Preparation method of sodium iron phosphate material and sodium iron phosphate material thereof

Abstract

This invention relates to a method for preparing sodium iron phosphate material and the sodium iron phosphate material itself. The method includes: 1) dissolving a divalent / trivalent iron source in deionized water to prepare solution A; 2) dissolving an alkaline substance in deionized water to prepare solution B, adding solution B dropwise to solution A, stirring until the solution pH = 4-8, and centrifuging and filtering to obtain a slurry; 3) dissolving chloride and / or fluoride, along with phosphate, in deionized water to prepare solution C, dispersing the slurry obtained in step 2) in solution C, stirring for 0.5-24 hours, filtering, and drying to obtain the target product. This invention proposes a novel method for the efficient preparation of nano-sized sodium iron phosphate under low-temperature conditions using a two-step particle size control method. This invention utilizes the rapid nucleation of precipitation reaction and the in-situ transformation of anion exchange to achieve the efficient, rapid, and nano-sized preparation of sodium iron phosphate product at room temperature.

Description

Technical Field

[0001] This invention relates to the field of electrode materials, specifically to a method for preparing sodium iron phosphate material and the sodium iron phosphate material itself, which can be used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium. Background Technology

[0002] Polyanionic compounds are high-performance electrode materials for alkali metal secondary batteries due to their excellent ion migration efficiency, good structure, and thermal stability. Vanadium phosphate / sodium iron phosphate, as a typical polyanionic compound, has attracted widespread attention due to its structural stability and high safety. Compared to sodium vanadium phosphate, sodium iron phosphate has a wider range of raw material sources and lower cost, making it more competitive in practical applications. Currently, traditional methods for preparing sodium iron phosphate materials mainly focus on high-temperature solid-state synthesis, sol-gel methods, and electrochemical synthesis methods. These methods often involve harsh conditions such as high vacuum, specific atmospheres, and high temperatures, making the operations cumbersome and the preparation costs high. Furthermore, the resulting sodium iron phosphate materials have large particle sizes, generally reaching the μm level. Due to the poor electronic conductivity of sodium iron phosphate, the large particle size limits the sodium storage performance of the prepared sodium iron phosphate materials. Prior to this, to address the poor conductivity of polyanionic compounds such as sodium vanadium phosphate, our research team proposed a nano-synthesis approach in Chinese invention patents (202210162593.6, 202210249477.8). Our research verified that smaller particle sizes of polyanionic compounds are beneficial for improving the electron / ion transport performance of materials. It is easy to infer that nano-design and preparation of sodium iron phosphate will improve the electron / ion transport efficiency of materials, thereby obtaining high-performance sodium iron phosphate products. However, to date, research on efficient nano-preparation techniques for sodium iron phosphate is scarce. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing sodium iron phosphate (SFP) material and the SFP material itself. A novel method for the efficient preparation of nano-sized SFP material using a two-step particle size control approach under low-temperature conditions is proposed. Based on the low Ksp characteristic of iron hydroxide and the large rate constant of precipitation reactions, iron ions are rapidly precipitated under alkaline conditions to form an iron hydroxide precursor with controllable particle size. Subsequently, PO4 is used... 3- F - Cl - Anions and OH - The ion exchange process yields nano-sized sodium iron phosphate materials. This invention utilizes the rapid nucleation of precipitation reactions and the in-situ transformation of anion exchange to achieve efficient, rapid, and nano-sized preparation of sodium iron phosphate products at room temperature.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A method for preparing sodium iron phosphate material, which involves a two-step particle size control method at room temperature to prepare nano-sized sodium iron phosphate material, specifically including the following steps:

[0006] 1) Dissolve a divalent / trivalent iron source in deionized water to prepare solution A. The divalent / trivalent iron source is one or more of the divalent / trivalent inorganic / organometallic 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 0.1–5.0 mol / L.

[0007] 2) An alkaline substance is dissolved in deionized water to prepare solution B. The alkaline substance is one or more of the following: sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, sodium bicarbonate, etc., whose aqueous solutions are alkaline. The concentration of the alkaline substance in solution B is 0.1–5.0 mol / L. Solution B is added dropwise to solution A at a certain dropping rate, and the mixture is stirred continuously until the pH of the solution reaches 4–8. The resulting slurry is then centrifuged and filtered.

[0008] 3) Dissolve the chloride and / or fluoride, along with the phosphate, in deionized water to prepare solution C. 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. Disperse the slurry obtained in step 2) in solution C, stirring continuously for 0.5–24 hours. Filter and dry to obtain the target product.

[0009] In solution C, the concentration ratio of chloride and / or fluoride to phosphate is 0 to 1:10, and the molar concentration ratio of divalent / trivalent iron source to phosphate is 1:1 to 1:3.

[0010] A method for preparing sodium iron phosphate material, the sodium iron phosphate material having the chemical formula Na x FeO y PO4F a Cl b , 0<x≤3, 0≤y≤1, 0≤a+b≤1, the microstructure is nanoparticles.

[0011] The particle size distribution is relatively concentrated. The preparation method described in this invention is simple and efficient, and can effectively control the particle size of sodium iron phosphate particles at room temperature, with the average particle size concentrated in the range of 50–200 nm. The sodium iron phosphate material described in this invention has good electrochemical performance and can be used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium.

[0012] The key feature of this invention is the use of a two-step particle size control method for the preparation of nano-sized sodium iron phosphate materials. By utilizing the relatively small Ksp of iron hydroxide and the large rate constant of the precipitation reaction, iron is rapidly precipitated to form iron hydroxide, thus achieving control over the precursor particle size. Then, an anion exchange method is used to... 3- F - Cl - Anions and OH - In-situ ion exchange enables multi-anion regulation, providing dual control over the particle size of the target product, resulting in small and uniformly distributed nano-sized sodium iron phosphate. The rapid nucleation rate of the precipitation reaction of iron hydroxide limits the growth of iron hydroxide crystal nuclei, thus controlling the particle size of the precursor. The ion exchange process not only avoids further crystal growth but also utilizes an in-situ transformation mechanism to achieve in-situ exfoliation of key components from the precursor, further reducing the product particle size. In short, through a two-step particle size control process, rapid, efficient, and nano-sized preparation of sodium iron phosphate can be achieved.

[0013] Compared with existing technologies, the beneficial effects of this invention are:

[0014] A two-step particle size control method involving alkaline iron precipitation and anion exchange was used to prepare nano-sized sodium iron phosphate materials with small and uniform particle size distribution. The rapid nucleation effect of the precipitation reaction facilitated the rapid formation of the iron hydroxide precursor, effectively controlling its particle size. Anion exchange was utilized to achieve the desired particle size distribution of PO4. 3- F - Cl - Anions and OH - In-situ transformation enables the regulation of structure (microstructure and electronic structure) and properties by multiple anions, thereby achieving efficient nano-scale preparation of sodium iron phosphate. This preparation method can effectively control the particle size and uniformity of sodium iron phosphate, achieving a nanoscale particle size distribution. - Cl - The introduction of anions improves the ionic / electronic conductivity of sodium iron phosphate materials, thus enhancing their electrochemical performance. Furthermore, the precipitation and ion exchange reactions are thorough, short-time, and can occur at room temperature, allowing the preparation method described in this invention to be completed efficiently and rapidly at room temperature, facilitating large-scale production. Due to the technical advantages of this method and the structural and performance advantages of the resulting product, it holds promise for overcoming the limitations of sodium iron phosphate materials in energy storage applications and has broad application prospects in the research of electrode materials for alkali metal secondary batteries such as lithium, sodium, and potassium. The method of this invention is simple to operate, highly efficient, and easily scaled up industrially, which is beneficial for promoting the research and application of sodium iron phosphate materials in the field of electrochemical energy storage. Attached Figure Description

[0015] Figure 1 The XRD curve of sodium iron phosphate prepared by the method of Example 1.

[0016] Figure 2 SEM characterization of the sodium iron phosphate material prepared by the method of Example 1.

[0017] Figure 3 EDS elemental analysis characterization of the sodium iron phosphate material prepared by the method of Example 1.

[0018] Figure 4 The particle size distribution of the sodium iron phosphate material prepared by the method in Example 2 is characterized.

[0019] Figure 5 BET characterization of the sodium iron phosphate material prepared by the method of Example 2. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are merely illustrative and are not intended to limit the present invention.

[0021] Example 1:

[0022] 1) Weigh 0.01 mol of ferrous sulfate and dissolve it in 50 mL of deionized water to prepare solution A.

[0023] 2) Weigh 0.1 mol of sodium hydroxide and dissolve it in 50 mL of deionized water to prepare solution B. Add solution B dropwise to solution A at a rate of one drop per second, stirring continuously until the pH of the solution reaches 5. Centrifuge and filter the resulting slurry.

[0024] 3) Weigh 0.01 mol of sodium fluoride and 0.03 mol of sodium dihydrogen phosphate, dissolve them in 50 ml of deionized water to prepare solution C. Disperse the slurry obtained in step 2) in solution C, stir continuously for 24 h, filter and dry to obtain the target product.

[0025] Depend on Figure 1 It can be seen that the curve shows the characteristic diffraction peaks of Na3Fe(Ⅲ)OPO4F at 11.2°, 13.2°, 18.2°, 19.5° and 23.1°, and the diffraction peaks have high intensity, indicating that the method of Example 1 successfully prepared sodium iron phosphate, and the obtained sodium iron phosphate has high purity and no impurities are generated.

[0026] Depend on Figure 2 It can be seen that the sodium iron phosphate prepared in Example 1 has a microstructure of nanoparticles with uniform particle size distribution, mainly concentrated at around 150 nm.

[0027] Depend on Figure 3 It can be seen that the sodium iron phosphate prepared 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 corresponding elements in Na3Fe(Ⅲ)OPO4F, further verifying that the prepared sodium iron phosphate sample is Na3Fe(Ⅲ)OPO4F.

[0028] Example 2:

[0029] 1) Weigh 0.01 mol of ferrous chloride and dissolve it in 50 mL of deionized water to prepare solution A.

[0030] 2) Weigh 0.1 mol of sodium hydroxide and dissolve it in 50 mL of deionized water to prepare solution B. Add solution B dropwise to solution A at a rate of one drop per second, stirring continuously until the pH of the solution reaches 7. Centrifuge and filter the resulting slurry.

[0031] 3) Weigh 0.01 mol potassium chloride and 0.02 mol disodium hydrogen phosphate, dissolve them in 50 ml of deionized water to prepare solution C. Disperse the slurry obtained in step 2) in solution C, stir continuously for 6 hours, filter and dry to obtain the target product.

[0032] Depend on Figure 4 It can be seen that the sodium iron phosphate prepared in Example 2 has a uniform particle size distribution, mainly concentrated at around 150 nm.

[0033] Depend on Figure 5 It can be seen that the sodium iron phosphate prepared in Example 2 has a high specific surface area (31.8 m²). 2 / g).

[0034] Example 3:

[0035] 1) Weigh 0.01 mol of ferrous oxalate and dissolve it in 50 mL of deionized water to prepare solution A.

[0036] 2) Weigh 0.1 mol of sodium bicarbonate and dissolve it in 50 mL of deionized water to prepare solution B. Add solution B dropwise to solution A at a rate of one drop per second, stirring continuously until the pH of the solution reaches 6. Centrifuge and filter the resulting slurry.

[0037] 3) Weigh 0.02 mol of sodium phosphate and dissolve it in 50 ml of deionized water to prepare solution C. Disperse the slurry obtained in step 2 in solution C, stir continuously for 16 h, filter and dry to obtain the target product.

[0038] Compare with Example 1:

[0039] In comparison, referring to the method for preparing sodium iron phosphate described in Chinese invention patent (202210454752.X) and making appropriate modifications, sodium iron phosphate was prepared by solid-phase method. The specific operation steps are as follows:

[0040] 1) Dry ball milling: Weigh 150.82g of ferric phosphate, 103.00g of sodium bicarbonate and 22.62g of glucose and add them to the ball mill jar for dry ball milling at 300rpm / min for 1h.

[0041] 2) Wet ball milling: Add 300g of deionized water to 1) and perform high-energy wet ball milling; the ball milling speed is 500rpm / min and the ball milling time is 5h; dry to obtain precursor powder material.

[0042] 3) Under an Ar atmosphere, the precursor powder material was loaded into a tube furnace for high-temperature calcination. Specifically, the temperature was increased to 350℃ at a rate of 2℃ / min and held for 4 hours; then, the temperature was increased to 700℃ at a rate of 5℃ / min and held for 12 hours; after cooling, the material was sieved and pulverized to obtain sodium iron phosphate cathode material.

[0043] Table 1 is a comparison of the discharge specific capacity of the sodium iron phosphate material prepared by the method of Example 3 and the sodium iron phosphate material prepared by Control Example 1.

[0044] Table 1. Comparison of discharge specific capacity of sodium iron phosphate prepared in Example 3 and Control Example 1

[0045]

[0046] As shown in Table 1, under a charge / discharge current density of 50 mA / g, the specific capacity of sodium vanadium phosphate prepared in Example 3 is 98 mAh / g, which is higher than that of sodium iron phosphate sample prepared by the method of Control Example 1 (91 mAh / g). The corresponding coin cell impedances are 160 Ω and 250 Ω, respectively. This indicates that the nano-prepared sodium iron phosphate has lower impedance and higher electronic / ionic conductivity, thus exhibiting better sodium storage performance.

[0047] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing sodium iron phosphate material, characterized in that, This method involves preparing nano-sized sodium iron phosphate materials at room temperature using a two-step particle size control approach, specifically including the following steps: 1) Dissolve the divalent / trivalent iron source in deionized water to prepare solution A; 2) Dissolve the alkaline substance in deionized water to prepare solution B. Add solution B dropwise to solution A and stir continuously until the pH of the solution is 4~8. Centrifuge and filter to obtain the slurry. 3) Dissolve chloride, fluoride, and phosphate in deionized water to prepare solution C. Disperse the slurry obtained in step 2) in solution C and stir continuously for 0.5 to 24 hours. Filter and dry to obtain the target product. In solution C, the concentration ratio of chloride and fluoride to phosphate is 0~1:10, and the molar concentration ratio of divalent / trivalent iron source to phosphate is 1:1~1:3; The aforementioned sodium iron phosphate material has the chemical formula Na. x FeO y PO4F a Cl b , 0 < x ≤ 3, 0 < y ≤ 1, 0 < a + b ≤ 1, the microstructure is nanoparticles.

2. The method for preparing sodium iron phosphate material according to claim 1, characterized in that, The divalent / trivalent iron source is one or more of ferrous sulfate, ferric sulfate, ferrous chloride, ferric nitrate, and ferrous oxalate.

3. The method for preparing sodium iron phosphate material according to claim 1, characterized in that, The concentration of the iron source in solution A is 0.1–5.0 mol / L.

4. The method for preparing sodium iron phosphate material according to claim 1, characterized in that, The alkaline substance is one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and sodium bicarbonate.

5. The method for preparing a sodium iron phosphate material according to claim 1, characterized in that, The concentration of alkaline substances in solution B is 0.1–5.0 mol / L.

6. The method for preparing a sodium iron phosphate material according to claim 1, characterized in that, 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. The method for preparing a sodium iron phosphate material according to claim 1, characterized in that, The average particle size of sodium iron phosphate material is 50~200 nm.

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