Method for treating ferric phosphate with abnormal pH

Abstract

The invention relates to the technical field of iron phosphate production, in particular to a treatment method of iron phosphate with abnormal pH. The invention discloses a treatment method of iron phosphate with abnormal pH. The treatment method comprises the following steps: step 1, adding an iron phosphate finished product with abnormal pH into a reaction kettle; adding water, and stirring to form slurry; step 2, heating the slurry obtained in the step 1, and adding phosphoric acid to adjust the pH value to 1.5-1.8; then continuously reacting; step 3, after the reaction in the step 2 is finished, filtering to obtain a filter cake, and washing the filter cake until the conductivity of washing water is less than 1000 [mu] s / cm; and step 4, drying and sintering the filter cake in the step 3 to obtain a qualified iron phosphate product. The treatment method provided by the invention solves the problem of unstable quality of an iron phosphate product due to abnormal pH, so that the iron phosphate product can meet the performance requirements of a key precursor of a lithium ion battery positive electrode material lithium iron phosphate.

Description

Technical Field

[0001] The invention relates to the technical field of ferric phosphate production, and in particular to a method for treating ferric phosphate with abnormal pH. Background Art

[0002] In the field of battery-grade iron phosphate, iron phosphate is a key precursor of lithium iron phosphate, a positive electrode material for lithium-ion batteries. Its quality directly affects the performance and safety of the battery. With the vigorous development of the new energy industry, the power and energy storage battery markets have increasingly stringent requirements for the performance stability of iron phosphate. However, in the production process of iron phosphate, pH abnormalities frequently occur, which seriously restricts product quality and production efficiency.

[0003] Common production methods for iron phosphate mainly include precipitation method, hydrothermal method, etc. The precipitation method usually uses ferrous salt and phosphate as raw materials, reacts under certain conditions to generate iron phosphate precipitate, and obtains the product through filtering, washing, drying and other processes. The hydrothermal method promotes the reaction and crystallization of raw materials to form iron phosphate in a high temperature and high pressure hydrothermal environment. These production processes are relatively mature in large-scale production, but it is still difficult to avoid abnormal pH of some iron phosphate products due to factors such as raw material impurities, fluctuations in reaction conditions, equipment aging or operating errors.

[0004] Causes and effects of abnormal pH iron phosphate:

[0005] 1. Causes

[0006] In terms of raw materials, if the ferrous salt contains more impurity metal ions (such as calcium, magnesium, etc.) or the purity of the phosphate is not enough, the pH balance of the system may change during the reaction, causing the pH of the ferric phosphate precipitation to deviate from the normal range. For example, some low-quality ferrous raw materials may contain a small amount of alkaline impurities, which will consume additional acid when reacting with phosphoric acid, causing the pH of the final product to increase.

[0007] The control accuracy of reaction conditions is crucial. Slight deviations in parameters such as reaction temperature, time, stirring speed, and solution concentration may cause pH abnormalities. For example, during the precipitation reaction, too high a temperature may accelerate certain side reactions and produce by-products that affect the pH; too long or too short a reaction time may lead to incomplete or over-reaction, thereby changing the pH of the system.

[0008] The material, cleanliness and operating stability of production equipment are also closely related to pH abnormalities. Corrosion products on the inner wall of the equipment may mix into the reaction system and become a factor affecting the pH. For example, if a reactor that has been used for a long time corrodes, the dissolution of metal ions will interfere with the synthesis environment of iron phosphate, resulting in abnormal pH of the product.

[0009] (II) Impact on product performance

[0010] Abnormal pH of iron phosphate will significantly affect its performance in subsequent applications in lithium iron phosphate materials. During the battery charge and discharge process, it will lead to increased capacity decay, reduced cycle life, and decreased charge and discharge efficiency. This is because abnormal pH may change the crystal structure and surface properties of iron phosphate, affecting its reaction activity with lithium sources and the diffusion rate of lithium ions. For example, iron phosphate with too high a pH may form a structure on the surface that is not conducive to the insertion and extraction of lithium ions, thereby hindering the normal charge and discharge process of the battery and reducing the overall performance and reliability of the battery.

[0011] Existing processing technology routes and defects:

[0012] (1) Simple washing method

[0013] Some companies try to use a simple water washing process to treat pH-abnormal iron phosphate. The abnormal product is placed in a large amount of water for multiple washings, hoping to remove the impurity ions that cause pH abnormalities through dilution and dissolution. However, this method has obvious defects. On the one hand, for some impurity ions that are tightly bound to iron phosphate or form co-precipitations, simple water washing is difficult to effectively remove, resulting in poor pH adjustment effects. On the other hand, large-scale water washing will produce a large amount of wastewater, increase environmental protection treatment costs, and may cause the loss of some iron phosphate products during the washing process, reducing product yields.

[0014] (II) Acid-base neutralization adjustment method

[0015] Some researchers use the method of adding acid or alkali to the abnormal pH iron phosphate for neutralization adjustment. In actual operation, it is difficult to accurately control the amount of acid and alkali added. If the amount added is insufficient, the pH cannot be adjusted to the ideal range; excessive addition will introduce new impurity ions, further affecting product quality. For example, when using hydrochloric acid to adjust the pH, if excessive addition is added, chloride ions will remain in the product, which may cause corrosion problems in subsequent battery applications and reduce battery safety and life.

[0016] (III) High temperature calcination method

[0017] By calcining pH-abnormal iron phosphate at high temperature, we attempt to use the decomposition and reorganization of substances in a high temperature environment to improve product performance and pH value. However, this method has many problems. During the high-temperature calcination process, iron phosphate is prone to agglomeration, resulting in uneven particle size distribution of the product particles, affecting its dispersibility in battery materials. At the same time, excessively high calcination temperatures may cause partial decomposition or phase change of the iron phosphate, destroying its crystal structure and reducing the electrochemical performance of the product. In addition, high-temperature calcination consumes huge energy, significantly increases production costs, and has poor economic benefits in large-scale industrial production.

[0018] (IV) Chemical Additive Method

[0019] Specific chemical additives are introduced to react with pH-abnormal iron phosphate to achieve the purpose of adjusting pH and improving performance. However, the selection and use of chemical additives are still in the exploratory stage. Many additives have problems such as high cost, complex and difficult to control reaction process, possible introduction of new impurities or potential harm to the environment. For example, some organic additives may remain in the product after the reaction, and may generate gas during battery use, affecting the stability and safety of the battery.

[0020] In summary, although there are many ways to treat pH-abnormal iron phosphate at present, they all have defects to varying degrees and are difficult to meet the growing needs of the battery industry. For this reason, this application proposes a method for treating pH-abnormal iron phosphate that is easy to produce. Summary of the invention

[0021] The present application discloses a method for treating an abnormal pH iron phosphate, wherein the finished iron phosphate product with abnormal pH is added to a reactor, and water is added to stir to form a slurry; then the temperature is raised and phosphoric acid is added to adjust the pH of the slurry to a range of 1.5-1.8, and the reaction is continued; after the reaction is completed, the filter cake is filtered to obtain a filter cake, and the filter cake is washed until the conductivity of the washing water is less than 1000μs / cm; finally, the filter cake is dried to a moisture content of less than 5%, and sintered at a temperature below 600°C to obtain a qualified iron phosphate product. The treatment method effectively improves the chemical properties and crystal structure of iron phosphate and reduces the impurity content by accurately adjusting the pH value, controlling the reaction conditions and subsequent treatment steps, thereby solving the problem of unstable quality of the iron phosphate product with abnormal pH, so that it can meet the performance requirements of the key precursor of lithium iron phosphate as the positive electrode material of lithium-ion batteries.

[0022] The technical solution adopted by this application to solve its technical problem is:

[0023] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0024] Step 1. Add the finished ferric phosphate product with abnormal pH into a reaction kettle; then add water and stir to form a slurry;

[0025] Step 2. The slurry of step 1 is heated, phosphoric acid is added to adjust the pH to 1.5-1.8; and then the reaction is continued;

[0026] Step 3. After the reaction in step 2 is completed, filtering is performed to obtain a filter cake, and the filter cake is washed until the conductivity of the washing water is less than 1000 μs / cm;

[0027] Step 4. Dry and sinter the filter cake from step 3 to obtain a qualified iron phosphate product.

[0028] In some specific embodiments, in step 1, the solid content of the slurry is 20-25%.

[0029] In some specific embodiments, in step 2, the temperature is raised to 70-80° C., and then the reaction is continued at 70-80° C. for 2-3 hours.

[0030] In some specific embodiments, in step 4, the filter cake is dried to a moisture content of less than 5% and then sintered.

[0031] In some specific embodiments, in step 4, the sintering temperature is less than 600°C.

[0032] In some specific embodiments, in step 1, the pH of the ferric phosphate product with abnormal pH is greater than 3.5 or less than 2.9.

[0033] In some specific embodiments, in step 4, the pH of the qualified ferric phosphate product is 3.0±0.1.

[0034] In some specific embodiments, in step 4, the mass content of S in the qualified ferric phosphate product is less than 20 ppm, and the mass content of K is less than 6 ppm.

[0035] In some specific embodiments, in step 4, the filter cake is dried to a moisture content of 1.5-4.5% and then sintered.

[0036] In some specific embodiments, in step 4, the sintering temperature is 400-450°C.

[0037] The beneficial effects of this application are:

[0038] The treatment method described in this application first mixes the finished iron phosphate product with abnormal pH with water to form a slurry, and adjusts the pH value of the slurry to 1.5-1.8 by heating and accurately adding phosphoric acid to ensure the effectiveness of the reaction and the stability of the properties of iron phosphate; then filtering and washing operations are performed to ensure product purity and reduce the adverse effects of impurities on subsequent performance; finally, the crystal structure and chemical composition of iron phosphate are optimized by controlling the moisture content and temperature conditions of the drying and sintering processes. Therefore, the treatment method described in the application successfully solves the product quality problem caused by abnormal pH in the production process of iron phosphate, improves the qualified rate and stability of iron phosphate products, and makes its key indicators such as pH value and impurity content meet the application requirements of battery-grade iron phosphate, which is conducive to improving the performance and safety of lithium-ion batteries, and meets the high-quality demand for iron phosphate in the power and energy storage battery markets. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0040] Figure 1 This is a SEM image of the iron phosphate prepared in Example 1 of the present application;

[0041] Figure 2 This is the XRD diagram of the iron phosphate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0042] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0043] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0044] In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or ab c, where a, b, c can be single or multiple, respectively.

[0045] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0046] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0047] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0048] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0049] Terminology explanation:

[0050] Conductivity: It is a physical quantity used to describe the electrical conductivity of a substance. In this article, the conductivity of the wash water <1000μs / cm is an indicator of the residual degree of impurity ions in the filter cake after washing. The lower the conductivity, the lower the concentration of impurity ions.

[0051] Hydrothermal method: A chemical synthesis method that promotes the reaction and crystallization of raw materials to form iron phosphate in a high temperature and high pressure hydrothermal environment. In this environment, the activity and reaction rate of the reactants will change, which is conducive to the formation of a specific crystal structure.

[0052] Precipitation method: using ferrous salt and phosphate as raw materials, reacting under certain conditions to generate ferric phosphate precipitate, and then filtering, washing, drying and other processes to obtain the product. By controlling the reaction conditions (such as temperature, pH value, solution concentration, etc.), the target product is precipitated in the form of precipitation.

[0053] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0054] Step 1. Add the finished ferric phosphate product with abnormal pH into a reaction kettle; then add water and stir to form a slurry;

[0055] Step 2. The slurry of step 1 is heated, phosphoric acid is added to adjust the pH to 1.5-1.8; and then the reaction is continued;

[0056] Step 3. After the reaction in step 2 is completed, filtering is performed to obtain a filter cake, and the filter cake is washed until the conductivity of the washing water is less than 1000 μs / cm;

[0057] Step 4. Dry and sinter the filter cake from step 3 to obtain a qualified iron phosphate product.

[0058] Specifically, in step 1, the pH of the ferric phosphate product with abnormal pH is greater than 3.5 or less than 2.9; the ferric phosphate product with abnormal pH is added to a reaction kettle, and then water is added and stirred to form a slurry with a solid content of 20-25%.

[0059] In step 1, the iron phosphate particles are dispersed in the water by stirring to avoid agglomeration, increase the contact area with the reagents added later, and facilitate the chemical reaction. At the same time, the solid content is controlled at 20-25% to ensure that the slurry has appropriate fluidity and reactivity, and neither too high a solid content will cause difficulty in stirring and uneven reaction, nor too low a solid content will affect production efficiency and cost-effectiveness.

[0060] Therefore, through step 1, the finished iron phosphate product with abnormal pH is evenly dispersed in water to form a stable slurry system, which provides a good material basis for subsequent pH adjustment and reaction, ensuring that the reaction can be carried out fully and evenly.

[0061] Specifically, in step 2, the slurry of step 1 is heated to 70-80° C., concentrated phosphoric acid is added to adjust the pH to 1.5-1.8, and then the reaction is continued at 70-80° C. for 2-3 hours.

[0062] In step 2, the temperature is raised to 70-80°C to provide suitable thermodynamic conditions for the reaction, accelerate the chemical reaction rate, and make the reaction between iron phosphate and phosphoric acid easier to proceed. In this temperature range, the degree of ionization and reaction activity of phosphoric acid are moderate, which can effectively adjust the pH of the system. When phosphoric acid is added to adjust the pH, the hydrogen ions (H+) generated by the ionization of phosphoric acid react with the impurity ions or abnormal pH substances in the slurry that affect the pH, thereby lowering the pH value of the system. Continuing the reaction for 2-3 hours can ensure that the reaction is fully carried out, optimize the crystal structure of iron phosphate, remove impurity components or abnormal structures that may affect product performance, and make the product performance closer to the qualified standards.

[0063] In step 2, if the reaction temperature is too high, it may cause excessive decomposition of iron phosphate or other side reactions, destroying its crystal structure, making the particle size distribution of the product uneven, affecting the dispersibility in the battery material, and thus reducing the electrochemical performance of the product. For example, too high a temperature may partially convert iron phosphate into other difficult-to-control phosphate compounds, changing the chemical composition and properties of the product, and failing to meet the requirements of battery-grade iron phosphate, resulting in a significant decrease in the performance of the final product when it is used in the preparation of lithium iron phosphate, such as capacity and cycle life.

[0064] In step 2, if the temperature is too low, the reaction rate will slow down, and the time required to reach the target pH and fully react will be greatly extended, reducing production efficiency. At the same time, it may lead to incomplete reaction, inability to effectively remove impurities and adjust the properties of iron phosphate, so that the product pH cannot be stabilized within the range of 1.5-1.8. The performance of the final product is still negatively affected by the abnormal pH, and in battery applications, it will show defects such as fast capacity decay and short cycle life.

[0065] Therefore, through step 2, phosphoric acid solution is used to accurately adjust the pH value of the slurry to 1.5-1.8, and the iron phosphate is fully reacted at an appropriate temperature to improve the chemical properties of the iron phosphate, laying the foundation for obtaining qualified products in the future. By controlling the pH and reaction conditions, the crystal structure and surface properties of the iron phosphate are transformed to an ideal state, reducing the adverse effects of abnormal pH on the performance of subsequent lithium iron phosphate materials, such as alleviating battery capacity attenuation, extending cycle life, and improving charge and discharge efficiency.

[0066] Specifically, in step 3, water is used to wash the filter cake until the conductivity of the washing water is less than 1000 μs / cm.

[0067] In step 3, the filtration process uses the pores of filter media such as filter cloth to separate the insoluble iron phosphate filter cake from the post-reaction solution. When washing the filter cake, use pure water to rinse it, and with the help of the dissolution and dilution effect of water, remove the soluble impurity ions remaining on the surface and internal pores of the filter cake, such as unreacted phosphoric acid, salts generated by the reaction, etc. Continuous washing is carried out until the conductivity of the washing water is less than 1000μs / cm, indicating that the concentration of impurity ions has been reduced to an acceptable level. At this time, the impurity content in the filter cake is greatly reduced, and the product purity is significantly improved.

[0068] If the conductivity of the washing water is too high, such as >1000μs / cm, it means that there are still many impurity ions remaining in the filter cake. These impurities will affect the crystal structure and chemical composition of iron phosphate in the subsequent drying and sintering process. For example, when the iron phosphate product is used in lithium iron phosphate materials, the battery's charge and discharge performance may decrease and the cycle life may be shortened, because impurities may interfere with the lithium ion embedding and extraction process, increase the battery's internal resistance, and reduce the battery's energy conversion efficiency. At the same time, the stability of the product will also be affected, and performance fluctuations are prone to occur, which is not conducive to large-scale industrial production and application.

[0069] Therefore, in step 3 of the present application, through filtering and washing operations, the impurity ions in the ferric phosphate filter cake are effectively removed and their content is reduced to ensure that the product purity meets the requirements, while reducing the adverse effects of impurities on the performance of subsequent products, thereby providing a guarantee for finally obtaining a qualified ferric phosphate product.

[0070] Specifically, in step 4, the moisture content of the filter cake is dried to less than 5%, and then sintered. The sintering temperature is less than 600° C., preferably 400-450° C. The pH of the qualified iron phosphate product is 3.0±0.1, the mass content of S is less than 10ppm, and the mass content of K is less than 2ppm.

[0071] In step 4, the water content in the filter cake is evaporated by heating, and the water content of the filter cake is reduced to <5% (preferably 1.5-4.5%). At a certain temperature (such as 180°C), the water content is converted into water vapor by heat and escapes, reducing the influence of the water content on the subsequent sintering process and product performance. The appropriate water content can prevent the product from being broken or having structural defects due to excessive internal stress caused by rapid evaporation of water during sintering, and also helps to control the particle size and agglomeration of the product.

[0072] Sintering is carried out at a temperature of <600°C (preferably 400-450°C) to allow the iron phosphate particles to undergo crystallization and densification. Within this temperature range, the crystal structure of iron phosphate is further optimized, and the atomic arrangement is more orderly, thereby improving its electrochemical performance and stability. At the same time, high-temperature sintering helps to remove residual organic impurities and some volatile inorganic impurities, further reducing the impurity content in the product, such as making the mass content of S <20ppm and the mass content of K <6ppm, thereby improving the purity of the product.

[0073] Therefore, in step 4, moisture and residual impurities in the filter cake are further removed through drying and sintering operations, so that the physical and chemical properties of the iron phosphate product meet the qualified standards, ensuring that it can meet the performance requirements of the key precursor of lithium iron phosphate as a positive electrode material for lithium-ion batteries, such as suitable pH value, low impurity content, good crystal structure and stability, etc.

[0074] If the moisture content of the iron phosphate is too high after drying (not reaching the range, such as 7%), the excessive moisture will vaporize quickly during the sintering process, generating a large vapor pressure, which may cause defects such as cracking and deformation of the product, seriously affecting the appearance and physical properties of the product. In addition, the presence of moisture will interfere with the diffusion and crystallization of the material during the sintering process, making the crystal structure of the product imperfect and reducing its electrochemical performance, resulting in reduced battery charge and discharge efficiency and accelerated capacity decay when applied to lithium iron phosphate materials.

[0075] If the sintering temperature is too high (such as reaching 650°C), the iron phosphate may be easily over-decomposed or phase-changed, destroying its original crystal structure and causing a serious decline in the electrochemical performance of the product. For example, the iron phosphate may be partially converted into other phosphates or metal oxides, changing the chemical composition and properties of the product, making it unable to meet the requirements of battery-grade iron phosphate. When used in batteries, it will greatly reduce the performance and safety of the battery, such as causing internal short circuits, thermal runaway and other problems.

[0076] The following examples and comparative examples further illustrate the method for treating pH-abnormal iron phosphate described in the present application.

[0077] Example 1

[0078] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0079] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:4kg of material:water, with a solid content of 20%.

[0080] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 70° C. and add phosphoric acid to control the pH to 1.54.

[0081] Step 3. The temperature was maintained at 70°C and stirring was continued for 2 hours. The material was pumped to a filter press by a delivery pump for filtration. The material was washed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (554 μs / cm).

[0082] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 4.5%.

[0083] Step 5. After drying, the filter cake is transported to a kiln and sintered at 500°C. After sintering, the material is packaged normally to obtain an iron phosphate product.

[0084] Example 2

[0085] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0086] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:3kg of material:water, with a solid content of 25%.

[0087] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 80° C. and add phosphoric acid to control the pH to 1.78.

[0088] Step 3. The temperature was maintained at 80°C, stirring was continued for 2 hours, and the material was pumped to a filter press by a delivery pump for filtration. Washing was performed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (752 μs / cm).

[0089] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 4.8%.

[0090] Step 5. After drying, the filter cake is transported to a kiln and sintered at 550°C. After sintering, the material is packaged normally to obtain an iron phosphate product.

[0091] Example 3

[0092] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0093] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:3kg of material:water, with a solid content of 25%.

[0094] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 80° C. and add phosphoric acid to control the pH to 1.62.

[0095] Step 3. The temperature was maintained at 80°C, stirring was continued for 3 hours, and the material was pumped to a filter press by a delivery pump for filtration. The material was washed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (354 μs / cm).

[0096] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 1.5%.

[0097] Step 5. After drying, the filter cake is transported to a kiln and sintered at 400°C. After sintering, the material is packaged normally to obtain an iron phosphate product.

[0098] Example 4

[0099] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0100] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:3kg of material:water, with a solid content of 25%.

[0101] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 80° C. and add phosphoric acid to control the pH to 1.66.

[0102] Step 3. The temperature was maintained at 80°C, stirring was continued for 3 hours, and the material was pumped to a filter press by a delivery pump for filtration. The material was washed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (122 μs / cm).

[0103] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 2.5%.

[0104] Step 5. After drying, the filter cake is transported to a kiln and sintered at 420°C. The sintering temperature is 450°C. After the sintering is completed, the material is normally packaged to obtain an iron phosphate product.

[0105] Example 5

[0106] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0107] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:3.3kg of material:water, with a solid content of 23%.

[0108] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 75° C. and add phosphoric acid to control the pH to 1.73.

[0109] Step 3. The temperature was maintained at 75°C, stirring was continued for 2.5 hours, and the material was pumped to a filter press by a delivery pump for filtration. Washing was performed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (437 μs / cm).

[0110] Step 4. The filter cake is dried at 180°C and the moisture content of the filter cake is controlled to be 3.2%;

[0111] Step 5. After drying, the filter cake is transported to a kiln and sintered at 420°C. After sintering, the material is packaged normally to obtain an iron phosphate product.

[0112] Comparative Example 1

[0113] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0114] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:4kg of material:water.

[0115] Step 2. Start stirring at 1500 r / min and increase the temperature while maintaining the slurry temperature at 35° C. and add phosphoric acid to control the pH to 1.58.

[0116] Step 3. Maintain the slurry temperature at 35°C, continue stirring for 2 hours, and pump the material to the filter press through a delivery pump. Wash with 50°C pure water, and test the conductivity of the washing water to be less than 1000μs / cm (543μs / cm).

[0117] Step 4: The filter cake is dried at 180°C and the moisture content of the filter cake is controlled to be less than 5%.

[0118] Step 5. After drying, the filter cake is transported to a kiln and sintered at 500°C. After sintering, the material is packaged normally to obtain the iron phosphate product.

[0119] Comparative Example 2

[0120] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0121] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:4kg of material:water.

[0122] Step 2. Start stirring at 1500 r / min and increase the temperature. At the same time, increase the temperature of the slurry to 70°C without adding phosphoric acid.

[0123] Step 3. The slurry was maintained at 70°C and stirred for 2 hours, and the material was pumped to a filter press by a delivery pump. The slurry was washed with 50°C pure water, and the conductivity of the washing water was tested to be less than 1000 μs / cm (561 μs / cm).

[0124] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 4.1%.

[0125] Step 5. After drying, the filter cake is transported to a kiln and sintered at 500°C. After sintering, the material is packaged normally to obtain the iron phosphate product.

[0126] Comparative Example 3

[0127] A method for treating ferric phosphate with abnormal pH, comprising the following steps:

[0128] Step 1. Add the abnormal pH ferric phosphate product into the tank for premixing at a ratio of 1kg:4kg of material:water.

[0129] Step 2. Start stirring at 1500 r / min and increase the temperature while maintaining the slurry temperature at 33°C without adding phosphoric acid.

[0130] Step 3. The slurry temperature was maintained at 33°C, stirring was continued for 2 hours, and the material was pumped to a filter press by a delivery pump for filtration. The slurry was washed with 50°C pure water, and the conductivity of the washing water was tested to be less than 5000 μs / cm (4537 μs / cm).

[0131] Step 4: The filter cake was dried at 180°C and the moisture content of the filter cake was controlled to be 4.2%.

[0132] Step 5. After drying, the filter cake is transported to a kiln and sintered at 500°C. After sintering, the material is packaged normally to obtain the iron phosphate product.

[0133] Examples 1-5 and Comparative Examples 1-3 were tested using the same abnormal pH ferric phosphate product in Table 1. The pH value was measured using a pH meter, and the mass contents of S and K were measured using inductively coupled plasma mass spectrometry (ICP-MS).

[0134] Table 1

[0135] sample pH S K Abnormal iron phosphate 3.95 320.6 60.7

[0136] The iron phosphates obtained in Examples 1-5 and Comparative Examples 1-3 were tested for impurities, and the test results are summarized in Table 2.

[0137] Table 2

[0138] sample pH S K Example 1 3.03 10.5 2.08 Example 2 3.08 18.6 5.32 Example 3 3.02 15.3 3.24 Example 4 3.04 13.1 4.89 Example 5 3.01 16.7 4.18 Comparative Example 1 3.38 172.8 27.91 Comparative Example 2 3.52 192.4 33.83 Comparative Example 3 3.71 243.1 54.25

[0139] The results in Table 1 and Table 2 show that the methods of Examples 1-5 have significant advantages in treating ferric phosphate with abnormal pH, and the specific performance and reasons are as follows:

[0140] 1. Effectively adjust pH value

[0141] The pH of the iron phosphate products after treatment in Examples 1-5 all reached around 3.0±0.1, which was significantly improved compared to the pH 3.95 (Table 1) of abnormal iron phosphate, and was closer to the target value than the results of Comparative Examples 1-3. This shows that the method can accurately adjust the pH to a suitable range, meet the strict pH requirements of battery-grade iron phosphate, and is conducive to maintaining good battery performance when subsequently applied to lithium iron phosphate materials, such as stable charge and discharge process, small capacity decay and long cycle life.

[0142] 2Significantly reduce impurity content

[0143] From the perspective of impurity content, the mass content of S in Examples 1-5 is less than 20ppm, and the mass content of K is less than 6ppm, while the S content in abnormal iron phosphate is as high as 320.6ppm, and the K content is 60.7ppm (Table 1), and the impurity content of Comparative Examples 1-3 is also much higher than that of the Examples. This shows that the method can effectively remove impurity elements in iron phosphate, improve product purity, reduce the adverse effects of impurities on the electrochemical performance of the product, and improve the stability and reliability of the product in battery applications.

[0144] 3. Cause Analysis

[0145] (1) Reasonable process steps and parameter control:

[0146] In step 1, the finished iron phosphate product with abnormal pH is stirred with water to form a slurry with a solid content of 20-25%, which ensures the uniform dispersion of the material and good reaction activity, and provides favorable conditions for subsequent pH adjustment and reaction. Step 2: After heating to 70-80°C and adding phosphoric acid to adjust the pH to 1.5-1.8, the reaction is continued for 2-3 hours. The appropriate temperature and pH range and sufficient reaction time allow phosphoric acid to fully react with impurities, effectively adjust the acidity and alkalinity of the system and remove some impurities, while optimizing the crystal structure of iron phosphate. For example, high temperature promotes the chemical reaction rate, making the reaction of impurities with phosphoric acid easier to proceed, and precise pH control ensures that the reaction proceeds in the direction of reducing the impurity content and adjusting the chemical properties of iron phosphate.

[0147] (2) Strict post-processing operations:

[0148] The filtering and washing operation in step 3 further removes the residual soluble impurities by washing the filter cake until the conductivity of the washing water is less than 1000 μs / cm, thereby ensuring the purity of the product. In step 4, the drying moisture and sintering temperature are strictly controlled, and the drying reduces the moisture to a suitable range, thereby avoiding the adverse effects of moisture on subsequent sintering. The sintering is carried out at a temperature of less than 600° C. (preferably 400-450° C.), which can not only achieve the crystallization and densification of the iron phosphate, but also prevent excessive decomposition or phase change, and further remove residual impurities, thereby comprehensively improving the quality of the product and achieving an ideal state in terms of pH value and impurity content.

[0149] The results in Table 1 and Table 2 show that the performance of the iron phosphate products obtained in Comparative Examples 1-3 is poor, and the specific analysis is as follows:

[0150] 1. Performance Results

[0151] The pH adjustment effect is not good: the pH of the iron phosphate product after treatment in Example 1 is 3.38, in Example 2 is 3.52, and in Example 3 is 3.71, all of which are obviously deviated from the pH range of 3.0±0.1 of qualified products, and the gap is large compared with Examples 1-5. This shows that these methods cannot effectively adjust the abnormal pH of iron phosphate to a suitable pH value, which will affect its subsequent application performance in lithium iron phosphate materials, such as causing problems such as increased battery capacity attenuation, reduced cycle life, and decreased charge and discharge efficiency.

[0152] Poor impurity removal ability: the mass content of S in Comparative Example 1 is 172.8ppm, and the mass content of K is 27.91ppm; the S content in Comparative Example 2 is 192.4ppm, and the K content is 33.83ppm; the S content in Comparative Example 3 is as high as 243.1ppm, and the K content is 54.25ppm, which is much higher than the impurity content standard of qualified products in Examples 1-5. This shows that these methods cannot effectively remove impurities in iron phosphate, the product purity is low, and the presence of impurities will interfere with the performance of iron phosphate in battery applications and reduce the stability and reliability of the battery.

[0153] 2. Cause Analysis

[0154] Comparative Example 1: The reaction temperature was only maintained at 35°C, which was lower than the appropriate range of 70-80°C. The low temperature resulted in a slow reaction rate, and the reaction between phosphoric acid and iron phosphate and impurities was insufficient, resulting in inadequate pH adjustment and incomplete impurity removal. At the same time, due to the incomplete reaction, more substances that affect the pH value may remain, causing the product pH to deviate from the target value, and the impurity content cannot be effectively reduced.

[0155] Comparative Example 2: When the temperature was raised to 70°C, phosphoric acid was not added for pH adjustment, and the key reagent for adjusting the pH was missing. This made it impossible to correct the original pH abnormality in the system, and the impurities could not be effectively removed by reacting with phosphoric acid, resulting in the product pH and impurity content not meeting the requirements.

[0156] Comparative Example 3: Not only was the reaction temperature maintained at 33°C, which was too low, but phosphoric acid was not added. The dual factors of low temperature and no phosphoric acid adjustment made it almost impossible for the reaction to proceed effectively, a large amount of impurities remained, and the pH abnormality of the product was serious, which greatly affected the product quality and made it unable to meet the performance requirements of battery-grade iron phosphate.

[0157] At the same time, according to the treatment method of Example 1, an experiment was carried out using the abnormal pH ferric phosphate product described in Table 3, and the pH of the obtained ferric phosphate product was detected. The results are summarized in Table 3.

[0158] Table 3

[0159] pH Abnormal Iron Phosphate (pH) Finished ferric phosphate product after treatment (pH) 3.8 3.02 3.75 2.98 4.02 3.05 3.68 3.04 2.65 3.01 2.71 3.01

[0160] As can be seen from Table 3, the results in Table 3 indicate that the treatment method has a good pH adjustment effect on iron phosphate with different initial pH values, and can stabilize it within the qualified range.

[0161] 1. Stability of pH adjustment:

[0162] It can be seen from Table 3 that for iron phosphate with an initial pH value fluctuating between 2.65 and 4.02, after being treated by the method of Example 1, the pH value of the final product can reach around 3.0±0.1, such as 3.02, 2.98, 3.05, 3.04, 3.01, etc. This shows that the treatment method has strong adaptability and stability, and can effectively treat iron phosphate with different degrees of pH abnormality to a pH range that meets the requirements, and is not affected by large fluctuations in the initial pH, providing a reliable technical means for dealing with various pH abnormalities in industrial production.

[0163] 2. Reliability of the method:

[0164] In actual production, abnormal pH iron phosphate may have different initial pH values, and this treatment method can always adjust it to the appropriate pH range, indicating that it is reasonable and effective in process control and chemical reaction mechanism. Through a series of operations such as slurry preparation in step 1, heating and adding phosphoric acid to adjust pH and reaction in step 2, filtration and washing in step 3, and drying and sintering in step 4, the pH value of iron phosphate can be stably and accurately controlled to ensure the consistency of product quality and meet the strict performance requirements of battery-grade iron phosphate for pH value, thereby ensuring its application effect in the production of lithium iron phosphate, a positive electrode material for lithium-ion batteries, and helping to improve the performance and stability of the battery.

[0165] from Figure 1 The microstructure of the treated iron phosphate can be observed in the figure. The morphology of the iron phosphate is normal, and no obvious agglomeration, deformation or other adverse microstructural changes are produced due to the treatment process. This shows that the treatment method of the present invention has a good effect in maintaining the microstructural integrity of the iron phosphate, which is conducive to maintaining stable performance in subsequent applications.

[0166] from Figure 2It can be seen that the crystal structure of the treated iron phosphate is normal. The characteristic peak position, intensity and peak shape in the XRD spectrum are consistent with the normal crystal structure characteristics of iron phosphate, indicating that after a series of treatment steps such as washing, drying and sintering of the present invention, the crystal structure of iron phosphate is not damaged and still maintains good crystallinity. It can be seen from Comparative Examples 1, 2 and 3 that high and low temperature reactions and whether phosphoric acid is added itself will not significantly affect the crystal structure of iron phosphate.

[0167] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for treating abnormal pH iron phosphate, characterized in that: The following steps are involved: Step 1. Add the finished ferric phosphate product with abnormal pH into the reactor; Add water and stir to form a slurry; Step 2. The slurry of step 1 is heated, phosphoric acid is added to adjust the pH to 1.5-1.8; and then the reaction is continued; Step 3. After the reaction in step 2 is completed, filtering is performed to obtain a filter cake, and the filter cake is washed until the conductivity of the washing water is less than 1000 μs / cm; Step 4. Dry and sinter the filter cake from step 3 to obtain a qualified iron phosphate product.

2. The processing method according to claim 1, characterized in that: In step 1, the solid content in the slurry is 20-25%.

3. The processing method according to claim 1, characterized in that: In step 2, the temperature is raised to 70-80° C., and then the reaction is continued at 70-80° C. for 2-3 hours.

4. The processing method according to claim 1, characterized in that: In step 4, the filter cake is dried to a moisture content of less than 5%, and then sintered.

5. The processing method according to claim 1, characterized in that: In step 4, the sintering temperature is less than 600°C.

6. The processing method according to claim 1, characterized in that: In step 1, the pH of the ferric phosphate product with abnormal pH is greater than 3.5 or less than 2.

9.

7. The processing method according to claim 1, characterized in that: In step 4, the pH of the qualified ferric phosphate product is 3.0±0.

1.

8. The processing method according to claim 1, characterized in that: In step 4, the mass content of S in the qualified ferric phosphate product is less than 20 ppm, and the mass content of K is less than 6 ppm.

9. The processing method according to claim 4, characterized in that: In step 4, the filter cake is dried to a moisture content of 1.5-4.5%, and then sintered.

10. The processing method according to claim 5, characterized in that: In step 4, the sintering temperature is 400-450°C.

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