Separator for electrochemical element, electrode assembly including the same, and secondary battery

Abstract

The present invention relates to a separator for an electrochemical device, an electrode assembly including the same, and a secondary battery. According to an embodiment of the present invention, there is provided a separator for an electrochemical device, comprising: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer including a binder polymer and inorganic particles, The thickness of both ends of the separator in a transverse direction (TD) is greater than the thickness of the central portion of the separator in the TD. The separator according to the present invention can prevent the phenomenon of insufficient adhesive strength at both TD ends during adhesion between the separator and the electrode by adjusting the thickness at both TD ends of the separator, thereby exhibiting uniform adhesive strength.

Description

Technical Field

[0001] The present invention relates to a separator for an electrochemical element, an electrode assembly including the same, and a secondary battery.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0133515 filed on October 7, 2021, and all of the contents disclosed in the specification and drawings of the application are incorporated into this application.

Background Art

[0003] Rechargeable secondary batteries have been in the spotlight as an alternative to fossil energy. Secondary batteries have mainly been used in traditional handheld devices such as mobile phones, video cameras, and power tools. However, recently, their application fields have been increasingly expanding to electrically driven vehicles (electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs)), large-capacity energy storage systems (ESSs), uninterruptible power supply devices (UPSs), and the like.

[0004] A secondary battery includes a positive electrode, a negative electrode, and an electrode assembly including a separator sandwiched therebetween, and an electrolyte that electrochemically reacts with the active materials coated on the positive electrode and the negative electrode. A representative example thereof is a lithium-ion secondary battery in which lithium ions act as working ions during charging and discharging to induce electrochemical reactions at the positive electrode and the negative electrode. In existing lithium-ion secondary batteries, lamination is applied during the assembly process to achieve the adhesive force between the electrodes and the separator in the electrode assembly. Lamination is a process of bonding the separator and the electrode. Lamination is a process of applying pressure to the separator and the electrode laminated one above the other and heating them for adhesion, and as a result, attempting to increase the adhesive force between the separator and the electrode.

[0005] Generally, an electrode, which is either a positive electrode or a negative electrode, is manufactured by applying an active material slurry onto a current collector and then drying it. However, when the active material slurry is applied onto the current collector, a sliding phenomenon occurs where the active material slurry flows towards both ends in the TD (Transverse Direction). For this reason, an active material layer with a thickness that gradually becomes thinner as it progresses towards both ends in the TD is formed.

[0006] Regarding this, FIG. 1 shows a structure in which a normal electrode and a separator are laminated. As is clear from FIG. 1, the separator 1 includes a porous coating layer 12 having a certain thickness on at least one surface of the porous polymer base material 11, and the electrode 2 includes an active material layer 22 on at least one surface of the current collector 21. The active material layer 22 has a thickness that gradually becomes thinner as it progresses towards both ends in the TD. For this reason, due to the insufficient thickness at both ends in the TD of the electrode, there has been a problem that even when the separator and the electrode are laminated, the adhesive force at both ends in the TD appears particularly low. In severe cases, there has been a problem that the phenomenon of the separator and the electrode floating without being adhered occurs.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been devised in view of the above circumstances, and aims to provide a separator for an electrochemical element that prevents the phenomenon of insufficient adhesive force occurring at both ends in the TD during the adhesion of the separator and the electrode, and exhibits a uniform adhesive force throughout the interface between the separator and the electrode.

[0008] Furthermore, the present invention aims to provide an electrode assembly and a secondary battery including the separator.

[0009] It will be easily understood that other objects and advantages of the present invention can be realized by the means and methods shown in the claims, and combinations thereof.

Means for Solving the Problems

[0010] The inventors have obtained the finding that the above object can be achieved by the following separator for an electrochemical element, an electrode assembly including the same, and a secondary battery.

[0011] A first aspect relates to a separator for an electrochemical element, wherein the separator includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a binder polymer and inorganic particles. The separator is characterized in that the thicknesses of both TD (transverse direction) end portions of the separator are further thicker than the thickness of the TD central portion.

[0012] A second aspect relates to the separator according to the first aspect, wherein the thicknesses of both TD end portions of the separator are 5 to 100% thicker than the thickness of the TD central portion.

[0013] A third aspect relates to the separator according to the first aspect or the second aspect, wherein both TD end portions of the separator include a region in which the thickness gradually increases along the direction away from the TD central portion.

[0014] A fourth aspect relates to the separator according to any one of the first aspect to the third aspect, wherein the length of one of the end portions of both end portions of the separator is 0.1 to 10% of the total length in the width direction of the separator.

[0015] A fifth aspect relates to an electrode assembly including a current collector and an electrode including an active material layer located on at least one surface of the current collector, and a separator located on at least one surface of the electrode, The separator includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a binder polymer and inorganic particles. It relates to an electrode assembly in which the thicknesses of both TD ends of the separator are further thicker than the thickness of the TD central part.

[0016] A sixth aspect is the electrode assembly according to the fifth aspect, wherein It relates to an electrode assembly characterized in that the thicknesses of both TD ends of the separator are 5 to 100% thicker than the thickness of the TD central part.

[0017] A seventh aspect is the electrode assembly according to the fifth aspect or the sixth aspect, wherein Both TD ends of the separator It relates to an electrode assembly characterized by having a shape corresponding to both TD ends of the active material layer.

[0018] An eighth aspect is the electrode assembly according to any one of the fifth to seventh aspects, wherein Both TD ends of the separator include a region where the thickness gradually increases along the direction away from the TD central part, It relates to an electrode assembly characterized in that both TD ends of the active material layer include a region where the thickness gradually decreases along the direction away from the TD central part.

[0019] A ninth aspect is the electrode assembly according to any one of the fifth to eighth aspects, wherein It relates to an electrode assembly in which the length of one end of both TD ends of the separator is 0.1 to 10% of the total length in the width direction of the separator.

[0020] A tenth aspect relates to a secondary battery including the electrode assembly according to any one of the fifth to ninth aspects.

[0021] An eleventh aspect is the secondary battery according to the tenth aspect, wherein The present invention relates to a secondary battery, characterized in that the secondary battery is a lithium secondary battery.

Advantages of the Invention

[0022] The separator for an electrochemical element, the electrode assembly including the same, and the secondary battery according to the present invention have a structure in which the thicknesses of both TD ends of the separator are adjusted according to the thicknesses of both TD ends of the electrode active material. Therefore, when the separator and the electrode are adhered, it is possible to prevent the phenomenon of insufficient adhesive force occurring at both TD ends, and to exhibit a uniform adhesive force over the entire interface between the separator and the electrode.

[0023] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention to be described later. Therefore, the present invention should not be construed as being limited only to the matters described in such drawings. On the other hand, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated for the purpose of emphasizing a clearer explanation.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0025] Hereinafter, the present invention will be described in detail. Terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. Instead, in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain the invention in the best way, they must be construed in accordance with the meaning and concept corresponding to the technical idea of the present invention.

[0026] Throughout this specification, when a part describes a certain component as "including" or "comprising", this means that, unless otherwise specified, it does not exclude other components, and it may further include or comprise other components.

[0027] Also, throughout this specification, the phrase "about" is used to mean at or near that numerical value when manufacturing and material tolerances specific to the recited meaning are presented, and is used to prevent an infringer from improperly using the disclosed content where an exact or absolute numerical value is recited to the detriment of understanding the present invention.

[0028] Throughout this specification, the description "A and / or B" means "A or B or both of them".

[0029] The present invention relates to a separator for an electrochemical element, an electrode assembly including the same, and a secondary battery.

[0030] Separator for electrochemical element

[0031] In the present invention, an electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, encompassing all elements that undergo electrochemical reactions. Specific examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor elements. In particular, the electrochemical device according to the present invention can be a secondary battery, and among the secondary batteries, it can be a lithium secondary battery that encompasses lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries, etc.

[0032] In the present invention, the separator may include a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate.

[0033] The separator of the present invention has a shape in which the thicknesses of both TD ends of the separator are even thicker than the thickness of the TD central portion. For example, the thicknesses of both TD ends of the separator may be generally 5 to 100%, or generally 10 to 50% thicker than the thickness of the TD central portion. Alternatively, both TD ends of the separator may include a region where the thickness gradually increases along the direction away from the TD central portion. In the present invention, by setting the thicknesses of both TD ends of the separator to be even thicker than the thickness of the TD central portion, the phenomenon of insufficient adhesive force appearing at both TD ends can be improved, and sufficient adhesive force can be ensured during the lamination of the separator and the electrode.

[0034] In the present invention, TD (Transverse Direction) means the width direction of the separator, that is, the direction perpendicular to the MD (Machine Direction), which is the longitudinal direction of the separator.

[0035] Specifically, in the present invention, in order to set the thicknesses of both TD ends of the separator to be even thicker than the thickness of the TD central portion, for example, while keeping the thickness of the porous polymer base material constant overall, the thicknesses of both TD ends of the porous coating layer may be set to be even thicker than the thickness of the TD central portion. For example, the thicknesses of both TD ends of the porous coating layer may be generally 10 to 150%, or generally 30 to 80% thicker than the thickness of the TD central portion. Alternatively, both TD ends of the porous coating layer may include a region where the thickness gradually increases along the direction away from the TD central portion.

[0036] In order to set the thicknesses of both TD ends of the porous coating layer to be even thicker than the thickness of the TD central portion, for example, the process of coating the porous coating layer on at least one surface of the porous polymer base material may be adjusted. Specifically, the design of the coating bar that can be used when coating the porous coating layer may be adjusted to adjust the thickness of each region of the porous coating layer.

[0037] Generally, in order to apply a slurry to form a porous coating layer on at least one surface of a porous polymer base material, first, after supplying the slurry to a coating bar, the coating bar may contact one surface of the porous polymer base material and rotate while the slurry is transferred to the porous polymer base material. The coating bar may be a wire bar in which a wire is wound around a cylindrical bar, and the slurry may be accommodated between adjacent wires and transferred to and coated on the porous polymer base material. The slurry transferred in this way is applied while being filled into the empty spaces in the pattern due to its fluidity, whereby a porous coating layer having an overall generally uniform thickness can be formed.

[0038] For example, as another method of applying the slurry, after applying the slurry to at least one surface of the porous polymer substrate, a predetermined coating bar is brought into contact with one surface of the porous polymer substrate and rotated to form a porous coating layer having a substantially uniform thickness. However, in the present invention, the method of applying the slurry to form the porous coating layer is not limited by the above description.

[0039] In the present invention, in order to adjust the thickness of each region of the porous coating layer, the design of the cylindrical bar and the wire may be adjusted. For example, in the present invention, the diameter of both ends of the cylindrical bar may be smaller than the diameter of the central portion. Also, the wire diameter of the wire wound around both ends of the cylindrical bar may be larger than the wire diameter of the wire wound around the central portion of the cylindrical bar. Thereby, since the amount of the coating liquid accommodated between the wires wound around both ends of the cylindrical bar is larger than that between the wires wound around the central portion of the cylindrical bar, the thickness of both ends of the porous coating layer can be adjusted.

[0040] In the present invention, the TD both ends of the separator mean both terminal ends in the width direction of the separator. Note that the TD both ends of the separator may also mean a portion corresponding to a portion where the thickness of the active material layer of the electrode becomes thin.

[0041] Specifically, the length of one of the two end portions of the separator may be approximately 0.1 to 10%, or approximately 0.2 to 5% of the total length in the width direction of the separator. By setting the end portion to have the length within the above range, it is possible to prevent the phenomenon that the adhesive force with the electrode becomes weak and exhibit a uniform adhesive force at all interfaces where the electrode and the separator are in contact. Also, if the content of the binder resin is increased or a separate adhesive layer is formed to ensure the adhesive force between the separator and the electrode, the resistance of the battery cell may increase or the thickness of the separator may increase, resulting in a loss in terms of the capacity of the battery cell. However, by forming only the TD both end portions of the separator thicker than the TD central portion, no loss occurs in terms of the capacity of the secondary battery.

[0042] FIG. 2 is a cross-sectional view schematically showing a structure in which a separator 1 and an electrode 2 are laminated according to an embodiment of the present invention. FIG. 2 shows a structure in which a pair of separators are laminated with the electrode as a boundary, but a plurality of electrodes and / or separators may be laminated.

[0043] The separator in FIG. 2 is formed to include a structure in which the thickness gradually increases along the direction away from the central portion at both end portions.

[0044] In the present invention, the porous polymer substrate is a porous ion-conducting barrier that blocks electrical contact between the negative electrode and the positive electrode while allowing ions to pass through, and means a substrate in which a large number of pores are formed inside. The pores have a structure that is interconnected with each other, and gas or liquid can pass from one surface of the substrate to the other surface. From the viewpoint of providing a shutdown function, a porous polymer film containing a thermoplastic resin can be used as such a porous polymer substrate. Here, the shutdown function refers to a function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the battery rises. Non-limiting examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polybutylene, and polypentene. On the other hand, from the aspect of the shutdown function, the melting point of the thermoplastic resin is preferably generally less than 200°C.

[0045] The thickness of the porous polymer substrate is not particularly limited, but specifically, it is generally 1 to 100 μm, more specifically, generally 5 to 50 μm, or generally 5 to 30 μm. The pores present in the porous polymer substrate are also not particularly limited, but it is preferably generally 10 to 95%, or generally 35 to 65%.

[0046] The porous coating layer is formed on at least one surface of the substrate and may contain a binder resin and inorganic particles.

[0047] In the present invention, in the porous coating layer, the inorganic particles are filled and in contact with each other, and are bound to each other by the binder resin. As a result, interstitial volumes are formed between the inorganic particles, and the interstitial volumes between the inorganic particles may have a structure that forms pores as empty spaces.

[0048] Further, in the present invention, specifically, the weight ratio of the inorganic particles to the binder resin in the porous coating layer may be 99:1 to 50:50.

[0049] In the present invention, the binder resin is not particularly limited as long as it can provide the binding force between inorganic particles and the binding force between the porous coating layer and the electrode. For example, the binder resin may be polyvinylidene fluoride-co-hexafluoro propylene (PVDF-co-HFP), polyvinylidene fluoride-co-trichloro ethylene, polyvinylidene fluoride-co-chlorotrifluoro ethylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, poly-n-propyl (meth) acrylate, polyisopropyl (meth) acrylate, poly-n-butyl (meth) acrylate, poly-t-butyl (meth) acrylate, poly-sec-butyl (meth) acrylate, polypentyl (meth) acrylate, poly-2-ethylbutyl poly (meth) acrylate, poly-2-ethylhexyl (meth) acrylate, poly-n-octyl (meth) acrylate, polyisooctyl (meth) acrylate, polyisononyl (meth) acrylate, polylauryl (meth) acrylate, poly-tetradecyl (meth) acrylate, poly-N-vinylpyrrolidone, polyacrylonitrile, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionateIt may be any one or a mixture of two or more selected from the group consisting of propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide.

[0050] Also, the binder resin may be a particulate binder polymer resin. For example, it may be an acrylic copolymer, styrene butadiene rubber, or a mixture of any two or more thereof, and the acrylic copolymer may include a copolymer of ethylhexyl acrylate and methyl methacrylate, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, a copolymer of butyl acrylate and methyl methacrylate, or a mixture of two or more thereof.

[0051] In the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. For example, the inorganic particles are not particularly limited as long as no oxidation and / or reduction reaction occurs in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li+). Non-limiting examples include ZrO2, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti yO3(PLZT), Pb(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia (HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, AlOOH, Al(OH)3, SiC, or a mixture thereof, etc.). On the other hand, in addition to these, 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 -based glass (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), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or may further contain any two or more of these inorganic particles.

[0052] Electrode assembly

[0053] The electrode assembly according to the present invention includes an electrode and a separator located on one surface of the electrode.

[0054] In the present invention, the electrode assembly may be stacked in a stack type or a stack-folding type to form a secondary battery, or may be wound in a jelly-roll shape to form a secondary battery.

[0055] The battery case for housing the electrode assembly may exhibit various shapes, for example, it may be a pouch-type case, a cylindrical case or a rectangular case.

[0056] In the electrode assembly of the present invention, the electrode may include a current collector and an active material layer located on at least one surface of the current collector. The separator may include a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a binder polymer and inorganic particles. In the electrode assembly of the present invention, the separator is as described above.

[0057] Generally, an electrode is manufactured by applying an active material slurry on a current collector and then drying it. However, when an active material slurry is applied on a current collector, a sliding phenomenon occurs in which the active material slurry flows as it advances toward both ends in the TD direction. For this reason, an active material layer having a thickness that gradually becomes thinner as it advances toward both ends in the TD direction is formed. Therefore, when laminating with a separator using the electrode, there has been a problem that sufficient adhesive force cannot be ensured in the region where the sliding phenomenon of the active material slurry occurs. For this reason, in the present invention, an attempt is made to solve the above problem by adjusting the thickness of the separator.

[0058] In the present invention, the separator has a shape in which the thicknesses of both ends in the TD direction of the separator are even thicker than the thickness of the TD central portion. For example, the thicknesses of both ends in the TD direction of the separator may be generally 5 to 100% or generally 10 to 50% thicker than the thickness of the TD central portion.

[0059] Alternatively, the TD both ends of the separator of the present invention may have a shape corresponding to the TD both ends of the active material layer.

[0060] Alternatively, the TD both ends of the active material layer may include a region where its thickness gradually decreases along the direction away from the TD central part, and the TD both ends of the separator may include a region where its thickness gradually increases along the direction away from the TD central part.

[0061] In the present invention, the electrode may be a positive electrode and / or a negative electrode.

[0062] The positive electrode is manufactured, for example, by applying a mixture of a positive electrode active material, a conductive agent, and a binder on a positive electrode current collector and then drying it. If necessary, a filler may be further added to the mixture.

[0063] The positive electrode active material includes layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), compounds substituted with one or more transition metals, and general formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, lithium copper oxide (Li2CuO2), vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, and general formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3) of Ni-site type lithium nickel oxide, general formula LiMn 2-x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn), LiMn2O4 in which a part of the general formula Li is substituted with alkaline earth metal ions, disulfide compounds, and Fe2(MoO4)3, etc., but not limited thereto.

[0064] The positive electrode current collector generally has a thickness of approximately 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector can also form fine irregularities on its surface to enhance the adhesive force of the positive electrode active material, and various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc. can be used.

[0065] The conductive agent is usually added at approximately 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive agent is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite, carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride, aluminum, nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives can be used.

[0066] The binder is a component that assists in the bonding between the active material and the conductive agent, etc., and the bonding to the current collector, and is usually added at approximately 1 to 50% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc.

[0067] The filler is a component that suppresses the expansion of the positive electrode, is selectively used, does not induce a chemical change in the battery, and is not particularly limited as long as it is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene, and fibrous substances such as glass fiber and carbon fiber are used.

[0068] The negative electrode is produced by applying and drying a negative electrode material on a negative electrode current collector, and may further contain the components as described above as necessary.

[0069] The negative electrode current collector is generally produced to have a thickness of approximately 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Similar to the positive electrode current collector, fine irregularities can be formed on the surface to strengthen the adhesion of the negative electrode active material, and various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics can be used.

[0070] The negative electrode material is, for example, carbon such as graphitizable carbon and graphite-based carbon, and 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), etc. Metal composite oxides, lithium metal, lithium alloys, silicon-based alloys, tin-based alloys, metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, conductive polymers such as polyacetylene, and Li-Co-Ni-based materials can be used.

[0071] In addition, the present invention provides a secondary battery including the electrode assembly, a battery module including this as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include a power tool that operates by receiving power supply, an automobile that operates by receiving power supply such as an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV), etc., an electric two-wheeler including an E-bike and an E-scooter, an electric golf cart, and an energy storage system, etc., but are not limited thereto.

[0072] Hereinafter, in order to assist in the understanding of the present invention, the present invention will be described in more detail with reference to examples. However, the examples according to the present invention can be deformed into various other forms, and it should not be construed that the scope of the present invention is limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the industry.

[0073] Examples

[0074] Each example and comparative example was manufactured according to the following method. Hereinafter, the examples and comparative examples will be described with reference to FIG. 3, Table 1 and Table 2.

[0075] Example 1

[0076] A slurry was prepared by charging polyethylene porous base material (thickness: 9 μm, porosity: 45%), polyvinylidene fluoride as a binder polymer, alumina (Al2O3) as inorganic particles (particle diameter: 500 nm), and acetone as a solvent.

[0077] After applying the slurry to one surface of the porous base material using a coating bar, it was dried to produce a separator.

[0078] The coating bar used at this time has a structure as shown in FIG. 3. The coating bar 30 in FIG. 3 is in the shape of a wire 32 wound around a cylindrical bar 31, with a wire having a large wire diameter wound around both ends B1 and B2, and a wire having a small wire diameter wound around the central portion A.

[0079] The total length of the coating bar is 250 mm, the central portion A is 200 mm, and both ends B1 and B2 are each 25 mm. The outer diameter of the coating bar used is constant. The diameter of the cylindrical bar in the central portion A is 12.7 mm, the wire diameter of the wire wound around the cylindrical bar in the central portion A is 0.4 mm, the diameter of the cylindrical bar at both ends B1 and B2 is 12.5 mm, and the wire diameter of the wire wound around the cylindrical bar at both ends B1 and B2 is 0.5 mm.

[0080] Example 2 and Comparative Example 1, Comparative Example 2

[0081] A separator was manufactured in the same manner as in the method of Example 1. However, as described in Table 1 below, the slurry was coated by changing the diameters of the cylindrical bars at the central portion A and both ends B1 and B2 of the coating bar and the wire diameters wound thereon.

[0082] [Table 1]

[0083] [Table 2]

[0084] Specifically, the electrode adhesion force (Lami strength, gf / 25mm) was evaluated by the following method. The active material [natural graphite and artificial graphite (weight ratio 5:5)], the conductive material [super P], and the binder [polyvinylidene fluoride (PVdF)] were mixed at a weight ratio of 92:2:6, dispersed in water, and then coated on a copper foil with a width of 250 mm to produce a negative electrode.

[0085] As in Examples 1 to 2 and Comparative Examples 1 to 2, separators with a width of 250 mm were manufactured and prepared.

[0086] After the prepared separator and the negative electrode were overlapped, they were sandwiched between 100-μm polyethylene terephthalate (PET) films and then adhered using a roll lamination machine. At this time, the conditions of the roll lamination machine were set to a temperature of 60°C, a pressure of 2.4 kgf / mm, and a speed of 5 m / min for adhesion.

[0087] The central part A and both end parts B1 and B2 of the adhered separator and negative electrode were cut into a size of 25 mm in width and 70 mm in length. After the end parts of the separator and the negative electrode were attached to a universal testing machine (UTM: Universal Testing Machine) (manufactured by Instron Corporation, Japan), a force was applied at 180° at a measurement speed of 300 mm / min to measure the force required for the separation of the negative electrode and the separator adhered to the negative electrode. [Description of Reference Numerals]

[0088] 1 Separator 11 Porous polymer substrate 12 Porous coating layer 2 Electrodes 21 Current collector 22 Active material layer 30 Coating bar 31 Cylindrical bar 32 Wire A Central part B1, B2 Ends

Claims

1. A separator for an electrochemical element, wherein the separator includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a binder polymer and inorganic particles, the thicknesses of both TD (transverse direction) ends of the separator are further thicker than the thickness of the TD central portion, both TD ends of the separator include a region where the thickness gradually increases along the direction away from the TD central portion, a separator, wherein the length of one of both ends of the separator is 0.1 to 10% of the total length in the width direction of the separator.

2. The separator according to claim 1, wherein the thicknesses of both TD ends of the separator are 5 to 100% thicker than the thickness of the TD central portion.

3. An electrode assembly including a current collector and an electrode including an active material layer located on at least one surface of the current collector, and a separator located on at least one surface of the electrode, wherein the separator includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a binder polymer and inorganic particles, the thicknesses of both TD ends of the separator are further thicker than the thickness of the TD central portion, the length of one of both ends of the separator is 0.1 to 10% of the total length in the width direction of the separator, both TD ends of the separator include a region where the thickness gradually increases along the direction away from the TD central portion, an electrode assembly, wherein both TD ends of the active material layer include a region where the thickness gradually decreases along the direction away from the TD central portion.

4. The electrode assembly according to claim 3, wherein the thicknesses of both TD ends of the separator are 5 to 100% thicker than the thickness of the TD central portion.

5. Both TD ends of the separator, The electrode assembly according to claim 3, having a shape corresponding to both TD ends of the active material layer.

6. A secondary battery including the electrode assembly according to any one of claims 3 to 5.

7. The secondary battery according to claim 6, wherein the secondary battery is a lithium secondary battery.

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