A flexible stretchable electrochromic device and a method of making the same

Abstract

The application discloses a kind of flexible stretchable electrochromic device and preparation method thereof, comprising: hydrogel-based flexible substrate, electrochromic layer and conductive electrode layer, hydrogel-based flexible substrate is 2-acrylamide-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel with excellent transparency, stretchability and ionic conductivity and acrylamide hydrogel with excellent transparency and stretchability, electrochromic layer is the uniform composite layer formed by drop coating after mixing the solution of tungsten oxide quantum dots prepared by hydrothermal method and poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution, and the conductive electrode layer is prepared by spin coating after compounding silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution.In the application, the flexible stretchable electrochromic device has excellent flexibility (cyclic stretching 1000 times under 200% tensile elongation), fast response speed and good optical contrast (DT=34%).

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochromic device preparation, and particularly relates to a flexible stretchable electrochromic device and a preparation method thereof. BACKGROUND

[0002] As a new intelligent soft electronic device, the flexible electrochromic device has the characteristics of high controllability, fast response speed and low power consumption, and can realize fast information interaction display between man and machine, and has wide application prospects in the fields of intelligent wearable devices, electronic skin and energy storage devices, and provides a feasible strategy for the development of the next generation of electronic products and is widely concerned. However, the flexible electrochromic device prepared at present is limited by the flexible substrate and the conductive electrode, and can only realize bending within a certain angle and stretching within a small degree. At the same time, due to the complexity of the device structure, there is a large modulus mismatch between the two material layers connected to each other when a large degree of deformation is borne, the mechanical and chemical compatibility at the interface is poor, and delamination phenomenon is easy to occur, which affects the response speed, optical contrast and the like of the device, resulting in low comprehensive performance of the electrochromic device. Therefore, in order to make the electrochromic device integrated into wearable devices or applied on non-planar surfaces to remain comfortable, shape-retaining and durable, it is very necessary to develop a visual, personalized and simple stretchable or deformable electrochromic device.

[0003] The flexible conductive electrode with high transparency, conductivity, excellent mechanical property and electrochemical stability is a key factor for constructing the stretchable electrochromic device. At present, the stretchable conductive electrode is usually prepared by mixing the conductive material with the elastomer or the polymer or by attaching the conductive material on the flexible substrate through various ways (drop coating, spin coating, spraying, blade coating, etc.). Among the conductive materials, the metal nanowires (silver nanowires, gold nanowires) and the conductive polymers (poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid, polyaniline, polypyrrole, etc.) are usually used as the active conductive substance due to their excellent flexibility, conductivity and electrochemical stability. Among them, the silver nanowire network is considered as a promising conductive material due to its high transparency and excellent conductivity. However, the bare silver nanowires are easy to be oxidized in the long-term electrochemical cycling environment or the humid environment, resulting in rapid deterioration of the electrode performance with the silver nanowire network. The flexible substrate is another key factor for realizing the stretchable electrochromic device. The commonly used flexible substrates at present include polydimethylsiloxane, hydrogenated styrene-butadiene-styrene (SEBS) triblock copolymer, Ecoflex, polyurethane and fabric with good elasticity, which all exhibit excellent transparency, flexibility and chemical stability. However, it is often necessary to adopt modification treatment, functional group endowment, composite of multiple materials and the like to realize the preparation of the flexible substrate with high stretchability, excellent ductility and adaptability, so that the Young's modulus can be matched with most soft tissues and the mechanical mismatch at the interface is reduced. SUMMARY

[0004] The present application aims to solve the technical problems that the existing flexible electrochromic device cannot simultaneously have arbitrary angle bending and large degree of stretching, fast response speed, repeated stretching cycle stability, etc., and thus provides a flexible electrochromic device and a preparation method thereof. In the present application, the flexible stretchable electrochromic device has excellent flexibility (200% tensile elongation rate, 1000 times of cyclic stretching), fast response speed and good optical contrast (DT=34%). Compared with other related reported devices, the tensile elongation rate of the device is increased by about 4 times, and the tensile cycle stability is increased by about 2.5 times on the basis of maintaining the electrochromic performance.

[0005] The present application adopts the following technical solutions:

[0006] A preparation method of a flexible stretchable electrochromic device, comprising the following steps:

[0007] (1) 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is prepared by taking acrylamide, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid and lithium chloride as raw materials;

[0008] (2) An acrylamide hydrogel-based flexible substrate is prepared by taking acrylamide as a raw material;

[0009] (3) A silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution is formed by taking ethylene glycol, isopropyl alcohol, poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution, silver nanowire and surfactant as raw materials;

[0010] (4) The silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution is prepared into a conductive electrode layer, and the acrylamide hydrogel flexible substrate is attached to form a conductive electrode layer on the surface of the acrylamide hydrogel flexible substrate;

[0011] (5) Tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid electrochromic solution is prepared by mixing tungsten oxide quantum dots, poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution and surfactant;

[0012] (6) The tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid electrochromic solution is prepared into an electrochromic layer, and then a 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is attached, so that the electrochromic layer is formed on the surface of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate; optionally, the electrochromic solution is drop-coated on the surface of a glass, so that an electrochromic layer is obtained, and then the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is attached, so that the electrochromic layer is transferred to the surface of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate; preferably, the plasma hydrophilic treatment conditions of the glass are as follows: the pressure is 60 Pa, the time is 10 min, and the power is 100 W; the volume of the drop-coated solution is 100 ul, the drying temperature of the oven is 60 DEG C, and the drying time of the oven is 30 min.

[0013] (7) The acrylamide hydrogel flexible substrate with a conductive electrode layer is attached to the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel flexible substrate with an electrochromic layer, so that a flexible stretchable electrochromic device is prepared.

[0014] In the present application, in step (1), the acrylamide, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, lithium chloride, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water are mixed to form a uniform solution, and then dried to prepare the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate. Preferably, the mass ratio of the acrylamide, acrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, lithium chloride, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water is (20-30):(10-17):(4-7):(10-20):(0.15-0.2):(0.1-0.15):(1.5-2):100.

[0015] In the present application, in step (2), the acrylamide, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water are mixed and stirred, and then dried to prepare the acrylamide hydrogel-based flexible substrate. Preferably, the mass ratio of the acrylamide, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water is (20-30):(0.15-0.2):(0.1-0.15):(1.5-2):100.

[0016] In the present application, in step (3), ethylene glycol and isopropanol constitute the cosolvent; the cosolvent is mixed with the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid solution and the surfactant to form a poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid / cosolvent composite solution, and the cosolvent is mixed with the silver nanowire to form a silver nanowire / cosolvent composite solution; the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid / cosolvent composite solution and the silver nanowire / cosolvent composite solution are mixed to form a silver nanowire / poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid composite solution. Preferably, the mass ratio of ethylene glycol to isopropanol is 1: (0.8-1.2); in the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid / cosolvent composite solution, the mass ratio of the cosolvent to the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid solution is 1: (3-5); in the silver nanowire / cosolvent composite solution, the mass ratio of the cosolvent to the silver nanowire is 1: (3-5); and the mass ratio of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid / cosolvent composite solution to the silver nanowire / cosolvent composite solution is (1.5-2.5):1. The stirring time for mixing the cosolvent with the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid and the silver nanowire with the cosolvent is 30 min. Preferably, according to the mass ratio, the proportion of the cosolvent is ethylene glycol:isopropanol=1:1, the mass ratio of the cosolvent to the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid solution is 1:4, the mass ratio of the cosolvent to the silver nanowire is 1:4, and the mass ratio of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid / cosolvent solution to the silver nanowire / cosolvent solution is 2:1.

[0017] In the present application, in step (4), the silver nanowire / poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid composite solution is spin-coated to prepare a conductive electrode layer; the spin-coating process is as follows: the spin-coating speed is 1000-3000 r / min, the spin-coating time is 50-70 s, and the adhering time is 5-15 min. Preferably, the spin-coating speed is 1000-3000 r / min, the spin-coating time is 60 s, and the hydrogel adhering time is 10 min.

[0018] In the present application, in step (5), tungsten oxide quantum dots are prepared by one-step hydrothermal method; the hydrothermal reaction temperature is 170-190 ℃, and the hydrothermal reaction time is 40-55 h; preferably, the hydrothermal reaction temperature is 180 ℃, and the hydrothermal reaction time is 48 h. In the tungsten oxide quantum dot / poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid electrochromic solution, the concentration of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid in the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid solution is 1.3%; the mass ratio of the poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid solution to the tungsten oxide quantum dot solution to H2O is 1:2:1, and the content of the surfactant is 0.25%.

[0019] The application discloses application of the flexible stretchable electrochromic device in preparation of a flexible electrochromic device or as a flexible electrochromic device.

[0020] The hydrogel-based flexible substrate of the flexible stretchable electrochromic device is a 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate and an acrylamide hydrogel-based flexible substrate; the electrochromic layer is prepared by drop coating of a tungsten oxide quantum dot / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution; and the conductive electrode layer is prepared by spin coating of a silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution.

[0021] Preferably, the thickness of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is 3-4 mm; the thickness of the acrylamide hydrogel-based flexible substrate is 3-4 mm; the thickness of the electrochromic layer is 0.357-2.56 um; and the thickness of the conductive electrode layer is 1-2 mm.

[0022] The application has the following beneficial effects:

[0023] (1) The electrochromic composite solution prepared by mixing the hydrothermally prepared tungsten oxide quantum dots and the poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution exhibits excellent response speed and good optical contrast, and the color change performance of the electrochromic solution can be regulated by regulating the mass ratio of the tungsten oxide quantum dots and the poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution, and the preparation process is simple, safe and reliable.

[0024] (2) The flexible electrochromic device prepared in the application uses a hydrogel to replace a traditional flexible material (polyester, polydimethylsiloxane, polyimide, etc.) as a flexible substrate, solves the defects of poor flexibility, poor stretch cycle stability and complex assembly of the existing flexible electrochromic device, and widens the application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to make the technical solutions of the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced below:

[0026] Figure 1 is a flow chart of the preparation of a flexible electrochromic device.

[0027] Figure 2 is the transmittance and stress-strain curve of acrylamide hydrogel and 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel.

[0028] Figure 3 is the sheet resistance of the conductive electrode layer prepared at different spin coating speeds.

[0029] Figure 4 is the transmittance curve of the conductive electrode layer prepared at different spin coating speeds.

[0030] Figure 5 is the transmission electron microscopy image and particle size distribution diagram of tungsten oxide quantum dots.

[0031] Figure 6 is the transmittance curve of the electrochromic layer prepared by drop coating different volumes of tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid electrochromic composite solution.

[0032] Figure 7 is the scanning electron microscopy cross-sectional image of the electrochromic layer prepared by drop coating different volumes of tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid electrochromic composite solution.

[0033] Figure 8 is the transmittance diagram of the flexible electrochromic device before and after electrochromism prepared by drop coating different volumes of electrochromic solution.

[0034] Figure 9 is the cyclic tensile property of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel of the transferred electrochromic layer in Example 1 and the electrochromic property after cyclic tensile.

[0035] Figure 10 is the scanning electron microscopy planar image of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel of the transferred electrochromic layer in Example 1 before and after cyclic tensile.

[0036] Figure 11 is the optical picture of the transferred working electrode composite photochromic hydrogel electrolyte layer with electrochromic layer after tensile.

[0037] Figure 12 is the stress-strain curve of the transferred working electrode composite photochromic hydrogel electrolyte layer with electrochromic layer. DETAILED DESCRIPTION

[0038] In the prior art, silver nanowires are easily oxidized in a long-term electrochemical cycling environment or a humid environment, resulting in rapid deterioration of the performance of an electrode with a silver nanowire network, and the substrate often needs to be subjected to modification treatment; the embedded structure, the coated structure and the protective layer structure designed in the present application can improve the stability of the silver nanowires; the hydrogel composed of a hydrophilic polymer has excellent chemical biocompatibility and mechanical biocompatibility, so that it can be well matched with soft tissues and exhibit excellent mechanical compliance, at the same time, the hydrogel exhibits excellent conductivity, adhesion and stretchability, which plays a crucial role in flexible electronics.

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. In the description of the present application, the mention of "embodiments", "one embodiment" or "other embodiments" means that the specific features, structures or characteristics described in connection with the embodiments are included in at least some of the embodiments, but not necessarily all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application. The raw materials used in the present application are all existing products, and the specific preparation operations and performance tests are conventional technologies.

[0040] The acrylic acid contained in the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel can induce the crystalline nanofiber structuring of the poly3,4-ethylenedioxythiophene chains in the tungsten oxide quantum dot / poly3,4-ethylenedioxythiophene-poly styrene sulfonic acid composite electrochromic layer, thereby isolating the positively charged poly3,4-ethylenedioxythiophene and the negatively charged polystyrene sulfonic acid, and improving the stretchability of the electrochromic layer. At the same time, based on the excellent flexibility and transparency of the hydrogel-based flexible substrate itself, the overall stretchability of the device is enhanced. Therefore, as shown in the present application, a flexible and stretchable electrochromic device is prepared by a transfer technology to construct a multilayer composite structure, so that it exhibits a broad application prospect in the fields of wearable devices, stretchable and portable display electronic products and the like. Figure 1

[0041] ​The raw materials and molds used in the application are existing products, and the specific preparation operation and performance test are conventional technologies. The poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution is a PH1000 type reagent produced by Healy Electronic Materials Company. The mechanical property test is performed by using a Mark-10 series f mesur type mechanical testing machine. The square resistance test of the conductive electrode is performed by using an ST-2258C digital four-probe. The transmittance and optical contrast test is performed by using an ultraviolet spectrophotometer to measure the transmittance of the conductive electrode and the electrochromic layer, and the transmittance difference of the device in the coloring and bleaching states at 550 nm wavelength. Example 1

[0042] A preparation method of a flexible stretchable electrochromic device, the steps are as follows:

[0043] (1) Preparation of 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel: weigh 5 g of acrylamide, 2.8 g of acrylic acid, 1.2 g of 2-acrylamido-2-methylpropane sulfonic acid and 3 g of lithium chloride in a beaker, add 20 g of deionized water, stir for 30 min to form a uniform mixed solution; then add 0.34 g of polyvinylpyrrolidone, 0.025 g of N,N-methylene bisacrylamide and 0.036 g of ammonium persulfate to the mixed solution, continue to stir for 30 min, then transfer to a common mold, place in a 60°C oven for 60 min, then increase the temperature to 80°C, continue to heat for 30 min, then take out and cool to room temperature to obtain 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel;

[0044] (2) Preparation of acrylamide hydrogel: weigh 5 g of acrylamide in a beaker, add 20 g of deionized water, and stir on a stirring table for 30 min to form a uniform mixed solution. Then add 0.34 g of polyvinylpyrrolidone, 0.025 g of N,N-methylene bisacrylamide and 0.036 g of ammonium persulfate to the mixed solution, continue to stir for 30 min, then transfer to a mold, place in a 60°C oven for 60 min, then increase the temperature to 80°C, continue to heat for 30 min, then take out and cool to room temperature to obtain acrylamide hydrogel;

[0045] (3) Preparation of silver nanowire / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid conductive solution: ethylene glycol and isopropyl alcohol were configured into a miscible solvent in a ratio of 1:1; 0.4 g of the miscible solvent and 1.6 g of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid solution and 0.025 g of Triton-X100 solution were weighed into a beaker and stirred and mixed for 30 min to form a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid / miscible solvent composite solution; 1 g of silver nanowire (isopropyl alcohol solvent, diameter 50 nm, concentration 20 mg / mL) was mixed with 4 g of miscible solvent, and continuous stirring was performed on a stirring table for 30 min to form a silver nanowire / miscible solvent composite solution; 2 g of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid / miscible solvent composite solution and 1 g of silver nanowire / miscible solvent composite solution were mixed, and continuous stirring was performed for 30 min to prepare a silver nanowire / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid composite solution without flocculent precipitation;

[0046] (4) Preparation of tungsten oxide quantum dots: 8.25 g of sodium tungstate dihydrate was dissolved in 25 g of deionized water solution, and after complete dissolution, a concentrated hydrochloric acid (37%) solution was added to form a white precipitate; then, centrifugal treatment was performed at a speed of 8000 r / min for 5 min, and after removing the supernatant solution, the precipitate was washed with deionized water, and this operation was repeated until the pH of the precipitate was neutral; then, the precipitate was mixed with 25 mL of ethylene glycol, and stirring was performed to form a transparent colorless solution, which was transferred to a 100 mL polytetrafluoroethylene reaction kettle, and heating reaction was performed in an oven at 180°C for 48 h, and the solution was cooled to room temperature; the obtained solution was placed in a 1000 molecular weight dialysis bag for dialysis treatment for 24 h, impurities in the solution were removed, and the solution was taken out to obtain a tungsten oxide quantum dot solution;

[0047] (5) Preparation of tungsten oxide quantum dot / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid composite electrochromic solution: 1 g of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid solution, 2 g of tungsten oxide quantum dot solution and 0.025 g of Triton-X100 solution were weighed into 1 g of deionized water to configure a mixed solution, and continuous stirring was performed for 24 h to prepare a tungsten oxide quantum dot / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid composite electrochromic solution;

[0048] (6) Preparation of the electrochromic layer: First, the glass sheet was sequentially placed in ethanol and deionized water solution and ultrasonically cleaned for 10 min, and then placed in an oven for drying. Subsequently, the cleaned glass sheet was placed in a plasma cleaning machine and plasma cleaned for 10 min under the conditions of a working power of 120 W and a working pressure of 300 Pa to improve the hydrophilicity of the glass surface. Then, 100 ul of tungsten oxide quantum dot / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid composite solution was drop-coated on the hydrophilic treated glass surface, and dried in a 60°C oven for 30 min to obtain the electrochromic layer;

[0049] (7) Preparation of the conductive electrode layer: The glass sheet was cleaned according to the above steps, and then silver nanowire / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid composite solution was spin-coated on the glass surface at a spin-coating speed of 2000 r / min for 60 s. The spin-coated glass was transferred to a 60°C oven for drying for 30 min to obtain the conductive electrode layer.

[0050] (8) Preparation of the electrochromic layer / 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel: The prepared electrochromic layer was transferred to the surface of the hydrogel by transfer. The specific method is as follows: First, the electrochromic solution was drop-coated on the glass surface, and dried in a 60°C oven for 30 min to obtain the electrochromic layer. Then, the prepared 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel was placed on the glass surface with the electrochromic layer, and the surface of the hydrogel was pressed against the electrochromic layer for 1 min. The electrochromic layer was transferred to the surface of the hydrogel after standing at room temperature for 10 min.

[0051] (9) Preparation of the conductive electrode layer / acrylamide hydrogel: The conductive electrode was transferred to the surface of the acrylamide hydrogel by referring to the method of step (8).

[0052] (10) Preparation of the flexible electrochromic device: The electrochromic layer / 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel and the conductive electrode layer / acrylamide hydrogel were compounded, and the electrochromic layer was tightly contacted with the conductive electrode layer by pressing for 2 min to obtain the flexible electrochromic device. The thickness of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate and the acrylamide hydrogel-based flexible substrate was 3 mm, and the thickness of the conductive electrode layer was 1 mm.

[0053] Figure 2 are the transmittance and stress-strain curves of the acrylamide hydrogel and the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel; from Figure 2It can be seen that the transmittance of the 2-acrylamido-2-methylpropanesulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel and the acrylamide hydrogel prepared above at 550 nm is 91.4% and 88.3%, respectively; the tensile breaking strength is 92 kPa and 87 kPa, respectively; and the tensile breaking elongation is 450% and 280%, respectively.

[0054] As shown in Table 1, the fabricated device exhibits excellent tensile elongation, tensile cycle stability, and optical contrast after coloring and fading, which are properties reported in most literatures, indicating that it has excellent flexibility, tensile strength, and tensile cycle stability. Example 2

[0055] Based on Example 1, the amount of tungsten oxide quantum dot / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid composite solution in step (6) was changed to 50 μL, and the spin coating speed in step (7) was changed to 1000 r / min. The rest remained the same, and conductive electrode layers prepared at different spin coating speeds were obtained. The rest remained the same, and a flexible stretchable electrochromic device was obtained. Example 3

[0056] Based on Example 1, the amount of tungsten oxide quantum dot / poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid composite solution in step (6) was changed to 200 μL, and the spin coating speed in step (7) was changed to 3000 r / min. The rest remained the same, and conductive electrode layers prepared at different spin coating speeds were obtained. The rest remained the same, and a flexible stretchable electrochromic device was obtained.

[0057] Figure 3 The sheet resistance of conductive electrode layers prepared at different spin coating speeds; Figure 4 These are the transmittance curves of conductive electrode layers prepared at different spin coating speeds. It can be seen that the sheet resistance of the conductive electrode layer prepared at a spin coating speed of 2000 r / min is 246 Ω / sq, and the transmittance is 78%; the sheet resistance of the conductive electrode layer prepared at a spin coating speed of 1000 r / min is 144 Ω / sq, and the transmittance is 68%; the sheet resistance of the conductive electrode layer prepared at a spin coating speed of 3000 r / min is 352 Ω / sq, and the transmittance is 80%.

[0058] Figure 5 The images show transmission electron microscopy (TEM) images and particle size distribution diagrams of tungsten oxide quantum dots. It can be seen that the present invention successfully prepared tungsten oxide quantum dots using a hydrothermal method, and the prepared tungsten oxide quantum dots can be uniformly distributed in aqueous solution, with an average particle size of 3.14 ± 0.55 nm.

[0059] Figure 6is the transmittance curve of the droplets of tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid electrochromic composite solution with different volumes; the electrochromic layer prepared by dropping 100 ul of electrochromic composite solution has a transmittance of 60%; the electrochromic layer prepared by dropping 50 ul of electrochromic composite solution has a transmittance of 70%; the electrochromic layer prepared by dropping 200 ul of electrochromic composite solution has a transmittance of 38%.

[0060] Figure 7 is the scanning electron microscope cross-sectional view of the electrochromic layer prepared by dropping tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-poly styrene sulfonic acid electrochromic composite solution with different volumes; the electrochromic layer prepared by dropping 100 ul of electrochromic composite solution has a thickness of 1.31 um; the electrochromic layer prepared by dropping 50 ul of electrochromic composite solution has a thickness of 357 nm; the electrochromic layer prepared by dropping 200 ul of electrochromic composite solution has a thickness of 2.56 um.

[0061] Figure 8 is the transmittance graph of the flexible electrochromic device before and after the electrochromic layer is prepared by dropping electrochromic solution with different volumes; the optical contrast of the flexible stretchable electrochromic device prepared by dropping 100 ul of electrochromic composite solution to form an electrochromic layer is 34% (Example 1); the optical contrast of the flexible stretchable electrochromic device prepared by dropping 50 ul of electrochromic composite solution to form an electrochromic layer is 15.7% (Example 2); the optical contrast of the flexible stretchable electrochromic device prepared by dropping 200 ul of electrochromic composite solution to form an electrochromic layer is 14.8% (Example 3).

[0062] Figure 9 is the cyclic stretching performance and electrochromic performance after cyclic stretching of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel transferred with the electrochromic layer; the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel transferred with the electrochromic layer can withstand cyclic stretching 1000 times (200% tensile elongation), and still maintains excellent electrochromic performance after stretching.

[0063] Figure 10 is the scanning electron microscope plan view of the 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel transferred with the electrochromic layer before and after cyclic stretching. The 2-acrylamido-2-methylpropane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel transferred with the electrochromic layer only has small ripples on the microstructure after 1000 cycles of stretching (200% tensile elongation), and no visible cracks appear, which has excellent cyclic stretching performance.

[0064] The present application synthesizes a silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid conductive electrode with stable electrochemical performance and a high-transparency, stretchable hydrogel polymer. At the same time, tungsten oxide quantum dots are synthesized by a hydrothermal method, and an electrochromic material with excellent fast response and cycle stability is prepared by compounding the tungsten oxide quantum dots with a poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution. By constructing a multi-layer composite structure, a high-performance flexible electrochromic device is prepared. The device exhibits excellent response speed, cycle stability and optical contrast, and can realize arbitrary angle bending, twisting and excellent stretchability. It has broad application prospects in wearable smart display and visual perception.

[0065] In the previously published patent application (CN2023104346258, Example 1), the stretchable fracture elongation of the working electrode composite photochromic hydrogel electrolyte layer with the transferred electrochromic layer was 50%, and after repeated stretching for 5 times at a stretchable elongation of 20%, visible cracks appeared in the electrochromic layer, which would cause the electrochromic performance to decrease, see Figure 11 , Figure 12 Compared with the previously published patent, the device prepared in the present application exhibits excellent stretchability and stretch cycle stability, and can maintain the integrity of the electrochromic layer after 1000 stretch cycles at a stretchable elongation of 200%. Moreover, it exhibits good optical contrast (DT=34%) and fast response speed. At the same time, the synthesis process of the hydrogel flexible substrate and the conductive electrode layer is adjusted and optimized, which exhibits more excellent transparency and conductivity.

[0066] Table 1 Comparison of stretchability and stretch cycle stability of Example 1 and related devices reported in the literature

[0067]

[0068] In Table 1, the references corresponding to serial numbers 1-5 are as follows:

[0069] [1] FAN Q, FAN H, LI K, et al. Stretchable, Electrochemically-Stable Electrochromic Devices Based on Semi-Embedded Ag@Au Nanowire Network [J]. Small, 2023, 19(22): 2208234.

[0070] [2] WU W, POH W C, LV J, et al. Self‐Powered and Light‐Adaptable Stretchable Electrochromic Display [J]. Adv Energy Mater, 2023, 13(18):2204103.

[0071] [3] OH S-J, BAE J W. All-in-One plasticized Ionogel-based stretchable electrochromic devices [J]. Chem Eng J, 2023, 467: 143367.

[0072] [4] LINDERHED U, PETSAGKOURAKIS I, ERSMAN P A, et al. Fully screenprinted stretchable electrochromic displays [J]. Flexible and Printed Electronics, 2021, 6(4): 045014.

[0073] [5] YUN T G, PARK M, KIM D-H, et al. All-Transparent Stretchable Electrochromic Supercapacitor Wearable Patch Device [J]. ACS Nano, 2019, 13(3): 3141-3150.

[0074] The above is based on the ideal embodiment of the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the scope of the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for the preparation of a flexible, stretchable electrochromic device, characterized in that, The method comprises the following steps: (1) 2-acrylamido-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is prepared by taking acrylamide, acrylic acid, 2-acrylamido-2-methyl propane sulfonic acid and lithium chloride as raw materials; (2) acrylamide hydrogel-based flexible substrate is prepared by taking acrylamide as raw material; (3) silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution is formed by taking ethylene glycol, isopropyl alcohol, poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution and silver nanowire as raw materials; (4) the silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution is prepared into a conductive electrode layer, and then the acrylamide hydrogel flexible substrate is attached to form a conductive electrode layer on the surface of the acrylamide hydrogel flexible substrate; (5) tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid electrochromic solution is prepared by mixing tungsten oxide quantum dots, poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution and surfactant; (6) the tungsten oxide quantum dots / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid electrochromic solution is prepared into an electrochromic layer, and then the 2-acrylamido-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate is attached to form an electrochromic layer on the surface of the 2-acrylamido-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate; (7) the acrylamide hydrogel flexible substrate with the conductive electrode layer is attached to the 2-acrylamido-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel flexible substrate with the electrochromic layer to prepare a flexible stretchable electrochromic device.

2. The method for preparing a flexible and stretchable electrochromic device according to claim 1, wherein: In step (1), acrylamide, acrylic acid, 2-acrylamido-2-methyl propane sulfonic acid, lithium chloride, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water are mixed to form a uniform solution, and then dried to obtain the 2-acrylamido-2-methyl propane sulfonic acid / acrylamide / acrylic acid / lithium chloride hydrogel-based flexible substrate.

3. The method of claim 1, wherein the flexible stretchable electrochromic device is prepared by: In step (2), acrylamide, ammonium persulfate, N,N-methylene bisacrylamide, polyvinylpyrrolidone and deionized water are mixed and stirred, and then dried to obtain the acrylamide hydrogel-based flexible substrate.

4. The method of claim 1, wherein the flexible, stretchable electrochromic device is prepared by: In step (3), ethylene glycol and isopropyl alcohol constitute a miscible solvent; the miscible solvent is mixed with the poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid solution to form a poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid / miscible solvent composite solution, and the miscible solvent is mixed with the silver nanowire to form a silver nanowire / miscible solvent composite solution; the poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid / miscible solvent composite solution and the silver nanowire / miscible solvent composite solution are mixed to form the silver nanowire / poly 3,4-ethylenedioxythiophene-polystyrene sulfonic acid composite solution.

5. The method for preparing a flexible and stretchable electrochromic device according to claim 4, characterized in that: The mass ratio of ethylene glycol and isopropanol is 1:(0.8-1.2); the mass ratio of the cosolvent and the PEDOT:PSS solution in the PEDOT:PSS / cosolvent composite solution is 1:(3-5); the mass ratio of the cosolvent and the silver nanowire in the silver nanowire / cosolvent composite solution is 1:(3-5); and the mass ratio of the PEDOT:PSS / cosolvent composite solution and the silver nanowire / cosolvent composite solution is (1.5-2.5):

1.

6. The method of claim 1, wherein the flexible, stretchable electrochromic device is prepared by: In step (4), the silver nanowire / PEDOT:PSS composite solution is spin-coated to prepare the conductive electrode layer; the spin-coating process is as follows: the spin-coating speed is 1000-3000 r / min, and the spin-coating time is 50-70 s; and the adhering time is 5-15 min.

7. The method of claim 1, wherein the flexible, stretchable electrochromic device is prepared by: In step (5), the tungsten oxide quantum dot solution is prepared by one-step hydrothermal method; the hydrothermal reaction temperature is 170-190 ℃, and the hydrothermal reaction time is 40-55 h; the mass ratio of the PEDOT:PSS solution, the tungsten oxide quantum dot solution and H2O in the tungsten oxide quantum dot / PEDOT:PSS electrochromic solution is 1:2:1, and the content of the surfactant is 0.25%.

8. The flexible stretchable electrochromic device prepared by the preparation method of the flexible stretchable electrochromic device according to claim 1.

9. The application of the flexible stretchable electrochromic device according to claim 8 in the preparation of a flexible electrochromic device or as a flexible electrochromic device.

10. The application of the flexible stretchable electrochromic device according to claim 8 in the preparation of a smart soft electronic device.

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