A highly stable sodium battery cathode and its preparation method

Abstract

This invention discloses a high-stability sodium battery cathode and its preparation method, comprising 3-15% PEDOT:PSS, 5-8% carbon nanotubes, 3-12% fluororubber, 0.5-5% nano-alumina, and the balance being cathode active material. The preparation method includes the following steps: S1. Carbon nanotubes and PEDOT:PSS are added sequentially to NMP and mixed to obtain a first dispersion; fluororubber powder is added to NMP at 80-100°C and dissolved to obtain a second dispersion; S2. The cathode active material and the first dispersion are mixed, then the second dispersion is added, and finally nano-alumina is added to obtain a cathode slurry; S3. The cathode slurry is coated onto the surface of an aluminum foil and then rolled to obtain the high-stability sodium battery cathode.

Description

Technical Field

[0001] This invention belongs to the field of sodium battery cathode technology, specifically a high-stability sodium battery cathode and its preparation method. Background Technology

[0002] Sodium-ion batteries have become a research hotspot in the energy storage field due to their significant advantages such as abundant resources and low cost. However, the performance bottleneck of cathode materials has always been a key factor restricting their commercial application and large-scale promotion. Traditional sodium-ion battery cathode materials, such as layered oxides, polyanionic compounds, and Prussian blue compounds, suffer from significant deficiencies in structural stability. During charging and discharging, as sodium ions insert and extract, the layered structure is prone to slippage and phase transitions, leading to gradual structural collapse and rapid capacity decay.

[0003] To improve the performance of these traditional cathode materials, researchers have tried various methods, such as element doping, surface coating, and structural modulation. While element doping can adjust the electronic and crystal structures of materials to some extent and enhance their structural stability, it may also introduce impurities, affecting the intrinsic properties of the material. Furthermore, the type and content of dopant elements are difficult to control precisely, leading to poor consistency in material performance. Surface coating can improve the interfacial compatibility between the material and the electrolyte to some extent and reduce side reactions, but the thickness and uniformity of the coating layer are difficult to guarantee, which may affect the transport of sodium ions and electrons, reducing the overall performance of the battery. Although structural modulation can design cathode materials with special structures, such as nanostructures and porous structures, to improve material performance, the fabrication processes for these special structures are often complex and costly, making large-scale industrial production difficult. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a highly stable sodium battery cathode and its preparation method. This invention utilizes a composite of Na3V2(PO4)3 and Na... 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2 enables complementary performance of active materials, while PEDOT:PSS and carbon nanotubes synergistically enhance conductivity, and fluororubber and nano-alumina strengthen structural stability. Ultimately, the highly stable sodium battery cathode achieves a balance between high-rate performance, cycle stability, and safety.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] The high-stability sodium battery cathode, by mass fraction, comprises 3-15% PEDOT:PSS (poly(3,4-ethylenedioxythiophene / polystyrene sulfonate), 5-8% carbon nanotubes, 3-12% fluororubber, 0.5-5% nano-alumina, and the balance being cathode active material; preferably, it comprises 5-12% PEDOT:PSS, 5-8% carbon nanotubes, 5-8% fluororubber, 1-3% nano-alumina, and the balance being cathode active material.

[0007] The positive electrode active material is sodium vanadium polyanion phosphate Na3V2(PO4)3 and layered sodium nickel manganese iron oxide Na2 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2.

[0008] According to some embodiments of the present invention, the Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 to Na3V2(PO4)3 is 2~6:1, with a preferred ratio of 3~5:1.

[0009] According to some embodiments of the present invention, the Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The specific surface area of ​​O2 is 5~20m². 2 / g, D50 is 0.5~5μm; preferably, the Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The specific surface area of ​​O2 is 8~12m². 2 / g, D50 is 1~3μm.

[0010] According to some embodiments of the present invention, the specific surface area of ​​the Na3V2(PO4)3 is 10~30 m². 2 / g, D50 is 0.5~2μm; the specific surface area of ​​Na3V2(PO4)3 is 15~20m². 2 / g, D50 is 0.5~1μm.

[0011] According to some embodiments of the present invention, the diameter of the carbon nanotube is 20~100 nm.

[0012] According to some embodiments of the present invention, the specific surface area of ​​the carbon nanotubes is 140~180 m². 2 / g.

[0013] According to some embodiments of the present invention, the nano-alumina has a purity ≥99.9%, a particle size of 10~100nm, and a specific surface area of ​​100~150m². 2 / g.

[0014] According to some embodiments of the present invention, the fluororubber is an elastomer copolymerized from vinylidene fluoride (VDF) and perfluoropropylene (HFP).

[0015] This invention also discloses a method for preparing the aforementioned highly stable sodium battery cathode, comprising the following steps:

[0016] S1. Carbon nanotubes and PEDOT:PSS are added sequentially to NMP and mixed well to obtain the first dispersion;

[0017] Fluororubber powder was dissolved in NMP at 80-100°C to obtain a second dispersion;

[0018] S2. After mixing the positive electrode active material and the first dispersion, the second dispersion is added, and finally nano-alumina is added to obtain the positive electrode slurry;

[0019] S3. Coat the positive electrode slurry onto the surface of aluminum foil and then roll it to obtain a high-stability sodium battery positive electrode.

[0020] According to some embodiments of the present invention, the solid content of the first dispersion is 5-15%, preferably 8-12%.

[0021] According to some embodiments of the present invention, the solid content of the second dispersion is 3-10%, preferably 5-8 wt%.

[0022] According to some embodiments of the present invention, the dissolution is carried out by stirring at 80~100°C for 120~150 min.

[0023] According to some embodiments of the present invention, the first dispersion is prepared by ultrasonic-assisted dispersion for 20-30 min, with an ultrasonic power of 300-500 W.

[0024] Before S2, the positive electrode active material needs to be pretreated, namely, the polyanionic sodium vanadium phosphate is heat-treated at 300~350℃ for 2~3h under inert gas protection, the layered sodium nickel manganese iron oxide is vacuum dried at 120~150℃ for 8~12h, and the pretreated sodium vanadium phosphate and layered sodium nickel manganese iron oxide are dry-mixed for 20~30min to obtain the positive electrode active material.

[0025] In S2, the mixing is carried out by stirring at 1000~1200 rpm for 120~150 min, and after the second dispersion is added, stirring is continued for 90~120 min.

[0026] In S2, the nano-alumina is dispersed at high speed at 2000-2200 rpm for 60-80 min after being added;

[0027] In S2, the viscosity of the positive electrode slurry is 3000~5000 mPs·s;

[0028] In S2, the positive electrode slurry is stirred in a vacuum during preparation, with a vacuum degree ≤ -0.09 MPa;

[0029] In S3, the thickness of the aluminum foil is 10~20μm, preferably 12~15μm;

[0030] In S3, the surface roughness Ra of the aluminum foil is 0.1~0.3μm;

[0031] In S3, the coating is performed using a slot coater;

[0032] In step S3, the coating speed is 0.5~3m / min, preferably 1~2m / min;

[0033] In S3, the thickness of the wet film coated is 80~100μm;

[0034] In S3, the solvent is removed by drying at 70~80℃ for 20~30 min, 100~120℃ for 30~40 min, and 140~150℃ for 40~60 min respectively after coating.

[0035] In S3, the temperature of the roller pressing is 60~80℃;

[0036] In S3, the pressure of the roller is 15~20MPa;

[0037] In S3, the speed of the roller pressing is 0.5~1m / min;

[0038] In step S3, the rolling process results in an electrode compaction density of 3.2~3.5 g / cm³. 3 .

[0039] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. This invention uses polyanionic sodium vanadium phosphate Na3V2(PO4)3 and layered sodium nickel manganese iron oxide Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5O2, as a composite positive electrode active material, and sodium vanadium polyanionic phosphate possess a stable three-dimensional framework structure. + The diffusion channels are unobstructed, resulting in excellent high-rate charge-discharge capability, but the specific capacity is relatively low. Layered sodium-nickel-manganese-iron oxides have high specific capacity, but exhibit low specific capacity at high rates. + The problems include high insertion / extraction resistance and poor cycle stability. When the two are combined in a certain proportion, the high ionic conductivity of sodium vanadium polyanionic phosphate can improve the rate performance of the layered material, while the high specific capacity of the layered material can compensate for the capacity limitation of the polyanionic material.

[0042] 2. Carbon nanotubes can construct long-distance electron transport channels, while PEDOT:PSS, a high-molecular conductive polymer, fills the gaps between the carbon nanotubes and bonds tightly to the surface of the active material. Compared to a single conductive agent, the electrode's electronic conduction resistance is reduced, ensuring rapid electron transport at high rates. The elastic segments of fluororubber can encapsulate the active material particles, buffering volume changes during cycling, while nano-alumina can act as a physical support point embedded between the active material and the binder, suppressing electrode structure collapse. The synergy of these two elements results in a high degree of structural integrity retention of the electrode after cycling.

[0043] 3. Therefore, the high-stability sodium battery cathode has high rate performance and excellent cycle stability. Compared with traditional cathodes, the risk of battery thermal runaway is reduced, thus balancing performance and safety. Detailed Implementation

[0044] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] The raw material information used in the following examples is as follows:

[0047] Carbon nanotubes are derived from the CR2000 series of Qingdao Chaorui Nanomaterials Technology Co., Ltd., with a diameter of 20~50nm and a specific surface area of ​​140~180m². 2 / g;

[0048] Fluororubber, derived from Zhonghao Chenguang Fluororubber FKM2604, is an elastomer copolymerized from vinylidene fluoride (VDF) and perfluoropropylene (HFP); its density is 1.81 g / cm³. 3 The tensile strength is 16.8 MPa and the elongation at break is 230%.

[0049] The nano-alumina has a purity of 99.99%, a particle size of 50 nm, and a specific surface area of ​​100~130 m². 2 / g;

[0050] The specific surface area of ​​Na3V2(PO4)3 is 15~20 m². 2 / g, D50 is 1.5μm;

[0051] Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The process involves weighing sodium nitrate, nickel nitrate, ferric nitrate, and manganese nitrate in a stoichiometric ratio of Na:Ni:Fe:Mn = 0.9:0.3:0.2:0.5, with an excess of 5% NaNO3 to compensate for sodium volatilization at high temperatures. The raw materials are then vacuum-dried at 80°C for 12 hours to remove water of crystallization. They are then placed in an agate mortar, and anhydrous ethanol is added as a dispersant. The mixture is ground for 10 minutes until homogeneous, forming a slurry. This mixture is then dried in an 80°C oven to remove the ethanol, yielding a dry powder. The powder is transferred to an alumina crucible and placed in a muffle furnace. The furnace is then heated in an air atmosphere: from room temperature (25°C) to 300°C and held for 2 hours, then further heated to 500°C and held for 4 hours. After natural cooling to room temperature, the powder is removed and ground again for 20 minutes to break up any agglomerated particles. The pre-calcined powder was reloaded into an alumina crucible and calcined a second time in air: the temperature was increased to 900-950℃ at a rate of 5℃ / min and held for 10-12 hours; the powder was then cooled to room temperature in the furnace to obtain black Na. 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2; its specific surface area is 8~12m². 2 / g, D50 is 3μm;

[0052] This includes, but is not limited to, the models from the above manufacturers.

[0053] Example 1

[0054] The high-stability sodium battery cathode of this embodiment includes 10% PEDOT:PSS, 7.3% carbon nanotubes, 6% fluororubber, 1.5% nano-alumina and the balance of cathode active material;

[0055] Na3V2(PO4)3 and Na in the positive electrode active material 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 is 3:1.

[0056] A method for preparing a high-stability sodium battery cathode includes the following steps:

[0057] S1. Place NMP in a suitable container, add carbon nanotubes and PEDOT:PSS in sequence according to the ratio, and then disperse using ultrasound-assisted dispersion for 25 minutes with the ultrasound power set to 400W. The purpose of ultrasound is to fully disperse carbon nanotubes and PEDOT:PSS in NMP and avoid agglomeration, ultimately obtaining a first dispersion with a solid content of 10%.

[0058] NMP was added to another container and heated to 90°C, then fluororubber powder was added. Fluororubber is an elastomer copolymerized from vinylidene fluoride (VDF) and perfluoropropylene (HFP), possessing good chemical stability and mechanical properties, and enhancing the adhesion of the electrode. The mixture was stirred continuously at 90°C for 130 minutes to fully dissolve the fluororubber powder, yielding a second dispersion with a solid content of 6%.

[0059] S2. Pretreatment of the positive electrode active material: Na3V2(PO4)3 was heat-treated in a high-temperature furnace at 320℃ for 2.5h under argon protection; Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2 was placed in a vacuum drying oven and dried under vacuum at 130°C for 10 hours. The pretreated Na3V2(PO4)3 and Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2 was placed in a dry mixer and dry-mixed at 1100 rpm for 25 minutes;

[0060] The obtained positive electrode active material was stirred with the first dispersion at 1100 rpm for 130 min to ensure thorough mixing. Then, the second dispersion was added, and stirring continued for 100 min. Finally, nano-alumina was added, and the stirring speed was increased to 2100 rpm for high-speed dispersion for 70 min, ultimately yielding a positive electrode slurry with a viscosity of 4000 mPs·s. The entire preparation process of the positive electrode slurry was carried out under vacuum, with the vacuum level controlled between -0.1 and -0.09 MPa.

[0061] S3. A slot coater is used for coating to evenly coat the positive electrode slurry onto the aluminum foil surface. The coating speed is controlled at 1.5 m / min, and the wet film thickness is 90 μm. After coating, the aluminum foil with the wet film is sent to a drying device for drying treatment, sequentially dried at 80℃ for 25 min, 110℃ for 35 min, and 150℃ for 50 min. The dried electrode then enters the rolling process. The rolling temperature is set at 70℃, the rolling pressure at 18 MPa, and the rolling speed at 0.8 m / min. After rolling, the electrode compaction density reaches 3.3 g / cm³. 3 .

[0062] Example 2

[0063] The difference between this embodiment and Embodiment 1 is as follows:

[0064] The high-stability sodium battery cathode of this embodiment includes 10% PEDOT:PSS, 6.5% carbon nanotubes, 7.3% fluororubber, 2.5% nano-alumina, and the balance of cathode active material.

[0065] Na3V2(PO4)3 and Na in the positive electrode active material 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 is 3:1;

[0066] The other raw materials, steps and parameters are the same as in Example 1.

[0067] Example 3

[0068] The difference between this embodiment and Embodiment 1 is as follows:

[0069] The high-stability sodium battery cathode of this embodiment includes 3% PEDOT:PSS, 7.3% carbon nanotubes, 6% fluororubber, 1.5% nano-alumina and the balance of cathode active material;

[0070] Na3V2(PO4)3 and Na in the positive electrode active material 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 is 2:1;

[0071] The other raw materials, steps and parameters are the same as in Example 1.

[0072] Example 4

[0073] The difference between this embodiment and Embodiment 1 is as follows:

[0074] The high-stability sodium battery cathode of this embodiment includes 3% PEDOT:PSS, 6.5% carbon nanotubes, 6.0% fluororubber, 2% nano-alumina, and the balance of cathode active material;

[0075] Na3V2(PO4)3 and Na in the positive electrode active material 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 is 6:1;

[0076] The other raw materials, steps and parameters are the same as in Example 1.

[0077] Example 5

[0078] The difference between this embodiment and Embodiment 1 is as follows:

[0079] The high-stability sodium battery cathode of this embodiment includes 3% PEDOT:PSS, 10% carbon nanotubes, 7.1% fluororubber, 2.9% nano-alumina, and the balance of cathode active material.

[0080] Na3V2(PO4)3 and Na in the positive electrode active material 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 is 6:1;

[0081] The other raw materials, steps and parameters are the same as in Example 1.

[0082] Example 6

[0083] The difference between this embodiment and Embodiment 1 is as follows:

[0084] In S3, after coating, it is dried at 120℃ for 3 hours;

[0085] In S3, the rolling temperature is 50℃;

[0086] In S3, the compacted density of the electrode sheet after rolling reaches 3.1 g / cm³. 3 ;

[0087] The other raw materials, steps and parameters are the same as in Example 1.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is as follows:

[0090] In this comparative example, the positive electrode active material is only Na3V2(PO4)3;

[0091] The other raw materials, steps and parameters are the same as in Example 1.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is as follows:

[0094] In this comparative example, the positive electrode active material is only Na. 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2;

[0095] The other raw materials, steps and parameters are the same as in Example 1.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 1 is as follows:

[0098] The high-stability sodium battery cathode in this comparative example contains 15% carbon nanotubes, 6.4% fluororubber, 1.2% nano-alumina, and the remainder positive electrode active material; it does not contain PEDOT:PSS.

[0099] The other raw materials, steps and parameters are the same as in Example 1.

[0100] Test case

[0101] The high-stability sodium battery positive electrodes prepared in the above embodiments and comparative examples were assembled into batteries. The CR2032 positive electrode shell was placed flat on the assembly table. Using tweezers, the pre-treated positive electrode sheet was placed in the center of the positive electrode shell. A glass fiber separator was then placed over the surface of the positive electrode sheet, ensuring complete coverage (the edge extending ≥2mm beyond the positive electrode sheet). Electrolyte was slowly added to the separator using a pipette, with a volume of 80μL, ensuring complete saturation. The mixture was allowed to stand for 5 minutes to allow the electrolyte to fully diffuse. A freshly treated sodium metal sheet was placed in the center of the separator using tweezers. A spring sheet and negative electrode shell were then placed in sequence, and the components were gently pressed together. The assembled battery was placed in a button cell battery sealing machine, with a sealing pressure of 10MPa and a holding time of 5s, to complete the sealing. After sealing, the battery appearance was inspected to ensure there was no electrolyte leakage and no deformation of the casing.

[0102] The sealed coin cells were left to stand at a constant temperature of 25±2℃ for 12 hours to allow the electrolyte to further penetrate into the pores of the positive electrode active material, thus completing the initial formation of the electrode-electrolyte interface and preparing for subsequent testing.

[0103] The assembled batteries were tested using a Blue Electric CT2001A battery testing system and an electrochemical workstation (CHI660E) under constant temperature and humidity conditions (temperature 25±1℃, relative humidity ≤30%), and cycled 100 times at a 1C rate within the range of 3.0~4.3V. The capacity decay rate after each cycle was recorded. Then, at 55±2℃, the batteries were charged and discharged at a 1C rate within the range of 2.0~3.2V for 100 cycles, and the capacity retention rate was recorded. The results are shown in Table 1.

[0104]

[0105] The following conclusions can be drawn from the test results:

[0106] As can be seen from the comparison between Examples 1 and 2, an excessive amount of fluororubber will slightly hinder the sodium ion transport channel, and an excessively high content of nano-alumina is prone to local agglomeration, which leads to a decrease in the ion diffusion efficiency inside the electrode.

[0107] As can be seen from Examples 3-5, PEDOT:PSS can fill the gaps between carbon nanotubes and bind tightly to the surface of active materials to reduce electronic conduction resistance. A reduction in its content will directly lead to a decrease in electron transport efficiency, and even adjusting the carbon nanotube content cannot completely compensate for this defect.

[0108] Example 6 did not use segmented drying, and low-temperature rolling resulted in low electrode compaction density, making the electrode structure prone to deformation during cycling.

[0109] Comparative Example 1 uses only Na3V2(PO4)3 as the positive electrode active material. Although it has a stable three-dimensional framework, its specific capacity is low, and its capacity decay during cycling is high. Comparative Example 2 uses only Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 Although O2 has a high specific capacity, its layered structure is prone to slippage during charging and discharging, resulting in poor cycle stability.

[0110] Comparative Example 3 does not contain PEDOT:PSS and relies solely on carbon nanotubes to construct the conductive network. The gaps between carbon nanotubes easily form electron transport blind zones, leading to a decrease in the overall conductivity of the electrode.

[0111] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A highly stable sodium battery cathode, characterized in that, By mass fraction, it includes 3-15% PEDOT:PSS, 5-8% carbon nanotubes, 3-12% fluororubber, 0.5-5% nano-alumina, and the balance positive electrode active material; The positive electrode active material is Na3V2(PO4)3 and Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 O2; the Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The mass ratio of O2 to Na3V2(PO4)3 is 2~6:1; The fluororubber is an elastomer copolymerized from vinylidene fluoride and perfluoropropylene.

2. The high-stability sodium battery cathode as described in claim 1, characterized in that, At least one of the following conditions a to b must be met: a.The Na 0.9 [Ni 0.3 Fe 0.2 Mn 0.5 The specific surface area of ​​O2 is 8~12m². 2 / g, D50 is 1~3μm; b. The specific surface area of ​​the Na3V2(PO4)3 is 15~20 m². 2 / g, D50 is 0.5~1μm.

3. The high-stability sodium battery cathode as described in claim 1, characterized in that, At least one of the following conditions a to b must be met: a. The diameter of the carbon nanotubes is 20~50nm; b. The specific surface area of ​​the carbon nanotubes is 140~180m². 2 / g.

4. The high-stability sodium battery cathode as described in claim 1, characterized in that... The nano-alumina has a particle size of 10~100nm and a specific surface area of ​​100~150m². 2 / g.

5. The method for preparing a high-stability sodium battery cathode as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Carbon nanotubes and PEDOT:PSS are added sequentially to NMP and mixed well to obtain the first dispersion; Fluororubber powder was dissolved in NMP at 80-100°C to obtain a second dispersion; S2. After mixing the positive electrode active material and the first dispersion, the second dispersion is added, and finally nano-alumina is added to obtain the positive electrode slurry; S3. Coat the positive electrode slurry onto the surface of aluminum foil and then roll it to obtain a high-stability sodium battery positive electrode.

6. The method for preparing a high-stability sodium battery cathode as described in claim 5, characterized in that, At least one of the following conditions a to d must be met: a. The solid content of the first dispersion is 5-15%; b. The solid content of the second dispersion is 3-10%; c. The dissolution is performed by stirring at 80-100℃ for 120-150 min; d. The first dispersion was prepared by ultrasonic-assisted dispersion for 20-30 minutes with an ultrasonic power of 300-500W.

7. The method for preparing a high-stability sodium battery cathode as described in claim 5, characterized in that, The positive electrode active material also needs to be pretreated, namely, the polyanionic sodium vanadium phosphate is heat-treated at 300~350℃ for 2~3h under inert gas protection, the layered sodium nickel manganese iron oxide is vacuum dried at 120~150℃ for 8~12h, and the pretreated sodium vanadium phosphate and layered sodium nickel manganese iron oxide are dry-mixed for 20~30min to obtain the positive electrode active material.

8. The method for preparing a high-stability sodium battery cathode as described in claim 7, characterized in that, At least one of the following conditions a to d must be met: a. The mixing is carried out by stirring at 1000-1200 rpm for 120-150 min, and stirring is continued for 90-120 min after the second dispersion is added; b. After the nano-alumina is added, it is dispersed at high speed at 2000~2200 rpm for 60~80 min; c. The viscosity of the positive electrode slurry is 3000~5000 mPs·s; d. The positive electrode slurry is stirred in a vacuum during preparation, with a vacuum degree ≤ -0.09MPa.

9. The method for preparing a high-stability sodium battery cathode as described in claim 5, characterized in that, At least one of the following conditions a to f must be satisfied: a. The thickness of the aluminum foil is 10~20μm; b. The surface roughness Ra of the aluminum foil is 0.1~0.3μm; c. The coating is performed using a slot coater; d. The coating speed is 0.5~3m / min; e. The thickness of the wet film coated is 80~100μm; f. After coating, the solvent is removed by drying at 70-80℃ for 20-30 min, 100-120℃ for 30-40 min, and 140-150℃ for 40-60 min.

10. The method for preparing a high-stability sodium battery cathode as described in claim 5, characterized in that, At least one of the following conditions a to b must be met: a. The thickness of the aluminum foil is 12~15μm; b. The coating speed is 1~2m / min.

11. The method for preparing a high-stability sodium battery cathode as described in claim 5, characterized in that, At least one of the following conditions a to d must be met: a. The temperature of the roller pressing is 60~80℃; b. The pressure of the roller pressing is 15~20MPa; c. The speed of the roller pressing is 0.5~1m / min; d. The rolling process results in an electrode compaction density of 3.2~3.5 g / cm³. 3 .

Images