A method for preparing positive electrode material, a pole piece, and a battery

Abstract

The invention belongs to the technical field of sodium battery preparation, and particularly relates to a method for preparing a positive electrode material, a pole piece, and a battery. The preparation method comprises the following steps: placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; ball-milling the premixed raw material through a ball mill; sending the ball-milled raw material into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; rolling and granulating the bonding body raw material through a roller granulator to obtain a sodium vanadium fluorophosphate precursor; and sintering the sodium vanadium fluorophosphate precursor once to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material. The carbon-coated sodium vanadium fluorophosphate positive electrode material obtained by the invention has good conductivity, high specific capacity, and can be continuously produced on a large scale; the obtained sodium vanadium fluorophosphate precursor has higher density, and therefore has a higher unit volume loading capacity during large-scale production, which is conducive to improving production capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium battery preparation, and in particular relates to a method for preparing a positive electrode material, a pole piece, and a battery. Background Art

[0002] Sodium vanadium fluorophosphate (Na3V2(PO4)2F3) is an important cathode material for sodium-ion batteries. It has high specific capacity and high energy density, and is considered one of the most promising high-voltage sodium-ion battery cathode materials. This material can provide high energy storage capacity, helping to improve the overall performance of sodium-ion batteries. However, the synthesis of this material is prone to F element loss, resulting in deviations in the material composition, insufficient purity, poor product consistency, and low specific capacity, making large-scale production difficult.

[0003] There are two existing methods for synthesizing sodium vanadium fluorophosphate: the first is a pure liquid phase high-temperature and high-pressure hydrothermal method: using water-soluble raw materials, which are dissolved and dispersed in a high-temperature and high-pressure hydrothermal reactor for reaction synthesis. Generally, secondary sintering carbon coating is required to improve conductivity, and a high-purity, good consistency, and high-specific capacity positive electrode material can be obtained; however, due to the complex process, it is not conducive to continuous large-scale production; the second is a liquid phase mixing + solid phase sintering process: the sodium source / fluorine source, vanadium source, phosphorus source, carbon source (citric acid), and pH adjuster (ammonia water) are dissolved, dispersed, spray-dried to obtain a precursor powder, and then solid-phase sintered to obtain the positive electrode material. Because this process is relatively simple, it can be continuously mass-produced and can be carbon-coated once; the pH is adjusted by ammonia water, combined with staged sintering to reduce the loss of F elements, and a large amount of ammonia nitrogen gas is generated at the same time, which puts a greater pressure on environmental treatment; the precursor is obtained by liquid phase mixing combined with spray drying. Since a large amount of gas will be generated during the process, the uniformity and density of the obtained precursor are poor, resulting in low powder compaction density and low loading capacity, thus affecting production capacity.

[0004] Therefore, it is necessary to design a method for preparing a positive electrode material that improves the above problems. Summary of the Invention

[0005] In order to solve the problems of the prior art, the present invention provides a method for preparing a positive electrode material, the preparation method comprising the following steps:

[0006] Step 1: putting the sodium vanadium fluorophosphate raw material, the carbon source and the fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a pre-mixed raw material;

[0007] Step 2: grinding the premixed raw materials into fine powder using a ball mill;

[0008] Step 3: The ball-milled raw materials are fed into a high-speed disperser for high-speed shear dispersion until a cohesive raw material is formed;

[0009] Step 4: Roll-pressing and granulating the bonded material through a roller granulator to obtain a sodium vanadium fluorophosphate precursor;

[0010] Step 5: sintering the sodium vanadium fluorophosphate precursor once to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material.

[0011] In some optional embodiments, in step 1, the sodium vanadium fluorophosphate raw material includes a sodium source / fluorine source, a phosphorus source and a vanadium source;

[0012] The sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid, and the vanadium source is vanadium pentoxide or ammonium metavanadate; wherein the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0013] The carbon source is glucose or citric acid, and the mass of the carbon source is 1-10wt% of the total mass of the sodium vanadium fluorophosphate raw material;

[0014] The fluorine replenishing agent is used to replenish fluorine loss, ensuring the completion and phase purity of the synthesized sodium vanadium fluorophosphate components; the fluorine replenishing agent also acts as a binder, and has a bonding effect on the particles during high-speed shear dispersion. After roller granulation, the density of the sodium vanadium fluorophosphate precursor is higher; wherein, the fluorine replenishing agent is polyvinylidene fluoride or polytetrafluoroethylene; the fluorine replenishing agent is polyvinylidene fluoride or polytetrafluoroethylene, and the mass of the fluorine replenishing agent is 1-8wt% of the total mass of the sodium vanadium fluorophosphate raw material.

[0015] In some optional embodiments, in step 2, the median particle size D50 of the raw material particles after ball milling is ≤6 microns.

[0016] In some optional embodiments, in step 3, when the high-speed disperser performs high-speed shear dispersion, the rotation speed of the high-speed disperser is 800-1800 rpm.

[0017] In some optional embodiments, in step 4, the roller pressing pressure of the roller granulator during roller granulation is ≥7 MPa.

[0018] In some optional embodiments, in step 5, the primary sintering is a step-by-step sintering, specifically:

[0019] After the sodium vanadium fluorophosphate precursor undergoes a first sintering reaction at a first sintering temperature, the temperature is raised to a second sintering temperature for a second sintering reaction;

[0020] Wherein, the conditions of the first sintering reaction are:

[0021] The first sintering temperature is 300-400℃, and the first sintering reaction time is 5-10h;

[0022] The conditions of the second sintering reaction are:

[0023] The second sintering temperature is 500-750° C., and the second sintering reaction time is 8-12 hours.

[0024] The second aspect of the present invention provides a carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above preparation method;

[0025] A third aspect of the present invention provides a pole piece comprising the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above-mentioned preparation method.

[0026] A fourth aspect of the present invention provides a battery comprising the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above-mentioned preparation method or the above-mentioned electrode sheet;

[0027] Beneficial effects of the present invention:

[0028] (1) The present invention uses a pure dry process, which is simpler than the hydrothermal process and can be continuously produced on a large scale. In addition, the pure dry process used in the present invention has less wastewater treatment in terms of environmental protection compared to the liquid phase + solid phase sintering process, and does not require a spray drying process, which has lower energy consumption;

[0029] (2) The process of the present invention is set up. Since there are many kinds of raw materials for the preparation of positive electrode materials, and the particle sizes of various raw materials are different, the raw materials are first pre-mixed by high-speed dispersion, and then the pre-mixed raw materials are refined by ball milling. Finally, high-speed dispersion is performed to ensure that the raw materials are evenly dispersed. The fluorine replenisher also serves as a binder. The fiberization of the binder is achieved by high-speed shear force, and the different particles in the raw materials after ball milling are bonded. The bonded raw materials are rolled and granulated by a roller granulator, and finally a sodium vanadium fluorophosphate precursor with higher density is obtained. Therefore, the unit volume loading capacity is higher in large-scale production, which is conducive to improving production capacity. The carbon-coated sodium vanadium fluorophosphate positive electrode material obtained by one-time sintering has good conductivity and high specific capacity, and can be continuously produced on a large scale.

[0030] (3) The preparation method of the positive electrode material of the present application uses low-cost carbon sources such as glucose and citric acid as raw materials, which reduces the production cost of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a scanning electron microscope image of the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared in Example 1 of the present invention;

[0032] Figure 2 This is the XRD pattern of the carbon-coated sodium vanadium fluorophosphate prepared in Example 1 of the present invention;

[0033] Figure 3 This is a schematic diagram of the charge and discharge curves of a battery made from the carbon-coated sodium vanadium fluorophosphate positive electrode material according to Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] A first aspect of the present invention provides a method for preparing a positive electrode material, the method comprising the following steps:

[0036] Step 1: putting the sodium vanadium fluorophosphate raw material, the carbon source and the fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a pre-mixed raw material;

[0037] Step 2: grinding the premixed raw materials into fine powder using a ball mill;

[0038] Step 3: The ball-milled raw materials are fed into a high-speed disperser for high-speed shear dispersion until a cohesive raw material is formed;

[0039] Step 4: Roll-pressing and granulating the bonded material through a roller granulator to obtain a sodium vanadium fluorophosphate precursor;

[0040] Step 5: sintering the sodium vanadium fluorophosphate precursor once to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material.

[0041] In some optional embodiments, in step 1, the sodium vanadium fluorophosphate raw material includes a sodium source / fluorine source, a phosphorus source and a vanadium source;

[0042] The sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid, and the vanadium source is vanadium pentoxide or ammonium metavanadate; wherein the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0043] The carbon source is glucose or citric acid, and the mass of the carbon source is 1-10wt% of the total mass of the sodium vanadium fluorophosphate raw material;

[0044] The fluorine replenishing agent is used to replenish fluorine loss, ensuring the completion and phase purity of the synthesized sodium vanadium fluorophosphate components; the fluorine replenishing agent also acts as a binder, and has a bonding effect on the particles during high-speed shear dispersion. After roller granulation, the sodium vanadium fluorophosphate precursor has a higher density; wherein, the fluorine replenishing agent is polyvinylidene fluoride or polytetrafluoroethylene, and the mass of the fluorine replenishing agent is 1-8wt% of the total mass of the sodium vanadium fluorophosphate raw material.

[0045] In some optional embodiments, in step 2, the median particle size D50 of the raw material particles after ball milling is ≤6 microns.

[0046] In some optional embodiments, in step 3, when the high-speed disperser performs high-speed shear dispersion, the rotation speed of the high-speed disperser is 800-1800 rpm.

[0047] In some optional embodiments, in step 4, the roller pressing pressure of the roller granulator during roller granulation is ≥7 MPa.

[0048] In some optional embodiments, in step 5, the primary sintering is a step-by-step sintering, specifically:

[0049] After the sodium vanadium fluorophosphate precursor undergoes a first sintering reaction at a first sintering temperature, the temperature is raised to a second sintering temperature for a second sintering reaction;

[0050] Wherein, the conditions of the first sintering reaction are:

[0051] The first sintering temperature is 300-400℃, and the first sintering reaction time is 5-10h;

[0052] The conditions of the second sintering reaction are:

[0053] The second sintering temperature is 500-750°C, and the second sintering reaction time is 8-12 hours.

[0054] The second aspect of the present invention provides a carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above preparation method;

[0055] A third aspect of the present invention provides a pole piece comprising the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above-mentioned preparation method.

[0056] A fourth aspect of the present invention provides a battery comprising the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the above-mentioned preparation method or the above-mentioned electrode sheet;

[0057] Example 1. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0058] The carbon source is glucose, the mass of the carbon source is 4wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine supplement is 2wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, sodium dihydrogen phosphate is 834.332g, glucose is 63.145g, and polytetrafluoroethylene is 31.573g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the premixed raw materials are ball-milled. The raw materials after curing are sent to a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1200 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is sintered once, and the once sintering is step-by-step sintering, the room temperature is heated to 350°C and kept warm for 8 hours, and then heated to 720°C and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0059] Example 2. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0060] The carbon source is glucose, the mass of the carbon source is 4wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine supplement is 3wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, glucose is 63.145g, and polyvinylidene fluoride is 47.359g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 5.0 microns; (3) the raw materials are ball-milled. The raw materials after curing are sent to a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1200 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is sintered once, and the once sintering is step-by-step sintering, the room temperature is heated to 350°C and kept warm for 8 hours, and then heated to 720°C and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0061] Example 3. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0062] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, citric acid is 55.252g, and polytetrafluoroethylene is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the raw materials are ball-milled. The refined raw materials are fed into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1400 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0063] Example 4. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is ammonium metavanadate, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0064] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, ammonium metavanadate is 565.651g, ammonium dihydrogen phosphate is 834.332g, citric acid is 55.252g, and polytetrafluoroethylene is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the raw materials are ball-milled. The refined raw materials are fed into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1400 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0065] Example 5. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is phosphoric acid, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0066] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, phosphoric acid is 827.843g, citric acid is 55.252g, and polytetrafluoroethylene is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the premixed raw materials are ball-milled. The raw materials after curing are sent to a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1400 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is sintered once, and the once sintering is step-by-step sintering, the room temperature is heated to 350°C and kept warm for 8 hours, and then heated to 720°C and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0067] Example 6. This example provides a method for preparing a positive electrode material, comprising the following steps: (1) placing a sodium vanadium fluorophosphate raw material, a carbon source, and a fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2;

[0068] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, citric acid is 55.252g, and polytetrafluoroethylene is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the raw materials are ball-milled. The refined raw materials are fed into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1400 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 9 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0069] Comparative Example 1, (1) sodium vanadium fluorophosphate raw material, a carbon source and a fluorine replenishing agent are put into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source and the vanadium source is 3:2:2;

[0070] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, citric acid is 55.252g, and polyvinylidene fluoride is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.9 microns; (3) the raw materials are ball-milled. The ground raw materials are fed into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 500 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours, to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0071] Comparative Example 2, (1) sodium vanadium fluorophosphate raw material, a carbon source and a fluorine replenishing agent are put into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source and the vanadium source is 3:2:2;

[0072] The carbon source is glucose, and the mass of the carbon source is 4wt% of the total mass of the sodium vanadium fluorophosphate raw materials. The raw materials are mixed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, glucose is 63.145g, and polyvinylidene fluoride is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.8 microns; (3) the ball-milled raw materials are fed into a high-speed disperser (4) the raw material of the adhesive is subjected to roller granulation by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for roller granulation is 7 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0073] Comparative Example 3, (1) sodium vanadium fluorophosphate raw material, a carbon source and a fluorine replenishing agent are put into a high-speed disperser for pre-dispersion and mixing to obtain a premixed raw material; wherein the sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid, and the vanadium source is vanadium pentoxide, and the molar ratio of the sodium source / fluorine source, the phosphorus source and the vanadium source is 3:2:2;

[0074] The carbon source is citric acid, the mass of the carbon source is 3.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, the mass of the fluorine replenisher is 1.5wt% of the total mass of the sodium vanadium fluorophosphate raw material, and the mixture is weighed according to the actual weight, wherein sodium fluoride is 304.561g, vanadium pentoxide is 439.736g, ammonium dihydrogen phosphate is 834.332g, citric acid is 55.252g, and polyvinylidene fluoride is 23.679g; (2) the premixed raw materials are ball-milled; the median particle size D50 of the raw material particles after ball milling is 4.9 microns; (3) the raw materials are ball-milled. The ground raw materials are fed into a high-speed disperser for high-speed shear dispersion until a bonding body raw material is formed; wherein the speed of the high-speed disperser is 1200 rpm; (4) the bonding body raw material is rolled and granulated by a roller granulator to obtain a sodium vanadium fluorophosphate precursor; wherein the roller pressure of the roller granulator for rolling granulation is 5 MPa; (5) the sodium vanadium fluorophosphate precursor is subjected to a single sintering, wherein the single sintering is a step-by-step sintering, the room temperature is raised to 350° C. and kept warm for 8 hours, and then the temperature is raised to 720° C. and kept warm for 10 hours to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material;

[0075] Performance testing: Performance testing of the materials provided in the examples and comparative examples;

[0076] (I) Detection method: 1. Scanning electron microscopy: The materials provided in the examples and comparative examples were subjected to scanning electron microscopy to observe the material morphology.

[0077] 2. XRD test: Powder X-ray diffractometer was used to perform powder test in the diffraction angle range of 10-80° 2θ.

[0078] 3. Coin Cell Fabrication: The positive electrode material, binder PVDF, and conductive carbon black (Super P) were mixed in a 94:3:3 ratio and dissolved in NMP. After thorough stirring and degassing, the mixture was filtered to obtain a slurry. The resulting slurry was applied to the surface of the current collector aluminum foil using an automatic coater. The coated electrode was dried at 105°C under both forced air and vacuum conditions for at least 12 hours. The positive electrode sheet was then roller-pressed to obtain the positive electrode sheet. The positive electrode sheet was punched into a 12mm diameter disc. The negative counter electrode was a sodium metal sheet, and a glass fiber membrane served as the separator. The electrolyte consisted of 1 mol / L NaPF6 dissolved in an organic solution with an EC:DEC ratio of 1:1. CR2032 coin cells were assembled in an argon-protected glove box with a water and oxygen content below 1 ppm. The battery was charged and discharged at a 1C current of 120 mA / g, and the cycling curve was measured over a voltage range of 2.5-4.3 V.

[0079] 4. Powder bulk density test: Weigh a certain amount of precursor powder and naturally feed it into a square sagger of a certain size and volume through a loader. Use a scraper to gently press and flatten the sagger. Weigh the mass of the empty sagger and the filled sagger respectively, and divide the mass by the volume of the sagger to obtain the powder bulk density.

[0080] 5. Powder compaction density test: Weigh a certain amount of powder sample and place it in a cylindrical mold. Apply pressure to compress the powder into a disc. After maintaining the pressure at 3T for a certain period of time, read the volume of the compressed material and calculate the powder compaction density by the mass-to-volume ratio.

[0081] (II) Test results. The performance test data of the positive electrode materials prepared in the examples and comparative examples are shown in Table 1 below.

[0082] Table 1

[0083]

[0084] Based on the performance test data of the positive electrode materials obtained from the above embodiments and comparative examples, it can be seen that: (1) the positive electrode materials obtained in each embodiment of the present invention have a high bulk density of the sodium vanadium fluorophosphate precursor, and the prepared positive electrode materials have a high powder compaction density, good conductivity, and high specific capacity. In comparative example 1, when preparing the positive electrode material, the rotation speed of the high-speed disperser is 500 rpm, so that the fluorine replenishing agent has no adhesive property, and the obtained precursor has a low bulk density. In comparative example 2, when preparing the positive electrode material, no fluorine replenishing agent is added to the sodium vanadium fluorophosphate raw material, and the obtained positive electrode material has many impurities, low purity, low bulk density of the precursor, low specific capacity, and low loading amount, which affects the improvement of production capacity; (2) Figure 1 This is a scanning electron microscope image of the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared in Example 1. Figure 1 It can be seen that the prepared carbon-coated sodium vanadium fluorophosphate cathode material is uniform nanoparticles, indicating that the sodium source / fluorine source, phosphorus source, vanadium source, carbon source and fluoride replenisher are in sufficient contact and react with each other; Figure 2 is the XRD pattern of the carbon-coated sodium vanadium fluorophosphate prepared in Example 1, Figure 2 The provided XRD diffraction pattern shows that the XRD diffraction spectrum of the prepared carbon-coated sodium vanadium fluorophosphate is completely consistent with the standard diffraction spectrum, indicating that the preparation method of the present invention adds a fluorine replenishing agent, which replenishes the F loss, so that the carbon-coated sodium vanadium fluorophosphate preparation process obtains pure phase sodium vanadium fluorophosphate; Figure 3 is the charge and discharge curve of the battery made from the positive electrode material of Example 1. Figure 3 It can be seen that the battery voltage made from the positive electrode material of Example 1 is 4.2V, and the constant current charging is performed at a charging current of 1C, and the discharge capacity is 118.5mAh / g; the carbon-coated sodium vanadium fluorophosphate positive electrode material obtained by the preparation method has a high specific capacity, and the battery made from the positive electrode material has a long cycle life;

[0085] It should be noted that: (1) The present invention uses a pure dry process, which is simpler than the hydrothermal process and can be produced continuously on a large scale, with the focus on the wastewater treatment capacity. Compared with the liquid phase + solid phase sintering process, the preparation method has the advantages of less wastewater treatment volume and no need for spray drying process, which has lower energy consumption. (2) The present invention uses a fluorine replenishing agent, which replenishes the F loss and ensures the component completion and phase purity. (3) The fluorine replenishing agent used in the preparation method also acts as a binder, and realizes the fiberization of the binder through high-speed shear force, so as to achieve bonding of different particles in the raw material after ball milling. The sodium vanadium fluorophosphate precursor obtained after the bonded raw material is roller-granulated by a roller granulator has higher density and better uniformity. Therefore, the unit volume loading capacity is higher in large-scale production, which is conducive to improving production capacity. (4) The preparation method obtains a carbon-coated sodium vanadium fluorophosphate positive electrode material after one-time sintering, which improves the conductivity of the positive electrode material. (5) The powder compaction density of the prepared carbon-coated sodium vanadium fluorophosphate positive electrode material is higher. (6) The carbon-coated sodium vanadium fluorophosphate positive electrode material obtained by the preparation method has a higher specific capacity.

[0086] It is worth noting that in the preparation method of the present application, the sodium vanadium fluorophosphate raw material, the carbon source and the fluorine replenishing agent are pre-dispersed and mixed to obtain a pre-mixed raw material, wherein the carbon source is glucose or citric acid, and the mass of the carbon source is 1-10wt% of the total mass of the sodium vanadium fluorophosphate raw material; the fluorine replenishing agent is polyvinylidene fluoride or polytetrafluoroethylene, and the mass of the fluorine replenishing agent is 1-8wt% of the total mass of the sodium vanadium fluorophosphate raw material; the pre-mixed raw material is ball-milled, and the median particle size D50 of the raw material particles after ball milling is ≤6 microns; the fluorine replenishing agent used is also used as a binder, and is passed through a high-speed The disperser disperses the ball-milled raw materials at high speed using shearing. The speed of the high-speed disperser is set to 800-1800 rpm. The high-speed shear force achieves fiberization of the adhesive, bonding the different particles in the ball-milled raw materials. The bonded raw materials are roller-granulated in a roller granulator. The resulting sodium vanadium fluorophosphate precursor has a higher density, thus increasing the unit volume loading capacity in large-scale production, which is conducive to increasing production capacity. The carbon-coated sodium vanadium fluorophosphate cathode material obtained by single-stage sintering has good conductivity and high specific capacity, and can be produced continuously on a large scale.

[0087] The method for preparing the positive electrode material provided by the present invention uses low-cost carbon sources such as glucose or citric acid as raw materials, thereby reducing the production cost of the positive electrode material.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The preparation method comprises the following steps: Step 1: putting the sodium vanadium fluorophosphate raw material, the carbon source and the fluorine replenishing agent into a high-speed disperser for pre-dispersion and mixing to obtain a pre-mixed raw material; Step 2: grinding the premixed raw materials into fine powder using a ball mill; Step 3: The ball-milled raw materials are fed into a high-speed disperser for high-speed shear dispersion until a cohesive raw material is formed; Step 4: Roll-pressing and granulating the bonded material through a roller granulator to obtain a sodium vanadium fluorophosphate precursor; Step 5: sintering the sodium vanadium fluorophosphate precursor to obtain a carbon-coated sodium vanadium fluorophosphate positive electrode material; In step 1, the sodium vanadium fluorophosphate raw materials include a sodium source / fluorine source, a phosphorus source and a vanadium source; The sodium source / fluorine source is sodium fluoride, the phosphorus source is ammonium dihydrogen phosphate or phosphoric acid, and the vanadium source is vanadium pentoxide or ammonium metavanadate; wherein the molar ratio of the sodium source / fluorine source, the phosphorus source, and the vanadium source is 3:2:2; The carbon source is glucose or citric acid, the carbon source mass is 1-10wt% of the total mass of the sodium vanadium fluorophosphate raw material; The fluorine replenishing agent is used to replenish fluorine loss, ensuring the completion and phase purity of the synthesized sodium vanadium fluorophosphate components; the fluorine replenishing agent also acts as a binder, bonding the particles during high-speed shear dispersion, and after roller granulation, the sodium vanadium fluorophosphate precursor has a higher density; wherein the fluorine replenishing agent is polyvinylidene fluoride or polytetrafluoroethylene, and the mass of the fluorine replenishing agent is 1-8wt% of the total mass of the sodium vanadium fluorophosphate raw material; In step 3, when the high-speed disperser performs high-speed shear dispersion, the speed of the high-speed disperser is 800-1800 rpm; In step 4, the roller granulator performs roller granulation at a roller pressure of ≥7 MPa.

2. The method for preparing the positive electrode material according to claim 1, wherein: In step 2, the median particle size D50 of the raw material particles after ball milling is ≤6 microns.

3. The method for preparing the positive electrode material according to claim 1, wherein: In step 5, the primary sintering is a step-by-step sintering, specifically: After the sodium vanadium fluorophosphate precursor undergoes a first sintering reaction at a first sintering temperature, the temperature is raised to a second sintering temperature for a second sintering reaction; Wherein, the conditions of the first sintering reaction are: The first sintering temperature is 300-400℃, and the first sintering reaction time is 5-10h; The conditions of the second sintering reaction are: The second sintering temperature is 500-750℃, and the second sintering reaction time is 8-12h.

4. A pole piece, characterized in that: The invention comprises a carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 3.

5. A battery, characterized in that: The invention comprises the carbon-coated sodium vanadium fluorophosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 3 or the electrode piece according to claim 4.

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