A preparation method and application of a three-dimensional composite material based on niobium boride and niobium oxide

Abstract

A preparation method and application of a niobium boride-niobium oxide composite three-dimensional material. The preparation method comprises the following steps: dissolving a niobium source and a boron source in a solvent containing an alkaline solution, adding a surfactant, and stirring the reaction under a protective atmosphere to produce a niobium boride-niobium oxide composite three-dimensional material. This invention is the first to apply niobium boride-niobium oxide in lithium-sulfur batteries. This not only physically confines polysulfides and inhibits their diffusion, but also creates a built-in electric field at the heterogeneous interface, enhancing charge transfer kinetics, promoting the conversion of elemental sulfur to polysulfides, preventing catalyst passivation, and improving the cycle and rate performance of lithium-sulfur batteries at low temperatures. Furthermore, niobium boride-niobium oxide can be used as a negative electrode material for lithium-ion batteries, exhibiting high discharge capacity and fast charging performance, and has promising application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a preparation method and application of a niobium boride-niobium oxide composite three-dimensional material. Background Art

[0002] With the rapid development of high-energy-consuming electronic devices, new energy vehicles and drone industries, people have paid attention to high-power-density secondary batteries, thus achieving new breakthroughs in fast-charging technology. Lithium-ion batteries have become the most advanced electrochemical energy storage systems in portable electronic devices, energy storage stations and electric vehicles due to their advantages such as high energy density and long cycle stability, attracting widespread attention from countries around the world. It is well known that negative electrode materials are the bottleneck in the development of high-power lithium-ion batteries. Graphite has a high theoretical capacity (372mAh g -1 ) is widely used as a commercial negative electrode material for lithium-ion batteries. However, its lithium insertion potential is low (0.1V vs.Li + / Li), which easily promotes the growth of lithium dendrites under low temperature and fast charging conditions, seriously affecting battery performance and safety. Therefore, there is an urgent need to find a high-power and high-energy-density lithium-ion battery anode material.

[0003] As a new energy storage system that surpasses lithium-ion batteries, lithium-sulfur batteries are based on conversion-type positive electrodes, in which active sulfur (S8) and lithium sulfide Electrochemical redox reaction occurs between the two, showing an extremely high theoretical energy capacity (1675mAh g -1 ), which is about ten times the theoretical energy density of common mainstream lithium-ion batteries. In addition, the theoretical energy density of lithium-sulfur batteries (2600Wh Kg -1 ) is high and the natural reserves of elemental sulfur are abundant, with lower cost and environmental friendliness, making it the next generation secondary battery with the greatest application potential. However, the practical application of lithium-sulfur batteries still faces the following key challenges: the electrical insulation of soluble intermediate polysulfides (Li2S8, Li2S6 and Li2S4) and solid sulfur species (S8, Li2S2 and Li2S) leads to a decrease in the electrochemical reaction rate, thereby reducing the utilization of active materials, especially under low temperature conditions; the tricky "shuttle effect" caused by the slow redox reaction kinetics of polysulfides will cause a large amount of active material to be lost, ultimately leading to a decrease in the reversible capacity of the battery; the large volume change of the S positive electrode during cycling will cause the electrode active material to fall off; the violent reaction of lithium polysulfides on the surface of the lithium negative electrode and repeated uneven deposition will cause corrosion and pulverization of metallic lithium, destroying the structure of the lithium anode, especially under high sulfur loading and poor electrolyte conditions. Summary of the Invention

[0004] Based on the above technical background, the present invention provides a niobium boride-niobium oxide composite three-dimensional material. This three-dimensional nanoscale material can be used as the host material for the sulfur positive electrode of lithium-sulfur batteries, alleviate the "shuttle effect" of polysulfides, and improve the cycle performance and rate performance of lithium-sulfur batteries at low temperatures; it can also be used as the negative electrode material of lithium-ion batteries, exhibiting high discharge capacity and fast charging characteristics.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a niobium boride-niobium oxide composite three-dimensional material comprises the following steps:

[0007] A niobium source and a boron source are dissolved in a solvent containing an alkaline solution in a molar ratio of 1:1.2-2.3, a surfactant is added, and the mixture is stirred at 0-120°C for 3-24 hours under a protective atmosphere. After the reaction, the products are centrifuged and collected using distilled water and anhydrous ethanol respectively, and then dried to obtain a niobium boride-niobium oxide composite three-dimensional material.

[0008] The stirring method is magnetic stirring or mechanical stirring, and the mixing time is 2-8 hours. The centrifugal speed is 5000-9000 r / min, and the centrifugal time is 3-6 minutes each time.

[0009] Furthermore, the niobium source includes one of niobium pentachloride, niobium ethanol, niobium oxalate, ammonium niobate oxalate and niobium pentoxide; the boron source includes one of boron dioxide, sodium borohydride and boron powder; the alkaline solution includes a combination of one or more of sodium hydroxide, potassium hydroxide and ammonia water; the solvent includes one or more of ultrapure water, oleylamine, ethanol, cyclohexane, isopropanol, glycerol, tetrahydrofuran, N-methylpyrrolidone and ethylene glycol; and the surfactant includes a combination of one or more of cetyltrimethylammonium bromide (CTAB), ethanolamine and polyvinylpyrrolidone (PVP).

[0010] Furthermore, the amount of alkaline substance in the alkaline solution is 0.5-2 times the molar ratio of the niobium source, and the amount of surfactant is 0.4-3 times the molar ratio of the niobium source.

[0011] An application of a niobium boride-niobium oxide composite three-dimensional material prepared by the method, wherein the niobium boride-niobium oxide composite three-dimensional material is used as a host material for sulfur in lithium-sulfur batteries or as a catalyst alone for adsorbing polysulfides.

[0012] Furthermore, when applied to lithium-sulfur batteries, the niobium boride-niobium oxide composite three-dimensional material is evenly mixed with graphyne to form a composite material, the composite material and the active material sublimated sulfur are ground and mixed into a uniform powder, which is then transferred into a polytetrafluoroethylene reactor or a magnetic boat. The container is placed in a blast drying oven or a tubular furnace and heated to 140-170°C for a constant temperature reaction for 4-20 hours. The mixture is naturally cooled to room temperature and taken out to obtain a mixture of sulfur, niobium boride-niobium oxide and graphyne, which is used as the positive electrode material of the lithium-sulfur battery.

[0013] Preferably, the heating temperature is 155° C. and the constant temperature reaction time is 15 h.

[0014] Furthermore, the mass ratio of the niobium boride-niobium oxide composite three-dimensional material to graphyne is 1:2-5, preferably, the mass ratio of the niobium boride-niobium oxide composite three-dimensional material to graphyne is 1:4; the mass ratio of the composite material to the active material sublimated sulfur is 2-4.5:6.5-8.5, preferably 3:7, 1:3, 2:8;

[0015] An application of the niobium boride-niobium oxide composite three-dimensional material prepared by the preparation method, wherein the niobium boride-niobium oxide composite three-dimensional material is used as a negative electrode active material in a lithium ion battery.

[0016] Furthermore, the niobium boride-niobium oxide composite three-dimensional material is dispersed in a solvent as a negative electrode active material with a conductive agent and a binder to obtain a negative electrode slurry. The negative electrode slurry is coated on a current collector, heated and dried, rolled and punched to obtain a negative electrode sheet.

[0017] The binder is polyvinylidene fluoride (PVDF) or an aqueous dispersion of acrylonitrile multi-polymer (LA133), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP) or ultrapure water.

[0018] The negative electrode active material accounts for 70-95% of the total mass of the negative electrode material (negative electrode active material, conductive agent, and binder), the conductive agent accounts for 2.5-20% of the total mass of the negative electrode material, and the binder accounts for 2.5-10% of the total mass of the negative electrode material. Preferably, the mass ratio of active material: conductive agent: binder is 90%:5%:5%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The niobium boride-niobium oxide composite three-dimensional material prepared by the present invention is in the form of a three-dimensional hollow sphere with a diameter of approximately 300nm. This invention is the first to apply niobium boride-niobium oxide (NbB-NbO2) in lithium-sulfur batteries. It can not only physically confine polysulfides and inhibit their diffusion, but also the built-in electric field formed at the heterogeneous interface can improve the charge transfer kinetics, promote the conversion of elemental sulfur to polysulfides, prevent catalyst passivation, and enhance the cycle and rate performance of lithium-sulfur batteries at low temperatures. In addition, niobium boride-niobium oxide (NbB-NbO2) can be used as a negative electrode material for lithium-ion batteries, exhibiting high discharge specific capacity and fast charging performance, and has good application prospects.

[0021] 2) The preparation method of the present invention is simple, low-cost, has low requirements on equipment, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD pattern of the niobium boride-niobium oxide composite three-dimensional material synthesized in Example 1;

[0023] Figure 2 This is an SEM image of the niobium boride-niobium oxide composite three-dimensional material synthesized in Example 1;

[0024] Figure 3 This is the charge and discharge curve of the lithium-sulfur battery in Example 1 at 0.2C;

[0025] Figure 4 This is the charge and discharge curve of the lithium-sulfur battery in Example 1 at 0°C and 0.5C;

[0026] Figure 5 This is an SEM image of the niobium boride-niobium oxide composite three-dimensional material synthesized in Example 2. DETAILED DESCRIPTION

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Example 1:

[0029] A synthesis method of a niobium boride-niobium oxide composite three-dimensional material comprises the following steps:

[0030] 0.811 g of niobium pentachloride and 0.189 g of sodium borohydride were added to a three-necked flask filled with argon and containing 70 mL of ultrapure water. 0.08 g of sodium hydroxide was then added, followed by mechanical stirring for 2 h. 0.5 g of CTAB was then added, followed by mechanical stirring at 0°C for 6 h to uniformly mix the above solutions. The above solutions were then centrifuged with distilled water and anhydrous ethanol for three times at 7000 rpm for 5 minutes each. The black product was collected and dried in a vacuum drying oven to obtain a niobium boride-niobium oxide composite three-dimensional material. The XRD spectrum is shown in FIG. Figure 1 As shown, the positions of all diffraction peaks in the figure are consistent with those of NbO2 (JCPDS card no.43-2043) and NbB (JCPDS card no.32-0709) standard cards. Figure 2 The SEM image of the prepared niobium boride-niobium oxide composite three-dimensional material shows that the morphology of the niobium boride-niobium oxide composite three-dimensional material is hollow nanospheres with a diameter of about 300 nm.

[0031] The niobium boride-niobium oxide composite three-dimensional material obtained in this embodiment can be used alone as a catalyst for adsorbing polysulfides, and can also be used as a host material for lithium-sulfur batteries to inhibit the "shuttle effect" of polysulfides and improve the cycle stability and rate performance of lithium-sulfur batteries at low temperatures.

[0032] When used in lithium-sulfur batteries, the prepared niobium boride-niobium oxide composite material is combined with graphyne in a 1:4 mass ratio to form a composite material. The composite material is then uniformly mixed with sublimed sulfur in a 1:3 mass ratio. The mixture is then ground in an agate mortar for 30 minutes until it is thoroughly mixed into a uniformly colored powder. The mixture is poured onto weighing paper and transferred to a weighing bottle. The weighing bottle is placed in a polytetrafluoroethylene-lined reactor and heated in a forced air drying oven at 150°C for 15 hours. After the reaction is complete, the reactor is cooled to room temperature and removed to produce a mixture of sulfur, niobium boride-niobium oxide, and graphyne.

[0033] A mixture of sulfur, niobium boride, niobium oxide and graphene is used as the positive electrode material of the lithium-sulfur battery, metallic lithium is used as the negative electrode, and the amount of commercial ether electrolyte is 10uLmg -1 , assemble lithium-sulfur batteries and test electrochemical performance. The charge and discharge curves at 0.2C are as follows Figure 3 As shown, the discharge capacity of the first cycle is 1359.3 mAh g -1 , the charge capacity is 1300.5mAh g -1 , the coulombic efficiency is 95.67%. The cycle test is carried out at 0℃, and the charge and discharge curve is as follows Figure 4 As shown. The first cycle discharge capacity at 0.2C is 1051.9 mAh g -1, the charge capacity is 1035.1mAh g -1 The first cycle discharge capacity at 0.5C is 935.0 mAh g -1 , the charge capacity is 928.1mAh g -1 Even at the fiftieth cycle, the discharge capacity is 690.5 mAh g -1 , charge capacity 690.0mAh g -1 , indicating that the assembled lithium-sulfur battery has good cycle stability.

[0034] Example 2

[0035] The difference between this example and Example 1 is that the 50 mL distilled water solvent is replaced with 50 mL isopropanol. In addition, ethanolamine is added instead of CTAB. The reaction conditions are changed to 25 ° C for 6 hours. The other parameters are the same as Example 1. The final niobium boride-niobium oxide is also a three-dimensional material. SEM image is shown as follows Figure 5 As shown, the three-dimensional hierarchical spherical material has a diameter of about 300 nm.

[0036] The niobium boride-niobium oxide composite three-dimensional material obtained in this embodiment is used as a negative electrode active material in button-type lithium-ion batteries. The three-dimensional hierarchical material can shorten the lithium ion diffusion distance, increase the effective contact area between the electrolyte and the interface, improve the charge transfer kinetics, and significantly improve the electrochemical performance of the lithium-ion battery. The binder used is polyvinylidene fluoride (PVDF), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP). The negative electrode slurry is composed of 80% niobium boride-niobium oxide composite three-dimensional material, 10% conductive agent and 10% binder by mass percentage. The counter electrode of the assembled button battery is metallic lithium, and the electrolyte is LiPF6 / EC / DMC (1 mol / L).

[0037] Example 3

[0038] The preparation of the niobium boride-niobium oxide composite three-dimensional material in this example differs from that in Example 1 in that the sodium borohydride in Example 1 was replaced with an equal molar amount of boron powder, the 50 mL distilled water solvent was replaced with 50 mL of NMP, and ethanolamine was added instead of CTAB. The reaction conditions were changed to a 4-hour reaction at 0°C in a homogeneous reactor. All other parameters remained the same as in Example 1.

[0039] Example 4

[0040] The preparation of niobium boride-niobium oxide composite three-dimensional material in this embodiment differs from that in Example 1 in that the niobium pentachloride in Example 1 is replaced with ammonium niobate oxalate in the same molar amount, and the sodium hydroxide is replaced with potassium hydroxide. In addition, ethanolamine is added instead of CTAB. The remaining parameters are the same as in Example 1.

[0041] Example 5

[0042] The preparation of niobium boride-niobium oxide composite three-dimensional material in this embodiment differs from that in Example 1 in that the 50 mL distilled water solvent in Example 1 is replaced with 50 mL oleylamine, and the sodium borohydride is replaced with the same molar amount of boron dioxide. The remaining parameters are the same as in Example 1.

[0043] The preparation method of the present invention is simple, low-cost, and has low equipment requirements. It is the first time to prepare a three-dimensional material of niobium boride-niobium oxide composite phase (NbB-NbO2). It utilizes the unique advantages of the interface of heterogeneous materials to prevent catalyst passivation. Combined with the built-in electric field effect of the heterogeneous interface, it improves the bonding ability with polysulfides and the charge transfer kinetics, promotes the conversion of elemental sulfur to polysulfides, inhibits the "shuttle effect" of lithium-sulfur batteries, and enhances the long cycle life and rate performance of lithium-sulfur batteries at low temperatures. At the same time, niobium boride-niobium oxide composite phase materials can also be used in lithium-ion battery negative electrode materials, showing high discharge capacity and fast charging characteristics, and have good application prospects.

[0044] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a niobium boride-niobium oxide composite three-dimensional material, characterized in that: The following steps are involved: A niobium source and a boron source are dissolved in a solvent containing an alkaline solution in a molar ratio of 1:1.2-2.3, a surfactant is added, and the mixture is stirred and reacted under a protective atmosphere. After the reaction is completed, the product is washed and dried to obtain a niobium boride-niobium oxide composite three-dimensional material; the niobium source comprises one of niobium pentachloride, niobium ethanol, niobium oxalate, ammonium niobate oxalate and niobium pentoxide; the boron source comprises one of boron dioxide, sodium borohydride and boron powder; the alkaline solution comprises a combination of one or more of sodium hydroxide, potassium hydroxide and ammonia water; the The solvent includes one or a combination of ultrapure water, oleylamine, ethanol, cyclohexane, isopropanol, glycerol, tetrahydrofuran, N-methylpyrrolidone and ethylene glycol; when the boron source is boron dioxide, the solvent is oleylamine; the surfactant includes one or a combination of cetyltrimethylammonium bromide, ethanolamine and polyvinylpyrrolidone; the alkaline substance in the alkaline solution is 0.5-2 times the molar ratio of the niobium source, and the amount of the surfactant is 0.4-3 times the molar ratio of the niobium source; the stirring reaction temperature is 0-120°C and the time is 3-24 hours.

2. An application of the niobium boride-niobium oxide composite three-dimensional material prepared by the method according to claim 1, characterized in that: The niobium boride-niobium oxide composite three-dimensional material is used as a host material of sulfur in lithium-sulfur batteries or as a catalyst alone to adsorb polysulfides.

3. The use according to claim 2, characterized in that: When used in lithium-sulfur batteries, the niobium boride-niobium oxide composite three-dimensional material is evenly mixed with graphyne to form a composite material. The composite material and the active material sublimated sulfur are ground and mixed into a uniform powder, which is then transferred into a polytetrafluoroethylene reactor or a magnetic boat and heated to 140-170°C for constant temperature reaction to obtain a mixture of sulfur, niobium boride-niobium oxide and graphyne, which is used as the positive electrode material of the lithium-sulfur battery.

4. The use according to claim 3, characterized in that: The mass ratio of the niobium boride-niobium oxide composite three-dimensional material to graphyne is 1:2-5, and the mass ratio of the composite material to the active material sublimated sulfur is 2-4.5:6.5-8.

5.

5. The use according to claim 3, characterized in that: Use a forced air drying oven or a tube furnace to heat to 140-170°C and maintain the constant temperature for 4-20 hours.

6. An application of a niobium boride-niobium oxide composite three-dimensional material prepared by the preparation method according to claim 1, characterized in that: The niobium boride-niobium oxide composite three-dimensional material is used as a negative electrode active material in a lithium ion battery.

7. The use according to claim 6, characterized in that: The niobium boride-niobium oxide composite three-dimensional material is dispersed in a solvent as the negative electrode active material with a conductive agent and a binder to obtain a negative electrode slurry. The negative electrode slurry is coated on a current collector, and the negative electrode sheet is obtained after heating, drying, rolling and punching.

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