Preparation method of sodium ferrovanadium phosphate material

Abstract

The invention relates to the technical field of sodium ion battery electrode materials, in particular to a preparation method of a sodium ferrovanadium phosphate material. The preparation method comprises the following steps: S1, sequentially adding an iron source, a vanadium source, a phosphorus source, a sodium source and a carbon source into grinding equipment, and carrying out dry grinding; s2, in a protective atmosphere, carrying out gradient sintering on the dry powder raw material, firstly sintering at 350 DEG C, then sintering at 650 DEG C, and finally sintering at a temperature T which is greater than or equal to 780 DEG C and less than or equal to 950 DEG C; and S3, the sodium ferrovanadium phosphate material obtained through gradient sintering is subjected to graded crushing, and the sodium ferrovanadium phosphate material with large, medium and small three-level particle size distribution is obtained. According to the method, water or any organic solvent is not adopted, dry ball milling is directly adopted, the three-level particle size distribution sodium ferrovanadium phosphate product is obtained through a step-by-step grinding mode, a gradient sintering mode and a graded smashing mode, and the prepared sodium ferrovanadium phosphate product has the advantages of being high in compaction density and high in discharge capacity.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium-ion battery electrode materials, and particularly relates to a preparation method of a sodium vanadium iron phosphate material. BACKGROUND

[0002] In recent years, the price of lithium carbonate is high, and the price of sodium carbonate is only one one-hundredth to one-fiftieth of that of lithium carbonate. Therefore, sodium-ion batteries are gradually favored by people due to the huge cost advantage. Sodium-ion batteries are mainly divided into three types according to different positive electrode materials: layered oxide ternary nickel-cobalt-manganese sodium-ion batteries, prussian series sodium-ion batteries and polyanion sodium-ion batteries. The layered oxide ternary nickel-cobalt-manganese sodium-ion battery has the advantages of high compaction density and high capacity, but the cost is relatively high due to the high cost of nickel, cobalt and manganese elements. The prussian series mainly includes prussian blue and prussian white, has the characteristics of high capacity and relatively low cost, but it is toxic and easy to produce toxic gas in thermal runaway, and the compaction density is low. The positive electrode material of the polyanion sodium-ion battery includes sodium vanadium iron phosphate, sodium iron phosphate and sodium iron pyrophosphate, and has the advantages of low cost, non-toxicity, environmental friendliness, high capacity and high compaction.

[0003] CN 107611429 A discloses a sodium-rich sodium vanadium iron phosphate material, a preparation method thereof and application thereof in a sodium-ion battery. In this technical solution, a sodium source, an iron source, a phosphorus source and a vanadium source are used to prepare a sodium vanadium iron phosphate positive electrode material through ball milling and sintering. However, flammable and explosive organic solvents such as acetone or anhydrous ethanol are needed as solvents in the ball milling process, and the prepared sodium vanadium iron phosphate material has poor electrical performance, and the initial discharge capacity is only 60-70 mAh / g, which is far lower than the theoretical discharge capacity of 120 mAh / g.

[0004] CN 115432686 A discloses a sodium vanadium iron phosphate material, a preparation method thereof and application thereof. In this technical solution, an iron source, a sodium source, a fluoride, a vanadium source and a phosphorus source are used as raw materials to realize high-efficiency nanometerization of the sodium vanadium iron phosphate material. The inexpensive iron element is used to replace the expensive vanadium element to reduce the preparation cost. The anion exchange technology, the reduction characteristics of the iron element and the coprecipitation effect are used to control the rapid nucleation and limited growth of the sodium vanadium phosphate material, so as to effectively control the particle size distribution of the sodium vanadium iron phosphate product and realize nanometerization. However, the fluoride is used as a raw material to react in an aqueous solution in the preparation process, the fluoride has strong corrosion, and the corrosion of the reaction equipment and pipelines is serious, which is not conducive to industrialization. In addition, the specific surface area of the prepared fluorophosphovanadium iron phosphate is as high as 46.5 m 2 / g, the specific surface area is too high, and the jelly is prone to be formed in the process of preparing the electrode. In addition, the discharge capacity of the sodium vanadium iron phosphate prepared by the technical scheme is only 109 mAh / g, and the discharge capacity is low. SUMMARY

[0005] In view of the technical problems that the existing sodium vanadium iron phosphate material preparation method needs to use flammable and explosive organic solvents in grinding, uses strong corrosive fluoride raw materials, or the discharge capacity of the prepared sodium vanadium iron phosphate material is low, the application provides a preparation method of sodium vanadium iron phosphate material, which does not use water or any organic solvent, directly uses dry ball milling, and obtains a sodium vanadium iron phosphate product with a three-level particle size distribution through a step-by-step grinding mode, a gradient sintering mode and a grading crushing mode. The prepared sodium vanadium iron phosphate product has the advantages of high compaction density and high discharge capacity.

[0006] The technical scheme of the application is as follows: A preparation method of sodium vanadium iron phosphate material, comprising the following steps: S1. Dry milling iron source, vanadium source, phosphorus source, sodium source and carbon source in sequence in a grinding device to obtain dry powder raw material; S2. Gradient sintering the dry powder raw material under a protective atmosphere, first sintering at 350 DEG C for 120 min, then sintering at 650 DEG C for 120 min to 180 min, and finally sintering at T temperature for 720 min to 840 min, T temperature is greater than or equal to 780 DEG C and less than or equal to 950 DEG C; S3. Grading crushing the sodium vanadium iron phosphate material obtained by gradient sintering to obtain a sodium vanadium iron phosphate material containing a three-level particle size distribution of large, medium and small.

[0007] It should be further pointed out that the iron source used in S1 is selected from at least one of diiron trioxide and triiron tetroxide; the vanadium source is selected from at least one of divanadium pentoxide, ammonium metavanadate and vanadyl sulfate; the phosphorus source is selected from at least one of monoammonium phosphate and diammonium phosphate; and the sodium source is selected from at least one of sodium carbonate and sodium bicarbonate.

[0008] The above raw materials are widely available on the market, and the price is relatively low, which reduces the cost of preparing the sodium vanadium iron phosphate material, so that the preparation method of the application is more economically feasible, and is beneficial to large-scale industrial production.

[0009] It should be further pointed out that in S1, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is 4:1-1.5:0.1-0.3:3-4.

[0010] The above ratio can make the raw materials fully react, reduce the occurrence of side reactions, improve the purity and yield of the target product sodium iron vanadium phosphate, and thus obtain a sodium iron vanadium phosphate material with excellent performance.

[0011] It should be further explained that the carbon source used in S1 is selected from at least one of sucrose, glucose and fructose.

[0012] Using the above sugar substances as the carbon source, on the one hand, the carbon produced by their decomposition in the subsequent sintering process can act as a reducing agent, participate in the reaction and promote the generation of the target product; on the other hand, the carbon can form a carbon coating layer on the surface of the material, improve the electrical conductivity of the material and improve the electrical performance of the sodium iron vanadium phosphate material.

[0013] It should be further explained that in S1, the molar ratio of carbon in the carbon source to iron in the iron source is 0.01-0.02:1.

[0014] The reasonable amount of carbon source is crucial to the performance of the sodium iron vanadium phosphate material. Under the above amount, the carbon source can form a uniform carbon coating layer on the surface of the material, which can neither effectively improve the electrical conductivity due to insufficient carbon content, nor affect other properties of the material, such as the compactness, due to excessive carbon content.

[0015] It should be further explained that S1 is specifically: (1) adding the iron source into a grinding device and dry grinding to a particle size of 150 nm-300 nm; (2) adding the vanadium source into the grinding device of step (1) and dry grinding to a particle size of 150 nm-400 nm; (3) adding the phosphorus source into the grinding device of step (2) and dry grinding for 3-5 h; (4) adding the sodium source into the grinding device of step (3) and dry grinding for 6-8 h; (5) adding the carbon source into the grinding device of step (4) and dry grinding for 9-11 h.

[0016] The step-by-step grinding method adopted by the present application can make the raw materials fully mixed and ground with the existing materials when added, improving the mixing uniformity of the raw materials. The grinding time and particle size control at different stages help to ensure the quality of the final dry powder raw materials, so that they have a suitable particle size distribution, providing a good foundation for the subsequent sintering process.

[0017] It should be further explained that after dry grinding in step (5), a dry powder raw material with a particle size range of 150 nm-400 nm is obtained.

[0018] The particle size range is conducive to uniform diffusion and reaction of the material during sintering, thereby obtaining a sodium iron vanadium phosphate material with high crystallinity and uniform structure.

[0019] It should be further explained that in S1, the total time of controlling dry grinding is 24 h-48 h.

[0020] It should be further explained that in S2, the protective atmosphere is a nitrogen atmosphere, a helium atmosphere or an argon atmosphere.

[0021] The protective atmosphere can prevent the raw material and the product from being oxidized during sintering, which helps to improve the purity and stability of the product and ensures that the performance of the sodium iron vanadium phosphate material is not affected by oxidation, thereby obtaining a high-quality product.

[0022] It should be further explained that in S3, the sodium iron vanadium phosphate is classified and crushed using an air flow mill, and the sodium iron vanadium phosphate material containing three levels of particle size distribution is obtained by adjusting the frequency of the classification wheel, specifically, the frequency of the classification wheel is first adjusted to 5 Hz-10 Hz for crushing, then the frequency of the classification wheel is adjusted to 10 Hz-20 Hz for crushing, and finally the frequency of the classification wheel is adjusted to 20 Hz-50 Hz for crushing.

[0023] The particles of the three levels of particle size fill each other, the gaps between the large particles are filled with medium particles, and the gaps between the medium particles are filled with small particles, forming a more compact packing structure, thereby significantly improving the compaction density of the material. High compaction density is crucial for battery electrode materials, as it allows more active material to be contained in a unit volume, thereby improving the energy density of the battery and increasing the endurance of the battery.

[0024] The classified particle size distribution helps to build more effective ion diffusion channels. Small particles can shorten the diffusion path of sodium ions and accelerate the diffusion speed of sodium ions inside the material, enabling the battery to be quickly charged and discharged at high current density and improving the rate performance of the battery. Medium particles and large particles act as a supporting skeleton to ensure the stability of the material structure and maintain the smoothness of the ion diffusion channel, further promoting the migration of sodium ions.

[0025] The beneficial effects of the present application are: The present application performs dry step-by-step grinding without adding water or any other solvent, and the ground material is dry powder containing no water, without the need for any drying operation. Then, gradient sintering is performed to obtain the desired sodium iron vanadium phosphate product, and finally, the sodium iron vanadium phosphate material containing three levels of particle size distribution is obtained by classification crushing, which has the advantages of simple process, easy operation and low energy consumption. Moreover, the existing lithium iron phosphate production line can be used for industrial production, and the obtained sodium iron vanadium phosphate material has high crystallinity, high compaction and good electrical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0027] Figure 1 This is an SEM image of the sodium ferrovanadium phosphate material finally obtained in step 4 of Example 3.

[0028] Figure 2 This is the particle size distribution diagram of the sodium ferrovanadium phosphate material finally obtained in step 4 of Example 3.

[0029] Figure 3 This is the particle size distribution diagram of the sodium ferrovanadium phosphate material finally obtained in step 4 of Comparative Example 2. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0031] A method for preparing sodium ferrovanadium phosphate material comprises at least the following steps: S1. Add an iron source, a vanadium source, a phosphorus source, a sodium source, and a carbon source sequentially into a grinding device for dry grinding to obtain a dry powder raw material. The step-by-step grinding method facilitates more complete and uniform grinding.

[0032] S2. Under a protective atmosphere, the dry powder raw material is subjected to a gradient sintering process, first at 350°C for 120 minutes, then at 650°C for 120 to 180 minutes, and finally at a temperature T for 720 to 840 minutes, where T is greater than or equal to 780°C and less than or equal to 950°C. Gradient sintering is beneficial for obtaining a powdered sodium ferrovanadium phosphate material with high crystallinity and no impurities.

[0033] S3. The sodium ferrovanadium phosphate material obtained by gradient sintering is graded and crushed to obtain a sodium ferrovanadium phosphate material having three particle size distributions of large, medium, and small. The graded and crushed sodium ferrovanadium phosphate material has the advantages of high compaction density and high discharge capacity.

[0034] In the S1 of the present application, the sequential addition here refers to the time gap between the addition of two substances, that is, after adding one substance into the grinding device, dry grinding is carried out for a period of time, and then the next substance is added, and after adding the last substance (carbon source), dry grinding is carried out on the material in the grinding device for a period of time; The dry grinding here refers to the process of reducing and refining the particles of solid materials by mechanical force without adding liquid medium, specifically, in the present application, the grinding objects (raw materials used) are all solid substances without water, ethanol, acetone or other liquids, and water, ethanol, acetone or other liquids do not need to be added into the grinding device during the grinding process.

[0035] More specifically, the specific operation steps of the S1 of the present application are as follows: First, the iron source is added into the grinding device for dry grinding, after t1 time, the vanadium source is added into the grinding device for dry grinding together with the iron source which has been ground for t1 time, after t2 time, the phosphorus source is added into the grinding device for dry grinding together with the iron source and the vanadium source in the grinding device, after t3 time, the sodium source is added into the grinding device for dry grinding together with the iron source, the vanadium source and the phosphorus source in the grinding device, after t4 time, the carbon source is added into the grinding device for dry grinding together with the iron source, the vanadium source, the phosphorus source and the sodium source in the grinding device, after t5 time, the step-by-step grinding of the raw materials is completed.

[0036] As a preferred embodiment of the present application, the raw materials (iron source, vanadium source, phosphorus source, sodium source and carbon source) used for preparing vanadium iron sodium phosphate are all powder.

[0037] As a preferred embodiment of the present application, the iron source can be selected from at least one of diiron trioxide (red iron oxide) and triiron tetroxide.

[0038] As a preferred embodiment of the present application, the vanadium source can be selected from at least one of di vanadium pentoxide, ammonium metavanadate and vanadyl sulfate.

[0039] As a preferred embodiment of the present application, the phosphorus source can be selected from at least one of monoammonium phosphate and diammonium phosphate.

[0040] As a preferred embodiment of the present application, the sodium source can be selected from at least one of sodium carbonate and sodium bicarbonate.

[0041] As a preferred embodiment of the present application, the carbon source can be selected from at least one of sucrose, glucose and fructose.

[0042] As a preferred embodiment of the present application, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source, and phosphorus provided by the phosphorus source is 4:1~1.5:0.1~0.3:3~4.

[0043] As a preferred embodiment of the present application, the molar ratio of carbon in the carbon source and iron in the iron source is 0.01~0.02:1.

[0044] As a preferred embodiment of the present application, the grinding time (t1, t2, t3, t4, t5) of each raw material can be controlled as a whole by the total grinding time, or individually controlled according to the set grinding time, or it can be judged whether the grinding is completed by comparing whether the particle size of the ground raw material reaches the expected particle size.

[0045] As a preferred embodiment of the present application, the total dry grinding time of S1 is 24 h~48 h.

[0046] As a preferred embodiment of the present application, after dry grinding for t1 time, the particle size range of the material (iron source) in the grinding equipment should be controlled in the range of 150 nm~300 nm.

[0047] As a preferred embodiment of the present application, after dry grinding for t2 time, the particle size range of the material (iron source and vanadium source) in the grinding equipment should be controlled in the range of 150 nm~400 nm.

[0048] As a preferred embodiment of the present application, after adding the phosphorus source, the phosphorus source is dry ground together with the iron source and the vanadium source in the grinding equipment for 3 h~5 h, i.e. t3 time is 3 h~5 h.

[0049] As a preferred embodiment of the present application, after adding the sodium source, the sodium source is dry ground together with the iron source, the vanadium source, and the phosphorus source in the grinding equipment for 6 h~8 h, i.e. t4 time is 6 h~8 h.

[0050] As a preferred embodiment of the present application, after adding the carbon source, the carbon source is dry ground together with the iron source, the vanadium source, the phosphorus source, and the sodium source in the grinding equipment for 9 h~11 h, i.e. t5 time is 9 h~11 h; and / or, after dry grinding for t5 time, the particle size range of the material (iron source, vanadium source, phosphorus source, sodium source, and carbon source) in the grinding equipment should be controlled in the range of 150 nm~400 nm.

[0051] As a preferred embodiment of the present application, the dry grinding adopts a ball mill, such as a planetary ball mill, which can be a vertical planetary ball mill or a horizontal planetary ball mill.

[0052] As a preferred embodiment of the present application, the ball-to-material ratio during ball milling is 5-10:1, and the rotation speed is 800 rpm-2000 rpm; in the stepwise feeding process, new grinding balls are added at the same time as new raw materials are added, so as to keep the ball-to-material ratio unchanged.

[0053] As a preferred embodiment of the present application, the grinding balls used in ball milling are selected from alumina, zirconia, silicon carbide or silicon nitride.

[0054] In S2 of the present application, the gradient sintering mode comprises a first temperature rising, a second temperature rising, a first temperature holding, a third temperature rising, a second temperature holding, a fourth temperature rising and a third temperature holding, which are sequentially performed; the first temperature rising refers to increasing the sintering environment temperature from room temperature (25℃) to 125℃, and the temperature rising time is 30 min, i.e. the temperature rising rate is 3.333℃ / min; The second temperature rising refers to increasing the sintering environment temperature from 125℃ to 350℃, and the temperature rising time is 75 min, i.e. the temperature rising rate is 3.0℃ / min; The first temperature holding refers to holding sintering at the sintering environment temperature of 350℃ for 120 min; The third temperature rising refers to increasing the sintering environment temperature from 350℃ to 650℃, and the temperature rising time is 75 min, i.e. the temperature rising rate is 4℃ / min; The second temperature holding refers to holding sintering at the sintering environment temperature of 650℃ for 120 min-180 min; The fourth temperature rising refers to increasing the sintering environment temperature from 650℃ to T temperature, wherein T temperature represents any specific temperature in the temperature range of 780℃-950℃, and the temperature rising time is 60 min-120 min; The third temperature holding refers to holding sintering at the sintering environment temperature of T temperature for 720 min-840 min.

[0055] As a preferred embodiment of the present application, the sintering equipment used in the sintering process can be a muffle furnace or a tube furnace, etc.

[0056] As a preferred embodiment of the present application, in the sintering process, nitrogen (N2) or inert gas is introduced into the interior of the sintering equipment to form a protective atmosphere, wherein the inert gas refers to an element in group 18 of the periodic table, including helium (He), argon (Ar), etc.

[0057] As a preferred embodiment of the present application, after the third temperature holding is completed, nitrogen is introduced into the interior of the sintering equipment to cool down, and after the temperature is reduced to room temperature, the sintering equipment is opened, and the gradient-sintered product is taken out, thereby obtaining the sodium iron vanadate phosphate.

[0058] In S3 of the present application, by controlling the process parameters in the crushing process, the sodium vanadium iron phosphate material obtained from S2 sintering is first crushed to obtain a part of sodium vanadium iron phosphate material with larger particle size, then the remaining sodium vanadium iron phosphate material is crushed to obtain a part of sodium vanadium iron phosphate material with medium particle size, and finally the remaining sodium vanadium iron phosphate material is crushed to a smaller particle size to obtain a product mixed by sodium vanadium iron phosphate materials with large, medium and small particle size distribution.

[0059] As a preferred embodiment of the present application, the crushing process is carried out by using an air flow mill. In the air flow crushing process, the particle size of the obtained particles can be changed by adjusting the frequency of the classification wheel of the air flow mill. Based on this feature, the present application first uses a smaller classification wheel frequency (for example, 5 Hz~10 Hz) to obtain a product with larger particle size, then increases the frequency of the classification wheel (for example, 10 Hz~20 Hz) to obtain a product with medium particle size, and finally further increases the frequency of the classification wheel (for example, 20 Hz~50 Hz) to obtain a product with smaller particle size.

[0060] Example 1 A sodium vanadium iron phosphate material is obtained according to the following preparation method: Step one: weigh 425 g of sodium carbonate powder as a sodium source, 160 g of iron trioxide powder as an iron source, 16.5 g of vanadyl sulfate powder as a vanadium source, and 345 g of monoammonium phosphate powder as a phosphorus source, and 3.5 g of sucrose powder as a carbon source, wherein the sodium carbonate, iron trioxide, vanadyl sulfate, monoammonium phosphate and sucrose are all analytically pure, at this time the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.01:0.1:3.

[0061] Step two: using dry ball milling method, without using water or any other liquid medium, first add 160 g of iron trioxide powder and 800 g of grinding balls weighed into the ball mill tank, place the ball mill tank in the ball mill, adjust the speed of the ball mill to 900 rpm for ball milling, to obtain raw material particles with a particle size of 200 nm; Then add 16.5 g of vanadyl sulfate powder and 82.5 g of grinding balls weighed into the ball mill tank, continue ball milling to obtain raw material particles with a particle size of 170 nm; Then add 345 g of monoammonium phosphate powder, 425 g of sodium carbonate powder and 3.5 g of sucrose powder weighed into the ball mill tank in turn for ball milling, according to the total ball-to-material ratio of 5:1, add the corresponding weight of grinding balls in turn, and the ball milling time is 3 h, 6 h and 9 h respectively; After a total of 28 h of ball milling, the dry raw powder with a particle size of 150 nm is obtained.

[0062] Step three: the raw material dry powder obtained after step two dry ball milling is placed in a sintering device, nitrogen is introduced into the sintering device, and after the air in the furnace is completely removed, gradient sintering is carried out starting from 25℃, and the sintering process is carried out in the order of one-stage temperature rise (25℃ to 125℃, sintering time 30 min), two-stage temperature rise (125℃ to 350℃, sintering time 75 min), one-stage temperature holding (350℃, sintering time 120 min), three-stage temperature rise (350℃ to 650℃, sintering time 75 min), two-stage temperature holding (650℃, sintering time 120 min), four-stage temperature rise (650℃ to 785℃, sintering time 80 min) and three-stage temperature holding (785℃, sintering time 760 min); After the gradient sintering is completed, nitrogen is continuously introduced to cool to room temperature, and then the sintered product is taken out, which is a powder vanadium iron sodium phosphate material.

[0063] Step four: the powder vanadium iron sodium phosphate material obtained by gradient sintering is subjected to airflow crushing, first adjusting the frequency of the classification wheel of the airflow mill to 7 Hz to obtain a larger particle size vanadium iron sodium phosphate material, then increasing the frequency of the classification wheel to 15 Hz to obtain a medium particle size vanadium iron sodium phosphate material, and finally continuously increasing the frequency of the classification wheel to 35 Hz to obtain a smaller particle size vanadium iron sodium phosphate material, and mixing the three vanadium iron sodium phosphate materials of different particle sizes to obtain a product of a mixture of vanadium iron sodium phosphate materials of large, medium and small particle sizes.

[0064] Example 2 A vanadium iron sodium phosphate material is obtained according to the following preparation method: Step one: 855 g of sodium carbonate powder is weighed as a sodium source, 492 g of iron trioxide powder is weighed as an iron source, 109.2 g of vanadium pentoxide powder is weighed as a vanadium source, and 690 g of monoammonium phosphate powder is weighed as a phosphorus source, and 10.7 g of sucrose powder is weighed as a carbon source, wherein the sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure, and at this time the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.5:0.3:3.

[0065] Step two: using a dry ball milling method, without using water or any other liquid medium, first 492 g of iron trioxide powder and 2.46 kg of grinding balls are added to the ball mill pot, the ball mill pot is placed in the ball mill, and the speed of the ball mill is adjusted to 1000 rpm for ball milling, to obtain raw material particles with a particle size of 210 nm; Then 109.2 g of vanadium pentoxide powder and 546 g of grinding balls are added to the ball mill pot, and the ball milling is continued, to obtain raw material particles with a particle size of 170 nm; Then, 690 g of ammonium dihydrogen phosphate powder, 855 g of sodium carbonate powder, and 10.7 g of sucrose powder were added in sequence and ball-milled. The ball-milling time was 4 h, 7 h, and 10 h, respectively. After a total of 32 h of ball-milling, the raw material dry powder with a particle size of 150 nm was obtained.

[0066] Step three: The raw material dry powder obtained after step two dry ball-milling was placed in a sintering device. Nitrogen was introduced into the sintering device. After the air in the furnace was completely removed, gradient sintering was performed starting from 25℃. The sintering process was performed in the following order: one-stage temperature rise (25℃ to 125℃, sintering time 30 min), two-stage temperature rise (125℃ to 350℃, sintering time 75 min), one-stage temperature holding (350℃, sintering time 120 min), three-stage temperature rise (350℃ to 650℃, sintering time 75 min), two-stage temperature holding (650℃, sintering time 160 min), four-stage temperature rise (650℃ to 825℃, sintering time 80 min), and three-stage temperature holding (825℃, sintering time 790 min). After the gradient sintering was completed, the nitrogen was continued to be introduced to cool to room temperature. Then, the sintered product was taken out, which was the powder vanadium iron sodium phosphate material.

[0067] Step four: The powder vanadium iron sodium phosphate material obtained by gradient sintering was subjected to airflow crushing. First, the classification wheel frequency of the airflow mill was adjusted to 8 Hz to obtain a larger particle size of the vanadium iron sodium phosphate material. Then, the classification wheel frequency was increased to 17 Hz to obtain a medium particle size of the vanadium iron sodium phosphate material. Finally, the classification wheel frequency was further increased to 41 Hz to obtain a smaller particle size of the vanadium iron sodium phosphate material. The three vanadium iron sodium phosphate materials with different particle sizes were mixed, and finally a product of a mixture of vanadium iron sodium phosphate materials with large, medium, and small particle sizes was obtained.

[0068] Example 3 A vanadium iron sodium phosphate material was obtained according to the following preparation method: Step one: 1.7 kg of sodium carbonate powder was weighed as a sodium source, 960 g of iron trioxide powder was weighed as an iron source, 218.4 g of vanadium pentoxide powder was weighed as a vanadium source, and 1.84 kg of ammonium dihydrogen phosphate powder was weighed as a phosphorus source. 28.5 g of sucrose powder was weighed as a carbon source. The sodium carbonate, iron trioxide, vanadium pentoxide, ammonium dihydrogen phosphate, and sucrose were all of analytical purity. At this time, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source, and phosphorus provided by the phosphorus source was about 4:1.49:0.3:4.

[0069] Step two: using dry ball milling method, without using water or any other liquid medium, first put 960 g of the weighed ferric oxide powder and 4.8 kg of grinding balls into the ball mill tank, place the ball mill tank in the ball mill, adjust the speed of the ball mill to 1800 rpm for ball milling, and obtain the raw material particles with a particle size of 210 nm; Then add 218.4 g of the weighed vanadium pentoxide powder and 1.09 kg of grinding balls into the ball mill tank, continue ball milling, and obtain raw material particles with a particle size of 170 nm; Then add 1.7 kg of sodium carbonate powder, 1.84 kg of monoammonium phosphate powder, and 28.5 g of sucrose powder in sequence for ball milling, and add the corresponding weight of grinding balls according to the total ball-to-material ratio of 5:1 in sequence, and the ball milling time is 5 h, 7 h, and 9 h, respectively; After a total of 38 h of ball milling, the raw material dry powder with a particle size of 150 nm is obtained.

[0070] Step three: place the raw material dry powder obtained after dry ball milling in step two into a sintering device, introduce nitrogen into the sintering device, and after completely removing the air in the furnace, start gradient sintering from 25℃, and perform the following procedures in sequence: one-stage heating (25℃ to 125℃, sintering time of 30 min), two-stage heating (125℃ to 350℃, sintering time of 75 min), one-stage holding (350℃, sintering time of 120 min), three-stage heating (350℃ to 650℃, sintering time of 75 min), two-stage holding (650℃, sintering time of 160 min), four-stage heating (650℃ to 875℃, sintering time of 90 min), and three-stage holding (875℃, sintering time of 820 min); After gradient sintering is completed, continue to introduce nitrogen to cool to room temperature, and then take out the sintered product, which is the powder vanadium iron sodium phosphate material.

[0071] Step four: air flow crushing is performed on the powder vanadium iron sodium phosphate material obtained by gradient sintering, first adjust the frequency of the classification wheel of the air flow mill to 10 Hz to obtain larger particle size vanadium iron sodium phosphate material, then increase the frequency of the classification wheel to 20 Hz to obtain medium particle size vanadium iron sodium phosphate material, and finally continue to increase the frequency of the classification wheel to 45 Hz to obtain smaller particle size vanadium iron sodium phosphate material, mix the three vanadium iron sodium phosphate materials with different particle sizes, and finally obtain a product mixed with vanadium iron sodium phosphate materials with large, medium, and small particle size distributions.

[0072] Under a scanning electron microscope (SEM), the morphology of the finally obtained vanadium iron sodium phosphate material is observed, as shown in Figure 1As shown, the material after airflow crushing mainly presents irregular flaky or granular shape, and the primary particle size is 300 nm-500 nm.

[0073] The particle size of the final product was analyzed, and it was found that the particle size distribution curve of the product was as shown in FIG. 3. Figure 2 As can be seen, the particle size distribution curve presents a multi-peak shape, which indicates that the sodium vanadium iron phosphate material treated by the fractional crushing in this embodiment 3 has multiple particle size distributions, and is not a single particle size. Specifically, the particle size distribution curve has a main peak at a particle size of about 1 μm, corresponding to a medium particle size sodium vanadium iron phosphate material, and the particle size distribution curve has secondary peaks at particle sizes of about 0.1 μm and 10 μm, respectively, corresponding to a smaller particle size sodium vanadium iron phosphate material and a larger particle size sodium vanadium iron phosphate material.

[0074] Comparative Example 1 A sodium vanadium iron phosphate material, different from the preparation method of embodiment 3, is that all raw materials are added together into a grinding device for wet ball milling, and a direct heating to the target temperature (875℃) for sintering is used instead of gradient sintering, and the powder sodium vanadium iron phosphate material is crushed at a single frequency of the classification wheel after sintering, to obtain a smaller particle size sodium vanadium iron phosphate material.

[0075] The specific preparation method of the sodium vanadium iron phosphate material of this comparative example 1 is as follows: Step one: 1.7 kg of sodium carbonate powder is weighed as a sodium source, 960 g of iron trioxide powder is weighed as an iron source, 218.4 g of vanadium pentoxide powder is weighed as a vanadium source, 1.84 kg of monoammonium phosphate powder is weighed as a phosphorus source, and 28.5 g of sucrose powder is weighed as a carbon source, wherein the sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure, and at this time, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.49:0.3:4.

[0076] Step two: the wet ball milling method is used, 960 g of iron trioxide powder, 218.4 g of vanadium pentoxide powder, 1.84 kg of monoammonium phosphate powder, 1.7 kg of sodium carbonate powder, 28.5 g of sucrose powder and 26.7 kg of grinding balls are added into a ball mill tank and water is added, the ball mill tank is placed in a ball mill, the rotation speed of the ball mill is adjusted to 1800 rpm, after a total of 38 h of ball milling, filtration and drying are performed to obtain raw material dry powder with a particle size of 150 nm.

[0077] Step three: Put the dry powder of raw materials obtained after step two into a sintering device, and introduce nitrogen into the sintering device. After the air in the furnace is completely removed, the temperature is increased from 25°C to 875°C at a rate of 550 min, and then the temperature is kept at 875°C for 820 min. After the gradient sintering is completed, the nitrogen is continuously introduced to cool to room temperature, and then the sintered product is taken out, which is the powder of the sodium iron vanadium phosphate material.

[0078] Step four: The sintered powder of the sodium iron vanadium phosphate material is subjected to airflow crushing, and the frequency of the classification wheel of the airflow mill is adjusted to 45 Hz to obtain a sodium iron vanadium phosphate material with smaller particle size.

[0079] Comparative Example 2 A sodium iron vanadium phosphate material, different from the preparation method of Example 3, is prepared by adding all the raw materials into a grinding device for wet ball milling, and the sintering process is replaced by directly increasing the temperature to the target temperature (875°C) for sintering. After sintering, the powder of the sodium iron vanadium phosphate material is crushed at a single classification wheel frequency to obtain a sodium iron vanadium phosphate material with larger particle size.

[0080] The specific preparation method of the sodium iron vanadium phosphate material of the present comparative example 2 is as follows: Step one: 1.7 kg of sodium carbonate powder is weighed as a sodium source, 960 g of iron trioxide powder is weighed as an iron source, 218.4 g of vanadium pentoxide powder is weighed as a vanadium source, 1.84 kg of monoammonium phosphate powder is weighed as a phosphorus source, and 28.5 g of sucrose powder is weighed as a carbon source. The sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure. At this time, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.49:0.3:4.

[0081] Step two: The wet ball milling method is used to add 960 g of iron trioxide powder, 218.4 g of vanadium pentoxide powder, 1.84 kg of monoammonium phosphate powder, 1.7 kg of sodium carbonate powder, 28.5 g of sucrose powder and 26.7 kg of grinding balls into a ball mill tank and add water. The ball mill tank is placed in a ball mill, and the speed of the ball mill is adjusted to 1800 rpm. After a total of 38 h of ball milling, the dry powder of raw materials with a particle size of 150 nm is obtained by filtration and drying.

[0082] Step three: Put the dry powder of raw materials obtained after step two into a sintering device, and introduce nitrogen into the sintering device. After the air in the furnace is completely removed, the temperature is increased from 25°C to 875°C at a rate of 550 min, and then the temperature is kept at 875°C for 820 min. After the gradient sintering is completed, the nitrogen is continuously introduced to cool to room temperature, and then the sintered product is taken out, which is the powder of the sodium iron vanadium phosphate material.

[0083] Step four: the sintered powder of sodium iron vanadium phosphate material is broken by airflow, and the frequency of the grading wheel of the airflow mill is adjusted to 10 Hz to obtain sodium iron vanadium phosphate material with larger particle size.

[0084] As shown in the particle size distribution of the sodium iron vanadium phosphate material obtained in Comparative Example 2 (as shown in the figure), the particle size distribution curve shows a unimodal shape, and the peak value is high. A large number of particles are concentrated in the same particle size, which means that the material is difficult to optimize in terms of physical and electrochemical properties through the synergistic effect of particles of different sizes. This result also proves that a combination of materials of various particle sizes can be obtained by the method of graded crushing. Figure 3 Comparative Example 3

[0085] A sodium iron vanadium phosphate material, different from the preparation method of Example 3, is that all the raw materials are added together into a grinding device for dry ball milling. The specific preparation method of the sodium iron vanadium phosphate material of this comparative example 3 is as follows:

[0086] Step one: 1.7 kg of sodium carbonate powder is weighed as a sodium source, 960 g of iron trioxide powder is weighed as an iron source, 218.4 g of vanadium pentoxide powder is weighed as a vanadium source, and 1.84 kg of monoammonium phosphate powder is weighed as a phosphorus source, and 28.5 g of sucrose powder is weighed as a carbon source, wherein the sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure, and at this time the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.49:0.3:4. Step two: using dry ball milling method, without using water or any other liquid medium, all the above weighed sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose powders are added into the ball mill pot, the ball mill pot is placed in the ball mill, and the speed of the ball mill is adjusted to 1800 rpm. After a total of 38 h of ball milling, the raw material dry powder with a particle size of 150 nm is obtained.

[0087] Step three: the raw material dry powder obtained after dry ball milling in step two is placed in a sintering device, nitrogen is introduced into the sintering device, and after the air in the furnace is completely removed, gradient sintering is started from 0°C, and the sintering process is carried out in the order of one-stage temperature rise (0°C to 25°C, sintering time 30 min), two-stage temperature rise (25°C to 350°C, sintering time 75 min), one-stage temperature holding (350°C, sintering time 120 min), three-stage temperature rise (350°C to 650°C, sintering time 75 min), two-stage temperature holding (650°C, sintering time 160 min), four-stage temperature rise (650°C to 875°C, sintering time 90 min) and three-stage temperature holding (875°C, sintering time 820 min).

[0088] ​After the gradient sintering is completed, nitrogen is continuously passed to cool to room temperature, and then the sintered product is taken out, which is a powder sodium iron vanadium phosphate material.

[0089] Step four: the powder sodium iron vanadium phosphate material obtained by gradient sintering is subjected to airflow crushing. First, the classification wheel frequency of the airflow mill is adjusted to 10 Hz to obtain a sodium iron vanadium phosphate material with a larger particle size. Then, the classification wheel frequency is increased to 20 Hz to obtain a sodium iron vanadium phosphate material with a medium particle size. Finally, the classification wheel frequency is continuously increased to 45 Hz to obtain a sodium iron vanadium phosphate material with a smaller particle size. The three sodium iron vanadium phosphate materials with different particle sizes are mixed, and finally a product of a mixture of sodium iron vanadium phosphate materials with large, medium and small particle sizes is obtained.

[0090] Comparative Example 4 A sodium iron vanadium phosphate material, different from the preparation method of Example 3, is sintered by directly heating to the target temperature (875℃) and holding sintering instead of gradient sintering.

[0091] The specific preparation method of the sodium iron vanadium phosphate material of Comparative Example 4 is as follows: Step one: 1.7 kg of sodium carbonate powder is weighed as a sodium source, 960 g of iron trioxide powder is weighed as an iron source, 218.4 g of vanadium pentoxide powder is weighed as a vanadium source, and 1.84 kg of monoammonium phosphate powder is weighed as a phosphorus source. 28.5 g of sucrose powder is used as a carbon source, wherein the sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure. At this time, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.49:0.3:4.

[0092] Step two: using a dry ball milling method, without using water or any other liquid medium, first put 960 g of iron trioxide powder and 4.8 kg of grinding balls into the ball mill pot, and place the ball mill pot in the ball mill. Adjust the speed of the ball mill to 1800 rpm for ball milling. Then add 218.4 g of vanadium pentoxide powder and 1.1 kg of grinding balls to the ball mill pot and continue ball milling. Then add 1.7 kg of sodium carbonate powder, 2.43 kg of monoammonium phosphate powder and 28.5 g of sucrose powder to the ball mill pot in sequence and ball mill for 5 h, 7 h and 9 h respectively. After a total of 38 h of ball milling, a raw dry powder with a particle size of 150 nm is obtained.

[0093] Step three: the raw material dry powder obtained after step two dry ball milling is placed in a sintering device, nitrogen is introduced into the sintering device, and after the air in the furnace is completely removed, the temperature is raised from 25℃ to 875℃, the temperature rising time is 550 min, then the temperature is kept at 875℃ for 820 min, after the gradient sintering is completed, the nitrogen is continued to be introduced to cool to room temperature, then the sintered product is taken out, which is the powder sodium iron vanadium phosphate material.

[0094] Step four: the powder sodium iron vanadium phosphate material obtained by gradient sintering is subjected to airflow crushing, first, the classification wheel frequency of the airflow mill is adjusted to 10 Hz to obtain a sodium iron vanadium phosphate material with a larger particle size, then the classification wheel frequency is increased to 20 Hz to obtain a sodium iron vanadium phosphate material with a medium particle size, and finally the classification wheel frequency is continuously increased to 45 Hz to obtain a sodium iron vanadium phosphate material with a smaller particle size, the three sodium iron vanadium phosphate materials with different particle sizes are mixed, and finally a product of a mixture of sodium iron vanadium phosphate materials with large, medium and small particle size distributions is obtained.

[0095] Comparative example 5 A sodium iron vanadium phosphate material, different from the preparation method of example 3, is sintered, and then the powder sodium iron vanadium phosphate material is crushed at a single classification wheel frequency to obtain a sodium iron vanadium phosphate material with a medium particle size.

[0096] The specific preparation method of the sodium iron vanadium phosphate material of the present comparative example 5 is as follows: Step one: 1.7 kg of sodium carbonate powder is weighed as a sodium source, 960 g of iron trioxide powder is weighed as an iron source, 218.4 g of vanadium pentoxide powder is weighed as a vanadium source, and 1.84 kg of monoammonium phosphate powder is weighed as a phosphorus source, and 28.5 g of sucrose powder is weighed as a carbon source, wherein the sodium carbonate, iron trioxide, vanadium pentoxide, monoammonium phosphate and sucrose are all analytically pure, at this time the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source and phosphorus provided by the phosphorus source is about 4:1.49:0.3:4.

[0097] Step two: using dry ball milling method, without using water or any other liquid medium, first put 960 g of iron trioxide powder and 4.8 kg of grinding balls weighed into the ball mill tank, put the ball mill tank into the ball mill, adjust the speed of the ball mill to 1800 rpm for ball milling; Then add 218.4 g of vanadium pentoxide powder and 1.1 kg of grinding balls weighed into the ball mill tank, continue to ball mill; Then add 1.7 kg of sodium carbonate powder, 1.84 kg of monoammonium phosphate powder and 28.5 g of sucrose powder weighed into the ball mill tank in turn, and add the corresponding weight of grinding balls according to the total ball-to-material ratio of 5:1 in turn, the ball milling time is 5 h, 7 h and 9 h respectively; After ball milling for a total of 38 h, the raw material dry powder with a particle size of 150 nm was obtained.

[0098] Step three: the raw material dry powder obtained after step two dry ball milling was placed in a sintering device, nitrogen was introduced into the sintering device, and after the air in the furnace was completely removed, gradient sintering was carried out starting from 25℃, and the sintering was carried out in the order of one-stage temperature rise (25℃ to 125℃, sintering time 30 min), two-stage temperature rise (125℃ to 350℃, sintering time 75 min), one-stage temperature holding (350℃, sintering time 120 min), three-stage temperature rise (350℃ to 650℃, sintering time 75 min), two-stage temperature holding (650℃, sintering time 160 min), four-stage temperature rise (650℃ to 875℃, sintering time 90 min) and three-stage temperature holding (875℃, sintering time 820 min); after the completion of gradient sintering, nitrogen was continuously introduced to cool to room temperature, and then the sintered product was taken out, which was the powder vanadium iron sodium phosphate material.

[0099] Step four: the sintered powder vanadium iron sodium phosphate material was subjected to airflow crushing, and the frequency of the classification wheel of the airflow mill was adjusted to 20 Hz to obtain a medium particle size vanadium iron sodium phosphate material.

[0100] The tap density of the vanadium iron sodium phosphate materials prepared in Examples 1-3 and Comparative Examples 1-5 was tested. Then the above eight vanadium iron sodium phosphate materials were used as electrode materials to make button cells, and their electrical properties were tested according to conventional methods in the art. The detection steps of each sample and the button cell preparation steps involved in the above tests were all carried out under the same process conditions.

[0101] The results are shown in Table 1 below, it can be seen that the electrical properties of the vanadium iron sodium phosphate materials prepared in Examples 1-3 are better, the 0.1 C discharge capacity reaches 118-119 mAh / g, close to the theoretical capacity of 120 mAh / g, and the prepared vanadium iron sodium phosphate product has high capacity and high voltage, thereby having high energy density, while the tap density and capacity of Comparative Examples 1-5 are lower than those of Examples 1-3, mainly because the present application adopts a classification grinding, gradient sintering mode and a special crushing method. Classification grinding makes the grinding more sufficient and the mixing more uniform; gradient sintering makes the reaction more sufficient, and the purity and crystallinity of the vanadium iron sodium phosphate product are higher; three-stage crushing forms a three-stage particle size distribution. In the three-stage particle size distribution of the vanadium iron sodium phosphate material prepared by the method of the present application, the medium particle size particles can fill the gaps between larger particles, and smaller particles can fill the gaps between medium particle size particles, thereby obtaining higher tap density. At the same time, the specific surface area of smaller particles is larger, which can provide more active sites for electrode reaction, helping to improve the charge and discharge efficiency of the battery and ensuring that the positive electrode material has good electrical properties.

[0102] Table 1. Performance test results of the sodium iron vanadate phosphate materials of various examples and comparative examples

[0103] Although the present application has been described in detail with reference to the preferred embodiments, the application is not limited to the preferred embodiments. Various equivalent modifications or replacements can be made to the embodiments of the present application by those skilled in the art without departing from the spirit and essence of the present application, and these modifications or replacements shall be within the scope of the present application. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or replacements, and these changes or replacements shall be within the protection scope of the present application.

Claims

1. A method for preparing sodium ferrovanadium phosphate material, characterized in that: The steps include: S1. Adding an iron source, a vanadium source, a phosphorus source, a sodium source, and a carbon source sequentially into a grinding device for dry grinding to obtain a dry powder raw material; S2. Under a protective atmosphere, the dry powder raw material is subjected to a gradient sintering process, first sintering at 350°C for 120 min, then sintering at 650°C for 120 min to 180 min, and finally sintering at a temperature T for 720 min to 840 min, where the temperature T is greater than or equal to 780°C and less than or equal to 950°C; S3. The sodium ferrous vanadium phosphate material obtained by gradient sintering is graded and crushed to obtain a sodium ferrous vanadium phosphate material having three particle size distributions of large, medium and small.

2. The method for preparing a sodium ferrovanadium phosphate material according to claim 1, wherein: The iron source used in S1 is selected from at least one of ferric oxide and ferrosoferric oxide; the vanadium source is selected from at least one of vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate; the phosphorus source is selected from at least one of monoammonium phosphate and diammonium phosphate; and the sodium source is selected from at least one of sodium carbonate and sodium bicarbonate.

3. The method for preparing a sodium ferrovanadium phosphate material according to claim 1 or 2, characterized in that: In S1, the molar ratio of sodium provided by the sodium source, iron provided by the iron source, vanadium provided by the vanadium source, and phosphorus provided by the phosphorus source is 4:1-1.5:0.1-0.3:3-4.

4. The method for preparing a sodium ferrovanadium phosphate material according to claim 1, wherein: The carbon source used in S1 is at least one selected from sucrose, glucose, and fructose.

5. The method for preparing a sodium ferrovanadium phosphate material according to claim 1 or 4, characterized in that: In S1, the molar ratio of carbon in the carbon source to iron in the iron source is 0.01-0.02:

1.

6. The method for preparing a sodium ferrovanadium phosphate material according to claim 1, wherein: S1 is specifically: (1) Add the iron source to the grinding equipment and dry grind until the particle size is 150 nm~300 nm; (2) adding the vanadium source to the grinding equipment of step (1) and dry grinding the vanadium source to a particle size of 150 nm to 400 nm; (3) Add the phosphorus source to the grinding equipment in step (2) and dry grind for 3 h to 5 h; (4) Add the sodium source to the grinding equipment in step (3) and dry grind for 6 h to 8 h; (5) Add the carbon source to the grinding equipment in step (4) and dry grind for 9 h to 11 h.

7. The method for preparing a sodium ferrovanadium phosphate material according to claim 6, wherein: After dry grinding in step (5), a dry powder raw material with a particle size range of 150 nm to 400 nm is obtained.

8. The method for preparing a sodium ferrovanadium phosphate material according to claim 1, 6 or 7, wherein: In S1, the total dry grinding time was controlled to be 24 h~48 h.

9. The method for preparing a sodium ferrovanadium phosphate material according to claim 1, wherein: In S3, the sodium ferrous vanadium phosphate is graded and crushed by using a jet mill, and the sodium ferrous vanadium phosphate material having three particle size distributions of large, medium and small is obtained by adjusting the frequency of the classifying wheel.

10. The method for preparing the sodium ferrovanadium phosphate material according to claim 9, wherein: First, adjust the frequency of the classifying wheel to 5 Hz ~ 10 Hz for crushing, then adjust the frequency of the classifying wheel to 10 Hz ~ 20 Hz for crushing, and finally adjust the frequency of the classifying wheel to 20 Hz ~ 50 Hz for crushing.

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