Preparation method for in-situ solid-phase synthesis of V2O5atV2CTx MXene supercapacitor electrode material

Abstract

The invention discloses a preparation method for in-situ synthesis of a V2O5 (at) V2CTx MXene supercapacitor electrode material, and an in-situ solid-phase synthesis method is a method for generating a target product through direct reaction of a solid precursor under heat treatment. The method has the advantages of uniform reaction, good interface contact, no solvent pollution and the like. According to the in-situ solid-phase synthesis method, V2O5 and V2CTx form a strongly coupled heterojunction on the nanoscale, and the electron transmission impedance is extremely low. The V2CTx framework effectively inhibits volume expansion / shrinkage of V2O5 in circulation, and super-long cycle life is obtained. The method is simple, does not need a complex template or post-treatment, and is easy for large-scale production. The composite material has the advantages of high specific capacity, excellent rate capability and excellent super-long cycle stability. The high-performance V2O5-coated V2CTx MXene supercapacitor electrode material is prepared, and the problems that the conductivity of V2O5 is poor and the interface is unstable in a traditional compounding method are solved. According to the method, atomic-scale interface coupling is realized, and the electrochemical performance of the composite material is improved to the greatest extent.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials technology, and particularly to a method for preparing electrode materials for high-performance asymmetric supercapacitors, specifically a method for preparing electrode materials in V2CT using a solid-state method. x Composite material of V2O5 nanosheets grown in situ on the surface of MXene. Background Technology

[0002] Supercapacitors have become an important electrochemical energy storage device due to their advantages such as high power density, long cycle life, and fast charge / discharge speed. Among them, asymmetric supercapacitors, by combining battery-type positive electrodes and capacitor-type negative electrodes with different operating potential windows, can significantly improve the energy density of the device and are currently a research hotspot.

[0003] As an electrode material for asymmetric supercapacitors, vanadium pentoxide (V₂O₅) needs to provide high specific capacitance and excellent rate performance. Vanadium pentoxide, due to its layered structure and abundant valence state changes (V₂O₅), is ideal. 3+ / V 4+ / V 5+ With its high theoretical specific capacity, bulk V2O5 is considered a highly promising electrode material. However, bulk V2O5 itself has poor conductivity, slow ion diffusion kinetics during charge and discharge, and poor structural stability, resulting in low actual specific capacity, poor rate performance, and short cycle life, which severely limits its commercial application.

[0004] MXenes are a new class of two-dimensional transition metal carbide / nitride materials with the general formula M. n+1 X n T x Where M represents a transition metal, X represents carbon or nitrogen, and T represents a transition metal. x Represents surface terminating groups (such as -OH, -O, -F, etc.). V2CT x MXene is one such example. It not only possesses the high conductivity, hydrophilicity, and rich surface chemistry common to the MXene family, but its constituent element vanadium (V) is the same as V₂O₅, providing a unique advantage for constructing a tight heterostructure between the two. Currently, although some research has explored combining MXene with other metal oxides, the utilization of V₂CT remains a challenge. x The structural similarity and elemental homology between V2CT and V2O5, through ingenious interface engineering design, allow for the application of V2CT in V2CT. x In-situ, directional growth of V2O5 on the surface to synergistically improve the conductivity, ion transport rate, and structural stability of composite materials remains a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To overcome the aforementioned technical bottlenecks, this invention proposes a novel structural construction strategy. This strategy utilizes V2CT... x Controlled thermal annealing of the MXene precursor induced an in-situ phase transition, partially converting it into V2O5 with high pseudocapacitive activity, thus successfully constructing a V2O5@V2CT. x Heterogeneous composite materials. The core advantages of this method are: firstly, the in-situ transformation process effectively inherits the two-dimensional morphological framework of the MXene precursor, thereby suppressing the self-stacking phenomenon of the sheets in subsequent processing; secondly, the V2O5 nanosheets generated in situ, as highly active electrochemical substances, form a tight interface with the conductive substrate, and the two work synergistically to significantly enhance the overall electrochemical performance and structural stability of the composite material.

[0006] This invention aims to overcome the technical defects of existing V2O5 electrode materials, such as low specific capacity, poor rate performance, and insufficient cycle stability due to low intrinsic conductivity and slow ion diffusion kinetics. Therefore, this invention provides a V2O5@V2CT electrode with high specific capacity, excellent rate performance, and long cycle stability. x MXene supercapacitor electrode composite material and its preparation method, which is simple, controllable, and easy to scale up; this method realizes the partial oxidation of V2O5 in V2CT through in-situ solid-phase synthesis. x In-situ, uniform growth of MXene nanosheets forms a stable synergistic conductive network, resulting in a composite material in which V2CT is uniformly distributed. x The V2O5 nanosheets on the surface of MXene sheets not only provide abundant chemically active sites to shorten the ion diffusion path, but also work synergistically with the highly conductive MXene matrix to significantly improve the overall charge transport dynamics and structural stability.

[0007] An in-situ solid-phase synthesis of V2O5@V2CT x The preparation method of MXene supercapacitor electrode material includes the following steps:

[0008] (1) The V2AlC MAX phase powder was placed in a mixed etching solution containing HCl and HF and reacted under constant temperature conditions to selectively etch away the Al atoms between the layers. After the reaction, the product was subjected to solid-liquid separation and repeated washing until the system was neutral. Finally, it was freeze-dried to obtain a multilayer V2CT. x MXene precursor.

[0009] (2) The V2CT obtained in step (1) x MXene precursor powder was placed in a tube furnace and subjected to programmed temperature heat treatment in an oxygen-containing atmosphere. By controlling the heat treatment parameters, V2CT was... xControlled in-situ partial oxidation occurs on the surface of MXene sheets, thereby growing uniformly dispersed V2O5 nanosheets in situ, ultimately yielding V2O5@V2CT with a two-dimensional / one-dimensional synergistic structure. x MXene composite electrode material.

[0010] As a preferred technical solution of the present invention, the heat treatment process parameters in step (2) are: heating rate of 3-10℃ / min, preferably 5℃ / min; calcination temperature of 250-450℃, preferably 350℃; and holding time of 2-4h, preferably 3h.

[0011] As a further preferred technical solution of the present invention, in step (1), the mixed etching solution is composed of a 12mol / L HCl solution and a 40wt% HF solution, and the volume of each solution is 5-10ml; the amount of V2AlC MAX phase powder is 0.5-1.0g; the temperature of the isothermal reaction is 40℃ and the time is 48h; the solid-liquid separation is carried out by centrifugation at a speed of 8000rpm, the single centrifugation time is 6min, and the washing is repeated 4-6 times; the temperature of the freeze drying is -60℃ and the time is 48h.

[0012] Secondly, this invention provides V2O5@V2CT prepared by any of the above preparation methods. x MXene composite electrode material.

[0013] Finally, the present invention also provides the V2O5@V2CT x Application of MXene composite electrode materials in the fabrication of supercapacitor devices.

[0014] Compared with the prior art, the present invention has the following significant advantages:

[0015] (1) Constructing a cooperative conductive network to improve rate performance: This invention utilizes highly conductive two-dimensional V2CT x MXene, as a conductive matrix, provides a rapid electron transport channel for the low-conductivity V2O5 nanosheets. The robust heterogeneous interface formed by the two constructs an efficient synergistic conductive network, significantly improving the rate performance of the composite material and overcoming the drawback of the sharp capacity decay of pure V2O5 at high current densities.

[0016] (2) Optimize ion transport pathways and enhance kinetics: The in-situ and uniform growth of V2O5 nanosheets on the MXene surface effectively shortens the diffusion distance of ions. At the same time, the excellent hydrophilicity of MXene promotes the full wetting of the electrolyte. The two work synergistically to greatly enhance the charge transport kinetics.

[0017] (3) Enhance structural stability and extend cycle life: V2O5 and V2CT x The strong chemical bonds formed between MXenes through in-situ oxidation effectively suppress the volume effect and structural pulverization of V2O5 during cycling, maintaining the structural integrity of the electrode material and thus endowing it with excellent long-term cycling stability.

[0018] (4) The process is simple and controllable, and has the potential for large-scale production: The two-step method of "acid etching-in-situ oxidation" adopted in this invention has a simple process flow, mild and controllable reaction conditions, and does not require complex equipment. It provides a practical and feasible technical solution for the low-cost and large-scale preparation of high-performance supercapacitor electrode materials. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention, and the illustrative embodiments of the invention and their descriptions are used to explain the invention.

[0020] Figure 1 The X-ray diffraction (XRD) pattern of the sample prepared in Example 2 of this invention;

[0021] Figure 2 This is a scanning electron microscope (SEM) image of the sample prepared in Example 2 of the present invention;

[0022] Figure 3 The nitrogen adsorption-desorption curve of the sample prepared in Example 2 of this invention;

[0023] Figure 4 V2O5@V2CT was prepared for Example 2 of this invention. x Cyclic voltammetry and constant current charge-discharge curves of MXene composite materials;

[0024] Figure 5 V2O5@V2CT in Embodiment 2 of the present invention x Comparison of the electrochemical performance of MXene composite material and V2O5 monomer. Detailed Implementation

[0025] Combined with appendix Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 The implementation method described in this application is as follows:

[0026] Example 1: In-situ solid-phase synthesis of V2O5@V2CT x Preparation method of MXene supercapacitor electrode material

[0027] (1) V2CT x Synthesis of MXene

[0028] 5 ml of 12M hydrochloric acid solution and 5 ml of 40% hydrofluoric acid solution were mixed in a polytetrafluoroethylene reactor liner and stirred for 0.5 hours to obtain an etching solution. 0.5 g of V2AlCT was then slowly added to the etching solution. x MAX phase powder was continuously stirred. The reactor liner was then transferred to a 40°C constant temperature water bath and reacted for 48 hours with stirring at 400 rpm. After the reaction, the resulting mixture was centrifuged. Specifically, the mixture was centrifuged at 8000 rpm for 6 minutes, and the supernatant was discarded. This washing-centrifugation step was repeated 4 to 6 times until the pH of the washing solution reached approximately 6. The final precipitate was collected and freeze-dried at -60°C for 48 hours to obtain V2CT. x MXene multilayer structure material.

[0029] (2) V2O5@V2CT x Synthesis of MXene composite materials

[0030] Take the V2CT prepared in step (1) x MXene powder was spread evenly in a ceramic boat. The boat containing V2CT was then placed inside. x A ceramic boat containing MXene powder was placed in the isothermal zone of a tube furnace. Under air atmosphere, the tube furnace was heated from room temperature to 300°C at a heating rate of 5°C / min and held at this temperature for 2.5 hours to carry out the in-situ partial oxidation reaction. After the holding period, the furnace was allowed to cool naturally to room temperature, and the product was collected to obtain V₂O₅@V₂CT. x MXene composite material.

[0031] (3) V2O5@V2CT x Fabrication of MXene composite supercapacitors

[0032] Take the V2O5@V2CT prepared in step (2) x The composite material, acting as the active agent, was mixed with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1. N-methylpyrrolidone was added as a solvent to this mixture, and the mixture was thoroughly stirred to form a homogeneous slurry. Subsequently, the slurry was uniformly coated onto a 1×1.5cm plate. 2 The working electrode is prepared by drying the carbon cloth current collector under vacuum conditions.

[0033] The working electrode, reference electrode (silver / silver chloride electrode), and counter electrode (platinum sheet) were placed together in an electrolyte (1M H2SO4 aqueous solution) to form a three-electrode testing system. The electrochemical performance of the working electrode was characterized using this system, including cyclic voltammetry, constant current charge-discharge testing, and AC impedance spectroscopy.

[0034] Example 2: In-situ solid-phase synthesis of V2O5@V2CT x Preparation method of MXene supercapacitor electrode material

[0035] (1) V2CT x Synthesis of MXene

[0036] The synthesis steps are the same as in Example 1.

[0037] (2) V2O5@V2CT x Synthesis of MXene composite materials

[0038] Take the V2CT prepared in step (1) x MXene powder was spread evenly in a ceramic boat. The boat containing V2CT was then placed inside. x A ceramic boat containing MXene powder was placed in the isothermal zone of a tube furnace. Under air atmosphere, the tube furnace was heated from room temperature to 350°C at a heating rate of 5°C / min and held at this temperature for 2.5 hours to carry out the in-situ partial oxidation reaction. After the holding period, the furnace was allowed to cool naturally to room temperature, and the product was collected to obtain V₂O₅@V₂CT. x MXene composite material.

[0039] (3) V2O5@V2CT x Fabrication of MXene composite supercapacitors

[0040] Take the V2O5@V2CT prepared in step (2) x The composite material, acting as the active agent, was mixed with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1. N-methylpyrrolidone was added as a solvent to this mixture, and the mixture was thoroughly stirred to form a homogeneous slurry. Subsequently, the slurry was uniformly coated onto a 1×1.5cm plate. 2 The working electrode is prepared by drying the carbon cloth current collector under vacuum conditions.

[0041] The working electrode, reference electrode (silver / silver chloride electrode), and counter electrode (platinum sheet) were placed together in an electrolyte (1MH2SO4 aqueous solution) to form a three-electrode testing system. The electrochemical performance of the working electrode was characterized using this system, including cyclic voltammetry, constant current charge-discharge testing, and AC impedance spectroscopy.

[0042] like Figure 1 As shown, it is the V2O5@V2CT prepared in this embodiment. x X-ray diffraction pattern of the composite material. This pattern also contains elements belonging to V2CT. x The composite material exhibits characteristic diffraction peaks of V2O5 and no other impurity peaks were observed, indicating that the composite material is composed of V2CT. x It consists of two phases, V2O5 and has high purity.

[0043] like Figure 2 As shown, it illustrates the V2O5@V2CT x Microstructure of the composite material. As can be observed from the figure, V₂O₅ is uniformly loaded onto V₂CT. x The surface of MXene nanosheets. This structure effectively prevents the recombination of two-dimensional MXene nanosheets due to van der Waals forces.

[0044] like Figure 3 As shown, this is the nitrogen adsorption-desorption isotherm of the material in this embodiment. Test results indicate that, thanks to the introduction of V₂O₅, V₂O₅@V₂CT x The specific surface area of ​​the composite material reaches 46.279 m². 2 g -1 This value is significantly higher than that of pure V2CT. x 28.975m 2 g -1 The increased specific surface area provides more active sites for electrochemical reactions, which in turn facilitates charge transfer and ion transport.

[0045] To evaluate the V2O5@V2CT described in this embodiment x The electrochemical properties of the composite material were tested by assembling it into a three-electrode test system as the working electrode.

[0046] like Figure 4 As shown, it is the V2O5@V2CT x Electrochemical response of composite electrode under different conditions. For example... Figure 4 As shown in the cyclic voltammetry curve of a, the integral area of ​​the curve increases accordingly as the scan rate increases from low to high, and it maintains an approximately mirror-symmetric rectangular shape at different scan rates. This indicates that the electrode material has excellent rate performance and good capacitance behavior. Figure 4 The constant current charge-discharge curves of b further show that, under different current densities, the charge-discharge curves all exhibit highly symmetrical triangular profiles, proving that the electrode material has high coulombic efficiency and fast reversible charge-discharge capability.

[0047] To further verify the performance advantages of the composite material of the present invention, it was compared with V2CT.x The monomer and V2O5 monomer were compared under the same conditions, and the results are as follows: Figure 5 As shown.

[0048] Figure 5 a at 20mVs -1 Comparison of cyclic voltammetry curves at different scan rates shows that V2O5@V2CT x The integral area of ​​the CV curve of the composite material is much larger than that of V2CT. x The monomer directly confirmed that the composite material has a significantly improved charge storage capacity. Figure 5 b in 1Ag -1 A comparison of constant current charge-discharge curves at current density shows that V2O5@V2CT x The discharge time of the composite material is significantly longer than that of the V2O5 monomer, indicating that it has a higher specific capacity. Figure 5 The volume contrast curves for c clearly quantify this advantage: at all tested scan rates, V2O5@V2CT x The specific capacity of the composite materials is higher than that of V2CT. x Both V2O5 monomers exhibited excellent rate capability. Furthermore, Figure 5 The AC impedance spectroscopy of d reveals the intrinsic mechanism behind the improved electrochemical performance of the composite material. In the low-frequency region, V2O5@V2CT x The composite material exhibits a steeper slope in its impedance spectrum, more closely perpendicular to the real axis, indicating faster ion diffusion kinetics. In the high-frequency region, the composite material has a smaller semi-circular radius, suggesting a significant reduction in charge transfer resistance. These EIS results collectively confirm that V₂O₅ and V₂CT... x The combined synergistic effect effectively optimizes the kinetic process of the electrode.

[0049] In summary, all electrochemical test results consistently demonstrate that the V2O5@V2CT prepared in this invention is effective. x Composite materials, their supercapacitor performance compared to V2CT x Significant improvements were achieved in both monomers and V2O5 monomers, validating the effectiveness and superiority of the composite material design.

[0050] Example 3: In-situ solid-phase synthesis of V2O5@V2CT x Preparation method of MXene supercapacitor electrode material

[0051] (1) V2CT x Synthesis of MXene

[0052] The synthesis steps are the same as in Example 1.

[0053] (2) V2O5@V2CT x Synthesis of MXene composite materials

[0054] Take the V2CT prepared in step (1) x MXene powder was spread evenly in a ceramic boat. The boat containing V2CT was then placed inside. x A ceramic boat containing MXene powder was placed in the isothermal zone of a tube furnace. Under air atmosphere, the tube furnace was heated from room temperature to 400 °C at a heating rate of 5 °C / min and held at this temperature for 2.5 hours to carry out the in-situ partial oxidation reaction. After the holding period, the furnace was allowed to cool naturally to room temperature, and the product was collected to obtain V₂O₅@V₂CT. x MXene composite material.

[0055] (3) V2O5@V2CT x Fabrication of MXene composite supercapacitors

[0056] Take the V2O5@V2CT prepared in step (2) x The composite material, acting as the active agent, was mixed with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1. N-methylpyrrolidone was added as a solvent to this mixture, and the mixture was thoroughly stirred to form a homogeneous slurry. Subsequently, the slurry was uniformly coated onto a 1×1.5cm plate. 2 The working electrode is prepared by drying the carbon cloth current collector under vacuum conditions.

[0057] The working electrode, reference electrode (silver / silver chloride electrode), and counter electrode (platinum sheet) were placed together in an electrolyte (1MH2SO4 aqueous solution) to form a three-electrode testing system. The electrochemical performance of the working electrode was characterized using this system, including cyclic voltammetry, constant current charge-discharge testing, and AC impedance spectroscopy.

[0058] Perform electrochemical performance testing

[0059] The materials obtained in Examples 1, 2, and 3 were used as the active materials for the working electrode. They were mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1 to form a slurry, which was then coated onto a nickel foam current collector to prepare an electrode sheet. Tests were conducted in a three-electrode system using 1M H₂SO₄ as the electrolyte, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode.

[0060] Test results: The composite material prepared in Example 1 showed a performance of 10 mV / s. -1 The specific capacity at the scan rate reached 408.2 Fg. -1 .

[0061] The composite material prepared in Example 2 was tested at 10 mV / s. -1 The specific capacity at the scan rate reached 607.8 Fg. -1 .

[0062] The composite material prepared in Example 3 was tested at 10 mV / s. -1 The specific capacity at the scan rate reached 489.5 Fg. -1 .

[0063] The electrode in Example 2 was at 10Ag -1 After 6000 charge-discharge cycles at the current density, the capacity retention rate was as high as 93.5%, while that of Comparative Example 1 and Example 3 was only 65.3% and 76.7%, respectively.

Claims

1. In-situ solid-phase synthesis of V2O5@V2C x The preparation method of the MXene supercapacitor electrode material is characterized in that, The method comprises the following steps: S1. Preparation of multilayer V2CT x MXene precursor: The V2AlC MAX phase powder is reacted in a mixed etching solution containing HF and HCl by using an acid etching method to selectively remove the aluminum layer therein, and then separated, washed to neutral and dried to obtain the multilayer V2CT x MXene precursor S2. In-situ oxidation compounding: The multilayer V2CT obtained in step S1 is subjected to heat treatment under an oxygen-containing atmosphere x The MXene precursor is subjected to heat treatment, so that the V2CT x The MXene sheet layer surface is subjected to in-situ partial oxidation, so that V2O5 nanosheets are formed in-situ, and finally the V2O5@V2CT x The MXene composite electrode material.

2. The production method according to claim 1, characterized by, The step S1 specifically comprises: S1-1. Mixing HF solution and HCl solution in a reaction container to form the mixed etching solution; S1-2. Adding V2AlC MAX phase powder into the mixed etching solution, continuously stirring at a constant temperature of 40℃ for 48 hours; S1-3. Performing solid-liquid separation on the reacted mixture, and washing the obtained solid phase product for multiple times until the pH value of the washing liquid approaches neutral; S1-4. The washed solid phase product is subjected to freeze-drying to obtain the multilayer V2CT x MXene precursor.

3. The preparation method according to claim 2, characterized in that: In the step S1-1, the concentration of the hydrochloric acid solution is 12 mol / L, and the amount used is 5-10 ml; the mass fraction of the hydrofluoric acid solution is 40wt%, and the amount used is 5-10 ml; and the mixing and stirring time is 0.5 hours.

4. The preparation method according to claim 2, characterized in that: In the step S1-2, the added amount of the V2AlC MAX phase powder is 0.5-1.0 g.

5. The preparation method according to claim 2, characterized in that: In the step S1-3, the solid-liquid separation is performed by centrifugation at a speed of 8000 rpm for 6 min; and the washing operation is repeated for 4-6 times.

6. The preparation method according to claim 2, characterized in that: In the step S1-4, the temperature for freeze-drying is -60℃, and the time is 48 hours.

7. The preparation method according to claim 1, characterized in that, The step S2 specifically comprises: The multi-layer V2CT x The MXene precursor is placed in a tube furnace, heated to 250-450°C at a heating rate of 5°C / min under an oxygen atmosphere, and held for 2-4 hours, and then naturally cooled to room temperature.

8. The preparation method according to claim 7, characterized in that: The temperature for heat treatment is 350℃, and the holding time is 3 hours.

9. A V2O5@V2C x MXene supercapacitor electrode composite material characterized in that, The method is prepared by the preparation method according to any one of claims 1-8.

10. A V2O5@V2C T as claimed in claim 9. x MXene supercapacitor electrode composite material, the preparation method thereof is based on in-situ solid-phase synthesis of V2O5@V2C T x Process for MXene supercapacitor electrode composite material.

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