Cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material and preparation method and application thereof

Abstract

The invention discloses a cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material and a preparation method and application thereof, the chemical formula of the positive electrode material is Na3V (2-x) MxO2 (PO4) 2F, M is Co, and the value range of x is 0.001-0.1. According to the cobalt-doped sodium vanadium oxyfluoride phosphate material provided by the invention, a proper amount of cobalt is used for replacing part of vanadium in situ, so that the electronic conductivity and the ion diffusion kinetics are improved, the rate capability of the material is remarkably improved, and the cycle life of the material is remarkably prolonged. Besides, according to the preparation method, room-temperature water-phase synthesis is adopted from the raw materials to the finished product, the production efficiency is high, the equipment requirement is low, operation is easy, environment friendliness is achieved, and compared with a high-temperature solid-phase method, a sol-gel method and other synthesis methods, the electrochemical performance of the material can be improved, and meanwhile the method is suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of battery positive electrode materials, and more specifically relates to a cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have similar physical and chemical properties to lithium, and have attracted considerable attention due to the cheapness and widespread distribution of sodium, and are considered a promising alternative 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-wheel vehicle markets, and be widely used in the energy storage field, which has high requirements for battery performance, safety and cycle stability.

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

[0004] However, the extremely low inherent electronic conductivity limits its overall electrochemical performance and practical application. In order to improve the conductivity and electrochemical performance of NVOPF, people have developed a variety of synthesis methods and modification strategies to obtain different microscopic morphologies and crystal structures. In the synthesis and preparation of NVOPF, a suitable synthesis method is particularly important. Nanostructured materials have the advantages of large specific surface area, short diffusion path, fast transmission kinetics, etc., and play an important role in improving the performance of electrode materials. NVOPF prepared by adjusting the hydrothermal temperature and pH value exhibits excellent sodium storage performance. For example, CN113036114B discloses a method for preparing a nano-sheet flower-shaped sodium vanadium fluoride phosphate electrode material, 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 fluoride phosphate electrode material. CN 115583644A discloses a method for preparing a sodium vanadium fluoride phosphate composite positive electrode material, in which the mixed dispersion of various components is improved by adding carbon sources and surfactants, and its rate cycle performance is improved, but the composition of the sodium vanadium fluoride phosphate electrode material is not fundamentally changed. CN 117446779A discloses a reduced graphene oxide modified sodium vanadium fluoride oxyphosphate positive electrode material and a preparation method thereof, which is modified by simple physical mixing and sintering of reduced graphene oxide and sodium vanadium fluoride oxyphosphate positive electrode material, but it does not change the components of the sodium vanadium fluoride oxyphosphate positive electrode material. Although the well-designed nanomaterials in the above-mentioned prior art have made great progress in improving 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 cobalt-doped sodium vanadium fluoride oxyphosphate positive electrode 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 fluorooxyphosphate positive electrode material and a preparation method and application thereof, so as to solve the problems of low specific capacity and poor electrochemical performance of fluorophosphate positive electrode materials in the above-mentioned prior art.

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

[0007] The first aspect of the present invention provides a cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material, the chemical formula of the positive electrode material is: Na3V 2-x M x O2(PO4)2F, wherein M is Co, and the value range of x is 0.001 to 0.1, preferably, the value range of x is 0.005 to 0.05, and more preferably, the value range of x is 0.01 to 0.03.

[0008] The second aspect of the present invention provides a method for preparing a cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material at room temperature, the steps comprising:

[0009] 1) dissolving a vanadium source in deionized water at room temperature and then adding a reducing agent to reduce the solution to obtain a solution 1;

[0010] 2) adding a cobalt source to the reduced solution 1 at room temperature to obtain solution 2;

[0011] 3) adding the fluorine source and the phosphorus source into deionized water at room temperature and stirring to obtain solution 3;

[0012] 4) adding solution 3 into solution 2, stirring, and then standing at room temperature to obtain the cobalt-doped sodium vanadium fluorooxyphosphate positive electrode material.

[0013] 5) The cobalt-doped sodium vanadium fluoride oxyphosphate positive electrode material was left to stand and washed alternately with deionized water and anhydrous ethanol for multiple times using a centrifuge, and then dried in a blast drying oven at 80° C. for 12 h to finally prepare Na3V 2-x M x O2(PO4)2F cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material.

[0014] Wherein, 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 pyrosulfite.

[0019] Among them, the molar ratio of vanadium source, phosphorus source and 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, and 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), deionized water and anhydrous ethanol are used for alternate washing 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] The fourth aspect of the present invention provides a positive electrode plate, the positive electrode plate comprises 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, foam nickel, foam copper, titanium-nickel shape memory alloy, stainless steel mesh, etc., the positive electrode active material layer comprises the above-mentioned cobalt-doped sodium vanadium fluoride oxyphosphate 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 of the two; and the solvent is selected from N-methylpyrrolidone. Meanwhile, the mass percentage of the positive electrode material, the conductive agent and the binder can be 80:10:10, which is only for exemplary display and is not specifically limited here.

[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 fluorooxyphosphate material provided by the present invention improves the electronic conductivity and ion diffusion kinetics by replacing part of the vanadium in situ with an appropriate amount of cobalt, and significantly improves 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. 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 3The figure shows the rate performance comparison of the positive electrode materials of Example 1 and Comparative Example 1.

[0034] Figure 4 The figure shows the rate performance comparison of the positive electrode materials of Example 2 and Comparative Example 1.

[0035] Figure 5 The figure shows the rate performance comparison of the positive electrode materials of Example 3 and Comparative Example 1. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0038] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may 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 associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0039] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0040] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0041] Unless otherwise specified, the room temperature and normal temperature referred to in the present invention 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, and cobalt acetate.

[0045] The sodium ion battery according to the present invention includes the above-mentioned positive electrode plate. Wherein, in addition to the positive electrode plate, the sodium ion battery also includes a negative electrode plate, a diaphragm, a sodium ion electrolyte and a battery shell. Wherein, 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) in a volume ratio of 1:1; the diaphragm can choose to use a glass fiber membrane or a ceramic diaphragm; the negative electrode plate can choose a metal sodium foil.

[0046] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If specific conditions are not specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0047] Example 1

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

[0049] S1: Sodium metavanadate and sodium pyrosulfite are weighed in a molar ratio of 1:2, and dissolved in deionized water at room temperature. After the dissolution is complete, the sodium metavanadate aqueous solution is mixed with the sodium pyrosulfite 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, dissolve the cobalt sulfate in deionized water at room temperature, and add the obtained cobalt sulfate aqueous solution to the solution 1 obtained in step S1 to obtain solution 2;

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

[0052] S4: adding solution 3 to solution 2 at room temperature, stirring, and then standing at room temperature for 24 hours to obtain 200 nm spherical nanoparticles of the cobalt-doped sodium vanadium fluorooxyphosphate positive electrode material.

[0053] S5: The cobalt-doped sodium vanadium fluoride oxyphosphate positive electrode material was washed alternately six times using a centrifuge with deionized water and anhydrous ethanol, and then dried in a forced air drying oven at 80° C. for 12 h to finally prepare Na3V2-x M x O2(PO4)2F cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material.

[0054] Example 2

[0055] Compared with Example 1, the only difference is that the molar ratio of sodium metavanadate to cobalt sulfate in step S2 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 the molar ratio of sodium metavanadate to cobalt sulfate in step S2 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 sodium vanadium fluorooxyphosphate positive electrode material at room temperature are as follows:

[0060] S1: Sodium metavanadate and sodium pyrosulfite are weighed in a molar ratio of 1:2, and are dissolved in deionized water at room temperature. After the dissolution is complete, the sodium metavanadate aqueous solution is mixed with the sodium pyrosulfite aqueous solution to obtain solution 1;

[0061] S2: ammonium dihydrogen phosphate and sodium fluoride were weighed and dissolved in deionized water at room temperature in a V:P:F molar ratio of 1:3:1.7 to obtain solution 2;

[0062] S3: adding solution 2 to solution 1 at room temperature, stirring, and then standing at room temperature to obtain the sodium vanadium fluorooxyphosphate positive electrode material.

[0063] S4: The sodium vanadium oxyfluoride phosphate positive electrode material is washed alternately six times using a centrifuge with deionized water and anhydrous ethanol, and then dried in a forced air drying oven at 80° C. for 12 h to finally prepare the sodium vanadium oxyfluoride phosphate positive electrode material Na3V2O2(PO4)2F.

[0064] The cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode materials prepared at room temperature in Examples 1 to 3 and the sodium vanadium oxyfluoride phosphate positive electrode materials prepared at room temperature in Comparative Example 1 were tested by X-ray diffraction (XRD) to obtain Figure 1 The data shown in Figure 1 show that the Na3V prepared in Examples 1 to 3 can be seen from the XRD diagram. 2-x Co x The XRD diffraction spectra of O2(PO4)2F are basically the same, indicating that the crystal structure of NVOPF is not significantly changed after cobalt doping. With the increase of Co content in the material, the (200), (103) and (202) peaks move to lower angles, indicating that the cobalt-doped NVOPF has a larger lattice constant than the undoped NVOPF. The XRD results show the successful introduction of cobalt.

[0065] Example 4

[0066] This embodiment provides a positive electrode sheet, and the preparation method thereof includes:

[0067] The positive electrode materials, acetylene black and polyvinylidene fluoride prepared in Examples 1 to 3 and Comparative Example 1 were respectively added to N-methylpyrrolidone and mixed evenly to obtain a positive electrode active slurry, which was coated on the surface of the carbon-coated aluminum foil of the current collector and dried to obtain a positive electrode sheet; wherein the usage ratio of the positive electrode material, acetylene black and polyvinylidene fluoride was 80:10:10 in percentage.

[0068] This embodiment provides a sodium ion battery, and the preparation method thereof includes:

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

[0070] Test Example 1

[0071] Each of the obtained positive electrode materials prepared in Example 4 was prepared into a positive electrode sheet, and then prepared into a sodium ion battery with a sodium sheet, and continuous charge and discharge tests were carried out at 0.5C, 1C, 5C, 10C, 20C, 40C, and 60C rates.

[0072] Figure 2 The charge and discharge curves of the sodium ion battery prepared by the positive electrode material of Example 1 at different rates are shown in FIG. Figure 2 It can be seen that the discharge capacities at rates of 0.5C, 1C, 5C, 10C, 20C, 40C, and 60C 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 For the comparison of the rate performance of sodium ion batteries prepared by using the positive electrode materials of Example 1, Example 2, Example 3 and Comparative Example 1, Figures 3 to 5It can be seen that compared with the undoped NVOPF material (Comparative Example 1), the cobalt doping prepared at room temperature can improve the intrinsic electronic conductivity and ion diffusion rate of the material, and improve the rate performance of the material.

[0074] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0075] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may 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 oxyfluoride phosphate positive electrode material, the chemical formula of the positive electrode material is: Na3V 2-x M x O2(PO4)2F, where M is Co, and the value range of x is 0.001 to 0.

1. Preferably, the value range of x is 0.005 to 0.05, and more preferably, the value range of x is 0.01 to 0.

03.

2. The method for preparing the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material according to claim 1, comprising the steps of: 1) dissolving a vanadium source in deionized water at room temperature and then adding a reducing agent to reduce the solution to obtain a solution 1; 2) adding a cobalt source to the reduced solution 1 at room temperature to obtain solution 2; 3) adding the fluorine source and the phosphorus source into deionized water at room temperature and stirring to obtain solution 3; 4) adding solution 3 to solution 2, stirring, and then standing at room temperature to obtain the cobalt-doped sodium vanadium fluoride oxyphosphate positive electrode material; 5) The cobalt-doped sodium vanadium fluoride oxyphosphate positive electrode material was left to stand and washed alternately with deionized water and anhydrous ethanol for multiple times using a centrifuge, and then dried in a forced air drying oven at 80° C. for 12 h to finally prepare Na3V 2-x M x O2(PO4)2F cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material.

3. The preparation method according to claim 2, characterized in that: The fluorine source in step 3) is sodium fluoride; Preferably, the vanadium source is one of vanadium pentoxide, ammonium metavanadate, vanadium pentafluoride, and sodium metavanadate; 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; Preferably, the cobalt source is one of cobalt chloride, cobalt nitrate, cobalt sulfate and cobalt acetate; The reducing agent is sodium pyrosulfite; Wherein, the molar ratio of vanadium source, phosphorus source and 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, preferably, the value range of x is 0.005 to 0.05, and more preferably, the value range of x is 0.01 to 0.03; The molar ratio of the reducing agent to the vanadium source is 2:1; Preferably, in step 5), deionized water and anhydrous ethanol are used for alternate washing 3-6 times.

4. Use of the cobalt-doped sodium vanadium oxyfluoride phosphate positive electrode material according to claim 1 in a sodium ion battery.

5. A positive electrode plate, comprising 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, foamed nickel, foamed copper, titanium-nickel shape memory alloy, stainless steel mesh, etc., and the positive electrode active material layer comprises the cobalt-doped sodium vanadium fluorooxyphosphate positive electrode material according to claim 1, a conductive agent, a binder and a solvent.

6. The positive electrode sheet according to claim 5, characterized in that: 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; and the mass percentage of the positive electrode material, the conductive agent and the binder can be 80:10:

10.

7. A sodium ion battery, characterized in that: The battery comprises the positive electrode sheet according to claim 5.

Images