Preparation Method and Application of a Core-Shell Structure CNT@VS4 Nano-Necklace Material

Abstract

The present invention discloses a preparation method and application of a core-shell structure CNT@VS4 nano-necklace material. The method is as follows: After acidifying multi-walled carbon nanotubes, they are dispersed in deionized water to obtain a carbon nanotube dispersion; dodecyl dimethyl betaine and ammonium metavanadate are heated and stirred to dissolve in the carbon nanotube dispersion to obtain solution A; thioacetamide is stirred and dissolved in ethylene glycol to obtain solution B; solution B is added to solution A and heated and stirred continuously, and then a precipitate is formed through a solvothermal reaction; the precipitate is washed and dried under vacuum to obtain the product. The method of the present invention has a simple process, uses green and environmentally friendly raw materials, and the prepared CNT@VS4 material has excellent electrochemical properties and is a promising cathode material for magnesium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for magnesium-ion batteries, and particularly relates to a preparation method and application of a core-shell structure CNT@VS4 nano-necklace material. Background Art

[0002] Due to advantages such as high energy density, long cycle life, and high working voltage, lithium-ion batteries have become the main power sources in fields such as electric vehicles, portable electronic devices, and even fixed energy storage systems. However, the scarcity of lithium resources and potential safety issues have hindered their further application in large-scale energy storage systems. In recent years, magnesium-ion batteries have attracted wide interest as a promising alternative. Magnesium is more abundant in nature than lithium, has a low price, and is in a diagonal position with lithium in the periodic table, with similar chemical properties. In addition, the redox potential of magnesium (Mg 2+ / Mg: –2.37V) is relatively low, and no dendrite effect will occur. Therefore, magnesium-ion batteries may have higher energy density, better rate performance, and safety, and also have greater potential in practical applications.

[0003] VS4 is a typical layered transition metal sulfide with a unique one-dimensional linear chain structure. The intermolecular chains are combined by van der Waals forces, and have a relatively large interlayer spacing and the relatively weak electrostatic force with Mg 2+ is more conducive to ion diffusion, so it is regarded as an ideal cathode material for magnesium-ion batteries. However, due to poor electronic conductivity and strong polarization effects, the development and application of unmodified VS4 materials are limited by poor cycle stability and rate capabilities.

[0004] In order to improve the electrochemical performance of VS4 materials in magnesium-ion batteries, in recent years, researchers have adopted various strategies, including designing unique nanostructures. For example, VS4 nano-urchin balls and VS4 nano-flowers have a relatively large specific surface area, which can increase the contact area between the active material and the electrolyte and provide more reactive sites. Element doping is another method to improve electrochemical performance. For example, Mo- or Mn-doped VS4 can improve conductivity, expand the interlayer spacing, generate a large number of sulfur vacancies, shorten the ion diffusion path, maintain structural stability, and obtain excellent magnesium storage performance. However, these modification methods usually make the synthesis steps more complex. From the perspective of cost savings, compounding with carbon materials is the most practical method. Summary of the Invention

[0005] To solve the above problems, the present invention discloses a preparation method of a core-shell structure CNT@VS4 nano-necklace material with excellent cycling performance and rate performance; and an application of the core-shell structure CNT@VS4 nano-necklace material prepared by the preparation method of the core-shell structure CNT@VS4 nano-necklace material.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] An object of the present invention is to provide a preparation method of a core-shell structure CNT@VS4 nano-necklace material, comprising the following steps:

[0008] (1) Acidify multi-walled carbon nanotubes (MWCNTs) and disperse them in deionized water to obtain a carbon nanotube dispersion;

[0009] (2) Heat and stir lauryl dimethyl betaine and ammonium metavanadate to dissolve them in the carbon nanotube dispersion to obtain solution A;

[0010] (3) Stir and dissolve thioacetamide in ethylene glycol to obtain solution B;

[0011] (4) Add solution B to solution A, continue heating and stirring, and then generate a precipitate through a solvothermal reaction;

[0012] (5) Wash and vacuum-dry the precipitate to obtain the core-shell structure CNT@VS4 nano-necklace material.

[0013] Further, in step (1), the concentration of the acidified carbon nanotubes in the carbon nanotube dispersion is 1.6 - 2.3 mg / mL. -1 .

[0014] Further, in step (1), the carbon nanotubes are acidified with a mixed solution of potassium permanganate, sodium nitrate, and concentrated sulfuric acid, and the mass ratio of potassium permanganate, sodium nitrate, and concentrated sulfuric acid is preferably 1:0.2:36.8.

[0015] Further, in step (2), the mass ratio of lauryl dimethyl betaine, ammonium metavanadate, and carbon nanotubes is 1:0.66 - 0.74:0.10 - 0.14.

[0016] Further, in step (2), the temperature of heating and stirring is 50 - 70 °C.

[0017] Further, in step (3), the concentration of thioacetamide is 0.38 - 0.62 mol / L. -1 .

[0018] Further, in step (4), the volume ratio of solution A to solution B is 1:0.9 - 1.1.

[0019] Furthermore, in the step (4), the solvothermal reaction temperature is 150 - 170 °C, and the reaction time is 12 - 18 h.

[0020] Furthermore, in the step (1), the diameter of the carbon nanotubes is 10 - 30 nm, and the length is 5 - 30 μm.

[0021] Another object of the present invention is to provide an application of the core - shell structure CNT@VS4 nano - necklace material prepared by the above - mentioned preparation method as a positive electrode material for a magnesium - ion battery.

[0022] In the synthesis process of the present invention, a simple and feasible surfactant - assisted solvothermal method is adopted. Using dodecyldimethylbetaine as a surfactant to regulate the morphology of VS4, and a unique VS4 nanoblock is formed in situ on the carbon nanotubes during the solvothermal process. The reaction has strong controllability and the obtained product has high purity. In the prepared core - shell structure CNT@VS4 nano - necklace material, VS4 presents a nanoblock morphology under the morphology - regulating action of dodecyldimethylbetaine, increasing the contact area between the active material and the electrolyte and promoting ion diffusion. In addition, this method uses carbon nanotubes as the growth carrier of VS4, which can not only induce the uniform nucleation and growth of VS4 nanoblocks, prevent excessive aggregation, but also form a good conductive network to promote the internal electron transport of the material. The process is simple, the design is ingenious, and the raw materials are green and environmentally friendly.

[0023] The core - shell structure CNT@VS4 nano - necklace material can be prepared by the method of the present invention. The unique VS4 nanoblock morphology is also beneficial to increasing the specific surface area of the material, providing more reactive sites, and is conducive to exhibiting a higher reversible capacity. Carbon nanotubes can not only provide a stable skeleton support for the growth of VS4 nanoblocks, improving the structural stability of the material, but also the three - dimensional conductive network formed by their interweaving is beneficial to the electron transfer along the carbon nanotubes between VS4 nanoblocks, greatly promoting the improvement of the material conductivity and enhancing the cycle stability and rate performance of the VS4 nanomaterial.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The CNT@VS4 material prepared by the method of the present invention has excellent electrochemical performance. As a positive electrode material for a magnesium - ion battery, CNT@VS4 can provide a reversible capacity of 170 mAh g -1 at 100 mA g -1 and a reversible capacity of 112.2 mAh g -1 at 500 mA g -1 It shows good cycle stability during 800 cycles, and the capacity retention rate is 68%. In addition, the CNT@VS4 material also has excellent rate performance at 2000 mA g-1 can still provide a reversible capacity of 77.2 mAh g -1 at a high magnification. Therefore, this core-shell structured CNT@VS4 nanonecklace material has good application potential as a high-performance and low-cost cathode material for magnesium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the XRD pattern of the CNT@VS4 material of the present invention;

[0027] Figure 2 are the XPS spectra of V, S, and C of the CNT@VS4 material of the present invention. Among them, a is the full XPS spectrum of the CNT@VS4 material, b is the XPS spectrum of V, c is the XPS spectrum of S, and d is the XPS spectrum of C;

[0028] Figure 3 is the SEM image of the CNT@VS4 material of the present invention;

[0029] Figure 4 are the TEM and HRTEM images of the CNT@VS4 material of the present invention. Among them, a and b are the TEM images of the CNT@VS4 material, and c is the HRTEM image of the CNT@VS4 material;

[0030] Figure 5 is the cyclic voltammogram of the CNT@VS4 electrode of the present invention;

[0031] Figure 6 is the charge / discharge curve of the CNT@VS4 electrode of the present invention;

[0032] Figure 7 is the rate performance graph of the CNT@VS4 of the present invention and the materials of Comparative Examples 1 and 2 at different current densities;

[0033] Figure 8 is the charge and discharge curve of the CNT@VS4 electrode of the present invention at different current densities;

[0034] Figure 9 is the cycle performance graph of the CNT@VS4 of the present invention and the materials of Comparative Examples 1 and 2 at 100 mA g -1 ;

[0035] Figure 10 is the cycle performance graph of the CNT@VS4 of the present invention and the materials of Comparative Examples 1 and 2 at 500 mA g -1 ;

[0036] Figure 11 is the SEM image of the VS4 nanosphere material of Comparative Example 1 of the present invention;

[0037] Figure 12TEM image of the VS4 nanosphere material of Comparative Example 1 of the present invention;

[0038] Figure 13 XRD pattern of the VS4 nanosphere material of Comparative Example 1 of the present invention;

[0039] Figure 14 SEM image of the VS4 microsphere material of Comparative Example 2 of the present invention;

[0040] Figure 15 TEM image of the VS4 microsphere material of Comparative Example 2 of the present invention;

[0041] Figure 16 XRD pattern of the VS4 microsphere material of Comparative Example 2 of the present invention;

[0042] Figure 17 SEM image of the VS4 / MWCNTs material of Comparative Example 3 of the present invention;

[0043] Figure 18 XRD pattern of the VS4 / MWCNTs material of Comparative Example 3 of the present invention. Detailed implementation manners

[0044] The present invention will be further clarified below in conjunction with the accompanying drawings and detailed implementation manners. It should be understood that the following detailed implementation manners are only used to illustrate the present invention and not to limit the scope of the present invention.

[0045] Example 1

[0046] Preparation of CNT@VS4 material:

[0047] (1) Add 1 g of multi-walled carbon nanotubes with a diameter of 10 - 30 nm and a length of 5 - 30 μm to a mixed solution containing 1 g of potassium permanganate, 0.2 g of sodium nitrate, and 36.8 g of concentrated sulfuric acid, and stir for 12 h. Then dilute with 200 mL of deionized water, add 10 mL of 30% hydrogen peroxide solution, continue stirring for 10 min, and centrifuge after standing overnight;

[0048] (2) Add 60 mg of acidified carbon nanotubes to 30 mL of deionized water, and ultrasonicate for 1 h to obtain a uniform carbon nanotube dispersion with a concentration of 2.0 mg / mL -1 ;

[0049] (3) Add 0.5 g of dodecyldimethylbetaine and 0.35 g of NH4VO3 to the carbon nanotube dispersion, and stir at 60 °C for 0.5 h to fully dissolve to obtain solution A;

[0050] (4) Stir and dissolve 1.13 g (0.015 mol) of thioacetamide in 30 mL of ethylene glycol to obtain solution B;

[0051] (5) Add solution B to solution A, continue heating and stirring for 0.5 h, then add the obtained mixture into a 100 mL hydrothermal reactor, place it in an oven and heat to 160 °C, and keep it at a constant temperature for 16 h;

[0052] (6) After cooling to room temperature, the obtained precipitate is separated by centrifugation, washed three times with deionized water and anhydrous ethanol respectively, and finally dried in vacuum at 80 °C.

[0053] Characterization of CNT@VS4 material:

[0054] Figure 1 is the XRD pattern of the CNT@VS4 material, which shows that the material is monoclinic VS4. In addition, the broad peak at 26° represents carbon nanotubes, proving the successful composite of VS4 and carbon nanotubes; Figure 2 a is the full XPS spectrum of CNT@VS4, which shows the presence of V, S, C and O elements; Figure 2 b, 2c and 2d are the XPS spectra of V, S and C respectively, which prove that the valence state of V is mainly +4 and the existing form of S is S2 2- , and VS4 and CNT are connected by a chemical bond C–S.

[0055] Analyze the size, morphology and microstructure of the obtained CNT@VS4 material by SEM, TEM and HRTEM images. Figure 3 is the SEM image of the CNT@VS4 material, which shows that the CNT@VS4 material has a special necklace-like morphology, with an average width of about 100 nm and a rough surface. Figure 4 a and 4b are the TEM images of CNT@VS4, which show that VS4 nanoblocks with a size of 10 - 40 nm grow on the surface of carbon nanotubes. Figure 4 c is the HRTEM image of CNT@VS4, which shows that the lattice spacings of the (110) plane of VS4 and the (002) plane of carbon nanotubes in CNT@VS4 are 0.56 and 0.34 nm respectively.

[0056] Electrochemical performance test:

[0057] Using 1-methyl-2-pyrrolidone as a solvent, grind and mix the CNT@VS4 prepared in this example, carbon black and polyvinylidene fluoride evenly at a mass ratio of 80:10:10, apply the obtained uniform slurry on a conductive carbon paper and dry it in vacuum at 80 °C for 12 h. Use 0.8 mol L -1 phenylmagnesium chloride (PhMgCl) and 0.4 mol L -1A solution of aluminum chloride (AlCl3) in tetrahydrofuran (THF) was mixed in equal volume as the electrolyte of the magnesium-ion battery, and glass fiber and metallic magnesium were used as the separator and counter electrode of the magnesium-ion battery, respectively. The electrochemical performance was tested using a CR2032 battery. The battery was assembled in a glove box filled with an argon atmosphere, and the water and oxygen concentrations were both less than 0.1 ppm. The constant current charge-discharge test of the battery was carried out at room temperature using a BlueTEC CT2001A multi-channel battery test system in a fixed voltage range of 0.2–2.2 V (vs. Mg 2+ / Mg). The specific performance is shown in Figures 5 to 10 .

[0058] Figure 5 Figure 2+ shows the cyclic voltammograms of the first three cycles of the CNT@VS4 electrode in the voltage range of 0.2–2.2 V vs. Mg -1 / Mg at a scan rate of 0.2 mV s Figure 6 Figure -1 is the charge / discharge curve of CNT@VS4 in the voltage range of 0.2–2.2 V at a current density of 100 mA g -1 , and the discharge capacity of the first cycle reaches 432 mAh g Figure 7 Figure -1 shows the rate performance of CNT@VS4, VS4 nanospheres of Comparative Example 1, and VS4 microspheres of Comparative Example 2 at different current densities. It can be seen that even at a high current density of 2 A g -1 , the capacity of CNT@VS4 can still reach 77.2 mAh g Figure 8 Figure Figure 9 and 10 are the cyclic performance diagrams of CNT@VS4, Comparative Example 1, and Comparative Example 2 at current densities of 100 and 500 mA g -1 , respectively. It is obvious that CNT@VS4 has a higher capacity and better cycle stability. After cycling 800 times at 500 mA g -1 , the capacity retention rate of CNT@VS4 reaches 68%.

[0059] Example 2

[0060] (1) 1 g of multi-walled carbon nanotubes with a diameter of 10–30 nm and a length of 5–30 μm was added to a mixed solution containing 1 g of potassium permanganate, 0.2 g of sodium nitrate, and 36.8 g of concentrated sulfuric acid and stirred for 12 h. Then it was diluted with 200 mL of deionized water, 10 mL of 30% hydrogen peroxide solution was added and stirred for another 10 min, and after standing overnight, it was separated by centrifugation;

[0061] (2) Add 50 mg of acidified carbon nanotubes to 30 mL of deionized water and ultrasonicate for 1 h to obtain a uniform carbon nanotube dispersion with a concentration of 1.6 mg / mL. -1 ;

[0062] (3) Add 0.5 g of dodecyldimethylbetaine and 0.33 g of NH4VO3 to the carbon nanotube dispersion, stir at 60 °C for 0.5 h to fully dissolve, and obtain Solution A.

[0063] (4) Stir and dissolve 0.87 g of thioacetamide in 30 mL of ethylene glycol to obtain Solution B.

[0064] (5) After adding Solution B to Solution A and continuing to heat and stir for 0.5 h, add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven, heat to 170 °C, and keep it at a constant temperature for 12 h.

[0065] (6) After cooling to room temperature, the resulting precipitate is separated by centrifugation, washed three times with deionized water and anhydrous ethanol respectively, and finally dried in vacuo at 80 °C.

[0066] The as-prepared CNT@VS4 material was characterized for its structure and tested for its electrochemical performance in the same manner as in Example 1. The results of its structural characterization were basically the same as those in Example 1, and the results of its electrochemical performance test are shown in Table 1.

[0067] Example 3

[0068] (1) Add 1 g of multi-walled carbon nanotubes with a diameter of 10 - 30 nm and a length of 5 - 30 μm to a mixed solution containing 1 g of potassium permanganate, 0.2 g of sodium nitrate, and 36.8 g of concentrated sulfuric acid, and stir for 12 h. Then dilute with 200 mL of deionized water, add 10 mL of 30% hydrogen peroxide solution, continue to stir for 10 min, and separate by centrifugation after standing overnight.

[0069] (2) Add 70 mg of acidified carbon nanotubes to 30 mL of deionized water and ultrasonicate for 1 h to obtain a uniform carbon nanotube dispersion with a concentration of 2.3 mg / mL. -1 ;

[0070] (3) Add 0.5 g of dodecyldimethylbetaine and 0.37 g of NH4VO3 to the carbon nanotube dispersion, stir at 60 °C for 0.5 h to fully dissolve, and obtain Solution A.

[0071] (4) Stir and dissolve 1.38 g of thioacetamide in 30 mL of ethylene glycol to obtain Solution B.

[0072] (5) Add solution B to solution A and continue heating and stirring for 0.5 h. Then add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat it to 150 °C, and keep it at a constant temperature for 18 h;

[0073] (6) After cooling to room temperature, the resulting precipitate is separated by centrifugation and washed three times with deionized water and anhydrous ethanol respectively, and finally placed in a vacuum dryer at 80 °C.

[0074] The as-prepared CNT@VS4 material was characterized for its structure and tested for its electrochemical performance in the same manner as in Example 1. The results of its structural characterization were basically the same as those in Example 1, and the results of its electrochemical performance test are shown in Table 1.

[0075] Example 4

[0076] (1) Add 1 g of multi-walled carbon nanotubes with a diameter of 10 - 30 nm and a length of 5 - 30 μm to a mixed solution containing 1 g of potassium permanganate, 0.2 g of sodium nitrate and 36.8 g of concentrated sulfuric acid, and stir for 12 h. Then dilute with 200 mL of deionized water, add 10 mL of 30% hydrogen peroxide solution and continue stirring for 10 min, and separate by centrifugation after standing overnight;

[0077] (2) Add 60 mg of acidified carbon nanotubes to 30 mL of deionized water and sonicate for 1 h to obtain a uniform carbon nanotube dispersion with a concentration of 2.0 mg / mL; -1

[0078] (3) Add 0.5 g of dodecyl dimethyl betaine and 0.35 g of NH4VO3 to the carbon nanotube dispersion, stir at 50 °C for 0.5 h to dissolve completely to obtain solution A;

[0079] (4) Stir and dissolve 1.13 g of thioacetamide in 27 mL of ethylene glycol to obtain solution B;

[0080] (5) Add solution B to solution A and continue heating and stirring for 0.5 h. Then add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat it to 150 °C, and keep it at a constant temperature for 15 h;

[0081] (6) After cooling to room temperature, the resulting precipitate is separated by centrifugation and washed three times with deionized water and anhydrous ethanol respectively, and finally placed in a vacuum dryer at 80 °C.

[0082] The as-prepared CNT@VS4 material was characterized for its structure and tested for its electrochemical performance in the same manner as in Example 1. The results of its structural characterization were basically the same as those in Example 1, and the results of its electrochemical performance test are shown in Table 1.

[0083] Example 5

[0084] (1) Add 1 g of multi-walled carbon nanotubes with a diameter of 10 - 30 nm and a length of 5 - 30 μm to a mixed solution containing 1 g of potassium permanganate, 0.2 g of sodium nitrate, and 36.8 g of concentrated sulfuric acid, and stir for 12 h. Then dilute with 200 mL of deionized water, add 10 mL of 30% hydrogen peroxide solution, continue to stir for 10 min, let stand overnight, and then perform centrifugal separation;

[0085] (2) Add 60 mg of acidified carbon nanotubes to 30 mL of deionized water, and ultrasonicate for 1 h to obtain a uniform carbon nanotube dispersion with a concentration of 2.0 mg / mL; -1

[0086] (3) Add 0.5 g of dodecyldimethylbetaine and 0.35 g of NH4VO3 to the carbon nanotube dispersion, stir at 70 °C for 0.5 h to fully dissolve, and obtain solution A;

[0087] (4) Stir and dissolve 1.13 g of thioacetamide in 33 mL of ethylene glycol to obtain solution B;

[0088] (5) After adding solution B to solution A and continuing to heat and stir for 0.5 h, add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat to 170 °C, and keep it at a constant temperature for 18 h;

[0089] (6) After cooling to room temperature, the resulting precipitate is separated by centrifugation, washed 3 times with deionized water and anhydrous ethanol respectively, and finally dried in vacuo at 80 °C.

[0090] The as-prepared CNT@VS4 material was characterized for its structure and tested for its electrochemical performance in the same manner as in Example 1. The results of its structural characterization were basically the same as those in Example 1, and the results of its electrochemical performance test are shown in Table 1.

[0091] Comparative Example 1

[0092] Preparation of VS4 nanosphere material:

[0093] (1) Add 0.5 g of dodecyldimethylbetaine and 0.35 g of NH4VO3 to 30 mL of deionized water, stir at 60 °C for 0.5 h to fully dissolve, and obtain solution A;

[0094] (2) Stir and dissolve 1.13 g of thioacetamide in 30 mL of ethylene glycol to obtain solution B;

[0095] (3) After adding solution B to solution A and continuing to heat and stir for 0.5 h, add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat to 160 °C, and keep it at a constant temperature for 16 h;

[0096] (4) After cooling to room temperature, the obtained precipitate was separated by centrifugation, washed three times with deionized water and anhydrous ethanol respectively, and finally placed in a vacuum dryer at 80 °C.

[0097] Electrochemical performance test:

[0098] Using 1-methyl-2-pyrrolidone as the solvent, the VS4 nanospheres prepared in this example were ground and mixed evenly with carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10. The obtained homogeneous slurry was coated on a conductive carbon paper and vacuum dried at 80 °C for 12 h. Using 0.8 mol L -1 phenylmagnesium chloride (PhMgCl) and 0.4 mol L -1 aluminum trichloride (AlCl3) in tetrahydrofuran (THF) solution were mixed in equal volume as the electrolyte for the magnesium-ion battery, and glass fiber and metallic magnesium were used as the separator and counter electrode for the magnesium-ion battery respectively. The electrochemical performance was tested using a CR2032 battery. The battery assembly was carried out in a glove box filled with an argon atmosphere, and the water and oxygen concentrations were both less than 0.1 ppm. The constant current charge-discharge test of the battery was carried out at room temperature using a BlueTEC CT2001A multi-channel battery test system in a fixed voltage range of 0.2–2.2 V vs. Mg 2+ / Mg.

[0099] The as-prepared VS4 nanosphere material was subjected to structural characterization and electrochemical performance test in the same method as in Example 1. Its morphology is as Figure 11 and 12 shown. Due to the lack of carbon nanotubes as the growth carrier, the VS4 nanoblocks self-assembled to form nanospheres with an average diameter of about 800 nm. Figure 13 The XRD results shown in Figure 7 indicated that its crystallinity was worse than that of Example 1. Figure 9 and 10 were the rate performance diagrams of CNT@VS4, VS4 nanospheres and VS4 microspheres at different current densities. The reversible capacity of CNT@VS4 was higher than that of VS4 nanospheres and VS4 microspheres; -1 and

[0100] were the comparison diagrams of the cycle performance of CNT@VS4, VS4 nanospheres and VS4 microspheres at current densities of 100 and 500 mA g

[0101] respectively. This diagram showed that the cycle stability of VS4 nanospheres and VS4 microspheres was far behind that of CNT@VS4; from the above tests, it can be seen that the magnesium storage electrochemical performance of VS4 nanospheres and VS4 microspheres was much inferior to that of CNT@VS4.

[0102] Comparative Example 2

[0101] Preparation of VS4 microsphere material:

[0102] (1) Add 0.35 g of NH4VO3 to 30 mL of deionized water, stir at 60 °C for 0.5 h to dissolve completely, and obtain solution A;

[0103] (2) Stir and dissolve 1.13 g of thioacetamide in 30 mL of ethylene glycol to obtain solution B;

[0104] (3) Add solution B to solution A, continue heating and stirring for 0.5 h, then add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat to 160 °C, and keep it at a constant temperature for 16 h;

[0105] (4) After cooling to room temperature, the resulting precipitate is separated by centrifugation, washed 3 times with deionized water and anhydrous ethanol respectively, and finally dried in vacuo at 80 °C.

[0106] The as-prepared VS4 microsphere material ( Figure 14 and 15 ) was tested for its electrochemical performance according to the same method as in Example 1. The results are shown in Table 1. Figure 16 The XRD results shown indicate that its crystallinity is worse than that of Example 1.

[0107] Comparative Example 3

[0108] Preparation of VS4 / MWCNTs material:

[0109] (1) Add 60 mg of unacidified multi-walled carbon nanotubes (MWCNTs) to 30 mL of deionized water, and ultrasonicate for 1 h to obtain a carbon nanotube dispersion with a concentration of 2.0 mg mL -1 ;

[0110] (2) Add 0.5 g of dodecyl dimethyl betaine and 0.35 g of NH4VO3 to the above-obtained carbon nanotube dispersion, stir at 60 °C for 0.5 h to dissolve completely, and obtain solution A;

[0111] (3) Stir and dissolve 1.13 g of thioacetamide in 30 mL of ethylene glycol to obtain solution B;

[0112] (4) Add solution B to solution A, continue heating and stirring for 0.5 h, then add the resulting mixture to a 100 mL hydrothermal reactor, place it in an oven and heat to 160 °C, and keep it at a constant temperature for 16 h;

[0113] (5) After cooling to room temperature, the resulting precipitate is separated by centrifugation, washed 3 times with deionized water and anhydrous ethanol respectively, and finally dried in vacuo at 80 °C.

[0114] The as-prepared VS4 / MWCNTs material was characterized for its structure and tested for its electrochemical performance according to the same method as in Example 1. Its morphology is as shown in Figure 17As shown, since the multi-walled carbon nanotubes were not acid-treated, the VS4 nanoblocks did not grow on the carbon nanotubes, but self-aggregated to form a nanosphere morphology with serious accumulation. The electrochemical performance test results of the VS4 / MWCNTs material are shown in Table 1. Figure 18 The XRD results shown indicate that its crystallinity is worse than that of Example 1.

[0115] Table 1 Electrochemical performance data

[0116]

[0117] It should be noted that the above content only illustrates the technical idea of the present invention and cannot limit the protection scope of the present invention. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements all fall within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a core-shell structure CNT@VS4 nano-necklace material, characterized in that, It includes the following steps: (1) Acidify multi-walled carbon nanotubes and disperse them in deionized water to obtain a carbon nanotube dispersion; (2) Heat and stir lauryl dimethyl betaine and ammonium metavanadate to dissolve them in the carbon nanotube dispersion to obtain Solution A; (3) Stir and dissolve thioacetamide in ethylene glycol to obtain Solution B; (4) Add Solution B to Solution A, continue heating and stirring, and then generate a precipitate through a solvothermal reaction; (5) Wash and vacuum-dry the precipitate generated in step (4) to obtain a core-shell structured CNT@VS4 nano-necklace material; In step (2), the mass ratio of lauryl dimethyl betaine, ammonium metavanadate, and carbon nanotubes is 1:0.66 - 0.74:0.10 - 0.14; in step (4), the temperature of the solvothermal reaction is 150 - 170 °C, and the time is 12 - 18 h; The core-shell structured CNT@VS4 nano-necklace material is used as a positive electrode material in a magnesium ion battery.

2. The preparation method of a core-shell structure CNT@VS4 nano-necklace material according to claim 1, characterized in that, In step (1), the concentration of the acidified carbon nanotubes in the carbon nanotube dispersion is 1.6 - 2.3 mg / mL -1 .

3. The preparation method of a core-shell structure CNT@VS4 nano-necklace material according to claim 1, characterized in that, In step (2), the temperature of the heating and stirring is 50 - 70 °C.

4. The preparation method of the core-shell structure CNT@VS4 nano-necklace material according to claim 1, wherein, In step (3), the concentration of thioacetamide in solution B is 0.38 - 0.62 mol / L -1 .

5. The preparation method of the core-shell structure CNT@VS4 nano-necklace material according to claim 1, wherein, In step (4), the volume ratio of Solution A and Solution B is 1:0.9 - 1.

1.

6. The preparation method of the core-shell structure CNT@VS4 nano-necklace material according to claim 1, characterized in that, In step (1), the diameter of the multi-walled carbon nanotubes is 10 - 30 nm, and the length is 5 - 30 μm.

7. Application of the core-shell structured CNT@VS4 nano-necklace material prepared by the preparation method of the core-shell structured CNT@VS4 nano-necklace material according to any one of claims 1 - 6 as a positive electrode material of a magnesium ion battery.

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