S, N-MXene / rGO composite flexible film and preparation method and application thereof

Abstract

The application discloses an S, N-MXene / rGO composite flexible film and a preparation method and application thereof. The composite flexible film has a layered hollow carbon sphere frame structure, the layer is a two-dimensional MXene layer loaded with large-size reduced graphene oxide and doped with sulfur atoms and nitrogen atoms, and the hollow carbon sphere frame is embedded into the two-dimensional MXene interlayer. The composite flexible film is obtained by mixing MXene, PMMA microsphere solution, graphene oxide and thiourea and heat treatment with PMMA as a template. 3 The composite flexible film has an excellent rate performance, and the volume capacity retention rate is 1580.5 F / cm 3 at 10 A / g. The capacity retention rate of an assembled asymmetric flexible supercapacitor reaches 81.8% after 5500 cycles, the energy density reaches 144.6 Wh / kg, and the power density reaches 875.9 W / kg.

Description

TECHNICAL FIELD

[0001] The present application relates to a hollow carbon sphere frame S, N-MXene / rGO composite material flexible film and its preparation and application, belonging to the field of organic composite electrode materials. BACKGROUND

[0002] Wind energy, solar energy, tidal energy and other environmentally friendly renewable energy sources are increasingly important for global sustainable development. However, these renewable energy sources are intermittent, which makes energy storage devices indispensable. Among the many energy storage technologies, supercapacitors have good commercialization potential due to their good flexibility, high power density, fast charging and discharging capability, and high safety performance. However, due to the low capacity and low cycle efficiency of existing supercapacitors, they cannot be applied to high-energy output devices. At the same time, due to the high internal resistance, they are easily limited during use. In order to overcome this shortcoming, it is urgent to develop new supercapacitor electrode materials. Therefore, in order to miniaturize to meet the needs of various flexible and portable electronic devices, many researchers have invested a lot of effort to improve the flexibility and energy density of supercapacitors. Two-dimensional MXenes exhibit many excellent properties, such as electrical conductivity, large specific surface area, large number of electrochemically active sites and open ion diffusion channels, and mechanical flexibility, making them a promising material for supercapacitors. However, due to the action of van der Waals forces, nanosheets will undergo highly dense re-deposition and aggregation, which severely limits the surface utilization and rate performance of MXenes, thereby adversely affecting their application in many fields.

[0003] In order to solve these problems, heteroatoms are doped into two-dimensional materials to meet the need for high energy density of electrode materials. Doping heteroatoms can greatly change the two-dimensional material (such as electron cloud density and chemical reactivity), increase the electrostatic repulsion between two-dimensional nanosheets, and thus effectively reduce the aggregation of two-dimensional nanosheets. Generally speaking, doping can be achieved in two different ways: surface functionalization of molecules by giving or taking away electrons, or by substituting / introducing heteroatoms in the lattice. S and N elements as dopants can effectively adjust the electronic state and electrochemical activity of MXene. Doping two different heteroatoms (N and S) into the material can provide more active sites while producing more defects, and affect the interlayer spacing of two-dimensional materials, achieving excellent energy storage performance. SUMMARY

[0004] Invention purposes: The first purpose of the present application is to provide a hollow carbon sphere frame S, N-MXene / rGO composite flexible film, the second purpose of the present application is to provide a preparation method of the S, N-MXene / rGO composite flexible film, the third purpose of the present application is to provide an electrode prepared by using the S, N-MXene / rGO composite flexible film, the fourth purpose of the present application is to provide a flexible asymmetric battery or a flexible supercapacitor comprising the S, N-MXene / rGO composite flexible film or the electrode prepared by using the S, N-MXene / rGO composite flexible film, and the fifth purpose of the present application is to provide a preparation method of the flexible asymmetric battery.

[0005] Technical scheme: The S, N-MXene / rGO composite flexible film provided by the present application has a layered hollow carbon sphere frame structure, wherein the lamella is doped with sulfur atoms and nitrogen atoms and carries large-size reduced graphene oxide two-dimensional MXene lamella, and the hollow carbon sphere frame is embedded into the two-dimensional MXene interlayer.

[0006] The preparation method of the S, N-MXene / rGO composite flexible film provided by the present application adopts a sacrifice template method, uses polymethyl methacrylate (PMMA) as a template, and comprises the following steps:

[0007] (A1) obtaining a MXene colloidal solution by etching Ti3AlC2;

[0008] (A2) dispersing PMMA in deionized water to obtain a PMMA colloidal solution;

[0009] (A3) mixing a thiourea aqueous solution, the PMMA colloidal solution, a GO aqueous solution and the MXene colloidal solution to obtain a mixed solution, stirring and reacting in an ice water bath, filtering, vacuum drying, calcining, and obtaining the S, N-MXene / rGO composite flexible film.

[0010] Further, in step (A1), the Ti3AlC2 powder is 200-400 mesh.

[0011] Further, in step (A1), the concentration of the MXene colloidal solution is 0.5-40 mg / mL.

[0012] Further, in step (A2), the concentration of the PMMA colloidal solution is 1-50 mg / mL.

[0013] Further, in step (A3), the concentration of the thiourea aqueous solution is 0.1-100 mg / mL.

[0014] Further, in step (A3), the concentration of the GO aqueous solution is 0.1-50 mg / mL.

[0015] Further, in step (A3), the mass ratio of thiourea to MXene in the mixed solution is 1:10-50:1, the mass ratio of PMMA to MXene is 1:1-20:1, and the mass ratio of MXene:GO is 1:20-50:1.

[0016] Further, in step (A3), the ice water bath stirring reaction time is 30-60 min.

[0017] Further, in step (A3), the vacuum drying temperature is 20-60℃, and the vacuum drying time is 1-12h.

[0018] Further, in step (A3), the calcination is under nitrogen protection, the heating rate is 0.5-8℃ / min, and the calcination temperature is 200-800℃ for 1-4h. Preferably, the calcination temperature is 400℃.

[0019] An S,N-MXene / rGO composite flexible film electrode comprises the S,N-MXene / rGO composite material flexible film described in the present application.

[0020] A flexible asymmetric zinc ion battery or a flexible supercapacitor comprises the S,N-MXene / rGO composite material flexible film described in the present application or the S,N-MXene / rGO composite material flexible film electrode described in the present application.

[0021] The preparation method of the flexible asymmetric zinc ion battery described in the present application comprises the following steps:

[0022] (B1) preparing a zinc salt solution;

[0023] (B2) preparing a PVA / zinc salt gel;

[0024] (B3) assembling the S,N-MXene / rGO composite flexible film electrode described in claim 8 with the PVA / zinc salt gel as the electrolyte to obtain a flexible asymmetric zinc ion battery.

[0025] Further, in step (B1), the zinc salt solution is obtained by dissolving a zinc salt in water, and the concentration of the zinc salt solution is 1-8mol / mL.

[0026] Further, in step (B2), the PVA / zinc salt gel is obtained by mixing the zinc salt solution and polyvinyl alcohol (PVA), stirring and heating, and vacuum drying.

[0027] Further, the amount of the zinc salt solution and PVA is 5:1-50:1.

[0028] Further, the heating and stirring is carried out at 80-90℃ for 1-4h.

[0029] Further, the temperature of vacuum drying is 20-90 DEG C, and the time of vacuum drying is 1-6 hours.

[0030] Further, in step (B3), when assembling the flexible asymmetric zinc battery, the S, N-MXene / rGO composite flexible film electrode and the zinc foil without the PVA / zinc salt gel on one end are connected by conductive silver paste.

[0031] Further, the preparation process of the flexible supercapacitor comprises a preparation step of the PVA / zinc salt gel.

[0032] Further, the preparation of the PVA / zinc salt gel comprises mixing deionized water, polyvinyl alcohol (PVA) and zinc salt, and heating and stirring to obtain colorless and transparent PVA / zinc salt gel.

[0033] Further, the flexible supercapacitor comprises a flexible symmetric supercapacitor and a solid-state flexible asymmetric supercapacitor.

[0034] The S, N-MXene / rGO flexible film is prepared by a sacrificial template method, and a layered porous structure S, N-MXene / rGO hybrid film is prepared by a one-step method of a sacrificial template, and excellent energy storage performance is achieved. The sacrificial template method is used, and PMMA (polymethyl methacrylate) is used as a template. MXene, PMMA microsphere solution, graphene oxide and thiourea are mixed into a mixed solution, and the mixed solution is filtered into a film to obtain a composite film with MXene as a substrate and PMMA as a template. The composite film is heated in a tube furnace under N2 protection to obtain a hollow carbon sphere frame S, N-MXene / rGO film modified by sulfur and nitrogen. The production of the S, N-MXene / rGO hybrid film with excellent energy storage performance is realized. The obtained flexible S, N-MXene / rGO hybrid film has an ultra-high volume capacity of 2414.6 F / cm 3 , and excellent rate performance, and the volume capacity retention rate is 1580.5 F / cm 3 at 10 A / g. In addition, the soft package bag battery S, N-MXene / rGO / / rGO for assembling the asymmetric flexible supercapacitor device has a capacity retention rate of 81.8% after 5500 cycles, an energy density of 144.6 Wh / kg, and a power density of 875.9 W / kg. The hollow carbon sphere frame S, N-MXene / rGO composite flexible film material prepared by the application solves the self-piling and aggregation problem of MXene due to its porous structure and S, N element doping, and provides a large number of active reaction sites for electron transfer in the internal cavity. At the same time, the complete and continuous MXene / rGO skeleton shortens the ion transmission path and reduces the resistance of the whole electrode, and improves the energy storage performance of the MXene electrode.

[0035] The application dopes heteroatoms (nitrogen atoms, sulfur atoms) in MXenes materials to reduce the risk of restacking of MXenes, protect the electroactive sites from being sacrificed, and improve the energy storage capacity of the electrode material. Heteroatom doping to reduce the risk of restacking of MXenes is an extremely effective method that can greatly change the electron cloud density and chemical reactivity of two-dimensional materials, increase the electrostatic repulsion between two-dimensional nanosheets, and thus effectively reduce the agglomeration of two-dimensional nanosheets. Thermal treatment of nitrogen doping can effectively release the restacking of MXene layers by forming wrinkles and increasing electrostatic repulsion, increase the number of surface defects and interlayer spacing of MXenes, and thus improve the accessibility of active sites. Therefore, by introducing heteroatoms to modify the surface terminal functional groups (-O, -OH and -F) and modify the underlying titanium carbide lattice, the performance of MXenes can be significantly improved. Doping two different heteroatoms (N and S) into MXenes materials can produce more defects and provide more active sites, while affecting the interlayer spacing of two-dimensional materials, and improving the energy storage capacity of the electrode material.

[0036] Advantages: Compared with the prior art, the application has the following obvious advantages:

[0037] (1) The S, N-MXene / rGO flexible film electrode prepared by the application adopts a novel preparation strategy of one-step sacrificial template method, successfully realizes the preparation of sulfur and nitrogen modified S, N-MXene / rGO with a layered hollow carbon sphere frame. This method not only simplifies the preparation process, but also effectively improves the preparation efficiency, so that the whole preparation process is easy to operate and efficient and time-saving.

[0038] (2) The layered hollow carbon sphere frame structure S, N-MXene / rGO composite flexible film electrode prepared by the application can improve the electronic structure and electrochemical activity of MXene through S, N element doping, thereby improving its electricity storage performance. And embedding the hollow carbon sphere frame into the MXene interlayer is beneficial to the penetration of electrolyte and the transmission of ions. In addition, the graphene oxide connects the MXene through hydrogen bonds to form a more stable network structure, which not only enhances the mechanical strength of the electrode, but also improves its flexibility.

[0039] (3) The hollow carbon sphere frame S, N-MXene / rGO composite flexible film electrode prepared by the application has good flexibility and ultra-high specific capacitance. The flexible electrode prepared by the S, N-MXene / rGO composite flexible film of the application has a weight specific capacitance and a volume specific capacitance of 742.9 F / g and 2414.6 F / cm 3 at a current density of 1 A / g (a volume specific capacitance of 2900.5 F / cm 3 ).

[0040] (4) The S, N-MXene / rGO asymmetric supercapacitor assembled by the composite flexible film electrode of the application can provide a high energy density of 144.6 Wh / kg at a power density of 875.9 W / kg, and has better performance than most of the reported heteroatom-doped MXene electrodes. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Cross-sectional scanning electron microscope image of undoped MXene obtained in Example 1;

[0042] Figure 2 Cross-sectional scanning electron microscope image of layered sandwich structure sulfur, nitrogen co-doped MXene obtained in Example 1;

[0043] Figure 3 Cross-sectional scanning electron microscope image of hollow carbon sphere frame S, N-MXene / rGO film obtained in Example 1;

[0044] Figure 4 Energy dispersive X-ray spectroscopy element mapping of the hollow carbon sphere frame S, N-MXene / rGO film obtained in Example 1;

[0045] Figure 5 CV plot of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode obtained in Example 1 at different scan rates;

[0046] Figure 6 GCD plot of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode obtained in Example 1 at different current densities;

[0047] Figure 7 CV plot of the layered sandwich structure S, N-MXene flexible film electrode provided in Examples 1-3 at a scan rate of 20 mV / s;

[0048] Figure 8 CV plot of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode provided in Examples 1, 4, 5, and 6 at a scan rate of 20 mV / s;

[0049] Figure 9 CV plot of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode provided in Examples 1, 7, 8, 9, and 10 at a scan rate of 20 mV / s;

[0050] Figure 10 Schematic diagram of the assembly of the hollow carbon sphere frame S, N-MXene / rGO flexible film battery provided in Example 1;

[0051] Figure 11 CV graph of the hollow carbon sphere frame S, N-MXene / rGO flexible supercapacitor device provided for Example 1;

[0052] Figure 12 GCD graph of the hollow carbon sphere frame S, N-MXene / rGO flexible supercapacitor device provided for Example 1. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be further described below in combination with the drawings.

[0054] Example 1

[0055] (1) Preparation of MXene nanosheets:

[0056] MXene was prepared by etching Ti3AlC2 by a conventional method. A MXene colloidal solution with a concentration of 3 mg / mL was obtained. 6 mL of the MXene colloidal solution was extracted, filtered into a film by a sand core filtering device, and dried in a 35℃ vacuum oven for 6 h to obtain flexible MXene nanosheets. The scanning electron microscope image is shown in Figure 1 .

[0057] (2) Thiourea was dissolved in deionized water to obtain a thiourea aqueous solution with a concentration of 6 mg / mL; PMMA with an average particle size of 1.8 μm was dispersed in deionized water to obtain a PMMA colloidal solution with a concentration of 10 mg / mL; GO was dissolved in deionized water to obtain a GO aqueous solution with a concentration of 1 mg / mL;

[0058] (3) Preparation of layered sandwich structure S, N co-doped MXene nanosheets:

[0059] 5 mL of the thiourea solution and 6 mL of the PMMA colloidal solution were mixed with 5 mL of the MXene colloidal solution 1 to prepare a layered sandwich structure S, N co-doped MXene nanosheet with a mass ratio of thiourea: MXene: PMMA of 2: 1: 4, and the total concentration of thiourea / PMMA / MXene in the mixed solution was controlled to be 2 mg / mL, and the reaction was stirred in an ice water bath for 30 min, filtered by a sand core filtering device, and then transferred to a vacuum box for drying at 30℃ for 12 h. The product was placed in a tubular furnace for calcination, the heating rate was 3℃ / min, and the annealing treatment was carried out at 400℃ under N2 for 2 h to obtain S, N-MXene nanosheets doped with sulfur and nitrogen in a layered sandwich structure. The scanning electron microscope image is shown in Figure 2 .

[0060] (4) In-situ preparation of macroporous hollow carbon sphere frame S, N-MXene / rGO film:

[0061] Take 1.1 mL of graphene oxide aqueous solution into 9 mL of thiourea: MXene: PMMA nanosphere mixed solution with mass ratio of 2:1:4 (thiourea / PMMA / MXene: GO mass ratio mixed according to the proportion of 16:1), then ice water bath stirring for 1 h, mixing uniformly, ultrasonic for 30 min, the mixed solution is filtered through the filter membrane with pore size of 200 nm, transferred to the vacuum box for drying at 30℃ for 12 h, then the S, N-MXene / GO nanosheet is placed in the tubular furnace for calcination, the heating rate is 3℃ / min, under N2 atmosphere at 400℃, heat treatment for 2 h, to obtain S, N-MXene / rGO composite flexible film with hollow carbon sphere frame. The scanning electron microscope image is shown in Figure 3 .

[0062] (5) Preparation of PVA-ZnSO4 gel electrolyte

[0063] In order to assemble flexible supercapacitors with S, N-MXene / rGO composite flexible film, PVA-ZnSO4 gel electrolyte is first prepared. Simply, 2 g of PVA (MW = 89000-98 000) is dissolved into 20 mL of ZnSO4 (1 M), stirring at 90℃ for 12 h, after cooling to room temperature, a uniform PVA / ZnSO4 gel electrolyte is formed.

[0064] (6) Preparation of rGO electrode

[0065] 5.6 mg of mixed material with mass ratio of rGO powder, acetylene black and polyvinylidene fluoride of 8:1:1 is coated on a zinc sheet with size of 2×2 cm as current collector, vacuum drying to obtain rGO electrode.

[0066] (7) Assembly of S, N-MXene / rGO quasi-solid flexible asymmetric supercapacitor

[0067] According to the size of 2×2 cm of S, N-MXene / rGO composite flexible film as electrode, the cut S, N-MXene / rGO flexible film electrode is evenly coated with cooled PVA / ZnSO4 gel electrolyte. Then the other side covered with PVA / ZnSO4 gel electrolyte is stacked with 2×2 cm of rGO coated zinc sheet and placed into the oven for drying at room temperature for 3 h. The two sides of S, N-MXene / rGO flexible film electrode and zinc electrode without PVA / ZnSO4 gel electrolyte are connected to the tab with conductive silver paste, and the outer layer is covered with aluminum plastic film to obtain S, N-MXene / rGO quasi-solid flexible asymmetric supercapacitor, and the prepared S, N-MXene / rGO quasi-solid flexible asymmetric supercapacitor is subjected to linear cyclic voltammetry test and constant current charge and discharge test. The assembly process is shown in Figure 10 .

[0068] A cross-sectional scanning electron microscope image of the undoped MXene flexible film prepared in this example is shown in FIG. 1A. As shown in FIG. 1A, after chemical etching of Al in Ti3AlC2, the MXene presents an accordion-like dense multilayer structure and well-arranged stacking structure, indicating that the Al atomic layer of Ti3AlC2 MAX is successfully exfoliated. Figure 1 A cross-sectional scanning electron microscope image of the layered sandwich structure S, N-MXene flexible film prepared in this example is shown in FIG. 2A. As shown in FIG. 2A, PMMA nanomicrosphere structures grow between the MXene layers and on the surface. A cross-sectional scanning electron microscope image of the hollow carbon sphere frame S, N-MXene / rGO flexible electrode film prepared in this example is shown in FIG. 3A. As shown in FIG. 3A, the PMMA nanomicrosphere structure disappears, but the S, N-MXene / rGO flexible electrode film still maintains the spherical pore structure, and as shown in FIG. 3B, the prepared hollow carbon sphere frame S, N-MXene / rGO flexible electrode film is successfully doped with S, N elements. Figure 2 A cross-sectional scanning electron microscope image of the layered sandwich structure S, N-MXene flexible film prepared in this example is shown in FIG. 2A. As shown in FIG. 2A, PMMA nanomicrosphere structures grow between the MXene layers and on the surface. A cross-sectional scanning electron microscope image of the hollow carbon sphere frame S, N-MXene / rGO flexible electrode film prepared in this example is shown in FIG. 3A. As shown in FIG. 3A, the PMMA nanomicrosphere structure disappears, but the S, N-MXene / rGO flexible electrode film still maintains the spherical pore structure, and as shown in FIG. 3B, the prepared hollow carbon sphere frame S, N-MXene / rGO flexible electrode film is successfully doped with S, N elements. Figure 3 A cross-sectional scanning electron microscope image of the layered sandwich structure S, N-MXene flexible film prepared in this example is shown in FIG. 2A. As shown in FIG. 2A, PMMA nanomicrosphere structures grow between the MXene layers and on the surface. A cross-sectional scanning electron microscope image of the hollow carbon sphere frame S, N-MXene / rGO flexible electrode film prepared in this example is shown in FIG. 3A. As shown in FIG. 3A, the PMMA nanomicrosphere structure disappears, but the S, N-MXene / rGO flexible electrode film still maintains the spherical pore structure, and as shown in FIG. 3B, the prepared hollow carbon sphere frame S, N-MXene / rGO flexible electrode film is successfully doped with S, N elements. Figure 4 A cross-sectional scanning electron microscope image of the layered sandwich structure S, N-MXene flexible film prepared in this example is shown in FIG. 2A. As shown in FIG. 2A, PMMA nanomicrosphere structures grow between the MXene layers and on the surface. A cross-sectional scanning electron microscope image of the hollow carbon sphere frame S, N-MXene / rGO flexible electrode film prepared in this example is shown in FIG. 3A. As shown in FIG. 3A, the PMMA nanomicrosphere structure disappears, but the S, N-MXene / rGO flexible electrode film still maintains the spherical pore structure, and as shown in FIG. 3B, the prepared hollow carbon sphere frame S, N-MXene / rGO flexible electrode film is successfully doped with S, N elements.

[0069] The undoped MXene, layered sandwich structure S, N-MXene, and hollow carbon sphere frame S, N-MXene / rGO flexible electrode films prepared in this example were subjected to cyclic voltammetry and galvanostatic charge-discharge tests, and the specific capacitances were 617.1, 1794.2, and 2414.6 F / cm2, respectively, at a scan rate of 1 A / g, and had good flexibility. The volume capacity of the assembled flexible asymmetric supercapacitor S, N-MXene / rGO / / rGO was 401.2 F / cm3, the energy density was 144.6 Wh / kg, and the power density was 875.9 W / kg, which was much higher than other related reported electrode materials. 3 3

[0070] Figure 5 CV curves of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode obtained in Example 1 at different scan rates; as shown in FIG. 4, the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode exhibits the largest integral area in the CV curve, showing a pair of wide redox peaks, indicating a pseudo-capacitive charge storage mechanism. Figure 5

[0071] GCD curves of the hollow carbon sphere frame S, N-MXene / rGO flexible film electrode obtained in Example 1 at different current densities; as shown in FIG. 5, the longest discharge time is exhibited in the GCD curve, indicating the highest volume capacity, and an approximately symmetric curve is shown, indicating excellent reversibility. Figure 6 Figure 6

[0072] Examples 2-3​​​​

[0073] The preparation process is the same as that of Example 1, except that the mass ratio of thiourea / MXene / PMMA nanospheres is changed

[0074] 2.5 mL, 10 mL of thiourea solution was mixed with 6 mL of PMMA colloidal solution and 5 mL of MXene solution, respectively, to prepare thiourea: MXene: PMMA nanospheres with a mass ratio of 1:1:4 and 4:1:4, respectively, and the total concentration of thiourea / PMMA / MXene in the mixed solution was controlled at 2 mg / mL. The mixed solution was stirred in an ice water bath for 30 min, filtered with a sand core filter device, and then transferred to a vacuum box for drying at 30°C for 12 h. The product was placed in a tubular furnace for calcination, with a heating rate of 3°C / min, and annealed at 400°C under N2for 2 h to obtain S,N-MXene nanosheets with a hierarchical porous structure. The other steps were the same as those of Example 1.

[0075] The S,N-MXene nanosheets prepared in this example were analyzed at a constant scan rate of 20 mV / s, and the results are shown in Figure 7 The specific capacitance of the composite flexible film electrode prepared by mixing thiourea: MXene: PMMA nanospheres with a mass ratio of 1:1:4 was up to 1587.1 F / cm 3 at a scan rate of 1 A / g, and had good flexibility. The specific capacitance of the composite flexible film prepared by mixing thiourea: MXene: PMMA nanospheres with a mass ratio of 4:1:4 was up to 999.5 F / cm 3 at a scan rate of 1 A / g, and had good flexibility.

[0076] The cyclic voltammograms (CV) of the S,N-MXene prepared in Examples 1-3 were compared at a constant scan rate of 20 mV / s, and the electrochemical energy was studied, and the results are shown in Figure 7 A pair of wide and symmetrical reversible anodic and cathodic peaks were shown on all CV curves, indicating that surface redox reactions were induced, resulting in pseudocapacitive behavior. The CV curve of the S,N-MXene prepared in Example 1 was the largest, indicating that the total charge stored was relatively high, and it exhibited strong capacitive behavior.

[0077] Examples 4-6

[0078] The preparation process is the same as that of Example 1, except that the addition of graphene oxide monomers is changed

[0079] 3.6 mL, 1.8 mL, 0.9 mL of the graphene oxide aqueous solution was added into 9 mL of the mixed solution of thiourea: MXene: PMMA nanospheres with a mass ratio of 2:1:4 (thiourea / PMMA / MXene: GO mass ratio was mixed according to the ratio of 5:1, 10:1, 20:1, respectively), then stirred in an ice water bath for 1 h, mixed uniformly, ultrasonic for 30 min, the mixed solution was filtered through a filter membrane with a pore size of 200 nm, transferred to a vacuum box and dried at 30℃ for 12 h, then the S, N-MXene / GO nanosheet was placed in a tubular furnace for calcination, the heating rate was 3℃ / min, and the heat treatment was carried out at 400℃ under N2 atmosphere for 2 h to obtain the S, N-MXene / rGO composite flexible film with conductive macroporous hollow carbon sphere framework. The other processes were the same as those in Example 1.

[0080] The S, N-MXene / rGO composite flexible film with hollow carbon sphere framework prepared in this example was analyzed at a constant scan rate of 20 mV / s, and the results are shown in Figure 8 The specific capacitance of the composite flexible film electrode obtained by the mass ratio of thiourea / PMMA / MXene: GO of 5:1 can reach 1630.6 F / cm 3 at a scan rate of 1 A / g, and has good flexibility. The specific capacitance of the composite flexible film obtained by the mass ratio of thiourea / PMMA / MXene: GO of 10:1 can reach 2019.5 F / cm 3 at a scan rate of 1 A / g, and has good flexibility. The specific capacitance of the composite flexible film obtained by the mass ratio of thiourea / PMMA / MXene: GO of 20:1 can reach 2205.9 F / cm 3 at a scan rate of 1 A / g, and has good flexibility.

[0081] In order to show the superiority of S, N-MXene / rGO prepared with different rGO ratios, the CV curves of the S, N-MXene / rGO composite flexible films prepared in Examples 1, 4, 5, and 6 were compared at a scan rate of 20 mV / s, as shown in Figure 8 The area enclosed by the CV curve is proportional to the specific capacitance of the active material. It can be seen from the CV curve that the CV curve area of Example 1 is the largest, and the corresponding specific capacitance is the highest among all samples.

[0082] Examples 7-10

[0083] The preparation process is the same as that in Example 1, except that the heat treatment temperature is changed

[0084] S, N-MXene / GO nanosheets were heat-treated at 200℃, 600℃, 800℃, 1000℃ under N2 atmosphere for 2h (heating rate of 3℃ / min) to obtain S, N-MXene / rGO composites with hollow carbon sphere frameworks. Other conditions were the same as Example 1.

[0085] The S, N-MXene / rGO composite flexible films with conductive macroporous hollow carbon sphere frameworks prepared in Examples 7-10 were analyzed at a constant scan rate of 20mV / s, and the results are shown in Figure 9 The composite flexible film obtained by heat treatment at 200℃ had a specific capacitance of 1328.7F / cm 3 at a scan rate of 1A / g, and had good flexibility. The composite flexible film obtained by heat treatment at 600℃ had a specific capacitance of 1806.3F / cm 3 at a scan rate of 1A / g, and had good flexibility. The composite flexible film obtained by heat treatment at 800℃ had a specific capacitance of 523.4F / cm 3 at a scan rate of 1A / g, and had good flexibility. The composite flexible film obtained by heat treatment at 1000℃ had a specific capacitance of 352.6F / cm 3 at a scan rate of 1A / g, and had good flexibility.

[0086] In order to characterize the effect of different heat treatment temperatures on the performance of the prepared S, N-MXene / rGO, the CV curves of the S, N-MXene / rGO composite flexible films prepared in Examples 1, 7, 8, 9, 10 were compared at a scan rate of 20mV / s, as shown in Figure 9 The area enclosed by the CV curve is proportional to the specific capacitance of the active material. As can be seen from the CV curve, the CV curve area of Example 1 is the largest, and the corresponding specific capacitance is the highest among all samples. In addition, the CV curve areas of Examples 9 and 10 are the smallest and smaller than that of the undoped MXene, which may be due to the collapse of the MXene layers at too high a temperature, resulting in poor performance. Therefore, the heat treatment temperature range should be 200-800℃, and the optimal temperature is 400℃.

[0087] The application evaluation of the S, N-MXene / rGO film prepared in Example 1 was assembled into a quasi-solid flexible asymmetric supercapacitor (as shown in Figure 10 For electrochemical testing, a voltage window of 0-1.75V was selected as the working voltage window of the device. The results are shown in Figures 11-12 As can be seen, the device has a Figure 11The device can work normally under the shown 1.75 V voltage window, and the CV curves obtained at a scan rate of 20-100 mV / s obviously show typical rectangular pseudo-capacitance behavior, and the CV curves change insignificantly at different scan rates, indicating that the device has excellent rate performance. The device can provide a high energy density of 144.6 Wh / kg at a power density of 875.9 W / kg. Figure 12 In the shown GCD curve, the specific capacitance of the S, N-MXene / rGO flexible supercapacitor device is 401.2 F / cm 3 In addition, the quasi-solid flexible device shows good cycle stability, and the prepared S, N-MXene / rGO supercapacitor can provide a high energy density of 144.6 Wh / kg at a power density of 875.9 W / kg. This indicates that the S, N-MXene / rGO quasi-solid flexible device has great potential in flexible energy storage and application.

Claims

1. An S, N-MXene / rGO composite flexible film, characterized in that, The S, N-MXene / rGO composite flexible film is a layered hollow carbon sphere frame structure, wherein the sheet layer is doped with sulfur atoms and nitrogen atoms, and carries a two-dimensional MXene sheet layer of large-size reduced graphene oxide, and the hollow carbon sphere frame is embedded in the two-dimensional MXene sheet layer.

2. The method of claim 1, wherein the S, N-MXene / rGO composite flexible film is prepared by the steps of: The sacrificial template method is used, and PMMA is used as the template, including the following steps: (1) obtaining a MXene colloidal solution by etching Ti3AlC2; (2) obtaining a PMMA colloidal solution by dispersing PMMA in deionized water; (3) mixing a thiourea aqueous solution, the PMMA colloidal solution, a GO aqueous solution, and the MXene colloidal solution to obtain a mixed solution, stirring and reacting in an ice water bath, filtering, vacuum drying, calcining, and obtaining the S, N-MXene / rGO composite flexible film.

3. The production method according to claim 2, characterized by, In step (1), the Ti3AlC2 powder is 200-400 mesh, and the concentration of the MXene colloidal solution is 0.5-40 mg / mL.

4. The production method according to claim 2, characterized by, In step (2), the concentration of the PMMA colloidal solution is 1-50 mg / mL.

5. The preparation method according to claim 2, characterized in that, In step (3), the concentration of the thiourea aqueous solution is 0.1-100 mg / mL, and the concentration of the GO aqueous solution is 0.1-50 mg / mL; the mass ratio of thiourea to MXene in the mixed solution is 1:10-50:1, the mass ratio of PMMA to MXene is 1:1-20:1, and the mass ratio of MXene to GO is 1:20-50:

1.

6. The preparation method according to claim 2, characterized in that, In step (3), the stirring and reaction time in the ice water bath is 30-60 min, the vacuum drying temperature is 20-60 ℃, the vacuum drying time is 1-12 h, and the calcining is carried out under nitrogen protection, the heating rate is 0.5-8 ℃ / min, the calcining temperature is 200-800 ℃, and the calcining time is 1-4 h.

7. A S, N-MXene / rGO composite flexible film electrode, characterized in that, The S, N-MXene / rGO composite flexible film of claim 1.

8. A flexible asymmetric zinc-ion battery or flexible supercapacitor, characterized in that, The S, N-MXene / rGO composite flexible film electrode of claim 7.

9. The method of claim 8, wherein the flexible asymmetric zinc-ion battery or the flexible supercapacitor is prepared by, The preparation method of the flexible asymmetric zinc ion battery includes the following steps: (B1) preparing a zinc salt solution; (B2) preparing a PVA / zinc salt gel; (B3) assembling the S, N-MXene / rGO composite flexible film electrode of claim 7 with the PVA / zinc salt gel as an electrolyte to obtain a flexible asymmetric zinc ion battery.

10. The method for preparing a flexible asymmetric zinc-ion battery or a flexible supercapacitor according to claim 9, characterized in that, In step (B1), the zinc salt solution is obtained by dissolving a zinc salt in water, and the concentration of the zinc salt solution is 1-8 mol / mL; in step (B2), the PVA / zinc salt gel is obtained by mixing and stirring a zinc salt solution and PVA and heating, and the amount ratio of the zinc salt solution to PVA is 5:1-50:1.

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