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 more particularly to a method for producing a sodium iron phosphate material used as an electrode material for secondary batteries of alkali metals such as lithium, sodium, and potassium, and the sodium iron phosphate material. [Background technology]

[0002] Polyanionic compounds are excellent electrode materials for alkali metal secondary batteries due to their excellent ion transfer efficiency and favorable structural and thermal stability. Vanadium-iron sodium phosphate, a typical polyanionic compound, has attracted widespread attention due to its structural stability and safety. Sodium iron phosphate has a broader raw material supply source and lower cost than sodium vanadium phosphate, making it a practically competitive alternative. Currently, conventional methods for producing sodium iron phosphate materials are limited to high-temperature solid-state synthesis, sol-gel synthesis, and electrochemical synthesis. These processes often involve harsh conditions, such as high vacuum, specific atmospheres, and high temperatures, resulting in complex operations and high production costs. The resulting sodium iron phosphate material has a relatively large microparticle size, typically on the order of micrometers. Because sodium iron phosphate has relatively low electronic conductivity, the large particle size limits the sodium storage performance of the resulting sodium iron phosphate material. To address the relatively low conductivity of polyanionic compounds such as sodium vanadium phosphate, members of this project team proposed the idea of ​​nanosynthesis in Chinese patent applications (202210162593.6, 202210249477.8). Research demonstrated that small-particle polyanionic compounds contribute to improved electron / ion transport performance in materials. It is anticipated that the design and production of nanosized sodium iron phosphate will improve the electron / ion transport efficiency of materials and result in superior-performance sodium iron phosphate products. However, to date, little research has been reported on the efficient production of nanosized sodium iron phosphate. Summary of the Invention [Problem to be solved by the invention]

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

[0004] In order to achieve the above object, the present invention employs the following technical means. The nano-sodium iron phosphate material is produced by a two-stage particle size control method under room temperature conditions, specifically comprising the following steps:

[0005] 1) A divalent or trivalent iron source is dissolved in deionized water to prepare solution A. The divalent or trivalent iron source is one or more of divalent or trivalent inorganic or 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 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 chloride and / or fluoride to phosphate in Solution C is 0 - 1:10, and the molar concentration ratio of the divalent or trivalent iron source to 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 of 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 being concentrated in the range of 50 to 200 nm. The sodium iron phosphate material of the present invention has good electrochemical performance and can be used as an electrode material for alkaline metal secondary batteries such as lithium, sodium, and potassium.

[0011] The present invention is characterized by the use of a two-stage particle size control method to produce nano-sodium iron phosphate material. By utilizing the characteristics of iron hydroxide, which has a relatively small Ksp, and the relatively large reaction rate constant of the precipitation reaction, iron ions are rapidly precipitated to form iron hydroxide, thereby achieving the goal of controlling the particle size of the precursor. Furthermore, an anion exchange method is used to convert PO4 3- , F - , Cl - and anions such as OH - In-situ ion exchange with cations and cations achieves the adjustment and control effect of polyanions. Dual control of the particle size of the target product results in a nano-sized sodium iron phosphate product with small particle sizes and uniform distribution. The rapid nucleation rate of the iron hydroxide precipitation reaction limits the growth of iron hydroxide crystal nuclei, controlling the particle size of the precursor. The ion exchange process not only does not contribute to further growth of the crystal nuclei, but also achieves in-situ exfoliation of key components of the precursor through an in-situ conversion mechanism, further reducing the particle size of the product. In other words, the two-stage particle size control process enables the rapid and efficient production of nano-sized sodium iron phosphate. [Effects of the Invention]

[0012] The present invention has the following advantageous effects compared to the prior art. By using a two-step particle size control method of iron precipitation under basic conditions and anion exchange, nano-sodium iron phosphate material with small particle size and uniform particle size distribution was successfully produced. The rapid nucleation action of the precipitation reaction quickly forms iron hydroxide precursor, and the particle size of the precursor is effectively controlled. The anion exchange action results in the rapid formation of PO43- , F - , Cl - and anions such as OH - This allows for in-situ conversion of sodium iron phosphate and polyanion to be achieved, allowing for the adjustment and control of structure (microstructure, electronic structure) and performance, and the efficient production of nanosized sodium iron phosphate. This manufacturing method effectively adjusts and controls the particle size and uniformity of sodium iron phosphate particles, achieving a nanoscale particle size distribution. - , Cl - The introduction of anions such as these contributes to improving the ionic and electronic conductivity of sodium iron phosphate materials and improving their electrochemical performance. Furthermore, because the precipitation and ion exchange reactions are efficient, have short reaction times, and can occur even at room temperature, the preparation method of the present invention can be completed efficiently and quickly at room temperature, making it easy to scale up. Due to its technical advantages and the structural and performance advantages of the resulting products, this method is expected to overcome limitations in the application of sodium iron phosphate-based materials in the energy storage field and may be widely used in research on electrode materials for alkaline metal secondary batteries such as lithium, sodium, and potassium. The method of the present invention has advantages such as simple operation, high efficiency, and amenable to industrial scale-up, facilitating research and application of sodium iron phosphate materials in the field of electrochemical energy storage. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an XRD graph of sodium iron phosphate produced by the method of Example 1. [Figure 2] 1 is an SEM characterization of the sodium iron phosphate material produced by the method of Example 1. [Figure 3] 1 is a characterization of the sodium iron phosphate material produced by the method of Example 1 by EDS elemental analysis. [Figure 4] 1 is a particle size distribution characterization of the sodium iron phosphate material produced by the method of Example 2. [Figure 5]1 is a BET characterization of the sodium iron phosphate material produced by the method of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the technical means in the embodiments of the present invention will be clearly and completely described with reference to the examples of the present invention, but it is clear 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 out and dissolved in 50 mL of deionized water to prepare solution B. Solution B was added dropwise to solution A at a rate of 1 drop / second, and stirring was continued until the solution reached a pH of 5. The mixture was then centrifuged and filtered 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 hours. The mixture was then filtered and dried to obtain the desired product.

[0016] As is clear from Figure 1, characteristic diffraction peaks of NaFe(III)OPOF appear at 11.2°, 13.2°, 18.2°, 19.5°, and 23.1° on the graph, and the diffraction peaks have high intensity, indicating that the method of Example 1 was successful in producing sodium iron phosphate, and that the obtained sodium iron phosphate was highly pure with no impurities.

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

[0018] As is clear from Figure 3, the sodium iron phosphate produced in Example 1 contains elements such as Na, Fe, P, O, and F, with the ratio of each element being 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 demonstrates 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 out and dissolved in 50 mL of deionized water to prepare solution B. Solution B was added dropwise to solution A at a rate of 1 drop / second, and stirring was continued until the solution reached pH 7. The mixture was then centrifuged and filtered 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 hours. The mixture was then filtered and dried to obtain the desired product.

[0020] As is clear from FIG. 4, the sodium iron phosphate produced in Example 2 has a uniform particle size distribution, with the particle sizes concentrated mainly around 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 out and dissolved in 50 mL of deionized water to prepare solution B. Solution B was added dropwise to solution A at a rate of 1 drop / second, and stirring was continued until the solution reached a pH of 6. The mixture was then centrifuged and filtered to obtain a slurry. 3) 0.02 mol of sodium phosphate was 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 16 hours. The mixture was then filtered and dried to obtain the target product.

[0023] Comparative Example 1 As a control, the sodium iron phosphate was prepared by the solid phase method with appropriate modifications based on the method for preparing sodium iron phosphate described in Chinese patent application (202210454752.X). The specific procedure is as follows:

[0024] 1) Raw material mixing by dry ball mill method: 150.82 g of iron phosphate, 103.00 g of sodium bicarbonate, and 22.62 g of glucose were weighed and placed in a ball mill tank, where the raw materials were mixed by dry ball mill method. The rotation speed was 300 rpm / min, and the mixing time by ball mill was 1 hour.

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

[0026] 3) The precursor powder material was placed in a tubular furnace and subjected to high-temperature firing under an Ar atmosphere. Specifically, the temperature was raised to 350°C at 2°C / min and maintained at that temperature for 4 hours, then raised to 700°C at 5°C / min and maintained at that temperature for 12 hours. After cooling, the material was sieved and pulverized to obtain sodium iron phosphate cathode material.

[0027] Table 1 compares the discharge specific capacity of the sodium iron phosphate material produced by the method of Example 3 and the sodium iron phosphate material produced in 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 the sodium iron phosphate prepared in Example 3 was 98 mAh / g, which was higher than the specific capacity (91 mAh / g) of the sodium iron phosphate sample prepared by the method of Comparative Example 1, and the impedances of the corresponding button batteries were 160 Ω and 250 Ω, respectively. The prepared nano-sized sodium iron phosphate was found to have lower impedance and higher electronic / ionic conductivity, thereby exhibiting better sodium storage performance.

[0030] The above-described embodiments are intended to illustrate, not limit, the technical means of the present invention. Although the present invention has been described in detail based on the above embodiments, it should be understood by those skilled in the art that modifications and equivalent substitutions can be made to the present invention, and that all modifications and partial substitutions made without departing from the spirit and scope of the present invention are included in the scope of the claims of the present invention.

Claims

1. A method for producing nano sodium iron phosphate material with the chemical formula Na x FeO y PO 4 F a Cl b (where 0<x≦3, 0≦y≦1, 0≦a+b≦1) is used under room temperature conditions using a two-stage particle size control method, and specifically includes the following steps: 1) preparing solution A by dissolving a divalent or trivalent iron source in deionized water; 2) dissolving a basic substance in deionized water to prepare solution B, adding solution B dropwise to solution A, stirring continuously until the pH of the solution reaches 4 to 8, and then centrifuging and filtering to obtain a slurry; and 3) Dissolve chloride and / or fluoride and phosphate in deionized water to prepare solution C, disperse the slurry obtained in step 2) in solution C, continue stirring for 0.5 to 24 hours, filter, and dry to obtain the target product.

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

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

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

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

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

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

3.

8. The chemical formula is Na ｘ FeO ｙ P.O. ４ F ａ Cl ｂ (where 0<x≦3, 0<y≦1, 0≦a+b≦1), and characterized in that the sodium iron phosphate material has a nanoparticulate microtopography.

9. A sodium iron phosphate material having the chemical formula Na x FeO y PO 4 F a Cl b (where x=3, 0≦y≦1, 0≦a+b≦1) and having a nanoparticulate microtopography.

10. 9. The sodium iron phosphate material according to claim 8, wherein the average particle size of the sodium iron phosphate material is 50 to 200 nm.

Images