A method for preparing a pure phase sodium ion battery positive electrode material

Abstract

This invention relates to a method for preparing a pure-phase sodium-ion battery cathode material, wherein the cathode material is a carbon-coated sodium iron pyrophosphate material, and the chemical formula of the sodium iron pyrophosphate is: Na a Fe b (PO4) c P2O7, wherein 3≤a≤4, 2≤b≤4, 1≤c≤3; its preparation method includes the following steps: weighing sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, citric acid and dispersant according to stoichiometric ratio; firstly, dissolving sodium carbonate and citric acid in a solvent to react and obtain a first slurry; mixing the first slurry, ferric phosphate, sodium dihydrogen phosphate and dispersant to obtain a second slurry; drying the second slurry to obtain a precursor; pre-sintering the precursor under a protective gas atmosphere, and then continuing to heat and sinter to obtain the cathode material; through the method of the present invention, pure phase sodium iron pyrophosphate cathode material can be obtained, effectively improving the electrochemical performance of the cathode material.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and more specifically, to a method for preparing a pure-phase sodium-ion battery cathode material. Background Technology

[0002] Sodium-ion batteries are considered the most promising alternative to lithium-ion batteries due to abundant sodium resources, low cost, and relatively high safety performance. In recent years, tremendous efforts have been made to develop key technologies for sodium-ion batteries, such as cathode materials, anode materials, and electrolytes.

[0003] In sodium-ion batteries, iron-based polyanion cathode materials have attracted widespread attention due to their low cost, environmental friendliness, excellent cycle performance, and good safety. In recent years, sodium iron pyrophosphate has been proven to be an electrochemically active cathode material. Na4Fe3(PO4)2P2O7 and Na3Fe2(PO4)P2O7 cathodes with specific compositions have theoretical capacities of 128 mAh / g and 119 mAh / g, respectively, showing great application potential. Na4Fe3(PO4)2P2O7, in particular, has high initial capacity, low raw material cost, and good cycle performance, making it suitable for large-scale energy storage systems.

[0004] Due to cost considerations, the main sodium, iron, and phosphorus sources used in the industrial production of sodium iron pyrophosphate are sodium carbonate, iron phosphate, and sodium dihydrogen phosphate. The preparation involves mixing these sources with a solvent, followed by drying to obtain a precursor. This precursor is then pre-sintered and sintered under a protective atmosphere to obtain the sodium iron pyrophosphate cathode material. However, this method results in poor cathode material performance due to the presence of the impurity phase NaFePO4, and sodium carbonate is prone to decomposition into gases during ball milling, posing a significant safety hazard. Summary of the Invention

[0005] Based on the aforementioned technical problems in the existing technology, the present invention provides a method for preparing a pure-phase sodium-ion battery cathode material. This method involves reacting sodium carbonate with a specific carbon source and combining it with specific mixing steps to obtain pure-phase sodium iron pyrophosphate.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a pure-phase sodium-ion battery cathode material, wherein the cathode material is a carbon-coated sodium iron pyrophosphate material, and the chemical formula of the sodium iron pyrophosphate is: Na a Fe b (PO4) c P2O7, wherein 3≤a≤4, 2≤b≤4, and 1≤c≤3, is prepared by the following steps:

[0008] S1. Weigh out sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, citric acid and dispersant according to the stoichiometric ratio;

[0009] S2. First, sodium carbonate and citric acid are dissolved in a solvent and reacted to obtain the first slurry;

[0010] S3. Combine the first slurry, ferric phosphate, sodium dihydrogen phosphate, and dispersant to obtain the second slurry;

[0011] S4. Dry the second slurry to obtain the precursor;

[0012] S5. The precursor is pre-sintered in a protective gas atmosphere, and then the temperature is increased to sinter it to obtain the cathode material.

[0013] In some embodiments, in step S2, citric acid is first dissolved in a solvent, and then sodium carbonate is added in batches to the citric acid solution over 10-30 minutes to carry out the reaction.

[0014] In some embodiments, in step S3, the first slurry, ferric phosphate, sodium dihydrogen phosphate, and dispersant are mixed and ball-milled at a ball-to-material ratio of 10-20:1. Preferably, the solid content of the slurry obtained after mixing is 40%-60%.

[0015] In some implementations, the ball milling rate is 400-800 rpm; the ball milling time is 8-24 h.

[0016] In some embodiments, in step S5, the pre-sintering temperature is 300-450°C; the sintering temperature is 500-800°C.

[0017] In some implementations, the pre-sintering time is 3-8 hours; the sintering time is 8-24 hours.

[0018] In some embodiments, the heating rate to both the pre-sintering temperature and the sintering temperature is 1-10°C / min; preferably, the heating rate is 2-5°C / min.

[0019] In some embodiments, the dispersant is at least one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

[0020] In some embodiments, in step S1, the raw materials are weighed according to a Na:Fe:P molar ratio of 4:3:4 and a citric acid to dispersant mass ratio of 2-4:1.

[0021] In some embodiments, the solvent is an alcohol solvent; preferably, it is ethylene glycol.

[0022] In some embodiments, step S4 involves vacuum drying at 70-100°C.

[0023] In some embodiments, the method also includes passing the dried material through a 250-500 mesh sieve.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention uses sodium carbonate, iron phosphate, and sodium dihydrogen phosphate as the sodium source, iron source, and phosphorus source, respectively, and citric acid as the carbon source. Sodium carbonate and citric acid are first mixed and reacted, then mixed with other raw materials, dried to obtain a precursor, which is then pre-sintered and sintered to obtain pure-phase sodium iron pyrophosphate. The scheme of this invention, by strictly controlling the raw material mixing steps—first mixing and reacting sodium carbonate and citric acid before mixing with other raw materials for subsequent steps—effectively solves the problem of poor material performance caused by impurities in the traditional process of preparing sodium iron pyrophosphate. This results in a pure-phase sodium iron pyrophosphate cathode material with a specific capacity closer to the theoretical specific capacity and better cycle stability. The use of a dispersant in this invention not only limits the growth of precursor particles but also, as an introduced new carbon source, further improves the conductivity of the cathode material, thereby enhancing its electrochemical performance.

[0026] In addition, the raw materials of the present invention are abundant and inexpensive, and can be used in the industrial production of sodium iron pyrophosphate cathode materials to effectively utilize raw materials and reduce production costs. Moreover, since sodium carbonate reacts with citric acid first, the problem of sodium carbonate generating gas in subsequent reactions, which could pose a danger to the subsequent reaction process, can be avoided. Attached Figure Description

[0027] Figure 1 Here is a SEM image of the Na4Fe3(PO4)2P2O7 / C cathode material prepared in Example 1;

[0028] Figure 2 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 / C cathode material prepared in Example 1.

[0029] Figure 3 The charge-discharge specific capacity diagram of the Na4Fe3(PO4)2P2O7 / C cathode material prepared in Example 1 is shown.

[0030] Figure 4 The graph shows the cycling performance of the Na4Fe3(PO4)2P2O7 / C cathode material prepared in Example 1 after 200 cycles at 0.5C. Detailed Implementation

[0031] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] Example 1

[0034] A method for preparing a pure-phase sodium-ion battery cathode material Na4Fe3(PO4)2P2O7 / C includes the following steps:

[0035] S1: Weigh the raw materials according to the stoichiometric ratio: 8g sodium carbonate, 22.85g ferric phosphate, 6.05g sodium dihydrogen phosphate, 30g citric acid, and 10g polyvinyl alcohol;

[0036] S2: First, dissolve citric acid in 20ml of ethylene glycol and stir. Then, slowly add sodium carbonate (in batches over 10 minutes), ultrasonically disperse for 10 minutes, and stir at 600rpm for 3 hours to obtain slurry 1.

[0037] S3: Dissolve ferric phosphate and sodium dihydrogen phosphate in 50 ml of ethylene glycol and stir. Disperse ultrasonically for 10 min and stir at 500 rpm for 5 h to obtain slurry 2.

[0038] S3: Add slurry 1, slurry 2 and dispersant together into a ball mill jar with a ball-to-material ratio of 10:1 and a solid-liquid ratio of 45%, and ball mill at 800 rpm for 12 hours;

[0039] S4: Place the ball-milled slurry in a vacuum oven and keep it at 80℃ for 12 hours;

[0040] S5: Sieve the dried material through a 400-mesh sieve, and collect the material that passes through the sieve to obtain the precursor;

[0041] S6: The precursor was placed in a tube furnace and heated to 300℃ under a nitrogen atmosphere and held for 5 hours; then heated to 530℃ and held for 10 hours. The heating rate was always 3℃ / min during the process to obtain Na4Fe3(PO4)2P2O7 / C material.

[0042] The obtained material was characterized by SEM and XRD, and the characterization results are as follows: Figure 1 and Figure 2 As shown.

[0043] like Figure 2 The Na4Fe3(PO4)2P2O7 / C material obtained in this embodiment completely overlaps with the standard card of Na4Fe3(PO4)2P2O7, with no impurity peaks, indicating that the material prepared in this embodiment is a pure phase material.

[0044] The obtained material was subjected to electrochemical performance testing, as detailed below:

[0045] The material obtained in this embodiment was used to prepare a positive electrode slurry at a mass ratio of Na4Fe3(PO4)2P2O7 / C: conductive carbon black: binder of 7:2:1. This slurry was then coated onto aluminum foil using a doctor blade coating method. The aluminum foil coated with the positive electrode slurry was placed in an oven and dried at 80°C for 8 hours, then cut into round pieces. Using a sodium metal sheet as the counter electrode, glass fiber as the separator, and a 1 mol / L sodium perchlorate solution of ethylene carbonate (EC) and diethyl carbonate (DEC) as the electrolyte (EC to DEC volume ratio of 1:1), a coin cell was assembled in a glove box. The electrochemical performance of the assembled coin cell was tested, and the test results are as follows: Figure 3 and Figure 4 As shown.

[0046] like Figure 3 The Na4Fe3(PO4)2P2O7 / C material obtained in this embodiment has a discharge specific capacity of 109.5mAh / g at a current density of 0.5C.

[0047] like Figure 4 The Na4Fe3(PO4)2P2O7 / C material obtained in this embodiment retains 95% of its capacity after 200 charge-discharge cycles at a current density of 0.5C.

[0048] Example 2

[0049] A method for preparing a pure-phase sodium-ion battery cathode material Na4Fe3(PO4)2P2O7 / C includes the following steps:

[0050] S1: Weigh the raw materials according to the stoichiometric ratio: 8g sodium carbonate, 22.85g ferric phosphate, 6.05g sodium dihydrogen phosphate, 30g citric acid, and 10g polyvinyl alcohol;

[0051] S2: First, dissolve citric acid in 20ml of ethylene glycol and stir. Then, slowly add sodium carbonate (in batches over 10 minutes), ultrasonically disperse for 10 minutes, and stir at 600rpm for 3 hours to obtain slurry 1.

[0052] S3: Dissolve ferric phosphate and sodium dihydrogen phosphate in 50 ml of ethylene glycol and stir. Disperse ultrasonically for 10 min and stir at 500 rpm for 5 h to obtain slurry 2.

[0053] S3: Add slurry 1, slurry 2 and dispersant together into a ball mill jar with a ball-to-material ratio of 10:1 and a solid-liquid ratio of 45%, and ball mill at 800 rpm for 12 hours;

[0054] S4: Place the ball-milled slurry in a vacuum oven and keep it at 80℃ for 12 hours;

[0055] S5: Sieve the dried material through a 400-mesh sieve, and collect the material that passes through the sieve to obtain the precursor;

[0056] S6: The precursor was placed in a tube furnace and heated to 300℃ under a nitrogen atmosphere and held for 5 hours; then heated to 550℃ and held for 10 hours. The heating rate was always 3℃ / min during the process to obtain Na4Fe3(PO4)2P2O7 / C material.

[0057] The Na4Fe3(PO4)2P2O7 / C material obtained in this embodiment was tested and found to have a discharge specific capacity of 110 mAh / g at a current density of 0.5C; after 200 charge-discharge cycles at a current density of 0.5C, the capacity retention rate was 96%.

[0058] Comparative Example 1

[0059] A method for preparing Na4Fe3(PO4)2P2O7 / C, a cathode material for sodium-ion batteries, includes the following steps:

[0060] S1: Weigh the raw materials according to the stoichiometric ratio: 8g sodium carbonate, 22.85g ferric phosphate, 6.05g sodium dihydrogen phosphate, 30g citric acid, and 10g polyvinyl alcohol;

[0061] S2: Sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, citrate and polyvinyl alcohol are added to 70 ml of ethylene glycol and stirred at 500 rpm for 5 hours to obtain a slurry;

[0062] S3: Add the obtained slurry into a ball mill jar with a ball-to-material ratio of 10:1 and a solid-liquid ratio of 45%, and ball mill at 800 rpm for 12 hours.

[0063] S4: Place the ball-milled slurry in a vacuum oven and keep it at 80℃ for 12 hours;

[0064] S5: Sieve the dried material through a 400-mesh sieve, and collect the material that passes through the sieve to obtain the precursor;

[0065] S6: The precursor was placed in a tube furnace and heated to 300℃ under a nitrogen atmosphere and held for 5 hours; then heated to 530℃ and held for 10 hours. The heating rate was always 3℃ / min during the process to obtain Na4Fe3(PO4)2P2O7 / C material.

[0066] The Na4Fe3(PO4)2P2O7 / C material obtained in this comparative example was tested and found to have a discharge specific capacity of 106 mAh / g at a current density of 0.5C; after 200 charge-discharge cycles at a current density of 0.5C, the capacity retention rate was 89%.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a pure-phase sodium-ion battery cathode material, characterized in that, The positive electrode material is carbon-coated sodium iron pyrophosphate, and the chemical formula of the sodium iron pyrophosphate is: Na a Fe b (PO4) c P2O7, wherein 3≤a≤4, 2≤b≤4, and 1≤c≤3, is prepared by the following steps: S1. Weigh out sodium carbonate, ferric phosphate, sodium dihydrogen phosphate, citric acid and dispersant according to the stoichiometric ratio; S2. First, sodium carbonate and citric acid are dissolved in a solvent and reacted to obtain the first slurry; S3. Mix the first slurry, ferric phosphate, sodium dihydrogen phosphate and dispersant to obtain the second slurry; S4. Dry the second slurry to obtain the precursor; S5. The precursor is pre-sintered in a protective gas atmosphere, and then the temperature is increased to sinter it to obtain the cathode material.

2. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, In step S2, citric acid is first dissolved in a solvent, and then sodium carbonate is added in batches to the citric acid solution over 10-30 minutes to carry out the reaction.

3. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, In step S3, the first slurry, ferric phosphate, sodium dihydrogen phosphate and dispersant are mixed and ball-milled at a ball-to-material ratio of 10-20:

1.

4. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 3, characterized in that, The ball milling speed is 400-800 rpm.

5. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, In step S5, the pre-sintering temperature is 300-450℃; the sintering temperature is 500-800℃.

6. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 5, characterized in that, The heating rate for both pre-sintering and sintering is 1-10℃ / min.

7. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, The dispersant is at least one of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol.

8. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, The solvent is an alcohol-based solvent.

9. The method for preparing the pure-phase sodium-ion battery cathode material according to claim 1, characterized in that, In step S1, the raw materials are weighed according to the molar ratio of Na:Fe:P of 4:3:4 and the mass ratio of citric acid to dispersant of 2-4:

1.

10. The cathode material obtained by the preparation method according to any one of claims 1-9.

Images