Secondary battery including seal tape

Abstract

The present specification relates to a secondary battery including a seal tape.SOLUTION: The present specification provides a secondary battery including a jelly-roll type electrode assembly in which a negative electrode is provided on an outer circumferential surface thereof, in which a seal tape, which absorbs an electrolyte and then expands, is attached to the outer circumferential surface of the electrode assembly to induce the electrode assembly to be unwound from the seal tape after the electrolyte is injected into a can, thereby increasing a contact area between the negative electrode located on the outer circumferential surface of the electrode assembly and the inside of the can and reducing resistance of the battery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery including a sealing tape.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0088822, filed with the Korean Intellectual Property Office on July 19, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. [Background technology]

[0003] In recent years, the demand for portable electronic products such as laptops, video cameras, and mobile phones has increased dramatically, and as the development of electric vehicles, energy storage batteries, robots, satellites, and other products has progressed in earnest, much research has been conducted on secondary batteries used as the driving power source for these products.

[0004] Such secondary batteries include, for example, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, etc. Among these, lithium secondary batteries are widely used in the field of cutting-edge electronic devices due to their advantages of being free to charge and discharge because they have almost no memory effect compared to nickel-based secondary batteries, a very low self-discharge rate, a high operating voltage, and a high energy density per unit weight.

[0005] In general, a lithium secondary battery is constructed by stacking or winding an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and then placing the electrode assembly in a metal can or a laminate sheet case, into which an electrolyte is injected or impregnated.

[0006] Electrode assemblies with a positive electrode / separator / negative electrode structure that make up secondary batteries can be broadly classified into jelly roll (wound) and stack (layered) types depending on their structure. The jelly roll type has a structure in which a long sheet-shaped positive electrode and negative electrode coated with active material are wound with a separator interposed between them, while the stack type has a structure in which multiple positive electrodes and negative electrodes of a predetermined size are stacked one on top of the other with a separator interposed between them. Among these, the jelly roll type electrode assembly has the advantages of being easy to manufacture, having a high energy density per weight, and being structurally stable.

[0007] Since cylindrical batteries including such jelly-roll type electrode assemblies are standardized, there is a need to maximize performance within a limited space. Summary of the Invention [Problem to be solved by the invention]

[0008] This specification provides a secondary battery including a jelly-roll type electrode assembly having a negative electrode disposed on its outer periphery, in which a sealing tape that absorbs an electrolyte and then expands is attached to the outer periphery of the electrode assembly, thereby inducing unraveling of the electrode assembly from the sealing tape after the electrolyte is injected into the can, thereby increasing the contact area between the negative electrode located on the outer periphery of the electrode assembly and the inside of the can, thereby reducing the resistance of the battery. [Means for solving the problem]

[0009] One embodiment of the present invention provides a secondary battery including: an electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator are wound; an electrolyte; and a can containing the electrode assembly and the electrolyte, wherein the negative electrode is located on an outer circumferential surface of the electrode assembly, and a sealing tape is provided on the outer circumferential surface of the electrode assembly, the sealing tape including a substrate and an adhesive layer provided on one surface of the substrate, and the adhesive layer has swelling properties in response to the electrolyte. [Effects of the Invention]

[0010] In the present invention, a sealing tape that swells in response to an electrolyte is attached to the negative electrode located on the outer periphery of the electrode assembly. When the electrolyte is poured into the battery can, the adhesive layer of the sealing tape absorbs the electrolyte and swells, causing the sealing tape to detach from the electrode assembly. As a result, the wound-up electrode assembly is partially unwound, increasing the contact area between the negative electrode on the outer periphery of the electrode assembly and the inside of the battery can, thereby providing low resistance characteristics for the battery. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram schematically illustrating a secondary battery according to an embodiment of the present invention. [Figure 2] 1 is a diagram schematically illustrating a secondary battery according to an embodiment of the present invention. [Figure 3] 1 shows CT images of batteries fabricated in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present specification will be explained in more detail below.

[0013] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0014] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when another member exists between the two members.

[0015] In this specification, when a part is said to be connected to another part, this includes not only a case where the part is directly connected to another part, but also a case where the part is indirectly connected via another element therebetween.

[0016] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below. However, in describing the operating principles of the preferred embodiments of the present invention in detail, if it is determined that a detailed description of related well-known functions or configurations may unnecessarily obscure the gist of the present invention, such detailed description will be omitted. Furthermore, the same reference numerals will be used throughout the drawings to designate parts having similar functions and operations.

[0017] One embodiment of the present invention provides a secondary battery including: an electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator are wound; an electrolyte; and a can containing the electrode assembly and the electrolyte, wherein the negative electrode is located on an outer periphery of the electrode assembly; a sealing tape is provided on the outer periphery of the electrode assembly; the sealing tape includes a substrate and an adhesive layer provided on one surface of the substrate; and the adhesive layer has swelling properties in response to the electrolyte.

[0018] Generally, cylindrical batteries including jelly-roll-type electrode assemblies have a separator positioned on the outer periphery of the electrode assembly. Because the electrode assembly is standardized, maximizing performance within a limited space is required. Typically, secondary battery performance is improved by maximizing capacity and reducing resistance. To maximize battery capacity, the amount of electrode material added must be increased, and to reduce resistance, the number of negative electrode tabs must be increased. However, it is difficult to infinitely increase the number of negative electrode tabs within the battery's internal space, and increasing the number of tabs can lead to problems such as reduced weldability with the battery can. Furthermore, increasing the electrode material content to maximize battery capacity reduces the internal space of the battery, making it difficult to add electrode tabs.

[0019] To address this issue, a method has been developed in which the negative electrode is positioned on the outer periphery of the electrode assembly, increasing the contact area between the negative electrode and the interior of the can and thereby reducing resistance. In this case, to maintain stable contact between the negative electrode and the interior of the can, the internal gap between the negative electrode and the interior of the can must be minimized.

[0020] However, before inserting the jelly-roll type electrode assembly into the can, a seal tape must be attached to the outer periphery of the electrode assembly to prevent the electrode assembly from unraveling, and a certain amount of internal gap must exist between the can and the electrode assembly for smooth insertion. If the gap is insufficient, the appearance of the electrode assembly may be damaged during insertion, and problems such as improper insertion may occur.

[0021] In this case, if existing sealing tape is used, the electrode assembly is tightly fixed, and stress caused by the contraction / expansion of the electrodes due to the charge / discharge of the secondary battery cannot be relieved, which can lead to problems such as electrode disconnection, cracks, and metal elution.

[0022] In the present invention, a negative electrode is positioned on the outer periphery of an electrode assembly, and a sealing tape that has swelling properties in response to an electrolyte and absorbs and expands in the electrolyte is used on the outer periphery of the electrode assembly. When the electrode assembly is inserted into a can and the electrolyte is poured into it, the adhesive layer of the sealing tape absorbs the electrolyte, losing its adhesiveness and expanding, thereby inducing unraveling of the electrode assembly.

[0023] Therefore, the electrode assembly unwraps due to the removal of the sealing tape and the contraction / expansion of the electrodes, increasing the contact area between the negative electrode located on the outer surface of the electrode assembly and the can, thereby reducing the resistance of the battery.

[0024] Furthermore, before inserting the electrode assembly into the can, the sealing tape stably fixes the jelly roll, thereby preventing the electrode assembly from coming undone and facilitating the insertion of the electrode assembly.

[0025] In one embodiment of the present invention, the sealing tape includes a substrate; and an adhesive layer provided on one surface of the substrate.

[0026] The adhesive layer included in the sealing tape will be specifically described below.

[0027] In one embodiment of the present invention, the adhesive layer has swelling properties due to the electrolyte solution. "Swelling properties due to the electrolyte solution" means that the adhesive layer changes its structure due to the electrolyte solution, for example, it absorbs the electrolyte solution and swells after coming into contact with the electrolyte solution. That is, the adhesive layer may be in a state in which it has absorbed the electrolyte solution and swelled.

[0028] The sealing tape can absorb an electrolyte solution and expand to form a three-dimensional structure. Specifically, the adhesive layer can absorb an electrolyte solution and expand to form a three-dimensional structure. For example, the adhesive layer can expand in the thickness direction and / or length direction upon contact with the electrolyte solution, thereby forming a three-dimensional structure. In the above, the "three-dimensional structure" of the sealing tape is formed by the action of the expansion force of the adhesive layer of the sealing tape in contact with the electrolyte solution and the peel force from the substrate, and can be a concept that includes all structures that allow the adhesive layer to be detached from the electrode assembly.

[0029] According to one example, the three-dimensional structure may include a plurality of protruding shapes in a direction perpendicular to the length direction of the adhesive layer. Here, "length direction" may refer to a direction perpendicular to the thickness direction of the adhesive layer when the adhesive layer is held flat. Furthermore, the terms "vertical" and "horizontal" refer to substantially vertical or horizontal within a range that does not impair the intended effect, and may include an error of, for example, ±10 degrees, ±5 degrees, or ±3 degrees.

[0030] In one embodiment of the present invention, the adhesive layer may have a center line average roughness value of 100 μm to 250 μm measured 24 hours after contact with the electrolyte solution.

[0031] Specifically, the center line average roughness (Ra) after contact with the electrolyte may be 150 μm to 240 μm, or 155 μm to 230 μm. The center line average roughness (Ra) may be a value measured on the surface of the adhesive layer 24 hours after contact with the electrolyte.

[0032] In the present invention, when the center line average roughness of the three-dimensional structure formed by the adhesive layer is adjusted within the above range, the sealing tape can be efficiently detached from the outer circumferential surface of the electrode assembly.

[0033] The "center line average roughness" means, for example, a value expressed in micrometers obtained by photographing a cross section of an adhesive layer forming a three-dimensional structure, mathematically remodeling the cross section of the three-dimensional structure using the photograph to obtain a roughness curve, extracting a reference length L from the roughness curve in the direction of the mean line, and expressing the roughness curve as y = f(x) with the mean line direction as the x-axis and the height direction as the y-axis, using the following formula 1:

[0034]

number

[0035] The centerline average roughness can be measured according to the standard of ASTM D4417, or can be determined as defined in JIS B0031 or JIS B0601.

[0036] In one embodiment of the present invention, the pressure-sensitive adhesive layer may include a cured product of a pressure-sensitive adhesive composition, or may include a polymer contained in the pressure-sensitive adhesive composition in a crosslinked form.

[0037] In one embodiment of the present invention, the pressure-sensitive adhesive composition may contain a polymer including polymerization units derived from a (meth)acrylic acid ester monomer, a monomer having a polar functional group, and a crosslinkable monomer containing a crosslinkable functional group.

[0038] In one example, in a secondary battery manufactured by attaching a sealing tape including an adhesive layer formed from the adhesive composition to an electrode assembly via the adhesive layer and inserting the electrode assembly into a battery can, the adhesive layer deforms, e.g., swells or expands, due to the polar functional groups present in the adhesive layer upon contact with the electrolyte solution injected into the secondary battery. In this case, the sealing tape forms a three-dimensional structure, and the surface of the adhesive layer has a specific range of surface roughness. As a result, the adhesive strength or peel strength between the electrode assembly and the adhesive layer is reduced, which can cause the adhesive layer to detach from the electrode assembly.

[0039] The pressure-sensitive adhesive composition includes a polymer having polymerization units, and the polymer may include, in a polymerized form, a (meth)acrylic acid ester monomer, a monomer having a polar functional group, and a crosslinkable monomer having a crosslinkable functional group.

[0040] The (meth)acrylic acid ester monomer contained in the polymerized units of the polymer may be, for example, an alkyl(meth)acrylate, and an alkyl(meth)acrylate having an alkyl group having 1 to 14 carbon atoms may be used in consideration of the cohesive strength, glass transition temperature, or adhesiveness of the adhesive. Examples of such a monomer include, but are not limited to, one or more of methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, t-butyl(meth)acrylate, sec-butyl(meth)acrylate, pentyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, 2-ethylbutyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylate, lauryl(meth)acrylate, and tetradecyl(meth)acrylate.

[0041] In the above, "(meth)acrylate" means acrylate or methacrylate, and similarly applies to other terms where "(meth)" is used.

[0042] The monomer having a polar functional group is a monomer having excellent affinity with an electrolyte solution and is included as a polymerization unit in the polymer of the adhesive composition so that an adhesive layer manufactured from the adhesive composition deforms, e.g., swells, when contacted with an electrolyte solution, thereby reducing the adhesive strength or peel strength between the electrode assembly and the adhesive layer. Furthermore, in the present application, by using a monomer having a specific structure as the monomer having a polar functional group, the sealing tape can form a three-dimensional structure with a specific surface roughness when contacted with an electrolyte solution. As a result, the sealing tape can be efficiently detached from the electrode assembly, thereby inducing isotropic volumetric expansion and contraction of the electrode assembly and efficiently preventing electrode disconnection.

[0043] In one embodiment of the present invention, the monomer having a polar functional group is represented by the following Chemical Formula 1:

[0044] [ka]

[0045] In the above Chemical Formula 1, R1 represents hydrogen or an alkyl group having 1 to 12 carbon atoms; R2 represents an alkylene group having 1 to 6 carbon atoms; R3 represents hydrogen, an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 24 carbon atoms, or an arylalkyl group having 6 to 48 carbon atoms; n is 0 or greater.

[0046] In the above Chemical Formula 1, the alkyl group having 1 to 12 carbon atoms may be a straight-chain or branched-chain alkyl group.

[0047] In 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, and examples thereof include hydrogen, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group. Preferably, R1 is hydrogen or a methyl group, but is not limited to these.

[0048] In addition, 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 be, for example, ethylene or propylene, but is not limited thereto.

[0049] 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 of R3 include hydrogen, a methyl group, an ethyl group, a propyl group, a phenyl group, a naphthalene group, a butylphenol group, a pentylphenol group, a hexylphenol group, a heptylphenol group, an octylphenol group, and a nonylphenol group, but are not limited to these.

[0050] Furthermore, the n may be 0 or more, for example, 1 or more, and preferably 2 or more.

[0051] In one embodiment of the present invention, the monomer represented by Chemical Formula 1 may be a monomer represented by Chemical Formula 2 below.

[0052] [ka]

[0053] In the above Chemical Formula 2, R1 and R3 are as defined above; p+q is greater than or equal to 1, p is a number from 0 to 100, and q is a number from 0 to 100.

[0054] Examples of the monomer represented by Chemical Formula 1 or Chemical Formula 2 include methoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, ethoxytriethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol methyl ether (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, propoxylated nonylphenol (meth)acrylate, ethoxylated phenol (meth)acrylate, and polypropylene glycol (meth)acrylate. Preferred examples include, but are not limited to, methoxyethyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, ethoxytriethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and polyethylene glycol methyl ether (meth)acrylate.

[0055] The monomer represented by Formula 1 or Formula 2 contains at least one oxygen atom, and the high electronegativity of the oxygen atom makes the monomer highly polar. Therefore, an adhesive layer containing the monomer has high affinity with a polar electrolyte solution and can swell upon contact with the electrolyte solution. Meanwhile, the term "electrolyte solution" in the above may refer to an ion-conducting medium used in, for example, a secondary battery. For example, the electrolyte solution may be, but is not limited to, an electrolyte solution that is a liquid medium. In this specification, the electrolyte solution may also be referred to as an electrolyte.

[0056] The polymer may contain, in a polymerized form, 30 to 300 parts by weight, for example, 40 to 280 parts by weight, or 44 to 250 parts by weight, of the monomer represented by Formula 1, relative to 100 parts by weight of the (meth)acrylic acid ester monomer, but is not limited thereto. The monomer represented by Formula 1 may be contained in an amount of 25 to 80 parts by weight, for example, 25 to 75 parts by weight, or 30 to 70 parts by weight, relative to 100 parts by weight of all monomers contained as polymerized units in the polymer. If the amount of the monomer represented by Formula 1 is too small, it may be difficult for the adhesive layer to expand sufficiently to detach from the electrode assembly upon contact with the electrolyte. If the amount of the monomer represented by Formula 1 is too large, excessive gelation may occur during the polymerization reaction of the polymer, making it difficult to achieve the adhesive properties of the adhesive. Therefore, taking this into consideration, the content of the monomer having a polar functional group may be adjusted within the above-mentioned range. In this specification, unless otherwise specified, "parts by weight" means relative "weight ratio".

[0057] The crosslinkable monomer having a crosslinkable functional group is a monomer that can be copolymerized with the (meth)acrylic acid ester monomer or other monomers contained in the polymer and, after copolymerization, can provide a crosslinking point in the main chain of the polymer that can react with a multifunctional crosslinking agent. The crosslinkable functional group may be a hydroxyl group, a carboxyl group, an isocyanate group, a glycidyl group, an amide group, or the like, and in some cases may be a photocrosslinkable functional group such as an acryloyl group or a methacryloyl group. The photocrosslinkable functional group can be introduced by reacting a compound having a photocrosslinkable functional group with the crosslinkable functional group provided by the copolymerizable monomer. Examples of the hydroxyl group-containing crosslinkable monomer include, but are not limited to, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxyethylene glycol (meth)acrylate, glycerol (meth)acrylate, and hydroxypropylene glycol (meth)acrylate, and mixtures of one or more of these monomers can also be used. Examples of the carboxyl group-containing monomer include, but are not limited to, (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. In addition, the crosslinkable monomer containing a glycidyl group may be, for example, glycidyl (meth)acrylate, epoxy alkyl (meth)acrylate, or epoxy cycloalkyl alkyl (meth)acrylate such as epoxy cyclohexyl methyl (meth)acrylate, but is not limited thereto.Examples of the crosslinkable monomer containing an isocyanate group that can be used include, but are not limited to, 2-isocyanate ethyl (meth)acrylate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, (meth)acryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, methacryloyl isocyanate, or allyl isocyanate; an acryloyl monoisocyanate compound obtained by reacting a diisocyanate compound or a polyisocyanate compound with 2-hydroxyethyl (meth)acrylate; and an acryloyl monoisocyanate compound obtained by reacting a diisocyanate compound or a polyisocyanate compound with a polyol compound and 2-hydroxyethyl (meth)acrylate. Examples of the amide group-containing monomer include, but are not limited to, (meth)acrylamide, diethylacrylamide, N-vinylpyrrolidone, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N'-methylenebisacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, and diacetone(meth)acrylamide. Examples of the amino group-containing monomer include, but are not limited to, aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and N,N-dimethylaminopropyl(meth)acrylate. Examples of the alkoxysilyl group-containing monomer include, but are not limited to, trimethoxysilylpropyl(meth)acrylate and allyloxyethyl(meth)acrylate.

[0058] The polymer may contain, in a polymerized form, 0.1 to 10 parts by weight, for example, 2.5 to 10 parts by weight, 2.9 to 9 parts by weight, or 2.9 to 8 parts by weight of a crosslinkable monomer relative to 100 parts by weight of a (meth)acrylic acid ester monomer, but is not limited thereto. The crosslinkable monomer may be contained in an amount of 0.1 to 5 parts by weight, for example, 0.5 to 3 parts by weight, or 1 to 2 parts by weight, relative to 100 parts by weight of all monomers contained in the polymerized units of the polymer. If the crosslinkable monomer content is too high, the peel strength may be too low, making it difficult for the adhesive layer to secure the electrode assembly. If the crosslinkable monomer content is too low, the adhesive layer may not expand sufficiently to detach from the electrode assembly upon contact with the electrolyte. Taking these factors into consideration, the content of the crosslinkable monomer may be adjusted within the above-mentioned range.

[0059] In one embodiment of the present invention, the adhesive layer may comprise a cured product of an adhesive composition comprising a polymer having polymerization units derived from a (meth)acrylic acid ester monomer, a monomer represented by Chemical Formula 1, and a crosslinkable monomer containing a crosslinkable functional group.

[0060] The polymer may further contain other functional comonomers in a polymerized form, if necessary, and examples thereof include a monomer represented by the following Chemical Formula 3.

[0061] [ka]

[0062] In the above Chemical Formula 3, R6 to R8 each independently represent hydrogen or an alkyl group, and R9 represents a cyano group; a phenyl group substituted or unsubstituted with an alkyl group; an acetyloxy group; or a COR 10 where R 10 represents an amino group or a glycidyloxy group which may or may not be substituted with an alkyl group or an alkoxyalkyl group.

[0063] R6 to R 10In the definition, the alkyl group or alkoxy group means an alkyl group or alkoxy group having 1 to 8 carbon atoms, and is preferably a methyl group, an ethyl group, a methoxy group, an ethoxy group, a propoxy group or a butoxy group.

[0064] Specific examples of the monomer of Formula 3 include, but are not limited to, nitrogen-containing monomers such as (meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-methyl(meth)acrylamide, (meth)acrylonitrile, N-vinylpyrrolidone, and N-vinylcaprolactam; styrene-based monomers such as styrene and methylstyrene; glycidyl(meth)acrylate; caprolactone; and vinyl esters of carboxylic acids such as vinyl acetate.

[0065] The polymer may be included in the composition in a crosslinked form using a multifunctional crosslinker. When the polymer is included in a crosslinked form, an adhesive layer prepared from the composition may have the property of expanding or swelling upon contact with an electrolyte, thereby preventing electrode disconnection. Furthermore, when the polymer is included in a crosslinked form, an adhesive layer prepared from the adhesive composition may have appropriate cohesive strength.

[0066] The type of polyfunctional crosslinking agent crosslinking the polymer is not particularly limited, and an appropriate crosslinking agent can be selected depending on the type of crosslinkable functional group present in the polymer from known crosslinking agents such as isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, metal chelate crosslinking agents, photocrosslinking agents, etc. Examples of the isocyanate crosslinking agent include diisocyanates such as tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoboron diisocyanate, tetramethylxylene diisocyanate, and naphthalene diisocyanate, as well as reaction products of the diisocyanates with polyols, and trimethylolpropane or the like can be used as the polyol. Examples of epoxy crosslinking agents that can be used include ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N,N,N',N'-tetraglycidylethylenediamine, and glycerin diglycidyl ether. Examples of aziridine crosslinking agents include N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), triethylenemelamine, bisisoprothaloyl-1-(2-methylaziridine), and tri-1-aziridinylphosphine oxide. Examples of metal chelate crosslinking agents include compounds in which a polyvalent metal is coordinated with a compound such as acetylacetone or ethyl acetoacetate. Examples of the polyvalent metal include aluminum, iron, zinc, tin, titanium, antimony, magnesium, and vanadium. Examples of photocrosslinking agents that can be used include polyfunctional acrylates. In the above, one or more crosslinking agents may be used in consideration of the type of crosslinkable functional group contained in the polymer.

[0067] The weight ratio of the multifunctional crosslinker in the pressure-sensitive adhesive composition can be adjusted to a range that ensures the desired peel strength or gel fraction (described below). For example, the crosslinker can be included in an amount of 0.001 to 10 parts by weight, e.g., 0.1 to 5 parts by weight, or 0.5 to 4 parts by weight, per 100 parts by weight of the total composition, but is not limited thereto. If the ratio of the multifunctional crosslinker is too low, the cohesive strength of the pressure-sensitive adhesive layer may not be adequately ensured, and if it is too high, the adhesive properties may be reduced. Therefore, an appropriate range should be selected taking these factors into consideration.

[0068] The polymer contained in the pressure-sensitive adhesive composition can be prepared by subjecting the mixture of monomers to a polymerization process such as solution polymerization, photopolymerization, bulk polymerization, suspension polymerization, or emulsion polymerization.

[0069] The polymer may have a weight average molecular weight (Mw) of approximately 300,000 to 2.5 million, 400,000 to 2 million, 500,000 to 2 million, 800,000 to 1.8 million, 600,000 to 1.2 million, 700,000 to 1.4 million, or 600,000 to 800,000. In this specification, the weight average molecular weight refers to a value converted to standard polystyrene measured by GPC (Gel Precipitation Chromatography), and unless otherwise specified, the molecular weight refers to the weight average molecular weight. If the molecular weight of the polymer is too low, the cohesive strength of the adhesive layer may decrease, and if it is too high, the adhesive properties may decrease. Therefore, an appropriate molecular weight can be selected taking these factors into consideration.

[0070] In addition to the above components, the PSA composition may further contain various additives known in the art, as needed. For example, the PSA composition may further contain a tackifier. Examples of tackifiers that can be used include, but are not limited to, rosin ester-based or styrene-based tackifiers, and appropriate types can be selected and used as needed. The content of the tackifier is also not particularly limited and can be adjusted taking into account factors such as the peel strength from the electrode assembly. For example, the tackifier may be used in a ratio of 1 to 25 parts by weight per 100 parts by weight of the polymer.

[0071] The pressure-sensitive adhesive composition may further contain additives such as an initiator such as a thermal initiator or a photoinitiator; an epoxy resin; a curing agent; an ultraviolet stabilizer; an antioxidant; a color-matching agent; a reinforcing agent; a filler; an antifoaming agent; a surfactant; a photopolymerizable compound such as a multifunctional acrylate; or a plasticizer, within a range that does not affect the intended effect.

[0072] For example, the polymer contained in the pressure-sensitive adhesive composition may be produced through photopolymerization by selecting a suitable photoinitiator known in the art. Examples of the photoinitiator include organic peroxides such as benzoyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-triethylcyclohexane, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxyisopropyl carbonate, di-2-ethylhexyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-3,3,5-trimethylhexanoyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dicumyl peroxide, and methyl ether ketone peroxide; butyl hydroperoxide; The photopolymerization method can be performed using, but is not limited to, hydroperoxides such as ammonium peroxide and cumyl hydroperoxide; oxidizing agents such as hydrogen peroxide, ammonium peroxydisulfate, nitric acid and its salts, perchloric acid and its salts, sulfuric acid and its salts, hypochloric acid and its salts, permanganic acid and its salts, chromic acid and its salts, lead dioxide, manganese dioxide, copper oxide, iron chloride, fluorine, chlorine, bromine, and iodine; reducing agents such as sodium borohydride, formaldehyde, acetaldehyde, amines, and hydrazine; azo compounds such as azobisisobutyronnitrile (hereinafter referred to as AIBN); irradiation with heat, light, ultraviolet light, or high-energy wavelengths; and electron transfer in an electrolyte.

[0073] The content of the photoinitiator is not particularly limited, but may be 0.01 to 5 parts by weight, for example, 0.01 to 1 part by weight, or 0.01 to 0.5 parts by weight, based on 100 parts by weight of the total monomer mixture.

[0074] The adhesive layer can be formed, for example, by coating a coating liquid containing the polymer and a multifunctional crosslinking agent on the substrate and inducing a crosslinking reaction between the polymer and the multifunctional crosslinking agent under appropriate conditions.

[0075] The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the intended use, for example, the desired peel strength, etc. The adhesive layer can be formed to have a thickness of, for example, about 2 μm to 100 μm, 3 μm to 50 μm, 4 μm to 25 μm, 4 μm to 15 μm, 4 μm to 10 μm, 4 μm to 9 μm, 4 μm to 7 μm, or 5 μm to 7 μm, but this can be changed depending on the intended purpose.

[0076] The adhesive layer may be provided on one side of the substrate in a pattern. Specifically, the pattern may be a closed figure pattern, a linear pattern, or a combination of a closed figure pattern and a linear pattern. In one example, the pattern may be a grid pattern or an S-shaped pattern, but is not limited thereto, and any suitable pattern known in the art may be used.

[0077] The pattern may include, but is not limited to, a wave pattern, a grid pattern, or an embossed pattern of a relief shape, and any suitable pattern known in the art may be adopted and applied.

[0078] The wavy pattern may refer to a pattern formed by wavy curves. In this case, the wavy curves may form convex or concave portions, and the uneven surface included in the adhesive layer may include such a pattern, thereby improving the adhesive strength of the adhesive layer.

[0079] The grid pattern may refer to a pattern formed by convex portions formed by the intersection of linear concave portions. Alternatively, it may refer to a pattern formed by concave portions formed by the intersection of linear convex portions. In this case, the formed convex portions or concave portions form a grid, and the shape of each grid may be any of a square, rectangle, parallelogram, and rhombus. When the uneven surface included in the adhesive layer includes such a pattern, the adhesive strength of the adhesive layer can be improved.

[0080] The embossed pattern of the relief shape may be, for example, a pattern in which spherical concaves and convexes are protruded in relief shape.

[0081] When the adhesive layer is provided (coated) in a patterned form, the contact area with the electrolyte increases, thereby accelerating the diffusion rate of the electrolyte into the adhesive layer. When the diffusion rate of the electrolyte increases, the adhesive layer also absorbs and expands the electrolyte at a faster rate, causing the sealing tape to detach from the electrode assembly more quickly. Therefore, the sealing tape detaches immediately after the electrolyte is poured into the battery can, inducing the electrode assembly to unravel, and more stably increasing the contact area between the negative electrode and the inside of the can. Furthermore, the shortened detachment time has the advantage of ensuring mass-production quality after battery production. However, if the detachment time is delayed and the sealing tape remains attached, there is a problem of increased battery resistance deviation during mass-production quality checks.

[0082] The sealing tape may be attached to the outer periphery of an electrode assembly in a secondary battery. In addition, in the sealing tape according to one embodiment of the present invention, the initial peel strength of the adhesive layer is not too high, and the sealing tape includes an adhesive layer containing the above-described monomer having a polar functional group. Therefore, when the sealing tape comes into contact with an electrolyte in a secondary battery, the adhesive layer absorbs the electrolyte and expands, so that the peel strength of the adhesive layer can be adjusted to a low level that allows the sealing tape to be detached from the electrode assembly.

[0083] In one embodiment of the present invention, the sealing tape may have an initial peel strength sufficient to secure the electrode assembly and detach from the electrode assembly upon contact with an electrolyte. If the initial peel strength of the electrode assembly is too high, the adhesive layer may be difficult to detach from the electrode assembly even after contact with the electrolyte. For example, the adhesive layer may have a peel strength of 370 gf / 25 mm or less, e.g., 350 gf / 25 mm or less, 315 gf / 25 mm or less, or 312 gf / 25 mm or less, measured at room temperature from glass at a peel speed of 5 mm / sec and a peel angle of 180 degrees. The lower limit of the adhesive layer's peel strength from glass is not particularly limited. For example, if the adhesive layer has a very low initial peel strength, the adhesive layer will lose its adhesive strength upon contact with the electrolyte, causing the sealing tape to detach from the electrode assembly, thereby preventing electrode disconnection. However, if the initial peel strength of the adhesive layer is too low, the adhesive layer may unravel without coming into contact with the electrolyte before the electrode assembly is placed in the can. In consideration of this, the lower limit of the peel strength of the adhesive layer from glass may be adjusted to 5 gf / 25 mm or more, for example, 10 gf / 25 mm or more, 20 gf / 25 mm or more, 30 gf / 25 mm or more, 40 gf / 25 mm or more, 50 gf / 25 mm or more, 60 gf / 25 mm or more, 70 gf / 25 mm or more, 80 gf / 25 mm or more, 85 gf / 25 mm or more, or 88 gf / 25 mm or more. When the adhesive layer has a peel strength from glass within this range, even when the adhesive layer is attached to the outer surface of the electrode assembly, it can exhibit an appropriate initial peel strength for detachment upon contact with the electrolyte, and the sealing tape can form a three-dimensional structure with a specific surface roughness when it comes into contact with the electrolyte.

[0084] In one embodiment of the present invention, the sealing tape may be detached from the outer peripheral surface of the electrode assembly, i.e., it may not be attached to the outer peripheral surface and may have lost its adhesive force.

[0085] The adhesive strength of the sealing tape after the electrolyte injection is reduced by 80% or more, specifically, 90% or more, 95% or more, or 99% or more, based on the adhesive strength of the sealing tape before the electrolyte injection.

[0086] In one embodiment of the present invention, the adhesive layer of the sealing tape absorbs the electrolyte and expands to form a three-dimensional structure, and the peel strength of the adhesive layer may be adjusted to be low enough to allow the adhesive layer to detach from the outer surface of the electrode assembly. According to one example, the sealing tape may detach from the outer surface of the electrode assembly after contacting the electrolyte, and preferably, 50% or more, for example, 60% or more, 70% or more, or 80% or more of the area of ​​the sealing tape attached to the outer surface of the electrode assembly may detach.

[0087] The thickness of the sealing tape can be appropriately selected depending on the desired peel strength, etc., and is not particularly limited. The sealing tape can be formed to a thickness of, for example, about 10 μm to 100 μm, 15 μm to 75 μm, 20 μm to 45 μm, 15 μm to 40 μm, 20 μm to 40 μm, or 20 μm to 30 μm, but this thickness may be changed depending on the purpose. If the thickness of the sealing tape is too thin, the effect of the expansion of the adhesive layer of the sealing tape may not be fully exerted. Conversely, if the thickness is too thick, the thickness of the electrode assembly may increase accordingly, which may result in significant damage to the electrode assembly due to reduced processability when inserting it into a battery case, or may cause a decrease in capacity for the same standard size.

[0088] The sealing tape may further include a release sheet attached to the adhesive layer to protect the adhesive layer before the sealing tape is used.

[0089] The substrate contained in the sealing tape will be specifically described below.

[0090] In one embodiment of the present invention, the substrate may include, but is not limited to, one or more films selected from the group consisting of polypropylene film, polyimide film, acrylic film, polyolefin film, polyamide film, polycarbonate film, polyurethane film, cellulose acetate film, and polyester film.

[0091] If the substrate comprises a polyester film, it may comprise at least one selected from the group consisting of polyethylene terephthalate film, polyethylene nitrate film, and polybutylene terephthalate film. If the substrate comprises a cellulose-based substrate, it may comprise at least one selected from the group consisting of cellulose acetate resin and cellulose alkylate resin, and may be manufactured by subjecting a mixture containing the resin to an extrusion or casting process. For example, cellulose acetate propionate or cellulose acetate butyrate may be used as the cellulose alkylate.

[0092] In order to shorten the removal time, the following base materials can be used as the base material of the sealing tape.

[0093] In one embodiment of the present invention, the substrate may have swelling properties in response to an electrolyte. Specifically, the substrate may absorb the electrolyte after contacting the electrolyte. Specifically, the substrate may absorb the electrolyte and undergo structural deformation. For example, the substrate may deform in the length direction after contacting the electrolyte.

[0094] When a substrate that absorbs the electrolyte after contact with it is used, the electrolyte can move more freely through the substrate, further accelerating the electrolyte absorption rate of the adhesive layer. Therefore, the sealing tape detaches faster than when a general substrate is used. This detachment occurs immediately after the electrolyte is poured into the battery can, inducing the loosening of the electrode assembly and more stably increasing the contact area between the negative electrode and the inside of the can. Furthermore, the shortened detachment time has the advantage of ensuring mass-production quality after battery production. However, if the detachment time is delayed and the sealing tape remains attached, there is a problem of increased battery resistance deviation during mass-production quality checks.

[0095] The term "length direction" as used herein may refer to a direction perpendicular to the thickness direction of the substrate when the substrate is held flat. Furthermore, the terms "vertical" and "horizontal" as used herein refer to substantially vertical or horizontal within a range that does not impair the intended effect, and may include an error of, for example, ±10 degrees, ±5 degrees, or ±3 degrees.

[0096] The substrate may be one that can deform, for example, expand, in any direction, including horizontal or vertical, or diagonal directions, in the plane of the substrate, so long as it has the property of deforming, for example, expanding, in the length direction.

[0097] In one embodiment of the present invention, the substrate may have a longitudinal distortion rate of 10% or more according to the following formula 2:

[0098] [Formula 2] Distortion rate in the longitudinal direction of the substrate = (L2-L1) / L1 x 100 In the formula 2, L1 is the initial length of the substrate before contact with the fluid, and L2 is the length of the substrate measured after contacting the substrate with the fluid for 24 hours at room temperature or 60°C.

[0099] When calculating Equation 2, the specific type of fluid that the substrate comes into contact with is not particularly limited. According to one example, the fluid may be a liquid electrolyte that is poured into the can. The term "electrolyte" may refer to, for example, an ion-conducting medium used in batteries. Furthermore, the term "room temperature" refers to a natural temperature that is not heated or cooled, and may refer to, for example, a temperature of about 10°C to about 30°C, about 20°C to about 30°C, or about 25°C.

[0100] The strain rate in the longitudinal direction of the substrate may be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The upper limit of the strain rate in the longitudinal direction of the substrate is not particularly limited. That is, the higher the strain rate value, the easier it is to induce detachment of the sealing tape. For example, the upper limit of the strain rate of the substrate may be 500%.

[0101] In Equation 2, L1 and L2 are the lengths of the substrate before and after contact with the fluid. The lengths are measured in a predetermined direction relative to the substrate, and the specific direction in which the lengths are measured is not particularly limited, as long as the same direction is applied when measuring L1 and L2.

[0102] For example, if the substrate is a rectangular sheet, the length of the substrate may be the horizontal, vertical, or diagonal length of the sheet, or the length in any direction on a plane. However, since the directions for measuring the lengths are the same when measuring L1 and L2, for example, if the horizontal length of the substrate is used as L1, the horizontal length of the substrate is also used as L2.

[0103] The shape of the substrate is not particularly limited and may be, for example, a film or sheet. The film or sheet substrate may have a rectangular, circular, triangular, or amorphous shape.

[0104] The substrate may have a Shore A hardness of 70A or more according to ASTM D2240. The substrate may have a Shore D hardness of 40D or more according to JIS K-7311. There is no particular upper limit to the hardness of the substrate, but, for example, the upper limit of the Shore A hardness may be 100A or 95A, and the upper limit of the Shore D hardness may be 100D or 85D.

[0105] The substrate may include a thermoplastic polyurethane film (TPU film). The substrate may have a single-layer structure of thermoplastic polyurethane film, or a multilayer structure, for example a two-layer structure, including at least one polyurethane film layer. The thermoplastic polyurethane film may be a uniaxially or biaxially stretched film, or a non-stretched film.

[0106] Known examples of the thermoplastic polyurethane film include polyester TPU film, polyether TPU film, and polycaprolactone TPU film. An appropriate type can be selected from these films, but polyester TPU film may be preferred. Furthermore, aromatic or aliphatic thermoplastic polyurethane films can be used. When using the thermoplastic polyurethane film, a release layer may be further included to ensure peel strength by adjusting adhesive strength.

[0107] The thermoplastic polyurethane film may be a reaction product of a mixture containing a polyol compound (e.g., a polyester polyol compound), a chain extender, and an isocyanate compound (e.g., an aromatic or aliphatic diisocyanate compound), and the ratio and type of the polyol compound that forms the soft chain and the chain extender and isocyanate compound that form the hard chain may be adjusted to provide a thermoplastic polyurethane film with desired physical properties. For example, the substrate may include a polyester-based thermoplastic polyurethane film, and if necessary, a film may be used in which the weight ratio of units derived from polyester polyol and units derived from the isocyanate compound and / or chain extender in the polyurethane is adjusted within an appropriate range.

[0108] When a thermoplastic polyurethane film is used as the substrate as described above, the electrolyte solution can move more freely through the substrate, and therefore the electrolyte solution absorption rate of the adhesive layer becomes even faster.

[0109] When the substrate includes another film in addition to the thermoplastic polyurethane film, the other film may be a polymer film or sheet manufactured to exhibit the above-described deformation, for example, expansion properties, when it comes into contact with a fluid due to the stretching or shrinking treatment conditions during the manufacturing process.

[0110] According to one example, the other film may be a film containing an ester bond or an ether bond or a cellulose ester compound, such as an acrylate-based film, an epoxy-based film, or a cellulose-based film.

[0111] In another embodiment, the substrate may include a film having a porous structure. Specifically, the porous film may be a separator, a nonwoven fabric, a fiber, or paper, but is not limited thereto, and any structure known in the art may be appropriately adopted.

[0112] When a film having a porous structure is used as the substrate, the electrolyte can move more freely through the substrate, resulting in a faster electrolyte absorption rate for the adhesive layer. Therefore, the sealing tape detaches more quickly than when a general substrate is used. This detachment occurs immediately after the electrolyte is poured into the battery can, inducing the loosening of the electrode assembly and more stably increasing the contact area between the negative electrode and the inside of the can. Furthermore, the shorter detachment time has the advantage of ensuring mass-production quality after battery production. However, if the detachment time is delayed and the sealing tape remains attached, there is a problem of increased battery resistance deviation during mass-production quality checks.

[0113] The method for producing the substrate is not particularly limited, and for example, a conventional film or sheet forming method such as extrusion or casting of a raw material containing the resin can be used. In this case, known additives can be added to the raw material containing the resin, if necessary.

[0114] When the substrate is in the form of a sheet or film, the thickness of the substrate is not particularly limited and may be, for example, about 10 μm to 200 μm, 10 μm to 100 μm, 10 μm to 50 μm, 15 μm to 30 μm, or 15 μm to 20 μm.

[0115] A secondary battery according to one embodiment of the present invention includes an electrode assembly having a wound structure of a positive electrode, a negative electrode, and a separator; an electrolyte; and a can containing the electrode assembly and the electrolyte, wherein the negative electrode is positioned on an outer circumferential surface of the electrode assembly and a sealing tape is provided on the outer circumferential surface. In this case, the sealing tape includes a substrate and an adhesive layer provided on one surface of the substrate, and the adhesive layer has swelling properties in response to the electrolyte so that it can absorb the electrolyte and swell after coming into contact with the electrolyte.

[0116] The electrode assembly may have a structure in which a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound up, and the negative electrode may be positioned on the outer periphery of the electrode assembly.

[0117] The sealing tape may be attached to the outer circumferential surface of the electrode assembly via the adhesive layer. The electrode assembly may be wound in a jelly roll shape.

[0118] In one embodiment of the present invention, the negative electrode may include a negative electrode coating portion and a negative electrode uncoated portion, and the negative electrode uncoated portion may be located on the outer periphery of the electrode assembly. That is, the negative electrode uncoated portion may be located on the outer periphery of the electrode assembly, and a sealing tape may be provided on the negative electrode uncoated portion.

[0119] In one embodiment of the present invention, the negative electrode may include a negative electrode coating portion and a negative electrode uncoated portion, and the negative electrode coating portion may be located on the outer circumferential surface of the electrode assembly. That is, the negative electrode coating portion may be located on the outer circumferential surface of the electrode assembly, and a sealing tape may be provided on the negative electrode coating portion.

[0120] In one embodiment of the present invention, the negative electrode may include a negative electrode coating portion and a negative electrode uncoating portion, and the negative electrode coating portion and the negative electrode uncoating portion may both be located on the outer circumferential surface of the electrode assembly. That is, the negative electrode coating portion coated with a negative electrode active material and the negative electrode uncoating portion not coated with a negative electrode active material may both be located on the outer circumferential surface of the electrode assembly, and sealing tape may be provided on the negative electrode coating portion and the negative electrode uncoating portion.

[0121] The positive electrode may include a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector. Specifically, the positive electrode includes a positive electrode coating portion in which a positive electrode active material layer is formed on the positive electrode current collector; and a positive electrode uncoated portion in which no positive electrode active material layer is formed on the positive electrode current collector. Specifically, the positive electrode coating portion may be formed by coating one or both sides of the positive electrode current collector with a positive electrode active material, and the positive electrode current collector may be exposed in the positive electrode uncoated portion where no positive electrode active material is coated. Here, the positive electrode current collector may be made of, for example, aluminum (Al) foil. In this case, the positive electrode active material may be, for example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron phosphate, or a compound or mixture containing at least one of these.

[0122] The negative electrode may include a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector. Specifically, the negative electrode includes a negative electrode coating portion having a negative electrode active material layer on the negative electrode current collector; and a negative electrode uncoated portion on the negative electrode current collector where no negative electrode active material layer is coated. Specifically, the negative electrode coating portion may be formed by coating one or both sides of the negative electrode current collector with a negative electrode active material, and the negative electrode current collector may be exposed in the negative electrode uncoated portion where no negative electrode active material is coated. Here, the negative electrode current collector may be formed of a foil made of, for example, copper (Cu) or nickel (Ni). In this case, the negative electrode active material may be formed of a material including, for example, artificial graphite. In addition, the negative electrode active material may be formed of, for example, lithium metal, lithium alloy, carbon, petroleum coke, activated carbon, graphite, silicon compound, tin compound, titanium compound, or an alloy thereof.

[0123] The separator separates and electrically insulates the positive electrode and the negative electrode. Here, the positive electrode and the negative electrode may be wound together with the separator to form a jelly roll type electrode assembly, or may be formed as a stack type or a stack and fold type.

[0124] The separator may be made of an insulating material and may be alternately stacked with the positive and negative electrodes, where the separator may be positioned between the positive and negative electrodes and on the outer surfaces of the positive and negative electrodes.

[0125] Any separator membrane that is normally used as a separator membrane in a secondary battery can be used without any particular limitation, and it is particularly preferable that the separator membrane has low resistance to the ion movement of the electrolyte and excellent ability to retain the electrolyte.

[0126] The separator may also be made of a ductile material. In this case, the separator may be formed of a polyolefin-based resin film, such as microporous polyethylene or polypropylene. Alternatively, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0127] In the above, the type of electrolyte, which is a fluid that deforms, for example, expands, the adhesive layer of the sealing tape, is not particularly limited, and any electrolyte known in this field can be used depending on the type of battery.

[0128] In one example, the electrolytic solution 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 manufacturing a secondary battery, but is not limited to these.

[0129] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0130] Examples of the non-aqueous organic solvent that may be used include 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, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0131] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with low-viscosity, low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte solution with high electrical conductivity can be prepared, and these cyclic carbonates are more preferably used.

[0132] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt can be 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 - It is possible to use one or more selected from the group consisting of: The concentration of the lithium salt in the electrolyte can vary depending on the application, and is usually within the range of 0.1M to 2.0M.

[0133] In addition to the components of the electrolyte solution, the electrolyte solution may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0134] The can containing the electrode assembly and the electrolyte may be, but is not limited to, a cylindrical can.

[0135] The secondary battery may be manufactured by attaching the sealing tape to an electrode assembly, placing the electrode assembly in a can, injecting an electrolyte into the can, and then sealing the can.

[0136] The sealing tape is inserted into the can while being fixed to the electrode assembly, and then absorbs the electrolyte injected into the can and expands, thereby reducing the peel strength between the adhesive layer and the electrode assembly, thereby allowing the adhesive layer of the sealing tape to detach from the electrode assembly. Therefore, the secondary battery according to one embodiment of the present invention may have a structure in which the electrode assembly is loosened to some extent, and the outer surface of the electrode assembly is in contact with the inside of the can.

[0137] FIG. 1 is a diagram schematically illustrating a secondary battery according to an embodiment of the present invention.

[0138] Referring to FIG. 1, the secondary battery includes an electrode assembly 11 and a sealing tape 12 attached to the outer circumferential surface of the electrode assembly 11.

[0139] Figure 1-1 is a schematic diagram of a secondary battery from the process of attaching the sealing tape 12 to the electrode assembly 11 to the process of storing it inside a can. The sealing tape 12 is attached to the outer surface of the electrode assembly 11, fixing the electrode assembly 11, and forming a certain amount of gap between the inside of the can 10 and the electrode assembly 11.

[0140] 1-2 is a schematic diagram of a secondary battery after an electrolyte solution has been injected into the can 10. As the sealing tape 12 absorbs the electrolyte solution and its peeling strength decreases, it becomes detached from the electrode assembly 11, causing the wound electrode assembly 11 to unwind to some extent, reducing the gap between the inside of the can 10 and the electrode assembly 11. At this time, although not clearly shown in FIG. 1-2, the outer circumferential surface of the electrode assembly may come into contact with the inside of the can.

[0141] That is, a secondary battery according to an embodiment of the present invention includes a region where the interior of the can and the outer periphery of the electrode assembly are in contact with each other. In this case, the contact area between the interior of the can and the outer periphery of the electrode assembly may be 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more, or may be 100% or less, 90% or less, 80% or less, 70% or less, or 60% or less, based on the total area of ​​the outer periphery of the electrode assembly.

[0142] 2 is a schematic diagram illustrating a secondary battery according to an embodiment of the present invention. Referring to FIG. 2, the sealing tape 12 may be attached to surround the outer periphery of the electrode assembly 11.

[0143] Specifically, the sealing tape 12 may be provided to surround the outer peripheral surface, including a finishing portion 21 where the outermost end of the outer peripheral surface of the electrode assembly 11 is located. That is, the sealing tape 12 may be provided to surround the outer peripheral surface in the width direction (direction perpendicular to the height direction) of the electrode assembly 11. In this case, the sealing tape being provided to surround the outer peripheral surface means that the sealing tape is provided continuously without being broken along the outer peripheral surface of the electrode assembly.

[0144] Specifically, the sealing tape 12 may be provided on each of the upper and lower portions 31 and 33 of the outer peripheral surface of the electrode assembly 11. That is, the sealing tape may be attached in two rows on the outer peripheral surface of the electrode assembly. In this case, the upper portion 31 and the lower portion 33 refer to the upper and lower regions, respectively, based on the center portion 32 of the outer peripheral surface. Furthermore, the upper end portion 41 and the lower end portion 42 of the outer peripheral surface of the electrode assembly may be provided so that the electrode assembly is exposed. However, this is not limited thereto, and the sealing tape may be attached at appropriate positions depending on the size and type of battery so that the detachment time can be appropriately adjusted.

[0145] The sealing tape 12 may be provided in an area that does not include the central portion 32 of the outer circumferential surface, based on the height of the electrode assembly 11. In this case, the central portion 32 may refer to an area within ±1% (height basis) above and below the center of the outer circumferential surface.

[0146] If the sealing tape is attached to the center of the outer periphery, it is difficult to induce unraveling of the electrode assembly even if the sealing tape absorbs and deforms the electrolyte, and the contact area between the negative electrode and the inside of the can is not ensured. On the other hand, if the sealing tape is attached to the upper and lower parts of the outer periphery without including the center, as in the present invention, it is easy to induce unraveling of the electrode assembly, and the contact area between the negative electrode and the inside of the can can be increased, making it easy to achieve low resistance characteristics.

[0147] The area of ​​the outer circumferential surface of the electrode assembly where the sealing tape is attached can be adjusted depending on the size and type of the battery so that the detachment time can be appropriately controlled. In one example, the area of ​​the sealing tape attached may be less than 80%, less than 70%, less than 60%, less than 50%, less than 40%, or less than 30% of the total area of ​​the outer circumferential surface of the electrode assembly, but may be 5% or more, 10% or more, or 20% or more, but is not limited thereto.

[0148] In another embodiment, the sealing tape may be provided on a finishing portion where the outermost end of the outer peripheral surface of the electrode assembly is located. Specifically, although not shown in the drawings, the sealing tape may be attached in the height direction on the finishing portion where the outermost end of the outer peripheral surface of the electrode assembly is located. That is, the sealing tape may be attached in a line so as to cover the finishing portion where the outermost end of the outer peripheral surface of the electrode assembly is located. However, this is not limited thereto, and the sealing tape may be attached at an appropriate position depending on the size and type of battery so as to appropriately adjust the unraveling of the electrode assembly.

[0149] When the sealing tape is attached in the height direction on the finishing portion of the electrode assembly, it can be attached in a form that continuously covers the finishing portion of the electrode, thereby preventing damage to the electrode assembly and increasing the contact area between the negative electrode and the inside of the cylindrical can, thereby easily achieving low resistance characteristics.

[0150] In one embodiment of the present invention, the average gap between the inside of the can and the outer peripheral surface of the electrode assembly before the sealing tape is removed, i.e., the difference between the average inner diameter of the can and the average outer diameter of the electrode assembly, may be more than 0.9% and not more than 2% based on the inner diameter of the can, specifically, not more than 1.5%, not more than 1.3%, not more than 1.2%, not more than 1.1%, or not more than 1%.

[0151] In one embodiment of the present invention, after the sealing tape is removed, the average gap between the inside of the can and the outer peripheral surface of the electrode assembly, i.e., the difference between the average inner diameter of the can and the average outer diameter of the electrode assembly, may be 0.9% or less based on the inner diameter of the can. Specifically, it may be 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, or 0.2% or less, or may be 0% or more, more than 0%, or 0.1% or more.

[0152] In one embodiment of the present invention, the electrode assembly may include one negative electrode tab. Generally, an electrode assembly having a separator located on its outer periphery includes multiple negative electrode tabs to achieve low resistance, but this can make it difficult to weld the negative electrode tabs and ensure sufficient internal space within the can. In contrast, the present invention positions the negative electrode on the outer periphery of the electrode assembly, increasing the contact area between the negative electrode and the interior of the can to achieve low resistance. This allows for highly low resistance characteristics even with a single negative electrode tab, while also reducing costs, ensuring sufficient internal space within the can, and ensuring sufficient weldability of the negative electrode tab.

[0153] [Example] Hereinafter, the present specification will be described in detail with reference to examples in order to specifically explain the present specification. However, the examples according to the present specification can be modified into various other forms, and the scope of the present application is not to be construed as being limited to the examples detailed below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art.

[0154] Example 1 (1) Manufacturing of sealing tape A 1000cc reactor equipped with a nitrogen gas reflux and a cooling device for easy temperature control was charged with a monomer mixture consisting of 68 parts by weight of n-butyl acrylate (n-BA), 30 parts by weight of methoxyethyl acrylate (MEA), and 2 parts by weight of hydroxybutyl acrylate (HBA), 0.02 parts by weight of n-dodecanethiol as a chain transfer agent, and 150 parts by weight of ethyl acetate (EAc) as a solvent. The mixture was then purged with nitrogen gas at 60°C for 60 minutes to remove oxygen, and then maintained at 60°C. After homogenizing the mixture, 0.04 parts by weight of azobisisobutyronitrile (AIBN) as a reaction initiator was added. The mixture was reacted for 8 hours to produce a polymer having a weight average molecular weight of 780,000. In the above, parts by weight means wt%.

[0155] 100 parts by weight of the polymer prepared as described above was added to an ethyl acetate solution of 0.3 parts by weight of a tolylene diisocyanate adduct of trimethylolpropane as a polyfunctional isocyanate crosslinking agent, and then diluted to an appropriate concentration in consideration of coating properties and mixed uniformly.

[0156] The adhesive composition prepared as described above was coated on one side of a PET (poly(ethylene terephthalate)) film (thickness: 12 μm) and dried to form a uniform adhesive layer with a thickness of 5 μm. A release film was then laminated on the coating layer, and the coating was then aged at a constant temperature (25°C) and humidity for 3 days to prepare a sealing tape.

[0157] (2) Secondary battery manufacturing A jelly-roll-shaped electrode assembly (cross-sectional diameter: 20.5 mm) was formed by winding the negative electrode, positive electrode, and separator together, with the negative electrode attached to the outer periphery. Sealing tape was applied to cover approximately 30% of the outer periphery, and the assembly was inserted into a cylindrical can (cross-sectional diameter: 21.05 mm). A carbonate-based electrolyte solution was then poured into the can, which was then sealed to prepare a secondary battery.

[0158] <Example 2> A secondary battery was manufactured in the same manner as in Example 1, except that a non-stretched PU film (thickness: 40 μm) made of thermoplastic polyurethane (TPU) was used as the substrate instead of the PET film in Example 1.

[0159] <Comparative Example 1> A secondary battery was manufactured in the same manner as in Example 1, except that a monomer mixture consisting of 98 parts by weight of n-butyl acrylate and 2 parts by weight of hydroxybutyl acrylate was used instead of the monomer mixture in Example 1.

[0160] <Experimental Example> For the secondary batteries manufactured in the examples and comparative examples, ACIR was measured at room temperature using a charge / discharge measuring device (P&E Solutions) by bringing the probes of the measuring device into contact with the positive and negative electrodes. In addition, the expansion of the adhesive layer of the sealing tape and the time it took for the sealing tape to detach from the electrode assembly were measured, and the results are shown in Table 1 below.

[0161] Figure 3 shows CT images of the batteries fabricated in Example 1 and Comparative Example 1. In Comparative Example 1, the sealing tape did not come off, creating a gap between the anode and the inside of the can. In Example 1, the sealing tape absorbed the electrolyte and expanded, causing the electrode assembly to unravel, resulting in almost no gap between the anode and the inside of the can.

[0162] [Table 1]

[0163] In Table 1, it was confirmed that in Examples 1 and 2, the adhesive layer contained a sealing tape that had swelling properties in response to the electrolyte, which induced the electrode assembly to unravel after the electrolyte was injected into the can, thereby increasing the contact area between the negative electrode and the can and reducing the internal resistance.

[0164] Furthermore, it was confirmed that in Example 2, the electrolyte solution diffused through the substrate, and the electrolyte solution had a high diffusion rate, so that the removal time of the sealing tape was faster.

[0165] On the other hand, in the case of Comparative Example 1, since the adhesive layer did not swell in response to the electrolyte, it was difficult to induce the electrode assembly to unravel, and the contact area between the negative electrode and the inside of the can could not be secured, resulting in high internal resistance.

[0166] While the present invention has been described above with reference to preferred embodiments, it will be understood by those skilled in the art that various modifications and variations can be made thereto without departing from the spirit and scope of the invention as set forth in the following claims. [Explanation of symbols]

[0167] 10 Cylindrical can 11...electrode assembly 12 Sealing tape 21 Finishing section 31 Upper part of outer periphery 32 Center of outer periphery 33 Lower part of outer periphery 41: Upper end of outer periphery 42 Lower end of outer periphery

Claims

1. A secondary battery comprising: an electrode assembly having a structure in which a positive electrode, a negative electrode, and a separator are wound; an electrolyte; and a can containing the electrode assembly and the electrolyte, the negative electrode is located on the outer circumferential surface of the electrode assembly, a sealing tape is provided on the outer circumferential surface of the electrode assembly; The sealing tape includes a substrate and an adhesive layer provided on one surface of the substrate, The adhesive layer has swelling properties in response to the electrolyte solution.

2. The secondary battery according to claim 1 , wherein the adhesive layer is in a swollen state after absorbing the electrolyte solution.

3. The secondary battery according to claim 1 , wherein the sealing tape is detached from the outer peripheral surface of the electrode assembly.

4. The secondary battery according to claim 1 , further comprising a region where the inside of the can and the outer circumferential surface of the electrode assembly are in contact with each other.

5. The secondary battery according to claim 1 , wherein the sealing tape is provided to surround the outer circumferential surface of the electrode assembly, including a finishing portion where an outermost end of the outer circumferential surface of the electrode assembly is located.

6. The secondary battery according to claim 1 , wherein the sealing tape is provided on both an upper portion and a lower portion of the outer circumferential surface of the electrode assembly.

7. The secondary battery according to claim 1 , wherein the sealing tape is provided in an area that does not include a center portion of the outer circumferential surface when the height of the electrode assembly is taken as a reference.

8. The secondary battery of claim 1 , wherein the negative electrode includes a negative electrode coating portion and a negative electrode uncoated portion, the negative electrode uncoated portion being located on an outer circumferential surface of the electrode assembly.

9. The secondary battery of claim 1 , wherein the negative electrode includes a negative electrode coating portion and a negative electrode uncoated portion, and the negative electrode coating portion is located on an outer circumferential surface of the electrode assembly.

10. The secondary battery according to claim 1, wherein the adhesive layer has a center line average roughness value of 100 μm to 250 μm measured 24 hours after contact with the electrolyte solution.

11. 10. The secondary battery of claim 1, wherein the adhesive layer comprises a cured product of an adhesive composition including a polymer having polymerization units derived from a (meth)acrylic acid ester monomer, a monomer represented by the following Chemical Formula 1, and a crosslinkable monomer having a crosslinkable functional group: 【Chemistry 1】 In the above Chemical Formula 1, R １ is hydrogen; or an alkyl group having 1 to 12 carbon atoms, R ２ is an alkylene group having 1 to 6 carbon atoms, R ３ is hydrogen; an alkyl group having 1 to 12 carbon atoms; an aryl group having 6 to 24 carbon atoms; or an arylalkyl group having 6 to 48 carbon atoms, n is 0 or greater.

12. The secondary battery according to claim 1 , wherein the adhesive layer is provided on one surface of the substrate in a patterned form.

13. The secondary battery according to claim 1 , wherein the substrate has swelling properties in response to the electrolyte solution.

14. The secondary battery according to claim 1, wherein the substrate has a longitudinal distortion rate of 10% or more according to the following formula 2: [Formula 2] Distortion rate in the longitudinal direction of the substrate = (L2 - L1) / L1 x 100 In the formula 2, L1 is the initial length of the substrate before contact with the fluid, and L2 is the length of the substrate measured after contacting the substrate with the fluid at room temperature or 60°C for 24 hours.

15. The secondary battery according to any one of claims 1 to 14, wherein the substrate comprises a thermoplastic polyurethane film.

16. The secondary battery according to claim 1 , wherein the substrate comprises a film including a porous structure.

17. The secondary battery of claim 1 , wherein the electrode assembly includes one negative electrode tab.

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