Separator for lithium secondary battery and method of manufacturing same

Abstract

The separator according to the present invention has an organic / inorganic composite porous coating layer formed on the surface of a polymer substrate, and the organic / inorganic composite porous coating layer has a first region with a high content of inorganic particles and a second region with a low content of inorganic particles. The first region improves the heat resistance of the side of the battery, thereby alleviating the problem of battery short-circuiting due to shrinkage at both ends of the separator.

Description

[Technical Field]

[0001] The present invention relates to a separator for a lithium secondary battery and a method for manufacturing the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2023-0026319 filed on February 27, 2023, and Korean Patent Application No. 10-2023-0125131 filed on September 19, 2023, the entire contents of which are incorporated herein by reference in their entirety in their specifications and drawings. [Background technology]

[0003] Due to their high applicability to a variety of products and their electrical properties such as high energy density, lithium secondary batteries are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are powered by electrical sources.

[0004] Currently, the operating voltage of a unit cell of a widely used secondary battery is approximately 2.5V to 4.5V. Therefore, if a higher output voltage is required, a battery pack can be configured by connecting multiple battery cells in series. Alternatively, a battery pack can be configured by connecting multiple battery cells in parallel depending on the charge / discharge capacity required for the battery pack. In this way, the number and electrical connection form of the battery cells included in the battery pack can be variously set depending on the required output voltage and / or charge / discharge capacity.

[0005] Meanwhile, known types of secondary battery unit cells include cylindrical, prismatic, and pouch types. In the case of a cylindrical secondary battery cell, a separator, which is an insulator, is interposed between a positive electrode and a negative electrode, and the separator is wound up to form a jelly-roll-shaped electrode assembly. This jelly-roll-shaped electrode assembly is then inserted into a battery can to form a battery. Strip-shaped electrode tabs are connected to the uncoated portions of the positive and negative electrodes, electrically connecting the electrode assembly to electrode terminals exposed to the outside. For reference, the positive electrode terminal is the cap plate of a seal that seals the opening of the battery can, and the negative electrode terminal is the battery can. However, conventional cylindrical battery cells with this structure have problems such as high resistance, large heat generation, and poor current collection efficiency due to current concentration at the strip-shaped electrode tabs connected to the uncoated portions of the positive electrode and / or negative electrode.

[0006] Small cylindrical battery cells with 18650 or 21700 form factors do not pose significant problems with resistance and heat generation, but when the form factor is increased to apply cylindrical battery cells to electric vehicles, a large amount of heat is generated around the electrode tabs during the fast charging process, both ends of the electrode assembly are compressed by the can, and repeated charging and discharging can cause partial deformation of the electrode assembly, which can rupture the separator and cause an internal short circuit.This internal short circuit can cause the cylindrical battery cell to catch fire.

[0007] Conventional separators have incorporated a porous coating layer containing inorganic particles to improve the thermal shrinkage characteristics of the separator's porous polymer substrate. However, when a separator including a porous coating layer having the same composition over its entire surface is applied to a large cylindrical battery, limitations may still be present in its heat resistance.

[0008] In addition, short circuits between electrodes occur due to the thermal shrinkage of the conventional separator, and the unique structure of the jelly roll results in uneven electrolyte impregnation paths during electrolyte injection, resulting in a large deviation in resistance between batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a separator membrane with improved heat shrinkage properties.

[0010] Specifically, the present invention aims to provide a separator that can be applied to large cylindrical batteries and has improved heat resistance at both ends, and an electrochemical device, particularly a lithium secondary battery, including the separator.

[0011] Another object of the present invention is to provide a separator having uniform electrolyte wettability that can be applied to large cylindrical batteries, and an electrochemical device, particularly a lithium secondary battery, including the separator.

[0012] It is yet another object of the present invention to provide a cylindrical battery cell including a separator with improved heat shrinkage properties, a battery pack including the same, and a vehicle including the battery pack.

[0013] However, the technical problems that the present invention aims to solve are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description of the invention. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides: A first aspect of the present invention provides a separator for an electrochemical device according to the following embodiment.

[0015] The separator for an electrochemical device according to the first embodiment is A separation membrane, The separation membrane includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate; the porous coating layer is divided into a first region disposed at both ends of the outermost portion of the separator in the width direction and a second region disposed between two portions of the first region; The first region and the second region each independently contain inorganic particles and a binder material, and the content ratio of the inorganic particles in the first region according to the following formula 1 is higher than the content ratio of the inorganic particles in the second region according to the following formula 2. [Formula 1] Content ratio (wt%) of inorganic particles in the first region = [amount of inorganic particles in the first region / (amount of inorganic particles in the first region + amount of binder material in the first region)] × 100 [Formula 2] Content ratio of inorganic particles in the second region (wt%)=[amount of inorganic particles in the second region / (amount of inorganic particles in the second region+amount of binder material in the second region)]×100

[0016] According to the second embodiment, in the first embodiment, In the porous coating layer, the porosity of the first region may be higher than the porosity of the second region.

[0017] According to the third embodiment, in the first or second embodiment, The content ratio of the inorganic particles in the second region may be lower than the content ratio of the inorganic particles in the first region, and may be 96 wt % or less.

[0018] According to a fourth embodiment, in any one of the first to third embodiments, The content ratio of the inorganic particles in the first region may be higher than the content ratio of the inorganic particles in the second region, and may be 70 wt % or more and 98 wt % or less.

[0019] According to the fifth embodiment, in any one of the first to fourth embodiments, The width of one of the first regions may be 5 to 35% of the entire width of the porous coating layer.

[0020] According to another embodiment of the present invention, there is provided a method for manufacturing a separator according to the following embodiment.

[0021] The method for manufacturing a separator according to the sixth embodiment includes: A method for manufacturing a separation membrane according to any one of the first to fifth embodiments, The method is carried out by a roll-to-roll process in which a long strip of porous polymeric substrate is continuously supplied; The method includes forming a first region having a predetermined width on both ends of a transverse direction (TD) perpendicular to a machine direction (MD) of the porous polymer substrate on at least one surface of the porous polymer substrate, and forming a second region between two portions of the first region, thereby obtaining a separation membrane strip including a composite porous coating layer having the first region and the second region.

[0022] According to the seventh embodiment, in the sixth embodiment, The first and second regions can be formed by applying a slurry for forming the first region and a slurry for forming the second region to respective partitioned portions using a double slot die.

[0023] According to the eighth embodiment, in the sixth or seventh embodiment, cutting the separation membrane strip to a predetermined length to obtain a separation membrane; In the resulting separation membrane, the side surfaces of the second region may be exposed at both ends in the MD direction of the porous polymer substrate.

[0024] According to other embodiments of the present invention, the following electrode assemblies and cylindrical battery cells are provided.

[0025] The electrode assembly according to the ninth embodiment includes: A jelly-roll type electrode assembly having a structure in which sheet-shaped first and second electrode plates and a separator interposed between the first and second electrode plates are wound in one direction, The separation membrane may be a separation membrane according to any one of the first to fifth embodiments.

[0026] The cylindrical battery cell according to the tenth embodiment is a jelly-roll type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction; a battery can in which the electrode assembly is housed; and a seal that seals an open end of the battery can, The separation membrane may be a separation membrane according to any one of the first to fifth embodiments.

[0027] According to the eleventh embodiment, in the tenth embodiment, The cylindrical battery cell may have a form factor ratio of 0.4 or greater.

[0028] The cylindrical battery cell can be a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, a 46800 cell, or a 46950 cell. [Effects of the Invention]

[0029] A separator according to one aspect of the present invention includes a porous coating layer formed on at least one surface of a porous polymer substrate, and the porous coating layer has first regions with a high content of inorganic particles disposed on both ends thereof, thereby improving the heat resistance of both ends of the separator.

[0030] In addition, by disposing a first region with a high content of inorganic particles and a second region with a low content of inorganic particles between two portions of the first region, it is possible to improve the wettability of the electrolyte through the breathable first region to the second region.

[0031] Therefore, according to another aspect of the present invention, it is possible to provide a cylindrical battery cell having low internal resistance and capable of preventing or eliminating internal short circuits, a battery pack including the same, and a vehicle. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a schematic diagram of a separation membrane according to one aspect of the present invention. [Figure 2] 1 is a schematic diagram illustrating a method for manufacturing a separation membrane according to one aspect of the present invention. [Figure 3] 1 is a schematic diagram illustrating a method for manufacturing a separation membrane according to one aspect of the present invention. [Figure 4] 1 is a photograph of the negative electrode surface taken out from the battery of Example 1. [Figure 5] 1 is a photograph of the negative electrode surface taken out from the battery of Example 2. [Figure 6] 1 is a photograph of the negative electrode surface taken out from the battery of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described in detail below.

[0034] Throughout this specification, when a part "comprises" a certain element, this does not mean excluding other elements, but means that it may further include other elements, unless otherwise specified.

[0035] Throughout this specification, the phrase "A and / or B" means "A or B, or all of them."

[0036] One aspect of the present invention relates to a separator for an electrochemical device.

[0037] The electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction and is a concept that includes primary batteries and secondary batteries. The secondary battery is capable of being charged and discharged and is a concept that includes lithium ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc.

[0038] In this specification, the separator serves as a porous ion-conducting barrier that blocks electrical contact between the negative and positive electrodes in an electrochemical device and allows ions to pass through. The separator has a plurality of pores formed therein, and preferably the pores are interconnected to allow gas and / or liquid to pass from one side of the separator to the other side.

[0039] A separator 100 according to one aspect of the present invention includes a porous polymer substrate 110 having a plurality of pores and including a polymer material. The separator also includes a porous coating layer 120 formed on at least one surface of the polymer substrate 110.

[0040] The porous coating layer may include inorganic particles and a binder material, and the inorganic particles may have a layered structure bound by the binder material. The coating layer has a porous structure due to interstitial volumes formed between the inorganic particles. This porous structure improves the electrolyte retention of the separator.

[0041] In one embodiment of the present invention, the porous coating layer may occupy 3 vol% to 40 vol% of the total volume (100 vol%) of the separator, and together with this, or independently, the thickness of the porous coating layer may be 5% to 50% of the total thickness (100%) of the separator.

[0042] In one embodiment of the present invention, the porous polymer substrate is a sheet-like porous membrane containing a polymer material and having a plurality of pores. For example, the polymer substrate may have a form including at least one sheet selected from porous polymer films and nonwoven fabrics. The pores include open pores, which have an interconnected structure and allow gas and / or liquid to pass from one side of the polymer substrate to the other side.

[0043] In one embodiment of the present invention, the polymer substrate may have an air permeability of 2,000 sec / 100 cc or less and a porosity of 30 vol% to 60 vol% in terms of battery output and cycle characteristics. 50 may have a range of 10 nm to 100 nm.

[0044] In the present invention, the air permeability refers to the time (seconds) required for 100 ml of air to pass through a polymer substrate or separation membrane of 1 square inch size under a constant air pressure of 4.8 inches. The air permeability can be measured, for example, using an EG01-55-1MR device manufactured by Asahi Seiko Co., Ltd.

[0045] In the present invention, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume, and is expressed in units of vol%. It may be used interchangeably with terms such as porosity and void ratio. The method for measuring the porosity in the present invention is not particularly limited, and may be measured, for example, by a Brunauer-Emmett-Teller (BET) measurement method using nitrogen gas or a mercury porosimeter. Alternatively, in one embodiment of the present invention, the true density of the object to be measured may be calculated from the density (apparent density) of the object to be measured for porosity, the composition ratio of the constituent components of the object, and the density of each component, and the porosity of the object may be calculated from the difference between the apparent density and the true density (net density).

[0046] In one embodiment of the present invention, the porosity increases as the content of inorganic particles increases, and thus the porosity of the first region may be higher than the porosity of the second region. The porosity may be measured, for example, from air permeability, and thus the air permeation time (sec / 100cc) of the first region may be shorter than that of the second region.

[0047] In one embodiment of the present invention, the porous polymer substrate may have a thickness of 5 μm to 20 μm to achieve a thinner electrochemical device and higher energy density. If the thickness of the polymer substrate is below this range, the conductive barrier function may be insufficient, while if the thickness exceeds this range (i.e., is too thick), the resistance of the separator may increase excessively.

[0048] In one embodiment of the present invention, the polymer material is preferably a thermoplastic resin having a melting point of 200°C or less, and may include one or more polyolefin-based resins, in order to provide a shutdown function. The shutdown function refers to the function of preventing thermal runaway of the battery by blocking ion migration between the positive and negative electrodes when the battery temperature rises and closing the pores of the polymer substrate by dissolving the polymer resin.

[0049] The polyolefin resin may include, for example, one or more selected from the group consisting of polyethylene, polypropylene, polybutene, and polypentene. In particular, the polyolefin resin may be polyethylene and / or polypropylene. In addition, the polymer material may further include, in addition to the polyolefin resin, one or more selected from polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene.

[0050] Next, the inorganic particles and binder material contained in the porous coating layer of the separation membrane will be described.

[0051] In one embodiment of the present invention, the inorganic particles are not particularly limited as long as they have a particle size smaller than the desired coating layer thickness, for example, a particle size of 1 / 2 to 1 / 1,000 of the coating layer thickness, and are electrochemically stable. For example, the diameter of the inorganic particles may be 10 nm or more. Meanwhile, for example, the average diameter D 50The particle size may be 10 μm or less, 7 μm or less, 5 μm or less, 2 μm or less, or 1 μm or less. That is, the inorganic particles are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). In particular, when inorganic particles having ion transfer ability are used, the ionic conductivity within the electrochemical device can be increased, thereby improving performance. Furthermore, when inorganic particles having a high dielectric constant are used as the inorganic particles, they can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0052] For the reasons described above, in a specific embodiment of the present invention, the inorganic particles may include inorganic particles with a high dielectric constant, such as a dielectric constant of 5 or more, or 10 or more, inorganic particles with lithium ion transport ability, or a mixture thereof. Non-limiting examples of inorganic particles with a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, where 0 <x<1、0<y<1である。)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, SiC, TiO2, etc. can be used alone or in combination of two or more. In particular, the above-mentioned BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, where 0 <x<1、0<y<1である。)、Pb(Mg 1 / 3 Nb 2 / 3Inorganic particles such as )O3-PbTiO3 (PMN-PT) and hafnia (HfO2) not only exhibit high dielectric constants of over 100, but also possess piezoelectricity, which generates a potential difference between the two surfaces when stretched or compressed under a certain pressure, preventing internal short circuits between the electrodes due to external impacts and improving the safety of electrochemical devices. Furthermore, when the aforementioned high dielectric constant inorganic particles are combined with inorganic particles with lithium ion transport capabilities, the synergistic effects can be multiplied.

[0053] In one specific embodiment of the present invention, the inorganic particles having lithium ion transport ability refer to inorganic particles that contain lithium element but have the function of transporting lithium ions without storing lithium. The inorganic particles having lithium ion transport ability can transport and transport lithium ions by a type of defect present inside the particle structure, thereby improving the lithium ion conductivity in the battery and thereby improving the battery performance. Non-limiting examples of the inorganic particles having lithium ion transport ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z (PO4)3,0 <x<2、0<y<1、0<z<3)、14Li2O-9Al2O3-38TiO2-39P2O5などのような(LiAlTiP) x O y Glass (0 <x<4、0<y<13)、リチウムランタンチタネート(Li x La y TiO3, 0 <x<2、0<y<3)、Li 3.25 Ge 0.25 P 0.75 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 such as Li3N (Li x N y , (0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , (0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z , (0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc. can be mentioned.

[0054] In one embodiment of the present invention, non-limiting examples of binder materials that can be used for the porous coating layer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, polyethylene oxide, and the like. The polymer resin may be any one selected from the group consisting of polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more of these polymer resins, but is not limited thereto.

[0055] In a separator for an electrochemical device according to one embodiment of the present invention, the porous coating layer is divided into a first region and a second region, specifically, the first region is disposed at both ends of the outermost portion of the separator in the width direction, and the second region is disposed between two portions of the first region.

[0056] In one aspect of the present invention, the separation membrane may have a rectangular shape. In this specification, the long side of the separation membrane may be referred to as the "length direction" and the short side of the separation membrane may be referred to as the "width direction." Furthermore, in consideration of the manufacturing process of the separation membrane, the long side of the separation membrane may be formed in the running direction of the separation membrane, and the short side may be formed in a direction perpendicular to the running direction. Therefore, the length direction of the separation membrane may be referred to as the "machine direction (MD)," and the width direction of the separation membrane may be referred to as the transverse direction (TD), which is perpendicular to the machine direction. Meanwhile, the machine direction and transverse direction of the separation membrane may also be distinguished as the long side and short side of the separation membrane, and may also be identified by the orientation direction of the polymer of the separation membrane substrate.

[0057] FIG. 1 shows a separator 100 according to an embodiment of the present invention.

[0058] Referring to FIG. 1, a separator according to an embodiment of the present invention includes a porous polymer substrate 110 having a porous coating layer 120 on at least one surface, for example, on both surfaces thereof, and the porous coating layer is divided into a first region 122 disposed at both ends in the outermost width direction and a second region 121 disposed between two portions of the first region.

[0059] In this case, the first region and the second region each independently contain inorganic particles and a binder material, and are characterized in that the content ratio of inorganic particles in the first region according to Formula 1 is higher than the content ratio of inorganic particles in the second region according to Formula 2. [Formula 1] Content ratio (wt%) of inorganic particles in the first region = [amount of inorganic particles in the first region / (amount of inorganic particles in the first region + amount of binder material in the first region)] × 100 [Formula 2] Content ratio of inorganic particles in the second region (wt%)=[amount of inorganic particles in the second region / (amount of inorganic particles in the second region+amount of binder material in the second region)]×100

[0060] According to an embodiment of the present invention, the porous coating layer has a first region and a second region having different inorganic particle content ratios. When the separator is provided in an electrode assembly, the porosity of the first region is higher than that of the second region, which promotes inflow of electrolyte into the second region through the first region, thereby reducing the internal resistance of the battery. Furthermore, when the separator is used in manufacturing a cylindrical battery cell, the improved heat resistance of the first region having a higher inorganic particle content reduces thermal contraction of the separator even at both ends of the cylindrical battery cell, thereby preventing or suppressing internal short circuits in the battery.

[0061] In one embodiment, the inorganic particle content of the second region may be less than the inorganic particle content of the first region, for example, 96 wt% or less, 95 wt% or less, 90 wt% or less, 89 wt% or less, 85 wt% or less, 80 wt% or less, or 75 wt% or less. In another embodiment, the inorganic particle content of the first region may be greater than the inorganic particle content of the second region, for example, 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, 80 wt% or more, 85 wt% or more, 88 wt% or more, 90 wt% or more, or 95 wt% or more. The inorganic particle content of the second region may be, for example, 60 wt% to 96 wt%, 70 wt% to 85 wt%, or 94 wt% to 95 wt%.

[0062] In one embodiment of the present invention, the content ratio of inorganic particles in the first region may be greater than the content ratio of inorganic particles in the second region, for example, 70 wt% to 98 wt%, 75 wt% to 95 wt%, 77.5 wt% to 95 wt%, 80 wt% to 95 wt%, 80 wt% to 90 wt%, 77.5 wt% to 80 wt%, or 95 wt% to 98 wt%.

[0063] In one embodiment of the present invention, the width of the first regions disposed at both lateral ends of the separator may be adjusted depending on the shape of the electrodes (positive and / or negative electrodes) in the electrode assembly. For example, the width of one of the first regions may be 0.1% to 40%, e.g., 5% to 35% or 10% to 30%, of the total lateral length of the porous coating layer. When the width of the first region is within this range, the heat resistance of both ends of the separator can be improved and the appropriate weight of the separator can be maintained, thereby achieving desirable effects in terms of improving the stability and energy density of the battery using the separator, but the present invention is not limited thereto.

[0064] Next, various embodiments of the porous coating layer will be described by way of examples. However, the provided embodiments are intended to aid in understanding the present invention and are not intended to limit the scope of the present invention.

[0065] In one embodiment of the present invention, the first region is disposed in a section around the second region such that at least a portion of a side surface of the second region is exposed to the outside. The first region is disposed so as to be in contact with the boundary of the second region. In the separator according to the present invention, the first region is disposed to improve the heat resistance of both outermost ends of the separator, and may also be disposed to promote inflow of the electrolyte into the coating layer.

[0066] The first region has a low binder resin content and a high inorganic particle content, resulting in a relatively higher porosity than the second region and a lower adhesive strength and cohesion with the electrode than the second region. This allows the electrolyte to more easily penetrate through the first region and reach the second region. During battery fabrication, the separator's top and bottom surfaces contact the electrodes, allowing the electrolyte to flow through the separator's sides. Therefore, if the entire area around the second region is surrounded by the first region, the wettability of the electrolyte to the second region can be further improved through the first region, which has a high inorganic particle content. However, because the separator is fabricated in a long strip shape along the machine direction during the separator fabrication process, it is preferable to form the first region only on both opposing edges of the second region to facilitate the process and reduce the separator's overall weight.

[0067] In a specific embodiment of the present invention, the second region may be disposed in a rectangular shape inside the surface of the polymer-based material, and the first region may have units disposed on one side and the other side opposite the first region, respectively, and the first region may not be disposed on the remaining two sides. When the first region is disposed in this manner, direct inflow of the electrolyte into the second region from the side of the second region where the first region is not disposed is promoted, and the use of such a separator can reduce the internal resistance of the electrode assembly.

[0068] According to another aspect of the present invention, there is provided a method for producing the separation membrane.

[0069] 2 is a schematic diagram illustrating a process for manufacturing a separation membrane according to an embodiment of the present invention, and a method for manufacturing a separation membrane will be described with reference to this figure.

[0070] Referring to FIG. 2, the separator may be manufactured by a continuous process using a roll-to-roll method. A long strip of polymer substrate 110 is continuously supplied by a traveling roll of a roll-to-roll device, and a coating layer-forming slurry is applied to the surface of the polymer substrate. The application of the slurry may be performed using a conventional coating device 300 such as a slot die. Meanwhile, the slurry may be divided into a slurry for forming the first region and a slurry for forming the second region, and each slurry may be prepared by adding inorganic particles and a binder material to an appropriate solvent.

[0071] After each slurry is prepared, the first region forming slurry is applied to both ends of the polymer substrate in the transverse direction TD, which is perpendicular to the running direction MD, and the second region forming slurry is applied between the two portions of the first region. The first region forming slurry and the second region forming slurry may be applied simultaneously using a double slot die, or may be applied by applying the first region forming slurry or the second region forming slurry first and then sequentially applying the remaining slurries. For example, the first region forming slurry may be applied to both ends of the polymer substrate in the width direction, and the second region forming slurry may be applied to a predetermined width inside the region where the first region slurry was continuously applied.

[0072] The applied slurry is then dried to obtain a separation membrane strip having a composite coating layer having a first region and a second region. The drying can be performed by passing the strip through a dryer 500 using heat or air. The separation membrane strip is then cut to a predetermined width using a cutter 400 or the like to obtain a separation membrane. In this case, the obtained separation membrane has the side surfaces of the second region exposed at both ends in the running direction of the polymer substrate.

[0073] In one embodiment of the present invention, after forming the porous coating layer on one side of the porous polymer substrate, a porous coating layer may be sequentially formed on the other side of the porous polymer substrate, or porous coating layers may be simultaneously formed on both sides of the porous polymer substrate by other means. The separator strip is then slit to a desired length to obtain a long strip of separator for application to a cylindrical battery cell. This results in a separator having first regions disposed at both ends of the outermost long side of the porous coating layer and a second region disposed between two portions of the first regions.

[0074] FIG. 3 is a schematic diagram illustrating a process for manufacturing a separator according to another embodiment of the present invention.

[0075] Referring to FIG. 3, a method for manufacturing a separator according to an embodiment of the present invention is as follows.

[0076] First, a long, unslit strip of porous polymer substrate 120 is prepared. A slurry for forming a first region and a slurry for forming a second region, each containing inorganic particles and a binder material and having different inorganic particle contents, are prepared. Then, one or both sides of the porous polymer substrate are coated with the first and second regions, such that the first regions 122 are disposed at both ends of the outermost lateral direction and the second regions 121 and 122 are alternately disposed between two portions of the first regions, and then dried to form a porous coating layer 120. The porous polymer substrate is then slit to a width required to assemble the desired battery cell, ultimately obtaining a separator including a porous coating layer partitioned into first regions with a high inorganic particle content at both ends of the outermost lateral direction of the separator and second regions with a low inorganic particle content between two portions of the first regions.

[0077] According to another aspect of the present invention, there is provided an electrochemical device, the separator for an electrochemical device being interposed between a positive electrode and a negative electrode. In one embodiment of the present invention, the electrochemical device may be a lithium ion secondary battery.

[0078] In one embodiment of the present invention, the electrochemical device may be fabricated by injecting a non-aqueous electrolyte solution, if necessary, into an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In this case, the positive electrode, the negative electrode, and the non-aqueous electrolyte solution constituting the electrode assembly may be those commonly used in the manufacture of lithium secondary batteries.

[0079] In one embodiment of the present invention, the electrochemical device may be a cylindrical battery cell.

[0080] In one embodiment of the present invention, the cylindrical battery cell includes a jelly-roll-type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction; a battery can in which the electrode assembly is housed; and a seal that seals an open end of the battery can, wherein the separator is the separator described above.

[0081] In one embodiment of the present invention, the cylindrical battery cell may be a large cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter Φ to the height H of a cylindrical battery, i.e., the diameter Φ divided by the height H) of about 0.4 or more.

[0082] In one embodiment of the present invention, the cylindrical battery cell may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 48750 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.418), a 48800 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), a 46800 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575), or a 46950 cell (diameter 46 mm, height 95 mm, form factor ratio 0.484). In the form factor number, the first two digits indicate the cell diameter, the next two digits indicate the cell height, and the final digit 0 indicates that the cell has a circular cross section.

[0083] In one embodiment of the present invention, the electrode assembly may be a jelly-roll type electrode assembly having a structure in which sheet-shaped first and second electrode plates and a separator interposed therebetween are wound in one direction, and in this case, the separator may be the separator described above.

[0084] The first electrode plate and the second electrode plate may each be a positive electrode or a negative electrode, and the configuration of the electrode assembly will be described below.

[0085] In one embodiment of the present invention, the positive electrode may be manufactured by forming a positive electrode mixture layer on a positive electrode current collector, which may be formed by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent onto the positive electrode current collector, followed by drying and rolling.

[0086] In a specific embodiment of the present invention, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like.

[0087] In a specific embodiment of the present invention, the positive electrode active material may be a compound capable of reversible intercalation and diintercalation of lithium (lithiated intercalation compound).

[0088] In one embodiment of the present invention, the positive electrode active material may include, but is not limited to, lithium transition metal oxides, lithium metal iron phosphates, lithium nickel-manganese-cobalt oxides, oxides in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal, or two or more of these. Specifically, the positive electrode active material may include, but is not limited to, layered compounds such as lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), or compounds substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3). 2-x M x Lithium manganese composite oxides represented by Li2Mn3MO8 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1); lithium metal phosphate oxides represented by LiMPO4 (where M is Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxides represented by Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); 1+x (Ni a Co b Mn c ) 1-x O2 (x=0~0.03, a=0.3~0.95, b=0.01~0.35, c=0.01~0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, in which a portion of the oxide is replaced by aluminum a [Ni b Co c Mn d Al e ] 1-f M1 fO2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1); an oxide in which a part of lithium nickel-manganese-cobalt oxide is substituted with another transition metal, Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo.). Disulfide compounds; Fe2(MoO4)3 and the like can be mentioned, but are not limited thereto.

[0089] In a specific embodiment of the present invention, the positive electrode may further optionally contain a conductive material. The conductive material may be porous. Thus, as long as the conductive material has porosity and conductivity, it can be used without limitation. For example, a porous carbon-based substance can be used. As such a carbon-based substance, carbon black, graphite, graphene, activated carbon, carbon fiber, carbon nanotube (CNT), etc. can be used. Also, as the conductive material, metal conductive materials such as metal fibers and metal meshes; metal powders such as copper, silver, nickel, and aluminum; or organic conductive materials such as polyphenylene derivatives can also be used. The conductive material can be used alone or in combination.

[0090] In a specific embodiment of the present invention, the positive electrode may further include a binder, which may be a thermoplastic resin or a thermosetting resin. More specifically, the binder may be polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or the like, which may be used alone or in combination, but is not necessarily limited to these, and any binder usable in the relevant technical field may be used.

[0091] In one specific embodiment of the present invention, the positive electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the solid content in the positive electrode slurry.

[0092] In one specific embodiment of the present invention, the solvent used in the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that results in a desired viscosity when the positive electrode active material and, optionally, a binder and a conductive material are included. For example, the solvent may be included so that the solids concentration in the slurry containing the positive electrode active material and, optionally, a binder and a conductive material is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0093] In one specific embodiment of the present invention, the positive electrode may be manufactured by mixing a positive electrode active material, an optional conductive material, and an optional binder to prepare a composition for forming a positive electrode active material layer, applying the composition to at least one surface of the positive electrode current collector, drying, and rolling. Alternatively, the positive electrode may be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, peeling it off from the support, and laminating the resulting film on the positive electrode current collector.

[0094] In one embodiment of the present invention, the negative electrode may be manufactured by forming a negative electrode mixture layer on a negative electrode current collector. The negative electrode mixture layer may be formed by coating a negative electrode current collector with a negative electrode slurry including a negative electrode active material, a binder, a conductive material, and a solvent, followed by drying and rolling.

[0095] In a specific embodiment of the present invention, the negative electrode active material may include lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of such a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, a transition metal oxide, or a mixture of two or more of these.

[0096] As an example of the negative electrode active material, the carbonaceous material capable of reversibly intercalating / deintercalating lithium ions may be any carbonaceous negative electrode active material commonly used in lithium ion secondary batteries, and representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous graphite, such as natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0097] As an example of the negative electrode active material, as the metal or an alloy of these metals and lithium, Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, or a mixture of two or more of these, or an alloy of these metals and lithium can be used.

[0098] As an example of the negative electrode active material, as the metal composite oxide, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≦x≦1), Li x WO2(0≦x≦1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), or a mixture of two or more of these can be used.

[0099] As an example of the negative electrode active material, as the material capable of doping and undoping lithium, Si, SiO x (0 < x ≦ 2), Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a mixture of two or more of these and is not Si), Sn, SnO2, Sn-Y (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element, or a mixture of two or more of these and is not Sn), etc. can be mentioned, and at least one of these can be mixed with SiO2 and used. The element Y can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a mixture of two or more of these.

[0100] Examples of the negative electrode active material include the transition metal oxide, such as lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

[0101] In one embodiment of the present invention, the negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of solids in the negative electrode slurry.

[0102] In one embodiment of the present invention, the negative electrode may optionally further include a binder. The binder is a component that aids in bonding between the active material and the current collector, or between the active material, the conductive material, and the current collector. The binder is typically added in an amount of 1 to 30 wt % based on the total weight of the solids in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0103] In a specific embodiment of the present invention, the negative electrode may optionally further include a conductive material. The conductive material is a component for further improving the conductivity of the negative electrode active material. When included, the conductive material may be added in an amount of 1 to 20 wt % based on the total weight of the solids in the negative electrode slurry. This conductive material may be the same as or different from the conductive material used in manufacturing the positive electrode. For example, carbon powders such as carbon black, acetylene black (or denka black), ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0104] In one embodiment of the present invention, the solvent used in the negative electrode slurry may include water or an organic solvent such as NMP or alcohol, and may be used in an amount that results in a desired viscosity when the negative electrode active material and, optionally, a binder and a conductive material are included. For example, the solvent may be included so that the solids concentration in the slurry containing the negative electrode active material and, optionally, a binder and a conductive material is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0105] In a specific embodiment of the present invention, when a non-aqueous electrolyte is used, the non-aqueous electrolyte may include a lithium salt and an organic solvent, and may further include additives commonly used in the art.

[0106] In one embodiment of the present invention, the lithium salt has Li as a cation. + Contains F as an anion - , Cl - , Br - , I - , NO3 - , N(CN)2 - , ClO4 - , BF4 -, AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - Or it may contain a mixture of two or more of these.

[0107] In one embodiment of the present invention, the lithium salt may be used alone or in combination of two or more kinds as needed. The lithium salt may be appropriately varied within a range that is normally usable, and may be contained in the non-aqueous electrolyte at a concentration of 0.01M to 5M, or 0.1M to 5M, or 0.1M to 3M.

[0108] In a specific embodiment of the present invention, the organic solvent is not limited as long as it minimizes decomposition due to oxidation during the charge / discharge process of the secondary battery and exhibits the desired properties together with the additives. For example, ether-based solvents, ester-based solvents, and amide-based solvents may be used alone or in combination.

[0109] In a specific embodiment of the present invention, the ether solvent among the organic solvents may be, but is not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, or a mixture of two or more thereof.

[0110] In one embodiment of the present invention, the ester solvent may include a cyclic carbonate compound, a linear carbonate compound, a linear ester compound, a cyclic ester compound, or a mixture of two or more thereof.

[0111] In one embodiment of the present invention, specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, fluoroethylene carbonate (FEC), and mixtures of two or more thereof.

[0112] In one embodiment of the present invention, specific examples of the linear carbonate compound include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, or a mixture of two or more thereof.

[0113] In one embodiment of the present invention, specific examples of the linear ester compound include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, or a mixture of two or more thereof.

[0114] In one embodiment of the present invention, specific examples of the cyclic ester compound include, but are not limited to, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, ε-caprolactone, or a mixture of two or more thereof.

[0115] In one embodiment of the present invention, the cyclic carbonate-based compound is a high-viscosity organic solvent with a high dielectric constant, which facilitates dissociation of the lithium salt in the electrolyte. Therefore, by mixing the cyclic carbonate-based compound with a linear carbonate-based compound and a linear ester-based compound, each of which has a low viscosity and a low dielectric constant, such as dimethyl carbonate or diethyl carbonate, in an appropriate ratio, a nonaqueous electrolyte solution having high electrical conductivity can be prepared.

[0116] A separator for a lithium secondary battery according to one aspect of the present invention effectively transports lithium ions and reduces side reactions between the separator for a lithium secondary battery containing an ion-conductive polymer material and the interface of an electrode, thereby significantly reducing the rate of increase in initial resistance inside the battery. As a result, a battery using the separator has improved power density characteristics and reduced irreversible capacity, thereby improving rate-limiting characteristics, thereby shortening the time required for charging or discharging the battery and improving charge / discharge life. Therefore, the separator is useful in portable devices that require fast charging speeds, such as mobile phones, laptops, digital cameras, and camcorders, electric vehicles such as hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), and medium- to large-scale energy storage systems.

[0117] In particular, the separator having the porous coating layer as described above has improved heat resistance at both outermost ends, making it useful for large cylindrical battery cells.

[0118] In order to facilitate understanding of the present invention, examples, comparative examples, and experimental examples are disclosed below. However, the following experimental examples are merely examples relating to the configuration and effects of the present invention, and the scope and effects of the present invention are not limited thereto.

[0119] [Separation membrane manufacturing] Example 1 PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 22.5:77.5 to prepare a first region forming slurry with a solid content of 20 wt%.

[0120] Next, PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 25:75 to prepare a slurry for forming a second region with a solid content of 20 wt%.

[0121] A polyethylene polymer film (thickness 9 μm, porosity 45 vol%, ventilation time 60 sec / 100 cc) was prepared, and the slurry for forming the first region and the slurry for forming the second region were applied sequentially as shown in Figure 1. The separation membrane was obtained by drying under humidified conditions of 23°C and a relative humidity of 45%. The total width of the separation membrane was 200 mm, and the width of the first region on both sides was 60 mm each.

[0122] Example 2. PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 20:80 to prepare a first region forming slurry with a solid content of 20 wt%.

[0123] Next, PVDF-HFP (molecular weight Mw 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 25:75 to prepare a slurry for forming a second region with a solid content of 20 wt%.

[0124] A polyethylene polymer film (thickness 9 μm, porosity 45 vol%, ventilation time 60 sec / 100 cc) was prepared, and the slurry for forming the first region and the slurry for forming the second region were applied sequentially as shown in Figure 1. The separation membrane was obtained by drying under humidified conditions of 23°C and a relative humidity of 45%. The total width of the separation membrane was 200 mm, and the width of the first region on both sides was 60 mm each.

[0125] Example 3 PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 5:95 to prepare a first region forming slurry with a solid content of 20 wt%.

[0126] Next, PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 25:75 to prepare a slurry for forming a second region with a solid content of 20 wt%.

[0127] A polyethylene polymer film (thickness 9 μm, porosity 45 vol%, ventilation time 60 sec / 100 cc) was prepared, and the slurry for forming the first region and the slurry for forming the second region were applied sequentially as shown in Figure 1. The separation membrane was obtained by drying under humidified conditions of 23°C and a relative humidity of 45%. The total width of the separation membrane was 200 mm, and the width of the first region on both sides was 60 mm each.

[0128] Comparative Example 1 PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 1 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 25:75 to prepare a slurry for forming a coating layer with a solid content of 20 wt%.

[0129] A polyethylene polymer film (thickness 9 μm, porosity 45 vol%, ventilation time 60 sec / 100 cc) was prepared, the slurry was applied, and the film was dried under humidified conditions of 23°C and 45% relative humidity to obtain a separation membrane. The total width of the separation membrane was 200 mm.

[0130] Comparative Example 2 PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 25:75 to prepare a first region forming slurry with a solid content of 20 wt%.

[0131] Next, PVDF-HFP (molecular weight Mw: 500,000 g / mol, HFP content: 15 wt%) and alumina (particle size 0.5 μm) were added to acetone in a weight ratio of 5:95 to prepare a slurry for forming a second region with a solid content of 20 wt%.

[0132] A polyethylene polymer film (thickness 9 μm, porosity 45 vol%, ventilation time 60 sec / 100 cc) was prepared, and the slurry for forming the first region and the slurry for forming the second region were applied sequentially as shown in Figure 1. The separation membrane was obtained by drying under humidified conditions of 23°C and a relative humidity of 45%. The total width of the separation membrane was 200 mm, and the width of the first region on both sides was 60 mm each.

[0133] [Evaluation of separation membrane properties] The physical properties of the separation membrane prepared above were evaluated according to the following evaluation methods, and the results are shown in Table 1 below and FIGS.

[0134] Evaluation method heat resistance The prepared separator was prepared to a length of 200 mm and a width of 200 mm, and dots were marked at intervals of 20 mm in both the horizontal and vertical directions. The separator was then placed in an oven at 130°C for 30 minutes, and the change in the spacing between the dots was observed.

[0135] The change in the distance between the first and second regions was measured in both the longitudinal and width directions, and then the shrinkage rate of the separator was calculated according to the following equation.

[0136] In the formula below, the "distance between points" was measured using a ruler on the sample after it had been left in the oven. The measurements were carried out on both the first and second regions, and the shrinkage rate was calculated from the average value of the measurements in each region. Shrinkage rate (%) = [(20 mm - distance between points in mm) / 20 mm] x 100

[0137] Ventilation time The air permeability of the separator was measured using an air permeability meter (Asahi Seiko, EGO-IT) according to JIS P 8117. To measure the air permeability of the first and second regions, the separator was manufactured and then divided into the first and second regions using a knife to obtain a sample for measuring the air permeability time.

[0138] Electrode adhesive strength The active material [natural graphite and artificial graphite (weight ratio 5:5)], conductive material [Super P], and binder [polyvinylidene fluoride (PVdF)] were mixed in a weight ratio of 92:2:6, dispersed in water, and then coated onto copper foil with a width of 250 mm to prepare the negative electrode.

[0139] Separation membranes were prepared as in Examples 1 to 3 and Comparative Examples 1 and 2.

[0140] The prepared separation membrane was divided into a first region and a second region using a knife.

[0141] The prepared separator and negative electrode were stacked on top of each other, sandwiched between 100 μm PET films, and bonded using a roll lamination device at 60°C, 2.4 kgf / mm pressure, and 5 m / min speed.

[0142] The bonded separator and anode were cut into a size of 25 mm wide and 70 mm long, and the ends of the separator and anode were attached to a UTM device (Instron). A force was applied at a 180° angle at a measurement speed of 300 mm / min to measure the force required to separate the separator from the anode.

[0143] As can be seen from Table 1, when the separators of Example 3 and Comparative Example 2 were used, the electrode assembly state was found to be unsuitable for the evaluation of electrolyte wettability due to poor adhesion in the second region or the first region, respectively, and therefore the results of the electrolyte wettability evaluation were omitted.

[0144] Checking the wettability of the electrolyte (1) Manufacturing of the negative electrode Anode slurry was prepared by mixing artificial graphite as the anode active material, carbon black as the conductive material, carboxymethyl cellulose (CMC) as the dispersant, and styrene-butadiene rubber (SBR, Zeon BM-L301) as the binder with water in a weight ratio of 95.8:1:1.2:2. The anode slurry was coated onto copper foil to a thickness of 50 μm to form a thin electrode plate, which was then dried at 135°C for at least 3 hours and pressed to prepare the anode.

[0145] (2) Manufacturing of the positive electrode A cathode slurry was prepared by mixing LiCoO2 as a cathode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder with N-methyl-2-pyrrolidone (NMP) in a weight ratio of 98:1:1. The cathode slurry was coated onto aluminum foil to a thickness of 20 μm to form a thin electrode plate, which was then dried at 135°C for at least 3 hours and pressed to prepare a cathode.

[0146] (3) Manufacture of lithium secondary batteries Next, the separator thus prepared was interposed between the negative electrode and the positive electrode, and then the electrodes were stacked to prepare a stacked electrode assembly. The stacked electrode assembly was then inserted into a pouch outer casing, and an electrolyte solution of 1M LiPF6 dissolved in a solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 30:70 was injected to prepare a lithium secondary battery.

[0147] The secondary battery fabricated as described above was disassembled at SOC 60 to observe wetting on the negative electrode surface. When wetting was good, a uniform charging state was observed across the entire negative electrode surface (FIGS. 4 and 5). However, when wetting was poor, dark, uncharged areas were observed on the negative electrode surface (FIG. 6).

[0148] Evaluation results [Table 1]

[0149] [Table 2]

[0150] As can be seen from the above results, it was confirmed that the heat resistance of the side portions of the separator was improved by providing the first regions with a high content of inorganic particles on both sides of the separator.

[0151] Therefore, when such a separator is applied to a jelly-roll type electrode assembly and used in a cylindrical battery, it is expected to effectively alleviate the problem of internal short circuits caused by shrinkage at both ends of the separator.

[0152] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is of course possible for a person skilled in the art to which the present invention pertains to make various modifications and variations within the technical spirit of the present invention and the equivalent scope of the following claims. [Explanation of symbols]

[0153] 100 separation membrane 110 Porous polymer substrate 120 Porous coating layer 121 Second area 122 1st area 300 Coating Equipment 400 Cutter 500 dryer

Claims

1. A separation membrane, The separation membrane includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate; the porous coating layer is divided into a first region disposed at both ends of the outermost portion of the separator in the width direction and a second region disposed between two portions of the first region; the first region and the second region each independently comprise inorganic particles and a binder material, and a content ratio of the inorganic particles in the first region according to the following formula 1 is higher than a content ratio of the inorganic particles in the second region according to the following formula 2: [Formula 1] Content ratio of inorganic particles in the first region (wt %)=[amount of inorganic particles in the first region / (amount of inorganic particles in the first region+amount of binder material in the first region)]×100 [Formula 2] Content ratio (wt %) of inorganic particles in second region=[amount of inorganic particles in second region / (amount of inorganic particles in second region+amount of binder material in second region)]×100

2. 2. The separator for an electrochemical device according to claim 1, wherein the porosity of the first region of the porous coating layer is higher than the porosity of the second region.

3. 2. The separator for an electrochemical device according to claim 1, wherein the content ratio of the inorganic particles in the second region is lower than the content ratio of the inorganic particles in the first region and is 96 wt % or less.

4. 2. The separator for an electrochemical device according to claim 1, wherein the content ratio of the inorganic particles in the first region is higher than the content ratio of the inorganic particles in the second region, and is 70 wt % to 98 wt %.

5. 2. The separator for an electrochemical device according to claim 1, wherein the width of one of the first regions is 5 to 35% of the entire width of the porous coating layer.

6. A method for producing the separation membrane according to any one of claims 1 to 5, comprising: The method is carried out by a roll-to-roll process in which a long strip of porous polymeric substrate is continuously supplied; a first region having a predetermined width at both ends of the porous polymer substrate in a transverse direction TD perpendicular to a running direction MD of the porous polymer substrate, and a second region between two portions of the first region, on at least one surface of the porous polymer substrate, thereby obtaining a separation membrane strip including a composite porous coating layer having the first region and the second region.

7. 7. The method of claim 6, wherein the first and second regions are formed by applying a slurry for forming the first region and a slurry for forming the second region to respective partitioned portions using a double slot die.

8. cutting the separation membrane strip to a predetermined length to obtain a separation membrane; The method for manufacturing a separation membrane according to claim 6, wherein the obtained separation membrane has side surfaces of the second region exposed at both ends in the MD direction of the porous polymer substrate.

9. A jelly-roll type electrode assembly having a structure in which sheet-shaped first and second electrode plates and a separator interposed between the first and second electrode plates are wound in one direction, An electrode assembly, wherein the separator is the separator according to any one of claims 1 to 5.

10. a jelly-roll type electrode assembly having a structure in which a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate are wound in one direction; a battery can in which the electrode assembly is housed; and a seal that seals an open end of the battery can, A cylindrical battery cell, characterized in that the separator is the separator according to any one of claims 1 to 5.

11. The cylindrical battery cell according to claim 10 , wherein the cylindrical battery cell has a form factor ratio of 0.4 or greater.

12. 11. The cylindrical battery cell according to claim 10, wherein the cylindrical battery cell is a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, a 46800 cell, or a 46950 cell.

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