A coating device and method for processing lithium battery composite separator

Abstract

The application discloses a coating device and method for processing lithium battery composite diaphragm, and relates to the technical field of lithium battery composite diaphragm production. The device comprises a diaphragm coating processing device, a first coating die head installed at a coating position of the diaphragm coating processing device, and a ladder auxiliary device located at the inner side of the first coating die head and used for dividing one-time coating into three-time coating forming. The ladder auxiliary device comprises a second coating die head and a third coating die head arranged at the inner side of the first coating die head, and the first coating die head, the second coating die head and the third coating die head are distributed in a ladder type. The application adopts a differentiated die lip structure with an arch shape, a concave shape and a flat shape matched with each other to replace a traditional single flat die lip, so that the tension shrinkage of high-speed transmission of the diaphragm can be compensated, coating microscopic defects can be smoothed, and edge thick edge accumulation can be eliminated from the source, and coating base material adhesion, full-width thickness uniformity and production yield can be simultaneously improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery composite separator production technology, specifically a coating apparatus and method for processing lithium battery composite separators. Background Technology

[0002] With the continuous improvement of energy density and safety performance requirements for power lithium batteries, composite separators, as the core insulating component of lithium batteries, have their surface ceramic coating uniformity, bonding strength, and edge morphology directly determining the battery's safety protection capability and cycle life. Slit extrusion coating is currently the mainstream preparation process for separator ceramic coatings, and the die lip structure of the coating die is the core component for controlling the slurry discharge distribution and determining the coating forming quality.

[0003] Existing conventional lithium battery separator coating equipment generally adopts a single flat die lip structure. The die lip has a uniform discharge gap along the width direction, and the slurry is discharged in a homogeneous manner with equal flow rate. This structure can meet the basic forming requirements under low-speed and thin-coating conditions, but under high-speed mass production and large-width coating scenarios, it has gradually revealed insurmountable technical limitations and can no longer meet the high-quality mass production requirements of high-end lithium battery composite separators.

[0004] The problems arising from existing technologies are as follows: During high-speed transmission, the diaphragm is subjected to both tension and surface tension of the slurry, which makes the coating edge prone to shrinkage. The flow rate of the flat die lip is uniformly distributed along the width, which cannot specifically increase the edge output to compensate for the shrinkage effect. In high-speed production, defects such as thin edges, broken edges, and exposed substrate are prone to occur, resulting in low product yield. Due to the inherent characteristics of slit coating fluid dynamics, the lateral resistance of the fluid at the end of the mold cavity is less than that in the middle, and there is a natural edge flow amplification effect. The flat mold lip cannot reverse the flow distribution from the discharge end to offset it, resulting in a cliff-like thick edge at the coating edge. This not only results in poor uniformity of thickness across the entire width and large loss during subsequent cutting and trimming, but also causes high concentration of curing stress at the thick edge. After cutting, problems such as ceramic particle powdering, edge burrs, and coating edge lifting are likely to occur, which seriously affect the performance of the diaphragm. Summary of the Invention

[0005] The purpose of this invention is to address the problems of existing lithium battery separator coating equipment using a single flat die lip, which cannot compensate for edge shrinkage caused by tension and slurry surface tension during high-speed transport of the separator, resulting in defects such as thin edges, broken edges, and exposed substrate. It also cannot counteract the edge flow amplification effect inherent in slot coating, which easily leads to abrupt thick edges and causes problems such as high edge trimming loss, stress concentration leading to powder shedding and edge curling, which seriously restrict product yield and separator performance. The invention provides a coating device and method for processing lithium battery composite separators.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a coating apparatus for processing lithium battery composite separators, comprising: A diaphragm coating processing apparatus and a first coating die installed in the coating section of the diaphragm coating processing apparatus; A step auxiliary device, located inside the first coating die, is used to divide a single coating process into three coating processes. The step auxiliary device includes a second coating die and a third coating die disposed inside the first coating die, and the first coating die, the second coating die, and the third coating die are distributed in a step-like manner. The die lip of the third coating die is closest to the inner diaphragm of the diaphragm coating processing device, and the die lip of the first coating die is furthest from the inner diaphragm of the diaphragm coating processing device.

[0007] As a further aspect of the present invention: the die lip of the third coating die head is arched, so that the material flow rate is distributed with more on both sides and less in the middle, thereby compensating for the edge shrinkage effect caused by tension during the transmission of the diaphragm.

[0008] As a further aspect of the present invention: the die lip of the second coating die head is concave, so that the material flow rate is distributed with less on both sides and more in the middle, smoothing out the fine vertical lines, pinholes and other defects on the surface of the first coating.

[0009] As a further aspect of the present invention: the die lips of both the second coating die and the third coating die are configured as wavy lip shapes, and the die lip of the third coating die is arched, so that the "cliff-like high-flow discharge" at the edge is decomposed into multi-stage gradual discharge, and the concentrated flow of the thick edge on one side is dispersed into multiple tooth peak-tooth valley gradual intervals, avoiding the accumulation of a large amount of edge slurry at one time to form a bulge and drip. In conjunction with the concave shape of the die lip of the second coating die, the "cliff-like throttling and narrowing" at the edge is transformed into multi-stage gradual material collection, avoiding the edge discharge discontinuity and edge shrinkage defects caused by the sudden return of the gap to zero; the edge slurry is continuously replenished by the micro discharge of the tooth peaks, and the edge liquid surface is kept stable while the thick edge is reduced.

[0010] As a further aspect of the present invention: the wavy lip of both the second coating die head and the third coating die head are staggered vertically, while the lip of the first coating die head is flat. By canceling out the positive and negative flow rates, a smooth and gentle slope-like edge thickness distribution is formed. Combined with the surface homogenization of the third straight die lip, the edge trimming loss can be greatly reduced, while ensuring the continuity of edge output and reducing the risk of powder falling off the edge.

[0011] As a further embodiment of the present invention: both the second coating die and the third coating die are provided with flow adapters on their inner sides. The flow adapters include straight grooves respectively opened on the inner sides of the second coating die and the third coating die. The lowest peak and valley of the wavy die lip of both the second coating die and the third coating die are provided with through holes communicating with the straight grooves.

[0012] As a further embodiment of the present invention: a first suspension seat is fixedly connected to the inner side of the first coating die head, a first adjusting screw is rotatably connected to the inner side of the first suspension seat, and one end of the first adjusting screw passes through to the outside of the first suspension seat and is fixedly connected to a first knob. The second coating die head is threadedly connected to the outer wall of the first adjusting screw and is also connected to the inner side of the first coating die head. A first limiting block is fixedly connected to both sides of the second coating die head, and a first limiting groove matching the first limiting block is opened on the inner side of the first coating die head.

[0013] As a further embodiment of the present invention: a second suspension seat is fixedly connected to the inner side of the first coating die head, a second adjusting screw is rotatably connected to the inner side of the second suspension seat, and one end of the second adjusting screw passes through to the outside of the second suspension seat and is fixedly connected to a second knob. The third coating die head is threadedly connected to the outer wall of the second adjusting screw. Second limiting blocks are fixedly connected to both sides of the third coating die head, and a second limiting groove matching the second limiting block is opened on the inner side of the first coating die head.

[0014] This invention also discloses a coating method for processing lithium battery composite separators, using the aforementioned coating apparatus for processing lithium battery composite separators, comprising the following steps: S1. The diaphragm coating processing device is equipped with a feeder for feeding the inner sides of the first coating die, the second coating die, and the third coating die. The first coating die, the second coating die, and the third coating die are arranged in a stepped manner, which breaks down a single thick coating into three stepped thin coatings. Through layering, the functions of wetting and anchoring, edge homogenization, and surface finishing can be achieved. This not only reduces coating solvent residue and curing internal stress, but also suppresses thick edge defects from the source and improves interlayer bonding, significantly improving the thickness uniformity and recycling reliability of the diaphragm coating. S2. The die lip of the third coating die is arched, and the die lip of the second coating die is concave. The discharge flow rate achieves thickness complementarity and edge gradient elimination. Together with the straight die lip of the first coating die, it completes surface homogenization and finishing, which can simultaneously improve the adhesion of the coating substrate, the uniformity of the thickness across the entire width, and reduce edge trimming loss. At the same time, the wavy die lips of the second and third coating dies are staggered vertically, and the discharge flow rates of the tooth peaks and tooth valleys complement each other, transforming the traditional cliff-like thick edge into a smooth, gentle slope edge, which can reduce edge trimming loss and reduce powdering defects caused by edge stress concentration. S3. During the coating process, when there is too much raw material inside the wavy peaks and valleys of the second coating die head and the third coating die head, it will enter the inside of the straight groove through the through hole. When the flow rate is too low, it will flow out from the inside of the through hole through the straight groove. This can smooth out the micro-flow fluctuations between adjacent teeth, stabilize the edge discharge state, and reduce the accumulation of material and skin in the dead corners of the tooth valleys. S4. Depending on the thickness of different coating materials, the operator can rotate the first knob and the second knob respectively, so that the first adjusting screw and the second adjusting screw rotate, thereby driving the second coating die head and the third coating die head to adjust their positions, thereby adjusting the distance between the first coating die head, the second coating die head and the third coating die head, so that the coating can be adapted to the processing of diaphragms of different thicknesses.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention replaces the traditional single flat die lip with a differentiated die lip structure that combines arched, concave, and flat shapes. This can compensate for the tension shrinkage of the diaphragm during high-speed transmission, smooth out micro-defects in the coating, and eliminate edge thick accumulation from the source. It can simultaneously improve the adhesion of the coating substrate, the uniformity of the overall thickness, and the production yield. 2. This invention achieves positive and negative coating flow complementarity, edge shrinkage compensation, and surface homogenization and finishing by using an arched third coating die, a concave second coating die, and a flat first coating die in a differentiated and coordinated manner. This can eliminate thick edge defects from the source, smooth out micro-coating defects, and simultaneously improve coating adhesion, full-width thickness uniformity, and production yield. 3. This invention sets staggered wavy lip at the ends of the second and third coating dies, combines the irregular profile characteristics of the two with the straight lip of the first coating die to complete the surface finishing, and constructs a gradient edge control system. This system can transform abrupt material discharge into multi-level gradual material discharge, and form a smooth, gentle slope edge by canceling out positive and negative flow rates. This ensures the continuity of edge material discharge while releasing curing stress, effectively reducing edge trimming loss and edge powdering defects. 4. The present invention achieves dynamic self-balancing of the slurry between the teeth through a flow adapter composed of a straight groove and a through hole. Combined with a fine-tuning mechanism composed of a second suspension seat, a second adjusting screw and a limiting slide, the position of the third coating die head is precisely adjusted. This stabilizes the edge discharge state, avoids material accumulation and skin formation in the tooth valleys, and can adapt to the coating requirements of diaphragms of different thicknesses, thereby improving the continuous production capacity and process adaptability of the equipment. 5. The present invention uses a dual-set independent fine-tuning mechanism consisting of a first suspension seat, a first adjusting screw and a corresponding limiting slide groove to drive the second coating die head and the third coating die head to slide smoothly and accurately. The stepped arrangement spacing of the three sets of dies head can be flexibly adjusted to adapt to coating conditions with different coating thicknesses and slurry characteristics, effectively broadening the process adaptability window and improving product changeover efficiency and coating forming stability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the coating section of the diaphragm coating processing apparatus 1 of the present invention; Figure 3 This is a schematic diagram of the first coating die head structure of the present invention; Figure 4 For the present invention Figure 3 Enlarged view of point A in the middle; Figure 5 This is a cross-sectional view of the end of the second coating die of the present invention; Figure 6 For the present invention Figure 5 Enlarged view at point B in the middle; Figure 7 This is a schematic diagram showing the misalignment of the second coating die head and the third coating die head of the present invention; Figure 8 This is a schematic diagram showing the stepped distribution of the first coating die, the second coating die, and the third coating die of the present invention.

[0017] In the figure: 1. Diaphragm coating processing device; 2. First coating die head; 3. Second coating die head; 4. Third coating die head; 5. First suspension seat; 6. First adjusting screw; 7. First knob; 8. Wave-shaped die lip; 9. Straight groove; 10. Through hole; 11. Second suspension seat; 12. Second adjusting screw; 13. Second knob. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention 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 invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this invention, it should be noted that unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," and "set up" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The following describes embodiments of the invention based on its overall structure.

[0020] Please see Figures 1 to 8 This embodiment provides a coating apparatus for processing lithium battery composite separators, including a separator coating processing apparatus 1. A first coating die 2 is mounted on the coating work station of the separator coating processing apparatus 1. A step auxiliary device is also provided inside the first coating die 2. This step auxiliary device is used to divide the traditional single-pass overall coating process into a three-layer coating forming process. The step auxiliary device includes a second coating die 3 and a third coating die 4, respectively, mounted inside the first coating die 2. The first coating die 2, second coating die 3, and third coating die 4 are arranged in a staggered, stepped configuration. Specifically, the die lip of the third coating die 4 is closest to the separator substrate inside the separator coating processing apparatus 1; the distance between the die lip of the second coating die 3 and the separator substrate is centered; and the die lip of the first coating die 2 is farthest from the separator substrate inside the separator coating processing apparatus 1. A dedicated feeder is fixedly installed on the diaphragm coating processing device 1. The feeder is connected to the feed ports of the first coating die 2, the second coating die 3 and the third coating die 4 respectively. It can stably and continuously supply coating slurry to the inside of the three sets of coating dies, ensuring the continuous operation of layer coating.

[0021] Most existing traditional lithium battery separator coating equipment adopts a single-head, single-thickness coating structure, lacking a stepped, multi-head, layered coating architecture. Relying solely on a single coating process to complete the overall coating formation results in numerous inherent technical defects. In the traditional single-thickness coating mode, the wet film thickness formed in a single pass is large. During curing, the surface slurry forms a skin and seals the coating, preventing the solvent inside the coating from evaporating quickly and evenly. This easily leads to excessive solvent residue, increased internal micropore defects, and a significant reduction in the separator's insulation and protective performance. Simultaneously, the uneven curing rate of the thick coating generates significant internal stress, easily causing quality problems such as edge lifting, cracking, and interlayer delamination. Furthermore, traditional single-thickness coating cannot achieve layered functional division, resulting in poor wetting and anchoring effects between the coating and the separator substrate, weak interlayer adhesion, and poor uniformity in coating width and thickness after coating formation, with severe edge accumulation and high subsequent edge trimming losses. After trimming, defects such as powder shedding and exposed substrate are prone to occur at the edges, seriously affecting the production yield and safety of lithium battery separators.

[0022] By employing a stepped, layered layout of the first coating die 2, the second coating die 3, and the third coating die 4, the traditional single-layer thick coating process is optimized into a three-stage, stepped, thin-layer superposition coating process. Utilizing the staggered arrangement of the three sets of dies, precise division of labor in coating is achieved, resulting in multiple technological benefits. The third coating die 4, closest to the diaphragm substrate, completes the first thin-layer coating, allowing the slurry to fully penetrate the micropores of the diaphragm substrate, forming a high-strength mechanical anchoring interface and improving the adhesion between the coating and the substrate from the source. The second coating die 3, with its centrally located spacing, completes the intermediate layer thickness filling and coating homogenization, effectively compensating for micro-thickness deviations in the first layer, smoothing out minor coating defects, and optimizing overall thickness uniformity. The first coating die 2, furthest from the substrate, completes the fine sealing coating, achieving surface densification, sealing surface micropores, and improving the overall smoothness and density of the coating.

[0023] The three-stage, stepped coating structure with three sets of die heads releases the internal stress during coating curing layer by layer, solving industry pain points such as stress concentration, cracking, and edge lifting associated with traditional single-coat thick coatings. Simultaneously, the layered, thin-layer curing method allows for complete solvent evaporation, significantly reducing residual solvent in the coating. Furthermore, the three-layer, step-by-step coating creates a functionally graded composite coating with tighter and stronger interlayer adhesion, effectively improving the overall structural stability of the coating. Moreover, the multi-layer complementary coating suppresses the problem of thick edge buildup at the coating edges from the source, significantly reducing subsequent edge trimming losses and the risk of edge powder shedding. This comprehensively improves the coating quality, production yield, and long-term reliability of the lithium-ion battery composite separator.

[0024] Most existing traditional lithium battery composite separator coating equipment uses a single, flat die lip for coating operations. The die lip has a uniform discharge gap along the width of the membrane, and the slurry flow distribution is fixed and uniform, making it impossible to differentiate flow compensation and defect correction based on coating conditions and membrane substrate characteristics. Therefore, traditional coating methods generally have many drawbacks: they cannot compensate for edge shrinkage caused by tension and surface tension of the slurry during high-speed membrane transport, easily leading to edge breakage and thin edge defects; single homogeneous discharge cannot smooth out microscopic defects such as pinholes and fine vertical lines generated during coating, resulting in poor overall coating smoothness; and due to fluid characteristics, thick edge slurry accumulation is prone to occur, resulting in poor thickness uniformity across the entire width, large subsequent edge trimming losses, and limited wetting and anchoring effect between the coating and the substrate, easily leading to problems such as powder shedding and delamination, seriously affecting the production yield and performance of composite separators.

[0025] Please refer to the figure. Figure 8 To address the aforementioned technical deficiencies, this application differentiates the die lip morphologies of the third coating die 4, the second coating die 3, and the first coating die 2, achieving complementary and precise coating through the coordinated operation of the three-layer die lip structure. Specifically, the die lip of the third coating die 4 has an overall arched structure, resulting in a narrower gap in the middle and wider gaps on both sides. This corresponds to a material flow distribution with less material in the middle and more on the sides. The smaller gap in the middle region of the die lip increases the slurry shear rate, enhances the slurry's penetration and wetting ability into the micropores of the diaphragm substrate, and improves the coating's anchoring bond. Simultaneously, the larger flow rate of material on both sides precisely compensates for the edge shrinkage effect caused by tension during high-speed transport of the diaphragm, effectively avoiding coating defects such as edge shrinkage, edge breakage, and material shortage, ensuring the continuity and integrity of the coating edges.

[0026] The die lip of the second coating die 3 is concave in shape, and the material discharge gap of the die lip has a structure that is wider in the middle and narrower on both sides. This corresponds to a material flow distribution that is more in the middle and less on both sides, which is completely opposite to the flow distribution of the third coating die 4. The large flow of slurry in the middle can fully fill and smooth out the microscopic defects such as fine vertical lines, pinholes, and local thin coatings left after the first coating of the third coating die 4, thus completing the filling and homogenization of the main coating thickness. At the same time, the small flow of slurry on both sides can offset the excessive slurry accumulation at the edge of the third coating die 4, so as to achieve the complementary offset of the thickness of the two layers of material flow, weaken and eliminate the problem of abrupt thick edges of the coating from the source, and achieve a smooth transition of the edge gradient.

[0027] Building upon this foundation, the first coating die 2 employs a flat die lip structure, enabling surface homogenization and finishing operations to be completed on top of the two differentiated complementary coating layers. This smooths out any microscopic thickness fluctuations and morphological marks remaining from the previous two coating layers, resulting in a dense, flat, and uniform surface coating. The three-layer die lip structure works in synergy to fundamentally solve the technical pain points of traditional flat die lip coatings, such as poor uniformity, numerous defects, severe thick edges, weak adhesion, and high edge trimming losses. This effectively improves the bonding strength between the coating and the separator substrate, the overall thickness uniformity, and the surface flatness of the coating, significantly reducing edge trimming losses during production. Ultimately, this significantly enhances the overall coating quality and long-term cyclic reliability of the lithium battery composite separator.

[0028] Existing traditional lithium battery composite separator coating dies mostly employ a flat, abrupt cliff-like structure at the die lip end, lacking a gradually wavy toothed structure and a coating system with bidirectional irregular profiles and staggered fits. In actual coating processes, traditional structures exhibit abrupt, abrupt flow rate distribution at the end: arched dies are prone to concentrated high flow rates at the edges, causing localized slurry accumulation, sagging, and the formation of thick, abrupt cliff-like edges; concave dies suffer from sudden narrowing of the end gap and instantaneous flow interruption, easily leading to defects such as intermittent edge discharge, edge shrinkage, and material shortage. Furthermore, traditional equipment lacks a flow regulation structure with complementary tooth peaks and valleys, resulting in a right-angle abrupt change in coating edge thickness. After curing, edge stress is highly concentrated, leading to large requirements for separator trimming allowance, high material loss, and a high likelihood of edge powdering, coating curling, and exposed substrate after trimming. It is impossible to simultaneously achieve continuous edge discharge, thick edge suppression, and finished product appearance quality, resulting in low mass production stability and product qualification rates.

[0029] Please see Figures 7-8 In response to the aforementioned technical deficiencies, this application provides wave-shaped wavy lip 8 at the ends of the lips of both the second coating die 3 and the third coating die 4. Combined with the differentiated profile and staggered layout structure of the lip itself, and with the straight lip of the first coating die 2, a complete gradient edge control system is formed. Among them, the third coating die head 4 with an arched structure, in conjunction with the end wave die lip 8, can decompose the traditional edge cliff-style high-flow concentrated discharge into a multi-stage gradual discharge with multiple sets of tooth peaks and tooth valleys. This evenly distributes the originally concentrated flow of thick edge to multiple gradual intervals, avoiding the formation of bulges, sagging, and localized ultra-thick edge defects due to the concentrated accumulation of edge slurry at one time. The second coating die head 3 with a concave structure, in conjunction with the end wave die lip 8, can transform the traditional end cliff-style sudden throttling and narrowing discharge method into a stable multi-stage gradual receiving structure. This eliminates the problems of discontinuous edge discharge, edge shrinkage, and material shortage caused by the sudden zeroing of the die lip end gap. At the same time, it relies on the tooth peaks to continuously discharge a small amount of slurry to compensate for the edge, effectively reducing the thickness of the thick edge while always maintaining a continuous and stable edge coating liquid surface.

[0030] Meanwhile, the wavy lip 8 of the second coating die 3 and the third coating die 4 are staggered vertically, utilizing the precise alignment of tooth peaks and valleys to achieve complementary and offsetting of positive and negative discharge flow rates. This transforms the traditional rigid, cliff-like thick-edge structure into a smooth, gently sloping edge thickness distribution, effectively releasing the concentrated stress generated by the curing shrinkage of the coating edge. This reduces defects such as edge powdering, coating cracking, and edge burrs caused by stress concentration at the structural root. Finally, the flat die lip of the first coating die 2 completes the surface homogenization and finishing process, smoothing out the microscopic tooth-like patterns and thickness fluctuations remaining from the previous two wavy die lip coatings, resulting in a smooth, dense coating surface with uniform overall thickness. This structural combination solves the technical pain points of traditional coatings, such as poor edge stability, severe thick edges, high edge trimming loss, and easy powdering after trimming. While ensuring continuous and stable material discharge at the coating edge throughout the process, it significantly reduces edge trimming loss in separator production, significantly improving the coating appearance quality and long-term reliability of lithium battery composite separators.

[0031] In existing technologies, coating dies with wavy comb lips generally lack built-in flow adaptation and compensation structures. The discharge of material from the peaks and valleys of the wavy dies relies entirely on the overall feeding pressure of the die head for passive discharge. Microscopic flow unevenness easily occurs between adjacent teeth due to slurry particle retention, microbubbles, and local flow field differences, often resulting in single-tooth overflow accumulation and localized material shortages and edge breakage. Furthermore, the valleys of traditional wavy dies are closed dead zones, where slurry tends to dry and form a skin over time, producing hard particles. This not only causes scratches and particle defects on the coating surface but also requires frequent shutdowns for cleaning, significantly shortening continuous production cycles and reducing mass production efficiency and product yield. In addition, traditional multi-layer die head structures are mostly fixed installations, unable to flexibly adjust the die head position according to different thicknesses of diaphragm products, resulting in poor process adaptability and difficulty in meeting the stable coating production needs of multi-specification products.

[0032] Please see Figures 5-6 This application specifically sets up a flow adaptive compensation structure and a die head position fine-tuning limiting structure, including: a flow adapter is installed on the inner side of both the second coating die head 3 and the third coating die head 4. The flow adapter includes straight grooves 9 respectively opened on the inner side of the second coating die head 3 and the third coating die head 4. The lowest peak and valley positions of the wave die lips 8 of the second coating die head 3 and the third coating die head 4 are respectively provided with through holes 10 that communicate with the corresponding straight grooves 9. At the same time, a second suspension seat 11 is fixedly installed on the inner side of the first coating die head 2. A second adjusting screw 12 is rotatably installed on the inner side of the second suspension seat 11. One end of the second adjusting screw 12 extends through to the outside of the second suspension seat 11 and is fixedly installed with a second knob 13. The third coating die head 4 is threadedly installed on the outer wall of the second adjusting screw 12. Second limiting blocks are fixedly set on both sides of the third coating die head 4. A second limiting slide groove matching the second limiting block is opened on the inner side of the first coating die head 2, which can realize the precise limiting sliding adjustment of the third coating die head 4.

[0033] In actual coating operations, dynamic self-balancing of flow between teeth is achieved by relying on the flow adapter: when excessive slurry accumulates at the peak and valley positions of the wave die lip 8 and overflow tends to occur, the excess slurry can be quickly collected into the straight groove 9 through the through hole 10 at the bottom of the peak and valley; when the flow rate of the local tooth valley is insufficient and there is a risk of material shortage, the slurry stored in the straight groove 9 can flow out through the through hole 10 in the opposite direction to compensate for the material shortage position in real time. This structure can effectively smooth out the micro-flow fluctuations between adjacent teeth, solve the defects of uneven material output, local overflow, material shortage and edge breakage of traditional wave die lip teeth, and stabilize the material output state of the coating edge throughout the process; at the same time, the connection structure between the straight groove 9 and the through hole 10 breaks the closed dead corner of the traditional tooth valley, so that the slurry at the tooth valley position always maintains a dynamic flow state, avoiding the problems of slurry stagnation and drying, and material accumulation and skin formation from the root, and greatly extending the continuous production cleaning-free cycle of the equipment. The fine-tuning limiting structure, consisting of the second adjusting screw 12, the second limiting block, and the second limiting groove, allows for precise adjustment of the installation position and coating spacing of the third coating die 4 by rotating the second knob 13. This adapts to the coating production needs of diaphragms of different thicknesses. The limiting structure ensures that the die head does not shift or wobble during adjustment, maintaining precise coating alignment accuracy. This effectively broadens the equipment's process adaptability and improves the coating stability and production versatility of products of different specifications.

[0034] In existing technologies, most three-layer stepped coating dies adopt an integral fixed installation structure, with a fixed spacing between the three coating dies. This makes it impossible to flexibly adjust the spacing according to different separator coating thicknesses and coating raw materials with different viscosity characteristics. The fixed spacing structure results in extremely poor equipment process adaptability: for ultra-thin coatings, excessively large die spacing can easily cause over-drying of the preceding coating, resulting in a lack of interlayer interface activity and defects such as coating delamination, decreased adhesion, powder shedding, and delamination. For thicker coatings, insufficient die spacing can lead to inadequate pre-drying of the wet film, making it easy for subsequent coatings to break up the preceding wet film, causing interlayer miscibility, coating sagging, uneven thickness, and other quality problems. Furthermore, the traditional fixed die structure requires complete disassembly and re-alignment and adjustment when switching between different product specifications. This is cumbersome, has poor alignment accuracy, and low changeover efficiency, failing to meet the mass production coating needs of multi-specification, multi-condition lithium battery composite separators.

[0035] Please see Figures 3-4This application specifically provides a precisely adjustable die head spacing adjustment and limiting structure, the specific structure of which is as follows: A first suspension seat 5 is fixedly connected to the inner side of the first coating die head 2, and a first adjusting screw 6 is rotatably mounted on the inner side of the first suspension seat 5. One end of the first adjusting screw 6 extends through to the outside of the first suspension seat 5 and is fixedly connected to a first knob 7; a second coating die head 3 is threadedly mounted on the outer wall of the first adjusting screw 6 and slidably mounted on the inner side of the first coating die head 2. First limiting blocks are fixedly provided on both sides of the second coating die head 3, and a first limiting groove that precisely matches the first limiting block is opened on the inner side of the first coating die head 2. Together with the aforementioned second suspension seat 11, second adjusting screw 12, second knob 13 on the inner side of the first coating die head 2 and the second limiting sliding structure matched with the third coating die head 4, two sets of independent and precise die head fine-tuning mechanisms are formed.

[0036] In the actual coating process, the operator can rotate the first knob 7 and the second knob 13 according to the coating thickness specifications of the diaphragm to be processed and the viscosity and solid content characteristics of the coating raw material. This drives the first adjusting screw 6 and the second adjusting screw 12 to rotate accordingly, thereby precisely adjusting the position of the second coating die 3 and the third coating die 4. The first limiting block and the first limiting groove, and the second limiting block and the second limiting groove, work together to precisely guide the die adjustment process, ensuring that the second coating die 3 and the third coating die 4 slide smoothly without deviation or deflection, and always maintain parallelism and alignment accuracy with the first coating die 2. This adjustable structure allows for flexible alteration of the stepped arrangement spacing between the first coating die 2, the second coating die 3, and the third coating die 4. This precisely matches the layered coating, wet film leveling, and gradient pre-drying requirements of diaphragms of different thicknesses, effectively addressing the technical pain points of traditional fixed-spacing dies that cannot adapt to multiple product specifications, have poor working condition adaptability, are cumbersome to change, and have numerous coating defects. It significantly broadens the equipment's process adaptability window, improves the stability of diaphragm coating and forming under different thicknesses and different slurry systems, and enhances the equipment's versatility and mass production adaptability.

[0037] The following describes a coating method for processing lithium battery composite separators, based on the aforementioned coating apparatus. The method includes the following steps: S1. The diaphragm coating processing device 1 is equipped with a feeder for feeding material to the inside of the first coating die 2, the second coating die 3 and the third coating die 4. The first coating die 2, the second coating die 3 and the third coating die 4 are arranged in a stepped manner, which divides the single thick coating into three thin layer coatings in a stepped manner. Through the layering, the functions of wetting and anchoring, edge elimination and homogenization and surface finishing can be achieved. This not only reduces the coating solvent residue and curing internal stress, but also suppresses thick edge defects from the source and improves the interlayer bonding force, which significantly improves the thickness uniformity and recycling reliability of the diaphragm coating. S2. The die lip of the third coating die 4 is arched, while the die lip of the second coating die 3 is concave. The discharge flow rate achieves thickness complementarity and edge gradient elimination. Together with the straight die lip of the first coating die 2, it completes surface homogenization and finishing. It can simultaneously improve the adhesion of the coating substrate, the uniformity of the thickness across the entire width, and reduce edge trimming loss. At the same time, the wavy die lips 8 of the second coating die 3 and the third coating die 4 are staggered vertically. Through the positive and negative complementarity of the discharge flow rate of the tooth peaks and tooth valleys, the traditional cliff-like thick edge is transformed into a smooth and gentle slope edge, which can reduce edge trimming loss and reduce powdering defects caused by edge stress concentration. S3. During the coating process, the lip of both the second coating die head 3 and the third coating die head 4 has a wavy shape. When there is too much raw material inside the peak and valley of the wavy die lip 8, it will enter the inside of the straight groove 9 through the through hole 10. When the flow rate is too low, it will flow out from the inside of the through hole 10 through the straight groove 9. This can smooth out the micro-flow fluctuations between adjacent teeth, stabilize the edge discharge state, and reduce the accumulation of material and skin in the dead corners of the tooth valleys. S4. Depending on the thickness of different coating materials, the operator can rotate the first knob 7 and the second knob 13 respectively, so that the first adjusting screw 6 and the second adjusting screw 12 rotate, thereby driving the second coating die 3 and the third coating die 4 to adjust their positions, thereby adjusting the distance between the first coating die 2, the second coating die 3 and the third coating die 4, so that the coating can be adapted to the processing of diaphragms of different thicknesses.

[0038] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A coating apparatus for processing composite separators for lithium batteries, characterized in that, include: A diaphragm coating processing apparatus (1) and a first coating die (2) installed on the coating part of the diaphragm coating processing apparatus (1); A step auxiliary device is located inside the first coating die (2) and is used to divide a single coating into three coatings. The step auxiliary device includes a second coating die (3) and a third coating die (4) disposed inside the first coating die (2). The first coating die (2), the second coating die (3) and the third coating die (4) are arranged in a step-like manner. The die lip of the third coating die (4) is closest to the inner diaphragm of the diaphragm coating processing device (1), and the die lip of the first coating die (2) is furthest from the inner diaphragm of the diaphragm coating processing device (1).

2. The coating apparatus for processing lithium battery composite separators according to claim 1, characterized in that, The die lip of the third coating die (4) is arched, which makes the material flow rate more on both sides and less in the middle, thereby compensating for the edge shrinkage effect caused by tension during the transmission of the diaphragm.

3. The coating apparatus for processing lithium battery composite separators according to claim 2, characterized in that, The die lip of the second coating die (3) is concave, which makes the material flow rate less on both sides and more in the middle, smoothing out the fine vertical lines, pinholes and other defects on the surface of the first coating.

4. The coating apparatus for processing lithium battery composite separators according to claim 3, characterized in that, The lip of both the second coating die (3) and the third coating die (4) is set as a wave-shaped wavy lip (8). The lip of the third coating die (4) is arched, which decomposes the "cliff-like large flow discharge" at the edge into multi-stage gradual discharge. The concentrated flow of the thick edge on one side is dispersed into the gradual interval of multiple tooth peaks and tooth valleys, avoiding the accumulation of a large amount of edge slurry at one time to form a bulge and drip. The lip of the second coating die (3) is concave, which transforms the "cliff-like throttling and narrowing" at the edge into multi-stage gradual material collection, avoiding the discontinuous edge discharge and edge shrinkage defects caused by the sudden return of the gap to zero. The edge slurry is continuously replenished by the micro discharge of the tooth peak, which maintains the stability of the edge liquid surface while pressing down the thick edge.

5. A coating apparatus for processing lithium battery composite separators according to claim 4, characterized in that, The second coating die (3) and the third coating die (4) both have wavy lip (8) in a staggered manner, which is consistent with the flat state of the lip of the first coating die (2). The positive and negative flow cancel each other out to form a smooth and gentle slope edge thickness distribution. Combined with the surface homogenization of the third straight die lip, the edge trimming loss can be greatly reduced, while ensuring the continuity of edge discharge and reducing the risk of edge trimming powder.

6. A coating apparatus for processing lithium battery composite separators according to claim 5, characterized in that, Both the second coating die (3) and the third coating die (4) are provided with flow adapters on their inner sides. The flow adapters include straight grooves (9) respectively opened on the inner sides of the second coating die (3) and the third coating die (4). The wavy lip (8) of both the second coating die (3) and the third coating die (4) has a through hole (10) that communicates with the straight groove (9) at the lowest peak and valley part.

7. A coating apparatus for processing lithium battery composite separators according to claim 6, characterized in that, The first coating die (2) is fixedly connected to the inner side of a first suspension seat (5), and the first suspension seat (5) is rotatably connected to the inner side of a first adjusting screw (6). One end of the first adjusting screw (6) passes through to the outside of the first suspension seat (5) and is fixedly connected to a first knob (7). The second coating die (3) is threadedly connected to the outer wall of the first adjusting screw (6) and is also connected to the inner side of the first coating die (2). The two sides of the second coating die (3) are fixedly connected to first limiting blocks. The inner side of the first coating die (2) is provided with a first limiting groove that matches the first limiting block.

8. A coating apparatus for processing lithium battery composite separators according to claim 7, characterized in that, The inner side of the first coating die (2) is fixedly connected to a second suspension seat (11), the inner side of the second suspension seat (11) is rotatably connected to a second adjusting screw (12), and one end of the second adjusting screw (12) passes through to the outside of the second suspension seat (11) and is fixedly connected to a second knob (13). The third coating die (4) is threadedly connected to the outer wall of the second adjusting screw (12), and the two sides of the third coating die (4) are fixedly connected to second limiting blocks. The inner side of the first coating die (2) is provided with a second limiting groove that matches the second limiting block.

9. A coating method for processing composite separators for lithium batteries, characterized in that, The coating apparatus for processing lithium battery composite separators according to claim 8 includes the following steps: S1. A feeder is installed on the diaphragm coating processing device (1) for feeding the inside of the first coating die (2), the second coating die (3) and the third coating die (4). The first coating die (2), the second coating die (3) and the third coating die (4) are arranged in a stepped manner, which divides the single thick coating into three thin layer coatings in a stepped manner. The functions of wetting and anchoring, edge elimination and homogenization and surface finishing can be achieved through layering. This not only reduces the coating solvent residue and curing internal stress, but also suppresses thick edge defects from the source and improves the interlayer bonding force, which significantly improves the thickness uniformity and recycling reliability of the diaphragm coating. S2. The die lip of the third coating die (4) is arched, and the die lip of the second coating die (3) is concave. The discharge flow rate achieves thickness complementarity and edge gradient elimination. With the flat die lip of the first coating die (2), the surface homogenization and finishing are completed. The adhesion of the coating substrate, the uniformity of the thickness of the whole width and the reduction of edge trimming loss can be improved simultaneously. At the same time, with the wavy die lip (8) of the second coating die (3) and the third coating die (4) being wavy in shape, they are staggered up and down. The discharge flow rate of the tooth peak and tooth valley complementarity and cancels each other, transforming the traditional cliff-like thick edge into a smooth and gentle slope edge. This can reduce edge trimming loss and reduce powdering defects caused by edge stress concentration. S3. During the coating process, when there is too much raw material inside the peak and valley of the wave-shaped die lip (8) of both the second coating die (3) and the third coating die (4), it will enter the inside of the straight groove (9) through the through hole (10). When the flow rate is too low, it will flow out from the inside of the through hole (10) through the straight groove (9). This can smooth out the micro-flow fluctuations between adjacent teeth, stabilize the edge discharge state, and reduce the accumulation and crusting of material in the dead corners of the tooth valleys. S4. Depending on the thickness of different coating materials, the operator can rotate the first knob (7) and the second knob (13) respectively, so that the first adjusting screw (6) and the second adjusting screw (12) rotate, thereby driving the second coating die (3) and the third coating die (4) to adjust their positions, thereby adjusting the distance between the first coating die (2), the second coating die (3) and the third coating die (4), so that the coating can be adapted to the processing of diaphragms of different thicknesses.

Images