Iron phosphate, its preparation method and production device and lithium iron phosphate positive electrode material

Abstract

The application provides iron phosphate, a preparation method and a production device thereof and a lithium iron phosphate positive electrode material, and relates to the technical field of iron phosphate. The iron phosphate provided by the application comprises spherical secondary particles, the secondary particles are composed of primary particles, the primary particles have an octahedral structure, and the average edge length of the primary particles is 200nm-800nm. In the application, the tap density of the iron phosphate is high, and thus the lithium iron phosphate positive electrode material prepared by using the iron phosphate has good electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of iron phosphate technology, specifically to an iron phosphate, its preparation method and production apparatus, and lithium iron phosphate cathode material. Background Technology

[0002] With the development of new energy technologies, lithium-ion batteries have been widely used in various fields such as mobile phones, laptops, and electric vehicles. Among these, the cathode material is a key component of lithium-ion batteries, determining their performance indicators such as energy density, cycle life, charge / discharge rate, and safety. In the 1990s, lithium iron phosphate was reported as a suitable cathode material for lithium-ion batteries, possessing high theoretical specific capacity and stable electrochemical performance, making it one of the most widely used cathode materials for lithium-ion batteries today.

[0003] Lithium iron phosphate (LFP) is generally prepared using a solid-state reaction method, which involves mixing iron phosphate and a lithium source in a specific ratio and then carrying out a solid-state reaction at high temperature to produce LFP. Currently, LFP is typically prepared using iron phosphate with primary particles in flake form and secondary particles in spherical form. However, this type of iron phosphate usually contains or introduces more impurities, and its tap density is low, resulting in poor electrochemical performance of the prepared LFP. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides iron phosphate, its preparation method and production apparatus, and lithium iron phosphate cathode material, aiming to solve the problems of high impurity content and low tap density of iron phosphate.

[0005] In a first aspect, embodiments of this application provide an iron phosphate, which includes spherical secondary particles composed of primary particles. The primary particles have an octahedral structure and an average side length of 200 nm to 800 nm.

[0006] In this embodiment, by regulating the structure of iron phosphate, its tap density can be significantly improved, and the iron phosphate with this morphology has fewer impurities, which helps to improve the electrochemical performance of the lithium iron phosphate cathode material made from this iron phosphate.

[0007] In some embodiments, the tap density of ferric phosphate is 1.15 g / cm³. 3 ~1.6g / cm 3 .

[0008] In this embodiment, controlling the tap density of iron phosphate within the above-mentioned range is beneficial for preparing lithium iron phosphate with good electrochemical performance.

[0009] In some embodiments, the particle size distribution coefficient of ferric phosphate is 0.7 to 1.3.

[0010] In this embodiment, by controlling the particle size distribution coefficient, the uniformity of iron phosphate is relatively high and the processing performance is good, which helps to improve the cycle performance and energy density of the lithium iron phosphate cathode material made from this iron phosphate.

[0011] In some embodiments, the crystal structure of iron phosphate is orthorhombic.

[0012] In this embodiment, the provided iron phosphate has a higher density and a higher tap density.

[0013] In some implementations, the average side length of the primary particles is 320 nm to 450 nm.

[0014] In this embodiment, by controlling the average side length of the primary particles, the obtained iron phosphate can have both high tap density and high purity.

[0015] Secondly, embodiments of this application provide a method for preparing ferric phosphate, comprising the following steps:

[0016] The oxidation reaction product is obtained by mixing a ferrous salt solution, a phosphate-containing solution, and an oxidant solution.

[0017] The oxidation reaction products were subjected to a first rinsing and pulping treatment in sequence to obtain a pulped material.

[0018] A portion of the pulped material is subjected to a first aging process to obtain the first aged material;

[0019] The first aged material and the remaining pulped material are mixed and subjected to a second aging process to obtain the second aged material;

[0020] The second aged material is subjected to a second rinse, drying and sintering in sequence to obtain iron phosphate.

[0021] In this embodiment, the oxidation reaction product is prepared by mixing ferrous salt solution, phosphate-containing solution and oxidant solution, which helps to increase the specific surface area of ​​the oxidation reaction product, increase the number of active sites, and thus improve the preparation efficiency. After the first rinsing, impurities can be removed, and the subsequent slurry treatment can promote the uniform dispersion of particles, which is conducive to pipeline transportation and continuous production. Subsequently, a portion of the slurry is first aged to obtain ferric phosphate seed crystals, so that the solid material in the remaining slurry can grow on the basis of the ferric phosphate seed crystals. The growth is highly ordered, and the primary ferric phosphate particles prepared are octahedral with high tap density.

[0022] In some embodiments, the concentration of ferrous ions in the ferrous salt solution is 0.5 mol / L to 1.5 mol / L; the concentration of phosphate ions in the phosphate-containing solution is 1.6 mol / L to 2.5 mol / L, and the pH value of the phosphate-containing solution is 6.8 to 7.2; the concentration of oxidant in the oxidant solution is 0.5 mol / L to 1 mol / L.

[0023] In this embodiment, the pH value can be adjusted by adding an alkali, such as sodium hydroxide or ammonia, to the phosphate-containing solution. Understandably, controlling the concentration and pH value of each reactant promotes the rapid formation of ferric phosphate and facilitates the formation of uniform nuclei, thus better promoting subsequent crystal growth. Furthermore, maintaining the solution concentration within the aforementioned range also helps reduce the adsorption of impurity ions by the product, thereby improving the purity of the ferric phosphate.

[0024] In some embodiments, an acid solution is used for pulping treatment; further, the acid solution is a phosphoric acid solution with a phosphoric acid concentration of 0.1 mol / L to 0.5 mol / L.

[0025] In this embodiment, the slurry treatment with acid solution can provide an acidic environment for the nucleation and growth of iron phosphate, which is beneficial for controlling the growth direction of iron phosphate crystals and promoting the formation of the target structure, namely the orthorhombic crystal structure.

[0026] In some embodiments, the temperature of the first aging is 85℃~100℃, and after the pulp changes color, it is aged for 5min~15min to obtain the first aged material; the temperature of the second aging is 85℃~100℃ and the time is 80min~150min.

[0027] In this embodiment, controlling the conditions of the first aging process can promote the formation of iron phosphate seed crystals, making their structure more regular and uniform, and their diameter spacing narrower. Simultaneously, controlling the conditions of the second aging process helps to promote the formation of iron phosphate particles, improving production efficiency.

[0028] In some embodiments, the drying temperature is 90°C to 110°C, the sintering temperature is 550°C to 650°C, and the sintering time is 1 hour to 3 hours.

[0029] In this embodiment, controlling the drying temperature helps improve drying efficiency and thus the production efficiency of ferric phosphate. Simultaneously, controlling the sintering temperature helps form orthorhombic ferric phosphate, thereby improving its tap density.

[0030] In some embodiments, the molar ratio of ferrous ions in the ferrous salt solution, phosphate ions in the phosphate-containing solution, and oxidant in the oxidant solution is 1:(0.95-1.05):(0.6-0.8).

[0031] In this embodiment, by controlling the molar ratio of ferrous ions, phosphate ions and oxidant, the iron-to-phosphorus ratio of the product can be made closer to the theoretical iron phosphate (FePO4), thereby improving the purity of the product.

[0032] In some embodiments, the first rinse is performed with water until the conductivity of the rinse water is <5 mS / cm; the second rinse is performed with water until the conductivity of the rinse water is <500 μS / cm.

[0033] In this embodiment, by controlling the endpoints of the first and second rinsing, impurities in the product can be effectively reduced while ensuring production efficiency.

[0034] In some embodiments, the pulping time is 30 min to 60 min; the solid content of the pulp is 10 wt% to 20 wt%.

[0035] In this embodiment, by controlling the slurry treatment time, it can be ensured that the iron phosphate particles are fully dispersed in the slurry; by controlling the solid content, it can be ensured that the slurry has appropriate viscosity and fluidity, so that the particles can change their microstructure under the action of acid solution, thereby improving electrochemical performance and processing performance.

[0036] In some embodiments, the ferrous salt in the ferrous salt solution is at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; the phosphate in the phosphate-containing solution is derived from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; and the oxidant in the oxidant solution is at least one of hydrogen peroxide, ammonium persulfate, and sodium persulfate.

[0037] In this embodiment, by controlling the types of ferrous salts, oxidants, and phosphate sources, the efficient chemical reaction can be ensured, product quality can be improved, and the cost can be relatively low.

[0038] Thirdly, embodiments of this application provide an apparatus for producing ferric phosphate, comprising the following units:

[0039] A feeding unit is used to provide raw materials for the oxidation reaction, which include ferrous salt solution, phosphate-containing solution and oxidant solution;

[0040] The reaction unit is used to carry out oxidation reactions and obtain oxidation reaction products;

[0041] The first rinsing unit is used to rinse the oxidation reaction products to obtain the first rinsed product.

[0042] The pulping unit is used to pulp the first rinse product to obtain pulped material;

[0043] An aging unit is used to sequentially perform a first aging treatment and a second aging treatment on the pulped material to obtain a second aged material;

[0044] The second rinsing unit is used to rinse the second aged material to obtain the second rinsed product.

[0045] The post-processing unit includes a drying subunit and a sintering subunit. The drying subunit is used to dry the second rinse product to obtain a dried material, and the sintering subunit is used to sinter the dried material to obtain ferric phosphate. The ferric phosphate is the ferric phosphate of the first aspect of this application or the ferric phosphate prepared by the preparation method of the second aspect of this application.

[0046] In this embodiment, by integrating units such as feeding, reaction, rinsing, pulping, aging, and post-processing, the preparation process of ferric phosphate is made continuous and automated, which can reduce manual intervention and improve the safety and stability of the production process.

[0047] In some embodiments, the feeding unit includes multiple storage tanks and multiple first discharge pipes disposed at the bottom of the multiple storage tanks, wherein the oxidation reaction raw materials are stored in the multiple storage tanks; the reaction unit includes a reactor and multiple first feed pipes disposed at the bottom of the reactor, and a first overflow port disposed at the top of the reactor, wherein the first feed pipes are connected to the first discharge pipes of the feeding unit, and the oxidation reaction raw materials undergo oxidation reaction in the reactor to obtain oxidation reaction products; the first rinsing unit includes a first belt filter and a first sprayer disposed on one side of the first belt filter, wherein the oxidation reaction products overflow from the overflow port at the top of the reactor in the reaction unit to the feed end of the first belt filter in the first rinsing unit, and are rinsed by the first sprayer to obtain a first rinsed product; the slurrying unit includes a slurrying reactor and a chute disposed on the slurrying reactor, and a second discharge pipe, wherein the chute is connected to the discharge end of the belt filter in the first rinsing unit, and the first rinsed product enters the slurrying reactor through the chute. The process involves several steps: First, a pulping process is performed in the pulping reactor to obtain a pulped material. Second, an aging unit is included, comprising an aging reactor, a second feed pipe located at the bottom of the aging reactor, and a second overflow port located at the top of the aging reactor. The second feed pipe is connected to the second discharge pipe of the pulping unit. The pulped material undergoes a first aging process and a second aging process sequentially in the aging reactor to obtain a second aged material. Third, a second rinsing unit is included, comprising a second belt filter and a second sprayer located on one side of the second belt filter. The second aged material overflows through the second overflow port at the top of the aging reactor in the aging unit to the feed end of the second belt filter, and is rinsed by the second sprayer to obtain a second rinsed product. Fourth, a drying and sintering unit is included, comprising a drying subunit and a sintering subunit. The drying subunit includes a drying chamber, and the sintering subunit includes a calcining furnace. The second rinsed product is dried in the drying chamber to obtain a dried material, which is then sintered in the calcining furnace to obtain ferric phosphate.

[0048] In this embodiment, by refining the specific structure of each unit, production efficiency and product quality are effectively improved, production costs and environmental impact are reduced, and favorable support is provided for the large-scale production of lithium iron phosphate cathode materials.

[0049] In some embodiments, the oxidizing reaction feedstock is fed into the reactor of the continuous reaction unit at a flow rate of 1 / 20 to 1 / 5 of the reactor volume in the continuous reaction unit per minute; the slurry is added to the aging reactor of the aging unit at a flow rate of 1 / 150 to 1 / 90 of the aging reactor volume in the aging unit per minute.

[0050] In this embodiment, by controlling the feed flow rates of the oxidation reaction raw materials and the slurry within the above-mentioned range, the equilibrium state within the reaction system can be maintained, improving the stability and controllability of the reaction process, which is beneficial to improving the purity and yield of ferric phosphate.

[0051] Fourthly, embodiments of this application provide a lithium iron phosphate cathode material.

[0052] In this embodiment, the lithium iron phosphate cathode material contains the aforementioned iron phosphate, and therefore has good electrochemical performance.

[0053] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0055] Figure 1 This is a schematic diagram of the ferric phosphate production apparatus in an embodiment of this application;

[0056] Figure 2 The image shows the XRD pattern of the second aged material in Example 1.

[0057] Figure 3 The XRD pattern of ferric phosphate in Example 1;

[0058] Figure 4 The XRD pattern of the aging reaction products in Comparative Example i is shown.

[0059] Figure 5 The XRD pattern of ferric phosphate in Comparative Example 1;

[0060] Figure 6 The XRD pattern of ferric phosphate in Example 9;

[0061] Figure 7 Here is a SEM image of ferric phosphate from Example 1;

[0062] Figure 8 Here is a SEM image of ferric phosphate from Example 2;

[0063] Figure 9 SEM image of ferric phosphate in Comparative Example 1;

[0064] Explanation of reference numerals in the attached drawings: 10, feeding unit; 20, reaction unit; 30, first rinsing unit; 40, pulping unit; 50, aging unit; 60, second rinsing unit; 70, post-processing unit. Detailed Implementation

[0065] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0066] Currently, the iron phosphate used to prepare lithium iron phosphate cathode materials generally has a secondary particle structure, with primary particles being plate-like and secondary particles being spherical. This type of iron phosphate usually contains more impurities and has a low tap density, which leads to poor electrochemical performance of the lithium iron phosphate cathode material prepared from this iron phosphate.

[0067] To address the technical problems of high impurity content and low tap density of iron phosphate, this application provides iron phosphate, its preparation method and production apparatus, and lithium iron phosphate cathode material. By controlling the structure of iron phosphate, the technical effects of reducing impurities and increasing the tap density of iron phosphate can be achieved, thereby improving the electrochemical performance of the lithium iron phosphate cathode material prepared from this iron phosphate.

[0068] In a first aspect, embodiments of this application provide an iron phosphate, which includes spherical secondary particles, the secondary particles being composed of primary particles, the primary particles having an octahedral structure, and the average side length of the primary particles being 200 nm to 800 nm.

[0069] In this application, compared to amorphous or irregularly shaped particles, the octahedral structure has a lower specific surface area. This reduced specific surface area means less opportunity for impurity ions to adsorb onto the particle surface during synthesis, thereby lowering the impurity content in ferric phosphate. Simultaneously, by controlling the edge length of the primary particles between 200 and 800 nm, the contact time between the particles and impurities in the solution during synthesis can be reduced, thus minimizing the adsorption and retention of impurity elements. Furthermore, the spherical shape of the secondary particles improves the flowability and filtration performance of the material. Compared to sheet-like structures, it offers less resistance and higher washing efficiency during filtration and washing, thus removing impurities more effectively. Moreover, during the formation of secondary particles, the ordered arrangement and specific size range of the octahedral primary particles contribute to a denser structure, thereby increasing the tap density. The spherical secondary particles have a lower porosity, and their morphology allows for tighter packing, reducing inter-particle gaps and providing higher mass, i.e., higher tap density, within the same volume.

[0070] Furthermore, in some embodiments, the tap density of ferric phosphate is 1.15 g / cm³.3 ~1.6g / cm 3 .

[0071] In this application, the tap density of iron phosphate is within the above-mentioned range, which is beneficial to improving the tap density of lithium iron phosphate prepared from the iron phosphate, thereby improving the electrochemical performance of lithium iron phosphate.

[0072] Furthermore, in some embodiments, the particle size distribution coefficient of ferric phosphate is 0.7 to 1.3.

[0073] In this application, the particle size distribution coefficient is (D90-D10) / D50. The closer the value is to 1, the higher the uniformity of iron phosphate. By controlling the particle size distribution coefficient within the above range, on the one hand, the material has high uniformity, which is beneficial for mixing and compaction; on the other hand, it is also beneficial to increase the contact area between the lithium iron phosphate cathode material made from this iron phosphate and the electrolyte, and shorten the diffusion path of lithium ions.

[0074] Furthermore, in some embodiments, the crystal structure of iron phosphate is orthorhombic.

[0075] In this application, orthorhombic iron phosphate exhibits high structural and thermal stability, and provides a path for lithium ions to diffuse along a specific lattice direction during charging and discharging, facilitating the rapid movement of lithium ions. Furthermore, the higher purity and density of the orthorhombic iron phosphate structure significantly contribute to improving the electrochemical performance of lithium iron phosphate cathode materials.

[0076] Furthermore, in some embodiments, the average side length of the primary particles is 320 nm to 450 nm.

[0077] In this application, the average side length of the primary particles is controlled within the above-mentioned range, which results in a weaker adsorption capacity for impurity ions during the growth process, thereby helping to reduce the impurity content in ferric phosphate.

[0078] Secondly, embodiments of this application provide a method for preparing ferric phosphate, comprising the following steps:

[0079] The oxidation reaction product is obtained by mixing a ferrous salt solution, a phosphate-containing solution, and an oxidant solution.

[0080] The oxidation reaction products were subjected to a first rinsing and pulping treatment in sequence to obtain a pulped material.

[0081] A portion of the pulped material is subjected to a first aging process to obtain the first aged material;

[0082] The first aged material and the remaining pulped material are mixed and subjected to a second aging process to obtain the second aged material;

[0083] The second aged material is subjected to a second rinse, drying and sintering in sequence to obtain iron phosphate.

[0084] In this application, the first rinsing reduces the impurity content during the synthesis process, removes unreacted raw materials, and improves the purity of the subsequent slurry. Simultaneously, the slurry treatment further optimizes the dispersibility of the material, which is beneficial for the formation of ferric phosphate seed crystals during the first aging process. Mixing the first aged material with the remaining slurry for a second aging process allows the growth of ferric phosphate to shift from amorphous to regular and ordered, which is beneficial for forming ferric phosphate with octahedral primary particles and spherical secondary particles. A second rinsing after the second aging process further reduces the impurity content in the product. The resulting ferric phosphate has an iron-to-phosphorus ratio close to 1:1, high purity, and high stability. The iron-to-phosphorus ratio is the molar ratio of iron to phosphorus. It should be noted that the aforementioned partial slurry refers to 8%–15% of the total slurry, and the remaining slurry refers to 85%–92% of the total slurry.

[0085] Furthermore, in some embodiments, the concentration of ferrous ions in the ferrous salt solution is 0.5 mol / L to 1.5 mol / L; the concentration of phosphate ions in the phosphate-containing solution is 1.6 mol / L to 2.5 mol / L, and the pH value of the phosphate-containing solution is 6.8 to 7.2; the concentration of oxidant in the oxidant solution is 0.5 mol / L to 1 mol / L.

[0086] In this application, limiting the concentration of each solution ensures sufficient contact and reaction of the reactants in the oxidation reaction, thereby optimizing the reaction rate, allowing the reaction to proceed rapidly and steadily, which is beneficial for forming the desired structure of ferric phosphate, and can reduce the waste of raw materials and save production costs. In addition, controlling the concentration of phosphate ions in the phosphate-containing solution within the above-mentioned range is beneficial for promoting the formation of octahedral primary particles, thereby improving the tap density of ferric phosphate.

[0087] Furthermore, in some embodiments, an acid solution is used for pulping treatment; preferably, the acid solution is a phosphoric acid solution with a phosphoric acid concentration of 0.1 mol / L to 0.5 mol / L.

[0088] In this application, an acid solution is used because the above-mentioned phosphoric acid solution for pulping treatment can have a positive impact on the microstructure of ferric phosphate. Phosphoric acid solution within this concentration range can promote the formation of primary particles and optimize secondary particles, thereby improving the tap density and morphological consistency of the finished ferric phosphate. Furthermore, using phosphoric acid solution for pulping will not introduce other impurities.

[0089] Furthermore, in some embodiments, the temperature of the first aging is 85℃~100℃, and after the pulp changes color, it is aged for 5min~15min to obtain the first aged material; the temperature of the second aging is 85℃~100℃ and the time is 80min~150min.

[0090] In this application, controlling the conditions of the first aging process can promote the initial shape formation of iron phosphate particles and control their size distribution, resulting in higher uniformity. Furthermore, controlling the conditions of the second aging process can further stabilize the crystal structure of iron phosphate and improve the cycle performance of the lithium iron phosphate cathode material prepared from this iron phosphate.

[0091] Furthermore, in some embodiments, the drying temperature is 90°C to 110°C, the sintering temperature is 550°C to 650°C, and the sintering time is 1 to 3 hours.

[0092] In this application, controlling the drying temperature can effectively remove moisture from the ferric phosphate slurry, avoiding crystal structure damage or phase transformation caused by drying; subsequently, sintering at 550℃~650℃ can ensure that the thermal stress during sintering is small and will not have a significant impact on the mechanical properties of ferric phosphate. At the same time, it can further improve the crystal structure of ferric phosphate and enhance the density and stability of the crystal.

[0093] Furthermore, in some embodiments, the molar ratio of ferrous ions in the ferrous salt solution, phosphate ions in the phosphate-containing solution, and oxidant in the oxidant solution is 1:(0.95-1.05):(0.6-0.8).

[0094] In this application, by controlling the molar ratio of each substance, the chemical reaction between phosphorus, iron and oxidant can be ensured to be more complete and controllable, which is conducive to forming iron phosphate with an iron-to-phosphorus ratio closer to the theoretical value and improving the purity of the material.

[0095] Furthermore, in some embodiments, the first rinse is performed with water until the conductivity of the rinse water after rinsing is <5 mS / cm; the second rinse is performed with water until the conductivity of the rinse water after rinsing is <500 μS / cm.

[0096] In this application, the conductivity of the rinse water after the first rinse is controlled to be <5 mS / cm, so that the ferric phosphate is deeply rinsed, thereby effectively reducing the impurity content in the prepared ferric phosphate.

[0097] Furthermore, in some embodiments, the pulping time is 30 min to 60 min; the solid content of the pulp is 10 wt% to 20 wt%.

[0098] In this application, setting the slurrying time to 30-60 minutes ensures that the material is fully dispersed and uniformly mixed in the solution, which is beneficial to the uniform growth of ferric phosphate crystals, thereby obtaining ferric phosphate with uniform morphology. In addition, controlling the solid content of the slurry can improve the fluidity and dispersibility of the slurry, thereby improving the efficiency of subsequent processing and shortening the aging time.

[0099] Furthermore, in some embodiments, the ferrous salt in the ferrous salt solution is at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; the phosphate-containing solution is derived from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid; and the oxidant in the oxidant solution is at least one of hydrogen peroxide, ammonium persulfate, and sodium persulfate.

[0100] In this application, controlling the types of ferrous salts, oxidants, and phosphate sources ensures efficient chemical reactions under different conditions, while reducing the formation of byproducts and increasing the yield and purity of the target product, iron phosphate.

[0101] Thirdly, embodiments of this application provide a production apparatus for iron phosphate, as shown in the schematic diagram below. Figure 1 As shown, it includes the following units:

[0102] The feeding unit 10 is used to provide raw materials for the oxidation reaction, including ferrous salt solution, phosphate-containing solution and oxidant solution;

[0103] Reaction unit 20 is used to carry out continuous oxidation reactions to obtain oxidation reaction products;

[0104] The first rinsing unit 30 is used to rinse the oxidation reaction products to obtain the first rinsed product.

[0105] The pulping unit 40 is used to pulp the first rinse product to obtain pulped material;

[0106] The aging unit 50 is used to sequentially perform a first aging treatment and a second aging treatment on the pulp to obtain a second aged material;

[0107] The second rinsing unit 60 is used to rinse the second aged material to obtain the second rinsed product;

[0108] The post-processing unit 70 includes a drying subunit and a sintering subunit. The drying subunit is used to dry the second rinsing product to obtain a dried material, and the sintering subunit is used to sinter the dried material to obtain iron phosphate.

[0109] In this application, the design of the feeding unit and reaction unit avoids the non-production time spent waiting for feeding and discharging in traditional batch production, enabling seamless connection between the reaction and processing processes, and significantly improving production efficiency and equipment utilization. Specifically, the first and second rinsing units effectively remove impurities and unreacted raw materials from the reaction products, improving product purity. The continuous operation of the pulping and aging units helps control the formation of the ferric phosphate microstructure, resulting in ferric phosphate with high tap density and an ideal iron-phosphorus ratio. The continuous design of the entire production unit facilitates integrated automated control, reduces manual intervention, lowers the labor intensity of operators, ensures the safety and stability of the production process, and is conducive to large-scale production.

[0110] Further, in some embodiments, the feeding unit 10 includes multiple storage tanks and multiple first discharge pipes disposed at the bottom of the multiple storage tanks, and the oxidation reaction raw materials are stored in the multiple storage tanks; the reaction unit 20 includes a reactor and multiple first feed pipes disposed at the bottom of the reactor, and an overflow port disposed at the top of the reactor, the first feed pipes being connected to the first discharge pipes of the feeding unit 10, and the oxidation reaction raw materials undergo oxidation reaction in the reactor to obtain oxidation reaction products; the first rinsing unit 30 includes a first belt filter and a first sprayer disposed on one side of the first belt filter, the oxidation reaction products overflow from the first overflow port at the top of the reactor in the reaction unit 20 to the feed end of the first belt filter in the first rinsing unit 30, and are rinsed by the first sprayer to obtain a first rinsed product; the slurry unit 40 includes a slurry reactor and a chute disposed on the slurry reactor, and a second discharge pipe, the chute being connected to the discharge end of the belt filter in the first rinsing unit 30, and the first rinsed product is fed into the chute. The material is fed into a pulping reactor and pulped to obtain pulped material. An aging unit 50 includes an aging reactor, a second feed pipe located at the bottom of the aging reactor, and a second overflow port located at the top of the aging reactor. The second feed pipe is connected to the second discharge pipe of the pulping unit 40. The pulped material undergoes a first aging process and a second aging process sequentially within the aging reactor to obtain second aged material. A second rinsing unit 60 includes a second belt filter and a first... The second sprayer is used to rinse the second aged material through the second overflow port at the top of the aging reactor in the aging unit 50 to the feed end of the second belt filter. The second aged material is then rinsed by the second sprayer to obtain the second rinsed product. The drying and sintering unit 70 includes a drying subunit and a sintering subunit. The drying subunit includes a drying box, and the sintering subunit includes a calcining furnace. The second rinsed product is dried in the drying box to obtain dried material. Subsequently, the dried material is sintered in the calcining furnace to obtain iron phosphate.

[0111] In this application, the design of multiple storage tanks and a first discharge pipe in the feeding unit 10 enables precise control of the flow rates of the ferrous salt solution, the phosphate-containing solution, and the oxidant solution, ensuring that these three oxidation reaction raw materials are continuously and stably supplied to the reaction unit according to a preset ratio, thereby improving reaction efficiency and raw material utilization. The reaction vessel in the reaction unit 20 is connected to the feeding unit through multiple first feed pipes at the bottom, enabling the simultaneous addition of multiple streams of oxidation reaction raw materials, which helps to fully mix and react rapidly within the reaction vessel. Simultaneously, the design of the first overflow port ensures that the oxidation reaction products can overflow to the subsequent rinsing unit, avoiding the waiting time for material transfer in traditional intermittent production and improving the continuity and efficiency of the entire production process. The first rinsing unit 30 and the second rinsing unit 60, respectively, utilize a first belt filter and a second belt filter, combined with a sprayer, to achieve continuous automatic washing of the oxidation reaction products and the second aged material.

[0112] Furthermore, in this application, the chute in the pulping unit 40 is connected to the outlet end of the belt filter in the first rinsing unit 30. The first rinsing product can enter the pulping reactor through the chute and be pulped to obtain pulped material. The second feed pipe in the aging unit 50 is connected to the second discharge pipe of the pulping unit 40. Part of the pulped material undergoes a first aging treatment in the aging reactor to prepare iron phosphate seed crystals. Subsequently, the remaining pulped material and iron phosphate crystals undergo a second aging treatment to obtain the second aged material. The portion of pulped material used for the first aging treatment accounts for 8% to 15% of the total pulped material, and the remaining pulped material used for the second aging treatment accounts for 85% to 92% of the total pulped material. In this application, effective coordination between the pulping unit 40 and the aging unit can be achieved, thereby improving the continuity and efficiency of the entire production process.

[0113] Furthermore, in this application, the iron phosphate production apparatus also includes a drying and sintering unit 70, which comprises a drying subunit and a sintering subunit, and can be used for drying and sintering the second rinse product to obtain iron phosphate. Therefore, this application, through a highly integrated and continuous process design, effectively improves the production efficiency and product quality of iron phosphate, reduces production costs and environmental impact, and thus provides strong support for the large-scale production and technological development of lithium iron phosphate cathode materials.

[0114] Furthermore, in some embodiments, the oxidizing reaction raw materials are fed into the reactor of the continuous reaction unit at a flow rate of 1 / 20 to 1 / 5 of the reactor volume in the continuous reaction unit per minute; the slurry material is added to the aging reactor of the aging unit at a flow rate of 1 / 150 to 1 / 90 of the aging reactor volume in the aging unit per minute.

[0115] In this application, by setting the flow rates of the oxidation reaction raw materials and the slurry to a specific ratio, it is possible to achieve stable control of the reaction process, optimize particle size distribution and microstructure, improve production efficiency and equipment utilization, reduce energy consumption and costs, and promote continuous optimization and automated management of process parameters.

[0116] Fourthly, this application provides a lithium iron phosphate cathode material, which is prepared from iron phosphate as described in the above embodiments or iron phosphate prepared by the methods described in the above embodiments. Therefore, it has good electrochemical performance.

[0117] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0118] I. Preparation Method

[0119] Example 1

[0120] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0121] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0122] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solutions will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 10 of the reactor volume.

[0123] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0124] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0125] S5. 10% of the total slurry material is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95℃. After the slurry changes from yellow to pink, it is kept at the temperature for 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e. the first aging material mentioned above) are obtained.

[0126] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 120 of the reactor volume per minute to obtain the second aging material.

[0127] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0128] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0129] Example 2

[0130] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0131] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.05 and a phosphorus molar concentration of 2.5 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.75 mol / L.

[0132] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is full, the solutions will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1.05:0.7, and the total amount of solution flowing into the reactor per minute is i / 15 of the reactor volume.

[0133] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0134] S4. Add a 0.1 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0135] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 90°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0136] S6. Maintain the system temperature at 90℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 90 of the reactor volume per minute to obtain the second aging material.

[0137] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0138] S8. The second rinse product is transferred to a drying oven and dried at 95°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 1.5 hours to obtain iron phosphate.

[0139] Example 3

[0140] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0141] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0142] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solution will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 20 of the reactor volume.

[0143] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0144] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0145] S5. 10% of the total slurry material is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95℃. After the slurry changes from yellow to pink, it is kept at the temperature for 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e. the first aging material mentioned above) are obtained.

[0146] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 150 of the reactor volume per minute to obtain the second aging material.

[0147] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0148] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0149] Example 4

[0150] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0151] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0152] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is full, the solution will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 5 of the reactor volume.

[0153] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0154] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0155] S5. 10% of the total slurry material is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95℃. After the slurry changes from yellow to pink, it is kept at the temperature for 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e. the first aging material mentioned above) are obtained.

[0156] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 100 of the reactor volume per minute to obtain the aging reaction product.

[0157] S7. The aging reaction product overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aging material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0158] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0159] Example 5

[0160] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0161] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0162] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solution will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 20 of the reactor volume.

[0163] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0164] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0165] S5. 10% of the total slurry material is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95℃. After the slurry changes from yellow to pink, it is kept at the temperature for 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e. the first aging material mentioned above) are obtained.

[0166] S6. Maintain the system temperature at 95°C, and add the remaining slurry to the aging reactor at a flow rate of 1 / 160 of the reactor volume per minute to obtain the second aging material.

[0167] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0168] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0169] Example 6

[0170] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0171] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.05 and a phosphorus molar concentration of 2.5 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.75 mol / L.

[0172] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solutions will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1.05:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 15 of the reactor volume.

[0173] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0174] S4. Add a 0.1 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0175] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 90°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0176] S6. Maintain the system temperature at 90℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 80 of the reactor volume per minute to obtain the second aging material.

[0177] S7. The aging reaction product overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aging material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0178] S8, the second rinse product is transported to a drying oven and dried at 95°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0179] Example 7

[0180] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0181] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0182] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is full, the solution will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 25 of the reactor volume.

[0183] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0184] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0185] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0186] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 150 of the reactor volume per minute to obtain the second aging material.

[0187] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0188] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0189] Example 8

[0190] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0191] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0192] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is full, the solution will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 3 of the reactor volume.

[0193] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0194] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0195] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0196] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 100 of the reactor volume per minute to obtain the second aging material.

[0197] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0198] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0199] Example 9

[0200] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0201] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0202] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solutions will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 10 of the reactor volume.

[0203] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0204] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0205] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0206] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 120 of the reactor volume per minute to obtain the second aging material.

[0207] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0208] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 540°C for 2 hours to obtain iron phosphate.

[0209] Example 10

[0210] One embodiment of the present invention provides a method for preparing ferric phosphate as follows:

[0211] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 1.5 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0212] S2. Start the stirring in the reactor and introduce the ferrous sulfate solution, phosphate solution, and oxidant solution into the reactor unit from the bottom in three streams. After the reactor is filled, the solutions will overflow naturally from the first overflow port at the top of the reactor into the first belt filter of the first rinsing unit. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7, and the total amount of solution flowing into the reactor per minute is 1 / 10 of the reactor volume.

[0213] S3. The material on the first belt filter is sprayed and rinsed with water using the first sprayer. After the conductivity of the rinsing water is <5ms / cm, the first rinsed product is transported from the discharge end of the first belt filter to the chute on the pulping reactor.

[0214] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor. Add the first rinsing product from the chute on the pulping reactor to the pulping reactor. After pulping for 30 minutes, the pulped material is obtained. Control the solid content of the pulped material to be 15%.

[0215] S5. A portion of the slurry, accounting for 10% of the total slurry, is transported to the aging reactor through the second feed pipe in the slurry unit. The material is added to the second overflow port, and stirring and heating are started. The heating temperature is 95°C. After the slurry changes from yellow to pink, it is kept at the temperature for another 10 minutes. After a total of 15 minutes of holding, iron phosphate seed crystals (i.e., the aforementioned first aging material) are obtained.

[0216] S6. Maintain the system temperature at 95℃, and add the remaining slurry to the aging reactor at a flow rate of 1 / 120 of the reactor volume per minute to obtain the second aging material.

[0217] S7. The second aged material overflows naturally into the second belt filter through the second overflow port of the aging reactor. The second aged material is then sprayed and rinsed by the second sprayer using water. After rinsing, the conductivity of the rinsing water is <500μs / cm, and the second rinsed product is obtained.

[0218] S8. The second rinse product is transferred to a drying oven and dried at 98°C to obtain a dried product. Subsequently, the dried product is sintered in a calcining furnace at 600°C for 2 hours to obtain iron phosphate.

[0219] Comparative Example 1

[0220] A type of iron phosphate, the preparation method of which is as follows:

[0221] S1. Prepare a ferrous sulfate solution with a ferrous ion molar concentration of 1 mol / L; prepare a phosphate solution with a pH of 7.0 and a phosphorus molar concentration of 2 mol / L by mixing ammonium dihydrogen phosphate, phosphoric acid, ammonia, and water; prepare an oxidizing agent solution with a hydrogen peroxide and pure water concentration of 0.8 mol / L.

[0222] S2. Start the stirring in the reactor. First, introduce the ferrous sulfate solution from the bottom of the reactor. Then, introduce the phosphate solution and the oxidant solution in two separate streams from the bottom of the reactor. The ferrous sulfate solution, phosphate solution, and oxidant solution are introduced into the reactor in a molar ratio of ferrous ions, phosphate ions, and oxidant of 1:1:0.7 to obtain the oxidation reaction product.

[0223] S3. Use a plate and frame filter press to rinse the oxidation reaction products. Rinse with water until the conductivity of the rinsing water is <5 mS / cm to obtain the filter cake.

[0224] S4. Add a 0.2 mol / L phosphoric acid solution to the pulping reactor, add the filter cake to the pulping reactor, and pulp for 30 minutes to obtain the pulped material. Control the solid content of the pulped material to be 15%.

[0225] S5. The slurry is transported to the aging reactor and fed to the second overflow port. Stirring and heating are started. The heating temperature is 95℃. After the slurry turns from yellow to pink, continue to keep it warm for 90 minutes. After a total of 120 minutes of keeping warm, the aging reaction product is obtained.

[0226] S6. Filter the aged product using a plate and frame filter press, and rinse with water until the conductivity of the rinse water is <500μs / cm to obtain the rinsed product.

[0227] S7. The rinsed product is transferred to a drying oven and dried at 98°C to obtain a dried product. The dried product is then sintered in a calcining furnace at 600°C to obtain ferric phosphate.

[0228] II. Performance Testing

[0229] (1) Average side length of primary particles: The average side length is calculated by statistically analyzing the side length of primary particles using SEM.

[0230] (2) Tap density: The test was conducted in accordance with GB / T 5162-2006. The test method is as follows: The powder was loaded into the sample tube and the sample tube was vibrated up and down. When the gap between the particles approached the limit and the volume of the powder no longer decreased, the volume and weight of the powder after vibration were entered into the computer and the tap density of the powder was automatically calculated. During the vibration, the amplitude was 3.0+0.1mm, the vibration frequency was 250±15 times / min, and the number of vibrations was 5000 times.

[0231] (3) Iron-to-phosphorus ratio: Refer to the national standard HG / T 4701-2021 and calculate according to the following formula: M=(w1 / w2)×0.5545, where w1 is the mass content of Fe and w2 is the mass content of P.

[0232] (4) Impurity element content (mass content: ppm): The impurity element content was determined by EDS energy spectrum.

[0233] (5) Morphology and structure: The morphology of iron phosphate was observed by scanning electron microscopy and the structure of iron phosphate was tested by XRD diffraction.

[0234] (6) Yield: The molar amount of iron added to the reaction vessel within 1 hour is taken as I. Fe R is defined as the molar amount of iron in the rinsing water within 1 hour. Fe Yield = (1-I) Fe / R Fe )×100%.

[0235] Table 1

[0236]

[0237] Table 2

[0238]

[0239] The test results above show that the iron phosphate obtained in Examples 1 to 10 of this application all have high tap density, exceeding 1.1 g / cm³. 3 Secondly, the impurity content is low, all below 180 ppm; in addition, the iron-to-phosphorus ratio is above 0.99, exhibiting good comprehensive performance and suitable for application in the preparation of high-performance lithium iron phosphate cathode materials.

[0240] Furthermore, comparing the test results of Examples 1 to 10, it can be found that when the crystal structure of iron phosphate is orthorhombic, its impurity content is relatively low. In addition, when the average side length of the primary particles of iron phosphate is 320 nm to 450 nm, the impurity content of iron phosphate can be further reduced, which is beneficial to improving the electrochemical performance of the lithium iron phosphate cathode material prepared by this iron phosphate.

[0241] In addition, the yield of ferric phosphate prepared by the method described in this application can reach more than 99%, which has good preparation efficiency. Furthermore, the yield of ferric phosphate is even higher when the oxidizing reaction raw material is added to the reactor of the continuous reaction unit at a flow rate of 1 / 20 to 1 / 5 of the reactor volume in the continuous reaction unit per minute, and the slurry is added to the aging reactor of the aging unit at a flow rate of 1 / 150 to 1 / 90 of the aging reactor volume in the aging unit per minute.

[0242] Figure 2 This is the XRD pattern of the second aged material in Example 1. Figure 3 The XRD pattern of ferric phosphate in Example 1; Figure 4 The image shows the XRD pattern of the aging reaction product in Comparative Example 1. Figure 5The XRD pattern of ferric phosphate in Comparative Example 1; for comparison Figures 2-3 and Figures 4-5 It can be seen that there are certain differences in the crystal structure of the second aged material in Example 1 and the aged reaction product in Comparative Example 1. Furthermore, the crystallinity of the second aged material in Example 1 is high, while the crystallinity of the aged reaction product in Comparative Example 1 is low. Although the structure of the final product iron phosphate is the same, the aged reaction product will affect the purity and tap density of the final product iron phosphate.

[0243] Figure 6 The image shows the XRD pattern of iron phosphate in Example 9. Its low crystallinity and numerous impurity peaks result in a low tap density of iron phosphate, which has a limited effect on improving the tap density of lithium iron phosphate cathode material.

[0244] Figures 7-8 The images shown are SEM images of ferric phosphate from Examples 1 and 2. Figure 9 The image shows the SEM image of iron phosphate in Comparative Example 1. As can be seen from the image, the iron phosphate in Examples 1 and 2 has a spherical secondary particle structure composed of primary particles, and these primary particles have an octahedral structure. In contrast, the iron phosphate in Comparative Example 1 has a loose and irregular structure. This morphological characterization indicates that the iron phosphate in Examples 1 and 2 has a more compact structure, which helps to improve the overall performance of the lithium iron phosphate cathode material prepared from this iron phosphate.

[0245] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. 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 this application, are also included in the scope of this application.

Claims

1. A type of iron phosphate, characterized in that, The iron phosphate comprises spherical secondary particles, which are composed of primary particles. The primary particles have an octahedral structure and an average side length of 200 nm to 800 nm.

2. The iron phosphate according to claim 1, characterized in that, The tap density of the ferric phosphate is 1.15 g / cm³. 3 ~1.6g / cm 3 .

3. The ferric phosphate according to claim 1 or 2, characterized in that, Includes at least one of the following features: (1) The particle size distribution coefficient of the iron phosphate is 0.7~1.3; (2) The crystal structure of the iron phosphate is orthorhombic; (3) The average side length of the primary particles is 320nm~450nm.

4. A method for preparing ferric phosphate according to any one of claims 1 to 3, characterized in that, Includes the following steps: The oxidation reaction product is obtained by mixing a ferrous salt solution, a phosphate-containing solution, and an oxidant solution. The oxidation reaction product is subjected to a first rinsing and pulping treatment in sequence to obtain a pulped material; A portion of the pulped material is subjected to a first aging treatment to obtain a first aged material; The first aged material and the remaining pulped material are mixed and subjected to a second aging process to obtain the second aged material; The second aged material is subjected to a second rinsing, drying and sintering in sequence to obtain the iron phosphate.

5. The method for preparing ferric phosphate according to claim 4, characterized in that, Includes at least one of the following features: (1) The concentration of ferrous ions in the ferrous salt solution is 0.5 mol / L to 1.5 mol / L; (2) The concentration of phosphate ions in the phosphate-containing solution is 1.6 mol / L to 2.5 mol / L, and the pH value of the phosphate-containing solution is 6.8 to 7.2; (3) The concentration of the oxidant in the oxidant solution is 0.5 mol / L to 1 mol / L; (4) The pulping process is carried out using an acid solution to obtain the pulped material; (5) The temperature of the first aging is 85℃~100℃. After the pulp changes color, it is aged for 5min~15min to obtain the first aged material. (6) The temperature for the second aging process is 85℃~100℃ and the time is 80min~150min; (7) The drying temperature is 90℃~110℃, the sintering temperature is 550℃~650℃, and the sintering time is 1h~3h.

6. The method for preparing ferric phosphate according to claim 5, characterized in that, Includes at least one of the following features: (1) The molar ratio of ferrous ions in the ferrous salt solution, phosphate ions in the phosphate-containing solution, and oxidant in the oxidant solution is 1:(0.95~1.05):(0.6~0.8). (2) The first rinsing is carried out by rinsing with water until the conductivity of the rinse water after rinsing is <5ms / cm; (3) The acid solution is a phosphoric acid solution with a phosphoric acid concentration of 0.1 mol / L to 0.5 mol / L; (4) The pulping treatment time is 30 min to 60 min; (5) The solid content of the slurry is 10wt%~20wt%; (6) The ferrous salt in the ferrous salt solution is at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; (7) The phosphate in the phosphate-containing solution is derived from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and phosphoric acid. (8) The oxidant in the oxidant solution is at least one of hydrogen peroxide, ammonium persulfate, and sodium persulfate; (9) The second rinsing is carried out by rinsing with water until the conductivity of the rinse water after rinsing is <500μs / cm.

7. A production apparatus for ferric phosphate, characterized in that, Includes the following units: A feeding unit is used to provide raw materials for the oxidation reaction, which include ferrous salt solution, phosphate-containing solution and oxidant solution; The reaction unit is used to carry out oxidation reactions and obtain oxidation reaction products; The first rinsing unit is used to rinse the oxidation reaction product to obtain the first rinsed product. The pulping unit is used to pulp the first rinsed product to obtain a pulped material; An aging unit is used to sequentially perform a first aging treatment and a second aging treatment on the slurry to obtain a second aged material; The second rinsing unit is used to rinse the second aged material to obtain the second rinsed product; The post-processing unit includes a drying subunit and a sintering subunit, wherein the drying subunit is used to dry the second rinsing product to obtain a dried material, and the sintering subunit is used to sinter the dried material to obtain iron phosphate; Wherein, the iron phosphate is the iron phosphate described in any one of claims 1 to 3, or the iron phosphate prepared by the method for preparing iron phosphate according to any one of claims 4 to 6; The feeding unit includes multiple storage tanks and multiple first discharge pipes disposed at the bottom of the multiple storage tanks, and the oxidation reaction raw materials are stored in the multiple storage tanks; The reaction unit includes a reaction vessel and a plurality of first feed pipes disposed at the bottom of the reaction vessel, and a first overflow port disposed at the top of the reaction vessel. The first feed pipes are connected to the first discharge pipe of the feeding unit. The oxidation reaction raw materials undergo an oxidation reaction in the reaction vessel to obtain the oxidation reaction product. The first rinsing unit includes a first belt filter and a first sprayer disposed on one side of the first belt filter. The oxidation reaction product overflows from the first overflow port at the top of the reactor in the reaction unit to the feed end of the first belt filter in the first rinsing unit, and the oxidation reaction product is rinsed by the first sprayer to obtain the first rinsed product. The pulping unit includes a pulping reactor and a chute disposed on the pulping reactor, as well as a second discharge pipe. The chute is connected to the discharge end of the belt filter in the first rinsing unit. The first rinsing product enters the pulping reactor through the chute and is pulped in the pulping reactor to obtain the pulped material. An aging unit includes an aging reactor and a second feed pipe disposed at the bottom of the aging reactor, and a second overflow port disposed at the top of the aging reactor. The second feed pipe is connected to the second discharge pipe of the slurry unit. The slurry undergoes the first aging treatment and the second aging treatment in the aging reactor in sequence to obtain the second aged material. The second rinsing unit includes a second belt filter and a second sprayer disposed on one side of the second belt filter. The second aged material overflows through the second overflow port at the top of the aging reactor in the aging unit to the feed end of the second belt filter. The second aged material is rinsed by the second sprayer to obtain the second rinsed product. The drying and sintering unit includes a drying subunit and a sintering subunit. The drying subunit includes a drying chamber, and the sintering subunit includes a calcining furnace. The second rinsed product is dried in the drying chamber to obtain the dried material. Subsequently, the dried material is sintered in the calcining furnace to obtain the iron phosphate.

8. The ferric phosphate production apparatus according to claim 7, characterized in that, Includes at least one of the following features: (1) The oxidation reaction raw material flows into the reactor in the reaction unit at a flow rate of 1 / 20 to 1 / 5 times the volume of the reactor in the reaction unit per minute; (2) The slurry is added to the aging reactor of the aging unit at a flow rate of 1 / 150 to 1 / 90 times the volume of the aging reactor in the aging unit per minute.

9. A lithium iron phosphate cathode material, characterized in that, It is prepared from ferric phosphate as described in any one of claims 1 to 3, or ferric phosphate prepared by any one of claims 4 to 6.

Images