Preparation method and application of boron-doped flaky defect niobium titanium oxide material grown on carbon tubes

Abstract

A preparation method and application of a boron-doped niobium-titanium oxide material with flaky defects grown on carbon nanotubes (CNTs) belongs to the technical field of positive electrode materials for lithium-selenium batteries. The method comprises the following steps: dissolving a niobium source, a titanium source, and carbon nanotubes in an organic solvent, adding a surfactant, and then adding an alkali source. After liquid-phase mixing and stirring, the mixture is transferred to a reactor for reaction at a certain temperature and pressure to form a composite precursor; the precursor and the boron source are then placed in a tubular furnace and calcined at high temperature to obtain a boron-doped niobium-titanium oxide composite material with flaky defects grown on CNTs. This composite material is then reacted with selenium to produce a selenium- and boron-doped niobium-titanium oxide composite material with flaky defects grown on CNTs. This composite material, which is used as a positive electrode active material for lithium-selenium batteries, has a flaky structure, boron doping, and oxygen defects that significantly enhance the reactivity of the substrate plane, promote the formation and dissolution of Li2S, and improve the cycling and rate performance of lithium-selenium batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-selenium battery positive electrode materials, and relates to a preparation method of a boron-doped flaky defect niobium-titanium oxide material grown on a carbon tube and its application in lithium-selenium batteries. Background Art

[0002] In recent years, the growing demand for high-energy-density energy storage devices has stimulated the exploration of next-generation lithium-ion battery alternatives. Among the many candidate batteries, lithium-sulfur batteries have attracted great attention due to their high theoretical energy density. As a cognate element of S, Se has a high capacity comparable to S (Se, 3268 mAh cm -3 vs S, 3467mAh cm -3 ), and its conductivity is about 1025 times higher than that of S (Se, 1×10 -5 S cm -1 vs S,5×10 -30 S cm -1 ), enabling faster kinetics. However, the commercialization of lithium-selenium batteries has been hampered by issues such as volume expansion / contraction caused by the large density difference between selenium and the discharge product, lithium selenide, during charge and discharge, slow catalytic reaction kinetics, low selenium utilization, and poor cycling stability due to selenium shuttling between the positive and negative electrodes.

[0003] To address these issues, researchers have designed and synthesized carbon materials with various structures, such as hollow carbon, porous carbon, graphene, and carbon nanotubes. However, traditional carbon materials exhibit weak interactions with polyselenides, resulting in insufficient long-term cycling stability and power characteristics in batteries. Therefore, developing a polar material with strong polarity and high catalytic activity to combine with carbon materials is expected to better modify existing selenium cathodes and improve the active material utilization and cycling performance of lithium-selenium batteries. Summary of the Invention

[0004] In order to improve the utilization rate of active materials and the cycle performance of lithium-selenium batteries, the present invention provides a preparation method of a boron-doped sheet-defect niobium titanium oxide material grown on carbon tubes and its application in lithium-selenium batteries. The specific structure can synergistically improve the conversion efficiency of the active material selenium through physical confinement, chemical adsorption and catalytic conversion. The lithium-selenium battery using this composite positive electrode has excellent cycle performance and fast charging performance.

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

[0006] A method for preparing a boron-doped flaky defect niobium-titanium oxide material grown on a carbon tube comprises the following steps:

[0007] Step 1: Weigh a niobium source and a titanium source in a molar ratio of 2:1, add the mixture to an organic solvent containing single-walled carbon nanotubes, and stir evenly. Then, add a surfactant and an alkali source, and stir at room temperature to mix evenly. Then, transfer the mixed solution to a reactor, place it in a homogeneous reactor, and react at 150-210° C. for 12-36 hours. After the reaction, collect the product by centrifugation with anhydrous ethanol at a centrifuge speed of 5500-8500 r / min, and each centrifugation time is 4-8 minutes. Then, dry the product to obtain a titanium niobium oxide composite precursor grown on the carbon nanotube.

[0008] The mass ratio of the sum of the niobium source and the titanium source to the carbon tube is 0.2-0.5:1;

[0009] The niobium source is one of niobium ethoxide, niobium pentachloride, ammonium niobate oxalate and niobium oxalate;

[0010] The titanium source is one of titanium sulfate, metatitanic acid, tetrabutyl titanate and isopropyl titanate;

[0011] The organic solvent is one or more of ethanol, methanol, cyclohexane, isopropanol, glycerol, tetrahydrofuran, N-methylpyrrolidone and ethylene glycol;

[0012] The surfactant is one of hexamethylenetetramine, cetyltrimethylammonium bromide, ethanolamine and polyvinylpyrrolidone;

[0013] The alkali source is ammonia water, potassium hydroxide and sodium hydroxide;

[0014] The amount of the alkali source is 1.5-6 times the molar ratio of the niobium source, and the amount of the surfactant is 3-5 times the molar ratio of the niobium source;

[0015] Step 2: Place the titanium niobium oxide composite precursor grown on the prepared carbon tube and the boron source in two magnetic boats in a certain proportion, and then transfer them to a tubular furnace for high-temperature calcination treatment at a temperature of 600-900°C and a calcination time of 3-8 hours to obtain boron-doped flaky defect niobium titanium oxide material B-TiNb2O7@CNT grown on carbon tubes.

[0016] The boron source is one of sodium borohydride, boron powder and boron dioxide;

[0017] The mass ratio of the titanium niobium oxide composite precursor grown on the carbon tube to the boron powder is 1:0.6-1.8;

[0018] The protective atmosphere of the tubular furnace is a mixed gas of argon and hydrogen (the volume ratio of argon and hydrogen is 95%:5%), argon, nitrogen, vacuum atmosphere or one of the following;

[0019] An application of a boron-doped flaky defect niobium-titanium oxide material grown on a carbon tube prepared by the preparation method. The boron-doped flaky defect niobium-titanium oxide material grown on a carbon tube is composited with selenium powder and used as a positive electrode material for a lithium-selenium battery, or is used alone as a catalyst for the adsorption of polyselenides.

[0020] When applied to lithium-selenium batteries, the specific application method is: the boron-doped flaky defect niobium-titanium oxide material grown on carbon tubes and the active material selenium powder are ground and mixed into a uniform powder, the powder is placed on a magnetic boat, and transferred to a tubular furnace in an argon atmosphere for constant temperature and high-temperature calcination; it is naturally cooled to room temperature and taken out to obtain a selenium- and boron-doped flaky defect niobium-titanium composite material grown on carbon tubes, which is used as the positive electrode material of the lithium-selenium battery.

[0021] The mass ratio of the boron-doped flaky defect niobium titanium oxide material grown on the carbon tube to the active material selenium powder is 3-5:2-1; the constant temperature of the tube furnace is 240-270° C., and the constant temperature time is 10-18 hours.

[0022] The generated selenium and boron doped sheet-defect niobium titanium oxide composite material grown on carbon tubes is dispersed in a solvent as an active material with a conductive agent and a binder to obtain a positive electrode slurry. The slurry is coated on the positive electrode collector, dried, rolled and punched to obtain a positive electrode sheet, and then a button battery is assembled.

[0023] 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.

[0024] The mass ratio of the positive electrode active material: the conductive agent: the binder is 70%-90%: 5%-20%: 5%-10%. Preferably, the mass ratio of the active material: the conductive agent: the binder is 80%: 10%: 10%.

[0025] The operating temperature range of the lithium-selenium battery is -30°C to 55°C.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) The present invention provides a selenium-based composite material comprising boron-doped defective niobium titanate with a two-dimensional sheet structure, nanotubular carbon, and selenium supported within the carbon nanotubes. Compared to traditional non-polar carbon materials, the niobium titanate grown on the carbon nanotubes can adsorb polyselenides through physical confinement and strong chemical bonding, suppressing the "shuttle effect." Furthermore, boron doping creates an empty σ orbital perpendicular to the substrate plane, maximizing overlap with the Se frontal orbital. The sheet structure and boron doping significantly enhance the reactivity of the substrate plane, promoting the conversion of polyselenides to final products and improving the cycling performance of lithium-selenium batteries.

[0028] 2) The preparation method of the present invention is simple, has mild conditions, a coherent process, strong controllability, low cost, low equipment requirements, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the XRD pattern of the boron-doped niobium-titanium oxide material grown on carbon nanotubes with plate-like defects synthesized in Example 1;

[0030] Figure 2 This is an SEM image of the boron-doped niobium-titanium oxide material grown on carbon nanotubes with plate-like defects synthesized in Example 1;

[0031] Figure 3 The cycle performance of the lithium-selenium battery of Example 1 at 0.5C;

[0032] Figure 4 The charge and discharge capacities of the lithium-selenium battery of Example 2 at different rates. DETAILED DESCRIPTION

[0033] 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.

[0034] Example 1:

[0035] The synthesis of a boron-doped flaky defect niobium-titanium oxide material grown on carbon nanotubes comprises the following steps:

[0036] Step 1: Dissolve 0.4g of niobium pentachloride, 0.252g of tetrabutyl titanate and 1.96g of single-walled carbon nanotubes in a mixed solution consisting of 25mL of ethylene glycol and 10mL of isopropanol, and place it on a magnetic stirrer and stir continuously for 30min. Subsequently, add 0.98g of urotropine and 0.4g of sodium hydroxide to the above mixed solution, stir at 30°C for 5h to mix it evenly, then transfer it to a 50mL reactor and heat it continuously at 190°C in a homogeneous reactor for 24h. After the reaction is completed, the product is centrifuged with anhydrous ethanol and collected after centrifugation at 7000rpm for 5 times. The product is then transferred to a vacuum oven for drying to obtain a titanium niobium oxide composite precursor grown on carbon tubes.

[0037] Step 2: Weigh the titanium niobium oxide composite precursor and boron powder in a mass ratio of 1:0.8, place the powders in two magnetic boats, transfer them to an argon atmosphere in a tube furnace, and heat at 5°C min -1 The temperature was raised to 750℃ at a rate of 100℃ and then calcined at 750℃ for 4 hours to obtain boron-doped flaky defect niobium titanium oxide material grown on carbon nanotubes. The XRD spectrum is shown in Figure 2. Figure 1 As shown, the positions of all diffraction peaks in the figure are consistent with the TiNb2O7 (JCPDS card no.77-1374) standard card. Figure 2 This is a SEM image of the boron-doped niobium titanium oxide material with sheet-like defects grown on carbon nanotubes. As can be seen from the image, niobium titanium oxide grows in sheet-like shapes on the carbon nanotube substrate, with a length of about 500 nm.

[0038] The boron-doped flaky defect niobium titanium oxide material grown on carbon tubes obtained in this embodiment and the selenium powder composite are used as positive electrode materials in lithium-selenium batteries, or used alone as a catalyst for the adsorption of polyselenides, thereby inhibiting the "shuttle effect" between polyselenides and improving the active material utilization and cycle stability of lithium-selenium batteries.

[0039] The specific application method is as follows: the prepared boron-doped flaky defect niobium titanium oxide material grown on carbon nanotubes is uniformly mixed with selenium powder in a mass ratio of 3:2. The mixture is added to an agate mortar and ground for 20 minutes until it is fully mixed into a powder with uniform color. The mixture is poured onto weighing paper, then transferred to a magnetic boat, placed in an argon atmosphere in a tube furnace, and heated at 2°C min -1 The sample was heated to 260°C at a heating rate of 1000 nm and calcined at a constant temperature of 260°C for 12 hours. After the time was up, the sample was allowed to stand and naturally cooled to room temperature and then taken out to obtain a mixture of selenium- and boron-doped flaky defect niobium titanium oxide grown on carbon nanotubes.

[0040] A mixture of selenium- and boron-doped flaky defective niobium titanium oxide grown on carbon nanotubes was used as the positive electrode active material of the lithium-selenium battery, with metallic lithium as the negative electrode, and a commercial ether electrolyte dosage of 10 μL mg -1 , assembled lithium selenium batteries and tested the electrochemical performance. The cycling stability at 0.5C is as follows Figure 3 As shown, the discharge capacity of the first cycle of 0.5C activation is 587.4mAhg -1 The first coulombic efficiency is 90.4%, and even at the 80th cycle, the discharge capacity is 459.1 mAh g -1 , higher than pure carbon tube lithium selenium battery (130mAhg -1 ), indicating that the lithium-selenium battery assembled in Example 1 of the present invention has good cycle stability.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that the mixed solvent of 25 mL ethylene glycol and 10 mL isopropanol is replaced with 35 mL ethanol. In addition, hexadecylammonium bromide is added instead of urotropine. The reaction conditions are 180°C for 16 hours. The other parameters are the same as those in embodiment 1. The prepared mixture of selenium and boron-doped sheet-shaped defective niobium titanium oxide grown on carbon tubes is used as the positive electrode active material of the lithium selenium battery to assemble the lithium selenium battery and test the electrochemical performance. The cycle stability at 0.5C is as follows. Figure 4 As shown, the discharge capacity at 0.5C is 616.8mAhg -1 Even when the discharge rate is 3C, the discharge capacity is 454.0mAhg -1 , indicating that the lithium-selenium battery composed of the composite positive electrode has excellent fast charging characteristics.

[0043] Example 3

[0044] This embodiment differs from Example 1 in that the mixed solvent of 25 mL of ethylene glycol and 10 mL of isopropanol is replaced with 20 mL of isopropanol and 10 mL of glycerol; in addition, hexadecylammonium bromide is added instead of hexamine; the reaction conditions are 190° C. for 16 h; the added base is changed from sodium hydroxide to ammonia water; the added boron source is changed to sodium borohydride; the mass ratio of the titanium niobium oxide composite precursor grown on the carbon nanotubes to the boron powder is changed to 1:0.5; and the remaining parameters are the same as in Example 1.

[0045] Example 4

[0046] This embodiment differs from Example 1 in that the mixed solvent of 25 mL of ethylene glycol and 10 mL of isopropanol is replaced with 35 mL of N-methylpyrrolidone; in addition, hexadecylammonium bromide is added instead of hexamine; the added base is changed from sodium hydroxide to ammonia water; and the mass ratio of the titanium niobium oxide composite precursor grown on the carbon nanotubes to the boron powder is changed to 1:1.2. The remaining parameters are the same as those in Example 1.

[0047] Example 5

[0048] This embodiment differs from embodiment 1 in that the mixed solvent of 25 mL of ethylene glycol and 10 mL of isopropanol is replaced with 20 mL of isopropanol and 10 mL of methanol; in addition, polyvinyl pyrrolidone is added instead of hexamethylenetetramine; the reaction conditions are changed to 200° C. for 24 h; the added base is changed from sodium hydroxide to potassium hydroxide; the mass ratio of the titanium niobium oxide composite precursor grown on the carbon nanotubes to the boron powder is changed to 1:1; and the remaining parameters are the same as those in embodiment 1.

[0049] 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 boron-doped flaky defect niobium-titanium oxide material grown on carbon nanotubes, characterized by: The following steps are involved: Step 1: adding a niobium source and a titanium source at a molar ratio of 2:1 to an organic solvent containing single-walled carbon nanotubes and stirring evenly, then adding a surfactant and an alkali source and stirring evenly to obtain a mixed solution; the surfactant is one of urotropine, cetyltrimethylammonium bromide and polyvinylpyrrolidone; the mass ratio of the sum of the niobium source and the titanium source to the single-walled carbon nanotubes is 0.2-0.5:1; the molar ratio of the alkali source is 1.5-6 times that of the niobium source, and the amount of the surfactant is 3-5 times that of the niobium source; Step 2: Transfer the mixed solution to a reaction kettle, place it in a homogeneous reactor and react at 150-210°C for 12-36 hours; Step 3: After the reaction is completed, the solid is collected by centrifugation and dried to obtain a titanium niobium oxide composite precursor grown on the carbon tube; Step 4: Place the titanium niobium oxide composite precursor grown on the carbon tube and the boron source in two magnetic boats respectively and transfer them to a tube furnace for high-temperature calcination. The high-temperature calcination temperature in the tube furnace is 600-900° C. and the calcination time is 3-8 hours to obtain a boron-doped flaky defect niobium titanium oxide material grown on the carbon tube; the mass ratio of the titanium niobium oxide composite precursor grown on the carbon tube to the boron source is 1:0.6-1.8; The boron-doped sheet-defect niobium titanium oxide material grown on the carbon tube is composited with selenium powder as a positive electrode material for a lithium-selenium battery, or is used alone as a catalyst for the adsorption of polyselenides.

2. The preparation method according to claim 1, wherein: In step 1, the niobium source is one of niobium ethanol, niobium pentachloride, ammonium niobate oxalate and niobium oxalate; the titanium source is one of titanium sulfate, metatitanic acid, tetrabutyl titanate and isopropyl titanate; the organic solvent is one of ethanol, methanol, cyclohexane, isopropanol, glycerol, tetrahydrofuran, N-methylpyrrolidone and ethylene glycol, or a combination of several thereof; and the alkali source is ammonia water, potassium hydroxide and sodium hydroxide.

3. The preparation method according to claim 1, wherein: In step 4, the boron source is one of sodium borohydride, boron powder and boron dioxide.

4. The preparation method according to claim 1, wherein: In step 4, the protective atmosphere of the tubular furnace is one of a mixed gas of argon and hydrogen, argon, nitrogen, and a vacuum atmosphere.

5. Use of a boron-doped niobium-titanium oxide material with plate-like defects grown on carbon nanotubes prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The boron-doped flaky defect niobium-titanium oxide material grown on carbon nanotubes is ground and mixed with active material selenium powder into a uniform powder, which is then transferred to a tubular furnace in an argon atmosphere for high-temperature constant-temperature calcination to obtain a selenium- and boron-doped flaky defect niobium-titanium oxide composite material grown on carbon nanotubes, which can be used as the positive electrode active material of a lithium-selenium battery; or used alone as a catalyst for the adsorption of polyselenides.

6. The use according to claim 5, characterized in that: The mass ratio of boron-doped flaky defect niobium titanium oxide material grown on carbon nanotubes to active material selenium powder is 3~5:2~1.

7. The use according to claim 5, characterized in that: The calcination constant temperature of the tubular furnace is 240-270°C and the calcination time is 10-18 hours.

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