Tungsten oxide paint for electrochromic elements, tungsten oxide thin film and dimming material

Abstract

This tungsten oxide paint for an electrochromic element is a paint for forming a tungsten oxide thin film having electrochromic properties, the paint being characterized by comprising a solvent, tungsten oxide nanoparticles dispersed in the solvent, and a binder, wherein: in the tungsten oxide nanoparticles, a half maximum full-width of the peak detected at 29°±1° as measured by the X-ray diffraction analysis (2θ) is at most 2°; and tungsten oxide nanoparticles have a primary particle size of 5-25 nm.

Description

[Technical Field]

[0001] The present invention relates to a technology relating to a tungsten oxide thin film used in an electrochromic element that changes color through an electrochemical oxidation-reduction reaction. [Background technology]

[0002] An electrochromic device (hereinafter also referred to as "ECD") is a color-changeable element that uses an electrochromic material (hereinafter also referred to as "EC material") that changes color through an electrochemical oxidation-reduction reaction. ECDs (electrochromic devices) are being considered for use in vehicle mirrors that control reflectance by changing color, and in car and building windows that can control light transmittance to improve air conditioning efficiency. Furthermore, ECDs are also being considered for use in displays, sunglasses, etc. ECDs include, for example, an EC material and a solid electrolyte.

[0003] In recent years, the application of ECD to light-control glass for buildings and vehicles has been actively investigated. Examples of EC materials used in light-control glass include metal oxides such as tungsten oxide (Patent Document 1), small molecules such as viologen (Patent Document 2), polymers such as PEDOT-PSS (Patent Document 3), and coordination polymers such as metal cyano complex nanoparticles (Patent Document 4).

[0004] Recently, ECDs using organic polymer materials and silver nanoparticles have also been developed. However, organic polymer materials generally have issues with light resistance and are not suitable for use in light-control glass. Furthermore, development of ECDs using silver nanoparticles has just begun, and light resistance and other aspects have not yet been fully evaluated.

[0005] In this way, inorganic materials are thought to have a certain advantage in terms of light resistance, etc. Among inorganic materials, metal oxides and metal cyano complex nanoparticles have already been commercialized.

[0006] However, in applications using tungsten oxide, the main EC material, various materials, including solid electrolytes, are mainly produced by physical processes such as magnetron sputtering, which means that mass production is problematic because it is a batch process using glass as the substrate.

[0007] Furthermore, flexible light-control films using resins as transparent substrates are being developed to balance convenience, portability, flexibility, cost, etc. (Patent Document 4). However, the technology in Patent Document 4 relies on process equipment and is expensive, particularly for reasons such as the need for a cooling device to prevent damage to the resin substrate due to the heat input during film formation, which is required for the solid electrolyte manufacturing method. Therefore, it is difficult to commercialize flexible light-control films using resin substrates.

[0008] For example, the market for Smart Glass, a general term for light-controlling glass, is expanding. However, like Low-E glass, Smart Glass is manufactured using a batch process using vapor deposition or sputtering. Therefore, the manufacturing costs and the introduction and running costs are barriers to its widespread adoption, and there is a strong demand for cost reductions through material and process development (Non-Patent Document 1).

[0009] From the viewpoint of reducing costs, an electrochromic element has been reported that combines an electrode formed by a method such as coating a dispersion liquid in which Prussian blue-type metal cyano complex nanoparticles are dispersed in water as an inorganic EC material with an electrode formed by a method such as coating a dispersion liquid in which tungsten oxide nanoparticles are dispersed in water, thereby producing a change between colored and transparent states (Patent Document 5). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 08-254717 [Patent Document 2] JP 2009-215166 A [Patent Document 3] Special table number 2005-519316 [Patent Document 4] Patent Publication No. 2011-180469 [Patent Document 5] Patent Publication No. 2018-021113 [Non-patent literature]

[0011] [Non-Patent Document 1] QUADRENNIAL TECHNOLOGY REVIEW, Chapter5, p.160, DOE, 2015 Summary of the Invention [Problem to be solved by the invention]

[0012] The combination of tungsten oxide and metal cyano complexes as light-control materials has attracted considerable attention. However, to popularize the wide variety of applications that utilize this combination, challenges remain: productivity (low cost, mass production), durability (number of uses, operating environment), ease of installation and control system, and reduced energy consumption. EC materials capable of high-contrast color changes between colored and colorless transparent states and fast response are particularly desirable, as are electrochromic devices utilizing such EC materials. Furthermore, for applications in energy-saving windows, it is desirable to develop new EC materials that offer high-efficiency thermal energy control while maintaining lightfastness.

[0013] The present invention has been made in consideration of the above circumstances, and aims to provide a new EC material that enables high-speed response and high-contrast color changes, as well as a dimming component as an electrochromic element using the same. [Means for solving the problem]

[0014] As a result of extensive research, the inventors investigated the manufacturing method and physical properties of tungsten oxide nanoparticles as EC materials, which have various characteristics such as crystallinity, amorphousness, and introduction of oxygen defects. They then discovered that a paint can be made by adding a binder to a dispersion liquid in which tungsten oxide nanoparticles, in which the half-width of the peak detected at 29°±1° in X-ray diffraction analysis (2θ) is 2° or less and the primary particle size is 5 to 25 nm, are dispersed in a solvent, and that a thin film formed using this paint has physical properties suitable for application in electrochromic devices, thereby completing the present invention.

[0015] [1] A tungsten oxide paint for electrochromic devices for forming a tungsten oxide thin film having electrochromic properties, comprising a solvent, tungsten oxide nanoparticles dispersed in the solvent, and a binder, wherein the tungsten oxide nanoparticles have a half-width of a peak detected at 29°±1° in X-ray diffraction analysis (2θ) of 2° or less and a primary particle size of 5 to 25 nm.

[0016] [2] The content of the tungsten oxide nanoparticles is 5% by mass or more and 30% by mass or less relative to the paint mass. [1] The tungsten oxide paint for an electrochromic device according to claim 1.

[0017] [3] The tungsten oxide paint for electrochromic devices according to [1] or [2], characterized in that the binder is one or more selected from polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), and hydroxyethyl cellulose (HEC), and the content of the binder is 0.1% by mass or more and 10% by mass or less relative to the mass of the paint.

[0018] [4] The tungsten oxide paint for electrochromic devices according to any one of [1] to [3], which contains a pH adjuster.

[0019] [5] The tungsten oxide paint for electrochromic devices according to [4], characterized in that the pH adjuster is one or more selected from potassium chloride (KCl), sodium chloride (NaCl), lithium chloride (LiCl), potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH).

[0020] [6] The tungsten oxide paint for electrochromic devices according to [4] or [5], which has a pH of 5 to 7.

[0021] [7] The tungsten oxide paint for electrochromic devices according to any one of [1] to [6], which is capable of forming a tungsten oxide thin film by a coating method.

[0022] [8] A thin film having electrochromic properties, comprising tungsten oxide nanoparticles and a binder, wherein the tungsten oxide nanoparticles have a half-width of a peak detected at 29°±1° in X-ray diffraction analysis (2θ) of 2° or less, and a primary particle size of 5 to 25 nm.

[0023] [9] The tungsten oxide thin film according to [8], which contains a pH adjuster.

[0024]

[10] The tungsten oxide thin film according to [8] or [9], characterized in that it undergoes an electrochromic reaction in an electrolyte containing one or more (trifluoromethanesulfonyl)imide salts selected from the group consisting of bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0025]

[11] A tungsten oxide thin film according to any one of [8] to

[10] ; The present invention is characterized by comprising: a metal cyano complex thin film containing metal cyano complex nanoparticles or an oxide thin film containing oxide nanoparticles, which undergoes the opposite coloring and decoloring changes due to an oxidation-reduction reaction to tungsten oxide; and an electrolyte layer located between the tungsten oxide thin film and the metal cyano complex thin film or the oxide thin film. Dimming component.

[0026] A dispersion is a mixture of tungsten oxide nanoparticles and a solvent, whereas the paint of the present invention is a dispersion to which a binder has been added. Therefore, the dispersion and the paint are distinguished from each other. [Effects of the Invention]

[0027] According to the present invention, by appropriately combining a thin film using tungsten oxide nanoparticles with a thin film using metal cyano complex nanoparticles, it is possible to manufacture and provide an electrochromic device that can switch between coloring and decoloring with high contrast and at high speed. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of an electrochromic element according to an embodiment. [Figure 2] FIG. 1 is a diagram showing the results of X-ray diffraction of tungsten oxide nanoparticles used in the examples. [Figure 3] 1 is a transmission electron microscope photograph of tungsten oxide nanoparticles used in the examples. [Figure 4] 1A and 1B are field emission scanning electron microscope photographs of tungsten oxide thin films according to examples and comparative examples. [Figure 5] 1 shows cyclic voltammograms of tungsten oxide thin films according to an example and a comparative example. [Figure 6] 1 shows changes in the visible light transmission spectrum of tungsten oxide thin films according to an example and a comparative example. [Figure 7] 1 is a comparison of cyclic voltammograms of tungsten oxide thin films according to examples. [Figure 8] 1 is a cyclic voltammogram of ECD1 according to an example. [Figure 9] 1 shows the visible light transmission spectrum of ECD1 according to an example. [Figure 10] 1 is a photograph of the color change of ECD1 according to an example. [Figure 11] 1 shows the total light transmittance spectrum of ECD1 according to an example. [Figure 12] 1 is a photograph of the color change of ECD2 according to an example. [Figure 13] 1 shows the total light transmittance spectrum of ECD2 according to an example. [Figure 14] 1 shows the total light transmittance spectrum of ECD3 according to an example. [Figure 15] 1 shows the total light transmittance spectrum of ECD4 according to an example. [Figure 16] 1 is a graph showing the relationship between the amount of tungsten oxide nanoparticles 1 added and the pH of the paint according to the example. [Figure 17] 1 is a graph showing the relationship between the amount of 0.1 M NaOH added and the pH of the paint for the example. [Figure 18] 1 shows changes in the visible light transmission spectrum of a tungsten oxide thin film according to an example. [Figure 19] 1 is a graph showing the results of a cycle test of ECD5 according to an example. [Figure 20] 1 is a graph showing the results of a cycle test of ECD5 according to an example. [Figure 21] 1 shows the change in visible light transmission spectrum when measuring the withstand voltage characteristics of ECD5 and ECD6 according to the examples. [Figure 22] 1 is a graph showing the results of a cycle test of ECD7 according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0029] [Tungsten oxide paint for electrochromic elements] The tungsten oxide (WO3) paint for electrochromic devices according to the present invention will be described. The tungsten oxide paint for electrochromic devices according to the present invention (hereinafter also referred to simply as "paint") is a paint for forming a tungsten oxide thin film with electrochromic properties, and is used in electrochromic devices. Specifically, the paint of the present invention contains a solvent, tungsten oxide nanoparticles dispersed in the solvent, and a binder.

[0030] In the following description, "A to B" indicating a range of values ​​is synonymous with "A or more and B or less."

[0031] The tungsten oxide nanoparticles used in the paint are characterized by a peak half-width of 2° or less detected at 29°±1° in X-ray diffraction analysis (2θ), and a primary particle size of 5 to 25 nm.

[0032] X-ray diffraction analysis (2θ) can be performed using, for example, Cu-Kα radiation (wavelength 1.54184 Å) with a tube voltage of 40 kV, a tube current of 40 mA, an operating axis of 2θ / θ, a scanning range (2θ) of 10° to 60°, a scanning speed of 0.1° / sec, and a step width of 0.02°.

[0033] The peak detected at 29°±1° used to determine the half-width is typically the strongest peak within the range of 29°±1°. The strongest peak is the peak with the largest intensity ratio. When measuring the half-width, the smaller of the values ​​at the base of the peak at either end is used as the reference value. The position from the reference value to the peak top is taken as the peak height. The width of the peak at half the peak height is then taken as the half-width. Note that if there are two peaks at 29°±1° and the bases of the peaks overlap, the half-width can also be determined by analysis using the X-ray diffraction instrument software.

[0034] X-ray diffraction indicates the crystallinity of tungsten oxide nanoparticles. Good crystallinity results in a sharp peak with a small half-width. When the half-width of the peak detected at 29°±1° in X-ray diffraction analysis (2θ) is 2° or less, this indicates that crystal defects are suppressed. Crystal defects are disruptions in the crystal arrangement. When crystal defects occur, defects are introduced at the lower end of the band gap conductor, narrowing the apparent band gap. This results in absorption in the visible light range. For these reasons, the upper limit of the half-width of the peak detected at 29°±1° in X-ray diffraction analysis (2θ) is 2° or less.

[0035] The lower limit of the half-width is not particularly limited, but is preferably 0.1° or more. A half-width of less than 0.1° means that the crystal repeatability is high. This indicates that the primary particle size of the primary particles is often greater than 25 nm. As the primary particle size increases, transmitted light is scattered, resulting in a decrease in transmittance across all wavelengths. For this reason, the lower limit of the half-width of the peak detected at 29°±1° in X-ray diffraction analysis (2θ) is preferably 0.1° or more.

[0036] The primary particle size of tungsten oxide nanoparticles is the diameter of the primary particle and can be identified, for example, by structural analysis using a transmission electron microscope (TEM). If ligands or other substances are adsorbed on the surface of the tungsten oxide nanoparticles, the primary particle size is calculated by excluding the ligands. The primary particle size is the length of the longest diagonal of the particle. The longest diagonal of the primary particle present in a TEM image with a field of view of 60 nm x 60 nm is measured. Only particles whose outlines are visible are counted. At least 10 primary particles are observed. For example, primary particles that overlap and whose outlines cannot be observed are not counted.

[0037] The upper limit of the primary particle size of the tungsten oxide nanoparticles is 25 nm or less from the viewpoint of increasing the specific surface area to improve the electrochemical response speed (i.e., the color change speed for switching between coloring and decoloring) and from the viewpoint of forming a smooth thin film. The lower limit of the primary particle size of the tungsten oxide nanoparticles is not particularly limited, but is, for example, 5 nm or more.

[0038] The lower limit of the content of the tungsten oxide nanoparticles is 5% by mass or more, preferably 10% by mass or more, based on the mass of the coating material (i.e., when the entire coating material is taken as 100% by mass). The upper limit of the content of the tungsten oxide nanoparticles is 30% by mass or less, preferably 25% by mass or less, based on the mass of the coating material. By keeping the content of the tungsten oxide nanoparticles within the above range, a homogeneous tungsten oxide thin film can be produced.

[0039] The tungsten oxide nanoparticles used in the coating material of the present invention can be produced by any known production technique. One example of the production method for tungsten oxide nanoparticles is as follows.

[0040] The method for producing tungsten oxide (WO) particles includes a sublimation process. The sublimation process is a process for producing tungsten oxide nanoparticles by sublimating a precursor or precursor solution of tungsten oxide nanoparticles in an oxygen atmosphere. The precursor of tungsten oxide nanoparticles is metallic tungsten powder or tungsten compound powder, and the precursor solution of tungsten oxide nanoparticles is a solution in which these precursors are dissolved in a solvent (e.g., water or alcohol).

[0041] As the tungsten compound, known compounds that can be used to produce tungsten oxide (WO3) particles can be used, such as various tungsten oxides (e.g., WO3, WO2), tungsten carbide, ammonium tungstate, calcium tungstate, and tungstic acid.

[0042] In the sublimation process, the precursor or precursor solution of tungsten oxide nanoparticles is sublimated in an oxygen atmosphere using any known technique, such as plasma treatment, arc discharge treatment, laser treatment, or electron beam treatment, with inductively coupled plasma treatment being preferred.

[0043] By appropriately setting the various conditions for the treatments (plasma treatment, arc discharge treatment, laser treatment, or electron beam treatment) performed in the sublimation process and the average particle size of the metallic tungsten powder and tungsten compound powder, it is possible to produce tungsten oxide nanoparticles with a primary particle size of 5 to 25 nm and a half-width of the peak detected at 29°±1° in X-ray diffraction analysis (2θ) of 2° or less.

[0044] The manufacturing method may include other steps besides the sublimation step, such as a heat treatment step after the sublimation step to increase the proportion of tungsten oxide (WO3) in the powder after the sublimation step.

[0045] The solvent used in the paint can be any solvent that can disperse tungsten oxide nanoparticles and does not affect the tungsten oxide nanoparticles. For example, water or alcohol can be used as the solvent. The alcohol can be one or more selected from isopropanol, ethanol, methanol, n-propanol, isobutanol, n-butanol, etc. From the viewpoint of improving the dispersibility of the tungsten oxide nanoparticles, for example, water alone is preferred.

[0046] The binder used in the coating material is not particularly limited, and one or more binders selected from organic binders or inorganic binders may be used. Examples of organic binders that can be used include cellulose derivatives, vinyl resins, fluorine-based resins, silicone resins, acrylic resins, epoxy resins, polyester resins, melamine resins, urethane resins, and alkyd resins. Examples of inorganic binders that can be used include products obtained by decomposing hydrolyzable silicon compounds such as alkyl silicates, silicon halides, and their partial hydrolyzates, organic polysiloxane compounds and their polycondensates, silica, colloidal silica, water glass, silicon compounds, phosphates such as zinc phosphate, metal oxides such as zinc oxide and zirconium oxide, biphosphates, cement, gypsum, lime, and enamel frit.

[0047] From the viewpoint of producing a uniform tungsten oxide thin film, it is preferable to use, as the binder, one or more types selected from, for example, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), and hydroxyethyl cellulose (HEC).

[0048] The lower limit of the binder content is 0.1% by mass or more, preferably 0.15% by mass or more, based on the paint mass (i.e., when the entire paint is taken as 100% by mass). The upper limit of the binder content is 10% by mass or less, preferably 5% by mass or less, and more preferably 2% by mass or less, based on the paint mass. By keeping the binder content within the above range, the pot life of the paint is extended, and the formed tungsten oxide thin film does not contain coarse aggregates, despite containing a binder.

[0049] The paint of the present invention may further contain a pH adjuster.

[0050] The pH adjuster used in the paint is not particularly limited, but one or more pH adjusters selected from those that do not inhibit the electrochemical reaction are optionally used. The electrochromic element according to the present invention is driven by an oxidation-reduction reaction involving, for example, lithium, potassium, or sodium, and therefore the pH adjuster is one or more selected from potassium chloride (KCl), sodium chloride (NaCl), lithium chloride (LiCl), potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH).

[0051] The content of the pH adjuster in the paint is appropriately controlled depending on the solid amount of the tungsten oxide nanoparticles. The pH of the paint containing the pH adjuster is, for example, 2 to 8. However, from the viewpoint of improving durability, the pH of the paint is preferably 3 or higher, more preferably 5 to 7, and even more preferably about 5.

[0052] In addition to the binder and pH adjuster, various other additives may be blended into the paint, such as antifoaming agents, crosslinking agents, curing catalysts, pigment dispersants, emulsifiers, film-forming aids, thickeners, neutralizing agents, and preservatives.

[0053] [ECD] An electrochromic device (hereinafter referred to as "ECD") according to the present invention will be described below. The electrochromic device is used as a light control member capable of adjusting light.

[0054] Fig. 1 is a cross-sectional view showing an example of an ECD 100 according to this embodiment. As shown in Fig. 1, the ECD 100 includes a first electrochromic layer 10 (an example of a "tungsten oxide thin film"), a second electrochromic layer 20 (an example of a "metal cyano complex thin film"), an electrolyte layer 30, a first transparent electrode layer 40, a second transparent electrode layer 50, a first insulating layer 60, and a second insulating layer 70. The ECD 100 is formed by stacking these layers (10, 20, 30, 40, 50, 60, 70).

[0055] The electrolyte layer 30 is located between the first electrochromic layer 10 and the second electrochromic layer 20. The first transparent electrode layer 40 is located on the surface of the first electrochromic layer 10 opposite the electrolyte layer 30. The second transparent electrode layer 50 is located on the surface of the second electrochromic layer 20 opposite the electrolyte layer 30. The first insulating layer 60 is located on the surface of the first transparent electrode layer 40 opposite the first electrochromic layer 10. The second insulating layer 70 is located on the surface of the second transparent electrode layer 50 opposite the second electrochromic layer 20.

[0056] The first electrochromic layer 10 and the second electrochromic layer 20 are layers with electrochromic properties, and their color changes reversibly through an oxidation-reduction reaction (they reversibly change between a colored state and a decolored state). The first electrochromic layer 10 is colored in a reduced state and decolored in an oxidized state. On the other hand, the second electrochromic layer 20 is decolored in a reduced state and colored in an oxidized state.

[0057] Generally, the ECD 100 is driven by applying a voltage between the first transparent electrode layer 40 and the second transparent electrode layer 50. Specifically, when a voltage is applied between the first transparent electrode layer 40 and the second transparent electrode layer 50, the ECD 100 changes between a first state and a second state.

[0058] In the first state, the first electrochromic layer 10 is in an oxidized state (i.e., a bleached state), and the second electrochromic layer 20 is in a reduced state (i.e., a bleached state). On the other hand, in the second state, the first electrochromic layer 10 is in a reduced state (i.e., a colored state), and the second electrochromic layer 20 is in an oxidized state (i.e., a colored state). As can be understood from the above explanation, it is possible to control the color change in the ECD 100 in response to the application of a voltage.

[0059] (1) First electrochromic layer 10 The first electrochromic layer 10 contains the above-mentioned tungsten oxide (WO) particles and a binder. That is, the first electrochromic layer 10 is a tungsten oxide thin film. The tungsten oxide nanoparticles are colorless (almost colorless and transparent) in an oxidized state and colored blue in a reduced state.

[0060] The thickness of the first electrochromic layer 10 is set appropriately depending on the purpose, and is, for example, 500 to 1500 nm. The thickness of the first electrochromic layer 10 may or may not be constant (i.e., it may vary depending on the position in the surface direction).

[0061] The present invention can also be conceived as a tungsten oxide thin film having electrochromic properties and comprising tungsten oxide nanoparticles and a binder, wherein the tungsten oxide nanoparticles have a half-width of a peak detected at 29°±1° in X-ray diffraction analysis (2θ) of 2° or less and a primary particle size of 5 to 25 nm. Furthermore, the tungsten oxide thin film of the present invention may contain the above-mentioned pH adjuster.

[0062] (2) Second electrochromic layer 20 The second electrochromic layer 20 contains a material that changes color and fade due to an oxidation-reduction reaction in the opposite manner to that of tungsten oxide used in the first electrochromic layer 10, and is preferably metal cyano complex nanoparticles or oxide nanoparticles. Note that the second electrochromic layer 20 containing metal cyano complex nanoparticles is an example of a metal cyano complex thin film, and the second electrochromic layer 20 containing oxide nanoparticles is an example of an oxide thin film.

[0063] When metal cyano complex nanoparticles or oxide nanoparticles are used in the second electrochromic layer 20, any type of nanoparticles may be used as long as they undergo a reversible oxidation-reduction reaction. Metal cyano complex or oxide nanoparticles are materials that become colored in an oxidized state and lose their color in a reduced state.

[0064] Hereinafter, a detailed description will be given of the case where metal cyano complex nanoparticles are used in the second electrochromic layer 20. The metal cyano complex particles are those represented by the general formula "AxM α [M β Particles of a Prussian blue-type metal cyano complex represented by "(CN)6]y·zH2O" are preferably used.

[0065] A is an atom selected from the group consisting of hydrogen, lithium, sodium, and potassium.

[0066] M α is one or more metal atoms selected from the group consisting of vanadium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, silver, zinc, lanthanum, europium, gadolinium, lutetium, barium, strontium, and calcium.

[0067] M β is one or more metal atoms selected from the group consisting of vanadium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, nickel, platinum, and copper, where x is 0 to 3, y is 0.3 to 1.5, and z is 0 to 30.

[0068] As the metal cyano complex, one type represented by the above general formula may be used, or a mixture of two or more types may be used.

[0069] The upper limit of the primary particle size of the metal cyano complex nanoparticles is 300 nm or less, preferably 100 nm or less, and more preferably 50 nm or less, from the viewpoint of increasing the specific surface area to improve the electrochemical response rate and forming a smooth thin film. The lower limit of the primary particle size of the metal cyano complex nanoparticles is not particularly limited, but is, for example, 4 nm or more, preferably 5 nm or more, and more preferably 6 nm or more. The method for measuring the primary particle size of the metal cyano complex nanoparticles is the same as that described above for the primary particle size of the tungsten oxide nanoparticles.

[0070] The thickness of the second electrochromic layer 20 is set appropriately depending on the purpose, and is, for example, 500 to 3000 nm. The thickness of the second electrochromic layer 20 may or may not be constant (i.e., it may vary depending on the position in the surface direction).

[0071] (3) Electrolyte layer 30 The electrolyte layer 30 is a layer containing an electrolyte. The first electrochromic layer 10 and the second electrochromic layer 20 undergo an electrochromic reaction in the electrolyte.

[0072] The electrolyte used in the electrolyte layer 30 preferably contains a (trifluoromethanesulfonyl)imide salt. The (trifluoromethanesulfonyl)imide salt includes one or more of bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide. Among these, potassium bis(trifluoromethanesulfonyl)imide is preferred.

[0073] The content of the electrolyte in the electrolyte layer 30 is not particularly limited, but from the viewpoint of improving the electrochemical response speed of the ECD 100, it is, for example, 0.1 to 1.5 mol / kg, and preferably 0.5 to 1.5 mol / kg.

[0074] Furthermore, the electrolyte layer 30 may contain a solvent or a resin in addition to the electrolyte. As the solvent contained in the electrolyte layer 30, a known solvent capable of dissolving the electrolyte contained in the electrolyte layer 30 can be used, and examples thereof include chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, aliphatic carboxylic acid esters such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and methyl trimethylacetate, aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate, lactones such as γ-butyrolactone and γ-valerolactone, lactams such as ε-caprolactam and N-methylpyrrolidone, tetrahydrofuran, 2 one or more of the following may be selected: cyclic ethers such as 1,2-diethoxyethane and ethoxymethoxyethane; sulfones such as ethyl methyl sulfone, sulfolane, 3-methyl sulfolane and 2,4-dimethyl sulfolane; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; phosphates such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate and triethyl phosphate; alcohols such as ethanol and 2-propanol; glycols such as ethylene glycol, propylene glycol and polyethylene glycol; water;

[0075] The resin contained in the electrolyte layer 30 is not particularly limited, and may be one or more selected from known resins such as acrylic resin, urethane resin, silicone resin, epoxy resin, vinyl chloride resin, ethylene resin, melamine resin, phenol resin, methyl methacrylate resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyethylene oxide resin, etc. When the electrolyte layer 30 contains a resin, the mechanical strength of the electrolyte layer 30 can be improved.

[0076] The electrolyte layer 30 may optionally contain various other additives within the range that does not impair the function of the electrolyte layer 30. Examples of known additives include an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, a tackifier, a color inhibitor, a flame retardant, and an antistatic agent.

[0077] The thickness of the electrolyte layer 30 is set appropriately depending on the purpose, and is, for example, 50 μm to 0.3 mm. The thickness of the electrolyte layer 30 may or may not be constant (i.e., it may vary depending on the position in the surface direction).

[0078] The electrolyte layer 30 may be colored or colorless (transparent). The color of the electrolyte layer 30 can be changed appropriately depending on the purpose.

[0079] (4) First Transparent Electrode Layer 40 and Second Transparent Electrode Layer 50 The first transparent electrode layer 40 and the second transparent electrode layer 50 are layers made of a transparent conductive material. The conductive material constituting the first transparent electrode layer 40 and the second transparent electrode layer 50 is not particularly limited as long as it does not cause corrosion or other deterioration to a practical extent when used as an electrochemical element. Examples of suitable conductive materials include indium tin oxide (ITO), zinc oxide, and conductive oxides such as those doped with aluminum, silver, or titanium; precious metals such as gold or platinum; alloys or metals such as stainless steel or aluminum that have corrosion resistance due to a passivation coating; and carbon materials such as graphene and carbon nanotubes. From the standpoint of durability, it is particularly preferable to use fluorine-doped tin oxide (FTO) or transparent conductive oxide (TCO) for the transparent electrode layers (40, 50).

[0080] The thickness of the first transparent electrode layer 40 and the second transparent electrode layer 50 is set appropriately depending on the purpose, and is, for example, 100 to 300 nm. The thickness of the first transparent electrode layer 40 and the second transparent electrode layer 50 may or may not be constant (i.e., may vary depending on the position in the surface direction).

[0081] However, from the viewpoint of increasing the contact area between the first electrochromic layer 10 and the first transparent electrode layer 40 and improving the electrochemical response speed, the thickness of the first transparent electrode layer 40 may be made non-uniform. Specifically, the surface of the first transparent electrode layer 40 is made uneven (i.e., the surface smoothness is reduced). The convex portions on the surface of the first transparent electrode layer 40 are formed, for example, from a conductive material. Similarly, from the viewpoint of increasing the contact area between the second electrochromic layer 20 and the second transparent electrode layer 50 and improving the response speed, the thickness of the second transparent electrode layer 50 may be made non-uniform.

[0082] The first transparent electrode layer 40 may contain known additives for the purposes of improving adhesion to the first electrochromic layer 10 and suppressing corrosion. Similarly, the second transparent electrode layer 50 may contain known additives for the purposes of improving adhesion to the second electrochromic layer 20 and suppressing corrosion. Examples of known additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, tackifiers, color inhibitors, flame retardants, and antistatic agents.

[0083] (5) First insulating layer 60 and second insulating layer 70 The first insulating layer 60 and the second insulating layer 70 are layers made of a transparent insulating material. For example, the first insulating layer 60 and the second insulating layer 70 are formed of resin or glass. Examples of resin include polyethylene terephthalate (PET), polycarbonate, and polyethylene naphthalate (PEN). The first insulating layer 60 and the second insulating layer 70 may contain known additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, tackifiers, color inhibitors, flame retardants, and antistatic agents.

[0084] The thickness of the first insulating layer 60 and the second insulating layer 70 is, for example, 50 μm to 1.1 mm. The thickness of the first insulating layer 60 and the second insulating layer 70 may or may not be constant (i.e., may vary depending on the position in the surface direction).

[0085] As described above, the ECD 100 changes between a first state and a second state when a voltage is applied. Here, we assume a configuration in which Prussian blue-type metal complex particles (e.g., iron-iron cyano complex particles) are used as metal cyano complex nanoparticles in the second electrochromic layer 20, and a transparent material is used for the electrolyte layer 30. In the above configuration, the ECD 100 hand exhibits a color change from dark blue to colorless and transparent. Tungsten oxide is nearly colorless and transparent in its oxidized state, and iron-iron cyano complex particles are nearly colorless and transparent in its reduced state. Therefore, ECD100 is colorless and transparent in its first state. On the other hand, tungsten oxide turns blue in its reduced state, and iron-iron cyano complex nanoparticles turn blue in its oxidized state. Therefore, ECD100 is dark blue in its second state.

[0086] The ECD 100 according to the present invention is not limited to the above configuration. For example, the first insulating layer 60 and the second insulating layer 70 may be omitted from the ECD 100. Furthermore, the ECD 100 may include layers other than the layers (10, 20, 30, 40, 50, 60, 70) described above. For example, another layer (e.g., an insulating layer) may be provided between the first transparent electrode and the first insulating layer 60. Similarly, another layer may be provided between the second transparent electrode and the second insulating layer 70.

[0087] The ECD of this embodiment combines a first electrochromic layer 10 containing tungsten oxide (WO3) nanoparticles with a second electrochromic layer 20 containing metal cyano complex nanoparticles, enabling high-speed response and achieving high-contrast color changes.

[0088] An example of a method for manufacturing an ECD is described below. For example, two commercially available substrates with transparent electrodes (e.g., ITO-coated glass) are used as the substrates. When ITO-coated glass is used as the substrate, the ITO corresponds to the first transparent electrode layer 40 and the second transparent electrode layer 50 in FIG. 1, and similarly, the glass corresponds to the first insulating layer 60 and the second insulating layer 70. The two substrates are referred to as the first substrate (second transparent electrode layer 50 + second insulating layer 70) and the second substrate (first transparent electrode layer 40 + first insulating layer 60), respectively.

[0089] First, a first film-forming substrate is manufactured by forming a second electrochromic layer 20 (metal cyano complex thin film) on a first substrate using a coating material containing metal cyano complex nanoparticles using a coating method such as slit coating, spin coating, bar coating, or spray coating, a wet coating process, etc. Similarly, a second film-forming substrate is manufactured by forming a first electrochromic layer 10 (tungsten oxide thin film) on a second substrate using the same method using the tungsten oxide coating material of the present invention. An electrolyte layer 30 is formed on the first film-forming substrate using a dispenser. Furthermore, a sealing structure is formed around the periphery using UV-curable resin. Alternatively, this sealing structure can be formed using commercially available electronic device sealing tape, etc.

[0090] The second film-formation substrate is then placed over the first film-formation substrate from above, and the two substrates are pressed and bonded together in a vacuum chamber. If sealing tape is used, bonding can be performed at room temperature and atmospheric pressure without any problems. In this way, an ECD consisting of a first insulating layer 60 / first transparent electrode layer 40 / first electrochromic layer 10 / electrolyte layer 30 / second electrochromic layer 20 / second transparent electrode layer 50 / second insulating layer 70 structure is obtained. [Example]

[0091] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0092] [Tungsten oxide nanoparticles] Tungsten oxide nanoparticles 1-4 were produced as follows.

[0093] <Tungsten oxide nanoparticles 1> Tungsten oxide nanoparticles produced using a sublimation process and then pulverized using a dry bead mill.

[0094] <Tungsten oxide nanoparticles 2> Tungsten oxide nanoparticles prepared using a sublimation process

[0095] <Tungsten oxide nanoparticles 3> Tungsten oxide nanoparticles prepared using a sublimation process and then calcined at 450°C in air

[0096] <Tungsten oxide nanoparticles 4> Tungsten oxide nanoparticles prepared using a sublimation process and then calcined at 550°C in air

[0097] Figure 2 shows the results of powder X-ray diffraction analysis of tungsten oxide nanoparticles 1-4. X-ray diffraction was performed using Cu-Kα radiation (wavelength 1.54184 Å). The diffraction information for tungsten oxide nanoparticles 1-4 matched the diffraction information for tungsten oxide nanoparticles searched from a standard sample database.

[0098] For tungsten oxide nanoparticles 1-4, the half-width of the peak (strongest peak) detected at 29°±1° in X-ray diffraction analysis (2θ) was determined. The determined half-width is as follows: Tungsten oxide nanoparticles 1:0.9° Tungsten oxide nanoparticles 2: 0.7° Tungsten oxide nanoparticles 3: 0.7° Tungsten oxide nanoparticles 4: 0.6°

[0099] In particular, a broad peak was observed in tungsten oxide nanoparticle 1, suggesting low crystallinity.

[0100] Figure 3 shows transmission electron microscope photographs of tungsten oxide nanoparticles 1 and tungsten oxide nanoparticles 4. It was confirmed that the primary particle size of both tungsten oxide nanoparticles 1 and tungsten oxide nanoparticles 4 was within the range of 5 to 25 nm. Specifically, tungsten oxide nanoparticles 1 were aggregates of nanoparticles (primary particles) with a diameter of approximately 10 nm or less, and tungsten oxide nanoparticles 4 were aggregates of nanoparticles with a diameter of approximately 20 nm.

[0101] [Tungsten oxide paint for electrochromic elements] As described below, a tungsten oxide paint for electrochromic devices according to an example and a dispersion according to a comparative example were prepared.

[0102] Example 1 25 g of tungsten oxide nanoparticles 1 (powder sample) were suspended in 75 mL of water, and then PVA was added as a binder to reduce the surface tension, followed by stirring to obtain the paint of Example 1. PVA was added so that the PVA solid content relative to the total paint was 0.63 mass%.

[0103] <Example 2> The same procedure as in Example 1 was carried out except that PVA was added so that the solid content of PVA relative to the total amount of the paint was 0.15% by mass.

[0104] Example 3 The same procedure as in Example 1 was carried out except that PVA was added so that the solid content of PVA relative to the total paint was 1.29% by mass.

[0105] Example 4 The procedure was the same as in Example 1, except that CMC was added as a binder instead of PVA. The solid content of CMC was added to the entire paint to be 1.32 mass %.

[0106] <Example 5> The procedure was the same as in Example 1, except that HPC was added as a binder instead of PVA. The solid content of HPC was added to the entire paint at 0.68 mass %.

[0107] Example 6 The procedure was the same as in Example 1, except that HEC was added as a binder instead of PVA. The HEC solid content relative to the total paint was 0.83 mass %.

[0108] <Comparative Example 1> The same as Example 1 except that no binder was added. That is, Comparative Example 1 is not a paint but simply a dispersion.

[0109] [Tungsten oxide thin film] Tungsten oxide thin films (first electrochromic layers) according to the examples and comparative examples were prepared as follows.

[0110] <Example 1-A> A tungsten oxide thin film according to Example 1-A was produced on an ITO-coated glass substrate consisting of glass (first insulating layer) covered with ITO (first transparent electrode layer) using the paint of Example 1. A spin coating method was used to form the tungsten oxide thin film.

[0111] First, the paint of Example 1 was filtered before use to adjust the viscosity to approximately 15 mPa·s. 2 ml of the paint was measured out with a micropipette and dropped onto a 100 mm square ITO-coated glass substrate placed on a spin coater. The substrate was then spun at 400 rpm for 10 seconds, followed by 800 rpm for 10 seconds to form a thin film. The thin film was then air-dried to obtain Example 1-A. The tungsten oxide thin film of Example 1-A had a thickness of approximately 1000 nm.

[0112] <Example 1-B> A tungsten oxide thin film according to Example 1-B was formed on an ITO-coated polyethylene terephthalate (PET) substrate consisting of polyethylene terephthalate (first insulating layer) coated with ITO (first transparent electrode layer) using the paint according to Example 1. A spin coating method was used to form the tungsten oxide thin film.

[0113] First, the paint of Example 1 was filtered before use to adjust the viscosity to approximately 15 mPa·s. 500 μl was measured using a micropipette and dropped onto a 50 mm square ITO-coated PET substrate placed on a spin coater. The substrate was spun at 400 rpm for 10 seconds, then at 800 rpm for 10 seconds to form a thin film. The thin film was then air-dried to obtain Example 1-B. The tungsten oxide thin film of Example 1-B had a thickness of approximately 1000 nm.

[0114] <Example 1-C> Example 1-C was the same as Example 1-B, except that the tungsten oxide thin film of Example 1-C was formed on an ITO-coated polycarbonate substrate made of polycarbonate (first insulating layer) coated with ITO (first transparent electrode layer). The thickness of the tungsten oxide thin film of Example 1-C was approximately 1000 nm.

[0115] <Example 1-D> Example 1-D was the same as Example 1-B, except that the tungsten oxide thin film of Example 1-D was formed on an ITO-coated polyethylene naphthalate (PEN) substrate consisting of polyethylene naphthalate (first insulating layer) coated with ITO (first transparent electrode layer). The thickness of the tungsten oxide thin film of Example 1-D was approximately 1000 nm.

[0116] <Example 2-A> A tungsten oxide thin film according to Example 2-A was formed on the same ITO-coated glass substrate as used in Example 1-A using the paint according to Example 2. A spin coating method was used to form the tungsten oxide thin film.

[0117] First, the paint of Example 2 was filtered before use to adjust the viscosity to approximately 15 mPa·s. 500 μl was measured using a micropipette and dropped onto a 50 mm square ITO-coated glass substrate placed on a spin coater. The substrate was spun at 400 rpm for 10 seconds, then at 800 rpm for 10 seconds to form a thin film. The thin film was then air-dried to obtain Example 2-A. The tungsten oxide thin film of Example 2-A had a thickness of approximately 1000 nm.

[0118] <Example 3-A> Example 2-A was the same as Example 2-A except that the paint according to Example 3 was used. The thickness of the tungsten oxide thin film according to Example 3-A was approximately 1000 nm.

[0119] <Example 4-A> A tungsten oxide thin film according to Example 4-A was formed on the same ITO-coated glass substrate as used in Example 1-A using the paint according to Example 4. A spin coating method was used to form the tungsten oxide thin film.

[0120] First, the paint of Example 4 was filtered before use to adjust the viscosity to approximately 15 mPa·s. 400 μl was measured using a micropipette and dropped onto a 50 mm square ITO-coated glass substrate placed on a spin coater. The substrate was rotated at 350 rpm for 5 minutes, and then at 1000 rpm for 5 seconds to form a thin film. The thin film was then allowed to dry naturally, yielding Example 4-A. The tungsten oxide thin film of Example 4-A had a thickness of approximately 1000 nm.

[0121] <Example 5-A> A tungsten oxide thin film according to Example 5-A was formed on the same ITO-coated glass substrate as used in Example 1-A using the paint according to Example 5. A spin coating method was used to form the tungsten oxide thin film.

[0122] First, the paint of Example 5 was filtered before use to adjust the viscosity to approximately 15 mPa·s. 400 μl was measured using a micropipette and dropped onto a 50 mm square ITO-coated glass substrate placed on a spin coater. The substrate was rotated at 250 rpm for 5 minutes, and then at 1000 rpm for 5 seconds to form a thin film. The thin film was then allowed to dry naturally, yielding Example 5-A. The tungsten oxide thin film of Example 5-A had a thickness of approximately 1000 nm.

[0123] <Example 6-A> Example 5-A was the same as Example 5-A except that the paint according to Example 6 was used. The thickness of the tungsten oxide thin film according to Example 6-A was about 1000 nm.

[0124] <Comparative example 1-A> Example 2-A was the same as Example 2-A except that the dispersion liquid according to Comparative Example 1 was used instead of the paint. The thickness of the tungsten oxide thin film according to Comparative Example 1-A was approximately 1000 nm.

[0125] <Evaluation of physical properties of tungsten oxide thin films> Figure 4 shows field emission scanning electron microscope photographs of Examples 1-A, 2-A, and 3-A and Comparative Example 1-A. As shown in Figure 4, Comparative Example 1-A, which does not contain a binder, exhibits poor adhesion to the ITO-coated glass substrate, and film peeling and large cracks are observed. In contrast, Examples 1-A, 2-A, and 3-A, which contain PVA, exhibit good adhesion, and neither film peeling nor large cracks are observed.

[0126] The electrochromic properties of Examples 1-A, 2-A, 3-A, and Comparative Example 1-A were evaluated by cyclic voltammetry. Specifically, a platinum wire was used as the counter electrode, a saturated silver / silver chloride electrode as the reference electrode, and a 1.5 mol / kg potassium bis(trifluoromethanesulfonyl)imide (KTFSI)-propylene carbonate solution was used as the electrolyte. Cyclic voltammograms were obtained at a scan rate of 5 mV / s. Figure 5 shows the cyclic voltammograms for Examples 1-A, 2-A, 3-A, and Comparative Example 1-A.

[0127] As shown in FIG. 5, it was found that Examples 1-A, 2-A, and 3-A exhibited a better oxidation-reduction reaction than Comparative Example 1-A.

[0128] Furthermore, for Examples 1-A, 2-A, and 3-A and Comparative Example 1-A, chronocoulometry was performed to obtain the visible light transmission spectra at the end potentials of -1.2 V (reduced state) and +1.0 V (oxidized state). Figure 6 shows the visible light transmission spectra of Examples 1-A, 2-A, and 3-A and Comparative Example 1-A.

[0129] As shown in Figure 6, the coating is colorless and transparent in the oxidized state at +1.0 V, and dark blue in the reduced state at -1.2 V. However, as the amount of PVA added increases, the amount of tungsten nanoparticles (WO3) decreases relatively, resulting in a poor redox reaction. Therefore, to achieve higher contrast, the amount of PVA added is preferably 0.1 to 1.0 mass% of the total coating material.

[0130] Furthermore, the electrochromic properties of Examples 4-A, 5-A, and 6-A were evaluated. Specifically, a platinum wire was used as the counter electrode, a saturated silver / silver chloride electrode as the reference electrode, and a 1.5 mol / kg potassium bis(trifluoromethanesulfonyl)imide (KTFSI)-propylene carbonate solution was used as the electrolyte. Cyclic voltammograms were obtained at a scan rate of 5 mV / s. Figure 7 shows the cyclic voltammograms for Examples 4-A, 5-A, and 6-A. As shown in Figure 7, it was found that the tungsten oxide thin films exhibited good redox reactions regardless of the binder used.

[0131] [Metal Cyano Complex Thin Film] As described below, a paint of metal cyano complex nanoparticles (Preparation Example 1) was prepared, and iron-iron cyano complex thin films (second electrochromic layer) according to Preparation Examples 1-A to 1-D were produced.

[0132] <Iron-iron cyano complex nanoparticles (Prussian blue)> First, 14.5 g of sodium ferrocyanide decahydrate was dissolved in 60 mL of water, and 30 mL of 16.2 g of iron nitrate nonahydrate was mixed and stirred for 5 minutes. The resulting blue iron-iron cyanide complex nanoparticles, Prussian blue, were centrifuged, washed three times with water, then once with methanol, and dried under reduced pressure to obtain iron-iron cyanide complex nanoparticles. The yield was 11.0 g, and the yield was Fe[Fe(CN)6] 0.75The purity was 97.4% as 3.75H2O. When the precipitate of the prepared iron-iron cyano complex nanoparticles AFe1 was analyzed using a powder X-ray diffractometer, the diffraction information matched that of Prussian blue, Fe4[Fe(CN)6]3, searched from a standard sample database. When measured using a transmission electron microscope, the iron-iron cyano complex nanoparticles were found to be an aggregate of nanoparticles (primary particles) with diameters of 5 to 25 nm.

[0133] <Adjustment example 1> Next, 0.40 g of the iron-iron cyano complex nanoparticles were suspended in 8 mL of water, and then 80 mg of sodium ferrocyanide decahydrate was added. Upon stirring, the solution turned into a blue, transparent solution. In this way, a paint containing iron-iron cyano complex nanoparticles according to Preparation Example 1 was obtained.

[0134] <Adjustment example 1-A> Using the paint of Preparation Example 1, an iron-iron cyano complex nanoparticle thin film of Preparation Example 1-A was produced by spin coating on an ITO-coated glass substrate. Specifically, a 50 mm square ITO-coated glass substrate was placed on a spin coater, and 500 μL of a mixture of the paint of Preparation Example 1 adjusted to 9% by mass and 10% by mass of PVA as a binder was dropped onto it. The substrate was rotated at 400 rpm for 10 seconds, and then at 900 rpm for 10 seconds to produce Preparation Example 1-A on the ITO-coated glass substrate. The film thickness of the iron-iron cyano complex nanoparticle thin film of Preparation Example 1-A was approximately 1000 nm.

[0135] <Adjustment example 1-B> ITO coating instead of ITO coated glass substrate Polyethylene terephthalate The same as Preparation Example 1-A except that a (PET) substrate was used. The thickness of the iron-iron cyano complex nanoparticle thin film in Preparation Example 1-B was about 1000 nm.

[0136] <Adjustment example 1-C> Instead of ITO coated glass substrate, ITO coated Membrane Po The other factors were the same as in Preparation Example 1-A, except that a recarbonate substrate was used. The thickness of the iron-iron cyano complex nanoparticle thin film in Preparation Example 1-C was approximately 1000 nm.

[0137] <Adjustment example 1-D> ITO coating instead of ITO coated glass substrate Polyethylene naphthalate The same as Preparation Example 1-A except that a (PEN) substrate was used. The film thickness of the iron-iron cyano complex nanoparticle thin film in Preparation Example 1-D was about 1000 nm.

[0138] [ECD] ECDs 1-4 according to the examples were fabricated by combining a tungsten oxide thin film (first electrochromic layer) and a metal cyano complex thin film (second electrochromic layer), and each of the fabricated ECDs was evaluated.

[0139] <ecd1> A tungsten oxide / iron-iron cyano complex nanoparticle ECD was prepared as ECD1, which was dark blue and colorless and transparent. Specifically, ECD1 was prepared by sandwiching an electrolyte layer between an ITO-coated glass substrate on which the tungsten oxide thin film of Example 1-A had been formed and an ITO-coated glass substrate on which the iron-iron cyano complex nanoparticle thin film of Preparation Example 1-A had been formed. The electrolyte layer was prepared by adding 30 parts by weight of methyl methacrylate polymer to 100 parts by weight of propylene carbonate to a 1.5 mol / kg potassium bis(trifluoromethanesulfonyl)imide (KTFSI)-propylene carbonate solution, and heating the solution at 60 to 80°C for approximately 24 hours to increase the viscosity. The potential of ECD1 was determined with the working electrode on the tungsten oxide thin film side.

[0140] Figure 8 shows the cyclic voltammogram of ECD1 measured at a scan rate of 5 mV / sec. As shown in Figure 8, ECD1 exhibits good redox reaction.

[0141] Figure 9 shows the results of acquiring the visible light transmission spectrum of ECD1. As shown in Figure 9, ECD1 exhibited a deep colored state when a voltage of -0.8 V was applied, and returned to a colorless and transparent state when a voltage of +1.2 V was applied. Figure 10 shows a photograph of the color change of ECD1.

[0142] Figure 11 shows the total light transmittance spectrum of ECD1. This measurement was performed using a ±1.5V dry cell battery. As shown in Figure 11, ECD1 is capable of switching transmittance over a wide wavelength range, including not only the visible light region but also the near-infrared region. Furthermore, the visible light transmittance and solar transmittance were calculated from the obtained measurement data using JIS R 3106:1998 (ISO 9050:2003). The visible light transmittance was 71.71% in the transparent state and 7.73% in the tinted state. The solar transmittance was 55.13% in the transparent state and 6.12% in the tinted state. These results demonstrate that this glass has effective performance as a light-control glass.

[0143] <ecd2> ECD2 was the same as ECD1, except that an ITO-coated PET substrate on which a tungsten oxide thin film according to Example 1-B was formed and an ITO-coated PET substrate on which an iron-iron cyano complex nanoparticle thin film according to Preparation Example 1-B was formed were used. ECD2 was set to a potential with the working electrode on the tungsten oxide thin film side.

[0144] Photographs of the changes in ECD2 are shown in Figure 12. ECD2 exhibited a deep colored state when a voltage of -0.8 V was applied, and returned to a colorless and transparent state when a voltage of +1.2 V was applied.

[0145] Figure 13 shows the total light transmittance spectrum of ECD2. This measurement was performed using a ±1.5V dry cell battery. As shown in Figure 13, ECD2 is capable of switching the transmittance over a wide wavelength range, from the visible light region to the near-infrared region. Furthermore, the visible light transmittance and solar transmittance were calculated from the obtained measurement data using JIS R 3106:1998 (ISO 9050:2003). The visible light transmittance was 78.98% in the transparent state and 1.64% in the colored state. The solar transmittance was 55.81% in the transparent state and 2.86% in the colored state. These results demonstrate that this film has effective performance as a light-control film.

[0146] <ecd3> ECD3 was the same as ECD1, except that it used an ITO-coated polycarbonate substrate with a tungsten oxide thin film formed thereon according to Example 1-C and an ITO-coated polycarbonate substrate with an iron-iron cyano complex nanoparticle thin film formed thereon according to Preparation Example 1-C. ECD3 was set to a potential with the working electrode on the tungsten oxide thin film side.

[0147] Figure 14 shows the total light transmittance spectrum of ECD3. This measurement was performed using a ±1.5V dry cell battery. As shown in Figure 14, ECD3 is capable of switching transmittance over a wide wavelength range, from the visible light region to the near-infrared region. Furthermore, the visible light transmittance and solar transmittance were calculated from the obtained measurement data using JIS R 3106:1998 (ISO 9050:2003). The visible light transmittance was 72.63% in the transparent state and 6.75% in the tinted state. The solar transmittance was 67.49% in the transparent state and 4.80% in the tinted state. These results demonstrate that this film has effective performance as a light-control film.

[0148] <ecd4> ECD4 was the same as ECD1, except that an ITO-coated PEN substrate on which a tungsten oxide thin film according to Example 1-D was formed and an ITO-coated PEN substrate on which an iron-iron cyano complex nanoparticle thin film according to Preparation Example 1-D was formed were used. ECD4 was set to a potential with the working electrode on the tungsten oxide thin film side.

[0149] Figure 15 shows the total light transmittance spectrum of ECD4. This measurement was performed using a ±1.5V dry cell battery. As shown in Figure 15, ECD4 is capable of switching transmittance over a wide wavelength range, including not only the visible light region but also the near-infrared region. Furthermore, the visible light transmittance and solar radiation transmittance were calculated from the obtained measurement data using JIS R 3106:1998 (ISO 9050:2003). The visible light transmittance was 67.90% in the transparent state and 4.47% in the tinted state. The solar radiation transmittance was 47.81% in the transparent state and 3.19% in the tinted state. These results demonstrate that the film has effective performance as a light-control film.

[0150] In the following description, an experiment was conducted to examine the relationship between the pH of the paint according to the present invention and the physical properties of the paint.

[0151] Example 7 Tungsten oxide nanoparticles 1 (powder sample) were suspended in water to a total amount of 0.10% by mass, and then PVA was added as a binder to reduce surface tension to a total amount of 0.01% by mass and stirred to obtain a paint. Similarly, a paint was obtained so that the total amount of tungsten oxide nanoparticles 1 was 1% by mass and the total amount of PVA was 0.1% by mass. Similarly, a paint was obtained so that the total amount of tungsten oxide nanoparticles 1 was 10% by mass and the total amount of PVA was 1% by mass. Similarly, a paint was obtained so that the total amount of tungsten oxide nanoparticles 1 was 20% by mass and the total amount of PVA was 2% by mass. Here, the case where the total amount of tungsten oxide nanoparticles 1 is 0% by mass refers to pure water produced from Milli-Q (registered trademark).

[0152] Fig. 16 is a graph showing the relationship between the amount (mass%) of tungsten oxide nanoparticles 1 added and the pH of the paint for Example 7. As shown in Fig. 16, the pH of the paint decreases relatively depending on the amount of tungsten oxide nanoparticles 1 added. Specifically, the pH was 4.83 when 0.10 mass% was added, the pH was 4.11 when 1 mass% was added, the pH was 3.15 when 10 mass% was added, and the pH was 2.87 when 20 mass% was added.

[0153] Example 8 The solid content of tungsten oxide nanoparticles 1 was adjusted to 0.1 mass% of the total paint, and PVA was added as a binder to 0.01 mass% of 20 mL of paint. The pH was then adjusted with HCl or NaOH to obtain paints with a pH of 2 to 7.

[0154] Table 1 shows the types of pH adjusters used in Example 8, the amounts added, and the pH after adjustment.

[0155] [Table 1]

[0156] As described above in Example 7, the pH decreased relatively depending on the amount of tungsten oxide nanoparticles added. Specifically, when the amount of tungsten oxide nanoparticles added was 0.1 mass%, the pH was approximately 4.83. As can be seen from Table 1, the pH of the paint can be adjusted using a pH adjuster. Specifically, the pH of the paint could be adjusted as desired by adding an acidic solvent (HCl) or a basic solvent (NaOH) to the paint.

[0157] Example 9 The solid content of tungsten oxide nanoparticles 1 was adjusted to 7.9 mass % or 20 mass % of the total paint, and 0.79 mass % or 2 mass % of PVA was added as a binder to 20 mL of paint, and the pH was adjusted with 0.1 M NaOH to prepare the paint of Example 9.

[0158] Figure 17 is a graph showing the relationship between the amount of 0.1 M NaOH added and the pH of the paint for Example 9. As in Figure 16, the higher the concentration of tungsten oxide nanoparticles, the more acidic the pH became. It was possible to adjust the pH by adjusting the amount of NaOH added for each concentration of tungsten oxide nanoparticles.

[0159] Example 10 Tungsten oxide thin films were prepared using 20 mL of a paint containing 20% ​​by weight of tungsten oxide nanoparticles 1 as a solids content and 2% by weight of PVA as a binder. The pH was adjusted by adding 0.1 M NaOH to the paint. Multiple tungsten oxide thin films were prepared using different amounts of 0.1 M NaOH added (i.e., pH). 400 μl of the paint was measured out with a micropipette and dropped onto a 50 mm square ITO-coated glass substrate mounted on a spin coater. The substrate was then spun at 500 rpm for 10 seconds, followed by 1000 rpm for 10 seconds to form a thin film. The thin film was then air-dried to obtain the tungsten oxide thin film of Example 10. It was confirmed that the thickness of the tungsten oxide thin film of Example 10 was affected by the pH of the paint. Specifically, the mean particle size was approximately 0.57 nm at pH 3 (1 ml of 0.1 M NaOH was added to 20 ml of paint), approximately 0.43 nm at pH 4 (3 ml of 0.1 M NaOH was added to 20 ml of paint), approximately 0.34 nm at pH 5 (6 ml of 0.1 M NaOH was added to 20 ml of paint), and approximately 0.33 nm at pH 6 (10 ml of 0.1 M NaOH was added to 20 ml of paint).

[0160] Figure 18 shows the change in the visible light transmission spectrum of the tungsten oxide thin film of Example 10. In Figure 18, the dashed line indicated by (1) represents the change in the visible light transmission spectrum in the initial state, the solid line indicated by (2) represents the change in the visible light transmission spectrum when the initial state is changed to a colored state, and the dashed line indicated by (3) represents the change in the visible light transmission spectrum when the colored state is changed back to a transparent state.

[0161] As shown in Figure 18, the tungsten oxide thin films were not negatively affected by the pH adjuster and exhibited a redox reaction. Over a 60-second period, the thin films exhibited a deep colored state when a voltage of 1.0 V was applied, and transitioned to a transparent state when a voltage of -1.2 V was applied. On the other hand, at pH 3, the thin films did not completely return to their original colorless and transparent state after 60 seconds, suggesting that a pH of around 5 provides an excellent contrast between the colored and transparent states.

[0162] ECDs with tungsten oxide thin films were fabricated using pH-adjusted paints using the same procedure as ECD1. Substrates were also compared using soda glass and PET film, and transparent electrode materials were ITO, FTO (fluorine-doped tin), and TCO (transparent conductive oxide).

[0163] <ecd5> ECD5 is an electrochromic device (using a glass substrate) equipped with a tungsten oxide thin film prepared from a pH 2.2 paint (adjusted so that the solid content of tungsten oxide nanoparticles 1 relative to the total paint was 13.9% by weight and the amount of PVA added was 0.7% by weight). A cycle test was conducted on ECD5 under the measurement conditions shown in Table 2 to examine the change in transmittance at 550 nm and 700 nm. As shown in Table 2, a cycle of alternating application of a voltage of -1.2 V (30 seconds) and a voltage of +1.0 V (30 seconds) was repeated 1,000 times (continuous measurement: approximately 16.6 hours). The results of the cycle test are shown in Figure 19.

[0164] [Table 2]

[0165] As shown in Figure 19, the high-durability TCO and FTO exhibited stable cycle durability, but rapid degradation was observed with ITO. This is thought to be due to the acidic tungsten oxide thin film attacking the ITO, causing it to corrode. The transparent electrode materials, high-durability TCO and FTO, have better chemical resistance and corrosion resistance than ITO, and are highly stable, resulting in good durability.

[0166] <ecd6> ECD6 is an electrochromic device (using a glass substrate) equipped with a tungsten oxide thin film fabricated from a pH 5.0 paint (5 mL of 0.1 M NaOH was added to 20 mL of paint adjusted to a solid content of 14.0 mass% tungsten oxide nanoparticles 1 and a PVA content of 0.7 wt% relative to the total paint). A cycle test was also conducted on ECD6 under the measurement conditions in Table 2 to examine the change in transmittance at 550 nm and 700 nm. The results of the cycle test are shown in Figure 20. As shown in Figure 20, the highly durable TCO and FTO exhibit stable cycle durability, while ITO exhibits gradual degradation. However, ECD6 exhibits higher durability than ECD5 for ITO. As can be seen from the above explanation, durability can be improved by adjusting the pH of the paint.

[0167] Figure 21 shows the changes in visible light transmission spectrum when the withstand voltage characteristics of ECD5 and ECD6 were measured under the conditions in Table 3. Here, after completing CV measurements at each applied voltage (high potential ⇒ low potential ⇒ final potential), the multi-potential step (MPS) method was used to raise and lower the voltage in 0.5 V increments, applying a negative potential to induce a coloring reaction, and then applying a positive potential to induce a bleaching reaction, and the device color (discoloration of the transparent conductive film and the color change state of the photochromic film) was monitored.

[0168] [Table 3]

[0169] As shown in Figure 21, when ITO was used, rapid degradation was observed with ECD5 (pH 2.2), especially at high voltages, and while degradation was also observed with ECD6 (pH 5.0), it was suppressed to some extent. In this way, adjusting the pH of the paint can also improve voltage resistance characteristics. Furthermore, when comparing transparent electrode materials, the highly durable TCO and FTO did not show much degradation even at high voltages, suggesting their superiority over ITO.

[0170] <ecd7> Electrochromic devices (using a PET substrate) equipped with tungsten oxide thin films prepared from pH-adjusted paints were subjected to cycle testing under the conditions shown in Table 2 to examine the change in transmittance at 550 nm and 700 nm. Tungsten oxide thin films were prepared using paints adjusted to pH 2.4 and pH 4.9 by adding 0.1 M NaOH to a paint prepared so that the solid content of tungsten oxide nanoparticles 1 and the PVA content were 15 wt% and 0.7 wt%, respectively. The results of the cycle testing are shown in Figure 22. As shown in Figure 22, even when the substrate was changed from a glass substrate to a PET substrate, the electrochromic device using a tungsten oxide thin film prepared from a pH 2.4 paint deteriorated rapidly, whereas the electrochromic device using a tungsten oxide thin film prepared from a pH 4.9 paint exhibited high durability. As can be seen from the above explanation, adjusting the pH of the paint is an effective method for improving durability.

[0171] As can be seen from the above explanation, the ECD of the present invention exhibits a large range of transmittance change. Since the larger the range of transmittance change, the higher the contrast, the ECD of the present invention can realize an electrochromic element that performs high-contrast coloring and bleaching without using an organic electrochromic material. This element is expected to be used in light-control glass and film, displays, indicators, and the like. Because it also has the ability to control long-wavelength components, it is also expected to be used as an energy-saving light-control component that can optimize the inflow of infrared rays, which are the heat component of solar energy, into automotive window glass and building window glass.

[0172] Although the embodiments of the present invention have been described above, the present invention is not necessarily limited to these, and a person skilled in the art will be able to find various alternative embodiments without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0173] 100:ECD 10: First electrochromic layer 20: Second electrochromic layer 30: Electrolyte layer 40: First transparent electrode layer 50: Second transparent electrode layer 60: First insulating layer 70: Second insulating layer

Claims

1. A coating material for forming a tungsten oxide thin film having electrochromic properties, a solvent, tungsten oxide nanoparticles dispersed in the solvent, and a binder; The tungsten oxide nanoparticles are When subjected to X-ray diffraction analysis (2θ), the half-value width of the peak detected at 29°±1° is 0.9° or less, The primary particle size is 5 to 25 nm, characterized in that the pH is 3 to 7 Tungsten oxide paint for electrochromic elements.

2. The content of the tungsten oxide nanoparticles is 5% by mass or more and 30% by mass or less relative to the paint mass. The tungsten oxide paint for electrochromic devices according to claim 1.

3. the binder is one or more selected from polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), and hydroxyethyl cellulose (HEC); The content of the binder is 0.1% by mass or more and 10% by mass or less relative to the paint mass. The tungsten oxide paint for electrochromic devices according to claim 1.

4. Contains pH adjuster The tungsten oxide paint for electrochromic devices according to claim 1.

5. The pH adjuster is one or more selected from potassium chloride (KCl), sodium chloride (NaCl), lithium chloride (LiCl), potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH). The tungsten oxide paint for electrochromic devices according to claim 4.

6. pH is 5 to 7 The tungsten oxide paint for electrochromic devices according to claim 4.

7. It is characterized by being able to form a tungsten oxide thin film by coating method. The tungsten oxide paint for electrochromic devices according to claim 1.

8. The tungsten oxide paint for electrochromic devices according to claim 1 is used. Tungsten oxide thin film.

9. Contains pH adjuster The tungsten oxide thin film according to claim 8.

10. The electrochromic reaction occurs in an electrolyte containing one or more (trifluoromethanesulfonyl)imide salts selected from the group consisting of bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide. The tungsten oxide thin film according to claim 8.

11. The tungsten oxide thin film according to claim 8; a metal cyano complex thin film containing metal cyano complex nanoparticles or an oxide thin film containing oxide nanoparticles, which undergoes coloring and decoloring due to an oxidation-reduction reaction opposite to that of tungsten oxide; The present invention is characterized in that it comprises an electrolyte layer positioned between the tungsten oxide thin film and the metal cyano complex thin film or the oxide thin film. Dimming component.

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