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

Abstract

The application provides a kind of iron phosphate material, its preparation method, positive electrode material, positive electrode sheet and secondary battery.The titanium element is doped in the iron phosphate material, at least part of the surface of the primary particle of the iron phosphate material is in laminated structure, in the multiple sheet layers of laminated structure, any two adjacent sheet layers are located on the side of each other respectively.The laminated structure forms a short-range ordered morphology, avoids the situation that sheet layer horizontal and vertical staggered causes space waste, can make the specific surface area and contact area of primary particle are more significantly improved.Moreover, the titanium element is also doped in the iron phosphate material, titanium element makes the iron phosphate material produce defects in the process of crystallization, hinders the growth of iron phosphate in a particular direction, is beneficial to the formation of laminated structure on the surface of iron phosphate particle.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to an iron phosphate material, a preparation method thereof, a positive electrode material, a positive electrode sheet and a secondary battery. Background Art

[0002] Lithium iron phosphate (LiFePO4) is a cathode material. Compared to other cathode materials, LiFePO4 offers both high safety and a suitable discharge capacity, making it widely used in lithium-ion batteries.

[0003] Iron phosphate is a common precursor material used in the production of lithium iron phosphate. A common process involves a solid-phase reaction of iron phosphate with lithium carbonate and glucose to form lithium iron phosphate. The properties and performance of the resulting lithium iron phosphate are largely determined by the iron phosphate material.

[0004] The microscopic morphology of iron phosphate has a significant impact on the macroscopic properties of iron phosphate. For example, the particle morphology in the iron phosphate material will directly affect the overall packing density and contact area of ​​the iron phosphate material. The primary particles of the iron phosphate material in traditional technologies are mostly dispersed irregular particles or spheres at the microscopic level. The sphere is the geometric shape with the smallest specific surface area, which leads to the overall specific surface area of ​​the iron phosphate material and the contact area with the outside world being relatively small. The charge and discharge efficiency of the positive electrode material prepared therefrom is relatively low. Some traditional technologies have also proposed iron phosphate materials with flaky primary particles, but the flaky particles are randomly and disorderly distributed, and there is obvious contact stacking and horizontal and vertical interlacing between the flakes, which has limited improvement in the specific surface area and contact area. The improvement in the charge and discharge efficiency of the prepared positive electrode material is also relatively limited.

[0005] Based on the above situation, further research is still needed to increase the specific surface area and contact area of ​​iron phosphate materials. Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present application provides an iron phosphate material, a preparation method thereof, a positive electrode material, a positive electrode plate, and a secondary battery. The iron phosphate material of the present application can effectively increase the specific surface area and contact area of ​​the iron phosphate material through structural design.

[0007] In a first aspect, an embodiment of the present application provides an iron phosphate material, wherein the iron phosphate material is doped with titanium, and at least a portion of the surface of the primary particles of the iron phosphate material has a laminated structure, wherein the laminated structure has a plurality of layers, and any two adjacent layers are located on one side of each other in a stacking direction;

[0008] Wherein, the stacking direction intersects with the extending direction of the sheet layer.

[0009] In this embodiment, the iron phosphate material is doped with titanium, which causes defects in the iron phosphate material during the crystallization process, hindering the growth of iron phosphate in a specific direction, and is conducive to the formation of a lamellar structure on the surface of the iron phosphate particles. A lamellar structure exists on the surface of the primary particles of the iron phosphate material. Any two adjacent layers of the multiple layers of the lamellar structure are located on one side of each other in the stacking direction. Unlike the traditional disordered flaky iron phosphate material, the lamellar structure forms a short-range ordered morphology, which avoids the situation where the layers are staggered horizontally and vertically to cause space waste, and can significantly improve the specific surface area and contact area of ​​the primary particles. In addition, since the ionic radius of titanium ions is smaller than that of iron ions, the ion channels at the sites occupied by titanium ions are widened. This is also conducive to improving the ion migration efficiency of the positive electrode material prepared therefrom during the charge-discharge process.

[0010] In some embodiments of the present application, the surface of the primary particles of the ferric phosphate material is split into the lamellar structure; and / or,

[0011] The surface of a single primary particle of the ferric phosphate material has a plurality of the lamellar structures; and / or,

[0012] In a single laminated structure, the number of the laminae is 2 to 4.

[0013] In this embodiment, the connection between the lamellar structure formed by the splitting of the surface of the primary particles and the matrix in which it is located is more stable, which is conducive to maintaining the integrity of the structure during subsequent processing, thereby enabling the structure of the iron phosphate material to be maintained more stable during subsequent processing and charge-discharge processes.

[0014] In this embodiment, the multiple lamellar structures can further increase the specific surface area and contact area of ​​a single primary particle, which is beneficial to further improve the charge-discharge performance of the positive electrode material prepared therefrom.

[0015] In this embodiment, 2 to 4 sheets are provided in the laminated structure, which is beneficial for taking into account both a larger specific surface area and the stability of a single laminated structure.

[0016] In some embodiments of the present application, the particle size of a single primary particle is 300 nm to 1000 nm; and / or,

[0017] In the laminated structure, the thickness of each of the laminae is 40 nm to 60 nm; and / or,

[0018] In the stacking direction, the maximum distance between two adjacent sheets is 20 nm to 50 nm.

[0019] In this embodiment, the particle size of a single primary particle is within the above range, which is conducive to forming a lamellar structure with larger size and gaps on the surface of the single primary particle, thereby generating a larger specific surface area and contact area.

[0020] In this embodiment, the thickness of the sheet and the maximum distance between two adjacent sheets are within the above ranges, which is beneficial for the iron phosphate material to have both high structural stability and large specific surface area.

[0021] In some embodiments of the present application, the chemical formula of the iron phosphate material is: Fe (1-n) Ti 0.75n PO4, where 0.02≤n≤0.04.

[0022] In this embodiment, the iron phosphate material having this chemical formula has a more regular lattice structure and a higher degree of crystallization, which helps ensure the lattice integrity of the positive electrode material prepared therefrom, thereby enabling the positive electrode material to have better ion mobility.

[0023] In some embodiments of the present application, the specific surface area of ​​the iron phosphate material is 9.4 m 2 / g~14m 2 / g; and / or,

[0024] The D50 particle size of the iron phosphate material is 30 μm to 60 μm; and / or,

[0025] The tap density of the iron phosphate material is 0.9 g / cm 3 ~1.05g / cm 3 .

[0026] In this embodiment, the iron phosphate material having the above-mentioned specific surface area is conducive to making the prepared positive electrode material have better charge-discharge performance.

[0027] In this embodiment, the iron phosphate material having the above-mentioned particle size characteristics is beneficial for improving the electrochemical performance of the positive electrode material prepared therefrom.

[0028] In this embodiment, the iron phosphate material having this tap density has a large specific surface area, and is also beneficial for improving the compaction density of the positive electrode material prepared therefrom.

[0029] In a second aspect, an embodiment of the present application provides a method for preparing an iron phosphate material, which comprises the following steps:

[0030] Providing a mixed solution including ferrous salt, titanium salt and phosphate;

[0031] mixing the mixed solution with a first alkali source to obtain a first slurry;

[0032] adding an oxidant and a second alkali source to the first slurry to obtain a second slurry;

[0033] performing a first solid-liquid separation process on the second slurry to obtain a filter cake;

[0034] mixing the filter cake with a phosphoric acid solution and subjecting the mixture to an aging treatment to obtain a third slurry;

[0035] The third slurry is subjected to a second solid-liquid separation process, dried, and calcined to obtain the iron phosphate material.

[0036] In this embodiment, when the first alkali source is added, ferrous ions and titanium ions can co-precipitate to form a mixed ferrous phosphate precipitate and titanium phosphate precipitate. Subsequently, an oxidant and a second alkali source are added so that the titanium element can be in-situ doped into the ferrous phosphate precipitate during the precipitation process. Then, during the aging process, the amorphous ferrous phosphate precipitate dissolves and recrystallizes to be converted into dihydrate ferric phosphate crystals. During the calcination process, the titanium element doped in the ferrous phosphate causes defects in the lattice, thereby hindering its growth in a specific direction, and the surface of the ferrous phosphate particles splits into multiple sheets arranged in sequence and spaced apart at the top, forming a laminated structure. The ferrous phosphate material in any of the above embodiments can be prepared by the preparation method of this embodiment.

[0037] In some embodiments of the present application, in the mixed solution, the ratio of the amount of iron element to the amount of titanium element is 1:(0.015-0.03); and / or,

[0038] In the mixed solution, the ratio of the amount of iron to the amount of phosphorus is 1:(0.97-1.07); and / or,

[0039] The oxidant includes hydrogen peroxide, and in the process of adding the oxidant and the second alkaline source to the first slurry, the ratio of the amount of hydrogen peroxide in the added hydrogen peroxide to the amount of ferrous ions in the mixed solution is (0.55-0.75):1; and / or,

[0040] The oxidant includes oxygen or compressed air. In the process of adding the oxidant and the second alkali source to the first slurry, the ratio of the amount of oxygen added to the amount of ferrous ions in the mixed solution is (0.275~0.375):1, or the ratio of the amount of oxygen in the added compressed air to the amount of ferrous ions in the mixed solution is (0.275~0.375):1.

[0041] In this embodiment, the above ratio of iron to titanium is selected to ensure that the formed iron phosphate has a good lattice structure during the subsequent deposition process, while allowing the titanium element to be fully doped into the iron phosphate. This further facilitates the formation of larger lamellar structures on the surface of the iron phosphate particles.

[0042] In this embodiment, selecting the above ratio of iron and phosphorus is beneficial to ensure sufficient precipitation of iron and titanium in the subsequent deposition process, thereby improving the utilization rate of iron and titanium.

[0043] In this embodiment, the oxidation product of hydrogen peroxide is only water, so the use of hydrogen peroxide as an oxidant will not substantially mix with impurity elements in the ferric phosphate precipitate, which is conducive to obtaining a relatively pure ferric phosphate precipitate. Further, by controlling the ratio of the amount of hydrogen peroxide to the amount of ferrous ion within the above range, it is possible to avoid introducing too many impurities while ensuring that the ferrous ion is fully oxidized. Oxygen and compressed air are gases, and when the oxidant is selected as oxygen or compressed air, it is also avoided that impurity elements are mixed with the ferric phosphate precipitate, which is conducive to obtaining a relatively pure ferric phosphate precipitate. Accordingly, the amount of oxygen in the oxygen or compressed air is controlled to be within the corresponding range with respect to the ratio of the amount of ferrous ion.

[0044] In some embodiments of the present application, the pH value of the mixed solution is 0.5-1.5; and / or,

[0045] After adding the first alkali source to the mixed solution, controlling the pH value of the formed first slurry to be 2.0-2.5; and / or,

[0046] During the process of adding the oxidant and the second alkaline source to the first slurry, the pH value is controlled to be 2.0-2.5.

[0047] In this embodiment, the mixed solution with a pH value in the above range is highly acidic, which can inhibit the hydrolysis and precipitation of ferrous ions and titanium ions, thereby ensuring that ferrous ions and titanium ions can form a uniformly mixed co-precipitate in the subsequent preparation process.

[0048] In this embodiment, controlling the pH value of the first slurry to 2.0-2.5 is beneficial for controlling the precipitation rate of ferrous and titanium ions to be lower, thereby making the particle size of the ferrous phosphate precipitate and the titanium phosphate precipitate smaller and more uniform, allowing them to be fully mixed during the precipitation process. Furthermore, in the subsequent deposition process, the titanium element can be uniformly doped into the ferrous phosphate precipitate.

[0049] In the embodiment, the pH value of the first slurry is controlled to be 2.0-2.5, the conversion rate of ferrous ions to ferric ions and the precipitation rate of ferric ions are both moderate, which is beneficial to the in-situ doping of titanium into the formed ferric phosphate precipitate in the precipitation process of iron. In addition, in the actual preparation process, when the pH value is too high, magnesium ions and potassium ions and other impurities will be mixed into the ferric phosphate material, thereby negatively affecting the powder resistance and discharge efficiency of the finally prepared positive electrode material.

[0050] In some embodiments of the present application, the step of aging treatment comprises: heating the mixture of the filter cake and the phosphoric acid solution to 85-98℃; and / or,

[0051] In the step of mixing the filter cake with the phosphoric acid solution, the ratio of the amount of substance of phosphoric acid in the phosphoric acid solution to the amount of substance of phosphate in the mixture is (0.1-0.2):1.

[0052] In the embodiment, after the ferric phosphate precipitate is dispersed in the phosphoric acid solution and then heated to 85-98℃, the ferric phosphate is allowed to nucleate and grow again after dissolution, which can fully convert the yellow amorphous ferric phosphate precipitate into white ferric phosphate dihydrate crystals.

[0053] In the embodiment, controlling the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixture within the above range can make the ferric phosphate precipitate fully dissolve while reducing or even avoiding the introduction of anionic impurities due to phosphoric acid. Moreover, when the ratio of the amount of substance of phosphoric acid in the phosphoric acid solution to the amount of substance of phosphate in the mixture is within the above range, the crystal type conversion is more likely to occur and proceed fully.

[0054] In some embodiments of the present application, the step of calcination treatment comprises: calcining the dried material at a temperature of 600-800℃ for 2-3h to form the ferric phosphate material.

[0055] In the embodiment, the above temperature range and heating time are used for calcination treatment, which can fully remove the crystal water in the crystal and promote the nucleation and growth of ferric phosphate again, and the stacking structure is formed on the surface of the particles during the growth process.

[0056] In a third aspect, the present application also provides a positive electrode material, wherein the preparation raw material of the positive electrode material comprises the ferric phosphate material according to any one of the above embodiments, or the preparation raw material of the positive electrode material comprises the ferric phosphate material prepared by the preparation method according to any one of the above embodiments.

[0057] In this embodiment, the iron phosphate material has a laminated structure and a large specific surface area. Accordingly, the positive electrode material prepared using it as raw material also has a large contact area and low internal resistance. The doped titanium ions also help widen the ion channels in the positive electrode material.

[0058] In some embodiments of the present application, the positive electrode material includes one or more of lithium iron phosphate and lithium manganese iron phosphate.

[0059] In a fourth aspect, the present application further provides a positive electrode plate, which includes a current collector and a positive electrode active layer disposed on the current collector, wherein the positive electrode active layer includes the positive electrode material as described in any of the above embodiments.

[0060] In this embodiment, the positive electrode plate includes the above-mentioned positive electrode material, which has a large contact area and a low internal resistance, so the positive electrode plate also has good charge-discharge performance.

[0061] In a fifth aspect, the present application further provides a secondary battery, which includes a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet of the secondary battery is the positive electrode sheet as described in the above embodiment.

[0062] In this embodiment, the secondary battery including the above-mentioned positive electrode sheet can exhibit high charge-discharge efficiency and cycle stability during the charge-discharge process.

[0063] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0065] Figure 1 Schematic diagram of the steps of the preparation method of the iron phosphate material of the present application;

[0066] Figure 2 This is a schematic diagram of the preparation process of the iron phosphate material of this application;

[0067] Figure 3 This is a surface morphology of the iron phosphate material prepared in Example 1;

[0068] Figure 4This is a surface morphology of the iron phosphate material prepared in Comparative Example 1;

[0069] Figure 5 These are X-ray diffraction test results of the iron phosphate materials prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0070] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0072] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0073] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0074] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0075] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0076] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0077] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0078] As analyzed in the background technology of this application, the primary particles of iron phosphate materials in traditional technologies are mostly spherical or flaky, and their actual specific surface areas are relatively low, which also limits the improvement of the specific surface area and contact area of ​​the positive electrode materials prepared therefrom.

[0079] In order to improve the above-mentioned problem, an embodiment of the present application provides an iron phosphate material, which is doped with titanium element, and at least part of the surface of the primary particles of the iron phosphate material is a laminated structure, and the laminated structure has multiple layers, and any two adjacent layers are located on one side of each other in the stacking direction; wherein the stacking direction intersects with the extension direction of the layers.

[0080] In this embodiment, the iron phosphate material is doped with titanium, which causes defects in the iron phosphate material during the crystallization process, hindering the growth of iron phosphate in a specific direction, and is conducive to the formation of a lamellar structure on the surface of the iron phosphate particles. A lamellar structure exists on the surface of the primary particles of the iron phosphate material. Any two adjacent layers of the multiple layers of the lamellar structure are located on one side of each other in the stacking direction. Unlike the traditional disordered flaky iron phosphate material, the lamellar structure forms a short-range ordered morphology, which avoids the situation where the layers are staggered horizontally and vertically to cause space waste, and can significantly improve the specific surface area and contact area of ​​the primary particles. In addition, since the ionic radius of titanium ions is smaller than that of iron ions, the ion channels at the sites occupied by titanium ions are widened. This is also conducive to improving the ion migration efficiency of the positive electrode material prepared therefrom during the charge and discharge process.

[0081] It is understood that a primary particle refers to a single smallest particle formed directly during the chemical synthesis process. Multiple primary particles will form secondary particles after agglomeration. The lamellar structure in the embodiments of the present application is formed directly on the surface of the particles during the synthesis process, so part of the structure of the primary particle acts as a lamellar structure.

[0082] In this embodiment, "any two adjacent layers are located on one side of each other in the stacking direction" means that: among any two adjacent layers, the first layer is located on one side of the second layer in the stacking direction, and the second layer is also located on one side of the first layer in the stacking direction, and the stacking direction and the extension direction of the layers can intersect perpendicularly or obliquely.

[0083] As an example of this embodiment, the surface of the primary particles of the iron phosphate material is split into a lamellar structure. The doped titanium element causes defects in the iron phosphate crystal structure, hindering the growth of the iron phosphate crystal structure in a specific direction, thereby allowing the surface to split into a lamellar structure.

[0084] In this example, the connection between the lamellar structure formed by the splitting of the primary particle surface and the matrix in which it is located is more stable, which is conducive to maintaining the integrity of the structure during subsequent processing, thereby enabling the structure of the iron phosphate material to remain more stable during subsequent processing and charge-discharge processes.

[0085] As an example of this embodiment, the surface of a single primary particle of the iron phosphate material has a plurality of lamellar structures.

[0086] In this example, the multiple lamellar structures can further increase the specific surface area and contact area of ​​a single primary particle, which is beneficial to further improve the charge-discharge performance of the positive electrode material prepared therefrom.

[0087] It is understood that in other examples, the surface of a single primary particle of ferric phosphate material may have only one lamellar structure. Furthermore, although not explicitly limited or described, in other examples, the surface of a primary particle of ferric phosphate material may have one or more disordered lamellar structures in addition to an ordered lamellar structure, or may have multiple lamellar structures distributed in other ordered ways.

[0088] As an example of this embodiment, in a single laminated structure, the number of layers is 2 to 4. For example, in a laminated structure, the number of layers can be 2, 3, or 4, or the number of layers can be between any two of the above numbers.

[0089] In this example, 2 to 4 layers are provided in the laminated structure, which is beneficial for taking into account both a larger specific surface area and the stability of a single laminated structure.

[0090] As an example of this embodiment, the particle size of a single primary particle is 300 nm to 1000 nm. For example, the particle size of a single primary particle is 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm. Alternatively, the particle size of a single primary particle can be between any two of the above particle sizes.

[0091] In this example, the particle size of a single primary particle is within the above range, which is conducive to forming a lamellar structure with larger size and gaps on the surface of the single primary particle, thereby generating a larger specific surface area and contact area.

[0092] As an example of this embodiment, in the laminated structure, the thickness of each layer is 40 nm to 60 nm. For example, the thickness of each layer can be 40 nm, 42 nm, 45 nm, 47 nm, 50 nm, 52 nm, 55 nm, 57 nm, or 60 nm, or the thickness of each layer can be between any two of the above thicknesses.

[0093] It is understood that in this embodiment, two adjacent sheets may be completely separated or at least partially separated. "Completely separated" means that there is no contact between the two adjacent sheets. "At least partially separated" means that the two adjacent sheets are partially in contact with each other and the other parts are separated to form a gap.

[0094] As an example of this embodiment, the distance between two adjacent sheets on the side close to the substrate where they are located is smaller than the distance between two adjacent sheets on the side away from the substrate where they are located.

[0095] As an example of this embodiment, the maximum spacing between two adjacent lamellae in the stacking direction is 20 nm to 50 nm. For example, the maximum spacing between two adjacent lamellae is 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm. Alternatively, the maximum spacing between two adjacent lamellae can be between any two of the above spacings. It will be understood that the spacing between two adjacent lamellae in the stacking direction can be uneven, i.e., the spacing in some areas is larger and in others is smaller. The maximum spacing refers to the maximum distance between two adjacent lamellae in the stacking direction.

[0096] In this example, the thickness of the sheet and the maximum distance between two adjacent sheets are within the above ranges, which is conducive to ensuring that the iron phosphate material has both high structural stability and a large specific surface area.

[0097] As an example of this embodiment, the chemical formula of the iron phosphate material is: Fe (1-n) Ti 0.75nPO4, wherein 0.02≤n≤0.04. For example, in the chemical formula of the iron phosphate material, n can be 0.02, 0.022, 0.024, 0.026, 0.028, 0.03, 0.032, 0.034, 0.036, 0.038, or 0.04, or n can be between any two of the above values.

[0098] In this example, the iron phosphate material having this chemical formula has a more regular lattice structure and a higher degree of crystallization, which helps ensure the lattice integrity of the positive electrode material prepared therefrom, resulting in better ion mobility of the positive electrode material.

[0099] As a further example of this embodiment, in the iron phosphate material, the mass content of the titanium element is 4000 ppm to 10000 ppm. For example, the mass content of the titanium element can be 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, or 10000 ppm, or the mass content of the titanium element can be between any two of the above mass contents.

[0100] In this example, when the mass content of the titanium element is within the above range, it is beneficial to significantly increase the specific surface area of ​​the iron phosphate material while minimizing the negative impact of the introduction of the titanium element on the charge and discharge capacity.

[0101] As a further example of this embodiment, the iron-phosphorus ratio of the ferrous phosphate material is 0.94-0.98, the mass content of the iron element in the ferrous phosphate material is 35.8%-36.4%, and the mass content of the phosphorus element in the ferrous phosphate material is 20.58%-20.64%.

[0102] The higher the titanium content in the iron phosphate material, the lower the iron-to-phosphorus ratio. When the iron-to-phosphorus ratio of the iron phosphate material is controlled within the range of 0.94 to 0.98 and the iron and phosphorus contents are within the above ranges, the iron phosphate material is more suitable as a precursor material for preparing a positive electrode material and ensures that the prepared positive electrode material has good charge-discharge performance. The iron-to-phosphorus ratio of the iron phosphate material is the ratio of the amount of iron to the amount of phosphorus in the iron phosphate material.

[0103] As an example of this embodiment, the specific surface area of ​​the iron phosphate material is 9.4 m 2 / g~14m 2 / g. For example, the specific surface area of ​​iron phosphate material is 9.4m 2 / g, 9.5m 2 / g, 9.6m 2 / g, 9.8m 2 / g、10m 2 / g, 10.5m 2 / g, 11 m 2 / g, 11.5 m 2 / g, 12 m 2 / g, 12.5 m 2 / g, 13 m 2 / g, 13.5 m 2 / g, 14 m 2 / g, or the specific surface area of the iron phosphate material can also be between any two of the above.

[0104] In this embodiment, the iron phosphate material having the above specific surface area is advantageous to make the prepared positive electrode material have better charge-discharge performance.

[0105] As an example of this embodiment, the D50 particle size of the iron phosphate material is 30 μm to 60 μm. For example, the D50 particle size of the iron phosphate material can be 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, or the D50 particle size of the iron phosphate material can also be between any two of the above.

[0106] The D50 particle size refers to the particle size corresponding to the cumulative particle size distribution of the iron phosphate material reaching 50%, and its physical meaning is that the particles with a particle size less than this value account for 50% of the total particles. The D50 particle size can be measured and obtained by a laser particle size instrument.

[0107] In this example, the iron phosphate material having the above particle size characteristics is advantageous to improve the electrochemical performance of the positive electrode material prepared therefrom.

[0108] As an example of this embodiment, the tap density of the iron phosphate material is 0.9 g / cm 3 ~1.05 g / cm 3 . For example, the tap density of the iron phosphate material can be 0.9 g / cm 3 , 0.92 g / cm 3 , 0.94 g / cm 3 , 0.96 g / cm 3 , 0.98 g / cm 3 , 1 g / cm 3 , 1.02 g / cm 3 , 1.04 g / cm 3 , 1.05 g / cm 3 , or the tap density of the iron phosphate material can also be between any two of the above.

[0109] In this example, the iron phosphate material having this tap density itself has a larger specific surface area, and is also advantageous to improve the tap density of the positive electrode material prepared therefrom.

[0110] In a second aspect, the present application also provides a method for preparing an iron phosphate material. Figure 1 Schematic diagram of the steps of the preparation method of the iron phosphate material. Figure 1 As shown, the preparation method includes the following steps S1 to S6.

[0111] Step S1, providing a mixed solution containing dissolved ferrous salt, titanium salt and phosphate.

[0112] As an example of this embodiment, the ferrous salt is selected from a salt that is soluble in water and ionizes ferrous ions. For example, the ferrous salt can be selected from, but is not limited to, any one or more of ferrous sulfate, ferrous chloride, and ferrous oxalate. This ferrous salt has good solubility and low material cost. Moreover, the anions in the ferrous salt are easily removed from the surface of the subsequently formed ferric phosphate, resulting in a low residual amount, which helps to ensure the purity of the ferric phosphate material.

[0113] As an example of this embodiment, the titanium salt is selected from salts that are soluble in water and ionize to produce titanium ions. For example, the titanium salt can be selected from, but is not limited to, any one or more of titanyl sulfate and titanium tetrachloride. This titanium salt has good solubility, and the anions therein are easily removed from the surface of the subsequently formed iron phosphate, resulting in a low residual amount, which helps ensure the purity of the iron phosphate material.

[0114] As an example of this embodiment, titanium salt can also use ilmenite and concentrated sulfuric acid mixed and filtered to obtain the filtrate, in which the mass fraction of titanium element is 7% to 10%, and the mass fraction of sulfate radical is 40% to 50%. For example, the mass fraction of titanium element can be 7.5%, 8%, 8.5%, 9%, 9.5%, or can be any numerical value between 7% and 10%, and the mass fraction of sulfate radical is 42%, 45%, 46%, 48% or any numerical value between 40% and 50%. The mass fraction of H2SO4 in the concentrated sulfuric acid used can be 50% to 60%, for example, 52%, 54%, 55%, 56%, 58%, or can be any numerical value between 50% and 60%.

[0115] As a further example of this embodiment, titanium salt can also be obtained by filtering the filtrate obtained by mixing ilmenite with concentrated sulfuric acid, and further includes iron and other impurity elements, wherein the mass fraction of iron is 3% to 4% (such as 3.1%, 3.25%, 3.35%, 3.5%, 3.65%, 3.95%, etc.), and the impurity elements include Al, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Na, Ni, Pb and Zn, and the content of the impurity elements does not exceed 5000 ppm.

[0116] As an example of the embodiment, the phosphate can be selected from, but not limited to, one or more of monobasic ammonium phosphate, dibasic ammonium phosphate, and sodium hydrogen phosphate. The phosphate has good solubility, and the cation therein is easy to remove from the surface of the subsequently formed iron phosphate, with less residual amount, which is conducive to ensuring the purity of the iron phosphate material.

[0117] As an example of the embodiment, in the mixed solution, the ratio of the amount of substance of the iron element to the amount of substance of the titanium element is 1:(0.015-0.03). For example, the ratio of the amount of substance of the iron element to the amount of substance of the titanium element can be 1:0.015, 1:0.016, 1:0.018, 1:0.02, 1:0.022, 1:0.024, 1:0.026, 1:0.028, 1:0.03, or the ratio of the amount of substance of the iron element to the amount of substance of the titanium element can also be between any two of the above ratios.

[0118] In this example, the above ratio of the iron element to the titanium element is selected, which is conducive to ensuring that the iron phosphate formed has a good lattice structure while enabling the titanium element to be fully doped into the iron phosphate during the subsequent deposition process. This further facilitates the formation of a good laminated structure on the surface of the iron phosphate particles.

[0119] As an example of the embodiment, in the mixed solution, the ratio of the amount of substance of the iron element to the amount of substance of the phosphorus element is 1:(0.97-1.07). For example, the ratio of the amount of substance of the iron element to the amount of substance of the phosphorus element is 1:0.97, 1:0.98, 1:0.99, 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.05, 1:1.07, or the ratio of the amount of substance of the iron element to the amount of substance of the phosphorus element can also be between any two of the above ratios.

[0120] In this example, the above ratio of the iron element to the phosphorus element is selected, which is conducive to ensuring the full precipitation of the iron element and the titanium element during the subsequent deposition process, and improving the utilization rate of the iron element and the titanium element.

[0121] As an example of the embodiment, the amount of substance of the phosphorus element can be correspondingly selected according to the amount of substance of the titanium element. For example, when the amount of substance of the titanium element is high, the amount of substance of the phosphorus element can also be set to be high, and when the amount of substance of the titanium element is low, the amount of substance of the phosphorus element can also be set to be low.

[0122] As an example of this embodiment, the pH value of the mixed solution can be 0.5-1.5 to ensure that the iron and titanium elements can be stably present in the aqueous solution. For example, the pH value of the mixed solution can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5. Alternatively, the pH value of the mixed solution can be between any two of the above pH values.

[0123] It is understood that different salt solutions may have different pH values. Therefore, when forming the mixed solution, a pH adjuster may be added to the mixed solution to control its pH value. The pH adjuster may be selected from, but not limited to, one or more of sulfuric acid, hydrochloric acid, sodium hydroxide, and ammonia water.

[0124] Step S2: mixing the mixed liquid with a first alkali source to obtain a first slurry.

[0125] In this embodiment, the addition of the first alkali source causes the precipitation of ferrous ions and titanium ions, thereby forming ferrous phosphate precipitate and titanium phosphate precipitate in the first slurry.

[0126] It is understood that the first alkali source is used to regulate the pH value of the first slurry formed by the mixed solution, and the amount of the first alkali source can be selected accordingly according to the desired pH value. As an example of this embodiment, after adding the first alkali source to the first mixed solution, the pH value of the first slurry formed is controlled to be 2.0-2.5 to form ferrous phosphate precipitate and titanium phosphate precipitate. For example, the pH value of the first slurry can be controlled to be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or the pH value of the first slurry can be controlled to be between any two of the above pH values.

[0127] In this example, controlling the pH value of the first slurry to 2.0-2.5 is beneficial to controlling the precipitation rate of ferrous ions and titanium ions to be lower, thereby making the particle size of ferrous phosphate precipitate and titanium phosphate precipitate smaller and more uniform, so that the two can be fully mixed during the precipitation process. Furthermore, in the subsequent deposition process, the titanium element can be evenly doped into the ferrous phosphate precipitate. Moreover, in the actual preparation process, when the pH value is too high, impurities such as magnesium ions and potassium ions will be mixed into the ferrous phosphate material, which will have a negative impact on the powder resistance and discharge efficiency of the final prepared positive electrode material.

[0128] It is understood that the pH value of the formed first slurry can be controlled by controlling the amount of the first alkali source added.

[0129] As an example of this embodiment, the alkaline substance in the first alkaline source can be selected from, but not limited to, one or more of ammonia, sodium hydroxide, sodium carbonate, and sodium bicarbonate. The cations of this alkaline substance are easily removed from the surface of the subsequently formed ferric phosphate, resulting in a small amount of residual material, which helps ensure the purity of the ferric phosphate material.

[0130] As an example of this embodiment, the ferrous phosphate precipitate may be ferrous dihydrogen phosphate.

[0131] In this embodiment, ferrous ions and titanium ions are first formed into a co-precipitate before oxidation, which can make the process of forming titanium-doped ferric phosphate precipitate smoother and prevent the subsequent addition of too much second alkali source due to the low pH value of the mixed solution, resulting in the local ferric phosphate precipitate forming too quickly and difficulty in uniform incorporation of the titanium element.

[0132] Step S3: adding an oxidant and a second alkali source to the first slurry to obtain a second slurry.

[0133] In this embodiment, the oxidant is used to oxidize the ferrous phosphate precipitate in the first slurry, thereby forming a ferric phosphate precipitate doped with titanium.

[0134] It can be understood that the second alkaline source is used to regulate the pH value of the first slurry during the oxidation precipitation process, and the amount of the second alkaline source added to the first slurry can be selected accordingly according to the desired pH value. As an example of this embodiment, in the process of adding the oxidant and the second alkaline source to the first slurry, the pH value is controlled to be 2.0~2.5. For example, the pH value in the process of adding the oxidant and the second alkaline source to the first slurry can be controlled to be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or the pH value in the process of adding the oxidant and the second alkaline source to the first slurry can be controlled to be between any two of the above pH values.

[0135] As the reaction between the oxidant and the ferrous phosphate proceeds, the product gradually reduces the pH of the first slurry. The added second alkaline source can be used to maintain the pH during the addition of the oxidant and the second alkaline source to the first slurry, thereby ensuring that the formed iron element is completely precipitated.

[0136] In this example, controlling the pH value during the addition of the oxidant and the second alkaline source to the first slurry to a range of 2.0 to 2.5 moderates the conversion rate of ferrous ions to ferric ions and the precipitation rate of ferric ions. This facilitates the in-situ doping of titanium into the resulting ferric phosphate precipitate during the precipitation of the iron element. Furthermore, in actual preparation processes, excessively high pH values ​​can lead to the incorporation of impurities such as magnesium and potassium ions into the ferric phosphate material, negatively impacting the powder resistance and discharge efficiency of the resulting cathode material.

[0137] As an example of this embodiment, the oxidant is selected from hydrogen peroxide. The oxidation product of hydrogen peroxide is only water, so the use of hydrogen peroxide as the oxidant will basically not mix impurities into the ferric phosphate precipitate, which is conducive to obtaining a relatively pure ferric phosphate precipitate.

[0138] As a further example of this embodiment, the mass fraction of hydrogen peroxide in hydrogen peroxide is 15% to 30%.

[0139] As a further example of this embodiment, during the process of adding the oxidant and the second alkaline source to the first slurry, the ratio of the amount of hydrogen peroxide in the added hydrogen peroxide to the amount of ferrous ions in the mixed solution is (0.55-0.75):1. For example, the ratio of the amount of hydrogen peroxide to the amount of ferrous ions is 0.55:1, 0.57:1, 0.6:1, 0.62:1, 0.65:1, 0.67:1, 0.7:1, 0.72:1, or 0.75:1. Alternatively, the ratio of the amount of hydrogen peroxide to the amount of ferrous ions may be between any two of the above ratios.

[0140] In this example, while excessive amounts of hydrogen peroxide have little impact on the composition and morphology of the resulting iron phosphate material, it can result in some waste of the raw material. However, insufficient amounts of hydrogen peroxide can lead to insufficient oxidation, resulting in a lower purity of the resulting iron phosphate material, further impacting the quality of the subsequently prepared cathode material.

[0141] As an example of this embodiment, the oxidant is selected from oxygen or compressed air.

[0142] As a further example of this embodiment, during the process of adding the oxidant and the second alkaline source to the first slurry, the ratio of the amount of oxygen added to the amount of ferrous ions in the mixed solution is (0.275-0.375): 1. For example, the ratio of the amount of oxygen added to the amount of ferrous ions in the mixed solution can be 0.285:1, 0.295:1, 0.305:1, 0.315:1, 0.325:1, 0.335:1, 0.345:1, 0.355:1, or 0.365:1, or can be any ratio between (0.275-0.375):1.

[0143] As a further example of this embodiment, during the process of adding the oxidant and the second alkaline source to the first slurry, the ratio of the amount of oxygen in the added compressed air to the amount of ferrous ions in the mixed solution is (0.275-0.375): 1. For example, the ratio of the amount of oxygen in the added compressed air to the amount of ferrous ions in the mixed solution can be 0.285:1, 0.295:1, 0.305:1, 0.315:1, 0.325:1, 0.335:1, 0.345:1, 0.355:1, or 0.365:1, or can be any ratio between (0.275-0.375):1.

[0144] In this example, oxygen and compressed air are gases. When oxygen or compressed air is selected as the oxidant, the incorporation of impurities into the ferric phosphate precipitate is also avoided, thereby facilitating the production of a relatively pure ferric phosphate precipitate. Accordingly, controlling the ratio of the amount of oxygen in the oxygen or compressed air to the amount of ferrous ions within a corresponding range facilitates the sufficient oxidation of the ferrous ions.

[0145] As an example of this embodiment, the alkaline substance in the second alkaline source can be selected from, but not limited to, one or more of ammonia water, sodium hydroxide, sodium carbonate, and sodium bicarbonate. The cations of this alkaline substance are easily removed from the surface of the subsequently formed ferric phosphate, resulting in a small amount of residual material, which helps ensure the purity of the ferric phosphate material.

[0146] As a further example of this embodiment, the second alkaline source is the same as the first alkaline source. Using the same first alkaline source and second alkaline source can avoid introducing a variety of different cations as much as possible, which is conducive to ensuring the purity of the ferric phosphate material.

[0147] As an example of this embodiment, the total time for adding the oxidant and the second alkaline source to the first slurry is 20 minutes to 60 minutes. For example, the total time for adding the oxidant and the second alkaline source can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 65 minutes, or the total time can be between any two of the above times.

[0148] In this example, controlling the total time of adding the oxidant and the second alkaline source within the above range is beneficial to controlling the formation process of the iron phosphate precipitate to be more gradual, which is beneficial to improving the uniformity of the distribution of the titanium element in the iron phosphate precipitate.

[0149] As a further example of this embodiment, after the addition of the oxidant and the second alkaline source is completed, the first slurry may be stirred for 30 minutes to 240 minutes. The stirring is continued to allow the reaction of forming the ferric phosphate precipitate to proceed fully.

[0150] Step S4: performing a first solid-liquid separation process on the second slurry to obtain a filter cake.

[0151] As an example of this embodiment, the first solid-liquid separation treatment of the second slurry may be performed by filtration.

[0152] As an example of this embodiment, after the second slurry is subjected to the first solid-liquid separation treatment, the method further includes a step of performing a first rinsing treatment on the iron phosphate precipitate.

[0153] In this example, the first rinsing treatment is used to remove anionic and cationic impurities attached to the surface of the ferric phosphate precipitate to obtain a purer ferric phosphate precipitate, and to reduce impurities inside the subsequently formed ferric phosphate dihydrate crystals, thereby improving the crystal quality.

[0154] As a further example of this embodiment, the step of performing a first rinsing treatment on the ferric phosphate precipitate includes: rinsing the ferric phosphate precipitate with flowing pure water, monitoring the conductivity of the outflowing rinsing water, and stopping the first rinsing treatment when the conductivity of the outflowing rinsing water is lower than a first preset conductivity value. The first preset conductivity value can be set according to actual needs.

[0155] As a further example of this embodiment, the first preset conductivity value may be 2 mS / cm to 10 mS / cm. For example, the first preset conductivity value may be 2 mS / cm, 3 mS / cm, 4 mS / cm, 5 mS / cm, 6 mS / cm, 7 mS / cm, 8 mS / cm, 9 mS / cm, or 10 mS / cm. Alternatively, the first preset conductivity value may be between any two of the above conductivities.

[0156] Step S5: mixing the filter cake with the phosphoric acid solution and subjecting the mixture to aging treatment to obtain a third slurry.

[0157] In this embodiment, after the filter cake is mixed with the phosphoric acid solution, the iron phosphate precipitate in the filter cake is dissolved in the phosphoric acid solution, and then the aging treatment is used to recrystallize the iron phosphate in the solution to form iron phosphate dihydrate crystals.

[0158] As an example of this embodiment, the aging step includes heating the mixture of the filter cake and the phosphoric acid solution to 85°C to 98°C to form ferric phosphate dihydrate crystals. In some examples, the mixture of the filter cake and the phosphoric acid solution can be heated to 85°C, 86°C, 87°C, 88°C, 90°C, 92°C, 94°C, 95°C, 96°C, 97°C, or 98°C, or to any temperature between the foregoing two temperatures.

[0159] In this example, the iron phosphate precipitate is dispersed in a phosphoric acid solution and then heated, allowing the iron phosphate to dissolve and re-nucleate, fully transforming the yellow amorphous iron phosphate precipitate into white iron phosphate dihydrate crystals. Furthermore, impurity ions adhering to the surface of the amorphous iron phosphate can be dissolved in the phosphoric acid solution, reducing the amount of impurities.

[0160] As a further example of this embodiment, after the mixture of the filter cake and the phosphoric acid solution is heated to 85° C. to 98° C., the mixture is kept warm for 3 h to 5 h.

[0161] As an example of this embodiment, the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixed solution is (0.1-0.2):1. For example, the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixed solution can be 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.18:1, 0.2:1, or the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixed solution can also be between any two of the above ratios. It can be understood that the phosphate ions of the phosphate in the mixed solution are substantially completely transferred to the ferric phosphate.

[0162] In this example, controlling the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixed solution within the above range can enable the ferric phosphate to be precipitated while being sufficiently dissolved, and reduce or even avoid the introduction of anionic impurities due to phosphoric acid. Moreover, when the ratio of the amount of substance of phosphoric acid to the amount of substance of phosphate in the mixed solution of the phosphoric acid solution is within the above range, the occurrence and sufficient progress of the crystal form conversion are more conducive.

[0163] As a further example of this embodiment, the pH value of the third slurry can be 1.0-2.0 to ensure that the ferric phosphate can be completely dissolved at room temperature. For example, the pH value of the third slurry can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 1.9, 2.0, or the pH value of the third slurry can also be between any two of the above pH values.

[0164] Step S6, after the second solid-liquid separation treatment of the third slurry, drying, calcination treatment, to obtain a ferric phosphate material.

[0165] In this embodiment, the third slurry is subjected to a second solid-liquid separation treatment to obtain a ferric phosphate dihydrate crystal. The ferric phosphate dihydrate crystal can form the desired ferric phosphate material with a laminated structure after calcination treatment.

[0166] As an example of this embodiment, the third slurry is subjected to a second solid-liquid separation treatment by filtration.

[0167] As an example of this embodiment, after the third slurry is subjected to a second solid-liquid separation treatment, a step of subjecting the ferric phosphate dihydrate crystal to a second rinsing treatment is further included.

[0168] In this example, the second rinsing treatment is used to remove anionic and cationic impurities attached to the surface of the ferric phosphate dihydrate crystal, to as far as possible avoid the influence of impurity ions on the morphology of the ferric phosphate material in the subsequent calcination process.

[0169] As a further example of this embodiment, the step of performing a second rinsing treatment on the ferric phosphate dihydrate crystals includes: rinsing the ferric phosphate dihydrate crystals with flowing pure water, monitoring the conductivity of the outflowing rinsing water, and stopping the second rinsing treatment when the conductivity of the outflowing rinsing water is lower than a second preset conductivity value. The second preset conductivity value can be set according to actual needs.

[0170] As a further example of this embodiment, the second preset conductivity value may be 100 μS / cm to 500 μS / cm. For example, the first preset conductivity value may be 100 μS / cm, 150 μS / cm, 200 μS / cm, 250 μS / cm, 300 μS / cm, 350 μS / cm, 400 μS / cm, 450 μS / cm, or 500 μS / cm. Alternatively, the second preset conductivity value may be between any two of the foregoing conductivities.

[0171] In this embodiment, the drying of the third slurry after the second solid-liquid separation treatment is carried out by drying. The drying temperature can be 80°C to 140°C, and the drying time can be 8 hours to 16 hours. For example, the drying temperature can be 85, 90, 92°C, 95°C, 96°C, 98°C, 100°C, 110°C, 120°C, 130°C, or any temperature between 80°C and 140°C. The drying time can be 9 hours, 10 hours, 12 hours, 15 hours, or any time between 8 hours and 16 hours. The drying can be carried out in an air atmosphere. Furthermore, the content of free water (by mass fraction) in the ferric phosphate dihydrate crystals obtained after drying is less than 1%. Free water is the opposite of crystallization water. Crystallization water refers to water molecules that are bound to ferric phosphate and together form the crystals, while free water refers to water molecules that are not bound to ferric phosphate and remain inside or on the surface of the ferric phosphate dihydrate crystals.

[0172] As an example of this embodiment, the step of calcining the ferric phosphate dihydrate crystals includes: heating the ferric phosphate dihydrate crystals at a temperature of 600° C. to 800° C. for more than 2 hours to form an ferric phosphate material.

[0173] As a further example of this embodiment, the calcination temperature during the calcination process can be 600°C, 620°C, 640°C, 650°C, 680°C, 700°C, 720°C, 740°C, 750°C, 780°C, 800°C, or the calcination temperature during the calcination process can be between any two of the above temperatures.

[0174] As a further example of this embodiment, the calcination time during the calcination process is 2 hours to 3 hours. For example, the calcination time can be 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.5 hours, 2.7 hours, 2.9 hours, or 3 hours, or the calcination time can be between any two of the above times.

[0175] As a further example of this embodiment, the heating rate to the calcination temperature during the calcination process can be 3°C / min to 8°C / min, for example, it can be 4°C / min, 5°C / min, 6°C / min, 7°C / min, or any heating rate between 3°C / min and 8°C / min.

[0176] As a further example of this embodiment, the calcination process may be performed under an air atmosphere.

[0177] In this example, calcining the dihydrate ferric phosphate crystals within the above-mentioned temperature range and heating time can fully remove the crystalline water in the crystals, promote the re-nucleation and growth of the ferric phosphate, and split on the particle surface to form a lamellar structure during the growth process.

[0178] Through the above steps S1 to S6, the iron phosphate material in the present application can be prepared.

[0179] In this embodiment, a ferrous salt solution, a titanium salt solution and a phosphate solution are premixed. When the first alkali source is added, ferrous ions and titanium ions can coprecipitate to form a mixed ferrous phosphate precipitate and a titanium phosphate precipitate. Subsequently, an oxidant and a second alkali source are added so that the titanium element can be in-situ doped into the ferrous phosphate precipitate during the precipitation process. Then, during the aging process, the amorphous ferrous phosphate precipitate dissolves and recrystallizes to be converted into dihydrate ferric phosphate crystals. During the calcination process, the titanium element doped in the ferrous phosphate causes defects in the lattice, thereby hindering its growth in a specific direction, and the surface of the ferrous phosphate particles splits into multiple sheets arranged in sequence and spaced apart at the top, forming a laminated structure. The ferrous phosphate material in any of the above embodiments can be prepared by the preparation method of this embodiment.

[0180] In a third aspect, another embodiment of the present application further provides a positive electrode material, wherein the raw material for preparing the positive electrode material comprises the iron phosphate material as in any of the above embodiments, or the raw material for preparing the positive electrode material comprises the iron phosphate material prepared by the preparation method as in any of the above embodiments.

[0181] In this embodiment, the iron phosphate material has a laminated structure and a large specific surface area. Accordingly, the positive electrode material prepared using it as raw material also has a large contact area and low internal resistance. In addition, the doped titanium ions also help widen the ion channels in the positive electrode material.

[0182] As an example of this embodiment, the positive electrode material includes one or more of lithium iron phosphate and lithium manganese iron phosphate.

[0183] In a fourth aspect, another embodiment of the present application further provides a positive electrode plate, which includes a current collector and a positive electrode active layer disposed on the current collector, and the positive electrode active layer includes the positive electrode material as described in any of the above embodiments.

[0184] In this embodiment, the positive electrode plate includes the above-mentioned positive electrode material, which has a large contact area and a low internal resistance, so the positive electrode plate also has good charge and discharge performance.

[0185] As an example of this embodiment, the positive electrode active layer may further include one or more of a conductive agent and a binder.

[0186] As a further example of this embodiment, in the positive electrode active layer, the conductive agent may be selected from one or more of conductive carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0187] As a further example of this embodiment, in the positive electrode active layer, the binder may be selected from one or more of polyvinyl pyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, and a copolymer of styrene and butadiene.

[0188] In a fifth aspect, another embodiment of the present application further provides a secondary battery, the secondary battery comprising a positive electrode plate and a negative electrode plate, the positive electrode plate of the secondary battery being the positive electrode plate as described in the above embodiment.

[0189] In this embodiment, the secondary battery including the above-mentioned positive electrode sheet can exhibit high charge and discharge efficiency and cycle stability during the charge and discharge process.

[0190] As an example of this embodiment, the negative electrode sheet includes a current collector and a negative electrode active layer disposed on the current collector, and the negative electrode active layer includes a negative electrode active material.

[0191] As a further example of this embodiment, the negative electrode active material includes one or more of graphite, silicon, silicon carbon, metallic lithium, and lithium titanate.

[0192] As a further example of this embodiment, the negative electrode active layer may further include one or more of a conductive agent and a binder.

[0193] As a further example of this embodiment, in the negative electrode active layer, the conductive agent may be selected from one or more of conductive carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0194] As a further example of this embodiment, in the negative electrode active layer, the binder may be selected from one or more of polyvinyl pyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, and a copolymer of styrene and butadiene.

[0195] The application will be described in further detail below with reference to specific examples, which are not to be understood as limiting the scope of the application as claimed.

[0196] Unless otherwise defined, all terms used in the description hereof, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. The terms used herein are for the purpose of describing specific embodiments and are not intended to limit the scope of the present application.

[0197] Some specific examples are listed below, it should be noted that the examples described below are exemplary, only for the purpose of explaining the present application, and can not be understood as limiting the present application. The technical or conditions not specified in the examples are according to the technical or conditions described in the literature in the art or according to the product manual. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by purchase.

[0198] I. Preparation method

[0199] Example 1

[0200] Anhydrous iron phosphate material is prepared by the process flow as shown in Figure 2 , and the specific process is as follows:

[0201] (1) Take ferrous sulfate (FeSO4) solution (mass concentration is 191.77 g / kg, pH value is 2.8), add titanium sulfate (TiOSO4) powder and ammonium dihydrogen phosphate ((NH4)2HPO4) powder to it, stir to dissolve the titanium sulfate powder and ammonium dihydrogen phosphate powder, and prepare a mixed solution for standby. In the mixed solution, the amount-of-substance ratio of iron, phosphorus and titanium is 1:1.02:0.0225, and the pH value of the mixed solution is 1.4.

[0202] (2) Add ammonia water to the mixed solution to raise the pH value of the first mixed solution to 2.20, so that the ferrous ions and titanium ions are converted into ferrous phosphate dihydrate precipitate and titanium phosphate precipitate respectively, and a first slurry is obtained.

[0203] (3) Gradually add hydrogen peroxide and ammonia water to the first slurry, and the overall dropwise adding time is controlled to be 30 min. After the dropwise adding is completed, continue to stir for 1 h to fully react, form a titanium-doped iron phosphate precipitate, and obtain a second slurry. The pH value of the first slurry during the reaction and the second slurry after the reaction is controlled to be 2.15. The amount-of-substance ratio of hydrogen peroxide in the added hydrogen peroxide to the amount of iron in step (1) is 0.65:1.

[0204] (4) After the iron phosphate precipitate is filtered, it is rinsed with pure water until the conductivity of the effluent water after rinsing reaches 5 mS / cm or less, and the rinsing is stopped.

[0205] (5) The rinsed iron phosphate was transferred to a dilute phosphoric acid solution (prepared by a mass ratio of pure water and concentrated phosphoric acid of 93.4:1.85, with a mass concentration of phosphoric acid in the concentrated phosphoric acid of 75%), and stirred thoroughly. The ratio of the amount of phosphoric acid to the amount of ammonium monohydrogen phosphate in step (1) was 0.115:1. The pH value of the formed slurry was 1.55. The mixture was then heated to 95°C and kept warm for 3 h to completely transform the yellow amorphous iron phosphate into white iron phosphate dihydrate crystals, thereby obtaining a third slurry.

[0206] (6) After filtering the third slurry, the ferric phosphate dihydrate crystals are rinsed with pure water until the conductivity of the effluent water after rinsing reaches below 200 μS / cm, and then the slurry is transferred to a 95°C oven and dried in an air atmosphere for 12 hours. After drying, the free water content in the ferric phosphate dihydrate crystals is less than 1 wt%.

[0207] (7) The ferric phosphate dihydrate crystals were crushed and placed in a muffle furnace, heated to 600 °C in an air atmosphere and kept at this temperature for 2 h for calcination, and then naturally cooled to form a white to light yellow ferric phosphate material.

[0208] Example 2

[0209] (1) Take a ferrous chloride (FeCl2) solution (mass concentration of 160.01 L / kg, pH 2.8), add ilmenite and concentrated sulfuric acid, filter the resulting filtrate (mass fraction of titanium 9.98%), and ammonium dihydrogen phosphate (NH4H2PO4) powder. Stir until the titanyl sulfate powder and ammonium dihydrogen phosphate powder are fully dissolved, and prepare a mixed solution for later use. In the mixed solution, the molar ratio of iron, phosphorus, and titanium is 1:1.03:0.03, and the pH of the mixed solution is 0.9.

[0210] (2) Adding sodium hydroxide solution to the mixed solution to increase the pH value of the mixed solution to 2.20, so that the ferrous ions and titanium ions are converted into ferrous dihydrogen phosphate precipitate and titanium phosphate precipitate, respectively, to obtain a first slurry.

[0211] (3) Compressed air and sodium hydroxide solution were gradually added to the first slurry, with the total addition time controlled to be 30 minutes. After the addition was completed, stirring was continued for 1 hour to fully react, forming a precipitate of iron phosphate doped with titanium, thereby obtaining a second slurry. The pH value of the first slurry during the reaction and the second slurry after the reaction was completed was controlled to be 2.15. The ratio of the amount of oxygen in the added air to the amount of iron in step (1) was 0.325:1.

[0212] (4) After filtering the iron phosphate precipitate, rinse it with pure water until the conductivity of the outflow water after rinsing reaches below 5mS / cm. Stop rinsing.

[0213] (5) The rinsed iron phosphate was transferred to a dilute phosphoric acid solution (prepared by a mass ratio of pure water and concentrated phosphoric acid of 93.4:1.85, with a mass concentration of phosphoric acid in the concentrated phosphoric acid of 75%), and stirred thoroughly. The ratio of the amount of phosphoric acid to the amount of ammonium monohydrogen phosphate in step (1) was 0.115:1. The pH value of the formed slurry was 1.55. The mixture was then heated to 98°C and kept warm for 5 hours to completely transform the yellow amorphous iron phosphate into white iron phosphate dihydrate crystals, thereby obtaining a third slurry.

[0214] (6) After filtering the third slurry, the ferric phosphate dihydrate crystals are rinsed with pure water until the conductivity of the effluent water after rinsing reaches below 200 μS / cm, and then the slurry is transferred to a 100°C oven and dried in an air atmosphere for 8 hours. After drying, the free water content in the ferric phosphate dihydrate crystals is less than 1 wt%.

[0215] (7) The ferric phosphate dihydrate crystals were crushed and placed in a muffle furnace, heated to 800 °C in an air atmosphere and kept at this temperature for 2 h for calcination, and then naturally cooled to form a white to light yellow ferric phosphate material.

[0216] Example 3

[0217] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Example 3 and Example 1 is that:

[0218] (1) Add titanium tetrachloride (TiCl4) and sodium monohydrogen phosphate (Na2HPO4) powder to a ferrous sulfate (FeSO4) solution (mass concentration 191.77 g / kg, pH 2.8) and stir until the titanium tetrachloride and sodium monohydrogen phosphate powders are fully dissolved. This mixture is then used as a standby solution. The molar ratio of iron, phosphorus, and titanium in the mixture is 1:1.01:0.015, and the pH of the mixture is 1.4.

[0219] (2) Sodium carbonate is added to the mixed solution to increase the pH value of the mixed solution to 2.20, so that the ferrous ions and titanium ions are converted into ferrous dihydrogen phosphate precipitates and titanium phosphate precipitates, respectively, to obtain a first slurry.

[0220] (3) Gradually add hydrogen peroxide and sodium carbonate to the first slurry, with the total addition time controlled to be 30 minutes. After the addition is completed, continue stirring for 1 hour to fully react to form a precipitate of iron phosphate doped with titanium, thereby obtaining a second slurry. The pH value of the first slurry during the reaction and the second slurry after the reaction is completed is controlled to be 2.15. The ratio of the amount of hydrogen peroxide in the added hydrogen peroxide to the amount of iron in step (1) is 0.65:1.

[0221] (4) After filtering the iron phosphate precipitate, rinse it with pure water until the conductivity of the outflow water after rinsing reaches below 5mS / cm. Stop rinsing.

[0222] (5) The rinsed iron phosphate was transferred to a dilute phosphoric acid solution (prepared by a mass ratio of pure water and concentrated phosphoric acid of 93.4:1.85, with a mass concentration of phosphoric acid in the concentrated phosphoric acid of 75%), and stirred thoroughly. The ratio of the amount of phosphoric acid to the amount of ammonium monohydrogen phosphate in step (1) was 0.115:1. The pH value of the formed slurry was 1.55. The mixture was then heated to 98°C and kept warm for 5 hours to completely transform the yellow amorphous iron phosphate into white iron phosphate dihydrate crystals, thereby obtaining a third slurry.

[0223] (6) After filtering the third slurry, the ferric phosphate dihydrate crystals are rinsed with pure water until the conductivity of the effluent water after rinsing reaches below 200 μS / cm, and then the slurry is transferred to a 90°C oven and dried in an air atmosphere for 16 hours. After drying, the free water content in the ferric phosphate dihydrate crystals is less than 1 wt%.

[0224] (7) The ferric phosphate dihydrate crystals were crushed and placed in a muffle furnace, heated to 700 °C in an air atmosphere and kept at this temperature for 3 h for calcination, and then naturally cooled to form a white to light yellow ferric phosphate material.

[0225] Example 4

[0226] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Example 4 and Example 1 is that in step (1), the molar ratio of iron element, phosphorus element and titanium element is 1:1.043:0.04.

[0227] Example 5

[0228] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Example 5 and Example 1 is that in step (1), the molar ratio of iron element, phosphorus element and titanium element is 1:0.997:0.01.

[0229] Example 6

[0230] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Example 6 and Example 1 is that in step (2), the amount of ammonia water was increased to increase the pH value of the mixed solution to 3.0, which was used as the first slurry.

[0231] Example 7

[0232] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Example 7 and Example 1 is that in step (3), the amount of ammonia water was increased, and the pH value of the first slurry during the reaction and the pH value of the second slurry after the reaction was controlled to be 3.0.

[0233] Comparative Example 1

[0234] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Comparative Example 1 and Example 1 is that in step (1), no titanium salt was added, and the molar ratio of iron element to phosphorus element was 1:1.4.

[0235] Comparative Example 2

[0236] Anhydrous ferric phosphate was prepared according to the method in Example 1. The difference between Comparative Example 2 and Example 1 is that after step (4), the rinsed ferric phosphate precipitate was directly placed in a muffle furnace, heated to 600°C and kept warm for 2 hours, calcined, and then naturally cooled.

[0237] 2. Test Method

[0238] 1. Titanium content detection

[0239] The titanium content in the iron phosphate materials prepared in each embodiment and comparative example was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES). The test results are shown in Table 1 below.

[0240] 2. Macro performance parameter test of iron phosphate material

[0241] BET specific surface area test: The specific surface area of ​​the iron phosphate materials prepared in each embodiment and comparative example was tested using the gas adsorption BET method. The test results are shown in Table 1 below.

[0242] Particle size: The D50 particle size of the ferric phosphate materials prepared in each embodiment and comparative example was measured by a laser particle size analyzer. The test results are shown in Table 1 below.

[0243] Determination of iron content: Under acidic conditions, most of the Fe in the sample solution was removed with stannous chloride. 3+ Reduction to Fe 2+ If necessary, add hydrogen peroxide to eliminate excess Sn 2+ Using sodium tungstate solution as an indicator, titanium trichloride was used to further convert Fe 3+ Reduction to Fe 2+The excess titanium trichloride was then reacted with potassium dichromate solution. Finally, the divalent iron was titrated with a standard potassium dichromate solution to determine the iron content. The iron content in the ferric phosphate materials prepared in each embodiment and comparative example is shown in Table 1 below.

[0244] Phosphorus content was determined using the quinoline molybdate gravimetric method. Under acidic conditions, orthophosphate reacts with the quinoline molybdate precipitant to form a yellow quinoline phosphomolybdate precipitate. The precipitate was filtered, washed, dried, and weighed, and the phosphorus content was calculated. The phosphorus content of the iron phosphate materials prepared in the Examples and Comparative Examples is shown in Table 1 below.

[0245] The iron-phosphorus ratio (Fe / P) is obtained by calculating the ratio of the molar number of iron element to the molar number of phosphorus element in the iron phosphate material. The results are shown in Table 1 below.

[0246] Tap density measurement: The tap density of each embodiment and comparative example was measured using a tap density meter.

[0247] 3. Crystal form and morphology test of iron phosphate materials

[0248] The surface morphologies of the iron phosphate materials of Example 1 and Comparative Example 1 were observed using a scanning electron microscope. The schematic diagrams of the surface morphologies of Example 1 and Comparative Example 1 are shown in FIG. Figure 3 and Figure 4 Shown.

[0249] The iron phosphate materials prepared in Example 1 and Comparative Example 1 were characterized by XRD using an X-ray powder diffractometer (XRD). Figure 5 shown. Figure 5 The peak position diagram at the bottom is a schematic diagram of the diffraction peak of standard iron phosphate.

[0250] 4. Application performance test of iron phosphate materials

[0251] First, the iron phosphate and lithium source (lithium carbonate) prepared in the above embodiments and comparative examples are sintered to obtain the corresponding lithium iron phosphate positive electrode material.

[0252] The compaction density of the lithium iron phosphate cathode materials prepared in each embodiment and comparative example was tested using a compaction density meter with a test pressure of 3T and a pressing time of 30S. The results can be seen in Table 2.

[0253] The powder resistivity of the lithium iron phosphate positive electrode materials prepared in each embodiment and comparative example was tested using a four-probe method at a pressure of 10 MPa. The results are shown in Table 2.

[0254] The lithium iron phosphate positive electrode material prepared in each example and comparative example was mixed with conductive carbon powder and PVDF binder in a mass ratio of 90:5:5, homogenized, coated on an aluminum foil, dried at 100°C, then rolled by a roll machine, and then punched into a 14mm diameter electrode sheet. The mass of the active material was obtained by weighing and deducting the mass of the aluminum foil. After drying the positive electrode sheet, a CR2032 button half cell was assembled in a UNlab type inert gas primary box of Braun Company in Germany. The button half cell was assembled in the order of negative electrode shell, lithium sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, spring, and positive electrode shell. The CR2032 button half cell was tested for charge-discharge electrochemical performance by using a Wuhan LanDian CT2001A type battery test system, and the voltage range was 2.0-4.6V. The test results are shown in Table 2.

[0255] Table 1

[0256]

[0257] Titanium element was not added to the initial mixture of Comparative Example 1, and titanium element was added to the initial mixture of Example 1. Referring to the content shown in Figure 4 , the lithium iron phosphate material prepared in Comparative Example 1 has an irregular granular shape, and each single particle is a primary particle. Referring to the content shown in Figure 3 , compared with Comparative Example 1, the lithium iron phosphate material prepared in Example 1 further has a plurality of laminated structures on the surface of the primary particle. Further, according to Figure 3 , the laminated structure generally includes 2-4 layers. The laminated structure is formed by splitting the original granular surface. The thickness of each single layer is between 40nm and 60nm, the particle size of each single primary particle is between 300nm and 1000nm, and the maximum distance between adjacent two layers is between 20nm and 50nm. The lithium iron phosphate materials prepared in Examples 2-7 have similar morphologies.

[0258] Referring to the content shown in Figure 5 , the lithium iron phosphate materials prepared in Example 1 and Comparative Example 1 have basically the same diffraction peak type, which indicates that the introduction of a small amount of titanium ions does not significantly change the phase characteristics of the lithium iron phosphate material. Compared with the diffraction peak type of Comparative Example 1, the diffraction peak type of Example 1 is slightly shifted to the left as a whole, which is mainly because the radius of titanium atom is smaller than that of iron atom, and the doping of titanium atom increases the interplanar spacing, and accordingly the incident angle corresponding to the diffraction peak is also reduced.

[0259] The main difference between Examples 1 to 5 lies in the relative contents of titanium and phosphorus in the mixed solution. Among them, the relative content of titanium in Example 1 is 0.0225, the relative content of titanium in Example 2 is 0.03, the relative content of titanium in Example 3 is 0.015, the relative content of titanium in Example 4 is 0.04, and the relative content of titanium in Example 5 is 0.01. The main difference between Examples 6 and 7 and Example 1 lies in the control of pH value in steps (2) and (3). As shown in Table 1, compared with Comparative Example 1, Examples 1 to 7 have shown varying degrees of improvement in specific surface area while the tap density remains basically unchanged, which is conducive to the subsequent preparation of positive electrode materials with both low internal resistance and high specific surface area.

[0260] In addition, compared to Comparative Example 1, although titanium was added to the mixed solution in Comparative Example 2, the amorphous iron phosphate precipitate was not first converted into iron phosphate dihydrate crystals during the subsequent preparation process, and calcination was performed directly. The iron phosphate material was formed based on the amorphous iron phosphate precipitate. This resulted in larger particles of the formed iron phosphate material and failed to split into a laminated structure. Accordingly, the tap density and specific surface area of ​​Comparative Example 2 were also low.

[0261] Table 2

[0262]

[0263] As shown in Tables 1 and 2, Comparative Example 1 was not doped with titanium, and its iron phosphate material did not have a laminated structure. The powder resistance of the lithium iron phosphate material prepared therefrom was 33.3Ω. During the charge-discharge process, it only exhibited a discharge efficiency of 96.3%.

[0264] Combined with Table 1 and Table 2, it can be seen based on Example 1, Example 2 and Example 4 that with the increase of titanium element in the iron phosphate material, although the specific surface area of ​​the iron phosphate material also increases and the powder resistance of the prepared lithium iron phosphate material decreases, the charge and discharge efficiency shows a trend of first increasing and then decreasing. This is mainly because the excessive addition of titanium element occupies the site of the iron element, resulting in a decrease in the discharge specific capacity of the prepared lithium iron phosphate material itself. Based on Example 1, Example 3 and Example 5, it can be seen that with the decrease of titanium element in the iron phosphate material, the specific surface area of ​​the lithium iron phosphate material shows a small decrease, the powder resistance of the prepared lithium iron phosphate material also increases a small amount, and accordingly its charge and discharge efficiency also decreases. It shows that when the amount of titanium element doping is too much or too little, it will have a certain negative impact on the charge-discharge efficiency of the prepared lithium iron phosphate material.

[0265] As shown in Tables 1 and 2, the lithium iron phosphate materials prepared in Examples 6 and 7 have significantly higher internal resistance and significantly lower charge and discharge efficiency compared to Example 1. This is primarily due to the use of a higher pH value during the preparation of the iron phosphate materials, which in turn results in higher levels of impurities such as magnesium salts and potassium salts in the iron phosphate materials.

[0266] As shown in Tables 1 and 2, despite titanium doping in Comparative Example 2, the internal resistance of the lithium iron phosphate powder prepared was significantly higher, even higher than that of Comparative Example 1. This was primarily because Comparative Example 2 was not recrystallized in a phosphoric acid solution to form neat iron phosphate dihydrate before subsequent calcination. This resulted in uneven size of the resulting lithium iron phosphate particles, significantly reducing charge and discharge performance.

[0267] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An iron phosphate material, characterized in that: The iron phosphate material is doped with titanium, and at least a portion of the surface of the primary particles of the iron phosphate material is in a lamellar structure. The surface of the primary particles of the iron phosphate material is split into the lamellar structure, and the lamellar structure is connected to the matrix in which it is located. The lamellar structure has multiple layers, and any two adjacent layers are located on one side of each other in the stacking direction. wherein the stacking direction intersects with the extending direction of the sheet layers; The specific surface area of ​​the iron phosphate material is 9.4 m 2 / g~14m 2 / g.

2. The iron phosphate material according to claim 1, characterized in that The surface of a single primary particle of the ferric phosphate material has a plurality of the lamellar structures; and / or, In a single laminated structure, the number of the laminae is 2 to 4.

3. The iron phosphate material according to claim 1, characterized in that The particle size of a single primary particle is 300 nm to 1000 nm; and / or, In the laminated structure, the thickness of each of the laminae is 40 nm to 60 nm; and / or, In the stacking direction, the maximum distance between two adjacent sheets is 20 nm to 50 nm.

4. The iron phosphate material according to any one of claims 1 to 3, characterized in that The chemical formula of the iron phosphate material is: Fe (1-n) Ti 0.75n PO4, where 0.02≤n≤0.

04.

5. The iron phosphate material according to any one of claims 1 to 3, characterized in that The D50 particle size of the iron phosphate material is 30 μm to 60 μm; and / or, The tap density of the iron phosphate material is 0.9 g / cm 3 ~1.05g / cm 3 .

6. A method for preparing an iron phosphate material, characterized in that: The following steps are involved: Providing a mixed solution including ferrous salt, titanium salt and phosphate; mixing the mixed solution with a first alkali source to obtain a first slurry; adding an oxidant and a second alkali source to the first slurry to obtain a second slurry; performing a first solid-liquid separation process on the second slurry to obtain a filter cake; mixing the filter cake with a phosphoric acid solution and subjecting the mixture to an aging treatment to obtain a third slurry; performing a second solid-liquid separation process on the third slurry, drying the slurry, and calcining the slurry to obtain the iron phosphate material; The iron phosphate material is doped with titanium, and at least part of the surface of the primary particles of the iron phosphate material presents a lamellar structure. The surface of the primary particles of the iron phosphate material is split into the lamellar structure, and the lamellar structure is connected to the matrix in which it is located. The lamellar structure has multiple layers, and any two adjacent layers are located on one side of each other in a stacking direction; the stacking direction intersects with the extension direction of the layers. The specific surface area of ​​the iron phosphate material is 9.4 m 2 / g~14m 2 / g.

7. The method for preparing the iron phosphate material according to claim 6, wherein: In the mixed solution, the ratio of the amount of iron element to the amount of titanium element is 1:(0.015-0.03); and / or, In the mixed solution, the ratio of the amount of iron to the amount of phosphorus is 1:(0.97-1.07); and / or, The oxidant includes hydrogen peroxide, and in the process of adding the oxidant and the second alkaline source to the first slurry, the ratio of the amount of hydrogen peroxide in the added hydrogen peroxide to the amount of ferrous ions in the mixed solution is (0.55-0.75):1; and / or, The oxidant includes oxygen or compressed air. In the process of adding the oxidant and the second alkali source to the first slurry, the ratio of the amount of oxygen added to the amount of ferrous ions in the mixed solution is (0.275~0.375):1, or the ratio of the amount of oxygen in the added compressed air to the amount of ferrous ions in the mixed solution is (0.275~0.375):

1.

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 mixed solution is 0.5-1.5; and / or, After adding the first alkali source to the mixed solution, controlling the pH value of the formed first slurry to be 2.0-2.5; and / or, During the process of adding the oxidant and the second alkaline source to the first slurry, the pH value is controlled to be 2.0-2.

5.

9. The method for preparing the iron phosphate material according to any one of claims 6 to 7, characterized in that: The aging step includes: heating the mixture of the filter cake and the phosphoric acid solution to 85° C. to 98° C.; and / or, In the step of mixing the filter cake with the phosphoric acid solution, the ratio of the amount of phosphoric acid in the phosphoric acid solution to the amount of phosphate in the mixed solution is (0.1-0.2):

1.

10. The method for preparing the iron phosphate material according to any one of claims 6 to 7, characterized in that: The calcination step includes: calcining the dried material at a temperature of 600° C. to 800° C. for 2 h to 3 h to form the iron phosphate material.

11. A positive electrode material, characterized in that The raw material for preparing the positive electrode material comprises the iron phosphate material according to any one of claims 1 to 5, or the raw material for preparing the positive electrode material comprises the iron phosphate material prepared by the preparation method according to any one of claims 6 to 10.

12. A positive electrode plate, characterized in that: The positive electrode sheet includes a current collector and a positive electrode active layer disposed on the current collector, and the positive electrode active layer includes the positive electrode material according to claim 11.

13. A secondary battery, characterized in that: The secondary battery includes a positive electrode sheet and a negative electrode sheet, and the positive electrode sheet of the secondary battery is the positive electrode sheet as claimed in claim 12.

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