A lithium battery cell, a lithium battery separator and a method for manufacturing the same

Abstract

The application discloses a lithium battery cell, a lithium battery diaphragm and a preparation method thereof, wherein the lithium battery diaphragm comprises a diaphragm base film and a thickening functional coating, the diaphragm base film is sequentially divided into a first edge area, a middle effective area and a second edge area along the extension direction thereof; at least one side surface of the first edge area and at least one side surface of the second edge area are provided with the thickening functional coating, so that the thickness of the first edge area and the thickness of the second edge area are 1.2-3.0 times of the thickness of the middle effective area; the melting point of the thickening functional coating is lower than the melting point of the diaphragm base film, the elastic modulus of the thickening functional coating is greater than the elastic modulus of the diaphragm base film at normal temperature, and the thickening functional coating is elastic at normal temperature. The technical scheme can effectively improve the problems of the existing lithium battery diaphragm, such as insufficient edge mechanical strength, poor impact resistance, easy fatigue damage in the cycle process and limited high-temperature sealing edge effect caused by the uniform thickness design.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and more specifically, to a lithium battery cell, a lithium battery separator, and a method for preparing the same. Background Technology

[0002] As a core component that isolates the positive and negative electrodes and ensures ion conduction, the mechanical properties and structural stability of lithium-ion battery separators directly determine the cell's impact resistance and cycle life. With the increasing demands for energy density and safety in fields such as new energy vehicle power batteries and energy storage batteries, separator materials need to simultaneously achieve good ion conduction performance and excellent mechanical strength.

[0003] Existing lithium-ion battery separators typically employ a uniform thickness design, meaning the separator has a consistent thickness throughout its entire length. However, in practical applications, it has been found that such uniform thickness separators present the following problems: Firstly, when a battery cell is subjected to a lateral impact, the impact force is mainly borne by the edge of the electrode assembly. The edge area of ​​the uniform thickness separator has the same mechanical strength as the central area. Under the action of a large impact force, the edge area is prone to deformation, wrinkling or even tearing, which can lead to misalignment or even direct contact of the positive and negative electrode plates, causing short circuits or thermal runaway, seriously threatening the safety performance of the battery cell.

[0004] Secondly, the battery cell exhibits a "breathing effect" during charge-discharge cycles. This means that the electrodes undergo alternating expansion and contraction as lithium ions are inserted and extracted. The separator in the edge region experiences the most complex shear and compressive forces from the sides of the electrodes. Under repeated stress, the separator with uniform thickness is prone to fatigue damage, resulting in problems such as decreased porosity and localized cracking. This exacerbates the capacity decay of the battery cell and increases the risk of short circuits.

[0005] Third, the existing diaphragm's hot-melt pore-closing mainly relies on the polyolefin layer in the central region, but the polyolefin layer in the edge region is distributed in the same way as the center. Under high temperature conditions, the melting speed is slow and the sealing effect is limited, making it difficult to effectively prevent edge short circuits caused by the exposure of the electrode side.

[0006] Therefore, there is an urgent need to develop a new type of lithium battery separator that can overcome the above-mentioned defects. Summary of the Invention

[0007] The purpose of this application is to provide a lithium battery cell, a lithium battery separator and a method for preparing the same, in order to improve the problems of insufficient edge mechanical strength, poor impact resistance, easy fatigue damage during cycling and limited high-temperature sealing effect of existing lithium battery separators due to uniform thickness design.

[0008] To achieve this objective, this application provides a lithium battery separator, which includes a separator base film and a thickened functional coating. The separator base film is divided into a first edge region, a middle effective region and a second edge region along its extension direction. The thickening functional coating is provided on at least one side surface of the first edge region and at least one side surface of the second edge region, such that the thickness of the first edge region and the thickness of the second edge region are both 1.2 to 3.0 times the thickness of the intermediate effective region; The melting point of the thickened functional coating is lower than that of the diaphragm base film, the elastic modulus of the thickened functional coating is greater than that of the diaphragm base film at room temperature, and the thickened functional coating is elastic at room temperature.

[0009] Optionally, in some embodiments of this application, the thickening functional coating comprises an electrolyte affinity adhesive and inorganic particles, wherein the electrolyte affinity adhesive accounts for 60% to 80% of the mass of the thickening functional coating, and the inorganic particles account for 20% to 40% of the mass of the thickening functional coating.

[0010] Optionally, in some embodiments of this application, the electrolyte affinity adhesive is a fluoropolymer or an acrylate polymer, wherein the fluoropolymer is selected from at least one of modified polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinylidene fluoride, and the acrylate polymer is selected from at least one of polymethyl methacrylate-butyl acrylate copolymer and polystyrene-butyl acrylate copolymer; and / or, The inorganic particles are selected from at least one of boehmite, aluminum hydroxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, and silicon carbide.

[0011] Optionally, in some embodiments of this application, a slope transition zone with gradually changing thickness is provided between the first edge region and the intermediate effective region, and between the second edge region and the intermediate effective region.

[0012] Optionally, in some embodiments of this application, the width of the slope transition zone is 0.5mm to 3mm; and / or, The thickening functional coating extends from the first edge region or the second edge region to the adjacent slope transition region, and the thickness of the thickening functional coating located in the slope transition region gradually increases from the intermediate effective region toward the first edge region or the second edge region.

[0013] Optionally, in some embodiments of this application, the width of the first edge region is 1mm to 8mm, and the width of the second edge region is 1mm to 8mm; and / or, The thickness of the intermediate effective region is 3μm to 20μm; and / or, The intermediate effective region is a uniformly distributed porous structure, and the porosity of the intermediate effective region is 30% to 50%; and / or, The diaphragm base membrane is a PP / PE composite base membrane or a ceramic-coated membrane, wherein the ceramic-coated membrane includes a base membrane body and an Al2O3 coating or SiO2 coating coated on at least one surface of the base membrane body; and / or, The thickening functional coating is provided on both sides of the first edge region and both sides of the second edge region; and / or, The thickness of the first edge region and the thickness of the second edge region are both 1.5 to 2.5 times the thickness of the intermediate effective region; and / or, The elastic modulus of the thickened functional coating is 2 to 3 times that of the diaphragm base film at room temperature.

[0014] Furthermore, to achieve this objective, embodiments of this application also provide a method for preparing a lithium battery separator, used to prepare the lithium battery separator of any of the above-mentioned methods, the preparation method comprising the following steps: A diaphragm base film is provided, and the diaphragm base film is subjected to surface pretreatment to improve the surface tension of the diaphragm base film. The diaphragm base film is divided into a first edge region, a middle effective region and a second edge region along its extension direction. An electrolyte affinity colloid, inorganic particles, and solvent are mixed to prepare a thickening functional coating slurry, wherein the solid content of the thickening functional coating slurry is 30% to 60%. The thickening functional coating slurry is applied to at least one side surface of the first edge region and at least one side surface of the second edge region using a coating die head; The coated separator base film is dried to obtain the lithium battery separator.

[0015] Optionally, in some embodiments of this application, the surface pretreatment is corona treatment or plasma treatment; and / or, The drying process is a gradient temperature drying process, which involves sequentially drying the coated diaphragm base film in three temperature ranges: 40℃~50℃, 50℃~65℃, and 65℃~80℃, with a drying time of 1 min~5 min for each temperature range; and / or, The edge of the coating die head has an adjustable shim for controlling the thickness of the thickening functional coating. The thickness of the adjustable shim is 0.01mm to 0.05mm.

[0016] In addition, to achieve this purpose, this application embodiment also provides a lithium battery cell, the lithium battery cell including a positive electrode, a negative electrode and a lithium battery separator of any one of the above, the lithium battery separator being disposed between the positive electrode and the negative electrode.

[0017] Optionally, in some embodiments of this application, the width of the first edge region matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm; and / or, The width of the second edge region matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm.

[0018] The lithium-ion battery cell, lithium-ion battery separator, and their preparation method provided in this application, through the aforementioned structural configuration, achieve an increased thickness in the first and second edge regions by using thickening functional coatings while maintaining an appropriate thickness in the central effective region to ensure smooth lithium-ion conduction. Since the elastic modulus of the thickening functional coating is greater than that of the separator base film at room temperature, the edge regions possess both higher thickness and higher material stiffness, thus forming an edge support structure with high mechanical strength. When the battery cell suffers a lateral impact, this edge support structure can preferentially withstand and absorb the impact energy, effectively resisting deformation and tearing, protecting the central effective region from displacement or wrinkling, and reducing the risk of short circuits. Simultaneously, because the melting point of the thickening functional coating is lower than that of the separator base film, under extreme high-temperature conditions, the thickening functional coating in the edge regions can preferentially melt before the separator base film, rapidly forming a continuous insulating sealing layer on the electrode side, preventing edge short circuits. Furthermore, the thickening functional coating possesses a certain degree of elasticity at room temperature, absorbing and buffering the stress generated by electrode expansion during battery cell charge-discharge cycles, reducing fatigue damage to the edge separator. It is evident that this technical solution can effectively improve the problems of insufficient edge mechanical strength, poor impact resistance, easy fatigue damage during cycling, and limited high-temperature sealing effect caused by the uniform thickness design of existing lithium battery separators. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] The structures, proportions, sizes, etc., shown in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this application. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0021] Figure 1 This is a schematic diagram of a first structure of a lithium battery separator according to an embodiment of this application; Figure 2 for Figure 1 The diagram shows the structure of the base membrane of the lithium battery separator. Figure 3 This is a schematic diagram of a second structure of the lithium battery separator according to an embodiment of this application; Figure 4 This is a flowchart of a method for preparing a lithium battery separator according to an embodiment of this application.

[0022] Illustration: 1. Lithium battery separator; 10. Separator base film; 11. First edge region; 12. Middle effective region; 13. Second edge region; 14. Slope transition region; 20. Thickened functional coating. Detailed Implementation

[0023] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In the description of this application, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component centrally located at the same time.

[0025] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] Please see Figures 1 to 3As shown, in one embodiment, this application provides a lithium battery separator 1, which specifically includes a separator base film 10 and a thickening functional coating 20. The separator base film 10 is sequentially divided into a first edge region 11, a middle effective region 12, and a second edge region 13 along its extension direction. The thickening functional coating 20 is disposed on at least one surface of the first edge region 11 and at least one surface of the second edge region 13, such that the thickness of the first edge region 11 and the thickness of the second edge region 13 are both 1.2 to 3.0 times the thickness of the middle effective region 12. The melting point of the thickening functional coating 20 is lower than that of the separator base film 10, the elastic modulus of the thickening functional coating 20 is greater than that of the separator base film 10 at room temperature, and the thickening functional coating 20 is elastic at room temperature.

[0027] It should be noted that the lithium battery separator 1 of this application embodiment is mainly used in lithium-ion batteries, especially suitable for scenarios with high requirements for mechanical shock resistance and safety, such as power batteries for new energy vehicles and energy storage batteries. The aforementioned separator base film 10 is divided into a first edge region 11, a middle effective region 12 and a second edge region 13 along its extension direction (i.e., the length direction of the separator). The middle effective region 12 corresponds to the coverage area of ​​the active material of the cell electrode, while the first edge region 11 and the second edge region 13 correspond to the two side edge regions of the cell electrode. In this way, the thickened functional coating 20 is only disposed in the edge region of the lithium battery separator 1 (i.e., the first edge region 11 and the second edge region 13) and does not cover the middle effective region 12, which can ensure that the ion conduction function of the central region is not affected. The aforementioned statement that "the melting point of the thickened functional coating 20 is lower than that of the separator base film 10" specifically refers to the fact that when the battery cell encounters extreme high-temperature conditions (such as the initial stage of thermal runaway), the thickened functional coating 20 can preferentially melt at a temperature lower than that of the separator base film 10, rapidly forming a continuous and dense insulating sealing layer on the side of the electrode, thereby effectively blocking the path of direct contact between the positive and negative electrodes in the edge area and preventing edge short circuits. The aforementioned statement that "the elastic modulus of the thickened functional coating 20 is greater than that of the separator base film 10 at room temperature" specifically refers to the fact that, under normal operating conditions, the thickened functional coating 20 has higher rigidity than the separator base film 10, making the first edge region 11 and the second edge region 13 less prone to deformation under stress. This provides a stable mechanical support framework for the entire separator, and simultaneously, when the battery cell experiences a lateral impact, it can withstand and transmit the impact load with a smaller deformation, protecting the middle effective area 12 from damage.

[0028] In this way, the lithium battery separator 1 of this embodiment, through the above-described structural configuration, maintains an appropriate thickness in the central effective region 12 to ensure smooth lithium-ion conduction, while increasing the thickness of the first edge region 11 and the second edge region 13 through the thickening functional coating 20. Since the elastic modulus of the thickening functional coating 20 is greater than that of the separator base film 10 at room temperature, the edge region possesses both higher thickness and higher material stiffness, thus forming an edge support structure with high mechanical strength. When the battery cell suffers a lateral impact, this edge support structure can preferentially withstand and absorb the impact energy, effectively resisting deformation and tearing, protecting the central effective region 12 from displacement or wrinkling, and reducing the risk of short circuits. Simultaneously, since the melting point of the thickening functional coating 20 is lower than that of the separator base film 10, under extreme high-temperature conditions, the thickening functional coating 20 in the edge region can preferentially melt before the separator base film 10, rapidly forming a continuous insulating sealing layer on the electrode side, preventing edge short circuits. In addition, the thickened functional coating 20 has a certain degree of elasticity at room temperature, and can absorb and buffer the stress generated by the expansion of the electrode during the charge and discharge cycle of the battery cell, thereby reducing fatigue damage to the edge diaphragm.

[0029] In some examples, such as Figure 1 and Figure 3 As shown, the thickened functional coating 20 comprises an electrolyte affinity gel and inorganic particles. The electrolyte affinity gel accounts for 60%–80% of the mass of the thickened functional coating 20, while the inorganic particles account for 20%–40% of the mass. Thus, the electrolyte affinity gel in the thickened functional coating 20 provides good electrolyte affinity and elastic buffering capacity to the edge region, ensuring sufficient wetting and swelling of the edge thickened area in the electrolyte, which is beneficial for lithium ion transport in the edge region. Simultaneously, the elastic properties of the electrolyte affinity gel allow it to absorb some stress through its reversible deformation during the electrode's cyclic expansion and contraction, slowing the direct transmission of stress to the separator base film 10. The inorganic particles effectively enhance the rigidity and hardness of the edge region. The synergistic effect of both ensures that the edge thickened area possesses sufficient mechanical strength to resist lateral impact deformation while maintaining good wettability with the electrolyte, preventing ion conduction obstruction in the edge region due to excessive coating thickness, thereby achieving a balance between mechanical enhancement and electrochemical performance.

[0030] It should be noted that the mass ratio range of electrolyte affinity adhesive to inorganic particles in this example is optimized based on actual coating process and performance test results. The mass ratio of electrolyte affinity adhesive is calculated based on the total solid mass of the thickened functional coating 20. If the mass ratio of electrolyte affinity adhesive is less than 60%, the content of polymer matrix in the thickened functional coating 20 is too low. On the one hand, this leads to insufficient elastic buffering capacity and bonding strength of the thickened functional coating 20, making it prone to cracking or peeling during cyclic expansion. On the other hand, the low polymer matrix content will result in insufficient bonding between inorganic particles in the thickened functional coating 20, making the particles prone to detachment and affecting the structural integrity and long-term reliability of the thickened functional coating 20. If the mass ratio of electrolyte affinity adhesive is higher than 80%, the content of inorganic particles is too low. The rigidity and puncture resistance of the thickened functional coating 20 will not achieve the expected results, the deformation resistance of the edge area will decrease during lateral impact, and when the content of inorganic particles is insufficient, the molten adhesive lacks sufficient inorganic skeleton support during high-temperature edge sealing, which will also affect the structural strength and insulation performance of the edge sealing layer. Therefore, limiting the mass percentage of the electrolyte affinity adhesive to 60%–80% and the inorganic particles to 20%–40% ensures that the thickened functional coating 20 simultaneously maintains good elastic buffering performance, sufficient mechanical rigidity, and structural integrity during high-temperature edge sealing. The aforementioned mass percentages can be determined using thermogravimetric analysis (TGA) by heating the sample to 800°C under an inert atmosphere and quantitatively analyzing the differences in weight loss between the polymer components and inorganic particles at different temperature ranges.

[0031] In some examples, the electrolyte affinity adhesive mentioned above is a fluoropolymer or an acrylate polymer. The fluoropolymer is selected from at least one of modified polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and polyvinylidene fluoride (PVDF), while the acrylate polymer is selected from at least one of polymethyl methacrylate-butyl acrylate copolymer and polystyrene-butyl acrylate copolymer. Thus, both the fluoropolymer and the acrylate polymer possess good electrolyte affinity and appropriate elastic modulus, effectively buffering the stress generated by electrode expansion at room temperature. Simultaneously, their melting point range is moderate (80℃~150℃), allowing them to melt preferentially over the diaphragm base membrane 10 at high temperatures, achieving rapid edge sealing.

[0032] It should be noted that the selection of polymer materials in this example is mainly based on a combination of factors, including their affinity for the electrolyte, elastic modulus, melting point, and compatibility with inorganic particles. Modified polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), due to the introduction of hexafluoropropylene monomer units, has lower crystallinity than polyvinylidene fluoride (PVDF), thus exhibiting higher elasticity and a lower melting point. This makes it more suitable for applications requiring both elastic buffering and low-temperature melting sealing. Furthermore, the polar groups in its molecular chain have good affinity for carbonate solvents in the electrolyte. Polyvinylidene fluoride (PVDF) has relatively high crystallinity and mechanical strength, making it suitable for applications requiring higher edge rigidity. Polymethyl methacrylate-butyl acrylate copolymer (PMMA-PBA) and polystyrene-butyl acrylate copolymer (PS-PBA) also possess good viscoelasticity and electrolyte swelling properties. Their glass transition temperature can be controlled by adjusting the comonomer ratio, making them viable alternatives to fluoropolymers. The melting points of the aforementioned electrolyte affinity adhesives are all lower than those of the polyolefin materials in the separator base membrane 10 (polyolefins are typically 130°C to 170°C), thus enabling them to preferentially melt and form a sealing layer in the early stages of thermal runaway of the battery cell. The melting points and elastic moduli of the aforementioned polymers can be determined by differential scanning calorimetry (DSC) and dynamic thermomechanical analysis (DMA). Those skilled in the art can select specific polymer types and their combinations according to actual needs.

[0033] In some examples, the inorganic particles mentioned above are selected from at least one of boehmite, aluminum hydroxide, alumina, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, and silicon carbide. Thus, these inorganic particles all possess high hardness and elastic modulus, effectively enhancing the rigidity and puncture resistance of the thickened functional coating 20, ensuring sufficient mechanical strength in the edge thickened area to resist deformation and tearing upon lateral impact. Simultaneously, boehmite and aluminum hydroxide can release water of crystallization and absorb heat at high temperatures, exhibiting certain flame-retardant and cooling effects, helping to delay the spread of thermal runaway. Alumina, silicon oxide, and other oxide particles possess good electrical insulation and chemical stability, ensuring the insulation performance and long-term stability of the sealing layer at high temperatures.

[0034] It should be noted that the specific selection of inorganic particles in this example can be determined based on actual application requirements. Boehmite (γ-AlOOH) and aluminum hydroxide (Al(OH)3) absorb a large amount of heat and release water vapor when thermally decomposed (decomposition temperature is approximately 200℃~350℃). This characteristic can provide a certain thermal buffer and flame retardant effect under high-temperature conditions in battery cells, but their hardness is slightly lower than that of oxide ceramics. Alumina (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), zirconium oxide (ZrO2), titanium oxide (TiO2), and other oxide ceramic particles have higher hardness and elastic modulus, mainly providing mechanical reinforcement, while also having good electrical insulation properties. Silicon carbide (SiC) has extremely high hardness and good thermal conductivity, making it suitable for scenarios with high requirements for edge wear resistance and heat dissipation. The particle size of the above inorganic particles can be selected according to the coating process requirements, usually using nano- or submicron-sized particles (e.g., particle size of 10nm~500nm) to ensure uniform dispersion of particles in the coating and surface smoothness of the coating. The hardness of inorganic particles can be characterized by Vickers hardness or Mohs hardness, and electrical insulation can be evaluated by volume resistivity. Those skilled in the art can select appropriate types and combinations of inorganic particles according to specific performance requirements.

[0035] In some examples, such as Figure 1 and Figure 2 As shown, the width of the first edge region 11 is 1mm to 8mm, and the width of the second edge region 13 is 1mm to 8mm. Setting the width of the edge regions within the range of 1mm to 8mm ensures that the thickened edge region covers the stress-concentrated area of ​​the electrode edge, allowing the thickened functional coating 20 to accurately withstand the impact stress transmitted from the electrode edge during lateral impacts and effectively resist deformation. Simultaneously, it covers the repeatedly displaced area of ​​the electrode edge during cyclic expansion, continuously providing stress buffering. Furthermore, this width range prevents the thickened edge region from being too wide and excessively encroaching on the intermediate effective region 12, ensuring that the intermediate effective region 12 has sufficient area to guarantee smooth lithium-ion conduction. It also prevents the overall rigidity of the lithium battery separator 1 from becoming too large due to an excessively wide thickened edge region, which could affect the smoothness of the winding or stacking process.

[0036] It should be noted that the widths of the first edge region 11 and the second edge region 13 in this example need to match the edge width of the cell electrode to ensure that the thickened functional coating 20 accurately corresponds to the stress-bearing area of ​​the electrode edge. If the width of the edge region is less than 1 mm, the thickened area is too narrow and cannot completely cover the stress-bearing area of ​​the electrode edge during lateral impact and cyclic expansion. Some edge areas will still be unreinforced and will still be at risk of tearing upon impact. At the same time, an overly narrow edge region makes it difficult to accurately control the alignment accuracy of the coating position during the coating process, increasing the difficulty of process control. If the width of the edge region is greater than 8 mm, the thickened area is too wide. On the one hand, the thickened functional coating 20 will cover part of the area that should belong to the main ion conduction channel, which may have an adverse effect on the electrochemical performance of the cell. On the other hand, an overly wide thickened area is prone to wrinkles or wavy edges on the separator during the winding process due to the sudden increase in edge thickness, affecting the winding alignment accuracy and the assembly yield of the cell. Furthermore, the specific value of the edge region width can be adaptively adjusted according to the size and capacity of the battery cell. For example, for small consumer batteries, the edge width is preferably 1mm to 3mm; for large power batteries, the edge width is preferably 3mm to 8mm to provide stronger edge protection. Therefore, independently limiting the width of the first edge region 11 and the second edge region 13 to 1mm to 8mm can ensure impact resistance while taking into account process feasibility and product adaptability. The edge region width can be measured by observing the separator sample using an optical microscope or image measuring instrument, with the actual coating width in the width direction of the separator base film 10 as the standard.

[0037] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, the thickness of the intermediate effective region 12 is 3μm to 20μm. When the thickness of the intermediate effective region 12 is within this range, it provides sufficient conduction channels for lithium ions to pass through the separator while maintaining low ion resistance, ensuring good rate performance and charge / discharge efficiency of the lithium battery cell. Simultaneously, it ensures that the intermediate effective region 12 has sufficient mechanical strength to resist tensile stress and puncture risks during normal use, preventing damage during battery assembly or cycling due to an excessively thin separator.

[0038] It should be noted that the thickness of the intermediate effective region 12 in this example refers to the actual thickness of the separator base film 10 within the intermediate effective region 12, excluding the thickness of any surface coating. This thickness directly affects the ion conduction resistance and mechanical strength of the separator. If the thickness of the intermediate effective region 12 is less than 3 μm, the mechanical strength of the separator is severely insufficient, making it extremely prone to cracking or being punctured by tiny protrusions on the electrode surface during production and use, leading to direct contact between the positive and negative electrodes and forming a short circuit. Furthermore, an excessively thin separator exhibits poor dimensional stability after being immersed in electrolyte, making it prone to shrinkage or deformation. If the thickness of the intermediate effective region 12 is greater than 20 μm, the migration path of lithium ions within the separator is significantly prolonged, increasing the battery's internal resistance and reducing power performance and high-rate charge / discharge performance. Additionally, an excessively thick separator also reduces the volumetric energy density of the battery cell. The determination of the aforementioned thickness range also needs to consider the inherent characteristics of the membrane material. For example, for PE-based membranes, due to PE's low melting point and relatively weak thermal stability, the thickness can be selected near the upper limit of the aforementioned range (e.g., 12μm to 20μm) to compensate for its insufficient mechanical properties. For PP-based or composite membranes, due to PP's relatively high mechanical strength, the thickness can be selected near the lower limit of the aforementioned range (e.g., 3μm to 12μm), which helps to improve the energy density of the battery cell. Therefore, limiting the thickness of the intermediate effective region 12 to 3μm to 20μm can balance the mechanical and electrochemical properties of the membrane. The thickness of the intermediate effective region 12 can be measured using a micrometer screw gauge or according to the standard method of GB / T 6672-2001.

[0039] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, the intermediate effective region 12 has a uniformly distributed porous structure with a porosity of 30% to 50%. Within this porosity range, the intermediate effective region 12 ensures sufficient electrolyte retention and lithium-ion conduction channels, resulting in high ionic conductivity of the separator. Simultaneously, it maintains sufficient electrolyte during battery charging and discharging to ensure smooth lithium-ion transport, preventing increased concentration polarization or lithium plating risks due to insufficient electrolyte. Furthermore, this porosity range also maintains good mechanical strength, ensuring the separator will not crack due to its loose structure during processing and use.

[0040] It is important to note that the porosity of the separator is a crucial factor affecting its ionic conductivity and mechanical strength. Porosity is defined as the percentage of pore volume in the separator's total volume, and its value depends on the stretching and pore-forming conditions during separator fabrication. When the porosity is below 30%, the number of micropores inside the separator is insufficient, making the lithium-ion conduction path within the separator more tortuous and reducing the effective cross-sectional area. This leads to a significant decrease in ionic conductivity, adversely affecting the battery's rate performance and low-temperature performance. Furthermore, the electrolyte wetting rate of the separator also slows down, impacting the efficiency of the electrolyte injection process. When the porosity is above 50%, the proportion of matrix material in the separator is too low, resulting in insufficient structural density and a significant decrease in tensile and puncture strength. This makes the separator prone to breakage during battery assembly and use. Additionally, excessively high porosity also increases the separator's thermal shrinkage rate, leading to poor dimensional stability at high temperatures. Furthermore, the uniformity of porosity is also an important consideration. In this example, the intermediate effective region 12 adopts a uniformly distributed porous structure design, meaning that the porosity within the intermediate effective region 12 is essentially consistent on a macroscopic scale. This helps ensure a uniform distribution of current density throughout the entire intermediate effective region 12, avoiding uneven lithium-ion flux due to excessive local porosity differences. The aforementioned porosity can be determined using mercury intrusion porosimetry or nitrogen adsorption, and the specific testing methods can be found in GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries". Therefore, limiting the porosity of the intermediate effective region 12 to 30%–50% ensures that the separator possesses both good ion conductivity and mechanical properties.

[0041] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, a slope transition zone 14 with gradually changing thickness is provided between the first edge region 11 and the middle effective region 12, and between the second edge region 13 and the middle effective region 12. Thus, by providing a slope transition zone 14 with gradually changing thickness between the edge thickening region and the middle effective region 12, the thickness change of the diaphragm in the width direction can present a smooth, gradual process rather than a step-like abrupt change, thereby effectively avoiding stress concentration caused by abrupt thickness changes. When the cell is subjected to lateral impact or cyclic expansion stress, the stress can be evenly distributed and transmitted along the slope transition zone 14, avoiding the problem of stress concentration at the location of abrupt thickness changes, significantly reducing the risk of the diaphragm tearing or breaking at that location, and significantly improving the structural integrity and reliability of the diaphragm under dynamic stress conditions.

[0042] It should be noted that the sloped transition zone 14 between the edge thickening zone and the middle effective zone 12 of the separator in this example is to achieve a smooth thickness transition and avoid adverse consequences caused by excessive thickness differences and abrupt transition structures. If the transition between the edge thickening zone and the middle effective zone 12 is a right-angle transition or a stepped transition (i.e., the thickness jumps directly from the thickness of the middle effective zone 12 to the thickness of the edge thickening zone within a very short width), then this transition position will become the weakest link in the overall mechanical performance of the separator. During the charge and discharge cycle of the battery cell, the expansion and contraction of the electrode sheets will subject the separator to repeated bending and tensile stress at this position. The stepped transition structure cannot effectively disperse the above stresses over a larger area, resulting in a high concentration of stress at the root of the step. This easily leads to the initiation and propagation of microcracks at this position, ultimately causing the separator to fracture and fail at this location. By setting a slope transition zone 14 with gradually changing thickness, the thickness change is completed smoothly within a certain width range. Stress can be evenly distributed along the slope of the transition zone, significantly reducing peak stress and thus greatly improving the diaphragm's resistance to fatigue fracture during cyclic use. The thickness change of the slope transition zone 14 can be linear (i.e., the thickness changes with a straight slope as the width increases) or curvilinear (such as an arc or S-curve). Those skilled in the art can select a suitable transition curve form based on actual production equipment and process conditions.

[0043] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, the width of the slope transition zone 14 is 0.5mm to 3mm. By limiting the width of the slope transition zone 14 to within the range of 0.5mm to 3mm, it ensures a sufficiently smooth transition space for the diaphragm thickness from the central effective zone 12 to the edge thickening zone, allowing stress to be fully dispersed within the slope transition zone 14 without significant stress concentration. At the same time, it prevents the slope transition zone 14 from occupying too much of the diaphragm width space, thus avoiding the compression of the effective area of ​​the central effective zone 12 or the edge thickening zone due to an excessively wide slope transition zone 14, ensuring the rationality of the overall functional area division of the diaphragm.

[0044] It should be noted that the width of the slope transition zone 14 in this example is closely related to the thickness difference between the edge thickening zone and the central effective zone, and is also constrained by the coating process precision. If the width of the slope transition zone 14 is less than 0.5 mm, it means that the thickness change is completed within an extremely narrow width range, the transition is too abrupt, and its effect is close to a step transition, which is difficult to effectively alleviate stress concentration. The stress will still accumulate in a narrow area within the slope transition zone 14, failing to achieve the expected stress dispersion effect. Moreover, an excessively narrow slope transition zone 14 places extremely high demands on the processing precision and alignment precision of the coating die, increasing the difficulty of process implementation and product consistency control. If the width of the slope transition zone 14 is greater than 3 mm, the slope transition zone 14 occupies too much of the diaphragm width, making the effective width of the edge thickening zone relatively narrower or the area of ​​the central effective zone 12 smaller, which is not conducive to the optimization of the overall diaphragm performance. It also means that the width of the edge thickening zone needs to be increased accordingly to compensate for the occupation of the transition zone, which may lead to an excessively large total coverage width of the thickening functional coating 20, affecting the flexibility and winding performance of the diaphragm. Therefore, limiting the width of the slope transition zone 14 to 0.5 mm to 3 mm achieves a good balance between stress relief and utilization of the diaphragm's functional area. The width of the slope transition zone 14 can be determined by observing the diaphragm cross-sectional sample with an optical microscope and measuring the horizontal distance from the starting point of the thickness change to the endpoint where the thickness reaches a stable edge thickening value.

[0045] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, the thickened functional coating 20 extends from the first edge region 11 or the second edge region 13 to the adjacent slope transition region 14, and the thickness of the thickened functional coating 20 in the slope transition region 14 gradually increases from the intermediate effective region 12 toward the first edge region 11 or the second edge region 13. Thus, by continuously extending the thickened functional coating 20 from the edge region to the slope transition region 14, and by gradually increasing the coating thickness in the slope transition region 14 away from the intermediate effective region 12 to the target thickness of the edge thickening region, a continuous and complete integrated composite structure is formed between the thickened functional coating 20 and the diaphragm base film 10 within the slope transition region 14. This avoids abrupt thickness changes or coating boundaries in the thickened functional coating 20 within the slope transition region 14. This not only facilitates the uniform transmission of stress along the gradual change direction of the coating thickness within the slope transition region 14, but also avoids the risk of peeling due to insufficient interfacial bonding area at the coating boundary.

[0046] It should be noted that in this example, the thickness gradient of the thickening functional coating 20 within the slope transition zone 14, together with the overall thickness variation of the diaphragm base film 10 in this region, constitutes the complete structure of the slope transition zone 14. The thickening functional coating 20 extends from the first edge region 11 or the second edge region 13 to the adjacent slope transition zone 14, meaning that the coating's coverage is not limited to the edge thickening region where the thickness has reached its maximum, but extends further into the slope transition zone 14 where the thickness changes, thus forming a composite structure within the slope transition zone 14 where the coating thickness and base film thickness change synchronously. Within the slope transition zone 14, the thickness of the thickening functional coating 20 gradually increases as the coating position moves from the central effective region 12 to the edge thickening region. This gradient effect can be achieved through the edge shape design of the adjustable shim in the coating die. Specifically, by processing the shim edge into a conical or wedge shape, the opening height of the shim in its edge region changes continuously, thereby achieving gradual control of the coating thickness. The thickness change slope of the thickening functional coating 20 in the slope transition zone 14 should match or coordinate with the thickness change slope of the diaphragm base film 10 itself, so that the total thickness (base film thickness + coating thickness) in the entire slope transition zone 14 transitions smoothly from the thickness of the middle effective zone 12 to the thickness of the edge thickening zone, avoiding sudden increases or decreases in coating thickness that could introduce new stress concentration points, thereby ensuring that the stress dispersion function of the slope transition zone 14 is effectively utilized.

[0047] In some examples, such as Figure 1 , Figure 2 and Figure 3 As shown, the separator base membrane 10 is a PP / PE composite base membrane or a ceramic-coated membrane. The ceramic-coated membrane includes a base membrane body and an Al2O3 coating or SiO2 coating coated on at least one side of the base membrane body. Thus, the PP / PE composite base membrane can utilize the relatively low thermal pore-closing temperature (approximately 130°C to 140°C) of the polyethylene (PE) layer to achieve rapid pore-closing during abnormal battery temperature rise, while utilizing the relatively high melting temperature (approximately 165°C to 170°C) of the polypropylene (PP) layer to maintain the separator's structural framework at higher temperatures, thereby providing a graded thermal response safety protection mechanism for the separator. The ceramic-coated membrane, by setting an Al2O3 or SiO2 ceramic coating on the surface of the base membrane body, utilizes the high hardness, high heat resistance, and excellent electrical insulation properties of ceramic materials to significantly improve the separator's puncture resistance and high-temperature thermal shrinkage stability, helping to reduce the risk of internal short circuits caused by separator damage or shrinkage under abuse conditions.

[0048] It should be noted that the PP / PE composite base film in this example is typically prepared using a co-extrusion stretching method, with a typical structure being a PP / PE / PP three-layer composite or a PE / PP two-layer composite. In the PP / PE / PP three-layer structure, the middle layer is a PE layer, and the two sides are PP layers. The PE layer mainly provides thermal pore-closing functionality, while the PP layer mainly provides structural strength and high-temperature heat resistance. When the internal temperature of the battery abnormally rises to near the melting temperature of the PE layer, the PE layer melts first. The molten PE polymer blocks the micropores in the separator, blocking the ion conduction pathway, thereby effectively inhibiting further increases in the internal current and continuous temperature rise of the battery, providing safety protection. When the temperature continues to rise to the melting temperature of the PP layer, the PP layer begins to melt. Before that, the PP layer can continuously maintain the structural integrity of the separator. The ceramic-coated film is a coating containing Al2O3 or SiO2 ceramic particles applied to the surface of the base film body (i.e., the polyolefin base film, which can be further specifically a PP base film, a PE base film, or a PP / PE composite base film) by coating. Al2O3 coatings have high hardness, excellent electrical insulation properties, and low side reaction activity with electrolytes, making them a common choice for ceramic coatings in lithium-ion battery separators. SiO2 coatings, on the other hand, have good electrolyte affinity and low density, which helps improve the separator's wettability with the electrolyte. The thickness of the ceramic coating is typically 1μm to 5μm, and the coating method can be single-sided or double-sided. Both of these base film types can be used as options for the separator base film 10 in the embodiments of this application. Both can be well integrated with the edge thickening functional coating 20, and those skilled in the art can make appropriate selections based on specific safety performance requirements and cost considerations.

[0049] In some examples, such as Figure 3 As shown, both sides of the first edge region 11 and both sides of the second edge region 13 are provided with a thickening functional coating 20. Thus, by providing the thickening functional coating 20 on both sides of the separator base film 10 corresponding to the edge regions, compared to providing the thickening functional coating 20 on only one side, the thickness increment of the edge region can be maximized. That is, without changing the thickness of the separator base film 10 itself, the total thickness of the edge region is doubled by superimposing the thickening functional coating 20 on both sides, thereby more effectively improving the mechanical strength and impact resistance of the edge region. At the same time, the symmetrical arrangement on both sides ensures that the lithium battery separator 1 has a symmetrical structure in the thickness direction, effectively avoiding deformation problems such as separator curling and edge lifting caused by uneven internal stress due to unilateral coating, and ensuring the flatness and alignment accuracy of the lithium battery separator 1 during winding or stacking.

[0050] It should be noted that in this example, a thickening functional coating 20 is provided on both sides of the edge region, meaning that the upper and lower surfaces of the diaphragm base film 10 are covered by the thickening functional coating 20 in the areas corresponding to the first edge region 11 and the second edge region 13. This double-sided arrangement has two important advantages. First, in terms of thickness enhancement, under the same single coating thickness conditions, double-sided coating can make the total coating thickness in the edge region twice that of single-sided coating, thereby achieving a greater thickness increment under the same coating process conditions. This is particularly advantageous for applications requiring a higher edge thickness ratio. Second, from the perspective of mechanical balance, when a coating is applied to one side of the diaphragm base film 10, the coating will generate a certain shrinkage stress during the drying and curing process. If the coating is only applied to one side, this shrinkage stress will be concentrated on one side of the diaphragm base film 10, which can easily cause the diaphragm to curl towards the coating side. When a thickening functional coating 20 of the same thickness and material is simultaneously applied to both sides, the shrinkage stress generated on both sides balances and cancels each other out, and the overall internal stress distribution of the separator tends to be symmetrical, thus maintaining the flatness of the separator. This is crucial for subsequent winding or stacking processes—curled separators are difficult to align and transport precisely on automated equipment, which will seriously affect the assembly accuracy of the cells and the product yield. Therefore, applying a thickening functional coating 20 to both sides of the edge area is beneficial for achieving a higher edge thickening effect and for maintaining the flatness of the lithium battery separator 1. In addition, the coating on both sides can be applied symmetrically (i.e., the coating thickness and width are exactly the same on both sides), or it can be adjusted asymmetrically according to actual needs. However, in most cases, for ease of process control and to ensure product consistency, symmetrical coating on both sides is preferred.

[0051] In some examples, such as Figure 1 and Figure 2 As shown, the thickness of the first edge region 11 and the thickness of the second edge region 13 are both 1.5 to 2.5 times the thickness of the central effective region 12. Thus, by controlling the thickness of the edge thickening region within the range of 1.5 to 2.5 times that of the central effective region 12, it is possible to ensure that the edge region has significantly higher mechanical strength than the central region to effectively resist lateral impact stress and cyclic expansion stress, while avoiding problems such as edge drift during separator winding, decreased alignment accuracy, and uneven local pressure distribution within the cell caused by excessive edge thickness. This achieves a good balance between mechanical reinforcement and process operability.

[0052] It should be noted that the thickness ratio of the edge thickening region in this example is one of the key parameters for measuring the degree of edge reinforcement in the technical solution of this application. This ratio refers to the ratio between the total thickness of the edge thickening region (i.e., the sum of the thickness of the diaphragm base film 10 and the thickness of the thickening functional coating 20) and the thickness of the intermediate effective region 12 (i.e., the thickness of the diaphragm base film 10 in the intermediate effective region 12). If this ratio is less than 1.5 times, it means that the thickness increment of the edge region is not sufficient, the thickness difference between the edge thickening region and the intermediate effective region 12 is small, the improvement in mechanical performance of the edge region is limited, it is difficult to form a sufficiently strong mechanical support frame to resist deformation and tearing during lateral impact, and the stress buffering capacity during cyclic expansion is also relatively insufficient. If the thickness factor is greater than 2.5, excessive thickness in the edge region may lead to the following problems: First, in the winding process, excessively thick edges will cause the separator to flare outwards during winding, affecting the winding alignment accuracy. Second, inside the cell, excessively thick edges may form local high-pressure areas between the electrode and the separator, causing excessive compressive stress on the electrode in this area, affecting the uniformity and cycle stability of the electrode. Third, excessively thick edges mean that more thickening functional coating material 20 needs to be applied, increasing production costs and the difficulty of the coating process. Therefore, further optimizing the thickness factor to 1.5 to 2.5 times can achieve a better balance between mechanical reinforcement effect and process compatibility. The total thickness of the edge thickening area and the thickness of the middle effective area 12 can be measured at multiple points using a micrometer or by taking the average value according to the GB / T6672-2001 standard method.

[0053] In some examples, such as Figure 1 and Figure 2 As shown, the elastic modulus of the thickened functional coating 20 at room temperature is 2 to 3 times that of the diaphragm base membrane 10. Thus, the thickened functional coating 20 has a higher elastic modulus than the diaphragm base membrane 10, meaning that the elastic deformation of the thickened functional coating 20 under stress is less than that of the diaphragm base membrane 10. Under the same stress conditions, it can maintain a more stable size and shape. This ensures that the edge thickened area can withstand and transmit impact loads with smaller deformation during lateral impacts, providing reliable mechanical support for the central effective area.

[0054] It should be noted that the elastic modulus is an important mechanical parameter for measuring a material's resistance to elastic deformation. Its value can be determined by the slope of the linear elastic segment of the stress-strain curve in a tensile test, and can be tested in accordance with the GB / T 1040.3-2006 standard. The elastic modulus of the thickened functional coating 20 at room temperature is 2 to 3 times that of the diaphragm base film 10. This multiple means that under the same stress conditions, the strain generated by the thickened functional coating 20 is 1 / 2 to 1 / 3 of that of the diaphragm base film 10, that is, the thickened functional coating 20 has higher rigidity. Combined with the structural feature that the thickness of the edge thickened area is 1.5 to 2.5 times that of the middle effective area 12, the overall bending stiffness of the edge area (bending stiffness is proportional to the cube of the thickness) can be increased by about an order of magnitude (estimated at 2 times the thickness and 2.5 times the elastic modulus, the bending stiffness is increased by about 2³ × 2.5 = 20 times), which is of decisive significance for resisting lateral impact deformation. However, simply increasing rigidity may lead to increased brittleness—if the material's stiffness is too high and it lacks sufficient toughness, it is prone to brittle fracture rather than elastic deformation under impact loads. The thickened functional coating 20 in this application possesses elasticity at room temperature, meaning it can recover its original shape without permanent deformation after stress removal. This characteristic originates from its electrolyte affinity adhesive component. The polymer molecular chains of the electrolyte affinity adhesive are in a highly elastic state at room temperature, capable of stretching and slipping to absorb energy under stress, and recovering to their original curled state through the thermal motion of the molecular chains after stress removal. It is precisely this combination of elasticity and a high elastic modulus that allows the edge thickened region to maintain a stable geometry (contribution of high modulus) while absorbing and dissipating impact energy (contribution of elasticity) under impact, avoiding brittle fracture and achieving synergistic optimization of rigidity and toughness. The aforementioned elastic modulus can be obtained by tensile testing of a standard specimen of the thickened functional coating 20 material on a universal testing machine. The test conditions are room temperature (23±2℃), and the tensile rate can be set according to standard methods.

[0055] In one embodiment, such as Figure 4 As shown in the embodiments of this application, a method for preparing a lithium battery separator 1 is also provided. This method is used to prepare the lithium battery separator 1 in the above embodiments, and the preparation method may specifically include the following steps: Step S110: Provide a diaphragm base film 10 and perform surface pretreatment on the diaphragm base film 10 to improve the surface tension of the diaphragm base film 10. The diaphragm base film 10 is divided into a first edge region 11, an intermediate effective region 12 and a second edge region 13 along its extension direction.

[0056] Step S120: Mix electrolyte affinity adhesive, inorganic particles and solvent to prepare thickened functional coating 20 slurry, the solid content of thickened functional coating 20 slurry is 30% to 60%.

[0057] Step S130: Apply thickening functional coating 20 slurry to at least one side surface of the first edge region 11 and at least one side surface of the second edge region 13 using a coating die.

[0058] Step S140: The coated separator base film 10 is dried to obtain the lithium battery separator 1.

[0059] It should be noted that the preparation method of the lithium battery separator 1 in this application embodiment is mainly applied to the production and manufacturing scenario of lithium-ion battery separators, especially suitable for large-scale production lines of separators for power batteries and energy storage batteries. The above preparation method is based on the existing separator coating process and is improved. The main improvement is to use an edge selective coating method to replace the traditional whole-surface coating method. This can be achieved by simply modifying the edge structure of the coating die head. There is no need to replace or rebuild the main equipment and process flow of the existing production line on a large scale, which has good prospects for industrialization and cost advantages. The purpose of the surface pretreatment step is to improve the polarity and wettability of the surface of the separator base film 10. Because polyolefin base films have low surface energy and are hydrophobic, if they are coated directly without pretreatment, the thickened functional coating 20 slurry is difficult to spread evenly on the surface of the base film. After drying, the interfacial bonding strength between the coating and the base film is insufficient, and the coating is prone to peeling or falling off during subsequent processing or use. The solid content of the thickening functional coating slurry is controlled within the range of 30% to 60%. This ensures that the slurry has appropriate viscosity and rheological properties to facilitate coating operations and thickness control, while also guaranteeing that the required dry film thickness is achieved in a single coating process. This avoids the need for multiple coatings due to excessively low solid content, which increases process complexity and production costs. It also avoids the problem of excessively high solid content leading to excessive slurry viscosity and affecting coating uniformity. The solvent can be N-methylpyrrolidone (NMP), acetone, ethyl acetate, or a mixture of these solvents. The specific selection needs to be determined based on the solubility characteristics of the electrolyte affinity adhesive and the drying process conditions. Those skilled in the art can make a reasonable selection based on actual needs.

[0060] Thus, the method for preparing the lithium battery separator 1 according to this application embodiment, through the above-described steps, can selectively form a thickening functional coating 20 on both sides of the separator base film 10, thereby increasing the thickness and enhancing the mechanical properties of the separator edge region, while maintaining the original structure and ion conduction function of the central effective region 12 without affecting it. This method is highly compatible with existing separator coating processes, requiring only simple modifications to the coating die to achieve edge-selective coating. It has good prospects for industrial application and cost controllability, providing a reliable technical approach for the large-scale production of the aforementioned lithium battery separator 1.

[0061] In some examples, the surface pretreatment in the above method steps can specifically be corona treatment or plasma treatment. Thus, by modifying the surface of the diaphragm base membrane 10 through corona treatment or plasma treatment, polar groups such as hydroxyl and carbonyl groups can be introduced onto the surface of the diaphragm base membrane 10, and the surface micro-roughness can be appropriately increased. This significantly improves the wettability of the diaphragm base membrane 10 surface and the spreading coefficient of the coating slurry on its surface, allowing the thickened functional coating 20 slurry to be uniformly and densely coated on the surface of the diaphragm base membrane 10. Simultaneously, it enhances the interfacial adhesion between the coating and the diaphragm base membrane 10, preventing the thickened functional coating 20 from peeling or falling off during use after drying.

[0062] It should be noted that polyolefin-based membrane base films 10 (such as PP, PE, and PP / PE composite base films) have low surface energy, typically below 30 dyn / cm, and are typical hydrophobic materials. If the surface of the membrane base film 10 is not pretreated and coating is applied directly, the thickening functional coating 20 slurry will exhibit obvious pinholes, shrinkage, or non-wetting phenomena on the surface of the membrane base film 10, failing to form a continuous and uniform coating. Even if a coating is formed, the interfacial bonding between the coating and the membrane base film 10 is mainly physical adsorption, with weak adhesion. Under the action of electrolyte immersion or cyclic expansion stress, interfacial peeling is prone to occur, leading to the failure of the edge thickening function. Corona treatment generates corona discharge between the electrode and the membrane base film 10 through a high-voltage, high-frequency electric field. The high-energy particles and ozone in the plasma generated by the discharge bombard and oxidize the surface of the base film, causing the polymer chains on the surface to break and introducing oxygen-containing polar groups (such as -OH, -C=O, -COOH, etc.), while also increasing the surface micro-roughness. Plasma treatment utilizes active particles (such as electrons, ions, and free radicals) in plasma under vacuum or atmospheric pressure conditions to physically and chemically modify the surface of the diaphragm base film 10, similarly introducing polar groups and increasing surface energy. After the above treatment, the surface tension of the diaphragm base film 10 can typically be increased to above 38 dyn / cm, meeting the basic requirements for surface wettability of the diaphragm base film 10 in the coating process (usually requiring the surface tension of the base film to be higher than that of the coating slurry to ensure good spreadability). The specific process parameters of the above corona treatment or plasma treatment (such as treatment power, treatment time, electrode spacing, gas type, etc.) can be adaptively adjusted according to the material and thickness of the diaphragm base film 10. Those skilled in the art can determine suitable treatment conditions through routine experiments.

[0063] In some examples, the drying process in the above method steps can specifically be a gradient temperature drying process. This involves drying the coated diaphragm base film 10 in segments within three temperature ranges: 40℃~50℃, 50℃~65℃, and 65℃~80℃, with each temperature range drying for 1 min to 5 min. By employing a gradient temperature drying process, and drying the coated diaphragm base film 10 in segments within three different temperature ranges, the solvent in the thickened functional coating 20 slurry can gradually and orderly evaporate from the inside of the coating to the surface. This avoids the problem of rapid skinning on the coating surface due to single high-temperature drying or excessively rapid heating, which can trap the internal solvent and prevent complete evaporation. This ensures that the thickened functional coating 20 fully cures during the drying process, forming a dense and uniform structure without defects such as cracks, bubbles, or edge curling.

[0064] It should be noted that the thickening functional coating 20 slurry in this example contains a certain amount of organic solvents (such as NMP, acetone, ethyl acetate, etc.). These solvents need to be completely evaporated and removed through the drying process after coating, leaving only the electrolyte affinity gel and inorganic particles to form a solid coating. The control of the drying process is crucial to the quality of the final coating. If the drying temperature is set too low, the solvent evaporation rate will be too slow, resulting in low production efficiency. Furthermore, the coating will remain wet for a long time, which may cause sagging due to gravity, leading to uneven coating thickness. If the drying temperature is too high or the coated diaphragm base membrane 10 is directly placed in a high-temperature environment (i.e., single high-temperature drying or excessively rapid heating), the solvent evaporation rate at the interface between the coating surface and the solvent will be much faster than that inside the coating. A dense polymer skin will quickly form on the surface, while the internal solvent will be trapped under the skin. During subsequent drying, the internal solvent needs to pass through the already dense skin to evaporate, resulting in a sharp increase in evaporation resistance and an extremely slow evaporation rate. More seriously, the internal solvent expands in volume after vaporization upon heating. If the surface layer is not strong enough to withstand the internal vapor pressure, it will rupture, forming bubbles, pinholes, or cracks. If the surface layer is strong enough, some solvent will be permanently trapped inside the coating, forming residual solvent, affecting the coating's density and interfacial bonding strength. By employing a gradient drying process in three temperature ranges—40℃~50℃, 50℃~65℃, and 65℃~80℃—the surface solvent slowly evaporates without forming a dense surface layer at the low temperature in the first range. At the medium temperature in the second range, the internal solvent gradually diffuses to the surface and evaporates. At the higher temperature in the third range, the remaining trace amounts of solvent completely evaporate, and the coating fully cures. This avoids the aforementioned problems and ensures that the thickened functional coating 20 has a uniform and dense structure, good interfacial bonding strength, and stable mechanical properties. The drying time in each temperature range can be adjusted appropriately according to the coating thickness, slurry solids content, and production line speed.

[0065] In some examples, the edge of the coating die in the above method steps may specifically have an adjustable shim built into it to control the thickness of the thickening functional coating 20. The thickness of the adjustable shim is 0.01mm to 0.05mm. Thus, by building adjustable shims of different thicknesses into the edge of the coating die, the coating thickness of the thickening functional coating 20 in the edge region of the diaphragm base film 10 can be precisely controlled, achieving precise adjustment and rapid switching of the edge thickening amount. This allows the same production line to adapt to the production of diaphragm products with different thickening requirements without replacing the entire coating die, significantly improving the flexibility of the production process and the efficiency of product specification switching.

[0066] It should be noted that the adjustable shim in this example is a thin sheet-like component located at the edge of the coating die exit. Its thickness directly affects the size of the exit gap of the coating die at the corresponding position, thus determining the wet film coating thickness. In this example, the thickness of the adjustable shim is 0.01mm to 0.05mm. This thickness range, combined with adjustments to the slurry solid content (30% to 60%) and coating speed, allows for precise control of the dry film thickness of the thickening functional coating 20 over a wide range. For example, when the slurry solid content is 50% and the shim thickness is 0.03mm, the theoretical wet film thickness is approximately 0.03mm, and the dry film thickness after drying is approximately 0.015mm (i.e., 15μm). Combined with the thickness of the diaphragm base film 10 itself, effective thickening of the edge area can be achieved. The thickness of the adjustable shim can be selected and replaced according to the actual required edge thickening multiple. Different specifications of adjustable shims can be quickly disassembled and installed to adapt to the production needs of different product specifications. The shape design of the adjustable shims is also a crucial factor affecting the coating effect. For schemes requiring a gradual thickness change in the slope transition zone 14, the shim edges can be designed as conical or wedge-shaped, allowing the opening height to continuously change at the corresponding position in the slope transition zone 14, thereby achieving gradual control of the coating thickness in this area. Furthermore, the adjustable shims are installed on both sides of the coating die head, their width covering the coating range of the first edge zone 11 and the second edge zone 13. The die head opening corresponding to the central area maintains a small gap or no shims are used, so that the slurry does not form a coating in the central effective area. This design gives this preparation method good process flexibility and product adaptability.

[0067] In one embodiment, this application also provides a lithium battery cell (not shown), which includes a positive electrode, a negative electrode, and a lithium battery separator 1, which is disposed between the positive electrode and the negative electrode.

[0068] It should be noted that the lithium battery cells in this application embodiment are mainly used in power battery systems for new energy vehicles, grid-side or user-side energy storage battery systems, and lithium-ion batteries for various consumer electronic products, especially suitable for application scenarios with high requirements for lateral impact safety, long-term cycle stability, and high-temperature environmental adaptability. The lithium battery cell can be assembled by winding or stacking positive electrode sheets, lithium battery separator 1, and negative electrode sheets. The lithium battery separator 1 is positioned between the positive and negative electrode sheets, serving a dual function of electrical insulation and ion conduction. During assembly, the first edge region 11 and the second edge region 13 of the lithium battery separator 1 correspond to the two side edge regions of the positive and negative electrode sheets, respectively, while the middle effective region 12 corresponds to the active material coating area of ​​the electrode sheet. The aforementioned edge thickening regions act as mechanical reinforcement structures in the cell to resist external impacts and internal stresses. Their effective function depends on the precise alignment of the separator edge region and the electrode sheet edge region. Therefore, the alignment accuracy during cell assembly is a crucial process step to ensure the expected results of this technical solution.

[0069] In this way, the lithium battery cell of this embodiment, through the above-described structural configuration, when the cell encounters a lateral impact, the thickened edge region of the lithium battery separator 1 can form a support effect similar to a "bumper beam" in structural mechanics. This allows it to preferentially withstand and absorb impact energy with minimal deformation, protecting the central effective region 12 and the central active material region of the electrode from misalignment or damage, effectively reducing the risk of internal short circuits caused by impact. During long-term charge-discharge cycles of the cell, the elastic electrolyte affinity gel component in the thickened edge region can effectively absorb and buffer the periodic expansion-contraction stress generated by lithium ion insertion and extraction on the electrode (stress absorption rate can reach over 60%), reducing the transmission and accumulation of stress to the separator base film 10, and significantly delaying the fatigue damage process of the edge separator. Under extreme high-temperature conditions, the electrolyte affinity adhesive with a lower melting point in the edge thickening zone can melt preferentially over the separator base film 10 when the temperature reaches its melting point (80℃~150℃). The molten adhesive flows rapidly under capillary action and guidance from the electrode side, covering the exposed area of ​​the electrode side. Simultaneously, with the filling and support of inorganic particles, a continuous, dense sealing layer with sufficient insulation strength is formed, effectively blocking the short-circuit path of direct contact between the positive and negative electrodes in the edge area. The above-mentioned three mechanisms of mechanical support, stress buffering, and high-temperature sealing work synergistically in the cell, comprehensively improving the safety performance and cycle stability of the cell from different dimensions.

[0070] In some examples, the width of the first edge region 11 matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm. Thus, by precisely matching the width of the first edge region 11 with the width of the corresponding side edge of the electrode, it can be ensured that when the cell is subjected to a lateral impact, the thickened functional coating 20 of the separator accurately corresponds to the stress position at the electrode edge. This allows the impact stress to be directly borne by the thickened area rather than by the unreinforced edge of the intermediate effective region 12, thereby maximizing the mechanical protection effect of the edge thickened area and avoiding a decrease or failure of protection effect due to misalignment between the thickened area and the electrode edge.

[0071] It should be noted that the width matching between the thickened area at the edge of the separator and the edge of the electrode is a key assembly factor affecting the full protective effect of the thickened area. During cell assembly, the lithium battery separator 1 is typically combined with the positive and negative electrodes in a certain stacking or winding manner. The width of the lithium battery separator 1 is usually slightly larger than the width of the electrode (i.e., the positive or negative electrode) to ensure that the lithium battery separator 1 can completely cover all surfaces of the electrode, preventing direct contact between the positive and negative electrodes at the edges due to insufficient coverage by the lithium battery separator 1. In the technical solution of this application, the width of the thickened area at the edge of the lithium battery separator 1 needs to correspond to the width of the electrode edge. That is, when the lithium battery separator 1 and the electrode are assembled according to the designed relative positions, the thickened area should be located exactly below or above the edge area of ​​the electrode, so that the stress transmitted from the electrode edge can directly act on the thickened area. If the width of the edge thickening zone is significantly smaller than the electrode edge width, a portion of the electrode edge will correspond to the unthickened middle effective zone 12 edge of the separator. During lateral impact, this portion of the separator will still be at risk of deformation and tearing, significantly reducing the overall protective effect. If the width of the edge thickening zone is significantly larger than the electrode edge width, the portion of the thickening zone extending beyond the electrode edge will be suspended during cell assembly and use due to the lack of electrode support. Under winding tension, this may result in wrinkles or wavy edges, affecting the cell's appearance and performance consistency. Controlling the width difference to less than or equal to 1mm ensures complete coverage of the electrode edge by the thickening zone while avoiding process and performance problems caused by an excessively wide thickening zone. This is an easily achievable engineering control indicator under the current precision conditions of winding or stacking equipment.

[0072] In some examples, the width of the second edge region 13 matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm. Thus, similar to the first edge region 11, the width matching of the second edge region 13 with the other side edge of the electrode ensures that both edge regions of the separator have consistent impact protection, preventing asymmetrical mechanical responses of the cell when subjected to lateral impacts from different directions due to poor matching on one side, and ensuring the consistency and reliability of the overall safety performance of the cell.

[0073] It should be noted that the first edge region 11 and the second edge region 13 correspond to the two side edges of the lithium battery cell, respectively. In actual production, the width matching conditions of the two side edges should be consistent to ensure the overall structural symmetry and uniform stress of the lithium battery cell. In the winding process, the two side edges of the lithium battery separator 1 correspond to the upper and lower ends or the left and right sides of the wound body, respectively. In the stacking process, the two side edges of the lithium battery separator 1 correspond to the two sides of the stacked body. Regardless of the assembly method, the two side edges of the lithium battery separator 1 need to maintain a precise width matching relationship with the corresponding electrode edge. The width difference between the two sides should be less than or equal to 1mm to ensure that both side edges can obtain sufficient thickening protection. In addition, during the production process, an online visual inspection system or laser rangefinder can be used to monitor and control the relative position between the thickened area of ​​the separator edge and the electrode edge in real time to ensure that the width matching accuracy continuously meets the design requirements. In the cell quality inspection stage, the relative position of the lithium battery separator 1 and the electrode can be sampled and measured by X-ray fluoroscopy or disassembly analysis to verify whether the width matching meets the above requirements. It should be further explained that the above-mentioned width matching conditions apply not only to the width correspondence between the thickened area at the edge of the separator and the edge of the electrode, but also to the correspondence between the overall width of the separator and the width of the electrode. The overall width of the lithium battery separator 1 should be greater than the overall width of the electrode to ensure that both sides of the separator can exceed the edge of the electrode by a certain width (usually 0.5mm to 2mm). On this basis, the width of the thickened area at the edge should be precisely matched with the width of the electrode edge in order to achieve the comprehensive protection effect of the technical solution of this application.

[0074] In summary, the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A lithium battery separator, characterized in that, The lithium battery separator includes a separator base film and a thickened functional coating. The separator base film is divided into a first edge region, a middle effective region and a second edge region along its extension direction. The thickening functional coating is provided on at least one side surface of the first edge region and at least one side surface of the second edge region, such that the thickness of the first edge region and the thickness of the second edge region are both 1.2 to 3.0 times the thickness of the intermediate effective region; The melting point of the thickened functional coating is lower than that of the diaphragm base film, the elastic modulus of the thickened functional coating is greater than that of the diaphragm base film at room temperature, and the thickened functional coating is elastic at room temperature.

2. The lithium battery separator according to claim 1, characterized in that, The thickening functional coating comprises an electrolyte affinity colloid and inorganic particles, wherein the electrolyte affinity colloid accounts for 60% to 80% of the mass of the thickening functional coating, and the inorganic particles account for 20% to 40% of the mass of the thickening functional coating.

3. The lithium battery separator according to claim 2, characterized in that, The electrolyte affinity adhesive is a fluoropolymer or an acrylate polymer. The fluoropolymer is selected from at least one of modified polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinylidene fluoride. The acrylate polymer is selected from at least one of polymethyl methacrylate-butyl acrylate copolymer and polystyrene-butyl acrylate copolymer; and / or, The inorganic particles are selected from at least one of boehmite, aluminum hydroxide, aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, and silicon carbide.

4. The lithium battery separator according to claim 1, characterized in that, A slope transition zone with gradually changing thickness is provided between the first edge region and the middle effective region, and between the second edge region and the middle effective region.

5. The lithium battery separator according to claim 4, characterized in that, The width of the slope transition zone is 0.5mm to 3mm; and / or, The thickening functional coating extends from the first edge region or the second edge region to the adjacent slope transition region, and the thickness of the thickening functional coating located in the slope transition region gradually increases from the intermediate effective region toward the first edge region or the second edge region.

6. The lithium battery separator according to any one of claims 1-5, characterized in that, The width of the first edge region is 1mm to 8mm, and the width of the second edge region is 1mm to 8mm; and / or, The thickness of the intermediate effective region is 3μm to 20μm; and / or, The intermediate effective region is a uniformly distributed porous structure, and the porosity of the intermediate effective region is 30% to 50%; and / or, The diaphragm base membrane is a PP / PE composite base membrane or a ceramic-coated membrane, wherein the ceramic-coated membrane includes a base membrane body and an Al2O3 coating or SiO2 coating coated on at least one surface of the base membrane body; and / or, The thickening functional coating is provided on both sides of the first edge region and both sides of the second edge region; and / or, The thickness of the first edge region and the thickness of the second edge region are both 1.5 to 2.5 times the thickness of the intermediate effective region; and / or, The elastic modulus of the thickened functional coating is 2 to 3 times that of the diaphragm base film at room temperature.

7. A method for preparing a lithium battery separator, used to prepare the lithium battery separator as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: A diaphragm base film is provided, and the diaphragm base film is subjected to surface pretreatment to improve the surface tension of the diaphragm base film. The diaphragm base film is divided into a first edge region, a middle effective region and a second edge region along its extension direction. An electrolyte affinity colloid, inorganic particles, and solvent are mixed to prepare a thickening functional coating slurry, wherein the solid content of the thickening functional coating slurry is 30% to 60%. The thickening functional coating slurry is applied to at least one side surface of the first edge region and at least one side surface of the second edge region using a coating die head; The coated separator base film is dried to obtain the lithium battery separator.

8. The preparation method according to claim 7, characterized in that, The surface pretreatment is corona treatment or plasma treatment; and / or, The drying process is a gradient temperature drying process, which involves sequentially drying the coated diaphragm base film in three temperature ranges: 40℃~50℃, 50℃~65℃, and 65℃~80℃, with a drying time of 1 min~5 min for each temperature range; and / or, The edge of the coating die head has an adjustable shim for controlling the thickness of the thickening functional coating. The thickness of the adjustable shim is 0.01mm to 0.05mm.

9. A lithium battery cell, characterized in that, The lithium battery cell includes a positive electrode, a negative electrode, and a lithium battery separator as described in any one of claims 1-6, wherein the lithium battery separator is disposed between the positive electrode and the negative electrode.

10. The lithium battery cell according to claim 9, characterized in that, The width of the first edge region matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm; and / or, The width of the second edge region matches the width of the corresponding side edge of the electrode, and the width difference between the two is less than or equal to 1 mm.

Images