary ammonium salt ionic liquid, pyrrole ionic liquid and quaternary phosphonium salt ionic liquid; the ratio of the gelator in the transparent supramolecular ionic gel is 0.1 to 10 weight percent. Compared with the traditional ionic liquid-polymer gel electrolyte, the transparent supramolecular ionic gel is used as the electrolyte of the electrochromic device, so that the transparent supramolecular ionic gel has higher transparency, and the performance of the electrochromic device is improved.

Description

Technical Field

[0001] The invention relates to the technical field of ion gel electrolytes, and in particular to a transparent supramolecular ion gel, a preparation method and application thereof as an electrolyte for an electrochromic device. Background Art

[0002] Electrochromic devices are electronic devices that use electrochromic materials and can achieve stable optical changes under the drive of external voltage. They are widely used in civilian and military fields such as anti-glare rearview mirrors, smart windows, electronic information displays, and military equipment camouflage. At present, most of the research on electrochromic devices is based on liquid electrolytes, which are mostly composed of salts (such as lithium perchlorate, lithium bromide, lithium hexafluorophosphate, etc.) and organic solvents (acetonitrile, propylene carbonate, ethylene carbonate, etc.). Although this type of electrolyte has good transparency and high ion mobility, it can be easily filled into the device, and the assembled device has good electrochromic effect, but there are also problems such as high toxicity, difficult packaging, easy leakage and flammability.

[0003] As a room temperature molten salt, ionic liquids have attracted widespread attention due to their non-flammability, low volatility, high ionic conductivity and thermal stability, as well as a wide electrochemical window. Current research includes the use of ionic liquids with polymers such as polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polymethyl methacrylate to prepare ion gels as electrolytes for use in electrochromic devices. Although it can avoid the problems of high toxicity, difficulty in packaging, easy leakage, and flammability of traditional liquid electrolytes, its low ionic conductivity and transparency will lead to reduced performance of electrochromic devices, limiting its practical application. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a transparent supramolecular ion gel, a preparation method and an application as an electrolyte for electrochromic devices, which solves the problems of low ionic conductivity and poor transparency of ionic liquid-polymer gel electrolytes, thereby improving the performance of electrochromic devices and expanding their applications.

[0006] (II) Technical solution

[0007] In a first aspect, the present invention provides a transparent supramolecular ionic gel, comprising a gelling factor and an ionic liquid; the gelling factor is at least one selected from sugars, stearic acid, surfactants and cholesterol-type gelling factors, and the molecular weight of the gelling factor does not exceed 1000; the proportion of the gelling factor in the transparent supramolecular ionic gel is 0.1-10wt%.

[0008] The molecular weight of the gel factor is no more than 1000, which helps to enhance the ionic conductivity of the gel and improve the transparency of the gel. At the same time, the relatively low molecular weight gel factor is more easily dissolved in the ionic liquid and may provide better processing properties, such as easy to form a uniform film or coating.

[0009] According to a preferred embodiment of the present invention, the transparent supramolecular ion gel is composed of a gel factor and an ionic liquid, and the gel factor accounts for 0.1-10 wt % of the total mass of the gel factor and the ionic liquid.

[0010] According to a preferred embodiment of the present invention, the transparent supramolecular ion gel further comprises a redox medium and an electrochromic material.

[0011] According to a preferred embodiment of the present invention, the redox medium is ferrocene, and the electrochromic material is a viologen small molecule compound, preferably a diheptyl-substituted viologen. The electrochromic material may also be other small molecule compounds or polymer color-changing materials.

[0012] According to a preferred embodiment of the present invention, the ionic liquid is selected from at least one of imidazole ionic liquids, quaternary ammonium salt ionic liquids, pyrrole ionic liquids and quaternary phosphonium salt ionic liquids.

[0013] According to a preferred embodiment of the present invention, the content of the redox medium in the transparent supramolecular ion gel is 0.5-1.0 wt %; the content of the electrochromic material in the transparent supramolecular ion gel is 2-4 wt %.

[0014] The explanations of sugar, stearic acid, surfactant and cholesterol gelling factors are as follows:

[0015] Carbohydrate gelling factors: This type of gelling factor usually contains one or more glycosyl units, which can be linked together by glycosidic bonds or combined with other types of molecules to form complex structures. For example, cyclodextrin (α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin) is a common carbohydrate gelling factor, which is a ring structure composed of glucose units. In addition, there are some gelling factors based on natural polysaccharide derivatives such as cellulose and chitosan.

[0016] Stearic acid gel factors: Stearic acid and its derivatives are typical examples. These compounds contain long-chain alkyl parts and polar head groups. Sodium stearate is a commonly used gel factor. Its long chains can be entangled and stacked with each other, and its carboxylate ions can strengthen this stacking through hydrogen bonds or other weak interactions, thus forming a stable gel network.

[0017] Surfactant gelators: This category includes various cationic, anionic and nonionic surfactants. They generally have a hydrophilic head and a hydrophobic tail, and can self-assemble into micelles, lamellar phases or other more complex structures under appropriate conditions. Some specific surfactants such as hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) can form gels at appropriate concentrations, especially when used with appropriate additives.

[0018] Cholesterol gelling factors: Cholesterol itself is an important gelling factor. Due to its unique rigid steroid skeleton, it can effectively participate in the formation and stabilization of membrane structure. Cholesterol gelling factors also include some cholesterol derivatives, such as cholesterol esters or cholesterol-grafted polymers, which can regulate the properties of gels by regulating the interactions between molecules.

[0019] In a second aspect, the present invention provides a method for preparing a transparent supramolecular ionic gel, comprising: S1, mixing a gel factor and an ionic liquid, and homogenizing the mixture to obtain a mixed solution;

[0020] S2, heating the mixed solution until it becomes a homogeneous transparent solution;

[0021] S3, cooling the homogeneous transparent solution to obtain the transparent supramolecular ion gel.

[0022] According to a preferred embodiment of the present invention, in S1, during the process of mixing the gel factor with the ionic liquid, a redox medium and an electrochromic material are also added; preferably, the redox medium is ferrocene, and the electrochromic material is a viologen small molecule compound, preferably a diheptyl-substituted viologen. Further, the content of ferrocene in the transparent supramolecular ion gel is 0.5-1.0wt%; the content of diheptyl-substituted viologen in the transparent supramolecular ion gel is 2-4wt%.

[0023] According to a preferred embodiment of the present invention, in S1, the homogenization process includes any one of stirring, shaking, pumping, and ultrasonic treatment.

[0024] According to a preferred embodiment of the present invention, in S2, the heating temperature is 110-120°C, and the heating time is 10-30 minutes.

[0025] In a third aspect, the present invention provides the use of the transparent supramolecular ion gel in the preparation of an electrochromic device.

[0026] In a fourth aspect, the present invention provides an electrochromic device, comprising a first transparent electrode layer, a transparent supramolecular ion gel electrolyte film layer and a second transparent electrode layer stacked in sequence;

[0027] The transparent supramolecular ion gel electrolyte membrane layer is formed by the transparent supramolecular ion gel of any of the above embodiments.

[0028] According to a preferred embodiment of the present invention, the first transparent electrode layer is composed of a first transparent electrode and a first electrochromic film covering its surface, and the second transparent electrode layer is composed of a second transparent electrode and a second electrochromic film covering its surface.

[0029] Preferably, the electrochromic device is a flexible electrochromic device or a rigid electrochromic device; specifically, when the first transparent electrode layer and the second transparent electrode layer are flexible, a flexible electrochromic device can be obtained; conversely, when the first transparent electrode layer and the second transparent electrode layer are rigid, a rigid electrochromic device can be obtained.

[0030] According to a preferred embodiment of the present invention, the first transparent electrode and the second transparent electrode are ITO electrodes.

[0031] According to a preferred embodiment of the present invention, the first electrochromic film is a PRODT polymer, and the second electrochromic film is a PEDOT:PSS polymer.

[0032] In a fifth aspect, the present invention provides a method for preparing an electrochromic device, comprising:

[0033] S1, mixing the gel factor and the ionic liquid, and homogenizing them to obtain a mixed solution;

[0034] S2, heating the mixed solution until it becomes a homogeneous transparent solution;

[0035] S3, injecting the homogeneous transparent solution between two electrochromic electrode layers, and after cooling, the homogeneous transparent solution forms a transparent supramolecular ion gel electrolyte; or, cooling the homogeneous transparent solution to form a transparent supramolecular ion gel, and then injecting the transparent supramolecular ion gel between two electrochromic electrode layers by injection.

[0036] Preferably, the first transparent electrode layer is composed of a first transparent electrode and a first electrochromic film covering its surface, and the second transparent electrode layer is composed of a second transparent electrode and a second electrochromic film covering its surface; the first electrochromic film is a PRODT polymer, and the second electrochromic film is a PEDOT:PSS polymer.

[0037] In electrochromic devices, ferrocene acts as a redox medium to assume the function of an electron transfer hub, and diheptyl substituted viologen acts as the main color-changing material to achieve optical response. The two achieve synergistic performance optimization through molecular design. Ferrocene can reduce the driving voltage of electrochromic devices, improve cycle stability, and shorten response time. Ferrocene itself is light yellow, which will also affect the color display of the device. Therefore, when selecting a redox medium, it is preferred to use colorless or lighter materials.

[0038] (III) Beneficial effects

[0039] The present invention adopts a gel factor and an ionic liquid to prepare a non-polymer-based gel, and directly heats and dissolves to form a homogeneous transparent solution. During the cooling process, the solution forms a supramolecular ionic gel based on the self-assembly effect of the gel factor. The entire preparation process is simple and convenient. Compared with traditional polymer ionic gels, the preparation method of the present invention is simpler.

[0040] Since the amount of gel factor used in the supramolecular ion gel is extremely low, usually less than 5wt%, this makes the supramolecular ion gel have high ionic conductivity and high optical transmittance close to that of pure ionic liquids, solving the problems of low ionic conductivity and poor transparency of ionic liquid-polymer gel electrolytes, thereby improving the performance of electrochromic devices and expanding their applications. In addition, the characteristics of the non-covalent self-assembly of the gel factor also give the gel self-healing properties.

[0041] The present invention uses this simple-to-prepare, high-ionic conductivity and optical transmittance, and self-repairing supramolecular ion gel as the electrolyte of the electronic color-changing device, which can not only avoid the problems of high toxicity, difficulty in packaging, easy leakage and flammability brought by traditional liquid electrolytes, but also improve the performance of the electrochromic device, such as response rate, coloring efficiency, optical contrast, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a photograph of the supramolecular ion gel of Example 1.

[0043] Figure 2 This is the test result of the ionic conductivity of the supramolecular ion gel of Example 1.

[0044] Figure 3 This is the SEM image of the supramolecular ion gel of Example 1.

[0045] Figure 4 The voltage-ultraviolet absorption spectrum test results of the electrochromic device of Example 9.

[0046] Figure 5 This is a comparison diagram of the electrochromic device of Example 9 before and after color change due to application of voltage.

[0047] Figure 6 This is the ultraviolet dynamic spectrum of the electrochromic device of Example 9.

[0048] Figure 7 This is a test chart of the color change cycle stability of the electrochromic device of Example 9.

[0049] Figure 8 This is a bending cycle test diagram of the flexible electrochromic device of Example 17.

[0050] Fig. 9 This is the voltage-UV absorption spectrum of the composite electrochromic device of Example 18.

[0051] Fig.10 This is the ultraviolet dynamic spectrum of the composite electrochromic device of Example 18.

[0052] Fig.11 This is a test chart of the color change cycle stability of the composite electrochromic device of Example 18. DETAILED DESCRIPTION

[0053] According to the inventor's research, in addition to polymers that can make ionic liquids form gels, some special small molecules can also make ionic liquids form gels, and these special small molecules are also called gel factors. First, the gel factor self-assembles into a slender fiber structure through non-covalent weak interactions such as hydrogen bonds, van der Waals effects, π-π stacking, hydrophobic effects, and electrostatic effects when cooling, and then the slender fibers are entangled with each other to form a three-dimensional network structure that can constrain and fix the solvent, and the ionic liquid is bound therein to obtain a supramolecular ion gel seen macroscopically. This type of supramolecular ion gel has the characteristics of simple preparation, high ionic conductivity and self-repair. If it is used as an electrolyte in an electrochromic ion gel, it can not only avoid the problems of large toxicity, difficult packaging, easy leakage and flammability of liquid electrolytes like polymerized ion gels, but also compared to traditional ionic liquid-polymer gel electrolytes, the supramolecular ion gel based on the gel factor provided by the present invention has higher ionic conductivity and transparency, so the performance of the electrochromic device can be significantly improved.

[0054] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with the accompanying drawings through specific implementation methods. In the following embodiments, the specific test methods and instruments used include:

[0055] Ionic conductivity test: Ray-Magnetic DZS-706-A multi-parameter analyzer;

[0056] Scanning electron microscope (SEM) test: TESCAN MIRA3 field emission scanning electron microscope;

[0057] Voltage-UV absorption spectrum test: Shimadzu UV-2600 UV-visible spectrophotometer is used in conjunction with Chenhua CHI760EA17427 electrochemical workstation, and the test mode is spectrum scanning;

[0058] UV kinetic spectrum test: Shimadzu UV-2600 UV-visible spectrophotometer was used in conjunction with Chenhua CHI760E A17427 electrochemical workstation, and the test mode was kinetic scanning;

[0059] Bending cycle test: Jiangsu Moxin MX-0580 electronic universal testing machine.

[0060] Example 1

[0061] This embodiment provides a supramolecular ion gel, and the preparation method thereof is as follows:

[0062] Use an electronic balance to accurately weigh 0.95 g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (BMIM[TFSI]) and 0.05 g of carbohydrate gel factor (β-cyclodextrin), add them to a sample bottle, and mix them evenly by ultrasonication for 10 minutes to obtain a mixed solution. The mixed solution is placed in a 120°C forced air drying oven and heated for 20 minutes until it becomes a homogeneous transparent solution. The homogeneous transparent solution is cooled to room temperature by self-heating, and the homogeneous transparent solution gradually becomes a gel, which is the supramolecular ionic gel of this embodiment (such as Figure 1 As shown), the gel factor content is 5wt%.

[0063] The supramolecular ion gel prepared in this example was tested, and the test results are as follows.

[0064] (1) Ionic conductivity test

[0065] The test results are as follows Figure 2 As shown in the figure, it can be seen that the ionic conductivity of the supramolecular ionic gel of this embodiment is 3.13mS / cm, which is close to 4.10mS / cm of pure ionic liquid. This is because the content of the gel factor used is extremely low, only 5wt%, which makes the binding force of the gel factor lower and the ionic liquid can be freely transmitted inside the gel.

[0066] (2) Scanning electron microscope (SEM) observation

[0067] The results are as follows Figure 3 As shown in the figure, in the microscopic morphology of supramolecular ion gel, the gel factor self-assembles through weak non-covalent interactions such as hydrogen bonds, van der Waals forces, and π-π stacking to form a slender fiber structure. These slender fibers are further entangled with each other to form a three-dimensional network structure, which binds the ionic liquid to form a gel observed from a macroscopic perspective.

[0068] Example 2

[0069] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the ionic liquid used is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]).

[0070] Example 3

[0071] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the ionic liquid used is a pyridine ionic liquid 1-butylpyridinium hexafluorophosphate ([BPy][PF6]).

[0072] Example 4

[0073] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the ionic liquid used is a quaternary ammonium salt ionic liquid tetrabutylammonium bistrifluoromethanesulfonyl imide salt ([N4441][TFSI]).

[0074] Example 5

[0075] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the ionic liquid used is a quaternary phosphonium salt ionic liquid trihexyltetradecylphosphonium bistrifluoromethanesulfonyl imide salt ([P66614][TFSI]).

[0076] Example 6

[0077] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the gel factor used is sodium stearate.

[0078] Example 7

[0079] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the gel factor used is hexadecyltrimethylammonium bromide (CTAB).

[0080] Example 8

[0081] This embodiment provides a supramolecular ion gel, and its preparation method and ion conductivity test method are consistent with those of Example 1. The difference is that the gel factor used is cholesterol benzoate.

[0082] Example 9

[0083] This embodiment provides an electrochromic device, and the preparation method thereof is as follows:

[0084] Use an electronic balance to accurately weigh 2.88g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (BMIM[TFSI]), 0.15g of carbohydrate gel factor (γ-cyclodextrin), 0.0186g of ferrocene and 0.092g of diheptyl substituted viologen (electrochromic material), add these substances to a sample bottle, and mix them evenly by ultrasonication for 10 minutes to obtain a mixed solution. The mixed solution is placed in a blast drying oven at 120°C and heated for 25 minutes until it becomes a homogeneous solution (gel factor content is 4.776wt%). Use double-sided tape to bond two 5*5cm ITO glasses, the bonding surface is the ITO surface, and the two sides are separated by double-sided tape, with a gap of about 0.1mm. Inject the heated homogeneous solution into the gap formed by the two ITO glasses with a syringe, and wait for the solution to cool to form an electrochromic gel. At this point, the electrochromic device is completed.

[0085] The electrochromic device prepared in this example was tested as follows:

[0086] (1) Voltage-UV absorption spectrum test

[0087] The electrochromic device was tested using a UV spectrometer under different voltages. Figure 4 As shown, the electrochromic device has a maximum absorption peak at 607nm. As the voltage increases, its absorbance also increases until it reaches -1.2V. Further increasing the voltage has a limited effect on the absorbance. At the same time, because excessive voltage will reduce the stability of the device, its best working voltage is -1.2V. The following tests are based on the applied voltage between -1.2V and 0V as the test conditions.

[0088] like Figure 5 As shown, it is a comparison chart of the electrochromic device before and after color change. It can be seen from the figure that when no voltage is applied, the color of the device is light yellow, which is due to the addition of yellow ferrocene. When -1.2V voltage is applied, the color of the device changes to blue.

[0089] (2) UV kinetic spectroscopy test

[0090] The ultraviolet dynamic spectrum of the electrochromic device was tested at 607nm between -1.2V and 0V. The test results are as follows Figure 6 As shown in the figure, it can be seen that the optical contrast of the electrochromic device is 91%, the coloring time is 21s, and the decolorization time is 48s.

[0091] (3) Electrochromic cycle stability test

[0092] The voltage was repeatedly applied between -1.2 V and 0 V, and the cycle stability of the electrochromic device was tested at 607 nm. The test results are as follows: Figure 7 As shown in the figure, after 1000 cycles, the optical contrast of the electrochromic device can still be maintained at 85.8% of the original value, indicating that the electrochromic device has good color change cycle stability. In practical applications, it is usually hoped that the optical contrast can reach at least 30% to 50%, and when the optical contrast reaches more than 60%, it is considered to have a very high contrast and can produce a very clear visual effect.

[0093] Example 10

[0094] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of Embodiment 9. The difference is that the ionic liquid used is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]).

[0095] Embodiment 11

[0096] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of Embodiment 9. The difference is that the ionic liquid used is a pyridine ionic liquid 1-butylpyridinium hexafluorophosphate ([BPy][PF6]).

[0097] Example 12

[0098] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of Embodiment 9. The difference is that the ionic liquid used is a quaternary ammonium salt ionic liquid tetrabutylammonium bistrifluoromethanesulfonyl imide salt ([N4441][TFSI]).

[0099] Embodiment 13

[0100] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of Embodiment 9. The difference is that the ionic liquid used is a quaternary phosphonium salt ionic liquid trihexyltetradecylphosphonium bistrifluoromethanesulfonyl imide salt ([P66614][TFSI]).

[0101] Embodiment 14

[0102] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of embodiment 9. The difference is that the gel factor used is sodium stearate.

[0103] Embodiment 15

[0104] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of Embodiment 9. The difference is that the gel factor used is cetyltrimethylammonium bromide (CTAB).

[0105] Example 16

[0106] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of embodiment 9. The difference is that the gel factor used is cholesterol benzoate.

[0107] Embodiment 17

[0108] This embodiment provides a flexible electrochromic device, and the preparation method thereof is as follows:

[0109] Use an electronic balance to accurately weigh 2.88g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (BMIM[TFSI]), 0.15g of carbohydrate gel factor (β-cyclodextrin), 0.0186g of ferrocene and 0.092g of diheptyl substituted viologen (electrochromic material), add these substances to a sample bottle, and mix them evenly by ultrasonication for 10 minutes to obtain a mixed solution (gel factor content is 4.776wt%). Place the mixed solution in a 120°C forced air drying oven and heat it for 25 minutes until it becomes a homogeneous solution. Use double-sided tape to attach two 4*4cm ITO-PET films (film thickness is about 200μm), with the attaching surface being the ITO surface, and the two sides separated by double-sided tape, with a gap of about 0.1mm. The heated homogeneous solution is injected into the gap formed by two ITO-PET films using a syringe, and the solution is allowed to cool to form an electrochromic gel. At this point, the bendable flexible electrochromic device is completed.

[0110] The flexible electrochromic device prepared in this example was subjected to a bending cycle test, and the results were as follows:

[0111] The flexible electrochromic device of this embodiment was placed in a universal testing machine and subjected to 50 and 1000 bending cycle tests with a compression amplitude of 10 mm. The test results are shown in FIG. Figure 8 As shown in the figure, after 50 times, the ultraviolet kinetic spectrum of the electrochromic device almost overlaps with the initial ultraviolet kinetic spectrum, and after 1000 bending cycles, the optical contrast of the flexible electrochromic device can still be maintained at more than 88% of the initial value. This shows that the flexible electrochromic device has good bendability.

[0112] Embodiment 18

[0113] This embodiment relates to a composite electrochromic device composed of a first transparent electrode layer, a transparent supramolecular ion gel electrolyte film layer and a second transparent electrode layer, and the preparation method is as follows:

[0114] 20 mg of electrochromic polymer PRODT was mixed with 10 mL of xylene to form solution A, and 4 mL of PEDOT:PSS was mixed with 16 mL of ethanol to form solution B. Solution A and solution B were sprayed on the ITO surface of 5*5 cm ITO glass respectively, and then placed in a blast drying oven at 80°C to form a film. The two ITO glasses that had been sprayed were bonded with double-sided tape, with the bonding surface being the ITO surface, and the gap between the two surfaces being about 0.1 mm.

[0115] Use an electronic balance to accurately weigh 0.95g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (BMIM[TFSI]) and 0.05g of carbohydrate gel factor (α-cyclodextrin), add them to the sample bottle, and mix them evenly by ultrasonication for 10 minutes to obtain a mixed solution. Heat the mixed solution in a 120°C forced air drying oven until it becomes a homogeneous and transparent solution. Inject the heated homogeneous solution into the gap formed by two pieces of sprayed ITO glass with a syringe, and wait for the solution to cool to form an electrochromic gel. At this point, the electrochromic device is completed.

[0116] The electrochromic device prepared in this example was tested, and the results were as follows:

[0117] (1) Voltage-UV absorption spectrum test

[0118] The electrochromic device was tested using a UV spectrometer under different voltages. The test results are as follows: Fig. 9 As shown in the figure, the electrochromic device has a maximum absorption peak at 548nm. As the voltage increases, its absorbance also increases until it reaches 0.8V. Further increasing the voltage has a limited effect on the absorbance. At the same time, because excessive voltage will reduce the stability of the device, its best working voltage is 0.8V. The following tests are conducted with the applied voltage between -0.8V and 0.8V as the test conditions.

[0119] (2) UV kinetic spectroscopy test

[0120] The ultraviolet kinetic spectrum of the electrochromic device was tested at 548 nm between 0.8 V and -0.8 V. The test results are as follows Fig.10 As shown: the optical contrast of the electrochromic device is 52%, the coloring time is 0.6s, the decolorization time is 0.4s, and the response speed is very fast, which is better than most of the currently known electrochromic devices.

[0121] (3) Cyclic stability test

[0122] A voltage between 0.8 V and -0.8 V was applied, and the cycling stability of the electrochromic device was tested at 548 nm. The test results are shown in Fig.11As shown, after 10,000 cycles, the optical contrast of the electrochromic device can still be maintained at 94.7% of the original value. This shows that the electrochromic device has excellent stability and also reflects that the supramolecular ion gel used has stable electrochemical properties.

[0123] Comparative Example 1

[0124] The carbohydrate gelling factor (β-cyclodextrin) in Example 1 was removed, and the ionic conductivity of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSI]) was directly tested.

[0125] Comparative Example 2

[0126] This embodiment provides a traditional polymer ion gel. The preparation method is as follows: 1.18g of polymer polymethyl methacrylate (PMMA, molecular weight of about 200000) and 2.75g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl imide) ([BMIM][TFSI]) are added to 20mL of tetrahydrofuran, stirred evenly for 30min, and then treated with an ultrasonic machine for 10min. The treated mixed solution is poured into a polytetrafluoroethylene mold and dried at 40°C for 24h, and the tetrahydrofuran is removed to obtain the polymer ion gel.

[0127] Comparative Example 3

[0128] This embodiment provides an electrochromic device, and its preparation method and testing method are consistent with those of embodiment 9. The difference is that the gelling factor γ-cyclodextrin is not used in the preparation process.

[0129] Comparative Example 4

[0130] The present embodiment provides an electrochromic device, and its preparation method is as follows. 1.18g of polymer polymethyl methacrylate (PMMA, molecular weight is about 200000) and 2.75g of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIM][TFSI]), 0.0186g of ferrocene and 0.092g of diheptyl substituted viologen (DHV[TFSI]2, electrochromic material) are added to 20mL of tetrahydrofuran, stirred evenly for 30min, and then treated with an ultrasonic machine for 10min. The treated mixed solution is poured into a polytetrafluoroethylene mold and baked at 40°C for 24h, and the tetrahydrofuran is removed to obtain a polymer gel. The obtained polymer is placed in two pieces of ITO-glass and taped tightly with double-sided tape to obtain the electrochromic device.

[0131] Table 1 shows the ion gel preparation parameters and ion conductivity test results of Examples 1 to 8 and Comparative Examples 1 to 2.

[0132]

[0133]

[0134] Table 2 shows the preparation parameters and performance test results of the electrochromic devices of Examples 9 to 16 and Comparative Examples 3 to 4.

[0135]

[0136] In combination with Table 1-2, by comparing Example 1 with Comparative Examples 1-2, it can be seen that when a gelling factor is added to the ionic liquid to form a gel, its ionic conductivity does not decrease much compared with the pure ionic liquid. When a traditional polymer is used to prepare a polymer gel, its ionic conductivity decreases by an order of magnitude.

[0137] It can be seen from Examples 1 to 8 that supramolecular ionic gels can still be formed by using other gelling factors or ionic liquids, and the ionic conductivity of the supramolecular ionic gel depends on the ionic conductivity of the ionic liquid itself, which is related to the size of its structure and the difficulty of dissociation, and is less affected by the gelling factor.

[0138] It can be seen from Example 9, Comparative Example 3 and Comparative Example 4 that when supramolecular ion gel is used as the electrolyte of the electrochromic device, the response time and cycle performance of the electrochromic device are not much different from those when pure ionic liquid is used as the electrolyte, but compared with the electrochromic device using traditional polymer ion gel as the electrolyte, the performance is better.

[0139] It can be concluded from Example 18 and Example 19 that the supramolecular ion gel can be used in electrochromic devices assembled from electrochromic polymers, and can also be used as an electrolyte for flexible electrochromic devices.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A transparent supramolecular ion gel, characterized in that: It comprises a gelling factor and an ionic liquid; the gelling factor is at least one selected from sugars, stearic acid, surfactants and cholesterol-based gelling factors, and the molecular weight of the gelling factor does not exceed 1000; the ionic liquid is at least one selected from imidazole ionic liquids, quaternary ammonium salt ionic liquids, pyrrole ionic liquids and quaternary phosphonium salt ionic liquids; the proportion of the gelling factor in the transparent supramolecular ionic gel is 0.1-10wt%.

2. The transparent supramolecular ion gel according to claim 1, characterized in that: The transparent supramolecular ion gel is composed of a gel factor and an ionic liquid; Alternatively, the transparent supramolecular ion gel contains a gel factor, an ionic liquid, a redox mediator and an electrochromic material.

3. The transparent supramolecular ion gel according to claim 2, characterized in that: The redox medium is ferrocene, and the electrochromic material is a viologen small molecule compound, preferably a diheptyl-substituted viologen.

4. The transparent supramolecular ion gel according to claim 2, characterized in that: The content of the redox medium in the transparent supramolecular ion gel is 0.5-1.0wt%; the content of the electrochromic material in the transparent supramolecular ion gel is 2-4wt%.

5. A method for preparing a transparent supramolecular ion gel, characterized in that: It includes: S1, mixing the gel factor and the ionic liquid, and homogenizing them to obtain a mixed solution; S2, heating the mixed solution until it becomes a homogeneous transparent solution; S3, cooling the homogeneous transparent solution to obtain the transparent supramolecular ion gel.

6. The preparation method according to claim 5, characterized in that: In S1, during the process of mixing the gel factor with the ionic liquid, a redox medium and an electrochromic material are also added.

7. The preparation method according to claim 5, characterized in that: In S1, the homogenization treatment includes any one of stirring, shaking, suction, and ultrasonic treatment; in S2, the heating temperature is 110-120° C., and the heating time is 10-30 min.

8. Use of the transparent supramolecular ion gel according to any one of claims 1 to 4 in the preparation of electrochromic devices.

9. An electrochromic device, characterized in that: It comprises a first transparent electrode layer, a transparent supramolecular ion gel electrolyte film layer and a second transparent electrode layer which are stacked in sequence; The transparent supramolecular ion gel electrolyte membrane layer is formed by the transparent supramolecular ion gel according to any one of claims 1 to 4.

10. The electrochromic device according to claim 9, characterized in that: The first transparent electrode layer is composed of a first transparent electrode and a first electrochromic film covering the surface thereof, and the second transparent electrode layer is composed of a second transparent electrode and a second electrochromic film covering the surface thereof.

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