A flexible copolymer with electrochromic and electrochemical energy storage performance and a preparation method and application thereof

Abstract

This invention belongs to the technical field of copolymers and their electrochemical applications, specifically relating to a flexible copolymer with electrochromic and electrochemical energy storage properties, its preparation method, and its applications. The preparation method of the flexible copolymer with electrochromic and electrochemical energy storage properties of this invention includes the following steps: adding 9-fluorenic acid and 3-bromo-4-methylthiophene to a BFEE, performing polymerization using an electrochemical workstation, and obtaining PBMTh-co-PFCA on the working electrode. The flexible copolymer with electrochromic and electrochemical energy storage properties, its preparation method, and its applications provided by this invention are rationally designed and easy to operate. The flexible copolymer of this invention, PBMTh-co-PFCA, has an interconnected porous network structure, increasing the contact area. Using the PBMTh-co-PFCA material of this invention to fabricate ESD significantly improves the electrochemical response and charge storage capacity.

Description

Technical Field

[0001] This invention belongs to the field of copolymers and their electrochemical applications, specifically relating to a flexible copolymer with electrochromic and electrochemical energy storage properties, its preparation method, and its applications. Background Technology

[0002] Electrochromism, a novel electrochemical color-regulating technology, allows for precise control of a material's light absorption, transmission, or reflection properties by applying an electric field. In recent years, the cross-disciplinary integration of electrochromic technology with other fields has spurred the development of various new smart devices and applications, including smart energy storage devices combined with supercapacitors, and energy storage-type smart window systems. The functionality of electrochromic devices (ECDs) has been extended to energy storage devices known as electrochromic supercapacitors (ECS). As an emerging energy storage technology, it possesses unique advantages over traditional energy storage devices: it can utilize an electric field to regulate its own optical properties, achieving reversible changes in color and transparency while simultaneously storing and releasing energy.

[0003] As the internet and microelectronics technologies gradually integrate into human production and daily life, people's interest in miniaturized, flexible, wearable, and intelligent electronic devices is growing stronger. Flexible electrochromic supercapacitors, as highly promising intelligent energy storage components for wearable smart electronic products, have received widespread attention and in-depth research. However, this field still faces many challenges: low device energy storage capacity, insufficient electrochromic contrast, poor accuracy in energy storage state recognition, and difficulties in large-scale fabrication of high-performance electrode materials.

[0004] The electrode materials commonly used in ECS (Electrochemical Creature Systems) mainly include conductive polymers and transition metal oxides. However, flexible ECS needs to withstand mechanical deformations such as bending, curling, and stretching, and the rigid crystal structure and low ductility of transition metal oxides present significant limitations. In contrast, conductive polymers, with their excellent electrochromic properties (multicolor changes, high contrast, and fast response), energy storage characteristics (high specific capacitance and fast charge / discharge rates), and especially their superior flexibility, have become ideal candidate materials for flexible wearable ECS.

[0005] Polyfluorene-based conductive polymers exhibit unique advantages in supercapacitor applications due to their high conjugation stability, high specific capacitance, and long cycle life. However, their electrochromic properties, such as a narrow color change range, moderate light contrast, and relatively long response time, limit their application in the ECS field.

[0006] To address this issue, copolymerizing polyfluorene with different conjugated units (such as thiophene, carbazole, and benzothiadiazole) can alter the conjugation length and energy level structure of the copolymer, thereby effectively improving its electrochromic properties and flexibility. For example, the paper "Dual redox-centered p(thiophene-TPA) conjugated polymers for high-performance flexible electrochromic supercapacitors" (Xu Cheng, Du Chunhui, et al.), published in *Chemical Engineering Journal*, Volume 510, April 15, 2025, 161744, reported that introducing a boron trifluoride diethyl ether system reduced the polymer's oxidation potential, mitigating the risk of structural degradation and active site deactivation in PTTPA electrode materials. However, electrochromic supercapacitors need to withstand repeated charge-discharge cycles and color switching; the long-term cycling stability of PTTPA materials requires further improvement, and there is a risk of thermal runaway at high temperatures.

[0007] Electrochemical polymerization is a common method for preparing conductive polymers, which can directly form a uniform conductive polymer film on the substrate surface. This film can then be used directly as the active layer of a device. This process avoids the introduction of inert components and interfacial voids by binders during device assembly, significantly simplifying the device fabrication process and improving device performance. However, when preparing copolymers using electrochemical polymerization, the comonomers need to have similar electrochemical oxidation potentials in the same electrolyte system, a condition that is often difficult to meet.

[0008] Typically, polyfluorene monomers have high electrochemical oxidation potentials, ranging from approximately 1.5 to 2.0 V in neutral electrolyte systems. In contrast, common monosubstituted thiophenes generally have lower electrochemical oxidation potentials, ranging from approximately 1 to 1.5 V in neutral electrolyte systems. In particular, the commonly used 3,4-ethylenedioxythiophene has an oxidation potential of approximately 1.0 V, which makes copolymerization of polyfluorene and polythiophene difficult to achieve. Summary of the Invention

[0009] The technical problem this invention aims to solve is to overcome the aforementioned deficiencies in existing technologies and provide a flexible copolymer with electrochromic and electrochemical energy storage properties, its preparation method, and its applications. The preparation method is rationally designed and simple to operate. The flexible copolymer of this invention is poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenylcarboxylic acid) (PBMTh-co-PFCA), which has an interconnected porous network structure, increasing the contact area. Using the PBMTh-co-PFCA material of this invention to fabricate a flexible electrochromic supercapacitor significantly improves the electrochemical response and charge storage capacity.

[0010] The present invention discloses a method for preparing a flexible copolymer with electrochromic and electrochemical energy storage properties, comprising the following steps: adding 9-fluorencarboxylic acid and 3-bromo-4-methylthiophene to boron trifluoride diethyl ether (BFEE), performing polymerization using an electrochemical workstation, and after polymerization, allowing it to air dry naturally to obtain the flexible copolymer poly(3-bromo-4-methylthiophene)-co-poly(9-fluorencarboxylic acid) on the working electrode. All solutions are degassed by a stream of dry argon before use, and a slight argon overpressure is maintained during the experiment.

[0011] Preferably, the working electrode of the electrochemical workstation is a PET-ITO electrode, the counter electrode is a platinum wire, and the reference electrode is an Ag / AgCl electrode. The diameter of the platinum wire used is 0.5 mm.

[0012] Preferably, the constant potential of the electrochemical workstation is 1.7~1.9V, more preferably 1.8V. The electrochemical workstation used is the KOST CS310M electrochemical workstation.

[0013] In any of the above preferred embodiments, the molar ratio of 9-fluorenic acid to 3-bromo-4-methylthiophene is 2:1 to 6:1, preferably 3:1.

[0014] Preferably, 9-fluorenic acid and 3-bromo-4-methylthiophene are added to boron trifluoride diethyl ether, wherein the concentration of 9-fluorenic acid is 0.04~0.08 mol / L, preferably 0.06 mol / L, and the concentration of 3-bromo-4-methylthiophene is 0.01~0.03 mol / L, preferably 0.02 mol / L.

[0015] The poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenylcarboxylic acid) (PBMTh-co-PFCA) of the present invention has a molecular weight of 1000-1500, preferably around 1200, which is determined by gel chromatography.

[0016] Preferably, the preparation method of PBMTh-co-PFCA includes the following steps: adding 9-fluorenic acid and 3-bromo-4-methylthiophene to boron trifluoride diethyl ether (BFEE), performing polymerization using an electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire as the counter electrode, and an Ag / AgCl electrode as the reference electrode, and obtaining PBMTh-co-PFCA on the working electrode.

[0017] A further preferred method for preparing PBMTh-co-PFCA includes the following steps: adding 9-fluorenic acid and 3-bromo-4-methylthiophene to boron trifluoride diethyl ether (BFEE), wherein the concentration of 9-fluorenic acid is 0.06 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.02 mol / L; performing polymerization using an electrochemical workstation, wherein the working electrode is a PET-ITO electrode, the counter electrode is a platinum wire, and the reference electrode is an Ag / AgCl electrode; and obtaining PBMTh-co-PFCA on the working electrode.

[0018] Application of the flexible copolymer with electrochromic and electrochemical energy storage properties: The obtained copolymer material is applied to the preparation of flexible electrochromic supercapacitors.

[0019] Preferably, the specific fabrication steps of the flexible electrochromic supercapacitor are as follows: Using an electrochemical workstation, an electrode coated with the prepared flexible copolymer poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenylcarboxylic acid) is used as the working electrode, and an electrode coated with poly(3,4-ethylenedioxythiophene) (PEDOT) is used as the counter electrode. A sandwich structure is formed between the working and counter electrodes by fixing them with a gel electrolyte. After drying, the flexible electrochromic supercapacitor is obtained. The drying temperature is maintained at a constant 65°C. All solutions are degassed by a dry argon gas flow before use, and a slight argon overpressure is maintained during the experiment. To maintain the balance of injected / output charges, the two electrodes (working and counter electrodes) need the same amount of charge during the redox process. Before constructing the device, the PBMTh-co-PFCA electrode is in a neutral state, while the PEDOT electrode is in an oxidized state.

[0020] The preparation steps of the poly(3,4-ethylenedioxythiophene) coated electrode are as follows: 3,4-ethylenedioxythiophene is added to acetonitrile (ACN) and boron tetrabutylammonium tetrafluoride (TBATFB). The concentration of PEDOT in ACN is 0.05 mol / L-0.1 mol / L, and the concentration of TBATFB in ACN is 0.1 mol / L. Polymerization is carried out using an electrochemical workstation, with PET-ITO as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential is 1.3~1.5V. The platinum wire used has a diameter of 0.5 mm. The electrochemical workstation used is a KOST CS310M electrochemical workstation. All solutions are degassed by a dry argon gas flow before use, and a slight argon overpressure is maintained during the experiment. After 3,4-ethylenedioxythiophene is polymerized on the electrode, the resulting poly(3,4-ethylenedioxythiophene) has a molecular weight of 600-1000, with a preferred molecular weight of 700.

[0021] The gel electrolyte is prepared by mixing lithium perchlorate, acetonitrile, polymethyl methacrylate, and polycarbonate. Preferably, lithium perchlorate, acetonitrile, polymethyl methacrylate, and polycarbonate are mixed in a mass ratio of 3:70:7:20 and stirred until a gel state is reached.

[0022] The preparation process of poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenic acid) of the present invention is as follows:

[0023] (n and m are determined by the molecular weight of the polymer).

[0024] This invention investigated the anodic polarization curves of FCA (9-fluorencarboxylic acid), BMTh (3-bromo-4-methylthiophene), and FCA+BMTh (FCA to BMTh molar ratio of 3:1) in a BFEE solution. The results showed that the electrochemical oxidation potentials of FCA and BMTh were similar, at 1.36 V and 1.44 V, respectively. This small potential difference allowed for the copolymerization of FCA and BMTh. The electrochemical oxidation potential of FCA+BMTh (FCA to BMTh molar ratio of 3:1) was between 1.36 V and 1.44 V (approximately 1.42 V), which is attributed to changes in the electrochemical environment caused by the continuous deposition of these two monomers during anodic oxidation. The results indicate that in BFEE, both FCA and BMTh monomers undergo simultaneous electrochemical oxidation, and the copolymer chains are composed of alternating amounts of these two monomers. The increase in redox current during continuous cyclic voltammetry scans indicates an increase in the amount of polymer on the electrode. Notably, the redox peak current value of PFCA is smaller compared to that of PBMTh. This indicates that the electrochemical polymerization of FCA is more difficult than that of BMTh. The redox peak potentials of PFCA in the 10th cycle are 1.32 V and 0.81 V, respectively. For PBMTh, the redox peak potentials in the 10th cycle are 1.46 V and 0.62 V, respectively. When FCA and BMTh are mixed, the redox peak positions are 1.38 V and 0.75 V, respectively, thus producing different potential values ​​in a new redox peak between the potentials of PFCA and PBMTh, indicating that a copolymerization reaction occurred between PFCA and PBMTh.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) The poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenic acid) copolymer material of the present invention has a porous network morphology, which effectively increases the specific surface area of ​​the material; it is self-supporting and has good flexibility; at the same time, the material also exhibits good electrochromic properties and electrochemical energy storage properties.

[0027] (2) The electrochromic supercapacitor constructed from the poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenyl carboxylic acid) copolymer material prepared in this invention has good electrochromic performance, high power, high energy density, good bending stability and constant current charge and discharge stability, and has great application value and broad application prospects in flexible wearable energy storage devices.

[0028] (3) The preparation method of the poly(3-bromo-4-methylthiophene)-co-poly(9-fluorencarboxylic acid) copolymer material of the present invention is reasonably designed and utilizes electrochemical copolymerization to solve the problem of the difficulty in achieving copolymerization of polyfluorene and polythiophene. Introducing electron-withdrawing groups on the thiophene monomer can improve its electrochemical oxidation potential, but it will also increase the difficulty of thiophene electrochemical polymerization. Previous studies have shown that after introducing two bromine atoms (3,4-dibromothiophene) at the 3,4 positions of thiophene, it is difficult for it to polymerize in conventional acetonitrile + tetrabutylammonium tetrafluoride electrolyte. At this time, it is necessary to regulate the electrochemical oxidation potential of thiophene through substituent modification. 3-bromo-4-methylthiophene contains both electron-withdrawing groups (bromine) and electron-donating groups (methyl), and its electrochemical oxidation potential is comparable to that of 9-fluorencarboxylic acid. Therefore, the copolymer prepared by copolymerization of 3-bromo-4-methylthiophene and 9-fluorencarboxylic acid has excellent electrochromic properties, supercapacitor properties and cycle stability by means of the synergistic effect of the two components. Attached Figure Description

[0029] Figure 1 Fourier transform infrared spectra of the PFCA, PBMTh, and PBMTh-co-PFCA copolymer of Example 1 are shown.

[0030] Figure 2 The image shows a scanning electron microscope (SEM) image of PFCA (A), PBMTh (B), and PBMTh-co-PFCA copolymer (C) from Example 1.

[0031] Figure 3 The molecular geometry diagram obtained by DFT calculation of the PBMTh-co-PFCA copolymer prepared in Example 1 is shown.

[0032] Figure 4 The potential of the PBMTh-co-PFCA copolymer prepared in Example 1 was scanned from -0.2V to 1.5V, and the absorbance changed with color (i.e. potential).

[0033] Figure 5 Electrochromic cycling diagrams of the PBMTh-co-PFCA copolymer prepared in Example 1 at two characteristic wavelengths of 520 nm and 730 nm.

[0034] Figure 6 The single-cycle transmittance-time response curves of the PBMTh-co-PFCA copolymer prepared in Example 1 at a wavelength of 520 nm are shown.

[0035] Figure 7 The single-cycle transmittance-time response curves of the PBMTh-co-PFCA copolymer prepared in Example 1 at a wavelength of 730 nm are shown.

[0036] Figure 8The image shows the charge-discharge (GCD) curve of the PBMTh-co-PFCA copolymer prepared in Example 1.

[0037] Figure 9 The image shows the TGA diagram of the PFCA, PBMTh, and PBMTh-co-PFCA copolymer from Example 1.

[0038] Figure 10 This is a schematic diagram of the sandwich structure of the ESD constructed in Example 6.

[0039] Figure 11 The spectroelectrochemical curves of the ESD constructed in Example 6 and its electrochromic cycling diagrams at different voltages are shown.

[0040] Figure 12 The single-cycle transmittance-time response curves of the ESD constructed for Example 6 at a wavelength of 485nm are shown.

[0041] Figure 13 The single-cycle transmittance-time response curves of the ESD constructed for Example 6 at a wavelength of 630 nm are shown.

[0042] Figure 14 The transmittance-time curves of the ESD constructed for Example 6 at a wavelength of 485nm.

[0043] Figure 15 The transmittance-time curves of the ESD constructed for Example 6 at a wavelength of 630 nm are shown.

[0044] Figure 16 The constant current charge-discharge (GCD) curve of the ESD constructed for Example 6.

[0045] Figure 17 A schematic diagram of the power density and energy density of the ESD constructed in Example 6.

[0046] Figure 18 A comparison of the cyclic voltammetry curves of the initial state of the ESD constructed in Example 6 and the cyclic voltammetry curves after 200 mechanical bends.

[0047] Figure 19 The figure shows the stability test results of the ESD constructed in Example 6 after constant current charge and discharge. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments.

[0049] Example 1

[0050] The preparation method of PBMTh-co-PFCA material of the present invention includes the following steps: 9-fluorenic acid (FCA) and 3-bromo-4-methylthiophene (BMTh) are added to boron trifluoride diethyl ether (BFEE) so that the concentration of 9-fluorenic acid is 0.06 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.02 mol / L. Electrochemical polymerization is carried out under computer control using a KOST CS310M electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire with a diameter of 0.5 mm as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential of 1.8V is used for 30 s. After polymerization is completed, the material is naturally air-dried for later use. PBMTh-co-PFCA is obtained on the PET-ITO electrode, and the molecular weight is determined to be 1200 by gel permeation chromatography.

[0051] All solutions were degassed by a stream of dry argon before use, and argon was kept under overpressure during the preparation process.

[0052] Poly-9-fluorenecarboxylic acid (PFCA): A high molecular weight compound formed by polymerization of 9-fluorenecarboxylic acid monomer, which is the same raw material as above. The degree of polymerization is 4 and the molecular weight is 835. (The preparation method is based on the article "Low-potential facile electrosyntheses of high-quality free-standing poly(fluorene-9-carboxylic acid) films" published by Nie Guangming et al. on November 20, 2007 in Electrochemistry Communications 10(2008) 186-189).

[0053] Poly(3-bromo-4-methylthiophene) (PBMTh): A high molecular weight compound formed by polymerization of the same raw material, 3-bromo-4-methylthiophene monomer, with a degree of polymerization of 4 and a molecular weight of 860. (The preparation method described in the graduate thesis of Qingdao University of Science and Technology, "Electrosynthesis and Electrochromic Properties of Conductive Polythiophene Derivatives" (Y1740322), completed and published on June 3, 2010).

[0054] (1) Fourier transform infrared spectroscopy experiments were conducted on the PFCA, PBMTh and PBMTh-co-PFCA copolymer prepared in the examples above. The experimental results are as follows: Figure 1 As shown in the figure, for PBMTh, the CH stretching vibration of the methyl group is at approximately 2900 cm⁻¹. -1This occurs at the 1400-1500 cm⁻¹, which is a typical region for alkyl CH vibrations. The C=C main chain stretching vibration of the thiophene ring is located at 1400-1500 cm⁻¹. -1 In this region, the CS stretching vibration of the thiophene ring is between 1000-1200 cm⁻¹. -1 The area was observed. It is located at 500-700 cm. -1 The absorption peak is attributed to the C-Br bond vibration. For PFCA, the C=C main chain stretching vibration of the fluorene ring is concentrated at 1400-1500 cm⁻¹. -1 The region. C=O stretching vibration is observed at 1700 cm. -1 A strong absorption peak is located at 3300 cm⁻¹. -1 The broad peaks are caused by the OH stretching vibration. They are located at 734, 816, and 887 cm⁻¹. -1 The absorption peak at 1024 cm⁻¹ is caused by the off-plane vibration of the CH group of the phenyl group, while the absorption peak at 1024 cm⁻¹ is caused by the off-plane vibration of the CH group of the phenyl group. -1 The absorption peaks at these locations are attributed to the in-plane vibrations of the phenyl group (C2 and C7). These spectra are similar to those of 1,2,4-trisubstituted benzene rings in terms of wavenumber and absorption bands. Therefore, it can be inferred that the polymerization sites of FCA are mainly located at C2 and C7. The infrared spectrum of the PBMTh-co-PFCA copolymer shows that its spectral absorption simultaneously encompasses the characteristic signals of both PBMTh and PFCA, proving that the copolymer was successfully prepared.

[0055] (2) Scanning electron microscope images of the above PFCA, PBMTh, and the PBMTh-co-PFCA copolymer prepared in the examples, as shown below. Figure 2 As shown, Figure 2In the figures, (A) represents PFCA, (B) represents PBMTh, and (C) represents PBMTh-co-PFCA. As can be seen, PFCA exhibits a granular structure with a particle size of approximately 0.6 μm. The particles are relatively large, tightly packed, and have few pores, representing a relatively dense morphology. PBMTh also exhibits a particle-aggregated structure, but the particle size is slightly smaller than that of PFCA. There are some loose pores between the particles, resulting in a particle-stacking morphology and low porosity. PBMTh-co-PFCA displays a large number of interconnected porous networks and a rough surface. Clearly, the specific surface area of ​​the prepared PBMTh-co-PFCA is significantly higher than that of the homopolymers PBMTh and PFCA. The average pore size of PBMTh-co-PFCA is 150 nm, the average particle size is 200 nm, and the average porosity is 55%. The porous network structure of PBMTh-co-PFCA can significantly increase the contact area between the electrode and the electrolyte, providing abundant ion transport channels, thereby achieving more thorough redox reactions and better reversibility. Meanwhile, its high specific surface area can provide more active sites, thereby significantly improving electrochemical response and charge storage capacity.

[0056] (3) The PBMTh-co-PFCA prepared in the above examples exhibits a self-supporting state and excellent flexibility. The formation of this self-supporting solid film is attributed to the hydrogen bond interaction between carboxyl groups in the copolymer structure, which enables the polymer to form a network structure. DFT calculations were performed on its structure, revealing two sites between the carbonyl oxygen atom and the hydroxyl hydrogen atom, resulting in molecular geometry bond lengths of 1.655 Å and 1.650 Å, respectively (e.g., ...). Figure 3 (As shown). This is because when flexible thiophene units and rigid fluorene units are copolymerized, the rigidity of the polyfluorene structure decreases, and the copolymer material exhibits excellent flexibility.

[0057] (4) The electrochromic properties of the PBMTh-co-PFCA prepared in this embodiment were tested:

[0058] a. For PBMTh-co-PFCA testing, the potential was swept from -0.2V to 1.5V, and the absorbance as a function of color (i.e., potential) is shown in the graph below. Figure 4 As shown, Figure 4The color blocks show that -0.2V corresponds to red, 1.0V to light blue, and 1.5V to bluish-violet. It can be seen that at -0.2V, an absorption peak appears at 520nm, which is due to the π electrons in the neutral state of PBMTh transitioning from the π orbital to the π antibonding orbital. When PBMTh-co-PFCA is in the neutral state, it exhibits a red color similar to PBMTh. As the potential gradually increases, the absorption peak at 520nm gradually weakens. When the applied potential increases to 1.0V, a new absorption peak appears at approximately 730nm. In this state, PBMTh-co-PFCA is in an oxidized state, and its color is light blue. As the potential continues to increase, the absorption peak at 730nm gradually strengthens. When the applied potential reaches 1.5V, PBMTh-co-PFCA exhibits bluish-violet. Therefore, the prepared copolymer PBMTh-co-PFCA has good electrochromic properties, and its color can reversibly change to red, light blue, and bluish-violet.

[0059] b. Using the chronopotentiometric method, the electrochromic cycling patterns of the PBMTh-co-PFCA copolymer at two characteristic wavelengths of 520 nm and 730 nm were measured, as follows: Figure 5 As shown, both curves exhibit regular, periodic rectangular waves, indicating that the material can rapidly and stably switch reversibly between the oxidized and reduced states, with no significant performance degradation within a 200-second test cycle, demonstrating excellent cycle stability. Specifically, the transmittance change (ΔT) at 520 nm is 22%, corresponding to the color switch between the neutral (red) and oxidized states; the transmittance change at 730 nm is even higher, reaching 42%, reflecting a stronger electrochromic contrast in the longer wavelength region, which perfectly corresponds to the conclusion in the aforementioned spectroelectrochemistry that the absorption peak at 730 nm increases with potential. Furthermore, the steep rise and fall edges of the curves indicate a fast response speed in switching between the two states, further verifying that the copolymer possesses good and stable reversible electrochromic properties.

[0060] c. Single-cycle transmittance-time response curves of the PBMTh-co-PFCA copolymer at two characteristic wavelengths of 520 nm and 730 nm, as shown in the figure. Figure 6-7 As shown, Figure 6 The graph shows the single-cycle transmittance-time response curve at 520nm. It can be seen that the initial transmittance of the material is about 48%, and the highest transmittance after switching is about 67%, with a transmittance change of ΔT=22%. The red box indicates that the rise time from low transmittance to high transmittance is 1.4s (the switching speed from reduced state to oxidized state), and the fall time from high transmittance back to low transmittance is 1.2s (the switching speed from oxidized state to reduced state). This indicates that at a wavelength of 520nm, the material switches between the two states relatively quickly, and the reduction process is slightly faster than the oxidation process. Figure 7 The single-cycle transmittance-time response curve at 730 nm shows that the initial transmittance is approximately 40%, and the highest transmittance after switching is approximately 82%, with a transmittance change of ΔT = 42% (significantly higher than the value at 520 nm). The red box indicates that the rise time is only 0.9 s (faster oxidation state switching) and the fall time is 1.5 s (slightly slower reduction state switching), with the overall response time within 1.5 s, demonstrating that the material exhibits a faster oxidation response and higher transmittance contrast in the long-wavelength region. Furthermore, the coloring efficiency of the PBMTh-co-PFCA film at 520 nm is calculated to be 186 cm⁻¹. 2 / C, at 730nm, is 293cm. 2 / C.

[0061] (5) The electrochemical energy storage performance of the PBMTh-co-PFCA copolymer material prepared in this embodiment was tested at different current densities. The galvanostatic charge-discharge (GCD) curves are shown in the figure. Figure 8 As shown, with time (s) on the horizontal axis and the potential (V) relative to the Ag / AgCl reference electrode on the vertical axis, different colored curves correspond to different current densities (1A / g, 2A / g, 3A / g, 5A / g, 10A / g). The rising phase of the curve corresponds to the charging process (potential increases, electrode stores charge), and the falling phase corresponds to the discharging process (potential decreases, electrode releases charge). These curves all exhibit a distorted triangular shape, indicating typical pseudocapacitive characteristics. When the current density is 1A / g, the specific capacitance of PBMTh-co-PFCA is 322F / g. The prepared PBMTh-co-PFCA copolymer has a high charge storage capacity, formed by the copolymerization reaction of thiophene (PBMTh) and fluorene (PFCA) units to form a continuous and stable large π-conjugated structure. The low charge transport resistance within the main chain provides a basis for rapid charge transfer. At the same time, the porous structure of the copolymer significantly increases the specific surface area of ​​the electrode, allowing the charge storage sites to be fully exposed. Electrolyte ions can come into contact with more active sites, thereby significantly increasing the amount of charge stored.

[0062] (6) Thermogravimetric analysis was performed on the thermal stability of the above PFCA, PBMTh, and the PBMTh-co-PFCA copolymer prepared in the examples. The results are as follows: Figure 9As shown, PBMTh materials exhibit a small mass loss before 100℃, due to the evaporation of adsorbed moisture. Within the 200–500℃ range, the mass decreases rapidly due to the thermal degradation of the thiophene conjugated backbone. For PFCA, the mass loss within the 200–300℃ range is likely caused by the decarboxylation of carboxyl groups. When the temperature rises to the 300–600℃ range, the mass loss is attributed to the thermal degradation of the fluorene ring conjugated backbone. The thermogravimetric curves of PBMTh-co-PFCA show that its thermal stability is superior to that of PBMTh and PFCA. Due to the gradual degradation of the conjugated backbone, the main period of weight loss occurs between 300 and 700 °C. This enhanced thermal stability is attributed to the copolymerization of rigid fluorene units and flexible thiophene units, forming a "rigid-flexible" conjugated backbone. The continuity of the conjugated large π system requires the disruption of longer and more stable conjugated segments to avoid thermal degradation; therefore, the decomposition temperature increases while the weight loss rate slows down. Simultaneously, the dipole-dipole interaction between the carboxyl groups of PFCA and the bromine substituents of PBMTh inhibits the decarboxylation reaction of the carboxyl groups, thus delaying the thermal decomposition of the material at the molecular level. Furthermore, the porous morphology of the copolymer effectively reduces intermolecular aggregation defects, resulting in a more uniform distribution of thermal stress in the backbone. This avoids rapid degradation caused by localized overheating and further improves thermal stability.

[0063] Example 2

[0064] The preparation method of PBMTh-co-PFCA material of the present invention includes the following steps: 9-fluorenic acid (FCA) and 3-bromo-4-methylthiophene (BMTh) are added to boron trifluoride diethyl ether (BFEE) so that the concentration of 9-fluorenic acid is 0.04 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.02 mol / L. Electrochemical polymerization is carried out under computer control using a KOST CS310M electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire with a diameter of 0.5 mm as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential of 1.8V is used for 30 s. After polymerization is completed, the material is naturally air-dried for later use. PBMTh-co-PFCA is obtained on the PET-ITO electrode. The average pore size of the PBMTh-co-PFCA copolymer material is measured to be 145 nm, the average particle size is 185 nm, and the average porosity is 52%. All solutions were degassed by a stream of dry argon before use, and argon was kept under overpressure during the preparation process.

[0065] Example 3

[0066] The preparation method of PBMTh-co-PFCA material of the present invention includes the following steps: 9-fluorenic acid (FCA) and 3-bromo-4-methylthiophene (BMTh) are added to boron trifluoride diethyl ether (BFEE) so that the concentration of 9-fluorenic acid is 0.08 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.02 mol / L. Electrochemical polymerization is carried out under computer control using a KOST CS310M electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire with a diameter of 0.5 mm as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential of 1.8V is used for 30 s. After polymerization is completed, the material is naturally air-dried for later use. PBMTh-co-PFCA is obtained on the PET-ITO electrode. The average pore size of the PBMTh-co-PFCA copolymer material is measured to be 155 nm, the average particle size is 210 nm, and the average porosity is 50%. All solutions were degassed by a stream of dry argon before use, and argon was kept under overpressure during the preparation process.

[0067] Example 4

[0068] The preparation method of PBMTh-co-PFCA material of the present invention includes the following steps: 9-fluorenic acid (FCA) and 3-bromo-4-methylthiophene (BMTh) are added to boron trifluoride diethyl ether (BFEE) so that the concentration of 9-fluorenic acid is 0.06 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.01 mol / L. Electrochemical polymerization is carried out under computer control using a KOST CS310M electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire with a diameter of 0.5 mm as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential of 1.8V is used for 30 s. After polymerization is completed, the material is naturally air-dried for later use. PBMTh-co-PFCA is obtained on the PET-ITO electrode. The average pore size of the PBMTh-co-PFCA copolymer material is measured to be 160 nm, the average particle size is 210 nm, and the average porosity is 49%. All solutions were degassed by a stream of dry argon before use, and argon was kept under overpressure during the preparation process.

[0069] Example 5

[0070] The preparation method of PBMTh-co-PFCA material of the present invention includes the following steps: 9-fluorenic acid (FCA) and 3-bromo-4-methylthiophene (BMTh) are added to boron trifluoride diethyl ether (BFEE) so that the concentration of 9-fluorenic acid is 0.06 mol / L and the concentration of 3-bromo-4-methylthiophene is 0.03 mol / L. Electrochemical polymerization is carried out under computer control using a KOST CS310M electrochemical workstation, with a PET-ITO electrode as the working electrode, a platinum wire with a diameter of 0.5 mm as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential of 1.8V is used for 30 s. After polymerization is completed, the material is naturally air-dried for later use. PBMTh-co-PFCA is obtained on the PET-ITO electrode. The average pore size of the PBMTh-co-PFCA copolymer material is measured to be 142 nm, the average particle size is 195 nm, and the average porosity is 45%. All solutions were degassed by a stream of dry argon before use, and argon was kept under overpressure during the preparation process.

[0071] Example 6

[0072] The specific fabrication steps of the flexible electrochromic supercapacitor of the present invention are as follows:

[0073] First, an electrode coated with poly(3,4-ethylenedioxythiophene) was prepared: 3,4-ethylenedioxythiophene was added to acetonitrile (ACN) and tetrabutylammonium boron tetrafluoride (TBATFB). The concentration of PEDOT in ACN was 0.05 mol / L, and the concentration of TBATFB in ACN was 0.1 mol / L. Polymerization was carried out using a KOST CS310M electrochemical workstation, with PET-ITO as the working electrode, a 0.5 mm platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential was 1.3 V, and the polymerization was carried out for 40 s. After the electrochemical reaction was completed, the electrode was naturally dried to obtain a poly(3,4-ethylenedioxythiophene) coated electrode. The mass of the poly(3,4-ethylenedioxythiophene) coating was 0.3 mg, and the area of ​​the coated surface was 1.5 cm². 2 The molecular weight is 700. All solutions were degassed with a stream of dry argon before use, and a slight argon overpressure was maintained during the experiment.

[0074] Secondly, a flexible electrochromic supercapacitor was prepared: the electrode with the flexible copolymer poly(3-bromo-4-methylthiophene)-co-poly(9-fluorencarboxylic acid) coating from Example 1 was used as the working electrode (wherein the mass of the PBMTh-co-PFCA coating was 0.5 mg and the coating area was 1.5 cm²). 2The electrode with the aforementioned poly(3,4-ethylenedioxythiophene) coating served as the counter electrode. Using a KOST CS310M electrochemical workstation, a sandwich structure was formed between the working electrode and the counter electrode by fixing it with 0.2g of gel electrolyte (lithium perchlorate, acetonitrile, polymethyl methacrylate, and polycarbonate mixed in a mass ratio of 3:70:7:20 and stirred until gelled). The mixture was then dried at 65℃ to obtain a flexible electrochromic supercapacitor (ESD). A schematic diagram of the obtained sandwich-structured ESD is shown below. Figure 10 As shown.

[0075] All solutions were degassed with a dry argon stream before use, and a slight argon overpressure was maintained during the experiment. To maintain the balance of injected / output charges, both electrodes (working and counter electrodes) required the same amount of charge during the redox process. The PBMTh-co-PFCA electrode was in a neutral state, while the PEDOT electrode was in an oxidized state before device construction.

[0076] (1) The electrochromic performance of the ESD constructed in the above embodiments was tested, such as... Figure 11 As shown, when a potential of -1.0V is applied, PBMTh-co-PFCA is in a reduced state (orange-red), while PEDOT is in an oxidized state (transparent light blue). Therefore, due to the superposition of these two colors, the ESD displays a brownish-red color. In this state, the absorption peak at approximately 485nm is mainly caused by the reduced state of PBMTh-co-PFCA. As the applied potential increases, PBMTh-co-PFCA gradually oxidizes to blue, while PEDOT decreases to a deep blue. During this process, the absorption peak at 485nm gradually weakens and eventually disappears, while a new absorption peak appears at 630nm, mainly caused by the reduced state of PEDOT. Therefore, when the applied potential is 1.5V, the ESD displays a deep blue color. This result indicates that the constructed ESD also exhibits excellent electrochromic properties.

[0077] (2) The electrochromic performance of the ESD constructed in the above embodiments was tested, such as... Figure 12-13 As shown, this demonstrates the performance at 485nm ( Figure 12 ) and 630nm ( Figure 13 The absorption curve for one cycle at the specified wavelength is shown. It can be seen that at 485 nm, the response time required for the device to transition from the reduced state to the oxidized state is 2.1 s, and the time to transition from the oxidized state to the reduced state is 2.6 s. The optical contrast ratio (ΔT%) is 35.2%, and the calculated colorimetric efficiency is 262 cm⁻¹. 2 / C. At 630 nm, the device takes 2.5 s to transition from a reduced state to an oxidized state, and 1.2 s to transition from an oxidized state to a reduced state. The optical contrast ratio (ΔT%) and coloring efficiency are 43.1% and 483 cm⁻¹, respectively. 2 / C.

[0078] (3) The electrochromic performance of the ESD constructed in the above embodiments was tested, such as... Figure 14-15 As shown, the device was recorded at 485nm ( Figure 14 ) and 630nm ( Figure 15 The absorption response at the ) indicates that the transmittance of the device remained almost unchanged after a long-term test of 1500s, which shows that the constructed device has excellent electrochromic stability.

[0079] (4) The electrochemical energy storage performance of the ESD constructed in the above embodiments was tested at different current densities, such as... Figure 16 As shown, the GCD curve of this device exhibits good symmetry and roughly a distorted triangular shape, reflecting typical characteristics of pseudocapacitance. The shape of the GCD curve does not change with increasing current density, indicating stable charge-discharge performance. At a current density of 1 A / g, the calculated specific capacitance of this device is 141 F / g. The corresponding power density and energy density are shown below. Figure 17 As shown in the figure, the power density and energy density of this device are 9082 W / kg and 56.6 Wh / kg, respectively. This result demonstrates that the constructed ESD device exhibits excellent electrochemical energy storage performance.

[0080] (5) The bending performance of the ESD constructed in the above embodiments was tested. The cyclic voltammetry (CV) curves in the initial state and the cyclic voltammetry (CV) curves after 200 mechanical bends (each bend at 90°) are shown in the figure. Figure 18 As shown, the blue curve represents the initial state, and the purple curve represents the state after 200 bends. The shapes, peak positions, and current densities of the two curves almost completely overlap, indicating that after 200 mechanical bends, the electrochemical active sites and charge transport capabilities of the device do not significantly decrease. This demonstrates that the constructed ESD device possesses excellent mechanical flexibility and electrochemical stability, maintaining a stable electrochemical response even under repeated bending conditions, making it suitable for applications in flexible wearable devices.

[0081] (6) Perform constant current charge-discharge stability testing on the ESD constructed in the above embodiments, such as... Figure 19 As shown, at a current density of 1 A / g, after 3000 charge-discharge cycles, the specific capacitance of the device is 111 Fg. -1(The capacitance retention rate is 78.7% compared to the initial specific capacitance value), demonstrating excellent GCD stability. Furthermore, by connecting the two devices in series, an LED can be lit, exhibiting good energy storage capacity. These results show that the porous structure formed by hydrogen bonds between carboxyl groups in the copolymer structure enables the device to maintain excellent electrochemical activity and cycling stability under bending conditions.

Claims

1. An application of a flexible copolymer with electrochromic and electrochemical energy storage properties, characterized in that: The obtained copolymer material was applied to the preparation of a flexible electrochromic supercapacitor. The steps were as follows: using an electrochemical workstation, the electrode with the obtained flexible copolymer poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenylcarboxylic acid) coating was used as the working electrode, and the electrode with the poly(3,4-ethylenedioxythiophene) coating was used as the counter electrode. The working electrode and the counter electrode were fixed in the middle by a gel electrolyte to form a sandwich structure. After drying, the flexible electrochromic supercapacitor was obtained. The preparation method of the flexible copolymer with electrochromic and electrochemical energy storage properties includes the following steps: adding 9-fluorenic acid and 3-bromo-4-methylthiophene to boron trifluoride diethyl ether, and using electrochemical polymerization. The constant potential of the electrochemical workstation is 1.7~1.9V, the working electrode is a PET-ITO electrode, the counter electrode is a platinum wire, and the reference electrode is an Ag / AgCl electrode. The flexible copolymer poly(3-bromo-4-methylthiophene)-co-poly(9-fluorenic acid) is prepared on the working electrode.

2. The application of the flexible copolymer with electrochromic and electrochemical energy storage properties according to claim 1, characterized in that: The molar ratio of 9-fluorenic acid to 3-bromo-4-methylthiophene is 2:1 to 6:

1.

3. The application of the flexible copolymer with electrochromic and electrochemical energy storage properties according to claim 2, characterized in that: 9-fluorenic acid and 3-bromo-4-methylthiophene were added to boron trifluoride diethyl ether, with the concentration of 9-fluorenic acid being 0.04~0.08 mol / L and the concentration of 3-bromo-4-methylthiophene being 0.01~0.03 mol / L.

4. The application of the flexible copolymer with electrochromic and electrochemical energy storage properties according to claim 1, characterized in that: The flexible copolymer with electrochromic and electrochemical energy storage properties has a molecular weight of 1000~1500.

5. The application of the flexible copolymer with electrochromic and electrochemical energy storage properties according to claim 1, characterized in that, The preparation steps of the poly(3,4-ethylenedioxythiophene) coated electrode are as follows: 3,4-ethylenedioxythiophene is added to acetonitrile and tetrabutylammonium boron tetrafluoride, and polymerization is carried out using an electrochemical workstation. PET-ITO is used as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The constant potential is 1.3~1.5V to obtain the poly(3,4-ethylenedioxythiophene) coated electrode.

6. The application of the flexible copolymer with electrochromic and electrochemical energy storage properties according to claim 1, characterized in that, The gel electrolyte is prepared by mixing lithium perchlorate, acetonitrile, polymethyl methacrylate, and polycarbonate.

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