Patent Publication Number: US-2012040235-A1

Title: Pouch having improved safety, pouch-type secondary battery including the same, and medium-to-large battery pack

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT international Application NO. PCT/KR2011/005637 filed on Jul. 30, 2011, which claims priority of Patent Application Nos. 10-2010-0075468, filed on Aug. 5, 2010, and 10-2011-0050759, filed on May 27, 2011, the entire contents of which are hereby incorporated by reference into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention disclosed herein relates to a pouch having improved safety, a secondary battery including the pouch, and a battery pack. 
     As the demand and technology for mobile devices increase, so do those for secondary batteries as an energy source for mobile devices. Of such secondary batteries, there are remarkable advances and commercialization being made for lithium secondary batteries that have high energy density and high discharge voltage. 
     According to structures of electrode assemblies including a positive electrode, a separator, and a negative electrode, secondary batteries may be classified into jellyroll (winding-type) electrode assemblies in which long sheet-shaped positive and negative electrodes are wound with a separator therebetween; stack-type electrode assemblies in which positive and negative electrodes cut to have certain sizes are sequentially stacked with a separator therebetween; and stack/folding-type electrode assemblies in which Bi-cells or full cells formed by stacking positive and negative electrodes having certain sizes with a separator therebetween are wound. 
       FIG. 1  is an exploded perspective view illustrating a typical pouch-type secondary battery in the related art. 
     Referring to  FIG. 1 , a pouch-type secondary battery  200  includes an electrode assembly  40  and a pouch-type battery case. 
     The electrode assembly  40  may be connected to electrode tabs  50  and  60  extending from the electrode assembly  40 , and electrode leads  70  and  80  welded to the electrode tabs  50  and  60 . The electrode tabs  50  and  60  or the electrode leads  70  and  80  may protrude in the same direction or different directions. In  FIG. 1 , the electrode tabs  50  and the electrode lead  70  protrude in the different direction from that of the electrode tabs  60  and the electrode lead  80 . 
     The pouch-type battery case includes a lower battery case  20  and an upper battery case  30 . The lower battery case  20  may be separated from the upper battery case  30  as illustrated in  FIG. 1 . Alternatively, although not shown, one of the four sides of the lower battery case  20  may be connected to the upper battery case  30 . Both the lower battery case  20  and the upper battery case  30  as illustrated in  FIG. 1 , or one thereof may be provided with a space part accommodating the electrode assembly  40 , and a sealing part for sealing the lower battery case  20  and the upper battery case  30 . 
     After the electrode assembly  40  is accommodated in the space part, the sealing part of the upper battery case  30  and the lower battery case  20  is sealed through heat welding, thereby completing the pouch-type secondary battery  200 . 
     The electrode assembly  40  is an electricity generating device in which a positive electrode and a negative electrode are sequentially stacked with a separator therebetween, and may have a jellyroll-type, stack-type, or stack/folding-type structure. The electrode tabs  50  and  60  extend from electrode plates of the electrode assembly  40 . The electrode leads  70  and  80  are electrically connected to the electrode tabs  50  and  60  extending from the electrode plates, e.g., through welding, and are partially exposed out of the lower battery case  20  and the upper battery case  30 . Insulating films  90  are attached to a portion of the top and bottom surfaces of the electrode leads  70  and  80  to improve sealing property and electrical insulation between the portion and the lower and upper battery cases  20  and  30 . 
     The lower battery case  20  and the upper battery case  30  include aluminum laminate sheets, and have a pouch shape as a whole, thereby constituting the pouch-type secondary battery  200 . 
     The electrode tabs  50  or  60  of the electrode assembly  40  that is a stack-type one in  FIG. 1  are integrally coupled in the form of a welding portion, e.g., through welding, and thus, the welding portion is connected to the electrode lead  70  or  80 . 
     Accordingly, the electrode leads  70  and  80  with ends opposed to welding portions being exposed are sealed by the lower battery case  20  and the upper battery case  30 . 
     One of main research efforts on such secondary batteries is to improve safety. A main area of research on secondary batteries is improving safety. When a secondary battery operates under abnormal conditions such as with an internal short circuit, in a charge state in which current and voltage exceed allowable thresholds, when exposure to high temperature, or subjected to an external impact or an impact from being dropped, the inner temperature and pressure of the battery may increase, causing the battery to explode. Such explosion may be a main defect of lithium secondary batteries, and thus, one of main research efforts on lithium secondary batteries is to improve safety. 
     Especially, secondary batteries used in a medium-to-large battery pack that is a power source for electric vehicles and hybrid vehicles are required to have long service life and are concentrated in the battery pack, safety is a critical issue. 
     Thus, technology for preventing the burning or explosion of a battery cell due to high pressure gas generated in the battery cell or high pressure gas generated under an unexpected condition is needed, thereby ensuring the service life and safety. 
     SUMMARY OF THE INVENTION 
     In the related art, a pouch-type secondary battery periodically discharges high pressure gas or includes a venting passage for discharging the gas, thereby preventing expansion of the secondary battery due to high temperature and pressure in the secondary battery, and explosion of the secondary battery due to the expansion. 
     However, the present invention provides a pouch-type battery case that deforms a pouch-type secondary battery in a predetermined shape with the pressure or force of gas generated in the secondary battery and expanding the secondary battery or bursting a sealing portion to discharge gas, thereby fundamentally cutting off electric current. That is, a pouch-type battery case according to the present invention is designed such that electrode tabs of an electrode assembly are separated from electrode leads when gas or high temperature and pressure generated in a secondary battery including the pouch type battery case damages the battery, thereby fundamentally cutting off electric current. 
     The present invention also provides a secondary battery including the pouch-type battery case, and a medium-to-large battery module including secondary batteries having the pouch-type battery case. 
     The present invention also provides a medium-to-large battery pack including medium-to-large battery modules having the secondary batteries. 
     In one embodiment, a pouch-type battery case includes: a space part accommodating an electrode assembly; an upper battery case; a lower battery case; and a sealing part for sealing the upper and lower battery cases, wherein each of the upper battery case and the lower battery case has a foldable structure formed by bending a spacing edge at least one time, and the spacing edge is disposed in a protruding direction of an electrode lead of the electrode assembly. 
     The foldable structure may be recessed and bent one time. 
     Electrode leads of the electrode assembly may protrude in the same direction, and spacing edges disposed over and under the electrode leads may be provided with foldable structures bent at least one time. 
     The foldable structure may be recessed and bent in a direction away from the electrode lead such that a folded portion faces the electrode lead. 
     The foldable structure may be recessed and bent toward the electrode lead from an opposite side to that of the electrode lead such that a folded portion faces the opposite side. 
     Electrode leads of the electrode assembly may protrude in both protruding directions, and the spacing edges disposed over and under the electrode leads may be provided with foldable structures bent at least one time. 
     Foldable structures may be disposed in the protruding directions of the electrode leads, and folded portions may face opposite sides. 
     Foldable structures may be disposed in the protruding directions of the electrode leads, and folded portions may face each other. 
     A folded portion of the foldable structure may have a length corresponding to an electrode non-coating portion of the electrode assembly. 
     The pouch-type battery case may further include a laminate sheet including a resin layer and a metal layer, wherein the battery case is sealed through heating welding after the electrode assembly is accommodated in the space part. 
     The laminate sheet may include an aluminum laminate sheet. 
     In another embodiment, a secondary battery includes: the pouch-type battery case; and an electrode assembly. 
     The electrode assembly may include a welding portion connecting an end of an electrode tab to an end of an electrode lead. 
     The welding portion may be configured such that bent surfaces formed by bending the end of the electrode tab and the end of the electrode lead face each other. 
     The electrode assembly may include at least one fractured recess in an end of an electrode tab or an end of an electrode lead. 
     The fractured recess may be disposed in an end of the electrode tab or an end of the electrode lead within the pouch-type battery case. 
     The secondary battery may be a lithium polymer secondary battery. 
     In another embodiment, a medium-to-large battery module includes: a plurality of unit batteries using the secondary battery as the unit battery, wherein the unit batteries are stacked toward both large side surfaces with respect to a protruding direction of an electrode lead of the secondary battery. 
     In another embodiment, a medium-to-large battery pack includes: a plurality of unit medium-to-large battery modules using the medium-to-large battery module as the unit medium-to-large battery module. 
     The medium-to-large battery pack may be used as a power source for power tools; electric vehicles including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); electric two-wheeled vehicles including an E-bike and an E-scooter; electric golf carts; electric trucks; and electric commercial vehicles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings: 
         FIG. 1  is an exploded perspective view illustrating a typical pouch-type secondary battery in the related art; 
         FIG. 2  is an exploded perspective view illustrating a pouch-type secondary battery according to an embodiment of the present invention; 
         FIG. 3  is a perspective view illustrating the pouch-type secondary battery of  FIG. 2 ; 
         FIG. 4  is a perspective view illustrating a state in which the pouch-type secondary battery of  FIG. 2  is expanded in a predetermined direction by expansion of gas in the secondary battery, to thereby separate electrode tabs from electrode leads; 
         FIGS. 5A and 5B  are a plan view and a side view illustrating the pouch-type secondary battery of  FIG. 3 ; 
         FIGS. 6A and 6B  are a plan view and a side view illustrating the pouch-type secondary battery of  FIG. 4 ; 
         FIG. 7  is an exploded perspective view illustrating the pouch-type secondary battery of  FIG. 2  provided with fractured recesses; 
         FIGS. 8A and 8B  are a plan view and a side view illustrating a pouch-type secondary battery according to another embodiment of the present invention; 
         FIGS. 9A and 9B  are a plan view and a side view illustrating a state in which the pouch-type secondary battery of  FIG. 8A  is expanded in a predetermined direction by expansion of gas in the secondary battery, to thereby separate electrode tabs from electrode leads; 
         FIGS. 10A and 10B  are a plan view and a side view illustrating a pouch-type secondary battery including electrode tabs and electrode leads protruding in the same direction according to another embodiment of the present invention; 
         FIGS. 11A and 11B  are a plan view and a side view illustrating a state in which the pouch-type secondary battery of  FIG. 10A  is expanded in a predetermined direction by expansion of gas in the secondary battery, to thereby separate the electrode tabs from the electrode leads; 
         FIGS. 12A to 12F  are plan views and side views illustrating welding portions of electrode tabs and electrode leads in pouch-type secondary batteries according to embodiments of the present invention; 
         FIG. 13  is a perspective view illustrating a battery module including pouch-type secondary batteries as illustrated in  FIG. 2 , according to an embodiment of the present invention; and 
         FIG. 14  is a perspective view illustrating a battery module including pouch-type secondary batteries as illustrated in  FIG. 10A , according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A secondary battery according to the present invention includes a pouch-type battery case including: a space part accommodating an electrode assembly; an upper battery case; a lower battery case; and a sealing part for sealing the upper and lower battery cases, wherein each of the upper battery case and the lower battery case has a foldable structure formed by bending a spacing edge at least one time, and the spacing edge is disposed in a protruding direction of an electrode lead of the electrode assembly. 
     Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
       FIG. 2  is an exploded perspective view illustrating a pouch-type secondary battery according to an embodiment of the present invention.  FIG. 3  is a perspective view illustrating the pouch-type secondary battery of  FIG. 2 .  FIG. 4  is a perspective view illustrating a state in which the pouch-type secondary battery of  FIG. 2  is expanded in a predetermined direction by expansion of gas in the secondary battery, to thereby separate electrode tabs from electrode leads. 
     Referring to  FIG. 2 , a pouch-type secondary battery  210  includes a pouch-type battery case. The pouch-type battery case includes a space part  110  accommodating an electrode assembly  40 ′, and a sealing part for sealing an upper battery case  30 ′ and a lower battery case  20 ′. Since the pouch-type battery case has foldable structures, spacing edges  130  of the upper battery case  30 ′ and spacing edges  120  of the lower battery case  20 ′, which are disposed in protruding directions of electrode leads  70 ′ and  80 ′ of the electrode assembly  40 ′, are folded at least one time. 
     The foldable structure is formed by recessing and bending the pouch-type battery case including the space part  110 , in a direction. The pouch-type battery case may be recessed and bent at least one time. For example, the pouch-type battery case may be recessed and bent one time according to an accommodating space and thickness of the secondary battery  210  including the pouch-type battery case. 
     As such, the upper battery case  30 ′ and the lower battery case  20 ′ of the secondary battery  210  are provided with at least one foldable structure disposed in the protruding direction of the electrode leads  70 ′ and  80 ′. Thus, when gas is generated or pressure is increased within the secondary battery  210 , the secondary battery  210  can be efficiently deformed in a predetermined direction. 
     The secondary battery  210  is more effective when being applied to a medium-to-large module formed by stacking and packaging a plurality of unit batteries using the secondary battery  210  as the unit battery, or to a medium-to-large battery pack including the medium-to-large module, than when being applied to a single secondary battery. 
     That is, since stacked and packaged unit batteries using the secondary battery  210  as the unit battery and constituting a medium-to-large module or battery pack overlap each other or are stacked in a z-direction of  FIG. 5A , even though inner pressure or gas of the unit batteries increases, expansion or deformation of the unit batteries in the z-direction is difficult. 
     As such, since deformation of the unit batteries in the z-direction is difficult within the medium-to-large module or battery pack, when high pressure gas is generated within the unit battery, high expansion stress is applied in an x-direction of  FIG. 5A , to thereby deform the unit battery in predetermined shape. 
     In detail, referring to  FIGS. 5A and 5B , the secondary battery  210  may have the foldable structure on at least one of the spacing edges  120  and  130  of the lower battery case  20 ′ and the upper battery case  30 ′ in the protruding direction of the electrode leads  70 ′ and  80 ′, that is, in the x-direction. 
     As such, when inner pressure of the secondary battery  210  having the foldable structure increases within a medium-to-large battery module or battery pack including the secondary battery  210  as a unit battery, since the unit batteries are stacked to apply pressure in a y-direction and the z-direction as illustrated in  FIGS. 5A and 5B , deformation of the unit battery in the y-direction and the z-direction is difficult, and thus, expansion due to inner gas is concentrated in the x-direction. 
     Accordingly, referring to  FIGS. 6A and 6B , expansion stress applied in the x-direction unfolds the foldable structures formed on the spacing edges  120  and  130 , and thus, the battery case expands in the x-direction. 
     When the battery case expands in the x-direction, the electrode leads  70 ′ and  80 ′ sealed together with the lower battery case  20 ′ and the upper battery case  30 ′ are pulled toward the outside of the secondary battery  210 . 
     Thus, when the unit battery, that is, the secondary battery  210  continually expands in the x-direction toward the outside thereof, and the foldable structures are maximally unfolded, the electrode leads  70 ′ and  80 ′ are separated from electrode tabs of the secondary battery  210  to cut off electric current. 
     The electrode leads  70 ′ and  80 ′ or the electrode tabs may be disposed at the same side or different sides. When the electrode leads  70 ′ and  80 ′ are disposed at different sides, the foldable structures may be disposed on at least two sides. 
     Alternatively, when the electrode leads  70 ′ and  80 ′ are disposed at the same side, the foldable structures may be disposed on one side. 
     The foldable structures are provided to both the spacing edges  120  and  130  of the lower and upper battery cases  20 ′ and  30 ′ in the protruding direction of the electrode leads  70 ′ and  80 ′, so that the foldable structures can be unfolded by expansion of inner gas. 
     When pulling force, which pulls the electrode leads  70 ′ and  80 ′, is balanced, maximum stress is applied to the electrode leads  70 ′ and  80 ′. Accordingly, the foldable structures are expanded and unfolded by inner pressure, and the electrode leads  70 ′ and  80 ′, can be efficiently separated from the electrode tabs. If the foldable structure is provided to one of the lower battery case  20 ′ and the upper battery case  30 ′, unfolding of a foldable part of the battery case due to expansion of inner gas may be difficult. 
     The foldable structures provided to the spacing edge  130  and the spacing edge  120  may be the same in shape and size to maximize the pulling force. 
     The foldable structures provided to the spacing edges  130  and the spacing edges  120  of the battery case as illustrated in  FIG. 2  are recessed and folded inward, and the degree of recessing of the battery case is not limited. 
     However, if the degree of recessing is too small, efficient separation of an electrode lead may be difficult, and thus, reliable cut off of electric current in an emergency may be difficult. On the contrary, if the degree of recessing is too great, deformation of a battery due to production of gas and high pressure in a battery may be delayed. Thus, the degree of recessing of the foldable structure provided to the spacing edge  120  or  130  may be adjusted at least such that the electrode lead  70 ′ or  80 ′ is completely separated from the electrode tab when the foldable structure is completely unfolded and protrudes outward. 
     For example, the foldable structure may be recessed inward up to an electrode non-coating portion of the electrode assembly  40 ′. 
     Since a method of forming the electrode non-coating portion on an electrode collector, or the shape of the electrode non-coating portion is well known in the art, a description thereof will be omitted. 
     The electrode non-coating portion is a portion of the electrode collector uncoated with an electrode active material, and connects the electrode collector to the electrode tab. Accordingly, the space of the electrode non-coating portion is irrelevant to the actual performance of the secondary battery  210 , and thus, may be minimized except for a space required by a process. Furthermore, the space required by a process may be used for another purpose. 
     To this end, according to the embodiment, the space of the electrode non-coating portion may be used as a space for recessing the foldable structures on the spacing edges  120  and  130  of the lower and upper battery cases  20 ′ and  30 ′. 
     As the degree of recessing of the foldable structure of the electrode case increases, separation of the electrode tab in an emergency is facilitated. Thus, the degree of recessing of the foldable structure may be maximized. However, the degree of recessing is limited due to a compact configuration of the secondary battery  210 . Thus, the space of the electrode non-coating portion may be used as a space for recessing the foldable structure, thereby achieving the compact configuration of the secondary battery  210  without negatively affecting the electrode assembly  40 ′. 
     As illustrated in  FIG. 2 , the battery case according to the embodiment is the same in structure as a well-known pouch-type battery case except that the battery case has the foldable structures on the spacing edges  120  and  130  of the lower battery case  20 ′ and the upper battery case  30 ′ in the protruding direction of the electrode leads  70 ′ and  80 ′. 
     That is, the battery case includes the space part  110  accommodating the electrode assembly  40 ′, and the upper battery case  30 ′ and the lower battery case  20 ′ are coupled to each other through heat welding at the sealing part extending around the space part  110 , thereby providing a pouch shape. 
     The foldable structure may have any shape provided that a bent surface is formed in a direction perpendicular to the protruding direction of the electrode leads  70 ′ and  80 ′. 
     When the electrode leads  70 ′ and  80 ′ protrude in both directions, bent surfaces may be formed in the direction perpendicular to the protruding direction of the electrode leads  70 ′ and  80 ′, and folded portions may be directed in opposite directions, that is, toward the electrode leads  70 ′ and  80 ′ as illustrated in  FIG. 2 , or folded portions may face each other as illustrated in  FIGS. 8A ,  8 B,  9 A and  9 B. 
     When the electrode leads  70 ′ and  80 ′ protrude in the same direction, bent surfaces may be formed in the direction perpendicular to the protruding direction of the electrode leads  70 ′ and  80 ′, and be recessed and bent in a direction away from the electrode leads  70 ′ and  80 ′ such that folded portions face the electrode leads  70 ′ and  80 ′ as illustrated in  FIGS. 10A ,  10 B,  11 A and  11 B, or bent surfaces may be recessed and bent toward the electrode leads  70 ′ and  80 ′ such that folded portions face the opposite side to that of the electrode leads  70 ′ and  80 ′. 
     For example, the foldable structure may be formed by heating and pressing a predetermined portion of the battery case with a heating jig having a shape corresponding to the foldable structure, but the present invention is not limited thereto. 
     The battery case may be constituted by a laminate sheet including a resin layer and a metal layer, and particularly, by an aluminum laminate sheet. 
     The laminate sheet includes an outer cover layer as a polymer film, a barrier layer as a metal film, and a polyolefin-based inner sealant layer. The outer cover layer has predetermined tensile strength and weatherability to efficiently resist the environment. To this end, an oriented nylon film or polyethylene terephthalate (PET) may be used to form the outer cover layer. 
     The barrier layer may be formed of aluminum to prevent introduction and discharge of a foreign substance such as gas and moisture, and reinforce the battery case. The inner sealant layer may be formed of a polyolefin based resin, which has heat welding property (heat adhesion) and low hygroscopicity to suppress introduction of electrolyte, and is resistant to expansion or corrosion due to electrolyte. More preferably, the inner sealant layer may be formed of cast polypropylene (cPP). 
     Insulating films  90 ′ are attached to a portion of the top and bottom surfaces of the electrode leads  70 ′ and  80 ′ to improve sealing property and electrical insulation between the portion and the lower and upper battery cases  20 ′ and  30 ′. 
     The sealing part of the battery case may further protrude outward than the foldable structures provided to the spacing edges  120  and  130 . 
     Accordingly, after the electrode assembly  40 ′ is accommodated in the space part  110 , sealing of the lower battery case  20 ′ and the upper battery case  30 ′ through heat welding is further facilitated. 
     Any method may be used to form the secondary battery  210 . For example, the secondary battery  210  may be formed by accommodating the electrode assembly  40 ′ in the battery case having the foldable structures through cutting, and then sealing the lower battery case  20 ′ and the upper battery case  30 ′ through heat welding. 
     Furthermore, the battery case may have a rectangular parallelepiped shape with an opening part that is opened in a predetermined protruding direction of an electrode lead. A bending area of the opening part may be provided to a dotted line shaped fractured portion that facilitates the formation of the foldable structure together with the sealing of the battery case after the electrode assembly  40 ′ is accommodated in the battery case. 
     Referring to  FIG. 7 , one or more fractured recesses  180  may be disposed in welding portions connecting the electrode leads  70 ′ and  80 ′ to the electrode tabs. 
     Accordingly, when pressure generated in the secondary battery  210  unfolds the foldable structures provided to the spacing edges  120  and  130 , to thereby apply the pulling force to the electrode leads  70 ′ and  80 ′, the welding portions can be more efficiently broken. 
     The positions and the number of the fractured recesses  180  are not limited. For example, the fractured recesses  180  may be disposed at both sides of the welding portion. A distance between the fractured recess  180  and the welding portion is not limited, provided that the fractured recess  180  is disposed in the electrode leads  70 ′ and  80 ′ and the electrode tabs in the battery case. 
     Also, the size and depth of the fractured recesses  180  are not limited, provided that the foldable structures of the battery case are unfolded in an emergency to more efficiently separate the electrode leads  70 ′ and  80 ′ from the electrode tabs, without negatively affecting service life and functions of the secondary battery  210 . 
       FIGS. 12A to 12F  are plan views and side views illustrating welding portions of electrode tabs and electrode leads, and a welding portion of an electrode tab and an electrode lead provided with fractured recesses  200 . 
     Referring to  FIG. 12A , the welding portion of the electrode tab and the electrode lead may be formed by coupling their overlapping ends through soldering or ultrasonic welding. Alternatively, referring to  FIG. 12C , ends of the electrode tab and the electrode lead may be bent, and then, the electrode tab and the electrode lead may be welded with bent surfaces contacting each other. 
     A pouch-type secondary battery according to the present invention may include any electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. For example, the electrode assembly may have a folding-type structure, a stack-type structure, a stack/folding-type structure, or stack/z-folding-type structure. 
     A secondary battery according to the present invention may be a lithium secondary battery, and particularly, be a so-called lithium ion polymer battery including an electrode assembly provided with electrolyte gel containing lithium. 
     A medium-to-large battery module according to the present invention includes the pouch-type secondary battery as a unit battery. 
       FIG. 13  is a perspective view illustrating a medium-to-large battery module including pouch-type secondary batteries with electrode leads protruding to both sides, according to an embodiment of the present invention.  FIG. 14  is a perspective view illustrating a medium-to-large battery module including pouch-type secondary batteries with electrode leads protruding to one side, according to an embodiment of the present invention. 
     The pouch-type secondary batteries of the medium-to-large battery module may include pouch-type battery cases having the same foldable structures or different foldable structures. 
     A medium-to-large battery pack according to the present invention includes the medium-to-large battery module. 
     Particularly, a secondary battery according to the present invention may be applied to a high power and capacity battery having long service life and excellent durability, a medium-to-large battery module including a plurality of unit batteries using the high power and capacity battery as the unit battery, or a medium-to-large battery pack including a plurality of unit batteries using the high power and capacity battery as the unit battery. 
     The medium-to-large battery pack may be used as a power source for power tools; electric vehicles including an electric vehicle (EV), a hybrid electric vehicle (REV), and a plug-in hybrid electric vehicle (PHEV); electric two-wheeled vehicles including an E-bike and an E-scooter; electric golf carts; electric trucks; and electric commercial vehicles. 
     Since the structure of the medium-to-large battery module or pack and a manufacturing method thereof are well known in the art, a description thereof will be omitted. 
     According to the embodiments of the present invention, when the pouch-type secondary battery is manufactured, an additional installing process or an additional installing space is unnecessary. In addition, since the pouch-type secondary battery fundamentally cuts off electric current when gas is generated therein, the service life and safety of the secondary battery can be significantly improved, and the manufacturing costs and the weight thereof can be reduced. Furthermore, the shape of the secondary battery can be easily modified. 
     Exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present disclosure as set forth in the following claims.