Secondary battery and battery module including the same

Abstract

A secondary battery according to an embodiment of the present application includes an electrode assembly including electrode sheets and separators positioned between the electrode sheets, a pouch-type battery case in which the electrode assembly is accommodated, an electrode lead connected to the electrode assembly and protruding outside the battery case, and a lead film surrounding the electrode lead and interposed between the electrode lead and the battery case. The lead film includes an outer layer surrounding the electrode lead and an inner layer positioned inside the outer layer, and the inner layer includes a material having higher gas permeability than the outer layer.

Description

TECHNICAL FIELD

[0001] This application claims the benefit of priority of Korean Patent Application No. 10-2020-0170441, filed on December 8, 2020, in the Republic of Korea, and Korean Patent Application No. 10-2021-0148399, filed on November 2, 2021, in the Republic of Korea.

[0002] The present disclosure relates to a secondary battery and a battery module including the same. In particular, the present disclosure relates to a secondary battery capable of discharging gas generated inside the same and a battery module including the same. BACKGROUND

[0003] Recently, as fossil fuels are depleted, the price of energy is rising, and the degree of concern about environmental pollution is increasing, and the demand for eco-friendly alternative energy is becoming an important factor in future life. In this regard, research on various power generation technologies such as nuclear power, solar power, wind power, and tidal power has been continuously ongoing. In addition, power storage systems for more efficient use of energy generated as described above have also received continuous attention.

[0004] In particular, as technology develops and the demand for mobile instruments increases, the demand for batteries as energy sources is also increasing. Accordingly, many studies have been conducted on batteries that satisfy various demands.

[0005] In general, there is a great demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries, which have advantages such as high energy density, discharge voltage, and output stability.

[0006] Secondary batteries can be classified according to the structure of an electrode assembly including a stack structure of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. In general, a secondary battery can include a jelly-roll type electrode assembly, the structure of which is formed by winding an elongated sheet-shaped positive electrode and a negative electrode with a separator interposed therebetween, a stacked electrode assembly, the structure of which is formed by sequentially stacking a plurality of positive electrodes and negative electrodes cut into predetermined sizes with a separator interposed therebetween, and the like. Recently, in order to solve the problems of the jelly-roll type electrode assembly and the stacked type electrode assembly, a stacked / folded type electrode assembly, which is a combination of the jelly-roll type and the stacked type, has been developed, and the structure of the stacked / folded type electrode assembly is formed by sequentially winding unit cells formed by stacking predetermined units of positive electrodes and negative electrodes with a separator interposed therebetween, and the unit cells are arranged on a separator.

[0007] Further, secondary batteries can be classified into cylindrical secondary batteries including an electrode assembly received in a cylindrical case, prismatic secondary batteries including an electrode assembly received in a prismatic case, and pouch-type secondary batteries including an electrode assembly received in a pouch-type case made of a laminated sheet, according to the shape of the case.

[0008] As the energy density of a secondary battery increases, the amount of gas generated inside the secondary battery also increases. In particular, in the case of a pouch-type secondary battery, when the internal pressure increases due to gas generated in the battery and exceeds the fusion strength limit of the pouch-type case, the secondary battery can be unsealed, thereby causing internal gas to be discharged. In this case, there is a problem in that the lifespan of the secondary battery is greatly reduced. Therefore, it is necessary to solve such a problem. SUMMARY

[0009] TECHNICAL PROBLEM

[0010] The present disclosure has been designed to solve the problems of the related art, and therefore aims to provide a secondary battery capable of effectively discharging gas generated inside the secondary battery and a battery module including the same.

[0011] However, the problems to be solved by embodiments of the present disclosure are not limited to the above-described problems, but can be variously extended within the scope of the present disclosure.

[0012] TECHNICAL SOLUTION

[0013] In one aspect of the present disclosure, a secondary battery according to any one of the following embodiments is provided.

[0014] According to a first embodiment, a secondary battery is provided, the secondary battery including: an electrode assembly including electrode sheets and a separator interposed between the electrode sheets; a pouch-type battery case in which the electrode assembly is received; an electrode lead connected to the electrode assembly and protruding from the battery case; and a lead film covering the electrode lead and interposed between the electrode lead and the battery case, wherein the lead film includes an outer layer covering the electrode lead and an inner layer disposed inside the outer layer, and the inner layer includes a material having higher gas permeability than the outer layer.

[0015] According to a second embodiment, a secondary battery as defined in the first embodiment is provided,

[0016] wherein an outer surface of the inner layer and an inner surface of the outer layer are adhered to each other.

[0017] According to a third embodiment, a secondary battery as defined in the first or second embodiment is provided,

[0018] wherein one end of the inner layer is exposed to the outside in the outside of the battery case, and the other end of the inner layer is covered by the outer layer in the inside of the battery case.

[0019] According to a fourth embodiment, there is provided a secondary battery as defined in the first or second embodiment,

[0020] wherein one end of the inner layer is exposed to the outside in the outside of the battery case, and the other end of the inner layer is exposed to an inside space of the battery case in the inside of the battery case.

[0021] According to a fifth embodiment, there is provided a secondary battery as defined in the first or second embodiment,

[0022] wherein one end of the inner layer is covered by the outer layer in the outside of the battery case, and the other end of the inner layer is exposed to an inside space of the battery case in the inside of the battery case.

[0023] According to a sixth embodiment, there is provided a secondary battery as defined in the first or second embodiment,

[0024] wherein one end of the inner layer is covered by the outer layer in the outside of the battery case, and the other end of the inner layer is covered by the outer layer in the inside of the battery case.

[0025] According to a seventh embodiment, there is provided a secondary battery as defined in the fifth or sixth embodiment,

[0026] wherein a width of the lead film of the outer layer covering one end of the inner layer in the extending direction of the electrode lead in the outside of the battery case is 2 mm or more.

[0027] According to an eighth embodiment, there is provided a secondary battery as defined in any one of the first to seventh embodiments,

[0028] wherein a thickness of the outer layer between the inner layer and the battery case is 100 pm to 300 pm.

[0029] According to a ninth embodiment, there is provided a secondary battery as defined in any one of the first to eighth embodiments,

[0030] wherein a thickness of the inner layer is 50 pm to 150 pm.

[0031] According to a tenth embodiment, there is provided a secondary battery as defined in any one of the first to ninth embodiments,

[0032] The outer layer has a gas permeability of 4 barrer to 40 barrer at 60°C.

[0033] According to an eleventh embodiment, there is provided a secondary battery as defined in any one of the first to tenth embodiments,

[0034] The outer layer has a water permeation amount of 0.02 g to 0.2 g at 25°C and 50% RH for 10 years.

[0035] According to a twelfth embodiment, there is provided a secondary battery as defined in any one of the first to eleventh embodiments,

[0036] The inner layer has a gas permeability of 1.6e 5 barrer to 1.6e 7 barrer.

[0037] According to a thirteenth embodiment, there is provided a secondary battery as defined in any one of the first to twelfth embodiments,

[0038] The outer layer includes a polyolefin-based resin, and the polyolefin-based resin includes at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinylidene fluoride (PVDF).

[0039] According to a fourteenth embodiment, there is provided a secondary battery as defined in any one of the first to thirteenth embodiments,

[0040] The inner layer includes at least one material selected from the group consisting of a polyolefin-based resin, a fluorinated resin, a natural material, a glass fiber, a ceramic fiber, and a metal fiber.

[0041] According to a fifteenth embodiment, there is provided a secondary battery as defined in the fourteenth embodiment,

[0042] The polyolefin-based resin includes at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinylidene fluoride (PVDF), the fluorinated resin includes at least one material selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride, and the natural material includes at least one material selected from the group consisting of cotton and wool.

[0043] According to a sixteenth embodiment, there is provided a secondary battery as defined in any one of the first to fifteenth embodiments,

[0044] A portion of the outer layer is disposed between the inner layer and one surface of the electrode lead.

[0045] According to a seventeenth embodiment, there is provided a secondary battery as defined in any one of the first to sixteenth embodiments,

[0046] The battery case includes an upper case and a lower case, an upper sealing portion of the upper case and a lower sealing portion of the lower case are combined with each other, and the lead film is disposed between the upper sealing portion and the lower sealing portion.

[0047] According to an eighteenth embodiment, there is provided a secondary battery as defined in the seventeenth embodiment,

[0048] The lead film is exposed in each of an inside and an outside of the battery case.

[0049] According to a nineteenth embodiment, there is provided a secondary battery as defined in the eighteenth embodiment,

[0050] An area of the lead film exposed to the outside of the battery case is the same as an area of the lead film exposed to the inside of the battery case.

[0051] According to a twentieth embodiment, there is provided a secondary battery as defined in the eighteenth embodiment,

[0052] An area of the lead film exposed to the outside of the battery case is greater than an area of the lead film exposed to the inside of the battery case.

[0053] According to a twenty-first embodiment, there is provided a secondary battery as defined in any one of the seventeenth to twentieth embodiments,

[0054] The outer layer includes an upper outer layer disposed between the upper sealing portion and the electrode lead and a lower outer layer disposed between the lower sealing portion and the electrode lead.

[0055] According to a twenty-second embodiment, there is provided a secondary battery as defined in the twenty-first embodiment,

[0056] The inner layer includes an upper inner layer covered by the upper outer layer and a lower inner layer covered by the lower outer layer.

[0057] According to a twenty-third embodiment, there is provided a secondary battery as defined in the twenty-second embodiment,

[0058] The upper outer layer includes a first upper outer layer and a second upper outer layer, and the upper inner layer is disposed between the first upper outer layer and the second upper outer layer.

[0059] According to a twenty-fourth embodiment, there is provided a secondary battery as defined in the twenty-second or twenty-third embodiment,

[0060] The lower outer layer includes a first lower outer layer and a second lower outer layer, and the lower inner layer is disposed between the first lower outer layer and the second lower outer layer.

[0061] According to a twenty-fifth embodiment, there is provided a secondary battery as defined in any one of the first to twenty-fourth embodiments,

[0062] The inner layer is in contact with one surface of the electrode lead.

[0063] In another aspect of the present disclosure, there is provided a battery module according to the following embodiments.

[0064] According to a twenty-sixth embodiment,

[0065] There is provided a battery module including a secondary battery as defined in the first embodiment.

[0066] Advantageous Effects

[0067] According to the present disclosure, by providing a lead film having high gas permeability in the vicinity of the electrode lead, gas generated inside the secondary battery can be effectively discharged.

[0068] Effects of the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned herein will become more fully apparent from the description of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 is an exploded perspective view of a secondary battery according to an embodiment of the present disclosure.

[0070] Figure 2 is a perspective view of a secondary battery shown in Figure 1 after sealing.

[0071] Figure 3 is a cross-sectional view taken along line A-A' in Figure 2 .

[0072] Figure 4 is a partial cross-sectional view of a portion "C" in Figure 3 .

[0073] Figure 5 is a cross-sectional view taken along line B-B' in Figure 2 .

[0074] Figure 6 is a cross-sectional view of a secondary battery according to another embodiment of the present disclosure.

[0075] Figure 7 is a partial cross-sectional view of a portion "D" in Figure 6 .

[0076] Figure 8 is a cross-sectional view of a secondary battery according to still another embodiment of the present disclosure.

[0077] Figure 9 is a cross-sectional view of a secondary battery according to still another embodiment of the present disclosure.

[0078] Figure 10 is a schematic view showing a detailed configuration of a lead film according to one embodiment of the present disclosure.

[0079] Figure 11 is a partial cross-sectional view showing a shape of a lead film according to a comparative example.

[0080] Figure 12 and Figure 13 are cross-sectional views respectively showing a shape of a lead film according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0081] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so as to be easily practiced by those skilled in the art. However, the present disclosure can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein.

[0082] In the present description, details of well-known features and techniques can be omitted in order not to unnecessarily obscure the presented embodiments, and the same or similar constituent elements are designated by the same reference numerals.

[0083] Further, each element in the drawings can be optionally shown in size and thickness for convenience of description, and thus the scope of the present disclosure is not limited to what is shown in the drawings. In the drawings, the thickness of several layers and regions is exaggerated for clarity. Further, the thickness of some layers and regions in the drawings is exaggerated for convenience of description.

[0084] Further, the expression that "a member such as a layer, a film, a region, or a plate is present on another member" encompasses that the member is directly present on the other member, and that the member is present on the other member with another member interposed therebetween. On the other hand, the expression that "a member is directly present on another member" means that there is no member interposed therebetween. Further, the expression that "is present on a member as a standard" encompasses the expression that "is present on or under the member as a standard" and does not necessarily mean "is present on or under in a direction opposite to a direction of gravity".

[0085] Throughout the specification, the expression that "a part includes a member" does not exclude the presence of any other member, but means that the part can further include the other member.

[0086] Further, throughout the specification, the term "plan view" refers to a planar shape of an object as viewed from above, and the term "cross-sectional view" refers to a vertical cross-section of an object as viewed from the side.

[0087] Figure 1 is an exploded perspective view of a secondary battery according to one embodiment of the present disclosure. Figure 2 is a perspective view showing Figure 1 is a perspective view of a secondary battery shown in Figure 3 is a cross-sectional view taken along Figure 2 line A-A' in

[0088] Referring to Figures 1 to 3 , a secondary battery 100 according to one embodiment of the present disclosure includes an electrode assembly 200 including electrode tabs 210, 220 and a separator 230 interposed between the electrode tabs 210, 220, a pouch-shaped battery case 300 in which the electrode assembly 200 is received, electrode leads 400, 500 connected with the electrode assembly 200 and protruding from the battery case, and a lead film 600 covering the electrode leads 400, 500 and interposed between the electrode leads 400, 500 and the battery case 300.

[0089] First, the electrode assembly 200 includes the electrode tabs 210, 220 having electrode tabs 210t, and the separator 230 interposed between the electrode tabs 210, 220. In particular, the electrode assembly 200 according to the present embodiment can be a stacked-type electrode assembly, a jelly-roll-type electrode assembly, or a stacked / folded-type electrode assembly. In Figure 3 , as one embodiment, a stacked-type electrode assembly is shown. In particular, the stacked-type electrode assembly can have a structure including a plurality of electrode tabs 210, 220 stacked together with a separator interposed between the electrode tabs.

[0090] Each of the electrode tabs 210, 220 can be formed by coating an electrode current collector with an electrode active material, and a portion of the electrode current collector can protrude, so that the electrode tab 210t can be provided. The electrode tabs 210, 220 can be classified into positive electrode tabs and negative electrode tabs, and the separator 230 can be interposed between the positive electrode tabs and the negative electrode tabs. For example, one of the electrode tabs 210 can be a positive electrode tab, and the electrode tab 210t protruding therefrom can be a positive electrode tab. The other of the electrode tabs 220 can be a negative electrode tab, and the electrode tab (not shown) protruding therefrom can be a negative electrode tab.

[0091] Further, according to the present embodiment, the electrode tabs can be connected with the electrode leads. For example, the electrode tab 210t having one polarity can be combined with one electrode lead 400, and the electrode tab (not shown) having another polarity can be combined with another electrode lead 500. The electrode leads 400, 500 can protrude from both ends of the battery case 300. In Figure 1 and Figure 2 In the above, it is shown that the two electrode leads 400, 500 protrude in opposite directions. However, the direction of protrusion is not particularly limited. In other words, the two electrode leads 400, 500 can protrude in the same direction from one side of the secondary battery 100. One of the two electrode leads 400, 500 can be a positive electrode lead, and the other can be a negative electrode lead. For example, when the electrode tab 210t shown in Figure 3 is a positive electrode tab, the electrode lead 400 combined therewith can be a positive electrode lead.

[0092] Meanwhile, the battery case 300 can be a pouch type case. The battery case 300 can include an upper case 310 and a lower case 320 coupled to each other. Although not particularly shown, the battery case 300 including the upper case 310 and the lower case 320 can be a laminate including a resin layer and a metal layer. In particular, each of the upper case 310 and the lower case 320 can include an inner resin layer for sealing, a metal layer for preventing the infiltration of materials, and an outer resin layer as an outermost layer.

[0093] The outer resin layer can have a high tensile strength and weather resistance based on its thickness, to protect the pouch type secondary battery 100 from external influences, and can exhibit electrical insulation properties. The outer resin layer can include a polyethylene terephthalate (PET) resin or a nylon resin. The metal layer can prevent the introduction of air or moisture into the interior of the pouch type secondary battery 100. The metal layer can include aluminum (Al). The inner resin layer can be bonded by heat and pressure applied thereto when the electrode assembly 200 is received in the battery case. The inner resin layer can include cast polypropylene (CPP) or polypropylene (PP).

[0094] Each of the upper case 310 and the lower case 320 can have a concave receiving portion 310R, 320R capable of receiving the electrode assembly 200, and the electrode assembly 200 can be stably received therein. The method for forming such a receiving portion 310R, 320R is not particularly limited, and a deep drawing process using a press punch can be employed.

[0095] The sealing portions 310S, 320S can be provided along the outer periphery of the receiving portions 310R, 320R of each of the upper case 310 and the lower case 320. The upper sealing portion 310S of the upper case 310 and the lower sealing portion 320S of the lower case 320 can be combined with each other, so that the battery case 3000 can be sealed. In particular, the inner resin layers of the upper sealing portion 310S and the lower sealing portion 320S can be partially melted by heat and pressure and combined with each other while the inner resin layers face each other. In other words, the combination between the upper sealing portion 310S and the lower sealing portion 320S or the combination of the upper sealing portion 310S, the lower sealing portion 320S, and the lead film 600 as described below can correspond to thermal fusion in which resin layers are combined with each other by applying heat and pressure thereto.

[0096] Meanwhile, in Figure 1 , it is shown that the upper case 310 and the lower case 320 each have a receiving portion and are separated from each other. However, a bag-shaped case made of a laminate sheet in which one side of the upper case and one side of the lower case are integrally formed with each other can also be used. A bag-shaped case having a sheet structure in which any one of the upper case and the lower case has a receiving portion and the other one does not have a receiving portion can also be used.

[0097] Hereinafter, the lead film 600 will be explained in more detail with reference to Figures 3 to 5 The lead film 600 will be explained in more detail. To avoid repetitive description, only one of the two electrode leads 400, 500, i.e., the electrode lead 400 will be explained, but the structure of the lead film 600 can also be formed in the other electrode lead 500.

[0098] Figure 4 is a partial cross-sectional view of a portion "C" in Figure 3 Figure 5 is a cross-sectional view taken along the center line B-B' in Figure 2

[0099] Referring to Figures 3 to 5 , the lead film 600 is formed to cover the electrode lead 400. The lead film 600 includes an outer layer 700 covering the electrode lead 400 and an inner layer 800 disposed inside the outer layer 700. The expression "the inner layer 800 is disposed inside the outer layer 700" means that the outer layer 700 is disposed so as to cover at least a portion of an outer surface of the inner layer 800.

[0100] ​​Further, the lead film 600 can be disposed between the upper sealing portion 310S of the upper case 310 and the lower sealing portion 320S of the lower case 320. The lead film 600 can be disposed at a portion of a partial region corresponding to the upper sealing portion 310S and the lower sealing portion 320S. In other words, in a region where the lead film 600 is not disposed, the inner resin layer of the upper sealing portion 310S and the inner layer of the lower sealing portion 320S face each other and are bonded to each other. However, in a region where the lead film 600 is disposed, each of the inner resin layer of the upper sealing portion 310S and the inner resin layer of the lower sealing portion 320S can be bonded to the outer layer of the lead film 600.

[0101] In particular, the outer layer 700 in the present embodiment is to enhance adhesion and sealing.

[0102] Accordingly, short circuiting between the electrode lead 400, 500 and the metal layer of the battery case 300 can be prevented, and the sealing of the pouch-type battery case 300 can be improved. When the metal electrode lead 400, 500 contacts the inner resin layer of the upper sealing portion 310S or the inner resin layer of the lower sealing portion 320S, there is relatively high contact resistance, thereby causing degradation of surface adhesion. However, when the outer layer 700 is provided according to the present embodiment, such degradation of adhesion can be prevented. Further, since the outer layer 700 has insulating properties, application of current from the electrode lead 400, 500 to the metal layer of the pouch-type battery case can be interrupted.

[0103] Further, the outer layer 700 can function together with the inner layer 800 to facilitate discharge of gas generated inside the secondary battery.

[0104] According to one embodiment of the present disclosure, the outer layer 700 can have a gas permeability of 4 to 40 Barrer, 5 to 20 Barrer, or 4 to 12 Barrer at 60℃. For example, the outer layer 700 can have a carbon dioxide permeability satisfying the above defined range. Further, based on a thickness of 200 μm, the outer layer 700 can have a gas permeability satisfying the above defined range at 60℃. When the outer layer 700 has a gas permeability satisfying the above defined range, gas generated inside the secondary battery can be more effectively discharged.

[0105] Here, the gas permeability can be determined as follows. Two kinds of secondary batteries equipped with a gas line through which gas can be injected from the outside are prepared. One kind of secondary battery is completely sealed except for the gas line. The other kind of secondary battery is sealed while a hole is formed, and an outer layer or an inner layer is attached to the hole. Then, after gas is injected from the outside through the gas line, a difference in internal pressure change between the battery not having the outer layer or the inner layer and the battery provided with the outer layer or the inner layer is determined. Here, the gas permeability of the outer layer or the inner layer can be determined by a correlation equation between the pressure change and the amount of gas injection. For example, the gas injected from the outside can be carbon dioxide.

[0106] According to one embodiment of the disclosure, the outer layer 700 can have a water permeation amount of 0.02 to 0.2 g, 0.02 to 0.04 g, or 0.06 to 0.15 g for 10 years at 25℃ and 50% RH. For example, when polypropylene is used as the outer layer 700, the water permeation amount of the outer layer can be 0.06 to 0.15 g. When the water permeation amount of the outer layer 700 satisfies the above defined range, the permeation of moisture introduced from the outer layer 700 can be more effectively prevented.

[0107] According to one embodiment of the disclosure, the outer layer 700 can have a gas permeability of 4 to 40 barrer at 60℃ and a water permeation amount of 0.02 to 0.2 g for 10 years at 25℃ and 50% RH. When the gas permeability and the water permeation amount of the outer layer 700 satisfy the above defined ranges, moisture can be more effectively prevented from permeating from the outside while discharging gas generated inside the secondary battery.

[0108] The water permeation amount of the outer layer can be determined by the method of ASTM F 1249. Here, a system officially certified by MCOON Company can be used to determine the water permeation amount.

[0109] According to one embodiment of the disclosure, the outer layer 700 can include a polyolefin-based resin. For example, the outer layer 700 can include a polyolefin-based resin satisfying the above defined ranges of gas permeability and / or water permeation amount. The polyolefin-based resin can include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinyl difluoride (PVDF). When the outer layer 700 includes polypropylene, the outer layer 700 can easily have a gas permeability of 4 to 40 barrer at 60℃.

[0110] Reference Figure 4 According to one embodiment of the disclosure, the outer layer 700 disposed between the inner layer 800 and the battery case 300 can have a thickness H of 100 μm to 300 μm or 100 μm to 200 μm. When the outer layer 700 satisfies the above defined thickness range, gas inside the battery case 300 can be more easily discharged to the outside.

[0111] Meanwhile, the inner layer 800 according to the present embodiment serves the purpose of discharging gas, and the inner layer 800 can include a material having a relatively higher air permeability (i.e., gas permeability) than the outer layer 700. In this way, during charging / discharging, gas generated inside the battery can be discharged to the outside through the inner layer 800. The expression "higher gas permeability" means that the amount of permeation of gas is relatively large when gas having a predetermined pressure is permeated in one direction. For example, the inner layer 800 can include a material having more pores than the outer layer 700. In other words, the inner layer 800 can include a material having a higher porosity per unit volume than the outer layer 700.

[0112] According to one embodiment of the present disclosure, the inner layer 800 can have a gas permeability of 1.6e 5 to 1.6e 7 Barrer, or 1e 6 to 3e 6 Barrer. For example, the inner layer 800 can have a carbon dioxide permeability satisfying the above defined range.

[0113] According to one embodiment of the present disclosure, the inner layer 800 can include at least one material selected from the group consisting of a polyolefin-based resin, a fluorinated resin, a natural material, a glass fiber, a ceramic fiber, and a metal fiber. For example, the inner layer 800 can include at least one material selected from the group consisting of a polyolefin-based resin, a fluorinated resin, a natural material, a glass fiber, a ceramic fiber, and a metal fiber satisfying the above defined range of gas permeability. The polyolefin-based resin can include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinylidene fluoride (PVDF). The fluorinated resin can include at least one material selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride, and the natural material can include at least one material selected from the group consisting of cotton and wool.

[0114] According to one embodiment of the present disclosure, the inner layer 800 can have a thickness of 50 µm to 150 µm or 50 µm to 100 µm. When the inner layer 800 has a thickness satisfying the above defined range, gas inside the battery case 300 can be more easily discharged to the outside.

[0115] As Figure 4 and Figure 5As shown in FIG. 8, the inner layer 800 can be disposed inside the outer layer 700. In particular, the inner layer 800 can be covered by the outer layer 700 in the x-axis or z-axis direction perpendicular to the protruding direction of the electrode lead 400. By providing the outer layer 700 having high sealing properties and then providing the inner layer 800 having higher gas permeability therein, the gas generated inside the battery case 300 can be more effectively discharged, while reducing the infiltration of moisture or foreign substances present outside the battery case 300 into the battery case 300. In other words, the gas generated inside the battery case 300 can be discharged through the inner layer 800 formed inside, while high sealing properties are provided by the outer layer 700 formed outside. As shown in FIG. 8, the inner layer 800 can be formed to have a smaller length than the outer layer 700 in the protruding direction of the electrode lead 400 (the direction parallel to the y-axis). In this case, the inner layer 800 can be exposed to each of the inside and outside of the battery case 300. The gas generated inside the battery case 300 can be discharged to the outside through the inner layer 800. Figure 4 As shown in FIG. 8, the gas generated inside the battery case 300 can be discharged to the outside of the battery case 300 through the inner layer 800.

[0116] In addition, as shown in FIGS. 9 and 10, the lead film 600 can be formed to have a larger length than the upper sealing portion 310S and the lower sealing portion 320S in the protruding direction of the electrode lead 400 (the direction parallel to the y-axis), and thus the lead film 600 can be exposed to each of the inside and outside of the battery case 300. Since the outer layer 700 has a certain degree of gas permeability, the gas generated inside the battery case 300 can be discharged to the outside not only through the inner layer 800 but also through the outer layer 700. Figure 3 and Figure 4 As shown in FIGS. 9 and 10, the lead film 600 can be formed to have a larger length than the upper sealing portion 310S and the lower sealing portion 320S in the protruding direction of the electrode lead 400 (the direction parallel to the y-axis), and thus the lead film 600 can be exposed to each of the inside and outside of the battery case 300. Since the outer layer 700 has a certain degree of gas permeability, the gas generated inside the battery case 300 can be discharged to the outside not only through the inner layer 800 but also through the outer layer 700.

[0117] The amount of gas discharge can be controlled by controlling the exposed area of the lead film 600 in each of the inside and outside of the battery case 300.

[0118] According to one embodiment of the disclosure, the exposed area of the lead film 600 in the outside of the battery case 300 can be the same as the exposed area of the lead film 600 in the inside of the battery case 300. According to another embodiment of the disclosure, the exposed area of the lead film 600 in the outside of the battery case 300 can be greater than the exposed area of the lead film 600 in the inside of the battery case 300. The amount of gas discharge is proportional to the gas discharge area and the pressure. When the exposed area of the lead film 600 in the outside of the battery case 300 is greater than the exposed area of the lead film 600 in the inside of the battery case 300, since the pressure in the inside of the battery case 300 is greater than the pressure in the outside of the battery case 300, the gas generated in the inside of the battery case 300 can be more easily discharged to the outside.

[0119] According to one embodiment of the disclosure, the exposed area of the lead film 600 in the outside of the battery case 300 can be 40 to 80 mm 2This is based on the internal pressure of 1 atmosphere at 60℃ can be discharged about 0.5 to 3 milliliters of gas per day such size. In addition, this is the amount of water penetration at 25℃ and 50% RH within 10 years can be 0.02 to 0.2 g such size.

[0120] Meanwhile, compared to the electrode lead 400, the lead film 600 can have a larger width and a smaller length. In this way, the lead film 600 can prevent the side surface of the electrode lead 400 from being exposed to the outside, while not interrupting the electrical connection of the electrode lead 400.

[0121] Here, reference is made to Figure 4 In the outside of the battery case 300, one end 800E1 of the inner layer 800 can be exposed to the outside to increase the gas discharge effect. In this way, the gas inside the battery case 300 can be discharged to the outside of the battery case 300 in the y-axis direction through the one end 800E1 of the inner layer 800. In addition, the outer layer 700 is provided with a certain degree of gas permeability, and the gas permeability of the inner layer 800 is not high, therefore, the gas diffused to the inside of the battery case of the inner layer 800 can also be discharged in the z-axis direction through the outer layer 700. For example, the gas inside the battery can be discharged in the z-axis direction through the outer layer 700 exposed to the outside of the battery case 300.

[0122] In addition, in the inside of the battery case 300, the other end 800E2 of the inner layer 800 can be formed to be covered by the outer layer 700. Here, the one end 800E1 and the other end 800E2 of the inner layer 800 can be opposite ends. According to the material used for the inner layer 800, the inner layer 800 for gas permeation can react with the electrolyte in the battery case 300, thereby affecting the internal constituent components and adversely affecting the battery performance. Therefore, in the present embodiment, the inner layer 800 is formed so as not to be directly exposed to the inside of the battery case 300, thereby providing the advantage that the gas discharge can be guided while protecting the internal constituent components compared to the simple layered arrangement of the gas permeable layer. In other words, when the material used for the inner layer 800 is a material that can react with the electrolyte in the battery case 300, it is preferable that, as described above, the other end 800E2 of the inner layer 800 is formed to be covered by the outer layer 700.

[0123] Hereinafter, reference will be made to Figure 6 and Figure 7 the lead film 600a according to another embodiment of the present disclosure will be explained in detail. However, the description of the part overlapping with the above will be omitted.

[0124] Figure 6 is a cross-sectional view of a secondary battery according to another embodiment of the present disclosure. Figure 7 is an enlarged view of a part "D" in Figure 6 Here,Figure 6 FIG. 7 is a cross-sectional view of a secondary battery according to another embodiment of the disclosure, taken along the yz plane. Figure 3 FIG. 8 is a cross-sectional view of a secondary battery according to another embodiment of the disclosure, taken along the yz plane. Figure 2 FIG. 9 is a cross-sectional view of a secondary battery according to another embodiment of the disclosure, taken along the yz plane.

[0125] Referring to FIG. 6, Figure 6 and Figure 7 According to another embodiment of the disclosure, the lead film 600a includes an adhesive outer layer 700a and a gas-permeable inner layer 800a.

[0126] Here, one end 800E1a of the inner layer 800a can be exposed to the outside in the outside of the battery case 300, and the other end 800E2a of the inner layer 800a can be exposed to the inside space of the battery case 300 in the inside of the battery case 300. In this way, it is possible to maximize the gas discharge effect. Here, the one end 800E1a and the other end 800E2a of the inner layer 800a can be opposite ends. In other words, the two ends 800E1a and 800E2a opposite to each other can be exposed to increase the gas discharge effect.

[0127] Here, the inner layer 800a preferably includes a material that is stable in an electrolyte environment, i.e., does not react with the electrolyte in the battery case 300. For example, the inner layer 800a can include at least one material selected from the group consisting of polypropylene, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene.

[0128] Hereinafter, the lead film 600b according to still another embodiment of the disclosure will be explained in detail with reference to Figure 8 However, a description of portions overlapping with the above will be omitted.

[0129] Figure 8 FIG. 10 is a cross-sectional view of a secondary battery according to still another embodiment of the disclosure, taken along the yz plane. Figure 8 FIG. 11 is a cross-sectional view of a secondary battery according to still another embodiment of the disclosure, taken along the yz plane. Figure 4 FIG. 12 is a cross-sectional view of a secondary battery according to still another embodiment of the disclosure, taken along the yz plane.

[0130] Referring to FIG. 10, Figure 8 According to still another embodiment of the disclosure, the lead film 600b includes an adhesive outer layer 700b and a gas-permeable inner layer 800b.

[0131] Here, in the outside of the battery case 300, one end 800E1b of the inner layer 800b is covered by the outer layer 700b. Also, in the inside of the battery case 300, the other end 800E2b of the inner layer 800b can be exposed to the inside space of the battery case 300. Since the one end 800E1b of the inner layer 800b is covered by the outer layer 700b, the gas generated in the inside of the battery case 300 can be sequentially discharged in the z-axis direction by means of the inner layer 800b and the outer layer 700b. For example, when the lead film 600 is exposed to the outside of the battery case 300, the gas generated in the inside of the battery case 300 can be sequentially discharged in the z-axis direction by means of the inner layer 800b and the outer layer 700b exposed to the outside of the battery case 300.

[0132] Here, the one end 800E1b and the other end 800E2b of the inner layer 800b can be opposite ends. When the inner layer 800b having a high permeability is exposed to the outside environment, there can be a problem in that the external components penetrate into the battery case 300. Accordingly, in the present embodiment, the inner layer 800b is configured such that the inner layer 800b can not be directly exposed to the outside of the battery case 300. In this way, compared to a simple layered arrangement of the gas permeable layer, the possibility of penetration of external components can be reduced. In contrast, the other end 800E2b of the inner layer 800b can be exposed to the inside space of the battery case 300 to complement the effect of gas discharge. Here, as described above, the inner layer 800b preferably includes a material that is stable in the electrolyte environment (i.e., does not react with the electrolyte in the battery case 300). For example, the inner layer 800a can include at least one material selected from the group consisting of polypropylene, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene.

[0133] Reference Figure 8 According to one embodiment of the present disclosure, in the outside of the battery case 300, the width W of the lead film 600b covering the outer layer 700b of the one end of the inner layer 800b in the electrode lead extension direction can be 2 mm or more, or 2 mm to 3 mm. When the width of the lead film 600b covering the outer layer 700b of the one end of the inner layer 800b in the electrode lead extension direction satisfies the above defined range, while the gas generated in the inside of the battery case 300 is discharged to the outside, it is possible to easily prevent the lead film 600b from being torn.

[0134] Hereinafter, the lead film 600c according to still another embodiment of the present disclosure will be explained in detail with reference to Figure 9 However, a description of portions overlapping with the above will be omitted.

[0135] Figure 9 is a cross-sectional view of a secondary battery according to still another embodiment of the present disclosure. Figure 9 With Figure 4a cross-sectional view similar to the cross-sectional view corresponding to the cross-section taken by the yz plane.

[0136] Referring to Figure 9 According to another embodiment of the present disclosure, the lead film 600c includes an adhesive outer layer 700c and a gas-permeable inner layer 800c.

[0137] Here, one end 800E1c of the inner layer 800c in the outside of the battery case 300 and the other end 800E2c of the inner layer 800c in the inside of the battery case 300 can be covered by the outer layer 700c. Here, the one end 800E1c and the other end 800E2c of the inner layer 800c can be opposite ends. As described above, the inner layer 800c for gas permeation is likely to react with the electrolyte in the battery case 300, thereby affecting the constituent components inside and adversely affecting the battery performance. In addition, when the inner layer 800c having a high permeation rate is exposed to the outside environment, there is a problem that external components can penetrate into the battery case 300. Therefore, according to the present embodiment, it is intended to reduce such a risk of the inner layer 800c reacting with the electrolyte in the battery case 300 and to mitigate the possibility of external material penetration by covering the opposite ends 800E1c, 800E2c of the inner layer 800c with the outer layer 700c.

[0138] Meanwhile, referring to Figure 3 , Figure 4 , Figure 7 , Figure 8 and Figure 9 According to the embodiments, the one end 800E1, 800E1a, 800E1b, 800E1c of the lead film 600, 600a, 600b, 600c can be disposed outside more than the outer surface of the battery case 300. In addition, the other end 800E2, 800E2a, 800E2b, 800E2c of the lead film 600, 600a, 600b, 600c can be disposed inside more than the inner surface of the battery case 300.

[0139] In this way, the lead film 600, 600a, 600b, 600c can maximize the area of the inner layer 800, 800a, 800b, 800c, thereby being able to effectively discharge the gas generated inside the battery case 300.

[0140] Hereinafter, the specific constitution of the lead film according to one embodiment of the present disclosure will be explained with reference to Figure 10

[0141] Figure 10 is a schematic view showing the specific constitution of the lead film according to one embodiment of the present disclosure.

[0142] Referring to Figure 10 ​According to one embodiment of the present disclosure, a lead film includes an adhesive outer layer 700 and a gas permeable inner layer 800 as described above.

[0143] Here, the outer layer 700 can include an upper outer layer 700U arranged between the upper sealing portion 310S of the upper case 310 and the electrode lead 400, and a lower outer layer 700L arranged between the lower sealing portion 320S of the lower case 320 and the electrode lead 400. Meanwhile, the inner layer 800 can include an upper inner layer 800U covered by the upper outer layer 700U and a lower inner layer 800L covered by the lower outer layer 700L.

[0144] Further, the upper outer layer 700U can include a first upper outer layer 710U and a second upper outer layer 720U, and the upper inner layer 800U can be arranged between the first upper outer layer 710U and the second upper outer layer 720U. Here, the first upper outer layer 710U and the second upper outer layer 720U can have a width d1 in a direction perpendicular to the protruding direction of the electrode lead 400 (a direction parallel to the x-axis) that is greater than a width d2 of the upper inner layer 800U in the corresponding direction.

[0145] In addition, the lower outer layer 700L can include a first lower outer layer 710L and a second lower outer layer 720L, and the lower inner layer 800L can be arranged between the first lower outer layer 710L and the second lower outer layer 720L. Similar to the upper outer layer 700U, the first lower outer layer 710L and the second lower outer layer 720L can have a width in a direction perpendicular to the protruding direction of the electrode lead 400 (a direction parallel to the x-axis) that is greater than a width of the lower inner layer 800L in the corresponding direction.

[0146] In the present embodiment, when the first upper outer layer 710U, the upper inner layer 800U, the second upper outer layer 720U, the first lower outer layer 710L, the lower inner layer 800L, and the second lower outer layer 720L are combined, heat and pressure are applied to the adjacent layers to be combined, and then the next layer is arranged and further heat and pressure are applied to the next layer to be combined. In other words, the operation of applying heat and pressure to two opposing layers is repeated for each layer to obtain the lead film according to the present embodiment.

[0147] The first upper outer layer 710U, the second upper outer layer 720U, the first lower outer layer 710L, and the second lower outer layer 720L are combined with each other to form the outer layer 700 covering the electrode lead 400. Referring to FIG. 7, the outer layer 700 can include the first upper outer layer 710U, the second upper outer layer 720U, the first lower outer layer 710L, and the second lower outer layer 720L. Figure 4 、 Figure 7 、 Figure 8 and Figure 9A portion of the outer layer 700, 700a, 700b, 700c can be disposed between the inner layer 800, 800a, 800b, 800c and one surface of the electrode lead 400. In other words, the inner layer 800, 800a, 800b, 800c can not be in direct contact with the electrode lead 400. This is because, as shown in Figure 10 the second upper outer layer 720U is disposed between the upper inner layer 800U and the electrode lead 40, and the first lower outer layer 710L is disposed between the lower inner layer 800L and the electrode lead 400.

[0148] Further, as described above, the first upper outer layer 710U, the second upper outer layer 720U, the first lower outer layer 710L, and the second lower outer layer 720L can have a width d1 in a direction perpendicular to the protruding direction of the electrode lead 400 (a direction parallel to the x-axis) that is greater than a width d2 of the upper inner layer 800U and the lower inner layer 800L in the corresponding direction, thereby allowing the inner layer 800 to be disposed inside the outer layer 700.

[0149] Further, each of the upper outer layer 700U, the lower outer layer 700L, the upper inner layer 800U, and the lower inner layer 800L can have a length in the protruding direction of the electrode lead 400 (a direction parallel to the y-axis) that is greater than a length of the upper sealing portion 310S and the lower sealing portion 320S in the corresponding direction, thereby allowing the lead film according to the present embodiment to be exposed to each of the inside and the outside of the battery case 300.

[0150] Hereinafter, advantages of the lead film according to one embodiment of the present disclosure will be explained in detail compared to the lead film of the comparative example shown in Figure 11 .

[0151] Figure 11 is a partial cross-sectional view showing the shape of the lead film according to the comparative example.

[0152] Referring to Figure 11 , according to the comparative example, the electrode lead 40 protrudes through a gap between the upper sealing portion 310S and the lower sealing portion 320S, and the electrode lead 40 is covered by the lead film 70 between the upper sealing portion 310S and the lower sealing portion 320S. Here, a gas permeable layer 80 for gas permeation can be formed on one surface of the electrode lead 40, which can be a metal permeable layer including a metal or alloy material. Since the lead film 70 includes a polymer resin for electrical insulation and sealing, the gas permeable layer 80 including a metal or alloy material can have a problem in terms of lamination ability with the lead film 70, which can adversely affect the sealing property of the secondary battery.

[0153] Unlike the comparative example, as shown in Figure 3 , Figure 4 , Figure 7 ,Figure 8 and Figure 9 As shown in FIGS. 1 to 3, the lead film 600 according to the embodiments of the present disclosure (i.e., the lead film 600, 600a, 600b, 600c) includes the inner layer 800, 800a, 800b, 800c having a relatively high gas permeability and disposed inside the outer layer 700, 700a, 700b, 700c. Thus, there is an advantage in that a gas discharge path can be provided in the battery case 300 without a problem of degradation in sealing.

[0154] Further, referring to Figure 3 , Figure 4 , Figure 7 , Figure 8 and Figure 9 , the lead film 600, 600a, 600b, 600c includes the inner layer 800, 800a, 800b, 800c disposed inside the outer layer 700, 700a, 700b, 700c, and the outer surface of the inner layer 800, 800a, 800b, 800c and the inner surface of the outer layer 700, 700a, 700b, 700c are adhered to each other.

[0155] Here, such adhesion encompasses fusion between the outer layer 700, 700a, 700b, 700c and the inner layer 800, 800a, 800b, 800c by means of heat or pressure application and adhesion between them by a separate adhesive.

[0156] Since the inner layer 800, 800a, 800b, 800c includes a material having a relatively high gas permeability and is adhered to the outer layer 700, 700a, 700b, 700c, the inner layer can function as a kind of physical support. In other words, according to the embodiments of the present disclosure, the inner layer 800, 800a, 800b, 800c not only functions as a gas discharge path, but also functions to supplement the durability and rigidity of the lead film 600, 600a, 600b, 600c. In this way, it is possible to prevent the problems that occur in the comparative examples, i.e., swelling of the lead film in upward and downward directions and local elongation of the lead film.

[0157] Hereinafter, a lead film according to another embodiment of the present disclosure will be explained with reference to Figure 12 and Figure 13 .

[0158] Figure 12 and Figure 13 are sectional views respectively showing the shape of a lead film according to another embodiment of the present disclosure.

[0159] Referring to Figure 12 and Figure 13The lead film 600', 600" can include the outer layer 700', 700" and the inner layer 800', 800". The description of the outer layer 700', 700" and the inner layer 800', 800" overlaps with the above description, and the overlapping description is omitted. However, in these embodiments, the inner layer 800', 800" can be adhered to one surface of the electrode lead 400. The inner layer 800', 800" disposed on the top can be in contact with the top surface of the electrode lead 400, and the inner layer 800', 800" disposed on the bottom can be in contact with the bottom surface of the electrode lead 400. Unlike the embodiments shown in Figure 4 、 Figure 7 、 Figure 8 and Figure 9 , the outer layer does not have a portion disposed between the inner layer 800, 800' and the electrode lead 400.

[0160] Figure 12 It is shown that one end 800E1' of the inner layer 800' is open, the other end 800E2' is covered with the outer layer 700', and Figure 13 It is shown that one end 800E1" of the inner layer 800" is covered with the outer layer 700", the other end 800E2" is open. Although not specifically shown, both the one end and the other end of the inner layer can be open, or both can be covered with the outer layer.

[0161] Referring to Figure 10 , the lead film 600', 600" shown in Figure 12 and Figure 13 can be obtained by eliminating the second upper outer layer 720U and the first lower outer layer 710L. In other words, the lead film 600', 600" having the inner layer 800', 800" in contact with one surface of the electrode lead 400 reduces the number of layers requiring heat fusion used in the manufacturing process, so the heat fusion step is also partially reduced. Therefore, it has advantages in terms of manufacturing process and cost saving.

[0162] According to the present disclosure, several directional terms (such as front, back, left, right, up and down) are used, but these directional terms are only used for the convenience of description, and can be changed according to the position of the object or the observer.

[0163] A plurality of the above-described secondary batteries can be assembled to form a battery module. Such a battery module can be installed together with various control and protection systems (such as a battery management system (BMS) and a cooling system) to form a battery pack.

[0164] The secondary battery, the battery module, or the battery pack can be applied to various devices, particularly, to transportation means (including electric bicycles, electric vehicles, and hybrid vehicles), but is not limited thereto. Accordingly, the secondary battery, the battery module, or the battery pack can be applied to various devices to which the secondary battery is applicable.

[0165] The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description.

Claims

1. A secondary battery comprising: an electrode assembly including electrode sheets and a separator interposed between the electrode sheets; a pouch-shaped battery case in which the electrode assembly is received; an electrode lead connected to the electrode assembly and protruding from the battery case; and a lead film covering the electrode lead and interposed between the electrode lead and the battery case, wherein the lead film includes an outer layer covering the electrode lead and an inner layer disposed inside the outer layer, the inner layer includes a material having higher gas permeability than the outer layer and is configured to provide a gas discharge path in the battery case, and an outer surface of the inner layer and an inner surface of the outer layer are adhered to each other. The air permeability of the inner layer is 1.6e 5 Baller to 1.6e 7 Baller.

2. The secondary battery according to claim 1, wherein One end of the inner layer is exposed to the outside in the outside of the battery case, and the other end of the inner layer is covered by the outer layer in the inside of the battery case.

3. The secondary battery according to claim 1, wherein One end of the inner layer is exposed to the outside in the outside of the battery case, and the other end of the inner layer is exposed to an inside space of the battery case in the inside of the battery case.

4. The secondary battery according to claim 1, wherein One end of the inner layer is covered by the outer layer in the outside of the battery case, and the other end of the inner layer is exposed to an inside space of the battery case in the inside of the battery case.

5. The secondary battery according to claim 1, wherein One end of the inner layer is covered by the outer layer in the outside of the battery case, and the other end of the inner layer is covered by the outer layer in the inside of the battery case.

6. The secondary battery according to claim 1, wherein The lead film covering one end of the inner layer in the outside of the battery case has a width of 2 mm or more in the extension direction of the electrode lead.

7. The secondary battery according to claim 5 or 6, wherein The outer layer has a thickness of 100 μm to 300 μm between the inner layer and the battery case.

8. The secondary battery according to claim 1, wherein The inner layer has a thickness of 50 μm to 150 μm.

9. The secondary battery according to claim 1, wherein The outer layer has a gas permeability of 4 barr to 40 barr at 60 °C.

10. The secondary battery according to claim 1, wherein The outer layer has a water permeation amount of 0.02 g to 0.2 g for 10 years at 25 °C and 50% RH.

11. The secondary battery according to claim 1, wherein The outer layer includes a polyolefin-based resin, and the polyolefin-based resin includes at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinylidene fluoride (PVDF).

12. The secondary battery according to claim 1, wherein The inner layer includes at least one material selected from the group consisting of a polyolefin-based resin, a fluorinated resin, a natural material, a glass fiber, a ceramic fiber, and a metal fiber.

13. The secondary battery according to claim 1, wherein The polyolefin-based resin includes at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinylidene fluoride (PVDF), 14. The secondary battery according to claim 13, wherein The fluorinated resin includes at least one material selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride, and The natural material includes at least one material selected from the group consisting of cotton and wool. A portion of the outer layer is disposed between the inner layer and one surface of the electrode lead such that the inner layer is not in direct contact with the electrode lead.

15. The secondary battery according to claim 1, wherein The battery case includes an upper case and a lower case, 16. The secondary battery according to claim 1, wherein an upper sealing portion of the upper case and a lower sealing portion of the lower case are combined with each other, and the lead film is disposed between the upper sealing portion and the lower sealing portion. ​ 17. The secondary battery according to claim 16, wherein The lead film is formed to have a greater length with respect to the upper and lower sealing portions in the protruding direction of the electrode lead, and the lead film is exposed in each of the inside and outside of the battery case.

18. The secondary battery according to claim 17, wherein An area of the lead film exposed to the outside of the battery case is the same as an area of the lead film exposed to the inside of the battery case.

19. The secondary battery of claim 17, wherein, An area of the lead film exposed to the outside of the battery case is greater than an area of the lead film exposed to the inside of the battery case.

20. The secondary battery of claim 16, wherein, The outer layer includes an upper outer layer disposed between the upper sealing portion and the electrode lead and a lower outer layer disposed between the lower sealing portion and the electrode lead.

21. The secondary battery according to claim 20, wherein The inner layer includes an upper inner layer covered by the upper outer layer and a lower inner layer covered by the lower outer layer.

22. The secondary battery of claim 21, wherein, The upper outer layer includes a first upper outer layer and a second upper outer layer, and The upper inner layer is disposed between the first upper outer layer and the second upper outer layer.

23. The secondary battery of claim 21, wherein, The lower outer layer includes a first lower outer layer and a second lower outer layer, and The lower inner layer is disposed between the first lower outer layer and the second lower outer layer.

24. The secondary battery of claim 1, wherein, The outer layer does not have a portion disposed between the inner layer and one surface of the electrode lead, such that the inner layer is in contact with the one surface of the electrode lead. 25.A battery module including the secondary battery according to any one of claims 1 to 24.

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