A method for preparing titanium-vanadium doped iron phosphate

Abstract

The application belongs to the field of phosphate inorganic material preparation, and relates to a method for preparing titanium-vanadium doped iron phosphate, which comprises the following steps: adding titanium and / or vanadium compounds into an iron phosphate complex solution to prepare an iron phosphate complex solution containing titanium and / or vanadium doped metal compounds, and then adding water into the mixed solution and heating to obtain titanium and / or vanadium ion doped iron phosphate; the titanium compound is selected from metatitanic acid, nano titanium dioxide, titanyl sulfate, titanyl oxalate, titanium citrate, titanium lactate or titanium tartrate; the vanadium compound is vanadium trioxide, vanadium dioxide (IV), vanadium pentoxide, vanadium monoxide, vanadium sulfate or vanadium trichloride. In addition, alternative solutions of adding sequence and adding timing change are provided. The application has simple process, is suitable for large-scale industrial production, and improves the electrochemical performance of lithium iron phosphate material in a power battery.

Description

Technical Field

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

[0002] Lithium iron phosphate (LiFePO4) batteries are experiencing explosive growth in demand in the power battery and energy storage fields due to their advantages such as lower raw material costs, higher operating voltage platform and thermal stability, and excellent electrochemical cycle performance. In the LiFePO4 crystal structure, lithium ions have a one-dimensional diffusion channel, while FeO6 octahedra are permeated 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.

[0006] CN118125410A discloses a method for preparing vanadium-doped iron phosphate and lithium iron phosphate, wherein an iron source, a phosphorus source and a vanadium source are mixed and ground, then dried and hydrogen peroxide is added and stirred to obtain a mixed solution.

[0007] CN118851127A discloses a titanium and vanadium-doped iron phosphate method. Titanium is first reacted with a ferrous salt to form a solution, which is then oxidized to obtain titanium-doped iron phosphate dihydrate (substance M). This solution is then mixed with a vanadium compound solution to obtain an iron phosphate product containing vanadium and titanium. This method uses ferrous sulfate as a raw material, and the mixing of vanadium with the solid iron phosphate results in uneven vanadium doping, with doping occurring only in the surface layer.

[0008] Achieving a uniform distribution of titanium / vanadium ions in lithium iron phosphate materials is an important way to improve the electrochemical performance of lithium iron phosphate materials. To date, there is a lack of a simple and low-cost process for preparing lithium iron phosphate with uniform titanium / vanadium doping. Summary of the Invention

[0009] This invention provides a method for preparing titanium and / or vanadium-doped iron phosphate. The titanium and / or vanadium doping method is simple and convenient, and the titanium / vanadium distribution in the prepared doped iron phosphate is uniform.

[0010] This application provides a method for preparing titanium and / or vanadium-doped iron phosphate, comprising the following steps:

[0011] S1. Preparation of iron phosphate complex solution containing titanium and / or vanadium: Add titanium and / or vanadium compounds to iron phosphate complex solution, heat and stir at a temperature between 50-160℃ to obtain iron phosphate complex solution containing titanium and / or vanadium doped metal compounds.

[0012] S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the titanium or vanadium-containing iron phosphate complex solution obtained in step S1. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150 ℃, keep warm for 10 min-24 h, and separate the solid and liquid to obtain titanium-doped iron phosphate dihydrate.

[0013] The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, the molar ratio of the dopant element to the iron element is (0.01-0.2):1, and the dopant element is titanium and / or vanadium.

[0014] In this invention, "titanium and / or vanadium-doped iron phosphate" includes three cases: titanium-doped iron phosphate, vanadium-doped iron phosphate, and titanium and vanadium-doped iron phosphate. The "molar ratio of the dopant element to iron" will correspond to three cases depending on the dopant element added: the molar ratio of titanium to iron, the molar ratio of vanadium to iron, or the molar ratio of the sum of titanium and vanadium to iron.

[0015] The titanium compound is metatitanic acid, nano-titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate, with metatitanic acid, nano-titanium dioxide, or titanium oxysulfate being preferred.

[0016] The vanadium compound is vanadium trioxide, vanadium dioxide (IV), vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride. Preferably, it is vanadium trioxide, vanadium dioxide (IV), vanadium pentoxide, or vanadium oxysulfate.

[0017] Preferably, the phosphorus-to-iron ratio in the ferric phosphate complex solution is (3-6):1, and the molar ratio of titanium, vanadium, or the sum of titanium and vanadium to iron is (0.05-0.2):1.

[0018] In step S2, the amount of water added is 0.5-4 times the volume of the complex solution, the heating temperature is controlled between 80-120℃, and the temperature is maintained between 10min-8h.

[0019] In this invention, the solid-liquid separation is a conventional solid-liquid separation method, such as filtration, centrifugation, or static separation.

[0020] As described above, the iron phosphate complex solution is prepared by any of the following methods:

[0021] Method 1: Mix ferric oxide with an excess of phosphoric acid solution with a concentration of 35-85 wt%, react at 60-160℃ to prepare a solution containing ferric phosphate complex, and remove insoluble matter by solid-liquid separation to obtain the ferric phosphate complex solution;

[0022] Method 2: Ferric phosphate is reacted with excess phosphoric acid (35-85 wt%) at 60-160℃ to prepare a solution containing ferric phosphate complex. The insoluble matter is removed by solid-liquid separation to obtain the ferric phosphate complex solution.

[0023] In this method, the phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1. When feeding raw materials in method 1 or method 2, the molar ratio of phosphoric acid to ferric oxide or ferric phosphate in the raw materials should be based on this phosphorus-to-iron ratio. This reference to the phosphorus-to-iron ratio indicates that the process is basically carried out according to this ratio, but slight adjustments may be made considering factors such as reaction losses and incomplete reactions. A ferric phosphate complex solution can only be formed in an environment where phosphoric acid is in significant excess to create a strong acid pH and the molar ratio of phosphoric acid to iron is greater than or equal to 2.5:1, such as 3:1, 4:1, 5:1, or 6:1.

[0024] Preferably, in methods 1 and 2, the reaction temperature is controlled between 70-110°C.

[0025] Furthermore, the timing of adding titanium or vanadium compounds can be adjusted to the preparation process of the ferric phosphate complex solution, as a simple method change.

[0026] The present invention also provides a method for preparing titanium and / or vanadium-doped iron phosphate, the method comprising:

[0027] S11. Preparation of iron phosphate complex solution containing doped elements: Iron oxide, phosphoric acid solution with a concentration of 35-85 wt%, titanium compound and / or vanadium compound are mixed and reacted at a reaction temperature between 60-160 ℃. After solid-liquid separation, iron phosphate complex solution containing titanium and / or vanadium is obtained.

[0028] S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the titanium and / or vanadium-containing iron phosphate complex solution obtained in step S11. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150 ℃, keep warm for 10 min-24 h, and separate the solid and liquid to obtain titanium and / or vanadium-doped iron phosphate dihydrate.

[0029] The mixing reaction described in step S11 can be carried out by any of the following methods: (a) direct mixing of ferric oxide, phosphoric acid solution, and titanium and / or vanadium compounds; (b) mixing ferric oxide with phosphoric acid solution first, then adding titanium and / or vanadium compounds for mixing and reaction; or (c) mixing titanium and / or vanadium compounds with phosphoric acid solution first, then adding titanium and / or vanadium compounds for mixing and reaction. The order in which the raw materials are added to the mixing reaction can be freely chosen according to the situation, and the reaction effect is almost the same.

[0030] The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, the molar ratio of the dopant element to iron element is (0.01~0.2):1, and the dopant element is titanium and / or vanadium;

[0031] The titanium compound is metatitanic acid, nano-titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate, preferably metatitanic acid, nano-titanium dioxide, or titanium oxysulfate. The vanadium compound is vanadium trioxide, vanadium(IV) dioxide, vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride; preferably vanadium trioxide, vanadium(IV) dioxide, vanadium pentoxide, or vanadium oxysulfate.

[0032] When the phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1, the molar ratio of phosphoric acid to ferric oxide in step S11 should be based on this phosphorus-to-iron ratio. An environment requiring a strong acid pH and a phosphoric acid-to-iron molar ratio of at least 2.5:1 is necessary for the formation of the ferric phosphate complex solution.

[0033] Preferably, the phosphorus-to-iron ratio in the iron phosphate complex solution is (3-6):1, the molar ratio of the dopant element to the iron element is (0.05-0.2):1, and the dopant element is titanium and / or vanadium.

[0034] In step S2, the amount of water added is 0.5-4 times the volume of the complex solution, the heating temperature is controlled between 80-120℃, and the temperature is maintained between 10min-8h.

[0035] Alternatively, the present invention also provides a method for preparing titanium and / or vanadium-doped iron phosphate, the method comprising:

[0036] S11. Preparation of iron phosphate complex solution with titanium and / or vanadium elements in one step: Iron oxide, phosphoric acid solution with a concentration of 35-85 wt%, titanium compound and / or vanadium compound are mixed and reacted at a reaction temperature between 60-160 ℃. After solid-liquid separation, iron phosphate complex solution containing titanium or vanadium is prepared.

[0037] S12. Preparation of iron phosphate complex solution with secondary doping of titanium and / or vanadium: Add titanium compound and / or vanadium compound to the iron phosphate complex solution with titanium and / or vanadium obtained in step S11, heat and stir at a temperature between 50-160℃, and separate solid and liquid or without solid and liquid separation to obtain iron phosphate complex solution with secondary doping of titanium and / or vanadium.

[0038] S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the titanium and / or vanadium-containing iron phosphate complex solution obtained in step S12. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150 °C. Keep warm for 10 min-24 h. Separate the solid and liquid to obtain titanium and / or vanadium-doped iron phosphate dihydrate.

[0039] This replacement method employs a two-stage doping process, introducing titanium and / or vanadium into the complex solution in two separate steps to increase the doping concentration of titanium and / or vanadium. Alternatively, titanium and vanadium can be doped sequentially during the two doping processes, ultimately achieving simultaneous doping of both. The order of titanium and vanadium doping during the two doping processes is not limited; it can be either titanium first followed by vanadium or vanadium first followed by titanium. Of course, three or more doping steps can also be performed, but the uneconomical nature and operational complexity associated with too many steps must be considered.

[0040] The mixing reaction described in step S11 can be carried out by any of the following methods: (a) direct mixing of ferric oxide, phosphoric acid solution, and titanium and / or vanadium compounds; (b) mixing ferric oxide with phosphoric acid solution first, then adding titanium and / or vanadium compounds for mixing and reaction; or (c) mixing titanium and / or vanadium compounds with phosphoric acid solution first, then adding titanium and / or vanadium compounds for mixing and reaction. The order in which the raw materials are added to the mixing reaction can be freely chosen according to the situation, and the reaction effect is almost the same.

[0041] The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, and the molar ratio of the dopant element to iron is (0.01-0.2):1, wherein the dopant element is titanium and / or vanadium. Preferably, the phosphorus-to-iron ratio in the iron phosphate complex solution is (3-6):1, and the molar ratio of the dopant element to iron is (0.05-0.2):1, wherein the dopant element is titanium and / or vanadium.

[0042] The titanium compound is metatitanic acid, nano titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate; the vanadium compound is vanadium trioxide, vanadium(IV) dioxide, vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride.

[0043] When the phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1, the molar ratio of phosphoric acid to ferric oxide in step S11 shall be based on this phosphorus-to-iron ratio.

[0044] Preferably, in step S11, a poorly soluble titanium or vanadium compound raw material is used, while in step S12, a readily soluble titanium or vanadium compound raw material is used.

[0045] Of course, the method of omitting step S12 and simultaneously adding the titanium compound and vanadium compound has been disclosed in the aforementioned method.

[0046] The solid-liquid separation is achieved through filtration, centrifugation, or settling.

[0047] The method yields doped ferric phosphate dihydrate, also known as hydrated ferric phosphate. Anhydrous ferric phosphate can be obtained from ferric phosphate dihydrate through high-temperature dehydration; the removal of water of crystallization is a well-known basic technique in this field.

[0048] The water mentioned in this application is soft water, deionized water, ultrapure water, or distilled water.

[0049] This application also provides a method for preparing titanium and / or vanadium-doped lithium iron phosphate cathode materials, the method comprising:

[0050] Titanium and / or vanadium-doped iron phosphate prepared by the aforementioned method is mixed with a lithium source and a carbon source, and then calcined at high temperature to prepare titanium and / or vanadium-doped lithium iron phosphate cathode material.

[0051] The method for preparing titanium and / or vanadium-doped lithium iron phosphate cathode materials adopts a commonly used method in the art for preparing lithium iron phosphate cathode materials.

[0052] the term:

[0053] Ferric phosphate dihydrate: also known as 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.

[0054] Titanium and / or vanadium-doped iron phosphate: This includes three cases: titanium-doped iron phosphate, vanadium-doped iron phosphate, and titanium and vanadium-doped iron phosphate. Titanium and vanadium indicate the presence of both titanium and vanadium elements.

[0055] Titanium-doped iron phosphate: Titanium is doped into iron phosphate crystals to form titanium-doped iron phosphate.

[0056] Vanadium-doped iron phosphate: Vanadium is doped into iron phosphate crystals to form vanadium-doped iron phosphate.

[0057] Titanium and vanadium-doped iron phosphate: Titanium and vanadium elements are doped into iron phosphate crystals to form titanium and vanadium-doped iron phosphate.

[0058] Titanium compound: In this application, it refers to a raw material compound used for titanium doping, the compound containing titanium and other non-metallic elements.

[0059] Vanadium compounds: In this application, vanadium compounds refer to raw material compounds used for vanadium doping, wherein the compounds contain vanadium and other non-metallic elements.

[0060] 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 (the molar ratio of phosphoric acid to iron is 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.

[0061] Iron oxide: also known as ferric oxide.

[0062] Phosphorus-iron ratio: refers to the molar ratio (molar ratio) of phosphorus to iron.

[0063] When the amount of substance, concentration, or other value or parameter is expressed as a range, 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, when the range "1-5" is disclosed, the described range should be interpreted as including ranges "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5", etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. Specifically, 0.3-10 times the amount of water added should be understood as meaning that multiples of water added, such as 0.3, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 times, can achieve the inventive purpose and effects of this invention. The range of 0.01-0.2 in "the molar ratio of dopant element 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 phosphorus-to-iron ratio in ferric phosphate is (2.5-8):1, where the range of 2.5-8 includes values ​​at the extremes and midpoints of 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 reaction temperature range of 60-150℃ includes values ​​such as 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, and 150℃. Similarly, the temperature ranges of 60-160℃, 70-110℃, and 80-120℃ should also include the midpoints of these values: 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, and 160℃ (covering the midpoints of 70-110℃ and 80-120℃). The reaction time range of 10min-8h includes the midpoints of 20min, 30min, 40min, 50min, 1h, 2h, 3h, 4h, 5h, 6h, and 7h.

[0064] Beneficial Effects: This application provides a novel method for uniformly doping iron phosphate with other metal elements, particularly for preparing titanium- and vanadium-doped iron phosphate. This invention utilizes a decomplexing method of iron phosphate complex solutions to obtain atomically uniformly doped iron phosphate products. This method also has the advantage of not significantly altering the iron phosphate synthesis method, maximizing the use 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

[0065] Figure 1 Example 4: Elemental distribution map (EDS mapping) of the product.

[0066] Figure 2 XRD pattern of the product in Example 4.

[0067] Figure 3 Example 5: Elemental distribution map (EDS mapping) of the product.

[0068] Figure 4 Example 5: Dual-beam electron microscopy image and elemental distribution map (EDS mapping) of product slices.

[0069] Figure 5 XRD pattern of the product in Example 5.

[0070] Figure 6 Example 9: Elemental distribution diagram (EDS mapping diagram) of the product. Detailed Implementation

[0071] Example 1

[0072] Take 31 ml of 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and 0.1 g of titanium dioxide nanoparticles, add them to the phosphoric acid solution, and heat the entire system to 90°C. Stir at 90°C 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 it at 90°C for 6 h to obtain a white precipitate with a mass of 14.2753 g. ICP test showed that the titanium content was 912 ppm.

[0073] Example 2

[0074] Take 31 ml of 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and 0.2 g of titanium dioxide powder, add them to the phosphoric acid solution, and heat the entire system to 90°C. Stir at 90°C 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 it at 100°C for 10 h to obtain a white precipitate with a mass of 13.1388 g. ICP test showed that the titanium content was 2184 ppm.

[0075] Example 3

[0076] 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 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.

[0077] Example 4

[0078] Take 31 ml of an 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Add 0.2043 g 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 dissolve completely. 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. Figure 1 This is an elemental distribution map (EDS mapping) of the obtained ferric phosphate dihydrate powder. From Figure 1 It can be seen that the Ti element is evenly distributed and consistent with the distribution of the main elements (oxygen, phosphorus, iron) in the material. Figure 2 The image shown is the XRD pattern of Example 4, which indicates that the product is doped with iron phosphate.

[0079] Alternatively, metatitanic acid and iron oxide can be added together to the phosphoric acid solution, or phosphoric acid and iron oxide can be mixed first, followed by the addition of metatitanic acid for a mixed reaction. Dissolving metatitanic acid in phosphoric acid solution first allows observation of its solubility, ensuring complete dissolution of all metatitanic acid.

[0080] Example 5

[0081] Take 31 ml of an 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and 0.4 g of vanadium trioxide powder, add them to the phosphoric acid solution, and heat the entire system to 90°C. Stir at 90°C for 3 h. After the reaction is complete, filter the system to obtain a dark green iron phosphate complex solution. Add 50 ml of H2O to the vanadium-containing iron phosphate complex solution and keep it at 90°C for 6 h to obtain a light yellow precipitate with a mass of 15.50 g. ICP test showed that the vanadium content was 5058.10 ppm.

[0082] Elemental distribution maps (EDS mapping) of ferric phosphate particles were prepared, and the test results are shown in [the table below]. Figure 3 , Figure 3 The vanadium-doped iron phosphate particles showed a uniform vanadium distribution on their surface. The particles were cut using a focused ion beam electron beam dual-beam electron microscope, and the distribution of O, P, Fe, and V in the cut sections was characterized by surface scanning of the elemental distribution map. The results are shown below. Figure 4 As shown. From Figure 4 It can be seen that the V element is evenly distributed in the cross-section of the particles. Figure 3 and Figure 4 This proves that the V element is uniformly distributed in the vanadium-doped iron phosphate particles. Figure 5 The image shown is the XRD pattern of Example 5, which indicates that the product is doped with iron phosphate.

[0083] Example 6

[0084] Take 31 ml of an 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and 0.6 g of vanadium trioxide powder, add them to the phosphoric acid solution, and heat the entire system to 90°C. Stir at 90°C for 3 h. After the reaction is complete, filter the system to obtain a dark green iron phosphate complex solution. Add 50 ml of H2O to the vanadium-containing iron phosphate complex solution and keep it at 90°C for 6 h to obtain a light yellow precipitate with a mass of 15.70 g. ICP test showed that the vanadium content was 7370.43 ppm.

[0085] Example 7

[0086] Take 31 ml of 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and 3.2 g of vanadium oxysulfate hydrate powder, add them to the phosphoric acid solution, heat the entire system to 90°C, and stir at 90°C for 3 h. After the reaction is complete, filter the system to obtain a dark green iron phosphate complex solution. Add 50 ml of H2O to the above complex solution and keep it at 90°C for 6 h to obtain a yellow precipitate with a mass of 14.90 g. ICP test showed that the vanadium content was 5399.24 ppm.

[0087] Example 8

[0088] Take 31 ml of an 85% phosphoric acid solution and add 19 ml of deionized water to form a 9 mol / L phosphoric acid solution. Accurately weigh 7.9845 g of iron oxide powder and add it to the phosphoric acid solution. Heat the system to 90°C and stir at 90°C for 3 h. After the reaction is complete, filter the system to obtain a purple-red iron phosphate complex solution. Add 1.8 g of vanadium pentoxide powder to the above complex solution, then add 50 ml of H2O, keep at 90°C for 15 min, filter, and keep the vanadium-containing filtrate at 100°C for 10 h to obtain a yellow precipitate with a mass of 14.8 g. ICP test shows that the vanadium content is 4090.60 ppm.

[0089] Example 9

[0090] 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 of metatitanic acid to the phosphoric acid solution, heat to 90℃, and keep warm for 1 h to allow the metatitanic acid to dissolve completely. Accurately weigh 7.9845 g of iron oxide and 0.4 g of vanadium trioxide powder and add them to the titanium-containing phosphoric acid solution. Heat the system to 90℃ and keep warm for 3 h. After the reaction is complete, filter the system to obtain a dark green iron phosphate complex solution. Add 50 ml of H2O to the dark green complex solution and keep warm at 100℃ for 17 h to obtain a pale yellow precipitate with a mass of 8.0569 g. ICP analysis showed that the titanium content in the iron phosphate dihydrate powder was 3522 ppm and the vanadium content was 27883 ppm. Figure 6 This is an elemental distribution map (EDS mapping) of the obtained ferric phosphate dihydrate powder. From Figure 6 It can be seen that Ti and V elements are evenly distributed and consistent with the distribution of the main elements (oxygen, phosphorus, and iron) in the material.

[0091] Alternatively, metatitanic acid and iron oxide can be added together to the phosphoric acid solution, or phosphoric acid and iron oxide can be mixed first, followed by the addition of metatitanic acid for a mixed reaction. Dissolving metatitanic acid in phosphoric acid solution first allows observation of its solubility, ensuring complete dissolution of all metatitanic acid.

[0092] Conclusions related to the embodiments: Based on the test results of the embodiments and the accompanying drawings, the method of the present invention can obtain a doped iron phosphate product with uniform distribution of doped elements. The doped titanium and vanadium are atomically dispersed in the iron phosphate lattice, exhibiting uniformity and consistency, which improves the electrochemical performance of downstream lithium iron phosphate products.

[0093] 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 and / or vanadium-doped iron phosphate, characterized in that, Includes the following steps: S1. Preparation of ferric phosphate complex solution containing titanium and / or vanadium: Add titanium compound and / or vanadium compound to ferric phosphate complex solution, heat and stir at a temperature between 50-160℃ to obtain ferric phosphate complex solution containing titanium and / or vanadium. S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the iron phosphate complex solution containing titanium and / or vanadium obtained in step S1. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150 ℃. Keep warm for 10 min-24 h. Separate the solid and liquid to obtain titanium and / or vanadium-doped iron phosphate dihydrate. The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, the molar ratio of the dopant element to the iron element is (0.01-0.2):1, and the dopant element is titanium and / or vanadium. The titanium compound is metatitanic acid, nano titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate. The vanadium compound is vanadium trioxide, vanadium dioxide, vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride.

2. The method as described in claim 1, characterized in that, In step S1, the phosphorus-to-iron ratio in the iron phosphate complex solution is (3-6):1, the molar ratio of the dopant element to the iron element is (0.05-0.2):1, and the dopant element is titanium and / or vanadium.

3. The method as described in claim 1, characterized in that, The titanium compound is metatitanic acid, nano titanium dioxide, or titanium oxysulfate, and the vanadium compound is vanadium trioxide, vanadium dioxide, vanadium pentoxide, or vanadium oxysulfate.

4. The method as described in claim 1, characterized in that, In step S2, the amount of water added is 0.5-4 times the volume of the complex solution, the heating temperature is controlled between 80-120℃, and the temperature is maintained between 10min-8h.

5. The method as described in claim 1, characterized in that, The iron phosphate complex solution is prepared by any one of the following methods: Method 1: Mix ferric oxide with a phosphoric acid solution with a concentration of 35-85 wt% and react at a temperature between 60-160℃ to prepare an ferric phosphate complex solution, or obtain an ferric phosphate complex solution by solid-liquid separation to remove insoluble matter; Method 2: React ferric phosphate with a phosphoric acid solution of 35-85 wt% at a reaction temperature of 60-160℃ to prepare a ferric phosphate complex solution, or obtain a ferric phosphate complex solution by solid-liquid separation to remove insoluble matter; The phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1, and the molar ratio of phosphoric acid to ferric oxide or ferric phosphate in the raw materials is based on this phosphorus-to-iron ratio.

6. A method for preparing titanium and / or vanadium-doped iron phosphate, characterized in that, Includes the following steps: S11. Preparation of iron phosphate complex solution containing doped elements: Iron oxide, phosphoric acid solution with a concentration of 35-85 wt%, titanium compound and / or vanadium compound are mixed and reacted at a reaction temperature between 60-160℃. After solid-liquid separation, iron phosphate complex solution containing titanium and / or vanadium is obtained. S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the iron phosphate complex solution containing titanium and / or vanadium obtained in step S11. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150℃. Keep warm for 10 min-24 h. Separate the solid and liquid to obtain titanium and / or vanadium-doped iron phosphate dihydrate. The mixing reaction described in step S11 is carried out by any of the following methods: (a) ferric oxide, 35-85 wt% phosphoric acid solution and titanium compound and / or vanadium compound are directly mixed and reacted; (b) ferric oxide and 35-85 wt% phosphoric acid solution are mixed first, and then titanium compound and / or vanadium compound are added and reacted; or (c) titanium compound and / or vanadium compound and 35-85 wt% phosphoric acid solution are mixed first, and then ferric oxide is added and reacted. The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, the molar ratio of the dopant element to iron element is (0.01-0.2):1, and the dopant element is titanium and / or vanadium; The titanium compound is metatitanic acid, nano titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate; the vanadium compound is vanadium trioxide, vanadium dioxide, vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride. When the phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1, the molar ratio of phosphoric acid to ferric oxide in step S11 shall be based on this phosphorus-to-iron ratio.

7. The method as described in claim 6, characterized in that, In step S11, the phosphorus-to-iron ratio in the iron phosphate complex solution is (3-6):1, the molar ratio of the dopant element to the iron element is (0.05-0.2):1, and the dopant element is titanium and / or vanadium; the titanium compound is metatitanic acid, nano titanium dioxide or titanium oxysulfate, and the vanadium compound is vanadium trioxide, vanadium dioxide, vanadium pentoxide or vanadium oxysulfate.

8. The method as described in claim 6 or 7, characterized in that, In step S2, the amount of water added is 0.5-4 times the volume of the complex solution, the heating temperature is controlled between 80-120℃, and the temperature is maintained between 10min-8h.

9. A method for preparing titanium and / or vanadium-doped iron phosphate, the method comprising: S11. Preparation of ferric phosphate complex solution with titanium and / or vanadium elements: Ferric oxide, phosphoric acid solution with a concentration of 35-85wt%, titanium compound and / or vanadium compound are mixed and reacted at a reaction temperature between 60-160℃. After solid-liquid separation, ferric phosphate complex solution containing titanium or vanadium is prepared. S12. Preparation of iron phosphate complex solution with secondary doping of titanium and / or vanadium: Add titanium compound and / or vanadium compound to the iron phosphate complex solution containing titanium or vanadium obtained in step S11, heat and stir at a temperature between 50-160℃, and separate solid and liquid or without solid and liquid separation to obtain iron phosphate complex solution with secondary doping of titanium and / or vanadium. S2. Preparation of titanium and / or vanadium-doped iron phosphate dihydrate: Add water to the iron phosphate complex solution of secondary doped titanium and / or vanadium obtained in step S12. The amount of water added is 0.3-10 times the volume of the complex solution. Heat and control the temperature between 60-150℃. Keep warm for 10 min-24 h. Separate the solid and liquid to obtain titanium and / or vanadium-doped iron phosphate dihydrate. The mixing reaction described in step S11 is carried out by any of the following methods: (a) ferric oxide, 35-85 wt% phosphoric acid solution and titanium compound and / or vanadium compound are directly mixed and reacted; (b) ferric oxide and 35-85 wt% phosphoric acid solution are mixed first, and then titanium compound and / or vanadium compound are added and reacted; or (c) titanium compound and / or vanadium compound are mixed first with 35-85 wt% phosphoric acid solution, and then added and reacted with ferric oxide. The phosphorus-to-iron ratio in the iron phosphate complex solution is (2.5-8):1, the molar ratio of the dopant element to iron element is (0.01-0.2):1, and the dopant element is titanium and / or vanadium; The titanium compound is metatitanic acid, nano titanium dioxide, titanium oxysulfate, titanium oxyoxalate, titanium citrate, titanium lactate, or titanium tartrate; the vanadium compound is vanadium trioxide, vanadium dioxide, vanadium pentoxide, vanadium monoxide, vanadium oxysulfate, or vanadium trichloride. When the phosphorus-to-iron ratio in the ferric phosphate complex solution is (2.5-8):1, the molar ratio of phosphoric acid to ferric oxide in step S11 shall be based on this phosphorus-to-iron ratio.

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