Preparation method of positive electrode slurry, positive electrode sheet and lithium ion battery

Abstract

The present invention provides a method for preparing a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The preparation method comprises: mixing a solvent, polyvinylidene fluoride, and a flexible conductive material to obtain a glue; mixing the glue with a positive electrode active material and a conductive agent to obtain a positive electrode slurry, wherein the flexible conductive material is selected from one or more of the group consisting of polypyrrole doped with sodium dodecylbenzenesulfonate, acrylic acid-pyrrole copolymer, and aniline-pyrrole copolymer. In the above-mentioned method for preparing the positive electrode slurry, polyvinylidene fluoride and a specific flexible conductive material are added to the positive electrode active material and the conductive agent. The positive electrode sheet is prepared using the above-mentioned positive electrode slurry. Under the combined action of the latter two materials, not only can the positive electrode sheet obtain a higher compaction density, but also the peel strength, flexibility, and processing performance of the positive electrode sheet can be greatly improved.

Description

Technical Field

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

[0002] Lithium-ion batteries are currently widely used in various areas of life, such as power batteries for new energy vehicles, 3C digital electronics, and power tools. Consequently, market demand for lithium-ion batteries is continuously increasing, and so are the requirements for product quality. Producing high-quality lithium-ion batteries requires ensuring the preparation of good positive and negative electrode slurries, which is the most critical step in the entire lithium-ion battery manufacturing process. As battery energy density increases, the required compaction density of the positive electrode sheet becomes increasingly stringent. If the positive electrode sheet is subjected to high compaction density, it will not be flexible and may become brittle after rolling. Poorly flexible electrode sheets are prone to breakage during die-cutting and winding due to the tension of the winding and unwinding process, resulting in lower process yields and increased electrode scrap rates. Therefore, improving the processing performance and flexibility of the positive electrode is crucial for increasing the compaction density of the positive electrode sheet, enhancing battery energy density, improving the manufacturing yield rate, and reducing battery production costs. Summary of the Invention

[0003] The main purpose of the present invention is to provide a method for preparing a positive electrode slurry, a positive electrode sheet and a lithium ion battery, so as to solve the problem that the existing high-density positive electrode materials have poor flexibility.

[0004] In order to achieve the above-mentioned object, the present invention provides a method for preparing a positive electrode slurry on one hand, which comprises: mixing a solvent, polyvinylidene fluoride and a flexible conductive material to obtain a glue; mixing the glue with a positive electrode active material and a conductive agent to obtain a positive electrode slurry, wherein the flexible conductive material is selected from one or more of the group consisting of polypyrrole doped with sodium dodecylbenzenesulfonate, acrylic acid-pyrrole copolymer and aniline-pyrrole copolymer.

[0005] Furthermore, the weight ratio of polyvinylidene fluoride to the flexible conductive material is (1-4):1.

[0006] Furthermore, the particle size of the polyvinylidene fluoride is 50 nm to 100 μm.

[0007] Furthermore, the positive electrode slurry includes, by weight, 90.0 to 97.5 parts of positive electrode active material, 1 to 5 parts of conductive agent, 1.5 to 2 parts of polyvinylidene fluoride and 0.5 to 1.5 parts of flexible conductive material.

[0008] Furthermore, the positive electrode active material is one or more selected from the group consisting of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide and lithium nickel cobalt aluminum oxide.

[0009] Furthermore, the conductive agent is selected from one or more of the group consisting of conductive carbon black, conductive graphite, carbon nanotubes, graphene, and nanocarbon fibers; preferably, the conductive carbon black is selected from one or more of the group consisting of acetylene black, Ketjen black, vapor-grown carbon fibers, and carbon nanotubes.

[0010] Furthermore, the viscosity of the positive electrode slurry is 8000-11000 mPa·s, the slurry particle size is 12-20 μm, and the slurry solid content is 58-65%.

[0011] Furthermore, the solvent is NMP.

[0012] Another aspect of the present application provides a positive electrode sheet, comprising a current collector and a positive electrode slurry coated on the current collector, wherein the positive electrode slurry is prepared by the above-mentioned preparation method.

[0013] Another aspect of the present application provides a lithium-ion battery, which includes the positive electrode sheet mentioned above.

[0014] Using the technical solution of the present invention, the above-mentioned positive electrode slurry preparation method adds polyvinylidene fluoride and a specific flexible conductive material to the positive electrode active material and conductive agent. The combined effect of these two materials in preparing positive electrode sheets not only enables the positive electrode sheets to achieve a higher compaction density, but also significantly improves the peel strength, flexibility, and processing performance of the positive electrode sheets. DETAILED DESCRIPTION

[0015] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0016] As described in the background art, existing high-density positive electrode materials have the problem of poor flexibility. To address the above technical issues, the present application provides a method for preparing a positive electrode slurry, the preparation method comprising: mixing a solvent, polyvinylidene fluoride, and a flexible conductive material to obtain a glue; and mixing the glue with a positive electrode active material and a conductive agent to obtain a positive electrode slurry, wherein the flexible conductive material includes, but is not limited to, one or more of the group consisting of polypyrrole doped with sodium dodecylbenzenesulfonate, acrylic acid-pyrrole copolymer, and aniline-pyrrole copolymer.

[0017] In the above-mentioned positive electrode slurry preparation method, polyvinylidene fluoride and a specific flexible conductive material are added to the positive electrode active material and conductive agent. The combined effect of these two materials in preparing positive electrode sheets not only achieves a higher compaction density but also significantly improves the peel strength, flexibility, and processing performance of the positive electrode sheet.

[0018] Since polypyrrole, acrylic acid-pyrrole copolymer and aniline-pyrrole copolymer doped with sodium dodecylbenzenesulfonate have good flexibility and conductivity regardless of the method used to prepare them, they are all suitable for the present application.

[0019] Preferably, the sodium dodecylbenzenesulfonate-doped polypyrrole can be prepared by electrochemical polymerization; the acrylic acid-pyrrole copolymer is obtained by copolymerization of acrylic acid and pyrrole at a molar ratio of 1:1; and the aniline-pyrrole copolymer is obtained by copolymerization of aniline and pyrrole at a molar ratio of 1:1.

[0020] In a preferred embodiment, the weight ratio of polyvinylidene fluoride to the flexible conductive material is (1-4):1. Limiting the usage ratio of polyvinylidene fluoride to the flexible conductive material within the above range can further improve the peel strength, flexibility, and processing performance of the subsequently produced positive electrode sheet.

[0021] The polyvinylidene fluoride used in the above preparation method can be produced by emulsion polymerization or suspension polymerization. In order to further improve the dispersibility of polyvinylidene fluoride in the glue solution and improve the performance stability of the positive electrode, in a preferred embodiment, the particle size of the polyvinylidene fluoride is 50nm to 100μm.

[0022] In a preferred embodiment, the positive electrode slurry comprises, by weight, 90.0-97.5 parts of positive electrode active material, 1-5 parts of conductive agent, 1.5-2 parts of polyvinylidene fluoride, and 0.5-1.5 parts of flexible conductive material. The amounts of the components in the positive electrode slurry include, but are not limited to, the aforementioned ranges. Limiting the amounts within these ranges can further improve the flexibility and peel strength of the positive electrode sheet produced from the positive electrode slurry.

[0023] The positive electrode material used in the above preparation method can be selected from commonly used types in the art. In a preferred embodiment, the positive electrode active material includes, but is not limited to, one or more of the group consisting of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and lithium nickel cobalt aluminum oxide.

[0024] The conductive agent used in the above preparation method can be selected from commonly used materials in the art. In a preferred embodiment, the conductive agent includes, but is not limited to, one or more of the group consisting of conductive carbon black, conductive graphite, carbon nanotubes, graphene, and carbon nanofibers. To further improve the conductivity of the positive electrode sheet, the conductive carbon black more preferably includes, but is not limited to, one or more of the group consisting of acetylene black, Ketjen black, VGCF, and carbon nanotubes.

[0025] In a preferred embodiment, the positive electrode slurry has a viscosity of 8,000 to 11,000 MPa·s, a slurry particle size of 12 to 20 μm, and a slurry solids content of 58 to 65%. Limiting the viscosity, particle size, and solids content of the positive electrode slurry within the above ranges helps further improve the processing performance of the positive electrode slurry when preparing positive electrode sheets.

[0026] The above preparation method can utilize organic solvents commonly used in the art. In a preferred embodiment, the solvent includes, but is not limited to, NMP. When the flexible conductive material is selected from polypyrrole doped with sodium dodecylbenzenesulfonate, acrylic acid-pyrrole copolymer, and aniline-pyrrole copolymer, NMP has good compatibility with the above flexible conductive materials and is inexpensive. Therefore, using NMP as the solvent in the positive electrode slurry can improve the overall performance of the subsequent positive electrode sheet while reducing its preparation cost.

[0027] On the other hand, the present application further 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 the positive electrode slurry prepared by the above-mentioned preparation method.

[0028] In the above-mentioned positive electrode slurry preparation method, polyvinylidene fluoride and a specific flexible conductive material are added to the positive electrode active material and conductive agent. The combined effect of these two materials in preparing positive electrode sheets not only achieves a higher compaction density but also significantly improves the peel strength, flexibility, and processing performance of the positive electrode sheet.

[0029] In another aspect, the present application provides a lithium-ion battery, which includes the positive electrode sheet mentioned above.

[0030] Since the positive electrode sheet containing the positive electrode slurry has good compaction density, flexibility and processing performance, the lithium ion battery prepared using the positive electrode sheet has good qualification rate and conductive performance.

[0031] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0032] The manufacturers of the raw materials used in the examples and comparative examples are shown in Table 1.

[0033] Table 1

[0034]

[0035] Example 1:

[0036] A method for preparing a positive electrode slurry for a lithium-ion battery (taking lithium nickel cobalt manganese oxide (8:1:1) as an example) comprises the following steps:

[0037] (1) A certain amount of solvent NMP was added to a stirring tank, and polyvinylidene fluoride and aniline-pyrrole copolymer were added to the stirring tank at a ratio of 2:1, stirred, dispersed, and dissolved in the solvent to form a glue solution with a viscosity of 6800 mPa·s and a solid content of 7 wt%.

[0038] (2) A certain amount of positive electrode active material (lithium nickel cobalt manganese oxide, 8:1:1) and a conductive agent (acetylene black) are added to a stirring tank, stirred and dispersed evenly, to obtain a lithium ion battery positive electrode slurry, wherein, based on the solid content of the positive electrode slurry, the positive electrode slurry includes: 95wt% positive electrode active material, 2wt% conductive agent, 1wt% aniline-pyrrole copolymer, and 2wt% polyvinylidene fluoride. The viscosity of the positive electrode slurry is 9857mPa·s, the solid content is 62.8%, and the particle size is 20μm.

[0039] Example 2

[0040] The difference from Example 1 is that the flexible conductive material is polypyrrole doped with sodium dodecylbenzenesulfonate, the viscosity of the positive electrode slurry is 9320 mPa·s, and the solid content of the slurry is 63.1%.

[0041] Example 3

[0042] The difference from Example 1 is that the flexible conductive material is polypyrrole doped with sodium dodecylbenzenesulfonate and acrylic acid-pyrrole copolymer (weight ratio 1:1), the viscosity of the positive electrode slurry is 10050 mPa·s, and the solid content of the slurry is 63.7%.

[0043] Example 4

[0044] The difference from Example 1 is that the flexible conductive material is polypyrrole doped with sodium dodecylbenzenesulfonate and aniline-pyrrole copolymer (weight ratio 1:1), the viscosity of the positive electrode slurry is 8652 mPa·s, and the solid content of the slurry is 62.3%.

[0045] Example 5

[0046] The difference from Example 1 is:

[0047] The solid materials in the positive electrode slurry include: 92 parts of positive electrode active material, 5 parts of conductive agent, 1.5 parts of polyvinylidene fluoride and 1.5 parts of flexible conductive material. The viscosity of the positive electrode slurry is 8850 MPa·s, and the solid content of the positive electrode slurry is 61.1%.

[0048] Example 6

[0049] The difference from Example 1 is:

[0050] The solid materials in the positive electrode slurry include: 96.5 parts of positive electrode active material, 1 part of conductive agent, 1.5 parts of polyvinylidene fluoride and 1 part of flexible conductive material, and the viscosity of the positive electrode slurry is 9890mPa·s, and the solid content of the positive electrode slurry is 64.3%.

[0051] Example 7

[0052] The difference from Example 6 is:

[0053] The solid materials in the positive electrode slurry include: 96.5 parts of positive electrode active material, 1 part of conductive agent, 2 parts of polyvinylidene fluoride and 0.5 parts of flexible conductive material, and the viscosity of the positive electrode slurry is 9205 MPa·s, and the solid content of the positive electrode slurry is 64.0%.

[0054] Example 8

[0055] The difference from Example 1 is that the weight ratio of polyvinylidene fluoride to the flexible conductive material is 1:1.

[0056] Example 9

[0057] The difference from Example 1 is that the weight ratio of polyvinylidene fluoride to the flexible conductive material is 5:1.

[0058] Comparative Example 1:

[0059] Compared with Example 1, the raw materials involved in Comparative Example 1 do not contain high molecular flexible composite materials, the solid substance in the glue system is only polyvinylidene fluoride, and the remaining substances and mass fractions, stirring parameters, stirring time, etc. are the same.

[0060] Comparative Example 2:

[0061] Compared with Example 9, the flexible material is thermoplastic polyurethane.

[0062] Performance testing:

[0063] The lithium nickel cobalt manganese oxide (8:1:1) positive electrode slurry prepared in Examples 1 to 9 and Comparative Examples 1 to 2 was coated on both sides of the aluminum foil, with the same surface density (surface density range 400g / m 2 ), after oven baking and roller pressing, the positive electrode sheet with uniform thickness was obtained. The rebound rate of the two types of electrode sheets after roller pressing was tested (compaction density 3.5g / m 3 ), conductivity, and peel strength. The positive electrode sheet was then bent 180° and the flexibility was tested by using a 2kg roller to press back and forth at the bend twice. The test results are shown in Table 2.

[0064] Table 2

[0065]

[0066] From Table 1 we can see that:

[0067] The rebound rate and conductivity of the electrode sheet of Example 1 7 days after rolling are similar to the test results of Comparative Example 1, and the peel strength of Example 1 is more than twice the peel strength of Example 1. From the bending experiment, it is known that under the condition of a compaction density of 3.5g / cc for the positive electrode of Example 1, the electrode sheet is bent 180°, and a roller with a certain weight is used to press the bend back and forth twice, and the electrode sheet does not break; under the condition of a compaction density of 3.5g / cc for the positive electrode of Comparative Example 1, the electrode sheet is bent 180°, and a roller with a certain weight is used to press the bend back and forth twice, and the electrode sheet breaks. By comparing Examples 1 to 4 and Comparative Example 2, it can be seen that the use of the specific flexible material of this application to prepare the positive electrode slurry can enable the positive electrode sheet obtained therefrom to obtain better comprehensive performance; by comparing Examples 1, 8 and 9, it can be seen that limiting the weight ratio of polyvinylidene fluoride to the flexible conductive material to the preferred range of this application is conducive to improving the positive electrode sheet to obtain better comprehensive performance. By comparing Examples 1, 5 to 7, it can be seen that limiting the composition of the positive electrode slurry to the preferred range of the present application to prepare the positive electrode slurry can enable the prepared positive electrode sheet to obtain better comprehensive performance.

[0068] In summary, compared to existing positive electrode sheets, the flexibility of the positive electrode sheet produced using the positive electrode slurry provided by this application is significantly improved, and after the positive electrode sheet is bent 180° and subjected to external force, the electrode sheet does not break, which is expected to significantly improve the electrode sheet processing performance and the battery assembly process qualification rate. Especially for wound batteries, the above-mentioned positive electrode sheet has strong adaptability. On the other hand, while improving the flexibility of the electrode sheet and the processing performance of the electrode sheet, the conductivity and peel strength of the electrode sheet are also significantly improved, and there is no adverse effect on the expansion of the electrode sheet.

[0069] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode slurry, characterized in that: The preparation method comprises: The solvent, polyvinylidene fluoride and the flexible conductive material are mixed to obtain a glue solution; The glue solution is mixed with a positive electrode active material and a conductive agent to obtain the positive electrode slurry, wherein the flexible conductive material is selected from one or more of the group consisting of polypyrrole doped with sodium dodecylbenzenesulfonate, acrylic acid-pyrrole copolymer, and aniline-pyrrole copolymer; the sodium dodecylbenzenesulfonate-doped polypyrrole has a doping amount of 8% sodium dodecylbenzenesulfonate, a molecular weight of 370,000, and a number average degree of polymerization of 900; the acrylic acid-pyrrole copolymer is obtained by polymerizing at a molar ratio of acrylic acid to pyrrole of 1:1, has a molecular weight of 200,000, and a number average degree of polymerization of 3000; the aniline-pyrrole copolymer is obtained by polymerizing at a molar ratio of aniline to pyrrole of 1:1, has a molecular weight of 210,000, and a number average degree of polymerization of 2600; The positive electrode slurry comprises, by weight, 90.0 to 97.5 parts of the positive electrode active material, 1 to 5 parts of the conductive agent, 1.5 to 2 parts of the polyvinylidene fluoride, and 0.5 to 1.5 parts of the flexible conductive material; the weight ratio of the polyvinylidene fluoride to the flexible conductive material is (1 to 4):1; the particle size of the polyvinylidene fluoride is 50 nm to 100 μm; The viscosity of the positive electrode slurry is 8000-11000 MPa•s, the slurry particle size is 12-20 μm, and the slurry solid content is 58-65%.

2. The preparation method according to claim 1, characterized in that The positive electrode active material is one or more selected from the group consisting of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide and lithium nickel cobalt aluminum oxide.

3. The preparation method according to claim 1 or 2, characterized in that The conductive agent is selected from one or more of the group consisting of conductive carbon black, conductive graphite, carbon nanotubes, graphene, and nano-carbon fibers.

4. The preparation method according to claim 3, characterized in that The conductive carbon black is selected from one or both of acetylene black and Ketjen black.

5. The preparation method according to claim 1, characterized in that The solvent is NMP.

6. A positive electrode sheet comprising a current collector and a positive electrode slurry coated on the current collector, characterized in that: The positive electrode slurry is prepared by the preparation method according to any one of claims 1 to 5.

7. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 6.

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