A layered phosphate vanadium-based positive electrode material and a synthesis method thereof, and a sodium-ion battery

Abstract

The present application uses sodium source, vanadium source, reducing acid and phosphoric acid as raw materials, synthesizes Na(VO)2(PO4)2.4H2O through wet ball milling, and then obtains layered vanadium phosphate-based positive electrode material Na(VO)2(PO4)2 after low-temperature sintering of the synthesized material. The present application realizes synthesis of pure-phase layered vanadium phosphate-based positive electrode material Na(VO)2(PO4)2 at room temperature. Compared with other phosphate positive electrode materials, the material has obviously improved electrical conductivity, shows excellent discharge capacity without carbon coating, and the synthesis method has low synthesis temperature, simple operation, low cost, strong controllability, good repeatability and suitability for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, specifically relating to the synthesis of layered vanadium phosphate-based cathode material Na(VO)2(PO4)2. Background Technology

[0002] In recent years, with the continuous development of clean and renewable energy, high-efficiency energy storage systems have attracted great attention, and various rechargeable batteries have been developed for power storage in distributed power plants and microgrids. Among them, lithium-ion batteries are the most widely used, but the continuous increase in demand has also exposed the shortcomings of insufficient lithium resources and supply security risks. Therefore, sodium-ion batteries, with their low cost and widespread availability of sodium resources, are becoming increasingly competitive in the field of large-scale electrochemical energy storage.

[0003] As a core component of sodium-ion batteries, the cathode material needs to possess the following characteristics: high discharge voltage; reversible sodium ion storage with a certain capacity; sufficiently fast diffusion and migration rates of sodium ions and electrons; good chemical stability, readily achievable through conventional preparation methods; and low process requirements, easily achieved through conventional stirring and coating processes. Many vanadium-based phosphates have attracted widespread attention due to their high redox potentials and stable reversibility. However, almost all vanadium-based phosphates possess a tunnel structure, where sodium ions migrate in a zigzag pattern within the crystal lattice, resulting in slow kinetics. Previous studies have found that vanadium-based phosphates with two-dimensional layered structures exhibit better lithium / sodium ion storage performance due to their higher ion diffusion rates compared to compounds with framework structures. However, during conventional high-temperature synthesis, vanadium-based phosphates tend to form thermally stable Na3V2(PO4)3 and tunnel-structured NaVOPO4. The synthesis of layered VOPO4 and NaVOPO4 is complex, time-consuming, and requires expensive reagents and harsh reaction conditions.

[0004] Patent document CN111646452A discloses a nanosheet-shaped sodium vanadium oxyphosphate hydrate cathode material, its preparation method, and its application. The method involves dissolving the raw material in deionized water as an electrolyte solution, then using vanadium sheets as the anode and platinum sheets as the cathode, performing an electrochemical stripping reaction of the vanadium sheets in the electrolyte solution. The anode is then replaced with a platinum sheet to continue the reaction. After the reaction is complete, repeated washing and drying yield the nanosheet-shaped sodium vanadium oxyphosphate hydrate. This preparation method involves complex equipment, high energy consumption, and complex processes in its electrochemical synthesis, making it unsuitable for large-scale production.

[0005] Patent document CN116395654A discloses a method for preparing sodium vanadium oxyphosphate (NaVOPO4) cathode material and its application. The method involves ball milling and mixing raw materials and carbon source, sieving the mixture, adding a grinding agent to wash it, drying and grinding the resulting suspension of mixed precursor and grinding agent to obtain precursor powder, and then sintering the precursor powder to obtain sodium vanadium oxyphosphate cathode material NaVOPO4. However, this material has the problem of high sodium ion migration energy barrier. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a layered vanadium phosphate-based cathode material Na(VO)2(PO4)2 and its synthesis method, as well as a sodium-ion battery.

[0007] To achieve the above objectives, the present invention proposes the following solution:

[0008] A method for synthesizing a layered vanadium phosphate-based cathode material includes:

[0009] (1) Sodium source, vanadium source, reducing acid, phosphoric acid and water are mixed and ball-milled to obtain product Na(VO)2(PO4)2·4H2O;

[0010] (2) After washing and drying the product, the crystal water is removed by low-temperature sintering to obtain layered vanadium phosphate-based cathode material Na(VO)2(PO4)2.

[0011] Preferably, the sodium source is one or more of NaOH, NaCl, NaF, and Na2CO3.

[0012] Preferably, the vanadium source is one or more of V2O5, NH4VO3, and VF5.

[0013] Preferably, the reducing acid is selected from any one or more of acetic acid and its hydrate, oxalic acid and its hydrate, citric acid and its hydrate, and ascorbic acid.

[0014] Preferably, the molar ratio of vanadium in the vanadium source to sodium in the sodium source and phosphoric acid is 2:2~6:7~17; and the molar ratio of vanadium in the vanadium source to hydrogen in the reducing acid is 1:1~3.

[0015] Preferably, in step (1), the solid-liquid ratio of the ball mill is 1:1 to 10; and the ball-to-material ratio of the ball mill is 5 to 40:1.

[0016] Preferably, in step (1), the rotation speed of the ball mill is 100~300 r / min; the ball milling time is 5~12h.

[0017] Preferably, in step (2), the temperature of the low-temperature sintering is 150~350℃; the time of the low-temperature sintering is 2~6h; and the low-temperature sintering is carried out in an inert atmosphere or a nitrogen atmosphere.

[0018] As a general inventive concept, the present invention also provides a layered vanadium phosphate-based cathode material, which is prepared by the aforementioned synthesis method.

[0019] As a general inventive concept, the present invention also provides a sodium-ion battery, including the aforementioned layered vanadium phosphate-based cathode material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention synthesizes a layered vanadium phosphate-based material Na(VO)2(PO4)2 at room temperature. The layered structure of Na(VO)2(PO4)2 provides a two-dimensional migration path for sodium ions, and its ion diffusion rate is higher than that of framework-structured compounds. Compared with other phosphate cathode materials, the layered vanadium phosphate-based material Na(VO)2(PO4)2 synthesized by the mechanochemical method has significantly improved conductivity, exhibits excellent discharge capacity without carbon coating, and the method has low synthesis temperature, simple operation, low cost, strong controllability, and good reproducibility, making it suitable for industrial production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a SEM image of the layered vanadium phosphate-based material Na(VO)2(PO4)2 material from Example 1 of this invention.

[0024] Figure 2 The XRD patterns are of Na(VO)2(PO4)2.4H2O prepared in Examples 1-4 of this invention.

[0025] Figure 3 These are the first charge-discharge curves for Embodiment 1 and Comparative Example 1 of the present invention.

[0026] Figure 4 The diagram shows the rate performance of Examples 1-4 and Comparative Example 1 of the present invention. Detailed Implementation

[0027] Some embodiments of the present invention provide a method for preparing a layered vanadium phosphate-based cathode material, comprising:

[0028] (1) Sodium source, vanadium source, reducing acid, phosphoric acid and water are mixed and ball milled. Under the action of mechanical force, the components are dispersed and reorganized, and physical and chemical transformations occur to obtain the product Na(VO)2(PO4)2·4H2O.

[0029] (2) After washing and drying the product, the crystal water is removed by low-temperature sintering to obtain layered vanadium phosphate-based cathode material Na(VO)2(PO4)2.

[0030] In some preferred embodiments, the sodium source is one or more of NaOH, NaCl, NaF, and Na2CO3.

[0031] In some preferred embodiments, the vanadium source is one or more of V2O5, NH4VO3, and VF5.

[0032] In some preferred embodiments, the reducing acid is selected from any one or more of acetic acid and its hydrate, oxalic acid and its hydrate, citric acid and its hydrate, and ascorbic acid.

[0033] In some preferred embodiments, the molar ratio of vanadium in the vanadium source to sodium in the sodium source and phosphoric acid is 2:2~6:7~17, and more preferably 2:2~6:9~17.

[0034] Hydrogen ion concentration affects crystal orientation and product purity. Excessive hydrogen ion concentration causes the material to grow along the direction of higher sodium ion migration energy barriers, while insufficient hydrogen ion concentration degrades product purity and easily introduces impurities. In some preferred embodiments, the molar ratio of vanadium in the vanadium source to hydrogen in the reducing acid is 1:1 to 3, more preferably 1:1.5 to 2.5, such as 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0035] In some preferred embodiments, in step (1), the solid-liquid ratio (mass ratio) of the ball mill is 1:1 to 10; if the solid-liquid ratio is too high, the reaction rate will be reduced, and if the solid-liquid ratio is too low, the crystal orientation will be affected, causing the material to grow along the direction of the high sodium ion migration energy barrier.

[0036] In some preferred embodiments, in step (1), the ball-to-material ratio (i.e., the mass ratio of grinding balls to solid materials) of the ball mill is 5 to 40:1.

[0037] In some preferred embodiments, in step (1), the rotation speed of the ball mill is 100~300 r / min, more preferably 100~250 r / min, such as 100 r / min, 125 r / min, 150 r / min, 175 r / min, 200 r / min, 225 r / min, 250 r / min, etc.; if the ball milling speed is too low, the reaction will be difficult to complete or even impossible to proceed, and if the ball milling speed is too high, the crystal structure will be destroyed.

[0038] In some preferred embodiments, in step (1), the ball milling time is 5 to 12 hours, more preferably 6 to 10 hours; if the ball milling time is too short, the reaction cannot proceed fully or the crystal growth will be insufficient, and if the ball milling time is too long, the crystal structure will be damaged.

[0039] In some preferred embodiments, in step (2), the temperature of the low-temperature sintering is 150~350℃, and more preferably 200~300℃.

[0040] In some preferred embodiments, in step (2), the low-temperature sintering time is 2~6h.

[0041] In some preferred embodiments, in step (2), the low-temperature sintering is carried out in an inert atmosphere or a nitrogen atmosphere.

[0042] Some embodiments of the present invention also provide a layered vanadium phosphate-based cathode material, which is prepared using the aforementioned preparation method.

[0043] Some embodiments of the present invention also provide a sodium-ion battery, including the aforementioned layered vanadium phosphate-based cathode material.

[0044] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] Example 1

[0048] (1) Weigh and measure V2O5 (1.1977g, equivalent to 6.552 mmol, purity 99.5%), NaOH (1.0921g, equivalent to 26.21mmol, purity 96%), H2C2O4·2H2O (1.6690g, equivalent to 13.106mmol, purity 99%), and H3PO4 (4.93ml, equivalent to 72.072mmol, purity 85%) in a molar ratio of 1:4:2:11, place them in an agate jar, add 20 mL of water, and add 8 times the solid mass of agate beads. Fix the agate tube in a planetary ball mill, set the rotation speed to 200 r / min and the time to 6h for ball milling reaction.

[0049] (2) After the reaction is complete, the obtained green powder material is taken out, washed three times with water and alcohol respectively, and placed in a 60℃ oven for 12 hours to obtain the dried product. The XRD pattern of the dried product is shown in the figure. Figure 2 As shown, from Figure 2 It can be seen that the XRD pattern of the sample without dehydrated crystallization matches well with the standard PDF card of Na(VO)2(PO4)2·4H2O, and the positions, shapes, and intensities of each characteristic peak correspond, proving that the target product was successfully synthesized. Furthermore, the characteristic peaks of the product in Example 1 are sharp and strong, with no impurity peaks present. This demonstrates that the product synthesized under the conditions of a rotation speed of 200 r / min and a time of 6 h has high crystallinity and is free of impurities.

[0050] (3) Place the dried product in a magnetic boat, put it into a muffle furnace, and heat it to 210°C at a heating rate of 5°C / min under an argon atmosphere. Hold the temperature for 3 hours to remove the water of crystallization and obtain the product.

[0051] The SEM image of the product obtained in Example 1 is shown below. Figure 1 As shown, from Figure 1 The synthesized material can be seen to be nanosheets of about 5 μm in size, which are stacked together.

[0052] Example 2

[0053] (1) Weigh and measure V2O5 (1.1977g, equivalent to 6.552 mmol, purity 99.5%), NaOH (1.6382g, equivalent to 39.320mmol, purity 96%), H2C2O4·2H2O (2.5034g, equivalent to 19.660mmol, purity 99%), and H3PO4 (4.93ml, equivalent to 72.072mmol, purity 85%) in a molar ratio of 1:6:3:11, place them in an agate jar, add 20 mL of water, and add 8 times the solid mass of agate beads. Fix the agate tube in a planetary ball mill, set the rotation speed to 200 r / min and the reaction time to 6h for the reaction.

[0054] (2) After the reaction is complete, the obtained green powder material is taken out, washed three times with water and alcohol respectively, and placed in a 60℃ oven for 12 hours to obtain the dried product. The XRD pattern of the dried product is shown in the figure. Figure 2 As shown, from Figure 2 As can be seen, the main peaks in the XRD pattern of the sample are consistent with the standard PDF card of Na(VO)2(PO4)2·4H2O, proving that the target product was successfully synthesized. Compared with Example 1, the intensity of the main peak at around 14° in Example 2 is significantly improved, while some weak peaks are not reflected in the XRD pattern. This proves that a high oxalic acid ratio is not conducive to the uniform growth of crystals and has a certain impact on crystal quality and integrity.

[0055] (3) Place the dried product in a magnetic boat, put it in a muffle furnace, and heat it to 210°C at a heating rate of 5°C / min under an argon atmosphere. Hold the temperature for 3 hours to remove the water of crystallization and obtain Na(VO)2(PO4)2.

[0056] Example 3

[0057] (1) Weigh and measure V2O5 (1.1977g, equivalent to 6.552 mmol, purity 99.5%), NaOH (1.0921g, equivalent to 26.21mmol, purity 96%), H2C2O4·2H2O (1.6690g, equivalent to 13.106mmol, purity 99%), and H3PO4 (4.93ml, equivalent to 72.072mmol, purity 85%) in a molar ratio of 1:4:2:11 and place them in an agate jar. Add 20 mL of water and add 8 times the solid mass of agate beads. Fix the agate tube in a planetary ball mill and set the rotation speed to 300 r / min and the reaction time to 6h.

[0058] (2) After the reaction is complete, the obtained green powder material is taken out, washed three times with water and alcohol respectively, and placed in a 60℃ oven for 12 hours to obtain the dried product. The XRD pattern of the dried product is shown in the figure. Figure 2 As shown, from Figure 2 As can be seen, the main peaks in the XRD pattern of the sample are in good agreement with the standard PDF card of Na(VO)2(PO4)2·4H2O, proving that the target product was successfully synthesized. However, the intensity of its characteristic peaks is significantly reduced, and several sharp peaks near 20° and 31° are transformed into extremely weak and broad peaks. This proves that the high rotation speed of 300 r / min reduces the crystallinity of the product.

[0059] (3) Place the dried product in a magnetic boat, put it into a muffle furnace, and heat it to 210°C at a heating rate of 5°C / min under an argon atmosphere. Hold the temperature for 3 hours to remove the water of crystallization and obtain the product.

[0060] Example 4

[0061] (1) Weigh and measure V2O5 (1.1977g, equivalent to 6.552 mmol, purity 99.5%), NaOH (1.0921g, equivalent to 26.21mmol, purity 96%), H2C2O4·2H2O (1.6690g, equivalent to 13.106mmol, purity 99%), and H3PO4 (4.93ml, equivalent to 72.072mmol, purity 85%) in a molar ratio of 1:4:2:11, place them in an agate jar, add 20 mL of H2O, and add 8 times the solid mass of agate beads. Fix the agate tube in a planetary ball mill, set the rotation speed to 200 r / min and the reaction time to 12h for the reaction.

[0062] (2) After the reaction is complete, the obtained green powder material is taken out, washed three times with water and alcohol respectively, and placed in a 60℃ oven for 12 hours to obtain the dried product. The XRD pattern of the dried product is shown in the figure. Figure 2 As shown, from Figure 2 It can be seen that, from Figure 2 As can be seen, the main peaks in the XRD pattern of the sample are in good agreement with the standard PDF card of Na(VO)2(PO4)2·4H2O, proving that the target product was successfully synthesized. However, similar to Example 3, the intensity of its characteristic peaks further decreased, and several sharp peaks near 20° and 31° were transformed into extremely weak and broad peaks. This proves that excessively long ball milling time also reduces the crystallinity of the product.

[0063] (3) Place the dried product in a magnetic boat, put it into a muffle furnace, and heat it to 210°C at a heating rate of 5°C / min under an argon atmosphere. Hold the temperature for 3 hours to remove the water of crystallization and obtain the product.

[0064] Comparative Example 1

[0065] NaVOPO4, a vanadium-based phosphate material prepared by water bath combined with high-temperature sintering:

[0066] Weigh 1.1977 g of V₂O₅ (equivalent to 6.552 mmol, purity 99.5%) and 1.6690 g of H₂C₂O₄·2H₂O (equivalent to 13.106 mmol, purity 99%) in a molar ratio of 1:2 and place them in a beaker containing 20 mL of H₂O. Heat the mixture in a 90°C water bath until the solid dissolves, yielding a blue solution A. Weigh 1.0921 g of NaOH (equivalent to 26.21 mmol, purity 96%) and 4.93 mL of H₃PO₄ (equivalent to 72.072 mmol, purity 85%) in a molar ratio of 4:11 and mix them. Add the mixture to solution A at a molar ratio of NaOH to V₂O₅ of 4:1. Continue the reaction for 6 hours, then wash, filter, and dry. Finally, sinter the solution at 800°C for 6 hours under an argon atmosphere to obtain the vanadium-based phosphate material NaVOPO₄.

[0067] The Na(VO)2(PO4)2 prepared in Examples 1-4 and the NaVOPO4 prepared by high-temperature sintering in Comparative Example 1 were assembled into coin cells according to the following method: a certain amount of ground powder was weighed, acetylene black was added as a conductive agent and PVDF (HSV-900) as a binder (7:2:1), and after thorough grinding, 0.2 mL of NMP was added to disperse and mix. After the slurry was uniformly mixed, it was stretched onto aluminum foil to form a positive electrode sheet. In an anaerobic glove box, a sodium metal sheet was used as the negative electrode, glass fiber was used as the separator, and sodium perchlorate was used as the electrolyte to assemble a CR2025 coin cell.

[0068] After the assembled battery was left to stand for 12 hours, its electrochemical performance was tested at a voltage range of 2.5–4.5V. The results are as follows: Figure 3-4 As shown.

[0069] from Figure 3-4 It can be seen that the battery assembled from the layered vanadium phosphate-based material Na(VO)2(PO4)2 synthesized by the mechanochemical method of this invention has high capacity and excellent rate performance, and the performance of Example 1 is significantly better than that of other examples, which is consistent with the XRD pattern.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing a layered vanadium phosphate-based cathode material, characterized in that, include: (1) A sodium source, a vanadium source, a reducing acid, phosphoric acid, and water are mixed and ball-milled to obtain the product; the molar ratio of vanadium in the vanadium source to sodium in the sodium source and phosphoric acid is 2:2~6:7~17; the molar ratio of vanadium in the vanadium source to hydrogen in the reducing acid is 1:1~3; the reducing acid is selected from any one or more of acetic acid and its hydrate, oxalic acid and its hydrate, citric acid and its hydrate, and ascorbic acid. (2) After washing and drying the product, the crystal water is removed by low-temperature sintering to obtain layered vanadium phosphate-based cathode material Na(VO)2(PO4)2; the low-temperature sintering temperature is 150~350℃, and the low-temperature sintering is carried out in an inert atmosphere or a nitrogen atmosphere.

2. The method for synthesizing the layered vanadium phosphate-based cathode material as described in claim 1, characterized in that, The sodium source is one or more of NaOH, NaCl, NaF, and Na2CO3.

3. The method for synthesizing the layered vanadium phosphate-based cathode material as described in claim 1, characterized in that, The vanadium source is one or more of V2O5, NH4VO3, and VF5.

4. The method for synthesizing the layered vanadium phosphate-based cathode material as described in claim 1, characterized in that, In step (1), the solid-liquid ratio of the ball mill is 1:1 to 10; the ball-to-material ratio of the ball mill is 5 to 40:

1.

5. The method for synthesizing the layered vanadium phosphate-based cathode material as described in claim 1, characterized in that, In step (1), the rotation speed of the ball mill is 100~300 r / min; the ball milling time is 5~12h.

6. The method for synthesizing the layered vanadium phosphate-based cathode material as described in claim 1, characterized in that, In step (2), the low-temperature sintering time is 2~6h.

7. A layered vanadium phosphate-based cathode material, characterized in that, It was prepared by the synthesis method described in any one of claims 1 to 6.

8. A sodium-ion battery, characterized in that, Including the layered vanadium phosphate-based cathode material as described in claim 7.

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