KR20060041650A - Organic/inorganic composite porous film and electrochemical device prepared thereby - Google Patents

Abstract

The present invention a) inorganic particles; And b) a polymer binder coating layer formed on part or all of the surface of the inorganic particles, wherein the inorganic binder particles are connected and fixed by the polymer binder coating layer, and an interstitial space between the inorganic particles is provided. Volume) provides an organic / inorganic composite porous film and a method for producing the same, characterized in that the pores of the micro-unit is formed. In another aspect, the present invention provides an electrochemical device comprising the organic / inorganic composite porous film.

The organic / inorganic composite porous film prepared according to the present invention has a pore structure of heat-resistant micro units present in the film, thereby increasing the space into which the liquid electrolyte enters, thereby improving lithium ion conductivity and electrolyte impregnation rate. The battery can achieve thermal safety and improved performance.

Inorganic materials, polymers, pores, films, separators, electrolytes, lithium secondary batteries, electrochemical devices

Description

Organic / inorganic composite porous film and electrochemical device using the same {ORGANIC / INORGANIC COMPOSITE POROUS FILM AND ELECTROCHEMICAL DEVICE PREPARED THEREBY}

1 is a schematic diagram of an organic / inorganic composite porous film prepared according to the present invention.

FIG. 2 is a SEM photograph of the organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ) prepared in Example 1. FIG.

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

4A and 4B illustrate lithium secondary batteries of Comparative Examples 1 and 1 each having a commercially available PP / PE / PP separator and an organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ) prepared in Example 1, respectively. Overcharge experiment comparison picture.

The present invention relates to an organic / inorganic composite porous film having a pore structure in micro units 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 is produced by coating 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 separator is interposed between the electrodes, 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 categories, the first is to prepare a composite solid electrolyte by using inorganic particles having lithium ion transfer capability alone or by mixing inorganic particles and polymer matrix having lithium ion transfer capability (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). However, it is known that no further progress is made due to the low ionic conductivity of inorganic materials and the increase of interfacial resistance between inorganic materials and polymers when mixed with polymers.

Second, an electrolyte is prepared by mixing an inorganic particle having no or no lithium ion transfer capacity 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.

However, the electrolyte prepared as described above did not faithfully serve as a separator even if no pores were present in the electrolyte or even if there were pores, due to the pore size and low porosity of the angstrom unit formed by plasticizer injection.

In order to solve the above-mentioned problems of the prior art, the present inventors introduced an organic / inorganic composite porous film having micropores formed using (1) inorganic particles and (2) binder polymers as constituents.

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) inorganic particles; And b) a polymer binder coating layer formed on part or all of the surface of the inorganic particles, wherein the inorganic binder particles are connected and fixed by the polymer binder coating layer, and an interstitial space between the inorganic particles is provided. Volume) provides an organic / inorganic composite porous film and an electrochemical device comprising the same, characterized in that the pores of the micro-unit is formed.

In addition, the present invention comprises the steps of a) dissolving the polymer in a solvent to prepare a polymer solution; b) adding and mixing the inorganic particles to the polymer solution of step a); And c) coating and drying the mixture of the inorganic particles and the polymer of step b) on a substrate and then desorbing the substrate.

Hereinafter, the present invention will be described in detail.

The organic / inorganic composite porous film of the present invention may be used as a separator by forming a porous structure of micro units having heat resistance using inorganic particles and a binder polymer as components. In addition, when using a gelable polymer when impregnated with liquid electrolyte as a component of the polymer, it can be used simultaneously as an electrolyte.

One of the main components of the organic / inorganic composite porous film according to the present invention are inorganic particles commonly used in the art. The inorganic particles serve as a main component for producing the final organic / inorganic composite porous film, and form micro pores by enabling an interstitial volume between the inorganic particles. It also serves as a kind of spacer to maintain physical shape. In addition, since the inorganic particles generally have a property that physical properties do not change even at a high temperature of 200 ° C. or more, the formed film has excellent heat resistance.

The inorganic particles of the present invention are preferably inorganic particles having a high dielectric constant of 5 or more, and more preferably inorganic particles having a dielectric constant of 10 or more and low density. This is because lithium ions moving 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 present invention is characterized by the use of inorganic particles, which have never been used as a conventional heat resistant separator component, for new purposes. That is, 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 ), hafnia (HfO ₂ ) not only exhibit high dielectric constants with dielectric constants of more than 100, but also piezoelectricity, in which electric charges are generated when tension or compression is applied under constant pressure, resulting in a potential difference between both sides. Due to the above characteristics, not only the internal short circuit of the positive electrode can be prevented from occurring due to an external impact, but also due to the potential difference generated in the particles, electron movement between the positive electrodes, that is, the flow of minute electric current, can be prevented. By gradually reducing the voltage of the battery, it is possible to prevent safety degradation such as sudden ignition and explosion.

The organic / inorganic composite electrolyte of the present invention can form pores in micro units by adjusting the size of the inorganic particles, the content of the inorganic particles, and the composition of the inorganic particles and the polymer, and also the pore size and porosity. I can regulate it.

The size of the inorganic particles is preferably in the range of 0.01 to 10㎛, but is not particularly limited thereto. If it is less than 0.01㎛ dispersibility is difficult to control the structure and physical properties of the organic / inorganic composite porous film, if it exceeds 10㎛ the thickness of the organic / inorganic composite porous film made of the same solid content increases The mechanical properties are lowered, and due to the excessively large pore size, there is a high probability of internal short circuit during charging and discharging of the battery.

The content of the inorganic particles is preferably in the range of 50 to 99% by weight, more preferably 60 to 95% by weight, per 100% by weight of the mixture of the inorganic material and the binder polymer constituting the organic / inorganic composite porous film. If the content is less than 50% by weight, the content of the polymer is too high, resulting in a decrease in pore size and porosity due to a decrease in the void space formed between the inorganic particles, resulting in deterioration of final cell performance. If the content exceeds 99% by weight, the polymer content is too small, and the mechanical properties of the final organic / inorganic composite porous film are reduced due to the weakening of the adhesion between the inorganic materials.

The other one of the main components of the organic / inorganic composite porous film according to the present invention is a polymer commonly used in the art. In particular, a polymer having a glass transition temperature (Tg) in the range of -200 to 200 ° C is preferable, because it can improve mechanical properties such as flexibility and elasticity.

The polymer faithfully plays a role of a binder for stably connecting and stably connecting the inorganic particles and the particles, thereby contributing to the reduction of mechanical properties of the organic / inorganic composite porous film to be manufactured.

In addition to the above-described function, the polymer of the present invention may have a feature that can exhibit a high degree of swelling of the electrolyte by gelling when the liquid electrolyte is impregnated. Accordingly, polymers having a solubility index of 15 to 45 MPa ^1/2 are preferred, particularly in the range of 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . 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 becomes difficult to be swelled by the conventional battery liquid electrolyte.

Non-limiting examples of the polymer having a glass transition temperature in the range of -200 to 200 ° C. and a solubility index of 15 to 45 MPa ^1/2 include polyvinylidene fluoride-hexafuluropropylene (polyvinylidene fluoride-co- hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl Acetate (polyvinylacetate), ethylene vinyl co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate (cellulose acetate propionate), cyanoethylpullulan, cyanoethylpol Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer butadiene copolymer, polyimide or a mixture thereof. In addition, any material can be used singly or in combination as long as it contains the above-described properties.

The organic / inorganic composite porous film of the present invention may further include other additives in addition to the above-described inorganic particles and polymers.

When manufacturing the organic / inorganic composite porous film of the present invention using a mixture containing inorganic particles and a polymer, three types of embodiments can be made, but are not limited thereto. The first is to form an organic / inorganic composite porous film alone using a mixture of inorganic particles and a polymer. The second is to form an organic / inorganic composite porous film by coating the mixture on a porous substrate having pores, wherein the film coated on the porous substrate has a surface of the porous substrate or a portion of the pores of the substrate of the inorganic particles and the polymer. An active layer coated with a mixture. Third, an organic / inorganic composite porous film may be prepared by coating the mixture on the positive electrode and / or the negative electrode, wherein the prepared film is integrated with the electrode.

In an embodiment of the organic / inorganic composite porous film of the present invention, the porous substrate coated with the mixture containing the inorganic particles and the polymer is a porous substrate including pores, and preferably has a melting resistance of 200 ° C. or higher. This is because it is possible to improve the safety deterioration of the organic / inorganic composite porous film of the present invention caused by external and / or internal heat stimulation.

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 10%, 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 forming a porous web, and may be in the form of 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.

The organic / inorganic composite porous film of the present invention manufactured using only a mixture of inorganic particles and polymers alone has a micropore structure due to the interstitial volume between the inorganic materials serving as a spacer and a supporter. Is formed. In addition, the organic / inorganic composite porous film of the present invention formed by coating the mixture on a porous substrate includes not only pores in the substrate itself, but also the pore structure of both the substrate and the active layer due to the void space between the inorganic particles formed on the substrate. Will form. Therefore, an increase in the space into which the electrolyte enters through the pores of the formed micro units may increase the diffusion and conductivity of lithium ions.

It is preferable that the organic / inorganic composite porous film of the present invention prepared by using a mixture of an inorganic material and a polymer alone or formed by coating the mixture on a porous substrate having pores has a pore size of 0.01 to 10 μm. . In addition, the porosity of the film is preferably in the range of 5 to 95%. In addition, the thickness of the organic / inorganic composite porous film of the present invention 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 part or all of the surface of the inorganic particle with a polymer may use a conventional coating method known in the art.

Hereinafter, describing an embodiment of the manufacturing method according to the present invention, a) dissolving a polymer in a solvent to prepare a polymer solution; b) adding and mixing the inorganic particles to the polymer solution of step a); And c) coating and drying the mixture of step b) on the substrate and then detaching the substrate.

1) First, the polymer is dissolved in a suitable organic solvent to prepare a polymer solution.

As the solvent, the solubility index is similar to that of the polymer to be used, and a 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.

2) Inorganic particles are added and dispersed in the prepared polymer solution to prepare inorganic particles and polymer mixture.

In the above, after adding an 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 0.01 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.

3) After coating and drying the prepared mixture of inorganic particles and polymer on a substrate (substrate), the organic / inorganic composite porous film of the present invention is obtained by desorbing the substrate.

The substrate is preferably a teflon sheet or a similar film commonly used in the art, but is not limited thereto.

In addition, the process of coating the mixture of inorganic particles and polymer may use a conventional coating method. In particular, it is preferable to apply by dip coating, die coating, roll coating, comma coating or a mixture thereof.

In the above step, the organic / inorganic composite porous film may be prepared by coating the mixture on the porous substrate or the electrode having pores, wherein the mixture of the inorganic particles and the polymer is formed on the surface of the porous substrate as well as the surface of the porous substrate having the pores. Some are also penetrated and coated. The porous substrate used does not require a desorption process in the manufacturing process.

The organic / inorganic composite porous film of the present invention prepared as described above may be used as a separator of a lithium secondary battery. At this time, when using a polymer that can be gelled during the liquid electrolyte solution impregnation of the polymer component of the film, after assembling the battery using the separator and the electrolyte and the polymer reacts by the injection of the electrolyte to gel to form a gel-type organic / inorganic composite electrolyte can do.

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 micro-pore structure, there are a lot of spaces filled with the liquid electrolyte to be injected, thereby exhibiting high ion conductivity and electrolyte impregnation rate. The performance is significantly improved. In addition, when the hydrophilic polymer is used as a component of the polymer, the wettability of the battery electrolyte is improved as compared to the conventional hydrophobic polyolefin-based separator, and there is an advantage in that the polar electrolyte solution for the battery, which has been difficult to use in the past, can be used.

In addition, the present invention provides an electrochemical device comprising an anode, a cathode, the organic / inorganic composite porous film of the present invention interposed between the anode and the cathode. 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. In particular, a lithium secondary battery is preferable among secondary batteries, and specific examples thereof include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The electrochemical device may be manufactured according to a conventional method known in the art, and for example, the electrochemical device may be manufactured by injecting an electrolyte into the assembly after assembling the electrode and the separator.

The organic / inorganic composite porous film included in the electrochemical device plays the role of a separator as in the present invention, and also plays a role of an electrolyte when using a gelable polymer when the liquid electrolyte is impregnated with a polymer among the film components.

The electrode to be used together with the organic / inorganic composite porous film is not particularly limited, but the cathode active material may be a conventional cathode active material that can be used for the anode of a conventional electrochemical device, in particular lithium manganese oxide (lithiated magnesium oxide), lithium Lithium intercalation materials and the like are preferred, such as a composite oxide formed by cobalt oxide, lithium nickel oxide, or a combination thereof. In addition, the negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, in particular lithium metal, or lithium alloy and carbon (carbon), petroleum coke, activated carbon (activated carbon) Lithium adsorption materials such as graphite or other carbons are preferable. The above-mentioned positive electrode active material is prepared by a positive electrode current collector, i.e., aluminum, nickel, or a combination thereof, and a foil and cathode current collector, i.e., copper, gold, nickel, or a copper alloy, or a combination thereof, respectively. The positive electrode is constituted in a form bound to the foil produced by the method.

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), dimethyl carbonate (DEC) and dimethyl carbonate ( dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran , N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate preferably dissolved and dissociated in an organic solvent consisting of carbonate, EMC), gamma butyrolactone or mixtures thereof.

As described above, the organic / inorganic composite porous film of the present invention prepared by using a gelable polymer when impregnating a liquid electrolyte with a polymer component is used when the battery is assembled using the film and the anode and the cathode and the electrolyte is injected therein. The polymer in the film may react with the electrolyte 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.

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

When the organic / inorganic composite porous film of the present invention is applied to the lamination process in the above process, the thermal safety improvement effect of the battery becomes remarkable. This is due to the heat shrinkage of the separator is more severe in the battery produced by the lamination and folding process than the battery produced by the general winding process. In addition, the lamination (lamination, stack) process has the advantage that can be easily assembled due to the excellent adhesion properties of the polymer in the organic / inorganic composite porous film of the present invention. At this time, the adhesion properties can be controlled by the content of the inorganic particles and the polymer as the main 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.

[Examples 1 to 7. Organic / Inorganic Composite Porous Film and Lithium Secondary Battery]

Example 1

1-1. Organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ ) Produce

A polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) polymer was added to tetrahydrofuran (THF) about 5% by weight, and then dissolved at a temperature of 50 ° C. for about 12 hours or more to prepare a polymer solution. . BaTiO ₃ powder having a particle size of about 400 nm was added to this polymer solution at 20 wt% of total solids and dispersed to prepare a mixed solution (BaTiO ₃ / PVdF-HFP = 80: 20 (weight ratio)). The mixed solution prepared using the doctor blade method was coated on a Teflon sheet substrate. Then, the solvent, THF, was dried and detached from the Teflon sheet to obtain a final organic / inorganic composite porous film (see FIG. 1). As a result of measuring by a porosimeter, the thickness of the final organic / inorganic composite porous film was about 30 μm, and the pore size and porosity were 0.4 μm and 60%, respectively.

1-2. Lithium secondary battery manufacturing

Anode manufacturing

A positive electrode mixture slurry was prepared by adding 94 wt% of LiCoO ₂ as a cathode active material, 3 wt% of carbon black as a conductive agent, and 3 wt% of PVdF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. . The positive electrode mixture slurry was coated and dried on a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, which is a positive electrode current collector.

Cathode manufacturing

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

Battery manufacturing

The positive electrode, the negative electrode, and the organic / inorganic composite porous film prepared in Example 1-1 were assembled using a stacking method, and 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in the assembled battery. An ethylene carbonate / propylene carbonate / diethyl carbonate (EC / PC / DEC = 30: 20: 50% by weight) based electrolyte was injected to prepare a lithium secondary battery.

Example 2

2-1. Organic / inorganic composite porous film (PVdF-HFP / BaTiO ₃ -Al ₂ O ₃ ) Produce

BaTiO ₃ powder instead of the BaTiO ₃ / Al ₂ O ₃ 20:80 was carried out in the same manner as in the above embodiment 1 except that the inorganic particles powder mixing ratio% by weight (see Fig. 1). As a result of measuring by the porosity measuring device, the final film thickness was 25 μm, and the pore size and porosity were 0.3 μm and 57%, respectively.

2-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured by the same method as Example 1, except that the organic / inorganic composite porous film prepared in Example 2-1 was used.

Example 3

3-1. Organic / Inorganic Composite Porous Film (PVdF-HFP / PMNPT) Manufacturing

The same procedure as in Example 1 was performed except that PMNPT powder was used instead of BaTiO ₃ powder (see FIG. 1). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 30㎛, pore size and porosity were 0.3㎛ and 60%, respectively.

3-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the organic / inorganic composite porous film prepared in Example 3-1 was used.

Example 4

4-1. 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 (See FIG. 1). As a result of measuring by the porosity measuring device, the thickness of the final organic / inorganic composite porous film was 25 μm, and the pore size and porosity were 0.4 μm and 58%, respectively.

4-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the organic / inorganic composite porous film prepared in Example 4-1 was used.

Example 5

5-1. Organic / Inorganic Composite Porous Film (PVdF-HFP / PZT) Manufacturing

Except for using the PZT powder instead of BaTiO ₃ powder, it was carried out in the same manner as in Example 1 (see Fig. 1). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 25 μm, and the pore size and porosity were 0.4 μm and 62%, respectively.

5-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the organic / inorganic composite porous film prepared in Example 5-1 was used.

Example 6

6-1. Organic / Inorganic Composite Porous Film (PVdF-HFP / PLZT) Manufacturing

Except for using the PLZT powder instead of BaTiO ₃ powder, it was carried out in the same manner as in Example 1 (see Fig. 1). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 25㎛, pore size and porosity were 0.3㎛ and 58%, respectively.

6-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured by the same method as Example 1, except that the organic / inorganic composite porous film prepared in Example 6-1 was used.

Example 7

7-1. Organic / Inorganic Composite Porous Film (PVdF-HFP / HfO ₂ ) Produce

The same procedure as in Example 1 was performed except that HfO ₂ powder was used instead of BaTiO ₃ powder (see FIG. 1). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 28㎛, pore size and porosity were 0.4㎛ and 60%, respectively.

7-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the organic / inorganic composite porous film prepared in Example 7-1 was used.

[Comparative Examples 1 to 3]

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the PP / PE / PP separator was used.

Comparative Example 2

2-1. Organic / Inorganic Composite Porous Film Manufacturing

An organic / inorganic composite porous film was prepared in the same manner as in Example 1, except that the composition ratio of BaTiO ₃ and PVdF-HFP was used in a ratio of 20:80 wt%. As a result of measuring the prepared BaTiO ₃ / PVdF-HFP by the porosity measuring device, the pore size of the organic / inorganic composite porous film was less than 0.01㎛, porosity was 10% level.

2-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured by the same method as Example 1, except that BaTiO ₃ / PVdF-HFP prepared in Comparative Example 2-1 was used.

Comparative Example 3

3-1. Preparation of Porous Film Using Plasticizer

After selecting dimethyl carbonate (DMC) as a plasticizer, a porous film was prepared using a composition ratio of PVdF-HFP as 30:70 wt% and THF as a solvent. The prepared film was extracted with dimethyl carbonate, which is a plasticizer, using methanol. As a result of measuring the prepared PVdF-HFP porous film with a porosity measuring device, the pore size was less than 0.01㎛, the porosity was 30% level.

3-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured by the same method as Example 1, except that the porous film prepared in Comparative Example 3-1 was used.

Experimental Example 1. Surface analysis of organic / inorganic composite porous film

In order to analyze the surface of the organic / inorganic composite porous film prepared according to the present invention, the following experiment was performed.

The PVdF-HFP / BaTiO ₃ film prepared in Example 1 was used as a sample.

As a result of confirming the surface by Scanning Electron Microscope (SEM), it was found that the inorganic particles, which are the main constituents of the organic / inorganic composite porous film of the present invention, form pores. In addition, it was confirmed that the polymer is coated on the surface of the inorganic particles (see FIG. 2).

Experimental Example 2 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.

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

After the samples were left at room temperature and 150 ° C. for 1 hour and collected and confirmed, the organic / inorganic composite porous film of the present invention and the control group showed good conditions at room temperature (see FIG. 3A). In the case where 1 hour has elapsed at a temperature of 150 ° C., different embodiments are shown. The control group PP / PE / PP membrane showed shrinkage due to high temperature and almost remained 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. 3B).

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

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.

3-1. Hot Box Experiment

The lithium secondary batteries prepared in Examples 1 to 7 were used, and the BaTiO ₃ / PVdF-HFP film having a 20: 80% by weight ratio of the battery of Comparative Example 1 using a commercially available PP / PE / PP separator as a control membrane was used as a separator. The battery of Comparative Example 2 used was used. Each cell was stored at 150 ° C. and 160 ° C. for 1 hour, respectively, after which the state of the cell is shown in Table 1 below.

As a result, the battery of Comparative Example 1 using a commercialized PP / PE / PP separator exhibited an explosion phenomenon of the battery when stored for 1 hour at a temperature of 160 ℃. This means that severe thermal contraction and melt fracture of the polyolefin-based separator proceeded by high temperature storage, causing internal short circuits of the positive electrode and the negative electrode of the battery. In comparison, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention showed no ignition and combustion even at a high temperature of 160 ° C., and showed a safe state (see Table 1).

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

Hot Box Experiment Conditions 150 ℃ / 1 hour 160 ℃ / 1 hour Example 1 O O Example 2 O O Example 3 O O Example 4 O O Example 5 O O Example 6 O O Example 7 O O Comparative Example 1 O X Comparative Example 2 O O

3-2. Overcharge Experiment

The lithium secondary batteries prepared in Examples 1 to 7 were used, and the BaTiO ₃ / PVdF-HFP film having a 20: 80% by weight ratio of the battery of Comparative Example 1 using a commercially available PP / PE / PP separator as a control membrane was used as a separator. The battery of Comparative Example 2 used was used. Each battery was charged under the conditions of 6V / 1A and 10V / 1A, and then the state of the battery is described in Table 2 below.

As a result, the battery of Comparative Example 1 using a commercialized PP / PE / PP separator exhibited an explosion phenomenon (see Figure 4a). This indicates that overcharging of the battery causes short-circuits of the electrodes due to shrinkage of the polyolefin-based separator and a decrease in safety of the battery. In comparison, the lithium secondary battery including the organic / inorganic composite porous film prepared in the present invention showed a safe state during overcharging (see Table 2 and FIG. 4B).

Overcharge Experiment Conditions 6V / 1A 10V / 1A Example 1 O O Example 2 O O Example 3 O O Example 4 O O Example 5 O O Example 6 O O Example 7 O O Comparative Example 1 X X Comparative Example 2 O O

Experimental Example 4. 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 1 to 7 were used, and BaTiO ₃ / PVdF-HFP consisting of 20: 80% by weight of the battery of Comparative Example 1 using a commercially available PP / PE / PP separator as a control group was used as a separator. The battery of Comparative Example 3 using the PVdF-HFP porous film prepared using the battery of Comparative Example 2 and the plasticizer as a separator was used. Each battery having a battery capacity of 760 mAh was cycled at a discharge rate of 0.5 C, 1 C, and 2 C, and their discharge capacities are shown in Table 3 by plotting C-rate characteristics.

As a result, the battery of Comparative Example 2 using an organic / inorganic composite porous film having a composition ratio of inorganic particles and a binder polymer in a ratio of 20: 80% by weight was more remarkable than the organic / inorganic composite porous film of the present invention and a conventional polyolefin-based separator. It is shown that the capacity for each discharge rate is reduced. This means that the amount of the inorganic particles is relatively smaller than that of the polymer, so that the pore size and porosity formed by the void space between the inorganic particles significantly decrease, resulting in deterioration of the battery performance.

In addition, the battery of Comparative Example 3 using the porous film formed with a pore structure as a separator using a plasticizer, the discharge rate compared to the battery containing the organic / inorganic composite porous film of the present invention and a conventional polyolefin-based separator like the battery of Comparative Example 2 Star doses were markedly reduced. In contrast, the lithium secondary battery having the organic / inorganic composite porous film of the present invention showed a high rate discharge (C-rate) characteristic comparable to the existing polyolefin-based separator up to a discharge rate of 2C (see Table 3).

Discharge rate 0.5C 1C 2C Example 1 757 746 694 Example 2 756 748 693 Example 3 756 744 691 Example 4 758 747 694 Example 5 759 750 698 Example 6 755 742 690 Example 7 758 747 694 Comparative Example 1 758 746 693 Comparative Example 2 695 562 397 Comparative Example 3 698 585 426

As described above, the organic / inorganic composite porous film of the present invention is connected and fixed between the inorganic particles due to the binder polymer, and due to the interstitial volume between the inorganic particles, the main component of the film, Since the pore structure is formed to increase the space to be filled with the electrolyte solution to improve the electrolyte impregnation rate and lithium ion conductivity, the lithium secondary battery using this as a separator can improve thermal safety and performance.

Claims (14)

a) inorganic particles; And b) a polymer binder coating layer formed on part or all of the surface of the inorganic particles In the organic / inorganic composite porous film comprising, the inorganic binder is connected and fixed by the polymer binder coating layer, characterized in that the pores of the micro-unit is formed due to the interstitial volume between the inorganic particles Inorganic composite porous film. The film of claim 1, wherein the inorganic particles are inorganic particles having a dielectric constant of 5 or more. The method of claim 2, 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 size of the inorganic particles ranges from 0.01 μm to 10 μm. The film of claim 1, wherein the content of the inorganic particles is 50 to 99 wt% per 100 wt% of the mixture including the inorganic particles and the binder polymer. The film of claim 1, wherein the polymer has a glass transition temperature (Tg) in the range of -200 to 200 ° C. The film of claim 1, wherein the polymer is a gelable polymer when impregnated with a liquid electrolyte, and has a solubility index of 15 to 45 MPa ^1/2 . 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 1 type selected from the group consisting of ethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer and polyimide Ideal film. The film of claim 1, wherein the pore size of the organic / inorganic composite porous film is in a range of 0.01 to 10 μm. The film of 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 Electrochemical device comprising a. The device of claim 12, wherein the electrochemical device further comprises a polyolefin-based separator. a) dissolving the polymer in a solvent to prepare a polymer solution; b) adding and mixing the inorganic particles to the polymer solution of step a); And c) coating and drying the mixture of the inorganic particles and the polymer of step b) on the substrate, and then desorbing the substrate. 12. A method for producing an organic / inorganic composite porous film as claimed in any one of claims 1 to 11.

Images