Preparation method of uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexing slow release

Abstract

The invention provides a preparation method of uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexing slow release, and relates to the technical field of lithium ion battery positive electrode material preparation, and the preparation method comprises the following steps: 1, a synthesis stage: pure water is used for bottoming, an iron source and a phosphorus source are mixed, hydrogen peroxide is added for oxidation, and a basic ammonium iron phosphate precursor is generated through a reaction; 2, a conversion stage: adding water into the basic ammonium iron phosphate precursor for slurrying, performing crystal transfer in a high-temperature acid environment to obtain iron phosphate dihydrate, adding a titanium slow-release agent in a crystal growth stage, and performing suction filtration and washing to obtain titanium-containing iron phosphate dihydrate; 3, post-treatment: washing and calcining the titanium-containing iron phosphate dihydrate to obtain titanium-doped iron phosphate; the invention provides a process for preparing titanium-doped iron phosphate by taking a titanium slow-release agent as a titanium source, a titanium sulfate solution and hydrogen peroxide are combined to form a relatively stable complex to replace a traditional titanium sulfate source, and the crystallinity and the grain size of iron phosphate crystals prepared by the process are not obviously influenced by titanium-doped ions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material preparation technology, specifically to a method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and other fields, lithium iron phosphate (LiFePO4) has become a mainstream cathode material, and its performance optimization has become a focus of industry attention. Titanium-doped iron phosphate (Ti-doped FePO4) is a key precursor for improving the conductivity and structural stability of lithium iron phosphate, and its doping uniformity directly affects the energy density, cycle life, and safety of the final battery. However, existing titanium doping processes still face significant technical bottlenecks in industrial production, such as the kinetic mismatch problem of direct doping (the solubility of titanium phosphate is extremely low, approximately 10). -29 Much lower than the Ksp≈10 of iron phosphate. -22 (Impatiens ions preferentially combine with phosphate to form independent precipitates), the side effects of coprecipitation methods and complexing agents (complexing agents such as citric acid and EDTA delay the release of titanium ions, but these complexing agents easily interfere with the ferric phosphate crystallization process and are difficult to meet the requirements of green production), and the industrialization obstacles of high uniformity processes (although sol-gel methods and hydrothermal methods can achieve atomic-level dispersion, they rely on organic titanium sources, high-temperature and high-pressure reaction conditions (>180℃) or complex post-processing processes, leading to a surge in production costs).

[0003] In the prior art: (1) Direct doping method (traditional process) Titanium salts (such as titanium sulfate and tetrabutyl titanate) are directly added during the synthesis of iron phosphate, and doping is achieved through co-precipitation or solid-state reaction. Its advantages are simple process and low cost, but titanium ions (Ti)... 4+ ) and phosphate (PO4) 3- If the combination is too rapid, it is very easy to form independent titanium phosphate precipitates (Ksp=10). -29 This leads to uneven doping and large fluctuations in electrochemical performance (such as fluctuations in ion diffusion coefficient of ±15%).

[0004] (2) Optimization of coprecipitation method The precipitation rate of titanium salts and phosphate ions can be slowed down by controlling pH, temperature, and stirring speed. The advantage is that it can partially improve the uniformity of titanium distribution, but the disadvantages are that it requires precise control of reaction conditions (e.g., pH = 2.5-3.5), has a narrow process window, and results in poor batch consistency.

[0005] (3) Sol-gel method Titanium and iron sources are mixed in a sol state and then dispersed at the atomic level through gelation. The advantage is high doping uniformity (EDS surface scan standard deviation <3%), but the process is complex (requiring high-temperature calcination), costly, and difficult to scale up.

[0006] (4) Hydrothermal / solventricular method In a closed high-pressure reactor, titanium ions are uniformly embedded into the iron phosphate lattice through high temperature and high pressure. The advantages are high product crystallinity and good doping uniformity, but the equipment investment is large, the energy consumption is high (reaction temperature >180℃), and the safety risks are high.

[0007] In other words, the traditional titanium-doped lithium iron phosphate preparation process has the following problems: ① Insufficient doping uniformity: The standard deviation of titanium distribution in the traditional process is >8%, resulting in poor batch consistency of the prepared lithium iron phosphate batteries; ② High process complexity: The hydrothermal method / sol-gel method is difficult to balance cost and performance; ③ Environmental pressure: Some processes use organic complexing agents (such as EDTA), resulting in high wastewater treatment costs. Summary of the Invention

[0008] Given the difficulty of obtaining uniform titanium-doped iron phosphate using traditional processes in an economical and rapid manner, this invention proposes a process for preparing titanium-doped iron phosphate using a titanium slow-release agent as the titanium source. This involves combining titanium sulfate solution with hydrogen peroxide to form a relatively stable complex, which replaces the traditional titanium sulfate source. This complex is introduced during the iron phosphate crystal growth stage. In the high-temperature, high-acid transformation environment of basic ammonium ferric phosphate, the complex slowly decomposes, thus achieving a match between the slow release of titanium ions and the crystallization kinetics of iron phosphate. This results in uniformly titanium-doped iron phosphate. This process effectively reduces the cost and difficulty of preparing titanium-doped iron phosphate, and the crystallinity and grain size of the iron phosphate crystals are not significantly affected by the titanium doping ions, as detailed below: A method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and sustained release includes the following steps: (1) Synthesis stage: pure water is used as the base, iron source and phosphorus source are mixed, hydrogen peroxide is added for oxidation, and the reaction produces a yellow one-wash filter cake, which is the basic iron ammonium phosphate precursor. (2) Conversion stage: The basic ammonium iron phosphate precursor obtained in step (1) is slurried with water and then crystallized into iron phosphate dihydrate in a high temperature acidic environment. Titanium slow-release agent is added during the crystal growth stage, and the filter cake is obtained by vacuum filtration and washing, which is titanium-containing iron phosphate dihydrate. (3) Post-processing: The titanium-containing iron phosphate dihydrate obtained in step (2) is washed and calcined to obtain titanium-doped iron phosphate.

[0009] Moreover, the specific operation method of step (1) is as follows: A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.2. Impurity-removed ferrous titanium dioxide was used as the iron source, and hydrogen peroxide was used as the oxidant. Pure water was used as the base. In a 10L reactor, the phosphorus source and iron source were added in parallel, followed by hydrogen peroxide. The reaction temperature was maintained at 30-60℃. After the feeding was completed, the temperature was kept for 25-35 minutes before the slurry was discharged. The slurry was filtered and washed until the conductivity of the wash water was lower than 4000 μS / cm, resulting in a yellow first-wash filter cake, which is the precursor of basic ammonium iron phosphate.

[0010] Furthermore, the concentration of the monoammonium phosphate solution is 0.5-2.0 mol / L, the concentration of ferrous titanium dioxide is 0.5-2.0 mol / L, and the molar ratio of ferrous titanium dioxide to monoammonium phosphate is 0.8-1.2.

[0011] Furthermore, the feeding rate of iron and phosphorus sources is 100-300 ml / min, and the feeding rate of hydrogen peroxide is 10-15 ml / min.

[0012] Moreover, the specific operation method of step (2) is as follows: Weigh 4-8 kg of water, add 2-3 kg of yellow first-wash filter cake and slurry. After slurrying for 20 minutes, add 200-700 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the slurry to 80-90℃. After the slurry turns white for 5 minutes, add titanium slow-release agent to the slurry. After keeping it warm for 1 hour, discharge the material and filter and wash to obtain a pink second-wash filter cake, which is titanium dihydrate ferric phosphate.

[0013] Furthermore, in step (2), the titanium slow-release agent is a complex formed by hydrogen peroxide and titanium sulfate, and the complex is [TiO(H2O2)] 2+ Complex.

[0014] Moreover, the preparation steps of the titanium slow-release agent include: weighing 3-12g of anhydrous titanium sulfate and dissolving it in 1L of pure water, and slowly adding 10-15g of hydrogen peroxide solution to the titanium sulfate solution under stirring to obtain a yellow hydrogen peroxide-titanium sulfate complex solution, which is the titanium slow-release agent.

[0015] Moreover, in step (2), the crystal growth stage is within 5 minutes after the slurry turns from yellow to white.

[0016] Moreover, in step (2), the high-temperature acidic environment of the conversion stage is: temperature of 80-90℃ and pH value of 1.5-2.5.

[0017] Moreover, in step (3), the calcination temperature is 500-700℃ and the calcination time is 2-4 hours.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes a process for preparing titanium-doped iron phosphate using a titanium slow-release agent as the titanium source. By combining titanium sulfate solution with hydrogen peroxide to form a relatively stable complex, this complex replaces the traditional titanium sulfate source. The complex is introduced during the iron phosphate crystal building and growth stage. In the high-temperature and high-acid crystallization environment of basic ammonium iron phosphate, the complex slowly decomposes, thereby achieving a match between the slow release of titanium ions and the crystallization kinetics of iron phosphate. This results in uniformly titanium-doped iron phosphate. This process effectively reduces the cost and difficulty of preparing titanium-doped iron phosphate, and the crystallinity and grain size of the iron phosphate crystals are not significantly affected by titanium doping ions.

[0019] 2. The titanium slow-release mechanism provided by this invention effectively solves the problem of uneven doping caused by the rapid combination of titanium ions and phosphate groups in the traditional direct doping method, significantly improving the doping uniformity of titanium-doped iron phosphate. Electron probe microanalysis (EPMA) reveals that titanium elements are distributed as tiny star-like spots in the iron phosphate crystals, without obvious bright aggregation spots, further demonstrating the effectiveness of the slow-release agent in improving doping uniformity. Using this slow-release agent for titanium doping requires no complex equipment or high-temperature, high-pressure conditions; it can be modified based on existing iron phosphate production lines, compatible with existing production lines and raw materials, without the need for additional raw material purchases or equipment modifications. This not only simplifies the process but also reduces production costs, making the industrial production of titanium-doped iron phosphate possible.

[0020] 3. This invention utilizes hydrogen peroxide-titanium sulfate complex as a titanium slow-release agent to solve the following industry pain points: ① Atomic-level dispersion (EDS standard deviation <2%) is achieved through titanium-hydrogen peroxide complexation slow release; ② The process is compatible with existing production lines and raw materials, without the need for additional raw material procurement and equipment modification; ③ A pollution-free complexing agent is used (H2O2 decomposes into H2O and O2). Attached Figure Description

[0021] Figure 1 This is a SEM scan image of the titanium-doped iron phosphate prepared in Example 3; Figure 2 This is an electron probe X-ray microscopy image of the titanium-doped iron phosphate prepared in Example 3; Figure 3 The X-ray diffraction pattern of the titanium-containing iron phosphate dihydrate prepared in Example 3 is shown below. Figure 4 The image shows the SEM scan of the iron phosphate prepared in Comparative Example 1. Figure 5 The X-ray diffraction pattern of the ferric phosphate dihydrate prepared in Comparative Example 1 is shown. Figure 6 The image shows the SEM scan of the iron phosphate prepared in Comparative Example 2. Figure 7Electron probe X-ray microscopy analysis of the iron phosphate prepared in Comparative Example 2; Figure 8 The X-ray diffraction analysis diagram of the iron phosphate dihydrate prepared in Comparative Example 2 is shown. Figure 9 This is a comparison chart of titanium slow-release agents. Detailed Implementation

[0022] Example 1 A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.2 and the concentration of monoammonium phosphate solution controlled at 0.5 mol / L. Impurity-removed ferrous titanium dioxide was used as the iron source, with the iron source concentration controlled at 0.5 mol / L and the ratio of ferrous titanium dioxide to monoammonium phosphate controlled between 0.8 and 1.2. Hydrogen peroxide was used as the oxidant. The overall process route can be divided into a synthesis stage and a conversion stage based on the temperature rise and conversion node. In order to reduce the impurity content in the finished product, a washing step was added between the two stages.

[0023] The process parameters for the synthesis stage are as follows: A 10L reactor is used as the reaction vessel. Pure water is used as the initial feed, and phosphorus and iron sources are added in parallel, followed by hydrogen peroxide. The feed rates for iron and phosphorus sources are 100 ml / min, and the feed rate for hydrogen peroxide is 10 ml / min. The reaction temperature is maintained at 30℃. After the feed is completed, the mixture is kept at this temperature for 25 minutes, and the slurry is discharged. It is then filtered and washed until the conductivity of the wash water is below 4000 μS / cm. At this point, a yellow first-wash filter cake is obtained, which is the basic ferric ammonium phosphate precursor.

[0024] The conversion stage then begins, during which hydrogen peroxide-titanium sulfate complex is used as a titanium slow-release agent. The preparation process of the slow-release agent is as follows: Weigh 3g of anhydrous titanium sulfate and dissolve it in 1L of pure water. Then, under stirring, slowly add 10g of hydrogen peroxide solution (controlling Ti(SO4)2:H2O2=1:2) to the titanium sulfate solution to obtain a yellow hydrogen peroxide-titanium sulfate complex solution. This solution is used as the titanium slow-release agent. Considering that the harsh environment of high temperature and high phosphorus during the early stage of conversion may cause premature decomposition of the titanium slow-release agent, the titanium slow-release agent is only introduced during the crystal growth stage after the slurry turns white. The process parameters for the conversion stage are as follows: Weigh 4 kg of pulping water, then add 2 kg of yellow first-wash filter cake for pulping. After 20 minutes of complete pulping, add 200 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the pulp to 80℃. After the pulp turns white for 5 minutes, add titanium slow-release agent to the pulp. After keeping it warm for 1 hour, discharge the material. After filtration and washing, obtain a pink second-wash filter cake. Dry, calcine, and pulverize the second-wash filter cake to obtain the finished titanium-doped iron phosphate.

[0025] Example 2 A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.2 and the concentration of monoammonium phosphate solution controlled at 2.0 mol / L. Impurity-removed ferrous titanium dioxide was used as the iron source, with the iron source concentration controlled at 2.0 mol / L and the ratio of ferrous titanium dioxide to monoammonium phosphate controlled between 0.8 and 1.2. Hydrogen peroxide was used as the oxidant. The overall process route can be divided into a synthesis stage and a conversion stage based on the temperature rise and conversion node. In order to reduce the impurity content in the finished product, a washing step was added between the two stages.

[0026] The process parameters for the synthesis stage are as follows: A 10L reactor is used as the reaction vessel. Pure water is used as the initial feed, and phosphorus and iron sources are added in parallel, followed by hydrogen peroxide. The feed rates for iron and phosphorus sources are 300 ml / min, and the feed rate for hydrogen peroxide is 15 ml / min. The reaction temperature is maintained at 60℃. After the feed is completed, the mixture is kept at this temperature for 35 minutes, and the slurry is discharged. It is then filtered and washed until the conductivity of the wash water is below 4000 μS / cm. At this point, a yellow first-wash filter cake is obtained, which is the basic ferric ammonium phosphate precursor.

[0027] The conversion stage then begins, during which hydrogen peroxide-titanium sulfate complex is used as a titanium slow-release agent. The preparation process of the slow-release agent is as follows: 12g of anhydrous titanium sulfate is weighed and dissolved in 1L of pure water. Then, 15g of hydrogen peroxide solution is slowly added dropwise to the titanium sulfate solution while stirring (controlling Ti(SO4)2:H2O2=1:3), thereby obtaining a yellow hydrogen peroxide-titanium sulfate complex solution. This solution is used as the titanium slow-release agent. Considering that the harsh environment of high temperature and high phosphorus during the early stage of conversion may cause premature decomposition of the titanium slow-release agent, the titanium slow-release agent is only introduced during the crystal growth stage after the slurry turns white. The process parameters for the conversion stage are as follows: Weigh 8 kg of pulping water, then add 2 kg of yellow first-wash filter cake for pulping. After 20 minutes of complete pulping, add 700 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the pulp to 90℃. After the pulp turns white for 5 minutes, add titanium slow-release agent to the pulp. After keeping it warm for 1 hour, discharge the material. After filtration and washing, a pink second-wash filter cake can be obtained. Dry, calcine, and pulverize the second-wash filter cake to obtain the finished titanium-doped iron phosphate.

[0028] Example 3 A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.2 and the concentration of monoammonium phosphate solution controlled at 1 mol / L. Impurity-removed ferrous titanium dioxide was used as the iron source, with the iron source concentration controlled at 1 mol / L and the ratio of ferrous titanium dioxide to monoammonium phosphate controlled between 0.8 and 1.2. Hydrogen peroxide was used as the oxidant. The overall process route can be divided into a synthesis stage and a conversion stage based on the temperature rise and conversion node. In order to reduce the impurity content in the finished product, a washing step was added between the two stages.

[0029] The process parameters for the synthesis stage are as follows: A 10L reactor was used as the reaction vessel. Pure water was used as the initial feed, and phosphorus and iron sources were added in parallel, followed by hydrogen peroxide. The feed rates for iron and phosphorus sources were 200 ml / min, and the feed rate for hydrogen peroxide was 12 ml / min. The reaction temperature was maintained at 45℃. After the feed was completed, the mixture was kept at this temperature for 30 minutes, and the slurry was discharged. It was then filtered and washed until the conductivity of the wash water was below 4000 μS / cm, at which point a yellow, first-wash filter cake was obtained.

[0030] The conversion stage then begins, during which hydrogen peroxide-titanium sulfate complex is used as a titanium slow-release agent. The preparation process of the slow-release agent is as follows: 8g of anhydrous titanium sulfate is weighed and dissolved in 1L of pure water. Then, 13g of hydrogen peroxide solution is slowly added dropwise to the titanium sulfate solution while stirring (controlling Ti(SO4)2:H2O2=1:2.5). This yields a yellow hydrogen peroxide-titanium sulfate complex solution, which is used as the titanium slow-release agent. Considering that the harsh environment of high temperature and high phosphorus during the early stage of conversion may cause premature decomposition of the titanium slow-release agent, the titanium slow-release agent is only introduced during the crystal growth stage after the slurry turns white. The process parameters for the conversion stage are as follows: Weigh 6 kg of pulping water, then add 2 kg of yellow first-wash filter cake for pulping. After 20 minutes of complete pulping, add 500 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the pulp to 85℃. After the pulp turns white for 5 minutes, add titanium slow-release agent to the pulp. After keeping it warm for 1 hour, discharge the material. After filtration and washing, a pink second-wash filter cake can be obtained. Dry, calcine, and pulverize the second-wash filter cake to obtain the finished titanium-doped iron phosphate.

[0031] The prepared titanium-doped iron phosphate was analyzed by SEM and electron probe microscopy. The results are shown in the figure. Figure 1 , Figure 2 Simultaneously, its physicochemical properties were determined, as detailed in Table 1. X-ray diffraction analysis was performed on the prepared pink two-wash filter cake (i.e., titanium-containing ferric phosphate dihydrate), and the results are shown in Table 1. Figure 3 .

[0032] The results above show that the introduction of titanium slow-release agent during the conversion process did not significantly affect the growth of iron phosphate crystals. Figure 1 It can be seen that after high-temperature calcination in a muffle furnace at 600℃, the primary particles adhered to each other, but the overall structure remained loose and porous. The particles were rounded and clearly defined, with no large pasty substances appearing, indicating that each individual grain was fully developed. Electron probe X-ray microscopy (EPMA) was used to analyze the uniformity of titanium element distribution in titanium-doped iron phosphate. This technique has higher accuracy than traditional energy scattering spectroscopy (EDS). Figure 2 As can be seen, the titanium element in the EPMA spectrum is distributed as tiny star-like dots, without obvious bright aggregates, indicating that the titanium element has achieved uniform doping at the nanoscale. Furthermore, from the X-ray diffraction pattern of ferric phosphate dihydrate (… Figure 3 No obvious titanium-related impurity peaks were found in the sample, indicating that the phase is a pure monoclinic phase. The high diffraction peak intensity and narrow half-peak width also indicate that the grains have good crystallinity.

[0033] As can be seen from Table 1, the high calcined specific surface area (BET=10.9) and the iron-to-phosphorus ratio of over 96.5% indicate that the incorporation of 2096 ppm titanium did not significantly affect the thermal stability and composition of the iron phosphate crystal structure. This suggests that it is feasible to prepare uniformly titanium-doped iron phosphate using hydrogen peroxide-titanium sulfate complex as a titanium slow-release agent.

[0034] Table 1 Physicochemical properties of iron phosphate in Example 3

[0035] Example 4

[0036] To better explain the mechanism of action of the hydrogen peroxide-titanium sulfate sustained-release agent, the thermal stability of this agent was investigated. Figure 9 A comparison was made with titanium slow-release agents (a complex formed by hydrogen peroxide and titanium sulfate: [TiO(H2O2))). 2+ The slow-release agent (complex) changed from an initial wine-red liquid to a transparent colorless liquid after being poured into 85°C pure water for 10 minutes. This process corresponds to the thermal decomposition of the slow-release agent. The decomposition process also produces a lot of small bubbles, indicating that hydrogen peroxide decomposes under the influence of high temperature, which in turn leads to the decomposition of the slow-release agent.

[0037] Comparative Example 1 To compare the impact of titanium slow-release agent on the process, compared with Example 3, Comparative Example 1 removed the step of adding titanium slow-release agent after whitening. A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.2 and the concentration of monoammonium phosphate solution controlled at 1 mol / L. The purified titanium dioxide ferrous iron was used as the iron source, with the iron source concentration controlled at 1 mol / L. The ratio of titanium dioxide ferrous iron to monoammonium phosphate was controlled between 0.8 and 1.2. Hydrogen peroxide was used as the oxidant. The overall process route can be divided into a synthesis stage and a conversion stage based on the temperature rise conversion node. In order to reduce the impurity content in the finished product, a washing step was added between the two stages.

[0038] The process parameters for the synthesis stage are as follows: A 10L reactor is used as the reaction vessel. Pure water is used as the initial feed, and phosphorus and iron sources are added in parallel, followed by hydrogen peroxide. The feed rates for iron and phosphorus sources are 200 ml / min, and the feed rate for hydrogen peroxide is 12 ml / min. The reaction temperature is maintained at 45℃. After feeding, the mixture is kept at this temperature for 30 minutes, and the slurry is discharged. It is then filtered and washed until the conductivity of the wash water is below 4000 μS / cm, at which point a yellow first-wash filter cake is obtained. The conversion stage then begins, with the following process parameters: 6 kg of pulping water is weighed and added to the filter cake for pulping. After 20 minutes of complete pulping, 500 g of phosphoric acid is added, and the oil bath is simultaneously turned on to raise the temperature. The final temperature of the slurry is controlled at 85℃. After holding at this temperature for 1 hour, the mixture is discharged. After filtration and washing, a pink second-wash filter cake is obtained. The second-wash filter cake is dried, calcined, and pulverized to obtain the finished titanium-doped iron phosphate.

[0039] The prepared titanium-doped iron phosphate was analyzed by SEM microscopy, and the results are shown in the figure. Figure 4 Simultaneously, its physicochemical properties were measured, as detailed in Table 2. X-ray diffraction analysis was performed on the prepared pink two-wash filter cake (i.e., ferric phosphate dihydrate), and the results are shown in Table 2. Figure 5 .

[0040] Table 2 Physicochemical properties of iron phosphate in Comparative Example 1

[0041] Comparing the physicochemical data in Tables 1 and 2, apart from the difference in titanium content due to the removal of the titanium doping step, the iron-phosphorus ratio, specific surface area, and moisture content of the two samples are quite similar. The introduction of the titanium slow-release agent, while achieving titanium doping, did not negatively affect the iron-phosphorus stoichiometry, specific surface area, or moisture content. This fully demonstrates the superiority of the strategy of using a titanium slow-release agent for titanium doping. Traditional doping methods, such as adding titanium sulfate to the iron salt at the synthesis stage or directly adding titanium sulfate before the conversion heating, significantly inhibit crystal growth, resulting in a sharp drop in the iron-phosphorus ratio of the finished product, a low anhydrous specific surface area after calcination, and blurred particle boundaries in the morphology. The hydrogen peroxide-titanium sulfate slow-release agent used in this invention overcomes these shortcomings.

[0042] from Figure 4As can be seen, the anhydrous ferric phosphate particles in Comparative Example 1 adhered to each other but remained loose and porous overall. This is because Comparative Example 1 did not incorporate titanium doping during the ferric phosphate crystallization process, thus avoiding interference from titanium ions and achieving higher ferric phosphate crystallinity. This increased particle burn-resistance manifested in the particles not easily fusing into large clumps; although adhered, they remained loose and porous. Theoretically, titanium isovalent ions would affect the ferric phosphate crystallization process, and the morphology of Comparative Example 1 is similar to that of the examples. This indicates that replacing traditional titanium sulfate with a hydrogen peroxide-titanium sulfate slow-release agent as the titanium source can significantly reduce the influence of titanium ions on the ferric phosphate crystallization process.

[0043] from Figure 5 It can be seen that the X-ray diffraction pattern of the ferric phosphate dihydrate prepared in Comparative Example 1 still shows a monoclinic phase with high peak intensity and narrow half-peak width, indicating that the material prepared in Comparative Example 1 has high crystallinity, which is consistent with... Figure 4 The high crystallinity morphology characteristics are consistent. The peak shapes of the X-ray diffraction patterns of Comparative Example 1 and the Examples are similar, which further indicates that using hydrogen peroxide-titanium sulfate as a titanium source can significantly reduce the influence of titanium ions on the iron phosphate crystallization process, demonstrating the superiority of this strategy. Figure 5 It can be seen that although the X-ray diffraction pattern of the ferric phosphate dihydrate prepared in Comparative Example 1 still shows a monoclinic phase, the overall peak intensity is not high. This indicates that the crystallization process of ferric phosphate may have been inhibited without the use of titanium slow-release agent, resulting in generally poor crystallinity. This is consistent with the conclusion in Comparative Example 1 that the ferric phosphate crystals are incompletely developed and have poor thermal stability.

[0044] In this invention, titanium sulfate and hydrogen peroxide can combine to form [TiO(H2O2)] 2+ The complex is formed by introducing [TiO(H2O2)] during the crystallization of basic ammonium ferric phosphate to produce ferric phosphate dihydrate. 2+ The complex, through its controllable decomposition under high phosphoric acid / high temperature conditions, enables the simultaneous release of titanium and crystal growth. In conventional doping processes, adding 2000 ppm titanium to iron phosphate typically reduces the iron-to-phosphorus ratio by more than 0.5% (compared to the undoped process). The similar iron-to-phosphorus ratios in Example 1 and Comparative Example 1 demonstrate that when the titanium ion release rate and the iron phosphate crystallization kinetics rate are close, the impact of titanium doping on iron phosphate crystals can be effectively reduced, highlighting the necessity of the hydrogen peroxide-titanium sulfate slow-release agent.

[0045] Comparative Example 2 To compare the differences between titanium slow-release agents and titanium sulfate doping, Comparative Example 2, compared to Example 3, replaced the titanium slow-release agent with titanium sulfate, while the titanium doping sites and amounts remained unchanged. Comparative Example 2 used a mixture of monoammonium phosphate and ammonia as the phosphorus source, with the pH controlled at 7.0-7.2 and the monoammonium phosphate solution concentration controlled at 1 mol / L. It used purified titanium dioxide ferrous oxide as the iron source, with the iron source concentration controlled at 1 mol / L. The ratio of titanium dioxide ferrous oxide to monoammonium phosphate was controlled between 0.8 and 1.2. Hydrogen peroxide was used as the oxidant. The overall process route can be divided into a synthesis stage and a conversion stage based on the temperature rise conversion node. To reduce the impurity content in the finished product, a washing step was added between the two stages.

[0046] The process parameters for the synthesis stage are as follows: A 10L reactor was used as the reaction vessel. Pure water was used as the initial feed, and phosphorus and iron sources were added in parallel, followed by hydrogen peroxide. The feed rates for iron and phosphorus sources were 200 ml / min, and the feed rate for hydrogen peroxide was 8 ml / min. The reaction temperature was maintained at 45℃. After the feed was completed, the mixture was kept at this temperature for 30 minutes, and the slurry was discharged. It was then filtered and washed until the conductivity of the wash water was below 4000 μS / cm, at which point a yellow, first-wash filter cake was obtained.

[0047] The conversion stage then begins, with the following process parameters: Weigh 6 kg of pulping water, then add the filter cake for pulping. After 20 minutes of complete pulping, add 500 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the pulp to 85°C. After the pulp turns white for 5 minutes, add titanium sulfate to the pulp. After keeping it warm for 1 hour, discharge the material. After filtration and washing, a pink secondary filter cake can be obtained. Dry, calcine, and pulverize the secondary filter cake to obtain the finished titanium-doped iron phosphate.

[0048] The prepared titanium-doped iron phosphate was analyzed by SEM and electron probe microscopy. The results are shown in the figure. Figure 6 , Figure 7 Simultaneously, its physicochemical properties were measured, as detailed in Table 3. X-ray diffraction analysis was performed on the prepared pink two-wash filter cake (i.e., ferric phosphate dihydrate), and the results are shown in Table 3. Figure 8 .

[0049] Table 3 Physicochemical properties of iron phosphate in Comparative Example 2

[0050] from Figure 6 and Figure 1The comparison shows that, compared to the anhydrous morphology of Example 3, the primary particles of Comparative Example 2 exhibit a partially fused and partially porous characteristic. At the same calcination temperature (600℃), the primary particles clearly fused, indicating poor thermal stability and disordered crystal structure. Compared to the loose and porous morphology of Comparative Example 1 without titanium doping, this demonstrates that directly adding titanium sulfate solution after whitening significantly affects the crystal development process. This is because titanium ions and iron ions have different valence states, ionic radii, and charge densities. Excessive replacement of iron ions by titanium ions in a short period during crystal development can deform the iron phosphate crystal structure and quench the crystallization process. Furthermore, smaller-sized iron phosphate with disordered crystal structures exhibits reduced thermal stability, leading to severe intergranular melting at conventional calcination temperatures.

[0051] We also used EPMA to analyze the uniformity of titanium element distribution, from Figure 7 As can be seen, many bright spots appeared in the EPMA (electron probe microanalysis) pattern, indicating that a large amount of titanium element was accumulated in this region. It is possible that the titanium element was not incorporated into the iron phosphate lattice, but formed a separate phase. This suggests that direct doping with titanium sulfate solution during the conversion process is very likely to result in uneven doping.

[0052] from Figure 8 As can be seen, the XRD pattern shows that the phase is still monoclinic, but the overall peak intensity is not high, which also indicates that the crystallization process is inhibited by the incorporation of titanium.

[0053] Table 3 shows the physicochemical properties of anhydrous ferric phosphate after calcination in Comparative Example 2. Compared with Example 3, the titanium content is similar, but the iron-phosphorus ratio is significantly reduced to only 96.08%, indicating that the ferric phosphate grains are not heat-resistant, have poor crystallinity, and the crystallization process is insufficient.

Claims

1. A method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and sustained release, characterized in that, Includes the following steps: (1) Synthesis stage: pure water is used as the base, iron source and phosphorus source are mixed, hydrogen peroxide is added for oxidation, and the reaction produces a yellow one-wash filter cake, which is the basic iron ammonium phosphate precursor. (2) Conversion stage: The basic ammonium iron phosphate precursor obtained in step (1) is slurried with water and then crystallized into iron phosphate dihydrate in a high temperature acidic environment. Titanium slow-release agent is added during the crystal growth stage, and the filter cake is obtained by vacuum filtration and washing, which is titanium-containing iron phosphate dihydrate. (3) Post-processing: The titanium-containing iron phosphate dihydrate obtained in step (2) is washed and calcined to obtain titanium-doped iron phosphate.

2. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 1, characterized in that, The specific operation method of step (1) is as follows: A mixture of monoammonium phosphate and ammonia was used as the phosphorus source, with the pH of the phosphorus source controlled at 7.0-7.

2. Ferrous titanium dioxide was used as the iron source, and hydrogen peroxide was used as the oxidant. Pure water was used as the base. In a 10L reactor, the phosphorus source and iron source were added in parallel, followed by hydrogen peroxide. The reaction temperature was maintained at 30-60℃. After the addition was completed, the temperature was maintained for 25-35 minutes before the slurry was discharged. The slurry was filtered and washed until the conductivity of the wash water was lower than 4000 μS / cm, resulting in a yellow first-wash filter cake, which is the precursor of basic ammonium iron phosphate.

3. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 2, characterized in that, The concentration of monoammonium phosphate solution is 0.5-2.0 mol / L, the concentration of ferrous titanium dioxide is 0.5-2.0 mol / L, and the molar ratio of ferrous titanium dioxide to monoammonium phosphate is 0.8-1.

2.

4. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 2, characterized in that, The feeding rate of iron and phosphorus sources is 100-300 ml / min, and the feeding rate of hydrogen peroxide is 10-15 ml / min.

5. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 1, characterized in that, The specific operation method of step (2) is as follows: Weigh 4-8 kg of water, add 2-3 kg of yellow first-wash filter cake and slurry. After slurrying for 20 minutes, add 200-700 g of phosphoric acid and simultaneously turn on the oil bath to raise the temperature. Control the final temperature of the slurry to 80-90℃. After the slurry turns white for 5 minutes, add titanium slow-release agent to the slurry. After keeping it warm for 1 hour, discharge the material and filter and wash to obtain a pink second-wash filter cake, which is titanium dihydrate ferric phosphate.

6. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 1, characterized in that, In step (2), the titanium slow-release agent is a complex formed by hydrogen peroxide and titanium sulfate, and the complex is [TiO(H2O2)] 2+ Complex.

7. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 6, characterized in that, The preparation steps of the titanium slow-release agent include: weighing 3-12g of anhydrous titanium sulfate and dissolving it in 1L of pure water, and slowly adding 10-15g of hydrogen peroxide solution to the titanium sulfate solution while stirring, to obtain a yellow hydrogen peroxide-titanium sulfate complex solution, which is the titanium slow-release agent.

8. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release as described in claim 1, characterized in that, In step (2), the crystal growth stage is within 5 minutes after the slurry turns from yellow to white.

9. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release according to claim 1, characterized in that, In step (2), the high-temperature acidic environment during the conversion stage is: temperature 80-90℃, pH value 1.5-2.

5.

10. The method for preparing uniform titanium-doped iron phosphate based on titanium-hydrogen peroxide complexation and slow release according to claim 1, characterized in that, In step (3), the calcination temperature is 500-700℃ and the calcination time is 2-4 hours.

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