KR101688010B1 - Separator containing coating layer, method for manufacturing the separator and battery using the separator - Google Patents

Abstract

The present invention relates to a separator having a coating layer and improved moisture resistance, a method for producing the same, and a battery using the same.
More specifically, it can exhibit heat resistance, strength and adhesive force suitable for a separation membrane including a binder and inorganic particles, as well as by controlling the composition of a solvent for forming a coating layer to reduce the moisture content in the separation membrane and reduce the degree of moisture adsorption The present invention relates to a separator having improved moisture resistance by suppressing an increase in moisture content under high humidity conditions, a method for producing the same, and a battery using the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a separation membrane including a coating layer, a method for producing the same, and a battery using the same. BACKGROUND ART [0002]

The present invention relates to a separation membrane including a coating layer, a method for producing the same, and a battery using the same.

A separator for an electrochemical cell means an interlayer that keeps the ion conductivity constant while isolating the positive electrode and the negative electrode from each other in the battery to enable charging and discharging of the battery. BACKGROUND ART [0002] In recent years, there has been an increasing demand for a battery having improved lifetime and stability, along with the trend of weight reduction and miniaturization of an electrochemical cell for improving the portability of electronic devices. In this connection, it is known that water content in the separator can be reduced to improve the life and performance of the battery.

Electrolyte interfase (SEI) and cathode active material (electrolyte) by preventing the electrolyte from decomposing due to moisture in the battery through moisture reduction in the separator and reducing the generation of acid (e.g., HF) Decomposition and the like can be minimized and the decrease of the battery capacity and the increase of the internal resistance can be suppressed. Therefore, in order to improve the performance of the electrochemical cell, not only the water content in the battery should be small, but also water penetration into the battery It is important.

Thus, by forming a coating layer with one or more hydrophobic substances on the surface of the separation membrane to impart hydrophobicity, the adsorption and influx of moisture in the separation membrane were reduced (Korean Patent Laid-Open No. 10-2008-0025433) The separator does not sufficiently exhibit heat resistance and mechanical strength, and the performance of the separator and the adhesion strength to the electrode are reduced, so that the separator is detached from the electrode during assembling the cell, so that it is difficult to secure the shape stability of the battery.

Korean Patent Publication No. 10-2008-0025433

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Disclosure of the Invention Problems to be solved by the present invention are to provide a separator having improved moisture resistance by decreasing the moisture content in the separator and reducing the re-adsorption and inflow of moisture to suppress moisture increase in the separator under high-humidity conditions, and a method for producing the same. .

Specifically, the present invention provides a separation membrane including a coating layer containing a binder and inorganic particles, which improves the moisture resistance of the separation membrane, and secures heat resistance, strength and adhesion suitable for the separator for a battery.

Another object of the present invention is to provide an electrochemical cell having excellent cell performance and shape stability by using a separator having improved heat resistance, strength and adhesion as well as moisture resistance.

According to an embodiment of the present invention,

A separator comprising a polyolefin film and a coating layer formed on one or both sides of the polyolefin film,

Wherein the moisture content of the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours is 1000 ppm or less,

Wherein the increase rate of the moisture content in the separation membrane according to the following formula 1 is 10% or less.

[Formula 1]

Increase rate of water content (%) = [(Y-X) / X] 100

In Equation (1)

X is the water content (ppm) in the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours,

Y is the moisture content (ppm) in the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours, and thereafter for 72 hours under the same conditions.

According to an embodiment of the present invention,

Applying a coating liquid on a polyolefin film to form a coating layer,

Wherein the coating liquid comprises a first solvent and a second solvent, wherein the first solvent has a polarity index of 4 or less, a boiling point of 100 占 폚 or less, and 35 weight% or less based on the total weight of the coating liquid , And a method for producing a separation membrane.

According to an embodiment of the present invention, there is provided a separator comprising a positive electrode, a negative electrode, and an electrolyte, the separator interposed between the positive electrode and the negative electrode, wherein the separator is a separator according to an embodiment of the present invention, An electrochemical cell, which is a separation membrane produced by the exemplary manufacturing method, is provided.

The separation membrane according to one embodiment of the present invention or the separation membrane manufactured through the manufacturing method of one embodiment reduces the moisture content in the separation membrane to prevent the decomposition of the electrolyte to generate less acid, The performance and lifetime of the battery can be improved.

In addition, it is possible to control moisture content increase rate by preventing moisture re-adsorption, and it is also possible to form a coating layer containing a binder and inorganic particles, thereby exhibiting properties such as heat resistance, strength and adhesive force suitable for a separator for electrochemical cells, The shape stability and heat stability of the chemical battery can be secured.

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

The separation membrane according to an embodiment of the present invention may include a polyolefin-based film and a coating layer formed on one or both sides of the polyolefin-based film.

The moisture content of the separation membrane of the present embodiment can be 1000 ppm or less after the separation membrane is allowed to stand at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours. More specifically, the moisture content in the separator may be 800 ppm or less, for example, 600 ppm or less. Within this range, the water content in the separator is low and the electrolyte in the battery can be prevented from being decomposed, and the decomposition of the negative electrode SEI film and the positive electrode active material can be reduced, thereby improving the performance and life of the battery.

The method for measuring the moisture content in the separator is not particularly limited, and examples thereof are as follows. After a separator having a coating layer is formed (with the package being removed in the case of packaging after manufacture) After storage for 72 hours at 28 ° C and 60% to 70% relative humidity, a total of 0.5 g to 1.0 g of the membrane is loaded into the capping vial. The vial was picked up on an 860 KF thermoprep (Metrom Inc.) and heated to 150 ° C. Using an automatic 831 KF coulometer (Metrom Inc.) for 10 minutes by Karl Fischer method, The content value (X ppm) is measured.

Further, the separation membrane according to the present embodiment may have an increase rate of the moisture content of 10% or less after being left to stand for 72 hours at a temperature of 25 to 28 DEG C and a relative humidity of 60 to 70%. Specifically, it may be 8% or less, more specifically 6% or less, and may have a negative value of, for example, less than 0%. The separation membrane according to the present embodiment has a low water re-adsorption rate in the separation membrane, which can further reduce moisture adsorption in the separation membrane even under conditions of high humidity. Particularly, when the water content increase rate has a negative value, it is possible to suppress moisture adsorption even after being left under a high humidity condition, thereby preventing deterioration of battery performance and service life due to moisture. The rate of increase of the moisture content was determined as X ppm in the separator after storage for 72 hours under the conditions of 25 ° C to 28 ° C and 60% to 70% relative humidity as described above. When the moisture content measured after storage for 72 hours under the conditions of relative humidity of 60% to 70% and Y is in ppm, can be calculated by the following equation (1). Specifically, the condition may be 25 캜 and a relative humidity of 65%.

[Formula 1]

Increase rate of water content (%) = [(YX) / X] x 100

The separator according to the present embodiment is further characterized in that the heat shrinkage rate in the machine direction (MD) or the transverse direction (TD) after being left at 120 ° C for 1 hour is 10% or less, specifically 8 Or less, more specifically, 7% or less. Within the above range, there is an advantage that the short circuit of the electrode is effectively prevented and the safety of the battery is improved.

The method of measuring the heat shrinkage percentage of the separation membrane is not particularly limited, and a method commonly used in the technical field of the present invention can be used. A method of measuring the heat shrinkage ratio of the separator is as follows: The separator is cut into a size of about 5 cm in length (MD) about 5 cm in length (TD) For 1 hour, and measuring the degree of shrinkage in the MD and TD directions of the separator to calculate the heat shrinkage ratio.

The separation membrane according to the embodiment may further have a tensile strength in the MD direction of 1,300 kgf / cm ² or more and a tensile strength in the TD direction of 1,100 kgf / cm ^{2 or} more. Specifically, the MD direction and the tensile strength of 1,400 kgf / cm ² to 2,100 kgf / cm ^2, may be the tensile strength in the TD direction of 1,200 kgf / cm ² to 2,000 kgf / cm ^2. More specifically, the tensile strength in the MD direction may be 1,500 kgf / cm ² to 1,800 kgf / cm ^2, and the tensile strength in the TD direction may be 1,300 kgf / cm ² to 1,700 kgf / cm ² .

The method for measuring the tensile strength of the separation membrane is not particularly limited, and a method commonly used in the technical field of the present invention can be used. The non-limiting examples of the method for measuring the tensile strength of the separator are as follows: The prepared separator was divided into 10 pieces of 10 pieces cut at 10 different points in a rectangular shape of 10 mm x MD (TD) 50 mm in width (MD) The specimens may be manufactured in such a manner that each of the specimens is mounted on a UTM (tensile tester) and the measured length is 20 mm, and then the specimens are pulled to measure the average tensile strength in the MD and TD directions.

The separation membrane according to the above embodiment may further have a puncture strength of 400 gf or more, for example, 410 gf to 590 gf.

Hereinafter, the polyolefin-based film and the coating layer included in the separation membrane of one embodiment of the present invention will be described in detail.

The base film of the separation membrane is not particularly limited as long as it is generally used for the separation membrane. However, in the case of the separation membrane for a secondary battery, a film having a shut down function can be used. Specifically, a polyolefin- The exemplary polyolefin-based film may be porous. Non-limiting examples of the polyolefin-based film include a separator selected from the group consisting of a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene double film, a polypropylene / polyethylene / polypropylene triple film, and a polyethylene / polypropylene / polyethylene triple film Can be used.

The polyolefin-based film may be formed using a polyolefin-based resin composition. The polyolefin-based resin composition may be composed of at least one polyolefin-based resin alone, or may be a mixed composition containing at least one polyolin-based resin, a resin other than a polyolefin-based resin, and / or an inorganic substance. Non-limiting examples of the polyolefin resin include polyethylene (PE), polypropylene (PP), polybutylene (PB), polyisobutylene (PIB) Poly-4-methyl-1-pentene (PMP), and the like. These may be used alone, or two or more of them may be used in combination, and a polyolefin-based resin copolymer or a mixture thereof may be used. Specifically, high density polyethylene (HDPE) having a weight average molecular weight (Mw) of less than 1,000,000 g / mol, for example, less than 100,000 g / mol to less than 1,000,000 g / mol, or an ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 g / Polyethylene (Ultrahigh Molecular Weight Polyethylene, UHMWPE), and the weight average molecular weight and the content of the polyolefin resin can be controlled according to the purpose. Non-limiting examples of the resin other than the polyolefin resin include polyamide (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polychlorotrifluoroethylene , PCTFE), polyoxymethylene (POM), polyvinyl fluoride (PVF), polyvinylidenefluoride (PVdF), polycarbonate (PC), polyarylate ), Polysulfone (PSF), polyetherimide (PEI), and the like. These may be used alone or in combination of two or more. Non-limiting examples of the inorganic substance include alumina, calcium carbonate, silica, barium sulfate, talc, and the like, and they may be used alone or in combination of two or more. The composition, content, and thickness of the polyolefin resin composition forming the film used in this embodiment are not particularly limited and can be appropriately adjusted according to the purpose.

The coating layer may be formed on one side or both sides of the film. The coating layer of the present embodiment may contain a binder for securing adhesion with an electrode and inorganic particles for improving heat resistance.

The thickness of one surface of the coating layer may be 0.1 to 10 탆, specifically 1 to 5 탆. It is possible to prevent the thickness of the entire separation membrane from becoming excessively thick within the above-mentioned thickness range, and to prevent the internal resistance of the battery from increasing. The method of measuring the thickness of the coating layer is not limited, but a non-limiting example can be measured using an SEM (Cross section) image and a micro-caliper. It is possible to form a coating layer having the above-mentioned thickness range to secure thermal stability, and it is possible to suppress an increase in the internal resistance of the battery.

Hereinafter, the binder and inorganic particles contained in the coating layer of the present embodiment will be specifically described.

end. bookbinder

The binder used in this embodiment may be an organic binder, or may be a homopolymer or a copolymer formed of two or more kinds of monomers. For example, fluorine-based binders; Acrylate binders; A nitrile binder; A polyvinyl binder; Polyester binders; A polyoxide binder; Cellulose based binders; Cyanide binders; Fluoran binder; Etc. may be used.

Specifically, polyvinylidenefluoride, polyvinylidenefluoride-hexafluoropropylene (PVDF-HFP), polyvinylidenefluoride-trichlorethylene (PVDF-TCE), polyvinylidene fluoride- , Fluorine-based binders such as polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE); Acrylate type binders such as polymers such as polymethylmethacrylate (PMMA) and polybutylmethacrylate PBMA, acrylate monomers and copolymers formed from monomers copolymerizable therewith; A nitrile binder such as polyacrylonitrile PAN; Polyvinyl-based binders such as polyvinylpyrrolidone (PVP), polyvinylacetate (PVAc), polyvinyl alcohol (PVA), and polyethylene-co-vinylacetate (PEVA); Polyester binders such as polyarylate (PAR); Polyoxide-based binders such as polyethylene oxide PEO and polypropylene oxide PPO; Cellulosic binders such as cellulose acetate (CA), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), and carboxyl methyl cellulose (CMC); Cyanide binders such as cyanoethylpullulan (CYEPL), cyanoethylpolyvinylalcohol (CRV), cyanoethyl cellulose (CEC), and cyanoethyl sucrose (CRU); And pullulan binders such as pullulan. These binders may be used alone or in combination of two or more.

The acrylate binder may be a copolymer obtained by polymerizing at least one monomer selected from the group consisting of methyl (meth) acrylate and butyl (meth) acrylate, or a copolymer of methyl (meth) acrylate, butyl (meth) Copolymers formed from possible monomers, copolymers obtained by copolymerizing acrylate monomers and vinyl acetate monomers, and the like. Specifically, a copolymer of butyl (meth) acrylate or a copolymer of at least one monomer selected from the group consisting of butyl (meth) acrylate, methyl (meth) acrylate, vinyl acetate and allylacetate can be used More specifically, ternary copolymers obtained by copolymerizing butyl (meth) acrylate, methyl (meth) acrylate and vinyl acetate can be used.

Even if the binder contained in the coating liquid is the same, the weight average molecular weight (Mw) may differ depending on the need. Even if two or more binders are included, the weight average molecular weight of each binder may be the same or different depending on the purpose. In this embodiment, the fluorine-based binder and the acrylate-based binder may be mixed in an appropriate ratio. Specifically, by containing the fluorine-based binder: acrylate-based binder in a weight ratio of 1: 0.25 to 1: 5, the binder can be sufficiently dispersed in the solvent, and the strength suitable for the separation membrane and the adhesion strength to the electrode can be ensured . Specifically, the weight ratio of the fluorine-based binder to the acrylate-based binder may be 1: 1 to 1: 5, and may be, for example, 1: 1 to 1: 1.5.

The fluorine-based binder may be polyvinylidene fluoride or polyvinylidenefluoride-hexafluoropropylene (PVDF-HFP), and the fluorine-based binder may include two kinds of binders having different weight average molecular weights Specifically a first fluorine-based binder having a weight average molecular weight of less than 1,000,000 g / mol and a second fluorine-based binder having a weight average molecular weight of less than 1,000,000 g / mol and having a weight-average molecular weight of 1,000,000 g / mol or more.

More specifically, the binder contained in the coating layer of the present embodiment may contain the first fluorine-based binder: the second fluorine-based binder: the acrylate-based binder in a weight ratio of 1: 1 to 2: 2 to 3. By using the binder in the present embodiment, the moisture content in the separator can be reduced to improve the performance and life of the battery, and the separator can be sufficiently impregnated into the electrolyte through the use of the binder, It is possible to provide a battery in which the electric power output is efficiently generated.

I. Inorganic particle

The kind of the inorganic particles contained in the coating layer is not particularly limited, and inorganic particles that are conventionally used in the art can be used. Non-limiting examples of the inorganic particles include Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO _2, and SnO ₂ . These may be used alone or in combination of two or more. For example, Al ₂ O ₃ (alumina) may be used.

The inorganic particles in the coating layer serve as a kind of spacer capable of maintaining the physical form of the coating layer. Accordingly, it is possible to prevent the inorganic particles in the coating layer from being detached during the assembling process of the battery or the like, thereby securing the shape stability and providing sufficient adhesion force between the coating layer and the film to suppress shrinkage of the film due to heat, Can be prevented from being short-circuited and excellent in high-temperature stability.

The size of the inorganic particles is not particularly limited, but may be an average particle diameter of 100 nm to 1000 nm, specifically 300 nm to 600 nm. When inorganic particles having the above-mentioned size range are used, it is possible to prevent degradation of the dispersibility of the inorganic particles in the coating liquid and the processability of the coating, and the thickness of the coating layer can be appropriately controlled. The inorganic particles may be contained in the coating layer in an amount of 50 to 95% by weight, for example 70 to 90% by weight.

Hereinafter, a method of manufacturing a separation membrane according to an embodiment of the present invention will be described. Specifically, the separation membrane according to the present embodiment may be formed by applying a coating liquid on a polyolefin film and then drying the coating liquid.

The polyolefin-based film may be porous, and the porous film may be formed by a generally known production method. As a non-limiting example, a dry method and a wet method are known. Specifically, the porous film of this embodiment can be produced by extruding a composition for a base film (for example, a polyolefin resin composition) and stretching to form fine pores in the film.

The coating solution may contain the binder and the inorganic particles described above. There is no particular limitation on the method of preparing the coating solution. However, the polymer solution in which the binder is dissolved and the inorganic dispersion in which the inorganic particles are dispersed are respectively prepared, The coating liquid may be prepared by mixing together.

The polymer solution and the solvent used for preparing the inorganic dispersion are not particularly limited as long as they can dissolve the polymeric binder and can sufficiently disperse the inorganic particles.

The polymer solution and the inorganic dispersion are further mixed with a solvent and then sufficiently stirred using a ball mill, a beads mill, a screw mixer or the like to prepare a coating solution in the form of a mixture .

Hereinafter, the additional solvent used for forming the coating solution together with the polymer solution and the inorganic dispersion in the separation membrane production method of this embodiment will be described in detail.

menstruum

The solvent may be a solvent that can be mixed with the polymer solution and the inorganic dispersion to exhibit stable liquid stability. In this embodiment, the first solvent and the second solvent may be used in combination.

The first solvent of this embodiment may be a solvent having a polarity of 4 or less and a boiling point of 100 占 폚 or less. The term " polarity degree " is a relative value determined in consideration of the interaction between the solvent and various polar solutes, and can be determined according to the structure of the molecule. The larger the value of the polarity is, the more the polarization in the molecular structure increases and the polarity becomes larger, so that the coupling with the polar solvent or the polar solute can be facilitated.

The term 'boiling point' can be used in combination with the boiling point, meaning that the pressure due to steam evolution in the corresponding solvent as the temperature increases equals the external pressure (eg atmospheric pressure = 1 atm) and starts to boil within the solvent do. The lower the boiling point of the solvent, the easier the drying process after coating the coating liquid on the separator.

Since the first solvent has relatively high hydrophilicity with respect to water (polarity of 10.2 and boiling point of 100 ° C) and has a high evaporation rate, it is possible to adsorb moisture in the air by the solvent when coating the separator (for example, The moisture content in the separator can be controlled.

delete

The first solvent can be selected according to the polarity and boiling point disclosed by commonly known literatures, and the polarity and boiling point according to the solvent are summarized as shown in Table 1 below.

menstruum The polarity index Boiling point (캜) Pentane 0.0 36 1,1,2-Trichlorotrifluoroethane 0.0 48 Cyclopentane 0.1 50 Heptane 0.1 98 n-Hexane 0.1 69 2,2,4-Trimethylpentane 0.1 98 Petroleum ether 0.1 30-60 Cyclohexane 0.2 81 n- Butyl Chloride 1.0 77 trichlorethylene 1.0 86 karbon tetraethylene 1.6 77 이리피opropyl ether 2.2 68 Toluene 2.4 111 Methyl t- Butyl Ether 2.5 55 o- Xylene 2.5 139 Chlorobenzene 2.7 132 o- Dichlorobenzene 2.7 180 benzene 2.7 80 Ethyl Ether 2.8 35 Diethyl ether 2.8 35 Dichloromethane 3.1 41 1,2-dichloroethane 3.5 84 n- Butyl Alcohol 3.9 117 isopropanol 3.9 82 n- Butyl Acetate 4.0 118 Isobutyl Alcohol 4.0 108 Tetrahydrofuran 4.0 65 n-propanol 4.0 97 Acetone 5.1 56 Water 10.2 100

The values shown in Table 1 are not absolute values that determine the polarity and boiling point of each solvent, and may vary within a range that does not impair the inherent properties of the solvent depending on the reference document.

The first solvent of the present embodiment may have a polarity of 4 or less, a boiling point of 100 ° C or less, and there is no particular limitation as long as it is a solvent belonging to the polarity and boiling point of the solvent. For example, n-hexane, Cyclohexane, carbon tetraethylene, methyl-t-butyl ether, 1,2-dichloroethane, tetrahydrofuran (THF) , 1,1,2-trichlorotrifluoroethane, 2,2,4-trimethylpentane, cyclopentane, petroleum ether (petroleum ether, benzene, n-Butyl Chloride, Ethyl Ether, dichloromethane, diethylether, heptane, pentane, n N-propanol, isopropanol, diisopropyl ether, trichloroethylene, etc. These may be used alone or in combination of two or more.

The first solvent may be contained in an amount of 35 wt% or less, specifically 10 to 35 wt%, based on the total weight of the coating solution. Within this range, not only the moisture reabsorption ratio in the separator can be reduced, but also the phase separation between the solvents does not occur when mixed with the polymer solution or the inorganic dispersion solution, so that the formation of the coating layer is easy.

The second solvent in the present embodiment is not particularly limited as long as it is a solvent capable of dissolving the binder to be contained in the coating liquid to stabilize liquid solution, and a second solvent can be used in the production of the polymer solution or the inorganic dispersion. Specific examples include acetone, acetone nitrile, tetramethylammonium chloride (TMAC), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc), dimethylcarbonate (DMC), and N-methylpyrrolidone (NMP). These may be used alone or in combination of two or more thereof. Or a mixture of two or more of them may be used.

The second solvent may be contained in the coating liquid in an amount of 50 wt% or more, specifically 60 wt% or more based on the total weight of the coating solution. More specifically, acetone may be used as the second solvent, By weight based on the total weight of the composition.

The solubility of the polymeric binder in the above range is excellent and the inorganic particles can be appropriately dispersed as well as the stability of the liquid solution can be ensured by mixing the polymer solution and the inorganic dispersion with the first and second solvents.

By using the first solvent and the second solvent in combination within the above range as in the present embodiment, the moisture content in the separation membrane can be reduced, and even in humidification conditions, the moisture adsorption can be reduced to suppress the increase of the moisture content , The performance and life of the battery can be improved.

Then, the coating solution containing the binder and / or the inorganic particles may be applied to coat the polyolefin film. The coating method is not particularly limited, and a method commonly used in the technical field of the present invention can be used. Examples of the coating method include a dip coating method, a die coating method, a roll coating method, and a comma coating method, and they may be used alone or in combination of two or more methods May be mixed and applied.

For example, the coating layer of the separation membrane according to the present embodiment may be formed using a dip coating method.

As described above, the coating liquid may be applied to coat the film and then dried to form a coating layer. The method of drying the coating liquid is not particularly limited, and a method commonly used in the technical field of the present invention can be used.

In the present invention, the drying of the coating layer can be performed by a method of drying by hot air, hot air, low-humidity air, vacuum drying, or irradiation of far-infrared rays or electron beams. The drying temperature and the drying time can be appropriately adjusted depending on the type of the solvent.

For example, it can be dried at a temperature of 60 to 120 캜 for 1 minute to 1 hour, more specifically at a temperature of 90 to 120 캜 for 1 to 30 minutes, or for 1 to 10 minutes .

As the phase transition phenomenon occurs in the drying process, a part of the solvent in the coating layer may be evaporated and dried to form micropores on the coating layer.

Hereinafter, an electrochemical cell according to an embodiment of the present invention will be described. An electrochemical cell according to an embodiment of the present invention includes an anode, a cathode, and an electrolyte, and a separator interposed between the anode and the cathode. At this time, the separation membrane may be a separation membrane according to embodiments of the present invention, or a separation membrane manufactured according to embodiments of the present invention.

The type of the electrochemical cell is not particularly limited and may be a battery of a kind known in the technical field of the present invention. For example, the secondary battery may be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The method for producing the electrochemical cell of this embodiment is not particularly limited, and a method commonly used in the technical field of the present invention can be used. A non-limiting example of the method for producing the electrochemical cell is as follows: A polyolefin-based porous separation membrane containing the organic and inorganic mixture coating layer of the present invention is placed between the anode and the cathode of a battery, The battery can be manufactured by filling.

The electrode constituting the electrochemical cell can be produced by binding an electrode active material to an electrode current collector by a method commonly used in the technical field of the present invention. The cathode active material of the electrode active material is not particularly limited, and a cathode active material conventionally used in the technical field of the present invention may be used. Non-limiting examples of the positive electrode active material include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, and lithium composite oxide in combination thereof. Of the electrode active materials used in the present invention, the negative active material is not particularly limited, and the negative active material conventionally used in the technical field of the present invention may be used. Non-limiting examples of the negative electrode active material include a lithium adsorbent material such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite or other carbon materials, and the like .

The electrode current collector is not particularly limited, and electrode current collectors commonly used in the technical field of the present invention can be used. Non-limiting examples of the positive electrode current collector material among the electrode current collectors include aluminum, nickel, or foil produced by a combination of these materials. As a non-limiting example of the cathode current collector material of the electrode current collector, copper, gold, nickel, a copper alloy, or a foil produced by a combination of these materials can be used.

The electrolytic solution is not particularly limited, and electrolytic solutions for electrochemical cells commonly used in the technical field of the present invention can be used. The electrolytic solution may be a salt having a structure such as A ⁺ B ^- dissolved or dissociated in an organic solvent. Non-limiting examples of the A ⁺ include alkali metal cations such as Li ⁺ , Na ^+, or K ⁺ , or cations made of combinations thereof. Non-limiting examples of B ^- include PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N ₃ SO ₂ ) ₂ ^- or C (CF ₂ SO ₂ ) ₃ ^- , or an anion composed of a combination of these.

Nonlimiting examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (Dipropyl carbonate, DPC), dimethyl sulfoxide (DMSO), acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran (THF), N-methyl- N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC) or gamma-butyrolactone (GBL). These may be used alone or in combination of two or more.

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

Preparation of polymer solution

PVdf-HFP (21216, manufactured by Solvay Co., Ltd.) having a weight average molecular weight (Mw) of 50 to 70,000 g / mol was added as a first polymer binder to acetone (purified gold) in an amount of 10 wt% Lt; / RTI > for 1 hour to prepare a first polymer solution.

A PVDF binder (KF 9300, Kureha) having a weight average molecular weight of 100-150,000 g / mol was added to acetone in an amount of 7 wt% as a second polymer binder, and the mixture was stirred at 40 ° C for 4 hours using a stirrer to obtain a second polymer solution .

Poly (butylmethacrylate) (Aldrich) having a weight average molecular weight of 30 to 350,000 g / mol as a third polymer binder was added to acetone in an amount of 5% by weight and stirred at 40 캜 for 4 hours using a stirrer to prepare a third To prepare a polymer solution.

Preparation of Inorganic Dispersions

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

Coating liquid ( coating slurry )

The first polymeric binder solution: the second polymeric binder solution: the third polymeric binder solution: the inorganic dispersion was mixed to a weight ratio of 1: 2: 5: 9, and n-hexane was added in an amount of 35% by weight based on the total weight of the coating solution. n-hexane and acetone were added thereto, followed by stirring at 25 캜 for 2 hours with a power mixer to prepare a coating solution.

Coating layer formation and separation membrane preparation

A polyethylene film (W Scope, PE) having a thickness of 9 占 퐉 was coated on both surfaces of the film by dip coating using the above coating solution and dried at 120 占 폚 for 1 minute to 3 minutes to form a 2 占 퐉 coating layer on both sides of the film Thereby forming a separator.

Example  2

A separator was prepared in the same manner as in Example 1 except that the coating solution was prepared using cyclohexane (tertiary decane) in place of n-hexane in the preparation of the coating solution.

Example  3

A separator was prepared in the same manner as in Example 1, except that the coating solution was prepared using carbon tetraethylene (pure heptane) instead of n-hexane in the preparation of the coating solution.

Example  4

A separator was prepared in the same manner as in Example 1 except that the coating solution was prepared using methyl-t-butyl ether (tert-butyl ether) instead of n-hexane in the preparation of the coating solution.

Example  5

A separator was prepared in the same manner as in Example 1, except that the coating liquid was prepared by using 1,2-dichloroethane (tertiary amine) instead of n-hexane in the preparation of the coating liquid.

Example  6

A separator was prepared in the same manner as in Example 1 except that the coating solution was prepared by using tetrahydrofuran (purified gold) instead of n-hexane in the preparation of the coating solution.

Example  7

In the preparation of the coating liquid in Example 1, the weight ratio of the first polymeric binder solution: second polymeric binder solution: third polymeric binder solution: inorganic dispersion = 1: 2: 5: 9 was mixed, Except that n-hexane and acetone were added in an amount of 17 wt% based on the weight of the coating solution to prepare a coating solution.

Example  8

In Example 7, the first polymeric binder solution: the second polymeric binder solution: the third polymeric binder solution: the inorganic dispersion was mixed in a weight ratio of 1: 2: 5: 9, and n-hexane was mixed with 10 Except that n-hexane and acetone were added so as to have a weight-average molecular weight of 5,000 to 10,000 by weight, to prepare a coating solution.

Example  9

A separator was prepared in the same manner as in Example 1, except that the coating solution was prepared using BMV (Butylmethacrylate-co-Methylmethacrylate-co-Vinylacetate) instead of PBMA in the preparation of the coating solution.

Comparative Example  One

A separation membrane was prepared in the same manner as in Example 1, except that n-hexane was not used as the first solvent in the preparation of the coating liquid.

Comparative Example  2

A separator was prepared in the same manner as in Example 1 except that the coating solution was prepared using toluene (purified gold) instead of n-hexane in the preparation of the coating solution.

Comparative Example  3

A separator was prepared in the same manner as in Example 1 except that the coating liquid was prepared using xylene (purified gold) instead of n-hexane in the preparation of the coating liquid.

Comparative Example  4

A separator was prepared in the same manner as in Example 1 except that n-hexane (n-hexane) was used instead of n-hexane to prepare a coating solution.

Comparative Example  5

The first polymeric binder solution: the second polymeric binder solution: the third polymeric binder solution: the inorganic dispersion = 1: 2: 5: 9 in the ratio of the first polymeric binder solution: the second polymeric binder solution: the third polymeric binder solution: % By weight of n-hexane and acetone to prepare a coating liquid.

Compositions included in the coating layer of the separator according to the above Examples and Comparative Examples are summarized in Table 2 below.

Fluorine series Acrylate series Al ₂ O ₃ Dispersion The first solvent (% by weight) 21216 solution 9300 solution PBMA solution BMV solution Example 1 One 2 5 - 9 n-hexane (35) Example 2 One 2 5 - 9 Cyclohexane (35) Example 3 One 2 5 - 9 Carbon Tetraethylene (35) Example 4 One 2 5 - 9 Methyl-t-butyl ether (35) Example 5 One 2 5 - 9 1,2-Dichloromethane (35) Example 6 One 2 5 - 9 THF (35) Example 7 One 2 5 - 9 n-hexane (17) Example 8 One 2 5 - 9 n-hexane (10) Example 9 One 2 - 5 9 n-hexane (35) Comparative Example 1 One 2 5 - 9 - Comparative Example 2 One 2 5 - 9 Toluene (35) Comparative Example 3 One 2 5 - 9 xylene (35) Comparative Example 4 One 2 5 - 9 n-butyl acetate (35) Comparative Example 5 One 2 - 5 9 n-hexane (45)

Experimental Example  One

Measurement of water content in the membrane

The following methods were performed to measure the water content in the separator prepared in the above Examples and Comparative Examples.

The separation membrane having the coating layer formed according to Examples and Comparative Examples was prepared, and the separation membrane was left for 72 hours at a temperature of 25 ° C and a relative humidity of 65%, and then 0.5 to 1.0 g of the separation membrane was loaded into the capping vial. The vial was taken out from an 860 KF Thermoprep (Metrom Co.), heated to 150 ° C, and subjected to automatic moisture measurement using an 831 KF coulometer (Metrom Inc.) for 10 minutes by Karl Fischer method The moisture content was measured. The measured moisture content was determined as the moisture content in the membrane X ppm.

Experimental Example  2

Measurement of water content increase rate of membrane

The following methods were performed to measure the water content increase rate of the separator prepared in the above Examples and Comparative Examples.

After the separation membrane having the coating layer formed according to the Examples and Comparative Examples was prepared, the separation membrane was allowed to stand for 72 hours at a temperature of 25 ° C and a relative humidity of 65%. Thereafter, After standing at 65% humidity for 72 hours, 0.5 to 1.0 g of the membrane was loaded into the capping vial. Thereafter, the water content Y ppm was measured by the Karl Fischer method using an 831 KF colometer in the same manner as in Experimental Example 1 above. The water content in the separation membrane measured by the method of Experimental Example 1 is referred to as X ppm. Using the X ppm and Y ppm measured as described above, the increase rate of the moisture content was calculated by the following formula 1.

[Formula 1]

Increase rate of water content (%) = [(Y-X) / X] 100

Experimental Example  3

Separator Heat shrinkage  Measure

The following methods were performed to measure the heat shrinkage of the separator prepared in the Examples and Comparative Examples.

Each of the membranes prepared according to Examples and Comparative Examples was cut into 5 cm (MD) 5 cm (length) (TD) 5 cm) to prepare seven samples. Each of the above samples was stored in a chamber at 120 ° C for 1 hour, and the degree of shrinkage in each of the MD and TD directions of each sample was measured, and the average value of the shrinkage was measured.

Experimental Example  4

Measurement of tensile strength of membrane

The following methods were performed to measure the tensile strength of the separator prepared in Examples and Comparative Examples.

Each of the membranes prepared according to the examples and comparative examples was subjected to ten specimens cut out at ten different points in a rectangular shape of 10 mm × 50 mm in width (MD), and each of the specimens UTM (tensile tester) to measure the length of 20 mm, and then the specimens were pulled to measure the average tensile strength in the MD and TD directions.

Experimental Example  5

Measurement of seepage strength of membranes

The following methods were carried out in order to measure the sting intensity of the membrane prepared in the above Examples and Comparative Examples.

Each of the membranes prepared according to the above Examples and Comparative Examples was cut into 10 pieces of MD 50 mm × TD 50 mm at different points and then 10 pieces of samples were prepared using KATO Tech G5 equipment The specimens were placed on a 10 cm hole, and the force was measured while pushing with a 1 mm probe. The stiffness of each of the above specimens was measured three times, and then the average value was calculated.

The measurement results according to Experimental Examples 1 to 5 are summarized in Table 3 below.

Moisture content in the membrane
(X ppm) Water content increase rate (%) Heat Shrinkage (%) The tensile strength
(kgf / cm ² ) Sting intensity
(gf) MD TD MD TD Example 1 450 -25.6 5 2 1545.91 1382.61 435 Example 2 468 -20.9 5 3 1681.62 1469.95 445 Example 3 501 -18.0 6 2 1643.84 1468.96 439 Example 4 520 -18.2 5 2 1846.65 1650.20 424 Example 5 548 -16.0 6 3 1763.61 1574.65 427 Example 6 570 -17.0 5 3 1701.06 1529.73 411 Example 7 526 -15.8 5 3 1588.90 1472.85 512 Example 8 580 -14.3 5 2 1807.28 1661.87 491 Example 9 448 -26.0 5 2 1780.85 1610.77 479 Comparative Example 1 740 +13.5 5 3 1372.20 1291.49 487 Comparative Example 2 580 +100.5 6 3 1607.92 1502.64 466 Comparative Example 3 610 +111.9 5 3 1708.74 1571.26 458 Comparative Example 4 680 +84.8 6 2 1525.91 1482.61 455 Comparative Example 5 Not measurable Not measurable Not measurable Not measurable Not measurable Not measurable Not measurable

In Examples 1 to 9, the first solvent having a polarity index of 4 or less and a boiling point of 100 占 폚 or less was contained in an amount of 35% by weight or less based on the total weight of the coating liquid, the water content in the separation membrane was 1000 ppm or less, After 72 hours at 25 ° C and a relative humidity of 65%, the measured increase in water content was less than 10%, and the moisture content was reduced without lowering the heat shrinkage, tensile strength and stamper strength, .

In addition, it has been confirmed that the performance and lifetime of the battery using the separator of the present invention can be improved by preventing the decomposition of the electrolyte at a point where the moisture content does not increase even under the condition of high humidity and is rather reduced.

On the other hand, when the coating liquid was prepared without using the first solvent having a polarity index of 4 or less and a boiling point of 100 ° C or less (Comparative Examples 1 to 4), the water content was greatly increased and the first solvent was changed to 35 In the case of using a coating solution containing more than 10% by weight (Comparative Example 5), alumina was not dispersed and the coating layer itself could not be formed by phase separation, and the physical properties according to Experimental Examples 1 to 5 were impossible to measure.

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

Claims (13)

A separator comprising a polyolefin film and a coating layer formed on one or both sides of the polyolefin film,
Wherein the moisture content of the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours is 1000 ppm or less,
Wherein the increase rate of the water content in the separation membrane according to the following formula (1) is 10% or less.
[Formula 1]
Increase rate of water content (%) = [(YX) / X] x 100
In Equation (1)
X is the water content (ppm) in the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours,
Y is the moisture content (ppm) in the separator after leaving the separator at 25 to 28 DEG C and a relative humidity of 60 to 70% for 72 hours, and thereafter for 72 hours under the same conditions. The separation membrane according to claim 1, wherein the coating layer contains a binder and inorganic particles. 3. The binder according to claim 2, wherein the binder is selected from the group consisting of a fluorine-based binder, an acrylate-based binder, a nitrile-based binder, a polyvinyl-based binder, a polyester-based binder, a polyoxide-based binder, a cellulose- Wherein the separation membrane comprises at least one selected from the group consisting of water, The separator according to claim 3, wherein the binder comprises a fluorine-based binder and the acrylate-based binder, wherein the weight ratio of the fluorine-based binder and the acrylate-based binder is 1: 0.25 to 1: 5. [5] The method according to claim 3, wherein the acrylate binder is at least one selected from the group consisting of methyl (meth) acrylate and butyl (meth) acrylate and at least one selected from the group consisting of allyl acetate and vinyl acetate. . ≪ / RTI > Applying a coating liquid on a polyolefin film to form a coating layer,
Wherein the coating liquid comprises a binder, a first solvent and a second solvent,
Wherein the binder comprises a fluorine-based binder and an acrylate-based binder,
Wherein the first solvent has a polarity index of 4 or less, a boiling point of 100 ° C or less, and a content of 35 wt% or less based on the total weight of the coating solution. 7. The method of claim 6, wherein the first solvent is selected from the group consisting of n-hexane, cyclohexane, carbon tetraethylene, methyl-t-butyl ether, , 1,2-dichloroethane, tetrahydrofuran (THF), 1,1,2-trichlorotrifluoroethane, 2,2,4-trimethyl But are not limited to, pentane (2,2,4-trimethylpentane), cyclopentane, petroleum ether, benzene, n-butyl chloride, ethyl ether, dichloromethane dichloromethane, diethylether, heptane, pentane, n-propanol, isopropanol, diisopropyl ether, and trichlorethylene. Wherein at least one selected from the group consisting of the above-mentioned materials is used. The method of claim 6, wherein the second solvent is selected from the group consisting of acetone, acetone nitrile, tetramethylammonium chloride (TMAC), tetrahydrofuran (THF), dimethylformamide, (DMF), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc), dimethylcarbonate (DMC), and N-methylpyrrolidone By weight based on the total weight of the coating liquid. The method for producing a separation membrane according to any one of claims 6 to 8, wherein the binder comprises the fluorine-based binder and the acrylate-based binder in a weight ratio of 1: 0.25 to 1: 5. [10] The method of claim 9, wherein the acrylate binder is at least one selected from the group consisting of methyl (meth) acrylate and butyl (meth) acrylate and at least one selected from the group consisting of allyl acetate and vinyl acetate. To form a copolymer. An anode, a cathode, and an electrolyte,
And a separator interposed between the anode and the cathode,
Wherein the separation membrane is a separation membrane according to any one of claims 1 to 5 or a separation membrane produced by the method according to any one of claims 6 to 8. 12. The electrochemical cell of claim 11, wherein the electrochemical cell is a secondary cell. 13. The electrochemical cell of claim 12, wherein the secondary battery is a lithium secondary battery.