KR20070082402A - Organic/inorganic composite porous film and electrochemical device prepared thereby - Google Patents

Abstract

An organic/inorganic composite porous film is provided to impart additional lithium ion conduction paths to a battery, to improve a degree of swelling with an electrolyte, and to improve the quality and thermal safety of a battery. An organic/inorganic composite porous film comprises: (a) porous inorganic particles having a plurality of pores therein; and (b) a binder polymer coating layer partially or totally formed on the surface of the inorganic particles. The inorganic particles are interconnected with each other and fixed to each other by the binder polymer, and the interstitial volumes in the inorganic particles form a pore structure. The porous inorganic particle is selected from the group consisting of inorganic particles having a dielectric constant of 5 or higher, and inorganic particles capable of lithium ion conduction.

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

3A is a photograph of the organic / inorganic composite porous film (PVdF-HFP / porous Al ₂ O ₃ ) prepared in Example 1 and the commercialized PP / PE / PP separator of Comparative Example 1 at room temperature, and FIG. 3B is The organic / inorganic composite porous film and the PP / PE / PP separator are photographs after being left at 150 ° C. for 1 hour.

4A and 4B illustrate Comparative Examples 1 and 1 each having a commercially available PP / PE / PP separator and an organic / inorganic composite porous film (PVdF-HFP / porous Al ₂ O ₃ ) prepared in Example 1, respectively. It is a comparison photograph of the overcharge experiment of a lithium secondary battery.

The present invention relates to an organic / inorganic composite porous film and an electrochemical device including the same, which can simultaneously achieve excellent thermal safety and improved performance.

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. Examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

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 physical properties that melt 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. Explosion may occur due to short circuit, discharge of electrical energy, etc. 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. However, it is known that no further progress has been made due to the lower ionic conductivity of inorganic materials and the increase of interfacial resistance between inorganic materials and polymers when mixed with polymers. In addition, the electrolyte prepared as described above did not faithfully perform its role as a separator due to the pore size and low porosity of the angstrom unit formed by the plasticizer injection even if there were no pores or electrolytes in the electrolyte.

The inventors have found that the organic / inorganic composite porous film formed by using (1) inorganic particles and (2) binder polymers as components may not only improve thermal stability, but also a pore structure formed by inorganic particles in the film. It has been found that can effectively fulfill the role as a separator that serves as a lithium ion migration channel.

In particular, when using the porous inorganic particles having a plurality of pore structures in the particles themselves as the inorganic particles, not only the pore structure formed between the inorganic particles described above, but also the total pores due to the plurality of pores present in the inorganic particles themselves. The increase of the additional lithium ion migration path and the increase of the electrolyte impregnation rate, thereby improving the performance and safety of the electrochemical device using the organic / inorganic composite porous film as a separator at the same time Revealed.

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

The present invention (a) a porous inorganic particles having a plurality of pores in the particles themselves; And (b) an organic / inorganic composite porous film including a binder polymer coating layer formed on part or all of the surface of the inorganic particles, and a method of manufacturing the same, an electrochemical device including the organic / inorganic composite porous film, preferably lithium secondary. Provide a battery.

Hereinafter, the present invention will be described in detail.

The organic / inorganic composite porous film of the present invention is an inorganic particle which is a main component of the freestanding organic / inorganic film, and is characterized by introducing porous inorganic particles.

The porous inorganic particles, unlike the non-porous inorganic particles used as coating and / or constituent components of the conventional separator, there are a number of pores having various sizes and porosities in the particles themselves, these pores are the movement path of lithium ions And to further increase the space to be impregnated with the electrolyte. Therefore, although the conventional organic / inorganic composite membrane composed of nonporous inorganic particles and polymers has excellent thermal stability compared to polyolefin-based separators, porous inorganic particles could not be faithfully performed as separators due to deterioration in performance. The organic / inorganic composite porous membrane of the present invention to which the is introduced is differentiated in that it can promote thermal safety and performance.

If more specific description of the characteristics of the organic / inorganic composite porous film, as follows.

1) The organic / inorganic composite porous film of the present invention not only prevents a short circuit between the positive electrode and the negative electrode, but also has a function of delivering electrolyte due to the pore structure, thereby effectively fulfilling the role of the separator. In particular, not only the pore structure in the film formed by the void spaces between the porous inorganic particles, but also the pore structure in the inorganic particles constituting the film itself can exhibit comparable performance with the conventional polyolefin-based separator (see Table 3). ).

2) In addition, the organic / inorganic mixed layer used as a constituent or coating component of the conventional separator could improve battery safety due to the use of inorganic particles. An increase in weight was brought about. In contrast, in the present invention, by using the porous inorganic particles having a plurality of pores in the particles themselves, not only can the above-mentioned safety and performance be improved, but also a significant weight reduction can be obtained. This weight reduction leads to weight reduction of the battery, resulting in an increase in energy density per unit weight of the battery.

3) Since the polyolefin-based separator has a melting point of 120 to 140 ° C., heat shrinkage occurs at high temperature, but the organic / inorganic composite porous film made of the inorganic particles and the binder polymer does not generate high temperature heat shrinkage due to the heat resistance of the inorganic particles. Therefore, in the electrochemical device using the organic / inorganic composite porous film as a separator, the safety deterioration due to the internal short circuit of the anode / cathode does not occur at all even under excessive conditions such as high temperature and overcharging, and thus it is very safe compared to conventional batteries. Will be displayed.

One of the constituents of the organic / inorganic composite porous film according to the present invention is an inorganic particle commonly used in the art, so long as it has pores in the particle itself, specific to pore size, porosity, component and / or shape, etc. no limits.

In this case, the pores may be micropore having a diameter of 2 nm or less, mesopores having a diameter of 2 to 50 nm, macropore having a diameter of 50 nm or more, or a mixed form thereof according to the International Pure Applied Chemistry (IUPAC) definition. It is preferably a large pore of 50nm or more. However, it is not limited thereto.

As described above, the porous inorganic particles provide additional movement paths and electrolyte impregnation spaces of lithium ions through the pore structure existing in themselves, thereby improving performance of the battery. In addition, by enabling an interstitial volume between the inorganic particles, it serves as a function of forming micro pores in the organic / inorganic composite porous coating layer and 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 organic / inorganic composite porous coating layer has excellent heat resistance.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range of the battery to be applied (for example, 0 to 5 V on the basis of Li / Li ⁺ ). In particular, in the case of using the inorganic particles having the ion transfer ability, since the ion conductivity in the electrochemical device can be improved to improve the performance, it is preferable that the ion conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is not only difficult to disperse during coating, but also has a problem of weight increase during battery manufacturing, and therefore, the smallest density is desirable. In addition, in the case of the inorganic material having a high dielectric constant, it is possible to improve the dissociation degree of the electrolyte salt, such as lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

For the foregoing reasons, the inorganic particles are preferably high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having a lithium ion transfer ability, or a mixture thereof.

Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO 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), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2, SiC Or mixtures thereof.

The inorganic particles having a lithium ion transfer capacity refers to the inorganic particles containing lithium element, but having a function of transporting lithium ions without storing lithium, and the inorganic particles having a lithium ion transfer capacity are inside the particle structure. Since lithium ions can be transferred and moved due to a kind of defect present in the battery, lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the 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 (LiAlTiP) _x O _y series glass such as ₂ 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 nitrides such as Li ₃ N (Li _x N _y , 0 <x <4, 0 <y <2), SiS ₂ series glass such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ (Li _x P ₂ S ₅ series glass (Li _x P _y S _z , 0 <, such as Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S _5, etc. x <3, 0 <y <3, 0 <z <7) or mixtures thereof. Specific examples thereof include (Li _0.5 La _0.5 ) TiO ₃ , Li _2x Ca _0.5-x TaO ₃ , Li _0.2 [Ca _1-y Sr _y ] _0.4 TaO ₃ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li ₃ VO ₄ , Li ₃ PO ₄ / Li ₄ SiO ₄ , Li ₂ S-GeS ₂ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ , Li ₂ S-GeS ₂ -Ga ₂ S ₃ , Li ₂ S-SiS ₂ , Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -SiS _2, and the like.

In the present invention, by controlling the pore size and porosity in the porous inorganic particles constituting the organic / inorganic composite porous coating layer, the size (particle diameter) of the porous inorganic particles, the content of the porous inorganic particles and the composition of the porous inorganic particles and the binder polymer, It is possible to form and control the pore structure of the organic / inorganic composite porous film. This pore structure is filled with the liquid electrolyte injected later, which results in a significant reduction in the interfacial resistance generated between the inorganic particles or between the inorganic particles and the binder polymer.

The size of the porous inorganic particles is not particularly limited, but is preferably in the range of 0.01 to 10㎛, more preferably 0.3 to 10㎛ range. If it is less than 0.01㎛ dispersibility is difficult to control the structure and physical properties of the organic / inorganic composite porous film, and if it exceeds 10㎛ the thickness of the organic / inorganic composite porous film made of the same solid content increases mechanical properties This can be degraded.

The pore size of the porous inorganic particles themselves may range from 0.1 nm to 1 μm, preferably 0.05 to 1 μm, but is not limited thereto. If the thickness is less than 0.1 nm, the pore size is so small that it is difficult for the electrolyte to penetrate. If the thickness is larger than 1 μm, the size of the porous inorganic particles increases, resulting in an increase in the thickness of the organic / inorganic composite porous film. . The porosity of the porous inorganic particles can be variously controlled in the range of 1 to 99%, but preferably 5 to 95%. If the porosity of the porous particles is less than 5%, it is difficult to expect the electrolyte impregnation into the pores present in the porous particles and thereby improve the performance of the battery. If the porosity exceeds 95%, the mechanical strength of the particles themselves may be weakened. have.

The content of the porous inorganic particles is not particularly limited, but may be in the range of 10 to 99 parts by weight per 100 parts by weight of the mixture of the porous inorganic particles and the binder polymer constituting the organic / inorganic composite porous film, preferably 50 to 95 parts by weight. It is wealth. If less than 10 parts by weight of the polymer content is too much may be reduced pore size and porosity due to the reduction of the void space formed between the inorganic particles may lead to a deterioration of the final battery performance. If the content exceeds 99% by weight, the polymer content is too small, and the mechanical properties may be degraded due to the weakening of the adhesion between the inorganic materials.

The other component of the organic / inorganic composite porous film according to the present invention is a binder polymer commonly used in the art. In particular, it is possible to use a glass transition temperature (Tg) as low as possible, preferably in the range of -200 to 200 ℃. This is because the mechanical properties such as flexibility and elasticity of the final film can be improved. The polymer faithfully plays a role of a binder for stably connecting and stably connecting the inorganic particles and the particles, thereby preventing a decrease in mechanical properties of the organic / inorganic composite porous film that is finally manufactured.

In addition, the binder polymer does not necessarily have an ion conducting ability, but when the polymer having an ion conducting ability is used, the performance of the electrochemical device may be further improved. Therefore, the binder polymer is preferably as high as possible dielectric constant. In fact, since the dissociation degree of the salt in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the higher the salt dissociation in the electrolyte of the present invention. The dielectric constant of the polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), particularly preferably 10 or more.

In addition to the above-described function, the binder polymer of the present invention may have a feature that can be gelled during the liquid electrolyte impregnation to exhibit a high degree of swelling. In fact, when the binder polymer is a polymer having excellent electrolyte impregnation rate, the electrolyte injected after battery assembly is permeated into the polymer, and the polymer having the absorbed electrolyte has electrolyte ion conducting ability. Therefore, it is possible to improve the performance of the electrochemical device as compared to the conventional organic / inorganic composite electrolyte. In addition, the polymer has a very good affinity to the electrolyte (affinity), there is an advantage that can be applied to the polar electrolyte solution for the battery which was difficult to use conventionally. In addition, when the polymer is a gelable polymer when the electrolyte is impregnated, then the injected electrolyte and the polymer react with each other to form a gel-type organic / inorganic composite electrolyte. The electrolyte thus formed is easier to manufacture than conventional gel electrolytes and exhibits high ionic conductivity and electrolyte impregnation rate, thereby improving battery performance. Therefore, polymers having a solubility index of 15 to 45 MPa ^1/2 are preferred if possible, with the range of 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 more preferred. If the solubility index is less than 15 MPa ^1/2 and ^greater than 45 MPa ^1/2 , it may be difficult to swell by conventional battery liquid electrolytes.

Non-limiting examples of binder polymers that can be used include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide ( polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol Cyanoethyl cellulose lcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide or these And mixtures thereof. In addition, any material can be used singly or in combination as long as it contains the above-described properties.

The thickness of the organic / inorganic composite porous film formed by coating a mixture of the porous inorganic particles and the binder polymer is not particularly limited, but may be adjusted in consideration of battery performance, and may be independently adjusted at the positive and negative electrodes. In the present invention, in order to reduce the internal resistance of the battery, it is preferable to adjust the thickness of the coating layer within a range of 1 to 100 μm, more preferably 1 to 30 μm.

In addition, the pore size and porosity of the organic / inorganic composite porous coating layer is mainly dependent on the size of the porous inorganic particles and the pore size present in the inorganic particles, such a pore structure is to be filled with the electrolyte solution to be injected later, The electrolyte thus filled plays a role of ion transfer. Therefore, the pore size and porosity are important influence factors for controlling the ionic conductivity of the coating layer. Pore size and porosity (porosity) of the organic / inorganic composite porous film of the present invention is preferably in the range of 0.1nm to 10㎛, 5 to 95%, but is not limited thereto.

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

The organic / inorganic composite porous film of the present invention may be applied to a battery using a microporous separator, such as a polyolefin-based separator, depending on the characteristics of the final battery.

The organic / inorganic composite porous film according to the present invention may be prepared according to a conventional method known in the art, for example, (a) dissolving a polymer in a solvent to prepare a polymer solution; (b) adding and mixing the porous inorganic particles to the polymer solution prepared in step (a); And (c) coating and drying the mixture of step (b) on the substrate and then detaching the substrate from the substrate.

First, 1) 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 binder polymer to be used, and the boiling point is preferably low. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used 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 porosity in the prepared polymer solution. After adding the porous inorganic particles to the prepared polymer solution, it is preferable to crush the inorganic particles. 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 the porous inorganic particles and the polymer 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.

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

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

In addition, the method of coating the mixture of the inorganic particles and the polymer on the substrate may be used a conventional coating method known in the art, for example, dip coating, die coating, roll coating, Various methods, such as a comma coating or a mixing method thereof, can be used.

The organic / inorganic composite porous film of the present invention prepared as described above may be used as a separator of an electrochemical device, preferably a lithium secondary battery. In addition, it is possible to use a separator by coating a conventional polymer known in the art, such as an electrolyte impregnable polymer, on one or both surfaces of the organic / inorganic composite porous film.

In this case, when a gelable polymer is used when the liquid electrolyte solution is impregnated with the binder polymer component of the film, after the battery is assembled using the separator, the injected electrolyte and the polymer react with each other 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 due to the micro-pore structure, a large amount of space to be filled with the injected liquid electrolyte provides high ionic conductivity and electrolyte impregnation rate. It can improve battery performance.

In addition, the present invention (a) a positive electrode; (b) a cathode; (c) the organic / inorganic composite porous film of the present invention interposed between the positive electrode and the negative electrode; And (d) provides an electrochemical device comprising an electrolyte.

Electrochemical devices include 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 including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery among the secondary batteries is preferable.

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.

In this case, in addition to the organic / inorganic composite porous film, a fine pore separation membrane may be additionally used. The micro pore separator may be a polyolefin-based separator or polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, With polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro and polyethylenenaphthalene It may be a porous substrate having a melting temperature of at least one selected from the group consisting of 200 ° C or more.

The electrochemical device may be manufactured according to conventional methods known in the art, and for example, an electrolyte may be injected after assembling the organic / inorganic composite porous film described above between an anode and a cathode. It can be prepared by.

The electrode to be applied together with the organic / inorganic composite porous film of the present invention is not particularly limited, and the electrode active material may be prepared in a form bound to the electrode current collector according to conventional methods known in the art.

Non-limiting examples of the positive electrode active material of the electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, in particular lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or Lithium intercalation materials such as composite oxides formed by combination are preferred. Non-limiting examples of the negative electrode active material may be a conventional negative electrode active material that can be used in the negative electrode of the conventional electrochemical device, in particular lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred.

Non-limiting examples of the positive electrode current collector is a foil made by aluminum, nickel or a combination thereof, and non-limiting examples of the negative electrode current collector by copper, gold, nickel or copper alloy or a combination thereof Foils produced.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and 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 ) Salts containing ions consisting of anions such as ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (γ-butyrolactone Or dissolved in an organic solvent consisting of a mixture thereof, but is not limited thereto.

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 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 adhesive properties of the polymer in the organic / inorganic composite porous film of the present invention. At this time, the adhesion properties may be controlled by the content of the inorganic particles and the polymer or the physical properties of the polymer, in particular, the more polar the polymer, the glass transition temperature (T _g ) or melting temperature (melting) The lower the point, T _m ), the better the adhesion between the organic / inorganic composite porous film and the electrode of the present invention.

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 and 2]

Example 1

1-1. Organic / inorganic composite porous film (PVdF-HFP / porous Al ₂ O 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. . To this polymer solution, a porous Al ₂ O ₃ powder having a particle size of about 1 μm, a pore size of 110 nm, and a porosity of 50% was added to 20% by weight of the total solids and dispersed, and mixed solution (porous Al ₂ O ₃ / PVdF-HFP = 80:20 (weight ratio)). The mixed solution prepared using the doctor blade method was coated on a Teflon sheet substrate. Coated and THF. After drying, it was detached from a Teflon sheet to obtain a final organic / inorganic composite porous film (see FIG. 1). The final film thickness was about 30 μm. As measured by a porosimeter, the average pore size and porosity of the final organic / inorganic composite porous film were 0.4 µm and 77%, 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 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

In the same manner as in Example 1, except that porous TiO ₂ powder having a pore size and porosity of 1 μm was used instead of the porous Al ₂ O ₃ powder having a pore size of 110 nm and a porosity of 50%. An organic / inorganic composite porous film (PVdF-HFP / porous TiO ₂ ) and a lithium secondary battery having the same were prepared (see FIG. 1). As a result of measuring by the porosity measuring device, the final organic / inorganic composite porous film thickness was 30㎛, the average pore size and porosity were 0.4㎛ and 76%, respectively.

[Comparative Examples 1 and 2]

Comparative example  One

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

An organic / inorganic composite porous film and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that the composition ratio of the non-porous Al ₂ O ₃ and PVdF-HFP was used in a ratio of 80: 20% by weight. It was. As a result of measuring the prepared non-porous Al ₂ O ₃ / PVdF-HFP by the porosity measuring device, the pore size of the organic / inorganic composite porous film was 0.3㎛, the average porosity was 52% level.

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.

As a sample, a PVdF-HFP / porous Al ₂ O ₃ film prepared in Example 1 was used.

The surface of the organic / inorganic composite porous film according to the present invention was confirmed by scanning electron microscopy (SEM). As a result, not only the pore structure is formed by the space between the inorganic particles, but also the inorganic particles themselves. I could see that there are a number of pores that exist. In addition, it was found that the polymer is coated on the surface of the porous 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 / porous Al ₂ O ₃ film prepared in Example 1 was used, and a PP / PE / PP separator of Comparative Example 1 was used as a control.

After leaving each sample for 1 hour at room temperature and 150 ℃, and collected and confirmed, as a result, both the organic / inorganic composite porous film and the control of the present invention showed a good state (see Fig. 3a), When 1 hour had elapsed at a temperature of 150 ° C, different embodiments were 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 using the porous inorganic particles of the present invention also has excellent thermal safety compared to the general PP / PE / PP separator.

Experimental Example  3. Safety Evaluation of 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 and 2 were used, and Comparative Example 1 using the non-porous Al ₂ O ₃ / PVdF-HFP film and the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control membrane The battery of 2 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. On the contrary, the lithium secondary battery including the organic / inorganic composite porous films of Comparative Example 2 using the non-porous inorganic particles and the inorganic inorganic particles of Examples 1 and 2 using the porous inorganic particles do not generate ignition and combustion even at a high temperature of 160 ° C. And 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 had excellent thermal safety.

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

3-2. Overcharge Experiment

The lithium secondary batteries prepared in Examples 1 and 2 were used, and Comparative Example 1 using the non-porous Al ₂ O ₃ / PVdF-HFP film and the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control membrane The battery of 2 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 Table 2 and Figure 4a). This indicates that a short circuit occurs between the positive electrodes due to the shrinkage of the polyolefin-based separator due to overcharging of the battery, and a decrease in safety of the battery occurs. In comparison, the lithium secondary battery including the battery of Comparative Example 2 using non-porous inorganic particles and the organic / inorganic composite porous films of Examples 1 and 2 using porous particles showed a safe state when overcharged (Table 2 and FIG. 4B). Based on these results, the organic / inorganic composite porous film of the present invention prepared using the porous inorganic particles not only has excellent stability compared to the PP / PE / PP separator of Comparative Example 1, but also a comparative example using conventional nonporous inorganic particles. It can be confirmed that the organic / inorganic composite porous film of 2 has comparable safety.

Condition Example 1 Example 2 Comparative Example 1 Comparative Example 2 6V / 1A O O X O 10V / 1A O O X 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 and 2 were used, and Comparative Example 2 using the non-porous Al ₂ O ₃ / PVdF-HFP as a separator and the cell of Comparative Example 1 using a commercially available PP / PE / PP separator as a control The battery of 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 composed of nonporous inorganic particles and a binder polymer as a separator has a reduced capacity by discharge rate compared to the organic / inorganic composite porous film of the present invention and a conventional polyolefin-based separator. Indicated. In contrast, the lithium secondary batteries of Example 1 and Example 2 having an organic / inorganic composite porous film using porous particles had a high rate discharge (C) comparable to that of the PP / PE / PP separator of Comparative Example 1 up to a discharge rate of 2C. -rate) characteristics (see Table 3). This means that due to the many pores present in the inorganic particles themselves, the movement path of lithium ions and the electrolyte impregnation space are added to improve the performance of the battery.

Through the experimental results, it was confirmed that the organic / inorganic composite porous film of the present invention prepared using the porous inorganic particles is improved in performance compared to the organic / inorganic composite porous film of Comparative Example 2 prepared using non-porous inorganic particles. Could.

Discharge rate Example 1 (mAh) Example 2 (mAh) Comparative Example 1 (mAh) Comparative Example 2 (mAh) 0.5C 758 759 758 748 1C 746 747 746 735 2C 694 693 693 678

Organic / inorganic composite porous film using porous inorganic particles according to the present invention by using a porous inorganic particles having a plurality of pores in the particles as a component, by the existing organic / inorganic composite porous film using non-porous particles In addition to the improved safety effect, the performance degradation pointed out by the problems of the organic / inorganic composite porous film using the conventional non-porous inorganic particles can be solved.

Claims (16)

(a) a porous inorganic particle having a plurality of pores in the particle itself; And (b) a binder polymer coating layer formed on part or all of the surface of the inorganic particles Organic / inorganic composite porous film comprising a. The organic / inorganic composite porous film of claim 1, wherein the inorganic polymer is connected and fixed between the inorganic particles by a binder polymer, and a pore structure is formed due to an interstitial volume between the inorganic particles. / Inorganic composite porous film. The film of claim 1, wherein the pore size in the porous inorganic particles is in the range of 0.1 nm to 1 μm, and the porosity is in the range of 5 to 95%. The film according to claim 3, wherein the pore size in the porous inorganic particles is a macropore of 50 nm or more. The film of claim 1, wherein the porous inorganic particles are at least one selected from the group consisting of (a) inorganic particles having a dielectric constant of 5 or more and (b) inorganic particles having a lithium ion transfer capacity. The inorganic particle having a dielectric constant of 5 or more is BaTiO 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), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O _3, TiO ₂ or SiC film. The method of claim 5, 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 (LixGeyPzSw, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Lithium Nitride (LixNy, 0 <x <4, 0 <y <2), SiS ₂ (LixSiySz, 0 <x <3, 0 Films with <y <2, 0 <z <4) series glass or P ₂ S ₅ (LixPySz, 0 <x <3, 0 <y <3, 0 <z <7) series glass The film of claim 1, wherein the porous inorganic particles range in size from 0.01 to 10 μm. The film of claim 1, wherein the content of the porous inorganic particles is 10 to 99 wt% per 100 wt% of the mixture including the porous inorganic particles and the binder polymer. The film of claim 1, wherein the binder polymer has a solubility parameter ranging from 15 to 45 MPa ^1/2 . The method of claim 1, wherein the binder polymer is polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene (polyvinylidene fluoride-co-trichloroethylene), Polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer, polyethylene oxide (polyethylene oxide), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol ), Cyanoethylcellulose, Group consisting of cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer and polyimide At least one film selected from. The film of claim 1, wherein the pore size of the organic / inorganic composite porous film is in the range of 0.1 nm to 10 μm, and the porosity 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. An electrochemical device comprising an anode, a cathode, a separator and an electrolyte, wherein the separator is an organic / inorganic hybrid porous film according to any one of claims 1 to 13. The electrochemical device of claim 14, wherein the electrochemical device is a lithium secondary battery. (a) dissolving a binder polymer in a solvent to prepare a polymer solution; (b) adding and mixing the porous inorganic particles to the polymer solution prepared in step (a); And (c) coating and drying the substrate using a mixture of the porous inorganic particles and the polymer of step (b) and then detaching the substrate from the substrate. Claim 1 to 13, wherein any one of the organic / inorganic composite porous film production method comprising a.

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