Preparation method of sodium iron phosphate pyrophosphate positive electrode material

Abstract

This invention belongs to the field of battery technology and relates to a method for preparing sodium iron pyrophosphate cathode material. This invention obtains high-compact sodium iron pyrophosphate cathode material by treating particles of different sizes at different high temperatures, thus significantly improving the energy density of the battery through a simple process. Furthermore, the preparation method of this invention is environmentally friendly, simple to operate, produces products with good consistency and repeatability, and is easy to scale up for mass production, allowing for the simple preparation of high-compact materials.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a method for preparing sodium iron pyrophosphate cathode material. Background Technology

[0002] Sodium-ion battery cathode materials mainly include phosphoric acid systems and metal oxide materials. Among them, phosphoric acid system batteries have high capacity, stable structure, and the material structure remains stable even under overcharging or high temperature conditions, exhibiting excellent safety and electrochemical stability. However, the low energy density greatly limits its application.

[0003] Therefore, using high-compaction sodium iron pyrophosphate cathode material is a good approach. Currently, commercially available sodium iron pyrophosphate cathode materials require increased compaction to improve the areal loading of the electrode and increase the energy density of the battery.

[0004] A good solution to improve the energy density of sodium iron pyrophosphate is to increase the compaction density of the cathode material. Currently, the commonly used methods for preparing this material have high environmental protection requirements, are complex to operate, difficult to control, costly, and have poor material repeatability. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the existing technology by providing a method for preparing sodium iron pyrophosphate cathode material that is simple in process, economical and environmentally friendly, low in cost, and can significantly improve the energy density of the battery.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a sodium iron pyrophosphate cathode material, the method comprising the following steps:

[0008] S1. Sodium source, phosphorus source, iron source and carbon source are uniformly mixed and then subjected to high temperature treatment in batches, and then dried separately to obtain granular material.

[0009] S2. Then, pre-treat different batches of granular material separately;

[0010] S3. Then, the pre-treated granules from different batches are mixed evenly, pressed into compacts, and finally sintered at high temperature.

[0011] In the above-mentioned method for preparing a sodium iron pyrophosphate cathode material, the high-temperature treatment temperature in step S1 is 150-250℃, and the high-temperature treatment time for each batch is n×(8-15)h; where n is the number of batches, specifically 2-4.

[0012] This invention achieves uniform grain growth by maximally controlling the reaction rate at a high-temperature treatment temperature of 150-250℃. Excessive reaction temperature leads to overly rapid crystal growth, excessively large average grain size, and an overly wide grain size distribution; conversely, insufficient temperature prevents complete crystallization. Furthermore, controlling the reaction time controls grain size, as the grain size gradually increases with prolonged hydrothermal reaction time. Additionally, the purity of the product phase increases, and its crystallinity improves.

[0013] In the above-mentioned method for preparing sodium iron pyrophosphate cathode material, the particle size of different batches of granules exhibits a gradient distribution.

[0014] This invention significantly improves the compaction density of materials by mixing different batches of granular materials with a gradient particle size distribution, ultimately increasing the energy density of the battery cell.

[0015] In the above-mentioned method for preparing sodium iron pyrophosphate cathode material, the particle size of the granules is 0.1-1.0 μm.

[0016] In the above-mentioned method for preparing a sodium iron pyrophosphate cathode material, in step S1, the sodium source is sodium carbonate, the phosphorus source is ammonium dihydrogen phosphate, the iron source is ferrous oxalate, and the carbon source is glucose.

[0017] In the above-mentioned method for preparing a sodium iron pyrophosphate cathode material, the pretreatment temperature in step S2 is 320-380℃ and the time is 5-6h.

[0018] In the above-mentioned method for preparing sodium iron pyrophosphate cathode material, the mixing mass ratio of different batches of pretreated granules is 1-1.5:1-3. By controlling the mixing mass ratio of different batches of pretreated granules to 1-1.5:1-3, this invention ensures a uniform distribution of particle size in the final cathode material, thereby improving material compaction.

[0019] In the above-mentioned method for preparing a sodium iron pyrophosphate cathode material, the pressure during step S3 pressing is 1-2 MPa and the holding time is 0.5-1.5 min.

[0020] In the above-mentioned method for preparing a sodium iron pyrophosphate cathode material, the high-temperature sintering temperature is 700-740℃, and the time is 5-8 hours. This invention maximizes battery performance by controlling the sintering temperature to 700-740℃; however, excessively high temperatures can lead to material structure damage and reduced battery life.

[0021] The present invention also provides a sodium-ion battery comprising the sodium iron pyrophosphate cathode material prepared by the above preparation method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention obtains a high-pressure compacted sodium iron pyrophosphate cathode material by preparing granules of different particle sizes through different high-temperature treatments. This high-pressure compacted sodium iron pyrophosphate cathode material greatly improves the energy density of the battery through a simple process.

[0024] 2. The preparation method of sodium iron pyrophosphate cathode material of the present invention is environmentally friendly, simple to operate, and produces products with good consistency and repeatability, which is convenient for large-scale production and can easily realize the preparation of high-compaction materials. Attached Figure Description

[0025] Figure 1 These are electron microscope comparison images of the sodium iron pyrophosphate cathode materials obtained in Examples 1-5 of this invention;

[0026] Figure 2 This is a comparison chart of the cycle performance of the sodium iron pyrophosphate cathode material obtained in Example 2 of the present invention. Detailed Implementation

[0027] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0028] Example 1:

[0029] S1. 5.365 kg of sodium carbonate, 3.596 kg of ferrous oxalate, 3.727 kg of ammonium dihydrogen phosphate, and 1.015 kg of glucose were placed in a hydrothermal reaction chamber and kept at 185°C in batches for 10 h and 20 h to obtain a precursor with an average particle size of 0.85 μm and a precursor with an average particle size of 0.55 μm.

[0030] S2. Pre-treat the precursors with an average particle size of 0.85 μm and 0.55 μm at 350 °C for 5 h respectively.

[0031] S3. Then, the precursor with an average particle size of 0.85 μm and the precursor with an average particle size of 0.55 μm are uniformly mixed and ground at a mass ratio of 1:1.5, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720°C for 6 hours.

[0032] Example 2:

[0033] S1. 5.365 kg of sodium carbonate, 3.596 kg of ferrous oxalate, 3.727 kg of ammonium dihydrogen phosphate, and 1.015 kg of glucose were placed in a hydrothermal reaction chamber at 185 °C and kept in batches for 10 h and 30 h to obtain a precursor with an average particle size of 0.85 μm and an average particle size of 0.35 μm.

[0034] S2. Pre-treat the precursors with an average particle size of 0.85 μm and 0.35 μm at 350 °C for 5 h respectively.

[0035] S3. Then, the precursor with an average particle size of 0.85 μm and the precursor with an average particle size of 0.35 μm are uniformly mixed and ground at a mass ratio of 1:1.5, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720°C for 6 hours.

[0036] Example 3:

[0037] S1. 5.365 kg of sodium carbonate, 3.596 kg of ferrous oxalate, 3.727 kg of ammonium dihydrogen phosphate, and 1.015 kg of glucose were placed in a hydrothermal reaction chamber at 185 °C and kept in batches for 10 h and 40 h to obtain a precursor with an average particle size of 0.85 μm and an average particle size of 0.2 μm.

[0038] S2. Pre-treat the precursors with an average particle size of 0.85 μm and 0.2 μm at 350 °C for 5 h respectively.

[0039] S3. Then, the precursor with an average particle size of 0.85 μm and the precursor with an average particle size of 0.2 μm are uniformly mixed and ground at a mass ratio of 1:1.5, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720 °C for 6 h.

[0040] Example 4:

[0041] S1. 5.365 kg of sodium carbonate, 3.596 kg of ferrous oxalate, 3.727 kg of ammonium dihydrogen phosphate, and 1.015 kg of glucose were placed in a hydrothermal reaction chamber and kept in batches at 185°C for 20 h and 30 h respectively to obtain a precursor with an average particle size of 0.55 μm and a precursor with an average particle size of 0.35 μm.

[0042] S2. Pre-treat the precursors with an average particle size of 0.55 μm and 0.35 μm at 350 °C for 5 h respectively.

[0043] S3. Then, the precursor with an average particle size of 0.55 μm and the precursor with an average particle size of 0.35 μm are uniformly mixed and ground at a mass ratio of 1:1.5, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720℃ for 6 hours.

[0044] Example 5:

[0045] S1. 5.365 kg of sodium carbonate, 3.596 kg of ferrous oxalate, 3.727 kg of ammonium dihydrogen phosphate, and 1.015 kg of glucose were placed in a hydrothermal reaction chamber at 185 °C and kept in batches for 20 h and 40 h to obtain a precursor with an average particle size of 0.55 μm and an average particle size of 0.2 μm.

[0046] S2. Pre-treat the precursors with an average particle size of 0.55 μm and 0.2 μm at 350 °C for 5 h respectively.

[0047] S3. Then, the precursor with an average particle size of 0.55 μm and the precursor with an average particle size of 0.2 μm are uniformly mixed and ground at a mass ratio of 1:1.5, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720 °C for 6 h.

[0048] Comparative Example 1:

[0049] The difference from Example 1 is that the precursor with an average particle size of 0.85 μm was directly ground, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720°C for 6 hours.

[0050] Comparative Example 2:

[0051] The difference from Example 1 is that the precursor with an average particle size of 0.55 μm was directly ground, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720°C for 6 hours.

[0052] Comparative Example 3:

[0053] The only difference from Example 2 is that the precursor with an average particle size of 0.35 μm was directly ground, pressed into a compact under a pressure of 5.5 MPa, and finally sintered at 720°C for 6 hours.

[0054] Comparative Example 4:

[0055] The only difference from Example 1 is that the sintering temperature in step S3 is 800°C.

[0056] Comparative Example 5:

[0057] The only difference from Example 1 is that the sintering temperature in step S3 is 600°C.

[0058] Table 1: Test results of compaction density of sodium iron pyrophosphate cathode materials prepared in Examples 1-5 and Comparative Examples 1-5

[0059] Example <![CDATA[Compaction density g / cm 3 > Example 1 2.21 Example 2 2.32 Example 3 2.28 Example 4 2.34 Example 5 2.38 Comparative Example 1 2.01 Comparative Example 2 2.11 Comparative Example 3 2.16 Comparative Example 4 2.06 Comparative Example 5 2.04

[0060] Figure 1These are electron microscope (EM) comparison images of the sodium iron pyrophosphate cathode materials obtained in Examples 1-5 of this invention. As can be seen from the images, all examples yielded cathode materials with particles of varying sizes. However, in Example 1, the larger particles were too large, resulting in a less than ideal compaction density. Example 5, on the other hand, achieved a well-balanced particle size distribution, effectively filling the gaps between particles and significantly improving compaction.

[0061] The batteries assembled in Examples 1-5 were tested for charge / discharge capacity and rate performance within a voltage range of 1.5-4.1V. Their 1C cycle data are as follows: Figure 2 As shown, the initial discharge specific capacity at 0.1C is 81.7 mAh g. -1 85.1mAh g -1 82.5mAh g -1 94.6mAh g -1 95.6mAh g -1 After 178 cycles, the capacity was 64.9 mAh g. -1 76.1mAh g -1 75.4mAh g -1 83.3mAh g -1 88.3mAh g -1 .

[0062] In summary, this invention obtains a high-pressure compacted sodium iron pyrophosphate cathode material by preparing granules of different particle sizes through different high-temperature treatments. This significantly improves the energy density of the battery through a simple process.

[0063] The embodiments described herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0064] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0065] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing a sodium iron pyrophosphate cathode material, characterized in that, The method includes the following steps: S1. Sodium source, phosphorus source, iron source and carbon source are uniformly mixed and then subjected to high temperature treatment in batches, and then dried separately to obtain granular material. S2. Then, pre-treat different batches of granular material separately; S3. Then, the pre-treated granules from different batches are mixed evenly, pressed into compacts, and finally sintered at high temperature. Step S1 involves high-temperature treatment at 150-250℃, with each batch undergoing high-temperature treatment for n×(8-15)h; where n is the number of batches, specifically 2-4. The particle size of the granules varies from batch to batch, ranging from 0.1 to 1.0 μm. In step S2, the pretreatment temperature is 320-380℃ and the time is 5-6 hours; The mixing mass ratio of pretreated granules from different batches is 1-1.5:1-3; The high-temperature sintering treatment is carried out at a temperature of 700-740℃ for 5-8 hours.

2. The method for preparing a sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In S1, the sodium source is sodium carbonate, the phosphorus source is ammonium dihydrogen phosphate, the iron source is ferrous oxalate, and the carbon source is glucose.

3. The method for preparing a sodium iron pyrophosphate cathode material according to claim 1, characterized in that, In step S3, the pressure during the pressing process is 1-2 MPa, and the holding time is 0.5-1.5 min.

4. A sodium-ion battery, characterized in that, This includes the sodium iron pyrophosphate cathode material prepared by the preparation method described in claim 1.

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