A self-supporting MXene-based composite thin film electrode material with wrinkle and interlayer macroporous structure and a preparation method thereof

Abstract

The application discloses a self-supporting MXene-based composite thin film electrode material with folds and interlayer macroporous structures and a preparation method thereof, and belongs to the technical field of supercapacitor electrode materials. + The method comprises the following steps: preparing a MXene nanosheet dispersion by etching and peeling a MAX phase through HCl / LiF; mixing the MXene with CNF, adding NaOH, and utilizing Na + The electrostatic bridge induces heterogeneous agglomeration and crumpling, and a wet film is obtained through vacuum suction filtration; interlayer macropores are formed through ice crystal growth and sublimation in freeze-drying; inert atmosphere heat treatment is performed to simultaneously realize CNF carbonization, removal of unstable functional groups on the surface of the MXene, and formation of Ti-O-C covalent bonds. The obtained electrode has a multi-level structure of "macroscopic fold-interlayer micrometer macropore-nanometer conductive network", and excellent electrochemical performance. The problem that MXene electrodes are prone to stacking and limit rapid ion transmission is solved, and the application has a wide application prospect in the fields of wearable electronics and flexible energy storage.

Description

Technical Field

[0001] This invention relates to the field of supercapacitor electrode materials technology, and in particular to a self-supporting MXene-based composite thin film electrode material with a wrinkled and interlayer macroporous structure and its preparation method. Background Technology

[0002] Supercapacitors, with their advantages of high power density, rapid charge / discharge capability, and long cycle life, have broad application prospects in wearable electronic devices, portable electronic instruments, and smart grids. Electrode materials are key components determining the performance of supercapacitors. Two-dimensional transition metal carbides / nitrides (MXenes, represented by Ti3C2) are considered highly promising supercapacitor electrode materials due to their high conductivity, high volumetric specific capacitance, and good hydrophilicity. However, in practical applications, MXene materials still face the problem of self-stacking caused by interlayer van der Waals forces, which severely hinders ion transport within the electrode material.

[0003] To improve ion transport performance, existing technologies typically employ methods such as introducing spacers (e.g., carbon nanotubes, graphene) or constructing three-dimensional porous structures. However, these methods largely rely on physical mixing and filtration to form films, but the physical interaction between MXene and carbon materials is weak, resulting in insufficient interfacial bonding strength and difficulty in forming interconnected hierarchical porous structures. Furthermore, some unstable functional groups on the MXene surface (e.g., -F, -OH) can lead to the loss of active sites and increased side reactions during electrochemical cycling, affecting the long-term cycling stability of the material.

[0004] Therefore, how to synergistically optimize from multiple dimensions such as preparation methods, interface chemistry and microstructure to improve the utilization rate of active sites and ion transport rate of MXene electrodes, while taking into account high electrochemical activity, long-term cycling stability and good mechanical flexibility, remains the core technical challenge facing this field. Summary of the Invention

[0005] The purpose of this invention is to provide a self-supporting MXene-based composite thin film electrode material with a wrinkled and interlayer macroporous structure and its preparation method, so as to solve the technical problems of low active site utilization, slow ion transport rate, weak interfacial bonding and poor cycle stability of existing MXene-based electrode materials mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides a method for preparing a self-supporting MXene-based composite thin film electrode material with a wrinkled and macroporous interlayer structure, specifically including the following steps: S1, Preparation of MXene nanosheet dispersion: MAX phase ceramic powder was added to HCl solution containing LiF and etched. After the reaction, the mixture was centrifuged and washed until neutral and a black supernatant appeared. The resulting mixed solution was ultrasonically exfoliated and the supernatant was collected by centrifugation to obtain the MXene nanosheet dispersion. S2, Electrostatic Assembly: The MXene nanosheet dispersion obtained in step S1 is mixed with the TEMPO oxidized cellulose nanofiber (CNF) dispersion. NaOH is added to adjust the pH of the system to alkaline. + The compressed double layer is used as an electrostatic bridge to cause heterogeneous aggregation and wrinkling of negatively charged MXene sheets and negatively charged CNF, forming composite flocculants, which are then obtained by vacuum filtration to obtain a self-supporting wet composite film. S3. Ice template forming and freeze-drying: The wet composite film obtained in step S2 is freeze-dried to form an interlayer macroporous structure inside the film by ice crystal growth and sublimation, thus obtaining a solid precursor film. S4. Heat-locking treatment: The solid precursor film obtained in step S3 is heat-treated in an inert atmosphere to achieve CNF carbonization, removal of -F and -OH functional groups on the MXene surface, and formation of Ti-OC covalent bonds, thereby obtaining a flexible composite thin film electrode material.

[0007] Preferably, in step S1, the MAX phase ceramic powder is Ti3AlC2; in the HCl solution containing LiF, the mass of LiF is 1-2g, and the concentration of HCl is 6-12mol / L; the etching reaction temperature is 35-60℃, and the time is 12-48h.

[0008] Preferably, in step S1, the ultrasonic stripping power is 100-500 W and the time is 30-120 min; the centrifugation speed is 2000-5000 rpm and the time is 1-30 min.

[0009] Preferably, in step S2, the concentration of the MXene nanosheet dispersion is 1-30 mg / mL; the mass of CNF solid accounts for 15%-55% of the total mass of the CNF and MXene mixed system.

[0010] Preferably, in step S2, NaOH is added to adjust the pH of the system to 8-13.

[0011] Preferably, the freeze-drying temperature is -50°C to -20°C, the vacuum degree is 1-20 Pa, and the time is 12-48 h.

[0012] Preferably, the inert atmosphere is nitrogen or argon; the heat treatment temperature is 300-500℃, the heating rate is 1-10℃ / min, and the holding time is 1-3 h.

[0013] The present invention also provides a self-supporting MXene-based composite thin film electrode material with a wrinkled and interlayer macroporous structure prepared by the above preparation method. The composite thin film electrode material has surface wrinkles, micron-level interlayer macropores and a nano-conductive network formed by carbonized CNF; MXene and carbonized CNF are bonded by Ti-OC covalent bonds.

[0014] Preferably, the diameter of the interlayer macropores is 50-400 μm.

[0015] Preferably, the mass fraction of CNF in the composite thin film electrode material is 15%-55%.

[0016] Therefore, the self-supporting MXene-based composite thin film electrode material with wrinkled and interlayer macroporous structure and its preparation method provided by the present invention have the following beneficial effects: (1) Methodological Innovation: This invention organically integrates three strategies—"electrostatic assembly," "ice template shaping," and "thermal locking"—to form a complete material preparation process from liquid-state control to solid-state shaping. Specifically, it first utilizes Na… + As an electrostatic bridge, the double layer between MXene and CNF is compressed to overcome the electrostatic repulsion caused by the negative surface charge, inducing heterogeneous aggregation and wrinkling, followed by vacuum filtration to form a film. Subsequently, freeze-drying is used to solidify the dynamic structure in the film into a solid precursor with oriented macropores through ice crystal growth and sublimation. Finally, a medium-temperature heat treatment at 400℃ simultaneously achieves partial carbonization of CNF to form a conductive framework, removal of some unstable functional groups (-F, -OH) on the MXene surface, and formation of Ti-OC covalent bonds at the interface, resulting in an integrated covalently cross-linked film with macroscopic surface wrinkles. This method is simple to operate, uses readily available raw materials, and has excellent reproducibility, providing a universal new strategy for the large-scale fabrication of high-performance flexible electrodes; its applicability can be extended to various MXene systems (such as V2CT). x Nb2CT x wait).

[0017] (2) Structural Innovation: This invention successfully constructed a composite thin-film electrode with cross-scale structural features using the above method. On a macroscopic scale, the film surface exhibits a rich wrinkled structure, significantly increasing the electrochemical active area. On a micrometer scale, the film interior forms interlayer macropores of hundreds of micrometers (approximately 240 μm), serving as an "ion highway" for electrolyte wetting and ion transport. On a nanometer scale, a conductive network formed by carbonized CNF runs through the MXene sheets, constructing an efficient electronic conduction pathway. This multi-level structural synergy of "macroscopic wrinkles - interlayer micrometer pores - nano-conductive network" effectively solves the problem of ion transport obstruction caused by the stacking of traditional MXene films, thereby improving electrochemical performance.

[0018] (3) Interface Innovation: This invention successfully constructed a Ti-OC covalent interface between MXene and partially carbonized CNF through alkaline treatment and medium-temperature heat treatment. Fourier transform infrared spectroscopy (FT-IR) analysis showed that at 805.5 cm⁻¹... -1 The appearance of a new peak at the Ti-OC bond confirms the construction of the Ti→O→C interfacial electronic channel. This strongly coupled interfacial structure not only endows the composite material with good mechanical stability but also provides an atomic-scale pathway for rapid interfacial charge transport.

[0019] (4) Excellent performance: The composite thin-film electrode prepared by this invention exhibits excellent comprehensive electrochemical performance. As a self-supporting structure, this electrode requires no binder or current collector and achieves high performance at 1 A g. -1 The specific capacitance reaches 756 F g at current density -1 Even at a high current density of 50 A g -1 It can still maintain 467.1 F g. -1 Its specific capacitance exhibits excellent rate performance. Electrochemical impedance spectroscopy tests show that its charge transfer resistance is as low as 0.22Ω, confirming its highly efficient interfacial charge transport capability.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fabrication process of the self-supported MXene / CNF composite thin film electrode obtained in Example 1 of the present invention; Figure 2 This is a photograph of the self-supporting MXene / CNF composite thin film electrode obtained in Embodiment 1 of the present invention; Figure 3 The images shown are scanning electron microscope images of the self-supporting MXene / CNF composite thin film electrode obtained in Example 1 of the present invention, wherein: (a) is a surface wrinkle morphology image; (b) is a cross-sectional interwoven network image after freeze-drying; and (c) is a cross-sectional image of interlayer macropores after heat treatment. Figure 4 The Fourier transform infrared spectrum of the self-supporting MXene / CNF composite thin film electrode obtained in Example 1 of the present invention is shown below. Figure 5 The thin film electrodes obtained in Embodiment 1, Comparative Example 1, and Comparative Example 2 of this invention were subjected to a temperature of 20 A g. -1 Electrochemical performance test curves at current density, where: (a) is the cyclic voltammetry curve; (b) is the galvanostatic charge-discharge curve; Figure 6The following are electrochemical performance test results of the self-supported MXene / CNF composite thin film electrode obtained in Example 1 of the present invention, wherein: (a) is the cyclic voltammetry curve at different scan rates; (b) is the galvanostatic charge-discharge curve at different current densities; (c) is the specific capacitance curve as a function of current density; and (d) is the AC impedance spectrum. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0023] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0024] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0025] Unless otherwise specified, all materials, reagents, instruments, and equipment used in this invention are commercially available and readily available to those skilled in the art. The testing standards used are all national or international standards commonly used in the field, and will not be further elaborated here.

[0026] Example 1 This embodiment provides a method for preparing a self-supporting MXene-based composite thin-film electrode material with wrinkled and interlayer macroporous structures. The preparation flowchart is shown below. Figure 1 As shown, firstly, in the presence of NaOH, using Na... +Electrostatic bridging induces heterogeneous aggregation and wrinkling of MXene and CNF; then freeze-drying and shaping with an ice template to form a solid precursor with a hierarchical porous structure; finally, heat treatment carbonizes CNF and forms Ti-OC covalent bonds, permanently locking the porous wrinkled structure to obtain a self-supporting flexible composite thin film electrode.

[0027] Specifically, the following steps are included: Preparation of S1 and MXene nanosheet dispersions: 1.6 g of LiF powder was added to 20 mL of 9 mol / L HCl solution and stirred for 15 min. Then, 1 g of Ti3AlC2MAX phase powder was slowly added, and the mixture was stirred at 40 °C for 24 h. After the reaction, the mixture was repeatedly washed with deionized water at 3500 rpm (1 min each time) until the supernatant had a pH of ≈6 and turned black. The resulting mixture was collected, ultrasonically exfoliated at 360 W for 30 min, and then centrifuged at 3500 rpm for 15 min. The supernatant was collected and diluted to a concentration of 10 mg / mL to obtain the MXene nanosheet dispersion.

[0028] S2, Electrostatic Assembly: 1.1 mL of the above MXene nanosheet dispersion (concentration 10 mg / mL) was mixed with 9 mL of TEMPO oxidized cellulose nanofiber (CNF) aqueous dispersion (concentration 0.1%), so that the CNF solid mass accounted for 45% of the total CNF and MXene solid mass (total solid mass of the system was 20 mg). The mixture was sonicated for 2 min to obtain a uniform black dispersion. While continuously stirring, 1.5 mL of NaOH solution (concentration 100 mg / mL) was added to adjust the pH of the system to 12. Stirring was continued for 30 min, and obvious flocculation and aggregation were observed in the system. After standing, the mixture separated into layers: a pale yellow clear liquid on top and a black precipitate on the bottom. Finally, vacuum filtration was performed to obtain a self-supporting wet composite film.

[0029] S3. Ice template forming and freeze-drying: The above-mentioned wet composite film was immediately placed on the surface of a copper platform and rapidly frozen with liquid nitrogen. It was then transferred to a freeze dryer and dried for 24 h at -50°C and a vacuum degree of <10 Pa. The interlayer macroporous structure was formed inside the film by ice crystal growth and sublimation, resulting in a self-supporting black precursor film.

[0030] S4. Heat-locking treatment: The solid precursor film was placed in a tube furnace and heated from 25°C to 100°C at a rate of 1.88°C / min under nitrogen protection, and then heated to 400°C at a rate of 5°C / min. The temperature was held for 2 hours and then naturally cooled to room temperature to obtain a dark gray self-supporting flexible MXene / CNF composite thin film electrode material with wrinkles and interlayer macroporous structure.

[0031] Example 2 The only difference between this embodiment and Embodiment 1 is that in step S2, the mass of CNF solid accounts for 15% of the total mass of the CNF and MXene mixed system. The remaining steps and parameters are the same and will not be repeated here.

[0032] Example 3 The only difference between this embodiment and Embodiment 1 is that in step S2, the mass of CNF solid accounts for 25% of the total mass of the CNF and MXene mixed system. The remaining steps and parameters are the same and will not be repeated here.

[0033] Example 4 The only difference between this embodiment and Embodiment 1 is that in step S2, the mass of CNF solid accounts for 35% of the total mass of the CNF and MXene mixed system. The remaining steps and parameters are the same and will not be repeated here.

[0034] Example 5 The only difference between this embodiment and Embodiment 1 is that in step S2, the mass of CNF solid accounts for 55% of the total mass of the CNF and MXene mixed system. The remaining steps and parameters are the same and will not be repeated here.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that CNF and NaOH were not added in step S2; instead, the same total solid mass (20 mg) of MXene dispersion as in step S2 was directly used for vacuum filtration. The remaining steps and parameters are the same and will not be repeated here.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that the heat-locking treatment in step S4 was not performed; that is, the solid precursor obtained in step S3 was directly used as the final electrode material. The remaining steps and parameters are the same and will not be repeated here.

[0037] The appearance morphology of the composite thin film material obtained in Example 1 was tested, and the results are as follows: Figure 2 As shown. By Figure 2 It is evident that the MXene / CNF composite film exhibits a distinct wrinkled structure on its surface, indicating that the three strategies of "electrostatic assembly," "ice template shaping," and "thermal locking" were used in synergy to successfully construct a rich wrinkled morphology on the film surface, which is beneficial for increasing the electrochemical active area.

[0038] The composite thin film material obtained in Example 1 was tested using scanning electron microscopy, and the results are as follows: Figure 3 As shown. Figure 3 (a) further demonstrates the micron-scale wrinkled morphology, confirming that the introduction of CNF effectively induces wrinkles in the MXene sheets, increases the contact area between the electrode and the electrolyte, and increases the electrochemical active area. Figure 3 (b) shows the interwoven network of MXene and CNF after freeze-drying, confirming that the electrostatic assembly and ice template strategy successfully constructed a three-dimensional interconnect skeleton. Figure 3 (c) shows the formation of interlayer macropores (approximately 240 μm in diameter) inside the composite film after heat treatment. These macropores can serve as rapid ion transport channels, significantly improving electrolyte wetting and rate performance.

[0039] Fourier transform infrared spectroscopy was performed on the composite thin film material obtained in Example 1, and the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that the composite film is at 805.5 cm. -1 A new characteristic absorption peak appeared nearby, which is attributed to the stretching vibration of the Ti-OC covalent bond. This indicates that an interfacial covalent bond was formed between MXene and CNF carbide through heat treatment, which is beneficial to enhancing the mechanical stability and charge transport efficiency of the material.

[0040] The electrochemical performance of the composite thin film materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 was tested at 20 Ag. -1 Its cyclic voltammogram and galvanostatic charge-discharge curve were tested at current density, and the results are as follows: Figure 5 As shown. Figure 5 As shown in (a), Example 1 has the largest CV integral area, indicating that it has the highest electrochemical activity; Figure 5 As shown in (b), Example 1 had the longest GCD discharge time, indicating that its electrochemical performance was significantly better than that of Comparative Example 1 and Comparative Example 2.

[0041] The electrochemical performance of the composite thin film material obtained in Example 1 was tested. Cyclic voltammetry curves were measured at different scan rates, and galvanostatic charge-discharge curves were measured at different current densities. The tests were conducted at open-circuit voltages with a frequency range from 0.01 Hz to 10 Hz. 5 AC impedance was tested under Hz conditions, and the results are as follows: Figure 6 As shown. Figure 6 As shown in (a), the material exhibits a distinct redox peak, demonstrating its pseudocapacitive properties. Figure 6 As shown in (b), the charge-discharge curves exhibit high symmetry, indicating excellent electrochemical reversibility. Figure 6 (c) shows that in 1 A g-1 At a current density of 756 F g, its specific capacitance can reach 756 F g. -1 Even at 50 Ag -1 Even at high current densities, its specific capacitance can still reach 467.1 F g. -1 This indicates that it has excellent electrochemical performance and rate performance; Figure 6 As shown in (d), its internal resistance is 1.77 Ω and its charge transfer resistance is 0.22 Ω, indicating that it has low impedance characteristics.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure, characterized in that, Specifically, the following steps are included: Preparation of S1 and MXene nanosheet dispersion: MAX phase ceramic powder was added to HCl solution containing LiF for etching reaction. After the reaction was completed, the mixture was centrifuged and washed until neutral and a black supernatant appeared. The resulting mixed solution was subjected to ultrasonic exfoliation, and the supernatant was collected by centrifugation to obtain the MXene nanosheet dispersion. S2, Electrostatic Assembly: The MXene nanosheet dispersion obtained in step S1 is mixed with the TEMPO oxidized cellulose nanofiber (CNF) dispersion. NaOH is added to adjust the pH of the system to alkaline. + The compressed double layer is used as an electrostatic bridge to cause heterogeneous aggregation and wrinkling of negatively charged MXene sheets and negatively charged CNF, forming composite flocculants, which are then obtained by vacuum filtration to obtain a self-supporting wet composite film. S3. Ice template forming and freeze-drying: The wet composite film obtained in step S2 is freeze-dried to form an interlayer macroporous structure inside the film by ice crystal growth and sublimation, thus obtaining a solid precursor film. S4. Heat-locking treatment: The solid precursor film obtained in step S3 is heat-treated in an inert atmosphere to achieve CNF carbonization, removal of -F and -OH functional groups on the MXene surface, and formation of Ti-OC covalent bonds, thereby obtaining a flexible composite thin film electrode material.

2. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S1, the MAX phase ceramic powder is Ti3AlC2; in the HCl solution containing LiF, the mass of LiF is 1-2 g and the concentration of HCl is 6-12 mol / L; the etching reaction temperature is 35-60℃ and the time is 12-48 h.

3. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S1, the ultrasonic stripping power is 100-500 W and the time is 30-120 min; the centrifugation speed is 2000-5000 rpm and the time is 1-30 min.

4. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S2, the concentration of the MXene nanosheet dispersion is 1-30 mg / mL; the mass of CNF solid accounts for 15%-55% of the total mass of the CNF and MXene mixed system.

5. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S2, NaOH is added to adjust the pH of the system to 8-13.

6. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S3, the freeze-drying temperature is -50℃ to -20℃, the vacuum degree is 1-20Pa, and the time is 12-48h.

7. The method for preparing a self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 1, characterized in that, In step S4, the inert atmosphere is nitrogen or argon; the heat treatment temperature is 300-500℃, the heating rate is 1-10℃ / min, and the holding time is 1-3h.

8. A self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure, characterized in that, The composite thin film electrode material is prepared by the preparation method described in any one of claims 1-7, and has surface wrinkles, micron-level interlayer macropores, and a nano-conductive network formed by carbonized CNF; MXene and carbonized CNF are bonded by Ti-OC covalent bonds.

9. The self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 8, characterized in that, The diameter of the interlayer macropores is 50-400 μm.

10. The self-supporting MXene-based composite thin-film electrode material with a wrinkled and interlayer macroporous structure according to claim 8, characterized in that, The mass fraction of CNF in the composite thin film electrode material is 15%-55%.

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