Carbon-coated high-entropy NASICON positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a carbon-coated high-entropy NASICON positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery electrode materials. The method comprises the following steps: adding a vanadium source, a carbon source, a chromium source, an iron source, a manganese source, a zinc source, an aluminum source, a sodium source and a phosphorus source into deionized water, heating and dissolving to obtain a clear solution; and heating the solution to form gel, and then carrying out the steps of vacuum drying, crushing, pre-sintering, calcining and the like to obtain the Na3V2-y (CrFeMnZnAl) y (PO4) 3 / C (0 < y < 1) positive electrode material. The positive electrode material has a stable NASICON structure, and the morphology is of a scaly structure. According to the invention, a high-entropy doping mode is adopted to replace part of vanadium sites in sodium vanadium phosphate, and the conductivity of the positive electrode material is improved through carbon coating, so that the prepared positive electrode material has relatively good cycling stability and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrode materials, and in particular to a carbon-coated high-entropy NASICON positive electrode material and a preparation method and application thereof. Background Art

[0002] Developing renewable and sustainable electrochemical energy storage technologies is an important approach to addressing the current energy crisis and environmental pollution. Lithium-ion batteries (LIBs) have been rapidly commercialized due to their advantages, such as high specific energy, long cycle life, wide charging power range, and good rate discharge performance. They are widely used in various portable mobile devices (such as laptops, mobile phones, digital cameras, etc.) and electric vehicles. However, the large-scale application of lithium-ion batteries is limited by the low abundance and uneven distribution of lithium resources in the Earth's crust. Sodium and lithium belong to the same main group, adjacent periodic elements, and have similar physical and chemical properties. Sodium resources are abundant and more evenly distributed than lithium. Therefore, sodium-ion batteries are considered to be a strong competitor for the next generation of energy storage devices.

[0003] Cathode materials serve as Na + The host material plays a vital role and determines the energy density of sodium-ion batteries. At present, the positive electrode materials of sodium-ion batteries mainly include layered metal oxides, Prussian blue materials and polyanion compounds. Layered metal oxides have problems such as multi-level structural phase transition and lattice distortion during the process of sodium insertion and extraction, which leads to a decrease in the stability of the material. During the synthesis of Prussian blue materials, there is more than 10% lattice water in the structure, which will decompose at high potential to produce a large amount of gas, causing the battery to swell and fail. Polyanion compounds have a stable 3D framework structure, good thermal stability and a high working potential, and are currently the best choice for sodium-ion battery positive electrode materials.

[0004] The sodium superion conductor (NASICON) type polyanion positive electrode material sodium vanadium phosphate (Na3V2(PO4)3) is considered to be a sodium ion battery positive electrode material with great application prospects due to its high voltage platform and high theoretical specific capacity (117mA h / g). However, since the framework of Na3V2(PO4)3 is connected by covalent bonds, it has poor electronic conductivity, which makes it difficult for its actual capacity to reach the theoretical value, and its rate performance is poor; in addition, the production cost of Na3V2(PO4)3 is high, and the environmental pollution problem cannot be ignored. Therefore, in order to improve the electrochemical properties of Na3V2(PO4)3, reduce production costs and alleviate environmental pollution problems, Na3V2(PO4)3 is generally doped or / and coated. For example, the prior art CN115207347A discloses a titanium-doped sodium manganese vanadium phosphate sodium ion battery positive electrode material with the chemical formula Na 3+xMnTi 1-x V x (PO4)3 (0.6≤x≤1) belongs to the rhombus NASICON structure with a space group of R-3c. The preparation method of the positive electrode material comprises the following steps: adding a sodium source, a manganese source, a titanium source, a vanadium source, ammonium dihydrogen phosphate and citric acid monohydrate to distilled water to obtain a mixed solution; subjecting the mixed solution to magnetic stirring in a constant temperature water bath to form a precursor wet gel; drying the wet gel and pre-calcining it, and then calcining it to obtain a precursor with a chemical formula of Na 3+x MnTi 1-x V x (PO4)3 battery positive electrode material. Although the patent application claims that the prepared Na 3+ x MnTi 1-x V x (PO4)3 positive electrode material has a high specific capacity, but the first-cycle discharge specific capacity of this positive electrode material at 0.5C is only 79.71m·Ah / g. When used as a positive electrode material for sodium ion batteries, this specific capacity still needs to be improved. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a carbon-coated high-entropy NASICON cathode material. The chemical formula of the cathode material is Na3V 2-y (CrFeMnZnAl) y (PO4)3 / C (0<y<1). The present invention replaces some vanadium sites in sodium vanadium phosphate by high entropy doping to obtain Na3V 2-y (CrFeMnZnAl) y (PO4)3 / C (0<y<1) positive electrode material increases the diffusion coefficient and electronic conductivity of sodium ions, thereby improving the electrochemical performance of sodium ion batteries.

[0006] Specifically, the present invention also provides the Na3V 2-y (CrFeMnZnAl) y The preparation method of (PO4)3 / C (0<y<1) positive electrode material comprises the following steps:

[0007] S1, adding a vanadium source and a carbon source into deionized water, heating and dissolving, to obtain a solution M1;

[0008] S2, adding a chromium source, an iron source, a manganese source, a zinc source and an aluminum source to the solution M1, heating and dissolving, to obtain a solution M2;

[0009] S3, adding a sodium source and a phosphorus source to the solution M2, heating and dissolving, to obtain a solution M3;

[0010] S4, heating the solution M3 to form a gel;

[0011] S5, vacuum drying the gel to obtain a xerogel;

[0012] S6. Crush the dry gel to obtain a powdery precursor, heat the powdery precursor to 300-400° C. under inert gas protection and pre-sinter for 2-4 hours, then continue heating to 700-800° C. and calcining for 8-10 hours to obtain the carbon-coated high-entropy NASICON positive electrode material.

[0013] In a preferred embodiment, the molar ratio of the vanadium source to the chromium source, iron source, manganese source, zinc source and aluminum source is (10-5y):y:y:y:y:y, wherein 0<y<1.

[0014] In a further preferred embodiment, the molar ratio of the vanadium source to the chromium source, iron source, manganese source, zinc source, and aluminum source is 45:1:1:1:1:1.

[0015] In a preferred embodiment, the molar ratio of the vanadium source to the carbon source in step S1 is 1:(3-4).

[0016] In a preferred embodiment, the conditions for heating and dissolving in step S1 are: heating to 60-80° C. and stirring for 30-60 minutes.

[0017] In a preferred embodiment, the vanadium source in step S1 is at least one of vanadium pentoxide, ammonium metavanadate, and sodium metavanadate.

[0018] In a preferred embodiment, the carbon source in step S1 is at least one of citric acid, oxalic acid, and glucose.

[0019] In a preferred embodiment, the conditions for heating and dissolving in step S2 are: heating to 60-80° C. and stirring for 10-20 minutes.

[0020] In a preferred embodiment, the chromium source in step S2 is at least one of chromium nitrate, chromium chloride, and chromium trioxide.

[0021] In a preferred embodiment, the iron source in step S2 is at least one of ferric nitrate, ferric chloride, and ferric oxide.

[0022] In a preferred embodiment, the manganese source in step S2 is manganese acetate and / or manganese carbonate.

[0023] In a preferred embodiment, the zinc source in step S2 is at least one of zinc nitrate, zinc chloride, and zinc oxide.

[0024] In a preferred embodiment, the aluminum source in step S2 is at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0025] In a preferred embodiment, the molar ratio of the sodium source in step S3 to the vanadium source in step S1 is 3:(2-y), wherein 0<y<1.

[0026] In a further preferred embodiment, the molar ratio of the sodium source in step S3 to the vanadium source in step S1 is 3:1.8.

[0027] In a preferred embodiment, the molar ratio of the phosphorus source in step S3 to the vanadium source in step S1 is 3:(2-y), wherein 0<y<1.

[0028] In a further preferred embodiment, the molar ratio of the phosphorus source in step S3 to the vanadium source in step S1 is 3:1.8.

[0029] In a preferred embodiment, the conditions for heating and dissolving in step S3 are: heating to 60-80° C. and stirring for 10-20 minutes.

[0030] In a preferred embodiment, the sodium source in step S3 is at least one of sodium fluoride, sodium acetate, sodium carbonate, and sodium nitrate.

[0031] In a preferred embodiment, the phosphorus source in step S3 is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

[0032] In a preferred embodiment, the heating condition in step S4 is: heating the oil bath to 80-90°C.

[0033] In a preferred embodiment, the vacuum drying conditions in step S5 are: vacuum drying at 100-120° C. for 20-24 hours.

[0034] In a preferred embodiment, the inert gas in step S6 is argon and / or nitrogen.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention replaces some vanadium sites in sodium vanadium phosphate by high entropy doping to obtain Na3V 1.8 (CrFeMnZnAl) 0.2 (PO4)3 / C cathode material. This cathode material has a stable NASICON framework, which not only facilitates the diffusion and transport of sodium ions, but also prevents structural distortion and internal stress problems caused during the charge and discharge process.

[0037] (2) Na3V 1.8 (CrFeMnZnAl) 0.2The multiple elements in the (PO4)3 / C positive electrode material work together (V, Mn and Cr exhibit electrochemical activity and improve the overall capacity, while other doping elements mainly play a role in stabilizing the structural framework), which can alleviate the volume change during charging and discharging, thereby giving sodium-ion batteries superior electrochemical performance.

[0038] (3) Na3V provided by the present invention 1.8 (CrFeMnZnAl) 0.2 The (PO4)3 / C cathode material is coated with carbon and has a scaly structure with numerous pores and gaps. This morphology increases the material's surface area, providing more active sites, accelerating the reaction rate, and significantly improving the material's electrical conductivity and sodium ion diffusion rate.

[0039] (4) At a current density of 1C, the Na3V 1.8 (CrFeMnZnAl) 0.2 The sodium-ion battery prepared with the (PO4)3 / C cathode material exhibited an initial discharge capacity of 113.9 mA h / g, reaching a capacity of 100.1 mA h / g after 100 cycles. At a current density of 20C, the initial discharge capacity was 97.1 mA h / g, and after 500 cycles, the capacity reached approximately 75.3 mA h / g, demonstrating excellent rate and cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 XRD patterns of the positive electrode materials of (PO4)3 / C, Na3V2(PO4)3 / C prepared in Comparative Example 1, and Na3V(CrFeMnZnAl)(PO4)3 / C prepared in Comparative Example 2;

[0041] Figure 2 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 SEM image of (PO4)3 / C cathode material;

[0042] Figure 3 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 TEM image of (PO4)3 / C cathode material;

[0043] Figure 4 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 The charge and discharge curve of the first cycle of charge and discharge process of (PO4)3 / C cathode material;

[0044] Figure 5 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 Cycling performance diagram of (PO4)3 / C cathode material at 1C current density;

[0045] Figure 6 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 Cycling performance diagram of (PO4)3 / C cathode material at 20C current density;

[0046] Figure 7 This is a graph showing the cycling performance of the Na3V2(PO4)3 / C cathode material prepared in Comparative Example 1 at a current density of 1C;

[0047] Figure 8 This is a cycling performance diagram of the Na3V(CrFeMnZnAl)(PO4)3 / C cathode material prepared in Comparative Example 2 at a current density of 1C;

[0048] Figure 9 This is the SEM image of the Na3V2(PO4)3 / C material prepared in Comparative Example 1;

[0049] Figure 10 This is the SEM image of Na3V(CrFeMnZnAl)(PO4)3 / C material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0050] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] A carbon-coated high-entropy NASICON cathode material (Na3V 1.8 (CrFeMnZnAl) 0.2 The preparation method of (PO4)3 / C) comprises the following steps:

[0053] S1. Dissolve 54 mmol of citric acid in 40 mL of deionized water and stir to obtain a clear aqueous solution of citric acid. Weigh 18 mmol of ammonium metavanadate and add it to the aqueous solution of citric acid. Heat to 80°C and stir for 30 minutes to obtain a clear solution M1.

[0054] S2. Add 0.4 mmol manganese acetate, 0.4 mmol chromium nitrate, 0.4 mmol zinc nitrate, 0.4 mmol iron nitrate and 0.4 mmol aluminum nitrate to solution M1, maintain stirring at 80° C. for 15 min to obtain a clear solution M2.

[0055] S3. Add 30 mmol of sodium acetate and 30 mmol of ammonium dihydrogen phosphate to solution M2, maintain stirring at 80° C. for 10 min, and obtain a blue clear solution M3.

[0056] S4. Heat solution M3 to 80°C in an oil bath and keep heating until most of the water is evaporated to form a blue gel.

[0057] S5. Place the blue gel in a vacuum drying oven and vacuum dry it at 120°C for 24 hours to obtain a light blue dry gel.

[0058] S6. Grind the dry gel with a pestle to obtain a powdered precursor. Place the powdered precursor in a tube furnace and, under the protection of an argon atmosphere, heat it to 400°C for 4 hours, then heat it to 750°C at a rate of 5°C / min and calcine it for 8 hours. Finally, cool it to room temperature in the tube furnace to obtain Na3V 1.8 (CrFeMnZnAl) 0.2 (PO4)3 / C positive electrode material.

[0059] Figure 1 The Na3V prepared in this example 1.8 (CrFeMnZnAl) 0.2 XRD (X-ray diffraction) pattern of (PO4)3 / C cathode material. Figure 1 It can be seen from the above that the material prepared in this example has good peak shape and peak intensity as well as good crystallinity. Figure 2 The Na3V prepared in this example 1.8 (CrFeMnZnAl) 0.2 SEM (scanning electron microscope) image of (PO4)3 / C cathode material. Figure 2 It can be seen from the above that the surface morphology of the material prepared in this embodiment is a scale-like structure with a large number of pores and gaps on the surface. Figure 3 The Na3V prepared in this example 1.8 (CrFeMnZnAl) 0.2 TEM (transmission electron microscope) image of (PO4)3 / C cathode material. Figure 3 As can be seen from the figure, the material is formed into a stacked morphology by flakes, which further confirms that the material is formed by basic flake units. 1.8 (CrFeMnZnAl) 0.2The specific surface area of ​​(PO4)3 / C cathode material is 154.1m 2 / g.

[0060] Example 2

[0061] A method for preparing a carbon-coated high-entropy NASICON cathode material comprises the following steps:

[0062] S1. Dissolve 72 mmol of oxalic acid in 40 mL of deionized water and stir to obtain a clear oxalic acid aqueous solution. Weigh 18 mmol of sodium metavanadate and add it to the oxalic acid aqueous solution. Heat to 75°C and stir for 45 minutes to obtain a clear solution M1.

[0063] S2. Add 0.4 mmol manganese carbonate, 0.4 mmol chromium chloride, 0.4 mmol zinc chloride, 0.4 mmol ferric chloride and 0.4 mmol aluminum chloride to solution M1, maintain stirring at 75° C. for 10 min to obtain a clear solution M2.

[0064] S3. Add 30 mmol of sodium carbonate and 30 mmol of diammonium hydrogen phosphate to solution M2, maintain stirring at 60° C. for 20 min, and obtain a blue clear solution M3.

[0065] S4. Heat solution M3 to 85°C in an oil bath and keep heating until most of the water is evaporated to form a blue gel.

[0066] S5. Place the blue gel in a vacuum drying oven and vacuum dry it at 100°C for 23 hours to obtain a light blue dry gel.

[0067] S6. Grind the dry gel with a pestle to obtain a powdered precursor. Place the powdered precursor in a tube furnace and, under the protection of a nitrogen atmosphere, heat it to 300°C for pre-calcination for 3 hours, then heat it to 800°C at a rate of 5°C / min and calcine it for 9 hours. Finally, cool it to room temperature in the tube furnace to obtain Na3V 1.8 (CrFeMnZnAl) 0.2 (PO4)3 / C positive electrode material.

[0068] Example 3

[0069] A method for preparing a carbon-coated high-entropy NASICON cathode material comprises the following steps:

[0070] S1. Dissolve 60 mmol of glucose in 40 mL of deionized water and stir to obtain a clear aqueous glucose solution. Weigh 18 mmol of vanadium pentoxide and add it to the aqueous glucose solution. Heat to 60°C and stir for 60 minutes to obtain a clear solution M1.

[0071] S2. Add 0.4 mmol manganese acetate, 0.4 mmol chromium oxide, 0.4 mmol zinc oxide, 0.4 mmol ferric oxide and 0.4 mmol aluminum sulfate to solution M1, maintain stirring at 60° C. for 20 min to obtain a clear solution M2.

[0072] S3. Add 30 mmol of sodium nitrate and 30 mmol of sodium dihydrogen phosphate to solution M2, maintain stirring at 70° C. for 15 min, and obtain a blue clear solution M3.

[0073] S4. Heat solution M3 to 90°C in an oil bath and keep heating until most of the water is evaporated to form a blue gel.

[0074] S5. Place the blue gel in a vacuum drying oven and vacuum dry it at 110°C for 20 h to obtain a light blue dry gel.

[0075] S6. Grind the dry gel with a pestle to obtain a powdered precursor. Place the powdered precursor in a tube furnace and, under the protection of a nitrogen atmosphere, heat it to 350°C for 2 hours, then heat it to 700°C at a rate of 5°C / min and calcine it for 10 hours. Finally, cool it to room temperature in the tube furnace to obtain Na3V 1.8 (CrFeMnZnAl) 0.2 (PO4)3 / C positive electrode material.

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing a Na3V2(PO4)3 / C positive electrode material, which specifically includes the following steps:

[0078] P1. Dissolve 60 mmol of citric acid in 40 mL of deionized water and stir to obtain a clear aqueous citric acid solution. Weigh 20 mmol of ammonium metavanadate and add it to the aqueous citric acid solution. Heat to 80°C and stir for 30 minutes to obtain a clear solution L1.

[0079] P2. Add 30 mmol of sodium acetate and 30 mmol of ammonium dihydrogen phosphate to solution L1 in sequence, keep heating and stirring at 80°C for 10 min, and obtain a blue clear solution L2.

[0080] P3. Heat solution L2 in an oil bath at 80°C until most of the water evaporates to form a blue gel.

[0081] P4. Transfer the blue gel to a vacuum drying oven and maintain vacuum drying at 120°C for 24 h to obtain a light blue dry gel.

[0082] P5. Grind the dry gel with a pestle to obtain a powdered precursor A. Place the powdered precursor A in a tubular furnace. Under the protection of an argon atmosphere, heat it to 400°C for pre-calcination for 4 hours, then heat it to 750°C at a rate of 5°C / min and calcine it for 8 hours. Finally, cool it to room temperature in the tubular furnace to obtain the Na3V2(PO4)3 / C positive electrode material.

[0083] Figure 9 The SEM image of the Na3V2(PO4)3 / C cathode material prepared in this comparative example is shown in FIG. Figure 9 It can be seen that the particles of the prepared Na3V2(PO4)3 / C material are agglomerated and the sample has no obvious flake structure; the specific surface area test result is 74.4m 2 / g.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing a Na3V(CrFeMnZnAl)(PO4)3 / C positive electrode material, which specifically includes the following steps:

[0086] R1. Dissolve 30 mmol of citric acid in 40 mL of deionized water and stir to obtain a clear aqueous solution of citric acid. Weigh 10 mmol of ammonium metavanadate and add it to the aqueous solution of citric acid. Heat to 80°C and stir for 30 minutes to obtain a clear solution N1.

[0087] R2. Add 2 mmol of manganese acetate, 2 mmol of chromium nitrate, 2 mmol of zinc nitrate, 2 mmol of iron nitrate and 2 mmol of aluminum nitrate to solution N1 in sequence, keep heating and stirring at 80°C for 15 minutes to obtain a clear solution N2.

[0088] R3. Add 30 mmol of sodium acetate and 30 mmol of ammonium dihydrogen phosphate to solution N2 in sequence, keep heating and stirring at 80°C for 10 min, and obtain a blue clear solution N3.

[0089] R4. Heat solution N3 to 80°C in an oil bath and maintain heating at 80°C until a large amount of water is evaporated to form a blue gel.

[0090] R5. Transfer the blue gel to a vacuum drying oven and dry it at 120°C for 24 h to obtain a light blue dry gel.

[0091] R6. Grind the obtained dry gel with a pestle to obtain a powdered precursor B. Place the powdered precursor B in a tubular furnace. Under the protection of an argon atmosphere, first heat it to 400°C and keep it warm for 4 hours. Then heat it to 750°C at a rate of 5°C / min and calcine it for 8 hours. Finally, cool it to room temperature in the tubular furnace to obtain the Na3V(CrFeMnZnAl)(PO4)3 / C positive electrode material.

[0092] Figure 10 The SEM image of the Na3V(CrFeMnZnAl)(PO4)3 / C cathode material prepared in this comparative example is shown in FIG. Figure 10 It can be seen that the prepared Na3V(CrFeMnZnAl)(PO4)3 / C material has almost no flake structure; the specific surface area test result is 54.1m 2 / g.

[0093] Application Examples

[0094] The composite materials prepared in Example 1 and Comparative Examples 1-2 were each mixed with a conductive agent (Super P) and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1. The mixture was then dispersed into N-methyl-2-pyrrolidone (NMP) solvent to form a uniform slurry. The slurry was then coated onto aluminum foil using a doctor blade or a four-sided coater to form a positive electrode sheet. The coated aluminum foil was placed in a drying oven and dried at 120°C for 12 hours. The dried aluminum foil was cut into circular electrode sheets with a diameter of 12 mm and assembled into button cells (CR2032) in a glove box. The electrochemical properties of the composite materials prepared in Example 1 and Comparative Examples 1-2 were tested using the composite materials prepared in Example 1 and Comparative Examples 1-2 as the working electrode and a sodium block as the counter electrode. The diaphragm was made of Whatman GF / A glass fiber filter paper, and the electrolyte system was a solute of 1M NaClO4 and a solvent of ethylene carbonate (EC) + dimethyl carbonate (DMC) + 5vol% fluoroethylene carbonate (FEC), with the volume ratio of EC and DMC being 1:1.

[0095] The assembled button batteries were subjected to electrochemical performance tests. The test instruments used for the electrochemical performance tests are as follows: LANHE-CT2001A multi-channel battery testing system produced by Wuhan Landian Electronics Co., Ltd., with a standing time of 12 hours, a voltage window range of 1.8-4.4V, a current density range of 100-2000mA / g, and a cycle number range of 100-1000 times.

[0096] Figure 4 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 The charge and discharge curve of the first cycle of the (PO4)3 / C cathode material. Figure 4 It can be clearly seen that there is a long voltage platform corresponding to charging and discharging respectively, and the cycle stability is excellent.

[0097] Figure 5 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2Cycling performance diagram of (PO4)3 / C cathode material at 1C current density. Figure 5 It can be seen that the positive electrode material still maintains a specific capacity of up to 100.1 mA·h / g after 100 cycles, showing good cycle stability.

[0098] Figure 6 Na3V prepared in Example 1 1.8 (CrFeMnZnAl) 0.2 Cycling performance diagram of (PO4)3 / C cathode material at 20C current density. Figure 6 It can be seen that the initial discharge specific capacity of the positive electrode material is 97.1 mA h / g, and after 500 cycles, it still maintains a specific capacity of up to 75.3 mA·h / g, showing good cycle stability and rate performance.

[0099] Figure 7 This is the cycle performance diagram of the Na3V2(PO4)3 / C positive electrode material prepared in Comparative Example 1 at a current density of 1C. The specific capacity and cycle stability are worse than those in Example 1.

[0100] Figure 8 This is the cycle performance diagram of the Na3V(CrFeMnZnAl)(PO4)3 / C positive electrode material prepared in Comparative Example 2 at a current density of 1C. The specific capacity and cycle stability are worse than those in Example 1.

[0101] The cycling performance of the positive electrode materials prepared in Example 1 and Comparative Examples 1-2 at a current density of 1C is shown in Table 1.

[0102] Table 1 Cycling performance of positive electrode materials of Example 1 and Comparative Examples 1-2 at 1C current density

[0103]

[0104] By comparing the cycle performance data of Example 1 and Comparative Examples 1-2, it can be seen that cation doping in an appropriate proportion can improve the specific capacity and cycle stability of the sodium vanadium phosphate positive electrode material.

[0105] In summary, the present invention studies Na3V 2-y (CrFeMnZnAl) y The preparation method of (PO4)3 / C (y=0, 0.2, 1) composite materials, the doping amount of high entropy materials, the material structure and morphology, and the electrochemical properties were studied. It was found that the high entropy doping strategy of replacing vanadium sites with five elements of Cr, Fe, Mn, Zn, and Al was adopted. When the molar ratio of the doping amount of these five elements to the vanadium element was 1:9, under the synergistic effect of these five elements, the obtained Na3V 1.8 (CrFeMnZnAl)0.2 (PO4)3 / C composite material has a scaly structure with many pores on the surface. This morphology makes the material have a larger specific surface area, can provide more active sites, and accelerate the reaction rate. At the same time, carbon coating greatly improves the conductivity of the material. 1.8 (CrFeMnZnAl) 0.2 When used as the positive electrode material for sodium ion batteries, (PO4)3 / C composite material has good cycle stability and rate performance.

[0106] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A carbon-coated high-entropy NASICON cathode material, characterized in that: The chemical formula of the carbon-coated high-entropy NASICON cathode material is Na3V 2-y (CrFeMnZnAl) y (PO4)3 / C, where 0<y<1.

2. The method for preparing the carbon-coated high-entropy NASICON cathode material according to claim 1, characterized in that: The following steps are involved: S1, adding a vanadium source and a carbon source into deionized water, heating and dissolving, to obtain a solution M1; S2, adding a chromium source, an iron source, a manganese source, a zinc source and an aluminum source to the solution M1, heating and dissolving, to obtain a solution M2; S3, adding a sodium source and a phosphorus source to the solution M2, heating and dissolving, to obtain a solution M3; S4, heating the solution M3 to form a gel; S5, vacuum drying the gel to obtain a xerogel; S6. Crush the dry gel to obtain a powdery precursor, heat the powdery precursor to 300-400° C. under inert gas protection and pre-sinter for 2-4 hours, then continue heating to 700-800° C. and calcining for 8-10 hours to obtain the carbon-coated high-entropy NASICON positive electrode material.

3. The preparation method according to claim 2, characterized in that The molar ratio of the vanadium source to the chromium source, iron source, manganese source, zinc source and aluminum source is (10-5y):y:y:y:y:y, wherein 0<y<1.

4. The preparation method according to claim 2, characterized in that The molar ratio of the vanadium source to the carbon source in step S1 is 1:(3-4); or / and, the molar ratio of the sodium source in step S3 to the vanadium source in step S1 is 3:(2-y), wherein 0<y<1; Or / and, the molar ratio of the phosphorus source in step S3 to the vanadium source in step S1 is 3:(2-y), wherein 0<y<1.

5. The preparation method according to claim 2, characterized in that The conditions for heating and dissolving in step S1 are: heating to 60-80°C and stirring for 30-60 minutes; Or / and, the conditions for heating and dissolving in step S2 are: heating to 60-80° C. and stirring for 10-20 minutes; Or / and, the conditions for heating and dissolving in step S3 are: heating to 60-80° C. and stirring for 10-20 minutes.

6. The preparation method according to claim 2, characterized in that The heating conditions in step S4 are: heating the oil bath to 80-90°C; Or / and, the vacuum drying condition in step S5 is: vacuum drying at 100-120° C. for 20-24 hours.

7. The preparation method according to claim 2, characterized in that The vanadium source in step S1 includes at least one of vanadium pentoxide, ammonium metavanadate, and sodium metavanadate; Or / and, the carbon source in step S1 includes at least one of citric acid, oxalic acid, and glucose.

8. The preparation method according to claim 2, characterized in that The chromium source in step S2 includes at least one of chromium nitrate, chromium chloride, and chromium trioxide; Or / and, the iron source in step S2 comprises at least one of ferric nitrate, ferric chloride, and ferric oxide; Or / and, the manganese source in step S2 is manganese acetate and / or manganese carbonate; Or / and, the zinc source in step S2 comprises at least one of zinc nitrate, zinc chloride, and zinc oxide; Or / and, the aluminum source in step S2 includes at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

9. The preparation method according to claim 2, characterized in that The sodium source in step S3 includes at least one of sodium fluoride, sodium acetate, sodium carbonate, and sodium nitrate; Or / and, in step S3, the phosphorus source includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate.

10. Use of the carbon-coated high-entropy NASICON cathode material according to claim 1 or the preparation method according to any one of claims 2 to 9 in preparing a cathode material for a sodium ion battery.

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