Preparation method of iron phosphate with high specific surface area and consistency

Abstract

The invention relates to a preparation method of iron phosphate with high specific surface area and consistency, which is characterized by comprising the following preparation steps: (1) synthesizing iron dihydrogen phosphate; (2) preparing amorphous iron phosphate, namely adding a surfactant and a dispersing agent into the iron dihydrogen phosphate solution in the step (1), uniformly stirring, adding 10-15% sodium hydroxide alkali liquor to adjust the pH value of a solution system in a reaction kettle to 1.8-2.2, mixing and stirring for 30-60 minutes under the condition of heat preservation at the temperature of 65-75 DEG C, filtering, washing, and drying to obtain the amorphous iron phosphate, wherein the addition amounts of the surfactant and the dispersing agent are respectively 0.3-0.7% and 1-3% of the total iron mass in the impurity-removed ferrous sulfate solution. After the suspension liquid is prepared, carrying out filter pressing and washing to remove impurities, so as to obtain an amorphous iron phosphate filter cake; (3) aging; and (4) preparing anhydrous iron phosphate. The preparation method has the beneficial effects that the performance of the prepared iron phosphate is ensured, and meanwhile, the high specific surface and the consistency are considered.

Description

Technical Field

[0001] The invention relates to the technical field of ferric phosphate, and in particular to a method for preparing ferric phosphate with high specific surface area and consistency. Background Art

[0002] Lithium iron phosphate cathode materials have the advantages of good cycle performance, high discharge capacity, safety and environmental protection, low price, and wide sources of raw materials. Therefore, they have become the preferred raw materials for the manufacture of power batteries and energy storage batteries in recent years. At present, the most mainstream synthesis route of lithium iron phosphate in the market is the solid phase method, which is to disperse, grind, dry, sinter, and crush the raw materials such as iron phosphate, lithium source, and carbon source to obtain lithium iron phosphate powder products. As one of the most used and most critical raw materials for the solid phase synthesis of lithium iron phosphate, iron phosphate is closely related to the development of new energy vehicles and energy storage industries.

[0003] At present, the three mainstream process routes on the market are 1) ferrous sulfate ammonia route; 2) sodium ferrous sulfate route; 3) iron route.

[0004] 1. Ammonia method: The ferrous sulfate solution reacts with industrial monoammonium phosphate, which is heated and stirred, and then filtered, washed, and flash evaporated.

[0005] Advantages:

[0006] 1. Obvious cost advantage;

[0007] 2. The by-product ammonium sulfate has high value;

[0008] 3. Product quality is more balanced;

[0009] Disadvantages:

[0010] 1. The compaction density is relatively low and is generally used in the field of energy storage;

[0011] 2. The amount of wastewater is large and the treatment cost is high;

[0012] 2. Sodium method: Use phosphoric acid + liquid alkali / soda ash + ferrous sulfate, heat with steam at 65-75℃, then age, filter and wash to obtain ferric phosphate.

[0013] Advantages:

[0014] 1. Suitable for combination with refined phosphoric acid;

[0015] 2. The compaction density of the sodium salt system is relatively high, generally around 2.7;

[0016] Disadvantages:

[0017] 1. Strict control requirements on sodium ion content in products;

[0018] 2. The by-product sodium sulfate is difficult to handle and has low value. The discharge of sodium sulfate needs to be combined with the relevant requirements of the plant site;

[0019] 3. Iron method: Use phosphoric acid + iron powder / iron block to heat and dissolve, then filter press, wash and flash evaporate.

[0020] Advantages:

[0021] 1. Good product quality, mainly targeting the fields of power batteries and high-end energy storage;

[0022] 2. This route produces less wastewater, less environmental pressure, and basically no by-products in the production process;

[0023] Disadvantages:

[0024] 1. High production cost and high price of pure iron;

[0025] 2. The product stability is relatively poor;

[0026] The iron phosphate industry has developed rapidly in recent years, especially driven by the new energy vehicle and energy storage markets, and the demand has increased significantly. With the gradual release of new production capacity in recent years, the supply of iron phosphate has increased significantly, market competition has intensified, and lithium iron phosphate has higher requirements for the performance and stability of iron phosphate. Therefore, it is very important to prepare high-performance and stable iron phosphate.

[0027] In view of this, the present invention develops anhydrous iron phosphate that combines high specific surface area and consistency without sacrificing the performance of iron phosphate by improving the process formula based on the existing sodium iron phosphate process. Summary of the invention

[0028] The purpose of the present invention is to provide a method for preparing ferric phosphate with high specific surface area and consistency.

[0029] The iron phosphate produced by the invention not only ensures performance but also takes into account high specific surface area and consistency.

[0030] More specifically, the particle size of the primary particles of iron phosphate can be controllably reduced within a certain range and the overall particle size distribution width can be reduced, thereby increasing the specific surface area and reaction activity of the material, reducing the iron-phosphorus ratio, and making the material have better consistency and dispersibility.

[0031] To achieve the above object, the present invention is implemented by the following technical solutions:

[0032] A method for preparing high specific surface area and consistency ferric phosphate comprises the following preparation steps:

[0033] (1) Synthesize ferrous dihydrogen phosphate;

[0034] (2) preparing amorphous iron phosphate;

[0035] (3) Aging;

[0036] (4) Preparation of anhydrous ferric phosphate.

[0037] As a further improvement of this solution, the (1) synthesis of ferrous dihydrogen phosphate specifically includes the following preparation steps:

[0038] A 1-1.05 mol / L ferrous sulfate solution is prepared and subjected to impurity removal treatment, and the impurity-removed ferrous sulfate solution, 85% phosphoric acid, and 27.5% hydrogen peroxide are sequentially pumped into a reaction kettle at a molar ratio of 1-1.05:1-1.05:0.5-0.75, wherein the impurity-removed ferrous sulfate solution is firstly pumped into the reaction kettle and a stirrer is turned on, phosphoric acid is added and mixed uniformly, and then hydrogen peroxide is added into the reaction kettle at a fixed adding rate within 30-45 minutes, and then stirred at 20-50° C. for 60-120 minutes to generate ferric dihydrogen phosphate.

[0039] As a further improvement of this solution, the (2) preparation of amorphous ferric phosphate specifically includes the following preparation steps:

[0040] A surfactant and a dispersant are added to the ferric dihydrogen phosphate solution in step (1).

[0041] The surfactant and dispersant are added in amounts of 0.3% to 0.7% and 1% to 3% of the total iron mass in the ferrous sulfate solution after impurities are removed, respectively; after stirring evenly, 10% to 15% sodium hydroxide alkali solution is added to adjust the pH value of the solution system in the reaction kettle to 1.8 to 2.2; after mixing and stirring for 30 to 60 minutes under the heat preservation condition of 65 to 75 DEG C, a suspension with a solid content of 8 to 15% is generated; after the suspension is prepared, it is filtered and washed to remove impurities to obtain an amorphous ferric phosphate filter cake.

[0042] As a further improvement of the present scheme, in the preparation of amorphous ferric phosphate in (2), the surfactant is at least one of alkylphenol polyoxyethylene ether (OP-10), cetyltrimethylammonium bromide (CTAB) and polysorbate (Tween 80).

[0043] As a further improvement of the present solution, in the preparation of amorphous ferric phosphate in (2), the dispersant is at least one of polyethylene glycol (PEG-200) and sodium dodecyl sulfate (SDS).

[0044] As a further improvement of this solution, the (3) aging specifically includes the following preparation steps:

[0045] The amorphous ferric phosphate filter cake of step (2) is slurried and dispersed, and then pumped into an aging kettle. At the same time, 85% phosphoric acid is added to the aging kettle, and the amount of phosphoric acid is 0.01 to 0.05 mol of the total iron mass in the ferrous sulfate solution after impurities are removed in step (1). The mixture is mixed and stirred at 85 to 105° C. until the slurry turns into a pink-white color, and then kept warm for 120 to 180 minutes.

[0046] As a further improvement of this solution, the (4) preparation of anhydrous ferric phosphate specifically includes the following preparation steps:

[0047] The solution obtained in step (3) is filtered and washed to remove impurities to obtain a dihydrate iron phosphate filter cake, which is dried in a flash dryer and then calcined in a rotary kiln to obtain anhydrous iron phosphate with crystal water removed.

[0048] As a further improvement of the present scheme, in the preparation of anhydrous ferric phosphate in (4), the drying temperature is 200-280° C.; the calcination temperature is 500-650° C.; and the calcination time is 4-8 h.

[0049] The method for preparing high specific surface area and consistency ferric phosphate of the present invention has the following beneficial effects:

[0050] 1) In the preparation process of the present invention, by adding an appropriate amount of surfactant (OP-10) and dispersant (PEG-200), the particle size of the primary iron phosphate particles can be significantly reduced and the overall particle size distribution width can be reduced, which not only improves the specific surface area and reaction activity of the material, but also makes the material have better consistency and dispersibility, and can also reduce the iron-phosphorus ratio, which is conducive to the preparation of nano-scale lithium iron phosphate with smaller particle size and higher compaction. And within a reasonable addition range, the amount of surfactant (OP-10) added has controllable regulation on the particle size, specific surface area and iron-phosphorus ratio of the primary particles of the material, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 : Preparation flow chart of the method for preparing high specific surface area and consistency ferric phosphate of the present invention;

[0052] Figure 2 : SEM (10kV*5k) microscopic morphology of the anhydrous ferric phosphate material in Example 1 of the present invention;

[0053] Figure 3 : EDS "O" element distribution diagram of anhydrous ferric phosphate material in Example 1 of the present invention;

[0054] Figure 4 : EDS "P" element distribution diagram of anhydrous ferric phosphate material in Example 1 of the present invention;

[0055] Figure 5: EDS "Fe" element distribution diagram of anhydrous ferric phosphate material in Example 1 of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following embodiments and the accompanying drawings are combined to illustrate the present invention. Figures 1 to 4 The present invention will be further described:

[0057] Example 1

[0058] This embodiment provides a method for preparing high specific surface area and consistency ferric phosphate, comprising the following steps:

[0059] (1) Synthesis of ferrous dihydrogen phosphate

[0060] A 1 mol / L ferrous sulfate solution is prepared and subjected to impurity removal treatment, and the impurity-removed ferrous sulfate solution, 85% phosphoric acid, and 27.5% hydrogen peroxide are successively pumped into a reactor at a molar ratio of 1:1:0.7, wherein the impurity-removed ferrous sulfate solution is first pumped into the reactor and a stirrer is turned on, phosphoric acid is added and mixed evenly, and then hydrogen peroxide is added to the reactor at a fixed addition rate within 30 minutes, and then stirred at 50° C. for 60 minutes to generate ferric dihydrogen phosphate;

[0061] (2) Preparation of amorphous iron phosphate

[0062] Adding a surfactant (OP-10) and a dispersant (PEG-200) to the ferrous dihydrogen phosphate solution of step (1), the added amounts being 0.5% and 1.5% of the total iron mass in the ferrous sulfate solution after impurities removal, respectively; stirring evenly; adding 12% sodium hydroxide lye to adjust the pH value of the solution system in the reactor to 1.9; mixing and stirring at 65° C. for 30 minutes to generate a suspension with a solid content of 12%; after the suspension is prepared, filtering and washing to remove impurities to obtain an amorphous ferric phosphate filter cake;

[0063] (3) Aging

[0064] The amorphous ferric phosphate filter cake of step (2) is slurried and dispersed, and then pumped into an aging kettle. At the same time, 85% phosphoric acid is added to the aging kettle, and the amount of phosphoric acid is 0.02 mol of the total iron mass in the ferrous sulfate solution after impurities are removed in step (1). Mix and stir at 95° C. until the slurry turns into a pink white color, and then keep warm for 120 minutes;

[0065] (4) Preparation of anhydrous ferric phosphate

[0066] The solution obtained in step (3) is filtered and washed to remove impurities to obtain a dihydrate iron phosphate filter cake, which is dried in a flash dryer at 220° C. and then calcined in a rotary kiln at 580° C. for 4 hours to obtain anhydrous iron phosphate with the crystal water removed.

[0067] Example 2

[0068] This embodiment provides a method for preparing high specific surface area and consistency ferric phosphate, comprising the following steps:

[0069] (1) Synthesis of ferrous dihydrogen phosphate

[0070] A 1 mol / L ferrous sulfate solution is prepared and subjected to impurity removal treatment, and the impurity-removed ferrous sulfate solution, 85% phosphoric acid, and 27.5% hydrogen peroxide are successively pumped into a reactor at a molar ratio of 1:1.05:0.7, wherein the impurity-removed ferrous sulfate solution is first pumped into the reactor and a stirrer is turned on, phosphoric acid is added and mixed uniformly, and then hydrogen peroxide is added to the reactor at a fixed addition rate within 40 minutes, and then stirred at 50° C. for 80 minutes to generate ferric dihydrogen phosphate;

[0071] (2) Preparation of amorphous iron phosphate

[0072] Adding a surfactant (OP-10) and a dispersant (PEG-200) to the ferrous dihydrogen phosphate solution of step (1), the added amounts being 0.5% and 1.5% of the total iron mass in the ferrous sulfate solution after impurities removal, respectively; stirring evenly; adding 10% sodium hydroxide lye to adjust the pH value of the solution system in the reactor to 1.8; mixing and stirring at 65° C. for 40 minutes to generate a suspension with a solid content of 12%; after the suspension is prepared, filtering and washing to remove impurities to obtain an amorphous ferric phosphate filter cake;

[0073] (3) Aging

[0074] The amorphous ferric phosphate filter cake of step (2) is slurried and dispersed, and then pumped into an aging kettle. At the same time, 85% phosphoric acid is added to the aging kettle, and the amount of phosphoric acid is 0.03 mol of the total iron mass in the ferrous sulfate solution after impurities are removed in step (1). Mix and stir at 95° C. until the slurry turns into a pink white color, and then keep warm for 120 minutes;

[0075] (4) Preparation of anhydrous iron phosphate

[0076] The solution obtained in step (3) is filtered and washed to remove impurities to obtain a dihydrate iron phosphate filter cake, which is dried in a flash dryer at 240° C. and then calcined in a rotary kiln at 600° C. for 4 hours to obtain anhydrous iron phosphate with crystal water removed.

[0077] Example 3

[0078] This embodiment provides a method for preparing high specific surface area and consistency ferric phosphate, comprising the following steps:

[0079] (1) Synthesis of ferrous dihydrogen phosphate

[0080] A 1 mol / L ferrous sulfate solution is prepared and subjected to impurity removal treatment, and the impurity-removed ferrous sulfate solution, 85% phosphoric acid, and 27.5% hydrogen peroxide are successively pumped into a reactor at a molar ratio of 1:1.05:0.6, wherein the impurity-removed ferrous sulfate solution is first pumped into the reactor and a stirrer is turned on, phosphoric acid is added and mixed evenly, and then hydrogen peroxide is added to the reactor at a fixed addition rate within 50 minutes, and then stirred at 50° C. for 80 minutes to generate ferric dihydrogen phosphate;

[0081] (2) Preparation of amorphous iron phosphate

[0082] Adding a surfactant (OP-10) and a dispersant (PEG-200) to the ferrous dihydrogen phosphate solution of step (1), the added amounts being 0.5% and 1.5% of the total iron mass in the ferrous sulfate solution after impurities removal, respectively; stirring evenly; adding 10% sodium hydroxide lye to adjust the pH value of the solution system in the reactor to 1.6; mixing and stirring at 75° C. for 40 minutes to generate a suspension with a solid content of 12%; after the suspension is prepared, filtering and washing to remove impurities to obtain an amorphous ferric phosphate filter cake;

[0083] (3) Aging

[0084] The amorphous ferric phosphate filter cake of step (2) is slurried and dispersed, and then pumped into an aging kettle. At the same time, 85% phosphoric acid is added to the aging kettle, and the amount of phosphoric acid is 0.04 mol of the total iron mass in the ferrous sulfate solution after impurities are removed in step (1). Mix and stir at 105° C. until the slurry turns into a pink white color, and then keep warm for 120 minutes;

[0085] (4) Preparation of anhydrous ferric phosphate

[0086] The solution obtained in step (3) is filtered and washed to remove impurities to obtain a dihydrate iron phosphate filter cake, which is dried in a flash dryer at 240° C. and then calcined in a rotary kiln at 620° C. for 4 hours to obtain anhydrous iron phosphate with crystal water removed.

[0087] Comparative Example 1

[0088] Compared with Example 1, the only difference is that no surfactant and dispersant are added in step (2).

[0089] Comparative Example 2

[0090] Compared with Example 1, the only difference is that only a surfactant (OP-10) is added in step (2). Specifically, the amount of surfactant (OP-10) added in step (2) of this example is 0.5%.

[0091] Comparative Example 3

[0092] Compared with Example 1, the only difference is that only a dispersant (PEG-200) is added in step (2). Specifically, the amount of the dispersant (PEG-200) added in step (2) of this example is 1.5%.

[0093] Comparative Example 4

[0094] Compared with Example 1, the only difference is that a surfactant (CTAB) and a dispersant (SDS) are added in step (2). Specifically, the amounts of surfactant (CTAB) and dispersant (SDS) added in step (2) of this example are 0.5% and 1.5%, respectively.

[0095] Comparative Example 5

[0096] Compared with Example 1, the only difference is that a surfactant (Tween 80) and a dispersant (SDS) are added in step (2). Specifically, in step (2) of this example, the amounts of surfactant (CTAB) and dispersant (SDS) added are 0.5% and 1.5%, respectively.

[0097] The particle size distribution, specific surface area and iron-phosphorus ratio of the anhydrous ferric phosphate prepared in Experimental Examples 1-3 and Comparative Examples 1-3 were analyzed, and the results are shown in Table 1 below.

[0098] Table 1 Particle size distribution and specific surface area of ​​each group of iron phosphate

[0099]

[0100] It can be seen from the data in Table 1 that the method of Examples 1-3 of the present invention can significantly reduce the particle size of the primary particles of iron phosphate and reduce the overall particle size distribution width, which not only improves the specific surface area and reaction activity of the material, but also makes the material have better consistency and dispersibility, and can also reduce the iron-phosphorus ratio of the iron phosphate material, which is conducive to the preparation of nano-scale lithium iron phosphate with smaller particle size and higher compaction.

[0101] It can be seen from the data of Comparative Examples 1-5 that the role of adding a surfactant (OP-10) when preparing amorphous iron phosphate is mainly to improve the interfacial properties in the liquid, reduce the surface tension, increase the contact area between the dispersed phase and the continuous phase, make the slurry more stable, promote the chemical reaction, improve the synthesis efficiency of phosphate and iron ions, thereby reducing the iron-phosphorus ratio, and the generated amorphous iron phosphate has better chemical activity.

[0102] The main reason for adding the dispersant (PEG-200) is that it is water-soluble and extremely stable, and is not easily affected by acids and alkalis. A large number of oxygen atoms in the PEG molecule can combine with the free hydroxyl groups on the surface of the colloidal particles through hydrogen bonds, coating the surface of the colloidal particles and hindering the agglomeration of the particles. After calcination, PEG is slowly removed, leaving pores, increasing the specific surface area and making the pore distribution uniform. The good dispersing effect of PEG-200 makes the interior of the amorphous iron phosphate reaction system more uniform, greatly improves the consistency of the particle size of the amorphous iron phosphate primary particles, reduces the agglomeration phenomenon between particles, and thus reduces the overall particle size distribution width of the material, making it have better consistency and dispersibility.

[0103] In summary, the synergistic effect of surfactant (OP-10) and dispersant (PEG-200) can significantly improve the performance of iron phosphate, thereby effectively enhancing its application effect in lithium-ion batteries. The other surfactants and dispersants mentioned in the above process have no significant effect.

[0104] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent changes made using the present invention are within the patent protection scope of the present invention.

Claims

1. A method for preparing high specific surface area and consistency ferric phosphate, characterized in that: The method comprises the following preparation steps: (1) Synthesizing ferrous dihydrogen phosphate; (2) preparing amorphous iron phosphate; (3) Aging; (4) Preparation of anhydrous ferric phosphate.

2. The method for preparing high specific surface area and consistency ferric phosphate according to claim 1, characterized in that: The (1) synthesis of ferrous dihydrogen phosphate specifically comprises the following preparation steps: A 1-1.05 mol / L ferrous sulfate solution is prepared and subjected to impurity removal treatment, and the impurity-removed ferrous sulfate solution, 85% phosphoric acid, and 27.5% hydrogen peroxide are sequentially pumped into a reaction kettle at a molar ratio of 1-1.05:1-1.05:0.5-0.75, wherein the impurity-removed ferrous sulfate solution is firstly pumped into the reaction kettle and a stirrer is turned on, phosphoric acid is added and mixed uniformly, and then hydrogen peroxide is added into the reaction kettle at a fixed adding rate within 30-45 minutes, and then stirred at 20-50° C. for 60-120 minutes to generate ferric dihydrogen phosphate.

3. The method for preparing high specific surface area and consistency ferric phosphate according to claim 1, characterized in that: The (2) preparation of amorphous ferric phosphate specifically includes the following preparation steps: A surfactant and a dispersant are added to the ferrous dihydrogen phosphate solution in step (1), and the added amounts are 0.3% to 0.7% and 1% to 3% of the total iron mass in the ferrous sulfate solution after impurities are removed, respectively. After stirring evenly, 10% to 15% sodium hydroxide alkali solution is added to adjust the pH value of the solution system in the reaction kettle to 1.8 to 2.

2. After mixing and stirring for 30 to 60 minutes under the condition of heat preservation of 65 to 75° C., a suspension with a solid content of 8 to 15% is generated. After the suspension is prepared, it is filtered and washed to remove impurities to obtain an amorphous ferric phosphate filter cake.

4. The method for preparing high specific surface area and consistency ferric phosphate according to claim 3, characterized in that: In the preparation of amorphous ferric phosphate in (2), the surfactant is OP-10.

5. The method for preparing high specific surface area and consistency ferric phosphate according to claim 3, characterized in that: In the preparation of amorphous ferric phosphate in (2), the dispersant is PEG-200.

6. The method for preparing high specific surface area and consistency ferric phosphate according to claim 1, characterized in that: The (3) aging specifically includes the following preparation steps: The amorphous ferric phosphate filter cake of step (2) is slurried and dispersed and then pumped into an aging kettle. At the same time, 85% phosphoric acid is added to the aging kettle. The amount of phosphoric acid is 0.01 to 0.05 mol of the total iron mass in the ferrous sulfate solution after impurities are removed in step (1). The mixture is mixed and stirred at 85 to 95° C. until the slurry turns into a pink-white color and then kept warm for 120 to 180 minutes.

7. The method for preparing high specific surface area and consistency ferric phosphate according to claim 1, characterized in that: The (4) preparation of anhydrous ferric phosphate specifically includes the following preparation steps: The solution obtained in step (3) is filtered and washed to remove impurities to obtain a dihydrate iron phosphate filter cake, which is dried in a flash dryer and then calcined in a rotary kiln to obtain anhydrous iron phosphate with crystal water removed.

8. The method for preparing high specific surface area and consistency ferric phosphate according to claim 7, characterized in that: In the preparation of anhydrous ferric phosphate in (4), the drying temperature is 200-280° C.; the calcination temperature is 500-650° C.; and the calcination time is 4-8 hours.

Images