Iron phosphate precursor, method for preparing the same and use thereof

Abstract

The application belongs to the technical field of iron phosphate preparation, and particularly relates to an iron phosphate precursor, a preparation method and application thereof. The iron phosphate precursor comprises secondary particles composed of flaky primary particles; the thickness of the primary particles is 10nm-50nm; and the sphericity of the secondary particles is 0.7-0.9. The iron phosphate precursor comprises secondary particles with a spherical shape composed of flaky primary particles, the flaky primary particles can increase the specific surface area of the iron phosphate precursor, the spherical structure of the secondary particles increases the tap density of the iron phosphate precursor, and thus is conducive to the preparation of a positive electrode material with higher tap density.

Description

Technical Field

[0001] This invention belongs to the field of iron phosphate preparation technology, specifically relating to an iron phosphate precursor, its preparation method, and its application. Background Technology

[0002] Iron phosphate, as one of the precursors of lithium iron phosphate (LFP) cathode materials for lithium-ion batteries, possesses core advantages such as high theoretical capacity, excellent thermal stability, and outstanding cycle life. Its structure features stable PO bonds and Fe bonds... 3+ The ion coordination system not only endows the material with good chemical stability but also effectively inhibits lithium dendrite growth, significantly improving battery safety. The morphology, tap density, specific surface area, and impurities of iron phosphate affect the microstructure of the prepared LiFePO4. Therefore, the preparation of iron phosphate directly impacts the subsequent LiFePO4 product.

[0003] To this end, CN116281914A discloses a method for preparing ferric phosphate, in which the amorphous ferric phosphate semi-finished product obtained by liquid-phase coprecipitation is dispersed in an acidic dispersion, and the hydrogen ion concentration (H+) is controlled. + / Fe 3+ The whitening process is achieved through a dissolution-recrystallization process, using a temperature range of 0.2~2 and an aging temperature of 60℃~100℃. This forms a well-crystallized monoclinic iron phosphate dihydrate (FePO4•2H2O). The primary particles are blocky or short columnar, while the secondary particles are nearly spherical with a wide particle size distribution (D50=5μm~10μm) and a tap density of approximately 1.2 g / cm³. 3 ~1.4g / cm 3 However, because the primary particles are blocky or short columnar, the secondary particles have insufficient sphericity, low specific surface area, and high sulfur content (usually >200ppm). Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes an iron phosphate precursor, its preparation method, and its applications, thereby resolving at least one aspect of the technical issues described above.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention provides an iron phosphate precursor comprising secondary particles composed of plate-like primary particles.

[0007] The thickness of the primary particles is 10nm~50nm;

[0008] The sphericity of the secondary particles is 0.7~0.9;

[0009] The preparation method of the iron phosphate precursor includes the following steps:

[0010] Preparation of seed crystal induction slurry: After adjusting the pH value of the first ferric phosphate slurry to 0.1~0.8, the slurry is kept at a certain temperature for crystallization to obtain the seed crystal induction slurry. The temperature for crystallization is 75℃~95℃.

[0011] Preparation process induction solution: Mix iron source solution and phosphorus source solution and adjust pH value to 1.5~3.0;

[0012] The molar ratio of iron in the iron source solution to phosphorus in the phosphorus source solution is 0.97~1.0:1;

[0013] The process induction liquid, the second ferric phosphate slurry, and the seed induction slurry are mixed and reacted.

[0014] In some possible implementations, the particle size distribution of the iron phosphate precursor is 0.5 to 0.75.

[0015] In some possible implementations, the average thickness of the primary particles is 20 nm to 40 nm.

[0016] In some possible implementations, the size of the primary particles is 0.2 μm to 1.5 μm.

[0017] In some possible implementations, the tap density of the iron phosphate precursor is 0.6 g / cm³. 3 ~1.5g / cm 3 .

[0018] In some possible implementations, the particle size D50 of the iron phosphate precursor is 1 μm to 30 μm.

[0019] In some possible implementations, the specific surface area of ​​the iron phosphate precursor is 2 g / cm³. 3 ~15g / cm 3 .

[0020] Secondly, the present invention provides a method for preparing the above-mentioned iron phosphate precursor, comprising the following steps:

[0021] Preparation of seed crystal induction slurry: After adjusting the pH value of the first ferric phosphate slurry to 0.1~0.8, the slurry is kept at a certain temperature for crystallization to obtain the seed crystal induction slurry. The temperature for crystallization is 75℃~95℃.

[0022] Preparation process induction solution: Mix iron source solution and phosphorus source solution and adjust pH value to 1.5~3.0;

[0023] The molar ratio of iron in the iron source solution to phosphorus in the phosphorus source solution is (0.97~1.0):1;

[0024] The process induction liquid, the second ferric phosphate slurry, and the seed induction slurry are mixed and reacted.

[0025] In some possible implementations, the mixing reaction includes the following steps: under heat preservation and stirring conditions, the second ferric phosphate slurry and the process induction liquid are fed into the seed induction slurry in parallel and then kept at a constant temperature to obtain a reaction slurry.

[0026] In some possible implementations, the mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed induction slurry is (5.0~9.0):(2.0~4.0):1.

[0027] In some possible implementations, the solid content of the first ferric phosphate slurry is 7.65% to 13.75%.

[0028] In some possible implementations, the solids content of the second ferric phosphate slurry is 7.65% to 13.75%.

[0029] In some possible implementations, the time for heat preservation and crystallization is 0.1h to 0.5h.

[0030] In some possible implementations, the temperature of the seed-inducing slurry is 75°C to 95°C.

[0031] In some possible implementations, the temperature of the second ferric phosphate slurry is 75°C to 95°C.

[0032] In some possible implementations, the temperature of the process induction liquid is 0°C to 50°C.

[0033] In some possible implementations, the solid content of the seed-inducing slurry is 0.1% to 0.5%.

[0034] In some possible implementations, the feeding time for the second slurry and the process induction liquid is 30 min to 60 min.

[0035] In some possible implementations, the holding temperature in the mixing reaction is 75°C to 95°C.

[0036] In some possible implementations, the holding time in the mixed reaction is 0.2h to 3.0h.

[0037] In some possible implementations, the preparation method further includes the steps of: obtaining the solids in the reaction slurry and performing post-processing; the post-processing includes washing, drying and calcination to obtain the iron phosphate precursor.

[0038] Thirdly, the present invention provides a lithium iron phosphate, the raw materials of which include the above-mentioned iron phosphate precursor.

[0039] Fourthly, the present invention provides a positive electrode material, wherein the positive electrode active material includes the aforementioned lithium iron phosphate.

[0040] Fifthly, the present invention provides a battery in which the positive electrode includes the above-mentioned positive electrode material.

[0041] In a sixth aspect, the present invention provides an electrical device comprising the battery described above.

[0042] The iron phosphate precursor and its preparation method provided by this invention have at least the following beneficial technical effects compared with the prior art:

[0043] (1) The iron phosphate precursor of the present invention comprises sheet-like primary particles (thickness of 10nm~50nm) forming spherical secondary particles. The sheet-like primary particles can increase the specific surface area of ​​the iron phosphate precursor, and the spherical structure of the secondary particles increases the tap density of the iron phosphate precursor, which is beneficial to preparing a cathode material with higher tap density.

[0044] (2) In the preparation method of the iron phosphate precursor of the present invention, the seed-inducing slurry provides the crystal nucleus and induces the growth of primary particles; the process inducing liquid promotes the growth of iron phosphate along a single crystal plane to form thin and wide plate-like primary particles, and further induces the plate-like primary particles to overlap and obliquely insert each other to form spherical secondary particles; after the second iron phosphate slurry is mixed with the seed-inducing slurry, it is dissolved and recrystallized under high temperature and low pH conditions, precipitating on the crystal nucleus, promoting the increase of the plate-like thickness of the primary particles, and thus increasing the size of the secondary particles. The synergistic effect of the seed-inducing slurry, the process inducing liquid, and the second iron phosphate slurry, along with the precise control of the preparation process conditions, ultimately forms the spherical secondary particle iron phosphate precursor. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this drawing 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 only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0046] Figure 1 This is a 1000x magnified SEM image of the iron phosphate precursor provided in Example 1 of the present invention.

[0047] Figure 2 This is a 5000x magnified SEM image of the iron phosphate precursor provided in Embodiment 1 of the present invention.

[0048] Figure 3This is a 20,000x magnified SEM image of the iron phosphate precursor provided in Example 1 of the present invention.

[0049] Figure 4 The image shows a 1000x magnified SEM image of the iron phosphate precursor prepared by the preparation method provided in Comparative Example 1 of this invention.

[0050] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described and illustrated below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments provided by this invention without inventive effort are within the scope of protection of this invention.

[0052] Obviously, the following description is merely some examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, modifications to design, manufacturing, or production based on the technical content disclosed in this invention are merely conventional technical means and should not be construed as insufficient disclosure of the present invention.

[0053] However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand the invention and is not intended to limit the subject matter of the claims.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0055] The first aspect of this invention provides an iron phosphate precursor comprising secondary particles composed of plate-like primary particles;

[0056] The average thickness of the primary particles is 10nm~50nm;

[0057] The sphericity of the secondary particles is 0.7~0.9.

[0058] The iron phosphate precursor provided in this embodiment of the invention has a plate-like primary particle that increases the specific surface area of ​​the iron phosphate precursor, and a spherical structure of secondary particles that increases the compaction density and tap density of the iron phosphate precursor, thereby improving the processing performance and electrochemical performance of lithium iron phosphate.

[0059] In some embodiments, the particle size D50 of the iron phosphate precursor is 1 μm to 30 μm. In this case, it facilitates finer milling during subsequent lithium iron phosphate preparation, controls particle size growth, and improves product yield.

[0060] In some embodiments, the particle size D50 of the iron phosphate precursor is 5 μm to 20 μm. In this case, it is beneficial to refine the particle size through milling during the preparation of lithium iron phosphate.

[0061] In some embodiments, the tap density of the iron phosphate precursor is 0.6 g / cm³. 3 ~1.5g / cm 3 .

[0062] In some embodiments, the tap density of the iron phosphate precursor is 0.9 g / cm³. 3 ~1.5g / cm 3 .

[0063] In some embodiments, the specific surface area of ​​the iron phosphate precursor is 2 g / cm³. 3 ~15g / cm 3 .

[0064] In some embodiments, the specific surface area of ​​the iron phosphate precursor is 6 g / cm³. 3 ~11g / cm 3 .

[0065] In some embodiments, the particle size distribution of the iron phosphate precursor is 0.5 to 0.75. In this case, the particle size distribution of the iron phosphate precursor is relatively concentrated, resulting in higher uniformity of the iron phosphate precursor material.

[0066] In some embodiments, the particle size distribution of the iron phosphate precursor is 0.6 to 0.7.

[0067] Particle size distribution refers to (D 90 -D 10 ) / D 50 The value of .

[0068] In some embodiments, the average thickness of the primary particles is 20 nm to 40 nm. In this case, the iron phosphate precursor maintains a high specific surface area while its structure is not easily damaged.

[0069] In some embodiments, the size (average width) of the primary particles is 0.2 μm to 1.5 μm. In this case, the primary particles have high structural stability and are not easily broken.

[0070] In some embodiments, the size (average width) of the primary particles is 0.5 μm to 1.2 μm.

[0071] In some embodiments, the average sphericity of the secondary particles is 0.75 to 0.9. In this case, the tap density of the precursor can be increased, thereby improving the electrical performance of the cathode material.

[0072] Sphericity refers to the ratio of the surface area of ​​a sphere of equal volume to that of the particle to the actual surface area of ​​the particle.

[0073] A second aspect of this invention provides a method for preparing the above-mentioned iron phosphate precursor, comprising the following steps:

[0074] S10. Preparation of seed crystal induction slurry: After adjusting the pH value of the first ferric phosphate slurry to 0.1~0.8, the slurry is kept at a constant temperature to crystallize and obtain the seed crystal induction slurry. The temperature for crystallization is 75℃~95℃.

[0075] S20. Preparation process induction solution: Mix the iron source solution and phosphorus source solution and adjust the pH value to 1.5~3.0;

[0076] The molar ratio of iron in the iron source solution to phosphorus in the phosphorus source solution is (0.97~1.0):1;

[0077] S30. Mix and react the process induction liquid, the second ferric phosphate slurry, and the seed induction slurry.

[0078] The method for preparing the ferric phosphate precursor provided in this invention involves preparing a seed-inducing slurry. The first ferric phosphate slurry contains a trivalent iron source and a phosphorus source. Crystallization is achieved by maintaining the temperature at 75°C to 95°C and a pH of 0.1–0.8. Since the solubility of ferric phosphate decreases with increasing temperature, phosphate and iron ions in the seed-inducing slurry precipitate crystal nuclei under high-temperature conditions, resulting in a seed-inducing slurry with a solid content of 0.1%–0.5%. Simultaneously, this provides H₂ for the dissolution and crystallization of the second ferric phosphate slurry. + The process induction solution promotes the growth of primary particles along a single crystal plane, eventually forming thin and wide sheets. The process induction solution, the second ferric phosphate slurry containing amorphous ferric phosphate, and the seed induction slurry are mixed and reacted. Under high temperature and low pH conditions, they are dissolved and recrystallized. When the second ferric phosphate slurry and the process induction solution are added to the seed induction slurry, the pH will rise accordingly. The iron and phosphorus elements in the second ferric phosphate slurry and the seed induction slurry can basically settle down and precipitate on the original crystal nuclei, eventually forming crystalline ferric phosphate with primary particles in sheet form and secondary particles in spherical shape.

[0079] In this embodiment, the pH value of the first ferric phosphate slurry is 0.1~0.8. In this case, if the pH value is too high, it cannot be guaranteed that the first ferric phosphate slurry will completely dissolve into an inducing liquid, thus affecting the effect of crystal nucleation by heating. If the pH value is too low, even if the temperature is raised to 75℃~95℃, only a small amount of crystal nuclei will precipitate, because low pH will promote the dissolution of crystal nuclei.

[0080] In this embodiment, the temperature for heat preservation and crystallization is 75℃~95℃. Under these conditions, if the temperature is too high, it approaches the boiling point, resulting in little improvement in effect but wasting heat and increasing costs. If the temperature is too low, the amount of crystal nuclei precipitated from the seed-induced slurry will be too small, or even impossible, leading to lower crystallinity in the prepared product. Furthermore, if the number of crystal nuclei is too small, the growth time of a single crystal nucleus will be prolonged, resulting in excessively large secondary particle size, high TD (transient precipitate), and conversely, low BET (best-to-crystal ratio).

[0081] In this embodiment, the pH of the process induction solution is adjusted to 1.5-3.0. In this case, if the pH is too high, ferric phosphate precipitate will form in the process induction solution at room temperature, affecting the induction effect and product morphology; if the pH is too low, the pH of the mixed reaction solution formed by the process induction solution, seed induction slurry, and second ferric phosphate slurry will be too low, thus affecting the precipitation ratio of ferric phosphate, ultimately resulting in small secondary ferric phosphate particle size and low yield.

[0082] In some embodiments, the preparation of the first ferric phosphate slurry in step S10 above includes the following steps:

[0083] S101. Under stirring conditions with a pH of 2.0~2.2 and a reaction temperature of 50℃~60℃, hydrogen peroxide and phosphate solution are introduced into ferrous salt solution in parallel flow for reaction, and then impurities are removed to obtain solid material.

[0084] S102. Mix the solid material with water to obtain the first ferric phosphate slurry.

[0085] In the preparation of the first ferric phosphate slurry, ferrous sulfate solution is used as the base liquid. Hydrogen peroxide and monoammonium phosphate solution are then mixed concurrently with the ferrous sulfate solution. The reaction is carried out at a low pH value to ensure the purity and yield of the ferric phosphate. The reaction temperature is 50℃~60℃; too low a temperature results in slow sedimentation, affecting the yield of ferric phosphate, while too high a temperature leads to crystallization, forming crystalline ferric phosphate. After the reaction, amorphous ferric phosphate is obtained. After removing impurities, it is mixed with water to obtain the first ferric phosphate slurry.

[0086] In some embodiments, in step S101 above, ammonia is used to control the pH value of the reaction to be maintained at 2.0~2.2.

[0087] In some embodiments, in step S101 above, the concentration of the ferrous salt solution is 0.5 mol / L to 1.4 mol / L.

[0088] In some embodiments, in step S101 above, the ferrous salt in the ferrous salt solution includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0089] In some embodiments, in step S101 above, the concentration of the phosphate solution is 1.0 mol / L to 2.5 mol / L.

[0090] In some embodiments, in step S101 above, the phosphate solution contains at least one of monoammonium phosphate, diammonium phosphate, and ammonium phosphate.

[0091] In some embodiments, in step S101 above, the molar ratio of ferrous salt, hydrogen peroxide and phosphate is 1:(0.95~1):0.2.

[0092] In some embodiments, in step S101 above, the stirring speed is 35Hz~45Hz.

[0093] In some embodiments, the reaction time in step S101 is 0.3h to 2h.

[0094] In some embodiments, in step S101 above, the impurity removal step includes: centrifuging and washing with deionized water 3 to 4 times.

[0095] In some embodiments, in step S101 above, the ratio of solid material to water is determined according to the solid content of the first ferric phosphate slurry.

[0096] In some embodiments, in step S10 above, the solid content of the first ferric phosphate slurry is 7.65% to 13.75%. In this case, if the solid content is below 7.65%, that is, the concentration of the reaction solution is too low, it will lead to a decrease in the sphericity of the secondary particles and too low production capacity, which is not conducive to mass production; while if the solid content is above 13.75%, the viscosity will be too high, making stirring and mixing difficult, and the co-precipitation reaction cannot occur quickly and uniformly.

[0097] In some embodiments, in step S10 above, the pH value of the first ferric phosphate slurry is adjusted to 0.1~0.8 using acid.

[0098] In some embodiments, the acid solution includes at least one of dilute sulfuric acid, dilute nitric acid, dilute hydrochloric acid, dilute phosphoric acid, oxalic acid, and acetic acid.

[0099] In some embodiments, in step S10 above, the time for heat preservation and crystallization is 0.1h to 0.5h.

[0100] In some embodiments, in step S10 above, the solid content of the seed-inducing slurry is 0.1% to 0.5%. In this case, although crystal nuclei will precipitate as the temperature increases, the number of precipitated crystal nuclei is limited due to the low pH of the reaction system, thus the solid content of the seed-inducing slurry is low.

[0101] In some embodiments, the preparation of the iron source solution in step S20 above includes the following steps:

[0102] S201. Iron source, acidic solution, oxidant and water are mixed.

[0103] In some embodiments, in step S201 above, the iron source includes at least one of ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous oxalate, and ferrous acetate.

[0104] In some embodiments, in step S201 above, the acidic solution includes dilute sulfuric acid.

[0105] In some embodiments, the concentration of dilute sulfuric acid is 2 mol / L to 4 mol / L. In this case, the pH value of the seed-inducing slurry can be effectively controlled with minimal impact on the solids content of the seed-inducing slurry.

[0106] In some embodiments, in step S201 above, the oxidant includes ozone, hydrogen peroxide, or sodium hypochlorite.

[0107] In some embodiments, the step of mixing the iron source, acidic solution, oxidant, and water in step S201 above includes:

[0108] S2011. Mix the iron source with water, then mix with an acidic solution and filter; mix the filtrate with an oxidizing agent to obtain an iron source solution.

[0109] In the above steps of mixing the iron source, acidic solution, oxidant and water, the acidic solution is used for the crystallization of the iron source; the oxidant is used to oxidize the ferrous ions in the system to form ferric ions.

[0110] In some embodiments, in step S2011 above, the molar ratio of iron source to oxidant is 1:(0.5~1).

[0111] In some embodiments, in step S20 above, the molar concentration of iron in the iron source solution is 0.2 mol / L to 1.5 mol / L.

[0112] In some embodiments, in step S20 above, the phosphorus source solution includes at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0113] In some embodiments, in step S20 above, the molar concentration of phosphorus in the phosphorus source solution is 0.2 mol / L to 2.5 mol / L.

[0114] In some embodiments, in step S20 above, a pH adjuster is used to adjust the pH value to 1.5~3.0.

[0115] In some embodiments, the pH adjuster includes at least one of ammonia and sodium hydroxide.

[0116] In some embodiments, in step S30 above, the temperature of the process induction liquid is 0°C to 50°C. In this case, if the temperature of the process induction liquid is too low, it is easy to freeze; if the temperature is too high, crystal nuclei will precipitate before the co-current feed, and the particle size distribution of the product will be affected after the co-current feed.

[0117] In some embodiments, the preparation of the second ferric phosphate slurry in step S30 above includes the following steps:

[0118] S301. Under stirring conditions with a pH of 2.0~2.2 and a reaction temperature of 50℃~60℃, hydrogen peroxide and phosphate solution are introduced into ferrous salt solution in parallel flow for reaction, and then impurities are removed to obtain solid material.

[0119] S302. Mix the solid material with water to obtain the first ferric phosphate slurry.

[0120] The preparation method and effect of the second ferric phosphate slurry are the same as those of the first ferric phosphate slurry, and will not be repeated here.

[0121] In some embodiments, in step S301 above, the solid content of the second ferric phosphate slurry is 7.65% to 13.75%. In this case, if the solid content is below 7.65%, that is, the concentration of the reaction solution is too low, it will lead to a decrease in the sphericity of the secondary particles and too low production capacity, which is not conducive to mass production; while if the solid content is above 13.75%, the viscosity will be too high, making stirring and mixing difficult, and the co-precipitation reaction cannot occur quickly and uniformly.

[0122] In some embodiments, in step S30 above, the temperature of the second ferric phosphate slurry is 75°C to 95°C.

[0123] In some embodiments, in step S30 above, the temperature of the seed induction slurry is 75°C to 95°C.

[0124] In some embodiments, in step S30 above, the mixing reaction includes the following steps:

[0125] S302. Under heat preservation and stirring conditions, the second ferric phosphate slurry and the process induction liquid are fed into the seed induction slurry in parallel and then kept at heat to obtain the reaction slurry.

[0126] In the above mixed reaction, the second ferric phosphate slurry and the process induction liquid are flowed into the seed induction slurry in parallel to ensure the synchronous growth of primary and secondary particles.

[0127] In some embodiments, in step S30 above, the mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed induction slurry is (5.0~9.0):(2.0~4.0):1. In this case, the higher the mass ratio of the seed induction slurry (i.e., the lower the proportion of the second ferric phosphate slurry), the more crystal nuclei are precipitated, resulting in smaller secondary particle size and smaller primary particle size in the final product. Conversely, the lower the mass ratio of the seed induction slurry, the fewer crystal nuclei are precipitated, the more material precipitates on the surface of the crystal nuclei, resulting in larger secondary particle size and larger primary particle size in the final product. Similarly, if the mass ratio of the process induction liquid is too high, the width of the plate-like primary particles will be too large, making them prone to breakage; if the mass ratio of the process induction liquid is too low, the size of the plate-like primary particles will be too small, making it impossible to prepare the target morphology. By adopting the above-mentioned mixing mass ratio, it is beneficial to obtain the target primary particle size, thereby obtaining secondary particles with high sphericity.

[0128] In some embodiments, in step S302 above, the feeding time of the second ferric phosphate slurry and the process induction liquid is 30 min to 60 min.

[0129] In some embodiments, in step S302 above, the heat preservation time is 0.2h to 3.0h.

[0130] In some embodiments, the heat preservation time in step S302 is 0.5h to 1.0h.

[0131] In some embodiments, the holding temperature in step S302 is 75°C to 95°C. In this case, the ferric phosphate is completely converted into crystals; if the holding temperature is too high, it approaches the boiling point, and the effect is not significantly improved, but heat is wasted and costs are increased; if the holding temperature is too low, the proportion of precipitated ferric phosphate is too low, affecting the yield, and it will also lead to low crystallinity of the ferric phosphate product.

[0132] In some embodiments, in step S302 above, the stirring speed is 100 rpm to 800 rpm. In this case, the ferric phosphate precursor can be uniformly nucleated, improving the sphericity of secondary particles and making the particle size distribution of the ferric phosphate precursor product uniform.

[0133] In some embodiments, in step S302 above, the stirring speed is 300 rpm to 500 rpm.

[0134] In some embodiments, the method for preparing the iron phosphate precursor further includes the following steps:

[0135] S40. Obtain the solids in the reaction slurry and perform post-processing to obtain the iron phosphate precursor.

[0136] In some embodiments, in step S40 above, the post-processing includes washing, drying, and calcination.

[0137] In some embodiments, the washing step includes:

[0138] The solid is washed with water.

[0139] In some specific embodiments, the washing steps are as follows:

[0140] In the centrifuge, the solid and water are circulated and washed 2 to 6 times. Then the conductivity of the wash water is tested. If the conductivity is qualified, the washing is stopped. Finally, the solid is centrifuged to remove water.

[0141] In some embodiments, the drying temperature is 100°C to 150°C. In some embodiments, the drying time is 10 hours to 12 hours. Within this temperature range, only free water in the product is removed, maintaining the crystallinity of the product.

[0142] In some embodiments, the calcination temperature is 500°C to 750°C. In some embodiments, the calcination time is 2 hours to 4 hours. In this case, the water of crystallization can be completely removed while maintaining the purity and crystallinity of the product phase, resulting in an anhydrous iron phosphate precursor with a high specific surface area.

[0143] A third aspect of the present invention provides a lithium iron phosphate, wherein the raw materials for preparation include the aforementioned iron phosphate precursor.

[0144] A fourth aspect of the present invention provides a positive electrode material, wherein the positive electrode active material includes the aforementioned lithium iron phosphate.

[0145] A fifth aspect of the present invention provides a battery in which the positive electrode includes the above-described positive electrode material.

[0146] A sixth aspect of the present invention provides an electrical device including the battery described above.

[0147] The following description, in conjunction with specific embodiments, provides further details.

[0148] Example 1

[0149] Example 1 provides an iron phosphate precursor, such as Figures 1-3 As shown, it consists of secondary particles composed of plate-like primary particles;

[0150] The primary particles have an average thickness of 20 nm and a size of 1.0 μm; the secondary particles have a sphericity of 0.88.

[0151] The particle size distribution of the iron phosphate precursor is 0.7.

[0152] This embodiment also provides a method for preparing the iron phosphate precursor provided in this embodiment, the steps of which are as follows:

[0153] E1. Preparation of the first ferric phosphate slurry:

[0154] Under the conditions of maintaining the pH value of the reaction system at 2.0~2.2 with ammonia water, the reaction temperature at 50℃~60℃, and the stirring speed at 40Hz, hydrogen peroxide and monoammonium phosphate solution were introduced into ferrous sulfate solution in a co-current flow and reacted for 1 hour. After centrifugation and washing three times with deionized water, solid material was obtained.

[0155] The concentration of ferrous sulfate solution is 1 mol / L; the concentration of monoammonium phosphate solution is 2.2 mol / L.

[0156] The molar ratio of ferrous sulfate, hydrogen peroxide, and monoammonium phosphate is 1:0.97:0.2.

[0157] E1.2 The solid material is mixed with water to obtain the first iron phosphate slurry, the solid content of the first iron phosphate slurry is 11.12%.

[0158] E2. Preparation of seed-inducing slurry:

[0159] The pH of the first ferric phosphate slurry was adjusted to 0.4 using 2 mol / L dilute sulfuric acid, and then kept at a constant temperature for crystallization to obtain a seed-induced slurry. The temperature for crystallization was 80℃ and the time was 0.3 h.

[0160] E3. Preparation of process induction solution:

[0161] E3.1 Ferrous sulfate and water are mixed, then mixed with dilute sulfuric acid and filtered; the filtrate is mixed with hydrogen peroxide to obtain an iron source solution; wherein the concentration of dilute sulfuric acid is 2 mol / L, the molar ratio of ferrous sulfate to hydrogen peroxide is 1:0.5, and the molar concentration of iron in the iron source solution is 1.0 mol / L.

[0162] E3.2 iron source solution and phosphoric acid with a molar concentration of 1.2 mol / L were thoroughly mixed at a molar ratio of iron to phosphorus of 0.98:1. The pH of the solution was then adjusted to 2.0 using ammonia water to obtain the process induction solution.

[0163] E4. Preparation of the second ferric phosphate slurry: The second ferric phosphate slurry with a solid content of 11.12% was prepared according to the preparation method of the first ferric phosphate slurry described above.

[0164] E5. Mixed Reaction:

[0165] Under the conditions of holding at 90℃ and stirring at 400rpm, the second ferric phosphate slurry at 90℃ and the process induction slurry at 30℃ were simultaneously introduced into the seed induction slurry at 90℃ within 45min. Then, the reaction was carried out at 80℃ for 0.8h to obtain the reaction slurry.

[0166] The mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed induction slurry is 7:3:1.

[0167] E6. Post-processing:

[0168] After obtaining the solids from the reaction slurry, the solids were washed with water three times, dried at 120℃ for 10 hours, and calcined at 610℃ for 3 hours.

[0169] Example 2

[0170] Example 2 provides an iron phosphate precursor composed of secondary particles consisting of plate-like primary particles;

[0171] The primary particles have an average thickness of 50 nm and a size of 1.3 μm; the secondary particles have a sphericity of 0.9.

[0172] The particle size distribution of the iron phosphate precursor is 0.5.

[0173] This embodiment also provides a method for preparing the iron phosphate precursor provided in this embodiment. The steps are basically the same as those in Example 1, except that:

[0174] In step E5, the time for introducing the second ferric phosphate slurry and the process induction liquid into the seed crystal induction slurry is 30 minutes;

[0175] The mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed crystal induction slurry is 5:2:1;

[0176] The temperature for the heat preservation reaction was 95℃, and the time was 0.5h.

[0177] Example 3

[0178] Example 3 provides an iron phosphate precursor composed of secondary particles consisting of plate-like primary particles;

[0179] The primary particles have an average thickness of 23 nm and a size of 1.2 μm; the secondary particles have a sphericity of 0.85.

[0180] The particle size distribution of the iron phosphate precursor is 0.6.

[0181] This embodiment also provides a method for preparing the iron phosphate precursor provided in this embodiment. The steps are basically the same as those in Example 1, except that:

[0182] In step E5, the time for introducing the second ferric phosphate slurry and the process induction liquid into the seed crystal induction slurry is 60 minutes;

[0183] The mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed crystal induction slurry is 9:4:1;

[0184] The temperature for the heat preservation reaction was 75℃, and the time was 2 hours.

[0185] Example 4

[0186] Example 4 provides an iron phosphate precursor composed of secondary particles consisting of plate-like primary particles;

[0187] The primary particles have an average thickness of 15 nm and a size of 0.8 μm; the secondary particles have a sphericity of 0.8.

[0188] The particle size distribution of the iron phosphate precursor is 0.65.

[0189] This embodiment also provides a method for preparing the iron phosphate precursor provided in this embodiment. The steps are basically the same as those in Example 1, except that:

[0190] In step E2, the pH value of the seed-inducing slurry is 0.1.

[0191] In step E3.2, the pH value of the process induction solution is 1.5.

[0192] Example 5

[0193] Example 5 provides an iron phosphate precursor composed of secondary particles consisting of plate-like primary particles;

[0194] The primary particles have an average thickness of 30 nm and a size of 1.5 μm; the secondary particles have a sphericity of 0.75.

[0195] The particle size distribution of the iron phosphate precursor is 0.55.

[0196] This embodiment also provides a method for preparing the iron phosphate precursor provided in this embodiment. The steps are basically the same as those in Example 1, except that:

[0197] In step E2, the pH value of the seed-inducing slurry is 0.8.

[0198] In step E3.2, the pH value of the process induction solution is 3.0.

[0199] Comparative Example 1

[0200] Comparative Example 1 provides a method for preparing an iron phosphate precursor, the steps of which are as follows:

[0201] D1. Preparation of the first ferric phosphate slurry:

[0202] D1.1 Under the conditions of maintaining the pH value of the reaction system at 2.0~2.2 with ammonia water, the reaction temperature at 50℃~60℃ and the stirring speed at 40Hz, hydrogen peroxide and monoammonium phosphate solution were introduced into ferrous sulfate solution in a co-current flow and reacted for 1 hour. After centrifugation and washing three times with deionized water, solid material was obtained.

[0203] The concentration of ferrous sulfate solution is 1 mol / L; the concentration of monoammonium phosphate solution is 2.2 mol / L.

[0204] The molar ratio of ferrous sulfate, hydrogen peroxide, and monoammonium phosphate is 1:0.97:0.2.

[0205] D1.2 The solid material is mixed with water to obtain the first iron phosphate slurry, which has a solid content of 11.12%.

[0206] D2. Preparation of seed-inducing slurry: The pH value of the first ferric phosphate slurry was adjusted to 0.4 with 2 mol / L dilute sulfuric acid, and the reaction was carried out at 80℃ for 0.3 h to obtain the seed-inducing slurry.

[0207] D3. Preparation of the second ferric phosphate slurry: The second ferric phosphate slurry with a solid content of 11.12% was prepared according to the preparation method of the first ferric phosphate slurry in D1.

[0208] D4. Mixed Reaction:

[0209] D4.1 Under the conditions of holding at 90℃ and stirring at 400rpm, the second ferric phosphate slurry at 90℃ was passed into the seed induction slurry at 90℃ and the reaction was carried out for 0.8h. The mass ratio of the second ferric phosphate slurry to the seed induction slurry was 7:1 to obtain the reaction slurry.

[0210] D4.2 Obtain the solids in the reaction slurry and perform post-processing to obtain the iron phosphate precursor; wherein, the solids are washed with water 3 times, dried at 120℃ for 10h, and calcined at 610℃ for 2h.

[0211] Comparative Example 2

[0212] Comparative Example 2 provides a method for preparing an iron phosphate precursor, the steps of which are basically the same as those in Example 1, except that:

[0213] In step E2, the pH value of the prepared seed-inducing slurry is 1.2.

[0214] Comparative Example 3

[0215] Comparative Example 3 provides a method for preparing an iron phosphate precursor, the steps of which are basically the same as those in Example 1, except that:

[0216] In step E5, the temperature of the process induction solution is 60°C.

[0217] Comparative Example 4

[0218] Comparative Example 4 provides a method for preparing an iron phosphate precursor, the steps of which are basically the same as those in Example 1, except that:

[0219] In step E5, the temperature of the process induction solution is -10℃.

[0220] Comparative Example 5

[0221] Comparative Example 5 provides a method for preparing an iron phosphate precursor, the steps of which are basically the same as those in Example 1, except that:

[0222] In step E5, the insulation temperature is 120℃.

[0223] Comparative Example 6

[0224] Comparative Example 6 provides a method for preparing an iron phosphate precursor, the steps of which are basically the same as those in Example 1, except that:

[0225] In step E5, the insulation temperature is 60℃.

[0226] To verify the advancement of the iron phosphate precursor and its preparation method provided in the embodiments of the present invention, the particle size D50, tap density and specific surface area of ​​the iron phosphate precursor or the prepared iron phosphate precursor provided in the embodiments and comparative examples of the present invention were tested, and the results are shown in Table 1 below.

[0227] The selected testing instruments include:

[0228] Particle size distribution: Malvern 3000 particle size analyzer.

[0229] BET: Surface area analyzer, model BSD-BET400, manufactured by Best Instrument Technology (Beijing) Co., Ltd.

[0230] Tap density: Tap density meter, model BT-313, manufactured by Dandong Better Instruments Co., Ltd.

[0231] Table 1

[0232]

[0233] From the table above and the accompanying drawings in the instruction manual, at least the following conclusions can be drawn:

[0234] (1) The iron phosphate precursor prepared by the method of the present invention consists of spherical secondary particles composed of plate-like primary particles. The plate-like primary particles significantly increase the specific surface area of ​​the iron phosphate precursor, and the spherical structure of the secondary particles increases the compaction density and tap density of the iron phosphate precursor.

[0235] (2) Data from Example 1 and Comparative Example 1 and Figures 1-4 It can be seen that when no process induction liquid was used in Comparative Example 1, the primary particles of the prepared iron phosphate precursor were small flakes and small spheres. This shows that in the preparation method of iron phosphate precursor provided by the present invention, the process induction liquid can promote the growth of iron phosphate along a single crystal plane, and finally form thin and wide flake-shaped primary particles; the seed induction slurry induces the flake-shaped primary particles to overlap and obliquely insert each other to form spherical secondary particles.

[0236] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A ferric phosphate precursor, characterized in that, Secondary particles consisting of flaky primary particles; The thickness of the primary particles is 10nm~50nm; The sphericity of the secondary particles is 0.7~0.9; The preparation method of the iron phosphate precursor includes the following steps: Preparation of seed crystal induction slurry: After adjusting the pH value of the first ferric phosphate slurry to 0.1~0.8, the slurry is kept at a certain temperature for crystallization to obtain the seed crystal induction slurry. The temperature for crystallization is 75℃~95℃. Preparation process induction solution: Mix iron source solution and phosphorus source solution and adjust pH value to 1.5~3.0; The molar ratio of iron in the iron source solution to phosphorus in the phosphorus source solution is 0.97~1.0:1; The process induction liquid, the second ferric phosphate slurry, and the seed induction slurry are mixed and reacted. The first ferric phosphate slurry and the second ferric phosphate slurry contain amorphous ferric phosphate; The preparation of the first ferric phosphate slurry includes the following steps: Under stirring conditions with a pH of 2.0~2.2 and a reaction temperature of 50℃~60℃, hydrogen peroxide and phosphate solution are introduced into ferrous salt solution in parallel flow for reaction, and then impurities are removed to obtain solid material. The solid material is mixed with water to obtain the first ferric phosphate slurry; The preparation of the second ferric phosphate slurry includes the following steps: Under stirring conditions with a pH of 2.0~2.2 and a reaction temperature of 50℃~60℃, hydrogen peroxide and phosphate solution are introduced into ferrous salt solution in parallel flow for reaction, and then impurities are removed to obtain solid material. The solid material is mixed with water to obtain a second ferric phosphate slurry; The mixing reaction includes the following steps: under heat preservation and stirring conditions, the second ferric phosphate slurry and the process induction liquid are introduced into the seed crystal induction slurry in parallel and then kept at heat to obtain the reaction slurry.

2. The iron phosphate precursor according to claim 1, characterized in that, The iron phosphate precursor shall satisfy at least one of the following characteristics (1) to (6): (1) The particle size distribution of the iron phosphate precursor is 0.5~0.75; (2) The average thickness of the primary particles is 20 nm to 40 nm; (3) The size of the primary particles is 0.2 μm to 1.5 μm; (4) The tap density of the iron phosphate precursor is 0.6 g / cm³. 3 ~1.5g / cm 3 ; (5) The particle size D50 of the iron phosphate precursor is 1 μm to 30 μm; (6) The specific surface area of ​​the iron phosphate precursor is 2m². 2 / g~15m 2 / g.

3. A method for preparing the iron phosphate precursor as described in claim 1 or 2, characterized in that, Includes the following steps: Preparation of seed crystal induction slurry: After adjusting the pH value of the first ferric phosphate slurry to 0.1~0.8, the slurry is kept at a certain temperature for crystallization to obtain the seed crystal induction slurry. The temperature for crystallization is 75℃~95℃. Preparation process induction solution: Mix iron source solution and phosphorus source solution and adjust pH value to 1.5~3.0; The molar ratio of iron in the iron source solution to phosphorus in the phosphorus source solution is 0.97~1.0:1; The process induction liquid, the second ferric phosphate slurry, and the seed induction slurry are mixed and reacted.

4. The method for preparing the iron phosphate precursor according to claim 3, characterized in that, The mixing reaction includes the following steps: under heat preservation and stirring conditions, the second ferric phosphate slurry and the process induction liquid are introduced into the seed crystal induction slurry in parallel and then kept at heat to obtain the reaction slurry.

5. The method for preparing the iron phosphate precursor according to claim 3 or 4, characterized in that, It satisfies at least one of the following characteristics (1) to (8): (1) The mass ratio of the second ferric phosphate slurry, the process induction liquid, and the seed crystal induction slurry is 5.0~9.0:2.0~4.0:1; (2) The solid content of the first ferric phosphate slurry is 7.65%~13.75%; (3) The solid content of the second ferric phosphate slurry is 7.65%~13.75%; (4) The time for heat preservation and crystallization is 0.1h~0.5h; (5) The temperature of the seed-inducing slurry is 75℃~95℃; (6) The temperature of the second ferric phosphate slurry is 75℃~95℃; (7) The temperature of the induction liquid in the process is 0℃~50℃; (8) The solid content of the seed-inducing slurry is 0.1%~0.5%.

6. The method for preparing the iron phosphate precursor according to claim 5, characterized in that, It satisfies at least one of the following characteristics (1) to (4): (1) The feeding time of the second ferric phosphate slurry and the process induction liquid is 30 min to 60 min; (2) In the mixed reaction, the holding temperature is 75℃~95℃; (3) In the mixed reaction, the heat preservation time is 0.2h~3.0h; (4) The preparation method further includes the steps of: obtaining the solid in the reaction slurry and performing post-treatment; the post-treatment includes washing, drying and calcination to obtain the iron phosphate precursor.

7. A lithium iron phosphate, characterized in that, The raw materials used in the preparation include the iron phosphate precursor as described in claim 1 or 2.

8. A positive electrode material, characterized in that, The active material in the cathode material includes lithium iron phosphate as described in claim 7.

9. A battery, characterized in that, The positive electrode of the battery includes the positive electrode material as described in claim 8.

10. An electrical device, characterized in that, Includes the battery as described in claim 9.

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