Synthesis method of battery-grade iron phosphate

Abstract

The invention discloses a synthesis method of battery-grade iron phosphate, which comprises the following steps: (1) preparing a ferrous sulfate aqueous solution with the concentration of 0.5-2 mol / L, adjusting the pH value to 1-2.5, and adding an oxidizing agent with the equivalent weight of ferrous ions of 1.1-1.2 to oxidize; (2) preparing a phosphoric acid aqueous solution, adjusting the pH value to 3-5, and adjusting the phosphorus-iron ratio of the phosphoric acid aqueous solution to the ferrous sulfate aqueous solution to 1.07-1.1; the surfactant is polyethylene glycol and / or ethylene glycol, and the addition amount of the surfactant is 0.1-1.5% of the theoretical mass of the iron phosphate; and (3) mixing the aqueous solution obtained in the step (1) and the aqueous solution obtained in the step (2) in equal proportion, reacting at 40-60 DEG C for not less than 0.5 hour, aging, and taking a solid to obtain the battery-grade iron phosphate. The iron phosphate obtained by the preparation method disclosed by the invention is battery grade, and the tap density is greater than or equal to 1.05 g / cm < 3 > and can reach 1.31 g / cm < 3 > at most; after corresponding raw material solutions are prepared, the raw material solutions are directly mixed, products are separated, and the iron phosphate with the expected tap density can be obtained, so that the manufacturing process is greatly simplified, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing ferric phosphate, and in particular to a method for synthesizing battery-grade ferric phosphate. Background Art

[0002] LiFePO4 (LFP) is widely used as the positive electrode material for power sources of electric vehicles (EVs), hybrid electric vehicles (HEVs), energy storage power stations and spacecraft. Iron phosphate (LF) is one of the raw materials for synthesizing lithium iron phosphate positive electrode materials, and its morphology will affect the performance of lithium iron phosphate.

[0003] The commonly used method for synthesizing ferric phosphate is co-precipitation, which uses iron salts and phosphoric acid or phosphates as raw materials. Under certain reaction conditions in the solution, ferric phosphate is precipitated to produce the product. Existing studies have shown that the raw material concentration, feed rate, reaction temperature, and the pH of the reaction system all have an impact on the tap density of ferric phosphate. Among them, adjusting the pH with a mixed solution of sodium hydroxide and ammonia water and strictly controlling the reaction system pH to 2.0 can increase the tap density of ferric phosphate to 1.34g / cm. 3 , ammonia as a complexing agent to adjust the Fe 3+ concentration, adjust the system pH, and control the nucleation rate of iron phosphate (Zhang Hongtao. Research on the preparation process of spherical iron phosphate precursor [D]. Tianjin University [2025-03-21]). However, in this scheme, the phosphorus-iron molar feed ratio is 1.5:1, and the phosphoric acid consumption is large; the invention patent application with publication number CN 119612472 A discloses a high-tap iron phosphate battery precursor, which uses basic ammonium ferric phosphate filter cake as raw material, adjusts the pH and two temperature gradients in two steps, the first pH is 0.8-1.2, the reaction temperature is 40-60 ° C, and polyethylene glycol is added, the second pH is 1.8-2.0, the second temperature is the aging temperature, reduces the amount of phosphoric acid, and increases the tap density to 1.13 g / cm 3 The invention patent application with publication number CN 118723959A discloses a method for preparing battery-grade iron phosphate with a high iron-phosphorus ratio. When preparing the iron salt solution and the phosphate solution, the pH of the two solutions is lowered to <1 in advance and then raised to 1-1.4 after mixing, thereby adjusting the tap density of the generated iron phosphate to 1.02 g / cm 3 ,These two solutions reduce the amount of phosphoric acid used, but there is still room for further improvement in its tap density. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for synthesizing battery-grade iron phosphate that can improve the tap density.

[0005] Technical solution: The method for synthesizing battery-grade iron phosphate described in the present invention comprises the following steps:

[0006] (1) configuring ferrous sulfate aqueous solution with concentration of 0.5-2 mol / L, adjusting pH=1-2.5, adding 1.1-1.2 equivalent of oxidant to oxidize ferrous ion;

[0007] (2) configuring phosphoric acid aqueous solution, adjusting pH=3-5, the phosphoric acid aqueous solution and ferrous sulfate aqueous solution have a phosphorus-iron ratio of 1.07-1.1; adding surfactant, the surfactant is polyethylene glycol and / or ethylene glycol, the adding amount is 0.1-1.5% of the theoretical mass of phosphoric iron;

[0008] (3) mixing the aqueous solutions obtained in steps (1) and (2) in equal proportions, reacting at 40-60°C for not less than 0.5 hours, aging, taking the solid, obtaining battery-grade phosphoric iron.

[0009] Preferably, in step (1), the pH is adjusted to 1.5-2.0 with concentrated sulfuric acid having a mass fraction of 95-98%.

[0010] Preferably, in step (1), the oxidant is hydrogen peroxide with a mass fraction of 20-30%.

[0011] Preferably, in step (1), the ferrous sulfate aqueous solution has a concentration of 1-1.5 mol / L.

[0012] Preferably, in step (2), when the surfactant is polyethylene glycol, the adding amount is 0.1-0.6% of the theoretical mass of phosphoric iron; when the surfactant is ethylene glycol, the adding amount is 0.4-0.6% of the theoretical mass of phosphoric iron.

[0013] Preferably, in step (2), the pH is adjusted to 3.5-4.2 with a sodium hydroxide solution having a mass fraction of 20-30%. Adjusting the pH of phosphoric acid with sodium hydroxide can promote the formation of phosphoric iron, and too high or too low pH will affect the reaction.

[0014] Preferably, in step (3), the reaction is carried out at 40-60°C for 0.5-2 hours.

[0015] Preferably, in step (3), the pumping speed during mixing is 5-10 mL / min.

[0016] Preferably, in step (3), the aging step is: continuing to heat to 80-95°C, stirring for 2-5 hours.

[0017] Preferably, in step (3), it further includes drying, the drying step is: taking the solid, drying at 100-150°C for 3-5 hours.

[0018] Preferably, in step (3), it further includes calcining and crushing, the calcining step is: taking the dried product, calcining at 550-700°C for 3-6 hours.

[0019] Advantages: compared with the prior art, the present application has the following remarkable advantages: 1. improving the compaction density: the prepared iron phosphate according to the preparation method of the present application is battery grade, and the tap density is ≥1.05 g / cm 3 , and can be up to 1.31 g / cm 3 ; 2. simplifying the process: after the corresponding raw material solution is prepared, the raw material solution is directly mixed, the product is separated, the iron phosphate with the expected tap density can be obtained, and no secondary separation, resolubilization, secondary pH adjustment and other steps are needed, so the process operation is greatly simplified; 3. reducing the cost: the amount of phosphoric acid is reduced to 1.1 times or less of the amount of iron source, and the amount of surface active agent is reduced to 1.5% or less; 4. ensuring the iron-phosphorus ratio: by controlling the phosphoric acid concentration, the phosphorus-iron ratio of the two solutions is controlled, the iron-phosphorus ratio of the product is ensured to be between 0.96 and 0.97, and the performance of the lithium iron phosphate prepared from the iron phosphate obtained by the process is stable; 5. the iron source solution is the by-product ferrous sulfate of purified titanium dioxide, which saves the production cost; 6. suitable for industrial production: the iron ion concentration is controlled within a certain range, which avoids increasing the wastewater treatment cost due to the too low iron ion concentration and avoids the precipitation of crystals in the solution due to the too high iron ion concentration. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the electron microscope image of the iron phosphate obtained in the second embodiment of the present application;

[0021] Figure 2 is the electron microscope image of the iron phosphate obtained in the first comparative example of the present application. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be further described below in combination with the drawings.

[0023] The preparation method of the battery grade iron phosphate in the present embodiment comprises the following steps:

[0024] (1) using the purified ferrous sulfate, a 1 mol / L solution is prepared, the pH is controlled to be about 1.6 (which can be 1.5-2.0) by adjusting with sulfuric acid, and the ferrous ion is oxidized by adding an excess of 20% hydrogen peroxide;

[0025] (2) a 1.06 mol / L phosphoric acid solution is prepared, the pH is adjusted to be about 4.0 (which can be 3.5-4.0) by using 25% sodium hydroxide solution to obtain a phosphoric acid solution, and a surface active agent PEG is added, and the amount of the surface active agent added is 0.3% of the theoretical mass of the iron phosphate;

[0026] (3) the two solutions are slowly (pump speed 5-10 mL / min) passed into a beaker placed in a water bath at a flow rate of 1:1, the water bath temperature is 50°C, heating and stirring are performed, the pH of the reaction solution is about 1.9-2.0, and the reaction is performed for about 1 h;

[0027] (4) The water bath is heated to 90°C, and heated and stirred for about 3 hours, and aged to obtain a light pink solution, i.e. iron phosphate dihydrate;

[0028] (5) The iron phosphate dihydrate is washed with water and dried at a temperature of 120°C for about 3 hours;

[0029] (6) The dried iron phosphate dihydrate is calcined at a temperature of 600°C for about 4 hours, and then crushed to obtain iron phosphate.

[0030] Example 2 The preparation method of the battery-grade iron phosphate of this example is similar to that of Example 1, except that in step (2), the amount of the surfactant PEG added is 0.5% of the theoretical mass of the iron phosphate.

[0031] Example 3 The preparation method of the battery-grade iron phosphate of this example is similar to that of Example 1, except that in step (2), the amount of the surfactant PEG added is 0.7% of the theoretical mass of the iron phosphate.

[0032] Example 4 The preparation method of the battery-grade iron phosphate of this example is similar to that of Example 1, except that in step (2), the surfactant is ethylene glycol, and the amount of the surfactant added is 0.3% of the theoretical mass of the iron phosphate.

[0033] Example 5 The preparation method of the battery-grade iron phosphate of this example is similar to that of Example 1, except that in step (2), the surfactant is ethylene glycol, and the amount of the surfactant added is 0.5% of the theoretical mass of the iron phosphate.

[0034] Example 6 The preparation method of the battery-grade iron phosphate of this example is similar to that of Example 1, except that in step (2), the surfactant is ethylene glycol, and the amount of the surfactant added is 0.7% of the theoretical mass of the iron phosphate.

[0035] Comparative Example 1 The preparation method of the iron phosphate of this comparative example is similar to that of Example 1, except that in step (2), no surfactant PEG is added.

[0036] Comparative Example 2 The preparation method of the iron phosphate of this comparative example is similar to that of Example 1, except that in step (2), the surfactant is SDS (sodium dodecyl sulfate), and the amount of the surfactant added is 0.3% of the theoretical mass of the iron phosphate.

[0037] Performance detection: The high-pressure iron phosphate prepared in Examples 1-6 and Comparative Examples 1-2 is subjected to performance testing, and the detection results are shown in Table 1.

[0038] Table 1:

[0039]

[0040]

[0041] From Table 1, Figure 1 and Figure 2 It can be seen that the liquid phase oxidation method, combined with appropriate and suitable amount of surfactant, one-pot reaction, can control the morphology and size of the primary particles of iron phosphate, and the crystal structure of the prepared iron phosphate is more compact. The compaction density of the prepared iron phosphate is greater than that prepared by the conventional physical and mechanical method.

Claims

1. A method for synthesizing battery-grade iron phosphate, characterized in that: The following steps are involved: (1) preparing a 0.5-2 mol / L ferrous sulfate aqueous solution, adjusting the pH to 1-2.5, and adding an oxidant with 1.1-1.2 equivalents of ferrous ions for oxidation; (2) preparing a phosphoric acid aqueous solution, adjusting the pH to 3-5, and the phosphorus-iron ratio of the phosphoric acid aqueous solution to the ferrous sulfate aqueous solution to be 1.07-1.1; adding a surfactant, wherein the surfactant is polyethylene glycol and / or ethylene glycol, and the added amount is 0.1-1.5% of the theoretical mass of the iron phosphate; (3) mixing the aqueous solutions obtained in step (1) and step (2) in equal proportions, reacting at 40-60° C. for not less than 0.5 hour, aging, and collecting the solid to obtain battery-grade iron phosphate.

2. The method for synthesizing battery-grade iron phosphate according to claim 1, wherein In step (1), concentrated sulfuric acid is used to adjust the pH to 1.5-2.0, wherein the mass fraction of the concentrated sulfuric acid is 95-98%.

3. The method for synthesizing battery-grade iron phosphate according to claim 1, wherein In step (1), the oxidant is hydrogen peroxide with a mass fraction of 20-30%.

4. The method for synthesizing battery-grade iron phosphate according to claim 1, wherein In step (2), when the surfactant is polyethylene glycol, the added amount is 0.1-0.6% of the theoretical mass of the iron phosphate; when the surfactant is ethylene glycol, the added amount is 0.4-0.6% of the theoretical mass of the iron phosphate.

5. The method for synthesizing battery-grade iron phosphate according to claim 1 or 2, characterized in that: In step (2), the pH is adjusted to 3.5-4.2 using a sodium hydroxide solution having a mass fraction of 20-30%.

6. The method for synthesizing battery-grade ferric phosphate according to claim 5, wherein: In step (3), during mixing, the pumping speed is 5 to 10 mL / min.

7. The method for synthesizing battery-grade ferric phosphate according to claim 1, wherein: In step (3), the reaction is carried out at 40-60°C for 0.5-2 hours.

8. The method for synthesizing battery-grade ferric phosphate according to claim 1, wherein: In step (3), the aging step is: continue to heat to 80-95°C and stir for 2-5 hours.

9. The method for synthesizing battery-grade ferric phosphate according to claim 1, wherein: In step (3), drying is also included. The drying step is: taking the solid, and drying it at 100-150° C. for 3-5 hours.

10. The method for synthesizing battery-grade iron phosphate according to claim 8, characterized in that: In step (3), calcination and crushing are also included. The calcination step is: taking the dried product, and calcining it at 550-700° C. for 3-6 hours.

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