Niobium boride / niobium nitride heterojunction material and preparation method and application thereof

Abstract

The invention belongs to the technical field of nano materials, and discloses a niobium boride / niobium nitride heterojunction material and a preparation method and application thereof. Commercial boron powder, niobium pentoxide, sodium chloride and potassium chloride are mixed and ground evenly, and the material is obtained through a one-step calcination method in the inert gas atmosphere of 950-1100 DEG C. And then preparing the sulfur / niobium boride / niobium nitride heterojunction through a vacuum melting diffusion reaction. The method is good in controllability, and more elemental sulfur can be fixed by the boride due to the unique electronic structure of the boride, rich active sites and amphiphilic sulfur properties. Meanwhile, the lithium-sulfur battery positive electrode material has a microcosmic nanorod-shaped structure, can solve the problem of poor fixity of elemental sulfur in the existing lithium-sulfur battery positive electrode material, inhibits dissolution of polysulfide, improves energy storage capacity, and fully releases active sites of boride, thereby solving and inhibiting the shuttle effect problem and the problem that a boride composite material is easy to agglomerate.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials, and particularly relates to a niobium boride / niobium nitride heterojunction material and a preparation method and application thereof. Background Art

[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 have low cost, abundant raw material reserves and high theoretical energy density (2600Wh·kg -1 ) has attracted widespread attention from researchers. However, the insulating properties of the active sulfur and the final discharge product lithium sulfide (Li2S) hinder the electron and ion transport during the charge and discharge process, and the lithium polysulfide that is easily soluble in the electrolyte undergoes a shuttle effect, resulting in the loss of active sulfur. Introducing polar sulfur host materials with high conductivity and catalytic properties to improve the conductivity of the positive electrode and accelerate the conversion of lithium polysulfide is one of the effective ways to inhibit the shuttle effect and improve sulfur utilization. Transition metal borides and transition metal nitrides, as new lithium-sulfur battery positive electrode materials, have gained increasing attention due to their unique crystal structure, excellent polysulfide adsorption capacity, high conductivity and good polysulfide catalytic conversion ability.

[0003] Boron has a large electronegativity (X=2.04), and the B atom in the boride is 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 sulfur- and lithium-philic effects capture lithium polysulfides based on strong MS or X-Li bonds (Lewis acid-base interactions) to reduce the shuttling of polysulfides. Therefore, boride heterojunctions have certain advantages in lithium-sulfur batteries.

[0004] However, most transition metal boride-nitride heterojunctions have complex preparation processes or use ammonia as a nitrogen source, which results in high risk factors, severe environmental pollution, and high temperatures. In addition, most borides are severely agglomerated during the preparation process and are mostly spherical or granular, with poor sulfur fixation ability and unable to fully contact with sulfur, thus failing to fully release their energy storage activity. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art boride-nitride heterojunction, such as complex preparation process, high temperature requirement, high risk factor, high pollution degree, poor conductivity and inability to fully release energy storage effect during use in lithium-sulfur batteries, the primary purpose of the present invention is to provide a method for preparing niobium boride / niobium nitride heterojunction material, which is obtained by a simple one-step calcination reaction method under a nitrogen atmosphere, can effectively fix elemental sulfur, inhibit the generation of soluble lithium polysulfide intermediates, and thus avoid severe shuttle effect.

[0006] Another object of the present invention is to provide a niobium boride / niobium nitride 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 invention is to provide an application of the above-mentioned niobium boride / niobium nitride heterojunction material in a lithium-sulfur battery.

[0008] The purpose of the present invention is achieved through the following technical solutions:

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

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

[0011] S2. The precursor obtained in step S1 is placed in a porcelain boat, transferred to a tube furnace, introduced with nitrogen, and the gas flow rate is maintained at 10-20 Nml / min. The temperature is heated to 950-1100°C in a nitrogen atmosphere, and kept warm for 1.5 hours to perform a melting heating reaction, and then cooled naturally to obtain a product after the reaction;

[0012] S3, adding deionized water to the reaction product obtained in step S2, leaving it to stand for 12 hours, then ultrasonically treating it for 1 hour, and drying the obtained product at 80°C;

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

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

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

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

[0017] Application of the above-mentioned niobium boride / niobium nitride heterojunction material in the field of lithium-sulfur batteries.

[0018] In the application process, the niobium boride / niobium nitride 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 / niobium boride / niobium nitride heterojunction material as a positive electrode material for a lithium-sulfur battery. The temperature of the vacuum melt diffusion reaction is 150-160°C and the time is 8-24 hours; the elemental sulfur accounts for 75% of the mass of the mixture.

[0019] The invention uses a one-step calcination method to prepare a nanorod-shaped niobium boride / niobium nitride heterojunction material in a nitrogen atmosphere at 950-1100° C., and then prepares a sulfur / niobium boride / niobium nitride heterojunction material through a vacuum melt diffusion reaction.

[0020] In addition, the present invention uses nitrogen as a nitrogen source. Since nitrogen is a gas and participates in the reaction only in the outermost layer, it can generate nanorod-shaped niobium nitride on its surface while generating niobium boride, thereby synthesizing a niobium boride / niobium nitride heterojunction material. On the one hand, the nano-scale niobium boride / niobium nitride heterojunction material has a small size and a large surface energy, and can effectively fix elemental sulfur, so that it can fix sulfur and adsorb polysulfides through stronger chemical reactions, reduce the content of high sulfides in the electrolyte, and inhibit the notorious shuttle effect in lithium-sulfur batteries. On the other hand, the contact between the niobium nitride generated on the surface and the niobium boride to form an interface can further improve the catalytic conversion efficiency, thereby greatly improving the electrochemical performance of the material in lithium-sulfur batteries.

[0021] The process of the invention is simple, the cost is low, and the controllability, safety and repeatability are good. 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, thereby solving the problem of poor fixation of sulfur element and inhibition of the shuttle effect caused by the dissolution of polysulfides in the existing lithium-sulfur battery positive electrode materials.

[0022] Compared with the prior art, the present invention has the following advantages and effects:

[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. While exerting the amphiphilic sulfur properties of niobium boride, the niobium nitride material can also greatly improve the conductivity of the boride, thereby fully releasing the energy storage activity, improving the catalytic performance, and increasing the conversion efficiency, greatly inhibiting the shuttle effect in the lithium-sulfur battery.

[0024] (2) The preparation method of the present invention is simple, easy to operate, safe and efficient, and avoids the environmental pollution and potential explosion hazard caused by using ammonia as a nitrogen source in the general nitride preparation process. At the same time, the reaction temperature is low, the cost is lower, and it is easy to scale up production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 2 This is the X-ray diffraction spectrum of the niobium boride / niobium nitride heterojunction material prepared in Example 1.

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

[0028] Figure 4 This is a comparison chart of the electrochemical impedance spectroscopy (EIS) of the lithium-sulfur battery positive electrode material of the sulfur / niobium boride / niobium nitride heterojunction material prepared in Example 1. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0030] Example 1

[0031] 1. Preparation:

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

[0033] S2. The precursor obtained in step S1 is placed in a porcelain boat and transferred to a tube furnace. Nitrogen is introduced, and the gas flow rate is maintained at 10 Nml / min. The temperature is heated to 950°C in a nitrogen atmosphere, and the temperature is kept for 1.5 hours to perform a melting heating reaction, and the reaction is allowed to cool naturally to obtain a product after the reaction;

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

[0035] S4, the product after ultrasonic treatment and drying in step S3 is washed with deionized water again, filtered, and freeze-dried to finally obtain a 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 the elemental sulfur accounts for 70% of the mass of the mixture, and the mixture is subjected to a vacuum melt diffusion reaction (the reaction temperature is 160° C. and the reaction time is 24 hours) 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 This is the SEM image of the niobium boride / niobium nitride heterojunction material, where a uniform nanorod structure can be seen; Figure 2 The X-ray diffraction spectrum and standard spectrum of the niobium boride / niobium nitride heterojunction material indicate the successful synthesis of the niobium boride / niobium nitride heterojunction material.

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

[0040] Example 2

[0041] 1. Preparation:

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

[0043] S2. The precursor obtained in step S1 is placed in a porcelain boat and transferred to a tube furnace. Nitrogen is introduced, and the gas flow rate is maintained at 20 Nml / min. The temperature is heated to 1000°C in a nitrogen atmosphere, and the temperature is kept for 1.5 hours to perform a melting heating reaction, and the reaction is allowed to cool naturally to obtain a product after the reaction;

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

[0045] S4. The product after ultrasonic treatment and drying in step S3 is washed with deionized water again, filtered, and freeze-dried to finally obtain a 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 the elemental sulfur accounts for 75% of the mass of the mixture, and the mixture is subjected to a vacuum melt diffusion reaction (the reaction temperature is 155° C. and the reaction time is 16 hours) to obtain a sulfur / niobium boride / niobium nitride heterojunction material.

[0047] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a niobium boride / niobium nitride heterojunction material, characterized in that The steps include: S1. Weigh commercial boron powder, niobium pentoxide, sodium chloride and potassium chloride, mix and grind to obtain a uniform precursor; S2, placing the precursor obtained in step S1 into a porcelain boat, transferring it to a tube furnace, introducing nitrogen, maintaining the gas flow rate at 10-20 Nml / min, heating the temperature to 950-1100°C in a nitrogen atmosphere, keeping the temperature for 1.5 hours, performing a melting heating reaction, and allowing it to cool naturally to obtain a product after the reaction; S3, adding deionized water to the reaction product obtained in step S2, leaving it to stand for 12 hours, then ultrasonically treating it for 1 hour, and drying the obtained product at 80°C; S4, the product after ultrasonic treatment and drying in step S3 is washed with deionized water again, filtered, and freeze-dried to finally obtain a niobium boride / niobium nitride heterojunction material.

2. The method for preparing a niobium boride / niobium nitride heterojunction material according to claim 1, characterized in that: The mass ratio of the total mass of the commercial boron powder and niobium pentoxide described in step S1 to the total mass of sodium chloride and potassium chloride is 1:7-1:

20.

3. The method for preparing a niobium boride / niobium nitride heterojunction material according to claim 1, characterized in that: The molar ratio of niobium pentoxide to commercial boron powder in step S1 is 1:3-1:

11.

4. A niobium boride / niobium nitride heterojunction material prepared by the preparation method according to any one of claims 1 to 3.

5. Application of the niobium boride / niobium nitride heterojunction material according to claim 4 in the field of lithium-sulfur batteries.

6. The use according to claim 5, characterized in that: During the application process, the niobium boride / niobium nitride 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 / niobium boride / niobium nitride heterojunction material as a positive electrode material for a lithium-sulfur battery.

7. The use according to claim 6, characterized in that: The temperature of the vacuum melting diffusion reaction is 150-160° C., and the time is 8-24 hours; the elemental sulfur accounts for 75% of the mass of the mixture.

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