Electrochromic device based on graphene counter electrode and preparation method thereof

Abstract

The invention discloses an electrochromic device based on a graphene counter electrode and a preparation method of the electrochromic device. The electrochromic device comprises a first substrate, a first electrochromic layer, a counter electrode, a second electrochromic layer and a second substrate from top to bottom in sequence, the first electrochromic layer and the second electrochromic layer are connected with the counter electrode through adhesive layers; each of the first substrate and the second substrate comprises a transparent substrate and a transparent conducting layer covering the surface of the transparent substrate; the middle part of the adhesive layer is electrolyte; the counter electrode layer is a graphene film. According to the invention, the graphene film is adopted as the counter electrode layer of the electrochromic device, so that the problem of unstable device performance of a counter electrode adopted in a traditional electrochromic device is solved, the stability of the electrochromic layer is ensured, and the performance of the electrochromic device is improved.

Description

Technical Field

[0001] This invention relates to the field of electrochromic device technology, and in particular to an electrochromic device based on a graphene counter electrode and its preparation method. Background Technology

[0002] The building sector accounts for approximately 40% of global carbon emissions. Developing efficient building energy-saving technologies, especially intelligent control technologies that can dynamically regulate solar radiation heat gain, plays a crucial supporting role in reducing building operating energy consumption. Buildings using electrochromic smart windows can reduce air conditioning energy consumption by 19%-26% annually and save 48%-67% on lighting energy. Electrochromism refers to the phenomenon where the optical properties of a material (reflectivity, transmittance, absorptivity, etc.) undergo stable and reversible changes under the influence of an applied electric field, manifesting as reversible changes in color or transparency. Electrochromic devices consist of a transparent electrode layer, an electrochromic layer, an ion-conducting (electrolyte) layer, a counter electrode (ion storage layer), and another transparent electrode layer. The counter electrode is the key functional layer in electrochromic devices for achieving charge and ion balance. It provides a site for redox reactions opposite to those of the working electrode (electrochromic layer) to achieve overall charge balance in the device, and simultaneously achieves ion balance through ion storage / release processes, thereby ensuring the device's electroneutrality during the electrochromic cycle and forming a complete electrochemical circuit. Therefore, the selection of electrode materials has a critical impact on the core performance of the device (such as response speed, coloring efficiency, cycle life, and optical contrast).

[0003] Currently, existing small-area electrochromic devices (approximately 1 cm²) exhibit optical contrast exceeding 40% and response times reduced to a few seconds, meeting the testing requirements of laboratory prototype devices. However, considering the needs of current electrochromic devices in practical production applications, further performance improvements are still necessary. Traditional electrochromic devices often use ITO glass as the counter electrode material (CN120742591A An electrochromic device based on ammonium ion aqueous electrolyte and its preparation method and application). However, because ITO glass cannot effectively accommodate ions in the device, the charge cannot be effectively balanced. Complementary coloring electrodes usually use electrochromic materials with complementary color-changing ranges (CN120972430A A long-life electrochromic smart window and its preparation method). The light modulation performance is enhanced by synchronously controlling the color change through dual color-changing electrodes, but the charge matching stability between the two is poor. Metal counter electrodes use the redox reaction of metal to provide charge compensation for the device (CN118818858A An electrochromic glass device and its preparation method). However, while continuously consuming the counter electrode, redox reactions of evolved gases are prone to occur. These factors greatly affect the performance and lifespan of electrochromic devices. In recent years, graphene thin film counter electrodes (CN113253534A: an electrochromic device and its manufacturing method) have attracted widespread attention due to their excellent properties such as high conductivity and ultra-large specific surface area, and are considered a potential solution to overcome the aforementioned defects. However, most current mainstream graphene-based counter electrode designs adopt the design of attaching graphene to the surface of ITO glass, which is still limited by the substrate performance. It is difficult to get rid of the limitations of the substrate on ion transport and charge balance, and cannot give full play to the intrinsic material advantages of graphene. Attaching graphene has certain requirements for adhesion ability and thickness, so the thickness is relatively thin and the conductivity is relatively low, which in turn restricts the further improvement of device response speed and cycle life. Summary of the Invention

[0004] The purpose of this invention is to provide an electrochromic device based on a graphene counter electrode and its preparation method. By using a graphene film as the counter electrode, the intrinsic material advantages of graphene are fully utilized to improve the response speed and cycle life of the electrochromic device.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an electrochromic device based on a graphene counter electrode, comprising, from top to bottom, a first substrate, a first electrochromic layer, a counter electrode, a second electrochromic layer, and a second substrate; The first and second electrochromic layers are connected to the counter electrode through an adhesive layer; Both the first and second substrates include a transparent substrate and a transparent conductive layer covering the surface of the transparent substrate; The middle portion of the adhesive layer is an electrolyte; The counter electrode layer is a graphene film.

[0006] In some possible implementations, the graphene film has a thickness of 70-100 μm.

[0007] In some possible implementations, the substrate comprises either glass or a polymer film coated with a transparent conductive layer.

[0008] In some possible embodiments, the electrolyte is a polycarbonate-based cationic electrolyte; the cation includes Li. + Na + K + Mg 2+ Al 3+ The electrolyte comprises at least one of perchlorate, hexafluorophosphate, and tetrafluoroborate.

[0009] Secondly, the present invention also provides a method for preparing the electrochromic device based on graphene counter electrode as described in the first aspect, comprising the following steps: The first substrate and the second substrate are processed by ultrasonic cleaning with acetone, ethanol and deionized water in sequence, drying with inert gas flow and irradiation with ultraviolet light. A first electrochromic layer and a second electrochromic layer are prepared. An electrochromic material is formed on the transparent conductive layer surface of the first substrate and the second substrate to form the first electrochromic layer and the second electrochromic layer, thereby obtaining a first substrate covered with the first electrochromic layer and a second substrate covered with the second electrochromic layer. A counter electrode layer is prepared by selecting a graphene film; An adhesive layer is prepared by attaching adhesive to the edges of the surfaces of the first substrate covered with a first electrochromic layer and the second substrate covered with a second electrochromic layer to form the adhesive layer; a cavity is provided in the middle of the adhesive layer; The first substrate covered with the first electrochromic layer, the adhesive layer, the counter electrode, the adhesive layer, and the second substrate covered with the second electrochromic layer are sequentially overlapped. Electrolyte is extracted and injected into the cavity through a tube to obtain a molded device; The molded device is encapsulated to obtain an electrochromic device based on a graphene counter electrode.

[0010] In some possible implementations, the ultrasonic cleaning time is set to 15–20 min.

[0011] In some possible implementations, the electrochromic material is deposited into an electrochromic layer by one of the following methods: electrodeposition, magnetron sputtering, hydrothermal method, sol-gel method, spin coating, and spray coating; the electrochromic material is one of Prussian blue and Prussian blue analogues, vanadium pentoxide, and tungsten trioxide.

[0012] In some possible implementations, the graphene film is a continuous, dense film with high electrical conductivity and high chemical stability.

[0013] In some possible implementations, the adhesive layer thickness is 1 mm.

[0014] In some possible implementations, the encapsulation specifically includes: encapsulating the molded device around an adhesive and curing it; the adhesive includes one of ultraviolet-curable adhesives and thermosetting optically transparent adhesives, and different types of adhesives need to be cured under different conditions.

[0015] This invention provides an electrochromic device based on a graphene counter electrode and its fabrication method. It solves the problem in existing technologies where graphene films need to be attached to a substrate for use, which is limited by the adhesion to the substrate and the charge transport capacity of the substrate material. By using a pure graphene film as the counter electrode to fabricate the electrochromic device, it features increased device cycle life, excellent electrode conductivity, fast electron transport, and fast response time. Compared with existing technologies, it has the following advantages: 1. This invention uses graphene film as the counter electrode of the electrochromic device, which overcomes the problems of easy oxidation-reduction reaction and charge mismatch that exist in traditional metal counter electrodes and conductive film electrodes, ensuring the stability of the color change of the electrochromic material and improving the quality and performance of the electrochromic device. 2. In the preparation method of the present invention, graphene film is directly used, eliminating the need for substrate material, and the preparation process is fast, which improves the preparation efficiency of electrochromic devices; 3. This invention uses commercially available graphene films and directly employs self-supporting graphene films as counter electrodes. These films exhibit stable performance and are easy to apply on a large scale, laying the foundation for the further commercial application of electrochromic devices. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an electrochromic device based on a graphene counter electrode provided by the present invention.

[0017] Wherein, 1-first substrate, 11-first transparent substrate, 12-first transparent conductive layer, 2-first electrochromic layer, 3-adhesive layer, 4-counter electrode layer, 5-second electrochromic layer, 6-second substrate, 61-second transparent conductive layer, 62-second transparent substrate. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. At the same time, in the description of the embodiments of this application, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0019] Example 1 This embodiment provides an electrochromic device based on a graphene counter electrode, comprising, from top to bottom, a first substrate, a first electrochromic layer, a counter electrode, a second electrochromic layer, and a second substrate.

[0020] The first and second electrochromic layers are connected to the counter electrode through an adhesive layer.

[0021] Both the first and second substrates include a transparent substrate and a transparent conductive layer covering the surface of the transparent substrate; the transparent substrate includes either glass or a polymer film covered with a transparent conductive layer, and is not limited to ITO glass.

[0022] The middle portion of the adhesive layer is an electrolyte; the electrolyte is a cationic electrolyte based on polycarbonate; the cations include Li. + Na + K + Mg 2+ Al 3+ At least one of the following, the electrolyte includes at least one of perchlorate, hexafluorophosphate, and tetrafluoroborate. In this embodiment, the cation is Na. + The electrolyte is a perchlorate electrolyte, specifically a sodium perchlorate electrolyte; the sodium perchlorate electrolyte is an organic electrolyte, wherein the organic solvent is polycarbonate. In other embodiments, the cation can be Li. + K + Mg 2+ Or Al 3+ At least one of them, the electrolyte can be hexafluorophosphate or tetrafluoroborate.

[0023] The counter electrode layer is a graphene film with a thickness of 100 μm. In other embodiments, the thickness can be 70 or 85 μm.

[0024] A method for fabricating an electrochromic device based on a graphene counter electrode includes the following steps: The first and second substrates are processed by sequentially ultrasonically cleaning them with acetone, ethanol, and deionized water for 15 minutes, followed by nitrogen gas drying and ultraviolet irradiation. In this embodiment, ITO glass is used as the material for both the first and second substrates, and their dimensions are 20 × 30 mm. In other embodiments, the ultrasonic cleaning time can be 20 or 18 minutes, the dimensions of the first and second substrates can be 30 × 40 or 40 × 50 mm, or other sizes, and gas drying can be performed using other inert gases.

[0025] A first electrochromic layer and a second electrochromic layer are prepared by depositing an electrochromic material on the transparent conductive layer surface of the first substrate and the second substrate to form the first electrochromic layer and the second electrochromic layer, resulting in a first substrate coated with the first electrochromic layer and a second substrate coated with the second electrochromic layer. The electrochromic material is Prussian blue, and the film is formed by a hydrothermal method. The thickness of the first electrochromic layer and the second electrochromic layer is 1.0 μm. In other embodiments, the electrochromic material may be a Prussian blue analogue, vanadium pentoxide, or tungsten trioxide, and the film may be formed by electrodeposition, magnetron sputtering, sol-gel method, spin coating, or spraying method.

[0026] The counter electrode layer was prepared by selecting a graphene film that had undergone graphitization at 3000 °C. The graphene film was a continuous and dense film with high conductivity and high chemical stability.

[0027] An adhesive layer is prepared by bonding a 1 mm thick adhesive layer to the edges of the surfaces of a first substrate covered with a first electrochromic layer and a second substrate covered with a second electrochromic layer, forming an adhesive layer; a cavity is provided in the middle of the adhesive layer. In this embodiment, the adhesive is 3M adhesive. In other embodiments, other adhesives can be selected, as long as they have a certain thickness and good adhesion. If the adhesive layer is too thin, there will be no space left for the electrolyte, which may lead to contact between the counter electrode and the working electrode, resulting in a short circuit.

[0028] A first substrate covered with a first electrochromic layer, an adhesive layer, a counter electrode, an adhesive layer, and a second substrate covered with a second electrochromic layer are sequentially stacked.

[0029] Electrolyte is extracted and injected into the cavity through a syringe to obtain a molded device.

[0030] An electrochromic device based on graphene counter electrodes is obtained by encapsulating the molded device around its perimeter with a UV-curable adhesive and then curing it with UV light. In other embodiments, a thermosetting optically transparent adhesive can be used for encapsulation and cured by heating.

[0031] Example 2 The only difference between this embodiment and Embodiment 1 is that the thickness of the first electrochromic layer and the second electrochromic layer is 0.6 μm.

[0032] Example 3 The only difference between this embodiment and Embodiment 1 is that the counter electrode layer is a graphene film with a thickness of 70 μm.

[0033] Example 4 The only difference between this embodiment and Embodiment 1 is that a graphene film that underwent graphitization at 1700 °C was selected. Example 5 The only difference between this embodiment and Embodiment 1 is that the electrolyte is sodium perchlorate gel electrolyte.

[0034] Comparative Example 1 The only difference between this comparative example and Example 1 is that the counter electrode layer is a zinc sheet with a thickness of 100 μm.

[0035] Comparative Example 2 The only difference between this comparative example and Example 1 is that the counter electrode layer is a copper sheet with a thickness of 100 μm.

[0036] Comparative Example 3 The only difference between this comparative example and Example 1 is that the counter electrode layer is made of carbon cloth with a thickness of 100 μm.

[0037] Comparative Example 4 The only difference between this comparative example and Example 1 is that the counter electrode layer is FTO glass with graphene attached by methods such as magnetron sputtering, electrodeposition, and spin coating, and the thickness is 100 μm.

[0038] Since other counter electrode materials are self-supporting, but graphene requires substrate support, the device constructed by attaching graphene differs somewhat from the construction method in Example 1. The electrochromic device of this comparative example includes, from top to bottom, a substrate, an electrochromic layer, a 3M adhesive layer, a counter electrode, and another substrate.

[0039] The following tests were performed on Examples 1-5 and Comparative Examples 1-4, and the results are shown in Table 1: Counter electrode conductivity: The resistivity of the counter electrode was measured using a four-probe method, and the conductivity was calculated based on the measured resistivity.

[0040] Response speed test: Apply a 3V step voltage to the device and measure the change in transmittance at a wavelength of 760nm. The time it takes for the transmittance change to reach 90% is the response time.

[0041] Cyclic life test: The device is subjected to constant voltage cycle test, with a coloring voltage of 3V and a fading voltage of -3V.

[0042] Table 1 Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. An electrochromic device based on a graphene counter electrode, characterized in that, include: From top to bottom, the components are: a first substrate, a first electrochromic layer, a counter electrode, a second electrochromic layer, and a second substrate. The first and second electrochromic layers are connected to the counter electrode through an adhesive layer; Both the first and second substrates include a transparent substrate and a transparent conductive layer covering the surface of the transparent substrate; The middle portion of the adhesive layer is an electrolyte; The counter electrode layer is a graphene film.

2. The electrochromic device based on a graphene counter electrode according to claim 1, characterized in that, The thickness of the graphene film is 70~100 μm.

3. The electrochromic device based on a graphene counter electrode according to claim 1, characterized in that, The substrate includes either glass or a polymer film coated with a transparent conductive layer.

4. The electrochromic device based on a graphene counter electrode according to claim 1, characterized in that, The electrolyte is a polycarbonate-based cationic electrolyte; the cation includes Li. + Na + K + Mg 2+ Al 3+ The electrolyte comprises at least one of perchlorate, hexafluorophosphate, and tetrafluoroborate.

5. A method for fabricating an electrochromic device based on a graphene counter electrode as described in any one of claims 1-4, comprising the following steps: The first substrate and the second substrate are processed by ultrasonic cleaning with acetone, ethanol and deionized water in sequence, drying with inert gas flow and irradiation with ultraviolet light. A first electrochromic layer and a second electrochromic layer are prepared. An electrochromic material is formed on the transparent conductive layer surface of the first substrate and the second substrate to form the first electrochromic layer and the second electrochromic layer, thereby obtaining a first substrate covered with the first electrochromic layer and a second substrate covered with the second electrochromic layer. A counter electrode layer is prepared by selecting a graphene film; An adhesive layer is prepared by attaching adhesive to the edges of the surfaces of the first substrate covered with a first electrochromic layer and the second substrate covered with a second electrochromic layer to form the adhesive layer; a cavity is provided in the middle of the adhesive layer; The first substrate covered with the first electrochromic layer, the adhesive layer, the counter electrode, the adhesive layer, and the second substrate covered with the second electrochromic layer are sequentially overlapped. Electrolyte is extracted and injected into the cavity through a tube to obtain a molded device; The molded device is encapsulated to obtain an electrochromic device based on a graphene counter electrode.

6. The preparation method according to claim 5, characterized in that, The ultrasonic cleaning time is set to 15-20 minutes.

7. The preparation method according to claim 5, characterized in that, The electrochromic material is deposited into an electrochromic layer by one of the following methods: electrodeposition, magnetron sputtering, hydrothermal method, sol-gel method, spin coating, and spraying method; the electrochromic material is one of Prussian blue and Prussian blue analogues, vanadium pentoxide, and tungsten trioxide.

8. The preparation method according to claim 5, characterized in that, The graphene film is a continuous and dense film with high conductivity and high chemical stability.

9. The preparation method according to claim 5, characterized in that, The thickness of the adhesive layer is 1 mm.

10. The preparation method according to claim 5, characterized in that, The encapsulation specifically includes: encapsulating the molded device around its perimeter with an adhesive and then curing it; the adhesive includes one of ultraviolet light curing adhesive and thermosetting optically transparent adhesive, and different types of adhesives need to be cured under different conditions.

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