High-speed response flexible passive electrochromic device and preparation method thereof

Abstract

The invention discloses a high-speed response flexible passive electrochromic device and a preparation method thereof, and belongs to the technical field of flexible electrochromic devices. The electrochromic device comprises a flexible substrate, a liquid metal layer and electrochromic writing ink, the liquid metal layer is arranged on one face of the flexible substrate, and the electrochromic writing ink is used for writing on the liquid metal layer. The flexible, passive and self-driven electrochromic device with high response speed is prepared, the comprehensive use performance of the electrochromic device is effectively improved, the application scene of the electrochromic device is expanded, the structure of the electrochromic device is simplified, the manufacturing cost of the electrochromic device is reduced, and energy conservation and consumption reduction are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of flexible electrochromic devices, and relates to a flexible passive electrochromic device with high-speed response and a preparation method thereof. Background Art

[0002] Electrochromism is a phenomenon in which the optical properties (reflectivity, transmittance, absorptivity, etc.) of a material undergo stable and reversible color changes under the action of an external electric field, which is manifested as reversible changes in color and transparency in appearance. Materials with electrochromic properties are called electrochromic materials, and devices made of electrochromic materials are called electrochromic devices. Electrochromic devices (ECDs) have received extensive attention in fields such as mobile phones, smart windows, automobiles, VR glasses, etc. For example, in modern society, people usually carry mobile devices for digital lightweight identity display, and in more important identity verification occasions, optical display devices with higher safety factors will be used. In the optical dimension, traditional display anti-counterfeiting devices are bulky, have poor portability, rely on power supplies, and are costly. Due to its low power consumption and reversibility, electrochromic materials are suitable for portable display devices and have become popular materials for portable display devices. However, for a typical "sandwich-type" electrochromic device, it has multiple functional structural layers, and the multi-layer structure complicates the logical interaction form between components, resulting in an interaction time of up to dozens of seconds for most electrochromic devices. Moreover, electrochromic devices rely on external power supplies for driving, which not only requires relatively complex circuit design, but also consumes more energy. And in some application scenarios where it is difficult to wire, such as the wild and mobile devices, external power supply driving becomes a major limiting factor for the application of electrochromic devices.

[0003] Therefore, it is necessary to provide a flexible passive electrochromic device with high-speed response and a preparation method thereof to improve the electrochromic performance of the electrochromic device and at the same time broaden the application scenarios of the electrochromic device. Summary of the Invention

[0004] In order to overcome the problems in the background art, the present invention prepares an electrochromic device with characteristics such as high-speed response, flexible and passive driving, effectively simplifies the device structure, eliminates components such as external power supplies and wires, makes the device thinner, lighter, enhances the portability and scene adaptability of the device, and passive driving helps to save energy and reduce costs; at the same time, the electrochromic device has better adhesion to components with curved surfaces such as wearable devices, flexible displays, and automotive glass, and can also adapt to dynamic deformations such as folding mobile phones and curling TVs, which is beneficial to broadening the application scenarios of electrochromic devices. And the electrochromic device of the present invention has high coloring efficiency, can be erased and reused repeatedly, further improving the usability and convenience of the electrochromic device.

[0005] To achieve the above object, the invention is realized through the following technical solutions:

[0006] On the one hand, the present invention provides a flexible passive electrochromic device with high-speed response. The electrochromic device includes a flexible substrate 1, a liquid metal layer 2, and electrochromic writing ink 3. The liquid metal layer 2 is disposed on one surface of the flexible substrate 1, and the electrochromic writing ink 3 is used for writing on the liquid metal layer 2. By injecting the electrochromic writing ink 3 into a commercially available water-based pen, the water-based pen can be used to write on the liquid metal layer. After writing, an electrochromic writing layer is formed.

[0007] The raw material of the flexible substrate 1 includes one of polyethylene terephthalate, polyimide-based material, and graphene / polydimethylsiloxane mixture. The raw material of the liquid metal layer 2 includes one of InSnBi, InGa, and InGaSn alloys. The raw material of the electrochromic writing ink 3 is a mixed solution of an ion-rich WO3 solution and a mixed hydrogel solution, and the mixed hydrogel solution is a mixture solution of hydrogel and lithium chloride. Among them, the flexible substrate 1 can directly use a polyimide (PDMA)-based film or a graphene / polydimethylsiloxane mixture film. For example, PDMA-4,4-diaminodiphenyl ether (ODA) film, PDMA-based film, and graphene / polydimethylsiloxane mixture film can all be obtained by direct purchase.

[0008] Preferably, the hydrogel is one of polyacrylamide-based hydrogel and polyvinyl alcohol-based hydrogel.

[0009] Preferably, the thickness of the flexible substrate 1 is 300 μm, and the thickness of the liquid metal layer 2 is 200 μm.

[0010] On the other hand, the present invention provides a preparation method of the above electrochromic device. The preparation method includes the following steps:

[0011] (1) Prepare an ion-rich WO3 solution and a mixed hydrogel solution respectively, and mix the mixed hydrogel solution and the ion-rich WO3 solution evenly to obtain electrochromic writing ink;

[0012] (2) Compose the liquid metal layer 2 and the flexible substrate 1 by rolling.

[0013] Preferably, in the electrochromic writing ink 3, the mass ratio of the ion-rich WO3 solution to the mixed hydrogel solution is ion-rich WO3 solution: mixed hydrogel solution = 1:1 - 3:1.

[0014] Preferably, in the step (1), the specific process for preparing the ion-rich WO3 solution is as follows: Disperse W powder into H2O2. After the complete reaction of W powder and H2O2, centrifuge the liquid to obtain the supernatant. Add excessive ethanol to the supernatant to prevent the continuous formation of internal complexes and simultaneously increase the ion concentration inside the supernatant. Then, dry the liquid to evaporate the ethanol and obtain the ion-rich WO3 solution. Since H2O is generated after the reaction of W powder and H2O2, thus, even after the evaporation of ethanol, the WO3 solution can still be obtained using the generated H2O as the solvent.

[0015] Preferably, the solid-liquid ratio of W powder to H2O2 is W powder: H2O2 = 1g: 4ml, the reaction temperature of W powder and H2O2 is 0 - 10°C, the centrifugation speed is 3500 rpm, the centrifugation time is 10 min, the drying temperature is 80°C, and the drying time is 1 h. The concentration of the WO3 solution prepared according to the foregoing ratio meets the requirements of the solution concentration of the present invention.

[0016] Preferably, in the step (1), the specific process for preparing the mixed hydrogel solution is as follows: Dissolve acrylamide monomer in deionized water to obtain an acrylamide monomer solution, then add lithium chloride to the acrylamide monomer solution to obtain a monomer mixed solution. Ultrasonically treat the monomer mixed solution until lithium chloride is completely dissolved, and then add N, N-dimethylacrylamide and ammonium persulfate to the monomer mixed solution and stir to obtain the mixed hydrogel solution.

[0017] Preferably, the solid-liquid ratio of acrylamide monomer to deionized water is acrylamide: deionized water = 3g: 20ml, the addition amount of lithium chloride satisfies 0 < addition amount of lithium chloride ≤ 10 mol / L based on the volume of the acrylamide monomer solution, the added mass of N, N-dimethylacrylamide is 0.1% of the mass of the acrylamide monomer solution, and the addition amount of ammonium persulfate is 0.2% of the mass of the acrylamide monomer solution.

[0018] Preferably, in the step (2), first perform plasma hydrophilic treatment on the flexible substrate 1 for 120 s before rolling, and the rolling temperature is 60°C. A vacuum plasma cleaner (model: TS-PL05) can be used to perform plasma hydrophilic treatment on the flexible substrate 1. Only the time parameter needs to be set, and other parameters can be set according to the initial settings of the plasma cleaner.

[0019] The beneficial effects of the present invention:

[0020] 1. By using a flexible substrate and a liquid metal layer with excellent flexibility in combination, the electrochromic device as a whole has excellent flexibility, has good adhesion to optical components such as curved surfaces and dynamic deformations, and has excellent adaptability to relatively complex usage scenarios.

[0021] 2. The present invention writes on the liquid metal layer by using electrochromic writing ink. When the electrochromic writing ink contacts the liquid metal, H + destroys the oxide layer on the surface of the liquid metal layer. After the oxide layer on the surface of the liquid metal layer is destroyed, the In alloy in the liquid metal layer acts as a chemical electrode to form an internal chemical potential difference with the W ions acting as electrodes in the electrochromic ink. Since the ink is rich in a large amount of H + , Li + is provided for ion exchange, and the change of W element from W 6+ →W 5+ can be quickly realized, achieving high-speed response passive color change, realizing fast optical information display, thereby simplifying the structure of the electrochromic device, making the electrochromic device lighter, saving energy and reducing consumption, enhancing the applicability and portability of the electrochromic device, and reducing costs.

[0022] 3. The present invention utilizes the characteristics of WO3 having better dispersion, shorter ion transport path, and larger surface area in liquid, enabling better interfacial contact between WO3 and liquid metal, thereby improving the coloring response speed of the electrochromic device. At the same time, in the electrochromic writing ink of the present invention, mixing WO3 with a hybrid hydrogel can endow the electrochromic writing ink with conductivity. A higher conductivity means a faster ion migration rate, which can meet the fast charge step required for electrochromic response, shorten the ion diffusion time, and thus shorten the coloring / bleaching response of the electrochromic device.

[0023] 4. The present invention uses WO3 as an electrochromic material and utilizes the unique band filling effect of WO3, that is, inserting Li + to make W 6+ reduce to W 5+ , generating strong near-infrared absorption, which can achieve a greater modulation of unit charge, thereby reducing the energy consumption of the electrochromic device.

[0024] 5. The electrochromic device of the present invention only includes two-layer structure (three-layer structure after writing), the structure is further optimized, the complexity of the structure is further reduced, the logical interaction between layers is simplified, and the performance loss between layers is reduced.

[0025] 6. For the electrochromic device of the present invention, the energized coloring time is 1 s. During the passive coloring process, the fastest response is 210 ms, and large-area coloring can be achieved at 810 ms. At least 49 erasures can be realized, having excellent coloring response speed and coloring efficiency, and at the same time can be used repeatedly for many times with a long service life.

[0026] 7. The preparation process of the electrochromic device of the present invention does not require expensive and large processing equipment compared with methods such as electrodeposition and magnetron sputtering. The preparation process is simple, easy to implement, and has a low cost, being suitable for industrial popularization and application. Description of the Drawings

[0027] Figure 1 Schematic structural diagram of the electrochromic device of the present invention;

[0028] Figure 2 Physical diagram of the ion-rich WO3 solution of the present invention and XRD elemental characterization

[0029] Figure 3 Morphology characterization and elemental analysis diagram of the WO3 solution of the present invention;

[0030] Figure 4 Morphology characterization diagram of the PAAm-LiCl freeze-dried hydrogel of the present invention;

[0031] Figure 5 Physical flexible effect display diagram of the electrochromic device of the present invention;

[0032] Figure 6 FTIR test result diagram of the electrochromic device of the present invention;

[0033] Figure 7 Ionic conductivity test result diagram of the PAAm-LiCl hydrogel solution of the examples and comparative examples of the present invention;

[0034] Figure 8 Ionic conductivity test result diagram of the electrochromic writing ink in the examples and comparative examples of the present invention;

[0035] Figure 9 Charge density test result diagram of the electrochromic writing ink in the examples and comparative examples of the present invention;

[0036] Figure 10 CV curves of the electrochromic writing ink in the examples and comparative examples of the present invention;

[0037] Figure 11 Peak current density and square root of scan rate of the electrochromic writing ink in the oxidized and reduced states in the examples and comparative examples of the present invention, where the left figure is the oxidized state diagram and the right figure is the reduced state diagram;

[0038] Figure 12 CV scan curves of the electrochromic writing ink in Example 1 of the present invention at a scan rate of 50 mV for the first 9 times (left figure) and the next 40 times (right figure);

[0039] Figure 13 Transmittance spectrum test result diagram of the electrochromic writing ink in the examples of the present invention;

[0040] Figure 14 Coloring rate and self-bleaching rate results of the electrochromic writing ink in Example 1 of the present invention in the energized state;

[0041] Figure 15 This is the graph of the coloring efficiency result of the electrochromic writing ink in Example 1 of the present invention;

[0042] Figure 16 This is the graph of the metal activity analysis result;

[0043] Figure 17 This is the schematic diagram of the self-driven coloring principle of the electrochromic device of the present invention;

[0044] Figure 18 This is the graph of the XPS analysis results of the electrochromic writing ink before and after coloring in Example 1 of the present invention;

[0045] Figure 19 This is the reflectance spectrum graph of the electrochromic device in different states in Example 1 of the present invention;

[0046] Figure 20 This is the self-coloring state graph of the electrochromic device in Example 1 of the present invention in the 120fps high-speed shooting mode;

[0047] Figure 21 This is the graph of the cyclic test results of 49 "coloring - erasing" of the electrochromic device in Example 1 of the present invention;

[0048] Figure 22 This is the graph for comparing the performance of the electrochromic device of the present invention with other electrochromic devices.

[0049] In the figure, 1 - flexible substrate, 2 - liquid metal layer, 3 - electrochromic writing ink. Detailed implementation manners

[0051] The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0052] In the examples and comparative examples of the present invention, chemical reagents not specifically stated were all used for experiments with commercially available analytical pure reagents.

[0053] Example 1

[0054] The electrochromic device was prepared by the following method in this example:

[0055] (1) Preparation of the ion-rich WO3 solution: 5 g of tungsten powder was dispersed in 20 ml of H2O2, and after fully reacting in an environment of 0 °C, it was centrifuged at 3500 rpm for 10 min, and the supernatant was extracted. At the same time, 40 ml of ethanol was added to prevent the continued formation of internal complexes and to increase the internal ion concentration. Finally, it was dried at 80 °C for 1 h to evaporate the ethanol, obtaining the ion-rich WO3 solution.

[0056] (2) Preparation of the mixed hydrogel solution: Dissolve 3 g of acrylamide monomer in 20 ml of deionized water, then add lithium chloride (LiCl) in a proportion of 6 mol / L, ultrasonicate until completely dissolved, and then add 0.018 g of N,N-dimethylacrylamide and 0.049 g of ammonium persulfate. After reaction, a mixed hydrogel solution, namely the PAAm-LiCl hydrogel solution, is obtained.

[0057] (3) Mix the ion-rich WO3 solution and the PAAm-LiCl hydrogel solution in a mass ratio of ion-rich WO3 solution: mixed hydrogel solution = 3:1 to obtain electrochromic writing ink.

[0058] (4) Under the heating condition of 60 °C, roll and form the InSnBi alloy and the polyethylene terephthalate film (i.e., the PET substrate) once, so that the InSnBi alloy forms a liquid metal layer and is compounded with the PET substrate.

[0059] After preparation, the electrochromic writing ink can be used to write on the liquid metal layer. After writing, the electrochromic device forms a three-layer structure, as Figure 1 shown, and the actual writing effect is as Figure 5 shown.

[0060] Example 2

[0061] This example prepares the electrochromic device in the same manner as Example 1, with the differences being: in this example, the reaction temperature of W powder and H2O2 is 5 °C, the raw material of the liquid metal layer is the InGa alloy, the flexible substrate 1 is the PDMA-ODA film, the hydrogel is the polyvinyl alcohol (PVA)-based hydrogel, and the WO3 solution and the PVA-LiCl hydrogel solution are in a mass ratio of ion-rich WO3 solution: mixed hydrogel solution = 1:1.

[0062] The electrochromic device prepared in this example has performance similar to that of the electrochromic device in Example 1.

[0063] Example 3

[0064] This example prepares the electrochromic device in the same manner as Example 1, with the differences being: in this example, the reaction temperature of W powder and H2O2 is 10 °C, the raw material of the liquid metal layer is the InGaSn alloy, the flexible substrate 1 is the graphene / polydimethylsiloxane mixture film, and the WO3 solution and the PAAm-LiCl hydrogel solution are in a mass ratio of ion-rich WO3 solution: mixed hydrogel solution = 2:1.

[0065] The electrochromic device prepared in this example has performance similar to that of the electrochromic device in Example 1.

[0066] Example 4

[0067] In this embodiment, the electrochromic device is prepared in the same manner as in Embodiment 1, except that: in this embodiment, the addition amount of LiCl is 2 mol / L.

[0068] The electrochromic device prepared in this embodiment has performance similar to that of the electrochromic device in Embodiment 1.

[0069] Embodiment 5

[0070] In this embodiment, the electrochromic device is prepared in the same manner as in Embodiment 1, except that: in this embodiment, the addition amount of LiCl is 4 mol / L.

[0071] The electrochromic device prepared in this embodiment has performance similar to that of the electrochromic device in Embodiment 1.

[0072] Embodiment 6

[0073] In this embodiment, the electrochromic device is prepared in the same manner as in Embodiment 1, except that: in this embodiment, the addition amount of LiCl is 8 mol / L.

[0074] The electrochromic device prepared in this embodiment has performance similar to that of the electrochromic device in Embodiment 1.

[0075] Embodiment 7

[0076] In this embodiment, the electrochromic device is prepared in the same manner as in Embodiment 1, except that: in this embodiment, the addition amount of LiCl is 10 mol / L.

[0077] The electrochromic device prepared in this embodiment has performance similar to that of the electrochromic device in Embodiment 1.

[0078] Comparative Example 1

[0079] In this comparative example, the electrochromic device is prepared in the same method as in Embodiment 1, except that: in this comparative example, the electrochromic writing ink is a WO3 solution and does not contain a mixed hydrogel solution.

[0080] Comparative Example 2

[0081] In this comparative example, the electrochromic device is prepared in the same method as in Embodiment 1, except that: in this comparative example, in the electrochromic writing ink, the mass ratio of the WO3 solution to the PAAm-LiCl hydrogel solution is rich ion WO3 solution: mixed hydrogel solution = 1:2.

[0082] Comparative Example 3

[0083] This comparative example uses the same method as Example 1 to prepare an electrochromic device, with the difference that: in the electrochromic writing ink of this comparative example, the WO3 solution and the PAAm-LiCl hydrogel solution are in a mass ratio of rich-ion WO3 solution: mixed hydrogel solution = 1:3.

[0084] Comparative Example 4

[0085] This comparative example uses the same method as Example 1 to prepare an electrochromic device, with the difference that: LiCl is not added to the electrochromic writing ink of this comparative example.

[0086] Through Figure 2 It can be seen that there are no obvious peaks in the XRD pattern of the rich-ion WO3 solution test, indicating that in the WO3 solution prepared by the present invention, the WO3 particles are amorphous. Compared with the closely arranged structure inside crystalline WO3, there are a large number of short-range disordered pores and channels inside the amorphous state, providing a low-barrier diffusion path for ions (such as H+, Li+), and accelerating the ion exchange speed.

[0087] Through Figure 3 It can be seen that WO3 is distributed in particles in the WO3 solution, and the particle size is about 200 μm.

[0088] Through Figure 4 It can be seen that after the PAAm-LiCl hydrogel is freeze-dried, the cross-sectional thickness is about 200 μm.

[0089] Through Figure 5 It can be seen that the electrochromic device prepared by the present invention can be bent at will and has excellent flexibility.

[0090] Through Figure 6 It can be seen that in the free water system, the electrochromic writing ink and the PAAm-LiCl hydrogel solution both show obvious O-H bond stretching vibration peaks in the range of 3200 - 3400 cm -1 However, in the PAAm-LiCl hydrogel solution, the weak peak at 2300 cm -1 may be a weak vibration related to Li + With the addition of WO3 particles, the original vibration mode is destroyed, and Li + may combine with the oxygen atoms in WO3. In addition, C=O stretching vibration peaks appear at 1600 cm -1 This is also a characteristic peak of the amide group in PAAm, and Li-O bonding vibration peaks appear at 570 cm -1 And the mixed solution shows a peak at 1038 cm -1A W-O vibration peak appears here, which was not found in the PAAm-LiCl hydrogel solution, proving that the successful introduction of WO3 particles can improve the conductivity. Higher conductivity means faster ion migration rate, which can meet the rapid charge compensation required for electrochromic response, shorten the diffusion time of ions in the electrolyte, and thus accelerate the coloring / bleaching response of electrochromism.

[0091] By Figure 7 It can be seen that adding LiCl to the hydrogel can effectively improve the conductivity of the PAAm-LiCl hydrogel solution. When the addition amount of LiCl is 6 mol / L, the ionic conductivity reaches the peak. Further increasing the addition amount of LiCl has a negative impact on the ionic conductivity. When the addition amount increases from 6 mol / L to 8 mol / L, the ionic conductivity shows a slight decrease. When it is further increased to 10 mol / L, the ionic conductivity does not decrease. The decrease in ionic conductivity may be due to too much LiCl added, and its own water absorption causes excessive water absorption, resulting in rapid solidification of the hydrogel and inability to mix well with the WO3 solution. Therefore, controlling the addition amount of LiCl between 0 - 10 mol / L is beneficial to improving the ionic conductivity of the electrochromic writing layer. Higher ionic conductivity can also effectively reduce the ionic diffusion barrier, accelerate the ion insertion / extraction in the redox reaction, and ultimately improve the coloring efficiency.

[0092] By Figure 8 It can be seen that compared with the pure WO3 solution, in the mixed solution obtained by mixing the WO3 solution with the PAAm-LiCl hydrogel solution, the ionic conductivity is improved. As the proportion of the WO3 solution in the mixed solution increases, the ionic conductivity of the mixed solution shows a slight decrease, probably due to the decrease in the Li + content. Therefore, the proportion of the WO3 solution in the mixed solution cannot be too large, otherwise the ionic conductivity will decrease excessively, causing too much negative impact on the electrochromic device.

[0093] By Figure 9 It can be seen that when the WO3 solution:PAAm-LiCl solution = 3:1, it shows a larger charge density (145.99 mC / cm 2 ). Considering the influence of the proportion of the WO3 solution on the ionic conductivity, it is determined that the WO3 solution:PAAm-LiCl solution = 3:1 is the optimal ratio, which can make the electrochromic device have a more significant color change.

[0094] By Figure 10 、 11It can be seen that when the ratio of WO3 solution to PAAm-LiCl solution is 3:1, the peak current is the largest, indicating that the ion transport rate is the fastest and the coloring and bleaching response times of the electrochromic device are shorter. In addition, by calculating the changes in the peak current density and the square root of the scan rate for the oxidized and reduced states of the electrochromic writing ink, it is further demonstrated that with the addition of the PAAm-LiCl hydrogel solution, the peak current density increases relative to the pure ion-rich WO3 solution, ultimately achieving a high-speed coloring response.

[0095] It can be seen that the results of the first 9 scans are different from those of the last 40 scans. From the results of the first 9 scan cycles, it can be observed that due to the storage of tungsten oxide ions and H Figure 12 + , Li + ions inside the electrochromic writing ink, as the scan time increases, the peak current at 0 V first increases and then decreases. The reason for the decrease is that as the number of CV cycle tests increases, a polymer deposit will form on the surface of the ITO electrode, and tungsten oxide ions are encapsulated inside the polymer. Since the tungsten oxide ions polymerize from the solution into the polymer, it also inhibits the electrochromic phenomenon of WO3. The last 40 cycles gradually show a linear trend, with a slope of approximately 1000 Ω, which is approximately equal to the resistance of the PAAm-LiCl hydrogel itself. On the one hand, it proves that the electrochromic device of the present invention can not only achieve self-powered driving but also perform writing and color change under an external power supply; on the other hand, it also proves that writing and color change under an external power supply will cause loss to the internal electrochromic material and affect the service life of the electrochromic device. Therefore, the electrochromic device of the present invention preferably operates in a self-powered driving mode.

[0096] It can be seen that the reflectance of the electrochromic device increases with the increase in the concentration of the ion-rich WO3 solution and shows a significant blue shift. When the mass fraction ratio of the ion-rich WO3 solution to the hydrogel solution is 3:1, the color is saturated, and compared with the mass fraction ratio of 1:1, the reflectance changes by about 20%. This further shows that when the mass fraction ratio of the ion-rich WO3 solution to the hydrogel solution is 3:1, the electrochromic writing ink has the best writing performance. Figure 13

[0097] It can be seen that for the mixed solution of the electrochromic device of the present invention, the coloring rate is 1 s under an external voltage of 5 V, which proves that the electrochromic device of the present invention not only has excellent coloring performance in the self-powered driving state but also has excellent coloring performance under an external voltage. At the same time, after the power is turned off for 297 s, the mixed solution can self-bleach because the WO3 ions are exchanged by Li Figure 14 + and H + ​​​Surrounding, on the one hand, proves that the electrochromic device of the present invention can bleach itself and be reused repeatedly, and on the other hand, it can prove that the electrochromic device of the present invention has a fast bleaching response performance.

[0098] Through Figure 15 It can be seen that the coloring efficiency of the mixed solution of the present invention is 274 cm at a wavelength of 480 nm -2 ·C -1 , and the coloring efficiency is relatively high. This is due to the unique band filling effect of WO3, that is, inserting Li + makes W 6+ reduce to W 5+ , generating strong near-infrared absorption, achieving greater light modulation per unit charge, and reducing the energy consumption of the device.

[0099] Through Figure 16 It can be seen that due to the strong mobility of liquid metals, their surface atoms are more easily captured by oxygen. Therefore, a nanoscale oxide layer is rapidly formed on the surface of liquid metals in air. However, the difference in oxidation potentials of different metal elements in liquid metals will lead to preferential oxidation. According to thermodynamics, the composition of the surface oxide of liquid metals is determined by the reactivity of individual metals in the melt. In has a lower oxidation potential in the InSnBi alloy and is more likely to be preferentially oxidized to form a surface In2O3 layer than Sn and Bi. The WO3 lattice forms Li x WO3 (a small amount of H + remaining may also react), and the W element changes from W 6+ to W 5+ , resulting in rapid coloring.

[0100] Through Figure 17 , 18 It can be seen that during the coloring process of the present invention, the difference in work functions between In (In / In 3+ =-0.34 V vs. the standard hydrogen electrode (SHE)) and tungsten trioxide (WO3 / Li x WO3 = +0.3 V vs. SHE) will drive In to release electrons and form In 3+ into the electrochromic writing ink. XPS test shows that WO3 spontaneously accepts electrons, while In 3+ enters the electrochromic writing ink, and at the same time inserts In 3+ ions, reducing W 6+ to W 5+ . The whole process can occur spontaneously without external voltage application, forming a chemical potential difference between the In element on the alloy and the W element in the electrochromic writing ink, thereby driving the directional migration of electrons and realizing passive electrochromism.

[0101] Through Figure 19It can be seen that the electrochromic device is light yellow in the colorless state, and at a wavelength of 532 nm, the reflectivity is 85.6%. In the colored state, it is blue. Due to the enhanced light absorption caused by carrier injection, the reflectivity in the visible light range is significantly reduced, and the reflectivity at 358 nm is 19%. After being erased by H2O2, an oxide layer is generated on the surface of the liquid metal, resulting in diffuse reflection. Due to the absorption of the oxide layer (about 40%), the reflectivity is low. Therefore, when using electrochromic writing ink to write on the liquid metal layer, obvious color changes occur.

[0102] Through Figure 20 It can be seen that starting from 110 ms, the electrochromic writing ink of the electrochromic device begins to be colored, and the color gradually turns blue. At 460 ms, a clear coloring state is shown. At 810 ms, a circular pattern with a diameter of 2 cm is completely colored. It fully proves that the electrochromic device of the present invention has a relatively high color change response rate.

[0103] Through Figure 21 It can be seen that we conduct a stability test of 50 writing-erasing cycles on the electrochromic device. Through the reflection spectrum, it can be observed that the average reflectivity value at 358 nm is 9%, and the error bar is ±5%. However, due to the action of hydrogen peroxide during the erasing process, the thickness and composition of the oxide layer on the surface of the liquid metal change, which has a certain impact on the optical performance, and the reflection spectrum floats more. The average reflectivity value at 358 nm is 40%, and the error bar is ±10%. It proves that the device of the present invention has high stability and can be repeatedly erased and written for a relatively large number of times.

[0104] Through Figure 22 It can be seen that the electrochromic device of the present invention has the fastest response time compared to 15 other electrochromic devices, fully proving that the electrochromic device of the present invention has excellent use performance.

[0105] In summary, the electrochromic device prepared by the present invention has relatively excellent flexibility, can achieve self-powered driving, and at the same time has a relatively high coloring and self-bleaching response rate, and can be repeatedly erased and reused for multiple times, with a wide range of applicable scenarios and excellent comprehensive use performance.

[0106] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A flexible passive electrochromic device with high-speed response, characterized in that: The electrochromic device includes a flexible substrate (1), a liquid metal layer (2), and electrochromic writing ink (3). The liquid metal layer (2) is disposed on one side of the flexible substrate (1), and the electrochromic writing ink (3) is used for writing on the liquid metal layer (2). The raw material of the flexible substrate (1) includes one of polyethylene terephthalate, polyimide-based material, and graphene / polydimethylsiloxane mixture. The raw material of the liquid metal layer (2) includes one of InSnBi, InGa, and InGaSn alloys. The raw material of the electrochromic writing ink (3) is a mixed solution of an ion-rich WO3 solution and a mixed hydrogel solution, and the mixed hydrogel solution is a mixture solution of a hydrogel and lithium chloride.

2. The flexible passive electrochromic device with high-speed response according to claim 1, characterized in that: The hydrogel is one of a polyacrylamide-based hydrogel and a polyvinyl alcohol-based hydrogel.

3. The flexible passive electrochromic device with high-speed response according to claim 1, characterized in that: The thickness of the flexible substrate (1) is 300 μm, and the thickness of the liquid metal layer (2) is 200 μm.

4. A method for preparing a high-speed response flexible passive electrochromic device according to any one of claims 1-3, characterized in that: The preparation method includes the following steps: (1) Prepare the ion-rich WO3 solution and the mixed hydrogel solution respectively, and mix the mixed hydrogel solution and the ion-rich WO3 solution evenly to obtain the electrochromic writing ink. (2) Compose the liquid metal layer (2) and the flexible substrate (1) by rolling.

5. The preparation method according to claim 4, characterized in that: In the electrochromic writing ink, the mass ratio of the ion-rich WO3 solution to the mixed hydrogel solution is ion-rich WO3 solution: mixed hydrogel solution = 1:1 - 3:

1.

6. The preparation method according to claim 4, characterized in that: In the step (1), the specific process of preparing the ion-rich WO3 solution is as follows: Disperse W powder into H2O2. After the W powder and H2O2 react completely, centrifuge the liquid to obtain the supernatant. Add excessive ethanol to the supernatant to prevent the continued formation of internal complexes and simultaneously increase the ion concentration inside the supernatant. Then, dry the liquid to evaporate the ethanol and obtain the ion-rich WO3 solution.

7. The preparation method according to claim 6, characterized in that: The solid-liquid ratio of the W powder to H2O2 is W powder: H2O2 = 1 g: 4 ml. The reaction temperature of the W powder and H2O2 is 0 - 10 °C. The centrifugation speed is 3500 rpm, and the centrifugation time is 10 min. The drying temperature is 80 °C, and the drying time is 1 h.

8. The preparation method according to claim 4, characterized in that: In the step (1), the specific process of preparing the mixed hydrogel solution is as follows: Dissolve acrylamide monomer in water to obtain an acrylamide monomer solution, then add lithium chloride to the acrylamide monomer solution to obtain a monomer mixed solution. Ultrasonically treat the monomer mixed solution until the lithium chloride is completely dissolved. Then, add N,N-dimethylacrylamide and ammonium persulfate to the monomer mixed solution and stir to obtain the mixed hydrogel solution.

9. The preparation method according to claim 8, characterized in that: The solid-liquid ratio of the acrylamide monomer to deionized water is acrylamide: deionized water = 3 g: 20 ml. The addition amount of lithium chloride satisfies 0 < addition amount of lithium chloride ≤ 10 mol / L based on the volume of the acrylamide monomer solution. The added mass of N,N-dimethylacrylamide is 0.1% of the mass of the acrylamide monomer solution. The added amount of ammonium persulfate is 0.2% of the mass of the acrylamide monomer solution.

10. The preparation method according to claim 4, characterized in that: In the step (2), before rolling, the flexible substrate (1) is first subjected to plasma hydrophilic treatment for 120 s, and the rolling temperature is 60°C.

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