Dotted morphology amorphous iron phosphate and continuous method for preparing same, anhydrous iron phosphate and method for preparing same

Abstract

The application provides a method for preparing point-shaped morphology amorphous iron phosphate by a continuous method, and the method comprises the following steps: under the condition of heating and stirring, a ferrous source solution, a phosphorus source solution, a pH regulator solution and an oxidizing agent are passed into a bottom liquid of a reaction kettle in parallel flow, the flow of the ferrous source solution, the reaction pH and the temperature are controlled, the reaction is carried out, and slurry is obtained through overflow; and the slurry is subjected to solid-liquid separation and washing to obtain point-shaped morphology amorphous iron phosphate. By adopting the continuous production process with an ultra-large flow, the operation is simple, the production capacity advantage is prominent, the method is suitable for industrial production, the prepared amorphous iron phosphate has a dispersed point-shaped morphology, the aging processing in the preparation process of anhydrous iron phosphate is facilitated, the production efficiency of the anhydrous iron phosphate is improved, and the production cost and the process difficulty are reduced. The application also provides point-shaped morphology amorphous iron phosphate prepared by the preparation method, anhydrous iron phosphate prepared based on the point-shaped morphology amorphous iron phosphate and a preparation method of the anhydrous iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to the preparation of dot-shaped lithium iron phosphate precursors. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has attracted much attention due to its non-toxicity, environmental friendliness, good safety, stable cycle performance, and theoretical capacity of 170 mAh / g. With increasingly specialized industrial applications, various industries have different requirements for the morphology and properties of LiFePO4 materials, leading to a diversification of synthesis methods, including discontinuous and continuous methods.

[0003] Currently, the mainstream method for preparing lithium iron phosphate precursors in the industry is the batch process. However, the batch process has low production efficiency, and the stability and uniformity of the product cannot be guaranteed, which is detrimental to the performance of lithium iron phosphate cathode materials. Compared to the continuous process, the batch process is more complex, consumes more energy, requires more additives, has a lower product yield, is difficult to automate, and involves bulky equipment with limited production capacity and higher costs. For example, patent application CN102030323A discloses a method for preparing lithium iron phosphate, which involves mixing ferrous sulfate and phosphoric acid, oxidizing with hydrogen peroxide, and adjusting the pH with excess sodium hydroxide solution to obtain the lithium iron phosphate product. This method has low production capacity and requires a large amount of washing water.

[0004] Compared to batch processes, continuous processes are particularly suitable for the large-scale, economical production of iron phosphate precursors. They simplify the process, facilitate automation, produce consistent products, reduce costs, and increase production capacity. For example, patent application CN115701828A discloses a quasi-continuous method for preparing battery-grade anhydrous iron phosphate using ferrous sulfate. Ferrous sulfate is mixed with hydrogen peroxide for pre-oxidation to create an iron salt solution, while sodium hydroxide and phosphoric acid solutions are mixed in a specific ratio to create a phosphorus source solution. The iron and phosphorus source solutions are continuously fed into a reactor equipped with stirring and temperature control devices using constant flow pumps. The solid-liquid mixture overflows continuously after filling the reactor. Strict control of the flow rates of these two solutions, as well as the temperature and pH of the reaction solution, is maintained. Continuous feeding and discharging yields large, spherical, amorphous iron phosphate particles with a certain particle size distribution. However, this method struggles to achieve high production capacity, and the resulting large, spherical particles are difficult to disperse during pulping. After aging, dissolution, and recrystallization, they easily form large-diameter agglomerated secondary particles, which is detrimental to the electrical performance of the cathode material. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a method for preparing amorphous ferric phosphate with low sphericity and dot-like morphology using a continuous method, amorphous ferric phosphate with dot-like morphology, anhydrous ferric phosphate, and their preparation methods.

[0006] To achieve the above objectives, this application proposes the following technical solution:

[0007] Firstly, a method for preparing amorphous iron phosphate with a dot-like morphology using a continuous process is provided, including:

[0008] S1. Under heating and stirring conditions, ferrous source solution, phosphorus source solution, pH adjuster solution and oxidant are fed concurrently into the bottom liquid of the reactor to carry out the reaction, and a slurry is obtained by overflow; the feed flow rate of the ferrous source solution is controlled to be 2.5%~4.5% of the reactor volume per minute; the pH of the system is maintained at 2.5~4.5 and the reaction temperature is 60~80℃ during the reaction process;

[0009] S2. After solid-liquid separation and washing, the slurry yields amorphous iron phosphate with a dot-like morphology.

[0010] Further, in step S1, the stirring speed is 100~800 rpm, preferably 150~450 rpm.

[0011] Furthermore, the flow rates of the ferrous source solution and the phosphorus source solution are determined according to the Fe / P molar ratio in the feed per unit time being 0.95~1.05:1, preferably 0.96~0.98:1.

[0012] Furthermore, the flow rates of the ferrous source solution and the oxidant are determined according to the molar ratio of Fe / oxidant in the feed per unit time being 1:0.5~1.

[0013] Further, the concentration of the ferrous source solution is 0.2~1.5 mol / L; preferably, the pH of the ferrous source solution is 1.2~1.4.

[0014] Furthermore, the ferrous source solution is prepared using a ferrous source, water, and an acidic solution.

[0015] Furthermore, the ferrous source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate;

[0016] Furthermore, the acidic solution is one or more of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, oxalic acid, and acetic acid.

[0017] Furthermore, the ratio of the molar amount of iron in the ferrous source to the molar amount of hydrogen ions in the acidic solution is 1:0.1~0.5.

[0018] Furthermore, the oxidant is one or more of ozone, hydrogen peroxide, and sodium hypochlorite.

[0019] Furthermore, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0020] Furthermore, the molar concentration of the phosphorus source solution is 0.2~2.5 mol / L, preferably 0.5~2.0 mol / L.

[0021] Furthermore, the pH adjuster is one or both of ammonia and sodium hydroxide.

[0022] Furthermore, the molar concentration of the pH adjusting agent solution is 5~12 mol / L.

[0023] Furthermore, the volume of the reactor is 50L or more, preferably 50L to 50m³. 3 .

[0024] Secondly, amorphous iron phosphate with a dot-like morphology is provided, which is prepared using the aforementioned preparation method.

[0025] Thirdly, a method for preparing anhydrous ferric phosphate is provided, including:

[0026] (1) The amorphous iron phosphate with dot-like morphology prepared by the above preparation method is formulated into a slurry to be aged, and aged to obtain an aged slurry;

[0027] (2) The aged slurry was separated into solid and liquid, dried and calcined to obtain anhydrous iron phosphate.

[0028] Furthermore, in step (1), the solid content of the slurry to be aged is 100~300g / L.

[0029] Furthermore, in step (1), the aging temperature is 80~100℃; the aging time is 1~5h.

[0030] Further, in step (1), the stirring speed during aging is 200~500 rpm.

[0031] Further, in step (1), during the aging process, 5-15 mL of phosphoric acid is added to every 100 g of ferric phosphate dihydrate in the slurry to be aged; the concentration of the phosphoric acid is 75-95%.

[0032] Furthermore, in step (2), the calcination temperature is 500~750℃.

[0033] Fourthly, anhydrous ferric phosphate is provided, prepared using the aforementioned method;

[0034] The anhydrous ferric phosphate satisfies at least one of conditions (a) to (c):

[0035] (a) The particle size D50 of the iron phosphate is 1~30μm, preferably 5~20μm;

[0036] (b) Tap density is 0.6~1.5 g / cm³ 3 ;

[0037] (c) Specific surface area is 2~15m² 2 / g, preferably 5~10m 2 / g.

[0038] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0039] The preparation method of this invention adopts a continuous production process with ultra-high flow rate, which is simple to operate, has outstanding capacity advantages, and is suitable for industrial production. The prepared amorphous ferric phosphate has a dispersed dot-like morphology, which facilitates the aging process in the preparation of anhydrous ferric phosphate, and helps to improve the production efficiency of anhydrous ferric phosphate and reduce production costs and process difficulty.

[0040] When the preparation method of the present invention uses a 100L reactor as the production equipment, the production capacity of amorphous iron phosphate can reach 27kg / h~45kg / h. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 SEM images of amorphous iron phosphate prepared in Example 1 at different magnifications.

[0043] Figure 2 The image shows an anhydrous ferric phosphate prepared in Example 1.

[0044] Figure 3 The images are SEM images of the amorphous iron phosphate prepared in Example 2 at different magnifications.

[0045] Figure 4 SEM images of the amorphous iron phosphate prepared in Example 3 at different magnifications.

[0046] Figure 5 The images are SEM images of the amorphous iron phosphate prepared in Example 4 at different magnifications.

[0047] Figure 6 The images are SEM images of the amorphous iron phosphate prepared in Example 5 at different magnifications.

[0048] Figure 7SEM images of the amorphous iron phosphate prepared in Example 6 at different magnifications.

[0049] Figure 8 SEM images of the amorphous iron phosphate prepared in Example 7 at different magnifications.

[0050] Figure 9 SEM images of the amorphous iron phosphate prepared in Example 8 at different magnifications.

[0051] Figure 10 SEM images of the amorphous iron phosphate prepared in Example 9 at different magnifications.

[0052] Figure 11 SEM images of the amorphous iron phosphate prepared in Example 10 at different magnifications.

[0053] Figure 12 SEM images of the amorphous iron phosphate prepared in Example 11 at different magnifications.

[0054] Figure 13 SEM images of amorphous iron phosphate prepared in Comparative Example 1 at different magnifications.

[0055] Figure 14 SEM images of amorphous iron phosphate prepared for Comparative Example 2 at different magnifications.

[0056] Figure 15 SEM images of amorphous iron phosphate prepared in Comparative Example 3 at different magnifications.

[0057] Figure 16 SEM images of the amorphous iron phosphate prepared in Comparative Example 4 at different magnifications. Detailed Implementation

[0058] This invention provides a continuous method for preparing amorphous iron phosphate with a dot-like morphology, comprising:

[0059] S1. Under heating and stirring conditions, ferrous source solution, phosphorus source solution, pH adjuster solution and oxidant are fed concurrently into the bottom liquid of the reactor to carry out the reaction, and a slurry is obtained by overflow; the feed flow rate of the ferrous source solution is controlled to be 2.5%~4.5% of the reactor volume per minute; the pH of the system is maintained at 2.5~4.5 and the reaction temperature is 60~80℃ during the reaction process;

[0060] S2. After solid-liquid separation and washing, the slurry yields amorphous iron phosphate with a dot-like morphology.

[0061] In the above preparation method, raw materials are fed in concurrently, and the product is continuously produced. This continuous process, with continuous feeding and output, keeps the slurry system in a dynamic equilibrium of nucleation, growth, re-nucleation, and regeneration. By significantly increasing the feed flow rate, the reactor can be compared to a shorter, vertical tubular reactor. The residence time of the material in the reactor is significantly shortened, achieving a reaction process dominated by nucleation and supplemented by growth. Secondary particles are discharged before they even have time to grow. This preparation method is simple to operate, significantly increases equipment capacity, and features a continuous production process with simultaneous feeding and output, a large feed flow rate, and huge capacity. The resulting product has stable quality and morphology. By controlling the feed flow rate of the ferrous source and reaction conditions, this method can produce amorphous ferric phosphate with a dispersed dot morphology, facilitating subsequent pulping and aging. This reduces the difficulty and cost of subsequent anhydrous ferric phosphate preparation methods and improves efficiency. Furthermore, this preparation method has a huge capacity; verification shows that a 100L reactor can achieve a capacity of 27kg / h~45kg / h of amorphous ferric phosphate when used as production equipment.

[0062] In the above preparation method, to obtain dispersed amorphous ferric phosphate, it is necessary to precisely control the feed flow rate of the ferrous source solution, the pH value of the reaction system, and the synthesis temperature simultaneously. If other conditions are met, a low feed flow rate will cause the primary particles to agglomerate into spheres, resulting in coarse amorphous ferric phosphate particles and preventing the formation of dispersed amorphous ferric phosphate. Conversely, a high feed flow rate will result in a short residence time of the material in the reactor, making it difficult to stably control the reaction conditions and affecting product stability. Similarly, if the temperature is too low, agglomeration into spheres will occur, preventing the formation of dispersed amorphous ferric phosphate. Conversely, a high temperature will directly cause aging and crystallization, resulting in a high impurity content in the product. Finally, if the pH is too low, agglomeration into spheres will occur, preventing the formation of dispersed amorphous ferric phosphate. Conversely, a high pH will result in excessive consumption of pH adjuster, increasing costs.

[0063] In the above preparation method, the feed flow rate of the ferrous source solution is controlled to be 2.5-4.5% of the volume of ferrous source solution per minute, such as 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, etc.

[0064] In the above preparation method, the pH of the system is maintained at 2.5~4.5 during the reaction process, for example, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.5, etc.

[0065] In the above preparation method, the reaction temperature is controlled at 60~80℃, for example, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, etc.

[0066] In some preferred embodiments, the volume of the reactor is 50L~50m³. 3 For example, 50L, 100L, 150L, ​​200L, 500L, 1m 3 5m 3 10m 3 15m 3 20m 3 25m 3 30m 3 35m 3 40m 3 45m 3 50m 3 wait.

[0067] In some preferred embodiments, in step S1, the stirring speed is 100~800 rpm, preferably 150~450 rpm, such as 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, etc.

[0068] In some preferred embodiments, the flow rates of the ferrous source solution and the phosphorus source solution are determined according to the Fe / P molar ratio in the feed per unit time of 0.95~1.05:1, preferably 0.96~0.98:1, such as 0.96:1, 0.97:1, 0.98:1, etc.

[0069] In some preferred embodiments, the flow rate of the ferrous source solution and the flow rate of the oxidant are determined according to the molar ratio of Fe / oxidant in the feed per unit time of 1:0.5 to 1, such as 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc.

[0070] In some preferred embodiments, the concentration of the ferrous source solution is 0.2~1.5 mol / L, for example 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.; preferably, the pH of the ferrous source solution is 1.2~1.4, for example 1.2, 1.3, 1.4, etc.

[0071] In some preferred embodiments, the ferrous source solution is prepared by using a ferrous source, water, and an acidic solution; preferably, the ferrous source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate; preferably, the acidic solution is one or more of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, oxalic acid, and acetic acid.

[0072] In some preferred embodiments, the ratio of the molar amount of iron in the ferrous source to the molar amount of hydrogen ions in the acidic solution is 1:0.1 to 0.5, for example, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.

[0073] In some preferred embodiments, the oxidant is one or more of ozone, hydrogen peroxide, and sodium hypochlorite.

[0074] In some preferred embodiments, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0075] In some preferred embodiments, the molar concentration of the phosphorus source solution is 0.2~2.5 mol / L, preferably 0.5~2.0 mol / L, such as 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, etc.

[0076] In some preferred embodiments, the pH adjuster is one or both of ammonia and sodium hydroxide.

[0077] In some preferred embodiments, the molar concentration of the pH adjuster solution is 5~12 mol / L, such as 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, etc.

[0078] The present invention also provides amorphous iron phosphate with a dot-like morphology, which is prepared by the aforementioned preparation method.

[0079] In some preferred embodiments, the tap density of the dot-shaped amorphous iron phosphate is 0.6 g / cm³. 3 The following is a further preferred value: 0.5 g / cm³ 3 The following is a further preferred value: 0.3~0.5 g / cm³. 3 ; Specific surface area is 20m² 2 / g or more, further preferably 25m 2 / g or more, more preferably 25~40m 2 / g.

[0080] This invention also provides a method for preparing anhydrous ferric phosphate, comprising:

[0081] (1) The amorphous iron phosphate with dot-like morphology prepared by the above preparation method is formulated into a slurry to be aged, and aged to obtain an aged slurry;

[0082] (2) The aged slurry was separated into solid and liquid, dried and calcined to obtain anhydrous iron phosphate.

[0083] The amorphous ferric phosphate with dot-like morphology prepared by the aforementioned preparation method is formulated into a slurry to be aged and then further processed to obtain anhydrous ferric phosphate. Since the amorphous ferric phosphate with dot-like morphology is easy to disperse and age after pulping, it helps to reduce the difficulty and cost of subsequent anhydrous ferric phosphate preparation methods and improve efficiency and production capacity.

[0084] In some preferred embodiments, in step (1), the solid content of the slurry to be aged is 100~300g / L, for example 100g / L, 150g / L, 200g / L, 250g / L, 300g / L, etc.

[0085] In some preferred embodiments, in step (1), the aging temperature is 80~100℃; the aging time is 1~5h.

[0086] In some preferred embodiments, in step (1), the stirring speed during aging is 200~500 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.

[0087] In some preferred embodiments, in step (1), during the aging process, 5-15 mL of phosphoric acid is added to every 100 g of ferric phosphate dihydrate in the slurry to be aged, for example, 5 mL, 6 mL, 7 mL, 8 mL, 9 mL, 10 mL, 11 mL, 12 mL, 13 mL, 14 mL, 15 mL of phosphoric acid are added to every 100 g of ferric phosphate dihydrate; the concentration of the phosphoric acid is 75-95%, for example, 75%, 80%, 85%, 90%, 95%, etc.

[0088] Preferably, in step (2), the calcination temperature is 500~750℃, for example 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, etc.

[0089] In step (2), the drying can be carried out using conventional drying methods in the art, such as baking, and the drying temperature can be conventional baking temperature in the art, such as 100~150℃.

[0090] In steps S2 and S3, the solid-liquid separation can be performed using conventional solid-liquid separation methods in the art, such as pressure filtration.

[0091] This invention provides anhydrous ferric phosphate, which is prepared using the aforementioned preparation method;

[0092] The anhydrous ferric phosphate satisfies at least one of conditions (a) to (c):

[0093] (a) The particle size D50 of the iron phosphate is 1~30μm, preferably 5~20μm, for example 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc.;

[0094] (b) Tap density is 0.6~1.5 g / cm³ 3 For example, 0.6 g / cm³ 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 wait;

[0095] (c) Specific surface area is 2~15m² 2 / g, preferably 5~10m 2 / g, for example 5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g etc.

[0096] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0097] In the following embodiments:

[0098] Particle size distribution was measured using a Malvern 3000 particle size analyzer.

[0099] BET was tested using a surface area analyzer, model BSD-BET400, manufactured by Best Instrument Technology (Beijing) Co., Ltd.

[0100] The tap density was measured using a tap density meter, model BT-313, manufactured by Dandong Better Instruments Co., Ltd.

[0101] Fe element testing method: redox titration.

[0102] P element test method: Quinomolybdate gravimetric method.

[0103] Example 1

[0104] Step S1, Preparation of iron source solution:

[0105] Ferrous sulfate was dissolved in deionized water to prepare a ferrous sulfate solution. Sulfuric acid solution was added, and the solution was filtered to obtain solution A. The molar concentration of ferrous sulfate in solution A was 1.0 mol / L, and the molar concentration of sulfuric acid in solution A was 0.12 mol / L.

[0106] Step S2, preparation of phosphorus source solution:

[0107] Ammonium dihydrogen phosphate was dissolved in deionized water to prepare a 2.0 mol / L solution, which was then filtered to obtain solution B.

[0108] Step S3, pH adjuster preparation:

[0109] Prepare a 6.0 mol / L ammonia solution, filter it, and obtain the solution as a pH adjuster for solution C;

[0110] Step S4, Preparation of oxidant:

[0111] Prepare a 9.0 mol / L hydrogen peroxide solution to serve as the oxidizing agent for solution D;

[0112] Step S5, Synthesis Reaction:

[0113] Add one-third volume of deionized water to a 100L synthesis reactor, heat to 70℃, and stir at 300 rpm. Simultaneously, introduce solution A at a flow rate of 3000 mL / min, solution B at a flow rate of 1546 mL / min, and solution D at a flow rate of 236 mL / min into the synthesis reactor. Use solution C to maintain the pH value in the synthesis reactor at 3.0±0.1. Stir the reaction thoroughly at 300 rpm and control the reaction temperature at 70℃. The reacted material flows out through the overflow port at the top of the synthesis reactor.

[0114] Step S6: The slurry prepared by the continuous method is pumped into a plate and frame filter press. After mother liquor separation, deionized water is added for washing until the pH is around 3.5. The slurry is then pressed dry and discharged to obtain amorphous ferric phosphate dihydrate. Its SEM image is shown below. Figure 1 As shown. From Figure 1It can be seen that the obtained amorphous iron phosphate dihydrate has a dot-like morphology and good dispersibility. The specific surface area and tap density data are shown in Table 1.

[0115] Step S7: The synthesized material is added to an aging reactor and pulped to form a uniform slurry with a solid content of 130 g / L. The stirring speed is 500 rpm, and the temperature is raised to 50°C. A certain volume of concentrated phosphoric acid is added (the volume of phosphoric acid is calculated based on 10 mL of phosphoric acid (concentration of 14.63 mol / L) / 100 g of ferric phosphate dihydrate). The slurry is heated to 90°C and aged for 2 hours. The aged material is then pumped into a centrifuge for washing for 1 hour and dehydration for 2 hours. The centrifuge speed is 37 Hz. After unloading, the material is placed in an oven and dried at 120°C for 10 hours to obtain ferric phosphate dihydrate. This ferric phosphate dihydrate is then calcined in a muffle furnace at 550°C for 2 hours to obtain a dry anhydrous ferric phosphate product. Its SEM image is shown below. Figure 2 As shown, the particle size D50 of the obtained anhydrous ferric phosphate was 7.28 μm, and the tap density TD was 0.92 g / cm³. 3 The specific surface area (BET) is 6.74 m². 2 / g, with an impurity S content of 5867ppm.

[0116] Example 2

[0117] The only difference between this embodiment and Embodiment 1 is that, in step S5, the flow rate of solution A is 2500 mL / min, the flow rate of solution B is 1289 mL / min, and the flow rate of solution D is 197 mL / min.

[0118] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 3 As shown. From Figure 3 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0119] Example 3

[0120] The only difference between this embodiment and Embodiment 1 is that, in step S5, the flow rate of solution A is 4500 mL / min, the flow rate of solution B is 2320 mL / min, and the flow rate of solution D is 354 mL / min.

[0121] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 4 As shown. From Figure 4 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0122] Example 4

[0123] The only difference between this embodiment and Embodiment 1 is that, in step S5, solution C is added to maintain the pH value in the synthesis vessel at 4.5 ± 0.1.

[0124] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 5 As shown. From Figure 5 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0125] Example 5

[0126] The only difference between this embodiment and Embodiment 1 is that, in step S5, solution C is added to maintain the pH value in the synthesis vessel at 2.5 ± 0.1.

[0127] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 6 As shown. From Figure 6 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0128] Example 6

[0129] The only difference between this embodiment and Embodiment 1 is that, in step S5, the reaction temperature is controlled at 60°C.

[0130] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 7 As shown. From Figure 7 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0131] Example 7

[0132] The only difference between this embodiment and Embodiment 1 is that, in step S5, the reaction temperature is controlled at 80°C.

[0133] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 8 As shown. From Figure 8 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0134] Example 8

[0135] The only difference between this embodiment and Embodiment 1 is that, in step S5, the stirring speed is controlled at 450 rpm.

[0136] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 9 As shown. From Figure 9It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0137] Example 9

[0138] The only difference between this embodiment and Embodiment 1 is that in step S5, the stirring speed is controlled at 700 rpm.

[0139] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 10 As shown. From Figure 10 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0140] Example 10

[0141] The only difference between this embodiment and Embodiment 1 is that, in step S5, the flow rate of solution B is 1579 mL / min and the flow rate of solution D is 167 mL / min.

[0142] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 11 As shown. From Figure 11 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0143] Example 11

[0144] The only difference between this embodiment and Embodiment 1 is that, in step S5, the flow rate of solution B is 1429 mL / min and the flow rate of solution D is 333 mL / min.

[0145] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 12 As shown. From Figure 12 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. The specific surface area, tap density and impurity S content data are shown in Table 1.

[0146] Comparative Example 1

[0147] The only difference between this comparative example and Example 1 is that, in step S5, the flow rate of solution A is 1500 mL / min, the flow rate of solution B is 773 mL / min, and the flow rate of solution D is 118 mL / min.

[0148] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 13 As shown in Table 1, the specific surface area, tap density, and impurity S content of the sample were tested. Figure 13It can be seen that the obtained amorphous iron phosphate secondary particles are basically agglomerated into spherical particles. Combined with Table 1, it can be seen that the tap density is significantly higher than that of the amorphous iron phosphate particles dispersed in Example 1.

[0149] Comparative Example 2

[0150] The only difference between this comparative example and Example 1 is that, in step S5, solution C is added to maintain the pH value in the synthesis vessel at 2.2 ± 0.1.

[0151] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 14 As shown in Table 1, the specific surface area, tap density, and impurity S content of the sample were tested. Figure 14 It can be seen that the resulting amorphous ferric phosphate secondary particles have high sphericity and are tightly bound. Therefore, on the one hand, more energy is required for dissolution and recrystallization during aging, and on the other hand, the primary ferric phosphate particles obtained after aging (dissolution and recrystallization) have larger particle sizes, which is not conducive to the performance of electrical properties.

[0152] Comparative Example 3

[0153] The only difference between this comparative example and Example 1 is that, in step S5, the reaction temperature is controlled at 55°C.

[0154] The SEM image of the obtained amorphous iron phosphate dihydrate is shown below. Figure 15 As shown in Table 1, the specific surface area, tap density, and impurity S content of the sample were tested. Figure 15 It can be seen that the obtained amorphous iron phosphate has high sphericity and tight bonding in its secondary particles. Therefore, on the one hand, more energy is required for dissolution and recrystallization during aging, and on the other hand, the primary particles of iron phosphate obtained after aging (dissolution and recrystallization) become larger, which is not conducive to the performance of electrical properties.

[0155] Comparative Example 4

[0156] The only difference between this comparative example and Example 1 is that, in step S5, the reaction temperature is controlled at 90°C.

[0157] The SEM image of the obtained ferric phosphate dihydrate is shown below. Figure 16 As shown in Table 1, the specific surface area, tap density, and impurity S content of the sample were tested. Figure 16 It can be seen that the obtained ferric phosphate dihydrate is in a crystalline state. As can be seen from Table 1, the impurity content of the product has increased significantly. Analysis shows that this may be due to the excessively high reaction temperature, which directly caused aging and crystallization, resulting in product agglomeration and a significant increase in the impurity content.

[0158] As can be seen from Table 1, the specific surface area of ​​the amorphous iron phosphate prepared in each embodiment is all above 25 m². 2The concentration of ferric phosphate is above / g. Furthermore, it can be concluded that compared to amorphous hydrated ferric phosphate with secondary particles agglomerated into spherical morphology, ferric phosphate with dispersed dot morphology has a more "loose" bond, i.e., lower tap and higher BET, and has a higher activation energy. In subsequent aging processes, it is more conducive to the realization of dissolution and recrystallization. It is possible to prepare anhydrous ferric phosphate with primary particles in the form of small spheres and secondary particles in the form of blocks. Currently, the industry generally believes that this morphology of ferric phosphate has excellent electrical properties.

[0159] Table 1

[0160]

[0161] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing amorphous iron phosphate with dispersed point morphology via a continuous process, characterized in that, include: S1. Under heating and stirring conditions, ferrous source solution, phosphorus source solution, pH adjuster solution, and oxidant are fed concurrently into the bottom liquid of the reactor for reaction, and a slurry is obtained by overflow. The feed flow rate of the ferrous source solution is controlled to be 2.5%~4.5% of the reactor volume per minute. The pH of the system is maintained at 2.5~4.5 and the reaction temperature is 60~80℃ during the reaction process. The flow rates of the ferrous source solution and the phosphorus source solution are determined according to the Fe / P molar ratio in the feed per unit time of 0.95~1.05:

1. The flow rates of the ferrous source solution and the oxidant are determined according to the Fe / oxidant molar ratio in the feed per unit time of 1:0.5~1. S2. After solid-liquid separation and washing, the slurry yields amorphous iron phosphate with a dispersed dot morphology.

2. The method for preparing dispersed, point-like amorphous iron phosphate by continuous method as described in claim 1, characterized in that, In step S1, the stirring speed is 100~800 rpm.

3. The method for preparing dispersed, dot-like amorphous iron phosphate by continuous method as described in claim 2, characterized in that, In step S1, the stirring speed is 150~450 rpm.

4. The method for preparing dispersed, point-like amorphous iron phosphate by continuous method according to any one of claims 1 to 3, characterized in that, The flow rates of the ferrous source solution and the phosphorus source solution are determined according to the Fe / P molar ratio in the feed per unit time being 0.96~0.98:

1.

5. The method for preparing dispersed, point-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The concentration of the ferrous source solution is 0.2~1.5 mol / L.

6. The method for preparing dispersed, dot-like amorphous iron phosphate by continuous method as described in claim 5, characterized in that, The pH of the ferrous source solution is 1.2 to 1.

4.

7. The method for preparing dispersed, dot-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The ferrous source solution is prepared by using a ferrous source, water, and an acidic solution.

8. The method for preparing dispersed, dot-like amorphous iron phosphate by continuous method as described in claim 7, characterized in that, The ferrous source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, and ferrous acetate; And / or, the acidic solution is one or more of sulfuric acid, hydrochloric acid, and acetic acid.

9. The method for preparing dispersed, point-like amorphous iron phosphate by continuous method as described in claim 7, characterized in that, The ratio of the molar amount of iron in the ferrous source to the molar amount of hydrogen ions in the acidic solution is 1:0.1~0.

5.

10. The method for preparing dispersed, dot-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The oxidant is one or more of ozone, hydrogen peroxide and sodium hypochlorite; And / or, the phosphorus source is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; And / or, the pH adjuster is one or both of ammonia and sodium hydroxide.

11. The method for preparing dispersed, point-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The molar concentration of the phosphorus source solution is 0.2~2.5 mol / L.

12. The method for preparing dispersed, point-like amorphous iron phosphate by continuous method as described in claim 11, characterized in that, The molar concentration of the phosphorus source solution is 0.5~2.0 mol / L.

13. The method for preparing dispersed, point-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The molar concentration of the pH adjuster solution is 5~12 mol / L.

14. The method for preparing dispersed, point-like amorphous iron phosphate by a continuous method according to any one of claims 1 to 3, characterized in that, The volume of the reactor is 50L or more.

15. The method for preparing dispersed, point-like amorphous iron phosphate by continuous method as described in claim 14, characterized in that, The volume of the reactor is 50L~50m³. 3 .

16. Amorphous iron phosphate with a dispersed, dot-like morphology, characterized in that, It is prepared by the method described in any one of claims 1 to 15.

17. A method for preparing anhydrous ferric phosphate, characterized in that, include: (1) Prepare the dispersed dot-shaped amorphous ferric phosphate as described in claim 16 into a slurry to be aged, and age it to obtain an aged slurry; (2) The aged slurry was separated into solid and liquid, dried and calcined to obtain anhydrous iron phosphate.

18. The method for preparing anhydrous ferric phosphate as described in claim 17, characterized in that, In step (1), the solid content of the slurry to be aged is 100~300g / L.

19. The method for preparing anhydrous ferric phosphate as described in claim 17, characterized in that, In step (1), the aging temperature is 80~100℃; the aging time is 1~5h.

20. The method for preparing anhydrous ferric phosphate as described in claim 17, characterized in that, In step (1), the stirring speed during aging is 200~500 rpm.

21. The method for preparing anhydrous ferric phosphate as described in claim 17, characterized in that, In step (1), during the aging process, 5-15 mL of phosphoric acid is added to every 100 g of ferric phosphate dihydrate in the slurry to be aged; the concentration of the phosphoric acid is 75-95%.

22. The method for preparing anhydrous ferric phosphate as described in claim 17, characterized in that, In step (2), the calcination temperature is 500~750℃.

23. Anhydrous ferric phosphate, characterized in that, It was prepared by the preparation method according to any one of claims 17 to 22; The anhydrous ferric phosphate satisfies at least one of conditions (a) to (c): (a) The particle size D50 of the anhydrous ferric phosphate is 1~30μm; (b) Tap density is 0.6~1.5 g / cm³ 3 ; (c) Specific surface area is 2~15m² 2 / g.

24. The anhydrous ferric phosphate as described in claim 23, characterized in that, The particle size D50 of the anhydrous iron phosphate is 5~20μm.

25. The anhydrous ferric phosphate as described in claim 23, characterized in that, The specific surface area of ​​the anhydrous ferric phosphate is 5~10 m². 2 / g.

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