KR20130059783A - Coating separator film for secondary battery and its preparing method - Google Patents

Abstract

PURPOSE: A coating separator film for secondary batteries is provided to have low heat shrinkage ratio and excellent thermal stability, thereby providing a secondary battery with high power and high stability. CONSTITUTION: A coating separator film for secondary batteries is in which an organic and inorganic composite coating layer is spread on one side or both sides of a polyolefin-based porous base film. The organic and inorganic composite coating layer comprises 100.0 parts by weight of cellulose-based resin; 1-20 parts by weight of polyvinyl fluoride-based resin; 1,000-6,000 parts by weight of inorganic filler; and 1-10 parts by weight of dispersant. The base film includes 100.0 parts by weight of polyethylene resin with a weight average molecular weight of 300,000-500,000, and a polypropylene resin with a weight average molecular weight of 200,000-400,000.

Description

Coated separator film for secondary battery and its preparing method

The present invention relates to a coating separator for a secondary battery and a method for manufacturing the same, which will be described in more detail, comprising a cellulose-based resin, a polyvinyl fluoride-based resin, and an inorganic filler (Inorganic filler) on one or both sides of a polyolefin-based microporous base film. In particular, the present invention relates to a coating separator for a secondary battery having a low organic heat-shrinkage ratio and excellent wettability with respect to an electrolyte due to an organic-inorganic composite coating layer applied thereto, and a method of manufacturing the same.

Recently, in the so-called Mobile Age, the demand for secondary batteries is explosively increasing as a source of energy for portable electronic devices such as mobile phones, laptops, tablet PCs and camcorders. As is well known, a secondary battery refers to a battery that can be repeatedly used through a charging process reverse to a discharge in which chemical energy is converted into electrical energy. Nickel cadmium batteries, nickel hydrogen batteries, lithium ion batteries and lithium Ion polymer batteries;

In general, the structure of a secondary battery is composed of a positive electrode material, a negative electrode material, a separator and an electrolyte, in which a separator film prevents an electrical short between the positive electrode and the negative electrode to secure the stability of the secondary battery and at the same time charge and discharge It is a very important component that facilitates the movement of lithium ions. Most of these separators are made of a polyolefin-based polymer resin having excellent chemical stability and electrical properties, and a number of micro pores are formed in the inside of the separator to serve as a passage for the ionic material. Depending on the distribution ratio and the orientation structure, the performance and stability of the secondary battery will vary.

As such, the thermal safety of the secondary battery depends on the shutdown temperature of the separator, the meltdown temperature, and the heat-shrinkage ratio at high temperature. In this case, the closing temperature refers to a temperature at which the micropores inside the separator are closed so that no more current can flow when the temperature inside the battery is abnormally increased, and the melt breaking temperature is a temperature at which the temperature inside the battery continues to rise above the closing temperature. It refers to the temperature at which the separator is melt broken and an electrical short occurs, and the thermal contraction rate refers to the degree to which the specification shrinks when the separator is exposed to a high temperature of 100 ° C. or higher. Therefore, in order to secure the stability of the secondary battery, it is necessary to develop a separator having a low closing temperature, a high melt fracture temperature, and a low thermal shrinkage rate.

Conventionally, a method of manufacturing a porous separator from a polyolefin resin is mainly a wet method, for example, as introduced in US Pat. No. 4,247,498, and a polyethylene resin is kneaded in a single phase with a pore-forming additive at a high temperature, A method of forming micropores in a polyethylene film by extruding in the form of a film and then phase separating the polyethylene resin and the pore-forming additive in a cooling process and then removing the pore-forming additive using an extraction solvent is used. Polyolefin-based separator prepared in this way is excellent in mechanical strength and ion permeability, uniform pore size is widely used in high capacity and high output lithium ion battery.

However, conventional polyolefin-based separators generally have insufficient thermal stability, which may cause considerable heat shrinkage at a high temperature of 120 ° C. or higher, and have a problem in that short circuit occurs easily due to external impact due to weak physical strength. In addition, since the polyolefin-based separator itself has hydrophobic properties, the so-called wettability is low due to lack of mutual affinity with the electrolyte solution, and thus, a lot of time is required for the electrolyte impregnation process in the secondary battery manufacturing process. There are drawbacks to using. In order to solve this problem, a technique commonly applied in recent years is a ceramic coating method.

For example, for the ceramic coating separator, domestic patent registration Nos. 379337, 858214, and 889207 may be coated with an active layer made of inorganic particles and a binder polymer on the surface of the polyolefin-based porous film, Polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylenevinylacetate copolymer, polyimide , Polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylflurane, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, flulan, carboxymethylcellulose and Using a resin selected from polyvinyl alcohol Ceramic and a method for producing a coated membrane is introduced.

As described above, the patent technologies describe that polyvinyl fluoride resin and cellulose resin can be used as the binder resin. However, in detail, the polyvinyl fluoride-based resin is used as a core component of the binder resin to form a ceramic coating layer, and the cellulose resin may be added or excluded only to give viscosity to the coating slurry. It is used as an optional ingredient that may be present.

As such, when the polyvinyl fluoride resin is used as a main component of the binder resin, the polyvinyl fluoride resin can improve the flexibility of the ceramic coating layer because the glass transition temperature is very low. The related problem cannot be solved, but there is a possibility that another problem of dissolving or gelling the membrane itself by the solvent component of the electrolyte may occur, and there is a need for improvement.

1.Patent Registration No. 739337 (2007.07.06. Registration; LG Chem Co., Ltd.) 2. Patent Registration No. 858214 (2008.09.04. Registered; LG Chem Co., Ltd.) 3. Patent registration No. 889207 (2009.03.06. Registered; LG Chem Co., Ltd.)

Therefore, the problem to be solved by the present invention is a fundamental problem of the polyolefin-based porous separator which is conventionally used to develop a large-capacity power storage device for commercializing electric vehicles and building a smart grid, which is the next-generation intelligent power grid. The present invention provides a porous coating separator for a secondary battery and a method of manufacturing the same, which ensure thermal stability at high temperature and at the same time, improve wettability of the electrolyte.

In general, when the ceramic coating layer is applied to the base film in order to improve the thermal stability of the polyolefin-based membrane, the ceramic coating layer has a problem that the air permeability of the membrane itself is greatly reduced by blocking the pores of the base film, the present invention solved Another challenge is to at least alleviate the problem of reduced permeability of the separator itself due to the ceramic coating layer.

In order to solve the above technical problem, the present inventors basically use a cellulose-based resin having a high glass transition temperature and excellent flexibility as a core constituent of the binder resin, and further, excellent in compatibility with the cellulose-based resin, thereby providing a ceramic coating layer. The present invention was completed by using a dispersion solvent capable of forming fine pores in the.

Coating separator for secondary batteries according to the present invention, 1 to 20 parts by weight of polyvinyl fluoride resin and 1,000 to 6,000 weight of inorganic filler on one or both sides of the polyolefin-based porous base film, based on 100 parts by weight of cellulose resin And an organic / inorganic composite coating layer including 1 to 10 parts by weight of a dispersant is applied.

In addition, the method for manufacturing a secondary battery coating separator according to the present invention comprises the steps of: a) preparing a polyolefin-based porous base film; b) 1 to 20 parts by weight of polyvinyl fluoride resin, 1,000 to 6,000 parts by weight of inorganic filler, 1,000 to 10,000 parts by weight of dispersion solvent, and 1 to 10 parts by weight of dispersant based on 100 parts by weight of cellulose resin. Preparing a coating slurry; c) applying the coating slurry to one or both surfaces of the base film and drying to form an organic-inorganic composite coating layer; Characterized in that consisting of.

The secondary battery coating separator according to the present invention is excellent in thermal stability due to low thermal shrinkage at high temperature, and is expected to contribute to the development of a secondary battery having high output and high stability in the future because it maintains good breathability despite the ceramic coating.

In addition, the coating separator for secondary batteries according to the present invention has an excellent wettability with respect to the electrolyte and facilitates an electrolyte impregnation process, and uses a relatively inexpensive cellulose-based resin as the main material of the coating slurry instead of the expensive polyvinyl fluoride-based resin. The manufacturing cost of the secondary battery can be significantly reduced.

In the porous separator for secondary batteries according to the present invention, a coating slurry containing a cellulose resin as a main material is applied to one or both surfaces of a polyolefin-based porous film to apply an organic-inorganic composite coating layer. For reference, in the present invention, 'coating slurry' refers to a raw material composition in a liquid state specially formulated to form the coating layer, and the 'organic-inorganic composite coating layer' refers to applying the coating slurry on a base film. It means the film in the solid state dried by. In addition, although the porous film itself, which is not coated with the coating layer, may also be used as a separator for secondary batteries, in the present invention, a state in which the coating slurry is not applied is referred to as a 'base film', and the organic film is inorganic or inorganic. The state in which the composite coating layer is applied is referred to as a 'coating separator'.

In the present invention, the base film serving as the base of the coating separator is made of a polymer resin of a polyolefin-based like the conventional secondary battery separator. The polyolefin resin is not particularly limited, but a polyethylene resin or a polypropylene resin is suitable, and among them, a high molecular weight polyethylene (HMWPE) having a melt index of 0.01 to 0.6 and a weight average molecular weight of 300,000 to 500,000. It is preferable to include.

If the melt index of the polyethylene resin is less than 0.01, the flowability of the resin itself is low, so that the mixing with the pore-forming additive is difficult to be achieved, and it is difficult to obtain a uniform film in the stretching process. In addition, if the melt index is 0.6 or more, the flowability is too high, there is a fear that the resin flows in the film extrusion step, there is a problem that the mechanical strength of the finished separator is lowered.

In addition, when the weight average molecular weight of the polyethylene resin is less than 300,000, the stretchability of the separator is improved, but the mechanical strength is weakened. On the contrary, when the weight average molecular weight is 500,000 or more, the mechanical strength of the separator is improved, but the stretching property and the kneading property are inferior. There is a problem that this is lowered and it is not easy to control the pore size.

In the present invention, the base film may be made of only the high molecular weight polyethylene (HMWPE) resin, or may be made of a mixed resin of the high molecular weight polyethylene and polypropylene. In this case, it is preferable that the weight average molecular weight of the polypropylene resin 5 to 50 parts by weight based on 100 parts by weight of polyethylene. If the content of the polypropylene resin is less than 5 parts by weight does not contribute to the improvement of heat resistance and mechanical strength, on the contrary, if more than 50 parts by weight, staining occurs on the surface of the thin film, or the load is increased during melt extrusion, making it difficult to work. Occurs.

The organic-inorganic composite coating layer applied to the base film includes 1 to 20 parts by weight of polyvinyl fluoride resin, 1,000 to 6,000 parts by weight of inorganic filler, and 1 to 10 parts by weight of a dispersant based on 100 parts by weight of cellulose resin. It is preferable that the thickness is 0.5-10 micrometers. At this time, if the thickness of the organic-inorganic composite coating layer is less than 0.5㎛, the heat resistance of the coating separator is insufficient, on the contrary, if it is 10㎛ or more, the air permeability is lowered and the thickness of the whole separator is too thick, the workability and enlargement of the secondary battery assembly Will have a negative impact on

Cellulose resin and polyvinyl fluoride resin among the components of the organic-inorganic composite coating layer serves as a binder resin for stably fixing the inorganic filler on the surface of the base film. Such cellulose resins include ethylcellulose, methylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and hydroxy. Hydroxyethyl cellulose, Carboxymethyl cellulose, Cellulose acetate, Cellulose triacetate, Cellulose acetate phthalate, Nitrocellulose and their ammonium or Any one or more selected from salts may be used. In addition to the above, cellulose acetate butyrate and cellulose acetate propionate may be used.

The cellulose-based resin contributes to improving heat resistance and controlling physicochemical properties of the separator through various chemical modifications.

Next, as the polyvinyl fluoride-based resin, polyvinyl fluoride homopolymer (PVDF HOMO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) or polyvinylidene fluoride-trichloroethylene (PVDF-CTFE) It is preferable to use any one or more selected from).

The polyvinyl fluoride resin is to provide flexibility to the coating film, and to improve the impregnation and chemical resistance to the electrolyte solution, if the content is less than 1 part by weight based on 100 parts by weight of the cellulose-based resin flexibility of the coating film There is such a problem that there is a problem that a small crack may occur at low temperatures due to this lack, on the contrary, if more than 20 parts by weight, the heat shrinkage rate at high temperatures is not preferable.

Next, the inorganic filler serves to improve the high temperature stability and the wettability of the base film. The inorganic filler is excellent in compatibility with the binder resin and must maintain a stable slurry when mixed with each other. As the inorganic filler, any one or more selected from calcium carbonate (CaCO ₃ ), barium oxide, silica (SiO ₂ ), aluminum oxide, aluminum hydroxide, silicon carbide (SiC), titanium oxide (TiO ₂ ), and talc (Talc) may be used. Can be used.

When the content of the inorganic filler is less than 1,000 parts by weight based on 100 parts by weight of the cellulose-based resin, there is a problem in that the high temperature heat shrinkage of the coating separator is rapidly increased. On the contrary, when the content of the inorganic filler is more than 6,000 parts by weight, precipitation of the inorganic filler occurs easily or coating is performed. There is a problem in that the dispersion stability of the coating slurry is reduced such that the viscosity becomes hardly high.

Lastly, the dispersant functions to maintain the uniform dispersion of the inorganic filler in the binder resin, and any one or more selected from oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, and sorbitan fatty acid esters may be used. It is possible to use high molecular weight polyamine amide carboxylic acid salts. If the content of the dispersant is less than 1 part by weight based on 100 parts by weight of the cellulose-based resin, there is a problem that the inorganic filler easily precipitates in the organic / inorganic composite slurry. There is a problem that the adhesion is reduced or impurities are generated by reaction with the electrolyte when assembling the secondary battery.

On the other hand, the method of manufacturing a porous coating separator for a secondary battery according to the present invention comprises the steps of (A) preparing a polyolefin-based porous base film, (B) preparing a coating slurry based on cellulose-based resin, and (C) The coating slurry is applied to one or both surfaces of the porous base film.

A. Preparation of Porous Base Film

First, the method for preparing a polyolefin-based porous base film is kneading a polyolefin-based resin with a pore-forming additive at a high temperature in a single phase, extruding it into a gel-like sheet, and then phase-separating the polyolefin-based resin and the pore-forming additive during cooling. And then removing the pore-forming additive using an extraction solvent.

The polyolefin-based resin is not particularly limited, but it is preferable to use a polyethylene resin having a weight average molecular weight of 300,000 to 500,000, and preferably a polypropylene resin having a weight average molecular weight of 200,000 to 400,000 with respect to 100 parts by weight of the polyethylene resin. 5 to 50 parts by weight is better to use.

The pore-forming additives include, for example, phthalic acid esters such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; Or aromatic ethers such as diphenyl ether and benzyl ether; And fatty acid esters can be used. Preferably, a solid paraffin wax and a liquid paraffin oil having good kneading ability with a polyolefin resin may be used, and in particular, 100 to 120 parts by weight of a solid paraffin wax having a weight average molecular weight of 3,000 to 5,000 and a weight average with respect to 100 parts by weight of the polyethylene resin. 80 to 100 parts by weight of liquid paraffin oil having a molecular weight of 400 to 1,000 is preferably used.

In the present invention, first, the polyolefin-based resin and the pore-forming additive are mixed together in the twin screw for extrusion, and in the form of a gel-like sheet having a thickness of 1000 to 4000 μm through a T-die at a temperature of 150 to 250 ° C. Extrude. At this time, the pore-forming additive uniformly distributed in the gel-like sheet aggregates in micro units while causing a phase transition phenomenon.

Then, the gel sheet is cooled while passing between a casting roll and a nip roll whose surface temperature is adjusted to 30 to 80 ° C. At this time, when the surface temperature of the phase casting roll is less than 30 ° C, the pore-forming additive is rapidly cooled and adhered to the roll surface so that irregularities are generated on the surface of the gel-like sheet or a sheet with a uniform thickness cannot be obtained. On the contrary, when the solid phase paraffin wax is not solidified at 80 ° C. or higher, it is difficult to form pores with a large size, wax is deposited on the surface of the casting roll, and a sliding phenomenon occurs, and the sheet cannot be stretched at a predetermined ratio.

Next, the cooled sheet is sequentially stretched by 5 to 15 times in the machine direction and the transverse direction, respectively, to prepare a thin film having a thickness of 10 to 30 μm. In this way, the thickness variation is reduced, and the pore size is uniformly distributed while the overall thickness distribution is uniform. Simultaneous biaxial stretching may be performed in addition to the sequential stretching process. However, in this case, since the stretching force is reduced, there is a problem that high speed or wide stretching is difficult, so it is preferable to use a sequential stretching process to obtain an excellent stretched molding film.

Next, the stretched sheet is immersed in an extraction solvent to remove the pore-forming additive, and heat-fixed at 100 to 180 ° C. in a heat setting chamber to remove residual stress of the thin film, thereby completing the polyolefin-based microporous base film. do. At this time, as the extraction solvent, hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, ethers such as hydrocarbon fluoride, diethyl ether and dioxane can be used. And if the heat setting temperature is less than 100 ℃ there is a problem that the heat resistance of the final coating separator is lowered, on the contrary, if more than 180 ℃ may cause a problem that the pores of the final coating separator is closed or finally broken.

The porous base film manufactured by the above method has a cross-sectional structure in which micropores are multi-layered when the cross section is observed by an electron microscope. That is, the fine fibers are arranged in the transverse direction, in which a number of fine pores are arranged in a layered layer, in particular, the size of the pores disposed in the inner layer of the film is larger than the pores arranged on both surface layers of the film. You can check it. As such, the base film may be used as a separator in itself, and may maintain high mechanical strength due to a multilayer-oriented separator pore structure, and have a high distribution ratio of open cells directly related to breathability. .

B. Coating Slurry  Produce

Next, the coating slurry characterized in that the present invention is 1 to 20 parts by weight of polyvinyl fluoride resin, 1,000 to 6,000 parts by weight of inorganic filler, and 1 to 10 parts by weight of dispersant and 1,000 to 10,000 parts of dispersant based on 100 parts by weight of cellulose resin. It is prepared by mixing parts by weight. Here, the cellulose resin, the polyvinyl fluoride resin, the inorganic filler, and the dispersant, which are binder resins, are the same as described above, and thus redundant description is omitted.

The dispersion solvent serves to dissolve the binder resin in a liquid state in which the binder resin can be applied, and it is preferable to use a solvent having a low boiling point and a high dissolving ability to the binder resin. Such dispersion solvents include tetrahydro furan, methylene chloride, chloroform, trichloro ethane, dimethyl formamide and N-methyl-2-pyrrolidone. One or more solvents selected from (N-methyl-pyrilridone), cyclohexane, toluene, toluene, methanol, ethanol, and water may be used. In particular, in the case of using water as a dispersion solvent, there is no risk of generating volatile toxic substances during the drying process after coating, which enables environmentally friendly operation. The dispersion solvent is all removed in the drying process after coating the coating slurry on the base film. Therefore, the dispersion solvent does not remain in the organic-inorganic composite coating layer in the finished state.

The dissolving solvent may increase the content of the binder resin as the dissolving power of the binder resin is higher, and the coating slurry may maintain a stable dispersion state. In addition, the lower the boiling point, the easier it is to remove the dispersion solvent in the process of drying the coating film. It is preferable that the breaking point of a dispersion solvent is 40-150 degreeC. If the content of the dispersion solvent is less than 1,000 parts by weight based on 100 parts by weight of the cellulose-based resin, the viscosity of the coating slurry becomes high, resulting in uneven coating thickness, which is a problem in the manufacturing process. Too low, there is a problem that the components of the coating film is not uniformly distributed.

On the other hand, in the present invention, in order to form abundant micropores in the coating film, it is preferable to use a composite solvent in which the binder resin, a good affinity solvent and a relatively low affinity solvent are used as a dispersion solvent. Among the dispersion solvents, solvents having good affinity with the binder resin include tetrahydrofuran, methylene chloride, chloroform, trichloroethane, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, toluene, and the like. Low affinity solvents include methanol, ethanol and water. Preferred complex solvents include a complex solvent of tetrahydrofuran and ethanol, a complex solvent of trichloroethane and methanol, and the like.

When the composite solvents having different affinity are used as described above, a relatively good affinity solvent is first removed in the process of drying the coating slurry after the coating slurry is applied to the base film, and then a low affinity solvent is removed later. . In this process, the binder resin component is first driven toward a good affinity solvent to form phase pores, and again, fine pores are formed in a place where a low affinity solvent is present, thereby forming abundant pores in the coating layer as a whole.

The coating slurry may be prepared using a conventional ball mill, roll mill, sand mill, pigment disperser, ultrasonic disperser, homogenizer, planetary mixer, or the like.

C) coating Slurry  Coating and drying

The final process is to apply the coating slurry prepared in step B) to one or both sides of the base film prepared in step A) and to dry to form an organic-inorganic composite coating layer having a thickness of 0.5 ~ 10㎛. In this case, the coating slurry may be coated using a conventional coating method, for example, dip coating, die coating, gravure coating, comma coating, or a mixture thereof. Various methods such as a method can be used.

In addition, as a method of drying the coating layer, a method of drying or vacuum drying or irradiating far-infrared rays or electron beams by hot air, hot air, or low humidity wind may be used. In addition, the drying temperature is different depending on the type of the dispersion solvent, but when the drying at a temperature of 60 ~ 120 ℃ generally can remove the dispersion solvent completely. In this drying process, the solvent and the non-solvent cause a phase transition phenomenon, whereby fine pores are formed in the coating layer.

Thus, in the present invention, by using a cellulose-based resin as the main component of the binder resin, at the same time by using a composite solvent in which a solvent having a relatively high affinity and a solvent having a low affinity is mixed as a dispersion solvent, The breathability of the composite coating layer was greatly improved.

Hereinafter, the present invention will be described in detail with reference to specific examples. However, the scope of the present invention is not limited by the following examples.

Example 1

10 parts by weight of polypropylene having a weight average molecular weight of 350,000 is added to 100 parts of polyethylene resin having a weight average molecular weight of 380,000, and 110 parts by weight of a solid paraffin wax having a weight average molecular weight of 3800 and a weight average molecular weight of 500 are pore-forming additives. A raw resin mixture was prepared by mixing 83 parts by weight of phosphorus liquid paraffin oil and 7 parts by weight of phosphite ester as an antioxidant.

Injecting the raw material resin mixture into an extruder equipped with a T-die, and maintaining the rotational speed of the twin screw at 400 rpm at a temperature of 200 ℃ extruded through a T-die to produce a gel sheet having a thickness of 2100㎛ Then, the gel sheet was cooled while passing between the casting roll and the nip roll.

Subsequently, the sheet was stretched 10 times in the transverse direction and 9 times in the longitudinal direction at a temperature of 120 ° C. using a biaxial stretching machine, and then the stretched sheet was immersed in methylene chloride solution to extract and remove the pore-forming additive. The stretched sheet was fixed to the frame and heat-set in an oven at 130 ° C. for 4 minutes to prepare a porous base film having a thickness of 20 μm.

Meanwhile, 3 parts by weight of ethyl cellulose, 0.1 part by weight of polyvinylidene fluoride-hexafluoropropylene, 37.9 parts by weight of tetrahydrofuran, 18.9 parts by weight of ethanol, and a polyamine amide carboxylic acid salt as a dispersant ('EFKA manufactured by Ciba Chemical Co., Ltd.) 5055 ') 0.1 weight part of each was mixed, melt | dissolved at 80 degreeC for 6 hours, and it was made to disperse | distribute uniformly. 40 parts by weight of a purity 99.99% hydrophilic silica (SiO ₂ ) was mixed and mixed for 12 hours using a ball mill to prepare a coating slurry.

Gravure coating the coating slurry on both sides of the polyethylene porous base film, and hot air dried at a temperature of 80 ℃ for 1 hour to complete the secondary battery coating separator according to the present invention.

[Examples 2 to 5]

A coating separator for a secondary battery was prepared in the same manner as in Example 1, except for changing the composition and content ratio of the coating slurry as shown in Table 1 below.

division Binder resin Inorganic filler Dispersed solvent Dispersant Example 1 Ethylcellulose
3 PVDF-HFP
0.1 SiO ₂
40 THF
37.9 ethanol
18.9 EFKA 5055
0.1 Example 2 Ethylcellulose
3 PVDF-HFP
0.2 SiO ₂
45 THF
34.5 ethanol
17.2 EFKA 5055
0.1 Example 3 Ethylcellulose
3 PVDF HOMO
0.1 SiO ₂
40 THF
37.9 ethanol
18.9 EFKA 5055
0.1 Example 4 Ethylcellulose
7 PVDF-HFP
0.5 SiO ₂
40 THF
35 ethanol
17.4 EFKA 5055
0.1 Example 5 Ethylcellulose
3 PVDF-HFP
0.1 Al ₂ O ₃
40 THF
37.9 ethanol
18.9 EFKA 5055
0.1

In Table 1, the numbers indicate the content (unit; parts by weight) of each component, 'PVDF-HFP' is fluoride-hexafluoropropylene, 'PVDF HOMO' is floridene homopolymer, and 'THF' is tetra Hydrofuran, 'EFKA 5055' is the product name of Ciba Chemical Co., Ltd. and is a high molecular weight polyamine amide carboxylic acid salt.

Comparative Example 1

Polyethylene porous base film was prepared in the same manner as in Example 1, and the coating slurry was not applied thereto.

Comparative Example 2

A polyethylene porous base film was prepared in the same manner as in Example 1, and a coating slurry was coated on both surfaces thereof, using 3 parts by weight of ethyl cellulose as a binder resin constituting the coating slurry, and 97 parts by weight of trichloroethane as a dispersion solvent. A coating separator was prepared in the same manner as in Example 1 except for the above.

[Comparative Example 3]

A polyethylene porous base film was prepared in the same manner as in Example 1, and a coating slurry was coated on both surfaces thereof, but 3 parts by weight of polyvinylidene fluoride-hexafluoropropylene was used as a binder resin constituting the coating slurry. 97 parts by weight of N-methyl-2-pyrrolidone was used as the coating slurry. After coating the coating slurry, the coagulated slurry was first solidified at room temperature for 10 minutes, and then evaporated and removed for 10 minutes at 75 ° C. to prepare a coating separator.

[Comparative Example 4]

A polyethylene porous base film was prepared in the same manner as in Example 1, and the film cross-section was plasma treated for 10 seconds using an argon (Ar) atmospheric pressure plasma without a coating slurry applied thereto.

Test result

Samples were taken for each of the separators prepared according to the Examples and Comparative Examples, their physical properties were measured, and the results are summarized in Tables 2 and 3.

Test Item (Unit) Example 1 Example 2 Example 3 Example 4 Example 5 Thickness (㎛) 25.9 26.0 26.0 25.9 26.0 Air permeability (sec / 100ml) 277 289.5 293.3 291 289 Tensile strength (kgf / cm2) 2297 2283 2270 2305 2293 Penetration Strength (Kgf / ㎠) 797.8 805.6 793 806.3 802.3 Closed
Temperature Start (℃) 145.9 145 146.5 147.5 148 End (℃) 146.9 147 148 148.8 149 Heat shrinkage rate; 130 ℃ / 10 minutes (%) 1.11 1.39 1.57 1.32 1.28 Heat shrinkage rate; 150 ° C / 10 min (%) 8.2 7.4 5.8 6.8 5.0 Impedance magnitude (Ω) 3.5 4.3 3.9 4.5 4.4 Wetting property against electrolyte (g) 0.0575 0.0557 0.0537 0.0578 0.0570

Test Item (Unit) Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Thickness (㎛) 19.9 25.9 26 25.9 Air permeability (sec / 100ml) 253.9 297 306 419 Tensile strength (kgf / cm2) 2287 2185 2235 2153 Penetration Strength (Kgf / ㎠) 797.8 796 771 763 Closed
Temperature Start (℃) 145 143.9 146.3 147.1 End (℃) 147 145.9 148.7 148.8 Heat shrinkage rate; 130 ℃ / 10 minutes (%) 59.1 15.2 16.3 58.7 Heat shrinkage rate; 150 ° C / 10 min (%) 70 35 34 66 Impedance magnitude (Ω) 3.9 4.4 4.0 8.0 Wetting property against electrolyte (g) 0.0237 0.0503 0.0483 0.0253

Test Methods

Test methods for the test items of Table 2 and Table 3 are as follows.

1) breathability (sec / 100ml); A sample having a size of 30 × 30 mm was taken with respect to the separator, and the time required for passage of 100 ml of air was measured using a Toyoseiki air permeability meter.

2) tensile strength (Kgf / cm 2); Samples each having a size of 20 x 200 mm in the MD and TD directions were taken with respect to the separator, and the force applied until the sample was broken using an Instron tensile strength tester was measured.

3) puncture strength (Kgf / cm 2); A sample having a size of 100 x 50 mm was taken with respect to the separator, and the force applied until the sample was punctured when a force was applied using a stick using a Katotech piercing strength meter was measured.

4) heat shrinkage (%); Using a separator prepared according to the above Examples and Comparative Examples to prepare a sample having a horizontal and vertical size of 10 x 10 Cm, sandwich the sample between A4 paper and put it in an oven, and then at a temperature of 150 ℃ each 10 minutes and After standing for 20 minutes, the shrinkage was measured.

5) impedance magnitude; The separator is cut into 16 pies and impregnated in the electrolyte for 30 seconds, and the impedance analyzer is attached by attaching a lead made of sus material of 15 pies to the electrodes of the impedance analyzer. After contacting both sides of the separator by the electrode of the electrode, the surface was in close contact with the material used in the porch cell (Pouch cell) and the impedance was measured.

6) wettability to electrolyte solution (g); Samples each having a size of 100 × 100 mm were taken for the separator, and the resultant was immersed in 10 ml of electrolyte for 1 minute, and then the increased weight was measured.

Comparison of physical properties

As can be seen from the results of Table 2 and Table 3, the coating separator prepared according to the embodiment of the present invention is used in Comparative Example 2 using only cellulose resin as the resin binder or Comparative Example 3 using only polyvinyl fluoride resin. Compared to the entire membrane air permeability showed a much better result. However, Comparative Example 1 or Comparative Example 4 did not have a ceramic coating, and thus showed much better breathability than other Examples or Comparative Examples with ceramic coating.

In addition, in Examples 1 to 5, the average heat shrinkage was 1.33% at 130 ° C., but only 6.64% at 150 ° C., while in Comparative Examples 2 and 3, 15.9% at 130 ° C. and 34.5% at 150 ° C. The heat shrinkage was much higher than that of the examples. In addition, the wettability of the electrolyte showed a slightly improved degree compared to Comparative Examples 2 and 3 of the present invention, but showed a result of more than two times improvement compared to Comparative Examples 1 and 4 without the ceramic coating.

From the above results, it was confirmed that the coating separator of the present invention has superior thermal stability and wettability to the electrolyte solution than the conventional coating separator, and in particular, can greatly reduce the decrease in air permeability due to the ceramic coating.

Claims (12)

On one side or both sides of the polyolefin-based porous base film, 1 to 20 parts by weight of polyvinyl fluoride resin, 1,000 to 6,000 parts by weight of inorganic filler, and 1 to 10 parts by weight of dispersant are included based on 100 parts by weight of cellulose resin. Coating separator for a secondary battery, characterized in that the organic-inorganic composite coating layer made by applying.
The secondary film of claim 1, wherein the base film comprises 5 to 50 parts by weight of polypropylene resin having a weight average molecular weight of 200,000 to 400,000 based on 100 parts by weight of polyethylene resin having a weight average molecular weight of 300,000 to 500,000. Coating separator for battery.
The method of claim 1, wherein the cellulose-based resin is ethyl cellulose (Ethylcellulose), methyl cellulose (Methylcellulose), hydroxypropyl cellulose (Hydroxypropyl cellulose), hydroxyethyl cellulose (Hydroxyethyl cellulose), hydroxypropyl methyl cellulose (Hydroxypropyl methyl cellulose), hydroxyethyl methyl cellulose, carboxymethyl cellulose, cellulose acetate, cellulose triacetate, cellulose acetate phthalate, nitro A coating separator for secondary batteries, characterized in that at least one selected from cellulose, cellulose acetate butylate, cellulose acetate propionate, and ammonium or salts thereof.
The polyvinyl fluoride-based resin according to claim 1 or 2, wherein the polyvinyl fluoride-based resin is any one or more selected from polyvinyl fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene. Secondary battery coating separator characterized in that.
The method of claim 1, wherein the inorganic filler is calcium carbonate (CaCO ₃ ), barium oxide, silica (SiO ₂ ), aluminum oxide, aluminum hydroxide, silicon carbide (SiC), titanium oxide (TiO ₂ ), talc Coating separator for a secondary battery, characterized in that any one or more selected from (Talc).
The coating separator of claim 1 or 2, wherein the dispersant is any one or more selected from oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, and sorbitan fatty acid esters.
3 to 7 weight of ethylcellulose on one or both sides of the polyolefin-based porous base film comprising 5 to 50 parts by weight of a polypropylene resin having a weight average molecular weight of 200,000 to 400,000 based on 100 parts by weight of polyethylene having a weight average molecular weight of 300,000 to 500,000. 0.1 to 0.5 parts by weight of polyvinylidene fluoride-hexafluoropropylene or polyvinyl floridene homopolymer, 40 to 45 parts by weight of silica (SiO ₂ ), and 0.1 parts by weight of polyamine amide carboxylic acid salt, A secondary battery coating separator, characterized in that the coating is made of an organic-inorganic composite coating layer having a thickness of 0.5 ~ 10㎛.
a) preparing a polyolefin-based porous base film;
b) 1 to 20 parts by weight of polyvinyl fluoride resin, 1,000 to 6,000 parts by weight of inorganic filler, 1,000 to 10,000 parts by weight of dispersion solvent, and 1 to 10 parts by weight of dispersant based on 100 parts by weight of cellulose resin. Preparing a coating slurry;
c) applying the coating slurry to one or both surfaces of the base film and drying to form an organic-inorganic composite coating layer; Method of manufacturing a coating separator for a secondary battery, characterized in that consisting of.
The method of claim 8, wherein the b) the dispersion solvent of the secondary cell, characterized in that for use as a dispersion solvent mixed with a cellulose-based resin and a relatively good affinity solvent and a relatively low affinity solvent. Method for producing a separator.
10. The method of claim 9, wherein the solvent having a relatively high affinity in the complex solvent is tetrahydrofuran, methylene chloride, chloroform, trichloroethane, dimethylformamide, N-methyl-2-pyrrolidone, cyclohexane, toluene Using any one of the solvent selected from the above, and a relatively low affinity solvent any one selected from methanol, ethanol, water using the manufacturing method of the coating separator for secondary batteries.
The method of claim 9 or 10. As the composite solvent, a composite solvent of tetrahydrofuran and ethanol or a composite solvent of trichloroethane and methanol is used.
a) Polyolefin resin consisting of 100 parts by weight of polyethylene having a weight average molecular weight of 300,000 to 500,000 and 5 to 50 parts by weight of polypropylene resin having a weight average molecular weight of 200,000 to 400,000, and a solid paraffin having a weight average molecular weight of 3,000 to 5,000 as a pore forming additive. Preparing a porous base film by adding 100 to 120 parts by weight of wax and 80 to 100 parts by weight of liquid paraffin oil having a weight average molecular weight of 400 to 1,000;
b) 0.1 to 0.5 parts by weight of polyvinylidene fluoride-hexafluoropropylene or polyvinyl fluoride homopolymer, 40 to 45 parts by weight of silica (SiO ₂ ), and 34 to tetrahydrofuran based on 3 to 7 parts by weight of ethyl cellulose. Preparing a coating slurry by mixing 38 parts by weight, 17 to 19 parts by weight of ethanol, and 0.1 part by weight of polyamine amide carboxylic acid salt;
c) applying the coating slurry to one or both surfaces of the base film and drying to form an organic-inorganic composite coating layer having a thickness of 0.5 to 10 μm; Method of manufacturing a coating separator for a secondary battery comprising a.