Preparation method of modified sodium vanadium phosphate positive electrode material

Abstract

This invention relates to the field of sodium-ion battery technology and discloses a method for preparing a modified sodium vanadium phosphate cathode material, comprising the following steps: Step 1: Add 1-4g of ammonium metavanadate and 0.8-2.6g of oxalic acid to 50-200mL of deionized water, stir and react at 60-120℃ for 20-80min, and after slight cooling, add sodium phosphate; after stirring, add cobalt sulfate heptahydrate, and then dry and grind the solution to obtain precursor powder. Step 2: Calcine the precursor powder in a high-temperature tubular furnace at 600-1200℃ for 8-24h to obtain the modified sodium-ion battery cathode material powder. This invention uses a chemical synthesis method to prepare the precursor and employs an energy-saving calcination process to prepare a cobalt particle-filled sodium vanadium phosphate cathode material for the first time. This process has the advantages of mild reaction conditions, high product purity, good particle size uniformity, and easy control of the proportion of each component, and can be continuously prepared and synthesized in large quantities.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a method for preparing a modified sodium vanadium phosphate cathode material. Background Technology

[0002] With the ever-increasing energy demands of human production and daily life, the massive consumption of fossil fuels such as oil and coal and their environmental pollution have limited the development of the energy sector. Therefore, future energy storage technologies are increasingly leaning towards sustainable and low-cost battery processes. In recent years, the rise of new energy vehicles and energy storage devices has led to excessive consumption of lithium resources, making the search for a rechargeable battery to replace lithium-ion batteries extremely important. Sodium and lithium belong to the same group of elements, sharing similar physical and chemical properties, while sodium resources are more abundant and less expensive than lithium resources. Therefore, sodium-ion batteries are gradually coming into focus and are considered one of the most promising alternatives to lithium-ion batteries.

[0003] Na3V2(PO4)3 of the NASICON type has advantages such as high voltage plateau, high ion diffusion rate and stable crystal structure, and is one of the candidate materials for future commercial sodium-ion batteries. However, the low intrinsic electronic conductivity, high price and toxicity of Na3V2(PO4)3 (hereinafter referred to as NVP) limit its industrial development. At present, the modification methods of NVP mainly focus on its poor conductivity, mainly in the following three aspects: (1) increasing the electronic conductivity of the material through carbon coating; (2) improving the intrinsic conductivity of the material through metal ion doping; (3) improving the electrochemical performance of the material through nanofabrication and special shape preparation. The traditional doping strategy of NVP materials is mainly to dope transition metal atoms to replace Na(1) and V sites, which can significantly increase the atomic lattice spacing, improve the voltage plateau, and improve the conductivity and theoretical specific capacity of the material. Therefore, metal element doping is considered an effective modification strategy.

[0004] While metal doping can improve specific capacity and stability to some extent, the energy density of sodium batteries is still far behind that of mature lithium-ion batteries. This is mainly because doping cannot effectively stimulate the performance of the non-potential polymer (NVP), failing to activate all sodium sites and maintain NVP stability, which greatly limits the practical application of this material. Secondly, different battery applications require materials to function well even at extreme temperatures, necessitating good structural stability to maintain good specific capacity and energy density. Most importantly, achieving fast charging while ensuring the lifespan of battery materials places high demands on the materials themselves. Therefore, it is essential to develop new NVP cathode material modification strategies to improve the overall performance of NVP materials at both room temperature and extreme temperatures, thereby promoting the practical application of sodium-ion batteries. Summary of the Invention

[0005] To address the technical problems mentioned in the background section, this invention provides a method for preparing a modified sodium vanadium phosphate cathode material.

[0006] This invention is achieved using the following technical solution: a method for preparing a modified sodium vanadium phosphate cathode material, comprising the following steps:

[0007] Step 1: Add 1-4g of ammonium metavanadate and 0.8-2.6g of oxalic acid to 50-200mL of deionized water. Stir and react at 60-120℃ for 20-80min. After slightly cooling, add sodium phosphate. After stirring, add cobalt sulfate heptahydrate. Then, dry the solution and grind it to obtain the precursor powder.

[0008] Step 2: Place the precursor powder in a high-temperature tubular calcination furnace and calcine it at a constant temperature of 600-1200℃ for 8-24 hours to obtain the modified sodium-ion battery cathode material powder.

[0009] Optionally, the ammonium metavanadate can be replaced with any one or a combination of at least two of sodium vanadate, sodium metavanadate, ammonium metavanadate, and vanadium pentoxide, and the proportions can be appropriately adjusted to achieve large-scale synthesis.

[0010] Optionally, the sodium phosphate may be replaced with any one or a combination of at least two of phosphoric acid, sodium phosphate, sodium metaphosphate, or sodium dihydrogen phosphate. Typical but non-limiting examples of such combinations include combinations of phosphoric acid and sodium phosphate, and combinations of sodium phosphate and sodium dihydrogen phosphate.

[0011] Optionally, the molar ratio of ammonium metavanadate, sodium phosphate, and oxalic acid is (1.5~6):(2.5~4.5):(3.0~5.5).

[0012] Optionally, after step 2, the following steps are also included: after taking out the sample, grind it thoroughly and wash and centrifuge it to remove the influence of impurities; when washing the sample, first place the sample powder in a centrifuge tube, add an appropriate amount of ethanol, sonicate it, set the speed to 12000 r / min, and the time to 5 min, and then dry and collect it.

[0013] A method for preparing an electrode includes the following steps: adding positive electrode active material (sodium vanadium phosphate powder prepared by any of the methods of claims 1-2), conductive black, and polyvinylidene fluoride (PVDF) in a mortar at a mass ratio of 8:1:1 and grinding for 20 minutes to make it uniform; then adding an appropriate amount of N-methylpyrrolidone (NMP) and grinding to form a uniform slurry; stirring the slurry in a vacuum mixer; then transferring the slurry to a ball mill and grinding it thoroughly at a speed of 100-400 r / min for 30 minutes; then coating the obtained slurry onto the surface of an aluminum foil and drying it to obtain a working electrode; and the electrode coating thickness is 10-30 μm.

[0014] A battery assembly method includes the following steps: assembling a sodium-ion battery in a glove box filled with argon atmosphere, then placing a positive electrode shell, a positive electrode sheet, adding an appropriate amount of electrolyte, then placing a separator, a sodium sheet, a stainless steel gasket, a spring sheet, and a negative electrode shell, and then using a start-up sealing machine to press and seal the battery.

[0015] Optionally, the positive electrode is a circular piece with a diameter of 12 mm made from the working electrode as described in claim 3.

[0016] Optionally, the active material loading of the electrode sheet is 1.5-1.7 mg / cm³. -2 .

[0017] Optionally, the glove box contains less than 0.01 ppm of water and less than 0.01 ppm of oxygen. During assembly, the electrolyte is a 1 mol / L NaClO4 solution, and 150 μL is added. The diaphragm is a glass fiber diaphragm with a specification of GF / D, and it is finally sealed using a pressure sealing machine.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention uses a chemical synthesis method to prepare the precursor and employs an energy-saving calcination process to prepare cobalt particle-filled sodium vanadium phosphate cathode material for the first time. This process has the advantages of mild reaction conditions, high product purity, good particle size uniformity, and easy control of the proportion of each component. It can be continuously prepared and synthesized in large quantities.

[0020] The cobalt particle-filled sodium vanadium phosphate (NVP) battery cathode material prepared by this invention simultaneously expands the sodium ion transport channels and improves conductivity, thereby improving the charge-discharge specific capacity and cycle stability of the NVP cathode material, providing new ideas and solutions for the further commercial application of sodium-ion batteries in the future. Attached Figure Description

[0021] Figure 1 This is a comparison of X-ray diffraction (XRD) images of the Co-NVP and NVP cathode materials prepared in this invention.

[0022] Figure 2 This is a scanning electron microscope (SEM) image of the Co-NVP cathode material prepared in this invention.

[0023] Figure 3 This is a comparison of the cyclic voltammetry (CV) curves of a sodium-ion battery using the Co-NVP cathode material prepared in this invention and a sodium-ion battery using conventional NVP materials at a scan rate of 0.2 mV / s.

[0024] Figure 4 X-ray photoelectron spectroscopy (XPS) of the Co-NVP cathode material prepared by this invention.

[0025] Figure 5 This is a charge-discharge curve of a sodium-ion battery using the Co-NVP cathode material prepared in this invention at a 0.2C rate.

[0026] Figure 6 This is a graph showing the long-cycle performance of a sodium-ion battery using the Co-NVP cathode material prepared in this invention at a 10C rate.

[0027] Figure 7 This is a rate performance diagram of a sodium-ion battery using the Co-NVP cathode material prepared in this invention at 1-50C.

[0028] Figure 8 This is a photograph of the appearance of a pouch cell assembled from the Co-NVP cathode material prepared in this invention.

[0029] Figure 9 This refers to the cycle performance of a pouch cell assembled with the Co-NVP cathode material prepared in this invention at a 5C rate.

[0030] Figure 10 This is a rate performance diagram of a soft-pack battery assembled with the Co-NVP cathode material prepared in this invention at 0.2-10C. Detailed Implementation

[0031] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0032] The chemical reagents used in this invention are all analytical grade ammonium metavanadate, sodium phosphate, oxalic acid, and cobalt sulfate heptahydrate. The purity of the inert gas (argon) used in step 1 is 99.999%. The aluminum foil and diaphragm used in step 2 were purchased from Suzhou Duoduo Chemical Technology Co., Ltd.

[0033] Example 1:

[0034] Step 1: Weigh ammonium metavanadate, sodium phosphate, oxalic acid, and cobalt sulfate heptahydrate according to the stoichiometric ratio. Add 1-4g of ammonium metavanadate and 0.8-2.6g of oxalic acid to 50-200mL of deionized water. Stir and react at 60-120℃ for 20-80min. After slight cooling, add sodium phosphate. After stirring, add cobalt sulfate heptahydrate. Then, dry the solution and grind it to obtain the precursor powder. Calcinate the precursor powder in a high-temperature tubular furnace at 600-1200℃ for 8-24h. This is the modified sodium-ion battery cathode material powder. After the sample is removed, grind it thoroughly and wash and centrifuge it to remove the influence of impurities. For washing, first place the sample powder in a centrifuge tube, add an appropriate amount of ethanol, sonicate, set the speed to 12000r / min, and the time to 5min, then dry and collect.

[0035] Step 2, preparation of electrode materials: Positive electrode active material, conductive black, and polyvinylidene fluoride (PVDF) are added to a mortar in a mass ratio of 8:1:1 and ground for 20 minutes to ensure uniformity. Then, an appropriate amount of N-methylpyrrolidone (NMP) is added and ground to form a uniform slurry. The resulting slurry is then coated onto an aluminum foil surface and dried to obtain the working electrode. This electrode is then formed into a circular electrode sheet with a diameter of 12 mm using a stamping machine. The active material loading of the electrode sheet is 1.5-1.7 mg / cm³. -2 .

[0036] Step 3, Sodium-ion battery assembly: The sodium-ion battery is assembled in a glove box filled with an argon atmosphere, where the water content is less than 0.01 ppm and the oxygen content is less than 0.01 ppm. During assembly, the positive electrode sheet prepared in Step 2 is placed in the positive battery casing, and 150 μL of sodium perchlorate electrolyte is added. The separator is a glass fiber separator, and the electrolyte is a 1M NaClO4 solution. The glove box is finally sealed using a pressure sealing machine. The prepared positive electrode material powder is subjected to phase and purity characterization tests, such as X-ray diffraction for phase analysis and X-ray photoelectron spectroscopy to determine the structure and distribution of each component in the analyte. After activation, the prepared battery is tested for electrochemical performance. The first three charge-discharge currents during activation are 0.2C, and then the test is performed at 1C, where 1C = 117.6 mAh / g, and the test voltage range is 2.3~4.2V. The initial charge-discharge curve of the material at 0.2C current is shown below. Figure 4 As shown, the long-cycle performance at 2200 cycles with a 10C magnification is as follows: Figure 5 As shown, the cyclic voltammetry curves at a scan rate of 0.2 mV / s are as follows: Figure 6 As shown, the rate performance at 1C~100C is as follows: Figure 7 As shown.

[0037] It can be seen that the initial discharge specific capacity of the sodium-ion battery modified with cobalt particles can reach 132.6 mAh / g. At a 10C rate, after 5000 charge-discharge cycles, the reversible discharge specific capacity of Co-NVP increases from 118.6 mAh / g. -1 Reduced to 113.3 mAh g -1 The capacity retention rate was 95.53%, demonstrating good long-term cycle stability under high current density. Furthermore, the pouch cell prepared after large-scale synthesis of positive electrode active materials successfully generated electricity and exhibited excellent cycle stability and rate performance.

[0038] Step 4, Assembly of the Soft-Pack Battery: First, the positive electrode sheet is prepared by mixing sodium vanadium phosphate powder, conductive carbon black, and polyvinylidene fluoride (PVDF) powder in a ratio of 8:1:1, with an appropriate amount of N-methylpyrrolidone (NMP). The mixture is then stirred in a vacuum mixer for 30 minutes to form a slurry. This slurry is then transferred to a ball mill and ground thoroughly at 300 rpm for 30 minutes, uniformly coating the slurry onto aluminum foil. After drying, the positive electrode sheet is cut into 4356 mm diameter pieces using a cutting machine. The sheet is then pulled between rotating rollers using the friction between the rollers, with a rolling thickness of 0.07 mm. Appropriate compaction density can increase the battery's discharge capacity, reduce internal resistance, reduce polarization loss, extend battery cycle life, and improve the utilization rate of lithium-ion batteries. After compaction, tabs are welded onto the electrode sheet, and an aluminum-plastic film punching machine is used to punch out aluminum-plastic film indentations that meet the battery dimensions. Secondly, the negative electrode is prepared according to a ratio of hard carbon: conductive carbon: polyvinylidene fluoride (PVDF) powder of 8:1:1. Except for the elimination of the ball milling step, all other steps are the same as described above. The negative electrode has a diameter of 4558 mm. After approximately 4 hours of pre-sodiumization, the negative electrode, separator, and positive electrode are stacked in an argon-filled glove box on a perforated aluminum-plastic film in that order. An appropriate amount of 1M NaClO4 solution is added, and top and side sealing processes are performed, completing the encapsulation. A photograph of the assembled pouch battery is shown below. Figure 8 As shown. The prepared battery underwent electrochemical performance testing after activation. During activation, the charge / discharge current for the first three cycles was 0.2C, and the test voltage range was 2.5~3.5V. The cycle performance after 100 charge / discharge cycles at 5C and the rate performance at 0.2-10C are shown below. Figure 9 As shown.

[0039] Results analysis:

[0040] As attached Figure 1As shown, X-ray diffraction was used to analyze the phase composition of the prepared cathode material, and the diffraction peaks obtained corresponded one-to-one with the standard card of NVP (JCPDS No. 53-0018). This indicates that the synthesized novel cathode material does not affect the integrity of the NVP crystal structure, and all are hexagonal NASICON structures without impurities. Furthermore, the diffraction peaks of the Co-NVP material contain peaks that match those of elemental cobalt (standard card PDF#89-7093), indicating that cobalt exists in elemental form in the synthesized NVP material.

[0041] As attached Figure 2 As shown in the aberration-corrected electron microscopy images, the cobalt particles are present on the surface or edges of the NVP material, rather than as independent particles, indicating that the cobalt particles have been successfully modified onto the NVP material.

[0042] As attached Figure 3 The figure shows a comparison of the cyclic voltammetry (CV) curves of sodium-ion batteries prepared with the modified cathode material of this invention and those prepared with traditional NVP materials at a scan rate of 0.2 mV / s. It can be seen that, compared with traditional NVP materials, both exhibit redox peaks around 3.4 V (corresponding to V...). 3+ / V 4+ The conversion potential of Co-NVP materials is approximately 3.9V, and this redox peak corresponds to a V0. 4+ / V 5+ The redox conversion indicates that the introduction of cobalt particles successfully activated V5+.

[0043] As attached Figure 4 As shown, X-ray photoelectron spectroscopy (XPS) analysis clearly shows that when Co-NVP is charged to the cutoff voltage, part of the V... 4+ Convert to V 5+ This indicates that the introduction of cobalt particles successfully activated multi-electron conversion, further improving the transport efficiency of sodium ions and enhancing the electrochemical performance of the NVP material. This result is also consistent with... Figure 3 The CV analysis graph in the figure is consistent.

[0044] As attached Figure 5 The figure shows the initial charge-discharge curve at 0.2C. As can be seen from the figure, this material exhibits the typical charge-discharge plateau curve characteristic of sodium-ion batteries. The initial discharge specific capacity of the sodium-ion battery modified with cobalt particles can reach 132.6 mAh / g, while the initial discharge specific capacity of the sodium-ion battery prepared with traditional NVP cathode material is only 116.5 mAh / g.

[0045] As attached Figure 6As shown, cycling performance was tested at a 10C rate. After 5000 cycles, the reversible discharge specific capacity of Co-NVP decreased from 118.6 mAh / g to 113.3 mAh / g, with a capacity retention of 95.53%, demonstrating good long-term cycling stability under high current density.

[0046] As attached Figure 7 As shown, the discharge specific capacities of the examples after 10 cycles at rates of 1C, 2C, 5C, 10C, 20C, 30C, and 50C were 129.56 mAh / g, 127.35 mAh / g, 125.73 mAh / g, 123.78 mAh / g, 120.87 mAh / g, 117.92 mAh / g, and 112.56 mAh / g, respectively. When the current was restored to 1C, the capacity recovered to 128.54 mAh / g, with a capacity retention rate of 99.21%. This fully demonstrates the excellent rate performance of the modified sodium-ion battery.

[0047] As attached Figure 8 , 9 As shown in Figure 10, the pouch battery prepared after synthesizing a large amount of positive electrode active material can successfully generate electricity. Moreover, after 100 cycles at a 5C rate, the discharge specific capacity only decreases from 104.25 mAh / g to 101.30 mAh / g. The discharge specific capacities after 5 cycles at each of the 0.2C, 0.5C, 1C, 2C, 5C, and 10C rates are 134.4 mAh / g, 129.5 mAh / g, 125.2 mAh / g, 118.3 mAh / g, 104.6 mAh / g, and 87.6 mAh / g, respectively. This indicates that it has excellent cycle stability and rate performance, verifying its great potential for practical production applications.

[0048] Therefore, the experimental data show that the modified cathode material in the examples significantly outperforms the comparative example in terms of discharge specific capacity, cycle performance, rate performance, and reaction kinetics in sodium-ion batteries, exhibiting better electrochemical performance and great development potential.

[0049] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a modified sodium vanadium phosphate cathode material, characterized in that, Includes the following steps: Step 1: Add 1-4g of component A and 0.8-2.6g of oxalic acid to 50-200mL of deionized water, stir and react at 60-120℃ for 20-80min, cool and add component B; after stirring, add cobalt sulfate heptahydrate, then dry the solution and grind it to obtain precursor powder; Step 2: Place the precursor powder in a high-temperature tubular furnace and calcine it at a constant temperature of 600-1200℃ for 8-24 hours to obtain the modified sodium vanadium phosphate cathode material. Component A is selected from any one or a combination of at least two of sodium vanadate, sodium metavanadate, ammonium metavanadate, and vanadium pentoxide. Component B is selected from any one or a combination of at least two of the following: phosphoric acid, sodium phosphate, sodium metaphosphate, or sodium dihydrogen phosphate. The molar ratio of component A, component B, and oxalic acid is (1.5~6):(2.5~4.5):(3.0~5.5).

2. The method for preparing a modified sodium vanadium phosphate cathode material as described in claim 1, characterized in that, After step 2, the following steps are also included: after taking it out, grind it thoroughly and wash and centrifuge it to remove the influence of impurities; when washing the sample, first put the sample powder into a centrifuge tube, add an appropriate amount of ethanol, sonicate it, set the speed to 12000 r / min, the time to 5 min, and then dry and collect it.

3. A method for preparing an electrode, characterized in that, The process includes the following steps: adding sodium vanadium phosphate powder, conductive black, and polyvinylidene fluoride prepared by the method described in claim 1 to a mortar in a mass ratio of 8:1:1 and grinding for 20 minutes to make the powder uniform; then adding an appropriate amount of N-methylpyrrolidone and grinding to form a uniform slurry; stirring the slurry in a vacuum mixer; then transferring the slurry to a ball mill and grinding for 30 minutes at a speed of 100-400 r / min; then coating the resulting slurry onto the surface of an aluminum foil and drying it to obtain a working electrode; and the electrode coating thickness is 10-30 μm.

4. A method for assembling a battery, characterized in that, The process includes the following steps: assembling a sodium-ion battery in a glove box filled with argon atmosphere, then sequentially placing the positive electrode shell, positive electrode plate, adding an appropriate amount of electrolyte, then placing the separator, sodium plate, stainless steel gasket, spring sheet, and negative electrode shell, and then using a start-up sealing machine to press and seal the battery. The positive electrode is a working electrode prepared by the electrode preparation method described in claim 3 and then cut into a circular piece with a diameter of 12 mm.

5. The battery assembly method as described in claim 4, characterized in that, The active material loading of the positive electrode is 1.5-1.7 mg / cm³. -2 .

6. The battery assembly method as described in claim 4, characterized in that, The glove box contains less than 0.01 ppm of water and less than 0.01 ppm of oxygen. During assembly, the electrolyte is a 1 mol / L NaClO4 solution, and the amount added is 150 μL. The diaphragm is a glass fiber diaphragm with a specification of GF / D, and it is finally sealed using a pressure sealing machine.

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