A wet lithium battery diaphragm asynchronous stretching production line MDO structure

Abstract

The present application relates to a kind of wet lithium battery diaphragm asynchronous stretching production line MDO structure, including the preheating unit, stretching unit and cooling setting unit being sequentially arranged along the direction of diaphragm;Multiple preheating rollers are arranged in the preheating unit in sequence;Multiple stretching rollers are arranged in the stretching unit in sequence;Multiple cooling rollers are arranged in the cooling setting unit in sequence;Its characterized in that, the stretching roller in the stretching unit is equipped with the oil removal roller matched therewith;The oil removal roller is vacuum adsorption type structure, is attached to the surface of the stretching roller, can remove the oil on diaphragm by extrusion and negative pressure adsorption;The roll diameter of the last preheating roller of the preheating unit is less than the roll diameter of other preheating rollers;The roll diameter of the first cooling roller of the cooling setting unit is less than the roll diameter of other cooling rollers.The present application effectively solves the problems encountered in current production, and creates favorable conditions for realizing MDO high ratio stretching.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator production, and in particular to a lithium battery separator stretching production line, specifically a wet-process lithium battery separator asynchronous stretching production line MDO structure. Background Technology

[0002] The preparation of wet-process lithium-ion battery separators typically involves processes such as mixing polyethylene and white oil, extrusion, casting, longitudinal stretching (MDO), transverse stretching, extraction, drying, and heat setting. Among these, the MDO longitudinal stretching process is the core step that determines the microstructure and macroscopic properties of the separator.

[0003] Currently, longitudinal stretching (MDO) typically consists of an extruder, die head, casting section, preheating section, stretching section, setting section, automatic winding section, and PLC electrical control system, usually containing multiple rollers. Functionally, they can be categorized as tension rollers, preheating rollers, stretching rollers, and cooling rollers. The stretching rollers are arranged in a staggered pattern. Each stretching roller is usually equipped with a pressure roller assembly to press the diaphragm tightly against the surface of the stretching roller.

[0004] The existing asynchronous stretching production line's MDO section has the following main shortcomings: 1. During the stretching process, the diaphragm surface is impregnated with a large amount of paraffin oil, which easily causes slippage on the roller surface under high-ratio stretching conditions, affecting stretching accuracy and thickness uniformity. Existing equipment in the industry lacks a dedicated degreasing device, making it impossible to effectively solve the oil film slippage problem under high-ratio stretching.

[0005] 2. The upper row of stretching rollers can only be raised and lowered as a whole, and individual rollers cannot be adjusted independently. During film threading and production debugging, the overall lifting structure lacks flexibility and cannot make fine adjustments to individual rollers for local tension fluctuations, thus limiting the scope for process optimization.

[0006] 3. Lack of real-time monitoring methods for the actual speed of the film surface. Existing equipment relies solely on roller speed encoders to indirectly calculate the film surface speed. When slippage occurs, it cannot be detected and reported in real time, making it difficult to detect and control product quality fluctuations in a timely manner.

[0007] 4. The pressing method and angle design of the pressure roller are not optimized enough, resulting in insufficient adhesion between the diaphragm and the stretching roller, which affects the tension control during the stretching process.

[0008] 5. The unreasonable layout and diameter configuration of the roller group limit the further improvement of the stretching ratio, and the temperature field at the end of the stretching process is not adjustable, which affects the uniformity of film crystallization.

[0009] The aforementioned deficiencies have a significant impact on high-ratio stretching of MDO, and therefore urgently need to be improved in order to better meet production needs. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of existing technologies by providing an MDO structure for a wet-process lithium battery separator asynchronous stretching production line, which effectively solves the problems encountered in current production and creates favorable conditions for achieving high-rate stretching of MDO.

[0011] The technical solution of this invention is: A wet-process lithium battery separator asynchronous stretching production line MDO structure includes a preheating unit, a stretching unit, and a cooling and shaping unit arranged sequentially along the separator direction. The preheating unit has multiple preheating rollers arranged sequentially. The stretching unit has multiple stretching rollers arranged sequentially. The cooling and shaping unit has multiple cooling rollers arranged sequentially. Each stretching roller in the stretching unit has a corresponding oil removal roller. The oil removal roller is pressed against the surface of the stretching roller and can remove oil from the separator through compression. The diameter of the last preheating roller in the preheating unit is smaller than the diameters of the other preheating rollers. The diameter of the first cooling roller in the cooling and shaping unit is smaller than the diameters of the other cooling rollers.

[0012] Furthermore, the degreasing roller includes a roller core and a sleeve; the roller core is a hollow, closed structure with multiple through-hole-shaped air holes on its circumferential sidewalls, and one end of it is connected to a vacuum pump through a rotary joint and pipeline; the sleeve is an open-ended cylindrical shape with a length equivalent to that of the roller core, and multiple micro-holes on its sidewalls; the sleeve is fitted onto the roller core, and retaining rings are provided at both ends; the gaskets are detachably connected to the roller core through a stop block to fix and seal the sleeve, thereby enabling the degreasing roller to remove oil from the diaphragm through negative pressure adsorption.

[0013] Furthermore, the sleeve is made of non-woven fabric; the micropores are evenly distributed.

[0014] Furthermore, each end of the degreasing roller is provided with a slide block; the slide block is rigidly connected to the shaft end of the roller core through a bearing to ensure synchronous movement at both ends.

[0015] Furthermore, each of the degreasing rollers is equipped with an independent lifting cylinder.

[0016] Furthermore, the number of preheating rollers in the preheating unit is 4 to 10, preferably 4 to 6; the number of preheating rollers in the upper row is equal to the number of preheating rollers in the lower row.

[0017] Furthermore, the diameter of the last preheating roller in the preheating unit is 210~230mm, for example, it can be 210mm, 215mm, 219mm, 220mm, 225mm, or 230mm; the diameter of the other preheating rollers is 390~410mm, for example, it can be 390mm, 395mm, 400mm, 405mm, or 410mm.

[0018] Furthermore, the last stretching roller in the stretching unit is a preheating roller, and it is equipped with an independent heating medium circulation pipeline and temperature control system to optimize the temperature field at the end of the stretching process.

[0019] Furthermore, the stretching rollers in the stretching unit are arranged in two rows, one above the other; the stretching rollers in the upper row and the stretching rollers in the lower row are staggered in the vertical direction.

[0020] Furthermore, the number of stretching rollers in the stretching unit is 5 to 11, preferably 5 to 9; the number of upper row stretching rollers is greater than the number of lower row stretching rollers, preferably, the difference between the number of upper row stretching rollers and the number of lower row stretching rollers is 1.

[0021] Furthermore, each of the stretching rollers in the upper row is equipped with an independent lifting cylinder.

[0022] Furthermore, the number of cooling rollers in the cooling unit is 2 to 8, preferably 2 to 6; the number of upper and lower cooling rollers is equal.

[0023] Furthermore, the diameter of the first cooling roller of the cooling unit is 210~230mm, for example, it can be 210mm, 215mm, 219mm, 220mm, 225mm, or 230mm; the diameter of the other cooling rollers is 390~410mm, for example, it can be 390mm, 395mm, 400mm, 405mm, or 410mm.

[0024] Furthermore, it also includes a speed detection unit, which is located on the inlet and outlet sides of the stretching unit and is electrically connected to the PLC control system.

[0025] Furthermore, the stretching roller is provided with a pressure roller that contacts it; the pressing angle between the pressure roller and the stretching roller is 18°~22°.

[0026] The beneficial effects of this invention are: This invention effectively improves the stretching ratio by adding an oil removal device, adjusting the angle of the pressure rollers, and optimizing the roller group layout. Thus, without replacing the entire production line, it comprehensively improves the puncture strength, thickness consistency, and product yield of the diaphragm, and has good application value. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of the oil removal roller of the present invention.

[0029] Among them, 1-sleeve; 2-air hole; 3-roller core; 4-stop block; 5-retaining ring; 6-bearing; 7-slide seat; 8-rotary joint; oil removal roller; 9-synchronous gear; 10-speed detection unit; 11-oil removal roller; 12-pressure roller. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 and 2 As shown.

[0032] A wet-process lithium battery separator asynchronous stretching production line MDO structure includes a preheating unit, a stretching unit, and a cooling and shaping unit arranged sequentially along the separator direction.

[0033] The preheating unit is equipped with multiple preheating rollers: L2-L7. These preheating rollers are arranged in an alternating pattern. Each preheating roller is equipped with a corresponding pressure roller 12 to ensure stable diaphragm operation. Preferably, the diameter of the last preheating roller L7 is 210~230mm, preferably 219mm, which is smaller than the diameter of the other preheating rollers (390~410mm, preferably 400mm). This allows it to match the diameter of the stretching zone rollers for a smooth tension transition, increases the wrap angle to enhance clamping force, and creates conditions for increasing the diaphragm stretch ratio. Simultaneously, a guide roller L1 is provided in front of the first preheating roller L2. This guide roller L1 has a tension detection function.

[0034] The stretching unit is equipped with multiple stretching rollers: L8-L14. These rollers are arranged in two rows, with the upper row staggered vertically from the lower row. Each upper row roller is equipped with an independent lifting cylinder. Each lifting cylinder has an independent air path branch pipe, solenoid valve, and pressure regulating valve, controlled separately by different control valves. This allows for independent lifting and lowering adjustment of the upper row rollers, facilitating position adjustment during film threading or maintenance.

[0035] Each of the stretching rollers is equipped with a pressure roller 12, and the pressing angle between the pressure roller and the stretching roller is 20° to ensure that the diaphragm is fully in contact with the stretching roller.

[0036] The stretching unit has an oil removal roller 11 that cooperates with the stretching roller. In this embodiment, due to the position limitation of the first stretching roller L8, an oil removal roller is not provided on L8.

[0037] The degreasing roller 11 includes a roller core 3 and a sleeve 1. The roller core 3 is a hollow, closed structure with multiple through-hole-shaped air holes 2 on its circumferential sidewalls. One end of the core is connected to a vacuum pump via a rotary joint 8 and a pipeline, allowing a negative pressure environment of -30 to -60 kPa to be created inside. Preferably, the roller core 3 is made of 304 stainless steel with a wall thickness of 30 mm. The air holes 2 are circular through holes with a diameter of 1.5 mm, arranged in an equilateral triangle staggered pattern with a center distance of 4 mm, achieving an open area ratio of approximately 13%.

[0038] The sleeve 1 is a cylindrical shape with open ends, its length being approximately equal to that of the roller core 3, and its sidewalls are provided with multiple micro-holes. The sleeve 1 is fitted onto the roller core 3, and each end is provided with a retaining ring 5. The retaining ring 5 is detachably connected to the roller core 3 via a stop block 4 to secure and seal the sleeve 1. Preferably, the sleeve 1 is made of a nonwoven fabric blended with nylon and special fibers, ensuring that the micro-holes are evenly distributed.

[0039] When the degreasing roller 11 is pressed against the surface of the stretching roller, it scrapes off the oil from the roller surface and the diaphragm surface by extrusion. Simultaneously, utilizing the negative pressure environment inside the roller core, an adsorption force is generated through the micropores on the sleeve surface, efficiently drawing the scraped oil and volatiles into the roller core and guiding them for collection. Preferably, the relative pressure between the degreasing roller and the steel roller surface is controlled at 0.2–0.5 MPa.

[0040] Each of the oil removal rollers is equipped with an independent lifting cylinder for vertical movement control. Additionally, one end of the roller core 3 is equipped with a synchronous gear 9 for driving its rotation.

[0041] The oil removal roller 11 is provided with slide blocks 7 at both ends. The slide blocks 7 are rigidly connected to the shaft end of the roller core through bearings to ensure synchronous movement at both ends.

[0042] Furthermore, the last stretching roller L14 of the stretching unit is a preheating roller, equipped with an independent heating medium circulation pipeline and temperature control system, and a temperature sensor is set on the roller surface to achieve closed-loop regulation in order to optimize the temperature field at the end of the stretching process.

[0043] Furthermore, in the stretching unit, each cylinder cooperating with the pressure rollers is equipped with an independent solenoid valve and pressure regulating valve, and the timing linkage is realized through a PLC control system: during film threading, the operation follows the sequence of "pressure roller disengagement → degreasing roller disengagement → lifting cylinder retraction", with each step signal interlocked; during production, the system resets in the sequence of "lifting cylinder extension → pressure roller pressing → degreasing roller pressing". The pneumatic control box integrates all solenoid valves, pressure regulating valves, and pressure gauges, and each circuit is independently adjustable.

[0044] The cooling and shaping unit includes multiple cooling rollers: L15-L18. These cooling rollers are arranged in two staggered rows, each equipped with a corresponding pressure roller. The first cooling roller, L15, has a diameter of 210-230 mm, preferably 219 mm, which is smaller than the diameters of the other cooling rollers (390-410 mm, preferably 400 mm). This allows it to match the diameter of the stretching zone rollers for a smooth tension transition, increases the wrap angle to enhance clamping force, and creates conditions for increasing the stretch ratio of the diaphragm. Simultaneously, a guide roller L19 is located behind the last cooling roller L18. This guide roller L19 has a tension detection function.

[0045] The stretching unit is equipped with speed detection units 10 at both the inlet and outlet sides to detect the moving speed of the diaphragm. Simultaneously, the signal lines of these speed detection units 10 are connected to the PLC control system along with the roller speed encoders of each stretching roller to compare the film surface speed with the roller surface linear speed in real time. When the deviation exceeds a set threshold, the system automatically alarms, allowing operators to adjust process parameters or check equipment status promptly. Preferably, the speed detection unit is a laser Doppler velocimeter with a speed measurement range of 1.8 m / min to 3000 m / min and a measurement accuracy of ±0.05% of the reading.

[0046] This invention successfully achieved high-rate stretching of MDO by comprehensively employing technical means such as roller diameter modification, functional redefinition, roller group layout optimization, pressure roller angle optimization, addition of oil removal device, and air control system upgrade, thus solving the key equipment bottleneck that restricts the improvement of wet-process lithium battery separator quality.

[0047] Actual production verification showed that the maximum allowable stretch ratio for stable operation of the modified MDO increased from the original 9.2-9.5 times to 10-12 times, and the actual ratio remained consistent with the set ratio, resulting in a 20% increase in the puncture strength of the prepared diaphragm. Regarding thickness uniformity, an online thickness tester (such as the SKEND HF3-4500-C) was used before winding to test the diaphragm thickness uniformity. Thickness data from one cycle along the TD direction (transverse) of the membrane, from left to right and from right to left, were collected as a set. The average thickness was measured, and the standard deviation of the diaphragm thickness was calculated using five sets of data. The standard deviation of the transverse thickness was reduced from twice the original 0.2-0.3 to approximately 0.15. Data on wavy edges caused by localized thickness unevenness was improved by 30% (wavy edge data measured immediately after diaphragm winding), and aging data was improved by 50% (wavy edge data measured 10 hours after diaphragm winding), significantly improving the diaphragm production yield.

[0048] The wavy edge test method is as follows: Cut a 2m long diaphragm sample and place it at the designated position on the flatness tester (Shenzhen Jingneng Precision Equipment Co., Ltd., JN-ZLJ-B2000-V30.2). Start the instrument to begin automatic edge-finding testing. The laser starts from the left side of the membrane, moves to the right end, and positions itself as the endpoint. At this point, the screen displays the diaphragm width, and the laser returns. After the laser returns to the starting point, the actual wavy edge is measured. As the measurement progresses, the screen displays the real-time status of the membrane surface undulation. After the test, the laser returns to zero. Based on the test diagram, read the values ​​at the left, center, and right positions on the diagram to calculate the wavy edge. Edge value: The height difference of the edge diaphragm (the vertical distance between the lowest point of the edge and the highest point of the whole).

[0049] The puncture strength test method is as follows: The test was conducted according to the method specified in GB / T 36363-2018. A diaphragm with a size of 50*100mm was cut along the TD direction. The diaphragm was fixed on the sample fixture of the puncture test machine (model: KES-GNDG5, KNC Technology Co., Ltd.). A steel needle with a diameter of 1.0 mm was used to puncture the diaphragm at a speed of 0.1cm / sec. The maximum load of the steel needle penetrating the diaphragm was read. The test was performed more than 5 times and the arithmetic mean was taken.

[0050] All parts not covered in this invention are the same as or can be implemented using existing technologies.

Claims

1. A wet-process lithium battery separator asynchronous stretching production line MDO structure, comprising a preheating unit, a stretching unit, and a cooling and shaping unit arranged sequentially along the separator direction; the preheating unit is provided with a plurality of preheating rollers arranged sequentially; the stretching unit is provided with a plurality of stretching rollers arranged sequentially; the cooling and shaping unit is provided with a plurality of cooling rollers arranged sequentially; characterized in that, The stretching unit has a matching oil removal roller on the stretching roller; the oil removal roller is pressed against the surface of the stretching roller and can remove the oil on the diaphragm by squeezing; the diameter of the last preheating roller in the preheating unit is smaller than the diameter of the other preheating rollers; the diameter of the first cooling roller in the cooling and shaping unit is smaller than the diameter of the other cooling rollers.

2. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, The oil removal roller includes a roller core and a sleeve. The roller core is a hollow, closed structure with multiple through-hole-shaped air holes on its circumferential sidewalls. One end of the roller core is connected to a vacuum pump via a rotary joint and a pipeline. The sleeve is a cylindrical shape with open ends, and its length is approximately the same as that of the roller core. It has multiple micro-holes on its sidewalls. The sleeve is fitted onto the roller core, and retaining rings are provided at both ends. The retaining rings are detachably connected to the roller core via a retaining block to fix and seal the sleeve. Thus, the oil removal roller can remove oil from the diaphragm through negative pressure adsorption.

3. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 2, characterized in that, The sleeve is made of non-woven fabric; the micropores are evenly distributed.

4. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 2, characterized in that, The oil removal roller is provided with slide blocks at both ends; the slide blocks are rigidly connected to the shaft end of the roller core through bearings to ensure synchronous movement at both ends.

5. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, Each of the oil removal rollers is equipped with an independent lifting cylinder.

6. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, The last stretching roller in the stretching unit is a preheating roller, and it is equipped with an independent heating medium circulation pipeline and temperature control system to optimize the temperature field at the end of the stretching process.

7. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, The stretching rollers in the stretching unit are arranged in two rows, one above the other; the stretching rollers in the upper row and the stretching rollers in the lower row are staggered in the vertical direction.

8. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 7, characterized in that, The stretching rollers in the upper row are each equipped with an independent lifting cylinder.

9. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, It also includes a speed detection unit, which is located on the inlet and outlet sides of the stretching unit and is electrically connected to the PLC control system.

10. The MDO structure of the wet-process lithium battery separator asynchronous stretching production line according to claim 1, characterized in that, The stretching roller is provided with a pressure roller that contacts it; the pressing inclination angle between the pressure roller and the stretching roller is 18°~22°.

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