Electrode material for improving consistency of sodium battery and preparation method thereof

Abstract

This invention discloses an electrode material for improving the uniformity of sodium-ion batteries and its preparation method, relating to the field of sodium-ion battery technology. The preparation method of the electrode material for improving the uniformity of sodium-ion batteries in this invention includes at least the following steps: mixing an organically coated sodium vanadium fluorophosphate composite material, polyacrylic acid-doped polyaniline, and a conductive agent to obtain the electrode material. The electrode material for sodium-ion batteries prepared by this invention exhibits good uniformity, high specific capacity, good rate performance, and excellent cycle stability, thus facilitating its application in large-scale energy storage batteries.

Description

Technical Field

[0001] This invention relates to the field of sodium battery technology, and more specifically to an electrode material for improving the consistency of sodium batteries and its preparation method. Background Technology

[0002] Since the Industrial Revolution, the global economy has experienced significant growth. However, while humanity has benefited from the rapid economic development driven by fossil fuels, overexploitation of energy has led to energy shortages, environmental pollution, and resource depletion, significantly impacting human survival and progress. Therefore, the development of new sustainable energy sources is urgently needed. Sodium-ion batteries have a similar structure and operating principle to lithium-ion batteries. These batteries function through the reversible insertion and extraction of sodium ions between the positive and negative electrodes, causing changes in electrode potential and thus enabling the charging and discharging process. This mechanism is often referred to as the "rocking chair" energy storage mechanism. The positive and negative electrodes of sodium-ion batteries are composed of two different materials capable of reversibly inserting and extracting sodium ions.

[0003] Sodium-ion batteries, as an important supplement to lithium-ion batteries, have attracted much attention due to the abundance and low cost of sodium resources. Among them, sodium vanadium fluorophosphate (NVPOF) is considered an ideal cathode material due to its stable NASICON framework structure, high operating voltage, and theoretical specific capacity. However, the core bottleneck in its industrialization lies in poor electrode consistency, specifically manifested in: uneven distribution of active materials: in traditional slurry coating processes, NVPOF particles are prone to sedimentation during drying; interface contact failure: commercial PVDF binders are insulators with excessively high modulus, failing to buffer cyclic stress and causing active material detachment; charge transport imbalance: weak bonding between the carbon coating layer and the active material interface leads to asynchronous ion / electron transport at high rates, resulting in localized polarization. From an industrialization perspective, the problem of insufficient battery consistency is amplified. This consistency defect not only increases the screening cost of battery packs but also severely restricts the application of sodium batteries in scenarios requiring long lifespan and high reliability, such as energy storage power stations. Therefore, developing an integrated technical solution that balances material synthesis uniformity and electrode interface stability has become crucial to overcoming the consistency bottleneck of sodium batteries. Summary of the Invention

[0004] The purpose of this invention is to provide an electrode material and its preparation method for improving the uniformity of sodium batteries, thereby solving the following technical problems: Existing sodium batteries suffer from poor consistency, low specific capacity, and short cycle life.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing an electrode material to improve the uniformity of sodium batteries, characterized by comprising at least the following preparation steps: Electrode materials are obtained by mixing organic-coated sodium vanadium fluorophosphate composite material, polyacrylic acid-doped polyaniline, and a conductive agent.

[0006] As a further aspect of the present invention: the mass ratio of the organic-coated sodium vanadium fluorophosphate composite material, the polyacrylic acid-doped polyaniline and the conductive agent is 7-8:1-2:1.

[0007] As a further aspect of the present invention: the preparation method of the organic-coated sodium vanadium fluorophosphate composite material includes at least the following steps: Sodium dihydrogen phosphate and sodium fluoride were added to a solution of vanadium oxalate, and ammonia was added to adjust the pH. After the reaction was completed, the solution was centrifuged, washed and dried to obtain sodium vanadium oxalate. Prepare a buffer solution containing Bis-TRIS and sodium chloride, add the sodium vanadium fluorophosphate, adjust the pH to neutral, stir, centrifuge, wash and dry, and then heat and carbonize at 600-700℃ to obtain an organically coated sodium vanadium fluorophosphate composite material.

[0008] As a further aspect of the present invention, the molar ratio of the vanadium oxalate, the sodium dihydrogen phosphate, and the sodium fluoride is 1:1.8-2.2:2.8-3.2.

[0009] As a further aspect of the present invention: the mass ratio of the tannic acid to the vanadium fluorophosphate is 0.15-0.25:1.

[0010] As a further aspect of the present invention: the method for preparing polyacrylic acid-doped polyaniline includes at least the following steps: A polyacrylic acid-hydrochloric acid solution and an aniline-hydrochloric acid solution were mixed, and ammonium persulfate was added. The mixture was reacted under nitrogen protection, and after filtration, washing, and drying, polyacrylic acid-doped polyaniline was obtained.

[0011] As a further aspect of the present invention, the mass ratio of the polyacrylic acid to the aniline is 1:14-17.

[0012] As a further aspect of the present invention: the conductive agent is one or more of conductive carbon black, carbon nanotubes, or graphene.

[0013] An electrode material for improving the consistency of sodium batteries is prepared by any one of the preparation methods described above.

[0014] The beneficial effects of this invention are: The electrode material prepared by this invention comprises an organically coated sodium vanadium fluorophosphate composite material, polyacrylic acid-doped polyaniline, and a conductive agent. Through the synergistic effect of the active material and the binder, the consistency of the sodium battery is improved. The organically coated sodium vanadium fluorophosphate composite material prepared by this invention forms a carbon layer with uniform thickness through organic coating with tannic acid followed by carbonization. This improves the material's conductivity and reduces the difference in contact resistance between particles. This uniform conductive network reduces the internal resistance dispersion of each battery cell, making electron conduction more synchronized during charging and discharging, and reducing voltage and capacity deviations. As the positive electrode active material of the sodium battery, the organically coated sodium vanadium fluorophosphate composite material exhibits improved particle size, composition, and carbon coating uniformity, reducing battery performance fluctuations caused by differences in the material itself.

[0015] This invention incorporates polyacrylic acid-doped polyaniline as a binder, which creates a synergistic effect with the active material, further enhancing consistency. The polyacrylic acid-doped polyaniline combines the strong adhesive properties of polyacrylic acid, reducing cracking caused by volume expansion during cycling, stabilizing the interface between the active material and the current collector, reducing shedding during cycling, and enhancing the conductivity of polyaniline, thereby improving the internal electron conduction of the electrode. This results in more uniform mechanical strength and conductivity across different areas of the electrode, preventing excessively fast or slow local reactions, reducing performance dispersion between batteries, and ensuring more synchronized reaction rates in different areas during charge and discharge, thus reducing the dispersion of voltage plateau and capacity retention. Simultaneously, the chemical doping of the composite binder polyacrylic acid and polyaniline leads to tighter interfacial bonding and more uniform electron transport. Detailed Implementation

[0016] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0017] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0018] The technical solution of the present invention will be further described in detail below with reference to several embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: The preparation method of the organic-coated sodium vanadium fluorophosphate composite material includes the following steps: Deionized water was placed in a beaker and heated in a water bath at 50°C with magnetic stirring. Vanadium pentoxide was dissolved in deionized water to obtain a vanadium pentoxide solution. 2.08 molar amounts of oxalic acid dihydrate of vanadium pentoxide were added. After reacting for 1 hour, 500 mL of 0.5 mol / L vanadium oxalate solution was obtained. 0.5 mol of sodium dihydrogen phosphate and 0.75 mol of sodium fluoride were weighed and added to the above vanadium oxalate solution. The pH was adjusted to neutral with 28% ammonia. The water bath temperature was set to 70°C and the reaction was carried out for 12 hours. After the reaction was completed, the reaction product was separated by centrifugation at 7000 r / min for 5 minutes. After washing and drying at 80°C, sodium vanadium oxyfluoride was obtained. NaCl was added to Bis-TRIS to prepare a 500 mL buffer solution containing 0.1 mol / L Bis-TRIS and 0.6 mol / L NaCl. Tannic acid was then added to achieve a concentration of 1.8 mg / mL. Hydrochloric acid was added to adjust the solution to neutral. 4 g of the aforementioned sodium vanadium fluorophosphate was then added and stirred. After centrifugation, the solution was washed with deionized water and vacuum-dried at 80 °C for 8 h. The solution was then heated in a tube furnace at 650 °C for 3 h. Ammonia gas was purged as a protective gas throughout the process, with a nitrogen flow rate of 10 mL / min, to obtain the organic-coated sodium vanadium fluorophosphate composite material.

[0020] Example 2: The preparation method of the organic-coated sodium vanadium fluorophosphate composite material includes the following steps: Deionized water was placed in a beaker and heated in a water bath at 50°C with magnetic stirring. Vanadium pentoxide was dissolved in deionized water to obtain a vanadium pentoxide solution. 2.08 molar amounts of oxalic acid dihydrate of vanadium pentoxide were added. After reacting for 1 hour, 500 mL of 0.5 mol / L vanadium oxalate solution was obtained. 0.5 mol of sodium dihydrogen phosphate and 0.75 mol of sodium fluoride were weighed and added to the above vanadium oxalate solution. The pH was adjusted to neutral with 28% ammonia. The water bath temperature was set to 70°C and the reaction was carried out for 12 hours. After the reaction was completed, the reaction product was separated by centrifugation at 7000 r / min for 5 minutes. After washing and drying at 80°C, sodium vanadium oxyfluoride was obtained. NaCl was added to Bis-TRIS to prepare a 500 mL buffer solution containing 0.1 mol / L Bis-TRIS and 0.6 mol / L NaCl. Tannic acid was then added to achieve a concentration of 1.8 mg / mL. Hydrochloric acid was added to adjust the solution to neutral. 5 g of the aforementioned sodium vanadium fluorophosphate was then added and stirred. After centrifugation, the solution was washed with deionized water and vacuum-dried at 80 °C for 8 h. The solution was then heated in a tube furnace at 650 °C for 3 h. Ammonia gas was purged as a protective gas throughout the process, with a nitrogen flow rate of 10 mL / min, to obtain the organic-coated sodium vanadium fluorophosphate composite material.

[0021] Example 3: The preparation method of polyacrylic acid-doped polyaniline includes the following steps: Weigh 500 mg of polyacrylic acid and dissolve it in 210 mL of 2 mol / L hydrochloric acid. Stir magnetically for 15 minutes until completely dissolved to form a homogeneous polyacrylic acid-hydrochloric acid solution. Weigh 7.5 g of aniline and dissolve it in 210 mL of 2 mol / L hydrochloric acid. Stir for 5 minutes to form an aniline-hydrochloric acid solution. Mix the above polyacrylic acid-hydrochloric acid solution and the above aniline-hydrochloric acid solution and place them at 5 °C. Add 25 g of ammonium persulfate and react for 6 h under nitrogen protection. After the reaction is complete, filter the mixture using a Buchner funnel and collect the filter cake. Wash the filter cake three times with 2 mol / L hydrochloric acid and then wash it three times with a 1:1 volume ratio ethanol-water solution. Transfer the washed filter cake to a vacuum drying oven and dry it at 60 °C for 24 h (vacuum degree ≤ -0.09 MPa) to obtain polyacrylic acid-doped polyaniline.

[0022] Example 4 A method for preparing an electrode material to improve the uniformity of sodium batteries includes the following steps: The organic-coated sodium vanadium fluorophosphate composite material prepared in Example 1, the polyacrylic acid-doped polyaniline prepared in Example 3, and conductive carbon black were mixed at a mass ratio of 7:2:1 to obtain an electrode material that improves the consistency of sodium batteries.

[0023] Example 5: A method for preparing an electrode material to improve the uniformity of sodium batteries includes the following steps: The organic-coated sodium vanadium fluorophosphate composite material prepared in Example 2, the polyacrylic acid-doped polyaniline prepared in Example 3, and conductive carbon black were mixed at a mass ratio of 7:2:1 to obtain an electrode material that improves the consistency of sodium batteries.

[0024] Example 6 A method for preparing an electrode material to improve the uniformity of sodium batteries includes the following steps: The organic-coated sodium vanadium fluorophosphate composite material prepared in Example 1, the polyacrylic acid-doped polyaniline prepared in Example 3, and conductive carbon black were mixed at a mass ratio of 8:1:1 to obtain an electrode material that improves the consistency of sodium batteries.

[0025] Example 7 A method for preparing an electrode material to improve the uniformity of sodium batteries includes the following steps: The organic-coated sodium vanadium fluorophosphate composite material prepared in Example 2, the polyacrylic acid-doped polyaniline prepared in Example 3, and conductive carbon black were mixed at a mass ratio of 8:1:1 to obtain an electrode material that improves the consistency of sodium batteries.

[0026] Compared with Example 4, Comparative Example 1 only replaced the organic-coated sodium fluorophosphate composite material prepared in Example 1 with sodium fluorophosphate prepared in Example 1 by the same mass. The remaining components and preparation methods were completely the same as those in Example 4.

[0027] Compared with Example 4, Comparative Example 2 only replaced the polyacrylic acid-doped polyaniline prepared in Example 3 with polyvinylidene fluoride (PVDF) in the same mass as in Example 4. The other components and preparation methods were completely the same as in Example 4.

[0028] Compared with Example 4, Comparative Example 3 only replaced the polyacrylic acid-doped polyaniline prepared in Example 3 with a physical mixture of polyacrylic acid and polyaniline in a mass ratio of 1:15. The remaining components and preparation methods were completely the same as in Example 4.

[0029] Performance testing Preparation of sodium batteries: Separator: The glass fiber diaphragm is cut into 18mm diameter round pieces using a mold. After drying the cut diaphragms in a vacuum drying oven at room temperature under vacuum, they are then placed in a glove box overnight.

[0030] Current collector: Cut the A1 foil current collector into strips of about 10cm x 25cm, then place them in anhydrous ethanol for ultrasonic cleaning three times, then clean them with distilled water, then soak them in oxalic acid solution, then clean them with distilled water and anhydrous ethanol, and finally soak them in ethanol solution for later use.

[0031] Gasket: Place a 16mm diameter stainless steel gasket in distilled water and anhydrous ethanol and sonicate for 10 minutes, then dry for later use.

[0032] Slurry preparation: The electrode materials obtained in Examples 4-7 and Comparative Examples 1-3 were added to the solvent NMP and magnetically stirred for 12 hours to obtain a uniform slurry.

[0033] Electrode sheet: The slurry was coated onto the current collector aluminum foil using a 200mm scraper, pre-dried using an infrared lamp, and then transferred to a vacuum drying oven at 80℃ for 12 hours. The dried electrode sheet was then cut into circular sheets using a slicing machine to obtain the positive electrode sheet. The electrode sheet diameter was 8mm, and the areal density of the positive electrode sheet was calculated to be 3.6mg / cm³. 2The negative electrode is a metal Na sheet. Since metal Na is very soft, it can be made into a negative electrode by rolling it with an iron rod in a glove box. The positive electrode and the negative electrode have the same area.

[0034] Assembly: CR-2025 type batteries were used. The batteries were assembled in a glove box filled with atmosphere (H2O and O2 were both less than 0.01ppm). The overall battery structure was as follows: positive electrode battery case - positive electrode pad assembly - positive electrode plate - separator - negative electrode plate - negative electrode pad assembly - negative electrode battery case. The electrolyte filled the positive and negative electrode plates and separator area. A 1 mol / L NaPF solution dissolved in a mixed solution of ethylene carbonate and diethyl carbonate (1:1 volume ratio) was used as the electrolyte. The electrolyte contained 5 wt% fluoroethylene carbonate (FEC) as a film-forming additive. After standing for 10 hours, subsequent electrochemical experiments were conducted.

[0035] Constant current charge-discharge testing (CCCD): CCCD is one of the fundamental testing methods in the field of electrochemistry. Its principle is to apply a constant current across the electrodes and observe the voltage change to obtain relevant information. By setting different current values, different voltage changes can be observed, thus obtaining information about the electrode's rate performance. If the voltage change curve under high current is closer to the voltage change curve under low current, it indicates better rate performance. By setting a fixed current and a certain range of charge-discharge voltage cutoff intervals, comparing the capacity changes after multiple CCCD tests yields information about the electrode material's cycle performance. If the electrode capacity is still largely maintained after multiple charge-discharge cycles, it indicates better cycle performance. In the experiments of this invention, a CT3002x multi-channel battery tester was used to test the battery's rate performance and cycle performance. In the rate performance test, the charge-discharge voltage range was set to 1.8-4.3V, and different rates were adjusted for charge-discharge. In the cycle performance test, the charge / discharge voltage range was set to 1.8-4.3V, the current ratio was 1C, and the cycle length was 500 times; the test results are shown in Table 1. Electrochemical Impedance Spectroscopy (EIS): EIS is mainly used to obtain electrochemical impedance spectroscopy. Its principle is to apply sinusoidal waves of different frequencies to the electrodes, and analyze the impedance response data to determine the physical properties of the electrode materials, such as impedance, capacitive reactance, and ion diffusion coefficient. Then, equivalent circuit simulation is used to solve for the desired physical properties. In this invention, a CHI760e electrochemical workstation was used to perform EIS on the assembled battery. The voltage for testing the EIS was set to 4.1V, the amplitude of the sinusoidal voltage was 5mV, and the frequency range of the sinusoidal voltage was 0.01Hz-100kHz; the test results are shown in Table 1. Table 1: Statistical Table of Sodium Battery Performance Test Data for Examples 4-7 and Comparative Examples 1-3

[0036] As shown in Table 1, the embodiments of the present invention, through the synergistic effect of the positive electrode material binder, outperform the comparative examples in terms of cycle stability, rate performance, and battery consistency. In Comparative Example 1, sodium vanadium fluoride phosphate was not organically coated, resulting in a decrease in the capacity retention and an increase in the interfacial impedance of the obtained sodium battery. This indicates that the carbon layer coated with the active material prepared in the present invention constructs a continuous conductive network, reducing the difference in contact resistance between particles. In Comparative Example 2, polyvinylidene fluoride was selected as the binder, and in Comparative Example 3, polyacrylic acid and polyaniline were not doped, resulting in a decrease in the performance of the obtained sodium battery. This indicates that the composite binder prepared in the present invention has both adhesive and conductive properties, avoiding uneven interfacial impedance, and the chemical doping makes the interfacial bonding tighter and the electron transport more uniform.

[0037] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing an electrode material that improves the uniformity of sodium batteries, characterized in that, It includes at least the following preparation steps: Electrode materials are obtained by mixing organic-coated sodium vanadium fluorophosphate composite material, polyacrylic acid-doped polyaniline, and a conductive agent.

2. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 1, characterized in that, The mass ratio of the organic-coated sodium vanadium fluorophosphate composite material, the polyacrylic acid-doped polyaniline, and the conductive agent is 7-8:1-2:

1.

3. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 1, characterized in that, The preparation method of the organic-coated sodium vanadium fluorophosphate composite material includes at least the following steps: Sodium dihydrogen phosphate and sodium fluoride were added to a solution of vanadium oxalate, and ammonia was added to adjust the pH. After the reaction was completed, the solution was centrifuged, washed and dried to obtain sodium vanadium oxalate. Prepare a buffer solution containing Bis-TRIS and sodium chloride, add the sodium vanadium fluorophosphate, adjust the pH to neutral, stir, centrifuge, wash and dry, and then heat and carbonize at 600-700℃ to obtain an organically coated sodium vanadium fluorophosphate composite material.

4. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 3, characterized in that, The molar ratio of the vanadium oxalate, the sodium dihydrogen phosphate, and the sodium fluoride is 1:1.8-2.2:2.8-3.

2.

5. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 4, characterized in that, The mass ratio of the tannic acid to the vanadium fluorophosphate is 0.15-0.25:

1.

6. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 1, characterized in that, The method for preparing polyacrylic acid-doped polyaniline includes at least the following steps: A polyacrylic acid-hydrochloric acid solution and an aniline-hydrochloric acid solution were mixed, and ammonium persulfate was added. The mixture was reacted under nitrogen protection, and after filtration, washing, and drying, polyacrylic acid-doped polyaniline was obtained.

7. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 6, characterized in that, The mass ratio of the polyacrylic acid to the aniline is 1:14-17.

8. The method for preparing an electrode material to improve the uniformity of sodium batteries according to claim 1, characterized in that, The conductive agent is one or more of conductive carbon black, carbon nanotubes, or graphene.

9. An electrode material for improving the uniformity of sodium batteries, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

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