Production process for jointly preparing lithium iron phosphate

Abstract

The invention provides a production process for joint preparation of lithium iron phosphate, relates to the technical field of lithium battery positive electrode materials, and solves the technical problems of limited utilization efficiency of lithium ions and iron phosphate ions and limited doping effect of the existing lithium iron phosphate preparation process. The method comprises the following steps: preparing lithium slurry; preparing iron phosphate slurry; lithium iron phosphate preparation: preparation of a first precursor: preparation of a second precursor: mixing the remaining lithium slurry and iron phosphate slurry, and adding the first precursor and the second precursor at the same time to obtain mixed slurry; adding a carbon source into the mixed slurry, carrying out wet ball milling, and then drying to obtain a mixture; and sintering the mixture in an inert atmosphere in two stages to obtain the lithium iron phosphate. The lithium and iron phosphate slurry production process is adopted, the liquid-solid phase combined production method is adopted, the product quality and performance can be controlled from the source, the product stability is good, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, and in particular to a production process for jointly preparing lithium iron phosphate. Background Art

[0002] Lithium-ion batteries have an irreplaceable function in energy regulation and have been widely used due to their high specific energy, long cycle life, no memory effect, and no environmental pollution.

[0003] At present, the manufacturing process of lithium-ion batteries is not perfect and the cost is high. The positive electrode material is mostly lithium iron phosphate, and the production of lithium iron phosphate requires materials such as iron phosphate source and lithium source to synthesize. The iron phosphate source usually uses ferrous phosphate or iron-containing phosphate ore as raw materials, such as ammonium ferrous phosphate (NH4FePO4·H2O) or phosphate iron ore; the lithium source generally uses lithium carbonate or lithium hydroxide. Most companies do not have the ability to produce the above raw materials at the same time, and most of them are purchased from outside. In addition, because lithium carbonate, lithium hydroxide, and iron phosphate raw materials are produced by different companies with different processes, their prices, quality, performance, etc. are uneven, resulting in poor stability of lithium iron phosphate products, low electrical performance indicators, and easy to be eliminated by the market. In addition, the electronic conductivity and Li+ diffusion coefficient of pure lithium iron phosphate materials are poor, which seriously affects its electrochemical performance and limits its further application. At present, ion doping, coating and other technologies are usually used to improve the electrochemical performance of lithium iron phosphate materials.

[0004] For example, the patent with publication number CN115133010A proposes a nitrogen-doped carbon-modified lithium iron phosphate positive electrode material, which is coated with a functionally modified carbon nanotube LiFePO4 material, overcoming the defect that carbon nanotubes are difficult to disperse, so that they can fully play the function of improving conductivity and mechanical properties in the lithium iron phosphate positive electrode material system. At the same time, by doping B, N and introducing iron ions and sodium ions, the enhancement effect of carbon nanotubes on conductivity can be further improved. The conventional method for lithium iron phosphate doping generally includes the following steps: precursor preparation; coprecipitation; calcination; crushing and molding. It requires the preparation of a liquid precursor, and then the solid lithium source and iron phosphate source are added to the precursor to react, and the ions to be doped are doped into the lithium iron phosphate to improve the electrochemical performance.

[0005] Precise control of the doping process is crucial to obtain doped lithium iron phosphate materials with excellent electrochemical properties. However, conventional preparation methods of lithium iron phosphate and its doping methods are to mix solid iron phosphate source and lithium source in water and then dry and sinter them. The utilization efficiency of lithium ions and iron phosphate ions is limited, and correspondingly, the doping effect on lithium iron phosphate is also limited.

[0006] In order to optimize the preparation process and method of lithium iron phosphate, the present invention provides a production process for jointly preparing lithium iron phosphate. Summary of the invention

[0007] The present invention provides a production process for jointly preparing lithium iron phosphate to solve the technical problems of limited utilization efficiency of lithium ions and iron phosphate ions and limited doping effect in the existing lithium iron phosphate preparation process.

[0008] The embodiments of the present invention are implemented by the following technical solutions:

[0009] A production process for jointly preparing lithium iron phosphate comprises the following steps:

[0010] S1: lithium slurry preparation;

[0011] S2: Preparation of iron phosphate slurry;

[0012] S3: Preparation of lithium iron phosphate: including the following steps:

[0013] C1: Preparation of the first precursor: taking part of the iron phosphate slurry and adding a titanium source to prepare the first precursor;

[0014] C2: Preparation of the second precursor: taking part of the lithium slurry and adding a nitrogen source to prepare the second precursor;

[0015] C3: while mixing the remaining lithium slurry and the iron phosphate slurry, adding the first precursor and the second precursor to obtain a mixed slurry;

[0016] C4: adding a carbon source to the mixed slurry, wet ball milling, and then drying to obtain a mixture;

[0017] C5: The mixture is sintered in two stages in an inert atmosphere to obtain lithium iron phosphate.

[0018] Preferably, in the step S1, the following steps are specifically included:

[0019] A1: Spodumene is roasted at 1100-1200°C to obtain roasted material;

[0020] A2: Sulfuric acid is added to the calcined material to obtain an acidified material, wherein the molar ratio of sulfuric acid to lithium oxide is 1:1.35-1.5;

[0021] A3: After the acidified material is cooled to 70-85°C, sodium hydroxide solution is added to adjust the Ph value to 5-6. After stirring for 25-35 minutes, sodium hydroxide solution is continued to be added to adjust the Ph value to 11-11.5 to obtain a mixed solution;

[0022] A4: The mixed solution is filtered and then evaporated by MVR to obtain the evaporated solution;

[0023] A5: Evaporation of liquid reaction and solid-liquid separation to obtain lithium slurry.

[0024] Preferably, in step A5, the lithium slurry may be one of lithium hydroxide slurry and lithium carbonate slurry;

[0025] After the evaporating liquid is added with sodium hydroxide for reaction, the mixed liquid is cooled to 0°C-5°C for solid-liquid separation to obtain a filtrate, which is lithium hydroxide slurry, wherein the molar ratio of sodium hydroxide to lithium oxide is 2-2.2:1;

[0026] After the evaporating liquid is added with sodium carbonate for reaction, the solid-liquid separation is performed to obtain a filter cake which is washed and slurried to obtain lithium carbonate slurry. The molar ratio of sodium carbonate to lithium oxide is 1-1.2:1.

[0027] Preferably, in step S2, the following steps are specifically included:

[0028] B1: Heat the ferrous sulfate solution to 80-85°C, add iron powder and adjust the Ph value to 3.5-4.5 for later use; add hydrogen peroxide with a molar ratio of 1.96-2:1 to the diammonium phosphate solution, then add ammonia water to adjust the Ph value to 6.5-7 for later use;

[0029] B2: Send the mixed solution of ferrous sulfate and iron powder to the reactor, heat and stir, slowly add diammonium phosphate solution with a volume ratio of 1:0.566-0.575, and react for 50min-60min;

[0030] B3: After the reaction, the mixed solution is filtered, the filter residue is washed and slurried for 30 minutes, then aged at 85°C-90°C for 1.2h-1.5h and washed again to obtain iron phosphate slurry.

[0031] Preferably, in step C1, the titanium source is titanium tetrachloride, and the molar ratio of titanium tetrachloride to phosphate ions in the iron phosphate slurry is 1:3.06-3.15.

[0032] Preferably, in step C2, the nitrogen source is a liquid nitrogen source, including one of acetonitrile, trimethylamine and methylimine; the molar ratio of the added nitrogen source to the lithium ions is 1:4.2-4.5, and the second precursor is added with water to adjust the Ph value to 9-11 for standby use.

[0033] Preferably, in step C3, the volume ratio of the lithium slurry, the iron phosphate slurry, the first precursor and the second precursor is 1-3:1-3:1-2:1-2.

[0034] Preferably, in step C4, the carbon source is one or more of sucrose, glucose, citric acid or polyethylene glycol, and the amount of the carbon source added is 3wt%-5wt% of the mixed slurry; after adding the carbon source and stirring for 1h-1.2h, wet grinding is performed to a final particle size of 0.32μm-0.35μm.

[0035] Preferably, in step C4, spray drying is adopted, the atomizing disk speed is 40Hz-42Hz, and the feed flow rate is 6.80m 3 / h-7.20m 3 / h, air inlet temperature 220℃-230℃, air outlet temperature 85℃-90℃.

[0036] Preferably, in step C5, the sintering temperature in the first stage is 580°C-600°C, and the sintering time is 1.5h-2.0h; the sintering temperature in the second stage is 750°C-760°C, and the sintering time is 1.6h-1.8h; nitrogen is used for protection to prevent oxidation, and the oxygen content is ≤0.2ppm;

[0037] The sintered materials are air flow crushed, batch mixed and packaged. The air flow crushing feeding frequency is 8Hz-10Hz, the classifying wheel frequency is 22Hz-25Hz, and the nitrogen flow rate is 396m 3 / h-400m 3 / h, nitrogen pressure 0.91Mpa-1.01Mpa, batch mixing time 30min.

[0038] The present invention adopts a production process for the joint preparation of lithium iron phosphate, which has the production process of lithium and iron phosphate slurry, and then uses the two slurries to prepare lithium iron phosphate. The liquid-solid combined production method can control the product quality and performance from the source, and the product has good stability, low cost and strong market competitiveness. And this joint production process can also be connected to produce lithium carbonate, lithium hydroxide and iron phosphate finished products and sell them out;

[0039] At the same time, the liquid raw material is easier to combine with the dopant, and the titanium source titanium tetrachloride is directly added to the iron phosphate slurry to obtain part of the titanium phosphate first; the nitrogen source is added to the lithium slurry, and the nitrogen source is an alkaline nitrogen source, and is added to the weakly alkaline lithium hydroxide or lithium carbonate, so as to ensure that the iron phosphate slurry and the lithium slurry are premixed with the dopant without destroying the first precursor and the second precursor, and the dopant mixing is more uniform, and the titanium doping is done by titanium phosphate doping, which can ensure that the titanium is doped in the iron position, but not in the lithium position;

[0040] The present invention premixes part of the iron phosphate slurry and the lithium slurry to obtain a precursor, and then mixes the precursor with the remaining iron phosphate slurry and the lithium slurry, so that the addition ratio of the dopant can be conveniently controlled by adjusting the ratio of the precursor to the remaining raw material slurry, and the dopant is premixed in the precursor in advance, so that the dopant and the raw material slurry that will react are premixed in advance to react, thereby obtaining a precursor mixed solution with a higher concentration that meets the reaction conditions of the raw material slurry;

[0041] When the subsequent raw material slurry reacts, the dopant precursor is mixed and adapted to the system. During the raw material reaction process, doping is carried out directly. Compared with ordinary liquid-solid doping, it is more uniform and has higher doping efficiency. Doping is completed simultaneously with the reaction, and the requirements for doping conditions are relatively low. Further solidification can be achieved by subsequent sintering; higher efficiency doping is achieved on the basis of easier doping.

[0042] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0043] 1. The present invention has the process of producing lithium and iron phosphate slurry at the same time, and then uses the two slurries to prepare lithium iron phosphate. The liquid-solid combined production method can control the product quality and performance from the source, and the product has good stability, low cost and strong market competitiveness;

[0044] 2. The present invention ensures that the iron phosphate slurry and the lithium slurry are premixed with the dopant without destroying the first precursor and the second precursor, and the dopant mixing is more uniform, and the titanium doping is done by titanium phosphate doping, which can ensure that the titanium is doped in the iron position but not in the lithium position;

[0045] 3. The present invention facilitates the control of the addition ratio of the dopant while allowing the dopant to be premixed in the precursor in advance, so that the dopant and the reacting raw material slurry are premixed in advance to react, thereby obtaining a precursor mixed solution with a higher concentration that meets the reaction conditions of the raw material slurry, thereby achieving more efficient doping while making doping easier. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 A schematic diagram of the process flow of the production process for the combined preparation of lithium iron phosphate provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0049] Example 1

[0050] A production process for jointly preparing lithium iron phosphate comprises the following steps:

[0051] S1: lithium slurry preparation;

[0052] S2: Preparation of iron phosphate slurry;

[0053] S3: Preparation of lithium iron phosphate: including the following steps:

[0054] C1: Preparation of the first precursor: taking part of the iron phosphate slurry and adding a titanium source to prepare the first precursor;

[0055] C2: Preparation of the second precursor: taking part of the lithium slurry and adding a nitrogen source to prepare the second precursor;

[0056] C3: while mixing the remaining lithium slurry and the iron phosphate slurry, adding the first precursor and the second precursor to obtain a mixed slurry;

[0057] C4: adding a carbon source to the mixed slurry, wet ball milling, and then drying to obtain a mixture;

[0058] C5: The mixture is sintered in two stages in an inert atmosphere to obtain lithium iron phosphate.

[0059] In this embodiment, step S1 specifically includes the following steps:

[0060] A1: Spodumene is roasted at 1200°C to obtain roasted material;

[0061] A2: Sulfuric acid is added to the calcined material to obtain an acidified material, wherein the molar ratio of sulfuric acid to lithium oxide is 1:1.35;

[0062] A3: After the acidified material is cooled to 80°C, sodium hydroxide solution is added to adjust the Ph value to 5.5. After stirring for 30 minutes, sodium hydroxide solution is continued to be added to adjust the Ph value to 11 to obtain a mixed solution;

[0063] A4: The mixed solution is filtered and then evaporated by MVR to obtain the evaporated solution;

[0064] A5: Evaporation of liquid reaction and solid-liquid separation to obtain lithium slurry.

[0065] In this embodiment, in the step A5, the lithium slurry may be lithium hydroxide;

[0066] After the evaporating liquid is added with sodium hydroxide for reaction, the mixed liquid is cooled to 5° C. for solid-liquid separation to obtain a filtrate, which is lithium hydroxide slurry, and the molar ratio of sodium hydroxide to lithium oxide is 2:1.

[0067] In this embodiment, step S2 specifically includes the following steps:

[0068] B1: Heat the ferrous sulfate solution to 80°C and add iron powder to adjust the Ph value to 4 for later use; add hydrogen peroxide with a molar ratio of 2:1 to the ammonium dihydrogen phosphate solution, and then add ammonia water to adjust the Ph value to 7 for later use;

[0069] B2: The mixed solution of ferrous sulfate and iron powder was sent to the reactor, heated and stirred, and diammonium phosphate solution with a volume ratio of 1:0.575 was slowly added and reacted for 60 minutes;

[0070] B3: After the reaction, the mixed solution was filtered, the filter residue was washed and slurried for 30 minutes, then aged at 90° C. for 1.2 hours and washed again to obtain iron phosphate slurry.

[0071] In this embodiment, in the step C1, the titanium source is titanium tetrachloride, and the molar ratio of the titanium tetrachloride to the phosphate ions in the iron phosphate slurry is 1:3.15.

[0072] In this embodiment, in step C2, the nitrogen source is liquid nitrogen source acetonitrile; the molar ratio of the added nitrogen source to lithium ions is 1:4.5, and water is added to the second precursor to adjust the Ph value to 11 for standby use.

[0073] In this embodiment, in step C3, the volume ratio of the lithium slurry, the iron phosphate slurry, the first precursor and the second precursor is 3:3:2:2.

[0074] In this embodiment, in step C4, the carbon source is glucose, and the amount of the carbon source added is 5 wt% of the mixed slurry; after adding the carbon source and stirring for 1.2 hours, wet grinding is performed to a final particle size of 0.32 μm.

[0075] In this embodiment, in step C4, spray drying is adopted, the atomizing disk speed is 40 Hz, and the feed flow rate is 7.20 m 3 / h, air inlet temperature 220℃, air outlet temperature 85℃.

[0076] In this embodiment, in step C5, the sintering temperature in the first stage is 600° C. and the sintering time is 1.5 h; the sintering temperature in the second stage is 750° C. and the sintering time is 1.6 h; nitrogen is used for protection to prevent oxidation, and the oxygen content is ≤0.2 ppm;

[0077] The sintered materials are subjected to air flow pulverization, batch mixing and packaging. The air flow pulverization feeding frequency is 10Hz, the classifying wheel frequency is 22Hz-25Hz, and the nitrogen flow rate is 400m 3 / h, nitrogen pressure 1.01Mpa, batch mixing time 30min.

[0078] Example 2

[0079] The difference between this embodiment and embodiment 1 is that, in this embodiment, in step A5, the lithium slurry is lithium carbonate slurry;

[0080] After the evaporating liquid is added with sodium carbonate for reaction, the solid-liquid separation is performed to obtain a filter cake which is washed and slurried to obtain lithium carbonate slurry, wherein the molar ratio of sodium carbonate to lithium oxide is 1.2:1.

[0081] Example 3

[0082] The difference between this embodiment and embodiment 1 is that, in this embodiment, step S2 specifically includes the following steps:

[0083] In this embodiment, in the step C1, the molar ratio of the titanium tetrachloride to the phosphate ions in the iron phosphate slurry is 1:3.06.

[0084] Example 4

[0085] The difference between this embodiment and embodiment 1 is that, in this embodiment, step S2 specifically includes the following steps:

[0086] In this embodiment, in the step C1, the molar ratio of the titanium tetrachloride to the phosphate ions in the iron phosphate slurry is 1:3.1.

[0087] Example 5

[0088] The only difference between this embodiment and embodiment 1 is that, in this embodiment, in step C2, the nitrogen source is liquid nitrogen source acetonitrile; and the molar ratio of the added nitrogen source to lithium ions is 1:4.2.

[0089] Example 6

[0090] The only difference between this embodiment and embodiment 1 is that, in this embodiment, in step C2, the nitrogen source is liquid nitrogen source acetonitrile; and the molar ratio of the added nitrogen source to lithium ions is 1:4.35.

[0091] Example 7

[0092] The only difference between this embodiment and Embodiment 1 is that, in this embodiment, in the step C3, the volume ratio of the lithium slurry, the iron phosphate slurry, the first precursor and the second precursor is 3:3:1:1.

[0093] Example 8

[0094] The only difference between this embodiment and Embodiment 1 is that, in this embodiment, in the step C3, the volume ratio of the lithium slurry, the iron phosphate slurry, the first precursor and the second precursor is 2:2:1:1.

[0095] Example 9

[0096] The difference between this embodiment and embodiment 1 is that, in this embodiment, in step C4, the amount of carbon source added is 3 wt % of the mixed slurry.

[0097] Example 10

[0098] The only difference between this embodiment and embodiment 1 is that, in this embodiment, in step C4, the amount of carbon source added is 4 wt % of the mixed slurry.

[0099] Comparative Example 1

[0100] The only difference between this comparative example and Example 1 is that the existing iron phosphate source and lithium source are used for synthetic doping.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that titanium doping and nitrogen doping are added after the reaction is completed.

[0103] Comparative Example 3

[0104] The only difference between this comparative example and Example 1 is that the titanium source and the nitrogen source are added to the whole raw material slurry for premixing.

[0105] The relevant data of the above embodiments and comparative examples are shown in Table 1 below:

[0106] Table 1. Data related to Examples 1-10 and Comparative Examples 1-3

[0107]

[0108] The electrochemical data of the above examples and comparative examples are listed in Table 2:

[0109] Table 2. Electrochemical experimental data related to Examples 1-10 and Comparative Examples 1-3

[0110]

[0111]

[0112] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A production process for the combined preparation of lithium iron phosphate, characterized in that: The steps include: S1: lithium slurry preparation; S2: Preparation of iron phosphate slurry; S3: Preparation of lithium iron phosphate: including the following steps: C1: Preparation of the first precursor: taking part of the iron phosphate slurry and adding a titanium source to prepare the first precursor; C2: Preparation of the second precursor: taking part of the lithium slurry and adding a nitrogen source to prepare the second precursor; C3: while mixing the remaining lithium slurry and the iron phosphate slurry, adding the first precursor and the second precursor to obtain a mixed slurry; C4: adding a carbon source to the mixed slurry, wet ball milling, and then drying to obtain a mixture; C5: The mixture is sintered in two stages in an inert atmosphere to obtain lithium iron phosphate.

2. A production process for combined preparation of lithium iron phosphate according to claim 1, characterized in that: In the step S1, the following steps are specifically included: A1: Spodumene is roasted to obtain roasted material; A2: adding sulfuric acid to the roasted material to acidify it to obtain an acidified material; A3: After the acidified material is cooled, add sodium hydroxide solution to adjust the Ph value, stir for 25min-35min, and continue to add sodium hydroxide solution to adjust the Ph value to obtain a mixed solution; A4: The mixed solution is filtered and then evaporated by MVR to obtain the evaporated solution; A5: Evaporation of liquid reaction and solid-liquid separation to obtain lithium slurry.

3. A production process for combined preparation of lithium iron phosphate according to claim 2, characterized in that: In the step A5, the lithium slurry may be one of lithium hydroxide slurry and lithium carbonate slurry; After the evaporating liquid is added with sodium hydroxide for reaction, the mixed liquid is cooled to 0°C-5°C for solid-liquid separation to obtain a filtrate, which is lithium hydroxide slurry, wherein the molar ratio of sodium hydroxide to lithium oxide is 2-2.2:1; After the evaporating liquid is added with sodium carbonate for reaction, the solid-liquid separation is performed to obtain a filter cake which is washed and slurried to obtain lithium carbonate slurry. The molar ratio of sodium carbonate to lithium oxide is 1-1.2:

1.

4. A production process for the combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In the step S2, the following steps are specifically included: B1: Heat the ferrous sulfate solution and add iron powder for later use; add hydrogen peroxide to the ammonium dihydrogen phosphate solution, and then add ammonia water to adjust the Ph value for later use; B2: Send the mixed solution of ferrous sulfate and iron powder to the reactor, heat and stir, slowly add diammonium phosphate solution and react for 50min-60min; B3: After the reaction, the mixed solution is filtered, the filter residue is washed and pulped for 30 minutes, then aged and washed again to obtain iron phosphate slurry.

5. A production process for the combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In the step C1, the titanium source is titanium tetrachloride, and the molar ratio of the titanium tetrachloride to the phosphate ions in the iron phosphate slurry is 1:3.06-3.

15.

6. A production process for combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In step C2, the nitrogen source is a liquid nitrogen source, including one of acetonitrile, trimethylamine and methylimine; the molar ratio of the added nitrogen source to the lithium ions is 1:4.2-4.5, and the second precursor is added with water to adjust the Ph value to 9-11 for standby use.

7. A production process for combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In the step C3, the volume ratio of the lithium slurry, the iron phosphate slurry, the first precursor and the second precursor is 1-3:1-3:1-2:1-2.

8. A process for the combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In step C4, the carbon source is one or more of sucrose, glucose, citric acid or polyethylene glycol, and the amount of the carbon source added is 3wt%-5wt% of the mixed slurry; after adding the carbon source, stirring for 1h-1.2h, wet grinding is performed to a final particle size of 0.32μm-0.35μm.

9. A production process for combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In step C4, spray drying is adopted, the atomizing disk speed is 40Hz-42Hz, and the feed flow rate is 6.80m 3 / h-7.20m 3 / h, air inlet temperature 220℃-230℃, air outlet temperature 85℃-90℃.

10. A process for the combined preparation of lithium iron phosphate according to any one of claims 1 to 3, characterized in that: In the step C5, the sintering temperature in the first stage is 580°C-600°C, and the sintering time is 1.5h-2.0h; the sintering temperature in the second stage is 750°C-760°C, and the sintering time is 1.6h-1.8h; nitrogen is used for protection to prevent oxidation, and the oxygen content is ≤0.2ppm; the sintered material is air flow crushed and batch mixed and packaged.

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