Tungsten oxide powder and electrochromic device using the same

Abstract

Provided is tungsten oxide powder having an average diameter of primary particles less than or equal to 100 nm, characterized in that the crystalline phase and the amorphous phase coexist in the primary particles of the tungsten oxide powder. Furthermore, preferably, the amorphous phase exists along 80%-100% of the perimeter of the crystalline phase in the primary particles. Furthermore, preferably, the amorphous phase exists along 100% of the perimeter of the crystalline phase in the primary particles. An electrochromic element using such tungsten oxide powder makes it possible to improve response speed and coloring efficiency.

Description

[Technical Field]

[0001] The embodiments described below generally relate to tungsten oxide powder and electrochromic devices using the same. [Background technology]

[0002] Electrochromic devices utilize an electrochemical oxidation-reduction reaction caused by the application of a voltage, which allows them to reversibly change from a transparent to a colored state. Electrochromic elements are used in displays and dimming systems. Dimming systems include photochromic glass, photochromic eyeglasses, and anti-glare mirrors. Dimming systems are also used in a variety of fields, including vehicles, aircraft, and buildings. For example, when used in building windows as photochromic glass, it can switch the sunlight on and off. Tungsten oxide powder is used as a material for electrochromic devices. For example, International Publication No. 2018 / 199020 (Patent Document 1) discloses a tungsten oxide powder that has a predetermined value measured by spectroscopic ellipsometry. It has been shown that using the tungsten oxide powder of Patent Document 1 in an electrochromic device improves the response speed. Furthermore, International Publication No. 2016 / 039157 (Patent Document 2) discloses the use of tungsten oxide powder having hopping conductivity in an electrochromic element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 199020 [Patent Document 2] International Publication No. 2016 / 039157 Summary of the Invention [Problem to be solved by the invention]

[0004] The use of the tungsten oxide powders disclosed in Patent Documents 1 and 2 in electrochromic elements improved the response speed, but no further improvement was observed. Furthermore, uneven coloring occurred during coloring. As a result of investigating the cause of this, it was found that each tungsten oxide powder required both a crystalline phase and an amorphous phase. In Patent Document 1, a deposited film with a thickness of 50 nm to 200 nm was required for measurement by spectroscopic ellipsometry. Similarly, in Patent Document 2, a film was required for measurement of activation energy. In Patent Documents 1 and 2, evaluation was performed using a tungsten oxide film. For this reason, the state of each powder was not necessarily understood. The present invention is intended to address these problems and to provide a tungsten oxide powder for electrochromic devices that has a crystalline phase and an amorphous phase. [Means for solving the problem]

[0005] The tungsten oxide powder according to the embodiment is a tungsten oxide powder having an average primary particle size of 100 nm or less, and the primary particles of the tungsten oxide powder are characterized in that a crystalline phase and an amorphous phase are mixed together. In addition, in the primary particles, the amorphous phase exists within a range of 80% to 100% of the perimeter of the crystalline phase. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of a tungsten oxide powder according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of how to determine the diameter of the crystalline phase and the width of the amorphous phase. [Figure 3] FIG. 3 is a diagram showing another example of a tungsten oxide powder according to an embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a cell structure of an electrochromic element. Embodiment

[0007] The tungsten oxide powder for electrochromic devices according to the embodiment is a tungsten oxide powder having an average primary particle size of 100 nm or less, and is characterized in that the primary particles of the tungsten oxide powder contain a mixture of a crystalline phase and an amorphous phase. FIG. 1 shows an example of a tungsten oxide powder for electrochromic devices according to an embodiment. 1 is tungsten oxide powder, 2 is a crystalline phase, and 3 is an amorphous phase. FIG. 1 illustrates primary particles of tungsten oxide powder. A primary particle is a single powder. Primary particles that aggregate to form a single powder are called secondary particles. Tungsten oxide powder for electrochromic devices is sometimes simply referred to as tungsten oxide powder.

[0008] In such tungsten oxide powder, the average particle size of the primary particles is 100 nm or less. If the average particle size exceeds 100 nm, the particles are large and transparency decreases. Although the lower limit of the average particle size is not particularly limited, it is preferably 2 nm or more. If the average particle size is small, the primary particles may be prone to aggregation. For this reason, the average particle size is preferably in the range of 2 nm to 100 nm, and more preferably 5 nm to 20 nm.

[0009] The average particle size is measured using a field emission scanning electron microscope (FE-SEM). A sample of tungsten oxide powder is observed using the FE-SEM, and an enlarged photograph is taken. The longest diagonal line of the tungsten oxide powder in the enlarged photograph is taken as the particle diameter of the powder particle. The average value of the particle diameters of 100 randomly selected powder particles is taken as the average particle size. The magnification of the enlarged photograph taken using the FE-SEM is 500,000 times or more.

[0010] Furthermore, the primary particles of the tungsten oxide powder are assumed to be a mixture of crystalline and amorphous phases. Analysis of the crystalline and amorphous phases is performed using HAADF-STEM. HAADF-STEM stands for High Angle Annular Dark Field-Scanning Transmission Electron Microscopy. Hereafter, HAADF-STEM images will also be simply referred to as STEM images. Furthermore, for STEM measurements, a thin film sample of the tungsten oxide powder is prepared using a microtome using the dispersion method. Furthermore, measurements are performed at an accelerating voltage of 200 kV and a magnification of 10,000,000x. The crystalline phase is an area where the regularity of the crystalline phase can be confirmed. In a STEM image, the crystalline phase is a surface where white dots are arranged in a checkerboard or border pattern at intervals of 0.3 nm to 0.5 nm. In other words, in the crystalline phase, white dots are regularly arranged in a STEM image. The checkerboard pattern here refers to a state in which white dots are regularly arranged in both the vertical and horizontal directions. The checkerboard pattern is synonymous with a chessboard pattern. Furthermore, the border pattern refers to a state in which the dots are regularly arranged, but the vertical spacing and horizontal spacing are different. In other words, the vertical spacing and horizontal spacing are the same, but the vertical spacing and horizontal spacing are different. Note that the vertical spacing and horizontal spacing being different means that the spacing differs by 0.1 nm or more. The amorphous phase is a region where the regularity of the crystal lattice cannot be confirmed. In the STEM image, it is a continuous white surface where no regular atomic arrangement can be seen. In Figure 1, the white dots of the crystalline phase 2 are shown as black dots.

[0011] Tungsten oxide is stable as tungsten trioxide (WO3) at room temperature. WO3 has a monoclinic crystal structure. In other words, conventional tungsten oxide powder has a monoclinic crystal structure and does not have an amorphous phase. The tungsten oxide powder according to the embodiment has a mixture of a crystalline phase and an amorphous phase. This allows for improved response speed and coloring efficiency.

[0012] In addition, it is preferable that the primary particles have an amorphous phase present within a range of 80% to 100% of the circumferential length of the crystalline phase, and that the primary particles have an amorphous phase present within a range of 100% of the circumferential length of the crystalline phase. The tungsten oxide powder according to the embodiment may be primary particles containing a mixture of a crystalline phase and an amorphous phase. Meanwhile, the presence of an amorphous phase within a range of 80% to 100% of the perimeter of the crystalline phase of the primary particles can improve the conductivity of the primary particles. The amorphous phase does not have a specific crystal structure. Therefore, there are no grain boundaries that cause resistance. This can improve the conductivity of the primary particles. Furthermore, the presence of an amorphous phase at 80% or more of the perimeter of the crystalline phase can improve the response speed of color change. This is because the presence of a low-resistance amorphous phase around the primary particles allows for a reaction regardless of the orientation of the powder. For this reason, it is preferable that the amorphous phase be present at 100% of the perimeter of the crystalline phase of the primary particles. Furthermore, a single crystal is an example of a state in which the tungsten oxide powder does not have an amorphous phase. In single crystal powder, there are no grain boundaries. On the other hand, when comparing the amorphous phase and the crystalline phase, the amorphous phase has a lower resistance value. As will be described later, when forming an electrochromic layer, the tungsten oxide powder comes into contact with itself. When the tungsten oxide powder comes into contact with itself, the presence of an amorphous phase can reduce the resistance. In the case of single crystal powders, the resistance value increases when the powders come into contact with each other. For this reason, it is preferable to have an amorphous phase.

[0013] The maximum width of the amorphous phase of the primary particle is preferably 0.1 nm or more and 5 nm or less. The width of the amorphous phase is the length of the amorphous phase on a line drawn from the periphery of the primary particle to the center point. The maximum width of the amorphous phase is the length of the largest amorphous phase in one primary particle. The center point of the primary particle refers to the center of gravity. An example of how to determine the width of each phase is shown in Figure 2. The symbols in the figure are the same as those in Figure 1. In the illustrated example, as shown by the solid lines, lines are drawn along the major and minor axes of the crystalline phase 2 of the tungsten oxide powder 1, with the intersection point being the center point. The center point of the tungsten oxide powder 1 is the center of gravity. The lengths of each line represent the major and minor axis widths of the crystalline phase 2. For the amorphous phase 3, as described above, the center point of the primary particle of the tungsten oxide powder 1 is used as the reference. In Figure 2, the center point of the primary particle is shown as the intersection point of the dashed lines along the major and minor axes. As in this example, the center point of the crystalline phase 2 may be located at a different position from the center point of the entire primary particle. Alternatively, the respective centers may be located at the same position. Lines are drawn from each point on the periphery of the primary particle to the center point (not shown), and the length of the amorphous phase along the lines represents the width at each point. If the maximum width of the amorphous phase is less than 0.1 nm, the effect of providing the amorphous phase may be insufficient. If the maximum width of the amorphous phase is greater than 5 nm, the proportion of the crystalline phase decreases. If the proportion of the crystalline phase decreases, the color change during coloring may decrease. Therefore, the maximum width of the amorphous phase of the primary particles is preferably in the range of 0.1 nm to 5 nm, and more preferably in the range of 0.2 nm to 4 nm. Furthermore, it is more preferably in the range of 0.5 nm to 3 nm. Furthermore, when the amorphous phase is present over 100% of the circumferential length of the crystalline phase of the primary particles, the maximum width of the amorphous phase is preferably 0.2 nm or more. Note that the width of the amorphous phase may be less than 0.1 nm in areas that do not exhibit the maximum width. Furthermore, the ratio of the maximum width of the amorphous phase to the maximum diameter of the primary particles is preferably within the range of 1 / 4 or less. This means that the maximum width of the amorphous phase / maximum diameter of the primary particles is 0.25 or less. If the ratio of the maximum width of the amorphous phase / maximum diameter of the primary particles exceeds 0.25, the proportion of the crystalline phase may decrease. If the ratio of the maximum width of the amorphous phase / maximum diameter of the primary particles is 0.25 or less, the effect of mixing the amorphous phase and the crystalline phase is easily achieved.

[0014] Furthermore, when the area of ​​the crystalline phase of the primary particles is A1 and the area of ​​the amorphous phase is B1, the ratio of the amorphous phase area B1 to the crystalline phase area A1 is preferably in the range of 0.2 to 0.8. When B1 / A1 is in the range of 0.2 to 0.8, the color change response speed and coloring efficiency can be improved. The B1 / A1 ratio is calculated as follows: Print the STEM image on paper. Print so that the primary particles on the paper are between 3cm and 10cm in diameter. A4 size paper is recommended. Cut out the crystalline phase and amorphous phase from the printed paper. Measure the cut-out pieces on a precision balance. The precision balance should be capable of measuring to 0.1mg. The ratio of the mass of the paper from which the amorphous phase was cut out to the mass of the paper from which the crystalline phase was cut out is taken as B1 / A1. This process is performed for five different particles, and the average value is taken as B1 / A1. In addition, if B1 / A1 can be determined by image analysis of a STEM image, image analysis may be used. In the case of using image analysis, the analysis is also performed on five different particles, and the average value is taken as B1 / A1. The color change response speed is the time it takes to change from a colored state to transparent (or from transparent to colored). The faster the response speed, the shorter the time it takes to change from a colored state to transparent (or from transparent to colored). The faster the response speed, the faster it is possible to switch between the colored state and the transparent state. The coloring efficiency is the amount of charge required for color change. 2 When the charge transfer coefficient (C) is large, a color change can occur with a small amount of charge.

[0015] If the B1 / A1 ratio is less than 0.2, the conductivity of the tungsten oxide powder may be insufficient. If the conductivity is reduced, the response speed may be insufficient. Furthermore, if the B1 / A1 ratio is greater than 0.8, the proportion of crystalline phase decreases. A decrease in the crystalline phase may result in a decrease in coloring efficiency. Therefore, it is preferable that the B1 / A1 ratio be in the range of 0.2 to 0.8, and more preferably in the range of 0.3 to 0.7. The area A1 of the crystalline phase is the total area of ​​the crystalline phase in one primary particle. The area B1 of the amorphous phase is the total area of ​​the amorphous phase in one primary particle. For example, if there are two amorphous phases in one primary particle, the total area of ​​the two locations is B1.

[0016] In the tungsten oxide powder according to the embodiment, a crystalline phase and an amorphous phase are mixed in the primary particles. Furthermore, performance can be improved by having the amorphous phase exist around the crystalline phase, controlling the maximum width of the amorphous phase, the area ratio of the amorphous phase to the crystalline phase, and the like. These may be used alone or in combination. Furthermore, the powder that satisfies all of these conditions will achieve the best performance improvement.

[0017] It is also preferable to provide tungsten oxide powder containing 0.01 mol% to 50 mol% of one or more of potassium, sodium, lithium, and magnesium. By incorporating these elements into tungsten oxide powder, the electrical conductivity of the tungsten oxide powder can be increased. Increasing the electrical conductivity of the tungsten oxide powder can increase the response speed. A content of less than 0.01 mol% results in insufficient effects. Furthermore, a content of more than 50 mol% reduces the benefits of tungsten oxide. Therefore, the content is preferably 0.01 mol% to 50 mol%, and even more preferably 1 mol% to 20 mol%. Furthermore, it is preferable that potassium, sodium, lithium, and magnesium are more highly distributed in the amorphous phase than in the crystalline phase. The amorphous phase has the effect of increasing electrical conductivity. By distributing these elements in the amorphous phase, the effect of increasing electrical conductivity can be more effectively achieved. The contents of potassium, sodium, lithium, and magnesium are calculated as elemental metals. For example, if potassium is added to tungsten oxide powder, it may exist as an oxide of potassium (including composite oxides). By calculating the contents as elemental metals, it becomes easier to measure the contents. The content of potassium and other elements can be measured using energy dispersive X-ray spectrometry (EDX). The following is an example of how to determine the potassium content. The sodium, lithium, and magnesium contents should be read by substituting potassium. The potassium contained in the tungsten oxide powder is color-mapped using EDX analysis. Measurement conditions are an accelerating voltage of 15.0 kV, area analysis is performed at a magnification of 1,000x or more, and the atomic ratio of K (potassium) to W (tungsten) obtained by the ZAF method is used. The ZAF method is a correction method that combines atomic number correction (Z), absorption correction (A), and fluorescence correction (F). Atomic number correction (Z) corrects the ratio of electrons irradiated onto the sample that are split into penetrating electrons and scattered electrons. Absorption correction (A) corrects the amount of characteristic X-rays generated within the sample that are absorbed before leaving the sample. Fluorescence (excitation) correction (F) corrects the intensity of fluorescent X-rays excited by X-rays generated within the sample. This is a common correction method for EDX.

[0018] The composition may also include secondary particles bonded to the primary particles via an amorphous phase. An example of a secondary particle is shown in FIG. 3. In the figure, 4 denotes a secondary particle of tungsten oxide powder. FIG. 3 shows a state in which primary particles 1 of tungsten oxide powder are bonded to each other via an amorphous phase 3. Here, "via an amorphous phase" refers to a state in which at least a portion of two particles of tungsten oxide powder are connected by an amorphous phase. This refers to a case in which an amorphous phase exists between crystalline phases of the tungsten oxide powder, or a state in which a portion of the crystalline phase is connected by an amorphous phase. While FIG. 3 illustrates a state in which two primary particles are bonded to each other, three or more primary particles may be bonded to each other. As mentioned above, the amorphous phase 3 has the effect of increasing the electrical conductivity of the tungsten oxide powder. Bonding via the amorphous phase 3 can increase the electrical conductivity.

[0019] Furthermore, with regard to the secondary particles, when the area of ​​the crystalline phase is A2 and the area of ​​the amorphous phase is B2, it is preferable that the ratio of the amorphous phase area B2 to the crystalline phase area A2 is within the range of 0.2 to 0.8. If the B2 / A2 ratio is within the range of 0.2 to 0.8, even if secondary particles are present, a decrease in conductivity can be suppressed. By controlling the B1 / A1 ratio of the primary particles and the B2 / A2 ratio of the secondary particles, performance can be improved. The crystalline phase area A2 of the secondary particles is the total area of ​​the crystalline phase in the secondary particles. The amorphous phase area B2 of the secondary particles is the total area of ​​the amorphous phase in the secondary particles.

[0020] The tungsten oxide powder described above can be used in electrochromic layers. Figure 4 shows an example of the cell structure of an electrochromic device. In the figure, 10 is the cell, 11 is the glass substrate, 12 is the transparent electrode, 13 is the electrochromic layer, 14 is the counter electrode, and 15 is the electrolyte. 4 is a schematic diagram of the cell structure of an electrochromic element. The glass substrate 11 has good light transmittance. If light transmittance is not desired, the substrate need not be glass. The transparent electrode 12 can be made of a material such as ITO. The electrochromic layer 13 uses the tungsten oxide powder according to the embodiment. The electrochromic layer 13 is formed by applying a tungsten oxide powder paste onto the transparent electrode 12 and drying it. The drying process is preferably carried out at a temperature between 120°C and 270°C. The counter electrode 14 may be made of platinum or the like. The counter electrode 14 is disposed on a glass substrate (not shown). An electrolyte 15 is filled between the electrochromic layer 13 and the counter electrode 14. The periphery of the electrolyte 15 is sealed. When a voltage is applied to the transparent electrode 12 and the counter electrode 14, the electrochromic layer 13 becomes transparent. Electrochromic elements can switch between transparent and colored states by turning an electric charge on and off. Electrochromic elements are used in displays and dimming systems. Examples of dimming systems include dimming glass, dimming eyeglasses, and anti-glare mirrors. Dimming systems are also used in a variety of fields, including vehicles, aircraft, and buildings. For example, when used as dimming glass in building windows, it can switch on and off the incidence of sunlight. It can also suppress the transmission of ultraviolet rays. In other words, electrochromic elements are suitable for controlling the on and off of the incidence of sunlight.

[0021] Furthermore, the electrochromic layer 13 preferably contains the tungsten oxide powder according to the embodiment in the range of 50% by mass to 100% by mass. If the content of the tungsten oxide powder according to the embodiment is small, the effect may be reduced. Furthermore, by containing 50% by mass or more of the tungsten oxide powder according to the embodiment, the electrochromic layer has a volume resistance of 1×10 5 The electrochromic layer including the tungsten oxide powder according to the embodiment can have a reduced volume resistance, thereby increasing the response speed.

[0022] Next, a method for producing the tungsten oxide powder according to the embodiment will be described. The method for producing the tungsten oxide powder according to the embodiment is not limited as long as it has the above-described configuration, but the following methods can be mentioned as methods for obtaining the tungsten oxide powder with a high yield. The tungsten oxide material according to the embodiment can be produced by two methods: a vapor phase method and a liquid phase method. In either method, a tungsten oxide precursor is first prepared.

[0023] When using the gas-phase method, a sublimation process is applied to a tungsten oxide precursor. Examples of tungsten oxide precursors include ammonium tungstate, WO, WO, and HWO. The tungsten oxide precursor is prepared as a powder or slurry. Furthermore, when potassium, sodium, lithium, or magnesium is added, their precursors are added. Potassium, sodium, lithium, and magnesium are called dopants, and their precursors are called dopant precursors. For example, the potassium precursor is K2WO4, the sodium precursor is Na2WO4, the lithium precursor is Li2WO4, and the magnesium precursor is MgWO4. The tungsten oxide precursor and the dopant precursor are mixed, and the mixture is subjected to a sublimation process. The dopant content can be controlled by adjusting the mixing ratio of the tungsten oxide precursor and the dopant precursor. The sublimation process uses a plasma flame. The precursor is introduced into the plasma flame using argon (Ar), nitrogen (N), or oxygen (O) as a carrier gas and sublimated. For example, the precursor mixture is sublimated by heating it to 10,000°C or higher in the plasma flame. The sublimated gas is rapidly cooled to room temperature in an oxygen atmosphere to obtain tungsten oxide powder. The particle size of the resulting powder particles can be controlled by controlling the rate at which the precursor is introduced into the plasma. For example, an average particle size of 100 nm or less can be achieved by introducing the sample at 6,000 g / h or less.

[0024] In addition, adjusting the volume ratio of the inert gas to the oxygen gas in the carrier gas is effective for controlling the area ratio of the amorphous phase. The inert gas is nitrogen or argon. The ratio of the inert gas volume to the (inert gas + oxygen gas) volume is preferably set within the range of 0.3 to 0.6. If the ratio of the inert gas volume to the (inert gas + oxygen gas) gas volume is less than 0.3, it is difficult to form an amorphous phase. Furthermore, the amount of oxygen is too large, which may result in the primary particles of the tungsten oxide powder becoming too large. Furthermore, if the ratio of the inert gas volume to the oxygen gas volume exceeds 0.6, there is too little oxygen, which may result in the production of metallic tungsten or WO2, thereby reducing the amount of WO3 produced. Therefore, by setting the ratio of the inert gas volume to the (inert gas + oxygen gas) volume within the range of 0.3 to 0.6, it is possible to control the proportion of the amorphous phase. Furthermore, the precursor feeding rate is preferably in the range of 200 g / h or more and 5000 g / h or less. As mentioned above, the feeding rate is effective in controlling the average particle size. Controlling the feeding rate is also effective in controlling the proportion of the crystalline phase. Controlling the feeding amount controls the contact time between the precursor and the plasma flame. Controlling the contact time between the precursor and the plasma flame can control the proportion of the crystalline phase. If the feeding rate is less than 200 g / h, the proportion of the crystalline phase may increase due to the small feeding amount. If the feeding rate is more than 5000 g / h, the proportion of the crystalline phase may decrease.

[0025] The liquid phase method involves dissolving a tungsten oxide precursor in an alkali, precipitating a tungsten oxide powder, and filtering and drying the resulting powder. Examples of the tungsten oxide precursor include ammonium tungstate, WO, WO, or HWO. Furthermore, when a dopant such as potassium is to be added, a dopant precursor is used. For example, K2WO4 or KOH can be used as the potassium precursor, Na2WO4 or NaOH can be used as the Na precursor, LiWO4 can be used as the Li precursor, and MgWO4 or Mg(OH)2 can be used as the Mg precursor. When a dopant is added, the dopant precursor is mixed in the process of dissolving the tungsten oxide precursor in alkali. In the process of dissolving the tungsten oxide precursor in an alkali, the tungsten oxide precursor is dispersed in water and dissolved by adjusting the pH to within the range of 9-11 with ammonia or KOH. This is a process of preparing the precursor into an alkaline aqueous solution.

[0026] The process for precipitating tungsten oxide powder involves adjusting the pH of the alkaline aqueous solution to within the range of 5-7 with a hydrochloric acid (HCl) solution. WO powder can be precipitated by neutralizing the alkaline aqueous solution. A sulfuric acid (HSO) solution or a nitric acid (HNO) solution may be used instead of hydrochloric acid. The width of the peripheral region (amorphous phase) is controlled by adjusting the HCl concentration (mass ratio) of the hydrochloric acid solution (e.g., an aqueous solution of hydrochloric acid) used for neutralization (adjusting the pH to 5-7). Precipitation using an HCl solution with a concentration of 30% or less first generates WO nuclei, and then an amorphous phase forms on their surface. Furthermore, it is preferable to set the mixing speed of the hydrochloric acid solution, from dissolving the precursor at pH 9-11, to completing neutralization within a range of 0.5 to 5 hours, and even more preferably within a range of 0.5 to 1.5 hours. This process allows for the production of tungsten oxide powder in which an amorphous phase is formed around a crystalline phase. If the neutralization completion time is less than 0.5 hours (30 minutes), the proportion of the crystalline phase may decrease. If the neutralization completion time is longer than 1.5 hours, the proportion of the crystalline phase may increase. The powdery precipitate obtained by neutralization is filtered and dried to recover the powder. The drying temperature is between 200°C and 400°C. Heating at temperatures above 400°C increases the area of ​​the crystalline phase and further increases the particle size. Drying at temperatures below 200°C may result in Cl (chlorine) remaining in the powder. The Cl content remaining in the tungsten oxide powder is preferably kept within the range of 0% to 0.1% by mass. Residual Cl in the tungsten oxide powder may combine with the electrolyte of the electrochromic device. Combination of the remaining Cl with the electrolyte may reduce the coloring efficiency of the electrochromic device. The Cl content in the tungsten oxide powder is measured using ion chromatography. The measurement device used is a Thermo Fisher Scientific ICS-2100 or equivalent. The sample used is a solution containing Cl extracted from tungsten oxide powder by hot-water pressure at 120°C for 8 hours. Note that a Cl content of 0% by mass includes values ​​below the measurement limit. Furthermore, tungsten oxide powder produced using a plasma flame does not use hydrochloric acid in the production process, so the Cl content is 0% by mass.

[0027] (Example) (Examples 1 to 11, Comparative Examples 1 to 3) Tungsten oxide powders according to Examples 1 to 9 and Comparative Examples 1 and 2 were prepared by a vapor phase method. A plasma flame at 10,000°C or higher was used in the vapor phase method. The carrier gas was a mixed gas of nitrogen and oxygen. The precursor, the nitrogen / oxygen volume ratio of the carrier gas, and the introduction rate were as shown in Table 1.

[0028] [Table 1]

[0029] Tungsten oxide powders according to the examples were produced using the above process. Example 6 contained 9 mol% potassium, Example 7 contained 50 mol% sodium, Example 8 contained 0.3 mol% lithium, and Example 9 contained 5 mol% magnesium. Comparative Example 1 had a carrier gas nitrogen / (nitrogen + oxygen) volume ratio and input amount outside the preferred range. Comparative Example 2 had a carrier gas nitrogen / oxygen volume ratio outside the preferred range.

[0030] Furthermore, in Examples 10 to 11 and Comparative Example 3, tungsten oxide powder was produced using a liquid phase synthesis method. Ammonium tungstate was used as the precursor. Ammonia was used in the process of dissolving the precursor in an alkali. Hydrochloric acid was used in the neutralization process. The time for neutralizing the pH of the alkaline aqueous solution and the drying temperature are as shown in Table 2.

[0031] [Table 2]

[0032] The amorphous and crystalline phases of the tungsten oxide powders according to the examples and comparative examples were also investigated. FE-SEM was used to measure the average particle size of the primary particles. STEM images were used to measure the amorphous and crystalline phases. Details are as described above. The results are shown in Tables 3 and 4.

[0033] [Table 3]

[0034] [Table 4]

[0035] As can be seen from the table, the amorphous phase was formed in a favorable state in the examples. The chlorine content of the tungsten oxide powders according to the examples and comparative examples was also measured, and the measurement results were all within the range of 0% by mass or more and 0.1% by mass or less. Next, electrochromic elements having electrochromic layers using the tungsten oxide powders according to the examples and comparative examples were fabricated. The electrochromic element had the structure shown in Figure 4. A transparent electrode 12 was provided on a glass substrate 11 with a width of 8 mm. The transparent electrode 12 was made of ITO. A tungsten oxide powder paste was applied to the transparent electrode 12 so that the dry film thickness was in the range of 0.3 μm to 3 μm. The electrochromic layer 13 was formed by drying at approximately 200°C. This was placed in a glass quartz cell with an optical path length of 1 cm. The cell was filled with an electrolyte. Platinum was used as the counter electrode 14. The counter electrode 14 was placed in the cell.

[0036] The volume resistance of the electrochromic layer was measured. The volume resistance was measured as follows: 1 g to 3 g of sample powder was filled into a cylindrical unit with a diameter of 20 mm. The measurement method used was the four-terminal method, with the four terminals arranged in a straight line with an electrode spacing of 3 mm. The volume resistivity was measured while applying pressures of 4 N (Newtons), 8 N, 12 N, 16 N, and 20 N to the sample using a hydraulic jack, and the lowest volume resistivity value was taken as the volume resistivity of the material. The reciprocal of the obtained volume resistivity was calculated and converted to conductivity.

[0037] The response speed and coloring efficiency of the electrochromic device were also investigated. The response speed (s) was measured as the time it took for the colored state to change to a transparent state (number of seconds). 2 / C) is the amount of charge required to cause a color change. The electrochromic device shown in Figure 4 was used to measure the response speed and coloring efficiency. The response speed was measured using an ultraviolet-visible absorption spectrophotometer, and was defined as the time it took for the transmittance of light with a wavelength of 600 nm to change from 20% to 70% when a voltage of 1.2 V was applied. The coloring efficiency was measured by measuring the absorbance with an ultraviolet-visible spectrophotometer and calculating it using the following formula: Coloring efficiency (cm 2 / C) = Change in absorbance at 600 nm / [(amount of applied charge (C)) / WO3 coating area (cm 2 )]. Here, the unit of charge is Coulomb (C). The thickness of the electrochromic layer was set to 1 μm. The results are shown in Table 5.

[0038] [Table 5]

[0039] As can be seen from the table, the electrochromic layer according to the example has a volume resistance of 4×10 5 The volume resistance was Ωcm or less. It can be seen that the volume resistance of the electrochromic layer was reduced. Improvements in response speed and coloring efficiency were also confirmed. Therefore, it was found that the electrochromic element using the tungsten oxide powder according to the example has improved performance.

[0040] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. The inventions described in the original claims of this application are set forth below. [1] A tungsten oxide powder having an average primary particle size of 100 nm or less, wherein the primary particles of the tungsten oxide powder are a mixture of a crystalline phase and an amorphous phase. [2] The tungsten oxide powder according to [1], wherein the primary particles have an amorphous phase present within a range of 80% to 100% of the perimeter of the crystalline phase. [3] The tungsten oxide powder according to any one of [1] and [2], wherein the primary particles have an amorphous phase present over 100% of the perimeter of the crystalline phase. [4] The tungsten oxide powder according to any one of [1] to [3], wherein the maximum width of the amorphous phase of the primary particles is 0.1 nm or more and 5 nm or less. [5] The tungsten oxide powder according to any one of [1] to [4], wherein, in the primary particles, when the area of ​​the crystalline phase is A1 and the area of ​​the amorphous phase is B1, the ratio of the area of ​​the amorphous phase B1 to the area of ​​the crystalline phase A1 is in the range of 0.2 to 0.8. [6] The tungsten oxide powder according to any one of [1] to [5], having an average particle size in the range of 5 nm to 20 nm. [7] The tungsten oxide powder according to any one of [1] to [6], which contains tungsten oxide powder containing 0.01 mol% to 50 mol% of one or more of potassium, sodium, lithium, and magnesium. [8] The tungsten oxide powder according to any one of [1] to [7], comprising secondary particles bonded to the primary particles via an amorphous phase. [9] The tungsten oxide powder according to [8], wherein the ratio of the area of ​​the amorphous phase B2 to the area of ​​the crystalline phase A2 is in the range of 0.2 to 0.8, where A2 is the area of ​​the crystalline phase and B2 is the area of ​​the amorphous phase.

[10] An electrochromic device using an electrochromic layer comprising the tungsten oxide powder according to any one of [1] to [9].

[11] The electrochromic layer has a volume resistivity of 1×10 5 The electrochromic device according to

[10] , having a resistivity of Ωcm or less.

[12] The tungsten oxide powder according to any one of [1] to [9], which is for use in an electrochromic device. [Explanation of symbols]

[0041] 1...Tungsten oxide powder (primary particles) 2...Crystal phase 3...Amorphous phase 4...Secondary particles of tungsten oxide powder 10...Cell (electrochromic element) 11...Glass substrate 12...Transparent electrode 13...Electrochromic layer 14...Counter electrode 15...Electrolyte

Claims

1. A tungsten oxide powder having an average primary particle size of 100 nm or less, wherein the primary particles of the tungsten oxide powder are a mixture of a crystalline phase and an amorphous phase, and the amorphous phase is present within a range of 80% to 100% of the circumferential length of the crystalline phase in the primary particles.

2. 2. The tungsten oxide powder according to claim 1, wherein the primary particles have an amorphous phase present over 100% of the perimeter of the crystalline phase.

3. 3. The tungsten oxide powder according to claim 1, wherein the maximum width of the amorphous phase of the primary particles is 0.1 nm or more and 5 nm or less.

4. 4. The tungsten oxide powder according to claim 1, wherein, in the primary particles, when an area of ​​a crystalline phase is A1 and an area of ​​an amorphous phase is B1, a ratio of the area of ​​the amorphous phase B1 / the area of ​​the crystalline phase A1 is within a range of 0.2 or more and 0.8 or less.

5. 5. The tungsten oxide powder according to claim 1, wherein the average particle size is in the range of 5 nm to 20 nm.

6. 6. The tungsten oxide powder according to claim 1, comprising a tungsten oxide powder containing 0.01 mol % to 50 mol % of one or more of potassium, sodium, lithium, and magnesium.

7. 7. The tungsten oxide powder according to claim 1, comprising secondary particles bonded to the primary particles via an amorphous phase.

8. 8. The tungsten oxide powder according to claim 7, wherein, when an area of ​​a crystalline phase is A2 and an area of ​​an amorphous phase is B2, a ratio of an area of ​​the amorphous phase B2 to an area of ​​the crystalline phase A2 is in the range of 0.2 or more and 0.8 or less.

9. An electrochromic device using an electrochromic layer comprising the tungsten oxide powder according to any one of claims 1 to 8.

10. The electrochromic layer has a volume resistance of 1×10 ５ 10. The electrochromic device according to claim 9, wherein the resistance is Ωcm or less.

11. The tungsten oxide powder according to any one of claims 1 to 8, which is for use in an electrochromic device.

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