Iron phosphate material and preparation method therefor, positive electrode material, positive electrode sheet, and secondary battery

Abstract

The present application belongs to the technical field of nanomaterials, and provides an iron phosphate material and a preparation method therefor, a positive electrode material, a positive electrode sheet, and a secondary battery, wherein the iron phosphate material comprises iron phosphate particles, the iron phosphate particles have a ring-like structure, and the D50 particle size of the iron phosphate particles is less than 1 μm. When the iron phosphate material of the present application is used as a precursor to prepare lithium iron phosphate, the energy consumption of a sanding process can be effectively reduced, and the process efficiency is improved.

Description

Iron phosphate materials and their preparation methods, cathode materials, cathode plates and secondary batteries Technical Field

[0001] This invention relates to the field of inorganic materials technology, specifically to an iron phosphate material and its preparation method, a positive electrode material, a positive electrode sheet, and a secondary battery. Background Technology

[0002] Ferric phosphate is a creamy white or grayish-white powder. It can form various hydrates, including ferric phosphate dihydrate, ferric phosphate tetrahydrate, and ferric phosphate octahydrate. Under normal conditions, it forms ferric phosphate dihydrate (relative molecular weight: 186.82), and begins to lose its water of crystallization when heated to around 160℃. Ferric phosphate possesses a rich framework structure, unique ion exchange properties, and electrochemical properties, making it an excellent material for preparing lithium iron phosphate, a cathode material for lithium-ion batteries widely used in new energy fields (such as new energy vehicles).

[0003] In existing technologies, the conductivity of lithium iron phosphate (LFP) is improved by nano-sizing iron phosphate, a key raw material in the synthesis of LFP or LMP. Currently, the particle size of LFP D50 prepared using conventional processes is typically between 2 μm and 30 μm. Therefore, to prepare LFP or LMP that achieves the desired conductivity, a large amount of energy is required to grind the iron phosphate particles to the nanoscale, resulting in significant energy consumption. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an iron phosphate material and its preparation method, a cathode material, a cathode electrode sheet and a secondary battery. The iron phosphate material provided by this application is easier to obtain nanoscale iron phosphate material, reduces the energy consumption required for nano-sizing and makes it easier to obtain iron phosphate material with smaller particle size, thereby making it easier to improve the conductivity of the prepared lithium iron phosphate material.

[0005] In a first aspect, embodiments of this application provide an iron phosphate material, which includes iron phosphate particles having a ring structure and a D50 particle size of less than 1 μm.

[0006] In the technical solution of this application embodiment, the iron phosphate material adopts small-sized iron phosphate particles with a ring structure and a D50 particle size of less than 1 μm. When preparing lithium iron phosphate as a precursor, it is beneficial to reduce the energy consumption required for nano-sizing and make it easier to obtain iron phosphate materials with smaller particle sizes, thereby making it easier to improve the conductivity of the prepared lithium iron phosphate material.

[0007] In some embodiments, the aggregation index of the particle size of the iron phosphate particles satisfies: 0.5≤(D90-D10) / D50≤2.

[0008] In this embodiment, the particle size distribution of iron phosphate particles is more concentrated, which is beneficial to improving grinding efficiency and obtaining uniformly sized nano-sized iron phosphate particles. This facilitates the uniform distribution of lithium ions in the iron phosphate particles during the subsequent lithium iron phosphate preparation process, resulting in lithium iron phosphate materials with high conductivity and excellent electrochemical performance.

[0009] In some embodiments, the ratio of the average inner diameter to the average outer diameter of the annular structure of the iron phosphate particles is (0.35 to 0.48):1.

[0010] In this embodiment, in the technical solution of this application, the ring diameter (the distance between the outer and inner diameters of the ring) affects the grinding efficiency and the morphology of the grinding particles. If the ring diameter is too large, it is not conducive to improving the grinding efficiency. If the ring diameter is too small, irregular fractures are likely to occur during the grinding process. Iron phosphate particles within the above-mentioned size range are beneficial to improving the grinding efficiency and obtaining nano-sized iron phosphate particles with regular morphology and uniform size, so that lithium ions can be uniformly distributed in the iron phosphate particles during the subsequent lithium iron phosphate preparation process.

[0011] In some embodiments, the average inner diameter of the cyclic structure of the iron phosphate particles ranges from 178 nm to 559 nm, and the average outer diameter of the cyclic structure of the iron phosphate particles ranges from 474.60 nm to 1188.90 nm.

[0012] In the above embodiments, iron phosphate particles within the above size range are beneficial for improving grinding efficiency and obtaining nanoscale iron phosphate particles with regular morphology and uniform size.

[0013] In some embodiments, the specific surface area of ​​the iron phosphate particles is 13 m². 2 / g~20m 2 / g.

[0014] In this embodiment, during the preparation of lithium iron phosphate, the larger specific surface area of ​​the iron phosphate particles facilitates the uniform distribution of lithium ions within the iron phosphate material and increases the contact area between the iron phosphate particles, promoting their bonding and thus improving the overall conductivity and cycle stability of the prepared lithium iron phosphate material. This application controls the specific surface area of ​​the iron phosphate material to be within the aforementioned range, which is beneficial for obtaining nanoscale iron phosphate particles with high specific surface area through grinding, thereby preparing lithium iron phosphate materials with high conductivity and high cycle performance.

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

[0016] Prepare an iron-phosphorus solution including ferrous ion source, chloride ion source and phosphate ion source, wherein the pH value of the iron-phosphorus solution is not greater than 1.5;

[0017] The iron-phosphorus solution is heated to above 70°C, and then an oxidant is added to the iron-phosphorus solution to obtain iron phosphate slurry.

[0018] Heat the ferric phosphate slurry to boiling. After the ferric phosphate slurry changes color, continue to maintain the boiling state for 1.5h to 4h to obtain the first slurry.

[0019] The first slurry is mixed with low-temperature dilution water to obtain the second slurry;

[0020] The second slurry was subjected to solid-liquid separation to obtain iron phosphate material.

[0021] In the technical solution of this application embodiment, the system for preparing iron phosphate material adopts a chloride ion system. The pH value of the iron-phosphorus solution is controlled to inhibit the hydrolysis of ferrous ions and reduce the aggregation of subsequently generated iron phosphate ions. The temperature of the iron-phosphorus solution is controlled and the ferrous ions are oxidized to obtain an iron phosphate slurry. Then, the iron phosphate slurry is heated to boiling. The volatility and complexing properties of hydrogen chloride are used to form an iron phosphate-hydrochloric acid complex with the iron phosphate particles in the iron phosphate slurry. Low-temperature dilution water is then added to the first slurry. Through dilution-cold activation decomposition, iron phosphate particles with a D50 particle size of less than 1 μm and a ring structure are finally prepared, thus making it easier to obtain nanoscale iron phosphate material. When this iron phosphate material is used as a precursor to prepare lithium iron phosphate, it is beneficial to reduce the energy consumption required for nano-sizing and make it easier to obtain iron phosphate material with smaller particle size, thereby making it easier to improve the conductivity of the prepared lithium iron phosphate material.

[0022] In some embodiments, the molar ratio of iron, phosphorus and chlorine in the iron-phosphorus solution is (0.8-1.2):(0.8-2):(0.5-3).

[0023] In the above embodiments, the iron, phosphorus, and chlorine elements in the reaction system affect the yield, size, and morphology of the generated iron phosphate particles. For example, a higher iron-chlorine ratio and a higher phosphorus-chlorine ratio are beneficial for iron phosphate precipitation to obtain a higher iron phosphate yield. A lower phosphorus-chlorine ratio is beneficial for the formation of iron phosphate-hydrochloric acid complexes during the high-temperature boiling stage, reducing iron phosphate agglomeration and obtaining iron phosphate materials with smaller size and better dispersibility. By controlling the iron, phosphorus, and chlorine elements to be within the above ratios, iron phosphate materials with a ring structure and a D50 particle size of less than 1 μm can be obtained with a higher yield.

[0024] In some embodiments, the molar ratio of iron, phosphorus and chlorine in the iron-phosphorus solution is 1:(1-1.2):(2-3).

[0025] In the above embodiments, controlling the iron, phosphorus and chlorine elements to be within the above range is beneficial to the full precipitation of iron to generate iron phosphate to obtain a higher yield, and the obtained iron phosphate material has a regular morphology and good particle dispersibility.

[0026] In some embodiments, the oxidant is selected from an aqueous solution of hydrogen peroxide, wherein the molar ratio of hydrogen peroxide to iron in the iron-phosphorus solution is (0.6-1):1, and the concentration of iron in the iron-phosphorus solution is 0.5 mol / L to 2.0 mol / L.

[0027] In the above embodiments, the ratio of hydrogen peroxide to iron in the iron-phosphorus solution and the concentration of iron affect the oxidation rate of ferrous ions, thereby affecting the nucleation rate and crystal growth rate of iron phosphate. Under the above conditions, it is beneficial to obtain iron phosphate slurry with smaller iron phosphate particles, which is beneficial to generate more iron phosphate-hydrochloric acid complex in the subsequent high-temperature boiling stage, and to ensure that the iron phosphate-hydrochloric acid complex is stably and uniformly dispersed in the first slurry, reducing the agglomeration of iron phosphate particles. This results in the generation of small-sized iron phosphate material with good particle dispersion in the subsequent dilution-cold activation decomposition and complexation stage.

[0028] In some embodiments, an aqueous solution of hydrogen peroxide is added to the iron-phosphorus solution by dropping for 5 to 15 minutes. After the dropping is completed, the mixture is stirred for 5 to 15 minutes to obtain an iron phosphate slurry.

[0029] In the above embodiments, the hydrogen peroxide dropping rate and stirring time affect the generation of iron phosphate nuclei and the growth of crystals. Under the above conditions, it is beneficial to rapidly generate iron phosphate nuclei and inhibit crystal growth, thereby obtaining an iron phosphate slurry with smaller iron phosphate particles. This allows for the generation of more iron phosphate-hydrochloric acid complexes in the subsequent high-temperature boiling stage, and facilitates the stable and uniform dispersion of the iron phosphate-hydrochloric acid complexes in the first slurry, reducing the agglomeration of iron phosphate particles. Consequently, in the subsequent dilution-cold activation decomposition and complexation stage, small-sized iron phosphate material with good particle dispersion is generated.

[0030] In some embodiments, the step of heating the iron-phosphorus solution to above 70°C and then adding an oxidant to the iron-phosphorus solution to obtain iron phosphate slurry includes:

[0031] Heat the iron-phosphorus solution to 70℃~80℃, and then add an aqueous solution of hydrogen peroxide to the iron-phosphorus solution.

[0032] In the above embodiments, using an aqueous solution of hydrogen peroxide and controlling the temperature of the iron-phosphorus solution to 70℃~80℃ is beneficial for the hydrogen peroxide to react fully with the iron-phosphorus solution, thereby improving the oxidation efficiency of ferrous ions. This facilitates the rapid generation of a large number of small-sized iron phosphate particles at this stage, which is beneficial for the subsequent high-temperature boiling stage to generate more iron phosphate-hydrochloric acid complexes. It also helps the iron phosphate-hydrochloric acid complexes to be stably and uniformly dispersed in the first slurry, thus preparing iron phosphate materials with small size and good particle dispersibility.

[0033] In some embodiments, the mass fraction of hydrogen peroxide in the aqueous solution of hydrogen peroxide is 20% to 30%.

[0034] In the above embodiments, hydrogen peroxide is within the above-mentioned content, which facilitates the rapid generation of ferric phosphate particles and can effectively reduce the decomposition loss of hydrogen peroxide itself during the oxidation of ferrous ions.

[0035] In some embodiments, the ferrous ion source is selected from one or more of ferrous nitrate and ferrous chloride.

[0036] In the above embodiments, the above-mentioned ferrous ion sources can all provide the necessary ferrous ions for the iron-phosphorus solution reaction system. When ferrous nitrate is used as the ferrous salt, the free nitrate ions in the system can be converted into nitric acid and volatilized and removed during the subsequent boiling process. When ferrous chloride is used as the ferrous salt, the free chloride ions in the system can be volatilized and removed in the form of hydrochloric acid during the subsequent boiling process, so as to reduce the acidity of the system and reduce impurities, and facilitate the subsequent acquisition of small-sized and high-yield iron phosphate.

[0037] In some embodiments, the ferrous ion source is selected from ferrous chloride.

[0038] In the above embodiments, ferrous chloride introduces chloride ions while providing ferrous ions, so that it can subsequently complex with ferric phosphate particles to form a ferric phosphate-hydrochloric acid complex, thereby reducing ferric phosphate agglomeration and avoiding the introduction of impurities such as nitrogen and oxygen.

[0039] In some embodiments, the chloride ion source is selected from at least one of hydrochloric acid and ferrous chloride.

[0040] In the above embodiments, both hydrochloric acid and ferrous chloride can provide the chloride ions required for the reaction and reduce the introduction of other impurity cations.

[0041] In some embodiments, the phosphate ion source is selected from at least one of H3PO4, (NH4)H2PO4, and (NH4)2HPO4.

[0042] In the above embodiments, H3PO4, (NH4)H2PO4, and (NH4)2HPO4 can provide the phosphate ions required for the reaction.

[0043] In some embodiments, the preparation steps of the iron-phosphorus solution are as follows:

[0044] A solution of iron and phosphorus is obtained by mixing ferrous ion source, chloride ion source, phosphate ion source and water and controlling the pH value to be no greater than 1.5.

[0045] In some embodiments, the desired iron-phosphorus solution can be obtained by directly mixing a ferrous ion source, a chloride ion source, a phosphate ion source, and water, which is a simple process.

[0046] In some embodiments, the ferrous ion source is ferrous chloride, the chloride ion source is selected from ferrous chloride and hydrochloric acid, and the phosphate ion source is phosphoric acid.

[0047] In the above embodiments, ferrous chloride serves as both a ferrous ion source and a chloride ion source, hydrochloric acid serves as a chloride ion source and provides acidity for the reaction, and phosphate serves as a phosphorus source and also provides acidity for the reaction. The pH value of the system and the elemental ratio of ferrous ions, phosphate ions, and chloride ions can be controlled by the proportions of the above raw materials. No additional acid or alkali (such as sulfuric acid, nitric acid, sodium hydroxide, ammonia, etc.) needs to be added. This process prepares a cyclic structured, small-sized iron phosphate material while minimizing impurity ions (such as sulfate, nitrate, sodium ions, NH4+). + By introducing materials such as lithium iron phosphate (Fe2+, etc.), high-purity Fe2+ materials can be prepared, thereby improving the cycle life and capacity retention of lithium iron phosphate prepared from these materials when applied to batteries.

[0048] In some embodiments, the preparation steps of the iron-phosphorus solution are as follows:

[0049] A dilute hydrochloric acid aqueous solution is heated to 50℃~70℃, and then elemental iron is added to react and obtain ferrous chloride solution. The concentration of the dilute hydrochloric acid aqueous solution is 1.0mol / L~4.0mol / L.

[0050] Add phosphoric acid and water to a ferrous chloride solution, mix, and control the pH value to be no greater than 1.5 to obtain an iron-phosphorus solution.

[0051] In the above embodiments, using elemental iron, hydrochloric acid aqueous solution, and phosphoric acid as raw materials to prepare iron-phosphorus solution can minimize the introduction of impurity ions and prepare high-purity iron phosphate material.

[0052] In some embodiments, the elemental iron material is selected from one or more of iron sheets, iron powder, and iron blocks.

[0053] In some embodiments, the pH value of the iron-phosphorus solution is 0.2 to 1.5.

[0054] In the above embodiments, the pH value of the iron-phosphorus solution affects the formation rate and yield of iron phosphate. A higher pH value is more likely to cause a large number of iron phosphate particles to agglomerate during the oxidation stage, while a lower pH value is not conducive to the precipitation of iron phosphate. Within the above pH value range, it is more conducive to obtaining iron phosphate materials with high yield and small size.

[0055] In some embodiments, the temperature difference between the second slurry and the first slurry is not less than 60°C.

[0056] In the above embodiments, the higher temperature difference is more conducive to the decomplexation of ferric phosphate and hydrochloric acid and cold quenching and refining, thereby generating smaller ferric phosphate materials.

[0057] In some embodiments, the temperature difference between the second slurry and the first slurry is further 70°C to 90°C.

[0058] In the above embodiments, controlling the temperature difference between the second slurry and the first slurry within this temperature range is more conducive to obtaining smaller-sized iron phosphate materials and achieving a higher yield.

[0059] In some embodiments, the mass ratio of the first slurry to low-temperature dilution water is 1:(10-20).

[0060] In the above embodiments, low-temperature dilution water is used for rapid cooling and dilution of the system, which is conducive to the decomposition of the iron phosphate-hydrochloric acid complex to generate iron phosphate material. The mass ratio of the first slurry to the low-temperature dilution water is within the above range, which is conducive to the rapid and complete decomposition of the iron phosphate-hydrochloric acid complex, thereby obtaining small-sized iron phosphate material with high purity and high yield.

[0061] In some embodiments, the first slurry is mixed with low-temperature dilution water and stirred until the color changes to obtain the second slurry.

[0062] In the above embodiments, during the high-temperature boiling process, an iron phosphate-hydrochloric acid complex was generated. After being mixed with low-temperature dilution water, the iron phosphate was decomplexed and precipitated, causing a change in the color of the slurry.

[0063] In some embodiments, the second slurry is subjected to solid-liquid separation, and the resulting solid is washed and dried at 90°C to 120°C to obtain iron phosphate material.

[0064] In the above embodiments, under the above conditions, moisture can be quickly removed to obtain iron phosphate material.

[0065] Thirdly, embodiments of this application provide a cathode material, including at least one of lithium iron phosphate material and lithium manganese iron phosphate material. The lithium iron phosphate material is prepared from the above-mentioned iron phosphate material or from iron phosphate material prepared by the above-mentioned method for preparing iron phosphate material. The lithium manganese iron phosphate material is prepared from the above-mentioned iron phosphate material or from iron phosphate material prepared by the above-mentioned method for preparing iron phosphate material.

[0066] Fourthly, embodiments of this application provide a positive electrode sheet, which includes the aforementioned positive electrode material.

[0067] In this embodiment, the positive electrode sheet contains the aforementioned positive electrode material, thus having the advantages of reducing the energy consumption and cost of positive electrode sheet preparation and improving the conductivity of the positive electrode sheet.

[0068] Fifthly, embodiments of this application provide a secondary battery, wherein the positive electrode used is the aforementioned positive electrode.

[0069] In this embodiment, the secondary battery includes the aforementioned positive electrode sheet, thus having the advantages of reducing the energy consumption and cost of secondary battery preparation and improving the electrochemical performance of the secondary battery.

[0070] Sixthly, embodiments of this application provide an electrical device including the aforementioned secondary battery.

[0071] In this embodiment, the electrical device includes the aforementioned secondary battery, thus having the advantages of reducing the energy consumption and cost of manufacturing the electrical device and improving its electrochemical performance.

[0072] 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, specific embodiments of this application are given below. Attached Figure Description

[0073] 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.

[0074] Figure 1 shows a scanning electron microscope (SEM) test result of the iron phosphate material prepared in Example 1;

[0075] Figure 2 shows a SEM test result of the iron phosphate material prepared in Example 1;

[0076] Figure 3 is a flowchart of the preparation method of iron phosphate material according to an embodiment of this application;

[0077] Figure 4 shows the X-ray diffraction (XRD) test results of the iron phosphate material prepared in Example 1, where the horizontal axis is the diffraction angle Two-Theta (°) and the vertical axis is the diffraction intensity Intensity (Counts).

[0078] Figure 5 shows the SEM test results of the iron phosphate material prepared in Comparative Example 6;

[0079] Figure 6 shows the SEM test results of the iron phosphate material prepared in Comparative Example 6;

[0080] Figure 7 shows the XRD test results of the iron phosphate material prepared in Comparative Example 6, where the horizontal axis is the diffraction angle Two-Theta (°) and the vertical axis is the diffraction intensity Intensity (Counts). Detailed Implementation

[0081] 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.

[0082] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0083] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0084] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0085] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0086] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0087] In the embodiments of this application, unless otherwise specified, the water can be at least one of distilled water, deionized water, pure water, and ultrapure water; the solvent used in the "solution" or "aqueous solution" is selected from at least one of distilled water, deionized water, pure water, and ultrapure water.

[0088] For those skilled in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to the specific circumstances. To address the technical problem of high energy consumption in the preparation of lithium iron phosphate, which requires a large amount of energy to grind iron phosphate particles to the nanoscale, this application provides an iron phosphate material and its preparation method, a cathode material, a cathode electrode, a secondary battery, and an electrical device. The iron phosphate material uses small-sized iron phosphate particles with a cyclic structure and a D50 particle size of less than 1 μm. When used as a precursor in the preparation of lithium iron phosphate, it is easier to obtain nanoscale iron phosphate materials, reducing the energy consumption required for nano-sizing and making it easier to obtain iron phosphate materials with smaller particle sizes. This makes it easier to improve the conductivity of the prepared lithium iron phosphate material, thereby reducing the energy consumption and cost in the preparation process of the cathode electrode, secondary battery, and electrical device, while also improving electrochemical performance.

[0089] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0090] Referring to Figures 1 and 2, in a first aspect, embodiments of this application provide an iron phosphate material comprising iron phosphate particles having a ring structure and a D50 particle size of less than 1 μm. Specifically, the D50 particle size can be 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, or 900 nm, or other values ​​within the above range, preferably 750 nm to 860 nm. Using the aforementioned small-sized iron phosphate particles with a ring structure and a D50 particle size of less than 1 μm as a precursor for preparing lithium iron phosphate helps reduce the energy consumption required for nano-sizing and makes it easier to obtain iron phosphate materials with smaller particle sizes, thereby improving the conductivity of the prepared lithium iron phosphate material.

[0091] Furthermore, in some embodiments, the aggregation index of the particle size of the iron phosphate particles satisfies: 0.5≤(D90-D10) / D50≤2, preferably 1.25≤(D90-D10) / D50≤1.81.

[0092] In the technical solution of this application embodiment, the particle size distribution of iron phosphate particles is more concentrated, which is beneficial to improve grinding efficiency and obtain uniformly sized nano-sized iron phosphate particles by sand milling. This facilitates the uniform distribution of lithium ions in the iron phosphate particles during the subsequent lithium iron phosphate preparation process, thereby obtaining lithium iron phosphate materials with high conductivity and excellent electrochemical performance.

[0093] Furthermore, in some embodiments, the ratio of the average inner diameter to the average outer diameter of the annular structure of the iron phosphate particles is (0.35 to 0.48):1, preferably (0.36 to 0.43):1.

[0094] In the technical solution of this application embodiment, the ring diameter (the distance between the outer diameter and the inner diameter of the ring) affects the grinding efficiency and the morphology of the grinding particles. If the ring diameter is too large, it is not conducive to improving the grinding efficiency. If the ring diameter is too small, irregular fractures are likely to occur during the grinding process. Iron phosphate particles within the above-mentioned size range are beneficial to improving the grinding efficiency and obtaining nano-sized iron phosphate particles with regular morphology and uniform size, so that lithium ions can be uniformly distributed in the iron phosphate particles during the subsequent lithium iron phosphate preparation process.

[0095] It should be noted that, in the technical solution of this application embodiment, the inner diameter of the annular structure of the iron phosphate particle refers to the distance between the two furthest points at the intersection of the straight line passing through the center of the annular structure of the iron phosphate particle in the radial direction and the iron phosphate particle, and the outer diameter of the annular structure of the iron phosphate particle refers to the distance between the two closest points at the intersection of the straight line passing through the center of the annular structure of the iron phosphate particle in the radial direction and the iron phosphate particle.

[0096] Preferably, in some embodiments, the average inner diameter of the cyclic structure of the iron phosphate particles ranges from 178 nm to 559 nm, and the average outer diameter of the cyclic structure of the iron phosphate particles ranges from 474.60 nm to 1188.90 nm; more preferably, the average inner diameter of the cyclic structure of the iron phosphate particles ranges from 240 nm to 371 nm, and the average outer diameter of the cyclic structure of the iron phosphate particles ranges from 614 nm to 901 nm.

[0097] In the technical solution of this application embodiment, iron phosphate particles within the above-mentioned size range are beneficial to improving grinding efficiency and obtaining nanoscale iron phosphate particles with regular morphology and uniform size.

[0098] Furthermore, in some embodiments, the specific surface area of ​​the iron phosphate particles is 13 m². 2 / g~20m 2 / g, preferably 13m 2 / g~17m 2 / g.

[0099] In the technical solution of this application embodiment, during the preparation of lithium iron phosphate, the larger specific surface area of ​​the iron phosphate particles is beneficial for the uniform mixing of various raw materials during the preparation process, and for the uniform distribution of lithium ions in the iron phosphate material. It also helps to improve the lithium ion insertion / extraction efficiency, thereby enhancing the rate performance and specific capacity of lithium iron phosphate. This application controls the specific surface area of ​​the iron phosphate material to be within the aforementioned range, which is beneficial for grinding to obtain nanoscale iron phosphate particles with high specific surface area, thereby preparing lithium iron phosphate materials with high rate performance and high specific capacity.

[0100] As shown in Figure 3, in a second aspect, embodiments of this application provide a method for preparing an iron phosphate material, comprising the following steps:

[0101] Prepare an iron-phosphorus solution including ferrous ion source, chloride ion source and phosphate ion source, wherein the pH value of the iron-phosphorus solution is not greater than 1.5;

[0102] The iron-phosphorus solution is heated to above 70°C, and then an oxidant is added to the iron-phosphorus solution to obtain iron phosphate slurry.

[0103] Heat the ferric phosphate slurry to boiling. After the ferric phosphate slurry changes color, continue to maintain the boiling state for 1.5h to 4h to obtain the first slurry.

[0104] The first slurry is mixed with low-temperature dilution water to obtain the second slurry;

[0105] The second slurry was subjected to solid-liquid separation to obtain iron phosphate material.

[0106] In the technical solution of this application embodiment, the system for preparing iron phosphate material adopts a chloride ion system. The pH value of the iron-phosphorus solution is controlled to inhibit the hydrolysis of ferrous ions and reduce the aggregation of subsequently generated iron phosphate ions. The temperature of the iron-phosphorus solution is controlled and the ferrous ions are oxidized to obtain an iron phosphate slurry. Then, the iron phosphate slurry is heated to boiling. The volatility and complexing properties of hydrogen chloride are used to form an iron phosphate-hydrochloric acid complex with the iron phosphate particles in the iron phosphate slurry. Low-temperature dilution water is added to the first slurry. Through dilution-cold activation decomposition, iron phosphate particles with a D50 particle size of less than 1 μm and a cyclic structure are finally prepared, thus making it easier to obtain nanoscale iron phosphate material. When this iron phosphate material is used as a precursor to prepare lithium iron phosphate, it is beneficial to reduce the energy consumption required for nano-sizing and make it easier to obtain iron phosphate material with smaller particle size, thereby making it easier to improve the conductivity of the prepared lithium iron phosphate material. By forming a ferric phosphate-hydrochloric acid complex under high-temperature conditions, ferric phosphate is protected in the form of a complex to prevent particle agglomeration. Then, a dilution-cold activation decomplexation method is used to decomplex the slurry containing ferric phosphate-hydrochloric acid under low-temperature conditions. Simultaneously, the principle of cold quenching is used to further refine the ferric phosphate particles, generating smaller-sized ferric phosphate particles, making it easier to obtain nanoscale ferric phosphate materials. This reduces the energy consumption required for nano-sizing and facilitates obtaining smaller particle sizes of ferric phosphate materials, improving the conductivity of lithium iron phosphate materials prepared from this ferric phosphate material. Furthermore, the high-temperature boiling method is beneficial for the full complexation of ferric phosphate particles to form the ferric phosphate-hydrochloric acid complex, and the free hydrochloric acid in the reaction system is evaporated to reduce acidity, thus facilitating the subsequent acquisition of small-sized and high-yield ferric phosphate, while also enabling the recovery of free hydrochloric acid. The preparation method of this application can prepare the ferric phosphate material as described above, with high yield and the ability to recover free hydrochloric acid.

[0107] Furthermore, in some embodiments, the molar ratio of iron, phosphorus, and chlorine in the iron-phosphorus solution is (0.8–1.2):(0.8–2):(0.5–3).

[0108] In the technical solutions of this application embodiment, the iron, phosphorus and chlorine elements in the reaction system affect the yield, size and morphology of the generated iron phosphate. For example, a higher iron-chlorine ratio and a higher phosphorus-chlorine ratio are conducive to the precipitation of iron phosphate to obtain a higher yield of iron phosphate. A lower phosphorus-chlorine ratio is conducive to the formation of iron phosphate-hydrochloric acid complex during the high-temperature boiling stage, reducing iron phosphate agglomeration and obtaining iron phosphate material with smaller size and better dispersibility. By controlling the iron, phosphorus and chlorine elements to be within the above ratio range, iron phosphate material with a ring structure and a D50 particle size of less than 1 μm can be obtained with a higher yield.

[0109] In some embodiments, the molar ratio of iron, phosphorus and chlorine in the iron-phosphorus solution is 1:(1-1.2):(2-3).

[0110] In the technical solution of this application embodiment, controlling the iron, phosphorus and chlorine elements to be within the above range is beneficial to the full precipitation of iron to generate iron phosphate to obtain a higher yield, and the obtained iron phosphate material has a regular morphology and good particle dispersibility.

[0111] In some embodiments, the oxidant is selected from an aqueous solution of hydrogen peroxide, wherein the molar ratio of hydrogen peroxide to iron in the iron-phosphorus solution is (0.6-1):1, and the concentration of iron in the iron-phosphorus solution is 0.5 mol / L to 2.0 mol / L.

[0112] In the technical solution of this application embodiment, the ratio of hydrogen peroxide to iron in the iron-phosphorus solution and the concentration of iron affect the oxidation rate of ferrous ions, thereby affecting the nucleation rate and crystal growth rate of iron phosphate. Under the above conditions, it is beneficial to obtain iron phosphate slurry with smaller iron phosphate particles, which is beneficial to generate more iron phosphate-hydrochloric acid complex in the subsequent high-temperature boiling stage, and to ensure that the iron phosphate-hydrochloric acid complex is stably and uniformly dispersed in the first slurry, reducing the agglomeration of iron phosphate particles, thereby generating small-sized iron phosphate material with good particle dispersion in the subsequent dilution-cold activation decomposition and complexation stage.

[0113] In some embodiments, an aqueous solution of hydrogen peroxide is added to the iron-phosphorus solution by dropping for 5 to 15 minutes. After the dropping is completed, the mixture is stirred for 5 to 15 minutes to obtain an iron phosphate slurry.

[0114] In the technical solution of this application embodiment, the hydrogen peroxide dropping rate and stirring time affect the generation of iron phosphate crystal nuclei and the growth of crystals. Under the above conditions, it is beneficial to rapidly generate iron phosphate crystal nuclei and inhibit crystal growth, thereby generating iron phosphate slurry with smaller iron phosphate particles. This allows for the generation of more iron phosphate-hydrochloric acid complexes in the subsequent high-temperature boiling stage, and facilitates the stable and uniform dispersion of iron phosphate-hydrochloric acid complexes in the first slurry, reducing the agglomeration of iron phosphate particles. As a result, small-sized iron phosphate material with good particle dispersion is generated in the subsequent dilution-cold activation decomposition and complexation stage.

[0115] In some embodiments, the iron-phosphorus solution is heated to 70°C to 80°C, and then an aqueous solution of hydrogen peroxide is added to the iron-phosphorus solution.

[0116] In the technical solution of this application embodiment, using an aqueous solution of hydrogen peroxide and controlling the temperature of the iron-phosphorus solution to 70℃~80℃ is beneficial for the hydrogen peroxide to react fully with the iron-phosphorus solution, improving the oxidation efficiency of ferrous ions, facilitating the rapid generation of a large number of small-sized iron phosphate particles at this stage, which is beneficial for the subsequent high-temperature boiling stage to generate more iron phosphate-hydrochloric acid complexes, and also facilitates the stable and uniform dispersion of the iron phosphate-hydrochloric acid complexes in the first slurry, thereby preparing iron phosphate material with small size and good particle dispersibility.

[0117] In some embodiments, the mass fraction of hydrogen peroxide in the aqueous solution of hydrogen peroxide is 20% to 30%.

[0118] In the technical solution of this application embodiment, hydrogen peroxide is within the above-mentioned content range, which facilitates the rapid generation of ferric phosphate particles and can effectively reduce the decomposition loss of hydrogen peroxide itself during the oxidation of ferrous ions.

[0119] In some embodiments, the ferrous ion source is selected from one or more of ferrous nitrate and ferrous chloride.

[0120] In the technical solutions of this application embodiment, the above-mentioned ferrous ion sources can all provide the necessary ferrous ions for the iron-phosphorus solution reaction system. When ferrous nitrate is used as the ferrous salt, the free nitrate ions in the system can be converted into nitric acid and volatilized and removed during the subsequent boiling process. When ferrous chloride is used as the ferrous salt, the free chloride ions in the system can be volatilized and removed in the form of hydrochloric acid during the subsequent boiling process, so as to reduce the acidity of the system and reduce impurities, and facilitate the subsequent acquisition of small-sized and high-yield iron phosphate.

[0121] In some embodiments, the ferrous ion source is selected from ferrous chloride.

[0122] In the technical solution of this application embodiment, ferrous chloride introduces chloride ions while providing ferrous ions, so that it can subsequently complex with ferric phosphate particles to form a ferric phosphate-hydrochloric acid complex, thereby reducing ferric phosphate agglomeration and avoiding the introduction of impurities such as nitrogen and oxygen.

[0123] In some embodiments, the chloride ion source is selected from at least one of hydrochloric acid and ferrous chloride.

[0124] In the technical solutions of this application embodiment, both hydrochloric acid and ferrous chloride can provide the chloride ions required for the reaction and reduce the introduction of other impurity cations.

[0125] In some embodiments, the phosphate ion source is selected from at least one of H3PO4, (NH4)H2PO4, and (NH4)2HPO4.

[0126] In the technical solutions of this application embodiment, H3PO4, (NH4)H2PO4, and (NH4)2HPO4 can provide the necessary phosphate ions for the reaction.

[0127] In some embodiments, the preparation steps of the iron-phosphorus solution are as follows:

[0128] A ferrous ion source, a chloride ion source, a phosphate ion source, and water are mixed, and the pH of the mixture is controlled to be no greater than 1.5 to obtain an iron-phosphorus solution.

[0129] In this embodiment, the desired iron-phosphorus solution can be obtained by directly mixing the ferrous ion source, chloride ion source, phosphate ion source, and water, which is a simple process.

[0130] In some embodiments, the ferrous ion source is ferrous chloride, the chloride ion source is selected from ferrous chloride and hydrochloric acid, and the phosphate ion source is phosphoric acid.

[0131] In the technical solution of this application embodiment, ferrous chloride serves as both a ferrous ion source and a chloride ion source, hydrochloric acid serves as a chloride ion source and provides acidity conditions for the reaction, and phosphate serves as a phosphorus source and also provides acidity conditions for the reaction. By adjusting the ratio of the above raw materials, the pH value of the system and the elemental ratio of ferrous ions, phosphate ions, and chloride ions can be controlled. There is no need to add additional acids or bases (such as sulfuric acid, nitric acid, sodium hydroxide, ammonia, etc.). At the same time, iron phosphate material with a cyclic structure and small size can be prepared, while minimizing the introduction of impurity ions (such as sulfate, nitrate, sodium, NH4, etc.), and high-purity iron phosphate material can be prepared. This can improve the cycle life and capacity retention of lithium iron phosphate prepared using this iron phosphate material as a raw material in batteries.

[0132] In some embodiments, the preparation steps of the iron-phosphorus solution are as follows:

[0133] A dilute hydrochloric acid aqueous solution is heated to 50℃~70℃, and then elemental iron is added to react and obtain ferrous chloride solution. The concentration of the dilute hydrochloric acid aqueous solution is 1.0mol / L~4.0mol / L.

[0134] Add phosphoric acid and water to a ferrous chloride solution, mix, and control the pH value to be no greater than 1.5 to obtain an iron-phosphorus solution.

[0135] In the technical solution of this application embodiment, an iron-phosphorus solution is prepared using elemental iron, hydrochloric acid aqueous solution, and phosphoric acid as raw materials. This minimizes the introduction of impurity ions and produces high-purity iron phosphate material. Specifically, phosphoric acid and water can be added to the ferrous chloride solution in the form of an aqueous phosphoric acid solution, or they can be added separately to the ferrous chloride solution. Specifically, in some embodiments, the elemental iron is selected from one or more of iron sheets, iron powder, and iron blocks.

[0136] Furthermore, in some embodiments, the pH value of the iron-phosphorus solution is 0.2 to 1.5.

[0137] In the technical solution of this application embodiment, the pH value of the iron-phosphorus solution affects the formation rate and yield of iron phosphate. A higher pH value is more likely to cause a large number of iron phosphate particles to agglomerate during the oxidation stage, while a lower pH value is not conducive to the precipitation of the target product iron phosphate. Within the above pH value range, it is more conducive to obtaining iron phosphate material with high yield and small size.

[0138] In some embodiments, the temperature difference between the second slurry and the first slurry is not less than 60°C.

[0139] In the technical solution of this application embodiment, the higher temperature difference is more conducive to the decomposition of iron phosphate-hydrochloric acid and cold quenching and refining, thereby generating smaller-sized iron phosphate materials.

[0140] In some embodiments, the temperature difference between the second slurry and the first slurry is further 70°C to 90°C.

[0141] In the technical solution of this application embodiment, controlling the temperature difference between the second slurry and the first slurry within this temperature range is more conducive to obtaining smaller-sized iron phosphate materials and achieving a higher yield.

[0142] In some embodiments, the mass ratio of the first slurry to low-temperature dilution water is 1:(10-20).

[0143] In the technical solution of this application embodiment, low-temperature dilution water is used for rapid cooling and dilution of the system, which is conducive to the decomposition of the iron phosphate-hydrochloric acid complex to generate iron phosphate material. The mass ratio of the first slurry to the low-temperature dilution water is within the above range, which is conducive to the rapid and complete decomposition of the iron phosphate-hydrochloric acid complex, thereby obtaining small-sized iron phosphate material with high purity and high yield.

[0144] In some embodiments, the first slurry is mixed with low-temperature dilution water and stirred until the color changes to obtain the second slurry.

[0145] In the technical solution of this application embodiment, during the high-temperature boiling treatment, an iron phosphate-hydrochloric acid complex is generated. After mixing with low-temperature dilution water, the iron phosphate precipitates after decomposition, and the slurry color changes. Specifically, the iron phosphate is a grayish-white or light red powder. The iron phosphate slurry containing iron phosphate particles obtained by oxidation with an oxidant is brownish-yellow. After high-temperature boiling (acid removal) treatment, no obvious iron phosphate precipitation occurs in the brownish-yellow iron phosphate slurry, and the slurry color becomes bright yellow, indicating that an iron phosphate-hydrochloric acid complex (e.g., [FeCl4]) is generated during the high-temperature boiling treatment. -When the complex is added to low-temperature dilution water and mixed, the ferric phosphate precipitates after decomplexing, and the slurry color changes from bright yellow to light white.

[0146] In some embodiments, the second slurry is subjected to solid-liquid separation, and the resulting solid is washed and dried at 90°C to 120°C to obtain iron phosphate material.

[0147] In the technical solution of this application embodiment, under the above conditions, moisture can be quickly removed to obtain iron phosphate material.

[0148] Thirdly, embodiments of this application provide a cathode material, including at least one of lithium iron phosphate material and lithium manganese iron phosphate material. The lithium iron phosphate material is prepared from the above-mentioned iron phosphate material or from iron phosphate material prepared by the above-mentioned method for preparing iron phosphate material. The lithium manganese iron phosphate material is prepared from the above-mentioned iron phosphate material or from iron phosphate material prepared by the above-mentioned method for preparing iron phosphate material.

[0149] Fourthly, embodiments of this application provide a positive electrode sheet, which includes the aforementioned positive electrode material. The positive electrode sheet containing the aforementioned positive electrode material has the advantage of reducing energy consumption and cost in the preparation of the positive electrode sheet.

[0150] Fifthly, embodiments of this application provide a secondary battery in which the positive electrode is the aforementioned positive electrode. The secondary battery includes the aforementioned positive electrode, thus offering advantages such as reduced energy consumption and cost in secondary battery manufacturing and improved electrochemical performance.

[0151] Sixthly, embodiments of this application provide an electrical device, such as a vehicle, including the battery as described in the above embodiments. The electrical device, comprising the aforementioned secondary battery, has the advantages of reducing energy consumption and cost in the manufacture of the electrical device and improving its electrochemical performance.

[0152] 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.

[0153] I. Preparation Method

[0154] Example 1

[0155] Step 1, Preparation of ferrous chloride: Take concentrated hydrochloric acid and add pure water to prepare a hydrochloric acid solution with a chloride ion concentration of 4.0 mol / L. Heat the dilute hydrochloric acid solution to 60℃. After reaching the temperature, add iron powder to the dilute hydrochloric acid solution (the iron powder is added in a molar ratio of Fe to Cl of 1:2). React until no more bubbles are produced. Filter to obtain ferrous chloride solution.

[0156] Step 2, preparation of iron-phosphorus solution: Take the prepared ferrous chloride solution, add phosphoric acid and pure water to mix, and prepare an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, phosphoric acid is added according to the molar ratio of Fe element to P element of 1:1). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.80.

[0157] Step 3, Preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in step 2 as the base liquid, heat the base liquid to 80℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 28%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element is 1.5:2.0). The dropwise addition time is controlled at 10 min. After the dropwise addition is completed, continue stirring for 10 min to obtain iron phosphate slurry.

[0158] Step four: Heat the ferric phosphate slurry prepared in step three to boiling point. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 2 hours to obtain the first slurry.

[0159] Step 5: Add the first slurry prepared in step 4 to low-temperature dilution water and stir until the slurry color changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 20℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:12).

[0160] Step 6: Filter the second slurry prepared in Step 5. The filtered solids are then washed countercurrently until the conductivity of the wash water is less than 500 μS / cm to obtain ferric phosphate filter cake. The filter cake is then dried at 98°C to obtain ferric phosphate.

[0161] The SEM results of the iron phosphate material prepared in Example 1 are shown in Figures 1 and 2. The microstructure of the iron phosphate material is cyclic, and the particle dispersion is good. The XRD results of the iron phosphate material are shown in Figure 4. The prepared small-sized iron phosphate material with a cyclic structure is a single iron phosphate phase. According to the particle size analysis data, the D50 particle size of the iron phosphate material is 0.82 μm, and the D100 particle size is only 3.846 μm. This application example prepared a small-sized iron phosphate material with a cyclic structure and a D50 particle size of less than 1 μm.

[0162] Example 2

[0163] Step 1, Preparation of ferrous chloride: Take concentrated hydrochloric acid and add pure water to prepare a hydrochloric acid solution with a chloride ion concentration of 4.0 mol / L. Heat the dilute hydrochloric acid solution to 50°C. After reaching the temperature, add iron powder to the dilute hydrochloric acid solution (the iron powder is added in a molar ratio of Fe to Cl of 1:2). React until no more bubbles are produced. Filter to obtain ferrous chloride solution.

[0164] Step 2, preparation of iron-phosphorus solution: Take the prepared ferrous chloride solution, add phosphoric acid and pure water to mix, and prepare an iron-phosphorus solution with a ferrous ion concentration of 0.5 mol / L (wherein, phosphoric acid is added according to the molar ratio of Fe element to P element of 1.0:1). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 1.2.

[0165] Step 3, Preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in step 2 as the base liquid, heat the base liquid to 70℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 20%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element of 0.6:1). The dropwise addition time is controlled at 5min. After the dropwise addition is completed, continue stirring for 5min to obtain iron phosphate slurry.

[0166] Step four: Heat the ferric phosphate slurry prepared in step three to boiling point. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 1.5 hours to obtain the first slurry.

[0167] Step 5: Add the first slurry prepared in step 4 to low-temperature dilution water and stir until the slurry color changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 10℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:30).

[0168] Step 6: Filter the second slurry prepared in Step 5. The filtered solids are then washed countercurrently until the conductivity of the wash water is less than 500 μS / cm to obtain ferric phosphate filter cake. The filter cake is then dried at 90°C to obtain ferric phosphate.

[0169] Example 3

[0170] Step 1, Preparation of ferrous chloride: Take concentrated hydrochloric acid and add pure water to prepare a hydrochloric acid solution with a chloride ion concentration of 4.0 mol / L. Heat the dilute hydrochloric acid solution to 70℃. After reaching the temperature, add iron powder to the dilute hydrochloric acid solution (the iron powder is added in a molar ratio of Fe to Cl of 1:2). React until no more bubbles are produced. Filter to obtain ferrous chloride solution.

[0171] Step 2, preparation of iron-phosphorus solution: Take the prepared ferrous chloride solution, add phosphoric acid and pure water to mix, and prepare an iron-phosphorus solution with a ferrous ion concentration of 2 mol / L (wherein, phosphoric acid is added according to the molar ratio of Fe element to P element of 1:1). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.6.

[0172] Step 3, preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in step 2 as the base liquid, heat the base liquid to 80℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 28%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element is 1:1). The dropwise addition time is controlled at 15min. After the dropwise addition is completed, continue stirring for 15min to obtain iron phosphate slurry.

[0173] Step four: Heat the ferric phosphate slurry prepared in step three to boiling point. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 4 hours to obtain the first slurry.

[0174] Step 5: Add the first slurry prepared in step 4 to low-temperature dilution water and stir until the slurry color changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 30℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:10).

[0175] Step 6: Filter the second slurry prepared in Step 5. The filtered solids are then washed countercurrently until the conductivity of the wash water is less than 500 μS / cm to obtain ferric phosphate filter cake. The filter cake is then dried at 120°C to obtain ferric phosphate.

[0176] Example 4

[0177] Step 1, Preparation of iron-phosphorus solution: Mix ferrous chloride, hydrochloric acid, H3PO4 and pure water to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous chloride, H3PO4 and hydrochloric acid are added in the molar ratio of Fe, P and Cl elements of 1:1:3). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.3.

[0178] Step 2, Preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in Step 1 as the base liquid, heat the base liquid to 80℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 28%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element is 1.5:2.0). The dropwise addition time is controlled at 10 min. After the dropwise addition is completed, continue stirring for 10 min to obtain iron phosphate slurry.

[0179] Step 3: Heat the ferric phosphate slurry prepared in Step 2 to boiling point. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 2 hours to obtain the first slurry.

[0180] Step 4: Add the first slurry prepared in Step 3 to low-temperature dilution water and stir until the color of the slurry changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 20℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:12).

[0181] Step 5: Filter the second slurry prepared in Step 4. The filtered solids are then washed countercurrently until the conductivity of the wash water is less than 500 μS / cm to obtain ferric phosphate filter cake. The filter cake is then dried at 98°C to obtain ferric phosphate.

[0182] Example 5

[0183] Step 1, Preparation of iron-phosphorus solution: Ferrous nitrate, hydrochloric acid, (NH4)H2PO4 and pure water are mixed to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous nitrate, hydrochloric acid and (NH4)H2PO4 are added in a molar ratio of Fe, P and Cl elements of 1:1:3). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.2.

[0184] Step 2, Preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in Step 1 as the base liquid, heat the base liquid to 70℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 20%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element of 0.6:1). The dropwise addition time is controlled at 5min. After the dropwise addition is completed, continue stirring for 5min to obtain iron phosphate slurry.

[0185] Step 3: Heat the ferric phosphate slurry prepared in Step 2 to boiling. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 1.5 hours to obtain the first slurry.

[0186] Step 4: Add the first slurry prepared in step 3 to low-temperature dilution water and stir until the slurry color changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 10℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:30).

[0187] Step 5: Filter the second slurry prepared in Step 4. Wash the filtered solids countercurrently until the conductivity of the washing water is less than 500 μS / cm to obtain ferric phosphate filter cake. Dry the filter cake at 90°C to obtain ferric phosphate.

[0188] Example 6

[0189] Step 1, Preparation of iron-phosphorus solution: Ferrous nitrate, hydrochloric acid, (NH4)2HPO4 and pure water are mixed to obtain an iron-phosphorus solution with a ferrous ion concentration of 2 mol / L (wherein, ferrous nitrate, hydrochloric acid and (NH4)2HPO4 are added in the molar ratio of Fe, P and Cl elements of 1.0:1.2:3). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.4.

[0190] Step 2, Preparation of iron phosphate slurry: Take the iron-phosphorus solution prepared in Step 1 as the base liquid, heat the base liquid to 80℃, and after reaching the temperature, add hydrogen peroxide dropwise to the base liquid (the mass fraction of hydrogen peroxide in hydrogen peroxide is 28%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element is 1:1). The dropwise addition time is controlled at 15min. After the dropwise addition is completed, continue stirring for 15min to obtain iron phosphate slurry.

[0191] Step 3: Heat the ferric phosphate slurry prepared in Step 2 to boiling. After the color of the ferric phosphate slurry gradually changes from brownish-yellow to bright yellow, continue to maintain the boiling state for 4 hours to obtain the first slurry.

[0192] Step 4: Add the first slurry prepared in Step 3 to low-temperature dilution water and stir until the slurry color changes from bright yellow to light white to obtain the second slurry (wherein, the temperature of the second slurry is 30℃, and the mass ratio of the first slurry to the low-temperature dilution water is 1:10).

[0193] Step 5: Filter the second slurry prepared in Step 4. Wash the filtered solids countercurrently until the conductivity of the washing water is less than 500 μS / cm to obtain ferric phosphate filter cake. Dry the filter cake at 120°C to obtain ferric phosphate.

[0194] Example 7

[0195] The only difference between this example and Example 4 is that ferrous chloride is replaced with ferrous nitrate in step one.

[0196] Example 8

[0197] The only difference between this example and Example 4 is that in step one, ferrous chloride is replaced with ferrous nitrate, and ferrous nitrate, H3PO4, and hydrochloric acid are added in a molar ratio of Fe, P, and Cl of 1:1:2. Step one is as follows:

[0198] Step 1, Preparation of iron-phosphorus solution: Mix ferrous nitrate, hydrochloric acid, H3PO4 and pure water to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous nitrate, H3PO4 and hydrochloric acid are added in the molar ratio of Fe, P and Cl elements of 1:1:2). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.45.

[0199] Example 9

[0200] The only difference from Example 4 is that in step one, ferrous chloride is replaced with ferrous nitrate, and ferrous nitrate, H3PO4, and hydrochloric acid are added in a molar ratio of Fe, P, and Cl of 1:1:0.5. Step one is as follows:

[0201] Step 1, Preparation of iron-phosphorus solution: Mix ferrous nitrate, hydrochloric acid, H3PO4 and pure water to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous nitrate, H3PO4 and hydrochloric acid are added in the molar ratio of Fe, P and Cl elements of 1:1:0.5). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.55.

[0202] Example 10

[0203] The only difference from Example 4 is that in step one, ferrous chloride is replaced with ferrous nitrate, and ferrous nitrate, H3PO4, and hydrochloric acid are added in a molar ratio of Fe, P, and Cl of 1:1:4. Step one is as follows:

[0204] Step 1, Preparation of iron-phosphorus solution: Mix ferrous nitrate, hydrochloric acid, H3PO4 and pure water to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous nitrate, H3PO4 and hydrochloric acid are added in the molar ratio of Fe, P and Cl elements of 1:1:4). After stirring evenly, the iron-phosphorus solution is obtained with a pH value of 0.25.

[0205] Example 11

[0206] The only difference between this and Example 4 is that the dripping time in step two is controlled at 25 minutes, and stirring continues for another 25 minutes after the dripping is completed.

[0207] Example 12

[0208] The only difference between this and Example 4 is that the temperature of the second slurry is controlled at 50°C in step three.

[0209] Comparative Example 1

[0210] The only difference between this and Example 4 is that in step one, ferrous chloride is replaced with ferrous nitrate and hydrochloric acid is replaced with nitric acid; in step three, the ferric phosphate slurry prepared in step two is heated to boiling and kept boiling for 2 hours to obtain the first slurry.

[0211] Comparative Example 2

[0212] The only difference between this example and Example 4 is that step one includes adjusting the pH of the iron-phosphorus solution to 2 using an alkaline solution. The specific steps of step one are as follows:

[0213] Ferrous chloride, hydrochloric acid, H3PO4, and pure water were mixed to obtain an iron-phosphorus solution with a ferrous ion concentration of 1.5 mol / L (wherein, ferrous chloride, H3PO4, and hydrochloric acid were added in a molar ratio of Fe, P, and Cl of 1:1:3). After stirring evenly, the iron-phosphorus solution was obtained. A 1 mol / L sodium hydroxide aqueous solution was added dropwise to the iron-phosphorus solution to adjust the pH of the iron-phosphorus solution to 2.

[0214] Comparative Example 3

[0215] The only difference between this and Example 4 is that the bottom liquid is heated to 65°C in step two.

[0216] Comparative Example 4

[0217] The only difference between it and Example 4 is that the boiling state is maintained for 30 minutes in step three.

[0218] Comparative Example 5

[0219] The only difference between this and Example 4 is that in step four, low-temperature dilution water was not used; instead, the mixture was naturally cooled to room temperature to obtain the second slurry.

[0220] Comparative Example 6

[0221] The specific steps for preparing iron phosphate using the traditional iron-based process are as follows:

[0222] Step 1, Preparation of ferrous dihydrogen phosphate: Take phosphoric acid and add pure water to prepare a 30% dilute phosphoric acid solution for later use. Heat the dilute phosphoric acid solution to 50°C. After reaching the temperature, add an appropriate amount of iron powder to the dilute phosphoric acid solution (the iron powder is added in a molar ratio of Fe to phosphorus of 1:2). After the reaction is completed, filter the slurry to obtain a ferrous dihydrogen phosphate solution.

[0223] Step 2, Preparation of ferric phosphate: Take the ferrous dihydrogen phosphate solution prepared in Step 1, add pure water to prepare a ferrous dihydrogen phosphate solution with a molar concentration of 1 mol / L, heat the prepared ferrous dihydrogen phosphate solution to 80℃, after heating, uniformly add hydrogen peroxide (the mass fraction of hydrogen peroxide in hydrogen peroxide is 28%, and the hydrogen peroxide is added according to the molar ratio of H2O2 to Fe element is 1.5:2.0) to the ferrous dihydrogen phosphate solution, control the addition time to 105 min, and keep warm for 60 min after the addition is completed to obtain ferric phosphate slurry.

[0224] Step 3: Filter the ferric phosphate slurry prepared in Step 2. Wash the filter material countercurrently until the conductivity of the washing water is less than 500 μS / cm to obtain ferric phosphate filter cake. Dry the filter cake at 98°C to obtain ferric phosphate.

[0225] The SEM images of the iron phosphate material prepared in Comparative Example 6 are shown in Figures 5 and 6, showing a sheet-like microstructure. The XRD pattern of the iron phosphate material is shown in Figure 7, indicating that the prepared iron phosphate material is a single iron phosphate phase. According to the particle size analysis data, the D50 particle size of the iron phosphate material prepared in Comparative Example 6 is 4.833 μm, and the D100 particle size is 15.721 μm, which are significantly larger than those of the iron phosphate material prepared in Example 1.

[0226] II. Testing Methods

[0227] 1. Property testing of iron phosphate materials

[0228] 1) The inner and outer diameters of the material were characterized by scanning electron microscopy (SEM). The inner diameter of the iron phosphate material was statistically analyzed and the average value was calculated to obtain the average inner diameter. The outer diameter of the material was statistically analyzed and the average value was calculated to obtain the average outer diameter. The average inner diameter, average outer diameter, and the ratio of the average inner diameter to the average outer diameter are shown in Table 1.

[0229] 2) The material was characterized using an X-ray diffractometer.

[0230] 3) The specific surface area of ​​the material was tested using the nitrogen adsorption BET test method, referring to the standard GB / T9587-2017. The test results of the specific surface area of ​​the iron phosphate materials prepared in the examples and comparative examples are shown in Table 1.

[0231] 4) The particle sizes D0 (μm), D10 (μm), D50 (μm), D90 (μm), D99 (μm), and D100 (μm) of the material were measured using a laser particle size analyzer. The particle size distribution (D90-D10) / D50 and the particle size test results are shown in Table 1.

[0232] 5) Sanding time test

[0233] The iron phosphate material was sand-milled until the D50 particle size was 350 nm. The sand-milling was then stopped, and the sand-milling time was recorded.

[0234] 6) The elemental composition of the material was analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES), and the results are shown in Table 2.

[0235] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0236] Table 1 Note: In Table 1, " / " indicates that the prepared iron phosphate material has a sheet-like structure and does not have data on its inner and outer diameters.

[0237] Table 2

[0238] As can be seen from the data in Table 1, the size of the iron phosphate materials prepared in Examples 1-12 of this application is significantly smaller than that of the iron phosphate materials prepared in Comparative Examples 1-6. Under the same conditions, the time required to mill the iron phosphate materials prepared in Examples 1-12 of this application to a D50 particle size of 350 nm is less than 100 min, which effectively reduces the energy consumption of the milling process and improves the process efficiency.

[0239] As can be seen from the comparison between Example 4 and Comparative Example 1, compared with the replacement of ferrous chloride and hydrochloric acid with ferrous nitrate and nitric acid respectively in Comparative Example 1, the size of the ferric phosphate material obtained in Example 4 is significantly reduced. This indicates that the all-chloride ion system using ferrous chloride and hydrochloric acid as the ferrous ion source and chloride ion source can make full use of the volatility and complexing properties of hydrogen chloride to form ferric phosphate-hydrochloric acid complexes with ferric phosphate particles in the ferric phosphate slurry. The ferric phosphate is protected in the form of complexes to prevent the ferric phosphate particles from agglomerating. Then, the slurry containing ferric phosphate-hydrochloric acid is decomplexed under low temperature conditions by dilution-cold activation decomplexing method, which is conducive to the generation of small-sized ferric phosphate particles.

[0240] As can be seen from the comparison between Example 4 and Comparative Example 2, compared with the pH value of the iron-phosphorus solution adjusted to 2 by sodium hydroxide aqueous solution in Comparative Example 2, the pH value of the iron-phosphorus solution was controlled to 0.3 in Example 4, and the size of the obtained iron phosphate material was significantly reduced. This shows that controlling the pH value of the iron-phosphorus solution to no more than 1.5 is beneficial to obtaining iron phosphate materials with smaller size.

[0241] As can be seen from Example 4 and Comparative Example 3, compared with Comparative Example 3, the iron-phosphorus solution in Example 4 was heated to above 70°C to prepare iron phosphate slurry, which improved the iron oxidation efficiency and facilitated the rapid generation of a large number of small iron phosphate particles. This was beneficial for the subsequent high-temperature boiling stage to generate more iron phosphate-hydrochloric acid complexes, and for the iron phosphate-hydrochloric acid complexes to be stably and uniformly dispersed in the slurry. The size of the obtained iron phosphate material was significantly reduced.

[0242] As can be seen from Example 4 and Comparative Example 4, compared with Comparative Example 4, the longer boiling state in Example 4 is beneficial for the iron phosphate particles in the system to fully complex and form iron phosphate-hydrochloric acid complex, thus protecting the iron phosphate in the form of a complex to avoid the agglomeration of iron phosphate particles, thereby obtaining iron phosphate material with smaller size.

[0243] As can be seen from Example 4 and Comparative Example 5, Comparative Example 5 did not add low-temperature dilution water, resulting in a reduced cold extraction effect. The overall size of the iron phosphate particles and the D50 particle size were significantly higher, and the time required to grind to a D50 particle size of 350 nm was longer.

[0244] As can be seen from Example 4 and Comparative Example 6, the iron phosphate particles prepared by the conventional iron-based process route of Comparative Example 6 have a larger D50 particle size, which is significantly higher than that of the iron phosphate material in Example 4.

[0245] A comparison between Examples 4 and 7 shows that, compared to Example 7 which uses ferrous nitrate as the ferrous source, i.e., simultaneously introducing nitrate anions and chloride anions, the all-chloride anion system used in Example 4 makes it easier to obtain smaller-sized iron phosphate materials.

[0246] Compared to Example 10, the D50 particle size, average inner diameter, and average outer diameter of Examples 8 and 9, which have a molar ratio of iron, phosphorus, and chlorine within (0.8–1.2):(0.8–2):(0.5–3), are significantly smaller than those of Example 10, which is more conducive to obtaining iron phosphate materials with smaller overall size.

[0247] A comparison of Examples 4 and 11 shows that controlling the hydrogen peroxide addition time to 5-15 minutes and the stirring time to 5-15 minutes yields smaller-sized iron phosphate materials. Compared to Example 11, Example 4, with its faster addition rate and shorter stirring time, facilitates the rapid formation of iron phosphate crystal nuclei and inhibits crystal growth. This, in turn, promotes the formation of more iron phosphate-hydrochloric acid complexes during the subsequent high-temperature boiling stage, ensuring the stable and uniform dispersion of the iron phosphate-hydrochloric acid complexes in the iron phosphate slurry, reducing the agglomeration of iron phosphate particles, and thus obtaining smaller-sized iron phosphate materials.

[0248] A comparison of Examples 4 and 12 shows that controlling the temperature difference between the second slurry and the first slurry to be no less than 60°C yields smaller-sized iron phosphate materials. Compared to Example 12, Example 4 uses a higher temperature difference, which is more conducive to the decomplexation of iron phosphate and hydrochloric acid and cold quenching refinement, thus facilitating the generation of smaller-sized iron phosphate materials.

[0249] As shown in Table 2, compared with Comparative Example 6, the metal impurity content of the iron phosphate materials prepared in Examples 1-12 of this application is generally lower. The high impurity element content of the iron phosphate prepared by the traditional iron method in Comparative Example 6 is mainly due to the large phosphorus excess coefficient in the traditional iron method (iron-phosphorus ratio: Fe / P = 1 / 2). After most of the Fe element is precipitated in the system, it forms phosphate precipitate with other impurity cations. However, the preparation method of iron phosphate materials provided in Examples 1-11 of this application controls the iron-phosphorus ratio to be 1:(1~1.2). After the iron phosphate precipitates, there are fewer free phosphate ions, and impurity cations are less likely to form phosphate precipitates.

[0250] 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 ferric phosphate material, characterized in that, The iron phosphate material includes iron phosphate particles, which have a ring structure and a D50 particle size of less than 1 μm.

2. The iron phosphate material according to claim 1, characterized in that, The aggregation index of the iron phosphate particles satisfies: 0.5≤(D90-D10) / D50≤2.

3. The iron phosphate material according to claim 1, characterized in that, The ratio of the average inner diameter to the average outer diameter of the annular structure of the iron phosphate particles is (0.35–0.48):1; The average inner diameter of the cyclic structure of the iron phosphate particles ranges from 178 nm to 559 nm, and the average outer diameter of the cyclic structure of the iron phosphate particles ranges from 474.60 nm to 1188.90 nm.

4. The iron phosphate material according to any one of claims 1 to 3, characterized in that, The specific surface area of ​​the iron phosphate particles is 13 m². 2 / g~20m 2 / g.

5. A method for preparing an iron phosphate material, characterized in that, Includes the following steps: Prepare an iron-phosphorus solution comprising a ferrous ion source, a chloride ion source, and a phosphate ion source, wherein the pH value of the iron-phosphorus solution is not greater than 1.5; The iron-phosphorus solution is heated to above 70°C, and then an oxidant is added to the iron-phosphorus solution to obtain iron phosphate slurry; The ferric phosphate slurry is heated to boiling. After the ferric phosphate slurry changes color, it is kept boiling for 1.5h to 4h to obtain the first slurry. The first slurry is mixed with low-temperature dilution water to obtain the second slurry; The second slurry was subjected to solid-liquid separation to obtain iron phosphate material.

6. The method for preparing the iron phosphate material according to claim 5, characterized in that, The molar ratio of iron, phosphorus, and chlorine in the iron-phosphorus solution is (0.8–1.2):(0.8–2):(0.5–3). The oxidant is selected from an aqueous solution of hydrogen peroxide, wherein the molar ratio of hydrogen peroxide to iron in the iron-phosphorus solution is (0.6-1):1, and the concentration of iron in the iron-phosphorus solution is 0.5 mol / L to 2.0 mol / L. The mass fraction of hydrogen peroxide in the aqueous solution is 20% to 30%. The ferrous ion source is selected from one or two of ferrous nitrate and ferrous chloride. The chloride ion source is selected from at least one of hydrochloric acid and ferrous chloride; The phosphate ion source is selected from at least one of H3PO4, (NH4)H2PO4, and (NH4)2HPO4.

7. The method for preparing the iron phosphate material according to claim 6, characterized in that, The preparation steps of the iron-phosphorus solution are as follows: A dilute hydrochloric acid aqueous solution is heated to 50℃~70℃, and then elemental iron is added to react and obtain ferrous chloride solution. The concentration of the dilute hydrochloric acid aqueous solution is 1.0mol / L~4.0mol / L. Phosphoric acid and water are added to the ferrous chloride solution, mixed, and the pH value is controlled to be no greater than 1.5 to obtain the iron-phosphorus solution. The steps of heating the iron-phosphorus solution to above 70°C and then adding an oxidant to the iron-phosphorus solution to obtain iron phosphate slurry include: The iron-phosphorus solution is heated to 70°C to 80°C, and then an aqueous solution of hydrogen peroxide is added to the iron-phosphorus solution. The step of mixing the first slurry with low-temperature dilution water to obtain the second slurry includes: The first slurry is mixed with the low-temperature dilution water and stirred until the color changes to obtain the second slurry; The step of performing solid-liquid separation on the second slurry to obtain the iron phosphate material includes: The second slurry is subjected to solid-liquid separation. The resulting solid is washed and dried at 90℃~120℃ to obtain the iron phosphate material.

8. The method for preparing the iron phosphate material according to any one of claims 6 to 7, characterized in that, The pH value of the iron-phosphorus solution is 0.2 to 1.5; The temperature difference between the second slurry and the first slurry is not less than 60°C; The mass ratio of the first slurry to the low-temperature dilution water is 1:(10-30).

9. A positive electrode material, characterized in that, The invention includes at least one of lithium iron phosphate and lithium manganese iron phosphate, wherein the lithium iron phosphate is prepared by the iron phosphate material according to any one of claims 1 to 4 or by the iron phosphate material prepared by the method of preparing the iron phosphate material according to any one of claims 5 to 8, and the lithium manganese iron phosphate is prepared by the iron phosphate material according to any one of claims 1 to 4 or by the iron phosphate material prepared by the method of preparing the iron phosphate material according to any one of claims 5 to 8.

10. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material as described in claim 9.

11. A secondary battery, comprising a positive electrode, characterized in that, The positive electrode used is the positive electrode as described in claim 10.

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