Electrode assembly and secondary battery containing the same

Abstract

The present invention provides a jelly roll type electrode assembly in which a first separation membrane, a negative electrode, a second separation membrane, and a positive electrode are sequentially laminated and wound together. [Solution] The positive electrode includes a first surface in the winding axis direction of the jelly roll type electrode assembly and a second surface opposite to the first surface, the core portion of the electrode assembly includes a separation membrane superposition portion in which the first separation membrane and the second separation membrane are superimposed in three or more layers between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the electrode assembly includes an adhesive tape positioned between the positive electrode and the first separation membrane facing the second surface of the positive electrode, or between the negative electrode adjacent to the second surface of the positive electrode and the first separation membrane.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2022-0165667, filed with the Korean Intellectual Property Office on December 1, 2022, and Korean Patent Application No. 10-2023-0171927, filed with the Korean Intellectual Property Office on December 1, 2023, and all of its contents are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a secondary battery including the same. More specifically, the present invention relates to an electrode assembly capable of preventing damage to the separation membrane located at the ends of the negative and positive electrodes due to swelling.

[0003] Furthermore, a secondary battery including the electrode assembly can be realized. [Background technology]

[0004] Generally, secondary batteries, unlike primary batteries which cannot be recharged, are batteries that can be charged and discharged, and such secondary batteries are widely used in advanced electronic devices such as telephones, laptops, and video cameras.

[0005] The stability of a secondary battery can be measured by a stability test that involves compressing one side of the secondary battery with a press and measuring internal short circuits.

[0006] Rechargeable batteries are classified according to the shape of the battery case into cylindrical and rectangular batteries, in which the electrode assembly is housed in a cylindrical or rectangular metal battery case, and pouch-type batteries, in which the electrode assembly is housed in a pouch-type battery case made of aluminum laminate sheet.

[0007] The electrode assemblies built into battery cases are chargeable and dischargeable power generation elements consisting of a stacked structure of positive electrode / separator membrane / negative electrode. They are classified into folding-type electrode assemblies (jelly roll-type electrode assemblies), in which a long sheet-like positive electrode coated with an active material is wound between a negative electrode with a separator membrane in between, and stack-type electrode assemblies, in which a number of positive and negative electrodes of a predetermined size are sequentially stacked with a separator membrane in between. Among these, jelly roll-type electrode assemblies have the advantages of being easy to manufacture and having a high energy density per unit weight.

[0008] A jelly roll electrode assembly is formed by winding together a positive electrode and a negative electrode, with a separator film interposed between them during the winding process. However, as hundreds to thousands of charge-discharge cycles progress, the jelly roll electrode assembly shrinks and expands. This causes bending deformation from the ends of the positive electrode in the center, eventually leading to cracks, which can result in disconnection or short circuits, significantly compromising the safety of the secondary battery. [Overview of the project] [Problems that the invention aims to solve]

[0009] Focusing on the problems of the conventional technology described above, the present invention provides an electrode assembly and a secondary battery including the same, which prevents the electrode ends from generating cracks on the separation membrane and other electrode surfaces when the electrodes contract and expand during charging and discharging of a secondary battery. [Means for solving the problem]

[0010] One embodiment of the present invention is a jelly roll type electrode assembly in which a first separation membrane, a negative electrode, a second separation membrane, and a positive electrode are sequentially laminated and wound, wherein the positive electrode includes a first surface that is the winding axis direction of the jelly roll type electrode assembly and a second surface that is the opposite surface of the first surface, and a core portion of the electrode assembly includes a separation membrane overlapping portion in which the first separation membrane and the second separation membrane are arranged to overlap three or more times between the positive electrode and the negative electrode facing the first surface of the positive electrode, and includes an adhesive tape located between the positive electrode and the first separation membrane facing the second surface of the positive electrode or between the negative electrode adjacent to the second surface of the positive electrode and the first separation membrane, to provide an electrode assembly.

[0011] One embodiment of the present invention provides a secondary battery including the electrode assembly; a battery case that has an opening on at least one surface and houses the electrode assembly, and a cap assembly coupled to the opening surface of the battery case.

[0012] One embodiment of the present invention provides a battery pack including the secondary battery.

[0013] One embodiment of the present invention provides a moving means including the battery pack.

Effects of the Invention

[0014] The electrode assembly and the secondary battery including the same according to the embodiment of the present invention provide three or more separation membranes located in the central direction of the jelly roll structure at a portion corresponding to the end of the portion where the winding of the positive electrode starts, and prevent cracking of the negative electrode at the portion in contact with the end of the positive electrode to prevent disconnection and short circuit, thereby improving the safety of the secondary battery.

[0015] Also, the electrode assembly and the secondary battery including the same according to the embodiment of the present invention provide three or more separation membranes overlapping on one surface of the positive electrode, and a separation membrane and an adhesive tape are arranged to overlap doubly on the other surface of the positive electrode, suppressing damage to the separation membrane due to slipping of the positive electrode, and preventing an internal short circuit of the secondary battery.

[0016] An adhesive tape containing a porous structure is positioned on the other side of the positive electrode, between the separation membrane and the negative electrode. This allows lithium ions from the negative electrode to move smoothly through the separation membrane and the adhesive tape, preventing a decrease in the capacity of the secondary battery due to the adhesive tape. [Brief explanation of the drawing]

[0017] [Figure 1] This is a perspective view showing an electrode assembly according to one embodiment of the present invention. [Figure 2] This is a plan view of a jelly roll type electrode assembly including a separation membrane superimposed portion according to one embodiment of the present invention. [Figure 3] Figure 2 is an enlarged plan view of a part of the assembly. [Figure 4] A schematic diagram shows the separation membrane superimposed portion of a jelly roll-type electrode assembly according to one embodiment of the present invention. [Figure 5] A schematic diagram shows the separation membrane superimposed portion of a jelly roll-type electrode assembly according to one embodiment of the present invention. [Figure 6] This is a cross-sectional view showing a secondary battery according to one embodiment of the present invention. [Figure 7] This is a perspective view showing a battery pack according to one embodiment of the present invention. [Figure 8] This is a perspective view showing a means of transport according to one embodiment of the present invention. [Figure 9] These are CT images showing the results of the cycle stability evaluation of secondary batteries based on the thickness of the adhesive tape in Example 1 and Comparative Example 1. [Figure 10] These are CT images showing the results of evaluating the cycle stability of secondary batteries based on the length of the adhesive tape used in Examples 1-4 and Comparative Example 2. [Figure 11] This figure shows a method for evaluating whether or not there is damage to the separation membrane in the core portion of a jelly roll type electrode assembly according to one embodiment of the present invention. [Modes for carrying out the invention]

[0018] The detailed description of the present invention is intended to fully explain the invention to a person having ordinary skill in the art. Wherever a part of the specification "includes" a component or "characterizes" a structure and shape, this does not exclude other components or other structures and shapes, unless otherwise stated, but rather means that other components, structures and shapes may be included.

[0019] Since the present invention can be subjected to various transformations and has various embodiments, specific embodiments are presented and described in detail in the detailed description. However, this is not intended to limit the scope of the invention by the examples, but rather to include all transformations, equivalents, or substitutes that fall within the spirit and technical scope of the present invention.

[0020] The present invention will be described in detail below with reference to the drawings. However, the drawings are for illustrative purposes only, and the scope of the present invention is not limited by the drawings.

[0021] The electrode assembly 100 according to the present invention is a chargeable and dischargeable power generation element comprising a positive electrode 110, a negative electrode 120, and separator membranes 130 and 140. The separator membranes 130 and 140 can be positioned between the positive electrode 110 and the negative electrode 120. Furthermore, the separator membranes 130 and 140 can be positioned on either one surface of the positive electrode 110 or one surface of the negative electrode 120.

[0022] In one embodiment, the electrode assembly 100 may include a jelly roll structure in which the positive electrode 110, the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 are stacked and then wound up. That is, the electrode assembly 100 may consist of the positive electrode 110, the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 stacked in order before winding.

[0023] One end 110a of the positive electrode can extend in the longitudinal direction of the positive electrode, and the one end 110a of the positive electrode may have a free-edge shape. This reduces the area of ​​the blank portion of the negative electrode current collector, thereby ensuring cost-effectiveness, and allows the slitting process to be performed after the active material layer is formed on the electrode, enabling the roll-to-roll process, including the slitting and winding processes, to be carried out more efficiently.

[0024] The slitting process involves cutting the electrode width to match the designed battery specifications using a slitter or cutter. For example, a slitter can cut a sheet of electrode to the height of the electrode assembly 100.

[0025] A roll-to-roll process may include all processes that use rolls to move a flexible material. For example, when manufacturing an electrode assembly, the electrode and separator membrane are supplied wound on a roll. The electrode and separator membrane are then moved and fed from the roll to a winding core and can be wound around the winding core. In this process, one end of the electrode and separator membrane can be moved and fed to the winding core via another roll.

[0026] The winding process refers to the process of winding electrodes and separation membranes onto a winding core.

[0027] The positive electrode 110 may include a positive electrode current collector 111, a positive electrode active material layer, and a positive electrode blank portion. The positive electrode current collector 111 is not particularly limited as long as it is conductive without inducing a chemical change in the battery. Specifically, the positive electrode current collector 111 may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. That is, the positive electrode current collector 111 may be provided in the form of surface-treated stainless steel, aluminum foil, etc.

[0028] The positive electrode current collector 111 can typically have a thickness of 3 to 50 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0029] The positive electrode 110 is formed by coating one or more sides of the positive electrode current collector 111 with positive electrode active material. The area coated with positive electrode active material is the positive electrode active material layer 112, and the area not coated with positive electrode active material is the positive electrode blank area. Since the positive electrode blank area is not coated with the positive electrode active material layer 112, the first electrode tab 150 can be joined to the positive electrode current collector 111.

[0030] The positive electrode active material may include lithium cobalt oxide, which has a high operating voltage and excellent capacity characteristics; lithium nickel oxide, which has high reversible capacity and facilitates the realization of large-capacity batteries; lithium nickel cobalt oxide, in which part of the nickel is replaced with cobalt; lithium nickel cobalt metal oxide, in which part of the nickel is replaced with manganese, cobalt, or aluminum; lithium manganese-based oxide, which has excellent thermal stability and is inexpensive; and lithium iron phosphate, which has excellent stability.

[0031] For more details, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (0 ≤ x ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-y M y Lithium nickel oxide of the Ni site type, represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ y ≤ 0.3); chemical formula LiMn 2-zLithium manganese composite oxides represented as MzO2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ z ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions, etc., are examples, but are not limited to these. The positive electrode may be Li metal.

[0032] According to one embodiment of the present invention, the positive electrode active material layer 112 may further include a positive electrode conductive material and a positive electrode binder. The positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it has electronic conductivity without undergoing a chemical change in the battery being constructed. Specifically, the positive electrode conductive material can be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Not only other materials similar to those described above, but any combination of such materials may be used as the positive electrode conductive material.

[0033] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0034] The negative electrode 120 may include a negative electrode current collector 121, a negative electrode active material layer, and a negative electrode blank portion. The negative electrode current collector 121 may include a thin metal plate with excellent conductivity, such as copper (Cu) or nickel (Ni) foil.

[0035] The negative electrode 120 is formed by coating one or both sides of the negative electrode current collector 121 with negative electrode active material, the negative electrode active material layer 122 is formed by coating or applying the negative electrode active material, and the negative electrode blank area is a region where the negative electrode current collector is exposed because the negative electrode active material is not coated or applied. Since the negative electrode blank area is not coated with negative electrode active material, the second electrode tab 160 can be joined to the negative electrode current collector 121.

[0036] The negative electrode active material may be, for example, carbon materials such as crystalline carbon, amorphous carbon, carbon composites, or carbon fibers, or lithium metal or lithium alloy. In this case, the negative electrode active material may further contain, for example, non-graphite-based SiO (silica) or SiC (silicon carbide) for high-capacity design.

[0037] The negative electrode active material layer 122 may include a negative electrode active material comprising at least one selected from the group consisting of silicon-based materials and carbon-based materials. The negative electrode active material layer 122 may further include a negative electrode conductive material and a negative electrode binder, and the negative electrode active material, negative electrode conductive material, and negative electrode binder may be any materials used in the industry without limitation.

[0038] According to one embodiment of the present invention, the negative electrode current collector 121 is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, the negative electrode current collector 121 can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that effectively adsorb carbon, such as copper and nickel, can be used as the negative electrode current collector 121. The thickness of the negative electrode current collector 121 may be 6 μm or more and 80 μm or less, but the thickness of the negative electrode current collector 121 is not limited thereto.

[0039] According to one embodiment of the present invention, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms thereof are substituted with Li, Na, or Ca, or it may contain various copolymers thereof.

[0040] According to one embodiment of the present invention, the negative electrode conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0041] The first electrode tab 150 and the second electrode tab 160 transmit electrons collected by the current collector to an external circuit and can protrude in directions opposite to each other relative to the electrode assembly of the jelly roll structure.

[0042] The separation membranes 130 and 140 can prevent internal short circuits that may occur due to contact between the positive electrode 110 and the negative electrode 120. The separation membranes 130 and 140 separate the negative electrode 120 and the positive electrode 110, providing a pathway for lithium ions to move. They can be used without particular limitations as long as they are the same type of separation membranes commonly used in secondary batteries, and those with low resistance to electrolyte ion movement while having excellent electrolyte moisture retention capacity are particularly preferred.

[0043] The separation membranes 130 and 140 may include a porous material to facilitate the movement of ions between electrodes. In one embodiment, the separation membranes 130 and 140 may include a substrate layer made of a porous material. The substrate layers 131 and 141 may include, for example, one selected from the group consisting of polyethylene (PE), polystyrene (PS), polypropylene (PP), and a copolymer of polyethylene (PE) and polypropylene (PP).

[0044] Alternatively, the base layers 131 and 141 may be porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. Furthermore, the separation membrane may typically have a thickness of 10 μm to 20 μm. Using the aforementioned separation membrane material as the base layer, a separation membrane can be used in which a slurry containing ceramic components or polymer substances is coated onto the base layer to ensure heat resistance or mechanical strength. It may be used selectively in a single-layer or multi-layer structure.

[0045] In other embodiments, the separation membranes 130 and 140 may include SRS (Safety Reinforced Separator) separation membranes. That is, the separation membranes 130 and 140 may include porous material substrate layers 131 and 141 and coating layers 132 and 142 formed by coating the substrate layers with a mixed slurry of inorganic particles and a binder polymer. Preferably, the coating layers 132 and 142 contain ceramic particles and have a uniform porous structure formed by the interstitial volume between the ceramic particles, which are the active layer components, along with the pore structure contained in the separation membrane substrate itself.

[0046] The coating layers 132 and 142 may contain ceramic particles comprising at least one selected from the group consisting of alumina, silica, TiO2, SiC, and MgAl2O4. Including such a coating layer can enhance the safety of the electrode assembly. The coating layer may further contain a lithium salt.

[0047] In another embodiment, the separation membranes 130 and 140 may each include coating layers 132 and 142 provided on at least one surface thereof, and the coating layers 132 and 142 may include an inorganic component, a binder component, and a lithium salt. By including the above-mentioned components in the separation membrane, although a binder for improving the adhesion to the electrode and an inorganic component for improving the mechanical strength of the separation membrane are included, an increase in internal resistance is not caused by the elution of the lithium salt contained in the coating layer, so it can be excellent in cell stability.

[0048] In addition, since the electrolyte impregnation level of the electrodes facing the separation membranes 130 and 140 can be increased, it can have advantageous performance from the viewpoint of long life. Specifically, the coating layers 132 and 142 may include the inorganic component, and the coating layers 132 and 142 including the inorganic component are advantageous in terms of the thermal shrinkage rate compared to a separation membrane made of a simple polymer material, so the separation membranes 130 and 140 including this can have better high-temperature safety.

[0049] Specifically, the lithium salt may be substantially the same as that contained in the electrolyte of a lithium secondary battery. For example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, and one or more selected from the group consisting of lithium 4-phenylborate may be used.

[0050] The inorganic component is not particularly limited as long as it does not cause an oxidation and / or reduction reaction, that is, an electrochemical reaction, with the positive or negative electrode current collector within the operating voltage range of the battery (for example, 0 to 5V based on the Li / Li+ standard) and does not impair the electrical conductivity. For example, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr1-y Ti y O3(PLZT), Pb(Mg3Nb) 2 / 3 )May be one or more selected from the group consisting of O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, and TiO2.

[0051] The binder is not particularly limited as long as it is a component that does not easily dissolve in the electrolyte, while exhibiting binding force with the electrodes laminated on the separation membrane and alternating binding force between the inorganic components and lithium salts in the mixed coating layer. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotrichloroetlene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate. It may be one or more mixtures selected from the group consisting of propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide, and preferably PVdF or PVdF-CTFE.

[0052] In one embodiment of the present invention, the positive electrode 110 includes a first surface facing the center (C, or core) of the jelly roll structure and a second surface facing away from the center C in the diametrical direction of the jelly roll. Here, the center C of the jelly roll structure is the center of the circular structure when the jelly roll structure is viewed from above, and represents a virtual region corresponding to the part where winding has begun.

[0053] More specifically, the “core” refers to a region that includes a hollow space located on the winding shaft of the electrode assembly and a portion of the wound-up laminated structure of the first separator / negative electrode / second separator / positive electrode, and can mean a region within two turns of the positive electrode from one longitudinal end of the positive electrode located at the innermost corner of the electrode assembly. “One turn” may also refer to the length required to wind the electrode or separator included in the electrode assembly 360° from a reference point, and the length may be determined according to the outer diameter of the winding core used for winding the electrode assembly, the thickness of the electrode or separator, and the number of turns of the electrode or separator located on the inside. For example, one turn of the positive electrode can refer to the length required to wind the positive electrode 360° from its longitudinal end in the direction in which the jelly roll type electrode assembly is wound, and this can be either clockwise or counterclockwise when viewed from above.

[0054] Referring to Figure 3, the electrode assembly 100 includes a separation film superposition section S where three or more layers of separation films 130 and 140 overlap between one surface of the positive electrode 110 and the negative electrode 120, specifically the negative electrode current collector (or negative electrode blank section, 121), at the innermost end of the positive electrode, i.e., the edge of the positive electrode adjacent to the center C of the jelly roll structure. That is, three or more layers of separation films 130 and 140 are placed between the first surface of the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode 110. Furthermore, an adhesive tape 180 is placed between the second surface of the positive electrode 110 and the negative electrode 120.

[0055] According to one embodiment of the present invention, the electrode assembly 100 includes a separation membrane superimposed portion S, which suppresses the sliding of the electrodes during battery charging and discharging, prevents damage to the negative electrode and separation membrane from deformation of the electrode assembly due to the contraction / expansion of the electrodes, and even if separation membrane damage occurs, the separation membrane superimposed portion prevents internal short circuits between the positive electrode and the negative electrode, thereby improving battery stability and lifespan characteristics.

[0056] The length of the separation membrane superimposed portion S may be 50% of the circumference of the electrode assembly 100, based on 100% of the circumference. That is, the separation membrane superimposed portion S can extend 180° around the electrode assembly. Preferably, the length of the separation membrane superimposed portion S may be more than half the circumference of the core portion C of the electrode assembly 100. More preferably, the length of the separation membrane superimposed portion S may be 6 mm or more in the direction opposite to the direction in which the core portion C of the electrode assembly 100 is located, from the end of the positive electrode 110 adjacent to the core portion C.

[0057] The electrode assembly 100 can be formed by fixing the separation membranes 130 and 140 to a winding core, and then supplying the negative electrode 120 and positive electrode 110 in that order to the winding core (not shown) and winding them up. Therefore, the first separation membrane 130, the second separation membrane 140, and the negative electrode 120 can be positioned at the front end of the end of the positive electrode 110. In other words, the first separation membrane 130, the second separation membrane 140, and the negative electrode current collector 121 can be formed extending from the front end of the end of the positive electrode 110, and the first separation membrane 130 and the second separation membrane 140 can be formed extending from the front end of the end of the negative electrode current collector 121. Here, the ends of the positive electrode 110 and the negative electrode 120 refer to the ends of the positive electrode 110 and the negative electrode 120 that are adjacent to the winding core in their longitudinal direction.

[0058] Then, after the negative electrode 120, positive electrode 110, and separation membranes 130 and 140 are wound up, the core is removed, thereby forming a core portion C in the center of the electrode assembly 100.

[0059] In other words, in the core portion C of the electrode assembly, the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 may extend beyond the longitudinal end of the positive electrode 110 and be further wound up. Specifically, the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 may extend beyond the longitudinal end 110a of the positive electrode and be further wound up.

[0060] After the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 are initially wound together, the positive electrode 110 may be wound together with the first separation membrane 130, the negative electrode 120, and the second separation membrane 140, starting from the longitudinal end 110a of the positive electrode. For example, the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 may be wound together around the core for at least one turn before being wound together with the positive electrode 110. That is, in the core portion C of the jelly roll type electrode assembly, the longitudinal ends 120a, 133, and 143 of the first separation membrane 130, the negative electrode 120, and the second separation membrane 140 may be located inside the longitudinal end 110a of the positive electrode.

[0061] The length and width of the negative electrode 120 may be greater than that of the positive electrode 110, and the length and width of the first separator membrane 130 and the second separator membrane 140 located on one and the opposite sides of the negative electrode 120 may also be greater than that of the positive electrode. If the first separator membrane 130, the negative electrode 120, and the second separator membrane 140 extend beyond the longitudinal end 110a of the positive electrode and are further wound up, the transfer of lithium ions from the positive electrode to the negative electrode in the chemical reaction of the lithium-ion battery may be more facilitated. If the length and width of the negative electrode are formed to be wider, the area of ​​the negative electrode that receives lithium ions increases, which can prevent a decrease in charge / discharge efficiency and can result in superior battery stability and life characteristics.

[0062] The separation membranes 130 and 140 located at the front ends of the negative electrode 120 and positive electrode 110 may be bent one or more times at the front end of the negative electrode 120 located towards the center of the jelly roll structure. In other words, the separation membranes 130 and 140 can be positioned in a form that is bent one or more times at the core portion C of the electrode assembly 100.

[0063] Furthermore, the separation membranes 130 and 140, which have been bent once or more and whose winding direction has been changed, may be laminated on one surface of the positive electrode 110. The separation membranes 130 and 140 extending from the negative electrode end may be bent in the direction opposite to the direction facing the winding shaft of the negative electrode and laminated on one surface of the positive electrode 110. Therefore, the separation membranes 130 and 140 can be triple-layered on one surface of the edge portion of the positive electrode 110 adjacent to the center of the electrode assembly 100, in the order of second separation membrane 140, second separation membrane 140', and first separation membrane 130'.

[0064] In other words, the separation membranes 130 and 140 are positioned circumferentially around the core portion C of the electrode assembly 100, and the first separation membrane 130 and the second separation membrane 140 are bent relative to each other at the bending portion B, so that they extend from the bending portion B in both clockwise and counterclockwise directions.

[0065] The separation membranes 130 and 140 bend relative to each other at least once, so that they have different winding directions (clockwise and counterclockwise or opposite winding direction and winding direction) relative to at least a portion of the electrode assembly 100. The separation membranes 130 and 140 may be laminated on one surface of the positive electrode 110. The separation membranes 130 and 140 extending in a first clockwise direction from the longitudinal end 120a of the negative electrode may bend relative to each other and extend in a counterclockwise direction. They may be laminated on one surface of the positive electrode 110 with respect to the winding shaft. Thus, the separation membranes 130 and 140 overlap to form four layers, the first separation membrane 130 is divided into two layers around the positive electrode 110, and three separation membrane layers can be formed within the separation membrane overlapping portion S.

[0066] In this case, the second separation membrane 140' located between the second separation membrane 140 and the first separation membrane 130' is the second separation membrane 140' located on one surface of the negative electrode 120, as the second separation membrane 140 is bent one or more times at the front end of the positive electrode edge. That is, the separation membrane superposition portion S allows the second separation membrane 140' located closest to the positive electrode 110 and the second separation membrane 140' extending from the longitudinal end of the negative electrode 120 in the core portion of the electrode assembly 100 to be in direct contact. In other words, the separation membrane superposition portion S allows the portion of the second separation membrane 140 closest to the positive electrode 110 in the radial direction and the portion of the second separation membrane 140' located further away from the positive electrode 110 in the radial direction to be in direct contact.

[0067] The core portion C of the electrode assembly includes a separation membrane superimposed portion between the positive electrode and the negative electrode facing the first surface of the positive electrode, and the separation membrane superimposed portion may have separation membranes arranged in three or more layers.

[0068] The core portion C of the electrode assembly includes a separation membrane superposition portion S between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode, and the separation membrane superposition portion S may mean a part of the region in which three or more layers of separation membrane are superimposed, with respect to the longitudinal end 110a of the positive electrode. Here, the separation membrane superposition portion S may mean the region up to the longitudinal end of the separation membrane superposition portion S, that is, the region having the same length in the direction of the core portion of the electrode assembly, with respect to the longitudinal end 110a of the positive electrode. In other words, the separation membrane superposition portion S can mean a region in which a single circumferential end Sa is defined at the position where three or more adjacent layers of separation membrane end. The separation membrane superimposed portion S can extend along three adjacent layers of the separation membrane from one circumferential end Sa to the other circumferential end Sb, where the circumferential end Sb opposite to the circumferential end Sa is defined by a position that is the same distance from the longitudinal end 110a of the positive electrode 110 as the distance from the circumferential end Sa to the longitudinal end 110a.

[0069] Figure 4 illustrates various relationships between electrodes and separation membranes disclosed herein. As shown in the figure, the separation membrane superimposed portion S may represent a region from the longitudinal end of the separation membrane superimposed portion S to a length L' equal to the distance L between the longitudinal end of the separation membrane superimposed portion S and the longitudinal end of the positive electrode, with respect to the longitudinal end 110a of the positive electrode, or it may represent a region having a length of L+L'=L+L=2L from the longitudinal end of the separation membrane superimposed portion S.

[0070] According to one embodiment of the present invention, the separation membrane superposition portion may be the core portion C of the electrode assembly in which the first separation membrane 130 and the second separation membrane 140 extending from the longitudinal end 120a of the negative electrode are superimposed. Specifically, the separation membrane superposition portion S may be the core portion C of the electrode assembly in which the first separation membrane 130 and the second separation membrane 140 extending from the longitudinal end 120a of the negative electrode are superimposed, and the first separation membrane 130 and the second separation membrane 140 may include regions extending from the longitudinal end 120a of the negative electrode. That is, the first separation membrane 130 and the second separation membrane 140 may extend longer than the longitudinal end 120a of the negative electrode and be further wound up.

[0071] In other words, the first separation membrane 130 and the second separation membrane 140 may be wound up to a predetermined length, and then wound up together with the negative electrode 120. The first separation membrane 130 and the second separation membrane 140 extending from the longitudinal end 120a of the negative electrode may be a portion of the first separation membrane 130 and the second separation membrane that were wound up before the negative electrode 120. The first separation membrane 130 and the second separation membrane 140 extending from the longitudinal end 120a of the negative electrode may include the first separation membrane 130' and the second separation membrane 140' that extend in the opposite direction to the winding direction. The folding and overlapping of such separation membranes forms the overlapping separation membrane portion S.

[0072] The separation membrane overlapping portion may be formed by a bent structure that extends integrally from the first and second separation membranes without providing a separate auxiliary separation membrane. This allows for adjustment so that the separation membrane constituting the separation membrane overlapping portion is three or more layers thick, using a simpler structure. Furthermore, when the separation membrane overlapping portion is formed by the first and second separation membranes overlapping and arranging to extend from the longitudinal end of the negative electrode, damage to the negative electrode and separation membrane can be prevented from deformation of the electrode assembly due to electrode contraction / expansion. Even if separation membrane damage occurs, the separation membrane overlapping portion can prevent internal short circuits between the positive and negative electrodes, thereby improving the battery's stability and lifespan characteristics.

[0073] According to one embodiment of the present invention, the first and second separation membranes may be folded together in the core portion of the electrode assembly in a direction opposite to the direction facing the winding shaft of the negative electrode, extending from the longitudinal end of the negative electrode, and superimposed between the positive electrode and the second separation membrane facing the first surface of the positive electrode. Specifically, the first separation membrane 130 and the second separation membrane 140 extending from the longitudinal end 120a of the negative electrode may be folded together in a direction opposite to the direction facing the winding shaft of the negative electrode, that is, toward the longitudinal end 110a of the positive electrode, and may be superimposed between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode to form a separation membrane superimposed portion S. This makes it possible to adjust the facing direction of the separation membranes constituting the separation membrane superimposed portion more easily, while making it possible to have three or more layers of separation membranes constituting the separation membrane superimposed portion with a simpler folding structure.

[0074] As described above, the separation membrane superposition section S may be stacked in the order of the first separation membrane 130', the second separation membrane 140', and the second separation membrane 140, with one surface of the positive electrode 110 as the reference. The separation membrane superposition section S may include a first interface and a second interface. The first interface refers to the surface where the second separation membranes 140 and 140' are in direct contact with each other, and the second interface refers to the surface where the second separation membrane 140' and the first separation membrane 130' are in direct contact.

[0075] Specifically, the separation membrane superposition section S may have three or more superimposed separation membranes, and may include one or more first separation membranes 130 and second separation membranes 140 and 140', and may include a first interface S1 where the second separation membrane 140 and the second separation membrane 140' are in direct contact, and a second interface S2 where the second separation membrane 140' and the first separation membrane 130 are in direct contact. In other words, the separation membrane superposition section is not a superimposed structure of a single separation membrane, but includes a superimposed structure of multiple separation membranes, namely first and second separation membranes, and may include interfaces where these membranes are in contact with each other. By including multiple interfaces in the separation membrane superposition section, it may be possible to easily adjust the facing direction of the separation membranes and the friction coefficient of each interface with a simpler bending structure.

[0076] According to one embodiment of the present invention, the coefficients of friction of the first interface and the second interface may each be 0.4 or greater. Specifically, the coefficients of friction of the first interface S1 and the second interface S2 may each be 0.42 or greater, 0.44 or greater, or 0.46 or greater. That is, the separation membrane superposition portion is not a superposition structure of a single separation membrane, but includes a superposition structure of a first separation membrane and a second separation membrane, which are multiple separation membranes, and includes multiple interfaces in contact with each other, but the coefficients of friction of the multiple interfaces may each be adjusted to be above a specific range. When the coefficients of friction of the first interface and the second interface satisfy the above range, the sliding of the positive electrode can be suppressed by the first separation membrane and the second separation membrane, which are integrally formed with the separation membrane superposition portion, during battery charging and discharging, and damage to the negative electrode and separation membrane can be prevented from deformation of the electrode assembly due to the contraction / expansion of the electrodes. Here, the coefficient of friction (μ) refers to the static friction coefficient measured according to the ASTM D1894 standard, and the coefficient of friction may be measured by a dry method, or it may have a larger value when measured by a wet method by impregnating the test piece in distilled water or electrolyte.

[0077] In other embodiments, the coefficients of friction of the first interface and the second interface of the electrode assembly 100 may be different. Preferably, the coefficient of friction of the first interface may be greater than that of the second interface. More preferably, the coefficient of friction of the first interface may be 0.6 or greater, and the coefficient of friction of the second interface may be 0.4 or greater. Specifically, the coefficients of friction of the first interface S1 and the second interface S2 may differ from each other depending on the type and facing direction of the first separation film 130, 130' and the second separation film 140, 140'. More specifically, the coefficient of friction of the first interface S1 may be 0.62 or greater or 0.66 or greater, and the coefficient of friction of the second interface S2 may be 0.42 or greater, 0.44 or greater, or 0.46 or greater. When the coefficient of friction of the interface of the separation membrane included in the separation membrane superimposed portion is adjusted to the aforementioned range, the sliding of the electrodes during battery charging and discharging is suppressed, damage to the negative electrode and separation membrane due to deformation of the electrode assembly caused by the contraction / expansion of the electrodes is prevented, and even if damage to the separation membrane occurs, the separation membrane superimposed portion prevents an internal short circuit between the positive electrode and the negative electrode, thereby improving the stability and lifespan characteristics of the battery.

[0078] According to one embodiment of the present invention, the first separation membrane and the second separation membrane may each include a coating layer provided on at least one surface.

[0079] Specifically, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include the coating layers 132, 132', 142, 142' and base layer layers 131, 131', 141, 141' provided on at least one surface, and the friction coefficient may be within a specific range depending on the composition, content, and particle size of the coating layers. Here, 130, 130', 140, and 140' indicate that at the bent portion B, the bending structure of the separation membrane causes the same separation membrane to extend in the opposite direction to the winding direction. Specifically, the friction coefficient between the coating layers of the separation membrane and the friction coefficient between the base layer may be greater than the friction coefficient between the coating layer and the base layer. Furthermore, the friction coefficient may be measured using a dry method, but a more significant difference may be observed when measured using a wet method, i.e., when impregnated with distilled water or an electrolyte.

[0080] When a coating layer is provided on at least one surface of the first and second separation membranes, the coefficient of friction of the interface of the separation membranes included in the overlapping separation membrane portion can be adjusted to a specific range by adjusting the facing direction of the coating layer provided on at least one surface of the first and second separation membranes, thereby suppressing the sliding of the electrodes during battery charging and discharging, and preventing damage to the negative electrode and separation membrane from deformation of the electrode assembly due to electrode contraction / expansion.

[0081] According to one embodiment of the present invention, the first separation membranes 130, 130' and the second separation membranes 140, 140' may each include a coating layer provided on at least one surface. Specifically, referring to Figure 4, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include a coating layer 132, 132', 142, 142' provided on one surface, and the surfaces of the first and second separation membranes with the coating layers may have a higher coefficient of friction than the surfaces of the first and second separation membranes without the coating layers. That is, when the coating layer is provided on the separation membrane, it can increase the coefficient of friction at the interface. By adjusting the facing direction of the coating layers provided on one surface of the first and second separation membranes, the coefficient of friction of the interface of the separation membranes included in the separation membrane superposition portion S is adjusted to a specific range, thereby suppressing the sliding of the electrodes during battery charging and discharging, and preventing damage to the negative electrode and separation membranes from deformation of the electrode assembly due to electrode contraction / expansion.

[0082] According to one embodiment of the present invention, the first separation membranes 130, 130' and the second separation membranes 140, 140' may have a coefficient of friction within a specific range through adjustment of the components, content, and particle size of the coating layer.

[0083] According to one embodiment of the present invention, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include a coating layer provided on one surface, and the first interface may be such that the coating layer of the second separation membranes 140, 140' and the coating layer of the second separation membrane are in direct contact. Specifically, referring to Figure 4, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include a coating layer 132, 132', 142, 142' provided on one surface, and the first interface S1 may be such that the coating layer 142 of the second separation membrane and the coating layer 142' of the second separation membrane are in direct contact. When the coating layer 142 of the second separation membrane and the coating layer 142' of the second separation membrane are in direct contact, that is, the coefficient of friction between the coating layers of the separation membrane may be greater than the coefficient of friction between the substrate layer and the substrate layer or the coefficient of friction between the coating layer and the substrate layer, and the coefficient of friction of the first interface may have a larger value. When the coating layer 142 of the second separation membrane and the coating layer 142' of the second separation membrane are in direct contact, the coefficient of friction of the interface of the separation membrane included in the separation membrane superimposed portion S increases, suppressing the sliding of the electrodes during battery charging and discharging, thereby preventing damage to the negative electrode and separation membrane from deformation of the electrode assembly due to the contraction / expansion of the electrodes.

[0084] According to one embodiment of the present invention, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include a coating layer provided on one surface, and the second interface may be such that the surface of the second separation membrane without a coating layer is in direct contact with the surface of the first separation membrane without a coating layer. Specifically, referring to Figure 4, the first separation membranes 130, 130' and the second separation membranes 140, 140' each include a coating layer 132, 132', 142, 142' provided on one surface, and the second interface S2 may be such that the surface of the second separation membrane without a coating layer, i.e., the second separation membrane substrate layer 141', and the surface of the first separation membrane without a coating layer, i.e., the first separation membrane substrate layer 131', are in direct contact. When the surface of the second separation membrane that does not have a coating layer and the surface of the first separation membrane that does not have a coating layer are in direct contact, that is, the coefficient of friction between the substrate layer of the separation membrane and the substrate layer may be greater than the coefficient of friction between the coating layer and the substrate layer, and the coefficient of friction of the second interface may have a larger value. When the surface of the second separation membrane that does not have a coating layer and the surface of the first separation membrane that does not have a coating layer are in direct contact at the second interface, the coefficient of friction of the interface of the separation membrane included in the separation membrane overlapping portion increases, and by suppressing the sliding of the electrodes during charging and discharging of the battery, damage to the negative electrode and separation membrane can be prevented from deformation of the electrode assembly due to the contraction / expansion of the electrodes.

[0085] According to one embodiment of the present invention, the first interface is the second separator membrane facing the first surface of the positive electrode; and the core portion of the electrode assembly, where the second separator membrane extending from the longitudinal end of the negative electrode may be in direct contact. Specifically, referring to Figures 2 to 4, the second separator membrane 140' extending from the longitudinal end 120a of the negative electrode may be superimposed between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode to form a separator membrane superimposed portion S. In this case, since the second separator membrane 140 is located between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode, the extended second separator membrane 140' may be in direct contact with the second separator membrane 140 located between the positive electrode 110 and the negative electrode 120. In other words, the second separation membrane 140 and the core portion of the electrode assembly may form a first interface S1 in direct contact with the second separation membrane 140' extending from the longitudinal end 120a of the negative electrode. This makes it easier to adjust the facing direction of the separation membranes constituting the separation membrane overlapping portion and the frictional force of the interface, while ensuring that the separation membranes constituting the separation membrane overlapping portion are three or more layers thick with a simpler bending structure.

[0086] According to one embodiment of the present invention, the second interface may be in direct contact between the first separator membrane extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly and the second separator membrane extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly. Specifically, referring to Figures 2 to 4, the first separator membrane 130' extending from the longitudinal end 120a of the negative electrode and the second separator membrane 140' extending from the longitudinal end of the negative electrode may be arranged superimposed between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode, forming a separator membrane superimposed portion S. In this case, a second interface S2 may be formed where the first separator membrane 130 extending from the longitudinal end 120a of the negative electrode and the second separator membrane 140' extending from the longitudinal end 120a of the negative electrode are in direct contact. This makes it easier to adjust the facing direction of the separation membranes and the frictional force of the interface, while ensuring that the separation membranes constituting the overlapping separation membrane section are three or more layers thick, using a simpler folding structure.

[0087] Figure 5 schematically shows the separation membrane superposition portion of a jelly roll type electrode assembly according to one embodiment of the present invention. Specifically, Figure 5(a) schematically shows the separation membrane superposition portion of a jelly roll type electrode assembly including a first separation membrane and a second separation membrane, each having a coating layer on both sides, and Figure 5(b) schematically shows the separation membrane superposition portion of a jelly roll type electrode assembly including a first separation membrane and a second separation membrane without a coating layer.

[0088] According to one embodiment of the present invention, the first separation membrane and the second separation membrane may each include a coating layer provided on at least one surface. Specifically, referring to Figures 3 and 5(a), the first separation membranes 130, 130' and the second separation membranes 140, 140' each include the coating layers 132, 132', 142, 142' and substrate layers 131, 131', 141, 141' provided on at least one surface, and the friction coefficient may be within a specific range depending on the composition, content, and particle size of the coating layer. Specifically, the friction coefficient between the coating layers of the separation membrane and the friction coefficient between the substrate layers may be greater than the friction coefficient between the coating layers and the substrate layers. Furthermore, the friction coefficient may be measured by a dry method, but a more significant difference may be observed when measured by a wet method, i.e., when impregnated with distilled water or an electrolyte.

[0089] When a coating layer is provided on at least one surface of the first and second separation membranes, the coefficient of friction of the interface of the separation membranes included in the overlapping separation membrane portion can be adjusted to a specific range by adjusting the facing direction of the coating layer provided on at least one surface of the first and second separation membranes, thereby suppressing electrode sliding during battery charging and discharging, and preventing damage to the negative electrode and separation membranes from deformation of the electrode assembly due to electrode contraction / expansion.

[0090] According to one embodiment of the present invention, the first separation membrane and the second separation membrane may each include a coating layer provided on at least one surface, and the coating layer may include an inorganic component, a binder component, and a lithium salt. Because the separation membrane contains the aforementioned components, even though it includes a binder for improving adhesion to the electrode and an inorganic component for improving the mechanical strength of the separation membrane, the elution of the lithium salt contained in the coating layer does not cause an increase in internal resistance, thus resulting in excellent cell stability.

[0091] According to one embodiment of the present invention, the length of the separation membrane superimposed portion S may be 30% or more of the circumference of the electrode assembly, based on 100% of the circumference. That is, the separation membrane superimposed portion S can extend approximately 108° around the electrode assembly.

[0092] Specifically, the length of the separation membrane superimposed portion may be 40% or more, or 50% or more, based on 100% of the circumference of the electrode assembly. That is, the separation membrane superimposed portion S can extend at least 144° around the electrode assembly.

[0093] Alternatively, the separation membrane layer may be folded to form a separation membrane superimposed portion S of 1 / 3 turn or more or 1 / 2 turn or more on the inner circumferential surface of the core portion of the electrode assembly.

[0094] Here, the perimeter of the electrode assembly may mean the perimeter of the inner surface of the electrode assembly, and the "inner surface perimeter" may mean a virtual circumference whose radius is the largest value among the distances from the winding shaft of the electrode assembly to the innermost corner layer that is in contact with the hollow of the electrode assembly. For example, the perimeter of the inner surface of the electrode assembly may be about 10 mm, but is not limited to this.

[0095] Furthermore, the longitudinal length of the separation membrane superimposed portion may mean a length of L+L'=L+L=2L. That is, the first separation membrane extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly, and the second separation membrane extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly, may be positioned between the positive electrode and the negative electrode facing the first surface of the positive electrode, with a length of 1 / 6 turn or more or 1 / 4 turn or more from the longitudinal end of the positive electrode. In this case, the longitudinal length of the separation membrane superimposed portion may be 1 / 3 turn or more or 1 / 2 turn or more. When the longitudinal length range of the separation membrane superimposed portion described above is met, the frictional force at the interface of the separation membrane included in the separation membrane superimposed portion may be sufficient to prevent damage to the negative electrode and separation membrane from deformation of the electrode assembly due to the contraction / expansion of the electrodes by suppressing the sliding of the electrodes during battery charging and discharging.

[0096] According to one embodiment of the present invention, the separation distance between the longitudinal end of the separation membrane superimposed portion and the longitudinal end of the positive electrode may be 3 mm or more. Specifically, referring to Figure 4, the separation distance L between the longitudinal end of the separation membrane superimposed portion and the longitudinal end of the positive electrode may be 4 mm or more, 5 mm or more, or 6 mm or more.

[0097] That is, the first separator membrane 130' extending from the longitudinal end of the negative electrode in the core portion of the electrode assembly, and the second separator membrane 140' extending from the longitudinal end 120a of the negative electrode in the core portion of the electrode assembly, may be positioned at least 3 mm from the longitudinal end 110a of the positive electrode between the positive electrode 110 and the negative electrode 120 facing the first surface of the positive electrode.

[0098] If the longitudinal length range of the aforementioned separation membrane superimposed portion is met, the separation membrane superimposed portion can be positioned between the positive electrode and the negative electrode facing the first surface of the positive electrode, even if process errors exist when the first and second separation membranes are introduced. Furthermore, the frictional force at the interface of the separation membrane included in the separation membrane superimposed portion can be sufficient to prevent damage to the negative electrode and separation membrane from deformation of the electrode assembly due to electrode contraction / expansion by suppressing the sliding of the electrodes during battery charging and discharging.

[0099] The electrode assembly 100 according to the present invention may further include a third electrode tab 170 in the core portion C. The third electrode tab 170 may be located at the front end of the longitudinal end of the positive electrode 110. In other words, the third electrode tab 170 can be in contact with the front end of the pocket-shaped separation membranes 130 and 140 in the direction of the core portion C.

[0100] The adhesive tape 180 is located on either one surface of the first separator membrane 130 facing the second surface of the positive electrode 110, or on one surface of the negative electrode 120. In other words, the adhesive tape 180 may be laminated on one surface of the first separator membrane 130 or one surface of the negative electrode 120 facing the edge portion of the positive electrode adjacent to the center of the jelly roll structure.

[0101] Furthermore, the adhesive tape 180 may include a substrate layer with a porous structure, such as the separation membranes 130 and 140.

[0102] The electrode assembly 100 may have three or more separation membranes 130, 140 superimposed between the first surface of the positive electrode 110 and the negative electrode 120, and two layers of the first separation membrane 130 and adhesive tape 180 superimposed between the second surface 110b of the positive electrode 110 and the negative electrode 120.

[0103] This configuration prevents cracks and overheating that may occur at the ends of the positive electrode 110. In other words, as the design requirements for high energy density increase, the density of the positive electrode inevitably increases due to the bonding of electrode tabs (second electrode tabs or in taps) to the core portion C of the electrode assembly 100, or the inclusion of more SiO in the negative electrode active material, resulting in increased stress at the positive electrode step portion. Here, the positive electrode step portion is the part where the thickness increases sharply to 100 μm to 200 μm at the starting point of the positive electrode due to the interposition of the positive electrode, and a physical step is formed within the jelly roll electrode assembly. This corresponds to the edge portion of the positive electrode 110 in the drawing.

[0104] For example, the in-tap is an electrode tab located on one side of the blank negative electrode area near the core C. In other words, the in-tap refers to the electrode tab closest to the longitudinal end of the negative electrode that forms the core C.

[0105] In such a stepped positive electrode portion, stress becomes high, and therefore, if this portion is continuously pressed during the contraction and expansion process due to charging and discharging, the separation membrane in the portion in contact with it will be damaged, increasing the risk of ignition due to cracks and short circuits. However, according to one embodiment of the present invention, as described above, a triple separation membrane is placed on the first surface of the positive electrode 110 at the edge of the positive electrode, and a double layer of separation membrane and adhesive tape is placed on the second surface of the positive electrode 110 at the edge of the positive electrode. This prevents damage to the separation membrane at the stepped positive electrode portion, enables a stable buffering effect, prevents cracks and short circuits caused by repeated contraction and expansion at the high-stress positive electrode end, and therefore reduces the risk of ignition.

[0106] In other words, as the charge-discharge cycle progresses hundreds to thousands of times, contraction and expansion of the electrodes may occur, causing bending deformation at the edge of the positive electrode 110, which can lead to cracks in the electrode. However, by placing a triple separation membrane on the first surface of the positive electrode 110 at the edge of the positive electrode and a double layer of separation membrane and adhesive tape on the second surface of the positive electrode 110 at the edge of the positive electrode, it is possible to prevent cracks and short circuits caused by contraction and expansion of the edge of the positive electrode 110, and the resulting ignition. In particular, in this embodiment, the triple separation membrane is placed on the first surface of the positive electrode, and the double layer of separation membrane and adhesive tape is placed on the second surface, rather than on just one surface of the positive electrode, so that cracks and short circuits in the electrode can be prevented on any surface.

[0107] An adhesive tape 180 according to one embodiment may include a porous substrate layer 181 and an adhesive layer 182 applied to one surface of the porous substrate layer. The adhesive layer 182 may be laminated over the entire surface of the porous substrate layer 181, or the adhesive layer 182 may be arranged in a pattern and laminated only over a portion of the surface of the porous substrate layer 181.

[0108] The porous substrate layer 181 of the adhesive tape 180 may be the separation membrane substrate layers 131 and 141 contained in the first separation membrane 130 and the second separation membrane 140. Furthermore, if the adhesive tape 180 includes a porous substrate layer and an adhesive layer 182, the adhesive layer 182 may contain a substance that facilitates the movement of ions, particularly lithium ions, or the adhesive layer 182 may absorb an electrolyte and expand, forming an ion transport path.

[0109] Therefore, the adhesive tape 180 facilitates the movement of ions between electrodes, similar to the separation membranes 130 and 140, and prevents lithium ions from precipitation even as the secondary battery 1 is charged and discharged.

[0110] Alternatively, the porous substrate layer 181 may be one or more films selected from the group consisting of, for example, acrylic film, polyolefin film, polyamide film, polycarbonate film, polyurethane film, cellulose acetate film, and polyester film, but is not limited thereto.

[0111] When a polyester film is used as the porous substrate layer 181, one or more films selected from the group consisting of polyethylene terephthalate film, polyethylene naphthalate film, and polybutylene terephthalate film can be used. When a cellulose-based porous substrate layer 181 is used as the porous substrate layer 181, for example, a porous substrate layer 181 containing cellulose acetate resin or cellulose alkylate resin can be used, which is produced by applying a mixture containing the resin to an extrusion or casting process. As the cellulose alkylate, for example, cellulose acetate propionate or cellulose acetate butylate can be used.

[0112] The method for producing the porous substrate layer 181 using the resin is not particularly limited. For example, a conventional film or sheet molding method, such as extrusion or casting, can be used to produce a raw material containing the resin and optionally known additives.

[0113] When the porous substrate layer 181 described above is in the form of a sheet or film, the thickness of the porous substrate layer 181 is not particularly limited and may be, for example, 10 to 200 μm, 10 to 100 μm, 10 to 50 μm, 15 to 30 μm, or approximately 15 to 20 μm.

[0114] The adhesive layer may contain polyethylene oxide (PEO, Poly-ethylene oxide, ether group). The polyethylene oxide acts with the electrolyte due to electrostatic polarity attraction, and the adhesive layer can attract the electrolyte that has flowed into the separation membrane through the porous substrate layer, causing the electrolyte to be absorbed into the adhesive layer.

[0115] Specifically, the adhesive layer 182 can be represented by the following chemical formula 1 (Chemical Formula 1).

[0116] [ka]

[0117] In the above chemical formula 1, R1 represents hydrogen or an alkyl group having 1 to 12 carbon atoms. R2 represents an alkylene group with 1 to 6 carbon atoms. R3 represents hydrogen, an alkyl group with 1 to 12 carbon atoms, an aryl group with 6 to 24 carbon atoms, or an arylalkyl group with 6 to 48 carbon atoms. n is greater than or equal to 0.

[0118] In the above chemical formula 1, R1 is hydrogen or an alkyl group having 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples include hydrogen, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, etc. Preferably, it may be hydrogen or a methyl group, but is not limited to these.

[0119] Furthermore, in the above chemical formula 1, R2 is an alkylene group having 1 to 6, 1 to 4, or 1 to 2 carbon atoms, and may, for example, be ethylene or propylene, but is not limited thereto.

[0120] The aforementioned R3 represents hydrogen; an alkyl group having 1 to 12, 1 to 8, 1 to 6, or 1 to 4 carbon atoms; an aryl group having 6 to 24, 6 to 20, 6 to 18, or 6 to 12 carbon atoms; or an arylalkyl group having 6 to 48, 6 to 30, 6 to 24, or 6 to 18 carbon atoms. Examples include, but are not limited to, hydrogen, methyl group, ethyl group, propyl group, phenyl group, naphthalate group, butylphenol group, pentylphenol group, hexylphenol group, heptylphenol group, octylphenol group, or nonylphenol group.

[0121] Furthermore, n may be 0 or greater, for example, 1 or greater, preferably 2 or greater.

[0122] Referring to Figure 6, in the secondary battery 1 according to the present invention, a double layer consisting of a first separation membrane 130 and an adhesive tape 180 is superimposed on the second surface of the positive electrode 110. This prevents damage to the separation membrane due to the step portion of the positive electrode and prevents internal short circuits in the secondary battery 1. Furthermore, lithium ions from the positive electrode move to the negative electrode via the electrolyte absorbed by the porous substrate layer and the adhesive layer. Thus, the secondary battery 1 according to the present invention can improve the capacity reduction problem caused by the adhesive layer.

[0123] Furthermore, the monomer represented by chemical formula 1 contains at least one oxygen atom, and due to the high electronegativity of the oxygen atom, the monomer exhibits very high polarity. Therefore, the adhesive layer containing the monomer has a high affinity for polar electrolytes and can expand upon contact with the electrolyte. In the above, the term "electrolyte" can mean, for example, an ion-conducting medium used in secondary batteries. For example, the electrolyte may be an electrolyte in liquid form, but is not limited to these. In this specification, electrolyte may also be expressed as electrolyte.

[0124] In other embodiments, the adhesive tape 180 may include a porous substrate layer 181 and a coating layer (not shown) on one surface of the porous substrate layer 181, which is a slurry of inorganic particles and a binder. The adhesive tape 180 can have adhesive properties due to the binder contained in the coating layer. For example, the adhesive tape 180 can be made by mixing an organic solvent with a slurry of inorganic particles and a binder, coating one surface of the porous substrate layer 181 with the slurry, and then adjusting the process conditions immediately before drying to induce phase separation so that the binder, which acts as an adhesive, is exposed on the surface.

[0125] The adhesive tape 180 according to another embodiment may include a porous substrate layer 181, a coating layer on one side of the porous substrate layer 181 coated with a slurry of inorganic particles and a binder, and an adhesive layer 182 applied to either one side of the coating layer or the other side of the porous substrate layer 181. Here, the side of the coating layer on which the adhesive layer 182 is applied means the side opposite to the side that is in direct contact with the substrate layer. The adhesive layer may have the same structure as the adhesive layer of the adhesive tape 180 according to one embodiment.

[0126] The adhesive tape 180 may be laminated in such a way that the base layer 181 of the adhesive tape 180 can be in direct contact with the positive electrode 110, or the adhesive layer 182 can be in direct contact with the negative electrode 120.

[0127] This configuration increases the frictional force between the positive electrode 110 and the negative electrode 120 and the adhesive tape 180, preventing the negative electrode 120 and the positive electrode 110 from sliding and preventing the core portion C from losing its shape (core deformation).

[0128] The adhesive tape 180 may be adhered so that the coating layer and adhesive layer are in direct contact with the second surface of the positive electrode 110, or it may be adhered to one surface of the negative electrode 120 that is opposite to the second surface of the positive electrode 110. Alternatively, the adhesive tape 180 may be adhered to one surface of the first separation membrane 130 located between the second surface 110b of the positive electrode 110 and the negative electrode 120, with the coating layer and adhesive layer in contact.

[0129] The adhesive tape 180, with its base layer, coating layer, and adhesive layer containing a porous structure, allows lithium ions from the negative electrode 120 to pass through, minimizing lithium deposition and ensuring the safety of the secondary battery even as charging and discharging of the electrode assembly 100 progresses.

[0130] The adhesive tape 180 according to the present invention may have a porous substrate layer 181 with a thickness of 13 μm or more, and an adhesive layer 182 with a thickness of more than 0 μm and 4 μm or less. Preferably, the porous substrate layer 181 may have a thickness of 15 μm or more, and the adhesive layer 182 may have a thickness of more than 0 μm and 3 μm or less. When the thickness of the porous substrate layer 181 is 13 μm or more, the total thickness of the adhesive tape 180 increases, which can prevent the ends of the negative or positive electrode from damaging or penetrating the separation membrane during core impingement. Furthermore, since the thickness of the adhesive layer 182 is 4 μm or less, the permeability of the electrolyte is high, and therefore the effect of increased ionic conductivity may occur.

[0131] Furthermore, the length of the adhesive tape 180 may be 5 mm or more. Preferably, the length of the adhesive tape 180 may be 10 mm or more. In addition, the length of the adhesive tape 180 that overlaps with the positive electrode may be 2 mm or more, preferably 5 mm or more.

[0132] In the adhesive tape 180, the porous substrate layer 181 and the substrate layer 131 of the first separation membrane face each other, and the length over which the porous substrate layer 181 and the substrate layer 131 of the first separation membrane face each other satisfies the aforementioned range. This suppresses electrode sliding due to the coefficient of friction between the separation membranes, and therefore prevents the shape of the core portion C from being distorted.

[0133] Furthermore, by ensuring that the overlapping length of the adhesive tape 180 and the positive electrode 110 satisfies the aforementioned range, the thickness of the region where the positive electrode edge is located increases. This increases the coefficient of friction due to the pressure applied by the adhesive tape 180 and the first separator membrane 130 during contraction and expansion of the electrode assembly 100, thereby preventing the electrodes from sliding.

[0134] The secondary battery 1 according to the present invention may include an electrode assembly 100, a battery case 200, and a cap assembly 300.

[0135] The secondary battery 1 may include an electrode assembly 100, a battery case 200, and a cap assembly 300.

[0136] The electrode assembly 100 is according to the embodiment described above.

[0137] The battery case 200 may be provided as a columnar structure with a space formed inside. The battery case 200 can house an electrode assembly 100 including electrodes and a separation membrane, and an electrolyte (not shown) in its internal space. The battery case 200 may have a structure in which at least one side is open (hereinafter referred to as the opening), and the other side may have a sealed structure. Here, one side and the other side of the battery case 200 refer to the ends located at the top and bottom along the direction of gravity or the central axis of the battery case 200.

[0138] A beading portion 210 folded toward the center of the secondary battery 1 may be provided on the upper side surface of the open battery case 200. Furthermore, a crimping portion 220 may be provided above the beading portion 210 of the battery case 200. That is, the crimping portion 220 can be located at the uppermost part of the battery case 200. Here, the upper part refers to the area from the center of the battery case 200 toward the opening.

[0139] The battery case 200 may be made of a lightweight conductive metal material such as aluminum or an aluminum alloy. It may also have a cylindrical shape.

[0140] Preferably, the battery case 200 according to the present invention may be cylindrical. Specifically, the battery case 200 may be cylindrical, rectangular, or pouch-shaped depending on the application, but when the battery case is cylindrical, it can be more suitable for housing a jelly roll-type electrode assembly, and when the battery case is cylindrical, the shape of the secondary battery including the jelly roll-type electrode assembly and the battery case for housing the electrode assembly may be cylindrical.

[0141] According to one embodiment of the present invention, the inside of the battery case may contain an electrolyte. Specifically, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the manufacture of lithium secondary batteries, but is not limited to these. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0142] According to one embodiment of the present invention, as the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0143] According to one embodiment of the present invention, the metal salt may be a lithium salt, and the lithium salt is a substance that is readily soluble in the non-aqueous organic solvent, for example, the anion of the lithium salt is F - Cl - , I - NO3 -, N(CN) 2- BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You can use one or more selected from the group consisting of the following.

[0144] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0145] The cap assembly 300 can be coupled to the open surface of the battery case 200 and may include a top cap 310, a safety vent 320, and a current interruption element 330.

[0146] The top cap 310 is located at the very top of the cap assembly 300 and can protrude away from the center of the battery case 200. The top cap 310 can act as an electrode terminal so that the protruding portion is electrically connected to the outside, for example, the top cap 310 can act as a positive terminal.

[0147] The top cap 310 can be joined to the edge of the top cap 310 and the sealing gasket 340, and the sealing gasket 340 may be located inside the crimping portion 220 of the battery case 200. The sealing gasket 340 can increase the sealing force between the top cap 310 and the battery case 200.

[0148] The top cap 310 may include a protruding portion extending upward, an edge portion that contacts and connects with the sealing gasket 340, and a first connecting portion that connects the protruding portion and the edge portion.

[0149] The safety vent 320 is located below the top cap 310 and can be electrically connected to the top cap 310. At least a portion of the surface of the safety vent 320 facing the top cap 310 can be in contact with the top cap 310. The safety vent 320 may be in contact with the top cap 310 for a certain length from its end, and the portion excluding the contact length may be located at a certain distance from the top cap 310. The portion of the safety vent 320 that is in contact with the top cap 310 can be coupled with the sealing gasket 340.

[0150] The safety vent 320 may have an increasing separation distance from the top cap 310 as it approaches the center of the safety vent 320 in the area where it contacts the top cap 310.

[0151] The safety vent 320 may include a contact portion that contacts the top cap 310, a central portion located in the center of the safety vent 320 that contacts the current interruption element, and a second connecting portion that connects the contact portion and the central portion. The safety vent 320 may also have bent portions (or notches) in the portions where the contact portion and the second connecting portion, and the second connecting portion and the central portion, come into contact.

[0152] In one embodiment, the end of the safety vent 320 may be positioned perpendicular to the axial direction of the battery case 200. In this case, the top cap 310 may also be positioned perpendicular to the axial direction of the battery case 200, similar to the safety vent 320. That is, the safety vent 320 and the top cap 310 can be positioned horizontally.

[0153] In another embodiment, the safety vent 320 may be provided such that its ends are bent to wrap around the outer surface of the top cap 310.

[0154] In the secondary battery 1 according to the present invention, the electrode assembly 100 housed inside the battery case 200 reacts with the electrolyte, generating gas and heat, which causes the internal pressure to rise.

[0155] When the pressure inside the secondary battery 1 rises, the safety vent 320 is subjected to force in the direction of the top cap 310, causing the bent portion to rupture and the gas inside the secondary battery 1 to be released.

[0156] The current interruptive device (CID) 330 is located below the safety vent 320 and may be connected to the safety vent 320 in some respects.

[0157] The current interruption element 330 disconnects from the safety vent 320 and interrupts the current when the safety vent 320 ruptures due to an increase in the internal pressure of the secondary battery 1.

[0158] The current interruption element 330 is connected to the safety vent 320 at its central portion and may include a connecting portion that protrudes upward toward an intermediate point along the direction in which the safety vent 320 is located, i.e., along the length of the current interruption element 330, an edge portion excluding the connecting portion, and a coupling portion that connects the connecting portion and the edge portion. Multiple coupling portions may be provided, and the multiple coupling portions may be located spaced apart from each other.

[0159] When the safety vent 320 is deformed in the direction in which the top cap 310 is positioned, the joint can break, and the connecting portion can be separated from the edge. That is, the connecting portion separates in the direction of the top cap 310 while still connected to the safety vent 320.

[0160] The CID gasket 350 encloses the edge of the current interruption element 330, electrically separating the edge and joint of the current interruption element 330 (excluding the connecting portion) from the safety vent 320.

[0161] According to one embodiment of the present invention, a battery pack 3 including any of the secondary batteries described above is provided.

[0162] Referring to Figure 7, the above embodiment shows a battery pack 3 in which a secondary battery 1 is included in a pack housing 2.

[0163] The battery pack according to the above embodiment has high output / high capacity.

[0164] According to one embodiment of the present invention, a means of transport including the aforementioned battery pack is provided.

[0165] Referring to Figure 8, the means of transport V, which includes a battery pack 3, is shown in the aforementioned example.

[0166] The means of transportation described above, by using a battery pack with high output / high capacity, is superior in terms of stability and safety.

[0167] While preferred embodiments of the present invention have been described above with reference to those skilled in the art, it will be understood that the present invention can be modified and altered in various ways without departing from the spirit and scope of the invention as set forth in the following claims.

[0168] Example 1 Manufacturing of electrode assemblies An Al foil with a thickness of 15 μm and a width of 63.9 mm was prepared as a positive electrode current collector. A positive electrode active material layer was formed on the positive electrode current collector by coating and drying a positive electrode active material slurry containing an NMCA (Ni-Mn-Co-Al) composite with a Ni content of 92% or more as the positive electrode active material and CNT (carbon nanotube) as a conductive material, thereby producing a positive electrode with a thickness of 154 μm.

[0169] Next, a Cu foil with a thickness of 8 μm and a width of 65.1 mm was prepared as the negative electrode current collector. A negative electrode active material slurry containing 50 parts by weight each of artificial graphite and natural graphite was applied to the negative electrode current collector and dried to form a negative electrode active material layer, thereby producing a negative electrode with a thickness of 187 μm.

[0170] On the other hand, two separation membranes were prepared, the first and second separation membranes, each consisting of a sheet-like polyethylene substrate layer with a coating layer formed on one surface containing Al2O3 as an inorganic component and a PVdF-based binder and a lithium salt as binder components.

[0171] Before winding the jelly roll electrode assembly, the base layers of the first and second separation membranes are superimposed so that the first and second base layers face each other. The first and second separation membranes are provided with an extension that extends long enough so that the superimposed portion where the first and second base layers face each other encloses the core of the electrode assembly by about three turns. The three turns extend in the opposite direction to the "winding direction," which is the direction in which the separation membrane and electrode are wound outward from the core, and extends outward rather than inward toward the core. In the electrode assembly shown in Figure 2, the winding direction is counterclockwise. The core may be the core of a jelly roll electrode assembly with an outer circumference of about 10 mm.

[0172] After the first and second separation membranes are wound approximately three times toward the core portion C, the separation membranes can be bent again and winding can be started so that they extend in the winding direction. The negative electrode and positive electrode are sequentially placed into the first and second separation membranes, and the negative electrode is placed closer to the core portion C to manufacture a jelly roll type electrode assembly. In this case, the core portion of the jelly roll type electrode assembly has a separation membrane overlap portion between one surface of the positive electrode in the winding axis direction and the second separation membrane located on one surface of the negative electrode, via extensions of the first and second separation membranes, and an adhesive tape is positioned on the opposite surface where the extensions are interposed, i.e., between the first separation membrane and the negative electrode, thereby having the structure shown in Figures 2 and 3.

[0173] In this case, the distance (L) between the longitudinal end of the separation membrane superimposed portion and the longitudinal end of the positive electrode was set to 3 mm, and the longitudinal length of the separation membrane superimposed portion (L + L' = 2L) was adjusted to 6 mm. The circumference of the inner surface of the manufactured jelly roll type electrode assembly was approximately 10 mm.

[0174] The adhesive tape had a porous substrate layer with a thickness of 16 μm, an adhesive layer with a thickness of 3 μm, and a length of 18 mm.

[0175] Manufacturing of rechargeable batteries After inserting the aforementioned jelly roll electrode assembly into a cylindrical battery case, an electrolyte solution prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a weight ratio of 4:9:3 and dissolving LiPF6 at a concentration of 15 wt% was poured into the case, and the cylindrical battery case was sealed with a cap assembly to produce a secondary battery.

[0176] Example 2 A jelly roll-type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that a 10 mm adhesive tape was used.

[0177] Example 3 A jelly roll-type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that a 15mm adhesive tape was used.

[0178] Example 4 A jelly roll-type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that a 5mm adhesive tape was used.

[0179] Comparative Example 1 A jelly roll-type electrode assembly and a secondary battery were manufactured in the same manner as in Example 1, except that the thickness of the porous substrate layer of the adhesive tape was 11 μm and the thickness of the adhesive layer was 5 μm.

[0180] Comparative Example 2 A jelly roll-type electrode assembly and a secondary battery were fabricated in the same manner as in Example 1, except that no adhesive tape was attached between the first separation membrane and the negative electrode.

[0181] Experimental example Experimental Example 1 - Evaluation of Core Impingement Evaluation of cycle stability based on adhesive tape thickness Secondary batteries manufactured in Example 1 and Comparative Example 1 were prepared, as well as secondary batteries that had been activated by performing two cycles of charging at 4.2V-2.5V and 0.2C, and discharging at 0.2C, respectively. Subsequently, secondary batteries that had been activated were prepared after 50 cycles under the conditions of 4.3V-2.5V 1C / 1C@24℃, and the short-term cycle stability was evaluated by checking for core impingement by computed tomography (CT) of the core portion, and the resulting images are shown in Figure 9.

[0182] Evaluation of cycle stability based on adhesive tape length Secondary batteries manufactured in Example 1 and Comparative Example 2 were prepared, as well as secondary batteries that had been activated by performing two cycles of charging at 4.2V-2.5V and 0.2C, and discharging at 0.2C, respectively. Subsequently, secondary batteries that had been activated were prepared after 50 cycles under the conditions of 4.3V-2.5V 1C / 1C@24℃, and the short-term cycle stability was evaluated by checking for core impingement by computed tomography (CT) of the core portion, and the resulting images are shown in Figure 10.

[0183] Evaluation of Core Impingement The presence or absence of core impingement in the secondary batteries of Example 1 and Comparative Example 1 was evaluated using the following method.

[0184] Figure 11 schematically illustrates the method for evaluating whether or not core impingement occurs. Specifically, Figure 11(a) schematically illustrates the method for evaluating whether or not core impingement occurs when deformation occurs in the negative electrode, and Figure 11(b) schematically illustrates the method for evaluating whether or not core impingement occurs when no deformation occurs in the negative electrode.

[0185] 1) On the first surface of the positive electrode 110, extend the straight line connecting the longitudinal end 110a of the positive electrode and a point 5 mm away from the end to draw the first extension line E1.

[0186] 2-1) If deformation occurs in the negative electrode In the core portion of the jelly roll-type electrode assembly, on the surface of the negative electrode 120 facing the first surface of the positive electrode, a straight line is drawn connecting two points within a distance of 5 mm from the longitudinal end 110a of the positive electrode, and a second extension line E2 is drawn by extending this line.

[0187] 2-2) When no deformation has occurred in the negative electrode On the radially inner surface of the positive electrode 110, a first extension line E1 is drawn by extending a straight line connecting the longitudinal end 110a of the positive electrode and a point 5 mm away from that end.

[0188] In the core portion of the jelly roll-type electrode assembly, on the surface of the negative electrode 120 facing the first surface of the positive electrode, a straight line is drawn connecting two points 5 mm apart from the longitudinal end 110a of the positive electrode, and a second extension line E2 is drawn by extending this line.

[0189] 3) A core impingement was determined to have occurred if the angle from the first extension line E1 to the second extension line E2 in a counterclockwise direction, based on the intersection point of the first extension line E1 and the second extension line E2, exceeded 25°.

[0190] On the other hand, the method for evaluating whether or not core impingement occurs can be applied by first evaluating whether or not core impingement occurs at the time of acquisition of an unknown cell, then re-evaluating whether or not core impingement occurs after 50 cycles, and comparing and analyzing the results with the core impingement conditions of the secondary battery according to the embodiment of the present invention.

[0191] Figure 9 is a CT image showing the cycle stability evaluation results based on the thickness of the adhesive tape of the secondary battery according to Example 1 and Comparative Example 1, and Figure 10 is a CT image showing the cycle stability evaluation results based on the length of the adhesive tape of the secondary battery according to Examples 1 to 4 and Comparative Example 2.

[0192] Referring to Figures 9 and 10, it was confirmed that the secondary battery manufactured in Example 1 did not experience core impingement in cycle stability evaluations based on the thickness and length of the adhesive tape. Similarly, it was confirmed that the secondary batteries manufactured in Examples 2 to 4 did not experience core impingement in cycle stability evaluations based on the length of the adhesive tape.

[0193] Core impingement was confirmed to occur in the secondary battery manufactured in Comparative Example 1 during cycle stability evaluation based on thickness, and core impingement was confirmed to occur in the secondary battery manufactured in Comparative Example 2 during cycle stability evaluation based on length.

[0194] Specifically, in both Comparative Example 1 and Comparative Example 2, it was confirmed that core impingement did not occur after activation, or that minute core impingement occurred. Furthermore, in both Comparative Example 1 and Comparative Example 2, it was confirmed that after 50 cycles, the frequency and extent of core impingement due to the contraction / expansion of the electrode assembly, i.e., damage to the negative electrode and separation membrane caused by the longitudinal end of the positive electrode, increased significantly.

[0195] In Example 1, the thickness of the porous substrate layer is greater, resulting in higher puncture strength than in Comparative Example 1. Therefore, it is possible to prevent punctures from occurring in the first separation membrane located between the positive and negative electrodes due to the positive and negative electrodes.

[0196] In Example 1 and Comparative Example 1, test specimens that change color upon contact with the acidic components of the electrolyte were placed between the adhesive layer and the porous substrate layer to confirm electrolyte permeability. The results showed that in Example 1, the adhesive layer was thin, resulting in ion conductivity through the adhesive tape, and therefore, the test specimen between the porous substrate layer and the adhesive layer turned red.

[0197] Furthermore, in Example 1, the thickness of the adhesive tape can increase the frictional force (stress) between the negative electrode and the separation membrane during negative electrode movement due to cycle progression, thereby reducing core impingement.

[0198] The secondary batteries manufactured in Examples 2-4 showed only a small difference in core impingement between activation and 50 cycles. In particular, when the overlap length between the adhesive tape and the positive electrode was 5 mm or more, the core impingement was confirmed to be 89% or more.

[0199] Through this, it can be seen that when the thickness of the adhesive tape between the first separation membrane and the negative electrode is 19 μm or more and the length is 5 mm or more, a higher coefficient of friction can be achieved compared to when there is no adhesive tape between the first separation membrane and the negative electrode or when the thickness of the adhesive tape is less than 19 μm, thereby suppressing electrode sliding and providing excellent protection against damage to the negative electrode and separation membrane even when the electrode contracts / expands.

[0200] The above detailed description is illustrative of the present invention. Furthermore, the foregoing describes only preferred embodiments of the present invention, and as stated above, the present invention can be used in a variety of other combinations, modifications, and environments, and can be modified or altered within the scope of the concept of the invention disclosed herein, within the scope equivalent to the foregoing disclosures, and / or within the scope of the art or knowledge of the art. Accordingly, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Furthermore, the appended claims should be construed to include other embodiments as well. [Explanation of Symbols]

[0201] 1 Secondary battery 100 electrode assembly 110 Positive electrode 110a Longitudinal end of the positive electrode 111 Positive electrode current collector 112 Cathode active material layer 120 negative electrode 120a Longitudinal end of the negative electrode 121 Negative electrode current collector 122 Negative electrode active material layer 130 First separation membrane 131 First separation membrane base layer 132 First separation film coating layer 140 Second separation membrane 141 Second separation membrane base layer 142 Second separation film coating layer 143 Longitudinal end of the second separation membrane 150 First electrode tab 160 Second electrode tab 170 Third electrode tab 180 Adhesive Tapes 181 Tape base layer 182 Adhesive layer 200 Battery Case 210 Beading section 220 Crimping section 300 Cap Assembly 310 Top Cap 320 Safety Vent 330 Current interruption element 340 Sealing Gasket 350 CID Gasket C Core S Separation membrane superimposed area B Folded section S1 1st interface S2 2nd interface S a The ends of one circle S b End S of the circumference a The ends of the circumference opposite each other L, L' Separation distance between the longitudinal end of the overlapping separation membrane and the longitudinal end of the positive electrode E1 1st extension line E2 2nd extension line

Claims

1. A first separation membrane, a negative electrode, a second separation membrane, and a positive electrode are sequentially stacked and wound together to form a jelly roll-type electrode assembly including a core. The positive electrode includes a first surface which is in the winding axis direction of the electrode assembly and a second surface which is the opposite surface of the first surface. The core portion of the electrode assembly includes a separation membrane superposition portion in which the first separation membrane and the second separation membrane are superimposed in three or more layers between the positive electrode and the negative electrode facing the first surface of the positive electrode. An electrode assembly including an adhesive tape positioned between the positive electrode and the first separator membrane facing the second surface of the positive electrode, or between the negative electrode adjacent to the second surface of the positive electrode and the first separator membrane.

2. The electrode assembly according to claim 1, wherein the lengths of the first separator membrane, the negative electrode, and the second separator membrane are each longer than the length of the positive electrode.

3. The electrode assembly according to claim 1, wherein the separation membrane superimposed portion extends from the end of the positive electrode in both the winding direction and the opposite direction of winding, and the first separation membrane and the second separation membrane are arranged in a superimposed manner.

4. The electrode assembly according to claim 1, wherein the first separation membrane and the second separation membrane are folded together in the core portion and extend in the winding direction and the opposite direction of winding, extending between the first surface of the positive electrode and the outer surface of the second separation membrane.

5. The aforementioned separation membrane superimposed portion is A first interface in which the second separation membrane extending in the opposite direction to the winding direction and the second separation membrane extending in the winding direction are in direct contact with each other, The second separation membrane, which extends in the direction opposite to the winding direction, and the first separation membrane, which extends in the winding direction, are in direct contact with each other, including a second interface. The electrode assembly according to claim 1, wherein the coefficients of friction of the first interface and the second interface are each 0.4 or greater.

6. The electrode assembly according to claim 5, wherein the coefficient of friction of the first interface is 0.6 or more, and the coefficient of friction of the second interface is 0.4 or more.

7. The first separation membrane and the second separation membrane each include a coating layer on at least one of their inner and outer surfaces. The electrode assembly according to claim 5, wherein the coefficient of friction of the coating layers of the first and second separation membranes is greater than the coefficient of friction of at least one uncoated portion of the inner and outer surfaces of the first and second separation membranes.

8. The first separation membrane and the second separation membrane are provided with a coating layer on at least one of their inner and outer surfaces. The electrode assembly according to claim 5, wherein the coating layer comprises an inorganic component, a binder component, and a lithium salt.

9. The first separation membrane and the second separation membrane each include a coating layer on at least one of their inner and outer surfaces. The electrode assembly according to claim 5, wherein the first interface is an interface in which the coating layer of the second separation film extending in the opposite direction to the winding direction and the coating layer of the second separation film extending in the winding direction are in direct contact with each other.

10. The first separation membrane and the second separation membrane each include a coating layer on at least one of their inner and outer surfaces. The electrode assembly according to claim 5, wherein the second interface is an interface in which the surface of the second separation film that does not have a coating layer is in direct contact with the surface of the first separation film that does not have a coating layer.

11. The electrode assembly according to claim 5, wherein the first interface is between one surface of the second separator membrane in contact with the negative electrode and one surface of the second separator membrane in contact with the first separator membrane.

12. The electrode assembly according to claim 5, wherein the second interface is between one surface of the first separator that is in contact with the longitudinal end of the positive electrode and one surface of the second separator that is separated from the longitudinal end of the positive electrode by a part of the first separator.

13. The electrode assembly according to claim 1, wherein the separation membrane superimposed portion extends at a rate of 108° or more around the circumference of the electrode assembly.

14. The separation film superimposed portion includes a first end extending in the opposite direction to winding, away from the longitudinal end of the positive electrode, and a second end extending in the winding direction opposite to the longitudinal end of the positive electrode. The electrode assembly according to claim 1, wherein at least one of the first end and the second end extends 3 mm or more from the longitudinal end of the positive electrode.

15. The electrode assembly according to claim 1, wherein the adhesive tape comprises a porous substrate layer and an adhesive layer on the porous substrate layer.

16. The electrode assembly according to claim 15, wherein the thickness of the porous substrate layer is 13 μm or more, and the thickness of the adhesive layer is greater than 0 μm and 4 μm or less.

17. The electrode assembly according to claim 1, wherein the length of the adhesive tape is 5 mm or more.

18. Electrode assembly according to any one of claims 1 to 17, A battery case having an opening on at least one side and housing the electrode assembly, and Cap assembly coupled to the opening surface of the battery case A secondary battery containing a battery.

19. The secondary battery according to claim 18, wherein the battery case is cylindrical.

Images