Graphene-based electrochromic composite film, preparation method and application thereof

Abstract

This invention belongs to the field of electrochromic materials technology, and relates to a graphene-based electrochromic composite film, its preparation method, and its application. The graphene-based electrochromic composite film comprises a substrate layer, a transparent conductive layer, a graphene-based interface coupling layer, a WO3-nanotube composite layer, a rare-earth-doped graphene layer, an electrolyte layer, a counter electrode layer, and a fluoropolymer coating layer, stacked sequentially. This invention constructs a high-performance electrochromic composite film through multilayer functional synergistic design, exhibiting good interfacial bonding and stability, a balance between light transmission and conductivity, excellent low-temperature performance, and good weather resistance.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic materials technology, and relates to a graphene-based electrochromic composite film, its preparation method and application. Background Technology

[0002] With the increasing demand for intelligent and comfortable vehicles, electrochromic panoramic sunroofs, as core components that can dynamically adjust light transmittance, have become standard equipment in high-end models. They achieve changes in light transmittance through the oxidation-reduction reaction of electrochromic materials such as WO3 under an electric field, which can reduce glare and lower in-vehicle energy consumption.

[0003] Traditional WO3 electrochromic canopies suffer from slow dimming speed and short cycle life. The industry has introduced highly conductive nanomaterials, such as graphene composite WO3, to improve performance. Graphene’s high specific surface area and high conductivity can shorten ion migration paths and accelerate electron transport, reducing dimming speed to 30-40 seconds.

[0004] In existing research, a transparent conductive layer, a graphene layer, a WO3 functional layer, an electrolyte layer, and a counter electrode layer are sequentially deposited on a glass substrate to form a symmetrical electrochromic structure. This utilizes the high conductivity of graphene to construct an electron transport network, shortening the electron transport distance in the WO3 layer; at the same time, the nanoscale structure of graphene increases the contact area between WO3 and the electrolyte, accelerating ion migration. However, the above technical solutions have the following problems: (1) Interface bonding defects: the surface energies of graphene and WO3 are large, there is no effective connecting layer, the interface is easy to peel off after composite, and the transmittance decreases by more than 30% after 10,000 cycles, resulting in insufficient stability; (2) Imbalance between transparency and conductivity: to ensure conductivity continuity, the amount of graphene used needs to be ≥0.3mg / cm 2 , resulting in visible light transmittance <80%, affecting the lighting inside the car; reducing the amount used will cause the conductive network to break, and the dimming speed will drop to more than 50s; (3) Low temperature ion migration bottleneck: the ion diffusion coefficient of WO3 lattice itself is low, and it will further decrease at low temperature, the ion insertion / extraction rate will decrease sharply, and the dimming time will be extended to more than 60s, which cannot be adapted to use in cold regions; (4) Poor weather resistance: long-term ultraviolet irradiation will cause graphene edge oxidation, and high temperature and high humidity environment will cause WO3 hydrolysis, with a service life of <2 years, which does not meet the requirement of more than 10 years of use for automobiles.

[0005] Therefore, there is an urgent need to develop an electrochromic film layer with good interfacial bonding and stability, light transmittance-conductivity balance, excellent low-temperature performance and good weather resistance to meet the high performance requirements of automotive sunroofs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a graphene-based electrochromic composite film, its preparation method, and its application. The high-performance electrochromic composite film is constructed through multi-layer functional synergistic design, featuring good interfacial bonding and stability, light transmittance-conductivity balance, excellent low-temperature performance, and good weather resistance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a graphene-based electrochromic composite film, wherein the graphene-based electrochromic composite film comprises a substrate layer, a transparent conductive layer, a graphene-based interface coupling layer, a WO3-nanotube composite layer, a rare earth-doped graphene layer, an electrolyte layer, a counter electrode layer, and a fluoropolymer coating layer, which are stacked sequentially.

[0009] This invention provides a graphene-based electrochromic composite film. It employs an interfacial covalent bond design in the graphene-based interface coupling layer, solving the problem of interfacial delamination between graphene and WO3. The charge compensation mechanism of rare-earth ion-doped graphene achieves a balance between high conductivity and high light transmittance at low dosages. The composite structure of nanotube-oriented ion channels and WO3 nanofilm accelerates low-temperature ion migration. The fluoropolymer coating enhances weather resistance.

[0010] Preferably, the substrate layer is made of ultra-white float glass.

[0011] Preferably, the thickness of the base layer is 2-3 mm, for example, it can be 2 mm, 2.2 mm, 2.5 mm, 2.8 mm or 3 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] Preferably, the light transmittance of the substrate layer is ≥92%, for example, it can be 92%, 95%, 96%, 98% or 99%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the transparent conductive layer comprises an ITO thin film.

[0014] Preferably, the thickness of the transparent conductive layer is 100-150nm, for example, it can be 100nm, 110nm, 120nm, 130nm or 150nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the sheet resistance of the transparent conductive layer is ≤10Ω / □, for example, it can be 10Ω / □, 8Ω / □, 5Ω / □, 3Ω / □ or 1Ω / □, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] It should be noted that "Ω / □" is the standard unit of sheet resistance, which is a parameter for measuring the conductivity of a film layer.

[0017] The sheet resistance of the transparent conductive layer is controlled to serve as the underlying conductive path.

[0018] Preferably, the thickness of the graphene-based interface coupling layer is 50-80 nm, for example, it can be 50 nm, 55 nm, 60 nm, 70 nm or 80 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the raw material of the graphene-based interface coupling layer includes graphene sheets, and also includes MXene nanosheets or hydroxylated graphene with hydroxyl functional groups on the surface, preferably MXene nanosheets with hydroxyl functional groups on the surface.

[0020] MXene nanosheets or hydroxylated graphene are covalently grafted onto the surface of graphene sheets. MXene nanosheets or hydroxylated graphene can act as a bridge to connect hydrophobic graphene and hydrophilic WO3, eliminating the risk of interfacial delamination.

[0021] Preferably, the graphene sheet has a thickness of 0.34 nm and a diameter of 5-10 μm.

[0022] The diameter of the graphene sheet is 5-10 μm, 5 μm, 6 μm, 8 μm, 9 μm or 10 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the MXene nanosheets include Ti3C2.

[0024] Preferably, the thickness of the MXene nanosheet is 5-10 nm, for example, it can be 5 nm, 6 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the WO3-nanotube composite layer includes a WO3-ZrO2 nanotube composite layer or a WO3-TiO2 nanotube composite layer.

[0026] The nanotubes in the WO3-nanotube composite layer provide ion-directed migration channels with a migration barrier of 0.2 eV, solving the problem of slow ion diffusion at low temperatures; the WO3 nanofilm shortens the ion insertion lattice distance.

[0027] Preferably, the WO3-nanotube composite layer comprises vertically arranged nanotubes and a WO3 nanofilm deposited on the nanotube walls.

[0028] Preferably, the nanotube has a diameter of 20-50 nm, a length of 500-800 nm, a wall thickness of 5-10 nm, and a porosity of 65-75%.

[0029] The diameter of the nanotube is 20-50nm, for example, it can be 20nm, 25nm, 30nm, 40nm or 50nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] The length of the nanotube is 500-800nm, for example, it can be 500nm, 550nm, 600nm, 700nm or 800nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The wall thickness of the nanotube is 5-10 nm, for example, it can be 5 nm, 6 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] The porosity of the nanotubes is 65-75%, for example, it can be 65%, 68%, 70%, 72% or 75%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the thickness of the WO3 nanofilm is 5-10 nm, for example, it can be 5 nm, 6 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the rare earth dopant ions in the rare earth-doped graphene layer include Y0. 3+ La 3+ or Nd 3+ Any one or at least two of the above, typical but non-limiting combinations include Y 3+ with La 3+ The combination, La 3+ With Nd 3+ The combination, or Y 3+ La 3+ With Nd 3+ The combination of .

[0035] Traditional processes require increased graphene dosage to ensure the continuity of the conductive network, resulting in visible light transmittance dropping below 80% and affecting the transparency of the canopy. Reducing the dosage, however, fails to create an effective conductive path, thus losing its electron transport enhancement effect. This invention uses rare-earth-doped graphene, where the rare-earth-doped ions fill the gaps between graphene sheets. These ions compensate for charge, reducing the graphene dosage to 0.15-0.2 mg / cm³. 2The light transmittance is increased to over 85%, achieving a balance between high conductivity and high light transmittance with low dosage.

[0036] Preferably, the thickness of the rare earth-doped graphene layer is 30-50 nm, for example, it can be 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the raw material of the electrolyte layer includes lithium-silver composite ionogel.

[0038] The electrolyte layer is made of lithium-silver composite ionogel with an ion conductivity of 10. -3 S / cm ensures ion migration.

[0039] Preferably, the counter electrode layer comprises a nickel oxide counter electrode.

[0040] The nickel oxide counter electrode can form a complementary color change with WO3, thereby enhancing contrast.

[0041] Preferably, the thickness of the fluoropolymer coating layer is 50-100 nm, for example, it can be 50 nm, 60 nm, 80 nm, 90 nm or 100 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the raw materials for the fluoropolymer coating layer include fluoropolymers and nano-oxides.

[0043] Preferably, the fluoropolymer includes fluorosiloxanes or fluoroacrylates.

[0044] Preferably, the fluorosiloxane includes any one or a combination of at least two of trifluoropropylsilane, fluorosilicone resin, or polytrifluoropropylsiloxane. Typical but non-limiting combinations include a combination of trifluoropropylsilane and fluorosilicone resin, a combination of fluorosilicone resin and polytrifluoropropylsiloxane, or a combination of trifluoropropylsilane, fluorosilicone resin, and polytrifluoropropylsiloxane.

[0045] Preferably, the fluorinated acrylate includes any one or a combination of at least two of ethyl trifluoroacrylate, methyl trifluorochloroacrylate, tetrafluoroethylene acrylate, styrene hexafluoroacrylate, or isooctyl fluorinated acrylate. Typical but non-limiting combinations include a combination of ethyl trifluoroacrylate and methyl trifluorochloroacrylate, a combination of tetrafluoroethylene acrylate, styrene hexafluoroacrylate, and isooctyl fluorinated acrylate, or a combination of ethyl trifluoroacrylate, methyl trifluorochloroacrylate, tetrafluoroethylene acrylate, styrene hexafluoroacrylate, and isooctyl fluorinated acrylate.

[0046] Preferably, the nano-oxide comprises nano-ZnO or nano-CeO2.

[0047] The fluoropolymer coating layer contains nano-ZnO or nano-CeO2 which can absorb ultraviolet light, and fluorosiloxane or fluorinated acrylate which is hydrophobic and moisture-resistant, preventing graphene oxidation and WO3 hydrolysis.

[0048] Preferably, the particle size of the nano-oxide is 5-10 nm, for example, it can be 5 nm, 6 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] In a second aspect, the present invention provides a method for preparing a graphene-based electrochromic composite film as described in the first aspect, the method comprising the following steps:

[0050] A transparent conductive layer is sputtered onto the surface of the substrate, and then a graphene-based interface coupling layer is deposited by coating and covalent bonding. A WO3-nanotube composite layer is prepared by anodic oxidation and atomic layer deposition, and then a rare earth-doped graphene layer is prepared and coated by reduction. After the electrolyte layer is infused to form an electrolyte layer, a counter electrode layer is sputtered, and then a fluoropolymer coating layer is deposited by dip coating and curing.

[0051] The method for preparing the graphene-based electrochromic composite film provided by this invention employs a coating and covalent bond solidification deposition of a graphene-based interface coupling layer to achieve interface enhancement; an anodic oxidation and atomic layer deposition are used to prepare a WO3-nanotube composite layer to accelerate ion migration; a reduction method is used to prepare and coat a rare earth-doped graphene layer to optimize the balance between conductivity and light transmittance; and a fluoropolymer coating layer is deposited through dip coating and solidification to enhance weather resistance.

[0052] Preferably, the substrate layer is ultrasonically cleaned for 30 minutes at 60°C using a mixture of deionized water and alcohol before sputtering.

[0053] Preferably, the sputtering power of the transparent conductive layer is 140-160W, for example, it can be 140W, 145W, 150W, 155W or 160W, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the specific steps of depositing the graphene-based interface coupling layer include: introducing carboxyl functional groups on the surface of the graphene sheet using plasma treatment, and then mixing it with MXene nanosheets or hydroxylated graphene containing hydroxyl functional groups on the surface, followed by coating and covalent bonding curing.

[0055] In this invention, carboxyl functional groups are introduced into graphene through plasma treatment, which then undergo dehydration condensation with MXene nanosheets containing hydroxyl functional groups on the surface or hydroxylated graphene to form covalent bonds. The resulting covalent bonds are deposited using a coating method and then thermo-cured to form -CO-Ti- covalent bonds, thus solving the problem of interfacial delamination between graphene and WO3.

[0056] The ratio of the graphene sheet to MXene nanosheets or hydroxylated graphene with hydroxyl functional groups on the surface is not specifically limited, and those skilled in the art can make an adaptive selection according to the actual application scenario.

[0057] Preferably, the coating method is spin coating, with a rotation speed of 2800-3200 rpm, such as 2800 rpm, 2900 rpm, 3000 rpm, 3100 rpm or 3200 rpm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the covalent bond is cured at a temperature of 115-125℃ for 0.8-1.2 hours.

[0059] The covalent bond solidification temperature is 115-125℃, for example, it can be 115℃, 118℃, 120℃, 122℃ or 125℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] The covalent bond curing time is 0.8-1.2h, for example, it can be 0.8h, 0.9h, 1h, 1.1h or 1.2h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Preferably, the specific steps for preparing the WO3-nanotube composite layer include: preparing nanotubes by anodic oxidation, using oxalic acid electrolyte, with the anode being a zirconium or titanium sheet and the cathode being an inert metal electrode, and the voltage being set to 20V; then depositing a WO3 nanofilm on the nanotube wall by atomic layer deposition at a deposition temperature of 150-250℃, using alternating reactions of a tungsten precursor and an oxygen source, and controlling the WO3 nanofilm thickness to be 5-10nm through 50-150 deposition cycles.

[0062] It should be noted that the present invention does not specifically limit the types of inert metal electrodes, tungsten precursors and oxygen sources, and those skilled in the art can make adaptive selections according to actual application scenarios.

[0063] The deposition temperature is 150-250℃, for example, it can be 150℃, 180℃, 200℃, 220℃ or 250℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] The number of deposition cycles is 50-150, for example, 50, 80, 100, 120 or 150, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] The thickness of the WO3 nanofilm is 5-10 nm, for example, it can be 5 nm, 6 nm, 8 nm, 9 nm or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] Preferably, the preparation steps of the rare earth-doped graphene layer include: mixing graphene oxide dispersion with yttrium nitrate solution and placing it in a closed reaction vessel, hydrothermally reacting at 160-200℃ for 4-12 hours, cooling and washing after the reaction to obtain rare earth-doped graphene slurry, and then coating it on the surface of WO3-nanotube composite layer.

[0067] The temperature of the hydrothermal reaction is 160-200℃, for example, it can be 160℃, 170℃, 180℃, 190℃ or 200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] The hydrothermal reaction time is 4-12 hours, for example, it can be 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] Preferably, the rare earth ion doping amount in the rare earth-doped graphene layer is 0.5-2 wt% of the total rare earth-doped graphene, for example, it can be 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt% or 2 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] It should be noted that sputtering the counter electrode layer after filling with electrolyte to form an electrolyte layer is a conventional process in the field. The specific parameters of the filling process and sputtering process are not specifically limited in this invention, and those skilled in the art can make adaptive selections according to the actual application scenario.

[0071] Preferably, the specific steps of depositing the fluoropolymer coating layer include: mixing the fluoropolymer with nano-oxide to prepare a sol, and then coating the obtained sol onto the surface of the counter electrode layer and curing it.

[0072] Preferably, the mass percentage of nano-oxides in the sol is 5-10 wt%, for example, it can be 5 wt%, 6 wt%, 8 wt%, 9 wt% or 10 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] Preferably, the dipping speed is 4-6 mm / s, for example, it can be 4 mm / s, 4.5 mm / s, 5 mm / s, 5.5 mm / s or 6 mm / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] Preferably, the curing temperature is 115-125℃ and the time is 1.8-2.2h.

[0075] The curing temperature is 115-125℃, for example, it can be 115℃, 118℃, 120℃, 122℃ or 125℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] The curing time is 1.8-2.2 hours, for example, it can be 1.8 hours, 1.9 hours, 2 hours, 2.1 hours or 2.2 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] Thirdly, the present invention provides an application of the graphene-based electrochromic composite film as described in the first aspect, wherein the graphene-based electrochromic composite film is used in automotive sunroofs.

[0078] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] (1) In view of the problem that the weak interfacial bonding between graphene and WO3 leads to the composite film being prone to interfacial peeling and poor cycle stability after multiple ion insertion / extraction cycles, the present invention adopts the interfacial covalent bond design of graphene-based interfacial coupling layer, which enhances the interfacial bonding between graphene and WO3, increases the cycle life to more than 400,000 cycles, and solves the stability problem.

[0081] (2) In view of the contradiction between the amount of graphene and transparency, the present invention adopts the charge compensation mechanism of rare earth ion doped graphene. Rare earth doping reduces the amount of graphene by 40% and increases the light transmittance to more than 85%, while the electrical conductivity does not decrease significantly, thus achieving a balance between high conductivity and high light transmittance with low dosage.

[0082] (3) This invention addresses the problem that the ion diffusion rate in the WO3 lattice drops sharply in low-temperature environments below -10℃, resulting in a significantly slower dimming speed that cannot meet the requirements for wide-temperature applications in vehicles. It employs a composite structure of nanotube-oriented ion channels and WO3 nanofilms, which accelerates low-temperature ion migration, shortening the dimming time at -10℃ to less than 37 seconds, and adapting to a wide temperature range of -40℃ to 85℃. Furthermore, the overall dimming speed is improved, resulting in a faster response.

[0083] (4) This invention addresses the problem that graphene is easily oxidized and WO3 is easily hydrolyzed when exposed to ultraviolet light, high temperature and high humidity for a long time, which leads to a decrease in conductivity and failure of the color-changing function. It adopts a fluoropolymer coating design, which makes the conductivity decrease rate as low as 20% after ultraviolet aging (1000h), and there is no hydrolysis under high temperature and high humidity, thus extending the service life and enhancing the weather resistance. Detailed Implementation

[0084] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0085] Example 1

[0086] This embodiment provides a graphene-based electrochromic composite film, which comprises, in sequence, a 2.5 mm thick ultra-white float glass with 98% light transmittance, a 120 nm thick ITO film with a sheet resistance of 3 Ω / □, a 60 nm thick graphene-based interface coupling layer, a WO3-ZrO2 nanotube composite layer, and a 40 nm thick Y-based interfacial coupling layer. 3+ The coating consists of a doped graphene layer, a lithium-silver composite ion gel layer, a nickel oxide counter electrode layer, and an 80 nm thick trifluoropropylsilane-nano ZnO coating layer.

[0087] The graphene-based interface coupling layer comprises graphene sheets and Ti3C2MXene nanosheets with hydroxyl functional groups on their surface. The graphene sheets have a thickness of 0.34 nm and a diameter of 8 μm, and the Ti3C2MXene nanosheets have a thickness of 8 nm. The WO3-ZrO2 nanotube composite layer comprises vertically arranged ZrO2 nanotubes and a WO3 nanofilm deposited on the walls of the ZrO2 nanotubes. The ZrO2 nanotubes have a diameter of 30 nm, a length of 600 nm, a wall thickness of 8 nm, and a porosity of 70%. The WO3 nanofilm has a thickness of 8 nm. The nano-ZnO has a particle size range of 5-10 nm.

[0088] The preparation method of the graphene-based electrochromic composite film includes the following steps:

[0089] Ultra-white float glass was ultrasonically cleaned for 30 min at 60℃ using a mixture of deionized water and alcohol. A transparent conductive layer was then sputtered onto the surface of the ultra-white float glass at a power of 150W. Carboxyl functional groups were introduced onto the surface of graphene sheets using plasma treatment. These graphene sheets were then mixed with MXene nanosheets containing hydroxyl functional groups and spin-coated at 3000 rpm, followed by covalent curing at 120℃ for 1 h. ZrO2 nanotubes were prepared using anodizing with oxalic acid electrolyte. The anode was a zirconium metal sheet, and the cathode was a platinum electrode. The voltage was set to 20V, and then WO3 nanofilms were deposited on the walls of ZrO2 nanotubes using atomic layer deposition at a deposition temperature of 200℃. The reaction was performed alternately with bis(tert-butylimino)bis(dimethylamino)tungsten(VI) and water, and the WO3 nanofilm thickness was controlled to be 8nm through 100 deposition cycles. Then, a graphene oxide dispersion was mixed with a yttrium nitrate solution and placed in a sealed reactor for hydrothermal reaction at 180℃ for 8 hours to obtain a rare-earth-doped graphene slurry, which was then coated onto the surface of the WO3-nanotube composite layer. 3+ Doping amount is Y 3+ The total amount of graphene doped is 1 wt%; after the electrolyte is poured in to form an electrolyte layer, the counter electrode layer is sputtered, and then trifluoropropylsilane is mixed with nano-ZnO to prepare a sol, wherein the mass percentage of nano-ZnO in the sol is 8 wt%; the obtained sol is dipped onto the surface of the counter electrode layer at a speed of 5 mm / s and then cured at 120°C for 2 h.

[0090] Example 2

[0091] This embodiment provides a graphene-based electrochromic composite film, which comprises, in sequence, a 2mm thick ultra-white float glass with 96% light transmittance, a 100nm thick ITO film with a sheet resistance of 5Ω / □, a 50nm thick graphene-based interface coupling layer, a WO3-ZrO2 nanotube composite layer, and a 30nm thick Y-based interfacial coupling layer. 3+ The coating consists of a doped graphene layer, a lithium-silver composite ion gel layer, a nickel oxide counter electrode layer, and a 50 nm thick trifluoropropylsilane-nano ZnO coating layer.

[0092] The graphene-based interface coupling layer comprises graphene sheets and Ti3C2MXene nanosheets with hydroxyl functional groups on their surface. The graphene sheets have a thickness of 0.34 nm and a diameter of 5 μm, and the Ti3C2MXene nanosheets have a thickness of 5 nm. The WO3-ZrO2 nanotube composite layer comprises vertically arranged ZrO2 nanotubes and a WO3 nanofilm deposited on the walls of the ZrO2 nanotubes. The ZrO2 nanotubes have a diameter of 20 nm, a length of 500 nm, a wall thickness of 5 nm, and a porosity of 65%. The WO3 nanofilm has a thickness of 5 nm. The nano-ZnO has a particle size range of 5-10 nm.

[0093] The preparation method of the graphene-based electrochromic composite film includes the following steps:

[0094] Ultra-white float glass was ultrasonically cleaned for 30 min at 60℃ using a mixture of deionized water and alcohol. A transparent conductive layer was then sputtered onto the surface of the ultra-white float glass at a power of 140W. Carboxyl functional groups were introduced onto the surface of graphene sheets using plasma treatment. These graphene sheets were then mixed with MXene nanosheets containing hydroxyl functional groups and spin-coated at 2800 rpm, followed by covalent curing at 115℃ for 1.2 h. ZrO2 nanotubes were prepared using anodizing with oxalic acid electrolyte. The anode was a zirconium metal sheet, and the cathode was a platinum electrode. The electrode was set to a voltage of 20V, and then WO3 nanofilms were deposited on the walls of ZrO2 nanotubes using atomic layer deposition at a deposition temperature of 150℃. The WO3 nanofilm thickness was controlled to 5nm by alternating reactions of bis(tert-butylimino)bis(dimethylamino)tungsten(VI) and water, with 50 deposition cycles. Then, a graphene oxide dispersion was mixed with a yttrium nitrate solution and placed in a sealed reactor for hydrothermal reaction at 160℃ for 12 hours to obtain a rare-earth-doped graphene slurry, which was then coated onto the surface of the WO3-nanotube composite layer. 3+ Doping amount is Y 3+ The total amount of graphene doped is 0.5 wt%; after the electrolyte layer is formed by pouring in electrolyte, the counter electrode layer is sputtered, and then trifluoropropylsilane is mixed with nano-ZnO to prepare a sol, wherein the mass percentage of nano-ZnO in the sol is 5 wt%; the obtained sol is dip-coated onto the surface of the counter electrode layer at a speed of 4 mm / s and then cured at 115 °C for 2.2 h.

[0095] Example 3

[0096] This embodiment provides a graphene-based electrochromic composite film, which comprises, in sequence, a 3mm thick ultra-white float glass with 92% light transmittance, a 150nm thick ITO film with a sheet resistance of 10Ω / □, an 80nm thick graphene-based interface coupling layer, a WO3-ZrO2 nanotube composite layer, and a 50nm thick Y-based interfacial coupling layer. 3+ The coating consists of a doped graphene layer, a lithium-silver composite ion gel layer, a nickel oxide counter electrode layer, and a 100 nm thick trifluoropropylsilane-nano ZnO coating layer.

[0097] The graphene-based interface coupling layer comprises graphene sheets and Ti3C2MXene nanosheets with hydroxyl functional groups on their surface. The graphene sheets have a thickness of 0.34 nm and a diameter of 10 μm, and the Ti3C2MXene nanosheets have a thickness of 10 nm. The WO3-ZrO2 nanotube composite layer comprises vertically arranged ZrO2 nanotubes and a WO3 nanofilm deposited on the walls of the ZrO2 nanotubes. The ZrO2 nanotubes have a diameter of 50 nm, a length of 800 nm, a wall thickness of 10 nm, and a porosity of 75%. The WO3 nanofilm has a thickness of 10 nm. The nano-ZnO has a particle size range of 5-10 nm.

[0098] The preparation method of the graphene-based electrochromic composite film includes the following steps:

[0099] Ultra-white float glass was ultrasonically cleaned for 30 min at 60℃ using a mixture of deionized water and alcohol. A transparent conductive layer was then sputtered onto the surface of the ultra-white float glass at a power of 160W. Carboxyl functional groups were introduced onto the surface of graphene sheets using plasma treatment. This mixture was then mixed with MXene nanosheets containing hydroxyl functional groups and spin-coated at 3200 rpm, followed by covalent curing at 125℃ for 0.8 h. ZrO2 nanotubes were prepared using anodizing with oxalic acid electrolyte. The anode was a titanium sheet, and the cathode was a platinum electrode. The voltage was set to 20V, and then WO3 nanofilms were deposited on the walls of ZrO2 nanotubes using atomic layer deposition at a deposition temperature of 250℃. The reaction was performed alternately with bis(tert-butylimino)bis(dimethylamino)tungsten(VI) and water, and the WO3 nanofilm thickness was controlled to be 10nm through 150 deposition cycles. Then, a graphene oxide dispersion was mixed with a yttrium nitrate solution and placed in a sealed reactor for hydrothermal reaction at 200℃ for 4 hours to obtain a rare-earth-doped graphene slurry, which was then coated onto the surface of the WO3-nanotube composite layer. 3+ Doping amount is Y 3+ The total amount of graphene doped is 2wt%; after the electrolyte layer is formed by pouring in electrolyte, the counter electrode layer is sputtered, and then trifluoropropylsilane is mixed with nano-ZnO to prepare a sol, wherein the mass ratio of nano-ZnO in the sol is 10wt%; the obtained sol is dip-coated onto the surface of the counter electrode layer at a speed of 6mm / s and then cured at 125℃ for 1.8h.

[0100] Example 4

[0101] This embodiment provides a graphene-based electrochromic composite film, which differs from Embodiment 1 in that, except for replacing the Ti3C2 MXene nanosheets with hydroxyl functional groups on the surface with hydroxylated graphene, the rest is the same as in Embodiment 1.

[0102] Example 5

[0103] This embodiment provides a graphene-based electrochromic composite film, which differs from Embodiment 1 in that the Y... 3+ Replace the doped graphene layer with La 3+ The graphene layer was doped, and the yttrium nitrate solution in the preparation method was replaced with a lanthanum nitrate solution, while the rest were the same as in Example 1.

[0104] Example 6

[0105] This embodiment provides a graphene-based electrochromic composite film, which differs from Embodiment 1 in that, except for replacing the ZrO2 nanotubes of the same size with TiO2 nanotubes, everything else is the same as in Embodiment 1.

[0106] Example 7

[0107] This embodiment provides a graphene-based electrochromic composite film, which differs from Embodiment 1 in that, except for replacing the trifluoropropylsilane-nano ZnO coating layer with methyl trifluorochloroacrylate and nano CeO2, the rest is the same as in Embodiment 1.

[0108] Example 8

[0109] This embodiment provides a graphene-based electrochromic composite film, the preparation method of which differs from that of Example 1 in that Y... 3+ Doping amount adjusted to Y 3+ The total amount of graphene doped was 0.1 wt%, and the rest were the same as in Example 1.

[0110] Example 9

[0111] This embodiment provides a graphene-based electrochromic composite film, the preparation method of which differs from that of Example 1 in that Y... 3+ Doping amount adjusted to Y 3+ The total amount of graphene doped was 2.5 wt%, and the rest was the same as in Example 1.

[0112] Example 10

[0113] This embodiment provides a graphene-based electrochromic composite film. The difference between its preparation method and that of Embodiment 1 is that the mass percentage of nano-ZnO in the sol is adjusted to 1 wt%, while the rest is the same as in Embodiment 1.

[0114] Example 11

[0115] This embodiment provides a graphene-based electrochromic composite film. The difference between its preparation method and that of Embodiment 1 is that the mass ratio of nano-ZnO in the sol is adjusted to 15wt%, while the rest is the same as in Embodiment 1.

[0116] Comparative Example 1

[0117] This comparative example provides a graphene-based electrochromic composite film. The difference from Example 1 is that the graphene-based interface coupling layer does not introduce Ti3C2 MXene nanosheets with hydroxyl functional groups on the surface, but only a single graphene layer. The rest is the same as in Example 1.

[0118] Comparative Example 2

[0119] This comparative example provides a graphene-based electrochromic composite film. The difference from Example 1 is that the WO3-ZrO2 nanotube composite layer is replaced with a single WO3 functional layer, while the rest is the same as in Example 1.

[0120] Comparative Example 3

[0121] This comparative example provides a graphene-based electrochromic composite film, which differs from Example 1 in that it does not include a Y-type electrochromic film. 3+ The graphene layer is doped, and everything else is the same as in Example 1.

[0122] Comparative Example 4

[0123] This comparative example provides a graphene-based electrochromic composite film, which differs from Example 1 in that it does not have a trifluoropropylsilane-nano ZnO coating layer, but is otherwise the same as Example 1.

[0124] Cyclic stability tests were conducted on the graphene-based electrochromic composite films provided in Examples 1-11 and Comparative Examples 1-4: an electrochemical workstation was used with a voltage range of ±2V and a current density of 1-2mA / cm². 2 The electrolyte was LiClO4 aqueous solution, and the test temperature was 25℃.

[0125] Visible light transmittance test: Visible light transmittance was measured using a UV-Vis spectrophotometer (300-800nm) at a temperature of 25℃.

[0126] Low-temperature dimming time test: At -10℃, the dimming response time of the electrochromic film was recorded using an electrochemical workstation and optical measurement equipment, with a voltage range of ±2V.

[0127] The dimming time test at room temperature (25℃) was conducted by using an electrochemical workstation and optical measurement equipment to record the dimming response time of the electrochromic film.

[0128] Test of conductivity decrease rate after UV aging: The conductivity change of the electrochromic film was measured using the four-probe method before and after UV irradiation (300-400nm wavelength, 1000h) at a test temperature of 25℃. The results are shown in Table 1.

[0129] Table 1

[0130]

[0131] As can be seen from Table 1, the graphene-based electrochromic composite film provided by the present invention has significantly improved stability, optimized light transmission-conductivity balance, improved low-temperature performance, enhanced weather resistance, and faster overall dimming speed.

[0132] A comparison of Examples 1 and 4 shows that using hydroxylated graphene to replace Ti3C2MXene nanosheets with hydroxyl functional groups on the surface can also connect graphene and WO3 through hydrogen bonds, but the overall performance is slightly lower than that of Example 1; a comparison of Examples 1 and 5 shows that using La 3+ Lanthanide ion substitution for Y 3+ Similarly, charge compensation can be achieved. A comparison of Examples 1 and 6 shows that using TiO2 nanotubes instead of ZrO2 nanotubes results in an ion migration barrier of 0.25 eV and a slightly longer low-temperature dimming time compared to ZrO2 nanotubes. A comparison of Examples 1 and 7 shows that using fluorinated acrylate and nano-CeO2 instead of fluorosiloxane-ZnO results in slightly weaker weather resistance. A comparison of Examples 1 and Examples 8 and 9 shows that too low a rare earth doping amount leads to insufficient charge compensation, decreased conductivity, and slower dimming speed; too high a rare earth doping amount leads to decreased conductivity, decreased interface stability, and a fragile film. A comparison of Examples 1 and Examples 10 and 11 shows that too low a mass percentage of nano-ZnO in the sol leads to decreased UV resistance, decreased conductivity, and reduced film stability; too high a mass percentage leads to decreased optical transparency, increased scattering, and reduced transmittance.

[0133] A comparison of Example 1 and Comparative Example 1 shows that the graphene-based interfacial coupling layer does not incorporate Ti3C2 MXene nanosheets with hydroxyl functional groups on its surface, and is only a single graphene layer. This results in poor interfacial adhesion, easy exfoliation, and affects the stability and lifespan of the film. A comparison of Example 1 and Comparative Example 2 shows that replacing the WO3-ZrO2 nanotube composite layer with a single WO3 functional layer leads to obstructed ion migration pathways, poor low-temperature dimming performance, and slow dimming speed. A comparison of Example 1 and Comparative Example 3 shows that without Y... 3+ The doping of graphene layers leads to insufficient charge compensation, poor conductivity, and affects the dimming speed and stability. As can be seen from the comparison between Example 1 and Comparative Example 4, the absence of a trifluoropropylsilane-nano ZnO coating layer results in poor weather resistance, decreased conductivity after UV aging, poor film stability, and decreased optical transparency.

[0134] In summary, this invention addresses the problem of weak interfacial bonding between graphene and WO3, which leads to poor interfacial delamination and cycling stability of the composite film after multiple ion insertion / extraction cycles. By employing an interfacial covalent bond design of a graphene-based interfacial coupling layer, the interfacial bonding between graphene and WO3 is enhanced, increasing the cycle life to over 400,000 cycles and solving the stability problem.

[0135] This invention addresses the contradiction between graphene dosage and transparency by employing a charge compensation mechanism using rare-earth ion-doped graphene. Rare-earth doping reduces the amount of graphene used by 40%, increases light transmittance to over 85%, and at the same time, the decrease in electrical conductivity is not significant, thus achieving a balance between high conductivity and high light transmittance with low dosage.

[0136] This invention addresses the problem of a sharp drop in ion diffusion rate in the WO3 lattice at temperatures below -10°C, resulting in a significantly slower dimming speed and failing to meet the requirements for wide-temperature applications in automotive applications. It employs a composite structure of nanotube-oriented ion channels and a WO3 nanofilm, which accelerates ion migration at low temperatures, reducing the dimming time at -10°C to less than 37 seconds, and adapting to a wide temperature range of -40°C to 85°C. Furthermore, the overall dimming speed is improved, resulting in a faster response.

[0137] This invention addresses the problem that graphene is easily oxidized and WO3 is easily hydrolyzed when exposed to ultraviolet light, high temperature and high humidity for a long time, resulting in decreased conductivity and failure of the color-changing function. It adopts a fluoropolymer coating design, which reduces the conductivity decrease rate to as low as 20% after ultraviolet aging (1000h), prevents hydrolysis under high temperature and high humidity, extends service life, and enhances weather resistance.

[0138] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A graphene-based electrochromic composite film, characterized in that, The graphene-based electrochromic composite film comprises a substrate layer, a transparent conductive layer, a graphene-based interface coupling layer, a WO3-nanotube composite layer, a rare earth-doped graphene layer, an electrolyte layer, a counter electrode layer, and a fluoropolymer coating layer, which are stacked sequentially.

2. The graphene-based electrochromic composite film according to claim 1, characterized in that, The substrate layer is made of ultra-white float glass; Preferably, the thickness of the base layer is 2-3 mm; Preferably, the transparent conductive layer comprises an ITO thin film; Preferably, the thickness of the transparent conductive layer is 100-150 nm.

3. The graphene-based electrochromic composite film according to claim 1 or 2, characterized in that, The thickness of the graphene-based interface coupling layer is 50-80 nm; Preferably, the raw material of the graphene-based interface coupling layer includes graphene sheets, and also includes MXene nanosheets or hydroxylated graphene with hydroxyl functional groups on the surface, preferably MXene nanosheets with hydroxyl functional groups on the surface. Preferably, the MXene nanosheets include Ti3C2.

4. The graphene-based electrochromic composite film according to any one of claims 1-3, characterized in that, The WO3-nanotube composite layer includes a WO3-ZrO2 nanotube composite layer or a WO3-TiO2 nanotube composite layer; Preferably, the WO3-nanotube composite layer comprises vertically arranged nanotubes and a WO3 nanofilm deposited on the nanotube walls; Preferably, the rare earth dopant ions in the rare earth-doped graphene layer include Y0. 3+ La 3+ or Nd 3+ Any one or at least two of them; Preferably, the thickness of the rare earth-doped graphene layer is 30-50 nm.

5. The graphene-based electrochromic composite film according to any one of claims 1-4, characterized in that, The thickness of the fluoropolymer coating layer is 50-100 nm; Preferably, the raw materials for the fluoropolymer coating layer include fluoropolymers and nano-oxides; Preferably, the fluoropolymer comprises fluorosiloxane or fluorinated acrylate; Preferably, the nano-oxide comprises nano-ZnO or nano-CeO2.

6. A method for preparing a graphene-based electrochromic composite film as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A transparent conductive layer is sputtered onto the surface of the substrate, and then a graphene-based interface coupling layer is deposited by coating and covalent bonding. A WO3-nanotube composite layer is prepared by anodic oxidation and atomic layer deposition, and then a rare earth-doped graphene layer is prepared and coated by reduction. After the electrolyte layer is infused to form an electrolyte layer, a counter electrode layer is sputtered, and then a fluoropolymer coating layer is deposited by dip coating and curing.

7. The preparation method according to claim 6, characterized in that, Before sputtering, the substrate layer was ultrasonically cleaned for 30 minutes at 60°C using a mixture of deionized water and alcohol. Preferably, the sputtering power of the transparent conductive layer is 140-160W; Preferably, the specific steps of depositing the graphene-based interface coupling layer include: introducing carboxyl functional groups on the surface of graphene sheets by plasma treatment, and then mixing it with MXene nanosheets or hydroxylated graphene containing hydroxyl functional groups on the surface, followed by coating and covalent bonding curing. Preferably, the coating method is spin coating, with a rotation speed of 2800-3200 rpm; Preferably, the covalent bond is cured at a temperature of 115-125℃ for 0.8-1.2 hours.

8. The preparation method according to claim 6 or 7, characterized in that, The specific steps for preparing the WO3-nanotube composite layer include: preparing nanotubes using an anodic oxidation method, using oxalic acid electrolyte, with the anode being a zirconium or titanium sheet and the cathode being an inert metal electrode, and the voltage being set to 20V; then depositing a WO3 nanofilm on the nanotube wall using atomic layer deposition, with a deposition temperature of 150-250℃, using an alternating reaction between a tungsten precursor and an oxygen source, and controlling the WO3 nanofilm thickness to be 5-10nm through 50-150 deposition cycles; Preferably, the preparation steps of the rare earth-doped graphene layer include: mixing graphene oxide dispersion with yttrium nitrate solution and placing it in a closed reaction vessel, and hydrothermally reacting it at 160-200℃ for 4-12 hours to obtain rare earth-doped graphene slurry, which is then coated on the surface of WO3-nanotube composite layer. Preferably, the amount of rare earth ions in the rare earth-doped graphene layer is 0.5-2 wt% of the total amount of rare earth-doped graphene.

9. The preparation method according to any one of claims 6-8, characterized in that, The specific steps for depositing the fluoropolymer coating layer include: mixing the fluoropolymer with nano-oxide to prepare a sol, and then coating the obtained sol onto the surface of the counter electrode layer and curing it. Preferably, the mass percentage of nano-oxides in the sol is 5-10 wt%. Preferably, the curing temperature is 115-125℃ and the time is 1.8-2.2h.

10. An application of the graphene-based electrochromic composite film as described in any one of claims 1-5, characterized in that, The graphene-based electrochromic composite film is used in automotive sunroofs.

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