Point-shaped amorphous iron phosphate and continuous preparation method thereof as well as anhydrous iron phosphate and preparation method thereof

Abstract

The invention provides a method for preparing amorphous iron phosphate with dotted morphology by a continuous method, which comprises the following steps: under the condition of heating and stirring, enabling a ferrous source solution, a phosphorus source solution, a pH regulator solution and an oxidizing agent to flow into a reaction kettle base solution in parallel, controlling the flow, reaction pH and temperature of the ferrous source solution, reacting, and obtaining slurry through overflowing; and carrying out solid-liquid separation and washing on the slurry to obtain the amorphous iron phosphate with the dotted morphology. By adopting an ultra-large flow continuous production process, the operation is simple, the productivity advantage is outstanding, the method is suitable for industrial production, the prepared amorphous iron phosphate is in a dispersed point-shaped morphology, aging processing in the anhydrous iron phosphate preparation process is facilitated, the production efficiency of the anhydrous iron phosphate is improved, and the production cost and the process difficulty are reduced. The invention further provides the amorphous iron phosphate with the dotted morphology prepared by the preparation method, anhydrous iron phosphate prepared based on the amorphous iron phosphate with the dotted morphology and a preparation method of the anhydrous iron phosphate.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials, and in particular relates to the preparation of a lithium iron phosphate precursor with a dot-like morphology. Background Art

[0002] Lithium iron phosphate has attracted much attention due to its non-toxicity, environmental friendliness, good safety, stable cycle performance, and theoretical capacity of 170mAh / g. With the increasing refinement of industrial applications, various industries have different requirements for the morphology and indicators of iron phosphate materials, so the synthesis methods are becoming more and more diversified, including discontinuous method, continuous method, etc.

[0003] At present, the mainstream method for preparing iron phosphate precursors in the industry is intermittent production. The intermittent production process has low production efficiency, and the product stability and uniformity cannot be guaranteed, which is not conducive to the performance of lithium iron phosphate positive electrode materials. Compared with the continuous method, the intermittent process is more complicated, the process consumes more energy, has more additives, the product yield is low, and it is not easy to automatically control. The production equipment is bulky, the production capacity is small, and the cost is high. For example, patent application CN102030323A discloses a method for preparing iron phosphate, which is to prepare ferrous sulfate and phosphoric acid into a mixed solution, then add hydrogen peroxide for oxidation, and add excess sodium hydroxide solution to adjust the pH to obtain an iron phosphate product. This method has low production capacity and a large amount of washing water.

[0004] Compared with the intermittent method, the continuous process is particularly suitable for the scale economy production of iron phosphate precursors, with simplified process, easy automatic control, good product consistency, reduced cost and increased production capacity. For example, patent application CN115701828A discloses a quasi-continuous method for preparing battery-grade anhydrous iron phosphate using ferrous sulfate, wherein ferrous sulfate is mixed with hydrogen peroxide for pre-oxidation as an iron salt solution, and sodium hydroxide solution and phosphoric acid solution are mixed in a certain ratio as a phosphorus source solution; the iron source solution and the phosphorus source solution are respectively continuously input into a reactor with a stirring and temperature control device by a constant flow pump, and the reaction solid-liquid mixture is naturally overflowed and continuously discharged after filling the reactor, and the flow rate of the two solutions and the temperature, pH value and other conditions of the reaction solution are strictly controlled, and the material is continuously fed and discharged, and the reaction obtains large-particle spherical amorphous iron phosphate with a certain particle size distribution, but the method is difficult to obtain high production capacity on the one hand, and the prepared spherical large particles are difficult to disperse during pulping on the other hand, and large-size agglomerated secondary particles are easily formed after aging, dissolving and recrystallization, which is not conducive to the performance of the electrical properties of the positive electrode material. Summary of the invention

[0005] In response to the above technical problems, the present application provides a method for continuously preparing amorphous iron phosphate with low sphericity and point-like morphology, amorphous iron phosphate with point-like morphology, anhydrous iron phosphate and a preparation method thereof.

[0006] To achieve the above objectives, this application proposes the following technical solutions: In a first aspect, a method for continuously preparing amorphous iron phosphate with a dot-like morphology is provided, comprising: S1. Under heating and stirring conditions, a ferrous source solution, a phosphorus source solution, a pH adjuster solution and an oxidant are simultaneously introduced into the bottom liquid of a reactor to react, and a slurry is obtained by overflow; the feed flow rate of the ferrous source solution is controlled to be 2.5% to 4.5% of the volume of the reactor per minute; during the reaction process, the pH of the system is maintained at 2.5 to 4.5, and the reaction temperature is 60 to 80°C; S2. The slurry is subjected to solid-liquid separation and washing to obtain amorphous iron phosphate with a dot-like morphology.

[0007] Furthermore, in step S1, the stirring speed is 100-800 rpm, preferably 150-450 rpm.

[0008] Furthermore, the flow rate of the ferrous source solution and the flow rate of the phosphorus source solution are determined according to the molar ratio of Fe / P in the feed per unit time of 0.95-1.05:1, preferably 0.96-0.98:1.

[0009] Furthermore, the flow rate of the ferrous source solution and the flow rate of the oxidant are determined according to a molar ratio of Fe / oxidant in the feed of 1:0.5-1 per unit time.

[0010] Furthermore, 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.

[0011] Furthermore, the ferrous source solution is prepared by using a ferrous source, water and an acidic solution.

[0012] Furthermore, the ferrous source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate; Furthermore, the acidic solution is one or more of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, oxalic acid, and acetic acid.

[0013] Furthermore, the ratio of the molar amount of iron contained in the ferrous source to the molar amount of hydrogen ions contained in the acidic solution is 1:0.1~0.5.

[0014] Furthermore, the oxidant is one or more of ozone, hydrogen peroxide and sodium hypochlorite.

[0015] 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.

[0016] Furthermore, the molar concentration of the phosphorus source solution is 0.2-2.5 mol / L, preferably 0.5-2.0 mol / L.

[0017] Furthermore, the pH regulator is one or both of ammonia water and sodium hydroxide.

[0018] Furthermore, the molar concentration of the pH regulator solution is 5-12 mol / L.

[0019] Furthermore, the volume of the reactor is greater than 50 L, preferably 50 L to 50 m 3 .

[0020] In a second aspect, amorphous iron phosphate with a dot-like morphology is provided, which is prepared by the aforementioned preparation method.

[0021] In a third aspect, a method for preparing anhydrous ferric phosphate is provided, comprising: (1) preparing the amorphous iron phosphate with a dot-shaped morphology obtained by the aforementioned preparation method into a slurry to be aged, and aging the slurry to obtain an aged slurry; (2) The aged slurry is subjected to solid-liquid separation, drying and calcination to obtain anhydrous iron phosphate.

[0022] Furthermore, in step (1), the solid content of the slurry to be aged is 100-300 g / L.

[0023] Furthermore, in step (1), the aging temperature is 80-100° C. and the aging time is 1-5 h.

[0024] Furthermore, in step (1), the stirring speed of the aging is 200-500 rpm.

[0025] Furthermore, 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%.

[0026] Furthermore, in step (2), the calcination temperature is 500-750°C.

[0027] In a fourth aspect, anhydrous ferric phosphate is provided, which is prepared by the aforementioned preparation method; The anhydrous ferric phosphate satisfies at least one of the conditions (a) to (c): (a) the particle size D50 of the iron phosphate is 1 to 30 μm, preferably 5 to 20 μm; (b) Tap density is 0.6~1.5g / cm 3 ; (c) Specific surface area is 2~15m 2 / g, preferably 5~10m 2 / g.

[0028] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: The preparation method of the present invention adopts a continuous production process with an ultra-large flow rate, is simple to operate, has outstanding production capacity advantages, is suitable for industrial production, and the prepared amorphous iron phosphate has a dispersed point-like morphology, which is convenient for aging processing during the preparation of anhydrous iron phosphate, is beneficial to improving the production efficiency of anhydrous iron phosphate and reducing production costs and process difficulty.

[0029] When the preparation method of the present invention adopts a 100L reactor as production equipment, the production capacity of amorphous ferric phosphate can reach 27kg / h~45kg / h. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 These are SEM images of the amorphous iron phosphate prepared in Example 1 at different magnifications.

[0032] Figure 2 This is the SEM image of the anhydrous ferric phosphate prepared in Example 1.

[0033] Figure 3 These are SEM images of the amorphous iron phosphate prepared in Example 2 at different magnifications.

[0034] Figure 4 These are SEM images of the amorphous iron phosphate prepared in Example 3 at different magnifications.

[0035] Figure 5 These are SEM images of the amorphous iron phosphate prepared in Example 4 at different magnifications.

[0036] Figure 6 These are SEM images of the amorphous iron phosphate prepared in Example 5 at different magnifications.

[0037] Figure 7 These are SEM images of the amorphous iron phosphate prepared in Example 6 at different magnifications.

[0038] Figure 8 These are SEM images of the amorphous iron phosphate prepared in Example 7 at different magnifications.

[0039] Fig. 9These are SEM images of the amorphous iron phosphate prepared in Example 8 at different magnifications.

[0040] Fig.10 These are SEM images of the amorphous iron phosphate prepared in Example 9 at different magnifications.

[0041] Fig.11 These are SEM images of the amorphous iron phosphate prepared in Example 10 at different magnifications.

[0042] Fig.12 These are SEM images of the amorphous iron phosphate prepared in Example 11 at different magnifications.

[0043] Fig.13 These are SEM images of the amorphous iron phosphate prepared in Comparative Example 1 at different magnifications.

[0044] Fig.14 These are SEM images of the amorphous iron phosphate prepared in Comparative Example 2 at different magnifications.

[0045] Fig.15 These are SEM images of the amorphous iron phosphate prepared in Comparative Example 3 at different magnifications.

[0046] Fig.16 These are SEM images of the amorphous iron phosphate prepared in Comparative Example 4 at different magnifications. DETAILED DESCRIPTION

[0047] The present invention provides a method for continuously preparing amorphous iron phosphate with a dot-like morphology, comprising: S1. Under heating and stirring conditions, a ferrous source solution, a phosphorus source solution, a pH adjuster solution and an oxidant are simultaneously introduced into the bottom liquid of a reactor to react, and a slurry is obtained by overflow; the feed flow rate of the ferrous source solution is controlled to be 2.5% to 4.5% of the volume of the reactor per minute; during the reaction process, the pH of the system is maintained at 2.5 to 4.5, and the reaction temperature is 60 to 80°C; S2. The slurry is subjected to solid-liquid separation and washing to obtain amorphous iron phosphate with a dot-like morphology.

[0048] In the above preparation method, raw materials are introduced in parallel, and the prepared product is continuously output. A continuous process of continuous feeding and continuous output of materials is adopted. The slurry system in the kettle is always in a dynamic balance of nucleation, growth, re-nucleation and re-growth. After greatly increasing the feed flow rate, the reactor can be compared to an upright, thicker and shorter tubular reactor, and the residence time of the material in the kettle is significantly shortened, so that the reaction process is mainly nucleation and supplemented by growth. The secondary particles can be discharged before they have time to grow up. The preparation method is simple to operate and can greatly improve the production capacity of the equipment. The continuous method generates a process with simultaneous feeding and output, a large feed flow rate, huge production capacity, and stable product quality and morphology. In the preparation method, by adjusting the feed flow rate of the ferrous source and the reaction conditions, amorphous iron phosphate with a dispersed point morphology can be prepared, which is convenient for subsequent slurrying and aging, and is conducive to reducing the difficulty and cost of the subsequent anhydrous iron phosphate preparation method and improving efficiency. In addition, the above preparation method has huge production capacity. It has been verified that the production capacity of a 100L reactor as a production equipment can reach 27kg / h~45kg / h of amorphous iron phosphate.

[0049] In the above preparation method, in order to obtain dispersed amorphous iron phosphate, it is necessary to accurately control the feed flow rate of the ferrous source solution, the pH value of the reaction system and the synthesis temperature at the same time. When other conditions meet the requirements, when the feed flow rate is too low, the primary particles tend to agglomerate into balls, which leads to coarser amorphous iron phosphate particles and failure to obtain dispersed amorphous iron phosphate. When the feed flow rate is too high, the material stays in the kettle for too short a time, and each reaction condition is difficult to stably control, affecting the stability of the product. When other conditions meet the requirements, if the temperature is too low, it tends to agglomerate into balls and it is impossible to obtain dispersed amorphous iron phosphate. If the temperature is too high, aging and crystallization will occur directly, and the product has a high impurity content. When other conditions meet the requirements, if the pH is too low, it tends to agglomerate into balls and it is impossible to obtain dispersed amorphous iron phosphate. If the pH is too high, the pH regulator is consumed more and the cost increases.

[0050] 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 the ferrous source solution introduced into the reactor per minute, for example, 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.

[0051] 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.

[0052] In the above preparation method, the reaction temperature during the reaction process is controlled to be 60~80°C, for example, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, etc.

[0053] In some preferred embodiments, the volume of the reactor is 50L~50m 3 , such as 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.

[0054] In some preferred embodiments, in step S1, the stirring speed is 100-800 rpm, preferably 150-450 rpm, for example, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, etc.

[0055] In some preferred embodiments, the flow rate of the ferrous source solution and the flow rate of the phosphorus source solution are determined according to the molar ratio of Fe / P in the feed per unit time of 0.95~1.05:1, preferably 0.96~0.98:1, for example 0.96:1, 0.97:1, 0.98:1, etc.

[0056] In some preferred embodiments, the flow rate of the ferrous source solution and the flow rate of the oxidant are determined according to a molar ratio of Fe / oxidant in the feed per unit time of 1:0.5 to 1, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, etc.

[0057] In some preferred embodiments, the concentration of the ferrous source solution is 0.2~1.5mol / L, for example, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, etc.; preferably, the pH of the ferrous source solution is 1.2~1.4, for example, 1.2, 1.3, 1.4, etc.

[0058] 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; In some preferred embodiments, the ratio of the molar amount of iron contained in the ferrous source to the molar amount of hydrogen ions contained in the acidic solution is 1:0.1-0.5, for example, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.

[0059] In some preferred embodiments, the oxidant is one or more of ozone, hydrogen peroxide and sodium hypochlorite.

[0060] 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.

[0061] 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, for example 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.

[0062] In some preferred embodiments, the pH adjuster is one or both of ammonia water and sodium hydroxide.

[0063] In some preferred embodiments, the molar concentration of the pH adjusting agent solution is 5-12 mol / L, for example, 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.

[0064] The present invention also provides amorphous iron phosphate with a dot-shaped morphology, which is prepared by the above-mentioned preparation method.

[0065] In some preferred embodiments, the tap density of the amorphous iron phosphate with a dotted morphology is 0.6 g / cm 3 Below, more preferably 0.5 g / cm 3 Below, more preferably 0.3~0.5g / cm 3 ; Specific surface area is 20m 2 / g or more, more preferably 25m 2 / g or more, more preferably 25 to 40 m 2 / g.

[0066] The present invention also provides a method for preparing anhydrous ferric phosphate, comprising: (1) preparing the amorphous iron phosphate with a dot-shaped morphology obtained by the aforementioned preparation method into a slurry to be aged, and aging the slurry to obtain an aged slurry; (2) The aged slurry is subjected to solid-liquid separation, drying and calcination to obtain anhydrous iron phosphate.

[0067] The amorphous iron phosphate with a dot-like morphology prepared by the aforementioned preparation method is prepared into a slurry to be aged and used as a raw material for further processing to obtain anhydrous iron phosphate. Since the amorphous iron phosphate with a dot-like morphology is convenient for aging after slurry dispersion, it is beneficial to reduce the difficulty and cost of the subsequent anhydrous iron phosphate preparation method and improve efficiency and production capacity.

[0068] In some preferred embodiments, in step (1), the solid content of the slurry to be aged is 100-300 g / L, for example, 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, etc.

[0069] In some preferred embodiments, in step (1), the aging temperature is 80-100° C. and the aging time is 1-5 h.

[0070] In some preferred embodiments, in step (1), the stirring speed of the aging is 200-500 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc.

[0071] In some preferred embodiments, in step (1), during the aging process, 5 to 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, etc. of phosphoric acid is added to every 100 g of ferric phosphate dihydrate; the concentration of the phosphoric acid is 75 to 95%, for example, 75%, 80%, 85%, 90%, 95%, etc.

[0072] Preferably, in step (2), the calcination temperature is 500-750°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, etc.

[0073] In step (2), the drying may be carried out by a conventional drying method in the art, such as oven drying, and the drying temperature may be a conventional drying temperature in the art, such as 100-150°C.

[0074] In step S2 and step S3, the solid-liquid separation may be carried out by a conventional solid-liquid separation method in the art, such as filter press.

[0075] The present invention provides anhydrous ferric phosphate, which is prepared by the above-mentioned preparation method; The anhydrous ferric phosphate satisfies at least one of the conditions (a) to (c): (a) the particle size D50 of the ferric phosphate is 1 to 30 μm, preferably 5 to 20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc.; (b) Tap density is 0.6~1.5g / cm 3 , for example 0.6 g / cm 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; (c) Specific surface area is 2~15m 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.

[0076] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0077] In the following embodiments: The particle size distribution was measured using a Malvern 3000 particle size analyzer.

[0078] BET is tested using a specific surface area tester, model BSD-BET400, manufactured by Best Instrument Technology (Beijing) Co., Ltd.

[0079] The compaction was tested by a compaction density meter, model BT-313, manufactured by Dandong Better Instrument Co., Ltd.

[0080] Fe element testing method: redox titration method.

[0081] P element testing method: quinoline molybdenum gravimetric method.

[0082] Example 1 Step S1, preparation of iron source solution: Dissolve ferrous sulfate in deionized water to prepare a ferrous sulfate solution, add sulfuric acid solution, and filter to obtain solution A, so that the molar concentration of ferrous sulfate in solution A is 1.0 mol / L, and the molar concentration of sulfuric acid in solution A is 0.12 mol / L; Step S2, preparation of phosphorus source solution: Dissolve ammonium dihydrogen phosphate in deionized water to prepare a 2.0 mol / L solution, and filter to obtain solution B; Step S3, preparation of pH adjusting agent: Prepare a 6.0 mol / L ammonia solution, filter, and obtain a pH regulator as solution C; Step S4, oxidant preparation: Prepare 9.0 mol / L hydrogen peroxide to obtain the oxidant as solution D; Step S5, synthesis reaction: Add one-third of the volume of deionized water into a 100L synthesis reactor, heat to 70°C, stir at 300rpm, and simultaneously introduce solution A at a flow rate of 3000mL / min, solution B at a flow rate of 1546mL / min, and solution D at a flow rate of 236mL / min into the synthesis reactor in parallel, use solution C to maintain the pH value in the synthesis reactor at 3.0±0.1, stir well to react, stir at 300rpm, control the reaction temperature at 70°C, and the materials after the reaction are discharged through the overflow port at the top of the synthesis reactor; Step S6, the slurry prepared by the continuous process is pumped into a plate-frame filter press, and after the mother liquor is separated, it is washed with deionized water until the pH is about 3.5, and then pressed and discharged to obtain amorphous ferric phosphate dihydrate, the SEM image of which is shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the obtained amorphous ferric phosphate dihydrate has a dot-like morphology and good dispersibility. After testing, its specific surface area and tap density data are shown in Table 1.

[0083] Step S7, put the synthetic material into an aging kettle for slurrying to form a uniform slurry with a solid content of 130g / L, stir at a speed of 500rpm, heat to 50°C, add a certain volume of concentrated phosphoric acid (the volume of phosphoric acid is calculated as 10mL phosphoric acid (phosphoric acid concentration 14.63mol / L) / 100g dihydrate iron phosphate), age and dehydrate the slurry to 90°C, and keep it warm for 2h; pump the aged material into a centrifuge for washing for 1h, dehydrate for 2h, and the centrifuge speed frequency is 37Hz. After unloading, put it into an oven and dry it at 120°C for 10h to obtain dihydrate iron phosphate, put it into a muffle furnace and calcine it at 550°C for 2h to obtain a dry anhydrous iron phosphate product, whose SEM picture is as follows Figure 2As shown in Figure 2, the particle size D50 of the obtained anhydrous ferric phosphate is 7.28 μm, and the tap density TD is 0.92 g / cm 3 ; BET surface area is 6.74m 2 / g, and the impurity S content is 5867ppm.

[0084] Example 2 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.

[0085] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 3 As shown. Figure 3 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0086] Example 3 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.

[0087] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 4 As shown. Figure 4 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0088] Example 4 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 reactor at 4.5±0.1.

[0089] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 5 As shown. Figure 5 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0090] Example 5 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 reactor at 2.5±0.1.

[0091] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 6 As shown. Figure 6It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0092] Example 6 The only difference between this embodiment and embodiment 1 is that in step S5, the reaction temperature is controlled to be 60°C.

[0093] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 7 As shown. Figure 7 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0094] Example 7 The only difference between this embodiment and embodiment 1 is that in step S5, the reaction temperature is controlled to be 80°C.

[0095] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Figure 8 As shown. Figure 8 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0096] Example 8 The only difference between this embodiment and embodiment 1 is that in step S5, the stirring speed is controlled to be 450 rpm.

[0097] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig. 9 As shown. Fig. 9 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0098] Example 9 The only difference between this embodiment and embodiment 1 is that in step S5, the stirring speed is controlled to be 700 rpm.

[0099] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.10 As shown. Fig.10 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0100] Example 10 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.

[0101] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.11 As shown. Fig.11 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0102] Embodiment 11 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.

[0103] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.12 As shown. Fig.12 It can be seen that the obtained amorphous iron phosphate has a dot-like morphology and good dispersibility. After testing, its specific surface area, tap density and impurity S content data are shown in Table 1.

[0104] Comparative Example 1 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.

[0105] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.13 As shown, after testing, its specific surface area, tap density and impurity S content data are shown in Table 1. Fig.13 It can be seen that the obtained amorphous iron phosphate secondary particles are basically agglomerated into spherical bodies. Combined with Table 1, it can be seen that the tap density is significantly higher than that of the amorphous iron phosphate dispersed in Example 1.

[0106] Comparative Example 2 The 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 reactor at 2.2±0.1.

[0107] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.14 As shown, after testing, its specific surface area, tap density and impurity S content data are shown in Table 1. Fig.14 It can be seen that the obtained amorphous iron 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. On the other hand, the particle size of the primary particles of iron phosphate obtained after aging (dissolution and recrystallization) becomes larger, which is not conducive to the performance of electrical properties.

[0108] Comparative Example 3 The only difference between this comparative example and Example 1 is that in step S5, the reaction temperature is controlled to be 55°C.

[0109] The SEM image of the obtained amorphous iron phosphate dihydrate is as follows Fig.15 As shown, after testing, its specific surface area, tap density and impurity S content data are shown in Table 1. Fig.15 It can be seen that the obtained amorphous iron phosphate has high sphericity of secondary particles and is tightly bound. Therefore, on the one hand, more energy is required for dissolution and recrystallization during aging. On the other hand, the primary particle size of the iron phosphate obtained after aging (dissolution and recrystallization) becomes larger, which is not conducive to the performance of electrical properties.

[0110] Comparative Example 4 The only difference between this comparative example and Example 1 is that in step S5, the reaction temperature is controlled to be 90°C.

[0111] The SEM image of the obtained iron phosphate dihydrate is as follows Fig.16 As shown, after testing, its specific surface area, tap density and impurity S content data are shown in Table 1. Fig.16 It can be seen that the obtained ferric phosphate dihydrate is partially crystalline, and it can be seen from Table 1 that the impurity content of the product is significantly increased. After analysis, this may be due to the excessively high reaction temperature, which directly leads to aging and crystallization, product agglomeration, and a significant increase in the impurity content of the product.

[0112] It can be seen from Table 1 that the specific surface area of ​​the amorphous iron phosphate prepared in each embodiment is 25 m 2 / g or more, and it can also be concluded that, relative to the amorphous hydrated iron phosphate in which the secondary particles are agglomerated into a spherical morphology, the iron phosphate in a dispersed point-like morphology is more "loosely" bound, that is, the tap compaction is lower, and the BET is higher, and it has a higher activation energy. In the subsequent aging process, it is more conducive to the realization of dissolution and recrystallization, and anhydrous iron phosphate with primary particles in the form of small spheres and secondary particles in the form of blocks can be prepared. At present, the industry generally believes that the iron phosphate in this morphology has excellent electrical properties.

[0113] Table 1 The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing amorphous iron phosphate with a dot-like morphology by a continuous process, characterized in that: include: S1. Under heating and stirring conditions, a ferrous source solution, a phosphorus source solution, a pH adjuster solution and an oxidant are simultaneously introduced into the bottom liquid of the reactor to react, and a slurry is obtained by overflow; the feed flow rate of the ferrous source solution is controlled to be 2.5% to 4.5% of the volume of the reactor per minute; the pH of the system is maintained at 2.5 to 4.5 during the reaction process, and the reaction temperature is 60 to 80°C; S2. The slurry is subjected to solid-liquid separation and washing to obtain amorphous iron phosphate with a dot-like morphology.

2. The method for preparing amorphous ferric phosphate with a dot-like morphology by a continuous process as claimed in claim 1, characterized in that: In step S1, the stirring speed is 100-800 rpm, preferably 150-450 rpm.

3. The method for preparing amorphous iron phosphate with dot-like morphology by continuous method according to claim 1 or 2, characterized in that: The flow rates of the ferrous source solution and the phosphorus source solution are determined according to the molar ratio of Fe / P in the feed per unit time of 0.95-1.05:1, preferably 0.96-0.98:

1.

4. The method for preparing amorphous ferric phosphate with a dot-like morphology by a continuous method according to any one of claims 1 to 3, characterized in that: 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 being 1:0.5-1.

5. The method for preparing amorphous ferric phosphate with dot-like morphology by a continuous method according to any one of claims 1 to 4, characterized in that: 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.

6. The method for preparing amorphous ferric phosphate with dot-like morphology by a continuous method according to any one of claims 1 to 5, characterized in that: 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; Preferably, the ratio of the molar amount of iron contained in the ferrous source to the molar amount of hydrogen ions contained in the acidic solution is 1:0.1-0.5; Preferably, the oxidant is one or more of ozone, hydrogen peroxide and sodium hypochlorite; Preferably, 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; Preferably, the molar concentration of the phosphorus source solution is 0.2-2.5 mol / L, preferably 0.5-2.0 mol / L; Preferably, the pH regulator is one or both of ammonia water and sodium hydroxide; Preferably, the molar concentration of the pH adjusting agent solution is 5-12 mol / L; Preferably, the volume of the reactor is 50L or more, preferably 50L~50m 3 .

7. Amorphous iron phosphate with dot-like morphology, characterized in that: The method is prepared according to any one of claims 1 to 6.

8. A method for preparing anhydrous ferric phosphate, characterized in that: include: (1) preparing the amorphous iron phosphate with a dot-like morphology as described in claim 7 into a slurry to be aged, and aging the slurry to obtain an aged slurry; (2) The aged slurry is subjected to solid-liquid separation, drying and calcination to obtain anhydrous iron phosphate.

9. The method for preparing anhydrous ferric phosphate according to claim 8, characterized in that: In step (1), the solid content of the slurry to be aged is 100-300 g / L; Preferably, in step (1), the aging temperature is 80-100° C. and the aging time is 1-5 h; Preferably, in step (1), the stirring speed of the aging is 200-500 rpm; Preferably, in step (1), during the aging process, 5 to 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 to 95%; Preferably, in step (2), the calcination temperature is 500-750°C.

10. Anhydrous ferric phosphate, characterized in that Prepared by the preparation method as claimed in claim 8 or 9; The anhydrous ferric phosphate satisfies at least one of the conditions (a) to (c): (a) the particle size D50 of the iron phosphate is 1 to 30 μm, preferably 5 to 20 μm; (b) Tap density is 0.6~1.5g / cm 3 ; (c) Specific surface area is 2~15m 2 / g, preferably 5~10m 2 / g.

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