Sodium vanadium fluorophosphate cathode material doped with cobalt, its preparation method and application

Abstract

The present invention discloses a cobalt-doped sodium vanadium fluorophosphate cathode material, its preparation method and application. The chemical formula of the cathode material is: Na<subgt;3< / subgt;V<subgt;2-x< / subgt;M<subgt;x< / subgt>O<subgt;2< / subgt>(PO<subgt;4< / subgt;)<subgt>2< / subgt>F, where M is Co and the value range of x is 0.001 to 0.1. The cobalt-doped sodium vanadium fluorophosphate material provided by the present invention in-situ replaces part of vanadium with an appropriate amount of cobalt, improves the electronic conductivity and ion diffusion kinetics, and significantly enhances the rate performance and cycle life of the material. In addition, the preparation method of the present invention adopts room-temperature aqueous-phase synthesis from raw materials to finished products, with high production efficiency, low equipment requirements, simple operation and environmental protection. Compared with synthesis methods such as high-temperature solid-phase method and sol-gel method, it can be suitable for large-scale production while taking into account the improvement of the electrochemical performance of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery cathode materials, and more specifically, relates to a sodium vanadium fluorophosphate cathode material doped with cobalt, and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have physical and chemical properties similar to those of lithium, and have attracted considerable attention due to the low cost and wide distribution of sodium, and are considered as promising alternatives to LIBs. In the future, sodium-ion batteries are expected to replace some low-end lithium iron phosphate batteries in the low-speed vehicle and two-wheeler markets, and be widely used in the energy storage field, where high requirements are placed on battery performance, safety, and cycle stability.

[0003] Among the components of the battery, the cathode material, as the component for storing active sodium, not only directly determines the electrochemical performance of the battery, but also affects the final cost of the battery. Polyanion-type compounds have the advantages of high and stable working voltage, diverse and stable structures, fast sodium-ion diffusion rate, good air stability, etc. In terms of electrochemical performance, NVOPF (sodium vanadium fluorophosphate) has a high theoretical specific capacity of 130 mAh g -1 , and has a high working voltage, so the energy density is also very high. In addition, the negligible volume change (<2%) during charge and discharge is particularly beneficial to long cycle stability.

[0004] However, its extremely low inherent electronic conductivity limits its overall electrochemical performance and practical applications. To improve the conductivity and electrochemical performance of NVOPF, various synthesis methods and modification strategies have been developed to obtain different micro-morphologies and crystal structures. In the synthesis of NVOPF, a suitable synthesis method is particularly important. Nanostructured materials have advantages such as a large specific surface area, short diffusion paths, and fast transport kinetics, and play an important role in improving the performance of electrode materials. Preparing NVOPF by adjusting the hydrothermal temperature and pH value shows excellent sodium storage performance. For example, CN113036114B discloses a preparation method of a sodium vanadium fluorophosphate electrode material with a nano-sheet flower-like shape, which controls the morphology of the final product by adding citric acid, polyethylene glycol, etc., but does not change the composition of the sodium vanadium fluorophosphate electrode material. CN 115583644A discloses a preparation method of a sodium vanadium fluorophosphate composite cathode material, in which the mixing and dispersion of various components are improved by adding a carbon source and a surfactant, etc., to improve its rate cycling performance, but it does not fundamentally change the composition of the sodium vanadium fluorophosphate electrode material. CN 117446779 A discloses a reduced graphene oxide modified sodium vanadium fluorophosphate cathode material and its preparation method, which realizes modification through simple physical mixing and sintering of reduced graphene oxide and the sodium vanadium fluorophosphate cathode material, but it also does not change the components of the sodium vanadium fluorophosphate cathode material. Although the well-designed nanomaterials in the above-mentioned prior arts have made good progress in improving the high-rate discharge performance, due to their inherent problems - slow Na ion diffusion kinetics and low electronic conductivity. Therefore, it is particularly important to select a suitable method to solve the problems of slow Na ion diffusion kinetics and low electronic conductivity. Therefore, the present invention introduces a cobalt-doped sodium vanadium fluorophosphate cathode material to solve the above problems. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a cobalt-doped sodium vanadium fluorophosphate cathode material and its preparation method and application to solve the problems of low specific capacity and poor electrochemical performance of the above-mentioned prior art fluorophosphate cathode materials.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] The first aspect of the present invention provides a cobalt-doped sodium vanadium fluorophosphate cathode material, and the chemical formula of the cathode material is: Na3V 2-x M x O2(PO4)2F, where M is Co, and the value range of x is 0.001 - 0.1. Preferably, the value range of x is 0.005 - 0.05. More preferably, the value range of x is 0.01 - 0.03.

[0008] The second aspect of the present invention provides a method for preparing a cobalt-doped sodium vanadium fluorophosphate cathode material at room temperature, and the steps include:

[0009] 1) Dissolve the vanadium source in deionized water at room temperature and then add a reducing agent to obtain Solution 1 after reduction;

[0010] 2) Add the cobalt source to the reduced Solution 1 at room temperature to obtain Solution 2;

[0011] 3) Add the fluorine source and the phosphorus source to deionized water at room temperature, stir and mix to obtain Solution 3;

[0012] 4) Add Solution 3 to Solution 2, stir, and then let it stand at room temperature to obtain the cobalt-doped sodium vanadium fluorophosphate cathode material.

[0013] 5) Use a centrifuge to alternately wash the cobalt-doped sodium vanadium fluorophosphate cathode material obtained by standing with deionized water and absolute ethanol for multiple times, and then dry it in a blast drying oven at 80 °C for 12 h, and finally prepare the Na3V 2-x M x O2(PO4)2F cobalt-doped sodium vanadium fluorophosphate cathode material.

[0014] Among them, preferably, the fluorine source in step 3) is sodium fluoride.

[0015] Preferably, the vanadium source is one of vanadium pentoxide, ammonium metavanadate, vanadium pentafluoride, and sodium metavanadate.

[0016] Preferably, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate.

[0017] Preferably, the cobalt source is one of cobalt chloride, cobalt nitrate, cobalt sulfate, and cobalt acetate.

[0018] The reducing agent is sodium metabisulfite.

[0019] Among them, the molar ratio of the vanadium source, the phosphorus source, and the fluorine source is 1:3:1.7.

[0020] The molar ratio of vanadium atoms in the vanadium source to cobalt atoms in the cobalt source is 2-x:x.

[0021] The value range of x is 0.001 to 0.1. Preferably, the value range of x is 0.005 to 0.05. More preferably, the value range of x is 0.01 to 0.03.

[0022] The molar ratio of the reducing agent to the vanadium source is 2:1.

[0023] Preferably, in step 5), it is alternately washed with deionized water and absolute ethanol 3-6 times.

[0024] The third aspect of the present invention provides the use of the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material in a sodium ion battery.

[0025] A fourth aspect of the present invention provides a positive electrode plate, comprising a current collector selected from carbon-coated aluminum foil, copper foil, aluminum foil, nickel foil, nickel foam, copper foam, titanium-nickel shape memory alloy, stainless steel mesh, and the like, and a positive electrode active material layer comprising the aforementioned cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material, a conductive agent, a binder, and a solvent. The positive electrode plate can be prepared according to conventional preparation techniques in the art.

[0026] For example, the conductive agent is selected from at least one of carbon black, carbon nanotubes, and acetylene black; the binder is selected from polyvinylidene fluoride, carboxymethyl cellulose, or a mixture thereof; and the solvent is selected from N-methylpyrrolidone. Furthermore, the mass ratio of the positive electrode material, conductive agent, and binder can be 80:10:10. This ratio is for illustrative purposes only and is not specifically limited herein.

[0027] A fifth aspect of the present invention provides a sodium ion battery, wherein the battery uses a positive electrode plate comprising the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material.

[0028] Beneficial technical effects of the present invention:

[0029] The cobalt-doped sodium vanadium oxyfluorophosphate material provided by the present invention improves electronic conductivity and ion diffusion kinetics by partially replacing vanadium with an appropriate amount of cobalt in situ, significantly enhancing the material's rate performance and cycle life. Furthermore, the preparation method of the present invention utilizes room-temperature aqueous synthesis from raw materials to finished product, resulting in high production efficiency, low equipment requirements, simple operation, and environmental friendliness. Compared with synthesis methods such as high-temperature solid-phase and sol-gel methods, the method is suitable for large-scale production while simultaneously improving the material's electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present application and should not be regarded as limiting the scope of the present application. In the drawings:

[0031] Figure 1 This is the XRD graph of the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material prepared in Examples 1 to 3.

[0032] Figure 2 The constant current charge and discharge curves of the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material prepared in Example 1 at different current densities.

[0033] Figure 3Comparison of the rate performance of the cathode materials in Example 1 and Comparative Example 1.

[0034] Figure 4 Comparison of the rate performance of the cathode materials in Example 2 and Comparative Example 1.

[0035] Figure 5 Comparison of the rate performance of the cathode materials in Example 3 and Comparative Example 1. Detailed implementation mode

[0036] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0037] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0038] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0039] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation modes of the present invention specification, which are obvious to those skilled in the art. Other implementation modes obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0040] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0041] Unless otherwise specified, room temperature and normal temperature as referred to in the present invention both refer to 25 ± 5°C.

[0042] In the present invention, the vanadium source is one of vanadium pentoxide, ammonium metavanadate, vanadium pentafluoride, and sodium metavanadate.

[0043] The phosphate is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate and sodium pyrophosphate.

[0044] The cobalt source is one of cobalt chloride, cobalt nitrate, sulfuric acid, cobalt acetate.

[0045] The sodium-ion battery according to the present invention includes the above-mentioned positive electrode sheet. Among them, in addition to the positive electrode sheet in the sodium-ion battery, it also includes a negative electrode sheet, a separator, a sodium-ion electrolyte and a battery case. Among them, the sodium-ion electrolyte can be a 1M sodium perchlorate solution containing 5% fluoroethylene carbonate (FEC), and the solvent in the electrolyte is a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) with a volume ratio of 1:1; the separator can be selected from a glass fiber membrane or a ceramic separator; the negative electrode sheet can be selected as a sodium metal foil.

[0046] The following will describe the implementation scheme of the present application in detail with specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0047] Example 1

[0048] The preparation steps of the cobalt-doped sodium vanadium fluorophosphate positive electrode material at room temperature are as follows:

[0049] S1: Weigh sodium metavanadate and sodium metabisulfite according to a molar ratio of 1:2 respectively, and dissolve them in deionized water at room temperature. After waiting for complete dissolution, mix the sodium metavanadate aqueous solution into the sodium metabisulfite aqueous solution to obtain solution 1;

[0050] S2: Weigh a certain amount of cobalt sulfate according to a molar ratio of V:Co of 1.99:0.01, then dissolve the cobalt sulfate in deionized water at room temperature, and add the obtained cobalt sulfate aqueous solution to solution 1 obtained in step S1 to obtain solution 2;

[0051] S3: Weigh ammonium dihydrogen phosphate and sodium fluoride according to a molar ratio of V:P:F of 1:3:1.7 and dissolve them in deionized water at room temperature to obtain solution 3;

[0052] S4: Add solution 3 to solution 2 at room temperature, stir, and then let it stand at room temperature for 24 h to obtain the cobalt-doped sodium vanadium fluorophosphate positive electrode material in the form of 200 nm spherical nanoparticles.

[0053] S5: Use a centrifuge to wash the obtained cobalt-doped sodium vanadium fluorophosphate positive electrode material 6 times alternately with deionized water and absolute ethanol, and then dry it in a blast drying oven at 80 °C for 12 h to finally prepare Na3V2-x M x Sodium cobalt-doped vanadium fluorophosphate Na3V2O2(PO4)2F cathode material.

[0054] Example 2

[0055] Compared with Example 1, the only difference is that in step S2, the molar ratio of sodium metavanadate to cobalt sulfate is 1.98:0.02. That is, the value of X is 0.02.

[0056] Example 3

[0057] Compared with Example 1, the only difference is that in step S2, the molar ratio of sodium metavanadate to cobalt sulfate is 1.97:0.03. That is, the value of X is 0.03.

[0058] Comparative Example 1: Undoped cobalt

[0059] The preparation steps of the sodium vanadium fluorophosphate cathode material at room temperature are as follows:

[0060] S1: Weigh sodium metavanadate and sodium metabisulfite according to a molar ratio of 1:2, and dissolve them in deionized water at room temperature respectively. After waiting for complete dissolution, mix the sodium metavanadate aqueous solution into the sodium metabisulfite aqueous solution to obtain Solution 1;

[0061] S2: Weigh ammonium dihydrogen phosphate and sodium fluoride according to a molar ratio of V:P:F of 1:3:1.7 and dissolve them in deionized water at room temperature to obtain Solution 2;

[0062] S3: Add Solution 2 to Solution 1 at room temperature, stir, and then let it stand at room temperature to obtain the sodium vanadium fluorophosphate cathode material.

[0063] S4: Use a centrifuge to wash the sodium vanadium fluorophosphate cathode material obtained by standing alternately with deionized water and absolute ethanol 6 times, and then dry it in a forced-air drying oven at 80 °C for 12 h to finally prepare the sodium vanadium fluorophosphate Na3V2O2(PO4)2F cathode material.

[0064] The cobalt-doped sodium vanadium fluorophosphate cathode materials prepared at room temperature in Examples 1 to 3 and the sodium vanadium fluorophosphate cathode material prepared at room temperature in Comparative Example 1 were obtained through X-ray diffraction testing (XRD) Figure 1 The data shown. It can be seen from the XRD pattern that the XRD diffraction patterns of Na3V 2-x Co x O2(PO4)2F prepared in Examples 1 to 3 are basically the same, indicating that the crystal structure of NVOPF has not been significantly changed after cobalt doping. As the Co content in the material increases, the (200), (103), and (202) peaks shift to lower angles, indicating that cobalt-doped NVCOPF has a larger lattice constant than undoped NVOPF. The XRD results indicate the successful introduction of cobalt element.

[0065] Example 4

[0066] This example provides a positive electrode sheet, and its preparation method includes:

[0067] The positive electrode materials, acetylene black, and polyvinylidene fluoride prepared in Examples 1 to 3 and Comparative Example 1 are respectively added to N-methylpyrrolidone and mixed evenly to obtain a positive electrode active paste. The positive electrode active paste is coated on the surface of a current collector carbon-coated aluminum foil and dried to obtain a positive electrode sheet; among them, the dosage ratio of the positive electrode material, acetylene black, and polyvinylidene fluoride is 80:10:10 by percentage.

[0068] This example provides a sodium-ion battery, and its preparation method includes:

[0069] Using the positive electrode sheet prepared above as the positive electrode, a sodium sheet as the negative electrode, a commercial ceramic separator as the separator, and a sodium-ion battery electrolyte selected to use a 1M sodium perchlorate solution containing 5% fluoroethylene carbonate (FEC). The solvent of this electrolyte is a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) with a volume ratio of 1:1. Then, battery assembly is carried out, and the assembly sequence is as follows: starting from the positive electrode case, assemble in the order of the positive electrode case, positive electrode sheet, 50 μL electrolyte, separator, sodium sheet, gasket, spring sheet, and negative electrode case to obtain a CR2032 type button battery. The whole process is assembled in an argon-filled glove box, where the moisture and oxygen content are maintained below 0.1 ppm for a long time.

[0070] Test Example 1

[0071] The positive electrode materials obtained in Example 4 are prepared into positive electrode sheets, and then sodium-ion batteries are prepared with sodium sheets and subjected to continuous charge and discharge tests at 0.5C, 1C, 5C, 10C, 20C, 40C, and 60C rates.

[0072] Figure 2 is the charge and discharge curves of the sodium-ion battery prepared with the positive electrode material of Example 1 at different rates. From Figure 2 it can be seen that the discharge capacities at 0.5C, 1C, 5C, 10C, 20C, 40C, and 60C rates are 129.5, 122.5, 115.1, 109.9, 101.6, 80.6, and 50.7 mAh·g -1 respectively, showing excellent rate discharge performance.

[0073] Figures 3 to 5 is the rate performance comparison of the sodium-ion batteries prepared with the positive electrode materials of Example 1, Example 2, Example 3, and Comparative Example 1 respectively. From Figures 3 to 5It can be seen that, compared with the undoped NVOPF material (Comparative Example 1), the cobalt-doped material prepared at room temperature can improve the intrinsic electronic conductivity and ion diffusion rate of the material, and enhance the rate performance of the material.

[0074] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other.

[0075] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cobalt-doped sodium vanadium fluorophosphate cathode material, and the chemical formula of the cathode material is: Na3V 2-x M x O2(PO4)2F, wherein, M is Co, where part of the cobalt replaces part of the vanadium in-situ, and the value range of x is 0.001 to 0.1; The sodium cobalt-doped vanadium fluorophosphate cathode material is prepared according to the following method, and the steps include: 1) Dissolve the vanadium source in deionized water at room temperature and then add a reducing agent to obtain Solution 1 after reduction; 2) Then add the cobalt source to the reduced Solution 1 at room temperature to obtain Solution 2; 3) Then add the fluorine source and the phosphorus source to deionized water and stir and mix to obtain Solution 3; 4) Add Solution 3 to Solution 2, stir, and then stand at room temperature to obtain the sodium cobalt-doped vanadium fluorophosphate cathode material; 5) The cobalt-doped sodium vanadium fluorophosphate cathode material obtained by standing is washed repeatedly with deionized water and absolute ethanol using a centrifuge, and then dried at 80 °C for 12 h in a forced-air drying oven. Finally, the sodium vanadium fluorophosphate cathode material doped with cobalt 2-x M x O2(PO4)2F is prepared.

2. The sodium vanadium fluorophosphate cathode material doped with cobalt according to claim 1, wherein The value range of x is 0.005 to 0.

05.

3. The sodium vanadium fluorophosphate cathode material doped with cobalt according to claim 1, characterized in that, The value range of x is 0.01 to 0.

03.

4. The sodium vanadium fluorophosphate cathode material doped with cobalt according to claim 1, characterized in that In step 3) of the preparation method of the sodium cobalt-doped vanadium fluorophosphate cathode material, the fluorine source is sodium fluoride; The vanadium source is one of vanadium pentoxide, ammonium metavanadate, vanadium pentafluoride, and sodium metavanadate; The phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, and sodium pyrophosphate; The cobalt source is one of cobalt chloride, cobalt nitrate, cobalt sulfate, and cobalt acetate; The reducing agent is sodium metabisulfite; Among them, the molar ratio of the vanadium source, the phosphorus source, and the fluorine source is 1:3:1.7; The molar ratio of vanadium atoms in the vanadium source to cobalt atoms in the cobalt source is 2 - x:x; The value range of x is 0.001 to 0.1; The molar ratio of the reducing agent to the vanadium source is 2:1; In step 5), wash alternately with deionized water and absolute ethanol 3 - 6 times.

5. The sodium vanadium fluorophosphate cathode material doped with cobalt according to claim 4, characterized in that The value range of x is 0.005 to 0.

05.

6. The sodium vanadium fluorophosphate cathode material doped with cobalt according to claim 5, characterized in that, The value range of x is 0.01 to 0.

03.

7. Application of the sodium cobalt-doped vanadium fluorophosphate cathode material according to any one of claims 1 to 3 in a sodium-ion battery.

8. A positive electrode sheet, the positive electrode sheet includes a current collector and a positive electrode active material layer, the current collector is selected from carbon-coated aluminum foil, copper foil, aluminum foil, nickel foil, nickel foam, copper foam, titanium-nickel shape memory alloy, stainless steel mesh, etc., and the positive electrode active material layer includes the sodium cobalt-doped vanadium fluorophosphate cathode material according to any one of claims 1 to 3, a conductive agent, a binder, and a solvent.

9. The positive electrode sheet according to claim 8, wherein, Among them, the conductive agent is selected from at least one of carbon black, carbon nanotubes, and acetylene black; the binder is selected from polyvinylidene fluoride, carboxymethyl cellulose, or a mixture of the two; the solvent is selected from N-methylpyrrolidone; at the same time, the mass percentages of the positive electrode material, the conductive agent, and the binder can be 80:10:

10.

10. A sodium-ion battery, characterized in that, The battery uses the positive electrode sheet according to claim 8.

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