A method for preparing modified iron phosphate by recycling, modified iron phosphate and application thereof

Abstract

The application discloses a method for preparing modified iron phosphate by recycling, the modified iron phosphate and application thereof, and belongs to the field of recycling and preparing iron phosphate, and comprises the following steps: S1, a precipitant is added to ferrous sulfate wastewater containing nickel for precipitation, and after filtration, an iron-rich filter cake and a nickel-rich filtrate are obtained; S2, the iron-rich filter cake is dispersed in a sulfuric acid solution, and iron powder is added for reduction, so that a primary solution is obtained; S3, ozone is introduced into the primary solution for oxidation reaction, so that a slurry is obtained; S4, a surface modifier and an initiator are added to the slurry for modification, so that a precursor slurry is obtained; and S5, the precursor slurry is subjected to a hydrothermal reaction, so that the modified iron phosphate is obtained. The modified iron phosphate doped with trace nickel is efficiently recycled and prepared from the ferrous sulfate wastewater containing nickel through the steps of precipitating and separating iron and nickel and copolymerization modification, so that the wastewater is utilized as a resource and pollutants are reduced, and meanwhile, the high-quality iron phosphate is prepared, and the electrochemical performance of lithium iron phosphate prepared in the subsequent step is excellent.

Description

Technical Field

[0001] This invention belongs to the field of recycling and preparation of ferric phosphate technology, specifically a method for recycling and preparing modified ferric phosphate, modified ferric phosphate and its applications. Background Technology

[0002] With the rapid development of the new energy vehicle and energy storage battery industries, the market demand for lithium iron phosphate (LFP) as the mainstream cathode material continues to rise, driving the large-scale production of LFP raw materials. At the same time, the discharge of nickel-containing ferrous sulfate wastewater from battery manufacturing, metallurgical processing, and other industries is increasing year by year. This type of wastewater contains high concentrations of Fe... 2+ Ni 2+ Direct discharge of valuable metal ions will cause pollution and waste of metal resources; while traditional wastewater treatment methods such as neutralization precipitation and chemical oxidation can only achieve pollutant discharge in compliance with standards, but cannot achieve efficient recycling of resources.

[0003] As the core precursor of lithium iron phosphate, the purity, dispersibility, and crystal structure of iron phosphate directly affect the performance of the final cathode material. Existing iron phosphate preparation technologies mainly include solid-state methods, liquid-phase precipitation methods, and hydrothermal methods. Among these, the hydrothermal method has become the mainstream process due to its high crystallinity and good particle uniformity, but it still has significant drawbacks: for example, to improve the dispersibility of iron phosphate, existing technologies often use physical coating methods to add modifiers. However, the modifiers are only physically adsorbed onto the particle surface and are prone to desorption during subsequent hydrothermal and sintering processes, leading to secondary particle agglomeration and making it impossible to guarantee long-term stable product performance; to improve the conductivity of lithium iron phosphate, existing technologies often use the addition of metal salts such as Ni, Co, and Mn as dopants, increasing raw material costs. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a method for recovering and preparing modified iron phosphate, the modified iron phosphate itself, and its applications. This invention utilizes a primary-secondary precipitant synergistic precipitation separation of iron and nickel, along with a copolymerization modification process, to efficiently recover and prepare trace amounts of nickel-doped modified iron phosphate from nickel-containing ferrous sulfate wastewater. This achieves both wastewater resource utilization and pollutant reduction, while also producing high-quality iron phosphate, which exhibits excellent electrochemical performance in subsequent lithium iron phosphate production.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a method for preparing modified iron phosphate by recycling, comprising the following steps: S1. Add a precipitant to the nickel-containing ferrous sulfate wastewater to precipitate it, and then filter it to obtain an iron-rich filter cake and a nickel-rich filtrate; The nickel-containing ferrous sulfate wastewater contains: Ni 2+ 8~40 g / L, Fe2+ 20~50 g / L; The precipitant consists of a main precipitant and an auxiliary precipitant; the main precipitant is trisodium phosphate or sodium pyrophosphate, preferably trisodium phosphate; the auxiliary precipitant is citric acid. S2. Disperse the iron-rich filter cake in sulfuric acid solution, control the pH between 1.0 and 2.0, and stir to dissolve at 60-80℃ for 0.5-2 hours. Add iron powder to reduce and obtain the primary solution. S3. Ozone is introduced into the primary solution to carry out an oxidation reaction and obtain a slurry; S4. Add surface modifier and initiator to the slurry and modify it at 35~65℃ for 0.5~4h. During the modification process, maintain the pH at 2.5~5.0 to obtain the precursor slurry. S5. Modified iron phosphate is obtained by hydrothermal reaction of the precursor slurry.

[0007] According to some embodiments of the present invention, in S1, the nickel-containing ferrous sulfate wastewater contains: Ni 2+ 8~40 g / L, Fe 2+ : 20~50 g / L, Cu: 1~35ppm, Cr: 1~60ppm, Pb: 1~25ppm.

[0008] According to some embodiments of the present invention, in S1, the nickel ferrous sulfate wastewater contains Cu, Pb and Cr impurity ions; the nickel ferrous sulfate wastewater contains Cu: 10~30ppm, Cr: 20~50ppm, and Pb: 10~20ppm.

[0009] According to some embodiments of the present invention, in S1, the precipitation is first stirred at 40~90°C for 0.5~3h, the pH at the reaction endpoint is controlled at 2~4.5, and then cooled to ≤20°C and allowed to stand; preferably, the precipitation is first stirred at 50~80°C for 1~2h, the pH at the reaction endpoint is controlled at 2.5~4.0, and then cooled to ≤15°C and allowed to stand.

[0010] This invention uses sulfuric acid solution and ammonia water to adjust the pH.

[0011] Further in S1, the amount of the main precipitant added, measured by a molar, is equal to the amount of Fe in the nickel-containing ferrous sulfate wastewater. 2+ 1.0 to 1.1 times the molar amount.

[0012] Further in S1, the amount of auxiliary precipitant added, measured by a molar, is equal to the Ni content in the nickel-containing ferrous sulfate wastewater. 2+ 0.9 to 1.1 times the molar amount.

[0013] The main precipitant and ferrous ions form phosphate precipitate, while citric acid, as an auxiliary precipitant, complexes with nickel ions to prevent a large amount of nickel from mixing into the filter cake, thus achieving efficient separation.

[0014] According to some embodiments of the present invention, in S2, the mass concentration of sulfuric acid in the sulfuric acid solution is 10-20%.

[0015] The addition of iron powder in this invention is not only to reduce ferric ions to ferrous ions, maintaining the same valence state, but also to remove trace amounts of heavy metal impurities such as Cu from the filter cake. 2+ and Pb 2+ .

[0016] According to some embodiments of the present invention, in S3, the ozone ventilation rate is 0.1~0.3 L / (L·min).

[0017] According to some embodiments of the present invention, in S3, the oxidation reaction continues until Fe in the solution... 2+ The concentration dropped to below 0.1 g / L.

[0018] According to some embodiments of the present invention, in S4, the solid content of the slurry is 10-40%. The solid content is determined by gravimetric method, i.e., the slurry is dried to constant weight, and the proportion of residual solid mass to the slurry is calculated.

[0019] According to some embodiments of the present invention, in S4, the surface modifier is a mixture of vinylphosphonic acid / itaconic acid in a molar ratio of 1 / 1 to 3.

[0020] According to some embodiments of the present invention, in S4, the amount of the surface modifier added accounts for 2 to 8% of the dry basis mass of the slurry, preferably 3 to 6%.

[0021] According to some embodiments of the present invention, in S4, the amount of the initiator added accounts for 0.3-3% of the dry basis mass of the slurry, preferably 0.5-2%.

[0022] According to some embodiments of the present invention, the modification process maintains the pH at 3.0 to 4.5 and is carried out at 40 to 60°C for 1 to 3 hours.

[0023] The modification of this invention utilizes phosphine groups to react with Fe. 3+ The covalent bonds formed through coordination and copolymerization, with the carboxyl groups providing steric hindrance, form a dense modified layer on the surface of iron phosphate particles under the initiation of ammonium persulfate. Subsequent hydrothermal reactions promote particle crystallization and solidification of the modified layer, which inhibits particle agglomeration and stabilizes the primary particle size of the product. This invention also utilizes trace amounts of nickel doping to regulate the electronic structure of iron phosphate, enhancing the lithium-ion diffusion rate and overcoming the shortcomings of traditional iron phosphate, such as poor conductivity and slow lithium-ion migration.

[0024] According to some embodiments of the present invention, in S5, the hydrothermal reaction is carried out at 130~190°C for 3~18 hours; preferably, the hydrothermal reaction is carried out at 150~180°C for 5~12 hours.

[0025] According to some embodiments of the present invention, in S5, the hydrothermal reaction is carried out in a hydrothermal reactor; According to some embodiments of the present invention, in S5, the hydrothermal reaction further includes a post-processing step, namely, a solid-liquid separation step, a solid washing step, and a solid drying step.

[0026] This invention also discloses a modified iron phosphate prepared by the aforementioned method, with the general chemical formula Fe. 1-x Ni x PO4, where x is 0.005~0.05, preferably x is 0.01~0.03.

[0027] According to some embodiments of the present invention, the average particle size of the modified iron phosphate is 1~50 μm, preferably 10~30 μm.

[0028] According to some embodiments of the present invention, the purity of the modified iron phosphate is ≥90%; this purity refers to Fe 1-x Ni x PO4 content.

[0029] The present invention also discloses the application of modified iron phosphate in the preparation of lithium iron phosphate, wherein modified iron phosphate and lithium carbonate are sintered to obtain lithium iron phosphate, and the addition ratio of modified iron phosphate and lithium carbonate is calculated according to the Li / (Fe+Ni) molar ratio of 1.01~1.03 / 1 (preferably 1.01~1.02 / 1); According to some embodiments of the present invention, the sintering temperature is 550~850℃, preferably 600~800℃.

[0030] According to some embodiments of the present invention, the holding time for sintering is 2 to 8 hours, preferably 3 to 6 hours.

[0031] According to some embodiments of the present invention, the heating rate of the sintering process is 3~12℃ / min. Preferably, it is 5~10℃ / min.

[0032] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0033] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a precipitant to initially precipitate ferrous ions, performing preliminary enrichment and purification steps. The trace amounts of residual nickel in the iron-rich filter cake can be used as a dopant to enhance the performance of lithium iron phosphate. Iron powder reduction not only unifies the valence state of iron ions but also facilitates the removal of heavy metal ions such as copper and lead ions. The purification process of this invention is cost-effective and removes impurities efficiently, ensuring consistent product performance.

[0034] 2. The precursor slurry of the present invention contains vinylphosphonic acid and itaconic acid copolymerized modified iron phosphate, wherein the phosphonic acid groups react with Fe... 3+ Coordination and carboxyl groups provide steric hindrance, forming a dense modified layer that effectively inhibits particle aggregation; the above modifications can promote crystal growth during hydrothermal processes.

[0035] 3. This invention uses nickel-containing ferrous sulfate wastewater as raw material and recovers nickel salts from nickel-rich filtrate. It does not require the addition of additional nickel salts, thus achieving resource recovery, reducing production costs, and eliminating the need for additional production equipment.

[0036] 4. The modified iron phosphate of the present invention can be used to prepare lithium iron phosphate. The prepared lithium iron phosphate material has excellent electrochemical performance and meets the requirements of high capacity, high rate and long cycle life as a cathode material of lithium-ion batteries. Attached Figure Description

[0037] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0038] Figure 1 The image shows a SEM image of the modified iron phosphate prepared in Example 1.

[0039] Figure 2 The image shows a SEM image of the modified iron phosphate prepared in Comparative Example 2.

[0040] Figure 3 The image shows a SEM image of the modified iron phosphate prepared in Comparative Example 3. Detailed Implementation

[0041] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0043] The raw material information used in the following examples is as follows: Nickel-containing ferrous sulfate wastewater contains: Ni 2+ 23 g / L, Fe 2+:36 g / L, Cu: 28ppm, Cr: 43ppm, Pb: 19ppm.

[0044] Ferric phosphate Example 1 S1. Inject nickel-containing ferrous sulfate wastewater into the reactor, start stirring (300 r / min), heat to 65℃, and proceed with Ni... 2+ Add 1.0 molar amount of auxiliary precipitant (citric acid) to the reactor, according to Fe 2+ Add the main precipitant (trisodium phosphate) slowly to the reactor at 1.05 times the molar amount, monitor the pH during the addition of trisodium phosphate, and stabilize the pH at the final reaction point at 3.0±1. Continue stirring for 1 hour, then turn off the heating and allow it to cool naturally to 12°C and stand for 4 hours. Plate and frame filtration (pressure 0.3 MPa) was used to collect iron-rich filter cake and nickel-rich filtrate.

[0045] S2. Dissolve the iron-rich filter cake in a 15% sulfuric acid solution, start stirring (250 r / min), heat to 70℃ and stir for 0.5 h, and check that the pH of the system is 1.5; since some ferrous ions are oxidized to ferric ions, iron powder needs to be added to reduce them back to ferrous ions. There should be some iron powder left over to ensure complete reduction. After reduction, filter to remove solid impurities and obtain the primary solution. S3. Turn on the ozone generator and introduce ozone into the primary solution, controlling the aeration rate at 0.2 L / (L⁻¹·min) (i.e., 0.2 L of ozone gas per minute per liter of primary solution), and continue aeration for oxidation; Fe 2+ When the concentration drops to 0.08 g / L, ozone is stopped, and slurry is obtained; the solid content of the slurry is 25% (gravimetric method: take 10 g of slurry, dry it to constant weight, and the residual solid mass is 2.5 g).

[0046] S4. Add a surface modifier (vinylphosphonic acid / itaconic acid molar ratio of 1 / 2) to the slurry, the amount of surface modifier added is 5% of the dry basis mass of the slurry; then add an initiator (ammonium persulfate), the amount of initiator added is 1.0% of the dry basis mass of the slurry; keep the system at 50℃ and pH 4.0±0.2 and stir (250 r / min) for 2 h to complete the modification reaction and obtain the precursor slurry.

[0047] S5. The precursor slurry was sealed in a hydrothermal reactor and heated to 160℃ for 6 hours. After the heating was completed, it was allowed to cool naturally to room temperature. The hydrothermal reactor was then opened, and the solid was collected by centrifugation. The solid was washed three times with deionized water and then dried in a vacuum drying oven at 80℃ for 12 hours to obtain modified iron phosphate. Its SEM image is shown below. Figure 1 The modified iron phosphate has a clear and regular surface, without any adhesion or stacking, and the surface is smooth and dense.

[0048] Example 2 The difference between this embodiment and Embodiment 1 is as follows: During S1, press Ni 2+ Add 1.0 times the molar amount of auxiliary precipitant (citric acid); The other raw materials, steps and parameters are the same as in Example 1.

[0049] Example 3 The difference between this embodiment and Embodiment 1 is as follows: In the S4 process, the ratio of vinylphosphonic acid to itaconic acid in the surface modifier is 2:1; The other raw materials, steps and parameters are the same as in Example 1.

[0050] Example 4 The difference between this embodiment and Embodiment 1 is as follows: The amount of surface modifier added accounts for 3% of the dry basis mass of the slurry; The other raw materials, steps and parameters are the same as in Example 1.

[0051] Example 5 The difference between this embodiment and Embodiment 1 is as follows: The amount of surface modifier added accounts for 10% of the dry basis mass of the slurry; The other raw materials, steps and parameters are the same as in Example 1.

[0052] Example 6 The difference between this embodiment and Embodiment 1 is as follows: During the modification of S4, the pH was controlled at 2.5±0.2; The other raw materials, steps and parameters are the same as in Example 1.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: In S2, the iron-rich filter cake was dissolved in an 11.5 wt% hydrochloric acid solution instead of a sulfuric acid solution. The other raw materials, steps and parameters are the same as in Example 1.

[0054] Comparative Example 2 This comparative example does not include the modification process in step S4; the slurry obtained in S3 is directly processed in step S5. The SEM image of the modified iron phosphate obtained in this comparative example is shown below. Figure 2 The particles in the figure are partially agglomerated, forming small-scale stacks with poor dispersibility; other raw materials, steps and parameters are the same as in Example 1.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: No auxiliary precipitant is added during the S1 process; The SEM image of the modified iron phosphate obtained in this comparative example is shown below. Figure 3 The particles in the image are severely agglomerated, forming large areas of blocky or flocculent stacks. The other raw materials, steps and parameters are the same as in Example 1.

[0056] Example of effect The physicochemical parameters of the modified iron phosphate prepared in the above embodiments and comparative examples are shown in Table 1; The chemical formula of the modified iron phosphate was determined by ICP-MS, and the purity of the modified iron phosphate was determined by ICP-OES. The average particle size was calculated by selecting 50 dispersed modified iron phosphate particles from the SEM image and averaging them.

[0057]

[0058] Lithium iron phosphate The modified iron phosphate obtained in the above examples and comparative examples were respectively prepared into lithium iron phosphate. The preparation process is as follows: Modified iron phosphate and lithium carbonate were fed into a planetary ball mill at a Li / (Fe+Ni) molar ratio of 1.02:1, with polyethylene glycol added as a dispersant. After ball milling, the particles were dried in a vacuum drying oven to remove moisture. The solid particles were then placed in a tubular sintering furnace, and argon gas was introduced. The temperature was raised to 700°C at a rate of 8°C / min and held for 6 hours. After sintering, the heating was turned off, and the argon gas flow rate was kept constant. The furnace was allowed to cool naturally to room temperature (25°C). The sintered solid powder was then pulverized and sieved (using a 200-mesh sieve) to remove large particles of impurities, yielding lithium iron phosphate.

[0059] The above-mentioned lithium iron phosphate was used as the positive electrode material to prepare half-cells and the following tests were performed. The test results are shown in Table 2. (1) Lithium iron phosphate: acetylene black: polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added to adjust the viscosity to 4000~8000 mPa·s to obtain a positive electrode slurry. (2) The positive electrode slurry is evenly coated on one surface (perpendicular to the thickness direction) of the aluminum foil (positive electrode current collector) and dried. Then, it is rolled and sheared to obtain a positive electrode sheet containing a positive electrode film.

[0060] (3) Using lithium hexafluorophosphate-ethyl methyl carbonate as electrolyte and polypropylene as separator, a button cell is made by combining the prepared positive electrode and negative lithium electrode.

[0061] The fabricated coin cells were tested using Blue Electric equipment to determine their discharge specific capacity at 0.2C and 1.0C within a voltage range of 2.0V to 3.8V, as well as their capacity retention after 100 cycles at 0.2C.

[0062]

[0063] Based on the above test results, the following should be noted: Example Group: Example 1, as a preferred embodiment, achieved a discharge specific capacity of 158 mAh / g, indicating high utilization of the active material and sufficient electrochemical reaction. At this rate, the capacity retention after 100 cycles was as high as 96.7%, demonstrating the good structural stability of the lithium iron phosphate cathode material prepared from modified iron phosphate. The crystal structure remained intact and decayed slowly during multiple lithium-ion intercalation / deintercalation processes. Furthermore, its discharge specific capacity remained at 149.2 mAh / g at a higher rate (1.0C), proving that the material possesses rapid lithium-ion diffusion kinetics and good electronic conductivity.

[0064] Comparative Example Group: Cl in Comparative Example 1 - Residues lead to crystallization defects, and aggregation hinders diffusion; while during the cycling process, Cl... - The destruction of lattice stability leads to gradual structural collapse during cycling. In Comparative Example 2, severe agglomeration and crystal defects resulted in extremely long and blocked lithium-ion diffusion paths. At high rates, diffusion was almost impossible, leading to incomplete electrode reactions. Agglomerates easily detached during cycling, and crystal defects caused rapid lattice collapse, resulting in the fastest capacity decay. In Comparative Example 3, agglomerates hindered lithium-ion diffusion, and numerous crystal defects obstructed insertion / extraction channels. At high rates, diffusion resistance was further amplified, significantly reducing the reaction rate. Crystal defects and agglomerates easily caused structural damage during cycling, and lattice collapse led to rapid capacity decay.

[0065] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for recovering and preparing modified iron phosphate, characterized in that, Includes the following steps: S1. Add a precipitant to the nickel-containing ferrous sulfate wastewater to precipitate it, and then filter it to obtain an iron-rich filter cake and a nickel-rich filtrate; The nickel-containing ferrous sulfate wastewater contains: Ni 2+ 8~40 g / L, Fe 2+ : 20~50 g / L, Cu: 1~35ppm, Cr: 1~60ppm, Pb: 1~25ppm; The precipitants are a primary precipitant and an auxiliary precipitant, with the primary precipitant being trisodium phosphate or sodium pyrophosphate, and the auxiliary precipitant being citric acid. S2. Disperse the iron-rich filter cake in a sulfuric acid solution, control the pH between 1.0 and 2.0, and stir to dissolve at 60-80℃ for 0.5-2 hours; add iron powder to reduce and obtain the primary solution; S3. Ozone is introduced into the primary solution to carry out an oxidation reaction and obtain a slurry; S4. Add surface modifier and initiator to the slurry and modify it at 35~65℃ for 0.5~4h. During the modification process, maintain the pH at 2.5~5.0 to obtain the precursor slurry. The surface modifier is a mixture of vinylphosphonic acid and itaconic acid in a molar ratio of 1 / 1 to 4; the initiator is ammonium persulfate; S5. Modified iron phosphate is obtained by hydrothermal reaction of the precursor slurry.

2. The method for preparing modified iron phosphate by recycling as described in claim 1, characterized in that, The precipitation process involves stirring at 40-90℃ for 0.5-3 hours, controlling the pH at the reaction endpoint to be 2-4.5, and then cooling to ≤20℃ and allowing it to stand.

3. The method for preparing modified iron phosphate by recycling as described in claim 2, characterized in that, The amount of the main precipitant added is the Fe in the nickel-containing ferrous sulfate wastewater. 2+ 1.0 to 1.1 times the molar amount; And / or, the amount of the auxiliary precipitant added is equal to the Ni content in the nickel-containing ferrous sulfate wastewater. 2+ 0.9 to 1.1 times the molar amount.

4. The method for preparing modified iron phosphate by recycling as described in claim 1, characterized in that, The sulfuric acid in the sulfuric acid solution has a mass concentration of 10-20%.

5. The method for preparing modified ferric phosphate by recycling as described in claim 1, characterized in that, The oxidation reaction continues until Fe in the solution... 2+ The concentration dropped to below 0.1 g / L; And / or, the solid content of the slurry is 10-40%.

6. The method for preparing modified iron phosphate by recycling as described in claim 1, characterized in that, The surface modifier is a mixture of vinylphosphonic acid and itaconic acid in a molar ratio of 1 / 1 to 3; And / or, the amount of the surface modifier added accounts for 2-8% of the dry basis mass of the slurry; And / or, the amount of the initiator added is 0.3-3% of the dry basis mass of the slurry.

7. The method for preparing modified iron phosphate by recycling as described in claim 1, characterized in that, The hydrothermal reaction was carried out at 130~190℃ for 3~18 hours; And / or, the hydrothermal reaction is carried out in a hydrothermal reactor; And / or, the hydrothermal reaction may further include a post-processing step, namely, solid-liquid separation, washing the solid, and drying the solid.

8. The modified iron phosphate prepared by the method according to any one of claims 1 to 7, characterized in that, Its general chemical formula is Fe 1-x Ni x PO4, where x = 0.01~0.

03.

9. The modified iron phosphate as described in claim 8, characterized in that, The modified iron phosphate has an average particle size of 1~50 μm.

10. The application of the modified iron phosphate as described in claim 8 or 9 in the preparation of lithium iron phosphate, characterized in that, Lithium iron phosphate was obtained by sintering modified iron phosphate and lithium carbonate; the addition ratio of modified iron phosphate and lithium carbonate was calculated according to the Li / (Fe+Ni) molar ratio of 1.01~1.02:

1. And / or, the sintering temperature is 550~850℃; And / or, the holding time for sintering is 2 to 8 hours; And / or, the heating rate of the sintering process is 3~12℃ / min.

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