Preparation method of ferric sodium pyrophosphate material

Abstract

The invention relates to the technical field of sodium ion battery electrode materials, in particular to a preparation method of a ferric sodium pyrophosphate material, which comprises the following steps: S1, mixing a ferric sulfate solution with a phosphorus salt solution to obtain a precipitate; s2, collecting the precipitate, adding water to prepare slurry, adding the slurry into a reaction kettle, and adding phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source and a soluble vanadium source to react; s3, sintering the reaction product to obtain an iron pyrophosphate precursor; s4, crushing the ferric pyrophosphate precursor, the powder sodium source and the powder carbon source to obtain dry powder; and S5, sintering the dry powder to obtain the ferric sodium pyrophosphate material. According to the preparation method, the ferric phosphate pyrophosphate precursor is prepared firstly, then the ferric phosphate pyrophosphate precursor, the powder sodium source and the powder carbon source are crushed and sintered together, the ferric phosphate pyrophosphate material is obtained, the process is simple, and the prepared ferric phosphate pyrophosphate material is good in consistency and stability, high in compaction density and excellent in electrical property.

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 iron phosphate pyrophosphate 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. The positive electrode material of the sodium ion battery mainly includes three types: ternary sodium battery material, prussian material and polyanion material. The ternary sodium battery material 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 material is cyanide, which will produce toxic gas when the battery is in thermal runaway. The polyanion material does not have the above two defects, and has the advantages of safety, non-toxicity and low cost. Among the polyanion materials, the synthesized sodium iron phosphate material is often a mineral phase and does not have electrochemical activity. Therefore, the sodium iron phosphate pyrophosphate material has attracted great attention and has become a popular positive electrode material of the sodium ion battery.

[0003] CN 117923452 A discloses a method for large-scale preparation of a composite sodium iron phosphate pyrophosphate material, which comprises the following steps: S1, first preparing a doped H y Fe (3-X) M X (PO4)4 precursor by a multi-element co-precipitation method, wherein M is one or a combination of multiple of Cr, Mn, Mg, Cu, Ni, Zn, V and Ti, H is a hydrogen ion, X is in the range of 0-1.5, and y is in the range of 0-3; S2, then adding a sodium source and a carbon source into the doped H y Fe (3-X) M X (PO4)4 precursor, uniformly mixing and then performing sintering to synthesize the composite sodium iron phosphate pyrophosphate material. The technical scheme has the defects that the iron in the prepared sodium iron phosphate pyrophosphate is divalent, and in the industrial production, ferrous sulfate is easily oxidized to cause the prepared product to be impure. Therefore, hydrogen peroxide or ascorbic acid needs to be additionally used as an antioxidant in the preparation process. Meanwhile, the prepared sodium iron phosphate pyrophosphate has a low discharge capacity of about 110 mAh / g.

[0004] CN 117902559 A proposes a preparation method of a fast-charging type sodium iron phosphate pyrophosphate positive electrode material to avoid the presence of other iron-based material impurities during the preparation of the sodium iron phosphate pyrophosphate material, thereby affecting the electrochemical performance of the material, the specific steps being: mixing iron phosphate, sodium dihydrogen phosphate and sodium carbonate according to the molar ratio of Na:Fe:P=4.2:3:4, adding glucose, the mass of the glucose accounting for 10% of the total mass of the iron phosphate, sodium dihydrogen phosphate, sodium carbonate and glucose, adding 200 mL of water, stirring, transferring to a sand mill for sand milling, the sand milling speed being 2000 rpm, the sand milling time being 1 h, obtaining a mixed slurry (D50 being less than 300 nm), the concentration of sodium dihydrogen phosphate in the mixed slurry being 0.25 g / mL; the mixed slurry is subjected to spray drying, the outlet temperature being controlled at 100℃, the flow rate being 35 mL / min, the obtained spherical precursor is transferred to a box furnace for first sintering, the first sintering procedure being that the temperature is raised from room temperature to 300℃ at a rate of 5℃ / min and sintered for 6 h, then second sintering is performed, the second sintering procedure being that the temperature is raised from 300℃ to 500℃ at a rate of 3℃ / min and sintered for 12 h, the obtained material is subjected to airflow crushing to obtain a sodium phosphate pyrophosphate positive electrode material Na4Fe3(PO4)2P2O7@4wt% Na2FeP2O7 with D50 being less than 5 μm. The technical solution has the disadvantage that the discharge capacity of the finally prepared sodium phosphate pyrophosphate positive electrode material is low, the initial discharge capacity in the voltage range of 0.2 C, 1.5 V-4.0 V being only 108 mAh / g. SUMMARY

[0005] In view of the technical problem of low discharge capacity of the sodium iron phosphate pyrophosphate material prepared by the existing method, the present application provides a preparation method of a sodium iron phosphate pyrophosphate material, which first prepares a sodium iron phosphate pyrophosphate precursor, and then crushes and sintering the precursor together with a powder sodium source and a powder carbon source to obtain the sodium iron phosphate pyrophosphate material, the process being simple, the prepared sodium iron phosphate pyrophosphate material being consistent and stable, having high compaction density and excellent electrical performance.

[0006] The technical solution of the present application is as follows: A preparation method of a sodium iron phosphate pyrophosphate material, comprising the following steps: S1, mixing a ferric sulfate solution and a phosphorus salt solution to obtain a precipitate at room temperature; S2, collecting the precipitate, adding water to prepare a slurry, and then adding the slurry to a reaction kettle, adding phosphoric acid, sodium phosphate salt, a soluble magnesium source, a soluble titanium source and a soluble vanadium source, and reacting at 85℃-95℃, continuing to react for 4 h-10 h after the material turns white; S3, the reaction product is filtered, washed, flash evaporated, crushed, and dried, and then sintered at a temperature of 800 DEG C for 1-2 h to obtain a ferric pyrophosphate precursor; S4, the ferric pyrophosphate precursor is crushed, then a powder sodium source and a powder carbon source are added and crushed to obtain a dry powder with a particle size of 200-500 nm; S5, the crushed dry powder is sintered under nitrogen protection at a temperature of 850 DEG C for 12-18 h to obtain a ferric sodium pyrophosphate material.

[0007] It should be further explained that in step S1, the preparation method of the ferric sulfate solution is as follows: Iron trioxide (red iron oxide) is added to a sulfuric acid solution, and the solution is stirred to form a ferric sulfate solution.

[0008] It should be further explained that in step S1, the phosphorus salt solution is a solution containing at least one of monammonium phosphate (dihydrogen ammonium phosphate, NH4H2PO4), diammonium phosphate (dihydrogen ammonium phosphate, (NH4)2HPO4), and triammonium phosphate (ammonium phosphate, (NH4)3PO4).

[0009] It should be further explained that in step S1, the phosphorus salt solution is added to the ferric sulfate solution, and the mixing is carried out by stirring, the stirring speed is controlled to be 50-150 rpm, and the addition time of the phosphorus salt solution is 7-10 h.

[0010] It should be further explained that in step S2, the precipitate obtained in step S1 is first filtered and washed.

[0011] It should be further explained that in step S2, the sodium phosphate salt is selected from at least one of monosodium phosphate (sodium dihydrogen phosphate, NaH2PO4), disodium phosphate (disodium hydrogen phosphate, monohydrogen sodium phosphate, Na2HPO4), and trisodium phosphate (sodium phosphate, Na3PO4).

[0012] It should be further explained that in step S2, the soluble magnesium source is selected from at least one of magnesium sulfate (MgSO4), magnesium chloride (MgCl2), and magnesium nitrate (Mg(NO3)2); The soluble titanium source is selected from at least one of titanium oxysulfate (TiOSO4), titanium trichloride (TiCl3), titanium tetrachloride (TiCl4), and titanium tetraiodide (TiI4); The soluble vanadium source is selected from at least one of vanadyl sulfate (VOSO4), sodium metavanadate (NaVO3), and sodium orthovanadate (Na3VO4).

[0013] It needs to be further explained that in step S2, the molar ratio of iron, phosphorus, magnesium, titanium, vanadium in the reaction system formed by mixing iron sulfate, phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source and a soluble vanadium source is 1:1-1.5:0.01-0.1:0.01-0.1:0.01-0.1.

[0014] It needs to be further explained that in step S2, the molar ratio of phosphoric acid to sodium phosphate is 1:0.1-0.2.

[0015] It needs to be further explained that in step S2, the stirring speed of the reaction kettle is controlled to be 50 rpm-150 rpm during the reaction.

[0016] It needs to be further explained that in step S3, the washing target is that the conductivity of the washing water is less than 500 us / cm.

[0017] It needs to be further explained that in step S3, the flash evaporation, crushing and drying treatment is carried out by using a flash evaporation, crushing and drying integrated machine, the air inlet temperature of the flash evaporation, crushing and drying integrated machine is set to be 120℃-180℃, the crushing disc frequency is 20 Hz-50 Hz, the air outlet temperature is 80℃-105℃, the grading wheel frequency is 20 Hz-50 Hz, and the moisture content of the material after drying is 15%-19%.

[0018] It needs to be further explained that in step S4, the powder sodium source is selected from at least one of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), monosodium phosphate (also known as sodium dihydrogen phosphate, NaH2PO4), disodium phosphate (also known as disodium hydrogen phosphate, Na2HPO4), and trisodium phosphate (also known as sodium phosphate, Na3PO4). The powder carbon source is selected from at least one of fructose, sucrose and glucose.

[0019] It needs to be further explained that in step S4, the molar ratio of sodium in the powder sodium source to carbon in the powder carbon source and iron in the iron pyrophosphate phosphate precursor is 4:0.03-0.06:3.

[0020] It needs to be further explained that in step S4, the iron pyrophosphate phosphate precursor is crushed by using a stirring crusher, and the stirring speed of the stirring crusher is controlled to be 350 rpm-500 rpm, and the crushing disc rotating speed is 600 rpm-1000 rpm.

[0021] The beneficial effects of the present application are: The application provides a preparation method of a sodium iron pyrophosphate material, which comprises the following steps: first, generating a ferric phosphate precipitate; mixing the precipitate with a magnesium source, a titanium source and a vanadium source to perform a reaction and then sintering to obtain a sodium iron pyrophosphate precursor; and then crushing the sodium iron pyrophosphate precursor together with a sodium source and a carbon source, and sintering the crushed material at a high temperature to obtain the sodium iron pyrophosphate material. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0023] Figure 1 is an X-ray diffraction pattern of the sodium iron pyrophosphate material obtained in step seven in Example 5.

[0024] Figure 2 is an X-ray diffraction pattern of the sodium iron pyrophosphate material obtained in step seven in Example 5.

[0025] Figure 3 is a scanning electron microscope picture of the sodium iron pyrophosphate material obtained in step seven in Example 5. DETAILED DESCRIPTION

[0026] In order to make the technical personnel in the art better understand the technical solutions in the present application, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative effort should belong to the protection scope of the present application.

[0027] A sodium iron pyrophosphate material, chemical formula is Na4Fe m Mg x Ti y V z (PO4)2P2O7, wherein m+x+y+z=3, m=2.70~2.97, x=0.01~0.10, y=0.01~0.10, z=0.01~0.10. The preparation method of the sodium iron pyrophosphate material comprises the following steps: S1, mixing a ferric sulfate solution with a phosphorus salt solution to obtain a precipitate at room temperature; S2, the precipitate is collected, water is added to make a slurry, and then added to a reaction kettle, phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source and a soluble vanadium source are added, and reacted at 85-95 DEG C, after the material turns white, continue to react for 4-10 hours; S3, the reaction product is filtered, washed, flash evaporated, crushed, and dried, then sintered, first heated from room temperature to 800 DEG C, then sintered at 800 DEG C for 1-2 hours, finally cooled from 800 DEG C to 200 DEG C and discharged, to obtain a ferric phosphate pyrophosphate precursor; S4, the ferric phosphate pyrophosphate precursor is crushed, then a powder sodium source and a powder carbon source are added and crushed, to obtain a dry powder with a particle size of 200-500 nm; S5, the crushed dry powder is sintered, first heated from room temperature to 850 DEG C, then sintered at 850 DEG C for 12-18 hours, and finally cooled from 850 DEG C to room temperature and discharged, to obtain a ferric phosphate pyrophosphate sodium material.

[0028] As a preferred embodiment of the present application, in step S1, the preparation method of the ferric sulfate solution is as follows: Iron sesquioxide is added to a sulfuric acid solution, and the solution is stirred to form a ferric sulfate solution.

[0029] The ferric sulfate solution is prepared by reacting iron sesquioxide with a sulfuric acid solution, the raw materials are widely available and relatively low in cost, and provide a relatively pure and stable iron source for subsequent preparation of ferric phosphate precipitate, which is conducive to ensuring the stability of the entire preparation process and the consistency of the product.

[0030] As a preferred embodiment of the present application, in step S1, the phosphorus salt solution is a solution containing at least one of monoammonium phosphate, diammonium phosphate, and triammonium phosphate.

[0031] These phosphorus salts can stably provide phosphate ions in solution, and their chemical properties are relatively stable, and can generate ferric phosphate precipitate relatively fully when reacting with the ferric sulfate solution. Moreover, these phosphorus salts are common chemical raw materials, which are easily available on the market and relatively low in price, which is conducive to reducing the preparation cost.

[0032] As a preferred embodiment of the present application, in step S1, the phosphorus salt solution is added to the ferric sulfate solution, and mixed by stirring, the stirring speed is controlled to be 50-150 rpm, and the addition time of the phosphorus salt solution is 7-10 hours.

[0033] The phosphorus salt solution and the iron sulfate solution can be fully mixed at the stirring speed of 50 rpm to 150 rpm, so that the reaction can be uniformly carried out, and local overfast or overslow reaction can be avoided to cause uneven particle size of the precipitate. The long addition time of the phosphorus salt solution can make the reaction more sufficient, and is beneficial to generating a more pure and better crystallinity iron phosphate precipitate, thereby laying a foundation for preparing high-quality sodium iron phosphate pyrophosphate material.

[0034] As a preferred embodiment of the present application, in step S2, the precipitate obtained in step S1 is first filtered and washed.

[0035] The filtering and washing treatment is to remove unreacted impurities, other ions in the solution, and impurity ions attached to the surface of the precipitate, so that the precipitate is more pure. The pure precipitate can reduce the interference of impurities in the subsequent reaction, improve the purity of the product, and thus improve the performance of the sodium iron phosphate pyrophosphate material.

[0036] As a preferred embodiment of the present application, in step S2, the sodium phosphate salt is at least one of monosodium phosphate, disodium phosphate, and trisodium phosphate.

[0037] These sodium phosphate salts are common inorganic salts, and the production process is mature, the market supply is sufficient, and they are easy to purchase and have low cost, which is conducive to controlling the preparation cost.

[0038] As a preferred embodiment of the present application, in step S2, the soluble magnesium source is at least one of magnesium sulfate, magnesium chloride, and magnesium nitrate.

[0039] These magnesium salts are common in the chemical raw material market, widely sourced, easy to obtain, and relatively low in price, which can reduce the production cost while ensuring the product performance.

[0040] As a preferred embodiment of the present application, in step S2, the soluble titanium source is at least one of titanyl sulfate, titanium trichloride, titanium tetrachloride, and titanium tetraiodide.

[0041] These soluble titanium salts have a relatively mature production and supply system in the chemical industry, and can be obtained through a regular channel and meet the demand for titanium source in the preparation process within a reasonable cost range.

[0042] As a preferred embodiment of the present application, in step S2, the soluble vanadium source is at least one of vanadyl sulfate, sodium metavanadate, and sodium orthovanadate.

[0043] These vanadium compounds are common vanadium salts, which are stably supplied on the market, relatively easy to obtain, and within an acceptable cost range, which is helpful to realize the economy of the preparation process.

[0044] As a preferred specific embodiment of the present invention, in step S2, in the reaction system formed by mixing iron sulfate, phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source and a soluble vanadium source, the molar ratio of iron, phosphorus, magnesium, titanium and vanadium is 1:1~1.5:0.01~0.1:0.01~0.1:0.01~0.1.

[0045] Preparing the precursor according to the above ratio can make the components in the reaction system react fully, and the appropriate amount of magnesium, titanium and vanadium elements can play a role in doping modification, and ultimately obtain sodium iron pyrophosphate material with the target chemical composition and structure.

[0046] As a preferred embodiment of the present invention, in step S2, the molar ratio of phosphoric acid to sodium phosphate is 1:0.1-0.2.

[0047] As a preferred embodiment of the present invention, in step S2, during the reaction process, the stirring speed of the reactor is controlled to be 50 rpm to 150 rpm.

[0048] At a stirring speed of 50 rpm~150 rpm, the components in the reaction system can be fully mixed, which is conducive to sufficient contact and reaction between the reactants, and thus conducive to the generation of products with uniform structure and stable performance, avoiding inconsistent product performance due to local reaction differences, thereby improving the quality stability of sodium ferric pyrophosphate materials.

[0049] As a preferred embodiment of the present invention, in step S3, the washing target is that the conductivity of the washing water is less than 500 us / cm.

[0050] Controlling the conductivity of the wash water to less than 500 us / cm can ensure that the impurity ions on the surface of the reaction product are fully removed. The high-purity reaction product can better form an ideal crystal structure in subsequent sintering and other processes, which is beneficial to improving the electrochemical properties of the sodium iron pyrophosphate material.

[0051] As a preferred specific embodiment of the present invention, in step S3, the flash evaporation, crushing, and drying processes are performed using a flash evaporation, crushing, and drying integrated machine. The inlet air temperature of the flash evaporation, crushing, and drying integrated machine is set to 120°C to 180°C, the crushing disk frequency is 20 Hz to 50 Hz, the outlet air temperature is 80°C to 105°C, and the classifying wheel frequency is 20 Hz to 50 Hz. The moisture content of the material after drying is 15% to 19%.

[0052] The flash evaporation, crushing and drying are integrated by using the flash evaporation crushing drying all-in-one machine, so that the process flow is simplified and the production efficiency is improved. By reasonably setting the parameters such as the inlet air temperature, the crushing disc frequency, the outlet air temperature and the grading wheel frequency, the material is fully crushed and uniformly dried, the moisture content of the material after drying is controlled in a suitable range, which is beneficial to guarantee the physical properties and chemical properties of the material, and provides good raw material conditions for subsequent sintering.

[0053] As a preferred embodiment of the present application, in step S4, the powder sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, monosodium phosphate, disodium phosphate and trisodium phosphate. These sodium salts are common chemical products, with large production scale, easy to buy on the market, low price, and can provide low-cost sodium source for preparing the sodium iron phosphate material.

[0054] As a preferred embodiment of the present application, in step S4, the molar ratio of sodium in the powder sodium source, carbon in the powder carbon source and iron in the iron pyrophosphate precursor is 4:0.03-0.06:3.

[0055] As a preferred embodiment of the present application, in step S4, the powder carbon source is selected from at least one of fructose, sucrose and glucose. These sugars are common carbohydrates in daily life, with abundant sources, easy to obtain, and relatively low price, so it is convenient and economical to use them as carbon sources, which is beneficial to reduce the preparation cost. At the same time, the powder carbon source can form a carbon coating layer at high temperature, which can improve the electrical conductivity of the material, reduce the side reaction between the material and the electrolyte, and also enhance the structural stability of the material, which is beneficial to improve the electrochemical performance of the sodium iron phosphate material.

[0056] As a preferred embodiment of the present application, in step S4, the stirring crusher is used to crush the iron pyrophosphate precursor, and the stirring speed of the stirring crusher is controlled to be 350 rpm-500 rpm, and the rotating speed of the crushing disc is controlled to be 600 rpm-1000 rpm.

[0057] Controlling the stirring speed of the stirring crusher to be 350 rpm-500 rpm and the rotating speed of the crushing disc to be 600 rpm-1000 rpm can fully crush and uniformly mix the iron pyrophosphate precursor, the powder sodium source and the powder carbon source added later, guarantee the particle size of the material to be 200 nm-500 nm, and control the specific surface area of the material in a reasonable range, so as to be beneficial to improve the electrochemical activity of the sodium iron phosphate material obtained by sintering.

[0058] Example 1 A kind of sodium iron phosphate material is prepared according to the following preparation method: Step one: 500 mL of 50% mass concentration sulfuric acid solution was added to a reaction kettle, while stirring, 180 g of 98% purity iron oxide red was added to the reaction kettle, the stirring speed of the reaction kettle was set to 50 rpm, and after the iron oxide red was completely dissolved, a ferric sulfate solution was obtained.

[0059] Step two: Then 150 g of 98% purity powdered diammonium hydrogen phosphate was added to the reaction kettle of step one, the reaction kettle was maintained at a stirring speed of 50 rpm during this period, and the addition speed of the powdered diammonium hydrogen phosphate was controlled so that the powdered diammonium hydrogen phosphate was added completely in 10 h, the powdered diammonium hydrogen phosphate reacted with the ferric sulfate to form yellow ferric phosphate precipitate.

[0060] Step three: After the reaction liquid was washed by pressure filtration, the yellow ferric phosphate precipitate was collected, the yellow ferric phosphate precipitate was made into a slurry with water, the slurry was added to the reaction kettle, the stirring device of the reaction kettle was opened, the stirring speed was set to 50 rpm, while stirring, phosphoric acid, powdered trisodium phosphate, powdered magnesium chloride, titanium tetrachloride, and powdered vanadyl sulfate were added to the reaction kettle, after the addition of the trisodium phosphate, magnesium chloride, titanium tetrachloride, and vanadyl sulfate was completely dissolved, a reaction system with a molar ratio of iron, phosphorus, magnesium, titanium, and vanadium of 1:1:0.01:0.01:0.01 was formed, the reaction system was heated to 85°C, and after the reaction system turned white was observed, the system was kept at temperature for 10 h.

[0061] Step four: After the temperature holding was completed, the reaction liquid was pressure filtered, and the separated white material was washed until the wash water conductivity was 400 us / cm, then the washed white material was sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine was set to 180°C, the crushing disc frequency was 20 Hz, the outlet air temperature was 100°C, and the grading wheel frequency was 20 Hz, finally a material with a moisture content of 15% was obtained.

[0062] Step five: The material obtained in step four was sent to a sintering furnace for sintering, first the temperature was raised from room temperature (25°C) to 800°C, the temperature raising time was 2 h, then the temperature was kept constant at 800°C for 1 h, finally the temperature was lowered from 800°C to 200°C and the furnace was discharged, the temperature lowering time was 2 h, and the ferric phosphate pyrophosphate precursor was obtained.

[0063] Step six: The sintered ferric phosphate pyrophosphate precursor was added to a stirring crusher, then 125 g of powdered sodium bicarbonate and 3.8 g of powdered sucrose were added to the stirring crusher, the stirring speed of the stirring crusher was set to 350 rpm, and the crushing disc speed was 600 rpm, until the particle size was 500 nm, and no water or other solvents were added during the process.

[0064] Step seven: the crushed material is placed in a sintering furnace and sintered under the protection of nitrogen, first heated from room temperature (25℃) to 850℃, the heating time is 2 h, then sintered at 850℃ for 12 h, finally cooled from 850℃ to room temperature (25℃) and discharged, the cooling time is 2 h, and the phosphoferric sodium material is obtained.

[0065] Example 2 A phosphoferric sodium material is prepared according to the following preparation method: Step one: 500 mL of 50% mass concentration sulfuric acid solution is added to the reaction kettle, while stirring, 180 g of 98% pure red iron oxide is added to the reaction kettle to dissolve, the stirring speed of the reaction kettle is set to 150 rpm, and after the red iron oxide is completely dissolved, a ferric sulfate solution is obtained.

[0066] Step two: then 168 g of 98% pure powder ammonium phosphate is added to the reaction kettle of step one, the reaction kettle is maintained at 150 rpm during the addition of the powder ammonium phosphate, and the addition speed of the powder ammonium phosphate is controlled so that the powder ammonium phosphate is added completely in 7 h, the powder ammonium phosphate reacts with the ferric sulfate to form a yellow ferric phosphate precipitate.

[0067] Step three: after the reaction solution is filtered and washed, the yellow ferric phosphate precipitate is collected, the yellow ferric phosphate precipitate is made into a slurry with water, the slurry is added to the reaction kettle, the stirring device of the reaction kettle is opened, the stirring speed is set to 150 rpm, and while stirring, phosphoric acid, powder disodium phosphate, powder magnesium nitrate, titanium trichloride, and powder sodium orthovanadate are added to the reaction kettle, after the addition of disodium phosphate, magnesium nitrate, titanium trichloride, and sodium orthovanadate is completely dissolved, a reaction system with a molar ratio of iron, phosphorus, magnesium, titanium, and vanadium of 1:1.5:0.1:0.1:0.1 is formed, the reaction system is heated to 95℃, and after the reaction system is observed to turn white, it is continuously incubated for 10 h.

[0068] Step four: after the incubation is completed, the reaction solution is filtered, and the separated white material is washed until the wash water conductivity is 300 us / cm, then the washed white material is sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine is set to 150℃, the frequency of the crushing disc is 50 Hz, the outlet air temperature is 90℃, and the frequency of the grading wheel is 50 Hz, finally a material with a moisture content of 19% is obtained.

[0069] Step five: the material obtained in step four is sent to a sintering furnace for sintering, first heated from room temperature (25℃) to 800℃, the heating time is 2 h, then sintered at 800℃ for 2 h, finally cooled from 800℃ to 200℃ and discharged, the cooling time is 2 h, and the phosphoferric sodium precursor is obtained.

[0070] Step six: the sintered iron phosphate pyrophosphate precursor was added to the stirring crusher, then 125 g of powdered sodium bicarbonate and 3.8 g of powdered sucrose were added to the stirring crusher, the stirring speed of the stirring crusher was set to 500 rpm, and the crushing disc rotation speed was set to 1000 rpm, until the particle size was 200 nm, and no water or other solvents were added during the process.

[0071] Step seven: the crushed material was placed in a sintering furnace and sintered under the protection of nitrogen, first heated from room temperature (25°C) to 850°C at a heating rate of 2 h, then sintered at 850°C for 18 h, and finally cooled from 850°C to room temperature (25°C) at a cooling rate of 2 h, to obtain the sodium iron phosphate pyrophosphate material.

[0072] Example 3 A sodium iron phosphate pyrophosphate material was prepared according to the following preparation method: Step one: 500 L of a 50% mass concentration sulfuric acid solution was added to a reaction kettle, and 249 kg of 98% pure red iron oxide was dissolved in the reaction kettle while stirring, the stirring speed of the reaction kettle was set to 100 rpm, and after the red iron oxide was completely dissolved, a ferric sulfate solution was obtained.

[0073] Step two: then 220 kg of 98% pure powdered ammonium dihydrogen phosphate was added to the reaction kettle of step one, the reaction kettle was maintained at a stirring speed of 100 rpm during the addition of the powdered ammonium dihydrogen phosphate, and the addition speed of the powdered ammonium dihydrogen phosphate was controlled so that the powdered ammonium dihydrogen phosphate was completely added in 8 h, the powdered ammonium dihydrogen phosphate reacted with the ferric sulfate to form a yellow iron phosphate precipitate.

[0074] Step three: after the reaction solution was filtered and washed, the yellow iron phosphate precipitate was collected, the yellow iron phosphate precipitate was added to water to form a slurry, the slurry was added to the reaction kettle, the stirring device of the reaction kettle was turned on, and the stirring speed was set to 100 rpm, then 18 kg of 85% mass concentration phosphoric acid, 2.3 kg of 98% pure powdered disodium phosphate, 9 kg of 99% pure powdered magnesium sulfate, 14.5 kg of 99% pure powdered titanyl sulfate, and 7.5 kg of 99% pure sodium metavanadate were added to the reaction kettle while stirring, after the disodium phosphate, magnesium sulfate, titanyl sulfate, and sodium metavanadate were completely dissolved, the reaction system was heated to 90°C, and after the reaction system turned white, the system was maintained at 90°C for 5 h.

[0075] Step four: after the end of the holding, the reaction liquid was pressure filtered, and the separated whitening material was washed to a washing water conductivity of 200 us / cm, then the washed whitening material was sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine was set to 130°C, the crushing disc frequency was 30 Hz, the outlet air temperature was 90°C, and the grading wheel frequency was 30 Hz, finally a material with a moisture content of 18% was obtained.

[0076] Step five: the material obtained in step four was sent to a rotary kiln for sintering, first heated from room temperature (25°C) to 800°C, the heating time was 2 h, then sintered at 800°C for 2 h, finally cooled from 800°C to 200°C and discharged, the cooling time was 2 h, to obtain a phosphoric acid pyrophosphate iron precursor.

[0077] Step six: the sintered phosphoric acid pyrophosphate iron precursor was added to a stirring crusher, then 219 kg of powdered sodium carbonate and 2.8 kg of powdered fructose were added to the stirring crusher, the stirring speed of the stirring crusher was set to 400 rpm, and the crushing disc speed was 700 rpm, until the particle size was 240 nm, without adding water or any other solvent during the process.

[0078] Step seven: the crushed material was placed in a roller kiln and sintered under the protection of nitrogen, first heated from room temperature (25°C) to 850°C, the heating time was 2 h, then sintered at 850°C for 15 h, finally cooled from 850°C to room temperature (25°C) and discharged, the cooling time was 2 h, to obtain a sodium phosphoric acid pyrophosphate iron material.

[0079] Example 4 A sodium phosphoric acid pyrophosphate iron material was prepared according to the following preparation method: Step one: a 2000 L sulfuric acid solution with a mass concentration of 50% was added to a reaction kettle, while stirring, 996 kg of red iron oxide with a purity of 98% was added to the reaction kettle to dissolve, the stirring speed of the reaction kettle was set to 100 rpm, and after the red iron oxide was completely dissolved, a ferric sulfate solution was obtained.

[0080] Step two: then 885 kg of powdered ammonium dihydrogen phosphate with a purity of 98% was added to the reaction kettle of step one, the reaction kettle was maintained at a stirring speed of 100 rpm during the addition, and the addition speed of the powdered ammonium dihydrogen phosphate was controlled so that the powdered ammonium dihydrogen phosphate was added completely in 9 h, the powdered ammonium dihydrogen phosphate reacted with the ferric sulfate to form a yellow ferric phosphate precipitate.

[0081] Step three: after the reaction solution is washed by pressure filtration, the yellow iron phosphate precipitate is collected, the yellow iron phosphate precipitate is added with water to form a slurry, the slurry is added into a reaction kettle, a stirring device of the reaction kettle is opened, a stirring speed is set to 100 rpm, 143 kg of phosphoric acid with a mass concentration of 85% is added into the reaction kettle while stirring, 18 kg of powder disodium phosphate with a purity of 98% is added into the reaction kettle while stirring, 36 kg of powder magnesium sulfate with a purity of 99% is added into the reaction kettle while stirring, 58 kg of powder titanyl sulfate with a purity of 99% is added into the reaction kettle while stirring, and 30 kg of sodium metavanadate with a purity of 99% is added into the reaction kettle while stirring, after the disodium phosphate, magnesium sulfate, titanyl sulfate and sodium metavanadate are completely dissolved, the reaction system is heated to 90 ℃, and after the reaction system is observed to be white, the reaction system is continuously heated for 5 h.

[0082] Step four: after the heating is completed, the reaction solution is subjected to pressure filtration, and the separated white material is washed until the washing water conductivity is 200 us / cm, and then the washed white material is sent to a flash crushing and drying all-in-one machine, an air inlet temperature of the flash crushing and drying all-in-one machine is set to 140 ℃, a crushing disc frequency is set to 30 Hz, an air outlet temperature is set to 90 ℃, and a grading wheel frequency is set to 30 Hz, and finally a material with a water content of 19% is obtained.

[0083] Step five: the material obtained in step four is sent to a rotary kiln for sintering, first, the rotary kiln is heated from room temperature (25 ℃) to 800 ℃, the heating time is 2 h, then the rotary kiln is sintered at 800 ℃ for 2 h, finally, the rotary kiln is cooled from 800 ℃ to 200 ℃, and the cooling time is 2 h, and finally, the iron pyrophosphate phosphate precursor is obtained.

[0084] Step six: the sintered iron pyrophosphate phosphate precursor is added into a stirring crusher, then 876 kg of powder sodium carbonate and 11.2 kg of powder fructose are added into the stirring crusher, a stirring speed of the stirring crusher is set to 400 rpm, and a crushing disc rotating speed is set to 700 rpm, until the particle size is 230 nm, and no water or other solvents are added in the process.

[0085] Step seven: the crushed material is placed in a roller kiln, and sintering is performed under the protection of nitrogen, first, the roller kiln is heated from room temperature (25 ℃) to 850 ℃, the heating time is 2 h, then the roller kiln is sintered at 850 ℃ for 12 h, finally, the roller kiln is cooled from 850 ℃ to room temperature (25 ℃), and the cooling time is 2 h, and finally, the sodium iron pyrophosphate phosphate material is obtained.

[0086] Example 5 A sodium iron pyrophosphate phosphate material is prepared according to the following preparation method: Step one: add 6000 L of 50% mass concentration sulfuric acid solution into the reaction kettle, and add 2988 kg of 98% purity iron oxide red into the reaction kettle while stirring, set the stirring speed of the reaction kettle to 100 rpm, and after the iron oxide red is completely dissolved, obtain the iron sulfate solution.

[0087] Step two: then add 2192 kg of 98% purity ammonium dihydrogen phosphate powder into the reaction kettle of step one, maintain the stirring state of the reaction kettle at 100 rpm during the process, and control the addition speed of the ammonium dihydrogen phosphate powder, so that the addition of the ammonium dihydrogen phosphate powder is completed in 9 h, and the yellow iron phosphate precipitate is generated by the reaction of the ammonium dihydrogen phosphate powder and the iron sulfate.

[0088] Step three: after the reaction liquid is washed by pressure filtration, the yellow iron phosphate precipitate is collected, the yellow iron phosphate precipitate is added with water to form a slurry, the slurry is added into the reaction kettle, the stirring device of the reaction kettle is opened, the stirring speed is set to 100 rpm, and 430 kg of 85% mass concentration phosphoric acid, 28 kg of 98% purity disodium phosphate powder, 108 kg of 99% purity magnesium sulfate powder, 174 kg of 99% purity titanyl sulfate powder, and 120 kg of 99% purity sodium metavanadate are added into the reaction kettle while stirring, after the disodium phosphate, magnesium sulfate, titanyl sulfate, and sodium metavanadate are completely dissolved, the reaction system is heated to 90℃, and after the reaction system is observed to turn white, the system is continuously kept at 90℃ for 5 h.

[0089] Step four: after the keeping at temperature is completed, the reaction liquid is subjected to pressure filtration, and the separated white material is washed until the washing water conductivity is 200 us / cm, then the washed white material is sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine is set to 145℃, the crushing disc frequency is 35 Hz, the outlet air temperature is 95℃, and the grading wheel frequency is 35 Hz, and finally a material with a moisture content of 17% is obtained.

[0090] Step five: the material obtained in step four is sent to a rotary kiln for sintering, first heated from room temperature (25℃) to 800℃, the heating time is 2 h, then sintered at 800℃ for 2 h, and finally cooled from 800℃ to 200℃ before discharging, the cooling time is 2 h, and the iron pyrophosphate phosphate precursor is obtained.

[0091] Step six: add the sintered iron pyrophosphate phosphate precursor into a stirring crusher, then add 2628 kg of sodium carbonate powder and 33.6 kg of fructose powder into the stirring crusher, set the stirring speed of the stirring crusher to 400 rpm, and the crushing disc speed to 700 rpm, until the particle size is 230 nm, and no water or other solvents are added during the process.

[0092] Step 7: Place the crushed material in a roller kiln and sinter it under the protection of nitrogen. First, heat it from room temperature (25°C) to 850°C for 2 hours, then sinter it at a constant temperature of 850°C for 15 hours, and finally cool it from 850°C to room temperature (25°C) and take it out of the furnace for 2 hours to obtain sodium iron pyrophosphate material.

[0093] The ferric phosphate pyrophosphate precursor obtained in step 5 of this Example 5 and the sodium ferric phosphate pyrophosphate material obtained in step 7 were sampled and subjected to X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) analysis.

[0094] Figure 1 In the figure, the red line is the standard XRD spectrum of ferric pyrophosphate, and the pink line is the standard XRD spectrum of iron phosphate. It can be calculated that the content of iron pyrophosphate in the ferric phosphate pyrophosphate precursor obtained in step 5 of this embodiment is 53.7%, and the content of iron phosphate is 46.3%.

[0095] Depend on Figure 2 It can be seen that the final sodium iron phosphate pyrophosphate material is Na4Fe 2.8 Mg 0.05 Ti 0.1 V 0.05 (PO4)2P2O7.

[0096] Depend on Figure 3 It can be seen that the final sodium iron pyrophosphate material is in the shape of irregular flakes.

[0097] Comparative Example 1 A sodium iron phosphate pyrophosphate material is prepared in a similar manner to Example 5, except that no soluble vanadium source, soluble magnesium source, or soluble titanium source is added in step 3. The specific preparation method is as follows: Step 1: Add 6000 L of 50% sulfuric acid solution to the reactor. While stirring, add 2988 kg of 98% pure red iron oxide to the reactor to dissolve. Set the stirring speed of the reactor to 100 rpm. After the red iron oxide is completely dissolved, a ferric sulfate solution is obtained.

[0098] Step 2: Then, 2192 kg of 98% pure powdered ammonium dihydrogen phosphate was added to the reactor in step 1. During this period, the reactor was stirred at 100 rpm, and the addition rate of the powdered ammonium dihydrogen phosphate was controlled so that the addition of the powdered ammonium dihydrogen phosphate was completed in 9 hours. The powdered ammonium dihydrogen phosphate reacted with ferric sulfate to form a yellow ferric phosphate precipitate.

[0099] Step three: after the reaction solution was washed by pressure filtration, the yellow iron phosphate precipitate was collected, and the yellow iron phosphate precipitate was made into a slurry with water, then the slurry was added into the reaction kettle, the stirring device of the reaction kettle was opened, the stirring speed was set to 100 rpm, while stirring, 430 kg of 85% mass concentration phosphoric acid and 28 kg of 98% purity disodium phosphate powder were added into the reaction kettle, after the added disodium phosphate was completely dissolved, the reaction system was heated to 90℃, after the reaction system turned white was observed, the system was continuously kept for 5 h.

[0100] Step four: after the heat preservation was completed, the reaction solution was pressure filtered, and the separated white material was washed until the washing water conductivity was 200 us / cm, then the washed white material was sent to a flash crushing and drying integrated machine, the inlet air temperature of the flash crushing and drying integrated machine was set to 145℃, the crushing disc frequency was 35 Hz, the outlet air temperature was 95℃, and the grading wheel frequency was 35 Hz, finally a material with a moisture content of 17% was obtained.

[0101] Step five: the material obtained in step four was sent to a rotary kiln for sintering, first heated from room temperature (25℃) to 800℃ for 2 h, then sintered at 800℃ for 2 h, finally cooled from 800℃ to 200℃ for 2 h before discharging, and a iron pyrophosphate phosphate precursor was obtained.

[0102] Step six: the sintered iron pyrophosphate phosphate precursor was added into a stirring crusher, then 2628 kg of sodium carbonate powder and 33.6 kg of fructose powder were added into the stirring crusher, the stirring speed of the stirring crusher was set to 400 rpm, and the crushing disc speed was set to 700 rpm, until the particle size was 230 nm, and no water or other solvents were added during the process.

[0103] Step seven: the crushed material was placed in a roller kiln and sintered under the protection of nitrogen, first heated from room temperature (25℃) to 850℃ for 2 h, then sintered at 850℃ for 15 h, finally cooled from 850℃ to room temperature (25℃) for 2 h before discharging, and a sodium iron pyrophosphate phosphate material was obtained.

[0104] The sodium iron pyrophosphate phosphate material obtained in step seven of the comparative example 1 was sampled and analyzed by scanning electron microscopy (SEM), and it was found that the prepared sodium iron pyrophosphate phosphate material was irregular flaky.

[0105] Comparative example 2 A sodium iron pyrophosphate phosphate material was prepared by a method similar to that of example 5, the main difference being that no soluble vanadium source, soluble magnesium source and soluble titanium source were added in step three, the sintering temperatures of steps five and seven were different, and step six used a wet grinding and spray drying process. The specific preparation method is as follows: Step one: 6000 L of 50% mass concentration sulfuric acid solution was added to a reaction kettle, while stirring, 2988 kg of 98% purity iron oxide red was added to the reaction kettle, the stirring speed of the reaction kettle was set to 100 rpm, after the iron oxide red was completely dissolved, a ferric sulfate solution was obtained.

[0106] Step two: then 2192 kg of 98% purity ammonium dihydrogen phosphate powder was added to the reaction kettle of step one, the reaction kettle was maintained at 100 rpm stirring state during the addition of the ammonium dihydrogen phosphate powder, and the addition speed of the ammonium dihydrogen phosphate powder was controlled, so that the ammonium dihydrogen phosphate powder was added completely in 9 h, the ammonium dihydrogen phosphate powder reacted with the ferric sulfate to generate yellow ferric phosphate precipitate.

[0107] Step three: after the reaction liquid was washed by pressure filtration, the yellow ferric phosphate precipitate was collected, the yellow ferric phosphate precipitate was added to water to form a slurry, the slurry was added to the reaction kettle, the stirring device of the reaction kettle was opened, the stirring speed was set to 100 rpm, while stirring, 430 kg of 85% mass concentration phosphoric acid and 28 kg of 98% purity disodium phosphate powder were added to the reaction kettle, after the disodium phosphate was completely dissolved, the reaction system was heated to 90℃, after the reaction system was observed to be white, the reaction system was continuously heated for 5 h.

[0108] Step four: after the heating was completed, the reaction liquid was pressure filtered, and the separated white material was washed to a washing water conductivity of 200 us / cm, then the washed white material was sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine was set to 145℃, the crushing disc frequency was 35 Hz, the outlet air temperature was 95℃, and the grading wheel frequency was 35 Hz, finally a material with a moisture content of 17% was obtained.

[0109] Step five: the material obtained in step four was sent to a sintering furnace, sintered at 600℃ for 2 h, and a ferric pyrophosphate phosphate precursor was obtained.

[0110] Step six: the sintered ferric pyrophosphate phosphate precursor was added to water together with 2628 kg of sodium carbonate powder and 33.6 kg of fructose powder, after stirring and beating, sand milling was performed until the particle size was 230 nm, the sand-milled slurry was spray dried, the spray temperature was controlled at 200℃, and the flow rate was 200 mL / min, and a mixed powder was obtained.

[0111] Step seven: the mixed powder was placed in a sintering furnace, sintered at 600℃ for 2 h under the protection of nitrogen, and a sodium ferric pyrophosphate phosphate material was obtained.

[0112] The sodium ferric pyrophosphate phosphate material obtained in step seven of the comparative example 2 was sampled and analyzed by scanning electron microscope (SEM), and it was found that the prepared sodium ferric pyrophosphate phosphate material was spherical.

[0113] Comparative Example 3 A sodium iron pyrophosphate material was prepared in a similar manner to Example 5, with the main difference being that a soluble vanadium source, a soluble magnesium source, and a soluble titanium source were added in step six, the sintering temperature of step five and step seven was different, and a wet grinding and spray drying process was used in step six. The specific preparation method is as follows: Step one: 6000 L of a 50% mass concentration sulfuric acid solution was added to a reaction kettle, while stirring, 2988 kg of 98% pure red iron oxide was added to the reaction kettle, the stirring speed of the reaction kettle was set to 100 rpm, and after the red iron oxide was completely dissolved, an iron sulfate solution was obtained.

[0114] Step two: Then 2192 kg of 98% pure powder ammonium dihydrogen phosphate was added to the reaction kettle of step one, the reaction kettle was maintained at a stirring speed of 100 rpm during the addition of the powder ammonium dihydrogen phosphate, and the addition speed of the powder ammonium dihydrogen phosphate was controlled so that the powder ammonium dihydrogen phosphate was added completely in 9 h, and the powder ammonium dihydrogen phosphate reacted with the iron sulfate to form a yellow iron phosphate precipitate.

[0115] Step three: After the reaction solution was filtered and washed, the yellow iron phosphate precipitate was collected, the yellow iron phosphate precipitate was added to water to form a slurry, the slurry was added to the reaction kettle, the stirring device of the reaction kettle was turned on, and the stirring speed was set to 100 rpm, while stirring, 430 kg of 85% mass concentration phosphoric acid and 28 kg of 98% pure powder disodium phosphate were added to the reaction kettle, after the added disodium phosphate was completely dissolved, the reaction system was heated to 90°C, after the reaction system turned white was observed, the system was continuously heated for 5 h.

[0116] Step four: After the heating was completed, the reaction solution was filtered, and the separated white material was washed until the wash water conductivity was 200 us / cm, then the washed white material was sent to a flash crushing and drying all-in-one machine, the inlet air temperature of the flash crushing and drying all-in-one machine was set to 145°C, the crushing disc frequency was 35 Hz, the outlet air temperature was 95°C, and the grading wheel frequency was 35 Hz, finally a material with a moisture content of 17% was obtained.

[0117] Step five: The material obtained in step four was sent to a sintering furnace, sintered at 600°C for 2 h, and a sodium iron pyrophosphate precursor was obtained.

[0118] Step six: the sintered iron pyrophosphate precursor was added into water together with 108 kg of 99% purity powder magnesium sulfate, 174 kg of 99% purity powder titanyl sulfate, 120 kg of 99% purity sodium vanadate, 2628 kg of powder sodium carbonate and 33.6 kg of powder fructose, and then the mixture was stirred and grinded until the particle size was 230 nm. The grinded slurry was spray dried at a temperature of 200°C and a flow rate of 200 mL / min to obtain a mixed powder.

[0119] Step seven: the mixed powder was sintered in a box furnace under the protection of nitrogen at 600°C for 2 h to obtain a sodium iron pyrophosphate material.

[0120] The sodium iron pyrophosphate material obtained in step seven of the comparative example 3 was sampled and analyzed by scanning electron microscopy (SEM), and it was found that the obtained sodium iron pyrophosphate material was spherical.

[0121] The sodium iron pyrophosphate materials prepared in examples 3-5 and comparative examples 1-3 were tested for tap density. Then, the above-mentioned five kinds of sodium iron pyrophosphate 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-mentioned tests were all carried out under the same process conditions.

[0122] The results are shown in Table 1 below, and it can be seen that the sodium iron pyrophosphate material prepared according to the method of the present application has high tap density and high capacity, with a 0.1 C discharge capacity of 130 mAh / g-133 mAh / g, thereby having high energy density and good electrical properties, and the process is simple to operate and has the ability to be industrialized.

[0123] Table 1: Performance test results of sodium iron pyrophosphate materials of examples and comparative examples

[0124] Although the present application has been described in detail with reference to the preferred embodiments, the present 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 should 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 should be within the protection scope of the present application.

Claims

1. A method for preparing sodium iron pyrophosphate material, characterized in that: The steps include: S1, mixing the ferric sulfate solution and the phosphate solution, reacting at room temperature to obtain a precipitate; S2. Collect the precipitate, add water to make a slurry, and then add it to the reactor. Add phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source, and a soluble vanadium source. React at 85°C to 95°C. Continue to react for 4 hours to 10 hours after the material turns white. S3, the reaction product is filtered, washed, flash evaporated, crushed, dried, and then sintered at a temperature of 800°C for 1 h to 2 h to obtain a ferric phosphate pyrophosphate precursor; S4, crushing the ferric phosphate pyrophosphate precursor, and then adding a powdered sodium source and a powdered carbon source to continue crushing to obtain a dry powder with a particle size of 200 nm to 500 nm; S5. Under nitrogen protection, the crushed dry powder is sintered at a temperature of 850°C for a time of 12 h to 18 h to obtain sodium iron pyrophosphate material.

2. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S1, the phosphate salt solution is a solution containing at least one phosphate salt selected from monoammonium phosphate, diammonium phosphate, and triammonium phosphate.

3. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S2, the sodium phosphate salt is selected from at least one of monosodium phosphate, disodium phosphate, and trisodium phosphate.

4. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S2, the soluble magnesium source is selected from at least one of magnesium sulfate, magnesium chloride, and magnesium nitrate; The soluble titanium source is selected from at least one of titanyl sulfate, titanium trichloride, titanium tetrachloride, and titanium tetraiodide; The soluble vanadium source is selected from at least one of vanadyl sulfate, sodium metavanadate and sodium orthovanadate.

5. The method for preparing a sodium iron pyrophosphate material according to claim 1 or 4, wherein: In step S2, in the reaction system formed by mixing ferric sulfate, phosphoric acid, sodium phosphate, a soluble magnesium source, a soluble titanium source and a soluble vanadium source, the molar ratio of iron, phosphorus, magnesium, titanium and vanadium is 1:1~1.5:0.01~0.1:0.01~0.1:0.01~0.

1.

6. The method for preparing the sodium iron pyrophosphate material according to claim 1, wherein: In step S2, the molar ratio of phosphoric acid to sodium phosphate is 1:0.1-0.

2.

7. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S3, flash evaporation, crushing, and drying are performed using a flash evaporation, crushing, and drying integrated machine. The inlet air temperature of the flash evaporation, crushing, and drying integrated machine is set to 120°C to 180°C, the crushing disk frequency is 20 Hz to 50 Hz, the outlet air temperature is 80°C to 105°C, and the classifying wheel frequency is 20 Hz to 50 Hz. The moisture content of the material after drying is 15% to 19%.

8. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S4, the powdered sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, monosodium phosphate, disodium phosphate, and trisodium phosphate; The powdered carbon source is selected from at least one of fructose, sucrose and glucose.

9. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S4 , the molar ratio of sodium in the powdered sodium source to carbon in the powdered carbon source and iron in the ferric phosphate pyrophosphate precursor is 4:0.03-0.06:

3.

10. The method for preparing a sodium iron pyrophosphate material according to claim 1, wherein: In step S4, the ferric pyrophosphate precursor is crushed by a stirring crusher, and the stirring speed of the stirring crusher is controlled to be 350 rpm~500 rpm, and the crushing disk speed is controlled to be 600 rpm~1000 rpm.

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