Patent Publication Number: US-11387508-B2

Title: Secondary battery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0080772, filed on Jul. 4, 2019 in the Korean Intellectual Property Office, the entire content of which is herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present invention relate to a secondary battery. 
     2. Description of the Related Art 
     A battery may be classified as a prismatic type, a cylindrical type, a pouch type, etc., according to the shape of a case. A prismatic or cylindrical battery may be manufactured by inserting an electrode assembly having a positive electrode, a negative electrode, and a separator into a metal can and sealing the electrode assembly, while a pouch type battery may be manufactured by enclosing an electrode assembly using an aluminum foil coated with an insulator. 
     Traditional battery can manufacturing methods may include a deep drawing process, an impact process, and so on. In an example, the deep drawing process is performed such that a sheet-shaped metal plate is placed on a molding die and punching operations are performed on the metal plate about ten times using a punch, thereby completing the can. In another example, the impact process is performed such that a slug in the form of a billet is placed on a molding die and a strong punching operation is performed on the slug about one time using a punch, thereby completing the can. The impact process can reduce the number of processing steps, thereby lowering the manufacturing cost. 
     However, the conventional deep drawing process and the conventional impact process are both limited in reducing a can thickness due to the respective manufacturing process characteristics and have a large deviation in the thickness of the can according to the area of the can. In addition, the conventional deep drawing process and the conventional impact process are problematic in that the manufacturing cost of the battery can is quite high. 
     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. 
     SUMMARY 
     According to an aspect of embodiments of the present invention, a secondary battery has a bending type can, or case, which may have no thickness deviation in various areas of the can by reducing the thickness of the can and increasing dimensional accuracy, and which has improved safety by providing curved portions at corners where three or four sides meet. 
     According to another aspect of embodiments of the present invention, a secondary battery has a bending type can, which includes desirably shaped curved portions by providing curvatures at corners where three or four sides meet, the curvatures overlapping with each other when the corners are bent, thereby preventing or substantially preventing pinholes from being generated during welding. 
     According to one or more embodiments of the present invention, a secondary battery includes: an electrode assembly; a case accommodating the electrode assembly, and a cap assembly coupled to the case to seal the case, wherein the case includes a bottom portion, long side portions bent and extended from the bottom portion, a first short side portion bent and extended from the bottom portion, and second short side portions bent and extended from the long side portions, the first short side portion and the second short side portions connected to each other to define a short side portion, and curvatures located between the first short side portion and the second short side portions. 
     The curvatures may be located at regions where the first short side portion and the second short side portions meet. 
     The curvatures may include a first curvature located in the first short side portion, and a second curvature located in each of the second short side portions. 
     The first curvature and the second curvature may overlap with each other. 
     The first curvature and the second curvature may be in an asymmetric configuration. 
     The first curvature may be larger than the second curvature. 
     The second curvature may be larger than the first curvature. 
     The first curvature may have a larger curvature radius than the second curvature. 
     The second curvature may have a larger curvature radius than the first curvature. 
     The secondary battery may further include curved portions located at regions where the bottom portion, the long side portions, and the short side portion including the first short side portion having the first curvature, and the second short side portion having the second curvature, meet. 
     The short side portion may further include welding portions, and the welding portions may include a first welding portion located between each of the curved portions and each of the first short side portion and the second short side portions, and a second welding portion located between the second short side portions. 
     The curvatures may be located at centers of regions where the first short side portion and the second short side portions meet. 
     The curvatures may be connected longer to the first short side portion than to the second short side portions, or the curvatures may be connected longer to the second short side portions than to the first short side portion. 
     The first short side portion may extend from both end portions of the bottom portion, the second short side portions may extend from both ends of the long side portions, and the short side portion may be defined on both sides of the bottom portion and the long side portions. 
     As described above, according to one or more embodiments of the present invention, a secondary battery having a bending type can is provided, which may have no thickness deviation in various areas of the can by reducing the thickness of the can and increasing dimensional accuracy, and which may improve safety by providing curved portions at corners where three or four sides meet. In some examples, asymmetrical curvatures are provided at vertexes (corners) where the first short side portion bent from the bottom portion and the second short portions bent from the long side portions meet, such that the asymmetrical curvatures overlap with each other when they are bent, thereby providing desirably shaped, symmetrical curved portions at the corners where the bottom portion, the long side portions, the first short side portion, and the second short side portions meet. 
     In addition, according to one or more embodiments of the present invention, a secondary battery having a bending type can is provided, which includes desirably shaped curved portions by providing curvatures at corners where three or four sides meet, the curvatures overlapping with each other when the corners are bent, thereby preventing or substantially preventing pinholes from being generated during welding. In some examples, according to the present invention, desirably shaped, symmetrical curved portions are provided by the asymmetrical curvatures overlapping with each other, and boundary regions between the first and second short side portions are spaced by a distance (e.g., a predetermined distance) apart from the curved portions, thereby easily performing welding without pinholes generated at the curved portions and the boundary regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an example secondary battery according to an embodiment of the present invention. 
         FIGS. 2A and 2B  are cross-sectional views illustrating example secondary batteries according to embodiments of the present invention. 
         FIGS. 3A and 3B  are perspective views illustrating an example method for manufacturing an example secondary battery according to an embodiment of the present invention. 
         FIGS. 4A to 4D  are partially enlarged plan views illustrating an example method for manufacturing an example secondary battery according to an embodiment of the present invention. 
         FIGS. 5A and 5B  are partially enlarged plan views illustrating an example method for manufacturing an example secondary battery. 
         FIGS. 6A to 6C  are perspective views illustrating an example method for manufacturing an example secondary battery according to an embodiment of the present invention. 
         FIGS. 7A and 7B  are partially enlarged plan views illustrating a method for manufacturing a secondary battery according to an example embodiment. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 100, 200: 
                 Secondary battery 
               
               
                 110:  
                 Electrode assembly 
               
               
                 120: 
                 First terminal 
               
               
                 130: 
                 Second terminal 
               
               
                 140: 
                 Can 
               
               
                 140A: 
                 Metal plate 
               
               
                 141: 
                 Bottom portion 
               
               
                 142, 143: 
                 Long side portion 
               
               
                 144, 145: 
                 Short side portion 
               
               
                 146: 
                 Welding portion 
               
               
                 147: 
                 Opening 
               
               
                 1440A, 1440B:  
                 Curvature 
               
               
                 1441:  
                 First curvature 
               
               
                 1442: 
                 Second curvature 
               
               
                 1550A, 1550B: 
                 Curved portion 
               
               
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION 
     Herein, some example embodiments of the present invention will be described in further 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 addition, in the accompanying drawings, sizes or thicknesses of various components may be exaggerated for brevity and clarity. Like numbers refer to like elements throughout. In addition, it is to be understood that when an element A is referred to as being “connected to” an element B, the element A may be directly connected to the element B or one or more intervening elements C may be present and the element A and the element B may be indirectly connected to each other. 
     The terminology used herein is for the purpose of describing particular embodiments 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 is to be further understood that the terms “comprise or include” and/or “comprising or including,” 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 is to 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 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. 
     Spatially relative terms, such as “below,” “beneath,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It is to be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “on” or “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. 
     The term “welding portion” used throughout this specification can be referred to as a temporary welding portion and/or a welding portion in some cases, which is for representing the welding sequence and function but is not intended to limit the invention. In addition, the term “welding” as used herein mainly means laser welding, and examples of a laser used for welding may include, but are not limited to, CO2 laser, fiber laser, disk laser, semiconductor laser, and/or yttrium aluminum garnet (YAG) laser. In addition, the terms “second short side portion” and “third short side portion” can be referred to as second short side portions, in some cases. 
     Unless otherwise defined, all terms used herein (including technical or scientific terms) have the same meanings as those generally understood by those skilled in the art to which the inventive concept pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having idealized or excessively formal meanings unless clearly defined herein. 
       FIG. 1  is a perspective view illustrating an example secondary battery according to an embodiment of the present invention. In the example shown in  FIG. 1 , a secondary battery  100  may include an electrode assembly  110  ( 110  and  210  in the examples shown in  FIGS. 2A and 2B ), a first terminal  120 , a second terminal  130 , a can, or case,  140 , and a cap assembly  150 . 
     In some examples, the can  140  may be provided by blanking and/or notching, bending, and welding a metal plate and may have a substantially hexahedral shape having an opening through which the electrode assembly  110  is inserted and placed and the cap assembly  150  is mounted. In some examples, the can  140  may include a rectangular bottom portion  141  having long sides and short sides, long side portions  142  and  143  bent and extended from the respective long sides of the bottom portion  141  to the cap assembly  150 , and short side portions  144  and  145  extended from the respective short sides of the bottom portion  141  and the long side portions  142  and  143 . 
     In  FIG. 1 , the can  140  and the cap assembly  150  assembled to each other are illustrated, such that the opening, which is a substantially opened part of a region corresponding to the cap assembly  150 , is not illustrated in  FIG. 1 . In an embodiment, the interior surface and/or the exterior surface of the can  140  may be subjected to insulation treatment such that the can  140  is insulated from the electrode assembly, the first terminal  120 , the second terminal  130 , and the cap assembly  150 . 
       FIGS. 2A and 2B  are cross-sectional views illustrating example secondary batteries  100  and  200 . In the example shown in  FIG. 2A , the secondary battery  100  may include an electrode assembly  110  having a winding axis extending in a horizontal direction (i.e., in a direction substantially parallel with a lengthwise direction of the cap assembly  150 ). In the example shown in  FIG. 2B , the secondary battery  200  may include an electrode assembly  210  having a winding axis extending in a vertical direction (i.e., in a direction substantially perpendicular to the lengthwise direction of the cap assembly  150 ). In some examples, the electrode assembly may be a stacked electrode assembly, rather than a wound electrode assembly. 
     The secondary battery  100  shown in  FIG. 2A  will now be described. The electrode assembly  110  may be formed by winding or stacking a stacked structure including a first electrode plate  111 , a separator  113 , and a second electrode plate  112 , which are thin plates or layers. In some examples, 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. In some examples, the first electrode plate  111  may be formed by coating a first active material, such as graphite or carbon, on a first electrode collector made of a metal foil, such as copper, a copper alloy, nickel, or a nickel alloy, and may include a first uncoated portion  111   a  that is not coated with the first active material. In some examples, the second electrode plate  112  may be formed by coating a second active material, such as a transition metal oxide, on a second electrode collector made of a metal foil, such as aluminum or an aluminum alloy, and may include a second uncoated portion  112   a  that is not coated with the second electrode material. In some examples, the separator  113 , which is located between the first and second electrode plates  111  and  112 , may prevent or substantially prevent short circuits between the first and second electrode plates  111  and  112 , and may allow lithium ions to move. In an embodiment, the separator  113  may include polyethylene, polypropylene, or a composite film of polyethylene and polypropylene. In an embodiment, the separator  113  may be replaced by an inorganic solid electrolyte, such as a sulfide-based compound, an oxide-based compound, or a sulphate compound, not necessitating a liquid- or gel-phase electrolyte solution. 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 located at opposite ends of the electrode assembly  110 . In some examples, the electrode assembly  110  may be accommodated in the can  140  with an electrolytic solution. In some examples, the electrolytic solution may include an organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC), and a lithium salt, such as LiPF 6  or LiBF 4 . In some examples, if the inorganic solid electrolyte is used, the electrolytic solution may be omitted. 
     The first terminal  120  may be made of a metal and may be electrically connected to the first electrode plate  111 . In some examples, the first terminal  120  may include a first collector plate  121 , a first terminal pillar  122 , and a first terminal plate  124 . In some examples, the first collector plate  121  may be brought into contact with the first uncoated portion  111   a  protruding at an end of the electrode assembly  110 . In an embodiment, the first collector plate  121  may be welded to the first uncoated portion  111   a . In some examples, the first collector plate  121  may be substantially in an inverted L-shaped (“┌”) configuration and may have a terminal hole  121   a  located in a top portion thereof. In some examples, the first terminal pillar  122  may be inserted into the terminal hole  121   a , followed by riveting and/or welding. In some examples, the first collector plate  121  may be made of copper or a copper alloy. In some examples, the first terminal pillar  122  penetrates the cap plate  151  to be described later and is electrically connected to the first collector plate  121  under the cap plate  151 . In addition, in some examples, while the first terminal pillar  122  is upwardly protruded and extended to an upper portion of the cap plate  151  by a length (e.g., a predetermined length), a flange  122   a  may be located below the cap plate  151  to prevent or substantially prevent the first terminal pillar  122  from being dislodged from the cap plate  151 . In an embodiment, a portion of the first terminal pillar  122  positioned below the flange  122   a  is fitted into the first terminal hole  121   a  of the first collector plate  121 , followed by riveting and/or welding. In some examples, the first terminal pillar  122  may be electrically insulated from the cap plate  151 . In some examples, boundary regions of the upwardly exposed first terminal pillar  122  and the first terminal plate  124  may be welded to each other. For example, a laser beam may be supplied to the boundary regions of the upwardly exposed first terminal pillar  122  and the first terminal plate  124  to melt the boundary regions, followed by cooling, thereby welding the boundary regions. The welded regions are designated by reference numeral  125  in  FIG. 2A . In an embodiment, a bus bar made of aluminum or an aluminum alloy may be welded to the first terminal plate  124 . 
     The second terminal  130  may also be made of a metal and may be electrically connected to the second electrode plate  112 . In some examples, the second terminal  130  may include a second collector plate  131 , a second terminal pillar  132 , and a second terminal plate  134 . In some examples, the second collector plate  131  may be brought into contact with the second uncoated portion  112   a  protruding at an end of the electrode assembly  110 . In some examples, the second collector plate  131  may be substantially in an inverted L-shaped (“┐”) configuration and may have a terminal hole  131   a  located in a top portion thereof. In some examples, the second terminal pillar  132  may be inserted into the terminal hole  131   a  and then coupled thereto. In some examples, the first collector plate  121  may be made of, for example, but is not limited to, aluminum or an aluminum alloy. In some examples, the second terminal pillar  132  penetrates 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, in some examples, while the second terminal pillar  132  is upwardly protruded and extended to an upper portion of the cap plate  151  by a length (e.g., a predetermined length), a flange  132   a  may be located below the cap plate  151  to prevent or substantially prevent the second terminal pillar  132  from being dislodged from the cap plate  151 . In an embodiment, a portion of the second terminal pillar  132  positioned below the flange  132   a  is fitted into the second terminal hole  131   a  of the second collector plate  131 , followed by riveting and/or welding. In an embodiment, the second terminal pillar  132  may be electrically insulated from the cap plate  151 . In some examples, the second terminal pillar  132  may be made of aluminum or an aluminum alloy. In an embodiment, 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, the second terminal pillar  132  is coupled to the hole  134   a  of the second terminal plate  134 . In an embodiment, the second terminal pillar  132  and the second terminal plate  134  may be riveted and/or welded to each other. In some examples, boundary regions of the upwardly exposed second terminal pillar  132  and the second terminal plate  134  may be welded to each other. For example, a laser beam may be supplied to the boundary regions of the upwardly exposed second terminal pillar  132  and the second terminal plate  134  to melt the boundary regions, followed by cooling, thereby welding the boundary regions. The welded regions are designated by reference numeral  135  in  FIG. 2A . In an embodiment, a bus bar made of aluminum or an aluminum alloy may be easily welded to the second terminal plate  134 . In an embodiment, the second terminal plate  134  may be electrically connected to the cap plate  151 . Thus, the cap plate  151  and the can  140 , which will be described below, may have the same polarity as the second terminal  130  (e.g., a positive polarity). 
     The cap assembly  150  may be coupled to the can  140 . In some examples, the cap assembly  150  may include the cap plate  151 , a seal gasket  152 , a plug  153 , a safety vent  154 , an upper coupling member  155 , and a lower insulating member  156 . The cap plate  151  may seal the opening of the case  140 , and may be made of a same material as the case  140 . In some examples, the cap plate  151  may be coupled to the can  140  by laser welding. As described above, in an embodiment, since the cap plate  151  has the same polarity as the second terminal  130 , the cap plate  151  and the can  140  may have the same polarity. The seal gasket  152  made of an insulating material may be located between each of the first terminal pillar  122  and the second terminal pillar  132  and the cap plate  151  at a bottom end of the cap plate  151  and may seal regions 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 or substantially prevent external moisture from permeating into the secondary battery  100  and prevent or substantially prevent the electrolyte accommodated in the secondary battery  100  from being effused outside. The plug  153  may seal an electrolyte injection hole  151   a  of the cap plate  151 . The safety vent  154  may be installed in a vent hole  151   b  of the cap plate  151  and may have a notch configured to be openable at a preset pressure. The upper coupling member  155  may be located between each of the first terminal pillar  122  and the second terminal pillar  132  and the cap plate  151  at a top end of the cap plate  151 . In addition, the upper coupling member  155  may closely contact the cap plate  151 . In addition, the upper coupling member  155  may also closely contact and the seal gasket  152 . In an embodiment, the upper coupling member  155  may insulate the first terminal pillar  122  and the second terminal pillar  132  from the cap plate  151 . In some examples, the upper coupling member  155  located in the second terminal pillar  132  may electrically connect the second terminal plate  134  and the cap plate  151  to each other. Accordingly, the second terminal  130  may have the same polarity as the cap plate  151  and the can  140 . The lower insulating member  156  may be located between each of the first collector plate  121  and the second collector plate  131  and the cap plate  151  and may prevent or substantially prevent an unnecessary short circuit from being generated. That is, the lower insulating member  156  may prevent or substantially prevent short circuits from being generated between the first collector plate  121  and the cap plate  151  and between the second collector plate  131  and the cap plate  151 . 
     The secondary battery  200  shown in  FIG. 2B  will now be described. The secondary battery  200  is different from the secondary battery  100  in terms of the construction of the electrode assembly  210  and the connection relationships between the electrode assembly  210  and each of the terminals  120  and  130 . A first electrode tab  211   a  may be positioned between the electrode assembly  210  and a first terminal pillar  122  of a first terminal  120 , and a second electrode tab  212   a  may be positioned between the electrode assembly  210  and a second terminal pillar  132  of a second terminal  130 . In an embodiment, the first electrode tab  211   a  may be extended 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 be electrically connected or welded to a planar flange  122   a  provided in the first terminal pillar  122 . In addition, the second electrode tab  212   a  may be extended from a top end of the electrode assembly  210  to a bottom end of the second terminal pillar  132  of the second terminal  130  to be electrically connected or welded to a planar flange  132   a  provided in the second terminal pillar  132 . The first electrode tab  211   a  may be either a first uncoated portion of the first electrode plate  211  of the electrode assembly  210 , which is not coated 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 a same material as the first electrode plate  211 , and the separate member may be 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 either a second uncoated portion of the second electrode plate  212  of the electrode assembly  210 , which is not coated with a second active material, or a separate member connected to the second uncoated portion. Here, the second uncoated portion may be made of a same material as the second electrode plate  212 , and the separate member may be 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, in an embodiment, since a winding axis of the electrode assembly and terminal axes of the terminals are parallel or horizontal with each other, the electrode assembly has excellent electrolyte impregnation capability when an electrolyte is injected, and internal gases may be rapidly transferred to a safety vent during overcharging to facilitate the safety vent  154  quickly operating. In an embodiment, electrode tabs (uncoated portions or separate members) of the electrode assembly are directly electrically connected to the terminals, which shortens electrical paths, thereby reducing internal resistance of the secondary battery  200  while reducing the number of components of the secondary battery  200 . 
     The can  140  manufactured by an example method, which will be described below, may be employed to the secondary batteries  100  and  200  shown in  FIGS. 1, 2A , and  2 B. 
       FIGS. 3A and 3B  are perspective views illustrating an example method for manufacturing example secondary battery  100 ,  200 .  FIG. 3A  shows a can  140  at an initial stage of manufacture. 
     In the example shown in  FIG. 3A , a substantially planar metal plate  140 A having a uniform thickness may be provided. In some examples, the metal plate  140 A may include any of aluminum (Al), iron (Fe), copper (Cu), titanium (Ti), nickel (Ni), magnesium (Mg), chromium (Cr), manganese (Mn), zinc (Zn), or alloys of these elements. In some examples, the metal plate  140 A may include nickel (Ni) plated iron (Fe) or SUS (e.g., SUS 301, SUS 304, SUS 305, SUS 316L, or SUS 321). 
     In some examples, the metal plate  140 A may have a thickness in a range from approximately 0.1 mm to approximately 10 mm, and a deviation in the thickness of the metal plate  140 A in all areas may be in a range from approximately 0.1% to approximately 1%. Therefore, the present invention may provide the can  140  that is relatively thin and has a small thickness deviation, compared to a conventional can. 
     In some examples, the metal plate  140 A may be preprocessed to facilitate a bending process, a notching process, and/or a welding process, which will be described below. In some examples, the metal plate  140 A may be subjected to annealing treatment performed in a gas atmosphere (e.g., a predetermined gas atmosphere) and a temperature range (e.g., a predetermined temperature range) for a period of time (e.g., a predetermined period of time). In some examples, the annealing treatment may be performed in an atmosphere of inert gas, such as argon (Ar) or nitrogen (N 2 ) at a temperature in a range from approximately 300° C. to approximately 1000° C. for approximately 10 seconds to approximately 60 minutes. The annealing treatment may increase the elastic modulus of the metal plate  140 A by approximately 5% to approximately 60%. Accordingly, the bending process of the metal plate  140 A, which will later be described, may be easily performed, and occurrence of a spring-back phenomenon may be minimized or reduced, particularly after the bending process. 
     In an embodiment, the metal plate  140 A may have a substantially planar top surface and a substantially planar bottom surface. In an embodiment, the top surface and/or the bottom surface of the metal plate  140 A may be subjected to insulation treatment. In some examples, a thin insulation film may be located on the top surface of metal plate  140 A by forming a thin oxide layer (e.g., an anodizing layer) through a metal oxidation process or coating or laminating an insulation resin (e.g., polyimide, polypropylene, or polyethylene). In some examples, the top surface of the metal plate  140 A may correspond to the interior surface of the can  140 , and the bottom surface of the metal plate  140 A may correspond to the exterior surface of the can  140 . These features of the metal plate  140 A may be commonly applied to all of the metal plates disclosed in the following embodiments. 
       FIG. 3B  shows the metal plate  140 A at a later stage of manufacture. 
     In the example shown in  FIG. 3B , the substantially planar metal plate  140 A having a uniform thickness may be provided using a blanking process and/or a notching process. In some examples, the metal plate  140 A may include a substantially rectangular bottom portion  141  having long sides and short sides, long side portions  142  and  143  (to later be bent from the bottom portion) horizontally extended from the respective long sides of the bottom portion  141 , and short side portions  144  and  145  (to later be bent from the bottom portion and the long side portions) horizontally extended from the bottom portion  141  and the respective long side portions  142  and  143 . 
     In some examples, one of the short side portions  144  may include a first short side portion  144   a  extended from the short side of the bottom portion  141  in a substantially triangular shape, a second short side portion  144   b  horizontally extended from an end of the long side portion  142 , and a third short side portion  144   c  horizontally extended from an end of the long side portion  143 . In an embodiment, the second short side portion  144   b  may include an inclined periphery located on a region facing the first short side portion  144   a , and the third short side portion  144   c  may also include an inclined periphery located on a region facing the first short side portion  144   a . In other words, the second and third short side portions  144   b  and  144   c  may be configured to match or correspond with the first short side portion  144   a . In an embodiment, the width of each of the long side portions  142  and  143  may be substantially equal to that of each of the long sides of the bottom portion  141 . In an embodiment, the width of the first short side portion  144   a  may be substantially equal to that of each of the short sides of the bottom portion  141 . In addition, the overall width of the second and third short side portions  144   b  and  144   c  may be substantially equal to the width of each of the short sides of the bottom portion  141 . In addition, the length of each of the long side portions  142  and  143  may be substantially equal to that of each of the short side portions  144  and  145 . In  FIG. 3B , dashed lines indicate bending lines in a subsequent process to be described later. 
       FIGS. 4A to 4D  are partially enlarged plan views illustrating an example method for manufacturing an example secondary battery. For clarity and brevity,  FIG. 4A  shows a first short side portion  144   a  extended from a bottom portion  141 , and second and third short side portions  144   b  and  144   c  extended from the long side portions  142  and  143 , respectively. 
     As shown in  FIG. 4B , in a region “ 4   b ,” in some examples, at least one or more curvatures  1440 A may be provided between the first short side portion  144   a  and the second short side portion  144   b , for example, a region where the first short side portion  144   a  and the second short side portion  144   b  meet, a connecting region where the first short side portion  144   a  and the second short side portion  144   b  are connected to each other, a vertex between the first short side portion  144   a  and the second short side portion  144   b , a corner between the first short side portion  144   a  and the second short side portion  144   b , or a corner joint region between the first short side portion  144   a  and the second short side portion  144   b.    
     In addition, as shown in  FIG. 4C , in a region “ 4   c ,” in some examples, at least one or more curvatures  1440 B may be provided between the first short side portion  144   a  and the third short side portion  144   c , for example, a region where the first short side portion  144   a  and the third short side portion  144   c  meet, a connecting region where the first short side portion  144   a  and the third short side portion  144   c  are connected to each other, a vertex between the first short side portion  144   a  and the third short side portion  144   c , a corner between the first short side portion  144   a  and the third short side portion  144   c , or a corner joint region between the first short side portion  144   a  and the third short side portion  144   c.    
     In some examples, the curvatures  1440 A may include a first curvature  1441  located in the first short side portion  144   a  and a second curvature  1442  located in the second short side portion  144   b.    
     In addition, in some examples, the curvatures  1440 B may include a first curvature  1441  located in the first short side portion  144   a , and a third curvature  1443  located in the third short side portion  144   c.    
     In addition, in some examples, the first curvature  1441  and the second curvature  1442  may be in an asymmetric configuration with respect to a bending line between the bottom portion  141  and the long side portion  142 . In addition, in some examples, the first curvature  1441  and the third curvature  1443  may be in an asymmetric configuration with respect to a bending line between the bottom portion  141  and the long side portion  143 . 
     As shown in  FIG. 4B , in some examples, the first curvature  1441  may be larger (e.g., have a larger area) than the second curvature  1442 . In addition, as shown in  FIG. 4C , in some examples, the first curvature  1441  may be larger (e.g., have a larger area) than the third curvature  1443 , or vice versa. 
     In some examples, the first, second, and third curvatures  1441 ,  1442 , and  1443  may be circular or elliptical. In addition, in some examples, if the first, second, and third curvatures  1441 ,  1442 , and  1443  are circular, the first curvature  1441  may have a larger curvature radius than the second curvature  1442 , as shown in  FIG. 4B . In addition, as shown in  FIG. 4C , the first curvature  1441  may have a larger curvature radius than the third curvature  1443 , or vice versa. 
     In some examples, the curvature radius of the first curvature  1441  may be approximately 5 to 11 times, and, in an embodiment, 7 to 9 times, that of the second curvature  1442 . Within this numerical range, a desirably shaped curved portion  1550 A (see  FIG. 6C ) may be provided at a region where the bottom portion  141 , the long side portion  142 , and the short side portions including the first short side portion  144   a  having the first curvature  1441 , and the second short side portion  144   b  having the second curvature  1442 , meet. In some examples, the curvature radius of the first curvature  1441  may be approximately 5 to 11 times, and, in an embodiment, 7 to 9 times, larger than that of the third curvature  1443 . Within this numerical range, a desirably shaped curved portion  1550 B (see  FIG. 6C ) may be provided at a region where the bottom portion  141 , the long side portion  143 , and the short side portions including the first short side portion  144   a  having the first curvature  1441 , and the third short side portion  144   c  having the third curvature  1443 , meet. 
     As described above and with reference to  FIG. 4D , in an embodiment, a curvature radius R 1  of the first curvature  1441  may be larger than a curvature radius R 2  of the second curvature  1442 , and the first curvature  1441  and the second curvature  1442  may be consecutively connected to each other. In an embodiment, the curvature radius of the first curvature  1441  may be larger than that of the third curvature  1443 , and the first curvature  1441  and the third curvature  1443  may be consecutively connected to each other. 
       FIGS. 5A and 5B  are partially enlarged plan views illustrating an example method for manufacturing an example secondary battery. As shown in  FIGS. 5A and 5B , in some examples, the second curvature  1442  may be larger (e.g., have a larger area) than the first curvature  1441 . In addition, as shown in  FIG. 5B , in some examples, the third curvature  1443  may be larger (e.g., have a larger area) than the first curvature  1441 . 
     In some examples, the first, second, and third curvatures  1441 ,  1442 , and  1443  may be circular or elliptical, and the second curvature  1442  may have a larger curvature radius than the first curvature  1441 . In addition, in some examples, the third curvature  1443  may have a larger curvature radius than the first curvature  1441 . In some examples, the first, second, and third curvatures  1441 ,  1442 , and  1443  are provided by blanking and/or notching the metal plate  140 A. Therefore, thicknesses of the first, second, and third curvatures  1441 ,  1442 , and  1443  may be equal to or similar to those of the bottom portion  141 , the first short side portion  144   a , the second short side portion  144   b , and the third short side portion  144   c.    
       FIGS. 6A to 6C  are perspective views illustrating an example method for manufacturing an example secondary battery.  FIGS. 6A and 6B  show the metal plate  140 A at a later stage of manufacture. In the example shown in  FIGS. 6A and 6B , the metal plate  140 A may be bent in a shape (e.g., a predetermined shape). In some examples, the metal plate  140 A may be bent in a predetermined shape after it is fixed by a bending machine or a press mold. 
     In some examples, the long side portions  142  and  143  bent and extended from the respective long sides of the bottom portion  141  in a substantially perpendicular direction, and the short side portions  144  and  145  bent and extended from the bottom portion  141  and the long side portions  142  and  143  in a substantially perpendicular direction, may be provided as the result of the bending process. That is, in an embodiment, the long side portions  142  and  143  may be bent approximately 90 degrees from the long sides of the bottom portion  141  to be extended, and the short side portions  144  and  145  may be bent approximately 90 degrees from the short sides of the bottom portion  141  to be extended and may be bent approximately 90 degrees from the long side portions  142  and  143  to be extended. 
     Therefore, the first short side portion  144   a , the second short side portion  144   b , and the third short side portion  144   c  may be positioned to face one another and their peripheries may contact one another. In an embodiment, an angle of a vertex of the first short side portion  144   a , facing the second and third short side portions  144   b  and  144   c  may be in a range from approximately 80 degrees to approximately 100 degrees, and, in an embodiment, 90 degrees. 
     In some examples, an angle defined between each of two upper peripheries of the first short side portion  144   a  and the short side of the bottom portion  141  may be in a range from approximately 40 degrees to approximately 50 degrees, and, in an embodiment, 45 degrees, an angle defined between the periphery of the second short side portion  144   b  facing an end of the periphery of the first short side portion  144   a  and an end of the long side portion  142  may be in a range from approximately 40 degrees to approximately 50 degrees, and, in an embodiment, 45 degrees, and an angle defined between the periphery of the third short side portion  144   c  facing another end of the periphery of the first short side portion  144   a  and an end of the long side portion  143  may be in a range from approximately 40 degrees to approximately 50 degrees, and, in an embodiment, 45 degrees. Accordingly, a vertex at which the bottom portion  141 , the end of the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  meet, and a vertex at which the bottom portion  141 , the end of the long side portion  143 , the first short side portion  144   a , and the third short side portion  144   c  meet, may be bent in a substantially round shape. 
     In some examples, a pair of asymmetrical curvatures  1440 A ( 1441  and  1442 ) are provided at a region or vertex where the first short side portion  144   a  and the second short side portion  144   b  meet, and a pair of asymmetrical curvatures  1440 B ( 1441  and  1443 ) are provided at a region or vertex where the first short side portion  144   a  and the third short side portion  144   c  meet, thereby providing a curved portion  1550 A (see  FIG. 6C ) at a region where the bottom portion  141 , the long side portion  142 , and the short side portions including the first short side portion  144   a  having the first curvature  1441  and the second short side portion  144   b  having the second curvature  1442 , meet, and a curved portion  1550 B (see  FIG. 6C ) at a region where the bottom portion  141 , the long side portion  143 , and the short side portions including the first short side portion  144   a  having the first curvature  1441  and the third short side portion  144   c  having the third curvature  1443  meet.  FIG. 6B  shows an example in which the short side portions  144  and  145  are bent from the long side portions  142  and  143 , respectively. That is,  FIG. 6B  shows an example in which the long side portions  142  and  143  have yet to be bent from the bottom portion  141 . 
       FIG. 6C  shows the can  140  at a later stage of manufacture. In the example shown in  FIG. 6C , a bending process and a welding process may be performed. 
     Similarly as above, in some examples, when the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  are bent with respect to the bottom portion  141 , the curvatures  1440 A, i.e., the first curvature  1441  and the second curvature  1442 , are positioned to overlap with each other or to be piled up one on another, thereby providing the symmetrical curved portion  1550 A at a corner where the bottom portion  141 , the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  meet. 
     In addition, in some examples, when the long side portion  143 , the first short side portion  144   a , and the third short side portion  144   c  are bent with respect to the bottom portion  141 , the curvatures  1440 B, i.e., the first curvature  1441  and the third curvature  1443 , are positioned to overlap with each other or to be piled up one on another, thereby providing the symmetrical curved portion  1550 B at a corner where the bottom portion  141 , the long side portion  143 , the first short side portion  144   a , and the third short side portion  144   c  meet. 
     In addition, in some examples, the welding portions  146  may be provided in the short side portions  144  and  145 . In some examples, the welding portions  146  may include a first welding portion  146   a , a second welding portion  146   b , and a third welding portion  146   c . The first welding portion  146   a  may extend from the curved portion  1550 A provided at a corner where the bottom portion  141 , the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  meet, and along a boundary region between the first short side portion  144   a  and the second short side portion  144   b . The second welding portion  146   b  may extend from the curved portion  1550 B provided at a corner where the bottom portion  141 , the long side portion  143 , the first short side portion  144   a , and the second short side portion  144   b  meet, and along a boundary region between the first short side portion  144   a  and the third short side portion  144   c . The third welding portion  146   c  may be located at a boundary region between the second short side portion  144   b  and the third short side portion  144   c.    
     In other words, the first welding portion  146   a  may be at an acute angle with respect to a short side of the bottom portion  141  in the curved portion  1550 A where the bottom portion  141 , the end of the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  meet, and the second welding portion  146   b  may be at an acute angle with respect to the short side of the bottom portion  141  in the curved portion  15506  where the bottom portion  141 , the end of the long side portion  143 , the first short side portion  144   a , and the third short side portion  144   c  meet. In addition, the third welding portion  146   c  may extend from a bottom end of the second and third short side portions  144   b  and  144   c  to a top end (i.e., an opening  147 ) of the second and third short side portions  144   b  and  144   c.    
     In some examples, the first and second welding portions  146   a  and  146   b  may be consecutively formed, and the third welding portion  146   c  may then be formed, or vice versa. In an embodiment, the welding process may be performed on the first welding portion  146   a , the third welding portion  146   c , and the second welding portion  146   b  in that order, or the welding order may be reversed. In addition, the welding process performed on the third welding portion  146   c  may be started from the bottom end and may be terminated at the top end, or vice versa. In some examples, the first, second, and third welding portions  146   a ,  146   b , and  146   c  may include a butt joint structure, a lap joint structure, an overlay joint structure, or an edge joint structure. In some examples, the welding portions  146  may be in a substantially inverted Y-shaped (“ ”) configuration. The welding portions  146  may be provided to have a solid-line shape. Therefore, the first short side portion  144   a  may be securely fixed to the second and third short side portions  144   b  and  144   c  due to the first and second welding portions  146   a  and  146   b , and the second and third short side portions  144   b  and  144   c  may be securely fixed to each other by the third welding portion  146   c.    
     In an embodiment, the first and second welding portions  146   a  and  146   b  connected to each other may be shaped as straight lines having at least one vertex, and the third welding portion  146   c  may be shaped as a straight line extending from the vertex, where the first and second welding portions  146   a  and  146   b  meet, to the opening  147 . In an embodiment, a vertex angle defined between the first welding portion  146   a  and the second welding portion  146   b  may be in a range from approximately 80 degrees to approximately 100 degrees, and, in an embodiment, 90 degrees. In addition, an angle in a range from approximately 40 degrees to approximately 50 degrees, and, in an embodiment, 45 degrees, may be defined between the first welding portion  146   a  and the short side of the bottom portion  141 , and an angle in a range from approximately 40 degrees to approximately 50 degrees, and, in an embodiment, 45 degrees, may also be defined between the second welding portion  146   b  and the short side of the bottom portion  141 . 
     As described above, one or more embodiments of the present invention provide the can  140  configured such that the first short side portion  144   a  is bent and extended from the bottom portion  141 , and asymmetrical curvatures  1440 A and  1440 B are provided at the vertex (corner) between the first short side portion  144   a  and the second short side portion  144   b  and at the vertex (corner) between the first short side portion  144   a  and the third short side portion  144   c , thereby providing symmetrical curved portions  1550 A and  15506 , which are naturally desirable, at regions where three or four sides meet, respectively. In addition, the first, second, and third welding portions  146   a ,  146   b , and  146   c  are provided from the curved portions  1550 A and  15506  along interfaces (e.g., cutting lines) between each of the first, second, and third short side portions  144   a ,  144   b , and  144   c  to be connected to one another to define a single short side portion  144 , thereby providing the can  140  having increased bending and welding workability and improved sealing efficiency to prevent or substantially prevent leakage of electrolyte. 
     Here, as the result of the bending process, curved portions may also be provided between the bottom portion  141  and the first short side portion  144   a , between the bottom portion  141  and each of the long side portions  142  and  143 , between the long side portion  142  and the second short side portion  144   b , and between the long side portion  143  and the third short side portion  144   c.    
     In some examples, as described above, the curved portion  1550 A having a round shape may be provided at the corner where the bottom portion  141 , the long side portion  142 , the first short side portion  144   a , and the second short side portion  144   b  meet by the asymmetrical curvatures  1440 A. In addition, as described above, the curved portion  15506  having a round shape may be provided at the corner where the bottom portion  141 , the long side portion  143 , the first short side portion  144   a  and the third short side portion  144   c  meet by the asymmetrical curvatures  1440 B. In some examples, the curvature radii of the curved portions  1550 A and  15506  located at regions where three or four sides meet may be smaller than those of the curved portions located at regions where the two sides meet, thereby providing the can  140  having a generally stable shape. 
     In some examples, prior to formation of the welding portions  146 , a temporary welding portion may first be provided at a boundary region between the first short side portion  144   a  and the second short side portion  144   b , a boundary region between the first short side portion  144   a  and the third short side portion  144   c , and/or a boundary region between the second short side portion  144   b  and the third short side portion  144   c . The temporary welding portion may include multiple temporary welding portions spaced apart from one another. In some examples, the temporary welding portions may be provided to have substantially dotted-line shapes. The temporary welding portions may prevent or substantially prevent a spring-back phenomenon from occurring to the long side portions  142  and  143 , the short side portions  144  and  145 , and the bottom portion  141 . In addition, the temporary welding portions may securely fix the long side portions  142  and  143  and the short side portions  144  and  145  to each other. Accordingly, the main welding portions  146  (i.e., the welding portions  146 ) may be easily provided. In an embodiment, the temporary welding portions may be provided by ultrasonic welding or resistance welding, as well as laser welding. 
       FIGS. 7A and 7B  are partially enlarged plan views illustrating a method for manufacturing a secondary battery according to an example embodiment. 
     As shown in  FIG. 7A , in some examples, a curvature  1440 C may be provided substantially at the center of a region where a first short side portion  144   a  and a second short side portion  144   b  (or a third short side portion) meet. In some examples, the curvature  1440 C may be provided substantially at the center of the region where the first short side portion  144   a  and the second short side portion  144   b  (or the third short side portion) meet, in a substantially symmetrically round shape, but the shape of the curvature  1440 C is not limited thereto. Rather, the curvature  1440 C may have any of the shapes of the above-described curvatures. 
     As shown in  FIG. 7B , in some examples, a curvature  1440 D may be connected longer (or more widely) to the second short side portion  144   b  (or the third short side portion) than to the first short side portion  144   a . In some other examples, the curvature  1440 D may be connected longer (or more widely) to the first short side portion  144   a  than to the second short side portion  144   b  (or the third short side portion). Accordingly, in some examples, the curvature  1440 D may have an asymmetric configuration around a region where the first short side portion  144   a  and the second short side portion  144   b  meet (e.g., a vertex or a corner). Similarly as above, the curvature  1440 D may be provided in a substantially round shape, but the shape of the curvature  1440 D is not limited thereto. Rather, the curvature  1440 D may have any of the shapes of the above-described curvatures. 
     As described above, when a metal plate is blanked and/or notched, the curvatures  1440 A,  14408 ,  1440 C, and  1440 D may be integrally formed at the boundary region between the first short side portion  144   a  and the second short side portion  144   b  or at the boundary region between the first short side portion  144   a  and the third short side portion  144   c.    
     In addition, in some examples, the long side portions  142  and  143  and the first short side portion  144   a  are bent from the bottom portion  141 , and the second and third short side portions  144   b  and  144   c  are bent from the long side portions  142  and  143 , as described above, the curvatures  1440 A,  1440 B,  1440 C, and  1440 D, to then be inserted or connected to the corner regions of three or four sides, where these side portions meet (for example, a region where the first short side portion  144   a  and the second short side portion  144   b  meet, and a region where the first short side portion  144   a  and the third short side portion  144   c  meet). 
     As described above, since the curvature(s) are located at the regions where the first short side portion bent from the bottom portion and the second and third short side portions bent from the long side portions meet, desirably shaped curved portions in a symmetric configuration may be provided at the regions (corners) where the bottom portion, the long side portions, and the first, second, and third short side portions meet by the curvatures when the first short side portion and the second and third short side portions are bent. In addition, since the desirably shaped curved portions in a symmetric configuration are provided by the curvature(s), and distances between boundary regions of the curved portions and the first, second, and third short side portions are reduced, welding can be easily performed, thereby preventing or substantially preventing pinholes from being generated at the boundary regions. In addition, when multiple batteries are assembled or stacked to manufacture a battery module or pack at a later stage, the symmetrical curved portions may not interfere with other batteries, thereby preventing or substantially preventing insulation breakdowns from occurring among the batteries. However, if the curved portions were asymmetrically configured, insulation layers of other neighboring batteries may be damaged by the asymmetrical curved portions, resulting in insulation breakdowns among the neighboring batteries. 
     While the secondary battery of the present invention has been particularly shown and described with reference to some example embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as set forth by the following claims.