KR101354708B1 - Method of manufacturing a multi-component separator film with ultra high molecule weight polyethylene for lithium secondary battery and a multi-component separator film for lithium secondary battery therefrom - Google Patents

Abstract

The present invention relates to a method for producing a multi-component separator for a lithium secondary battery comprising ultra high molecular weight polyethylene, and to a multi-component separator for a lithium secondary battery prepared therefrom, and more particularly, to a liquid electrolyte of a lithium secondary battery having a higher permeability. A method for preparing a multi-component separator for a lithium secondary battery comprising ultra-high molecular weight polyethylene having not only improved ion conductivity but also improved mechanical strength by increasing affinity with one component of vinylidene fluoride series, that is, adhesion thereto It relates to a multi-component separator for a lithium secondary battery. To this end, the method for preparing a multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention is mixed by using a compatibilizer to easily mix vinylidene fluoride-based polymer, ultra high molecular weight polyethylene, and high density polyolefin. And dissolving the mixture mixed in the mixing step with liquid paraffin, and extruding and casting the dissolved mixture to prepare a sheet of an ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer form. Simultaneously, biaxially stretching the cast sheet to produce a separator, washing the biaxially stretched separator with a volatile solvent to remove liquid paraffin from the biaxially stretched separator, and the washed biaxially stretched Stage to open and set separator , Characterized in that comprises the features that it comprises the ultra-high molecular weight polyethylene.

Compatibilizers, vinylidene fluoride, polyolefins, liquid paraffin, lithium secondary batteries, separators, multicomponent systems, multilayers, separators, separators.

Description

METHOD OF MANUFACTURING A MULTI-COMPONENT SEPARATOR FILM WITH ULTRA HIGH MOLECULE WEIGHT POLYETHYLENE FOR LITHIUM SECONDARY BATTERY AND A MULTI- COMPONENT SEPARATOR FILM FOR LITHIUM SECONDARY BATTERY THEREFROM}

The present invention relates to a method for producing a multi-component separator for a lithium secondary battery comprising ultra high molecular weight polyethylene, and to a multi-component separator for a lithium secondary battery prepared therefrom, and more particularly, to a liquid electrolyte of a lithium secondary battery having a higher permeability. A method for preparing a multi-component separator for a lithium secondary battery comprising ultra-high molecular weight polyethylene having not only improved ion conductivity but also improved mechanical strength by increasing affinity with one component of vinylidene fluoride series, that is, adhesion thereto It relates to a multi-component separator for a lithium secondary battery.

In general, separators are well known in the art to be prepared by forming a melt mixture of inorganic powders such as polyolefins, organic solvents and silica particulate powder into sheets and then extracting organic solvents and inorganic powders from the sheets. On the other hand, since the inorganic powder has to be extracted, the permeability of the final separator largely dependent on the particle size of the inorganic powder is difficult to be adjusted to the desired level.

Various methods for producing membranes from ultra high molecular weight polyethylene are disclosed in Japanese Patent Laid-Open Nos. 60-242035, 61-195132, 61-195133, 63-39602 and the like. In this method, ultrahigh molecular weight polyethylene having a weight average molecular weight of 7 × 10 ⁵ and higher is dissolved in a nonvolatile solvent to prepare a solution and heated to prepare a gel-like sheet, wherein the amount of nonvolatile solvent in the sheet is nonvolatile. Adjust by removal of solvent. The gel-like sheet is then elongated while heating, and residual nonvolatile solvent is removed from the elongated sheet by extraction to prepare a separator.

In this method a number of pores are formed by elongation of the gel-like sheet after solidification by cooling. Therefore, the separator formed in the method is characterized by the distribution of the size of the small hole and the size of the narrow hole. However, this method does not provide a polyolefin separator having a large pore size and high permeability suitable for high-precision filtration membranes, battery separators, and the like.

In the present invention as described above, the present invention is a polyolefin membrane having excellent permeability to prepare a polyolefin composition solution containing an ultra-high molecular weight component, extrusion of the extruder into the sheet by the die lip, to prepare a gel-like sheet It was confirmed that a rapid separation of the extruded sheet, and preferably also a separator excellent in ion conductivity.

In general, a separator of a lithium secondary battery has been used in various forms such as a polyolefin-based alone or a porous sheet or film made of polyolefin-based and ultra high molecular weight polyethylene.

Conventional technology related to the production of a separator that plays an important role in the performance and safety of such a lithium secondary battery is US Patent No. 6,413,676 (Lithium ion polymer electrolytes), in which the polyvinylidene fluoride is used The prepared membrane shows high ionic conductivity due to its good affinity with liquid electrolytes, while its mechanical properties are poor, and thus the separator is not commercialized as a separator for lithium secondary batteries requiring high mechanical properties in the manufacturing process. there was. In addition, the study on membranes prepared by coating PVdF on PE nonwoven fabrics (Novel porous separator based on PVdF and PE non-woven matrix for rechargeable lithium batteries, Journal of Power Sources, 139 (2005) 235-241) and PVdF only Korean Patent No. 0805760 and a paper (Preparation and characterization of new microporous stretched membrane for lithium rechargeable battery, Journal of Power Sources, 163 (2006) 247-251) have been published for the prepared separator.

Meanwhile, currently commercialized polyethylene separators are inferior in affinity with liquid electrolytes, need to improve ion conductivity, and studies on improving permeability of higher separators are urgently needed.

The present invention has been made to solve the above problems, an object of the present invention has a higher high permeability, and enhances the affinity with the vinylidene fluoride series, which is one component of the liquid electrolyte of the lithium secondary battery, that is, adhesion In order to provide a method of manufacturing a multi-component separator for ultra-high molecular weight polyethylene including ultra-high molecular weight polyethylene having not only further improved ion conductivity but also improved mechanical strength, and to provide a multi-component separator for lithium secondary battery comprising ultra-high molecular weight polyethylene prepared therefrom It is.

These and other objects and advantages of the present invention will become more apparent from the following description, taken in conjunction with the accompanying drawings, illustrating preferred embodiments of the invention.

The object is to mix the vinylidene fluoride-based polymer, ultra-high molecular weight polyethylene and high-density polyolefin with a compatibilizer to easily kneading, and dissolving the mixture in the mixing step with liquid paraffin And extruding and casting the dissolved mixture to produce a sheet having a high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer form, and simultaneously biaxially stretching the cast sheet to prepare a separator; And washing the biaxially stretched separator with a volatile solvent to remove the liquid paraffin from the biaxially stretched separator, and heat-setting the washed biaxially stretched separator, including ultrahigh molecular weight polyethylene. Multicomponent for Lithium Secondary Battery It is achieved by the separation membrane.

Herein, the ultra high molecular weight polyethylene has a weight average molecular weight of 1,500,000 to 3,000,000, the high density polyolefin has a weight average molecular weight of 300,000 to 600,000, and the vinylidene fluoride-based polymer has a weight average molecular weight of 50,000 to 500,000.

In addition, Mw / Mn (weight average molecular weight / number average molecular weight) of the high density polyolefin and the vinylidene fluoride-based polymer is characterized in that 4 to 8.

In addition, the vinylidene fluoride-based polymer is characterized in that it contains 10 to 60% by weight of the total weight of the ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition.

In addition, the ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition and the liquid paraffin is characterized in that the weight ratio of 2-5: 5-8.

In addition, the compatibilizer is aluminum stearate (aluminum stearate), the aluminum stearate is characterized in that it contains 3 to 30% by weight relative to the total weight of the ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition do.

The vinylidene fluoride-based polymer may be at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, or a mixture thereof. It features.

The object is also achieved by a multi-component separator for a lithium secondary battery comprising an ultra-high molecular weight polyethylene, characterized in that prepared according to the method for producing a multi-component separator for a lithium secondary battery comprising the ultra-high molecular weight polyethylene.

According to the present invention, it has higher permeability and improves affinity with vinylidene fluoride series, which is one component of the liquid electrolyte of the lithium secondary battery, that is, adhesion, thereby not only improving ion conductivity but also improving mechanical strength. It has the effect of having.

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings of the present invention. It will be apparent to those skilled in the art that these embodiments are provided by way of illustration only for the purpose of more particularly illustrating the present invention and that the scope of the present invention is not limited by these embodiments .

Referring to the manufacturing method of the multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention.

First, the vinylidene fluoride-based polymer is mixed using a compatibilizer to easily knead ultra-high molecular weight polyethylene and high density polyolefin. Here, aluminum stearate may be used as a compatibilizer used for good kneading of the vinylidene fluoride-based polymer, ultrahigh molecular weight polyethylene, and high density polyolefin.

The vinylidene fluoride-based polymer is 10 to 60% by weight, more preferably 20 to 50% by weight of the total amount of the ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition. In this case, the ultra high molecular weight polyethylene has a weight average molecular weight of 1,500,000 to 3,000,000, the high density polyolefin has a weight average molecular weight of 300,000 to 600,000, and the vinylidene fluoride-based polymer uses a polymer having a weight average molecular weight of 50,000 to 500,000. desirable.

Further, the Mw / Mn (weight average molecular weight / number average molecular weight) of the high density polyolefin and the vinylidene fluoride series polymer is less than 10, preferably 4 to 8. This is because, when Mw / Mn is 10 or more, the solubility becomes good, but the strength improvement of the resulting separator is insufficient.

The high density polyolefin used in the method for producing a multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention is obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, or the like. Crystalline homopolymers or copolymers. In addition, various additives such as antioxidants, ultraviolet absorbers, lubricants, antiblocking agents, pigments, dyes, inorganic fillers, and the like may be added to the polyolefins without departing from the object of the present invention.

In addition, the vinylidene fluoride-based polymer used in the method for producing a multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention is a copolymer of polyvinylidene fluoride, vinylidene fluoride and hexafluoropropylene, Separation membranes can be prepared by selectively combining at least one polymer of vinylidene fluoride and tetrafluoroethylene or a mixture thereof in any order.

Next, the mixture is mixed with the liquid paraffin to dissolve in the mixing step. When the ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer composition is dissolved in liquid paraffin, the ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer composition and the liquid paraffin are in a weight ratio of 2 to 5: 5. It is preferably ˜8, wherein the dissolved solution is extruded and cast at high temperature to produce a sheet.

The ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer solution as a raw material in the present invention is prepared by heating and dissolving the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer in a solvent. The solvent is not particularly limited as long as it can sufficiently dissolve the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, liquid paraffin, or mineral oils whose boiling points correspond to them may be used. In order to obtain, a nonvolatile solvent such as liquid paraffin is preferable. Several properties are contemplated, such as the boiling range of suitable inert solvents such as liquid paraffin. The heat dissolution is carried out by stirring the ultra-high molecular weight polyethylene and the high-density polyolefin at a temperature which completely dissolves in the solvent, or by uniformly mixing and dissolving in the extruder. In the case of dissolving while stirring in a solvent, the temperature varies depending on the polymer and the solvent used. For example, in the case of high density polyethylene, the temperature is in the range of 140 to 250 ° C. When preparing a separator from a high concentration solution of ultra high molecular weight polyethylene and high density polyolefin, it is preferable to dissolve in an extruder. When melt | dissolving in an extruder, the ultra-high molecular weight polyethylene and the high density polyolefin which were mentioned above are first supplied to the extruder which has a side feeder etc., and is melted. It is necessary to supply a liquid solvent from the side feeder to the ultra high molecular weight polyethylene and the high density polyolefin in the molten state to the ultra high molecular weight polyethylene and the high density polyolefin in the molten state. In heating dissolution, it is preferable to add an antioxidant for preventing the oxidation of the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride series polymer.

Next, the heating solution of this ultrahigh molecular weight polyethylene and a high density polyolefin is preferably extruded from a die and molded. As the die, a sheet die having a mold shape having a rectangular inlet is used. A double cylindrical inflation die may be used. When the sheet die is used, the die cap is usually 0.1 to 5 mm, and the extrusion concentration is 140 to 250 ° C. The extrusion speed at this time is 20-30 cm / min. In this way, the solution extruded from the die is formed into a molded product in a gel-like state by cooling. Cooling is preferably performed at a rate of 50 ° C./minute or more up to at least the gelling temperature. In general, when the cooling rate is slow, the higher-order structure of the composition in a gel-like state becomes rougher, and the pseudo cell units forming the higher-order structure become larger, but when the cooling rate is faster, they become dense cell units. If the cooling rate is less than 50 ° C / min, the degree of crystallinity is increased to form a gel-like composition suitable for stretching. Therefore, by adjusting the cooling rate, it is possible to change the pore diameter of the resulting membrane. As the cooling method, cold air, cooling water, a method of making direct contact with another cooling medium, a method of making contact with a roller cooled as a refrigerant, and the like can be used. In addition, the solution extruded from the die may be taken out before the cooling or during the cooling as a drawing ratio of 1 to 10, preferably 1 to 5. If the take-out ratio is 10 or more, it is not preferable because the tightening force becomes large and breaks easily when stretching.

The ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride series sheet thus prepared is drawn in at least one axial direction to prepare a stretched film. The stretching method is not limited to this, but a tentering method, a roll method, a calendering method, or the like can be used. Among these methods, simultaneous biaxial stretching by the tentering method is preferable. The stretching temperature is from room temperature to the melting point of the polymer gel, preferably 80 to 130 ° C, more preferably 100 to 125 ° C. The stretching ratio is 4 to 200 times, preferably 8 to 100 times, and more preferably 16 to 50 times in terms of area.

The ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based separator through the above process removes residual liquid paraffin by washing with a solvent. As the cleaning solvent, volatile solvents such as hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorohydrocarbons such as ethane trifluoride, diethyl ether and dioxane and the like can be used. . These solvents are appropriately selected according to the solvent used for dissolving the ultra high molecular weight polyethylene and the high density polyolefin, and used alone or in combination. The washing method is performed by a method of immersion in a solvent, a method of spraying a solvent, a method of combining them, or the like.

The cleaning as described above is performed until the liquid paraffin in the stretched molding is less than 1% by weight. Thereafter, the cleaning solvent may be dried. The drying method of the cleaning solvent may be performed by heating drying, drying by hot air, contact with a heating roll, or immersion in a heating medium. It is preferable to heat-set a dry extending | stretching composition in the temperature range of crystal dispersion temperature-melting | fusing point. If the heat setting temperature exceeds the melting point, the resin will melt. Although the time of heat setting treatment changes with heat setting temperature, it is preferable to carry out for 10 second-10 minutes.

The ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based separator prepared by the method for preparing a multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention has a porosity of 30 to 95% and a film thickness. As the separation membrane having a thickness of 25 μm, the air permeability is preferably 2000 sec / 100 cc or less, more preferably 200-1000 sec / 100 cc, and the average pore diameter is preferably 0.005-1 μm, more preferably 0.01-0.2 μm, The tensile breaking strength is preferably 800 kg / cm 2 or more, more preferably 900 kg / cm 2 or more, and the puncture strength is preferably 450 g or more.

In addition, the thickness of the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based separator is appropriately selected, but is preferably about 0.1 to 50 µm, more preferably 1 to 25 µm. It is because the thickness is not practical because the mechanical strength of the film is less than 0.1 mu m, and when the thickness exceeds 50 mu m, the thickness is so thick that the effective resistance becomes large.

The method for preparing a separator by introducing ultra high molecular weight polyethylene, high density polyolefin and vinylidene fluoride-based polymer according to the present invention will be described in detail.

First, a vinylidene fluoride-based polymer having a weight average molecular weight (Mw) of 50,000 to 500,000, a high density polyolefin having a weight average molecular weight (Mw) of 300,000 to 600,000, and a weight average using aluminum stearate as a compatibilizer Ultra high molecular weight polyethylene having a molecular weight (Mw) of 1,500,000 to 3,000,000 is mixed, the mixture is heated and dissolved in liquid paraffin, and the dissolved solution is extruded and cast at a high temperature to obtain ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride series A sheet in the form of a polymer is prepared.

In this case, the vinylidene fluoride-based polymer is 10 to 60% by weight, more preferably 20 to 50% by weight of the total amount of the ultra high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition, which is a compatibilizer Aluminum stearate is added in an amount of 3 to 30% by weight based on the total amount of the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer. When dissolving the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition in liquid paraffin, the ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition and the liquid paraffin are in a weight ratio of 2-5: 5-8. It is desirable to. In heating dissolution, it is preferable to add an antioxidant for preventing oxidation of the polyolefin. The heating solution of this polyolefin is preferably molded by extruding from a die. As the die, a sheet die having a mold shape having a rectangular inlet is used. A double cylindrical inflation die may be used. When the sheet die is used, the die cap is usually 0.1 to 5 mm, and the extrusion concentration is 140 to 250 ° C. The extrusion speed at this time is 20-30 cm / min. In this way, the solution extruded from the die is formed into a molded product in a gel-like state by cooling. Cooling is preferably performed at a rate of 50 ° C./minute or more up to at least the gelling temperature.

The ultrahigh molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based sheet thus prepared is subjected to simultaneous biaxial stretching by the tentering method to prepare a separator. The stretching temperature is from room temperature to the melting point of the polymer gel, preferably 80 to 130 ° C, more preferably 100 to 125 ° C. The stretching ratio is 4 to 200 times, preferably 8 to 100 times, and more preferably 16 to 50 times in terms of area.

The ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based separator through the above process removes residual liquid paraffin using a solvent. As the washing solvent, volatile solvents such as hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride and fluorohydrocarbons such as ethane trifluoride, diethyl ether and dioxane and the like can be used. These solvents are appropriately selected depending on the solvent used for dissolving the polyolefin, and used alone or in combination. The washing method is performed by a method of immersion in a solvent, a method of spraying a solvent, a method of combining them, or the like. The cleaning as described above is performed until the liquid paraffin in the stretched molding is less than 1% by weight. Thereafter, the cleaning solvent may be dried. The drying method of the cleaning solvent may be performed by heating drying, drying by hot air, contact with a heating roll, or immersion in a heating medium. It is preferable to heat-set a dry extending | stretching composition in the temperature range of crystal dispersion temperature-melting | fusing point. If the heat setting temperature exceeds the melting point, the resin will melt. Although the time of heat setting treatment changes with heat setting temperature, it is preferable to carry out for 10 second-10 minutes.

Hereinafter, this invention is shown concretely by the following Example and a comparative example. However, the scope of the present invention is not limited by these.

≪ Example 1 >

Ultra high molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition and compatibilizer composed of 20% by weight of polyvinylidene fluoride-based polymer, 5% by weight of ultra high molecular weight polyethylene, and 75% by weight of high density polyethylene Aluminum stearate (aluminum stearate) was added by mixing 6% by weight relative to the total amount of the ultra-high molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition. Then, the ultra high molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition and liquid paraffin are dissolved in the polymer composition at a ratio of 4: 6 to form a solution, and then extruded and cast at a high temperature. After axial stretching, the liquid paraffin was removed with a volatile solvent and subjected to heat setting to prepare a final separator.

<Example 2>

The final membrane was prepared in the same manner as in Example 1 except that the ultrahigh molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition was set to 10% by weight ultrahigh molecular weight polyethylene and 70% by weight high density polyethylene.

<Example 3>

The final membrane was prepared in the same manner as in Example 1 except that the ultrahigh molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition was set to 15% by weight of ultra high molecular weight polyethylene and 65% by weight of high density polyethylene.

<Example 4>

The ultrahigh molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition was prepared in the same manner as in Example 1 except that 30% by weight of polyvinylidene fluoride and 5% by weight of ultra high molecular weight polyethylene and 65% by weight of high density polyethylene were used. The final separator was prepared.

<Example 5>

In the ultrahigh molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition, a final separation membrane was prepared in the same manner as in Example 4 except that 10% by weight of ultra high molecular weight polyethylene and 60% by weight of high density polyethylene were used.

<Example 6>

The final membrane was prepared in the same manner as in Example 4 except that the ultrahigh molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition was set to 15% by weight ultrahigh molecular weight polyethylene and 55% by weight high density polyethylene.

&Lt; Comparative Example 1 &

A final membrane was prepared in the same manner as in Example 1, except that the membrane was prepared without including ultra high molecular weight polyethylene.

Table 1 shows the composition and components of the Examples and Comparative Examples.

[Table 1]

Item Ultra high molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition Compatibilizer
Of the total weight of the polymer composition Ultra high molecular weight polyethylene-high density polyethylene-polyvinylidene fluoride polymer composition: liquid paraffin
(ratio) Polyvinylidene
Fluoride
(weight%) Ultra high molecular weight
Polyethylene
(weight%) High density polyethylene
(weight%) Aluminum stearate
(weight%) Example 1 20 5 75 6 4: 6 Example 2 20 10 70 6 4: 6 Example 3 20 15 65 6 4: 6 Example 4 30 5 65 6 4: 6 Example 5 30 10 60 6 4: 6 Example 6 30 15 55 6 4: 6 Comparative Example 1 20 Not used 100 6 4: 6

       Table 2 summarizes the results of the Examples and Comparative Examples.

[Table 2]

Item Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Sheet formability Good Good Good Good Good Good Good Thickness (㎛) 25 23 26 24 24 25 25 Air permeability
(Sec / 100cc) 45 42 40 43 41 37 52 Average diameter (μm) 0.30 0.34 0.40 0.32 0.37 0.43 0.23

As can be seen in Table 2, the membrane made of ultra high molecular weight polyethylene-high density polyolefin-polyvinylidene fluoride polymer composition by introducing ultra high molecular weight polyethylene according to the present invention has better air permeability than the membrane without ultra high molecular weight. And a large ball size suitable for a battery separator and the like.

1 is a manufacturing process diagram of a multi-component separator for a lithium secondary battery including ultra high molecular weight polyethylene according to the present invention.

Claims (8)

In the method for producing a multi-component separator for a lithium secondary battery containing ultra high molecular weight polyethylene, Mixing vinylidene fluoride-based polymer, ultra high molecular weight polyethylene, and high density polyolefin using a compatibilizer to easily knead, Dissolving the mixture mixed in the mixing step with liquid paraffin; Extruding and casting the dissolved mixture to produce a sheet in the form of ultra high molecular weight polyethylene-high density polyolefin-vinylidenefluoride-based polymer; Simultaneously biaxially stretching the cast sheet to produce a separator; Washing the biaxially stretched separator with a volatile solvent to remove liquid paraffin from the biaxially stretched separator; And heat-setting the washed biaxially stretched separator, the multi-component separator for lithium secondary battery comprising ultra high molecular weight polyethylene. The method of claim 1, The ultra high molecular weight polyethylene has a weight average molecular weight of 1,500,000 to 3,000,000, the high density polyolefin has a weight average molecular weight of 300,000 to 600,000, and the vinylidene fluoride-based polymer has a weight average molecular weight of 50,000 to 500,000, ultra high molecular weight Multi-component separator for lithium secondary battery containing polyethylene. The method of claim 1, Mw / Mn (weight average molecular weight / number average molecular weight) of the high density polyolefin and the vinylidene fluoride-based polymer is characterized in that 4 to 8, a multi-component separator for a lithium secondary battery containing ultra-high molecular weight polyethylene. The method of claim 1, The vinylidene fluoride-based polymer is characterized in that it contains 10 to 60% by weight of the total weight of the ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition, a multi-component system for a lithium secondary battery containing ultra high molecular weight polyethylene Separator. The method of claim 1, The ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition and the liquid paraffin is characterized in that the weight ratio of 2 to 5: 5 to 8, multi-component separator for a lithium secondary battery containing ultra-high molecular weight polyethylene. The method of claim 1, Compatibilizer is aluminum stearate (aluminum stearate), characterized in that the aluminum stearate contains 3 to 30% by weight relative to the total weight of the ultra-high molecular weight polyethylene-high density polyolefin-vinylidene fluoride-based polymer composition, Multi-component separator for lithium secondary battery containing ultra high molecular weight polyethylene. The method of claim 1, The vinylidene fluoride-based polymer is at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, or a mixture thereof. To, the multi-component separator for a lithium secondary battery containing ultra high molecular weight polyethylene. The multi-component separator for a lithium secondary battery comprising ultra-high molecular weight polyethylene, characterized in that prepared according to any one of claims 1 to 7.

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