Preparation method for sodium iron phosphate material, and sodium iron phosphate material

Abstract

A preparation method for a sodium iron phosphate material, and a sodium iron phosphate material. The preparation method comprises: 1) dissolving a divalent / trivalent iron source in deionized water to formulate a solution A; 2) dissolving an alkaline substance in deionized water to formulate a solution B, adding the solution B to the solution A dropwise, stirring the mixed solution until the pH of the solution is 4-8, and centrifugally filtering same to obtain a slurry; and 3) dissolving a chloride and / or fluoride, and a phosphate in deionized water to formulate a solution C, dispersing the slurry obtained in step 2) in the solution C, stirring same for 0.5-24 h, and filtering and drying same to obtain a target product. The method is a new method for efficiently preparing nano sodium iron phosphate by using a two-step particle size control method under low-temperature conditions, and achieves rapid and efficient nano-crystallization preparation of the sodium iron phosphate product by using the rapid nucleation of a precipitation reaction and an in-situ conversion effect of anion exchange at room temperature.

Description

A preparation method of sodium iron phosphate material and sodium iron phosphate material Technical Field

[0001] The present invention relates to the field of electrode materials, and in particular to a preparation method of a sodium iron phosphate material and the sodium iron phosphate material. The material can be used as an electrode material for secondary batteries of alkali metals such as lithium, sodium and potassium. Background Art

[0002] Polyanionic compounds are a class of excellent alkali metal secondary battery electrode materials due to their outstanding ion migration efficiency, good structure and thermal stability. Vanadium / sodium iron phosphate, as a typical polyanionic compound, has attracted widespread attention due to its advantages such as stable structure and high safety. Compared with sodium vanadium phosphate, sodium iron phosphate has a wider source of raw materials and lower cost, and is more competitive in practical applications. At present, the preparation methods of traditional sodium iron phosphate materials are mainly concentrated in high-temperature solid-phase synthesis, sol-gel method, electrochemical synthesis method and other methods. The preparation process often involves harsh conditions such as high vacuum, specific atmosphere, and high temperature. The operation is relatively cumbersome and the preparation cost is high. At the same time, the microscopic particle size of the prepared sodium iron phosphate material is large, generally reaching the μm level. Due to the poor electronic conductivity of sodium iron phosphate, the larger particle size will restrict the sodium storage performance of the prepared sodium iron phosphate material. Prior to this, in order to solve the problem of poor conductivity of polyanionic compounds such as sodium vanadium phosphate, the project team proposed a nano-synthesis idea in the Chinese invention patents (202210162593.6, 202210249477.8). Through research, it was verified that polyanionic compounds with smaller particle sizes are beneficial to improving the electron / ion migration performance of the material. It is not difficult to infer that by nano-designing and preparing sodium iron phosphate, it will be beneficial to improve the electron / ion transport efficiency of the material, thereby obtaining a sodium iron phosphate product with excellent performance. However, so far, there have been few reports on the research on the efficient preparation technology of sodium iron phosphate nano-crystallization.

[0003] Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing sodium iron phosphate material and the sodium iron phosphate material thereof, and propose a new method for efficiently preparing nano sodium iron phosphate under low temperature conditions by using a two-step particle size control method. Based on the characteristics of the small Ksp of iron hydroxide and the large reaction rate constant of the precipitation reaction, the iron ions are rapidly precipitated under alkaline conditions to form an iron hydroxide precursor with controllable particle size. Subsequently, PO4 3- 、F - 、Cl - Anions and OH -The present invention utilizes the rapid nucleation of precipitation reaction and the in-situ conversion of anion exchange to achieve room temperature, rapid, nano-scale and efficient preparation of sodium iron phosphate products.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A method for preparing a sodium iron phosphate material, wherein the method is to prepare a nano sodium iron phosphate material at room temperature using a two-step particle size control method, specifically comprising the following steps:

[0007] 1) Dissolve a divalent / trivalent iron source in deionized water to prepare Solution A. The divalent / trivalent iron source is one or more divalent / trivalent inorganic / organic metal salts of iron, such as ferrous sulfate, ferrous 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.

[0008] 2) Dissolve an alkaline substance in deionized water to form Solution B. The alkaline substance is one or more substances with alkaline aqueous solutions, such as sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and sodium bicarbonate. The concentration of the alkaline substance in Solution B is 0.1 to 5.0 mol / L. Add Solution B dropwise to Solution A at a constant dropwise addition rate, stirring continuously until the solution pH reaches 4 to 8, and centrifuge to filter the resulting slurry.

[0009] 3) Dissolve a chloride and / or fluoride, and a 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, stir continuously for 0.5 to 24 hours, filter, and dry to obtain the target product.

[0010] 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 / trivalent iron source to the phosphate is 1:1 to 1:3.

[0011] A method for preparing sodium iron phosphate material The sodium iron phosphate material prepared has the chemical formula Na x FeO y PO4F a Cl b , 0<x≤3, 0≤y≤1, 0≤a+b≤1, the microscopic morphology is nano-granular.

[0012] The particle size distribution is relatively concentrated. The preparation method described in the present invention is simple and efficient, and can effectively control the particle size of sodium iron phosphate particles at room temperature, with an average particle size concentrated in the range of 50 to 200 nm. The sodium iron phosphate material described in the present invention has excellent electrochemical properties and can be used as an electrode material for alkali metal secondary batteries such as lithium, sodium, and potassium.

[0013] The present invention is characterized in that: a two-step particle size control method is used to prepare nano sodium iron phosphate materials. By taking advantage of the small Ksp of iron hydroxide, the precipitation reaction has a large reaction rate constant, and quickly precipitating iron to form iron hydroxide, the purpose of controlling the precursor particle size is achieved. Then, the anion exchange method is used to control the size of the precursor through PO4 3- 、F - 、Cl - Anions and OH - The in-situ exchange of multiple anions is achieved, which doubles the control of the particle size of the target product, thereby obtaining a nano-sodium iron phosphate product with small particle size and uniform distribution. Due to the fast nucleation rate of the precipitation reaction of iron hydroxide, the growth of the iron hydroxide crystal nucleus is limited, and the particle size of the precursor is controlled. The ion exchange process not only does not involve further growth of the crystal nucleus, but also uses the in-situ conversion mechanism to achieve in-situ stripping of the key components of the precursor, promoting further reduction in the product particle size. That is, through two-step particle size control steps, rapid, efficient, and nano-scale preparation of sodium iron phosphate can be achieved.

[0014] Compared with the existing technology, the beneficial effects of the present invention are:

[0015] Through the two-step particle size control method of alkaline iron precipitation and anion exchange, a small and uniformly distributed nano-sodium iron phosphate material was prepared. Due to the rapid nucleation effect of the precipitation reaction, the iron hydroxide precursor was quickly formed, effectively controlling the particle size of the precursor. By using the anion exchange effect, PO4 3- 、F - 、Cl - Anions and OH - The in-situ conversion of the sodium iron phosphate can achieve the regulation of the structure (microstructure, electronic structure) and performance of the multi-anion, thereby realizing the efficient nano-scale preparation of sodium iron phosphate. Through this preparation method, the particle size and uniformity of sodium iron phosphate can be effectively regulated to achieve nano-scale distribution of particle size. - 、Cl -The introduction of anions is beneficial to improving the ion / electronic conductivity of the sodium iron phosphate material and improving the electrochemical performance. At the same time, since the precipitation reaction and the ion exchange reaction are fully reactive, the reaction time is short, and both can occur at room temperature, the preparation method involved in the present invention can be completed efficiently and quickly at room temperature, and it is easy to achieve scaled-up preparation. Due to the technical advantages of this method and the structural and performance advantages of the product obtained by the method, it is expected to improve the limitations of sodium iron phosphate materials in the application of energy storage, and has broad application prospects in the research of alkali metal secondary battery electrode materials such as lithium, sodium, and potassium. The method of the present invention has the advantages of simple operation, high efficiency, and easy industrial amplification, which is conducive to promoting the research and application promotion of sodium iron phosphate materials in the field of electrochemical energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is an XRD curve of sodium iron phosphate prepared by the method of Example 1.

[0017] FIG2 is an SEM characterization of the sodium iron phosphate material prepared by the method of Example 1.

[0018] FIG3 is an EDS elemental analysis characterization of the sodium iron phosphate material prepared by the method of Example 1.

[0019] FIG4 is a particle size distribution representation of the sodium iron phosphate material prepared by the method of Example 2.

[0020] FIG5 is a BET characterization of the sodium iron phosphate material prepared by the method of Example 2. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only for illustration and are not intended to limit the present invention.

[0022] Example 1:

[0023] 1) Weigh 0.01 mol of ferrous sulfate and dissolve it in 50 mL of deionized water to prepare solution A.

[0024] 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 while stirring continuously until the solution reaches a pH of 5. Centrifuge and filter the resulting slurry.

[0025] 3) Weigh 0.01 mol of sodium fluoride and 0.03 mol of sodium dihydrogen phosphate and 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 hours, filter, and dry to obtain the target product.

[0026] As can be seen from Figure 1, the characteristic diffraction peaks of Na3Fe(III)OPO4F appear at 11.2°, 13.2°, 18.2°, 19.5° and 23.1° on the curve, 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 is of high purity and no impurities are generated.

[0027] As can be seen from FIG2 , the microscopic morphology of the sodium iron phosphate prepared in Example 1 is nano-particle-like, and the particle size distribution is uniform, mainly concentrated around 150 nm.

[0028] As can be seen from Figure 3, the sodium iron phosphate prepared in Example 1 contains elements such as Na, Fe, P, O, and F, and the ratio of the corresponding elements 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.

[0029] Example 2:

[0030] 1) Weigh 0.01 mol of ferrous chloride and dissolve it in 50 mL of deionized water to prepare solution A.

[0031] 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 while stirring continuously until the solution reaches pH 7. Centrifuge and filter the resulting slurry.

[0032] 3) Weigh 0.01 mol potassium chloride and 0.02 mol sodium hydrogen phosphate and 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.

[0033] As can be seen from FIG4 , the sodium iron phosphate prepared in Example 2 has a uniform particle size distribution, mainly concentrated around 150 nm.

[0034] As can be seen from Figure 5, the sodium iron phosphate prepared in Example 2 has a higher specific surface area (31.8m 2 / g).

[0035] Example 3:

[0036] 1) Weigh 0.01 mol of ferrous oxalate and dissolve it in 50 mL of deionized water to prepare solution A.

[0037] 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 while stirring continuously until the solution reaches pH 6. Centrifuge and filter the resulting slurry.

[0038] 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 hours, filter, and dry to obtain the target product.

[0039] Comparative Example 1:

[0040] For comparison, referring to the preparation method of sodium iron phosphate described in Chinese invention patent (202210454752.X) and making appropriate changes, sodium iron phosphate was prepared by solid phase method. The specific operation steps are as follows:

[0041] 1) Dry ball milling: 150.82 g of ferric phosphate, 103.00 g of sodium bicarbonate, and 22.62 g of glucose were weighed and added to a ball mill for dry ball milling at a speed of 300 rpm / min for 1 h.

[0042] 2) Wet ball milling: 300 g of deionized water was added to the mixture prepared in 1) and subjected to high-energy wet ball milling; the ball milling speed was 500 rpm / min and the ball milling time was 5 h; and the mixture was dried to obtain a precursor powder material.

[0043] 3) The precursor powder material was placed in a tube furnace and calcined at high temperature under an Ar atmosphere. Specifically, the temperature was raised at 2°C / min to 350°C and held for 4 hours; then, the temperature was raised at 5°C / min to 700°C and held for 12 hours. After cooling, the material was sieved and crushed to obtain the sodium iron phosphate cathode material.

[0044] Table 1 is a comparison table of the discharge specific capacities of the sodium iron phosphate material prepared by the method of Example 3 and the sodium iron phosphate material prepared by the comparative example 1;

[0045] Table 1 Comparison of discharge specific capacity of sodium iron phosphate prepared in Example 3 and Comparative Example 1

[0046] As can be seen from Table 1, under the charge and discharge current density of 50 mA / g, the specific capacity of the sodium vanadium phosphate prepared in Example 3 is 98 mAh / g, which is higher than the sodium iron phosphate sample prepared by the method of Control Example 1 (91 mAh / g). The corresponding button battery impedances are 160 and 250 Ω, respectively, indicating that the sodium iron phosphate prepared by nano-sizing has smaller impedance and higher electronic / ionic conductivity, thus showing better sodium storage performance.

[0047] The above embodiments are only used to illustrate rather than 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 the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a sodium iron phosphate material, characterized in that: The method is to prepare nano sodium iron phosphate material by a two-step particle size control method at room temperature, and specifically comprises the following steps: 1) Dissolve a divalent / trivalent iron source in deionized water to prepare solution A; 2) dissolving alkaline substances in deionized water to prepare solution B, adding solution B dropwise to solution A, stirring continuously until the solution pH is 4-8, and centrifugally filtering the resulting slurry; 3) Dissolve the chloride and / or fluoride and phosphate in deionized water to prepare solution C, disperse the slurry obtained in step 2) in solution C, stir continuously for 0.5 to 24 hours, filter and dry to obtain the target product.

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

3. The method for preparing a 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 a sodium iron phosphate material according to claim 1, characterized in that: The alkaline substance is one or more of sodium hydroxide, potassium hydroxide, ammonia water, 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 the alkaline substance in solution B is 0.1 to 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: In the above 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 / trivalent iron source to the phosphate is 1:1 to 1:

3.

8. A sodium iron phosphate material, characterized in that: The sodium iron phosphate material is prepared by the preparation method of the sodium iron phosphate material according to any one of claims 1 to 7, and its chemical formula is Na x FeO y PO4F a Cl b , 0<x≤3, 0≤y≤1, 0≤a+b≤1, the microscopic morphology is nano-granular.

9. A sodium iron phosphate material according to claim 8, characterized in that: The average particle size of the sodium iron phosphate material is between 50 and 200 nm.

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