KR100739337B1 - Organic/inorganic composite porous film and electrochemical device prepared thereby - Google Patents

Abstract

The present invention is an organic / inorganic composite porous film comprising a porous substrate having pores and an active layer coated with a mixture of inorganic particles and a binder polymer having a pore portion of the substrate or a surface of the substrate having a lithium ion transfer ability and a method of manufacturing the same. It provides an electrochemical device comprising the same.

The organic / inorganic composite porous film prepared according to the present invention improves the lithium ion conductivity of the final film as well as the pores contained in both the porous substrate and the active layer by using inorganic particles having lithium ion transfer ability as the active layer component of the film. Since the electrolyte impregnation rate is improved due to the structure, the lithium secondary battery using the same may exhibit an improvement in performance.

Porous substrate, lithium ion, conductivity, inorganic material, polymer, separator, gel polymer electrolyte, lithium secondary battery

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 structural diagram of an organic / inorganic composite porous film prepared according to the present invention.

FIG. 2 is an SEM image of the organic / inorganic composite porous film (LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP) prepared in Example 1. FIG.

Figure 3a is a photograph of the organic / inorganic composite porous film (LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP) prepared in Example 1 and commercialized PP / PE / PP separator at room temperature storage, Figure 3b It is a photograph after leaving the / inorganic composite porous film and the PP / PE / PP separator at 150 ° C. for 1 hour, respectively.

The present invention relates to an organic / inorganic composite porous film having improved lithium ion conductivity and electrolyte impregnation rate 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 aluminum foil and copper foil, which are current collectors, respectively, to form a positive electrode. It is prepared, and the electrolyte is injected after the separator interposed between the two electrodes. 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 the inorganic electrolyte and the increase of the interfacial resistance between the inorganic and the polymer when mixed with the polymer.

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 composite electrolyte prepared as described above has a problem in that lithium ion conductivity is significantly reduced due to the addition of inorganic particles added to improve safety. In addition, even if no pores existed in the electrolyte, or even if there were pores, the pore size and low porosity of the angstrom unit did not serve as a separator.

In order to solve the problems of the prior art mentioned above, the present inventors have an organic / inorganic composition consisting of (1) a porous substrate having pores and (2) an active layer comprising inorganic particles having lithium ion transfer capability as main components. A 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 provides an organic / inorganic composite porous film comprising a) a porous substrate having pores, and b) an active layer coated with a mixture of inorganic particles and a binder polymer having a portion of pores on the surface of the substrate or a substrate having lithium ion transfer ability. And it provides an electrochemical device comprising the same.

In addition, the present invention comprises the steps of a) dissolving the polymer in a solvent; b) adding and mixing inorganic particles having lithium ion transfer capability to the polymer solution of step a); And c) coating and drying the surface of the porous substrate having pores or a portion of the pores of the substrate with the mixture of step b).

Hereinafter, the present invention will be described in detail.

The organic / inorganic composite porous film of the present invention is coated on the surface of the porous substrate having the pores or a portion of the pores of the substrate using inorganic particles having a lithium ion transfer capacity and a binder polymer as the active layer component, when using this as a separator The effect of improving the ion conductivity can be obtained. In this case, the film has an improved electrolyte impregnation rate due to the pore structure included in both the substrate and the active layer in the film. 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.

In the organic / inorganic composite porous film according to the present invention, one of the active layer components formed by coating a portion of the pores of the surface of the porous substrate or the substrate contains inorganic particles, preferably lithium element, having lithium ion transfer ability, It is an inorganic particle having a function of transferring lithium ions without storing. Inorganic particles having lithium ion transfer ability can transfer and move lithium ions due to a kind of defect present in the particle structure, thereby improving lithium ion conductivity in the battery, thereby improving battery performance. Can be. Non-limiting examples of inorganic particles having a lithium ion transfer capacity include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ (LiAlTiP) _x O _y series glass such as O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3) , Li germanium thiophosphate such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5 ), Lithium nitride such as Li ₃ N (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ based glass such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ (Li _x Si P ₂ S ₅ series glass (Li _x P _y S _z , 0 <x, such as _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S _5, etc. <3, 0 <y <3, 0 <z <7) or mixtures thereof.

The organic / inorganic composite porous film of the present invention controls the size of the inorganic particles having the lithium ion transport ability, which is a constituent of the active layer of the film, the content of the inorganic particles, and the composition of the inorganic particles and the polymer, thereby controlling the active layer together with the pores included in the porous substrate. The pore structure of the can be formed, and also the pore size and porosity can be adjusted together.

The size of the inorganic particles is not limited, but is preferably in the range of 0.01 to 10㎛. 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 Deterioration in mechanical properties and excessively large pore size increase the probability of internal short circuits during battery charging and discharging.

The content of the inorganic particles having the lithium ion transfer capacity is preferably in the range of 50 to 99 wt%, more preferably 60 to 95 wt%, per 100 wt% of the mixture of the inorganic particles and the polymer constituting the organic / inorganic composite porous film. Do. 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 the final cell performance. Due to the weakening of the adhesion between the inorganic materials, the mechanical properties of the final organic / inorganic composite porous film is reduced.

Inorganic particles having lithium ion transfer ability as one of the active layer components of the present invention may further include inorganic particles commonly used in the art. Non-limiting examples thereof include SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, CaO, ZnO, Y ₂ O ₃ , 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 ) or SrTiO ₃ have.

In the organic / inorganic composite porous film according to the present invention, the other of the active layer components formed by coating a portion of the pores of the surface of the porous substrate or the substrate 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 of the final film.

The polymer faithfully plays a role of a binder that connects and stably fixes the inorganic particles and the particles, the surface of the inorganic particles and the porous substrate, and a part of the pores of the substrate, thereby mechanically preparing the organic / inorganic composite porous film to be manufactured. Prevents degradation of physical properties.

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-co-hexafluoropropylene. ), Polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate (polyvinylacetate), ethylene vinyl co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate propionate), cyanoethylpullulan, cyanoethylpoly 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. In the case of using the polymer having a solubility index of 15 to 45 MPa ^1/2 , in addition to the binder role of the inorganic particles described above, the polymer can be gelled by being swelled without being dissolved in the electrolyte, thereby contributing to the improvement of the electrolyte impregnation rate.

The active layer constituting the organic / inorganic composite porous film of the present invention may further include a solvent and other additives in addition to the inorganic particles and the polymer having lithium ion transfer ability.

In the organic / inorganic composite porous film according to the present invention, a substrate coated with a mixture of inorganic particles and a binder polymer having lithium ion transfer ability as the active layer component is a porous material having pores commonly used in the art. It is a base material. This is because there are a lot of spaces to be filled with the electrolyte solution to facilitate the transfer of lithium, thereby improving battery performance.

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.

The polyethylene-based separator, which is a porous substrate used in the related art, has a poor thermal safety and has a problem in that the safety of a battery is greatly reduced by internal and external stimuli. Therefore, the porous substrate of the organic / inorganic composite porous film according to the present invention is preferably a heat resistant substrate having a melting temperature 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 the 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, the 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 organic / inorganic composite porous film of the present invention formed by coating a mixture of inorganic particles and a binder polymer having lithium ion transfer ability on the porous substrate includes not only pores in the substrate itself, but also inorganic materials in the active layer formed on the substrate. Due to the interstitial volume between the particles, both the substrate and the active layer form a pore structure. Therefore, the electrolyte impregnation rate is improved by increasing the space for the electrolyte solution due to the pore structure.

It is preferable that the organic / inorganic composite porous film of the present invention formed by coating the mixture on a porous substrate having pores includes pores having a 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.

Compared with the conventional technology in which inorganic particles are coated on a polyolefin-based porous substrate, the organic / inorganic composite porous film of the present invention is used as an active layer component by mixing together inorganic particles and a binder polymer having lithium ion transfer ability on the porous substrate. By doing so, it is possible to improve the lithium ion conductivity of the final film and thereby improve the performance of the battery. In addition, when a heat resistant substrate having a melting temperature of 200 ° C. or more is used as a porous substrate having pores, the thermal stability of the final film can be improved, and when it is included as a separator, problems such as an internal short circuit of a battery due to high temperature heat shrinkage are solved. The safety of the battery can be raised. In addition, when a polymer having a solubility index of 15 to 45 MPa ^1/2 is used as the polymer component of the active layer constituting the film, the polymer may be gelled when the liquid electrolyte is impregnated to exhibit a high electrolyte impregnation rate, thereby improving battery performance.

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 inorganic particles and polymers having lithium ion transfer ability to the pores of the substrate or the surface of the porous substrate having pores may use conventional coating methods known in the art.

Hereinafter, for one embodiment of the production method according to the present invention, a) dissolving a polymer in a solvent; b) adding and mixing inorganic particles having lithium ion transfer capability to the polymer solution of step a); And c) coating and drying the surface of the porous substrate having pores or a portion of the pores in the substrate with the mixture of step b).

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) A mixture of inorganic particles and a polymer is prepared by adding and dispersing inorganic particles having lithium ion transfer ability to the prepared polymer solution.

In the above, after adding the inorganic particle which has a lithium ion transfer ability 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.

Although the composition of the mixture consisting of inorganic particles and polymers having lithium ion transfer ability is not particularly limited, the thickness, pore size and porosity of the organic / inorganic composite porous film of the present invention can be adjusted accordingly.

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) The mixture of the inorganic particles and the polymer having a lithium ion transfer capacity is coated on the prepared porous substrate, and then dried to obtain the organic / inorganic composite porous film of the present invention.

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 may be used as a separator of a lithium secondary battery. In this case, when using a polymer that can be gelled during liquid electrolyte impregnation as the polymer component of the active layer forming the film, after the assembly of the battery using the separator, the electrolyte and the polymer react by the injection of the electrolyte to form a gel-type organic / inorganic composite electrolyte. have.

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 has a large amount of space filled with the liquid electrolyte injected due to the pore structure included in both the porous substrate and the active layer, thereby providing high ion conductivity. And an electrolyte solution impregnation rate, which can significantly improve battery performance. In particular, lithium ion conductivity increases due to the lithium ion transport ability of the inorganic material. 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 includes 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 pores, polymers 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 may be 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 (NMP), ethyl methyl carbonate yl carbonate, EMC), gamma butyrolactone or a mixture thereof is preferably dissolved and dissociated.

As described above, the organic / inorganic composite porous film of the present invention prepared by using a gelable polymer when the liquid electrolyte is impregnated with the polymer component of the active layer is assembled with a battery using the film and the positive electrode and the negative electrode and injected into the electrolyte In this case, 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.

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.

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 in the battery produced by the lamination and folding process is more severe 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.

Example 1

1-1. Organic / Inorganic Composite Porous Film (PVdF-HFP / LiTi) ₂ (PO ₄ ) 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. . LiTi ₂ (PO ₄ ) ₃ powder was added to this polymer solution at a concentration of 20 wt% of total solids and dispersed to prepare a mixed solution (LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP = 80/20 (wt%)). It was. The mixed solution thus prepared was coated on a polyethylene terephthalate porous substrate (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 0.4 μm and 58%, respectively, and the structure thereof is shown in FIG. 1.

1-2. Lithium secondary battery manufacturing

Anode manufacturing

A positive electrode mixture slurry was prepared by adding 94 wt% of LiCoO ₂ as a positive electrode 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 / LiTi) ₂ (PO ₄ ) ₃ -BaTiO ₃ ) Produce

LiTi ₂ (PO _{4) 3} powder instead of BaTiO ₃ and LiTi ₂ (PO _{4) 3} of the powder mixture (weight ratio = 50:50), except that a was performed in the same manner as in Example 1. The pore size and porosity were 0.3 µm and 53%, respectively, as measured by the porosity measuring device (see FIG. 1).

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.

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. The pore size of the prepared organic / inorganic composite porous film was less than 0.01㎛, porosity was 5% level.

Comparative Example 2

2-1. Organic / Inorganic Composite Porous Film Manufacturing

LiTi ₂ (PO ₄ ) ₃ and An organic / inorganic composite porous film was prepared in the same manner as in Example 1, except that the composition ratio of PVdF-HFP was used in a ratio of 10: 90% by weight. As a result of measuring the prepared LiTi ₂ (PO ₄ ) 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 5% level.

2-2. Lithium secondary battery manufacturing

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP film prepared in Comparative Example 2-1 was used.

Comparative Example 3

3-1. Organic / Inorganic Composite Porous Film Manufacturing

A PP / PE / PP separator was used as the porous substrate, and the composition of BaTiO ₃ and PVdF-HFP having no lithium transfer capacity was used in a ratio of 10: 90% by weight. An inorganic composite porous film was prepared. 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㎛, the porosity was 5% level.

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 of 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.

Examples of the sample include LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP film was used.

As a result of confirming the surface by Scanning Electron Microscope (SEM), the organic / inorganic composite porous film of the present invention is not only porous substrate, but also inorganic particles are injected into the surface of the porous substrate or a part of the pores of the substrate to form a pore structure. It was confirmed that (see Figure 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.

Examples of the sample include LiTi ₂ (PO ₄ ) ₃ / PVdF-HFP film was used, and a commercialized PP / PE / PP separator was used as a control.

After leaving the samples for 1 hour at room temperature and 150 ℃, and collected and confirmed them, the organic / inorganic composite porous film and the control of the present invention showed a good state at room temperature (see Figure 3a) In the case where 1 hour has elapsed at a temperature of 150 ° C., different embodiments are shown. As a control, commercialized PP / PE / PP separators showed shrinkage at high temperature due to the low melting point of PP and PE (PP ~ 165 ℃, PE ~ 135 ℃), but remained almost in the form of organic / inorganic The composite porous film showed no heat shrink at all and 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

Lithium secondary batteries prepared in Examples 1 and 2 were used, the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control, LiTi ₂ (PO ₄ ) ₃ / PVdF- consisting of a ratio of 10: 90% by weight Separation membrane of organic / inorganic composite porous film prepared by applying inorganic material and polymer (BaTiO ₃ / PVdF-HFP) having no lithium transfer capability to the battery of Comparative Example 2 and the substrate of PP / PE / PP separator using HFP film as separator The battery of Comparative Example 3 used as was. 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, an oil prepared by applying inorganic material and polymer (BaTiO ₃ / PVdF-HFP) without lithium transfer ability to the battery of Comparative Example 1 using a commercialized PP / PE / PP separator and a substrate of PP / PE / PP separator The battery of Comparative Example 3 in which the inorganic / inorganic composite porous film was used as a separator exhibited an explosion phenomenon of the battery when stored at 160 ° C. for 1 hour. 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 a safe state without ignition and combustion even at a high temperature of 160 ° C. (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 had excellent thermal safety.

Condition Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 150 ℃ / 1 hour O O O O O 160 ℃ / 1 hour O O X O X

3-2. Overcharge Experiment

Lithium secondary batteries prepared in Examples 1 and 2 were used, the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control, LiTi ₂ (PO ₄ ) ₃ / PVdF- consisting of a ratio of 10: 90% by weight An organic / inorganic composite porous film prepared by applying an inorganic material and a polymer (BaTiO ₃ / PVdF-HFP) having no lithium transfer capability to the battery of Comparative Example 2 and the substrate of PP / PE / PP separator using HFP film as a separator was used as a separator. The battery of Comparative Example 3 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 oil prepared by applying inorganic material and polymer (BaTiO ₃ / PVdF-HFP) without lithium transfer capability to the battery of Comparative Example 1 using the commercialized PP / PE / PP separator and the substrate of PP / PE / PP separator The battery of Comparative Example 3 using the inorganic composite porous film as the separator exhibited an explosion phenomenon. 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 when overcharged (see Table 2).

Condition Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 6V / 1A O O X O X 10V / 1A O O X O X

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.

Lithium secondary batteries prepared in Examples 1 and 2 were used, the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control, LiTi ₂ (PO ₄ ) ₃ / PVdF- consisting of a ratio of 10: 90% by weight An organic / inorganic composite porous film prepared by applying an inorganic material and a polymer (BaTiO ₃ / PVdF-HFP) having no lithium transfer capability to the battery of Comparative Example 2 and the substrate of PP / PE / PP separator using HFP film as a separator was used as a separator. The battery of Comparative Example 3 used was used. Each battery having a battery capacity of 560mAh was cycled at a discharge rate of 0.5C, 1C, and 2C, and their discharge capacities are shown in Table 3 by plotting C-rate characteristics.

As a result of the experiment, the inorganic particles and the polymer having no lithium transfer ability on the battery of Comparative Example 2 and the PP / PE / PP separator base material using the film having the composition ratio of the inorganic particles having the lithium ion transfer capacity and the binder polymer ratio of 10: 90% by weight as the separator. The battery of Comparative Example 3 using the organic / inorganic composite porous film prepared by applying (BaTiO ₃ / PVdF-HFP = 90/10) as a separator was discharged compared to the organic / inorganic composite porous film of the present invention and the conventional polyolefin-based separator. The rate-specific dose was shown to decrease. This shows that the effect of improving the lithium ion conductivity is insufficient due to the inorganic particles having a small amount of lithium ion transfer ability. In addition, the amount of the inorganic particles that constitute the active layer component of the film is relatively small compared to the polymer, which means that the pore size and porosity of the final film is reduced, thereby degrading the performance of the battery. In addition, the battery of Comparative Example 3 using the organic / inorganic composite film having a composition ratio of 10:90 weight ratio of an inorganic material and a polymer having no lithium transfer capability as the separator of the organic / inorganic composite porous film of the present invention and Compared with the existing polyolefin-based separator, the capacity of each discharge rate is decreased. In addition, it was observed that the deterioration of performance was caused more than the battery of Comparative Example 2 due to the lack of lithium transfer ability. 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 Example 1 (mAh) Example 2 (mAh) Comparative Example 1 (mAh) Comparative Example 2 (mAh) Comparative Example 3 (mAh) 0.5C 556 557 558 430 412 1C 545 547 546 382 351 2C 492 491 493 270 234

The organic / inorganic composite porous film of the present invention can improve the lithium ion conductivity of the final film by using inorganic particles having lithium ion transfer ability as the active layer component of the film. In addition, due to the pore structure included in both the porous substrate and the active layer, there are a lot of spaces for the electrolyte to enter, so that the electrolyte impregnation rate is improved, and thus the lithium secondary battery using the same may provide an improvement in performance.

Claims (15)

(a) a porous substrate having pores; And (b) the surface of the substrate or a portion of the pores of the substrate includes an active layer coated with a mixture of inorganic particles and a binder polymer having a lithium ion transfer capacity, the inorganic particles having a lithium ion transfer capacity contains a lithium element Organic / inorganic composite porous film, characterized in that the particles themselves can move lithium ions without storing lithium. The method of claim 1, wherein the inorganic particles having a lithium ion transfer capacity is lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3 ), Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO _3, 0 <x <2, 0 <y <3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), lithium nitride (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4) Series glass and P ₂ S ₅ (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7) at least one film selected from the group consisting of glass. 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 having the lithium ion transfer ability is 50 to 99 wt% per 100 wt% of the mixture of the inorganic particles and the 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 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 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 porous substrate is a heat resistant substrate having a melting temperature of 200 ° C. or higher. The method of claim 8, 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 pore size of the porous substrate is in a range of 0.01 to 50 μm, and 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 12, 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 13, wherein the electrochemical device further comprises a polyolefin-based separator. a) dissolving the polymer in a solvent; b) adding and mixing inorganic particles having lithium ion transfer capability to the polymer solution of step a); And c) coating and drying the surface of the porous substrate with pores or a portion of the pores in the substrate with the mixture of step b) The method of manufacturing an organic / inorganic composite porous film according to any one of claims 1 to 12.

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