A solid-state polymer electrolyte, a flexible electrochromic device and a preparation method

Abstract

The application discloses a solid-state polymer electrolyte, a flexible electrochromic device and a preparation method, and relates to the technical field of electrochromic technology. The preparation method of the solid-state polymer electrolyte comprises the following steps: mixing polyethylene glycol dimethacrylate, thermoplastic polyurethane and a lithium salt, and performing cross-linking polymerization to obtain the solid-state polymer electrolyte. Through the preparation method, a semi-interpenetrating network is formed by the reversible physical action of a covalently cross-linked polyethylene glycol dimethacrylate three-dimensional network and thermoplastic polyurethane, and a solid-state electrolyte with high ionic conductivity and good mechanical flexibility is prepared, thereby effectively solving the problem that the existing solid-state electrolyte based on polyethylene glycol dimethacrylate cannot simultaneously consider good ion migration performance and mechanical flexibility.

Description

Technical Field

[0001] This invention relates to the field of electrochromic technology, and more particularly to a solid polymer electrolyte, a flexible electrochromic device, and a preparation method thereof. Background Technology

[0002] With the rapid development of flexible electronics technology and novel functional materials, electronic devices are gradually evolving towards lightweight, bendable, and curved surface integration. However, traditional electrochromic devices rely on rigid, transparent conductive substrates, which are prone to interface instability and performance degradation under curved configurations and cyclic bending conditions, thus limiting their expansion in emerging flexible application scenarios. Against this backdrop, flexible electrochromic devices (FECDs) that integrate controllable optical modulation capabilities and excellent mechanical compliance are particularly important and are considered promising candidates in fields such as flexible displays, dynamic anti-counterfeiting labels, and curved smart windows.

[0003] The normal operation of flexible electrochromic devices relies on the electrolyte, which serves as the ion transport medium, and it must maintain its optical performance even when bent. Solid polymer electrolytes (SPEs) have attracted considerable attention due to their leak-proof properties, excellent thin-film molding capabilities, and structural flexibility. An ideal SPE not only needs high ionic conductivity but also good mechanical strength. These key characteristics directly determine the overall performance of flexible electrochromic devices. Poly(ethylene glycol)-based polymer networks in SPEs, such as polyethylene glycol dimethacrylate (PEGDMA), are often used as ion-conducting matrices due to their abundant etheroxy groups. However, highly cross-linked PEGDMA networks can inhibit chain migration and limit ion transport; while reducing the cross-linking density can improve ion mobility, it is difficult to guarantee the structural stability of the device under repeated bending.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a solid polymer electrolyte, a flexible electrochromic device and a preparation method, which aims to solve the problem that existing PEGDMA-based polymer electrolytes are difficult to simultaneously achieve good ion migration performance and mechanical flexibility.

[0006] The technical solution of the present invention is as follows: A first aspect of the present invention provides a method for preparing a solid polymer electrolyte, comprising the following steps: The solid polymer electrolyte is obtained by mixing PEGDMA, thermoplastic polyurethane (TPU) and lithium salt and then performing crosslinking polymerization.

[0007] Optionally, the preparation method of the solid polymer electrolyte specifically includes the following steps: PEGDMA, lithium salt and photoinitiator are mixed to obtain the first mixture; TPU is mixed with an organic solvent to obtain a second mixture; The second mixture is added to the first mixture, and after cross-linking polymerization under ultraviolet light for a preset time, the solid polymer electrolyte is obtained.

[0008] Optionally, the lithium salt includes at least one of LiTFSI, LiClO4, LiBF4, and LiPF6; and / or, the organic solvent includes N,N-dimethylformamide.

[0009] Optionally, the mass ratio of PEGDMA, lithium salt, and photoinitiator is 0.8:(0.5~0.7):(0.2~0.4); and / or; The TPU mass accounts for 0% to 60% of the total mass of the first mixture and the TPU, but not 0%; and / or, The preset time is 0.5~1 h.

[0010] In a second aspect, the present invention provides a solid polymer electrolyte, wherein it is prepared by the preparation method described above.

[0011] A third aspect of the present invention provides a flexible electrochromic device, wherein the flexible electrochromic device includes a first flexible electrode, a second flexible electrode, and an electrochromic film located between the first flexible electrode and the second flexible electrode, the electrochromic film including the solid polymer electrolyte of the present invention as described above, and viologen-based electrochromic material and ferrocene dispersed in the solid polymer electrolyte.

[0012] Optionally, the viologen-based electrochromic material is R is at least one of a single chemical bond, furanyl, thiophene, selenyl, ethylenedioxythiophene, and benzothiadiazole.

[0013] A fourth aspect of the present invention provides a method for fabricating a flexible electrochromic device, comprising the following steps: PEGDMA, TPU, lithium salt, viologen-based electrochromic material and ferrocene were mixed and cross-linked to obtain an electrochromic film. A first flexible electrode and a second flexible electrode are respectively disposed on both sides of the electrochromic film to obtain the flexible electrochromic device.

[0014] In a fifth aspect, the present invention provides a pharmaceutical anti-counterfeiting label, wherein the pharmaceutical anti-counterfeiting label includes the flexible electrochromic device described above.

[0015] In a sixth aspect, the present invention provides a smart window, wherein the smart window includes the flexible electrochromic device of the present invention as described above.

[0016] Beneficial effects: The solid polymer electrolyte prepared by the preparation method provided by the present invention has both high ionic conductivity and good mechanical flexibility, which effectively solves the problem that existing PEGDMA-based solid electrolytes are difficult to simultaneously achieve good ion migration performance and mechanical flexibility.

[0017] Specifically, this invention utilizes a covalently cross-linked PEGDMA three-dimensional network and the reversible physical interaction of TPU to synergistically form a semi-interpenetrating network, constructing a solid polymer electrolyte with both excellent ion transport capabilities and mechanical flexibility, applicable to flexible electrochromic devices. During the cross-linking polymerization of PEGDMA and TPU, PEGDMA, acting as a bifunctional cross-linking agent, opens its double bonds at both ends, forming a molecular covalently cross-linked network with other PEGDMAs. Simultaneously, it copolymerizes with reactive sites on the TPU chain, forming dynamically reversible physical cross-linking points. PEGDMA provides a chemically cross-linked framework to construct continuous ion transport channels, while the polyether segments abundant in the PEGDMA three-dimensional cross-linked network provide continuous transport channels for electrolyte ion migration, thus ensuring high ionic conductivity. The introduction of TPU to construct a flexible polymer framework, through physical entanglement and hydrogen bonding interactions between chain segments, improves the ductility and mechanical stability of the solid polymer electrolyte, enabling it to maintain structural integrity and electrochemical stability under bending or deformation conditions. Specifically, the hard segments in TPU form physical cross-linking points through hydrogen bonding, enhancing the mechanical flexibility of the solid polymer electrolyte, while the soft segments impart high flexibility to the chain segments, enabling the solid polymer electrolyte to maintain structural integrity and electrochemical stability under bending or deformation conditions. Additionally, Li... + It dissociates and complexes with the C=O and -COC groups in the thermoplastic polyurethane structure, further enhancing ionic conductivity through a "coordination-dissociation" relay conduction mechanism. The synergistic effect of these two factors gives the solid polymer electrolyte high ionic conductivity and mechanical flexibility, providing rapid ionic compensation and a stable interfacial environment for the redox process of electrochromic materials, thereby improving electrochromic kinetic performance and enhancing the structural reliability and electrochemical stability of devices based on the solid polymer electrolyte under bending conditions. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the solid polymer electrolyte in an embodiment of the present invention.

[0019] Figure 2 This is a flowchart illustrating the fabrication process of the flexible electrochromic device in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the flexible electroluminescent thin film in Example 1 and its material structure formula.

[0021] Figure 4 The Fourier transform infrared spectrum of the solid polymer electrolyte in Example 1 is shown.

[0022] Figure 5 This is a stress-strain curve of the solid polymer electrolyte in Example 1.

[0023] Figure 6 This is the electrochemical impedance spectroscopy diagram of the solid polymer electrolyte in Example 1.

[0024] Figure 7 The graph shows the ionic conductivity results of the solid polymer electrolyte in Example 1.

[0025] Figure 8 Photographs of HV[TFSI]2FECD and SHV[TFSI]2FECD at different voltages.

[0026] Figure 9 The result is a graph showing the response time of HV[TFSI]2FECD.

[0027] Figure 10 The result is a graph showing the response time of SHV[TFSI]2FECD.

[0028] Figure 11 The cyclic voltammetry diagram of HV[TFSI]2FECD under bending conditions.

[0029] Figure 12 The cyclic voltammetry diagram of SHV[TFSI]2FECD under bending conditions.

[0030] Figure 13 The images show actual HV[TFSI]2FECD and SHV[TFSI]2FECD labels used for anti-counterfeiting of pharmaceuticals.

[0031] Figure 14 The graph shows the temperature changes over time between a conventional window and a smart window equipped with HV[TFSI]2FECD under continuous solar radiation.

[0032] Figure 15 The graph shows the temperature changes over time between a conventional window and a smart window equipped with SHV[TFSI]2FECD under continuous solar radiation. Detailed Implementation

[0033] This invention provides a solid polymer electrolyte, a flexible electrochromic device, and a method for preparing it. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0035] If the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0036] To address the challenge of existing PEGDMA-based solid electrolytes simultaneously achieving good ion migration performance and mechanical flexibility, this invention introduces TPU into a crosslinking system. TPU possesses a microphase-separated structure with hard and soft segments. The hard segments form crosslinking points, while the soft segments impart chain flexibility, enabling the construction of a covalent-physical synergistic network. This, in turn, alleviates the limitations imposed by high crosslinking degree on ion migration while maintaining mechanical stability. Specifically, this invention provides a method for preparing a solid polymer electrolyte, comprising the following steps: The solid polymer electrolyte is obtained by mixing PEGDMA, TPU and lithium salt and then performing crosslinking polymerization.

[0037] In this embodiment, a semi-interpenetrating network is formed synergistically by the covalently cross-linked PEGDMA three-dimensional network and the reversible physical interaction of TPU, constructing a solid polymer electrolyte with both good ion transport capability and mechanical flexibility, which can be applied to flexible electrochromic devices. During the cross-linking polymerization of PEGDMA and TPU, PEGDMA, as a bifunctional cross-linking agent, opens its double bonds at both ends and forms a molecular covalently cross-linked network with other PEGDMAs. Simultaneously, it copolymerizes with reactive sites on the TPU chain to form dynamically reversible physical cross-linking points. PEGDMA provides a chemically cross-linked framework to construct continuous ion transport channels, and the polyether segments abundant in the PEGDMA three-dimensional cross-linked network provide continuous transport channels for electrolyte ion migration, thereby ensuring high ionic conductivity of the system. The introduction of TPU to construct a flexible polymer framework, through physical entanglement and hydrogen bonding interactions between chain segments, improves the ductility and mechanical stability of the solid polymer electrolyte, enabling it to maintain structural integrity and electrochemical stability under bending or deformation conditions. Specifically, the hard segments in TPU form physical cross-linking points through hydrogen bonding, enhancing the mechanical flexibility of the solid polymer electrolyte, while the soft segments impart high flexibility to the chain segments, enabling the solid polymer electrolyte to maintain structural integrity and electrochemical stability under bending or deformation conditions. Additionally, Li... + It dissociates and complexes with the C=O and -COC groups in the TPU structure, further enhancing ionic conductivity through a "coordination-dissociation" relay conduction mechanism. The synergy of these two factors gives the solid polymer electrolyte high ionic conductivity and mechanical flexibility, providing rapid ionic compensation and a stable interfacial environment for the redox process of electrochromic materials, thereby improving electrochromic kinetic performance and enhancing the structural reliability and electrochemical stability of devices based on the solid polymer electrolyte under bending conditions.

[0038] Therefore, the solid polymer electrolyte prepared by the preparation method provided by the present invention has both high ionic conductivity and good mechanical flexibility, effectively solving the problem that existing PEGDMA-based solid electrolytes are difficult to simultaneously achieve good ion migration performance and mechanical flexibility.

[0039] In some embodiments, the lithium salt includes, but is not limited to, at least one of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiClO4 (lithium perchlorate), LiBF4 (lithium tetrafluoroborate), and LiPF6 (lithium hexafluorophosphate).

[0040] In some implementations, such as Figure 1 As shown, the preparation method of the solid polymer electrolyte specifically includes the following steps: S11. Mix PEGDMA, lithium salt and photoinitiator to obtain the first mixture; S12. Mix TPU with an organic solvent to obtain a second mixture; S13. The second mixture is added to the first mixture, and crosslinking polymerization is carried out under ultraviolet light for a preset time to obtain the solid polymer electrolyte.

[0041] In this embodiment, PEGDMA is used as the crosslinking monomer, and a stable three-dimensional crosslinked network is formed through in-situ polymerization initiated by ultraviolet light. The polyether segments rich in this network provide continuous transport channels for ion migration in the solid polymer electrolyte, thereby ensuring that the system has high ionic conductivity. At the same time, TPU is introduced to construct a flexible polymer skeleton. Through physical entanglement and hydrogen bonding interactions between the chain segments, the ductility and mechanical stability of the solid polymer electrolyte are improved, enabling the solid polymer electrolyte to maintain structural integrity and electrochemical stability under bending or deformation conditions, while further improving ionic conductivity.

[0042] Specifically, the photoinitiator absorbs photons under ultraviolet light irradiation, causing α-cleavage and generating active free radicals. These free radicals attack the acrylate double bonds (C=C) at both ends of the PEGDMA molecule, initiating the polymerization reaction. As a bifunctional crosslinking agent, PEGDMA, after its double bonds are opened, forms a molecular covalent crosslinking network with other PEGDMA molecules and also undergoes free radical copolymerization with reactive sites on the TPU chain, forming dynamically reversible physical crosslinking points, i.e., hydrogen bonds are formed between the -NH- group of TPU and the C=O or -O- group of PEGDMA. Under the influence of an electric field, the lithium salt dissociates into Li... + It will coordinate with the ether oxygen atom (-O-) on the PEGDMA chain, Li + It can "jump" between different ether oxygen sites, and Li + It will also dissociate and complex with the C=O and -COC groups in the TPU structure, thereby improving the ionic conductivity through a "coordination-dissociation" relay conduction mechanism.

[0043] In step S11, in some embodiments, the mass ratio of PEGDMA, lithium salt and photoinitiator is 0.8:(0.5~0.7):(0.2~0.4), for example, it can be 0.8:0.5:0.2, 0.8:0.5:0.4, 0.8:0.7:0.2 or 0.8:0.7:0.4, etc.

[0044] In some specific embodiments, the photoinitiator includes, but is not limited to, 2-hydroxy-2-methylphenylacetone (HOMPP).

[0045] In step S12, in some embodiments, the ratio of TPU to organic solvent is (0~2.0) g: (1~5) mL, and 0 g of TPU is not used.

[0046] In some embodiments, the organic solvent includes N,N-dimethylformamide (DMF).

[0047] In some embodiments, the total mass of the TPU accounts for 0% to 60% of the total mass of the first mixture and the TPU, but is not 0%. The addition of TPU can improve the ionic conductivity and mechanical flexibility of the solid polymer electrolyte.

[0048] In step S13, in some embodiments, the preset time is 0.5 to 1 hour, for example, it can be 30 minutes, 40 minutes, 50 minutes or 1 hour.

[0049] This invention also provides a solid polymer electrolyte, which is prepared using the preparation method described above.

[0050] This invention also provides a flexible electrochromic device, wherein the flexible electrochromic device includes a first flexible electrode, a second flexible electrode, and an electrochromic film located between the first flexible electrode and the second flexible electrode. The electrochromic film includes the solid polymer electrolyte of this invention as described above, as well as viologen-based electrochromic material and ferrocene dispersed in the solid polymer electrolyte.

[0051] In this embodiment, the solid polymer electrolyte exhibits high ionic conductivity, good ductility and mechanical stability, and maintains structural integrity and electrochemical stability even under bending or deformation conditions. The viologen-based electrochromic material and the ferrocene serving as the counter electrode achieve stable color transitions through a reversible redox reaction. This flexible electrochromic device not only demonstrates stable optical modulation capabilities and fast response characteristics, but also maintains good operational stability under repeated bending conditions, providing a promising technical solution for applications in flexible displays, smart windows, and dynamic anti-counterfeiting labels.

[0052] In some embodiments, the first flexible electrode includes a first flexible substrate and a first conductive metal oxide located on the first flexible substrate, and the second flexible electrode includes a second flexible substrate and a second conductive metal oxide located on the second flexible substrate. The first flexible substrate includes polyethylene terephthalate (PET), the first conductive metal oxide includes indium tin oxide (ITO), the second flexible substrate includes PET, and the second conductive metal oxide includes ITO.

[0053] In some embodiments, the viologen-based electrochromic material is R is at least one of the following: a chemical single bond, furanyl, thiophene, selenophene, ethylenedioxythiophene, and benzothiadiazolyl. It represents the bis(trifluoromethanesulfonyl)imide anion.

[0054] In this embodiment, the viologen-based electrochromic material has good redox reversibility and strong electron acceptor properties, and can undergo stable and reversible transitions between different redox states, accompanied by significant spectral changes.

[0055] In its initial state, the viologen-based electrochromic material mainly exists in a divalent cation state (V... 2+ When the viologen divalent cation is present, its absorption of visible light is weak, and the device appears pale yellow. When a reduction voltage is applied, the viologen divalent cation gains electrons and is reduced to a free radical cation state (V•). + Meanwhile, ferrocene, as the redox substance of the counter electrode, plays a charge compensation role, converting neutral ferrocene (Fc) into ferrocene cations (Fc). + ), releasing electrons to maintain the charge balance of the system.

[0056] This invention also provides a method for fabricating a flexible electrochromic device, wherein, as... Figure 2 As shown, it includes the following steps: S21. PEGDMA, TPU, lithium salt, viologen-based electrochromic material and ferrocene are mixed and cross-linked to obtain an electrochromic film. S22. A first flexible electrode and a second flexible electrode are respectively disposed on both sides of the electrochromic film to obtain the flexible electrochromic device.

[0057] In this invention, PEGDMA, TPU, lithium salt, viologen-based electrochromic material, and ferrocene are mixed and cross-linked to form an electrochromic film. PEGDMA and TPU form a semi-interpenetrating network, improving the ionic conductivity and mechanical flexibility of the electrochromic film. The viologen-based electrochromic material and ferrocene are dispersed within this network, achieving color change through redox reactions. The flexible electrochromic device prepared in this embodiment not only exhibits stable optical modulation capabilities and fast response characteristics but also maintains good operational stability under repeated bending conditions, providing a promising technical solution for applications in flexible displays, smart windows, and dynamic anti-counterfeiting labels.

[0058] In step S21, the specific selection of lithium salt and viologen-based electrochromic materials is described above and will not be repeated here.

[0059] In some implementations, step S21 specifically includes the following steps: S211. Mix PEGDMA, lithium salt and photoinitiator to obtain the first mixture; S212. Mix TPU with an organic solvent to obtain a second mixture; S213. The second mixture is added to the first mixture, and then viologen-based electrochromic material and ferrocene are added. After mixing, crosslinking polymerization is carried out under ultraviolet light for a preset time to obtain the solid polymer electrolyte.

[0060] In this embodiment, PEGDMA is used as the crosslinking monomer, and a stable three-dimensional crosslinked network is formed by in-situ polymerization initiated by ultraviolet light. The polyether segments rich in this network provide continuous transport channels for ion migration in the solid polymer electrolyte, thereby ensuring that the system has high ionic conductivity. At the same time, TPU is introduced to construct a flexible polymer skeleton. Through physical entanglement and hydrogen bonding interactions between the chain segments, the ductility and mechanical stability of the solid polymer electrolyte are improved, enabling the solid polymer electrolyte to maintain structural integrity and electrochemical stability under bending or deformation conditions.

[0061] The viologen-based electrochromic material and ferrocene, serving as the counter electrode, achieve stable color changes through a reversible redox reaction. This flexible electrochromic device not only exhibits stable optical modulation capabilities and fast response characteristics, but also maintains good operational stability under repeated bending conditions, providing a promising technical solution for applications in flexible displays, smart windows, and dynamic anti-counterfeiting labels.

[0062] Specifically, the photoinitiator absorbs photons under ultraviolet light irradiation, causing α-cleavage and generating active free radicals. These free radicals attack the acrylate double bonds (C=C) at both ends of the PEGDMA molecule, initiating the polymerization reaction. As a bifunctional crosslinking agent, PEGDMA, after its double bonds are opened, forms a molecular covalent crosslinking network with other PEGDMA molecules and also undergoes free radical copolymerization with reactive sites on the TPU chain, forming dynamically reversible "physical crosslinking points," i.e., hydrogen bonds are formed between the -NH- group of TPU and the C=O or -O- group of PEGDMA. Under the influence of an electric field, the lithium salt dissociates into Li... + It will coordinate with the ether oxygen atom (-O-) on the PEGDMA chain, Li + It can "jump" between different ether oxygen sites, and Li + It will also dissociate and complex with the C=O and -COC groups in the TPU structure, further improving the ionic conductivity through a "coordination-dissociation" relay conduction mechanism.

[0063] This invention also provides a drug anti-counterfeiting label, wherein the drug anti-counterfeiting label includes the flexible electrochromic device described above in this invention.

[0064] This invention also provides a smart window, wherein the smart window includes the flexible electrochromic device described above in this invention embodiment.

[0065] The present invention will be further described below through specific embodiments.

[0066] In the following embodiments, unless otherwise specified, the raw materials and equipment used are all commercially available products.

[0067] In the following embodiments, PEGDMA ( Purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number: P909886-250ML, with a number-average molecular weight (M). n The concentration is 550, containing 270–330 ppm of 2,6-di-tert-butyl-p-cresol (BHT) and 80–120 ppm of p-hydroxyanisole (MEHQ) as polymerization inhibitors.

[0068] The TPU used ( The 1185A10 is from BASF Germany, and its weight-average molecular weight (M) is... w The value is 80,000.

[0069] In the following embodiments, the ITO / PET substrate consists of a PET film and an ITO film with a thickness of 150 nm formed on the PET film.

[0070] Example 1: Preparation of Solid Polymer Electrolytes Mix 0.8 g of PEGDMA, 0.5 g of LiTFSI and 0.3 g of HOMPP and stir magnetically for 1 hour to obtain a homogeneous first mixture. Prepare four identical portions at the same time.

[0071] Different masses of TPU (0 g, 0.4 g, 1.08 g and 2.4 g, respectively) were added to DMF (5 mL) and stirred continuously at 70 °C until a clear and homogeneous second mixture with different TPU contents was obtained.

[0072] The second mixtures with different TPU contents were slowly added to the four portions of the first mixture, and stirred at 70 °C for 1 hour to ensure complete homogenization. After the mixtures were cooled to room temperature, solid polymer electrolyte mixture a (without TPU, as a control), solid polymer electrolyte mixture b (corresponding to the addition of 0.4 g of TPU), solid polymer electrolyte mixture c (corresponding to the addition of 1.08 g of TPU) and solid polymer electrolyte mixture d (corresponding to the addition of 2.4 g of TPU) were obtained.

[0073] Solid polymer electrolyte mixtures a, b, c, and d were irradiated with ultraviolet light for 1 hour to perform crosslinking polymerization, resulting in thin film solid polymer electrolytes a (denoted as LiFTP-0%), b (denoted as LiFTP-20%), c (denoted as LiFTP-40%), and d (denoted as LiFTP-60%).

[0074] test: (1) Chemical structural characterization of solid polymer electrolytes The chemical structure of the solid polymer electrolyte was analyzed using a Bruker Vertex 70V Fourier transform infrared spectroscopy system. The results are as follows: Figure 3 As shown, the solid polymer electrolytes LiFPT-20%, LiFPT-40%, and LiFPT-60% after the addition of TPU show a decrease in viscosity from 3300 cm⁻¹. -1 up to 3400 cm -1 A distinct vibrational band was observed nearby, corresponding to the -NH stretching vibration mode, indicating that TPU was successfully polymerized into the solid polymer electrolyte.

[0075] (2) Characterization of the mechanical properties of solid polymer electrolytes The mechanical properties of solid polymer electrolytes were analyzed using a ZQ-990B universal testing machine, and the results are as follows: Figure 4 As shown, the fracture strain of LiFPT-0% is only 20%, while the fracture strains of LiFPT-20%, LiFPT-40%, and LiFPT-60% significantly increase to 579%, 930%, and 1243%, respectively. These results indicate that the addition of TPU effectively improves the flexibility and ductility of solid polymer electrolytes.

[0076] (3) Characterization of the electrochemical performance of solid polymer electrolytes A thin-film solid polymer electrolyte was placed between two steel plates, and its electrochemical impedance was measured using an electrochemical workstation. The effective area of ​​the thin-film solid polymer electrolyte was 2 cm². 2 The electrochemical workstation used was a CHI760e. The electrochemical impedance spectroscopy results for the solid polymer electrolyte film are as follows: Figure 5 As shown, its ionic conductivity was calculated based on electrochemical impedance, and the results are as follows. Figure 6As shown, the ionic conductivity of LiFPT-0% is 0.43 mS / cm, while the ionic conductivity of LiFPT-20%, LiFPT-40%, and LiFPT-60% are 0.46 mS / cm, 0.55 mS / cm, and 1.43 mS / cm, respectively. The ionic conductivity of LiFPT-60% (1.43 mS / cm) is 3.3 times that of LiFPT-0% (0.43 mS / cm). This demonstrates that the addition of TPU can effectively improve the ionic conductivity of solid polymer electrolytes.

[0077] Example 2: Fabrication of a flexible electrochromic device The synthetic routes for HV[TFSI]2 and SHV[TFSI]2 are as follows:

[0078] Preparation of HV[TFSI]2: Following the synthetic route described above, 4,4'-bipyridine (i.e., compound a, 0.11 mg, 0.7 mmol) and 1-bromoheptane (2.51 mg, 7 mmol) were added to DMF (3 mL), and the mixture was stirred continuously at 130 °C for 72 hours. After the reaction was complete, the precipitate was filtered to obtain the crude product (yellow solid). The crude product was purified by column chromatography to obtain a pure product. The product was dissolved in 100 mL of hot water (65 °C), and excess LiTFSI was added (for ion exchange), separating the yellow precipitate. After filtration, the crude product was washed with water to remove excess lithium salt, yielding pure HV[TFSI]2 in 64% yield. The 1H NMR spectrum of the prepared HV[TFSI]2 is as follows: 1 ¹H NMR (400 MHz, DMSO-d⁶) δ 9.39 (s, 4H), 8.78 (s, 4H), 4.66 (s, 4H), 1.98 (s, 4H), 1.33 (s, 16H), 0.89 (s, 6H). The carbon NMR data are as follows: 13 C NMR (101 MHz, DMSO-d6) δ 149.12, 146.19, 127.08, 145.40, 124.74, 121.54, 118.34, 115.14, 61.432, 31.48, 28.52, 25.85, 22.42, 14.35. Fluorine NMR data are as follows: 19 F NMR (376 MHz, DMSO-d6) delta-78.8.

[0079] Preparation of SHV[TFSI]2: Following the above synthetic route, 2,5-bis(4-pyridyl)thiophene (i.e., compound b, 1.25 mg, 0.7 mmol) and 1-bromoheptane (2.51 mg, 7 mmol) were added to DMF (3 mL), and the mixture was stirred continuously at 130 °C for 72 hours. After the reaction was complete, the precipitate was filtered to obtain the crude product (yellow solid). The crude product was purified by column chromatography to obtain the pure product. The product was dissolved in 100 mL of hot water (65 °C), and excess LiTFSI was added (for ion exchange), separating the yellow precipitate. After filtration, the crude product was washed with water to remove excess lithium salt, yielding pure SHV[TFSI]2 in 68% yield. The 1H NMR spectrum of the prepared SHV[TFSI]2 is as follows: 1 ¹H NMR (400 MHz, DMSO-d6) δ 9.39 (s, 4H), 8.78 (s, 6H), 4.66 (s, 4H), 1.98 (s, 4H), 1.33 (s, 16H), 0.89 (s, 6H). The carbon NMR data are as follows: 13 C NMR (101 MHz, DMSO-d6) δ 147.09, 145.63, 143.00, 134.08, 124.74, 123.66, 121.54, 118.34, 115.14, 60.64, 31.48, 31.09, 28.55, 22.43, 14.36. Fluorine NMR data are as follows: 19 F NMR (376 MHz, DMSO-d6) delta-78.8.

[0080] Preparation of four solid polymer electrolyte mixtures with different TPU contents: 0.8 g of PEGDMA, 0.5 g of LiTFSI, and 0.3 g of HOMPP were mixed and magnetically stirred for 1 hour to obtain a homogeneous first mixture. Four identical portions were prepared simultaneously. Different masses of TPU (0 g, 0.4 g, 1.08 g, and 2.4 g, respectively) were added to DMF (5 mL) and stirred continuously at 70 °C until a clear and homogeneous second mixture with different TPU contents was obtained. The second mixtures with different TPU contents were slowly added to the four portions of the first mixture, and stirred continuously at 70 °C for 1 hour to ensure complete homogenization. The resulting mixtures were cooled to room temperature and stored to obtain solid polymer electrolyte mixture a (without TPU, as a control), solid polymer electrolyte mixture b (corresponding to the addition of 0.4 g of TPU), solid polymer electrolyte mixture c (corresponding to the addition of 1.08 g of TPU), and solid polymer electrolyte mixture d (corresponding to the addition of 2.4 g of TPU), respectively.

[0081] Fabrication of flexible electrochromic device based on HV[TFSI]2: 0.1 mM HV[TFSI]2 and 0.12 mM ferrocene were added to solid polymer electrolyte mixtures a to d, respectively, and ultrasonically treated for 5 minutes. Then, the mixture was magnetically stirred at room temperature for 12 hours to ensure complete dissolution and equilibrium, thereby obtaining a homogeneous third mixture. A 70 μm thick sealing film was applied to the ITO side of an ITO / PET substrate, and a circular opening with a diameter of 1.6 cm was formed in the sealing film. A pre-prepared third mixture was then injected into this circular opening. Next, a second ITO / PET substrate was carefully placed on the sealing film, allowing the third mixture to spread evenly, and then irradiated under UV light for 1 hour to promote crosslinking. Copper foil strips were then attached to the edges of the two ITO / PET substrates for conductivity. Finally, the device was sealed with UV-cured adhesive to prevent leakage and ensure structural integrity.

[0082] Fabrication of flexible electrochromic devices based on SHV[TFSI]2: The fabrication method is basically the same as that of flexible electrochromic devices based on HV[TFSI]2, except that HV[TFSI]2 is replaced with SHV[TFSI]2.

[0083] The flexible electrochromic devices based on HV[TFSI]2 and SHV[TFSI]2 are named HV[TFSI]2FECD and SHV[TFSI]2FECD, respectively, and the effective active area of ​​each flexible electrochromic device is 2 cm².

[0084] like Figure 7 As shown, in this embodiment, the flexible electrochromic device includes two ITO / PET substrates and an electrochromic film (EC film) located between the two ITO / PET substrates. The materials used to prepare the electrochromic film include HV[TFSI]2 or SHV[TFSI]2, and LiTFSI (…). ), PEGDMA ), TPU ( ) and diceroxide ( ).

[0085] test: (1) Coloring and fading images and response time characterization of flexible electrochromic devices like Figure 8As shown, HV[TFSI]2FECD is colored at a wavelength of 606 nm by applying a voltage of -1.3 V for 50 s and then bleached by applying a voltage of 0.5 V for 150 s. SHV[TFSI]2FECD is colored at a wavelength of 575 nm by applying a voltage of -1.2 V for 50 s and then bleached by applying a voltage of 0.5 V for 150 s. During coloring, HV[TFSI]2FECD and SHV[TFSI]2FECD are blue and red, respectively. After bleaching, HV[TFSI]2FECD and SHV[TFSI]2FECD are light yellow.

[0086] The transmittance was measured using a UV-Vis spectrophotometer (PerkinElmer λ 650s) to characterize the response time of the flexible electrochromic device. The results are as follows: Figure 9 and Figure 10 As shown. By Figure 9 It can be seen that the time required for HV[TFSI]2FECD to change its transmittance by 90% after coloring and bleaching is 3.6 s (t c ) and 9.8 s (t b Its optical contrast ( The figure is 81.8%. Figure 10 It can be seen that the time required for SHV[TFSI]2FECD to change its transmittance by 90% after coloring and bleaching is 3.2 s (t). c ) and 8.4 s (t b Its optical contrast ( The accuracy rate was 81.9%, indicating that the device exhibited a fast response time and high optical contrast.

[0087] (2) Cyclic voltammetry test of flexible electrochromic devices under bending conditions Cyclic voltammetry testing of the flexible electrochromic device was performed using a three-electrode system at a scan rate of 100 mV / s over a potential range of -1.8 V to 0.5 V, using an electrochemical workstation of model CHI760e.

[0088] Test results are as follows Figure 11 and Figure 12 As shown. The bending diameter of the device is 5 cm. After 500 bending cycles, the current density of both devices is consistent with the curve after 0 cycles, and after 1000 cycles, the current density decreases slightly. Despite the deterioration in device characteristics, the electrochromic film exhibits high durability even after 1000 cycles of repeated bending tests, without mechanical damage.

[0089] Example 3: Flexible electrochromic devices used in anti-counterfeiting labels for pharmaceuticals Specific testing steps: The flexible electrochromic devices (HV[TFSI]2FECD and SHV[TFSI]2FECD) prepared in Example 2 were attached to a drug with a diameter of 5 cm, and voltage was applied to color the drug to achieve anti-counterfeiting. The electrochemical workstation used was a CHI760e.

[0090] like Figure 13 As shown, in the initial state, the coded patterns such as "CAS," "NAME," and "SUST," as well as the star pattern, are almost indistinguishable. After applying an external voltage of -1 V, the flexible electrochromic device exhibits distinct blue and red hues. Therefore, the pre-designed pattern is displayed with high contrast. When the voltage is removed or reversed, the device returns to its initial state, and the pattern disappears. This electrically triggered reversible display process enables dynamic information verification, thus providing an effective strategy for anti-counterfeiting applications in pharmaceuticals.

[0091] Example 4: Fabrication of Flexible Electrochromic Devices for Smart Windows Using the HV[TFSI]2FECD and SHV[TFSI]2FECD prepared in Example 2, a miniature house model with a 5cm × 5cm smart window was constructed (size: 18.1 cm × 12.7 cm × 15.0 cm). A conventional window (made of polyvinyl chloride plastic) was used as a control. Solar radiation was transmitted through the smart window into the indoor space using an AM1.5 solar simulator. The photothermal regulation capability was evaluated by monitoring changes in indoor temperature.

[0092] The results are as follows Figure 14 and Figure 15 As shown, after 30 minutes of sunlight exposure, the indoor temperature of a traditional window gradually rises to 26.0 ℃, while the indoor temperature of a house equipped with HV[TFSI]2FECD and SHV[TFSI]2FECD smart windows only reaches 23.5 ℃ and 22.8 ℃ respectively during the same period. Compared to traditional windows, the smart windows reduce the indoor temperature by 2.5 ℃ and 3.5 ℃ respectively when in operation. This smart window demonstrates excellent energy-saving performance and has great potential for application in the field of energy-efficient buildings.

[0093] The results above demonstrate that the flexible electrochromic device constructed from viologen-based electrochromic materials and solid polymer electrolytes exhibits stable and reversible electrochromic properties. Even after 1000 bending cycles, the device maintains excellent optical characteristics, structural integrity, and relatively stable electrochemical performance. When applied to smart windows, the prepared flexible electrochromic device can effectively reduce solar radiation entering the room by adjusting light transmittance, thereby reducing indoor heat accumulation and lowering the ambient temperature, thus reducing building energy consumption to a certain extent and meeting the energy-saving control requirements of smart windows. Furthermore, the prepared flexible electrochromic device also has potential application value in the field of pharmaceutical anti-counterfeiting.

[0094] In summary, this invention provides a solid polymer electrolyte, a flexible electrochromic device, and a preparation method thereof. The solid polymer electrolyte prepared using the method provided by this invention possesses both high ionic conductivity and good mechanical flexibility, effectively solving the problem that existing PEGDMA-based solid electrolytes struggle to simultaneously achieve good ion migration performance and mechanical flexibility.

[0095] Specifically, this invention utilizes a covalently cross-linked PEGDMA three-dimensional network and the reversible physical interaction of TPU to synergistically form a semi-interpenetrating network, constructing a solid polymer electrolyte with both excellent ion transport capabilities and mechanical flexibility, applicable to flexible electrochromic devices. During the cross-linking polymerization of PEGDMA and TPU, PEGDMA, acting as a bifunctional cross-linking agent, opens its double bonds at both ends, forming a molecular covalently cross-linked network with other PEGDMAs. Simultaneously, it copolymerizes with reactive sites on the TPU chain, forming dynamically reversible physical cross-linking points. PEGDMA provides a chemically cross-linked framework to construct continuous ion transport channels, while the polyether segments abundant in the PEGDMA three-dimensional cross-linked network provide continuous transport channels for electrolyte ion migration, thus ensuring high ionic conductivity. The introduction of TPU to construct a flexible polymer framework, through physical entanglement and hydrogen bonding interactions between chain segments, improves the ductility and mechanical stability of the solid polymer electrolyte, enabling it to maintain structural integrity and electrochemical stability under bending or deformation conditions. Specifically, the hard segments in TPU form physical cross-linking points through hydrogen bonding, enhancing the mechanical flexibility of the solid polymer electrolyte, while the soft segments impart high flexibility to the chain segments, enabling the solid polymer electrolyte to maintain structural integrity and electrochemical stability under bending or deformation conditions. Additionally, Li... +It dissociates and complexes with the C=O and -COC groups in the thermoplastic polyurethane structure, further enhancing ionic conductivity through a "coordination-dissociation" relay conduction mechanism. The synergistic effect of these two factors gives the solid polymer electrolyte high ionic conductivity and mechanical flexibility, providing rapid ionic compensation and a stable interfacial environment for the redox process of electrochromic materials, thereby improving electrochromic kinetic performance and enhancing the structural reliability and electrochemical stability of devices based on the solid polymer electrolyte under bending conditions.

[0096] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a solid polymer electrolyte, characterized in that, Includes the following steps: Polyethylene glycol dimethacrylate, thermoplastic polyurethane, and lithium salt were mixed and crosslinked to obtain the solid polymer electrolyte.

2. The preparation method according to claim 1, characterized in that, The preparation method of the solid polymer electrolyte specifically includes the following steps: Polyethylene glycol dimethacrylate, lithium salt and photoinitiator are mixed to obtain the first mixture; Thermoplastic polyurethane is mixed with an organic solvent to obtain a second mixture; The second mixture is added to the first mixture, and after cross-linking polymerization under ultraviolet light for a preset time, the solid polymer electrolyte is obtained.

3. The preparation method according to claim 2, characterized in that, The lithium salt includes at least one of LiTFSI, LiClO4, LiBF4, and LiPF6; and / or, the organic solvent includes N,N-dimethylformamide.

4. The preparation method according to claim 2, characterized in that, The mass ratio of polyethylene glycol dimethacrylate, lithium salt, and photoinitiator is 0.8:(0.5~0.7):(0.2~0.4); and / or; The thermoplastic polyurethane accounts for 0% to 60% of the total mass of the first mixture and the thermoplastic polyurethane, but not 0%; and / or, The preset time is 0.5~1 h.

5. A solid polymer electrolyte, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. A flexible electrochromic device, characterized in that, The flexible electrochromic device includes a first flexible electrode, a second flexible electrode, and an electrochromic film located between the first flexible electrode and the second flexible electrode. The electrochromic film includes the solid polymer electrolyte of claim 5, as well as viologen-based electrochromic material and ferrocene dispersed in the solid polymer electrolyte.

7. The flexible electrochromic device according to claim 6, characterized in that, The viologen-based electrochromic material is R is at least one of a single chemical bond, furanyl, thiophene, selenyl, ethylenedioxythiophene, and benzothiadiazole.

8. A method for fabricating a flexible electrochromic device, characterized in that, Includes the following steps: Polyethylene glycol dimethacrylate, thermoplastic polyurethane, lithium salt, viologen-based electrochromic material and ferrocene are mixed and crosslinked to obtain an electrochromic film. A first flexible electrode and a second flexible electrode are respectively disposed on both sides of the electrochromic film to obtain the flexible electrochromic device.

9. A pharmaceutical anti-counterfeiting label, characterized in that, The anti-counterfeiting label for pharmaceuticals includes the flexible electrochromic device as described in any one of claims 6-7.

10. A smart window, characterized in that, The smart window includes the flexible electrochromic device according to any one of claims 6-7.

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