A binder for lithium ion batteries and a positive electrode sheet for lithium ion batteries

Abstract

The present application belongs to the technical field of battery pole piece, and particularly relates to a binder for lithium ion battery and a positive pole piece for lithium ion battery. The binder for lithium ion battery is an oil-soluble polyurethane containing 1,6-hexane diisocyanate (HDI) and polyether polyol block, and the terminal is capped by hydroxypropyl acrylate (HPA). The positive pole piece for lithium ion battery comprises a positive material, a binder and a conductive agent. An intermittent coating method is adopted. Part of the polyurethane solution is used to pre-coat the positive material, and a layer of polyurethane film is attached to the surface of the positive material to form an artificial SEI film. The coated positive material has a certain elasticity, which can effectively relieve the stress generated in the charging and discharging cycle process of the positive material, improve the structural stability of the positive material, and has good lithium ion conduction effect, which helps to improve the battery conductivity.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode technology, specifically relating to a binder for lithium-ion batteries and a positive electrode for lithium-ion batteries. Background Technology

[0002] With the deepening research into the reaction mechanism of lithium-ion batteries and the development of lithium-ion battery material technology, the application of lithium-ion batteries in production and daily life is constantly expanding. In recent years, the proportion of new energy vehicles in my country's total vehicle market has increased for four consecutive years. The technological level of the new energy vehicle industry has significantly improved, and the competitiveness of enterprises has been greatly enhanced. According to the "White Paper on the Development of China's New Energy Vehicle Industry (2022)," the production and sales volume of new energy vehicles reached 6.7 million units in 2021, and it is estimated that by 2030, global sales of new energy vehicles will exceed 47.8 million units, making new energy vehicles a major driving force for the development of the automotive industry. As a key component of new energy vehicles, lithium-ion batteries must maintain a basic balance in terms of charging speed, driving range, and exhaust emissions to promote the sustainable development of the automotive industry.

[0003] Currently, the mainstream cathode materials for rechargeable batteries are lithium iron phosphate (LFP) cathodes and nickel-cobalt-manganese (NCM) ternary cathodes. NCM ternary cathodes possess high charging voltage and energy density, making them ideal next-generation cathode materials for rechargeable batteries. According to the "Lithium-ion Battery Industry Standard Conditions" (2021 Edition) and the "Interim Measures for the Administration of Lithium-ion Battery Industry Standard Announcements" issued by the Ministry of Industry and Information Technology in 2021, the energy density of a single cell using ternary cathode materials must be ≥210Wh / kg, while the energy density of other single cells only needs to be ≥160Wh / kg.

[0004] Lithium-ion batteries using nickel-cobalt-manganese ternary cathode materials have achieved energy densities of up to 300 Wh / kg, while lithium-ion batteries using lithium iron phosphate cathode materials have energy densities of around 200 Wh / kg. However, traditional ternary battery slurries still consist of cathode materials, polyvinylidene fluoride (PVDF) binders, and conductive carbon black. The degradation rate of the cathode material is much higher than that of the lithium iron phosphate cathode. PVDF binders are high-molecular-weight linear polymers. When added as binders, they cannot effectively cover the surface of the cathode material. During battery charging and discharging, the exposed surface of the cathode material is in direct contact with the electrolyte. The high-potential electrode material's contact with the electrolyte solvent leads to solvent decomposition, forming an SEI film on the cathode material surface. This consumes a large number of active lithium ions, causing a decrease in capacity. With each charge-discharge cycle, the SEI film thickness increases, leading to an irreversible decrease in capacity.

[0005] Typical ternary lithium-ion batteries exhibit significant capacity decay after 800 charge-discharge cycles. After 1000-1200 cycles, their capacity drops to 70-80% of their initial capacity, reaching the point of replacement. Severe capacity decay occurs after 1500 cycles, necessitating replacement. Therefore, compared to lithium iron phosphate batteries, ternary lithium-ion batteries only offer an advantage in terms of single-cycle driving range; they do not provide a significant advantage over the entire battery lifespan. Especially at higher current densities, the concentration polarization within the battery increases, causing the cutoff voltage to be reached prematurely during charging and discharging, resulting in a decrease in specific capacity. Therefore, maintaining high capacity in ternary lithium-ion batteries over long-term charge-discharge cycles is crucial. Summary of the Invention

[0006] The purpose of this invention is to provide a binder for lithium-ion batteries and a positive electrode sheet for lithium-ion batteries containing the binder, ultimately obtaining a positive electrode sheet that can effectively improve the cycle performance of the battery and prevent the problem of excessively rapid capacity decay in lithium-ion batteries with ternary positive electrode materials during charging and discharging.

[0007] The present invention is achieved by the following scheme: the binder for lithium-ion batteries is an oil-soluble polyurethane containing 1,6-hexamethylene diisocyanate (HDI) and polyether polyol blocks, and the end is capped with hydroxypropyl acrylate (HPA).

[0008] This oil-soluble polyurethane binder has a low molecular weight, abundant oxygen-containing functional groups, and double-bond-terminated polyurethane, effectively circumventing the insulating properties of traditional polyurethane. It can provide a large number of lithium-ion transport sites and has good lithium-ion transport performance. Through HPA end-capping, molecular network cross-linking can be achieved, and it is attached to the surface of the positive electrode material in a form similar to an SEI film. The presence of its dual soft segments makes the polyurethane more elastic after forming a coating on the surface. Compared with traditional polyurethane, it reduces the passivation of the active material surface by phenyl hard segments. At high temperatures, it undergoes a cross-linking reaction and transforms into thermosetting polyurethane, which is difficult to be dissolved by solvents, thus maintaining the integrity of the lithium-ion battery electrode. At the same time, it provides a faster lithium-ion transport pathway, increases structural stability, and significantly improves the cycle performance of lithium-ion batteries under high current.

[0009] Furthermore, the molecular weight of oil-soluble polyurethane is 9,000 to 12,000, and its viscosity at 25°C is 60,000 to 80,000 mPa·s.

[0010] The present invention also provides a positive electrode sheet for lithium-ion batteries, comprising a positive electrode material, the above-mentioned binder and conductive agent.

[0011] Furthermore, the mass percentages of the positive electrode material, conductive agent, and binder are 80.0–85.0%, 7.0–10.0%, and 8.0–10.0%, respectively.

[0012] The above-mentioned method for preparing the positive electrode sheet for lithium-ion batteries is an intermittent preparation method, which includes the following steps:

[0013] (1) Add oil-soluble polyurethane to an organic solvent and stir to obtain a polyurethane solution;

[0014] (2) Add the polyurethane solution and organic solvent from step (1) to the cathode material in sequence, stir and dry to obtain polyurethane modified cathode material;

[0015] (3) Add the polyurethane solution, conductive agent, and remaining organic solvent from step (1) to the polyurethane modified cathode material in step (2) in sequence, and stir until uniform to obtain cathode slurry.

[0016] (4) Coat the positive electrode slurry onto the surface of the aluminum foil, use a scraper on an automatic coating machine to coat it evenly, dry, compact, and punch to obtain the positive electrode sheet.

[0017] An intermittent preparation method is adopted. First, a portion of the polyurethane solution is used to pre-coat the cathode material, and a layer of polyurethane film is attached to the surface of the cathode material to form an artificial SEI film. The dual soft segment polyurethane gives the coated cathode material good elasticity, which can effectively relieve the stress generated by the cathode material during charge and discharge cycles, improve the structural stability of the cathode material, and has good lithium ion conduction, which helps to improve the battery conductivity.

[0018] Furthermore, the organic solvent is one or more of polyvinylpyrrolidone, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide, preferably N-methylpyrrolidone.

[0019] Further, in step (1), the mass ratio of oil-soluble polyurethane to organic solvent in the polyurethane solution is 1:1.5 to 4, the stirring speed is 800 to 1000 rpm, and the time is 4 to 8 hours.

[0020] Furthermore, the cathode material is one or both of the ternary cathode materials nickel-cobalt-manganese 811 and nickel-cobalt-manganese 523.

[0021] Furthermore, in step (2), the mass ratio of polyurethane solution, positive electrode material, and organic solvent is 1:70-80:150-160.

[0022] Furthermore, in step (2), the stirring speed is 800-1600 rpm, the time is 8-24 h, and the high-temperature drying temperature is 80-110℃, the time is 8-30 h.

[0023] Furthermore, in step (3), the mass ratio of the conductive agent, polyurethane solution, ternary cathode material, and organic solvent is 1:2~3:8~30:20~30.

[0024] Furthermore, the conductive agent is one or more of conductive carbon black, conductive graphite, and carbon fiber, preferably conductive carbon black.

[0025] Furthermore, in step (3), the stirring speed is 800-1500 rpm and the time is 1-3 min.

[0026] Furthermore, in step (4), the high-temperature drying temperature is 80-110℃ and the time is 4-8h.

[0027] Furthermore, in step (4), the height of the scraper is 23–25 μm.

[0028] The specific method for manufacturing a lithium-ion battery using the above-mentioned positive electrode sheet is as follows: in an inert atmosphere glove box, the positive electrode shell, positive electrode sheet, separator, negative electrode sheet, gasket, spring sheet, and negative electrode shell are assembled in that order from bottom to top, and then pressurized to form a lithium-ion battery.

[0029] Furthermore, the press pressure is 50–60 MPa, and the pressing time is 8–10 seconds.

[0030] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0031] (1) By utilizing the good lithium-ion transport capability of hydroxypropyl acrylate (HPA) end-capped polyurethane adhesive and combining it with an intermittent preparation method to form a structurally stable artificial SEI film, a lithium-ion battery with good electrochemical performance was prepared.

[0032] (2) Hydroxypropyl acrylate (HPA) end-capped polyurethane binder contains abundant oxygen-containing functional groups, which can provide a large number of lithium-ion transport sites, improve the lithium-ion transport rate under high current density, and enhance the fast charging capacity of lithium-ion batteries.

[0033] (3) Hydroxypropyl acrylate (HPA) end-capped polyurethane adhesive achieves molecular network cross-linking after high-temperature curing, and is attached to the surface of the positive electrode material in a form similar to SEI film, which increases the structural stability of lithium-ion battery.

[0034] (4) The intermittent preparation method attaches an artificial SEI film to the surface of the cathode material, which makes the coated cathode material have a certain elasticity, effectively relieving the stress generated by the cathode material during charge and discharge cycles and improving the structural stability of the cathode material. Attached Figure Description

[0035] Figure 1 This is a graph showing the cycle data of the lithium-ion battery obtained in Example 1;

[0036] Figure 2 This is a graph showing the rate data of the lithium-ion battery obtained in Example 1;

[0037] Figure 3 These are SEM images of the lithium-ion battery electrode obtained in Example 1 before and after 200 cycles;

[0038] Figure 4 This is a graph showing the cycle data of the lithium-ion battery obtained in Comparative Example 1;

[0039] Figure 5 This is a graph showing the rate data of lithium-ion batteries obtained from Comparative Example 1;

[0040] Figure 6 These are SEM images of the lithium-ion battery electrode obtained in Comparative Example 1 before and after 180 cycles. Detailed Implementation

[0041] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0042] The polyurethane used in the following examples is EBECRIL 4491 from Allnex, a hydroxypropyl acrylate (HPA)-terminated polyurethane binder with an average molecular weight of 7,000–12,000 and a viscosity of 60,000–80,000 mPa·s at 25°C. The cathode material is NCM811 from Ningbo Ronbay New Energy Technology Co., Ltd.

[0043] Example 1

[0044] The preparation method of the positive electrode sheet for lithium-ion batteries and the lithium-ion battery in this embodiment is as follows:

[0045] (1) Mix polyurethane (average molecular weight of 7000, viscosity of 60000 mPa·s at 25℃) with N-methylpyrrolidone at a mass ratio of 1:2 and stir at 1000 rpm for 4 hours to fully dissolve the polyurethane.

[0046] (2) Take 0.1g of polyurethane solution and add it to 8g of ternary cathode material. Add 16g of N-methylpyrrolidone and stir at 1500rpm for 24h to make the cathode material and polyurethane solution evenly mixed. Transfer the stirred cathode slurry to a large evaporating dish to ensure that the cathode slurry is spread evenly. Dry it in a high-temperature oven at 100℃ for 24h to completely remove moisture. Collect it for later use.

[0047] (3) Mix 0.8g of ternary cathode material, 0.3g of polyurethane solution, 0.1g of conductive carbon black and 2.0g of N-methylpyrrolidone in a high-speed mixer at 1000rpm for 2min to make them evenly mixed. Transfer the mixture to one side of the aluminum foil laid flat on the glass plate and coat it evenly with a scraper on an automatic coating machine. The scraper height is 25μm. Coat the cathode slurry evenly on the smooth aluminum foil surface. Bake it at 80℃ for 6h in a high-temperature oven. After compacting it with a roller press, use a 14mm punching machine to cut the electrode into a circular cathode electrode.

[0048] (4) In an inert atmosphere glove box, the positive electrode shell, positive electrode plate, separator, negative electrode plate, gasket, spring sheet and negative electrode shell are assembled in that order from bottom to top. The CR2032 button lithium-ion battery is prepared by stabilizing the pressure at 50MPa for 10s using a press.

[0049] Example 2

[0050] The preparation method of the positive electrode sheet for lithium-ion batteries and the lithium-ion battery in this embodiment is as follows:

[0051] (1) Mix polyurethane (average molecular weight of 9000, viscosity of 70000 mPa·s at 25℃) with N-methylpyrrolidone at a mass ratio of 1:2 and stir at 1000 rpm for 4 hours to fully dissolve the polyurethane.

[0052] (2) Take 0.1g of polyurethane solution and add it to 7.5g of ternary cathode material. Add 15g of N-methylpyrrolidone and stir at 1500rpm for 24h to make the cathode material and polyurethane solution evenly mixed. Transfer the stirred cathode slurry to a large evaporating dish to ensure that the cathode slurry is spread evenly. Dry it in a high-temperature oven at 100℃ for 24h to completely remove moisture. Collect it for later use.

[0053] (3) Mix 0.8g of ternary cathode material, 0.3g of polyurethane solution, 0.1g of conductive carbon black and 2.0g of N-methylpyrrolidone in a high-speed mixer at 1000rpm for 2min to make them evenly mixed. Transfer the mixture to one side of the aluminum foil laid flat on the glass plate and coat it evenly with a scraper on an automatic coating machine. The scraper height is 25μm. Coat the cathode slurry evenly on the smooth aluminum foil surface. Bake it at 80℃ for 6h in a high-temperature oven. After compacting it with a roller press, use a 14mm punching machine to cut the electrode into a circular cathode electrode.

[0054] (4) In an inert atmosphere glove box, the positive electrode shell, positive electrode plate, separator, negative electrode plate, gasket, spring sheet and negative electrode shell are assembled in that order from bottom to top. The CR2032 button lithium-ion battery is prepared by stabilizing the pressure at 50MPa for 10s using a press.

[0055] Example 3

[0056] The preparation method of the positive electrode sheet for lithium-ion batteries and the lithium-ion battery in this embodiment is as follows:

[0057] (1) Mix polyurethane (average molecular weight of 10,000, viscosity of 80,000 mPa·s at 25℃) with N-methylpyrrolidone at a mass ratio of 1:3 and stir at 1000 rpm for 4 hours to fully dissolve the polyurethane.

[0058] (2) Take 0.1g of polyurethane solution and add it to 8g of ternary cathode material. Add 16g of N-methylpyrrolidone and stir at 1500rpm for 24h to make the cathode material and polyurethane solution evenly mixed. Transfer the stirred cathode slurry to a large evaporating dish to ensure that the cathode slurry is spread evenly. Dry it in a high-temperature oven at 100℃ for 24h to completely remove moisture. Collect it for later use.

[0059] (3) Mix 0.7g of ternary cathode material, 0.3g of polyurethane solution, 0.1g of conductive carbon black and 2.5g of N-methylpyrrolidone in a high-speed mixer at 1000rpm for 2min to make them evenly mixed. Transfer the mixture to one side of the aluminum foil laid flat on the glass plate and coat it evenly with a scraper on an automatic coating machine. The scraper height is 25μm. Coat the cathode slurry evenly on the smooth aluminum foil surface. Bake it at 80℃ for 6h in a high-temperature oven. After compacting it with a roller press, use a 14mm punching machine to cut the electrode into a circular cathode electrode.

[0060] (4) In an inert atmosphere glove box, the positive electrode shell, positive electrode plate, separator, negative electrode plate, gasket, spring sheet and negative electrode shell are assembled in that order from bottom to top. The CR2032 button lithium-ion battery is prepared by stabilizing the pressure at 50MPa for 10s using a press.

[0061] Comparative Example 1

[0062] The comparative example of the positive electrode sheet for lithium-ion batteries and the preparation method of lithium-ion batteries are as follows:

[0063] (1) Mix 0.8g of ternary cathode material, 0.3g of polyvinylidene fluoride, 0.1g of conductive carbon black and 2.0g of N-methylpyrrolidone in a high-speed mixer at 1000rpm for 2min to make them evenly mixed. Transfer the mixture to one side of the aluminum foil laid flat on the glass plate and coat it evenly with a scraper on an automatic coating machine. The scraper height is 25μm. Coat the cathode slurry evenly on the smooth aluminum foil surface. Bake it at 80℃ for 6h in a high-temperature oven. After compacting it with a roller press, use a 14mm punching machine to cut the electrode into a circular cathode electrode.

[0064] (2) In an inert atmosphere glove box, the positive electrode shell, positive electrode plate, separator, negative electrode plate, gasket, spring sheet and negative electrode shell are assembled in that order from bottom to top. The CR2032 button lithium-ion battery is prepared by stabilizing the pressure at 50MPa for 10s using a press.

[0065] Comparative Example 2

[0066] The comparative example of the positive electrode sheet for lithium-ion batteries and the preparation method of lithium-ion batteries are as follows:

[0067] (1) Mix 0.8g of ternary cathode material, 0.3g of polyurethane solution, 0.1g of conductive carbon black and 2.0g of N-methylpyrrolidone in a high-speed mixer at 1000rpm for 2min to make them evenly mixed. Transfer the mixture to one side of the aluminum foil laid flat on the glass plate and coat it evenly with a scraper on an automatic coating machine. The scraper height is 25μm. Coat the cathode slurry evenly on the smooth aluminum foil surface. Dry it in a high-temperature oven at 80℃ for 6h. After compacting it with a roller press, use a 14mm punching machine to cut the electrode into a circular cathode electrode.

[0068] (2) In an inert atmosphere glove box, the positive electrode shell, positive electrode plate, separator, negative electrode plate, gasket, spring sheet and negative electrode shell are assembled in that order from bottom to top. The CR2032 button lithium-ion battery is prepared by stabilizing the pressure at 50MPa for 10s using a press.

[0069] Comparative Example 3

[0070] The only difference between Comparative Example 3 and Example 1 is that the polyurethane used is waterborne polyurethane LX-110 from Guilin Xinmei Environmental Protection Technology Co., Ltd.

[0071] The lithium-ion batteries obtained in the above examples and comparative examples were tested for cycle performance at a current density of 0.5C (1C = 205 mA / g), and for rate performance at current densities of 0.2C, 0.5C, 1.0C, 2.0C, and 5.0C. Specific data are shown in Table 1.

[0072] Table 1. Electrochemical performance of lithium-ion batteries obtained from examples and comparative examples.

[0073]

[0074] according to Figure 1 , Figure 2 Based on the data in Table 1, the lithium-ion battery obtained in Example 1 achieved a capacity retention rate of 88.9%, and the battery electrodes remained relatively intact after 200 cycles (e.g., Figure 3 As shown), it exhibits good structural stability. At a high current density of 5.0C, the capacity is 91mAh / g. After a high current density charge-discharge cycle, the capacity still reaches 173mAh / g at a second charge-discharge cycle at a current density of 1.0C. Examples 2 and 3 also show good cycle performance and rate performance. Comparative Example 1, which uses polyvinylidene fluoride as a binder, has a capacity retention rate of only 63.9%. After 200 cycles, the surface of the battery electrode is covered with cracks (such as...). Figure 6 As shown in the figure, the structure has poor stability. At a high current density of 5.0C, the capacity is only 63 mAh / g, indicating low capacity at high current densities. The conductivity is also poor. After a high current density charge-discharge cycle, the capacity at a second charge-discharge cycle at a 1.0C current density is 157 mAh / g, recovering to 95.0% of the capacity at the first 1.0C current density. The electrochemical stability is also poor. Comparative Example 2 uses polyurethane solution as a binder to prepare lithium-ion battery electrodes in a one-step process, but the capacity retention rate is only 65.2%, and at a high current density of 5.0C, the capacity is only 54 mAh / g. The capacity was low at high current densities (mAh / g), and the conductivity was poor. After high current density charge-discharge, the capacity was 147 mAh / g at the second charge-discharge at 1.0C, recovering to 91.9% of the capacity at the first 1.0C current density. Electrochemical stability was poor. Comparative Example 3 used conventional aqueous polyurethane as a binder, whose hard segments were benzene rings or benzene homologues, resulting in severe surface passivation and easy dissolution in the electrolyte. The film structure formed at high temperatures was unstable, leading to low capacity retention and low capacity at high current densities in the lithium-ion battery. This demonstrates that the method used in this application, employing hydroxypropyl acrylate (HPA) end-capped polyurethane binder and an intermittent preparation method to attach an artificial SEI film to the surface of the positive electrode material, gives the coated positive electrode material a certain degree of elasticity. This effectively alleviates the stress generated during charge-discharge cycles, improves the structural stability of the positive electrode material, and produces a lithium-ion battery with good cycle performance and rate performance.

[0075] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A positive electrode sheet for a lithium-ion battery, characterized in that, This includes positive electrode materials, conductive agents, and binders; The adhesive is an oil-soluble polyurethane containing 1,6-hexamethylene diisocyanate and polyether polyol blocks, and the ends of the oil-soluble polyurethane are capped with hydroxypropyl acrylate. The positive electrode sheet is prepared by an intermittent preparation method; The intermittent preparation method includes the following steps: (1) Add oil-soluble polyurethane to an organic solvent and stir to obtain a polyurethane solution; (2) Add the polyurethane solution and organic solvent from step (1) to the cathode material in sequence, stir and dry to obtain polyurethane modified cathode material; (3) Add the polyurethane solution, conductive agent, and remaining organic solvent from step (1) to the polyurethane modified cathode material in step (2) in sequence, and stir until uniform to obtain cathode slurry. (4) Coat the positive electrode slurry onto the surface of the aluminum foil, use a scraper on an automatic coating machine to coat it evenly, dry, compact, and punch to obtain the positive electrode sheet.

2. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, The oil-soluble polyurethane in the adhesive has a molecular weight of 9,000 to 12,000 and a viscosity of 60,000 to 80,000 mPa·s at 25°C.

3. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, The mass percentages of the positive electrode material, conductive agent, and binder are 80.0–85.0%, 7.0–10.0%, and 8.0–10.0%, respectively.

4. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, In step (1) of the intermittent preparation method, the mass ratio of oil-soluble polyurethane to organic solvent in the polyurethane solution is 1:1.5-4, the stirring speed is 800-1000 rpm, and the time is 4-8 h.

5. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, In step (2) of the intermittent preparation method, the mass ratio of polyurethane solution, positive electrode material, and organic solvent is 1:70-80:150-160.

6. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, In step (2) of the intermittent preparation method, the stirring speed is 800-1600 rpm and the time is 8-24 h. The high-temperature drying temperature is 80-110℃ and the time is 8-30 h.

7. The positive electrode sheet for lithium-ion batteries according to claim 1, characterized in that, In step (3) of the intermittent preparation method, the mass ratio of conductive carbon black, polyurethane solution, polyurethane modified cathode material, and organic solvent is 1:2~3:8~30:20~30.

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