Lead tab for joining electrode tab, method for joining the same to electrode tab, and lithium secondary battery including the structure in which the lead tab is joined to the electrode tab

Abstract

A lead tab for joining an electrode tab, which can prevent deformation due to exposure of a lithium negative electrode tab and improve the physical strength and safety of the joining portion, a method for joining the lead tab to an electrode tab, and a lithium secondary battery including a structure in which the lead tab is joined to the electrode tab are disclosed. The lead tab for joining an electrode tab is joined to an electrode tab of an electrode assembly for a lithium secondary battery and includes a first metal lead; and a second metal lead, one end of which contacts the first metal lead and caps the electrode tab to form a joining portion.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0175173 dated December 14, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a lead tab for joining an electrode tab, a method for joining the lead tab to an electrode tab, and a lithium secondary battery having a structure in which the lead tab is joined to the electrode tab. More particularly, the present invention relates to a lead tab for joining an electrode tab, which can prevent deformation due to exposure of a lithium negative electrode tab and improve the physical strength and safety of the joining portion, a method for joining the lead tab to an electrode tab, and a lithium secondary battery having a structure in which the lead tab is joined to the electrode tab. [Background technology]

[0003] As interest in energy storage technology continues to grow, its application fields have expanded to include mobile phones, tablets, laptops, and video cameras, as well as the energy sources of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development of electrochemical devices is steadily increasing. Electrochemical devices are a field that has attracted the most attention from this perspective, and the development of lithium secondary batteries, such as lithium-sulfur batteries, which are capable of charging and discharging, has become a focus of attention. Recently, the development of such batteries has led to research and development of new electrodes and battery designs to improve capacity density and specific energy.

[0004] During the manufacture of such lithium secondary batteries, welding is performed to connect tabs between unit electrodes to obtain output suited to the intended application, and a process of joining the electrode tab and lead tab is also performed. FIG. 1 is a perspective view showing the joined electrode tab and lead tab in a typical secondary battery, and FIG. 2 is a plan view of the lead tab joined to the electrode tab in a typical secondary battery. As shown in FIG. 1, a typical secondary battery requires an electrode tab (positive electrode tab or negative electrode tab, 2) to electrically connect the positive and negative electrode plates constituting the electrode assembly 1 to an external device. This electrode tab 2 is joined by welding to a lead tab (positive electrode lead tab or negative electrode lead tab, 3) as shown in FIG. 2. As shown in FIG. 2, the lead tab 3 includes a metal lead 3a and a lead film 3b located locally on one or both sides of the metal lead 3a, and the metal lead 3a located on one side is joined so as to overlap the electrode tab.

[0005] More specifically, most lithium secondary batteries generally use ultrasonic welding, laser welding, or resistance welding to join the negative electrode tab (copper) or positive electrode tab (aluminum) to the lead tab (copper, nickel, etc.). For example, in lithium-ion batteries, copper (Cu) is applied to the negative electrode tab, and this is then welded to the lead tab (Ni) to join the electrode tab and lead tab.

[0006] However, lithium-sulfur batteries, which are attracting attention as next-generation secondary batteries that can replace lithium-ion batteries, use only pure lithium metal (Li-metal) without a separate current collector for the anode. In other words, the anode of a lithium-sulfur battery is composed solely of lithium. However, lithium has a lower melting point than other metals and is brittle, making it easily broken or deformed. It also poses a risk of explosion when exposed to air, making it difficult to actively use as a battery material. Furthermore, these unique properties of lithium make it difficult to join the lithium anode tab and the lead tab that electrically connects it.

[0007] In other words, if the lead tab connected to the negative electrode tab of a general lithium secondary battery is applied to a lithium-sulfur battery, problems caused by lithium will inevitably occur. Therefore, there is a need to develop a new lead tab that can be applied to a lithium-sulfur battery and prevent problems such as deformation of the lithium negative electrode tab. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a lead tab for joining an electrode tab, which can prevent deformation due to exposure of a lithium negative electrode tab and improve the physical strength and safety of the joining portion, a method for joining the lead tab to an electrode tab, and a lithium secondary battery including a structure in which the lead tab is joined to the electrode tab. [Means for solving the problem]

[0009] To achieve the above object, the present invention provides a lead tab for joining an electrode tab to an electrode tab of an electrode assembly for a lithium secondary battery, the lead tab including: a first metal lead; and a second metal lead having one end contacting the first metal lead and capping the electrode tab to form a joint.

[0010] The present invention also provides a method for joining an electrode tab and a lead tab of an electrode assembly for a lithium secondary battery, the method including: a) positioning the electrode tab at one end of the second metal lead of the lead tab; b) winding the second metal lead so that both ends of the second metal lead, which are positioned in a direction perpendicular to the joining direction with the electrode tab, are in contact with each other, and capping a surface of the electrode tab; and c) joining the second metal lead and the electrode tab by non-contact welding.

[0011] The present invention also provides a lithium secondary battery having a structure in which the lead tab is joined to an electrode tab. [Effects of the Invention]

[0012] The lead tab for joining an electrode tab, the method for joining the lead tab to an electrode tab, and the lithium secondary battery including the structure in which the lead tab is joined to the electrode tab according to the present invention have the advantages of preventing deformation due to exposure of the lithium negative electrode tab by capping the lithium negative electrode tab with a specific member of the lead tab and improving the physical strength of the joining portion.

[0013] In addition, the lead tab for joining an electrode tab, the method for joining the lead tab to an electrode tab, and the lithium secondary battery including the structure in which the lead tab is joined to the electrode tab according to the present invention have the advantage that the capping can be made more robust by further providing a joining film on a specific member of the lead tab.

[0014] In addition, the lead tab for joining an electrode tab, the method for joining the lead tab to an electrode tab, and the lithium secondary battery including the structure in which the lead tab is joined to the electrode tab according to the present invention have the advantage that a protective film can be further provided on a specific member of the lead tab, thereby further physically protecting the joining portion between the lithium negative electrode tab and the lead tab and even providing an insulating effect. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing an electrode tab and a lead tab joined together in a typical secondary battery. [Figure 2] FIG. 2 is a plan view of a lead tab joined to an electrode tab in a typical secondary battery. [Figure 3] 1 is a plan view of a lead tab for joining an electrode tab according to an embodiment of the present invention; [Figure 4]Figure 4a is a vertical cross-sectional view showing the positional relationship between a first metal lead and a lead film in a lead tab for joining an electrode tab according to one embodiment of the present invention, and Figure 4b is a vertical cross-sectional view showing the positional relationship between the first metal lead and a second metal lead when the first metal lead protrudes through the lead film in a lead tab for joining an electrode tab according to one embodiment of the present invention. [Figure 5] 1 is a schematic view showing an electrode tab capped with a lead tab for joining an electrode tab according to the present invention; [Figure 6] 10 is a plan view of a lead tab for joining an electrode tab according to another embodiment of the present invention; FIG. [Figure 7] 7 is a vertical cross-sectional view showing the state in which the electrode tab is capped with the lead tab of FIG. 6. FIG. [Figure 8] 10 is a vertical cross-sectional view of a lead tab for joining an electrode tab according to still another embodiment of the present invention; [Figure 9] 9 is a vertical cross-sectional view showing the state in which the electrode tab is capped with the lead tab of FIG. 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below with reference to the accompanying drawings so that a person skilled in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be embodied in various forms, and therefore the present invention is not limited to the embodiments described below. Furthermore, it will be apparent that well-known parts that are not essential components may be omitted from the drawings in order to more clearly explain the features of the present invention.

[0017] 3 is a plan view of a lead tab for joining an electrode tab according to one embodiment of the present invention. The lead tab for joining an electrode tab (100) according to the present invention is to be joined with an electrode tab of an electrode assembly for a lithium secondary battery, and as shown in FIG. 3, includes a (flat) first metal lead (110) and a second metal lead (130) whose one end contacts the first metal lead (110) and caps the electrode tab to form a joint.

[0018] The lead tab may further include a lead film 120 located locally on one or both sides of the first metal lead 110. For example, the second metal lead 130 may extend from the lead film 120, but both ends thereof perpendicular to the direction of joining with the electrode tab may be separated from the lead film 120.

[0019] The electrode tab of the electrode assembly for a lithium secondary battery is preferably a lithium negative electrode tab of an electrode assembly for a lithium-sulfur battery.

[0020] Generally, when manufacturing lithium secondary batteries, welding is performed to connect tabs between unit electrodes to obtain the output required for the intended purpose, and this requires a process of joining a regular lead tab (as shown in Figure 2) to an electrode tab (as shown in Figure 1) by welding. Most lithium secondary batteries generally use ultrasonic welding, laser welding, or resistance welding to join the negative electrode tab (copper) or positive electrode tab (aluminum) to the lead tab (copper, nickel, etc.). For example, in lithium-ion batteries, copper (Cu) is used for the negative electrode tab, and this is then welded to the lead tab (Ni) to join the electrode tab and lead tab.

[0021] However, lithium-sulfur batteries, which are attracting attention as next-generation secondary batteries that can replace lithium-ion batteries, do not use a separate current collector for the negative electrode, but instead use only pure lithium metal. Lithium has a lower melting point than other metals, is brittle, easily breaks or deforms, and poses a risk of explosion when exposed to air, making it difficult to actively use as a battery material. These unique properties of lithium also make it difficult to connect the lithium negative electrode tab and the lead tab that electrically connects it. In other words, it is not easy to apply the lead tab used for connecting the negative electrode tab, which is used in general lithium secondary batteries, to lithium-sulfur batteries.

[0022] Therefore, the present applicant has added a specific member (second metal lead 130) to a conventional lead tab and capped the lithium negative electrode tab with this additional member to prevent deformation due to exposure of the lithium negative electrode tab. The lead tab for joining an electrode tab according to the present invention will now be described in more detail.

[0023] First, the first metal lead (110) of the present invention and the lead film (120) that may be locally positioned on one or both sides of the first metal lead (110) may be conventional. That is, the first metal lead (110) may be made of a metal lead material, such as nickel, that is commonly used to bond with lithium negative electrode tabs. The lead film (120) may also be made of the same material, such as polypropylene, that is commonly used to bond with lithium negative electrode tabs.

[0024] The second metal lead (130) may be sheet-shaped, and may be wound around an electrode tab to form a joint. This prevents deformation due to exposure of the lithium negative electrode tab and prevents physical contact with other components inside the cell except for the lithium negative electrode tab and the lead tab. The first metal lead (110) may or may not be included in the joint. When the joint further includes one end of the first metal lead (110), one end of the first metal lead (110) is interposed between the electrode tab and the second metal lead (130) in a certain section based on a vertical cross section of the joint. Even when the first metal lead (110) is not included in the joint, the first metal lead (110) contacts the second metal lead (130) at least at one end or at one cross section. Whether the first metal lead (110) is included in the joint or not, the first metal lead (110) and the second metal lead (130) can be brought into contact with each other by welding, for example. However, there are no particular limitations on the means for bringing the first metal lead (110) and the second metal lead (130) into contact with each other, as long as they can be brought into contact with each other.

[0025] 4a is a vertical cross-sectional view showing the positional relationship between a first metal lead and a lead film in a lead tab for joining an electrode tab according to an embodiment of the present invention, and FIG. 4b is a vertical cross-sectional view showing the positional relationship between a first metal lead and a second metal lead when the first metal lead protrudes through the lead film in a lead tab for joining an electrode tab according to an embodiment of the present invention. Here, a case will be described in which the lead tab further includes a lead film (120) locally positioned on one or both sides of the first metal lead (110). The lead film (120) may be locally positioned on both the top and bottom of the first metal lead (110) in a form that surrounds the first metal lead (110), as shown in FIG. 4a. In this case, one side end of the first metal lead (110) positioned in the direction of joining with the electrode tab (lithium negative electrode tab) may be positioned only up to the point where one end of the lead film (120) is positioned (i.e., the interface between the lead film and the second metal lead), or it may be positioned so as to pass through the interface between the lead film (120) and the second metal lead (130) and overlap the top surface of the second metal lead (130), as shown in Figure 4b.

[0026] If one end of the first metal lead 110, which is positioned in the direction to be joined to the electrode tab, is located at the interface between the lead film 120 and the second metal lead 130, a conductive structure is formed in the order of the electrode tab, the second metal lead 130, and the first metal lead 110. If one end of the first metal lead 110, which is positioned in the direction to be joined to the electrode tab, passes through the interface between the lead film 120 and the second metal lead 130 and is positioned so as to overlap the upper surface of the second metal lead 130, both the first metal lead 110 and the second metal lead 130 will come into contact with the electrode tab. Among these, when the lead tab is configured so that both the first metal lead (110) and the second metal lead (130) are in contact with the electrode tab, it is easier to manufacture than when the lead tab is fabricated so that the conductive structure is formed in the order of the electrode tab, the second metal lead (130), and the first metal lead (110), and the electrical conductivity can also be at the same or higher level.

[0027] Figure 5 is a schematic diagram showing the state of capping an electrode tab with a lead tab for electrode tab joining according to the present invention. Figure 5a shows the state before the electrode tab is positioned on the second metal lead (130) of the lead tab, and Figure 5b shows the state after the electrode tab is positioned on the second metal lead (130) of the lead tab and the remaining portion of the second metal lead (130) where the electrode tab is not positioned is folded and the electrode tab is capped. As shown in Figure 5, the remaining portion of the second metal lead (130) where the electrode tab (140) is not positioned (i.e., one or more of both ends) can be folded in a direction perpendicular to the length of the first metal lead (110) to cap the electrode tab (140). Therefore, after the electrode tab (140) is capped with the second metal lead (130) of the lead tab (100), the electrode tab (140) is contained within the second metal lead (130) and is not exposed to the outside.

[0028] 3 and 5, the dotted lines on the second metal lead 130 indicate the portion that is bent when capping the electrode tab 140, and this is merely one embodiment shown for ease of understanding. Therefore, as long as the second metal lead 130 caps the electrode tab 140 and prevents the electrode tab 140 from being exposed to the outside, there are no particular restrictions on the portion that is bent on the second metal lead 130. Furthermore, when capping the electrode tab 140 with the second metal lead 130, the second metal lead 130 can be wound into a circular shape without being bent, and in this case, the bent portion is also not necessary.

[0029] The material of the second metal lead (130) may be selected from the group consisting of nickel, metals having similar or identical physical properties, and alloys containing two or more of these metals. The second metal lead may have a structure or form in which one metal is plated on the surface of another metal, for example, a form in which a thin film of nickel is plated on the surface of copper. The material of the second metal lead (130) may be the same as or different from that of the first metal lead (110). However, it is preferable that the material of the second metal lead (130) be the same as that of the first metal lead (110) so as to form a stable conductive structure and exhibit consistent electrical conductivity. The thickness of the second metal lead (130) may vary depending on the thickness of the electrode tab (negative lithium tab), but the thickness ratio of the electrode tab to the second metal lead (130) may be 7 to 15:1, preferably 9 to 12:1, and more preferably about 10:1.

[0030] The length of the second metal lead (130) (i.e., the length perpendicular to the length of the first metal lead) is sufficient to cap and enclose the electrode tab (140). The width of the second metal lead (130) is also sufficient to cap and enclose the electrode tab (140). Therefore, it is preferable to appropriately adjust the length and width of the second metal lead (130) according to the specifications of the electrode tab (140).

[0031] Meanwhile, as described above, one side end of the first metal lead (110) positioned in the direction of joining to the electrode tab can be positioned at the interface between the lead film (120) and the second metal lead (130), or it can pass through the interface between the lead film (120) and the second metal lead (130) and be positioned so as to overlap the upper surface of the second metal lead (130), as shown in FIG. 4b. In the former case, the second metal lead (130) can be attached to the end surface of the first metal lead (110) in the direction of the electrode tab and the end surface of the lead film (120) in the direction of the electrode tab using an adhesive. However, it is preferable not to adhere the portion of the second metal lead (130) that is bent to cap the electrode tab. And in the latter case, the second metal lead (130) can be attached to the lower surface of the first metal lead (110) using an adhesive.

[0032] FIG. 6 is a plan view of a lead tab for joining an electrode tab according to another embodiment of the present invention, and FIG. 7 is a vertical cross-sectional view showing the state in which the electrode tab is capped with the lead tab of FIG. 6. Meanwhile, the lead tab (200) for joining an electrode tab according to another embodiment of the present invention further includes lead bonding films (150) attached (provided) in a form extending from each end of the second metal lead (130) (based on a direction perpendicular to the length direction of the first metal lead) as shown in FIG. 6, if necessary. The lead bonding films (150) are intended to prevent problems that may occur when capping the electrode tab using only the second metal lead (130). When the lead bonding films (150) are attached in a form extending from each end of the second metal lead (130), the second metal lead (130) is fixed through the bonding between the lead bonding films (150a, 150b) when the electrode tab is capped with the second metal lead (130), as shown in FIG. 7. When this is expressed as a case where the electrode tab is capped with the second metal lead (130), both ends of the second metal lead (130) in the winding direction are fixed with the lead bonding film (150).

[0033] More specifically, when the lead bonding film 150 is not attached to the second metal lead 130, i.e., as shown in FIG. 3, both ends of the second metal lead 130 can be touched or folded so that they overlap when capping the electrode tab. While touching both ends of the second metal lead 130 does not pose any particular problems, overlapping both ends of the second metal lead 130 can result in tolerances. Therefore, when the electrode tab is capped with the lead bonding film 150 attached to both ends of the second metal lead 130, bonding or adhesion is possible only between one lead bonding film 150a and the other lead bonding film 150b, thereby eliminating the possibility of tolerances occurring. In addition, even if the lead bonding film 150a is not used, the length of the second metal lead 130 in the winding direction may be the same as or shorter than the circumference of the electrode tab. The lead bonding film 150 may be made of a material selected from the group consisting of polypropylene, polymer compounds having similar or identical physical properties, and mixtures thereof, and among these, polypropylene alone may be most preferred.

[0034] Figure 8 is a vertical cross-sectional view of a lead tab for joining an electrode tab according to another embodiment of the present invention, and Figure 9 is a vertical cross-sectional view showing an electrode tab capped with the lead tab of Figure 8. Meanwhile, the lead tab (300) for joining an electrode tab according to another embodiment of the present invention may further include one or more protective films (170) attached to (provided with) the lower surface of the second metal lead (130) as shown in Figure 8 (or the second metal lead may further include one or more protective films attached to its lower surface), if necessary. That is, the protective film (170) serves as a component for further capping the second metal lead (130) that caps the electrode tab (140) as shown in Figure 9 (i.e., when the electrode tab is capped with the second metal lead, the protective film is located at the outermost edge of the capping portion (or joining portion)). This not only provides better physical protection for the electrode tab (140), but also provides an insulating effect and seals the portion where the electrode tab is pulled out from the electrode assembly. The protective film 170 may be made of a material selected from the group consisting of polypropylene, polymer compounds having similar or identical physical properties, and mixtures thereof, with polypropylene being most preferred.

[0035] Next, a method for joining a lead tab to an electrode tab according to the present invention will be described with reference to Figure 5. The method for joining a lead tab to an electrode tab is a method for joining an electrode tab of an electrode assembly for a lithium secondary battery to the above-described lead tab, and includes the steps of: a) positioning the electrode tab (140) at one end of the second metal lead (130) of the lead tab (100), b) winding the second metal lead (130) so that both ends thereof, which are positioned perpendicular to the joining direction with the electrode tab (140), are in contact with each other, and capping the surface of the electrode tab (140), and c) joining the second metal lead (130) and the electrode tab (140) by non-contact welding.

[0036] In the method of joining the lead tab to the electrode tab, the second metal lead (130) may have lead joining films (150) attached to both ends (see FIGS. 6 to 9). Also, the second metal lead (130) may have a protective film (170) attached to its lower surface (see FIGS. 8 and 9). In other words, the second metal lead (130) of step a) may further include a protective film attached to its lower surface, and in this case, a step of heat-sealing the protective film may be further included after step c).

[0037] The heat sealing not only provides better physical protection for the electrode tab 140 but also improves the sealing effect of the portion where the electrode tab 140 extends from the electrode assembly. Therefore, when the protective film 170 is used, the lead tab and the electrode tab are first joined by welding, and then the protective film 170 is heat-sealed at a temperature of approximately 110 to 150°C, preferably approximately 120 to 140°C. The protective film 170 then connects the second metal lead 130 to the portion where the electrode tab 140 extends from the electrode assembly, thereby achieving a more secure seal. The specific method for joining the lead tab and the electrode tab is as described above. Meanwhile, the non-contact welding may be any common welding method known as non-contact welding, such as ultrasonic welding or laser welding. Therefore, no special restrictions are imposed on the welding conditions.

[0038] Next, a lithium secondary battery according to the present invention will be described. The lithium secondary battery has a structure in which the lead tab described above is joined to an electrode tab, i.e., a structure in which the electrode tab of the electrode assembly for a lithium secondary battery is capped with a second metal lead of "a lead tab for joining an electrode tab for joining with an electrode tab of an electrode assembly for a lithium secondary battery, the lead tab including a first metal lead; and a second metal lead, one end of which contacts the first metal lead and caps the electrode tab to form a joint." The lithium secondary battery is preferably a lithium-sulfur battery, and the electrode tab of the electrode assembly for a lithium secondary battery is preferably a lithium negative electrode tab.

[0039] In one embodiment of the present invention, the lithium secondary battery may include a positive electrode, a negative electrode, an electrolyte interposed between the positive electrode and the negative electrode, and a separator. The lithium secondary battery may be fabricated by a known method and with a structure known in the art, except for the lead tab and the structure in which the lead tab is joined to the electrode tab. The positive electrode, separator, and electrolyte will now be briefly described.

[0040] The positive electrode included in the lithium secondary battery of the present invention may include a positive electrode active material, a binder, a conductive material, etc. The positive electrode active material may be a sulfur-carbon composite (C2S) in which sulfur is supported on a porous carbon material. x ) n : x=2.5 to 50, n≧2). The sulfur may be elemental sulfur (S8), a sulfur-based compound, or a mixture thereof. The sulfur-based compound is specifically Li2S n (n≧1) or an organic sulfur compound, etc. The carbon material may be any one of carbon nanotubes, graphene, graphite, carbon black such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, and lamp black, carbon fiber, and a mixture containing two or more of these.

[0041] The binder is a component that aids in bonding the positive electrode active material to the conductive material and the current collector, and may be, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof, but is not limited thereto.

[0042] The conductive material is not particularly limited as long as it does not induce side reactions in the internal environment of the lithium secondary battery, does not induce chemical changes in the battery, and has excellent electrical conductivity. Representative examples include graphite or conductive carbon. Examples include, but are not limited to, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, and lamp black; carbon-based materials having a graphene or graphite crystal structure; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0043] The positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, conductive material, etc. in a dispersion medium (solvent) to prepare a slurry, which is then applied to a positive electrode current collector, dried, and rolled. The dispersion medium may be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or a mixture thereof.

[0044] The positive electrode current collector may be made of, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO), FTO (F-doped SnO), alloys thereof, or aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be in the form of a foil, film, sheet, punched, porous, foam, or the like.

[0045] The separator is interposed between the positive electrode and the negative electrode to prevent short circuits between them and provide a path for lithium ions to move. The separator may be made of an olefin polymer such as polyethylene or polypropylene, glass fiber, or the like, in the form of a sheet, multi-layer membrane, microporous film, woven fabric, or nonwoven fabric, but is not limited to these. Meanwhile, when a solid electrolyte such as a polymer (e.g., an organic solid electrolyte, an inorganic solid electrolyte, or the like) is used as the electrolyte, the solid electrolyte may also serve as the separator.

[0046] The electrolyte may be a solid electrolyte or a liquid electrolyte, and the liquid electrolyte may be, for example, a non-aqueous electrolyte solution. The non-aqueous electrolyte solution may be, but is not limited to, carbonate, ester, ether, or ketone, which may be used alone or in combination. For example, aprotic organic solvents such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, phosphate triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but are not limited to these.

[0047] The electrolyte may further contain a lithium salt. Examples of the lithium salt include known lithium salts that are easily dissolved in non-aqueous electrolytes, such as LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium tetraphenylborate, lithium imide, etc., but are not limited to these.

[0048] Meanwhile, the lithium secondary battery according to the present invention can be applied to a battery cell used as a power source for small devices, and is particularly suitable for use as a unit battery of a battery module, which is a power source for medium- to large-sized devices. In this regard, the present invention also provides a battery module including two or more lithium secondary batteries electrically connected (in series or parallel). The number of lithium secondary batteries included in the battery module can be adjusted in various ways, taking into account the application and capacity of the battery module. Furthermore, the present invention also provides a battery pack in which the battery modules are electrically connected according to conventional techniques in the art. The battery module and battery pack can be used as a power source for one or more medium- to large-sized devices, including, but not limited to, power tools; electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric trucks; electric commercial vehicles; and power storage systems.

[0049] Preferred examples will be described below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0050] [Example 1] Bonding of electrode tab and lead tab An electrode assembly was fabricated by stacking a unit cell including a positive electrode containing the sulfur-carbon composite as a positive electrode active material, a lithium metal negative electrode, and a polyethylene separator interposed therebetween.

[0051] Separately, a lead tab was manufactured that included a planar first metal lead (nickel), a lead film (polypropylene) located locally on one surface of the first metal lead, and a second metal lead (nickel) that extended from the lead film and had both ends separated from the lead film. (*Joining conditions for the first metal lead and the second metal lead - Weld time: 0.02~0.03sec, Hold time: 0.02~0.03sec, Amp(%): 70~80%)

[0052] Next, each negative electrode tab (lithium) was positioned at the center of the second metal lead of the lead tab, and then the second metal lead was folded so that both ends of the second metal lead were in contact, the surface of the negative electrode tab was capped, and the capped portion was ultrasonically welded to join the negative electrode tab and the lead tab.

[0053] [Example 2] Bonding of electrode tab and lead tab The negative electrode tab and the lead tab were bonded in the same manner as in Example 1, except that instead of the second metal lead used in Example 1, a second metal lead was used in which a lead bonding film (polypropylene) was attached to each end of the second metal lead in an extended form, and the lead bonding films were bonded to each other when the negative electrode tab was capped using the second metal lead.

[0054] [Example 3] Bonding of electrode tab and lead tab The negative electrode tab and the lead tab were joined in the same manner as in Example 1, except that instead of the second metal lead used in Example 1, a second metal lead with a protective film (polypropylene) attached to its lower surface was used, so that the protective film was positioned at the outermost periphery of the capping area after capping.

[0055] [Comparative Example 1] Bonding of electrode tab and lead tab The negative electrode tab and the lead tab were bonded in the same manner as in Example 1, except that a normal lead tab (based on Example 1, including only the first metal lead and the lead film) without a second metal lead was used, and thus the negative electrode tab was simply bonded to one side of the first metal lead.

[0056] [Experimental Example 1] Strength measurement of the electrode tab and lead tab joint The tensile strength of the bonded portions of the electrode tabs and lead tabs bonded in Examples 1 to 3 and Comparative Example 1 was measured, and the results are shown in the following Table 1. The tensile strength was measured using a UTM device manufactured by AMETEK and a 600 N weight.

[0057] [Table 1]

[0058] As described above, the tensile strength of the bonded portion of the electrode tab and lead tab bonded in Examples 1 to 3 and Comparative Example 1 was measured. As a result, it was confirmed that Examples 1 to 3, in which the surface of the lithium negative electrode tab was capped to prevent it from being exposed, had significantly superior tensile strength compared to Comparative Example 1, in which a conventional lead tab was used.

[0059] Furthermore, it was found that among Examples 1 to 3, Example 3, which was configured so that the protective film was located on the outermost surface after capping, had the best tensile strength. [Explanation of symbols]

[0060] 100, 200, 300: Lead tab 110: First metal lead 120: Lead film 130: Second metal lead 140: Electrode tab 150: Lead bonding film 170: Protective film

Claims

1. A lead tab for joining an electrode tab of an electrode assembly for a lithium secondary battery, a first metal lead; and a second metal lead, one end of which contacts the first metal lead and caps the electrode tab to form a joint; A lead tab for joining an electrode tab.

2. 2. The lead tab for joining an electrode tab according to claim 1, wherein the second metal lead is in a sheet shape, and the sheet-shaped second metal lead is wound around an electrode tab to form a joint in which the second metal lead is wound around the electrode tab.

3. 3. The lead tab for joining an electrode tab according to claim 2, wherein the joining portion further includes one end of the first metal lead, and the one end of the first metal lead is interposed between the electrode tab and the second metal lead in a certain section based on a vertical cross section of the joining portion.

4. 2. The lead tab for joining an electrode tab according to claim 1, wherein the material of the second metal lead is the same as that of the first metal lead.

5. 3. The lead tab for joining an electrode tab according to claim 2, wherein the length of the second metal lead in the winding direction is equal to or shorter than the periphery of the electrode tab.

6. 6. The lead tab for joining an electrode tab according to claim 5, wherein both ends of the second metal lead in the winding direction are fixed by a lead joining film.

7. 2. The lead tab for joining an electrode tab according to claim 1, further comprising one or more protective films attached to a lower surface of the second metal lead, the protective films being located at the outermost periphery of the joining portion when the electrode tab is capped.

8. 2. The lead tab for joining an electrode tab according to claim 1, further comprising a lead film locally positioned on one or both surfaces of the first metal lead.

9. 10. The lead tab for joining an electrode tab according to claim 1, wherein the electrode tab of the electrode assembly for a lithium secondary battery is a lithium negative electrode tab of an electrode assembly for a lithium-sulfur battery.

10. A method for joining an electrode tab of an electrode assembly for a lithium secondary battery to the lead tab for electrode tab joining according to any one of claims 1 to 9, a) positioning the electrode tab on either end of the second metal lead of the electrode tab joining lead tab; b) winding the second metal lead so that both ends of the second metal lead, which are positioned in a direction perpendicular to the direction of joining with the electrode tab, are in contact with each other, and capping the surface of the electrode tab; c) joining the second metal lead and the electrode tab by non-contact welding; 10. A method for joining a lead tab to an electrode tab, comprising:

11. 11. The method of joining a lead tab to an electrode tab according to claim 10, wherein after the electrode tab is capped with the second metal lead of the lead tab, the electrode tab is contained inside the second metal lead and is not exposed to the outside.

12. The method for joining a lead tab to an electrode tab according to claim 10, wherein the non-contact welding is ultrasonic welding or laser welding.

13. 11. The method of claim 10, further comprising: a protective film attached to a lower surface of the second metal lead in step a); and a step of thermally fusing the protective film after step c).

14. A lithium secondary battery having a structure in which the lead tab for electrode tab joining according to claim 1 is joined to an electrode tab.

15. 15. The lithium secondary battery of claim 14, wherein the thickness ratio of the electrode tab to the second metal lead is 7 to 15:

1.

16. 15. The lithium secondary battery according to claim 14, wherein the lithium secondary battery is a lithium-sulfur battery, and the electrode tab is a lithium negative electrode tab.

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