Method for preparing iron phosphate by circulating oxygen oxidation and application

Abstract

The invention provides a method for preparing iron phosphate by circulating oxygen oxidation and application, and the method comprises the following steps: (1) weighing a certain amount of ferroferric oxide powder, adding into a reaction kettle filled with deionized water, starting a stirring device, uniformly stirring, slowly adding a proper amount of phosphorus-containing solution, raising the temperature, continuously stirring and reacting for 1-2 hours, and filtering to obtain a filtrate; then adding a proper amount of a reducing agent into the reaction kettle, and continuously stirring and reacting for 1-2 hours to obtain a ferrous dihydrogen phosphate solution; (2) mounting a circulating air pump on the reaction kettle in the step (1), adjusting the reaction temperature and the stirring speed, introducing oxygen into the ferrous dihydrogen phosphate solution, and controlling the oxygen introducing speed and the reaction time, so that a mixture is generated in the reaction kettle; and (3) after the reaction in the step (2) is finished, carrying out suction filtration on the mixture in the reaction kettle to obtain an iron phosphate crude product, washing the iron phosphate crude product with deionized water, drying, and roasting in a muffle furnace at 500-700 DEG C for 2-4 hours to obtain the iron phosphate. According to the method for preparing the iron phosphate, oxygen is used for oxidation, oxygen water can be recycled, the cost is reduced, the yield of the iron phosphate is increased, the content of impurity ions in the iron phosphate is reduced, and the method is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing iron phosphate, and particularly relates to a method and application for preparing iron phosphate by cyclic oxygen oxidation. 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 cycling performance, and safety.

[0003] In the oxidation process of preparing iron phosphate, there are many drawbacks in the selection and use of oxidants. When using hydrogen peroxide as an oxidant, although it has strong oxidation ability and can react under relatively mild conditions, hydrogen peroxide has poor stability and is prone to thermal decomposition, resulting in low actual utilization rate of the oxidant. In addition, hydrogen peroxide is relatively expensive, and large-scale use will significantly increase production costs, which is not conducive to cost control in industrial production. When using oxygen as an oxidant, although it has the advantages of low cost and wide source, the solubility of oxygen in the solution is limited, which greatly limits the oxidation reaction rate. The oxidation reaction usually has extremely strict requirements on reaction conditions such as temperature, pH value, stirring speed, etc. Too high temperature may cause side reactions and generate impurity phases, affecting the purity of the iron phosphate product. In the oxidation process, impurities are easily introduced due to factors such as oxidants, catalysts, and reaction vessels. If industrial-grade oxidants or catalysts are used, they may contain a small amount of heavy metal impurities, which will be mixed into the iron phosphate product during the reaction process, seriously affecting the quality of the product. Especially for iron phosphate applied in the battery field, too high impurity content will reduce key indicators such as the charge and discharge performance and cycle life of the battery, having an adverse impact on the downstream industry.

[0004] Aiming at the problems existing in the prior art, how to provide a preparation method of iron phosphate with low production cost, high product purity, and high yield 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 and application for preparing iron phosphate by cyclic oxygen oxidation to solve the problems of high production cost, low product purity, and low yield in the prior art.

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

[0007] The present invention provides a method for preparing iron phosphate by cyclic oxygen oxidation, and the preparation method includes the following steps:

[0008] (1) Weigh a certain amount of ferric ferrocyanide powder, add it to a reaction kettle filled with deionized water, turn on the stirring device, stir evenly, slowly add an appropriate amount of phosphorus-containing solution, and at the same time raise the temperature. Continuously stir and react for 1 - 2 hours, then add an appropriate amount of reducing agent to the reaction kettle and continue to stir and react for 1 - 2 hours to obtain ferrous dihydrogen phosphate solution;

[0009] (2) Install a circulating air pump on the reaction kettle in step (1), adjust the reaction temperature and stirring speed, introduce oxygen into the ferrous dihydrogen phosphate solution, control the rate of oxygen introduction and the reaction time, and make a mixture form in the reaction kettle;

[0010] (3) After the reaction in step (2) is completed, filter the mixture in the reaction kettle to obtain crude iron phosphate. Wash the crude iron phosphate with deionized water, dry it, and then place it in a muffle furnace at 500 - 700 °C for roasting for 2 - 4 hours to obtain iron phosphate.

[0011] Further, the mass concentration of the phosphorus-containing solution in step (1) is 80 - 90%.

[0012] Further, the stirring speed in step (1) is 300 - 500 r / min, and the reaction temperature is 80 - 90 °C.

[0013] Further, the phosphorus-containing solution in step (1) is a mixture of one of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and water.

[0014] Further, the reducing agent in step (1) is one or a mixture of oxalic acid, ascorbic acid, maltose, glucose, sodium sulfite, etc.

[0015] Further, the volume concentration of oxygen in the reaction kettle in step (2) is 25 - 40%.

[0016] Further, the stirring speed in step (2) is 300 - 500 r / min.

[0017] Further, the oxygen flow rate in step (2) is 0.5 - 1 L / min.

[0018] Further, the reaction temperature in step (2) is 40 - 60 °C and the reaction time is 3 - 5 hours.

[0019] Further, the application of the iron phosphate prepared by a method of cyclic oxygen oxidation for preparing iron phosphate is used as a raw material for large-scale production of the cathode material of lithium batteries.

[0020] Beneficial effects:

[0021] A method for preparing iron phosphate by cyclic oxygen oxidation provided by the present invention uses oxygen oxidation. The unreacted oxygen in the upper part of the reaction kettle is recovered by a circulating gas pump and re-introduced into the reaction kettle for recycling. During the circulation process, the oxygen content in the circulating gas can be regularly detected, and the oxygen supplement amount can be adjusted according to the content to maintain the oxygen concentration required for the reaction. The oxygen water can be recycled, reducing the cost, increasing the yield of iron phosphate, and reducing the content of impurity ions in iron phosphate, which is suitable for large-scale production. Specific Embodiments

[0022] The following will illustrate the present invention in conjunction with specific implementation embodiments. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, and not used to limit 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.

[0023] Unless otherwise specified, the chemical reagents used in the present invention are all ordinary commercially available analytical pure.

[0024] Preparation of a phosphorus-containing solution with a mass fraction of 85%: Weigh 85 g of phosphoric acid and 15 g of water, and then stir and dissolve to obtain.

[0025] Preparation of a phosphorus-containing solution with a mass fraction of 80%: Weigh 80 g of phosphoric acid and 20 g of water, and then stir and dissolve to obtain.

[0026] Preparation of a phosphorus-containing solution with a mass fraction of 90%: Weigh 90 g of phosphoric acid and 10 g of water, and then stir and dissolve to obtain.

[0027] Example 1:

[0028] (1) Weigh 11 g of ferric oxide powder, add it to a reaction kettle containing 500 mL of deionized water, turn on the stirring device, stir evenly, slowly add 62 g of a phosphorus-containing solution with a mass fraction of 85%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 6 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain a ferrous dihydrogen phosphate solution;

[0029] (2) Install a vortex gas pump on the reaction kettle in step (1), adjust the temperature in the reaction kettle to 50 °C, start the vortex gas pump, turn on the stirring, the stirring speed is 300 r / min, introduce oxygen into the ferrous dihydrogen phosphate solution at a speed of 1 L / min, control the volume concentration of oxygen to be 30%, and react for 4 hours to form a mixture in the reaction kettle;

[0030] (3) After the reaction in step (2) is completed, the mixture in the reaction kettle is filtered by suction to obtain crude iron phosphate. The crude iron phosphate is washed with deionized water, dried at 100 °C for 24 hours, and then calcined in a muffle furnace at 700 °C for 3 hours to obtain iron phosphate, with a yield of 83.1%.

[0031] Example 2:

[0032] (1) Weigh 11 g of ferric oxide powder and add it to a reaction kettle containing 500 mL of deionized water. Start the stirring device, stir evenly, slowly add 62 g of a phosphorus-containing solution with a mass fraction of 80%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 6 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain ferrous dihydrogen phosphate solution;

[0033] (2) Install a vortex air pump on the reaction kettle in step (1), adjust the temperature in the reaction kettle to 50 °C, start the vortex air pump, start stirring, with a stirring speed of 500 r / min, and introduce oxygen into the ferrous dihydrogen phosphate solution at a speed of 0.8 L / min, control the volume concentration of oxygen to be 40%, and react for 4 hours to form the mixture in the reaction kettle;

[0034] (3) After the reaction in step (2) is completed, the mixture in the reaction kettle is filtered by suction to obtain crude iron phosphate. The crude iron phosphate is washed with deionized water, dried at 100 °C for 24 hours, and then calcined in a muffle furnace at 500 °C for 3 hours to obtain iron phosphate, with a yield of 80.8%.

[0035] Example 3:

[0036] (1) Weigh 11 g of ferric oxide powder and add it to a reaction kettle containing 500 mL of deionized water. Start the stirring device, stir evenly, slowly add 60 g of a phosphorus-containing solution with a mass fraction of 90%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 5 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain ferrous dihydrogen phosphate solution;

[0037] (2) Install a vortex air pump on the reaction kettle in step (1), adjust the temperature in the reaction kettle to 60 °C, start the vortex air pump, start stirring, with a stirring speed of 300 r / min, and introduce oxygen into the ferrous dihydrogen phosphate solution at a speed of 0.5 L / min, control the volume concentration of oxygen to be 25%, and react for 5 hours to form the mixture in the reaction kettle;

[0038] (3) After the reaction in step (2) is completed, the mixture in the reaction kettle is filtered by suction to obtain crude iron phosphate. The crude iron phosphate is washed with deionized water, dried at 100 °C for 24 hours, and then calcined in a muffle furnace at 700 °C for 3 hours to obtain iron phosphate, with a yield of 81.4%.

[0039] Example 4:

[0040] (1) Weigh 11 g of ferric ferrooxide powder and add it to a reaction kettle filled with 500 mL of deionized water. Start the stirring device, stir evenly, slowly add 62 g of a phosphorus-containing solution with a mass fraction of 85%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 6 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain a ferrous dihydrogen phosphate solution;

[0041] (2) Install a vortex air pump on the reaction kettle in step (1), adjust the temperature in the reaction kettle to 60 °C, start the vortex air pump, start stirring, the stirring speed is 300 r / min, and introduce oxygen into the ferrous dihydrogen phosphate solution at a speed of 0.8 L / min, control the volume concentration of oxygen to be 20%, react for 4 hours, and the mixture in the reaction kettle is formed;

[0042] (3) After the reaction in step (2) is completed, filter the mixture in the reaction kettle to obtain crude iron phosphate, wash the crude iron phosphate with deionized water, dry it at 100 °C for 24 hours and then place it in a muffle furnace at 500 °C for roasting for 3 hours to obtain iron phosphate, and the yield is 76.4%.

[0043] Comparative Example 1:

[0044] (1) Weigh 11 g of ferric ferrooxide powder and add it to a reaction kettle filled with 500 mL of deionized water. Start the stirring device, stir evenly, slowly add 62 g of a phosphorus-containing solution with a mass fraction of 85%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 6 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain a ferrous dihydrogen phosphate solution;

[0045] (2) Charge 7.5 g of oxygen into the ferrous dihydrogen phosphate solution prepared in step (1), the temperature is 50 °C, and the stirring rate is 500 r / min, and react for 5 hours;

[0046] (3) After the reaction in step (2) is completed, filter, wash with distilled water to obtain crude iron phosphate, place it in a muffle furnace at 700 °C for roasting to obtain iron phosphate, and the yield is 68.8%.

[0047] Comparative Example 2:

[0048] (1) Weigh 11 g of ferric ferrooxide powder and add it to a reaction kettle filled with 500 mL of deionized water. Start the stirring device, stir evenly, slowly add 62 g of a phosphorus-containing solution with a mass fraction of 85%, while raising the temperature to 85 °C, continuously stir and react for 2 hours, then add 6 g of oxalic acid to the reaction kettle, and continue to stir and react for 2 hours to obtain a ferrous dihydrogen phosphate solution;

[0049] (2) adding 30% mass concentration of hydrogen peroxide to the ferrous dihydrogen phosphate solution prepared in step (1), wherein the molar ratio of ferrous dihydrogen phosphate to hydrogen peroxide is 1:0.5, stirring and heating to 40° C., and reacting for 5 hours;

[0050] (3) After the reaction in step (2) is completed, the mixture is filtered and washed with distilled water to obtain a crude iron phosphate, which is then calcined in a muffle furnace at 700° C. to obtain iron phosphate with a yield of 72.3%.

[0051] The impurity ion content of the iron phosphate prepared in Example 1-4 and Comparative Example 1-2 was measured by the following test method:

[0052] Impurity ions: Tested in accordance with HG / T4701-2014 "Iron phosphate for batteries" standard.

[0053] The test results are shown in Table 1, as follows:

[0054] Table 1

[0055]

[0056] It can be seen from Examples 1-3 that the ferric phosphate prepared by the present invention has a high yield, a low content of impurity ions in the ferric phosphate, controls the amount of oxygen introduced, and recycles oxygen for oxidation. The preparation method can greatly reduce costs and bring benefits when applied to scale-up industrial production; from the comparison between Example 4 and Example 1, it can be seen that when the oxygen concentration when oxygen is introduced into the ferrous dihydrogen phosphate solution is unreasonable, the impurity ion content of the prepared ferric sulfate final product is higher and the yield is lower; from the comparison between Comparative Example 1 and Example 1, it can be seen that when oxygen is introduced once as an oxidant, oxygen cannot be fully utilized, resulting in a higher impurity ion content and a lower yield in the prepared ferric sulfate final product; from the comparison between Comparative Example 2 and Example 1, it can be seen that when hydrogen peroxide is used as an oxidant, the yield of preparing ferric phosphate becomes lower and the impurity ion content becomes higher.

[0057] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing ferric phosphate by cyclic oxygen oxidation, characterized in that: The synthesis of the ferric phosphate comprises the following steps: (1) Weigh a certain amount of ferrosoferric oxide powder, add it to a reactor filled with deionized water, turn on the stirring device, stir evenly, slowly add an appropriate amount of phosphorus-containing solution, increase the temperature at the same time, continue stirring and reacting for 1-2 hours, then add an appropriate amount of reducing agent to the reactor, continue stirring and reacting for 1-2 hours, and obtain a ferrous dihydrogen phosphate solution; (2) installing a circulating air pump on the reactor of step (1), adjusting the reaction temperature and stirring speed, introducing oxygen into the ferrous dihydrogen phosphate solution, and controlling the rate of oxygen introduction and the reaction time to generate a mixture in the reactor; (3) After the reaction in step (2) is completed, the mixture in the reaction kettle is filtered to obtain a crude iron phosphate product, which is washed with deionized water, dried, and then calcined in a muffle furnace at 500-700° C. for 2-4 hours to obtain iron phosphate.

2. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: The mass concentration of the phosphorus-containing solution in step (1) is 80-90%.

3. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: The phosphorus-containing solution in step (1) is a mixture of one of phosphoric acid, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate and water.

4. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: The stirring speed in step (1) is 300-500 r / min, and the reaction temperature is 80-90°C.

5. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: In the step (1), the reducing agent is a mixture of one or more of oxalic acid, ascorbic acid, maltose, glucose and sodium sulfite.

6. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: The volume concentration of oxygen in the reactor in step (2) is 25-40%.

7. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 6, characterized in that: The stirring speed in step (2) is 300-500 r / min.

8. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: The oxygen flow rate in step (2) is 0.5-1 L / min.

9. The method for preparing ferric phosphate by cyclic oxygen oxidation according to claim 1, characterized in that: In the step (2), the reaction temperature is 40-60° C. and the reaction time is 3-5 hours.

10. Use of the iron phosphate prepared by the method for preparing iron phosphate by cyclic oxygen oxidation according to any one of claims 1 to 9, characterized in that: Raw materials for large-scale production of positive electrode materials for lithium batteries.

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