Composite separator for electrochemical device and electrochemical device including the same

Abstract

To provide a composite separation film for an electrochemical element.SOLUTION: The present invention provide a composite separation film for an electrochemical element, and the electrochemical element containing them, in which a porous polymer substrate having a plurality of gas cavities, and a porous coating layer that is formed to at least one surface of the porous polymer substrate, and contains a binder that is positioned to one part or a whole part of a plurality of particles and a front surface of the particles, and connects and fixes between the particles are contained. Each particle is an inorganic particle and / or an organic particle, and has a meltdown temperature of 170°C or larger.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite separator for an electrochemical device and an electrochemical device including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2019-0092560, filed on July 30, 2019, the entire contents of which are incorporated herein by reference in their entirety. [Background technology]

[0003] In recent years, interest in energy storage technology has been growing. As its application fields expand to include mobile phones, camcorders, laptops, and even electric vehicles, research and development efforts in electrochemical devices have become increasingly focused. Electrochemical devices are a field that has attracted the most attention in this regard, and the development of rechargeable secondary batteries in particular has been attracting attention. In recent years, research and development efforts have been conducted on new electrode and battery designs to improve capacity density and specific energy in the development of such batteries.

[0004] Among the electrochemical elements currently in use, lithium secondary batteries, which were developed in the early 1990s, are attracting attention due to their advantages of higher operating voltage and significantly higher energy density compared to conventional batteries that use aqueous electrolytes, such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries.

[0005] A lithium secondary battery refers to a battery in which a non-aqueous electrolyte containing lithium ions is injected into an electrode assembly including a cathode including a cathode active material capable of absorbing and desorbing lithium ions, an anode including an anode active material capable of absorbing and desorbing lithium ions, and a porous separator interposed between the cathode and the anode.

[0006] The cathode active materials used in lithium secondary batteries include transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium-manganese oxide (LiMn2O4), and lithium-nickel oxide (LiNiO2), as well as composite oxides in which some of these transition metals are replaced with other transition metals.

[0007] Among the cathode active materials, LiCoO2 is widely used due to its excellent physical properties such as cycle characteristics. However, its low safety and high cost due to the limited availability of cobalt as a raw material limit its mass use as a power source in fields such as electric vehicles.

[0008] Lithium-manganese oxides such as LiMnO2 or LiMn2O4 are attracting attention as cathode active materials that can replace LiCoO2 due to their advantages of using manganese, which is an abundant and environmentally friendly raw material. However, lithium-manganese oxides have disadvantages such as low capacity and poor cycle characteristics.

[0009] On the other hand, LiNiO2 or lithium oxides containing manganese, cobalt, and / or other transition metals and nickel as the main component are less expensive than the cobalt-based oxides and exhibit high discharge capacities when charged to 4.3 V, with the reversible capacity of doped LiNiO2 approaching approximately 200 mAh / g, exceeding that of LiCoO2 (approximately 165 mAh / g).

[0010] Therefore, despite somewhat lower average discharge voltages and volumetric densities, commercial batteries containing nickel-based lithium oxides as cathode active materials exhibit improved energy densities, and high-capacity batteries using such cathode active materials are being actively researched and developed.

[0011] However, while nickel-based lithium oxides have the advantage of high capacity, they also suffer from problems such as rapid phase transitions in the crystal structure due to volume changes during charge-discharge cycles, which can lead to particle cracks and voids at grain boundaries, potentially damaging the separator and reducing safety. Therefore, a separator with enhanced safety is needed. In particular, LiNiO2 cathode active material not only has the above problems, but also has difficulty in applying to secondary batteries due to the lack of smooth reversible reactions, so it needs to be supplemented with small amounts of components such as Co or Al.

[0012] Polyolefin-based porous polymer substrates, which are commonly used as separators in electrochemical devices, exhibit severe thermal shrinkage at temperatures above 100°C due to material properties and manufacturing process characteristics, including stretching, causing short circuits between the cathode and anode.

[0013] To solve the safety issues of such electrochemical devices, a composite separator has been proposed, in which a porous coating layer is formed by coating at least one surface of a porous polymer substrate having a large number of pores with a mixture of an excess amount of inorganic particles and a binder.

[0014] The composite separator with such a porous coating layer has shutdown and meltdown temperature ranges similar to those of the porous polymer substrate before the porous coating layer is applied. As a result, the composite separator hardly shrinks as a function of temperature, but when the temperature exceeds the meltdown temperature, the composite separator ruptures, causing a large-scale short circuit between the cathode and anode, which can lead to fire and explosion of the battery.

[0015] Therefore, when a battery operates abnormally, such as when a short circuit occurs, the shutdown function must be activated at a lower temperature than conventional methods to quickly cut off the current, preventing a sudden short circuit caused by an increase in internal resistance (IR) and suppressing a sudden rise in battery temperature. In particular, the shutdown temperature must be designed to be managed below the self-heating temperature, which is the temperature at which the cathode active material experiences thermal runaway. The meltdown function must be activated at a higher temperature than conventional methods to delay the point at which a major short circuit occurs, and a separator must be developed that can safely reduce the battery voltage by quickly cooling itself compared to the amount of heat generated. Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, an object of the present invention is to provide a composite separator for an electrochemical device, which comprises a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer containing a binder and inorganic particles, and which has a meltdown temperature of 170°C or higher.

[0017] Another object of the present invention is to provide a composite separator for electrochemical devices, in which the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices is 30°C or more.

[0018] Another object of the present invention is to provide a composite separator for an electrochemical device, in which the packing density of the porous coating layer is improved.

[0019] Another object of the present invention is to provide a composite separator for an electrochemical device, in which the porous coating layer has improved pore uniformity.

[0020] A further object of the present invention is to provide an electrochemical device having enhanced safety, which includes the above-mentioned composite separator for an electrochemical device. [Means for solving the problem]

[0021] In order to solve the above-mentioned technical problems, one aspect of the present invention provides a composite separator for an electrochemical device according to the following embodiment.

[0022] According to a first embodiment of the present invention, there is provided a composite separator for an electrochemical device, comprising: a porous polymer substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer comprising a plurality of particles and a binder located on some or all of the surfaces of the particles to connect and fix the particles, wherein the particles are inorganic particles and / or organic particles, and the composite separator has a meltdown temperature of 170°C or higher.

[0023] According to a second embodiment of the present invention, the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for an electrochemical device in the first embodiment and the meltdown temperature of the composite separator for an electrochemical device may be 30°C or more.

[0024] According to a third embodiment of the present invention, in the first or second embodiment, the porous polymer substrate may have a shutdown temperature of 140° C. or less.

[0025] According to a fourth embodiment of the present invention, in any one of the first to third embodiments, the composite separator for an electrochemical device may have a meltdown temperature of 170 to 220°C.

[0026] According to a fifth embodiment of the present invention, in any one of the first to fourth embodiments, the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices may be 30°C to 90°C.

[0027] According to a sixth embodiment of the present invention, in any one of the first to fifth embodiments, the plurality of particles are packed and bound to each other by the binder while in contact with each other, thereby forming interstitial volumes between the particles, and the interstitial volumes between the particles become empty spaces to form pores, and the ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate may be 2.0 or less.

[0028] According to a seventh embodiment of the present invention, in any one of the first to sixth embodiments, the ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate may be 0.75 to 1.25.

[0029] According to an eighth embodiment of the present invention, in any one of the first to seventh embodiments, the particles may be inorganic particles, and the average particle size of the inorganic particles may be 10 to 450 nm.

[0030] According to a ninth embodiment of the present invention, in any one of the first to eighth embodiments, the particles may be organic particles, and the average particle size of the organic particles may be 10 to 150 nm.

[0031] According to a tenth embodiment of the present invention, in any one of the first to eighth embodiments, the binder may be polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, an acrylic copolymer, or a mixture thereof.

[0032] In order to solve the above-mentioned technical problems, another aspect of the present invention provides an electrochemical device according to the following embodiment.

[0033] According to an eleventh embodiment of the present invention, there is provided an electrochemical device including a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the composite separator for an electrochemical device according to any one of the first to tenth embodiments.

[0034] According to a twelfth embodiment of the present invention, in the eleventh embodiment, the electrochemical device may be a lithium secondary battery. [Effects of the Invention]

[0035] The composite separator for electrochemical devices according to the present invention has a meltdown temperature of 170°C or more. In one embodiment of the present invention, the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices may be 30°C or more. This allows the shape of the separator to be maintained, preventing phenomena such as sudden explosion, and ensuring the safety of the electrochemical device.

[0036] In addition, the composite separator for an electrochemical device according to the present invention uses inorganic particles with very small particle diameters in the porous coating layer, thereby significantly improving the packing density and pore uniformity of the porous coating layer and suppressing short circuits between the cathode and anode even when the electrochemical device is overheated. This makes it possible to provide a composite separator for an electrochemical device with improved stability, and an electrochemical device including the same.

[0037] Furthermore, when a nickel-based cathode active material is used as the cathode of the electrochemical device, the crystalline structure of the cathode active material undergoes a rapid phase transition due to volume changes that occur during charge-discharge cycles. This may result in cracks in the particles or voids at the grain boundaries, but the composite separator is not damaged, thereby enhancing the safety of the electrochemical device including such a composite separator. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be described in detail below. The terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts that correspond to the technical concept of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0039] According to one embodiment of the present invention, there is provided a composite separator for an electrochemical device, comprising: a porous polymer substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer comprising a plurality of particles and a binder located on some or all of the surfaces of the particles to connect and fix the particles, wherein the particles are inorganic particles and / or organic particles and have a meltdown temperature of 170°C or higher.

[0040] According to one embodiment of the present invention, there is provided a composite separator for an electrochemical device, comprising: a porous polymer substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer comprising a plurality of particles and a binder located on some or all of the surfaces of the particles to connect and fix the particles, wherein the particles are inorganic particles and / or organic particles; wherein the composite separator for an electrochemical device has a meltdown temperature of 170°C or more; and the porous polymer substrate has a shutdown temperature of 140°C or less.

[0041] In the present invention, the term "meltdown" refers to a phenomenon in which the shape of a composite separator or a porous polymer substrate is melted and lost, and the temperature at which this phenomenon occurs is defined as the meltdown temperature.

[0042] In the present invention, the "meltdown temperature" is measured by applying a load of 0.01 N to a composite separator or porous polymer substrate prepared in a size of 4 mm x 8 mm using a thermomechanical analyzer (TMA). The degree of deformation is measured while the temperature is increased at a rate of 5°C / min. The temperature at which the composite separator or porous polymer substrate contracts with the increase in temperature and then expands again to break is measured. This temperature is defined as the meltdown temperature of the composite separator or porous polymer substrate.

[0043] In the present invention, "shutdown" refers to a characteristic in which, when a charged electrochemical device is short-circuited, the potential difference between the cathode and anode suddenly decreases, causing an exothermic reaction, which decomposes the electrolyte and generates gases such as methane, hydrogen, and carbon dioxide, potentially leading to an explosion. In this case, the porous polymer substrate used as a separator melts and blocks the pores, slowing the flow of current and terminating the battery and exothermic reactions, thereby ensuring stability. Therefore, in this specification, the shutdown temperature is defined as the temperature at which the pores of the porous polymer substrate are completely blocked. This shutdown is divided into stages depending on the degree to which the pores of the porous polymer substrate are blocked. As the temperature increases, i.e., near the melting point of the porous polymer substrate, the pores of the porous polymer substrate begin to block. This is defined as the first-stage shutdown temperature, i.e., the shutdown onset temperature. The temperature at which all pores of the porous polymer substrate are blocked as the temperature further increases is defined as the second-stage shutdown temperature, i.e., the shutdown end temperature. In this specification, the term "shutdown end temperature" is used interchangeably with the term "shutdown temperature."

[0044] The shutdown temperature was measured by fixing the separation membrane or porous polymer substrate to a frame (outer diameter: 15 cm × 15 cm, inner diameter: 10 cm × 10 cm) with polyimide tape and then exposing it to a convection oven at a heating rate of 3 °C / min from 80 °C. The aeration time was measured as the temperature at which the aeration time (Gurley value) first exceeded 10,000 sec / 100 ml. The aeration time was measured using an air permeability measuring device (Asahi Seiko Co., Ltd., Model: EG01-55-1MR) as the time (seconds) required for 100 ml of air to pass through the separation membrane or porous polymer substrate at a constant pressure (0.05 MPa).

[0045] The meltdown temperature of the composite separator for an electrochemical device according to the present invention is 170°C or higher, and according to one embodiment of the present invention, the meltdown temperature of the composite separator for an electrochemical device may be 170 to 220°C, 170 to 200°C, 170 to 179°C, or 174 to 179°C. When the meltdown temperature of the composite separator for an electrochemical device satisfies this range, the separator will not meltdown even if the temperature rises to a higher level after shutdown, and the shape of the separator will be maintained, thereby preventing phenomena such as battery fire and sudden explosion due to a large-scale short circuit between the cathode and anode.

[0046] The composite separator for an electrochemical device may have a shutdown temperature of 140°C or less, 120 to 140°C, 122 to 136°C, or 124 to 133°C.

[0047] The difference between the meltdown temperature and the shutdown temperature of the composite separator for electrochemical devices may be 40 to 120° C., 50 to 110° C., or 60 to 100° C. Such a large difference between the meltdown temperature and the shutdown temperature allows for early shutdown when a short circuit occurs in the electrochemical device, blocking the pores of the porous polymer substrate and cutting off the current, thereby suppressing a temperature rise. Furthermore, even if the temperature rises further after shutdown, the separator does not melt down and the shape of the separator is maintained, preventing phenomena such as a sudden explosion.

[0048] According to one embodiment of the present invention, the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices may be 30° C. or more, 30° C. to 90° C., 30° C. to 70° C., 30° C. to 40° C., or 30° C. to 35° C. When the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices satisfies this range, the meltdown temperature of the composite separator is sufficiently higher than the meltdown temperature of the porous polymer substrate, thereby delaying battery ignition and explosion due to a large-scale short circuit between the cathode and anode, thereby improving battery stability.

[0049] A composite separator for an electrochemical device according to one embodiment of the present invention includes a porous polymer substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer including a plurality of particles and a binder located on a part or all of the surface of the particles to connect and fix the particles together. The binder in the porous coating layer can adhere the particles to each other (i.e., connect and fix the particles) so that the particles remain bound to each other. The binder can also maintain the particles and the porous polymer substrate in a bound state. The particles in the porous coating layer can be in substantial contact with each other to form an interstitial volume, and the interstitial volume can have a particle-packed structure (closely packed or densely packed). The interstitial volume between the particles is a space defined by particles that are substantially in contact with each other, and the interstitial volume between the particles has a structure that allows the formation of pores in the porous coating layer as vacant spaces, and the ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate may be less than 2.0. The particles are inorganic particles and / or organic particles.

[0050] The ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate may be 2.0 or less, 0.5 to 2.0, or 0.75 to 1.25. When the ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate satisfies this range, the separator may have the required porosity and the temperature difference between the meltdown temperature of the porous polymer substrate and the meltdown temperature of the porous coating layer may be desired.

[0051] In this specification, the porosity of a porous polymer substrate is determined by dividing the "true density (X) (weight per unit area / thickness) of the porous polymer substrate" by the "theoretical density (Y) of the porous polymer substrate" as shown in the following Equation 1, and multiplying this by 100 to express it as a percentage (%).

[0052] [Formula 1] Porosity of porous polymer substrate (%) = [1-X / Y] x 100

[0053] In this specification, the porosity of the porous coating layer is expressed as a percentage (%) by dividing the "true density (W) of the porous coating layer (weight per unit area / thickness)" by the "theoretical density (Z) of the porous coating layer material," subtracting the result from 1, and multiplying the result by 100, as shown in Equation 2 below.

[0054] [Formula 2] Porosity of porous coating layer (%) = [1-W / Z] x 100

[0055] In this specification, the average particle size of the porous polymer substrate is measured using a capillary flow porometer manufactured by PMI.

[0056] In this specification, the average particle size of the porous coating layer is measured using a capillary flow porometer manufactured by PMI after coating a nonwoven fabric support with a composition for forming the porous coating layer. This measurement method requires the application of pressure, so it is impossible to measure without a support such as a nonwoven fabric support. Since this experiment measures the minimum pore size in the thickness direction, the use of a nonwoven fabric support with large pores does not significantly affect the experimental results.

[0057] In one embodiment of the present invention, when inorganic particles are used as the particles, the inorganic particles may have an average particle size of 10 to 450 nm, 10 to 400 nm, 15 to 400 nm, or 15 to 380 nm. When organic particles are used as the particles, the organic particles may have an average particle size of 10 to 150 nm, 15 to 130 nm, 15 to 100 nm, 15 to 80 nm, or 15 to 70 nm. When the average particle sizes of the inorganic particles and organic particles satisfy these ranges, respectively, microshorts between the cathode and anode can be prevented, maintaining isolation function, and smooth lithium ion movement can be maintained.

[0058] It is also more desirable that the particles have a uniform size.

[0059] The average particle size is D95(V), which means the particle size corresponding to 95% based on the volume average particle size, that is, the particle size (median diameter) corresponding to 95% of the total volume when measuring particle sizes and accumulating the volume from the smallest particle.

[0060] In one embodiment of the present invention, when the particles are inorganic particles, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport ability, or a mixture thereof.

[0061] The inorganic particles having a dielectric constant of 5 or more are BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, 0 <x<1)、Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、(1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-xIt may be PbTiO3 (PMN-PT, 0 < x < 1), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, γ-AlO(OH), SiC, TiO2 or a mixture of two or more of these.

[0062] The inorganic particles having the lithium ion transfer ability are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)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 TiO3, 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), Li x Si y S z series glass (0 < x < 3, 0 < y < 2, 0 < z < 4) and Li x P y S z series glass (0 < x < 3, 0 < y < 3, 0 < z < 7) or a mixture of two or more of these.

[0063] In one embodiment of the present invention, the inorganic particles may be alumina particles, silica particles or a mixture of these. The alumina particles are a compound of aluminum and oxygen having the chemical formula of Al2O3. The silica particles are a compound of silicon and oxygen having the chemical formula of SiO2. <​In one embodiment of the present invention, the inorganic particles may be embodied in various shapes, such as spherical and plate-like shapes.

[0065] In an embodiment of the present invention, when the particles are organic particles, the organic particles are not particularly limited as long as they are commonly used in the art, and non-limiting examples thereof include polystyrene, polyethylene, polyimide, melamine-based resin, phenol-based resin, cellulose, modified cellulose, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide, polyimide, and mixtures thereof.

[0066] According to one embodiment of the present invention, the thickness of the porous coating layer may be in the range of 0.5 μm to 3.0 μm, 1.0 μm to 2.5 μm, or 1.0 μm to 2.0 μm.

[0067] According to one embodiment of the present invention, the pore size of the porous coating layer is preferably uniform and equal to the pore size of the porous polymer substrate so that the composite separator for an electrochemical device has uniform ionic conductivity throughout. Therefore, the size of the particles contained in the porous coating layer is preferably uniform and the particles preferably have the above-mentioned average particle size. Furthermore, the more non-uniform the particle size, the more difficult it is to ensure the uniformity of the thickness of the porous coating layer. Therefore, the particles preferably have a monomodal particle size distribution. As used herein, monomodal can be defined as a standard deviation of 1% or more to less than 40%, preferably 1% or more to 35%, when analyzed using a particle size analyzer (Dynamic Light Scattering (DLS), Nicomp 380). Bimodal or multimodal can be defined as a standard deviation of 40% or more when particle size and distribution are determined using the particle size analyzer. When the standard deviation is 40% or more, two or more particle size peaks may appear.

[0068] According to one embodiment of the present invention, the use of very small particles significantly improves the density and mechanical properties of the porous coating layer, thereby increasing the meltdown temperature of the composite separator for electrochemical devices and minimizing the shutdown temperature of the porous polymer substrate.

[0069] In the composite separator for an electrochemical device according to one embodiment of the present invention, the binder used to form the porous coating layer may be a water-dispersible emulsion-type binder that is not dissolved but dispersed in a medium used to form the porous coating layer, or a soluble binder that is dissolved in the medium.

[0070] Generally, a water-dispersed emulsion type binder is included in a composition for forming a porous coating layer and is in a particulate state when applied to a porous polymer substrate. Therefore, the water-dispersed emulsion type binder can exhibit adhesive strength by surrounding the surfaces of inorganic or organic particles while deforming under the drying temperature conditions of the composition. Therefore, since the particles of the water-dispersed emulsion type binder must deform under the drying temperature conditions, the glass transition temperature (T g ) is preferably 40°C or less. When the glass transition temperature of the particles of the water-dispersed emulsion-type binder satisfies this temperature range, it can function as a binder that improves the binding strength between inorganic particles or organic particles. On the other hand, a soluble-type binder generally has a glass transition temperature of 100°C or higher and has heat resistance, and can be used to complement the heat shrinkage rate and heat resistance of a separator.

[0071] As described above, in one embodiment of the present invention, the inorganic particles may have an average particle size of 10 nm to 450 nm, and the organic particles may have an average particle size of 10 nm to 150 nm. Meanwhile, the average particle size of conventionally used particles may be 500 nm to 800 nm. The emulsion binder may have an average particle size of 100 to 500 nm, and such an emulsion binder can easily bind conventional particles with a large average particle size.

[0072] Meanwhile, the inorganic or organic particles according to an embodiment of the present invention may have a relatively smaller average particle size than particles conventionally used, and in order to bind such inorganic or organic particles according to an embodiment of the present invention, it may be more advantageous to use a mixture of an emulsion-type binder and a soluble binder that can easily surround fine powder particles.

[0073] In particular, the glass transition temperature (T g ) can be used as a binder because it can improve the mechanical properties, such as flexibility and elasticity, of the porous coating layer that is finally formed. Such a binder effectively binds and stably fixes inorganic particles together, thereby contributing to preventing a decrease in the mechanical properties of a composite separator for an electrochemical device incorporating a porous coating layer. Specifically, the emulsion-type binder may have a glass transition temperature of -200 to 40°C, and the solution-type binder may have a glass transition temperature of 50 to 200°C.

[0074] Furthermore, the binder does not necessarily have to have ion-conducting ability, but using a polymer with ion-conducting ability can further improve the performance of the electrochemical device. Therefore, the binder can be used with as high a dielectric constant as possible. In fact, since the degree of salt dissociation in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the binder, the more the degree of salt dissociation in the electrolyte can be improved. The dielectric constant of such binders can be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and can particularly be 10 or higher.

[0075] In addition to the above-mentioned functions, the binder may exhibit a high degree of swelling in the liquid electrolyte by gelling when impregnated with the liquid electrolyte, and therefore the solubility index of the binder, i.e., Hildebrand solubility parameter, is 15 to 45 MPa. 1 / 2 , 15 to 25 MPa 1 / 2 or 30 to 45 MPa 1 / 2 Therefore, it is more preferable to use a hydrophilic polymer having many polar groups than a hydrophobic polymer such as polyolefins. 1 / 2 Less than or 45MPa 1 / 2 If the content is too high, swelling by a typical liquid electrolyte for batteries may be difficult.

[0076] Non-limiting examples of such binders include polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, acrylic copolymers, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxymethyl cellulose, but are not limited to these.

[0077] The acrylic copolymer may be a copolymer containing two or more repeating units selected from the group consisting of a repeating unit derived from a monomer having a cyano group, a repeating unit derived from a monomer having a carboxy group, and a repeating unit derived from a monomer having an alkyl group having 1 to 14 carbon atoms.

[0078] The cyano group-containing monomer may be at least one selected from the group consisting of (meth)acrylonitrile, 2-(vinyloxy)ethanenitrile, and 2-(vinyloxy)propanenitrile. Preferably, the cyano group-containing monomer may be (meth)acrylonitrile, which has hardness and can maintain the shape of the binder.

[0079] The monomer having a carboxy group may be one or more selected from the group consisting of (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropionic acid, 4-(meth)acryloyloxybutyric acid, acrylic acid dimer, itaconic acid, maleic acid, and maleic anhydride. Preferably, the monomer having a carboxy group is (meth)acrylic acid, which can be distributed on the surface of the binder to improve dispersibility.

[0080] The monomer having an alkyl group of 1 to 14 carbon atoms may be methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, or tetradecyl (meth)acrylate, and may be used alone or in combination of two or more. If the alkyl group contains more than 14 carbon atoms, the alkyl group may be too long and non-polar, which may reduce the packing density of the porous coating layer. Preferably, the monomer having an alkyl group having 1 to 14 carbon atoms may be 2-ethylhexyl (meth)acrylate, which can improve the impregnation of the electrolyte.

[0081] The acrylic copolymer may further include one or more repeating units derived from a non-acrylic monomer (e.g., a styrene-based monomer, a butadiene-based monomer, a vinyl-based monomer, etc.) in addition to the repeating units derived from the above monomers.

[0082] Specific examples of the acrylic copolymer include ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, butadiene-acrylic acid copolymer, butadiene-methacrylic acid copolymer, and the like.

[0083] In this case, when the average particle size of the particles to be applied is small, a soluble binder polymer that can easily surround fine particles and exert binding strength is advantageous, and examples thereof include polyvinyl alcohol, polyacrylic acid, or a mixture thereof. Among these, polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid are preferred because they are hydrophilic and therefore have excellent dispersibility without a separate surface treatment. The polyacrylic acid may be non-crosslinked or crosslinked. The crosslinked polyacrylic acid is advantageous in that it not only has excellent dispersibility without a separate surface treatment but also reduces the resistance of the porous coating layer, while the non-crosslinked polyacrylic acid may be advantageous for dispersing inorganic or organic particles. When using a hydrophobic polymer as a binder, it is preferable to modify the surfaces of the inorganic and organic particles to make them hydrophobic.

[0084] The weight ratio of the particles to the binder is in the range of 80:20 to 99:1, 85:15 to 98:2, or 90:10 to 97:3. When the particle to binder content ratio satisfies the above range, it is possible to prevent the problem of reduced pore size and porosity of the coating layer formed due to an increased binder content, and to solve the problem of weakened peel resistance of the coating layer formed due to a decreased binder content.

[0085] The composite separator for an electrochemical device according to one embodiment of the present invention may further include other additives as components of the porous coating layer in addition to the above-described particles (one or more of inorganic particles and organic particles) and binder.

[0086] Specifically, the porous polymer substrate may be a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

[0087] The porous polymer film substrate or porous polymer nonwoven fabric substrate may be a polyolefin-based porous polymer film or porous polymer nonwoven fabric substrate such as polyethylene or polypropylene, and such a polyolefin-based porous polymer film substrate or porous polymer nonwoven fabric substrate exhibits a shutdown function at a temperature of, for example, 80 to 140°C.

[0088] In this case, the polyolefin-based porous polymer film substrate or porous polymer nonwoven fabric substrate can be formed from a polyolefin-based polymer such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, polypentene, etc., either alone or in combination of two or more of these polymers.

[0089] The porous polymer film substrate or porous polymer nonwoven fabric substrate can also be manufactured using various polymers such as polyester in addition to polyolefin. The porous polymer film substrate or porous polymer nonwoven fabric substrate can also be formed into a laminated structure of two or more layers, and each layer can be formed from the above-mentioned polymers such as polyolefin and polyester alone or a mixture of two or more of them.

[0090] In addition to the polyolefins described above, the porous polymer film substrate and the porous nonwoven fabric substrate can be formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, either alone or in combination.

[0091] The thickness of the porous polymer substrate is not particularly limited, and may be, for example, in the range of 1 to 30 μm, 2 to 20 μm, 3 to 15 μm, or 4 to 12 μm. When the porous polymer substrate has such a thickness range, it does not act as a resistor but can have the appropriate mechanical strength required for a separator.

[0092] The size of the pores present in the porous polymer substrate may be in the range of 10 to 100 nm, 15 to 80 nm, or 20 to 70 nm. When the porous polymer substrate has pores in this size range, it can have an appropriate separating function required for a separation membrane without acting as a resistance.

[0093] The porosity of the porous polymer substrate may be in the range of 30 to 80%, 35 to 70%, 38 to 65%, or 43 to 55%. When the porous polymer substrate has such a porosity range, it does not act as a resistor but can have the appropriate mechanical strength required for a separator.

[0094] A composite separator for an electrochemical device according to one embodiment of the present invention can be manufactured by preparing a composition for forming a porous coating layer, including particles and a binder, applying the composition to at least one surface of a porous polymer substrate, and drying the composition.

[0095] First, the composition for forming the porous coating layer can be prepared by dissolving / dispersing a binder in a solvent, adding particles (one or more of inorganic particles and organic particles), and dispersing the mixture. The particles can be added in a state where they have been crushed to a predetermined average particle size, or they can be added to a binder solution / dispersion, and then crushed and dispersed using a ball mill or other method while controlling the particles to have a predetermined average particle size.

[0096] The method for coating the porous polymer substrate with the composition for forming the porous coating layer is not particularly limited, but is preferably slit coating or dip coating. Slit coating is a method in which a composition supplied through a slit die is applied to the entire surface of a porous polymer substrate, and the thickness of the coating layer can be controlled by adjusting the flow rate supplied from a metering pump. Dip coating is a method in which a porous polymer substrate is immersed in a tank filled with the composition, and the thickness of the coating layer can be controlled by adjusting the concentration of the composition and the speed at which the substrate is pulled up from the tank. To more accurately control the coating thickness, the substrate may be post-weighed using a Mayer bar or the like after immersion.

[0097] Thereafter, the porous polymer substrate coated with the composition for forming a porous coating layer is dried in an oven to form a coating layer on at least one surface of the porous polymer substrate.

[0098] In the porous coating layer, the particles are packed together and in contact with each other, and are bound to each other by the binder, thereby forming interstitial volumes between the particles, which become empty spaces and form pores.

[0099] That is, the binder adheres the particles to each other so that they can maintain their bonded state, i.e., the binder connects and fixes the particles to each other. Also, the pores of the porous coating layer are pores formed by the interstitial volume between particles as empty spaces, which are spaces limited by particles that are substantially in contact with each other in a particle-packed structure (closely packed or densely packed).

[0100] The thickness of the porous coating layer is not particularly limited, and may be, for example, in the range of 0.5 to 3 μm, 1.0 to 2.5 μm, or 1.0 to 2.0 μm. When the porous coating layer has such a thickness range, it does not act as a resistor but can have the appropriate mechanical strength required for a separator.

[0101] In addition, the average diameter of the pores formed in the porous coating layer may be in the range of 10 to 100 nm, 15 to 80 nm, 20 to 70 nm, or 33 to 48 nm. When the porous coating layer has an average diameter of the pores in this range, lithium ions can move smoothly without acting as a resistance.

[0102] The ratio (a / b) of the average diameter of the pores (a) formed in the porous coating layer to the average diameter of the pores (b) formed in the porous polymer substrate may be 2.0 or less, 0.5 to 2.0, 0.75 to 1.25, or 0.938 to 1.363. When the ratio (a / b) of the average diameter of the pores (a) formed in the porous coating layer to the average diameter of the pores (b) formed in the porous polymer substrate satisfies this range, micro-short circuits between the cathode and anode are prevented, maintaining isolation function, and smooth lithium ion movement is maintained.

[0103] The porosity of the porous coating layer may be 30 to 80%, 35 to 70%, 38 to 65%, or 51 to 65%. When the porous coating layer has such a porosity range, lithium ions can move smoothly without acting as a resistance.

[0104] An electrochemical device according to one aspect of the present invention includes a cathode, an anode, and a separator interposed between the cathode and the anode, where the separator is the composite separator according to one embodiment of the present invention described above.

[0105] Such an electrochemical device includes all devices that perform an electrochemical reaction, specifically, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor devices. 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 desirable.

[0106] Both electrodes, the cathode and the anode, applied together with the composite separation membrane for the electrochemical device of the present invention are not particularly limited, and can be manufactured in a form in which an electrode active material is bound to an electrode current collector by a usual method well known in the art.

[0107] As non-limiting examples of the cathode active material among the electrode active materials, ordinary cathode active materials used in the cathodes of conventional electrochemical devices can be used, and in particular, it is desirable to use lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these. In particular, a lithium oxide containing nickel as a main component, for example, Li a (Ni 1-x-y-z Co x Mn y M z )O2 (where M is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), 0.95 ≦ a ≦ 1.3, x ≦ (1 - x - y - z), y ≦ (1 - x - y - z), z ≦ (1 - x - y - z), 0 < x < 1, 0 ≦ y < 1, 0 ≦ z < 1), and can be a cathode active material represented by such, and non-limiting examples of such a cathode active material include LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.85 Co 0.1 Al 0.05 O2 is one example.

[0108] Non-limiting examples of the anode active material include conventional anode active materials used in electrochemical device anodes, particularly lithium metal or lithium alloys, and lithium-absorbing materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons. Non-limiting examples of the cathode current collector include foils made of aluminum, nickel, or a combination thereof. Non-limiting examples of the anode current collector include foils made of copper, gold, nickel, copper alloys, or a combination thereof.

[0109] The electrolyte used in the electrochemical element of the present invention is A + B - A salt with the structure + Li + , Na + , K. + or a combination thereof, such as B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 -or a salt containing an anion such as the above or a combination thereof, dissolved or dissociated in an organic solvent such as 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), ethyl methyl carbonate (EMC), γ-butyrolactone, or a mixture thereof, but is not limited thereto.

[0110] The electrolyte may be injected at an appropriate stage in the battery manufacturing process depending on the manufacturing process and desired physical properties of the final product, i.e., before battery assembly or at the final stage of battery assembly.

[0111] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0112] Example 1 (1) Manufacturing of composite separation membranes The porous polymer substrate was a 11 μm thick polyethylene porous film (WL11B, manufactured by Double Scope Co., Ltd., porosity 43%, theoretical density of the porous polymer substrate 0.973 g / cm). 3 , the actual density of the porous polymer substrate is 0.555 g / cm 3 , pore size 48 nm, shutdown temperature 140°C, meltdown temperature 147°C).

[0113] To form a porous coating layer, cross-linked polyacrylic acid (PAA) (Aekyung Oil Chemicals, developed product) was prepared as a binder, and inorganic particles with an average particle size of 20 nm and a specific surface area of ​​81 g / m were used. 2Alumina (Al2O3) particles (SpectrAl 81, manufactured by Cabot Corporation) were prepared. 10 parts by weight of cross-linked polyacrylic acid (PAA) (Aekyung Oil & Chemicals, developed product) was dissolved in 100 parts by weight of water to prepare a binder solution. The inorganic particles were added to and dispersed in the binder solution so that the weight ratio of binder to inorganic particles was 5:95, thereby preparing a composition for forming a porous coating layer.

[0114] The composition for forming the porous coating layer was coated on one side of the porous polymer substrate to a thickness of 1.5 μm and dried to prepare a composite separator. The porosity of the formed porous coating layer was measured to be 51% (theoretical density of the porous coating layer material was 3.88 g / cm). 3 , the actual density of the porous coating layer material is 1.90g / cm 3 ), the meltdown temperature of the composite separator was improved to 179°C, and the shutdown temperature after removing the coating layer was confirmed to be 140°C.

[0115] The ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate was 0.938.

[0116] In addition, the increase in meltdown temperature due to the formation of the porous coating layer (composite), i.e., the difference between the meltdown temperature of the porous polymer substrate used in the composite separator and the meltdown temperature of the composite separator, was 32°C.

[0117] (2) Fabrication of porous coating layer for measuring pore size To form a porous coating layer, cross-linked polyacrylic acid (PAA) (Aekyung Oil Chemicals, developed product) was prepared as a binder, and inorganic particles with an average particle size of 20 nm and a specific surface area of ​​81 g / m were used. 2Alumina (Al2O3) particles (SpectrAl 81, manufactured by Cabot Corporation) were prepared. 10 parts by weight of cross-linked polyacrylic acid (PAA) (Aekyung Oil & Chemicals, developed product) was dissolved in 100 parts by weight of water to prepare a binder solution. The inorganic particles were added to and dispersed in the binder solution so that the weight ratio of binder to inorganic particles was 5:95, thereby preparing a composition for forming a porous coating layer.

[0118] A nonwoven fabric (Mitsubishi Paper Mills, LN1-1511, pore size 5.1 μm) was prepared. The nonwoven fabric (Mitsubishi Paper Mills, LN1-1511, pore size 5.1 μm) was used as a support, and the composition for forming the porous coating layer was coated onto one side of the support by dip coating to form a coating thickness of 5 μm. The pore size measured for the semi-finished product was 45 nm.

[0119] (3) Manufacturing of electrochemical elements (lithium secondary batteries) 1) Cathode and anode production 96 parts by weight of LiNi as the cathode active material 0.7 Co 0.1 Mn 0.2 O2, 2 parts by weight of acetylene black as a conductive material, and 2 parts by weight of polyvinylidene fluoride (PVDF) as a binder were added to and mixed with NMP (N-methyl-2-pyrrolidone) to prepare a cathode active material slurry, which was then coated on an aluminum (Al) current collector and dried to prepare a cathode.

[0120] An anode was manufactured by adding and mixing 96 parts by weight of graphite as an anode active material, 0.5 parts by weight of acetylene black as a conductive material, 1.0 part by weight of carboxymethyl cellulose (CMC) as a thickener, and 2.5 parts by weight of SBR as a binder to water to prepare an anode active material slurry, which was then coated on a copper (Cu) current collector and dried.

[0121] 2) Manufacture of lithium secondary batteries A pouch-type cell was fabricated using the prepared cathode, anode, and composite separator, and an electrolyte (EC / EMC = 1 / 2 (volume ratio), LiPF 61 mol) was injected into the fabricated cell to fabricate a lithium secondary battery.

[0122] Example 2 Inorganic particles with an average particle size of 20 nm and a specific surface area of ​​51 g / m 2 A composite separator and a lithium secondary battery using the same were manufactured in the same manner as in Example 1, except that the alumina (Al2O3) particles (SpectrAl 51, manufactured by Cabot Corporation) were used.

[0123] The porosity of the coating layer of the manufactured composite separator was measured to be 52% (theoretical density of the porous coating layer material was 3.88 g / cm 3 , the actual density of the porous coating layer material is 1.86g / cm 3 ), the meltdown temperature of the composite separator increased to 177°C, and the shutdown temperature after removing the coating layer was confirmed to be 140°C. The ratio of the pore size of the porous coating layer to the pore size of the porous polymer substrate was 0.979 (substrate pore size: 48nm, coating layer pore size: 47nm), and the meltdown temperature increased by 30°C due to the formation of the porous coating layer (composite formation).

[0124] Example 3 The porous polymer substrate was a 15 μm thick polyethylene porous film (Toray Industries, F15CK2, porosity 49%, theoretical density of the porous polymer substrate 0.973 g / cm). 3 , the actual density of the porous polymer substrate is 0.496 g / cm 3 A composite separator and a lithium secondary battery using the same were manufactured in the same manner as in Example 1, except that the conditions were changed to 1.0, 1.2, 1.4, 1.6, 1.8, 1.9, 1.4, 1.6, 1.8, 1.8, 1.9 ...

[0125] The porosity of the coating layer of the manufactured composite separator was measured to be 51% (the theoretical density of the porous coating layer material was 3.88 g / cm 3, the actual density of the porous coating layer material is 1.90g / cm 3 ), the meltdown temperature of the composite separator increased to 179°C, and the shutdown temperature after removing the coating layer was confirmed to be 140°C. The ratio of the pore size of the porous coating layer to the pore size of the porous polymer substrate was 1.216 (substrate pore size: 37 nm, coating layer pore size: 45 nm), and the increase in meltdown temperature due to the formation of the porous coating layer (composite formation) was 31°C.

[0126] Example 4 The porous polymer substrate was a 10 μm thick polyethylene porous film (Senior, SW710H, porosity 55%, theoretical density of the porous polymer substrate 0.968 g / cm). 3 , the actual density of the porous polymer substrate is 0.436 g / cm 3 A composite separator and a lithium secondary battery using the same were manufactured in the same manner as in Example 1, except that the porous coating layer was changed to an acrylic emulsion (CSB130, manufactured by Toyo Ink Co., Ltd.) and the pore size was changed to 33 nm, the shutdown temperature was changed to 134°C, and the meltdown temperature was changed to 147°C).

[0127] Example 5 A composite separator and a lithium secondary battery using the same were manufactured in the same manner as in Example 4, except that a 1:1 mixture of cross-linked polyacrylic acid (PAA) (Aekyung Oil & Chemicals, developed product) and acrylic emulsion (Toyo Ink, CSB130) was used as a binder for forming the porous coating layer.

[0128] Comparative Example 1 A composite separator and a lithium secondary battery using the same were manufactured in the same manner as in Example 1, except that the inorganic particles were changed to alumina particles (AES11, manufactured by Sumitomo Chemical Co., Ltd.) having an average particle size of 800 nm.

[0129] The pore size of the porous coating layer of the manufactured composite separator was 154 nm, and the porosity of the porous coating layer was 59% (theoretical density of the porous coating layer material was 3.88 g / cm). 3 , the actual density of the porous coating layer material is 1.59g / cm 3 ), and the meltdown temperature of the composite separator was measured to be 150°C.

[0130] The ratio of the pore size of the porous coating layer to the pore size of the porous polymer substrate was 3.208, and the increase in meltdown temperature due to the composite was 3°C.

[0131] Measurement method The porosity of the porous polymer substrate, the porosity of the porous coating layer, the pore size of the porous polymer substrate, the pore size of the porous coating layer, the shutdown temperature and the meltdown temperature of the porous polymer substrate of the composite separators prepared in Examples 1 to 5 and Comparative Example 1 were measured as follows, and the results are shown in Table 1 below.

[0132] Porosity of porous polymer substrates The porosity of a porous polymer substrate is determined by dividing the "true density (X) of the porous polymer substrate (weight per unit area / thickness)" by the "theoretical density (Y) of the porous polymer substrate" as shown in the following Equation 1, and multiplying this by 100 to express it as a percentage (%).

[0133] [Formula 1] Porosity of porous polymer substrate (%) = [1-X / Y] x 100

[0134] Porosity of porous coating layer The porosity of the porous coating layer is expressed as a percentage (%) by dividing the "true density (W) of the porous coating layer (weight per unit area / thickness)" by the "theoretical density (Z) of the porous coating layer material" as shown in Equation 2 below, subtracting the result from 1, and multiplying the result by 100.

[0135] [Formula 2] Porosity of porous coating layer (%) = [1-W / Z] x 100

[0136] Average diameter of pores formed in porous polymer substrate (b) Measurement is carried out using a capillary flow porometer manufactured by PMI.

[0137] Average diameter of pores formed in the porous coating layer (a) The composition for forming the porous coating layer is coated on a nonwoven fabric support, and then the porous coating layer is measured using a capillary flow porometer manufactured by PMI.

[0138] Shutdown temperature of porous polymer substrates The shutdown temperature was determined by dissolving and removing the porous coating layer formed on the composite separator, and then fixing only the porous polymer substrate to a frame (outer diameter: 15 cm × 15 cm, inner diameter: 10 cm × 10 cm) with polyimide tape and exposing it to a convection oven at a heating rate of 3 °C / min from 80 °C. The air permeability time was measured by measuring the temperature at which the air permeability time (Gurley value) first exceeded 10,000 sec / 100 ml. The air permeability time was measured using an air permeability tester (Asahi Seiko Co., Ltd., Model: EG01-55-1MR) as the time (seconds) required for 100 ml of air to pass through the porous polymer substrate at a constant pressure (0.05 MPa).

[0139] Measuring the meltdown temperature The meltdown temperature was measured by applying a load of 0.01 N to a composite separator membrane measuring 4 mm x 8 mm using a thermomechanical analyzer (TMA). The temperature was increased at a rate of 5°C / min, and the degree of deformation was measured. The temperature at which the membrane contracted with the increase in temperature, then stretched again and broke was measured, and this temperature was defined as the meltdown temperature of the composite separator membrane.

[0140] In addition, the porous coating layer formed on the composite separator was dissolved and removed in the same manner as in measuring the shutdown temperature, and then the meltdown temperature of the porous polymer substrate was measured using the meltdown temperature measurement method described above.

[0141] Battery stability evaluation The lithium secondary batteries produced in Examples 1 to 5 and Comparative Example 1 were subjected to high-temperature storage evaluation, and the results are shown in Table 1.

[0142] For the high-temperature storage evaluation, a fully charged lithium secondary battery was heated from room temperature (25°C) to 150°C at a rate of 5°C per minute, and once it reached 150°C, it was maintained at that temperature for one hour. If ignition occurred during this time, it was rated as "ignition," and if not, it was rated as "pass."

[0143] [Table 1]

[0144] In the table above, "meltdown temperature increase" refers to the difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices. Table 1 shows that the composite separators of Examples 1 to 5 had meltdown temperature increases of 30°C or more, while the composite separator of Comparative Example 1 had a smaller increase of 3°C. As a result, the lithium secondary battery of Comparative Example 1 ignited during a battery stability test. However, the lithium secondary batteries of Examples 1 to 5 exhibited improved stability even when exposed to heating conditions at 150°C for one hour, as the composite separator was able to prevent short circuits between the cathode and anode.

Claims

1. A composite separator for an electrochemical device, a porous polymer substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer including a plurality of particles and a binder located on a part or all of the surfaces of the particles to connect and fix the particles to each other; the particles are inorganic particles, The inorganic particles have an average particle size in the range of 15 nm to 380 nm, The size of the pores present in the porous polymer substrate is 20 nm to 70 nm; The average particle size of the pores formed in the porous coating layer is 20 nm to 70 nm; the porous polymeric substrate has a shutdown temperature of 140°C or less; having a meltdown temperature of 170°C or higher; The difference between the meltdown temperature of the porous polymer substrate used in the composite separator for electrochemical devices and the meltdown temperature of the composite separator for electrochemical devices is 30°C to 40°C; The composite separator for an electrochemical element, wherein the binder is one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, and an acrylic copolymer.

2. 2. The composite separator for electrochemical devices according to claim 1, wherein the composite separator for electrochemical devices has a meltdown temperature of 170 to 220°C.

3. the plurality of particles are packed together and in contact with one another and bound to one another by the binder, thereby forming interstitial volumes between the particles, and the interstitial volumes between the particles become empty spaces and form pores; 2. The composite separator for electrochemical devices according to claim 1, wherein the ratio (a / b) of the average diameter (a) of the pores formed in the porous coating layer to the average diameter (b) of the pores formed in the porous polymer substrate is 2.0 or less.

4. 4. The composite separator for electrochemical devices according to claim 3, wherein a ratio (a / b) of an average diameter (a) of pores formed in the porous coating layer to an average diameter (b) of pores formed in the porous polymer substrate is in the range of 0.75 to 1.

25.

5. An electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode, An electrochemical device, wherein the separation membrane is the composite separation membrane for electrochemical devices according to claim 1 .

6. 6. The electrochemical device according to claim 5, wherein the electrochemical device is a lithium secondary battery.

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