Electrode assembly and lithium secondary battery including the same

Abstract

The present invention relates to an electrode assembly including: a positive electrode including a positive electrode active material layer; a negative electrode including a negative electrode active material layer; an electrode stack including a separator interposed between the positive electrode and the negative electrode; and at least one fixing member that wraps and fixes the electrode stack in an entire width direction, wherein the positive electrode includes a positive electrode sliding portion where the thickness of the positive electrode active material layer decreases, and the at least one fixing member is disposed to overlap a region corresponding to the positive electrode sliding portion.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183641, filed December 23, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly and a lithium secondary battery including the same, and more particularly to an electrode assembly developed to suppress the occurrence of lithium plating in an electrode slide portion and a lithium secondary battery including the same. [Background technology]

[0003] With the development of technologies for electric vehicles, energy storage systems (ESS), portable electronic devices, etc., the demand for lithium secondary batteries as an energy source is rapidly increasing.

[0004] Lithium secondary batteries are classified into pouch types, can types, etc. depending on the material of the case that houses the electrode assembly, and the electrode assemblies are classified into wound types (jelly roll types), stack types, stack and lamination types, stack and folding types, etc. depending on the manufacturing method and shape.

[0005] Among them, pouch-type secondary batteries are manufactured by pressing a flexible pouch film laminate to form a cup, placing an electrode assembly in the cup, injecting electrolyte, and sealing the seal.Can-type secondary batteries are manufactured by placing an electrode assembly in a metal can, injecting electrolyte, and assembling a top cap on the top of the can to seal it.

[0006] The electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. The positive and negative electrodes are fabricated by coating a current collector with electrode slurry to form an active material layer, followed by drying and rolling. When fabricating an electrode by coating the electrode slurry, a sliding portion is formed at the end of the active material layer, where the thickness of the active material layer gradually decreases. In the region where the electrode sliding portion is formed, the distance between the positive and negative active material layers increases, reducing adhesion to the separator and making lithium plating more likely to occur.

[0007] In addition, as lithium secondary batteries are repeatedly charged and discharged, the electrolyte is consumed and the amount of electrolyte decreases. When the amount of electrolyte in the battery decreases, the electrolyte cannot reach the end of the electrode, and the impregnation of the electrolyte decreases. As a result, the mobility of lithium ions decreases, and lithium plating may occur.

[0008] Meanwhile, as lithium secondary batteries are increasingly used as power sources for electric vehicles, lithium secondary batteries (hereinafter referred to as "long cells" for convenience) with a length that is relatively long relative to the width have been developed in consideration of the storage space and position of the battery. Such long-cell lithium secondary batteries have the advantages of being able to achieve higher capacity and having superior space efficiency compared to conventional lithium secondary batteries, but they have the problem that as charging and discharging are repeated, the pressure at the end portion of the electrode assembly near the electrode tab decreases, reducing the adhesion between the separator and the electrode, which exacerbates lithium plating.

[0009] Therefore, there is a need for the development of an electrode assembly capable of preventing lithium plating at the electrode slide portion and a lithium secondary battery including the same. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above problems, and aims to provide an electrode assembly that has been developed to improve adhesion between the electrode and the separator by arranging a fixing member so as to overlap with a positive electrode slide portion, and to maintain a pressure force at the end of the electrode assembly, thereby suppressing the occurrence of lithium plating.

[0011] Another object of the present invention is to provide a lithium secondary battery that includes the electrode assembly and is capable of preventing deterioration in battery performance and safety due to lithium precipitation. [Means for solving the problem]

[0012] According to one embodiment, the present invention provides an electrode assembly including: a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, an electrode stack including a separator interposed between the positive electrode and the negative electrode, and at least one fixing member that wraps and fixes the electrode stack in a width direction, wherein the positive electrode includes a positive electrode sliding portion where the thickness of the positive electrode active material layer decreases, and the at least one fixing member is disposed to overlap a region corresponding to the positive electrode sliding portion.

[0013] Meanwhile, the negative electrode may include a negative electrode sliding portion where the thickness of the negative electrode active material layer is reduced, and the fixing member may be disposed to overlap at least a portion of a region corresponding to the negative electrode sliding portion.

[0014] On the other hand, the electrode laminate may have a ratio L / W of 3 or more, where L is the total length L to the total width W, and preferably 3-7.

[0015] The electrode assembly according to the present invention may include 2 to 10 fixing members, and the fixing members may be arranged symmetrically along the entire length. Preferably, the fixing members may be arranged at equal intervals.

[0016] The fixing member may include a porous structure, and specifically may be a tape having an adhesive layer formed on one surface of a substrate having a porous structure.

[0017] The fixing member may have a width of 10 to 50 mm.

[0018] According to another embodiment, the present invention provides a lithium secondary battery including the electrode assembly according to the present invention, an electrolyte, and a battery case for accommodating the electrode assembly and the electrolyte, wherein the battery case may be a pouch-type battery case. [Effects of the Invention]

[0019] In the electrode assembly according to the present invention, the fixing member is disposed to overlap the region where the positive electrode sliding portion is formed, thereby firmly maintaining adhesion between the electrode sliding portion and the separator. As a result, it is possible to minimize a decrease in lithium mobility due to poor adhesion at the interface between the electrode sliding portion and the separator and to prevent lithium from being deposited from the electrode sliding portion.

[0020] Furthermore, when a fixing member is disposed as in the present invention in a long cell having a large overall length relative to its overall width, it is possible to suppress a decrease in the pressure at the end of the electrode assembly as charging and discharging progresses, thereby minimizing the phenomenon of electrolyte reduction in the electrode slide portion and preventing a decrease in battery performance.

[0021] Therefore, when the electrode assembly according to the present invention is applied, excellent performance and safety can be achieved throughout the life of the lithium secondary battery. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a top view of an electrode assembly according to one embodiment of the present invention. [Figure 2] FIG. 2 is a side view of an electrode stack according to one embodiment of the present invention. [Figure 3]5 is a photograph showing the state of a lithium secondary battery including an electrode assembly manufactured according to an embodiment after cycling; [Figure 4] 5 is a photograph showing the state of a lithium secondary battery including an electrode assembly manufactured according to a comparative example after cycling; DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be specifically described below.

[0024] The present inventors conducted extensive research to develop a lithium secondary battery that can achieve excellent performance and safety throughout its entire lifespan. As a result, they discovered that by fixing the electrode stack with a fixing member during the formation of the electrode assembly and arranging the fixing member so that it overlaps the positive electrode sliding portion region, not only can the interfacial adhesion between the electrode sliding portion and the separator be improved, but also a relatively uniform pressure can be maintained up to the end of the electrode assembly even during repeated charge and discharge. As a result, deterioration in battery performance can be minimized throughout the battery's lifespan, and excellent safety can be achieved by suppressing fires and / or explosions due to lithium plating, which led to the completion of the present invention.

[0025] Specifically, the electrode assembly according to the present invention is characterized by including an electrode stack including a positive electrode, a negative electrode, and a separator, and at least one fixing member that wraps around and fixes the outer surface of the electrode stack in the entire width direction, and the at least one fixing member is arranged to overlap an area corresponding to the positive electrode sliding portion.

[0026] When the fixing member is disposed so as to overlap the positive electrode sliding portion region as described above, the fixing member maintains the distance between the electrode sliding portion and the separator, and prevents the distance between the electrode sliding portion and the separator from increasing even when the volume of the positive electrode active material layer and / or the negative electrode active material layer changes due to repeated charge and discharge. As a result, even when repeated charge and discharge are performed, the interfacial adhesion between the separator and the electrode and the electrolyte impregnation at the end of the electrode assembly can be maintained and lithium plating due to a decrease in lithium mobility can be suppressed.

[0027] Fig. 1 shows a top view of an electrode assembly according to an embodiment of the present invention, and Fig. 2 shows a side view of an electrode stack according to the present invention. The present invention will be described in more detail below with reference to the drawings. However, the drawings are merely examples for explaining the present invention, and the scope of the present invention is not limited to those shown in the drawings. Various modifications are possible within the scope of the present invention.

[0028] As shown in FIG. 1, an electrode assembly 1 according to the present invention includes an electrode stack 100 and at least one fixing member 200 that fixes the electrode stack 100 by wrapping it in the width direction.

[0029] 2, the electrode stack 100 includes a positive electrode 10 including positive electrode active material layers 12a and 12b, a negative electrode 20 including negative electrode active material layers 22a and 22b, and a separator 30 interposed between the positive electrode 10 and the negative electrode 20. The electrode stack 100 may be a stack-type electrode stack formed by cutting a positive electrode, a separator, and a negative electrode to a predetermined size and then stacking them.

[0030] The positive electrode 10 may have a structure in which positive electrode active material layers 12a, 12b are formed on one or both sides of a positive electrode current collector 14. The positive electrode active material layers include a positive electrode center portion 12a where the thickness of the positive electrode active material layer is relatively constant and a positive electrode slide portion 12b where the thickness of the positive electrode active material layer decreases. The positive electrode 10 also includes a positive electrode tab 16 for electrical connection to an external power source.

[0031] The positive electrode 10 of the lithium secondary battery is manufactured by coating one or both surfaces of a positive electrode current collector 14 with a positive electrode slurry prepared by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the coated positive electrode slurry to remove the solvent. The coated positive electrode slurry is then rolled. When the positive electrode active material layer is formed by the wet coating method, the amount of the positive electrode slurry applied to the end portion of the positive electrode active material layer decreases, forming a positive electrode slide portion 12b.

[0032] Meanwhile, various positive electrode current collectors used in the art can be used as the positive electrode current collector 14. For example, the positive electrode current collector can be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector can typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0033] Meanwhile, the positive electrode active material layers 12a and 12b may include a positive electrode active material, a conductive material, and a binder.

[0034] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and various positive electrode active materials used in the art can be used, and the type is not particularly limited. For example, the positive electrode active material can be a lithium iron phosphate oxide (e.g., LiFe 1-x M xPO4, 0 ≦ x < 1), lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (0 < Y < 1), LiMn 2-z Ni z O4 (0 < Z < 2), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (0 < Y1 < 1), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (0 < Z1 < 2), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p1 Co q1 Mn r1 )O2 (0 < p1 < 1, 0 < q1 < 1, 0 < r1 < 1, p1 + q1 + r1 = 1) or Li(Ni p2 Co q2 Mn r2 )O4 (0 < p2 < 2, 0 < q2 < 2, 0 < r2 < 2, p2 + q2 + r2 = 2), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p3 Co q3 Mn r3 M s3 )O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p3, q3, r3, and s3 are the atomic fractions of the respective independent elements, 0 < p3 < 1, 0 < q3 < 1, 0 < r3 < 1, 0 < s3 < 1, and p2 + q2 + r3 + s2 = 1) or combinations thereof can be used.

[0035] The positive electrode active material can be contained at 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight based on the total weight of the positive electrode active material layer.

[0036] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the resulting battery and has electronic conductivity can be used without particular limitations. Specific examples include 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, carbon fiber, and carbon nanotubes; 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; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0037] The binder improves adhesion between positive electrode active material particles and 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders can be used alone or in combination. The binder can be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0038] The negative electrode 20 may have a structure in which negative electrode active material layers 22a, 22b are formed on one or both sides of a negative electrode current collector 24. The negative electrode active material layers include a negative electrode central portion 22a where the thickness of the negative electrode active material layer is relatively constant and a negative electrode slide portion 22b where the thickness of the negative electrode active material layer decreases. The negative electrode 20 also includes a negative electrode tab 26 for electrical connection to an external power source.

[0039] The negative electrode 20 of a lithium secondary battery is fabricated by coating one or both surfaces of a negative electrode current collector 24 with a negative electrode slurry, which is prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the coated negative electrode slurry to remove the solvent. The coating is then rolled. When the negative electrode active material layer is formed using the wet coating method, the amount of negative electrode slurry applied to the edge of the negative electrode active material layer decreases, forming a negative electrode sliding portion 22b. While this varies depending on the negative electrode loading amount and coating conditions, the negative electrode sliding portion 22b is generally longer than the positive electrode sliding portion 12b.

[0040] The negative electrode current collector may be a negative electrode current collector commonly used in the art, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector typically has a thickness of 3 to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be provided with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0041] Meanwhile, the negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0042] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium, which is generally used in the relevant technical field, can be used, and the type thereof is not particularly limited. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiO y (where 0 < Y < 2), silicon-based materials such as Si-C composites; lithium metal thin films; metal materials capable of alloying with lithium such as Sn and Al; etc. Any one or a mixture of two or more of these can be used.

[0043] The negative electrode active material can be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight based on the total weight of the negative electrode active material layer.

[0044] The conductive material is used to impart conductivity to the negative electrode. In the battery to be constructed, as long as it does not cause a chemical change and has electron conductivity, it can be used without particular limitation. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight based on the total weight of the negative electrode active material layer.

[0045] The binder functions to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0046] The separator 30 separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular limitations. Specifically, the separator can be 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. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Separators coated with ceramic components or polymeric materials can also be used to ensure heat resistance or mechanical strength.

[0047] In the case of the present invention, when the positive and negative electrodes include electrode slide portions where the active material layer thickness is reduced at their ends, the separator and the electrode active material layer are not in close contact at the electrode slide portions, resulting in lower lithium mobility than at the center of the electrode. As a result, lithium ions generated at the positive electrode during discharge are not inserted into the negative electrode and are instead deposited on the surface of the negative electrode, a phenomenon known as lithium plating. Furthermore, as the overall length of the electrode assembly increases, the pressure at the ends of the electrode assembly decreases, further reducing the adhesion between the electrode assembly and the separator at the ends. As the electrolyte is consumed through repeated charge and discharge, the electrolyte no longer comes into contact with the electrode slide portions, which can lead to a decrease in battery performance and an accelerated lithium plating phenomenon.

[0048] The present invention addresses these problems by arranging a fixing member 200 so that it overlaps the positive electrode sliding portion 12b, thereby improving the adhesion between the positive electrode sliding portion 12b and the separator 30. When the fixing member 200 is arranged as in the present invention, it is possible to minimize a decrease in lithium mobility due to poor adhesion at the interface between the electrode sliding portion and the separator, suppress a decrease in the pressure force at the end of the electrode assembly as charge and discharge progress, and minimize a decrease in the electrolyte at the electrode sliding portion.

[0049] More preferably, the fixing member 200 may be disposed to overlap at least a portion of the region corresponding to the negative electrode sliding portion 22 b. When the fixing member 200 is disposed to overlap at least a portion of the negative electrode sliding portion, the interfacial adhesion between the positive electrode and the separator and the interfacial adhesion between the negative electrode and the separator are both increased, thereby providing a better effect in suppressing lithium plating and performance degradation.

[0050] Meanwhile, the electrode stack may have a ratio L / W of the total length L to the total width W of 3 or more, preferably 3 to 7, and more preferably 4 to 6. Here, the total width and total length refer to the width and length, respectively, of the largest components among the positive electrode, negative electrode, and separator constituting the electrode stack. A ratio of the total length to the total width of an electrode stack of 3 or more has the advantage of achieving high capacity. However, when the total length is long relative to the total width, the cell pressure at the end portions in the total length direction may be weak, resulting in a problem of reduced electrolyte impregnation at the end portions when the electrolyte is consumed during charging and discharging. However, when the fixing member is arranged to overlap the positive electrode slide portion as in the present invention, the pressure is maintained relatively uniformly all the way to the end of the electrode stack, thereby solving this problem.

[0051] Specifically, the electrode laminate according to the present invention can have an overall width of 50 mm to 200 mm, preferably 70 mm to 200 mm, and more preferably 70 mm to 150 mm, and an overall length of 200 mm to 1,000 mm, preferably 300 mm to 800 mm, and more preferably 400 mm to 600 mm.

[0052] Meanwhile, the fixing member 200 may have a porous structure. When the fixing member has a porous structure, the electrolyte can pass through the fixing member and be impregnated into the electrode stack, preventing the fixing member from reducing the electrolyte impregnation of the electrode stack. Specifically, the fixing member 200 may be, but is not limited to, a finishing tape having an adhesive layer formed on one side of a base layer made of a porous polymer material. The polymer material may be, but is not limited to, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), etc.

[0053] The fixing member 200 preferably has a width of about 10 to 50 mm or 20 to 40 mm in the overall width direction of the electrode stack. If the width of the fixing member 200 is too wide, the area of ​​the outer surface of the electrode stack 100 covered by the fixing member 200 increases, reducing the contact area with the electrolyte and possibly reducing the electrolyte impregnation. If the width is too narrow, the fixing effect of the electrode stack may be reduced.

[0054] Meanwhile, the electrode assembly according to the present invention may include 2 to 10, preferably 2 to 8, and more preferably 3 to 7 fixing members. Here, the fixing members may be arranged symmetrically along the entire length, and preferably, the fixing members may be arranged at equal intervals. When a plurality of fixing members are provided and arranged as described above, an electrode stack having a long-cell structure with a long overall length can be firmly fixed, and a change in pressure depending on the position on the electrode stack can be prevented.

[0055] Next, the lithium secondary battery according to the present invention will be described.

[0056] A lithium secondary battery according to the present invention includes an electrode assembly according to the present invention, an electrolyte, and a battery case containing the electrode assembly and the electrolyte. Since the electrode assembly has been described above, only the remaining components will be described below.

[0057] The lithium secondary battery according to the present invention may be manufactured by housing an electrode assembly in a battery case, injecting an electrolyte, and sealing the battery case.

[0058] Here, the battery case may be, for example, a pouch-type battery case.

[0059] The pouch-type battery case may include a barrier layer, a substrate layer disposed on one side of the barrier layer, and a sealant layer disposed on the other side of the barrier layer, and may include at least one cup portion recessed in one direction.

[0060] Specifically, the pouch-type battery case can be manufactured by a method in which a flexible pouch film laminate having a base layer, a barrier layer, and a sealant layer laminated in that order is inserted into a press molding device, and pressure is applied to a portion of the pouch film laminate with a punch to stretch it, thereby forming a cup portion having a recessed shape in one direction.

[0061] Here, the substrate layer is disposed on the outermost layer of the pouch-type battery case, and serves to protect the electrode assembly from external impact and to provide electrical insulation.

[0062] The substrate layer may be made of a polymer material, for example, one or more polymer materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon (registered trademark).

[0063] The substrate layer may have a single layer structure or a multi-layer structure in which different polymer films are laminated together. When the substrate layer has a multi-layer structure, an adhesive layer may be interposed between the polymer films.

[0064] For example, the base layer may have a laminate structure of a polyethylene terephthalate (PET) film and a nylon film, where the nylon film is preferably disposed on the barrier layer side, i.e., the inner side, and the polyethylene terephthalate film is disposed on the outer surface side of the pouch.

[0065] Polyethylene terephthalate (PET) films have excellent durability and electrical insulation properties, and when placed on the surface, these properties are also excellent. However, PET films have poor adhesion to the aluminum alloy thin film that constitutes the barrier layer and exhibit different stretching behavior. Therefore, when a PET film is placed on the barrier layer side, peeling between the substrate layer and the barrier layer can occur during the molding process, resulting in an uneven stretching of the barrier layer and reduced moldability. In contrast, nylon films have similar stretching behavior to the aluminum alloy thin film that constitutes the barrier layer, and placing a nylon film between the polyethylene terephthalate and the barrier layer can improve moldability.

[0066] The polyethylene terephthalate film may have a thickness of 5 μm to 20 μm, preferably 5 μm to 15 μm, and more preferably 7 μm to 15 μm, and the nylon film may have a thickness of 10 μm to 40 μm, preferably 10 μm to 35 μm, and more preferably 15 μm to 25 μm. When the thicknesses of the polyethylene terephthalate film and the nylon film satisfy the above ranges, excellent formability and rigidity after forming are achieved.

[0067] Meanwhile, the total thickness of the substrate layer may be 10 μm to 60 μm, preferably 20 μm to 50 μm, and more preferably 30 μm to 50 μm. When the substrate layer has a multilayer structure, the thickness includes the thickness of the adhesive layer. When the substrate layer satisfies the above range, the durability, insulating properties, and moldability are excellent. If the thickness of the substrate layer is too thin, durability decreases and damage to the substrate layer may occur during the molding process. If the thickness is too thick, moldability may decrease, the total thickness of the pouch may increase, the battery storage space may decrease, and the energy density may decrease.

[0068] The barrier layer is intended to ensure the mechanical strength of the pouch-type battery case, to block the entry and exit of gas or moisture outside the secondary battery, and to prevent leakage of electrolyte.

[0069] The barrier layer may be made of a metal material, for example, an aluminum alloy thin film, which may contain aluminum and one or more metal elements other than aluminum, for example, iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0070] The barrier layer may have a thickness of 40 μm to 100 μm, more preferably 50 μm to 80 μm, and even more preferably 60 μm to 80 μm. When the thickness of the barrier layer satisfies this range, moldability is improved, the molding depth of the cup portion is increased, and even during two-cup molding, cracks and / or pinholes are reduced, improving resistance to external stress after molding.

[0071] The sealant layer is bonded by thermocompression to seal the pouch-shaped battery case, and is located on the inner layer of the battery case.

[0072] The sealant layer is the surface that comes into contact with the electrolyte and the electrode assembly after the pouch is formed, and therefore must have insulating and corrosion resistance. It must also have high sealing properties because it must completely seal the interior and prevent the movement of substances between the inside and the outside.

[0073] The sealant layer may be made of a polymer material, for example, one or more selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon (registered trademark). Among these, it is particularly preferable to use polypropylene (PP), which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, and chemical properties such as corrosion resistance.

[0074] More specifically, the sealant layer may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0075] The sealant layer may have a single layer structure or a multi-layer structure including two or more layers made of different polymer materials.

[0076] The sealant layer may have a total thickness of 60 μm to 100 μm, preferably 60 μm to 90 μm, and more preferably 70 μm to 90 μm. If the sealant layer is too thin, the durability and insulating properties of the seal may decrease, while if it is too thick, the flexibility may decrease, the total thickness of the pouch film laminate may increase, and the energy density per volume may decrease.

[0077] Next, the electrolyte is used to transfer lithium ions generated by an electrochemical reaction of an electrode during charging and discharging of a secondary battery. Various electrolytes for lithium secondary batteries known in the art may be used, and the type of electrolyte is not particularly limited.

[0078] For example, the electrolyte can include an organic solvent and a lithium salt.

[0079] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0080] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt concentration is preferably within a range of 0.1 to 5.0 M, and more preferably 0.1 to 3.0 M. When the lithium salt concentration is within this range, the electrolyte exhibits appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0081] In addition to the constituent components of the electrolyte, the electrolyte may further contain additives for the purposes of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, and improving the discharge capacity of the battery.

[0082] The present invention will now be described in more detail with reference to specific examples.

[0083] Example A positive electrode of 70 mm x 500 mm, a negative electrode of 75 mm x 505 mm, and a separator of 80 mm x 510 mm were prepared, and the positive electrode / separator / negative electrode were stacked in this order to form an electrode stack.

[0084] Here, the positive electrode was prepared by coating a positive electrode slurry onto a 500 mm long aluminum current collector so that the total length of the positive electrode active material layer was 490 mm, followed by drying and rolling. 8 mm long positive electrode slide portions were formed on both ends of the positive electrode active material layer.

[0085] The negative electrode was fabricated by coating the negative electrode slurry on a copper current collector having a length of 505 mm so that the total length of the negative electrode active material layer was 495 mm, drying, and rolling, and negative electrode slide portions having a length of 10 mm were formed on both ends of the negative electrode active material layer.

[0086] Next, five fixing members were wrapped around the outer surface of the electrode stack in the full width direction to fabricate an electrode assembly. The fixing members at both ends of the electrode stack were positioned 5 mm from the end of the positive electrode, and the fixing members were arranged at equal intervals. A 30 mm wide finishing tape (0.022T, PET, Daehyunst, ST-5595DG(HF)) was used as the fixing members.

[0087] Comparative Example An electrode assembly was produced in the same manner as in Example 1, except that the fixing member was positioned 30 mm from the end of the positive electrode.

[0088] Experimental Example The electrode assemblies prepared in the examples and comparative examples were placed in a pouch-type battery case having a cup portion formed by sequentially stacking nylon / polyethylene terephthalate / Al alloy thin film / polypropylene, and an electrolyte solution was injected into the case, followed by sealing to prepare lithium secondary batteries.

[0089] Thereafter, the fabricated lithium secondary battery was charged to 4.22 V at 0.33 C and discharged to 2.5 V at 0.33 C as one cycle, and after repeating charge and discharge for 800 cycles, the electrode stack was separated and visually inspected for the occurrence of lithium plating.

[0090] Fig. 3 is a photograph showing the condition of a lithium secondary battery using the electrode assembly of the example after 800 cycles, and Fig. 4 is a photograph showing the condition of a lithium secondary battery using the electrode assembly of the comparative example after 800 cycles. Referring to Figs. 3 and 4, it can be seen that lithium plating did not occur in the lithium secondary battery using the electrode assembly of the example, but lithium plating occurred in the lithium secondary battery using the electrode assembly of the comparative example. [Explanation of symbols]

[0091] 1 Electrode assembly 10 positive electrode 20 negative electrode 30 Separator 100 Electrode laminate 200 Fixing member 300 electrolytes

Claims

1. an electrode laminate including a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer, and a separator interposed between the positive electrode and the negative electrode; an electrode assembly including at least one fixing member that fixes the electrode stack by wrapping it in a width direction, the positive electrode includes a positive electrode slide portion where the thickness of the positive electrode active material layer decreases, the at least one fixing member is disposed to overlap a region corresponding to the positive electrode sliding portion.

2. The electrode assembly according to claim 1 , wherein the negative electrode includes a negative electrode slider portion where the thickness of the negative electrode active material layer decreases.

3. The electrode assembly according to claim 2 , wherein the fixing member is disposed so as to overlap at least a portion of the region corresponding to the negative electrode sliding portion.

4. The electrode assembly according to claim 1 , wherein the electrode stack has a ratio L / W of a total length L to a total width W of 3 or more.

5. 2. The electrode assembly of claim 1, wherein the electrode stack has a ratio of a total length L to a total width W of 3 to 7.

6. the electrode assembly includes 2 to 10 fixing members; The electrode assembly according to claim 1 , wherein the fixing members are arranged at bilaterally symmetrical positions along the entire length.

7. The electrode assembly of claim 6 , wherein the securing members are equally spaced apart.

8. The electrode assembly of claim 1 , wherein the fixing member comprises a porous structure.

9. The electrode assembly according to claim 1 , wherein the fixing member is a tape having a substrate with a porous structure and an adhesive layer formed on one surface thereof.

10. The electrode assembly according to claim 1 , wherein the fixing member has a width of 10 to 50 mm.

11. A lithium secondary battery comprising: the electrode assembly according to claim 1 ; an electrolyte; and a battery case for accommodating the electrode assembly and the electrolyte.

12. The lithium secondary battery according to claim 11 , wherein the battery case is a pouch-type battery case.

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