KR20160051664A - A method for manufacturing a separator for a lithium secondary battery and the separator fabricated by the same - Google Patents

Abstract

The present invention relates to a method for manufacturing an organic-inorganic hybrid porous separator, wherein damage to a separator is minimized and properties such as air permeability can be adjusted easily in the process of manufacturing a separator, and the separator. The separator for a secondary battery manufactured according to the method for manufacturing a separator according to the present invention has excellent heat resistance and mechanical properties owing to little surface defect generation in the process of drying the separator and has excellent air permeability owing to inorganic particles not too much condensed in an organic-inorganic hybrid porous layer. The method for manufacturing a porous separator for a secondary battery comprises the steps of: preparing a porous separator substrate; manufacturing slurry for forming an inorganic-organic hybrid porous layer to be applied to at least one side surface of the porous separator substrate; applying the slurry to at least one side surface of the porous separator substrate; and drying the separator substrate having the slurry applied thereto.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator for a secondary battery, and a separator prepared by the method. BACKGROUND ART [0002]

The present invention relates to a process for producing a separator for a secondary battery and a separator for a secondary battery produced from the process. More particularly, the present invention relates to a method for manufacturing a separation membrane for a secondary battery, which minimizes damage to the separation membrane during manufacturing and facilitates control of physical properties such as air permeability, and a separation membrane therefor.

Lithium-ion batteries are based on anode / cathode / separator / electrolytic solution and are widely used in small electronic equipment such as mobile phones and laptops because they are highly energy- . In recent years, hybrid electric vehicles (HEV), plug-in EVs, electric bikes (e-bikes) and energy storage systems (Energy Storage System, ESS) is rapidly expanding.

Lithium ion secondary battery is a stable electrochemical device that is insulated by a separator. However, since an anode or a cathode is short-circuited due to an abnormal phenomenon of internal or external battery or impact, there is a possibility of heat generation and explosion. Therefore, thermal / Securing safety is the most important consideration.

A commercially available polyolefin-based separator used in a lithium secondary battery is a porous film that functions to prevent electrical short-circuiting between the anode and the cathode while providing pores serving as a passage for lithium ion. Commercially, a polyolefin- It is widely used. When the battery is elevated to a high temperature by internal or external stimulation at a temperature of 100 ° C or higher, the polyolefin-based porous separator can not avoid a volume change such as shrinkage or melting of the separator, resulting in an electrical short between the anode and the cathode Explosion or the like may occur. In addition, when the separator ruptures due to dendrite growth in the battery, there is also a problem that the explosion of the battery due to an internal short circuit can be induced. In order to suppress the thermal shrinkage due to the high temperature and the instability of the battery due to the dendrites, the inorganic particles are coated with the binder on one or both sides of the porous separator substrate to give the function of suppressing the shrinkage of the substrate, Inorganic composite porous layer which provides a more secure separation membrane by the action of the organic / inorganic composite porous layer. At this time, the porous layer may cause coating defects on the surface due to cracks generated during the manufacturing process, for example, drying process. As a result, the organic / inorganic composite porous layer can easily be desorbed when the secondary battery is assembled or when the battery is used, which leads to a decrease in the safety of the battery. In addition, the porous layer-forming slurry applied to the separator substrate for forming the porous layer has a problem that the packing density is increased due to increased density of the particles during drying, thereby lowering the air permeability. Korean Patent Laid-Open Publication No. 10-2010-0092988 discloses a method of coating a slurry of inorganic particles and organosilane on a nonwoven fabric separating membrane without introducing a polymer binder to induce chemical bonding between inorganic particles. However, since the high temperature condition is higher than the melting temperature of a polyolefin such as polyethylene or polypropylene, it can not be applied to a polyolefin-based separator. There is a problem. Therefore, there is a demand for a new method for preparing a composite membrane for ensuring excellent cell characteristics.

It is an object of the present invention to provide a method for producing a separation membrane for a secondary battery, which is capable of obtaining a separation membrane excellent in air permeability due to few defects generated on the surface of the separation membrane and an excessive concentration of inorganic particles. It is still another object of the present invention to provide a production method capable of easily controlling intrinsic properties of a separation membrane such as air permeability by controlling the content of a binder and / or a thickener. Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention provides a slurry for forming an organic / inorganic composite porous layer for a secondary battery in order to solve the above problems. Said slurry comprising: a) an inorganic particle; And b) a solid component comprising a polymeric resin is dispersed in a solvent, and the content of the solid component in the slurry is less than 5% by weight to less than 15% by weight based on 100% by weight of the slurry.

Here, the inorganic particles may be selected from the group consisting of inorganic particles that do not undergo oxidation and / or reduction reaction within the operating voltage range of the electrochemical device, inorganic particles that have lithium ion transfer capability, inorganic particles that have a dielectric constant of 5 or more Or more.

Here, the polymer resin may have a glass transition temperature of -200 to 200 캜.

Here, the content ratio of a) and b) may be 70:30 to 99.9: 0.1 in terms of weight ratio.

The solvent may be selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone -2-pyrrolidone, NMP), cyclohexane, water, and mixtures of two or more.

The present invention also relates to (S10) preparing a porous membrane substrate; (S20) preparing a slurry for forming an organic / inorganic composite porous layer for application to at least one side of the porous membrane substrate; (S30) applying the slurry to at least one side of the porous membrane base material; And (S40) drying the separation membrane substrate having the slurry applied thereon. The present invention also provides a method for manufacturing a porous separation membrane for a secondary battery.

Here, the slurry for forming the organic / inorganic composite porous layer in the step (S20) may include: a) inorganic particles; And b) a polymeric resin is dispersed in a solvent, and the content of the solid component in the slurry may be 5 wt% to 15 wt% based on 100 wt% of the slurry.

Here, the drying may be carried out at a temperature of from 85 캜 to 135 캜.

Here, the drying can be performed for 1 minute to 10 minutes.

Here, the drying may be carried out at a temperature of 80 to 135 DEG C for 1 to 10 minutes.

The present invention also relates to a porous substrate; Inorganic complex porous layer formed on at least one surface of the porous substrate, wherein the organic / inorganic composite porous layer has a solid content of 5 wt% to 100 wt% of the total slurry including the solvent, 15% by weight of a slurry is coated on at least one surface of the porous substrate, and the solid component comprises: a) an inorganic particle; And b) a polymer resin.

Here, the secondary battery separator may have an air permeability of 100 to 250 sec / 100 cc.

Here, the organic / inorganic composite porous layer has a porous structure according to an interstitial volume in which inorganic materials are formed by mutual interaction.

The present invention also includes a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
FIG. 1 schematically shows an organic / inorganic composite separator for a secondary battery commonly used in the art.
2 is a process flow diagram schematically showing a method for producing a separation membrane according to one embodiment of the present invention.
3 and 4 are SEM images of the separation membrane surface according to Comparative Example 3. Fig.

The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

FIG. 1 shows a composite separator 10 generally used in the secondary battery field. In general, the conventional composite separator comprises a polyolefin porous film (1) and an organic / inorganic composite porous layer formed on one side or both sides of the film, wherein the organic / inorganic composite porous layer comprises a plurality of inorganic particles (3) And a binder resin (5). However, conventional composite membranes have a problem in that surface defects due to cracks generated during the drying process are generated, and the inorganic particles are easily separated from the organic / inorganic composite porous layer, thereby lowering safety. In addition, there is a problem that a portion where the inorganic particles are excessively concentrated in the porous layer is generated during the drying process of the composite separator, thereby lowering the air permeability.

The present invention provides a slurry for forming an organic / inorganic composite porous layer for the production of a composite separator for a secondary battery having less surface defects and excellent air permeability, and a method for producing the separator for a secondary battery using the same.

FIG. 2 is a process flow chart schematically showing a method for producing a separation membrane for a secondary battery according to a specific embodiment of the present invention. Hereinafter, a method for producing a slurry and a composite separator for forming an organic / inorganic composite porous layer will be described with reference to FIG.

A method of manufacturing a composite membrane according to an embodiment of the present invention includes: preparing a porous membrane substrate (S10); (S20) of preparing a slurry for forming an organic / inorganic composite porous layer; Applying the slurry to at least one side of the porous membrane substrate (S30); And drying (S40) drying the separator substrate coated with the slurry. Hereinafter, the present invention will be described in detail with reference to a process flowchart shown in FIG.

First, a porous substrate for a composite separator of a secondary battery is prepared (S10). The porous substrate can provide a path for lithium ions while electrically insulating the negative electrode and the positive electrode while preventing a short circuit. The porous substrate can be used without particular limitation as long as it can be used in a separation membrane of an electrochemical device. Examples of such a porous substrate include polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyether sulfone, polyphenylene oxide, polyphenyl And a porous substrate formed by mixing any two or more selected from among rhenium sulfide, polyethylene naphthalene, and the like, but the present invention is not limited thereto. As the porous substrate, a thin film or nonwoven fabric in the form of a film may be used singly or in combination. In the present invention, the thickness of the porous substrate may be 5 to 50 탆. In the present invention, the thickness of the porous substrate is not particularly limited to the above-mentioned range. However, when the thickness is too thinner than the lower limit described above, the mechanical properties are deteriorated and the separator may be easily broken during use of the battery. On the other hand, the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 탆 and 10% to 95%, respectively.

In one specific embodiment of the present invention, the porous substrate may be produced according to a wet method or a dry method. In one embodiment of the present invention, the porous substrate may be manufactured according to a wet method or a dry method, and the porous substrate may be prepared without applying a heat fixing process and / or an annealing process have. In this case, as described later, the temperature of the organic / inorganic composite porous layer slurry drying step may be adjusted to adjust the temperature to fix the porous substrate together, thereby removing the thermal history of the porous substrate.

For example, the wet method will be described in detail. A mixture of a polyethylene resin and a pore-forming agent such as paraffin is used to obtain an extrudate using a twin-screw extruder, and the extrudate obtained is placed on a T-die And then passed through a cooling roll to produce an extruded sheet. Next, the extruded sheet is stretched in the longitudinal direction and the transverse direction. Then, in the stretched sheet, the pore-forming agent may be removed to obtain a porous substrate, wherein the heat-setting step is not performed separately.

Next, a slurry for forming an organic / inorganic composite porous layer on one side of the porous substrate is prepared (S20).

In general, the polyolefin-based separator is accompanied by a volume change such as shrinkage or melting of the separator when the battery rises to a high temperature due to internal or external stimulation. As a result, electrical short circuit between the anode and the cathode, And the like. In order to prevent such heat shrinkage at a high temperature, the heat and mechanical properties of the separator can be improved by forming an organic / inorganic composite porous layer containing inorganic particles on one surface or both surfaces of the polyolefin porous substrate. The organic / inorganic composite porous layer has a porous structure according to an interstitial volume, which is a space filled with the inorganic particles and formed by mutual interaction.

According to a specific embodiment of the present invention, the slurry comprises a) a solid and a solvent, wherein a) the solid content is a component excluding the solvent in the slurry, a1) a plurality of inorganic particles and a2) . In one embodiment of the present invention, the slurry has a solid content dispersed in a predetermined solvent, and the solid content of the slurry is less than 5 wt% to 15 wt% or 5 wt% to 11 wt% % Or 7 wt% to 10 wt%.

The polymer resin includes a binder resin. The binder resin provides binding force between the inorganic particles and provides a binding force between the composite porous layer and the porous substrate. In addition, the polymer resin may further include a thickener optionally in order to control the viscosity of the slurry.

In the present invention, the content ratio of the inorganic particles to the polymer resin is determined in consideration of the thickness, pore size, and porosity of the organic / inorganic composite porous layer of the present invention, The inorganic particles are 50 to 99.9% by weight or 70 to 99.5% by weight.

If the content of the inorganic particles is less than 50% by weight, the polymer resin may be contained in an excessive amount, resulting in a decrease in pore size and porosity due to a decrease in void space formed between the inorganic particles. On the other hand, when the content exceeds 99.9% by weight, the mechanical properties of the final organic / inorganic composite porous layer are deteriorated due to the weak adhesive force between the inorganic particles because the polymer content is too small.

In the present invention, as the ratio of the inorganic particles (I) to the polymer resin (P) increases, the porosity of the organic / inorganic composite porous layer of the present invention increases, Inorganic particle weight + polymer resin weight), the thickness of the organic / inorganic composite porous layer is improved. Also, the possibility of pore formation between inorganic particles increases, and the pore size increases. At this time, as the size (particle size) of the inorganic particles increases, the interstitial distance between the inorganic particles increases.

According to one embodiment of the present invention, the slurry can be prepared by charging the inorganic particles and the polymer resin into a solvent and uniformly dispersing them. The method for producing the slurry is not limited to any particular method as far as it is a method for obtaining a uniform dispersion mixture. One specific embodiment thereof will be described as follows.

First, a polymer solution is prepared by dissolving a polymer resin in an appropriate organic solvent. It is preferable that the solvent has a similar solubility index to the polymer resin to be used and a low boiling point. This is to facilitate uniform mixing of the slurry and solvent removal during subsequent drying. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or mixtures thereof.

Next, a plurality of inorganic particles are added to and dispersed in the polymer solution to obtain a slurry for forming an organic / inorganic composite porous layer.

As described above, the slurry for forming an organic / inorganic composite porous layer according to the present invention has a solid content of less than 15%. Conventionally, a slurry for solid organic matter having a solid content of 20% to 40% or more is mainly used as a slurry for forming an organic / inorganic composite porous layer. However, as described later, such a solid content high-content slurry causes a large amount of surface defects during the drying process of the composite porous layer, which is a cause of a high defect rate of the separation membrane. In addition, when such a solid content high-content slurry is used, the packing density of the inorganic particles in the composite porous layer is increased, and the inorganic particles are densely packed, resulting in a problem of lowering the porosity.

Accordingly, the present invention is advantageous in that it is possible to prevent the surface defects of the separator in the separation membrane manufacturing process by reducing the solid content of the slurry and alleviate the packing density of the inorganic particles, thereby obtaining a separation membrane having excellent porosity characteristics.

On the other hand, it is preferable to add inorganic particles to the polymer solution and then crush the inorganic particles. In this case, the disintegration time is preferably 1 to 20 hours, and the particle size of the disintegrated inorganic particles is preferably 0.001 to 10 mu m as mentioned above. As the crushing method, a conventional method can be used, and a ball mill method is particularly preferable.

In the present invention, the inorganic particles contained in the slurry are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance. When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, so that the ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having lithium ion-transporting ability, or a mixture thereof. Nonlimiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 - ω} La _ω Zr _{1 - ψ} Ti _ψ O ₃ (PLZT, Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO , NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, and TiO ₂ may be used alone or in combination of two or more. In particular, the above-mentioned BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1 - ω} La _ω Zr _{1 - ψ} Ti _ψ O ₃ (PLZT where 0 <x <1, 0 < Inorganic particles such as Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) exhibit a high dielectric constant of 100 or more, And a piezoelectricity is generated so that a potential difference is generated between both sides by generating a charge when being stretched or compressed so as to prevent the occurrence of an internal short circuit between the two electrodes due to an external impact so as to improve the safety of the electrochemical device can do. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion-transferring ability are mixed, their synergistic effect can be doubled.

In the present invention, the inorganic particles having a lithium ion-transferring ability refer to inorganic particles containing a lithium element but not lithium and having a function of moving lithium ions. The inorganic particles having a lithium ion- Since lithium ions can be transferred and transferred due to a kind of defect present, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _ω Ti _ψ (PO ₄ ) ₃ , 0 <x <2, 0 <y <3) , lithium aluminum titanium phosphate _{(Li ω Al ψ Ti ξ (} PO 4) 3, 0 <x <2, 0 <y <1, 0 <z <3), 14Li 2 O-9Al 2 O 3 -38TiO 2 -39P ₂ O ₅ as such (LiAlTiP) _ω O _ψ series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li ω La ψ TiO 3,} 0 <x <2, 0 <y <3 ), Li _{3 . 25 Ge 0 .25 P 0. 75 S} 4 Mani lithium germanium thiophosphate Titanium _{(Li ω Ge ψ P ξ S} ψ, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w such as <5), Li ₃ N lithium nitride _{(Li ω N ψ, 0 <} x <4, 0 <y <2) such _{as, Li 3 PO 4 -Li 2 S} -SiS 2 SiS ₂ based P ₂ S ₅ based, such as _{glass (Li ω Si ψ S ξ} , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 , such as glass ( Li _? P _? S _?, 0 <x <3, 0 <y <3, 0 <z <7), or a mixture thereof.

On the other hand, the pore size and porosity of the organic / inorganic composite porous layer depends mainly on the size of the inorganic particles. For example, when inorganic particles having a particle size of 1 탆 or less are used, pores to be formed also become 1 탆 or less. Such a pore structure is filled with an electrolyte solution to be injected at a later stage, and the filled electrolyte serves as an ion transfer function. Therefore, the pore size and porosity are important factors for controlling the ionic conductivity of the organic / inorganic composite porous layer. The pore size and porosity of the organic / inorganic composite porous layer of the present invention are preferably in the range of 0.001 to 10 μm, or 0.01 to 1 μm, and 5 to 95%, respectively.

In addition, the thickness of the organic / inorganic composite porous layer of the present invention is not particularly limited, but may be adjusted in consideration of cell performance. More preferably in the range of 1 to 100 mu m, and particularly preferably in the range of 2 to 30 mu m. By adjusting the thickness range, battery performance can be improved.

In the separation membrane according to an embodiment of the present invention, the inorganic particle size of the organic / inorganic composite porous layer is not limited, but may be in the range of 0.001 to 10 μm for the formation of a uniform porous layer and proper porosity. When the inorganic particle size satisfies this range, the dispersibility is maintained, the physical properties of the separator are easily controlled, the increase in the thickness of the organic / inorganic composite porous layer can be avoided, and the mechanical properties can be improved , And an excessively large pore size may reduce the probability of an internal short circuit occurring during charging and discharging of the battery.

In the present invention, the polymer resin, particularly, the binder resin may preferably be a polymer resin having a low glass transition temperature (Tg), and the glass transition temperature may be -200 to 200 ° C, 200 ° C to 170 ° C or -200 ° C to 150 ° C. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer resin faithfully performs a binder function to connect and stably fix inorganic particles and particles, thereby contributing to prevention of deterioration of mechanical properties of the final organic / inorganic composite porous layer. In addition, although the polymer resin does not necessarily have the ion-conducting ability, the performance of the electrochemical device can be further improved by using a polymer having ion-conducting ability. Therefore, it is preferable that the polymer resin has a high permittivity constant. In fact, since the degree of dissociation of the salt in the electrolyte depends on the permittivity constant of the electrolyte solvent, the higher the permittivity constant of the polymer resin, the better the salt dissociation in the electrolyte of the present invention. The dielectric constant of the polymer resin may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), preferably 10 or more. In addition to the above-mentioned functions, the polymer resin of the present invention can be characterized by being capable of exhibiting a high degree of swelling by gelation upon impregnation with a liquid electrolyte. Accordingly, a solubility parameter of 15 to 45 MPa ^1/2 of a polymer resin is preferable, and more preferably 15 to 25 MPa ^1/2, and 30 to 45 MPa ^1/2 range. Therefore, hydrophilic polymer resins having many polar groups are preferred over hydrophobic polymer resins such as polyolefins. If the solubility is more than 15 MPa ^1/2 and less than 45 MPa ^1/2 hard to be impregnated with a conventional liquid electrolyte batteries.

Non-limiting examples of the polymer resin that can be used in the present invention include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, Polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, and the like. vinyl acetate, co-vinyl acetate, polyethylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethyl Cyanoethylsucrose, pullulan and carboxy Butyl cellulose may be any one or a mixture of two or more of those selected from the group consisting of (carboxyl methyl cellulose). However, the present invention is not limited thereto.

In the present invention, the thickening agent is selected from the group consisting of cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylcellulose, cyanoethylsucrose ), Pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof. However, the present invention is not limited thereto.

Next, the slurry is applied to at least one side of the prepared porous membrane substrate (S30). The method of coating the slurry on the porous substrate is not limited to any particular method, and conventional coating methods known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof can be used.

Next, the separator substrate coated with the slurry is dried (S40). The drying step is suitably set so as to minimize the occurrence of surface defects on the surface of the composite porous layer. In the present invention, the drying temperature is from 80 캜 to 135 캜, or from 100 캜 to 130 캜. The drying time is 1 minute to 10 minutes, or 1 minute to 5 minutes. The drying may be carried out within a suitable range using a drying aid such as a drying oven or hot air.

In the case of drying the slurry in the temperature range described above, the slurry is dried and the inorganic particles and the binder resin in the slurry are not localized in the slurry until the organic / inorganic composite porous layer is formed, and the slurry is uniformly applied on the surface of the porous substrate . If the temperature is lower than the above range, the slurry is left in a dry state at a low temperature for a long period of time, resulting in packing of particles or slippage of the slurry, resulting in poor coverage of the porous substrate by the organic / inorganic composite porous layer Problems can arise. That is, there is a problem that the porous substrate is not sufficiently covered with the organic / inorganic composite porous layer, so that the heat stability of the separation membrane is not secured.

Also, when the porous substrate is provided in a state in which the porous substrate is not subjected to heat setting and / or annealing, the drying of the slurry and the heat setting of the porous substrate can be simultaneously performed, have.

The composite separator of the present invention thus produced can be used as a separator of an electrochemical device, preferably a lithium secondary battery. The composite separator according to the present invention has an air permeability of 100 sec / 100cc to 250sec / 100cc. The shrinkage ratio in the MD direction and the shrinkage ratio in the TD direction are 3% or less.

Also, the present invention provides a positive electrode comprising: (a) a positive electrode; (b) a cathode; (c) an organic / inorganic hybrid separator of the present invention interposed between the anode and the cathode; And (d) an electrolytic solution. The electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include all kinds of primary and secondary batteries, fuel cells, solar cells, and capacitors. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferable.

The electrochemical device may be manufactured according to a conventional method known in the art, and may be manufactured, for example, by assembling the positive electrode and the negative electrode with the separator interposed therebetween, and then injecting an electrolyte solution .

In one embodiment of the present invention, the electrode is not particularly limited, and an electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, A lithium intercalation material such as a composite oxide formed by a combination thereof, and the like are preferable. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is PF _{6 ^{-, BF 4 -, Cl -}} , Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, NCF 3 SO 2) 2 -, CCF 2 SO 2) 3 - (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone (gamma -butyrolactone), or a mixture of these compounds. Or dissolving or dissociating in an organic solvent composed of a mixture, but the present invention is not limited thereto.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell. As a process for applying the organic / inorganic composite porous layer of the present invention to a battery, a lamination, stacking and folding process of a separator and an electrode can be performed in addition to a general winding process.

When the separator according to the present invention is applied to the lamination process in the above process, the thermal stability improvement effect of the battery becomes remarkable. This is due to the fact that the heat shrinkage of the separator more severely occurs in the battery produced by the lamination and folding process than the cell produced by the general winding process. In addition, the lamination and stacking process is advantageous in that the organic / inorganic composite porous layer of the present invention can be easily assembled due to the excellent adhesive property of the polymer. In this case, the adhesive force characteristics can be controlled by the content of the inorganic particles and the main polymer or the physical properties of the polymer. Particularly, as the polymer shows polarity, the glass transition temperature (Tg) or the melting point , Tm), the adhesion between the organic / inorganic composite porous layer of the present invention and the electrode is improved.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Manufacturing example

Based on 100 wt.% Of the total weight of a mixture of polyethylene (high density polyethylene, weight average molecular weight 500,000, melting temperature 135 DEG C) and a pore former (liquid paraffin oil, kinetic viscosity at 40 DEG C of 40 cSt) 35% by weight and 65% by weight, respectively. The mixture was extruded at 220 占 폚 using a twin-screw extruder to obtain an extrudate. The resulting extrudate was passed through a T-die and then passed through a cooling roll to prepare an extruded sheet. The extruded sheet thus prepared was stretched four times in the longitudinal direction and eight times in the transverse direction using a biaxial stretching machine. The longitudinal (MD) stretching temperature is 125 占 폚, and the transverse stretching temperature is 115 占 폚. In the stretched sheet, pore forming agent was removed using methylene chloride as a solvent, and a porous substrate was obtained.

Example  One

Al ₂ O ₃ A slurry for forming a porous coating layer was prepared by mixing a binder (SX8686 (H) 7, JRS Co., Ltd.) / water at a weight ratio of 9: 1: 90. The slurry was coated on one surface of a porous substrate (thickness 12 占 퐉) prepared in the above Preparation Example using a doctor blade method to a thickness of 3 to 4 占 퐉 and dried and heat-fixed at a rate of 5 m / min at 130 占 폚 for 2 minutes Composite membranes were prepared.

Example  2

Al ₂ O ₃ A composite membrane was prepared in the same manner as in Example 1, except that the weight ratio of 9 / 1.6 / 89.4 was used to mix the powder (Nippon Light Metal, LS235) / acrylic binder (SX8686 (H) 7, .

Example  3

Al ₂ O ₃ A composite separator was prepared in the same manner as in Example 1, except that the weight ratio of the powder (Nippon Light Metal, LS235) / acrylic binder (SX8686 (H) 7, JRS) / water was mixed at a weight ratio of 8.5 / .

Comparative Example  One

Al ₂ O ₃ (LS235) / acrylic binder (SX8686 (H) 7, JRS) / water were mixed at a weight ratio of 19: 1: 80 to prepare a slurry for forming a porous coating layer. The slurry was applied on one side of a polyethylene film (W scope, WL11B, thickness 11 탆) of the porous base material prepared in Preparation Example 1 using a doctor blade method to a thickness of 3 to 4 탆 and dried at 130 캜 at 5 m / min Respectively.

Comparative Example  2

Al ₂ O ₃ A composite separator was prepared in the same manner as in Comparative Example 1, except that the weight ratio of the powder (Nippon Light Metal, LS235) / acrylic binder (SX8686 (H) 7, JRS) / water was mixed at a weight ratio of 10/10/80 .

Comparative Example  3

Al ₂ O ₃ A slurry for forming a porous coating layer was prepared by mixing a binder (SX8686 (H) 7, JRS Co., Ltd.) / water at a weight ratio of 9: 1: 90. The slurry was coated on one surface of a porous substrate (thickness 12 占 퐉) prepared in the above Preparation Example using a doctor blade method to a thickness of 3 to 4 占 퐉 and dried and heat-fixed at a rate of 5 m / min at 50 占 폚 for 2 minutes Composite membranes were prepared.

Comparative Example  4

Al ₂ O ₃ A slurry for forming a porous coating layer was prepared by mixing a binder (SX8686 (H) 7, JRS Co., Ltd.) / water at a weight ratio of 9: 1: 90. The slurry was applied on one side of a polyethylene film (W scope, WL11B, thickness 11 μm) to a thickness of 3 to 4 μm using a doctor blade method and dried at 50 ° C. at a rate of 5 m / min for 2 minutes to form a composite membrane .

Experimental Example

1. Aeration and Contraction ratio  relation

The permeability and shrinkage of the membranes prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were measured and summarized as shown in Table 1 below.

Comparison of properties of membranes No. The thickness of the composite porous layer (mu m) Air permeability (sec / 100cc) Shrinkage (%) Amount of solid loading (g / m ² ) MD TD Example 1 16.5 165 2.0 1.6 6.7 Example 2 15.0 226 2.8 2.8 5.8 Example 3 15.2 220 2.8 1.6 5.3 Comparative Example 1 14.5 183 4.0 3.1 6.7 Comparative Example 2 15.9 498 5.0 4.9 4.8

As can be seen in Table 1, in the case of Examples 1 to 3, the air permeability was 230 sec / 100 cc or less, which indicated a level of air permeability suitable for use as a separator of a secondary battery. In addition, Examples 1 to 3 of the present invention showed superior aspects in the MD and TD direction shrinkage as compared with Comparative Examples 1 and 2.

In the above table, the air permeability characteristics were similar to those of the above examples, but the air permeability was increased as compared with Example 1 in which the loading amount of the solid was the same, and the shrinkage ratio in the MD and TD directions was 3% Respectively.

From the measurement results, it was confirmed that the composite membrane prepared using the solid low-content slurry of the present invention exhibited improved characteristics in terms of air permeability and shrinkage as compared with the separator using the solid content high-content slurry.

2. Comparison of physical properties according to drying temperature

Solid content (%) Drying temperature (캜) Composite film thickness
(탆) Ventilation
(sec / 100 ml) Shrinkage (%) MD TD Example 1 10 130 16.6 165 2.0 1.6 Comparative Example 3 10 50 15 350 3.0 8.0 Comparative Example 4 10 50 16.5 150 3.2 8.5

As shown in Table 2, in Comparative Examples 3 and 4, the shrinkage ratio was very high and it was confirmed that the heat stability was lowered than in Example 1. In the case of Comparative Example 4, the air permeability value alone is the same as that in Example 1, but the reason is that the concentration of the porous substrate due to the composite porous layer is uneven. FIG. 3 and FIG. 4 are SEM images of the surface of the separation membrane according to Comparative Example 3, confirming that the inorganic particles in the composite porous layer were not uniformly distributed on the surface of the porous substrate but were localized.

1 ... Porous substrate
3 ... inorganic particles
5 ... polymer resin
10 ... membrane

Claims (14)

a) inorganic particles; And b) a solid component including a polymer resin is dispersed in a solvent, and the content of the solid component in the slurry is less than 5% by weight to less than 15% by weight based on 100% by weight of the slurry. Slurry for forming.
The method according to claim 1,
Wherein the inorganic particles are at least one selected from the group consisting of inorganic particles that do not undergo oxidation and / or reduction reaction within the operating voltage range of the electrochemical device, inorganic particles having lithium ion transfer capability, and inorganic particles having a dielectric constant of 5 or more , A slurry for forming a porous organic / inorganic composite layer for a secondary battery.
The method according to claim 1,
Wherein the polymer resin has a glass transition temperature of -200 to 200 占 폚.
The method according to claim 1,
Inorganic composite porous layer for a secondary battery, wherein the content ratio of a) to b) is 70:30 to 99.9: 0.1 in terms of weight ratio.
The method according to claim 1,
The solvent may be selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, inorganic composite porous layer for a secondary battery, wherein the mixture is one or a mixture of two or more selected from the group consisting of pyrrolidone, NMP, cyclohexane, and water.
(S10) preparing a porous membrane substrate;
(S20) preparing a slurry for forming an organic / inorganic composite porous layer for application to at least one side of the porous membrane substrate;
(S30) applying the slurry to at least one side of the porous membrane base material; And
(S40) drying the separator substrate coated with the slurry;
Wherein the porous separator is formed of a porous material.
The method according to claim 6,
The slurry for forming the organic / inorganic composite porous layer in the step (S20) comprises: a) an inorganic particle; And b) a solid component comprising a polymer resin is dispersed in a solvent, and the content of the solid component in the slurry is 5 wt% to 15 wt% based on 100 wt% of the slurry. Way.
The method according to claim 6,
Wherein the drying is performed at a temperature of from 85 캜 to 135 캜.
The method according to claim 6,
Wherein the drying is performed for 1 minute to 10 minutes.
The method according to claim 6,
Wherein the drying is carried out at a temperature of 80 to 135 캜 for 1 to 10 minutes.
A porous substrate; And an organic / inorganic composite porous layer formed on at least one surface of the porous substrate,
Wherein the organic / inorganic composite porous layer is formed by coating a slurry having a solid content of 5 wt% to 15 wt% on at least one surface of the porous substrate with respect to 100 wt% of the total slurry including the solvent,
The solid component comprises a) an inorganic particle; And b) a polymer resin.
12. The method of claim 11,
Wherein the separation membrane for a secondary battery has an air permeability of 100 to 250 sec / 100 cc.
12. The method of claim 11,
Wherein the organic / inorganic composite porous layer has a porous structure according to an interstitial volume in which the inorganic materials are formed to be in contact with each other.
A cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator according to any one of claims 11 to 13.

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