A niobium boride / nitride heterojunction material, a preparation method and application thereof

Abstract

The application belongs to the technical field of nanomaterials, and discloses a niobium boride / niobium nitride heterojunction material and a preparation method and application thereof. Commercial boron powder, di-niobium pentoxide, sodium chloride and potassium chloride are uniformly mixed and ground, and the material is obtained through one-step calcination at 950-1100 DEG C under an inert gas atmosphere. The sulfur / niobium boride / niobium nitride heterojunction obtained through vacuum melting diffusion reaction can be prepared. The application has good controllability. Due to the unique electronic structure of borides, 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-nanorod 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 borides, and thus solve and inhibit the problem of shuttle effect and the problem of easy agglomeration of boride composite materials.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, and specifically relates to a niobium boride / niobium nitride heterojunction material, its preparation method, and its application. Background Technology

[0002] With the rapid development of mobile electronic devices, energy storage power supplies, and electric vehicles, there is an urgent need to develop energy storage systems with higher energy density. Lithium-sulfur batteries are advantageous due to their low cost, abundant raw material reserves, and high theoretical energy density (2600 Wh·kg⁻¹). -1 This has attracted widespread attention from researchers. However, the insulating properties of sulfur, the active material, and lithium sulfide (Li2S), the final discharge product, hinder electron and ion transport during the charge and discharge process. Furthermore, lithium polysulfides, which are readily soluble in the electrolyte, exhibit a shuttle effect, leading to the loss of sulfur. Introducing polar sulfur host materials with high conductivity and catalytic performance to improve the conductivity of the cathode and accelerate the conversion of lithium polysulfides is one effective way to suppress the shuttle effect and improve sulfur utilization. Transition metal borides and transition metal nitrides, as novel cathode materials for lithium-sulfur batteries, are gaining increasing attention due to their unique crystal structure, excellent polysulfide adsorption capacity, high conductivity, and good polysulfide catalytic conversion ability.

[0003] Boron has a relatively high electronegativity (X = 2.04), and the B atoms in borides have an electron-deficient structure, which can capture polysulfides by forming BS bonds. Therefore, in transition metal borides, both B atoms and metal atoms can chemically bond with polysulfide anions. Studies have found that these polar materials with chalcophilic and lithiophilic effects capture lithium polysulfides based on strong MS or X-Li bond (Lewis acid-base interaction) interactions, thereby mitigating polysulfide shuttle. Therefore, boride heterojunctions have certain advantages in lithium-sulfur batteries.

[0004] However, most transition metal boride nitride heterojunctions are complex to prepare, or use ammonia as a nitrogen source, which is dangerous, causes significant environmental pollution, and requires high temperatures. In addition, most borides agglomerate severely during the preparation process, and are mostly spherical or granular, resulting in poor sulfur fixation ability and insufficient contact with sulfur, thus failing to fully release their energy storage activity. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, such as complex boride / nitride heterojunction preparation processes, high temperature requirements, high risk factors, high pollution levels, poor conductivity, and incomplete energy storage performance in lithium-sulfur batteries, the primary objective of this invention is to provide a method for preparing niobium boride / niobium nitride heterojunction materials. This method involves a simple one-step calcination reaction under a nitrogen atmosphere, which can effectively fix elemental sulfur, suppress the generation of soluble lithium polysulfide intermediates, and thus avoid the material with severe shuttle effect.

[0006] Another objective of this invention is to provide a niobium boride / niobium nitride heterojunction material prepared by the above-described preparation method; this material can also effectively buffer the volume change of the cathode material and improve the conductivity of the electrode material.

[0007] Another object of the present invention is to provide an application of the above-mentioned niobium boride / niobium nitride heterojunction material in lithium-sulfur batteries.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a niobium boride / niobium nitride heterojunction material includes the following steps:

[0010] S1. Weigh commercial boron powder, niobium pentoxide, sodium chloride and potassium chloride, mix and grind them to obtain a uniform precursor;

[0011] S2. Place the precursor obtained in step S1 into a ceramic boat, transfer it to a tube furnace, introduce nitrogen gas, maintain the gas flow rate at 10-20 Nml / min, heat the temperature to 950-1100℃ in a nitrogen atmosphere, hold for 1.5h, carry out the melting heating reaction, and let it cool naturally to obtain the product after the reaction.

[0012] S3. Add the product obtained in step S2 to deionized water, let it stand for 12 hours, then sonicate for 1 hour, and dry the product at 80°C.

[0013] S4. The product dried by ultrasonic treatment in step S3 is washed again with deionized water, filtered, and freeze-dried to finally obtain niobium boride / niobium nitride heterojunction material.

[0014] The total mass of the commercial boron powder and niobium pentoxide mentioned in step S1 is in a mass ratio of 1:7 to 1:20 to the total mass of sodium chloride and potassium chloride.

[0015] The molar ratio of niobium pentoxide to commercial boron powder in step S1 is 1:3 to 1:11.

[0016] A niobium boride / niobium nitride heterojunction material prepared by the above-described preparation method.

[0017] The above-mentioned niobium boride / niobium nitride heterojunction materials are used in the field of lithium-sulfur batteries.

[0018] In the application process, niobium boride / niobium nitride heterojunction material is first mixed with elemental sulfur to obtain a mixture. This mixture is then subjected to a vacuum melt-diffusion reaction to obtain a sulfur / niobium boride / niobium nitride heterojunction material, which serves as the cathode material for lithium-sulfur batteries. The vacuum melt-diffusion reaction is carried out at a temperature of 150–160°C for 8–24 hours; the elemental sulfur constitutes 75% of the mixture by mass.

[0019] This invention prepares nanorod-shaped niobium boride / niobium nitride heterojunction materials by calcination at 950-1100℃ in a nitrogen atmosphere using a one-step calcination method, and then prepares sulfur / niobium boride / niobium nitride heterojunction materials by vacuum melt diffusion reaction.

[0020] In addition, this invention uses nitrogen as the nitrogen source. Since nitrogen is a gas, it only participates in the reaction on the outermost layer, allowing the formation of niobium boride and niobium nitride nanorods on the niobium boride surface simultaneously, thus synthesizing a niobium boride / niobium nitride heterojunction material. On one hand, the nanoscale niobium boride / niobium nitride heterojunction material has a small size and high surface energy, which can effectively fix elemental sulfur. This allows it to fix sulfur and adsorb polysulfides through stronger chemical interactions, reducing the content of high-sulfide compounds in the electrolyte and suppressing the notorious shuttle effect in lithium-sulfur batteries. On the other hand, the interface formed by the surface-generated niobium nitride and niobium boride can further improve the catalytic conversion efficiency, thereby greatly enhancing the electrochemical performance of this material in lithium-sulfur batteries.

[0021] The process of this invention is simple, low-cost, and has good controllability, safety, and repeatability. The prepared material has a nanorod structure, which can solve the problem of agglomeration of boride heterojunctions during the preparation process and fully release its active sites. This solves the problem of poor sulfur fixation and the shuttle effect caused by the suppression of polysulfide dissolution in existing lithium-sulfur battery cathode materials.

[0022] The present invention has the following advantages and effects compared with the prior art:

[0023] (1) The present invention prepares a niobium boride / niobium nitride heterojunction material with a three-dimensional nanorod structure, which can effectively avoid the agglomeration of niobium boride and give full play to the amphiphilic sulfur properties of niobium boride. At the same time, the niobium nitride material can also greatly improve the conductivity of borides, thereby fully releasing the energy storage activity, improving the catalytic performance, improving the conversion efficiency, and greatly suppressing the shuttle effect in lithium-sulfur batteries.

[0024] (2) The preparation method of the present invention is simple, safe and efficient, avoiding environmental pollution and potential explosion hazards caused by using ammonia as a nitrogen source in the general preparation of nitrides. At the same time, the reaction temperature is lower, the cost is lower, and it is easy to scale up production. Attached Figure Description

[0025] Figure 1 This is a SEM image of the niobium boride / niobium nitride heterojunction material prepared in Example 1.

[0026] Figure 2 The image shows the X-ray diffraction pattern of the niobium boride / niobium nitride heterojunction material prepared in Example 1.

[0027] Figure 3 The rate performance diagram of the sulfur / niobium boride / niobium nitride heterojunction material provided in Example 1 of the present invention as the positive electrode of a lithium-sulfur battery is shown.

[0028] Figure 4 The image shows a comparison of the electrochemical impedance spectroscopy (EIS) of the lithium-sulfur battery cathode materials prepared in Example 1, which are sulfur / niobium boride / niobium nitride heterojunction materials. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] Example 1

[0031] 1. Preparation:

[0032] S1. Weigh 0.195g of commercial B powder, 0.364g of Nb2O5, 2.795g of NaCl and 2.795g of KCl, mix and grind to obtain a uniform precursor;

[0033] S2. Place the precursor obtained in step S1 into a ceramic boat and transfer it to a tube furnace. Pour nitrogen gas into the furnace and maintain the gas flow rate at 10 N ml / min. Heat the furnace to 950 °C under a nitrogen atmosphere and hold for 1.5 h to carry out a melting heating reaction. Allow the furnace to cool naturally to obtain the product after the reaction.

[0034] S3. Add the product obtained in step S2 to deionized water, let it stand for 12 hours, then sonicate for 1 hour, and dry the product at 80°C.

[0035] S4. The product dried by ultrasonic treatment in step S3 is washed again with deionized water, filtered, and freeze-dried to finally obtain niobium boride / niobium nitride heterojunction material.

[0036] S5. The niobium boride / niobium nitride heterojunction material obtained in S4 is mixed with elemental sulfur to obtain a mixture, wherein elemental sulfur accounts for 70% of the mass of the mixture. The mixture is then subjected to a vacuum melt diffusion reaction (the reaction temperature is 160℃ and the time is 24h) to obtain a sulfur / niobium boride / niobium nitride heterojunction material.

[0037] 2. Characterization and performance testing:

[0038] The niobium boride / niobium nitride heterojunction material prepared above was characterized and its performance was tested. Figure 1 The image shows a SEM image of a niobium boride / niobium nitride heterojunction material, revealing a uniform nanorod structure. Figure 2 The X-ray diffraction pattern and standard pattern of the niobium boride / niobium nitride heterojunction material demonstrate the successful synthesis of the material.

[0039] Figure 3 The charge-discharge performance of the obtained sulfur / niobium boride / niobium nitride heterojunction material as a positive electrode of lithium-sulfur battery is higher than that of pure niobium boride material at 0.1, 0.2, 0.5, 1 and 2C. Figure 4 The figure shows a comparison of the electrochemical impedance spectroscopy (EIS) of the sulfur / niobium boride / niobium nitride heterojunction material prepared in Example 1 with that of niobium boride. As can be seen from the figure, the impedance of the sulfur / niobium boride / niobium nitride heterojunction material is significantly lower than that of pure niobium boride. This indicates that the introduction of niobium nitride and niobium nitride can effectively improve the conductivity of the material, reduce the material resistance, and improve the electrochemical performance.

[0040] Example 2

[0041] 1. Preparation:

[0042] S1. Weigh 0.195g of commercial B powder, 0.364g of Nb2O5, 2.795g of NaCl and 2.795g of KCl, mix and grind to obtain a uniform precursor;

[0043] S2. Place the precursor obtained in step S1 into a ceramic boat and transfer it to a tube furnace. Pour in nitrogen gas and maintain the gas flow rate at 20 N ml / min. Heat the temperature to 1000 °C under a nitrogen atmosphere and hold for 1.5 h to carry out a melting heating reaction. Allow it to cool naturally to obtain the product after the reaction.

[0044] S3. Add the product obtained in step S2 to deionized water, let it stand for 12 hours, then sonicate for 1 hour, and dry the product at 80°C.

[0045] S4. The product dried by ultrasonic treatment in step S3 is washed again with deionized water, filtered, and freeze-dried to finally obtain niobium boride / niobium nitride heterojunction material.

[0046] S5. The niobium boride / niobium nitride heterojunction material obtained in S4 is mixed with elemental sulfur to obtain a mixture, wherein elemental sulfur accounts for 75% of the mass of the mixture. The mixture is then subjected to a vacuum melt diffusion reaction (at a temperature of 155°C and a time of 16 hours) to obtain a sulfur / niobium boride / niobium nitride heterojunction material.

[0047] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a niobium boride / niobium nitride heterojunction material, characterized in that... The following steps are included: S1. Weigh commercial boron powder, niobium pentoxide, sodium chloride and potassium chloride, mix and grind them to obtain a uniform precursor; the mass ratio of the total mass of the commercial boron powder and niobium pentoxide to the total mass of sodium chloride and potassium chloride is 1:7-1:20; the molar ratio of niobium pentoxide to commercial boron powder is 1:3-1:

11. S2. Place the precursor obtained in step S1 into a ceramic boat, transfer it to a tube furnace, introduce nitrogen gas, maintain the gas flow rate at 10-20 Nml / min, heat the temperature to 950-1100 ℃ under nitrogen atmosphere, hold for 1.5h, carry out the melting heating reaction, and let it cool naturally to obtain the product after the reaction. S3. Add the product obtained in step S2 to deionized water, let it stand for 12 hours, then sonicate for 1 hour, and dry the product at 80°C. S4. The product dried by ultrasonic treatment in step S3 is washed again with deionized water, filtered, and freeze-dried to finally obtain niobium boride / niobium nitride heterojunction material.

2. A niobium boride / niobium nitride heterojunction material prepared by the preparation method described in claim 1.

3. The application of the niobium boride / niobium nitride heterojunction material according to claim 2 in the field of lithium-sulfur batteries.

4. The application according to claim 3, characterized in that: In the application process, niobium boride / niobium nitride heterojunction material is first mixed with elemental sulfur to obtain a mixture. The mixture is then processed through a vacuum melt diffusion reaction to obtain sulfur / niobium boride / niobium nitride heterojunction material, which is used as a cathode material for lithium-sulfur batteries.

5. The application according to claim 4, characterized in that: The vacuum melt diffusion reaction is carried out at a temperature of 150–160°C for 8–24 hours; the elemental sulfur accounts for 75% of the mass of the mixture.

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