A method for preparing titanium-doped iron phosphate

Abstract

The application belongs to the technical field of phosphate inorganic materials, and relates to a method for preparing titanium-doped iron phosphate. The method comprises the following steps: S1, preparing a titanium-containing iron phosphate complex solution; S2, mixing a part of the titanium-doped iron phosphate complex solution obtained in S1 with water, heating and controlling the temperature to be between 60-150 DEG C, and keeping warm for 10 min-2 h to form a titanium-doped iron phosphate suspension; S3, adding the remaining titanium-containing iron phosphate complex solution into the suspension obtained in S2, heating and controlling the temperature to be between 60-150 DEG C, keeping warm for 10 min-24 h, and performing solid-liquid separation to obtain a titanium-doped iron phosphate hydrate. The method can improve the yield of titanium-doped iron phosphate, increase the titanium doping amount, and overcome the problem that increasing the input amount of titanium compounds leads to a sharp reduction in the yield of iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of phosphate inorganic material preparation, specifically relating to a method for preparing titanium-doped iron phosphate. Background Technology

[0002] Due to its advantages such as lower raw material costs, higher operating voltage platform and thermal stability, and excellent electrochemical cycle performance, the demand for lithium iron phosphate (LiFePO4) batteries in the fields of power batteries and energy storage is experiencing explosive growth. In the LiFePO4 crystal structure, lithium ions have a one-dimensional diffusion channel, while FeO6 octahedra are surrounded by PO4. 3- The tetrahedral structure prevents the formation of a continuous FeO6 octahedral network, resulting in low electronic conductivity and ion mobility. Surface carbon coating can effectively improve the electronic conductivity of the material; however, a high amount of carbon coating tends to reduce the material's compaction density, thereby reducing the energy density of the power battery.

[0003] To address the aforementioned issues, LiFePO4 materials can be modified through ion doping. Ion doping refers to doping the LiFePO4 lattice with certain highly conductive metal ions (such as Ti, V, and Ni) to reduce the conductivity of Li. + The resistance to diffusion along a one-dimensional path promotes the migration and diffusion of lithium ions and electrons, thereby improving the rate performance and electrochemical performance of LiFePO4 materials.

[0004] CN 117842954 A describes the preparation of titanium ion-doped iron phosphate by mixing soluble titanium salt, iron phosphate dihydrate, and a solvent, followed by high-temperature sintering. However, this process may suffer from uneven titanium ion dispersion during industrialization.

[0005] CN 119018867 A describes the preparation of titanium-doped iron phosphate precursors by uniformly mixing phosphorus, iron, and titanium sources and then combining this with a hydrothermal reaction. However, the hydrothermal reaction requires high temperature and high pressure conditions, making large-scale industrialization difficult. Summary of the Invention

[0006] The applicant investigated a method for doping titanium and vanadium during the preparation of ferric phosphate using ferric phosphate complex decomposition, a method described in another patent application. However, during the preparation of titanium-doped ferric phosphate materials, the applicant discovered that increasing the amount of titanium compound used to obtain a high titanium doping level resulted in an inverse relationship between increasing titanium content and the yield of titanium-doped ferric phosphate. Specifically, increasing the amount of titanium compound used could lead to a sharp decrease in the ferric phosphate yield or require an excessively long decomposition and crystallization reaction time, but the increase in titanium doping level was not significant. This is highly detrimental to the industrial production of titanium-doped ferric phosphate products, especially for the preparation of high-titanium-doped ferric phosphate products.

[0007] This invention provides a simple and low-cost method for preparing titanium-doped iron phosphate with high titanium doping content, uniform doping, and high yield.

[0008] This application provides a method for preparing titanium-doped iron phosphate, the method comprising:

[0009] S1. Preparation of titanium-containing ferric phosphate complex solution: The titanium-containing ferric phosphate complex solution is prepared by any one of the following methods 1-4:

[0010] Method 1: Add the titanium compound to the iron phosphate complex solution, heat and stir, and mix at a temperature controlled between 60-160℃ to obtain the final product;

[0011] Method 2: Ferric oxide, 35-85 wt% phosphoric acid solution, and titanium compound are directly mixed and reacted, with the reaction temperature controlled between 60-160℃;

[0012] Method 3: First mix ferric oxide with 35-85wt% phosphoric acid solution, then add titanium compound to mix and react. The reaction temperature is controlled between 60-160℃.

[0013] Method 4: First mix the titanium compound with 35-85wt% phosphoric acid solution, then add it to the mixture with ferric oxide, and react at a temperature controlled between 60-160℃.

[0014] S2. Preparation of titanium-doped iron phosphate hydrate suspension: Take a portion of the titanium-doped iron phosphate complex solution obtained in S1, mix it with water, heat and control the temperature between 60-150℃, keep it at this temperature for 10 min-2 h to form a titanium-doped iron phosphate hydrate suspension. The volume of the titanium-doped iron phosphate complex solution taken out from S1 is 3-20% of the total volume of the titanium-doped iron phosphate complex solution obtained in S1.

[0015] S3. Preparation of titanium-doped iron phosphate: Add the remaining titanium-doped iron phosphate complex solution obtained in S1 to the suspension obtained in S2, heat and control the temperature between 60-150℃, keep warm for 10min-24h, and separate the solid and liquid to obtain titanium-doped iron phosphate hydrate.

[0016] in,

[0017] In step S1, the phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1. In the method for preparing the iron phosphate complex solution or the titanium-containing iron phosphate complex solution, the molar ratio of phosphoric acid to ferric oxide is based on this phosphorus-to-iron ratio to form an environment with a strong acid pH and a phosphoric acid-to-iron molar ratio of at least 2.5:1, in order to form the iron phosphate complex solution.

[0018] According to the present invention, in step S1, the molar ratio of doped titanium to iron is (0.01-0.2):1, preferably (0.05-0.2):1.

[0019] According to the present invention, in step S1, the reaction temperature is preferably controlled between 70-110°C. Higher temperature is beneficial to increase the reaction rate, but excessively high temperature leads to higher energy consumption and higher operational risks.

[0020] According to the present invention, in step S1, the titanium compound is metatitanic acid, nano-titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate; preferably, the titanium compound is metatitanic acid, nano-titanium dioxide, or titanium oxysulfate.

[0021] According to the present invention, the volume of water used in step S2 is 0.5-10 times the volume of the titanium-containing iron phosphate complex solution, preferably 0.5-4 times; the preferred reaction temperature is 70-110°C, and the reaction time is 0.5-1.5 h.

[0022] In step S2, the titanium-containing iron phosphate complex solution is mixed with a large amount of water, which causes the titanium-doped iron phosphate hydrate to precipitate rapidly and form a (solid-liquid) suspension.

[0023] According to the present invention, in step S3, the remaining titanium-containing iron phosphate complex solution obtained in step S1 can be added at once or in batches continuously; the reaction temperature is preferably 70-110°C, and the reaction time is 1-10h.

[0024] Furthermore, the preparation method further includes:

[0025] S4. Reuse the mother liquor obtained from S3 filtration to replace 35-85 wt% of phosphoric acid in the preparation of the titanium-containing iron phosphate complex solution in step S1.

[0026] The mother liquor filtered in step S3 contains substances such as titanium, iron phosphate complex, and phosphoric acid. It can be returned to step S1 to replace 35-85 wt% of the phosphoric acid. As long as the phosphorus-to-iron ratio and the molar ratio of doped titanium to iron are controlled within the ranges specified above during reuse, it will be fine.

[0027] As an alternative, this application also provides a method for preparing titanium-doped iron phosphate, comprising the following steps:

[0028] S1. Prepare a titanium-containing ferric phosphate complex solution; the titanium-containing ferric phosphate complex solution is prepared by any one of the following methods 1-4:

[0029] Method 1: Add the titanium compound to the iron phosphate complex solution, heat and stir, and mix at a temperature controlled between 60-160℃ to obtain the final product;

[0030] Method 2: Ferric oxide, 35-85 wt% phosphoric acid solution, and titanium compound are directly mixed and reacted, with the reaction temperature controlled between 60-160℃;

[0031] Method 3: First mix ferric oxide with 35-85wt% phosphoric acid solution, then add titanium compound to mix and react. The reaction temperature is controlled between 60-160℃.

[0032] Method 4: First mix the titanium compound with 35-85wt% phosphoric acid solution, then add it to the mixture with ferric oxide, and react at a temperature controlled between 60-160℃.

[0033] S22. Mix titanium-doped iron phosphate hydrate seed crystals with water to form a suspension containing titanium-doped iron phosphate hydrate.

[0034] S33. Add the titanium-containing iron phosphate complex solution obtained in S1 to the suspension in S22, heat and control the temperature at 60-150℃, react for 10 min-24 h, separate the solid and liquid, and prepare titanium-doped iron phosphate hydrate.

[0035] The volume ratio of water in S22 to the volume of titanium-containing iron phosphate complex solution in S33 is between 1:2 and 4:1.

[0036] According to the present invention, in step S1, the molar ratio of titanium to iron in the titanium-containing iron phosphate complex solution is (0.01-0.2):1, and the phosphorus-iron ratio is (2.5-8):1.

[0037] Preferably, in step S22, the titanium-doped iron phosphate hydrate seed crystals are nanoparticles or microparticles, which are prepared by grinding or direct preparation.

[0038] In some embodiments of the present invention, titanium-doped iron phosphate hydrate seed crystals are obtained by mixing a titanium-doped iron phosphate complex solution with 5-40 times its volume of water, heating to 60-160°C for 10 min-1 h, to obtain a titanium-doped iron phosphate hydrate crystal suspension, followed by solid-liquid separation to obtain titanium-doped iron phosphate hydrate particles as seed crystals, i.e., titanium-doped iron phosphate hydrate seed crystals. The titanium-doped iron phosphate complex solution can be prepared using any of the aforementioned methods 1-4.

[0039] As an alternative, the suspension obtained in step S2, the suspension before solid-liquid separation in step S3, or the suspension before solid-liquid separation in step S33 can be directly used. This suspension, mixed with water, serves as the suspension for step S22 and can then be used as the seed suspension for the next batch of titanium-doped iron phosphate preparation. For example, a large quantity of nanocrystalline suspension can be prepared in advance according to step S2, and used in batches, diluted with water to form a seed suspension, which can then be used as the seed for the next batch of titanium-doped iron phosphate preparation. Another example: the suspension obtained in step S3 or S33 before solid-liquid separation can be used in batches, diluted with water to form a seed suspension, which can then be used as the seed for the next batch of titanium-doped iron phosphate preparation. In these alternatives, the volume ratio of water to the volume of the titanium-doped iron phosphate complex solution added during the preparation of the next batch of titanium-doped iron phosphate is between 1:2 and 4:1.

[0040] This application provides a method for preparing titanium-doped lithium iron phosphate cathode material, the method comprising:

[0041] The titanium-doped iron phosphate prepared by the aforementioned method was mixed with a lithium source and a carbon source, and then calcined at high temperature to prepare a titanium-doped lithium iron phosphate cathode material.

[0042] the term

[0043] Ferric phosphate dihydrate: also known as ferric phosphate dihydrate, ferric phosphate dihydrate, ferric phosphate dihydrate or ferric phosphate dihydrate, is ferric phosphate containing two water molecules of crystallization. When ferric phosphate precipitates from solution, it often contains two water molecules of crystallization. In this application, ferric phosphate sometimes refers to ferric phosphate dihydrate.

[0044] Titanium-doped iron phosphate: Titanium is doped into iron phosphate crystals to form titanium-doped iron phosphate. Titanium-doped iron phosphate dihydrate is titanium-doped iron phosphate containing two molecules of water of crystallization.

[0045] Titanium compound: In this application, it refers to a raw material compound used for titanium doping, which contains titanium and other non-metallic elements.

[0046] Ferric phosphate complex: Ferric phosphate-phosphoric acid complex formed by ferric phosphate and phosphoric acid exists in solution form. In ferric phosphate complex solutions, phosphoric acid is in excess (molar ratio of phosphoric acid to iron greater than 2.5:1), and the acidity is high (pH value below 1, or even below 0). The phosphorus-iron ratio in the ferric phosphate complex solution essentially corresponds to the molar ratio of phosphoric acid to iron in the reactants.

[0047] Titanium-containing ferric phosphate complex solution: A solution of ferric phosphate complex containing a soluble titanium compound dispersed in the solution. The titanium-containing ferric phosphate complex solution can be prepared by directly dispersing the soluble titanium compound in the complex solution, or by reacting the titanium compound with phosphoric acid during the synthesis of the ferric phosphate complex, thereby dispersing it in the ferric phosphate complex solution. In this application, it is sometimes also referred to as a titanium-containing ferric phosphate complex solution, or simply a titanium-containing ferric phosphate complex solution.

[0048] Titanium-doped iron phosphate hydrate seed crystals: These are essentially titanium-doped iron phosphate hydrate particles. In this application, they refer to titanium-doped iron phosphate hydrate particles (solid particles) used as seed crystals for the production of the next batch of titanium-doped iron phosphate hydrate. There are two methods to obtain these seed crystals. The first method involves adding a small amount of titanium-doped iron phosphate complex solution to a large amount of water, heating it, rapidly decomposing the complex, and obtaining nano-sized particles (seed crystals) through solid-liquid separation. The second method involves using the previous batch of titanium-doped iron phosphate hydrate product, which is then ground and pulverized to obtain micron or nano-sized particles.

[0049] Iron oxide: also known as ferric oxide.

[0050] Phosphorus-iron ratio: refers to the molar ratio (molar ratio) of phosphorus to iron.

[0051] The next batch: refers to the batch that follows the previous batch in the preparation process of at least two batches.

[0052] When the amount of substance, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, the phosphorus-to-iron ratio in ferric phosphate is (2.5-8):1, where the numerical range of (2.5-8):1 includes values ​​at endpoints and intermediate points such as 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, or 8:1. The range of (0.01-0.2):1 in the statement "the molar ratio of titanium to iron is (0.01-0.2):1" includes the endpoints and midpoints of values ​​such as 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1, and 0.20:1. The range of 3-20% includes midpoints of values ​​such as 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, and 19%. The addition of water in the range of "0.5-10" or "0.5-4" times should be understood as meaning that multiples of 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 can achieve the inventive purpose and effect of this invention (also covering the endpoints and intermediate points covered by 0.5-4). A volume ratio of 1:2 to 4:1 should be understood as including endpoints and intermediate points such as 1:2, 1:1, 2:1, 3:1, and 4:1. The reaction temperature range of 60-160℃ includes values ​​such as 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, and 155℃. Similarly, the temperature ranges of 60-150℃ and 70-110℃ should also include the midpoints of these values, such as 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, and 145℃ (also covering the endpoints and midpoints of the 70-110℃ range).The reaction time range of 10 min to 24 h includes intermediate points such as 20 min, 30 min, 40 min, 50 min, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, and 23 h. Similarly, the range of 0.5 h to 1.5 h and 1 h to 10 h also includes intermediate points between the endpoints.

[0053] Beneficial Effects: This application provides a method for uniformly doping titanium metal element into iron phosphate. The invention utilizes a method of decomplexing an iron phosphate complex solution to obtain an atomically titanium-doped iron phosphate product. More importantly, the method provided in this application can improve the yield of titanium-doped iron phosphate while simultaneously increasing the titanium doping amount. This overcomes the problem that increasing the amount of titanium compound input leads to a sharp decrease in iron phosphate yield. Furthermore, this method has the advantage of not significantly altering the iron phosphate synthesis method, maximizing the utilization of the original iron phosphate complex solution decomplexing process and equipment for producing iron phosphate, and reducing the cost of industrial production. Attached Figure Description

[0054] Figure 1 This is an EDS mapping diagram of the elemental distribution of the titanium-doped iron phosphate product in Example 3.

[0055] Figure 2 This is the XRD pattern of Example 3. Detailed Implementation

[0056] The purpose of this application is to provide an improved method for preparing titanium-doped iron phosphate. The specific implementation includes two parts: the first part is a comparative example (hereinafter referred to as the "simple method"), and the second part is an example embodying the method of the present invention (hereinafter referred to as the "seed method"). It should be noted that the comparative example is also a novel preparation method, which has been separately applied for. To demonstrate the innovativeness of the present invention, relevant examples of the simple method are introduced as comparative examples to provide a basis for comparison.

[0057] Comparative Example 1

[0058] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 0.3812 g (0.0039 mol) of metatitanic acid to the mixture and incubate at 90 °C for 1 h to allow the metatitanic acid to dissolve completely. Then add 7.9845 g of ferric oxide powder to the titanium-containing phosphoric acid solution and incubate at 90 °C for 3 h. After incubation, filter to obtain a purple-red filtrate. Add 100 mL of water to the purple-red complex solution and incubate at 100 °C for 4 h to stop the reaction. After filtration, washing, and drying, obtain titanium-doped iron phosphate dihydrate powder, weighed to a mass of 0.1004 g, with a yield of 0.54%.

[0059] Comparative Example 2

[0060] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 7.9845 g of ferric oxide powder to the mixture and incubate at 90 °C for 3 h. After incubation, filter to obtain a purple-red filtrate. Weigh 0.5 g (0.0031 mol) of titanium oxysulfate powder and add it to the ferric phosphate complex solution. Incubate at 90 °C for 40 min. After incubation, filter the mixture to obtain a Ti-containing ferric phosphate complex solution. Add 100 mL of water to the titanium-containing ferric phosphate complex solution and incubate at 90 °C for 4 h to stop the reaction. Then filter, wash, and dry to obtain titanium-doped ferric phosphate dihydrate powder, weighed to be 0.0807 g, with a yield of 0.43%.

[0061] Comparative Example 3

[0062] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 7.9845 g of ferric oxide powder to the mixture and incubate at 90℃ for 3 h. After incubation, filter to obtain a purple-red filtrate. Weigh 0.1 g (0.0006 mol) of titanium oxysulfate powder and add it to the ferric phosphate complex solution. Incubate at 90℃ for 40 min. After incubation, filter the mixture to obtain a ferric phosphate complex solution containing dissolved Ti. Add 50 mL of deionized water to the ferric phosphate complex solution containing dissolved Ti and incubate at 90℃ for 6 h. The precipitate mass is 7.2168 g. ICP test shows a titanium content of 788 ppm.

[0063] Comparative Example 4

[0064] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a 9 mol / L phosphoric acid solution. Add 0.2043 g (0.002 mol) of metatitanic acid to the phosphoric acid solution, heat to 90°C, and keep at this temperature for 1 h to allow the metatitanic acid to completely dissolve. Accurately weigh 7.9845 g of iron oxide powder and add it to the titanium-containing phosphoric acid solution. Heat the system to 90°C and keep at this temperature for 3 h. After the reaction is complete, filter the system to obtain a purple-red iron phosphate complex solution. Add 50 mL of H2O to the purple-red complex solution and keep at 100°C for 15 h to obtain a white precipitate with a mass of 7.8761 g. ICP test showed that the titanium content was 2940 ppm. In Comparative Example 4, after keeping at 100°C for 6 h, very little product was observed; further reaction was needed to obtain more product.

[0065] A comparison of Comparative Examples 1-3 shows that increasing the amount of titanium significantly reduces the yield of titanium-doped iron phosphate. The inventors have not yet determined the exact reason for this. A comparison of Comparative Example 4 and Comparative Example 3 indicates that increasing the amount of titanium significantly slows down the rate of decomposition and formation of titanium-doped iron phosphate from the titanium-containing iron phosphate complex. Consequently, Comparative Example 4 requires a reaction time of 15 hours to achieve a yield comparable to that of Comparative Example 3.

[0066] Example 1

[0067] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 0.3812 g (0.0039 mol) of metatitanic acid to the mixture and incubate at 90 °C for 1 h to allow the metatitanic acid to dissolve completely. Then add 7.9845 g of ferric oxide powder to the titanium-containing phosphoric acid solution and incubate at 90 °C for 3 h. After incubation, filter to obtain a purple-red filtrate, which is the ferric phosphate complex solution of dissolved Ti. Take 6 mL of the ferric phosphate complex solution of dissolved Ti and add it to 100 mL of deionized water. Turbidity appears after addition. After incubation at 100 °C for 1 h, pump the remaining 44 mL of the ferric phosphate complex solution of dissolved Ti into the system at a pump rate of 1 mL / min. After pumping, incubate at 100 °C for 4 h to stop the reaction. After filtration, washing, and drying, titanium-doped iron phosphate dihydrate powder was obtained, weighed to a mass of 11.3767 g, and the Ti content was determined to be 10595.78 ppm by ICP testing.

[0068] Compared with Comparative Example 1, the method (seed method) of Example 1 increased the yield of iron phosphate by 113 times. Although the Ti content of Comparative Example 1 could not be accurately measured due to its low yield, the Ti content of Example 1 reached 10595.78 ppm, far exceeding the target doping amount of 4000 ppm.

[0069] Example 2

[0070] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 7.9845 g of ferric oxide powder to the mixture and incubate at 90℃ for 3 h. After incubation, filter to obtain a purple-red filtrate. Weigh 0.5 g of titanium oxysulfate powder and add it to the ferric phosphate complex solution. Incubate at 90℃ for 40 min. After incubation, filter the mixture to obtain a ferric phosphate complex solution containing dissolved Ti. Take 6 mL of the ferric phosphate complex solution containing dissolved Ti and add it to 100 mL of deionized water. Turbidity appears after addition. Incubate at 90℃ for 1 h. Then, pump the remaining 44 mL of the ferric phosphate complex solution containing dissolved Ti into the system at a pump rate of 6 mL / min. After pumping, incubate at 90℃ for 4 h and then stop the reaction. The product mass is 13.7547 g, which is 170 times that of the simple method. ICP test shows that the Ti content is 5966.49 ppm.

[0071] Compared with Comparative Example 2, Example 2 showed that the method (seed method) yielded 170 times more iron phosphate. Although the Ti content could not be accurately measured in Comparative Example 2 due to its low yield, Example 2 achieved a Ti content of 5966.49 ppm, far exceeding the target doping level of 4000 ppm.

[0072] Example 3

[0073] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 7.9845 g of ferric oxide powder to the mixture and incubate at 90℃ for 3 h. After incubation, filter to obtain a purple-red filtrate. Weigh 0.7 g of titanium oxysulfate powder and add it to the ferric phosphate complex solution. Incubate at 90℃ for 40 min. After incubation, filter the mixture to obtain a ferric phosphate complex solution containing dissolved Ti. Take 6 mL of the ferric phosphate complex solution containing dissolved Ti and add it to 100 mL of deionized water. Turbidity appears after addition. Incubate at 100℃ for 1 h. Then, pump the remaining 44 mL of the ferric phosphate complex solution containing dissolved Ti into the system at a pump rate of 6 mL / min. After pumping, incubate at 100℃ for 4 h and then stop the reaction. The product mass is 12.1148 g, and the Ti content determined by ICP is 8051.22 ppm. The elemental distribution map (EDS mapping) of the obtained titanium-doped ferric phosphate particles is shown in [reference needed]. Figure 1 The XRD pattern of titanium-doped iron phosphate is shown in [reference needed]. Figure 2 .

[0074] Example 4

[0075] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 7.9845 g of ferric oxide powder to the mixture and incubate at 90 °C for 3 h. After incubation, filter to obtain a purple-red filtrate. Weigh 0.3 g (0.0018 mol) of titanium oxysulfate powder and add it to the ferric phosphate complex solution. Incubate at 90 °C for 40 min. After incubation, filter the mixture to obtain a ferric phosphate complex solution containing dissolved Ti. Take 6 mL of the ferric phosphate complex solution containing dissolved Ti and add it to 100 mL of deionized water. Turbidity appears after addition. Incubate at 90 °C for 30 min. Then, pump the remaining 44 mL of the ferric phosphate complex solution containing dissolved Ti into the system at a pump rate of 1 mL / min. After pumping, incubate at 90 °C for 4 h and then stop the reaction. The product mass is 13.6460 g, and the Ti content is 4213 ppm according to ICP test.

[0076] Example 5

[0077] Take 31 mL of 85% phosphoric acid solution and add 19 mL of deionized water to form a mixed solution. Add 0.3812 g (0.0039 mol) of metatitanic acid to the solution and incubate at 90 °C for 1 h to allow the metatitanic acid to dissolve completely. Then add 7.9845 g of ferric oxide powder to the titanium-containing phosphoric acid solution and incubate at 90 °C for 3 h. After incubation, filter to obtain a purple-red filtrate. Take 6 mL of the ferric phosphate complex solution containing dissolved Ti and add it to 100 mL of deionized water. Turbidity appears after addition. After incubation at 100 °C for 1 h, pump the remaining 44 mL of the ferric phosphate complex solution containing dissolved Ti into the system at a pump rate of 1 mL / min. After pumping, incubate at 100 °C for 4 h to stop the reaction, obtaining a slurry of titanium-doped ferric phosphate dihydrate. This slurry is used as a seed crystal for other batches of synthesis.

[0078] Take 12 mL of the slurry, add 50 mL of water, and then slowly pour in 50 mL of freshly prepared complex solution containing dissolved Ti (repeating the previous method for preparing the complex to obtain a fresh 50 mL complex solution). Keep warm at 100℃ for 4 h to obtain titanium-doped ferric phosphate dihydrate. After filtration, washing, drying, and weighing, the mass is 3.6727 g.

[0079] Although the yield of Example 5 was not ideal, it was significantly improved compared with Comparative Example 1 and Comparative Example 2 within the same reaction time.

[0080] Comparing the results of Examples 1-4, the yield of iron phosphate obtained using the simple method (non-seed method) decreases with increasing addition of titanium compounds, and the reaction time is prolonged. More importantly, the titanium doping level is difficult to reach above 4000 ppm, which cannot meet application requirements. However, the results of Examples 1-5 show that the seed method can achieve: 1) increased yield of titanium-doped iron phosphate, 2) increased titanium doping level, and 3) uniform titanium doping with atomic-level dispersion.

[0081] The above embodiments of the present invention, including those cited in previous patent applications, are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing titanium-doped iron phosphate, characterized in that, Includes the following steps: S1. Preparation of titanium-containing ferric phosphate complex solution: The titanium-containing ferric phosphate complex solution is prepared by any one of the following methods 1-4: Method 1: Add the titanium compound to the iron phosphate complex solution, heat and stir, and mix at a temperature controlled between 60-160℃ to obtain the final product; Method 2: Ferric oxide, 35-85 wt% phosphoric acid solution, and titanium compound are directly mixed and reacted, with the reaction temperature controlled between 60-160℃; Method 3: First mix ferric oxide with 35-85wt% phosphoric acid solution, then add titanium compound to mix and react. The reaction temperature is controlled between 60-160℃. Method 4: First mix the titanium compound with 35-85wt% phosphoric acid solution, then add it to the mixture with ferric oxide, and react at a temperature controlled between 60-160℃. S2. Preparation of titanium-doped iron phosphate hydrate suspension: Take a portion of the titanium-doped iron phosphate complex solution obtained in S1, mix it with water, heat and control the temperature between 60-150℃, keep it at this temperature for 10 min-2 h to form a titanium-doped iron phosphate hydrate suspension. The volume of the titanium-doped iron phosphate complex solution taken out from S1 is 3-20% of the total volume of the titanium-doped iron phosphate complex solution obtained in S1. S3. Preparation of titanium-doped iron phosphate: Add the remaining titanium-doped iron phosphate complex solution obtained in S1 to the suspension obtained in S2, heat and control the temperature between 60-150℃, keep warm for 10min-24h, and separate the solid and liquid to obtain titanium-doped iron phosphate hydrate. in, In step S1, the phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, and the molar ratio of doped titanium to iron is (0.01-0.2):1; the titanium compound is metatitanic acid, nano-titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate. The volume of water used in step S2 is 0.5-10 times the volume of the titanium-containing ferric phosphate complex solution.

2. The method as described in claim 1, characterized in that, In step S1, the reaction temperature is controlled between 70-110℃, and the titanium compound is metatitanic acid, nano titanium dioxide, or titanium oxysulfate, with a molar ratio of titanium to iron of (0.05-0.2):

1.

3. The method as described in claim 1, characterized in that, In step S2, the volume of water used is 0.5-4 times the volume of the titanium-containing iron phosphate complex solution, the temperature is controlled at 70-110℃, and the holding time is 0.5-1.5h; in step S3, the remaining complex solution is added either all at once or in batches, the temperature is controlled at 70-110℃, and the holding time is 1h-10h.

4. The method according to any one of claims 1-3, characterized in that, The method further includes the following steps: S4. Reuse the mother liquor obtained from S3 filtration to replace 35-85 wt% of phosphoric acid in the preparation of the titanium-containing iron phosphate complex solution in step S1.

5. The method as described in claim 1, characterized in that, Step S2 is replaced by S22, and step S3 is replaced by S33. Steps S22 and S33 are as follows: S22. Mix titanium-doped iron phosphate hydrate seed crystals with water to form a suspension containing titanium-doped iron phosphate hydrate. S33. Add the titanium-containing iron phosphate complex solution obtained in S1 to the suspension in S22, heat and control the temperature between 60-150℃, react for 10 min-24 h, separate the solid and liquid, and prepare titanium-doped iron phosphate hydrate. The volume ratio of water in S22 to the volume of titanium-containing iron phosphate complex solution in S33 is between 1:2 and 4:

1.

6. The method as described in claim 5, characterized in that, Titanium-doped iron phosphate hydrate seed crystals are nanoparticles or microparticles, which are prepared by grinding or direct preparation.

7. The method as described in claim 5 or 6, characterized in that, Titanium-doped iron phosphate hydrate seed crystals are obtained by mixing a titanium-containing iron phosphate complex solution with 5-40 times its volume of water, heating to 60-150℃, and reacting for 10 min-1 h to obtain a titanium-doped iron phosphate crystal suspension. Solid-liquid separation is then performed to obtain titanium-doped iron phosphate hydrate particles used as seed crystals.

8. The method as described in claim 5, characterized in that, The suspension obtained before solid-liquid separation in step S3 of claim 1 or before solid-liquid separation in step S33 of claim 5 is mixed with water to replace the suspension in the next batch of step S22 for the preparation of the next batch of titanium-doped iron phosphate hydrate, wherein the volume ratio of the water to the volume of the titanium-doped iron phosphate complex solution added in the next batch is between 1:2 and 4:1.

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