A method for continuously synthesizing low-iron phosphorus ratio high-quality ferric phosphate

Abstract

The application discloses a preparation method of continuously synthesizing low-iron-phosphorus high-quality iron phosphate, which comprises the following steps: preparing an iron salt solution; preparing a phosphorus salt solution; pumping the two solutions into a continuous synthesizer after accurate metering to obtain a synthesis slurry; aging the synthesis slurry at a certain temperature until the crystal transformation is completed and the slurry is whitened; after prolonging the whitened slurry for a period of time, solid-liquid separation is performed, the filter cake is washed on line; and the filter cake after washing is dried and calcined, so that the low-Fe / P, high-purity and good-consistency iron phosphate product is obtained. The amount of sulfuric acid and the amount of ammonia water added in the iron salt and the phosphorus salt and the synthesis temperature play an important role in the nucleation and growth of the iron phosphate, meanwhile, the continuous synthesis influences the consistency and stability of the iron phosphate product, and the stability of the reaction environment and the concentration is maintained in the synthesis process.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material preparation technology, and in particular to a method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio. Background Technology

[0002] Lithium iron phosphate (LiFePO4) batteries have become the mainstream choice for power batteries due to their high safety, long cycle life, and low cost. Currently, the mainstream equipment for synthesizing LiFePO4 is still the batch reactor. However, due to the large size of the reactor, problems exist such as large batch-to-batch variations, easy adsorption / encapsulation of metal ions, low precision in controlling the iron-to-phosphorus ratio (Fe / P), and high sulfur content. Furthermore, in conventional processes, uneven mixing of the iron source (e.g., FeSO3) and phosphorus source (e.g., H3PO3) can easily lead to localized supersaturation crystallization, resulting in a wide particle size distribution, irregular morphology, and poor consistency of the product. The Fe / P ratio, purity, and morphology of LiFePO4 all affect the electrochemical performance of LiFePO4. A low Fe / P ratio can increase the proportion of Li sites in LiFePO4, while low purity allows impurity particles to easily clog Li+ channels, increasing Li+ migration resistance. Currently, there is little information available on technologies for precisely controlling the Fe / P ratio and maintaining high quality and consistency in continuous synthesis.

[0003] Based on this, this patent describes a continuous synthesis method for preparing iron phosphate with low Fe / P ratio, high quality, and good consistency. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the continuous synthesis of high-quality iron phosphate with a low iron-to-phosphorus ratio.

[0005] The objective of this invention is achieved through the following technical solution: a method for continuous synthesis of high-quality iron phosphate with a low iron-to-phosphorus ratio, comprising the following steps:

[0006] (1) Take ferric sulfate solution and add acid to adjust the pH to 0.9-1.5 to obtain ferric salt solution;

[0007] (2) Take the phosphate salt solution and add alkali to adjust the pH to 4-6 to obtain the phosphate salt solution;

[0008] (3) After precise metering, the iron salt solution and phosphate salt solution are simultaneously pumped into the continuous synthesizer, and the outlet temperature is controlled to obtain a slurry with a pH of 0.9 to 1.5;

[0009] (4) The slurry prepared in step (3) is placed into the reactor for aging and kept warm until it turns white and crystallizes;

[0010] (5) The whitening slurry is extended for a period of time, solid-liquid separation is performed, the filter cake is washed online, and the washed filter cake is dried and calcined to obtain the final product;

[0011] In step (1), the Fe concentration of the ferric phosphate solution is 46–65 g / L;

[0012] In step (1), the acid added is one or both of sulfuric acid and phosphoric acid;

[0013] In step (2), the concentration of P in the phosphate salt solution is 40–50 g / L;

[0014] In step (2), the phosphate salt solution is either ammonium dihydrogen phosphate or diammonium hydrogen phosphate;

[0015] In step (2), the added alkali is one or both of ammonia and sodium hydroxide;

[0016] In step (3), the measured nP / nFe ratio is 1.0 to 1.2;

[0017] In step (3), the outlet temperature of the continuous synthesizer is controlled at 55-75℃;

[0018] In step (4), the aging temperature is 75–90℃;

[0019] In step (5), the drying temperature is 85–105°C, and the calcination temperature is 550–600°C. This invention has the following advantages:

[0020] This invention controls the reaction pH of iron salts and phosphate salts, accurately measures the pH, and uses a continuous flow synthesizer to ensure that the reaction pH of the synthesis slurry is between 0.9 and 1.5. At the same time, continuous flow is used to enhance heat and mass transfer and maintain environmental stability, ultimately producing high-quality and consistent iron phosphate with a low Fe / P ratio of 0.960 to 0.965. Attached Figure Description

[0021] Figure 1 This is a SEM image of the iron phosphate dihydrate prepared in Example 4.

[0022] Figure 2 The image shows the SEM image of the anhydrous iron phosphate prepared in Example 4.

[0023] Figure 3 SEM image of ferric phosphate dihydrate prepared for Comparative Example 1.

[0024] Figure 4 SEM image of anhydrous iron phosphate prepared for Comparative Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Example 1: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0032] (1) Take ferric sulfate solution and add acid to adjust the pH to 0.9-1.5 to obtain ferric salt solution;

[0033] (2) Take the phosphate salt solution and add alkali to adjust the pH to 4-6 to obtain the phosphate salt solution;

[0034] (3) After precise metering, the iron salt solution and phosphate salt solution are simultaneously pumped into the continuous synthesizer, and the outlet temperature is controlled to obtain a slurry with a pH of 0.9 to 1.5;

[0035] (4) The slurry prepared in step (3) is placed into the reactor for aging and kept warm until it turns white and crystallizes;

[0036] (5) The whitening slurry is extended for a period of time, solid-liquid separation is performed, the filter cake is washed online, and the washed filter cake is dried and calcined to obtain the final product;

[0037] In step (1), the Fe concentration of the ferric phosphate solution is 46–65 g / L;

[0038] In step (1), the acid added is one or both of sulfuric acid and phosphoric acid;

[0039] In step (2), the concentration of P in the phosphate salt solution is 40–50 g / L;

[0040] In step (2), the phosphate salt solution is either ammonium dihydrogen phosphate or diammonium hydrogen phosphate;

[0041] In step (2), the added alkali is one or both of ammonia and sodium hydroxide;

[0042] In step (3), the measured nP / nFe ratio is 1.0 to 1.2;

[0043] In step (3), the outlet temperature of the continuous synthesizer is controlled at 55-75℃;

[0044] In step (4), the aging temperature is 75–90℃;

[0045] In step (5), the drying temperature is 85-105℃ and the calcination temperature is 550-600℃.

[0046] Example 2: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0047] (1) Take ferric sulfate solution and add acid to adjust the pH to 0.9 to obtain ferric salt solution;

[0048] (2) Adjust the pH of the phosphate salt solution to 4 by adding alkali to obtain the phosphate salt solution;

[0049] (3) After precise metering, iron salt solution and phosphate salt solution are simultaneously pumped into the continuous synthesizer, and the outlet temperature is controlled to obtain a slurry with pH of 0.9;

[0050] (4) The slurry prepared in step (3) is placed into the reactor for aging and kept warm until it turns white and crystallizes;

[0051] (5) The whitening slurry is extended for a period of time, solid-liquid separation is performed, the filter cake is washed online, and the washed filter cake is dried and calcined to obtain the final product;

[0052] In step (1), the Fe concentration of the ferric phosphate solution is 46 g / L;

[0053] In step (1), the acid added is sulfuric acid;

[0054] In step (2), the concentration of P in the phosphate salt solution is 40 g / L;

[0055] In step (2), the phosphate salt solution is ammonium dihydrogen phosphate;

[0056] In step (2), the added alkali is one or two types of ammonia water;

[0057] In step (3), the measured nP / nFe = 1.0;

[0058] In step (3), the outlet temperature of the continuous synthesizer is controlled at 55°C;

[0059] In step (4), the aging temperature is 75℃;

[0060] In step (5), the drying temperature is 85℃ and the calcination temperature is 550℃.

[0061] Example 3: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0062] (1) Take ferric sulfate solution and add acid to adjust the pH to 1.5 to obtain ferric salt solution;

[0063] (2) Adjust the pH of the phosphate salt solution to 6 by adding alkali to obtain the phosphate salt solution;

[0064] (3) After precise metering, iron salt solution and phosphate salt solution are simultaneously pumped into the continuous synthesizer, and the outlet temperature is controlled to obtain a slurry with pH of 1.5.

[0065] (4) The slurry prepared in step (3) is placed into the reactor for aging and kept warm until it turns white and crystallizes;

[0066] (5) The whitening slurry is extended for a period of time, solid-liquid separation is performed, the filter cake is washed online, and the washed filter cake is dried and calcined to obtain the final product;

[0067] In step (1), the Fe concentration of the ferric phosphate solution is 65 g / L;

[0068] In step (1), the acid added is phosphoric acid;

[0069] In step (2), the concentration of P in the phosphate salt solution is 50 g / L;

[0070] In step (2), the phosphate salt solution is diammonium hydrogen phosphate;

[0071] In step (2), the added alkali is sodium hydroxide;

[0072] In step (3), the measured nP / nFe = 1.2;

[0073] In step (3), the outlet temperature of the continuous synthesizer is controlled at 75°C;

[0074] In step (4), the aging temperature is 90℃;

[0075] In step (5), the drying temperature is 105℃ and the calcination temperature is 600℃.

[0076] Example 4: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0077] (1) Take a ferric sulfate solution with Fe concentration = 50 g / L, add sulfuric acid to adjust the pH to 1.1, and prepare an iron salt solution;

[0078] (2) Take the prepared ammonium dihydrogen phosphate solution (P=40g / L) and add ammonia water to adjust the pH to 4.5 to obtain the phosphate salt solution;

[0079] (3) The iron salt solution and phosphate salt solution are accurately metered with nP / nFe=1.15 and then pumped into the continuous synthesizer simultaneously to ensure that the outlet temperature is 65℃ and to obtain a slurry with a pH of 1.2.

[0080] (4) The slurry synthesized in step (3) is placed into a reactor and aged at 85°C until the crystallization is completed and the mixture turns white.

[0081] (5) After the whitening slurry is extended for 30 minutes, solid-liquid separation is performed, and the filter cake is washed online. The washed filter cake is dried and then calcined. The drying temperature is 105℃ and the calcination temperature is 600℃ to obtain the product anhydrous ferric phosphate.

[0082] Example 5: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0083] (1) Take a ferric sulfate solution with Fe concentration = 50 g / L, add sulfuric acid to adjust the pH to 1.0, and prepare an iron salt solution;

[0084] (2) Take the prepared ammonium dihydrogen phosphate solution (P=40g / L) and add ammonia water to adjust the pH to 5 to obtain the phosphate salt solution;

[0085] (3) The iron salt solution and phosphate salt solution are accurately metered with nP / nFe=1.15 and then pumped into the continuous synthesizer simultaneously to ensure that the outlet temperature is 65℃ and to obtain a slurry with a pH of 1.2.

[0086] (4) The slurry synthesized in step (3) is placed into a reactor and aged at 85°C until the crystallization is completed and the mixture turns white.

[0087] (5) After the whitening slurry is extended for 30 minutes, solid-liquid separation is performed, and the filter cake is washed online. The washed filter cake is dried and then calcined. The drying temperature is 105℃ and the calcination temperature is 600℃ to obtain the product anhydrous ferric phosphate.

[0088] Example 6: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0089] (1) Take a ferric sulfate solution with Fe concentration = 50 g / L, add sulfuric acid to adjust the pH to 0.9, and prepare an iron salt solution;

[0090] (2) Take the prepared ammonium dihydrogen phosphate solution (P=45g / L) and add ammonia water to adjust the pH to 5.0 to obtain the phosphate salt solution;

[0091] (3) The iron salt solution and phosphate salt solution are accurately metered with nP / nFe=1.15 and then pumped into the continuous synthesizer simultaneously to ensure that the outlet temperature is 65℃ and to obtain a slurry with a pH of 1.0.

[0092] (4) The slurry synthesized in step (3) is placed into a reactor and aged at 85°C until the crystallization is completed and the mixture turns white.

[0093] (5) After the whitening slurry is extended for 30 minutes, solid-liquid separation is performed, and the filter cake is washed online. The washed filter cake is dried and then calcined. The drying temperature is 105℃ and the calcination temperature is 600℃ to obtain the product anhydrous ferric phosphate.

[0094] Example 7: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0095] (1) Take a ferric sulfate solution with Fe concentration = 50 g / L, add sulfuric acid to adjust the pH to 1.0, and prepare an iron salt solution;

[0096] (2) Take the prepared ammonium dihydrogen phosphate solution (P=40g / L) and add ammonia water to adjust the pH to 5.0 to obtain the phosphate salt solution;

[0097] (3) The iron salt solution and phosphate salt solution are accurately metered with nP / nFe=1.2 and then pumped into the continuous synthesizer simultaneously to ensure that the outlet temperature is 65℃ and to obtain a slurry with a pH of 1.2.

[0098] (4) The slurry synthesized in step (3) is placed into a reactor and aged at 85°C until the crystallization is completed and the mixture turns white.

[0099] (5) After the whitening slurry is extended for 30 minutes, solid-liquid separation is performed, and the filter cake is washed online. The washed filter cake is dried and then calcined. The drying temperature is 105℃ and the calcination temperature is 600℃ to obtain the product anhydrous ferric phosphate.

[0100] Example 8: A method for continuous synthesis of high-quality iron phosphate with low iron-to-phosphorus ratio, comprising the following steps:

[0101] (1) Take a ferric sulfate solution with Fe concentration = 56 g / L, add sulfuric acid to adjust the pH to 0.9, and prepare an iron salt solution;

[0102] (2) Take the prepared diammonium phosphate solution (P=45g / L) and add ammonia water to adjust the pH to 6 to obtain the phosphate salt solution;

[0103] (3) The iron salt solution and phosphate salt solution are accurately metered with nP / nFe=1.11 and then pumped into the continuous synthesizer simultaneously to ensure that the outlet temperature is 55℃ and to obtain a slurry with a pH of 1.25.

[0104] (4) The slurry synthesized in step (3) is placed in a reactor and aged at 85°C until the crystallization is completed and the slurry turns white.

[0105] (5) After the whitening slurry is extended for 30 minutes, solid-liquid separation is performed, and the filter cake is washed online. The washed filter cake is dried and then calcined. The drying temperature is 105℃ and the calcination temperature is 600℃ to obtain the product anhydrous ferric phosphate.

[0106] Comparative Example 1: This comparative example is a comparative experimental example of Example 4. The raw material parameters and experimental parameters are the same as those of Example 4, except that the reactor is changed from a continuous synthesizer to a reaction vessel, and phosphate salt is used as the base material and ferric solution is used as the dropping liquid. The dropping time is controlled within 30 minutes. After the addition is completed, the temperature is raised directly for aging and crystallization. The subsequent treatment method is the same as that of Example 4.

[0107] Comparative Example 2: This comparative example is a comparative experimental example of Example 5. The only difference between it and Example 5 is that the pH of the iron salt solution is adjusted to 0.7 and the pH of the slurry obtained in step (3) is 0.8. All other conditions are the same as those in Example 5.

[0108] Comparative Example 3: This comparative example is a comparative experimental example of Example 6. The only difference between this example and Example 6 is that the outlet temperature of the continuous synthesizer is reduced to 45°C. All other conditions are the same as those in Example 6.

[0109] Comparative Example 4: This comparative example is a comparative experiment of Example 7. The raw material parameters are the same as those of Example 7, except that the reactor is changed from a continuous synthesizer to a reaction vessel. A dropwise addition method is adopted, with phosphate salt solution as the base material and iron salt solution as the drop liquid. The dropwise addition time is controlled at 30 min. After addition, the temperature is directly raised for aging and crystallization. The subsequent treatment method is the same as that of Example 7.

[0110] Comparative Example 5: This comparative example is a comparative experimental example of Example 8. The only difference from Example 8 is that the continuous synthesizer is replaced with a reaction vessel. The iron salt solution and phosphate salt solution are precisely metered with nP / nFe=1.12 and then pumped into the reaction vessel simultaneously. The other parameters are the same as in Example 8, and the subsequent processing method is the same as in Example 8.

[0111] Comparative Example 6: This comparative example is a comparative experimental example of Example 7. The only difference between it and Example 7 is that phosphoric acid was added to the phosphate salt solution to adjust the pH to 6.5, and the pH of the slurry obtained in step (3) was 1.6. The subsequent processing method is the same as that of Example 7.

[0112] The anhydrous ferric phosphates prepared in Examples 4-8 and Comparative Examples 1-6 were subjected to physicochemical analysis, and the specific components are shown in Tables 1 and 2.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] As can be seen from Tables 1 and 2, in Examples 4-7 and Comparative Examples 1-4, the Fe / P ratio, impurity content, and particle size distribution of the products changed with the change of reactor neutralization and synthesis conditions. In general, under the condition of fixed iron salt and phosphate salt, using a continuous synthesizer can produce iron phosphate with low Fe / P ratio (0.960-0.965), high quality (low impurity content), and good consistency.

[0118] Lithium iron phosphate was prepared from the anhydrous iron phosphate of Examples 4 and 5 and Comparative Examples 1 and 2, and its electrochemical performance was tested. The data are shown in Table 3.

[0119] Table 3

[0120]

[0121] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for continuously synthesizing low-iron phosphorus ratio high-quality ferric phosphate, characterized by, The method comprises the following steps: (1) taking a ferric sulfate solution and adjusting the pH to 0.9-1.5 by adding acid to prepare a ferric salt solution; (2) taking a phosphorus salt solution and adjusting the pH to 4-6 by adding alkali to prepare a phosphorus salt solution; (3) precisely metering the ferric salt solution and the phosphorus salt solution and simultaneously feeding them into a continuous synthesizer by a pump, controlling the outlet temperature to be 55-75 ℃, and obtaining a slurry with a pH of 0.9-1.5; (4) putting the slurry prepared in step (3) into a reaction kettle for aging, and keeping the temperature until the crystal transformation is complete and the slurry is white; (5) prolonging the time of the white slurry, separating the solid and the liquid, washing the filter cake on line, drying and calcining the filter cake after washing to obtain the product.

2. The method of claim 1, wherein the method is a continuous method of synthesizing low-iron phosphorus ratio high-quality ferric phosphate. In step (1), the Fe concentration of the ferric phosphate solution is 46-65 g / L.

3. The method of claim 1, wherein the method is continuous. In step (1), the acid added is one or both of sulfuric acid and phosphoric acid.

4. The method of claim 1, wherein the method is continuous. In step (2), the P concentration of the phosphorus salt solution is 40-50 g / L.

5. The method of claim 1, wherein the method is continuous. In step (2), the phosphorus salt solution is one of ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

6. The method of claim 1, wherein the method is continuous. In step (2), the alkali added is one or both of ammonia and sodium hydroxide.

7. The method of claim 1, wherein the method is continuous. In step (3), the nP / nFe after metering is 1.0-1.

2.

8. The method of claim 1, wherein the method is continuous. In step (4), the aging temperature is 75-90 ℃.

9. The method of claim 1, wherein the method is continuous. In step (5), the drying temperature is 85-105 ℃, and the calcination temperature is 550-600 ℃.

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