Cathode slurry, cathode sheet, preparation method thereof and lithium ion battery

Abstract

This invention provides a positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery. The positive electrode slurry comprises a positive electrode active material, a conductive agent, a first binder, a dispersant, and a first solvent. The solids content of the positive electrode slurry is 69-71%, and the viscosity is 5000-8000 mPa·s. The dispersant is a combination of polyethylene glycol and ethanolamine. The solids content of the positive electrode slurry in this application is higher than that of conventional positive electrode slurries, avoiding the formation of inter-soluble virtual edges. Controlling the viscosity of the positive electrode slurry within the above range helps improve the stability and uniformity of the slurry coating on the current collector, while further helping to avoid the formation of inter-soluble virtual edges. By reducing the virtual edge problem, it helps to improve the electrochemical performance of the battery, reduce dependence on specific coating parameters or process conditions, expand the process adjustment window, and improve production yield.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery. Background Technology

[0002] The positive electrode active material is characterized by its small particle size, large specific surface area, and high particle count per unit volume. Its solid content in the resulting slurry is typically between 60% and 65%. In contrast, insulating ceramics (boehmite / alumina) have relatively larger particle sizes, and their solid content in the resulting ceramic slurry is typically between 28% and 35%. Both the positive electrode slurry and the insulating ceramic slurry use N-methylpyrrolidone as the solvent, exhibiting the "like dissolves like" principle. Because the particle size of the positive electrode active material is much smaller than that of the insulating ceramic, the solid content of the positive electrode slurry is greater than that of the insulating ceramic slurry. Therefore, the surface tension of the positive electrode slurry is greater than that of the insulating ceramic.

[0003] To balance the forces, materials with lower surface tension migrate towards those with higher surface tension, causing ceramic slurry to migrate towards the positive electrode slurry. Since the particle size of the positive electrode active material is much smaller than that of the insulating ceramic, the insulating ceramic cannot integrate into the positive electrode slurry interlayer and thus migrates upwards towards the positive electrode slurry. During the coating oven baking process, the positive electrode slurry, due to its high solid content, dries first. At the solid-liquid boundary, the surface tension difference between the ceramic and ceramic slurries reaches its maximum, resulting in the strongest migration of the ceramic slurry towards the positive electrode slurry, leading to the phenomenon of interleaved edges. Currently, there is no fundamental solution to the interleaved edge problem. Adjusting the process methods cannot fundamentally solve the problem; the adjustment window is narrow. Subsequently, the interleaved edge problem leads to poor electrode edge gripping, resulting in a large number of defective products. Summary of the Invention

[0004] The main objective of this invention is to provide a positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery, in order to solve the problem in the prior art where the positive electrode sheet has a false edge due to the simultaneous coating of the positive electrode slurry and the ceramic slurry.

[0005] To achieve the above objectives, according to one aspect of the present invention, a positive electrode slurry is provided, the positive electrode slurry comprising a positive electrode active material, a conductive agent, a first binder, a dispersant and a first solvent, wherein the solid mass content of the positive electrode slurry is 69-71%, the viscosity is 5000-8000 mPa·s, and the dispersant is a combination of polyethylene glycol and ethanolamine.

[0006] Furthermore, the mass content of the dispersant in the positive electrode slurry is 0.05~0.5%.

[0007] Furthermore, the mass ratio of polyethylene glycol to ethanolamine is 1:(0.1~0.3).

[0008] Furthermore, the number-average molecular weight of polyethylene glycol is 400-600 g / mol; and / or, the ethanolamine is selected from any one or more of monoethanolamine, diethanolamine, and triethanolamine; and / or, the average particle size of the positive electrode active material is 1.0-1.5 µm (D50); and / or, the specific surface area of ​​the positive electrode active material is 11-14 m². 2 / g.

[0009] Further, the mass ratio of the positive electrode active material, the conductive agent, and the first binder is (96~97.5):(0.5~1.0):(1.5~2.5); and / or, the positive electrode active material is selected from any one or more of lithium iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide; and / or, the conductive agent is selected from any one or more of super conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and carbon fibers; and / or, the first binder is selected from any one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polytetrafluoroethylene; and / or, the first solvent is selected from any one or more of N-methylpyrrolidone, ethanol, dimethylformamide, and dimethyl sulfoxide.

[0010] According to another aspect of the present invention, a method for preparing a positive electrode sheet is provided, the method comprising: coating the aforementioned positive electrode slurry and ceramic slurry together on a current collector and drying them to obtain a positive electrode sheet.

[0011] Furthermore, the drying temperature is 100~200℃.

[0012] Furthermore, the solids content of the ceramic slurry is 28-35%.

[0013] According to another aspect of the present invention, a positive electrode is provided, which is prepared by the aforementioned preparation method.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0015] Applying the technical solution of this invention, polyethylene glycol, being a long chain with ether bonds, can form steric hindrance between particles; ethanolamine, as a surfactant, helps reduce the surface tension of the cathode slurry. The cathode slurry of this application uses a combination of polyethylene glycol and ethanolamine as a dispersant, which helps increase the solids content of the cathode slurry and regulates its viscosity, controlling the solids content to be 69-71% and the viscosity to be in the range of 5000-8000 mPa·s. The higher solids content of the cathode slurry compared to conventional cathode slurries allows for rapid drying during baking to form the active cathode layer, preventing the ceramic slurry and cathode slurry from exhibiting "like dissolves like" conditions, thus preventing the ceramic slurry from migrating towards the cathode slurry and avoiding the formation of mutually soluble edges. Controlling the viscosity of the cathode slurry within the above range helps improve the stability and uniformity of the slurry coating on the current collector, while further helping to avoid the formation of mutually soluble edges. Reducing virtual edge issues helps lower the DC internal resistance of the battery, improve its electrochemical performance, reduce dependence on specific coating parameters or process conditions, expand the process debugging window, and improve production yield. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 An optical photograph of the positive electrode sheet in Embodiment 1 of this application is shown;

[0018] Figure 2 An optical photograph of the positive electrode in Comparative Example 1 of this application is shown.

[0019] The above figures include the following reference numerals:

[0020] 1. Ceramic region; 2. Positive electrode region. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] As analyzed in the background section of this application, the prior art has the problem of virtual edges appearing on the positive electrode sheet due to the simultaneous coating of the positive electrode slurry and the ceramic slurry. In order to solve the above problems, this application provides a positive electrode slurry, a positive electrode sheet, a method for preparing the same, and a lithium-ion battery.

[0023] In a typical embodiment of this application, a positive electrode slurry is provided, which includes a positive electrode active material, a conductive agent, a first binder, a dispersant and a first solvent. The solid content of the positive electrode slurry is 69-71% by mass, the viscosity is 5000-8000 mPa·s, and the dispersant is a combination of polyethylene glycol and ethanolamine.

[0024] Polyethylene glycol (PEG) is a long chain with ether bonds, which can create steric hindrance between particles; ethanolamine, as a surfactant, helps reduce the surface tension of the cathode slurry. The cathode slurry of this application uses a combination of PEG and ethanolamine as a dispersant, which helps increase the solids content of the cathode slurry and regulates its viscosity, controlling the solids content to be 69-71% and the viscosity to be in the range of 5000-8000 mPa·s. The higher solids content of the cathode slurry compared to conventional cathode slurries allows for rapid drying during baking to form the active cathode layer, preventing the ceramic slurry and cathode slurry from exhibiting the "like dissolves like" condition, thus preventing the ceramic slurry from migrating towards the cathode slurry and avoiding the formation of mutually soluble edges. Controlling the viscosity of the cathode slurry within the above range helps improve the stability and uniformity of the slurry coating on the current collector, while further helping to avoid the formation of mutually soluble edges. Reducing virtual edge issues helps lower the DC internal resistance of the battery, improve its electrochemical performance, reduce dependence on specific coating parameters or process conditions, expand the process debugging window, and improve production yield.

[0025] In one embodiment of this application, the mass content of the dispersant in the above-mentioned positive electrode slurry is 0.05~0.5%, specifically 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, and any range between two values.

[0026] Controlling the mass content of dispersant in the cathode slurry within the above range helps to adjust the surface tension of the cathode slurry without affecting its electrical properties, allowing it to quickly form a dense layer during the drying process. This disrupts the "like dissolves like" condition between the ceramic slurry and the cathode slurry, further preventing the formation of miscible edges.

[0027] In order to further enhance the interaction between polyethylene glycol and ethanolamine, thereby reducing the DC internal resistance of the battery and avoiding the generation of virtual edges, in one embodiment of this application, the mass ratio of the polyethylene glycol to ethanolamine is 1:(0.1~0.3).

[0028] In one embodiment of this application, the number average molecular weight of the polyethylene glycol is 400-600 g / mol; and / or, the ethanolamine is selected from any one or more of monoethanolamine, diethanolamine, and triethanolamine; and / or, the average particle size of the positive electrode active material is D50 of 1.0-1.5 µm; and / or, the specific surface area of ​​the positive electrode active material is 11-14 m². 2 / g.

[0029] Controlling the number-average molecular weight of polyethylene glycol within the aforementioned range helps to increase the solid content of the cathode slurry without affecting the battery's internal resistance, thereby helping to avoid the formation of virtual edges. In this application, the average particle size and specific surface area of ​​the cathode active material remain within the aforementioned range without exhibiting mutual-soluble virtual edges. Furthermore, controlling the average particle size and specific surface area of ​​the cathode active material within these ranges helps to increase the diffusion rate of lithium ions during charging and discharging, thereby improving the battery's rate performance.

[0030] In one embodiment of this application, the mass ratio of the above-mentioned positive electrode active material, conductive agent and first binder is (96~97.5):(0.5~1.0):(1.5~2.5); and / or, the positive electrode active material is selected from any one or more of lithium iron phosphate, lithium cobalt oxide and lithium nickel cobalt manganese oxide; and / or, the conductive agent is selected from any one or more of super conductive carbon black, acetylene black, Ketjen black, carbon nanotubes and carbon fibers; and / or, the first binder is selected from any one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber and polytetrafluoroethylene; and / or, the first solvent is selected from any one or more of N-methylpyrrolidone, ethanol, dimethylformamide and dimethyl sulfoxide.

[0031] The proportion and types of components in the positive electrode slurry of this application are not limited to the above range. This application controls the mass ratio and types of positive electrode active material, conductive agent and first binder within the above range, which helps to improve the synergistic effect with the dispersant, thereby helping to further improve the charge and discharge efficiency, capacity retention, cycle stability and rate characteristics of the battery while avoiding mutual dissolution and virtual edges.

[0032] In another typical embodiment of this application, a method for preparing a positive electrode sheet is provided, the method comprising: coating the aforementioned positive electrode slurry and ceramic slurry together on a current collector and drying them to obtain a positive electrode sheet.

[0033] By using a parallel coating method, both the positive electrode slurry and the ceramic slurry are simultaneously coated onto the current collector in a very short time, followed by immediate drying. Because the positive electrode slurry of this application has a high solid content and relatively high surface tension, a stable and dense coating can be rapidly formed during the drying process. This characteristic breaks the existing "like dissolves like" condition, effectively preventing the migration of ceramic slurry to the positive electrode slurry, thereby reducing the phenomenon of ceramic mutual dissolution and improving the edge integrity of the positive electrode sheet.

[0034] In order to further improve the drying speed of the cathode slurry, avoid the generation of false edges and reduce production costs, in one embodiment of this application, the drying temperature is 100~200℃.

[0035] In one embodiment of this application, the solid mass content of the above-mentioned ceramic slurry is 28-35%.

[0036] Controlling the solid content of the ceramic slurry within the above-mentioned range helps to improve the uniformity of the coating, reduce the occurrence of delamination, bubbles or discontinuities, and thus help to improve the coating quality.

[0037] In one embodiment of this application, the ceramic slurry includes a ceramic material, a second binder, and a second solvent, wherein the mass ratio of the ceramic material to the second binder is (10~30):1; and / or, the ceramic material may be boehmite and / or alumina; and / or, the second binder may be polyvinylidene fluoride; and / or, the second solvent may be N-methylpyrrolidone.

[0038] The proportion and types of components in the ceramic slurry of this application are not limited to the above range. This application controls the mass ratio and types of ceramic material, second binder and second solvent within the above range, which helps to improve the insulation performance and mechanical strength of the coating.

[0039] In another typical embodiment of this application, a positive electrode is provided, which is prepared by the aforementioned preparation method.

[0040] Since the above-mentioned positive electrode sheet is prepared by the preparation method of this application, the positive electrode sheet does not have a virtual edge.

[0041] In another typical embodiment of this application, a lithium-ion battery is provided, including a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0042] Since the positive electrode in the above-mentioned lithium-ion battery is the positive electrode of this application, the lithium-ion battery has high specific capacity, cycle stability and consistency.

[0043] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0044] Example 1

[0045] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, which was a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2. The positive electrode slurry was obtained with a dispersant content of 0.1% and a solid content of 70%. The viscosity was 5800 mPa·s.

[0046] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0047] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0048] Example 2

[0049] The difference from Example 1 is that the mass content of the dispersant in the positive electrode slurry is 0.05%;

[0050] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, which was a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2. The positive electrode slurry was obtained with a dispersant content of 0.05% and a solid content of 69%. The viscosity was 5000 mPa·s.

[0051] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0052] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0053] Example 3

[0054] The difference from Example 1 is that the mass content of the dispersant in the positive electrode slurry is 0.5%;

[0055] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, which was a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2. The positive electrode slurry was obtained with a dispersant content of 0.5% and a solid content of 70.5%. The viscosity was 7000 mPa·s.

[0056] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0057] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0058] Example 4

[0059] The difference from Example 1 is that the mass content of the dispersant in the positive electrode slurry is 0.6%;

[0060] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, which was a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2. The positive electrode slurry was obtained with a dispersant content of 0.6% and a solid content of 71%. The viscosity was 8000 mPa·s.

[0061] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0062] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0063] Example 5

[0064] The difference from Example 1 is that the mass ratio of polyethylene glycol to diethanolamine is 1:0.1;

[0065] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.1. The positive electrode slurry had a solids content of 70%, a viscosity of 5796 mPa·s, and a dispersant content of 0.1%.

[0066] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0067] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0068] Example 6

[0069] The difference from Example 1 is that the mass ratio of polyethylene glycol to diethanolamine is 1:0.3;

[0070] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.3 to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%, the viscosity was 5840 mPa·s, and the mass content of the dispersant in the positive electrode slurry was 0.1%.

[0071] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0072] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0073] Example 7

[0074] The difference from Example 1 is that the mass ratio of polyethylene glycol to diethanolamine is 1:0.4;

[0075] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.4. The positive electrode slurry had a solids content of 70%, a viscosity of 5943 mPa·s, and a dispersant content of 0.1%.

[0076] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0077] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0078] Example 8

[0079] The difference from Example 1 is that the number average molecular weight of polyethylene glycol is 400 g / mol;

[0080] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 400 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%, the viscosity was 6012 mPa·s, and the mass content of the dispersant in the positive electrode slurry was 0.1%.

[0081] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0082] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0083] Example 9

[0084] The difference from Example 1 is that the number average molecular weight of polyethylene glycol is 600 g / mol;

[0085] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 600 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%, the viscosity was 5978 mPa·s, and the mass content of the dispersant in the positive electrode slurry was 0.1%.

[0086] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0087] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0088] Example 10

[0089] The difference from Example 1 is that the number average molecular weight of polyethylene glycol is 700 g / mol;

[0090] The lithium iron phosphate (D50 is 1.17µm, specific surface area is 13.6m²) was used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97:0.7:2. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 700 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%, the viscosity was 6047 mPa·s, and the mass content of the dispersant in the positive electrode slurry was 0.1%.

[0091] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0092] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 150°C to obtain a positive electrode sheet.

[0093] Example 11

[0094] The difference from Example 1 is that lithium iron phosphate (D50 is 1µm, specific surface area is 14m²) is used.2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 96:1:1.5. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2 to obtain a positive electrode slurry. The solid content of the positive electrode slurry was 70%, the viscosity was 6002 mPa·s, and the mass content of the dispersant in the positive electrode slurry was 0.1%.

[0095] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0096] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated on aluminum foil and then dried at 200°C to obtain a positive electrode sheet.

[0097] Example 12

[0098] The difference from Example 1 is that lithium iron phosphate (D50 is 1.5µm, specific surface area is 11m²) is used. 2 The conductive agent super conductive carbon black and the first binder polyvinylidene fluoride were added to N-methylpyrrolidone in a mass ratio of 97.5:0.5:2.5. After high-speed stirring and dispersion, a pre-positive electrode slurry was obtained. A dispersant, a combination of polyethylene glycol (number average molecular weight of 500 g / mol) and diethanolamine, was added to the pre-positive electrode slurry in a mass ratio of 1:0.2. The positive electrode slurry had a solids content of 70%, a viscosity of 5909 mPa·s, and a dispersant content of 0.1%.

[0099] Boehmite and the second binder, polyvinylidene fluoride, were added to N-methylpyrrolidone at a mass ratio of 20:1 and dispersed by high-speed stirring to obtain a ceramic slurry (solid mass content of 30%).

[0100] The above-mentioned positive electrode slurry and the above-mentioned ceramic slurry are coated onto aluminum foil and then dried at 100°C to obtain a positive electrode sheet.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that polyvinylpyrrolidone was used instead of the combination of polyethylene glycol and ethanolamine to obtain the positive electrode sheet.

[0103] Comparative Example 2

[0104] The difference from Example 1 is that the addition of polyethylene glycol and ethanolamine is omitted, the solid content of the positive electrode slurry is 65%, the viscosity is 4000 mPa·s, and the positive electrode sheet is finally obtained.

[0105] The results of observing whether the positive electrode sheets prepared in the examples and comparative examples show whether virtual edges appear are shown in Table 1.

[0106] The positive electrode, polyethylene separator, and graphite negative electrode prepared in the examples and comparative examples are assembled into a dry cell. Lithium hexafluorophosphate electrolyte is injected into the dry cell, and then sealing, standing, hot and cold pressing, formation, and capacity testing are performed to obtain a lithium-ion battery.

[0107] The lithium-ion batteries prepared above were tested by DC charge-discharge method, and the DC internal resistance of the batteries was calculated using Ohm's law. The test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] Figure 1 This is an optical photograph of the positive electrode sheet in Embodiment 1 of this application. Figure 2 This is an optical photograph of the positive electrode in Comparative Example 1 of this application, from... Figure 1 and Figure 2 The comparison shows that Figure 2 The positive electrode plate has a distinct virtual edge at the junction of ceramic region 1 and positive electrode region 2.

[0111] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0112] Polyethylene glycol (PEG) is a long chain with ether bonds, which can create steric hindrance between particles; ethanolamine, as a surfactant, helps reduce the surface tension of the cathode slurry. The cathode slurry of this application uses a combination of PEG and ethanolamine as a dispersant, which helps increase the solids content of the cathode slurry and regulates its viscosity, controlling the solids content to be 69-71% and the viscosity to be in the range of 5000-8000 mPa·s. The higher solids content of the cathode slurry compared to conventional cathode slurries allows for rapid drying during baking to form the active cathode layer, preventing the ceramic slurry and cathode slurry from exhibiting the "like dissolves like" condition, thus preventing the ceramic slurry from migrating towards the cathode slurry and avoiding the formation of mutually soluble edges. Controlling the viscosity of the cathode slurry within the above range helps improve the stability and uniformity of the slurry coating on the current collector, while further helping to avoid the formation of mutually soluble edges. Reducing virtual edge issues helps lower the DC internal resistance of the battery, improve its electrochemical performance, reduce dependence on specific coating parameters or process conditions, expand the process debugging window, and improve production yield.

[0113] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode slurry, characterized in that, The positive electrode slurry includes a positive electrode active material, a conductive agent, a first binder, a dispersant, and a first solvent. The solid content of the positive electrode slurry is 69-71% by mass, and the viscosity is 5000-8000 mPa·s. The dispersant is a combination of polyethylene glycol and ethanolamine.

2. The positive electrode slurry according to claim 1, characterized in that, The mass content of the dispersant in the positive electrode slurry is 0.05~0.5%.

3. The positive electrode slurry according to claim 1 or 2, characterized in that, The mass ratio of polyethylene glycol to ethanolamine is 1:(0.1~0.3).

4. The positive electrode slurry according to any one of claims 1 to 3, characterized in that, The number-average molecular weight of the polyethylene glycol is 400-600 g / mol; and / or, the ethanolamine is selected from any one or more of monoethanolamine, diethanolamine, and triethanolamine; And / or, the average particle size of the positive electrode active material is 1.0~1.5µm with a D50; and / or, the specific surface area of ​​the positive electrode active material is 11~14m². 2 / g.

5. The positive electrode slurry according to any one of claims 1 to 4, characterized in that, The mass ratio of the positive electrode active material, the conductive agent, and the first binder is (96~97.5):(0.5~1.0):(1.5~2.5). And / or, the positive electrode active material is selected from any one or more of lithium iron phosphate, lithium cobalt oxide, and lithium nickel cobalt manganese oxide; And / or, the conductive agent is selected from any one or more of super conductive carbon black, acetylene black, Ketjen black, carbon nanotubes and carbon fibers; And / or, the first adhesive is selected from any one or more of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber and polytetrafluoroethylene; And / or, the first solvent is selected from any one or more of N-methylpyrrolidone, ethanol, dimethylformamide, and dimethyl sulfoxide.

6. A method for preparing a positive electrode sheet, characterized in that, The preparation method includes: The positive electrode slurry and ceramic slurry as described in any one of claims 1 to 5 are coated onto the current collector and dried to obtain the positive electrode sheet.

7. The preparation method according to claim 6, characterized in that, The drying temperature is 100~200℃.

8. The preparation method according to claim 6 or 7, characterized in that, The solid content of the ceramic slurry is 28-35%.

9. A positive electrode plate, characterized in that, The positive electrode sheet is prepared by the preparation method according to any one of claims 6 to 8.

10. A lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode, characterized in that, The positive electrode is the positive electrode as described in claim 9.

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