Preparation method of sheet-like iron phosphate and lithium iron phosphate thereof

Abstract

This invention discloses a method for preparing layered iron phosphate and lithium iron phosphate. The method includes: preparing a ferrous phosphate mixture; filtering the ferrous phosphate mixture to obtain a refined ferrous phosphate filtrate; taking a portion of the refined ferrous phosphate filtrate and adding crude iron phosphate seed crystals to it, mixing evenly, and using it as a reaction base solution; continuously adding the remaining refined ferrous phosphate filtrate and an oxidant to the reaction base solution in a parallel flow, and carrying out a precipitation reaction at a specific temperature; the reaction product is washed and calcined to obtain battery-grade layered iron phosphate. This invention combines "seed induction" and "co-current co-precipitation" processes to control the nucleation and growth process of iron phosphate crystals, successfully preparing a uniform, large-particle-size layered iron phosphate product. This method can prepare uniform-size, tightly packed layered iron phosphate precursors, obtaining high-density lithium iron phosphate cathode materials, while improving the production yield and reducing washing water consumption, and has good process production application value.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate preparation technology, and more specifically, to a method for preparing layered iron phosphate and lithium iron phosphate. Background Technology

[0002] Lithium-ion batteries, as a new generation of green high-energy chemical power sources, are widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their advantages such as high energy density, long cycle life, no memory effect, and low self-discharge rate. Among the many lithium-ion battery cathode materials, lithium iron phosphate (LiFePO4) has become one of the most competitive cathode materials in the fields of power batteries and energy storage batteries due to its excellent cycle stability, high safety (good thermal stability), environmental friendliness, and abundant raw material sources.

[0003] Lithium iron phosphate is typically prepared by sintering the precursor iron phosphate (FePO4) with a lithium source using a high-temperature solid-state or liquid-state method. Therefore, the physical and chemical properties of the precursor iron phosphate (such as morphology, particle size, tap density, specific surface area, crystallinity, and iron-to-phosphorus ratio) directly determine the electrochemical performance of the final lithium iron phosphate product.

[0004] In existing technologies, the mainstream methods for preparing ferric phosphate include: ① iron sheet phosphating, ② hydrothermal / solvothermal methods, and ③ precipitation methods. Among these, precipitation methods (especially liquid-phase co-precipitation under normal pressure) are the most widely used due to their simple process, mild conditions, and ease of large-scale industrial production. Traditional liquid-phase co-precipitation methods typically use ferrous salts (such as ferrous sulfate) and phosphorus sources (such as phosphoric acid and sodium phosphate) as raw materials. An oxidant (such as hydrogen peroxide) is added, and the mixture reacts at a specific pH value to generate amorphous or low-crystallinity ferric phosphate precipitate.

[0005] However, iron phosphate obtained through traditional processes using iron phosphate precursors often consists of severely agglomerated, irregularly shaped particles, resulting in low compaction density and poor electrochemical performance in lithium iron phosphate cathode materials. To overcome this drawback, researchers have focused on controlling the morphology of iron phosphate and lithium iron phosphate. Constructing low-dimensional nanomaterials (such as nanowires and nanosheets) is considered an effective strategy. In particular, layered (or nanosheet) iron phosphate structures offer significant advantages. Currently, studies have employed hydrothermal methods, template methods, or the use of organic additives to prepare layered iron phosphate. However, these methods suffer from complex processes, high costs, and difficulties in industrial-scale production.

[0006] Therefore, there is an urgent need to develop a simple, low-cost, and easily industrialized method to prepare uniformly sized, layered iron phosphate precursors, thereby obtaining high-density lithium iron phosphate cathode materials. Summary of the Invention

[0007] In view of the above, the present invention provides a method for preparing layered iron phosphate and lithium iron phosphate, which can prepare a uniform particle size and layered iron phosphate precursor, thereby obtaining a high-density lithium iron phosphate cathode material. At the same time, the method is simple, low-cost and easy to industrialize.

[0008] The first aspect of the present invention provides a method for preparing lamellar iron phosphate, comprising the following steps:

[0009] S1: Prepare a ferrous phosphate solution;

[0010] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0011] S3: Take a portion of the refined ferrous filtrate obtained in step S2, add crude ferric phosphate as seed crystals, mix well and use it as the reaction base liquid;

[0012] S4: Under stirring conditions, the remaining portion of the refined ferrous filtrate and the oxidant are continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. After the reaction is completed, the precipitate is collected, washed, and crude ferric phosphate is obtained.

[0013] S5: Calcine the crude iron phosphate obtained in step S4 to obtain battery-grade layered iron phosphate.

[0014] In step S1, the ferrous phosphate mixture is prepared by reacting an iron source with 30-40 wt% phosphoric acid at 50-70°C for 12-36 hours. The iron source includes pure iron blocks, iron powder, and pig iron blocks. The molar ratio of iron to phosphorus is Fe:P = 1:1.8-2.2. This step provides a ferrous phosphate mixture with a precisely controllable iron-to-phosphorus ratio. By reacting the iron source with phosphoric acid under mild conditions, preliminary dissolution and mixing are performed, effectively removing insoluble impurities and providing a high-purity ferrous phosphate mixture for subsequent processes. Furthermore, setting the Fe:P molar ratio to 1:1.8-2.2, maintaining an excess of phosphorus, not only ensures the complete completion of the subsequent oxidation precipitation reaction and inhibits the formation of impurity phases, guaranteeing the high purity of the ferric phosphate product, but also ensures that the excess phosphate (PO4) ions... 3- Adsorbed on the surface of seed crystals and newly formed crystals, it can regulate the growth rate of each crystal facet and work synergistically with subsequent seed induction to help the final iron phosphate product form a regular lamellar morphology.

[0015] In step S2, filtration removes insoluble solid impurities, yielding a high-purity refined ferrous filtrate, thus avoiding the influence of impurity elements on the purity of the final ferric phosphate product. Furthermore, this step purifies a highly homogeneous liquid-phase reaction system with a defined chemical composition, creating a clean, stable, and controllable reaction environment for the subsequent precise control of the "seed induction" and "co-current co-precipitation" processes. This is a prerequisite for ensuring the large-scale, reproducible preparation of lamellar ferric phosphate with regular morphology and concentrated particle size distribution. Without this purification step, the presence of impurities will interfere with the directional induction of the seed crystals, leading to uncontrolled ferric phosphate crystallization and preventing the acquisition of the lamellar morphology required by this invention.

[0016] In step S3, the volume of the refined ferrous filtrate is 1 / 20 to 1 / 5 of the total volume of the refined ferrous filtrate obtained in step S2; the amount of crude ferric phosphate added, calculated as iron element, has a molar ratio of 0.5~1.5:10 with the iron element in the refined ferrous filtrate. This step is the core step in achieving controllable synthesis of the lamellar morphology of ferric phosphate products, and its function is to construct a reaction substrate containing seed crystals. Since crude ferric phosphate is readily available and possesses a lamellar morphology, it can serve as a template for inducing the formation of lamellar ferric phosphate. This invention creatively uses crude ferric phosphate as a seed crystal and mixes it with a portion of the refined ferrous filtrate at a specific molar ratio (0.5~1.5:10). Using crude ferric phosphate as a seed crystal not only effectively induces heterogeneous nucleation but also effectively achieves the replication and growth of the lamellar morphology, greatly reducing costs while obtaining superior morphology control. In this step, based on the "seed-induced epitaxial growth" mechanism, the crude ferric phosphate seed crystals in the reaction substrate act as a pre-designed "growth template." When subsequent reactants are added, the newly generated ferric phosphate molecules (FePO4) preferentially undergo heterogeneous nucleation and epitaxial growth on the seed crystal surface, thereby inheriting and amplifying the lamellar morphology of the seed crystal, achieving precise control over the microstructure of the final ferric phosphate product. Furthermore, using only 1 / 20 to 1 / 5 of the total volume of the refined ferrous filtrate mixed with the crude ferric phosphate seed crystals as the reaction substrate significantly reduces the initial supersaturation of the reactants, effectively inhibiting homogeneous nucleation and forcing the reaction to proceed entirely through seed crystal growth. This completely solves the problems of uncontrollable nucleation and wide particle size and morphology distribution in traditional co-precipitation methods, ensuring high consistency and reproducibility in batch production.

[0017] In step S4, the oxidant is hydrogen peroxide, and its addition amount is 105%~115% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate. The precipitation reaction temperature is 55~85℃, and the reaction time is 0.5~1.5h. The precipitation reaction is carried out under stirring conditions at a stirring speed of 15~25 Hz. This step is a key execution stage for achieving precise control of the morphology and particle size of the ferric phosphate product. In this step, a co-current co-precipitation method is used, where the remaining refined ferrous filtrate and oxidant are continuously and uniformly added to the reaction substrate containing the seed template to precisely control the supersaturation of the reaction system, maintaining it at an optimal window below the homogeneous nucleation critical value but above the concentration required for seed growth. This completely suppresses explosive homogeneous nucleation, avoiding the generation of small, disordered new crystal nuclei; at the same time, all newly generated ferric phosphate molecules (FePO4) are epitaxially deposited on the surface of the pre-added crude ferric phosphate seed crystals only through heterogeneous nucleation, thereby achieving controllable growth of ferric phosphate crystals. The "co-precipitation" process in this step, in synergy with the "seed induction" technique in step S3, ensures that the lamellar morphology of the crude ferric phosphate seed crystals is replicated and amplified, ultimately yielding lamellar ferric phosphate (FePO4·2H2O) with uniform composition, concentrated particle size distribution, and regular morphology. Furthermore, this invention preferably conducts the precipitation reaction at a temperature of 55–85°C and a stirring speed of 15–25 Hz for 0.5–1.5 h, further optimizing crystallinity and particle dispersibility, providing the optimal reaction environment for obtaining a lamellar ferric phosphate product with uniform particle size.

[0018] In step S5, the calcination temperature is 500-800℃, and the calcination time is 1-3 hours. At this optimized temperature of 500-800℃, the water of crystallization in the precursor is completely removed, achieving a complete phase transformation from ferric phosphate dihydrate (FePO4·2H2O) to anhydrous ferric phosphate (FePO4). Simultaneously, the calcination process involves high-temperature annealing, effectively repairing defects within the ferric phosphate crystals and significantly improving the crystallinity of the ferric phosphate product, thereby giving ferric phosphate higher structural and chemical stability.

[0019] A second aspect of the present invention provides a method for preparing lithium iron phosphate, comprising mixing the layered iron phosphate with a lithium source and a carbon source, ball milling the mixture, and sintering it under an inert atmosphere to obtain lithium iron phosphate. The lithium source is lithium carbonate, and the carbon source is at least one of glucose and polyethylene glycol. The molar ratio of iron phosphate to lithium carbonate is Fe:Li = 1:1.01~1.05. The amount of carbon source added is 4~6% of the mass of the iron phosphate. The sintering temperature is 700~800℃, and the sintering time is 6~10 h.

[0020] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0021] This invention proposes using readily available crude iron phosphate as seed crystals. By combining "seed induction" and "co-current co-precipitation" processes, the nucleation and growth process of iron phosphate crystals is effectively controlled, successfully preparing large-particle-size lamellar iron phosphate products with uniform particle size to improve the compaction density and electrochemical performance of battery cathodes. This method is simple, low-cost, and easy to industrialize. The preparation method of this invention can effectively change the morphology of iron phosphate and increase the particle size of the finished iron phosphate product, improve the product qualification rate, reduce washing water consumption, and has significant value for technological production applications. Attached Figure Description

[0022] Figure 1 This is a SEM image of the lamellar iron phosphate prepared according to the present invention;

[0023] Figure 2 This is the XRD pattern of the lamellar iron phosphate prepared according to the present invention;

[0024] Figure 3 These are the charge-discharge curves of lithium iron phosphate in Examples 1, 4 and Comparative Example 1 of this invention. Detailed Implementation

[0025] The embodiments of this application will now be described in more detail. This application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the application. It should be understood that the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0026] Example 1:

[0027] 1. A method for preparing layered iron phosphate, comprising the following steps:

[0028] S1: Prepared by reacting pure iron blocks with 35wt% phosphoric acid at 60℃ for 24h, and then preparing a ferrous phosphate mixture; wherein the molar ratio of iron to phosphorus is Fe∶P=1∶2;

[0029] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0030] S3: Take a portion of the refined ferrous filtrate obtained in step S2 and add crude ferric phosphate as seed crystals. The amount added is calculated based on iron element, and the molar ratio of crude ferric phosphate to iron element in the refined ferrous filtrate is 1:10. After mixing evenly, it is used as the reaction base liquid. The volume of the refined ferrous filtrate accounts for 1 / 10 of the total volume of the refined ferrous filtrate obtained in step S2.

[0031] S4: Under stirring conditions at a speed of 20 Hz, the remaining portion of the refined ferrous filtrate and the oxidant are continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. The precipitation reaction temperature is 75℃, and the reaction time is 1 h. After the reaction is completed, the precipitate is collected and washed to obtain crude ferric phosphate. The oxidant is hydrogen peroxide, and its addition amount is 110 mol% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

[0032] S5: The crude iron phosphate obtained in step S4 is calcined at a temperature of 550°C for 3 hours to obtain battery-grade layered iron phosphate.

[0033] 2. A method for preparing lithium iron phosphate, comprising mixing the above-mentioned lamellar iron phosphate with a lithium source and a carbon source and then ball milling the mixture, wherein the lithium source is lithium carbonate, the carbon source is glucose, the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.01, the amount of carbon source added is 4% of the mass of iron phosphate, and sintering is carried out under an inert atmosphere at a temperature of 700℃ for a time of 6h to obtain lithium iron phosphate powder.

[0034] Example 2:

[0035] 1. A method for preparing layered iron phosphate, comprising the following steps:

[0036] S1: Prepared by reacting iron powder with 30wt% phosphoric acid at 50℃ for 24h, and then preparing a ferrous phosphate mixture; wherein the molar ratio of iron to phosphorus is Fe∶P=1∶1.8;

[0037] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0038] S3: Take a portion of the refined ferrous filtrate obtained in step S2 and add crude ferric phosphate as seed crystals. The amount added is calculated based on iron element, and the molar ratio of crude ferric phosphate to iron element in the refined ferrous filtrate is 0.5:10. After mixing evenly, it is used as the reaction base liquid. The volume of the refined ferrous filtrate accounts for 1 / 20 of the total volume of the refined ferrous filtrate obtained in step S2.

[0039] S4: Under stirring conditions at a stirring speed of 20 Hz, the remaining portion of the refined ferrous filtrate and the oxidant are continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. The precipitation reaction temperature is 55℃, and the reaction time is 0.5 h. After the reaction is completed, the precipitate is collected and washed to obtain crude ferric phosphate. The oxidant is hydrogen peroxide, and its addition amount is 105 mol% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

[0040] S5: The crude iron phosphate obtained in step S4 is calcined at a temperature of 500℃ for 2 hours to obtain battery-grade layered iron phosphate.

[0041] 2. A method for preparing lithium iron phosphate, comprising mixing the above-mentioned lamellar iron phosphate with a lithium source and a carbon source and then ball milling the mixture, wherein the lithium source is lithium carbonate, the carbon source is polyethylene glycol, the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.03, the amount of carbon source added is 5% of the mass of iron phosphate, and sintering is carried out under an inert atmosphere at a temperature of 750℃ for 8 hours to obtain lithium iron phosphate powder.

[0042] Example 3:

[0043] 1. A method for preparing layered iron phosphate, comprising the following steps:

[0044] S1: Prepared by reacting pig iron blocks with 40wt% phosphoric acid at 70℃ for 36h, and then preparing a ferrous phosphate mixture; wherein the molar ratio of iron to phosphorus is Fe∶P=1∶2.2;

[0045] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0046] S3: Take a portion of the refined ferrous filtrate obtained in step S2 and add crude ferric phosphate as seed crystals. The amount added is calculated based on iron element, and the molar ratio of crude ferric phosphate to iron element in the refined ferrous filtrate is 1.5:10. After mixing evenly, it is used as the reaction base liquid. The volume of the refined ferrous filtrate accounts for 1 / 5 of the total volume of the refined ferrous filtrate obtained in step S2.

[0047] S4: Under stirring conditions at a speed of 20 Hz, the remaining portion of the refined ferrous filtrate and the oxidant were continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. The precipitation reaction temperature was 85℃, and the reaction time was 1.5 h. After the reaction was completed, the precipitate was collected and washed to obtain crude ferric phosphate. The oxidant was hydrogen peroxide, and its addition amount was 115 mol% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

[0048] S5: The crude iron phosphate obtained in step S4 is calcined at a temperature of 800℃ for 1 hour to obtain battery-grade layered iron phosphate.

[0049] 2. A method for preparing lithium iron phosphate, comprising mixing the above-mentioned layered iron phosphate with a lithium source and a carbon source and then ball milling the mixture, wherein the lithium source is lithium carbonate, the carbon source is glucose and polyethylene glycol, the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.05, the amount of carbon source added is 6% of the mass of iron phosphate, and sintering is carried out under an inert atmosphere at a temperature of 800℃ for 10h to obtain lithium iron phosphate powder.

[0050] Example 4:

[0051] 1. A method for preparing layered iron phosphate, comprising the following steps:

[0052] S1: Prepared by reacting pure iron blocks with 35wt% phosphoric acid at 60℃ for 24h, and then preparing a ferrous phosphate mixture; wherein the molar ratio of iron to phosphorus is Fe∶P=1∶2;

[0053] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0054] S3: Take a portion of the refined ferrous filtrate obtained in step S2 and add crude ferric phosphate as seed crystals. The amount added is calculated based on iron element, and the molar ratio of crude ferric phosphate to iron element in the refined ferrous filtrate is 1:10. After mixing evenly, it is used as the reaction base liquid. The volume of the refined ferrous filtrate accounts for 1 / 10 of the total volume of the refined ferrous filtrate obtained in step S2.

[0055] S4: Under stirring conditions at a stirring speed of 20 Hz, the remaining portion of the refined ferrous filtrate and the oxidant are continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. The precipitation reaction temperature is 55℃, and the reaction time is 1 h. After the reaction is completed, the precipitate is collected and washed to obtain crude ferric phosphate. The oxidant is hydrogen peroxide, and its addition amount is 110 mol% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

[0056] S5: The crude iron phosphate obtained in step S4 is calcined at a temperature of 550°C for 3 hours to obtain battery-grade layered iron phosphate.

[0057] 2. A method for preparing lithium iron phosphate, comprising mixing the above-mentioned lamellar iron phosphate with a lithium source and a carbon source and then ball milling the mixture, wherein the lithium source is lithium carbonate, the carbon source is glucose, the molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.01, the amount of carbon source added is 4% of the mass of iron phosphate, and sintering is carried out under an inert atmosphere at a temperature of 700℃ for a time of 6h to obtain lithium iron phosphate powder.

[0058] Comparative Example 1:

[0059] 1. A method for preparing ferric phosphate, using a single-inlet hydrogen peroxide solution, comprising the following steps:

[0060] S1: Prepared by reacting pure iron blocks with 35wt% phosphoric acid at 60℃ for 24h, and then preparing a ferrous phosphate mixture; wherein the molar ratio of iron to phosphorus is Fe∶P=1∶2;

[0061] S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate;

[0062] S3: Under stirring conditions at a speed of 20 Hz, the oxidant was continuously added to the refined ferrous filtrate to carry out a precipitation reaction. The precipitation reaction temperature was 70℃, and the reaction time was 1 h. After the reaction was completed, the precipitate was collected and washed to obtain crude ferric phosphate. The oxidant was hydrogen peroxide, and the amount added was 110 mol% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

[0063] S4: The crude iron phosphate obtained in step S3 is calcined at a temperature of 550°C for 2 hours to obtain battery-grade iron phosphate.

[0064] 2. The above-mentioned iron phosphate was mixed with lithium source and carbon source and then ball-milled. The lithium source was lithium carbonate and the carbon source was glucose. The molar ratio of iron phosphate to lithium carbonate was Fe:Li=1:1.01. The amount of carbon source added was 4% of the mass of iron phosphate. Sintering was carried out under an inert atmosphere at a temperature of 700℃ for 6 hours to obtain lithium iron phosphate powder.

[0065] from Figure 1 and Figure 2 It can be seen that the embodiments of the present invention successfully prepared battery-grade iron phosphate, and the prepared battery-grade iron phosphate has a lamellar structure with a particle size in the micrometer range. The lamellars are arranged regularly and tightly, and a small number of small-sized lamellae exist on the surface. Table 1 is a comparison table of the iron phosphate particle size of the embodiments and comparative examples of the present invention. As can be seen from Table 1, the iron phosphate particle size prepared by Example 1 using dual liquid inlet is significantly larger than that of the iron phosphate particle size of Comparative Example 1 using single liquid inlet. In addition, the physicochemical analysis of the battery-grade iron phosphate prepared in Examples 1-4 was performed, and the test results are shown in Table 2. Table 2 shows that the iron-to-phosphorus ratio (Fe / P) and other elements of the iron phosphate prepared in Examples 1-4 of the present invention meet the corresponding requirements.

[0066] Electrical performance testing method: First, battery assembly was performed. Lithium iron phosphate powder, polyvinylidene fluoride (PVDF), and conductive carbon obtained in Examples 1, 4, and Comparative Example 1 were poured into a homogenizer at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added for homogenization. The slurry was then uniformly coated onto aluminum foil and dried in a vacuum oven for 24 hours. The dried material was sliced ​​to obtain a positive electrode sheet, and its active material loading was calculated. The battery was assembled in the order of positive electrode shell, positive electrode sheet, separator, lithium sheet, gasket, spring sheet, and negative electrode shell, and an appropriate amount of electrolyte was added. The cells were then encapsulated to obtain a coin cell. The electrical performance of the coin cells assembled from lithium iron phosphate obtained in Examples 1, 4, and Comparative Example 1 was then tested using a Newway battery testing system, with a voltage range of 2.5~4.3V at room temperature.

[0067] Figure 3 The figures show the 0.1C charge-discharge curves of the coin cells containing the cathode materials prepared in Example 1, Comparative Example 1, and Example 4. A comparison reveals that the charge-discharge specific capacity of the coin cells containing lithium iron phosphate prepared in Example 1 is significantly higher, as is the compaction density. This indicates that the charge-discharge specific capacity and compaction performance of the coin cells containing lithium iron phosphate prepared in Example 1 are significantly improved. This may be because the iron phosphate in Example 1 is a tightly packed lamellar structure, which facilitates both improved compaction and easier lithium-ion insertion / extraction, thereby enhancing the electrochemical activity of the cathode material and increasing both the battery compaction density and specific capacity.

[0068] Table 1. Comparison of ferric phosphate particle size between embodiments and comparative examples of the present invention.

[0069]

[0070] Table 2 Test results of iron phosphate in the embodiments of the present invention

[0071]

[0072] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A method for preparing layered iron phosphate, characterized in that, Includes the following steps: S1: Prepare a ferrous phosphate solution; S2: Filter the ferrous phosphate mixture obtained in step S1 to obtain a refined ferrous filtrate; S3: Take a portion of the refined ferrous filtrate obtained in step S2, add crude ferric phosphate as seed crystals, mix well and use it as the reaction base liquid; S4: Under stirring conditions, the remaining portion of the refined ferrous filtrate and the oxidant are continuously and concurrently added to the reaction substrate to carry out a precipitation reaction. After the reaction is completed, the precipitate is collected, washed, and crude ferric phosphate is obtained. S5: Calcine the crude iron phosphate obtained in step S4 to obtain battery-grade layered iron phosphate.

2. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S1, the ferrous phosphate mixture is prepared by reacting an iron source with phosphoric acid at a concentration of 30-40 wt% at 50-70°C for 12-36 hours; wherein the iron source includes pure iron blocks, iron powder, and pig iron blocks.

3. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In the ferrous phosphate mixture, the molar ratio of iron to phosphorus is Fe∶P=1∶1.8~2.

2.

4. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S3, the volume of the refined ferrous filtrate accounts for 1 / 20 to 1 / 5 of the total volume of the refined ferrous filtrate obtained in step S2.

5. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, The amount of crude ferric phosphate added, calculated as iron element, has a molar ratio of 0.5~1.5:10 with the iron element in the partially refined ferrous filtrate.

6. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S4, the oxidant is hydrogen peroxide, and the amount added is 105% to 115% of the theoretical amount required to completely oxidize the ferrous ions in the refined ferrous filtrate.

7. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S4, the precipitation reaction is carried out at a temperature of 55~85℃ for 0.5~1.5h.

8. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S4, the precipitation reaction is carried out under stirring conditions at a stirring speed of 15-25 Hz.

9. The method for preparing lamellar ferric phosphate according to claim 1, characterized in that, In step S5, the calcination temperature is 500~800℃ and the calcination time is 1~3h.

10. A method for preparing lithium iron phosphate, characterized in that, The lamellar iron phosphate described in any one of claims 1 to 9 is mixed with a lithium source and a carbon source and then ball-milled and sintered under an inert atmosphere to obtain lithium iron phosphate.

11. The method for preparing lithium iron phosphate according to claim 10, characterized in that, The lithium source is lithium carbonate, and the carbon source is at least one of glucose and polyethylene glycol.

12. The method for preparing lithium iron phosphate according to claim 10, characterized in that, The molar ratio of iron phosphate to lithium carbonate is Fe∶Li=1∶1.01~1.

05.

13. The method for preparing lithium iron phosphate according to claim 10, characterized in that, The amount of carbon source added is 4-6% of the mass of the iron phosphate.

14. The method for preparing lithium iron phosphate according to claim 10, characterized in that, The sintering temperature is 700~800℃, and the sintering time is 6~10h.

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