Patent Publication Number: US-11031580-B2

Title: Secondary battery with embossed safety vent

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a National Phase Patent Application of International Patent Application Number PCT/KR2017/007704, filed on Jul. 18, 2017, which claims priority of Korean Patent Application No. 10-2016-0119916, filed Sep. 20, 2016. The entire contents of both of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a secondary battery. 
     BACKGROUND ART 
     In general, unlike a primary battery that cannot be charged, a secondary battery can be charged and discharged. A low-capacity secondary battery packaged in the form of a pack comprised of one single cell is used as the power source for various portable small-sized electronic devices, such as smart phones, digital cameras, laptop computers, tablets, and so on. A high-capacity secondary battery in which several tens of cells are connected in a battery pack is used as the power source for motor drives, such as those in electric scooters, hybrid vehicles, or electric vehicles. 
     A secondary battery may be manufactured in various shapes, including, for example, a prismatic type, a cylindrical type and a pouch type. The secondary battery is generally constructed by accommodating an electrode assembly formed by interposing a separator between positive and negative electrode plates in a case together with an electrolytic solution and then installing a cap plate in the case. In some cases, a solid electrolyte as an ion conductor may be interposed between positive and negative electrode plates without an electrolytic solution. Of course, a positive electrode terminal and a negative electrode terminal are connected to the electrode assembly and are then exposed and protruded to the outside through the cap plate. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     Technical Problems to be Solved 
     Various embodiments of the present invention provide a secondary battery having an embossed safety vent, which is not damaged by an external force generated during a manufacturing process, can clearly define a rupture area or shape, and makes process management for rupture area or shape easy. 
     Technical Solutions 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by providing a secondary battery including a case, a cap plate which is installed in the case and has a vent hole, and a safety vent which is coupled to the vent hole of the cap plate and ruptures when the internal pressure of the case is greater than a reference pressure, wherein the safety vent includes an embossed portion, and a notch portion formed in the embossed portion. 
     The embossed portion may include a first embossed portion formed along the periphery of the embossed portion and protruding in a first direction, a second embossed portion formed in the first embossed portion and protruding in a second direction opposite to the first direction, and a third embossed portion formed in the second embossed portion and protruding in the first direction. 
     The notch portion may be formed in the third embossed portion. 
     The first embossed portion and the third embossed portion may have semicircular cross sections protruding in the first direction. 
     The third embossed portion may have a rectangular cross section protruding in the second direction. 
     The second embossed portion may be shaped to have multiple portions divided by the third embossed portion, and the divided second embossed portions may be all coplanar. 
     The third embossed portions may have +-shaped, X-shaped, or I-shaped planes. 
     The first embossed portion may have an elliptical plane. 
     The safety vent may include a sloping portion outwardly extending from the first embossed portion in the first direction, and a peripheral portion outwardly extending from the sloping portion and coupled to a peripheral portion of a vent hole of the cap plate. 
     Advantageous Effects 
     As described above, various embodiments of the present invention provides a secondary battery having an embossed safety vent, which is not damaged by an external force generated during a manufacturing process, can clearly define a rupture area or shape, and can facilitate process management for the rupture area or shape. 
     That is to say, according to various embodiments of the present invention, the safety vent includes a first embossed portion protruding in a downward direction, a second embossed portion protruding in an upward direction while inwardly extending to the first embossed portion, the second embossed portion specifically having a perfectly planar top surface, a third embossed portion protruding in a downward direction while inwardly extending to the second embossed portion, and a notch portion formed in the third embossed portion. Therefore, the safety vent, including the first, second and third embossed portions and the notch portion, may rarely undergo a spring back phenomenon, irrespective of the elongation of a metal. In particular, since the spring back phenomenon rarely occurs to the first, second and third embossed portions and the notch portion, safety vents produced in large quantities may have uniformly managed shapes and dimensions (heights). 
     Therefore, in the secondary batteries employing the above-described safety vent, rupture pressures may be all equally set, thereby improving safety and reliability. That is to say, according to various embodiments of the present invention, a rupture area or shape of the safety vent can be clearly defined, and the process management for the rupture area or shape can be facilitated. 
     In addition, since the notch portion is finally formed after forming the first, second and third embossed portions, it is possible to suppress the safety vent from being damaged during a manufacturing process. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a secondary battery according to various embodiments of the present invention. 
         FIG. 2  is a cross-sectional view taken along the line  2 - 2  of  FIG. 1 . 
         FIGS. 3A and 3B  are a front perspective view and a rear view illustrating an embossed safety vent and a cap plate with the same installed therein in the secondary battery according to various embodiments of the present invention. 
         FIGS. 4A and 4B  are cross-sectional views taken along lines  4   a - 4   b  of  FIG. 3  and  FIG. 4C  is a cross-sectional view illustrating another exemplary safety vent. 
         FIGS. 5A and 5B  are front perspective views and  FIG. 5C  is a rear perspective view illustrating a method of manufacturing an embossed safety vent in the secondary battery according to various embodiments of the present invention. 
         FIGS. 6A and 6B  are a front perspective view and a rear view illustrating an embossed safety vent and a cap plate with the same installed therein in the secondary battery according to various embodiments of the present invention. 
         FIGS. 7A and 7B  are a front perspective view and a rear view illustrating an embossed safety vent and a cap plate with the same installed therein in the secondary battery according to various embodiments of the present invention. 
         FIG. 8  is a cross-sectional view illustrating a general safety vent for a secondary battery. 
         FIGS. 9A and 9B  are an exploded perspective view and a cross-sectional view of another exemplary secondary battery with an embossed safety vent according to various embodiments of the present invention. 
         FIG. 10  is a perspective view of a battery module including secondary batteries according to various embodiments of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a preferred embodiment of the present invention will be described in detail. 
     Various embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to the example embodiments set forth herein. Rather, these example embodiments of the disclosure are provided so that this disclosure will be thorough and complete and will convey inventive concepts of the disclosure to those skilled in the art. 
     In the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” and/or “comprising,” when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various members, elements, regions, layers and/or sections, these members, elements, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one member, element, region, layer and/or section from another. Thus, for example, a first member, a first element, a first region, a first layer and/or a first section discussed below could be termed a second member, a second element, a second region, a second layer and/or a second section without departing from the teachings of the present disclosure. 
       FIG. 1  is a perspective view of a secondary battery according to various embodiments of the present invention, and  FIG. 2  is a cross-sectional view taken along the line  2 - 2  of  FIG. 1 . 
     As illustrated in  FIGS. 1 and 2 , the secondary battery  100  according to various embodiments of the present invention includes an electrode assembly  110 , a first terminal  120 , a second terminal  130 , a case  140  and a cap assembly  150 . 
     The electrode assembly  110  has a wound or laminated stacked structure including a first electrode plate  111 , a separator  113 , and a second electrode plate  112 , which are thin plates or layers. In this embodiment, the first electrode plate  111  may operate as a negative electrode and the second electrode plate  112  may operate as a positive electrode, or vice versa. 
     The first electrode plate  111  may include a first electrode collector formed of a metal foil made of, for example, copper, a copper alloy, nickel or a nickel alloy, and a first electrode active material, such as, graphite or carbon, on the first electrode collector. In addition, the first electrode plate  111  may include a first electrode uncoated portion  111   a  where the first electrode active material is not applied. The first electrode uncoated portion  111   a  may function as a passage for current flowing between the first electrode plate  111  and an exterior of the first electrode plate  111 . However, embodiments of the present invention are not limited to the material of the first electrode plate  111  listed herein. 
     The second electrode plate  112  may include a second electrode collector formed of a metal foil made of, for example, aluminum or an aluminum alloy, and a second electrode active material, such as, a transition metal oxide, on the second electrode collector. In addition, the second electrode plate  112  may include a second electrode uncoated portion  112   a  where the second electrode active material is not applied. The second electrode uncoated portion  112   a  may function as a passage for current flowing between the second electrode plate  112  and an exterior of the second electrode plate  112 . However, embodiments of the present invention are not limited to the material of the second electrode plate  112  listed herein. 
     In other embodiments, polarities of the first and second electrode plates  111  and  112  may differ from what is described above. 
     The separator  113  may be positioned between the first electrode plate  111  and the second electrode plate  112  to prevent electrical short circuits and to allow movement of lithium ions. The separator  113  may be made of, but not limited to, a material selected from the group consisting of polyethylene, polypropylene, a copolymer of polypropylene and polyethylene, and combinations thereof. In addition, the separator  113  may be replaced by an inorganic solid electrolyte not requiring a liquid- or gel-phase electrolytic solution, such as a sulfide-based, oxide-based or phosphate-based compound. 
     The first terminal  120  and the second terminal  130  electrically connected to the first electrode plate  111  and the second electrode plate  112 , respectively, are positioned at opposite ends of the electrode assembly  110 . For example, the electrode assembly  110  is accommodated in the case  140  with an electrolyte, but embodiments of the present invention are not limited thereto. The electrolytic solution may include an organic solvent, such as EC (ethylene carbonate), PC (propylene carbonate), DEC (diethyl carbonate), EMC (ethyl methyl carbonate), or DMC (dimethyl carbonate), and a lithium salt, such as LiPF 6 , or LiBF 4 . In addition, the electrolyte may be in a liquid, solid or gel phase. As described above, when an inorganic solid electrolyte is used, the electrolyte may not be employed. 
     The first terminal  120  is made of a metal and is electrically connected to the first electrode plate  111 . The first terminal  120  includes a first collector plate  121 , a first terminal pillar  122  and a first terminal plate  124 . 
     The first collector plate  121  is brought into contact with the first electrode uncoated portion  111   a  protruding to one end of the electrode assembly  110 . The first collector plate  121  is welded to the first electrode uncoated portion  111   a . The first collector plate  121  may have a roughly shape and has a terminal hole  121   a  formed at its top portion. The first terminal pillar  122  is fitted into the terminal hole  121   a  to then be riveted and/or welded. The first collector plate  121  is made of, for example, copper or a copper alloy, but embodiments of the present invention are not limited to the material of the first collector plate  121  to those listed herein. 
     The first terminal pillar  122  upwardly protrudes a predetermined length and extends while penetrating through a cap plate  151 , which will be described later, and is electrically connected to the first collector plate  121  under the cap plate  151 . In addition, while upwardly protruding a predetermined length and extending from the cap plate  151 , the first terminal pillar  122  has a flange  122   e  formed under the cap plate  151  to prevent the first terminal pillar  122  from being dislodged from the cap plate  151 . A region of the first terminal pillar  122  positioned under the flange  122   e  is fitted into the first terminal hole  121   a  of the first collector plate  121  to then be riveted and/or welded. Here, the first terminal pillar  122  is electrically insulated from the cap plate  151 . The first terminal pillar  122  may be made of, for example, copper, a copper alloy, aluminum or an aluminum alloy, but embodiments of the present invention are not limited to the material of the first collector terminal  122  listed herein. 
     The first terminal plate  124  has a hole  124   a , and the first terminal pillar  122  is coupled to the hole  124   a  to then be riveted and/or welded. For example, boundary regions of the upwardly exposed first terminal pillar  122  and the first terminal plate  124  are welded to each other, but embodiments of the present invention are not limited thereto. For example, laser beam is applied to the boundary regions of the upwardly exposed first terminal pillar  122  and the first terminal plate  124 , and the boundary regions are welded to each other to then be cooled, followed by welding. The welded regions are marked with reference numeral  25  in  FIG. 2 . 
     Meanwhile, a busbar (not shown) made of aluminum or an aluminum alloy may be welded to the first terminal plate  124 . 
     The second terminal  130  is also made of a metal and is electrically connected to the second electrode plate  112 . The second terminal  130  includes a second collector plate  131 , a second terminal pillar  132  and a second terminal plate  134 . 
     The second collector plate  131  is brought into contact with the second electrode uncoated portion  112   a  protruding to the other end of the electrode assembly  110 . The second collector plate  131  may have a roughly shape and has a terminal hole  131   a  formed at its top portion. The second terminal pillar  132  is fitted into the terminal hole  131   a  to then be coupled thereto. The second collector plate  131  is made of, for example, aluminum or an aluminum alloy, but embodiments of the present invention are not limited to the material of the second collector plate  131  to those listed herein. 
     The second terminal pillar  132  upwardly protrudes a predetermined length and extends while penetrating through the cap plate  151  to be described later, and is electrically connected to the second collector plate  131  under the cap plate  151 . In addition, while upwardly protruding a predetermined length and extending from the cap plate  151 , the second terminal pillar  132  has a flange  132   e  formed under the cap plate  151  to prevent the second terminal pillar  132  from being dislodged from the cap plate  151 . A region of the second terminal pillar  132  positioned under the flange  132   e  is fitted into the second terminal hole  131   a  of the second collector plate  131  to then be riveted and/or welded. Here, the second terminal pillar  132  is electrically insulated from the cap plate  151 . The second terminal pillar  132  may be made of, for example, aluminum or an aluminum alloy, but embodiments of the present invention are not limited to the material of the second terminal pillar  132  listed herein. 
     The second terminal plate  134  has a hole  134   a . In addition, the second terminal plate  134  is coupled to the second terminal pillar  132 . That is to say, the second terminal pillar  132  is coupled to the hole  134   a  of the second terminal plate  134 . In addition, the second terminal pillar  132  and the second terminal plate  134  are riveted and/or welded to each other. For example, boundary regions of the upwardly exposed second terminal pillar  132  and the second terminal plate  134  are welded to each other, but embodiments of the present invention are not limited thereto. For example, laser beam is applied to the boundary regions of the upwardly exposed second terminal pillar  132  and the second terminal plate  134 , and the boundary regions are welded to each other to then be cooled, followed by welding. 
     Additionally, a busbar (not shown) made of aluminum or an aluminum alloy is easily welded to the second terminal plate  134 . Here, the second terminal plate  134  may be electrically connected to the cap plate  151 . Therefore, the cap plate  151  and the case  140 , which will be described below, may have the same polarity with the second terminal  130  (e.g., a positive polarity). 
     Here, a winding axis of the electrode assembly  110  (that is, a horizontal axis extending in the left-right direction in  FIG. 2 ) is substantially perpendicular to or maintained at approximately 90 degrees with respect to a terminal axis of the first terminal pillar  122  of the first terminal  120  (a vertical axis extending in the top-down direction in  FIG. 2 ) and a terminal axis of the second terminal pillar  132  of the second terminal  130  (a vertical axis extending in the top-down direction in  FIG. 2 ). 
     The case  140  is made of, for example, a conductive metal, such as aluminum, an aluminum alloy or nickel plated steel, but embodiments of the present invention are not limited to the material of the case  140  listed herein. The case  140  may have an approximately hexahedral shape having an opening through which the electrode assembly  110 , the first terminal  120  and the second terminal  130  may be inserted and placed. In  FIG. 2 , the case  140  and the cap assembly  150  assembled to each other are illustrated. Thus, the opening, which is a substantially opened part of the peripheral edge of the cap plate  150 , is not illustrated in  FIG. 2 . Meanwhile, the interior surface of the case  140  is subjected to insulation treatment such that it maintains electrical isolation from the electrode assembly  110 , the first terminal  120 , the second terminal  130  and the cap assembly  150 . 
     The cap assembly  150  is coupled to the case  140 . In detail, the cap assembly  150  includes the cap plate  151 , a seal gasket  152 , a plug  153 , a safety vent  154 , an upper insulation member  155  and a lower insulation member  156 . 
     The cap plate  151  may seal the opening of the case  140  and may be made of the same material with the case  140 . For example, the cap plate  151  may be coupled to the case  140  by laser welding, but embodiments of the present invention are not limited thereto. Here, since the cap plate  151  may have the same polarity with the second terminal  130 , as described above, the cap plate  151  and the case  140  may also have the same polarity. 
     The seal gasket  152  is formed between each of the first terminal pillar  122  and the second terminal pillar  132  and the cap plate  151  using an insulating material, and seals gaps between each of the first terminal pillar  122  and the second terminal pillar  132  and the cap plate  151 . The seal gasket  152  may prevent external moisture from penetrating into the secondary battery  100  or may prevent internal electrolyte contained in the secondary battery  100  from flowing out. 
     The plug  153  hermetically seals an electrolyte injection hole  151   a  of the cap plate  151 , and the safety vent  154  is installed in a vent hole  151   b  of the cap plate  151  and has a notch portion ( 154   a  of  FIGS. 3B, 4A and 4B ) formed to be opened at a preset pressure. 
     The upper insulation member  155  is formed between each of the first terminal pillar  122  and the second terminal pillar  132  and the cap plate  151 . In addition, the upper insulation member  155  is brought into close contact with the cap plate  151 . Further, the upper insulation member  155  may also be brought into close contact with the seal gasket  152 . The upper insulation member  155  insulates the first terminal pillar  122  and the second terminal pillar  132  from the cap plate  151 . 
     The lower insulation member  156  is formed between each of the first collector plate  121  and the second collector plate  131  and the cap plate  151  and prevents unnecessary electrical short circuits from occurring therebetween. That is to say, the lower insulation member  156  prevents electrical short circuits from occurring between the first collector plate  121  and the cap plate  151  and between the second collector plate  131  and the cap plate  151 . 
       FIGS. 3A and 3B  are a front perspective view and a rear view illustrating an embossed safety vent  154  and a cap plate  151  with the same installed therein in the secondary battery  100  according to various embodiments of the present invention, and  FIGS. 4A and 4B  are cross-sectional views taken along lines  4   a - 4   b  of  FIG. 3  and  FIG. 4C  is a cross-sectional view illustrating another exemplary safety vent  154 D. 
     As illustrated in  FIGS. 3A and 3B  and  FIGS. 4A and 4B , the safety vent  154  is coupled to an inner wall of the inclined vent hole  151   b  of the cap plate  151 . When the internal pressure of the case  140  is greater than a reference pressure, the safety vent  154  ruptures to allow the internal gas of the case  140  to be rapidly released to the outside, thereby avoiding a dangerous situation of the secondary battery  100 . 
     To this end, the safety vent  154  includes a peripheral portion  154   a  coupled to the inner wall or stepped portion of the vent hole  151   b , a sloping portion  154   b  extending from the peripheral portion  154   a , an embossed portion  154 G planarly extending from the sloping portion  154   b  in a substantially horizontal direction, and a notch portion  154   f  formed in the embossed portion  154 G. 
     The peripheral portion  154   a  may be welded to the inner wall or stepped portion of the vent hole  151   b  by, for example, laser welding, but embodiments of the present invention are not limited thereto. To perform welding, the peripheral portion  154   a  may have a thickness greater than that of the sloping portion  154   b  or the embossed portion  154 G. 
     The sloping portion  154   b  may extend from the peripheral portion  154   a  to be inclined in an inwardly downward direction (for example, in a first direction), but embodiments of the present invention are not limited thereto. Here, the sloping portion  154   b  may be brought into close contact with and fixed to, for example, the inclined inner wall of the vent hole  151   b , but embodiments of the present invention are not limited thereto. Therefore, when the secondary battery  100  is in a normal state, it is possible to prevent the internal electrolyte from leaking out along the interfacial surface between the safety vent  154  and the vent hole  151   b.    
     The embossed portion  154 G extends from the sloping portion  154   b  and is formed to be substantially planar in a horizontal direction. That is to say, the embossed portion  154 G may include a first embossed portion  154   c  protruding in a downward direction (for example, in the first direction), a second embossed portion  154   d  protruding in an upward direction (for example, in a second direction), and a third embossed portion  154   e  protruding in the downward direction. 
     The first embossed portion  154   c  is connected to the sloping portion  154   b  and has, for example, a substantially semicircular cross section protruding in the downward direction, but embodiments of the present invention are not limited thereto. In addition, the second embossed portion  154   d  is connected to the first embossed portion  154   c  and has, for example, a substantially rectangular cross section protruding in an upward direction, but embodiments of the present invention are not limited thereto. Here, a top surface of the second embossed portion  154   d  may be substantially or perfectly planar. The third embossed portion  154   e  is connected to the second embossed portion  154   d  and has, for example, a substantially semicircular section protruding in the downward direction, but embodiments of the present invention are not limited thereto. 
     Here, the first embossed portion  154   c  has, for example, a substantially a rectangular or elliptical plane. That is to say, the first embossed portion  154   c  is in the shape of a rectangle having four rounded corners in a planar view. In addition, the second embossed portion  154   d  is in the shape of, for example, a plane having multiple portions divided by the third embossed portion  154   e  in a planar view, but embodiments of the present invention are not limited thereto. That is to say, the third embossed portion  154   e  has, for example, a substantially +-shaped plane, but embodiments of the present invention are not limited thereto. Of course, ends of the third embossed portion  154   e  may be connected to the first embossed portion  154   c.    
     As illustrated in  FIGS. 3A and 3B , the second embossed portion  154   d  may also have a plane having four portions divided by the +-shaped third embossed portion  154   e  in a planar view. Of course, top surfaces of the four divided portions of the second embossed portion  154   d  are all coplanar, and bottom surfaces thereof are also coplanar. That is to say, according to embodiments of the present invention, as illustrated in  FIG. 4A , heights of the four divided portions of the second embossed portion  154   d , as denoted by “X” values, are all equal to one another. In addition, the X values for various types of the safety vent  154  may be equally managed without a deviation. That is to say, during formation of the first embossed portion  154   c , the second embossed portion  154   d  and the third embossed portion  154   e , a spring back phenomenon can be minimized, irrespective of the elongation of a metal used in forming the safety vent  154 , and the X values can be uniformly managed to equal values without a deviation in the X values depending on the type of the safety vent  154  manufactured. 
     Therefore, according to various embodiments of the present invention, the rupture area or shape of the safety vent  154  can be clearly defined, and a process management for the rupture area or shape can be facilitated. 
     Meanwhile, in order to reduce a dead volume of the case  140 , bottom ends of the first embossed portion  154   c  and the third embossed portion  154   e  of the safety vent  154  are preferably positioned lower than a bottom surface of the cap plate  151 . In addition, in order to make pressures converge on the vent hole  151   b , a top end of the second embossed portion  154   d  is preferably positioned inside the vent hole  151   b , that is, above the bottom surface of the cap plate  151 . 
     In addition, a thickness of the embossed portion  154 G, that is, the overall thickness of the first, second and third embossed portions  154   c ,  154   d  and  154   e , may vary according to characteristics of the secondary battery  100 , but may be generally in the range of approximately 0.2 mm to approximately 2 mm. Accordingly, the notch portion  154   f  may have a thickness in the range of, for example, approximately 0.01 mm to approximately 1 mm, but embodiments of the present invention are not limited to the thickness of the notch portion  154   f  disclosed herein. As described above, such dimension values may change in various manners according to design characteristics of a secondary battery. 
     The notch portion  154   f  may be formed along the third embossed portion  154   e . That is to say, the notch portion  154   f  may have, for example, a substantially +-shaped plane, which is the same with or substantially the same with the third embossed portion  154   e , but embodiments of the present invention are not limited thereto. The notch portion  154   f  may be formed along the center of the bottom surface of the third embossed portion  154   e . In some cases, however, notch portion  154   f  may be formed along the center of the top surface of the third embossed portion  154   e . As described above, since the third embossed portion  154   e  and the notch portion  154   f  are formed in substantially +-shaped configurations, the safety vent  154  may rupture in a substantially +-shaped configuration when the internal pressure of the case  140  is greater than the reference pressure. 
     In addition, as illustrated in  FIG. 4C , in the safety vent  154   d  according to another embodiment of the present invention, only a sloping portion  154   b  can be directly welded to an inner wall of the vent hole  151   b  of the cap plate  151  without a relatively thick peripheral portion  154   a . Since the peripheral portion  154   a  having a stepped portion is not provided in the safety vent  154   d , the vent hole  151   b  formed on the cap plate  151  with an inclination can be easily processed and the safety vent  154  can also be easily processed. Of course, the welding is performed along the interfacial surface formed between the top end of the sloping portion  154   b  and the inner wall of the vent hole  151   b.    
       FIGS. 5A and 5B  are front perspective views and  FIG. 5C  is a rear perspective view illustrating a method of manufacturing an embossed safety vent in the secondary battery  100  according to various embodiments of the present invention. 
     As illustrated in  FIG. 5A , a planar metal plate may be subjected to a first forging process, for example, to be processed to turn into a first preliminary safety vent  154 A, including a substantially planar peripheral portion  154   a , a sloping portion  154   b  extending from the peripheral portion  154   a  to be inclined in an inwardly downward direction, and a planar portion  154   c ′ planarly extending from the sloping portion  154   b  in a substantially horizontal direction, but embodiments of the present invention are not limited thereto. Here, the sloping portion  154   b  and the planar portion  154   c ′ may be formed more thinly than the peripheral portion  154   a . Of course, the peripheral portion  154   a  may not be provided in some cases. 
     Here, the first forging process may include, for example, providing a lower mold having an opening and an upper mold having a punch to be coupled to the opening, placing a planar metal plate between the lower mold and the upper mold, and coupling the punch of the upper mold to the opening of the lower mold to allow the planar metal plate placed between the lower mold and the upper mold to be processed to turn into the first preliminary safety vent  154 A including the peripheral portion  154   a , the sloping portion  154   b  and the planar portion  154   c ′, but embodiments of the present invention are not limited thereto. 
     Meanwhile, the planar metal plate may be, for example, one selected from the group consisting of general aluminum, an aluminum alloy and an equivalent thereof, but embodiments of the present invention are not limited thereto. 
     As illustrated in  FIG. 5B , the planar portion  154   c ′ of the first preliminary safety vent  154 A may be processed to turn into a first embossed portion  154   c , a second embossed portion  154   d  and a third embossed portion  154   e  by, for example, a second forging process, but embodiments of the present invention are not limited thereto. Here, the second embossed portion  154   d  and the third embossed portion  154   e  may be formed after forming the first embossed portion  154   c , the first embossed portion  154   c  may be formed after forming the second embossed portion  154   d  and the third embossed portion  154   e , or the first embossed portion  154   c , the second embossed portion  154   d  and the third embossed portion  154   e  may be formed at the same time. Practically, the second embossed portion  154   d  may be a portion that is naturally formed or defined as the result of forming the first embossed portion  154   c  and the third embossed portion  154   e.    
     Here, the first embossed portion  154   c  may be formed to have, for example, a substantially semicircular cross section protruding in a downward direction (i.e., in a first direction), but embodiments of the present invention are not limited thereto. In addition, the first embossed portion  154   c  may be formed to have, for example, a substantially elliptical plane, but embodiments of the present invention are not limited thereto. Practically, the first embossed portion  154   c  may be formed along boundary surfaces between the planar portion  154   c ′ and the sloping portion  154   b.    
     In addition, the second embossed portion  154   d  may be formed to have, for example, a rectangular cross section protruding in an upward direction (i.e., in a second direction), that is, a top surface of the second embossed portion  154   d  may be perfectly planar, but embodiments of the present invention are not limited thereto. In addition, the second embossed portion  154   d  may be formed to have, for example, a substantially rectangular plane having a rounded portion at its one side, but embodiments of the present invention are not limited thereto. 
     The third embossed portion  154   e  may be formed to have, for example, a substantially semicircular cross section protruding in the downward direction and a substantially +-shaped plane. Here, an end of the third embossed portion  154   e  may be connected to the first embossed portion  154   c . In addition, the second embossed portion  154   d  is practically divided by the third embossed portion  154   e , yielding multiple second embossed portions  154   d . Here, all of the divided second embossed portions  154   d  may have the same area. 
     Of course, even after the dividing, all of top surfaces of the divided second embossed portions  154   d  may still have the same height or may still be coplanar. That is to say, heights ranging from an imaginary line connecting bottom ends of the first embossed portion  154   c  and the second embossed portions  154   d  to planar bottom surfaces or planar top surfaces of the multiple second embossed portions  154   d  are all the same with one another, which means that the X values are equal to one another, as described above. 
     Moreover, these constructional characteristics commonly apply to all types of the safety vents  154  manufactured according to embodiments of the present invention. In other words, the above-described first and second forging processes bring about minimized spring back phenomena, irrespective of the intrinsic elongation of a metal, which is because the above-described constructional characteristics commonly apply to all of the manufactured safety vents  154 . 
     Here, the second forging process may include, for example, providing a lower mold having a trench and an upper mold having a protrusion to be coupled to the trench, placing the first preliminary safety vent  154 A between the lower mold and the upper mold, and coupling the protrusion of the upper mold to the trench of the lower mold to allow the planar portion  154   c ′ of the first preliminary safety vent  154 A placed between the lower mold and the upper mold to be processed to turn into a second preliminary safety vent  154 B, including the first embossed portion  154   c , the second embossed portion  154   d  and the third embossed portion  154   e , but embodiments of the present invention are not limited thereto. 
     Here, planar shapes of the trench of the lower mold and the protrusion of the upper mold may substantially correspond to those of the first embossed portion  154   c  and the third embossed portion  154   e.    
     As illustrated in  FIG. 5C , a notch portion  154   f  may be formed along the third embossed portion  154   e . The notch portion  154   f  may be formed along, for example, a bottom end of the third embossed portion  154   e , but embodiments of the present invention are not limited thereto. Here, since the third embossed portion  154   e  is formed in a substantially +-shaped configuration, the notch portion  154   f  is also formed in a substantially +-shaped configuration. In addition, the notch portion  154   f  may be shorter than the third embossed portion  154   e  or may be longer than the third embossed portion  154   e . That is to say, in some cases, the notch portion  154   f  may be formed to have a predetermined length along the bottom end of the first embossed portion  154   c  as well as the bottom end of the third embossed portion  154   e . Moreover, in some cases, the notch portion  154   f  may be formed in the first embossed portion  154   c  only, instead of the third embossed portion  154   e.    
     In addition, although the notch portion  154   f  formed along the bottom surface of the third embossed portion  154   e  is illustrated in  FIG. 5C , it may also be formed along a top surface of the third embossed portion  154   e . Of course, the notch portion  154   f  may be formed along the top surfaces of the third embossed portion  154   e  and the first embossed portion  154   c  or along the top surface of the first embossed portion  154   c.    
     In addition, the notch portion  154   f  is configured to rupture when the internal pressure of the case  140  is greater than a reference pressure, thereby rapidly making the internal pressure of the case  140  equalized to atmospheric pressure. Therefore, the notch portion  154   f  is formed to have a smaller thickness (to be more thinly) than the third embossed portion  154   e . Of course, in a case where the notch portion  154   f  is formed in the first embossed portion  154   c , the notch portion  154   f  is formed to have a smaller thickness than the first embossed portion  154   c.    
     In such a way, according to various embodiments of the present invention, since the notch portion  154   f  is formed at a final stage, it is possible to provide the secondary battery  100  including the embossed safety vent  154 , which is unlikely damaged during a manufacturing process, can clearly define a rupture area or shape, and can facilitate process management for the rupture area or shape. 
     Meanwhile, the notch portion  154   f  can be formed in various manners. For example, the notch portion  154   f  can be formed using laser beam or an etching process. In addition, the notch portion  154   f  may also be formed using a mold. For example, in a state in which the top surface of the third embossed portion  154   e  is coupled to an upper mold having a semicircular protrusion formed therein, the bottom surface of the third embossed portion  154   e  is pressed by a lower mold having a substantially +-shaped protrusion, thereby forming the notch portion  154   f . Moreover, the notch portion  154   f  may also be formed together during formation of the first, second third embossed portions  154   c ,  154   d.    
       FIGS. 6A and 6B  are a front perspective view and a rear view illustrating an embossed safety vent  254  and a cap plate  151  with the same installed therein in the secondary battery  100  according to various embodiments of the present invention. 
     As illustrated in  FIGS. 6A and 6B , the safety vent  254  according to the embodiment of the present invention may include a third embossed portion  254   e  having, for example, a substantially X-shaped plane, but embodiments of the present invention are not limited thereto. Accordingly, a notch portion  254   f  may also be formed to have, for example, a substantially X-shaped plane, but embodiments of the present invention are not limited thereto. In addition, the notch portion  254   f  may be formed not only in the third embossed portion  254   e  but also in a portion of a first embossed portion  154   c . Moreover, with this configuration of the X-shaped third embossed portion  254   e , the safety vent  254  may include second embossed portions  254   d  having different areas. That is to say, the areas of two of the second embossed portions  254   d  divided by the third embossed portion  254   e  may be greater than those of the other two second embossed portions  254   d . As described above, since the third embossed portion  254   e  and the notch portion  254   f  are formed in substantially X-shaped configuration in a planar view, the safety vent  254  may rupture in a substantially X-shaped configuration when the internal pressure of the case  140  is greater than a reference pressure. 
       FIGS. 7A and 7B  are a front perspective view and a rear view illustrating an embossed safety vent  354  and a cap plate  151  with the same installed therein in the secondary battery  100  according to various embodiments of the present invention. 
     As illustrated in  FIGS. 7A and 7B , the safety vent  354  according to the embodiment of the present invention may include a third embossed portion  354   e  having, for example, a substantially I-shaped plane, but embodiments of the present invention are not limited thereto. Accordingly, a notch portion  354   f  may also be formed to have, for example, a substantially I-shaped plane, but embodiments of the present invention are not limited thereto. In addition, the notch portion  354   f  may be formed not only in the third embossed portion  354   e  but also in a portion of a first embossed portion  154   c . Moreover, with this configuration of the I-shaped third embossed portion  354   e , the safety vent  354  may include second embossed portions  354   d  having the same area. That is to say, the areas of two of the second embossed portions  354   d  divided by the third embossed portion  354   e  may be equal to each other. As described above, since the third embossed portion  354   e  and the notch portion  354   f  are formed in substantially I-shaped configuration in a planar view, the safety vent  354  may rupture in a substantially I-shaped configuration when the internal pressure of the case  140  is greater than a reference pressure. 
       FIG. 8  is a cross-sectional view illustrating a general safety vent  10  for a secondary battery. 
     As illustrated in  FIG. 8 , the general safety vent  10  may include a relatively thick peripheral portion  11 , a relatively thin planar portion  12  inwardly extending from the peripheral portion  11  in a substantially horizontal direction, and a notch portion  13  formed roughly at the center of the planar portion  12 . 
     Here, the planar portion  12  is subjected to a forging process to be formed in a substantially gull-winged configuration in a sectional view. As illustrated in  FIG. 8 , the planar portion  12  may have irregular X values due to elongation of a metal used in forming the safety vent  10  or a spring back phenomenon. Particularly, since the respective X values of various safety vents  10  are different, the safety vents  10  may rupture (operate) at different points in time in various secondary batteries employing the same, thereby lowering the battery safety or reliability. The term X value used herein may be defined as a distance between bottommost and topmost ends of the planar portion  12  where the notch portion  13  is formed. 
     According to the present invention, however, as described above, the first embossed portion  154   c , the second embossed portion  154   d  and the third embossed portion  154   e  are willfully formed in the safety vent  154 , the second embossed portion  154   d  is formed to be perfectly planar as a whole, and the notch portion  154   f  is formed along the third embossed portion  154   e  and/or the first embossed portion  154   c , thereby minimizing a spring back phenomenon, irrespective of the elongation of the metal forming the safety vent  154 , and ultimately eliminating a deviation in the X value. Therefore, in the secondary battery  100  employing the safety vent  154  according to the embodiments of the present invention, the safety vent  154  may operate at an equal point in rupturing time, thereby improving the safety and reliability of the secondary battery  100 . 
       FIGS. 9A and 9B  are an exploded perspective view and a cross-sectional view of another exemplary secondary battery with an embossed safety vent according to various embodiments of the present invention.  FIG. 10  is a perspective view of a battery module including secondary batteries according to various embodiments of the present invention. 
     The secondary battery  200  according to various embodiments of the present invention is different from the secondary battery  100  according to the previous embodiment in view of a configuration of an electrode assembly  210  and a connection relationship between the electrode assembly  210  and first and second terminals  120  and  130 . 
     As illustrated in  FIGS. 9A and 9B , a winding axis of the electrode assembly  210  is substantially parallel to or substantially horizontal with a terminal axis of a first terminal pillar  122  of the first terminal  120  and a terminal axis of a second terminal pillar  132  of the second terminal  130 . Here, the winding axis and the terminal axes may mean axes extending in the top-down direction in  FIGS. 9A and 9B , and it is meant that when a winding axis and a terminal axis are referred to as being substantially parallel to or substantially horizontal with each other, they may not meet each other even by being lengthened or may meet each other by being lengthened extremely long. 
     In addition, a first electrode tab  211   a  is interposed between the electrode assembly  210  and the first terminal pillar  122  of the first terminal  120 , and a second electrode tab  212   a  is interposed between the electrode assembly  210  and the second terminal pillar  132  of the second terminal  130 . That is to say, the first electrode tab  211   a  extends from a top end of the electrode assembly  210  to a bottom end of the first terminal pillar  122  of the first terminal  120  to then be electrically connected to or welded to a planar flange  122   e  provided in the first terminal pillar  122 . In addition, the second electrode tab  212   a  extends from the top end of the electrode assembly  210  to a bottom end of the second terminal pillar  132  of the second terminal  130  to then be electrically connected to or welded to a planar flange  132   e  provided in the second terminal pillar  132   
     Practically, the first electrode tab  211   a  may be a first uncoated portion itself, which is not coated on a first electrode plate  211  of the electrode assembly  210  with a first active material  211   b , or a separate member connected to the first uncoated portion. Here, the first uncoated portion may be made of the same material with the first electrode plate  211 , and the separate member may be made of one selected from the group consisting of nickel, a nickel alloy, copper, a copper alloy, aluminum, an aluminum alloy and equivalents thereof. 
     In addition, the second electrode tab  212   a  may be practically a second uncoated portion itself, which is not coated on a second electrode plate  212  of the electrode assembly  210  with a first active material  212   b , or a separate member connected to the second uncoated portion. Here, the second uncoated portion may be made of the same material with the second electrode plate  212 , and the separate member may be made of one selected from the group consisting of aluminum, an aluminum alloy, nickel, a nickel alloy, copper, a copper alloy, and equivalents thereof. 
     As described above, since the winding axis of the electrode assembly and the terminal axes of the terminals are configured to be substantially parallel to or substantially horizontal with each other, the electrode assembly demonstrate excellent wettability with respect to an electrolyte during injection of the electrolyte and the safety vent rapidly operates owing to rapid movement of internal gases in an event of overcharging. 
     In addition, since an electrode tab (an uncoated portion itself or a separate member) of the electrode assembly is directly electrically connected to the terminal to shorten an electrical path, internal resistance of the secondary battery can be reduced and the number of components can be reduced. 
       FIG. 10  is a perspective view of a battery module including secondary batteries according to various embodiments of the present invention. 
     As illustrated in  FIG. 10 , a plurality of secondary batteries  100  are arranged in a line and a plurality of busbars  220  are coupled to the arranged secondary batteries  100 , thereby completing a battery module  1000 . For example, a first terminal  120  of one of the secondary batteries  100  is welded to a second terminal  130  of another adjacent secondary battery  100  by a busbar  220 , thereby providing the battery module  1000  having the plurality of secondary batteries  100  connected to one another in series. 
     Here, since the busbars  220  are made of aluminum or an aluminum alloy, and the first terminal plate  124  of the first terminal  120  and the second terminal plate  134  of the second terminal  130  are also made of aluminum or an aluminum alloy, the busbars  220  can be easily welded to the first terminal  120  and the second terminal  130 . 
     Although the foregoing embodiments have been described to practice the secondary battery of the present invention, these embodiments are set forth for illustrative purposes and do not serve to limit the invention. Those skilled in the art will readily appreciate that many modifications and variations can be made, without departing from the spirit and scope of the invention as defined in the appended claims, and such modifications and variations are encompassed within the scope and spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     Various embodiments of the present invention relate to a secondary battery.