Patent Publication Number: US-2023163386-A1

Title: Battery Cell and Battery Module Including the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry under 35 U.S.C. § 371 of the International Application No. PCT/KR2022/001174, filed on Jan. 21, 2022, which claims the benefit of priority to Korean Patent Application No. 10-2021-0016111 filed on Feb. 4, 2021, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a battery cell and a battery module including the same, and more particularly, to a battery cell with improved external emission of gas generated inside the battery cell, and a battery module including the same. 
     BACKGROUND OF THE INVENTION 
     As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. In particular, secondary batteries are of great interest as energy sources not only for mobile devices such as mobile phones, digital cameras, notebooks and wearable devices, but also for power devices such as electric bicycles, electric vehicles and hybrid electric vehicles. 
     Depending on the shape of a battery case, these secondary batteries are classified into a cylindrical battery and a prismatic battery in which a battery assembly is included in a cylindrical or prismatic metal can, and a pouch-type battery in which the battery assembly is included in a pouch-type case of an aluminum laminate sheet. Here, the battery assembly included in the battery case is a power element including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and capable of charging and discharging, and is classified into a jelly-roll type in which long sheet-type positive and negative electrodes coated with an active material are wound with a separator being interposed therebetween, and a stack type in which a plurality of positive and negative electrodes are sequentially stacked with a separator being interposed therebetween. 
     Among them, in particular, a pouch-type battery in which a stack-type or stack/folding-type battery assembly is included in a pouch-type battery case made of an aluminum laminate sheet is being used more and more due to low manufacturing cost, small weight, and easy modification. 
       FIG.  1    is a top view showing a conventional battery cell.  FIG.  2    is a cross-sectional view, taken along the axis  2 - 2  of  FIG.  1   . Referring to  FIGS.  1  and  2   , a conventional battery cell  10  includes a battery case  20  having an accommodation portion  21  in which a battery assembly  11  is mounted, and a sealing portion  25  formed by sealing an outer periphery thereof. Here, the battery cell  10  includes an electrode lead  30  protruding out of the battery case  20  via the sealing portion  25 , and a lead film  40  is located between upper and lower portions of the electrode lead  30  and the sealing portion  25 . 
     However, as the energy density of the battery cell increases in recent years, there is a problem that the amount of gas generated inside the battery cell also increases. In the case of the conventional battery cell  10 , a component capable of discharging the gas generated inside the battery cell is not included, so a venting may occur in the battery cell due to gas generation. In addition, moisture may penetrate into the battery cell damaged by the venting, which may cause side reactions, and there is a problem that battery performance deteriorates and additional gas is generated. Accordingly, there is an increasing need to develop a battery cell with improved external emission of gas generated inside the battery cell. 
     BRIEF SUMMARY OF THE INVENTION 
     The present disclosure is directed to providing a battery cell with improved external emission of gas generated inside the battery cell, and a battery module including the same. 
     The object to be solved by the present disclosure is not limited to the above-mentioned object, and the objects not mentioned here may be clearly understood by those skilled in the art from this specification and the accompanying drawings. 
     In one aspect of the present disclosure, there is provided a battery cell, comprising: 
     a battery case having an accommodation portion in which an electrode assembly is mounted, and a sealing portion formed by sealing an outer periphery thereof; an electrode lead electrically connected to an electrode tab included in the electrode assembly and protruding out of the battery case via the sealing portion; and a lead film located at a portion corresponding to the sealing portion in at least one of an upper portion and a lower portion of the electrode lead, wherein the lead film has a dented portion that is recessed in an outer direction of the battery case, the dented portion is opened toward the inside of the battery case, the dented portion includes a first dented portion and a second dented portion, and a width of the second dented portion is greater than a width of the first dented portion. 
     The second dented portion may be located farther from the accommodated electrode assembly than the first dented portion. 
     A part of the first dented portion may be located at a position corresponding to the sealing portion. 
     A part of the second dented portion may be located at a positon not corresponding to the sealing portion. 
     The lead film may have a width greater than a width of the sealing portion and smaller than a length of the electrode lead. 
     The second dented portion may be located between an end of the sealing portion and an end of the lead film. 
     The first dented portion may extend along a protruding direction of the electrode lead, and the second dented portion may extend along a longitudinal direction of the sealing portion. 
     The second dented portion may have a circular, triangular, rectangular or uneven shape. 
     An inner surface of the dented portion may be closed based on a protruding direction of the electrode lead. 
     The lead film may further include an inner layer configured to cover at least one surface of inner surfaces of the dented portion of the lead film. 
     A material of the inner layer may have a higher melting point compared to a material of the lead film and may not react with an electrolytic solution. 
     The lead film may contain a polyolefin-based material. 
     The inner layer may contain at least one of polyolefin-based materials, fluorine-based materials and porous ceramic-based materials. 
     The dented portion may be located over the electrode lead. 
     The lead film may have a length greater than a width of the electrode lead. 
     The dented portion may be located between an end of the electrode lead and an end of the lead film. 
     The lead film may include a first lead film and a second lead film, the first lead film may be located at an upper portion of the electrode lead, and the second lead film may be located at a lower portion of the electrode lead. 
     The electrode lead may be located between the first lead film and the second lead film, and the first lead film and the second lead film may be connected to each other. 
     The dented portion may be located in at least one of the first lead film and the second lead film. 
     An end of the dented portion at an outermost side of the battery case may be located outer than an outer surface of the battery case. 
     An end of the dented portion opened toward the inside of the battery case may be located inner than an inner surface of the battery case. 
     Based on a protruding direction of the electrode lead, a width of the lead film surrounding a front surface of the dented portion may be 2 mm or more. 
     A thickness of the lead film surrounding an upper surface of the dented portion may be 100 μm to 300 μm. 
     The lead film may have gas permeability of 20 Barrer to 60 Barrer at 60° C. The lead film may have a moisture penetration amount of 0.02 g to 0.2 g for 10 years at 25° C., 50% RH. 
     In another aspect of the present disclosure, there is also provided a battery module, comprising the battery cell described above. 
     According to the embodiments, the present disclosure provides a battery cell, which includes an electrode lead to which a lead film having a dented portion dented in the outer direction of the battery case and opened toward the inside of the battery case is formed, and a battery module including the battery cell, thereby improving the external emission of gas generated inside the battery cell. 
     According to embodiments, in the present disclosure, since the dented portion includes a first dented portion and a second dented portion so that the width of the second dented portion is greater than the width of the first dented portion, it is possible to improve the external emission of gas generated inside the battery cell and to improve the durability of the lead film. 
     The effect of the present disclosure is not limited to the above effects, and the effects not mentioned here will be clearly understood by those skilled in the art from this specification and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a top view showing a conventional battery cell. 
         FIG.  2    is a cross-sectional view, taken along the axis  2 - 2  of  FIG.  1   . 
         FIG.  3    is a top view showing a battery cell according to this embodiment. 
         FIG.  4    is a perspective view showing an electrode lead included in the battery cell of  FIG.  3   . 
         FIGS.  5 ( a ) and ( b )  are cross-sectional views, taken along the axis  5 ( a ), ( b )- 5 ( a )( b ) of  FIG.  4   . 
         FIGS.  6 ( a ) and ( b )  are cross-sectional views, taken along the axis  6 ( a ), ( b )- 6 ( a ), ( b ) of  FIG.  4   . 
         FIGS.  7 ( a ) and ( b )  are cross-sectional views, taken along the axis  7 ( a ), ( b )- 7 ( a ), ( b ) of  FIG.  4   . 
         FIGS.  8 ( a ) and ( b )  are enlarged views showing the electrode lead in the battery cell of  FIG.  3   . 
         FIGS.  9 ( a ) and ( b )  are enlarged views showing the electrode lead according to a location of the sealing portion in  FIG.  8 ( a ) . 
         FIG.  10    is an enlarged view showing the electrode lead in the battery cell of  FIG.  3    according to another embodiment of the present disclosure. 
         FIG.  11    is an enlarged view showing the electrode lead in the battery cell of  FIG.  3    according to another embodiment of the present disclosure. 
         FIG.  12    is an enlarged view showing the electrode lead in the battery cell of  FIG.  3    according to another embodiment of the present disclosure. 
         FIG.  13    is a cross-sectional view, taken along the axis  13 - 13  of  FIG.  3   . 
         FIG.  14    is a diagram showing the flow of gas generated in the battery cell and discharged to the outside in  FIG.  13   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the accompanying drawings, various embodiments of the present disclosure will be described in detail so as to be easily implemented by those skilled in the art. The present disclosure may be implemented in various different forms and is not limited to the embodiments described herein. 
     In order to clearly explain the present disclosure, parts irrelevant to the description are omitted, and identical or similar components are endowed with the same reference signs throughout the specification. 
     In addition, since the size and thickness of each component shown in the drawings are arbitrarily expressed for convenience of description, the present disclosure is not necessarily limited to the drawings. In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. Also, in the drawings, for convenience of explanation, the thickness of some layers and regions is exaggerated. 
     In addition, throughout the specification, when a part “includes” a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. 
     In addition, throughout the specification, when referring to “top view”, it means that the target part is viewed from above, and when referring to “cross-sectional view”, it means that a vertically-cut section of the target part is viewed from a side. 
     Hereinafter, a pouch battery cell  100  according to an embodiment of the present disclosure will be described. However, here, the description will be made based on one side surface of both side surfaces of the pouch battery cell  100 , but it is not necessarily limited thereto, and the same or similar contents may be described in the case of the other side surface. 
       FIG.  3    is a top view showing a battery cell according to this embodiment. 
     Referring to  FIG.  3   , the battery cell  100  according to this embodiment includes a battery case  200 , an electrode lead  300 , and a lead film  400 . 
     The battery case  200  includes an accommodation portion  210  in which an electrode assembly  110  is mounted, and a sealing portion  250  formed by sealing an outer periphery thereof. The sealing portion  250  may be sealed by heat, laser, or the like. The battery case  200  may be a laminate sheet including a resin layer and a metal layer. More specifically, the battery case  200  may be made of a laminate sheet, and may include an outer resin layer forming the outermost layer, a barrier metal layer preventing penetration of materials, and an inner resin layer for sealing. 
     Also, the electrode assembly  110  may have a structure of a jelly-roll type (winding type), a stack type (lamination type), or a composite type (stack/folding type). More specifically, the electrode assembly  110  may include a positive electrode, a negative electrode, and a separator disposed therebetween. 
     Hereinafter, the electrode lead  300  and the lead film  400  will be mainly described. 
       FIG.  4    is a perspective view showing an electrode lead included in the battery cell of  FIG.  3   . 
     Referring to  FIGS.  3  and  4   , the electrode lead  300  is electrically connected to an electrode tab (not shown) included in the electrode assembly  110 , and protrudes out of the battery case  200  via the sealing portion  250 . In addition, the lead film  400  is located at a portion corresponding to the sealing portion  250  in at least one of an upper portion and a lower portion of the electrode lead  300 . Accordingly, the lead film  400  may improve the sealing properties of the sealing portion  250  and the electrode lead  300  while preventing a short circuit from occurring in the electrode lead  300  during sealing. 
       FIGS.  5 ( a ) and ( b )  are cross-sectional views, taken along the axis  5 ( a ),( b )- 5 ( a )( b ) of  FIG.  4   .  FIGS.  6 ( a ) and ( b )  cross-sectional views, taken along the axis  6 ( a ), ( b )- 6 ( a ), ( b ) of  FIG.  4   .  FIGS.  7 ( a ) and ( b )  are cross-sectional views, taken along the axis  7 ( a ), ( b )- 7 ( a ), ( b ) of  FIG.  4   . 
     Referring to  FIGS.  5 ( a ) and ( b ) , the lead film  400  has a dented portion  450  that is recessed in an outer direction of the battery case  200 , and the dented portion  450  is opened toward the inside of the battery case  200 . In addition, the inner surface of the dented portion  450  may be closed based on the protruding direction of the electrode lead  300 . 
     Accordingly, in the lead film  400 , if the gas generated inside the battery case  200  exceeds a predetermined pressure, the gas may be discharged to the dented portion  450 , and the gas introduced into the dented portion  450  may be discharged to the outside of the battery according to the pressure difference between the inside and outside. In addition, since the dented portion  450  of the lead film  400  is opened toward the inside and simultaneously the inner surface of the dented portion recessed in the outward direction of the lead film  400  is closed, there is an advantage in that airtightness and durability of the pouch can also be secured. In addition, in the lead film  400 , the gas permeation area may be maximized by the dented portion  450 , so that a large amount of gas can be discharged. 
     Referring to  FIGS.  6 ( a ), ( b ) and  7 ( a ), ( b ) , the dented portion  450  includes a first dented portion  451  and a second dented portion  455 , and the width of the second dented portion  455  is greater than the width of the first dented portion  451 . 
     In this specification, the width of the second dented portion  455  refers to a maximum value of the distance between one end and the other end of the second dented portion  455  in a direction orthogonal to the protruding direction of the electrode lead  300 , and the width of the first dented portion  451  refers to a maximum value of the distance between one end and the other end of the first dented portion  451  in a direction orthogonal to the protruding direction of the electrode lead  300 . 
     If the curvature generated as the lead film  400  expands to the outside by pressure increases since the gas inside the battery case  200  flows into the dented portion  450 , the stress applied to the interface between the lead film  400  and the electrode lead  300  also increases. 
     If the dented portion  450  has the same width entirely, as the curvature of the expanded lead film  400  increases, the durability of the lead film  400  may be weakened due to the stress applied to the interface between the lead film  400  and the electrode lead  300 . 
     Meanwhile, if the dented portion  450  includes the first dented portion  451  and the second dented portion  455  having different widths, since the curvature of the lead film  400  expanded in the first dented portion  451  having a relatively small width is smaller than the curvature of the lead film  400  expanded in the second dented portion  455  having a relatively great width, the stress applied to the interface of the lead film  400  and the electrode lead  300  is small, so it is possible to improve durability and improve gas emission. 
     In addition, referring to  FIGS.  5 ( a ),( b ) to  7 ( a ), ( b ) , the lead film  400  may further include an inner layer  410  covering at least one of the inner surfaces of the dented portion  450 . 
     For example, referring to  FIGS.  5 ( a ) to  7 ( a ) , the inner layer  410  in the dented portion  450  may cover the entire surface of the lead film  400 . That is, the inner layer  410  may be formed on the entire inner surface of the dented portion  450 , except for the opened surface. 
     Accordingly, even if the lead film  400  is sealed together with the sealing portion  250  in a state of being located in at least one of the upper and lower portions of the electrode lead  300 , the dented portion  450  may be preserved in a non-sealed state by the inner layer  410 . 
     As another example, referring to  FIGS.  5 ( b ) to  7 ( b ) , the inner layer  410  may cover an upper surface or a lower surface among the inner surfaces of the dented portion  450 . That is, the dented portion  450  may have an inner layer  410  formed on at least one of the upper and lower surfaces facing each other. 
     Accordingly, while the lead film  400  minimizes the inner layer  410  formed in the dented portion  450 , the dented portion  450  may be preserved in a non-sealed state by the inner layer  410 . In addition, the manufacturing process may be simplified and the cost may be reduced. 
     More specifically, the inner layer  410  may be made of a material having a higher melting point compared to the material constituting the lead film  400 . In addition, the inner layer  410  may be made of a material that does not react with the electrolytic solution contained in the battery case  200 . Accordingly, since the inner layer  410  is made of the above-described material, the inner layer  410  does not separately react with the electrolytic solution and does not cause heat fusion, thermal deformation, or the like in the high-temperature sealing process, so that the dented portion  450  may be kept blank. In addition, the gas generated in the battery case  200  may be easily discharged to the outside. 
     In one embodiment of the present disclosure, the thickness of the inner layer  410  may be 100 μm or less. 
     In one embodiment of the present disclosure, the gas permeability of the inner layer  410  may be 40 Barrer or more. For example, the carbon dioxide permeability of the inner layer  410  may satisfy the above range. 
     For example, the inner layer  410  may include at least one of polyolefin-based materials, fluorine-based materials, and porous ceramic-based materials. For example, the inner layer  410  may include at least one of polyolefin-based materials, fluorine-based materials, and porous ceramic-based materials that satisfies the above gas permeability value. The polyolefin-based material may include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinyl difluoride (PVDF). The fluorine-based material may include at least one material selected from the group consisting of polytetrafluoroethylene and polyvinylidene fluoride. In addition, the inner layer  410  may include a getter material, so that gas permeability may be increased while water permeability may be minimized. As an example, the getter material may be calcium oxide (CaO), barium oxide (BaO), lithium chloride (LiCl), silica (SiO 2 ), or the like, and any material reacting with water (H 2 O) can be used without being limited thereto. 
     The inner layer  410  may have an adhesive material between the lead film  400  and the inner layer  410  or may be extruded together with the lead film  400  and adhered to the lead film  400 . The adhesive material may include an acryl-based material. In particular, when the inner layer  410  is extruded together with the lead film  400 , the gas permeability of the inner layer  410  may be 40 Barrer or more. 
     Referring to  FIGS.  4  to  7   ( a ), ( b ), the lead film  400  may include a first lead film and a second lead film, the first lead film may be located at an upper portion of the electrode lead  300 , and the second lead film may be located at a lower portion of the electrode lead  300 . At this time, the electrode lead  300  may be sealed together with the sealing portion  250  in a state of being located between the first lead film and the second lead film, so that the first lead film and the second lead film may be connected to each other. 
     Accordingly, the lead film  400  may prevent the side surface of the electrode lead  300  from being exposed to the outside, while improving the sealing properties of the sealing portion  250  and the electrode lead  300 . 
     For example, in the lead film  400 , the dented portion  450  may be located in at least one of the first lead film and the second lead film. More specifically, in the lead film  400 , the dented portion  450  may be formed in the first lead film or the second lead film based on the electrode lead  300 , or the dented portion  450  may be formed in both the first lead film and the second lead film based on the electrode lead  300 . However, the number of the dented portion  450  is not limited to the above, and the lead film  400  may be formed in an appropriate number. 
     Accordingly, by adjusting the number of the dented portions  450  formed in the lead film  400 , the durability and airtightness of the lead film  400  may be controlled. In addition, by minimizing the number of the dented portion  450  as necessary, it is possible to simplify the manufacturing process and reduce the cost. 
       FIGS.  8 ( a ) and ( b )  are enlarged views showing the electrode lead in the battery cell of  FIG.  3   .  FIGS.  9 ( a ) and ( b )  are enlarged views showing the electrode lead according to a location of the sealing portion in  FIG.  8 ( a ) . 
     Referring to  FIGS.  8 ( a ) and ( b ) , the second dented portion  455  may be located farther from the accommodated electrode assembly  110  than the first dented portion  451 . 
     At this time, the second dented portion  455  may play a role of discharging the gas generated inside the battery case  200  to the outside of the battery case  200 . Accordingly, since the width of the second dented portion  455  is greater than the width of the first dented portion  451 , the area through which the gas is discharged to the outside is further increased, and thus it may be easier to increase the emission of gas. 
     In addition, the first dented portion  451  having a relatively smaller width may serve as a passage through which the gas generated inside the battery case  200  flows into the dented portion  450 , and may increase durability of the lead film  400 . 
     Referring to  FIGS.  8 ( a ), ( b ) , a part of the first dented portion  451  may be located at a position corresponding to the sealing portion  250 . For example, the second dented portion  455  may be located farther from the accommodated electrode assembly  110  than the first dented portion  451 , and also a part of the first dented portion  451  may be located at a position corresponding to the sealing portion  250 . 
     Referring to  FIGS.  8 ( a ), ( b ) , a part of the second dented portion  455  may be located at a position that does not correspond to the sealing portion  250 . In this case, as the area in which the second dented portion  455  does not correspond to the sealing portion  250  increases, the area in which the gas inside the battery case  200  is discharged to the outside of the battery case  200  may increase. For example, while the second dented portion  455  is located farther from the accommodated electrode assembly  110  than the first dented portion  451 , a part of the second dented portion  455  may be located at a position that does not correspond to the sealing portion  250 . 
     In an embodiment of the present disclosure, the width of the lead film  400  may be greater than the width of the sealing portion  250  and may be smaller than the length of the electrode lead  300 . In this specification, the length of the lead film  400  means a maximum value of the distance between one end and the other end of the lead film  400  in the protruding direction of the electrode lead  300 . The width of the sealing portion  250  means a maximum value of the distance between one end and the other end of the sealing portion  250  in the protruding direction of the electrode lead  300 . The length of the electrode lead  300  means a maximum value of the distance between one end and the other end of the electrode lead  300  in the protruding direction of the electrode lead  300 . At this time, the second dented portion  455  may be located between the end of the sealing portion  250  and the end of the lead film  400 . For example, the second dented portion  455  may be entirely located at a position that does not correspond to the sealing portion  250 . 
     In the lead film  400 , the dented portion  450  may be formed in various shapes. 
     Referring to  FIGS.  8 ( a ), ( b ) , the first dented portion  451  may extend along the protruding direction of the electrode lead  400 , and the second dented portion  455  may extend along the longitudinal direction of the sealing portion  250 . In this specification, the longitudinal direction of the sealing portion  250  refers to a direction orthogonal to the protruding direction of the electrode lead  300 . 
     In the lead film  400 , the dented portion  450  may be formed at various positions with respect to the electrode lead  300 . 
     For example, as shown in  FIG.  8 ( a ) , in the lead film  400 , the dented portion  450  may be located over the electrode lead  300 . More specifically, the dented portion  450  may be formed at a position corresponding to the center of the electrode lead  300 . 
     As another example, as shown in  FIG.  8 ( b ) , the length of the lead film  400  may be greater than the width of the electrode lead  300 , and the dented portion  450  may be located between the end of the electrode lead  300  and the end of the lead film  400 . Here, the length of the lead film  400  means a maximum value of the distance between one end and the other end of the lead film  400  in a direction orthogonal to the protruding direction of the electrode lead  300 , and the width of the electrode lead  300  means a maximum value of the distance between one end and the other end of the electrode lead  300  in a direction orthogonal to the protruding direction of the electrode lead  300 . In other words, in the lead film  400 , the dented portion  450  may be formed at a position avoiding the electrode lead  300 . However, the position of the dented portion  450  is not limited to the above, and the dented portion  450  may be formed at an appropriate position within the lead film  400 . 
     Accordingly, by adjusting the position of the dented portion  450  formed in the lead film  400 , the durability and airtightness of the lead film  400  may be controlled. In addition, if necessary, by adjusting the size of the dented portion  450  according to the position of the dented portion  450 , it is possible to simplify the manufacturing process and reduce the cost. 
     Referring to  FIGS.  9 ( a ), ( b ) , in the lead film  400 , an end of the dented portion  450  opened toward the inside may be formed adjacent to the end of the lead film  400  toward the inner side of the battery case  200 , and an end of the dented portion  450  at the outermost side of the battery case  200 , which is recessed toward the outside, may be located between the end of the sealing portion  250  and the end of the lead film  400 . In this specification, the term “the end at the outermost side of the battery case  200 ” refers to an end of the dented portion  450  located at the outermost side with respect to the protruding direction of the electrode lead  300  among the ends of the dented portion. 
     In addition, the end of the dented portion  450  recessed toward the outside may be spaced apart from the end of the sealing portion  250  by a predetermined distance, or may be located adjacent thereto. 
     For example, if comparing  FIGS.  9 ( a ) and  9 ( b ) , even if the position of the sealing portion  250  in contact with the lead film  400  is changed, it may be found that the area of the dented portion  450  located outside the battery case  200  is not affected. 
     Accordingly, in this embodiment, within the error range according to the positions of the lead film  400  and the sealing portion  250  generated during the sealing process, the area where the dented portion  450  is located outside with respect to the battery case  200  may be uniformly maintained, and the area in which the gas in the battery case  200  can be introduced into and discharged from the dented portion  450  may also be maintained uniformly. Accordingly, there is an advantage in that the gas exhaust effect by the dented portion  450  can also be maintained. 
       FIGS.  10  to  12    are enlarged views showing the electrode lead in the battery cell of  FIG.  3    according to other embodiments of the present disclosure. 
     Referring to  FIGS.  10  to  12   , the second dented portion  455  may have a circular, triangular, or uneven shape, but is not limited thereto, and may have, for example, a rectangular shape as shown in  FIGS.  8 ( a ), ( b ) . 
     Accordingly, by adjusting the shape of the dented portion  450  formed in the lead film  400 , durability and airtightness of the lead film  400  can be controlled. In addition, if necessary, the shape of the dented portion  450  may be changed to simplify the manufacturing process and reduce cost. 
       FIG.  13    is a cross-sectional view, taken along the axis  13 - 13  of  FIG.  3   .  FIG.  14    is a diagram showing the flow of gas generated in the battery cell and discharged to the outside in  FIG.  13   . 
     Referring to  FIG.  13   , the end of the dented portion  450  at the outermost side of the battery case  200  may be located outer than the outer surface of the battery case  200 . In this specification, the outer surface of the battery case  200  means an end of the sealing portion  250  of the battery case  200  at an outer side of the battery. Accordingly, it may be easier to sufficiently secure an area through which the gas can be discharged to the outside of the battery. 
     In addition, the end of the dented portion  450  that is opened toward the inside of the battery case  200  may be located inner than the inner surface of the battery case  200 . In this specification, the inner surface of the battery case  200  means an end of the sealing portion  250  of the battery case  200  at an inner side of the battery. Accordingly, the gas in the battery may more easily flow into the dented portion  450 . 
     In the above case, the lead film  400  may maximize the area of the dented portion  450  so that the permeation area of the gas generated inside the battery case  200  may be maximized, so a large amount of gas may be discharged. 
     Referring to  FIG.  13   , the thickness H of the lead film  400  surrounding the upper surface of the dented portion  450  may be 100 μm to 300 μm, or 100 μm to 200 μm. If the thickness H of the lead film  400  surrounding the upper surface of the dented portion  450  satisfies the above range, the gas inside the battery case  200  may be more easily discharged to the outside. In this specification, the lead film  400  surrounding the upper surface of the dented portion  450  refers to the lead film  400  between the dented portion  450  and the electrode lead  300 . 
     Referring to  FIG.  13   , based on the protruding direction of the electrode lead  300 , the width W of the lead film  400  surrounding the front surface of the dented portion  450  may be 2 mm or more, or 2 mm to 3 mm. In this specification, the width of the lead film  400  surrounding the front surface of the dented portion  450  means a maximum value of the distance between the recessed end of the lead film  400  at the outermost side of the battery case  200  and the end of the lead film  400  at the outer side of the battery case  200 . If the width W of the lead film  400  surrounding the front surface of the dented portion  450  satisfies the above range, it may be easier to prevent the lead film  400  from being torn while the gas generated inside the battery case  200  is discharged to the outside. 
     Referring to  FIG.  14   , the gas generated inside the battery cell  100  may be discharged toward the dented portion  450  of the lead film  400 . Here, since the dented portion  450  is opened toward the inside, the pressure inside the dented portion  450  may be the same as the pressure inside the battery case  200 . 
     The pressure inside the dented portion  450  is higher than the pressure outside the battery cell  100 , and the resulting pressure difference may act as a driving force of the gas. Accordingly, the gas introduced into the dented portion  450  may be easily discharged toward the outside. In addition, the emission amount of gas generated inside the battery cell  100  may also be increased. 
     At this time, the gas generated inside the battery case  200  may be discharged along the Z-axis direction via the dented portion  450  and the lead film  400  surrounding the upper surface of the dented portion. For example, when the dented portion  450  is exposed to the outside of the battery case  200 , the gas generated inside the battery case  200  may be discharged along the Z-axis direction via the dented portion  450  and the lead film  400  surrounding the upper surface of the dented portion. In particular, when the recessed end of the dented portion  450  at the outermost side of the battery case is located outer than the outer surface of the battery case  200 , gas may be discharged along the Z-axis direction through the lead film  400  between the recessed end the dented portion  450  at the outermost side of the battery case  200  and the outer surface of the battery case  200 . 
     In one embodiment of the present disclosure, the gas permeability of the lead film  400  may be 20 Barrer to 60 Barrer, or 30 Barrer to 40 Barrer at 60° C. For example, the carbon dioxide permeability of the lead film  400  may satisfy the above range. In addition, the gas permeability may satisfy the above range at 60° C. based on the thickness of the lead film  400  of 200 μm. If the gas permeability of the lead film  400  satisfies the above range, the gas generated inside the secondary battery may be more effectively discharged. 
     In this specification, the gas permeability may be measured by ASTM F2476-20. 
     In one embodiment of the present disclosure, the moisture penetration amount of the lead film  400  may be 0.02 g to 0.2 g, or 0.02 g to 0.04 g, or 0.06 g, or 0.15 g for 10 years at 25° C., 50% RH. If the moisture penetration amount of the lead film  400  satisfies the above range, the penetration of moisture from the lead film  400  may be more effectively prevented. 
     The moisture penetration amount of the lead film  400  may be measured by adopting the ASTM F 1249 method. At this time, the moisture penetration amount may be measured using equipment officially certified by MCOON. 
     In one embodiment of the present disclosure, the lead film  400  may have a gas permeability of 20 Barrer to 60 Barrer at 60° C. and a moisture penetration amount of 0.02 g to 0.2 g at 25° C., 50% RH for 10 years. If the gas permeability and the moisture penetration amount of the lead film  400  satisfy the above ranges, the penetration of moisture from the outside may be more effectively prevented while discharging the gas generated inside the secondary battery. 
     In one embodiment of the present disclosure, the lead film  400  may include a polyolefin-based resin. For example, the lead film  400  may include a polyolefin-based resin satisfying the gas permeability and/or moisture penetration amount values described above. The polyolefin-based resin may include at least one material selected from the group consisting of polypropylene, polyethylene, and polyvinyl difluoride (PVDF). While the lead film  400  contains polypropylene, the gas permeability of the lead film  400  may be 20 Barrer to 60 Barrer at 60° C. Also, the moisture penetration amount may be 0.06 g to 0.15 g. In this case, the gas generated inside the secondary battery may be more effectively discharged, and the penetration of moisture from the outside may be easily prevented. 
     In addition, since the lead film  400  is made of the above-described material, the lead film  400  may maintain the airtightness of the battery cell  100  and prevent leakage of the internal electrolytic solution. 
     A battery module according to another embodiment of the present disclosure includes the battery cell described above. Meanwhile, one or more battery modules according to this embodiment may be packaged in a pack case to form a battery pack. 
     The battery module described above and the battery pack including the same may be applied to various devices. These devices may be transportation means such as electric bicycles, electric vehicles, hybrid electric vehicles, and the like, but the present disclosure is not limited thereto, and the present disclosure may be applied various devices that can use a battery module and a battery pack including the same, which is also within the scope of the right of the present disclosure. 
     Although the preferred embodiment of the present disclosure has been described in detail above, the scope of the right of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present disclosure defined in the appended claims also fall within the scope of the right of the present disclosure.