KR101661671B1 - A method for manufacturing porous separators for use of secondary cell using nano steam, separators made by the method, and secondary cell - Google Patents

Abstract

The present invention relates to a method for producing a porous separator for a secondary battery using nano-vapor, a separator prepared by the method, and a secondary battery including the separator.

Description

Technical Field [0001] The present invention relates to a method for producing a porous separator for a secondary cell using nano-vapor, a separator prepared using the same, and a secondary cell using the same,

The present invention relates to a method for producing a porous separator for a secondary battery using nano-vapor, a separator prepared by the method, and a secondary battery including the separator.

The porous separator for a secondary battery refers to an interlayer that keeps the anode and the cathode in a battery while maintaining the ion conductivity and enables charging and discharging of the battery.

In recent years, electrochemical cells for increasing the portability of electronic devices have become more lightweight and miniaturized, and there is a tendency to require high-output large capacity batteries for use in electric vehicles and the like. Therefore, in the case of a separator for a secondary battery, it is required to reduce its thickness and weight, and at the same time, it is required to have excellent shape stability by heat and high tension in order to improve the productivity of a high capacity battery.

The electrode assembly composed of the anode / separator / cathode may have a laminated structure, but may have a structure in which a plurality of electrodes are laminated with a separator interposed therebetween and then bonded to each other by heating / pressing. In this case, the coupling of the electrode and the separation membrane is achieved by heating / pressing the electrode with the adhesive layer formed on the separation membrane facing each other. Therefore, a binder polymer is generally coated on the separator in order to improve adhesion and shrinkage ratio to the electrode. A high boiling point solvent such as DMF (dimethylformamide) is usually used to dissolve the binder polymer in the preparation of the coating solution. When the solvent remains in the drying process after coating, an electrochemical side reaction occurs in the secondary battery, Which adversely affects performance. In order to reduce the solvent content after coating, the drying conditions must be over-applied, and excessive drying conditions adversely affect the raw material separation membrane. For example, in the prior art (Korean Patent Registration No. 0877161), when the boiling point of the costing agent is less than 100 캜, drying is preferably performed at 100 캜 to remove the costing agent, and when the boiling point of the costing agent is 100 캜 or higher It is preferable to perform vacuum drying at 90 占 폚. However, both the method of drying at 100 占 폚 and the method of vacuum drying at 90 占 폚 all involve high temperature heat applied to the secondary battery porous separator, so that contraction and deformation of the separator due to heat can not be avoided. In addition, in order to secure a certain level of air permeability, air containing moisture must be used. In this case, excessive water content after coating occurs. For example, when the water content in the battery increases, the lithium secondary battery generates an acid by causing decomposition of the electrolyte, and the acid thus produced is decomposed into a negative electrode SEI (solid electrolyte interface) and a side reaction And ultimately causes problems such as a decrease in battery capacity and an increase in internal resistance. That is, since the performance of the lithium secondary battery is greatly influenced by the moisture content in the battery, it is most important to prevent the penetration of moisture in the manufacturing process of the battery.

Korea Patent No. 0877161

none

The present invention has been devised to provide a separation membrane excellent in stability against heat by solving the problem of shrinkage or deformation of the separation membrane due to heat in a conventional method of heating and drying solvent and moisture by heating or vacuum at a high temperature as described above.

The present invention also solves all problems such as the decomposition of a negative electrode SEI (solid electrolyte interface), the dissolution of a cathode active material, the reduction of a battery capacity, and the increase of internal resistance, .

The present invention can effectively remove the solvent and moisture of the separation membrane by drying at a relatively low temperature by introducing a drying step using the nano-vapor during the drying process of the porous separation membrane for a secondary battery.

A method of manufacturing a porous separation membrane for a secondary battery according to an embodiment of the present invention comprises coating a base material with a coating composition comprising a binder polymer and a solvent to prepare a coated separation membrane and drying the coated separation membrane using a nano- Lt; / RTI >

First, a coating layer is formed on a substrate. Specifically, the binder polymer and the solvent are sufficiently stirred using a ball mill, a bead mill or a screw mixer to form a coating composition in the form of a mixture, and then the coating composition is applied on at least one side of the base by a dip coating method, A roll coating method, or a comma coating method. The coating method may be used alone or in combination of two or more methods. The thickness of the coating layer formed by the above method may be in the range of 0.01 to 10 mu m, for example, in the range of 1 to 5 mu m.

The substrate may be polyolefin-based. For example, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene and polypropylene can be used as long as it is a polyolefin-based polymer, and a single film structure formed of a single layer, Structure. The thickness of the substrate may be between 1 탆 and 50 탆, for example between 4 탆 and 25 탆. The pore size and porosity of the substrate are not critical, but appropriate mechanical properties and air permeability can be secured within the above range. The substrate may also be in the form of a fiber or membrane.

Then, the coated separator is first dried using nano vapor. In the present invention, the nano vapor refers to a vapor whose particle size is controlled to 1 μm or less. Specifically, the steam generated through the steam generator is passed through a nano-vapor converter equipped with an induction coil heater to control the steam particle size to 1 μm or less. The term 'steam' means a gas generated by heating water. Therefore, the particle size of water vapor in the nano vapor is 1 탆 or less. Specifically, it may be 500 to 1000 nm.

According to the embodiments of the present invention, not only can the separator be dried at a low temperature by drying the separator using the nano-vapor, but also can be uniformly dried through the separator thus produced. As a result, It is possible to prevent the phenomenon that the physical properties such as the characteristics are lowered. Hereinafter, the effect of the nano vapor of the present invention will be described in more detail with reference to FIG. 1 is a schematic view schematically showing the principle of drying a separation membrane using nano-vapor. FIG. 1 (a) shows the conventional hot air type separation membrane drying, and FIG. 1 (b) shows separation membrane drying using the nano vapor according to the present invention. 1 (a) and 1 (b), the separator comprises a substrate 1 and a coating layer 2. In the case of the hot air type as shown in FIG. 1 (a), since hot air can not pass through the separator, only a part of the surface coat layer 2 of the separator is dried first. The inside of the separator is not dried yet, and water and solvent remain therein, which causes deterioration of properties (adhesion and thermal characteristics, etc.) later. On the other hand, in the case of the nano vapor system as shown in FIG. 1 (b), since the nano vapor is dried to the inside of the surface coating layer 2 of the separator, not only the solvent can be dried in a short time at low temperature, It is possible to prevent the deterioration of physical properties caused by the above.

In the first drying using the nano-vapor, dry air containing 10 to 50 vol%, specifically 10 to 30 vol%, of nano-vapor relative to the total air may be used. Within the above range, drying can sufficiently take place and a separation membrane can be obtained in which the physical properties are appropriately maintained. When the amount of the nano-vapor is less than the above range, drying is not sufficient. When the amount of the nano-vapor is larger than the above range, phase separation occurs between the binder and the inorganic particles in the coating layer, have. The first drying can be performed while passing the dried air containing the nano vapor through the separation membrane at a rate of 0.5 to 5 m ³ / min, for example, 1 to 3 m ³ / min. Sufficient drying can be performed without affecting the physical properties of the separator within the above-mentioned speed range. In the present invention, the 'dry air' means air passing through the separator of the present invention to dry the separator. For example, air having a dew point of -30 ° C or less may be used.

The first drying may be performed at 50 to 100 ° C, and the drying may be performed to ensure proper physical properties within the range. By using the nano-vapor during the first drying, the drying temperature can be lowered than otherwise, and the deterioration of the physical properties due to the high temperature can be suppressed.

In the first drying, the drying may be divided into a plurality of drying sections, and the drying temperatures in the respective sections may be the same or different. For example, the first and second drying zones may be divided into a first drying zone and a first drying zone, and the drying temperatures of the first drying zone and the first drying zone may be respectively 50 to 100 ° C. For example, the drying temperatures of the first and second drying zones may be 50 to 90 ° C, respectively. The drying temperatures of the first and second drying zones may be different from or identical to each other. In one example, the drying temperatures of the first and second drying zones may be 50 ° C, 55 ° C, 60 ° C, 65 ° C, 70 ° C, 75 ° C, 80 ° C, 85 ° C, or 90 ° C, respectively. In addition to the first and second drying zones, 1 - 3 drying zone, 1 - 4 drying zone and 1 - 5 drying zone using nano vapor may be additionally performed. If the drying zone is divided into several drying zones, it may be advantageous to have a different temperature for each zone.

The method may further include a second drying step of performing thermal drying in a temperature range of 35 to 90 ° C before or after the drying using the nano-vapor. For example, the second drying may be carried out after the first drying. For example, the second drying may be performed before the first drying. The second drying step may be performed by controlling the drying temperature and the drying time in one drying zone. However, the drying may be performed sequentially by dividing the drying zone into several drying zones and varying the temperature and time of each drying zone. For example and not by way of limitation, the second drying zone and the second drying zone may be divided and dried, and the drying temperatures of the second drying zone and the second drying zone may be 35 ° C to 90 ° C, respectively. The drying temperatures of the second drying zone and the second drying zone may be different from each other or may be the same. In one example, the drying temperatures of the second _ 1 drying zone and the second _ 2 drying zone are 35 ° C., 40 ° C., 45 ° C., 50 ° C., 55 ° C., 60 ° C., 65 ° C., 70 ° C., 75 ° C., , Or 90 < 0 > C. In addition to the second-1 drying zone and the second drying zone 2, a second drying zone 3, a second drying zone 4, and the like may be additionally provided. Also, the second drying may be performed at the same temperature interval as the first drying. The second drying may be performed while passing the separation membrane at a rate of 0.5 to 10 m ³ / min, for example, 1 to 5 m ³ / min, to the air heated in the thermal drying step. Sufficient drying can be performed without affecting the physical properties of the separator within the above-mentioned speed range. The first drying step and the second drying step according to an embodiment of the present invention will be described in more detail with reference to FIG. 2 is a schematic diagram of a separation membrane drying process according to an embodiment of the present invention. 2, the nano vapor generated in the nano-steam generator 3 is sprayed into the first-first drying zone 5 together with the dry air provided in the dry air supplier 4 to dry the separation membrane 10. Thereafter, the separation membrane can be further dried while passing through the second _ 1 drying zone 7 and the second _ 2 drying zone 9 of the general hot air dryer. At this time, the nano-vapor can be injected through the punching plate 6 of the first-first drying zone 5, and the general hot-air steam can be supplied to the second-1 drying zone 7 and the second- Lt; / RTI >

The second drying may be performed at a temperature of about 20 to 60 DEG C lower than a temperature required for thermal drying or vacuum drying in order to reduce the solvent and the water content to a predetermined amount without passing through the first drying according to the embodiment of the present invention. Therefore, it is possible to dry at low temperature through the introduction of nano vapor, so that heat shrinkage or thermal deformation of the separator due to high temperature drying can be prevented. Conventionally, in the case of a high boiling point solvent (for example, a boiling point of 200 ° C or higher, or 250 ° C or higher), it is necessary to heat the boiling point to a temperature above the boiling point and heat shrinkage and deformation of the separation membrane due to heating, The use of the solvent was limited and there were restrictions on the kinds of the binder polymer that can be selected. The present invention can effectively remove the solvent and / or moisture through the nano-vapor process and the low-temperature thermal drying step by a method suitable for high boiling point solvents. Therefore, the solvent to which the nano-vapor drying method of the present invention can be applied is not particularly limited, and generally, a solvent used for a binder polymer of a porous separation membrane for a secondary battery can be applied. Examples of the solvent include acetone, N-methyl-2-pyrollidinone, tetrahydrofuran, dimethylformamide, methylene chloride, chloroform chloroform, cyclohexane, water, or mixtures thereof.

The polymeric binder that can be used in the present invention is not particularly limited as long as it has a binding force with the electrode stacked on the separation membrane and is not easily dissolved by the electrolyte solution. For example, it is possible to use polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinylidene fluoride (trichlorethylene) fluoride-trichlorethylene (PVdF-TCE), polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethylmethacrylate, polyacrylonitrile, But are not limited to, polyvinylpyrollidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate propionate, cyanoethylpulluran, cyanoethylpolyvinyl alcohol (cyanoe thylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethyl cellulose, acrylonitrile styrene butadiene copolymer, acrylonitrile styrene butadiene copolymer, Polyimide, styrene butadiene rubber (SBR), and the like. For example, PVdF or PVdF-HFP or both can be used, and SBR is an excellent synthetic rubber having excellent heat resistance, abrasion resistance, aging resistance, water resistance, gas permeability and the like. In one embodiment of the present invention, the polymer binder may be a PVdF homopolymer having a weight average molecular weight (g / mol) of 110000 and / or a PVdF-HFP copolymer having a weight average molecular weight (g / mol) of 300,000.

In the present invention, the coating composition may further include inorganic particles. By adding inorganic particles to the polymeric binder, the mechanical strength of the separator can be increased to ensure safety of the battery due to external force and the like, and heat resistance can be improved.

The inorganic particles that can be used in the present invention are not particularly limited as long as they do not cause oxidation and / or reduction reaction with the positive electrode or the negative electrode current collector, that is, do not cause electrochemical reaction in the operating voltage range of the battery, , SnO ₂ , Ga ₂ O ₃ , MgO, NiO, B ₂ O ₃ , Ga ₂ O ₃ , SiO ₂ and TiO ₂ . And may be at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ and TiO ₂ .

The porous separator for a secondary battery according to an embodiment of the present invention may have a residual solvent amount of 80 ppm or less and a water content of 500 ppm or less. Specifically, the residual solvent amount may be 70 ppm or less and the water content may be 400 ppm or less.

Another aspect of the present invention is a method for producing a polymer electrolyte membrane, comprising the steps of: (a) preparing a first binder polymer solution by adding a first solvent to a first binder polymer and stirring at 15 to 35 ° C, (b) (C) preparing a coating composition by mixing the first binder polymer solution and the inorganic dispersion solution prepared in the steps (a) and (b); (d) Coating the composition; and (e) drying the coated separator using nano-vapor. The present invention also provides a method of manufacturing a porous separator for a secondary battery.

The coating liquid may be prepared by stirring the inorganic particles with the binder polymer and the first solvent in the step (a) without performing the steps (b) and (c). When the above-mentioned (b) and (c) are separately carried out, there is an advantage that the dispersibility of the inorganic particles and the binder and stability of the liquid bath can be improved.

Accordingly, another aspect of the present invention is a process for preparing a coating composition comprising: (a) preparing a coating composition comprising a binder polymer, a solvent and inorganic particles; (b) coating the coating composition on one or both sides of the substrate; And (c) drying the coated separator using nano-vapor. The present invention also provides a method of manufacturing a porous separator for a secondary battery.

The method may further include a second drying step of performing thermal drying at a temperature ranging from 35 to 90 ° C before or after the first drying step using the nano-vapor. The thermal drying step may be performed after the drying step of the nano vapor. The second drying step may be performed by controlling the drying temperature and the drying time in one drying zone. However, the drying may be performed sequentially by dividing the drying zone into several drying zones and varying the temperature and time of each drying zone. For example and not by way of limitation, the second drying zone and the second drying zone may be divided and dried, and the drying temperatures of the second drying zone and the second drying zone may be 35 ° C to 90 ° C, respectively. The drying temperatures of the second drying zone and the second drying zone may be different from each other or may be the same. In one example, the drying temperatures of the second _ 1 drying zone and the second _ 2 drying zone are 35 ° C., 40 ° C., 45 ° C., 50 ° C., 55 ° C., 60 ° C., 65 ° C., 70 ° C., 75 ° C., , Or 90 < 0 > C. In addition to the second-1 drying zone and the second drying zone 2, a second drying zone 3, a second drying zone 4, and the like may be additionally provided.

The dispersion medium of the inorganic particles may be, for example, acetone, and the inorganic particles may be dispersed in a dispersion medium, preferably using a ball mill or a bead mill, and dispersed in an appropriate size. The inorganic particles may be dispersed by using the ball mill or the bead mill for 0.5 hour to 4.5 hours and dispersed, and more preferably for 1 to 3.5 hours.

The method may further include the step of adding a second solvent to the second binder polymer after the step (a) and stirring the mixture at 15 to 35 ° C to prepare a second binder polymer solution, wherein the second binder polymer solution May be used to prepare the coating composition of step (c).

In the above embodiments, the first binder polymer, the second binder polymer or the binder polymer may be the same binder polymer mentioned in the present invention. In the above embodiments, the first solvent, the second solvent, or the solvent may be the same solvent as mentioned in the present invention. In the above embodiments, the inorganic particles and the substrate may be the same inorganic particles and substrate as those mentioned in the present invention.

The porous separation membrane for a secondary battery produced by the manufacturing method described herein may have a residual solvent amount of 80 ppm or less and a water content of 500 ppm or less. For example, the residual solvent amount may be 70 ppm or less and the water content may be 400 ppm or less. Specifically, the residual solvent amount may be 60 ppm or less and the water content may be 300 ppm or less.

When the porous separator for a secondary battery is dried at 45 ° C for 160 hours, the rate of change L _{1 in} the vertical direction (MD) of the following formula ( ₁ ) is 1.5% ) length change ratio (L ₂₎ of this can be not more than 1.0%.

[Formula 1]

L ₁ = │L _m1 - L _m0 / L _m0

L ₂ = L _t1 - L _t0 / L _t0

Wherein, L _m0 and L _t0 denotes an initial vertical length and an initial horizontal length of the produced separation membrane in accordance with an embodiment of the invention, L _m1 and L _t1 are respectively kept the membrane at 45 ℃ 160 sigan And the length in the vertical direction and the length in the horizontal direction. For example, L _m0 and L _t0 may each be 50 mm.

The present invention minimizes heat shrinkage or thermal deformation of the separator due to the conventional high temperature drying since it can be dried at low temperature through the introduction of nano vapor. When the length change rate L ₁ of the vertical direction MD and the length change rate L ₂ of the horizontal direction TD are within the above range, the short circuit of the electrodes can be effectively prevented and the safety of the battery can be improved. Method of measuring the length change ratio (L ₂₎ in the longitudinal change ratio (L ₁₎ and a horizontal direction (TD) in the vertical direction (MD) are:

Ten specimens were prepared by cutting the membrane at 10 different points on the cross (MD) 50 mm × longitudinal (TD) 50 mm. Each of the specimens was left in an oven at 45 ° C. for 160 hours. Direction and a change in length in the TD direction are measured to calculate an average length change rate.

The residual solvent amount of the porous separator for a secondary battery according to aspects of the present invention may be 80 ppm or less and the water content may be 500 ppm or less. The air permeability of the porous separator for a secondary battery may be 300 sec / 100cc or less.

In another aspect, the present invention provides a porous separator for a secondary battery, manufactured according to an embodiment; anode; And a negative electrode. The secondary battery may be a lithium secondary battery. Lithium may be suitable for producing electricity having a large electric capacity per unit mass because the atomic amount of the element itself is small. The positive electrode has a positive electrode active material formed in a predetermined region, and examples of the positive electrode active material include a lithium-based oxide. The negative electrode has a negative electrode active material formed in a predetermined region, and examples of the negative electrode active material include a carbon material. The porous separation membrane is positioned between the anode and the cathode to prevent a short-circuit and to allow movement of lithium ions. The secondary battery includes a liquid electrolyte or a polymer electrolyte, and typical examples of the secondary battery include a cylindrical, square, and pouch type.

The separation membrane according to the present invention is advantageous in that heat shrinkage or thermal deformation of the separation membrane due to high temperature drying can be prevented because it can be dried at a low temperature through introduction of nano vapor. Also, since the solvent and / or moisture can be effectively removed from the high-boiling point solvent through the low-temperature thermal drying step after or after the application of the nano-vapor, there is no limitation in solvent selection.

The method for preparing a separator according to the present invention and the separator produced thereby can minimize the side reaction in the battery due to a solvent or moisture by including a solvent and moisture at a predetermined amount or less.

1 is a schematic view schematically showing the principle of drying a separation membrane using nano-vapor. FIG. 1 (a) shows the conventional hot air type separation membrane drying, and FIG. 1 (b) shows separation membrane drying using the nano vapor according to the present invention.
2 is a schematic diagram of a separation membrane drying process according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail by describing Examples, Comparative Examples and Experimental Examples. However, the following examples, comparative examples and experimental examples are merely examples of the present invention, and the present invention should not be construed as being limited thereto.

Example  One

(1) Preparation of coating agent

1) Polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer (21216, Solvay) having a weight average molecular weight of 300,000 g / mol was added to acetone in an amount of 10% by weight, Followed by stirring for 4 hours to prepare a first polymer solution.

2) 10% by weight of polyvinylidene fluoride (PVdF) homopolymer (5130, Solvay) having a weight average molecular weight of 1,100,000 g / mol was added to dimethylformamide (DMF) (purified gold) Followed by stirring at 25 캜 for 4 hours to prepare a second polymer solution.

3) 25% by weight of Al ₂ O ₃ (LS235, Japan light metal) was added to acetone (purified water) at 25% by weight and milled for 3 hours at 25 ° C using a bead mill to prepare an inorganic dispersion.

The first polymer solution, the second polymer solution and the inorganic dispersion were mixed at a composition ratio of the first polymer solution: second polymer solution: inorganic dispersion: solvent (acetone) = 1: 1: 3: 6, Lt; 0 > C for 2 hours to prepare a coating agent.

(2) Preparation of separator

The prepared coating agent was coated on both sides of a polyethylene single-membrane base film (Selgard PE) having a thickness of 9 μm by dip coating method, and then the substrate film was coated with a nano-scale apparatus (trade name: DOYA TEST COATER, 10 vol%) nano-vapor-containing dry air was applied at a rate of 2 m ³ / min and dried in a first 1 _ 1 drying zone at 85 ° C. Thereafter, the resultant was dried in a first _2 drying zone at 85 ° C using the same conditions of nano vapor, and sequentially dried in a second _ 1 drying zone at 85 ° C and a second drying zone at 85 ° C using hot air applied at a rate of 2 m ³ / min. Thereby preparing a porous separator for a secondary battery according to Example 1. At this time, air having a dew point of -50 DEG C was used as the dry air.

Example  2

The separation membrane of Example 2 was prepared in the same manner as in Example 1, except that the amount of nano-vapor used in Example 1 was changed to 20 vol%, and the drying process was changed as shown in Table 1.

Example  3

The separation membrane of Example 3 was prepared in the same manner as in Example 1 except that the amount of nano-vapor used in Example 1 was changed to 30 vol% and the drying process was changed as shown in Table 1.

Example  4

The separation membrane of Example 4 was prepared in the same manner as in Example 1, except that the amount of nano-vapor used in Example 1 was changed to 40 vol% and the drying process was changed as shown in Table 1.

Comparative Example  1 and 2

The separation membranes of Comparative Examples 1 and 2 were prepared in the same manner as in Example 1 except that the nano vapor was not applied in Example 1 and the drying process was changed as shown in Table 1. [

Nano Steam Consumption
(Dry air consumption) First drying (drying nano steam) Second drying (hot air drying) 1 zone 2 zones 1 zone 2 zones 3 Zone 4 zones Example 1 10 (90) 85 ℃ 85 ℃ 85 ℃ 85 ℃ - - Example 2 20 (80) 75 ℃ 75 ℃ 75 ℃ 75 ℃ - - Example 3 30 (70) 70 ℃ 70 ℃ 70 ℃ 70 ℃ - - Example 4 40 (60) 60 ° C 60 ° C 60 ° C 60 ° C - - Comparative Example 1 unused - - 120 DEG C 110 ° C 100 ℃ 100 ℃ Comparative Example 2 unused - - 110 ° C 110 ° C 100 ℃ 100 ℃

Experimental Example

1. Remaining amount of solvent

The residual amount of the solvent DMF in the separation membrane prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was measured by gas chromatography (Model: HP-6890) under the measurement conditions shown in Table 2 below.

Parameter Conditions Column Front: HP-INNOWAX (length 30 m, ID 0.53 mm, film thickness 1.00 m)
Back: HP-1 (length 30 M, ID 0.53 mm, film thickness 0.88 m) Temp. Prog. 40 캜 (4 min) - 20 캜 / min - 250 캜 (4 min) 유율 10 mL / min Injector S / SL injector Split ratio 5: 1 Detector FID Injection Vol. 1 μl Injector temp. 200 ℃

2. Water content

For the measurement of the moisture content of the membranes prepared in Examples 1 to 4 and Comparative Examples 1 and 2, 0.1 ± 0.02 g of a sample was sampled and the moisture content was measured using an 831 KF Coulometer and 860 KF Thermoprep (manufacturer: Metrohm) .

3. Measurement of permeability of membrane

In order to measure the air permeability of the membrane prepared in Examples 1 to 4 and Comparative Examples 1 and 2, the following experiment was conducted.

Each of the separators prepared in the above examples and comparative examples was cut to a size of 50 mm (TD direction) X 100 mm (MD direction), and then an air permeability measuring apparatus (Asahi Seiko Co., model: EG01-55-1MR) was used And the time for passing 100 cc of air through each of the specimens was measured. The time was measured five times each, and the average value was calculated to measure the air permeability.

4. Vertical direction ( MD ) ≪ / RTI > L _One ) And horizontal direction ( TD ) ≪ / RTI > L ₂ )

In order to measure the rate of change of the membrane prepared in Examples 1 to 4 and Comparative Examples 1 and 2, the following experiment was performed.

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 10 pieces of MD 50 mm × TD 50 mm. Ten specimens were prepared. Each of the specimens was allowed to stand in an oven at 45 ° C for 160 hours, and the degree of change in length in the MD direction and the TD direction of each specimen was measured to calculate the average length change rate.

The results of measurement of residual solvent amount, moisture content, air permeability and rate of change according to the above Experimental Example are shown in Table 3 below.

Moisture content
(ppm) Remaining amount of DMF
(ppm) MD length change rate (%) TD length change rate (%) Ventilation
(sec / 100cc) Example 1 250 25 0.8 0 179 Example 2 280 28 0.5 0 185 Example 3 320 31 0.3 0 190 Example 4 368 32 0.2 0 198 Comparative Example 1 950 120 3 2 328 Comparative Example 2 1200 130 2 2 389

As can be seen from the results of Table 3, the process for producing a separator using nano-vapor according to the present invention is characterized in that the rate of change in length in the TD and MD directions is small and the air permeability is also excellent, while maintaining the water content and the solvent residual amount at 500 ppm or less and 80 ppm or less, respectively On the other hand, in Comparative Examples 1 and 2 in which high temperature heat drying was performed in comparison with the present invention, not only the amount of water and the amount of solvent remained, but also the rate of heat and shrinkage in the TD and MD direction increases.

Claims (15)

At least one side of the substrate is coated with a coating composition comprising a binder polymer and a solvent to prepare a coated separator,
And a second step of drying the coated separator using water vapor having a particle size of 1 m or less. The method for producing a porous separation membrane according to claim 1, further comprising a second drying step of performing thermal drying at a temperature of 35 to 90 캜 before or after the first drying. delete The method of claim 1, wherein the water vapor is injected in an amount of 10 to 50 vol% based on the total injection air in the first drying using water vapor having a particle size of 1 m or less. 5. The method of claim 4, wherein the injection rate of the total injection air is 0.5 to 5 m < ³ > / min. The method of claim 1, wherein the coating composition further comprises inorganic particles. The method for producing a porous separation membrane according to claim 1, wherein the substrate is a polyolefin-based single membrane. The method for producing a porous separation membrane according to claim 7, wherein the polyolefin-based single membrane has a thickness of 4 탆 to 25 탆. The method according to any one of claims 1, 2, and 4 to 8, wherein the binder polymer is selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF- HFP), polyvinylidene fluoride-trichlorethylene (PVdF-TCE), polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrole Polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, pullulan, At least one member selected from the group consisting of carboxymethyl cellulose, acrylonitrile styrene butadiene copolymer, polyimide and styrene butadiene rubber A method for producing a porous separator. The method for producing a porous separation membrane according to any one of claims 1, 2, and 4 to 8, wherein the solvent remaining amount of the porous separation membrane is 80 ppm or less and the water content is 500 ppm or less. The method according to claim 1,
It is preferred that the coated separator is prepared,
(a) a first solvent is added to a first binder polymer, and the mixture is stirred at 15 to 35 DEG C to prepare a first binder polymer solution,
(b) an inorganic dispersion in which the inorganic particles are dispersed in a dispersion medium is prepared,
(c) mixing the first binder polymer solution and the inorganic dispersion prepared in the steps (a) and (b) to prepare a coating composition,
(d) coating the coating composition on at least one side of the substrate. A porous separator comprising a porous substrate and a coating layer formed on at least one side of the substrate, wherein the coating layer comprises a binder polymer and inorganic particles, wherein the porous separator has a longitudinal rate of change (MD) (L ₁ ) is 1.5% or less and the longitudinal rate of change (L ₂ ) in the horizontal direction (TD) is 1.0% or less, and the longitudinal rate of change L ₁ and L ₂ are as shown in the following formula (1).
[Formula 1]
_{L 1 = │L m1 - L m0} │ / L m0
_{L 2 = │L t1 - L t0} │ / L t0
L _m0 and L _t0 represent the initial vertical length and initial horizontal length of the separator, respectively, and L _m1 and L _t1 indicate the vertical length and horizontal length measured after storing the separator at 45 ° C for 160 hours, respectively. Indicates direction length.) 13. The porous separator for a secondary battery according to claim 12, wherein the residual solvent amount of the porous separator for a secondary battery is 80 ppm or less and the water content is 500 ppm or less. 14. The porous separator for a secondary battery according to claim 12 or 13, wherein the porous separator for a secondary battery has an air permeability of 300 sec / 100cc or less. 13. A secondary battery comprising a cathode, an anode, and a porous separator for a secondary battery according to claim 12 or 13 located between the anode and the cathode.

Images