A method for producing compact spherical iron phosphate

Abstract

The application discloses a method for preparing dense spherical iron phosphate, wherein a divalent iron source and a phosphorus source are mixed to obtain a mixed solution; the phosphorus source is a monobasic acid phosphorus source or a dibasic acid phosphorus source; hydrogen peroxide is added to the mixed solution for oxidation, sulfuric acid is used to adjust the pH to 1.90-1.94, phosphoric acid is added, and reaction is carried out for 10-20 min to obtain a reaction liquid; finally, the reaction liquid is filtered and washed, aged and crystallized, and calcined to obtain iron phosphate. In the preparation process of the iron phosphate, the morphology of the iron phosphate can be controlled to obtain a dense spherical or spherical structure, and the process stability and product consistency are improved. In addition, the preparation method can realize the control of the performance of the iron phosphate without adding complex equipment, and the process is simple and easy to be industrialized and enlarged.

Description

Technical Field

[0001] This invention belongs to the field of iron phosphate preparation technology, and particularly relates to a method for preparing dense spherical iron phosphate. Background Technology

[0002] Iron phosphate, as one of the raw materials for preparing lithium iron phosphate (LiFePO4) cathode materials, plays a decisive role in improving the safety and cycle stability of LiFePO4 batteries. The performance of LiFePO4 batteries is mainly determined by iron phosphate; therefore, optimizing its preparation process and controlling costs are of great significance for improving battery performance and reducing production costs. Iron phosphate dihydrate (FePO4·2H2O), as the core precursor for preparing LiFePO4 cathode materials, directly determines the rate performance, cycle stability, and energy density of subsequent LiFePO4 materials due to its crystal integrity, morphological characteristics, impurity phase content, and doping uniformity, playing a crucial role in the overall performance of power batteries and energy storage batteries.

[0003] The current main process route for producing anhydrous ferric phosphate using the ammonium ferric phosphate method involves using ferrous iron as a base, producing ferric phosphate precursors by adding phosphate salts and hydrogen peroxide, and then decomposing them to obtain anhydrous ferric phosphate. However, the anhydrous ferric phosphate produced by this process has primary crystals that are multidimensional nanosheets. If the process is not well controlled, irregular shapes such as needle-like, tree-like, branch-like, and elongated crystals may also appear. During secondary agglomeration, the nanosheets stack randomly, forming loose aggregates; the secondary particles have a wide particle size distribution (large D50 fluctuations), with large particles and ultrafine powders coexisting; the particle surfaces are rough, with disordered pores and a high BET specific surface area, making it difficult to form dense spherical particles, resulting in low compaction density and poor compaction performance.

[0004] Based on this, we are now studying a production process for iron phosphate, which simultaneously controls the morphology of iron phosphate during the preparation process to form dense spherical or near-spherical anhydrous iron phosphate particles, effectively improving the compaction performance. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a production process for anhydrous ferric phosphate, so as to achieve the control of its morphology during the production process, forming spherical or near-spherical anhydrous ferric phosphate particles with a dense structure, and effectively improving the compaction performance.

[0006] Technical solution: The present invention provides a method for preparing dense spherical iron phosphate, comprising the following steps:

[0007] (1) Mix the ferrous iron source and the phosphorus source to obtain a mixed solution; the phosphorus source is a monocarboxylic acid phosphorus source or a dicarboxylic acid phosphorus source;

[0008] (2) After adding hydrogen peroxide to the mixed solution for oxidation, the pH is adjusted to 1.90-1.94 with sulfuric acid, and phosphoric acid is added. The reaction is carried out for 10-20 minutes to obtain the reaction solution.

[0009] (3) The reaction solution was filtered, washed, aged, crystallized, and calcined to obtain ferric phosphate;

[0010] The total phosphorus content of the phosphorus source and phosphoric acid is in a molar ratio of (1.0-1.2):1 to the iron content of the iron source, and the total molar ratio of phosphoric acid to the total phosphorus source and phosphoric acid is in a molar ratio of (0.026-0.1):1.

[0011] Furthermore, in step (1) of the preparation method, the divalent iron source is selected from at least one of ferrous sulfate heptahydrate, ferrous nitrate, ferrous oxalate, or ferrous chloride.

[0012] Furthermore, in step (1) of the preparation method, the phosphorus source is selected from at least one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate, or potassium dihydrogen phosphate. More preferably, the phosphorus source is an ammonium salt phosphorus source, selected from ammonium monohydrogen phosphate or ammonium dihydrogen phosphate.

[0013] Furthermore, in step (2) of the preparation method, the amount of hydrogen peroxide added is 1.0-1.2 times the number of moles required to oxidize ferrous iron to ferric iron.

[0014] Furthermore, in step (2) of the preparation method, after adding the phosphoric acid, the pH value of the reaction solution is (1.90-1.94) ± 0.02.

[0015] Furthermore, in step (3) of the preparation method, the reaction temperature of the aging crystallization is 80-100℃ and the reaction time is 120min-240min.

[0016] Furthermore, in step (3) of the preparation method, the calcination temperature is 500-650℃ and the calcination time is 3-7h.

[0017] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are that the preparation method can simultaneously control the morphology of iron phosphate during the preparation process to obtain a dense spherical or near-spherical structure, thereby improving process stability and product consistency; in addition, the preparation method can control the properties of iron phosphate without adding complex equipment, and the process is simple and easy to scale up for industrial production. Attached Figure Description

[0018] Figure 1 This is a SEM image of the iron phosphate prepared in Example 1 of the present invention;

[0019] Figure 2This is a SEM image of the iron phosphate prepared in Comparative Example 1 of this invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] Example 1

[0022] The preparation method of ferric phosphate in this embodiment includes the following steps:

[0023] (1) Prepare 1L of ferrous sulfate heptahydrate solution with a total iron concentration of 60g / L (i.e., 1.07mol iron) and 0.5L of ammonium hydrogen phosphate solution with a phosphorus content of 70g / L (i.e., 1.13mol phosphorus). Mix the two to obtain a mixed solution with a pH of 1.98.

[0024] (2) Add 8% hydrogen peroxide by mass to the mixed solution using a peristaltic pump, and adjust the pH to about 1.94 using sulfuric acid; the amount of hydrogen peroxide used is 1.2 times the number of moles required to oxidize ferrous iron in ferrous sulfate heptahydrate to ferric iron.

[0025] (3) Add 3.34 g of 85% phosphoric acid (i.e. 0.03 mol of phosphorus, accounting for 2.6% of the total phosphorus) to step (2) for 90 min. At this time, the pH value of the system is 1.94 ± 0.02.

[0026] (4) After stirring and reacting continuously for 20 minutes at a stirring rate of 250 rpm in the reactor, the resulting slurry is filtered and washed, and the amount of washing water used is 10 times the theoretical yield of iron phosphate.

[0027] (5) After washing, put it in a water bath and heat it to 84-85℃, keep it warm for 180 minutes to obtain ferric phosphate slurry.

[0028] (6) The obtained ferric phosphate slurry is filtered and washed to obtain filter cake. The washing water is 10 times the theoretical yield of ferric phosphate.

[0029] (7) The filter cake was calcined at 550°C for 4 hours to obtain anhydrous ferric phosphate.

[0030] Example 2

[0031] The preparation method of ferric phosphate in this embodiment is basically the same as that in Example 1, except for the amount of phosphoric acid added in step (3), as follows:

[0032] (3) Add 6.86g of 85% phosphoric acid (i.e. 0.06mol of phosphorus, accounting for 5% of the total phosphorus) to step (2) for 90min. At this time, the pH value of the system is 1.94±0.02.

[0033] Example 3

[0034] The preparation method of ferric phosphate in this embodiment is basically the same as that in Example 1, except for the amount of phosphoric acid added in step (3), as follows:

[0035] (3) Add 10.56g of 85% phosphoric acid (i.e. 0.09mol of phosphorus, accounting for 7.4% of the total phosphorus) to step (2) for 90min. At this time, the pH value of the system is 1.94±0.02.

[0036] Example 4

[0037] The preparation method of ferric phosphate in this embodiment is basically the same as that in Example 1, except that in step (2), sulfuric acid is used to adjust the pH to about 1.90, and the amount of phosphoric acid added in step (3) is as follows:

[0038] (3) Add 14.47g of 85% phosphoric acid (i.e. 0.126mol of phosphorus, accounting for 10% of the total phosphorus) to step (2) for 90min. At this time, the pH value of the system is 1.90±0.015.

[0039] Comparative Example 1

[0040] The preparation method of this comparative example of iron phosphate is the same as that used in Example 1, and includes the following steps:

[0041] (1) Prepare 1L of ferrous sulfate heptahydrate solution with a total iron concentration of 60g / L (i.e., 1.07mol iron) and 0.513L of ammonium hydrogen phosphate solution with a phosphorus content of 70g / L (i.e., 1.16mol phosphorus). Mix the two solutions to obtain a mixed solution with a pH of 1.98.

[0042] (2) Add 8% hydrogen peroxide by mass to the mixed solution using a peristaltic pump, and adjust the pH to about 1.94 using sulfuric acid; the amount of hydrogen peroxide used is 1.2 times the number of moles required to oxidize ferrous iron in ferrous sulfate heptahydrate to ferric iron.

[0043] (3) After stirring and reacting continuously for 20 minutes at a stirring rate of 250 rpm in the reactor, the resulting slurry is filtered and washed, and the amount of washing water used is 10 times the theoretical yield of iron phosphate.

[0044] (4) After washing, put it in a water bath and heat it to 84-85℃, keep it warm for 180 minutes to obtain ferric phosphate slurry.

[0045] (5) The obtained ferric phosphate slurry is filtered and washed to obtain filter cake. The washing water is 10 times the theoretical yield of ferric phosphate.

[0046] (6) The filter cake was calcined at 550°C for 4 hours to obtain anhydrous ferric phosphate.

[0047] Comparative Example 2

[0048] Comparative Example 2 is basically the same as Example 1, except that it also uses a stepwise addition of the phosphorus source, but the phosphorus source in step (3) is also an ammonium hydrogen phosphate solution. Specifically:

[0049] (1) Prepare 1L of ferrous sulfate heptahydrate solution with a total iron concentration of 60g / L (i.e., 1.07mol iron) and 0.5L of ammonium hydrogen phosphate solution with a phosphorus content of 70g / L (i.e., 1.13mol phosphorus). Mix the two to obtain a mixed solution with a pH of 1.98.

[0050] (2) Add 8% hydrogen peroxide by mass to the mixed solution using a peristaltic pump, and adjust the pH to about 1.94 using sulfuric acid; the amount of hydrogen peroxide used is 1.2 times the number of moles required to oxidize ferrous iron in ferrous sulfate heptahydrate to ferric iron.

[0051] (3) Add 0.053L of ammonium hydrogen phosphate solution with a phosphorus content of 70g / L (i.e. 0.12mol of phosphorus, accounting for 10% of the total phosphorus) to step (2) for 90min. At this time, the pH value of the system is 1.94±0.02.

[0052] (4) After stirring and reacting continuously for 20 minutes at a stirring rate of 250 rpm in the reactor, the resulting slurry is filtered and washed, and the amount of washing water used is 10 times the theoretical yield of iron phosphate.

[0053] (5) After washing, put it in a water bath and heat it to 84-85℃, keep it warm for 180 minutes to obtain ferric phosphate slurry.

[0054] (6) The obtained ferric phosphate slurry is filtered and washed to obtain filter cake. The washing water is 10 times the theoretical yield of ferric phosphate.

[0055] (7) The filter cake was calcined at 550°C for 4 hours to obtain anhydrous ferric phosphate.

[0056] Morphological characteristics

[0057] The morphology of the iron phosphate prepared in Example 1 and Comparative Example 1 was characterized, and the results are as follows: Figure 1 and Figure 2 As shown.

[0058] Performance Characterization

[0059] The particle size (unit μm), specific surface area, and iron-phosphorus ratio of the iron phosphate samples prepared in the above examples and comparative examples were measured, and the results are shown in Table 1.

[0060] Table 1 Performance data of the examples and comparative examples

[0061]

[0062] As shown in Figures and Table 1, in Examples 1 to 4 of this invention, the specific surface area decreases with decreasing D50. This verifies that the preparation method of this invention can effectively improve the density and tapping performance of the prepared iron phosphate, resulting in a dense morphological structure. Furthermore, calculations of the span values ​​for Examples 1 and 4 show that when their span values ​​are similar, the specific surface area decreases significantly with decreasing D50. This further verifies that, under similar particle size distributions, the iron phosphate particles prepared in Example 4 have lower surface porosity and higher tapping performance.

[0063] Compared with the data from Example 1 and Comparative Example 1, and Example 4 and Comparative Example 2, it can be seen that the present invention, by adopting a stepwise addition of the phosphorus source, and adding phosphoric acid as the phosphorus source in the second step, not only does not affect the pH value of the system, but also can regulate the morphology of the primary iron phosphate particles, forming a regular spherical or near-spherical structure. This avoids the formation of a disordered, loose, honeycomb structure during secondary agglomeration. Figure 1 and Figure 2 The comparison shows that Example 1 has a spherical appearance and high tapping density; Comparative Example 1 has an amorphous shape, low tapping density, and poor flowability.

Claims

1. A method for preparing dense spherical iron phosphate, characterized in that, Includes the following steps: (1) Mix the ferrous iron source and the phosphorus source to obtain a mixed solution; the phosphorus source is a monocarboxylic acid phosphorus source or a dicarboxylic acid phosphorus source; (2) After adding hydrogen peroxide to the mixed solution for oxidation, the pH is adjusted to 1.90-1.94 with sulfuric acid, and phosphoric acid is added. The reaction is carried out for 10-20 minutes to obtain the reaction solution. (3) The reaction solution was filtered, washed, aged, crystallized, and calcined to obtain ferric phosphate; The molar ratio of total phosphorus in the phosphorus source and phosphoric acid to iron in the iron source is (1.0-1.2):1, and the molar ratio of phosphoric acid to total phosphorus in the phosphorus source and phosphoric acid is (0.026-0.15):

1.

2. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (1), the divalent iron source is selected from at least one of ferrous sulfate heptahydrate, ferrous nitrate, ferrous oxalate, or ferrous chloride.

3. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (1), the phosphorus source is selected from at least one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate, or potassium dihydrogen phosphate.

4. The method for preparing dense spherical iron phosphate according to claim 3, characterized in that, The phosphorus source is an ammonium salt phosphorus source, selected from monoammonium phosphate or diammonium phosphate.

5. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (2), the amount of hydrogen peroxide added is 1.0-1.2 times the number of moles required to oxidize ferrous iron to ferric iron.

6. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (2), after adding the phosphoric acid, the pH value of the reaction solution is (1.90-1.94) ± 0.

02.

7. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (3), the reaction temperature for aging crystallization is 80-100℃ and the reaction time is 120min-240min.

8. The method for preparing dense spherical iron phosphate according to claim 1, characterized in that, In step (3), the calcination temperature is 500-650℃ and the calcination time is 3-7h.

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