A composite single crystal sodium vanadium oxyfluorophosphate material with a nanocarbon material, and a preparation method and application thereof

Abstract

The present invention discloses a nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material, its preparation method and application. A vanadium source compound and a reducing agent compound are dissolved in water, heated and stirred for a reduction reaction, and a sodium source compound, a fluorine source compound and a phosphorus source compound are added to obtain a mixed solution; the nano-carbon material is dispersed in water to obtain a dispersion liquid, and the dispersion liquid is mixed with the mixed solution to obtain a reaction solution; the reaction solution is added to a hydrothermal reactor for hydrothermal reaction and subjected to multiple washing treatments to obtain a nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate precursor; after drying and grinding, heat treatment and cooling are carried out to obtain the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material; through the nano-carbon material composite single-crystal, the present invention can form carbon material-single-crystal surface adhesion, surface embedding and bulk phase penetration structures, which can effectively improve the electron / ion transport efficiency, specific capacity, cycle efficiency, rate performance and cycle stability of the sodium vanadium oxyfluorophosphate material.

Description

Technical Field

[0001] The present invention belongs to the field of sodium-ion batteries, relates to a cathode material for sodium-ion batteries, and particularly relates to a nano-carbon material composite single-crystal sodium vanadium fluorophosphate material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the intermittency and uncertainty of green energy power generation, it is imperative to develop and utilize large-scale energy storage devices. Since the large-scale commercial application of lithium-ion batteries in 1991, they have been widely used in the fields of energy storage devices, new energy vehicles, and 3C electronic devices. However, the limited lithium resources and the continuously expanding demand have led to a rapid increase in the prices of basic lithium battery materials such as lithium carbonate / lithium hydroxide. Therefore, it is extremely urgent to develop new electrochemical energy storage batteries with excellent quality and low cost. Sodium-ion batteries have a rocking-chair charge and discharge mechanism similar to that of lithium-ion batteries; at the same time, sodium resources are abundant, the cost is low, and the processing technology is mature. Therefore, sodium-ion batteries have become the best choice and the best alternative to relieve the application pressure of lithium-ion batteries.

[0003] Sodium-ion batteries are mainly composed of a cathode material, an anode material, a separator, an electrolyte, a current collector, and a casing. Among them, the cathode material generally accounts for the highest cost proportion, and at the same time, the cathode material is also the bottleneck that determines the electrochemical performance of the battery at present. Sodium vanadium fluorophosphate (Na3V2O2(PO4)2F) is a very promising cathode material for sodium-ion batteries, which has the advantages of high potential and high energy density. However, there are problems such as low intrinsic electronic conductivity, poor crystallinity in the sol-gel method synthesis, many defects, and easy decomposition at high-temperature sintering. Modifying sodium vanadium fluorophosphate to obtain a cathode material for sodium-ion batteries with excellent performance is an important research topic at present. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a nano-carbon material composite single-crystal sodium vanadium fluorophosphate material, a preparation method thereof, and an application thereof, so as to solve the technical problems such as low intrinsic electronic conductivity, poor crystallinity in the sol-gel method synthesis, many defects, and easy decomposition at high-temperature sintering of sodium vanadium fluorophosphate in the prior art.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method of a nano-carbon material composite single-crystal sodium vanadium fluorophosphate material, comprising the following steps:

[0007] 1) Dissolve a vanadium source compound and a reducing agent compound in water, heat and stir until the vanadium ions are reduced and appear green, then add a sodium source compound, a fluorine source compound, and a phosphorus source compound to obtain a mixed solution. The molar ratio of Na, V, P, and F elements in the obtained mixed solution is 3:2:2:(1-5); disperse the nano-carbon material in water to obtain a dispersion, and mix the dispersion with the mixed solution and stir evenly to obtain a reaction solution;

[0008] 2) Add the reaction solution prepared in step 1) to a hydrothermal autoclave and carry out hydrothermal reaction at 100 - 250 °C for 0.5 h - 50 h to prepare an initial nano-carbon material composite single-crystal sodium vanadyl fluorophosphate mixed solution;

[0009] 3) Centrifuge or filter and wash the initial nano-carbon material composite single-crystal sodium vanadyl fluorophosphate mixed solution prepared in step 2) at a centrifugation rate of 1000 - 12000 r / min for multiple times to obtain a nano-carbon material composite single-crystal sodium vanadyl fluorophosphate precursor;

[0010] 4) Dry and grind the nano-carbon material composite single-crystal sodium vanadyl fluorophosphate precursor in step 3), then heat-treat it in an Ar / N2 atmosphere at a heating rate of 1 - 20 °C / min to 300 - 800 °C for 1 min - 20 h, and then naturally cool it to room temperature to finally obtain a nano-carbon material composite single-crystal sodium vanadyl fluorophosphate material.

[0011] Further, the vanadium source compound in step 1) is one or more of ammonium metavanadate, vanadyl sulfate, vanadium trichloride, vanadyl acetylacetonate, vanadyl oxalate, vanadium pentoxide, vanadium dioxide, vanadium trioxide, sodium metavanadate, and sodium vanadate; the reducing agent compound is one or more of citric acid, glucose, oxalic acid, sucrose, and ascorbic acid.

[0012] Further, the sodium source compound in step 1) is one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium fluoride, sodium sulfate, sodium hydroxide, and sodium nitrate; the phosphorus source compound is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium-containing phosphates, and potassium-containing phosphates; the fluorine source compound is one or more of sodium fluoride, lithium fluoride, ammonium fluoride, and potassium fluoride.

[0013] Further, the nano-carbon material is a carbon material with at least one dimension of the dispersed phase scale less than 100 nm, including graphene, carbon nanotubes, carbon nanofibers, and nano-carbon spheres.

[0014] Further, the nano-carbon material is one or several of non-functionalized, hydroxylated, aminated, nitrated, carboxylated, sulfonated, and free-radical addition-modified nano-carbon materials.

[0015] Further, the specific method for preparing the dispersion of the nano-carbon material in step 1) is: the nano-carbon material is subjected to ice-water bath ultrasonic dispersion treatment in an ultrasonic instrument or a cell disruptor, or is subjected to ball milling dispersion treatment to obtain a dispersion.

[0016] Further, when the dispersion is mixed with the mixed solution in step 1), the addition amount of the nano-carbon material is 0.01 - 50% of the mass of sodium vanadyl fluorophosphate expected to be generated in the mixed solution.

[0017] Further, in the step 1), the temperature for the reduction reaction of vanadium ions when the vanadium source compound and the reducing agent compound are dissolved in water and the temperature is raised is 20-180 °C, and the time is 0.1-10 h.

[0018] Application of a nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material as a cathode material in a sodium-ion battery.

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

[0020] 1) By adopting the preparation method of the present invention, the nano-carbon material adheres to the surface, is embedded in the surface and penetrates the single crystal of sodium vanadium oxyfluorophosphate in the bulk phase and is coated on the surface of the single crystal of sodium vanadium oxyfluorophosphate. On the one hand, the three-dimensional conductive network of the nano-carbon material inside and on the surface of the formed single crystal particles provides more channels for the diffusion of sodium ions and the conduction of electrons. On the other hand, the surface defects of the nano-carbon material during the hydrothermal process induce the nucleation of sodium vanadium oxyfluorophosphate and the rapid growth of crystal grains, significantly improving the yield and particle size of the single crystal of sodium vanadium oxyfluorophosphate, thereby greatly improving the specific capacity, cycle efficiency, rate performance and cycle stability of the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material; the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material prepared by the present invention is different from the simple carbon-coated structure on the surface of the existing cathode material. First, the present invention prepares large particle single crystal materials, rather than simple polycrystalline particle mixtures. At the same time, the large particle single crystal and the nano-carbon material prepared by the present invention form different novel composite structures such as surface coating, surface embedding and bulk phase penetration, which can improve the electronic and ionic conductivity on the surface and inside of the single crystal, and is the key technology to promote the industrial application of large particle single crystals of phosphates.

[0021] 2) In the preparation process of the present invention, the hydrothermal method is selected for the hydrothermal reaction, and the chemical reaction raw materials are uniformly mixed at the molecular ion level in a liquid phase environment at a low temperature (below 250 °C) to synthesize single crystal particles of sodium vanadium oxyfluorophosphate. After heat treatment (300-800 °C), the crystallinity of the material is further improved, and the internal defects of the single crystal are reduced, thereby effectively ensuring the crystallinity of the material and shortening the sintering time, suppressing the decomposition reaction of the material, and making the prepared nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material have higher specific capacity, rate performance and better cycle stability when assembled as a cathode material in a sodium-ion battery. Description of the Drawings

[0022] Figure 1 Microscopic SEM image of the NVPF-10 sample prepared for Comparative Example 1;

[0023] Figure 2 Microscopic SEM image of the NVPF@CNTs-pure-10 sample prepared for Example 1;

[0024] Figure 3Microscopic SEM images of the NVPF@CNTs-OH-10 sample prepared in Example 2;

[0025] Figure 4 Microscopic SEM images of the NVPF@CNTs-NH2-10 sample prepared in Example 3;

[0026] Figure 5 Microscopic SEM images of the NVPF@CNTs-SO3H-10 sample prepared in Example 4;

[0027] Figure 6 Microscopic SEM images of the NVPF@CNTs-COOH-0.5 sample prepared in Example 5;

[0028] Figure 7 Microscopic SEM images of the NVPF@CNTs-COOH-50 sample prepared in Example 6;

[0029] Figure 8 Microscopic SEM images of the NVPF-50 sample prepared in Comparative Example 2;

[0030] Figure 9 Microscopic SEM images of the NVPF@SP-NH2-20 sample prepared in Example 9;

[0031] Figure 10 Microscopic SEM images of the NVPF@CNF-NH2-20 sample prepared in Example 9;

[0032] Figure 11 Microscopic SEM images of the NVPF@RGO-NH2-20 sample prepared in Example 10;

[0033] Figure 12 High-magnification SEM images of the NVPF@CNTs-NH2-10 sample in Example 3;

[0034] Figure 13 XRD patterns of the NVPF-10, NVPF@CNTs-pure-10, NVPF@CNTs-OH-10, NVPF@CNTs-NH2-10, NVPF@CNTs-SO3H-10, and NVPF@CNTs-COOH-0.5 samples;

[0035] Table 1 shows the 0.2C-1C cycling performance graphs of the NVPF-10, NVPF@CNTs-pure-10, NVPF@CNTs-OH-10, NVPF@CNTs-NH2-10, NVPF@CNTs-SO3H-10, and NVPF@CNTs-COOH-0.5 samples after heat treatment at 600 °C for 2 h in an argon atmosphere. Detailed implementation mode

[0036] The following further elaborates on the present invention in detail in conjunction with specific embodiments, which is an explanation rather than a limitation of the present invention.

[0037] The preparation method of the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material proposed by the present invention utilizes the high electronic conductivity and surface groups of the nano-carbon material to realize the in-situ growth of single-crystal sodium vanadium oxyfluorophosphate particles induced by the surface groups of the nano-carbon material, so as to adhere, surface-embed, and bulk-phase penetrate the single-crystal sodium vanadium oxyfluorophosphate on the surface of the nano-carbon material and coat it on the surface of the single crystal, thereby improving the specific capacity, cycle efficiency, rate performance, and cycle stability of the obtained product, the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material (sodium vanadium oxyfluorophosphate@C single-crystal composite material), so as to be used as a cathode material in sodium-ion batteries, and further obtaining a sodium-ion battery with excellent electrochemical performance.

[0038] In order to enable those skilled in the art to further understand the technical solution of the present invention, the technical solution of the present invention is further elaborated in detail below in the form of embodiments.

[0039] Example 1

[0040] The preparation method of the carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate material in this example includes the following steps:

[0041] 1) According to the elemental molar ratio of Na:V:P:F = 3:2:2:3, weigh a certain mass of NH4VO3 and oxalic acid and dissolve them in 45 mL of water. Heat to 70 °C and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and NH4H2PO4 and continue stirring for 1 h to obtain a uniformly mixed mixed solution mainly composed of sodium vanadium oxyfluorophosphate.

[0042] 2) Add non-functionalized carbon nanotubes (tube diameter 50 nm) and a dispersant to a beaker containing 40 mL of water, and perform ice-water bath ultrasonic dispersion in an ultrasonic cell crusher to obtain a dispersion.

[0043] 3) Mix the dispersion with the mixed solution in step 1) at 5% of the mass of sodium vanadium oxyfluorophosphate in the mixed solution by carbon nanotubes. The mixed solution is placed on a magnetic stirring table and stirred for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution.

[0044] 4) Add the reaction solution to a 100 mL hydrothermal autoclave, keep it at 180 °C in a blast drying oven for 10 h, and then perform centrifugal cleaning with ultrapure water three times and alcohol twice (10000 r / min) to obtain a carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate precursor, denoted as NVPF@CNTs-pure-10 sample.

[0045] 5) The prepared carbon nanotube composite single-crystal sodium vanadium fluorophosphate precursor was dried in a blast dryer at 80 °C for 12 h, and then ground in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0046] 6) The powdery material was placed in a tubular furnace and heat-treated at 600 °C for 2 h under Ar atmosphere protection. After that, the sample was taken out and ground twice. The obtained carbon nanotube composite single-crystal sodium vanadium fluorophosphate material was denoted as NVPF@CNTs-pure-10-S composite material.

[0047] Example 2

[0048] The preparation method of the carbon nanotube composite single-crystal sodium vanadium fluorophosphate material in this example includes the following steps:

[0049] 1) According to the element molar ratio of Na:V:P:F = 3:2:2:3, a certain mass of NH4VO3 and oxalic acid were weighed and dissolved in 45 mL of water. The temperature was raised to 70 °C and stirred at 400 r / min for 3 h until the vanadium ions were reduced to green. Then, NaF and NH4H2PO4 were added and stirring was continued for 1 h to obtain a uniformly mixed liquid mainly composed of sodium vanadium fluorophosphate;

[0050] 2) Hydroxylated carbon nanotubes (with a diameter of 50 nm) and a dispersant were added to a beaker containing 40 mL of water, and ultrasonic dispersion was carried out in an ice-water bath using an ultrasonic cell disruptor to obtain a dispersion;

[0051] 3) The dispersion was mixed with the mixed solution in step 1) at a ratio of 5% of the mass of carbon nanotubes to sodium vanadium fluorophosphate in the mixed solution. The mixed solution was placed on a magnetic stirring table and stirred for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution;

[0052] 4) The reaction solution was added to a 100 mL hydrothermal autoclave and maintained at 180 °C for 10 h in a blast drying oven. Then, it was centrifugally washed three times with ultrapure water and twice with alcohol (10000 r / min) to obtain a carbon nanotube composite single-crystal sodium vanadium fluorophosphate precursor, denoted as NVPF@CNTs-OH-10 sample.

[0053] 5) The prepared carbon nanotube composite single-crystal sodium vanadium fluorophosphate precursor was dried in a blast dryer at 80 °C for 12 h, and then ground in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0054] 6) The powdery material was placed in a tubular furnace and heat-treated at 600 °C for 2 h under Ar atmosphere protection. After that, the sample was taken out and ground twice. The obtained carbon nanotube composite single-crystal sodium vanadium fluorophosphate material was denoted as NVPF@CNTs-OH-10-S composite material.

[0055] Example 3

[0056] The preparation method of the carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate material in this example includes the following steps:

[0057] 1) According to the elemental molar ratio of Na:V:P:F = 3:2:2:3, weigh a certain mass of NH4VO3 and oxalic acid and dissolve them in 45 mL of water. Heat to 70 °C and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and NH4H2PO4 and continue stirring for 1 h to obtain a uniformly mixed liquid mainly composed of sodium vanadium oxyfluorophosphate;

[0058] 2) Add the amino-functionalized carbon nanotubes (with a diameter of 50 nm) and a dispersant into a beaker containing 40 mL of water, and perform ice-water bath ultrasonic dispersion in an ultrasonic cell disruptor to obtain a dispersion;

[0059] 3) Mix the dispersion with the mixed solution in step 1) according to 5% of the mass of the carbon nanotubes in the sodium vanadium oxyfluorophosphate in the mixed solution. Stir the mixed solution on a magnetic stirring table for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution;

[0060] 4) Add the reaction solution to a 100 mL hydrothermal autoclave, keep it at 180 °C in a blast drying oven for 10 h, and then perform three centrifugal cleanings with ultrapure water and two centrifugal cleanings with alcohol (10000 r / min) to obtain the carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate precursor, denoted as NVPF@CNTs-NH2-10 sample.

[0061] 5) Dry the prepared carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate precursor in a blast drying oven at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0062] 6) Put the powdery material into a tubular furnace, perform heat treatment at 600 °C for 2 h under Ar atmosphere protection, then take out the sample and grind it twice. The obtained carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate material is denoted as NVPF@CNTs-NH2-10-S composite material.

[0063] Example 4

[0064] The preparation method of the carbon nanotube composite single-crystal sodium vanadium oxyfluorophosphate material in this example includes the following steps:

[0065] 1) Weigh a certain mass of NH4VO3 and oxalic acid and dissolve them in 45 mL of water according to the molar ratio of elements Na:V:P:F = 3:2:2:3. Heat the solution to 70 °C and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and NH4H2PO4 and continue stirring for 1 h to obtain a uniformly mixed solution mainly composed of sodium vanadium oxyfluorophosphate.

[0066] 2) Add sulfonated functionalized carbon nanotubes (with a diameter of 50 nm) and a dispersant into a beaker containing 40 mL of water, and perform ultrasonic dispersion in an ice-water bath using an ultrasonic cell disruptor to obtain a dispersion.

[0067] 3) Mix the dispersion with the mixed solution from step 1) at a ratio of 5% of the mass of carbon nanotubes to sodium vanadium oxyfluorophosphate in the mixed solution. Stir the well-mixed solution on a magnetic stirring platform for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution.

[0068] 4) Add the reaction solution into a 100 mL hydrothermal autoclave, keep it at 180 °C in a blast drying oven for 10 h, and then centrifuge and wash it three times with ultrapure water and twice with alcohol (at 10000 r / min) to obtain a carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate precursor, denoted as the NVPF@CNTs-SO3H-10 sample.

[0069] 5) Dry the prepared carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate precursor in a blast drying oven at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material.

[0070] 6) Place the powdery material in a tubular furnace, perform heat treatment at 600 °C for 2 h under Ar atmosphere protection, then take out the sample and grind it again. The obtained carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material is denoted as the NVPF@CNTs-SO3H-10-S composite material.

[0071] Example 5

[0072] The preparation method of the carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material in this example includes the following steps:

[0073] 1) Weigh a certain mass of V2O5 and citric acid and dissolve them in 50 mL of water according to the molar ratio of elements Na:V:P:F = 3:2:2:3. Heat the solution to 100 °C and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and (NH4)2HPO4 and continue stirring for 1 h to obtain a uniformly mixed solution mainly composed of sodium vanadium oxyfluorophosphate.

[0074] 2) Add carboxylated carbon nanotubes (with a diameter of 50 nm) and a dispersant into a beaker containing 40 mL of water, and perform ultrasonic dispersion in an ice-water bath using an ultrasonic cell disruptor to obtain a dispersion;

[0075] 3) Mix the dispersion with the mixed solution in step 1) at a ratio of 5% of the mass of carbon nanotubes to the sodium vanadyl phosphate fluoride in the mixed solution. Stir the well-mixed solution on a magnetic stirring table for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution;

[0076] 4) Add the reaction solution into a 100 mL hydrothermal autoclave, maintain it at 250 °C in a blast drying oven for 0.5 h, and then perform centrifugal cleaning three times with ultrapure water and twice with alcohol (10000 r / min) to obtain a carbon nanotube composite single crystal sodium vanadyl phosphate fluoride precursor, denoted as NVPF@CNTs-COOH-0.5 sample.

[0077] 5) Dry the prepared carbon nanotube composite single crystal sodium vanadyl phosphate fluoride precursor by blowing air at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0078] 6) Place the powdery material in a tubular furnace, perform heat treatment at 300 °C for 20 h under Ar atmosphere protection, then take out the sample and grind it twice. The obtained carbon nanotube composite single crystal sodium vanadyl phosphate fluoride material is denoted as NVPF@CNTs-COOH-0.5-S composite material.

[0079] Example 6

[0080] The preparation method of the carbon nanotube composite single crystal sodium vanadyl phosphate fluoride material in this example includes the following steps:

[0081] 1) Weigh a certain mass of NH4VO3 and sucrose and dissolve them in 45 mL of water according to the element molar ratio of Na:V:P:F = 3:2:2:1. Heat it to 70 °C and stir at 400 r / min for 3 h until the vanadium ions are reduced to green, then add NaF and H3PO4 and continue stirring for 1 h to obtain a well-mixed mixed solution mainly composed of sodium vanadyl phosphate fluoride;

[0082] 2) Add carboxylated carbon nanotubes (with a diameter of 50 nm) and a dispersant into a beaker containing 40 mL of water, and perform ultrasonic dispersion in an ice-water bath using an ultrasonic cell disruptor to obtain a dispersion;

[0083] 3) Mix the dispersion with the mixed solution in step 1) at a ratio of 5% of the mass of carbon nanotubes to the sodium vanadyl phosphate fluoride in the mixed solution. Stir the well-mixed solution on a magnetic stirring table for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution;

[0084] 4) Add the reaction solution to a 100 mL hydrothermal reactor, maintain it at 120 °C in a blast drying oven for 5 h, and then centrifuge and wash it three times with ultrapure water and twice with alcohol (10,000 r / min) to obtain a carbon nanotube composite single-crystal sodium vanadyl fluorophosphate precursor, denoted as the NVPF@CNTs-COOH-50 sample.

[0085] 5) Dry the prepared carbon nanotube composite single-crystal sodium vanadyl fluorophosphate precursor in a blast drying oven at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0086] 6) Place the powdery material in a tube furnace, perform heat treatment at 800 °C for 1 min under Ar atmosphere protection, then take out the sample and grind it twice. The obtained carbon nanotube composite single-crystal sodium vanadyl fluorophosphate material is denoted as the NVPF@CNTs-COOH-50-S composite material.

[0087] Example 7

[0088] The preparation method of the carbon nanotube composite single-crystal sodium vanadyl fluorophosphate material in this example includes the following steps:

[0089] 1) Weigh a certain mass of vanadyl sulfate and glucose according to the elemental molar ratio of Na:V:P:F = 3:2:2:3, dissolve them in 50 mL of water, heat up to 100 °C, and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and (NH4)2HPO4 and continue stirring for 1 h to obtain a uniformly mixed mixture mainly composed of sodium vanadyl fluorophosphate;

[0090] 2) Add hydroxylated carbon nanotubes (tube diameter 50 nm) and a dispersant to a beaker containing 40 mL of water, and perform ultrasonic dispersion in an ice-water bath using an ultrasonic cell disruptor to obtain a dispersion;

[0091] 3) Mix the dispersion with the mixed solution in step 1) according to 50% of the mass of carbon nanotubes in the sodium vanadyl fluorophosphate in the mixed solution. Stir the mixed solution on a magnetic stirring platform for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution;

[0092] 4) Add the reaction solution to a 100 mL hydrothermal reactor, maintain it at 100 °C in a blast drying oven for 50 h, and then centrifuge and wash it three times with ultrapure water and twice with alcohol (10,000 r / min) to obtain a carbon nanotube composite single-crystal sodium vanadyl fluorophosphate precursor, denoted as the NVPF@CNTs-OH-250-0.5 sample.

[0093] 5) Dry the prepared carbon nanotube composite single-crystal sodium vanadyl fluorophosphate precursor in a blast drying oven at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material;

[0094] 6) The powder material is placed in a tube furnace and heat-treated at 300 °C for 0.1 h under Ar atmosphere protection. Then the sample is taken out and ground twice. The obtained carbon nanotube composite single-crystal sodium vanadium fluorophosphate material is denoted as NVPF@CNTs-OH-250-0.5-S composite material.

[0095] Example 8

[0096] The preparation method of the nano-carbon sphere (Super P) composite single-crystal sodium vanadium fluorophosphate material in this example includes the following steps:

[0097] 1) According to the elemental molar ratio of Na:V:P:F = 3:2:2:1, a certain mass of VCl3 and glucose are weighed and dissolved in 60 mL of water. The temperature is raised to 20 °C and stirred at 400 r / min for 3 h until the vanadium ions are reduced to green. Then NaF and NaH2PO4 are added and stirring is continued for 1 h to obtain a uniformly mixed liquid mainly composed of sodium vanadium fluorophosphate.

[0098] 2) The amino-functionalized nano-carbon spheres and a dispersant are added to a beaker containing 20 mL of water and ball-milled in a ball mill at 400 r / min for 10 h for dispersion to obtain a dispersion.

[0099] 3) The dispersion is mixed with the mixed solution in step 1) at a ratio of 0.1% of the nano-carbon spheres to the mass of sodium vanadium fluorophosphate in the mixed solution. The mixed solution is placed on a magnetic stirring table and stirred for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution.

[0100] 4) The reaction solution is added to a 100 mL hydrothermal autoclave and maintained at 180 °C in a forced-air oven for 20 h. Then it is centrifugally washed three times with ultrapure water and twice with alcohol (12000 r / min) to obtain a nano-carbon sphere composite single-crystal sodium vanadium fluorophosphate precursor, denoted as NVPF@SP-NH2-10 sample.

[0101] 5) The prepared nano-carbon sphere composite single-crystal sodium vanadium fluorophosphate precursor is dried in a forced-air oven at 80 °C for 12 h, and then ground in an agate mortar for 30 min to obtain a uniformly ground powdery material.

[0102] 6) The powder material is placed in a tube furnace and heat-treated at 600 °C for 2 h under Ar atmosphere protection. Then the sample is taken out and ground twice. The obtained nano-carbon sphere composite single-crystal sodium vanadium fluorophosphate material is denoted as NVPF@SP-NH2-20-S composite material.

[0103] Example 9

[0104] The preparation method of the carbon fiber (CNF) composite single crystal sodium vanadium fluorophosphate material of this embodiment includes the following steps:

[0105] 1) Weigh a certain mass of vanadium trioxide, NaF, and NaH2PO4 according to the element molar ratio of Na:V:P:F = 3:2:2:1. Dissolve vanadium trioxide and sucrose in 60 mL of water, heat up to 20 °C, and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and NaH2PO4 and continue to stir for 1 h to obtain a uniformly mixed liquid mainly composed of sodium vanadium fluorophosphate.

[0106] 2) Add the aminated carbon fiber (diameter 50 nm) and a dispersant into a beaker containing 20 mL of water, and ball-mill at 400 r / min in a ball-mill tank for 10 h to disperse and obtain a dispersion.

[0107] 3) Mix the dispersion with the mixed solution in step 1) according to 0.1% of the mass of the carbon fiber to the sodium vanadium fluorophosphate in the mixed liquid. Place the well-mixed solution on a magnetic stirring table and stir for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution.

[0108] 4) Add the reaction solution into a 100 mL hydrothermal autoclave, keep it at 180 °C in a blast drying oven for 20 h, and then centrifuge and wash it three times with ultrapure water and twice with alcohol (10000 r / min) to obtain a carbon fiber composite single crystal sodium vanadium fluorophosphate precursor, denoted as NVPF@CNF-NH2-20 sample.

[0109] 5) Dry the prepared carbon fiber composite single crystal sodium vanadium fluorophosphate precursor by blowing air at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material.

[0110] 6) Put the powdery material into a tubular furnace, perform heat treatment at 600 °C for 2 h under Ar atmosphere protection, then take out the sample and grind it twice. The obtained carbon fiber composite single crystal sodium vanadium fluorophosphate material is denoted as NVPF@CNF-NH2-20-S composite material.

[0111] Example 10

[0112] The preparation method of the graphene (Graphene) composite single crystal sodium vanadium fluorophosphate material of this embodiment includes the following steps:

[0113] 1) Weigh a certain mass of vanadium trioxide, NaF, and NaH₂PO₄ according to the elemental molar ratio of Na:V:P:F = 3:2:2:5. Dissolve vanadium trioxide and sucrose in 60 mL of water, heat it to 20 °C, and stir at 400 r / min for 3 h until the vanadium ions are reduced to green. Then add NaF and NaH₂PO₄ and continue stirring for 1 h to obtain a uniformly mixed solution mainly composed of sodium vanadium oxyfluorophosphate.

[0114] 2) Add the aminated graphene (with a diameter of 50 nm) and a dispersant into a beaker containing 20 mL of water, and ball-mill at 400 r / min in a ball-milling tank for 10 h to obtain a dispersion.

[0115] 3) Mix the dispersion with the mixed solution in step 1) according to 0.1% of the mass of graphene in the sodium vanadium oxyfluorophosphate in the mixed solution. Stir the well-mixed solution on a magnetic stirring platform for 1 h at a magnetic stirring speed of 400 r / min to obtain a reaction solution.

[0116] 4) Add the reaction solution into a 100 mL hydrothermal autoclave, keep it at 180 °C in a blast drying oven for 20 h, and then centrifuge and wash it three times with ultrapure water and twice with alcohol (at 10000 r / min) to obtain a graphene composite single crystal sodium vanadium oxyfluorophosphate precursor, denoted as NVPF@RGO-NH₂-20 sample.

[0117] 5) Dry the prepared graphene composite single crystal sodium vanadium oxyfluorophosphate precursor in a blast drying oven at 80 °C for 12 h, and then grind it in an agate mortar for 30 min to obtain a uniformly ground powdery material.

[0118] 6) Put the powdery material into a tube furnace, and perform heat treatment at 600 °C for 2 h under Ar atmosphere protection. Then take out the sample and grind it twice. The obtained graphene composite single crystal sodium vanadium oxyfluorophosphate material is denoted as NVPF@RGO-NH₂-20-S composite material.

[0119] The vanadium source compound can also be one or more of vanadyl acetylacetonate, vanadium oxyacetylacetonate, vanadium pentoxide, vanadium dioxide, sodium metavanadate, and sodium vanadate; the reducing agent compound can also be ascorbic acid; the sodium source compound can also be one or more of sodium carbonate, sodium bicarbonate, disodium hydrogen phosphate, sodium phosphate, sodium sulfate, sodium hydroxide, and sodium nitrate; the phosphorus source compound can also be one or more of sodium-containing phosphates and potassium-containing phosphates; the fluorine source compound can also be one or more of lithium fluoride, ammonium fluoride, and potassium fluoride.

[0120] The nanocarbon material is a carbon material with at least one dimension of the dispersed phase scale less than 100 nm, and can also be nitrated nanocarbon materials such as graphene, carbon nanotubes, or nanocarbon spheres.

[0121] Comparative Example 1

[0122] The difference between this comparative example and Examples 1-10 is that the in-situ growth of sodium vanadium oxyfluorophosphate single crystal particles induced by carbon nanotubes is not utilized.

[0123] 1) According to Na:V:P:F = 3:2:2:3, a certain mass of NH4VO3 and oxalic acid were weighed and dissolved in 85 mL of water. The temperature was raised to 70 °C and stirred at 400 r / min for 3 h until the vanadium ions were reduced to green. Then, two reagents, NaF and NH4H2PO4, were added and stirred for another 1 h to obtain a uniformly mixed solution. The mixed solution of the raw materials was added to a 100 mL hydrothermal autoclave and maintained at 180 °C in a blast drying oven for 10 h. After centrifugal washing with ultrapure water three times and alcohol twice (8000 r / min), the single crystal sodium vanadium oxyfluorophosphate precursor was obtained, denoted as the NVPF-10 comparative sample.

[0124] 2) The prepared single crystal sodium vanadium oxyfluorophosphate precursor was dried in a blast drying oven at 80 °C for 12 h. After drying, it was ground in an agate mortar for 30 min to obtain a uniformly ground powdery material. The powdery material was placed in a tube furnace and heat-treated at 600 °C for 2 h under Ar atmosphere protection. Then the sample was taken out and ground again. The obtained single crystal sodium vanadium oxyfluorophosphate composite material was denoted as the NVPF-10-S composite material.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Examples 1-10 is that the in-situ growth of sodium vanadium oxyfluorophosphate single crystal particles induced by carbon nanotubes is not utilized.

[0127] 1) According to Na:V:P:F = 3:2:2:3, a certain mass of NH4VO3 and oxalic acid were weighed and dissolved in 85 mL of water. The temperature was raised to 70 °C and stirred at 400 r / min for 3 h until the vanadium ions were reduced to green. Then, two reagents, NaF and NH4H2PO4, were added and stirred for another 1 h to obtain a uniformly mixed solution. The mixed solution of the raw materials was added to a 100 mL hydrothermal autoclave and maintained at 180 °C in a blast drying oven for 50 h. After centrifugal washing with ultrapure water three times and alcohol twice (8000 r / min), the single crystal sodium vanadium oxyfluorophosphate precursor was obtained, denoted as the NVPF-50 comparative sample.

[0128] In step 2), the prepared single crystal sodium vanadium oxyfluorophosphate precursor was dried in a blast drying oven at 80 °C for 12 h. After drying, it was ground in an agate mortar for 30 min to obtain a uniformly ground powdery material. The powdery material was placed in a tube furnace and heat-treated at 600 °C for 2 h under Ar atmosphere protection. Then the sample was taken out and ground again. The obtained single crystal sodium vanadium oxyfluorophosphate composite material was denoted as the NVPF-50-S composite material.

[0129] Figure 1 Microscopic SEM image of the NVPF-10 comparative sample prepared in Comparative Example 1; Figure 2 Microscopic SEM image of the NVPF@CNTs-pure-10 sample prepared in Example 1, Figure 3 Microscopic SEM image of the NVPF@CNTs-OH-10 sample prepared in Example 2, Figure 4 Microscopic SEM image of the NVPF@CNTs-NH2-10 sample prepared in Example 3, Figure 5 Microscopic SEM image of the NVPF@CNTs-SO3H-10 sample prepared in Example 4. By analyzing Figures 1-5 the microscopic organizational structures of the five graphs therein, it can be seen that among them, the functionalized carbon nanotubes affect the grain size of single-crystal sodium vanadium fluorophosphate. The surface groups on the functionalized carbon nanotubes act as heterogeneous nucleation sites during the hydrothermal process, adsorb and aggregate ions, induce nucleation, inhibit homogeneous nucleation during the hydrothermal process, and promote grain growth. As a result, the synthesized single-crystal sodium vanadium fluorophosphate sample has larger single-crystal particles and stronger XRD peak intensity than the comparative sample. Moreover, the hydroxylated carbon nanotubes are successfully embedded on the surface of the single crystal, which can effectively improve the surface electron transport efficiency of the material.

[0130] Figure 6 Microscopic SEM image of the NVPF@CNTs-COOH-0.5 sample prepared in Example 5, Figure 7 Microscopic SEM image of the NVPF@CNTs-COOH-50 sample prepared in Example 6. By analyzing Figure 6 and Figure 7 the microscopic organizational structures of the graphs therein, it can be observed that the carboxylated carbon nanotubes induce the growth process of single-crystal sodium vanadium fluorophosphate during the hydrothermal process.

[0131] Figure 8 Microscopic SEM image of the NVPF-50 comparative sample prepared in Comparative Example 2. Combining Figure 7 with the microscopic SEM image of the NVPF@CNTs-COOH-50 sample prepared in Example 6. By analyzing Figure 7 and Figure 8 the microscopic organizational structures of the graphs therein, it can be clearly seen that the carboxylated carbon nanotubes can induce the growth of sodium vanadium fluorophosphate.

[0132] Figure 9 Microscopic SEM image of the NVPF@SP-NH2-10 sample prepared in Example 8. By analyzing Figure 9 the microscopic organizational structure of the graph therein, it can be seen that the nanocarbon spheres adhere to and embed in the surface of the single crystal.

[0133] Figure 10 Microscopic SEM image of the NVPF@CNF-NH2-20 sample prepared in Example 9, Figure 11Microscopic SEM image of the NVPF@RGO-NH2-20 sample prepared in Example 10. By analyzing Figure 10 and 11 the microscopic organizational structure in the spectrum, it can be seen that carbon fibers and graphene are embedded inside the single crystal, forming a nano-carbon material - single crystal composite structure.

[0134] Figure 12 High-magnification SEM image of the NVPF@CNTs-NH2-10 sample in Example 3. It can be clearly seen from the figure that carbon nanotubes are attached to the surface of the single crystal, embedded in the surface of the single crystal and penetrate through the inside of the single crystal, forming a nano-carbon material - single crystal composite structure.

[0135] Figure 13 XRD patterns of the samples of Comparative Example 1 NVPF-10, Examples 1 - NVPF@CNTs-pure-10, NVPF@CNTs-OH-10, NVPF@CNTs-NH2-10, and NVPF@CNTs-SO3H-10. It can be seen that the peak intensity of sodium vanadium fluorophosphate single crystal induced by amino-functionalized carbon nanotubes is the highest and the crystallinity is the best.

[0136] Table 1

[0137]

[0138] By analyzing Table 1, it can be seen that the initial specific capacities of the samples of Comparative Example 1 NVPF-10-S, Example 1 NVPF@CNTs-pure-10-S, Example 2 NVPF@CNTs-OH-10-S, Example 3 NVPF@CNTs-NH2-10-S, Example 4 NVPF@CNTs-SO3H-10, and Example 5 NVPF@CNTs-COOH-0.5-S at a rate of 0.2C are 118.8, 94.3, 110.7, 124.2, 118.5, and 122.6 mAh g -1 , respectively, and the initial specific capacities at a rate of 1C are 112.9, 93.0, 106.7, 118.2, 107.1, and 122.1 mAh g -1 , respectively. After 800 cycles, the retention rates are 81.6%, 87.8%, 81.8%, 95.0%, 81.2%, and 94.8%, respectively. Finally, among them, the nano-carbon material composite sodium vanadium fluorophosphate single crystal cathode material in Example 3 exhibits the most excellent rate and cycling performance.

[0139] Using the preparation method of the present invention, carbon nanotubes adhere to the surface, are embedded in the surface, and penetrate the bulk of sodium vanadium oxyfluorophosphate single crystals and are coated on the surface of sodium vanadium oxyfluorophosphate single crystals. As shown in the SEM image of Example 3, on the one hand, the three-dimensional conductive network of carbon nanotubes inside and on the surface of the formed single crystal particles provides more channels for sodium ion diffusion and electron conduction. On the other hand, during the hydrothermal process, the surface defects of carbon nanotubes induce the nucleation and growth of sodium vanadium oxyfluorophosphate, significantly increasing the particle size of sodium vanadium oxyfluorophosphate single crystal particles, thereby greatly improving the specific capacity, cycle efficiency, rate performance, and cycle stability of the carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material. As a result, the carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material is used as the positive electrode material of a sodium ion battery, showing more excellent performance than sodium vanadium oxyfluorophosphate and other types of composite materials.

[0140] In the preparation process of the present invention, the hydrothermal method is selected for the hydrothermal reaction. The chemical reaction raw materials are uniformly mixed at the molecular ion level in a liquid phase environment at a low temperature (below 250 °C) to form and grow sodium vanadium oxyfluorophosphate single crystal particles, and then the crystallinity of the material is further improved and the internal defects of the single crystal are reduced after heat treatment (300 - 800 °C). Compared with the traditional sol-gel method and solid-phase sintering method, the hydrothermal method is more likely to form uniform sodium vanadium oxyfluorophosphate single crystal particles in the synthesized product, effectively ensuring the crystallinity of the material, shortening the sintering time, and inhibiting the decomposition reaction of the material. Therefore, the carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material prepared by hydrothermal method has higher specific capacity, rate performance, and better cycle stability when assembled as the positive electrode material in a sodium ion battery. Through X-ray diffraction testing, the peak value of the strongest peak of the sample in Example 3 increased by about 50% compared with the comparison samples in Comparative Examples 1 and 2. At the same time, the electrochemical performance test results show that the specific capacity after 800 cycles at 1C also increased by 10% - 20% compared with the comparison samples, indicating that the addition of carbon nanotubes has a very significant effect on improving the crystallinity and electrochemical performance of the carbon nanotube composite single crystal sodium vanadium oxyfluorophosphate material.

Claims

1. A preparation method of a composite single crystal sodium vanadium oxyfluorophosphate material with a nanocarbon material, characterized in that It includes the following steps: 1) Dissolve the vanadium source compound and the reducing agent compound in water, heat up and stir until the vanadium ions are reduced and show green, then add the sodium source compound, the fluorine source compound and the phosphorus source compound to obtain a mixed solution. The molar ratio of Na, V, P and F elements in the obtained mixed solution is 3:2:2:(1-5); Disperse the nanocarbon material in water to obtain a dispersion, and mix the dispersion with the mixed solution and stir evenly to obtain a reaction solution; The nanocarbon material is one of hydroxylated, aminated, nitrated, carboxylated, sulfonated and free radical adduct nanocarbon materials; 2) Add the reaction solution prepared in step 1) to a hydrothermal reactor and carry out hydrothermal reaction at 100-250 °C for 0.5 h-50 h to prepare an initial nanocarbon material composite single crystal sodium vanadium fluorophosphate mixed solution; 3) Carry out multiple centrifugation or suction filtration cleaning treatment on the initial nanocarbon material composite single crystal sodium vanadium fluorophosphate mixed solution prepared in step 2) at a centrifugation rate of 1000-12000 r / min to obtain a nanocarbon material composite single crystal sodium vanadium fluorophosphate precursor; 4) Dry and grind the nanocarbon material composite single crystal sodium vanadium fluorophosphate precursor in step 3), then heat it to 300-800 °C at a rate of 1-20 °C / min in an Ar / N2 atmosphere for heat treatment for 1 min-20 h, and then naturally cool it to room temperature to finally obtain a nanocarbon material composite single crystal sodium vanadium fluorophosphate material; The prepared nanocarbon material composite single crystal sodium vanadium fluorophosphate material enables the nanocarbon material to adhere to the surface, be embedded in the surface and penetrate the bulk of the sodium vanadium fluorophosphate single crystal and coat the surface of the sodium vanadium fluorophosphate single crystal.

2. The preparation method of the sodium vanadium oxyfluorophosphate material composite with nano-carbon materials according to claim 1, characterized in that: In step 1), the vanadium source compound is one or more of ammonium metavanadate, vanadyl sulfate, vanadium trichloride, vanadium acetylacetonate, vanadyl acetylacetonate, vanadium pentoxide, vanadium dioxide, vanadium trioxide, sodium metavanadate and sodium vanadate; The reducing agent compound is one or more of citric acid, glucose, oxalic acid, sucrose and ascorbic acid.

3. The preparation method of the sodium vanadium oxyfluorophosphate material composite with carbon nanomaterials according to claim 1, characterized in that: In step 1), the sodium source compound is one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium fluoride, sodium sulfate, sodium hydroxide and sodium nitrate; The phosphorus source compound is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, sodium-containing phosphate and potassium-containing phosphate; The fluorine source compound is one or more of sodium fluoride, lithium fluoride, ammonium fluoride and potassium fluoride.

4. The preparation method of the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material according to claim 1, wherein: The nanocarbon material is a carbon material with at least one dimension of the dispersed phase scale less than 100 nm, including graphene, carbon nanotubes, carbon nanofibers and carbon nanospheres.

5. The preparation method of the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material according to claim 1, wherein: The specific method for preparing the dispersion of the nanocarbon material in step 1) is: the nanocarbon material is ultrasonically dispersed in an ice-water bath by an ultrasonic instrument or a cell crusher, or is dispersed by ball milling to obtain a dispersion.

6. The preparation method of the nano-carbon material composite single-crystal sodium vanadium oxyfluorophosphate material according to claim 1, wherein: When the dispersion is mixed with the mixed solution in step 1), the addition amount of the nanocarbon material is 0.01-50% of the mass of sodium vanadium fluorophosphate expected to be generated in the mixed solution.

7. The preparation method of the sodium vanadium oxyfluorophosphate material composite with nano-carbon materials according to claim 1, characterized in that: In step 1), the temperature for the vanadium source compound and the reducing agent compound to be dissolved in water and the vanadium ion reduction reaction to occur during heating is 20-180 °C, and the time is 0.1-10 h.

8. A sodium vanadium oxyfluorophosphate material of a nanocarbon material composite single crystal prepared by the preparation method according to any one of claims 1-7.

9. Use of the sodium vanadium oxyfluorophosphate material of a nanocarbon material composite single crystal as described in claim 8 as a cathode material in a sodium ion battery.

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