CN110165122B - Polyethylene microporous membrane and preparation method and application thereof - Google Patents
Polyethylene microporous membrane and preparation method and application thereof Download PDFInfo
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- CN110165122B CN110165122B CN201910402940.6A CN201910402940A CN110165122B CN 110165122 B CN110165122 B CN 110165122B CN 201910402940 A CN201910402940 A CN 201910402940A CN 110165122 B CN110165122 B CN 110165122B
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- H—ELECTRICITY
- 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
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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
Abstract
The invention relates to a polyethylene microporous membrane and a preparation method and application thereof, wherein the method comprises the steps of carrying out melt blending treatment on polyethylene resin and a diluent so as to form a melt; shaping and cooling the melt to obtain a sheet, the cooling causing phase separation of the melt; subjecting the sheet to a longitudinal stretching treatment and a first transverse stretching treatment so as to obtain a base film; subjecting the base film to an extraction treatment to remove the diluent; drying the base membrane from which the diluent is removed so as to remove the extractant; carrying out second transverse stretching treatment on the base film after drying treatment; and (3) subjecting the second transverse stretching treatment product to three-stage transverse thermal relaxation treatment so as to obtain the polyethylene microporous membrane. The method is simple to operate and strong in controllability, and when the production speed of the prepared polyethylene microporous membrane is 50-80m/min, the transverse heat shrinkage rate can be as low as-0.5% -0%, and meanwhile, the longitudinal heat shrinkage rate can be as low as 2% -2.5%.
Description
Technical Field
The invention relates to the field of microporous membranes, in particular to a polyethylene microporous membrane, a preparation method and application thereof, and more particularly relates to a preparation method of the polyethylene microporous membrane, the polyethylene microporous membrane and a lithium ion battery.
Background
The currently used lithium ion battery separator is mainly composed of porous organic polymers, and the thermal shrinkage rate of the separator is one of the important parameters of the separator. The thermal shrinkage resistance of the diaphragm is improved, safety problems such as thermal runaway of the battery and the like caused by short circuit of the diaphragm can be effectively prevented, and the method is an important method for improving the thermal shock resistance of the battery. In addition, thermal shrinkage may affect the pore size and pore size distribution of the lithium battery separator, thereby affecting the internal resistance of the lithium battery separator and its battery performance. Therefore, for the lithium ion battery separator, reducing the thermal shrinkage rate has an important significance for improving the safety and the service performance of the lithium battery, and has gradually become the focus of attention of lithium battery separator manufacturers and lithium battery manufacturers in recent years.
The TD (transverse direction) heat shrinkage has a greater effect on the cylindrical battery performance than the MD (machine direction) heat shrinkage, and therefore, the heat shrinkage in the width TD direction is generally required to be as low as possible. However, the polyolefin microporous membrane prepared by the current method has high transverse heat shrinkage rate, and can not meet the production requirements of lithium battery diaphragm manufacturers and lithium battery manufacturers, and the transverse heat shrinkage rate becomes the index which is most difficult to adjust in the physical and chemical properties of the current diaphragm.
Therefore, the method for preparing polyolefin microporous membranes needs to be further studied.
Disclosure of Invention
The present application is based on the discovery and recognition by the inventors of the following facts and problems:
the speed of a conventional wet method for preparing the diaphragm is generally 25-50 m/min, the speed of the conventional wet method is low, and the production speed needs to be increased in order to improve the production efficiency. However, after the production speed is increased (for example, 50-80m/min), the transverse heat shrinkage rate of the diaphragm prepared by the conventional wet method is high (can reach more than 0.7 percent), and the actual production requirement cannot be met at all. Based on the above problems, the inventors have made extensive experimental studies and proposed a novel method for preparing a polyethylene microporous membrane, and surprisingly found that the polyethylene microporous membrane prepared by the method has a transverse heat shrinkage rate as low as-0.5% to 0% (under the heat shrinkage test condition of 105 ℃,1 hour) and a longitudinal heat shrinkage rate as low as 2% to 2.5% at a production speed of 50 to 80 m/min.
To this end, in a first aspect of the present invention, a method for preparing a polyethylene microporous membrane is provided. According to an embodiment of the invention, the method comprises: carrying out melt blending treatment on polyethylene resin and a diluent so as to form a melt; shaping and cooling the melt to obtain a sheet, the cooling causing phase separation of the melt; subjecting the sheet to a longitudinal stretching treatment and a first transverse stretching treatment so as to obtain a base film; subjecting the base film to an extraction treatment to remove the diluent; drying the base membrane from which the diluent is removed so as to remove the extractant; carrying out second transverse stretching treatment on the base film after drying treatment; performing three-stage transverse thermal relaxation treatment on the second transverse stretching treatment product so as to obtain a polyethylene microporous membrane; in the three-stage transverse thermal relaxation treatment, the ratio of the width of the retracted film in the second stage of thermal relaxation treatment to the width of the retracted film in the first stage of thermal relaxation treatment is 0.86-0.88, such as 0.863, 0.865, 0.867, 0.869, 0.87, 0.873, 0.875, 0.877 or 0.879; the ratio of the width of the retracted film in the third stage of thermal relaxation treatment to the width of the retracted film in the second stage of thermal relaxation treatment is 0.95-0.99, such as 0.953, 0.955, 0.957, 0.96, 0.963, 0.965, 0.967, 0.97, 0.973, 0.975, 0.977, 0.98, 0.983, 0.985 or 0.987. The second transverse stretching treatment can be used for shaping, stretching and rectifying deviation of the film, and ensures that the residual extracting agent on the film is completely volatilized. The width of the shrink film refers to the width of the film that is heat-shrunk in each thermal relaxation treatment; in the invention, the second-stage retraction ratio (the width of the second-stage retraction film/the width of the first-stage retraction film) is minimum, and the retraction ratio is 0.86-0.88; the third stage shrink ratio (third stage shrink film width/second stage shrink film width) is the greatest. The inventors found that if the ratio of the width of the contracted film in the three-stage transverse thermal relaxation treatment is not within the above range, that is, if the width of the film contracted in the first stage, second stage or third stage thermal relaxation treatment is too large or too small, the stress in the resin cannot be sufficiently removed, and the microporous polyethylene film produced has a high transverse thermal shrinkage ratio and a weak resistance to thermal shrinkage. When the ratio of the width of the retraction film in the three-stage transverse thermal relaxation treatment is in the range, the stress in the resin can be sufficiently removed, and the prepared polyethylene microporous film has low transverse thermal shrinkage rate and strong heat shrinkage resistance. The method provided by the embodiment of the invention is simple to operate and strong in controllability, and when the production speed of the prepared polyethylene microporous membrane is 50-80m/min, the transverse heat shrinkage rate is as low as-0.5% -0% (105 ℃,1h), and the longitudinal heat shrinkage rate is as low as 2% -2.5%, so that the longitudinal heat shrinkage rate is considered while the lower transverse heat shrinkage rate is ensured, and the transverse heat shrinkage rate and the longitudinal heat shrinkage rate are relatively balanced.
According to an embodiment of the present invention, the method may further include at least one of the following additional technical features:
according to the embodiment of the invention, the temperature of the three-stage transverse thermal relaxation treatment is 132-135 ℃, such as 132.2, 132.4, 132.6, 132.8, 133, 133.2, 133.4, 133.6, 133.8, 134, 134.2, 134.4, 134.6 or 134.8 ℃. The temperature range of the three-stage transverse thermal relaxation treatment means that the temperature of each stage of transverse thermal relaxation treatment is selectable within the range of 132-135 ℃, i.e. the temperature of each stage of transverse thermal relaxation treatment is not necessarily the same. The inventor finds that if the temperature of the multi-stage transverse thermal relaxation treatment is too high, the tensile strength of the prepared polyethylene microporous membrane is too low; if the temperature of the multi-section transverse thermal relaxation treatment is too low, the stress in the resin cannot be sufficiently removed, and the prepared polyethylene microporous membrane has high transverse thermal shrinkage rate and weak heat shrinkage resistance. When the temperature of the multi-section transverse thermal relaxation treatment is 132-135 ℃, the stress in the resin can be more fully removed, the transverse thermal shrinkage rate of the prepared polyethylene microporous membrane is lower, the heat shrinkage resistance is higher, and the proper tensile strength is kept.
According to an embodiment of the invention, in the three-stage transverse thermal relaxation treatment, the time of the first stage of thermal relaxation treatment is 20 s-40 s, such as 25, 30 or 35 s; the time of the second stage of thermal relaxation treatment is 20s to 40s, such as 25, 30 or 35 s; the time of the third stage of thermal relaxation treatment is 20s to 40s, such as 25, 30 or 35 s. It should be noted that, the processing time of each stage of the transverse thermal relaxation processing can be realized by adjusting the length of the multi-stage transverse thermal relaxation processing equipment and/or the overall vehicle speed, and the time of each stage of the transverse thermal relaxation processing is not necessarily the same. The length of the multi-section transverse thermal relaxation treatment equipment refers to the length of the diaphragm which is transmitted in the longitudinal advancing direction after a clamp of the tenter type thermal relaxation treatment equipment clamps the diaphragm, and the adjustment range is 80-100 m; the integral vehicle speed refers to the speed of the thermal relaxation treatment of the diaphragm, and the adjustment range is 50-80 m/min. When the processing time of each section in the three-section transverse thermal relaxation processing is in the range, the prepared polyethylene microporous membrane has lower transverse thermal shrinkage rate and stronger heat shrinkage resistance.
According to an embodiment of the present invention, after the three-stage transverse thermal relaxation treatment, the method further comprises: the three-stage transverse thermal relaxation treatment product is subjected to a hot roll treatment to obtain a polyethylene microporous film. In some embodiments, the temperature of the hot roll treatment is 130 to 135 ℃, such as 131, 132, 133, or 134 ℃. The inventors found that when the temperature of the heat roll treatment is in the above range, not only the TD heat shrinkage ratio can be further reduced, but also the MD/TD heat shrinkage ratio can be adjusted to be within an appropriate range.
According to an embodiment of the invention, the diluent is a paraffinic oil. In some embodiments, the extractant comprises a solvent selected from dichloromethane, methanol, ethanol, C1-6At least one of a halogenated alkane, chloroform, or 1, 2-dichloroethane. In some embodiments, the cooling process is performed by a cast sheet roll.
According to the embodiment of the invention, the mass ratio of the polyolefin resin to the diluent is (20-40): (60-80), such as 30: 70. in some embodiments, the polyolefin resin has an average molecular weight of 40 to 80 million, such as 40, 50, 60, 70, or 80 million.
According to an embodiment of the invention, the longitudinal stretching treatment has a stretching ratio of 5 to 8, such as 5.5, 6.0, 6.5, 7.0, 7.5 or 8.0. In some embodiments, the first transverse stretching process has a stretch ratio of 5 to 9, such as 5, 6, 7, 7.5, 8, or 9.
In a second aspect of the present invention, a method for preparing a polyethylene microporous membrane is provided. According to an embodiment of the invention, the method comprises: carrying out melt blending treatment on polyethylene resin and paraffin oil so as to form a melt; shaping and cooling the melt to obtain a sheet, the cooling being performed by a casting roll, the cooling causing phase separation of the melt; subjecting the sheet to a longitudinal stretching treatment and a first transverse stretching treatment so as to obtain a base film; extracting the basement membrane to remove the paraffin oil; drying the base membrane from which the paraffin oil is removed so as to remove the extractant; carrying out second transverse stretching treatment on the base film after drying treatment; performing three-stage transverse thermal relaxation treatment on the second transverse stretching treatment product at the temperature of 132-135 ℃; carrying out hot roller treatment on the three-stage thermal relaxation treatment product at the temperature of 130-135 ℃ so as to obtain the polyethylene microporous membrane; in the three-stage transverse thermal relaxation treatment, the ratio of the width of a retracted film subjected to second-stage thermal relaxation treatment to the width of a retracted film subjected to first-stage thermal relaxation treatment is 0.86-0.88, the ratio of the width of a retracted film subjected to third-stage thermal relaxation treatment to the width of a retracted film subjected to second-stage thermal relaxation treatment is 0.95-0.99, the time of the first-stage thermal relaxation treatment is 20-40 s, the time of the second-stage thermal relaxation treatment is 20-40 s, and the time of the third-stage thermal relaxation treatment is 20-40 s. The method provided by the embodiment of the invention is simple to operate and strong in controllability, and the prepared polyethylene microporous membrane has lower transverse thermal shrinkage rate, more balanced transverse and longitudinal thermal shrinkage rates and stronger heat shrinkage resistance.
In a third aspect of the present invention, a polyethylene microporous membrane is presented. According to the embodiment of the invention, under the conditions that the thermal shrinkage test temperature is 105 ℃ and the time is 1h, the transverse thermal shrinkage rate of the polyethylene microporous membrane is-0.5-0%, and the longitudinal thermal shrinkage rate is 2-2.5%. In some embodiments, the polyethylene microporous membrane is prepared by the method of any of the above.
In a fourth aspect of the present invention, a lithium ion battery is presented. According to an embodiment of the invention, the battery comprises: a cathode, an anode, and a microporous polyethylene membrane as described above or prepared according to the method of any of the above, the separator being positioned between the anode and the cathode.
Detailed Description
The following detailed description of embodiments of the invention is intended to be illustrative, and not to be construed as limiting the invention.
It should be noted that the heat shrinkage test conditions (105 ℃,1h) in the present invention are the test conditions (temperature, time) commonly used in the industry by those skilled in the art.
The invention relates to the research field of lithium ion battery microporous membranes, in particular to a wet preparation method of a single-layer polyolefin microporous membrane with low thermal shrinkage. The inventor optimizes the transverse thermal relaxation treatment under the condition that the vehicle speed is 50-80m/min, takes the transverse thermal relaxation treatment temperature and the relaxation mode as entry points, reduces the thermal shrinkage rate of the diaphragm at 105 ℃, avoids the diaphragm from shrinking and deforming to a greater extent, and reduces the probability of short circuit caused by the contact of the anode and the cathode of the lithium battery.
Specifically, the invention provides a method for preparing a polyolefin microporous membrane by a wet method, which comprises the steps of extruding a casting sheet, longitudinally drawing, transversely drawing, extracting and drying, transversely secondarily thermally stretching and transversely thermally relaxing. When the vehicle speed is 50-80m/min, the thermal shrinkage rate of the polyolefin microporous membrane can be obviously reduced by optimizing transverse thermal relaxation treatment, and other parameters can be correspondingly adjusted according to actual requirements. The preparation method of the diaphragm provided by the invention is simple to operate and strong in controllability, ensures the transverse thermal shrinkage rate and gives consideration to longitudinal thermal shrinkage, and the transverse and longitudinal thermal shrinkage rates are relatively balanced. The polyolefin microporous membrane prepared by the invention has a transverse heat shrinkage rate of 0.5 percent to 0 percent and a longitudinal heat shrinkage rate of 2 percent to 2.5 percent at 105 ℃ for 1 hour.
The preparation method comprises the following steps:
(1) mixing polyethylene resin and diluent paraffin oil, putting into a double-screw extruder, melting and mixing, then extruding a casting film, cooling a casting sheet roller, and casting into a thick sheet;
(2) carrying out longitudinal stretching (MDO) on the thick sheet obtained in the step (1) through a stretching roller, fixing two sides of the thin film through a clamp, and carrying out first transverse stretching (TDO 1);
(3) drawing the microporous oil film obtained in the step (2) into an extraction drying device;
(4) fixing the microporous dry film obtained in the step (3) by using clamps at two sides, and performing transverse secondary hot stretching heat setting treatment (TDO 2);
(5) performing multi-section transverse thermal relaxation treatment on the diaphragm obtained in the step (4);
(6) and (5) carrying out hot roller treatment on the diaphragm obtained in the step (5).
In some embodiments, in step (5), the multi-stage transverse thermal relaxation treatment step is divided into three stages of retraction. The second-stage retraction ratio (second-stage retraction film width/first-stage retraction film width) is minimum, and the retraction ratio is 0.86-0.88; the third stage retraction ratio (third stage retraction film width/second stage retraction film width) is maximum, and the retraction ratio is 0.95-0.99.
In some embodiments, in the step (5), the multi-stage transverse thermal relaxation treatment step has a thermal relaxation temperature of 132-135 ℃.
In some embodiments, in the three-stage transverse thermal relaxation treatment, the time of the first stage of thermal relaxation treatment is 20 s-40 s, the time of the second stage of thermal relaxation treatment is 20 s-40 s, and the time of the third stage of thermal relaxation treatment is 20 s-40 s.
In some embodiments, the multi-stage transverse thermal relaxation treatment equipment has a length of 80-100 m.
In some embodiments, the overall vehicle speed (speed of the thermal relaxation process of the diaphragm) is 50-80 m/min.
In some embodiments, the temperature of the hot roll treatment is 130 to 135 ℃.
The invention will be further explained with reference to specific examples.
Example 1
1) Polyolefin resin and diluent paraffin oil are blended and put into a double-screw extruder according to the mass ratio of 30:70 and the average molecular weight of the polyolefin resin of 50 ten thousand, and are melted and mixed, and then are conveyed into an extrusion die head through a metering pump. Then extruding a casting film, cooling a casting sheet roller, and casting into a thick sheet;
2) the resulting slab was longitudinally stretched (MDO) by a stretching roll at a longitudinal stretching ratio of 6.5, then both sides of the film were fixed with a jig and subjected to a first transverse stretching (TDO1) at a transverse stretching ratio of 7;
3) and (3) extracting and drying the microporous oil film, fixing the microporous oil film by using a clamp at two sides, and performing transverse secondary thermal stretching (TDO2) and multi-section transverse thermal relaxation treatment. The temperature of the thermal relaxation treatment was 132.5 deg.C (for each stage), the time of the first stage thermal relaxation treatment was 40s, the time of the second stage thermal relaxation treatment was 40s, and the time of the third stage thermal relaxation treatment was 40 s. Three-stage retraction, the second-stage retraction ratio (second-stage retraction film width/first-stage retraction film width) was 0.87, and the third-stage retraction ratio (third-stage retraction film width/second-stage retraction film width) was 0.96. After retraction, the dried film was subjected to a hot roll treatment at 130 ℃;
4) and (6) rolling the diaphragm.
As a result: separator thickness 12.5 μm, porosity 39.3%, thermal shrinkage (105 ℃,1 h): MD 2.32% and TD-0.16%.
Example 2
1) Polyolefin resin and diluent paraffin oil are blended and put into a double-screw extruder according to the mass ratio of 30:70 and the average molecular weight of the polyolefin resin of 80 ten thousand, melted and mixed, and conveyed into an extrusion die head through a metering pump. Then extruding a casting film, cooling a casting sheet roller, and casting into a thick sheet;
2) the resulting slab was longitudinally stretched (MDO) by a stretching roll at a stretch ratio of 7, then both sides of the film were fixed with a jig and subjected to a first transverse stretching (TDO1) at a transverse stretch ratio of 7.5;
3) and (3) extracting and drying the microporous oil film, fixing the microporous oil film by using a clamp at two sides, and performing transverse secondary thermal stretching (TDO2) and multi-section transverse thermal relaxation treatment. The thermal relaxation temperature was 133.3 deg.C (per stage). The time for the first stage of thermal relaxation treatment is 40s, the time for the second stage of thermal relaxation treatment is 40s, and the time for the third stage of thermal relaxation treatment is 40 s. Three-stage retraction, wherein the second-stage retraction ratio (the second-stage retraction film width/the first-stage retraction film width) is 0.86, and the third-stage retraction ratio (the third-stage retraction film width/the second-stage retraction film width) is 0.98. After retraction, the dried film was subjected to a hot roll treatment at 132 ℃;
4) and (6) rolling the diaphragm.
As a result: separator thickness 12 μm, porosity 38.6%, thermal shrinkage (105 ℃,1 h): MD 2.50% and TD-0.25%.
Example 3
1) Polyolefin resin and diluent paraffin oil are blended and put into a double-screw extruder according to the mass ratio of 30:70 and the average molecular weight of the polyolefin resin of 80 ten thousand, melted and mixed, and conveyed into an extrusion die head through a metering pump. Then extruding a casting film, cooling a casting sheet roller, and casting into a thick sheet;
2) the resulting slab was longitudinally stretched (MDO) by a stretching roll at a longitudinal stretching magnification of 6, then both sides of the film were fixed with a jig and subjected to a first transverse stretching (TDO1) at a transverse stretching magnification of 7;
3) and (3) extracting and drying the microporous oil film, fixing the microporous oil film by using a clamp at two sides, and performing transverse secondary thermal stretching (TDO2) and multi-section transverse thermal relaxation treatment. The thermal relaxation temperature was 134 ℃ (per stage). The time for the first stage of thermal relaxation treatment is 40s, the time for the second stage of thermal relaxation treatment is 40s, and the time for the third stage of thermal relaxation treatment is 40 s. Three-stage retraction, the second-stage retraction ratio (second-stage retraction film width/first-stage retraction film width) was 0.87, and the third-stage retraction ratio (third-stage retraction film width/second-stage retraction film width) was 0.98. After retraction, the dried film was subjected to a hot roll treatment at 133 ℃;
4) and (6) rolling the diaphragm.
As a result: separator thickness 11.7 μm, porosity 38.5%, thermal shrinkage (105 ℃,1 h): MD 2.26% and TD-0.11%.
Comparative example 1
The preparation method is basically the same as that of example 1, except that: the thermal relaxation treatment temperature was 130 deg.C (for each stage). And a third stage of retraction (i.e., third stage retracted film width/second stage retracted film width is 1), which corresponds to only two stages of retraction.
As a result: the separator prepared by the method of comparative example 1 had a thickness of 12 μm, a porosity of 38.5%, a heat shrinkage ratio (105 ℃,1 h): MD 2.69% and TD 0.46%.
Comparative example 2
1) Polyolefin resin and diluent paraffin oil are blended and put into a double-screw extruder according to the mass ratio of 30:70 and the average molecular weight of the polyolefin resin of 50 ten thousand, and are melted and mixed, and then are conveyed into an extrusion die head through a metering pump. Then extruding a casting film, cooling a casting sheet roller, and casting into a thick sheet;
2) the resulting slab was longitudinally stretched (MDO) by a stretching roll at a longitudinal stretching ratio of 6.5, then both sides of the film were fixed with a jig and subjected to a first transverse stretching (TDO1) at a transverse stretching ratio of 7.8;
3) and (3) extracting and drying the microporous oil film, fixing the microporous oil film by using a clamp at two sides, and performing transverse secondary thermal stretching (TDO2) and multi-section transverse thermal relaxation treatment. The thermal relaxation temperature was 130 deg.C (per stage). The time for the first stage of thermal relaxation treatment is 40s, the time for the second stage of thermal relaxation treatment is 40s, and the time for the third stage of thermal relaxation treatment is 40 s. Three-stage retraction, the second-stage retraction ratio (second-stage retraction film width/first-stage retraction film width) was 0.94, and the third-stage retraction ratio (third-stage retraction film width/second-stage retraction film width) was 0.99. After retraction, the dried film is subjected to hot roll treatment at 80 ℃;
4) and (6) rolling the diaphragm.
As a result: the separator prepared by the method of comparative example 2 had a thickness of 12 μm, a porosity of 38.5%, a heat shrinkage ratio (105 ℃,1 h): MD 2.87% and TD 0.62%.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (11)
1. A preparation method of a polyethylene microporous membrane is characterized by comprising the following steps:
melt blending the polyethylene resin with a diluent to form a melt,
shaping and cooling the melt to obtain a sheet, the cooling causing phase separation of the melt,
subjecting the sheet to a longitudinal stretching treatment and a first transverse stretching treatment to obtain a base film,
subjecting the base film to an extraction treatment to remove the diluent,
drying the base membrane from which the diluent is removed to remove the extractant,
the base film after the drying treatment is subjected to a second transverse stretching treatment,
subjecting the second transverse stretching treatment product to three-stage transverse thermal relaxation treatment so as to obtain a polyethylene microporous membrane,
in the three-stage transverse thermal relaxation treatment, the ratio of the width of the retraction film subjected to the second stage of thermal relaxation treatment to the width of the retraction film subjected to the first stage of thermal relaxation treatment is 0.86-0.88, and the ratio of the width of the retraction film subjected to the third stage of thermal relaxation treatment to the width of the retraction film subjected to the second stage of thermal relaxation treatment is 0.95-0.99.
2. The method of claim 1, wherein the temperature of the three-stage transverse thermal relaxation treatment is 132 to 135 ℃.
3. The method according to claim 1, wherein in the three-stage transverse thermal relaxation treatment, the time of the first stage of thermal relaxation treatment is 20 s-40 s, the time of the second stage of thermal relaxation treatment is 20 s-40 s, and the time of the third stage of thermal relaxation treatment is 20 s-40 s.
4. The method of claim 1, wherein after the three-stage transverse thermal relaxation treatment, further comprising: the three-stage transverse thermal relaxation treatment product is subjected to a hot roll treatment to obtain a polyethylene microporous film.
5. A method as set forth in claim 4, characterized in that the temperature of the hot roll treatment is 130-135 ℃.
6. The method of claim 1, wherein the diluent is a paraffinic oil.
7. The method of claim 1, wherein the extractant comprises a solvent selected from the group consisting of dichloromethane, methanol, ethanol, C1-6At least one of a halogenated alkane, chloroform, or 1, 2-dichloroethane.
8. The method of claim 1, wherein the cooling is performed by a cast sheet roll.
9. A preparation method of a polyethylene microporous membrane is characterized by comprising the following steps:
the polyethylene resin and the paraffin oil are subjected to melt blending treatment so as to form a melt,
shaping and cooling the melt to obtain a sheet, the cooling being performed by a casting roll, the cooling causing phase separation of the melt,
subjecting the sheet to a longitudinal stretching treatment and a first transverse stretching treatment to obtain a base film,
subjecting the basement membrane to an extraction treatment to remove the paraffinic oil,
drying the base membrane from which the paraffin oil is removed to remove the extractant,
the base film after the drying treatment is subjected to a second transverse stretching treatment,
performing three-stage transverse thermal relaxation treatment on the second transverse stretching treatment product at the temperature of 132-135 ℃, wherein the ratio of the width of a retraction film subjected to second-stage thermal relaxation treatment to the width of the retraction film subjected to first-stage thermal relaxation treatment is 0.86-0.88, the ratio of the width of the retraction film subjected to third-stage thermal relaxation treatment to the width of the retraction film subjected to second-stage thermal relaxation treatment is 0.95-0.99, the time of the first-stage thermal relaxation treatment is 20-40 s, the time of the second-stage thermal relaxation treatment is 20-40 s, and the time of the third-stage thermal relaxation treatment is 20-40 s,
and carrying out hot roller treatment on the three-stage thermal relaxation treatment product at the temperature of 130-135 ℃ so as to obtain the polyethylene microporous membrane.
10. The microporous polyethylene membrane is characterized by being prepared by the method of any one of claims 1 to 9, and having a transverse heat shrinkage rate of-0.5% to 0% and a longitudinal heat shrinkage rate of 2% to 2.5% under the conditions that a heat shrinkage test temperature is 105 ℃ and a time is 1 h.
11. A lithium ion battery, comprising:
a cathode electrode, which is provided with a cathode,
an anode, a cathode, a anode and a cathode,
a polyethylene microporous membrane as defined in claim 10 or prepared according to the method of any one of claims 1 to 9, the polyethylene microporous membrane being located between the anode and the cathode.
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