Hybrid polyanionic vanadium-based positive electrode material and preparation method thereof, and sodium ion battery

Abstract

The application provides a hybrid polyanion vanadium-based positive electrode material and a preparation method thereof. By preparing an organic acid and a vanadium source into a solution state, and then adding other raw materials for reaction, a pure-phase hybrid polyanion vanadium-based positive electrode material can be synthesized at a lower synthesis temperature. The method has the advantages of low synthesis temperature, short reaction time, low energy consumption and cost, simple operation, real-time monitoring and regulation of the pH of the reaction system in the subsequent reaction process, improved control precision of the pH value, ensured synthesis of a nanosheet product with high purity, good controllability of the process, good repeatability, and suitability for industrial production. The preparation method of the application not only avoids the shortcomings of a traditional hydrothermal reaction, such as long time consumption, high energy consumption, and inconvenience for observation and process control, but also effectively improves the purity, yield, consistency, and controllability of the product.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage materials, and particularly relates to a sodium ion battery positive electrode material, in particular to a hybrid polyanion vanadium-based positive electrode material A x A preparation method of (VO)2(HPO4)2R and application thereof. BACKGROUND

[0002] In recent years, sodium ion batteries, which are mainly composed of abundant and economical raw materials, have become a new star in the field of energy storage batteries. However, the sodium ion batteries do not have competitive performance in terms of energy density and cycle life, which has become a key factor restricting commercial application. Therefore, researchers start from each component of the sodium ion battery, and improve the comprehensive performance through selecting suitable materials, exploring synthesis methods, applying modification processes, optimizing formula and structure and many other ways. Through these researches, it has been proved that the positive electrode system plays a decisive role in the performance of the sodium ion battery. At present, the widely studied sodium ion battery positive electrode materials mainly include low-cost layered metal oxides, sodium polyanion compounds, prussian blue compounds and the like.

[0003] The sodium polyanion compound NaM(XO4) (X represents phosphorus, sulfur, vanadium, silicon and the like, and M represents a transition metal element with variable valence) is composed of an anion structural unit and a MO x polyhedron with strong covalent bonds. The bonding of the anion unit constructs a three-dimensional network structure, which provides a high-coordination gap that can be occupied by metal cations. Among several types of sodium ion battery positive electrode materials, the polyanion compound exhibits advantages in terms of working voltage, cycle life, safety and the like. This is due to the fast ion conduction channel provided by the anion unit and the stability of the charging and discharging redox potential by the "inductive effect". However, there is still a lack of a simple process and environmentally friendly preparation and modification method for the sodium polyanion positive electrode material, which has become an obstacle to the industrial application of the polyanion positive electrode material.

[0004] In order to explore a greater prospect of the application of phosphate positive electrode materials in sodium ion batteries, new preparation and modification methods for polyanion positive electrode materials are constantly being proposed. Although progress has been made, the main purpose of exploring new methods is to synthesize new materials and improve the electrochemical performance, and the process optimization and energy-saving and environmental protection attempts are still lacking.

[0005] CN116598447A discloses a carbon material coated sodium vanadium fluorophosphate and a preparation method and application thereof as a sodium ion battery positive electrode material, comprising preparing a sodium vanadium fluorophosphate material and mixing a carbon material with the sodium vanadium fluorophosphate material and ball milling to obtain a carbon coated sodium vanadium fluorophosphate material. It utilizes iron elements to partially replace vanadium elements in sodium vanadium phosphate, reduces the cost, and improves the electrochemical performance of the material through doping of fluorine elements and coating of carbon materials. However, due to the multiple material manufacturing steps and complex process flow, a large amount of organic waste liquid is generated in the process, resulting in greater pollution and poor environmental performance.

[0006] CN113328086A discloses a sodium vanadyl pyrophosphate@graphene composite positive electrode material and a preparation and application thereof, which is prepared by mixing a sodium source, a phosphorus source, a vanadium source and deionized water, then adding graphene oxide, followed by spray drying or freeze drying, and finally calcining to obtain a pyrophosphate composite material. The sodium vanadyl pyrophosphate is coated with few-layer or multi-layer graphene, and thus has good rate characteristics and charge and discharge specific capacity. However, due to the need for spray drying or freeze drying and high-temperature calcination, the technology is difficult, the energy consumption is large, and the process cost is high.

[0007] CN109546117A discloses a layered metal organic phosphate framework sodium ion positive electrode material and a preparation method thereof, which is prepared by adding a sodium source, a vanadium source, phosphoric acid and oxalic acid into water, then preparing a base material through a hydrothermal reaction, and then mixing and grinding with a carbon conductive agent. The positive electrode material has good electrochemical performance and is a new attempt in the field of sodium ion battery positive electrode materials. However, the hydrothermal reaction requires a high reaction temperature and a slow reaction rate, and thus requires a long reaction time, resulting in high energy consumption, and the synthesized product is often large and dense, resulting in poor conductivity and sodium ion diffusion; and when hydrothermal reaction occurs, the material continuously dissolves into the liquid phase with the increase of temperature and time, resulting in a continuous change of pH value and unmonitorable, and the consistency of changes between different experiments cannot be estimated, thus causing poor consistency of the reaction and poor consistency of different batches of products and uncontrollable morphology. SUMMARY

[0008] In view of the above technical problems, the purpose of the present application is to provide a hybrid poly-anion vanadium-based positive electrode material and a preparation method and a sodium ion battery thereof.

[0009] To achieve the above purpose, the present application proposes the following solutions:

[0010] The present application provides a hybrid poly-anion vanadium-based positive electrode material, the chemical general formula of which is A x(V0)2(HPO4)2R, A is one or more of Li, Na, K, R is one or more of acetate, oxalate, citrate, 1≤x≤3; the crystal structure of the hybrid polyanion vanadium-based positive electrode material is a monoclinic structure of chiral non-centrosymmetric space group, and the unit cell volume is 560~660 Å 3 ; the hybrid polyanion vanadium-based positive electrode material has a nanosheet structure, and the width of the nanosheet is 2.5~10 μm.

[0011] As preferred, the molecular structure of the hybrid polyanion vanadium-based positive electrode material is: VO 2+ and HPO4 2- to form a 2D structure [(VO)2(HPO4)2(R)] x- layer, alkali metal ions and water molecules are located between the [(VO)2(HPO4)2(R)] x- layers.

[0012] As a general inventive concept, the present application provides a preparation method of a hybrid polyanion vanadium-based positive electrode material, comprising:

[0013] S1, dissolving a vanadium source in an organic acid solution to obtain solution A;

[0014] S2, mixing solution A with an alkali metal source and a phosphorus source to obtain solution B;

[0015] S3, adjusting the pH value of solution B to 1~6 with phosphoric acid, and performing a reaction under heating conditions, wherein the pH value of the reaction system is maintained at 1~6 during the reaction, and after the reaction is completed, solid-liquid separation, washing and drying are performed, and then sintering is performed to remove crystallization water, to obtain a hybrid polyanion vanadium-based positive electrode material A x (VO)2(HPO4)2R.

[0016] As preferred, in step S1, the vanadium source is one or more of vanadium pentoxide, vanadium dioxide, and ammonium metavanadate.

[0017] As preferred, in step S1, the organic acid is one or more of acetic acid, oxalic acid, citric acid and hydrates thereof.

[0018] As preferred, in step S2, the phosphorus source is one or more of phosphoric acid, lithium phosphate, sodium phosphate, and potassium phosphate.

[0019] As preferred, in step S2, the alkali metal source is a salt or hydroxide of at least one of Li, Na, and K.

[0020] Preferably, in step S1, the dissolving is carried out under heating and stirring; the temperature of the heating is 50-100 DEG C; the speed of the stirring is 100-400 r / min.

[0021] Preferably, in step S3, the temperature of the reaction is 50-100 DEG C; the time of the reaction is 6-24 h; the reaction is carried out under stirring; the speed of the stirring is 100-400 r / min.

[0022] Preferably, the molar ratio of vanadium in the vanadium source, alkali metal in the alkali metal source and phosphate radical in the phosphorus source is 1:2-4:1; the molar ratio of vanadium in the vanadium source and hydrogen ion in the organic acid is 1:2-2.5.

[0023] Preferably, in step S1, the organic acid solution is prepared by dissolving the organic acid in hot water; the concentration of the organic acid solution is 0.6-1 mol / L; the temperature of the hot water is 50-100 DEG C.

[0024] Preferably, in step S3, the sintering is carried out under vacuum environment or inert atmosphere protection; the temperature of the sintering is 120-350 DEG C; the time of the sintering is 1-6 h; the heating rate of the sintering is 3-10 DEG C / min.

[0025] As one general inventive concept, the application further provides a sodium ion battery comprising the hybrid polyanionic vanadium-based positive electrode material A x (VO)2(HPO4)2R or the hybrid polyanionic vanadium-based positive electrode material A obtained by the preparation method. x (VO)2(HPO4)2R.

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

[0027] The preparation method of the application can synthesize the pure-phase hybrid polyanionic vanadium-based positive electrode material at a lower synthesis temperature by first preparing a solution of the organic acid and the vanadium source and then adding other raw materials for reaction, and the method has the advantages of low synthesis temperature, short reaction time, low energy consumption and cost, simple operation, real-time monitoring and control of the pH of the reaction system in the subsequent reaction process, improved control precision of the pH value, ensured synthesis of products with good purity, good controllability and repeatability of the process and suitability for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative effort based on these drawings.

[0029] Figure 1 SEM images of reaction products prepared in Example 1 and Comparative Example 1, wherein (a) is an SEM image of the reaction product prepared in Example 1, and (b) is an SEM image of the reaction product prepared in Comparative Example 1.

[0030] Figure 2 XRD of reaction products prepared in Example 1-2 and Comparative Example 1-2 of the present application.

[0031] Figure 3 The first circle charge-discharge curve of the button cell assembled by the product obtained in Example 1 and Comparative Example 1 of the present application.

[0032] Figure 4 The rate performance graph of the button cell assembled by the product obtained in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0033] Some embodiments of the present application provide a hybrid poly-anion vanadium-based positive electrode material, with a general chemical formula of A x (VO)2(HPO4)2R, A is one or more than two of Li, Na, and K, R is one or more than two of acetate, oxalate, and citrate, and 1≤x≤3; the crystal structure of the hybrid poly-anion vanadium-based positive electrode material is a single-clinic crystal structure of chiral non-centrosymmetric space group, with a unit cell volume of 560-660 Å 3 ; the hybrid poly-anion vanadium-based positive electrode material has a nanosheet structure, and the width of the nanosheet is 2.5-10 μm.

[0034] In some embodiments, the molecular structure of the hybrid poly-anion vanadium-based positive electrode material is: VO 2+ and HPO4 2- form a long chain [(VO)(HPO4)], and the R group bridges each long chain to form a 2D structure [(VO)2(HPO4)2(R)] x- layer, and alkali metal ions and water molecules are located between the [(VO)2(HPO4)2(R)] x- layers.

[0035] As a general inventive concept, the present application also provides a preparation method of a hybrid poly-anion vanadium-based positive electrode material, comprising:

[0036] S1, dissolving a vanadium source in an organic acid solution to obtain a solution A;

[0037] S2, mixing the solution A with an alkali metal source and a phosphorus source to obtain a solution B;

[0038] S3, adjusting the pH value of the solution B to 1-6 by using phosphoric acid, and performing a reaction under a heating condition, wherein the pH value of the reaction system is maintained at 1-6 during the reaction, and after the reaction, the obtained powder is separated, washed, dried, and then sintered at a low temperature to remove the crystal water, thereby obtaining a hybrid poly-anionic vanadium-based positive electrode material A x (VO)2(HPO4)2R.

[0039] In the present application, the organic acid is added into a hot aqueous solution under a certain temperature and stirring, and after the organic acid is dissolved to obtain an organic acid solution, the vanadium source is added, and after a period of reaction, a precursor solution is obtained, and then the alkali metal source and the phosphorus source are added into the solution. Subsequently, the pH of the reaction system is adjusted to a suitable range by using phosphoric acid, and the pH value in the reaction process is detected and controlled in a suitable range. After the reaction, the obtained powder containing water is separated. The obtained powder containing water is sintered at a low temperature to remove the crystal water and change the crystallinity, thereby obtaining a hybrid poly-anionic vanadium-based positive electrode material.

[0040] The present applicant has found that by first dissolving the vanadium source in the organic acid solution, and then adding the alkali metal source and the phosphorus source, the reaction conditions can be reduced, and the reaction efficiency can be significantly improved, and the reaction does not need to be performed under hydrothermal conditions. In the preparation method of the present application, the reaction is performed in an open space, and the precipitation generation time, color change, pH change, and reaction state can be observed in real time, which is convenient for process parameter adjustment and control and experience summary. It is found through analysis that the above advantages are because, compared with the method of adding each raw material in the form of a solid into water and reacting under hydrothermal conditions, the reaction of the present application is performed in a liquid phase, and various elements required by the target product exist in the form of ions in the aqueous solution, so the ion concentration is high, the contact area is large, and thus a faster reaction rate can be provided, the reaction time and the reaction temperature are reduced, and the pure-phase hybrid poly-anionic vanadium-based positive electrode material can be synthesized at a lower synthesis temperature.

[0041] In some preferred embodiments, in step S3, the pH value of the reaction system is adjusted to 1-5, for example, 1, 2, 3, 4, 5, etc.

[0042] In some preferred embodiments, in step S1, the vanadium source is at least one of vanadium pentoxide, vanadium dioxide, and ammonium metavanadate.

[0043] In some preferred embodiments, in step S1, the organic acid is at least one of acetic acid, oxalic acid, citric acid, and a hydrate thereof.

[0044] In some preferred embodiments, in step S2, the phosphorus source is at least one of phosphoric acid, lithium phosphate, sodium phosphate, potassium phosphate.

[0045] In some preferred embodiments, in step S2, the alkali metal source is at least one of Li, Na, K in the form of a salt or hydroxide.

[0046] In some preferred embodiments, in step S1, the dissolving is carried out under heating and stirring; the temperature of the heating is 50-100℃; the speed of the stirring is 100-400 r / min.

[0047] In some preferred embodiments, in step S1, the organic acid solution is prepared by dissolving an organic acid in hot water; the concentration of the organic acid solution is 0.6-1 mol / L; the temperature of the hot water is 50-100℃.

[0048] In some preferred embodiments, in step S3, the temperature of the reaction is 50-100℃, further preferably 50-95℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc.; the time of the reaction is 6-24 h.

[0049] In some preferred embodiments, in step S3, the reaction is carried out under stirring; the speed of the stirring is 100-400 r / min.

[0050] In some preferred embodiments, the molar ratio of vanadium in the vanadium source, alkali metal in the alkali metal source, and phosphate in the phosphorus source is 1:2-4:1, and the molar ratio of vanadium in the vanadium source to hydrogen ions in the organic acid is 1:2-2.5, such as 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0051] In some preferred embodiments, in step S3, the sintering is carried out under vacuum or in an inert atmosphere; the temperature of the sintering is 120-350℃, further preferably 150-300℃, such as 150℃, 180℃, 200℃, 220℃, 250℃, 280℃, 300℃, etc.; the time of the sintering is 1-6 h; the heating rate of the sintering is 3-10℃ / min.

[0052] As a general inventive concept, the present application also provides a sodium-ion battery comprising the hybrid polyanionic vanadium-based positive electrode material A x (VO)2(HPO4)2R or the hybrid polyanionic vanadium-based positive electrode material A obtained by the preparation method described above x (VO)2(HPO4)2R.

[0053] In order to facilitate the understanding of the present application, the present application will be described in more detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0054] Unless otherwise defined, all the professional terms used herein have the same meaning as understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0055] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased on the market or can be prepared by existing methods.

[0056] Example 1

[0057] (1) A beaker containing 40 mL of water was placed in a constant temperature water bath heated to 90°C, and 0.026 mol of H2C2O4·2H2O was added to the beaker under magnetic stirring at 100 r / min. After the oxalic acid was dissolved, 0.013 mol of V2O5 was added, and the reaction was carried out for 15 min to obtain solution A1.

[0058] (2) Under the magnetic stirring at 100 r / min, 0.052 mol of NaOH and 0.026 mol of H3PO4 were sequentially added to the solution A1 obtained in step (1) to obtain solution B1, and phosphoric acid was added dropwise to solution B1 during the reaction to adjust the pH to 3, and the reaction was carried out for 10 h. After the reaction was completed, the water-containing powder obtained in the reaction was separated, washed with water and anhydrous ethanol for 3 times respectively, and vacuum dried at 60°C for 12 h to obtain the reaction product. The SEM image of the obtained product is shown in Figure 1 (a), and the product is stacked by nanosheets with a width of about 3 μm, the surface of the nanosheet is smooth, the shape is regular, and the crystallization is good. The XRD pattern is shown in Figure 1 (a), and the product is stacked by nanosheets with a width of about 3 μm, the surface of the nanosheet is smooth, the shape is regular, and the crystallization is good. The XRD pattern is shown in Figure 2 (a), and the product is stacked by nanosheets with a width of about 3 μm, the surface of the nanosheet is smooth, the shape is regular, and the crystallization is good. The XRD pattern is shown in Figure 2 It can be seen that the XRD pattern of the sample without removing the crystal water is in good agreement with the standard PDF card of Na2(VO)2(HPO4)2C2O4·2H2O, and the position, shape and intensity of each characteristic peak can be matched, which proves that the target product is successfully synthesized. The characteristic peaks of the product of Example 1 are sharp and strong, and there is no impurity peak. This proves that the product synthesized under the condition of not excessive oxalic acid and pH of 3 has high crystallinity and no impurities. The obtained product was sintered at a low temperature of 200°C for 2 h to remove the crystal water and change the crystallinity.

[0059] Example 2

[0060] (1) A beaker containing 40 mL of water was placed in a constant temperature water bath heated to 90°C, and 0.026 mol of H2C2O4.2H2O was added to the beaker under magnetic stirring at 100 r / min. After the oxalic acid was dissolved, 0.013 mol of V2O5 was added, and the reaction was allowed to proceed for 15 min to obtain solution A2.

[0061] (2) 0.052 mol of NaOH and 0.026 mol of H3PO4 were added to solution A2 obtained in step (1) under magnetic stirring at 100 r / min to obtain solution B2. During the reaction, phosphoric acid was added dropwise to solution B2 to adjust the pH to 6, and the reaction was allowed to proceed for 10 h. After the reaction was completed, the water-containing powder obtained in the reaction was separated, washed with water and anhydrous ethanol three times each, and vacuum-dried at 60°C for 12 h to obtain a reaction product. The reaction product was subjected to phase analysis, and the XRD pattern thereof is shown in Figure 2 Figure 2 It can be seen from the XRD pattern of Example 2 that the XRD pattern thereof is consistent with the standard PDF card of Na2(VO)2(HPO4)2C2O4.2H2O, and the positions and shapes of the characteristic peaks can be matched, which proves that the target product is successfully synthesized. However, the overall intensity of the characteristic peaks is decreased, and especially the strongest peak near 10.5° is decreased, and slight impurity peaks appear near 18° and 22°. This proves that the sample synthesized under the condition of insufficient acidity and pH of 6 is affected by insufficient acidity, the growth of the product is inhibited, the crystallinity is reduced, and a small amount of impurities is generated.

[0062] The product obtained was sintered at a low temperature of 250°C for 2 h to remove the crystal water and change the crystallinity.

[0063] Comparative Example 1

[0064] (1) A beaker containing 40 mL of water was placed in a constant temperature water bath heated to 90°C, and 0.026 mol of H2C2O4.2H2O was added to the beaker under magnetic stirring at 100 r / min. After the oxalic acid was dissolved, 0.013 mol of V2O5 was added, and the reaction was allowed to proceed for 15 min to obtain solution A2.

[0065] (2) 0.052 mol of NaOH and 0.026 mol of H3PO4 were added to solution A2 obtained in step (1) under magnetic stirring at 100 r / min to obtain solution B2. During the reaction, phosphoric acid was added dropwise to solution B2 to adjust the pH to 6, and the reaction was allowed to proceed for 10 h. After the reaction was completed, the water-containing powder obtained in the reaction was separated, washed with water and anhydrous ethanol three times each, and vacuum-dried at 60°C for 12 h to obtain a reaction product. The reaction product was subjected to phase analysis, and the XRD pattern thereof is shown in Figure 2 Figure 2 ​​The XRD pattern of Comparative Example 1 matches the standard PDF card of Na(VO)(HPO)C·2O. The positions of the characteristic peaks correspond, but the overall intensity of the characteristic peaks decreases, some weak peaks are obscured, and obvious miscellaneous peaks appear near 11°, 12°, 19°, 22°, and 27°. This proves that the product synthesized under the conditions of excess oxalic acid and pH 3 contains the target product, but due to the influence of excessive oxalate ions, significant impurities are generated.

[0066] The obtained product was sintered at 150 °C for 2 h to remove crystal water and change the crystallinity.

[0067] Comparative Example 2

[0068] (1) Weigh and measure 0.013 mol V2O5, 0.052 mol NaOH, 0.026 mol H2C2O4·2H2O, 0.026 mol H3PO4, and 40 mL H2O in a polytetrafluoroethylene container. Adjust the pH to 3 with phosphoric acid, sonicate for 30 min, and place in a hydrothermal autoclave for reaction at 90°C for 10 h.

[0069] (2) After the reaction is completed, the solid-liquid separation is performed to obtain the powder material, which is washed three times with water and alcohol respectively, and placed in a 60°C oven for 12 hours to obtain a dried product. The dried product is sintered at a low temperature to remove the crystal water and change the crystallinity to obtain the product. The SEM image of the obtained product is shown in FIG. Figure 1 (b) is shown by Figure 1 As shown in (b), the sample is composed of rough nano-scale flakes stacked into irregular rectangular blocks of varying sizes, indicating that the crystal growth has not yet been completed and the surface is still reacting. The dried product was analyzed for phase, and the XRD pattern is shown in Figure 2 As shown, from Figure 2 The XRD pattern of Comparative Example 1 shows that the positions of the characteristic peaks generally correspond to those of the standard PDF card of Na₂(VO)₂(HPO₄)₂C₂O₄·2H₂O. However, the peaks near 15° are offset, have different peak shapes, and are significantly lower in intensity. This suggests that at the same temperature and reaction time, the hydrothermally synthesized material in Comparative Example 2 is still in a transitional state, with incomplete incorporation of oxalic acid and incomplete material growth.

[0070] contrast Figure 1 It can be seen from (a) and 1 (b) that, at the same temperature and time, the material synthesized by hydrothermal method (the preparation of comparative example 2 can be regarded as a generalized hydrothermal reaction) is in the form of small flakes, and the crystal growth is not complete, while the material synthesized by water bath has formed complete flake crystals with good dispersibility.

[0071] The XRD results of Examples 1-2, Comparative Example 1 and Comparative Example 2 are as follows:Figure 2 At the same temperature and time, the hydrothermally synthesized material is still in a transition state, and oxalic acid is not fully combined. It is proved that water bath increases the reaction rate, reduces the synthesis temperature and shortens the synthesis time. Comparison of XRD patterns between different pH and oxalic acid dosage examples shows that the optimization of oxalic acid amount and phosphoric acid to adjust pH value is beneficial to the synthesis of pure phase material.

[0072] The Na2(VO)2(HPO4)2(C2O4) prepared in Examples 1-2 and Comparative Examples 1-2 and the Na2(VO)2(HPO4)2(C2O4) prepared by hydrothermal method in Comparative Example 1 were assembled into button cells according to the following method: first, the Na2(VO)2(HPO4)2(C2O4) powder and acetylene black were ball milled at a ratio of 7:2. Then, a certain amount of ball milling material and binder PVDF (HSV-900) (9:1) were weighed, and after grinding, 0.4 mL of NMP was added for dispersion and mixing. After uniform mixing, the slurry was coated on an aluminum foil to form a positive electrode sheet, and vacuum dried. Finally, in an anaerobic glove box, a CR2025 button cell was assembled with a metal sodium sheet as the negative electrode, glass fiber as the separator, and sodium perchlorate as the electrolyte.

[0073] After the assembled battery was placed for 12 h, the electrochemical performance test was carried out at a voltage range of 2.5-4.5 V, and the results are shown in Figures 3-4 .

[0074] As can be seen from Figures 3-4 , compared with Comparative Example 1, the battery assembled from the hybrid polyanionic vanadium-based positive electrode material Na2(VO)2(HPO4)2(C2O4) synthesized in Example 1 has high capacity and excellent rate performance.

[0075] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a hybrid polyanionic vanadium-based cathode material, characterized in that, The preparation method comprises the following steps: S1, dissolving a vanadium source in an organic acid solution to obtain solution A; the organic acid is one or more than two of acetic acid, oxalic acid, citric acid and hydrates thereof; S2, mixing solution A with an alkali metal source and a phosphorus source to obtain solution B; S3, the pH value of solution B is adjusted to 1-6 by phosphoric acid, and the reaction is carried out under heating, the pH value of the reaction system is maintained at 1-6 during the reaction, after the reaction is completed, solid-liquid separation, washing and drying are carried out, and then sintering is carried out to remove crystallization water, to obtain a hybrid poly-anion vanadium-based positive electrode material A x (VO)2(HPO4)2R, wherein A is one or two or more of Li, Na and K, R is one or two or more of acetate, oxalate and citrate, 1≤x≤3; the temperature of the reaction is 50-100 DEG C; and the temperature of the sintering is 120 DEG C-350 DEG C.

2. The method for preparing the hybrid polyanion vanadium-based cathode material according to claim 1, wherein: In step S1, the vanadium source is one or more than two of vanadium pentoxide, vanadium dioxide and ammonium metavanadate; In step S2, the phosphorus source is one or more than two of phosphoric acid, lithium phosphate, sodium phosphate and potassium phosphate; In step S2, the alkali metal source is at least one of Li, Na and K in the form of a salt or hydroxide.

3. The method for preparing the hybrid polyanion vanadium-based cathode material according to claim 1, wherein: In step S1, the dissolving is performed under heating and stirring; the temperature of the heating is 50-100℃; the stirring speed is 100-400 r / min.

4. The method for preparing the hybrid polyanion vanadium-based cathode material according to claim 1, wherein: In step S3, the reaction time is 6-24 h; the reaction is performed under stirring; the stirring speed is 100-400 r / min.

5. The method for preparing the hybrid polyanion vanadium-based cathode material according to claim 1, wherein: The molar ratio of vanadium in the vanadium source, alkali metal in the alkali metal source, hydrogen in the organic acid and phosphate in the phosphorus source is 1:2-4:1; the molar ratio of vanadium in the vanadium source and hydrogen in the organic acid is 1:2-2.

5.

6. The method for preparing the hybrid polyanion vanadium-based cathode material according to claim 1, wherein: In step S1, the organic acid solution is prepared by dissolving the organic acid in hot water; the concentration of the organic acid solution is 0.6-1 mol / L; the temperature of the hot water is 50-100℃.

7. The production method according to claim 1, wherein In step S3, the sintering is performed under vacuum or in an inert atmosphere; the sintering time is 1-6 h; the sintering heating rate is 3-10℃ / min.

8. A hybrid poly-anionic vanadium-based cathode material, characterized in that, The preparation method is prepared according to any one of claims 1-7.

9. The hybrid poly-anionic vanadium-based cathode material of claim 8, wherein, The crystal structure of the hybrid poly-anion vanadium-based positive electrode material is a single-clinic crystal structure of chiral non-centrosymmetric space group, and the unit cell volume is 560-660 Å 3 The hybrid poly-anion vanadium-based positive electrode material has a nanosheet structure, and the width of the nanosheet is 2.5-10 μm.

10. The hybrid poly-anionic vanadium-based cathode material of claim 8 or 9, wherein, The molecular structure of the hybrid poly-anionic vanadium-based positive electrode material is: VO 2+ and HPO4 2- compositions [(VO)(HPO4)] long chains, R groups bridge each long chain to form a 2D structure [(VO)2(HPO4)2(R)] x- layer, alkali metal ions are located between the [(VO)2(HPO4)2(R)] x- layers.

11. A sodium-ion battery, characterized in that, Hybrid polyanionic vanadium-based positive electrode material A according to any one of claims 8 to 10 x (Vo)2(HPO4)2R.

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