Current collectors for sodium-ion secondary batteries and their preparation methods and equipment

Abstract

This invention relates to sodium-ion secondary batteries, specifically to a current collector for sodium-ion secondary batteries and its preparation method and equipment. The current collector for the positive electrode of the sodium-ion secondary battery includes an intermediate metal foil layer and coatings located on both sides of the intermediate layer; the coatings contain nano-cellulose and a conductive agent. This invention's current collector for the positive electrode of the sodium-ion secondary battery isolates the contact between the sodium-ion positive electrode material and the aluminum foil, overcoming the problems in existing sodium-ion secondary batteries such as low electrode compaction density, reduced battery capacity, and reduced lifespan caused by chemical reactions between the positive electrode material and the aluminum foil.

Description

Technical Field

[0001] This invention relates to sodium-ion secondary batteries, and more specifically to a current collector for sodium-ion secondary batteries and its preparation method and equipment. Background Technology

[0002] In the 21st century, lithium batteries have been applied in numerous fields, including mobile phones, computers, wearable devices, electric vehicles, bicycles, power tools, and streetlights. In recent years, lithium resource consumption has been characterized by high demand and rapid depletion, with lithium production growth failing to keep pace. This is due to two main reasons: firstly, lithium resources are finite, primarily existing as spodumene ore and lithium from salt lakes; and secondly, lithium extraction from salt lakes is impossible during winter. In contrast, sodium is widely available and abundant, with reserves 420 times that of lithium, and its price is significantly lower. In recent years, with the soaring price of lithium, sodium-ion batteries have attracted widespread attention due to their potential cost reduction of 30-50% compared to lithium-ion batteries, particularly in energy storage, hybrid power, and lead-acid battery replacement, where they hold promising application prospects.

[0003] Currently, the preparation method of the positive electrode of sodium-ion batteries involves: using Na3V2(PO4)3 and NaFe... 1 / 3 Ni 1 / 3 Mn 1 / 3 One of the three materials, O3, Prussian blue, and conductive agent, is mixed with a binder to form a slurry, which is then coated onto aluminum foil and prepared through processes such as drying, rolling, and slitting.

[0004] Compared to lithium-ion secondary battery cathode materials, sodium-ion secondary battery cathode materials are more alkaline. Due to the contact between the cathode material and the aluminum foil, a certain chemical reaction occurs, which leads to a decrease in the compaction density of the cathode sheet during the rolling process and loss of cathode material, thereby reducing the capacity and cycle life of the finished sodium-ion secondary battery. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the prior art.

[0006] This invention provides a current collector for the positive electrode of a sodium-ion secondary battery, as well as a method and apparatus for its preparation. The current collector isolates the contact between the sodium-ion positive electrode material and the aluminum foil, overcoming the problems of low electrode compaction density, reduced battery capacity, and reduced lifespan caused by chemical reactions between the positive electrode material and the aluminum foil in existing sodium-ion secondary batteries.

[0007] A sodium-ion secondary battery positive electrode current collector includes an intermediate metal foil layer and coatings located on both sides of the intermediate layer; the coatings contain nanocellulose and a conductive agent.

[0008] The current collector of the present invention adopts a three-layer structure, with the top and bottom layers being coatings and the middle layer being a metal foil (e.g., aluminum foil); the nanocellulose component in the coating prevents the positive electrode material from contacting the aluminum foil, thus preventing a chemical reaction between the two; since nanocellulose is non-conductive, a highly conductive component is added to the coating to achieve electronic conduction between the positive electrode material and the current collector.

[0009] According to embodiments of the present invention, the metal foil is selected from aluminum foil or copper foil. Optionally, the thickness of the metal foil is 10-20 μm, for example 15 μm.

[0010] According to an embodiment of the present invention, the thickness of the coating is 0.5-5 μm, for example 1-2 μm.

[0011] According to an embodiment of the present invention, the coating contains 30-75 wt% nanocellulose, optionally 60-72 wt%; the coating contains 10-40 wt% conductive agent, optionally 25-37 wt%.

[0012] According to an embodiment of the present invention, the nanocellulose is selected from one or two of cellulose nanocrystals and cellulose nanofibers.

[0013] Optionally, the cellulose nanocrystals have a diameter of 5-70 nm and a length of 25-300 nm; preferably a diameter of 5-20 nm and a length of 25-100 nm; more preferably a diameter of 15-20 nm and a length of 35-45 nm.

[0014] Optionally, the cellulose nanofibers have a diameter of 5-60 nm and a length of 100-3000 nm; preferably a diameter of 5-20 nm and a length of 500-1500 nm; more preferably a diameter of 5-10 nm and a length of 500-650 nm.

[0015] In some embodiments, the nanocellulose is a mixture of cellulose nanofibers and nanofibers in a mass ratio of 1:1; the cellulose nanocrystals have a diameter of 15-20 nm and a length of 35-45 nm; the cellulose nanofibers have a diameter of 5-10 nm and a length of 500-650 nm.

[0016] According to an embodiment of the present invention, the conductive agent is selected from one or more of carbon black, acetylene black, carbon nanotubes, Ketjen black, and carbon fiber; preferably, acetylene black and carbon nanotubes are used in a mass ratio of 1:1.

[0017] According to an embodiment of the present invention, the coating further contains a binder, the content of which may be 1-5 wt%, and more preferably 2-5 wt%.

[0018] According to embodiments of the present invention, the adhesive is polyvinylidene fluoride (PVDF), preferably with a molecular weight of 800,000 to 1,200,000, for example, 1,000,000. Studies have found that if the molecular weight of PVDF is too low, the adhesion is poor; if the molecular weight is too high, dissolution is difficult.

[0019] According to an embodiment of the present invention, the coating further contains a dispersant, the content of which may be selected as 0.5-3 wt%, and more preferably 1-3 wt%.

[0020] According to embodiments of the present invention, the dispersant is polyvinylpyrrolidone (PVP), preferably with a molecular weight of 600,000 to 1,200,000, for example, 800,000. Studies have found that if the molecular weight of polyvinylpyrrolidone is too low, its dispersibility is poor, and if the molecular weight is too high, it is difficult to dissolve.

[0021] According to an embodiment of the present invention, the raw materials for preparing the coating further include a solvent, which may be N-methylpyrrolidone (NMP). Typically, the solvent in the coating evaporates substantially after drying.

[0022] According to an embodiment of the present invention, the coating contains nanocellulose, conductive agent, binder and dispersant. Optionally, the mass ratio of nanocellulose, conductive agent, binder and dispersant is (30-75):(10-40):(1-5):(0.5-3).

[0023] The present invention also provides a method for preparing the above-mentioned sodium-ion secondary battery positive electrode current collector, comprising:

[0024] 1) Mix nanocellulose, conductive agent, binder, dispersant and solvent according to the formula to prepare a slurry with a solid content of 5-50wt%;

[0025] 2) The slurry is evenly coated on the upper and lower surfaces of the metal foil and then dried;

[0026] 3) The metal foil coated in step 2) is oxidized under a NO2 atmosphere;

[0027] 4) The oxidized metal foil from step 3) is hot-rolled to obtain a current collector.

[0028] Optionally, the solid content of the slurry in step 1) is 10-20 wt%. If the solid content of the slurry is too low, the manufacturing cost is high; if the solid content of the slurry is too high, it is difficult to uniformly disperse the various substances.

[0029] Optionally, in step 1), the dispersion is carried out in the Hongyun DL-500L equipment with a dispersion disc linear speed of 10-200m / min, preferably 60-100m / min. If the speed is too low, it will be difficult to disperse fully; if the speed is too high, it will easily break the dispersed material. The dispersion time is 120-240min.

[0030] Optionally, step 2) involves coating on a Kejing Zhida Technology MG200 micro-gravure coating machine. Optionally, the coating conveyor speed is 2-10 m / min, and the drying temperature is 80-130℃. Optionally, the coating thickness after drying is 0.5-5 μm, and more preferably 1-2 μm.

[0031] Optionally, in step 3), the NO2 flow rate is 10-30 L / min, and the oxidation temperature is 60-120℃. Studies have found that high temperatures are beneficial to the oxidation reaction. Oxidation can eliminate the hydroxyl groups in the nanocellulose material, preventing it from chemically reacting with the highly oxidized cathode material after battery charging.

[0032] Optionally, in step 4), the pressure of hot rolling is 0.1-2 MPa, and the temperature of hot rolling is 60-80℃. Hot rolling is beneficial for enhancing the adhesion between the coating and the metal foil.

[0033] In some specific examples, the preparation method of the positive electrode current collector of the sodium-ion secondary battery includes:

[0034] 1) Disperse nanocellulose, conductive agent, binder, dispersant and solvent in the Hongyun DL-500L equipment according to the formula to prepare a slurry with a solid content of 5-50wt%; the dispersion disc linear speed is 10-200m / min, preferably 60-100m / min, and the dispersion time is 120-240min;

[0035] 2) The slurry is uniformly coated on the upper and lower surfaces of the metal foil using a Kejing Zhida Technology MG200 micro-gravure coating machine. The coating conveyor speed is 2-10 m / min, and the drying temperature is 80-130℃. After drying, the coating thickness is 0.5-5 μm, preferably 1-2 μm.

[0036] 3) The metal foil coated in step 2) is oxidized in a NO2 atmosphere; the NO2 flow rate is 10-30 L / min and the oxidation temperature is 60-120℃.

[0037] 4) The oxidized metal foil from step 3) is hot-rolled to obtain a current collector; the hot-rolling pressure is 0.1-2 MPa, and the hot-rolling temperature is 60-80℃.

[0038] To better prepare the above-mentioned sodium-ion secondary battery positive electrode current collector, the present invention also provides an apparatus, comprising: an unwinding shaft; a transfer shaft; a first microgravure coating machine; a first drying oven; a second microgravure coating machine; a second drying oven; an NO2 oxidation device; a hot press roller; and a take-up shaft, connected in sequence. The NO2 oxidation device is provided with an NO2 outlet and an NO2 inlet.

[0039] The present invention also includes a sodium-ion secondary battery positive electrode current collector prepared by the above method.

[0040] The present invention also includes the application of the above-mentioned sodium-ion secondary battery positive electrode current collector in the preparation of sodium-ion secondary batteries.

[0041] The present invention also provides a positive electrode sheet for a sodium-ion secondary battery, comprising the aforementioned positive current collector for a sodium-ion secondary battery. In some embodiments, it further includes a positive electrode slurry coated on the positive current collector. Optionally, the positive electrode slurry comprises NaFe. 1 / 3 Ni 1 / 3 Mn 1 / 3 One or more of the following: O3, sodium vanadium phosphate, sodium vanadium fluorophosphate, Prussian white, etc.

[0042] The present invention also provides a sodium-ion secondary battery, including the above-mentioned sodium-ion secondary battery positive electrode sheet; or including the above-mentioned sodium-ion secondary battery positive current collector.

[0043] The nanocellulose in the coating of this invention isolates the contact between the positive electrode material and the aluminum foil, preventing the chemical reaction between them. Compared with sodium-ion secondary batteries that use traditional aluminum foil as the positive electrode current collector, the compaction density of the positive electrode sheet of the sodium-ion secondary battery prepared by this invention is increased by 0.1-0.3 g / cm3, the capacity of the sodium-ion battery is increased by 20-30%, and the cycle life is increased by 70-110%. Attached Figure Description

[0044] Figure 1 A schematic diagram of the positive electrode current collector of a sodium-ion secondary battery according to an embodiment of the present invention.

[0045] Figure 2 A schematic diagram of the equipment used to prepare the positive electrode current collector for sodium-ion secondary batteries according to an embodiment of the present invention. Detailed Implementation

[0046] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the examples, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0047] It should be noted that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0048] like Figure 1As shown, an embodiment of the present invention provides a positive electrode current collector for a sodium-ion secondary battery, comprising an intermediate metal foil 2, and coatings 1 and 3 respectively located on both sides of the intermediate layer; the coatings contain nanocellulose and a conductive agent.

[0049] like Figure 2 As shown, this embodiment of the invention provides an apparatus for preparing a positive electrode current collector for a sodium-ion secondary battery, comprising, in sequence, an unwinding shaft 1; a transfer shaft 2; a first microgravure coating machine 3; a first drying oven 4; a second microgravure coating machine 5; a second drying oven 6; an NO2 oxidation device 7; a hot press roller 10; and a take-up shaft 11. The NO2 oxidation device 7 is provided with an NO2 outlet 8 and an NO2 inlet 9.

[0050] like Figure 2 As shown, the working process of the equipment is as follows: the aluminum foil is unwound on the unwinding shaft 1; it is then sent to the first microgravure coating machine 3 via the transfer shaft 2, where a slurry (cellulose slurry) is coated on the upper surface of the aluminum foil and dried in the first oven 4; subsequently, it enters the second microgravure coating machine 5, where a slurry (cellulose slurry) is coated on the lower surface of the aluminum foil and dried in the second oven 6; then, the cellulose is oxidized in the NO2 oxidation equipment 7; subsequently, it is rolled at the hot press roller 10; and finally, it is wound up at the take-up shaft 11.

[0051] In some embodiments, the coating slurry can be prepared by the following embodiments, or by using slurries prepared using existing technologies.

[0052] The following sodium-ion secondary battery positive electrode current collectors can be used Figure 2 The equipment shown is used for preparation.

[0053] Example 1

[0054] This embodiment provides a positive electrode current collector for a sodium-ion secondary battery, and the preparation method is as follows:

[0055] 1) Nanocellulose, conductive agent, binder and dispersant are added to NMP in a mass ratio of 72:25:2:1 and fully dispersed in Hongyun DL-500L equipment to prepare a slurry with a solid content of 10%; the dispersion disc linear speed is 75m / min and the dispersion time is 180min.

[0056] Nanocellulose consists of cellulose nanocrystals with a diameter of 15-20 nm and a length of 35-45 nm; the conductive agent is acetylene black with a particle size distribution of 35-45 nm; the binder is PVDF with a molecular weight of 1 million; and the dispersant is PVP with a molecular weight of 800,000.

[0057] 2) The above slurry was uniformly coated on the upper and lower surfaces of a 15μm thick aluminum foil using a Kejing Zhida Technology MG200 micro-gravure coating machine. The coating belt speed was 3m / min, and the drying temperature was 110℃. The coating thickness after drying was 1μm.

[0058] 3) The coated current collector in step 2) is oxidized under a NO2 atmosphere with a NO2 flow rate of 15 L / min and an oxidation temperature of 100 °C;

[0059] 4) The current collector after oxidation in step 3) is hot rolled under a certain pressure of 0.25 MPa and the hot rolling temperature is 80℃.

[0060] Example 2

[0061] This embodiment provides a positive electrode current collector for a sodium-ion secondary battery, and the preparation method is as follows:

[0062] 1) Nanocellulose, conductive agent, binder and dispersant are added to NMP in a mass ratio of 72:25:2:1 and fully dispersed in Hongyun DL-500L equipment to prepare a slurry with a solid content of 10%; the dispersion disc linear speed is 75m / min and the dispersion time is 180min.

[0063] Nanocellulose is a mixture of cellulose nanofibers and cellulose nanofibers in a mass ratio of 1:1; the cellulose nanocrystals have a diameter of 15-20 nm and a length of 35-45 nm; the cellulose nanofibers have a diameter of 5-10 nm and a length of 500-650 nm.

[0064] The conductive agent is a mixture of acetylene black and carbon nanotubes, with a mass ratio of acetylene black to carbon nanotubes of 1:1; the particle size of acetylene black is 35-45nm; the carbon nanotubes have a diameter of 5-10mm and a length of 50-80nm; the binder is PVDF with a molecular weight of 1 million; and the dispersant is PVP with a molecular weight of 800,000.

[0065] 2) The above slurry was uniformly coated on the upper and lower surfaces of a 15μm thick aluminum foil using a Kejing Zhida Technology MG200 micro-gravure coating machine. The coating belt speed was 3m / min, and the drying temperature was 110℃. The coating thickness after drying was 1μm.

[0066] 3) The coated current collector in step 2) is oxidized under a NO2 atmosphere with a NO2 flow rate of 15 L / min and an oxidation temperature of 100 °C;

[0067] 4) The current collector after oxidation in step 3) is hot rolled under a certain pressure of 0.25 MPa and the hot rolling temperature is 80℃.

[0068] Example 3

[0069] This embodiment provides a positive electrode current collector for a sodium-ion secondary battery, and the preparation method is as follows:

[0070] 1) Nanocellulose, conductive agent, binder and dispersant are added to NMP in a mass ratio of 60:37:2:1 and fully dispersed in Hongyun DL-500L equipment to prepare a slurry with a solid content of 10%; the dispersion disc linear speed is 75m / min and the dispersion time is 180min.

[0071] Nanocellulose is a mixture of cellulose nanofibers and nanocrystals in a 1:1 mass ratio; cellulose nanocrystals have a diameter of 15-20 nm and a length of 35-45 nm; cellulose nanofibers have a diameter of 5-10 nm and a length of 500-650 nm; the conductive agent is a mixture of acetylene black and carbon nanotubes in a 1:1 mass ratio; the acetylene black particle size is 35-45 nm; the carbon nanotubes have a diameter of 5-10 mm and a length of 50-80 nm; the binder is PVDF with a molecular weight of 1 million; the dispersant is PVP with a molecular weight of 800,000.

[0072] 2) The above slurry was uniformly coated on the upper and lower surfaces of a 15μm thick aluminum foil using a Kejing Zhida Technology MG200 micro-gravure coating machine. The coating belt speed was 3m / min, and the drying temperature was 110℃. The coating thickness after drying was 1μm.

[0073] 3) The coated current collector in step 2) is oxidized under a NO2 atmosphere with a NO2 flow rate of 15 L / min and an oxidation temperature of 100 °C;

[0074] 4) The current collector after oxidation in step 3) is hot rolled under a certain pressure of 0.25 MPa and the hot rolling temperature is 80℃.

[0075] Comparative Example 1

[0076] The difference between the sodium-ion secondary battery positive electrode current collector and Example 1 is that the mass ratio of nanocellulose, conductive agent, binder, and dispersant is 92:5:2:1.

[0077] Comparative Example 2

[0078] The difference between the sodium-ion secondary battery positive electrode current collector and Example 1 is that the mass ratio of nanocellulose, conductive agent, binder, and dispersant is 10:87:2:1.

[0079] Experimental Example

[0080] NaFe 1 / 3 Ni 1 / 3 Mn 1 / 3O3 positive electrode slurry was coated onto current collectors for sodium-ion secondary batteries prepared in Examples 1-3 and Comparative Examples 1-2, as well as commercially available ordinary aluminum foil (1060 aluminum foil from Guangzhou Nano New Material Technology Co., Ltd., 15 μm thick). After drying at 95°C and rolling, positive electrode sheets were obtained. Further slitting and winding yielded 26650 cylindrical sodium-ion secondary batteries. The mass fraction of the positive electrode sheet was: NaFe... 1 / 3 Ni 1 / 3 Mn 1 / 3 O3 94%, Super P 3%, PVDF 3%.

[0081] The method for testing the maximum compaction density of the electrode sheet is as follows: after coating, the electrode sheet is cut into 200×200mm sizes, the pressure of the roller press is set to 30-60 tons, and the electrode sheet is rolled. After rolling, the electrode sheet is folded in half. The electrode sheet with a gap but no breakage after folding is compacted, which is the maximum compaction of the electrode sheet.

[0082] Electrode impedance test method: Cut the rolled electrode into a square size of 4cm×8cm, place the cut electrode between the probes of the BER2200 tester, apply a pressure of 5MPa, and read the value.

[0083] Battery internal resistance test method: The battery internal resistance is tested using an RJ3563 internal resistance meter at 1000Hz.

[0084] For the fabricated batteries, five batteries from each design were subjected to a cyclic test at 25°C for N cycles. The discharge capacity of the battery in the Nth cycle and the first cycle was recorded, and the discharge retention rate was calculated. Discharge retention rate = (Nth discharge capacity / First discharge capacity) × 100%. The cyclic test was terminated when the cyclic discharge retention rate reached 80%, and the number of cycles was recorded. The test results are shown in Table 1.

[0085] Table 1 Performance Test Results

[0086]

[0087] As can be seen from the table above, the sodium-ion secondary battery prepared using the current collector of this invention has significantly improved the maximum compaction density of the positive electrode, battery capacity, and cycle life compared to the sodium-ion secondary battery prepared using traditional aluminum foil. The battery using the composite nanocellulose scheme has slightly better maximum compaction density of the electrode, battery capacity, and cycle life than the battery using single nanocellulose. Increasing the conductive agent content in the current collector coating can further improve the cycle life of the battery.

[0088] As can be seen from Example 1 and Comparative Example 1, adding too much polyacrylonitrile increases the maximum compaction density of the electrode, but reduces the battery capacity and cycle life due to decreased conductivity. As can be seen from Example 1 and Comparative Example 2, adding too little polyacrylonitrile decreases the maximum compaction density of the electrode, reduces alkali resistance, leads to increased electrode impedance, reduced battery capacity, and decreased cycle life.

[0089] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A positive electrode current collector for a sodium-ion secondary battery, characterized in that, The device comprises an intermediate metal foil layer and coatings located on both sides of the intermediate layer; the coatings contain nanocellulose and a conductive agent; the metal foil is selected from aluminum foil or copper foil, and has an oxidation temperature of 60-120℃; the coatings contain 30-75 wt% nanocellulose and 10-40 wt% conductive agent. The method for preparing the positive electrode current collector of the sodium-ion secondary battery includes: 1) Mix nanocellulose, conductive agent, binder, dispersant and solvent according to the formula to prepare a slurry with a solid content of 5-50wt%; 2) Apply the slurry evenly to both the upper and lower surfaces of the metal foil and allow it to dry; 3) The metal foil coated in step 2) is oxidized under a NO2 atmosphere; 4) The oxidized metal foil from step 3) is hot-rolled to obtain a current collector.

2. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, The thickness of the metal foil is 10-20 μm; and / or the thickness of the coating is 0.5-5 μm.

3. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, The coating contains 60-72 wt% nanocellulose and 25-37 wt% conductive agent.

4. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, The nanocellulose is selected from one or two of cellulose nanocrystals and cellulose nanofibers; The conductive agent is selected from one or more of carbon black, acetylene black, carbon nanotubes, Ketjen black, and carbon fiber.

5. The sodium-ion secondary battery positive electrode current collector according to claim 4, characterized in that, The conductive agent is acetylene black and carbon nanotubes in a mass ratio of 1:

1.

6. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, The coating also contains a binder at a content of 1-5 wt%; The adhesive is polyvinylidene fluoride; The coating also contains a dispersant at a content of 0.5-3 wt%. The dispersant is polyvinylpyrrolidone.

7. The sodium-ion secondary battery positive electrode current collector according to claim 6, characterized in that, The binder content in the coating is 2-5 wt%; The polyvinylidene fluoride has a molecular weight of 800,000 to 1,200,000. The dispersant content in the coating is 1-3 wt%; The molecular weight of the polyvinylpyrrolidone is 600,000 to 1,200,000.

8. The sodium-ion secondary battery positive electrode current collector according to any one of claims 1-7, characterized in that, The coating contains nanocellulose, conductive agent, binder, and dispersant.

9. The sodium-ion secondary battery positive electrode current collector according to claim 8, characterized in that, The mass ratio of nanocellulose, conductive agent, binder and dispersant is (30-75):(10-40):(1-5):(0.5-3).

10. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, Step 1) The solid content of the slurry is 10-20 wt%; and / or, Step 1) Perform thorough dispersion in the Hongyun DL-500L equipment, with a dispersion disc linear speed of 10-200 m / min; dispersion time of 120-240 min; and / or, Step 2) Coating is performed on the Kejing Zhida Technology MG200 micro-gravure coating machine; the coating belt speed is 2-10 m / min, and the drying temperature is 80-130℃; the coating thickness after drying is 0.5-5 μm; and / or, Step 3) The NO2 flow rate is 10L-30L / min; and / or, Step 4) The pressure of the hot roller pressing is 0.1-2MPa, and the temperature of the hot roller pressing is 60-80℃.

11. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, Step 1) The linear velocity of the dispersing disc is 60-100 m / min.

12. The sodium-ion secondary battery positive electrode current collector according to claim 1, characterized in that, Step 2) The coating thickness after drying is 1-2 μm.

13. The application of the sodium-ion secondary battery positive electrode current collector according to any one of claims 1-12 in the preparation of sodium-ion secondary batteries.

14. A positive electrode sheet for a sodium-ion secondary battery, characterized in that, Includes the positive electrode current collector of the sodium-ion secondary battery as described in any one of claims 1-12.

15. A sodium-ion secondary battery, characterized in that, It includes the positive electrode of the sodium-ion secondary battery as described in claim 14; or it includes the positive current collector of the sodium-ion secondary battery as described in any one of claims 1-12.

16. An apparatus for preparing a positive electrode current collector for a sodium-ion secondary battery, characterized in that, It includes, in sequence, an unwinding shaft; a transfer shaft; a first microgravure coating machine; a first drying oven; a second microgravure coating machine; a second drying oven; a NO2 oxidation device; a hot press roller; and a take-up shaft.

17. The apparatus for preparing a sodium-ion secondary battery positive electrode current collector according to claim 16, characterized in that, The NO2 oxidation equipment is equipped with a NO2 outlet and a NO2 inlet.

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