Preparation method of sodium ion positive electrode material with high humidity adaptability, positive electrode material, positive electrode sheet and sodium ion battery

Abstract

The application discloses a preparation method of a sodium-ion positive electrode material with high humidity adaptability, a positive electrode material, a positive electrode sheet and a sodium-ion battery. The method comprises the following steps: S1, fluorinated graphene is ground or ball-milled for pretreatment to obtain fluorinated graphene fine powder; S2, the fluorinated graphene fine powder is dispersed in a first organic solvent to form a first dispersion liquid; S3, an organic molecule with a structural general formula of R-PEG-X is dissolved in a second organic solvent to form a second solution; S4, the second solution and the first dispersion liquid are mixed under stirring; S5, a sodium-ion layered oxide positive electrode material is added into the pre-assembled composite unit dispersion liquid and is subjected to ultrasonic treatment; and S6, a mixed liquid obtained in S5 is subjected to vacuum rotary evaporation, and a solvent is removed, so that the pre-assembled composite unit is coated on the surface of the positive electrode material particles, and the sodium-ion positive electrode material with high humidity adaptability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a sodium-ion battery cathode material, and more particularly to a sodium-ion cathode material with high humidity adaptability, its preparation method, a cathode sheet containing the cathode material, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries (SIBs) have shown broad application prospects in large-scale energy storage and low-speed electric vehicles due to the abundance and low cost of sodium resources. Layered transition metal oxides (such as sodium nickel iron manganese oxide and sodium copper iron manganese oxide) have advantages as cathode materials for SIBs, including high specific capacity, suitable voltage platform, and mature synthesis process.

[0003] However, layered oxide cathode materials are extremely sensitive to water and carbon dioxide in the air. The alkaline compounds remaining on their surface (such as NaOH and Na₂CO₃) are strongly hydrophilic and will preferentially adsorb water molecules in humid environments, triggering Na₂CO₃ oxidation. + / H + Exchange and surface alkalization reactions lead to irreversible structural phase transitions in the material, resulting in a sharp decline in electrochemical performance. This problem severely restricts the storage, transportation, and large-scale application of this type of cathode material, while also increasing the reliance on extremely dry environments during battery manufacturing and raising production costs.

[0004] Currently, the main methods for improving the air stability of cathode materials include elemental doping and surface coating. Among these, surface coating has been widely studied due to its relatively simple process and significant effects. Common coating materials include metal oxides (such as Al2O3 and TiO2), phosphates, and carbon materials. However, existing technologies still have the following drawbacks: (1) Limitations of single-function materials: Although metal oxide coatings can block moisture, their poor conductivity / ion conductivity will seriously degrade the rate performance of the material; although carbon materials (such as graphene) can improve electronic conductivity, their overly hydrophobic surface will hinder electrolyte wetting and increase interfacial impedance.

[0005] (2) Complex process or poor effect: Chemical vapor deposition (CVD), atomic layer deposition (ALD) and other processes are costly and have low yield, making it difficult to achieve large-scale production; while simple physical mixing cannot form a uniform, dense and functionally distinct coating layer, resulting in limited protection effect.

[0006] (3) Key contradictions remain unresolved: Most existing coating technologies use single-function materials or simple composites, making it difficult to achieve a balance between the contradictory requirements of "efficiently isolating water vapor (hydrophobic)" and "maintaining excellent electrolyte wetting and ion transport (liquiophilic / non-oleophobic)".

[0007] Therefore, there is an urgent need to develop a new coating technology that can effectively block water molecule erosion while ensuring electrode processing performance and electrochemical performance. Summary of the Invention

[0008] The present invention aims to solve the technical problem of poor stability of existing sodium ion cathode materials in humid air, and to provide a sodium ion cathode material with high humidity adaptability and its preparation method.

[0009] Specifically, the present invention aims to achieve the following technical effects simultaneously: (1) significantly improve the hydrophobic and moisture-resistant properties of the cathode material and reduce its stringent requirements for storage and transportation environments; (2) ensure that the material has excellent dispersibility and processing performance in electrode slurry processing; and (3) ensure that the material has good electrolyte wettability, ionic / electronic conductivity and long-cycle stability in battery cycling.

[0010] To achieve the above objectives, the present invention provides the following technical solution: This invention proposes an innovative "component-structure-process" strategy to construct a hybrid coating layer with a "conductive skeleton-flexible interface layer" composite structure on the surface of cathode material particles.

[0011] (a) Component selection Fluorinated graphene serves as a conductive framework, providing rigid support, efficient electron channels, and a chemical passivation barrier. The CF bonds on the surface of fluorinated graphene endow it with strong hydrophobicity and chemical inertness, while the nanochannels between its two-dimensional sheet structures facilitate the selective transport of sodium ions.

[0012] R-PEG-X type organic molecules serve as flexible interface layers, where R is a hydrophobic alkyl chain (C8-C22), PEG is a solvent-friendly segment (degree of polymerization n=10-200), and X is an anchoring group (selected from amino, carboxyl, mercapto, hydroxyl, or hydrogen atom).

[0013] (II) Structural Design The hybrid coating layer has a unique "core-shell" ordered structure. R-PEG-X molecules are anchored to the surface of fluorinated graphene through hydrophobic interactions with their hydrophobic alkyl chains (R). PEG segments extend outward to form a pre-assembled composite unit with fluorinated graphene as the "core" and R-PEG-X as the "shell". This unit is uniformly coated on the surface of the cathode material particles.

[0014] (III) Key Processes The “liquid-phase pre-self-assembly” process is adopted to first allow fluorinated graphene and R-PEG-X to form a regular pre-assembled composite unit in a pure system, and then coat the unit onto the surface of the cathode material, thereby ensuring the uniformity and functional synergy of the composite structure.

[0015] III. Technical Principles The technical principle behind this invention, which achieves "hydrophobic but not oleophobic" electrochemical performance, is summarized as follows: (1) Regarding the hydrophobic mechanism: The CF bond of fluorinated graphene itself has strong hydrophobicity; at the same time, the long-chain alkyl (R) extending outward in the R-PEG-X molecule further enhances the hydrophobic properties of the coating layer surface. The synergistic effect of the two makes it difficult for water molecules to approach the surface of the cathode material, thereby effectively inhibiting the surface alkalization reaction and structural degradation.

[0016] (2) Regarding the non-oleophobic / hydrophilic mechanism: The outwardly extending PEG segments in the R-PEG-X molecule have excellent compatibility with carbonate electrolytes. The ether oxygen atoms in the PEG segments can react with the Li in the electrolyte. + / Na + Coordination occurs, and hydrogen bonds are formed with solvent molecules, thereby significantly reducing the contact angle of the electrolyte on the coating surface and achieving rapid and complete electrolyte wetting. This is the key difference between this invention and traditional simple hydrophobic coatings (such as only fluorinated graphene coatings)—the latter, although hydrophobic, have poor surface compatibility with the electrolyte, resulting in a significant increase in interfacial impedance.

[0017] (3) Regarding the conduction and ion transport mechanism: Fluorinated graphene forms a continuous conductive network, providing a fast transport channel for electrons; the nano gaps between fluorinated graphene sheets and the flexibility of PEG segments provide a convenient path for the cross-interface transport of sodium ions, avoiding the obstruction of ion transport by the dense coating layer.

[0018] (4) Regarding the synergistic effect mechanism: Fluorinated graphene and R-PEG-X are not simply a superposition of their respective functions. On the one hand, fluorinated graphene, as a "skeleton," provides regular anchoring points for R-PEG-X, guiding the organic molecules to arrange in an orderly manner and forming a complete and defect-free coating layer. On the other hand, R-PEG-X, as an "interface layer," solves the interfacial compatibility problem between fluorinated graphene and the electrolyte. At the same time, its flexible characteristics can alleviate the stress cracking of the coating layer caused by the volume change of the positive electrode material during charging and discharging. The combined effect of the two is to retain the high conductivity and chemical stability of fluorinated graphene, solve its "oleophobic" defect, and compensate for the poor electronic conductivity of a single organic coating layer.

[0019] The "liquid-phase pre-self-assembly" process (S4) of this invention is the key to forming the above-mentioned regular "core-shell" structure. If this step is omitted and simple mixing is used (such as in Comparative Example 4), organic molecules will be adsorbed on the surface of fluorinated graphene and cathode material at the same time, and it will be impossible to form an ordered pre-assembled unit, which will lead to a disordered coating layer structure and a significant decrease in performance.

[0020] The present invention specifically employs the following preparation method: A method for preparing a sodium-ion cathode material with high humidity adaptability includes the following steps: S1. Fluorinated graphene pretreatment: Fluorinated graphene is ground or ball-milled to obtain fine fluorinated graphene powder with a particle size D90 of less than 1 micrometer.

[0021] S2. Preparation of fluorinated graphene dispersion: The fluorinated graphene fine powder obtained in S1 is dispersed in the first organic solvent and subjected to ultrasonic treatment to form a uniform and stable first dispersion.

[0022] S3. Preparation of organic molecule solution: Dissolve an organic molecule with the general structural formula R-PEG-X in a second organic solvent, and then heat and stir to form a second solution.

[0023] Wherein, R is a straight-chain or branched alkyl group of C8-C22, PEG is a polyethylene glycol segment with a degree of polymerization n=10-200, and X is selected from one of amino, carboxyl, mercapto, hydroxyl or hydrogen atoms.

[0024] S4. Liquid-phase pre-self-assembly: Under stirring conditions, the second solution is added to the first dispersion. Utilizing the hydrophobic interaction and van der Waals forces between the C8-C22 alkyl chains in the R-PEG-X organic molecules and the surface of the fluorinated graphene, the R-PEG-X organic molecules are adsorbed onto the surface of the fluorinated graphene through physical self-assembly, forming a pre-assembled composite unit dispersion with fluorinated graphene as the core and R-PEG-X as the shell.

[0025] S5. Coating the cathode material: Sodium ion layered oxide cathode material powder is added to the pre-assembled composite unit dispersion and ultrasonically treated to make the pre-assembled composite unit and cathode material particles uniformly mixed.

[0026] S6. Solvent Removal and Drying: The mixture obtained in S5 is subjected to vacuum rotary evaporation to remove the organic solvent, so that the pre-assembled composite unit is uniformly coated on the surface of the cathode material particles, thus obtaining the sodium ion cathode material with high humidity adaptability.

[0027] Preferably, the amount of fluorinated graphene is 0.1-5 wt% of the mass of sodium ion layered oxide. The mass ratio of the fluorinated graphene to the R-PEG-X organic molecule is 1:0.5 to 1:5, preferably 1:1.5 to 1:2.

[0028] Preferably, the first organic solvent and the second organic solvent are each independently selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, ethanol or isopropanol, and are preferably N-methylpyrrolidone.

[0029] Preferably, the mass concentration of the fluorinated graphene in the first organic solvent is 0.1-5 mg / mL; and the mass concentration of the R-PEG-X organic molecule in the second organic solvent is 0.5-10 mg / mL.

[0030] Preferably, the mixing temperature in S4 is 20-60°C, the stirring time is 1-5 hours, and the ultrasonic power in S5 is 100-500 W, and the ultrasonic time is 0.5-4 hours.

[0031] Preferably, the temperature of the water bath in S6 for vacuum rotary evaporation is 60-100℃.

[0032] Preferably, the sodium ion layered oxide cathode material is selected from one or more of sodium nickel iron manganese oxide, sodium nickel cobalt manganese oxide, sodium copper iron manganese oxide, sodium nickel copper iron manganese oxide, or lithium nickel copper iron manganese oxide, and the R-PEG-X organic molecule is preferably octadecyl polyethylene glycol amino (C18-PEG-NH2).

[0033] Compared with the prior art, the present invention has the following beneficial effects: This invention constructs a composite coating layer of fluorinated graphene and R-PEG-X, wherein the CF bonds of the fluorinated graphene and the alkyl chains of the R-PEG-X molecules provide strong hydrophobicity, effectively blocking water vapor erosion. Experimental data show that after the materials of the embodiments of this invention are exposed to air for 72 hours, the residual alkali and pH value on their surface remain almost unchanged, while the residual alkali content of the uncoated materials increases significantly.

[0034] In this invention, the PEG segments exhibit excellent compatibility with carbonate-based electrolytes, ensuring thorough electrolyte wetting (non-oleophobic); the fluorinated graphene conductive framework provides efficient electron channels. The synergistic effect of these two components results in the material of this invention exhibiting significantly superior rate performance and cycle stability compared to materials coated with only a single component. Experimental data show that the 5C rate capacity of the material of this invention is far higher than the comparative examples of "fluorinated graphene only" and "organic molecules only," producing an unexpected technical effect of "1+1>2."

[0035] The X group (such as amino group) of R-PEG-X molecule can combine with trace amounts of hydroxyl or oxygen atoms on the surface of the cathode material through hydrogen bonding, thereby enhancing the adhesion between the coating layer and the substrate. At the same time, the flexibility of the PEG chain segment can adapt to the volume changes of the cathode material during charging and discharging, preventing the coating layer from cracking and peeling off.

[0036] This invention employs a wet coating process combining liquid-phase self-assembly and vacuum rotary evaporation, which is characterized by mild conditions, simple operation, low cost, and ease of industrial-scale production. Attached Figure Description

[0037] The above and other objects, features, and advantages of the invention will become clearer through a more detailed description of the preferred embodiments illustrated in the accompanying drawings. The same reference numerals denote the same parts throughout the drawings, and the drawings are not intentionally drawn to scale with actual dimensions; the focus is on illustrating the gist of the invention.

[0038] Figure 1 This is a flowchart illustrating the manufacturing process of the present invention.

[0039] Figure 2 This is a schematic diagram of the preparation process of the present invention.

[0040] Figure 3 This is a SEM image of the surface of sodium copper iron manganese oxide material coated with fluorinated graphene and organic molecule C18-PEG-NH2 in Example 2. Detailed Implementation

[0041] To facilitate understanding of the present invention, it is further described below with reference to specific embodiments and comparative examples. However, the following embodiments are only used to illustrate the principles and effects of the present invention and should not be construed as limiting the scope of protection of the present invention. All equivalent modifications or substitutions made based on the above-described ideas of the present invention should be included within the scope of protection of the present invention.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. As used herein, open-ended terms such as “comprising” and “including” mean the presence of a stated feature, step, or component, but do not exclude the presence or addition of one or more other features, steps, or components.

[0043] I. Raw Materials and Reagents Fluorinated graphene (FG): purity >99%, particle size D90 <1μm, Shandong Zhongshan Optoelectronic Materials Co., Ltd.; Octadecyl-polyethylene glycol-amino (C18-PEG-NH2): n≈45, molecular weight approximately 2000, Shanghai Maclean Biochemical Technology Co., Ltd.; Sodium copper iron manganese oxide (Na0.9Cu0. 22 Fe0.3Mn0. 48 O2): Prepared by laboratory co-precipitation method; N-methylpyrrolidone (NMP): Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0044] II. Performance Testing Methods 1. Residual alkali content and pH value test: Mix 2g of sample with 40mL of pure water, stir for 10 minutes, filter and take the filtrate, and measure the pH value with a pH meter; use a high-frequency infrared carbon and sulfur analyzer to test the residual alkali content.

[0045] 2. Air exposure experiment: Spread the sample flat in a petri dish and expose it in a constant temperature and humidity chamber at 25℃ and 60% relative humidity for 72 hours. After taking it out, test the residual alkali and pH according to the above method.

[0046] 3. Electrochemical Performance Testing: The prepared positive electrode material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 90:5:5. An appropriate amount of NMP was added, and the mixture was ground into a uniform slurry. This slurry was coated onto aluminum foil, vacuum dried, and then cut into φ12 mm discs as the positive electrode. Using a sodium metal sheet as the negative electrode, a GF / D glass fiber membrane as the separator, and 1 M NaPF6 dissolved in EC / DEC (volume ratio 1:1) as the electrolyte, CR2032 coin cells were assembled in an argon glove box. Constant current charge-discharge tests were conducted in a 25℃ constant temperature chamber, with a voltage range of 2.5-4.2 V.

[0047] 4. Contact angle test: The sample powder is pressed into a disc, and the contact angle of water and electrolyte on the disc surface is measured using a contact angle measuring instrument.

[0048] III. Examples Example 1 This embodiment provides a sodium-ion cathode material with high humidity adaptability, and its preparation method includes the following steps: S1. Place 50 mg of fluorinated graphene in an agate ball mill jar, add agate balls, and ball mill in a high-energy ball mill at 1300 rpm for 6 hours (pause for 0.5 hours every 2 hours of ball milling) to obtain fine powder of fluorinated graphene.

[0049] S2. Disperse the ball-milled fluorinated graphene powder in 20 mL of N-methylpyrrolidone and sonicate it at 300 W for 2.5 hours to form a uniform and stable first dispersion.

[0050] S3. Dissolve 75 mg of C18-PEG-NH2 in 15 mL of N-methylpyrrolidone and stir magnetically in a 40°C water bath for 1 hour to form a second solution.

[0051] S4. Under stirring conditions at 45℃, the second solution is slowly added dropwise to the first dispersion, and stirring is continued for 2 hours, so that C18-PEG-NH2 is adsorbed onto the surface of fluorinated graphene through physical self-assembly to form a pre-assembled composite unit dispersion (the mass ratio of fluorinated graphene to C18-PEG-NH2 is 1:1.5).

[0052] S5. Add 5 g of sodium copper iron manganese oxide cathode material to the above pre-assembled composite unit dispersion and sonicate at 300 W for 2 hours.

[0053] S6. Place the mixture in a rotary evaporator and vacuum rotary evaporate it in an 80°C water bath to remove the NMP solvent, thereby obtaining the sodium copper iron manganese oxide material coated with fluorinated graphene and C18-PEG-NH2 (the amount of fluorinated graphene is 1 wt% of sodium copper iron manganese oxide).

[0054] Example 2 The only difference between this embodiment and Example 1 is that: the amount of fluorinated graphene used in S1 is 100 mg, the amount of NMP used in S2 is 40 mL; the amount of C18-PEG-NH2 used in S3 is 150 mg, and the amount of NMP used is 30 mL; the amount of fluorinated graphene used is 2 wt% of sodium copper iron manganate. The remaining steps and parameters are the same as in Example 1.

[0055] Example 3 The only difference between this embodiment and Example 1 is that: the amount of fluorinated graphene used in S1 is 150 mg, the amount of NMP used in S2 is 60 mL; the amount of C18-PEG-NH2 used in S3 is 225 mg, and the amount of NMP used is 45 mL; the amount of fluorinated graphene used is 3 wt% of sodium copper iron manganate. The remaining steps and parameters are the same as in Example 1.

[0056] Example 4 The only difference between this embodiment and Example 2 is that the amount of C18-PEG-NH2 used in S3 is 100 mg (the mass ratio of fluorinated graphene to C18-PEG-NH2 is 1:1). The remaining steps and parameters are the same as in Example 2.

[0057] Example 5 The only difference between this embodiment and Example 2 is that the amount of C18-PEG-NH2 used in S3 is 200 mg (the mass ratio of fluorinated graphene to C18-PEG-NH2 is 1:2). The remaining steps and parameters are the same as in Example 2.

[0058] IV. Comparative Example Comparative Example 1 (Uncovered) Sodium copper iron manganese oxide material without any coating treatment was used, and its source was the same as in the example.

[0059] Comparative Example 2 (fluorinated graphene coating only) The difference between this comparative example and Example 2 is that C18-PEG-NH2 is not added (i.e., steps S3 and S4 are omitted). The specific steps are as follows: after preparing the fluorinated graphene dispersion according to steps S1 and S2 of Example 2, 5g of positive electrode material is directly added and ultrasonically treated for 2 hours. Then, the solvent is evaporated by vacuum rotation to obtain a positive electrode material coated only with fluorinated graphene (the amount of fluorinated graphene is 2wt%).

[0060] Comparative Example 3 (C18-PEG-NH2 coating only) The difference between this comparative example and Example 2 is that fluorinated graphene is not added (i.e., steps S1, S2, and S4 are omitted). The specific steps are as follows: 150 mg of C18-PEG-NH2 is dissolved in 30 mL of NMP to form a solution, 5 g of positive electrode material is added and ultrasonically treated for 2 hours, and then the solvent is evaporated under vacuum to obtain a positive electrode material coated only with C18-PEG-NH2 (the amount of C18-PEG-NH2 is 3 wt%).

[0061] Comparative Example 4 (Non-self-assembly simple mixed coating) The difference between this comparative example and Example 2 is that the S4 pre-self-assembly step is omitted, and the fluorinated graphene, C18-PEG-NH2, and cathode material are directly mixed. The specific steps are as follows: Fluorinated graphene fine powder is prepared according to S1 of Example 2; 5g of cathode material, 100mg of fluorinated graphene powder, and 150mg of C18-PEG-NH2 powder are weighed, simply mixed, and then 60mL of NMP is added. The mixture is ultrasonically treated for 2 hours, and then the solvent is evaporated under vacuum to obtain the composite-coated cathode material.

[0062] V. Performance Test Results

[0063] Table 1 Comparison of air stability in various cases It should be noted that the pH value in Table 1 refers to the pH value of the solution measured using a pH meter after weighing 2g of each case material and 40ml of pure water, stirring for 10 minutes. The residual alkali concentration refers to the residual alkali in each case measured using a high-frequency infrared carbon-sulfur analyzer. The test method involves weighing 0.2g of standard sample and 0.5g of test sample, and heating at a temperature of 2000-4000℃. As shown in Table 1, after 72 hours of exposure to air, the residual alkali and pH value of the materials in Examples 1-5 of this invention showed almost no change, significantly better than the uncoated Comparative Example 1 and the Comparative Example 2 coated only with fluorinated graphene, and also better than the Comparative Example 4 using a non-self-assembly process.

[0064]

[0065] Table 2 Comparison of initial rate performance for each case (mAh / g) It should be noted that the rate performance of the embodiments in Table 2 was obtained by assembling CR2032 batteries and conducting constant current charge-discharge tests at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C in a 25°C constant temperature chamber, with a voltage range of 2.5V-4.2V. As can be seen from Table 2, the 5C rate capacity of Embodiment 2 of the present invention (119 mAh / g) is significantly higher than that of Comparative Example 2 (68 mAh / g) and Comparative Example 3 (76 mAh / g), proving that fluorinated graphene and C18-PEG-NH2 have a synergistic effect.

[0066]

[0067] Table 3. Comparison of rate performance (mAh / g) of each case after 72 hours of exposure It should be noted that the rate performance of the embodiments in Table 3 was obtained by assembling each embodiment into CR2032 batteries after 72 hours of exposure to air and then conducting constant current charge-discharge tests at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C in a 25°C constant temperature chamber, with a voltage range of 2.5V-4.2V. As can be seen from Table 3, the materials of the embodiments of the present invention can still maintain excellent rate performance after 72 hours of exposure to air, proving that their high humidity adaptability is significantly better than that of the comparative examples.

[0068]

[0069] Table 4 Comparison of 1C Cyclic Stability in Various Cases It should be noted that the electrochemical performance of each embodiment in Table 4 was obtained by assembling CR2032 batteries and testing them in a 25°C constant temperature chamber at a constant current of 1C, with a voltage range of 2.5V-4.2V. The coulombic efficiency and capacity retention after 500 cycles were further calculated. As can be seen from Table 4, the capacity retention after 500 cycles of Embodiment 2 of this invention is as high as 87.2%, far superior to the comparative embodiments.

[0070]

[0071] Table 5 Contact Angle Test Results As shown in Table 5, although Comparative Example 2 (FG only) has strong hydrophobicity, its electrolyte contact angle is as high as 58°, indicating poor compatibility with the electrolyte ("oleophobic"). Comparative Example 3 (R-PEG-X only) has an electrolyte contact angle of 25°, which is hydrophilic but lacks a conductive framework. Example 2 of the present invention achieves both high hydrophobicity (water contact angle 132°) and excellent electrolyte wettability (contact angle 22°), that is, the ideal state of "hydrophobic but not oleophobic".

Claims

1. A method for preparing a sodium-ion cathode material with high humidity adaptability, characterized in that, Includes the following steps: S1. Fluorinated graphene is pretreated by grinding or ball milling to obtain fluorinated graphene fine powder; S2. Disperse the fluorinated graphene fine powder in a first organic solvent to form a first dispersion; S3. Dissolve an organic molecule with the general structural formula R-PEG-X in a second organic solvent to form a second solution; wherein R is a straight-chain or branched alkyl group of C8-C22, PEG is a polyethylene glycol segment with a degree of polymerization n=10-200, and X is selected from one of amino, carboxyl, mercapto, hydroxyl or hydrogen atoms. S4. Under stirring conditions, the second solution is mixed with the first dispersion. The hydrophobic interaction and van der Waals forces between the C8-C22 alkyl chain in the R-PEG-X organic molecule and the surface of the fluorinated graphene are utilized to allow the R-PEG-X organic molecule to be adsorbed onto the surface of the fluorinated graphene through physical self-assembly, forming a pre-assembled composite unit dispersion. S5. Add the sodium ion layered oxide cathode material to the pre-assembled composite unit dispersion and perform ultrasonic treatment; S6. The mixture obtained in S5 is subjected to vacuum rotary evaporation to remove the solvent, so that the pre-assembled composite unit is coated on the surface of the cathode material particles, thereby obtaining the sodium ion cathode material with high humidity adaptability.

2. The preparation method according to claim 1, characterized in that, The amount of fluorinated graphene used is 0.1-5 wt% of the mass of the sodium ion layered oxide cathode material; the mass ratio of the fluorinated graphene to the R-PEG-X organic molecule is 1:0.5 to 1:

5.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the fluorinated graphene to the R-PEG-X organic molecule is 1:1.5 to 1:

2.

4. The preparation method according to claim 1, characterized in that, The mass concentration of the fluorinated graphene in S2 in the first organic solvent is 0.1-5 mg / mL; the mass concentration of the R-PEG-X organic molecule in S3 in the second organic solvent is 0.5-10 mg / mL.

5. The preparation method according to claim 1, characterized in that, The mixing temperature in S4 is 20-60℃, and the stirring time is 1-5 hours; the ultrasonic power in S5 is 100-500 W, and the ultrasonic time is 0.5-4 hours.

6. The preparation method according to claim 1, characterized in that, The first organic solvent and the second organic solvent are the same, both being N-methylpyrrolidone.

7. The preparation method according to claim 1, characterized in that, The R-PEG-X organic molecule is octadecyl-polyethylene glycol-amino (C18-PEG-NH2).

8. A sodium-ion cathode material with high humidity adaptability prepared by the preparation method according to any one of claims 1-7, characterized in that, The surface of the cathode material particles is coated with a hybrid coating layer formed by the physical self-assembly of fluorinated graphene and R-PEG-X organic molecules; the coating layer has a conductive framework-flexible interface layer composite structure, wherein fluorinated graphene constitutes the conductive framework, R-PEG-X molecules are anchored to the surface of fluorinated graphene with their alkyl chains, and PEG segments extend outward.

9. A positive electrode sheet, characterized in that, It includes the sodium ion cathode material as described in claim 8.

10. A sodium-ion battery, characterized in that, It includes the positive electrode sheet as described in claim 9.

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