Lithium battery microporous membrane, preparation method thereof and vacuum adsorption device of casting piece of lithium battery microporous membrane

Abstract

The invention discloses a lithium battery microporous membrane and a preparation method thereof and a vacuum adsorption device of a microporous membrane casting piece, and the vacuum adsorption device of the microporous membrane casting piece comprises an upper plate, a front plate and a rear plate which are respectively fixed on the front side and the rear side of the upper plate, and side plates which are respectively fixed on the left side and the right side of the upper plate, the upper plate, the front plate, the rear plate and the two side plates are fixedly connected together to form a sealing cover with an opening in the lower part, an oil baffle plate is arranged in the sealing cover, the bottom surfaces of the side plates are cambered surfaces matched with the bottom surface of a chilling roller, and the side surfaces, close to the front plate, of the side plates are attached to the side surface of an outlet of a die head; the upper plate is provided with two oil fume outlets which are symmetrically arranged left and right, each oil fume outlet is connected with an oil fume pipeline, and each oil fume pipeline is connected with a negative pressure fan. The casting pieces in the sealing cover are adsorbed through the double fans, the consistency of wind fields on the two sides in the sealing cover is guaranteed, the attaching capacity of the casting pieces is improved, the cooling speed of a casting body is increased, oil fume can be rapidly adsorbed, and oil fume accumulation is reduced.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery microporous membrane, its preparation method, and a vacuum adsorption device for microporous membrane castings, belonging to the field of lithium-ion battery separator manufacturing technology. Background Technology

[0002] Lithium-ion batteries are a core component of new energy vehicles, and the separator is one of its key materials. The performance of the lithium-ion battery separator (microporous membrane) determines the battery's interface structure and internal resistance, directly affecting its capacity, cycle life, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of the battery. Currently, in the lithium-ion battery separator production process, after the extruder die extrudes the cast sheet, a four-sided sealed cover is typically used. A single fan is used to extract the contents from the vacuum adsorption system. However, the adsorption effect on both sides of the adsorption device is inconsistent, leading to uneven adhesion between the cast sheet and the cooling roller, poor oil fume removal, and an unreasonable internal airflow design. This can easily result in oil droplet accumulation, which drips onto the cast sheet, causing thin spots and oil fume carbonization, resulting in scratches and bright lines on the membrane surface. Furthermore, current vacuum adsorption devices require periodic replacement of the internal oil-absorbing cloth, which is slow and inefficient. Summary of the Invention

[0003] The purpose of this invention is to provide a lithium battery microporous membrane that reduces thin spots; another purpose of this invention is to provide a method for preparing the lithium battery microporous membrane; yet another purpose of this invention is to provide a vacuum adsorption device for improving the bonding ability of cast sheets and improving membrane surface defects during the production process of lithium-ion battery separators, so as to solve the technical problems of uneven casting sheet bonding, slow cooling speed, and insufficient cooling causing thin spots in the existing separator production process.

[0004] To achieve the above objectives, the lithium battery separator of the present invention adopts the following technical solution: a lithium battery microporous membrane, one side of the microporous membrane is a glossy surface and the other side is a matte surface, the area of ​​insufficient cooling thin spots on the microporous membrane is less than 3% of the total area of ​​the glossy surface of the microporous membrane, and the insufficient cooling thin spots refer to the areas that show higher light transmittance and grayscale greater than 150 on the defect detector.

[0005] As a preferred option, the area of ​​insufficiently cooled thin spots on the microporous membrane is less than 2.6% of the total smooth surface area of ​​the microporous membrane.

[0006] The preparation method of the lithium battery microporous membrane of the present invention adopts the following technical solution: A preparation method of lithium battery microporous membrane, characterized in that it includes the following steps: (1) mixing of ingredients: polyethylene or polypropylene and pore-forming agent are mixed evenly in proportion to obtain a mixture; (2) extrusion casting: the mixture obtained in step (1) is extruded through an extruder to obtain a high-temperature melt, the high-temperature melt is accurately metered and fed into a die head, the cast sheet extruded through the die head is cooled on a chilling roller to form a casting sheet, when the casting sheet is cooled on the chilling roller, the sealing cover above the chilling roller is used to vacuum adsorb the casting sheet, and the casting sheet is connected to the sealing cover. (3) Biaxial stretching: The cast film is sent into the biaxial stretching machine for stretching; (4) Extraction and drying: The biaxially stretched film is introduced into the extraction tank for extraction, the extractant is removed, and the extracted film is dried; (5) Waste edge trimming: The dried film is pulled a second time and the waste edge is trimmed before entering the transverse stretching device; (6) Transverse stretching: The film after the waste edge trimming is introduced into the transverse stretching process for transverse stretching treatment; (7) Heat setting and winding: The transversely stretched film is heat set, the stress is removed, and then it is wound by an online winding machine to obtain the diaphragm.

[0007] As a preferred solution, after vacuum adsorption and accelerated cooling, after steps (3)-(7), after the heat setting step in step (7), the thin spot defect is detected by a defect detector to form a membrane morphology defect image.

[0008] As a preferred embodiment, in the (1) ingredient mixing step, an antioxidant may be further added to the mixture; wherein the mass ratio of polyethylene or polypropylene to pore-forming agent is (10-50):(50-90); the pore-forming agent is white oil, nonane, or naphthane, and white oil may be selected.

[0009] As a preferred option, in the extrusion casting step (2), the extrusion pressure is 4-8 MPa, the die extrusion temperature is 140-270℃, the extrusion speed is 0.2-15 m / min, and the film thickness can be adjusted by adjusting the extrusion amount of the polyolefin resin composition; the quenching roller temperature is 8-20℃.

[0010] As a preferred embodiment, in the biaxial stretching step (3), the biaxial stretching can be either biaxial synchronous stretching or biaxial asynchronous stretching; the uniaxial stretching magnification factor can be 2 times or more, for example, 3-30 times. In the case of biaxial stretching, the stretching magnification factor in each direction can be 3 times or more, for example, 4-30 times. Furthermore, the amount of stretching in each direction does not need to be the same, and the magnification factor affects the film size in a multiplicative manner.

[0011] As a preferred option, in the transverse stretching step (6), the stretching temperature can be 80-130℃; the stretching ratio is 1-1.8 times.

[0012] The vacuum adsorption device for microporous membrane castings of the present invention adopts the following technical solution: A vacuum adsorption device for microporous membrane castings includes an upper plate, a front plate and a rear plate respectively fixed on the front and rear sides of the upper plate, and side plates respectively fixed on the left and right sides of the upper plate. The upper plate, the front plate, the rear plate and the two side plates are fixedly connected together to form a sealing cover with an opening at the bottom. An oil baffle is provided inside the sealing cover. The bottom surface of the side plate is an arc surface adapted to the bottom surface of the quenching roller. The side of the side plate near the front plate is attached to the side of the die head outlet. Two symmetrically arranged fume outlets are opened on the upper plate. Each fume outlet is connected to a fume duct, and each fume duct is connected to a negative pressure fan.

[0013] As a preferred embodiment, the oil baffle includes a frame installed on the inner wall of the sealing cover, with a first oil-absorbing plate and a second oil-absorbing plate connected to the frame. The first oil-absorbing plate is connected to the front plate and slopes upward from the front plate to the middle of the sealing cover. The second oil-absorbing plate is connected to the rear plate and slopes downward from the rear plate to the middle of the sealing cover. Both the first oil-absorbing plate and the second oil-absorbing plate have oil-absorbing material on their surfaces.

[0014] As a preferred embodiment, the plane on which the oil baffle frame is located is parallel to the plane on which the upper plate is located, the angle between the side of the oil baffle frame that is attached to the front plate and the first oil suction plate is 120°~170°, and the angle between the side of the oil baffle frame that is attached to the rear plate and the second oil suction plate is 80°~90°.

[0015] As a preferred embodiment, the fume outlet is a rectangular opening extending to the left and right, and the fume duct includes a bottom pipe connected to the upper circle below the rectangular opening, with a curved pipe with a circular cross-section connected to the upper end of the bottom pipe.

[0016] As a preferred embodiment, the upper plate is provided with a rotating interface, which is located between the two fume outlets.

[0017] As a preferred embodiment, the side plate includes a support plate, a connecting plate, and a lateral sealing plate. The support plate is welded to the upper plate, the connecting plate is fixedly connected to the lower part of the support plate by bolts, and the lateral sealing plate is fixedly connected to the lower part of the connecting plate by bolts. The lateral sealing plate is made of PTFE.

[0018] As a preferred embodiment, the inner wall of the sealing cover is provided with a support boss, the support boss is fixed on the inner wall of the connecting plate, the oil baffle is placed on the support boss, and the support bosses on the connecting plates on the left and right sides of the sealing cover support the oil baffle.

[0019] As a preferred embodiment, the upper surface of the support boss is flat and the lower surface is curved, and the oil baffle is supported on the flat surface of the support boss.

[0020] As a preferred embodiment, the front plate and the upper plate are welded together, and the fume duct is welded to the fume outlet of the upper plate.

[0021] As a preferred embodiment, the rear plate and the upper plate are fixedly connected by bolts, and a rear sealing plate is bolted to the lower part of the rear plate. The oil baffle is fixed inside the sealing cover by bolts between the rear plate and the rear sealing plate. The rear sealing plate is made of PTFE.

[0022] The beneficial effects of this invention are as follows: The vacuum adsorption device for the lithium battery microporous membrane casting in this invention can improve the bonding ability of the casting and improve membrane surface defects. It is installed in the casting process. After the membrane surface is processed by the extruder, it emerges from the lip to form a cast sheet. The vacuum adsorption device is fixed to the die head and adheres as closely as possible to the lower cooling roller. A fan draws air, creating negative pressure inside the vacuum adsorption, allowing the membrane surface to adhere to the cooling roller surface faster and better, accelerating the cooling speed of the cast sheet and reducing the occurrence of thin spots due to uneven cooling. Specifically, because the adsorption force and speed between the casting and the cooling roller are increased, the casting and the cooling roller can adhere to the cooling roller faster and better (the side of the casting that adheres to the cooling roller ultimately forms the smooth surface of the microporous membrane). Therefore, it increases the cooling speed of the casting and reduces thin spots caused by oil fume condensation. Thus, this invention can reduce the area of ​​insufficiently cooled thin spots and improve the quality of the separator.

[0023] This invention employs dual fans to adsorb the casting sheets inside the sealing cover, ensuring consistent airflow on both sides of the sealing cover, improving the adhesion of the casting sheets, and accelerating the cooling speed of the cast body; the two fans adsorb the casting sheets through two right eye pipes, which can quickly adsorb oil fumes, reduce oil fume accumulation, effectively promote the casting sheets to adhere to the cooling roller as soon as possible, and accelerate the cooling time.

[0024] Preferably, the oil baffle inside the sealing cover includes two oil-absorbing plates, which can effectively absorb oil fumes, reduce the risk of oil dripping, avoid the formation of thin oil dripping spots on the casting sheet and scratches on the casting sheet due to carbonization of oil fumes, and improve the product A-grade rate.

[0025] Preferably, the two oil suction plates are within the aforementioned angle range, which allows the interior of the sealing cover to maintain a large air pressure and air volume.

[0026] Preferably, the fume extraction duct adopts a channel design with a round top and a square bottom to improve the efficiency of fume passage and reduce the risk of oil droplets condensing due to the impact of fume on sharp edges.

[0027] Preferably, the rotary interface can be used to connect devices such as sensors, and can measure data such as wind speed and wind pressure inside the sealed enclosure.

[0028] Preferably, the oil baffle is supported by a support boss, allowing the oil baffle to be installed in a drawer-like manner, which can significantly reduce the time for replacing the oil-absorbing material and improve production efficiency.

[0029] Preferably, the bottom surface of the support boss adopts a rounded structure, which can further reduce the risk of oil condensation and accumulation forming oil droplets.

[0030] Preferably, the main components of the sealing cover are fixed by welding or bolting, which can improve design and assembly efficiency and make installation and debugging convenient and quick.

[0031] On the other hand, the present invention provides a microporous membrane prepared using the above-described vacuum adsorption device.

[0032] The microporous membrane prepared by this invention has a thin spot rate of 1% to 3% due to insufficient cooling. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the vacuum adsorption device for a lithium battery separator casting according to an embodiment of the present invention. Figure 2 yes Figure 1 A diagram on the front side; Figure 3 yes Figure 1 A schematic diagram from a low angle after removing one side panel; Figure 4 yes Figure 1 Usage status diagram; Figure 5 This is a partial schematic diagram of the side panel and oil baffle. Figure 6 yes Figure 3 A schematic diagram of the internal oil baffle plate; Figure 7 yes Figure 6 A plan view; Figure 8 yes Figure 1 Schematic diagram of the upper and middle plates; Figure 9 yes Figure 1 Schematic diagram of the middle support plate and connecting plate; Figure 10 This is a schematic diagram of the connection between the front panel and the side panel; Figure 11 This is a schematic diagram of the connecting plate; Figure 12 yes Figure 11 A plan view; Figure 13 yes Figure 1 Side interior view; Figure 14 yes Figure 1 3D view and side view of the front panel; Figure 15 This is a simulation result of the center distance data at the bottom of the fume extraction duct; Figure 16These are the simulation results of the angle data of the two oil suction plates in the oil baffle.

[0034] In the diagram: 1-Front plate, 2-Upper plate, 2.1-Fume outlet, 3-Side plate, 3.1-Support plate, 3.2-Connecting plate, 3.3-Side sealing plate, 4-Fume duct, 4.1-Bottom duct, 4.2-Bend, 5-Rear plate, 5.1-Rear sealing plate, 6-Oil baffle, 6.1-Frame, 6.2-First oil suction plate, 6.3-Second oil suction plate, 7-Support boss, 8-Rotating interface, 9-Die head, 10-Quick cooling roller, 11.1-Screw, 11.2-Wing nut. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0036] An embodiment of the lithium battery separator of the present invention: A lithium battery separator comprising a microporous membrane, wherein in the casting stage, the cast sheet extruded by the die is cooled on a chilling roller to form a cast sheet, and the cast sheet is vacuum adsorbed by a sealing cover above the chilling roller, and the cast sheet is adsorbed onto the chilling roller under the action of two negative pressure fans connected to the sealing cover; the side of the cast sheet that is in contact with the chilling roller is stretched to form a glossy film surface, and the other side of the cast sheet is stretched to form a matte film surface.

[0037] An embodiment of the lithium battery separator preparation method of the present invention: A method for preparing a lithium battery separator, characterized by comprising the following steps: (1) Mixing of ingredients: Polyethylene (25 parts by weight) and white oil (75 parts by weight) are mixed evenly to obtain a mixture; (2) Extrusion casting: The mixture obtained in step (1) is extruded through an extruder to obtain a high-temperature melt, the high-temperature melt is accurately metered and fed into a die head, the die head temperature is 215°C, the extrusion pressure is 5.5 MPa, the cast sheet extruded through the die head is cooled on a chilling roller to form a casting sheet, wherein the chilling roller temperature is 12°C, when the casting sheet is cooled on the chilling roller, the casting sheet is vacuum adsorbed by a sealing cover above the chilling roller, the casting sheet is connected to the two (3) Biaxial stretching: The casting sheet is fed into the biaxial stretching machine for stretching, and the biaxial stretching ratio is 7 times. (4) Extraction and drying: The biaxially stretched membrane is introduced into the extraction tank for extraction, the extractant is removed, and the extracted membrane is dried at a temperature of 45°C. (5) Waste edge trimming: The dried membrane is pulled a second time and the waste edge is trimmed before entering the transverse stretching device. (6) Transverse stretching: The membrane after the waste edge is trimmed is introduced into the transverse stretching process for transverse stretching, and the transverse stretching ratio is 1.5 times and the stretching temperature is 110°C. (7) Heat setting and winding: The transversely stretched membrane is heat set, the stress is removed, and then it is wound by an online winding machine to obtain the diaphragm. After the heat setting step (7), the thin point defect is displayed by the defect detector to form a diaphragm morphology defect image.

[0038] The specific structure of one embodiment of the lithium battery separator vacuum adsorption device of the present invention is as follows: Figures 1 to 14 As shown, the vacuum adsorption device for improving the bonding ability of the casting sheet and improving the defects of the diaphragm in this embodiment includes an upper plate 2, a front plate 1 and a rear plate 5 respectively fixed on the front and rear sides of the upper plate 2, and side plates 3 respectively fixed on the left and right sides of the upper plate 2. The upper plate 2, the front plate 1, the rear plate 5 and the two side plates 3 are fixedly connected together to form a sealing cover with an opening at the bottom. An oil baffle 6 is provided inside the sealing cover. The bottom surface of the side plate 3 is an arc surface adapted to the bottom surface of the chilling roller 10. The side of the side plate 3 near the front plate 1 is attached to the side of the die head 9 outlet. Two symmetrically arranged fume outlets 2.1 are opened on the upper plate 2. Each fume outlet 2.1 is connected to a fume duct 4, and each fume duct 4 is connected to a negative pressure fan.

[0039] like Figure 8 As shown, the fume outlet 2.1 is a rectangular opening extending left and right. The fume duct 4 includes a bottom duct 4.1 connected to the upper circle below the rectangular opening. The upper end of the bottom duct 4.1 is connected to a curved pipe 4.2 with a circular cross-section. The upper plate 2 has a rotating interface 8, which is located between the two fume outlets 2.1.

[0040] The oil baffle 6 includes a frame 6.1 mounted on the inner wall of the sealing cover. A first oil-absorbing plate 6.2 and a second oil-absorbing plate 6.3 are connected to the frame 6.1. The first oil-absorbing plate 6.2 is connected to the front plate 1 and slopes upwards from the front plate 1 to the middle of the sealing cover. The second oil-absorbing plate 6.3 is connected to the rear plate 5 and slopes downwards from the rear plate 5 to the middle of the sealing cover. Both the first oil-absorbing plate 6.2 and the second oil-absorbing plate 6.3 have oil-absorbing material on their surfaces. The plane of the frame 6.1 of the oil baffle 6 is parallel to the plane of the upper plate 2. The angle between the side of the frame 6.1 of the oil baffle 6 that is in contact with the front plate 1 and the first oil-absorbing plate 6.2 is 120°~170°, and the angle between the side of the frame 6.1 of the oil baffle 6 that is in contact with the rear plate 5 and the second oil-absorbing plate 6.3 is 80°~90°.

[0041] The side plate 3 includes a support plate 3.1, a connecting plate 3.2, and a lateral sealing plate 3.3. The support plate 3.1 is welded to the upper plate 2. The connecting plate 3.2 is fixedly connected to the lower part of the support plate 3.1 by bolts. The lateral sealing plate 3.3 is fixedly connected to the lower part of the connecting plate 3.2 by bolts. The lateral sealing plate 3.3 is a PTFE plate.

[0042] The inner wall of the sealing cover is provided with a support boss 7, which is fixed to the inner wall of the connecting plate 3.2. The oil baffle 6 is placed on the support boss 7, and the support bosses 7 on the connecting plates on the left and right sides of the sealing cover support the oil baffle 6. The upper surface of the support boss 7 is flat and the lower surface is curved. The oil baffle 6 is supported on the flat surface of the support boss 7.

[0043] The front plate 1 is welded and fixed together with the upper plate 2, and the fume duct 4 is welded to the fume outlet 2.1 of the upper plate 2. The rear plate 5 is fixedly connected to the upper plate 2 by bolts, and the lower part of the rear plate 5 is connected to the rear sealing plate 5.1 by bolts. The oil baffle 6 is fixed inside the sealing cover by bolts between the rear plate 5 and the rear sealing plate 5.1. The rear sealing plate 5.1 is made of PTFE.

[0044] The sealing cover of this invention is fully welded to prevent gaps between components, which would result in poor adsorption. The front plate 1 and the upper plate 2 are welded together. The support plate 3.1 reinforces the front plate 1 and the upper plate 2 and is welded together to fix them. The upper plate 1 is fixed to the side of the mold head 9 outlet. A PTFE gasket is placed at the contact position with the mold head 9 to prevent oil fumes from entering the contact gap and condensing and dripping onto the casting body, forming defects. A rotating interface 8 is provided at the center of the upper plate 2 to facilitate the installation of a pressure gauge to monitor the internal pressure in real time. The upper plate 2 is welded together with the oil fume duct 4. The upper bend 4.2 of the oil fume duct 4 is welded to the lower square tube 4.1 to ensure sealing. The two sides of the bend 4.2 are connected to a negative pressure fan (not shown in the attached figure) through flexible hoses (not shown in the attached figure) to draw negative pressure into the sealing cover, keeping the adsorption effect on both sides of the casting sheet consistent, ensuring stable adhesion on both sides of the casting sheet, and allowing the oil fumes inside the sealing cover to be discharged smoothly.

[0045] The upper bend 4.2 of the fume extraction duct 4 is a circular pipe, with an overall circular design above the bend. The internal channel is smooth and rounded without any sharp edges, ensuring smooth and unobstructed flow of fumes without condensation or accumulation. The bottom pipe 4.1 of the fume extraction duct 4 adopts an upper circular structure with a lower circular structure. The bottom of the bottom pipe 4.1 is welded and fixed to the fume outlet 2.1 of the upper plate 2, facilitating the flow of fumes. The optimal center-to-center distance between the bottoms of the two fume extraction ducts, after simulation design, is 400mm~440mm (e.g., 400mm, 405mm, 410mm, 415mm, 420mm, 425mm, 430mm, 435mm, 440mm). Figure 15 The table provides some simulation data. Calculations show that when the center-to-bottom distance between the two fume ducts is in the range of 425mm to 440mm, the adsorption effect is the best and the proportion of thin spots due to insufficient cooling is the smallest. When considering both air volume and air pressure, the center-to-bottom distance between the two fume ducts can be selected as 425mm.

[0046] The upper plate 2 and the rear plate 5 are fixed with wing nuts 11.2. A threaded rod 11.1 is welded to the rear of the upper plate 2 to speed up disassembly and improve efficiency. Oil-absorbing cloth is installed on the two oil-absorbing plates on the oil baffle 6 to absorb oil droplets condensed from the fumes inside the sealing cover. The oil baffle 6 is circumferentially fitted to the inner circumferential surface of the sealing cover to ensure its sealing performance, preventing condensed oil droplets from dripping onto the casting surface. The oil baffle 6 is placed on the support boss 7 of the connecting plate 3.2. The support boss 7 supports the oil baffle 6, forming a drawer-type installation method, simplifying the cumbersome installation process, increasing the replacement speed of the oil baffle 6, reducing replacement time, and minimizing cost losses. The bottom of the support boss 7 is an arc surface, forming an arc-shaped boss structure. The arc-shaped boss effectively ensures the passage of fumes and prevents condensation, thus preventing oil droplets from sliding off.

[0047] The oil baffle 6 adopts an integrated pull-out design and is fixed to the upper plate 2 with a wing nut to prevent loosening. The rear end of the first oil suction plate is slightly longer than the front end of the second oil suction plate to prevent possible oil droplets from falling onto the casting plate. The gap between the two oil suction plates is straight, facilitating the smooth entry of oil fumes into the exhaust duct and preventing condensation inside the sealing cover. The angles of the two oil suction plates were calculated and simulated to achieve the optimal angles. Specifically, the angle between the side of the frame that is attached to the front plate and the first oil suction plate is 120°~170°, and the angle between the side of the frame that is attached to the rear plate and the second oil suction plate is 80°~90°. Figure 16 The following is a partial simulation data provided: Data simulations and calculations revealed that the optimal suction effect, balancing airflow and pressure, is achieved when the angle between the frame / front panel and the first oil-absorbing plate is 150°~170°, and the angle between the frame / rear panel and the second oil-absorbing plate is 86°~90°. The best results are achieved when the angle between the frame / front panel and the first oil-absorbing plate is 150°, and the angle between the frame / rear panel and the second oil-absorbing plate is 86°. Therefore, during manufacturing, an integrated oil-absorbing plate structure is customized based on these angles (e.g., ...). Figure 6 (As shown).

[0048] The connecting plate 3.2 and the support plate 3.1 are fixed with screws. The connecting plate 3.2 is located on both sides of the sealing cover, and the support plate 3 is used to support the sealing cover and prevent deformation on both sides of the sealing cover. Figure 10 As shown, the connecting plate 3.2 is slightly longer than the front plate 1. Through the mutual assembly and fixation of the components, gaps between the connecting parts are eliminated, ensuring the overall sealing performance of the sealing cover. The connecting plate 3.2 is welded with a threaded rod, and a wing nut is used to fix the side sealing plate 3.3 for easy installation. The rear side of the oil baffle plate 6 is fixed to the rear plate 5 and the rear sealing plate 5.1 with screws, enabling overall disassembly and rapid replacement in a short time, improving production efficiency and reducing cost waste.

[0049] The present invention has the following advantages: (1) The sealing cover of the present invention is fixed by welding, bolts and threaded rods with butterfly nuts, which can improve the design and assembly efficiency and make the installation and debugging convenient and quick; (2) The present invention uses a double fan to adsorb the sealing cover, ensuring the consistency of the air field on both sides inside the sealing cover, improving the bonding ability of the casting sheet, and accelerating the cooling speed of the casting body; (3) The oil fume duct adopts a channel design with an upper circle and a lower circle to improve the oil fume passage efficiency and reduce the risk of oil fume impact and condensation of oil droplets caused by the presence of sharp edges; in the simulation experiment, the adsorption effect reached the best when the center distance between the bottom of the two oil fume ducts was 425mm; (4) The oil baffle adopts a drawer-type design, which can greatly reduce the time for replacing the oil absorbent cotton and improve production efficiency; after the simulation experiment, the angle of the oil absorbent plate was determined to be 150° for the first oil absorbent plate and 86° for the second oil absorbent plate when the adsorption effect was optimal; (5) The bottom surface of the support boss adopts a circular arc structure, which can further reduce the risk of oil fume condensation and accumulation to form oil droplets.

[0050] Using the vacuum adsorption device of this invention in the casting stage of diaphragm production increases the adsorption force and speed between the casting and the quenching roller, allowing the casting and quenching roller to adhere to each other more quickly and effectively. This improves the cooling rate of the casting and reduces thin spots caused by oil fume condensation. Therefore, this invention reduces the area of ​​insufficiently cooled thin spots and improves diaphragm quality. The microporous membrane prepared using the vacuum adsorption device of this invention has an insufficient cooling thin spot ratio of 1% to 3%.

[0051] The foregoing has shown and described the basic structure, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the scope of protection of the present invention in any way, and all technical solutions obtained by equivalent substitution or other means fall within the scope of protection of the present invention.

[0052] All parts not covered in this invention are the same as or can be implemented using existing technologies.

Claims

1. A lithium battery microporous membrane, wherein one side of the microporous membrane is glossy and the other side is matte, characterized in that: The area of ​​insufficiently cooled thin spots on the microporous membrane is less than 3% of the total area of ​​the smooth surface of the microporous membrane. Insufficiently cooled thin spots refer to areas that show higher light transmittance and a grayscale greater than 150 on the defect detector.

2. A method for preparing a microporous membrane for a lithium battery, characterized in that, Includes the following steps: (1) Mixing of ingredients: Mix polyethylene or polypropylene with pore-forming agent in proportion to obtain a mixture; (2) Extrusion casting: The mixture obtained in step (1) is extruded through an extruder to obtain a high-temperature melt. The high-temperature melt is accurately metered and fed into a die. The cast sheet extruded through the die is cooled on a chilling roller to form a casting. When the casting is cooled on the chilling roller, the casting is vacuum-adsorbed by the sealing cover above the chilling roller. The casting is adsorbed onto the chilling roller by the two negative pressure fans connected to the sealing cover. (3) Biaxial stretching: The casting is fed into a biaxial stretching machine for stretching; (4) Extraction and drying: The biaxially stretched membrane is introduced into the extraction tank for extraction to remove the extractant, and the extracted membrane is dried. (5) Trimming waste edges: After the dried film is pulled twice and the waste edges are trimmed, it enters the transverse stretching device; (6) Lateral stretching: The film after the waste edges are cut is introduced into the lateral stretching process for lateral stretching treatment; (7) Heat setting and winding: After the transverse stretching of the membrane, heat setting is performed to remove stress, and then the membrane is wound on an online winding machine to obtain the microporous membrane.

3. The method for preparing the lithium battery microporous membrane according to claim 2, characterized in that: After vacuum adsorption and accelerated cooling, after steps (3)-(7), after the heat setting step in step (7), the thin spot defects on the smooth surface of the microporous membrane are detected by a defect detector to form a microporous membrane morphological defect image.

4. A vacuum adsorption device for lithium battery microporous membrane castings, characterized in that: It includes an upper plate, a front plate and a rear plate fixed to the front and rear sides of the upper plate respectively, and side plates fixed to the left and right sides of the upper plate respectively. The upper plate, the front plate, the rear plate and the two side plates are fixedly connected together to form a sealing cover with an opening at the bottom. An oil baffle is provided inside the sealing cover. The bottom surface of the side plate is an arc surface adapted to the bottom surface of the chilling roller. The side of the side plate near the front plate is attached to the side of the die head outlet. Two symmetrically arranged fume outlets are opened on the upper plate. Each fume outlet is connected to a fume duct, and each fume duct is connected to a negative pressure fan.

5. The vacuum adsorption device for lithium battery microporous membrane castings according to claim 4, characterized in that: The oil baffle includes a frame installed on the inner wall of the sealing cover. A first oil-absorbing plate and a second oil-absorbing plate are connected to the frame. The first oil-absorbing plate is connected to the front plate and slopes upward from the front plate to the middle of the sealing cover. The second oil-absorbing plate is connected to the rear plate and slopes downward from the rear plate to the middle of the sealing cover. The surfaces of the first oil-absorbing plate and the second oil-absorbing plate are covered with oil-absorbing material.

6. The vacuum adsorption device for lithium battery microporous membrane castings according to claim 5, characterized in that: The plane on which the oil baffle frame is located is parallel to the plane on which the upper plate is located. The angle between the side of the oil baffle frame that is attached to the front plate and the first oil suction plate is 120°~170°. The angle between the side of the oil baffle frame that is attached to the rear plate and the second oil suction plate is 80°~90°.

7. The vacuum adsorption device for lithium battery microporous membrane castings according to claim 4, characterized in that: The fume outlet is a rectangular opening extending to the left and right. The fume duct includes a bottom pipe connected to the upper circle below the rectangular opening, and a curved pipe with a circular cross-section is connected to the upper end of the bottom pipe. The upper plate has a rotating interface located between the two fume outlets.

8. The vacuum adsorption device for lithium battery microporous membrane castings according to claim 4, characterized in that: The side plate includes a support plate, a connecting plate, and a lateral sealing plate. The support plate is welded to the upper plate. The connecting plate is fixedly connected to the lower part of the support plate by bolts. The lateral sealing plate is fixedly connected to the lower part of the connecting plate by bolts. The lateral sealing plate is made of PTFE. The front plate is welded to the upper plate. The fume duct is welded to the fume outlet of the upper plate. The oil baffle is fixed inside the sealing cover by bolts between the rear plate and the rear sealing plate. The rear sealing plate is made of PTFE.

9. The vacuum adsorption device for lithium battery microporous membrane castings according to claim 4, characterized in that: The inner wall of the sealing cover is provided with a support boss, which is fixed on the inner wall of the connecting plate. The oil baffle is placed on the support boss, and the support bosses on the connecting plates on the left and right sides of the sealing cover support the oil baffle. The upper surface of the support boss is flat and the lower surface is curved. The oil baffle is supported on the flat surface of the support boss.

10. The microporous membrane prepared by the vacuum adsorption device of the lithium battery microporous membrane casting according to any one of claims 4 to 9.

Images