Positive electrode conductive paste, positive electrode sheet and lithium-ion battery

Abstract

The present invention relates to a positive electrode conductive paste, which comprises the following components by mass percentage: 0.1-3% carbon nanotubes, 0.1-10% dispersant, and the remainder being a solvent; wherein the dispersant comprises a first polymer and a second polymer in a mass ratio of 20 to 1:1, the first polymer being a carboxylate of a 1,1-difluoroethylene polymer having a weight-average molecular weight of 1,000 to 20,000, and the second polymer being a 1,1-difluoroethylene polymer having a weight-average molecular weight of 500,000 to 2,000,000. The present invention also relates to a method for preparing the positive electrode conductive paste, as well as a positive electrode sheet and a lithium-ion battery using the positive electrode conductive paste. The positive electrode conductive paste of the present invention has the advantages of good dispersibility and higher solid content, which is conducive to reducing the cost of use and is suitable for lithium-ion secondary batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode conductive slurry, and in particular to a positive electrode conductive slurry, a positive electrode sheet and a lithium ion battery. Background Art

[0002] With the development of society, lithium-ion secondary batteries have been widely used in mobile phones, computers, headphones, and even electric vehicles. Currently, the most commonly used cathode materials for lithium-ion secondary batteries include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials (lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide). However, these cathode materials all suffer from low electrical conductivity, which results in insufficient rapid charging capability for lithium-ion batteries and restricts their application. Adding a conductive agent can build an electronic conductive network in the positive electrode, increasing the electron conduction rate and maximizing the positive electrode's performance. Carbon nanotubes, particularly those with a high aspect ratio, are excellent conductors. They not only form a long-range conductive network but also bridge and bind different active cathode particles, improving the bonding stability of the positive electrode.

[0003] Due to their large surface area and strong interactions between carbon nanotubes, they easily aggregate and have poor dispersion properties. They typically need to be prepared into a dispersed slurry before they can be used in lithium-ion batteries. Existing carbon nanotube slurries with small diameters (≤5 nm) and high aspect ratios (≥1000) are difficult to disperse and stabilize. Commonly used conductive carbon nanotube dispersants for lithium-ion battery positive electrodes are polyvinylpyrrolidone (PVP) and N-methylpyrrolidone (NMP). The resulting conductive slurries typically have low solids content and high costs. For example, OCSiAl's commercially available TUBALL single-walled carbon nanotubes have a maximum solids content of only 0.4%, which increases the cost of carbon nanotubes and limits their market application.

[0004] Therefore, the development of carbon nanotube conductive slurries with better dispersion performance and higher solid content is of great significance for the application of carbon nanotubes in the field of lithium-ion secondary batteries. Summary of the Invention

[0005] Based on this, the present invention provides a positive electrode conductive slurry, which has the advantages of good dispersibility and higher solid content, is conducive to reducing the cost of use, and is suitable for lithium-ion secondary batteries.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A positive electrode conductive paste comprises the following components by mass percentage:

[0008] Carbon nanotubes 0.1~3%, dispersant 0.1~10%, and the rest is solvent;

[0009] The dispersant comprises a first polymer and a second polymer in a mass ratio of 20 to 1: 1, wherein the first polymer is a carboxylate of a 1,1-difluoroethylene polymer with a weight-average molecular weight of 1,000 to 20,000, and the second polymer is a 1,1-difluoroethylene polymer with a weight-average molecular weight of 500,000 to 2,000,000.

[0010] In the positive electrode conductive slurry designed by the present invention, the dispersant is compounded by two polymers in a specific ratio. The first polymer is a low-molecular-weight 1,1-difluoroethylene polymer, which is a charged carboxylate. The low-molecular-weight first polymer easily migrates and adsorbs to the surface of the carbon nanotubes, forming a spatially positioned polymer layer in the middle of the carbon nanotubes, thereby effectively dispersing the carbon nanotubes. At the same time, a charge layer is formed on the surface of the carbon nanotubes, which plays a charge repulsive role and further inhibits the agglomeration of the carbon nanotubes; the second polymer is a high-molecular-weight 1,1-difluoroethylene polymer, which mainly increases the slurry viscosity, prevents the slurry from settling, improves storage stability, and is conducive to achieving a higher solid content.

[0011] The conductive agent slurry of the present invention utilizes the synergistic effect of the first and second polymers to achieve a high solids content and good dispersibility, with no noticeable sedimentation or agglomeration after six months of long-term storage. Positive electrodes using this conductive slurry exhibit improved conductivity, and the resulting lithium-ion batteries exhibit low internal resistance and excellent rapid charge and discharge performance.

[0012] In addition, the dispersant of the positive electrode conductive paste of the present invention is mainly 1,1-difluoroethylene polymer, which is the same material as the general positive electrode adhesive PVDF. It not only has good electrochemical stability, but also can improve the peel strength of the electrode.

[0013] Preferably, the structural formula of the first polymer is as follows:

[0014]

[0015] Wherein, n and m are the degree of polymerization, 0≤n / (m+n)≤50%, and M is at least one of Li, Na or K.

[0016] The first polymer is a 1,1-difluoroethylene polymer containing carboxylates at both ends. The anionic carboxylates at both ends can better form a charge layer on the surface of the carbon nanotubes, play a charge repulsion role, and inhibit the agglomeration of the carbon nanotubes to a greater extent, effectively improving the dispersibility and stability of the positive electrode conductive slurry, allowing it to achieve a higher solid content.

[0017] Preferably, the carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and triple-walled carbon nanotubes, with a tube diameter of 1-5 nm and an aspect ratio of 1000-5000:1.

[0018] Preferably, the second polymer is a vinylidene fluoride homopolymer.

[0019] Preferably, the solvent is N-methylpyrrolidone.

[0020] The present invention also provides a method for preparing the positive electrode conductive slurry, comprising the following steps:

[0021] (1) uniformly mixing a first polymer and a solvent to obtain a first dispersion;

[0022] (2) adding carbon nanotubes to the first dispersion and mixing them evenly to obtain a second dispersion;

[0023] (3) Adding a solvent and a second polymer to the second dispersion and mixing them evenly to obtain the positive electrode conductive slurry.

[0024] Preferably, the solid content of the first dispersion obtained in step (1) is adjusted to 20%, and the viscosity of the positive electrode conductive slurry obtained in step (3) is 3000-50000 mPa·s.

[0025] The present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode slurry coated on the current collector, wherein the positive electrode slurry comprises a positive electrode active material, a conductive slurry, an adhesive and a solvent, and the conductive slurry is the positive electrode conductive slurry.

[0026] Preferably, the positive electrode active material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium manganate, lithium manganate phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum oxide; and the binder is a 1,1-difluoride polymer.

[0027] The present invention also provides a lithium ion battery, which includes the positive electrode sheet. DETAILED DESCRIPTION

[0028] The positive electrode conductive paste of the present invention comprises the following components by mass percentage: 0.1-3% carbon nanotubes, 0.1-10% dispersant, and the remainder being solvent;

[0029] The dispersant comprises a first polymer and a second polymer in a mass ratio of 20 to 1: 1, wherein the first polymer is a carboxylate of a 1,1-difluoroethylene polymer with a weight-average molecular weight of 1,000 to 20,000, and the second polymer is a 1,1-difluoroethylene polymer with a weight-average molecular weight of 500,000 to 2,000,000.

[0030] The structural formula of the first polymer is as follows:

[0031]

[0032] Wherein, n and m are the degree of polymerization, 0≤n / (m+n)≤50%, and M is at least one of the alkali metal elements Li, Na or K.

[0033] The carbon nanotubes may be one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and triple-walled carbon nanotubes, preferably oligo-walled carbon nanotubes (a mixture of at least two of single-walled carbon nanotubes, double-walled carbon nanotubes, and triple-walled carbon nanotubes). More preferably, the carbon nanotubes have a diameter of 1 to 5 nm and an aspect ratio of 1000 to 5000:1.

[0034] The second polymer is a 1,1-difluoroethylene polymer (i.e., PVDF resin), which can be a polymer obtained by homopolymerizing 1,1-difluoroethylene monomer or copolymerizing it with a modified monomer. The modified monomer can be selected from trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, etc. The second polymer is preferably a 1,1-difluoroethylene homopolymer.

[0035] The solvent is specifically N-methylpyrrolidone.

[0036] The method for preparing the positive electrode conductive slurry comprises the following steps:

[0037] (1) uniformly mixing a first polymer and a solvent to obtain a first dispersion;

[0038] (2) adding carbon nanotubes to the first dispersion and mixing them evenly to obtain a second dispersion;

[0039] (3) Adding a solvent and a second polymer to the second dispersion and mixing them evenly to obtain the positive electrode conductive slurry.

[0040] More preferably, the solid content of the first dispersion obtained in step (1) is adjusted to 20%; and the viscosity of the positive electrode conductive slurry obtained in step (3) is 3000-50000 mPa·s.

[0041] The positive electrode sheet of the present invention includes a current collector and a positive electrode slurry coated on the current collector. The positive electrode slurry includes a positive electrode active material, the positive electrode conductive slurry, a binder and a solvent.

[0042] Specifically, the positive electrode active material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium manganate, lithium manganate phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum oxide. The binder is a vinylidene fluoride polymer (i.e., PVDF resin), preferably the same as the second polymer. The solvent is N-methylpyrrolidone. The current collector is aluminum foil.

[0043] The lithium ion battery of the present invention uses the positive electrode sheet.

[0044] Example 1

[0045] S1. Preparation of positive electrode conductive slurry

[0046] In a 20 mL high-speed stirring tank, add 1 g of dicarboxylate polymer LiOOC-(CH2CF2)m-COOLi (i.e., in the aforementioned structural formula, n=0, n / (m+n)=0, M is Li, the molecular weight of the polymer Mw=1310, and the molecular weight distribution PDI=1.88) and 4 g of N-methylpyrrolidone, mix and stir at a speed of 200 r / min and a temperature of 25°C for 30 min to obtain a uniform first dispersion with a solid content of 20%.

[0047] 0.5 g of oligo-walled carbon nanotubes (diameter 1-5 nm, aspect ratio 1000-3000:1) was added to the first dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a second dispersion.

[0048] The second dispersion was transferred to a 1 L high-speed stirring tank, and 1.0 g of PVDF resin (Mw = 1.92 million, PDI = 1.87) and 493.5 g of N-methylpyrrolidone were added. The mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a positive electrode conductive slurry with a viscosity of 3230 mPa·s.

[0049] S2. Preparation of positive electrode sheet:

[0050] Calculated by solid mass percentage, 97% of lithium nickel cobalt manganese oxide (NCM 811) active material, 0.8% of the above-mentioned positive electrode conductive slurry and 1.2% of PVDF resin were taken, and N-methylpyrrolidone (NMP) was gradually added and fully stirred to obtain a positive electrode slurry. The solid content of the slurry was adjusted to 50% with NMP. The positive electrode slurry was evenly coated on both sides of the aluminum foil current collector, and the positive electrode sheet was obtained after drying and roller pressing.

[0051] S3. Preparation of negative electrode sheet

[0052] Calculated by solid mass percentage, 1.3% sodium carboxymethyl cellulose (CMC), 1.8% styrene-butadiene latex (SBR), 0.8% conductive carbon black and 96.1% artificial graphite were added to deionized water and stirred thoroughly to obtain a negative electrode slurry with a solid content of 50%. The negative electrode slurry was coated on a copper foil current collector and dried and roller-pressed to obtain a negative electrode sheet.

[0053] S4. Preparation of Lithium-ion Batteries

[0054] The diaphragm was selected as a single-sided ceramic PE film (base film 9 um, Al2O3 ceramic layer 3 um), and the electrolyte was prepared by mixing 1.0 M LiPF6 / ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). The volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) was EC:EMC:DEC = 30:50:30.

[0055] The positive electrode sheet, negative electrode sheet and separator were vacuum dried at 100°C for 24 hours, and then cut, stacked, shelled, injected with liquid, pre-sealed, formed, double-sealed and fixed in volume to obtain a lithium-ion soft-pack battery.

[0056] Example 2

[0057] In this embodiment, a positive electrode conductive paste is first prepared according to the following step S1, and then the positive electrode conductive paste is used to prepare a positive electrode sheet, a negative electrode sheet and a lithium-ion battery by taking the same steps S2-S4 as in embodiment 1.

[0058] S1. Preparation of positive electrode conductive slurry

[0059] In a 700 mL high-speed stirring tank, add 10 g of dicarboxylate polymer NaOOC-(CH2CF2)m-COONa (i.e., in the aforementioned structural formula, n=0, n / (m+n)=0, M is Na, the polymer has a molecular weight Mw=5340, and a molecular weight distribution PDI=1.82) and 40 g of N-methylpyrrolidone, and mix and stir at a speed of 200 r / min and 25°C for 30 min to obtain a uniform first dispersion with a solid content of 20%.

[0060] 5 g of oligo-walled carbon nanotubes (diameter 1-5 nm, aspect ratio 1000-3000:1) were added to the first dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and 25° C. for 240 min to obtain a second dispersion.

[0061] 1.0 g of PVDF resin (Mw = 1.12 million, PDI = 1.82) and 444.0 g of N-methylpyrrolidone were added to the second dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a conductive paste with a viscosity of 15620 mPa·s.

[0062] Example 3

[0063] In this embodiment, a positive electrode conductive paste is first prepared according to the following step S1, and then the positive electrode conductive paste is used to prepare a positive electrode sheet, a negative electrode sheet and a lithium-ion battery by taking the same steps S2-S4 as in embodiment 1.

[0064] S1. Preparation of positive electrode conductive slurry

[0065] In a 700 mL high-speed stirring tank, 50 g of dicarboxylate polymer KOOC-(CH2CF2)m-COOK (i.e., in the aforementioned structural formula, n=0, n / (m+n)=0, M is K, molecular weight Mw=5460, molecular weight distribution PDI=1.81) and 200 g of N-methylpyrrolidone were added and mixed and stirred at a speed of 200 r / min and 25°C for 30 min to obtain a uniform first dispersion with a solid content of 20%.

[0066] 5 g of oligo-walled carbon nanotubes (diameter 1-5 nm, aspect ratio 3000-5000:1) were added to the first dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and 25° C. for 240 min to obtain a second dispersion.

[0067] 2.5 g of PVDF resin (Mw = 1.12 million, PDI = 1.82) and 242.5 g of N-methylpyrrolidone were further added to the second dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a positive electrode conductive slurry with a viscosity of 21280 mPa·s.

[0068] Example 4

[0069] In this embodiment, a positive electrode conductive paste is first prepared according to the following step S1, and then the positive electrode conductive paste is used to prepare a positive electrode sheet, a negative electrode sheet and a lithium-ion battery by taking the same steps S2-S4 as in embodiment 1.

[0070] S1. Preparation of positive electrode conductive slurry

[0071] In a 700 mL high-speed stirring tank, 10 g of a dicarboxylate polymer NaOOC-(CH2CF2)m-(CF2CF(CF3)n-COONa (i.e., in the aforementioned structural formula, n / (m+n)=45%, M is Na, the polymer has a molecular weight Mw = 10300, and a molecular weight distribution PDI = 2.25) and 40 g of N-methylpyrrolidone were added, and the mixture was mixed and stirred at a speed of 200 r / min and 25°C for 30 min to obtain a uniform first dispersion with a solid content of 20%.

[0072] 10 g of oligo-walled carbon nanotubes (diameter 1-5 nm, aspect ratio 3000-5000:1) were added to the first dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and 25° C. for 240 min to obtain a second dispersion.

[0073] 5.0 g of PVDF resin (Mw = 1.12 million, PDI = 1.82) and 435.0 g of N-methylpyrrolidone were further added to the second dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a positive electrode conductive slurry with a viscosity of 36860 mPa·s.

[0074] Example 5

[0075] In this embodiment, a positive electrode conductive paste is first prepared according to the following step S1, and then the positive electrode conductive paste is used to prepare a positive electrode sheet, a negative electrode sheet and a lithium-ion battery by taking the same steps S2-S4 as in embodiment 1.

[0076] S1. Preparation of positive electrode conductive slurry

[0077] In a 700 mL high-speed stirring tank, 15 g of a dicarboxylate polymer NaOOC-(CH2CF2)m-(CF2CF(CF3)n-COONa (i.e., in the aforementioned structural formula, n / (m+n)=9%, M is Na, the polymer has a molecular weight Mw = 18600, and a molecular weight distribution PDI = 2.14) and 60 g of N-methylpyrrolidone were added, and the mixture was mixed and stirred at a speed of 200 r / min and 25°C for 30 min to obtain a uniform first dispersion with a solid content of 20%.

[0078] 15 g of oligo-walled carbon nanotubes (diameter 1-5 nm, aspect ratio 3000-5000:1) were added to the first dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and 25° C. for 240 min to obtain a second dispersion.

[0079] 1.5 g of PVDF resin (Mw = 550,000, PDI = 2.14) and 408.5 g of N-methylpyrrolidone were further added to the second dispersion, and the mixture was stirred and dispersed at a speed of 1000 r / min and a temperature of 25°C for 240 min to obtain a positive electrode conductive slurry with a viscosity of 48980 mPa·s.

[0080] Comparative Example 1

[0081] A commercially available single-walled carbon nanotube conductive agent (TUBALL brand product of OCSiAl) was used as the positive electrode conductive paste, and steps S2-S4 similar to those in Example 1 were followed to prepare a positive electrode sheet, a negative electrode sheet, and a lithium-ion battery.

[0082] Comparative Example 2

[0083] Commercially available conductive carbon black (Super P product of Temeco) was used as the positive electrode conductive agent, and steps S2-S4 similar to those in Example 1 were followed to prepare a positive electrode sheet, a negative electrode sheet, and a lithium-ion battery.

[0084] Solid content and viscosity determination

[0085] The solid content and viscosity of the positive electrode conductive pastes of Examples 1-5 and Comparative Example 1 were measured respectively. The measurement results are shown in Table 1 below:

[0086] Table 1 Viscosity and solid content of conductive paste

[0087]

[0088] As can be seen from Table 1, using carbon nanotubes as the conductive agent, the solid content of the positive electrode conductive paste obtained in the embodiment of the present invention is substantially higher than that of the commercially available product in Comparative Example 1. This indicates that the formulation of the present invention can produce a conductive paste with better carbon nanotube dispersion, which is conducive to achieving higher stability. Compared with existing products, the positive electrode conductive paste of the present invention has a superior cost advantage.

[0089] At the same time, the viscosity of the positive electrode conductive paste obtained in the embodiment of the present invention is substantially higher than that of the commercially available product in Comparative Example 1, indicating that the positive electrode conductive paste of the present invention has stronger adhesion to the current collector.

[0090] Performance Testing

[0091] The following performance tests were performed on the positive electrode sheets and lithium-ion soft-pack batteries prepared in Examples 1-5 and Comparative Examples 1-2, respectively.

[0092] 1. Pole peel strength test

[0093] The rolled positive electrode sheet was cut into 20 x 200 mm strips. One side of the sample was adhered to 3M double-sided tape, and the other side was adhered to a 25 x 200 mm stainless steel plate. A 2 kg rubber roller was used to roll the double-sided tape adhesive area back and forth three times to ensure that the positive electrode sheet, double-sided tape, and steel plate were completely adhered. The specimen was then bent 180° in the opposite direction. A universal electronic tensile testing machine was used for testing. One end of the stainless steel plate was fixed to the lower fixture of the tensile machine, and the bent end of the specimen was fixed to the upper fixture. The specimen angle was adjusted to ensure that the upper and lower ends were in a vertical position. The specimen was then stretched at a speed of 50 mm / min until it was completely peeled from the substrate. The displacement and applied force during the process were recorded. The force at which the forces are balanced is generally considered to be the adhesion force of the positive electrode sheet.

[0094] 2. Battery performance test

[0095] 1) Battery capacity

[0096] At 25±5°C, discharge the cell at a constant current of 0.33 C to 3.0 V and let it rest for 10 min. Then charge it at a constant current of 0.33 C to 4.3 V. Then switch to constant voltage charging until the charging current is ≤0.02C. The capacity during the constant current charging stage is Q1, and the capacity during the constant voltage charging stage is Q2. The battery capacity is Q1+Q2.

[0097] 2) Internal resistance test

[0098] When the battery cell is charged to 50% capacity, use a 1 kHz voltage internal resistance tester to detect the internal resistance of the battery.

[0099] 3) Rate discharge capacity retention

[0100] At 25±5°C, charge the cell at a constant current of 0.33C to 4.3V, let it rest for 10 minutes, then switch to constant voltage charging until the charging current is ≤0.02C. After 10 minutes, discharge it at a rate of 3C to 3.0V. The constant current charging capacity is Q1, the constant voltage charging capacity is Q2, and the 2C discharge capacity is Q3. The 2C discharge capacity retention rate = Q3 / (Q1+Q2).

[0101] The performance test results are shown in Table 2 below:

[0102] Table 2 Performance test data of the embodiments and comparative examples

[0103]

[0104] As can be seen from Table 2, the positive electrode conductive pastes prepared in Examples 1-5 of the present invention have good electrode sheet adhesion, and the lithium ion batteries prepared therefrom have low internal resistance and good rate discharge performance.

[0105] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A positive electrode conductive paste, characterized in that: The components include the following by mass percentage: Carbon nanotubes 0.1~3%, dispersant 0.1~10%, and the rest is solvent; The dispersant comprises a first polymer and a second polymer in a mass ratio of 20 to 1: 1, wherein the first polymer is a carboxylate of a 1,1-difluoroethylene polymer having a weight average molecular weight of 1,000 to 20,000, and the second polymer is a 1,1-difluoroethylene polymer having a weight average molecular weight of 500,000 to 2,000,000; The vinylidene fluoride polymer is a polymer obtained by homopolymerizing vinylidene fluoride monomer or copolymerizing it with a modified monomer, and the modified monomer is selected from one or more of trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, and hexafluoropropylene.

2. The positive electrode conductive paste according to claim 1, characterized in that The structural formula of the first polymer is as follows: Wherein, n and m are the degree of polymerization, 0≤n / (m+n)≤50%, and M is at least one of Li, Na or K.

3. The positive electrode conductive paste according to claim 1 or 2, characterized in that The carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and triple-walled carbon nanotubes, with a tube diameter of 1-5 nm and an aspect ratio of 1000-5000:

1.

4. The positive electrode conductive paste according to claim 1 or 2, characterized in that: The second polymer is a vinylidene fluoride homopolymer.

5. The positive electrode conductive paste according to claim 1 or 2, characterized in that: The solvent is N-methylpyrrolidone.

6. A method for preparing the positive electrode conductive paste according to any one of claims 1 to 5, characterized in that: The steps include: (1) uniformly mixing a first polymer and a solvent to obtain a first dispersion; (2) adding carbon nanotubes to the first dispersion and mixing them evenly to obtain a second dispersion; (3) Adding a solvent and a second polymer to the second dispersion and mixing them evenly to obtain the positive electrode conductive slurry.

7. The method according to claim 6, wherein The solid content of the first dispersion obtained in step (1) is adjusted to 20%, and the viscosity of the positive electrode conductive slurry obtained in step (3) is 3000-50000 mPa·s.

8. A positive electrode sheet, characterized in that: The invention comprises a current collector and a positive electrode slurry coated on the current collector, wherein the positive electrode slurry comprises a positive electrode active material, a conductive slurry, a binder and a solvent, and the conductive slurry is the positive electrode conductive slurry according to any one of claims 1 to 5.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode active material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; and the binder is a 1,1-difluoroethylene polymer.

10. A lithium ion battery, characterized in that: Including the positive electrode sheet according to claim 8 or 9.

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