Carbon-co-oxide-coated sodium vanadium fluorophosphate composite positive electrode material and preparation method thereof, and sodium ion battery composite positive electrode

Abstract

The invention relates to the field of battery manufacturing, in particular to a carbon-co-oxide-coated sodium vanadium fluorophosphate composite positive electrode material and a preparation method thereof and a sodium ion battery composite positive electrode. The preparation method comprises the steps that a carbon source is added into mixed acid for reaction, then KMnO4 is added for water bath reaction, and the carbon-co-oxide-coated sodium vanadium fluorophosphate composite positive electrode material is obtained; finally, adding a hydrogen peroxide solution for a co-oxidation reaction, and washing and drying after the reaction to obtain a co-oxidation carbon source; wherein the carbon source is a mixture of a one-dimensional carbon source and a two-dimensional carbon source; mixing and grinding the co-oxidation carbon source obtained in the step 1 with a vanadium source, a sodium source, phosphate and a fluorine source to obtain precursor powder, and presintering the precursor powder to obtain a sodium vanadium fluorophosphate intermediate product; and sintering the sodium vanadium fluorophosphate intermediate product at high temperature to obtain the carbon-co-oxide-coated sodium vanadium fluorophosphate composite positive electrode material. The prepared positive electrode material has the advantages of high conductivity, high magnification, high discharge capacity, high power and good cycle stability, and can be used for preparing a sodium ion battery composite positive electrode.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing, specifically to a co-oxidized carbon-coated sodium vanadium fluoride phosphate composite cathode material, its preparation method, and a sodium-ion battery composite cathode. Background Technology

[0002] Energy security, as a core component of the national security system, is a crucial foundation for maintaining the sustainable development of the national economy and a "strategic resource" driving high-quality economic development. Building a new energy system urgently requires the development of electrochemical energy storage technologies that combine high energy density, high power density, low cost, and long cycle life. Among numerous energy storage solutions, sodium-ion batteries have become a global research hotspot due to their significant resource endowment advantages (sodium is abundant in the Earth's crust at 2.74%) and cost competitiveness (raw material costs are 30%–50% lower than lithium batteries). This technology not only shares a similar working principle with lithium-ion batteries but is also compatible with existing mature lithium battery production processes, thus being regarded as a strategic solution for large-scale energy storage.

[0003] As a core component of sodium-ion batteries, the cathode material directly determines the battery's energy density and overall performance. Developing cathode active materials with high specific capacity, excellent rate performance, and long cycle stability is a key technological challenge for advancing the commercial application of sodium-ion batteries. Among numerous candidate materials, sodium vanadium fluoride phosphate (Na3V2(PO4)2F3) stands out due to its high operating voltage platform (-3.8 V vs. Na...). + With its high theoretical specific capacity (128 mAh / g) and vanadium fluoride (Na₂F), sodium fluoride is widely recognized as one of the most promising high-energy-density sodium electrode materials. However, as a typical representative of vanadium-based polyanionic compounds, sodium fluoride is still limited by its low intrinsic electronic conductivity (-10 mAh / g). -10 Bottlenecks such as S / cm and sluggish ion diffusion kinetics have resulted in its actual electrochemical performance falling far short of theoretical expectations.

[0004] CN105655565 A discloses a composite cathode material for sodium-ion batteries and its preparation method. This method improves the electronic conductivity of sodium vanadium phosphate and sodium fluorophosphate, as well as the rate performance and cycle performance of the battery, by coating nanoscale sodium vanadium phosphate and sodium fluorophosphate with an amorphous carbon layer. Utilizing the strong adhesion properties of dopamine during polymerization, it is used as a carbon source and calcined to form a complete amorphous carbon coating layer, increasing electron transport in the active material. Then, a conductive polymer is introduced after polymerization. This method improves the overall rate performance and cycle performance of the composite cathode material to some extent. However, due to the structural limitations of amorphous carbon, problems such as low specific capacity and unsatisfactory long-cycle performance still exist.

[0005] In recent years, carbon coating and ion doping technologies have gradually become research hotspots for improving the performance of sodium vanadium fluorophosphate. However, these methods are generally complex to operate, costly, and their effectiveness needs further improvement. Therefore, it is necessary to continue to seek new improvement methods to enhance battery performance and reduce costs. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems and provide a co-oxide carbon-coated sodium vanadium fluorophosphate composite cathode material with high discharge capacity, high power, excellent cycle stability, high conductivity, and high rate capability.

[0007] Another objective of this invention is to provide a method for preparing a co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material that uses simple raw materials, involves a simple process, and has low cost.

[0008] The present invention also provides a sodium-ion battery composite cathode containing the above-mentioned co-oxidized carbon-coated sodium vanadium fluoride phosphate composite cathode material.

[0009] The technical solution describes a method for preparing a carbon-coated sodium vanadium fluorophosphate composite cathode material, comprising the following steps: Step 1: Add the carbon source to the mixed acid for reaction, then add KMnO4 for water bath reaction, and finally add hydrogen peroxide solution for co-oxidation reaction. After the reaction, wash and dry to obtain the co-oxidized carbon source; wherein, the carbon source is a mixture of one-dimensional carbon source and two-dimensional carbon source.

[0010] Step 2: The co-oxidation carbon source obtained in Step 1 is mixed with vanadium source, sodium source, phosphate and fluorine source and ground into a precursor powder. The precursor powder is pre-sintered at 300℃~400℃ for 4~6h under a protective atmosphere to obtain sodium fluorophosphate intermediate. Step 3: The sodium vanadium fluorophosphate intermediate obtained in Step 2 is sintered at 550℃~800℃ for 6~10h under a protective atmosphere to obtain a carbon-coated sodium vanadium fluorophosphate composite cathode material.

[0011] Here, the one-dimensional carbon source refers to carbonaceous raw materials with one-dimensional nanostructures, which mainly act as "conductive bridges" in composite materials, such as carbon nanotubes, carbon nanofibers, or carbon nanowires. The two-dimensional carbon source can be listed as graphene, mesophase carbon microspheres, acetylene black, flake graphite, or porous carbon, which serve as "supporting structures." The two sources increase interfacial bonding by introducing various functional groups such as hydroxyl and carboxyl groups. Compared with the traditional single oxidation strategy, this co-oxidation strategy forms a more stable and conductive three-dimensional network structure.

[0012] Preferably, in step 1, the mixing mass ratio of the one-dimensional carbon source and the two-dimensional carbon source is 1 to 3:1.

[0013] In step 1, the reaction temperature of the carbon source and the mixed acid is 25-40°C, and the reaction time is 20 min. The mixed acid is any two of sulfuric acid, hydrochloric acid, or nitric acid. The amount of carbon source added is 2% of the mass of the mixed acid. Adding too much carbon source will result in insufficient oxidation of some carbon materials, resulting in an incomplete structure. Adding too little carbon source will result in over-oxidation and destruction of the carbon material structure.

[0014] In step 1, the amount of KMnO4 added is 1 to 1.2 times the mass of the carbon material. If the amount added is too high, the reaction will be extremely violent, resulting in exothermic runaway and destructive damage to the carbon structure. If the amount added is too low, the oxidation process will be uneven. After adding KMnO4, the water bath reaction temperature is 30 to 50°C, and the reaction time is 3 to 5 hours. Preferably, after the water bath reaction, water can be added and the mixture can be left to stand for a period of time to release the heat of reaction.

[0015] In step 1, the amount of hydrogen peroxide added is 10% of the amount of KMnO4 added, to fully reduce high-valence manganese impurities. Insufficient addition will lead to impure products, while excessive addition may cause structural damage and physical harm, both of which need to be avoided. The co-oxidation reaction temperature is 35–40°C. Compared to high temperatures, room temperature reactions are milder, which is beneficial for introducing oxygen-containing functional groups while maximizing the preservation of the overall network structure of the composite carbon material and reducing voids and fragments caused by excessive oxidation.

[0016] In step 2, the amount of the co-oxidized carbon source added is 5% to 30% of the total mass of the vanadium source, sodium source, phosphate, and fluorine source.

[0017] In step 2, the molar ratio of sodium, vanadium, phosphorus, and fluorine in the vanadium source, sodium source, phosphate, and fluorine source is 3:2:2:3. Further, the vanadium source is at least one of V₂O₃, NaVO₃, Na₃VO₄, V₂O₅, or NH₄VO₃. The sodium source is at least one of NaOH, CH₃COONa, NaNO₃, Na₂CO₃, NaF, NaH₂PO₄, Na₂HPO₄, or Na₃PO₄. The phosphate is at least one of NH₄H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄, NaH₂PO₄, Na₂HPO₄, or Na₃PO₄. The fluorine source is at least one of NaF and NH₄F. Preferably, in step 2, the mixing and grinding step can use various existing grinding methods to mix the raw materials evenly, such as ball milling, with a rotation speed of 400-600 rpm and a time of 4-8 hours. The ball milling solvent can be at least one of deionized water, methanol, and ethanol. After ball milling, the material is dried to obtain precursor powder.

[0018] The co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material of the present invention is prepared by the above-described preparation method.

[0019] The present invention relates to a sodium-ion battery composite cathode, comprising a substrate and a coating material on the surface of the substrate, wherein the coating material comprises at least the aforementioned co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material, a conductive material, and a binder.

[0020] Beneficial effects: 1) This invention ingeniously utilizes the microscopic composite of one-dimensional and two-dimensional carbon sources, essentially constructing a "multi-dimensional, multi-scale carbon network." The one-dimensional carbon source plays multiple roles as a "conductive bridge" and "structural bridge," while the two-dimensional carbon source provides a "conductive plane" and a "mechanical matrix." This synergistic effect fundamentally solves the respective bottlenecks of easy stacking of two-dimensional carbon sources and easy agglomeration of one-dimensional carbon sources, giving rise to groundbreaking applications in energy storage, conversion, flexible electronics, and high-end composite materials. This is a paradigm of designing material properties at the nanoscale. Further considering the distribution of both in the conductive three-dimensional network, the amount of one-dimensional carbon source added should not be less than that of two-dimensional carbon source. The preferred mixing mass ratio of the two-dimensional carbon source is 1–3:1. Excessive addition of one-dimensional carbon source will lead to agglomeration, while insufficient addition will result in an unstable three-dimensional network structure that is easily destroyed.

[0021] 2) In this invention, a carbon source is reacted with mixed acid to achieve intercalation and preliminary oxidation of multiple carbon materials. KMnO4 is then added to react and the three-dimensional framework is oxidized in a deep and controllable manner, introducing oxygen-containing functional groups such as hydroxyl and epoxy groups. Finally, a co-oxidation reaction with hydrogen peroxide is carried out to remove high-valence manganese impurities, resulting in a 3D conductive carbon network with interpenetrating surfaces and lines. The co-oxidized carbon source obtained through the above reaction process has the characteristics of high conductivity and stable 3D structure, and can be widely used as an additive coating material for various battery materials.

[0022] 3) Based on the mixing of one-dimensional and two-dimensional carbon sources used in step 1, to achieve efficient composite carbon oxide material and battery material, the mixed and finely ground precursor powder is sintered twice. During pre-sintering, the temperature is strictly controlled at 300℃~400℃. Excessive pre-sintering temperature leads to fluorine loss, destroying the three-dimensional network structure of the carbon source, which is detrimental to the material's cycle performance and rate performance. Insufficient pre-sintering temperature results in incomplete removal of volatile components from some raw materials, and the unremoved volatile components will destroy the three-dimensional network structure of the carbon source, preventing uniform composite with the raw materials. The pre-sintering time is 4~6 hours. Finally, the sodium vanadium fluorophosphate intermediate obtained after pre-sintering is sintered at a high temperature of 550℃~800℃ to obtain a composite cathode material with a stable three-dimensional conductive network structure, strong interfacial bonding, high discharge capacity, high conductivity, and good cycle stability.

[0023] 4) This invention utilizes a high-temperature solid-state method to prepare carbon-coated sodium vanadium fluorophosphate cathode materials. The co-oxidation treatment of the composite carbon forms abundant functional groups (such as -COOH and -OH) on its surface, enhancing the chemical bonding with sodium vanadium fluorophosphate particles and forming a three-dimensional conductive network. This structure significantly improves the overall electronic conductivity of the composite material and reduces polarization during charging and discharging. The oxygen-containing groups of the co-oxidized carbon coordinate with ions on the surface of sodium vanadium fluorophosphate, reducing interfacial charge transfer impedance (e.g., a decrease in charge transfer impedance Rct in EIS testing). The flexible carbon skeleton of the co-oxidized carbon coats the surface of sodium vanadium fluorophosphate particles (as shown in the SEM image), forming a "buffer layer" that effectively inhibits the volume expansion and particle breakage of sodium vanadium fluorophosphate. The oxygen-containing groups on the surface of the co-oxidized carbon material form chemical bonds (such as COV bonds) with sodium vanadium fluorophosphate, enhancing interfacial bonding and reducing the shedding of active material during cycling. Therefore, this co-oxidized carbon-coated sodium vanadium fluorophosphate cathode material exhibits high discharge capacity, high conductivity, and good cycle stability. Sodium-ion batteries containing positive electrode materials have high safety performance and a high operating voltage platform (-3.8 V vs. Na). + / Na) and high specific capacity (128.7 mAh·g -1 It is applicable to fields such as new energy vehicles and energy storage. Attached Figure Description

[0024] Figure 1 (a~d) and Figure 2 (a-d) are SEM images of sodium vanadium fluorophosphate cathode materials in Examples 1-4 and Comparative Examples 1-4; Figure 3 and Figure 4 The images show the XRD patterns of sodium vanadium fluorophosphate cathode materials in Examples 1-4 and Comparative Examples 1-4. Figure 5 and Figure 6 The above are charge-discharge curves of sodium vanadium fluorophosphate cathode materials in Examples 1-4 and Comparative Examples 1-4 at a 1C rate. Figure 7 and Figure 8 The following are rate cycling diagrams of sodium vanadium fluorophosphate cathode materials in Examples 1-4 and Comparative Examples 1-4; Figure 9 and Figure 10 The graph shows the cycling performance of sodium vanadium fluorophosphate cathode materials in Examples 1-4 and Comparative Examples 1-4 at a rate of 20C. Detailed Implementation

[0025] The technical solution of the present invention will be described in detail below with reference to the embodiments. The described embodiments are only some embodiments of the present invention, not all embodiments, and should not be construed as limiting the scope of protection of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. All raw materials in the following embodiments are commercially available.

[0026] Example 1 0.5 g of carbon nanotubes and 0.5 g of mesophase carbon microspheres were added to 80 mL of mixed acid solution and reacted for 20 min. Then, 1.2 g of KMnO4 was added and reacted in a water bath at 35 °C for 3 h. After dilution with 100 mL of distilled water, the mixture was allowed to stand for 10 min and then 8 mL of 30% hydrogen peroxide solution was added and reacted at 35 °C for 8 h. After the reaction, the mixture was washed until pH=4 and dried for 8 h to obtain the co-oxidized carbon source.

[0027] Then, ammonium metavanadate, sodium fluoride, ammonium phosphate, and the oxidized carbon source were added to the ball milling solvent and mixed evenly. The mixture was ball milled for 4 hours and dried for 8 hours to obtain the precursor powder. The total mass of carbon in the carbon source was 15% of the total mass of the vanadium source, sodium source, phosphate, and fluorine source. The amounts of ammonium metavanadate, sodium fluoride, and ammonium phosphate were used in a molar ratio of sodium, vanadium, phosphorus, and fluorine of 3:2:2:3.

[0028] The precursor powder was pre-sintered at 350°C for 5 hours under an argon atmosphere, and then ground into powder to obtain sodium vanadium fluorophosphate intermediate. Finally, the sodium vanadium fluorophosphate intermediate was sintered at 600°C for 6 hours under an argon atmosphere and manually ground into powder to obtain carbon oxide-coated sodium vanadium fluorophosphate composite cathode material, which was named NVPF@O-MCMB / CNT. Example 2 1.0 g of carbon nanotubes and 0.5 g of graphene were added to 80 mL of mixed acid solution and reacted for 20 min. Then, 1.5 g of KMnO4 was added and reacted in a water bath at 40 °C for 4 h. After dilution with 100 mL of distilled water, the mixture was allowed to stand for 10 min and then 10 mL of 30% hydrogen peroxide solution was added and reacted at 40 °C for 6 h. After the reaction, the mixture was washed until pH=4 and dried for 8 h to obtain the co-oxidized carbon source.

[0029] Then, vanadium pentoxide, sodium acetate, ammonium dihydrogen phosphate, ammonium fluoride, and the oxidized carbon source are manually ground and mixed evenly to obtain precursor powder. The total mass of carbon in the carbon source is 20% of the total mass of the vanadium source, sodium source, phosphate, and fluorine source. The amount of vanadium pentoxide, sodium acetate, ammonium dihydrogen phosphate, and ammonium fluoride used is such that the molar ratio of sodium, vanadium, phosphorus, and fluorine is 3:2:2:3.

[0030] Precursor powder was pre-sintered at 300℃ for 5 hours under an argon atmosphere, and then manually ground into powder to obtain sodium vanadium fluorophosphate intermediate. Finally, the sodium vanadium fluorophosphate intermediate was sintered at 700℃ for 8 hours under an argon atmosphere, and then manually ground into powder to obtain carbon oxide-coated sodium vanadium fluorophosphate composite cathode material, named NVPF@O-GN / CNT. Example 3 1.5g of carbon nanofibers and 0.5g of flake graphite were added to 80mL of mixed acid solution and reacted for 20min. Then, 2.2g of KMnO4 was added and reacted in a water bath at 38℃ for 5h. After dilution with 100mL of distilled water, the mixture was allowed to stand for 10min and then 15mL of 30% hydrogen peroxide solution was added and reacted at 38℃ for 10h. After the reaction, the mixture was washed until pH=4 and dried for 8h to obtain the co-oxidized carbon source.

[0031] Then, vanadium oxide, sodium fluoride, diammonium hydrogen phosphate and the oxidized carbon source were added to the ball milling solvent and mixed evenly. The mixture was ball milled for 4 hours and dried for 8 hours to obtain the precursor powder. The total mass of carbon in the carbon source was 10% of the total mass of the vanadium source, sodium source, phosphate and fluorine source. The molar ratio of sodium, vanadium, phosphorus and fluorine in the amounts of vanadium oxide, sodium fluoride and diammonium hydrogen phosphate was 3:2:2:3.

[0032] The precursor powder was pre-sintered at 400℃ for 5 hours under an argon atmosphere, and then manually ground into powder to obtain sodium vanadium fluorophosphate intermediate. Finally, the sodium vanadium fluorophosphate intermediate was sintered at 800℃ for 10 hours under an argon atmosphere, and then manually ground into powder to obtain carbon oxide-coated sodium vanadium fluorophosphate composite cathode material, which was named NVPF@O-Gr / CNT.

[0033] Example 4 1.0 g of carbon nanotubes and 0.5 g of acetylene black were added to 80 mL of mixed acid solution and reacted for 20 min. Then, 1.5 g of KMnO4 was added and reacted in a water bath at 40 °C for 3 h. After dilution with 100 mL of distilled water, the mixture was allowed to stand for 10 min and then 10 mL of 30% hydrogen peroxide solution was added and reacted at 40 °C for 10 h. After the reaction, the mixture was washed until pH=4 and dried for 8 h to obtain the co-oxidized carbon source.

[0034] Then, ammonium metavanadate, sodium fluoride, ammonium dihydrogen phosphate, and the oxidized carbon source were added to the ball milling solvent and mixed evenly. The mixture was ball milled for 4 hours and dried for 8 hours to obtain the precursor powder. The total mass of carbon in the carbon source was 15% of the total mass of the vanadium source, sodium source, phosphate, and fluorine source. The amounts of ammonium metavanadate, sodium fluoride, and ammonium dihydrogen phosphate were used in a molar ratio of sodium, vanadium, phosphorus, and fluorine of 3:2:2:3.

[0035] The precursor powder was pre-sintered at 350°C for 5 hours under an argon atmosphere, and then manually ground into powder to obtain sodium vanadium fluorophosphate intermediate. Finally, the sodium vanadium fluorophosphate intermediate was sintered at 700°C for 8 hours under an argon atmosphere, and then manually ground into powder to obtain carbon oxide-coated sodium vanadium fluorophosphate composite cathode material, which was named NVPF@O-AB / CNT.

[0036] Comparative Example 1 In this comparative example, carbon nanotubes and graphene were directly mixed with vanadium pentoxide, sodium acetate, ammonium dihydrogen phosphate, and ammonium fluoride instead of undergoing an oxidation step. The rest was the same as in Example 1. The resulting sample was named NVPF@GN / CNT.

[0037] Comparative Example 2 In this comparative example, the carbon source was replaced with graphite and mesophase carbon microspheres, and the rest was the same as in Example 1. The resulting sample was named NVPF@O-Gr / MCMB.

[0038] Comparative Example 3 In this comparative example, the carbon source was replaced with graphene and carbon nanotube materials, and the pre-sintering operation step was not performed. The rest was the same as in Example 1. The obtained sample was named NVPF@O-Gr / CNT-1.

[0039] Comparative Example 4 In this comparative example, the carbon source was replaced with acetylene black and carbon nanotube material. The pre-sintering operation was carried out in an argon atmosphere at 500°C for 5 hours. The rest was the same as in Example 1. The obtained sample was named NVPF@O-AB / CNT-1.

[0040] Experimental Example Figure 1 Figure 2 shows scanning electron microscope (SEM) images of the cathode materials in Examples 1-4 and Comparative Examples 1-4. It can be seen that the materials in all four examples are uniformly mixed and show no agglomeration. The materials in Examples 1 and 4, pre-sintered at 350℃, have a larger number of porous structures compared to the materials in Examples 2 and 3, pre-sintered at 300℃ and 400℃, increasing the specific surface area and providing more "active sites" and a shorter "reaction path" for the electrode reaction. In contrast, the four comparative examples show a large number of material particles agglomerated, and the carbon material is not uniformly coated into the material. This indicates that the simple composite carbon material without oxidation treatment, the composite carbon material with two two-dimensional carbon materials after oxidation treatment, and the cathode materials without pre-sintering and pre-sintered at 500℃ are not as effective as the cathode material with co-oxidation coating of one-dimensional and two-dimensional carbon materials.

[0041] Figure 3Figure 4 shows the XRD patterns of sodium vanadium fluorophosphate cathode materials prepared in Examples 1-4 and Comparative Examples 1-4. It can be seen that the diffraction peaks of the cathode materials in the XRD patterns of Examples 1-4 and Comparative Examples 1-4 are consistent with the standard PDF card of sodium vanadium fluorophosphate, and the sharp peaks in the figure indicate that these powders have good crystallinity.

[0042] Active material, conductive carbon black, and polyvinylidene fluoride were thoroughly mixed in a mass ratio of 7:2:1. N-methylpyrrolidone was then added, and the mixture was coated onto carbon-coated aluminum foil. After cutting, the foil was dried in an oven at 100°C for 10 hours to obtain the positive electrode sheet. Different sodium-ion battery positive electrodes were assembled into batteries in the following order: negative electrode shell, counter electrode sodium sheet, separator, electrolyte, positive electrode material, gasket, spring sheet, and positive electrode shell. The charge-discharge electrochemical performance of different batteries was tested at 1C. Figure 5 As can be seen from Figure 6, the cathode material coated with carbon using both one-dimensional and two-dimensional carbon sources exhibits a higher specific capacity. Specifically, Examples 1 and 4 show a first-cycle discharge specific capacity of 126.6 mAh·g at 1C rate. -1 and 120.5 mAh·g -1 Approximately theoretical specific capacity of 128 mAh·g -1 However, the highest first-cycle discharge specific capacity of the four comparative samples prepared without oxidation, oxidation with two two-dimensional carbon sources, and without pre-sintering or pre-sintering at 500℃ was 85.4 mAh·g. -1 The results show that the composite carbon materials obtained by oxidation with one-dimensional and two-dimensional carbon sources have better conductivity and structural stability, and the sodium vanadium fluorophosphate cathode material pre-calcined at 350°C has a higher specific capacity.

[0043] Figure 7 Figure 8 shows the rate performance graphs of the cathode materials in Examples 1-4 and Comparative Examples 1-4. It can be seen that the cathode materials with one-dimensional and two-dimensional carbon sources co-oxidized with carbon exhibit superior rate performance. In contrast, the specific capacity in the 0.1-10C rate performance graphs of the four comparative examples does not exceed 100 mAh·g. -1 The specific capacity of Example 1 is significantly lower than that of the four embodiments. Example 1, at 0.1C, achieves a specific capacity as high as 122.5 mAh·g. -1 The specific capacity at 1C is 126.6 mAh·g. -1 The specific capacity at 10C is 110.3 mAh·g. -1 The specific capacity at 20C is 105.6 mAh·g. -1In summary, the composite carbon material without oxidation treatment (Comparative Example 1) and the cathode material formed by oxidizing and coating two kinds of two-dimensional carbon materials (Comparative Example 2) did not form a stable three-dimensional network structure, and their specific capacity was significantly lower than that of the cathode material coated with one-dimensional and two-dimensional carbon materials. The cathode material pre-sintered at 350℃ performed better than the cathode material without pre-sintering and pre-sintered at 300, 400, and 500℃.

[0044] Figure 9 and Figure 10 As can be seen, the cathode material co-coated with one-dimensional and two-dimensional carbon sources and pre-sintered at 350℃ exhibits extremely high specific capacity and good cycle stability; after 5000 cycles at 20C, Example 1 retains a capacity of up to 81.57%, while the specific capacity of the four comparative examples at 20C does not exceed 90 mAh·g. -1 Furthermore, the degradation is extremely severe. These results demonstrate that the co-oxidized carbon layer coated sodium vanadium fluorophosphate cathode material prepared in this invention exhibits excellent cycle performance.

[0045] In summary, this invention utilizes co-oxidized carbon materials. Compared to traditional methods that simply do not involve carbon oxide coating or perform single oxidation treatment, this invention exhibits superior coating performance for sodium vanadium fluorophosphate cathode materials. It expands the specific surface area of ​​the material, enhancing the battery's conductivity and structural stability, and further improving the battery's cycle stability and rate performance. Furthermore, it boasts low production costs, high safety performance, and a high operating voltage platform (-3.8 V vs. Na). + / Na) and high specific capacity (126.6mAh·g) -1 It is applicable to fields such as new energy vehicles and energy storage.

[0046] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material, characterized in that, Includes the following steps: Step 1: Add the carbon source to the mixed acid for reaction, then add KMnO4 for water bath reaction, and finally add hydrogen peroxide solution for co-oxidation reaction. After the reaction, wash and dry to obtain the co-oxidized carbon source; wherein, the carbon source is a mixture of one-dimensional carbon source and two-dimensional carbon source; Step 2: The co-oxidation carbon source obtained in Step 1 is mixed with vanadium source, sodium source, phosphate and fluorine source and ground into a precursor powder. The precursor powder is pre-sintered at 300℃~400℃ for 4~6h under a protective atmosphere to obtain sodium fluorophosphate intermediate. Step 3: The sodium vanadium fluorophosphate intermediate obtained in Step 2 is sintered at 550℃~800℃ for 6~10h under a protective atmosphere to obtain a carbon-coated sodium vanadium fluorophosphate composite cathode material.

2. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1, characterized in that, In step 1, the one-dimensional carbon source is at least one of carbon nanotubes, carbon nanofibers, and carbon nanowires, and the two-dimensional carbon source is at least one of graphene, mesophase carbon microspheres, acetylene black, flake graphite, and porous carbon.

3. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1 or 2, characterized in that, In step 1, the mixing mass ratio of the one-dimensional carbon source and the two-dimensional carbon source is 1 to 3:

1.

4. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1 or 2, characterized in that, In step 1, the reaction temperature of the carbon source with the mixed acid is 25-40°C and the reaction time is 20 min. The mixed acid is any two of sulfuric acid, hydrochloric acid or nitric acid. The amount of carbon source added is 2% of the mass of the mixed acid.

5. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1, characterized in that, In step 1, the amount of KMnO4 added is 1 to 1.2 times the mass of the carbon source, and the water bath reaction temperature after adding KMnO4 is 30 to 50°C for 3 to 5 hours.

6. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1 or 5, characterized in that, In step 1, the amount of hydrogen peroxide added is 10% of the mass of KMnO4, the co-oxidation reaction temperature is 35-40℃, and the time is 6-10h.

7. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1, characterized in that, In step 2, the amount of the co-oxidized carbon source added is 5% to 30% of the total mass of the vanadium source, sodium source, phosphate, and fluorine source.

8. The preparation method of the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 1 or 7, characterized in that, In step 2, the molar ratio of sodium, vanadium, phosphorus and fluorine in the vanadium source, sodium source, phosphate and fluorine source is 3:2:2:

3.

9. A co-oxide-coated sodium vanadium fluorophosphate composite cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. A sodium-ion battery composite positive electrode, characterized in that, The coating material includes a substrate and a coating material on the substrate surface, wherein the coating material includes at least the co-oxidized carbon-coated sodium vanadium fluorophosphate composite cathode material as described in claim 9, a conductive material, and a binder.

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