Preparation method and application of low-cost iron phosphate

Abstract

The invention provides a preparation method of low-cost iron phosphate, which comprises the following steps: weighing ferroferric oxide and a phosphorus source compound, adding into distilled water, continuously stirring and heating to 40-90 DEG C, then adding a compound additive, and continuously stirring and reacting to obtain a ferrous dihydrogen phosphate solution; and adding an oxidizing agent for reaction and post-treatment to obtain the iron phosphate. The preparation method can improve the yield of the iron phosphate, reduce the content of impurity ions and improve the tap density of the iron phosphate, and the iron-containing reaction aid and the reducing agent are mixed to serve as the compound aid, so that the cost can be greatly reduced, the income can be improved, and the preparation method is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic new materials, and particularly relates to a method for preparing low-cost iron phosphate. Background Art

[0002] Iron phosphate (FePO 4 ) as a key precursor for the cathode material of lithium iron phosphate (LiFePO 4 ) plays a crucial role in the field of lithium-ion batteries. With the rapid growth of the new energy vehicle and energy storage markets, the demand for high-performance and low-cost battery materials is becoming increasingly urgent. Iron phosphate has become an ideal choice for preparing lithium iron phosphate due to its stable structure, good cycle performance and safety.

[0003] The main methods for preparing iron phosphate include the following: 1. Ferrous sulfate method: Ferrous sulfate reacts with phosphoric acid to produce iron phosphate. The advantages of this method are that the raw materials are easily available and the cost is relatively low, but the disadvantages are that the introduction of sulfate radicals may lead to low product purity and a large amount of sulfate-containing wastewater is generated, causing pressure on the environment; 2. Iron powder reduction method: This method uses pure iron (iron blocks or iron powder) as the iron source and reacts with phosphoric acid to produce iron phosphate. The advantage of this method is high product purity, but the cost is relatively high; 3. Iron red method: Iron oxide reacts with phosphoric acid to produce iron phosphate. This method is suitable for large-scale production, but the product purity and performance are greatly affected by the raw materials, and the tapped density of the prepared iron phosphate is relatively low, which is not suitable for the cathode material of lithium batteries.

[0004] Aiming at the problems existing in the prior art, how to provide a method for preparing iron phosphate with low production cost, high product purity, high yield and high tapped density is an urgent problem to be solved by the present invention. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing low-cost iron phosphate to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing low-cost iron phosphate, and the preparation method includes the following steps:

[0008] (1) Weigh ferric oxide and a phosphorus source compound, add them to distilled water, continuously stir and heat up to 40-90 °C, then add a composite auxiliary agent, continue to stir and react for 20-40 min. After the reaction ends, post-treatment is carried out to obtain a ferrous dihydrogen phosphate solution;

[0009] (2) An oxidant is added to the ferrous dihydrogen phosphate solution, and the mixture is stirred and heated to 40 - 90 °C for 1 - 3 h. After the reaction ends, post-treatment is carried out to obtain crude iron phosphate, which is then calcined at 450 - 750 °C to obtain iron phosphate;

[0010] The composite auxiliary agent is a mixture of an iron-containing reaction auxiliary agent and a reducing agent.

[0011] As a further improvement, the iron-containing reaction auxiliary agent can be any iron-containing substance, including but not limited to iron oxide, ferrous oxide, magnetite, or a combination thereof.

[0012] As a further improvement, the reducing agent is at least one of oxalic acid, ascorbic acid, maltose, glucose, sodium bisulfite, sodium sulfite, phosphorous acid and its salts, hypophosphorous acid and its salts, and hydrazine hydrate.

[0013] As a further improvement, the reducing agent is at least one of oxalic acid, ascorbic acid, and glucose.

[0014] As a further improvement, the molar addition amount of the iron-containing reaction auxiliary agent in step (1) is 10 - 50% of the molar amount of magnetite.

[0015] As a further improvement, the total molar addition amount of the composite auxiliary agent in step (1) is 0.5 - 2 times the molar amount of magnetite.

[0016] As a further improvement, the phosphorus source compound is at least one of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0017] Preferably, the phosphorus source compound is phosphoric acid.

[0018] As a further improvement, the addition amount of the phosphorus source compound in step (1) is 2 - 3 times the molar amount of iron in magnetite.

[0019] As a further improvement, the oxidant is at least one of hydrogen peroxide, ozone, and oxygen.

[0020] As a further improvement, the oxidant is a hydrogen peroxide solution with a mass concentration of 20 - 50%.

[0021] Preferably, the oxidant is a hydrogen peroxide solution with a mass concentration of 30%.

[0022] As a further improvement, the application of the low-cost iron phosphate prepared by the method for preparing a low-cost iron phosphate in a cathode material of a lithium battery.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The iron phosphate prepared by the method for preparing low-cost iron phosphate provided by the present invention has a high yield, low content of impurity ions, high tapped density, and the use of a mixture of an iron-containing reaction assistant and a reducing agent as a composite assistant can greatly reduce costs and increase benefits, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD pattern of the iron phosphate prepared in Example 2;

[0026] Figure 2 SEM image of the iron phosphate prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention will be described below in conjunction with specific implementation embodiments. It should be noted that the following examples are examples of the present invention, only for explaining the present invention, and not for limiting the present invention. Without departing from the gist or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0028] In the following examples, the compound monomers and related reagents used can be purchased from the market. Among them, ferrous oxide, iron oxide, and magnetite are purchased from Shandong Luyin New Material Technology Co., Ltd., ascorbic acid is purchased from Xi'an Lavia Biotechnology Co., Ltd., and glucose is purchased from Henan Fango Environmental Protection Materials Co., Ltd.

[0029] The preparation method of Example 1 includes the following steps:

[0030] (1) Weigh 23.2 g of magnetite and 78.4 g of phosphoric acid, add them to 200 mL of distilled water, continuously stir and heat up to 65 °C, then add 18.0 g of glucose and 0.8 g of ferrous oxide, continue to stir and react for 30 min. After the reaction is completed, filter to obtain a ferrous dihydrogen phosphate solution;

[0031] (2) Add 35 mL of a hydrogen peroxide solution with a mass concentration of 30% dropwise to the ferrous dihydrogen phosphate solution, stir and react at 80 °C for 3 h. After the reaction is completed, filter, wash with distilled water to obtain a crude iron phosphate product, and calcine it in a muffle furnace at 700 °C to obtain iron phosphate, with a yield of 97.9%.

[0032] The preparation method of Example 2 includes the following steps:

[0033] (1) Weigh 23.2 g of magnetite and 78.4 g of phosphoric acid, add them to 200 mL of distilled water, continuously stir and heat up to 65 °C, then add 4.5 g of oxalic acid and 4.6 g of magnetite, continue to stir and react for 30 min. After the reaction is completed, filter to obtain a ferrous dihydrogen phosphate solution;

[0034] (2) 35 mL of 30% hydrogen peroxide solution was added dropwise to the ferrous dihydrogen phosphate solution, and the mixture was stirred at 80 °C for 3 h. After the reaction, it was filtered and washed with distilled water to obtain crude iron phosphate, which was calcined in a muffle furnace at 700 °C to obtain iron phosphate with a yield of 99.2%.

[0035] The preparation method of Example 3 includes the following steps:

[0036] (1) 23.2 g of iron tetroxide and 78.4 g of phosphoric acid were weighed and added to 200 mL of distilled water. The mixture was continuously stirred and heated to 65 °C, and then 8.8 g of ascorbic acid and 3.2 g of iron(III) oxide were added. Stirring was continued for 30 min. After the reaction, it was filtered to obtain a ferrous dihydrogen phosphate solution.

[0037] (2) 35 mL of 30% hydrogen peroxide solution was added dropwise to the ferrous dihydrogen phosphate solution, and the mixture was stirred at 80 °C for 3 h. After the reaction, it was filtered and washed with distilled water to obtain crude iron phosphate, which was calcined in a muffle furnace at 700 °C to obtain iron phosphate with a yield of 98.7%.

[0038] The preparation method of Comparative Example 1 includes the following steps:

[0039] (1) 23.2 g of iron tetroxide and 78.4 g of phosphoric acid were weighed and added to 200 mL of distilled water. The mixture was continuously stirred and heated to 65 °C, and then 4.5 g of oxalic acid and 0.7 g of hydrochloric acid were added. Stirring was continued for 30 min. After the reaction, it was filtered to obtain a ferrous dihydrogen phosphate solution.

[0040] (2) 35 mL of 30% hydrogen peroxide solution was added dropwise to the ferrous dihydrogen phosphate solution, and the mixture was stirred at 80 °C for 3 h. After the reaction, it was filtered and washed with distilled water to obtain crude iron phosphate, which was calcined in a muffle furnace at 700 °C to obtain iron phosphate with a yield of 80.8%.

[0041] The preparation method of Comparative Example 2 includes the following steps:

[0042] (1) 23.2 g of iron tetroxide and 78.4 g of phosphoric acid were weighed and added to 200 mL of distilled water. The mixture was continuously stirred and heated to 65 °C, and then 4.5 g of oxalic acid and 6.9 g of iron tetroxide were added. Stirring was continued for 30 min. After the reaction, it was filtered to obtain a ferrous dihydrogen phosphate solution.

[0043] (2) 35 mL of 30% hydrogen peroxide solution was added dropwise to the ferrous dihydrogen phosphate solution, and the mixture was stirred at 80 °C for 3 h. After the reaction, it was filtered and washed with distilled water to obtain crude iron phosphate, which was calcined in a muffle furnace at 700 °C to obtain iron phosphate with a yield of 85.2%.

[0044] The preparation method of Comparative Example 3 includes the following steps:

[0045] (1) Weigh 23.2 g of iron tetroxide and 78.4 g of phosphoric acid, add them to 200 mL of distilled water, continuously stir and heat up to 65 °C, then add 18 g of oxalic acid, continue to stir and react for 30 min. After the reaction ends, filter to obtain a ferrous dihydrogen phosphate solution;

[0046] (2) Add 35 mL of hydrogen peroxide solution with a mass concentration of 30% dropwise to the ferrous dihydrogen phosphate solution, stir and react at 80 °C for 3 h. After the reaction ends, filter, wash with distilled water to obtain crude iron phosphate, and calcine it in a muffle furnace at 700 °C to obtain iron phosphate, with a yield of 91.7%.

[0047] The impurity ion content and tapped density of the iron phosphates prepared in Examples 1-3 and Comparative Examples 1-3 were measured, and the test methods are as follows:

[0048] Impurity ions: Tested according to the standard of HG / T 4701-2014 "Iron Phosphate for Batteries";

[0049] Tapped density: Tested according to the standard of GB / T 5126-2020.

[0050] The test results are shown in Tables 1-2, as follows:

[0051] Table 1

[0052]

[0053] Table 2

[0054]

[0055]

[0056] From the comparison between Example 2 and Comparative Example 1, it can be seen that compared with the preparation of iron phosphate using oxalic acid and nickel phosphide as composite additives, using oxalic acid and iron tetroxide as composite additives, the prepared iron phosphate has a higher yield, lower impurity ion content and higher tapped density. This shows that this method is more efficient, has better purity, the particles are closely packed, and it is more suitable as the cathode material of lithium batteries. It shows that adding an iron-containing reaction additive during this reaction process can adjust the redox potential of the reaction system, promote the progress of the reaction, and improve the reaction efficiency.

[0057] It can be seen from the comparison between Example 2 and Comparative Example 2 that, compared with the preparation of iron phosphate when the addition amount of the iron-containing reaction aid is not within the appropriate range while the total addition amount of the composite aid is within the appropriate range, when both the iron-containing reaction aid and the total addition amount of the composite aid are within the appropriate range, the yield of the prepared iron phosphate is higher, the content of impurity ions is lower, indicating that this method is more efficient, has better purity, and can improve the tap density to a certain extent.

[0058] It can be seen from the comparison between Example 2 and Comparative Example 3 that, compared with the preparation of iron phosphate by adding a large amount of oxalic acid, when oxalic acid and magnetite are used in combination, even if the total mass of oxalic acid and magnetite is lower than the amount of oxalic acid added alone, the prepared iron phosphate still has a higher yield, a lower content of impurity ions and a higher tap density, and the addition of magnetite does not increase the content of impurity ions. Moreover, when using oxalic acid alone, the large addition of oxalic acid also increases the production cost and reduces the economic benefit, which is not suitable for large-scale industrial production.

[0059] It can be seen from the test results of Examples 1-3 that the preparation method of a low-cost iron phosphate provided by the present invention can improve the yield of iron phosphate, reduce the content of impurity ions, indicating that this method is efficient, has good purity, and the tap density of iron phosphate is high, indicating that the particles of this method are closely packed, and it is more suitable as the cathode material of lithium batteries. Using a mixture of an iron-containing reaction aid and a reducing agent as a composite aid can adjust the redox potential of the reaction system, promote the reaction, and greatly reduce the cost and increase the benefit, which is suitable for large-scale production.

[0060] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing low-cost iron phosphate, characterized in that: The following steps are involved: (1) Weighing ferroferric oxide and a phosphorus source compound, adding them to distilled water, stirring continuously and heating to 40-90° C., then adding a composite auxiliary agent, continuing to stir and react for 20-40 minutes, and after the reaction is completed, post-processing is performed to obtain a ferrous dihydrogen phosphate solution; (2) adding an oxidant to the ferrous dihydrogen phosphate solution, stirring and heating to 40-90° C., reacting for 1-3 hours, and after the reaction is completed, post-processing to obtain a crude ferric phosphate, and then calcining at 450-750° C. to obtain ferric phosphate; The composite auxiliary agent is a mixture of an iron-containing reaction auxiliary agent and a reducing agent.

2. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The reducing agent is at least one of oxalic acid, ascorbic acid, maltose, glucose, sodium bisulfite, sodium sulfite, phosphorous acid and its salts, hypophosphorous acid and its salts, and hydrazine hydrate.

3. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The reducing agent is at least one of oxalic acid, ascorbic acid and glucose.

4. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The molar amount of the iron-containing reaction aid added in step (1) is 10-50% of the molar amount of ferrosoferric oxide.

5. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The total molar amount of the composite auxiliary agent added in step (1) is 0.5-2 times the molar amount of ferrosoferric oxide.

6. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: In the step (1), the phosphorus source compound is at least one of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

7. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The amount of the phosphorus source compound added in step (1) is 2-3 times the molar amount of iron in ferroferric oxide.

8. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: The oxidant in step (2) is at least one of hydrogen peroxide, ozone and oxygen.

9. The method for preparing low-cost ferric phosphate according to claim 1, characterized in that: In the step (2), the oxidant is a hydrogen peroxide solution with a mass concentration of 20-50%.

10. Use of low-cost iron phosphate prepared by the method for preparing low-cost iron phosphate according to any one of claims 1 to 9 in positive electrode materials for lithium batteries.

Images