Cobalt-doped iron phosphate and preparation method thereof
By using a mixed solution of amorphous iron phosphate, divalent cobalt salt, and persulfate for heating and aging during the preparation of iron phosphate, the problems of low cobalt content and difficulty in uniform mixing in cobalt-doped iron phosphate were solved, achieving efficient cobalt doping and improving the electrochemical performance of iron phosphate.
Patent Information
- Application Number
- CN202511747124.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-25
- Publication Date
- 2026-02-13
AI Technical Summary
The existing cobalt-doped lithium iron phosphate batteries have low cobalt content and it is difficult to mix cobalt and iron at the molecular level, which affects the improvement of the electrochemical performance of lithium iron phosphate batteries.
By mixing amorphous iron phosphate material with a mixed solution containing divalent cobalt salt and persulfate, and then subjecting it to a high-temperature aging treatment, the persulfate generates highly oxidizing sulfate radicals at high temperatures, which oxidize divalent cobalt ions to trivalent cobalt ions, achieving uniform mixing at the molecular level. Cobalt-doped iron phosphate is then obtained through washing, drying, and sintering.
The precipitation efficiency and doping amount of cobalt were improved, the crystal structure of iron phosphate was changed, the conductivity and ion migration path of iron phosphate were enhanced, and high-performance cobalt-doped iron phosphate was prepared.
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Figure CN121516833A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of iron phosphate doping modification technology, specifically to a cobalt-doped iron phosphate and its preparation method. Background Technology
[0002] With the widespread application of lithium iron phosphate (LFP) batteries in the new energy vehicle sector, their market share is gradually increasing, and the market is also placing higher demands on them. Traditional methods to improve the electrochemical performance of LFP batteries include introducing metal oxides into the wet ball milling process during LFP preparation to achieve metal cation doping. However, this method makes it difficult to achieve uniform mixing of dopant ions and other raw materials at the molecular level, resulting in limited performance improvement and difficulty in further enhancing the performance of LFP batteries. This makes them unable to meet the increasingly stringent performance requirements of LFP materials in the current industry.
[0003] To further improve the performance of lithium iron phosphate (LFP) batteries, metal cation doping can be transferred to the LFP preparation process. By doping LFP and then using the doped LFP as a precursor, high-performance LFP can be prepared. Since lithium cobalt phosphate has better conductivity and a higher voltage plateau than LFP, doping LFP with cobalt ions is significant for improving LFP performance.
[0004] However, when cobalt doping is carried out during the preparation of iron phosphate, it is still difficult for cobalt and iron to be uniformly mixed at the molecular level, and the precipitation efficiency of cobalt is usually low, resulting in a low cobalt content in the final cobalt-doped iron phosphate, which affects the doping effect. Summary of the Invention
[0005] In view of the technical problems existing in the background art, this application provides a cobalt-doped iron phosphate and its preparation method, aiming to solve the technical problems of low cobalt content and difficulty in uniformly mixing cobalt and iron elements at the molecular level in existing cobalt-doped iron phosphate.
[0006] In a first aspect, embodiments of this application provide a method for preparing cobalt-doped iron phosphate, comprising the following steps: Amorphous iron phosphate materials and mixed solutions containing divalent cobalt salts and persulfates are provided; Amorphous iron phosphate material is mixed with a mixed solution to obtain a mixed slurry; The mixed slurry was subjected to a heating and aging treatment to obtain cobalt-doped iron phosphate dihydrate; Cobalt-doped iron phosphate dihydrate was washed, dried, and sintered to obtain cobalt-doped iron phosphate.
[0007] In the technical solution of this application embodiment, divalent cobalt salt and persulfate can achieve uniform mixing at the molecular level in a mixed solution. By mixing this mixed solution with amorphous iron phosphate material and subjecting it to a temperature aging treatment, the persulfate can be activated at high temperature to generate sulfate free radicals with strong oxidizing properties, which uniformly oxidize divalent cobalt ions into trivalent cobalt ions. At the same time, the oxidized trivalent cobalt ions react with phosphate ions in the mixed slurry, thereby obtaining cobalt-doped iron phosphate with high cobalt content and uniform mixing of iron and cobalt at the molecular level with high cobalt precipitation efficiency. By using cobalt doping to change the crystal structure of iron phosphate, the performance of iron phosphate is effectively improved.
[0008] In some embodiments, the mixed solution also contains phosphoric acid; and / or, the amorphous iron phosphate material is formed by reacting an iron salt solution and a phosphate solution, wherein the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(1.05~1.30).
[0009] In this embodiment, by adding phosphoric acid to the mixed solution and / or controlling the appropriate excess of phosphorus in the amorphous iron phosphate material, a phosphate-rich environment can be formed in the mixed slurry. This promotes the homogeneous precipitation of trivalent cobalt ions formed by homogeneous oxidation during the heating and aging process with the phosphate-rich ions in the mixed slurry, thus preventing the trivalent cobalt ions from being reduced to divalent cobalt ions in the liquid phase and effectively improving the precipitation efficiency of cobalt.
[0010] In some embodiments, the aging process includes: heating to 75~90°C, maintaining the temperature until the mixed slurry changes color, and then maintaining the temperature for another 60~120 minutes.
[0011] In this embodiment, by controlling the conditions of the heating and aging treatment, the persulfate ions in the mixed slurry can be fully activated at high temperature to generate sulfate free radicals with strong oxidizing properties. These sulfate free radicals are then used to uniformly oxidize the divalent cobalt ions in the mixed slurry into trivalent cobalt ions, which are then used for doping, effectively improving the precipitation efficiency and doping amount of cobalt.
[0012] In some embodiments, the molar ratio of cobalt to persulfate ions in the mixed solution is 1:(1.0~4.0).
[0013] In this embodiment, by controlling the molar ratio between cobalt and persulfate ions in the mixed solution, an excess of persulfate can be ensured so that sufficient sulfate free radicals are generated after the temperature aging treatment, which fully oxidize the divalent cobalt ions in the mixed solution to trivalent cobalt ions, thereby improving the precipitation efficiency of cobalt.
[0014] In some embodiments, the molar ratio of iron to cobalt in the mixed slurry is 1-x : x, where 0 < x ≤ 0.02.
[0015] In this embodiment, by controlling the molar ratio of iron and cobalt in the mixed slurry, it is beneficial to prepare cobalt-doped iron phosphate with appropriate cobalt content. This allows the appropriate amount of cobalt to replace the iron in the iron phosphate, achieving lattice doping and effectively improving the performance of iron phosphate.
[0016] In some embodiments, the method for preparing the amorphous iron phosphate material includes: Iron salts are dissolved in water to obtain an iron salt solution; Phosphate, hydrogen peroxide, and water are mixed to obtain a phosphate solution; A phosphate solution is added to an iron salt solution, and after the reaction, an amorphous iron phosphate material is obtained. Among them, Fe in iron salt solution 2+ The molar concentration of phosphorus in the phosphate solution is 0.5~1.2 mol / L, and the molar concentration of phosphorus in the phosphate solution is 1.0~2.0 mol / L.
[0017] In this embodiment, iron salt solution and phosphate solution are prepared separately, and the Fe in the iron salt solution is... 2+ By controlling the molar concentration of Fe in the iron salt solution and the molar concentration of phosphorus in the phosphate solution, the Fe concentration in the iron salt solution can be controlled. 2+ After oxidation with hydrogen peroxide, it reacts fully with phosphate ions in the phosphate solution to generate amorphous iron phosphate material.
[0018] In some embodiments, when the mixed solution contains phosphoric acid, the pH value of the phosphate solution is 6.5~7.5, the molar ratio of iron in the iron salt solution to hydrogen peroxide in the phosphate solution is 1:(0.6~1.0), and the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(0.9~1.10).
[0019] In this embodiment, by controlling the pH value of the phosphate solution and the molar ratio of iron in the ferric salt solution to hydrogen peroxide in the phosphate solution, it is beneficial to promote the full oxidation of ferrous ions in the ferric salt solution to ferric ions by hydrogen peroxide, which then reacts fully with phosphate ions in the phosphate solution to form amorphous iron phosphate material. Simultaneously, under the condition that the mixed solution contains phosphoric acid, by controlling the molar ratio of iron in the ferric salt solution to phosphorus in the phosphate solution, the iron-to-phosphorus ratio in the generated amorphous iron phosphate material can be regulated, which is beneficial to forming a phosphate-rich environment in the mixed slurry.
[0020] In some embodiments, when the mixed solution contains phosphoric acid, the step of mixing amorphous iron phosphate material with the mixed solution to obtain a mixed slurry includes: Amorphous iron phosphate material was subjected to solid-liquid separation and washing to obtain filter cake; Mix the filter cake with the mixed solution and disperse by slurrying for 30-60 minutes to obtain the mixed slurry. The molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material is (0.1~0.3):1.
[0021] In this embodiment, by performing solid-liquid separation and washing on the amorphous iron phosphate material, impurities in the amorphous iron phosphate material can be effectively removed, which is beneficial for preparing cobalt-doped iron phosphate with low impurity content. Then, by pulping and dispersing treatment, the amorphous iron phosphate material is uniformly mixed with the mixed solution, and by adjusting the molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material, a phosphate-rich environment is formed, so as to achieve cobalt doping of the amorphous iron phosphate material by homogeneous precipitation of trivalent cobalt ions in the phosphate-rich environment.
[0022] In some embodiments, the washing step includes rinsing with water until the conductivity of the rinse water is ≤500 μs / cm; and / or, the drying step includes drying at 90~100°C for 10~14 h; and / or, the sintering step includes sintering at 550~650°C.
[0023] In this embodiment, by adjusting the relevant parameters in the washing, drying and sintering processes, it is beneficial to remove impurities from cobalt-doped ferric phosphate dihydrate and convert it into cobalt-doped anhydrous ferric phosphate.
[0024] Secondly, embodiments of this application provide a cobalt-doped iron phosphate, which is prepared by the preparation method provided in the first aspect.
[0025] In the technical solution of this application embodiment, the iron and cobalt elements in cobalt-doped iron phosphate are mixed at the molecular level, and the cobalt element can replace some of the iron sites in the iron phosphate crystal, change the crystal lattice structure of iron phosphate, and realize lattice doping, thereby giving cobalt-doped iron phosphate a wider ion migration path and better conductivity.
[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0027] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.
[0028] Figure 1 This is a process flow diagram of the preparation of cobalt-doped iron phosphate in Example 1 of this application; Figure 2 The images show the XRD patterns of cobalt-doped iron phosphate dihydrate and cobalt-doped iron phosphate prepared in Example 1 of this application. Figure 3 The XRD patterns of cobalt-doped iron phosphate dihydrate and cobalt-doped iron phosphate prepared in Comparative Example 1 of this application are shown. Figure 4 The images show the XRD patterns of cobalt-doped iron phosphate dihydrate and cobalt-doped iron phosphate prepared in Comparative Example 2 of this application. Detailed Implementation
[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0034] When cobalt doping iron phosphate, conventional cobalt doping methods often result in difficulty in uniformly mixing cobalt and iron at the molecular level, and the precipitation efficiency of cobalt during the doping process is usually low. This leads to a low cobalt content in the final cobalt-doped iron phosphate, affecting the doping effect and making it difficult to effectively improve the performance of iron phosphate.
[0035] To address the technical problems of low cobalt content and difficulty in achieving uniform molecular-level mixing of cobalt and iron in existing cobalt-doped iron phosphate, this application provides a cobalt-doped iron phosphate and its preparation method. The method involves preparing a mixed slurry by combining amorphous iron phosphate material with a mixed solution containing divalent cobalt salt and persulfate, achieving uniform molecular-level mixing of the raw materials under liquid-phase conditions. Then, a heating and aging treatment is used to homogeneously oxidize and precipitate the divalent cobalt ions in the mixed slurry, thereby obtaining cobalt-doped iron phosphate with high cobalt content and uniform molecular-level mixing of iron and cobalt with high cobalt precipitation efficiency. By utilizing cobalt doping to alter the crystal structure of iron phosphate, the performance of iron phosphate is effectively improved.
[0036] In a first aspect, embodiments of this application provide a method for preparing cobalt-doped iron phosphate, comprising the following steps: Amorphous iron phosphate materials and mixed solutions containing divalent cobalt salts and persulfates are provided; Amorphous iron phosphate material is mixed with a mixed solution to obtain a mixed slurry; The mixed slurry was subjected to a heating and aging treatment to obtain cobalt-doped iron phosphate dihydrate; Cobalt-doped iron phosphate dihydrate was washed, dried, and sintered to obtain cobalt-doped iron phosphate.
[0037] In this application, persulfate is used as an oxidant. It does not react with divalent cobalt salts at room temperature, but when mixed with divalent cobalt salts, it forms a clear mixed solution, achieving uniform mixing at the molecular level. Then, by mixing the mixed solution with amorphous iron phosphate material and subjecting the mixed slurry to a high-temperature aging treatment, the persulfate in the mixed slurry is activated at high temperature to generate sulfate free radicals with strong oxidizing properties. This uniformly oxidizes the divalent cobalt ions in the mixed slurry to trivalent cobalt ions. The oxidized trivalent cobalt ions can also homogeneously precipitate with the phosphate ions in the mixed slurry to form cobalt phosphate. Moreover, the precipitation efficiency of trivalent cobalt ions is significantly higher than that of divalent cobalt ions. This allows the technical solution provided in this application to obtain cobalt-doped iron phosphate with high cobalt content and uniform mixing of iron and cobalt at the molecular level with high cobalt precipitation efficiency.
[0038] Furthermore, in some embodiments, the mixed solution also contains phosphoric acid; and / or, the amorphous iron phosphate material is formed by reacting an iron salt solution and a phosphate solution, wherein the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(1.05~1.30).
[0039] In this application, to address the problem that trivalent cobalt ions are easily reduced to divalent cobalt ions in the liquid phase, a phosphate-rich environment is created in the mixed slurry. By utilizing the small solubility product constant of trivalent cobalt phosphate, the trivalent cobalt ions generated by homogeneous oxidation are precipitated homogeneously with the phosphate ions abundant in the mixed slurry, thus promoting the forward chemical reaction and preventing the reduction of trivalent cobalt ions, effectively improving the precipitation efficiency of cobalt.
[0040] One way to create a phosphate-rich environment in the mixed slurry is by adding phosphoric acid to the mixed solution, controlling the excess phosphorus in the amorphous iron phosphate material, or both adding phosphoric acid to the mixed solution and controlling the excess phosphorus in the amorphous iron phosphate material. Specifically, when controlling the excess phosphorus in the amorphous iron phosphate material, the molar ratio of iron in the iron salt solution used to prepare the amorphous iron phosphate material to phosphorus in the phosphate solution can be any value within the range of 1:1.05, 1:1.10, 1:1.15, 1:1.20, 1:1.25, 1:1.30, or 1:(1.05~1.30).
[0041] Furthermore, in some embodiments, the temperature aging treatment includes: heating to 75~90°C, maintaining the temperature until the mixed slurry changes color, and then maintaining the temperature for another 60~120 minutes.
[0042] In this application, by controlling the conditions of the heating and aging treatment, the persulfate ions in the mixed slurry can be fully activated at high temperature to generate sulfate free radicals with strong oxidizing properties. These sulfate free radicals are then used to uniformly oxidize the divalent cobalt ions in the mixed slurry into trivalent cobalt ions, so that the trivalent cobalt ions can be used for doping. Compared with the conventional method of using divalent cobalt for doping, this method effectively improves the precipitation efficiency and doping amount of cobalt, which is beneficial to improving the performance of the prepared cobalt-doped iron phosphate.
[0043] If the temperature during the aging process is too low, the activation effect on persulfate ions will be poor, thus affecting its oxidation effect on divalent cobalt ions. If the temperature during the aging process is too high, it will cause the persulfate ions to decompose violently, and the decomposition product is oxygen, which has a poor oxidizing effect, also affecting the oxidation effect on divalent cobalt ions. Specifically, the temperature during the aging process can be any value within the range of 75℃, 80℃, 85℃, 90℃, or 75~90℃. After holding at the corresponding temperature until the mixed slurry changes color, continue holding for a period of time to convert the amorphous cobalt-doped ferric phosphate formed after homogeneous precipitation into crystalline cobalt-doped ferric phosphate dihydrate. The holding time can be any value within the range of 60min, 80min, 100min, 120min, or 60~120min.
[0044] Furthermore, in some embodiments, the molar ratio of cobalt to persulfate ions in the mixed solution is 1:(1.0~4.0).
[0045] In this application, by controlling the molar ratio between cobalt and persulfate ions in the mixed solution, an excess of persulfate ions can be ensured. This allows the persulfate ions to generate sufficient sulfate free radicals after high-temperature activation, thereby fully oxidizing the divalent cobalt ions in the mixed solution to trivalent cobalt ions, effectively improving the cobalt precipitation efficiency. Specifically, the molar ratio of cobalt to persulfate ions can be any value within the range of 1:1.0, 1:1.5, 1:2.0, 1:2.5, 1:3.0, 1:3.5, 1:4.0, or 1:(1.0~4.0).
[0046] Furthermore, in some embodiments, the molar ratio of iron to cobalt in the mixed slurry is 1-x : x, where 0 < x ≤ 0.02.
[0047] In this application, by controlling the molar ratio of iron and cobalt in the mixed slurry, the amount of cobalt in the prepared cobalt-doped iron phosphate can be effectively adjusted. This allows the appropriate amount of doped cobalt to replace the iron in the iron phosphate, changing the crystal structure of the iron phosphate and achieving lattice doping. Compared with undoped iron phosphate, this effectively broadens the lithium-ion migration path and improves its conductivity.
[0048] Furthermore, in some embodiments, the method for preparing the provided amorphous iron phosphate material includes: Iron salts are dissolved in water to obtain an iron salt solution; Phosphate, hydrogen peroxide, and water are mixed to obtain a phosphate solution; A phosphate solution is added to an iron salt solution, and after the reaction, an amorphous iron phosphate material is obtained. Among them, Fe in iron salt solution2+ The molar concentration of phosphorus in the phosphate solution is 0.5~1.2 mol / L, and the molar concentration of phosphorus in the phosphate solution is 1.0~2.0 mol / L.
[0049] In this application, iron salt solution and phosphate solution are prepared separately, and the Fe in the iron salt solution is... 2+ By controlling the molar concentration of Fe in the iron salt solution and the molar concentration of phosphorus in the phosphate solution, the Fe concentration in the iron salt solution can be controlled. 2+ After oxidation with hydrogen peroxide, it reacts fully with phosphate ions in the phosphate solution to generate amorphous iron phosphate material. Specifically, the Fe in the iron salt solution... 2+ The molar concentration can be 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, or any value within the range of 0.5 to 1.2 mol / L. The molar concentration of phosphorus in the phosphate solution can be 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, or any value within the range of 1.0 to 2.0 mol / L. Preferably, the ferric salt includes at least one of ferrous sulfate, ferrous nitrate, and ferrous chloride; the phosphate includes at least one of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate, or is a mixture of phosphoric acid and ammonia.
[0050] Furthermore, in some embodiments, when the mixed solution contains phosphoric acid, the pH value of the phosphate solution is 6.5~7.5, the molar ratio of iron in the iron salt solution to hydrogen peroxide in the phosphate solution is 1:(0.6~1.0), and the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(0.9~1.10).
[0051] In this application, by controlling the pH value of the phosphate solution and the molar ratio of iron in the ferric salt solution to hydrogen peroxide in the phosphate solution, it is beneficial to promote the complete oxidation of ferrous ions in the ferric salt solution to ferric ions by hydrogen peroxide, which then reacts fully with phosphate ions in the phosphate solution to form amorphous iron phosphate material. Specifically, the pH value of the phosphate solution can be 6.5, 6.8, 7.0, 7.2, 7.5, or any value within the range of 6.5 to 7.5; the molar ratio of iron in the ferric salt solution to hydrogen peroxide in the phosphate solution can be any value within the range of 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, or 1:(0.6 to 1.0). Simultaneously, under the condition that the mixed solution contains phosphoric acid, by controlling the molar ratio of iron in the ferric salt solution used to prepare amorphous iron phosphate material to phosphorus in the phosphate solution, it is beneficial to form a phosphate-rich environment in the mixed slurry, thereby improving the precipitation efficiency of cobalt. Specifically, the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution can be any value within the range of 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.10, or 1: (0.9~1.10).
[0052] Furthermore, in some embodiments, when the mixed solution contains phosphoric acid, the step of mixing the amorphous iron phosphate material with the mixed solution to obtain the mixed slurry includes: Amorphous iron phosphate material was subjected to solid-liquid separation and washing to obtain filter cake; Mix the filter cake with the mixed solution and disperse by slurrying for 30-60 minutes to obtain the mixed slurry. The molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material is (0.1~0.3):1.
[0053] In this application, by performing solid-liquid separation and washing on amorphous iron phosphate material, impurities in the amorphous iron phosphate material can be effectively removed, which is beneficial for preparing cobalt-doped iron phosphate with low impurity content. Then, by pulping and dispersing, the amorphous iron phosphate material is uniformly mixed with the mixed solution. By controlling the molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material, a phosphate-rich environment is formed. This allows for the homogeneous precipitation of trivalent cobalt ions in the phosphate-rich environment to achieve cobalt doping of the amorphous iron phosphate material, which is beneficial for preparing cobalt-doped iron phosphate with a high cobalt content and uniform mixing of iron and cobalt at the molecular level. Specifically, the molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material is any value within the range of 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, or (0.1~0.3):1. Preferably, when washing amorphous iron phosphate materials, pure water is used for washing, and the conductivity of the final rinse water is controlled to be ≤10 mS / cm.
[0054] Furthermore, in some embodiments, the mixed solution contains divalent cobalt salt, persulfate, phosphoric acid, and water; when the mixed solution is mixed with amorphous iron phosphate material, the mass of the mixed solution = the amount of iron in the amorphous iron phosphate material ÷ (1.5~2.5 mol / kg). The divalent cobalt salt includes at least one of cobalt sulfate, cobalt nitrate, and cobalt chloride; the persulfate includes at least one of sodium persulfate and potassium persulfate.
[0055] Furthermore, in some embodiments, when the mixed solution does not contain phosphoric acid, the molar concentration of cobalt in the mixed solution is 0.5~1.0 mol / L, the pH value of the iron phosphate solution is 2.5~4.5, the molar ratio of iron in the iron salt solution to hydrogen peroxide in the phosphate solution is 1 : (0.6~1.0), and the molar ratio of iron to phosphorus in the amorphous iron phosphate material is 1 : (1.05~1.30).
[0056] In this application, although the mixed solution does not contain phosphoric acid, the excess phosphate ions in the amorphous iron phosphate material can be utilized to form a phosphate-rich environment in the mixed slurry through the above-described method. Furthermore, the amorphous iron phosphate material prepared by this method does not require washing or pulping and can be directly mixed with the mixed solution to prepare the mixed slurry. Compared to adding phosphoric acid to the mixed solution, this effectively shortens the process flow and saves energy and production costs. However, the final cobalt-doped iron phosphate contains slightly higher levels of impurities such as magnesium, manganese, and sulfur, approximately 200 ppm.
[0057] Further, in some embodiments, the washing step includes rinsing with water until the conductivity of the resulting rinse water is ≤500 μs / cm; and / or, the drying step includes drying at 90~100℃ for 10~14h; and / or, the sintering treatment step includes sintering at 550~650℃.
[0058] In this application, by controlling the conductivity of the rinsing water after washing, the impurity content in the cobalt-doped ferric phosphate dihydrate is reduced; further, through drying and sintering, the cobalt-doped ferric phosphate dihydrate can be converted into cobalt-doped anhydrous ferric phosphate. During the sintering process, the sintering time at 550-650°C is preferably 1-4 hours.
[0059] Secondly, embodiments of this application provide a cobalt-doped iron phosphate, which is prepared by the preparation method provided in the first aspect.
[0060] In this application, iron and cobalt elements are mixed at the molecular level in cobalt-doped iron phosphate, and cobalt can replace some of the iron sites in the iron phosphate crystal, changing the crystal lattice structure of iron phosphate and achieving lattice doping. This results in cobalt-doped iron phosphate having a wider ion migration path and better conductivity. Based on the cobalt-doped iron phosphate of this application, it is beneficial for preparing high-performance lithium iron phosphate materials.
[0061] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0062] I. Preparation Method Example 1 This embodiment provides a method for preparing cobalt-doped iron phosphate, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include the following: S1. Mix ferrous sulfate with pure water until homogeneous to prepare Fe... 2+ A ferric salt solution with a molar concentration of 1 mol / L.
[0063] S2. Mix phosphoric acid, ammonia, pure water and hydrogen peroxide evenly to prepare a phosphate solution with a pH of 7.0; in this phosphate solution, the molar concentration of phosphorus is 1.5 mol / L and the concentration of hydrogen peroxide is 0.9 mol / L.
[0064] S3. Place the iron salt solution prepared in step S1 into a reaction vessel and stir. Use a peristaltic pump to add the phosphate solution prepared in step S2 dropwise into the reaction vessel, controlling the dropping time to be 30 minutes. After the dropping is complete, stir and mix for another 45 minutes to obtain an amorphous iron phosphate material in a slurry state. In the reaction vessel, the molar ratio of iron in the iron salt solution to phosphorus in the added phosphate solution is 1:1, and the molar ratio of iron in the iron salt solution to hydrogen peroxide in the added iron phosphate solution is 1:0.6.
[0065] S4. The amorphous iron phosphate material obtained in step S3 is subjected to pressure filtration and rinsed with pure water. The conductivity of the final rinse water is controlled to be ≤10 ms / cm to obtain filter cake.
[0066] S5. Mix cobalt sulfate, sodium persulfate, phosphoric acid, and pure water, and stir until homogeneous to obtain a mixed solution. The mass of this mixed solution is calculated by dividing the amount of iron in the amorphous iron phosphate material obtained in step S3 by 2 mol / kg; and the molar ratio of cobalt to iron in the mixed solution is 0.01:0.99, the molar ratio of phosphoric acid to iron in the amorphous iron phosphate material is 0.15:1, and the molar ratio of cobalt to persulfate ions is 1:3.
[0067] S6. Use the mixed solution obtained in step S5 as the pulping solution and transfer it to the reaction vessel. Add the filter cake obtained in step S4 to the reaction vessel and pulp and disperse for 45 minutes to obtain the mixed slurry.
[0068] S7. The mixed slurry obtained in step S6 is subjected to a heating and aging treatment to obtain cobalt-doped iron phosphate dihydrate. Specifically, the heating and aging process involves: first heating the mixed slurry to 85°C, maintaining this temperature until the slurry changes color, and then continuing to maintain the temperature for another 75 minutes to obtain cobalt-doped iron phosphate dihydrate (Fe). 0.99 Co 0.01 PO4·2H2O).
[0069] S8. The cobalt-doped ferric phosphate dihydrate obtained in step S7 is subjected to pressure filtration and rinsed with pure water, controlling the conductivity of the rinsing water to be ≤500 μs / cm; then the rinsed cobalt-doped ferric phosphate dihydrate is dried at 95℃ for 12 h, and after drying, it is sintered at 600℃ for 4 h to convert the ferric phosphate dihydrate into anhydrous ferric phosphate, thus obtaining cobalt-doped ferric phosphate (Fe). 0.99 Co 0.01 PO4).
[0070] In this embodiment, the contents of each impurity element in the prepared cobalt-doped iron phosphate are shown in Table 1.
[0071] Table 1. Content (ppm) of each impurity element in the cobalt-doped iron phosphate prepared in Example 1. Comparative Example 1 This comparative example provides a method for preparing iron phosphate. Compared with Example 1, the only difference is that in step S5, only phosphoric acid and pure water are added when preparing the mixed solution, and cobalt sulfate and sodium persulfate are not added. The mass of the mixed solution and the molar ratio of phosphoric acid and iron in the amorphous iron phosphate material in the mixed solution are the same as in Example 1. The remaining steps are the same as in Example 1, and will not be repeated here.
[0072] Since no cobalt sulfate or sodium persulfate was added in this comparative example, it was not cobalt doped, and the product obtained was anhydrous iron phosphate.
[0073] Comparative Example 2 This comparative example provides a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that the sodium persulfate used in step S5 is replaced with hydrogen peroxide, and the amount of hydrogen peroxide is equal to the amount of sulfur in the sodium persulfate used in Example 1. The remaining steps are the same as in Example 1 and will not be repeated here.
[0074] Comparative Example 3 This comparative example provides a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that phosphoric acid is not added when preparing the mixed solution in step S5. The mass of the mixed solution and the amount of cobalt and persulfate in the mixed solution are the same as in Example 1. The remaining steps are the same as in Example 1 and will not be repeated here.
[0075] Example 2 This embodiment provides a method for preparing cobalt-doped iron phosphate, including the following steps: S1. Mix ferrous sulfate with pure water until homogeneous to prepare Fe... 2+ A ferric salt solution with a molar concentration of 1 mol / L.
[0076] S2. Mix phosphoric acid, ammonia, pure water and hydrogen peroxide evenly to prepare a phosphate solution with a pH of 3.5; in this phosphate solution, the molar concentration of phosphorus is 1.5 mol / L and the concentration of hydrogen peroxide is 0.75 mol / L.
[0077] S3. Place the iron salt solution prepared in step S1 into a reaction vessel and stir. Use a peristaltic pump to add the phosphate solution prepared in step S2 dropwise into the reaction vessel, controlling the dropping time to be 30 minutes. After the dropping is completed, stir and mix for another 45 minutes to obtain an amorphous iron phosphate material in a slurry state. In the reaction vessel, the molar ratio of iron in the iron salt solution to phosphorus in the added phosphate solution is 1:1.2, and the molar ratio of iron in the iron salt solution to hydrogen peroxide in the added iron phosphate solution is 1:0.6.
[0078] S4. Mix cobalt sulfate, sodium persulfate, and pure water, and stir until homogeneous to obtain a mixed solution. In this mixed solution, the molar concentration of cobalt is 0.75 mol / L, and the molar ratio of cobalt to iron in the amorphous iron phosphate material is 0.01:0.99. The molar ratio of cobalt to persulfate ions in this mixed solution is 1:3.
[0079] S5. Pour the mixed solution obtained in step S4 into the amorphous iron phosphate material obtained in step S3, and stir for 8 minutes to obtain a mixed slurry.
[0080] S6. The mixed slurry obtained in step S5 is subjected to a heating and aging treatment to obtain cobalt-doped iron phosphate dihydrate. Specifically, the heating and aging process involves: first, heating the mixed slurry to 85°C, maintaining this temperature until the slurry changes color, and then continuing to maintain the temperature for another 75 minutes to obtain cobalt-doped iron phosphate dihydrate (Fe). 0.99 Co 0.01 PO4·2H2O).
[0081] S7. The cobalt-doped ferric phosphate dihydrate obtained in step S6 is subjected to pressure filtration and rinsed with pure water, controlling the conductivity of the rinsing water to be ≤500 μS / cm; then the rinsed cobalt-doped ferric phosphate dihydrate is dried at 95℃ for 12 h, and after drying, it is sintered at 600℃ for 4 h to convert the ferric phosphate dihydrate into anhydrous ferric phosphate, thus obtaining cobalt-doped ferric phosphate (Fe). 0.99 Co 0.01 PO4).
[0082] In this embodiment, the contents of each impurity element in the prepared cobalt-doped iron phosphate are shown in Table 2.
[0083] Table 2. Content (ppm) of each impurity element in the cobalt-doped iron phosphate prepared in Example 2. The method for preparing cobalt-doped iron phosphate provided in this embodiment omits the rinsing and pulping processes for amorphous iron phosphate materials compared to Example 1, resulting in a shorter process flow and reduced production costs. However, a comparison of Tables 1 and 2 shows that the content of impurity elements Mg and Mn in the cobalt-doped iron phosphate prepared in this embodiment is significantly higher than that in Example 1.
[0084] Examples 3-4 and Comparative Examples 3-5 Examples 3-4 and Comparative Examples 3-5 respectively provide a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that the heating temperature of the aging treatment in step S7 and the holding time after the slurry changes color are changed, as shown in Table 3. The remaining steps are the same as in Example 1 and will not be repeated here.
[0085] Table 3. Heating temperatures and holding times in Examples 3-4 and Comparative Examples 3-5 Examples 5-7 and Comparative Examples 6-8 Examples 5-7 and Comparative Examples 6-8 respectively provide a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that the molar ratio of cobalt and persulfate ions in the mixed solution and the molar ratio of cobalt and iron in the amorphous iron phosphate material in step S5 are changed, as shown in Table 4. The remaining steps are the same as in Example 1 and will not be repeated here.
[0086] Table 4. Relevant molar ratios in Examples 5-7 and Comparative Examples 6-8 II. Testing Methods 1. Phase analysis: The products prepared in Example 1 and Comparative Examples 1-2 were characterized by X-ray powder diffraction (XRD).
[0087] 2. Material content test: The content of each impurity element in the cobalt-doped iron phosphate prepared in each example and comparative example was tested by inductively coupled plasma atomic emission spectrometry.
[0088] III. Analysis of Test Results for Each Embodiment and Comparative Example By comparison Figure 2-4 It can be seen that the diffraction peaks of the cobalt-doped iron phosphate dihydrate and cobalt-doped iron phosphate prepared in Example 1 are the same as the diffraction peaks of the pure phase of iron phosphate dihydrate and the pure phase of anhydrous iron phosphate obtained without cobalt doping in Comparative Example 1. No derivative peaks of cobalt impurities appeared in Example 1, indicating that the cobalt element doped in Example 1 replaced the iron sites in the iron phosphate lattice, thus achieving lattice doping.
[0089] The cobalt content and cobalt precipitation efficiency in the cobalt-doped iron phosphates prepared in Examples 1-9 and Comparative Examples 1-10 are shown in Table 5.
[0090] Table 5. Detection data from Examples 1-7 and Comparative Examples 1-8 The cobalt precipitation efficiency is calculated as follows: Cobalt precipitation efficiency = y M1 / (1000000 x M2).
[0091] In the above formula, y represents the cobalt content in cobalt-doped iron phosphate, in ppm; x represents the amount of cobalt doping in cobalt-doped iron phosphate (i.e., Fe). 1-x Co x In PO4, x), M1 and M2 are the relative molecular weight of anhydrous iron phosphate and the relative atomic weight of cobalt, respectively.
[0092] As can be seen from Table 5, the cobalt-doped iron phosphate preparation methods provided in each embodiment of this application can achieve cobalt doping with a high cobalt precipitation efficiency (>82%).
[0093] Specifically, by comparing Example 1 and Comparative Examples 1-2, it can be seen that when hydrogen peroxide is used as an oxidant in Comparative Example 2, since divalent cobalt ions cannot be oxidized to trivalent cobalt ions, only divalent cobalt ions can be used for doping. The cobalt content in the resulting cobalt-doped iron phosphate is only slightly higher than that in Comparative Example 1 without cobalt doping, and the cobalt precipitation efficiency is extremely low. In contrast, in Example 1, sodium persulfate is used as an oxidant, and after activation, divalent cobalt ions are oxidized to trivalent cobalt ions. Compared with Comparative Example 2, this effectively improves the cobalt content and cobalt precipitation efficiency in cobalt-doped iron phosphate.
[0094] Comparing Examples 1, 2, and 3, it can be seen that in Comparative Example 3, no phosphoric acid was added during the preparation of the mixed solution in step S5. Therefore, a phosphate-rich environment was not formed, resulting in the reduction of some trivalent cobalt ions to divalent cobalt ions. This affected the cobalt content and precipitation efficiency of the cobalt-doped iron phosphate obtained from Comparative Example 3. Although no phosphoric acid was added in Example 2, the proportion of phosphate used in the preparation of amorphous iron phosphate was increased. This also created a phosphate-rich environment, preventing the reduction of trivalent cobalt ions and resulting in a higher cobalt content in the prepared cobalt-doped iron phosphate.
[0095] Comparing Examples 1, 3-4, and 3-5, it can be seen that the heating temperature and the holding time during the aging treatment have a significant impact on the cobalt content in the prepared cobalt-doped iron phosphate. In Comparative Examples 3-5, excessively high or low heating temperatures or excessively short holding times are detrimental to the activation of sodium persulfate, thus affecting the oxidation effect on divalent cobalt ions. This leads to a decrease in the content of trivalent cobalt ions formed in Comparative Examples 3-5, resulting in a lower cobalt content in the final prepared cobalt-doped iron phosphate.
[0096] Comparative studies of Examples 1, 5-7, and 6-8 show that the molar ratio of cobalt to persulfate ions in the mixed solution affects the cobalt precipitation efficiency. If the persulfate ratio is too low, the lack of sufficient oxidant to oxidize divalent cobalt ions leads to a significant decrease in cobalt precipitation efficiency. Conversely, while a high persulfate ratio improves precipitation efficiency, it results in significant raw material waste with little improvement in efficiency, and excessive sulfate residue may lead to excessive sulfur content in the resulting iron phosphate. Furthermore, variations in the molar ratio of cobalt to iron in the mixed solution affect the cobalt doping level. Higher doping levels result in higher cobalt content in the cobalt-doped iron phosphate. Appropriately increasing the cobalt doping level within a certain range can improve precipitation, but excessively high levels reduce precipitation efficiency and decrease the proportion of lithium iron phosphate in the resulting lithium iron phosphate battery, thus affecting the battery's electrochemical performance.
[0097] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A method for preparing cobalt-doped iron phosphate, characterized in that, Includes the following steps: Amorphous iron phosphate materials and mixed solutions containing divalent cobalt salts and persulfates are provided; The amorphous iron phosphate material is mixed with the mixed solution to obtain a mixed slurry; The mixed slurry was subjected to a heating and aging treatment to obtain cobalt-doped iron phosphate dihydrate; The cobalt-doped iron phosphate dihydrate was washed, dried, and sintered to obtain cobalt-doped iron phosphate.
2. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The mixed solution also contains phosphoric acid; and / or, The amorphous iron phosphate material is formed by reacting an iron salt solution and a phosphate solution, wherein the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(1.05~1.30).
3. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The heating and aging process includes: heating to 75~90℃, maintaining the temperature until the mixed slurry changes color, and then maintaining the temperature for another 60~120 minutes.
4. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, In the mixed solution, the molar ratio of cobalt to persulfate ions is 1:(1.0~4.0).
5. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, In the mixed slurry, the molar ratio of iron to cobalt is 1-x : x, where 0 < x ≤ 0.
02.
6. The method for preparing cobalt-doped iron phosphate according to claim 2, characterized in that, The method for preparing the amorphous iron phosphate material provided includes: Iron salts are dissolved in water to obtain an iron salt solution; Phosphate, hydrogen peroxide, and water are mixed to obtain a phosphate solution; The phosphate solution is added to the iron salt solution, and after the reaction, an amorphous iron phosphate material is obtained. Among them, Fe in the iron salt solution 2+ The molar concentration of phosphorus in the phosphate solution is 0.5~1.2 mol / L, and the molar concentration of phosphorus in the phosphate solution is 1.0~2.0 mol / L.
7. The method for preparing cobalt-doped iron phosphate according to claim 6, characterized in that, When the mixed solution contains phosphoric acid, the pH value of the phosphate solution is 6.5~7.5, the molar ratio of iron in the iron salt solution to hydrogen peroxide in the phosphate solution is 1:(0.6~1.0), and the molar ratio of iron in the iron salt solution to phosphorus in the phosphate solution is 1:(0.9~1.10).
8. The method for preparing cobalt-doped iron phosphate according to claim 2, characterized in that, When the mixed solution contains phosphoric acid, the step of mixing the amorphous iron phosphate material with the mixed solution to obtain a mixed slurry includes: The amorphous iron phosphate material was subjected to solid-liquid separation and washing to obtain a filter cake; The filter cake is mixed with the mixed solution and dispersed by slurrying for 30-60 minutes to obtain a mixed slurry. The molar ratio of phosphoric acid in the mixed solution to iron in the amorphous iron phosphate material is (0.1~0.3):
1.
9. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The washing steps include: rinsing with water until the conductivity of the resulting rinse water is ≤500 μs / cm; and / or, The drying step includes: drying at 90~100℃ for 10~14 hours; and / or, The sintering process includes sintering at 550~650℃.
10. A cobalt-doped iron phosphate, characterized in that, It is prepared by any one of the preparation methods according to claims 1-9.