Method for preparing low-aluminum titanium-doped iron phosphate material by utilizing ferrophosphorus slag

Abstract

The invention provides a method for preparing a low-aluminum titanium-doped iron phosphate material by utilizing ferrophosphorus slag, which comprises the following steps: S1, crushing the ferrophosphorus slag, and dissolving the crushed ferrophosphorus slag in an acid solution to prepare a primary leaching solution; s2, acid is continuously added into the leaching residues for dissolution, and secondary leaching liquid is prepared; s3, adding an alkaline substance into the primary leachate to obtain an iron-phosphorus mixture; s4, mixing the secondary leachate with an iron-phosphorus mixture; s5, preparing a yellow material; s6, pulping the yellow material, and adding a phosphoric acid solution to obtain the yellow material; s7, the yellow material is heated and then subjected to heat preservation; s8, naturally cooling, filtering, washing and dehydrating to obtain iron phosphate dihydrate; and S9, drying the dehydrated iron phosphate dihydrate in a drying oven, and calcining to obtain the low-aluminum titanium-doped anhydrous iron phosphate. The titanium element in the iron-phosphorus adjusting liquid is doped into the iron phosphate material, so that the crystal structure and the performance of the iron phosphate material are optimized, the preparation process is simplified, and the titanium doping cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of iron phosphate materials, and specifically relates to a method for preparing a low-aluminum and titanium-doped iron phosphate material by using phosphorus iron slag. Background Art

[0002] Iron phosphate is an important cathode material widely used in lithium-ion batteries. Its main function is to provide positive charges to electrons to achieve the discharge of the battery. Compared with other cathode materials, iron phosphate has the advantages of high stability, good safety, and long cycle life. However, its capacity is relatively low and cannot meet the requirements of modern electronic products for high-performance batteries. Therefore, the technology of titanium-doped iron phosphate has emerged, aiming to improve the performance of iron phosphate by doping titanium elements.

[0003] Titanium-doped iron phosphate materials have broad application prospects in the field of lithium-ion batteries due to their excellent performance. It can be used as the cathode material of lithium-ion batteries to improve the energy density, cycle stability, and safety of the batteries. In addition, with the rapid development of fields such as electric vehicles and energy storage systems, the demand for titanium-doped iron phosphate materials will also continue to grow.

[0004] There are various preparation methods for titanium-doped iron phosphate materials, mainly including hydrothermal method, solid-phase method, sol-gel method, and co-precipitation method. The present invention adopts the co-precipitation method, mixing three solutions at a certain rate to form a precipitate, and after transformation, calcining to obtain a titanium-doped battery-grade iron phosphate material.

[0005] Patent CN115818601B, "Titanium-Doped Battery-Grade Iron Phosphate and Its Preparation Method", includes the following steps: adding iron titanium ore to a ferrous sulfate solution to obtain a first mixed system; then separately adding it to a reaction vessel with a phosphate solution to obtain a second mixed system, adding a catalyst, and introducing an oxygen-containing gas for catalytic oxidation reaction to obtain a third mixed system, then performing solid-liquid separation, collecting the solid matter, and washing and drying it; the ferrous sulfate is a by-product in the production process of titanium white by the sulfuric acid method; the ferrous sulfate solution also contains titanium elements; the addition time of the iron titanium ore is 4 - 8 minutes. The present invention uses the ferrous sulfate by-produced in the production process of titanium white by the sulfuric acid method as the raw material, and through the above operations, removes impurities in the preparation process of iron phosphate, retains a small amount of titanium to co-precipitate uniformly with iron phosphate, realizes the doping of the original acid, and obtains a uniform and stable product.

[0006] Patent CN117756076B, "Titanium-doped anhydrous iron phosphate material, its preparation method and application". The preparation method includes the following steps: providing a titanium-containing ferrous sulfate raw material solution and a titanium-free ferrous sulfate raw material solution; mixing the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution to obtain a mixed solution; mixing the mixed solution with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate; aging, rinsing, drying and sintering the slurry in sequence to obtain a titanium-doped anhydrous iron phosphate material.

[0007] Patent CN119018867A, "A method for improving the grain morphology and crystallinity of titanium-doped iron phosphate by hydrothermal method". The preparation method includes: S1. Raw material preparation: preparing ammonium phosphate solution, phosphoric acid solution, titanium white ferrous solution, and hydrogen peroxide for standby; S2. Synthesis: putting the ammonium phosphate solution, titanium white ferrous solution, and hydrogen peroxide into a reaction vessel to react to obtain a slurry; filtering and washing the slurry to obtain a yellow first-washed filter cake; S3. Transformation: taking 2.5 - 3.5 kg of the yellow first-washed filter cake, adding 8.0 - 12.0 kg of water, 200 - 800 g of phosphoric acid solution, and 120 - 180 g of titanium sulfate, pulping and stirring evenly, filtering and washing to obtain a light pink second-washed filter cake; S4. Calcination: drying the light pink second-washed filter cake to obtain dihydrate iron phosphate, and calcining and pulverizing the dihydrate iron phosphate to obtain the finished iron phosphate.

[0008] However, Patent CN115818601B and Patent CN117756076B have problems of uneven distribution of doping elements, which affect the physical and chemical indexes and performance of the finished product. Patent CN119018867A has problems such as high requirements for reaction equipment, long reaction time, being not conducive to industrialization, and it is difficult to ensure the uniformity of titanium element distribution. Summary of the Invention

[0009] To solve the above technical problems, the purpose of the present invention is to provide a low-aluminum titanium-doped iron phosphate material. This technology realizes the improvement of the performance of iron phosphate by changing the crystal structure of iron phosphate, improving chemical activity, enhancing ion and electron conductivity, and stabilizing the crystal structure, specifically as follows: A method for preparing a low-aluminum titanium-doped iron phosphate material by using phosphorus iron slag, including the following steps: S1. Adding phosphorus iron slag with a titanium content of 0.20% - 1.10% of the iron molar amount in the raw material into a crusher for crushing, grinding, and screening to obtain particulate materials. Dissolving the particulate materials in an acid solution for primary leaching, controlling the pH at 0.5 - 1.5, the temperature at 20 - 40 °C, reacting for 10 - 50 minutes, and filtering to obtain a primary leachate and a leaching residue; S2. Continuing to add an acid solution to the leaching residue obtained in step S1 for secondary leaching to prepare a secondary leachate for standby; S3. Add an alkaline substance to the primary leachate obtained in step S1 to adjust the pH of the system to 1.0 - 1.8, filter to obtain the precipitate, which is the iron-phosphorus mixture; S4. Mix the secondary leachate obtained in step S2 with the iron-phosphorus mixture obtained in step S3, and adjust the iron-phosphorus ratio of the system to 1:1 to obtain the iron-phosphorus adjustment solution; S5. Take 5 - 20% by volume of the iron-phosphorus adjustment solution, heat it to 60 °C, add the remaining iron-phosphorus adjustment solution and an alkaline substance to obtain the yellow material; S6. Pulp the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:1.5 - 2, and add a phosphoric acid solution to obtain the white material; S7. Heat the above-mentioned white material to 85 - 98 °C and then keep it warm; S8. Naturally cool to room temperature, filter, wash, and dehydrate to obtain iron phosphate dihydrate; S9. Dry the dehydrated iron phosphate dihydrate in an oven and then calcine it in a muffle furnace to obtain low-aluminum and titanium-doped anhydrous iron phosphate.

[0010] Preferably, in step S1, in the method for preparing a low-aluminum and titanium-doped iron phosphate material using phosphorus iron slag, it is characterized in that in step S1, the phosphorus iron slag is a solid mixture rich in iron phosphate and graphite after lithium extraction from waste lithium iron phosphate; Preferably, in steps S1 and S2, the acid solution is one of sulfuric acid, hydrochloric acid, and perchloric acid, and the molar ratio of hydrogen element to iron element in the phosphorus iron slag in the acid solution is 2 - 5:1.

[0011] Preferably, in step S1, the primary leachate contains iron ions, phosphoric acid, titanium ions, and aluminum ions.

[0012] Preferably, in step S2, the secondary leachate mainly contains iron ions, phosphoric acid, and titanium ions, and the purpose of the secondary leaching is to continue to dissolve the remaining phosphorus iron slag after the primary leaching.

[0013] Preferably, in steps S3 and S5, the alkaline substance is one or more of sodium hydroxide, potassium hydroxide, magnesium oxide, and ammonia water.

[0014] Preferably, in step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjustment solution is n(Ti):n(Fe) = 0.3% - 1.2%.

[0015] Preferably, in step S6, the phosphorus element in the added phosphoric acid solution is in a molar ratio of 0.25 - 0.55:1 to the iron element in the iron-phosphorus adjustment solution.

[0016] Preferably, in step S7, the heat preservation time is 60 - 150 min.

[0017] Preferably, in step S8, the content of low-aluminum titanium-doped anhydrous iron phosphate is 2-10 ppm, and the titanium content is 1200-6000 ppm.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The core of the low-aluminum titanium-doped iron phosphate material of the present invention is that the phosphorus-iron slag is subjected to two-stage leaching to obtain a phosphorus-iron adjustment solution, and the titanium element contained in the iron-phosphorus adjustment solution is incorporated into the iron phosphate material in a certain manner, avoiding the additional process steps of doping titanium, and simplifying the preparation process; the titanium ions in the iron-phosphorus adjustment solution are evenly distributed and can be evenly doped in the iron phosphate material to optimize the crystal structure and performance of the iron phosphate material. At the same time, the in-situ titanium directly comes from the raw material (phosphorus-iron slag) without the need to additionally add titanium compounds, greatly reducing the cost of doping titanium at the phosphorus-iron end and the lithium iron phosphate end.

[0019] 2. In the present invention, the phosphorus-iron slag after lithium extraction from waste lithium iron phosphate batteries is directly used as the raw material, avoiding the waste of pure iron source and phosphorus source required for traditional iron phosphate preparation, and greatly reducing the raw material cost.

[0020] 3. In the present invention, after the step-by-step leaching of steps S1 and S2 and the pH gradient regulation of S3, aluminum in the system is preferentially dissolved and separated in the iron-phosphorus precipitation stage. The aluminum content of the final product is only 2-10 ppm, far lower than the industry conventional level (usually >50 ppm), and finally achieving the effect that the 1C discharge capacity reaches 141 mAh / g when the sintering compaction density is reduced to 2.44 g / cm 3 ³.

[0021] 4. The titanium ions in the iron-phosphorus adjustment solution are evenly distributed and can be evenly doped in the iron phosphate material to optimize the crystal structure and performance of the iron phosphate material. At the same time, the in-situ titanium directly comes from the raw material (phosphorus-iron slag) without the need to additionally add titanium compounds, greatly reducing the cost of doping titanium at the phosphorus-iron end and the lithium iron phosphate end. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the flow chart for preparing iron phosphate from phosphorus-iron slag; Figure 2 is the electron microscope image of anhydrous iron phosphate in Example 1; Figure 3 is the electron microscope image of anhydrous iron phosphate in Example 2; Figure 4 is the electron microscope image of anhydrous iron phosphate in Example 3; Figure 5 is the electron microscope image of anhydrous iron phosphate in Example 4; Figure 6 is the electron microscope image of anhydrous iron phosphate in Comparative Example 1; Figure 7 is the electron microscope image of anhydrous iron phosphate in Comparative Example 2; Figure 8 It is the electron microscope image of ferric phosphate anhydrous for Comparative Example 3. Specific Embodiments

[0023] Example 1 A method for preparing low-aluminum and titanium-doped ferric phosphate material by using phosphorus-iron slag, comprising the following steps ( Figure 1 ): S1. Add phosphorus-iron slag (black slag) with a titanium content of 0.20% of the molar amount of iron in the raw materials into a crusher for crushing and grinding, and screen to obtain granular materials, dissolve them in an acid solution to prepare a primary leaching solution; S2. Continue to add an acid solution to the leaching residue obtained in step S1 for secondary leaching to prepare a secondary leaching solution for standby; S3. Add magnesium oxide to the primary leaching solution to adjust the pH of the system to 1.3, stir for 30 min to prepare a precipitate of the primary leaching solution, and filter out the precipitate to obtain an iron-phosphorus mixture; S4. Mix the secondary leaching solution with the iron-phosphorus mixture, and add a phosphorus-containing mother liquor to adjust the iron-phosphorus ratio of the system to 1:1 to obtain an iron-phosphorus adjusted solution; S5. Heat the iron-phosphorus adjusted solution with a volume ratio of 5% to 60 °C, and at the same time add the iron-phosphorus adjusted solution and an alkaline substance to obtain a yellow material; S6. Pulp the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:1.5, and add a phosphoric acid solution to obtain a white material; S7. Heat the above white material to 88 °C and then keep it warm; S8. Naturally cool to room temperature, filter and wash, wash until the conductivity is below 600 μs / cm, and then dehydrate to obtain ferric phosphate dihydrate; S9. Dry the dehydrated ferric phosphate dihydrate in an oven and then calcine it in a muffle furnace to obtain low-aluminum and titanium-doped ferric phosphate anhydrous.

[0024] Preferably, in step S1, the phosphorus-iron slag is a solid mixture rich in ferric phosphate and graphite after lithium extraction from waste lithium iron phosphate, and the acid is sulfuric acid; Preferably, in step S1, the hydrogen element in the primary leaching sulfuric acid solution is twice the molar amount of the iron element in the phosphorus-iron slag, stir at 40 °C for 50 min, and filter to obtain the primary leaching solution; Preferably, in step S1, the primary leaching solution mainly contains iron ions, phosphoric acid, titanium ions and aluminum ions; Preferably, in step S2, the filtered leaching residue is continuously dissolved with sulfuric acid to obtain a secondary leaching solution, and the hydrogen element in the secondary leaching sulfuric acid solution is five times the molar amount of the iron element in the phosphorus-iron slag; Preferably, in step S2, the secondary leaching solution mainly contains iron ions, phosphoric acid and titanium ions, and the purpose of secondary leaching is to continue to dissolve the remaining phosphorus-iron slag in the primary leaching.

[0025] Preferably, in step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjusting solution is n(Ti):n(Fe) = 0.3%.

[0026] Preferably, in step S5, the volume of the partial iron-phosphorus adjusting solution is 5% of the entire system. The alkaline substance is ammonia water. The ammonia water and the iron-phosphorus adjusting solution are fed in two streams, and the addition amount of ammonia water is controlled so that the synthesis pH < 2.1 to obtain yellow material. After filtration and centrifugation, an ammonium ferric phosphate hydroxide filter cake is obtained; Preferably, in step S6, the ammonium ferric phosphate hydroxide filter cake is slurried with pure water for 30 min, and a phosphoric acid solution is added and stirred for another 10 min. The phosphorus element in the added phosphoric acid solution is in a molar ratio of 0.25:1 to the iron element in the iron-phosphorus adjusting solution; Preferably, in step S7, the white material is heated to 88 °C, turned white, and then kept warm for 90 min; Preferably, in step S8, the content of low-aluminum titanium-doped anhydrous ferric phosphate is 7.42 ppm, and the titanium content is 1217 ppm.

[0027] Example 2 A method for preparing a low-aluminum titanium-doped ferric phosphate material from phosphorus iron slag, comprising the following steps: S1. Add phosphorus iron slag (black slag) with a titanium content of 0.50% of the iron molar amount in the raw material into a crusher for crushing and grinding, and screen to obtain particulate matter, which is dissolved in an acid solution to prepare a primary leaching solution; S2. Continue to leach the leaching residue obtained in step S1 with an acid solution for secondary leaching to prepare a secondary leaching solution for standby; S3. Add magnesium oxide to the primary leaching solution obtained in step S1 to adjust the system pH to 1.3, stir for 30 min, filter to obtain a precipitate, namely an iron-phosphorus mixture; S4. Mix the secondary leaching solution obtained in step S2 with the iron-phosphorus mixture obtained in step S3, and adjust the iron-phosphorus ratio of the system to 1:1 to obtain an iron-phosphorus adjusting solution; S5. Heat the iron-phosphorus adjusting solution with a volume ratio of 10% to 60 °C, add the remaining iron-phosphorus adjusting solution and an alkaline substance to obtain yellow material; S6. Slurry the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:2, and add a phosphoric acid solution to obtain white material; S7. Heat the above-mentioned white material to 90 °C and then keep it warm; S8. Naturally cool to room temperature, filter and wash, wash until the conductivity is below 600 μs / cm, and then dehydrate to obtain ferric phosphate dihydrate; S9. Dry the dehydrated ferric phosphate dihydrate in an oven and then calcine it in a muffle furnace to obtain low-aluminum titanium-doped anhydrous ferric phosphate.

[0028] Preferably, in step S1, the ferrophosphorus slag is a solid mixture rich in iron phosphate and graphite after lithium extraction from waste lithium iron phosphate, and the acid is sulfuric acid; Preferably, in step S1, the hydrogen element in the primary leaching sulfuric acid solution is twice the molar amount of the iron element in the ferrophosphorus slag, stirred at 40 °C for 30 min, and filtered to obtain the primary leaching solution; Preferably, in step S1, the primary leaching solution mainly contains iron ions, phosphoric acid, titanium ions and aluminum ions; Preferably, in step S2, the leaching residue after filtration is continuously dissolved with sulfuric acid to obtain a secondary leaching solution, and the hydrogen element in the secondary leaching sulfuric acid solution is three times the molar amount of the iron element in the ferrophosphorus slag; Preferably, in step S2, the secondary leaching solution mainly contains iron ions, phosphoric acid and titanium ions, and the purpose of secondary leaching is to continuously dissolve the remaining ferrophosphorus slag after primary leaching.

[0029] Preferably, in step S3, the alkaline substance is magnesium oxide to adjust the pH of the system to 1.3, stirred for 30 min, and filtered to obtain an iron-phosphorus mixture; Preferably, in step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjustment solution is n(Ti):n(Fe) = 0.50%; Preferably, in step S5, the volume of a part of the iron-phosphorus adjustment solution is 10% of the whole system. The alkaline substance is ammonia water, and the ammonia water and the iron-phosphorus adjustment solution are fed in parallel, and the addition amount of ammonia water is controlled so that the synthesis pH < 2.1 to obtain yellow material, and after filtration and centrifugation, an ammonium ferric phosphate hydroxide filter cake is obtained; Preferably, in step S6, the ammonium ferric phosphate hydroxide filter cake is slurried with pure water for 30 min, phosphoric acid solution is added and stirred for another 10 min, and the phosphorus element in the added phosphoric acid solution is 0.35:1 to the iron element molar amount in the iron-phosphorus adjustment solution; Preferably, in step S7, the white material is heated to 90 °C and turned white and then kept warm for 110 min; Preferably, in step S8, the content of low-aluminum and titanium-doped anhydrous iron phosphate is 6.38 ppm, and the titanium content is 2039 ppm.

[0030] Example 3 A method for preparing low-aluminum and titanium-doped iron phosphate material from ferrophosphorus slag, comprising the following steps: S1. Add ferrophosphorus slag (black slag) with a titanium content of 0.80% of the iron molar amount to a crusher for crushing and grinding, and screen to obtain particulate matter and dissolve it in an acid solution to prepare a primary leaching solution; S2. Continuously leach the leaching residue obtained in step S1 with an acid solution for secondary leaching to prepare a secondary leaching solution for standby; S3. Add magnesium oxide to the primary leachate obtained in step S1 to adjust the pH of the system to 1.3, stir for 30 min, filter to obtain the precipitate, i.e., the iron-phosphorus mixture; S4. Mix the secondary leachate obtained in step S2 with the iron-phosphorus mixture obtained in step S3, and adjust the iron-phosphorus ratio of the system to 1:1 to obtain the iron-phosphorus adjusted solution; S5. Heat 15% by volume of the iron-phosphorus adjusted solution to 60 °C, add the remaining iron-phosphorus adjusted solution and the alkaline substance to obtain the yellow material; S6. Pulp the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:1.8, and add phosphoric acid solution to obtain the white material; S7. Heat the above white material to 95 °C and keep it warm; S8. Naturally cool to room temperature, filter and wash, wash until the conductivity is below 600 μs / cm, and then dehydrate to obtain iron phosphate dihydrate; S9. Dry the dehydrated iron phosphate dihydrate in an oven, and then calcine it in a muffle furnace to obtain low-aluminum and titanium-doped anhydrous iron phosphate.

[0031] Preferably, in step S1, the phosphorus-iron slag is a solid mixture rich in iron phosphate and graphite after lithium extraction from waste lithium iron phosphate, and the acid is sulfuric acid. Preferably, in step S1, the hydrogen element in the primary leaching sulfuric acid solution is twice the molar amount of the iron element in the phosphorus-iron slag, stir at 40 °C for 50 min, and filter to obtain the primary leachate; Preferably, in step S1, the primary leachate mainly contains iron ions, phosphoric acid, titanium ions and aluminum ions; Preferably, in step S2, the leaching residue after filtration is continuously dissolved with sulfuric acid to obtain the secondary leachate, and the hydrogen element in the secondary leaching sulfuric acid solution is five times the molar amount of the iron element in the phosphorus-iron slag; Preferably, in step S2, the secondary leachate mainly contains iron ions, phosphoric acid and titanium ions, and the purpose of secondary leaching is to continuously dissolve the remaining phosphorus-iron slag after primary leaching.

[0032] Preferably, in step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjusted solution is n(Ti):n(Fe)=0.85%; Preferably, in step S5, the volume of the partial iron-phosphorus adjusted solution is 15% of the whole system. The alkaline substance is ammonia water. Ammonia water and the iron-phosphorus adjusted solution are fed in two streams, and the amount of ammonia water added is controlled so that the synthesis pH < 2.1 to obtain the yellow material. After filtration and centrifugation, an ammonium ferric phosphate hydroxide filter cake is obtained; Preferably, in step S6, the ammonium ferric phosphate hydroxide filter cake is slurried with pure water for 30 min, phosphoric acid solution is added and stirred for another 10 min, and the phosphorus element in the added phosphoric acid solution is 0.45:1 to the molar amount of the iron element in the iron-phosphorus adjusted solution; Preferably, in step S7, the white material is heated to 95 °C, turned white, and then kept warm for 120 min; Preferably, in step S8, the content of low-aluminum and titanium-doped anhydrous iron phosphate is 7.11 ppm, and the titanium content is 2973 ppm.

[0033] Example 4 A method for preparing low-aluminum and titanium-doped iron phosphate material by using phosphorus iron slag, comprising the following steps: S1. Add phosphorus iron slag (black slag) with a titanium content of 1.10% of the iron molar amount in the raw material into a crusher for crushing and grinding, and screen to obtain particulate materials, which are dissolved in an acid solution to prepare a primary leaching solution; S2. Continue to add an acid solution to the leaching residue obtained in step S1 for secondary leaching to prepare a secondary leaching solution for standby; S3. Add magnesium oxide to the primary leaching solution obtained in step S1 to adjust the pH of the system to 1.3, stir for 30 min, filter to obtain a precipitate, i.e., an iron-phosphorus mixture; S4. Mix the secondary leaching solution obtained in step S2 with the iron-phosphorus mixture obtained in step S3, and adjust the iron-phosphorus ratio of the system to 1:1 to obtain an iron-phosphorus adjusted solution; S5. Heat the iron-phosphorus adjusted solution with a volume ratio of 20% to 60 °C, and simultaneously add the iron-phosphorus adjusted solution and an alkaline substance to obtain a yellow material; S6. Pulp the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:1.6, and add a phosphoric acid solution to obtain a white material; S7. Heat the above white material to 98 °C and then keep it warm; S8. Naturally cool to room temperature, filter and wash, wash until the conductivity is below 600 μs / cm, and then dehydrate to obtain iron phosphate dihydrate; S9. Dry the dehydrated iron phosphate dihydrate in an oven, and then calcine it in a muffle furnace to obtain low-aluminum and titanium-doped anhydrous iron phosphate.

[0034] Preferably, in step S1, the phosphorus iron slag is a solid mixture rich in iron phosphate and graphite after lithium extraction from waste lithium iron phosphate, and the acid is sulfuric acid; Preferably, in step S1, the hydrogen element in the primary leaching sulfuric acid solution is twice the molar amount of the iron element in the phosphorus iron slag, stir at 40 °C for 50 min, and filter to obtain a primary leaching solution; Preferably, in step S1, the primary leaching solution mainly contains iron ions, phosphoric acid, titanium ions and aluminum ions; Preferably, in step S2, the filtered leaching residue is continuously dissolved with sulfuric acid to obtain a secondary leaching solution, and the hydrogen element in the secondary leaching sulfuric acid solution is five times the molar amount of the iron element in the phosphorus iron slag; Preferably, in step S2, the secondary leaching solution mainly contains iron ions, phosphoric acid and titanium ions. The purpose of secondary leaching is to continue dissolving the phosphorus iron slag remaining after primary leaching.

[0035] Preferably, in step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjustment solution is n(Ti):n(Fe) = 1.40%. Preferably, in step S5, the volume of a part of the iron-phosphorus adjustment solution is 20% of the whole system. The alkaline substance is ammonia water. The ammonia water and the iron-phosphorus adjustment solution are fed in two streams, and the addition amount of ammonia water is controlled so that the synthesis pH < 2.1 to obtain yellow material. After filtration and centrifugation, an ammonium ferric phosphate hydroxide filter cake is obtained. Preferably, in step S6, the ammonium ferric phosphate hydroxide filter cake is slurried with pure water for 30 min, and phosphoric acid solution is added and stirred continuously for 10 min. The molar amount of phosphorus element in the added phosphoric acid solution is 0.55:1 to the iron element molar amount in the iron-phosphorus adjustment solution. Preferably, in step S7, the white material is heated to 98 °C, turned white and then kept warm for 150 min. Preferably, in step S8, the content of low-aluminum titanium-doped anhydrous ferric phosphate is 6.26 ppm, and the titanium content is 4826 ppm.

[0036] Comparative Example 1 A preparation method of ferric phosphate. Comparative Example 1 is similar to the steps of Example 1, the difference being that in this comparative example, phosphorus iron slag (ferric phosphate waste) without titanium element is used in step S1, and the molar ratio of titanium to iron in the solution is controlled at n(Ti):n(Fe) = 0.00%.

[0037] Comparative Example 2 A preparation method of ferric phosphate. Comparative Example 2 is similar to the steps of Example 1, the difference being that in this comparative example, phosphorus iron slag with a titanium content of 1.5% of the iron molar amount is used in step S1.

[0038] Comparative Example 3 A preparation method of ferric phosphate. Comparative Example 3 is similar to the steps of Example 1, the difference being that in this comparative example, aluminum sulfate is added in step S4.

[0039] The following table shows the physical and chemical indexes of the ferric phosphate prepared in Examples 1 to 4 and Comparative Examples 1 to 3 of the present invention.

[0040] Table 1 Physical and Chemical Indexes of Examples and Comparative Examples

[0041] As can be seen from Table 1, when there is no titanium ion in the iron phosphate adjustment liquid in Comparative Example 1, the iron content in anhydrous iron phosphate is relatively high, the phosphorus content is relatively low, and the iron-phosphorus ratio is relatively high. As the titanium content in the raw material increases, the iron content in the prepared anhydrous iron phosphate decreases, the phosphorus content increases, and the corresponding iron-phosphorus ratio decreases; in Comparative Example 2, when the titanium content in the raw material is 1.50% of the molar amount of iron, that is, the titanium content is 5546 ppm, the iron content of the prepared iron phosphate is lower than 36.00%, the phosphorus content is higher than 20.90%, and the iron-phosphorus ratio is lower than 96.00%; in Comparative Example 3, aluminum sulfate was additionally added in step S4, resulting in the aluminum content in the final product rising to 728 ppm. Aluminum impurities will hinder the diffusion of lithium ions and reduce the capacity and rate performance of lithium iron phosphate (LiFePO4). It should be noted that except for Comparative Example 3, the content of low-aluminum titanium-doped anhydrous iron phosphate prepared is lower than 10 ppm.

[0042] The iron phosphates prepared in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3 were made into lithium iron phosphate button cells, and their electrochemical performances were detected. The detection indexes are shown in Table 2.

[0043] Table 2 Indexes of lithium iron phosphate prepared in examples and comparative examples

[0044] As can be seen from Table 2, the sintered compaction density of the examples is relatively high and much higher than that of the comparative examples. The 1C discharge capacities of Examples 1, 2, 3, and 4 are 137, 139, 140, and 141 mAh / g respectively, and increase with the increase of the titanium doping amount. On the one hand, as the titanium doping amount increases, the crystal plane spacing of the iron phosphate crystal will change. The increase of the crystal plane spacing is beneficial to the intercalation and deintercalation process of lithium ions, thus improving the electrical performance of lithium iron phosphate. On the other hand, the incorporation of titanium elements can also improve the ionic conductivity and electronic conductivity of iron phosphate, which makes it easier for iron phosphate to release and store energy, thus improving the charge and discharge speed and capacity of the battery. The results of Comparative Examples 1 and 2 show that when no titanium is doped and the titanium doping amount is higher than a certain value (n(Ti):n(Fe)=1.50%), it shows lower electrochemical activity. And when the iron phosphate contains too much electrochemically inactive impurity aluminum, the electrical performance of its lithium iron phosphate is only 131 mAh / g, which will seriously affect the electrical performance of lithium iron phosphate.

[0045] Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 、 Figure 8Respectively shown are the electron microscope images of the anhydrous iron phosphate prepared in Example 1, Example 2, Example 3, Example 4 of the present invention, and Comparative Example 1, Comparative Example 2, and Comparative Example 3. It can be seen from the figure that when the titanium doping amount in Comparative Example 3 and Examples 1 to 4 is between 0.30% and 1.40%, the particles are evenly distributed and stacked in an orderly manner, and the boundaries between the particles are clear. This morphology not only increases the specific surface area of the material, improves the reaction activity, but also facilitates the rapid diffusion and insertion of lithium ions, while improving the overall mechanical properties and stability of the material. When no titanium element is doped and the titanium doping amount is 1.50%, the fusion between particles is relatively serious. It can be seen from Comparative Example 3 and Example 1 that there is no special difference in the morphology between high-aluminum iron phosphate and low-aluminum iron phosphate, and their differences are mainly reflected in the performance after being made into lithium iron phosphate.

Claims

1. A method for preparing low-aluminum titanium-doped iron phosphate material using ferrophosphorus slag, characterized in that, It includes the following steps: S1. Add phosphoric iron slag with a titanium content in the raw material of 0.20%-1.10% of the molar amount of iron into a crusher for crushing, grinding, and screening to obtain granular materials. Dissolve the granular materials in an acid solution for primary leaching, control the pH = 0.5-1.5, the temperature at 20-40 °C, react for 10-50 minutes, and filter to obtain the primary leachate and leaching residue; S2. Continue to add an acid solution to the leaching residue obtained in step S1 for secondary leaching to obtain a secondary leachate; S3. Add an alkaline substance to the primary leachate obtained in step S1 to adjust the system pH = 1.0-1.8, filter to obtain the precipitate, i.e., the iron-phosphorus mixture; S4. Mix the secondary leachate obtained in step S2 with the iron-phosphorus mixture obtained in step S3, and adjust the iron-phosphorus ratio in the system to 1:1 to obtain an iron-phosphorus adjustment solution; S5. Take 5-20% by volume of the iron-phosphorus adjustment solution, heat it to 60 °C, add the remaining iron-phosphorus adjustment solution and an alkaline substance to obtain a yellow material; S6. Pulp the yellow material obtained in step S5 with pure water at a material-liquid mass ratio of 1:1.5-2, and add a phosphoric acid solution to obtain a white material; S7. Heat the above white material to 85-98 °C and then keep it warm; S8. Naturally cool to room temperature, filter, wash, and dehydrate to obtain iron phosphate dihydrate; S9. Dry and calcine the iron phosphate dihydrate in an oven to obtain low-aluminum and titanium-doped anhydrous iron phosphate, i.e., anhydrous iron phosphate.

2. The method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S1, the phosphoric iron slag is a solid mixture rich in iron phosphate and graphite after lithium extraction from waste lithium iron phosphate.

3. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In steps S1 and S2, the acid solution is one of sulfuric acid, hydrochloric acid, and perchloric acid; The hydrogen element in the acid solution is in a ratio of 2-5:1 to the molar amount of iron element in the phosphoric iron slag.

4. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S1, the primary leachate contains iron ions, phosphoric acid, titanium ions, and aluminum ions.

5. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S2, the secondary leachate mainly contains iron ions, phosphoric acid, and titanium ions.

6. The method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, wherein In steps S3 and S5, the alkaline substance is one or several of sodium hydroxide, potassium hydroxide, magnesium oxide, and ammonia water.

7. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S4, the molar ratio of titanium ions to iron ions in the iron-phosphorus adjustment solution is n(Ti):n(Fe)=0.3%-1.2%.

8. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S6, the phosphorus element in the added phosphoric acid solution is in a ratio of 0.25-0.55:1 to the molar amount of iron element in the iron-phosphorus adjustment solution.

9. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S7, the heat preservation time is 60-150 min.

10. A method for preparing a low-aluminum titanium-doped iron phosphate material using phosphorus iron slag according to claim 1, characterized in that, In step S8, in the low-aluminum and titanium-doped anhydrous iron phosphate, the aluminum content is 2-10 ppm, and the titanium content is 1200-6000 ppm.

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