Composite conductive agent for positive electrode, positive plate and preparation method of positive plate

Abstract

The invention relates to the field of lithium ion batteries, and discloses a composite conductive agent for a positive electrode, a positive plate and a preparation method of the positive plate, the conductive agent comprises conductive carbon black, conductive graphite and a nano carbon material; the mass ratio of the conductive carbon black to the conductive graphite to the nano carbon material is 1: (0.5-2): (0.5-2). According to the invention, through the synergistic effect of the conductive carbon black, the conductive graphite and the nano carbon material, on one hand, a multi-scale and multi-layer electron conduction network can be formed, so that rapid transmission of electrons in the whole electrode is ensured; secondly, uniform distribution of the conductive agent in the electrode material can be ensured, the agglomeration phenomenon is reduced, local nonuniformity of current density is reduced, and overheating and failure of the battery are prevented; thirdly, the structural stability and the mechanical performance of the electrode can be remarkably enhanced, the active material can be prevented from falling off in the circulation process, and the capacity and the circulation performance of the battery are improved; and fourthly, the thermal management and chemical stability of the battery can be improved, and the safety and service life of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a composite conductive agent for the positive electrode, a positive electrode sheet, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, excellent rate performance, and environmental friendliness, making them one of the most attractive energy storage systems and playing an increasingly important role in modern society. Lithium-ion batteries are widely used in the compact electronic device market (such as mobile phones, vacuum cleaners, and high-end cameras). With the continuous development of society, higher requirements are being placed on the electrochemical and safety performance of lithium-ion batteries.

[0003] However, the impact of conductive agents on battery performance is often overlooked. In existing technologies, the types of conductive agents are mostly limited, and they have many disadvantages in terms of performance. For example, conductive carbon black has poor thermal conductivity, mechanical strength, and flexibility. Using conductive carbon black will lead to difficulties in battery thermal management and affect the structural temperature characteristics of the electrodes. On the other hand, nano-carbon materials have excellent conductivity, but they are difficult to disperse uniformly and are prone to agglomeration, which affects conductivity. Summary of the Invention

[0004] To overcome the shortcomings of existing conductive agents that cannot simultaneously achieve conductivity, dispersibility, mechanical properties, and thermal management capabilities, thus affecting battery performance, this invention provides a composite conductive agent for the positive electrode, a positive electrode sheet, and a method for preparing the same, which can improve battery capacity and cycle performance.

[0005] The first aspect of this invention provides a composite conductive agent for a positive electrode, comprising conductive carbon black, conductive graphite, and nano-carbon materials;

[0006] The mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.5-2:0.5-2.

[0007] Preferably, the mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.8-1.2:0.8-1.2.

[0008] Preferably, the conductive carbon black is Li-435;

[0009] Preferably, the conductive graphite is KS6;

[0010] Preferably, the nano-carbon material is Inano-NO3-D4.

[0011] A second aspect of the present invention provides a battery positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active coating coated on the positive current collector, the positive active coating comprising 90-98 wt% positive active material, 1-5 wt% conductive agent and 1-5 wt% binder;

[0012] The conductive agent is the conductive agent provided in the first aspect of the present invention.

[0013] A third aspect of the present invention provides a method for preparing the positive electrode sheet provided in the second aspect of the present invention, comprising the following steps:

[0014] (1) In the presence of a solvent, binder, positive electrode active material and conductive agent are mixed to obtain positive electrode slurry;

[0015] (2) The obtained positive electrode slurry is coated on the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained.

[0016] In this invention, through the synergistic effect of conductive carbon black, conductive graphite, and nano-carbon materials, firstly, a multi-scale, multi-layered electronic conduction network can be formed, thereby ensuring rapid electron transport throughout the electrode; secondly, the conductive agent can be uniformly distributed in the electrode material, reducing agglomeration and local non-uniformity of current density, preventing battery overheating and failure; thirdly, the structural stability and mechanical properties of the electrode can be significantly enhanced, helping to prevent the shedding of active materials during cycling and improving battery capacity and cycle performance; and fourthly, the thermal management and chemical stability of the battery can be improved, enhancing battery safety and lifespan. Attached Figure Description

[0017] Figure 1 This is a cycle performance diagram of batteries made with conductive agents provided by the present invention and comparative technical solutions at 25°C.

[0018] Figure 2 This is a cycle performance diagram of the battery made with the conductive agent provided by the present invention and the comparative technical solution at 45°C.

[0019] Figure 3 This invention describes the performance of batteries made with the conductive agent provided by this invention at different discharge rates at 25°C. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The first aspect of this invention provides a composite conductive agent for a positive electrode, comprising conductive carbon black, conductive graphite, and nano-carbon materials;

[0022] The mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.5-2:0.5-2.

[0023] In this invention, through the synergistic effect of conductive carbon black, conductive graphite, and nano-carbon materials, firstly, a multi-scale, multi-layered electronic conduction network can be formed, thereby ensuring rapid electron transport throughout the electrode; secondly, the conductive agent can be uniformly distributed in the electrode material, reducing agglomeration and local non-uniformity of current density, preventing battery overheating and failure; thirdly, the structural stability and mechanical properties of the electrode can be significantly enhanced, helping to prevent the shedding of active materials during cycling and improving battery capacity and cycle performance; and fourthly, the thermal management and chemical stability of the battery can be improved, enhancing battery safety and lifespan.

[0024] According to a preferred embodiment of the present invention, the mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.8-1.5:0.8-1.5.

[0025] In this invention, the conductive agent in the above-mentioned specific ratio can further improve the battery capacity and cycle performance.

[0026] In this invention, the conductive carbon black can be selected from conductive carbon blacks such as Li-435, Printex XE2B, Vulcan XC-72 and Acetylene Black.

[0027] According to a preferred embodiment of the present invention, the conductive carbon black is Li-435.

[0028] In this invention, the conductive graphite can be selected from, for example, KS6, KS-15, SFG6, and... Conductive graphite such as KS44.

[0029] According to the present invention, preferably, the conductive graphite is KS6.

[0030] In this invention, the nano-carbon material can be selected from nano-carbon materials such as Inano-NO3-D4, Arkema Graphistrength C100, Cheap Tubes MWNTs, and Nanocyl NC7000.

[0031] According to the present invention, preferably, the nanocarbon material is Inano-NO3-D4.

[0032] In this invention, Li-435, KS6, and Inano-NO3-D4 work synergistically to further enhance the performance of the conductive agent and improve the battery capacity and cycle performance compared to other types of conductive carbon black, conductive graphite, and nano-carbon materials, especially within a mass ratio of 1:0.5-2:0.5-2.

[0033] A second aspect of the present invention provides a battery positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active coating coated on the positive current collector, the positive active coating comprising 90-98 wt% positive active material, 1-5 wt% conductive agent and 1-5 wt% binder;

[0034] The conductive agent is the conductive agent provided in the first aspect of the present invention.

[0035] In this invention, when the composition of the positive electrode active coating is within the above-mentioned range, higher battery capacity and capacity retention can be obtained.

[0036] According to a preferred embodiment of the present invention, the positive electrode active coating comprises 96-98 wt% positive electrode active material, 1-2 wt% conductive agent and 1-2 wt% binder.

[0037] According to the present invention, preferably, the adhesive is selected from at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polymethyl methacrylate (PMMA).

[0038] According to the present invention, preferably, the positive electrode active material is lithium nickel cobalt manganese oxide.

[0039] According to the present invention, more preferably, the positive electrode slurry further includes 0.1-0.5 wt% lithium carbonate.

[0040] In this invention, compared with other conventional positive electrode active materials, lithium nickel cobalt manganese oxide can better cooperate with the conductive agent provided by this invention, resulting in better battery capacity and cycle performance.

[0041] According to a preferred embodiment of the present invention, the positive current collector is aluminum foil.

[0042] According to the present invention, preferably, the tensile strength of the aluminum foil is ≥270MPa.

[0043] In this invention, the high tensile strength current collector can reduce the risk of electrode deformation during battery manufacturing and use, better maintain the integrity of the electrode, thereby reducing the battery's internal resistance, further improving the battery's energy density and safety, and effectively reducing costs.

[0044] According to the present invention, preferably, the thickness of the positive current collector is 14-16 μm.

[0045] In this invention, the thickness of the positive electrode current collector is beneficial for achieving higher battery energy density.

[0046] Furthermore, a positive current collector with high tensile strength can ensure the strength of the electrode even with a relatively thin thickness.

[0047] According to a preferred embodiment of the present invention, the thickness of the positive electrode sheet is 150-153 μm.

[0048] According to the present invention, preferably, the compaction density of the positive electrode sheet is 3.40-3.45 g / cm³. 3 .

[0049] A third aspect of the present invention provides a method for preparing the positive electrode sheet provided in the second aspect of the present invention, comprising the following steps:

[0050] (1) In the presence of a solvent, binder, positive electrode active material and conductive agent are mixed to obtain positive electrode slurry;

[0051] (2) The obtained positive electrode slurry is coated on the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained.

[0052] According to a preferred embodiment of the present invention, the solid content of the positive electrode slurry is 65-75 wt%, and the viscosity is 5000-7000 mPa·s.

[0053] In this invention, a solid content in the positive electrode slurry within the above-mentioned range is more conducive to coating.

[0054] According to the present invention, preferably, the positive electrode slurry is mixed in step (1) by planetary dispersion vacuum stirring, with an orbital speed of 20-25 rpm and a rotational speed of 800-1800 rpm.

[0055] The present invention does not impose any particular limitations on the coating and drying of the positive electrode slurry, and those skilled in the art can make conventional choices.

[0056] According to a preferred embodiment of the present invention, the coating speed of the positive electrode slurry is 15-25 m / min.

[0057] According to the present invention, preferably, the drying method in step (2) is oven baking.

[0058] According to the present invention, preferably, the baking temperature is 90-120°C and the air frequency is 35-45Hz.

[0059] The present invention does not particularly limit the specific type of solvent, and those skilled in the art can conventionally choose, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, and acetone.

[0060] In this invention, preferably, the negative electrode slurry comprises 82-83 wt% artificial graphite, 13-14 wt% silicon carbide material, 0.5-0.6 wt% conductive carbon black, 0.08-0.1 wt% single-walled carbon nanotubes, 1.2-1.3 wt% dispersant and 2.0-2.2 wt% binder.

[0061] In this invention, the negative electrode sheet made from the negative electrode slurry with the specific composition and ratio described above can better cooperate with the positive electrode sheet provided by this invention, thereby further improving the battery capacity and cycle performance.

[0062] In this invention, the solid content of the negative electrode slurry is preferably 48-52 wt%, and the viscosity is preferably 3000-5000 mPa·s.

[0063] In this invention, the mixing, coating, drying, and rolling of the negative electrode slurry can be performed using the same methods as the mixing, coating, drying, and rolling of the positive electrode slurry.

[0064] In this invention, the negative electrode current collector is preferably copper foil.

[0065] Preferably, the thickness of the negative electrode current collector is 8-10 μm.

[0066] In this invention, the thickness of the negative electrode sheet is preferably 117-120 μm.

[0067] Preferably, the compaction density of the negative electrode sheet is 1.62-1.67 g / cm³. 3 .

[0068] The present invention will be described in detail below through embodiments.

[0069] In the following embodiments, unless otherwise specified, all parts refer to parts by mass.

[0070] Capacity retention rate = Discharge capacity after a certain number of cycles / Initial discharge capacity × 100%.

[0071] Unless otherwise specified, all reagents were commercially available, specifically:

[0072] The conductive carbon black was purchased from DENKA Corporation of Japan, and its grade was Li-435.

[0073] The conductive graphite was purchased from Erystal Micron Company, and its grade was KS6.

[0074] The nano-carbon material was purchased from Jiangxi Jinxi Nanomaterials Co., Ltd., with the grade Inano-N03-D4;

[0075] SWCNT was purchased from Shanghai Haiyi Company, and its brand / specification is TUBALL™ BATT H2O 0.4%.

[0076] The artificial graphite was purchased from Qingdao Taidongrui New Energy Materials Co., Ltd., and its grade / specification was TG8C.

[0077] The silicon carbon material was purchased from Liyang Tianmu Pioneer Battery Materials Technology Co., Ltd., and its grade / specification is SC2A.

[0078] The high tensile aluminum foil was purchased from Hangzhou Wuxing Aluminum Co., Ltd., with a thickness of 15μm and a tensile strength of ≥270MPa.

[0079] The copper foil was purchased from Gansu Hailiang New Energy Materials Co., Ltd., and its thickness was 8μm.

[0080] The diaphragm was purchased from Hebei Jinli New Energy Technology Co., Ltd., with a thickness of 12μm and a ceramic coating with a thickness of 3μm.

[0081] The electrolyte was purchased from Hunan Dajing New Materials Co., Ltd., and its brand name is DJ197.

[0082] Example 1

[0083] 1.2 parts of polyvinylidene fluoride (PVDF) powder were mixed with N-methyl-2-pyrrolidone (NMP) to prepare a PVDF solution with a solid content of 8 wt%. The PVDF solution was then mixed with 97.2 parts of lithium nickel cobalt manganese oxide, 0.4 parts of Li-435, 0.5 parts of KS6, and 0.5 parts of Inano-NO3-D4. The mixture was stirred in a planetary dispersion vacuum mixer at a revolution speed of 20 rpm and a rotation speed of 1000 rpm for 3.5 h to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70 wt%, and the viscosity was 5800 mPa·s.

[0084] 1.2 parts of carboxymethyl cellulose (CMC) powder were mixed with water to prepare a CMC solution with a solid content of 2 wt%. The CMC solution was then mixed with 82.58 parts of artificial graphite, 13.44 parts of silicon carbide, 0.5 parts of Li-435, and 0.08 parts of single-walled carbon nanotubes (SWCNTs) in a planetary dispersion vacuum mixer at a revolution speed of 24 rpm and a rotation speed of 1300 rpm for 3.5 h. Then, 2.2 parts of polymethyl methacrylate (PMMA) were added, and the mixture was stirred in the same mixer at a revolution speed of 20 rpm and a rotation speed of 800 rpm for 0.5 h to obtain the negative electrode slurry. The solid content of the negative electrode slurry was 48 wt%, and the viscosity was 4000 mPa·s.

[0085] The above-mentioned positive electrode slurry was coated onto a 15μm thick high-tensile aluminum foil using a gap extrusion coating machine at a coating speed of 20m / min. The foil was then placed in an oven for baking at 100℃ and a fan frequency of 38Hz, resulting in a single-sided density of 230g / m³. 2 The positive electrode plate.

[0086] The above-mentioned negative electrode slurry was coated onto an 8μm thick copper foil using a gap extrusion coating machine at a coating speed of 18m / min, and then placed in an oven for baking at a temperature of 120℃ and a wind frequency of 42Hz, resulting in a single-sided density of 90g / m³. 2 The negative electrode.

[0087] The positive electrode sheet was rolled to a thickness of 150 μm using a roller press, and the negative electrode sheet was rolled to a thickness of 117 μm. They were then cut into strips with widths of 57.5 mm and 59 mm, respectively, and placed in a vacuum drying oven to dry at 120°C for 10 h.

[0088] The positive and negative electrode sheets and the separator are wound into a battery cell, which is then placed inside a steel shell along with the upper and lower insulating sheets. The negative electrode tab is connected to the steel shell by spot welding. After grooving, electrolyte is injected and the shell is sealed to obtain an 18650 battery.

[0089] Inject electrolyte, evacuate and let stand at 20°C for 36 hours.

[0090] At 25℃, the voltage was charged to 4.2V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.02C, and discharged to 2.75V using 1C. This charge-discharge cycle was repeated 500 times. The performance after 500 cycles is as follows: Figure 1 As shown, the battery's initial discharge capacity at 25°C was measured to be 3.16 Ah, and after 500 cycles, the discharge capacity was 2.70 Ah, with a capacity retention rate of 85.4%.

[0091] At 45℃, the voltage was charged to 4.2V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.02C, and discharged to 2.75V using 1C. This charge-discharge cycle was repeated 500 times. The performance after 500 cycles is as follows: Figure 2 As shown, the battery's initial discharge capacity at 45℃ was measured to be 3.15 Ah, and after 500 cycles, the discharge capacity was 2.72 Ah, with a capacity retention rate of 86.3%.

[0092] The performance of this battery at different discharge rates at 25°C is as follows: Figure 3 As shown.

[0093] Comparative Example 1

[0094] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1.4 parts Li-435 and no other conductive agents were added.

[0095] The battery's cycle performance at 25°C after 500 cycles is as follows: Figure 1 As shown, the initial discharge capacity of the battery at 25°C was measured to be 3.14 Ah, and the discharge capacity after 500 cycles was 2.62 Ah, with a capacity retention rate of 83.4%.

[0096] The battery's cycle performance at 45°C for 500 cycles is as follows: Figure 2 As shown, the initial discharge capacity of the battery at 45°C was measured to be 3.16 Ah, and the discharge capacity after 500 cycles was 2.70 Ah, with a capacity retention rate of 85.4%.

[0097] Comparative Example 2

[0098] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1.4 parts KS6 and no other conductive agents were added.

[0099] The battery's cycle performance at 25°C after 500 cycles is as follows: Figure 1 As shown, the initial discharge capacity of the battery at 25°C was measured to be 3.15 Ah, and the discharge capacity after 500 cycles was 2.60 Ah, with a capacity retention rate of 82.5%.

[0100] The battery's cycle performance at 45°C for 500 cycles is as follows: Figure 2 As shown, the initial discharge capacity of the battery at 45°C was measured to be 3.15 Ah, and the discharge capacity after 500 cycles was 2.67 Ah, with a capacity retention rate of 84.8%.

[0101] Comparative Example 3

[0102] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 0.6 parts Li-435 and 0.8 parts Inano-NO3-D4.

[0103] The battery's cycle performance at 25°C after 500 cycles is as follows: Figure 1 As shown, the initial discharge capacity of the battery at 25°C was measured to be 3.15 Ah, and the discharge capacity after 500 cycles was 2.53 Ah, with a capacity retention rate of 80.3%.

[0104] The battery's cycle performance at 45°C for 500 cycles is as follows: Figure 2 As shown, the initial discharge capacity of the battery at 45°C was measured to be 3.14 Ah, and the discharge capacity after 500 cycles was 2.62 Ah, with a capacity retention rate of 83.4%.

[0105] Example 2

[0106] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1 part Li-435, 0.8 parts KS6 and 1.5 parts Inano-NO3-D4.

[0107] The battery's initial discharge capacity at 25°C was measured to be 3.16 Ah, and after 500 cycles, the discharge capacity was 2.69 Ah, with a capacity retention rate of 85.1%.

[0108] The battery's initial discharge capacity at 45°C was measured to be 3.16 Ah, and after 500 cycles, the discharge capacity was 2.72 Ah, with a capacity retention rate of 86.1%.

[0109] Example 3

[0110] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1 part Li-435, 1.5 parts KS6 and 0.8 parts Inano-NO3-D4.

[0111] The battery's initial discharge capacity at 25°C was measured to be 3.15 Ah, and after 500 cycles, the discharge capacity was 2.67 Ah, with a capacity retention rate of 84.8%.

[0112] The battery's initial discharge capacity at 45°C was measured to be 3.19 Ah, and after 500 cycles, the discharge capacity was 2.74 Ah, with a capacity retention rate of 85.9%.

[0113] Example 4

[0114] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1 part Li-435, 0.5 parts KS6 and 2 parts Inano-NO3-D4.

[0115] The battery's initial discharge capacity at 25°C was measured to be 3.14 Ah, and after 500 cycles, the discharge capacity was 2.65 Ah, with a capacity retention rate of 84.4%.

[0116] The battery's initial discharge capacity at 45°C was measured to be 3.18 Ah, and after 500 cycles, the discharge capacity was 2.73 Ah, with a capacity retention rate of 85.8%.

[0117] Example 5

[0118] The battery was prepared and tested according to the method of Example 1, except that the conductive agent was 1 part Li-435, 2 parts KS6 and 0.5 parts Inano-NO3-D4.

[0119] The battery's initial discharge capacity at 25°C was measured to be 3.15 Ah, and after 500 cycles, the discharge capacity was 2.65 Ah, with a capacity retention rate of 84.1%.

[0120] The battery's initial discharge capacity at 45°C was measured to be 3.14 Ah, and after 500 cycles, the discharge capacity was 2.69 Ah, with a capacity retention rate of 85.6%.

[0121] The results of the above embodiments and comparative examples show that the battery using the conductive agent provided by the present invention has significantly better specific capacity and cycle performance.

[0122] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite conductive agent for positive electrodes, characterized in that, This includes conductive carbon black, conductive graphite, and nano-carbon materials; The mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.5-2:0.5-2.

2. The conductive agent according to claim 1, characterized in that, The mass ratio of the conductive carbon black, conductive graphite and nano-carbon material is 1:0.8-1.5:0.8-1.

5.

3. The conductive agent according to claim 1 or 2, characterized in that, The conductive carbon black is Li-435; And / or, the conductive graphite is KS6; And / or, the nano-carbon material is Inano-NO3-D4.

4. A battery positive electrode sheet, characterized in that, The positive electrode sheet includes a positive current collector and a positive active coating coated on the positive current collector. The positive active coating includes 90-98 wt% positive active material, 1-5 wt% conductive agent and 1-5 wt% binder. The conductive agent is the conductive agent described in any one of claims 1-3.

5. The positive electrode sheet according to claim 4, characterized in that, The positive electrode active coating comprises 96-98 wt% positive electrode active material, 1-2 wt% conductive agent and 1-2 wt% binder; Preferably, the adhesive is selected from at least one of polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polymethyl methacrylate; Preferably, the positive electrode active material is lithium nickel cobalt manganese oxide; More preferably, the positive electrode active coating further includes 0.1-0.5 wt% lithium carbonate.

6. The positive electrode sheet according to claim 4 or 5, characterized in that, The positive current collector is aluminum foil; Preferably, the tensile strength of the aluminum foil is ≥270MPa; Preferably, the thickness of the positive electrode current collector is 14-16 μm.

7. The positive electrode sheet according to any one of claims 4-6, characterized in that, The thickness of the positive electrode sheet is 150-153 μm; Preferably, the compaction density of the positive electrode sheet is 3.4-3.45 g / cm³. 3 .

8. A method for preparing the positive electrode sheet according to any one of claims 4-7, characterized in that, Includes the following steps: (1) In the presence of a solvent, binder, positive electrode active material and conductive agent are mixed to obtain positive electrode slurry; (2) The obtained positive electrode slurry is coated on the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained.

9. The method according to claim 8, characterized in that, The positive electrode slurry has a solid content of 68-72 wt% and a viscosity of 5000-7000 mPa·s; And / or, the revolution speed of the mixture in step (1) is 20-25 rpm and the rotation speed is 800-1800 rpm.

10. The method according to claim 8 or 9, characterized in that, The coating speed of the positive electrode slurry is 15-25 m / min; And / or, the drying method in step (2) is oven baking; Preferably, the baking temperature is 90-120℃ and the air frequency is 35-45Hz.

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