Tungsten oxide material, tungsten oxide powder set for electrochromic element, and slurry for electrochromic element production

Abstract

The present invention aims to improve the speed of the reversible reaction of electrochromism, making possible the high-efficiency production of electrochromic elements. According to the embodiments, a potassium-containing tungsten oxide material (1) is provided. The tungsten oxide material has a particle shape with a central portion (2) and a surrounding portion (3) adjacent to the central portion, and an average particle diameter of 100 nm or less. The periodicity of the crystal is different between the central portion and the surrounding portion. Furthermore, a tungsten oxide powder set for electrochromic elements containing 80 mass% or more and 100 mass% or less of the tungsten oxide material is provided. In addition, a slurry for the production of electrochromic elements containing the above-described tungsten oxide material is provided.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to tungsten oxide material, tungsten oxide powder set for electrochromic element, and slurry for electrochromic element production. BACKGROUND

[0002] An electrochromic element is an element that utilizes a reversible change in optical properties when an electric charge is applied to a substance. Electrochromic elements are used for displays and light control systems by utilizing changes in optical properties. As light control systems, light control glass, light control glasses, anti-glare mirrors, and the like can be cited. Furthermore, light control systems have been used in various fields such as vehicles, aircraft, buildings, and the like.

[0003] As a material for an electrochromic element, a tungsten oxide powder can be cited. The reversible reaction when an electric charge is applied to a material exhibiting electrochromic properties is a redox reaction in which electrons are taken in and out. Therefore, as a means to improve the speed of reversible reaction, attempts have been made to impart hopping conduction characteristics to the electrochromic element material.

[0004] Furthermore, in order to improve the initial performance of the electrochromic element, attempts have been made to contain an alkali metal salt in a coating solution used for forming an electrochromic layer containing tungsten oxide and molybdenum oxide. Specifically, the purpose is to add alkali metal ions to the electrochromic oxide layer from the initial state in advance, to form an electrochromic element that immediately functions after production.

[0005] Furthermore, attempts have been made to suppress the deterioration of the initial properties at the time of repeated color development / color fading operation by using an electrochromic substance layer in which lithium tungstate, sodium tungstate, potassium tungstate, and the like are added to the tungsten oxide as a color former of the electrochromic element. That is, the purpose of this means is to obtain a long-life electrochromic element in which the substance exhibiting electrochromic properties has been improved.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: International Publication No. 2016 / 039157

[0009] Patent Literature 2: Japanese Patent Application Laid-Open No. H9-512112

[0010] Patent Literature 3: Japanese Patent Application Laid-Open No. H3-43716 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] An object of the embodiments is to provide a tungsten oxide material that can increase the speed of reversible reaction when used as a material for an electrochromic element, and that can be efficiently manufactured when manufacturing an electrochromic element, an electrochromic element tungsten oxide powder set, and a slurry for manufacturing an electrochromic element.

[0013] Means for solving the problem

[0014] According to the embodiments, a potassium-containing tungsten oxide material can be provided. The tungsten oxide material has a particle shape including a central portion and a surrounding portion adjacent to the central portion, and an average particle diameter of 100 nm or less. The periodicity of the crystal is different between the central portion and the surrounding portion. Further, an electrochromic element tungsten oxide powder set containing 80 mass% or more and 100 mass% or less of the tungsten oxide material can be provided. In addition, a slurry for manufacturing an electrochromic element containing the above-described tungsten oxide material can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a cross-sectional view schematically showing an example of a tungsten oxide powder particle to which the embodiments relate.

[0016] Figure 2 is a cross-sectional view schematically showing another example of a tungsten oxide powder particle to which the embodiments relate.

[0017] Figure 3 is a cross-sectional view schematically showing the periodicity of a crystal within a tungsten oxide powder particle to which the embodiments relate.

[0018] Figure 4 is Figure 3 is an enlarged cross-sectional view of the E portion of

[0019] Figure 5 is an enlarged view schematically showing the molecular structure in the M portion of Figure 4

[0020] Figure 6 is a diagram showing the concept of a method for measuring the angle of repose of a tungsten oxide powder to which the embodiments relate. DETAILED DESCRIPTION

[0021] The tungsten oxide material to which the embodiments relate contains a tungsten oxide powder containing particles having an average particle diameter of 100 nm or less. The powder contains potassium, and the periodicity of the crystal is different between the surrounding portion and the central portion when the powder is analyzed using a scanning transmission electron microscope (STEM).

[0022] ​The tungsten oxide material according to the embodiment exhibits electrochromic properties, that is, a reversible change in optical properties is observed when an electric charge is applied to the material. Therefore, the tungsten oxide material can be used as an electrochromic element, for example, as an electrochromic element. That is, the tungsten oxide material according to the embodiment can function as a tungsten oxide material for an electrochromic element. Hereinafter, the tungsten oxide material is sometimes referred to as a tungsten oxide powder for an electrochromic element, or simply as a tungsten oxide powder. In addition, the tungsten oxide material is sometimes described as K-WO3 because it contains potassium (K) in the powder particles of tungsten oxide (WO3).

[0023] The tungsten oxide material can improve the response speed of color change when used in an electrochromic element. The tungsten oxide material can further improve the response speed compared to when the hopping conduction characteristics are imparted by having the above-described configuration.

[0024] Figure 1 and Figure 2 Examples of powder particles of the tungsten oxide material according to the embodiment are shown in FIGS. 1 to 4. Figure 1 and Figure 2 Cross sections of one particle contained in the powder-like tungsten oxide material are shown schematically in FIGS. 1 to 4. The tungsten oxide powder particle 1 shown in the figures includes a central portion 2 and a peripheral portion 3 that are different in periodicity from each other. The peripheral portion 3 is adjacent to the central portion 2. Figure 1 An example in which the width of the peripheral portion 3 is uniform around the entire cross section is shown in FIG. 1. Figure 2 An example in which the width of the peripheral portion 3 is different depending on the site is shown in FIG. 2. The width of the peripheral portion 3 can be uniform or non-uniform. That is, the peripheral portion 3 can exist as a layer having a uniform thickness on the central portion 2 as a core, or can exist as a layer having a non-uniform thickness on the central portion 2 as a core. In the example shown in the figures, the central portion 2 has a rectangular cross section, but the shape of the central portion 2 is not limited to the example shown in the figures, and can have a square and a trapezoidal cross-sectional shape, for example, and a cross-sectional shape similar to these shapes.

[0025] In any of FIGS. 1 to 4, Figure 1 and Figure 2 An example in which the peripheral portion 3 covers the entire periphery of the central portion 2 is shown in any of FIGS. 1 to 4. It is preferable that the peripheral portion 3 exist on 80% or more and 100% or less of the outer periphery of the central portion 2.

[0026] The average particle diameter of the powder particles of the tungsten oxide material is 100 nm or less. The average particle diameter referred to herein is the average primary particle diameter of the tungsten oxide powder, i.e., the average primary particle diameter. The average particle diameter can be calculated as follows. A sample of the tungsten oxide powder is observed by FE-SEM (Field Emission Scanning Electron Microscope), and a magnified photograph is taken. The longest diagonal line of the K-WO3 powder as represented in the magnified photograph is taken as the particle diameter of the powder particles. The average of the particle diameters of 100 powder particles arbitrarily extracted is taken as the average particle diameter. Further, the magnification of the FE-SEM photograph is set to 50,000x or more.

[0027] Specifically, the FE-SEM image is used. The particle diameters of 100 primary particles clearly visible in the FE-SEM image are measured, and the average thereof is taken as the average particle diameter. In a case where the primary particles cannot be confirmed only by the secondary particles, the primary particles formed by pulverizing the secondary particles can also be measured. Further, the average particle diameter based on the FE-SEM observation can also be measured for a film containing the tungsten oxide powder, such as an electrochromic layer contained in an electrochromic element, and the like, for a part containing the powder in a device using the tungsten oxide powder. For example, the cross section of such a film is subjected to FE-SEM observation, a magnified photograph of the cross section is taken, and the average particle diameter is calculated using the obtained FE-SEM image as described above.

[0028] If the average particle diameter of the tungsten oxide powder exceeds 100 nm, the surface area cannot be obtained. Therefore, the average particle diameter is preferably 100 nm or less. Further, the lower limit of the average particle diameter is not particularly limited, but is preferably 5 nm or more. If a powder material having an average particle diameter of 5 nm or more is used, the workability at the time of manufacturing the electrochromic element becomes good. Therefore, an average particle diameter of 5 nm or more and 100 nm or less is preferred, and an average particle diameter of 10 nm or more and 50 nm or less is more preferred.

[0029] The tungsten oxide powder contains potassium (K). The potassium can be present as metallic potassium or a potassium compound. As the potassium compound, oxides (including composite oxides) and the like can be given. By containing potassium, the conductivity of the tungsten oxide powder can be improved.

[0030] In the tungsten oxide material, the potassium is not mixed with the WO3 powder only in the form of independent powder particles of metallic potassium and potassium compounds, but is contained in each of the powder particles contained in the tungsten oxide powder. Therefore, in the electrochromic element using the K-WO3 powder, the distribution of the potassium in the electrochromic layer is uniform.

[0031] Further, the periodicity of the WO3 crystal differs between the center portion and the peripheral portion when the tungsten oxide powder is subjected to STEM analysis (Scanning Transmission Electron Microscopy analysis). The STEM analysis employs a HAADF-STEM image. HAADF-STEM is High Angle Annular Dark Field-Scanning Transmission Electron Microscopy. Hereinafter, the HAADF-STEM image is also sometimes referred to simply as a STEM image. Further, when the STEM measurement is performed, a thin film sample of the tungsten oxide powder is produced by a microtome using a dispersion method. Further, the acceleration voltage of the STEM is set to 200 kV, and the measurement is performed at a magnification of 10000000 times.

[0032] The periodicity of the crystal differs between the center portion and the peripheral portion means that there are regions in the powder particle in which the interatomic distance differs. Figure 3 and Figure 4 A schematic cross-sectional view showing the concept of the periodicity of the crystal is shown in FIG. 1. Further, Figure 4 is Figure 3 an enlarged cross-sectional view of the E portion shown in FIG. 1. The tungsten oxide material has a crystal structure in which a plurality of phases that are parallel to each other in a direction intersecting the direction from the inside of the tungsten oxide powder particle 1 toward the surface are arranged in order in the direction toward the surface of the particle. In the tungsten oxide powder particle 1, the interatomic distance I c between adjacent phases among the plurality of phases in the center portion 2 differs from the interatomic distance I p between adjacent phases among the plurality of phases in the peripheral portion 3. If the periodicity of the crystal is the same throughout the particle, the interatomic distance is constant. Further, the interatomic distance being constant means that the deviation of the interatomic distance in the enlarged photograph based on the STEM is 1 (angstrom) or less. The deviation of the interatomic distance is the deviation from the average value of any five interatomic distances.

[0033] The plurality of phases can each be a phase having a layered structure. The interatomic distance is found based on the crystal structure in which these phases are arranged in parallel. Details are described with reference to Figure 5 . Figure 5 is an enlarged view of the M portion shown in FIG. 1, and is a diagram schematically showing the molecular structure in this portion. Figure 4 schematically shows the molecular structure in the peripheral portion 3 of the tungsten oxide powder particle 1. Figure 5

[0034] In each of the plurality of phases that are parallel to each other and arranged in order in the direction 23 from the center toward the surface of the tungsten oxide powder particle 1, for example, as shown in Figure 5 ​As shown, the first crystal phase 7 in which tungsten atoms 4 and oxygen atoms 5 are arranged side by side to form a layered structure, and the second crystal phase 8 in which potassium atoms 6, tungsten atoms 4 and oxygen atoms 5 are arranged side by side to form a layered structure, can be included. These first crystal phase 7 and second crystal phase 8 can cross the direction 23 toward the surface of the powder particle. Further, the first crystal phase 7 and second crystal phase 8 can be alternately arranged along the direction 23 toward the surface. The interatomic distance indicates the interval of the first crystal phase 7 in which tungsten atoms 4 and oxygen atoms 5 are arranged side by side to each other. For example, the second crystal phase 8 in which potassium atoms 6, tungsten atoms 4 and oxygen atoms 5 are arranged side by side to each other can not be considered. That is, the interval at which the layers of tungsten atoms 4 and oxygen atoms 5 are arranged in order in the direction 23 from the center of the powder particle toward the surface can be regarded as the interatomic distance, and the STEM analysis can be performed. That is, the periodicity of the crystal as referred to herein can be said to indicate the periodicity of the first crystal phase which corresponds to the crystal of WO3 not containing potassium. Further, the direction 23 from the inside of the powder particle toward the surface can cross the interface between the center portion 2 and the surrounding portion 3.

[0035] Figure 5 The molecular structure of the surrounding portion 3 of the tungsten oxide powder particle 1 is shown, but the interatomic distance I p corresponding to the interval between the first crystal phase 7 in which tungsten atoms 4 and oxygen atoms 5 are connected in the surrounding portion 3 in the direction 23 toward the surface c . That is, the interval between the mutually parallel crystal phases in which tungsten atoms and oxygen atoms are connected in the center portion 2 can be regarded as the interatomic distance I c .

[0036] By making the periodicity of the crystal different between the center portion and the surrounding portion, the conductivity of the tungsten oxide powder can be improved. The improvement in the conductivity means the reduction in the resistance value. Thus, when the tungsten oxide material is used for an electrochromic element, the response speed of the color change can be improved.

[0037] Further, the ratio I p / I c of the interatomic distance I p in the surrounding portion to the interatomic distance I c in the center portion is preferably in the range of 1.1 or more and 3 or less. If the ratio I p / I c of the interatomic distance in the center portion to the interatomic distance in the surrounding portion is 1.1 or more, the periodicity of the crystal is significantly different between the respective regions, and thus the above-described effects can be exerted. On the other hand, if the ratio I p / I c of the interatomic distance in the center portion to the interatomic distance in the surrounding portion is 3 or less, the regularity of the crystal in the surrounding portion is easily maintained. Thus, the interatomic distance I pInteratomic distance I from the center c The ratio between I p / I c Preferably, it is in the range of 1.1 or higher and 3 or lower, more preferably in the range of 1.5 or higher and 2.5 or lower.

[0038] Preferred interatomic distance I at the center c exist (E) and above and Within the following range. If the interatomic distance at the center is I c Within the aforementioned range, because the interatomic distance is of a suitable size, it is easy to control the interatomic distance I with the surrounding parts. p The ratio of I p / I c Furthermore, if the interatomic distance at the center is I... c Staying at This makes it easier to maintain the regularity of the crystal structure in the central part. Furthermore, a suitable interatomic distance I in the surrounding area is preferred. p exist The above and Within the following range.

[0039] Furthermore, the amount of potassium present is preferably greater in the periphery than in the center. By having a greater amount of potassium in the periphery, the interatomic distance of the crystals in the periphery can be increased. This, in turn, improves the conductivity of the tungsten oxide powder. As described above, if the conductivity increases, the resistance decreases, thus improving the response speed of color changes in the electrochromic element. The tungsten oxide material according to the embodiments may contain powder particles that contain no potassium in the center but only in the periphery.

[0040] The proportion of potassium present can be determined by energy-dispersive X-ray spectrometry (EDX). EDX analysis allows for the color distribution mapping of potassium in tungsten oxide powder. The measurement conditions involve setting the accelerating voltage to 15.0 kV and performing surface analysis at a magnification of over 1000 times. The proportion is determined from the atomic ratio of K (potassium) to W (tungsten) obtained by the ZAF method.

[0041] The ZAF method combines three correction methods: atomic number correction (Z), absorption correction (A), and fluorescence correction (F). Atomic number correction (Z) corrects the ratio of incoming electrons to scattered electrons when they irradiate the sample. Absorption correction (A) corrects the amount of characteristic X-rays absorbed until they exit the sample. Fluorescence (excitation) correction (F) corrects the intensity of fluorescent X-rays excited by X-rays generated in the sample. This is a common correction method for EDX.

[0042] Further, the peripheral portion preferably has a maximum width of 1.5 nm or more and 5 nm or less. If the maximum width of the peripheral portion is 1.5 nm or more, the proportion of the existence of the peripheral portion 3 is sufficient, and the above-described effects can be obtained. Further, if the maximum width of the peripheral portion is 5 nm or less, the proportion of the existence of the peripheral portion 3 can be moderate. Further, the interatomic distance I p is 1.5 nm or more and 5 nm or less. The maximum width of the peripheral portion is preferably 1.5 nm or more and 5 nm or less in the above-described range.

[0043] The width of the peripheral portion substantially coincides with the region in which potassium exists more. That is, in the tungsten oxide material according to the embodiment, the periodicity of the crystal is changed by the existence of potassium in the peripheral portion. By the existence of potassium in the peripheral portion, the conductivity of the tungsten oxide powder can be improved. Further, the change in color in the electrochromic element is a reversible reaction caused by the entry and exit of electrons. By the existence of the peripheral portion at a prescribed proportion, the entry and exit of electrons in the peripheral portion is facilitated. That is, by the entry and exit of electrons on the surface of the powder particle, the speed of the reversible reaction can be accelerated. Therefore, the maximum width of the peripheral portion is preferably in the range of 1.5 nm or more and 5 nm or less, and more preferably in the range of 2 nm or more and 4 nm or less. Further, the peripheral portion can be thinner than this at a place other than the maximum width.

[0044] The tungsten oxide powder in which the maximum width of the peripheral portion is in the range of 2 nm or more and 4 nm or less has a tendency to be preferred in the range in which the flowability is easily achieved according to the layer formation described later. As described later, the flowability of the tungsten oxide powder can be evaluated based on the angle of repose.

[0045] The method of calculating the maximum width of the peripheral portion is described below. First, the interface between the central portion and the peripheral portion in the tungsten oxide powder particle is confirmed in the STEM image showing the cross section of the tungsten oxide powder particle. The interface is regarded as the outer periphery of the central portion, and a line perpendicular to the tangent line with respect to the outer periphery of the central portion is drawn from the outer periphery of the central portion to the surface of the powder particle. The length of the line thus drawn straight outward from the central portion is regarded as the width of the peripheral portion at this point, and the longest width among these widths is regarded as the maximum width of the peripheral portion. For example, in the tungsten oxide powder particle 1 of the example shown in FIG. 1, Figure 3 and Figure 4 in the example shown in FIG. 1, Figure 4 the width W MAX corresponds to the maximum width of the peripheral portion 3. Further, the STEM image of the primary particle of the tungsten oxide powder particle 1 is measured.

[0046] Further, the proportion of the peripheral portion existing on the outer periphery of the central portion can be determined by STEM analysis. In the STEM image showing the cross section of the tungsten oxide powder particle, in the portion where the central portion and the peripheral portion are contiguous, the interface thereof is regarded as the outer periphery of the central portion, and in the portion where the outer side of the central portion and the peripheral portion are not contiguous, the surface of the particle is regarded as the outer periphery of the central portion. The proportion of the portion where the contiguous peripheral portion exists in the total outer periphery of the central portion where these outer peripheries are added is confirmed.

[0047] The content of potassium in the tungsten oxide powder is preferably in the range of 1 mol% or more and 50 mol% or less. The content of potassium in the tungsten oxide powder herein refers to the amount of potassium contained in the tungsten oxide powder. That is, it refers to the total amount of potassium contained in the central portion and the peripheral portion. If the content of potassium in the tungsten oxide powder is 1 mol% or more, the above-described effects obtained by containing potassium can be sufficiently exerted. Further, by making the content of potassium 50 mol% or less, good cost performance can be achieved. This is because even if potassium is contained in an amount exceeding 50 mol%, the effects of more than 50 mol% cannot be obtained. Therefore, the content of potassium contained in the tungsten oxide powder is preferably in the range of 1 mol% or more and 50 mol% or less, and more preferably in the range of 5 mol% or more and 35 mol% or less.

[0048] The content of potassium in the tungsten oxide powder can be analyzed by Inductively Coupled Plasma (ICP) emission spectroscopy. ICP emission spectroscopy is a method of measuring the wavelength of light when a sample is gasified into an atomic state by applying energy to the sample. Since light corresponding to the atoms of the sample is emitted, analysis can be performed in units of elements. Further, since the object of measurement is gasified, the content of the entire sample can be measured. In ICP emission spectroscopy, first, the sample is dissolved into a liquid with an acid and a base, and then introduced into an argon plasma. The concentration of K (potassium) and W (tungsten) is measured by measuring the excitation emission light of the sample with a detector. The measured concentration of K is converted into the amount of potassium atoms of the element, and the concentration of W is converted into the amount of WO3 molecules. These values obtained by converting the concentrations of K and W into potassium and WO3, respectively, are used to calculate the content of potassium by regarding the tungsten oxide powder as a K-WO3 powder containing K and WO3.

[0049] Further, when the amount of potassium is measured by X-Ray Photoelectron Spectroscopy (XPS) analysis of the above-described tungsten oxide powder, the content of potassium K XPS sought by XPS is preferably 1.05 or more. ICP The ratio K XPS / K ICP is preferably 1.05 or more.

[0050] XPS analysis is a method of irradiating a soft X-ray to a sample and measuring photoelectrons released with ionization of the sample. It is an effective analysis method for measuring elements present in the vicinity of several nm deep from the surface of the sample. As described above, ICP analysis is an effective method for quantifying the amount of the element present in the whole of the sample. In contrast, XPS analysis is an effective method for quantifying the amount of the element present in the vicinity of the surface of the sample.

[0051] The ratio K of the amount of potassium obtained by XPS analysis to the amount of potassium obtained by ICP analysis XPS / K ICP is 1.05 or more, indicating that the amount of potassium present in the vicinity of the surface in the powder particles of the tungsten oxide powder is large. In other words, the ratio K of the amounts of potassium based on these analysis methods XPS / K ICP is less than 1.05, indicating that the amount of potassium present on the surface of the particles is small. This indicates that the amount of potassium in the surrounding portion is small. Controlling the amount of potassium present is effective in controlling the above-mentioned interatomic distance.

[0052] Further, the upper limit of the ratio K of the potassium content XPS / K ICP is preferably 5 or less. By keeping this ratio at 5 or less, it is easy to accommodate the ratio of the interatomic distances of the central portion and the surrounding portion within a prescribed range.

[0053] Further, as the measurement conditions for XPS analysis, it is prescribed that the X-ray source is a single-crystal spectrometer Al Kα ray, the X-ray power is 50.0 W, the analysis area is φ 200 μm, and the angle between the surface of the sample and the detector is 45°.

[0054] With the tungsten oxide powder for an electrochromic element as described above, the conductivity is improved. Since the conductivity is high, the resistance value can be reduced by the tungsten oxide powder. Further, by providing the surrounding portion in the tungsten oxide powder, the entry and exit of electrons can be performed mainly in the surrounding portion. Thus, the speed of the entry and exit of electrons is improved.

[0055] Specifically, the conductivity of the tungsten oxide powder can be 1 x 10 -5 / Ωcm or more and 3 x 10 -3 / Ωcm or less. The conductivity referred to here is the conductivity based on the 4-terminal method. The conductivity of the potassium-free tungsten oxide powder (WO3) is less than 1 x 10 -5 / Ωcm. As described above, by containing potassium, the conductivity can be improved. Further, by keeping the conductivity at 1 x 10 -3 / Ωcm, the response reaction of an erroneous color change due to unintentional charge movement, which can occur due to the conductivity being excessively improved, can be prevented. Thus, the conductivity of the tungsten oxide powder is preferably 1 x 10 -5 / Ωcm or more and 3 x 10-3 in the range of 5 x 10 -5 in the range of 1 x 10 -3 in the range of 1 x 10

[0056] Further, the measurement method of the electrical conductivity can be measured as described below. In a φ 20 mm cylindrical cell, 1 g to 3 g of the sample powder is filled. As the measurement method, a 4-terminal method is adopted, and 4 terminals are arranged at an interval of 3 mm in the straight line direction. By an oil pressure jack, a pressure of 4 N (Newton), 8 N, 12 N, 16 N, or 20 N is applied to the sample, and in this state, the volume resistivity is measured, and the lowest value of the volume resistivity is taken as the volume resistivity of the material. The reciprocal of the obtained volume resistivity is calculated, and converted into the electrical conductivity.

[0057] In measuring the repose angle of the tungsten oxide powder, the repose angle is preferably in the range of 30° or more and 45° or less. The repose angle indicates the flowability of the powder. The smaller the repose angle, the better the flowability of the powder. If the flowability of the powder is good, the powder can be uniformly dispersed when a layer is formed using the powder. That is, an electrochromic layer in which the tungsten oxide powder is uniformly dispersed can be formed. By having a repose angle of 30° or more, the flowability is appropriately high, and the supply amount is stable. Further, if the repose angle is 45° or less, the flowability is good, and agglomeration that can occur when the flowability is low is less likely to occur.

[0058] For the measurement of the repose angle, a Scott Volumeter prescribed in Tungsten Molybdenum Industries Standard TMIAS0101 (Powder Property Test Method: 2010) is used. TMIAS0101 is an industry standard issued by Japan Tungsten & Molybdenum Industries Association.

[0059] Figure 6 A conceptual diagram showing a method of obtaining a repose angle is shown in FIG. 8. The repose angle is measured using a Scott Volumeter. A tungsten oxide powder sample 10 is poured into a hopper of the Scott Volumeter. The tungsten oxide powder sample 10 is poured into a measuring cup 9 provided directly below the hopper to form a cup until it overflows to the surroundings. The angle of the upper surface of the measuring cup 9 and the pile of the tungsten oxide powder sample 10 is measured, and taken as the repose angle AR. When the tungsten oxide powder sample 10 does not naturally fall into the measuring cup 9, the upper part of the metal mesh provided in the hopper is gently stirred with a brush to allow the powder to flow in.

[0060] When the above-described tungsten oxide material is used as a material for an electrochromic element, an electrochromic element tungsten oxide powder group containing 80% by mass or more and 100% by mass or less of the tungsten oxide material is preferably formed. By containing the tungsten oxide material having a peripheral portion according to the embodiment in a proportion of 80% by mass or more, the above-described improved electrical conductivity can be obtained. Therefore, an electrochromic element tungsten oxide powder group containing 80% by mass or more, further 90% by mass or more, of the electrochromic element tungsten oxide powder according to the embodiment is preferable. In other words, in the powder material for an electrochromic element, a tungsten oxide powder not having a peripheral portion can also be contained in an amount of 20% by mass or less. Alternatively, a compound powder other than a tungsten oxide powder exhibiting electrochromic properties, such as a molybdenum oxide powder, can also be contained in an amount of 20% by mass or less.

[0061] Further, a slurry containing the tungsten oxide material according to the embodiment can also be used as a slurry for manufacturing an electrochromic element. By specifying the slurry as a tungsten oxide material, an electrochromic layer can be formed by coating. For example, in a sputtering method, film formation over a large area is difficult. By specifying the slurry, coating over a large area becomes easy.

[0062] The slurry is a mixture of the electrochromic element tungsten oxide powder according to the embodiment and a solvent. As the solvent, water, an organic substance, or the like can be exemplified. Of the compound contained in the slurry that exhibits a color change with the application of an electric charge, i.e., a compound having electrochromic properties, 80% by mass or more and 100% by mass or less is preferably the tungsten oxide material according to the embodiment. For example, by mixing the above-described electrochromic element tungsten oxide powder group and a solvent, a slurry can be prepared.

[0063] Next, a manufacturing method of the tungsten oxide material according to the embodiment will be described. As long as the tungsten oxide material according to the embodiment has the above-described composition, the manufacturing method thereof is not limited, but as a method for obtaining a high yield, the following methods can be exemplified.

[0064] As the manufacturing method of the tungsten oxide material according to the embodiment, both a gas phase method and a liquid phase method can be exemplified. In either manufacturing method, first, a precursor of tungsten oxide and a precursor of potassium are prepared.

[0065] When the gas phase method is employed, the K-WO3 powder according to the embodiment can be produced, for example, as follows. The precursor of tungsten oxide and the precursor of potassium are mixed to obtain a mixture. The obtained mixture is subjected to a sublimation process to produce the tungsten oxide powder. Specifically, in the synthesis in a gas phase, the process of mixing the precursor of tungsten oxide and the precursor of potassium to obtain a mixture, sublimating the mixture, and cooling the sublimated gas to cause it to be desublimated is performed.

[0066] As precursors of tungsten oxide, for example, ammonium tungstate, WO3, WO2, and H2WO4 can be listed. Further, as a precursor of potassium, for example, K2WO4 can be listed. Since impurities are hardly mixed in when these compounds are used as precursors, these precursors are preferred.

[0067] As the mixing step, the respective precursors are mixed in a powder state or a slurry state in such a manner that the molar ratio of K and W reaches an amount corresponding to the target composition. In this mixing step, the ratio of K and W in the resulting K-WO3 is controlled by adjusting the mixing ratio of K and W.

[0068] Here, the width of the peripheral portion is controlled by adjusting the mixing ratio (molar ratio) of tungsten and potassium. For example, when the raw material mixing ratio of potassium to tungsten ([molar amount of K] / [molar amount of W]) in the raw materials, i.e., the respective precursors, is 0.01 or less, it is difficult to obtain a peripheral portion having a maximum width in the above-mentioned preferred range. Further, if the mixing ratio (molar ratio) is set to 0.5 or more, not only the maximum width of the peripheral portion is greater than the preferred range, but also K2WO4 is generated, so it is preferred that the mixing ratio (molar ratio) of potassium to tungsten in the mixture of the precursors is less than 0.5.

[0069] The mixed powder or slurry is introduced into a plasma flame with argon (Ar), nitrogen (N), or oxygen (O) as a carrier gas to sublimate it. For example, the mixture of the precursors is heated to 10,000°C or more in the plasma flame to sublimate it. By quenching the sublimated gas to room temperature in an oxygen atmosphere, a mixed oxide of potassium and tungsten is obtained. By controlling the speed of introducing the sample into the plasma, the particle diameter of the resulting powder particles can be controlled. For example, by introducing the sample at 100 g / min or less, the average particle diameter can be made to be 100 nm or less.

[0070] When the liquid phase method is employed, for example, the K-WO3 powder according to the embodiment is produced as follows. In the synthesis in a liquid phase, the processes of dissolving a precursor of tungsten oxide with a base, dissolving a precursor of potassium in water, mixing these two solutions, precipitating a powder, and recovering it by filtering and drying the resulting powder are performed.

[0071] Here, as a precursor of tungsten oxide, for example, ammonium tungstate, WO3, WO2, or H2WO4 can be used. The precursor of tungsten oxide is dispersed in water and dissolved by adjusting the pH to the range of 9 to 11 with ammonia or KOH.

[0072] Next, as a precursor of potassium, for example, K2WO4 (potassium tungstate) or KOH (potassium hydroxide) can be used. Here, both K2WO4 and KOH are dissolved by mixing with water.

[0073] The aqueous solution of the tungsten oxide precursor and the aqueous solution of the potassium precursor are mixed in the desired amounts. When KOH is used to dissolve the tungsten oxide precursor, the W amount and the K amount are mixed so as to reach the desired amounts including the K amount of the KOH used for the dissolution. Here, the W amount and the K amount are noted. In the above-described vapor phase method, the K added by the raw material (the potassium precursor) is all precipitated as a solid at the time of sublimation, so the mixing ratio of the respective precursors can be adjusted depending on the desired ratio of W and K in the K-W03. In the liquid phase synthesis, even if the powder is precipitated, a portion of the K and W remains in the mixed solution, and K remains in the liquid more than W. Therefore, the K amount is mixed in a larger amount than the amount corresponding to the desired ratio.

[0074] Next, as described above, the pH of the solution obtained by dissolving the raw material (the respective precursors) with the aqueous alkali solution is adjusted to a range of pH 5 to 7 with a hydrochloric acid (HC1) solution, so that the K-W03 powder is precipitated. Instead of the hydrochloric acid, a sulfuric acid (H2S04) solution or a nitric acid (HNO3) solution can be used. Here, by adjusting the HC1 concentration (mass ratio) of the HC1 solution (for example, an aqueous HC1 solution) at the time of neutralization (adjustment to pH 5 to 7), the width of the surrounding portion can be controlled. By precipitating it in an HC1 solution having a concentration of 30 mass% or less, a core of W03 is first formed, and a surface layer containing K is formed on the surface thereof. That is, a surface layer having a large amount of K as the surrounding portion can be formed on the surface of the core having a small amount of K as the central portion. If it is precipitated in a solution having a concentration exceeding 30 mass%, W and K are precipitated at the same time, and a core of W03 as the central portion cannot be formed. Therefore, the surrounding portion and the central portion, which differ in periodicity of the crystal, cannot be formed. The HC1 concentration of the HC1 solution used in the neutralization process is preferably 5 mass% or more and 30 mass% or less.

[0075] The precipitate in powder form obtained by the neutralization is filtered and dried, whereby the powder is recovered. The drying temperature is set to a range of 200°C or more and 400°C or less. If heating is performed at a temperature exceeding 400°C, the particle size increases. At a drying temperature lower than 200°C,

[0076] The tungsten oxide material according to the embodiment is a tungsten oxide powder containing potassium and containing particles having an average particle diameter of 100 nm or less. When the powder is analyzed by STEM, the periodicity of the crystal differs between the surrounding portion and the central portion. In this tungsten oxide material, the speed of the reversible reaction when used as a material for an electrochromic element is improved. Furthermore, an electrochromic element using this tungsten oxide material can be efficiently manufactured.

[0077] [Example]

[0078] (Examples 1-7, Comparative Examples 1-3)

[0079] By the above-described production method, potassium-containing tungsten oxide powder was produced. In Examples 1, 2, 4, 6, and 7, and Comparative Examples 1 and 3, the precipitation step was performed in the gas phase. However, in Comparative Example 1, the precipitation step in the gas phase was performed using only a precursor of tungsten oxide. Further, in Examples 3 and 5, and Comparative Examples 2 and 4, the precipitation step was performed in the liquid phase.

[0080] In detail, in Examples 1, 2, 4, 6, and 7, and Comparative Examples 1 and 3, the powder-like tungsten oxide material was produced by the above-described gas phase method under the following conditions. As the precursors, powders of WO3and K2WO3were prepared. These precursor powders were mixed in the mixing amounts shown in Table 1 to prepare samples. The prepared samples were transported into an oxygen plasma together with a mixed gas of N2:Ar = 1:1 at the feeding rates shown in Table 1. The samples that passed through the plasma were discharged into a recovery machine under conditions of an atmospheric atmosphere, an atmospheric pressure, and room temperature, and the powder produced by solidification was recovered therein.

[0081] Table 1

[0082]

[0083] In Examples 3 and 5, and Comparative Examples 2 and 4, the powder-like tungsten oxide material was produced by precipitation in the liquid phase under the following conditions. As the precursors, K2WO4and H2WO4were prepared. These precursors were dissolved in an alkaline aqueous solution in the mixing amounts shown in Table 2. The alkaline aqueous solution was set to a range of pH 9 to 11. In the aqueous solution containing the dissolved precursors, an aqueous hydrochloric acid solution (HCl aqueous solution) was added in the concentration shown in Table 2, and the alkalinity was neutralized. The neutralized aqueous solution was set to a range of pH 5 to 7. The precipitate that was precipitated was recovered by filtration and dried to obtain a powder.

[0084] Table 2

[0085]

[0086] The tungsten oxide powder obtained in each of the examples and comparative examples was investigated for the average particle diameter of the particles contained in the powder, the presence or absence of the central portion and the peripheral portion in which the periodicity of the crystal was different, the potassium content (ICP analysis and XPS analysis), the interatomic distance (central portion and peripheral portion), and the width of the peripheral portion, using the above-described method. The results are shown in Tables 3 and 4 below. Specifically, in Table 3, the average particle diameter of the powder particles, the potassium content obtained by ICP analysis and XPS analysis, respectively, and the ratio K XPS / K ICP In Table 4, the interatomic distance in the central portion and the peripheral portion of the powder particles, the interatomic distance in the peripheral portion (I p) relative to the interatomic distance (I c ) of the center portion p / I c ) and the maximum width of the surrounding portion. Further, in Comparative Examples 1 and 4, as shown in Table 3, the center portion and the surrounding portion in which the periodicity of the crystal was different were not confirmed. Therefore, in these Comparative Examples, for the sake of convenience, the values of the interatomic distance of all the particles were described in Table 4 for both the center portion and the surrounding portion. Further, in these Comparative Examples, since there was no surrounding portion, the width thereof was zero.

[0087] Table 3

[0088]

[0089] Table 4

[0090]

[0091] As shown in Table 3, in the tungsten oxide powders relating to Examples 1 to 7, the surrounding portion in which the periodicity of the crystal was different from the center portion was formed. Further, in these Examples, the values of the ratio K XPS / K ICP of the potassium content obtained by the various analysis methods were 1.05 or more. Therefore, it was found that the potassium was contained in a large amount in the surface of the tungsten oxide powder.

[0092] Next, the electric conductivities of the tungsten oxide powders relating to each of the Examples and Comparative Examples were measured. The measurement of the electric conductivity was performed by the 4-terminal method as described above. Further, the repose angles of the respective powders were measured by the method as described above. The results thereof are shown in the following Table 5.

[0093] Table 5

[0094]

[0095] As shown in Table 5, the tungsten oxide powders relating to Examples 1 to 7 showed good electric conductivities. Further, the repose angles were in the range of 30° or more and 45° or less. It was found that the electric conductivity and the flowability were improved in the tungsten oxide powders relating to Examples 1 to 7.

[0096] On the contrary, in Comparative Example 1, the electric conductivity was low since the potassium was not contained. Further, in Comparative Example 2 and Comparative Example 3, the flowability was poor since the average particle diameter of the powder particles exceeded 100 nm. In Comparative Example 2, it was also considered that since the particle diameter was extremely large, the inter-particle voids were easily generated in the content of the powder, and the electric conductivity was reduced. In the tungsten oxide powder relating to Comparative Example 4, the center portion and the surrounding portion in which the periodicity of the crystal was different were not obtained in the particles of the material containing the potassium, and thus the electric conductivity was low.

[0097] (Examples 8 to 11)

[0098] In addition, potassium-containing tungsten oxide powder was produced. In Example 11, powder of tungsten oxide was produced by the same vapor phase method as in Example 1, except that the mixed amount of WO3and K2WO3powders as precursors and the feeding speed at the time of delivery into the oxygen plasma were changed as shown in Table 6. Furthermore, in Examples 8 to 10, powder of tungsten oxide was produced by the same liquid phase method as in Example 3, except that the mixed amount of K2WO4and H2WO4as precursors and the concentration of aqueous hydrochloric acid (HCl aqueous solution) were changed as shown in Table 7.

[0099] Table 6

[0100]

[0101] Table 7

[0102]

[0103] The tungsten oxide powder obtained in Examples 8 to 11 was investigated for the average particle diameter of the particles contained in the powder, the presence or absence of the center portion and the peripheral portion in which the periodicity of the crystal was different, the potassium content (ICP analysis and XPS analysis), the interatomic distance (center portion and peripheral portion), and the width of the peripheral portion, by the methods described above. The results are shown in Tables 8 and 9 below. The contents of Tables 8 and 9 relating to Examples 8 to 11 correspond to the contents of Tables 3 and 4 relating to Examples 1 to 7 and Comparative Examples 1 to 4.

[0104] Table 8

[0105]

[0106] Table 9

[0107]

[0108] As shown in Table 8, in the tungsten oxide powder relating to Examples 8 to 11, the peripheral portion in which the periodicity of the crystal was different from the center portion was also formed.

[0109] Next, the electric conductivity and the rest angle of the tungsten oxide powder relating to Examples 8 to 11 were measured. The measurement was performed by the same method as in the powder relating to Examples 1 to 7. The results are shown in Table 10 below.

[0110] Table 10

[0111]

[0112] As shown in Table 10, the tungsten oxide powder relating to Examples 8 to 11 showed a good electric conductivity to the same extent as the tungsten oxide powder relating to Examples 1 to 7, and a value of the rest angle was obtained to approximately the same extent.

[0113] According to one or more of the above-described embodiments and examples, a tungsten oxide material containing potassium and a tungsten oxide powder set for an electrochromic element and a slurry for manufacturing an electrochromic element can be provided. The tungsten oxide material has a particle shape with an average particle diameter of 100 nm or less. The particle of the tungsten oxide material includes a central portion and a peripheral portion adjacent to the central portion, and the periodicity of the crystal is different between the central portion and the peripheral portion. By using these tungsten oxide materials, the tungsten oxide powder set for an electrochromic element, and the slurry for manufacturing an electrochromic element as a material for an electrochromic element, the speed of reversible reaction of the obtained electrochromic element can be increased. Further, by using these tungsten oxide powder set for an electrochromic element and the slurry for manufacturing an electrochromic element, an electrochromic element can be efficiently manufactured.

[0114] The embodiments of the present application have been described, but these embodiments are suggested as examples, and the intention is not to limit the scope of the application. These novel embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made within the scope of the gist of the application. These embodiments and modifications thereof are included in the scope and gist of the application, and are included in the range of the application and its equivalents described in the claims.

[0115] Symbol explanation

[0116] 1 - Tungsten oxide powder particle, 2 - Central portion, 3 - Peripheral portion, 4 - Tungsten atom, 5 - Oxygen atom, 6 - Potassium atom, 7 - First crystal phase, 8 - Second crystal phase, 9 - Measuring cup, 10 - Tungsten oxide powder sample.

Claims

1. A tungsten oxide material containing potassium, having a particle shape comprising a central portion and a peripheral portion adjacent to the central portion, with an average particle size of less than 100 nm, wherein the periodicity of the crystals differs between the central portion and the peripheral portion, the tungsten oxide material having a crystal structure in which multiple phases parallel to each other are sequentially arranged in a direction intersecting from the interior of the particle toward the surface, and the interatomic distance between the multiple phases adjacent to each other in the peripheral portion is I. p Relative to the interatomic distance I between the plurality of phases adjacent in the central portion c The ratio of I p / I c Within the range of 1.1 and 3.

2. The tungsten oxide material of claim 1, wherein, The content of potassium is in a range of 1 mol% or more and 50 mol% or less.

3. The tungsten oxide material of claim 1 or 2, wherein, The content K of the potassium as determined by X-ray photoelectron spectroscopy XPS The content K of the potassium as determined by inductively coupled plasma emission spectroscopy ICP The ratio K XPS / K ICP is 1.05 or more.

4. The tungsten oxide material of claim 1 or 2, wherein, The peripheral portion has a maximum width of 1.5 nm or more and 5 nm or less.

5. The tungsten oxide material of claim 1, wherein, The interatomic distance I c In The above and The following ranges.

6. A tungsten oxide powder group for an electrochromic element, comprising 80 mass% or more and 100 mass% or less of the tungsten oxide material according to any one of claims 1 to 5.

7. A slurry for manufacturing an electrochromic element, comprising the tungsten oxide material according to any one of claims 1 to 5.

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