Anhydrous iron phosphate material as well as preparation method and application thereof

Abstract

The invention provides an anhydrous iron phosphate material and a preparation method and application thereof, and belongs to the technical field of lithium batteries, the BET of the anhydrous iron phosphate material is 10.37-1456 m / g, and the total amount of impurity elements of Cr, Cu, Ni, Pb and Zn contained in the anhydrous iron phosphate material is less than or equal to 60 ppm. The anhydrous iron phosphate provided by the invention is relatively high in BET and low in impurity content, and is beneficial to preparation of a positive electrode material with relatively good electrochemical performance, so that a positive electrode plate and a secondary battery with relatively good electrochemical performance are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate batteries, and in particular to an anhydrous iron phosphate material and a preparation method and application thereof. Background Art

[0002] As the main raw material for preparing lithium iron phosphate batteries, iron phosphate can be used in new energy vehicles, so it has attracted much attention from relevant technical personnel in the new energy field. At present, the main preparation method of iron phosphate is to directly mix ferrous sulfate solution, phosphate solution, and oxidant to form iron phosphate precipitation, and then obtain iron phosphate products through subsequent treatment. This process is relatively mature. However, this method will result in a high impurity content in the final product and a low specific surface area of ​​the material due to the inability to effectively remove impurities during the preparation of iron phosphate, resulting in poor electrochemical performance of the prepared positive electrode material.

[0003] Therefore, it is necessary to provide a new method for preparing iron phosphate, so that the specific surface area of ​​the prepared iron phosphate material is increased while reducing the impurity content. Summary of the invention

[0004] In view of the technical problems existing in the background technology, the present application provides an anhydrous iron phosphate material and a preparation method and application thereof, aiming to solve the technical problem of how to increase the specific surface area of ​​iron phosphate while reducing the impurity content.

[0005] In the first aspect, the embodiments of the present application provide an anhydrous iron phosphate material, the BET value range of which is 10.37-14.56m² / g; wherein the total amount of impurity elements Cr, Cu, Ni, Pb, and Zn is ≤60ppm.

[0006] In the technical solution of the embodiment of the present application, the anhydrous ferric phosphate provided has a large specific surface area and high purity, which is beneficial to improving the reaction activity of the anhydrous ferric phosphate and further improving the electrochemical performance of the positive electrode material prepared using the anhydrous ferric phosphate.

[0007] In a second aspect, the present invention provides a method for preparing anhydrous ferric phosphate material, comprising the following steps: The ammonium phosphate solution is mixed with the ferrous solution, and the pH range of the mixed solution is controlled to be 3-4.5, and a first slurry containing ferrous phosphate precipitate is obtained through reaction; an oxidant is added to the first slurry for primary oxidation, and then filtering and washing are performed once to obtain a first filter cake; phosphoric acid and water are added to the first filter cake for slurrying, and then an oxidant is added for secondary oxidation to obtain a second slurry; the second slurry is heated and aged, and then filtering and washing are performed twice to obtain a second filter cake; the second filter cake is dried and sintered to obtain anhydrous iron phosphate material.

[0008] In the technical scheme of the embodiment of the present application, a ferrous phosphate precipitate is first formed, and the ferrous phosphate particle structure is oxidized, and the ferrous phosphate particles are converted into ferrous phosphate particles by utilizing the solid-state characteristics of the ferrous phosphate particles, and the crystal structure is reorganized and the crystal form is transformed, so that the ferrous phosphate particles are agglomerated and the specific surface area is increased; the steps of primary oxidation-slurrying-secondary oxidation are adopted to overcome the defects that the ferrous phosphate particles cannot be completely oxidized due to the solid state and the impurities are precipitated and coated, and the impurity content of the iron phosphate is reduced, and it is conducive to the stable growth of the crystal to increase the specific surface area of ​​the iron phosphate. At the same time, the washing step after the primary oxidation is also conducive to the reduction of impurities; and then through aging, secondary washing, drying, and sintering, the impurities of the iron phosphate are further reduced and the phase change is carried out to obtain battery-grade iron phosphate. Therefore, the anhydrous iron phosphate material obtained in the present application has the advantages of large specific surface area and low impurity content.

[0009] In some embodiments, the oxidant includes at least one of oxygen, ozone, and hydrogen peroxide; and / or, the time for the first oxidation is 20-30 minutes, and the time for the second oxidation is 10-15 minutes.

[0010] In this embodiment, the object of the first oxidation is the first slurry containing ferrous phosphate precipitate, and the object of the second oxidation is the slurry after slurrying. The unoxidized ferrous phosphate particles after slurrying are more dispersed and easy to oxidize. Therefore, the time of the first oxidation is longer than the time of the second oxidation to achieve full oxidation of ferrous ions without excessively extending the reaction time, thereby further increasing the specific surface area of ​​ferric phosphate and reducing the impurity content of ferric phosphate.

[0011] In some embodiments, the endpoint conductivity of the washing water used for the first filtration washing is lower than 4 mS / cm, and the endpoint conductivity of the washing water used for the second filtration washing is lower than 0.5 mS / cm; and / or, the washing water used for the first filtration washing and the washing water used for the second filtration washing are both pure water.

[0012] In this embodiment, the purpose of the first washing and the second washing is to reduce the impurity content. The lower the endpoint conductivity is, the less the impurity content is.

[0013] In some embodiments, the ammonium phosphate salt solution includes at least monoammonium hydrogen phosphate, diammonium phosphate, phosphoric acid, and ammonia water, and the pH range of the ammonium phosphate salt solution is 6-8; and / or, the ferrous solution includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate, and the pH range of the ferrous solution is 3-4; and / or, the molar ratio of the iron element in the ferrous solution to the phosphorus element in the ammonium phosphate salt is (1-1.2):1.

[0014] In this embodiment, the ammonium phosphate salt provides phosphate ions and ammonium ions, and the ferrous solution provides ferrous ions to form a ferrous phosphate precipitate. Under the pH value limit of the ammonium phosphate salt, the concentration of the ammonium phosphate salt can be controlled. Under the pH value limit of the ferrous solution, the concentration of ferrous ions can be controlled and the oxidation of ferrous ions can be inhibited.

[0015] In some embodiments, the molar ratio of the oxidant used in the first oxidation to the ferrous ions in the ferrous solution is (0.6-0.8):1, and the molar ratio of the oxidant used in the second oxidation to the oxidant used in the first oxidation is (0.1-0.2):1.

[0016] In this embodiment, sufficient oxidation of ferrous iron is achieved by limiting the amount of oxidant used in the primary oxidation and the secondary oxidation without increasing the cost.

[0017] In some embodiments, the aging temperature is 90-100°C; and / or the drying temperature is 80-120°C, and the sintering temperature is 540-580°C.

[0018] In this embodiment, if the aging temperature is too high, the quality of iron phosphate will not be significantly improved, but a large amount of energy consumption costs will be increased; if the aging temperature is too low, the iron phosphate will not be fully aged, the crystallinity will be reduced, and the use requirements of battery-grade iron phosphate will not be met.

[0019] Furthermore, in this embodiment, free water in the second filter cake is removed by drying, and bound water of iron phosphate in the filter cake is removed by sintering, thereby finally obtaining anhydrous iron phosphate.

[0020] In a third aspect, an embodiment of the present application provides a positive electrode material, which is prepared using the aforementioned anhydrous iron phosphate material, or is prepared using the anhydrous iron phosphate material prepared using the aforementioned method for preparing the anhydrous iron phosphate material.

[0021] In this embodiment, the positive electrode material is prepared using the above-mentioned anhydrous iron phosphate as a precursor. Since anhydrous iron phosphate has the characteristics of large specific surface area and low impurity content, the obtained positive electrode material is beneficial to improving the cycle performance and energy density of the battery.

[0022] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, comprising the aforementioned positive electrode material.

[0023] In this embodiment, the positive electrode plate includes the above-mentioned positive electrode material, and thus the obtained positive electrode plate also has better electrochemical performance.

[0024] In a fifth aspect, an embodiment of the present application provides a secondary battery, comprising the aforementioned positive electrode plate.

[0025] In this embodiment, the secondary battery includes the above-mentioned positive electrode plate, and thus also has better electrochemical performance.

[0026] 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. DETAILED DESCRIPTION

[0027] The following is a detailed description of the embodiments of the technical solution of the present application. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field 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" in the specification and claims of this application and the above description and any variations thereof are intended to cover non-exclusive inclusions.

[0029] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0030] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0031] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0032] 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).

[0033] 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. indicate orientations or positional relationships based on the orientations or positional relationships shown, 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0034] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0035] In the related art, the main preparation method of iron phosphate is to directly mix ferrous sulfate solution, phosphate solution and oxidant to form iron phosphate precipitation, and then obtain iron phosphate product through subsequent treatment. This process is relatively mature. However, this method will cause the impurities in the preparation process of iron phosphate to be unable to be effectively removed, resulting in a high impurity content in the final product and a low specific surface area of ​​the material, which leads to poor electrochemical performance of the prepared positive electrode material.

[0036] In order to solve the technical problem of increasing the specific surface area of ​​iron phosphate while reducing the impurity content, the present application provides an anhydrous iron phosphate material and its preparation method and application, wherein the provided anhydrous iron phosphate material has a high specific surface area and a low impurity content, and when it is applied to a positive electrode sheet or a secondary battery, the electrochemical performance of the positive electrode sheet or the secondary battery can be improved.

[0037] In the first aspect, the embodiments of the present application provide an anhydrous iron phosphate material, the BET value range of which is 10.37-14.56m² / g; wherein the total amount of impurity elements Cr, Cu, Ni, Pb, and Zn is ≤60ppm.

[0038] In the technical solution of the embodiment of the present application, the anhydrous iron phosphate provided has a large specific surface area and high purity, which is beneficial to improving the reaction activity of the anhydrous iron phosphate and ultimately improving the electrochemical performance of the positive electrode material prepared using the anhydrous iron phosphate of the present application.

[0039] In a second aspect, the present invention provides a method for preparing anhydrous ferric phosphate material, comprising the following steps: S1, mixing the ammonium phosphate solution and the ferrous solution, and controlling the pH range of the mixed solution to be 3-4.5, and obtaining a first slurry containing ferrous phosphate precipitate through reaction; S2, adding an oxidant to the first slurry for primary oxidation, and then filtering and washing once to obtain a first filter cake; S3, adding phosphoric acid and water to the first filter cake for slurrying, and then adding an oxidant for secondary oxidation to obtain a second slurry; S4, heating the second slurry for aging, and then filtering and washing it twice to obtain a second filter cake; S5. Drying and sintering the second filter cake to obtain anhydrous ferric phosphate material.

[0040] In the technical scheme of the embodiment of the present application, a ferrous phosphate precipitate is first formed, and the ferrous phosphate particle structure is oxidized, and the ferrous phosphate particles are converted into iron phosphate particles by utilizing the solid-state characteristics of the ferrous phosphate particles, and the crystal structure is reorganized and the crystal form is transformed, so that the iron phosphate particles are agglomerated and the specific surface area is increased; the steps of primary oxidation-slurrying-secondary oxidation are adopted to overcome the defects that the ferrous phosphate particles cannot be completely oxidized due to the solid state and the impurities are precipitated and coated, and the impurity content of iron phosphate is reduced, and it is also conducive to the stable growth of crystals to increase the specific surface area of ​​iron phosphate. At the same time, the washing step after the primary oxidation is also conducive to the reduction of impurities; and then through aging, secondary washing, drying, and sintering, the impurities of iron phosphate are further reduced and a phase change is performed to obtain battery-grade iron phosphate. Therefore, the anhydrous iron phosphate material obtained in the present application has the advantages of large specific surface area and low impurity content.

[0041] Specifically, the reaction process and mechanism of the present application are as follows: The ammonium phosphate solution and the ferrous salt solution react under the condition of pH range of 3-4.5 to obtain a first slurry containing ferrous phosphate precipitate, wherein the ferrous phosphate precipitate includes ferrous phosphate octahydrate, ferrous hydrogen phosphate coated with ferrous phosphate octahydrate and impurities; wherein, when the pH value is lower than 3, the precipitation rate will be reduced, the reaction efficiency will be reduced and the crystallinity of the microcrystals will be deteriorated, resulting in no ferrous phosphate or ferrous phosphate existing in the solution in an ionic state, and compared with the oxidized ferrous phosphate precipitate, the oxidized ferrous phosphate in an ionic state will cause the disadvantage of reduced BET; when the pH value is higher than 4.5, it means that too much phosphorus source is added, which will affect the reaction system during subsequent aging, resulting in poor crystal transformation effect, and then leading to the negative effects of reduced specific surface area of ​​the prepared iron phosphate and increased impurity content.

[0042] Further, in the present application, by carrying out a primary oxidation to the first slurry, the ferrous phosphate precipitate is partially oxidized, and a preliminary impurity removal treatment is carried out by a filtering and washing to obtain the first filter cake, the first filter cake includes ferrous phosphate, ferrous phosphate and impurities; thereafter, phosphoric acid is used to pulp the first filter cake, so that the coated ferrous salt is dispersed in the slurry, an oxidant is added for secondary oxidation, and the complete oxidation of the ferrous phosphate precipitate is achieved to obtain the second slurry, the second slurry includes ferrous phosphate and water; in the process, the purpose of the primary oxidation is to partially oxidize the ferrous phosphate, but the ferrous phosphate coated inside cannot be oxidized, so it is necessary to disperse the ferrous phosphate coated inside into the slurry after pulping, and then oxidize the remaining unoxidized divalent iron by secondary oxidation, and finally achieve the purpose of fully oxidizing the ferrous phosphate precipitate. If in the process, only one oxidation is used, the oxidation is insufficient, and only secondary oxidation is used, which is not conducive to the aging crystal transformation, and the specific surface area of ​​ferrous phosphate is further increased. Therefore, the advantage of adding phosphoric acid for slurrying and then performing secondary oxidation is that during slurrying, phosphoric acid reduces the pH of the slurry to a stable and appropriate level, and can allow the divalent iron that was not completely precipitated during the previous oxidation reaction to continue to undergo oxidation reaction, thereby improving the overall reaction efficiency. At the same time, it can also allow the crystals to grow stably on the original basis, which is beneficial to increasing the specific surface area of ​​the iron phosphate, and is also beneficial to preventing impurities from being coated in the precipitated particles, thereby reducing the impurity content of the iron phosphate.

[0043] Furthermore, in the present application, the second slurry is aged, and the iron phosphate and water are phase-changed to obtain a more stable dihydrate iron phosphate. After removing soluble impurities through secondary washing, the free water in the second filter cake is removed by drying, and then sintering is performed to obtain battery-grade anhydrous iron phosphate.

[0044] Furthermore, in some embodiments, the oxidant includes at least one of oxygen, ozone, and hydrogen peroxide; and / or, the time for the first oxidation is 20-30 minutes, and the time for the second oxidation is 10-15 minutes.

[0045] In the technical scheme of the embodiment of the present application, the object of the primary oxidation is the first slurry containing the precipitation of ferrous phosphate, and the object of the secondary oxidation is the slurry after slurrying. The unoxidized ferrous phosphate particles after slurrying are more dispersed and easy to oxidize. Therefore, the duration of the primary oxidation is longer than the duration of the secondary oxidation to achieve full oxidation of ferrous ions, and the reaction time will not be excessively extended. On the other hand, since the actual growth time of the crystallites will affect the particle structure, the extension of the oxidation time is conducive to the reorganization of the primary particle structure to fill in the particle gap, the particles agglomerate, and increase the specific surface area of ​​ferric phosphate. However, the excessive oxidation time aggravates the particle agglomeration phenomenon, reduces the original crystal gap, and reduces the specific surface area of ​​ferric phosphate. Therefore, the present application controls the duration of the segmented oxidation under the premise of ensuring full oxidation through the secondary oxidation, which can further improve the specific surface area of ​​ferric phosphate and reduce the impurity content of ferric phosphate.

[0046] Furthermore, in some embodiments, the time for adding the ammonium phosphate salt solution to the ferrous solution is 45-55 minutes.

[0047] In the technical solution of the embodiment of the present application, the addition rate of ammonium phosphate will affect the nucleation rate of ferrous phosphate, and then affect the specific surface area of ​​ferric phosphate. If the speed is too fast, the specific surface area will be small, and some impurities will be coated in the precipitated particles, resulting in a high impurity content. If the speed is too slow, the specific surface area will also be small, the quality of anhydrous ferric phosphate cannot be optimized, and the corresponding energy consumption will increase.

[0048] Furthermore, in some embodiments, the endpoint conductivity of the washing water used for the first filtration washing is lower than 4 mS / cm, and the endpoint conductivity of the washing water used for the second filtration washing is lower than 0.5 mS / cm; the washing water used for the first filtration washing and the washing water used for the second filtration washing are both pure water.

[0049] In the technical solution of the embodiment of the present application, the purpose of the first washing and the second washing is to reduce the impurity content. The lower the endpoint conductivity, the less impurity content. Among them, reducing the impurity content by controlling the first washing is beneficial to reducing the difficulty of phase change during subsequent aging, so as to increase the specific surface area of ​​ferric phosphate.

[0050] Further, in some embodiments, the ammonium phosphate salt solution includes at least monoammonium hydrogen phosphate, diammonium phosphate, phosphoric acid, and ammonia water, and the pH value of the ammonium phosphate salt is 6-8; and / or the ferrous solution includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate, and the pH value of the ferrous solution is 3-4; and / or the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate salt is (1-1.2):1.

[0051] Specifically, the pH value of the ammonium phosphate salt can be 6, 6.5, 7, 7.5, 8 or any value between 6 and 8, the pH value of the ferrous solution can be 3, 3.5, 4 or any value between 3 and 4, and the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate salt can be 1:1, 1.1:1, 1.2:1 or any value between (1-1.2):1.

[0052] In the technical solution of the embodiment of the present application, the ammonium phosphate salt provides phosphate ions and ammonium ions, and the ferrous solution provides ferrous ions to form a ferrous phosphate precipitate. Under the pH value limit of the ammonium phosphate salt, the concentration of the ammonium phosphate salt can be controlled. Under the pH value limit of the ferrous solution, the concentration of ferrous ions can be controlled and the oxidation of ferrous ions can be prevented.

[0053] Furthermore, in some embodiments, the molar ratio of the oxidant used in the first oxidation to the ferrous ions in the ferrous solution is (0.6-0.8):1, and the molar ratio of the oxidant used in the second oxidation to the oxidant used in the first oxidation is (0.1-0.2):1.

[0054] Specifically, the molar ratio of the oxidant used in the primary oxidation to the ferrous ions in the ferrous solution can be any value between 0.6:1, 0.7:1, 0.8:1 or (0.6-0.8):1, and the molar ratio of the oxidant used in the secondary oxidation to the ferrous ions in the ferrous solution can be any value between 0.1:1, 0.2:1 or (0.1-0.2):1. By limiting the amount of oxidant used in the primary oxidation and the secondary oxidation, sufficient oxidation of ferrous iron can be achieved without increasing costs.

[0055] Further, in some embodiments, the aging temperature is 90-100°C; and / or the drying temperature is 80-120°C, and the sintering temperature is 540-580°C.

[0056] Specifically, the aging temperature can be 90°C, 92°C, 94°C, 96°C, 98°C, 100°C or any value between 90-100°C. Understandably, in the present embodiment, if the aging temperature is too high, the crystal structure of the iron phosphate will be destroyed, resulting in the failure of the iron phosphate, and the side reaction will be promoted, and the impurities will increase; and if the aging temperature is too low, the iron phosphate will not be aged sufficiently, the crystallinity will be reduced, and the use requirements of battery-grade iron phosphate will not be met. As is well known to those skilled in the art, aging is a necessary process commonly used in the preparation of iron phosphate, and its purpose is to promote the growth and perfection of iron phosphate crystals and the homogenization of particle size, and to improve the stability of iron phosphate.

[0057] Furthermore, the drying temperature may be 80° C., 90° C., 100° C., 110° C., 120° C. or any value between 80-120° C., and the sintering temperature may be 540° C., 550° C., 560° C., 570° C., 580° C. or any value between 540-580° C. Free water in the second filter cake is removed by drying, and then bound water of iron phosphate in the filter cake is removed by sintering, and finally anhydrous iron phosphate is obtained.

[0058] In a third aspect, an embodiment of the present application provides a positive electrode material prepared using anhydrous iron phosphate material.

[0059] In the technical solution of the embodiment of the present application, the positive electrode material is prepared by conventional means using the above-mentioned anhydrous iron phosphate as a precursor. Since anhydrous iron phosphate has the characteristics of large specific surface area and low impurity content, the obtained positive electrode material is beneficial to improving the cycle performance and energy density of the battery.

[0060] In a fourth aspect, an embodiment of the present application provides a positive electrode plate, comprising the aforementioned positive electrode material.

[0061] In this embodiment, the positive electrode plate includes the above-mentioned positive electrode material, and thus the obtained positive electrode plate also has better electrochemical performance.

[0062] In a fifth aspect, an embodiment of the present application provides a secondary battery, comprising the aforementioned positive electrode plate.

[0063] In this embodiment, the secondary battery includes the above-mentioned positive electrode plate, and thus also has better electrochemical performance.

[0064] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0065] 1. Preparation method Example 1 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain a phosphate ammonium salt solution, and the phosphate ammonium salt solution is added to a ferrous sulfate solution with a pH of 4 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the phosphate ammonium salt is 1.005:1, and the dripping time of the phosphate ammonium salt solution is controlled to 50 minutes, and the pH of the mixed solution is adjusted to 4.5. After the reaction, a first slurry containing ferrous phosphate precipitate is obtained; (2) adding hydrogen peroxide to the first slurry for primary oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 20 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the primary filtration and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for the primary oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying, stirring for 25 minutes, and then adding hydrogen peroxide for secondary oxidation for 15 minutes to obtain a second slurry, wherein the molar ratio of hydrogen peroxide used in the secondary oxidation to the hydrogen peroxide used in the primary oxidation is 0.1:1; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0066] Example 2 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain an ammonium phosphate solution, and the ammonium phosphate solution is added to a ferrous sulfate solution with a pH of 4 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate solution is 1.005:1, and the dripping time of the ammonium phosphate solution is controlled to 30 minutes. The pH of the mixed solution is adjusted to 4.5, and after the reaction, a first slurry containing ferrous phosphate precipitate is obtained; (2) adding hydrogen peroxide to the first slurry for primary oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 20 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the primary filtration and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for the primary oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying, stirring for 25 minutes, and then adding hydrogen peroxide for secondary oxidation for 15 minutes to obtain a second slurry, wherein the molar ratio of hydrogen peroxide used in the secondary oxidation to the hydrogen peroxide used in the primary oxidation is 0.1:1; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0067] Example 3 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain an ammonium phosphate solution, and the ammonium phosphate solution is added to a ferrous sulfate solution with a pH of 4 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate solution is 1.005:1, and the dripping time of the ammonium phosphate solution is controlled to 70 minutes. The pH of the mixed solution is adjusted to 4.5, and after the reaction, a first slurry containing ferrous phosphate precipitate is obtained; (2) adding hydrogen peroxide to the first slurry for primary oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 20 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the primary filtration and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for the primary oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying, stirring for 25 minutes, and then adding hydrogen peroxide for secondary oxidation for 15 minutes to obtain a second slurry, wherein the molar ratio of hydrogen peroxide used in the secondary oxidation to the hydrogen peroxide used in the primary oxidation is 0.1:1; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0068] Example 4 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain a phosphate ammonium salt solution, and the phosphate ammonium salt solution is added to a ferrous sulfate solution with a pH of 4 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the phosphate ammonium salt is 1.005:1, and the dripping time of the phosphate ammonium salt solution is controlled to 50 minutes. The pH of the mixed solution is adjusted to 3, and after the reaction, a first slurry containing ferrous phosphate precipitate is obtained; (2) adding hydrogen peroxide to the first slurry for primary oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 20 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the primary filtration and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for the primary oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying, stirring for 25 minutes, and then adding hydrogen peroxide for secondary oxidation for 15 minutes to obtain a second slurry, wherein the molar ratio of hydrogen peroxide used in the secondary oxidation to the hydrogen peroxide used in the primary oxidation is 0.1:1; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0069] Example 5 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain a phosphate ammonium salt solution, and the phosphate ammonium salt solution is added to a ferrous sulfate solution with a pH of 4 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the phosphate ammonium salt is 1.005:1, and the dripping time of the phosphate ammonium salt solution is controlled to 50 minutes, and the pH of the mixed solution is adjusted to 4.5. After the reaction, a first slurry containing ferrous phosphate precipitate is obtained; (2) adding hydrogen peroxide to the first slurry for primary oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 10 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the primary filtration and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for the primary oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying, stirring for 25 minutes, and then adding hydrogen peroxide for secondary oxidation for 15 minutes to obtain a second slurry, wherein the molar ratio of hydrogen peroxide used in the secondary oxidation to the hydrogen peroxide used in the primary oxidation is 0.1:1; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0070] Comparative Example 1 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 6.5 by adjusting the amount of raw materials to obtain a phosphate ammonium salt solution, and under stirring, the mixed solution of the phosphate ammonium salt solution and hydrogen peroxide is added to a ferrous sulfate solution with a pH of 4, wherein the molar ratio of iron in the ferrous solution to phosphorus in the phosphate ammonium salt is 1.005:1, and the dripping time of the mixed solution of the phosphate ammonium salt solution and hydrogen peroxide is controlled to be 50 minutes, and the pH of the mixed solution is adjusted to 4.5. After reaction, a slurry is obtained, and the amount of hydrogen peroxide used is the sum of the amounts of hydrogen peroxide used in the secondary oxidation in Example 1; (2) filtering and washing the slurry once until the end point conductivity of the washing water used for the first filtering and washing is lower than 4 mS / cm to obtain a filter cake; (3) Add phosphoric acid and water to the filter cake for slurrying and stir for 25 minutes to obtain a slurry; (4) heating the slurry to 95° C. for aging, and filtering and washing the slurry for a second time after the slurry changes from yellow to white, until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a washing product; (5) The washed material is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0071] Comparative Example 2 A method for preparing anhydrous ferric phosphate material, the other contents of which are the same as those of Example 1, except that step (3) does not include adding hydrogen peroxide for secondary oxidation.

[0072] Comparative Example 3 A method for preparing anhydrous ferric phosphate material, the other contents of which are the same as those of Example 1, except that step (3) does not include a slurrying step.

[0073] Comparative Example 4 A method for preparing anhydrous ferric phosphate material, the other contents are the same as those of Example 1, except that step (1) is replaced by mixing ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water, and adjusting the pH of the solution to 4.5 by adjusting the amount of raw materials to obtain an ammonium phosphate salt solution, and adding the ammonium phosphate salt solution to a ferrous sulfate solution with a pH of 3 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate salt is 1.005:1, the dripping time of the ammonium phosphate salt solution is controlled at 50 minutes, the pH of the mixed solution is adjusted to 2, and the ferrous phosphate solution is obtained after the reaction.

[0074] Comparative Example 5 A method for preparing anhydrous ferric phosphate material, the other contents are the same as those of Example 1, except that step (1) is replaced by mixing ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water, and adjusting the pH of the solution to 4.5 by adjusting the amount of raw materials to obtain an ammonium phosphate salt solution, and adding the ammonium phosphate salt solution to a ferrous sulfate solution with a pH of 3 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the ammonium phosphate salt is 1.005:1, the dripping time of the ammonium phosphate salt solution is controlled to 50 minutes, the pH of the mixed solution is adjusted to 5, and the ferrous phosphate solution is obtained after the reaction.

[0075] Comparative Example 6 A method for preparing anhydrous ferric phosphate material comprises the following steps: (1) ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid and ammonia water are mixed, and the pH of the solution is controlled to 4.5 by adjusting the amount of raw materials to obtain a phosphate ammonium salt solution, and the phosphate ammonium salt solution is added to a ferrous sulfate solution with a pH of 3 under stirring, wherein the molar ratio of iron in the ferrous solution to phosphorus in the phosphate ammonium salt is 1.005:1, and the dripping time of the phosphate ammonium salt solution is controlled to 50 minutes, and the pH of the mixed solution is adjusted to 2, and a ferrous phosphate solution is obtained after the reaction; (2) adding hydrogen peroxide to the ferrous phosphate solution for oxidation, wherein the dripping time of the hydrogen peroxide is controlled within 35 min, and then filtering and washing once until the endpoint conductivity of the washing water used for the filtering and washing is lower than 4 mS / cm, thereby obtaining a first filter cake, wherein the molar ratio of the hydrogen peroxide used for oxidation to the ferrous ions in the ferrous solution is 0.6:1; (3) adding phosphoric acid and water to the first filter cake for slurrying and stirring for 25 minutes to obtain a second slurry; (4) heating the second material slurry to 95° C. for aging, and after the second slurry changes from yellow to white, filtering and washing for the second time until the end point conductivity of the washing water used for the second filtration and washing is lower than 0.5 mS / cm, thereby obtaining a second filter cake; (5) The second filter cake is dried at 100°C and then sintered at 540°C to obtain anhydrous iron phosphate material.

[0076] 2. Test Method Property test of anhydrous ferric phosphate material The BET test of anhydrous ferric phosphate material is carried out in accordance with GB / T 19587, and the impurity content test is carried out in accordance with HG / T4701-2021, where the impurity types include Cr, Cu, Ni, Pb, and Zn.

[0077] III. Analysis of test results of various embodiments and comparative examples The test results of anhydrous ferric phosphate are shown in Table 1.

[0078] Table 1 Performance results of anhydrous ferric phosphate

[0079] In Table 1, Examples 1-3 changed the time for adding phosphate ammonium salt. The results showed that if the time for adding phosphate ammonium salt solution was too long or too short, BET would decrease. Moreover, as the time for adding phosphate ammonium salt solution increased, the total amount of impurities increased. Therefore, the time for adding phosphate ammonium salt solution in Example 1 would obviously affect BET and impurity content. Compared with Example 1, the pH value of the mixed solution in step (1) was reduced in Example 4. The results showed that BET value decreased and impurity content increased. Compared with Example 1, the time for one oxidation was shortened in Example 5. The results showed that BET value decreased and impurity content increased. Examples 1-5 illustrate that appropriate control of the time for adding phosphate ammonium salt solution and the reaction pH is conducive to the improvement of BET and the reduction of impurity content.

[0080] Compared with Example 1, in Comparative Example 1, sufficient amounts of hydrogen peroxide and ammonium phosphate solution were directly mixed and reacted with ferrous solution. The results showed that the BET value dropped significantly and the impurity content increased sharply, indicating that the formation of precipitated ferrous phosphate first and then secondary oxidation was more conducive to the improvement of BET and the control of impurity content; Compared with Example 1, Comparative Example 2 did not perform secondary oxidation. The results showed that the BET value dropped and the impurity content increased, indicating that by secondary oxidation, the duration of segmented oxidation was controlled under the premise of ensuring sufficient oxidation, the specific surface area of ​​ferric phosphate could be further increased and the impurity content of ferric phosphate could be reduced; Compared with Example 1, Comparative Example 3 was not slurried, but the strips of primary oxidation were The results show that the BET value decreases and the impurity content increases, indicating that the slurrying step after the primary oxidation is conducive to the improvement of BET and the reduction of impurity content; compared with Example 1, Comparative Examples 4 and 5 adjust the reaction pH of step (1) so that ferrous phosphate is in an ionic state for subsequent reactions. The results show that the BET value decreases significantly and the impurity content increases, indicating that precipitated ferrous phosphate is more conducive to the improvement of BET and the control of impurity content than ionic ferrous phosphate; compared with Example 1, Comparative Example 6 combines the secondary oxidation into the primary oxidation, and allows ferrous phosphate to be in an ionic state for subsequent reactions. The results show that the BET value decreases and the impurity content increases.

[0081] In summary, it is shown that the anhydrous iron phosphate material produced through the process steps of the present application has the characteristics of high BET and low impurity content.

[0082] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An anhydrous iron phosphate material, It is characterized in that The BET value range is 10.37-14.56m² / g; among them, the total amount of impurity elements Cr, Cu, Ni, Pb, and Zn is ≤60ppm.

2. A method for preparing the anhydrous ferric phosphate material as claimed in claim 1, It is characterized in that The following steps are involved: The ammonium phosphate solution and the ferrous solution are mixed, and the pH range of the mixed solution is controlled to be 3-4.5, and a first slurry containing ferrous phosphate precipitate is obtained through reaction; adding an oxidant to the first slurry for primary oxidation, and then filtering and washing to obtain a first filter cake; Phosphoric acid and water are added to the first filter cake for slurrying, and then an oxidant is added for secondary oxidation to obtain a second slurry; The second slurry is heated and aged, and then filtered and washed twice to obtain a second filter cake; The second filter cake is dried and sintered to obtain the anhydrous ferric phosphate material.

3. The method for preparing anhydrous ferric phosphate material according to claim 2, It is characterized in that The oxidant comprises at least one of oxygen, ozone and hydrogen peroxide; and / or The time of the first oxidation is 20-30 minutes, and the time of the second oxidation is 10-15 minutes.

4. The method for preparing anhydrous ferric phosphate material according to claim 2, It is characterized in that The endpoint conductivity of the washing water used in the first filtration and washing is lower than 4 mS / cm, and the endpoint conductivity of the washing water used in the second filtration and washing is lower than 0.5 mS / cm; and / or The washing water used for the first filtration and washing and the washing water used for the second filtration and washing are both pure water.

5. The method for preparing anhydrous ferric phosphate material according to claim 2, It is characterized in that The ammonium phosphate salt solution comprises at least ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, and ammonia water, and the pH range of the ammonium phosphate salt solution is 6-8; and / or The ferrous solution comprises at least one of ferrous sulfate, ferrous chloride and ferrous nitrate, and the pH range of the ferrous solution is 3-4; and / or The molar ratio of the iron element in the ferrous solution to the phosphorus element in the ammonium phosphate salt is (1-1.2):

1.

6. The method for preparing anhydrous ferric phosphate material according to claim 2, It is characterized in that The molar ratio of the oxidant used in the primary oxidation to the ferrous ions in the ferrous solution is (0.6-0.8):1, and the molar ratio of the oxidant used in the secondary oxidation to the oxidant used in the primary oxidation is (0.1-0.2):

1.

7. The method for preparing anhydrous ferric phosphate material according to claim 2, It is characterized in that The aging temperature is 90-100° C.; and / or The drying temperature is 80-120°C, and the sintering temperature is 540-580°C.

8. A positive electrode material, It is characterized in that The anhydrous ferric phosphate material is prepared by the anhydrous ferric phosphate material as described in claim 1, or the anhydrous ferric phosphate material is prepared by the preparation method of the anhydrous ferric phosphate material as described in claims 2-7.

9. A positive electrode sheet, It is characterized in that Comprising the positive electrode material as claimed in claim 8.

10. A secondary battery, It is characterized in that Comprising the positive electrode sheet as claimed in claim 9.

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