An electrolyte for zinc-based electrochromic devices

Abstract

An electrolyte for a zinc-based electrochromic device belongs to the technical field of functional materials and devices. The electrolyte includes a mixed solvent, a zinc salt solute and an additive; wherein the mixed solvent is a mixed solution formed by water and one of alcohol and nitrile organic solvents, and the additive is a cryptand additive. The present invention uses a mixed solution formed by water and one of alcohol and nitrile organic solvents as a mixed solvent, and its high ionic conductivity, low viscosity and high dielectric constant can ensure a rapid reversible deposition process of zinc ions; at the same time, the hydroxyl or cyano polar groups can effectively dissolve zinc salts; and the introduction of alcohol and nitrile organic solvents can reduce the occurrence of interfacial side reactions and improve reversibility. Using cryptand as an additive, the oxygen atoms of the cryptand additive form a multi-element coordination with zinc ions, reduce the content of interfacial water, thereby improving reversibility, and further improving the uniformity of zinc film deposition.

Description

Technical Field

[0001] The invention belongs to the technical field of functional materials and devices, and in particular relates to an electrolyte for a zinc-based electrochromic device. Background Art

[0002] Electrochromism is a phenomenon in which certain materials undergo a stable and reversible color change due to a redox reaction that occurs under the influence of an applied electric field. In recent years, electrochromic devices have become increasingly popular for use in displays, sensors, and smart windows.

[0003] Traditional electrochromic devices can adjust the transmittance by applying different voltages to change the type and depth of color. However, with the rapid development of smart and interactive electronics, traditional electrochromic devices are often difficult to adapt to the requirements of practical applications. The main development trend in the future will be to design and manufacture electrochromic devices with multiple states and higher reversibility to meet consumer needs and expand the scope of application.

[0004] Zinc-based electrochromic devices achieve color and transmittance control by reversibly depositing zinc ions in the electrolyte on the conductive film. The three states of transparency, translucency and complete opacity can be achieved by changing the deposition time of zinc, which has great application prospects in the field of smart color-changing windows. However, the electrolyte used in devices with this working mode is usually an aqueous solution of zinc sulfate. Due to the uneven electric field at the zinc plating interface and the side reactions caused by the solvent water, its reversibility is very low, resulting in uneven deposition of zinc on the conductive film and poor reversibility. Summary of the invention

[0005] The purpose of the present invention is to propose an electrolyte for a zinc-based electrochromic device in view of the problems existing in the background technology.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An electrolyte for a zinc-based electrochromic device comprises a mixed solvent, a zinc salt solute and an additive; wherein the mixed solvent is a mixed solution formed by water and one of alcohol and nitrile organic solvents, and the additive is a cryptand additive.

[0008] Furthermore, the alcohol organic solvent is methanol, ethanol, ethylene glycol, glycerol, isopropanol, or their alcohol isomers or derivatives; the nitrile organic solvent is acetonitrile, malononitrile, acetonenitrile, succinonitrile, adiponitrile, or their nitrile isomers or derivatives.

[0009] Furthermore, the volume ratio of water to the alcohol or nitrile organic solvent is 1:(1-10).

[0010] Furthermore, the zinc salt solute is one or more of zinc sulfate, zinc trifluoromethanesulfonate, zinc chloride, zinc bromide, zinc iodide, zinc bis(trifluoromethylsulfonyl)imide, zinc perchlorate, zinc tetrafluoroborate, zinc nitrate, and zinc acetate.

[0011] Furthermore, in the electrolyte, the concentration of zinc salt is 0.1-4 mol / L.

[0012] Furthermore, the additive is one or more of cryptands such as cryptands 222, cryptands 221, and cryptands 211.

[0013] Furthermore, the additive is added in an amount of 0.1 wt% to 1 wt% of the electrolyte mass.

[0014] The invention provides an electrolyte for a zinc-based electrochromic device, which is applied in a reflective electrochromic device or a transmissive electrochromic device.

[0015] Furthermore, when the above-mentioned electrolyte is applied to a reflective electrochromic device, the color-changing layer is selected to be a conductive film that allows reversible electroplating and stripping of zinc, such as a copper mesh, an aluminum mesh, a silver mesh, a zinc mesh, a stainless steel mesh or gold-plated nylon 66, etc.; the electrode material is selected to be zinc, or an alloy formed by zinc and copper, aluminum, silver, magnesium, manganese, etc.

[0016] Furthermore, when the above-mentioned electrolyte is applied to a transmissive electrochromic device, the color-changing layer is selected to be a conductive film that allows reversible electroplating and stripping of zinc, such as FTO, ITO or conductive PET; the electrode material is selected to be zinc, or an alloy formed by zinc and copper, aluminum, silver, magnesium, manganese, etc.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides an electrolyte for a zinc-based electrochromic device, which uses a mixed solution formed by water and one of alcohol and nitrile organic solvents as a mixed solvent. Its high ionic conductivity, low viscosity, and high dielectric constant can ensure a rapid reversible zinc ion deposition process; at the same time, the hydroxyl or cyano polar groups can effectively dissolve zinc salts; and the introduction of alcohol and nitrile organic solvents can reduce the occurrence of interfacial side reactions and improve reversibility. Using cryptand as an additive, the oxygen atoms of the cryptand additive form a multi-element coordination with zinc ions, reducing the content of interfacial water to improve reversibility, and then improving the uniformity of zinc film deposition. In summary, the electrolyte of the present invention has a low melting point, low viscosity, high dielectric constant, good redox stability, and low price, and is very suitable for use as an electrolyte for highly reversible zinc-based electrochromic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a zinc-based electrochromic device based on the electrolyte of the present invention;

[0020] Figure 2 A schematic diagram of the interaction between cryptand 222 molecules and zinc ions in the electrolyte prepared in Example 1;

[0021] Figure 3 This is a comparison chart of the color change effect achieved by the electrolyte prepared in Example 1 and the traditional electrolyte;

[0022] Figure 4 The schematic diagram of the color change effect achieved by the electrolyte prepared in Example 1 and the traditional electrolyte;

[0023] Figure 5 This is a SEM image of a coating formed on ITO by the electrolyte prepared in Example 2;

[0024] Figure 6 The constant current coloring and fading curves of the electrolyte prepared in Example 3;

[0025] Figure 7 These are photos of the coatings of the electrolyte prepared in Example 4 at different coloring times. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described with the following specific embodiments, but the present invention is not limited to these examples.

[0027] Example 1

[0028] A mixture of water and succinonitrile in a volume ratio of 1:4 was used as a mixed solvent, zinc tetrafluoroborate was dissolved in it at a molar concentration of 4 mol / L, and 0.5% of cryptand 222 was used as an additive. ITO was used as the color-changing electrode and the zinc ring was used as the counter electrode to assemble a zinc-based electrochromic device. The schematic diagram of the device structure is shown in FIG. Figure 1 As shown. The mixed solvent can reduce the interface side reactions such as water-induced corrosion and gas generation. At the same time, the cryptand molecules can replace water molecules to form coordination with zinc ions to induce the uniform deposition of zinc ions during the electroplating process. The schematic diagram of the interaction between zinc ions and cryptand 222 is shown in Figure 2 After applying a -1.3V potential to the device for 1 minute, zinc ions deposited on the ITO to form a uniform gray area, thus changing the color and transmittance of the ITO glass ( Figure 3 ). If the traditional 2M ZnSO4 pure water solution is used for coloring under the same conditions for 1 minute, the uneven electroplating of zinc will be caused by the uneven electric field at the interface, and the coloring of the ITO surface will be relatively uneven. The principle diagram of the color change effect achieved by the two electrolytes is shown in the figure below. Figure 4 shown.

[0029] Example 2

[0030] A mixture of water and ethylene glycol in a volume ratio of 1:1 was used as a mixed solvent, zinc trifluoromethanesulfonate was dissolved therein at a molar concentration of 2 mol / L, and 0.1% of the mass fraction of cryptand 222 was used as an additive. Using ITO as the color-changing electrode and a copper-zinc alloy ring as the counter electrode, a zinc-based electrochromic device was assembled. The ethylene glycol molecules in the mixed solvent can reduce the interfacial side reactions such as corrosion and gas production caused by water. At the same time, the cryptand molecules can replace water molecules to form coordination with zinc ions to further reduce the adverse reactions of zinc ions during the electroplating process. After applying a potential of -1.3V to the device for 3 minutes, a scanning electron microscope test was performed on the gray area formed on the ITO, and it was found that due to the presence of the cryptand molecules, the zinc ions were deposited more evenly on the ITO, and no obvious dendritic zinc was produced, which proved that the electrolyte of the present invention is conducive to the application of zinc-based electrochromic devices ( Figure 5 ).

[0031] Example 3

[0032] A mixture of water and acetonitrile in a volume ratio of 1:1 was used as a mixed solvent, zinc chloride was dissolved in it at a molar concentration of 1 mol / L, and 0.1% of cryptand 211 was used as an additive. ITO was used as a color-changing electrode and a zinc ring was used as a counter electrode to assemble a zinc-based electrochromic device. The acetonitrile molecules in the mixed solvent can reduce the interfacial side reactions such as water-induced corrosion and gas production. At the same time, the cryptand molecules can replace water molecules to form coordination with zinc ions to further reduce the adverse reactions of zinc ions during the electroplating process. Apply 1 mA cm to the device. -2 After 30 seconds, the current density was 1 mA cm -2 The zinc coating on ITO is stripped off at a current density of 1.58kV. The electroplating and stripping curves are shown in Figure 6 As shown. It can be seen that due to the use of a mixed solvent of acetonitrile and water, the water decomposition reaction at the interface is suppressed, and the coulombic efficiency of zinc plating and stripping is higher than that of the case when the traditional electrolyte is used, indicating that most of the zinc can be reversibly plated and stripped, which shows that the electrolyte of the present invention has high reversibility when used in zinc-based electrochromic devices.

[0033] Example 4

[0034] A mixture of water and glycerol in a volume ratio of 1:1 was used as a mixed solvent, zinc trifluoromethanesulfonate was dissolved therein at a molar concentration of 2 mol / L, and 0.1% of cryptand 221 was used as an additive. ITO was used as a color-changing electrode and a zinc ring was used as a counter electrode to assemble a zinc-based electrochromic device. The glycerol molecules in the mixed solvent can reduce the interface side reactions such as corrosion and gas production caused by water. At the same time, the cryptand 221 molecules can replace water molecules to form coordination with zinc ions to further reduce the content of water molecules introduced to the interface during the electroplating process. After applying a -1.3V potential to the device for 10 minutes, the gray area gradually formed on the ITO was further energized for 30 minutes, and zinc formed a mirror surface on the ITO, which was completely opaque. The voltage was then reversed, that is, after applying a 1.1V potential to the device for 10 minutes, the zinc coating on the ITO surface completely disappeared and became transparent again ( Figure 7 ). The use of traditional electrolytes not only results in uneven coating, but also leaves a large amount of zinc particles remaining after reverse current is applied, which indicates that the electrolyte of the present invention can realize a highly reversible zinc-based electrochromic device.

Claims

1. An electrolyte for a zinc-based electrochromic device, characterized in that: The invention comprises a mixed solvent, a zinc salt solute and an additive; wherein the mixed solvent is a mixed solution of water and ethylene glycol, the additive is cryptand 222, and the zinc salt solute is zinc trifluoromethanesulfonate; the volume ratio of water to ethylene glycol is 1:1; the amount of the additive added is 0.1wt% of the mass of the electrolyte; and the concentration of the zinc salt in the electrolyte is 2mol / L.

2. Use of the electrolyte according to claim 1 in a reflective electrochromic device or a transmissive electrochromic device.

3. According to the use described in claim 2, when the electrolyte is applied to a reflective electrochromic device, the color-changing layer is a copper mesh, an aluminum mesh, a silver mesh, a zinc mesh, a stainless steel mesh or a gold-plated nylon 66; and the electrode material is zinc.

4. According to the use described in claim 2, when the electrolyte is applied to a transmissive electrochromic device, the color-changing layer is FTO, ITO or conductive PET; and the electrode material is zinc.

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