MXene-based flexible conductive film and preparation method and application thereof

Abstract

The application provides a MXene-based flexible conductive film and a preparation method thereof, and is prepared by the following method: titanium aluminum carbide is etched by hydrochloric acid and lithium fluoride to obtain a single-layer MXene dispersion liquid; a reduced graphene oxide aqueous dispersion liquid, the single-layer MXene dispersion liquid and a PEDOT:PSS solution are mixed and uniformly mixed under nitrogen protection, NaOH solution is added, and stirring and suspension are carried out; a self-supporting film is obtained by vacuum filtration; the film is peeled off by freeze-drying, immersed in concentrated hydrochloric acid, washed and dried to obtain the MXene-based flexible conductive film. The flexible conductive film has high specific surface area and good cycle performance. A flexible solid-state supercapacitor is prepared by using the flexible conductive film, and the flexible solid-state supercapacitor has high energy density and power density, and good electrochemical stability and mechanical flexibility. The application has simple process, low cost and is suitable for large-scale production, and is suitable for flexible wearable energy storage devices and has great popularization and application value.

Description

Technical Field

[0001] This invention belongs to the field of flexible conductive thin film materials, specifically relating to a high specific surface area flexible conductive thin film based on MXene / reduced graphene oxide / PEDOT:PSS, its preparation method, and its application in flexible wearable energy storage devices. Background Technology

[0002] With the rapid advancement and development of electronic information technology, electronic devices are evolving towards portability, flexibility, and wearability. One of the biggest challenges in developing flexible electronics technology is finding lightweight and flexible electrochemical energy storage devices to match. Flexible supercapacitors have attracted widespread attention due to their high specific capacitance, excellent long-cycle charge-discharge stability, and good mechanical flexibility, and have broad application prospects in fields such as flexible displays, flexible electronic sensors, and flexible energy storage devices.

[0003] MXene, a two-dimensional transition metal carbonitride material, is considered an ideal electrode material for flexible supercapacitors due to its high conductivity, excellent mechanical flexibility, and good electrochemical activity. However, MXene nanosheets tend to stack during film formation, leading to a decrease in specific surface area and hindered ion transport, thus limiting its electrochemical performance. Traditional preparation methods, such as in-situ polymerization and slurry coating, suffer from problems such as complex processes, high energy consumption, dense film structures, and few active sites. Furthermore, commonly used binders such as PVDF can reduce the ionic conductivity of the electrode. While PEDOT:PSS exhibits good conductivity, its high content of the non-conductive PSS component negatively impacts overall electrochemical performance.

[0004] Therefore, developing a simple preparation method that can significantly improve the specific surface area and electrochemical performance of MXene-based thin films is of great scientific significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high specific surface area MXene-based flexible conductive films that is simple, low-cost, and suitable for large-scale production, as well as its applications. The flexible conductive film of this invention possesses advantages such as high specific surface area and excellent electrochemical performance, while also exhibiting good mechanical flexibility. Furthermore, applying the above-mentioned flexible conductive film to flexible supercapacitors yields advantages such as high energy density, long cycle life, and good bending stability.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing an MXene-based flexible conductive thin film, the method comprising the following steps:

[0008] (1) Preparation of monolayer MXene dispersion

[0009] Titanium aluminum carbide was etched with hydrochloric acid and lithium fluoride to obtain a monolayer MXene dispersion;

[0010] Furthermore, the mass ratio of the titanium aluminum carbide to lithium fluoride is 1:1~2.

[0011] The concentration of the hydrochloric acid is preferably 8-12 M.

[0012] The volume of the hydrochloric acid is 10~35 mL / g based on the mass of lithium fluoride.

[0013] The etching temperature is preferably 30~50℃, more preferably 40℃. The etching time is preferably 12~48 hours.

[0014] After etching, the resulting reaction product was centrifuged and washed, then ultrasonically exfoliated in an ice bath to obtain a monolayer MXene dispersion.

[0015] (2) The aqueous dispersion of reduced graphene oxide, the single-layer MXene dispersion, and the PEDOT:PSS solution are mixed and mixed evenly under nitrogen protection. NaOH solution is added and stirred to form a suspension. The suspension is obtained by vacuum filtration. The film is then freeze-dried to peel off the film, immersed in concentrated hydrochloric acid, washed and dried to obtain the MXene-based flexible conductive film.

[0016] The concentration of the reduced graphene oxide aqueous dispersion is 3~6 mg / mL.

[0017] The concentration of the monolayer MXene dispersion is 3~8 mg / mL.

[0018] The concentration of the PEDOT:PSS solution is 1~2 wt.%, preferably 1.5%.

[0019] The concentration of the NaOH solution is 100~200 mg / mL.

[0020] The volume ratio of the reduced graphene oxide aqueous dispersion, the monolayer MXene dispersion, the PEDOT:PSS solution, and the NaOH solution is 2~10 : 6~10 : 0.5~1 : 0.5~1.

[0021] The vacuum filtration produces a self-supporting membrane. The vacuum degree of the vacuum filtration is -80 to -100 kPa, and the filtration generally uses a filter membrane with a pore size of 0.22 μm.

[0022] The concentrated hydrochloric acid treatment time is 12 to 48 hours.

[0023] The present invention also provides MXene-based flexible conductive films prepared by the above method.

[0024] This invention also provides the application of MXene-based flexible conductive films in flexible supercapacitors.

[0025] Furthermore, this invention provides MXene-based flexible conductive films as flexible electrodes for use in the fabrication of flexible supercapacitors.

[0026] Furthermore, the method of application is as follows:

[0027] The MXene flexible conductive film is cut into two thin electrode sheets of the same size. The thin film electrodes are fixed onto the polyimide film. A gel electrolyte is coated on the surface of the two electrode sheets. The two electrolyte-coated electrodes are overlapped and a cellulose membrane is sandwiched between the electrodes to prevent short circuits. The stacked assembly consisting of the two electrodes and the membrane is pressed together to ensure tight contact between all components. Then, it is encapsulated with polyimide tape to prevent electrolyte leakage, thus assembling a flexible supercapacitor.

[0028] The present invention also provides a flexible supercapacitor, the flexible supercapacitor comprising the MXene-based flexible conductive film.

[0029] Furthermore, the flexible supercapacitor uses an MXene-based flexible conductive film as a flexible electrode.

[0030] The flexible supercapacitor can be prepared by the following method: fixing thin-film electrodes onto polyimide films, coating gel electrolyte onto the surfaces of the two electrodes, overlapping the two electrodes coated with electrolyte, and sandwiching a cellulose membrane between the electrodes to prevent short circuits; pressing the laminated assembly consisting of the two electrodes and the membrane together to ensure tight contact between all components, and then encapsulating it with polyimide tape to prevent electrolyte leakage, thereby assembling the flexible supercapacitor.

[0031] Preferably, the gel electrolyte is a PVA / H3PO4 gel electrolyte.

[0032] The two ends of the flexible supercapacitor are connected by conductive tape, and the conductive tape is electrically connected to the testing equipment for electrochemical and mechanical performance testing.

[0033] The flexible supercapacitors can be combined in series and / or in parallel to form a combined device, thereby increasing the output voltage and output power.

[0034] This invention also provides the application of flexible supercapacitors in flexible wearable energy storage devices.

[0035] This invention uses PEDOT:PSS and rGO as intercalation materials to suppress the self-stacking of MXene nanosheets, thereby preserving accessible active surfaces and promoting ion diffusion pathways. Alkali treatment significantly accelerates the vacuum filtration process by affecting the solution pH, which is beneficial for large-scale film production. Hydrochloric acid treatment of the film effectively removes a large number of low-conductivity PSS chains from PEDOT:PSS, forming a porous and interconnected conductive network. This step not only significantly increases the specific surface area of ​​the film but also exposes more electroactive sites and improves charge transport kinetics. Finally, a flexible conductive film (A-MGP5 flexible conductive film) with high specific surface area and good electrochemical performance is prepared.

[0036] The flexible conductive film of this invention has a high specific surface area of ​​62.92 m² / g and a specific capacitance of 361 F / g at 1 A / g, retaining 87% of its capacitance after 10,000 cycles. When this flexible conductive film is assembled into a symmetrical flexible solid-state supercapacitor, it achieves an energy density of 14.5 Wh / kg and a power density of 398.4 W / kg. This flexible supercapacitor exhibits high energy and power densities, good electrochemical stability and scalability, excellent mechanical flexibility, good bending stability, and good cycling performance. The invention features a simple process, low cost, and suitability for mass production, making it suitable for flexible wearable energy storage devices and possessing significant potential for widespread application. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the preparation process of MXene-redox graphene-PEDOT:PSS flexible conductive film.

[0038] Figure 2 SEM images of MXene, rGO, PEDOT:PSS and A-MGP5 films.

[0039] Figure 3 Optical and cross-sectional SEM images and EDS elemental distribution maps of different thin films.

[0040] Figure 4 XRD, FTIR, and Raman spectral characterization results for different raw materials and thin films.

[0041] Figure 5 Nitrogen adsorption-desorption isotherms, pore size distributions, and XPS spectra of different thin films.

[0042] Figure 6 The results show the electrochemical performance of different thin films.

[0043] Figure 7This is a schematic diagram of the assembly and performance characterization of a flexible symmetrical supercapacitor.

[0044] Figure 8 This demonstrates the series-parallel performance, bending performance, and practical applications of the devices. Detailed Implementation

[0045] To make the technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with the embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0046] Example 1: Preparation of MXene-redox graphene-PEDOT:PSS flexible conductive film (A-MGP5), the preparation flow chart is as follows. Figure 1 As shown.

[0047] Preparation of MXene dispersion: 2 g Ti3AlC2 powder was added to 40 mL of 9 M HCl solution containing 3.2 g LiF. The mixture was stirred at 40 °C for 48 hours, centrifuged and washed until neutral, and then ultrasonically exfoliated in an ice bath to obtain a 5 mg / mL monolayer MXene dispersion. 25 mg rGO was ultrasonically dispersed in 6 mL of deionized water, mixed with 6 mL of the 5 mg / mL MXene dispersion and 0.5 mL of 1.5% PEDOT:PSS solution, and stirred for 30 minutes under nitrogen protection. 0.5 mL of NaOH solution (150 mg / mL) was quickly added, and the mixture was stirred to form a suspension. The suspension was then vacuum filtered at -80 kPa for 40 seconds to form a membrane (0.22 μm pore size). After freeze-drying and exfoliation, the membrane was immersed in concentrated hydrochloric acid for 24 hours, washed, and dried to obtain the A-MGP5 membrane.

[0048] MXene films are prepared by the following method:

[0049] A 12 ml MXene dispersion (5 mg / ml) was vacuum filtered for 40 seconds at -80 kPa to form a membrane (0.22 μm pore size). The membrane was then freeze-dried and peeled off to obtain a self-supporting membrane.

[0050] MGP films are prepared by the following method:

[0051] 25 mg rGO was dispersed in 6 ml of deionized water and sonicated for 15 minutes to obtain an aqueous dispersion (approximately 4 mg / ml). This rGO dispersion was then mixed with 6 ml of MXene dispersion and 0.5 ml of PEDOT:PSS solution. The mixture was purged with nitrogen for 2 minutes and then stirred under sealed conditions for 30 minutes. The suspension was then filtered through a 0.22 μm pore size membrane using vacuum-assisted filtration (-80 kPa), followed by freeze-drying to remove the membrane and obtain a self-supporting membrane.

[0052] A-MGP4 thin films are prepared by the following method:

[0053] 25 mg rGO was dispersed in 6 mL of deionized water and sonicated for 15 minutes to obtain an aqueous dispersion (approximately 4 mg / mL). This rGO dispersion was then mixed with 5 mL of 5 mg / mL MXene dispersion and 0.5 mL of 1.5% PEDOT:PSS solution. The mixture was purged with nitrogen for 2 minutes and then sealed. After continuous stirring for 30 minutes, NaOH solution (150 mg / mL) was rapidly added to form a suspension. The suspension was then filtered through a 0.22 μm pore size membrane using vacuum-assisted filtration (-80 kPa) to form a self-supporting membrane. The resulting membrane was freeze-dried to remove the filter membrane, and then immersed in hydrochloric acid solution for 12 hours. Finally, it was washed three times with deionized water and dried.

[0054] A-MGP6 thin films are prepared by the following method:

[0055] 25 mg rGO was dispersed in 6 mL of deionized water and sonicated for 15 minutes to obtain an aqueous dispersion (approximately 4 mg / mL). This rGO dispersion was then mixed with 7 mL of 5 mg / mL MXene dispersion and 0.5 mL of 1.5% PEDOT:PSS solution. The mixture was purged with nitrogen for 2 minutes and then sealed. After continuous stirring for 30 minutes, NaOH solution (150 mg / mL) was rapidly added to form a suspension. The suspension was then filtered through a 0.22 μm pore size membrane using vacuum-assisted filtration (-80 kPa) to form a self-supporting membrane. The resulting membrane was freeze-dried to remove the filter membrane, and then immersed in hydrochloric acid solution for 12 hours. Finally, it was washed three times with deionized water and dried.

[0056] SEM images of MXene, rGO, PEDOT:PSS and A-MGP5 films are shown below. Figure 2 As shown, (a) is MXene, (b) is rGO, (c) is PEDOT:PSS, and (d) is A-MGP5 film.

[0057] Optical and cross-sectional SEM images and EDS elemental distribution maps of different thin films are shown below. Figure 3 As shown, (a) is an optical and cross-sectional SEM image of different thin films, (b) is an EDS elemental distribution map of pure MXene thin film, and (c) is an EDS elemental distribution map of A-MGP5 thin film.

[0058] Compared to dense MGP films, A-MGP flexible films treated with alkali and acid in sequence exhibit greater thickness and a more porous internal structure at the same MXene content.

[0059] Characterization results of XRD, FTIR, and Raman spectra of different raw materials and thin films are as follows: Figure 4 As shown, (a) is the XRD pattern of MXene, MGP, and Ti3AlC2, (b) is the XRD pattern of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6, (c) is the FTIR pattern of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6, and (d) is the Raman spectrum of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6.

[0060] XRD patterns show that the (002) diffraction peak of the MGP, A-MGP4, A-MGP5, and A-MGP6 films decreased from 7.4° to 5.6°, indicating an increase in the internal space of the films. Alkali and acid treatments in sequence significantly increased the specific surface area of ​​the films.

[0061] FTIR spectra show that, compared with MGP films, A-MGP films have more oxygen (-O) functional groups, indicating better conductivity; sulfur (-S) functional groups are reduced, indicating a decrease in PSS content (acid treatment removes a large amount of S-containing PSS components), and an increase in internal space of the film.

[0062] Raman spectroscopy shows that, compared with MGP films, A-MGP films have a smaller D / G band ratio, indicating that the carbon structure inside the film is more ordered, the charge transfer rate is higher, and the electrochemical performance is better after the base-acid sequential treatment.

[0063] Nitrogen adsorption-desorption isotherms, pore size distributions, and XPS spectra of different thin films are shown below. Figure 5 As shown, (a) is the nitrogen adsorption-desorption isotherm of MXene and A-MGP5 films, (b) is the pore size distribution of MXene and A-MGP5 films, and (c) to (f) are the XPS spectra of MXene, MGP and A-MGP5.

[0064] Nitrogen adsorption-desorption isotherms and pore size distribution diagrams show that, compared with pure MXene films, A-MGP5 films have higher specific surface area and larger pore size, indicating that the alkali-acid sequential treatment can significantly increase the specific surface area of ​​the film and form a porous structure inside.

[0065] XPS spectra show that, compared to MGP films, A-MGP films treated with alternating base and acid have more oxygen-containing functional groups and fewer fluorine-containing functional groups on their surface, indicating that alternating base and acid treatment can effectively regulate the functional groups on the film surface and improve the electrochemical performance of the film.

[0066] The electrochemical performance of the A-MGP5 thin-film electrode was tested in a three-electrode system (2 M H2SO4 electrolyte). The electrode was cut into 1 cm × 1 cm pieces and placed in a fixture.

[0067] Electrochemical performance results of different thin films are as follows: Figure 6 As shown, (a) is the cyclic voltammetry curve of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6; (b) is the galvanostatic charge-discharge (GCD) curve of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6; (c) is the CV curve of A-MGP5 thin film electrode at different scan rates; (d) is the GCD curve of A-MGP5 thin film electrode at different current densities; (e) is the specific capacitance distribution of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6 thin film electrodes; (f) is the Nyquist plot of MXene, MGP, A-MGP4, A-MGP5, and A-MGP6 thin film electrodes; (g) is the CV curve of A-MGP5 thin film electrode (the shaded area represents the contribution of surface control capacitance); (h) is the diffusion control capacitance of A-MGP5 thin film electrode at different scan rates and its percentage contribution; (i) The figure shows the constant current charge-discharge (GCD) cycle stability test of the A-MGP5 thin film electrode.

[0068] Test results show that the A-MGP5 film treated with alternating alkali and acid has a specific capacitance of 361 F / g, an internal resistance of 2.007 Ω, and a charge transfer resistance of 0.822 Ω at 1 A / g. Furthermore, after 10,000 constant current charge-discharge (GCD) cycles at a current density of 5 A g⁻¹, the A-MGP5 film electrode exhibits 87% specific capacitance retention and 99.8% coulombic efficiency, demonstrating excellent charge-discharge cycle stability.

[0069] Example 2: Assembly of a flexible symmetrical supercapacitor

[0070] The A-MGP5 film was cut into two 1 cm × 2 cm electrode sheets, and each sheet was then fixed onto a separate polyimide film. A PVA / H3PO4 gel electrolyte was coated onto the electrode surface. The two electrolyte-coated electrodes were then overlapped, with a cellulose membrane sandwiched between them to prevent short circuits. The stacked assembly was gently pressed together to ensure tight contact between all components. Finally, the assembly was sealed with polyimide tape to prevent electrolyte leakage, resulting in a flexible supercapacitor. Conductive wires were connected to the electrodes of the flexible supercapacitor via conductive tape, and these wires were electrically connected to a testing device for electrochemical and mechanical performance testing.

[0071] Assembly diagram and performance characterization of flexible symmetrical supercapacitors are shown below. Figure 7 As shown, the device's series and parallel performance, bending performance, and practical applications are demonstrated as follows. Figure 8 As shown.

[0072] Figure 7 In the figure, (a) is a schematic diagram of the assembly structure of the flexible symmetrical supercapacitor; (b) is a test result of the A-MGP5 flexible device at different voltage windows with a scan rate of 50 mV / s; (c) is a test result of the A-MGP5 flexible device at different voltage windows with a current density of 1 A / g; (d) is a test result of the CV curve of the A-MGP5 flexible device at different scan rates; (e) is a test result of the GCD curve of the A-MGP5 flexible device at different current densities; (f) is a Nyquist plot of the A-MGP5 flexible device, an inset of locally magnified high-frequency region, and an equivalent circuit diagram; (g) is a comparison of the Ragone plot of the A-MGP5 flexible device with other MXene-based capacitors.

[0073] Test results show that the A-MGP5 flexible device exhibits the best electrochemical performance at 0-0.8V, a specific capacitance of 135 F / g at a current density of 1 A / g, and a low charge transfer resistance (1.92 Ω). Compared with other flexible supercapacitors, the A-MGP5 flexible device demonstrates higher energy density and power density, exhibiting competitive and advantageous electrochemical performance.

[0074] Figure 8In the figure, (a) is the CV curve of a single A-MGP5 flexible device and two series / parallel devices; (b) is the GCD curve of a single A-MGP5 flexible device and two series / parallel devices; (c) is the CV curve of the A-MGP5 device at different bending angles; (d) is the optical image of the A-MGP5 flexible device at different bending angles; (e) is the CV curve of the A-MGP5 flexible device at a 90° bending angle with different number of repeated bending cycles; (f) is the optical image of four A-MGP5 flexible devices connected in series lighting an LED; and (g) is the test result of the charge-discharge cycle stability of the A-MGP5 flexible device at a current density of 2 A / g.

[0075] Test results show that the A-MGP5 flexible device exhibits good electrochemical stability and scalability, as well as excellent mechanical flexibility and structural stability. The assembled A-MGP5 flexible device achieves an energy density of 14.5 Wh / kg at a power density of 398.4 W / kg, while maintaining a capacitance retention of 73% and a coulombic efficiency close to 100% after 8000 consecutive charge-discharge cycles. This demonstrates the excellent energy density, cycle stability, and mechanical flexibility of the A-MGP5 flexible supercapacitor, showcasing significant application potential in wearable technology.

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing an MXene-based flexible conductive thin film, characterized in that... The method includes the following steps: (1) Preparation of monolayer MXene dispersion: Titanium aluminum carbide was etched with hydrochloric acid and lithium fluoride to obtain a monolayer MXene dispersion; (2) The aqueous dispersion of reduced graphene oxide, the single-layer MXene dispersion, and the PEDOT:PSS solution are mixed and mixed evenly under nitrogen protection. NaOH solution is added and stirred to form a suspension. The suspension is obtained by vacuum filtration. The film is then freeze-dried to peel off the film, immersed in concentrated hydrochloric acid, washed and dried to obtain the MXene-based flexible conductive film.

2. The method as described in claim 1, characterized in that... In step (1), the mass ratio of titanium aluminum carbide to lithium fluoride is 1:1~2; the concentration of hydrochloric acid is 8~12M; and the volume of hydrochloric acid is 10~35mL / g based on the mass of lithium fluoride.

3. The method as described in claim 1, characterized in that... In step (2), the concentration of the reduced graphene oxide aqueous dispersion is 3~6 mg / mL; the concentration of the monolayer MXene dispersion is 3~8 mg / mL; the concentration of the PEDOT:PSS solution is 1~2 wt.%; and the concentration of the NaOH solution is 100~200 mg / mL.

4. The method as described in claim 1, characterized in that... In step (2), the volume ratio of the reduced graphene oxide aqueous dispersion, the monolayer MXene dispersion, the PEDOT:PSS solution, and the NaOH solution is 2~10:6~10:0.5~1:0.5~1.

5. The method as described in claim 1, characterized in that... In step (2), the concentrated hydrochloric acid treatment time is 12 hours to 48 hours.

6. The MXene-based flexible conductive film prepared by the method according to any one of claims 1 to 5.

7. The application of the MXene-based flexible conductive film as described in claim 6 in flexible supercapacitors.

8. The application as described in claim 7, characterized in that... MXene-based flexible conductive films are used as flexible electrodes to fabricate flexible supercapacitors.

9. A flexible supercapacitor, characterized in that... The flexible supercapacitor includes the MXene-based flexible conductive film as described in claim 6.

10. The application of the flexible supercapacitor as described in claim 9 in flexible wearable energy storage devices.

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