Preparation method of cobalt-doped iron phosphate

Abstract

The invention provides a preparation method of cobalt-doped iron phosphate, and belongs to the field of new energy battery positive electrode material metal doping, the preparation method of cobalt-doped iron phosphate comprises the following steps: providing a CoOOH solution and amorphous iron phosphate; mixing the CoOOH solution with amorphous iron phosphate, and then carrying out slurrying treatment to obtain first slurry; aging the first slurry to obtain a ferrocobalt solid solution; and drying and calcining the ferrocobalt solid solution to obtain the cobalt-doped iron phosphate. According to the application, Co < 3 + > is adopted for doping, so that CoPO4 and FePO4 which are consistent in crystal structure can generate a ferrocobalt solid solution more easily in the aging process, and therefore, the utilization rate of cobalt and the content of cobalt in cobalt-doped iron phosphate can be increased.

Description

Preparation method of cobalt-doped iron phosphate Technical Field

[0001] This invention relates to the field of metal doping in cathode materials for new energy batteries, specifically to a method for preparing cobalt-doped iron phosphate. Background Technology

[0002] LiFePO4 (lithium iron phosphate) batteries possess excellent thermal stability, a cycle life far exceeding other types of lithium-ion batteries, relatively low cost, and environmental friendliness. They can store electrical energy and power vehicle electric motors, making them one of the mainstream power battery technologies in the new energy vehicle sector. However, with the continuous development of new energy vehicles, the limitations of LiFePO4 batteries have gradually become apparent. These limitations stem from the low conductivity (10⁻⁶) of LiFePO4 due to its inherent structural constraints. -9 S·cm -1 The slow lithium-ion diffusion rate and other issues result in a low discharge potential, making it difficult to achieve full capacity and thus limiting the electrochemical performance of LiFePO4 cathode materials.

[0003] In existing technologies, researchers have proposed various solutions to address the technical challenges of improving the electronic conductivity and ion diffusion rate of LiFePO4 batteries, primarily including carbon coating and metal ion doping. Metal ion doping involves introducing small amounts of specific metal ions (such as magnesium, titanium, aluminum, cobalt, etc.) into the crystal structure of LiFePO4, replacing the original lithium or iron ion positions in the crystal lattice. By incorporating other metal ions, the intrinsic electronic structure and / or crystal structure parameters of LiFePO4 are altered, thereby increasing electronic conductivity and accelerating ion diffusion rate.

[0004] Currently, the conventional method for doping cobalt into LiFePO4 is to react cobalt sulfate with phosphate and carbonate to prepare cobalt phosphate, and then react the cobalt phosphate with iron phosphate to form a cobalt-iron solid solution. That is, using Co... 2+ Doping is performed in the form of Co. However, Co 2+ With PO4 3- Precipitation requires a relatively high pH (5.5-6.5), and impurities also tend to precipitate at this pH and be introduced into the target product, affecting product performance. Furthermore, Co... 2+ With PO4 3- The resulting product is Co3(PO4)2. Since Co3(PO4)2 has a different crystal structure than iron phosphate (FePO4), forming a cobalt-iron solid solution is more difficult, directly affecting the cobalt doping rate. Therefore, under the combined influence of the aforementioned factors, the performance of cobalt-doped LiFePO4 remains significantly limited. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method for preparing cobalt-doped iron phosphate, which aims to solve the technical problems of easy introduction of impurities and low doping rate during the preparation of cobalt-doped iron phosphate.

[0006] This application provides a method for preparing cobalt-doped iron phosphate, comprising the following steps: providing a CoOOH solution and amorphous iron phosphate; mixing the CoOOH solution and the amorphous iron phosphate and then performing a slurry treatment to obtain a first slurry; aging the first slurry to obtain a cobalt-iron solid solution; and drying and calcining the cobalt-iron solid solution to obtain cobalt-doped iron phosphate.

[0007] In the technical solution of this application embodiment, CoOOH is first reacted with phosphoric acid through a slurry treatment to generate CoPO4 precipitate, while CoPO4 is uniformly mixed with amorphous iron phosphate; then, through aging treatment, CoPO4 with a uniform crystal structure reacts with FePO4 to generate cobalt-iron solid solution; finally, the crystallinity is improved by drying and calcination to prepare cobalt-doped iron phosphate. This application uses Co... 3+ Doping makes CoPO4 and FePO4 with consistent crystal structures more likely to form cobalt-iron solid solutions during aging, which helps to increase the cobalt content in cobalt-doped iron phosphate and thus improve the electrochemical performance of LiFePO4 cathode materials.

[0008] In some embodiments, the pH environment of the pulping treatment is 1.6 to 2.0.

[0009] In this embodiment, impurity elements are less likely to precipitate when the pH environment is 1.6~2.0. By performing pulping treatment under pH conditions of 1.6~2.0, CoOOH and phosphoric acid can fully react to generate CoPO4 precipitate while reducing the introduction of impurity elements.

[0010] In some embodiments, the preparation method of the provided CoOOH solution includes the following steps: mixing water with a first pH adjuster to obtain a base liquid; adding cobalt salt and a second pH adjuster to the base liquid to obtain a second slurry; adding a first oxidant and a third pH adjuster to the second slurry to obtain a third slurry; and stirring the third slurry to obtain a CoOOH solution; wherein the pH values ​​of the base liquid, the second slurry, and the third slurry are all 9.0 to 9.5.

[0011] In this embodiment, the base liquid provides an alkaline environment to generate the hydroxide intermediate Co(OH)2, and the second and third slurries provide an alkaline environment to over-oxidize Co(OH)2 to obtain CoOOH, thereby allowing Co to exist stably in the slurry in the +3 oxidation state.

[0012] In some embodiments, the molar ratio of the cobalt salt to the first oxidant is 1:(0.8~1.0); and / or, the first pH adjuster, the second pH adjuster, and the third pH adjuster are each independently selected from at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate; and / or, the cobalt salt includes at least one of cobalt sulfate heptahydrate, cobalt chloride, cobalt nitrate, and cobalt acetate; and / or, the first oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

[0013] In this embodiment, optimizing the molar ratio of cobalt salt to the first oxidant facilitates the complete conversion of divalent cobalt in the cobalt salt into trivalent cobalt. Optimizing the types of raw materials for the pH adjuster, cobalt salt, and oxidant facilitates the successful preparation of high-purity CoOOH. Furthermore, the wide availability and low cost of these raw materials are beneficial for industrial production.

[0014] In some embodiments, the method for preparing the amorphous ferric phosphate includes the following steps: mixing a ferrous salt with water to obtain a ferrous salt solution; mixing a phosphate salt with water and a second oxidizing agent to obtain a phosphate salt solution; adding the phosphate salt solution to the ferrous salt solution, and reacting to obtain amorphous ferric phosphate.

[0015] In this embodiment, a co-precipitation method is used to prepare amorphous iron phosphate by reacting a ferrous salt solution with an oxidant and a phosphate solution. Specifically, ferrous ions are oxidized to ferric ions by the oxidant under acidic conditions. These ferric ions then immediately react with phosphate ions in the solution to form amorphous iron phosphate precipitate with extremely low solubility.

[0016] In some embodiments, the molar ratio of the ferrous salt to the phosphate salt and the second oxidant is 1:(1.0~1.1):(0.5~1.0); and / or, the concentration of ferrous ions in the ferrous salt solution is 0.5~1.5 mol / L; and / or, the mass concentration of phosphorus in the phosphate salt solution is 3~9%; and / or, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the phosphate salt includes at least one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, and diammonium hydrogen phosphate; and / or, the second oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

[0017] In this embodiment, by optimizing the feeding ratio of ferrous salt to the second oxidant, it is possible to ensure that Fe 2+ It is fully oxidized, avoiding the introduction of impurities such as ferrous phosphate (Fe3(PO4)2). Simultaneously, by optimizing the feed ratio of ferrous salt to phosphate salt, it is possible to ensure that Fe is fully oxidized. 3+ It is completely converted to FePO4, avoiding Fe 3+Impurities are introduced after precipitation in the form of other iron oxides. Furthermore, by optimizing the types of raw materials for ferrous salts, phosphate salts, and the second oxidant, as well as the concentrations of ferrous ions and phosphorus, it is beneficial to control the nucleation rate of FePO4 within the optimal range, thereby obtaining amorphous FePO4 particles with uniform particle size distribution and regular morphology.

[0018] In some embodiments, the pulping process includes: adding the CoOOH solution and the amorphous ferric phosphate to a mixture containing water and phosphoric acid, and pulping; wherein the molar ratio of iron in the amorphous ferric phosphate to CoOOH in the CoOOH solution is 1:(0.025~0.1); and the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:(0.2~0.3).

[0019] In this embodiment, through slurry processing, CoOOH can be dissolved in a mixture containing water and phosphoric acid, releasing Co. 3+ Co 3+ With PO4 3- The reaction produces CoPO4 precipitate, which is then uniformly dispersed and mixed with amorphous ferric phosphate through slurrying. The phosphoric acid in the mixture helps regulate the pH environment of the slurry treatment, preventing the reduction of trivalent cobalt to divalent cobalt and reducing the formation of impurity precipitates, thus avoiding the introduction of impurities into the target product. Furthermore, optimizing the molar ratio of iron to CoOOH in the amorphous ferric phosphate helps control the cobalt doping level within an optimal range. Further optimization of the molar ratio of iron to phosphoric acid in the amorphous ferric phosphate helps provide a suitable acidic environment and phosphorus compensation.

[0020] In some embodiments, the aging process includes: aging the first slurry at 90~100°C, and after the first slurry changes color, keeping it at that temperature for 2~2.5 hours.

[0021] In this embodiment, the aging process provides sufficient energy and time for CoPO4 and FePO4, which is beneficial for the rearrangement of ions in the first slurry. Specifically, because the crystal structures of CoPO4 and FePO4 are highly similar, the Fe atoms on the surface or in the lattice of amorphous iron phosphate... 3+ It is more likely to be partially replaced by Co 3+ This process enables cobalt doping and improves the doping amount and utilization rate of cobalt. At the same time, iron phosphate can transform from a disordered state into a more stable ordered crystal structure, ultimately yielding a cobalt-iron solid solution.

[0022] In some embodiments, the drying temperature is 95~110℃ and the drying time is 12~14h; and / or, the calcination temperature is 600~650℃ and the calcination time is 2~3h.

[0023] In this embodiment, drying removes moisture from the cobalt-iron solid solution, which facilitates subsequent calcination and prevents material splashing, agglomeration, or uneven product formation during calcination. Simultaneously, calcination promotes grain growth and defect repair in the cobalt-iron solid solution, leading to cobalt-doped iron phosphate with higher crystallinity.

[0024] In some embodiments, the cobalt-doped iron phosphate has the general molecular formula Fe. 1-x Co x PO4, where 0 < x ≤ 0.1.

[0025] In this embodiment, the cobalt doping ratio is less than or equal to 10%, which is beneficial to improve the electrochemical performance of the cathode material while reducing the consumption of precious metals and lowering production costs.

[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 is a flowchart of the preparation route of cobalt-doped iron phosphate in Example 1 of this application; Figure 2 is the XRD pattern of cobalt-doped iron phosphate in Example 1 of this application; Figure 3 is the SEM image of cobalt-doped iron phosphate in Example 1 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] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0035] Currently, the conventional method for doping cobalt into LiFePO4 is to react cobalt sulfate with phosphate and carbonate to prepare cobalt phosphate, and then react the cobalt phosphate with iron phosphate to form a cobalt-iron solid solution. That is, using Co... 2+ The cobalt-iron solid solution is produced by this method, but it is difficult to generate the cobalt-iron solid solution, resulting in a low cobalt doping rate. In addition, impurities are easily introduced during the preparation process, which limits the performance of cobalt-doped LiFePO4.

[0036] To address the challenges of generating a cobalt-iron solid solution during the preparation of cobalt-doped LiFePO4, which leads to low cobalt doping rates and the easy introduction of impurities, this application provides a method for preparing cobalt-doped iron phosphate. First, a slurry treatment is used to react CoOOH with phosphoric acid to generate CoPO4 precipitate, while simultaneously mixing CoPO4 with amorphous iron phosphate. Next, an aging treatment is performed to allow the CoPO4 with a uniform crystal structure to react with FePO4 to form a cobalt-iron solid solution. Finally, drying and calcination are used to improve crystallinity, yielding cobalt-doped iron phosphate. In this application, Co... 3+Doping makes CoPO4 and FePO4 with consistent crystal structures more likely to form cobalt-iron solid solutions during aging, which is beneficial to improving the utilization rate of cobalt and the cobalt content in cobalt-doped iron phosphate, thereby improving the electrochemical performance of LiFePO4 cathode materials.

[0037] Specifically, this application provides a method for preparing cobalt-doped iron phosphate, comprising the following steps: S1. providing a CoOOH solution and amorphous iron phosphate; S2. mixing the CoOOH solution and amorphous iron phosphate and then performing a slurry treatment to obtain a first slurry; S3. aging the first slurry to obtain a cobalt-iron solid solution; S4. drying and calcining the cobalt-iron solid solution to obtain cobalt-doped iron phosphate.

[0038] In this application, CoOOH is mixed with amorphous ferric phosphate and then subjected to a slurry treatment. During stirring, CoOOH dissolves and transforms into CoPO4 precipitate. Simultaneously, CoPO4 and amorphous ferric phosphate are uniformly mixed and dispersed in the solution, with some CoPO4 adsorbing onto the amorphous ferric phosphate, resulting in a first slurry. Subsequently, the first slurry is aged, which allows the uniformly mixed or adsorbed CoPO4 to rearrange with the amorphous ferric phosphate. Specifically, CoPO4 adsorbs some Fe from the surface or lattice of the amorphous ferric phosphate. 3+ Replace with Co 3+ Simultaneously, the aging process transforms ferric phosphate from a disordered state into a more stable, ordered crystal structure, thus yielding a cobalt-iron solid solution. Finally, the cobalt-iron solid solution is first dried to remove moisture, and then calcined to remove the Co from the solid solution. 3+ Locked within the lattice of iron phosphate, it completely replaces some Fe sites, achieving cobalt doping and promoting grain growth and crystal defect repair in the cobalt-iron solid solution. This is beneficial for improving crystallinity and obtaining long-range ordered and high-purity cobalt-doped iron phosphate.

[0039] This application adopts Co 3+ Doping can produce CoPO4 with the same crystal structure as FePO4. Both are more likely to form cobalt-iron solid solution during aging, which helps to reduce the difficulty of preparing cobalt-doped iron phosphate, promote its industrialization, improve the utilization rate of cobalt and the cobalt content in cobalt-doped iron phosphate, thereby improving the activity and energy density of LiFePO4 cathode material and enhancing its electrochemical performance.

[0040] Furthermore, in some embodiments, the pH environment for the pulping treatment is 1.6 to 2.0.

[0041] In this application, by precisely controlling the pH environment of the pulping process, the Co in CoOOH is made more cohesive. 3+At lower pH values, CoPO4 precipitate with a smaller solubility product preferentially forms, and mixes uniformly with amorphous ferric phosphate, which also has a small solubility product, under stirring and they adsorb each other. This facilitates the removal of some Fe from the amorphous ferric phosphate during subsequent aging treatment. 3+ Replace with Co 3+ Meanwhile, since common impurity elements are not easily precipitated in an environment with a pH value of 1.6 to 2.0, this application controls the pH environment of the pulping process at 1.6 to 2.0, which helps to reduce the introduction of impurity elements and promotes the full reaction of CoOOH with phosphoric acid to form CoPO4 precipitate. Specifically, the pH environment of the pulping process can be 1.6, 1.7, 1.8, 1.9, 2.0, or any value within the range of 1.6 to 2.0.

[0042] Further, in some embodiments, the method for preparing the provided CoOOH solution includes the following steps: mixing water with a first pH adjuster to obtain a base liquid; adding cobalt salt and a second pH adjuster to the base liquid to obtain a second slurry; adding a first oxidant and a third pH adjuster to the second slurry to obtain a third slurry; and stirring the third slurry to obtain a CoOOH solution; wherein the pH values ​​of the base liquid, the second slurry, and the third slurry are all 9.0~9.5.

[0043] In this application, by adjusting the pH of the base solution, the cobalt salt, upon being added to the base solution, reacts instantly to form a Co(OH)₂ precipitate that remains insoluble. By adjusting the pH of the second slurry, the Co(OH)₂ precipitate is stably present in the slurry, and after the addition of the first oxidant, the Co(OH)₂ precipitate is over-oxidized to CoOOH with good crystallinity and uniform morphology, rather than other Co oxides. By adjusting the pH of the third slurry, the Co(OH)₂ precipitate reacts fully with the first oxidant to form CoOOH, and the stability of CoOOH is ensured, so that Co always exists stably in the slurry in the +3 valence form. Specifically, the pH values ​​of the base solution, the second slurry, and the third slurry can be 9, 9.1, 9.2, 9.3, 9.4, 9.5, or any value within the range of 9 to 9.5.

[0044] Further, in some embodiments, the molar ratio of cobalt salt to the first oxidant is 1:(0.8~1.0); and / or, the first pH adjuster, the second pH adjuster, and the third pH adjuster are each independently selected from at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate; and / or, the cobalt salt includes at least one of cobalt sulfate heptahydrate, cobalt chloride, cobalt nitrate, and cobalt acetate; and / or, the first oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

[0045] In this application, by optimizing the molar ratio of cobalt salt to the first oxidant, it is beneficial to accurately convert the Co(OH)2 precipitate generated under alkaline conditions into CoOOH, rather than other cobalt oxides, to obtain stable trivalent cobalt. Furthermore, by optimizing the types of raw materials—pH adjuster, cobalt salt, and oxidant—it is beneficial to control the reaction route and successfully prepare high-purity CoOOH. At the same time, the aforementioned raw materials are widely available and inexpensive, allowing for selection based on actual conditions, which is beneficial for industrial production. Specifically, the molar ratio of cobalt salt to the first oxidant is any value within the range of 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, or 1:(0.8~1.0).

[0046] Furthermore, in some embodiments, the cobalt salt and the second pH adjuster are added at a time of 10-30 minutes; the first oxidant and the third pH adjuster are added at a time of 10-30 minutes; and the third slurry is stirred and reacted at a time of 20-40 minutes.

[0047] In this application, by controlling the addition time of each raw material and the stirring reaction time, it is beneficial to promote the full progress of the reaction, so as to efficiently prepare high-purity CoOOH.

[0048] Furthermore, in some embodiments, the method for preparing amorphous ferric phosphate includes the following steps: mixing ferrous salt with water to obtain a ferrous salt solution; mixing phosphate salt with water and a second oxidizing agent to obtain a phosphate salt solution; adding the phosphate salt solution to the ferrous salt solution, and reacting to obtain amorphous ferric phosphate.

[0049] In this application, amorphous iron phosphate was prepared using a co-precipitation method. Specifically, stable ferrous salt and phosphate solutions were first prepared. The phosphate solution was then added to the ferrous salt solution, allowing the ferrous ions in the ferrous salt solution to be oxidized to ferric ions under acidic conditions. These ferric ions immediately react with phosphate ions in the solution to form FePO4. Since FePO4 has extremely low solubility, it precipitates instantly before it can form a regular crystal structure, resulting in a disordered amorphous iron phosphate precipitate. This disordered structure facilitates the thermal diffusion of cobalt ions into the iron phosphate crystal lattice.

[0050] Further, in some embodiments, the molar ratio of ferrous salt to phosphate salt and the second oxidant is 1:(1.0~1.1):(0.5~1.0); and / or, the concentration of ferrous ions in the ferrous salt solution is 0.5~1.5 mol / L; and / or, the mass concentration of phosphorus in the phosphate salt solution is 3~9%; and / or, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the phosphate salt includes at least one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, and diammonium hydrogen phosphate; and / or, the second oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

[0051] In this application, by optimizing the feed ratio of ferrous salt to the second oxidant, it is possible to ensure that all Fe... 2+ All were fully oxidized to Fe 3+ To avoid residual unoxidized Fe 2+ The reaction with phosphoric acid produces impurities such as ferrous phosphate (Fe3(PO4)2), which severely affects the electrochemical performance of the LiFePO4 cathode material. Meanwhile, by optimizing the feed ratio of divalent iron salt to phosphate salt, the optimal Fe2+ / Fe2+ / Fe3+ / Fe2+ / Fe3+ / Fe3+ / Fe4+ / Fe3 ... 3+ It is completely converted to FePO4, avoiding excess Fe. 3+ Precipitation in the form of Fe(OH)3 or other iron oxides introduces impurities into ferric phosphate. Furthermore, by optimizing the types of raw materials (ferrous salts, phosphate salts, oxidants, and the concentrations of ferrous ions and phosphorus), the nucleation rate of FePO4 can be controlled within an optimal range. This avoids the instantaneous generation of a large number of crystal nuclei, resulting in excessively fine particles that are difficult to process later. It also avoids excessive crystal growth leading to overly large particle sizes or localized crystallization, thus obtaining amorphous FePO4 particles with uniform particle size distribution and regular morphology.

[0052] Specifically, the molar ratio of ferrous salt to phosphate salt can be any value within the range of 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, or 1:(1.0~1.1); the molar ratio of ferrous salt to second oxidant can be any value within the range of 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or 1:(0.5~1.0).

[0053] Furthermore, in some embodiments, the phosphate salt solution is added at a time of 10-30 minutes; the reaction time between the phosphate salt solution and the ferrous salt solution is 40-60 minutes.

[0054] In this application, by controlling the addition time of the raw materials and the reaction time, it is beneficial to control the nucleation rate of FePO4 and promote the complete reaction, so that Fe3+ It is fully transformed into amorphous FePO4 particles with uniform particle size distribution and regular morphology.

[0055] Further, in some embodiments, the pulping process includes: adding CoOOH solution and amorphous ferric phosphate to a mixture containing water and phosphoric acid, and pulping; wherein the molar ratio of iron in the amorphous ferric phosphate to CoOOH in the CoOOH solution is 1:(0.025~0.1); and the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:(0.2~0.3).

[0056] In this application, by adding a CoOOH solution to a mixture containing water and phosphoric acid, CoOOH can dissolve and release Co under acidic conditions and stirring. 3+ Co 3+ With PO4 3- The reaction produces CoPO4 precipitate. Simultaneously, CoPO4 and amorphous ferric phosphate are uniformly mixed and dispersed in the solution through slurrying. Some CoPO4 and amorphous ferric phosphate adsorb each other, which facilitates the removal of some Fe from the amorphous ferric phosphate through thermal diffusion during subsequent aging treatment. 3+ Replace with Co 3+ The phosphoric acid in the mixture helps regulate the pH environment of the slurry treatment, preventing trivalent cobalt from being reduced to divalent cobalt and reducing the formation of impurity precipitates. Optimizing the molar ratio of iron to CoOOH in amorphous iron phosphate helps control the cobalt doping amount within the optimal range, maximizing the performance of cobalt-doped iron phosphate. Optimizing the molar ratio of iron to phosphoric acid in amorphous iron phosphate also helps provide a suitable acidic environment and phosphorus compensation, ensuring the stable presence of amorphous iron phosphate and CoPO4 in the slurry. Controlling the molar ratio of iron in amorphous iron phosphate to CoOOH in the CoOOH solution helps regulate the cobalt doping ratio.

[0057] Specifically, the molar ratio of iron in amorphous ferric phosphate to CoOOH in the CoOOH solution can be any value within the range of 1:0.025, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, or 1:(0.025~0.1); the molar ratio of iron in amorphous ferric phosphate to phosphoric acid in the mixture can be any value within the range of 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, 1:0.29, 1:0.3, or 1:(0.2~0.3).

[0058] Furthermore, in some embodiments, the aging process includes: aging the first slurry at 90~100°C, and after the first slurry changes color, keeping it at that temperature for 2~2.5 hours.

[0059] In this application, the aging treatment provides sufficient energy and time for CoPO4 and FePO4, which is conducive to the rearrangement of ions in the first slurry. During the ion rearrangement process, Fe in the amorphous iron phosphate surface or lattice... 3+ Partially replaced by Co 3+ This allows for cobalt doping, and because the crystal structures of CoPO4 and FePO4 are highly similar, Co... 3+ Compared to Co 2+ It is easier to convert Fe 3+ The substitution and formation of a cobalt-iron solid solution facilitates the full doping of cobalt into iron phosphate, increasing the cobalt doping amount and utilization rate, while simultaneously reducing the difficulty of preparing cobalt-doped iron phosphate. This application, through aging at higher temperatures, enables iron phosphate to transform from a disordered state into an ordered crystal structure, ultimately yielding a more stable cobalt-iron solid solution.

[0060] Furthermore, in some embodiments, the drying temperature is 95~110°C and the drying time is 12~14h; and / or, the calcination temperature is 600~650°C and the calcination time is 2~3h.

[0061] In this application, drying removes moisture from the cobalt-iron solid solution, which facilitates subsequent calcination and avoids material splashing, agglomeration, or uneven product formation during calcination. Calcination promotes grain growth and defect repair in the cobalt-iron solid solution, resulting in cobalt-doped iron phosphate with higher crystallinity.

[0062] Furthermore, in some embodiments, the general molecular formula of cobalt-doped iron phosphate is Fe. 1-x Co x PO4, where 0 < x ≤ 0.1.

[0063] In this application, x represents the cobalt doping ratio. By adjusting the cobalt doping ratio, it is beneficial to improve the electrochemical performance of the cathode material while reducing the consumption of precious metals and lowering production costs. Specifically, the cobalt doping ratio can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the range of 0 to 10%, but not including 0.

[0064] 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.

[0065] I. Preparation Method Example 1 Please refer to Figure 1. This example provides a method for preparing cobalt-doped iron phosphate, including the following steps: S1. Provide CoOOH solution and amorphous iron phosphate.

[0066] (1) Preparation of CoOOH solution: CoSO4·7H2O was prepared into a 1 mol / L CoSO4 solution with deionized water. 1000 mL of a base solution with a pH of 9.0-9.5 was prepared by mixing deionized water with NaOH and placed in a synthesis reactor. 1000 mL of CoSO4 solution and 8% NaOH solution were simultaneously added dropwise to the base solution for 30 min to obtain the second slurry. Then, 108.8 mL of 25% hydrogen peroxide and 8% NaOH solution were simultaneously added dropwise to the second slurry for 30 min to obtain the third slurry. During the addition of CoSO4 solution and hydrogen peroxide, the mixture was continuously stirred, and the pH of the second and third slurries was adjusted to 9-9.5 by controlling the dropwise rate of NaOH solution. After the addition of CoSO4 solution and hydrogen peroxide was completed, the mixture was stirred for another 30 min to obtain the CoOOH solution. The molar ratio of CoSO4 to hydrogen peroxide is 1:0.88.

[0067] (2) Preparation of amorphous ferric phosphate: FeSO4 was prepared into a 1 mol / L FeSO4 solution with deionized water. A phosphate salt solution with a phosphorus concentration of 5.5% was prepared using sodium dihydrogen phosphate, deionized water, and hydrogen peroxide, wherein the molar ratio of phosphorus to hydrogen peroxide in the phosphate salt solution was 1.02:0.6. Then, 574.92 mL of the phosphate salt solution was added dropwise to 1000 mL of FeSO4 solution and reacted for 50 min to obtain amorphous ferric phosphate. The amorphous ferric phosphate was washed with deionized water until the conductivity of the washing solution was less than or equal to 3.5 mS / cm to obtain water-washed amorphous ferric phosphate. The dropwise addition time of the phosphate salt solution was 30 min, and the molar ratio of ferrous ions in the FeSO4 solution to phosphorus in the phosphate salt solution was 1:1.02.

[0068] S2. Add 200 mL of CoOOH solution and the washed amorphous ferric phosphate to a mixture containing water and phosphoric acid. Pulping is carried out for 30 min at a pH of 1.7–1.8 to obtain the first slurry. The molar ratio of iron in the amorphous ferric phosphate to CoOOH in the CoOOH solution is 1:0.1, and the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:0.25.

[0069] During the pulping process, the reaction formula for the formation of CoPO4 from CoOOH and phosphoric acid is CoOOH + H3PO4 + (Y-2)H2O → CoPO4·YH2O.

[0070] S3. Place the first slurry into an aging reactor and age it at 98°C. After the first slurry changes color, keep it at that temperature for 2 hours to obtain a cobalt-iron solid solution. Wash the cobalt-iron solid solution with deionized water until the conductivity of the washing solution is less than or equal to 350 μS / cm to obtain the washed cobalt-iron solid solution.

[0071] During the aging process, the reaction formula for the formation of cobalt-iron solid solution from CoPO4 and FePO4 is FePO4·YH2O + 0.1CoPO4·YH2O → FeCo 0.1 PO4·2H2O+(Y-2)H2O.

[0072] S4. The cobalt-iron solid solution after washing with water is dried at 98°C for 12 hours and then calcined at 600°C for 2 hours to obtain cobalt-doped iron phosphate.

[0073] Example 2 This example provides a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in amorphous iron phosphate to CoOOH in the CoOOH solution is changed in step S2. In this example, the molar ratio of iron in amorphous iron phosphate to CoOOH in the CoOOH solution is 1:0.08. The remaining steps are the same as in Example 1 and will not be repeated here.

[0074] In this embodiment, during the aging process, the reaction formula for the formation of cobalt-iron solid solution from CoPO4 and FePO4 is FePO4·YH2O + 0.08CoPO4·YH2O → FeCo 0.08 PO4·2H2O+(Y-2)H2O.

[0075] Example 3 This example provides a method for preparing cobalt-doped ferric phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in amorphous ferric phosphate, CoOOH in the CoOOH solution, and phosphoric acid in the mixture is changed in step S2. In this example, the molar ratio of iron in amorphous ferric phosphate to CoOOH in the CoOOH solution is 1:0.05. The remaining steps are the same as in Example 1 and will not be repeated here.

[0076] In this embodiment, during the aging process, the reaction formula for the formation of cobalt-iron solid solution from CoPO4 and FePO4 is FePO4·YH2O + 0.05CoPO4·YH2O → FeCo 0.05 PO4·2H2O+(Y-2)H2O.

[0077] Example 4 This example provides a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in amorphous iron phosphate, CoOOH in the CoOOH solution, and phosphoric acid in the mixture is changed in step S2. In this example, the molar ratio of iron in amorphous iron phosphate to CoOOH in the CoOOH solution is 1:0.025. The remaining steps are the same as in Example 1 and will not be repeated here.

[0078] In this embodiment, during the aging process, the reaction formula for the formation of cobalt-iron solid solution from CoPO4 and FePO4 is FePO4·YH2O + 0.025CoPO4·YH2O → FeCo 0.025 PO4·2H2O+(Y-2)H2O.

[0079] Example 5 This example provides a method for preparing cobalt-doped ferric phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture in step S2 is changed to 1:0.30. That is, the pulping is carried out under the condition of pH 1.6~1.7. The remaining steps are the same as in Example 1, and will not be repeated here.

[0080] Example 6 This example provides a method for preparing cobalt-doped ferric phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixed solution is changed to 1:0.24 in step S2. That is, the pulping is carried out under the condition of pH 1.8~1.9. The remaining steps are the same as in Example 1, and will not be repeated here.

[0081] Example 7 This example provides a method for preparing cobalt-doped ferric phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixed solution is changed to 1:0.20 in step S2. That is, the pulping is carried out under the condition of pH 1.9~2.0. The remaining steps are the same as in Example 1, and will not be repeated here.

[0082] Comparative Example 1 This comparative example provides a method for preparing ferric phosphate, which differs from Example 1 in that cobalt is not doped during the preparation of ferric phosphate. In this comparative example, the method for preparing ferric phosphate includes the following steps: S1. Preparation of amorphous ferric phosphate: A 1 mol / L FeSO4 solution is prepared using FeSO4 and deionized water. A phosphate salt solution with a phosphorus element mass concentration of 5.5% is prepared using sodium dihydrogen phosphate, deionized water, and hydrogen peroxide, wherein the molar ratio of phosphorus element to hydrogen peroxide in the phosphate salt solution is 1.02:0.6. 574.92 mL of the phosphate salt solution is added dropwise to 1000 mL of FeSO4 solution and reacted for 50 min to obtain amorphous ferric phosphate. The amorphous ferric phosphate is washed with deionized water until the conductivity of the washing solution is less than or equal to 3.5 mS / cm to obtain water-washed amorphous ferric phosphate. The dropwise addition time of the phosphate salt solution is 30 min, and the molar ratio of ferrous ions in the FeSO4 solution to phosphorus element in the phosphate salt solution is 1:1.02.

[0083] S2. Add the washed amorphous ferric phosphate to a mixture containing water and phosphoric acid, and beat for 30 minutes at a pH of 1.7-1.8 to obtain the first slurry. The molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:0.25.

[0084] S3. Place the first slurry into an aging reactor and age it at 98°C. After the first slurry changes color, keep it at this temperature for 2 hours to obtain a solid solution. Wash the cobalt-iron solid solution with deionized water until the conductivity of the washing solution is less than or equal to 350 μS / cm to obtain a water-washed solid solution. S4. Dry the water-washed solid solution at 98°C for 12 hours, and then calcine it at 600°C for 2 hours to obtain iron phosphate.

[0085] Comparative Example 2 provides a method for preparing cobalt-doped iron phosphate. The only difference from Example 1 is that phosphoric acid is not added to the mixture in step S2. That is, the pulping is carried out under conditions of pH 3.0. The remaining steps are the same as in Example 1 and will not be repeated here.

[0086] Comparative Example 3 provides a method for preparing cobalt-doped ferric phosphate. Compared with Example 1, the only difference is that the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture in step S2 is changed to 1:0.6. That is, the pulping is carried out under the condition of pH 1.0. The remaining steps are the same as in Example 1 and will not be repeated here.

[0087] Comparative Example 4 provides a method for preparing cobalt-doped iron phosphate. The difference between this method and Example 1 is the use of Co... 2+ Preparation of cobalt-doped ferric phosphate. Specifically, step S1 does not require the preparation of a CoOOH solution; in step S2, the washed amorphous ferric phosphate and cobalt sulfate are added to a mixture containing water and phosphoric acid, and the mixture is stirred for 30 minutes at a pH of 1.7-1.8 to obtain the first slurry. The molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:0.25; the molar ratio of iron in the amorphous ferric phosphate to CoOOH in the cobalt sulfate solution is... 2+ The molar ratio is 1:0.1.

[0088] Comparative Example 5 provides a method for preparing cobalt-doped iron phosphate. Compared with Example 1, the difference is that the CoOOH solution prepared in Example 1 is replaced with a mixture of cobalt sulfate and hydrogen peroxide, wherein the molar ratio of cobalt sulfate to hydrogen peroxide is 1:0.88.

[0089] Specifically, in step S1, a mixture of cobalt sulfate and hydrogen peroxide is prepared: CoSO4·7H2O is prepared with deionized water to form a 1 mol / L CoSO4 solution, and 108.8 mL of 25% hydrogen peroxide is added dropwise to the CoSO4 solution to obtain a mixture of cobalt sulfate and hydrogen peroxide.

[0090] In step S2, the mixture of washed amorphous ferric phosphate, cobalt sulfate, and hydrogen peroxide is added to a mixture containing water and phosphoric acid. The mixture is then pulped for 30 minutes at a pH of 1.7–1.8 to obtain the first pulp. The molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:0.25; the molar ratio of iron in the amorphous ferric phosphate to cobalt sulfate in the mixture is [missing value]. 2+ The molar ratio is 1:0.1.

[0091] II. Test Methods 1. XRD Test The cobalt-doped iron phosphate prepared in Example 1 was tested using an X-ray diffractometer.

[0092] 2. SEM testing: The cobalt-doped iron phosphate prepared in Example 1 was tested using a scanning electron microscope, and the D50 particle size was measured.

[0093] 3. Elemental analysis: The cobalt-doped iron phosphate or iron phosphate prepared in each example and comparative example were tested using an elemental analyzer, and the iron content, phosphorus content and cobalt content were recorded.

[0094] 4. The specific surface area was determined by the gas adsorption BET method for the cobalt-doped iron phosphate or iron phosphate prepared in Example 1, with reference to standard GB / T 19587-2017.

[0095] III. Analysis of Test Results of Each Example and Comparative Example Figure 2 is the XRD pattern of cobalt-doped iron phosphate prepared in Example 1. As can be seen from Figure 2, the diffraction peak positions of the cobalt-doped iron phosphate sample prepared in Example 1 are consistent with those of the standard card of iron phosphate, and there are no other impurity peaks. This indicates that the preparation method of cobalt-doped iron phosphate provided in this application effectively achieves cobalt doping and does not contain impurity phases.

[0096] Figure 3 is a SEM image of the cobalt-doped iron phosphate prepared in Example 1. As can be seen from Figure 3, the primary particles of the cobalt-doped iron phosphate sample prepared in Example 1 have a uniform particle size distribution, regular morphology, and a clean surface without impurities, indicating that this application effectively reduces the introduction of impurity phases.

[0097] The cobalt-doped iron phosphate sample prepared in Example 1 had a D50 particle size of 5.92 μm and a specific surface area of ​​8.62 m². 2 / g, which is beneficial for preparing highly active LiFePO4 cathode materials.

[0098] Table 1. Elemental comparison of cobalt-doped iron phosphate or iron phosphate prepared in each embodiment and comparative example. As shown in Table 1, applying the technical solution of this application helps to increase the cobalt doping content (cobalt content) in iron phosphate, thereby improving cobalt utilization and the performance of cobalt-doped iron phosphate. Improved cobalt utilization means that, with the cobalt addition amount remaining constant, the cobalt doping content in iron phosphate increases significantly.

[0099] Comparing the data from Examples 1-4 and Comparative Example 1, it can be seen that by adjusting the molar ratio of iron in amorphous iron phosphate to CoOOH in the CoOOH solution, the cobalt content in cobalt-doped iron phosphate can be stably and accurately controlled, indicating that the preparation method provided in this application has high stability.

[0100] Comparing the data from Examples 1, 5-7, and Comparative Examples 2-3, it can be seen that Comparative Example 2, without the addition of phosphoric acid, had a pH of 3 and a cobalt content of only 1013.66 ppm, which is much lower than that of Example 1. This indicates that phosphoric acid helps maintain a suitable pH environment during pulping and promotes the conversion of CoOOH to CoPO4. In contrast, Comparative Example 3 further increased the amount of phosphoric acid and lowered the pH to 1, resulting in a slight decrease in cobalt content compared to Example 1. This suggests that an excessively low pH may be detrimental to the stability of CoPO4 or the formation of a solid solution. Controlling the pH environment of pulping within the range of 1.6-2.0 helps to significantly improve the utilization rate of cobalt.

[0101] Comparing the data from Example 1 and Comparative Examples 4-5, it can be seen that Comparative Example 4 uses Co 2+ The cobalt content was only 103.23 ppm, compared to Comparative Example 5 which used Co 2+ Compared to hydrogen peroxide, the cobalt content is only 13.71 ppm, while Example 1 used Co... 3+， The cobalt content reached 10171.94 ppm, indicating that Co... 3+ The resulting CoPO4 has the same crystal structure as FePO4, making it more likely to form a solid solution; Co 2+ It is difficult to be oxidized to Co by hydrogen peroxide in an acidic environment. 3+ Furthermore, the structure of the resulting Co3(PO4)2 differs greatly from that of FePO4, making it difficult to form a cobalt-iron solid solution, which leads to a significant decrease in the cobalt doping rate.

[0102] 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, The process includes the following steps: providing a CoOOH solution and amorphous ferric phosphate; mixing the CoOOH solution and the amorphous ferric phosphate and then performing a slurry treatment to obtain a first slurry; aging the first slurry to obtain a cobalt-iron solid solution; and drying and calcining the cobalt-iron solid solution to obtain cobalt-doped ferric phosphate.

2. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The pH environment for the pulping treatment is 1.6~2.

0.

3. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The method for preparing the CoOOH solution includes the following steps: mixing water with a first pH adjuster to obtain a base solution; adding cobalt salt and a second pH adjuster to the base solution to obtain a second slurry; adding a first oxidant and a third pH adjuster to the second slurry to obtain a third slurry; and stirring the third slurry to obtain a CoOOH solution; wherein the pH values ​​of the base solution, the second slurry, and the third slurry are all 9.0~9.

5.

4. The method for preparing cobalt-doped iron phosphate according to claim 3, characterized in that, The molar ratio of the cobalt salt to the first oxidant is 1:(0.8~1.0); and / or, the first pH adjuster, the second pH adjuster, and the third pH adjuster are each independently selected from at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate; and / or, the cobalt salt includes at least one of cobalt sulfate heptahydrate, cobalt chloride, cobalt nitrate, and cobalt acetate; and / or, the first oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

5. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The method for preparing the amorphous ferric phosphate includes the following steps: mixing ferrous salt with water to obtain a ferrous salt solution; mixing phosphate salt with water and a second oxidizing agent to obtain a phosphate salt solution; adding the phosphate salt solution to the ferrous salt solution, and reacting to obtain amorphous ferric phosphate.

6. The method for preparing cobalt-doped iron phosphate according to claim 5, characterized in that, The molar ratio of the ferrous salt to the phosphate salt and the second oxidant is 1:(1.0~1.1):(0.5~1.0); and / or, the concentration of ferrous ions in the ferrous salt solution is 0.5~1.5 mol / L; and / or, the mass concentration of phosphorus in the phosphate salt solution is 3~9%; and / or, the ferrous salt includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; and / or, the phosphate salt includes at least one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, and diammonium hydrogen phosphate; and / or, the second oxidant includes at least one of hydrogen peroxide, ozone, and sodium hypochlorite.

7. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The pulping process includes: adding the CoOOH solution and the amorphous ferric phosphate to a mixture containing water and phosphoric acid, and pulping; wherein the molar ratio of iron in the amorphous ferric phosphate to CoOOH in the CoOOH solution is 1:(0.025~0.1); and the molar ratio of iron in the amorphous ferric phosphate to phosphoric acid in the mixture is 1:(0.2~0.3).

8. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The aging process includes: aging the first slurry at 90~100℃, and keeping it at that temperature for 2~2.5h after the first slurry changes color.

9. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The drying temperature is 95~110℃, and the drying time is 12~14h; and / or, the calcination temperature is 600~650℃, and the calcination time is 2~3h.

10. The method for preparing cobalt-doped iron phosphate according to claim 1, characterized in that, The general molecular formula of the cobalt-doped iron phosphate is Fe. 1-x Co x PO4, where 0 < x ≤ 0.1.

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