KR100409019B1 - Multi-layer microporous membrane and methods of preparing the same - Google Patents

Abstract

The present invention relates to a multilayer microporous membrane and a method of manufacturing the same, and more particularly, to a multilayer microporous membrane and a method for producing the microporous coating layer through a phase separation method on the surface of a support layer of a polymer membrane.

The present invention for this purpose, a) a support layer of the polymer film; And b) a nonporous polymer layer having a melting point applied to one or both surfaces of the support layer lower than the melting point of the support layer polymer, and a method of manufacturing the same.

Multi-layered microporous membrane according to the present invention is a polymer material having a low melting point on the surface of the support separator to form a microporous membrane through a phase separation method, so that the microporous membrane has a very low degree of nonporosity and hardly loses the shape retaining force without damaging the permeability of the support separator. ), It is possible to manufacture a battery separator excellent in safety.

Description

Multi-layer microporous membrane and its manufacturing method {MULTI-LAYER MICROPOROUS MEMBRANE AND METHODS OF PREPARING THE SAME}

The present invention relates to a multilayer microporous membrane and a method of manufacturing the same, and more particularly, to a multilayer microporous membrane and a method for producing the microporous coating layer through a phase separation method on the surface of a support layer of a polymer membrane.

The battery separator basically separates the positive electrode and the negative electrode to prevent the two electrodes from contacting and short-circuit, and also serves to pass electrolyte and ions between the two electrodes. The material itself is inert because it does not participate in electrochemical reactions, but its physical performance greatly affects the performance and safety of the battery.

In particular, lithium ion or lithium polymer secondary batteries require more demanding properties due to the high reactivity of lithium. In addition to the functions of the general separator described above, micropores may be formed when overcharged or an external short circuit occurs. It is necessary to close the circuit of the battery by closing it. The cutting function of the battery circuit by the closing of the micropores is referred to as a no-porosity or a shutdown function. When the non-porosity occurs, the movement of the electrolyte and ions is blocked, so that the current becomes almost zero, and further battery reaction is stopped, thereby preventing the battery from being exploded. However, since the temperature can continue to rise to a certain degree even after the non-porosity occurs and the current is cut off, the shape of the separator should not be lost even above the no-pore start temperature. If the separator breaks and loses its shape, the two electrodes are in direct contact and short-circuited. Therefore, in the safety of the lithium secondary battery, together with the aforementioned non-porous onset temperature, the shape integrity (melt integrity) from the start of non-porous to the membrane breaking temperature becomes an important factor.

Various materials may be used as the separator, but due to the demanding requirements of the lithium secondary battery, all of the currently commercially available polyolefins such as polyethylene or polypropylene are used. Although the polyethylene has a melting point of about 130 to 135 ° C., it is possible to lower the non-porous temperature slightly compared to the separator using polypropylene. However, the polyethylene separator is incomplete in terms of safety since the shape holding force is not guaranteed to a high temperature. . The separator made of polypropylene has advantages such as better mechanical strength than that made of polyethylene. However, since the melting point of polypropylene is as high as about 160 to 165 ° C, there is insufficient point to expect safety due to non-porosity. Thus, in order to compensate for the disadvantages of polyethylene and polypropylene, a polyethylene membrane is sandwiched between two layers of polypropylene membranes, thereby making a separator having a low non-porous onset temperature and good shape retention (US Pat. No. 5,691,077). However, this method is difficult to process and has various problems such as interface adhesion problem.

In addition, in the case of high density polyethylene mainly used for the production of the separator, the melting point is 135 ° C, which is still high as a safe non-vaporization start temperature.

In view of the problems of the prior art, an object of the present invention is to provide a microporous membrane having high safety by forming a microporous coating film having a lower melting point by a phase separation method on a surface of a battery membrane support layer for a battery, thereby lowering the degree of nonporosity.

Another object of the present invention is to provide a method for preparing the multilayer microporous membrane by a phase separation method.

It is another object of the present invention to provide a lithium ion secondary battery or a lithium ion polymer secondary battery comprising the multilayer microporous membrane having excellent safety with low non-porous temperature without impairing permeation of the support separator as a separator. .

In order to achieve the above object, the present invention is a) a pore size of 0.001 to 100 ㎛, the thickness of the support layer of a polymer membrane of 1 to 50 ㎛; And b) a non-porous layer having a melting point applied to one or both sides of the support layer 40 to 75 ℃ lower than the support layer polymer of the a), the pore size is 0.001 to 100 ㎛, thickness 0.01 to 20 ㎛ Including;

The air permeability of the multilayer microporous membrane is a maximum of 5,000 seconds / 100cc at a temperature below the melting point of the non-porous layer, and provides a multilayer microporous membrane, characterized in that at least 10,000 seconds / 100cc at a temperature above the melting point of the non-porous layer.

In addition, the present invention

In the manufacturing method of the multilayer microporous membrane,

a) providing a support layer of a polymer membrane;

b) lower than the melting point of the support layer polymer on one or both sides of the support layer

Applying a polymer solution containing a polymer having a silver melting point; And

c) drying the coating film as it is, or drying after impregnation with a non-solvent

Forming an Uncoated Layer by Phase Separation Method

It provides a method for producing a multilayer microporous membrane comprising a.

The present invention also provides a lithium ion secondary battery or a lithium ion polymer secondary battery comprising the multilayer microporous membrane of the substrate as a separator.

Hereinafter, the present invention will be described in detail.

The present invention is to provide a multi-layer microporous membrane and a method of manufacturing the same by applying a microporous polymer membrane having a lower melting point to one or both surfaces of a support having a microporous membrane to form a non-porous layer by a phase separation method. According to this method, it has a low non-porous start temperature and shows high safety, and is suitable for use as a battery separator, a lithium ion secondary battery, and a lithium ion polymer secondary battery.

To this end, the present invention is based on the support layer of the polymer membrane that has already been made, and a polymer solution containing a polymer having a melting point lower than the melting point of the support layer polymer is applied to one or both surfaces thereof to apply a microporous membrane to the phase separation method. To produce a multilayer microporous membrane.

The polymers of the support layer and the non-coating layer used in the present invention are different from each other in melting point, and in particular, the melting point of the non-coating layer polymer is 40 to 75 ° C. lower than the melting point of the support layer polymer. According to this method, it is possible to manufacture a separator having excellent safety by maintaining the shape holding force up to the melting point of the support layer of the polymer film (for example, about 165 ° C, which is the melting point of polypropylene) while having a low non-porous starting temperature. The pores of the non-porous layer thus formed lose their shape above the melting point. The base material serves as a so-called 'supporting layer', and the coating layer serves as a so-called 'uncoated layer'.

The material of the support layer is a polymer having a melting point of 130 to 200 ° C., and is made of polyethylene, polypropylene, or the like, and may be used regardless of whether it is manufactured dry or wet. Specific examples of the polymer of the support layer are high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, Poly-1-butene, polyethylene-propylene copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, Polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, Polystyrene, polyphenylene oxide, polysulfone, polycarbonate, polyester ( polyester, polyamide, polyurethane, polyacrylate, polyvinylidene chloride, polyvinylidene fluoride, polysiloxane, polyolefin ionomer ), Polymethyl pentene and derivatives thereof, preferably at least one selected from the group consisting of, and more preferably, a polypropylene separator. In addition, the support layer of the polymer film may be manufactured in the form of a blend or laminate of the polymer materials.

In addition, the present invention uses a polymer having a melting point of 90 to 125 ℃ lower melting point than the support layer polymer in order to initiate the shutdown at a desired temperature (shutdown). Specific examples include high density polyethylene, low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene, high crystalline polypropylene, poly Poly 1-butene, ethylene vinyl acetate copolymer (EVA; poly (ethylene-co-vinyl acetate)), polyethylene-propylene copolymer, polyethylene-butylene copolymer (polyethylene- butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butyl Polystyrene-ethylene-butylene-styrene copolymer, polystyrene, polyvinylidene fluoride, poly Polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyurethane, polyacrylonitrile, polyacrylate, polyacrylic acid acid, polyamide, polyacrylamide, polyvinylacetate, polyvinylpyrrolidone, polytetraethylene glycol diacrylate, polysulfone , Polyvinylidene chloride (polyvinylidene chloride), polyolefin ionomers (ionomers) and derivatives thereof are preferably selected from the group consisting of one or more, and in addition to the various polymers can be selected and used according to the conditions.

In addition, the multilayer microporous membrane of the present invention is prepared by a phase separation method. This will be described in more detail as follows.

In the present invention, the phase separation method used for forming the non-porous layer is made of a homogeneous polymer solution, and then separated into a phase region in which the polymer is mostly and a phase region in which the polymer is mostly by dropping the solubility of the polymer by a constant method. This is how you do it. After the solvent is removed in the above method, only the polymer phase remains, so that the porous membrane is formed. As a method of separating the phases by lowering the solubility, a method by evaporation of a solvent, a method of lowering a temperature (thermally induced phase separation), a method of adding a third nonsolvent, and the like may be used. . Preferably, the present invention uses, but is not limited to, a method in which a sample coated with a coating solution containing a non-porous layer-forming polymer is evaporated or impregnated with a non-solvent in air at room temperature.

As described above, phase separation can be carried out using all conventionally known methods, and the morphology of the non-porous layer is determined by the composition of the solution and the phase separation conditions. In the present invention, for fine morphology control, the temperature of the atmosphere is preferably changed or the atmosphere is filled with vapor of a solvent or a nonsolvent. Either method can be used to produce a porous coating membrane, and if prepared under the optimum conditions according to the present invention, it is possible to produce a final separator having a nonporous function with little loss of permeability of the support layer of the polymer membrane.

In addition, according to the present invention there is an advantage that the non-porous layer can be formed in a simple process without affecting the physical properties of the support layer of the polymer film as the base material. Moreover, since the non-porous layer is formed on the surface of the base material, the mechanical properties of the non-porous layer itself are not greatly restricted, so that a film having as large porosity as possible can be produced. Therefore, the non-porous layer can be formed with little loss of permeability of the base material isolation membrane. At this time, if the manufacturing method of the support layer and the non-porous layer to be bonded separately without the present invention, there will be a lot of restrictions on the porosity, thickness and permeability due to the handling problem during the process.

Hereinafter, a method of manufacturing the multilayer microporous membrane by the phase separation method will be described in detail.

First, a) providing a support layer of a polymer membrane is carried out. The present invention produces a microporous membrane to be used as a support layer by a dry or wet method.

Thereafter, b) applying a polymer solution containing a polymer having a melting point lower than the melting point of the support layer polymer on one or both sides of the support layer. In the present invention, the polymer solution includes 1 to 10% by volume of the non-porous layer material polymer, and 90 to 99% by volume of the solvent. It is heated to 45 ~ 125 ℃ to make a homogeneous solution to prepare a coating solution. Then, the step of applying the solution to the surface of the support layer separator as the base material. In this case, the coating method may be used brushing (brushing), casting (casting), or dip coating (dip coating).

In addition, the solvent used in the coating solution for forming the non-porous layer is 1-methyl-2-pyrrolidone (1-methyl-2-pyrrolidone, NMP), n-hexane (n-hexane), diethyl ether (diethyl ether, dimethyl formamide (DMF), dimethylacetamide (DMAc), dioxane, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), cyclohexane ), Benzene, toluene, and xylene are preferably selected from the group consisting of one or more solvents. Other solvents may also be used depending on the type and conditions of the polymer. In addition, in consideration of solubility, permeability of the nonsolvent, evaporation of the solvent, etc., 1 to 50% by volume of one or more other solvents or nonsolvents may be used.

Next, the present invention is carried out the step of forming a non-porous layer by c) drying the coating as it is, or by impregnating the non-solvent and drying.

The present invention forms a non-porous layer by a method of drying the coated support layer separator as it is by evaporation, or a phase separation method of separating a polymer and a solvent phase after being impregnated in a non-solvent storage tank.

The nonsolvent used for the impregnation is water, acetone, methanol, ethanol, n-propanol, n-butanol, n-methylpyrrolidone (NMP; N-methyl pyrrolidone) and their It is preferably selected from the group consisting of mixtures.

The drying is carried out under a vapor atmosphere surrounded by a gas selected from all kinds of gases including nitrogen, oxygen, carbon dioxide, air and the like, with a relative humidity of 0 to 100%, below the saturated vapor pressure of the solvent used. It is desirable to.

The above describes the whole process for the production of the film having the optimum physical properties, some processes may be changed or omitted depending on the desired final physical properties, and additional processes may be added. That is, in the present invention, a process of applying a non-porous polymer solution to the support layer separator and a drying process, or phase separation methods in which a non-solvent is impregnated, each process may be selectively combined regardless of the order of at least one, The microporous membrane which is a composite membrane can be obtained.

According to the present invention, each of the supporting layer separator and the non-porous layer has at least one or more multilayered structures, and has a multilayered structure of at least two or more layers as a whole.

The pore size of the support layer is 0.001 to 100 ㎛, the thickness of the support layer is preferably 1 to 50 ㎛.

In addition, the pore size of the non-porous layer formed by the phase separation method of the present invention is 0.001 to 100 ㎛, thickness is 0.1 to 20 ㎛.

In addition, the multilayer microporous membrane has a permeability of 5,000 sec / 100 cc or less at the melting point of the non-porous layer or less, and the multilayer microporous membrane has a permeability of 10,000 sec / 100 cc or more at the melting point of the non-porous layer.

The multi-layer microporous membrane thus prepared has a low non-porous initiation temperature and excellent stability, and thus may be used as a battery separator. In addition, the separator may be used in a lithium ion secondary battery.

In addition, the microporous membrane of the present invention can be used as a separator in a lithium ion polymer secondary battery containing a gel-like polymer electrolyte.

Hereinafter, the present invention will be described with reference to the following Examples and Comparative Examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example 1

Preparation of multilayer microporous membranes 1

The support layer polypropylene separator was prepared by the well-known dry method. Subsequently, 5% by volume of low density polyethylene (LDPE; melt index = 50 g / min, density = 0.916 g / cm 3 melting point = 103 ° C) was mixed with 95% by volume of cyclohexane and heated to 75 ° C to apply a homogeneous polymer. After the solution was prepared, it was dip-coated to the support layer separator thus prepared and dried at room temperature to form a non-porous layer. The physical properties of the final product thus prepared were measured in the following manner and the results are shown in Table 1 below.

[Property Test Method]

Air permeability: JIS P8117

Air permeability after heating at 120 ° C for 15 minutes: JIS P8117

Shutdown temperature

Membrane integrity temperature

Example 2

Preparation of multilayer microporous membranes 2

As in Example 1, a support layer polypropylene separator was prepared. Thereafter, 4% by volume of low density polyethylene (LDPE; melt index = 50 g / min, density = 0.916 g / cm 3 melting point = 103 ° C), 9% by volume of acetic acid, and 87% by weight of cyclohexane Heated to 75 ° C. to produce a homogeneous polymer coating solution, and then dip coating the previously prepared support layer separator. After drying for 30 seconds in room temperature air, the phases were separated by impregnation with ethanol. The physical properties of the prepared final product was measured in the same manner as described above for the air permeability, the start temperature of the non-porosity, the membrane breaking temperature and the results are shown in Table 1 below.

Comparative Example 1

PP / PE / PP 3-layer separator

For conventionally used polypropylene / polyethylene / polypropylene three-layer separator E157 (Celgard, Inc., USA), the air permeability, non-porous start temperature, and membrane breaking temperature were measured in the same manner as described above. It was.

division Example 1 Example 2 Comparative Example 1 Breathability (sec / 100cc) 400 300 370 Aeration after heating (sec / 100cc; 120 ° C, 15 minutes) 12,000 8,000 450 Non-Carburization Start Temperature (℃) 102 102 132 Membrane Break Temperature (℃) 165 165 165

In Table 1, the non-porous onset temperature of Example 1 and Example 2 was much lower than that of Comparative Example 1 at 102 ° C. In addition, when comparing the air permeability starting temperature and the air permeability after heating to 120 degreeC with the comparative example 1, it turns out that the battery isolation membrane of Example 1 produced the outstanding safety.

As described above, the multilayer microporous membrane according to the present invention has a low melting point polymer material formed on the surface of the support separation membrane to form a microporous membrane through a phase separation method, and has a very low degree of nonporosity without substantially impairing the permeability of the support separation membrane. Since the shape holding force is also excellent, a battery separator excellent in safety can be produced.

Claims (14)

(correction) a) a support layer of a polymer membrane having a pore size of 0.001 to 100 µm and a thickness of 1 to 50 µm; And b) a non-porous layer having a melting point applied to one or both sides of the support layer containing a polymer 40 to 75 ℃ lower than the support layer polymer of the a), the pore size of 0.001 to 100 ㎛, thickness 0.01 to 20 ㎛ Include, The air permeability of the multi-layer microporous membrane is a maximum of 5,000 seconds / 100cc at a temperature below the melting point of the non-porous layer, at least 10,000 seconds / 100cc at a temperature above the melting point of the non-porous layer, characterized in that the multilayer microporous membrane. (delete) The method of claim 1, The multi-layer microporous membrane of the a) the support layer is in the form of a blend or laminate (laminate). The method according to claim 1 or 3, The material of the support layer of a) is high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, polyethylene-propylene air. Copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, polystyrene, polyphenylene oxide, polysulfone At least one selected from the group consisting of polycarbonates, polyesters, polyamides, polyurethanes, polyacrylates, polyvinylidene chlorides, polyvinylidene fluorides, polysiloxanes, polyolefin ionomers, polymethyl pentenes and derivatives thereof Multilayer microporous membrane selected. The method according to claim 1 or 2, The material of the non-coating layer of b) is high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, ethylene vinyl Acetate copolymer, polyethylene-propylene copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, polystyrene , Polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene copolymer, polyethylene oxide, polyurethane, polyacrylonitrile, polyacrylate, polyacrylic acid, polyamide, polyacrylamide, polyvinylacetate, polyvinyl Pyrrolidone, Polytetraethylene Glycol Acrylate, polysulfone, polyvinylidene chloride, polyolefin ionomer (ionomer), and a multi-layer micro-pore membrane being at least one selected from the group consisting of their derivatives. (delete) (delete) (delete) In the manufacturing method of the multilayer microporous membrane, a) providing a support layer of a polymer membrane; b) lower than the melting point of the support layer polymer on one or both sides of the support layer Applying a polymer solution containing a polymer having a silver melting point; And c) drying the coating film as it is, or drying after impregnation with a non-solvent Forming an Uncoated Layer by Phase Separation Method Method for producing a multi-layer microporous membrane comprising a. The method of claim 9, The material of the supporting layer of step a) is high density polyethylene (high density polyethylene), low density polyethylene (low density polyethylene), linear low density polyethylene (poly low density polyethylene), polypropylene, high crystalline polypropylene (high crystalline polypropylene), polyethylene- Propylene copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, polystyrene, polyphenylene oxide, From the group consisting of polysulfones, polycarbonates, polyesters, polyamides, polyurethanes, polyacrylates, polyvinylidene chlorides, polyvinylidene fluorides, polysiloxanes, polyolefin ionomers, polymethyl pentenes and derivatives thereof Method for producing a multilayer microporous membrane selected from more than one species . The method of claim 9, The coating of step b) is a method of manufacturing a multilayer microporous membrane is carried out by a dip coating, casting, or brushing method. The method of claim 9, The polymer solution of step b) is Iii) high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, ethylene vinyl acetate copolymer, polyethylene-propylene Copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, polystyrene, polyvinylidene fluoride, Polyvinylidene fluoride hexafluoropropylene copolymer, polyethylene oxide, polyurethane, polyacrylonitrile, polyacrylate, polyacrylic acid, polyamide, polyacrylamide, polyvinylacetate, polyvinylpyrrolidone, polytetraethylene Glycol diacrylate, polysulfone 1 to 10% by volume of a polymer selected from the group consisting of polyvinylidene chloride, polyolefin ionomer and derivatives thereof; And Ii) group consisting of 1-methyl-2-pyrrolidone, n-hexane, diethyl ether, dimethylformamide, dimethylacetamide, dioxane, tetrahydrofuran, dimethylsulfoxide, cyclohexane, benzene, toluene, and xylene 90-99% by volume of at least one solvent selected from Method for producing a multi-layer microporous membrane comprising a. The method of claim 9, The non-solvent of step c) is multi-layered micropores selected from the group consisting of water, acetone, methanol, ethanol, n-propanol, n-butanol, and N-methylpyrrolidone (NMP; N-methyl pyrrolidone) Method of Making Membranes. A lithium ion secondary battery or lithium ion polymer secondary battery comprising the multilayer microporous membrane of claim 1 as a separator.