A positive electrode sheet, a method for manufacturing the same, and a lithium ion battery

Abstract

The application provides a positive plate, a preparation method thereof and a lithium ion battery. The positive plate comprises a positive current collector and a coating area and a blank foil area arranged on at least one side of the positive current collector; the coating area is provided with a positive active material layer; the edge of the coating area is provided with an insulating adhesive layer; the insulating adhesive layer comprises a first adhesive layer, an intermediate layer and a second adhesive layer which are sequentially stacked from bottom to top; and the bonding strength of the first adhesive layer is greater than that of the second adhesive layer. By arranging the insulating adhesive layer on the surface of the positive plate, the problem of foreign matter introduction caused by the winding, tab rubbing and welding of the battery cell is solved, the wrinkling of the positive plate in the rolling process is avoided, and the quality of the positive plate and the safety performance of the lithium ion battery are comprehensively improved.

Description

Technical Field

[0001] This invention belongs to the field of insulating adhesive materials technology, specifically relating to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have attracted widespread attention due to their high energy density and long cycle life, and are widely used in portable electronic devices, electric vehicles, and smart grids. In the production process of lithium-ion batteries, the preparation of the positive electrode typically involves slitting and rolling. The purpose of these operations is primarily to ensure a tight bond between the active material layer and the current collector, reducing porosity and electron transport distance, thereby improving the compaction density and utilization rate of the electrode.

[0003] Currently, during the slitting process of positive electrode sheets, issues such as exposed current collectors and burrs on the cut edges are common, leading to safety hazards. Furthermore, during the rolling process, the different extensibility of the current collector and active material layer under roller pressure results in inconsistent stretching across different parts of the electrode sheet. This manifests as wavy edges on the foil and can even create fine wrinkles, ultimately reducing the finished product quality and process yield.

[0004] To address the aforementioned issues, existing technologies disclose a solution involving coating the electrode edge with a ceramic insulating layer. While this can alleviate the generation of metal burrs, it presents several problems during use: Firstly, the ceramic insulating layer itself lacks adhesive properties, making it prone to generating metal foreign objects during processing (e.g., winding, folding, or welding). Due to its lack of adhesiveness, it cannot prevent foreign objects generated during production from entering the core, leading to high short-circuit rates in the battery cell and high self-discharge. Secondly, after coating the electrode edge with ceramic particles, the rigidity and resistance to deformation of these particles cause the positive electrode active material to slip during the electrode rolling process, squeezing the edge-coated ceramic particle area and ultimately resulting in electrode wrinkling or cracking of the edge-coated ceramic insulating coating.

[0005] Therefore, there is an urgent need in this field to develop an insulating coating that can not only avoid the burr problem generated during the slitting process of the electrode, but also make the electrode maintain consistent ductility during the rolling process, and reduce the wrinkling of the electrode and the slippage of the active material. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a positive electrode sheet, its preparation method, and a lithium-ion battery. By setting an insulating adhesive layer on the surface of the positive electrode sheet, the present invention not only solves the problem of foreign matter introduction during the winding, tab flattening, and welding processes of the battery cell, but also avoids wrinkling of the electrode sheet during rolling, thus comprehensively improving the quality of the electrode sheet and the safety performance of the lithium-ion battery.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a coated area and an empty foil area disposed on at least one side of the positive current collector;

[0009] The coating area is provided with a layer of positive active material;

[0010] An insulating adhesive layer is provided at the edge of the paste application area;

[0011] The insulating adhesive layer comprises, from bottom to top, a first adhesive layer, an intermediate layer, and a second adhesive layer stacked sequentially.

[0012] The adhesive strength of the first adhesive layer is greater than that of the second adhesive layer.

[0013] This invention designs two adhesive layers with different bonding strengths. The first adhesive layer, closer to the electrode, has a higher bonding strength, firmly adhering to the surface of the positive current collector and active material layer, and preventing the insulating adhesive layer from detaching. The middle layer is mainly designed to improve the mechanical strength of the insulating adhesive layer. The second adhesive layer, farther from the electrode, provides a lower bonding strength. This layer design not only adheres to foreign objects but also prevents excessive bonding strength from causing the electrode to stick to the rollers during rolling. Therefore, the insulating adhesive layer provided by this invention can reduce the Hi-pot defect rate and lower the risk of cell failure.

[0014] Furthermore, in existing technologies, after coating the electrode edges with ceramic particles, the particles are not easily deformed. During the rolling process, the particles in the active material layer move outwards, resulting in significant slippage. However, the slippage at the electrode edges is relatively small, meaning the edge elongation is less than the elongation of the active material layer. This ultimately leads to problems such as electrode wrinkling or cracking of the ceramic coating at the edges. The insulating coating material provided by this invention has excellent flexibility, ensuring that the edge elongation is not less than the elongation of the active material layer, thereby significantly reducing defects such as electrode wrinkling caused by rolling.

[0015] Preferably, the first adhesive layer is made of a polymer.

[0016] Preferably, the monomers of the polymer include any one or a combination of at least two of imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene. For example, it can be imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0017] Preferably, the thickness of the first adhesive layer is 2-10 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0018] Preferably, the bonding strength of the first adhesive layer to the positive electrode current collector is 10 N / m-500 N / m, for example, it can be 10 N / m, 15 N / m, 20 N / m, 25 N / m. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0019] Preferably, the material of the intermediate layer includes any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene, or polyimide. For example, it can be polyethylene terephthalate, polypropylene, or polyimide. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0020] Preferably, the thickness of the intermediate layer is 11-30 μm, for example, it can be 11 μm, 13 μm, 15 μm, 17 μm, 20 μm, 22 μm, 25 μm, 28 μm, or 30 μm. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0021] Preferably, the second adhesive layer comprises a combination of inorganic materials and adhesives.

[0022] Preferably, the inorganic material includes any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, or barium titanate. For example, it can be alumina, boehmite, magnesium hydroxide, or barium titanate. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0023] Preferably, the adhesive comprises any one or a combination of at least two of polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride or styrene-butadiene rubber. For example, it may be polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride or styrene-butadiene rubber. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0024] Preferably, the inorganic content in the second adhesive layer is 2%-30% by mass, more preferably 8%-15%, for example, it can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0025] In this invention, by controlling the mass percentage of inorganic matter in the second adhesive layer, the bonding strength of the second adhesive layer can be adjusted according to actual usage requirements. If the content is too low, the bonding strength of the second adhesive layer will be too high, causing the second adhesive layer to come into contact with the roller surface during the rolling process of the electrode, resulting in problems such as sticking to the roller and wrinkling of the electrode, which in turn affects the process. Conversely, if the content is too high, the bonding strength of the second adhesive layer will be too low, resulting in a weak ability to adsorb impurities and increasing the risk of foreign objects falling into the core.

[0026] Preferably, the thickness of the second adhesive layer is 2-10 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0027] Preferably, the adhesion strength of the second adhesive layer to the positive electrode current collector is 2-6 N / m, for example, it can be 2 N / m, 3 N / m, 4 N / m, 5 N / m, or 6 N / m. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0028] Preferably, the distance by which the insulating adhesive layer covers one side of the paste-coated area is 0.3-0.7 mm, for example, it can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, or 0.7 mm. For the sake of brevity, the values ​​within the above range will not be listed one by one.

[0029] Preferably, the distance by which the insulating adhesive layer covers one side of the empty foil area is 2.3-7.7 mm, for example, it can be 2.3 mm, 2.8 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, or 7.7 mm. For the sake of brevity, the values ​​in the above range will not be listed one by one.

[0030] In this invention, by adjusting the distance between the insulating adhesive layer covering the paste area and the empty foil area, the structure of the paste area covered by the insulating adhesive layer is kept intact during rolling, and cracks will not appear due to compression.

[0031] Preferably, the width of the insulating adhesive layer is 3-8 mm, for example, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, or 8 mm; the thickness is 15-50 μm, for example, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm. For the sake of brevity, the values ​​within the above range will not be listed one by one.

[0032] In a second aspect, the present invention provides a method for preparing a positive electrode sheet according to the first aspect, the method comprising the following steps:

[0033] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the intermediate layer respectively. After drying, an insulating adhesive is obtained. Then, the insulating adhesive is laminated to the edge of the paste-coated area to obtain the positive electrode sheet.

[0034] Preferably, the first adhesive layer slurry comprises a polymer and a first solvent.

[0035] Preferably, the monomers of the polymer include any one or a combination of at least two of imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene. For example, it can be imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0036] Preferably, the first solvent comprises any one or a combination of at least two of N-methylpyrrolidone, acetone, dimethylacetamide, or water.

[0037] Preferably, the solid content of the first adhesive layer slurry is 4%-10%.

[0038] Preferably, the second adhesive layer slurry comprises a combination of inorganic substances and binders, as well as a second solvent.

[0039] Preferably, the inorganic material includes any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, or barium titanate. For example, it can be alumina, boehmite, magnesium hydroxide, or barium titanate. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0040] Preferably, the adhesive comprises any one or a combination of at least two of polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride or styrene-butadiene rubber. For example, it may be polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride or styrene-butadiene rubber. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0041] Preferably, the second solvent comprises any one or a combination of at least two of N-methylpyrrolidone, acetone, dimethylacetamide, or water.

[0042] Preferably, the solid content of the second adhesive layer slurry is 10%-15%.

[0043] Preferably, the material of the intermediate layer includes any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene, or polyimide.

[0044] Preferably, the coating method includes either gravure coating or blade coating.

[0045] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode is the positive electrode according to the first aspect.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] This invention provides a positive electrode sheet with two adhesive layers having different bonding strengths. The first adhesive layer, closer to the electrode sheet, has a higher bonding strength, firmly adhering to the surface of the positive electrode current collector and active material layer, and preventing the insulating adhesive layer from detaching. The middle layer is mainly designed to improve the mechanical strength of the insulating adhesive layer. The second adhesive layer, farther from the electrode sheet, provides a lower bonding strength. This adhesive layer design not only adheres to foreign objects but also prevents excessive bonding strength from causing the electrode sheet to stick to the rollers during rolling. Therefore, the insulating adhesive layer provided by this invention can reduce the Hi-pot defect rate and lower the risk of cell failure.

[0048] Furthermore, in existing technologies, after coating the electrode edges with ceramic particles, the particles are not easily deformed. During the rolling process, the particles in the active material layer move outwards, resulting in significant slippage. However, the slippage at the electrode edges is relatively small, meaning the edge elongation is less than the elongation of the active material layer. This ultimately leads to problems such as electrode wrinkling or cracking of the ceramic coating at the edges. The insulating coating material provided by this invention has excellent flexibility, ensuring that the edge elongation is not less than the elongation of the active material layer, thereby significantly reducing defects such as electrode wrinkling caused by rolling. Attached Figure Description

[0049] Figure 1 The diagram shows the structure of the positive electrode sheet provided in Example 1, where 1-aluminum foil, 2-second adhesive layer, 3-intermediate layer, 4-first adhesive layer, 5-active material layer, 6-width covering the aluminum foil, and 7-width covering the active material layer. Detailed Implementation

[0050] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0051] Example 1

[0052] This embodiment provides a positive electrode, such as Figure 1 As shown, the positive electrode sheet includes an aluminum foil with a thickness of 15 μm and a paste-coated area and an empty foil area disposed on both sides of the aluminum foil. The paste-coated area is provided with a positive electrode active material layer. An insulating adhesive layer with a width of 5 mm and a thickness of 35 μm is disposed at the edge of the paste-coated area. The insulating adhesive layer includes a first adhesive layer, an intermediate layer and a second adhesive layer stacked sequentially from bottom to top. The distance of the insulating adhesive layer covering the side of the paste-coated area is 0.5 mm and the distance of the insulating adhesive layer covering the side of the empty foil area is 4.5 mm.

[0053] The first adhesive layer is made of polyacrylate with a thickness of 10 μm and an adhesion strength of 40 N / m to aluminum foil; the middle layer is made of PET with a thickness of 15 μm; the second adhesive layer consists of polyacrylate and alumina, with the alumina content in the second adhesive layer being 12% by mass, a thickness of 10 μm, and an adhesion strength of 4 N / m to aluminum foil.

[0054] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method of which is as follows:

[0055] Polyacrylate and N-methylpyrrolidone solvent were mixed to obtain a first adhesive layer slurry with a solid content of 8 wt.%.

[0056] Alumina with a median particle size of 1 μm, polyacrylate binder and N-methylpyrrolidone were mixed and stirred to obtain a uniformly dispersed second adhesive layer slurry with a solid content of 12 wt.%.

[0057] Conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone were mixed to prepare a conductive adhesive solution. Then, lithium iron phosphate active material was stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The solid content of the positive electrode slurry was 55 wt.%, and the solid components of the positive electrode slurry included 94 wt.% lithium iron phosphate, 3 wt.% polyvinylidene fluoride, and 3 wt.% conductive carbon black.

[0058] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the PET intermediate layer, and after drying, an insulating adhesive is obtained. Then, the positive electrode slurry is coated on both sides of the aluminum foil, dried, and then rolled. The insulating adhesive is then attached to the edge of the active material layer to obtain the positive electrode sheet.

[0059] Example 2

[0060] This embodiment provides a positive electrode sheet, which includes an aluminum foil with a thickness of 15 μm and a paste-coated area and an empty foil area disposed on both sides of the aluminum foil. The paste-coated area is provided with a positive electrode active material layer, and the edge of the paste-coated area is provided with an insulating adhesive layer with a width of 4 mm and a thickness of 35 μm. The insulating adhesive layer covers the side of the paste-coated area by 0.4 mm and covers the side of the empty foil area by 3.6 mm. The insulating adhesive layer includes a first adhesive layer, an intermediate layer and a second adhesive layer stacked sequentially from bottom to top.

[0061] The first adhesive layer is made of polyacrylate with a thickness of 10 μm and an adhesion strength of 210 N / m to aluminum foil; the middle layer is made of PET with a thickness of 15 μm; the second adhesive layer consists of polyacrylate and alumina, with the alumina content in the second adhesive layer being 10% by mass, a thickness of 10 μm, and an adhesion strength of 5 N / m to aluminum foil.

[0062] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method of which is as follows:

[0063] Polyacrylate and N-methylpyrrolidone solvent were mixed to obtain a first adhesive layer slurry with a solid content of 6 wt.%.

[0064] Alumina with a median particle size of 1 μm, polyacrylate binder and N-methylpyrrolidone were mixed and stirred to obtain a uniformly dispersed second adhesive layer slurry with a solid content of 12 wt.%.

[0065] Conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone were mixed to prepare a conductive adhesive solution. Then, lithium iron phosphate active material was stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The solid content of the positive electrode slurry was 55 wt.%, and the solid components of the positive electrode slurry included 94 wt.% lithium iron phosphate, 3 wt.% polyvinylidene fluoride, and 3 wt.% conductive carbon black.

[0066] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the PET intermediate layer, and after drying, an insulating adhesive is obtained. Then, the positive electrode slurry is coated on both sides of the aluminum foil, dried, and then rolled. The insulating adhesive is then attached to the edge of the active material layer to obtain the positive electrode sheet.

[0067] Example 3

[0068] This embodiment provides a positive electrode sheet, which includes an aluminum foil with a thickness of 15 μm and a paste-coated area and an empty foil area disposed on both sides of the aluminum foil. The paste-coated area is provided with a positive electrode active material layer, and the edge of the paste-coated area is provided with an insulating adhesive layer with a width of 6 mm and a thickness of 30 μm. The insulating adhesive layer covers the side of the paste-coated area by 0.6 mm and the side of the empty foil area by 5.4 mm. The insulating adhesive layer includes a first adhesive layer, an intermediate layer and a second adhesive layer stacked sequentially from bottom to top.

[0069] The first adhesive layer is made of polyacrylate with a thickness of 8μm and an adhesion strength of 357N / m to aluminum foil; the middle layer is made of PET with a thickness of 15μm; the second adhesive layer consists of polyacrylate and alumina, with the alumina content in the second adhesive layer being 13% by mass, a thickness of 7μm, and an adhesion strength of 3N / m to aluminum foil.

[0070] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method of which is as follows:

[0071] Polyacrylate and N-methylpyrrolidone solvent were mixed to obtain a first adhesive layer slurry with a solid content of 8.2 wt.%.

[0072] Alumina with a median particle size of 1 μm, polyacrylate binder and N-methylpyrrolidone were mixed and stirred to obtain a uniformly dispersed second adhesive layer slurry with a solid content of 12 wt.%.

[0073] Conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone were mixed to prepare a conductive adhesive solution. Then, lithium iron phosphate active material was stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The solid content of the positive electrode slurry was 55 wt.%, and the solid components of the positive electrode slurry included 94 wt.% lithium iron phosphate, 3 wt.% polyvinylidene fluoride, and 3 wt.% conductive carbon black.

[0074] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the PET intermediate layer, and after drying, an insulating adhesive is obtained. Then, the positive electrode slurry is coated on both sides of the aluminum foil, dried, and then rolled. The insulating adhesive is then attached to the edge of the active material layer to obtain the positive electrode sheet.

[0075] Example 4

[0076] This embodiment provides a positive electrode sheet, which includes an aluminum foil with a thickness of 15 μm and a paste-coated area and an empty foil area disposed on both sides of the aluminum foil. The paste-coated area is provided with a positive electrode active material layer, and the edge of the paste-coated area is provided with an insulating adhesive layer with a width of 3 mm and a thickness of 15 μm. The insulating adhesive layer covers the side of the paste-coated area by 0.3 mm and the side of the empty foil area by 2.7 mm. The insulating adhesive layer includes a first adhesive layer, an intermediate layer and a second adhesive layer stacked sequentially from bottom to top.

[0077] The first adhesive layer is made of polyacrylonitrile, with a thickness of 2μm and an adhesion strength of 10N / m to aluminum foil; the middle layer is made of polypropylene, with a thickness of 11μm; the second adhesive layer includes polyimide and magnesium hydroxide, with a magnesium hydroxide content of 30% by mass in the second adhesive layer, a thickness of 2μm, and an adhesion strength of 2N / m to aluminum foil.

[0078] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method of which is as follows:

[0079] Polyacrylonitrile and N-methylpyrrolidone solvent were mixed to obtain a first adhesive layer slurry with a solid content of 6 wt.%.

[0080] Magnesium hydroxide with a median particle size of 1 μm, polyimide binder and N-methylpyrrolidone were mixed and stirred to obtain a uniformly dispersed second adhesive layer slurry with a solid content of 12 wt.%.

[0081] Conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone were mixed to prepare a conductive adhesive solution. Then, lithium iron phosphate active material was stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The solid content of the positive electrode slurry was 55 wt.%, and the solid components of the positive electrode slurry included 94 wt.% lithium iron phosphate, 3 wt.% polyvinylidene fluoride, and 3 wt.% conductive carbon black.

[0082] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the polypropylene intermediate layer, and after drying, an insulating adhesive is obtained. Then, the positive electrode slurry is coated on both sides of the aluminum foil, dried, and then rolled. The insulating adhesive is then attached to the edge of the active material layer to obtain the positive electrode sheet.

[0083] Example 5

[0084] This embodiment provides a positive electrode sheet, which includes an aluminum foil with a thickness of 15 μm and a paste-coated area and an empty foil area disposed on both sides of the aluminum foil. The paste-coated area is provided with a positive electrode active material layer, and the edge of the paste-coated area is provided with an insulating adhesive layer with a width of 8 mm and a thickness of 50 μm. The insulating adhesive layer covers the side of the paste-coated area by 0.7 mm and the side of the empty foil area by 7.7 mm. The insulating adhesive layer includes a first adhesive layer, an intermediate layer and a second adhesive layer stacked sequentially from bottom to top.

[0085] The first adhesive layer is made of polyacrylonitrile, with a thickness of 10 μm and an adhesion strength of 10 N / m to aluminum foil; the middle layer is made of polypropylene, with a thickness of 30 μm; the second adhesive layer includes polyimide and magnesium hydroxide, with a magnesium hydroxide content of 2% by mass and a thickness of 10 μm, and an adhesion strength of 6 N / m to aluminum foil.

[0086] This embodiment also provides a method for preparing the above-mentioned positive electrode sheet, the method of which is as follows:

[0087] Polyacrylonitrile and N-methylpyrrolidone solvent were mixed to obtain a first adhesive layer slurry with a solid content of 6 wt.%.

[0088] Magnesium hydroxide with a median particle size of 1 μm, polyimide binder and N-methylpyrrolidone were mixed and stirred to obtain a uniformly dispersed second adhesive layer slurry with a solid content of 12 wt.%.

[0089] Conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone were mixed to prepare a conductive adhesive solution. Then, lithium iron phosphate active material was stirred at high speed to obtain a uniformly dispersed positive electrode slurry. The solid content of the positive electrode slurry was 55 wt.%, and the solid components of the positive electrode slurry included 94 wt.% lithium iron phosphate, 3 wt.% polyvinylidene fluoride, and 3 wt.% conductive carbon black.

[0090] The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the polypropylene intermediate layer, and after drying, an insulating adhesive is obtained. Then, the positive electrode slurry is coated on both sides of the aluminum foil, dried, and then rolled. The insulating adhesive is then attached to the edge of the active material layer to obtain the positive electrode sheet.

[0091] Example 6

[0092] The difference between this embodiment and Embodiment 1 is that the bonding strength of the first adhesive layer is 6 N / m, while all other aspects are the same as in Embodiment 1.

[0093] Example 7

[0094] The difference between this embodiment and Embodiment 1 is that the bonding strength of the second adhesive layer is 1 N / m, and the mass percentage of alumina in the second adhesive layer slurry is 32 wt.%, while all other aspects are the same as in Embodiment 1.

[0095] Example 8

[0096] The difference between this embodiment and Embodiment 1 is that the bonding strength of the second adhesive layer is 9 N / m, and the mass percentage of alumina in the second adhesive layer slurry is 9.5 wt.%, while all other aspects are the same as in Embodiment 1.

[0097] Example 9

[0098] The difference between this embodiment and Embodiment 1 is that the distance of the insulating adhesive layer covering the paste area is 0mm, and the distance covering the empty foil area is 4.5mm. All other aspects are the same as in Embodiment 1.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is that no insulating adhesive layer is provided; otherwise, they are the same as Example 1.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that the insulating adhesive layer is replaced with a boehmite insulating layer of equal thickness, and the average particle size of the boehmite is 1 μm. All other aspects are the same as in Example 1.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is that no second adhesive layer is provided in the insulating adhesive layer; otherwise, they are the same as in Example 1.

[0105] Application Examples 1 to 9 and Comparative Application Examples 1 to 3

[0106] Lithium-ion batteries were prepared using the positive electrode sheets provided in Examples 1 to 9 and Comparative Examples 1 to 3, and the preparation methods are as follows:

[0107] Preparation of the negative electrode sheet: Conductive carbon black and sodium carboxymethyl cellulose aqueous solution are mixed to prepare a conductive adhesive solution. Then, natural graphite active material is added to the conductive adhesive solution and dispersed by high-speed stirring to obtain a semi-finished product. Finally, styrene-butadiene latex binder is added and slowly stirred and mixed to prepare the negative electrode slurry. The solid content of the negative electrode slurry is 55%, wherein the solid components of the negative electrode slurry include 94 wt.% natural graphite, 1.8 wt.% sodium carboxymethyl cellulose, 1.7 wt.% conductive carbon black, and 2.5 wt.% styrene-butadiene latex.

[0108] The above-mentioned negative electrode slurry is coated on both sides of a copper foil current collector with a thickness of 10 μm, and then the electrode is compacted using a roller press to obtain the negative electrode sheet.

[0109] Lithium-ion battery fabrication: A wet-process separator is used, with a base film thickness of 9 μm. A coating with a thickness of 3 μm is applied to the surface of the base film, and the coating material is boehmite. The above-mentioned positive electrode, negative electrode, and separator are used to fabricate a battery cell, which is then processed through electrolyte injection, encapsulation, and formation processes to obtain a lithium-ion battery.

[0110] Test conditions

[0111] The positive electrode sheets provided in Application Examples 1 to 9 and Comparative Application Examples 1 to 3 were tested, and the preparation methods are as follows:

[0112] Adhesive strength of insulating adhesive layer: The test surface is adhered to aluminum foil, and the adhesive strength of the corresponding test surface is tested by using a tensile testing machine with a 180° tensile method.

[0113] The lithium-ion batteries provided in Application Examples 1 to 9 and Comparative Application Examples 1 to 3 were tested using the following methods:

[0114] (1) Hi-pot defect rate: Apply a 500V DC voltage to the positive and negative poles of the core for 2 seconds, test the resistance of the core, and set the core resistance ≤20MΩ as a defective product. Record the number of defective products. Defect rate = (number of defective products / total number of processed products) × 100%.

[0115] (2) High-temperature performance test:

[0116] A. First, under conditions of 25℃ temperature and 40% humidity, charge the battery with a 1C current to the cutoff voltage of 3.65V;

[0117] B. Under conditions of 25°C and 40% humidity, discharge at 0.5C to 2.5V and measure the discharge capacity.

[0118] C. Repeat step A;

[0119] D. After standing at 60℃ for 30 days and the battery temperature returns to 25℃, discharge it at 0.5C with a cutoff voltage of 2.5V to test the remaining capacity of the lithium-ion battery.

[0120] Remaining capacity percentage = (remaining battery capacity / initial battery capacity) × 100%.

[0121] The test results are shown in Tables 1 and 2:

[0122] Table 1

[0123]

[0124]

[0125] Table 2

[0126]

[0127] As can be seen from Tables 1 and 2, the positive electrode sheet provided by the present invention has two adhesive layers with different bonding strengths. The above-mentioned adhesive layer setting can not only stick to foreign objects, but also avoid the phenomenon of sticking to the roller when the electrode sheet is rolled due to excessive adhesive strength. Therefore, the insulating adhesive layer provided by the present invention can reduce the Hi-pot defect rate and reduce the risk of cell failure.

[0128] Compared to Example 1, Example 6 shows that the adhesive strength of the first adhesive layer is too low, which will cause delamination; Examples 7 and 8 show that by adjusting the mass percentage of inorganic matter in the second adhesive layer, the adhesive strength of the second adhesive layer can be adjusted according to actual usage requirements; Example 9 shows that not covering the paste area will increase the Hi-pot defect rate.

[0129] Compared with Example 1, the alumina insulating coating and the insulating coating with only one layer of adhesive disclosed in the prior art cannot achieve the technical effect of the positive electrode sheet provided by the present invention.

[0130] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a paste area and an empty foil area disposed on at least one side of the positive current collector; The coating area is provided with a layer of positive active material; An insulating adhesive layer is provided at the edge of the paste application area; The insulating adhesive layer comprises, from bottom to top, a first adhesive layer, an intermediate layer, and a second adhesive layer stacked sequentially. The adhesive strength of the first adhesive layer is greater than that of the second adhesive layer; The bonding strength of the first adhesive layer to the positive electrode current collector is 10 N / m-500 N / m; The second adhesive layer has an adhesion strength of 2-6 N / m to the positive electrode current collector.

2. The positive electrode sheet according to claim 1, characterized in that, The first adhesive layer is made of polymer.

3. The positive electrode sheet according to claim 2, characterized in that, The monomers of the polymer include any one or a combination of at least two of imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene.

4. The positive electrode sheet according to claim 1, characterized in that, The thickness of the first adhesive layer is 2-10 μm.

5. The positive electrode sheet according to claim 1, characterized in that, The material of the intermediate layer includes any one or a combination of at least two of polyethylene terephthalate, polypropylene, or polyimide.

6. The positive electrode sheet according to claim 1, characterized in that, The thickness of the intermediate layer is 11-30 μm.

7. The positive electrode sheet according to claim 1, characterized in that, The second adhesive layer comprises a combination of inorganic materials and adhesives.

8. The positive electrode sheet according to claim 7, characterized in that, The inorganic material includes any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, or barium titanate.

9. The positive electrode sheet according to claim 7, characterized in that, The adhesive comprises any one or a combination of at least two of the following: polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride, or styrene-butadiene rubber.

10. The positive electrode sheet according to claim 1, characterized in that, The inorganic content in the second adhesive layer is 2%-30% by mass.

11. The positive electrode sheet according to claim 10, characterized in that, The inorganic content in the second adhesive layer is 8%-15% by mass.

12. The positive electrode sheet according to claim 1, characterized in that, The thickness of the second adhesive layer is 2-10 μm.

13. The positive electrode sheet according to claim 1, characterized in that, The distance by which the insulating adhesive layer covers one side of the paste-coated area is 0.3-0.7 mm.

14. The positive electrode sheet according to claim 1, characterized in that, The distance by which the insulating adhesive layer covers one side of the empty foil area is 2.3-7.7 mm.

15. The positive electrode sheet according to claim 1, characterized in that, The width of the insulating adhesive layer is 3-8 mm, and the thickness is 15-50 μm.

16. A method for preparing a positive electrode sheet according to any one of claims 1-15, characterized in that, The method includes the following steps: The first adhesive layer slurry and the second adhesive layer slurry are coated on both sides of the intermediate layer respectively. After drying, an insulating adhesive is obtained. Then, the insulating adhesive is laminated to the edge of the paste-coated area to obtain the positive electrode sheet.

17. The method according to claim 16, characterized in that, The first adhesive layer slurry comprises a polymer and a first solvent.

18. The method according to claim 17, characterized in that, The monomers of the polymer include any one or a combination of at least two of imide, acrylic acid, acrylate, acrylonitrile, styrene, urethane, vinylidene fluoride, butadiene, or styrene.

19. The method according to claim 17, characterized in that, The first solvent includes any one or a combination of at least two of N-methylpyrrolidone, acetone, dimethylacetamide, or water.

20. The method according to claim 16, characterized in that, The solid content of the first adhesive layer slurry is 4%-10%.

21. The method according to claim 16, characterized in that, The second adhesive layer slurry comprises a combination of inorganic substances and binders, as well as a second solvent.

22. The method according to claim 21, characterized in that, The inorganic material includes any one or a combination of at least two of alumina, boehmite, magnesium hydroxide, or barium titanate.

23. The method according to claim 21, characterized in that, The adhesive comprises any one or a combination of at least two of the following: polyimide, polyacrylic acid, polyacrylate, polyacrylonitrile, polystyrene, polyurethane, polyvinylidene fluoride, or styrene-butadiene rubber.

24. The method according to claim 21, characterized in that, The second solvent includes any one or a combination of at least two of N-methylpyrrolidone, acetone, dimethylacetamide, or water.

25. The method according to claim 16, characterized in that, The solid content of the second adhesive layer slurry is 10%-15%.

26. The method according to claim 16, characterized in that, The material of the intermediate layer includes any one or a combination of at least two of polyethylene terephthalate, polypropylene, or polyimide.

27. The method according to claim 16, characterized in that, The coating method includes either gravure coating or blade coating.

28. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode is the positive electrode according to any one of claims 1-15.

Images