Tungsten oxide powder slurry, method for producing the same, and method for producing electrochromic element using the same

Abstract

A tungsten oxide powder slurry characterized by being a tungsten oxide powder slurry obtained by mixing a tungsten oxide powder with an aqueous solvent, wherein the tungsten oxide powder in the slurry has a particle size cumulative curve in which D 50 is 20 nm or more and 10,000 nm or less, D 90 is 100,000 nm or less, and a half-value width of the strongest peak detected at 29° ± 1° when X-ray diffraction analysis (2θ) is performed is 2° or less.

Description

Technical Field

[0001] The embodiments described later relate to tungsten oxide powder slurry, a method for manufacturing the same, and a method for manufacturing an electrochromic element using the same. Background Technology

[0002] Tungsten oxide powder is used in various fields such as electrochromic materials, battery electrode materials, photocatalysts, and sensors. For example, International Publication No. 2018 / 199020 (Patent Document 1) discloses tungsten oxide powder with an average particle size of less than 50 nm. Patent Document 1 uses tungsten oxide powder with a specified value obtained by elliptic polarization spectroscopy. The tungsten oxide powder of Patent Document 1 shows improved photocatalytic performance. Furthermore, it shows improved response speed of electrochromic elements.

[0003] For example, an electrochromic element is a light-emitting element that switches between transparent and colored states by switching on and off charges. When using tungsten oxide powder as described in Patent Document 1 to form the electrochromic element, a problem of reduced transparency occurred. Upon investigation, it was found that there was a problem with the agglomeration of the tungsten oxide powder.

[0004] The electrode layer of the electrochromic element is formed using a coating process. The coating process uses a paste containing tungsten oxide powder. The paste is a substance obtained by mixing an organic binder in an aqueous solvent. The paste is prepared by mixing tungsten oxide powder with an aqueous dispersion to obtain a slurry. Organic substances such as binders are mixed into the slurry to form the paste.

[0005] For example, Japanese Patent No. 5641926 (Patent Document 2) discloses a method for controlling the particle size D of tungsten oxide powder. 50 D 90 The slurry is described in Patent Document 2 as a slurry made by mixing tungsten oxide powder with an aqueous solvent. However, even when using the slurry in Patent Document 2, problems with agglomeration arise.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2018 / 199020

[0009] Patent Document 2: Japanese Patent No. 5641926

[0010] Patent Document 3: International Publication No. 2020 / 196720 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Patent Document 2 describes a slurry that controls the particle size distribution of tungsten oxide powder. However, if the slurry, formed by mixing tungsten oxide powder with an aqueous solvent, is left to stand for an extended period, the tungsten oxide powder agglomerates. As a result, the particle size distribution of the tungsten oxide powder, which was previously found in an aqueous solvent, cannot be maintained.

[0013] This invention addresses such problems by providing a tungsten oxide powder slurry that can suppress agglomeration even after prolonged storage.

[0014] Methods for solving problems

[0015] The tungsten oxide powder slurry of the embodiment is characterized in that it is a tungsten oxide powder slurry prepared by mixing tungsten oxide powder with an aqueous solvent, and the particle size accumulation curve of the tungsten oxide powder in the slurry is shown in Figure D. 50 For wavelengths above 20nm and below 10000nm, D 90 The wavelength is below 100,000 nm, and the half-width of the strongest peak detected at 29°±1° during X-ray diffraction analysis (2θ) is below 2°. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating an example of the particle size distribution of the tungsten oxide powder slurry according to an embodiment.

[0017] Figure 2 This is a diagram showing an example of X-ray diffraction (2θ) of the tungsten oxide powder slurry of the embodiment.

[0018] Figure 3 This is a graph showing an example of the absorbance of the tungsten oxide powder slurry according to the embodiment.

[0019] Figure 4 This is a diagram showing an example of an electrochromic element. Detailed Implementation

[0020] The tungsten oxide powder slurry of the embodiment is characterized in that it is a tungsten oxide powder slurry prepared by mixing tungsten oxide powder with an aqueous solvent, and the particle size accumulation curve of the tungsten oxide powder in the slurry is shown in Figure D. 50 For wavelengths above 20nm and below 10000nm, D 90 The wavelength is below 100,000 nm, and the half-width of the strongest peak detected at 29°±1° during X-ray diffraction analysis (2θ) is below 2°.

[0021] Tungsten oxide powder is preferably WO3-compliant. 3-x, powders with 0 ≤ x < 0.3. The tungsten oxide powder has the property of showing intercalation. Intercalation is a reversible reaction in which electrons or ions enter and exit the nanoparticles of the metal compound. By actively carrying out the intercalation reaction, the performance as a semiconductor is improved. In addition, the movement of electrons generated by flowing an electric current or irradiating light becomes active. Therefore, the tungsten oxide powder becomes a material suitable for various fields such as photocatalysts, electrochromic elements, battery electrode materials, and sensors.

[0022] In addition, when used as a material for an electrochromic element or a photocatalyst material, the tungsten oxide powder is preferably WO3 with x = 0. In addition, when used as a battery electrode material or a sensor, the tungsten oxide powder is preferably WO 3-x , 0 < x < 0.3. WO3 with x = 0 means no oxygen deficiency. Without oxygen deficiency, it is less likely to agglomerate.

[0023] In addition, the aqueous dispersion is a liquid having water as a main component. The water is preferably pure water. If there are many impurities like tap water, it may affect the cohesiveness. The pure water is the pure water that meets A1 described in JIS-K-0557 (1998).

[0024] In the particle size cumulative curve graph of the tungsten oxide powder in the slurry, D 50 is 20 nm or more and 10,000 nm or less, and D 90 is 100,000 nm or less. Figure 1 shows an example of the particle size distribution of the tungsten oxide powder slurry of the embodiment. In the figure, the horizontal axis is the particle diameter (μm), the left vertical axis is the frequency (%), and the right vertical axis is the cumulative (%)). When using the values of the particle size cumulative curve graph, the vertical axis becomes the cumulative (%). When using the values of the particle size frequency curve graph, the vertical axis becomes the frequency (%). In addition, both the frequency (%) and the cumulative (%) are the number ratios. D 50 is the particle diameter at the stage of the number ratio of 50%. D 90 is the particle diameter at the number ratio of 90%.

[0025] Furthermore, particle size distribution was determined using dynamic light scattering. The sample used was a slurry containing tungsten oxide powder at a concentration of 0.01% to 0.1% by mass. If the tungsten oxide powder content in the slurry was more than 0.1% by mass, the sample was prepared by dilution. If the tungsten oxide powder content in the slurry was less than 0.01% by mass, the sample was prepared by removing water. The sample concentration was set to be 0.01% to 0.1% by mass to control agglomeration at low concentrations. This is because if agglomeration occurs at low concentrations, more agglomeration will occur at higher concentrations. The measurement was performed within one hour after dilution. The measurement time was set to 30 seconds. Three measurements were performed on the same sample, and the average value was used. It should be noted that the sample was thoroughly stirred after one hour of dilution, and the measurement was performed within one hour after stirring.

[0026] For the particle size distribution measurement apparatus using dynamic light scattering, a Microtrac NANOTRAC UPA-EX or equivalent apparatus was used. The measurement time for a single measurement was set to 30 seconds, and the average of three measurements was taken as the result. Furthermore, the refractive index of the tungsten oxide powder was set to 1.81, the particle shape to non-spherical, and the density to 7.3 g / cm³ as input values ​​to the measuring apparatus. 3 The ratio is calculated based on the volume distribution.

[0027] The particle size determined by dynamic light scattering is the size of a mixture of primary and secondary particles. A primary particle is a single powder. Secondary particles are powders aggregated together to form a single powder. Sometimes, aggregated particles are also called aggregated particles.

[0028] Regarding tungsten oxide powder slurry, D in the cumulative particle size curve of tungsten oxide powder in the slurry... 50 For wavelengths above 20nm and below 10000nm, D 90 The particle size is below 100,000 nm. Sometimes, the particle size cumulative curve (particle size cumulative curve) is simply referred to as the cumulative curve.

[0029] D of the cumulative curve 50 For those above 20nm and below 10000nm, D 90 A value below 100,000 nm indicates the absence of large condensed particles. If D... 50 Particle sizes below 20 nm (0.02 μm) may be too small, increasing manufacturing overhead. Furthermore, if D... 50 Large particles exceeding 10000 nm (10 μm) will form aggregated particles when the slurry is left to stand for a long time. Similarly, when D... 90When a paste exceeding 100,000 nm (100 μm) is left to stand for an extended period, it will form aggregated particles. For example, in the case of electrochromic elements, this results in switching between transparency and color. If large aggregated particles are present, it becomes difficult to increase light transmittance.

[0030] Therefore, the D of the cumulative curve 50 Preferably, the wavelength is 20nm or larger and 10000nm or smaller, and further down to 500nm or smaller. Furthermore, the cumulative curve D... 90 Preferably, the wavelength is below 100,000 nm, and further below 1,000 nm.

[0031] Furthermore, the present invention is characterized in that the half-width of the strongest peak detected at 29°±1° when X-ray diffraction analysis (2θ) is less than 2°.

[0032] Figure 2 An example of X-ray diffraction (2θ) of the tungsten oxide powder slurry of the embodiment is shown. In the figure, the vertical axis represents the X-ray diffraction intensity, and the horizontal axis represents the diffraction angle (2θ).

[0033] For the X-ray diffraction apparatus, Bruker D8 ADVANCE is used; for the detector, YNEYE-XE high-speed one-dimensional detector is used; and for the X-ray tube, KFL-Cu-2KDC or an equivalent X-ray tube is used.

[0034] The X-ray diffraction measurement method uses a Cu target, tube voltage of 40 kV, tube current of 40 mA, operating axis of 2θ / θ, scanning range (2θ) of 10°–60°, scanning speed of 0.1° / sec, and step size of 0.02°. Furthermore, the sample used is a slurry with a tungsten oxide powder concentration of 10% by mass or more and 40% by mass or less. It should be noted that a slurry with a tungsten oxide powder concentration of 30% by mass is recommended. If the tungsten oxide powder concentration varies, it can be adjusted by removing or adding an aqueous solvent. The sample is placed in a cell (container) with a depth of 1 mm. The height is adjusted so that the surface of the slurry placed in the cell becomes a reflecting surface. Setting the tungsten oxide powder concentration of the sample to 10% by mass or more and 40% by mass or less facilitates the measurement. Setting the surface of the slurry placed in the cell as a reflecting surface also facilitates the measurement.

[0035] Furthermore, the half-value width is determined using the strongest peak detected at 29°±1°. The half-value width is determined by setting the smaller value in the root portion of the peak as the reference value. The position from the reference value to the peak apex is set as the peak height. The peak width at half the peak height is set as the half-value width. It should be noted that the strongest peak detected at 29°±1° represents the peak with the largest peak intensity detected between 28° and 30°. Therefore, large peaks may also exist outside this range.

[0036] X-ray diffraction reveals the crystallinity of tungsten oxide powder. Good crystallinity yields sharp peaks with small half-widths (WWHMs). A WWHM of less than 2° for the strongest peak detected at 29° ± 1° during X-ray diffraction analysis (2θ) indicates suppressed crystal defects. Good crystallinity also prevents aggregation even after prolonged storage of the slurry. Crystal defects represent disordered crystalline arrangement, indicating that the regularity of the atomic arrangement in the crystal structure collapses beyond necessary limits. Introducing crystal defects creates defects at the lower end of the band gap, narrowing the apparent band gap. This results in absorption in the visible light domain and a reduction in transmittance.

[0037] The lower limit of the half-width is not particularly limited, but is preferably 0.1° or higher. A half-width below 0.1° indicates high crystallization repeatability. This means there are more primary particles larger than 20 nm. If the primary particle size increases, transmitted light scattering occurs, potentially reducing transmittance across the entire wavelength range. Consequently, the stability of the slurry also decreases due to the larger particle size. Furthermore, if the primary particle size is large, the aggregated particles become even larger. If the aggregated particles become larger, D... 50 There is a tendency for the peak to become excessively high. Therefore, the half-width of the strongest peak detected at 29°±1° during X-ray diffraction analysis (2θ) is preferably 0.1° or more and 2° or less.

[0038] By possessing particle size distribution and crystallinity as described above, it is possible to provide a slurry that can suppress agglomeration.

[0039] Furthermore, the particle size frequency curve of tungsten oxide powder is preferably in the range of D0 to D10. 90 A peak is considered a single peak within a given range. Sometimes, the particle size frequency curve is simply referred to as a frequency curve. A peak in a frequency curve is defined as an upward trend → peak (apex) → downward trend, and any peak whose apex has a convex shape exceeding 1% is counted as a peak. The frequency curve has D0 to D... 90 Within a certain range, there is only one peak representing an upward → peak → downward combination. This indicates that the grain size distribution is centered on the grain size at the peak (the apex). For example, if peaks exist in both small and large grain sizes, it is possible that the large grains are essentially aggregated particles. That is, it indicates that not only the D of the cumulative curve... 50 D90 Furthermore, the shape of the frequency curve is also important.

[0040] Furthermore, the content of tungsten oxide powder in the slurry is preferably in the range of 5% by mass or more and 50% by mass or less. When the amount of tungsten oxide powder is less than 5% by mass, the efficiency of the coating process may be reduced due to the low content. In addition, if the amount of tungsten oxide powder exceeds 50% by mass, the fluidity of the slurry may be reduced. The reduction in fluidity makes it easier to form agglomerated particles. Therefore, the content of tungsten oxide powder in the slurry is preferably in the range of 5% by mass or more and 50% by mass or less, and further, 10% by mass or more and 40% by mass or less.

[0041] In addition, the content of tungsten oxide powder in the slurry can be adjusted by the amount added when mixing with an aqueous solvent.

[0042] Furthermore, the method for determining the tungsten oxide powder content from the tungsten oxide powder slurry is as follows: First, the mass of the glass container is measured. The mass of the glass container is set as mass A. Next, 4g to 5g of slurry is added to the glass container. The mass of the glass container with the added slurry is measured. The mass of the glass container with the added slurry is set as mass B. Mass B is set as the value measured using a precision balance capable of measuring with an accuracy of 0.1mg. Next, the glass container with the added slurry is placed on a hot plate heated to 120°C. Drying is carried out until the liquid in the slurry is completely evaporated. The dried glass container is cooled to room temperature. Then, the mass of the dried glass container is measured. The mass of the dried glass container is set as mass C. The mass (%) of tungsten oxide powder in the slurry is calculated by [(mass C - mass A) / (mass B - mass A)] × 100%.

[0043] In addition, aqueous solvents may also contain alcohols. Aqueous solvents are liquids with water as their main component. Here, "with water as the main component" means that the solvent contains more than 50% by mass of water. When water is set as 100 parts by mass, it may also contain less than 50 parts by mass of alcohol.

[0044] Furthermore, the tungsten oxide powder slurry preferably contains one or more ingredients selected from ammonia, potassium hydroxide, and sodium hydroxide. Ammonia (NH3), potassium hydroxide (KOH), and sodium hydroxide (NaOH) have the effect of adjusting the pH of the slurry. They are water-soluble and suitable for pH adjustment. The pH is preferably 2 or higher, and more preferably 4 or higher. By adjusting the pH, the surface potential of the tungsten oxide powder can be increased. If the surface potential increases, the repulsive force between the powders becomes stronger. If the repulsive force becomes stronger, it becomes less likely to form aggregated particles. It should be noted that there is no particular upper limit to the pH, but it is preferred to be below 8. If the pH exceeds 8, it may be too alkaline, which may adversely affect the coating process.

[0045] Furthermore, if the pH of the tungsten oxide powder slurry exceeds 8, the tungsten oxide powder may dissolve. If the tungsten oxide powder dissolves, it may have an adverse effect on particle size and crystallinity.

[0046] Furthermore, when the aqueous solvent is removed, the average particle size of the tungsten oxide powder is preferably 20 nm or less. An average particle size of 20 nm or less after removing the aqueous solvent indicates a low number of aggregated particles. While there is no particular limitation on the lower limit of the average particle size after removing the aqueous solvent, it is preferably 5 nm or more. When the average particle size is less than 5 nm, the repeatability of the crystal structure decreases due to the small particle size. If the repeatability of the crystal structure decreases, good electrochromic properties may not be exhibited. Furthermore, if the particle size exceeds 20 nm, light scattering increases, potentially reducing transmittance. Moreover, as an electrochromic material, a large particle size increases the influence of the ion diffusion rate within the particles, potentially slowing down the color change rate.

[0047] The particle size in the tungsten oxide powder slurry appears different from that after removing the aqueous solvent. This is because the grain boundaries of the primary particles in the tungsten oxide powder are clearly visible after removing the aqueous solvent.

[0048] The method for determining the average particle size of tungsten oxide powder after removing aqueous solvents is as follows: A slurry is added to a glass container. The glass container with the slurry is placed on a hot plate heated to 120°C. The aqueous solvent is completely removed. The sample remaining in the glass container is removed and observed using TEM (scanning transmission electron microscopy). The TEM is set to a magnification of 1,000,000. The longest diagonal of the tungsten oxide powder in the TEM image is taken as the particle size. Since overlapping particles of tungsten oxide powder are aggregated particles, the outline of one powder is counted for the overlapping portions. This operation is performed on 20 particles, and their average value is taken as the average particle size.

[0049] Furthermore, the tungsten oxide powder may contain 0.01 mol% or more and 50 mol% or less of one or more of potassium (K), sodium (Na), lithium (Li), and magnesium (Mg). By including these elements in the tungsten oxide powder, the conductivity of the tungsten oxide powder can be increased. Moreover, these elements can be included without reducing crystallinity. For example, in fields where electricity is applied, such as in electrochromic elements, the color change reaction can be accelerated by increasing conductivity. When the content is less than 0.01 mol%, the effect is insufficient. Furthermore, if the content exceeds 50 mol%, the benefits of tungsten oxide cannot be utilized. Therefore, the content is preferably 0.01 mol% or more and 50 mol% or less, and further, 1 mol% or more and 20 mol% or less. Furthermore, when using tungsten oxide powder containing potassium, etc., it is sufficient that at least one portion of the tungsten oxide powder in the slurry contains potassium, etc. Alternatively, all of the tungsten oxide powder in the slurry may contain potassium, etc.

[0050] It should be noted that the potassium content does not include KOH or similar substances added for pH adjustment of the slurry. The potassium content in the tungsten oxide powder referred to here is essentially the content of potassium in the tungsten oxide powder particles. Furthermore, the potassium content can be, for example, 0.01% by mass or more and 50% by mass or less.

[0051] Furthermore, the absorbance of the slurry at a wavelength of 600 nm is preferably 1 or less. Additionally, the ratio of absorbance at 350 nm to absorbance at 600 nm is preferably 3 or more.

[0052] The absorbance was measured using the following method. First, a quartz cell with a 1 cm optical path was prepared. As a sample, a slurry containing 0.01% by mass of tungsten oxide powder was prepared. Additionally, as a reference, a sample consisting only of pure water was prepared. The sample and reference were set in the absorbance measuring apparatus. The measurement was set to be performed in 1 nm increments from 300 nm to 800 nm.

[0053] For the spectrophotometer device, it is set to use the Shimadzu UV-2700i or an equivalent device.

[0054] A paste with an absorbance of less than 1 at a wavelength of 600 nm indicates good visible light transmittance. Good visible light transmittance indicates high transparency. For example, it is sometimes used in window glass for electrochromic elements. In addition, it is sometimes coated on walls for photocatalysts. High transparency can reduce undesirable changes in appearance. Therefore, it can be considered a handy paste.

[0055] Furthermore, a absorbance ratio of 350nm to 600nm for the slurry is greater than 3, indicating that ultraviolet light is difficult to pass through while visible light can pass through easily. For example, when applied to window glass, this can create a coating film that is difficult for ultraviolet light to pass through but allows visible light to pass through easily.

[0056] Furthermore, there is no particular upper limit to the ratio of absorbance at wavelength 350 nm to absorbance at wavelength 600 nm, but it is preferably 25 or less.

[0057] When the absorbance at 350 nm / absorbance at 600 nm is less than 3, the large particle size may cause light scattering, resulting in reduced transmittance across the entire wavelength range. Alternatively, the particles may be excessively fragmented, introducing defects into the crystal structure. If the absorbance at 350 nm / absorbance at 600 nm exceeds 25, the particles become smaller than 5 nm, potentially reducing the color change rate as an electrochromic material. Therefore, the ratio of absorbance at 350 nm / absorbance at 600 nm is preferably 3 or more and 25 or less, and more than 3 or more and 15 or less.

[0058] The tungsten oxide powder slurry described above can suppress the formation of agglomerated particles. Furthermore, even after prolonged storage, the formation of agglomerated particles can be suppressed. The tungsten oxide powder slurry is a slurry formed by mixing tungsten oxide powder with an aqueous solvent. If left for a long time, the tungsten oxide powder in the slurry gradually settles. As a result, agglomerated particles of tungsten oxide powder are formed. The tungsten oxide powder slurry of the embodiment can suppress the formation of agglomerated particles even after being left for more than 24 hours.

[0059] Such tungsten oxide powder slurry can be applied to various fields such as electrochromic materials, battery electrode materials, photocatalyst materials, and sensor materials.

[0060] An electrochromic element is a device that causes a reversible change in photoelectric properties by applying an electric charge. This allows it to switch between a transparent state and a colored state.

[0061] In addition, photocatalysts are substances that decompose harmful substances (such as acetaldehyde) in gases by contacting the photocatalyst material with the gas (such as air).

[0062] In addition, electrode materials for batteries are substances used as electrode materials for Li-ion secondary batteries and capacitors.

[0063] Furthermore, gas sensors can be cited as examples of sensors. For instance, a sensor containing tungsten oxide powder can be placed in an atmosphere containing methane gas (CH4). The resistance value changes depending on the amount of methane gas adsorbed on the tungsten oxide powder. This property allows for the fabrication of a methane gas sensor.

[0064] To suit various applications, a coating film is formed. The coating film is applied using a paste. The paste is a substance obtained by mixing organic matter into a tungsten oxide powder slurry. Examples of organic matter include adhesives. Due to the inclusion of organic matter, the paste has higher viscosity compared to the slurry. The tungsten oxide powder slurry of the embodiment suppresses the formation of agglomerated particles; therefore, even when a paste using it is used, the formation of agglomerated particles can be suppressed. Furthermore, even when the tungsten oxide powder slurry is left for more than 24 hours, the formation of agglomerated particles can still be suppressed, making it a suitable slurry.

[0065] Furthermore, the tungsten oxide powder slurry is preferably a slurry used for manufacturing electrochromic elements. As described above, the tungsten oxide powder slurry exhibits excellent visible light transmittance. Therefore, a coating film with excellent visible light transmittance can be obtained. The electrochromic element can switch between transparent and colored states by switching on a charge. Electrochromic elements are used in displays and dimming systems. Examples of dimming systems include dimming glass, dimming glasses, and anti-glare glasses. In addition, dimming systems are used in various fields such as vehicles, aircraft, and buildings. For example, if used as dimming glass in building windows, it can switch the on / off state of sunlight incidence. Furthermore, it can suppress the transmission of ultraviolet rays. In other words, it can be said to be an electrochromic element suitable for controlling the on / off state of sunlight incidence.

[0066] Figure 4 An example of an electrochromic element is shown in the figure. In the figure, 1 is a glass substrate, 2 is a transparent electrode, 3 is an electrochromic layer, 4 is a counter electrode, 5 is an electrolyte, and 10 is a cell. Figure 4 This is a schematic diagram of the cell structure of the electrochromic element. Furthermore, the glass substrate 1 has good light transmittance. However, a non-glass substrate is not required if light transmission is not desired. Additionally, materials such as ITO can be used for the transparent electrode 2.

[0067] The electrochromic layer 3 uses the tungsten oxide powder paste of the embodiment. The electrochromic layer 3 is formed by coating the tungsten oxide powder paste onto the transparent electrode 2 and drying it. The drying process is preferably in the range of 120°C or higher and 270°C or lower.

[0068] The counter electrode 4 can be made of materials such as platinum. The counter electrode 4 is disposed on a glass substrate (not shown). Furthermore, an electrolyte 5 is filled between the electrochromic layer 3 and the counter electrode 4. The electrolyte 5 is then sealed around itself. When a voltage is applied to the transparent electrode 2 and the counter electrode 4, the electrochromic layer 3 becomes transparent.

[0069] Next, the method for manufacturing the tungsten oxide powder slurry of the embodiment will be described. The manufacturing method of the tungsten oxide powder slurry of the embodiment is not limited as long as it has the above-described structure, but the following methods can be listed as methods for obtaining a good yield.

[0070] First, tungsten oxide powder is prepared. The tungsten oxide powder is preferably a powder with an average particle size of 10 μm or less, and further, 50 nm or less. Methods for manufacturing tungsten oxide powder include sublimation and liquid-phase synthesis. The sublimation process is preferably any one of plasma treatment, arc treatment, laser treatment, or electron beam treatment. Plasma treatment is preferred. Examples of plasma treatment are illustrated in Patent Documents 1 and 2. Furthermore, the liquid-phase synthesis process is a method of precipitating the metal compound by dissolving a precursor of the metal compound in a solution and changing the pH or temperature of the solution. Examples of the liquid-phase synthesis process are illustrated in International Publication No. 2020 / 196720 (Patent Document 3).

[0071] In addition, when it contains one or more of potassium, sodium, lithium, and magnesium, it is preferable to add them during the sublimation process or the liquid-phase synthesis process.

[0072] Next, a crushing process is performed to break down the tungsten oxide powder. Bead milling is preferred as the crushing process. Tungsten oxide powder tends to agglomerate. Therefore, the agglomerated particles (secondary particles) must be broken down into primary particles through the crushing process.

[0073] A bead mill is a media pulverizer that uses media called beads. Furthermore, the beads are preferably beads with a particle size of 0.05 mm or more and 0.5 mm or less. Moreover, the beads are preferably beads with zirconium oxide as the main component.

[0074] Ball milling is a crushing process. Ball milling uses media with a diameter of 2 mm or more. Sufficient crushing cannot be achieved using media with a diameter of 2 mm or more. Furthermore, crushing processes using homogenizers also cannot achieve sufficient crushing. A homogenizer is a crushing device that combines stationary and rotating blades. Since it is a method that does not use media, sufficient crushing cannot be achieved. Therefore, ball mills are preferred.

[0075] Furthermore, if the bead size is less than 0.05 mm or larger than 0.5 mm, the crushing efficiency may decrease. Therefore, the bead size is preferably 0.05 mm or more and 0.5 mm or less, and further 0.1 mm or more and 0.3 mm or less.

[0076] Furthermore, beads made primarily of zirconium oxide are preferred. Other suitable materials for beads include zirconium oxide, alumina, and soda glass. Zirconia beads exhibit low aggression towards tungsten oxide powder. That is, they can be effectively broken down with minimal damage to the tungsten oxide powder. Therefore, the tungsten oxide powder is less prone to crystal defects.

[0077] By suppressing the generation of crystal defects, the half-width of the strongest peak detected at 29°±1° during X-ray diffraction analysis (2θ) can be set to below 2°. It should be noted that zirconia beads are ceramic sintered bodies with zirconia as the main component, and may also contain sintering aids.

[0078] The phrase "zirconia as the main component" here means that each bead contains 50% or more zirconia by mass. Furthermore, the zirconia content is preferably 90% or more by mass.

[0079] Next, the tungsten oxide powder, which has undergone a crushing process, is added to an aqueous solvent. Furthermore, the aqueous dispersion is a liquid with water as its main component. The water is preferably pure water. If it contains many impurities, such as tap water, it may affect coagulation. Pure water is water that meets the A1 standard described in JIS-K-0557 (1998). In addition, the aqueous solvent may also contain alcohol. When water is set to 100 parts by mass, alcohol may be present in the range of 50 parts by mass or less.

[0080] Furthermore, the content of tungsten oxide powder in the slurry is preferably set to be in the range of 5% by mass or more and 50% by mass or less.

[0081] Furthermore, as needed, the tungsten oxide powder slurry preferably contains one or more of ammonia, potassium hydroxide, and sodium hydroxide. These are water-soluble and suitable for pH adjustment. The pH is preferably 2 or higher, and more preferably 4 or higher. By adjusting the pH, the surface potential of the tungsten oxide powder can be increased. If the surface potential increases, the repulsive force between the powders becomes greater. If the repulsive force becomes greater, it becomes difficult to form aggregated particles. It should be noted that there is no particular upper limit to the pH, but a pH of 8 or lower is preferred.

[0082] Ammonia and similar substances are effective at adjusting pH. However, they are also difficult to handle. Therefore, for ease of handling, it is preferable to omit the addition of ammonia and similar substances unless absolutely necessary.

[0083] Preferably, the mixture of water and tungsten oxide is stirred using a mixer or ultrasonic waves.

[0084] Furthermore, the bead mill preferably sets the bead filling rate in the disperser to a range of 40% by volume or more and 90% by volume or less. The bead filling rate is the amount of beads fed when the volume in the disperser is set to 100% by volume. If the bead filling rate is within the range of 40% by volume or more and 90% by volume or less, the contact between the beads and the tungsten oxide powder can be made more uniform. Therefore, the bead filling rate is preferably 40% by volume or more and 90% by volume or less, and further preferably 60% by volume or more and 80% by volume or less.

[0085] Furthermore, when the volume of the disperser in the bead mill is set to 100% by volume, the total amount of water and tungsten oxide powder added is preferably in the range of 10% by volume or more and 60% by volume or less. The bead mill rotates either by rotating the disperser containing the beads or by rotating the beads using stirring blades provided within the disperser. If the total amount of beads and tungsten oxide powder added is too high, the impact force of rotation may decrease. Conversely, if the total amount of beads and tungsten oxide powder added is too low, the manufacturing efficiency decreases. Therefore, the amount added to the disperser is preferably 10% by volume or more and 60% by volume or less, and further, 20% by volume or more and 40% by volume or less. It should be noted that when ammonia or the like is added, the amount added is calculated based on the assumption that ammonia is also included in the water.

[0086] Furthermore, the impact force generated by the bead mill is preferably in the range of 100G or more and 500G or less. To achieve this impact force, the rotational speed of the disperser is preferably set to 7 m / sec or more. In addition, the crushing time is preferably 20 minutes or more.

[0087] Through the above processes, tungsten oxide powder slurry can be manufactured. It can then be stored in a container. Furthermore, the container is selected to be resistant to deterioration caused by the tungsten oxide powder slurry. Glass containers or polymer containers are preferred as such containers.

[0088] The tungsten oxide powder slurry of the embodiment can suppress the formation of agglomerated particles. Therefore, even when stored in a static state, the formation of agglomerated particles can be suppressed.

[0089] (Example)

[0090] (Examples 1-6, Comparative Examples 1-6)

[0091] Tungsten oxide powder was prepared by plasma treatment. Examples 1-3 were tungsten oxide powders. Example 4 was tungsten oxide powder with 5 mol% potassium added. Example 5 was tungsten oxide powder with 4 mol% sodium added. Example 6 was tungsten oxide powder with 2 mol% lithium added. The average particle size before slurry preparation is shown in Table 1.

[0092] Pure water was prepared as an aqueous dispersion. The pure water was pure water that met the A1 standard described in JIS-K-0557 (1998). In addition, ammonia was prepared as a pH adjuster.

[0093] Tungsten oxide powder is mixed with water. Additionally, ammonia is added to adjust the pH if necessary. This process produces a tungsten oxide powder slurry.

[0094] Next, the tungsten oxide powder slurry undergoes a crushing process. The crushing process is performed under the conditions shown in Table 1. The media are beads from a bead mill and balls from a ball mill. Furthermore, the amount of media added to the disperser is the total volume percentage of the media added when the volume inside the disperser is set to 100% by volume. Additionally, the amount of slurry added to the disperser is the volume percentage of the tungsten oxide powder slurry added when the volume inside the disperser is set to 100% by volume. Furthermore, the rotational speed of the disperser in the bead mill is set to 7 m / sec or higher.

[0095] Comparative Example 1 used a ball mill. Comparative Example 2 reduced the particle size of the beads. Furthermore, Comparative Example 3 used Al2O3 to make the beads. Comparative Example 4 reduced the amount of beads fed into the mill. Comparative Example 5 used a homogenizer. Comparative Example 6 did not involve a crushing process.

[0096] Table 1

[0097]

[0098] Through the above processes, tungsten oxide powder slurry that has undergone a crushing process was prepared. Ammonia was added to adjust the pH in Examples 1, 3, 1, 2, and 4.

[0099] The tungsten oxide powder slurry was placed in a polymer container. The time shown in Table 2 was set for a static state. Then, particle size distribution, X-ray diffraction, and absorbance were measured. The methods described above were used for the determination of particle size distribution, X-ray diffraction, and absorbance. The results are shown in Table 3.

[0100] Table 2

[0101]

[0102] Table 3

[0103]

[0104] D is shown in Table 3. 50 and D 90 The values ​​were obtained using dynamic light scattering with the slurry as the sample. Furthermore, the particle size in Table 2 was determined by TEM observation of the tungsten oxide powder obtained after removing the moisture from the slurry. Moreover, the tungsten oxide powder content in Table 2 was determined by measuring the mass of the tungsten oxide powder remaining after removing the moisture from the slurry.

[0105] As can be seen from the table, the tungsten oxide powder slurry of the known examples did not form aggregated particles even after standing for more than 24 hours (1 day). Furthermore, in the particle size frequency curve, particles appear from D0 to D... 90There is only one peak within the range up to this point. Furthermore, the absorbance at 600 nm is less than 1. Additionally, the ratio of absorbance at 350 nm to absorbance at 600 nm is 3 or more. It is known that ultraviolet light is blocked, allowing visible light to pass through.

[0106] In contrast, the half-width of Comparative Example 1 exceeded 2°. Comparative Examples 2 and 4 showed reduced absorbance due to poor crystallinity. Furthermore, Comparative Examples 1, 3, 5, and 6 showed reduced absorbance due to the formation of many aggregated particles.

[0107] Next, electrochromic elements were fabricated using the tungsten oxide powder slurries from the examples and comparative examples. A binder was added to each slurry to form a paste. The paste was then used in a coating process to form an electrochromic layer.

[0108] As an electrochromic element for transmittance measurement, it is configured to have Figure 4 The components of the structure shown are as follows. A transparent electrode 2 is disposed on a glass substrate 1 with a width of 8 mm. The transparent electrode 2 is made of ITO. A tungsten oxide powder paste is coated on the transparent electrode 2. An electrochromic layer 3 is formed by drying at approximately 200°C. This layer is placed in a glass quartz cell with an optical path length of 1 cm. An electrolyte is filled into the cell. Furthermore, platinum is used as a counter electrode 4. The counter electrode 4 is disposed in the cell. The counter electrode 4 is arranged in a manner that does not overlap with the light used for transmittance measurement.

[0109] The measurement was performed by applying a voltage to the transparent electrode 2 and the counter electrode 4. A positive voltage was applied to the electrodes when the electrode was transparent, and the color change was observed until the transmittance became unchanged. Once the transmittance became unchanged, the voltage application was stopped, and the measurement was performed within 5 minutes. The transmittance of the electrochromic element at a wavelength of 600 nm when it was transparent was measured.

[0110] The results are shown in Table 4.

[0111] Table 4

[0112] Transmittance (%) at a wavelength of 600 nm Example 1 90 Example 2 80 Example 3 85 Example 4 87 Example 5 82 Example 6 90 Comparative Example 1 60 Comparative Example 2 30 Comparative Example 3 30 Comparative Example 4 95 Comparative Example 5 55 Comparative Example 6 40

[0113] As can be seen from the table, the electrochromic element using the paste of the embodiment has a high transmittance at a wavelength of 600 nm. Therefore, it is known that it becomes a highly transparent element after applying a positive voltage. In contrast, the elements of Comparative Examples 1-3 and Comparative Examples 5-6 have reduced transmittance.

[0114] also, Figure 3The figure shows the results of measuring the absorbance of Examples 1, 3, and Comparative Example 1. In the figure, the vertical axis represents absorbance and the horizontal axis represents wavelength. As can be seen from the figure, the absorbance in the visible light region (400 nm to 800 nm) of Examples 1 and 3 is lower. That is, the transmittance of visible light beyond wavelength 600 nm is also good.

[0115] It should be noted that, in Comparative Example 4, the transmittance is good due to the small particle size. However, the color change rate is slow due to the poor crystallinity of tungsten oxide. The color change rate of the electrochromic element in the embodiment is faster than that of any of the comparative examples. Therefore, it is known that the tungsten oxide powder slurry of the embodiment can balance transmittance and color change rate.

[0116] The above examples illustrate several embodiments of the present invention, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These variations of the embodiments are included in the scope and spirit of the invention, and are also included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above-described embodiments can be combined with each other.

[0117] Explanation of symbols

[0118] 1…glass substrate

[0119] 2…Transparent electrode

[0120] 3… Electrochromic layer

[0121] 4…opposite electrode

[0122] 5… Electrolyte

[0123] 10… pool

Claims

1. A tungsten oxide powder slurry, which is a tungsten oxide powder slurry prepared by mixing tungsten oxide powder with an aqueous solvent, said tungsten oxide powder slurry being used for manufacturing electrochromic elements. In the cumulative particle size curve of the tungsten oxide powder in the slurry, D 50 For wavelengths above 20nm and below 10000nm, D 90 Below 100,000 nm During X-ray diffraction analysis (2θ), the strongest peak detected at 29°±1° had a half-width of less than 2°. The absorbance of the tungsten oxide powder slurry at a wavelength of 600 nm is less than 1.

2. The tungsten oxide powder slurry according to claim 1, wherein, D 50 For wavelengths below 500nm, D 90 Below 1000nm.

3. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, The particle size frequency curve of the tungsten oxide powder is in the range of D0 to D10. 90 Within the range, there is one peak.

4. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, The content of tungsten oxide powder in the slurry is in the range of 5% by mass or more and 50% by mass or less.

5. The tungsten oxide powder slurry according to claim 3, wherein, The content of tungsten oxide powder in the slurry is in the range of 5% by mass or more and 50% by mass or less.

6. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, It contains one or more of the following: ammonia, potassium hydroxide, and sodium hydroxide.

7. The tungsten oxide powder slurry according to claim 3, wherein, It contains one or more of the following: ammonia, potassium hydroxide, and sodium hydroxide.

8. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, When the aqueous solvent is removed, the average particle size of the tungsten oxide powder is less than 20 nm.

9. The tungsten oxide powder slurry according to claim 3, wherein, When the aqueous solvent is removed, the average particle size of the tungsten oxide powder is less than 20 nm.

10. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, The tungsten oxide powder slurry contains 0.01% by mass and less than 50% by mass of any one or two or more of potassium, sodium, lithium, and magnesium tungsten oxide powder.

11. The tungsten oxide powder slurry according to any one of claims 1 to 2, wherein, The absorbance at 350nm is greater than or equal to the absorbance at 600nm.

12. A method for manufacturing an electrochromic element, wherein the tungsten oxide powder slurry according to any one of claims 1 to 11 is used.

13. A method for manufacturing tungsten oxide powder slurry according to any one of claims 1 to 11, comprising the steps of: crushing the tungsten oxide powder using a bead mill with beads of zirconium oxide as the main component having a particle size of 0.05 mm or more and 0.5 mm or less; and mixing the crushed tungsten oxide powder with the aqueous solvent. In the bead mill, when the volume inside the disperser is set to 100% by volume, the amount of beads fed into the mill is set to be between 40% and 90% by volume.

14. The method for manufacturing tungsten oxide powder slurry according to claim 13, wherein, In the process of mixing the tungsten oxide powder with the aqueous solvent, when the volume in the disperser is set to 100% by volume, the total amount of water and the tungsten oxide powder is set to be between 10% by volume and 60% by volume.

15. The method for manufacturing tungsten oxide powder slurry according to claim 13 or 14, wherein, In the crushing process using the bead mill, the impact force generated by the bead mill is in the range of 100G or more and 500G or less.

16. The method for manufacturing tungsten oxide powder slurry according to claim 15, wherein, The speed of the disperser is above 7 m / sec.

17. The method for manufacturing tungsten oxide powder slurry according to claim 13 or 14, wherein, In the crushing process using the aforementioned bead mill, the crushing time is 20 minutes or more.

18. The method for manufacturing tungsten oxide powder slurry according to claim 15, wherein, In the crushing process using the aforementioned bead mill, the crushing time is 20 minutes or more.

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