Mylar film, preparation method thereof and lithium battery pole group

Abstract

The invention provides a mylar film, a preparation method thereof and a lithium battery pole group. The mylar film comprises a polyester base film and a functional layer arranged on at least one side surface of the polyester base film, wherein the surface of one side, far away from the polyester base film, of the functional layer is provided with a reticulate pattern array of which the density is arranged in a gradient manner, and adjacent reticulate patterns are communicated with each other to form a capillary liquid guide channel. The preparation method comprises the following steps: (1) preparing lyophilic coating slurry; (2) pretreating the surface of at least one side of the polyester base film; (3) coating the surface of the pretreated polyester base film with the lyophilic coating slurry, and drying to form a functional layer; and (4) pressing a reticulate pattern array of which the density is in gradient arrangement on the surface of the functional layer to prepare the mylar film. The Mylar film provided by the invention not only can improve the infiltration performance of an electrolyte and solve the problem of non-uniform infiltration, but also can ensure the insulating strength and avoid the risk of short circuit due to chip falling, and meanwhile, ensures that the process is simple and the cost is controllable.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, and relates to a Mylar membrane, and more particularly to a Mylar membrane, its preparation method, and lithium battery electrode assembly. Background Technology

[0002] Mylar film, also known as polyester film, possesses excellent insulation properties, mechanical strength, and chemical corrosion resistance. It is a core material for lithium-ion battery electrode pack coating, primarily used to isolate the electrode pack, prevent short circuits, and also protect the electrode pack and fix the electrode sheets. As lithium-ion batteries develop towards higher rate performance, longer cycle life, larger capacity, and higher energy density, higher requirements are placed on the electrolyte wetting performance of the electrode pack—the electrolyte needs to quickly and uniformly wet the interior of the electrode pack, reducing injection time and formation time, and avoiding problems such as dry areas at the top and liquid accumulation at the bottom, thereby improving the cycle performance and rate performance of lithium-ion batteries.

[0003] In the existing technology, in order to improve the liquid absorption and electrolyte wetting performance of Mylar membranes, the relevant improvement schemes mainly focus on the following aspects: First, opening through holes or grooves on the surface of the Mylar membrane to increase the contact area and flow channels of the electrolyte and accelerate the wetting speed; second, setting protrusions or stripes on the surface of the Mylar membrane to enhance the spreading ability of the electrolyte; and third, adopting capillary structures or integrally formed flow channels to achieve directional flow of electrolyte.

[0004] However, the above-mentioned improvement schemes all have obvious drawbacks: simply creating through holes will damage the insulation structure of the Mylar membrane, reduce its insulation withstand voltage performance, and easily generate debris at the edges of the through holes, which can easily cause short circuits if it enters the electrode assembly; simply setting grooves or bumps results in poor directionality of electrolyte wetting, still leading to uneven wetting and dry areas at the top, and cannot improve the electrolyte retention capacity of the Mylar membrane; capillary structures or integrally molded channels are difficult to process, costly, and prone to clogging, and their wetting performance will significantly decrease after long-term use. In addition, the existing Mylar membranes have low surface energy and poor compatibility with electrolytes, further restricting the electrolyte wetting speed and electrolyte retention effect.

[0005] Therefore, it is evident that providing a Mylar film for lithium battery electrode pack coating that can improve electrolyte wetting performance, solve the problem of uneven wetting, ensure insulation strength, avoid the risk of short circuit due to shedding, and at the same time ensure simple process and controllable cost has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a Mylar membrane, its preparation method, and a lithium battery electrode assembly, which can improve electrolyte wetting performance, solve the problem of uneven wetting, ensure insulation strength, avoid the risk of short circuit due to shedding, and ensure simple process and controllable cost.

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

[0008] In a first aspect, the present invention provides a Mylar film, comprising a polyester base film and a functional layer disposed on at least one surface of the polyester base film.

[0009] The functional layer has a grid pattern with a gradient density on the side of the surface away from the polyester base film, and adjacent grid patterns are interconnected to form capillary liquid channels.

[0010] The depth of the mesh pattern is less than the thickness of the functional layer, and the mesh pattern array is hydrophilic.

[0011] In a second aspect, the present invention provides a method for preparing a Mylar membrane as described in the first aspect, comprising the following steps:

[0012] (1) Preparation of hydrophilic coating slurry;

[0013] (2) Pretreatment is performed on at least one surface of the polyester film;

[0014] (3) Apply the hydrophilic coating slurry to the surface of the pretreated polyester base film and dry it to form a functional layer;

[0015] (4) A mesh pattern with a gradient density is pressed onto the surface of the functional layer to obtain the Mylar film.

[0016] Steps (1) and (2) are not in any particular order.

[0017] Thirdly, the present invention provides a lithium battery electrode assembly coated with a Mylar film as described in the first aspect.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) This invention abandons the single improvement method of simply drilling, grooving and setting protrusions in the prior art, and adopts a combination design of "layered composite + gradient mesh array + hydrophilic modification", which not only solves the problems of slow and uneven wetting of existing Mylar membranes, but also avoids the risk of damage to insulation performance and shedding. Among them, the polyester base film serves as the substrate to ensure the basic insulation performance and mechanical strength of the Mylar membrane; the functional layer improves the compatibility between the Mylar membrane and the electrolyte and enhances the liquid retention capacity through material modification. The mesh array on its surface can serve as the liquid storage space for the electrolyte and provide a channel for the rapid diffusion of the electrolyte. The depth of the mesh is less than the thickness of the functional layer, that is, the mesh does not penetrate the membrane body, thus avoiding damage to the insulation structure. Moreover, the gradient arrangement structure can form a capillary driving force from bottom to top, guiding the electrolyte to diffuse directionally from the bottom of the electrode group to the top, effectively solving the problems of dry area at the top and liquid accumulation at the bottom.

[0020] (2) The preparation method provided by the present invention is simple and the process is controllable. The functional layer and the mesh array can be formed in one step by the "coating + hot pressing" method. No secondary punching is required, which avoids the damage to the Mylar membrane structure caused by secondary processing. At the same time, the key parameters such as mesh array density and porosity can be quantitatively controlled by adjusting the coating thickness and hot pressing parameters, which is convenient for large-scale industrial production and has a low production cost, making it suitable for promotion and application. Attached Figure Description

[0021] Figure 1 These are schematic diagrams of the cross-sections of the Mylar membrane provided in Examples 1-8.

[0022] Wherein: 1-Polyester base film; 2-Functional layer.

[0023] Figure 2 It is the mesh array on the surface of the functional layer in the Mylar membrane provided in Example 1.

[0024] Wherein: 21-bottom mesh array; 22-middle mesh array; 23-top mesh array. Detailed Implementation

[0025] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0026] One embodiment of the present invention provides a Mylar film, comprising a polyester base film and a functional layer disposed on at least one surface of the polyester base film.

[0027] The functional layer has a grid pattern with a gradient density on the side of the surface away from the polyester base film, and adjacent grid patterns are interconnected to form capillary liquid channels.

[0028] The depth of the mesh pattern is less than the thickness of the functional layer, and the mesh pattern array is hydrophilic.

[0029] This invention abandons the single improvement method of simply drilling, grooving, and adding protrusions in existing technologies, and adopts a combined design of "layered composite + gradient mesh array + hydrophilic modification". This not only solves the problems of slow and uneven wetting of existing Mylar membranes, but also avoids the risks of insulation damage and shedding. The polyester base film serves as the substrate, ensuring the basic insulation performance and mechanical strength of the Mylar membrane. The functional layer, through material modification, improves the compatibility between the Mylar membrane and the electrolyte, enhances its electrolyte retention capacity, and the mesh array on its surface serves as a storage space for the electrolyte, while also providing channels for rapid electrolyte diffusion. The depth of the mesh is less than the thickness of the functional layer, meaning the mesh does not penetrate the membrane, avoiding damage to the insulation structure. Furthermore, the gradient arrangement structure can form a capillary driving force from bottom to top, guiding the electrolyte to diffuse directionally from the bottom of the electrode assembly to the top, effectively solving the problems of dry areas at the top and liquid accumulation at the bottom.

[0030] In some embodiments, the mesh array is a non-through porous structure with a porosity of 15% to 40%, for example, 15%, 20%, 25%, 30%, 35% or 40%, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] This invention limits the porosity of the mesh array to the range of 15% to 40%, which can ensure sufficient liquid storage space and liquid conduction channels, while avoiding excessive porosity that could lead to functional layer detachment or decreased insulation performance.

[0032] In some embodiments, the electrolyte contact angle of the mesh array is ≤30°, for example, it can be 5°, 10°, 15°, 20°, 25° or 30°, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] This invention limits the electrolyte contact angle of the mesh array to below 30°, which ensures rapid electrolyte spreading and wetting, thereby improving the wetting speed.

[0034] In some embodiments, the raw materials for preparing the functional layer include ceramic particles and a polar binder.

[0035] Among them, ceramic particles have excellent insulation and high temperature resistance, which can enhance the mechanical strength and insulation performance of the functional layer, while the hydroxyl groups on their surface can improve the hydrophilicity; polar binder has good hydrophilicity and adhesion, which can firmly bond ceramic particles to the surface of polyester base film, while forming a connected porous structure.

[0036] In some embodiments, the ceramic particles are made of at least one of alumina, silica, or boehmite.

[0037] The ceramic particles of the above materials all have excellent insulation properties, hydrophilicity, and mechanical strength.

[0038] In some embodiments, the particle size of the ceramic particles is 50~500nm, for example, it can be 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] This invention limits the particle size of ceramic particles to the range of 50~500nm, which can ensure that the ceramic particles are uniformly dispersed in the binder to form a connected porous structure.

[0040] In some embodiments, the polar binder includes at least one of polyvinylidene fluoride, polyamide, or polyurethane.

[0041] The aforementioned polar binders all possess excellent hydrophilicity, adhesion, and resistance to electrolyte corrosion, making them suitable for the working environment of lithium batteries and ensuring the stability of the functional layer.

[0042] In some embodiments, the gradient arrangement level of the mesh array is ≥2, for example, it can be 2, 3, 4 or 5, and the bottom mesh array density is greater than the top mesh array density.

[0043] In some embodiments, the gradient arrangement level of the mesh array is 2, including a bottom mesh array and a top mesh array; wherein, the density of the bottom mesh array is 1.2 to 2 times the density of the top mesh array, for example, it can be 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times or 2 times, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0044] In some embodiments, the gradient arrangement of the mesh array has three levels, including a bottom mesh array, a middle mesh array, and a top mesh array; wherein, the density of the bottom mesh array is 1.2 to 1.5 times that of the middle mesh array, for example, it can be 1.2 times, 1.3 times, 1.4 times, or 1.5 times; the density of the bottom mesh array is 1.5 to 2 times that of the top mesh array, for example, it can be 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, or 2 times; but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0045] The aforementioned gradient arrangement of the mesh array allows the capillary driving force at the bottom to be greater than that at the top, forming a bottom-up directional flow that promotes rapid diffusion of the electrolyte from the bottom to the top of the electrode assembly, completely eliminating the dry area phenomenon at the top. At the same time, the dense mesh array at the bottom can increase the contact area between the electrolyte and the Mylar membrane, accelerating the absorption and diffusion of the electrolyte at the bottom.

[0046] It should be noted that the Mylar membrane is generally placed in a continuous roll, with the bottom, middle, and top mesh arrays arranged along the axial direction of the Mylar membrane roll. That is, one end of the axial direction of the Mylar membrane roll corresponds to the bottom mesh array (or top mesh array), the other end corresponds to the top mesh array (or bottom mesh array), and the middle area of ​​the roll corresponds to the middle mesh array. In practical applications, the bottom mesh array generally corresponds to the bottom area of ​​the electrode assembly, and the top mesh array corresponds to the top area of ​​the electrode assembly. Of course, the bottom area of ​​the electrode assembly is placed at the bottom of the cell casing, where there is sufficient electrolyte, while the top of the electrode assembly is located at the top of the cell casing. This allows the electrolyte to diffuse upwards through the mesh array of the Mylar membrane when the electrolyte level at the top decreases or becomes insufficient, preventing a dry area at the top.

[0047] In some embodiments, the mesh shape of the mesh array includes at least one of rhombus, stripe, or spiral.

[0048] The aforementioned mesh shape can form an interconnected capillary fluid-conducting network, improving the diffusion efficiency of the electrolyte.

[0049] In some embodiments, the mesh depth of the mesh array is 1~5μm, for example, it can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, and the mesh width is 2~8μm, for example, it can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm or 8μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0050] The coordinated use of the above-mentioned mesh depth and mesh width can ensure sufficient capillary driving force without damaging the structural integrity of the functional layer, thus avoiding problems such as functional layer shedding and flaking.

[0051] In some embodiments, the thickness of the functional layer is 1 to 10 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0052] This invention limits the thickness of the functional layer to the range of 1~10μm, which can avoid increasing the overall thickness of the Mylar membrane while ensuring the hydrophilic and hydroconductive properties, thus not affecting the packaging size of the electrode assembly.

[0053] In some embodiments, the thickness of the polyester base film is 10~25μm, for example, it can be 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm or 25μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0054] This invention limits the thickness of the polyester-based film to the range of 10~25μm, which ensures that the Mylar film has sufficient insulation and mechanical strength to meet the requirements for electrode group coating.

[0055] One embodiment of the present invention also provides a method for preparing the Mylar membrane described in any of the above embodiments, comprising the following steps:

[0056] (1) Preparation of hydrophilic coating slurry;

[0057] (2) Pretreatment is performed on at least one surface of the polyester film;

[0058] (3) Apply the hydrophilic coating slurry to the surface of the pretreated polyester base film and dry it to form a functional layer;

[0059] (4) A mesh pattern with a gradient density is pressed onto the surface of the functional layer to obtain the Mylar film.

[0060] Steps (1) and (2) are not in any particular order.

[0061] The preparation method provided by this invention is simple and controllable. It can achieve one-time molding of functional layer and textured array by "coating + hot pressing" without secondary punching, thus avoiding damage to the Mylar membrane structure caused by secondary processing. At the same time, by adjusting the coating thickness and hot pressing parameters, key parameters such as textured array density and porosity can be quantitatively controlled, which is convenient for large-scale industrial production and has low production cost, making it suitable for widespread application.

[0062] In some embodiments, the preparation method of the hydrophilic coating slurry in step (1) includes: mixing ceramic particles, polar binder and solvent, stirring evenly and then grinding and filtering to obtain the hydrophilic coating slurry.

[0063] In some embodiments, the mass ratio of the ceramic particles, polar binder and solvent is (30~50):(10~20):(30~60), for example, it can be 30:10:60, 35:10:55, 40:15:45, 45:20:35 or 50:20:30, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] In some embodiments, the solvent includes N-methylpyrrolidone and / or acetone.

[0065] In some embodiments, the particle size of the hydrophilic coating slurry is 100~500nm, for example, it can be 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0066] This invention ensures uniform dispersion of the slurry by thoroughly grinding and filtering the hydrophilic coating slurry to achieve a particle size within the range of 100~500nm, thus avoiding agglomeration.

[0067] In some embodiments, the pretreatment in step (2) includes plasma modification treatment to improve the adhesion of the base film surface.

[0068] In some embodiments, the power of the plasma modification treatment is 100~300W, for example, it can be 100W, 120W, 140W, 160W, 180W, 200W, 220W, 240W, 260W, 280W or 300W, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0069] In some embodiments, the plasma modification treatment time is 10 to 30 seconds, for example, 10 seconds, 12 seconds, 14 seconds, 16 seconds, 18 seconds, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds or 30 seconds, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0070] In some embodiments, the atmosphere for the plasma modification treatment includes air or oxygen.

[0071] The plasma modification treatment under the above process conditions can increase the active groups on the surface of the polyester film, improve the adhesion between the hydrophilic coating slurry and the polyester film, and effectively prevent the subsequent functional layer from falling off.

[0072] In some embodiments, the coating method in step (3) includes blade coating or slot coating.

[0073] In some embodiments, the coating thickness of the hydrophilic coating slurry in step (3) is 1~10μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0074] In some embodiments, the drying temperature in step (3) is 80~120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0075] In some embodiments, the drying time in step (3) is 10 to 30 minutes, for example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0076] After drying under the above process conditions, a porous structure with a porosity of 15% to 40% is formed inside the functional layer.

[0077] In some embodiments, the pressing method described in step (4) includes hot pressing microforming.

[0078] In some embodiments, the hot pressing temperature for the hot pressing microforming is 80~120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0079] In some embodiments, the applied pressure for the hot pressing microforming is 0.3 to 0.8 MPa, for example, it can be 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa or 0.8 MPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0080] In some embodiments, the holding time for the hot-press microforming is 10 to 30 seconds, for example, it can be 10 seconds, 12 seconds, 14 seconds, 16 seconds, 18 seconds, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds or 30 seconds, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] In some embodiments, the hot pressing mold used in the hot pressing microforming is a mold with a mesh array structure.

[0082] This invention, by limiting the process conditions of hot pressing microforming and the hot pressing mold, can ensure that the mesh array is a non-penetrating porous structure, and that the depth, width and density meet the design requirements, while avoiding damage to the polyester base film.

[0083] One embodiment of the present invention also provides a lithium battery electrode assembly covered with the Mylar film described in any of the above embodiments.

[0084] In some embodiments, the Mylar membrane, after coating the lithium battery electrode assembly, presents an integral bent structure, including an interconnected top surface, a first side surface, a bottom surface, and a second side surface.

[0085] The Mylar membrane at least partially overlaps at the first or second side.

[0086] This invention defines the Mylar membrane as an integral bent structure, which can adapt to the coating requirements of the electrode assembly. The Mylar membrane overlaps at least partially on the first or second side to avoid gaps at the joints of the Mylar membrane. At the same time, the through-type capillary liquid guiding channel can realize the uniform diffusion of electrolyte on all surfaces of the electrode assembly, further improving the wetting uniformity and ensuring that all parts of the electrode assembly can be fully wetted by electrolyte.

[0087] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0088] Example 1

[0089] This embodiment provides a Mylar film for coating lithium battery electrode packs, such as Figure 1 As shown, the Mylar membrane includes a polyester base film 1 and a functional layer 2 disposed on one side surface of the polyester base film 1. The polyester base film 1 has a thickness of 15 μm, the functional layer 2 has a thickness of 5 μm, and the raw materials for preparing the functional layer 2 include alumina ceramic particles (particle size of 200 nm) and polyvinylidene fluoride binder in a mass ratio of 40:15.

[0090] like Figure 2 As shown, the functional layer 2 has a gradient-arranged mesh pattern on the surface away from the polyester base film 1, with adjacent mesh patterns interconnected to form capillary liquid guiding channels. Specifically, the mesh pattern array is a non-penetrating porous structure with a porosity of 25%, and the gradient arrangement of the mesh pattern array has three levels, including a bottom mesh pattern array 21, a middle mesh pattern array 22, and a top mesh pattern array 23. The density of the bottom mesh pattern array 21 is 1.2 times that of the middle mesh pattern array 22, and the density of the bottom mesh pattern array 21 is 1.5 times that of the top mesh pattern array 23. The mesh pattern of the mesh pattern array is rhomboid, with a mesh depth of 3 μm and a mesh width of 5 μm. After coating the lithium battery electrode assembly, the Mylar membrane presents an integrated bent structure, with the mesh patterns on the top, side (including the first and second side) and bottom surfaces being continuous, forming a through-type capillary liquid guiding channel.

[0091] The above-mentioned method for preparing the Mylar membrane includes the following steps:

[0092] (1) Preparation of hydrophilic coating slurry: 40 parts of alumina ceramic particles, 15 parts of polyvinylidene fluoride and 45 parts of N-methylpyrrolidone were mixed, stirred evenly and then ground to a particle size of 300 nm. After filtration, a uniformly dispersed hydrophilic coating slurry was obtained.

[0093] (2) Base film pretreatment: Plasma modification treatment was performed on one side surface of polyester base film 1. The power was set to 200W, the treatment time was 20s, and the treatment atmosphere was air.

[0094] (3) Coating: The hydrophilic coating slurry is uniformly coated on the surface of the pretreated polyester base film 1 using a doctor blade coating method, and the coating thickness is controlled to be 5μm. Then, it is dried at 100℃ for 20min to form the functional layer 2.

[0095] (4) Mesh array molding: The hot pressing micro-molding process is adopted. The hot pressing temperature is set to 100℃, the applied pressure is 0.5MPa, and the holding time is 20s. The mesh array with a mesh array structure is pressed on the surface of the functional layer 2 to form a gradient mesh array, thus obtaining the Mylar film.

[0096] Example 2

[0097] This embodiment provides a Mylar film for coating lithium battery electrode packs, such as Figure 1 As shown, the Mylar membrane includes a polyester base film 1 and a functional layer 2 disposed on one side surface of the polyester base film 1. The polyester base film 1 has a thickness of 10 μm, the functional layer 2 has a thickness of 1 μm, and the functional layer 2 is prepared from silica ceramic particles (50 nm in diameter) and polyamide binder in a mass ratio of 30:10.

[0098] In this embodiment, the functional layer 2 has a gradient-arranged mesh pattern on its surface away from the polyester base film 1, with adjacent mesh patterns interconnected to form capillary liquid guiding channels. Specifically, the mesh pattern array is a non-penetrating porous structure with a porosity of 15%, and the gradient arrangement of the mesh pattern array has two levels, including a bottom mesh pattern array and a top mesh pattern array. The density of the bottom mesh pattern array is 1.2 times that of the top mesh pattern array. The mesh pattern of the mesh pattern array is strip-shaped, with a mesh depth of 1 μm and a mesh width of 2 μm. After coating the lithium battery electrode assembly, the Mylar membrane presents an integrated bent structure, with the mesh patterns on the top, side (including the first and second side) and bottom surfaces being continuous to form a through-type capillary liquid guiding channel.

[0099] The above-mentioned method for preparing the Mylar membrane includes the following steps:

[0100] (1) Preparation of hydrophilic coating slurry: Mix 30 parts of silica ceramic particles, 10 parts of polyamide and 60 parts of acetone, stir evenly and grind to a particle size of 100 nm, filter and obtain a uniformly dispersed hydrophilic coating slurry;

[0101] (2) Base film pretreatment: Plasma modification treatment was performed on one side surface of polyester base film 1. The power was set to 100W, the treatment time was 10s, and the treatment atmosphere was oxygen.

[0102] (3) Coating: The hydrophilic coating slurry is uniformly coated on the surface of the pretreated polyester base film 1 using a slit coating method, and the coating thickness is controlled to be 1 μm. Then, it is dried at 80°C for 30 min to form the functional layer 2.

[0103] (4) Mesh array molding: The hot pressing micro-molding process is adopted. The hot pressing temperature is set to 80℃, the applied pressure is 0.3MPa, and the holding time is 10s. The mesh array with a mesh array structure is pressed on the surface of the functional layer 2 to form a gradient mesh array, thus obtaining the Mylar film.

[0104] Example 3

[0105] This embodiment provides a Mylar film for coating lithium battery electrode packs, such as Figure 1 As shown, the Mylar membrane includes a polyester base film 1 and a functional layer 2 disposed on one side surface of the polyester base film 1. The polyester base film 1 has a thickness of 25 μm, the functional layer 2 has a thickness of 10 μm, and the raw materials for preparing the functional layer 2 include boehmite ceramic particles (500 nm in diameter) and polyurethane binder in a mass ratio of 50:20.

[0106] In this embodiment, the functional layer 2 has a gradient-arranged mesh pattern on the surface away from the polyester base film 1, with adjacent mesh patterns interconnected to form capillary liquid guiding channels. Specifically, the mesh pattern array is a non-penetrating porous structure with a porosity of 40%, and the gradient arrangement of the mesh pattern array has three levels, including a bottom mesh pattern array, a middle mesh pattern array, and a top mesh pattern array. The density of the bottom mesh pattern array is 1.5 times that of the middle mesh pattern array, and the density of the bottom mesh pattern array is twice that of the top mesh pattern array. The mesh pattern of the mesh pattern array is spiral-shaped, with a mesh depth of 5 μm and a mesh width of 8 μm. After coating the lithium battery electrode assembly, the Mylar membrane presents an integrated bent structure, with the mesh patterns on the top, side (including the first and second side) and bottom surfaces being continuous, forming a through-type capillary liquid guiding channel.

[0107] The above-mentioned method for preparing the Mylar membrane includes the following steps:

[0108] (1) Preparation of hydrophilic coating slurry: 50 parts of boehmite ceramic particles, 20 parts of polyurethane and 30 parts of N-methylpyrrolidone were mixed, stirred evenly and then ground to a particle size of 500 nm. After filtration, a uniformly dispersed hydrophilic coating slurry was obtained.

[0109] (2) Base film pretreatment: Plasma modification treatment was performed on one side surface of polyester base film 1. The power was set to 300W, the treatment time was 30s, and the treatment atmosphere was air.

[0110] (3) Coating: The hydrophilic coating slurry is uniformly coated on the surface of the pretreated polyester base film 1 using a doctor blade coating method, and the coating thickness is controlled to be 10 μm. Then, it is dried at 120℃ for 10 min to form the functional layer 2.

[0111] (4) Mesh array molding: The hot pressing micro-molding process is adopted, the hot pressing temperature is set to 120℃, the applied pressure is 0.8MPa, and the holding time is 30s. The mesh array with a mesh array structure is pressed on the surface of the functional layer 2 to form a gradient arrangement of mesh array density, and the Mylar film is obtained.

[0112] Example 4

[0113] This embodiment provides a Mylar film for coating lithium battery electrode packs. Except for adjusting the applied pressure of the hot pressing microforming process to change the mesh depth of the mesh array to 0.5 μm, the rest of the structure and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0114] Example 5

[0115] This embodiment provides a Mylar film for coating lithium battery electrode packs. Except for adjusting the coating thickness of the hydrophilic coating slurry to change the thickness of the functional layer 2 to 0.5 μm, the rest of the structure and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0116] Example 6

[0117] This embodiment provides a Mylar film for coating lithium battery electrode packs. Except for changing the thickness of the polyester base film 1 to 8μm, the rest of the structure and conditions are the same as in Embodiment 1, and will not be described in detail here.

[0118] Example 7

[0119] This embodiment provides a Mylar film for coating lithium battery electrode packs. Except for changing the mass ratio of alumina ceramic particles and polyvinylidene fluoride binder to 20:30, the rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0120] Example 8

[0121] This embodiment provides a Mylar film for coating lithium battery electrode packs. Except for changing the mass ratio of alumina ceramic particles and polyvinylidene fluoride binder to 60:5, the rest of the structure and conditions are the same as in Example 1, and will not be described again here.

[0122] Comparative Example 1

[0123] This comparative example provides a Mylar film for coating lithium battery electrode packs. Except for adjusting the mesh array structure of the pressing mold, changing the original gradient mesh array to an equal density mesh array, i.e., the mesh array density in each region is the same, the rest of the structure and conditions are the same as in Example 1, and will not be described in detail here.

[0124] Comparative Example 2

[0125] This comparative example provides a Mylar film for coating lithium battery electrode packs. Except for step (4), which is not performed, i.e., no mesh array is set on the surface of the functional layer, the rest of the structure and conditions are the same as those in Example 1, and will not be described in detail here.

[0126] Comparative Example 3

[0127] This comparative example uses a perforated polyester film (15 μm thick) as the Mylar film for coating lithium battery electrode packs.

[0128] Performance testing

[0129] The lithium battery electrode groups were coated with Mylar films obtained from the above embodiments and comparative examples. The electrolyte contact angle, wetting speed, insulation withstand voltage, shedding, and electrode group wetting uniformity of various Mylar films were tested. The relevant test results are shown in Table 1 below.

[0130] Table 1

[0131]

[0132] As can be seen, the present invention ensures that the electrolyte contact angle is ≤30° through the synergistic effect of the functional layer and the mesh array, which greatly improves the wetting speed compared with conventional Mylar membranes and shortens the injection time and formation time; the directional capillary driving force formed by the mesh array with a density gradient accelerates the uniform wetting of the electrolyte.

[0133] In addition, the textured array design does not damage the overall insulation structure of the Mylar membrane, while the ceramic particles in the functional layer can enhance the insulation performance, ensuring that the insulation withstand voltage performance of the Mylar membrane meets the requirements of lithium battery electrode pack coating, and avoiding the defect of easy shedding of existing perforated Mylar membranes.

[0134] Furthermore, after the Mylar membrane is coated with lithium battery electrode assembly, it presents an integrated bent structure that can be adapted to lithium battery electrode assembly of different specifications. At the same time, parameters such as mesh shape, mesh array density, and porosity can be adjusted according to actual needs to meet the usage requirements of different types of lithium batteries such as high rate and long cycle.

[0135] The preparation method provided by this invention adopts conventional coating and hot pressing processes, which do not require complex equipment and can achieve quantitative control and large-scale industrial production. Compared with existing capillary and one-piece molded flow channel solutions, the production cost is significantly reduced, making it suitable for widespread application.

[0136] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A Mylar membrane, characterized in that, The Mylar membrane includes a polyester base film and a functional layer disposed on at least one surface of the polyester base film; The functional layer has a grid pattern with a gradient density on the surface away from the polyester base film, and adjacent grid patterns are interconnected to form capillary liquid channels. The depth of the mesh pattern is less than the thickness of the functional layer, and the mesh pattern array is hydrophilic.

2. The Mylar membrane according to claim 1, characterized in that, The textured array is a non-penetrating porous structure with a porosity of 15% to 40%. And / or, the electrolyte contact angle of the mesh array is ≤30°.

3. The Mylar membrane according to claim 1 or 2, characterized in that, The raw materials for preparing the functional layer include ceramic particles and polar binders; The ceramic particles are made of at least one of alumina, silicon dioxide, or boehmite. And / or, the particle size of the ceramic particles is 50~500nm; And / or, the polar binder includes at least one of polyvinylidene fluoride, polyamide, or polyurethane.

4. The Mylar membrane according to claim 1 or 2, characterized in that, The gradient arrangement level of the mesh array is ≥2, and the density of the bottom mesh array is greater than that of the top mesh array.

5. The Mylar membrane according to claim 4, characterized in that, The gradient arrangement level of the mesh array is 2, including a bottom mesh array and a top mesh array; The density of the bottom mesh array is 1.2 to 2 times that of the top mesh array.

6. The Mylar membrane according to claim 4, characterized in that, The gradient arrangement level of the mesh array is 3, including a bottom mesh array, a middle mesh array and a top mesh array; The bottom mesh array density is 1.2 to 1.5 times that of the middle mesh array density, and the bottom mesh array density is 1.5 to 2 times that of the top mesh array density.

7. The Mylar membrane according to claim 1 or 2, characterized in that, The mesh shape of the mesh array includes at least one of rhombus, stripe, or spiral. And / or, the mesh depth of the mesh array is 1~5μm and the mesh width is 2~8μm.

8. The Mylar membrane according to claim 1 or 2, characterized in that, The thickness of the functional layer is 1~10μm; And / or, the thickness of the polyester base film is 10~25μm.

9. A method for preparing a Mylar membrane as described in any one of claims 1 to 8, characterized in that, The preparation method includes the following steps: (1) Preparation of hydrophilic coating slurry; (2) Pretreatment is performed on at least one surface of the polyester film; (3) Apply the hydrophilic coating slurry to the surface of the pretreated polyester base film and dry it to form a functional layer; (4) A mesh pattern with a gradient density is pressed onto the surface of the functional layer to obtain the Mylar film; Steps (1) and (2) are not in any particular order.

10. The method for preparing the Mylar membrane according to claim 9, characterized in that, The preparation method of the hydrophilic coating slurry in step (1) includes: mixing ceramic particles, polar binder and solvent, stirring evenly and then grinding and filtering to obtain the hydrophilic coating slurry; The mass ratio of the ceramic particles, polar binder and solvent is (30~50):(10~20):(30~60); And / or, the solvent includes N-methylpyrrolidone and / or acetone; And / or, the particle size of the hydrophilic coating slurry is 100~500nm.

11. The method for preparing the Mylar membrane according to claim 9, characterized in that, The pretreatment method described in step (2) includes plasma modification treatment; The power of the plasma modification treatment is 100~300W; And / or, the plasma modification treatment time is 10~30s; And / or, the atmosphere of the plasma modification treatment includes air or oxygen.

12. The method for preparing the Mylar membrane according to claim 9, characterized in that, The coating method described in step (3) includes blade coating or slot coating; And / or, the coating thickness of the hydrophilic coating slurry in step (3) is 1~10μm; And / or, the drying temperature in step (3) is 80~120℃; And / or, the drying time in step (3) is 10~30 min.

13. The method for preparing the Mylar membrane according to claim 9, characterized in that, The pressing method described in step (4) includes hot pressing microforming; The hot pressing temperature for the hot pressing micro-forming is 80~120℃; And / or, the applied pressure for the hot pressing microforming is 0.3~0.8MPa; And / or, the holding time for the hot-press microforming is 10~30s; And / or, the hot pressing mold used in the hot pressing microforming is a mold with a mesh array structure.

14. A lithium battery electrode assembly, characterized in that, The lithium battery electrode assembly is covered with a Mylar film as described in any one of claims 1 to 8.

15. The lithium battery electrode assembly according to claim 14, characterized in that, The Mylar membrane, after being used to coat the lithium battery electrode assembly, presents an integral bent structure, including an interconnected top surface, a first side surface, a bottom surface, and a second side surface. The Mylar membrane at least partially overlaps at the first or second side.

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