A preparation method of a dual-carbon coordinated sodium ion battery positive electrode material Na3V2(PO4)3 / C

Abstract

The application discloses a preparation method of a double-carbon coordinated sodium ion battery positive electrode material Na3V2(PO4)3 / C, which comprises the following steps: (1) taking a high-valence vanadium source compound, a phosphorus source compound, a sodium source compound and a reducing agent as raw materials, taking carbon nanotubes as a carbon source, weighing reaction raw materials according to a set proportion, mechanically ball-milling for 1-24 hours, reducing the high-valence vanadium into low-valence vanadium at normal temperature, and obtaining a precursor; and (2) performing calcination treatment on the precursor obtained in the step (1) to obtain the Na3V2(PO4)3 / C material. The technical problem of "a complex synthesis process, a complicated procedure, a long synthesis period caused by drying in a liquid phase reaction, difficulty in control, only carbon coating, poor conductivity of the obtained sodium vanadium phosphate carbon composite material, and influence on the play of electrochemical performance" in the prior art is solved; the preparation method has the advantages of a short process, easy control and low cost, the prepared Na3V2(PO4)3 / C has high purity and high crystallinity, and is easy to realize large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium-ion battery cathode materials, and relates to a high-performance sodium-ion battery cathode material, in particular to a preparation method of a double-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C. BACKGROUND

[0002] Lithium-ion batteries have been widely used in electronic devices and electric vehicles due to their light weight, small size, high energy density, and no memory effect. However, lithium-ion batteries still have problems in battery safety, cycle life, and cost. Moreover, with the development of human society, the demand for lithium-ion batteries will inevitably increase, but the reserves of metal lithium in the earth's crust are limited, only 0.002%, and the distribution of lithium resources is uneven, most of which are concentrated above 4000 meters above sea level, making it difficult to exploit. Its application in large-scale energy storage technology will ultimately be restricted by lithium resources. These problems have greatly limited the application of lithium-ion batteries in large-scale energy storage. Therefore, developing a new energy storage battery system with abundant resources, reasonable price, high safety factor, and high comprehensive performance is the key to the development of today's society. In comparison, sodium is abundant in the earth's crust and widely distributed, and sodium and lithium elements are in the same main group and have similar charging and discharging mechanisms. Therefore, sodium-ion batteries have environmental and resource advantages and are one of the important choices for future energy storage power grids and the most promising candidate material for the next generation.

[0003] Polyanionic materials have high operating potential, stable structure framework, and good safety, so they are considered to be one of the most promising cathode materials in SIB (Sodium-ion battery). NASICON has a large three-dimensional network structure and high sodium ion conductivity, and has a stable framework to meet the ultra-high speed and reversible Na + extraction / insertion. Among them, Na3V2(PO4)3 / C material is a sodium super ionic conductor, that is, it has a NASICON structure and contains a three-dimensional open channel, which can realize the rapid migration of sodium ions. However, due to the slight twist of the VO6 octahedron arrangement and the large V-O orbital energy difference, the polyanionic electrode material has inherent low conductivity, which limits its rate capability and cycle capability.

[0004] In the prior art, a liquid phase reaction method is often used to first prepare a precursor, and then calcination is performed under an inert atmosphere to obtain a target product. For example, CN 202111300358.2 provides a sodium vanadium phosphate carbon composite material and a preparation method and application thereof, including the following steps: (1) 4 mmol of ammonium vanadate and 12 mmol of oxalic acid are added to 10 ml of deionized water, and the solution is stirred at 70 DEG C for 2 hours. After the solution is clear, 6 mmol of sodium dihydrogen phosphate and 1 mmol of sucrose are added, and the solution is stirred at room temperature for 4 hours until the solution is clear to obtain a precursor solution; (2) the precursor solution is mixed with ethylene glycol at a mass ratio of 1:5, and continuously stirred for 3 hours, then transferred to a hydrothermal reaction kettle for solvothermal reaction, and after being kept at 180 DEG C for 12 hours, the sample is taken out, centrifuged, washed with ethanol and dried to obtain an intermediate product; (3) the intermediate product is ground and placed in a tube furnace under an argon atmosphere, heated to 350 DEG C at a rate of 5 DEG C / min, kept for 4 hours, then further heated to 800 DEG C at a rate of 5 DEG C / min, kept for 6 hours, and naturally cooled to obtain a sodium vanadium phosphate carbon composite material. The synthesis process of the above patent is complex and tedious, and the liquid phase reaction needs to be dried, resulting in a long synthesis period, which is not easy to control. Moreover, only carbon coating is performed, and the conductivity of the obtained sodium vanadium phosphate carbon composite material is still poor, which affects the play of its electrochemical performance. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a sodium vanadium phosphate carbon composite material Na3V2(PO4)3 / C, to solve the technical problems of the prior art that the synthesis process is complex and tedious, the liquid phase reaction needs to be dried, resulting in a long synthesis period, which is not easy to control, and only carbon coating is performed, and the conductivity of the obtained sodium vanadium phosphate carbon composite material is still poor, which affects the play of its electrochemical performance. The preparation method has the advantages of short process, easy control and low cost, and the prepared Na3V2(PO4)3 / C has high purity and high crystallinity, and is easy to realize large-scale production.

[0006] In order to achieve the above purpose, the present application provides the following technical solutions:

[0007] The present application provides a preparation method of a sodium vanadium phosphate carbon composite material Na3V2(PO4)3 / C, including the following steps:

[0008] (1) high-valent vanadium source compound, phosphorus source compound, sodium source compound, reducing agent and carbon nanotube are used as raw materials, the reaction raw materials are weighed according to the set proportion, and mechanical ball milling is performed for 1-24 hours. Dry milling is used in mechanical ball milling to reduce high-valent vanadium to low-valent vanadium at room temperature to obtain a precursor;

[0009] (2) calcining the precursor obtained in step (1) to obtain a Na3V2(PO4)3 / C material.

[0010] In a preferred embodiment, the high-valence vanadium source compound is one or more of a combination of ammonium metavanadate, vanadium pentoxide and vanadium dioxide. The selected vanadium source is high-valence vanadium, which greatly reduces the cost of synthesis conditions and raw materials.

[0011] In a preferred embodiment, the phosphorus source is one or more of a combination of sodium dihydrogen phosphate, sodium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0012] In a preferred embodiment, the sodium source is one or more of a combination of sodium dihydrogen phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium hydroxide and sodium citrate.

[0013] In a preferred embodiment, the reducing agent is one or more of a combination of oxalic acid, ascorbic acid, citric acid, malic acid, glycolic acid, glucose and sucrose.

[0014] In a preferred embodiment, in step (1), mechanical ball milling is performed for 3-10 hours; a stainless steel tank is used, the grinding medium is stainless steel beads, the ball-to-material ratio is 50-100:1, the mass ratio of large, medium and small beads is 5:2:3, the diameter of large beads is 1 cm, the diameter of medium beads is 0.6 cm, the diameter of small beads is 0.4 cm, and the rotation speed is 200-600 rpm.

[0015] In a preferred embodiment, in step (1), the molar ratio of sodium, vanadium and phosphorus elements is 3:2:3, the molar ratio of the reducing agent to the high-valence vanadium source compound is 1:1-30:1, and the mass ratio of carbon nanotubes to the high-valence vanadium source compound is 1:200-1:10.

[0016] In a preferred embodiment, in step (1), the molar ratio of the reducing agent to the high-valence vanadium source compound is 3:1-15:1, and the mass ratio of carbon nanotubes to the high-valence vanadium source compound is 1:100-1:50.

[0017] In a preferred embodiment, in step (2), the precursor obtained in step (1) is transferred into an inert atmosphere or a reducing atmosphere, and is kept at 200-400℃ for 2-6 hours, then heated to 600-900℃ for 4-8 hours, with a heating rate of 5℃ / min.

[0018] The method uses a low-temperature solid-phase chemical reduction method to reduce high-valence vanadium to low-valence vanadium, which can achieve sufficient and uniform reduction of vanadium, and can achieve sufficient mixing of reaction raw materials. Carbon coating increases the interface conduction, and carbon nanotubes increase the conduction between particles. Then, calcination treatment is performed to obtain a sodium ion battery cathode material Na3V2(PO4)3 / C with double carbon synergy.

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

[0020] 1) The application discloses a preparation method of a sodium-ion battery cathode material Na3V2(PO4)3 / C.

[0021] 2) The Na3V2(PO4)3 / C material prepared by the application has a first-week discharge capacity of 110 mAh / g in a range of 2.5-4.0 V as a cathode material of a secondary sodium-ion battery.

[0022] 3) The Na3V2(PO4)3 / C material prepared by the application has good electrochemical performance (very excellent rate discharge performance), high safety, low price, simple synthesis process and easy control, and can be applied to energy storage equipment, backup power supply, reserve power supply and the like.

[0023] 4) The preparation method of the sodium-ion battery cathode material Na3V2(PO4)3 / C has the advantages of short synthesis period, low-cost raw materials, simple process, easy control, obvious practical value and good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is an X-ray diffraction pattern of the Na3V2(PO4)3 / C material in Example 1 of the application.

[0025] Figure 2 is an X-ray diffraction pattern of the Na3V2(PO4)3 / C material in Comparative Example 1 of the application.

[0026] Figure 3 is an SEM image of the Na3V2(PO4)3 / C material in Example 1 of the application.

[0027] Figure 4 is a STEM image of the Na3V2(PO4)3 / C material in Example 1 of the application.

[0028] Figure 5 is a CV graph of the Na3V2(PO4)3 / C material in Comparative Example 1 of the application.

[0029] Figure 6 is a charge-discharge curve graph of the Na3V2(PO4)3 / C material in Comparative Example 1 of the application.

[0030] Figure 7 is a 1C cycle performance graph of the Na3V2(PO4)3 / C electrode in Example 1 of the application in an electrolyte.

[0031] Figure 8is a 1C cycle performance graph of the Na3V2(PO4)3 / C electrode in the electrolyte in the present application comparative example 1.

[0032] Figure 9 is a rate performance graph of the Na3V2(PO4)3 / C electrode in the electrolyte in the present application example 1.

[0033] Figure 10 is a rate performance graph of the Na3V2(PO4)3 / C electrode in the electrolyte in the present application comparative example 1.

[0034] Figure 11 is an AC impedance graph of the Na3V2(PO4)3 / C electrode in the electrolyte in the present application example 1.

[0035] Figure 12 is an AC impedance graph of the Na3V2(PO4)3 / C electrode in the electrolyte in the present application comparative example 1. DETAILED DESCRIPTION

[0036] The technical solutions in the examples of the present application will be described clearly and completely below. Obviously, the described examples are only some of the examples of the present application, but not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] Unless otherwise specified, the reagents used in the present examples are all commercially available or prepared by conventional means, and the equipment used is conventional in the art. The following are some examples from the inventors' experiments:

[0038] Example 1

[0039] Sodium dihydrogen phosphate, ammonium metavanadate, sodium carbonate, ascorbic acid, and carbon nanotubes were used as raw materials, wherein the molar ratio of sodium, vanadium, and phosphorus was 3:2:3, the molar ratio of ascorbic acid and ammonium metavanadate was 2:1, and the mass ratio of carbon nanotubes and ammonium metavanadate was 1:50. The raw materials were mechanically ball milled for 3 hours. A stainless steel tank was used as the grinding medium, with a ball-to-material ratio of 72:1 and a large-to-medium-to-small bead mass ratio of 5:2:3. The large beads had a diameter of 1 cm, the medium beads had a diameter of 0.6 cm, and the small beads had a diameter of 0.4 cm. The rotation speed was 400 revolutions per minute. A precursor was obtained. The precursor was transferred to a tube furnace and heated to 300°C in a nitrogen atmosphere. After holding for 4 hours, the temperature was increased to 650°C and held for 6 hours at a constant rate of 5°C / min. After cooling, the Na3V2(PO4)3 / C material was obtained.

[0040] Example 2

[0041] Sodium phosphate dibasic, ammonium metavanadate, sodium carbonate, ascorbic acid, carbon nanotubes as raw materials, wherein the molar ratio of sodium, vanadium and phosphorus is 3:2:3, the molar ratio of ascorbic acid and ammonium metavanadate is 2:1, the mass ratio of carbon nanotubes and ammonium metavanadate is 1:100, the raw materials are mechanically ball milled for 3 hours, a stainless steel tank is used, the grinding medium is stainless steel beads, the ball-to-material ratio is 72:1, the mass ratio of large, medium and small beads is 5:2:3, the diameter of large beads is 1cm, the diameter of medium beads is 0.6cm, the diameter of small beads is 0.4cm, and the rotation speed is 400rpm / min, to obtain a precursor. The precursor is transferred into a tube furnace, heated to 300℃ in an argon atmosphere, kept at 300℃ for 4 hours, then heated to 650℃, kept at 650℃ for 6 hours, the heating rate is controlled at 5℃ / min, and after cooling, Na3V2(PO4)3 / C material is obtained.

[0042] Example 3

[0043] Sodium phosphate dibasic, ammonium metavanadate, sodium carbonate, ascorbic acid, carbon nanotubes as raw materials, wherein the molar ratio of sodium, vanadium and phosphorus is 3:2:3, the molar ratio of ascorbic acid and ammonium metavanadate is 3:1, the mass ratio of carbon nanotubes and ammonium metavanadate is 1:50, the raw materials are mechanically ball milled for 3 hours, a stainless steel tank is used, the grinding medium is stainless steel beads, the ball-to-material ratio is 72:1, the mass ratio of large, medium and small beads is 5:2:3, the diameter of large beads is 1cm, the diameter of medium beads is 0.6cm, the diameter of small beads is 0.4cm, and the rotation speed is 400rpm / min, to obtain a precursor. The precursor is transferred into a tube furnace, heated to 300℃ in an argon atmosphere, kept at 300℃ for 4 hours, then heated to 650℃, kept at 650℃ for 6 hours, the heating rate is controlled at 5℃ / min, and after cooling, Na3V2(PO4)3 / C material is obtained.

[0044] Comparative Example 1

[0045] Sodium phosphate dibasic, ammonium metavanadate, sodium carbonate, ascorbic acid as raw materials, wherein the molar ratio of sodium, vanadium and phosphorus is 3:2:3, the molar ratio of ascorbic acid and ammonium metavanadate is 1:1, the raw materials are mechanically ball milled for 3 hours to obtain a precursor. The precursor is transferred into a tube furnace, heated to 300℃ in an argon atmosphere, kept at 300℃ for 4 hours, then heated to 650℃, kept at 650℃ for 6 hours, and after cooling, a sodium ion battery positive electrode material is obtained.

[0046] Comparative Example 2

[0047] Sodium phosphate dibasic, ammonium metavanadate, sodium carbonate as raw materials, wherein the molar ratio of sodium, vanadium and phosphorus is 3:2:3, the raw materials are mechanically ball milled for 5 hours to obtain a precursor. The precursor is transferred into a tube furnace, heated to 300℃ in an argon atmosphere, kept at 300℃ for 4 hours, then heated to 650℃, kept at 650℃ for 6 hours, and after cooling, a sodium ion battery positive electrode material is obtained.

[0048] Comparative Example 3

[0049] The sodium-ion battery positive electrode material is obtained by using sodium dihydrogen phosphate, ammonium metavanadate, sodium carbonate, ascorbic acid and carbon nanotubes as raw materials, wherein the molar ratio of sodium, vanadium and phosphorus is 3:2:3, the molar ratio of ascorbic acid and ammonium metavanadate is 2:1, and the mass ratio of carbon nanotubes and ammonium metavanadate is 1:50; the raw materials are wet ground for 3 hours to obtain a mixed slurry; the mixed slurry is dried and treated, and then crushed and transferred into a tube furnace; the temperature is raised to 300 DEG C in a nitrogen atmosphere, and kept for 4 hours; then the temperature is raised to 650 DEG C, and kept for 6 hours; and after cooling, the sodium-ion battery positive electrode material is obtained.

[0050] The sodium-ion battery positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-3 are used as active materials, respectively, and mixed in a mass ratio of 8:1:1 of active material: acetylene black: polyvinylidene fluoride (PVDF), and then a proper amount of N-methyl pyrrolidone is added to form a viscous slurry, which is coated on an aluminum foil with rough surface, baked in a vacuum drying oven at 80 DEG C for 8 hours, and then the whole electrode sheet is cut into a circular sheet electrode with a diameter of 14 mm by using a sheet cutting machine. A 2016 button cell is assembled in an argon glove box, with metallic sodium as the counter electrode, glass fiber as the separator, and 1 mol / L NaClO4 (1:1 volume ratio of EC and DEC) as the electrolyte. The battery is tested in a voltage range of 2.5-4.0 V, and the electrochemical cycle performance is tested at 1C=120 mA g -1 , 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, 0.1C, respectively. The specific values are shown in Table 1.

[0051] Table 1 shows the electrochemical performance test of the sodium-ion battery polyanion positive electrode active material obtained in Examples 1-3 and Comparative Examples 1-3.

[0052]

[0053]

[0054] Comparative analysis of Example 1 and Comparative Example 2 shows that the sample after adding carbon nanotubes and carbon coating has higher electrochemical capacity, better rate performance and capacity retention rate, which indicates that the sample after carbon coating has better electronic conductivity, increases the conduction between interfaces, the addition of carbon nanotubes forms a carbon network that tightly connects the particles, increases the conduction between the particles, reduces the ion transmission path, is conducive to the storage and transportation of sodium ions, and provides higher capacity rate performance and cycle stability.

[0055] Comparative Examples 1-3, it can be seen that too much ascorbic acid and carbon nanotube addition results in a decrease in the electrochemical capacity of the material, and the possible reason is that too much ascorbic acid addition increases the thickness of the outer carbon coating layer of the material, affecting the interface conduction of the positive electrode material. Too much carbon nanotube insertion on the surface of the positive electrode material affects the transmission between particles.

[0056] Comparative analysis of Examples 1-3, it can be seen that the 1C capacity retention rate of the material described in Examples 1-3 of the present application is maintained in the range of 95.8-97.3%, and the 1C initial discharge capacity is maintained at 105.4-109.0 mAh / g. The discharge specific capacity at 10C rate is maintained at 80.3-87.9 mAh / g. This shows that the series of polyanion materials described in the present application all exhibit excellent structural stability, cycle stability and good rate performance.

[0057] Comparative analysis of Comparative Examples 1 and 2, it can be seen that the sample without carbon coating has poorer cycle stability, lower discharge specific capacity at 1C and poorer rate performance. Especially Comparative Example 2, at a large current density of 10C, exhibits a discharge specific capacity of 20.4 mAh / g. This is because the sample without carbon coating exhibits the inherent shortcomings of this type of material, i.e. low electronic conductivity, thereby affecting the electrochemical performance of the material.

[0058] Comparative analysis of Example 1 and Comparative Example 3, although the electrochemical performance of the two is not much different, the sample of Example 1 still has good electrochemical performance. Dry ball milling of Example 1 compared to wet ball milling of Comparative Example 3 has a simple synthesis process, is easy to control, avoids the use of alcohol during the experiment, is safe, is cheaper, has more significant practical value and good application prospects.

[0059] Figure 1 is the X-ray diffraction pattern of the Na3V2(PO4)3 / C composite material of Example 1 of the present application. It can be observed that the synthesized material has obvious diffraction peaks, and the position and peak intensity of the diffraction peaks can be well attributed to the NASICON structure of the rhombohedron, with a space group of R3C. At the same time, no impurity peaks are observed in the XRD pattern, and the addition of CNTs has no effect on the crystal structure of the undoped CNT material.

[0060] Figure 2This is the X-ray diffraction pattern of the Na3V2(PO4)3 / C composite material of Comparative Example 1 of this invention. It can be observed that the synthesized material has obvious diffraction peaks, and the positions and intensities of these peaks can be well attributed to the orthorhombic NASICON structure, with space group R3C. Meanwhile, no impurity peaks were observed in the XRD pattern. In comparison, the XRD diffraction peak intensities of the composite material in Example 1 are slightly lower than those in Comparative Example 1. This is partly due to the higher carbon content of the Example 1 sample, and partly because the presence of porosity in the three-dimensional structure also has a certain impact on the crystallinity of the composite material.

[0061] Figure 3 This is a SEM image of the composite material in Example 1, from... Figure 3 It can be seen that the material particles produced by this invention are significantly smaller and do not show obvious agglomeration.

[0062] Figure 4 This is a STEM image of the composite material in Example 1. It can be seen that the material particles prepared by this method are significantly smaller. The smaller particle size not only shortens the diffusion distance of ions, making it easier for them to reach the interior of the particles and accelerating ion transport, but also promotes electrolyte wetting and enhances the interaction between the electrode and the electrolyte. Carbon coating increases interfacial conductivity between the particles, and the addition of carbon nanotubes forms a carbon network between the particles.

[0063] Figure 5 The cyclic voltammetry curves of the composite material in Comparative Example 1 show more clearly that Comparative Example 1 has two reduction peaks and exhibits relatively small polarization.

[0064] Figure 6 The figures show the charge-discharge curves of the composite material in Comparative Example 1 at 1C. Two phase transition plateaus generated during the discharge process in Example 1 are clearly visible. The phase transition plateaus are 3.34V and 3.21V, respectively.

[0065] Figure 7 This is a 1C cycle performance graph of the Na3V2(PO4)3 / C electrode in the electrolyte according to Example 1 of the present invention. The test results are as follows... Figure 7 Within the 2.5-4V range, the initial discharge capacity was 109.0 mAh / g, and the capacity retention rate of this composite material remained at 96.1% after 200 cycles, demonstrating good electrochemical performance.

[0066] Figure 8 This is a graph showing the 1C cycle performance of the comparative example 1Na3V2(PO4)3 / C electrode in the electrolyte. The test results are as follows: Figure 8 Within the 2.5-4V range, the initial discharge capacity of the prepared Na3V2(PO4)3 / C electrode was 84.2 mAh / g, and the capacity retention rate after 200 cycles was still 92.6%.

[0067] Figure 9 is a plot of the rate capability of the Na3V2(PO4)3 / C electrode of Example 1 of the present application in electrolyte. The material shows excellent rate capability, still delivering a specific capacity of 87.9 mAh / g at 10 C current density. The prepared material of Example 1 improves the electrochemical activity and reversibility of the positive electrode compared to the material of Comparative Example 1, which is attributed to the fast ion reaction kinetics and high electronic conductivity induced by the carbon coating and carbon nanotube transport network.

[0068] Figure 10 is a plot of the rate capability of the Na3V2(PO4)3 / C electrode of Comparative Example 1 of the present application in electrolyte. Still delivering a specific capacity of 74.9 mAh / g at 10 C current density.

[0069] Figure 11 is a plot of the AC impedance of the Na3V2(PO4)3 / C electrode of Example 1 of the present application in electrolyte. The material in Example 1 has a smaller impedance.

[0070] Figure 12 is a plot of the AC impedance of the Na3V2(PO4)3 / C electrode of Comparative Example 1 of the present application in electrolyte. It can be seen from the Nyquist curves of both that the composite material in Example 1 has a smaller semicircle size than the composite material of Comparative Example 1, indicating that the conductivity of the composite material of Example 1 is higher than that of Comparative Example 1, which is conducive to obtaining better rate capability. In addition, the difference in the slope of the straight line in the low frequency region of the composite materials of Example 1 and Comparative Example 1 indicates the difference in the diffusion rate of sodium ions in the two materials. As can be seen from the figure, the composite material of Example 1 not only has good electrical conductivity, but also has a faster diffusion rate of sodium ions, which is also the reason why the composite material of Example 1 has good rate capability and cycle performance.

[0071] While embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a dual-carbon synergistic sodium-ion battery positive electrode material Na3V2(PO4)3 / C, characterized in that, The method comprises the following steps: (1) taking high-valence vanadium source compound, phosphorus source compound, sodium source compound, reducing agent and carbon nanotube as raw materials, weighing the reaction raw materials according to the set proportion, and mechanically ball milling for 1-24 hours, wherein the dry milling is adopted to reduce the high-valence vanadium into low-valence vanadium at room temperature, so as to obtain a precursor; (2) performing calcination treatment on the precursor obtained in step (1) to obtain a Na3V2(PO4)3 / C material; The carbon coating increases the interface conduction of the particles, and the addition of the carbon nanotube forms a carbon network between the particles. The reducing agent is one or more combinations of oxalic acid, ascorbic acid, citric acid, malic acid, glycolic acid, glucose and sucrose.

2. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, The high-valence vanadium source compound is one or more combinations of ammonium metavanadate, vanadium pentoxide and vanadium dioxide.

3. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, The phosphorus source is one or more combinations of sodium dihydrogen phosphate, sodium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

4. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, The sodium source is one or more combinations of sodium dihydrogen phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium hydroxide and sodium citrate.

5. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, In step (1), the mechanical ball milling is performed for 3-10 hours; a stainless steel tank is adopted, the grinding medium is stainless steel beads, the ball-to-material ratio is 50-100:1, the mass ratio of large, medium and small beads is 5:2:3, the diameter of large beads is 1 cm, the diameter of medium beads is 0.6 cm, the diameter of small beads is 0.4 cm, and the rotation speed is 200-600 revolutions / minute.

6. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, In step (1), the molar ratio of sodium, vanadium and phosphorus elements is 3:2:3, the molar ratio of the reducing agent and the high-valence vanadium source compound is 1:1-30:1, and the mass ratio of the carbon nanotube and the high-valence vanadium source compound is 1:200-1:

10.

7. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 6, characterized in that, In step (1), the molar ratio of the reducing agent and the high-valence vanadium source compound is 3:1-15:1, and the mass ratio of the carbon nanotube and the high-valence vanadium source compound is 1:100-1:

50.

8. The preparation method of the dual-carbon synergistic sodium-ion battery cathode material Na3V2(PO4)3 / C according to claim 1, characterized in that, In step (2), the precursor obtained in step (1) is transferred into an inert atmosphere or a reducing atmosphere, and then heated at 200-400℃ for 2-6 hours, and then heated to 600-900℃ for 4-8 hours, with the heating rate being controlled at 5℃ / min.

9. A Na3V2(PO4)3 / C positive electrode material for a dual-carbon and sodium-ion battery, which is prepared by the preparation method according to any one of claims 1-8.

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