Bamboo-based composite polypyrrole flexible membrane electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of flexible energy storage materials, in particular to a bamboo-based composite polypyrrole flexible membrane electrode material and a preparation method thereof.The preparation method comprises the steps that TEMPO oxidized cellulose nanofibers or UMCNF mechanically ground cellulose nanofibers are stirred and mixed with deionized water, and suspension liquid with the mass fraction of 0.2%-1% is prepared; carrying out vacuum filtration on the suspension by adopting a 0.22-0.45 mu m filter membrane to form a uniform wet membrane, freeze-drying the wet membrane to constant weight, and then carrying out die casting at room temperature by adopting a hot press to obtain a bamboo nanofiber flexible membrane; the method comprises the following steps: dissolving ferric trichloride hexahydrate in deionized water at room temperature to obtain an oxidant solution; mixing pyrrole, the bamboo nanofiber flexible membrane and an oxidizing agent solution according to a ratio, stirring, standing, freezing and carrying out in-situ polymerization to obtain a polymerization reaction solution; carrying out suction filtration on the polymerization reaction solution by adopting a 0.22-0.45 mu m filter membrane to obtain a membrane material, freeze-drying the membrane material to constant weight, and carrying out die casting by adopting a hot press to obtain the electrode material, and the material obtained by the method is good in electrical property and good in mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of flexible energy storage materials technology, specifically to a bamboo-based composite polypyrrole flexible membrane electrode material, its preparation method, and its application. Background Technology

[0002] With the growth of global energy demand and the development of flexible electronics technology, flexible supercapacitors, due to their combination of fast charging and discharging, long cycle life, and flexibility, have become core energy storage devices in fields such as wearable devices. Electrode materials, as the key to the performance of flexible supercapacitors, directly determine their energy density, power density, and cycle stability. Existing technologies suffer from the following drawbacks: Limitations of carbon-based materials: Although carbon-based electrodes such as graphene and carbon nanotubes have excellent conductivity, they have low energy density (usually <15Wh / kg) and their preparation process relies on non-renewable resources, resulting in high costs.

[0003] Defects of transition metal oxides: Although manganese dioxide, ruthenium oxide, etc. have high theoretical specific capacitance, they have poor conductivity (conductivity < 1 S / m) and insufficient flexibility. After 1000 cycles, the specific capacitance retention rate is often less than 60%.

[0004] Conductive polymers such as polyaniline and polypyrrole tend to agglomerate when used alone, resulting in low mechanical strength and rapid decay of specific capacitance (retention rate <70% after 500 cycles).

[0005] Bottlenecks in biomass-based materials: Existing bamboo fiber-based electrodes mostly use freeze-drying processes, resulting in rough membrane material surfaces and fiber agglomeration, leading to uneven loading of conductive polymers, unstable electrochemical performance, and difficulty in achieving both flexibility and high capacitance.

[0006] Furthermore, the preparation process of traditional electrode materials is complex and relies on toxic chemical reagents, which does not meet the requirements of green and sustainable development. Therefore, developing flexible electrode materials based on renewable biomass that combine high specific capacitance, excellent flexibility, and environmental friendliness has become the key to breaking through the bottleneck of flexible energy storage technology. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a bamboo-based composite polypyrrole flexible film electrode material with good electrical properties and good mechanical strength, as well as its preparation method and application.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by the present invention is as follows: a method for preparing a bamboo-based composite polypyrrole flexible film electrode material, comprising: mechanically grinding TEMPO oxidized cellulose nanofibers or UMCNF cellulose nanofibers and mixing them with deionized water to prepare a suspension with a mass fraction of 0.2% to 1%; The above suspension was vacuum filtered using a 0.22-0.45μm filter membrane to form a uniform wet membrane. The wet membrane was freeze-dried to constant weight and then die-cast using a hot press at room temperature to obtain a bamboo nanofiber flexible membrane. At room temperature, ferric chloride hexahydrate is dissolved in deionized water to obtain an oxidizing agent solution; Pyrrole, bamboo nanofiber flexible membrane and oxidant solution were mixed in proportion, stirred and then allowed to stand and freeze for in-situ polymerization to obtain polymerization reaction solution. The polymerization reaction solution was filtered through a 0.22-0.45 μm filter membrane to obtain a membrane material. The membrane material was freeze-dried to constant weight and then die-cast using a hot press at room temperature to obtain a bamboo nanofiber-based polypyrrole composite flexible membrane electrode material.

[0009] In one embodiment, the molar ratio of ferric chloride hexahydrate to pyrrole is 1:1 to 1:3, and the mass ratio of pyrrole to bamboo nanofiber flexible membrane is 1:20 to 1:50.

[0010] In one embodiment, die casting using a hot press at room temperature is performed by die casting for 5-10 minutes at a pressure of 5-20 MPa and room temperature.

[0011] In one embodiment, the freeze-drying to constant weight is performed by freezing at -50°C to -20°C for 3-4 hours, followed by drying to constant weight under a vacuum of ≤10Pa.

[0012] In one embodiment, the static freezing in-situ polymerization is a polymerization reaction at 0°C to 4°C for more than 12 hours.

[0013] In one embodiment, the concentration of the oxidant solution is 0.05-0.2 mol / L.

[0014] Based on the same inventive concept, a bamboo-based composite polypyrrole flexible film electrode material obtained by the above method is also provided, wherein the specific capacitance retention rate of the bamboo-based composite polypyrrole flexible film electrode material is ≥88% after 100 180° bending.

[0015] Based on the same inventive concept, an application of the above-mentioned bamboo-based composite polypyrrole flexible film electrode material in the electrode assembly of flexible supercapacitors, energy storage modules of wearable electronic devices or smart sensors is also provided.

[0016] In one embodiment, the flexible supercapacitor has an energy density ≥5Wh / kg, a power density ≥100W / kg, and a specific capacitance retention rate ≥85% after 1000 cycles.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: In the preparation method of the above-mentioned bamboo-based composite polypyrrole flexible membrane electrode material, the membrane material is prepared by replacing the traditional freeze-drying method with a vacuum filtration method and freeze-drying. The two-dimensional oriented arrangement of fibers is achieved by die-casting driven by a hot press, improving the surface smoothness of the membrane material by 40% and reducing the fiber agglomeration rate by 60%, providing a good substrate for uniform polypyrrole loading. Hydroxyl groups on the surface of the bamboo nanofiber flexible membrane form hydrogen bonds with polypyrrole, inhibiting polypyrrole agglomeration and simultaneously constructing continuous conductive channels, reducing charge transfer resistance. By adjusting the concentration of the bamboo nanofiber suspension and the amount of pyrrole, the density and porosity of the membrane material are balanced. The constructed porous structure provides abundant transport channels for electrolyte ions, and the high polypyrrole loading enhances the pseudocapacitive contribution. The obtained bamboo-based composite polypyrrole flexible film electrode material exhibits a specific capacitance of up to 32.75 F / g at a current density of 0.02 A / g, and maintains a specific capacitance retention rate of over 85% within the current density range of 0.02-0.1 A / g. It operates stably at various charge and discharge rates, making it suitable for high-power applications. The charge transfer resistance is as low as 15 Ω, and the ion diffusion coefficient reaches 1.2 × 10⁻⁶. -6 cm 2 / s; After 1000 charge-discharge cycles, the specific capacitance retention rate remains above 90%. The bamboo-based composite polypyrrole flexible film electrode material can withstand 100 repeated 180° bends, with a specific capacitance retention rate of ≥88% after bending, and no surface cracks or peeling. Stress-strain tests show that its elongation at break reaches 8.5%, and its tensile strength is as high as 25MPa, meeting the daily deformation requirements of wearable devices. Processing adaptability: The electrode material can be cut into any shape, and the thickness is adjustable to adapt to the assembly of flexible energy storage devices of different sizes. The above preparation process uses only deionized water as a solvent, with no toxic chemical reagent emissions; bamboo material is low in cost and conforms to the concept of green manufacturing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 shows a comparison of the macroscopic morphology of the bamboo nanofiber-based flexible membrane under different conditions according to one embodiment; where (a) is Comparative Example 1, (b) Example 1, (c) Example 3, (d) Comparative Example 3, (e) Example 2, and (f) Example 4. Figure 2 shows the SEM microstructure of a bamboo nanofiber-based flexible membrane according to one embodiment; wherein (a) is Comparative Example 1, (b) Example 1, (c) Example 3, (d) Comparative Example 3, (e) Example 2, and (f) Example 4; Figure 3 shows the mechanical properties of a bamboo nanofiber-based flexible membrane according to one embodiment; (a) a comparison of stress-strain curves of bamboo nanofiber-based flexible membranes of Example 1 and Comparative Example 1, (b) a cross-section of the bamboo nanofiber-based flexible membrane of Comparative Example 1, (c) a cross-section of the bamboo nanofiber-based flexible membrane of Example 1, (d) a schematic diagram of the bending of the bamboo nanofiber-based flexible membrane of Comparative Example 1, and (e) a schematic diagram of the bending of the bamboo nanofiber-based flexible membrane of Example 1. Figure 4 shows the SEM microstructure of the composite electrode according to one embodiment; (a) Comparative Example 1, (b) Example 1, (c) Example 3, (d) Comparative Example 3, (e) Example 2, (f) Example 4; Figure 5 shows the CV curve (a), CP curve (b), and AC impedance spectrum (c) of the composite electrode in Example 1. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] Example 1: The bamboo-based composite polypyrrole flexible membrane electrode material provided in this embodiment includes the following raw materials (by mass): UMCNF mechanically ground cellulose nanofibers (mass concentration 1.35%), deionized water (prepared as 20g of 0.2% concentration suspension), pyrrole 0.201g, ferric chloride hexahydrate 0.1352g, and deionized water 20mL.

[0024] Its preparation method includes the following steps: (1) Preparation of suspension Mix 50g of 1.35% UMCNF-CNF with 287.5g of deionized water by mass, and stir at 500rpm for 2h at room temperature to obtain a suspension with a mass concentration of 0.2% for later use. (2) Preparation of flexible membrane: Take 20g of suspension, filter it with a 0.22μm filter membrane (-0.09MPa), freeze dry (-50℃, ≤10Pa), and press cast it at 5MPa for 5min to obtain a bamboo nanofiber flexible membrane, denoted as U. 0.2 Bamboo nanofiber flexible membrane; (3) In-situ polymerization: Ferric chloride hexahydrate was dissolved in 20 mL of deionized water, and 0.201 g of pyrrole was added. The U obtained above... 0.2 Bamboo nanofiber flexible membrane was mixed, stirred at 300 rpm for 30 min, and allowed to stand at 0℃ for 12 h; then filtered through a 0.22 μm filter membrane, dried (-50℃, ≤10 Pa), and die-cast (5 MPa for 5 min) to obtain U 0.2 / PPy-3 electrode material.

[0025] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, the specific capacitance is 32.75 F / g at a current density of 0.02 A / g; the specific capacitance retention rate is 95% after 100 180° bends; the charge transfer resistance is 15 Ω; the elongation at break is 8.5%; and the tensile strength is 25 MPa.

[0026] Example 2: The bamboo-based composite polypyrrole flexible membrane electrode material provided in this embodiment includes the following raw materials (by mass): TEMPO oxidized cellulose nanofibers (concentration 1.10%), deionized water (prepared as 20g of 0.2% concentration suspension), pyrrole 0.201g, ferric chloride hexahydrate 0.1352g, and deionized water 20mL.

[0027] Preparation method: Same as in Example 1, except that the substrate was replaced with TEMPO-CNF to obtain T 0.2 Bamboo nanofiber flexible membrane, then prepared to obtain T 0.2 / PPy-3 electrode.

[0028] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, the specific capacitance is 24.325 F / g at a current density of 0.02 A / g; the specific capacitance retention rate is 92% after 100 bends; the charge transfer resistance is 22 Ω; the elongation at break is 7.1%; and the tensile strength is 20.83 MPa.

[0029] Example 3: The bamboo-based composite polypyrrole flexible membrane electrode material provided in this embodiment includes the following raw materials (by mass): UMCNF mechanically ground cellulose nanofibers (concentration 1.35%), deionized water (prepared as 20g of 0.5% concentration suspension), pyrrole 0.201g, ferric chloride hexahydrate 0.1352g, and deionized water 20mL.

[0030] Its preparation method includes the following steps: Preparation method: Same as in Example 1, except the suspension concentration was changed to 0.5%, yielding U 0.5 / PPy-3 electrode.

[0031] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, the specific capacitance is 25.12 F / g at a current density of 0.02 A / g; after 100 bends, the specific capacitance retention rate is 94%, the charge transfer resistance is 17 Ω, the elongation at break is 7.9%, and the tensile strength is 23.4 MPa.

[0032] Example 4: The bamboo-based composite polypyrrole flexible membrane electrode material provided in this embodiment includes the following raw materials (by mass): TEMPO oxidized cellulose nanofibers (concentration 1.10%), deionized water (prepared as 20g of 0.5% concentration suspension), pyrrole 0.201g, ferric chloride hexahydrate 0.1352g, and deionized water 20mL.

[0033] Preparation method: Same as in Example 1, except that the substrate was replaced with TEMPO-CNF to obtain T 0.5 / PPy-3 electrode.

[0034] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, the specific capacitance is 22.7 F / g at a current density of 0.02 A / g; the specific capacitance retention rate is 88% after 100 bends; the charge transfer resistance is 23 Ω; the elongation at break is 6.4%; and the tensile strength reaches 18.8 MPa.

[0035] Comparative Example 1: Preparation of U by freeze-drying 冷冻0.2 / PPy-3 flexible membrane The difference from Example 1 is that: after the suspension is prepared, the bamboo nanofiber flexible membrane material is directly obtained by freeze-drying (without filtration), and after in-situ polymerization, it is directly freeze-dried and die-cast to obtain U. 冷冻0.2 / PPy-3 electrode.

[0036] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, at a current density of 0.02 A / g, the specific capacitance is 20.35 F / g (a decrease of 37.9% compared to Example 1), the charge transfer resistance increases to 26; the surface roughness increases by 60%, the polypyrrole loading is uneven, cracks appear only after 50 bends, the elongation at break is only 5.3%, and the tensile strength is 15.6 MPa. Compared with Example 1, the mechanical properties such as elongation at break and tensile strength, as well as the electrochemical properties, are significantly reduced.

[0037] Comparative Example 2: Polypyrrole loading multiple 1x The difference from Example 1 is that the amount of pyrrole added was changed to 0.067g, resulting in U 0.2 / PPy-1 electrode.

[0038] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, at a current density of 0.02 A / g, the specific capacitance is 20.225 F / g (a decrease of 38.2% compared to Example 1); the charge transfer resistance increases to 30 Ω, the elongation at break decreases to 6.1%, and the tensile strength is 18.4 MPa. Its mechanical properties such as flexibility and electrochemical properties are significantly reduced.

[0039] Comparative Example 3: Preparation of T by freeze-drying 冷冻0.2 / PPy-3 flexible membrane The difference from Example 1 is that: after the suspension is prepared, bamboo nanofiber flexible membrane material is obtained directly by freeze-drying (without filtration), followed by in-situ polymerization, freeze-drying, and die-casting. Furthermore, the substrate is replaced with TEMPO-CNF to obtain T. 冷冻0.2 / PPy-3 electrode.

[0040] The electrode material prepared above will be subjected to performance tests. The test results are as follows: in 1 mol / L hydrochloric acid electrolyte, the specific capacitance at a current density of 0.02 A / g is 21.1 F / g (a decrease of 35.6% compared to Example 1); the charge transfer resistance increases to 32 Ω, the elongation at break decreases to 6.2%, and the tensile strength is 18.8 MPa. Its mechanical properties such as flexibility and electrochemical properties are significantly reduced.

[0041] Figure 1 Comparison images of the macroscopic morphology of bamboo nanofiber-based flexible membranes under different conditions; where (a) is Comparative Example 1, (b) Example 1, (c) Example 3, (d) Comparative Example 3, (e) Example 2, and (f) Example 4; according to Figure 1 It is known that thin film materials prepared from bamboo nanofibers of different concentrations exhibit macroscopic differences: thin film materials prepared with lower concentrations have higher surface transmittance and greater porosity, while as the concentration of the raw material increases, the prepared thin film materials become smoother and denser, with fewer deformation defects. Furthermore, the filtration + freezing process of this invention produces thin film materials that are smoother and denser, with significantly fewer deformation defects, compared to thin film materials obtained by freezing alone.

[0042] according to Figure 3It can be seen that the bamboo nanofiber-based flexible membrane obtained by the preparation method of the present invention exhibits yielding after strain increases with stress. In contrast, the film material of Comparative Example 1 yields directly under lower stress. During the stretching process, the film material of Example 1 fractures after a certain amount of slippage, while the film material of Comparative Example 1 fractures directly. The film material obtained by the preparation method of the present invention has a superior elongation at break. The flexible film material prepared by freeze-drying in Comparative Example 1 exhibits poor mechanical integrity, which is related to the porous structure formed by the sublimation of ice crystals.

[0043] according to Figure 5 It can be seen that, within the voltage window of 0~0.8V and tested at a scan rate of 0.1V / s, the cyclic voltammetry curve of U0.2 / PPy-3 is close to rectangular in shape and has a large closed area, indicating that the material has good charge storage capacity and a large capacitance. Further testing of Example 1 U using chronopotentiometric method was performed. 0.2 The charge-discharge performance of the / PPy-y electrode, including the charging time curve U at a current density of 0.02 A / g. 0.2 / PPy-yC and discharge curve U 0.2 / PPy-3-D / C (as shown) Figure 5 As shown in (b) of the diagram, U 0.2 / PPy-3 exhibits a discharge time close to 250 s, indicating that the electrode prepared under these conditions possesses the best capacitance performance, consistent with the results of the CV curve. The specific capacitance calculated based on the discharge time reaches 32.75 F / g. Further analysis of U can be performed using electrochemical impedance spectroscopy (IMP). 0.2 The mass transfer process of / PPy-y electrode materials in the electrolyte, such as Figure 5 As shown in (c) in the figure, by U 0.2 The spectrum of / PPy-3 shows that its low-frequency slope is small, indicating that its charge transfer resistance is small. The calculated charge transfer resistance is close to 15Ω, and the corresponding capacitance is large.

[0044] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a bamboo-based composite polypyrrole flexible film electrode material, characterized in that, include: TEMPO oxidized cellulose nanofibers or UMCNF mechanically ground cellulose nanofibers were mixed with deionized water to prepare a suspension with a mass fraction of 0.2% to 1%. The above suspension was vacuum filtered using a 0.22-0.45μm filter membrane to form a uniform wet membrane. The wet membrane was freeze-dried to constant weight and then die-cast using a hot press at room temperature to obtain a bamboo nanofiber flexible membrane. At room temperature, ferric chloride hexahydrate is dissolved in deionized water to obtain an oxidizing agent solution; Pyrrole, bamboo nanofiber flexible membrane and oxidant solution were mixed in proportion, stirred and then allowed to stand and freeze for in-situ polymerization to obtain polymerization reaction solution. The polymerization reaction solution was filtered through a 0.22-0.45μm filter membrane to obtain a membrane material. The membrane material was freeze-dried to constant weight and then die-cast using a hot press at room temperature to obtain a bamboo nanofiber-based polypyrrole composite flexible membrane electrode material.

2. The method for preparing the bamboo-based composite polypyrrole flexible film electrode material according to claim 1, characterized in that, The molar ratio of ferric chloride hexahydrate to pyrrole is 1:1-1:3, and the mass ratio of pyrrole to bamboo nanofiber flexible membrane is 1:20-1:

50.

3. The method for preparing the bamboo-based composite polypyrrole flexible film electrode material according to claim 1, characterized in that, Die casting using a hot press at room temperature involves casting for 5-10 minutes at a pressure of 5-20 MPa at room temperature.

4. The method for preparing the bamboo-based composite polypyrrole flexible film electrode material according to claim 1, characterized in that, The freeze-drying to constant weight is performed by freezing at -50℃ to -20℃ for 3-4 hours, followed by drying to constant weight under a vacuum of ≤10Pa.

5. The method for preparing the bamboo-based composite polypyrrole flexible film electrode material according to claim 1, characterized in that, The static freezing in-situ polymerization is a polymerization reaction at 0℃~4℃ for more than 12 hours.

6. The method for preparing the bamboo-based composite polypyrrole flexible film electrode material according to claim 1, characterized in that, The concentration of the oxidant solution is 0.05-0.2 mol / L.

7. A bamboo-based composite polypyrrole flexible film electrode material obtained by the preparation method according to any one of claims 1-6, wherein the bamboo-based composite polypyrrole flexible film electrode material can retain a specific capacitance of ≥88% after 100 180° bending cycles.

8. The application of the bamboo-based composite polypyrrole flexible film electrode material according to claim 7 in the electrode assembly of flexible supercapacitors, energy storage modules of wearable electronic devices or smart sensors.

9. The application according to claim 8, characterized in that, The flexible supercapacitor has an energy density of ≥5Wh / kg, a power density of ≥100W / kg, and a specific capacitance retention rate of ≥85% after 1000 cycles.

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