A hydrangea-shaped bismuth vanadate-MXene heterojunction and its preparation method and application

Abstract

The present invention discloses a hydrangea-shaped bismuth vanadate-MXene heterojunction and its preparation method and application, belonging to the field of nanofunctional materials technology. The preparation method obtains a hydrangea-shaped bismuth vanadate-MXene heterojunction by selecting a bismuth source and controlling the reaction conditions. It is not only simple to operate but also has low requirements for equipment and has the potential for industrialization. The hydrangea-shaped bismuth vanadate-MXene heterojunction obtained by this preparation method has a novel structure. The array structure of the hydrangea-shaped surface can significantly increase the contact area with the electrolyte, achieving better ion transmission effect and greatly alleviating volume expansion during battery charging and discharging. At the same time, the built-in electric field at the heterojunction interface can promote charge transfer, further improving electrochemical performance, and has good application prospects in sodium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of nano-functional materials, and specifically relates to a hydrangea-shaped bismuth vanadate-MXene heterojunction and a preparation method and application thereof. Background Art

[0002] Bismuth vanadate (BVO) has an orthorhombic crystal structure, with each bismuth atom surrounded by six oxygen atoms and each vanadium atom by four. This structure creates a layered structure, making it a semiconductor with a specific framework. It undergoes both conversion and alloying reactions, resulting in a high theoretical specific capacity, making it a promising anode material for batteries. However, its band gap is 2.26 eV, resulting in poor conductivity. Furthermore, the volume expansion caused by alloying reactions can disrupt the structure, hindering the long cycle life of sodium-ion batteries. Existing modifications have primarily focused on altering the morphology of the material itself, such as creating needle-like, dendritic, and nanoparticle-like structures, to form heterostructures with MXenes. However, homologous heterostructures of vanadium-based MXenes have yet to be reported. Summary of the Invention

[0003] The first object of the present invention is to provide a method for preparing a hydrangea-shaped bismuth vanadate-MXene heterojunction, which is simple to operate, has low requirements on equipment, and can simply and efficiently prepare a hydrangea-shaped bismuth vanadate-MXene heterojunction.

[0004] The second object of the present invention is to provide a hydrangea-shaped bismuth vanadate-MXene heterojunction, which is prepared by the above-mentioned preparation method of the hydrangea-shaped bismuth vanadate-MXene heterojunction. Its structure is novel, and its unique hydrangea-shaped microstructure can effectively increase the contact area with the electrolyte when used in sodium ion batteries, promote ion transport, and reduce the diffusion barrier. The staggered surface layers can alleviate the volume expansion during the charge and discharge process, thereby increasing the battery life and stability and better maintaining the battery capacity.

[0005] The third object of the present invention is to provide an application of a hydrangea-shaped bismuth vanadate-MXene heterojunction in a sodium ion battery.

[0006] Based on the above objectives, the present invention adopts the following technical solutions:

[0007] A method for preparing a hydrangea-shaped bismuth vanadate-MXene heterojunction, comprising:

[0008] (1) The V2AlC powder was stirred and etched in a hydrofluoric acid solution. After the reaction was completed, the solution was repeatedly washed with deionized water until the pH was neutral. The suspension obtained was filtered and freeze-dried to obtain the first V2C powder.

[0009] (2) Mix the first V2C powder with water to form a suspension, add BiCl3, and at the same time, dropwise add H2O2 solution. After stirring evenly, transfer it into a reactor and perform hydrothermal reaction at 140-180℃ for 12-20 hours. After cooling, centrifugation, and drying, the product is obtained.

[0010] This invention utilizes in-situ growth of bismuth vanadate on V2C MXene to form a hydrangea-shaped bismuth vanadate-MXene heterostructure. The key to achieving this hydrangea-shaped structure is the selection of a bismuth source; the second key is controlling process parameters, particularly temperature, as the formation of the hydrangea-shaped structure is extremely sensitive to temperature.

[0011] Furthermore, in step (1), the concentration of the hydrofluoric acid solution is 49 wt %, the etching temperature of the V2AlC powder in the hydrofluoric acid solution is 55-65° C., and the etching time is 50 h-60 h.

[0012] Furthermore, in step (2), the H2O2 solution concentration is 30 wt%, and the volume mass ratio of the H2O2 solution to the first V2C powder is 1 mL:120 mg. Hydrogen peroxide is highly oxidizing, and excessive use will produce over-oxidized products, which is not conducive to the formation of heterogeneous structures.

[0013] Furthermore, in step (2), the molar ratio of BiCl3 to the first V2C powder is 1:5-6. At this ratio, the surface morphology growth effect of the heterostructure is better and the hydrothermal reaction effect is better.

[0014] Furthermore, in step (2), the temperature is raised to 140-180°C at a rate of 5-10°C / min.

[0015] Preferably, the hydrothermal reaction temperature is 160°C for 16 hours. During the hydrothermal reaction, the temperature is raised from room temperature to 160°C at a rate of 5-10°C / min and maintained at 160°C for 16 hours. Slow heating is crucial for obtaining the hydrangea-shaped bismuth vanadate-MXene heterostructure. Too rapid a heating rate results in a rapid reaction, hindering the formation of the structural surface morphology. However, too slow a heating rate results in inefficient preparation.

[0016] A hydrangea-shaped bismuth vanadate-MXene heterojunction is prepared by the above-mentioned preparation method of the hydrangea-shaped bismuth vanadate-MXene heterojunction.

[0017] An application of the above-mentioned hydrangea-shaped bismuth vanadate-MXene heterojunction in sodium ion batteries.

[0018] Furthermore, the hydrangea-shaped bismuth vanadate-Mxene, conductive carbon black, and carboxymethyl cellulose were mixed with deionized water in a weight ratio of 7:2:1, ground into a uniform slurry, coated on a clean copper foil, dried, and sliced ​​to serve as the negative electrode of a sodium ion battery. The loading amount of the hydrangea-shaped bismuth vanadate-Mxene on the copper foil was 1-1.2 mg cm -2 .

[0019] Furthermore, a copper foil loaded with hydrangea-shaped bismuth vanadate-Mxene was used as the negative electrode and a diethylene glycol dimethyl ether solution of NaPF6 was used as the electrolyte to assemble a sodium ion battery.

[0020] The concentration of the NaPF6 diethylene glycol dimethyl ether solution is 1 mol / L.

[0021] The hydrangea-shaped bismuth vanadate-MXene heterostructure prepared by the present invention has a unique hydrangea-shaped heterostructure that can effectively increase the electrolyte contact surface when used in sodium ion batteries, promote ion transport and diffusion, thereby increasing the reaction rate and reducing the diffusion barrier. The built-in electric field at its interface can promote electron transport. At the same time, the staggered array surface can effectively alleviate the volume expansion during the battery charge and discharge process, improve battery stability, and increase battery life. This sodium ion battery still has 233 mAh g after 2000 cycles of constant current charge and discharge at 2A. -1 The above capacity has a better effect on capacity retention.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a hydrangea-shaped bismuth vanadate-MXene heterostructure, its preparation method, and application. This preparation method, through the selection of a bismuth source and control of reaction conditions, produces a flower-shaped bismuth vanadate heterojunction. This method is not only simple to operate but also requires minimal equipment, showing potential for industrialization. The resulting flower-shaped bismuth vanadate heterostructure is novel, and the hydrangea-shaped surface array significantly increases the contact area with the electrolyte, achieving better ion transport and significantly mitigating volume expansion during battery charge and discharge. This method has promising application prospects in sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1This is a scanning electron microscope image of the first powder provided in Example 1 of the present invention;

[0026] Figure 2 This is a scanning electron microscope image of the hydrangea-shaped bismuth vanadate-MXene heterostructure provided in Example 1 of the present invention;

[0027] Figure 3 This is a transmission electron microscopy image of the hydrangea-shaped bismuth vanadate-MXene heterostructure provided in Example 1 of the present invention;

[0028] Figure 4 This is a scanning electron microscopy image of the hydrangea-shaped bismuth vanadate-MXene heterostructure provided in Example 2 of the present invention;

[0029] Figure 5 This is a scanning electron micrograph of the sheet-like array bismuth vanadate-MXene heterostructure provided in Example 3 of the present invention;

[0030] Figure 6 Stability diagram of the sodium ion battery made of hydrangea-shaped bismuth vanadate-MXene heterostructure provided in the experimental example of the present invention. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0032] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0033] Example 1

[0034] This embodiment provides a method for preparing a hydrangea-shaped bismuth vanadate-MXene heterostructure, and the process is as follows:

[0035] S1. Use a graduated cylinder to measure 20 mL of 49 wt% HF solution and add it to a polytetrafluoroethylene beaker. Weigh 1 g of V2AlC and slowly add it to the beaker. Seal the beaker with plastic film and stir at an appropriate rate on a magnetic stirrer. Etch at 60°C for 55 h. Centrifuge and wash to a neutral pH. Freeze-dry in a vacuum freeze dryer (-55°C to -60°C) for 24 h to obtain the first powder, V2CMXene. The scanning electron microscope image is shown below. Figure 1 As shown, it is a layered structure;

[0036] S2. Weigh 120 mg of V2C MXene (1 mmol) and mix with 30 mL of water to form a suspension. Weigh 63 mg of BiCl3 (0.2 mmol) and slowly add it to the suspension. At the same time, dropwise add 1 mL of 30% H2O2 solution (tested to be the appropriate amount; too much or too little is not suitable for forming heterostructures). Stir for 30 minutes and then transfer to the reactor. At this time, the solution is yellow-green. The temperature is raised to 160°C at a heating rate of 8°C / min. The hydrothermal reaction is carried out at 160°C for 16 hours. After the reaction is completed, it is cooled to room temperature, washed three times with deionized water and ethanol, and dried in a vacuum at 70°C to obtain a hydrangea-shaped bismuth vanadate-MXene heterostructure. Its scanning electron microscopy and transmission electron microscopy images are shown below. Figure 2 , Figure 3 As shown, the bismuth vanadate-MXene heterostructure is hydrangea-shaped.

[0037] Example 2

[0038] This embodiment provides a method for preparing a hydrangea-shaped bismuth vanadate-MXene heterostructure, and the process is as follows:

[0039] S1. Use a graduated cylinder to measure 20 mL of a 49 wt% HF solution and add it to a polytetrafluoroethylene beaker. Slowly add 1 g of vanadium-alcohol-based MXene (V2AlC) to the beaker, seal the beaker with plastic film, and stir at an appropriate rate on a magnetic stirrer. Etch the mixture at 60°C for 55 h. Centrifuge, wash the mixture to a neutral pH, and freeze-dry it in a vacuum freeze dryer for 24 h to obtain the first vanadium-alcohol-based MXene powder.

[0040] S2. Weigh 120 mg of V2C MXene (1 mmol) and mix with 30 mL of water to form a suspension. Weigh 63 mg of BiCl3 (0.2 mmol) and slowly add it to the suspension. Simultaneously, dropwise add 1 mL of 30% H2O2 solution (tested to be the appropriate amount; too much or too little is not suitable for forming a heterostructure). Stir for 30 minutes and then transfer to a reactor. The solution is now yellow-green. The temperature is raised to 160°C at a heating rate of 2°C / min. The hydrothermal reaction is carried out at 160°C for 16 hours. After the reaction, the solution is cooled to room temperature, washed three times with deionized water and three times with ethanol, and then dried in a vacuum at 70°C. This yields a hydrangea-shaped bismuth vanadate-MXene heterostructure. The scanning electron microscopy image is shown below. Figure 4 Shown is a partial hydrangea.

[0041] Example 3

[0042] This embodiment provides a method for preparing a lamellar array bismuth vanadate-MXene heterostructure, the process is as follows:

[0043] S1. Use a graduated cylinder to measure 20 mL of a 49 wt% HF solution and add it to a polytetrafluoroethylene beaker. Slowly add 1 g of V2AlC to the beaker, seal the beaker with plastic film, and stir at an appropriate rate on a magnetic stirrer. Etch the mixture at 60°C for 55 h. Centrifuge, wash to a neutral pH, and freeze-dry in a vacuum freeze dryer for 24 h to obtain the first V2C MXene powder.

[0044] S2. Weigh 120 mg of V2C MXene (1 mmol) and mix with 30 mL of water to form a suspension. Weigh 63 mg of BiCl3 (0.2 mmol) and slowly add it to the suspension. Simultaneously, dropwise add 1 mL of 30% H2O2 solution (tested to be the appropriate amount; too much or too little is not suitable for forming a heterostructure). Stir for 30 minutes and then transfer to a reactor. The solution is now yellow-green. The temperature is raised to 160°C at a heating rate of 12°C / min. The hydrothermal reaction is carried out at 160°C for 16 hours. After the reaction, the solution is cooled to room temperature, washed three times with deionized water and three times with ethanol, and then dried in a vacuum at 70°C. This yields a hydrangea-shaped bismuth vanadate-MXene heterostructure. The scanning electron microscopy image is shown below. Figure 5 As shown, it is a lamellar array without the presence of flower-like structures.

[0045] Comparative Example 1

[0046] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that BiCl3 is replaced by Bi(NO3)3.

[0047] Comparative Example 2

[0048] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that the hydrothermal reaction time of 16 h is replaced by 12 h.

[0049] Comparative Example 3

[0050] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that the hydrothermal reaction time of 16 h is replaced by 20 h.

[0051] Comparative Example 4

[0052] This comparative example provides a preparation method of bismuth vanadate-Mxene, which is basically the same as Example 1, except that the hydrothermal reaction temperature is 180° C. and the time is 16 h.

[0053] Comparative Example 5

[0054] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that the hydrothermal reaction temperature is 140° C. and the time is 16 h.

[0055] Comparative Example 6

[0056] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that the amount of V2C MXene is 90 mg.

[0057] Comparative Example 7

[0058] This comparative example provides a preparation method of bismuth vanadate-MXene, which is basically the same as Example 1, except that the amount of V2C MXene is 150 mg.

[0059] Test Example 1

[0060] The bismuth vanadate-MXene of Examples 1 to 3 and Comparative Examples 1 to 7 were used to observe and record their structural shapes under an electron microscope. The recorded results are shown in Table 1.

[0061] Table 1. Comparison of the structure and shape of bismuth vanadate-MXene

[0062]

[0063] As can be seen from Table 1, when other bismuth sources are used instead of BiCl3 (Comparative Example 1), no hydrangea-like structure can be obtained. It can be seen that anions play an important role in the formation of the hydrangea-like structure, but the specific mechanism of action needs further study. Comparative Examples 2 and 3 changed the time of the hydrothermal reaction, and the resulting bismuth vanadate heterojunction became partially hydrangea-like and cluster-like structures, indicating that the time of the hydrothermal reaction has an impact on the structure formation. Comparative Examples 4 and 5 changed the temperature of the hydrothermal reaction and obtained a cluster-like structure, indicating that the temperature of the hydrothermal reaction also has a certain influence on the formation of the structure. On this basis, Comparative Examples 6 and 7 changed the ratio of the reaction precursor V2C MXene, and the resulting structures changed greatly, indicating that the ratio of MXene has a great influence on the formation of the structure.

[0064] Test Example 2

[0065] The electrochemical performance of the hydrangea-shaped bismuth vanadate-MXene heterostructure prepared in Example 1 and the amorphous bismuth vanadate-MXene prepared in Comparative Example 1 as anode materials for sodium-ion batteries was tested in CR2032 coin cells. The hydrangea-shaped bismuth vanadate-MXene or amorphous bismuth vanadate-MXene was mixed with conductive carbon black and carboxymethyl cellulose (CMC) in a weight ratio of 7:2:1 with deionized water droplets. The mixture was then manually ground to obtain a uniform slurry, which was spread onto a clean copper foil using a coater. After vacuum drying at 60°C for 12 hours, the copper foil was cut into electrodes with a diameter of approximately 14 mm. The active material loading on the electrodes (hydrangea-shaped bismuth vanadate-MXene or amorphous bismuth vanadate-MXene) was approximately 1-1.2 mg cm -2 In a vacuum glove box, a sodium ion half-cell was assembled in the following order: CR2032 negative electrode shell - material electrode - PP diaphragm - glass fiber diaphragm - sodium-loaded gasket - spring - CR2032 positive electrode shell. The electrolyte used was a 1M NaPF6 diethylene glycol dimethyl ether solution, and about 200 μL of electrolyte was used for one cell. The assembled button cell was tested on a blue power test system. The test results are shown in Table 2 and Figure 6 As shown:

[0066] Table 2. Comparison of sodium ion battery performance

[0067]

[0068] From Table 2 and Figure 6 It can be seen that the sodium ion battery prepared by the hydrangea-shaped bismuth vanadate-MXene heterostructure provided by the embodiment of the present invention can maintain a capacity of 233 mAh g after 2000 cycles at 2A. -1 , and the downward trend is slow. In contrast, the comparative example 1 has only 181mAh g -1 , and is still declining significantly. It is speculated that the hydrangea-shaped bismuth vanadate-MXene heterostructure can alleviate the volume expansion during the charge and discharge process, making the battery cycle life significantly longer than the control sample and more stable.

[0069] In summary, the present invention provides a hydrangea-shaped bismuth vanadate-MXene heterostructure, its preparation method, and application. This preparation method obtains a hydrangea-shaped bismuth vanadate-MXene heterostructure by selecting a bismuth source and controlling the reaction conditions. It is not only simple to operate but also has low equipment requirements, allowing for industrial production. The resulting bismuth vanadate-MXene heterostructure has a novel structure. The unique hydrangea-shaped structure can greatly increase the contact surface with the electrolyte when used in sodium ion batteries, thereby promoting ion transport and diffusion, while alleviating volume expansion during charge and discharge, and better maintaining battery capacity. It has good application prospects in sodium ion batteries.

[0070] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrangea-shaped bismuth vanadate-MXene heterojunction, characterized in that: The process is as follows: (1) The V2AlC powder was stirred and etched in a hydrofluoric acid solution. After the reaction was completed, the solution was repeatedly washed with deionized water until the pH was neutral. The suspension obtained was filtered and freeze-dried to obtain the first V2C powder. (2) The first V2C powder was mixed with water to form a suspension, BiCl3 was added, and H2O2 solution was added dropwise at the same time. After stirring evenly, the suspension was transferred into a reactor and heated to 160°C at a rate of 5-10°C / min for hydrothermal reaction for 16 hours. The product was obtained after cooling, centrifugation, and drying. The concentration of the H2O2 solution was 30wt%, the volume mass ratio of the H2O2 solution to the first V2C powder was 1mL:120mg, and the molar ratio of BiCl3 to the first V2C powder was 1:

5.

2. The preparation method according to claim 1, characterized in that In step (1), the concentration of the hydrofluoric acid solution is 49 wt %, and the etching temperature of the V2AlC powder in the hydrofluoric acid solution is 55-65° C.

3. A hydrangea-shaped bismuth vanadate-MXene heterojunction prepared by the preparation method according to claim 1 or 2.

4. An application of the hydrangea-shaped bismuth vanadate-MXene heterojunction as claimed in claim 3 in a sodium ion battery.

5. The use according to claim 4, characterized in that Hydrangea-shaped bismuth vanadate-Mxene, conductive carbon black and carboxymethyl cellulose were mixed with deionized water in a weight ratio of 7:2:1, ground into a uniform slurry, coated on a clean copper foil, dried and sliced ​​to serve as the negative electrode of sodium ion batteries.

6. The use according to claim 5, characterized in that The loading of hydrangea-shaped bismuth vanadate-Mxene on copper foil is 1-1.2 mg cm -2 .

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