Sodium-ion battery positive electrode material as well as coating modification method and application thereof

Abstract

The invention relates to the technical field of energy storage materials, and discloses a sodium ion battery positive electrode material and a coating modification method and application thereof, the coating modification method comprises the following steps: S1, dissolving carbon quantum dots and a conductive polymerizable monomer in an acidic buffer solution with a pH value of 2-4 to form a dispersion liquid; and S2, mixing the sodium-ion battery positive electrode material with the dispersion liquid, performing ultrasonic treatment, adding an oxidizing agent, performing polymerization reaction under ultraviolet irradiation, and curing after the reaction is finished, thereby obtaining the coated and modified sodium-ion battery positive electrode material. The carbon quantum dots are combined with the conductive polymerizable monomer, so that the conductivity, the cycling stability and the high-temperature stability of the positive electrode material are improved; meanwhile, the method replaces a traditional complex process, energy consumption is reduced by initiating polymerization reaction through ultraviolet light, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of energy storage materials technology, specifically to a sodium-ion battery cathode material, its coating modification method, and its application. Background Technology

[0002] With the global energy structure transformation and the rapid expansion of renewable energy power generation, the importance of energy storage systems is becoming increasingly prominent. Compared to traditional lithium-ion battery technology, sodium-ion batteries have become an important supplement to the lithium-ion battery system due to the abundance of sodium resources, their high crustal abundance, low cost potential, and certain compatibility with lithium battery technology. In recent years, among the various components of sodium-ion batteries, cathode materials have received particular attention because their performance directly determines the battery's energy density, cycle life, rate performance, and safety. Industry research has found that among many cathode material systems, layered transition metal oxides (with the general formula NaNi) are particularly important. x Fe y Mn (1-x-y) O2 (represented by Na) is considered one of the most promising cathode materials for sodium-ion batteries due to its high theoretical specific capacity, suitable discharge voltage platform, and good tunable composition mechanism. Na-based layered oxides possess advantages such as ease of synthesis, a good electrochemical voltage platform, and suitability for large-scale production. Furthermore, their structure can be regulated by various transition metal elements such as Ni, Fe, and Mn to optimize charge-discharge capacity, cycle stability, and rate performance. However, these materials still face challenges in practical applications, including structural collapse, drastic phase transitions, rapid capacity decay, and insufficient cycle life. Therefore, improving the electrochemical stability and conductivity / ion transport performance of this system through surface modification, coating, and doping has become a research hotspot.

[0003] While existing technologies employing carbon nanoparticle-based plasma fluorination coating have improved the cycling stability of materials to some extent, they still have several drawbacks. First, plasma treatment equipment is costly and the process is complex. Second, the unique morphology of carbon nanoparticles makes it difficult to control the uniformity of the coating layer. Third, coating with a single carbon material has limited effect on improving electron conductivity. Finally, fluorination treatment may introduce defects into the material surface, thereby affecting the material's stability. Summary of the Invention

[0004] This invention provides a sodium-ion battery cathode material and its coating method, to address the shortcomings of existing sodium-ion battery cathode materials in terms of conductivity, cycle stability, and high-temperature stability. In a first aspect, the present invention provides a method for coating modification of a sodium-ion battery cathode material, specifically comprising the following steps: S1: Dissolve carbon quantum dots and conductive polymerizable monomers in an acidic buffer solution with a pH of 2-4 to form a dispersion; S2: The sodium-ion battery cathode material and the dispersion are mixed, ultrasonically treated, and then an oxidant is added. The mixture is then subjected to a polymerization reaction under ultraviolet light irradiation. After the reaction is completed, the mixture is aged to obtain the coated and modified sodium-ion battery cathode material.

[0005] In one optional embodiment, the sodium-ion battery cathode material is a layered sodium-ion battery cathode material with the general chemical formula NaNi. x Fe y Mn (1-x-y) O2, wherein 0.2≤x≤0.5, 0.1≤y≤0.4, preferably NaNi 0.33 Fe 0.33 Mn 0.33 O2.

[0006] In one alternative embodiment, the carbon quantum dots have a particle size of 2-8 nm. This particle size range allows the carbon quantum dots to have a large specific surface area and form a relatively dense three-dimensional conductive network structure in the battery. These small-sized carbon quantum dots not only significantly improve electronic conductivity and reduce volume resistivity, but also enhance the overall performance of the battery, especially exhibiting high stability and low internal resistance during rapid charge and discharge. By controlling the particle size of the carbon quantum dots, the electrochemical characteristics of the battery can be optimized, improving its energy density and cycle life.

[0007] As an example, the particle size of the carbon material can be 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, or within any of the above values.

[0008] Furthermore, the conductive polymerizable monomer is selected from at least one of pyrrole, thiophene, pyrrole derivatives, and thiophene derivatives; the mass ratio of the sodium-ion battery cathode material to the dispersion is 1:1-3, preferably 1:2.5.

[0009] In one optional embodiment, the acidic buffer solution is a citric acid and sodium citrate buffer solution. This buffer solution provides a stable acidic environment, ensuring that the conductive polymerizable monomers maintain good polymerizability and conductivity during synthesis. The combination of citric acid and sodium citrate not only effectively adjusts the pH value, preventing the effects of excessively acidic or alkaline conditions on the reaction, but also maintains a certain ionic strength during the reaction, promoting the polymerization reaction of conductive monomers. Using citric acid and sodium citrate as a buffer solution helps improve the conductivity and long-term stability of battery materials, especially in the preparation of sodium-ion battery materials, effectively improving the charge-discharge efficiency and cycle life of the battery.

[0010] In one optional embodiment, the ultrasonic power is set to 250-350W, and the ultrasonic time is set to 35-55min. By optimizing the ultrasonic power and time, the dispersibility of the material can be improved, promoting uniform mixing among the reactants. Ultrasonic treatment helps improve the bonding between carbon quantum dots and conductive polymers, further enhancing the conductivity of the battery. Appropriate ultrasonic power and time can balance energy input and material stability, avoiding damage to the material structure.

[0011] In one optional embodiment, the oxidant is a persulfate, preferably ammonium persulfate or potassium persulfate, and its amount is 0.5-2 times the molar amount of the polymerizable monomer. Persulfate is a strong oxidant that can effectively promote the polymerization reaction of conductive polymerizable monomers and improve conductivity. In this embodiment, the use of ammonium persulfate and potassium persulfate can control the reaction rate under certain conditions, ensure the degree of polymerization of the material, and avoid the reaction being too fast or too slow, which would affect the electrochemical performance of the final product.

[0012] In one optional embodiment, the ultraviolet irradiation conditions are a wavelength of 365 nm and an intensity of 10-50 mW / cm². 2 Ultraviolet (UV) irradiation can effectively initiate polymerization reactions. By adjusting the irradiation intensity and time, the formation of the coating layer can be precisely controlled, ensuring its uniformity and stability. Insufficient UV intensity hinders the polymerization reaction, while excessively high UV intensity is detrimental to the stability of the coating layer. When the UV intensity exceeds a certain range, the properties of the resulting coated material are significantly compromised.

[0013] As an example, the ultraviolet light intensity can be 10 mW / cm². 2 20mW / cm 2 30mW / cm 2 40mW / cm 2 50mW / cm 2 , or within the range of any of the above values.

[0014] In one optional embodiment, the curing time is 2-6 hours, and the inert gas is nitrogen, argon, or other gases that do not react with the reactants. Suitable curing temperature and time contribute to the curing and stability of the coating layer. Simultaneously, the use of an inert gas for protection avoids possible oxidation reactions during the coating process, thus improving the quality and performance of the coating layer.

[0015] As an example, the curing time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or within any of the above values.

[0016] Secondly, the present invention also provides a method for preparing a modified sodium-ion battery cathode material. By using the above method, the conductivity, cycle stability and high-temperature stability of the sodium-ion battery cathode material are significantly improved through the modified coating layer, thereby enhancing battery performance.

[0017] Thirdly, the present invention also provides a sodium-ion battery cathode material prepared by the above method.

[0018] Carbon quantum dots (CQDs), also known as carbon dots or carbon nanodots, are a class of zero-dimensional carbon nanomaterials with remarkable fluorescence properties. They consist of ultrafine, dispersed, quasi-spherical carbon nanoparticles with a size of less than 10 nm. CQDs possess numerous advantages, including excellent optical properties, good water solubility, low toxicity, environmental friendliness, wide availability of raw materials, low cost, and good biocompatibility. CQDs have a wide range of applications, showing promising prospects in many fields such as medical imaging technology, environmental monitoring, chemical analysis, catalyst preparation, and energy development.

[0019] The core of the technical principle in this invention lies in the organic combination of three major innovations: ultraviolet light-induced polymerization, carbon quantum dot (CQD) embedding, and acidic buffer system.

[0020] Ultraviolet light (365nm wavelength) is used to initiate the polymerization reaction of polymerizable monomers (such as pyrrole, thiophene, aniline, etc.) on the surface of the cathode material. Under ultraviolet light irradiation, the monomers undergo free radical polymerization to form polymer chains. These polymer chains form a strong bond with the surface of the cathode material through chemical reactions. Ultraviolet light not only provides precise reaction energy but also controls the polymerization rate and molecular weight, ensuring the uniformity and stability of the coating layer.

[0021] Carbon quantum dots (CQDs) form chemical bonds (e.g., -COOH···O-Mn) with metal ions (such as manganese) on the cathode material surface through their abundant carboxyl groups (-COOH). This chemical bonding enhances the adhesion between CQDs and the cathode material, ensuring the stability of the coating layer. The nanoscale size and high specific surface area of ​​CQDs enable them to effectively fill the material surface, forming a three-dimensional conductive network and significantly improving the material's conductivity. The carbon quantum dots in the coating layer not only improve the material's conductivity but also effectively reduce the structural degradation of sodium ions during cycling, thus enhancing the battery's cycle stability.

[0022] Acidic buffer solutions (such as citrate-sodium citrate buffer, pH 2-4) provide an ideal reaction environment for the entire coating reaction. In this acidic environment, polymerizable monomers can polymerize efficiently to form a conductive polymer coating layer. The acidic buffer system optimizes the monomer polymerization behavior by controlling the pH value, while ensuring the uniformity and stability of the polymerization reaction. Furthermore, the acidic environment promotes the chemical bonding between carbon quantum dots and the cathode material, contributing to the formation of a stronger and more stable interface.

[0023] The technical principle of this invention lies in improving the overall performance of the cathode material by constructing stable chemical bonds and a three-dimensional conductive network. Specifically, a key advantage of using carbon quantum dots as a conductive material is the abundance of carboxyl groups on their surface. These carboxyl groups can form stable chemical bonds with metal elements (such as manganese) in the cathode material, thereby achieving a tight and stable surface bond. This chemical bonding not only allows carbon quantum dots to firmly adhere to the surface of the cathode material, improving the stability of the coating layer, but also optimizes the interfacial interaction between the cathode material and the coating layer at the microscopic level. Furthermore, the three-dimensional conductive network constructed by the conductive polymer and carbon quantum dots further enhances the electron conduction efficiency, enabling more efficient electron transfer during battery charging and discharging.

[0024] The technical solution of this invention has the following advantages: (1) This invention constructs a "conductive polymer-conductive material" composite coating layer by combining conductive materials such as carbon quantum dots, carbon nanotubes, and graphene with polymerizable monomers (such as pyrrole and thiophene). This composite structure forms a three-dimensional conductive network, significantly improving the electronic conductivity of the cathode material and reducing the volume resistivity to 1.2 × 10⁻⁶. -3 The Ω·cm is reduced by approximately 33% compared to the previous technology, further improving the overall performance of the battery.

[0025] (2) In the aging and post-treatment steps, the present invention optimizes the ultraviolet irradiation conditions, the amount of oxidant, and the protection of the inert atmosphere, making the coating layer more uniform and stable, thereby significantly improving the performance of the battery in high-temperature environments. For example, the capacity retention rate reaches 92.3% after 200 cycles at 1C rate; the high-temperature storage stability is improved, and the capacity retention rate is >95% after 7 days at 60℃, which is significantly better than the prior art.

[0026] (3) The coating modification method of the present invention replaces the traditional plasma treatment process with ultraviolet light-initiated polymerization, making the entire process simpler, less energy-consuming, and more suitable for large-scale production. This improvement not only solves the problems of complex equipment and high energy consumption in the prior art, but also improves production efficiency and economy. The present invention also has significant cost advantages. By reducing raw material costs by about 40% and equipment investment by about 60%, the present invention significantly reduces manufacturing costs while maintaining high performance, and has broad prospects for industrial application. Detailed Implementation

[0027] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0028] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0029] The carbon quantum dot material used in this invention was purchased from the Maclean's reagent website.

[0030] Example 1 Take NaNi 0.33 Fe 0.33 Mn 0.33 5g of O2 cathode material, 50mg of carbon quantum dots (5nm particle size), and 0.5ml of pyrrole monomer were dissolved in 100ml of citrate buffer solution (pH=3) to form a dispersion. The mass ratio of cathode material to dispersion was 1:2.5. The solution was sonicated at 300W for 45min. Then, 0.8g of ammonium persulfate was added to the solution, and the mixture was exposed to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiation was performed for 20 minutes. The amount of ammonium persulfate was 1 times the molar amount of pyrrole monomer. The mixture was then transferred to a 60°C oil bath and matured under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0031] Example 2 Take NaNi 0.5 Fe 0.4 Mn 0.15g of O2 cathode material, 50mg of carbon quantum dots (8nm particle size), and 0.5ml of pyrrole monomer were dissolved in 100ml of citrate buffer solution (pH=3) to form a dispersion. The mass ratio of cathode material to dispersion was 1:1. The solution was sonicated at 250W for 35min. Then, 0.8g of potassium persulfate was added to the solution, and the solution was exposed to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiate for 20 min. The amount of potassium persulfate is 0.5-2 times the molar amount of pyrrole monomer. Then, transfer to a 60℃ oil bath and mature under nitrogen protection for 4 h. The product is washed with ethanol and vacuum dried at 80℃ for 12 h to obtain the final modified material.

[0032] Example 3 Take NaNi 0.2 Fe 0.1 Mn 0.7 5g of O2 cathode material, 50mg of carbon quantum dots (2nm particle size), and 0.5ml of pyrrole monomer were dissolved in 100ml of citrate buffer solution (pH=3) to form a dispersion. The mass ratio of cathode material to dispersion was 1:3. The solution was sonicated at 350W for 55min. Then, 0.8g of ammonium persulfate was added to the solution, and the mixture was exposed to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiation was performed for 20 minutes. The amount of ammonium persulfate was 0.5-2 times the molar amount of pyrrole monomer. The mixture was then transferred to a 60°C oil bath and matured under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0033] Example 4 Take NaNi 0.33 Fe 0.33 Mn 0.33 5g of O2 cathode material, 50mg of carbon quantum dots (5nm particle size), and 0.5ml of 3,4-ethylenedioxythiophene were dissolved in 100ml of citrate buffer solution (pH=3) to form a dispersion. The mass ratio of cathode material to dispersion was 1:2.5. The solution was sonicated at 300W for 45min. Then, 0.8g of potassium persulfate was added to the solution, and the solution was subjected to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiation was performed for 20 minutes. The amount of potassium persulfate was 0.5-2 times the molar amount of 3,4-ethylenedioxythiophene. The product was then transferred to a 60°C oil bath and aged under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0034] Example 5 Take NaNi 0.33 Fe 0.33 Mn 0.335g of O2 cathode material, 50mg of carbon quantum dots (5nm particle size), and 0.5ml of 3,4-ethylenedioxythiophene were dissolved in 100ml of citrate buffer solution (pH=4) to form a dispersion. The mass ratio of cathode material to dispersion was 1:2.5. The solution was sonicated at 300W for 45min. Then, 0.8g of ammonium persulfate was added to the solution, and the solution was subjected to 365nm ultraviolet light (intensity 30mW / cm²). 2 The mixture was irradiated for 20 minutes. The amount of ammonium persulfate was 0.5-2 times the molar amount of 3,4-ethylenedioxythiophene. It was then transferred to a 60°C oil bath and aged under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0035] Example 6 Take NaNi 0.33 Fe 0.33 Mn 0.33 5g of O2 cathode material, 50mg of carbon quantum dots (5nm particle size), and 0.5ml of 3,4-ethylenedioxythiophene were dissolved in 100ml of citrate buffer solution (pH=2) to form a dispersion. The mass ratio of cathode material to dispersion was 1:2.5. The solution was sonicated at 300W for 45min. Then, 0.8g of ammonium persulfate was added to the solution, and the solution was subjected to 365nm ultraviolet light (intensity 30mW / cm²). 2 The mixture was irradiated for 20 minutes. The amount of ammonium persulfate was 0.5-2 times the molar amount of 3,4-ethylenedioxythiophene. It was then transferred to a 60°C oil bath and aged under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0036] Example 7 Take NaNi 0.33 Fe 0.33 Mn 0.33 5g of O2 cathode material, 50mg of carbon quantum dots (5nm particle size), and 0.5ml of 3,4-ethylenedioxythiophene were dissolved in 100ml of citrate buffer solution (pH=2) to form a dispersion. The mass ratio of cathode material to dispersion was 1:2.5. The solution was sonicated at 300W for 45min. Then, 0.8g of potassium persulfate was added to the solution, and the solution was subjected to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiation was performed for 20 minutes. The amount of potassium persulfate was 0.5-2 times the molar amount of 3,4-ethylenedioxythiophene. The product was then transferred to a 60°C oil bath and aged under nitrogen protection for 4 hours. The product was washed with ethanol and vacuum dried at 80°C for 12 hours to obtain the final modified material.

[0037] Comparative Example 1: This comparative example provides a sodium-ion battery cathode material and its coating modification method, which uses existing technology to coat it with carbon nanofibers. The specific steps are as follows: Take NaNi 0.33 Fe 0.33 Mn 0.33 5g of O2 cathode material and 50mg of carbon nanotubes were dispersed in 100ml of 1wt% ethanol to form a dispersion. The solution was ultrasonically treated for 30min, and then the treated material was placed in a CF4 atmosphere for plasma fluorination at 200W for 10min. The treated material was then annealed in an argon (Ar) atmosphere at 400℃ for 2h. The product was washed with ethanol and vacuum dried at 80℃ for 12h to obtain the final modified material.

[0038] Comparative Example 2: This comparative example provides a sodium-ion battery cathode material and its coating modification method, which differs from Example 1 in that it does not use carbon quantum dots.

[0039] Comparative Example 3: This comparative example provides a sodium-ion battery cathode material and its coating modification method. The difference between this material and Example 1 is that the ultraviolet light intensity is insufficient, only 5 mW / cm². 2 .

[0040] Comparative Example 4: This comparative example provides a sodium-ion battery cathode material and its coating modification method. The difference between this material and Example 1 is that the ultraviolet light intensity is excessively high, at 60 mW / cm². 2 .

[0041] Comparative Example 5: This comparative example provides a sodium-ion battery cathode material and its coating modification method. The difference between this material and Example 1 is that the pH value of the citric acid buffer solution is too low, and pH=1 is used.

[0042] Comparative Example 6: This comparative example provides a sodium-ion battery cathode material and its coating modification method. The difference from Example 1 is that the pH value of the citric acid buffer solution is too high; pH=5 is used. Methods or standards for detecting performance data. The prepared positive electrode material, using polyvinylidene fluoride (PVDF) as a binder and conductive carbon black (SP) as a conductive agent, was mixed at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as a solvent, and the mixture was stirred to form a slurry. This slurry was coated onto aluminum foil, dried, and rolled to obtain the positive electrode sheet. The electrolyte consisted of a 1 mol / L NaPF6 propylene carbonate (PC) solution with 5 vol% fluoroethylene carbonate (FEC) added. A sodium metal sheet served as the counter electrode, and a polypropylene (PP) membrane was used as the separator. The cells were assembled into coin cells in an argon-filled glove box, maintaining a pressure of 8-10 MPa during encapsulation to ensure interface contact. Finally, the assembled cells underwent electrical performance testing.

[0043] The assembled battery was subjected to cycle performance testing at 25°C. In the first cycle, under a constant temperature environment of 25℃, the secondary battery was charged to 4.1V at 0.1C, and then charged at 4.1V at a constant voltage until the current was less than or equal to 0.05mA. After standing for 5 minutes, it was discharged to 2.0V at 0.1C.

[0044] In the second cycle, under a constant temperature environment of 25°C, the secondary battery was charged at 1C to 4.1V, and then charged at a constant voltage of 4.1V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.0V. This process was repeated 200 times, and the capacity retention rate was recorded.

[0045] The resistivity, cycle stability and thermal stability of the cathode materials prepared in Examples 1-6 and Comparative Examples 1-6 are shown in Table 1.

[0046] Table 1. Test results of resistivity, cyclic stability, and thermal stability.

[0047] analyze: (1) As can be seen from the data in Table 1, the sodium-ion battery cathode materials of Examples 1 to 7 all exhibit excellent and stable comprehensive performance in terms of volume resistivity, cycle stability, and thermal stability. Among them, Example 1 has the lowest volume resistivity, which is only 1.18 × 10⁻⁶. -3 The capacity retention rate after 200 cycles was 92.3% (Ω·cm), and after 7 days of storage at 60°C, it reached 95.7%, indicating excellent conductivity, electrochemical stability, and thermal stability. Although Examples 2-7 differed in parameters such as cathode material composition, carbon quantum dot particle size, monomer type, and buffer pH, their volume resistivity was consistently below 1.52 × 10⁻⁶. -3 The Ω·cm cyclic retention rate was higher than 88%, and the capacity retention rate after 7 days of storage at 60℃ was mostly higher than 90%, indicating that the method of this application has good process adaptability and stability.

[0048] (2) Compared with the examples, the overall performance of Comparative Examples 1-6 all decreased to varying degrees. Comparative Example 1 used existing technology to coat carbon nanofibers with horns combined with plasma treatment, and its volume resistivity was 1.67 × 10⁻⁶. -3 Although the cycle retention rate was 93.0% at Ω·cm, its high-temperature storage performance decreased significantly. After 7 days of storage at 60°C, the capacity retention rate was only 79.3%, which was significantly lower than that of the example, indicating that the method is insufficient in terms of thermal stability.

[0049] (3) Comparative Example 2, which did not use carbon quantum dots, showed a significant increase in volume resistivity to 2.29 × 10⁻⁶. -3 The Ω·cm, cycle retention rate and high-temperature storage performance decreased to 85.9% and 86.3%, respectively, indicating that carbon quantum dots played a key role in constructing a continuous conductive network and reducing interfacial impedance. Comparative Examples 3 and 4 used excessively low and excessively high ultraviolet light intensities, respectively, with volume resistivity of 2.01 × 10⁻⁶. -3 Ω·cm and 1.87×10 -3 The Ω·cm and cycle retention rates were all below 85%, indicating that the intensity of ultraviolet light has a significant impact on the in-situ polymerization process. Insufficient or excessive light intensity is not conducive to the formation of a uniform and dense conductive polymer coating layer.

[0050] (4) Comparative Examples 5 and 6 used citric acid buffer solutions with excessively low (pH=1) and excessively high (pH=5) pH values, respectively, with volume resistivity of 2.12 × 10⁻⁶. -3 Ω·cm and 1.99×10 -3 The Ω·cm, cycle retention rate, and high-temperature storage performance were significantly lower than those of the example. This indicates that the pH value of the buffer solution has a significant impact on the polymerization reaction and the stability of the coating layer structure; excessively acidic or alkaline conditions will destroy the uniformity and stability of the coating layer.

[0051] In summary, the experimental results in Table 1 demonstrate that the embodiments of this application, through the use of a suitable pH buffer solution, appropriate ultraviolet light intensity, and a persulfate initiation system in the presence of carbon quantum dots, achieve in-situ uniform coating of conductive polymers on the surface of the cathode material, thereby significantly reducing volume resistivity and simultaneously improving cycle stability and thermal stability. Compared with Comparative Examples 1-6, the embodiments exhibit significant advantages in conductivity, electrochemical stability, and high-temperature storage performance, fully demonstrating the effectiveness and superiority of the technical solution of this application.

[0052] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A coating modification method of a sodium-ion battery cathode material, characterized in that, Includes the following steps: S1: Dissolve carbon quantum dots and conductive polymerizable monomers in an acidic buffer solution with a pH of 2-4 to form a dispersion; S2: The sodium-ion battery cathode material and the dispersion are mixed, ultrasonically treated, and then an oxidant is added. The mixture is then subjected to a polymerization reaction under ultraviolet light irradiation. After the reaction is completed, the mixture is aged to obtain the coated and modified sodium-ion battery cathode material.

2. The method of claim 1, wherein, The sodium ion battery positive electrode material is a sodium ion battery layered positive electrode material, and the chemical general formula is NaNi x Fe y Mn (1-x-y) O2, wherein 0.2≤x≤0.5, 0.1≤y≤0.

4.

3. The method according to claim 1 or 2, characterized in that, The carbon quantum dots described in S1 have a particle size of 2-8 nm; And / or, the conductive polymerizable monomer is selected from at least one of pyrrole, thiophene, pyrrole derivatives, and thiophene derivatives; And / or, the mass ratio of the sodium-ion battery cathode material to the dispersion is 1:1-3.

4. The method of claim 1, wherein, The acidic buffer solution is a citric acid and sodium citrate buffer solution.

5. The method according to claim 1 or 2, characterized in that, The ultrasonic power is 250-350W, and the ultrasonic time is 35-55min.

6. The method of claim 1 or 2, wherein, The oxidant is a persulfate, preferably selected from ammonium persulfate and / or potassium persulfate; And / or, the amount of the oxidant is 0.5-2 times the molar amount of the conductive polymerizable monomer.

7. The method of claim 1 or 2, wherein, The UV light irradiation conditions are wavelength 365 nm, intensity 10-50 mW / cm 2 .

8. The method of claim 1, wherein, The curing time is 2-6 hours; And / or, the curing process is carried out in a nitrogen or inert gas atmosphere; After the curing process is completed, the curing products are also subjected to steps of filtration, washing, and drying.

9. A coated modified sodium-ion battery cathode material, characterized in that, It is prepared by the coating modification method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, Including the coated modified sodium-ion battery cathode material as described in claim 9.

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