KR20060003665A - New organic/inorganic composite porous film and electrochemical device prepared thereby - Google Patents

Abstract

The present invention is a porous substrate having pores, the melting temperature is 200 ℃ or more; And an active layer coated with a mixture of inorganic particles having a dielectric constant constant of 5 or more on the surface of the substrate or the substrate, and a polymer having a solubility parameter of 15 to 45 MPa ^1/2 . Provided are a porous film and a method of manufacturing the same, and an electrochemical device including the same.

The organic / inorganic composite porous film prepared according to the present invention has pores and has excellent structural and physical properties by using an active layer containing a porous substrate having a melting temperature of 200 ° C. or higher, a high dielectric constant inorganic particles, and a polymerizable gelable polymer. In addition to showing safety, lithium ion transfer is significantly improved during electrolyte impregnation and the electrolyte impregnation rate is excellent, and thus, a lithium secondary battery using the same may provide excellent battery safety and performance improvement.

Porous substrates, pores, inorganic materials, polymers, active layers, films, separators, gel polymer electrolytes, lithium secondary batteries, electrochemical devices

Description

New Organic / Inorganic Composite Porous Films and Electrochemical Devices Using Them {NEW ORGANIC / INORGANIC COMPOSITE POROUS FILM AND ELECTROCHEMICAL DEVICE PREPARED THEREBY}

1 is a structural diagram of an organic / inorganic composite porous film prepared in Example 1. FIG.

Figure 2a is a photograph of the organic / inorganic composite porous film prepared in Example 1 (PVdF-CTFE / BaTiO ₃ ) and commercialized PP / PE / PP separator at room temperature storage, Figure 2b is the organic / inorganic composite porous film And a photograph after leaving the PP / PE / PP separator at 150 ° C. for 1 hour.

The present invention relates to an organic / inorganic composite porous film having an excellent safety and performance improvement, and an electrochemical device including the same.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebooks and PCs, and even electric vehicles, efforts for research and development of batteries are becoming more concrete. The electrochemical device is the most attracting field in this respect, and among them, the development of a secondary battery capable of charging and discharging has been the focus of attention.

Secondary batteries are chemical cells capable of repeating charging and discharging using reversible interconversion of chemical and electrical energy, and are classified into Ni-MH secondary batteries and lithium secondary batteries. Lithium secondary batteries include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries.

A lithium ion battery coats a positive electrode active material (eg, LiCoO ₂ ) and a negative electrode active material (eg, graphite) having a crystal structure on an aluminum foil and a copper foil, which are current collectors, respectively. After the preparation, the separator is interposed between the electrodes, and the electrolyte is injected. When the battery is charged, lithium inserted in the positive electrode active material crystal is detached and enters the negative electrode active material crystal structure. On discharge, lithium in the negative electrode active material is detached and inserted into the crystal in the positive electrode. As the charge and discharge as described above, lithium ions move energy between the positive electrode and the negative electrode to transfer energy, and thus, are called rocking chair batteries. Lithium ion batteries having such an operation mechanism may be divided into lithium ion liquid battery (LiLB), lithium ion polymer battery (LiPB), and lithium polymer battery (LPB) according to the electrolyte used. That is, LiLB uses a liquid electrolyte, LiPB uses a gel polymer electrolyte, and LPB uses a solid polymer electrolyte.

Lithium secondary batteries are currently produced by many companies because of their high operating voltage and high energy density, compared to conventional Ni-MH batteries using aqueous electrolyte solutions, but their safety characteristics are different. The safety evaluation and safety of the battery are the most important considerations, and accordingly, the safety standard of the lithium secondary battery strictly regulates ignition and smoke in the battery.

Lithium ion batteries and lithium ion polymer batteries currently in production use polyolefin-based separators to prevent short circuits between the positive and negative electrodes. Since the polyolefin-based separator has a property of melting at 200 ° C. or lower, when the battery rises to a high temperature due to internal and / or external magnetic poles, a volume change such as shrinkage or melting of the separator occurs. An explosion may occur due to a short circuit, the release of electrical energy, or the like. Therefore, there is a demand for development of a separator in which heat shrinkage does not occur at high temperatures.

In an effort to improve the problems of the polyolefin-based separators mentioned above, there have been many attempts to develop an electrolyte to which inorganic substances are applied while serving as a separator, which is one of research directions of a general polymer electrolyte. If these are largely classified into two, first, inorganic particles are used, and composite electrolytes are prepared by using inorganic particles having lithium ion transfer capability alone or by mixing polymers having lithium ion transfer capability together. However, it is known that there is no further progress due to the lower ionic conductivity of the inorganic electrolyte and the increased interfacial resistance between the inorganic and the polymer when mixed with the polymer (Japanese Laid-Open Publication No. 2003-022707; Solid State Ionics , vol. 158, n.3, p275, 2003; Journal of Power Sources , vol. 112, n.1, p209, 2002; Electrochimica Acta , vol. 48, n.14, p2003, 2003).

Second, an electrolyte is prepared by mixing inorganic particles having lithium ion transfer ability or lithium ion transfer ability with a gel polymer electrolyte composed of a polymer and a liquid electrolyte. In this case, the inorganic material is added in a small amount compared to the polymer and the liquid electrolyte, and has an auxiliary function to assist the lithium ion transfer made by the liquid electrolyte.

On the other hand, when manufacturing a composite electrolyte from a solution state, it also has a structure in which pores are formed in the composite electrolyte depending on the type of inorganic material (US Patent No. 6,544,689; Japanese Laid-Open No. 2002-008724; 314995; WO 02/092638; WO 00/038263; Journal of Electrochemical Society , v.147, p1251, 2000; Solid State Ionics , v.159, n.1, p111, 2003; Journal of Power Sources , v .110, n.1, p38, 2002; Electrochimica Acta , v.48, n.3, p227, 2002).

In US Pat. No. 6,203,949 and US Pat. No. 6,599,664, attempts have been made to prepare an organic / inorganic composite electrolyte using a sol-gel process. However, problems due to the complexity of the sol-gel process and volume shrinkage after gel formation have not been solved yet, and are still far from practical use.

Looking at the common problems of the conventional studies using the inorganic particles as described above, the first is that when the liquid electrolyte is not used, the interfacial resistance between the inorganic material or between the inorganic material and the polymer is very large and the performance is reduced. Second, when an excess of minerals is used, the electrolyte tends to brittle easily. This causes a problem that the battery assembly is difficult to handle because it is not easy to handle. In particular, most of the studies conducted to date have attempted to develop a composite electrolyte containing an inorganic material in the form of a free standing film, but in this case, it is difficult to apply a battery due to poor mechanical properties such as a tendency to break. . Even in the case of improving the mechanical properties by reducing the inorganic content, if the battery is assembled after mixing with the liquid electrolyte in advance, the mechanical properties are greatly reduced by the liquid electrolyte, which makes the assembly of the battery impossible. In this case, since the polymer content is high in the organic / inorganic composite membrane, it takes a very long time to disperse the electrolyte in the battery, and the actual electrolyte wettability is also poor.

In addition, US Pat. No. 6,432,586 prepared a composite membrane by coating silica and the like on a polyolefin-based separator. This was to improve the easily broken mechanical properties of the composite electrolyte described above, but did not show a great effect on the safety including high temperature heat shrinkage.

In order to solve the above-mentioned problems of the prior art, the present inventors have (1) a substrate having excellent thermal stability and (2) an active layer composed of an active layer which is excellent in lithium ion transfer capacity and electrolyte impregnation rate and gelable by electrolyte impregnation. / Inorganic composite porous film was introduced.

Accordingly, an object of the present invention is to provide an organic / inorganic composite porous film and a method of manufacturing the same.

Another object of the present invention is to provide an electrochemical device including the organic / inorganic composite porous film.

The present invention a) a porous substrate having pores, the melting temperature of 200 ℃ or more; And b) an active layer coated with a mixture of inorganic particles having a dielectric constant of at least 5 on the surface of the substrate or the substrate, and a polymer having a solubility parameter of 15 to 45 MPa ^1/2 . An inorganic composite porous film and an electrochemical device including the same are provided.

In addition, the present invention comprises the steps of a) dissolving a polymer having a solubility index of 15 to 45 MPa ^1/2 in a solvent; b) adding and mixing inorganic particles having a dielectric constant of at least 5 to the polymer solution of step a); And c) coating and drying a surface of the porous substrate having a pore and a part of the pores in the substrate having a melting temperature of 200 ° C. or more with the mixture of step b). do.

Hereinafter, the present invention will be described in detail.

The organic / inorganic composite porous film of the present invention can be used not only as a separator by using a porous substrate having pores, but also has a high dielectric constant and can be used simultaneously as an electrolyte because it contains a polymer that can be gelled by electrolyte impregnation. .

Polyolefin-based separators, which are porous substrates used in the related art, have poor thermal safety and have a problem in that battery safety is greatly reduced by internal and external stimuli.                     

Accordingly, in order to prevent internal short circuits that may occur under excessive conditions such as high temperature of the battery and overcharging, the substrate in the organic / inorganic composite porous film of the present invention preferably has a melting temperature of 200 ° C. or higher. In addition, the substrate is preferably porous including a pore portion. This is because there is a lot of space to be filled with the electrolyte solution to facilitate the transfer of lithium can improve the battery performance. Non-limiting examples of the porous base material having the pore portion and the melting temperature of 200 ℃ or more include polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene (polyethylenenaphthalene) or mixtures thereof, and other heat-resistant engineering plastics can be used without limitation.

The thickness of the porous substrate is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm. If it is less than 1㎛ it is difficult to maintain the mechanical properties, if it exceeds 100㎛ acts as a resistive layer.

Pore size and porosity of the porous substrate is not particularly limited, porosity is preferably 5 to 95%. The pore size (diameter) is preferably 0.01 to 50 µm, more preferably 0.1 to 20 µm. When the pore size and porosity are less than 0.01 μm and 5%, respectively, it acts as a resistive layer, and when the pore size and porosity exceeds 50 μm and 95%, it becomes difficult to maintain mechanical properties.

The porous substrate may be in the form of fibers or membranes, and in the case of fibers, a nonwoven fabric that forms a porous web, and may be in the form of a spunbond or melt blown composed of long fibers. desirable.

The spawn bond method is a single continuous process, receives heat and melts to form long fibers, and is stretched by hot air to form a web. The melt blown process is a process of spinning a polymer capable of forming a fiber through a spinneret formed of hundreds of small orifices. It is a three-dimensional fiber with a spider-web structure.

In the organic / inorganic composite porous film of the present invention, one of the active layer components formed by coating a part of the pores of the surface of the porous substrate or the substrate is preferably an inorganic particle having a high dielectric constant constant of 5 or more, in particular a high dielectric constant of 10 or more And inorganic particles having a low density are more preferable. This is because lithium ions in the battery can be easily transferred. Non-limiting examples of inorganic particles having a high dielectric constant of 5 or more include Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), BaTiO ₃ , hafnia (HfO ₂ ), SrTiO ₃ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, CaO, ZnO, Y ₂ O ₃ or a mixture thereof.

The size of the inorganic particles is not limited, but is preferably in the range of 1nm to 10㎛. If it is less than 1 nm, it is difficult to control the structure and physical properties of the active layer due to the deterioration of dispersibility, and if it exceeds 10 μm, the mechanical properties may be reduced by reducing the pore size and pore portion of the organic / inorganic composite porous film. .

In the prior art, the inorganic particles are coated on the porous substrate alone or coated with an organic binder such as polyvinyl alcohol to improve the adhesion of the inorganic particles, but the structural safety of the electrolyte is not only lowered but the organic binder is also reduced. I was completely dissolved in the electrolyte, resulting in a weakening of the adhesion between the inorganic materials and the breakage of the pore structure.

Accordingly, the present invention is not dissolved in the electrolyte, but by using a polymer that can be gelated by swelling the electrolyte, not only stably fixing the inorganic particles but also improving structural safety, and by increasing the ionic conductivity and the impregnation rate for the electrolyte Battery performance can be improved.

Therefore, in the organic / inorganic composite porous film of the present invention, a polymer having a solubility index of 15 to 45 MPa ^1/2 is preferable as another component in the porous substrate surface or an active layer formed by coating a portion of the pores in the substrate. In particular, the range of 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 is more preferred. This is because the polymer is gelled by the electrolyte solution impregnation, thereby not only fulfilling the role of the binder of the inorganic particles but also exhibiting a high degree of electrolyte impregnation (degree of swelling). Therefore, hydrophilic polymers having many polar groups are preferable to hydrophobic polymers such as polyolefins. When the solubility index is less than 15 MPa ^{1/2 and more} than 45 MPa ^1/2 , it is difficult to be swelled by a conventional battery liquid electrolyte, and in the range of 25 to 30 MPa ^1/2 of the above range, The solubility index of the liquid electrolyte for phosphorus batteries and the solubility index are almost the same and can be dissolved in the electrolyte beyond gelation.

In addition, polymers having a glass transition temperature (Tg) in the range of -200 to 100 ° C are preferred. This is because mechanical properties such as flexibility and elasticity can be improved.

Non-limiting examples of the polymer having a glass transition temperature in the range of 200 to 100 ° C. and a solubility index of 15 to 45 MPa ^1/2 are polyvinylidene fluoride-co-hexafluoropropylene. , Polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate ( polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), Cyanoethylpullulan, cyanoethylpolylue Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, or mixtures thereof. In addition, any material can be used singly or in combination as long as it contains the above-described properties.

The composition ratio (weight%) of the inorganic particles to the polymer is not particularly limited, but 10:90 to 99: 1 is appropriate, and 50:50 to 99: 1 is preferable. If the composition ratio is less than 10:90, a desired level of porosity is hardly formed in the active layer, thereby deteriorating battery performance. If the composition ratio of 99: 1 is exceeded, mechanical properties are degraded due to weak adhesion between inorganic materials.

The active layer of the present invention may further include a solvent and other additives in addition to the inorganic particles and the polymer described above.

Compared to the conventional technology in which the polyolefin-based porous substrate is coated with inorganic particles having lithium ion transfer ability, the organic / inorganic composite porous film of the present invention not only promotes physical safety by using a porous substrate having a melting temperature of 200 ° C. or higher but also inherently It is possible to improve the structural safety by mixing together the electrophoretic inorganic particles and the polymer having a solubility index of 15 to 45 MPa ^1/2 as the active layer component.

After coating an active layer made of a mixture of inorganic material and polymer on the porous substrate, the pore size of the organic / inorganic composite porous film is preferably in the range of 0.001 μm (1 nm) to 10 μm, and porosity is 5 to 5. The 95% range is preferred. The organic / inorganic composite porous film of the present invention not only includes pores in the substrate itself, but also forms a porous structure in both the substrate and the active layer due to the space between the inorganic particles in the active layer formed on the substrate, thereby allowing the electrolyte solution to enter. The increase in space may have an effect of increasing the diffusion and conductivity of lithium ions.

The thickness of the organic / inorganic composite porous film is preferably in the range of 1 to 100 μm, more preferably in the range of 2 to 30 μm. By adjusting the thickness range, battery performance can be improved.

The organic / inorganic composite porous film of the present invention can be applied to a battery using a conventional polyolefin-based pore separator according to the characteristics of the final battery.

According to the present invention, a method of coating a mixture of high dielectric constant inorganic particles and gelable polymers on the surface of a porous substrate having a pore portion and a melting temperature of 200 ° C. or higher in the pores of the substrate may be a conventional coating method known in the art. have.

Hereinafter, for one embodiment of the production method according to the present invention, a) dissolving a polymer having a solubility index of 15 to 45 MPa ^1/2 in a solvent; b) adding and mixing inorganic particles having a dielectric constant of at least 5 to the polymer solution of step a); And c) coating and drying the surface of the porous substrate having a pore, a melting temperature of 200 ° C. or more, or a portion of the pores of the substrate with the mixture of step b).

First, a polymer solution is prepared by dissolving a polymer having a solubility index of 15 to 45 MPa ^1/2 in an appropriate organic solvent.

As the solvent, the solubility index is similar to that of the polymer, and the boiling point is preferably low. This is because mixing can be made uniform, and then the solvent can be easily removed. Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N -methyl-2-pyrrolidone, nmP), cyclohexane, water or a mixture thereof.

The inorganic particles and the polymer mixture are prepared by adding and dispersing high dielectric constant inorganic particles in the prepared polymer solution.

In the above, after adding a high dielectric constant inorganic particle to a polymer solution, it is preferable to grind | pulverize an inorganic particle. In this case, the crushing time is suitably 1 to 20 hours, and the particle size of the crushed inorganic particles is preferably 1 nm to 10 μm as mentioned above. As the shredding method, a conventional method can be used, and a ball mill method is particularly preferable.

The composition of the mixture consisting of inorganic particles and polymers is not particularly limited, and thus the thickness, pore size and porosity of the organic / inorganic composite porous film of the present invention can be adjusted.

That is, as the ratio (ratio = I / P) of the inorganic particles (I) to the polymer (P) increases, the porosity of the organic / inorganic composite porous film of the present invention increases, which is the same solid content (inorganic particle weight + High molecular weight) resulting in an increase in the thickness of the organic / inorganic composite porous film. In addition, the pore size of the inorganic particles increases, so that the pore size increases. At this time, as the size (particle diameter) of the inorganic particles increases, the interstitial distance between the inorganic particles increases, thereby increasing the pore size.

The mixture of the prepared inorganic particles and the polymer is coated on the prepared porous substrate and then dried. In this case, the process of coating the mixture of the inorganic particles and the polymer on the porous substrate may use a conventional coating method, Dip coating, Die coating, roll coating, comma coating Or it is preferable to apply | coat through these mixing system.

The organic / inorganic composite porous film of the present invention prepared as described above is assembled into a battery using a separator of a lithium secondary battery, and then gelled by reacting an electrolyte solution with a polymer by injection of an electrolyte solution. Can be formed.

The gel-type organic / inorganic composite electrolyte of the present invention is easier to manufacture than the gel polymer electrolyte of the prior art, and due to the porous structure, there are a large number of spaces filled with the liquid electrolyte to be injected, thereby exhibiting high ion conductivity and electrolyte impregnation rate. Can be significantly improved. In addition, by using a hydrophilic inorganic material and a polymer compared to the conventional hydrophobic polyolefin-based separator, the wettability (wetting) for the battery electrolyte is not only improved, but there is an advantage that can be used for the polar electrolyte solution for the battery, which was difficult to use in the prior art.

In addition, the present invention comprises an anode, a cathode, the organic / inorganic composite porous film and the electrolyte of the present invention interposed between the anode and the cathode, the electrolyte is impregnated in the pores, polymer or both in the organic / inorganic composite porous film It provides an electrochemical device characterized in that. In this case, in addition to the organic / inorganic composite porous film of the present invention can be used and applied with the existing polyolefin-based separator.

The electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary cells, fuel cells, solar cells, or capacitors. The organic / inorganic composite porous film included in the electrochemical device functions as a separator and an electrolyte as in the present invention.

Additionally, the present invention provides a positive electrode comprising a) a positive electrode active material capable of occluding and releasing lithium; b) a negative electrode comprising a negative electrode active material capable of occluding and releasing lithium; c) the organic / inorganic composite porous film; And it provides a lithium secondary battery comprising an electrolyte solution.

The lithium secondary battery includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

The lithium secondary battery may be manufactured by a conventional method known in the art, and for example, the organic / inorganic composite porous film is inserted between a positive electrode and a negative electrode and then a liquid electrolyte is added thereto.

The electrode to be used together with the organic / inorganic composite porous film is not particularly limited, but the positive electrode active material is lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, or a combination thereof. The main component is a lithium intercalation material such as a composite oxide formed by the anode, and the anode is bound to a foil manufactured by a cathode current collector, that is, aluminum, nickel, or a combination thereof. It is composed.

The negative electrode material is mainly composed of lithium metal or lithium alloy and lithium adsorption material such as carbon, petroleum coke, activated carbon, graphite or other carbons. The negative electrode is configured in the form of a binder bound to a current collector, that is, a foil made of copper, gold, nickel or a copper alloy or a combination thereof.

An electrolytic solution used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, and comprising an alkali metal cation or an ion composed of a combination thereof, such as K ^+, B ^- is PF ₆ ^{- _{, BF 4 -, Cl -,}} Br -, I -, ClO 4 -, ASF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2 ₃ ) Salts containing ions consisting of anions such as ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (dimethyl). carbonate, DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, nmP), ethyl methyl carbonate preferably dissolved and dissociated in an organic solvent consisting of hyl carbonate, EMC), gamma butyrolactone or mixtures thereof.

As described above, when the battery is assembled using the organic / inorganic composite porous film prepared according to the present invention and the positive electrode and the negative electrode and the electrolyte is injected therein, the polymer in the active layer coated on the organic / inorganic composite porous film is the electrolyte solution. It can react with to form a gel polymer electrolyte.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the battery assembly or at the end of battery assembly.

As a process of applying the organic / inorganic composite porous film of the present invention to a battery, a lamination and folding process of a separator and an electrode may be performed in addition to a general winding process.

In the above process, in particular the lamination process (lamination) has the advantage that can be easily assembled due to the excellent adhesion properties of the active layer in the organic / inorganic composite porous film of the present invention. At this time, the adhesion property may be controlled by the content of the inorganic particles and the polymer of the active layer component.

The invention is explained in more detail based on the following examples and experimental examples. However, Examples and Experimental Examples are for illustrating the present invention and are not limited to these.                     

Example 1. Organic / Inorganic Composite Porous Film (PVdF-CTFE / BaTiO) ₃ ) Produce

A polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVdF-CTFE) polymer was added to acetone in about 5% by weight, and then dissolved at a temperature of 50 ° C. for about 12 hours or more to prepare a polymer solution. A slurry was prepared by adding BaTiO ₃ powder to the polymer solution at a concentration of 20% by weight of solids and crushing and dispersing BaTiO ₃ powder at about 300 nm using a ball mill method for 12 hours or more. The slurry thus prepared was coated on a polyethylene terephthalate pore membrane (porosity 80%) having a thickness of about 20 μm by using a dip coating method, and the coating thickness was adjusted to about 2 μm. The porosity and porosity in the active layer impregnated and coated on the polyethylene terephthalate porous substrate were 0.3 μm and 55%, respectively, and the structure thereof is shown in FIG. 1.

Example 2. Preparation of Organic / Inorganic Composite Porous Film

The same procedure as in Example 1 was repeated except that PMNPT powder was used instead of BaTiO ₃ powder. As a result of measuring by the porosity measuring apparatus, pore size and porosity were 0.4 micrometer and 60%, respectively (refer FIG. 1).

Example 3. Preparation of Organic / Inorganic Composite Porous Film

BaTiO ₃ powder instead of BaTiO ₃ and the mixture powder of the Al ₂ O ₃ (weight ratio = 30:70), except that a was performed in the same manner as in Example 1. As a result, the pore size and porosity were 0.2 μm and 50%, respectively, measured by the porosity measuring device (see FIG. 1).

Example 4. Organic / Inorganic Composite Porous Film (CMC / BaTiO) ₃ ) Produce

Carboxyl Methyl Cellulose (CMC) was added to the polymer about 2% by weight in water and dissolved for at least 12 hours at a temperature of 60 ℃, except that the polymer solution was prepared in the same manner as in Example 1 It was. As measured by the porosity measuring device, the pore size and porosity in the active layer impregnated and coated on the polyethylene terephthalate porous substrate were 0.4 μm and 58%, respectively (see FIG. 1).

Example 5-8. Lithium secondary battery

Anode manufacturing

92% by weight of LiCoO ₂ as a positive electrode active material, 4% by weight carbon black as a conductive material and 4% by weight PVdF as a binder were added to N-methyl-2pyrrolidone (nmP) as a solvent to prepare a positive electrode mixture slurry. Prepared. The positive electrode mixture slurry was coated and dried on an aluminum thin film having a thickness of about 20 μm, which is a positive electrode current collector, to prepare a positive electrode, and then roll press was performed.

Cathode manufacturing

The negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material at 96% by weight, 3% by weight, and 1% by weight, respectively, to NMP as a solvent. Was prepared. The negative electrode mixture slurry was coated and dried on a copper thin film having a thickness of 10 μm, which is a negative electrode current collector, to prepare a negative electrode, and then roll press was performed.

Battery manufacturing

The positive electrode, the negative electrode, and each of the organic / inorganic composite porous films prepared in Examples 1 to 4 were assembled using a stacking method, in which 1 M lithium hexafluorophosphate (LiPF ₆ ) was dissolved. The lithium secondary batteries of Examples 5 to 8 were prepared by injecting an ethylene carbonate / ethyl methyl carbonate (EC / EMC = 1: 2, volume ratio) electrolyte.

Comparative Example 1. Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 5, except that the PP / PE / PP separator was used.

Experimental Example 1. Heat shrinkage analysis of organic-inorganic composite porous film

In order to compare the organic / inorganic composite porous film prepared according to the present invention with a conventional separator, the following experiment was performed.

PVdF-CTFE / BaTiO ₃ prepared in Example 1 was used as a sample, and a PP / PE / PP separator was used as a control.

After leaving each sample for 1 hour at room temperature and 150 ℃, and collected and confirmed, the organic / inorganic composite porous film and the control of the present invention showed a good state at room temperature (see Figure 2a) In the case where 1 hour has elapsed at a temperature of 150 ° C., different embodiments are shown. The PP / PE / PP separator of the control group showed shrinkage due to high temperature and remained almost in shape. However, the organic / inorganic composite porous film of the present invention showed no heat shrinkage at all, and thus showed the same good condition as at room temperature. (See FIG. 2B).

As a result, it was confirmed that the organic / inorganic composite porous film of the present invention has excellent thermal safety.

Experimental Example 2. Performance Evaluation of Lithium Secondary Battery

In order to measure the charge and discharge capacity of the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention, it was performed as follows.

The lithium secondary batteries prepared in Examples 5 to 8 were used, and the battery of Comparative Example 1 using a commercially available PP / PE / PP separator was used as a control. Each battery having a battery capacity of 760mAh was cycled at a discharge rate of 0.5C, 1C, and 2C, and their discharge capacities are shown in Table 1 by plotting C-rate characteristics.

As a result, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention showed excellent high-rate discharge (C-rate) characteristics up to 2C discharge rate compared to the existing polyolefin-based separator (see Table 1).

Discharge rate Example 1 Example 2 Example 3 Example 4 Comparative Example 1 0.5C 756 757 758 755 752 1C 745 747 746 742 741 2C 692 694 693 691 690

Experimental Example 3. Safety Evaluation of a Lithium Secondary Battery

In order to evaluate the safety of the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention, it was performed as follows.

The lithium secondary batteries prepared in Examples 5 to 8 were used, and the battery of Comparative Example 1 using a commercially available PP / PE / PP separator was used as a control. Each cell was stored for 1 hour at a high temperature of 160 ℃, after which the state of the cell is shown in Table 2 below.

As a result of the experiment, the battery of Comparative Example 1 using a commercialized PP / PE / PP separator fired. This indicates that the safety of the battery is reduced by internal short circuiting of the two electrodes, the positive electrode and the negative electrode, due to high temperature storage. In comparison, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention did not generate ignition and combustion even at a high temperature of 160 ° C., and showed a safe state (see Table 2).

As a result, it was confirmed that the lithium secondary battery including the organic / inorganic composite porous film of the present invention had excellent safety.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Fire X X X X O

As described above, since the heat shrinkage phenomenon does not occur using the heat-resistant porous substrate having a melting temperature of 200 ° C. or higher, the organic / inorganic composite porous film of the present invention solves a problem such as an internal short circuit of the battery due to high temperature heat shrinkage. Can improve the safety.                     

In addition, by coating a polymer mixture having a high dielectric constant inorganic particles and a solubility index of 15 to 45 MPa ^{1/2 on} the surface of the porous substrate or a part of the pores of the substrate to form a porous structure, lithium ion dissociation is improved and the electrolyte impregnation Excellent rate can improve battery performance. In addition, due to the high adhesive strength by controlling the content of the inorganic material and the polymer in the active layer, it is possible to increase the economics of the battery assembly process requiring a lamination process (lamination). In addition, the organic / inorganic composite porous film may be used as an electrolyte to improve fragile mechanical properties that may be caused when the film is formed in a free form.

Claims (15)

a) a porous substrate having pores and having a melting temperature of 200 ° C. or higher; And b) an active layer coated with a mixture of inorganic particles having a dielectric constant of at least 5 and a surface of the substrate or a polymer having a solubility parameter of 15 to 45 MPa ^1/2 Organic / inorganic composite porous film comprising a. The method of claim 1, wherein the porous substrate is polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide and poly At least one film selected from the group consisting of phenylene sulfide and polyethylene naphthalene. The film of claim 1, wherein the porous substrate has a pore size of 0.01 to 50 μm. The film of claim 1, wherein the porosity of the porous substrate is 5 to 95%. The method of claim 1, wherein the inorganic particles are Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O _{With 3} -PbTiO ₃ (PMN-PT), BaTiO ₃ , hafnia (HfO ₂ ), SrTiO ₃ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, CaO, ZnO and Y ₂ O ₃ At least one film selected from the group consisting of. The film of claim 1, wherein the inorganic particles range in size from 1 nm to 10 μm. The method of claim 1, wherein the polymer is polyvinylidene fluoride-co-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), poly Methyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide ( polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol Cyanoethylcellulose, cyano Til sucrose (cyanoethylsucrose), pullulan (pullulan) and carboxyl methyl cellulose film, at least one member selected from the group consisting of (carboxyl methyl cellulose). The film of claim 1, wherein the inorganic particles and the polymer have a weight ratio of 10:90 to 99: 1. The film of claim 1 wherein the pore size of the organic / inorganic composite porous film is in the range of 1 nm (0.001 μm) to 10 μm. The film according to claim 1, wherein the porosity of the organic / inorganic composite porous film is in the range of 5 to 95%. The film of claim 1, wherein the organic / inorganic composite porous film has a thickness in a range of 1 to 100 μm. a) an anode; b) a cathode; c) an organic / inorganic composite porous film according to any one of claims 1 to 11, interposed between the anode and the cathode; And d) electrolyte An electrochemical device comprising an electrochemical device, characterized in that the electrolyte is impregnated in the pores, polymers or both in the organic / inorganic composite porous film. The device of claim 12, wherein the electrochemical device further comprises a polyolefin-based separator. The device of claim 12, wherein the electrochemical device is a lithium ion secondary battery. a) dissolving a polymer having a solubility index of 15 to 45 MPa ^1/2 in a solvent; b) adding and mixing inorganic particles having a dielectric constant of at least 5 to the polymer solution of step a); And c) coating and drying the surface of the porous substrate having pores and having a melting temperature of at least 200 ° C. or a portion of the pores in the substrate with the mixture of step b). 12. A method for producing an organic / inorganic composite porous film as claimed in any one of claims 1 to 11.

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