Electrochromic smart windows and methods of making the same

Abstract

The application relates to the field of building intelligent windows, and provides an electrochromic intelligent window and a preparation method thereof. The electrochromic intelligent window comprises oppositely arranged first and second working electrodes and an ion conductive medium layer; the first and second working electrodes respectively comprise first and second electrochromic layers; the ion conductive medium layer comprises an electrolyte layer formed by a liquid electrolyte and a counter electrode, wherein the first and second electrochromic layers contain a polyacid, and the liquid electrolyte contains an aluminum salt and a zinc salt. The intelligent window has the characteristics of high contrast and high cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building smart windows, and in particular, provides an electrochromic smart window and a preparation method thereof. BACKGROUND

[0002] Electrochromism refers to the phenomenon that the optical properties of a material, such as transmittance, absorbance or reflectance, change reversibly and continuously under the action of an external electric field, through the electrochemical reaction of ions (such as H + , Li + , etc.) injected or removed from the material. This change is not limited to the visible light range observable by the naked eye, but also includes the ultraviolet light range, the infrared light range and most of the electromagnetic wave range. In recent years, electrochromic technology has attracted much attention due to its unique advantages: on the one hand, the color of the material can be conveniently adjusted by adjusting the voltage; on the other hand, the technology has non-volatility (memory effect) and low energy consumption characteristics; most importantly, its optical response has excellent reversibility and cycle stability. These characteristics make electrochromic technology have broad application prospects in the fields of smart display, automobile anti-dazzling rearview mirror, building energy-saving light-adjusting window (such as smart glass) and the like.

[0003] Traditional electrochromic smart windows generally have a symmetrical sandwich structure, including a first transparent substrate layer, a first transparent conductive layer, an electrochromic layer, an electrolyte layer, an ion storage layer, a second transparent conductive layer and a second transparent substrate layer which are sequentially stacked. The electrochromic layer is the core layer, and the electrochromic material therein undergoes redox reaction under voltage driving to produce reversible color change; the electrolyte layer is a pure ionic conductor, usually containing a solution of perchlorate (such as lithium perchlorate, sodium perchlorate, etc.) or a solid electrolyte material; the ion storage layer mainly balances the electric charge and stores the counter ions when the electrochromic material undergoes redox reaction. Generally, the electrolyte layer adopts a single perchlorate system, but in electrochromic applications, such electrolytes based on monovalent cations (such as , , ) still have significant limitations: for example, are corrosive, have limited resource reserves and high cost, and have large ionic radius, resulting in slow deintercalation kinetics in the material. In addition, the ion storage layer needs to have complementary optical properties (usually needs to remain colorless) to the electrochromic layer, so as to achieve effective charge compensation when the latter undergoes color change. This traditional multi-layer structure design containing multiple independent functional layers not only increases the complexity of the device, but also is the structural root cause of the limitations of the aforementioned electrolyte and ion storage layer, thereby limiting the further improvement of the performance of the electrochromic device and the application expansion.

[0004] Electrochromic smart windows typically rely on metal oxide materials (such as WO3) as the core color-changing layer. However, these materials face numerous challenges in practical applications: limited color change (mainly blue), slow response speed, insufficient cycling stability, and difficulty in simultaneously achieving high optical modulation rate and excellent electrochemical reversibility. Furthermore, as mentioned above, traditional structures require complex multi-layer stacking to realize device functionality, which introduces interface problems, limiting device performance and large-scale application.

[0005] Polyoxometalates (polyacids) are a class of inorganic clusters with defined metal-oxygen frameworks. Due to their excellent structural stability, abundant multi-electron reversible redox properties, tunable molecular composition, and high intrinsic electrochemical activity, they are considered promising electrochromic materials. Of particular note is the inherent pseudocapacitive property of polyacids, which gives them unique technological value in integrating electrochromic and energy storage functions. However, effectively applying polyacid-based materials to high-performance electrochromic devices still requires addressing the following key issues: 1) Poor film formation and interfacial compatibility: Pure polyacid materials are difficult to directly form uniform, dense, and strongly adherent functional films on commonly used substrates, posing a challenge to the long-term interfacial stability with adjacent functional layers; 2) Limited optical properties in the colored state: Most polyacids exhibit relatively limited hues in their reduced (colored) state, which is insufficient for achieving broad-band, tunable multicolor electrochromism; 3) Operating voltage and stability: Driving significant optical modulation of polyacids usually requires high operating voltages, which may be accompanied by the risk of electrolyte side reactions and potentially affect the long-term cycling stability of the device. Summary of the Invention

[0006] The purpose of this invention is to provide an electrochromic smart window and its preparation method. The electrochromic smart window of this invention is a polyacid-based electrochromic smart window, which features high contrast and high cycling stability.

[0007] In a first aspect, the present invention provides an electrochromic smart window, comprising: a first working electrode and a second working electrode disposed opposite to each other, and an ion-conducting dielectric layer located between the two.

[0008] The first working electrode comprises a first transparent substrate, a first transparent conductive layer, and a first electrochromic layer stacked sequentially;

[0009] The second working electrode comprises a second transparent substrate, a second transparent conductive layer, and a second electrochromic layer stacked sequentially;

[0010] The ion-conducting dielectric layer includes:

[0011] an electrolyte layer formed by a liquid electrolyte, the liquid electrolyte occupying a space between the first electrochromic layer and the second electrochromic layer and being in contact with the first electrochromic layer and the second electrochromic layer, respectively; and

[0012] a counter electrode composed of two metal sheets, the two metal sheets being arranged at opposite ends of the electrolyte layer and spaced apart from each other, each metal sheet having a main section embedded in the electrolyte layer and an extension section extending out of the electrolyte layer;

[0013] The first electrochromic layer and the second electrochromic layer each contain a polyacid, and the polyacid is a niobium-substituted heteropolytungstate; the liquid electrolyte further contains an aluminum salt and a zinc salt.

[0014] As some preferred embodiments, the thickness of the first electrochromic layer and the second electrochromic layer is independently 5-7 μm.

[0015] In a second aspect, the present application provides a method for preparing the electrochromic smart window of the first aspect of the present application, comprising the following steps:

[0016] (1) preparing a first working electrode and a second working electrode

[0017] providing a first transparent substrate having a first transparent conductive layer formed on the surface thereof and a second transparent substrate having a second transparent conductive layer formed on the surface thereof;

[0018] applying a precursor solution containing the polyacid to the surface of the first transparent conductive layer and the second transparent conductive layer, respectively, to form a first electrochromic layer and a second electrochromic layer;

[0019] (2) constructing an ion conductive medium layer

[0020] applying the liquid electrolyte to the surface of the first electrochromic layer and the second electrochromic layer, respectively, to form an electrolyte layer between the first electrochromic layer and the second electrochromic layer;

[0021] embedding a metal sheet at opposite ends of the electrolyte layer, respectively, so that each metal sheet has a main section and an extension section, to obtain a counter electrode.

[0022] The electrochromic smart window of the present application is a symmetrical structure design with an ion conductive medium layer as the center. The design uses aluminum salt and zinc salt as the main components in the electrolyte layer, which can improve the ion conductivity and improve the optical modulation amplitude of the smart window. The electrochromic layer in contact with the electrolyte layer is a heteropolytungstate with niobium substitution as the color-changing material, which can effectively improve the coloring efficiency and optical response speed, and significantly widen the optical modulation range to the ultraviolet-visible-near infrared wide band (350~1300nm). Moreover, in the smart window of the present application, the counter electrode (two metal sheets) is located in the middle region of the device (i.e., the smart window), and the working electrodes are distributed on both sides. This layout optimizes the charge transport path, and the aluminum salt and zinc salt as the electrolyte and the heteropolytungstate with niobium substitution synergistically improve the charge storage capacity and ion transport dynamics of the device. This combination not only enhances the optical modulation capability (high contrast, wide spectral range), but also realizes the synergistic effect of electrochromism and energy storage function, giving the device high cycle stability.

[0023] In addition, compared with the traditional tungsten trioxide smart window (which relies on complementary electrodes and magnetron sputtering process) and polymer-based smart window (which has poor cycle stability), the present application simplifies the device architecture (without complex complementary electrodes and sputtering equipment) based on maintaining the color-changing performance of the device, significantly improves the durability relying on the synergistic effect of the materials, and has wide spectral response and energy storage function, providing a new direction for the development of smart window and energy integrated devices.

[0024] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0026] Figure 1 A physical image of the polyacid {P2W 15 Nb3} prepared in Preparation Example 1;

[0027] Figure 2 A thermogravimetric curve of the polyacid {P2W 15 Nb3} prepared in Preparation Example 1;

[0028] Figure 3 An electrochromic structure diagram of the electrochromic smart window according to an embodiment of the present application;

[0029] Figure 4 A structure schematic diagram of the ion conductive medium layer and a schematic diagram of the counter electrode connection conductive connection according to an embodiment of the present application;

[0030] Figure 5 A schematic diagram showing the reversible switching between colorless and blue for the electrochromic smart window according to an embodiment of the present application;

[0031] Figure 6 A real photo showing the reversible switching between colorless and blue for the electrochromic smart window of Example 1;

[0032] Figure 7 A scanning electron microscope image showing the morphology of the electrochromic layer in the electrochromic smart window of Example 1;

[0033] Figure 8 An electrochemical impedance spectrogram of the electrochromic layer of Example 1;

[0034] Figure 9 A cyclic voltammetry spectrogram of the electrochromic smart window of Example 1;

[0035] Figure 10 A galvanostatic charge-discharge spectrogram of the electrochromic smart window of Example 1;

[0036] Figure 11 A transmittance spectrogram showing the change of the transmittance of the electrochromic smart window of Example 1 when reversibly switching between colorless and blue;

[0037] Figure 12 A response time spectrogram showing the reversible switching between colorless and blue for the electrochromic smart window of Example 1;

[0038] Figure 13 A transmittance spectrogram showing the change of the transmittance of the electrochromic smart window of Example 1 when reversibly switching between colorless and blue for 50000 seconds.

[0039] BRIEF DESCRIPTION OF DRAWINGS

[0040] 100: electrochromic smart window; 10: first working electrode; 20: second working electrode; 30: ion conductive medium layer; 11: first transparent substrate; 12: first transparent conductive layer; 13: first electrochromic layer; 21: second transparent substrate; 22: second transparent conductive layer; 23: second electrochromic layer; 31: electrolyte layer; 32: counter electrode; 32a: main section; 32b: extension section; 40: conductive connector. DETAILED DESCRIPTION

[0041] Embodiments of the present application are described in detail below. The embodiments described below are examples for explaining the present application and should not be construed as limiting the present application.

[0042] The "scope" disclosed in this invention is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0043] In this invention, the terms "first", "second" and "I" and "II" are used only for distinguishing and descriptive purposes, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0044] In this invention, unless otherwise specified, all embodiments and optional embodiments of this invention can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this invention.

[0045] This invention provides an electrochromic smart window. According to some embodiments, such as... Figure 3 and Figure 4 As shown, the electrochromic smart window 100 includes a first working electrode 10 and a second working electrode 20 disposed opposite to each other, and an ion-conducting dielectric layer 30 located between the two, wherein,

[0046] The first working electrode 10 includes a first transparent substrate 11, a first transparent conductive layer 12 and a first electrochromic layer 13 stacked in sequence, and the second working electrode 20 includes a second transparent substrate 21, a second transparent conductive layer 22 and a second electrochromic layer 23 stacked in sequence.

[0047] The ion-conducting dielectric layer 30 includes:

[0048] The electrolyte layer 31 is formed of liquid electrolyte, which occupies the space between the first electrochromic layer 13 and the second electrochromic layer 23, and is in contact with the first electrochromic layer 13 and the second electrochromic layer 23 respectively.

[0049] The electrode 32 consists of two metal sheets, which are respectively disposed at opposite ends of the electrolyte layer 31 and spaced apart from each other. Each metal sheet has a main section 32a and an extension section 32b. The main section 32a is embedded inside the electrolyte layer 31, and the extension section 32b extends out of the electrolyte layer 31.

[0050] In the present application, both the first electrochromic layer and the second electrochromic layer comprise a polyacid, and the polyacid is a niobium-substituted heteropolytungstate, which can be a Dawson-type tungstophosphate tri-substituted with niobium, for example. Preferably, the niobium-substituted heteropolytungstate is K8H[P2W 15 (N b O2)3O 59 ]·12H2O.

[0051] Preferably, the first electrochromic layer and the second electrochromic layer further comprise TiO2 distributed therein. The TiO2 is usually used as a carrier to improve the film-forming property of the polyacid: on the one hand, TiO2 is a fine particle (usually microspheres) which, when distributed in the electrochromic layer, can increase the specific surface area of the electrochromic layer; on the other hand, the surface of the TiO2 particle is rich in hydroxyl groups which can form hydrogen bonding with the oxygen atoms or the proton donors in the polyacid molecules, so that the polyacid can be effectively fixed on the surface of the TiO2, realizing the stable construction of the polyacid thin film (i.e. the electrochromic layer).

[0052] Preferably, the thickness of the first electrochromic layer and the second electrochromic layer is independently 5-7 μm, for example 5 μm, 5.5 μm, 6 μm, 7 μm, etc. In this case, on the one hand, the comprehensive performance of the smart window can be avoided due to the too thin electrochromic layer; on the other hand, the possibility of the film layer falling off due to the too thick electrochromic layer can also be reduced. More preferably, the thickness of the first electrochromic layer and the second electrochromic layer is the same.

[0053] In the present application, the electrolyte layer is formed by a liquid electrolyte, and the liquid electrolyte comprises an aluminum salt and a zinc salt. Compared with the traditional alkali metal salt electrolyte (such as lithium salt, sodium salt), the aluminum salt and the zinc salt also have the characteristics of low cost and high safety. Preferably, the aluminum salt is aluminum perchlorate (Al(ClO4)3), and the zinc salt is zinc perchlorate (Zn(ClO4)2).

[0054] As a preferred embodiment, the molar ratio of the aluminum salt and the zinc salt is 1:(0.8-1.2), for example 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2. This ratio helps to reduce the possibility of reducing the service life of the smart window due to the relative excess of the aluminum salt, while minimizing the risk of prolonging the response time due to the excessive zinc salt.

[0055] In the present application, the liquid electrolyte can further comprise a solvent, which is preferably an organic solvent. The use of an organic solvent can reduce the hydrolysis of the polyacid, prevent the precipitation of Al 3+ and Zn 2+ , and play a role in protecting the conductive layer, thereby improving the cycle stability of the device. More preferably, the organic solvent is selected from at least one of propylene carbonate (PC), ethylene carbonate (EC), acetonitrile (ACN).

[0056] In some embodiments, the total concentration of aluminum and zinc salts in the liquid electrolyte is 0.8-1.5 mol / L, such as 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0057] In some embodiments, the thickness of the ionically conductive medium layer (i.e., the thickness of the electrolyte layer) is 1-2.5 mm, such as 1 mm, 1.2 mm, 1.4 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, etc.

[0058] In the present application, the counter electrode comprises two metal sheets, which are not particularly limited in the present application and can be selected according to the prior art of smart windows, such as various conductive metal foils, specific examples of which include but are not limited to zinc foil, copper foil, nickel foil. According to some embodiments, the thickness of the metal sheet is 20-60 μm, such as 20 μm, 30 μm, 40 μm, 50 μm, 55 μm, 60 μm, etc.

[0059] In the present application, the two metal sheets can be arranged in parallel with the first electrochromic layer and the second electrochromic layer (the angle between the metal sheet and one of the electrochromic layers is ≤5°). In addition, the metal sheet can be inserted into the electrolyte layer with its long axis perpendicular to the embedding path (the direction from the end to the middle of the electrolyte layer), or it can be inserted into the electrolyte layer with its short axis perpendicular to the embedding path. Among them, the main section is defined as the effective area where the metal sheet is in macroscopic contact with the liquid electrolyte, and the exposed area which is not in contact with the liquid electrolyte is uniformly referred to as the extension section, which is used to connect the external wire. The extension section can also be a single block area or a multi-block area, as the metal sheet is conductive as a whole, and only needs to select any extension area to connect. According to some embodiments, as shown in FIG. 2A, A and B are the cross-sectional view and top view of the ionically conductive medium layer, respectively, and C shows two sections of a single metal sheet, as shown in FIGS. 2A-C, part of the metal sheet is embedded in the electrolyte layer 31, the embedded part is the main section 32a, and the area exposed outside the electrolyte layer 31 is the extension section 32b. Generally, the total area of the main sections of the two metal sheets can be 20%-50% of the light-emitting area of the smart window. Figure 4

[0060] The transparent substrate is not particularly limited in the present application and can be selected according to the prior art of smart windows. According to some embodiments, the first transparent substrate and the second transparent substrate are both glass. Preferably, the materials of the first transparent conductive layer and the second transparent conductive layer are independently selected from at least one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), and antimony-doped tin oxide (ATO).​

[0061] In some embodiments, the thickness of the first and second transparent conductive layers can be 0.1-1 μm, for example, 0.1 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.7 μm, 0.8 μm, etc.

[0062] In some embodiments, the ratio of the thicknesses of the first transparent substrate, the first transparent conductive layer and the first electrochromic layer 13 is (200-400):(0.02-0.1):1.

[0063] In some embodiments, the ratio of the thicknesses of the second transparent substrate, the second transparent conductive layer and the second electrochromic layer is (200-400):(0.02-0.1):1.

[0064] As a preferred embodiment, the first working electrode and the second working electrode are the same, i.e., the compositions and thicknesses of the layers are the same, respectively.

[0065] In the smart window structure of the present application, a common counter electrode is provided between the two oppositely arranged working electrodes, forming a parallel structure of a double electrochromic loop and realizing the synergistic color change of the two electrochromic layers. Referring to Figure 5 As shown, the working mode can be: applying a voltage to drive the electrolyte ions to insert into the electrochromic layer, causing coloring; after reversing the voltage polarity, the ions are extracted, and the electrochromic layer returns to the transparent state, thereby realizing reversible optical regulation. In addition, since the two electrochromic layers can realize synchronous response under the same bias, the superposition effect can obtain more optimized overall optical modulation effect.

[0066] The present application also provides a preparation method of the electrochromic smart window, comprising the following steps:

[0067] (1) preparing a first working electrode and a second working electrode

[0068] providing a first transparent substrate with a first transparent conductive layer formed on the surface and a second transparent substrate with a second transparent conductive layer formed on the surface;

[0069] applying a precursor solution containing the polyacid to the surface of the first and second transparent conductive layers, respectively, to form a first electrochromic layer and a second electrochromic layer;

[0070] (2) constructing an ion conductive medium layer

[0071] applying a liquid electrolyte to the surface of the first and second electrochromic layers, respectively, to form an electrolyte layer between the first and second electrochromic layers;

[0072] The two metal sheets are respectively embedded at opposite ends of the electrolyte layer, so that each metal sheet has a main section and an extension section, and an opposite electrode is obtained.

[0073] In step (1), the precursor solution can be applied on the conductive layer by electrochemical deposition or coating method to form the electrochromic layer. When electrochemical deposition is used, the precursor solution is an electrodeposition solution; when coating method is used, the precursor solution is a coating solution. The specific formulation of the electrodeposition solution and the coating solution is determined according to the respective process requirements, and the conventional components thereof are well known in the art.

[0074] As a preferred embodiment, the first electrochromic layer and the second electrochromic layer are prepared by chemical electrodeposition. In this case, the precursor solution is an electrodeposition solution containing the polyacid; wherein the electrodeposition solution further contains water and an electrolyte salt. The electrolyte salt can be selected from at least one of lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4). In the electrodeposition solution, the concentration of the polyacid can be 0.5-2 mmol / L, for example, 0.5 mmol / L, 1 mmol / L, 1.2 mmol / L, 1.5 mmol / L, etc., and the concentration of the electrolyte salt can be 0.05-2 mol / L, for example, 0.05 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.

[0075] Further, step (1) includes the following procedure:

[0076] First, a TiO2 matrix layer is formed on the surface of the first transparent conductive layer and the second transparent conductive layer, respectively, to obtain a deposition working electrode;

[0077] Then, each deposition working electrode is placed in a precursor solution containing a polyacid (i.e., an electrodeposition solution), a voltage of -1 V to 0.3 V is applied, and the potential is cycled at a scan rate of 0.05-0.1 V / s for 10-50 cycles to form a polyacid on the TiO2 matrix layer, thereby obtaining a first electrochromic layer and a second electrochromic layer.

[0078] In which, the TiO2 slurry can be coated on the conductive layer by doctor blade method or screen printing method to form a wet film, and sintered at a high temperature of 450-550°C for 0.5-1.5 h, until the slurry is solidified to form a transparent thin film (i.e., TiO2 matrix layer). In which, the solid content of the TiO2 slurry can be 15%-25%, and the thickness of the wet film can be 20-40 μm. The TiO2 slurry can be obtained by commercial purchase, for example, the product of Dyesol Company, with the trade name of 18NR-T. The deposition is prepared on an electrochemical workstation by cyclic voltammetry, and the reference electrode can be Ag / AgCl electrode, and the deposition counter electrode can be platinum sheet.

[0079] In step (2), the liquid electrolyte can be applied by perfusion or coating to form the electrolyte layer between the first electrochromic layer and the second electrochromic layer, and preferably the coating method is used to form the electrolyte layer.

[0080] Preferably, step (2) comprises the following process:

[0081] The liquid electrolyte is uniformly coated on the surface of the electrochromic layer of each working electrode to form an electrolyte coating. The two sets of working electrodes with electrolyte coatings are placed face to face to make the coatings opposite and in contact to obtain an electrolyte layer. Two conductive metal foils are taken as counter electrodes, the metal foils are partially inserted into the electrolyte layer from the end, and the electrolyte layer is ensured to be continuous and through (i.e. the two metal foils are arranged at intervals), thereby obtaining an ion conductive medium layer.

[0082] In some embodiments, the preparation method of the present application further comprises:

[0083] (3) Formation of external electrodes and device packaging

[0084] The first conductive connector and the second conductive connector are respectively arranged at the edge regions of the first working electrode and the second working electrode, and the third conductive connector is arranged at the extended section of the metal sheet, and finally the entire smart window is packaged with a packaging material (such as epoxy resin) to obtain an electrochromic smart window with a symmetrical electrode structure. The conductive connectors described above can include copper foil conductive adhesive tape.

[0085] The following describes the embodiments of the present application. The embodiments described below are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application.

[0086] Preparation Example 1

[0087] This preparation example is used to illustrate the polyacid K8H[P2W 15 (N b O2)3O 59 ]·12H2O and the preparation method thereof.

[0088] 1) Preparation of K6[α-P2W 18 O 62 ]·14H2O (abbreviated as "{P2W 18}")

[0089] A solution of 100 g Na2WO4.2H2O in water was heated to boiling, and 150 mL of phosphoric acid solution (concentration of 85 wt%) was added dropwise under stirring. After the addition was completed, the resulting yellow-green solution was continuously stirred and refluxed for 12 h. After the reaction was completed, the resulting reaction solution was cooled to room temperature, and 100 g KCl was added, resulting in a large amount of precipitate in the solution. The precipitate was collected by filtration and redissolved in hot water, and the solution was left to stand at 5 °C for 12 h. After crystallization, the product was dried to obtain a crystalline product.

[0090] A solution of 70 g of the above crystalline product in 250 mL of hot water (water temperature of 80 °C) was prepared, and bromine water (0.05 mL) was added under stirring. The solution was then cooled to room temperature. Under stirring, 10 wt% of an aqueous KHCO3 solution was continuously added dropwise to the solution. It was observed that a precipitate was first formed in the solution, and the precipitate dissolved as continuous stirring was applied, and the solution turned colorless and transparent. To the resulting mixture, 110 mL of hydrochloric acid (concentration of 6 mol / L) was added to obtain a light yellow solution. The solution was boiled for 1 h and filtered. After filtration, 100 g of KCl was added to the solution and stirred until completely dissolved. The resulting mixed solution was left to stand at 5 °C for 12 h, and yellow crystals were formed. After drying, the sample {P2W 18} was collected.

[0091] (2) K 10 [α-P2W 17 O 61 ]·20H2O (hereinafter referred to as “{P2W 17}”)

[0092] A solution of 80 g of the sample {P2W 18} in water was prepared, and 250 mL of a 0.2 mol / L aqueous KHCO3 solution was added. The solution was stirred for 1 h, and a white precipitate was formed to obtain a solid-liquid mixture. The solid-liquid mixture was suction filtered to recover the white precipitate. The white precipitate was redissolved in boiling water, and then cooled to room temperature. Snowflake-shaped recrystallization was observed, and the recrystallization product was collected by filtration and dried to obtain a sample {P2W 17}.

[0093] (3) Preparation of K7[P2W 17 (NbO2)O 61 ]·8H2O (hereinafter referred to as “{P2W 17 Nb”)

[0094] A solution of 0.25 g of K7HNb6O 19 ·13H2O in hydrogen peroxide (concentration of 30 wt%) was prepared, and the pH of the solution was adjusted to 1 by dropwise addition of 1 mol / L hydrochloric acid. Subsequently, 4.5 g of the sample {P2W 17} and continue stirring for 15 minutes, then add 20g KCl, a yellow solid precipitates, continue stirring for 10 minutes, filter the yellow precipitate and recrystallize it in water to obtain sample {P2W 17 Nb}.

[0095] (4) Na 12 [P2W 15 O 56 ]·24H2O (abbreviated as "{P2W) 15 Preparation of}”

[0096] 38.5g sample {P2W 18 Dissolve the substance in water, and add 35g of NaClO4·H2O. Stir the resulting system vigorously for 20 minutes to obtain a solution. Continue stirring the solution in an ice-water bath for 3 hours, and then filter. Add 100mL of 1mol / L Na2CO3 aqueous solution to the filtrate, and a white precipitate forms. Filter, wash, and dry the precipitate to obtain the product {P2W}. 15}

[0097] (5) K8H[P2W 15 (NbO2)3O 59 ]·12H2O (abbreviated as "{P2W) 15 Preparation of Nb3}

[0098] 0.8g K7HNb6O 19 • 13H2O was dissolved in hydrogen peroxide (30wt%), and the pH of the solution system was adjusted to 1 by adding 1 mol / L hydrochloric acid to obtain solution I.

[0099] 5g sample {P2W 15 Dissolve it in 50 mL of 1 mol / L LiCl aqueous solution, and add 1 mL of 1 mol / L hydrochloric acid to obtain solution II.

[0100] Solution I and solution II were mixed and stirred for 20 minutes. Then, 20 g of KCl was added, and a yellow precipitate began to form. Stirring continued for another 10 minutes, and the resulting yellow precipitate was collected by filtration. The precipitate was recrystallized in hot water to obtain the target product {P2W}. 15 Nb3}.

[0101] like Figure 1 As shown, the {P2W} obtained in this preparation example 15 Nb3 is a yellow solid. Figure 2 It can be seen that {P2W} in this preparation example 15 Nb3 loses only 5% of its mass (water of crystallization) at 600℃, which indicates that it has excellent thermal stability and is suitable for use in electrochromic devices.

[0102] The following examples are used to illustrate the electrochromic smart window and the preparation method thereof of the present application. Figure 1

[0103] Example 1

[0104] S1: Preparation of two groups of working electrodes using the same process

[0105] FTO conductive glass (specification 3.5 cm x 3.5 cm) was sequentially cleaned in water, acetone, and ethanol for 20 minutes each, and then dried with high-pressure nitrogen.

[0106] TiO2 slurry was uniformly coated on the FTO conductive layer of the conductive glass using a screen printing method, with the wet film thickness controlled at 30 μm (the mesh number of the screen printing screen used was 200 mesh), and then placed in a muffle furnace for sintering at 500°C for 1 h, followed by natural cooling to room temperature, to form a transparent TiO2 film, obtaining the pretreated FTO glass.

[0107] The pretreated FTO glass was used as the deposition working electrode, with an Ag / AgCl electrode as the reference electrode and a platinum sheet electrode as the counter electrode, and the three electrodes were placed in a deposition solution ({P2W 15 Nb3} was 1 mmol / L and LiClO4 was 0.1 mol / L in water). Using cyclic voltammetry, the P2W 15 Nb3 film was deposited on the FTO surface in a voltage range of -1.0 V ~ 0.3 V (vs. Ag / AgCl) at a scan rate of 0.1 V / s for 30 cycles, obtaining an electrochromic layer (EC layer).

[0108] After deposition, the surface of the electrochromic layer was cleaned with deionized water, and then dried at 150°C for 0.5 h, obtaining a working electrode with the structure of FTO glass / electrochromic layer.

[0109] S2: Construction of an electrochromic smart window

[0110] Al(ClO4)3 and Zn(ClO4)2 were dissolved in PC at a molar ratio of 1:1, stirred until completely dissolved, and prepared into a transparent liquid electrolyte with a concentration of 1 mol / L. The liquid electrolyte was dried in a forced air drying oven at 50°C for 6 h to remove water.

[0111] The liquid electrolyte was uniformly coated on the surface of the electrochromic layer of the two groups of working electrodes to form a coating. The two groups of working electrodes were then placed in parallel and opposite to each other, with the coating in contact, obtaining an electrolyte layer, and two pieces of zinc foil were used as the counter electrode, which was inserted into the electrolyte layer from the end relative to the EC layer (the main section area of each zinc foil was 0.5 cm x 2 cm).​

[0112] S3: Formation of external electrode and device packaging

[0113] The copper foil conductive tape is pasted on the edge of the FTO glass as a lead wire to lead out the positive and negative electrodes of the smart window, and the copper foil conductive tape is pasted on the extended section of the zinc foil. Finally, the entire smart window is packaged with epoxy resin to obtain an electrochromic smart window with a symmetrical electrode structure.

[0114] In the smart window of the present embodiment, the sheet resistance of the FTO glass is 13 Ω / square, the thickness of the glass substrate is 2.2 mm, the thickness of the FTO conductive layer is 400 nm, the electrochromic layer contains TiO2 microspheres and {P2W 15 Nb3} polyacid adsorbed thereon, and the layer thickness is 6 μm. The thickness of the electrolyte layer is 2 mm, which is a liquid electrolyte formed by Zn(ClO4)2 / Al(ClO4)3 and propylene carbonate, and the thickness of the zinc foil is 5 μm.

[0115] Figure 7 The SEM images of the electrochromic layer (EC layer) are shown, in which the left image is the cross-sectional morphology, the lower layer is the FTO glass, and the upper layer is the EC layer. The right image is the surface morphology of the EC layer. As can be seen from the right image, the EC layer is formed by a large number of fine particles, and the surface presents a loose and porous structure. Such morphology is beneficial to the penetration of the electrolyte and the exposure of active sites, and meets the structural requirements of an ideal electrochromic layer.

[0116] Figure 6 The reversible conversion of the smart window between colorless and blue is shown (the device is in a colored state at an operating condition of 1.4 V, and is in a bleached state at 1.8 V), in which the color developing area is 2 cm x 2 cm.

[0117] Comparative Example 1

[0118] The electrochromic smart window is prepared by the method of Reference Example 1, except that lithium perchlorate in an equimolar amount (the total of zinc salt and aluminum salt) is used as the electrolyte when preparing the liquid electrolyte.

[0119] Comparative Example 2

[0120] The electrochromic smart window is prepared by the method of Reference Example 1, except that the polyacid {P2W 15 Nb3} in the deposition solution is replaced by polyacid {P5W 30} (specifically K 12.5 Na 1.5 [NaP5W 30 O 110 ]·15H2O).

[0121] Comparative Example 3

[0122] The electrochromic smart window was prepared according to the method of Example 1, except that the thickness of each electrochromic layer was adjusted. Specifically, a TiO2 slurry was uniformly coated on the FTO conductive layer of the conductive glass by screen printing, with the wet film thickness controlled at 3 μm (the mesh number of the screen printing screen used was 420), and then the conductive glass was placed in a muffle furnace and sintered at 500°C for 0.5 h, followed by natural cooling to room temperature, to form a transparent TiO2 film, thereby obtaining the pretreated FTO glass. The pretreated FTO glass was used as the working electrode for deposition, and a polyacid was deposited thereon according to the electrochemical deposition method of Example 1 to obtain an electrochromic layer. The thickness of each EC layer was 500 nm.

[0123] Test Example

[0124] The test example was used to illustrate the electrochemical and optical properties of the electrochromic smart windows prepared in the above examples and comparative examples.

[0125] 1. Test method for coloring voltage and bleaching voltage

[0126] A step voltage was applied to the device by an electrochemical workstation (Shanghai Chenhua, model CHI 660E, same below), while the color change of the device was observed to determine the voltage required to cause complete coloring (colorless to blue) and the voltage required to cause complete bleaching (blue to colorless).

[0127] 2. Impedance test: A three-electrode system was used, with the FTO glass / electrochromic layer of Example 1 as the working electrode, a platinum sheet as the counter electrode, and Ag / AgCl (3 M KCl) as the reference electrode. A sinusoidal AC perturbation signal with an amplitude of 5 mV was applied at an open circuit potential, with a frequency scanning range of 0.01 Hz to 10 6 Hz, and the initial voltage was set to 0.05 V. The test data was analyzed by fitting the equivalent circuit model using ZView software.

[0128] 3. Transmittance test: The transmittance was tested using a UV-visible-near infrared spectrophotometer (Hitachi UH4150), with a scanning range of 350 to 1300 nm.

[0129] 4. Cycle stability test: The smart window was repeatedly switched between the coloring voltage and the bleaching voltage for multiple cycles, and the transmittance change was monitored. The contrast ratio retention rate at 650 nm after 250 cycles was calculated, and the contrast ratio retention rate D was calculated according to the following formula:

[0130] D = (T n / T0) x 100%, where T0 represents the initial contrast ratio, and T n represents the contrast ratio obtained after 250 cycles.

[0131] The results are shown in Table 1.

[0132] Table 1

[0133]

[0134] In combination with the data in Table 1, it can be seen that the smart window of Example 1 has a higher contrast ratio and high cycle stability, and also has a lower working voltage, compared with Comparative Examples 1-3.

[0135] Figure 8 P2W 15 The electrochemical impedance spectrum of the Nb3thin film in the liquid electrolyte (composition same as Example 1) environment. As can be seen from the figure, in the high frequency region, there is an incomplete semicircle feature associated with the surface charge transfer process of the material; in the low frequency region, a upward sloping line form associated with the diffusion behavior of ions inside the film is presented, which indicates that the film exhibits a small internal resistance characteristic during the redox reaction process, which can improve the color change speed and reduce the voltage required for color change.

[0136] Figure 9 The cyclic voltammogram of the smart window of Example 1, as can be seen from the figure, at a working voltage of -1.4V, it can be converted from colorless transparent state to blue opaque state, and at a voltage of 1.8V of opposite polarity, the smart window can be changed back to the original colorless transparent state.

[0137] Figure 10 The charge-discharge current curve of the smart window under 1mA charging current, as can be seen from the figure, the discharge time of the smart window is 204s, and after calculation, the area specific capacity of the device is 141mAh / m 2 , which indicates that the smart window not only can adjust the color change, but also has the function of energy storage.

[0138] Figure 11 The transmittance curve of the smart window in the visible light spectral range in the transparent state and the colored state is shown, compared with the traditional inorganic material (such as nickel oxide) electrochromic smart window, the spectral response range of the smart window is widened from 350~800nm to 350~1300nm, not only can it be optically modulated in the visible light band, but also can have spectral response in the near-infrared band, at 850nm, the bleached state transmittance of the smart window is 86%, the colored state transmittance is 6%, and the optical modulation value is 80%, at 1200nm, the bleached state transmittance of the smart window is 96%, the colored state transmittance is 17%, and the optical modulation value is 79%. It can be seen that the smart window realizes about 80% high optical modulation in the near-infrared band (850~120 nm), and has a high contrast ratio.

[0139] Figure 12The optical response time of the device is shown, and according to the figure, the bleaching time is 13 s and the coloring time is 7 s, and it can be seen that the optical response of the smart window is fast.

[0140] Figure 13 The cycle stability of the smart window at a wavelength of 650 nm is shown, and it is calculated that the initial optical modulation amplitude retention rate of the smart window can still be 84% after 50000 seconds (i.e., 250 cycles) of reversible conversion between colorless and blue.

[0141] In summary, the smart window of the present application significantly widens the spectral response range to the near-infrared band, making it have the functions of adjusting visible light transmittance and near-infrared heat, and being able to realize the dual regulation of visible light and near-infrared heat in the solar spectrum, and the smart window has low working voltage, high cycle stability and high contrast, and the device can be used not only for display but also for energy storage, making it show broad application prospects in the fields of building energy saving, smart buildings, and improving indoor comfort.

[0142] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An electrochromic smart window, characterized in that, include: A first working electrode and a second working electrode are arranged opposite to each other, and an ion-conducting dielectric layer is located between them; The first working electrode comprises a first transparent substrate, a first transparent conductive layer, and a first electrochromic layer stacked sequentially; The second working electrode comprises a second transparent substrate, a second transparent conductive layer, and a second electrochromic layer stacked sequentially; The ion-conducting dielectric layer includes: An electrolyte layer is formed of a liquid electrolyte, which occupies the space between the first electrochromic layer and the second electrochromic layer, and is in contact with the first electrochromic layer and the second electrochromic layer respectively. as well as The electrode consists of two metal plates, which are respectively disposed at opposite ends of the electrolyte layer and spaced apart from each other. Each metal plate has a main section and an extension section. The main section is embedded inside the electrolyte layer, and the extension section extends out of the electrolyte layer. Both the first electrochromic layer and the second electrochromic layer contain polyacids, and the polyacids are K8H[P2W] 15 (N b O2)3O 59 ·12H2O; the liquid electrolyte comprises aluminum salt and zinc salt; The thicknesses of the first electrochromic layer and the second electrochromic layer are independently 5~7 μm.

2. The electrochromic smart window according to claim 1, characterized in that, The first electrochromic layer and the second electrochromic layer further contain TiO2 distributed in the layers.

3. The electrochromic smart window according to claim 1, characterized in that, The aluminum salt is aluminum perchlorate, and the zinc salt is zinc perchlorate; and / or The molar ratio of the aluminum salt to the zinc salt is 1:(0.8~1.2).

4. The electrochromic smart window according to claim 1 or 3, characterized in that, The liquid electrolyte further comprises an organic solvent, wherein the organic solvent is selected from at least one of propylene carbonate, ethylene carbonate, and acetonitrile; In the liquid electrolyte, the total concentration of the aluminum salt and zinc salt is 0.8~1.5 mol / L.

5. The electrochromic smart window according to claim 1, characterized in that, Both the first transparent substrate and the second transparent substrate are glass; The materials of the first transparent conductive layer and the second transparent conductive layer are independently selected from at least one of indium tin oxide, fluorine-doped tin oxide, aluminum-doped zinc oxide, gallium-doped zinc oxide, and antimony-doped tin oxide.

6. The electrochromic smart window according to claim 1, characterized in that, The thickness ratio of the first transparent substrate, the first transparent conductive layer and the first electrochromic layer is (200~400):(0.02~0.1):1; the thickness ratio of the second transparent substrate, the second transparent conductive layer and the second electrochromic layer is (200~400):(0.02~0.1):

1.

7. The electrochromic smart window according to claim 1, characterized in that, The thickness ratio of the ion-conducting dielectric layer to the thickness of the first working electrode is (0.5~1.5):

1.

8. A method for preparing the electrochromic smart window according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Preparation of the first working electrode and the second working electrode A first transparent substrate having a first transparent conductive layer formed on its surface and a second transparent substrate having a second transparent conductive layer formed on its surface are provided; A precursor solution containing the polyacid is applied to the surface of the first transparent conductive layer and the second transparent conductive layer, respectively, to form a first electrochromic layer and a second electrochromic layer. (2) Constructing an ion-conducting dielectric layer The liquid electrolyte is applied to the surfaces of the first electrochromic layer and the second electrochromic layer respectively to form an electrolyte layer between the first electrochromic layer and the second electrochromic layer. A metal sheet is embedded at each of the opposite ends of the electrolyte layer, so that each metal sheet has a main section and an extension section, thus obtaining a counter electrode.

9. The preparation method according to claim 8, characterized in that, Step (1) includes the following process: First, TiO2 matrix layers are formed on the surfaces of the first transparent conductive layer and the second transparent conductive layer, respectively, to obtain a deposited working electrode; Then, each deposition electrode was placed in a precursor solution containing polyacids, and a voltage of -1V to 0.3V was applied. The electrode was then cyclically scanned for 10 to 50 cycles at a scan rate of 0.05 to 0.1V / s to deposit polyacids on the TiO2 matrix layer. The precursor solution containing polyacids further comprises water and an electrolyte salt, wherein the electrolyte salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate and lithium tetrafluoroborate. In the precursor solution containing polyacids, the concentration of polyacids is 0.5~2 mmol / L, and the concentration of electrolyte salts is 0.05~2 mol / L.

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