Tungsten oxide particles and method for producing tungsten oxide particles

Abstract

Tungsten oxide particles according to an embodiment have an average primary particle diameter of 10 nm to 100 nm inclusive. With respect to an infrared absorption spectrum thereof obtained by an infrared total reflectance measurement method, if a straight line connecting a point at which the minimum value of absorbance is measured within the range of 3,950 cm-1 to 4,000 cm-1 inclusive and a point at which the minimum value of absorbance is measured within the range of 2,150 cm-1 to 2,200 cm-1 inclusive is defined as a base line, the maximum value X of the absorbance of 1,000 cm-1 to 1,100 cm-1 inclusive and the maximum value Y of the absorbance of 2,300 cm -1 to 2,400 cm-1 inclusive satisfy the following relational expression (1): 0.01 ≤ Y / X ≤ 0.1.

Description

Tungsten oxide particles and method for producing tungsten oxide particles

[0001] Embodiments of the present invention relate to tungsten oxide particles and methods for producing tungsten oxide particles.

[0002] Tungsten oxide particles are used in a variety of applications, including battery electrode materials, photocatalysts, sensors, and electrochromic elements. Efforts have been made to improve the performance of tungsten oxide particles. For example, Patent Document 1 describes tungsten oxide particles with improved performance achieved by imparting hopping conductivity. The tungsten oxide particles described in Patent Document 1 can be manufactured by a plasma method. Furthermore, Patent Document 2 describes tungsten oxide particles with improved performance using spectroscopic ellipsometry. The tungsten oxide particles described in Patent Document 2 can be manufactured by liquid-phase synthesis.

[0003] International Publication No. 2016 / 039157, International Publication No. 2018 / 199020

[0004] Conventionally, tungsten oxide particles have been produced by plasma methods, as described in Patent Document 1, or by liquid-phase synthesis, as described in Patent Document 2. While plasma methods can produce tungsten oxide particles with small particle sizes, they have the problem of higher production costs compared to liquid-phase synthesis. On the other hand, when tungsten oxide particles are produced by liquid-phase synthesis, the particles become coarser during precipitation, and further aggregate during drying, resulting in larger particle sizes for the produced tungsten oxide particles. As a result, the surface area of ​​the particles decreases, leading to a problem of reduced visible light absorption when used as a photocatalyst. Therefore, there has been a need to reduce the production cost of tungsten oxide particles without reducing the amount of visible light absorbed.

[0005] Embodiments of the present invention provide tungsten oxide particles having a visible light absorption amount equal to or greater than that of conventional tungsten oxide particles, and having reduced manufacturing costs, as well as a method for producing the tungsten oxide particles.

[0006] The above problem is solved by the following embodiments. <1> The average primary particle diameter is from 10 nm to 100 nm, and in an infrared absorption spectrum obtained by total reflection infrared measurement, 3950 cm －１ to 4000 cm －１ where the minimum absorbance is measured within the range, and 2150 cm －１ to 2200 cm －１ where the minimum absorbance is measured within the range is used as a baseline, 1000 cm －１ to 1100 cm －１ the maximum absorbance X within the range and 2300 cm －１ to 2400 cm －１ the maximum absorbance Y within the range satisfy the following relational expression (1): 0.01 ≤ Y / X ≤ 0.1 (1). Tungsten oxide particles. <2> The maximum value X and the maximum value Y satisfy the following relational expression (2): 0.018 ≤ Y / X ≤ 0.030 (2). The tungsten oxide particles according to <1>. <3> The tungsten oxide particles according to <1> or <2>, wherein the average secondary particle diameter is from 50 nm to 10000 nm. <4> The BET specific surface area is 10 m ２ / g to 200 m ２ / g. The tungsten oxide particles according to any one of <1> to <3>. <5> The tungsten oxide particles according to any one of <1> to <4>, wherein a nitrogen content is from 0.01% by mass to 0.2% by mass. <6> In an ultraviolet-visible absorption spectrum obtained by Kubelka-Munk transformation of a diffuse reflectance spectrum obtained by a diffuse reflection method, absorbance at 375 nm is A ３７５ and absorbance at 400 nm is A ４００ when the following formula (4): B = (400 - 375) × (0 - A ４００ ) / (A ４００ - A ３７５) + 400 ... (4) is 450 or more and 500 or less, wherein the tungsten oxide particles according to any one of <1> to <5>. <7> Tungsten oxide particles according to any one of <1> to <6>, used for one or more selected from the group consisting of photocatalytic materials, electrochromic materials and electrode materials for batteries. <8> A method for producing tungsten oxide particles, comprising in this order: a dissolution step of dissolving tungstic acid in an aqueous solution of a nitrogen-containing polymer to obtain an aqueous tungstic acid solution, and a heat treatment step of performing heat treatment at a temperature of 350°C or more and 600°C or less to obtain tungsten oxide particles, wherein the average primary particle diameter of the tungsten oxide particles is 10 nm or more and 100 nm or less. <9> The method for producing tungsten oxide particles according to <8>, wherein the nitrogen-containing polymer is polyethyleneimine. <10> A method for producing tungsten oxide particles according to <8> or <9>, further comprising a drying step of heating the tungstic acid aqueous solution at a temperature of 100°C to 180°C between the dissolution step and the heat treatment step. <11> A method for producing tungsten oxide particles according to any one of <8> to <10>, further comprising a grinding step of grinding the tungsten oxide particles after the heat treatment step. <12> A method for producing tungsten oxide particles according to <11>, further comprising a classification step of sieving the tungsten oxide particles after the grinding step.

[0007] Figure 1 is a conceptual diagram of an energy storage device. Figure 2 shows the infrared absorption spectra of tungsten oxide particles from Example 6 and Comparative Example 1. Figure 3 shows the ultraviolet-visible absorption spectra of tungsten oxide particles from Example 4 and Comparative Example 1.

[0008] <Tungsten Oxide Particles> The tungsten oxide particles according to this embodiment may exist as primary particles or as secondary particles. Primary particles refer to a state in which individual particles are not aggregated, i.e., a single particle. Secondary particles refer to a state in which primary particles are aggregated.

[0009] The average primary particle diameter of the tungsten oxide particles according to this embodiment is 10 nm or more and 100 nm or less, preferably 10 nm or more and 70 nm or less, and more preferably 10 nm or more and 50 nm or less. Here, the average primary particle diameter is the average particle size of the primary particles of the tungsten oxide particles. If the average primary particle diameter of the tungsten oxide particles exceeds 100 nm, the surface area cannot be obtained. Furthermore, using tungsten oxide particles with an average primary particle diameter of 10 nm or more improves the manufacturability when manufacturing electrochromic elements.

[0010] The average primary particle diameter is measured as follows: Tungsten oxide particles are observed using an FE-SEM (Field Emission Scanning Electron Microscope), and magnified images are obtained. The magnification of the FE-SEM images is set to 50,000x or higher. The longest diagonal of a single tungsten oxide particle visible in the magnified image is taken as the primary particle diameter of that particle. The average of the primary particle diameters of 100 randomly selected particles is taken as the average primary particle diameter of the tungsten oxide particles.

[0011] The average secondary particle diameter of the tungsten oxide particles according to this embodiment is preferably 50 nm to 10,000 nm, more preferably 100 nm to 5,000 nm, and even more preferably 200 nm to 3,000 nm. Here, the average secondary particle diameter is the average particle size of the secondary particles of the tungsten oxide particles.

[0012] The average secondary particle size is measured by the following wet method: 0.01 g of tungsten oxide particles is directly introduced into a measuring device (Microtrac HRA, manufactured by HONEWELL) circulating pure water as the dispersion medium, and the particle size distribution is measured using a laser diffraction / light scattering wet particle size distribution meter. The median diameter (D50) is determined from the obtained particle size distribution data, and this median diameter is taken as the average secondary particle size of the tungsten oxide particles. For the measurement, the refractive index of pure water is assumed to be 1.33, and the refractive index of the tungsten oxide particles is assumed to be 1.81.

[0013] The BET specific surface area of ​​the tungsten oxide particles according to this embodiment is preferably 10 m². ２ / g or more 200m２ It is less than or equal to / g, and more preferably 13m ２ / g or more 100m ２ It is less than or equal to / g, and more preferably 15m ２ / g or more 80m ２ The value is less than or equal to / g. A BET specific surface area above the lower limit improves the activity of the photocatalyst. A BET specific surface area below the upper limit reduces the manufacturing cost of tungsten oxide particles.

[0014] The BET specific surface area can be measured in accordance with JIS-Z-8830:2013. The measuring device used is the TriStar3000 automatic specific surface area and pore distribution analyzer (manufactured by Shimadzu Corporation). In this measurement, 1 g of sample is thoroughly degassed under vacuum conditions at 20°C for 4 hours, and the BET specific surface area is measured using nitrogen gas as the adsorption gas.

[0015] As described later, the tungsten oxide particles according to the embodiment are manufactured using a nitrogen-containing polymer. Therefore, the tungsten oxide particles according to the embodiment are pure tungsten oxide (WO ３ It is not composed of ) and contains nitrogen (N) as an impurity. The nitrogen content is, for example, 0.01% by mass or more and 0.2% by mass or less, preferably 0.01% by mass or more and 0.1% by mass or less, and more preferably 0.02% by mass or more and 0.04% by mass or less.

[0016] The nitrogen content is measured using an oxygen and nitrogen analyzer (LECO ON836) by the inert gas fusion-infrared absorption method.

[0017] The tungsten oxide particles according to this embodiment exhibit an infrared absorption spectrum of 3950 cm⁻¹ obtained by infrared total internal reflection measurement. －１ More than 4000cm －１ The point where the minimum absorption value was measured was within the following range and at 2150 cm. －１ More than 2200cm －１ The baseline is the straight line connecting the point where the minimum absorption value was measured within the following range, at 1000 cm. －１ More than 1100cm －１ The following maximum absorption value X and 2300 cm －１More than 2400cm －１ The maximum value Y of the absorption degree below preferably satisfies the following relation (1): 0.01 ≤ Y / X ≤ 0.1 ... (1), the following relation (2): 0.018 ≤ Y / X ≤ 0.030 ... (2), and more preferably satisfies the following relation (3): 0.018 ≤ Y / X ≤ 0.025 ... (3).

[0018] When the infrared absorption spectrum of tungsten oxide particles was measured using the infrared total internal reflection method, it was found to be at 1000 cm⁻¹. －１ More than 1100cm －１ An absorption peak originating from nitrogen, which is present as an impurity, is observed at the following position. Therefore, at 1000 cm⁻¹ －１ More than 1100cm －１ The maximum absorbance value below refers to the maximum absorbance value due to nitrogen absorption.

[0019] The tungsten oxide particles according to this embodiment are manufactured using a nitrogen-containing polymer and therefore contain N-H bonds derived from the nitrogen-containing polymer. When the infrared absorption spectrum of the tungsten oxide particles according to this embodiment is measured by infrared total internal reflection, it is 2300 cm⁻¹. －１ More than 2400cm －１ An absorption peak originating from the N-H bond is observed at the following position. Therefore, 2300 cm⁻¹ －１ More than 2400cm －１ The maximum absorbance value below refers to the maximum absorbance value due to absorption originating from the N-H bond.

[0020] The tungsten oxide particles according to this embodiment, when measured using the infrared total internal reflection method, show an infrared absorption spectrum of 3950 cm⁻¹. －１ More than 4000cm －１ The following locations and 2150 cm －１ More than 2200cm －１ Absorption peaks are generally not observed at the following positions. Therefore, in this embodiment, 3950 cm⁻¹ －１ More than 4000cm －１ The point where the minimum absorption value was measured was within the following range and at 2150 cm. －１ More than 2200cm －１The baseline is defined as the straight line connecting the point where the minimum absorption value was measured within the following range. When this straight line is used as the baseline, the 1000 cm distance is defined as follows: －１ More than 1100cm －１ The following maximum absorption values ​​X and 2300 cm －１ More than 2400cm －１ By using the maximum absorbance value Y below, it is possible to eliminate fluctuations that appear in the infrared absorption spectrum due to the measurement environment, etc. When the above straight line is used as the baseline, the absorbance due to N-H bond absorption relative to the absorbance due to nitrogen absorption can be expressed as Y / X. Y / X represents the relative magnitude of the absorbance due to N-H bond and is an indicator of the extent to which N-H bonds are contained in tungsten oxide particles.

[0021] When determining the baseline, 3950cm －１ More than 4000cm －１ If the minimum absorption value is measured at multiple locations within the following range, the point determined as follows should be 3950 cm. －１ More than 4000cm －１ The point at which the minimum absorption value within the following range was measured is 3950 cm. －１ More than 4000cm －１ The minimum absorption value within the following range is 2150 cm². －１ More than 2200cm －１ If the absorption value is less than the minimum value within the following range, 3950 cm －１ More than 4000cm －１ Among the multiple points within the following range where the minimum absorption value was observed, the measurement point at the position with the smallest wavenumber was 3950 cm. －１ More than 4000cm －１ The point at which the minimum absorption value within the following range was measured is 3950 cm. －１ More than 4000cm －１ The minimum absorption value within the following range is 2150 cm². －１ More than 2200cm －１ If the absorption value is greater than or equal to the minimum value within the following range, 3950 cm －１ More than 4000cm －１Among a plurality of points at which the minimum absorbance is observed within the following range, the measurement point at the position having the largest wavenumber is defined as 3950 cm －１ or more and 4000 cm －１ the point at which the minimum absorbance within the following range is measured.

[0022] When determining a baseline, 2150 cm －１ or more and 2200 cm －１ when the minimum absorbance within the following range is measured at a plurality of positions, the point determined as follows is defined as 2150 cm －１ or more and 2200 cm －１ the point at which the minimum absorbance within the following range is measured. 3950 cm －１ or more and 4000 cm －１ when the minimum absorbance within the following range is equal to or greater than the minimum absorbance within 2150 cm －１ or more and 2200 cm －１ the following range, among a plurality of points at which the minimum absorbance is observed within 2150 cm －１ or more and 2200 cm －１ the following range, the measurement point at the position having the smallest wavenumber is defined as 2150 cm －１ or more and 2200 cm －１ the point at which the minimum absorbance within the following range is measured. 3950 cm －１ or more and 4000 cm －１ when the minimum absorbance within the following range is equal to or greater than the minimum absorbance within 2150 cm －１ or more and 2200 cm －１ the following range, among a plurality of points at which the minimum absorbance is observed within 2150 cm －１ or more and 2200 cm －１ the following range, the measurement point at the position having the largest wavenumber is defined as 2150 cm －１ or more and 2200 cm －１ the point at which the minimum absorbance within the following range is measured.

[0023] When Y / X is 0.01 or more or 0.018 or more, the tungsten oxide particles can absorb visible light of 450 nm or more and 500 nm or less. When Y / X is 0.1 or less, 0.030 or less or 0.025 or less, the tungsten oxide particles have fewer crystal defects. As a result, the recombination probability of electrons and holes generated by light absorption decreases, and high photocatalytic activity can be obtained.

[0024] The infrared absorption spectrum measured by total infrared reflection measurement method is obtained by measurement via the diffuse reflection method using a Fourier transform infrared spectrometer (FT / IR-6600 manufactured by JASCO Corporation) under the following measurement conditions. (Measurement conditions) Atmosphere: Vacuum atmosphere (100 Pa) Incident angle: 45 degrees Resolution: 4 cm －１ Measurement wavenumber range: 1000 to 4000 cm －１ Number of integrations: 50 times

[0025] In the tungsten oxide particles according to the embodiment, in the ultraviolet-visible absorption spectrum obtained by Kubelka-Munk transformation (K-M transformation) of the diffuse reflection spectrum obtained by the diffuse reflection method, the absorbance at 375 nm is defined as A ３７５ and when the absorbance at 400 nm is defined as A ４００ , the following formula (4): B = (400-375) × (0-A ４００ ) / (A ４００ -A ３７５ ) + 400 ··· (4), B represented by the formula is preferably 450 or more and 500 or less.

[0026] The tungsten oxide particles according to the embodiment are powders having an average primary particle diameter of 10 nm or more and 100 nm or less, so it is difficult to directly measure the absorbance of the tungsten oxide particles to obtain an ultraviolet-visible absorption spectrum. For the tungsten oxide particles according to the embodiment, a diffuse reflection spectrum is obtained by the diffuse reflection method, and an ultraviolet-visible absorption spectrum can be obtained by performing Kubelka-Munk transformation on the diffuse reflection spectrum. In the ultraviolet-visible absorption spectrum, the absorbance A at 375 nm ３７５ and the absorbance A at 400 nm ４００If the value differs from the above, the straight line connecting the measurement point at 375 nm and the measurement point at 400 nm intersects with the horizontal line indicating zero absorbance. In equation (4) above, B represents the wavelength value at the point where the straight line passing through the two measurement points at 375 nm and 400 nm intersects with the horizontal line indicating zero absorbance. In addition, B in equation (4) above represents the longest wavelength that tungsten oxide particles can absorb.

[0027] When B is 450 or higher, the amount of photons available when tungsten oxide particles are used as a photocatalyst increases, improving the photocatalytic properties. When B is 500 or lower, the tungsten oxide particles have fewer crystal defects. As a result, the probability of recombination between electrons and vacancies created by light absorption decreases, and high photocatalytic activity is obtained.

[0028] The diffuse reflectance spectrum is measured as follows: Tungsten oxide particles are densely packed into the micro-sample measuring holder (Shimadzu Corporation, sample amount 0.1 g) of a UV-Vis absorbance spectrophotometer (Shimadzu Corporation UV-2700i) using an integrating sphere. Then, the reflectance of light with wavelengths between 300 nm and 800 nm is measured to obtain the diffuse reflectance spectrum. The integrating sphere used is the Shimadzu Corporation ISR-2600. The slit width is set to 5 nm. Calibration of the UV-Vis absorbance spectrophotometer is performed by filling the micro-sample measuring holder with barium sulfate and placing it behind the integrating sphere. Reflectance measurement is performed with the micro-sample measuring holder placed behind the integrating sphere. A black plate is placed on the back of the micro-sample measuring holder.

[0029] <Applications of Tungsten Oxide Particles> Next, we will explain the applications of tungsten oxide particles.

[0030] The tungsten oxide particles according to this embodiment can be used as one or more selected from the group consisting of photocatalytic materials, electrochromic materials, and battery electrode materials.

[0031] For example, when used in photocatalytic materials, it can improve decomposition performance. When used in electrochromic materials, it can improve black-and-white reversal speed and durability. Furthermore, when used in battery electrode materials, it improves power density, energy density, and capacity retention.

[0032] Among these, it is preferable to use it in energy storage devices, which are a type of electrode material for batteries. An energy storage device is a device in which a negative electrode and a positive electrode face each other with a non-conductive layer in between, and which uses an electrolyte, for example, is capable of repeatedly accumulating (charging) and releasing (discharging) electric charge through oxidation-reduction reactions or ion adsorption and desorption.

[0033] Figure 1 shows a conceptual diagram illustrating the configuration of an energy storage device. In the diagram, 10 is the energy storage device, 11 is the negative electrode layer, 12 is the negative electrode layer, 13 is the separator layer, 14 is the positive electrode layer, and 15 is the positive electrode layer. Figure 3 shows the structure of the cell portion.

[0034] The negative electrode layer 11 and the positive electrode layer 15 are formed from conductive materials. Examples of conductive materials include aluminum, copper, stainless steel, platinum, ITO, IZO, FTO, and SnO. ２ InO ３ Examples include the above. Furthermore, a thickness within the range of 5 μm to 50 μm is preferable.

[0035] Furthermore, it is preferable to use the tungsten oxide powder according to the embodiment in either the negative electrode layer 12 or the positive electrode layer 14. It is also preferable to use the tungsten oxide powder according to the embodiment in the negative electrode layer 12. Furthermore, it is preferable that the negative electrode layer 12 contains 50% by mass or less of the tungsten oxide powder according to the embodiment. Additionally, it is preferable that the porosity of the negative electrode layer 12 is 10% by volume or more and 60% by volume or less.

[0036] Furthermore, the positive electrode layer 14 contains LiCoO ２ LiMnO ２ LiNiO ２It is preferable to use Li composite oxides such as the above. With respect to the Li counter electrode, the one with a lower potential becomes the negative electrode, and the one with a higher potential becomes the positive electrode. In combination with the positive electrode layer described above, the electrode layer according to the embodiment becomes the negative electrode layer. The Li composite oxide is a general-purpose positive electrode active material. In other words, by changing the negative electrode layer to that of the embodiment, the performance as an energy storage device can be imparted.

[0037] Furthermore, the separator layer 13 is intended to provide a certain distance between the negative electrode layer 12 and the positive electrode layer 14. Examples of porous layers for the separator layer 13 include polyethylene porous layers and polypropylene porous layers. The separator layer 13 is impregnated with an electrolyte containing Li ions. Organic solvents and ionic liquids can be used as the electrolyte. Examples of organic solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-BL), valerolactone (VL), and mixed solvents thereof. LiPF4 is used as the electrolyte. ６ LiBF ４ LiClO ４ LiCF ３ SO ３ These and mixed electrolytes are examples.

[0038] <Method for producing tungsten oxide particles> Next, a method for producing tungsten oxide particles according to the embodiment will be described.

[0039] The method for producing tungsten oxide particles according to this embodiment comprises, in this order, a dissolution step of dissolving tungstic acid in an aqueous solution of a nitrogen-containing polymer, and a heat treatment step of performing heat treatment at a temperature of 350°C to 600°C to obtain tungsten oxide particles. The method for producing tungsten oxide particles according to this embodiment may also include a drying step between the dissolution step and the heat treatment step, in which the aqueous solution of the nitrogen-containing polymer is dried at a temperature of 100°C to 180°C. The method for producing tungsten oxide particles according to this embodiment may also include a pulverization step after the heat treatment step in which the tungsten oxide particles are pulverized. The method for producing tungsten oxide particles according to this embodiment may also include a classification step after the pulverization step in which the tungsten oxide particles are sieved. The tungsten oxide particles described above can be obtained by the method for producing tungsten oxide particles according to this embodiment. Each step will be described below.

[0040] A nitrogen-containing polymer is used in the dissolution process. By using a nitrogen-containing polymer, the tungstic acid is surrounded by the polymer in the aqueous solution, preventing the growth of tungsten-containing polymer complexes that precipitate in the drying process or tungsten oxide particles that precipitate in the heat treatment process. As a result, tungsten oxide particles with a small average primary particle diameter are obtained. The nitrogen-containing polymer is not particularly limited as long as it is a polymer containing nitrogen atoms, but examples include polyethyleneimine, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, polyoxyethylene alkylamine, and ethylenediaminetetrakis(propoxylate-block-ethoxylate)tetrol. Among these, polyethyleneimine is preferred.

[0041] Polyethyleneimine may have a linear structure or a network structure. Among these, polyethyleneimine with a network structure is preferred. Polyethylene with a network structure is less expensive than polyethyleneimine with a linear structure, which can reduce the manufacturing cost of tungsten oxide particles. Furthermore, compared to polyethyleneimine with a linear structure, polyethyleneimine with a network structure can maintain a greater distance from the tungsten (W) atoms in tungstic acid, improving the dispersibility of the aqueous solution. The molecular weight of polyethyleneimine is preferably 300 to 1800, and more preferably 600 to 1200. If the molecular weight of polyethyleneimine is too high, the viscosity of the aqueous solution will increase, causing the solution to adhere to stirrers or other equipment and become difficult to remove, resulting in a lower yield of tungsten oxide particles. If the molecular weight of polyethyleneimine is too low, the effect of preventing particle growth will be reduced.

[0042] Nitrogen-containing polymers may be used individually or in combination of two or more types.

[0043] An aqueous solution of nitrogen-containing polymer is obtained by dissolving the nitrogen-containing polymer in water. For example, pure water is used. The pure water is of grade A1 to A4 as specified in JIS-K-0557:1998. For example, the nitrogen-containing polymer is mixed with water so that the concentration of the nitrogen-containing polymer is 50% by mass or more and 97% by mass or less to obtain an aqueous solution of nitrogen-containing polymer. When mixing the nitrogen-containing polymer with water, stirring may be performed. The stirring time is, for example, 1 minute or more and 60 minutes or less. If the concentration of nitrogen-containing polymer is less than 50% by mass, the nitrogen-containing polymer cannot sufficiently cover the tungstic acid, and the tungsten-containing polymer complex that precipitates in the drying process or the tungsten oxide particles that precipitate in the heat treatment process will aggregate, making it difficult to obtain particles with a small particle size. Also, if the concentration of nitrogen-containing polymer exceeds 97% by mass, the viscosity will increase, and the oxide will not be uniformly dispersed within the nitrogen-containing polymer.

[0044] In the dissolution process, for example, tungstic acid is added to an aqueous solution of a nitrogen-containing polymer, and the tungstic acid is dissolved in the aqueous solution of the nitrogen-containing polymer to obtain an aqueous tungstic acid solution. The mass of water contained in the aqueous solution of the nitrogen-containing polymer is preferably 1 to 30 relative to the mass of tungstic acid. If the amount of tungstic acid added is too small, the amount of tungsten oxide particles obtained at one time will be small, and the manufacturing efficiency will deteriorate. If the amount of tungstic acid added is too large, it will be difficult for the tungstic acid to disperse uniformly in the aqueous solution.

[0045] In the drying step, the tungstic acid aqueous solution is heated at a temperature of 100°C to 180°C. The drying step is performed to remove water contained in the tungstic acid aqueous solution. Since it is also possible to remove water along with excess nitrogen-containing polymer in the heat treatment step described later, the method for producing tungsten oxide particles according to the embodiment does not necessarily have a drying step. However, from the viewpoint of recovering water and nitrogen-containing polymer separately and reducing the disposal cost of nitrogen-containing polymer, it is preferable that the method for producing tungsten oxide particles according to the embodiment has a drying step.

[0046] The drying temperature is 100°C to 180°C, preferably 120°C to 160°C, and more preferably 125°C to 150°C. Below 100°C, it takes a long time to remove moisture by evaporation or boiling. Above 180°C, particles may grow or react with the atmosphere. Furthermore, the drying process may be carried out in the atmosphere at the above temperatures.

[0047] The drying time can be appropriately set depending on the amount of tungstic acid aqueous solution and the drying temperature. From the viewpoint of sufficiently removing moisture, it is preferable to lengthen the drying time when the amount of tungstic acid aqueous solution is large, and it is also preferable to lengthen the drying time when the drying temperature is low. For example, if the amount of water contained in the tungstic acid aqueous solution is 30 g, the drying time is preferably 1 hour or more and 10 hours or less, more preferably 2 hours or more and 8 hours or less, and even more preferably 4 hours or more and 6 hours or less.

[0048] In the heat treatment process, tungsten oxide particles are obtained by heat treatment at a temperature between 350°C and 600°C. Heat treatment removes excess nitrogen-containing polymers present in the tungsten oxide particles. Furthermore, if the heat treatment process is performed without a drying process, moisture can be removed along with the excess nitrogen-containing polymers.

[0049] If the drying process is not followed, the target of heat treatment in the heat treatment process is the tungstic acid aqueous solution. On the other hand, if the drying process is followed, the water is removed by drying and the tungsten-containing polymer complex precipitates, so the target of heat treatment in the heat treatment process is the tungsten-containing polymer complex. Whether or not the drying process is followed, tungsten oxide particles are generated by the heat treatment process.

[0050] The heat treatment temperature is 350°C to 600°C, preferably 500°C to 600°C, and more preferably 550°C to 600°C. Below 350°C, nitrogen-containing polymers cannot be sufficiently removed, and high-purity tungsten oxide particles cannot be obtained. Above 600°C, the particles grow, making it difficult to obtain particles with a small particle size. Furthermore, the heat treatment process may be carried out in the atmosphere at the above temperatures.

[0051] The heat treatment time can be appropriately set depending on the amount of tungstic acid aqueous solution and the heat treatment temperature. From the viewpoint of sufficiently removing carbon components contained in nitrogen-containing polymers, it is preferable to lengthen the heat treatment time when the amount of tungstic acid aqueous solution is large, and it is also preferable to lengthen the heat treatment time when the heat treatment temperature is low. The heat treatment time is, for example, 1 hour or more and 24 hours or less, preferably 3 hours or more and 18 hours or less, and more preferably 6 hours or more and 12 hours or less.

[0052] In the grinding step, the tungsten oxide particles obtained in the heat treatment step are ground. Even without grinding, the visible light absorption of the tungsten oxide particles obtained by the manufacturing method according to this embodiment can be equivalent to that of conventional tungsten oxide particles, but grinding can further increase the visible light absorption. The grinding method is not particularly limited, and for example, grinding in a mortar and pestle is one example. The grinding time is, for example, 5 minutes or more and 60 minutes or less.

[0053] In the classification process, tungsten oxide particles are sieved. Sieving makes it easier to obtain tungsten oxide particles of the desired particle size. In particular, if the material was not sufficiently ground in the grinding process, sieving can remove larger particles. The sieving method is not particularly limited; for example, sieving can be performed using stainless steel sieves with mesh sizes of 212 μm, 150 μm, 100 μm, 75 μm, 45 μm, and 20 μm in sequence. The amount of tungsten oxide particles passed through the stainless steel sieve at one time is, for example, 3 g or less. The time spent sieving with each stainless steel sieve is, for example, 5 minutes or less.

[0054] Next, specific examples of the embodiments and their evaluation results will be described.

[0055] [Example 1] 5 g of polyethyleneimine with a molecular weight of 1200 was added to 30 mL of pure water and stirred for 10 minutes to dissolve the polyethyleneimine. In this way, aqueous solution A of nitrogen-containing polymer was prepared. 3 g of tungstic acid was added to aqueous solution A and stirred for 30 minutes to dissolve the tungstic acid. In this way, aqueous solution B with a mass ratio of water to tungstic acid (water / tungstic acid) of 10 was prepared. Aqueous solution B was dried at 150°C for 6 hours to remove the water contained in the aqueous solution and precipitate the tungsten-containing polymer complex. Then, heat treatment was performed at 500°C for 6 hours to remove polyethyleneimine and obtain tungsten oxide particles. The tungsten oxide particles were ground in a mortar for 5 minutes to obtain the tungsten oxide particles of Example 1.

[0056] [Example 2] Tungsten oxide particles of Example 2 were obtained in the same manner as in Example 1, except that polyethyleneimine with a molecular weight of 600 was used instead of polyethyleneimine with a molecular weight of 1200.

[0057] [Example 3] Tungsten oxide particles of Example 3 were obtained in the same manner as in Example 1, except that polyethyleneimine with a molecular weight of 300 was used instead of polyethyleneimine with a molecular weight of 1200, and the heat treatment time was changed from 6 hours to 1 hour.

[0058] [Example 4] Tungsten oxide particles of Example 4 were obtained in the same manner as in Example 1, except that polyethyleneimine with a molecular weight of 1800 was used instead of polyethyleneimine with a molecular weight of 1200, and the heat treatment temperature was changed from 500°C to 600°C.

[0059] [Example 5] Except for changing the heat treatment temperature from 500°C to 550°C and not performing the 5-minute grinding, tungsten oxide particles of Example 5 were obtained in the same manner as in Example 1.

[0060] [Example 6] Tungsten oxide particles of Example 6 were obtained in the same manner as in Example 1, except that the heat treatment temperature was changed from 500°C to 550°C.

[0061] [Example 7] Except for changing the amount of tungstic acid added from 3 g to 1 g, changing the heat treatment temperature from 500°C to 550°C, and changing the heat treatment time from 1 hour to 12 hours, tungsten oxide particles of Example 7 were obtained in the same manner as in Example 3.

[0062] [Example 8] Except for changing the amount of tungstic acid added from 3 g to 30 g, changing the heat treatment temperature from 500°C to 600°C, and changing the heat treatment time from 6 hours to 12 hours, tungsten oxide particles of Example 8 were obtained in the same manner as in Example 2.

[0063] [Example 9] Except for changing the heat treatment temperature from 500°C to 350°C and the heat treatment time from 1 hour to 24 hours, tungsten oxide particles of Example 9 were obtained in the same manner as in Example 3.

[0064] [Example 10] Tungsten oxide particles of Example 10 were obtained in the same manner as in Example 9, except that the heat treatment time was changed from 24 hours to 15 hours.

[0065] [Example 11] Tungsten oxide particles of Example 11 were obtained in the same manner as in Example 9, except that the heat treatment time was changed from 24 hours to 5 hours.

[0066] [Comparative Example 1] Tungsten oxide particles of Comparative Example 1 were obtained in the same manner as in Example 5, except that polyethyleneimine was not added to pure water, the heat treatment temperature was changed from 550°C to 600°C, and the heat treatment time was changed from 6 hours to 1 hour.

[0067] [Comparative Example 2] Tungsten oxide particles of Comparative Example 2 were obtained in the same manner as in Example 1, except that the heat treatment temperature was changed from 500°C to 700°C and the heat treatment time was changed from 6 hours to 1 hour.

[0068] [Comparative Example 3] Particles for Comparative Example 3 were obtained in the same manner as in Example 5, except that the heat treatment temperature was changed from 550°C to 300°C and the heat treatment time was changed from 6 hours to 24 hours. In Comparative Example 3, because the heat treatment temperature was low, excess polyethyleneimine could not be sufficiently removed, and tungsten oxide particles could not be obtained; instead, black particles were obtained.

[0069] [Measurement of Average Primary Particle Diameter] Tungsten oxide particles from Examples 1 to 11 and Comparative Examples 1 and 2 were observed using FE-SEM, and magnified images were obtained. The magnification of the FE-SEM images was set to 50,000x. For 100 tungsten oxide particles visible in the magnified images, the longest diagonal was measured, and the average value of the 100 measurements was calculated.

[0070] [Measurement of Average Secondary Particle Size] A dispersed slurry filled with pure water and circulated was directly loaded with 0.01 g of tungsten oxide particles from Example 1 into a measuring device (Microtrac HRA, manufactured by HONEWELL), and the particle size distribution was measured using a laser diffraction / light scattering wet particle size distribution analyzer. The median diameter (D50) was determined from the obtained particle size distribution data. The median diameter was taken as the average secondary particle size of the tungsten oxide particles. For the measurement, the refractive index of pure water was set to 1.33 and the refractive index of the tungsten oxide particles was set to 1.81. The average secondary particle size was determined in the same manner for the tungsten oxide particles of Examples 2 to 11 and Comparative Examples 1 and 2.

[0071] [Measurement of BET specific surface area] The BET specific surface area was measured for each of the tungsten oxide particles of Examples 1 to 11 and Comparative Examples 1 and 2 in accordance with JIS-Z-8830:2013. The measurement device used was the automatic specific surface area and pore distribution analyzer TriStar3000 (manufactured by Shimadzu Corporation). For the measurement of the BET specific surface area, 1 g of tungsten oxide particles was thoroughly degassed under vacuum conditions at 20°C for 4 hours, and nitrogen gas was used as the adsorption gas.

[0072] [Measurement of Infrared Absorption Spectra] For each of the tungsten oxide particles of Examples 1 to 11 and Comparative Examples 1 and 2, the infrared absorption spectrum was measured by diffuse reflectance using a Fourier transform infrared spectrometer (FT / IR-6600, manufactured by JASCO Corporation) under the following measurement conditions. (Measurement conditions) Atmosphere: Vacuum atmosphere (100 Pa) Angle of incidence: 45 degrees Resolution: 4 cm －１ Measurement wavefrequency range: 1000-4000 cm －１ Number of calculations: 50. In the infrared absorption spectrum obtained, at 3950 cm⁻¹ －１ More than 4000cm －１ The point where the minimum absorption value was measured was within the following range and at 2150 cm. －１ More than 2200cm －１ Draw a straight line passing through the point where the minimum absorption value was measured within the following range, and use this line as the baseline for 1000 cm. －１ More than 1100cm －１ The following maximum absorption values ​​X and 2300 cm－１ More than 2400cm －１ The maximum value Y of the absorption was determined, and Y / X was calculated.

[0073] [Measurement of Visible Absorbance] Tungsten oxide particles from Examples 1 to 11 and Comparative Examples 1 and 2 were densely packed into the micro-sample measuring holder (Shimadzu Corporation, sample amount 0.1 g) of a UV-Vis spectrophotometer (Shimadzu Corporation, UV-2700i) using an integrating sphere. The reflectance of light with wavelengths between 300 nm and 800 nm was then measured to obtain diffuse reflectance spectra. The integrating sphere used was the ISR-2600 manufactured by Shimadzu Corporation. The slit width was set to 5 nm. Calibration of the UV-Vis spectrophotometer was performed by filling the micro-sample measuring holder with barium sulfate and placing it behind the integrating sphere. Reflectance measurements were performed with the micro-sample measuring holder placed behind the integrating sphere. A black plate was placed on the back of the micro-sample measuring holder. The diffuse reflectance spectrum of tungsten oxide particles was obtained from the difference between the ultraviolet-visible absorption spectrum obtained when tungsten oxide particles were packed into the trace sample measurement holder and the ultraviolet-visible absorption spectrum obtained when barium sulfate was packed into the holder. The obtained diffuse reflectance spectrum was subjected to a Kuberkar-Munk transform using the attached software to obtain the ultraviolet-visible absorption spectrum. From the obtained ultraviolet-visible absorption spectrum, the absorbance A at 375 nm was obtained. ３７５ The value and absorbance A at 400 nm ４００ The values ​​of and were determined, and B was calculated using the above formula (4).

[0074] [Evaluation of Photocatalytic Activity] 50 mg of tungsten oxide particles from Examples 1-11 and Comparative Examples 1 and 2 were applied to a 5 x 10 cm frosted glass plate and dried. Then, they were placed in a 3 L container and 10 ppm of acetaldehyde was sealed inside. White light was irradiated for 10 minutes at an illuminance of 6000 lux while blocking ultraviolet light with wavelengths below 400 nm using an ultraviolet-cutting filter. The gas decomposition rate was determined from the amount of decomposed acetaldehyde. A higher gas decomposition rate indicates stronger photocatalytic activity of the tungsten oxide particles.

[0075] [Yield Calculation] The mass of tungstic acid used is W ０The mass of the obtained tungsten oxide particles is W １ The yield of tungsten oxide particles in Examples 1 to 11 and Comparative Examples 1 and 2 was calculated using the following formula (5): Yield [%] = (W １ ( / 231.8)÷(W) ０ / 249.8) × 100 ... (5)

[0076] The results are shown in Table 1. Figure 2 shows the infrared absorption spectra of tungsten oxide particles from Example 6 and Comparative Example 1. Figure 3 shows the ultraviolet-visible absorption spectra of tungsten oxide particles from Example 4 and Comparative Example 1.

[0077]

[0078] As is clear from Table 1, the tungsten oxide particles of Examples 1 to 10 exhibited photocatalytic activity equal to or greater than that of the tungsten oxide particles of Comparative Example 1, which were produced by a conventional method. The tungsten oxide particles of Example 11, produced at a low heat treatment temperature and short heat treatment time, showed weak photocatalytic activity. In applications where particularly strong photocatalytic activity is not required, it is possible to further reduce manufacturing costs by producing tungsten oxide particles at a low heat treatment temperature and short heat treatment time.

[0079] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0080] 10 Energy storage device 11 Negative electrode layer 12 Negative electrode layer 13 Separator layer 14 Positive electrode layer 15 Positive electrode layer

Claims

1. The average primary particle diameter is between 10 nm and 100 nm, and the infrared absorption spectrum obtained by total infrared reflection measurement is 3950 cm⁻¹. －１ More than 4000cm －１ The point where the minimum absorption value was measured was within the following range and at 2150 cm. －１ More than 2200cm －１ The baseline is the straight line connecting the point where the minimum absorption value was measured within the following range, at 1000 cm. －１ More than 1100cm －１ The following maximum absorption value X and 2300 cm －１ More than 2400cm －１ Tungsten oxide particles such that the maximum absorbance Y satisfies the following relationship (1): 0.01 ≤ Y / X ≤ 0.1 ... (1).

2. The tungsten oxide particles according to claim 1, wherein the maximum value X and the maximum value Y satisfy the following relation (2): 0.018 ≤ Y / X ≤ 0.030 ... (2).

3. Tungsten oxide particles according to claim 1 or 2, wherein the average secondary particle diameter is 50 nm or more and 10,000 nm or less.

4. A tungsten oxide particle according to claim 1 or 2, which has a BET specific surface area of 10 m ２ / g or more and 200 m ２ / g or less.

5. Tungsten oxide particles according to claim 1 or 2, wherein the nitrogen content is 0.01% by mass or more and 0.2% by mass or less.

6. In the UV-Vis absorption spectrum obtained by the Kubelkar-Munk transform of the diffuse reflectance spectrum obtained by the diffuse reflectance method, the absorbance at 375 nm is A. ３７５ And the absorbance at 400 nm is A ４００ In that case, the following equation (4): B = (400 - 375) × (0 - A ４００ ) / ( A ４００ -A ３７５ Tungsten oxide particles according to claim 1 or 2, wherein B, represented by ) + 400 ... (4), is 450 or more and 500 or less.

7. Tungsten oxide particles according to claim 1 or 2, used for one or more selected from the group consisting of photocatalytic materials, electrochromic materials, and battery electrode materials.

8. A method for producing tungsten oxide particles, comprising, in this order: a dissolution step of dissolving tungstic acid in an aqueous solution of a nitrogen-containing polymer to obtain an aqueous tungstic acid solution; and a heat treatment step of performing heat treatment at a temperature of 350°C to 600°C to obtain tungsten oxide particles, wherein the average primary particle diameter of the tungsten oxide particles is 10 nm to 100 nm.

9. The method for producing tungsten oxide particles according to claim 8, wherein the nitrogen-containing polymer is polyethyleneimine.

10. A method for producing tungsten oxide particles according to claim 8 or 9, comprising a drying step of heating the tungstic acid aqueous solution at a temperature of 100°C to 180°C between the dissolution step and the heat treatment step.

11. A method for producing tungsten oxide particles according to claim 8 or 9, further comprising a grinding step of grinding the tungsten oxide particles after the heat treatment step.

12. A method for producing tungsten oxide particles according to claim 11, further comprising a classification step of sieving the tungsten oxide particles after the grinding step.

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