KR20170029399A - Method for manufacturing porous film, the porous film, and electro-chemical battery or separator comprising the porous film - Google Patents

Abstract

The present invention relates to a method of producing a porous film, a porous film produced by the method, and a separator or an electrochemical cell comprising the porous film, the method of producing a porous film including: extrusion-molding a composition comprising a crystalline resin, capable of forming a lamellar, and pore-forming particles so as to form a precursor film; annealing the precursor film at a temperature between (Tm-80)C and (Tm-3)C; and first-stretching the annealed precursor film to between 50% and 400% at 0-50C, wherein the pore-forming particles are included to be 5 parts by volume to 40 parts by volume with respect to 100 parts by volume of the entire composition, and wherein Tm is the melting temperature of the crystalline resin.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous film, a porous film produced therefrom, and a separator or an electrochemical cell containing the same. BACKGROUND ART [0002]

The present invention relates to a process for producing a porous film and a porous film produced by the process. The present invention also relates to a separation membrane or an electrochemical cell including the porous film.

A separator for an electrochemical cell is an interlayer which separates an anode and a cathode from each other in a battery while maintaining the ionic conductivity to enable charging and discharging of the battery. The separator is made of a porous film.

Examples of the method for producing such a porous film include a dry process and a wet process. The dry process is a process in which a precursor film is extruded and then the orientation of the lamellar is controlled through heat treatment such as annealing and stretched to form pores. Since the dry process (Korean Patent Publication No. 2008-0085922) does not use an extraction solvent as compared with a wet process, it is eco-friendly and cost-competitive, but since it forms pores by stretching between crystals and amorphous of a single substance, There is a problem that the tensile strength in the direction is lowered. In addition, when pores are formed between crystalline and amorphous materials, the pore size is determined by the difference in the strength of crystal and amorphous material, and thus the pore size is determined by the type of material. Therefore, in the case of polyethylene, the pore size is excessively large, making it difficult to use it as a separator for a secondary battery.

The wet process refers to a method of mixing a polymer material with a plasticizer, extruding the polymer material to form a sheet, and removing the plasticizer from the sheet to form pores. In the wet process, the size of the pores is determined by controlling the compatibility with the plasticizer. However, it is difficult to apply the same process to other materials except polyethylene.

Korean Patent Publication No. 2008-0085922

The present invention provides two types of pores having different morphology and size, which are easier to manufacture and more efficient in production process than those of the above-mentioned prior arts, and have excellent air permeability, porosity, tensile strength and thermal stability To provide a porous film. Furthermore, it is intended to improve cell safety and long-term reliability in an electrochemical cell including the pore by controlling the porosity and air permeability while keeping the average size of pores of the porous film small.

One embodiment of the present invention is a porous film comprising a pore-forming particle and a crystalline resin capable of forming a lamellar, wherein the porous film has a first pore formed by the pore-forming particles, Wherein the volume of the first pore is larger than the volume of the second pore.

Another embodiment of the present invention provides a separator comprising the porous film or a functional layer formed on one side or both sides of the porous film.

Another embodiment of the present invention relates to a method for producing a precursor film, which comprises extruding a composition comprising a crystalline resin capable of forming a lamellar and pore-forming particles to form a precursor film and heating the precursor film to a temperature of (Tm-80) 3) 占 폚, and stretching the annealed film at a low temperature of 0 占 폚 to 50 占 폚 by 50% to 400%, wherein the Tm is the crystalline resin ≪ / RTI >

The porous film according to one embodiment of the present invention is easy to manufacture and has a high production efficiency, so that the manufacturing cost can be remarkably reduced. Also, it is possible to provide a porous film having two types of pores having different morphologies and sizes, having a small pore size, and having excellent air permeability, porosity, tensile strength and thermal stability. Further, by controlling the average size of the pores, battery safety and long-term reliability can be improved in an electrochemical cell including a porous film.

 By including two types of pores having different morphologies and sizes, the electrochemical cell including the same can have a low probability of occurrence of electrical short-circuit, and can improve long-term battery reliability and improve battery safety.

In addition, compared with the conventional dry method, there is an advantage that the average size of the pores is remarkably reduced and the cell safety is improved.

1 is a scanning electron microscope (SEM) photograph of a porous film made of polyethylene (PE) made according to Example 1. Fig.
FIG. 2 is a scanning electron microscope (SEM) image of a porous film made of PE according to Comparative Example 3. FIG.
3 is a scanning electron microscope (SEM) photograph of a porous film of polypropylene (PP) made according to Example 4. Fig.
4 is a scanning electron microscope (SEM) image of a porous film made of PP produced according to the conventional dry method.
5 is an exploded perspective view of an electrochemical cell according to an example of the present invention.

Hereinafter, the present invention will be described in more detail. Those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Hereinafter, a method of manufacturing a porous film according to an embodiment of the present invention will be described. A method of manufacturing a porous film according to an embodiment of the present invention includes the steps of forming a precursor film by extrusion molding a composition comprising a crystalline resin and pore-forming particles, heating the precursor film to a temperature of (Tm-80) 3) 占 폚, and stretching the annealed film at a low temperature of 0 占 폚 to 50 占 폚 by 50% to 400%.

First, a composition including a crystalline resin and pore-forming particles may be extruded in an extruder to produce a precursor film. A method of extrusion molding is not particularly limited, but a film can be formed by melting a crystalline resin using a T-die or a ring-shaped die using a single screw or twin screw extruder. Specifically, the composition is melt-kneaded with respective components such as a crystalline resin and pore-forming particles, extruded and discharged, and solidified through casting to form a uniform precursor film. In one embodiment, pellets compounded with a composition comprising a crystalline resin and pore-forming particles are placed in a hopper of an extruder equipped with a tie die and extruded at an extruder temperature set at 170 ° C to 330 ° C. The extrudate is extruded to a casting roll set at (Tg + 10) ° C to (Tm-10) ° C to adjust the draw ratio to be 30-150, for example, 40-100, . When the stretching ratio is lower than 30, uniform pores are hardly formed, and when the stretching ratio is higher than 150, breakage occurs easily in the stretching process. The thickness of the precursor film is in the range of from 1 탆 to 500 탆, for example from 5 탆 to 300 탆, in embodiments from 5 탆 to 100 탆, more specifically from 5 탆 to 40 탆, 30 mu m. In one example, two or more precursor films extruded may be laminated together to produce a multilayer precursor film of two or more layers. In another example, coextrusion can be used to produce a multilayer precursor film of two or more layers. In the case of a multilayer precursor film of two or more layers, for example, it may be a three-layer structure of crystalline polypropylene / crystalline polyethylene / crystalline polypropylene, or a two-layer structure of crystalline polyethylene / crystalline polypropylene.

The crystalline resin that can be used is a polymer resin compound containing a part of crystals capable of forming a lamellar, for example, poly (4-methylpentene), polyethylene, polypropylene, a copolymer thereof or a combination thereof . Specifically, high density polyethylene (HDPE), polypropylene, or a copolymer thereof may be used. The crystallinity thereof may be in the range of 5% to 95%, for example, 20% to 95%, or 50% . Specifically, a polyethylene resin having a crystallinity of 50 to 95% or a polypropylene resin having a crystallinity of 40 to 80% can be used. In the case of polypropylene, a resin having an isotacticity of 85 to 99% as measured from the solubility of xylene can be used. When the polyolefin compound is used, the crystallinity and the crystal orientation are controlled, so that it is possible to manufacture a porous film having a unique morphology with a thin layer between the lamellae. In one example, a polyethylene having a melting index of 10 or less, specifically 5 or less, for example, 3 or less, or a polypropylene having a melt index of 8 or less, more specifically 5 or less, Can be used. When the melt index exceeds the above range, it is difficult to easily produce the film, and the stretchability in the stretching process is lowered and the film is broken. In another example, the crystalline resin may be a compound having a glass transition temperature (Tg) or a melting temperature (Tm) of 100 ° C or higher. When a compound having a glass transition temperature or a melting temperature in the above range is used, not only the heat resistance of the porous film can be improved but also the pore size can be more advantageously controlled for the desired physical property. In another example, the crystalline resin may include other resins besides the above-mentioned compounds. Examples of other resins include fluorine-based polymers, polyimides, polyesters, polyamides, polyetherimides, polyamideimides, and polyacetals. When other resins are included, the above-mentioned crystalline resin and other resins may be blended by a known method to produce a crystalline resin. In another example, the crystalline resin may comprise a copolymer of an olefin and a non-olefin monomer.

The pore-forming particles that can be used may be inorganic particles, organic particles or composite particles thereof. Examples of the inorganic particles include alumina, silica, titania, zirconia, magnesia, ceria, zinc oxide, iron oxide, silicon nitride, , Calcium carbonate, barium sulfate, aluminum sulfate, aluminum hydroxide, barium titanate, calcium titanate, talc, calcium silicate and magnesium silicate. Examples of the organic particles include double bonds made by emulsion polymerization or suspension polymerization Polymerized crosslinked polymer, polymer precipitate made in solution through controlled compatibility, and the like. Specific examples include non-crosslinked or crosslinked polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyurethane (PU) (PMP), polyethylene terephthalate (PET), polycarbonate (PC), polyester, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polymethylene oxide (PMO) (PAI), polysulfone (PSF), polyethylsulfone (PES), polyvinylidene fluoride (PVP), polyvinylidene chloride (PMMA), polyethylene oxide , Polyphenylene sulfide (PPS), polyarylate (PAR), polyimide (PI), polyaramid (PA), cellulose, cellulose modified product, melamine resin and phenol resin One or more organic particles can be used . More specifically, a crosslinked silicone rubber composition comprising a silicone rubber, an ethylene-methyl acrylate copolymer, a polystyrene (PS), a polyethylene (PE), a polypropylene (PP), a polysulfone (PSF), and a polyimide (Ethylene-methyl acrylate copolymer), polystyrene (PS), or polyethylene (PE) may be used as the cross-linking agent. The size of the pore-forming particles may be 0.1 to 50 times the thickness of the lamella formed from the crystalline resin. Specifically, the average particle size of the pore-forming particles may be 30 nm to 300 nm. More specifically from 30 nm to 250 nm, and even more specifically from 30 nm to 200 nm, for example from 30 nm to 100 nm, from 50 nm to 100 nm. When the particle size is less than 30 nm, it is difficult to uniformly disperse in the polymer. When the particle size is larger than 300 nm, there is no problem in dispersibility, but the size of pores generated increases and the safety of the separation membrane decreases. Using pore-forming particles having the above-described range may be advantageous in terms of controlling the size of pores, uniformity of pores, and air permeability. The pore-forming particles may be treated with a surfactant or the like to improve the dispersibility in the composition. The pore-forming particles in the precursor-forming composition may be included in a volume of from 5 parts by volume to 40 parts by volume, specifically from 5 parts by volume to 30 parts by volume, more specifically from 10 parts by volume to 30 parts by volume, based on the total volume of the composition. When the pore-forming particles are included in the precursor-forming composition in the above-described range, the uniformity of the pores can be improved, the separation membrane having excellent air permeability, mechanical strength and thermal stability can be formed, and the processability can be improved. The precursor-forming composition may contain an appropriate amount of an antioxidant, an antistatic agent, a neutralizing agent, a dispersant, an introblocking agent, and a slip agent, if necessary.

The extruded nonporous precursor film can then be annealed at a temperature of (Tm-80) DEG C to (Tm-3) DEG C. Annealing is a heating process for improving the crystal structure and orientation structure by heat treatment to promote the formation of micropores upon stretching. If the stretching ratio is appropriately adjusted to have a value of 40 or more, the annealing process may be shortened. Through the annealing process, the elasticity recovery rate of the precursor film can be adjusted to 5% to 80%, specifically 10% to 70%, more specifically, 20% to 60%. When the elastic recovery rate is within the above range, pore formation and pore size control can be easily performed in a subsequent drawing step, and it is easy to realize a morphology including the first pore and the second pore. For example, annealing can be accomplished by heating the precursor film extruded through hot air in a tenter or IR heater, or the like, into a heated oven in which the precursor film is placed in roll form, In the presence of a catalyst. The annealing temperature and time may be adjusted depending on the stretching ratio in the production of the precursor film. For example, in the case of polyethylene, 80 to 135 ° C, in the case of polypropylene, 100 to 150 ° C, Can be processed at a temperature 3 [deg.] C to 80 [deg.] C lower than the temperature (Tm).

Thereafter, a step of first stretching the annealed film at a low temperature of 50% to 400%, specifically, 50% to 200% may be performed. The low-temperature stretching process is a process for forming pores between the particles and the polymer and inducing crazing over the entire area of the film to form uniform pores. For example, Direction) in a roll-like manner. The low temperature stretching temperature may vary depending on the type of the crystalline resin, but may be, for example, a glass transition temperature of the crystalline resin-50 ° C to a glass transition temperature of the crystalline resin + 160 ° C, Deg.] C to 50 [deg.] C, and 10 [deg.] C to 50 [deg.] C. If the stretching ratio is within the above range, uniform pores of small size can be formed on each part and surface of the film, and further, the problem that the tensile force is similar to the breaking strength and is easily broken can be avoided. The stretching ratio for keeping the tensile force low may be 300% or less, more specifically 200% or less, more specifically 150% or less.

Further, when the stretching ratio is in the above range, cracks are sufficiently formed in the low temperature stretching step, and the desired air permeability and porosity can be achieved.

Hereinafter, a method of manufacturing a porous film according to another embodiment of the present invention will be described. The method for producing a porous film according to the above-described embodiment comprises the steps of extruding a composition containing a crystalline resin and pore-forming particles to form a precursor film and heating the precursor film to a temperature of (Tm-80) (Tm-70) DEG C to (Tm-3) DEG C at a temperature of from 0 DEG C to 50 DEG C, and the first stretched film is annealed at a temperature of Lt; RTI ID = 0.0 > 40% < / RTI > The above embodiment differs from the above-described embodiment only in that it additionally includes a second stretching, so that the second stretching will be mainly described below. When the second elongation is added, the pore size can be increased and the pore uniformity can be increased to improve the air permeability of the separation membrane.

When the magnification of the second stretching is less than 40%, it is difficult to realize the process characteristic of improving the air permeability by enlarging the pores of the lamellar-fibril structure produced in the first stretching. When the magnification of the second stretching is 400% It is not suitable because it is highly likely to break. For securing a uniform pore structure and distribution, the second stretching may be conducted at a temperature of (Tm-70) ° C to (Tm-3) ° C, for example, in a longitudinal direction (MD direction) The magnification may be 40% to 400% in the longitudinal direction, for example, 40% to 250%, for example, 50% to 150%. The second stretching can be controlled depending on the kind of the precursor film, but it can be carried out, for example, in the range of 90 ° C to 135 ° C for polyethylene and 110 ° C to 150 ° C for polypropylene.

It is more appropriate to carry out the first stretching and the second stretching separately in order to maintain the pore uniformity of the surface.

Thereafter, heat fixing can be additionally performed as necessary. The hot fixation includes stretching 110% to 150% longitudinally or transversely with heat applied using a roll-type apparatus, and then relaxing 80% to 100% of the stretched longitudinal or transverse length. Heat setting is a process of reducing residual stress and shrinkage. The heat setting may be performed at a temperature of (Tm-80) DEG C to (Tm-3) DEG C. When heat fixation is further carried out, a porous film having improved heat resistance can be produced. For example, the shrinkage rate at high temperature is reduced, so that thermal stability and safety can be improved when used in a battery.

Hereinafter, a porous film according to an embodiment of the present invention will be described.

The porous film according to one embodiment of the present invention may be a porous film manufactured by the manufacturing method according to the above embodiments. The porous film of this embodiment includes pore-forming particles and a crystalline resin. The pore-forming particles and the crystalline resin are as described above in the production method according to the embodiments of the present invention, and the crystallinity of the crystalline resin can be controlled through extrusion molding, annealing, drawing, and the like. The crystallinity of the crystalline resin in the porous film may be 10% to 60%. Specifically, it may be 20% to 50%. And a second pore formed between the lamella of the crystalline resin and the volume of the first pore may be larger than the volume of the second pore. In addition, the volume of the entire first pore may be smaller than the volume of the entire second pore. The average size of the pores including the first pore and the second pore may be 100 nm or less, for example, 80 nm or less, specifically 10 nm to 70 nm.

Hereinafter, the pore structure of the porous film according to this embodiment will be described in more detail with reference to FIGS. 1 and 2. FIG. FIG. 1 is a scanning electron microscope (SEM) photograph of a porous film made of polyethylene (PE) produced according to Example 1 of the present invention, FIG. 2 is a photograph of a porous film made of PE according to a conventional dry method, It is a photograph.

Referring to FIG. 1, the porous film of the present embodiment simultaneously includes a first pore 5 formed by pore-forming particles and a second pore 6 formed between the lamella of a crystalline resin, Is greater than the volume of the second pore. The first pore 5 has a / b of 1 to 7, for example, 1 to 6, while the length of the major axis of the pore is a and the length of the minor axis is b, a / b may be 0.5 or more. When the porous film is a polyethylene film, the a / b of the first pores 5 is 1 to 7, for example, 1 to 6, and the second pores 6 have a / b of more than 7 or more than 9 , Or greater than 10. When the porous film is a polypropylene film, a / b of the first pores 5 is 1 to 7, for example, 1 to 6, and the second pores 6 have a / b of more than 0.5, For example, it may be from 0.5 to 5. Referring again to Fig. 1, the porous film of the present embodiment includes a fibril 8 formed between the lamella 7 and the lamella 7, and between the neighboring fibrils 8, second pores 6 May be formed. In the porous film according to the present embodiment, the thickness of the lamella may vary depending on the kind of the crystalline resin used, but may be 200 nm or less, more specifically 100 nm or less, and more specifically 80 nm or less . For example, in the case of a polyethylene crystalline resin, it is 100 nm or less, for example, 10 nm to 100 nm, for a polypropylene crystalline resin, 100 nm or less, specifically 80 nm or less, more specifically 5 nm to 60 A lamellar having a thickness of nm can be formed.

Referring to FIG. 2, it can be seen that the thickness of the lamella 7 'is about 300 nm to 500 nm in the case of the porous film manufactured by the conventional dry method, which is thicker than the lamella 7 of the porous film according to the embodiments of the present invention have. Although not shown in detail in FIGS. 1 and 2, the lamellar structure of the porous film of the present embodiment is formed into a lamellar structure having five or less layers, The porous film obtained by the conventional dry method can be formed into a layered structure in which at least ten or more layers are laminated. The thickness of the lamellar structure having ten or more layered structures may be thicker than that of the porous film of this embodiment. The porosity of the porous film according to this embodiment may be 40% to 70%, specifically 45% to 65%, and the air permeability may be 400 sec / 100cc or less, specifically 300 sec / 100cc or less, sec / 100cc. In addition, the thickness of the porous film may be 7 [mu] m to 30 [mu] m and the thickness variation may be less than 10% of the thickness.

Hereinafter, a separation membrane according to an embodiment of the present invention will be described. The separation membrane according to this embodiment may include the porous film according to one embodiment of the present invention. For example, the porous film may be formed of only the porous film according to one embodiment of the present invention, or may further include a functional layer formed on one or both sides of the porous film. The functional layer may be a porous adhesive layer for enhancing the adhesive force with the electrode or a heat-resistant porous layer for improving heat resistance. The functional layer may comprise a binder resin and / or particles.

According to one embodiment of the present invention, there is provided an electrochemical cell comprising a porous film comprising a crystalline resin and pore-forming particles as described herein, and an anode and a cathode, and filled with an electrolyte.

The type of the electrochemical cell is not particularly limited and may be a battery of a kind known in the technical field of the present invention.

The electrochemical cell according to an embodiment of the present invention may be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The method of manufacturing the electrochemical cell according to an embodiment of the present invention is not particularly limited, and a method commonly used in the technical field of the present invention can be used.

5 is an exploded perspective view of an electrochemical cell according to one embodiment. The electrochemical cell according to one embodiment is explained as an example of square type, but the present invention is not limited thereto, and may be applied to various types of cells such as a lithium polymer battery and a cylindrical battery.

5, an electrochemical cell 100 according to an embodiment includes an electrode assembly 40 wound around a separator 30 between an anode 10 and a cathode 20, an electrode assembly 40 (Not shown). The anode 10, the cathode 20 and the separator 30 are impregnated with an electrolyte (not shown).

The separation membrane 30 is as described above.

The anode 10 may include a cathode current collector and a cathode active material layer formed on the cathode current collector. The cathode active material layer may include a cathode active material, a binder, and optionally a conductive material.

The cathode current collector may be aluminum (Al), nickel (Ni) or the like, but is not limited thereto.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specifically, it is possible to use at least one of cobalt, manganese, nickel, aluminum, iron or a composite oxide or composite phosphorus of metal and lithium in combination thereof. More specifically, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate or a combination thereof may be used.

The binder not only adheres the positive electrode active materials to each other well but also adheres the positive electrode active material to the positive electrode current collector. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride , Carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like. These may be used alone or in combination of two or more.

The conductive material imparts conductivity to the electrode. Examples of the conductive material include, but are not limited to, natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, and metal fiber. These may be used alone or in combination of two or more. The metal powder and the metal fiber may be made of metals such as copper, nickel, aluminum, and silver.

The cathode 20 may include a negative electrode collector and a negative electrode active material layer formed on the negative collector.

The negative electrode current collector may be copper (Cu), gold (Au), nickel (Ni), copper alloy, or the like, but is not limited thereto.

The negative electrode active material layer may include a negative electrode active material, a binder, and optionally a conductive material.

Examples of the negative electrode active material include a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, a transition metal oxide, Can be used.

Examples of the material capable of reversibly intercalating and deintercalating lithium ions include carbonaceous materials, and examples thereof include crystalline carbon, amorphous carbon, and combinations thereof. Examples of the crystalline carbon include amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like. As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used. As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-C composite, Si-Y alloy, Sn, SnO ₂ , Sn-C composite, Sn- And at least one of them may be mixed with SiO ₂ . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The kinds of the binder and the conductive material used for the cathode are the same as those used for the anode and the conductive material.

The positive electrode and the negative electrode may be prepared by mixing each active material and a binder with a conductive material in a solvent to prepare each active material composition and applying the active material composition to each current collector. The solvent may be N-methyl pyrrolidone or the like, but is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The electrolytic solution includes an organic solvent and a lithium salt.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples thereof may be selected from a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent and an aprotic solvent.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate Carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Specifically, when a mixture of a chain carbonate compound and a cyclic carbonate compound is used, it can be prepared from a solvent having a high viscosity and a high dielectric constant. Here, the cyclic carbonate compound and the chain carbonate compound may be mixed in a volume ratio of 1: 1 to 1: 9.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, Mevalonolactone, caprolactone, and the like. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. Examples of the ketone-based solvent include cyclohexanone, and examples of the alcohol-based solvent include ethyl alcohol, isopropyl alcohol, and the like.

The organic solvents may be used alone or in combination of two or more. When two or more of them are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the battery to enable the operation of a basic electrochemical cell and to accelerate the movement of lithium ions between the positive electrode and the negative electrode.

For example the lithium salt _{is, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiN (SO 3 C 2 F 5) 2, LiN (CF 3 SO 2) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2 , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) where x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) _2, .

The concentration of the lithium salt can be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, and thus can exhibit excellent electrolytic solution performance, and lithium ions can effectively move.

Hereinafter, the present invention will be described in more detail with reference to Examples, Comparative Examples and Experimental Examples. It should be understood, however, that these examples, comparative examples and experimental examples are merely illustrative of the present invention, and thus the scope of the present invention is not limited thereto.

Example 1

Polyethylene 100 parts (PE 5202BS (Prime Polymer Co., MI 0.3, crystallinity 80%, Tm 136 ° C) / PE 5000S (Lotte Petrochemical MI 0.9, crystallinity 60%, Tm 130 ° C) = 50/50 And 15 parts of CaCO ₃ surface-treated with fatty acids (aliphatic calcium and oxalylated RA), the extrusion conditions were 190 to 250 ° C., and the draw ratio 40 to 45, and the precursor film thus formed was annealed at 120 DEG C for 2 minutes (after the annealing, the elasticity recovery rate was 30%), and the first precursor film was subjected to 100% first elongation (Low-temperature stretching), followed by 100% second stretching (high-temperature stretching) at 120 ° C in the MD direction to prepare a porous film having a thickness of 20 to 25 μm.

The morphology of the porous film was observed with a scanning electron microscope (SEM) and the results are shown in Fig.

Example 2

The porous film of Example 2 was prepared in the same manner as in Example 1, except that the low-temperature stretching was conducted at 25 占 폚 in the MD direction once at 50%.

Example 3

The porous film of Example 3 was prepared in the same manner as in Example 1, except that the low-temperature stretching was conducted at 150 占 폚 for one time in the MD direction at 25 占 폚.

Example 4

Except that a polypropylene homopolymer having a melt flow index of 2.0 (polyvinyl alcohol S801, crystallinity of 58%) was used instead of the polyethylene in Example 1, the annealing was performed at 140 占 폚 and the second stretching was performed at 140 占 폚 The porous film of Example 4 was prepared in the same manner as in Example 1.

Example 5

A porous film of Example 5 was prepared in the same manner as in Example 1 except that 100% stretching (high temperature stretching) was not performed in the MD direction at 120 캜 after the low temperature stretching in Example 1 .

Example 6

A porous film of Example 6 was prepared in the same manner as in Example 1 except that a precursor film having a thickness of 30 탆 was formed at a drawing ratio of 100 in Example 1.

Comparative Example 1

A porous film of Comparative Example 1 was prepared in the same manner as in Example 1 except that the low temperature stretching ratio was changed to 30%.

Comparative Example 2

A porous film of Comparative Example 2 was prepared in the same manner as in Example 4, except that the low temperature stretching ratio was changed to 30%.

Comparative Example 3

(PE prime polymer, 5202BS) was formed into a precursor film having a thickness of 30 탆 at an extrusion temperature of 190 to 250 캜 and a draw ratio of 120, and the precursor film thus formed was heated at 120 캜 (Low-temperature stretching) once at 40 占 폚 in the MD direction at 25 占 폚 and then subjected to a second stretching (high-temperature stretching) at 200 占 폚 in the MD direction at 120 占 폚 to obtain a porous film having a thickness of 20 to 25 占 퐉 And its morphology was observed with a scanning electron microscope (SEM). The results are shown in Fig.

Comparative Example 4

A polypropylene porous film (product name: C201) of Celgard manufactured by the dry method was purchased and its morphology was observed with a scanning electron microscope (SEM). The results are shown in FIG.

Comparative Example 5

A porous film was prepared in the same manner as in Example 1 except that CaCO ₃ was used in a volume ratio of 2 in Example 1.

The compositions of the porous films of Examples 1 to 6 and Comparative Examples 1, 2, 3 and 5 are summarized in Tables 1 and 2 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Crystalline resin PE PE PE PP PE PE Pore-forming particles
Volume ratio 15 15 15 15 15 15 Draw ratio 40 to 45 40 to 45 40 to 45 40 to 45 40 to 45 100 Annealing temperature 120 DEG C 120 DEG C 120 DEG C 140 ° C 120 DEG C 120 DEG C The first stretching condition (MD) 25 ° C, 100% 25 ° C, 50% 25 ° C, 150% 25 ° C, 100% 25 ° C, 100% 25 ° C, 100% The second stretching condition (MD) 120 ° C, 100% 120 ° C, 100% 120 ° C, 100% 140 ° C, 100% - 120 ° C, 100%

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 5 Crystalline resin PE PP PE PE Pore forming particle volume ratio 15 15 - 2 Draw ratio 40 to 45 40 to 45 120 40 to 45 Annealing temperature 120 DEG C 140 ° C 120 DEG C 120 DEG C The first stretching condition (MD) 25 ° C, 30% 25 ° C, 30% 25 ° C, 40% 25 ° C, 100% The second stretching condition (MD) 120 ° C, 100% 140 ° C, 100% 120 ° C, 200% 120 ° C, 100%

Experimental Example  One

Measurement of air permeability of porous film

In order to measure the air permeability of the porous film of each of Examples 1 to 6 and Comparative Examples 1 to 5, each of the porous films was cut at 10 different points in a size capable of entering a circle having a diameter of 1 inch or more. Then, the time for passing 100 cc of air through each of the above specimens was measured using an air permeability measuring apparatus (Asahi Seiko Co., Ltd.). The time was measured five times each, and the average value was calculated to measure the air permeability.

Experimental Example  2

Porosity measurement of porous film

The porosity of the porous films of Examples 1 to 6 and Comparative Examples 1 to 5 was measured as follows. The volume (cm ³ ) and mass (g) of the porous film were determined, and the density (g / cm ³ ) of the film and the film was calculated using the following equation. The density of the film was calculated from the density of the material.

Porosity (%) = (volume-mass / density of porous film) / volume x 100

Experimental Example  3

Annealing  after Elastic recovery rate

After annealing in Examples 1 to 6 and Comparative Examples 1 to 5, the elastic recovery rate was measured at room temperature using a universal testing machine (UTM). The porous film was measured at a grip interval of 50 mm (L ₀ ) / min, and the length (L ₁ ) at the time when the residual stress was zero when the steel sheet was recovered at a speed of 50 mm / min immediately after the elongation at 100% was measured and then calculated using the following equation.

[Formula 1]

ER (%) = (L ₁ -L ₀ ) / L ₀ X 100

Experimental Example  4

Pore size

PMI capillary flow porometer. The maximum pore size was calculated from the bubble point. As the wetting solution, a Galwick solution having a surface tension of 15.9 dynes / cm was used. The size of the sample was 2.5 inches in diameter. The samples were each averaged by measuring 10 samples.

Experimental Example  5

Evaluating process failure rate

LCO (LiCoO2) was coated on both sides of a 14 μm thick aluminum foil with a thickness of 94 μm, dried and rolled to obtain a positive electrode having a total thickness of 108 μm . Natural graphite and artificial graphite (1: 1) were coated on both sides of copper foil with thickness of 8μm as anode active material and dried and rolled to prepare a negative electrode having a total thickness of 128 ㎛. The electrolytic solution was 1.5M LiPF ₆ mixed in an organic solvent of EC / EMC / DEC + 0.2% LiBF ₄ + 5.0% FEC + 1.0% VC + 3.00% SN + 1.0% PS + 1.0% SA (PANAX ETEC CO., LTD.) Was used. A separator was interposed between the positive electrode and the negative electrode and wound into an electrode assembly of 7 cm x 6.5 cm. 3 seconds to the electrode assembly at 100 ℃, 5kgf / cm ² And sealed in an aluminum coated pouch (8 cm x 12 cm) at the adjacent two corners at a temperature of 143 ° C. Then, 6.5 g of the electrolyte solution was introduced, and the air inside the cell was degassed for 3 minutes or more using a degassing machine Was left. 120 seconds at 110 ℃ after aging (aging) of the manufactured battery at 12 hours 25 ℃, 20kgf / cm ² Lt; RTI ID = 0.0 &gt; cm2 &lt; / RTI &gt;

The defective rate was calculated by measuring a decrease in OCV in the chemical conversion process for the produced battery. When the defect rate is less than 2%, it is indicated as Ο, and when the defect rate is more than 2%, it is indicated as Χ.

The measurement results according to Experimental Examples 1 to 5 are shown in Tables 3 and 4 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Ventilation rate (sec / 100cc) 250 262 280 260 400 150 Porosity (%) 52 51 48 51 46 53 Elasticity recovery after annealing (%) 30 30 30 40 30 58 Pore size (nm) 50 40 55 10 35 52 Defect ratio (%) O O O O O O

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Ventilation rate (sec / 100cc) 750 800 750 480 1530 Porosity (%) 46 45 42 43 32 Elasticity recovery after annealing (%) 30 40 85 - 30 Pore size (nm) 100 90 200 140 150 Defect ratio (%) X X X X X

As can be seen from Tables 3 and 4, the porous films of Examples 1 to 6 had a good air permeability and porosity, a very small pore size of 100 nm or less and a low defective rate, while the porous films of Comparative Examples 1 to 5 The pore size was relatively large and the uniformity of the pores was smaller than that of the example, resulting in a large defect occurrence rate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that such detail is solved by the person skilled in the art without departing from the scope of the invention. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (20)

A porous film comprising pore-forming particles and a crystalline resin,
Wherein the porous film includes a first pore formed by the pore-forming particles and a second pore formed between the lamella of the crystalline resin, wherein the volume of the first pore is larger than the volume of the second pore, The average particle diameter of the particles is 30 nm to 100 nm, the pore-forming particles are contained as 10 to 30 parts by volume of the total volume of the porous film,
Wherein the average size of the pores including the first pores and the second pores is 100 nm or less. The porous film according to claim 1, wherein the pore-forming particles are organic particles or inorganic particles. The porous film according to claim 1, wherein the pore-forming particles are surface-treated with a surfactant. The method of claim 2, wherein the organic particles are selected from the group consisting of polystyrene (PS), polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) (PU), poly methylpentene (PMP), polyethylene terephthalate (PET), polycarbonate (PC), polyester, polyvinyl alcohol (PVA), polyacrylonitrile (PMO), polyethylene oxide (PEO), polyamide (PA), polyamideimide (PAI), polysulfone (PSF), polyetherimide (PES), polyphenylene sulfide (PPS), polyarylate (PAR), polyimide (PI), polyaramid (PA), cellulose, modified cellulose, melamine resin and phenol resin Wherein the organic particles are at least one selected from the group consisting of Porous film. The method of manufacturing a semiconductor device according to claim 2, wherein the inorganic particles are at least one selected from the group consisting of alumina, silica, titania, zirconia, magnesia, ceria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, calcium carbonate, barium sulfate, barium titanate, , Calcium titanate, talc, calcium silicate, or magnesium silicate. The porous film of claim 1, wherein the crystalline resin is a high density polyethylene (HDPE), poly (4-methylpentene), polyethylene terraplat, ultra high molecular weight polyethylene (UHMWPE), polypropylene, or a combination thereof. The porous membrane according to claim 1, wherein a / b is 1 to 7, and the second pore is a porous membrane having a / b of 0.5 or more, wherein the first pore has a length of a major axis of the pore a and a length of the minor axis b. film. The porous film of claim 1, wherein the second pore is formed in a fibril structure between the lamella and the neighboring lamella. The porous film according to claim 1, wherein the lamellar thickness is 200 nm or less. The porous film according to claim 1, wherein the air permeability of the porous film is 400 sec / 100cc or less. A separator comprising a porous film according to any one of claims 1 to 10, or a functional layer formed on one or both sides of the film. Forming a precursor film by extrusion-molding a composition comprising a crystalline resin capable of forming a lamellar and pore-forming particles,
The precursor film is annealed at a temperature of (Tm-80) DEG C to (Tm-3) DEG C,
Wherein the annealed precursor film is first stretched by 50% to 400% at 0 to 50 ° C to produce a porous film,
The pore-forming particles are included in 10 to 30 parts by volume of the total volume of the composition,
The average particle diameter of the pore-forming particles is 30 nm to 100 nm,
Tm means a melting temperature of the crystalline resin,
The Draw ratio in forming the precursor film is 40 to 100,
Wherein the average pore size of the prepared porous film is 100 nm or less. 13. The method of claim 12, comprising second stretching the first stretched precursor film at a temperature of (Tm-70) DEG C to (Tm-3) DEG C from 40% to 400%. 14. The method of claim 13, further comprising stretching from 110% to 150% in the longitudinal or transverse direction after said second stretching, followed by relaxing to 80% to 100% of said stretched longitudinal or transverse length. A method for producing a porous film. 13. The method of producing a porous film according to claim 12, wherein the pore-forming particles are organic particles or inorganic particles. 13. The method of claim 12, wherein the crystalline resin is a high density polyethylene (HDPE), poly (4-methylpentene), polyethylene terraplat, ultra high molecular weight polyethylene (UHMWPE), polypropylene, or combinations thereof. The method of producing a porous film according to claim 12, wherein the elasticity recovery rate after annealing is 5% to 80%. The process for producing a porous film according to claim 17, wherein the elasticity recovery rate after annealing is 20% to 60%. An electrochemical cell comprising a porous film, a cathode, a cathode, and an electrolyte according to any one of claims 1 to 10. 20. The electrochemical cell of claim 19, wherein the electrochemical cell is a lithium secondary battery.

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