CN111933869A - Membrane preparation method based on oil content feedback process - Google Patents
Membrane preparation method based on oil content feedback process Download PDFInfo
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- CN111933869A CN111933869A CN202011087551.8A CN202011087551A CN111933869A CN 111933869 A CN111933869 A CN 111933869A CN 202011087551 A CN202011087551 A CN 202011087551A CN 111933869 A CN111933869 A CN 111933869A
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
A membrane preparation method based on an oil content feedback process comprises the steps of mixing and heating polyethylene, paraffin oil, silica nanoparticles and 4, 4' -thiobis (6-tert-butyl-m-cresol) in batches, extruding and molding, stretching transversely and longitudinally respectively, and then stretching in two dimensions. And after the stretching is finished, the film is sent into an oil content analysis device, and the oil removal device is optimally controlled according to the distribution condition of oil stains on the oil absorption material, so that the lithium battery diaphragm with low oil content is finally prepared.
Description
Technical Field
The invention relates to the technical field of lithium battery diaphragms and preparation thereof.
Background
The diaphragm is an important component in the lithium battery, and directly determines the service performance and safety of the lithium battery. Typically the separator is an insulating material having a porous structure. In the case of a separator, it is generally necessary to ensure a certain porosity and pore size so that ions can smoothly migrate. Too high results in a decrease in the strength of the separator, and too low results in an increase in the internal resistance. The uniformity of the film also affects the electrolyte wetting of the film, thereby affecting the internal resistance of the cell. Moreover, in abnormal situations, an excessive current will cause the temperature to rise to T1, closing the membrane opening, stopping ion migration and avoiding further danger. But if the temperature is raised too high to T2, it also causes the membrane to rupture, thereby damaging the cell. Only by appropriately lowering the temperature T1, the temperature T2 can be raised to make the battery safer to use. Therefore, for the lithium battery diaphragm, the parameters affect the safety and performance of the subsequent battery during use.
At present, the above problems are solved by adopting a more complex process mode in the industry, for example, a PE diaphragm is bombarded by gamma rays and reacts with polar methoxy polyethylene oxide acrylate to form a film; or mixing Al2O3And the nano ceramic particles are uniformly coated on the surface of the PE diaphragm to form a film and the like. Although the existing various modes solve the problems to a certain extent, the effect is limited, the cost is high, a new process needs to be introduced, and the process maturity is yet to be improved.
The industry mostly performs one-by-one optimization of single parameters to achieve security and improve performance. The membrane thickness is detected, for example, with an optical device. However, this is time consuming and laborious and the multi-parameter crossover is difficult to control. Meanwhile, the consistency of comprehensive performance of all parameters is not realized, and the significance on the safety and the performance improvement of the battery is achieved.
However, if a method capable of comprehensively representing each parameter is selected for process control, the control precision requirement of the process is high, and how to realize the process control of the composite parameter by using a simple method is not mentioned in the prior art.
In addition, grease or other solvents are inevitably used in the preparation process of the film, although extraction is carried out in the process, a small amount of residue still can be left, and whether the grease is extracted cleanly or not has great influence on the performance parameters of the film. If the grease is not extracted completely, the porosity and air permeability of the diaphragm are directly influenced, and the internal resistance, the cyclicity and the like of the battery are further influenced. The existing oil content detection method is usually a destructive test, is complex to operate, cannot be applied to online feedback of a production line, cannot be directly applied to an optimized production process, and can only be used as a detection result of a final product.
Therefore, a method for preparing a lithium battery diaphragm by fully utilizing the existing process method and efficiently realizing better safety and better electrical property of the battery on the basis of optimizing the preparation process is urgently needed.
Disclosure of Invention
In view of the above problems, the present invention has been made to provide a lithium battery separator and a method for preparing the same, which overcome or at least partially solve the above problems.
Membrane preparation method based on oil content feedback process
The raw material A is polyethylene and comprises the following two parts
A1: polyethylene particles having a molecular weight of 6.5X 106 to 8.5X 106;
a2: polyethylene pellets having a density of 0.966 to 0.983g/cm 3;
the raw material B is paraffin oil; the raw material C is silicon dioxide nano particles with the diameter of 20-30 nm; the raw material D is 4, 4' -thiobis (6-tert-butyl-m-cresol);
step 1: heating and mixing the raw materials in the step 4 in batches;
step 2: and injecting the mixed slurry into an extruder to extrude the mixed slurry into a thick film.
And step 3: sequentially carrying out longitudinal stretching and transverse stretching on the thick film at a stretching ratio of 6-7 to obtain a thin film, and extracting after the stretching is finished;
and 4, step 4: the film is conveyed to a two-dimensional stretching device, light transmittance abnormal points on the film are obtained, and a stretching area is determined according to the distribution of the abnormal points;
and 5: correspondingly controlling a two-dimensional stretching device to perform a film two-dimensional stretching process according to the determined stretching area;
step 6: the film delivery roller conveys the film forward so that it passes through the oil absorbing embossing area and is finally transported from this area to the next equipment; simultaneously, the oil absorption imprinting material conveying roller synchronously conveys the oil absorption imprinting material to an oil absorption imprinting area, and the oil absorption imprinting material conveying roller is positioned above the thin film in parallel in the area and is in contact with the thin film;
and 7: when the film and the oil absorption imprinting material are conveyed between the press rollers positioned in the oil absorption imprinting area, the film and the oil absorption imprinting material are in sufficient contact under the extrusion of the press rollers, so that the oil of the film is separated out under the action of external force, the oil is absorbed by the oil absorption imprinting material, and oil stains are left on the surface of the oil absorption imprinting material.
And 8: the oil absorption imprinting material conveying roller continuously conveys the oil absorption imprinting material stained with oil stains upwards to enable the oil absorption imprinting material to be vertically arranged, and the oil absorption surface faces the camera;
and step 9: and the camera synchronously acquires an image of the lattice-shaped oil stain pattern on the oil absorption surface of the vertical area of the oil absorption imprinting material.
Step 10: and comparing the oil stain patterns with different oil contents tested and stored in a database in advance, analyzing the thickness and the color depth of each grid in the grid-shaped oil stain patterns, and judging the oil content in the current film.
Step 11: and adjusting the oil removing process according to the oil content analysis result.
The oil-absorbing imprinting material is of a composite structure and comprises a plane substrate and grid-shaped protrusions positioned on the substrate. Thus, under the external force extrusion, the grid-shaped protrusions can adsorb more grease, so that an obvious grease stain pattern is formed.
The oil removal process includes extraction in an extraction tank.
The oil removing process comprises the step of removing oil through a squeezing roller in an oil removing device.
A membrane based on an oil content feedback process, prepared using the above method.
Invention and technical effects
1. The oil absorption material and the film are jointly extruded to form the oil absorption pattern, so that the oil content of the film can be conveniently and simply judged through image identification and judgment. And can accurately judge which region has abnormal oil content distribution. Therefore, the production process can be accurately optimized and improved by using the result, so that the film with low oil content can be conveniently and efficiently produced, and the performance of the product can be improved.
2. The preparation materials, the flow steps and the process parameters are optimized, the raw material for preparing the lithium battery diaphragm and the corresponding preparation method are provided, the opening can be closed when the temperature of the battery is abnormally increased, the mechanical strength of the film is high, the high temperature resistance and the low internal resistance are realized, the high-performance lithium battery diaphragm is prepared, the lithium battery diaphragm can be protected in time when the temperature of the battery is abnormal, and the lithium battery diaphragm is high in temperature resistance, low in resistance, high in safety and excellent in electrical performance.
3. The consistency of all parameters of the battery diaphragm is provided for the first time, so that the influence on the safety and the battery performance is large. The method comprehensively optimizes a plurality of parameters, utilizes the light transmittance capable of comprehensively representing a plurality of conventional diaphragm parameters as a consistency standard, and utilizes the light transmittance to control the manufacture of the diaphragm, thereby efficiently realizing the high-safety and high-performance diaphragm and being particularly suitable for large-batch actual production processes.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a flow chart of a process for making a separator
FIG. 2 is a top view of a two-dimensional stretching process of a separator
FIG. 3 is a rear view of a two-dimensional stretching process of a separator
FIG. 4 is a front view of a process for stretching a separator in two dimensions
FIG. 5 is a schematic diagram of a two-dimensional stretching process of a separator
FIG. 6 is a schematic diagram of oil content detection
Fig. 7 is a schematic view of the structure of the oil absorbing material.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
Diaphragm preparation method
The feedstock a is polyethylene, and in particular, may comprise the following two fractions, and the preferred weight ratio of the two is 1:1.53, according to a number of experiments.
A1: molecular weight 6.5X 106-8.5×106The polyethylene particles of (a);
a2: the density is 0.966-0.983g/cm3The polyethylene particles of (a);
the raw material B is paraffin oil; the raw material C is silicon dioxide nano particles with the diameter of 20-30 nm; the raw material D is 4, 4' -thiobis (6-tert-butyl-m-cresol);
wherein the weight ratio of the raw material A to the raw material B is 27: 43, the weight ratio of the raw material C to the raw material A is 1.3: 100, the weight ratio of the raw material D to the raw material A is 0.7: 100.
step 1: mixing the raw material A1, the raw material D and half of the raw material B by weight, heating to 70-110 ℃, stirring for 25 minutes, and keeping the stirring speed at 340 r/min.
Step 2: adding the raw material A2 and the other half of the raw material B by weight into the stirred material in the step 1, mixing, heating to 90-130 ℃, stirring for 5 minutes, and keeping the stirring speed at 340 r/min.
And step 3: and (3) adding the raw material C into the stirred material obtained in the step (2), keeping the temperature at 140-170 ℃, stirring for 30 minutes, and increasing the stirring speed to 520 r/min to finally obtain the slurry.
And 4, step 4: and injecting the mixed slurry into an extruder for extrusion, and keeping the temperature of the extruder at 170-230 ℃ and the extrusion rate at 1100 g/min.
And 5: cooling and solidifying the extrudate on a cooling roller to form a thick film with the thickness of 400-2500 μm, wherein the cooling temperature is 20-70 ℃, and solid-liquid phase separation or liquid-liquid phase separation occurs in the cooling and solidifying process, so that a microporous structure is formed in the extrudate.
Step 6: setting the temperature of a preheating roller, a longitudinal stretching roller and a cooling roller to be 90 ℃, 120 ℃ and 20 ℃, and longitudinally stretching the thick film through the preheating roller, the longitudinal stretching roller and the cooling roller in sequence to obtain a semi-thick film with the extension ratio of 6-7;
and 7: setting the temperature of a preheating roller, the temperature of a transverse stretching roller and the temperature of a cooling roller to be 100 ℃, 125 ℃ and 90 ℃, and carrying out transverse stretching on the semi-thick film through the preheating roller, the transverse stretching roller and the cooling roller in sequence to obtain a film with the elongation ratio of 6-7;
and 8: and (3) conveying the film into a dichloromethane extraction box for extraction, wherein the temperature in the extraction box is 20-35 ℃, and the extraction time is 4 hours. Drying after extraction;
and step 9: the film is conveyed to a two-dimensional stretching device for fine adjustment stretching in the transverse and longitudinal directions, and the stretching temperature is kept at 130-150 ℃. Meanwhile, the light transmittance distribution of the film is monitored in the stretching process, so that the force of the stretching device at different stretching positions is controlled, the light transmittance consistency of the film at different positions is adjusted, and the film with better consistency is finally obtained.
Step 10: and cooling to form the film after the two-dimensional stretching is finished.
Step 11: and (5) testing parameters such as thickness, cleanliness, strength, wettability, air permeability and the like by using detection equipment.
The diaphragm prepared according to the raw material proportion and the process can timely close the open pore when the temperature of the battery is abnormally increased, and can be kept at a higher temperature without the problem of membrane rupture. Meanwhile, the internal resistance is low, and the stability is good.
Wherein thick film is understood in the art to mean a thicker film formed from the paste extruded in the extruder; the semi-thick film is a film with reduced thickness after being stretched in one direction; the film is a film with the thickness close to that of a final finished product after the two-direction stretching process.
In step 3, the mixture may be directly heated to the desired temperature as described above. In particular, however, the heating in step 3 may be performed by alternating heating-holding-heating to give sufficient contact reaction time for each material to obtain better film properties. Specifically, the heating in step 3 may be performed according to the following formula:
T= a*(sin(t)+b*t2)+X
where T is the heating temperature, T is the time, a, b are empirical coefficients, preferably a =5, b =0.1, and X is the temperature in step 2, typically 90-130 ℃. Where T is in units of deg.C, T is in units of minutes and X is in units of deg.C.
In this case, it is necessary to maintain the temperature and stir the mixture after the heating temperature T reaches the temperature required in step 3.
Two-dimensional stretching process in diaphragm manufacturing
In the stretching process, only the thickness of the film is generally monitored to ensure thickness consistency and thus improve the performance of the film. In practice, a number of parameters of the film affect its performance. For example: porosity, pore size, film density, breathability, etc. These properties are usually measured only after the film has been produced, using a number of different devices, to determine whether the film is acceptable. First, doing so requires more equipment; secondly, the detection is post detection, and the produced inferior products cannot be avoided.
The invention provides the detection of the film parameters in the film stretching process and controls the stretching action at the same time, thereby ensuring that the film with higher quality is stretched. However, if a plurality of devices are used for parameter detection, the devices are abnormally complicated, and it is difficult for the control algorithm to balance a plurality of parameters. However, it has been found that, over many years, the above-mentioned non-uniformities in various parameters are ultimately reflected in non-uniformities in the light transmission of the film. Therefore, in order to rapidly control the stretching device in production practice, the invention proposes to use the light transmittance to perform the control of the film stretching, thereby comprehensively controlling the above parameters and obtaining a higher quality diaphragm. Therefore, this is also one of the points of the present invention, and the process thereof will be set forth in detail below.
The two-dimensional stretching equipment comprises a left moving roller 1, a right moving roller 2, an upper left clamping roller 3-1, a lower left clamping roller 3-2, an upper right clamping roller 4-1, a lower right clamping roller 4-2, a rear side edge clamping part 5-1, a rear side edge lower clamping part 5-2, a front side edge clamping part 6-1, a front side edge lower clamping part 6-2, a rear side edge driving part 5-3, a front side edge driving part 6-3, a camera 7 and a surface light source 8.
The left moving roller 1 and the right moving roller 2 are respectively positioned at two ends of the device and used for transmitting the film M, and are simultaneously used for generating left or right pulling force on the film M positioned on the left moving roller and the right moving roller when the film M is respectively translated leftwards or rightwards, and when the other end of the film M is relatively fixed, the longitudinal stretching of the diaphragm is realized.
The upper left clamping roller 3-1 and the lower left clamping roller 3-2 are arranged oppositely up and down and used for clamping the left side of the film M. Wherein the left lower clamping roller 3-2 is fixedly arranged, and the left upper clamping roller 3-1 can move up and down. The upper left pinch roller 3-1 moves downward when the pinching is required, thereby forming the pinching of the left side edge of the film M with the lower left pinch roller 3-2. The upper left clamping roller 3-1 is a plurality of short rollers which can move up and down independently, and the up-and-down movement distance is accurate and controllable. The lower left pinch roll 3-2 is a long roll.
The upper right clamping roller 4-1 and the lower right clamping roller 4-2 are arranged oppositely up and down and used for clamping the right side of the film M. Wherein the right lower clamping roller 4-2 is fixedly arranged, and the right upper clamping roller 4-1 can move up and down. The upper right pinch roller 4-1 moves downward when the pinching is required, thereby forming the pinching of the right side edge of the film M with the lower right pinch roller 4-2. The upper right pinch roll 4-1 is a single long roll, the distance of which up and down moves is precisely controllable. The lower right pinch roll 4-2 is a long roll.
When the upper left pinch roller 3-1 at different positions moves downward by different distances, different intervals are formed at different positions from the lower left pinch roller 3-2, thereby generating different pinching forces to the film M at the corresponding positions. At this time, if the right moving roller 2 moves rightwards, the film M is driven to move rightwards, and at this time, the clamping forces at different positions on the left side of the film M are different, so that for the driving force fixed by the right moving roller 2, the stretching degrees of the longitudinal strip regions of the film M at different positions in the transverse direction are different, and thus different stretching ratios can be generated for the longitudinal strip regions at different positions. Therefore, by controlling the different pitches formed by the upper left pinch roller 3-1 and the lower left pinch roller 3-2 at different positions, the draw ratio of the corresponding sliver region can be controlled. For more precise control, a denser, greater number of upper left pinch rollers may be provided, typically 10, but for higher control resolution, 20-30 may be provided.
When the upper right pinch roller 4-1 moves downwards to form a pinch on the right side edge of the film M together with the lower right pinch roller 4-2, if the left moving roller 1 moves leftwards, the film M is driven to move leftwards, and the film M is uniformly and longitudinally stretched.
Each back side edge clamping part 5-1 and each back side edge lower clamping part 5-2 are arranged oppositely up and down to form a back side edge clamping part together. A plurality of which are arranged along the rear side of the film M for clamping the rear side of the film M. The front side edge clamping part 6-1 and the front side edge lower clamping part 6-2 are arranged oppositely up and down and are a section of a whole, and the front side edge clamping part and the front side edge lower clamping part jointly form a front side edge clamping part used for clamping the front side edge of the film M. The main bodies of the rear side edge clamping part 5-1, the rear side edge lower clamping part 5-2, the front side edge clamping part 6-1 and the front side edge lower clamping part 6-2 are all made of rubber, and the film is prevented from being damaged during clamping. Meanwhile, the rubber is doped with fine iron particles during molding, thereby enhancing the strength of the rubber on the one hand and simultaneously being used for being attracted by the driving part.
The rear side driving part 5-3 is composed of electromagnets and is positioned at the rear side of the rear side edge clamping part 5-1 and the rear side edge lower clamping part 5-2, and the number of the rear side driving parts 5-3 is also a plurality and respectively corresponds to the rear side edge clamping parts which are arranged. The transverse strip-shaped area is used for attracting the corresponding rear side clamping part after being electrified, so that the transverse strip-shaped area corresponding to the position of the film clamped by the rear side clamping part is stretched. Therefore, by controlling the current magnitude of the different rear side driving portions 5-3, the backward stretching force of the rear side clamping portions corresponding to different positions can be controlled, thereby controlling the stretching ratio of the transverse strip-shaped area corresponding to the film. Of course, the front side holding part should fixedly hold the front side of the film while controlling the rear side driving part 5-3 to stretch.
The front side driving portion 6-3 is composed of electromagnets and is located on the front side of the front side clamping portion 6-1 and the front side of the front side lower clamping portion 6-2, and a plurality of rear side driving portions 6-3 are evenly distributed on the front side of the front side clamping portion and used for attracting the corresponding front side clamping portion after being electrified, so that the film clamped by the front side clamping portion is stretched. Although the front side upper holding part 6-1 and the front side lower holding part 6-2 are both single, the main body thereof is made of rubber, and has a certain flexibility. Therefore, by controlling the current of a certain front side driving portion 6-3, the relatively largest pulling force can be generated at the position of the front side clamping portion directly opposite to the front side driving portion 6-3, and the next largest pulling force can be generated at the position adjacent to the position of the front side clamping portion directly opposite to the front side driving portion 6-3. That is, even if only one of the front side driving portions 6-3 is energized, the entire front side of the film can be stretched, but the position corresponding to the front side driving portion 6-3 is stretched most, and the other positions are successively decreased in accordance with the stretch ratio at a distance therefrom. However, since the entire front-side holding portion is an integral whole along the front side of the film, the variation in the stretch ratio at such different positions is actually very small. Therefore, it is very suitable for the case where the stretching ratio at a certain position needs to be finely adjusted. Therefore, the method does not cause drastic change of consistency with an adjacent area due to control of micro stretching of a certain area, thereby ensuring accuracy and high efficiency of process control, and is also one of the invention points. Of course, in the two-dimensional stretching apparatus, only a fine stretching operation is performed, defects at individual positions are adjusted, and a large stretching ratio operation is not performed.
A surface light source 8 is provided above the film, and a plurality of surface light sources 8 may be provided since the film may be large. However, if the multi-surface light source combination is carried out, the light intensity of any position of the film is the same. The surface light source 8 is used to provide uniform illumination to the film.
The camera 7 is arranged below the film, and the film can be large and the field of view of the camera is limited, so that a plurality of cameras 7 can be arranged to splice the field of view. The camera 7 is for emitting light transmitted through the film from the light source 8 on the receiving surface, and taking an image of the film.
The obtained image is sent to a processor to carry out the following operations:
(1) each pixel point in the image is positionally mapped to an actual point on the film.
(2) Obtaining the gray value P of each pixel point in the imagei。
(3) Determining the mean gray-scale value P of the image0。
(4) If Pi-P0|/ P0>Q, then P isiThe corresponding film position point is marked as an abnormal point, wherein Q is a set threshold range, and can be selected according to the level of the requirement on the film consistency, and in order to take account of speed and precision, the Q value can be initially set to be small, for example, 0.01, so that a large number of abnormal points appear, but in this case, the inconsistency of many abnormal points is not unacceptable in practice. Further accurate screening is therefore required.
(5) Abandoning the isolated abnormal points, selecting the area with concentrated abnormal points, controlling the area light source 8 corresponding to the area to weaken the light intensity to 30% of the standard light intensity, recalculating the gray value of each pixel and the average gray value, and re-marking the abnormal points according to the relationship between the gray value and the average gray value. Thus, areas where the transmission is below normal will decay more rapidly and more severely, and will therefore be marked significantly. And controlling the area light source 8 corresponding to the area to improve the light intensity to 250% of the standard light intensity again, recalculating the gray value and the average gray value of each pixel, and re-marking the abnormal points according to the relationship between the gray value and the average gray value. Thus, areas with higher than normal transmission will have a faster and more severe gray scale value rise and will therefore also be marked clearly. Thus, the outlier can be redetermined. Through this kind of mode, can accurate screening anomaly to can avoid excessive and unnecessary tensile operation, practice thrift the production time, improve the film forming ability.
(6) And determining the distribution area of the newly determined abnormal points, and selecting a rectangular frame with the smallest area to cover the abnormal points, wherein the rectangular frame is used as an area to be stretched in two dimensions and is called a stretching area. Individual outliers that are isolated can be discarded from consideration.
The control method for longitudinal stretching and transverse stretching comprises the following steps:
firstly, when the stretching areas are uniformly distributed at all positions of the film, the upper right clamping roller 4-1 and the lower right clamping roller 4-2 are controlled to approach to clamp the right side of the film, and the left moving roller 1 moves leftwards.
When the stretching areas are distributed in a longitudinal strip shape, controlling the upper left clamping roller 3-1 at the corresponding position to gradually approach the lower left clamping roller 3-2, and generating the maximum clamping force on the position of the film with the minimum distance; the left upper nip roll 3-1 in the remaining positions is also close to the left lower nip roll 3-2, but at a larger pitch, producing less or even no nip force for that position of the film. And controlling the right moving roller 2 to translate to the right, so that the area corresponding to the maximum clamping force is intensively longitudinally stretched, and the rest area is slightly stretched or even not longitudinally stretched.
Thirdly, when the stretching areas are distributed in a transverse strip shape,
if the abnormal condition in the area is serious, inputting large current to the rear side driving part 5-3 at the corresponding position so as to generate large pulling force; and the rear side driving part 5-3 at the other positions inputs small current, thereby generating small tension even without generating tension. Such that the respective regions are laterally stretched and the remaining regions are slightly or not laterally stretched. At this time, the front side edge holding portion holds the side edge of the film as a whole.
If there is only a slight abnormal condition in the area, the difference from the peripheral light transmission condition is small. A large current is inputted to the front side driving part 6-3 at the corresponding position, so that a large tensile force is generated and the region corresponding to the position is laterally stretched. However, since the front side edge holding portion 6-1 and the front side edge lower holding portion 6-2 are single, a transverse tension is generated in other positions in the longitudinal direction of the film. But because the main body of the front side clamping part is made of rubber, the front side clamping part has certain flexibility. Therefore, the transverse tension generated at other positions is not greatly different from the transverse tension generated at the abnormal position. Thereby it is avoided that a certain position is stretched in the transverse direction, resulting in excessive stretching. At this time, the rear side edge holding portion holds the side edge of the film as a whole.
Through the raw material proportion and the preparation process, the T1 temperature of the finally obtained film is 100 ℃, the T2 temperature is 220 ℃, and the safety of the battery can be effectively ensured. Meanwhile, the thickness error is not more than 0.01 percent because the thickness of the film is 23 mu m; the uniformity of parameters such as the size, porosity, pore distribution and wettability of the film openingPreferably, the sheet resistance is less than 0.41. omega. cm2When assembled into a lithium battery, the internal resistance is 20.4% lower than that of the conventional film.
Those skilled in the art will appreciate that the above stretching process is best suited for use in conjunction with the preparation of the films proposed by the present invention. This does not mean that the stretching process cannot be used for the manufacture of other films. The conventional lithium battery separator may be manufactured using the above-described stretching process.
Oil content optimization process
The paraffin oil is used in the preparation process of the film, and the paraffin oil is extracted by dichloromethane subsequently, but the paraffin oil is extracted cleanly, so that the performance parameters of the film are greatly influenced. If the grease is not extracted completely, the porosity and air permeability of the diaphragm are directly influenced, and the internal resistance, the cyclicity and the like of the battery are further influenced. In the prior art, chemical extraction is adopted to prolong the extraction time or extract for multiple times, but the time and the economic cost are increased. Therefore, the method is particularly important for measuring the oil content of the film.
In the prior art, a part of a sample is intercepted, and the oil content of the sample is tested by using a chemical reagent or an evaporation mode. However, this method is only suitable for the later test, and the sample cannot be intercepted on the production line, which may cause damage to the whole film. And the later-stage test result can only be used for judging whether the film is qualified or not, and the production process cannot be controlled on line in real time according to the result.
The invention provides an online oil content testing method applicable to a production line, which comprises the following steps:
the film conveying device comprises a film conveying roller 11-1, a film conveying device and a film conveying device, wherein the film conveying roller comprises a left roller and a right roller and is used for conveying a film M to an oil absorption stamping area; the oil-absorbing imprinting material 11-4 is used for separating out oil in the film under the action of external force and forming oil stains on the surface of the material; the oil absorption imprinting material conveying roller 11-2 is used for conveying the oil absorption imprinting material 11-4 to the position above the film in the oil absorption imprinting area; the pressing rollers 11-3 are arranged in the oil absorption pressing area and are divided into an upper row and a lower row, each row is provided with a plurality of rollers and is positioned on the outer sides of the oil absorption pressing material 11-4 and the thin film M, when the upper row and the lower row of pressing rollers rotate and extrude, the oil absorption pressing material 11-4 is fully contacted with the thin film M, oil in the thin film M is separated out, and oil stains are printed on the oil absorption pressing material 11-4; the oil-absorbing imprinting material conveying roller 11-2 further comprises a roller positioned on the upper side and used for vertically conveying the oil-absorbing imprinting material 11-4 subjected to oil-absorbing imprinting upwards, and the oil-absorbing surface of the oil-absorbing imprinting material 11-4 is vertically exposed; and the camera 11-5 is used for acquiring an image of the oil absorption side of the exposed oil absorption imprinting material 11-4, comparing the acquired image with a standard image in a database, and analyzing the oil content in the film.
In general, the oil-absorbing material is a planar sheet structure, but in order to enable the judgment of the oil content with higher resolution, the oil-absorbing imprint material 11-4 of the present invention adopts a composite structure comprising a planar base 11-4-1 and lattice-like projections 11-4-2 on the base. Thus, under the external force extrusion, the grid-shaped protrusions can adsorb more grease, so that an obvious grease stain pattern is formed. The general plane oil absorption material can form a planar oil stain and is not suitable for judging the oil content, and the lattice-shaped pattern of the oil stain can accurately judge the oil content according to the thickness and the color depth of a lattice line, so that the detection of a camera is more accurate and convenient. This is also one of the points of the present invention.
The operation is carried out according to the following steps:
(1) the film feed roller 11-1 conveys the film M forward so that the film passes through the oil-absorbing embossing area and is finally conveyed from the area to the next apparatus;
(2) meanwhile, the oil-absorbing imprinting material conveying roller 11-2 synchronously conveys the oil-absorbing imprinting material 11-4 to an oil-absorbing imprinting area, and the oil-absorbing imprinting material is positioned above the thin film in parallel and is in contact with the thin film in the area;
(3) when the film M and the oil-absorbing imprinting material 11-4 are conveyed to a position between the press rolls 11-3 in the oil-absorbing imprinting area, the film M and the oil-absorbing imprinting material are in sufficient contact with each other under the pressing of the press rolls, so that the oil of the film M is separated out under the action of external force and absorbed by the oil-absorbing imprinting material 11-4, and oil stains are left on the surface of the oil-absorbing imprinting material 11-4.
(4) The oil absorption impression material conveying roller 11-2 continuously conveys the oil absorption impression material 11-4 stained with oil stains upwards to enable the oil absorption impression material to be vertically arranged, and the oil absorption surface faces the camera 11-5;
(5) the camera synchronously acquires the image of the oil absorption surface of the vertical area of the oil absorption imprinting material 11-4. Since the oil-absorbing imprint material 11-4 has lattice-shaped protrusions 11-4-2 on the surface thereof, if oil is adsorbed, the oil is preferentially adsorbed on the protrusions, or more oil is adsorbed on the protrusions than on the base 11-4-2. Therefore, the collected image has a lattice-shaped oil stain pattern.
(6) And comparing the oil stain patterns with different oil contents tested and stored in a database in advance, analyzing the thickness and the color depth of each grid in the grid-shaped oil stain patterns, and judging the oil content in the current film.
(7) And adjusting the extraction time in the process according to the oil content analysis result, and controlling an action mechanism if the oil content is higher so as to soak the film in the extraction tank for a longer time. If the oil content is lower than the standard value, the action mechanism can be controlled, so that the film can pass through the extraction box more quickly. The above steps are realized by automatic analysis and control of the processor, manual intervention operation is not needed, and the method is more convenient and accurate.
Furthermore, in the step (6), in addition to obtaining the oil content of the whole film, according to the oil distribution in the oil pattern, the oil content distribution condition of the film can be determined, and according to the condition, the oil content can be fed back to the oil removing device, namely, the oil content is fully separated out by performing extrusion for a long time with a large extrusion force in an area with high oil content. The specific grease removing process comprises the following steps:
the oil removing device comprises a left film conveying roller and a right film conveying roller which are used for bearing the films and conveying the films through the oil removing device; the upper oil adsorption device and the lower oil adsorption device respectively comprise a left conveying roller, a right conveying roller and oil absorption materials, wherein the left conveying roller and the right conveying roller of each oil adsorption device are used for conveying the upper oil absorption material and the lower oil absorption material to the upper part and the lower part of the film respectively to generate contact adsorption, and the film M is clamped between the two oil absorption materials; the squeezing rollers comprise a plurality of rollers which are oppositely arranged up and down, are respectively arranged at the outer sides of the two oil absorption materials and are used for squeezing the two oil absorption materials inwards to enable the two oil absorption materials to be fully contacted with the film and generate certain mechanical squeezing force on the film. The oil in the film is transferred to the oil absorbing material under the double action of adsorption and extrusion.
The specific operation method comprises the following steps:
(1) the film conveying roller conveys the film from left to right, conveys the film to the extrusion roller and adsorbs grease after extrusion;
(2) meanwhile, the upper oil absorption device and the lower oil absorption device respectively convey the upper oil absorption material and the lower oil absorption material to the squeezing rollers through oil absorption material conveying rollers, and the upper oil absorption material and the lower oil absorption material are respectively positioned at the upper side and the lower side of the thin film;
(3) the squeezing rollers apply pressure to the upper oil absorption material and the lower oil absorption material, so that the upper oil absorption material and the lower oil absorption material are tightly attached to and squeeze the film M clamped in the middle, and therefore the grease in the film M is separated out and is absorbed by the oil absorption materials.
In order to realize the controllability of the grease removing operation, the extrusion rollers are respectively arranged on the upper surface and the lower surface of the film, and each surface of the extrusion rollers is provided with a plurality of extrusion rollers, and preferably, the adjacent two extrusion rollers have different diameters. Meanwhile, each extrusion roller on the upper surface is in a plurality of sections in the transverse direction of the film, and the extrusion force of each section can be independently controlled. The gap between each section of the upper transverse squeezing roller and the lower squeezing roller can be controlled as required, so that the squeezing degree of the film in different areas can be controlled, and the oil removing strength of different areas of the film can be realized.
By utilizing the oil content testing and process optimizing technology, the internal resistance of the lithium battery diaphragm is reduced by 6.1 percent.
Although the above process can ensure the uniformity of the film, the adsorption of impurities on the surface of the film is inevitable during the production process of the film, and although the whole production can be carried out in an ultra-clean room, the adsorption is still not completely avoided. Such surface impurities can have a significant effect on the performance of the battery after the battery is formed. Particularly, it is affected that the battery is broken in the region where the impurities are present even when the temperature of T2 is not reached, thereby greatly affecting the safety of the battery.
Particularly, static electricity is inevitably generated during the production and transfer of the thin film, and thus a small amount of impurities such as dust in the space are adsorbed even in the ultra-clean room. This makes the current method for removing impurities on the surface of the thin film less effective. And the cost of adding the static electricity removing device is higher.
Therefore, the invention creatively arranges the water spraying device and the cleaning device, and can more thoroughly remove the impurities adsorbed on the surface by utilizing the characteristic that the film is less influenced by static electricity in the water absorption state. The concrete structure and method are as follows:
and after the film is stretched and before the film is rolled, spraying water to wet the film, and cleaning and drying the film after wetting. The cleaning process comprises the following steps.
Cleaning device includes the box, is provided with three transport roller in the box for the film gets into from box below input port, exports from the upper right delivery outlet, and the whole vertical condition that is of film. The two sides of the vertical part of the film are respectively provided with a dust collector, a dust blower and a dust collector in a straight line from top to bottom in sequence. The dust collector is used for absorbing impurities on the surface and the periphery of the film, and the dust blower is used for blowing air to the surface of the film, so that the impurities firmly adsorbed on the surface of the film are blown off. The arrangement of the dust collector and the dust blower can blow off impurities on the surface of the film, but the impurities can be absorbed instantly, and secondary pollution to the box body cannot be caused.
The negative pressure device is positioned at the input port and the output port of the box body and is used for ensuring that air at the input port and the output port flows outwards when the box body is cleaned; and a dust suction port for sucking foreign substances possibly existing in the space of the cabinet.
After the stretching is finished, water spraying operation is carried out to ensure certain water content of the film. At the moment, the film is conveyed to the cleaning device, the dust collector and the dust blower are started to remove dust on the film, and meanwhile, the negative pressure device can be started to prevent external dust from entering. At this time, the film has a water content, so that the influence of static electricity on the film is negligible, and dust and impurities on the film are blown off and absorbed more easily. Therefore, it is one of the inventions of the present invention to perform the cleaning step after the completion of the water absorption operation. And after the dust blowing operation is finished, the obtained product is dried and coiled in a drying device.
Those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than others, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.
Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.
Claims (5)
1. A membrane preparation method based on an oil content feedback process is characterized by comprising the following steps:
the raw material A is polyethylene and comprises the following two parts
A1: molecular weight 6.5X 106-8.5×106The polyethylene particles of (a);
a2: the density is 0.966-0.983g/cm3The polyethylene particles of (a);
the raw material B is paraffin oil; the raw material C is silicon dioxide nano particles with the diameter of 20-30 nm; the raw material D is 4, 4' -thiobis (6-tert-butyl-m-cresol);
step 1: heating and mixing the 4 raw materials in batches;
step 2: injecting the mixed slurry into an extruder to extrude into a thick film;
and step 3: sequentially carrying out longitudinal stretching and transverse stretching on the thick film, wherein the stretching ratio is 6-7, obtaining a thin film, and extracting after the stretching is finished;
and 4, step 4: the film is conveyed to a two-dimensional stretching device, light transmittance abnormal points on the film are obtained, and a stretching area is determined according to the distribution of the abnormal points;
and 5: correspondingly controlling a two-dimensional stretching device to perform a film two-dimensional stretching process according to the determined stretching area;
step 6: the film delivery roller conveys the film forward so that it passes through the oil absorbing embossing area and is finally transported from this area to the next equipment; simultaneously, the oil absorption imprinting material conveying roller synchronously conveys the oil absorption imprinting material to an oil absorption imprinting area, and the oil absorption imprinting material conveying roller is positioned above the thin film in parallel in the area and is in contact with the thin film;
and 7: when the film and the oil-absorbing impression material are conveyed between the press rollers positioned in the oil-absorbing impression area, the film and the oil-absorbing impression material are fully contacted under the extrusion of the press rollers, so that the oil of the film is separated out under the action of external force, and is absorbed by the oil-absorbing impression material, and oil stains are left on the surface of the oil-absorbing impression material;
and 8: the oil absorption imprinting material conveying roller continuously conveys the oil absorption imprinting material stained with oil stains upwards to enable the oil absorption imprinting material to be vertically arranged, and the oil absorption surface faces the camera;
and step 9: a camera synchronously collects an image of a latticed oil stain pattern on the oil absorption surface of the vertical area of the oil absorption imprinting material;
step 10: comparing the oil stain pattern with oil stain patterns with different oil contents tested and stored in a database in advance, analyzing the thickness and the color depth of each grid in the grid-shaped oil stain pattern, and judging the oil content in the current film;
step 11: and adjusting the oil removing process according to the oil content analysis result.
2. The method of claim 1, wherein: the oil-absorbing imprinting material is of a composite structure and comprises a planar substrate and grid-shaped protrusions positioned on the substrate, so that under the extrusion of external force, the grid-shaped protrusions can adsorb more grease, and an obvious oil stain pattern is formed.
3. The method of claim 1, wherein: the oil removal process includes extraction in an extraction tank.
4. The method of claim 1, wherein: the oil removing process also comprises the step of removing oil in an oil removing device through a squeezing roller.
5. A membrane based on an oil content feedback process is characterized in that: prepared using a process as claimed in any preceding claim.
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| CN101041722A (en) * | 2006-03-22 | 2007-09-26 | 赛尔格有限责任公司 | Membrane made of a blend of uhmw polyolefins |
| CN107698837A (en) * | 2017-08-31 | 2018-02-16 | 浙江百浩工贸有限公司 | A kind of preparation method of PVB barrier films |
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| CN109980156A (en) * | 2018-12-24 | 2019-07-05 | 中材锂膜有限公司 | A kind of wet process lithium ion battery separator degreasing unit |
| CN111615422A (en) * | 2018-09-11 | 2020-09-01 | 株式会社Lg化学 | Crosslinked polyolefin separator and method for producing same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101041722A (en) * | 2006-03-22 | 2007-09-26 | 赛尔格有限责任公司 | Membrane made of a blend of uhmw polyolefins |
| KR20180112524A (en) * | 2017-04-04 | 2018-10-12 | 명성티엔에스주식회사 | Method manufacturing for separator of secondary battery |
| CN107698837A (en) * | 2017-08-31 | 2018-02-16 | 浙江百浩工贸有限公司 | A kind of preparation method of PVB barrier films |
| CN111615422A (en) * | 2018-09-11 | 2020-09-01 | 株式会社Lg化学 | Crosslinked polyolefin separator and method for producing same |
| CN109980156A (en) * | 2018-12-24 | 2019-07-05 | 中材锂膜有限公司 | A kind of wet process lithium ion battery separator degreasing unit |
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