Preparation method and application of battery-grade iron phosphate

Abstract

The invention discloses a preparation method and application of battery-grade iron phosphate. The method comprises the following steps: S1, obtaining a ferric trichloride solution; s2, obtaining a phosphoric acid solution; s3, mixing the ferric trichloride solution and the phosphoric acid solution to form a mixed solution; s4, heating the mixed solution, and carrying out a reaction I to obtain an iron phosphate dihydrate precipitate; the reaction temperature of the reaction I is 70-110 DEG C, and the reaction time is 10-20 hours; s5, separating, washing and drying the iron phosphate dihydrate precipitate to obtain iron phosphate dihydrate; and S6, calcining the iron phosphate dihydrate to obtain the battery-grade iron phosphate. The method disclosed by the invention is simple to operate, no other impurity ions are introduced, and high-purity battery-grade iron phosphate can be obtained; the recycled hydrochloric acid can be directly used as a chemical raw material, so that the cost can be reduced, the economic benefit can be improved and the recycling of resources is facilitated while the performance requirements of the lithium ion battery positive electrode material are met.

Description

Technical Field

[0001] The invention belongs to the field of chemical technology, and in particular relates to a preparation method and application of battery-grade iron phosphate Background Art

[0002] Ferric chloride is a major chemical raw material. Every year, the electronics industry and ore smelting produce a large amount of ferric chloride. Ferric chloride is converted into battery-grade iron phosphate. Generally, double decomposition reaction is used to directly add soluble phosphates, such as sodium phosphate, sodium monohydrogen phosphate, potassium phosphate and ammonium phosphate, to the ferric chloride solution. The product after the reaction is not only the hydrate of iron phosphate, but also the corresponding chloride salts, such as sodium chloride, potassium chloride and ammonium chloride, etc. The added value of the above-mentioned chloride salts is low, and it is difficult to reuse them. They are often directly discharged, which not only causes waste, but also causes pollution, as shown in patent CN202011039726. If ferric chloride is directly reacted with phosphoric acid, since the product is hydrochloric acid, which is more acidic than phosphoric acid, under general conditions, the reaction cannot be carried out. However, if the reaction can be carried out, not only iron phosphate can be obtained, but also hydrochloric acid with higher added value can be obtained, and there is no other metal impurities in the iron phosphate, and the purity is higher.

[0003] Therefore, how to utilize the material properties of ferric chloride and ferric phosphate to prepare battery-grade iron phosphate has become an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present invention provides a method for preparing battery-grade iron phosphate, the main purpose of which is to solve the technical problem that iron phosphate cannot be prepared using phosphoric acid and ferric chloride.

[0005] In one aspect, the present invention provides a method for preparing battery-grade iron phosphate, comprising the following steps:

[0006] S1: Obtain ferric chloride solution;

[0007] S2: obtaining a phosphoric acid solution;

[0008] S3: The ferric chloride solution and the phosphoric acid solution are mixed to form a mixed solution;

[0009] S4: The mixed solution is heated and reacted I to obtain a ferric phosphate dihydrate precipitate;

[0010] The reaction temperature of the reaction I is 70-110° C., and the reaction time is 10-20 h;

[0011] S5: The ferric phosphate dihydrate precipitate in step S4 is separated, washed, and dried to obtain ferric phosphate dihydrate;

[0012] S6: After calcining the dihydrated iron phosphate in step S5, battery-grade iron phosphate is obtained.

[0013] The present invention is based on the problems existing in the prior art. Through a large number of scientific research practices, it is found that although hydrochloric acid is more acidic than phosphoric acid, it is also a volatile acid. Therefore, as long as the reaction temperature is reasonably controlled and a small amount of hydrochloric acid generated in the solution is transferred away in time, the entire reaction can be promoted. The chemical reaction formula is: FeCl 3 +H 3 PO 4 →FePO 4 ↓+3HCl↑, this reaction does not violate the basic principle of double decomposition reaction, and the specific chemical reaction process is as follows. The solubility product and weak acid dissociation constant in the chemical reaction equation were calculated, and it was found that when the pH in the solution>2.2, hydrated ferric phosphate would be generated in theory. In this way, as long as the hydrogen chloride in the system is removed in time, the continuous generation of hydrated ferric phosphate can be guaranteed. The present invention adopts a heating method, which can utilize the gasification of water to take away the hydrogen chloride and promote the reaction. This method can effectively avoid other impurity ions (such as Na + , K + Mg 2+ At the same time, hydrochloric acid with higher added value can be obtained.

[0014]

[0015] Therefore, the present invention uses ferric chloride solution as an iron source and battery-grade phosphoric acid as a phosphorus source to prepare battery-grade iron phosphate, and the process comprises: configuring ferric chloride and phosphoric acid into a mixed solution with a certain proportion and concentration, heating the mixed solution, and reasonably controlling the reaction temperature to volatilize the solvent, wherein the volatilized solvent is hydrochloric acid, and the hydrochloric acid is recovered; and a precipitate is obtained at the same time, and the precipitate is washed, dried, and calcined to obtain battery-grade iron phosphate.

[0016] Optionally, in step S4, the reaction temperature of reaction I is 80-100° C., and the reaction time is 12-15 h.

[0017] Optionally, in step S4, the reaction temperature of the reaction I is selected from any value of 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, or any range between two of them.

[0018] Optionally, in step S3, the molar ratio of the P element to the Fe element in the mixed solution is 1-2.

[0019] Optionally, in step S3, the molar ratio of the P element to the Fe element in the mixed solution is 1.2 to 1.8.

[0020] Optionally, in step S3, the molar ratio of the P element to the Fe element in the mixed solution is selected from any value of 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or any range between two of them.

[0021] Optionally, in step S1, the molar concentration of the ferric chloride solution is 0.1 to 5 mol / L.

[0022] Optionally, in step S1, the molar concentration of the ferric chloride solution is 0.2-1.0 mol / L.

[0023] Optionally, in step S1, the molar concentration of the ferric chloride solution is selected from any value in 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, or a range between any two of them.

[0024] Optionally, in step S2, the mass concentration of the phosphoric acid solution is 10wt% to 80wt%.

[0025] Optionally, in step S2, the mass concentration of the phosphoric acid solution is 20wt% to 50wt%.

[0026] Optionally, in step S2, the mass concentration of the phosphoric acid solution is selected from any value of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or any range between two of them.

[0027] Optionally, in step S4, the mixed solution is heated and reacted to obtain a dihydrated iron phosphate precipitate and volatile hydrochloric acid, and the volatile hydrochloric acid is collected;

[0028] In step S4, during the heating and reaction I, water is added to the reaction I system to adjust the volume of the reaction solution to be the same from the beginning of the reaction to the end of the reaction.

[0029] The preparation method of the present invention is accompanied by the volatilization of hydrochloric acid during the heating process, so the hydrochloric acid needs to be collected; in addition, in order to ensure that the volume of the mixed solution in the system remains unchanged, water (preferably deionized water) needs to be continuously added so that the reaction process can be carried out in an appropriate amount of aqueous solution system.

[0030] Optionally, in step S6, the calcination temperature is 400-700° C., and the calcination time is 1-10 h.

[0031] Optionally, in step S6, the calcination temperature is 450-600° C., and the calcination time is 2-8 hours.

[0032] Optionally, in step S6, the calcination temperature is selected from any value of 400°C, 420°C, 450°C, 470°C, 500°C, 520°C, 550°C, 570°C, 600°C, 620°C, 650°C, 670°C, 700°C or any range between two of them.

[0033] Optionally, in step S2, the phosphoric acid solution is obtained by extracting, purifying and diluting phosphoric acid in sequence to obtain the phosphoric acid solution.

[0034] Optionally, in step S2, the extraction agent used for the extraction is a kerosene solution containing tributyl phosphate.

[0035] In a second aspect, the present invention provides the use of battery-grade iron phosphate prepared by the above-mentioned method for preparing battery-grade iron phosphate in battery materials.

[0036] In a third aspect, the present invention provides a positive electrode material for a lithium-ion battery, wherein the raw material of the positive electrode material is selected from the battery-grade iron phosphate prepared by the above-mentioned preparation method of the battery-grade iron phosphate.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The invention overcomes the principle that a weak acid cannot react with a strong acid in a double decomposition reaction by utilizing the volatility of hydrochloric acid; a ferric chloride solution and battery-grade phosphoric acid are used as raw materials, and a suitable reaction temperature is controlled so that ferric chloride and volatile hydrochloric acid are generated by reaction to prepare battery-grade iron phosphate; the method is simple to operate, and no other impurity ions are introduced, so that high-purity battery-grade iron phosphate can be obtained; meanwhile, the recovered hydrochloric acid can be directly used as a chemical raw material, and while meeting the performance requirements of a lithium-ion battery positive electrode material, the cost can be reduced, the economic benefit can be improved, and the recycling of resources is beneficial. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the chemical reaction for preparing hydrated ferric phosphate provided by the present invention;

[0040] Figure 2 The XRD pattern of the iron phosphate dihydrate provided in Example 1 of the present invention;

[0041] Figure 3 This is the XRD spectrum of the battery-grade iron phosphate provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The present application is further described below in conjunction with specific embodiments. The following are only a few embodiments of the present application, and are not intended to limit the present application in any form. Although the present application discloses the following preferred embodiments, they are not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the above disclosed technical content to make some changes or modifications are equivalent to equivalent implementation cases and are within the scope of the technical solution.

[0043] Unless otherwise specified, the raw materials in the examples of the present application were purchased from commercial sources and used directly without any special treatment.

[0044] Example 1

[0045] Prepare raw materials: prepare 0.5M ferric chloride solution; extract and purify phosphoric acid, using a kerosene solution containing tributyl phosphate as an extractant, and then dilute the purified phosphoric acid into a 50wt% phosphoric acid solution.

[0046] Reaction process: 500mL of 0.5M ferric chloride solution and 73.5g of 50wt% phosphoric acid solution are mixed, and the molar ratio of P element to Fe element is 1.5 to form a translucent mixed solution; the mixed solution is heated and stirred, and the reaction temperature is controlled to be 100°C; during the heating process, hydrochloric acid will volatilize, and the hydrochloric acid is collected. In order to ensure that the volume of the mixed solution in the reaction system remains unchanged, pure water needs to be continuously added to the reaction system; after reacting for 12 hours, a dihydrated iron phosphate precipitate is obtained; the precipitate is separated, washed and dried to obtain battery-grade dihydrated iron phosphate; the theoretical mass of dihydrated iron phosphate is calculated to be 46.7g, and the actual mass is 37.6g, with a yield of 80.5%; the phase structure is as follows Figure 2 As shown, it is shown that the intermediate product is pure phase dihydrated iron phosphate; the reaction parameters are shown in Table 1.

[0047] Calcination process: The above-mentioned dihydrated iron phosphate is calcined at a temperature of 600°C for 2 hours to obtain battery-grade iron phosphate; the physical structure is as follows Figure 3 As shown, it shows that the product is a pure phase iron phosphate structure without any impurity peaks; the purity test of battery-grade iron phosphate is shown in Table 2.

[0048] Example 2

[0049] The difference between Example 2 and Example 1 is that the raw material ratio is different, and the parameters such as reaction temperature and calcination temperature are different; the preparation steps are the same, see Table 1 for details.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is that the raw material ratio is different, and the parameters such as reaction temperature and calcination temperature are different; the preparation steps are the same, see Table 1 for details.

[0052] Example 4

[0053] The difference between Example 4 and Example 1 is that the raw material ratio is different, and the parameters such as reaction temperature and calcination temperature are different; the preparation steps are the same, see Table 1 for details.

[0054] Example 5

[0055] The difference between Example 5 and Example 1 is that the raw material ratio is different, and the parameters such as reaction temperature and calcination temperature are different; the preparation steps are the same, see Table 1 for details.

[0056] Table 1. Reaction parameters of Examples 1-5

[0057]

[0058] Table 2. Purity test of battery-grade iron phosphate in Example 1

[0059] Example 1 purity Fe / P(mol) Na(ppm) K(ppm) Battery Grade Iron Phosphate 99.8 0.987 16 8

[0060] According to Table 1, Table 2, Figure 2 and Figure 3 It can be seen that battery-grade iron phosphate can be prepared by the method of Example 1, and it is pure phase without impurities, its purity reaches about 99.8, and there are no other impurity ions.

[0061] Similarly, by adjusting the raw material ratio and reaction parameters of Examples 2 to 5, the XRD spectrum of the final product prepared is similar to the spectrum morphology of Example 1, indicating that the products prepared in Examples 2 to 5 are battery-grade iron phosphate, and are all pure phases without impurities, with a purity of about 99.0 to 99.9%, and no other impurity ions.

[0062] It can be seen from the experimental results of Examples 1 to 5 above that high-purity battery-grade iron phosphate can be prepared by the preparation method designed by the present invention.

[0063] The invention uses ferric chloride solution as an iron source and battery-grade phosphoric acid as a phosphorus source to prepare battery-grade iron phosphate. The process comprises: configuring ferric chloride and phosphoric acid into a mixed solution with a certain proportion and concentration, heating the mixed solution, controlling the reaction temperature to volatilize the solvent, the volatilized solvent is hydrochloric acid, and recovering the hydrochloric acid; and obtaining a precipitate, washing, drying and calcining the precipitate to obtain the battery-grade iron phosphate.

[0064] Specifically, the reaction temperature is controlled to be 70 to 110°C, preferably 80 to 100°C, more preferably 90 to 105°C, and further preferably 95 to 105°C.

[0065] The molar ratio of the P element to the Fe element in the mixed solution is controlled to be 1 to 2, preferably 1.2 to 1.8.

[0066] The molar concentration of the ferric chloride solution is controlled to be 0.1 to 5 mol / L, preferably 0.2 to 1.0 mol / L.

[0067] The mass concentration of the phosphoric acid solution is controlled to be 10% to 80%, preferably 20% to 50%.

[0068] The calcination temperature is controlled to be 400-700°C, preferably 450-600°C.

[0069] In the prior art, an iron source (such as ferrous sulfate, ferrous chloride, ferric chloride, ferric nitrate, ferrous nitrate, etc.) and phosphoric acid are reacted in an alkaline solution. The pH value of the reaction system needs to be adjusted to about 2.3-2.5 using an alkaline solution (such as one or more of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate). The reaction is stirred at 50-60° C. in a reactor for 1-12 hours to obtain a crude iron phosphate product. In order to remove the introduced impurity ions, a certain amount of phosphoric acid solution and the crude iron phosphate product are used again to continue to react at 140-170° C. in a pressurized reactor (closed system) for 1-12 hours to obtain a hydrated iron phosphate precipitate. The precipitate is separated, dried, and then calcined to obtain anhydrous iron phosphate.

[0070] In the above-mentioned prior art, the crude iron phosphate can be precipitated by adjusting the pH value with alkaline solution to a certain condition, and the crude product is converted into iron phosphate hydrate by pressurization and temperature increase, and finally calcined to form anhydrous iron phosphate. The iron phosphate generation process of this technology is relatively complicated, and alkaline ions are introduced, and then phosphoric acid is used to remove the alkaline ions, which increases the impurity removal process and makes the whole reaction steps complicated; the impurity removal process is reacted in a closed high-pressure and high-temperature environment, which has low safety and cannot continuously prepare products; the preparation method has high energy consumption, high cost, and complex operation, which is not conducive to actual production.

[0071] The present invention overcomes the principle that weak acid cannot react with strong acid in double decomposition reaction by utilizing the volatility of hydrochloric acid; by using ferric chloride solution and battery-grade phosphoric acid as raw materials, controlling the appropriate reaction temperature, and timely transferring a small amount of hydrochloric acid generated in the solution, the whole reaction can be promoted. The chemical reaction formula is: FeCl 3 +H 3 PO 4 →FePO 4 ↓+3HCl↑; the reaction generates ferric chloride and volatile hydrochloric acid to prepare battery-grade iron phosphate; the preparation method is carried out under normal pressure and open conditions, the operation is relatively simple and safe, no alkaline adjustment is required, other impurity ions will not be introduced, and no impurity removal process is required, and finally high-purity battery-grade iron phosphate can be prepared. The preparation method of the present invention can effectively avoid other impurity ions (such as Na + , K + Mg 2+ At the same time, it can also recover hydrochloric acid with higher added value.

[0072] The high-purity battery-grade iron phosphate prepared by the present invention can be used as a raw material in battery materials; in particular, it can be used as a positive electrode material for lithium-ion batteries.

[0073] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing battery-grade iron phosphate, characterized in that: The preparation method comprises the following steps: S1: Obtain ferric chloride solution; S2: obtaining a phosphoric acid solution; S3: The ferric chloride solution and the phosphoric acid solution are mixed to form a mixed solution; S4: The mixed solution is heated and reacted I to obtain a ferric phosphate dihydrate precipitate; The reaction temperature of the reaction I is 70-110° C., and the reaction time is 10-20 h; S5: The ferric phosphate dihydrate precipitate in step S4 is separated, washed, and dried to obtain ferric phosphate dihydrate; S6: After calcining the dihydrated iron phosphate in step S5, battery-grade iron phosphate is obtained.

2. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S4, the reaction temperature of reaction I is 80-100° C., and the reaction time is 12-15 h.

3. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S3, the molar ratio of the P element to the Fe element in the mixed solution is 1 to 2; Preferably, in step S3, the molar ratio of the P element to the Fe element in the mixed solution is 1.2 to 1.

8.

4. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S1, the molar concentration of the ferric chloride solution is 0.1 to 5 mol / L; Preferably, in step S1, the molar concentration of the ferric chloride solution is 0.2-1.0 mol / L.

5. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S2, the mass concentration of the phosphoric acid solution is 10wt% to 80wt%; Preferably, in step S2, the mass concentration of the phosphoric acid solution is 20wt% to 50wt%.

6. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S4, the mixed solution is heated and reacted to obtain a dihydrated iron phosphate precipitate and volatile hydrochloric acid, and the volatile hydrochloric acid is collected; In step S4, during the heating and reaction I, water is added to the reaction I system to adjust the volume of the reaction solution to be the same from the beginning of the reaction to the end of the reaction.

7. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S6, the calcination temperature is 400-700° C., and the calcination time is 1-10 hours; Preferably, in step S6, the calcination temperature is 450-600° C., and the calcination time is 4-6 hours.

8. The method for preparing battery-grade iron phosphate according to claim 1, characterized in that: In step S2, the phosphoric acid solution is obtained by extracting, purifying and diluting phosphoric acid in sequence to obtain the phosphoric acid solution; Preferably, in step S2, the extraction agent used for the extraction is a kerosene solution containing tributyl phosphate.

9. Use of the battery-grade iron phosphate prepared by the method for preparing the battery-grade iron phosphate according to any one of claims 1 to 8 in battery materials.

10. A positive electrode material for a lithium ion battery, characterized in that: The raw material of the positive electrode material is selected from the battery-grade iron phosphate prepared by the preparation method of the battery-grade iron phosphate according to any one of claims 1 to 8.

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