MXene-Al / CNF-PANI-3 composite film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of new energy materials and flexible energy storage devices, in particular to an MXene-Al / CNF-PANI-3 composite film and a preparation method and application thereof.The composite film is of a soft-hard hierarchical structure formed by alternation of flexible layer MXene nanosheets and rigid layers CNF-PANI, CNF-PANI and Al < 3 + > serve as spacing layers to be inserted between the MXene nanosheets, and the thickness of the flexible layer MXene nanosheets and the thickness of the rigid layer CNF-PANI are larger than that of the rigid layer CNF-PANI. A stable three-dimensional network structure is formed by electrostatic acting force and hydrogen bonds, a symmetric supercapacitor assembled by using the three-dimensional network structure as a self-supporting electrode does not need a current collector and a binder, the capacity retention ratio is greater than or equal to 89.7% after 5000 charge-discharge cycles, and the three-dimensional network structure is suitable for flexible wearable electronic energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of new energy materials and flexible energy storage devices, specifically to an MXene-Al / CNF-PANI-3 composite thin film, its preparation method, and its application. Background Technology

[0002] With the global energy transition towards renewable energy and the widespread adoption of portable electronic devices, developing efficient, stable, environmentally friendly, and mechanically flexible energy storage technologies has become a common goal for both academia and industry. Supercapacitors, due to their advantages such as high power density, fast charge / discharge rates, and long cycle life, have demonstrated significant application value in new energy vehicles, smart grids, and wearable electronic devices. Their core performance characteristics—capacitance and rate capability—are highly dependent on the structural design and intrinsic properties of the electrode materials.

[0003] Currently, supercapacitor electrode materials mainly include carbon-based materials (activated carbon, carbon nanotubes, graphene), conductive polymers (polyaniline, polypyrrole), and transition metal compounds. However, traditional powder electrodes require the addition of binders and conductive agents, increasing inactive mass and reducing overall energy density. Two-dimensional materials such as MXene (e.g., Ti3C2T) are being explored. x Due to its metallic conductivity, tunable interlayer spacing, and abundant surface functional groups, MXene has become an ideal candidate electrode material. However, the strong van der Waals forces between MXene nanosheets can easily lead to stacking, reducing the effective specific surface area and ion transport channels, thus limiting the full realization of its electrochemical performance. In addition, the mechanical strength of MXene itself is insufficient to meet the reliability requirements of flexible electronics under repeated bending.

[0004] Existing technologies attempt to suppress MXene stacking by introducing intercalating agents (such as conductive polymers and carbon nanofibers). For example, intercalating polyaniline (PANI) into the MXene interlayer can improve charge storage capacity, but PANI is prone to volume expansion and contraction during multiple charge-discharge cycles, leading to structural pulverization. Although cellulose nanofibers (CNF) can improve mechanical strength, their insulating properties sacrifice conductivity, and the resulting composite electrodes often have low capacitance values, making it difficult to achieve both capacitance and mechanical strength. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention aims to provide an MXene-Al / CNF-PANI-3 composite thin film, its preparation method, and its application. The MXene-Al / CNF-PANI-3 composite thin film possesses excellent flexibility, high conductivity, and high energy storage density, providing a flexible supercapacitor constructed from the thin film, thus realizing an all-solid-state energy storage device without the need for current collectors.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An MXene-Al / CNF-PANI-3 composite film is described, wherein the composite film has a soft-hard hierarchical structure consisting of alternating flexible MXene nanosheets and rigid CNF-PANI layers, wherein CNF-PANI and Al... 3+ Inserted as a spacer layer between MXene nanosheets, it forms a stable three-dimensional network structure through electrostatic forces and hydrogen bonds.

[0007] A method for preparing an MXene-Al / CNF-PANI-3 composite thin film includes the following steps: Ti3AlC2 powder was etched by adding hydrochloric acid solution and LiF powder to obtain MXene nanosheet suspension.

[0008] CNF dispersion was mixed with hydrochloric acid solution and aniline monomer, and (NH4)2S2O8 was added as an initiator to carry out oxidative polymerization reaction to obtain CNF-PANI suspension.

[0009] The MXene nanosheet suspension, soluble aluminum salt, and CNF-PANI suspension were physically mixed to obtain a homogeneous dispersion.

[0010] The homogeneous dispersion was vacuum filtered and dried to obtain a flexible self-supporting composite film of MXene-Al / CNF-PANI-3.

[0011] In a preferred embodiment of the present invention, the mass concentration of the MXene nanosheet suspension is 1.0 mg / mL to 2.0 mg / mL, and the concentration of the CNF dispersion is 3.0 mg / mL to 7.0 mg / mL.

[0012] In a preferred embodiment of the present invention, the volume ratio of MXene nanosheet suspension, CNF-PANI suspension and AlCl3·6H2O solution is 35-45:4-16:6-18, the soluble aluminum salt is AlCl3·6H2O, and the concentration of AlCl3·6H2O is 0.005mol / L-0.02mol / L.

[0013] In a preferred embodiment of the present invention, the concentration of hydrochloric acid solution during the preparation of CNF-PANI suspension is 0.8 mol / L-1.5 mol / L, and the concentration of hydrochloric acid solution during the preparation of MXene nanosheet suspension is 8.0 mol / L-12.0 mol / L.

[0014] In a preferred embodiment of the present invention, nitrogen gas is introduced for protection during the oxidative polymerization reaction, and an ice-water bath is also required for protection.

[0015] In a preferred embodiment of the present invention, the vacuum filtration uses a filter membrane with a pore size of 0.1μm-0.4μm, a drying temperature of 40℃-60℃, and a drying time of 8h-15h.

[0016] A supercapacitor electrode comprising the aforementioned MXene-Al / CNF-PANI-3 composite film.

[0017] A supercapacitor includes copper foil, the MXene-Al / CNF-PANI-3 composite thin film electrode, a gel electrolyte, the MXene-Al / CNF-PANI-3 composite thin film electrode, and copper foil stacked sequentially.

[0018] The gel electrolyte is a PVA / H2SO4 gel electrolyte.

[0019] The specific preparation method of the PVA / H2SO4 gel electrolyte of the present invention includes: dissolving 2g of polyvinyl alcohol (PVA) in 1mol / L H2SO4 at 95°C and continuously stirring to form a transparent gel electrolyte.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. The MXene-Al / CNF-PANI-3 composite film of the present invention, Al 3+ Using CNF-PANI as a spacer, it inhibits the self-stacking of MXene nanosheets, thereby improving the rate performance of the composite film; on the other hand, it constructs a "soft-hard" hierarchical porous structure inside the thin-film electrode, accelerating the penetration and transport of electrolyte ions. Furthermore, Al... 3+ The ionic and hydrogen bonds induced by CNF enhance the bonding between adjacent MXene nanosheets and optimize the conductive path; while the encapsulation of PANI by the MXene sheets effectively alleviates the structural collapse caused by the conductive polymer during long-term charge-discharge cycles, thereby extending the cycle life of the composite film.

[0021] 2. In this invention, MXene provides high conductivity and abundant reactive sites, ensuring rapid electron transport and efficient charge storage. CNF, with polyhydroxy and carboxyl functional groups, serves as a polymerization template for PANI, effectively mitigating the volume deformation of the conductive polymer during long-term charge-discharge cycles. At the same time, adjacent MXene nanosheets are connected through hydrogen bonding, thereby improving the specific capacity and structural stability of the composite film.

[0022] 3. The MXene-Al / CNF-PANI-3 flexible self-supporting composite film prepared by this invention has a robust structure, high conductivity, good flexibility, and excellent electrochemical performance. The MXene-Al / CNF-PANI-3 flexible self-supporting composite film can be directly used as an electrode without the need to introduce additional conductive agents and binders. When the prepared MXene-Al / CNF-PANI-3 flexible self-supporting composite film is used as an electrode material to assemble a flexible symmetrical supercapacitor, the device exhibits excellent specific capacitance, and the capacitance performance is almost unaffected under deformation conditions such as bending and folding, proving its good electrochemical stability. Therefore, the MXene-Al / CNF-PANI-3 self-supporting composite film has broad application prospects in the field of flexible electronic energy storage.

[0023] 4. This invention adopts a "one-pot" electrostatic self-assembly combined with conventional vacuum filtration, which does not require complex and expensive equipment, has a wide range of raw material sources, and the process parameters are easy to control, making it suitable for large-scale production. Compared with complex processes such as screen printing or electrochemical deposition, the ease of operation of this invention greatly reduces production costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating a simplified preparation process of the MXene-Al / CNF-PANI-3 flexible self-supporting composite film described in this invention.

[0025] Figure 2 In Figure 1, a is a transmission electron microscope (TEM) image of MXene obtained in Comparative Example 6, b is a physical image of MXene obtained in Comparative Example 6, and c is a scanning electron microscope (SEM) image of the cross-section of the MXene-Al / CNF-PANI-3 composite film obtained in Example 1.

[0026] Figure 3 In the figure, a is the conductivity curve of the samples obtained from Comparative Examples 3, 5, 6 and Example 1; b is the conductivity curve of the samples obtained from Comparative Examples 1 to 4; c is the stress-strain curve of the samples obtained from Comparative Examples 3, 5, 6 and Example 1; and d is the stress-strain curve of the samples obtained from Comparative Examples 1 to 4.

[0027] Figure 4 The XRD patterns, XPS total spectra, C spectra, and O spectra of the samples obtained from Comparative Examples 3, 5, 6, and 1 are respectively.

[0028] Figure 5 In the figure, ab represents the CV curve and GCD curve of the sample obtained in Example 1 as a self-supporting electrode, respectively. cd represents the specific capacitance curve and EIS curve of the sample obtained in Comparative Example 3, Comparative Example 5, Comparative Example 6 and Example 1 as a self-supporting electrode under different current densities, respectively.

[0029] Figure 6 The diagrams in the middle and the image below are, respectively, a schematic diagram, a CV curve, a GCD curve, and a CV curve at different bending angles of the flexible symmetrical supercapacitor assembled with the sample obtained in Example 1 as a self-supporting electrode.

[0030] Figure 7 Figures a, b, and c respectively show the cyclic stability test and actual demonstration of the flexible symmetrical supercapacitor assembled with the sample obtained in Example 1 as a self-supporting electrode. Detailed Implementation

[0031] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1 A method for preparing an MXene-Al / CNF-PANI-3 composite membrane, such as... Figure 1 As shown, it includes the following steps: S1. Preparation of MXene nanosheet suspension, specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. Stir continuously in an ice bath for 30 min to form a homogeneous solution.

[0034] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min. Then stir it in an oil bath at 50°C for 48 h.

[0035] (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min.

[0036] (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0037] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0038] S3. Preparation of MXene-Al / CNF-PANI-3 flexible self-supporting composite film, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1, add 12 mL of CNF-PANI suspension from step S2 and sonicate for 10 min, then introduce 10 mL of 0.01 mol / L AlCl3·6H2O to initiate electrostatic self-assembly, and obtain a homogeneous dispersion of MXene-Al / CNF-PANI after sonication. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene-Al / CNF-PANI-3 flexible self-supporting composite membrane.

[0039] Example 2 A method for preparing MXene-Al / CNF-PANI-1 S1. Preparation of MXene nanosheet suspension, specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. Stir continuously in an ice bath for 30 min to form a homogeneous solution.

[0040] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min. Then stir it in an oil bath at 50°C for 48 h.

[0041] (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min.

[0042] (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0043] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0044] S3. Preparation of MXene-Al / CNF-PANI-1 flexible self-supporting composite film, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1, add 4 mL of CNF-PANI suspension from step S2 and sonicate for 10 min, then introduce 18 mL of 0.01 mol / L AlCl3·6H2O to initiate electrostatic self-assembly, and obtain a homogeneous dispersion of MXene-Al / CNF-PANI after sonication. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene-Al / CNF-PANI-1 flexible self-supporting composite membrane.

[0045] Example 3 A method for preparing MXene-Al / CNF-PANI-2 S1. Preparation of MXene nanosheet suspension, specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. Stir continuously in an ice bath for 30 min to form a homogeneous solution.

[0046] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min. Then stir it in an oil bath at 50°C for 48 h.

[0047] (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min.

[0048] (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0049] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0050] S3. Preparation of MXene-Al / CNF-PANI-2 flexible self-supporting composite film, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1, add 8 mL of CNF-PANI suspension from step S2 and sonicate for 10 min, then introduce 14 mL of 0.01 mol / L AlCl3·6H2O to initiate electrostatic self-assembly, and obtain a homogeneous dispersion of MXene-Al / CNF-PANI after sonication. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50°C for 12 h to obtain an MXene-Al / CNF-PANI-2 flexible self-supporting composite membrane.

[0051] Example 4 A method for preparing MXene-Al / CNF-PANI-4 S1. Preparation of MXene nanosheet suspension, specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. Stir continuously in an ice bath for 30 min to form a homogeneous solution.

[0052] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min. Then stir it in an oil bath at 50°C for 48 h.

[0053] (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min.

[0054] (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0055] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0056] S3. Preparation of MXene-Al / CNF-PANI-4 flexible self-supporting composite film, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1, add 16 mL of CNF-PANI suspension from step S2 and sonicate for 10 min, then introduce 6 mL of 0.01 mol / L AlCl3·6H2O to initiate electrostatic self-assembly, and obtain a homogeneous dispersion of MXene-Al / CNF-PANI after sonication. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene-Al / CNF-PANI-4 flexible self-supporting composite membrane.

[0057] Application Example 1 A method for fabricating a supercapacitor, comprising the following specific steps: (1) 2 g of PVA powder and 30 mL of 1 mol / L H2SO4 solution were stirred continuously at 95 °C for 3 h to form a transparent PVA / H2SO4 gel electrolyte. (0) A conductive copper foil, an MXene-Al / CNF-PANI-3 membrane electrode, a gel electrolyte, an MXene-Al / CNF-PANI-3 membrane electrode, and a conductive copper foil are stacked sequentially. They are pressed together under a pressure of 5 MPa to obtain an all-solid-state flexible symmetrical supercapacitor.

[0058] Comparative Example 1 A method for preparing an MXene / CNF-PANI-1 composite membrane includes the following steps: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0059] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50°C for 48 h. (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0060] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0061] S3. Preparation of MXene / CNF-PANI flexible self-supporting composite film, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1 and 4 mL of CNF-PANI suspension from step S2, mix them, and then sonicate to obtain a homogeneous dispersion of MXene / CNF-PANI-1. (7) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene / CNF-PANI-1 composite membrane.

[0062] Comparative Example 2 A method for preparing an MXene / CNF-PANI-2 composite membrane is as follows: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0063] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50°C for 48 h. (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0064] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0065] S3. Preparation of MXene / CNF-PANI-2 flexible self-supporting composite film, specifically including the following steps: 1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1 and 8 mL of CNF-PANI suspension from step S2, mix them, and then sonicate to obtain a homogeneous dispersion of MXene / CNF-PANI-2. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene / CNF-PANI-2 composite membrane.

[0066] Comparative Example 3 A method for preparing an MXene / CNF-PANI-3 composite film is as follows: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0067] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50°C for 48 h. (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0068] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0069] S3. Preparation of MXene / CNF-PANI-3 flexible self-supporting composite film, specifically including the following steps: 1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1 and 12 mL of CNF-PANI suspension from step S2, mix them, and then sonicate to obtain a homogeneous dispersion of MXene / CNF-PANI-3. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene / CNF-PANI-3 composite membrane.

[0070] Comparative Example 4 A method for preparing an MXene / CNF-PANI-4 composite film is as follows: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0071] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50°C for 48 h. (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0072] S2. Preparation of CNF-PANI suspension, specifically including the following steps: (1) CNF-PANI suspension was prepared by in-situ oxidative polymerization using CNF as a biological template; (2) Weigh an appropriate amount of CNF (0.65%) gel and dissolve it in deionized water to form a uniform dispersion of 5 mg / mL. Store it in a refrigerator for later use. (3) Place 20 mL of the above CNF colloidal solution in an Erlenmeyer flask, add 40 mL of 1 mol / L HCl solution, stir thoroughly, and cover the mouth of the flask with plastic wrap to carry out the reaction under closed conditions. Then add 0.4 g of aniline monomer and stir at room temperature for 30 min. (4) 0.6 g (NH4)2S2O8 was added to the above reaction mixture to initiate oxidative polymerization. The polymerization process was continuously stirred in an ice bath for 12 h to finally obtain CNF-PANI suspension.

[0073] S3. Preparation of MXene / CNF-PANI-4 flexible self-supporting composite film, specifically including the following steps: 1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1 and 16 mL of CNF-PANI suspension from step S2, mix them, and then sonicate to obtain a homogeneous dispersion of MXene / CNF-PANI-4. (8) (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene / CNF-PANI-4 composite membrane.

[0074] Comparative Example 5 A method for preparing an MXene-Al flexible self-supporting composite thin film is as follows: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (1) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0075] (2) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50°C for 48 h. (3) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (4) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (5) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (6) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0076] S2. Preparation of MXene-Al flexible self-supporting composite films, specifically including the following steps: (1) Take 40 mL of 1.5 mg / mL MXene nanosheet suspension from step S1 and mix it with 10 mL of 0.01 mol / L AlCl3·6H2O. After sonication for 10 min, obtain a homogeneous MXene-Al dispersion. (2) The above homogeneous dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene-Al composite membrane.

[0077] Comparative Example 6 A method for preparing an MXene thin film is as follows: S1. Preparation of MXene nanosheet suspension; specifically including the following steps: (9) Weigh 3.0 g of LiF and dissolve it in 40 mL of 9 mol / L HCl solution. The reaction system is carried out in a polytetrafluoroethylene liner. The solution is stirred continuously in an ice bath for 30 min to form a homogeneous solution.

[0078] (10) Weigh 2.0 g Ti3AlC2 powder and slowly add it to the above mixture for 15 min, and then stir it in an oil bath at 50 °C for 48 h. (11) After the reaction in step (2) is completed, the mixture is washed multiple times by centrifugation with deionized water until the pH value of the supernatant is greater than 6. The lower precipitate is collected. Each centrifugation is performed at a speed of 6000 rpm / min for 10 min. (12) The precipitate obtained above is redispersed in deionized water and ultrasonically treated with an ultrasonic power of 150 W for 30 min. Note that nitrogen gas is introduced for protection during the process, and an ice-water bath is required to prevent the ultrasonic exothermic effect from affecting the material properties. (13) After ultrasonic treatment, the obtained dispersion was centrifuged at 3500 rpm / min for 30 min. The upper suspension obtained by centrifugation was collected and stored in a refrigerator. (14) A certain volume of the above suspension was filtered by a simple vacuum filtration method, then dried and weighed, and the mass concentration of the above MXene suspension was calculated to be 1.5 mg / mL.

[0079] S2. Preparation of MXene thin films, specifically including the following steps: (1) Take 40 mL of the 1.5 mg / mL MXene nanosheet suspension from step S1; (2) The above dispersion was vacuum filtered through an aqueous mixed cellulose ester membrane with a pore size of 0.2 μm to form a uniform wet membrane, and then dried on a hot plate at 50 °C for 12 h to obtain an MXene film.

[0080] Results Analysis Figure 2 Image a is a transmission electron microscope (TEM) image of MXene obtained in Comparative Example 6, showing that MXene exhibits a sheet-like shape; image b is a physical image of MXene obtained in Comparative Example 6, and both exhibit obvious Tyndall effect under laser illumination, indicating the colloidal properties and stable dispersibility of the prepared MXene suspension; image c is a scanning electron microscope (SEM) image of the cross-section of the MXene-Al / CNF-PANI-3 composite film obtained in Example 1, clearly showing that CNF-PANI successfully inserted into the MXene nanosheets, effectively increasing the interlayer spacing of the MXene nanosheets, which is beneficial for exposing more active sites and promoting ion diffusion and storage.

[0081] Figure 3 In Figure 1, a represents the conductivity curves of the samples obtained from Comparative Examples 3, 5, 6, and 1; b represents the conductivity curves of the samples obtained from Comparative Examples 1 to 4. It can be seen that the conductivity of the MXene-Al / CNF-PANI-3 film prepared in Example 1 can reach 136.17 S / cm, exhibiting ultra-high conductivity. In Figure 2, c represents the stress-strain curves of the samples obtained from Comparative Examples 3, 5, 6, and 1; d represents the stress-strain curves of the samples obtained from Comparative Examples 1 to 4. It can be seen that the tensile strength of the MXene-Al / CNF-PANI-3 film prepared in Example 1 can reach up to 19.29 MPa, exhibiting good mechanical properties.

[0082] Figure 4 The images in the middle (ad) are, in order, the XRD patterns, XPS total spectra, C spectra, and O spectra of the samples obtained from Comparative Examples 3, 5, 6, and 1, respectively. Figure 4As can be seen from Figure a, the MXene-Al / CNF-PANI-3 film prepared in Example 1 has a smaller diffraction angle at the 002 crystal plane. 3+ The introduction of CNF-PANI opened up the layer space of MXene, increasing the interlayer spacing of MXene nanosheets. Figure 4 As shown in Figure b, the MXene-Al / CNF-PANI-3 film prepared in Example 1 exhibits an N peak and an enhanced Al peak, confirming that Al³⁺ and CNF-PANI were successfully inserted into the MXene interlayer; from Figure 4 The CD image shows that the CO and OC=O peaks of the MXene-Al / CNF-PANI-3 film prepared in Example 1 are shifted to the left to obtain a higher binding energy, indicating that electrostatic and hydrogen bonding interactions are generated between the metal Al³⁺ and the oxygen-containing functional groups of MXene and CNF.

[0083] Figure 5 Figures a and b show the CV and GCD curves of the sample obtained in Example 1 as a self-supporting electrode, respectively. Figure a shows that the CV curve has a slightly distorted rectangular shape, indicating that the electrochemical storage capacity comes from the combination of pseudocapacitance and double-layer capacitance. Figures c and d show the specific capacitance and EIS curves of the samples obtained in Comparative Examples 3, 5, 6 and Example 1 as self-supporting electrodes at different current densities, respectively. Figures b and c show that the charge-discharge curves have a slightly distorted isosceles triangular shape, further indicating the presence of pseudocapacitance. The areal capacitance of the MXene-Al / CNF-PANI-3 membrane electrode prepared in Example 1 is as high as 4286 mF / cm² (8 mA / cm²), proving its excellent capacitance storage capacity. Figure d shows that the MXene-Al / CNF-PANI-3 membrane electrode (Rct = 0.22 Ω) exhibits a lower charge transfer resistance than other membrane electrodes, further proving the rapid charge transfer and ion transport inside the membrane electrode.

[0084] Figure 6 Figures a and ac respectively show schematic diagrams, CV curves, GCD curves, and CV curves at different bending angles of the flexible symmetrical supercapacitor assembled using the sample obtained in Example 1 as self-supporting electrodes. Figure a shows that the two membrane electrodes are separated by a solid gel electrolyte PVA / H2SO4, and the electrode surface is a conductive copper foil. Figures b and c show that the CV curves are symmetrical and rectangular at low scan rates, which is consistent with the characteristics of an ideal capacitor. At 2 mA / cm², the CV curves are relatively stable. 2The calculated surface capacitance at the current density is 1035.8 mF / cm², indicating that the device has good capacitance storage performance. Figure d shows that the CV curves at all test angles are almost overlapping, and the performance degradation is almost negligible, proving that the assembled device has excellent mechanical flexibility and good electrochemical stability under deformation, and can be applied to flexible wearable electronic devices.

[0085] Figure 7 Figures a and b respectively show the cycle stability test and actual demonstration of the flexible symmetrical supercapacitor assembled with the sample obtained in Example 1 as a self-supporting electrode. This device retains 89.7% of its initial capacitance after 5000 GCD cycles, demonstrating excellent cycle stability. Furthermore, the integrated device formed by series connection can power an electronic display, proving its great application potential in practical energy storage systems.

[0086] In summary, a self-supporting MXene-Al / CNF-PANI-3 composite film exhibiting high conductivity, good flexibility, and excellent energy storage performance was successfully constructed through electrostatic self-assembly and vacuum-assisted filtration. CNF, with its various hydroxyl and carboxyl functional groups, serves as a polymerization template for PANI, effectively mitigating volume deformation of the conductive polymer during long-term charge-discharge cycling. Simultaneously, it connects adjacent MXene nanosheets through hydrogen bonding, thereby improving the specific capacity and structural stability of the composite film. The introduction of highly charged Al³⁺ ions allows CNF and MXene to self-assemble through electrostatic interactions, forming strong ionic bonds that enhance the interfacial bonding and electron transport between CNF-PANI and MXene. CNF-PANI and Al³⁺ together constitute the spacer layer within MXene, forming a directional, layered "soft-hard" structure in the composite film. This not only effectively inhibits the self-stacking of MXene nanosheets but also significantly improves the transport efficiency of electrolyte ions, thus achieving superior electrochemical performance. This patented symmetrical supercapacitor device, assembled using a flexible self-supporting composite thin film of MXene-Al / CNF-PANI-3, exhibits excellent electrochemical performance, with high areal capacitance and electrochemical stability, and has broad application potential in the field of energy storage.

[0087] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0088] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An MXene-Al / CNF-PANI-3 composite film, characterized in that, The composite film has a soft-hard hierarchical structure consisting of alternating flexible MXene nanosheets and rigid CNF-PANI layers, wherein CNF-PANI and Al 3+ Inserted as a spacer layer between MXene nanosheets, it forms a three-dimensional network structure through electrostatic forces and hydrogen bonds.

2. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 1, characterized in that, Includes the following steps: Ti3AlC2 powder was etched by adding hydrochloric acid solution and LiF powder to obtain MXene nanosheet suspension; CNF dispersion was mixed with hydrochloric acid solution and aniline monomer, and (NH4)2S2O8 was added as an initiator to carry out oxidative polymerization reaction to obtain CNF-PANI suspension; The MXene nanosheet suspension, soluble aluminum salt, and CNF-PANI suspension were physically mixed to obtain a homogeneous dispersion. The homogeneous dispersion was vacuum filtered and dried to obtain a flexible self-supporting composite film of MXene-Al / CNF-PANI-3.

3. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 2, characterized in that, The mass concentration of MXene nanosheet suspension was 1.0 mg / mL-2.0 mg / mL, and the concentration of CNF dispersion was 3.0 mg / mL-7.0 mg / mL.

4. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 2, characterized in that, The volume ratio of MXene nanosheet suspension, CNF-PANI suspension and AlCl3·6H2O solution was 35-45:4-16:6-18, the soluble aluminum salt was AlCl3·6H2O, and the concentration of AlCl3·6H2O was 0.005mol / L-0.02mol / L.

5. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 2, characterized in that, The concentration of hydrochloric acid solution in the preparation of CNF-PANI suspension is 0.8 mol / L-1.5 mol / L, and the concentration of hydrochloric acid solution in the preparation of MXene nanosheet suspension is 8.0 mol / L-12.0 mol / L.

6. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 2, characterized in that, Nitrogen gas is required for protection during the oxidative polymerization reaction, and an ice-water bath is also needed for protection.

7. The method for preparing the MXene-Al / CNF-PANI-3 composite film according to claim 2, characterized in that, The vacuum filtration uses a filter membrane with a pore size of 0.1μm-0.4μm, a drying temperature of 40℃-60℃, and a drying time of 8h-15h.

8. A supercapacitor electrode, characterized in that, Includes the MXene-Al / CNF-PANI-3 composite film as described in claim 1.

9. A supercapacitor, characterized in that, It includes copper foil, the MXene-Al / CNF-PANI-3 composite thin film electrode as described in claim 8, a gel electrolyte, the MXene-Al / CNF-PANI-3 composite thin film electrode as described in claim 8, and copper foil stacked in sequence.

10. The supercapacitor according to claim 9, characterized in that, The gel electrolyte is a PVA / H2SO4 gel electrolyte.

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