Preparation method of polyanionic sodium ion battery positive electrode material

Abstract

The invention provides a preparation method of a sodium ferric pyrophosphate positive electrode material (NFPP), which is simple in process flow, high in product yield, good in carbon coating effect, high in activity phase and excellent in comprehensive performance, and relates to the technical field of sodium ion batteries. The sodium ferric phosphate pyrophosphate positive electrode material is synthesized through a high-temperature hydrothermal one-step method, the method can avoid the tedious process that high-temperature calcination is performed again after a precursor is synthesized through a traditional hydrothermal method, and the sodium ferric phosphate pyrophosphate positive electrode material obtained through the method does not contain inactive impure phases and has high charge-discharge capacity.

Description

Technical Field

[0001] This application relates to the technical field of sodium-ion batteries, and particularly to a polyanionic cathode material and a preparation method thereof. Background Art

[0002] Currently, lithium-ion batteries are more widely used in the market, and their commercial technologies are relatively mature. However, sodium-ion batteries also have their own unique advantages. For example, sodium reserves are more abundant than lithium, and there is an advantage in terms of price. Therefore, the research and development of sodium-ion batteries have become a new trend in the battery industry. Currently, the mainstream sodium-ion cathode materials include layered oxides, polyanionic types, and Prussian types. Compared with the other two types of materials, polyanionic cathode materials, especially cathode materials with a NASICON crystal structure, can quickly intercalate and deintercalate Na + , have a stable structure, excellent thermal stability, good rate performance, and excellent cycling performance, showing great commercial potential. Among them, sodium iron pyrophosphate phosphate (NFPP) cathode materials composed of abundant and widely sourced sodium, iron, and phosphorus have suitable working voltages (3.1V vs. Na+ / Na), high theoretical capacities (up to 129 mAh / g), open three-dimensional frameworks, and are safe and non-toxic, making such materials have potential market value and application significance in the field of energy storage technology. However, the synthesis conditions of sodium iron pyrophosphate phosphate cathode materials are harsh, and a large number of inactive impurities easily exist in the synthesis products, which will seriously affect their electrochemical performance. There is an urgent need to develop a suitable preparation method to synthesize high-activity-phase sodium iron pyrophosphate phosphate cathode materials.

[0003] At present, the preparation processes for sodium iron pyrophosphate cathode materials are divided into two types: one is the solid-phase ball milling process. For example, in patent CN115881948A, sodium iron pyrophosphate cathode materials are prepared by solid-phase mixing. Insoluble metal salts, sodium salts, phosphorus sources, and carbon sources (such as glucose, citric acid, sucrose, etc.) are mixed and ball milled or sand milled, and the final product is obtained after calcination. However, the solid-phase ball milling process cannot ensure uniform mixing among Na, M, and PO4, resulting in a large amount of inactive heterophases in the final product, seriously affecting the electrochemical performance of the material. The other is the liquid-phase process. For example, in patent CN115148976A, organic phosphoric acid, sodium organic acid, nano iron phosphate, and a carbon source are added to deionized water and stirred, and the precursor powder is obtained by spray drying, ground, sintered under nitrogen protection, and naturally cooled to obtain sodium iron pyrophosphate / carbon, the cathode material for sodium-ion batteries. However, the above-mentioned water-soluble metal salts are extremely hygroscopic, and the carbon sources such as glucose, citric acid, and sucrose have relatively low melting points and high viscosities, resulting in serious powder sticking to the wall during the spray drying process, unable to collect materials normally, easily leading to uneven carbon coating of the final material, high material loss, and the need for drying and re-calcination processes after the precursor is collected, with a complex process. Therefore, there is an urgent need to develop a preparation method with a simple process flow, high product yield, good carbon coating effect, high active phase, and excellent comprehensive performance of the material. Summary of the Invention

[0004] The purpose of this application is to provide a preparation method for sodium iron pyrophosphate cathode materials with a simple process flow, high product yield, good carbon coating effect, high active phase, and excellent comprehensive performance of the material.

[0005] To achieve the above purpose, the technical solution of this application is as follows:

[0006] This application provides a preparation method for sodium iron pyrophosphate cathode materials, including the following steps:

[0007] Dissolve the sodium source, iron source, phosphorus source, and carbon source in deionized water according to a ratio to form a mixed solution, and then add a reducing agent to the mixed solution; add the obtained mixed solution to a reaction kettle for hydrothermal reaction, and take out the reaction product, which is centrifuged, vacuum dried, and airflow pulverized to obtain the sodium iron pyrophosphate cathode material.

[0008] In the present invention, the sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium nitrate, sodium sulfate, sodium oxalate, sodium phosphate, sodium pyrophosphate, disodium dihydrogen pyrophosphate, trisodium hydrogen pyrophosphate, sodium citrate, and sodium gluconate, and preferably sodium dihydrogen phosphate.

[0009] In the present invention, the iron source includes at least one of iron / ferrous oxalate, iron / ferrous nitrate, iron / ferrous sulfate, iron / ferrous phosphate, iron / ferrous acetate, and iron / ferrous chloride, and preferably ferrous oxalate.

[0010] In the present invention, the phosphorus source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate, monosodium hydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, pyrophosphoric acid, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and trisodium hydrogen pyrophosphate, and preferably sodium dihydrogen phosphate.

[0011] In the present invention, the carbon source includes at least one of citric acid, glucose, sucrose, maltose, lactose, cyclodextrin, and water-soluble starch, and preferably glucose.

[0012] In the present invention, the reducing agent includes at least one of hydrazine hydrate, sodium borohydride, and ascorbic acid, and preferably hydrazine hydrate.

[0013] In the present invention, the molar ratio of sodium:iron:phosphorus:carbon in the sodium source, iron source, phosphorus source, and carbon source is 4:(2.8 - 3.2):(3.8 - 4.2):1 - 2, and the mass ratio of the deionized water added to the total mass of the raw materials is 1 - 3:1.

[0014] In the present invention, the ratio of the reducing agent to the raw materials is 5 - 15% wt, and preferably 8 - 12% wt.

[0015] In the present invention, the temperature of the hydrothermal reaction is 260 - 370 °C, preferably 300 - 330 °C, and the time of the hydrothermal reaction is 7 - 15 h, preferably 10 - 12 h.

[0016] In the present invention, the rotation speed of the centrifuge is 5000 - 10000 r / min, and the centrifugation time is 1 - 5 min.

[0017] In the present invention, the drying temperature is 100 - 200 °C, the drying time is 1 - 8 h, and the D50 of the sodium iron pyrophosphate phosphate cathode material obtained after pulverization is 1.5 - 10.5 μm.

[0018] In the present invention, the chemical formula of the sodium iron pyrophosphate phosphate cathode material is Na4Fe3(PO4)2(P2O7).

[0019] In the present invention, the XRD diffraction peak intensities I(200):I(210):I(222) of the sodium iron pyrophosphate phosphate cathode material are 1:0.75 - 0.85:0.73 - 0.82, where I(200), I(210), and I(222) represent the XRD diffraction peak intensities of the sodium iron pyrophosphate phosphate cathode material in three directions.

[0020] The beneficial effects of the present invention are as follows:

[0021] This application synthesizes the sodium iron pyrophosphate phosphate cathode material by a one-step high-temperature hydrothermal method, avoiding the cumbersome process of high-temperature calcination required after synthesizing the precursor by the traditional hydrothermal method, and the process flow is simple. At the same time, the hydrothermal method can accurately control the reaction temperature to synthesize the sodium iron pyrophosphate phosphate cathode material with the required highly active phase and uniform carbon coating. The sodium iron pyrophosphate phosphate synthesized by this method has no impurity phase, has a high charge-discharge capacity, excellent electrochemical performance, and has good application prospects. Brief Description of the Drawings

[0022] Figure 1 It is the XRD pattern of the sodium iron pyrophosphate phosphate cathode material prepared in Example 1 of the present invention. Detailed Embodiments

[0023] Raw Materials and Sources

[0024] Raw material Source Sodium dihydrogen phosphate Shijiazhuang Jinghuang Ferrous oxalate Hefei Yalong Glucose Heilongjiang Jinxiang Hydrazine hydrate Tianjin Damao Ascorbic acid Tianjin Fuchen

[0025] Testing Methods

[0026] Crystal Structure Testing: An X-ray powder diffractometer (PANalytical Aeris) is used, with CuKα radiation as the radiation source, and the radiation wavelength The scanning diffraction angle range is 5° to 55°, and the scanning rate is 2.78° / min.

[0027] Capacity Testing: The fabricated coin-type half-cell is placed in an incubator for testing, and the testing temperature is 25 ± 1°C. Using a Neware battery tester, the working step is set to "constant current and constant voltage charging", the voltage is set to 4V, first charge at a rate of 0.2C to 4.0V, then the constant voltage charging current drops to 0.02C, and the initial charging capacity C1 of the sodium-ion battery is tested. Then, discharge at a constant current of 0.2C to 2.0V, and the initial discharge capacity C2 of the sodium-ion battery is tested. The formula for the first efficiency (Eff . ) is: Eff . = C2 / C1 * 100%.

[0028] Rate Performance (Rate Discharge): The fully charged battery is discharged to the cut-off voltage at 0.2C / 2.0C respectively, and the capacity retention rate is calculated, that is, the value of 0.2C / 2C.

[0029] Example 1

[0030] Dissolve 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose in 300 ml of deionized water to form a mixed solution, and then add 30 ml of hydrazine hydrate to the mixed solution as a reducing agent. Add the obtained mixed solution to a reaction kettle, heat it to 315 °C for hydrothermal reaction for 11 h, take out the reaction product, centrifuge it at 6000 r / min for 3 min, dry it in a vacuum oven at 120 °C for 4 h, and pulverize it with a jet mill to obtain a sodium iron pyrophosphate phosphate cathode material with D50 = 3 μm.

[0031] Example 2

[0032] Dissolve 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose in 300 ml of deionized water to form a mixed solution, and then add 15 ml of hydrazine hydrate to the mixed solution as a reducing agent. Add the obtained mixed solution to a reaction kettle, heat it to 260 °C for hydrothermal reaction for 7 h, take out the reaction product, centrifuge it at 6000 r / min for 3 min, dry it in a vacuum oven at 120 °C for 4 h, and pulverize it with a jet mill to obtain a sodium iron pyrophosphate phosphate cathode material with D50 = 3 μm.

[0033] Example 3

[0034] Dissolve 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose in 300 ml of deionized water to form a mixed solution, and then add 45 ml of hydrazine hydrate to the mixed solution as a reducing agent. Add the obtained mixed solution to a reaction kettle, heat it to 370 °C for hydrothermal reaction for 15 h, take out the reaction product, centrifuge it at 6000 r / min for 3 min, dry it in a vacuum oven at 120 °C for 4 h, and pulverize it with a jet mill to obtain a sodium iron pyrophosphate phosphate cathode material with D50 = 3 μm.

[0035] Example 4

[0036] Dissolve 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose in 300 ml of deionized water to form a mixed solution, and then add 30 ml of ascorbic acid to the mixed solution as a reducing agent. Add the obtained mixed solution to a reaction kettle, heat it to 315 °C for hydrothermal reaction for 11 h, take out the reaction product, centrifuge it at 6000 r / min for 3 min, dry it in a vacuum oven at 120 °C for 4 h, and pulverize it with a jet mill to obtain a sodium iron pyrophosphate phosphate cathode material with D50 = 3 μm.

[0037] Comparative Example 1

[0038] Without using the hydrothermal method, 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose were directly dissolved in 300 ml of deionized water to form a mixed solution. After grinding with a sand mill, precursor particles were prepared by spray drying. The precursor was sintered at 500 °C for 20 h in a nitrogen atmosphere in a box furnace. The reaction product was taken out and pulverized by a jet mill to obtain a sodium iron pyrophosphate positive electrode material with D50 = 3 μm.

[0039] Comparative Example 2

[0040] 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose were dissolved in 300 ml of deionized water to form a mixed solution without adding a reducing agent. The obtained mixed solution was added to a reaction kettle and heated to 315 °C for hydrothermal reaction for 11 h. The reaction product was taken out and centrifuged at 6000 r / min for 3 min, dried in a vacuum oven at 120 °C for 4 h, and pulverized by a jet mill to obtain a sodium iron pyrophosphate positive electrode material with D50 = 3 μm.

[0041] Comparative Example 3

[0042] 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose were dissolved in 300 ml of deionized water to form a mixed solution, and then 30 ml of hydrazine hydrate was added to the mixed solution as a reducing agent. The obtained mixed solution was added to a reaction kettle and heated to 150 °C for hydrothermal reaction for 11 h. The reaction product was taken out and centrifuged at 6000 r / min for 3 min, dried in a vacuum oven at 120 °C for 4 h, and pulverized by a jet mill to obtain a sodium iron pyrophosphate positive electrode material with D50 = 3 μm.

[0043] Comparative Example 4

[0044] 72.1 g of sodium dihydrogen phosphate, 81.1 g of ferrous oxalate, and 6.8 g of glucose were dissolved in 300 ml of deionized water to form a mixed solution, and then 30 ml of hydrazine hydrate was added to the mixed solution as a reducing agent. The obtained mixed solution was added to a reaction kettle and heated to 315 °C for hydrothermal reaction for 1 h. The reaction product was taken out and centrifuged at 6000 r / min for 3 min, dried in a vacuum oven at 120 °C for 4 h, and pulverized by a jet mill to obtain a sodium iron pyrophosphate positive electrode material with D50 = 3 μm.

[0045] Table 1: Crystal structure data of the sodium iron pyrophosphate positive electrode materials prepared in Examples 1 - 4

[0046] I(200):I(210):I(222) Example 1 1:0.81:0.78 Example 2 1:0.78:0.75 Example 3 1:0.84:0.81 Example 4 1:0.80:0.78

[0047] Table 2: 0.2C discharge capacity, first efficiency (2.0 - 4.0 V), and 2C capacity of the sodium iron pyrophosphate positive electrode materials prepared in Examples 1 - 4 and Comparative Examples 1 - 4

[0048]

[0049]

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of sodium iron pyrophosphate phosphate cathode material, comprising the following steps: Dissolve a sodium source, an iron source, a phosphorus source, and a carbon source in deionized water in a ratio to form a mixed solution, and then add a reducing agent to the mixed solution; add the obtained mixed solution to a reaction kettle for hydrothermal reaction, and take out the reaction product, followed by centrifugal separation, vacuum drying, and air flow pulverization to obtain the sodium iron pyrophosphate phosphate cathode material; the temperature of the hydrothermal reaction is 260-370 °C, preferably 300-330 °C, and the time of the hydrothermal reaction is 7-15 h, preferably 10-12 h.

2. The preparation method according to claim 1, characterized in that, The sodium source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium nitrate, sodium sulfate, sodium oxalate, sodium phosphate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, trisodium hydrogen pyrophosphate, sodium citrate, and sodium gluconate, preferably sodium dihydrogen phosphate.

3. The preparation method according to claim 1 or 2, characterized in that, The iron source includes at least one of iron oxalate, ferrous oxalate, iron nitrate, ferrous nitrate, iron sulfate, ferrous sulfate, iron phosphate, ferrous phosphate, iron acetate, ferrous acetate, iron chloride, and ferrous chloride, preferably ferrous oxalate.

4. The preparation method according to any one of claims 1-3, characterized in that, The phosphorus source includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate, sodium hydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium hydrogen phosphate, sodium phosphate, pyrophosphoric acid, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and trisodium hydrogen pyrophosphate, preferably sodium dihydrogen phosphate.

5. The preparation method according to any one of claims 1-4, characterized in that, The carbon source includes at least one of citric acid, glucose, sucrose, maltose, lactose, cyclodextrin, and water-soluble starch, preferably glucose.

6. The preparation method according to any one of claims 1-5, characterized in that, The reducing agent includes at least one of hydrazine hydrate, sodium borohydride, and ascorbic acid, preferably hydrazine hydrate.

7. The preparation method according to any one of claims 1-6, characterized in that, The molar ratio of sodium:iron:phosphorus:carbon in the sodium source, iron source, phosphorus source, and carbon source is 4:(2.8-3.2):(3.8-4.2):1-2, and the mass ratio of the added deionized water to the total mass of the raw materials is 1-3:1; and / or, the ratio of the reducing agent to the raw materials is 5-15% wt, preferably 8-12% wt.

8. The preparation method according to any one of claims 1-7, characterized in that, The rotation speed of the centrifuge is 5000-10000 r / min, and the centrifugation time is 1-5 min; and / or, the drying temperature is 100-200 °C, the drying time is 1-8 h, and the D50 of the sodium iron pyrophosphate phosphate cathode material obtained after pulverization is 1.5-10.5 μm.

9. A sodium iron pyrophosphate phosphate cathode material prepared by the preparation method according to any one of claims 1-8.

10. The sodium iron pyrophosphate phosphate cathode material according to claim 9, wherein The XRD diffraction peak intensities I(200):I(210):I(222) of the sodium iron pyrophosphate phosphate cathode material are 1:0.75-0.85:0.73-0.82, where I(200), I(210), and I(222) represent the XRD diffraction peak intensities of the sodium iron pyrophosphate phosphate cathode material in three directions.

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