Tungsten oxide powder and electrochromic element using the same

Abstract

The present application provides tungsten oxide powder having an average primary particle size of 100 nm or less, characterized in that a crystalline phase and an amorphous phase are mixedly present in the primary particles of the tungsten oxide powder. Further, in the primary particles, it is preferable that the amorphous phase be present in a range of 80% or more and 100% or less of the circumference of the crystalline phase. Further, in the primary particles, it is preferable that the amorphous phase be present in 100% of the circumference of the crystalline phase. An electrochromic element using such tungsten oxide powder can improve response speed and coloring efficiency.

Description

Technical Field

[0001] The embodiments described later generally relate to tungsten oxide powder and electrochromic elements using the same. Background Technology

[0002] Electrochromic elements are devices that utilize electrochemical redox reactions caused by the application of voltage. Thus, electrochromic elements can reversibly change from a transparent state to a colored state.

[0003] Electrochromic elements are used in displays and dimming systems. Examples of dimming systems include dimming glass, dimming glasses, and anti-glare mirrors. Furthermore, dimming systems are used in various fields such as vehicles, aircraft, and buildings. For instance, if used as dimming glass in building windows, it can switch the amount of sunlight entering the building.

[0004] Tungsten oxide powder has been used as a material for electrochromic elements. For example, International Publication No. 2018 / 199020 (Patent Document 1) discloses tungsten oxide powder having a specified value determined by a spectroscopic ellipsometry. By using the tungsten oxide powder of Patent Document 1 in an electrochromic element, it has been shown that the response speed can be improved.

[0005] Furthermore, International Publication No. 2016 / 039157 (Patent Document 2) discloses the use of tungsten oxide powder with hopping conductivity in electrochromic elements.

[0006] Existing technical documents

[0007] Patent documents

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

[0009] Patent Document 2: International Publication No. 2016 / 039157 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] An improvement in response speed was observed by using tungsten oxide powder from Patent Document 1 or Patent Document 2 in the electrochromic element. However, no improvement beyond that was observed. Furthermore, uneven coloring occurred during coloring.

[0012] The investigation revealed that the presence of both crystalline and amorphous phases in each tungsten oxide powder is necessary. In Patent Document 1, a deposition film with a thickness of 50 nm to 200 nm is required for measurement using ellipsometry. Similarly, in Patent Document 2, film formation is necessary for measuring the activity energy. Both Patent Documents 1 and 2 evaluated the activity by forming tungsten oxide films. Therefore, it may not be possible to accurately determine the state of each powder.

[0013] The present invention was made to solve such problems, and its object is to provide tungsten oxide powder for electrochromic elements having both crystalline and amorphous phases.

[0014] Methods for solving problems

[0015] The tungsten oxide powder involved in the embodiments is a tungsten oxide powder with an average primary particle size of less than 100 nm, characterized in that: the primary particles of the tungsten oxide powder contain a crystalline phase and an amorphous phase mixed together. Attached Figure Description

[0016] Figure 1 This is an illustration showing an example of tungsten oxide powder involved in the embodiment.

[0017] Figure 2 This is a diagram illustrating an example of how to determine the diameter of a crystalline phase and the width of an amorphous phase.

[0018] Figure 3 This is an illustration showing another example of tungsten oxide powder involved in the embodiment.

[0019] Figure 4 This is a diagram illustrating an example of the cell structure of an electrochromic element. Detailed Implementation

[0020] The tungsten oxide powder for electrochromic elements involved in the embodiments is tungsten oxide powder with an average particle size of less than 100 nm for primary particles, characterized in that: crystalline phase and amorphous phase are mixed in the primary particles of the tungsten oxide powder.

[0021] Figure 1 An example of tungsten oxide powder for an electrochromic element according to an embodiment is shown. 1 is tungsten oxide powder, 2 is a crystalline phase, and 3 is an amorphous phase. Figure 1 The diagram shows primary particles of tungsten oxide powder. A primary particle is simply a piece of powder. A particle that aggregates with each other to form a powder is called a secondary particle. Furthermore, the term "tungsten oxide powder" is sometimes used simply to refer to electrochromic elements.

[0022] In the aforementioned 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 transparency decreases due to the large particle size. There is no particular limitation on the lower limit of the average particle size, but it is preferably 2 nm or more. If the average particle size is small, there is a possibility that the primary particles may easily aggregate. Therefore, the average particle size is preferably in the range of 2 nm or more and 100 nm or less, more preferably in the range of 5 nm or more and 20 nm or less.

[0023] Furthermore, the method for determining the average particle size was set to use FE-SEM (Field Emission Scanning Electron Microscope). A magnified photograph of the tungsten oxide powder sample was obtained by observing it using FE-SEM. The longest diagonal of the tungsten oxide powder in the magnified photograph was taken as the particle size of that powder. The average particle size was taken as the average of the particle sizes of 100 randomly selected powder samples. Moreover, the magnification of the FE-SEM photographs was specified to be 500,000x or higher.

[0024] Furthermore, the primary particles of tungsten oxide powder are configured to contain a mixture of crystalline and amorphous phases. Analysis of the crystalline and amorphous phases can be performed using HAADF-STEM. HAADF-STEM is a high-angle Annular Dark Field-Scanning Transmission Electron Microscopy. Hereinafter, HAADF-STEM images are sometimes simply referred to as STEM images. Furthermore, when performing STEM measurements, it is specified that thin film samples of tungsten oxide powder are prepared using a dispersive slicer. Furthermore, it is specified that the STEM accelerating voltage is set to 200 kV, and the measurement is performed at a magnification of 10,000,000x.

[0025] A crystalline phase is a region in which the regularity of the crystalline phase can be identified. In STEM images, a crystalline phase appears as white dots arranged in a checkerboard or border pattern with intervals between 0.3 nm and 0.5 nm.

[0026] In other words, for crystalline phases, white dots are arranged regularly in STEM images. The checkerboard pattern mentioned here refers to the regular arrangement of white dots in both the vertical and horizontal directions. The checkerboard pattern is synonymous with a chessboard pattern. Furthermore, the border pattern refers to a regular arrangement where the vertical and horizontal spacings differ. That is, it means that the vertical and horizontal spacings are the same, but the vertical and horizontal spacings are different. Moreover, the difference between the vertical and horizontal spacings indicates a difference of more than 0.1 nm.

[0027] Furthermore, the so-called amorphous phase refers to regions where the regularity of the crystal lattice cannot be confirmed. In STEM images, these are continuous white surfaces without a regular arrangement of atoms. Moreover, in... Figure 1 In the diagram, the white dots of crystalline phase 2 are represented by black dots.

[0028] Tungsten oxide is stable at room temperature as tungsten trioxide (WO3). WO3 has a monoclinic crystal structure. That is, conventional tungsten oxide powders have a monoclinic crystal structure and do not contain an amorphous phase. The tungsten oxide powder according to the embodiments contains both crystalline and amorphous phases. As a result, the reaction speed and coloring efficiency can be improved.

[0029] Furthermore, it is preferable that an amorphous phase is present in the primary particles within a range of 80% to 100% of the perimeter of the crystalline phase. Furthermore, it is preferable that an amorphous phase is present in the primary particles within 100% of the perimeter of the crystalline phase.

[0030] For the tungsten oxide powder involved in the embodiments, any primary particles consisting of a mixture of crystalline and amorphous phases are acceptable. On the other hand, the presence of an amorphous phase within 80% to 100% of the perimeter of the crystalline phase in the primary particles improves the conductivity of the primary particles. The amorphous phase does not have a specific crystal structure. Therefore, there are no grain boundaries that constitute resistance. This further improves the conductivity of the primary particles. Furthermore, the presence of an amorphous phase within 80% or more of the perimeter of the crystalline phase improves the response speed to color changes. Because the presence of a low-resistance amorphous phase around the primary particles allows for reactions independent of the powder's orientation. Therefore, it is preferable that the amorphous phase is present within 100% of the perimeter of the crystalline phase in the primary particles.

[0031] Furthermore, as a state in which tungsten oxide powder lacks an amorphous phase, single crystals can be cited as an example. If it is a single-crystal powder, grain boundaries are absent. On the other hand, comparing the amorphous phase and the crystalline phase, the amorphous phase has a lower resistivity. When forming the electrochromic layer as described later, the tungsten oxide powders are in contact with each other. When the tungsten oxide powders are in contact with each other, the resistivity can be reduced by having an amorphous phase. If they are single-crystal powders, the resistivity increases when the powders are in contact. Therefore, having an amorphous phase is preferable.

[0032] Furthermore, it is preferable that the maximum width of the amorphous phase of the primary particle is 0.1 nm or more and 5 nm or less. The width of the amorphous phase is defined as the length of the amorphous phase along a straight line drawn from the outer periphery of the primary particle towards its center point. The maximum width of the amorphous phase within a single primary particle is defined as the length of the largest amorphous phase. Furthermore, the center point of the primary particle refers to the centroid.

[0033] Figure 2 The diagram shows an example of how to calculate the width of each phase. The symbols in the diagram are... Figure 1The symbols are the same. In the illustrated example, if solid lines are used, lines are drawn along the major and minor axes with the center point of the crystalline phase 2 of tungsten oxide powder 1 as the intersection point. The center point of tungsten oxide powder 1 is called the centroid. The length of each line is taken as the major and minor axis widths of the crystalline phase 2. Regarding the amorphous phase 3, the center point of the primary particles of tungsten oxide powder 1 is used as the reference as described above. Figure 2 In this example, the center point of the primary particle is shown as the intersection of the dashed lines along the major and minor axes, respectively. As in this example, the position between the center point of crystalline phase 2 and the center point of the primary particle as a whole can be different. All center points can also be in 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 this line is taken as the width at each point.

[0034] If the maximum width of the amorphous phase is less than 0.1 nm, the effect of setting 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, it is preferable that the maximum width of the amorphous phase of the primary particles is in the range of 0.1 nm or more and 5 nm or less, more preferably in the range of 0.2 nm or more and 4 nm or less. Furthermore, it is even more preferable that it is in the range of 0.5 nm or more and 3 nm or less. In addition, when the amorphous phase is present on 100% of the perimeter of the crystalline phase of the primary particles, the maximum width of the amorphous phase is preferably 0.2 nm or more. Furthermore, for the parts where the maximum width is not shown, the width of the amorphous phase may be less than 0.1 nm.

[0035] Furthermore, the ratio of the maximum width of the amorphous phase to the maximum diameter of the primary particle is preferably in the range of 1 / 4 or less. This means that the ratio of the maximum width of the amorphous phase to the maximum diameter of the primary particle is 0.25 or less. If the ratio of the maximum width of the amorphous phase to the maximum diameter of the primary particle is greater than 0.25, there is a possibility that the proportion of the crystalline phase will decrease. If the ratio of the maximum width of the amorphous phase to the maximum diameter of the primary particle is 0.25 or less, it is easy to obtain the effect of allowing the amorphous phase and the crystalline phase to coexist.

[0036] Furthermore, it is preferable that, for the aforementioned primary particles, when the area of ​​the crystalline phase is set as A1 and the area of ​​the amorphous phase is set as 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 or higher and 0.8 or lower. If B1 / A1 is in the range of 0.2 or higher and 0.8 or lower, the response speed of color change and the coloring efficiency can be improved.

[0037] The B1 / A1 ratio is calculated as follows: Print the STEM image onto paper. Print particles once onto the printed paper, with a particle size ranging from 3 cm to 10 cm. A4 size paper is recommended. Cut out the crystalline and amorphous phases separately from the printed paper. Measure the cut crystalline and amorphous phases using a precision balance. The precision balance should be able to measure to a depth of 0.1 mg. The ratio of the mass of the paper with the amorphous phase cut out to the mass of the paper with the crystalline phase cut out is taken as B1 / A1. Perform this operation on 5 different particles and take the average value as B1 / A1.

[0038] Furthermore, image analysis can also be used to determine B1 / A1 when analyzing STEM images. When using image analysis, it is specified that the analysis is performed on five different particles, and the average value is taken as B1 / A1.

[0039] The so-called color change response speed refers to the time it takes for a color to change from a tinted state to a transparent state (or from a transparent state to a tinted state). A faster response speed means a shorter time to change from a tinted state to a transparent state (or from a transparent state to a tinted state). A faster response speed also means that the switching between tinted and transparent states can be performed quickly.

[0040] Furthermore, the so-called coloring efficiency is the amount of charge required for a color change. If the coloring efficiency (cm²) 2 If the charge level is high, then a small amount of charge can produce a color change.

[0041] If the B1 / A1 ratio is below 0.2, the conductivity of the tungsten oxide powder may be insufficient. Decreased conductivity may lead to insufficient response speed. Furthermore, if the B1 / A1 ratio exceeds 0.8, the proportion of the crystalline phase decreases. A reduction in the crystalline phase may result in decreased coloring efficiency. Therefore, it is preferable that the B1 / A1 ratio is in the range of 0.2 or higher and 0.8 or lower, more preferably in the range of 0.3 or higher and 0.7 or lower.

[0042] Furthermore, the area A1 of the crystalline phase is the total area of ​​the crystalline phase in a single primary particle. Similarly, the area B1 of the amorphous phase is the total area of ​​the amorphous phase in a single primary particle. For example, if there are two locations of amorphous phase in a single primary particle, the total area of ​​those two locations is set as B1.

[0043] For the tungsten oxide powder involved in the embodiments, a mixture of crystalline and amorphous phases exists in the primary particles. Furthermore, performance can be improved by ensuring the amorphous phase exists around the crystalline phase, controlling the maximum width of the amorphous phase, and the area ratio of the amorphous phase to the crystalline phase. These can be used individually or in combination. Moreover, tungsten oxide powder that satisfies all conditions exhibits the best performance.

[0044] Furthermore, it is preferable to have tungsten oxide powder containing one or more of potassium, sodium, lithium, and magnesium at a concentration of 0.01 mol% or more and 50 mol% or less. The presence of these elements in the tungsten oxide powder improves its conductivity. Increased conductivity leads to improved response speed. If the concentration is below 0.01 mol%, the effect of these elements is insufficient. Furthermore, if the concentration exceeds 50 mol%, the advantages of tungsten oxide cannot be effectively utilized. Therefore, a concentration of 0.01 mol% or more and 50 mol% or less is preferred, and more preferably 1 mol% or more and 20 mol% or less is more desirable. Additionally, it is preferable that potassium, sodium, lithium, and magnesium are more abundant in the amorphous phase than in the crystalline phase. The amorphous phase has the effect of improving conductivity. By distributing these elements in the amorphous phase, the effect of further improving conductivity can be achieved.

[0045] Furthermore, the contents of potassium, sodium, lithium, and magnesium are calculated using elemental metal conversions. For example, if potassium is present in tungsten oxide powder, it may also exist as potassium oxides (including complex oxides). By specifying the metal element conversions, the contents can be easily determined.

[0046] The proportions of potassium and other minerals can be determined using energy dispersive X-ray spectrometry (EDX). The method for determining potassium content is shown below. The contents of sodium, lithium, and magnesium are determined by displacing potassium.

[0047] Potassium contained in tungsten oxide powder was color-mapped using EDX analysis. For the measurement conditions, the accelerating voltage was set to 15.0 kV, and surface analysis was performed at a magnification of 1000x or higher. The atomic ratio of K (potassium) to W (tungsten) was determined from the ZAF method.

[0048] The ZAF method combines three correction methods: atomic number correction (Z), absorption correction (A), and fluorescence correction (F). Atomic number correction (Z) corrects the ratio of electrons entering the sample to scattered electrons. Absorption correction (A) corrects the amount of absorption of characteristic X-rays generated in the sample before they are exposed outside the sample. Fluorescence (excitation) correction (F) corrects the intensity of fluorescent X-rays excited by X-rays generated in the sample. As a correction method for EDX, it is a common approach.

[0049] In addition, it can also have secondary particles formed by the combination of the aforementioned primary particles through amorphous materials. Figure 3 An example of secondary particles is shown in the figure. In the figure, 4 is a secondary particle of tungsten oxide powder. Figure 3This refers to the state in which primary particles 1 of tungsten oxide powder are bonded together by an amorphous phase 3. Here, "bonded by an amorphous phase" means that at least a portion of two tungsten oxide powder particles are connected through an amorphous phase. Therefore, this illustrates the case where an amorphous phase exists between the crystalline phases of tungsten oxide powder, and the state where a portion of the crystalline phase is connected through an amorphous phase. Furthermore, Figure 3 The diagram shows a state where two primary particles are combined, but it can also show a state where three or more primary particles are combined.

[0050] As mentioned earlier, amorphous phase 3 has the effect of improving the conductivity of tungsten oxide powder. As long as the amorphous phase 3 is involved in the bonding, the conductivity can be improved.

[0051] Furthermore, regarding the aforementioned secondary particles, when the area of ​​the crystalline phase is defined as A2 and the area of ​​the amorphous phase as B2, it is preferable that the ratio of the area of ​​the amorphous phase B2 to the area of ​​the crystalline phase A2 is within the range of 0.2 or higher and 0.8 or lower. As long as the ratio of B2 / A2 is within the range of 0.2 or higher and 0.8 or lower, even if secondary particles are present, the decrease in conductivity can be suppressed. By controlling the ratio of B1 / A1 as primary particles and the ratio of B2 / A2 as secondary particles, performance can be improved. Moreover, the area A2 of the crystalline phase in the secondary particles is the total area of ​​the crystalline phase in the secondary particles. Furthermore, the area B2 of the amorphous phase in the secondary particles is the total area of ​​the amorphous phase in the secondary particles.

[0052] The tungsten oxide powder described above can be used in electrochromic layers. Figure 4 The figure shows an example of a test cell structure for an electrochromic element. In the figure, 10 is the test 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.

[0053] Figure 4 This is a simplified diagram of the cell structure of the electrochromic element. Furthermore, the glass substrate 11 has good light transmittance. It can also be a non-glass substrate when light transmission is not desired. Additionally, materials such as ITO can be used as the transparent electrode 12.

[0054] The electrochromic layer 13 uses tungsten oxide powder as described in the embodiment. The electrochromic layer 13 is formed by coating a tungsten oxide powder paste onto the transparent electrode 12 and then drying it. Preferably, the drying process is performed at a temperature between 120°C and 270°C. Furthermore, platinum or the like can be used as the counter electrode 14. 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 electrolyte 15 is then sealed around itself. When a voltage is applied to the transparent electrode 12 and the counter electrode 14, the electrochromic layer 13 becomes transparent.

[0055] Electrochromic elements can switch between transparent and tinted states by switching on and off charges. They are widely used in displays and dimming systems. Examples of dimming systems include smart glass, smart glasses, and anti-glare lenses. Furthermore, dimming systems are used in various fields such as vehicles, aircraft, and buildings. For instance, when used as smart glass in building windows, it can switch the on / off state of sunlight. It can also suppress the transmission of ultraviolet rays. In other words, electrochromic elements are arguably the most suitable for controlling the on / off state of sunlight.

[0056] Furthermore, it is preferable that the electrochromic layer 13 contains tungsten oxide powder according to the embodiment in the range of 50% by mass or more and 100% by mass or less. If the content of tungsten oxide powder according to the embodiment is low, the effect may be reduced. In addition, by containing 50% by mass or more of tungsten oxide powder according to the embodiment, the volume resistivity of the electrochromic layer can be made to be less than 1×10⁻⁶. 5 Below Ωcm. The electrochromic layer containing the tungsten oxide powder according to the embodiment can reduce the volume resistivity. Therefore, the response speed can be improved.

[0057] Next, a method for manufacturing the tungsten oxide powder according to the embodiments will be described. The manufacturing method is not limited as long as the tungsten oxide powder according to the embodiments has the above-described structure; however, the following methods can be listed as manufacturing methods with high yield.

[0058] Regarding the manufacturing methods of the tungsten oxide material involved in the embodiments, two methods can be listed: the gas-phase method and the liquid-phase method. Regardless of the manufacturing method, a tungsten oxide precursor is first prepared.

[0059] When using the gas-phase method, a sublimation process is specified for the tungsten oxide precursor. Examples of tungsten oxide precursors include ammonium tungstate, WO3, WO2, and H2WO4. Furthermore, the tungsten oxide precursor is prepared into powder or slurry.

[0060] Furthermore, when adding potassium, sodium, lithium, and magnesium, their precursors are specified. Potassium, sodium, lithium, and magnesium are referred to as dopants, and their precursors are referred to as dopant precursors. For example, K₂WO₄ can be listed as a precursor for potassium, Na₂WO₄ as a precursor for sodium, Li₂WO₄ as a precursor for lithium, and MgWO₄ as a precursor for magnesium. The tungsten oxide precursor and the dopant precursor are mixed. A sublimation process is specified for the mixture. By adjusting the mixing ratio of the tungsten oxide precursor and the dopant precursor, the dopant content can be controlled.

[0061] The sublimation process utilizes a plasma flame. Precursors are introduced into the plasma flame using argon (Ar), nitrogen (N), or oxygen (O) as a carrier gas, causing them to sublimate. For example, the mixture of precursors can be sublimated by heating it to above 10,000°C in a plasma flame. Tungsten oxide powder can be obtained by rapidly cooling the sublimated gas to room temperature in an oxygen atmosphere. The particle size of the desired powder particles can be controlled by adjusting the rate at which the precursor is introduced into the plasma. For example, by introducing the sample at a rate of 6000 g / h or less, an average particle size of less than 100 nm can be achieved.

[0062] Furthermore, adjusting the volume ratio of the inert gas to oxygen in the carrier gas is effective in controlling the area ratio of the amorphous phase. The inert gas is nitrogen or argon. Preferably, the volume ratio of the inert gas to (inert gas + oxygen) is set within the range of 0.3 to 0.6. If the volume ratio of the inert gas to (inert gas + oxygen) is below 0.3, it is difficult to form an amorphous phase. Furthermore, excessive oxygen content may lead to an excessive increase in the primary particles of tungsten oxide powder. Additionally, if the volume ratio of the inert gas to oxygen exceeds 0.6, insufficient oxygen may result in the formation of metallic tungsten and WO2, thus potentially reducing the amount of WO3 formed. Therefore, by setting the volume ratio of the inert gas to (inert gas + oxygen) within the range of 0.3 to 0.6, the proportion of the amorphous phase can be controlled.

[0063] Furthermore, the feed rate of the precursor is preferably within the range of 200 g / h or higher and 5000 g / h or lower. As mentioned above, the feed rate is effective for controlling the average particle size. Moreover, controlling the feed rate is also effective for controlling the proportion of the crystalline phase. Controlling the feed rate becomes controlling the contact time between the precursor and the plasma flame. Controlling the contact time between the precursor and the plasma flame allows control over the proportion of the crystalline phase. If the feed rate is less than 200 g / h, there is a possibility that the proportion of the crystalline phase may increase due to the low feed rate. Furthermore, if the feed rate is greater than 5000 g / h, there is a possibility that the proportion of the crystalline phase may decrease.

[0064] Furthermore, when using the liquid-phase method, the procedures include dissolving the tungsten oxide precursor with an alkali, precipitating the tungsten oxide powder, and filtering and drying the obtained powder. For example, ammonium tungstate, WO3, WO2, or H2WO4 can be used as the tungsten oxide precursor.

[0065] Furthermore, when dopants such as potassium are present, a dopant precursor is specified. For example, K₂WO₄ or KOH can be used as a potassium precursor, Na₂WO₄ or NaOH can be used as a Na precursor, LiWO₄ can be used as a Li precursor, and MgWO₄ or Mg(OH)₂ can be used as a Mg precursor. Additionally, when adding dopants, it is specified that the dopant precursor is mixed during the process of dissolving the tungsten oxide precursor with an alkali.

[0066] In the process of dissolving the tungsten oxide precursor with alkali, the tungsten oxide precursor is dispersed in water and dissolved by adjusting the pH to the range of 9-11 using ammonia or KOH. This is a process of preparing the precursor in an alkaline aqueous solution.

[0067] The process of precipitating tungsten oxide powder involves adjusting the pH of the aforementioned alkaline aqueous solution to a range of pH 5-7 using hydrochloric acid (HCl) solution. Neutralizing the alkaline aqueous solution allows WO3 powder to precipitate. Alternatively, sulfuric acid (H2SO4) solution or nitric acid (HNO3) solution can be used instead of hydrochloric acid. Here, the width of the surrounding portion (amorphous phase) can be controlled by adjusting the HCl concentration (mass ratio) of the hydrochloric acid solution (e.g., an aqueous solution of hydrochloric acid) during neutralization (adjusting to pH 5-7). By precipitating it with an HCl solution of concentration 30% or less, WO3 nuclei are first formed, and then an amorphous phase forms on their surface.

[0068] Furthermore, regarding the mixing rate of the hydrochloric acid solution, the time from the dissolution of the precursor at pH 9-11 to the end of neutralization is preferably specified to be in the range of 0.5 hours or more and 5 hours or less, more preferably in the range of 0.5 hours or more and 1.5 hours or less. Through this process, tungsten oxide powder with an amorphous phase formed around the crystalline phase can be obtained. If the neutralization end time is less than 0.5 hours (30 minutes), the proportion of the crystalline phase may decrease. Conversely, if the neutralization end time is greater than 1.5 hours, the proportion of the crystalline phase may increase.

[0069] The powder obtained after neutralization can be recovered by filtering and drying. The drying temperature is specified to be above 200°C and below 400°C. If heating is performed at a temperature above 400°C, the area of ​​the crystalline phase increases, and the particle size increases. If the drying temperature is below 200°C, there is a possibility that Cl (chlorine) may remain in the powder.

[0070] Preferably, the residual Cl in the tungsten oxide powder is in the range of 0% by mass or more and 0.1% by mass or less. If Cl remains in the tungsten oxide powder, there is a possibility that it may combine with the electrolyte of the electrochromic element. If the residual Cl combines with the electrolyte, the coloring efficiency of the electrochromic element may decrease. Furthermore, the amount of Cl in the tungsten oxide powder is determined by ion chromatography. The measuring apparatus used is the ICS-2100 model or equivalent measuring apparatus manufactured by Thermo Fisher Scientific. Regarding the sample, the portion obtained by applying hot water pressure to the tungsten oxide powder at 120°C for 8 hours and extracting the solution containing Cl is used. In addition, 0% by mass of Cl also includes the determination limit. Furthermore, tungsten oxide powder manufactured using plasma flame has a Cl content of 0% by mass because hydrochloric acid is not used in the manufacturing process.

[0071] (Example)

[0072] (Examples 1-11, Comparative Examples 1-3)

[0073] The tungsten oxide powders described in Examples 1-9 and Comparative Examples 1-2 were prepared using a gas-phase method. A plasma flame at or above 10,000°C was used in the gas-phase method. Furthermore, the carrier gas was a mixture of nitrogen and oxygen. The precursor, the nitrogen / oxygen volume ratio of the carrier gas, and the injection rate are shown in Table 1.

[0074] Table 1

[0075]

[0076] Through the above processes, the tungsten oxide powder involved in the embodiments was produced. Furthermore, Example 6 is an example containing 9 mol% potassium, Example 7 is an example containing 50 mol% sodium, Example 8 is an example containing 0.3 mol% lithium, and Example 9 is an example containing 5 mol% magnesium. Additionally, Comparative Example 1 is an example where the volume ratio of nitrogen to (nitrogen + oxygen) in the carrier gas deviates from the preferred range. Furthermore, Comparative Example 2 is an example where the volume ratio of nitrogen to oxygen in the carrier gas deviates from the preferred range.

[0077] Furthermore, as Examples 10-11 and Comparative Example 3, tungsten oxide powder was prepared using a liquid-phase synthesis method. Ammonium tungstate was used as a precursor. Ammonia was used in the step of dissolving the precursor with alkali. In addition, hydrochloric acid was used in the neutralization step. The time for neutralizing the pH of the alkaline aqueous solution and the drying temperature are shown in Table 2.

[0078] Table 2

[0079]

[0080] In addition, the amorphous and crystalline phases of the tungsten oxide powders involved in the examples and comparative examples were 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.

[0081] Table 3

[0082]

[0083] Table 4

[0084]

[0085] As shown in the table, the amorphous phase is formed in the preferred state in the embodiments.

[0086] In addition, the chlorine content of the tungsten oxide powders involved in the examples and comparative examples was determined. The results were all in the range of 0% by mass or more and 0.1% by mass or less.

[0087] Next, an electrochromic element having an electrochromic layer using the tungsten oxide powder described in the examples and comparative examples was fabricated.

[0088] As an electrochromic element, it is specified to have Figure 4 The structure is shown. A transparent electrode 12 is disposed on a glass substrate 11 with a width of 8 mm. The transparent electrode 12 is specified as ITO. Tungsten oxide powder paste is coated on the transparent electrode 12 in such a way that the dried film thickness is 0.3 μm or more and 3 μm or less. It is dried at about 200°C, thereby forming an electrochromic layer 13. It is placed in a glass quartz test cell with an optical path length of 1 cm. The test cell is filled with an electrolyte. In addition, platinum is used as the counter electrode 14. The counter electrode 14 is placed in the test cell.

[0089] The volume resistivity of the electrochromic layer was determined. The method for determining the volume resistivity is as follows: 1g to 3g of sample powder was filled into a cylindrical unit with a diameter of 20mm. The four-terminal method was used, with the four terminals arranged in a straight line at 3mm intervals. Pressures of 4N, 8N, 12N, 16N, and 20N were applied to the sample using a hydraulic jack, and the volume resistivity was measured under these conditions. 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 into conductivity.

[0090] In addition, the response speed and coloring efficiency of the electrochromic element were studied.

[0091] Regarding the response speed (s), the speed (in seconds) from the tinted state to the transparent state was measured. Furthermore, the tinting efficiency (cm²) was also measured. 2 / C) is the amount of charge used to induce color change. It is used in the determination of response rate and coloring efficiency. Figure 4 The electrochromic device shown.

[0092] The response rate was measured using a UV-Vis absorbance spectrophotometer. The time it took for the transmittance of light with a wavelength of 600 nm to change from 20% to 70% was measured when a voltage of 1.2V was applied.

[0093] The method for determining coloring efficiency involves measuring absorbance using a UV-Vis spectrophotometer and calculating the coloring efficiency from the following formula: Coloring efficiency (cm²) 2 / C) = Change in absorbance at 600nm / [(Applied charge (C)) / Coating area of ​​WO3 (cm²) 2 Here, the unit of charge is coulomb (C). Furthermore, the thickness of the electrochromic layer is specified as 1 μm. The results are shown in Table 5.

[0094] Table 5

[0095]

[0096] As shown in the table, the volume resistivity of the electrochromic layer in the embodiment is 4 × 10⁻⁶. 5 Below Ωcm. It was found that the volume resistivity decreased as an electrochromic layer. Furthermore, it was confirmed that the response speed and coloring efficiency were improved. Therefore, it was found that the performance of the electrochromic element using the tungsten oxide powder described in the examples was improved.

[0097] The above embodiments of the present invention have been illustrated, but these embodiments are shown as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included within the scope of the invention as described in the claims and their equivalents. Furthermore, the above-described embodiments can also be implemented by combining with each other.

[0098] Symbol Explanation

[0099] 1: Tungsten oxide powder (primary particles)

[0100] 2: Crystalline phase

[0101] 3: Amorphous phase

[0102] 4: Secondary particles of tungsten oxide powder

[0103] 10: Test cell (electrochromic element)

[0104] 11: Glass substrate

[0105] 12: Transparent Electrode

[0106] 13: Electrochromic layer

[0107] 14: Opposite electrode

[0108] 15: Electrolyte

Claims

1. A tungsten oxide powder which is a tungsten oxide powder having secondary particles, wherein, The secondary particles of the tungsten oxide powder are formed by agglomeration of primary particles each having an average particle diameter of 100 nm or less, the primary particles have a crystalline phase and an amorphous phase mixed therein, and the amorphous phase is present in a range of 80% or more and 100% or less of the circumference of the crystalline phase, and the primary particles in the secondary particles are combined via the amorphous phase.

2. The tungsten oxide powder according to claim 1, wherein In the primary particles, the amorphous phase is present in 100% of the circumference of the crystalline phase.

3. The tungsten oxide powder according to any one of claims 1 to 2, wherein The maximum width of the amorphous phase of the primary particles is 0.1 nm or more and 5 nm or less.

4. The tungsten oxide powder according to any one of claims 1 to 2, wherein In the primary particles, when the area of the crystalline phase is set as Al and the area of the amorphous phase is set as Bl, the ratio of the area Bl of the amorphous phase to the area Al of the crystalline phase is in a range of 0.2 or more and 0.8 or less.

5. The tungsten oxide powder according to claim 3, wherein In the primary particles, when the area of the crystalline phase is set as Al and the area of the amorphous phase is set as Bl, the ratio of the area Bl of the amorphous phase to the area Al of the crystalline phase is in a range of 0.2 or more and 0.8 or less.

6. The tungsten oxide powder according to any one of claims 1 to 2, wherein The average particle diameter is in a range of 5 nm or more and 20 nm or less.

7. The tungsten oxide powder according to claim 5, wherein The average particle diameter is in a range of 5 nm or more and 20 nm or less.

8. The tungsten oxide powder according to any one of claims 1 to 2, wherein The tungsten oxide powder contains any one or two or more of potassium, sodium, lithium, and magnesium in a range of 0.01 mol% or more and 50 mol% or less.

9. The tungsten oxide powder according to any one of claims 1 to 2, wherein, For the secondary particles, when the area of the crystalline phase is set as A2 and the area of the amorphous phase is set as B2, the ratio of the area B2 of the amorphous phase to the area A2 of the crystalline phase is in a range of 0.2 or more and 0.8 or less.

10. An electrochromic element using an electrochromic layer provided with the tungsten oxide powder according to any one of claims 1 to 9.

11. The electrochromic element according to claim 10, wherein The volume resistivity of the electrochromic layer is 1 x 10 5 Ωcm or less.

12. The tungsten oxide powder according to any one of claims 1 to 2, which is used for an electrochromic element.

13. The tungsten oxide powder according to claim 7, which is used for an electrochromic element.

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