Iron phosphate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of inorganic new materials, and provides iron phosphate and a preparation method and application thereof.The preparation method of the iron phosphate comprises the following steps that ferroferric oxide and a phosphorus source compound are added into distilled water, a compound additive is added after the temperature is increased, the mixture is stirred to react, and a ferrous dihydrogen phosphate solution is obtained; the compound additive is a mixture of an iron-containing reaction additive and a reducing agent, the addition amount of the compound additive is 0.5-2 times of the molar weight of the ferroferric oxide, and the addition amount of the iron-containing reaction additive is 10-50% of the molar weight of the ferroferric oxide; adding an oxidizing agent into the ferrous dihydrogen phosphate solution, stirring, heating and reacting to obtain an iron phosphate crude product; and roasting the iron phosphate crude product at 450-750 DEG C 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

[0001] This invention is a divisional application based on the application filed on March 13, 2025, with application number 202510298543.4 and entitled "A method for preparing low-cost iron phosphate and its application". Technical Field

[0002] This invention belongs to the field of inorganic new materials technology, and particularly relates to iron phosphate, its preparation method and application. Background Technology

[0003] Iron phosphate (FePO4) plays a crucial role in the field of lithium-ion batteries as a key precursor for lithium iron phosphate (LiFePO4) cathode materials. 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. Due to its stable structure, good cycle performance and safety, iron phosphate has become an ideal choice for the preparation of lithium iron phosphate.

[0004] The main methods for preparing iron phosphate include the following: 1. Ferrous sulfate method: Iron phosphate is produced by reacting ferrous sulfate with phosphoric acid. The advantage of this method is that the raw materials are readily available and the cost is low. However, the disadvantage is that the introduction of sulfate ions may lead to low product purity and generate a large amount of sulfate-containing wastewater, which puts 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 high. 3. Iron oxide red method: Iron phosphate is produced by reacting iron oxide with phosphoric acid. This method is suitable for large-scale production, but the product purity and performance are greatly affected by the raw materials. The tap density of the iron phosphate produced is low, which is not suitable for the positive electrode material of lithium batteries.

[0005] In view of the problems existing in the prior art, how to provide a method for preparing ferric phosphate with low production cost, high product purity, high yield and high tap density is the problem that this invention urgently needs to solve. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing iron phosphate to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing ferric phosphate, comprising the following steps: (1) Add iron(III) oxide and phosphorus source compound to distilled water, heat up and add composite auxiliaries, stir to react and obtain ferrous dihydrogen phosphate solution; the composite auxiliaries are a mixture of iron-containing reaction auxiliaries and reducing agents, the amount of the composite auxiliaries added is 0.5-2 times the molar amount of iron(III) oxide, and the amount of the iron-containing reaction auxiliaries added is 10-50% of the molar amount of iron(III) oxide; (2) Add an oxidant to the ferrous dihydrogen phosphate solution, stir and heat to react, and obtain crude ferric phosphate; (3) The crude ferric phosphate is roasted at 450-750℃ to obtain ferric phosphate.

[0008] Preferably, the amount of phosphorus source compound added is 2-3 times the molar amount of iron in iron(III) oxide.

[0009] Preferably, the phosphorus source compound is at least one selected from phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0010] More preferably, the phosphorus source compound is phosphoric acid.

[0011] Preferably, in step (1), the composite additive is added after the temperature is raised to 40-90℃, and the stirring reaction time is 20-40℃.

[0012] Preferably, the iron-containing reaction aid is at least one of iron oxide, ferrous oxide, and iron(III) oxide.

[0013] Preferably, the reducing agent is at least one selected from oxalic acid, ascorbic acid, maltose, glucose, sodium bisulfite, sodium sulfite, phosphorous acid and its salts, hypophosphorous acid and its salts, and hydrazine hydrate.

[0014] More preferably, the reducing agent is at least one of oxalic acid, ascorbic acid, and glucose.

[0015] Preferably, the stirring and heating reaction in step (2) is carried out by stirring and heating to 40-90°C and then reacting for 1-3 hours.

[0016] Preferably, the oxidant is at least one of hydrogen peroxide, ozone, and oxygen.

[0017] Preferably, the oxidant is a hydrogen peroxide solution with a mass concentration of 20-50%.

[0018] Preferably, the oxidant is a hydrogen peroxide solution with a mass concentration of 30%.

[0019] The present invention also provides an iron phosphate prepared by the method described in any one of the above-mentioned methods.

[0020] The present invention also provides an application of iron phosphate prepared by any of the above methods in lithium battery cathode materials.

[0021] Compared with the prior art, the beneficial effects of the present invention are: The present invention provides a method for preparing ferric phosphate with high yield, low impurity ion content, and high tap density. Furthermore, the method uses a mixture of iron-containing reaction aids and reducing agents as a composite aid, which can greatly reduce costs and increase profits, making it suitable for large-scale production. Attached Figure Description

[0022] Figure 1 The XRD pattern of the iron phosphate prepared in Example 2; Figure 2 The image shows the SEM image of the iron phosphate prepared in Example 2. Detailed Implementation

[0023] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0024] In the following examples, the monomers and related reagents used were all commercially available. Ferrous oxide, ferric oxide, and ferric oxide were purchased from Shandong Luyin New Material Technology Co., Ltd., ascorbic acid was purchased from Xi'an Lavia Biotechnology Co., Ltd., and glucose was purchased from Henan Fangao Environmental Protection Materials Co., Ltd.

[0025] Example 1 This embodiment provides a method for preparing ferric phosphate, including the following steps: (1) Weigh 23.2g of iron(II,III) oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 18.0g of glucose and 0.8g of ferrous oxide, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 97.9%.

[0026] Example 2 This embodiment provides a method for preparing ferric phosphate, including the following steps: (1) Weigh 23.2g of iron(III) oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 4.5g of oxalic acid and 4.6g of iron(III) oxide, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 99.2%.

[0027] Example 3 This embodiment provides a method for preparing ferric phosphate, including the following steps: (1) Weigh 23.2g of ferric oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 8.8g of ascorbic acid and 3.2g of ferric oxide, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 98.7%.

[0028] Comparative Example 1 This comparative example provides a method for preparing iron phosphate, including the following steps: (1) Weigh 23.2g of iron(III) oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 4.5g of oxalic acid and 0.7g of hydrochloric acid, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 80.8%.

[0029] Comparative Example 2 This comparative example provides a method for preparing iron phosphate, including the following steps: (1) Weigh 23.2g of iron(III) oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 4.5g of oxalic acid and 6.9g of iron(III) oxide, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 85.2%.

[0030] Comparative Example 3 This comparative example provides a method for preparing iron phosphate, including the following steps: (1) Weigh 23.2g of iron(III) oxide and 78.4g of phosphoric acid, add them to 200mL of distilled water, stir continuously and heat to 65℃, then add 18g of oxalic acid, continue stirring and react for 30min, the reaction is finished, filter, and obtain ferrous dihydrogen phosphate solution. (2) Add 35 mL of 30% hydrogen peroxide solution to the ferrous dihydrogen phosphate solution, stir the reaction at 80 °C for 3 h, filter the solution, wash with distilled water to obtain crude ferric phosphate, and calcine it in a muffle furnace at 700 °C to obtain ferric phosphate with a yield of 91.7%.

[0031] The impurity ion content and tap density of the ferric phosphates prepared in Examples 1-3 and Comparative Examples 1-3 were determined using the following methods: Impurity ions: Tested according to HG / T4701-2014 "Iron Phosphate for Batteries" standard; Tap density: Tested according to GB / T 5126-2020 standard.

[0032] The test results are shown in Table 1-2, as follows: Table 1

[0033] Table 2

[0034] The comparison between Example 2 and Comparative Example 1 shows that, compared with the preparation of iron phosphate using oxalic acid and nickel phosphide as composite additives, the preparation of iron phosphate using oxalic acid and iron(III) oxide as composite additives has a higher yield, lower impurity ion content, and higher tap density. This indicates that the method is more efficient, has better purity, and produces denser particle packing, making it more suitable as a cathode material for lithium batteries. This demonstrates that adding iron-containing reaction additives during the reaction process can adjust the redox potential of the reaction system, promote the reaction, and improve the reaction efficiency.

[0035] The comparison between Example 2 and Comparative Example 2 shows that, compared to the method where the amount of iron-containing reaction aid is not within a suitable range, the method where the total amount of composite aid is within a suitable range results in a higher yield and lower impurity ion content when iron-containing reaction aid is used and the total amount of composite aid is within a suitable range. This indicates that the method is more efficient, has better purity, and can improve the tap density to a certain extent.

[0036] The comparison between Example 2 and Comparative Example 3 shows that, compared to adding a large amount of oxalic acid to prepare ferric phosphate, when oxalic acid and iron oxide are used together, even if the total mass of oxalic acid and iron oxide is lower than the amount of oxalic acid added alone, the resulting ferric phosphate still has a higher yield, lower impurity ion content, and higher tap density. Moreover, the addition of iron oxide does not increase the content of impurity ions. Furthermore, when oxalic acid is used alone, the large amount of oxalic acid added also increases production costs and reduces economic benefits, making it unsuitable for industrial scale-up production.

[0037] The test results of Examples 1-3 show that the low-cost iron phosphate preparation method provided by the present invention can improve the yield of iron phosphate and reduce the content of impurity ions, indicating that the method is efficient and has good purity. The high tap density of iron phosphate indicates that the particles are tightly packed, making it more suitable as a positive electrode material for lithium batteries. The composite additive, which uses a mixture of iron-containing reaction aids and reducing agents, can adjust the redox potential of the reaction system, promote the reaction, and greatly reduce costs and increase profits, making it suitable for large-scale production.

[0038] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ferric phosphate, characterized in that, Includes the following steps: (1) Add iron(III) oxide and phosphorus source compound to distilled water, heat up and add composite auxiliaries, stir to react and obtain ferrous dihydrogen phosphate solution; the composite auxiliaries are a mixture of iron-containing reaction auxiliaries and reducing agents, the amount of the composite auxiliaries added is 0.5-2 times the molar amount of iron(III) oxide, and the amount of the iron-containing reaction auxiliaries added is 10-50% of the molar amount of iron(III) oxide; (2) Add an oxidant to the ferrous dihydrogen phosphate solution, stir and heat to react, and obtain crude ferric phosphate; (3) The crude ferric phosphate is roasted at 450-750℃ to obtain ferric phosphate.

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

3. The method for preparing ferric phosphate according to claim 1, characterized in that, The phosphorus source compound is at least one of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

4. The method for preparing ferric phosphate according to claim 1, characterized in that, In step (1), after heating to 40-90℃, add the composite additive and stir the reaction for 20-40℃.

5. The method for preparing ferric phosphate according to claim 1, characterized in that, The iron-containing reaction aid is at least one of iron oxide, ferrous oxide, and iron(III) oxide. 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.

6. The method for preparing ferric phosphate according to claim 1, characterized in that, The stirring and heating reaction described in step (2) is to stir and heat to 40-90℃ and then react for 1-3 hours.

7. The method for preparing ferric phosphate according to claim 1, characterized in that, The oxidant is at least one of hydrogen peroxide, ozone, and oxygen.

8. The method for preparing ferric phosphate according to claim 1, characterized in that, The oxidant is a hydrogen peroxide solution with a mass concentration of 20-50%.

9. Ferric phosphate prepared by the method of any one of claims 1-8.

10. The application of iron phosphate prepared by the method according to any one of claims 1-8 in the cathode material of lithium battery.

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