Vanadium boride / vanadium nitride / MXene heterojunction material and preparation method and application thereof

Abstract

The application belongs to the technical field of nanomaterials, and discloses a vanadium boride / vanadium nitride / MXenes heterojunction material and a preparation method and application thereof. Commercial boron powder, vanadium pentoxide, MXenes, sodium chloride and potassium chloride are uniformly mixed and ground, and the material is obtained through one-step calcination at 900-1100 DEG C in an inert gas atmosphere. Then, the sulfur / vanadium boride / vanadium nitride / MXenes heterojunction prepared through a vacuum melting diffusion reaction can be obtained. The application has good controllability. Due to the unique electronic structure of the boride, the rich active sites, and the dual sulfur property, the application can fix more sulfur elements. At the same time, the application has a micro-laminated structure, can solve the problem of poor sulfur element fixation in the existing lithium-sulfur battery positive electrode material, inhibit the dissolution of polysulfides, improve the energy storage capacity, fully release the active sites of the boride, and thus solve and inhibit the problem of shuttle effect and the problem of easy agglomeration of the boride composite material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterials, and particularly relates to a vanadium boride / vanadium nitride / MXenes heterojunction material and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for renewable energy, advanced energy storage devices require more environmental protection and economy. Among the various battery types studied, lithium-sulfur batteries stand out due to their safety and high energy density, attracting the attention of researchers. The theoretical specific capacity of elemental sulfur used in the positive electrode of lithium-sulfur batteries is 1675 mAh / g, and it is considered to be the most promising low-cost, high-energy-density energy storage battery of the next generation. Transition metal borides as a new type of lithium-sulfur battery positive electrode material have attracted more and more attention due to their unique crystal structure, excellent polysulfide adsorption capacity, high conductivity and good polysulfide catalytic conversion capacity.

[0003] Boron has a large electronegativity (X=2.04), so it can effectively slow down the oxidation of metals and increase the active sites. The modified electronic structure between transition metals and boron can also reduce the kinetic energy barrier in the electrochemical process, so it can exhibit excellent electrocatalytic performance. At the same time, the B atom in boride belongs to an electron-deficient structure, which can capture polysulfides by forming B-S bonds. Therefore, both B atoms and metal atoms in transition metal borides can chemically bond with polysulfide anions. This dual sulfur property can enrich the chemical anchoring sites and catalytic active sites.

[0004] However, most transition metal borides are mainly synthesized at high temperatures, and the preparation process is complex, the temperature is high, and most borides are severely agglomerated during the preparation process, mostly spherical or granular, and have poor sulfur fixation capacity, so they cannot fully contact with sulfur, thereby cannot fully release their energy storage activity. SUMMARY

[0005] In order to overcome the shortcomings and deficiencies of the prior art that the preparation process of boride heterojunction is complex, the required temperature is high, and the agglomeration is serious, and the conductivity is poor and the energy storage effect cannot be fully released in the use of lithium-sulfur batteries, the primary purpose of the present application is to provide a preparation method of vanadium boride / vanadium nitride / MXenes heterojunction material. The material obtained by the simple one-step calcination reaction method can effectively fix elemental sulfur and inhibit the generation of soluble lithium polysulfide intermediates, thereby avoiding serious shuttle effect.

[0006] Another purpose of the present application is to provide a vanadium boride / vanadium nitride / MXenes heterojunction material prepared by the above preparation method; the material can also effectively buffer the volume change of the positive electrode material and improve the conductivity of the electrode material.

[0007] Another object of the present application is to provide an application of the above-mentioned vanadium boride / vanadium nitride / MXenes heterojunction material in a lithium-sulfur battery.

[0008] The object of the present application is achieved by the following technical solutions:

[0009] A preparation method of a vanadium boride / vanadium nitride / MXenes heterojunction material, comprising the following operation steps:

[0010] S1, weigh commercial boron powder, vanadium pentoxide, MXenes, sodium chloride and potassium chloride, mix and grind to obtain a uniform precursor;

[0011] S2, the precursor obtained in step S1 is transferred to a tube furnace in a porcelain boat, nitrogen is introduced as a nitrogen source, the temperature is heated to 900-1100 DEG C under a nitrogen atmosphere, and the temperature is kept for 2 hours to perform a melting heating reaction, and the product after reaction is obtained after natural cooling;

[0012] S3, the product after reaction obtained in step S2 is washed with 80 DEG C deionized water and ultrasonic treated for 2 hours;

[0013] S4, the product after ultrasonic treatment in step S3 is subjected to suction filtration, deionized water washing and freeze drying, and finally a vanadium boride / vanadium nitride / MXenes heterojunction material is obtained.

[0014] The MXenes in step S1 are Ti3C2.

[0015] The mass ratio of the total mass of the commercial boron powder and vanadium pentoxide to the total mass of sodium chloride and potassium chloride in step S1 is 1:10.

[0016] The molar ratio of vanadium pentoxide to commercial boron powder in step S1 is 1:3-1:11.

[0017] The molar ratio of MXenes to commercial boron powder in step S1 is 1:1-1:5.

[0018] A vanadium boride / vanadium nitride / MXenes heterojunction material prepared by the above-mentioned preparation method.

[0019] The above-mentioned vanadium boride / vanadium nitride / MXenes heterojunction material is applied in the field of lithium-sulfur batteries.

[0020] In the application process, the vanadium boride / vanadium nitride / MXenes heterojunction material is mixed with elemental sulfur to obtain a mixture, and the sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material is prepared by vacuum melting diffusion reaction. The temperature of the vacuum melting diffusion reaction is 140-160 DEG C, and the time is 0.5-24 hours; the elemental sulfur accounts for 70% of the mass of the mixture.

[0021] The present application is prepared by calcining vanadium boride / nitride vanadium / MXenes heterojunction material in a nitrogen atmosphere at 900-1100 DEG C by one-step calcination method, and then the sulfur / vanadium boride / nitride vanadium / MXenes heterojunction material is prepared by vacuum melting diffusion reaction. In the present application, because MXenes have a high specific surface area and a large number of active sites, they can be used as a substrate material for the reaction of boron with vanadium pentoxide in a molten state at high temperature to generate boride, avoiding the agglomeration of boride and fully releasing the catalytic activity and energy storage capacity of boride. At the same time, experiments show that the introduction of MXenes can reduce the generation temperature of boride from above 1300 DEG C to 900-1100 DEG C, optimizing the reaction temperature. The reaction principle is:

[0022] 2V2O5 (s) + 18B (s) → 4VB2 (s)+ 5B2O2 (g)

[0023] In addition, the present application uses nitrogen as a nitrogen source. Because nitrogen is a gas, it only participates in the reaction at the outermost layer, and can generate layered nitride vanadium on the surface of boride at the same time of generating boride, thereby synthesizing boride / nitride vanadium / MXenes heterojunction material. On the one hand, the boride / nitride vanadium / MXenes heterojunction material with a layered nanoscale size and a large surface energy can effectively fix elemental sulfur, so that it can fix sulfur and adsorb polysulfides through stronger chemical action, reduce the content of high sulfur compounds in the electrolyte, and inhibit the notorious shuttle effect in lithium-sulfur batteries. On the other hand, because the electron transfer that occurs when materials with different work functions contact can regulate the electron density of the metal catalytic center, the surface electron structure and catalytic efficiency of the transition metal-based catalyst can be effectively regulated, and therefore the contact between the generated nitride vanadium and boride at the surface can further improve the catalytic conversion efficiency, thereby greatly improving the electrochemical performance of the material in lithium-sulfur batteries.

[0024] The present application has simple process, low cost, good controllability, safety and repeatability, and the prepared material has a layered structure, which can solve the problem of agglomeration of boride heterojunction during preparation, fully release the active sites, and thus solve the problem of poor sulfur elemental fixation and inhibition of the shuttle effect caused by polysulfide dissolution in the existing lithium-sulfur battery cathode material.

[0025] The application adopts one-step heating calcination, uses the high specific surface and a large number of active sites of MXene to adsorb vanadium pentoxide and boron powder in a molten state at high temperature, and prepares a vanadium boride / nitrogen vanadium / MXenes heterojunction grown on MXenes through one-step reaction. The characteristics of the high specific surface and a large number of active sites of MXene can improve the sulfur loading, reduce the reaction temperature, provide growth sites for vanadium boride, avoid the agglomeration of vanadium boride, and thus release the catalytic activity of vanadium boride. At the same time, the nanoscale vanadium boride / nitrogen vanadium / MXenes heterojunction has small size and large surface energy, can effectively fix elemental sulfur, can fix sulfur and adsorb polysulfides through stronger chemical action, reduces the content of high polysulfides in the electrolyte, greatly improves the conversion efficiency, and catalyzes the fast conversion of soluble lithium polysulfide into insoluble Li2S2 / Li2S, greatly inhibiting the shuttle effect in lithium-sulfur batteries.

[0026] The application has the following advantages and effects compared with the prior art.

[0027] (1) The application prepares a vanadium boride / nitrogen vanadium / MXenes heterojunction with a three-dimensional layered structure, can effectively avoid the agglomeration of vanadium boride, release the energy storage activity, improve the catalytic performance, improve the conversion efficiency, and catalyze the fast conversion of soluble lithium polysulfide into insoluble Li2S2 / Li2S, greatly inhibiting the shuttle effect in lithium-sulfur batteries.

[0028] (2) The preparation process is simple and easy to implement, has lower temperature, lower cost, and is convenient for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 SEM image of the vanadium boride / nitrogen vanadium / MXenes heterojunction material prepared in Example 1.

[0030] Figure 2 X-ray diffraction spectrum of the vanadium boride / nitrogen vanadium / MXenes heterojunction material prepared in Example 1.

[0031] Figure 3 Rate performance diagram of the sulfur / vanadium boride / nitrogen vanadium / MXenes heterojunction material provided in Example 1 as a lithium-sulfur battery positive electrode;

[0032] Figure 4 Electrochemical impedance (EIS) comparison diagram of the lithium-sulfur battery positive electrode material of the sulfur / vanadium boride / nitrogen vanadium / MXenes heterojunction material prepared in Example 1. DETAILED DESCRIPTION

[0033] The application will be further described in detail below in combination with examples and drawings, but the embodiments of the application are not limited thereto.

[0034] Example 1

[0035] 1. Preparation:

[0036] S1, take 0.195g of commercial B powder, 0.364g of V2O5, 2.795g of NaCl, 2.795g of KCl, and 90mg of MXenes, mix and grind to obtain a uniform precursor;

[0037] S2, put the precursor in S1 into a porcelain boat and transfer it to a tube furnace, introduce nitrogen, heat to a temperature of 900℃ under a nitrogen atmosphere, and keep the temperature for 2h to perform a melting heating reaction, and then naturally cool to obtain a reacted product;

[0038] S3, wash the reacted product in S2 with 80℃ deionized water, transfer it into a beaker and ultrasonic for 2;

[0039] S4, perform suction filtration, deionized water washing, and freeze-drying on the ultrasonic treated product in S3 to finally obtain a vanadium boride / vanadium nitride / MXenes heterojunction material.

[0040] 2. Characterization and performance test:

[0041] The above prepared vanadium boride / vanadium nitride / MXenes heterojunction material is characterized and tested for performance. Figure 1 The SEM image of the vanadium boride / vanadium nitride / MXenes heterojunction material shows a uniform layered structure; Figure 2 The X-ray diffraction spectrum and standard spectrum of the vanadium boride / vanadium nitride / MXenes heterojunction material show the successful synthesis of the vanadium boride / vanadium nitride / MXenes heterojunction material.

[0042] Mix the vanadium boride / vanadium nitride / MXenes heterojunction material with elemental sulfur to obtain a mixture, with elemental sulfur accounting for 70% of the mass of the mixture, and then prepare a sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material by vacuum melting diffusion reaction (reaction temperature is 150℃ and time is 12h). Figure 3 The charge-discharge performance of the sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material as a lithium-sulfur battery positive electrode is that the first circle discharge capacity reaches 1556mA h g -1 , which is much higher than that of boron vanadium / MXenes 1038mA h g -1 and boron vanadium 867mA h g -1 . Figure 4The electrochemical impedance (EIS) comparison chart of the sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material prepared in Example 1 and vanadium boride, as shown in the figure, the impedance of the sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material is obviously smaller than that of pure vanadium boride, which indicates that the introduction of vanadium nitride and MXenes can effectively improve the conductivity of the material, reduce the material resistance and improve the electrochemical performance.

[0043] Example 2

[0044] 1. Preparation:

[0045] S1. Take 0.13 g of commercial B powder, 0.364 g of V2O5, 2.47 g of NaCl, 2.47 g of KCl, and 50 mg of MXenes, mix and grind to obtain a uniform precursor;

[0046] S2. Put the precursor in S1 into a porcelain boat and transfer it to a tube furnace, introduce nitrogen, heat to a temperature of 900℃ under a nitrogen atmosphere, and keep the temperature for 2 h to perform a melting and heating reaction. After natural cooling, the reacted product is obtained;

[0047] S3. Wash the reacted product in S2 with 80℃ deionized water and transfer it into a beaker for ultrasonic treatment for 2 h.

[0048] S4. Perform suction filtration, deionized water washing, and freeze-drying on the ultrasonically treated product in S3 to finally obtain a vanadium boride / vanadium nitride / MXenes heterojunction material.

[0049] S5. Mix the vanadium boride / vanadium nitride / MXenes heterojunction material obtained in S4 with elemental sulfur to obtain a mixture, with elemental sulfur accounting for 70% of the mass of the mixture. The mixture is subjected to vacuum melting and diffusion reaction (reaction temperature is 140℃, and reaction time is 24 h) to obtain a sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material.

[0050] Example 3

[0051] 1. Preparation:

[0052] S1. Take 0.195 g of commercial B powder, 0.364 g of V2O5, 2.795 g of NaCl, 2.795 g of KCl, and 90 mg of MXenes, mix and grind to obtain a uniform precursor;

[0053] S2. Put the precursor in S1 into a porcelain boat and transfer it to a tube furnace, introduce nitrogen, heat to a temperature of 900℃ under a nitrogen atmosphere, and keep the temperature for 3 h to perform a melting and heating reaction. After natural cooling, the reacted product is obtained;

[0054] S3. The product after reaction in S2 is washed with 80℃ deionized water, and is transferred into a beaker for ultrasonic treatment for 2h.

[0055] S4. The product after ultrasonic treatment in S3 is subjected to suction filtration, deionized water washing, and freeze-drying, to finally obtain a vanadium boride / vanadium nitride / MXenes heterojunction material.

[0056] S5. The vanadium boride / vanadium nitride / MXenes heterojunction material obtained in S4 is mixed with elemental sulfur to obtain a mixture, the elemental sulfur accounting for 70% of the mass of the mixture, and the mixture is subjected to vacuum melt diffusion reaction (the reaction temperature is 160℃, and the reaction time is 10h) to obtain a sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material.

[0057] Example 4

[0058] 1. Preparation:

[0059] S1. 0.195g of commercial B powder, 0.364g of V2O5, 2.795g of NaCl, 2.795g of KCl, and 90mg of MXenes are mixed and ground to obtain a uniform precursor;

[0060] S2. The precursor in S1 is placed into a porcelain boat and is transferred into a tube furnace, nitrogen is introduced, and heating is performed under a nitrogen atmosphere, the temperature range is 1100℃, the holding time is 2h, melt heating reaction is performed, and the product after reaction is obtained after natural cooling;

[0061] S3. The product after reaction in S2 is washed with 80℃ deionized water, and is transferred into a beaker for ultrasonic treatment for 2h.

[0062] S4. The product after ultrasonic treatment in S3 is subjected to suction filtration, deionized water washing, and freeze-drying, to finally obtain a vanadium boride / vanadium nitride / MXenes heterojunction material.

[0063] S5. The vanadium boride / vanadium nitride / MXenes heterojunction material obtained in S4 is mixed with elemental sulfur to obtain a mixture, the elemental sulfur accounting for 70% of the mass of the mixture, and the mixture is subjected to vacuum melt diffusion reaction (the reaction temperature is 150℃, and the reaction time is 20h) to obtain a sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material.

[0064] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement modes, and all shall be included in the protection scope of the present application.

Claims

1. A method for preparing a vanadium boride / vanadium nitride / MXenes heterojunction material, characterized in that The following steps are included: S1. Weigh commercial boron powder, vanadium pentoxide, MXenes, sodium chloride, and potassium chloride, mix and grind to obtain a uniform precursor; S2. Place the precursor obtained in step S1 into a porcelain boat and transfer it to a tube furnace. Add nitrogen as a nitrogen source and heat the mixture to 900-1100° C. in a nitrogen atmosphere. Maintain the temperature for 2 h to perform a melt heating reaction. Allow the mixture to cool naturally to obtain a product. S3, washing the reaction product obtained in step S2 with 80°C deionized water and ultrasonically treating for 2h; S4. The product subjected to ultrasonic treatment in step S3 is filtered, washed with deionized water, and freeze-dried to finally obtain a vanadium boride / vanadium nitride / MXenes heterojunction material.

2. The preparation method according to claim 1, wherein: The MXenes described in step S1 is Ti3C2.

3. The preparation method according to claim 1, wherein: The mass ratio of the total mass of the commercial boron powder and vanadium pentoxide described in step S1 to the total mass of sodium chloride and potassium chloride is 1:

10.

4. The preparation method according to claim 1, wherein: The molar ratio of vanadium pentoxide to commercial boron powder in step S1 is 1:3-1:

11.

5. The preparation method according to claim 1, wherein: The molar ratio of MXenes to commercial boron powder described in step S1 is 1:1-1:

5.

6. A vanadium boride / vanadium nitride / MXenes heterojunction material prepared by the preparation method according to any one of claims 1 to 5.

7. Application of the vanadium boride / vanadium nitride / MXenes heterojunction material according to claim 6 in the field of lithium-sulfur batteries.

8. The use according to claim 7, characterized in that: During the application process, the vanadium boride / vanadium nitride / MXenes heterojunction material is first mixed with elemental sulfur to obtain a mixture, and the mixture is subjected to a vacuum melt diffusion reaction to obtain a sulfur / vanadium boride / vanadium nitride / MXenes heterojunction material.

9. The use according to claim 8, characterized in that: The temperature of the vacuum melting diffusion reaction is 140-160° C., and the time is 0.5-24 h; the elemental sulfur accounts for 70% of the mass of the mixture.

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