KR20190049604A - Porous separating film and electrochemical device containing the same - Google Patents

Abstract

Proposed are a porous separating film and an electrochemical device including the same. According to the present invention, the porous separating film comprises: a plurality of inorganic particles; and a binder polymer located on a part or on all of a surface of the inorganic particles, and connecting the inorganic particles to each other, wherein the binder polymer has a weight average molecular weight of 1,200,000 to 1,600,000 gram per mol and the weight of the binder polymer relative to the total weight of the porous separating film is 17 to 25 wt%.

Description

TECHNICAL FIELD [0001] The present invention relates to a porous separator and an electrochemical device including the porous separator. [0002] POROUS SEPARATING FILM AND ELECTROCHEMICAL DEVICE CONTAINING THE SAME [

The present invention relates to a porous separator and an electrochemical device including the same, and more particularly, to a porous separator having improved mechanical properties and suppressed dimensional change in an electrolyte, and an electrochemical device including the same.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. Electrochemical devices have attracted the greatest attention in this respect, among which the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve the capacity density and specific energy in developing such batteries, And research and development on the design of the battery.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium ion battery has safety problems such as ignition and explosion when using an organic electrolytic solution, and it is disadvantageous in that it is difficult to manufacture.

Recently, the lithium ion polymer battery is considered to be one of the next generation batteries by improving the weak point of the lithium ion battery. However, since the capacity of the battery is still relatively low as compared with the lithium ion battery, Is urgently required.

Such electrochemical devices are produced in many companies, but their safety characteristics are different. It is very important to evaluate the safety and safety of such an electrochemical device. The most important consideration is that the electrochemical device should not injure the user in case of malfunction. For this purpose, the safety standard strictly regulates the ignition and fuming in the electrochemical device. In the safety characteristics of the electrochemical device, there is a high possibility that the electrochemical device will be overheated to cause thermal runaway or explosion if the separator is penetrated. Particularly, a polyolefin-based porous substrate commonly used as a separator of an electrochemical device exhibits extreme heat shrinkage behavior at a temperature of 100 ° C or higher due to the normal characteristics of the manufacturing process including material properties and elongation, .

In order to solve the safety problem of such an electrochemical device, a separator in which a porous organic-inorganic coating layer is formed by coating a mixture of an excess of inorganic particles and a binder polymer on at least one surface of a polyolefin-based porous substrate having a plurality of pores is proposed .

However, at this time, the porous layer may cause coating defects on the surface due to cracks generated during the manufacturing process, for example, drying process. As a result, the organic / inorganic composite porous layer can easily be desorbed when the secondary battery is assembled or when the battery is used, which leads to a decrease in the safety of the battery. In addition, the porous layer-forming slurry applied to the polyolefin-based porous substrate for forming the porous layer has a problem that packing density is increased due to increased density of particles during drying, resulting in lowered air permeability characteristics .

Therefore, there is still a demand for solving the problem of the decrease in the air permeability characteristic due to the provision of the polyolefin-based porous substrate.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a porous separator having improved tensile strength and elongation, and reduced rate of dimensional change in an electrolyte.

Another object of the present invention is to provide an electrochemical device comprising the separator.

According to an aspect of the present invention, there is provided a separator of the following embodiments.

In a first embodiment,

A plurality of inorganic particles, and a binder polymer disposed on at least a part of the surface of the inorganic particles to connect and fix the inorganic particles,

Wherein the binder polymer has a weight average molecular weight of 1,200,000 g / mol to 1,600,000 g / mol,

And a binder polymer in an amount of 17 to 25% by weight based on the total weight of the porous separation membrane.

The second embodiment, in the first embodiment,

Wherein the binder polymer has a weight average molecular weight of 1,300,000 g / mol to 1,500,000 g / mol.

The third embodiment is, in the first embodiment or the second embodiment,

And a binder polymer in an amount of 18 to 22% by weight based on the total weight of the porous separation membrane.

The fourth embodiment is, in any one of the first to third embodiments,

The inorganic particles are inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, or mixtures thereof.

The fifth embodiment is, in any one of the first through fourth embodiments,

Wherein the binder polymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutylene terephthalate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide (polyethylene) oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpyrrolidone, Polyvinyl alcohol (cyanoethylpolyviny a mixture of two or more kinds selected from the group consisting of lanolin, lanolin, lanolin, lanolin, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. Separator.

The sixth embodiment is, in any one of the first through fifth embodiments,

In the porous separation membrane, the inorganic particles are charged and bound to each other by the binder polymer in contact with each other, thereby forming an interstitial volume between the inorganic particles, The interstitial volume is an empty space,

According to another aspect of the present invention, there is provided an electrochemical device of the following embodiments.

A seventh embodiment is an electrochemical device including a cathode, an anode, a separator interposed between the cathode and the anode, wherein the separator is a porous separator of any one of the first to sixth embodiments, Device.

The eighth embodiment is, in the seventh embodiment,

And the electrochemical device is a lithium secondary battery.

According to another aspect of the present invention, there is provided a process for producing a porous separator of the following embodiments.

The ninth embodiment includes the steps of preparing a composition for forming a porous separation membrane comprising inorganic particles and a binder polymer, and applying the composition to one surface of the releasable substrate, drying the same, and then removing the releasable substrate , or

Preparing a composition for forming a porous separator, which comprises inorganic particles and a binder polymer; and applying the composition for forming a porous separator to one surface of at least one electrode layer of the cathode and the anode, Comprising the steps of: preparing a composite of an electrode and a porous separator;

The present invention relates to a method for producing a porous separator according to any one of the first to sixth embodiments.

The tenth embodiment is, in the ninth embodiment,

The method for applying the composition for forming a porous separation membrane to the releasable base material or the electrode layer is a method for manufacturing a porous separation membrane which is a method of a slurry coating or a dip coating method.

According to one embodiment of the present invention, both the weight average molecular weight and the content of the binder polymer are adjusted to an optimum range. As a result, the tensile strength and the elongation are improved, the rate of change of the dimension in the electrolyte is decreased, Can be provided.

In addition, since the porous separator according to an embodiment of the present invention does not have a porous polymer substrate, it is possible to reduce the cost and control the pore size and porosity of the entire separator membrane to achieve a uniform porous separator. So that the weight can be reduced. In addition, there is no phenomenon such as heat shrinkage even when exposed to a high temperature of 120 DEG C or more, and safety can be improved.

1 is a graph showing tensile strengths of the porous separator prepared in Example 1 and Comparative Examples 1 to 3. FIG.
2 is a graph showing elongation ratios of the porous separation membranes prepared in Example 1 and Comparative Examples 1 to 3. FIG.
3 is a graph showing the dimensional change rate of the porous separator prepared in Example 1 and Comparative Examples 1 to 3 upon impregnation with an electrolyte.
4 is a graph showing the insulation resistance of the lithium secondary battery manufactured in Example 1 and Comparative Examples 1 to 3. FIG.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The porous separator according to one aspect of the present invention comprises a plurality of inorganic particles and a binder polymer which is located on a part or the whole of the surface of the inorganic particles to connect and fix the inorganic particles, The molecular weight is 1,200,000 g / mol to 1,600,000 g / mol, and the weight of the binder polymer based on the total weight of the porous separator is 17 to 25% by weight.

Since the porous separation membrane of the present invention is interposed between the cathode and the anode to serve as a separator as described later, the porous separation membrane may correspond to a porous separation layer, And an inorganic material, which may be an organic-inorganic complex.

Since the organic-inorganic composite is composed only of an inorganic material and a binder polymer without a porous polymer substrate such as a polyolefin, a tensile strength and an elongation are lower than those of a polymer substrate, and therefore there is a problem in that a separation membrane is torn or an internal micro- have. Also, since the organic-inorganic composite is composed only of inorganic particles and a binder polymer, appearance failure may occur when the secondary battery is applied due to the swelling phenomenon during impregnation into the electrolyte solution.

In the present invention, in order to increase the tensile strength and elongation of the porous separator and simultaneously suppress the swelling phenomenon upon electrolyte impregnation, the physical properties of the binder polymer, in particular, the weight average molecular weight is controlled to 1,200,000 g / mol to 1,600,000 g / mol, The weight of the binder polymer with respect to the total weight of the porous separator was controlled to be 17 to 25 wt%, thereby solving the above problem.

According to an embodiment of the present invention, the weight average molecular weight of the binder polymer is 1,200,000 to 1,600,000 g / mol, or 1,300,000 to 1,500,000 g / mol, or 1,350,000 to 1,450,000 g / mol, Or from 1,350,000 g / mol to 1,430,000 g / mol, 1,430,000 g / mol to 1,600,000 g / mol, 1,200,000 g / mol to 1,430,000 g / mol. When the weight average molecular weight of the binder polymer is less than 1,200,000 g / mol, the strength of the separator is very low or a free standing film having no porous substrate can not be realized. When the weight average molecular weight of the binder polymer is more than 1,600,000 g / mol , The viscosity is very high, which is disadvantageous in the production process of the porous separator. Even after the production of the porous separator, the tensile strength can be weakened because the ratio of the binder polymer capable of sufficiently contacting the inorganic particles is low.

The weight average molecular weight (Mw) of the binder polymer is a polystyrene reduced weight average molecular weight (Mw) measured by gel permeation chromatography (GPC).

In the porous separator according to one aspect of the present invention, a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C may be used as the binder polymer, Mechanical properties such as flexibility and elasticity can be improved. Such a binder polymer faithfully performs a binder function to connect and stably fix inorganic particles, thereby contributing to prevention of degradation of mechanical properties of the porous separator.

In addition, although the binder polymer does not necessarily have ion conductivity, the performance of the electrochemical device can be further improved by using a polymer having ion conductivity. Therefore, the binder polymer having a high permittivity constant can be used. Actually, the dissociation degree of the salt in the electrolytic solution depends on the permittivity constant of the solvent of the electrolyte. Therefore, the higher the permittivity constant of the binder polymer, the better the salt dissociation degree in the electrolyte. The permittivity constant of the binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and may be 10 or more.

In addition to the above-mentioned functions, the binder polymer may have a characteristic of exhibiting a high degree of swelling of the electrolyte due to gelation upon impregnation with a liquid electrolyte. Accordingly, the solubility index of the binder polymer, that is, the Hildebrand solubility parameter is in the range of 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . Therefore, hydrophilic polymers having many polar groups can be used more than hydrophobic polymers such as polyolefins. If the solubility index exceeds 15 MPa ^1/2 and exceeds 45 MPa ^1/2 , it may be difficult to swell by a conventional liquid electrolyte for a battery.

In the porous separation membrane, the inorganic particles are charged and bound to each other by the binder polymer in contact with each other, thereby forming an interstitial volume between the inorganic particles, The volume (Interstitial Volume) becomes empty space to form pores.

That is, the binder polymer attaches the inorganic particles to each other so that the inorganic particles can remain bonded to each other, for example, the binder polymer connects and fixes the inorganic particles. In addition, the pores of the porous separation membrane are pores formed by the interstitial volume between the inorganic particles as void spaces, which is an inorganic matter that is substantially interviewed in a closed packed or densely packed structure It is the space defined by the particles.

Examples of such a binder polymer include polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile ), Polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose (cellulose acetate) acetate), cellulose acetate butylate but are not limited to, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, ), Pullulan, and carboxyl methyl cellulose, but the present invention is not limited thereto.

Non-limiting examples of the inorganic particles include high-permittivity inorganic particles having a dielectric constant of 5 or more and specifically 10 or more, inorganic particles having lithium ion-transporting ability, or mixtures thereof.

Nonlimiting examples of the 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) 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 , AlO (OH) ₂ , Al ₂ O ₃ .H ₂ O, or a mixture thereof.

The inorganic particles having lithium ion-transferring ability refer to inorganic particles containing a lithium element but not lithium and having a function of transferring lithium ions. Examples of inorganic particles having lithium ion transferring ability include, but are not limited to, It is a 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 _{(LixAl y Ti z (PO 4} ) (LiAlTiP) _x O _y series glass such as LiNiO ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ , Lithium such as lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), Li _3.25 Ge _0.25 P _0.75 S ₄ , germanium Mani help thiophosphate _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li 3 N lithium nitride (Li, such as _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS ₂ SiS ₂ family, such as _{glass (Li x Si y S z} , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 There is P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof as such.

In addition, the weight of the binder polymer relative to the total weight of the porous separation membrane may be 17 to 25 wt%, and more specifically, 18 to 22 wt%. The volume of the binder polymer with respect to the total volume of the porous separation membrane may be 27 to 40% by volume, or 28 to 33% by volume. When the weight of the binder polymer satisfies the above range, it is possible to prevent the decrease of the pore size and porosity due to the presence of excessive binder polymer in the pores of the formed porous separation membrane, The inorganic particles can be stably fixed by the binder polymer without being separated during storage or operation of the electrochemical device having the porous separation membrane.

As can be seen from the evaluation results of Examples and Comparative Examples described later, the effect exhibited by the porous separator of the present invention satisfies only one of the weight range of the binder polymer and the weight average molecular weight of the binder polymer with respect to the total weight of the porous separator But can be realized only when a binder polymer having a weight average molecular weight of 1,200,000 g / mol to 1,600,000 g / mol and a weight of 17 to 25% by weight based on the total weight of the porous separator is applied.

The porous separator according to an aspect of the present invention may further include other additives in addition to the inorganic particles and the binder polymer.

The porous separation membrane according to an embodiment of the present invention may be prepared by preparing a composition for forming a porous separation membrane comprising inorganic particles and a binder polymer, applying the composition to one surface of a releasable substrate, drying the same, . Alternatively, the composition for forming a porous separation membrane may be directly applied to one surface of one or more electrode layers of the cathode and the anode, and dried to form a composite of the electrode-porous separation membrane bonded directly to the electrode layer.

First, the composition for forming a porous separation membrane can be prepared by dissolving a binder polymer in a solvent, and then adding and dispersing inorganic particles. The inorganic particles may be added in a state of being crushed to have a predetermined average particle diameter or inorganic particles may be added to the solution of the binder polymer and then crushed while controlling the inorganic particles to have a predetermined average particle diameter by using a ball mill method or the like Dispersed.

The method for coating (coating) the composition for forming a porous separation membrane on the releasable base material or the electrode layer is not particularly limited, but it is preferable to use a slip coating method or a dip coating method. The slurry coating is capable of adjusting the thickness of the coating layer according to the flow rate supplied from the metering pump in such a manner that the composition supplied through the slat die is applied to the entire surface of the substrate. The dip coating method is a method of coating a substrate by immersing the substrate in a tank containing the composition. The thickness of the coating layer can be adjusted according to the concentration of the composition and the speed at which the substrate is taken out from the composition tank. And the like.

The porous substrate coated with the composition for forming a porous membrane is dried using a drier such as an oven, and then the porous substrate is removed by removing the substrate. As such a releasable substrate, a glass plate, a polyethylene film, a polyester film, or the like can be used, but the present invention is not limited thereto.

Or a composition for forming a porous separator may be directly coated on the electrode layer, it may be dried in the same manner to form a composite of the electrode-porous separator bonded to the electrode layer.

An electrochemical device according to an aspect of the present invention includes a cathode, an anode, a separator interposed between the cathode and the anode, and the separator is a porous separator according to an embodiment of the present invention described above.

 Such an electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, or super capacitor devices. Particularly, 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 is preferable.

The cathode and the anode both to be used together with the porous separator of the present invention are not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use a lithium composite oxide. As a non-limiting example of the anode active material, a conventional anode active material that can be used for an anode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the cathode current collector include aluminum, nickel, or a combination thereof, and examples of the anode current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

The electrolytic solution which can be used in the electrochemical device of the present invention is a salt having a structure such as A ⁺ B ^- , wherein A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , K ^{+ -} it 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} ^- anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl (DMP), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone -Butyrolactone), or a mixture thereof, but the present invention 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 required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Measurement of weight average molecular weight (Mw)

The weight average molecular weight was measured by gel permeation chromatography (GPC), and the conditions were as follows.

- Appliance: 1200 series from Agilent Technologies

- Column: Using 2 PLgel mixed B from Polymer laboratories

- Solvent: THF

- Column temperature: 40 ° C

- Sample concentration: 1 mg / mL, 100 L injection

Standard: Polystyrene (Mp: 3900000, 723000, 316500, 52200, 31400, 7200, 3940, 485)

Example 1

&Lt; Preparation of cathode and anode >

96.7 parts by weight of LiCoO ₂ serving as a cathode active material, 1.3 parts by weight of graphite serving as a conductive agent, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) serving as a binder were mixed to prepare a cathode mixture. The resulting cathode mixture was dispersed in 1-methyl-2-pyrrolidone serving as a solvent to prepare a cathode mixture slurry. The slurry was coated on both sides of an aluminum foil having a thickness of 20 탆, dried, and pressed to prepare a cathode.

97.6 parts by weight of graphite serving as an anode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) serving as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC) were mixed to prepare an anode mix. This anode mix was dispersed in ion-exchange water functioning as a solvent to prepare an anode mix slurry. The slurry was coated on both sides of a copper foil having a thickness of 20 탆, dried and pressed to prepare an anode.

&Lt; Preparation of porous separator &

16 parts by weight of PVdF (polyvinylidene fluoride) having a weight average molecular weight of 1,430,000 g / mol as a binder polymer was added to 184 parts by weight of acetone at a ratio of 8% by weight of solid content and dissolved at 50 DEG C for about 12 hours or more to obtain a binder polymer solution Prepared. Alumina was added to the prepared binder polymer solution so that the weight ratio of the binder polymer to the inorganic particles of 500 nm in average alumina (Al ₂ O ₃ ) was 22:78 and dispersed to prepare a slurry for the porous separator. At this time, the weight of the binder polymer with respect to the total weight of the porous separator was 22 wt% (corresponding to 33 vol%).

The slurry thus prepared was coated on a polyester film substrate by a dip coating method and dried in an oven at 150 캜 for about 10 minutes by adjusting the coating thickness to about 20 탆, A separator was prepared.

&Lt; Production of lithium secondary battery >

LiPF ₆ was dissolved in an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) in a composition of 3: 3: 4 (volume ratio) so as to have a concentration of 1.0 M to prepare a nonaqueous electrolytic solution .

The porous separator was laminated between the cathode and the anode, and the electrolyte was injected into the pouch to prepare a lithium secondary battery.

Example 2

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of the binder polymer to the inorganic particles was 18:82. At this time, the weight of the binder polymer with respect to the total weight of the porous separator was 18 wt% (corresponding to 28 vol%).

Comparative Example 1

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1, except that PVdF (polyvinylidene fluoride) having a weight average molecular weight of 1,100,000 g / mol was used as the binder polymer.

Comparative Example 2

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1, except that PVdF (polyvinylidene fluoride) having a weight average molecular weight of 1,650,000 g / mol was used as the binder polymer.

Comparative Example 3

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1, except that PVdF (polyvinylidene fluoride) having a weight average molecular weight of 2,000,000 g / mol was used as the binder polymer.

Comparative Example 4

The porous separator was prepared in the same manner as in Example 1, except that the weight ratio of the binder polymer to the inorganic particles was 5:95. At this time, the weight of the binder polymer with respect to the total weight of the porous separator was 5 wt% (corresponding to 8 vol%). However, since the strength of the binder polymer is low, it is impossible to form the porous separator.

Comparative Example 5

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1 except that the weight ratio of the binder polymer to the inorganic particles was 11:89. At this time, the weight of the binder polymer with respect to the total weight of the porous separator was 11% by weight (corresponding to 18% by volume).

Comparative Example 6

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1, except that the weight ratio of the binder polymer to the inorganic particles was 15:85. At this time, the weight of the binder polymer with respect to the total weight of the porous separator was 15 wt% (corresponding to 24 vol%).

Comparative Example 7

A porous separator and a lithium secondary battery were prepared in the same manner as in Example 1 except that the weight ratio of the binder polymer to the inorganic particles was 30:70. At this time, the weight of the binder polymer based on the total weight of the porous separator was 30 wt% (corresponding to 43% by volume).

Property evaluation

Tensile Strength Evaluation

The tensile strengths of the porous membranes prepared in Example 1 and Comparative Examples 1 to 3 were measured by the following methods, and the results are shown in FIG. The tensile strengths of the porous separators prepared in Examples 1, 2 and Comparative Examples 5 to 7 were measured by the following methods, and the results are shown in Table 1.

<Tensile Strength Measurement Method>

Six pieces of the porous separator were prepared with a size of 20x20 mm, and the strength was measured by pulling at 500 mm / min from the room temperature through an Instron equipment until fracture. The average value of the six porous membranes was determined as the tensile strength.

Elongation evaluation

The elongation percentage of the porous separator prepared in Example 1 and Comparative Examples 1 to 3 was measured by the following method, and the results are shown in FIG. The elongation of the porous separator prepared in Examples 1, 2, and 5 to 7 was measured by the following method, and the results are shown in Table 1.

<Estimation method of elongation>

Six porous membranes were prepared with a size of 20x20 mm. The elongated length of the membranes was measured by pulling them at a rate of 500 mm / min from the room temperature through an Instron instrument, and the ratio of the increased porosity to the initial porous membrane length was calculated. The average value of the six porous membranes was determined by elongation.

Evaluation of dimensional change rate

The dimensional change rate of the porous separator prepared in Example 1 and Comparative Examples 1 to 3 upon impregnation with the electrolyte was measured by the following method, and the results are shown in FIG. The dimensional change rates of the porous separator membranes prepared in Examples 1, 2 and Comparative Examples 5 to 7 were measured by the following methods, and the results are shown in Table 1.

&Lt; Measurement method of dimensional change rate &

The porous separator was prepared in a size of 100x100 mm, impregnated in a 500 ml Nalgen bottle containing 20 ml of electrolyte, placed on the PET film for 1 hour, and the length was measured in transverse length from the initial value. The average value of the two porous membranes was defined as the rate of dimensional change.

Insulation resistance evaluation

The insulation resistance of the lithium secondary battery manufactured in Example 1 and Comparative Examples 1 to 3 was measured by the following method, and the results are shown in FIG. The insulation resistance of the porous separator prepared in Examples 1, 2, and 5 to 7 was measured by the following method, and the results are shown in Table 1.

<Method of measuring insulation resistance>

Two pieces of the prepared porous separator were prepared in size of 100x100 mm, and the volume resistance (Rv) of the separator was measured after 3 seconds by applying a voltage of 100V using a Hioki insulation resistance measuring device (Super Megohm meter SM7120) To obtain an insulation resistance (volume insulation resistance). The average value of the two porous membranes was defined as the rate of dimensional change.

ρ ((volume) insulation resistance, Ω · cm) = (electrode area of measuring equipment (19.6 cm ² )) X Rv (measured volume resistivity value) / [thickness of porous separator

Comparative Example 4 Comparative Example 5 Comparative Example 6 Example 2 Example 1 Comparative Example 7 Content of binder polymer
(weight%) 5 11 15 18 22 30 Content of binder polymer (% by volume) 8 18 24 28 33 43 Tensile strength (kgf / cm ² ) No strength 70 90 130 151 200 Elongation (%) 14 17 18 25 30 Insulation resistance (TΩ · cm) 40 65 70 84 100 Dimensional change ratio (%) 2.4 3.0 3.4 3.8 6.5

Referring to FIGS. 1 to 4 and Table 1, when the weight ratio of the binder polymer to the total weight of the porous separator of the present invention is in the range of 17 to 25 wt% (22 wt% ), The tensile strength, the elongation, the insulation resistance, and the dimensional change rate were remarkably lowered as compared with Example 1 when the weight average molecular weight of the binder polymer deviated from 1,200,000 g / mol to 1,600,000 g / mol. Also, as in Comparative Examples 4 to 6, when the binder polymer of the present invention meets the weight average molecular weight range of 1,200,000 g / mol to 1,600,000 g / mol (1,430,000 g / mol), the binder polymer If the weight of the porous separator was outside the range of 17 to 25% by weight, the membrane would not be formed into a porous separator itself, or the ratio of tensile strength, elongation, insulation resistance and dimensional change would be significantly lower than those of Examples 1 and 2.

From this, it can be seen that the porous separator of the present invention exhibiting a synergistic effect of improving the tensile strength and elongation, reducing the rate of dimensional change in the electrolyte, and securing the insulation resistance is characterized in that the weight ratio of the binder polymer to the total weight of the porous separator Binder polymer having a weight average molecular weight of 1,200,000 g / mol to 1,600,000 g / mol and a weight of 17 to 25% by weight based on the total weight of the porous separator is not achieved, It can be seen that the present invention can be implemented only when it is applied.

Claims (10)

A plurality of inorganic particles, and a binder polymer disposed on at least a part of the surface of the inorganic particles to connect and fix the inorganic particles,
Wherein the binder polymer has a weight average molecular weight of 1,200,000 g / mol to 1,600,000 g / mol,
Wherein the weight of the binder polymer with respect to the total weight of the porous separator is 17 to 25 wt%. The method according to claim 1,
Wherein the binder polymer has a weight average molecular weight of 1,300,000 g / mol to 1,500,000 g / mol. The method according to claim 1,
Wherein the weight of the binder polymer relative to the total weight of the porous separator is 18 to 22 wt%. The method according to claim 1,
Wherein the inorganic particles are inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, or mixtures thereof. The method according to claim 1,
Wherein the binder polymer is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, But are not limited to, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate ), Polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan ( cyanoethylpullulan, cyanoethylpullulan, And any one selected from the group consisting of polyvinyl alcohol (cyanoethylpolyvinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, or two of them By weight of the porous separator. The method according to claim 1,
In the porous separation membrane, the inorganic particles are charged and bound to each other by the binder polymer in contact with each other, thereby forming an interstitial volume between the inorganic particles, The interstitial volume is a porous membrane that forms voids by forming voids. 7. An electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the porous separator according to any one of claims 1 to 6. 8. The method of claim 7,
Wherein the electrochemical device is a lithium secondary battery. Comprising the steps of: preparing a composition for forming a porous separator, which comprises inorganic particles and a binder polymer; and applying the composition to one surface of a releasable substrate, drying the same, and then removing the releasable substrate; or
Preparing a composition for forming a porous separator, which comprises inorganic particles and a binder polymer; and applying the composition for forming a porous separator to one surface of at least one electrode layer of the cathode and the anode, Comprising the steps of: preparing a composite of an electrode and a porous separator;
A method for producing a porous separation membrane according to any one of claims 1 to 6. 10. The method of claim 9,
The method for applying the composition for forming a porous separation membrane to the releasable base material or the electrode layer is a method of a slot coating or a dip coating method.

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