Method for producing sodium iron phosphate material and sodium iron phosphate material

Abstract

The present invention relates to a method for manufacturing a sodium iron phosphate material and a sodium iron phosphate material. Such a method includes: 1) a step of dissolving a divalent or trivalent iron source in deionized water to prepare solution A; 2) a step of dissolving a basic substance in deionized water to prepare solution B, dropping solution B into solution A, stirring until the pH of the solution reaches 4-8, and centrifuging and filtering to obtain a slurry; and 3) a step of dissolving a chloride and / or fluoride and a phosphate in deionized water to prepare solution C, dispersing the slurry obtained in step 2) in solution C, stirring for 0.5-24 h, filtering, and drying to obtain a target product. The present invention proposes a novel method for efficiently manufacturing sodium nano iron phosphate by using a two-step particle size control method under low-temperature conditions. The present invention utilizes rapid nucleation by precipitation reaction and in-situ conversion action by anion exchange to rapidly and efficiently manufacture a sodium nano iron phosphate product at room temperature.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials, and specifically, to a method for manufacturing a sodium iron phosphate material used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium, and to the sodium iron phosphate material.

Background Art

[0002] Polyoxyanion-based compounds are excellent electrode materials for alkali metal secondary batteries with excellent performance because they have excellent ion migration efficiency and good structural and thermal stability. Sodium vanadium iron phosphate, as a typical polyoxyanion-based compound, has attracted wide attention because of its stable structure and high safety. Sodium iron phosphate has a wider raw material supply source and lower cost compared to sodium vanadium phosphate, so it has great practical competitiveness. At present, the manufacturing methods of conventional sodium iron phosphate materials are mainly limited to methods such as high-temperature solid-phase synthesis method, sol-gel method, and electrochemical synthesis method. The manufacturing process often involves harsh conditions such as high vacuum, specific atmosphere, and high temperature. The operation is relatively complicated, the manufacturing cost is relatively high, and the micro particle size of the obtained sodium iron phosphate material is relatively large, usually reaching about μm. Since sodium iron phosphate has relatively low electronic conductivity, the large particle size restricts the sodium storage performance of the manufactured sodium iron phosphate material. So far, in order to solve problems such as the relatively low conductivity of polyoxyanion-based compounds such as sodium vanadium phosphate, the members of this project team have proposed the idea of nano-synthesis in Chinese patent applications (202210162593.6, 202210249477.8), and verified through research that polyoxyanion-based compounds with small particle sizes contribute to the improvement of the electron / ion migration performance of the material. It can be inferred that by performing nano-design and manufacturing of sodium iron phosphate, the electron / ion transport efficiency of the material can be improved, and sodium iron phosphate products with excellent performance can be obtained. However, so far, there has been little reported research on the technology for efficiently manufacturing nano-sodium iron phosphate.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present invention aims to provide a method for producing a sodium iron phosphate material and a sodium iron phosphate material, and proposes a novel method for efficiently producing nano-sodium iron phosphate by using a two-stage particle size control method under low-temperature conditions. Due to the characteristic of relatively small Ksp of iron hydroxide and the characteristic of relatively large reaction rate constant of the precipitation reaction, iron ions are rapidly precipitated under basic conditions to form an iron hydroxide precursor with controllable particle size. Subsequently, by utilizing the ion exchange action between anions such as PO4 3- , F - , Cl - and OH - , a nano-sodium iron phosphate material is obtained. The present invention utilizes rapid nucleation by precipitation reaction and in-situ conversion action by anion exchange to rapidly and efficiently produce a nano-sized sodium iron phosphate product at room temperature.

Means for Solving the Problems

[0004] In order to achieve the above object, the present invention adopts the following technical means. Under room temperature conditions, a nano-sodium iron phosphate material is produced by using a two-stage particle size control method, specifically a method for producing a sodium iron phosphate material including the following steps.

[0005] 1) Dissolve a divalent or trivalent iron source in deionized water to prepare solution A. The divalent or trivalent iron source is any one or more of divalent or trivalent inorganic / organic metal salts of iron such as ferrous sulfate, ferric sulfate, ferrous chloride, ferric nitrate, and ferrous oxalate. The concentration of the iron source in solution A is 0.1 to 5.0 mol / L.

[0006] 2) Dissolve the basic substance in deionized water to prepare Solution B. The basic substance is any one or more of substances whose aqueous solutions such as sodium hydroxide, potassium hydroxide, aqueous ammonia, sodium carbonate, and sodium bicarbonate exhibit basicity. The concentration of the basic substance in Solution B is 0.1 - 5.0 mol / L. Drop Solution B into Solution A at a predetermined dropping rate, continue stirring until the pH of the solution reaches 4 - 8, and perform centrifugation and filtration to obtain a slurry.

[0007] 3) Dissolve the chloride and / or fluoride and phosphate in deionized water to prepare Solution C. The chloride is any one or more of sodium chloride, potassium chloride, and ammonium chloride, the fluoride is any one or more of sodium fluoride, potassium fluoride, and ammonium fluoride, and the phosphate is any one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate. Disperse the slurry obtained in Step 2) in Solution C, continue stirring for 0.5 - 24 h, filter, and dry to obtain the target product.

[0008] The concentration ratio of the chloride and / or fluoride to the phosphate in Solution C is 0 - 1:10, and the molar concentration ratio of the divalent or trivalent iron source to the phosphate is 1:1 - 1:3.

[0009] A sodium iron phosphate material produced by the method for producing a sodium iron phosphate material, with the chemical formula Na x FeO y PO4F a Cl b (where 0 < x ≤ 3, 0 ≤ y ≤ 1, 0 ≤ a + b ≤ 1), and the microtopography is in the form of nanoparticles.

[0010] The particle size distribution is relatively concentrated. The manufacturing method according to the present invention is simple and efficient, and can achieve efficient adjustment and control of the particle size of sodium iron phosphate particles under room temperature conditions, with the average particle size concentrated in the range of 50 to 200 nm. The sodium iron phosphate material according to the present invention has good electrochemical performance and can be applied to electrode materials for alkali metal secondary batteries such as lithium, sodium, and potassium.

[0011] The feature of the present invention is to manufacture a nano sodium iron phosphate material by using a two-step particle size control method. By utilizing the characteristics that iron hydroxide has a relatively small Ksp and the precipitation reaction has a relatively large reaction rate constant, iron ions are rapidly precipitated to form iron hydroxide, achieving the purpose of controlling the particle size of the precursor. Furthermore, by using the method of anion exchange, in-situ ion exchange between anions such as PO4 3- , F - , Cl - and OH - is carried out to achieve the adjustment and control effect by polyanions. By double-controlling the particle size of the target product, a nano sodium iron phosphate product with a small particle size and a uniform distribution is obtained. Due to the fast nucleation rate of the iron hydroxide precipitation reaction, the growth of iron hydroxide crystal nuclei is limited, and the particle size of the precursor is controlled. The ion exchange process not only does not participate in the further growth of crystal nuclei, but also achieves the in-situ peeling of important components of the precursor through the in-situ conversion mechanism, promoting the further reduction of the particle size of the product. That is, through the two-step particle size control process, the rapid and efficient production of nanosized sodium iron phosphate can be achieved.

Advantages of the Invention

[0012] Compared with the prior art, the present invention has the following beneficial effects. By using a two-step particle size control method of iron precipitation under basic conditions and anion exchange, a nano sodium iron phosphate material with a small particle size and a uniform particle size distribution can be manufactured. Due to the rapid nucleation effect of the precipitation reaction, an iron hydroxide precursor is rapidly formed, and the particle size of the precursor is effectively controlled. Due to the anion exchange effect, PO43- , F - , Cl - and other anions such as OH - are converted in situ with OH, the structure (microstructure, electronic structure) and performance adjustment and control effects by polyanions are achieved, and efficient production of nano-sized sodium iron phosphate is achieved. By this production method, the particle size and uniformity of sodium iron phosphate particles are effectively adjusted and controlled, and a nano-scale distribution of the particle size of the particles is achieved. F - , Cl - and other anions contribute to the improvement of the ion / electron conductivity of the sodium iron phosphate material and improve the electrochemical performance. In addition, the precipitation reaction and the ion exchange reaction are sufficient, the reaction time is short, and both can occur even under room temperature conditions. Therefore, the production method according to the present invention can be efficiently and quickly completed under room temperature conditions, and it is easy to achieve scale-up production. This method is expected to improve the limitations of the application of sodium iron phosphate-based materials in the field of energy storage due to its technical advantages and the structural and performance advantages of the manufactured products, and may be widely applied in the research of electrode materials for alkali metal secondary batteries such as lithium, sodium, and potassium. The method of the present invention has advantages such as simple operation, high efficiency, and easy industrial scale-up, and promotes the research and application development of sodium iron phosphate materials in the field of electrochemical energy storage.

Brief Description of Drawings

[0013]

Figure 1

Figure 2

Figure 3

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Embodiments for Carrying out the Invention

[0014] Hereinafter, with reference to the examples of the present invention, the technical means in the embodiments of the present invention will be clearly and completely described. However, it is obvious that the described embodiments are merely examples and do not limit the present invention.

[0015] Example 1 1) 0.01 mol of ferrous sulfate was weighed and dissolved in 50 mL of deionized water to prepare solution A. 2) 0.1 mol of sodium hydroxide was weighed and dissolved in 50 mL of deionized water to prepare solution B. Solution B was dropped into solution A at a rate of 1 drop / second, and stirring was continued until the pH of the solution reached 5. Then, centrifugation and filtration were performed to obtain a slurry. 3) 0.01 mol of sodium fluoride and 0.03 mol of sodium dihydrogen phosphate were weighed and dissolved in 50 mL of deionized water to prepare solution C. The slurry obtained in step 2) was dispersed in solution C, and stirring was continued for 24 h. Then, filtration and drying were performed to obtain the target product.

[0016] As is clear from FIG. 1, characteristic diffraction peaks of Na3Fe(III)OPO4F appear at 11.2°, 13.2°, 18.2°, 19.5° and 23.1° of the graph, and moreover, the diffraction peaks have high intensity. This indicates that the production of sodium iron phosphate by the method of Example 1 was successful, and the purity of the obtained sodium iron phosphate is high and no impurities are generated.

[0017] As is clear from FIG. 2, the sodium iron phosphate produced in Example 1 has a nanoparticle-like microtopography, and the particle size distribution is uniform and mainly concentrated at about 150 nm.

[0018] As is clear from Fig. 3, the sodium iron phosphate produced in Example 1 contains elements such as Na, Fe, P, O, and F, and the ratio of each element is Na:Fe:P:O:F = 25:7:10:36:8, which is consistent with the stoichiometric ratio of the constituent elements in Na3Fe(III)OPO4F. This further demonstrated that the produced sodium iron phosphate sample is Na3Fe(III)OPO4F.

[0019] Example 2 1) 0.01 mol of ferrous chloride was weighed and dissolved in 50 mL of deionized water to prepare solution A. 2) 0.1 mol of sodium hydroxide was weighed and dissolved in 50 mL of deionized water to prepare solution B. Solution B was dropped into solution A at a rate of 1 drop / second, and stirring was continued until the pH of the solution reached 7. Then, centrifugation and filtration were carried out to obtain a slurry. 3) 0.01 mol of potassium chloride and 0.02 mol of disodium hydrogen phosphate were weighed and dissolved in 50 mL of deionized water to prepare solution C. The slurry obtained in step 2) was dispersed in solution C, and stirring was continued for 6 h. Then, filtration and drying were carried out to obtain the target product.

[0020] As is clear from Fig. 4, the sodium iron phosphate produced in Example 2 has a uniform particle size distribution and is mainly concentrated at about 150 nm.

[0021] As is clear from Fig. 5, the sodium iron phosphate produced in Example 2 has a relatively high specific surface area (31.8 m 2 / g).

[0022] Example 3 1) 0.01 mol of ferrous oxalate was weighed and dissolved in 50 mL of deionized water to prepare solution A. 2) 0.1 mol of sodium bicarbonate was weighed and dissolved in 50 mL of deionized water to prepare solution B. Solution B was dropped into solution A at a rate of 1 drop / second, and stirring was continued until the pH of the solution reached 6. Then, centrifugation and filtration were carried out to obtain a slurry. 3) Weighed 0.02 mol of sodium phosphate, dissolved it in 50 mL of deionized water to prepare Solution C. The slurry obtained in Step 2) was dispersed in Solution C, stirring was continued for 16 h, followed by filtration and drying to obtain the target product.

[0023] Comparative Example 1 As a control, with appropriate modifications referring to the method for producing sodium iron phosphate described in Chinese Patent Application (202210454752.X), sodium iron phosphate was produced by the solid-phase method. The specific procedure is as follows.

[0024] 1) Raw material mixing by dry ball milling method: Weighed 150.82 g of iron phosphate, 103.00 g of sodium bicarbonate, and 22.62 g of glucose, put them into the ball mill tank, and carried out raw material mixing by the dry ball milling method. The rotation speed was set at 300 rpm / min, and the mixing time by the ball mill was set at 1 h.

[0025] 2) Raw material mixing by wet ball milling method: Added 300 g of deionized water to 1) and carried out mixing by the high-energy wet ball milling method. The rotation speed of the ball mill was set at 500 rpm / min, the mixing time by the ball mill was set at 5 h, and then dried to obtain the precursor powder material.

[0026] 3) Under an Ar atmosphere, the precursor powder material was put into a tubular furnace for high-temperature calcination. Specifically, the temperature was raised to 350 °C at a rate of 2 °C / min and held for 4 h, then the temperature was raised to 700 °C at a rate of 5 °C / min and held for 12 h. After cooling, it was sieved and pulverized to obtain the sodium iron phosphate cathode material.

[0027] Table 1 is a comparison table of the discharge specific capacities of the sodium iron phosphate material produced by the method of Example 3 and the sodium iron phosphate material produced by Comparative Example 1.

[0028]

Table 1

[0029] As is clear from Table 1, under the condition of a charge-discharge current density of 50 mA / g, the specific capacity of sodium iron phosphate produced in Example 3 was 98 mAh / g, which was higher than that of the sodium iron phosphate sample produced by the method of Comparative Example 1 (91 mAh / g), and the impedances of the corresponding button cells were 160 Ω and 250 Ω, respectively. The produced nano-sized sodium iron phosphate was found to exhibit better sodium storage performance because it had a smaller impedance and higher electron / ion conductivity.

[0030] The above-described embodiments are for illustrative purposes and do not limit the technical means of the present invention. Although the present invention has been described in detail based on the above embodiments, it is possible to make changes and equivalent substitutions to the present invention, and it should be understood by those skilled in the art that any changes and some substitutions made without departing from the spirit and scope of the present invention are all included in the claims of the present invention.

Claims

1. A method for producing a sodium iron phosphate material by using a two-stage particle size control method under room temperature conditions, specifically comprising the following steps. 1) A step of dissolving a divalent or trivalent iron source in deionized water to prepare solution A. 2) A step of dissolving a basic substance in deionized water to prepare solution B, dropping solution B into solution A, continuing stirring until the pH of the solution reaches 4-8, and performing centrifugation and filtration to obtain a slurry. 3) A step of dissolving a chloride and / or fluoride and a phosphate in deionized water to prepare solution C, dispersing the slurry obtained in step 2) in solution C, continuing stirring for 0.5-24 h, filtering, and drying to obtain the target product.

2. The method for producing a sodium iron phosphate material according to claim 1, wherein the divalent or trivalent iron source is any one or more of ferrous sulfate, ferric sulfate, ferrous chloride, ferric nitrate, and ferrous oxalate.

3. The method for producing a sodium iron phosphate material according to claim 1, wherein the concentration of the iron source in solution A is 0.1-5.0 mol / L.

4. The method for producing a sodium iron phosphate material according to claim 1, wherein the basic substance is any one or more of sodium hydroxide, potassium hydroxide, aqueous ammonia, sodium carbonate, and sodium bicarbonate.

5. The method for producing a sodium iron phosphate material according to claim 1, wherein the concentration of the basic substance in solution B is 0.1-5.0 mol / L.

6. The method for producing a sodium iron phosphate material according to claim 1, wherein the chloride is any one or more of sodium chloride, potassium chloride, and ammonium chloride, the fluoride is any one or more of sodium fluoride, potassium fluoride, and ammonium fluoride, and the phosphate is any one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate.

7. In step 3) of the method for producing a sodium iron phosphate material according to claim 1, the concentration ratio of the chloride and / or fluoride to the phosphate in solution C is 0-1:10, and the molar concentration ratio of the divalent or trivalent iron source to the phosphate is 1:1-1:

3.

8. A sodium iron phosphate material produced by the method for producing a sodium iron phosphate material according to any one of claims 1 to 7, having a chemical formula of Na ｘ FeO ｙ PO ４ F ａ Cl ｂ (where 0 < x ≤ 3, 0 ≤ y ≤ 1, 0 ≤ a + b ≤ 1), and characterized in that the microtopography is in the form of nanoparticles.

9. The sodium iron phosphate material according to claim 8, characterized in that the average particle diameter of the sodium iron phosphate material is 50 to 200 nm.

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