KR20220085098A - A separator and a method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention, a porous support; and a cross-linked electrolyte swellable polymer filled in the pores of the porous support, having an ionic conductivity of 1.0 * 10 ^-4 S/cm or more, and a puncture strength of 300 gf or more, and a method for manufacturing the same.

Description

Separator and its manufacturing method

The present invention relates to a separation membrane and a method for manufacturing the same.

Lithium secondary batteries are widely used as a power source for various electric products that require miniaturization and weight reduction, such as smartphones, laptops, and tablet PCs. The development of large, long-life, and high-stability lithium secondary batteries is required.

As a means for achieving the above object, a separator with micropores that separates the positive electrode and the negative electrode to prevent an internal short and facilitates the movement of lithium ions during charging and discharging, in particular, heat-induced phase separation (Thermally Induced Phase Separation) R&D on microporous membranes using polyolefins such as polyethylene, which is advantageous for pore formation, economical, and easy to meet the physical properties required for membranes, is active.

However, a separator using polyethylene having a low melting point of about 135° C. may undergo shrinkage deformation at a high temperature higher than the melting point due to heat generation of the battery. When a short circuit occurs due to such deformation, a thermal runaway phenomenon of the battery may occur, resulting in safety problems such as ignition.

On the other hand, the conventionally widely used polyolefin-based separator has weak heat resistance and mechanical strength, so when exposed at a temperature of 150° C. for about 1 hour, heat shrinkage occurs at 50 to 90%, and the function of the separator is lost. , there is a problem that an internal short circuit is highly likely to occur in the event of an external impact. In order to compensate for this problem, a technique of coating a heat-resistant layer containing ceramic particles on the surface of a separator has been proposed.

However, such a heat-resistant layer leaves significant technical challenges with respect to air permeability and conductivity (resistance), which are factors that have a very important effect on the performance of the separator. That is, when a heat-resistant layer containing ceramic particles is formed on the surface of the porous substrate, the heat resistance of the separator is improved, but the ceramic particles included in the heat-resistant layer close the pores formed in the porous substrate, thereby reducing the air permeability of the separator, and Accordingly, there is a problem in that the ion movement path between the positive electrode and the negative electrode is greatly reduced, and as a result, the charging and discharging performance of the secondary battery is greatly reduced.

In addition, as the heat-resistant layer is continuously exposed to the electrolyte inside the battery, the ceramic particles may be partially and continuously detached from the porous substrate, and in this case, the heat resistance of the separator may also be gradually reduced.

A method of improving heat resistance by crosslinking a polyolefin separator has been proposed. Japanese Patent Application Laid-Open Nos. Hei 11-144700 and 11-172036 disclose the invention of improving heat resistance by manufacturing a cross-linked separator using silane-modified polyolefin. There is a problem of being vulnerable to an external force applied to it, which is difficult to improve even through the coating as described above.

The present invention is to solve the problems of the prior art described above, and an object of the present invention is to improve the mechanical properties of the separator, in particular, the resistance to external force applied perpendicular to the surface of the separator, and to improve heat resistance and ionic conductivity An object of the present invention is to provide a separation membrane that can be implemented in a balanced manner and a method for manufacturing the same.

One aspect of the present invention, a porous support; and a crosslinked electrolyte swellable polymer filled in the pores of the porous support, having an ionic conductivity of 1.0 * 10 ^-4 S/cm or more, and a puncture strength of 300 gf or more.

In one embodiment, the filling ratio of the pores of the porous support of the electrolyte swellable polymer crosslinked body may be 90% or more.

In one embodiment, the porosity of the separation membrane may be 10% or less.

In one embodiment, the porous support may include one selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

In one embodiment, the porosity of the porous support is 30 ~ 90%, the average pore size is 20 ~ 100nm, the thickness may be 5㎛ or more.

In one embodiment, the porous support may further include an inorganic filler.

In one embodiment, the electrolyte swellable polymer crosslinked product may be produced by a crosslinking reaction of a polyfunctional monomer activated by an initiator.

In one embodiment, the separation membrane may satisfy one or more of the following conditions (i) to (iii).

(i) a meltdown temperature of 200°C or higher; (ii) 60% or less of longitudinal heat shrinkage at 150°C; (iii) Membrane resistance 150 mΩ or less.

Another aspect of the present invention comprises the steps of: (a) applying a monomer solution containing a polyfunctional monomer, an initiator, and a solvent having a boiling point of 150° C. or less to one surface of the first release film to generate a first layer; (b) laminating a porous support on the first layer; (c) forming a second layer by applying the monomer solution on the porous support; (d) laminating a second release film on the second layer, and then pressing the first and second release films to contact the porous support to move the first and second layers into the pores of the porous support penetrating and integrating; (e) applying energy to the integrated first and second layers to crosslink the polyfunctional monomer; and (f) removing the first and second release films.

In one embodiment, the content of the polyfunctional monomer in the monomer solution may be 10 to 30% by weight.

Separation membrane according to an aspect of the present invention, a porous support; And it is possible to significantly improve mechanical properties and heat resistance by including the cross-linked electrolyte swellable polymer filled in the pores of the porous support, and to secure the required level of ionic conductivity based on the electrolyte permeability according to the swelling behavior of the cross-linked polymer. can

It should be understood that the effects of the present invention are not limited to the above-described effects, and include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 and 2 are schematic diagrams of the swelling characteristics of the electrolyte swellable polymer crosslinked product according to an embodiment of the present invention and the electrolyte permeation principle thereof.
3 is a schematic diagram of a method for manufacturing a separator according to an embodiment of the present invention.

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case where it is "directly connected" but also the case where it is "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

One aspect of the present invention, a porous support; and a crosslinked electrolyte swellable polymer filled in the pores of the porous support, having an ionic conductivity of 1.0 * 10 ^-4 S/cm or more, and a puncture strength of 300 gf or more.

The porous support may supplement the weak mechanical properties and stability of the electrolyte swellable polymer crosslinked body by fixing and supporting the electrolyte swellable polymer crosslinked body in the separation membrane. In addition, the electrolyte swellable polymer crosslinked product may exist in a crosslinked state inside the pores of the porous support, and in some cases, polymer chains included in the inner wall of the pores, for example, adjacent ones of polyolefin chains are crosslinked By doing so, the mechanical properties and heat resistance of the porous support can be improved.

The electrolyte swellable polymer crosslinked body is substantially completely filled in the pores of the porous support, preferably not only the pores located on the surface of the porous support, but also the pores located at the center of the porous support to significantly lower the porosity of the separation membrane, so the separation membrane It is possible to improve the resistance to the external force applied perpendicular to the surface of the.

90% or more, preferably, 95% or more, more preferably, 99% or more of the total volume of the pores of the porous support may be completely impregnated and filled with the electrolyte swellable polymer crosslinked product. If the filling ratio of the electrolyte swellable polymer crosslinked body to the pores of the porous support is less than 90%, the electrolyte swellable polymer crosslinked body cannot be continuously formed from one side of the porous support to the other surface. In this case, at least a portion of the separation membrane There is a problem in that it is difficult to secure a required level of ionic conductivity because the movement path of the electrolyte is blocked by the crosslinked electrolyte swellable polymer in the region.

In addition, in a state in which the electrolyte swellable polymer crosslinked body is filled in the pores of the porous support, the porosity of the separator may be 10% or less, preferably 5% or less, more preferably 1% or less. When the porosity of the separator is more than 10%, resistance to external force applied perpendicular to the surface of the separator may be lowered like a conventional separator including micropores.

1 and 2 are schematic diagrams of the swelling characteristics of the electrolyte swellable polymer crosslinked product according to an embodiment of the present invention and the electrolyte permeation principle according thereto.

Referring to FIG. 1 , the electrolyte swellable polymer crosslinked product may be reversibly converted into a swelling and deswelling state depending on whether or not it is in contact with an electrolyte having a predetermined concentration. Specifically, when the electrolytic solution swellable polymer crosslinked body comes into contact with a predetermined electrolyte solution, some regions of the polymer crosslinked body, for example, a side chain, may be charged, and the adjacent side chain also has the same charge, so that the repulsive force between the adjacent side chains is increased. can work This repulsive force may swell the polymer crosslinked body by separating the polymer chains constituting the polymer crosslinked body from each other. Conversely, when the electrolyte solution is removed from the electrolytic solution swellable polymer crosslinked body, the charge imparted to some regions of the polymer crosslinked body and the resulting repulsive force disappear, and the polymer crosslinked body may be de-swelled.

The electrolyte swellable polymer crosslinked product filled in the pores of the porous support may permeate the electrolyte according to the swelling-deswelling behavior as described above when in contact with a liquid electrolyte, that is, the electrolyte. Referring to Figure 2, the electrolyte swellable polymer crosslinked product in contact with the electrolyte of a predetermined concentration can be gradually swollen up to the maximum degree of swelling allowed over time, and after swelling to the maximum degree of swelling (s ₁ ) (t ₀ ) reaches a steady state and no longer swells, and in the swollen state, the substances contained in the electrolyte present on both sides of the separation membrane, for example, depending on the concentration gradient of various ions, these ions are formed in the separation membrane. can be permeable. The maximum swelling degree of the electrolyte swellable polymer crosslinked product, that is, the critical value that can swell to the extent that it does not dissolve may depend on the concentration of the electrolyte solution, so it is necessary to appropriately adjust the concentration of the electrolyte solution so that the electrolyte solution swellable polymer crosslinked product does not dissolve there is

In this way, in the separation membrane, the electrolyte swellable polymer crosslinked body is continuously formed by filling and penetrating the pores of the porous support, so that various ions contained in the electrolyte solution can permeate according to the swelling-deswelling behavior, so the ions of the separation membrane Conductivity may be improved, and uniform ionic conductivity may be implemented in the entire region of the separation membrane.

The ionic conductivity of the separator may be 1.0*10 ^-4 S/cm or more, preferably, 2.0*10 ^-4 S/cm or more, more preferably, 4.0*10 ^-4 S/cm or more, and the The puncture strength may be 300 gf or more, preferably 500 gf or more, and more preferably, 680 gf or more.

The porous support may include a plurality of pores having a substantially uniform average size, and these pores may contribute to improvement of resistance properties and ionic conductivity of the separation membrane. In addition, the separation membrane can be thinned to a required thickness due to high porosity and high mechanical strength.

The porosity of the porous support may be 30 to 90%, preferably, 30 to 80%, more preferably, 30 to 70%. As used herein, the term “porosity” refers to the ratio of the volume occupied by pores to the total volume in any porous article. If the porosity of the porous support is less than 50%, air permeability and ionic conductivity may be reduced, and if it exceeds 90%, mechanical properties such as tensile strength and puncture strength may be reduced.

The average size of the pores included in the porous support may be 20 ~ 100nm, preferably, 20 ~ 80nm, more preferably, 30 ~ 60nm. If the average size of the pores is less than 20 nm, air permeability and ionic conductivity may be reduced, and if it exceeds 100 nm, mechanical properties such as tensile strength and puncture strength may be reduced.

The thickness of the porous support is 5 μm or more, preferably, 5 μm or more, in terms of ion conductivity, heat resistance, and mechanical properties of the separation membrane, in terms of thinning and high energy density of the electrochemical device including the separation membrane It may be ~20㎛, more preferably, 8 ~ 15㎛. If the thickness of the porous support is less than 5㎛, mechanical properties, in particular, the puncture strength may be reduced.

The porous support may include a polymer resin having electrical insulation, and the polymer resin may include a thermoplastic resin in consideration of shutdown characteristics. As used herein, the term "shutdown characteristic" means that when the temperature of the battery is increased due to overheating, the polymer resin melts and closes the pores of the porous support to block the movement of ions. From this point of view, the melting point of the polymer resin or the thermoplastic resin may be 200° C. or less.

The thermoplastic resin may include, for example, one selected from the group consisting of polyethylene, polypropylene, polypentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. , preferably, at least one of polyethylene and polypropylene, and more preferably, polyethylene.

The polyethylene is ultra high molecular weight polyethylene (UHMWPE, Mw: 1,000,000 ~ 7,000,000 g / mol), high molecular weight polyethylene (HMWPE, Mw: 100,000 ~ 1,000,000 g / mol), high density polyethylene (HDPE, Mw: 100,000 ~ 1,000,000 g / mol), It may be one selected from the group consisting of low-density polyethylene (LDPE, Mw: 10,000 to 100,000 g/mol), homogeneous linear and linear low-density polyethylene (LLDPE), and combinations of two or more thereof.

For example, the polyethylene may be a high-density polyethylene having a weight average molecular weight (M _w ) of 250,000 to 450,000. If the weight average molecular weight of the polyethylene is more than 450,000, the viscosity may increase and processability may be deteriorated. If the weight average molecular weight of the polyethylene is less than 250,000, the viscosity is excessively low and the dispersibility with pore formers and antioxidants used to prepare the porous support is extremely low. and, in some cases, phase separation or layer separation may occur.

The porous support may be a so-called crosslinked porous support having a structure in which at least a portion of polyethylene is crosslinked by a crosslinkable compound. For example, the crosslinked porous support may include a continuous phase matrix including polyethylene and a silane-modified polyethylene crosslinked in the continuous phase matrix to support the continuous phase matrix.

The silane-modified polyethylene may mean that alkoxyvinylsilane is grafted in a polyethylene chain, and the alkoxyvinylsilane grafted in the polyethylene chain may react with moisture under a predetermined condition to cross-link the polyethylene chain. .

Since the crosslinked porous support has a higher meltdown temperature than the uncrosslinked porous support, the heat resistance of the separator can be significantly improved, but tensile properties of the separator may be deteriorated by crosslinking, so the content of the silane-modified polyolefin in the separator may be adjusted to 0.1 to 50% by weight, preferably 0.1 to 30% by weight.

The electrolyte swellable polymer crosslinked product may be produced by a crosslinking reaction of a polyfunctional monomer activated by an initiator. The type of the initiator is not particularly limited as long as the initiator is capable of imparting a radical to the polyfunctional monomer and inducing a crosslinking reaction between the polyfunctional monomers by the radical.

The type of the polyfunctional monomer is not particularly limited as long as it can be activated and crosslinked by energy such as heat, light, or a combination thereof in the presence of an initiator. The polyfunctional monomer may have 2 or more, preferably 2 to 6 functional groups per molecule. If the number of functional groups per molecule of the polyfunctional monomer is less than two, crosslinking may be delayed, and if more than six, it is difficult to control crosslinking.

The polyfunctional monomer is, for example, trimethylolpropane-ethoxylate triacrylate, acrylic acid (acrylic acid), carboxyethyl acrylate (carboxyethyl acrylate), polyacrylic acid (poly acrylic acid), carboxy Methyl cellulose, alginate, polyvinyl alcohol, agarose, polyethylene glycol diacrylate, triethylene glycol diacrylate, trimethyl Allpropane ethoxylate triacrylate, bisphenol-A ethoxylate dimethaacrylate, carboxyethyl acrylate, methyl cyanoacrylate , ethyl cyanoacrylate, ethyl cyano ethoxyacrylate, cyano acrylic acid, hydroxyethyl methacrylate, hydroxypropyl acrylate ( hydroxypropyl acrylate), derivatives thereof, and a combination of two or more thereof may be selected from the group consisting of, but is not limited thereto.

The porous support may further include an inorganic filler. The inorganic filler may supplement or improve mechanical properties deteriorated as the porosity of the porous support increases.

The inorganic filler is, for example, silica (SiO ₂ ), TiO ₂ , Al ₂ O ₃ , zeolite, AlOOH, BaTiO ₂ , talc (Talk), Al(OH) ₃ , CaCO ₃ and 2 of these It may be one selected from the group consisting of the above combinations, preferably, spherical nanoparticles having an average particle size of 10 to 1,000 nm, more preferably, nanoparticles whose surface is hydrophobized or hydrophilized. For example, silica (SiO ₂ ) may have a hydrocarbon layer formed of hydrophobic linear hydrocarbon molecules on its surface. Since silica itself has hydrophilic properties, in order to improve compatibility with hydrophobic polyethylene, spherical silica nanoparticles coated with linear hydrocarbon molecules, for example, (poly)ethylene, are suitable.

The content of the inorganic filler in the porous support may be 10 to 70% by weight, preferably, 10 to 60% by weight. If the content of the inorganic filler is less than 10% by weight, mechanical strength, acid resistance, chemical resistance, and flame retardancy of the porous support may be reduced, and if it is more than 70% by weight, flexibility and workability of the porous support may be reduced.

The separation membrane may satisfy one or more of the following conditions (i) to (iii), preferably, all of the conditions (i) to (iii). (i) a meltdown temperature of 200°C or higher, preferably, 210°C or higher, more preferably, 210 to 350°C; (ii) 60% or less of longitudinal heat shrinkage at 150°C, preferably 50% or less; (iii) Film resistance 150 mΩ or less, preferably 120 mΩ or less.

3 is a schematic diagram of a method for manufacturing a separator according to an embodiment of the present invention. Referring to FIG. 3 , in the method of manufacturing a separator according to another aspect of the present invention, (a) a monomer comprising a polyfunctional monomer, an initiator, and a solvent having a boiling point of 150° C. or less on one surface of the first release film 11 applying the solution to create a first layer (21); (b) laminating a porous support 30 on the first layer 21; (c) forming a second layer 22 by applying the monomer solution on the porous support 30; (d) laminating a second release film 12 on the second layer 22 and then pressing the first and second release films 11 and 12 to contact the porous support 30 to Infiltrating and integrating the first and second layers (21, 22) into the pores (31) of the porous support (30); (e) applying energy to the integrated first and second layers (21, 22) to crosslink the polyfunctional monomer; and (f) removing the first and second release films 11 and 12 .

In step (a), a monomer solution containing a polyfunctional monomer, an initiator, and a solvent having a boiling point of 150° C. or less is applied to one surface of the first release film 11 to produce the first layer 21. . The first release film 11 may be a resin film through which the energy applied in step (e) can be transmitted, and the first layer 21 and The opposing surface may be physically and/or chemically treated.

The solvent may be a solvent having a boiling point of 150° C. or less, preferably 100° C. or less, and more preferably, 30-100° C. Such solvents are, for example, water, alcohols, ethoxyethanol, methoxyethanol, lactone, acetonitrile, acetone, methylethylketone, tetrahydrofuran, dimethylformaldehyde, cyclohexane, n-methyl-2-pyrroly. Don (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, water, and may be one selected from the group consisting of a combination of two or more thereof, but is not limited thereto.

The solvent can be easily removed at a temperature of 100° C. or less after crosslinking the polyfunctional monomer in the monomer solution filled in the pores of the porous support, and the polyfunctional monomer inside the pores of the porous support in the separation membrane The electrolytic solution swellable polymer crosslinked product formed by crosslinking may be introduced.

If the boiling point of the solvent is greater than 150° C., excess energy may be consumed to remove it, and when the drying temperature is lowered to avoid this, a solvent having no conductivity inside the pores of the porous support remains, so that the ions of the separator Conductivity may be reduced. In addition, the solvent remaining inside the pores of the porous support may lower the bonding force between the inner wall of the pores and the electrolyte swellable polymer crosslinked body, thereby reducing the puncture strength of the separator.

In addition, the first release film 11 may have various physical properties according to the type of energy applied in step (e). For example, when the energy is light, preferably UV, it may transmit such UV, and when the energy is heat, it may be capable of sufficiently conducting such heat, and the energy is light and heat. In the case of a combination, it may be one that transmits light and conducts heat at the same time.

The content of the polyfunctional monomer in the monomer solution may be 10 to 30% by weight. If the content of the polyfunctional monomer in the monomer solution is less than 10% by weight, the polyfunctional monomer filled in the pores is not sufficiently crosslinked, or even if crosslinked, the amount of the electrolyte swellable polymer crosslinked product generated inside the pores is very small. The puncture strength and heat resistance of the separator may be lowered, and the ionic conductivity may be significantly lowered. In addition, if the content of the polyfunctional monomer in the monomer solution is more than 30% by weight, the crosslinking density of the electrolyte swellable polymer crosslinked product filled in the pores of the porous support is excessively increased, so that swelling-de-swelling behavior may be inhibited, Accordingly, the ionic conductivity of the separation membrane may be reduced.

The monomer solution may include a polyfunctional monomer, an initiator, and a solvent having a boiling point of 150° C. or less, and the functional effects, ratios, types, etc. of the polyfunctional monomer, initiator and solvent are the same as described above.

In step (b), the porous support 30 may be laminated on the first layer 21 . The porous support 30 is laminated on top of the first layer 21 in a state in which the first layer 21 is not dried and/or gelled, that is, in a state having a certain level of fluidity and flowability, At this time, a portion of the first layer 21 may penetrate to a predetermined depth into the pores 31 located on the contact surface when in contact with the porous support 30 due to the capillary effect. The operational effects, materials, properties, specifications, etc. of the porous support 30 are the same as those described above.

In step (c), the second layer 22 may be formed by applying the monomer solution on the porous support 30 . The monomer solution for forming the second layer 22 may be the same as that used for forming the first layer 21, and its components, effects, ratios, types, etc. are the same as those described above. Since the second layer 22 applied on the porous support 30 also has a non-dried and/or gelled state, that is, a certain level of fluidity and flowability, some of the second layer 22 is When in contact with the porous support 30 due to the capillary effect, it can penetrate to a predetermined depth into the pores 31 located on the contact surface.

In step (d), a second release film 12 is laminated on the second layer 22 , and then the first and second release films 11 and 12 are brought into contact with the porous support 30 . The first and second layers 21 and 22 may be penetrated into the pores 31 of the porous support 30 and integrated therein.

Referring to FIG. 3 , the first and second layers 21 and 22 applied to both sides of the porous support 30 in steps (a) to (c) are formed by the capillary effect of the porous support 30 ) can only penetrate to a certain depth into the pores 31 located on both surfaces of the surface, and the first and second layers 21 and 22 are the inside of the porous support 30 only by this capillary effect, preferably , there is a problem that it cannot penetrate to the pores located in the center.

That is, the first and second layers 21 and 22 cannot be continuously formed from one surface to the other surface of the porous support 30 only by penetration by the capillary effect, and in this case, at least a portion of the separation membrane, specifically As a result, the conductive path by the first and second layers 21 and 22 is blocked at the center, so there is a problem in that it is difficult to secure a required level of ionic conductivity.

Therefore, by pressing the first and second release films 11 and 12 toward the center of the porous support 30 in step (d), the first and second layers 21 and 22 are the porous It is possible to completely penetrate up to the pores 31 located in the center of the support 30 , and the first and second layers 21 and 22 are in contact with each other in the pores 31 located in the center of the porous support 30 . can be integrated.

This pressurization may be made until the first and second release films 11 and 12 come into contact with both surfaces of the porous support 30, respectively.

When the pressing is terminated in a state in which the first and second release films 11 and 12 are not in contact with both surfaces of the porous support 30, respectively, that is, the first and second release films 11, When a certain amount of the first and second layers 21 and 22 remain between 12) and both sides of the porous support 30, both sides of the porous support 30 by subsequent steps (e) and (f). Also, a layer including the electrolyte swellable polymer crosslinked product may be formed to a predetermined thickness.

Such a layer may also exhibit swelling-deswelling behavior when in contact with the electrolyte, and since its cross-sectional area is large compared to the cross-sectional area of the pores 31 of the porous support 30, trying to penetrate the separation membrane at the interface between the layer and the pores The movement of ions through the separation membrane may be inhibited by a substance, for example, a so-called “bottleneck” in which ions are concentrated and overcrowded. Therefore, by pressing the first and second release films 11 and 12 to contact the porous support 30 in step (d), these layers are generated on both sides of the porous support 30 can be prevented

The second release film 12 may also be a resin film through which the energy applied in step (e) can be transmitted, and the second layer 22 and The opposing surface may be physically and/or chemically treated.

In addition, the second release film 12 may have various physical properties depending on the type of energy applied in step (e). For example, when the energy is light, preferably UV, it may be one capable of transmitting such UV, and when the energy is heat, it may be one capable of sufficiently conducting such heat, and the energy is light and heat. In the case of a combination, it may be one that transmits light and conducts heat at the same time.

In step (e), by applying energy to the integrated first and second layers 21 and 22 to crosslink the polyfunctional monomer filled in the pores 310 of the porous support 30, the electrolyte swellability A polymer crosslinked body can be formed. The energy may be one selected from the group consisting of heat, light, electron beam, and a combination of two or more thereof, preferably, heat or light, more preferably, UV, but is not limited thereto. Through the step (e), the polyfunctional monomer included in the monomer solution may be cross-linked to gel (harden) the integrated first and second layers 21 and 22.

In the step (f), the porous support 30 by removing the first and second release films 11 and 12; and an electrolyte-swellable polymer crosslinked body 20 filled in the pores 30 of the porous support 30 can be obtained.

At this time, it is necessary to minimize damage to the surfaces of the first and second layers 21 and 22 as the first and second release films 11 and 12 are peeled off. When the release film is peeled off, when some of the first and/or second layers that have been in contact with the release film are peeled off together, the effect of the crosslinked electrolyte swellable polymer filled in the pores of the porous support is appropriately evaluated. Because it cannot be implemented.

As such, in order to selectively remove only the first and second release films 11 and 12 without damaging the surfaces of the first and second layers 21 and 22, the first and second release films 11 , 12), but with different thicknesses, it is preferable to first remove the thin release film among them in step (f), and then remove the thick release film later. Each of the first and second release films 11 and 12 may have a thickness of 1 to 100 μm, preferably, 10 to 100 μm, but is not limited thereto.

Within the above range, the thickness of the first release film 11 may be 25 to 100 μm, and the thickness of the second release film 12 may be 1 to 24 μm, and in this case, step (f) By removing the first release film 11 after removing the second release film 12 from the have.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

(1) Preparation of monomer solution

A monomer solution was prepared by uniformly mixing 90 g of ethanol, 10 g of polyethylene glycol 400 diacrylate (PEG(400) DA), and 1 g of trimethylbenzoyl phenylphosphinate (TPO).

(2) Preparation of separation membrane

The monomer solution was applied to one side of a polyethylene terephthalate (PET) release film having a thickness of 50 μm, and then a polyethylene porous membrane (permeability: 150 sec/100 ml, thickness: 14 μm, porosity: 45 vol%) was laminated. . After applying the monomer solution on the polyethylene porous film, a polyethylene terephthalate (PET) release film having a thickness of 23 μm was laminated, and the release film and the polyethylene porous film were roll-pressed to form the release film with the polyethylene porous film. A structure in which the polyethylene porous membrane interposed between the release films was completely impregnated in the monomer solution was obtained.

100W UV is irradiated to both sides of the structure for 5 seconds to impregnate the pores of the polyethylene porous membrane, and to cure the monomer solution applied to the surface, and then laminated on both sides of the structure to have a thickness of 23 μm The release film and the release film having a thickness of 50 μm were sequentially removed to obtain a precursor film. The precursor film was left in an oven preheated to 90° C. to remove ethanol remaining in the precursor film to prepare a separator.

Example 2

(1) Preparation of monomer solution

Ethanol 80g, polyethylene glycol 400 diacrylate (Polyethylene Glycol 400 Diacrylate, PEG(400)DA) 20g, trimethylbenzoyl phenylphosphinate (Trimethylbenzoyl Phenylphosphinate, TPO) 1g was uniformly mixed to prepare a monomer solution.

(2) Preparation of separation membrane

A separation membrane was prepared in the same manner as in Example 1.

Example 3

(1) Preparation of monomer solution

A monomer solution was prepared in the same manner as in Example 2 above.

(2) Preparation of separation membrane

Except for using a polyethylene porous membrane (permeability: 100 sec/100ml, thickness: 5.5㎛, porosity: 32 vol%) instead of a polyethylene porous membrane (permeability: 150 sec/100ml, thickness: 14㎛, porosity: 45 vol%) A separation membrane was prepared in the same manner as in Example 1.

Example 4

(1) Preparation of monomer solution

Ethanol 70g, polyethylene glycol 400 diacrylate (Polyethylene Glycol 400 Diacrylate, PEG(400)DA) 30g, trimethylbenzoyl phenylphosphinate (Trimethylbenzoyl Phenylphosphinate, TPO) 1g was uniformly mixed to prepare a monomer solution.

(2) Preparation of separation membrane

A separation membrane was prepared in the same manner as in Example 1.

Example 5

(1) Preparation of monomer solution

A monomer solution was prepared in the same manner as in Example 2.

(2) Preparation of separation membrane

29.5 parts by weight of high-density polyethylene having a weight average molecular weight (M _w ) of 350,000, molecular weight distribution (M _w /M _n ) of 5, 0.5 parts by weight of silane-modified high-density polyethylene, and 70 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40°C The mixture was mixed and put into a twin screw extruder (inner diameter 58mm, L/D=56, twin screw extruder). Dibutyltin dilaurate, a crosslinking catalyst, was pre-dispersed in a part of the paraffin oil, and added through the side injector of the twin-screw extruder so as to be 0.5 wt% based on the total weight of the material passing through the twin-screw extruder. After discharging from the twin-screw extruder to a T-die having a width of 300 mm under the conditions of 200° C. and a screw rotation speed of 40 rpm, a base sheet having a thickness of 800 μm was prepared by passing it through a casting roll having a temperature of 40° C.

A stretched film was prepared by stretching the base sheet 6 times in the longitudinal direction (MD) in a roll stretching machine at 110° C., and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 125° C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 50° C. for 5 minutes.

Thereafter, after heating to 125° C. in a tenter stretching machine, it was stretched 1.45 times in the transverse direction (TD) and then relaxed and heat-set so as to be 1.25 times compared to before stretching. The film was cross-linked in a constant temperature and humidity bath at 85 ° C. and humidity of 85% for 72 hours to form a cross-linked polyethylene porous membrane (permeability: 129 sec/100 ml, thickness: 9.6 μm, porosity: 52 vol%, meltdown temperature: 210 ° C). prepared.

The polyethylene porous membrane (permeability: 150 sec/100ml, thickness: 14㎛, porosity: 45 vol%) instead of a cross-linked polyethylene porous membrane (permeability: 129 sec/100ml, thickness: 9.6㎛, porosity: 52 vol%, meltdown temperature : 210° C.), a separation membrane was prepared in the same manner as in Example 1, except that it was used.

Comparative Example 1

(1) Preparation of monomer solution

A monomer solution was prepared in the same manner as in Example 2.

(2) Preparation of separation membrane

A separator was prepared in the same manner as in Example 1, except that a polyethylene porous membrane (permeability: 150 sec/100ml, thickness: 14 μm, porosity: 45 vol%) was not used.

Comparative Example 2

The polyethylene porous membrane used in Example 1 and the like (permeability: 150 sec/100ml, thickness: 14㎛, porosity: 45% by volume) was applied as a separator.

Comparative Example 3

(1) Preparation of monomer solution

Ethanol 92g, polyethylene glycol 400 diacrylate (Polyethylene Glycol 400 Diacrylate, PEG(400)DA) 8g, trimethylbenzoyl phenylphosphinate (Trimethylbenzoyl Phenylphosphinate, TPO) 1g was uniformly mixed to prepare a monomer solution.

(2) Preparation of separation membrane

A separation membrane was prepared in the same manner as in Example 1.

Comparative Example 4

(1) Preparation of monomer solution

Ethanol 68g, polyethylene glycol 400 diacrylate (Polyethylene Glycol 400 Diacrylate, PEG(400)DA) 32g, trimethylbenzoyl phenylphosphinate (Trimethylbenzoyl Phenylphosphinate, TPO) 1g was uniformly mixed to prepare a monomer solution.

(2) Preparation of separation membrane

A separation membrane was prepared in the same manner as in Example 1.

Experimental Example 1

The physical properties of the separation membranes prepared according to Examples and Comparative Examples were measured and evaluated according to the following method, and the results are shown in Tables 1 and 2 below. Unless otherwise stated, measurements were made at room temperature (25° C.).

-Thickness (㎛): The thickness of the separator specimen was measured using a micro-thickness meter.

- Porosity (%): Based on ASTM F316-03, the porosity of the separator having a radius of 25 mm was measured using a capillary porometer manufactured by PMI.

-Puncture strength (gf): Using KATO TECH's KES-G5 puncture strength measuring instrument model, apply force to a separator sample with a size of 100 × 50 mm with a stick with a diameter of 0.5 mm at a rate of 0.05 cm/sec. The force applied when the specimen was pierced was measured.

-Heat shrinkage rate (%): After placing a 200 × 200 mm separator sample in an oven at 140° C. and 150° C. for 1 hour and leaving it in between A4 paper, it is cooled to room temperature to shrink the length of the specimen in the longitudinal direction (MD) was measured and the heat shrinkage rate was calculated using the following formula.

Heat shrinkage (%)=(l ₃ -l ₄ )/l ₃ *100

(In the above formula, l ₃ is the longitudinal length of the specimen before contraction, and l ₄ is the longitudinal length of the specimen after contraction.)

-Meltdown temperature (MDT, ℃): Using a thermomechanical analysis (TMA), a force of 0.01N was applied to the separator specimen, and then the temperature was raised at a rate of 5°C/min to measure the degree of deformation of the separator specimen. The temperature at which the specimen was fractured was taken as the meltdown temperature.

division Example 1 Example 2 Example 3 Example 4 Example 5 support thickness 14 14 5.5 14 9.6 Separator thickness 14 14 5.5 14 9.6 Membrane Porosity ≤1.0 ≤0.5 ≤0.5 ≤0.1 ≤0.5 punching strength 684 792 402 804 828 Heat shrinkage (MD, 140℃) 42 40 40 39 37 Thermal shrinkage (MD, 150℃) 49 45 55 44 41 Meltdown temperature 205 210 203 214 225

division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 support thickness no support 14 14 14 Separator thickness 20 14 14 14 Membrane Porosity 0 50 ≤1.0 ≤0.1 punching strength Measurable 634 651 833 Heat shrinkage (MD, 140℃) Measurable 65 46 38 Thermal shrinkage (MD, 150℃) Measurable 68 57 43 Meltdown temperature Measurable 145 187 231

Experimental Example 2

A coin cell was manufactured by inserting the separator prepared according to the above Examples and Comparative Examples between the SUS electrodes having a thickness of 1 mm. As the electrolyte solution, LiPF ₆ dissolved in a concentration of 1.15M in a solvent in which ethylene carbonate and methylene carbonate were mixed in a volume ratio of 30:70, respectively, was used.

The impedance and ionic conductivity of the separator inserted into the coin cell were measured 5 times using EIS (Electrochemical Mpedance Spectroscopy) at a frequency of 10 ⁴ to 10 ⁶ Hz, a current of 10.0 mV, a voltage range of ±10V, and a temperature of 25°C. The average value was obtained, and the results are shown in Table 3 below.

division Impedance (mΩ) Ion Conductivity (S/cm) Example 1 128 4.9 E-04 Example 2 120 5.2 E-04 Example 3 116 2.1 E-04 Example 4 115 5.4 E-04 Example 5 118 3.6 E-04 Comparative Example 1 207 4.3 E-04 Comparative Example 2 70 8.9 E-04 Comparative Example 3 Measurable (uncured) Measurable (uncured) Comparative Example 4 702 8.9 E-05

The description of the present invention described above is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

11: first release film
12: second release film
20: electrolyte swellable polymer crosslinked product
21: first floor
22: second floor
30: porous support
31: Qigong

Claims (10)

porous support; and
Including an electrolyte swellable polymer crosslinked body filled in the pores of the porous support,
The ionic conductivity is 1.0*10 ^-4 S/cm or more, and the puncture strength is 300gf or more, the separation membrane. According to claim 1,
The filling ratio of the electrolyte swellable polymer crosslinked body with respect to the pores of the porous support is 90% or more, the separation membrane. According to claim 1,
The porosity of the separation membrane is 10% or less, the separation membrane. According to claim 1,
The porous support is a separator comprising one selected from the group consisting of polyethylene, polypropylene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. According to claim 1,
The porosity of the porous support is 30 ~ 90%, the average pore size is 20 ~ 100nm, the thickness is 5㎛ or more, the separation membrane. 4. The method of claim 3,
The porous support further comprises an inorganic filler, the separation membrane. According to claim 1,
The electrolyte swellable polymer crosslinked product is a separator that is generated by a crosslinking reaction of a polyfunctional monomer activated by an initiator. According to claim 1,
The separation membrane satisfies one or more of the following conditions (i) to (iii), a separation membrane:
(i) a meltdown temperature of 200°C or higher;
(ii) 60% or less of longitudinal heat shrinkage at 150°C;
(iii) Membrane resistance 150 mΩ or less. In the method for manufacturing the separation membrane according to any one of claims 1 to 8,
(a) forming a first layer by applying a monomer solution containing a polyfunctional monomer, an initiator, and a solvent having a boiling point of 150° C. or less on one surface of the first release film;
(b) laminating a porous support on the first layer;
(c) forming a second layer by applying the monomer solution on the porous support;
(d) laminating a second release film on the second layer, and then pressing the first and second release films to contact the porous support to move the first and second layers into the pores of the porous support penetrating and integrating;
(e) applying energy to the integrated first and second layers to crosslink the polyfunctional monomer; and
(f) removing the first and second release films; comprising, a method of manufacturing a separator. 10. The method of claim 9,
The content of the polyfunctional monomer in the monomer solution is 10 to 30% by weight, the method of manufacturing a separation membrane.

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