Abstract:
There is provided a secondary battery comprising an electrode assembly including a first electrode plate having a first electrode tab, a second electrode plate having a second electrode tab and a separator between the first electrode plate and the second electrode plate, a case including a body accommodating the electrode assembly, a cap plate covering a top portion of the body, and a bottom plate covering a bottom portion of the body, a first electrode terminal electrically connected to the first electrode tab, a second electrode terminal electrically connected to the second electrode tab through the case, and a connection plate electrically connected to the second electrode tab and configured to bend away from the bottom plate, the connection plate being on the bottom plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0139031, filed on Oct. 2, 2015 in the Korean Intellectual Property Office, the content of which is incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of embodiments of the present invention relate to a secondary battery. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, in order to fabricate a high-capacity battery, as many electrode plates as possible should be wound and placed in a can having a given volume. In addition, in order to increase an amount of active material coated on the electrode plates, the volume of the can occupied by a current collector should be reduced. However, because current collecting efficiency should be maintained to fabricate a high-power battery, an electrode tab is welded to an electrode assembly whenever each of the turns of the winding is accomplished to fabricate the high-power battery. The fully-fabricated electrode assembly is referred to as a multi-tab electrode assembly. 
         [0006]    In the conventional process for attaching an electrode tab of an electrode assembly to a case, an auxiliary tab is welded to the electrode tab and the auxiliary tab is then welded to a cap plate or a bottom plate of the case. Here, the auxiliary tab has a primary bending structure formed at a portion welded to the electrode tab and has a secondary bending structure formed by assembling the cap plate or the bottom plate into the case. 
         [0007]    The aforementioned process, however, may undesirably increase processing costs due to additional equipment for attaching and bending processes. In addition, when stress, such as vibrations or electrical or mechanical shocks, is applied to the bent portion of the auxiliary tab for an extended period of time, the bent portion of the auxiliary tab may be cut due to the stress. 
       SUMMARY 
       [0008]    Aspects of embodiments of the present invention are directed to a secondary battery having improved durability against stress, such as vibrations or electrical or mechanical shocks, by reducing (e.g., minimizing) a welded and bent portion of an electrode tab by directly connecting an electrode assembly to a case. 
         [0009]    The above and other aspects of the present invention will be described in or be apparent from the following description of exemplary embodiments. 
         [0010]    According to some embodiments of the present invention, there is provided a secondary battery comprising: an electrode assembly including a first electrode plate having a first electrode tab, a second electrode plate having a second electrode tab and a separator between the first electrode plate and the second electrode plate; a case including a body accommodating the electrode assembly, a cap plate covering a top portion of the body, and a bottom plate covering a bottom portion of the body; a first electrode terminal electrically connected to the first electrode tab; a second electrode terminal electrically connected to the second electrode tab through the case; and a connection plate electrically connected to the second electrode tab and configured to bend away from the bottom plate, the connection plate being on the bottom plate. 
         [0011]    In an embodiment, the connection plate is formed by stamping a peripheral portion of a region of the bottom plate. 
         [0012]    In an embodiment, a connecting part connected to the bottom plate and a stamping part formed in a single line processed by stamping form a periphery of the connection plate, and the stamping part is configured to separate the peripheral portion of the connection plate from the bottom plate. 
         [0013]    In an embodiment, the connection plate is on a same line as the bottom plate. 
         [0014]    In an embodiment, a coupling groove is on an outer surface of the bottom plate and a portion of a bottom surface of the coupling groove constitutes the connection plate. 
         [0015]    In an embodiment, the bottom plate further includes a cover plate placed in the coupling groove and fastened with the coupling groove to seal the connection plate. 
         [0016]    In an embodiment, the secondary battery further includes a bottom insulation member between the electrode assembly and the bottom plate, wherein an opening through which the second electrode tab penetrates is in a region of the bottom insulation member, the region corresponding to the connection plate. 
         [0017]    In an embodiment, a spacer protruding from a top surface of the bottom plate forms a space between the bottom plate and the bottom insulation member, and wherein a portion of the second electrode tab connected to the connection plate is bent and positioned in the space. 
         [0018]    In an embodiment, the second electrode plate is connected to the bottom plate through the second electrode tab and the connection plate. 
         [0019]    In an embodiment, the first electrode tab extends in a direction extending from the first electrode plate to the cap plate and the second electrode tab extends in a direction extending from the second electrode plate to the bottom plate. 
         [0020]    As described above, according to some embodiments of the present invention, the secondary battery having improved durability against stress can be provided by reducing (e.g., minimizing) a welded and bent portion of an electrode tab by directly connecting an electrode assembly to a case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0022]      FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention; 
           [0023]      FIG. 2  is a cross-sectional view taken along the line I-I′ of  FIG. 1 ; 
           [0024]      FIG. 3  is a cross-sectional view taken along the line II-II′ of  FIG. 1 ; 
           [0025]      FIG. 4  is a plan view of a bottom plate illustrating a connection plate according to an embodiment of the present invention; 
           [0026]      FIG. 5  is a diagram illustrating a connection method of a second electrode tab and a connection plate according to an embodiment of the present invention; and 
           [0027]      FIGS. 6-9  are diagrams illustrating an assembling sequence of a second electrode tab and a bottom plate according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Hereinafter, examples of embodiments of the invention will be described in detail with reference to the accompanying drawings such that they can readily be made and used by those skilled in the art. 
         [0029]      FIG. 1  is a perspective view of a secondary battery according to an embodiment of the present invention,  FIG. 2  is a cross-sectional view taken along the line I-I′ of  FIG. 1 ,  FIG. 3  is a cross-sectional view taken along the line II-II′ of  FIG. 1 ,  FIG. 4  is a plan view of a bottom plate illustrating a connection plate according to an embodiment of the present invention, and  FIG. 5  is a diagram illustrating a connection method of a second electrode tab and a connection plate according to an embodiment of the present invention. 
         [0030]    Referring to  FIGS. 1 to 5 , the secondary battery  100  according to an embodiment of the present invention includes an electrode assembly  110 , a case  120  and an electrode terminal portion  130 . In addition, the secondary battery  100  may further include a bottom insulation member  140 . 
         [0031]    The electrode assembly  110  may include a first electrode plate  111 , a second electrode plate  112  and a separator  113 . 
         [0032]    The first electrode plate  111  may be formed by coating a first electrode active material  111   b  (e.g., graphite or carbon) on a first electrode current collector  111   a  made of a metal foil (e.g., a copper or nickel foil). The first electrode plate  111  may include a plurality of first electrode tabs  111   c  extending and protruding from a region of the first electrode current collector  111   a,  which is not coated with the first electrode active material  111   b,  toward the cap plate  122 . The first electrode tabs  111   c  may be formed (e.g., aligned) at a preset or predetermined position through a winding process in the course of fabricating the electrode assembly  110 , thereby forming a multi-tab structure. Each of the first electrode tabs  111   c  is electrically connected to a first electrode terminal  131 , thereby establishing a path for the flow of current between the first electrode plate  111  and the first electrode terminal  131 . 
         [0033]    The second electrode plate  112  may be formed by coating a second electrode active material  112   b,  e.g., a transition metal oxide, on a second electrode current collector  112   a  made of a metal foil, e.g., an aluminum foil. The second electrode plate  112  may include a plurality of second electrode tabs  112   c  extending and protruding from a region of the second electrode current collector  112   a,  which is not coated with the second electrode active material  112   b,  toward the bottom plate  123 . Thus, the second electrode tabs  112   c  may extend in the opposite direction to the first electrode tabs  111   c.  The second electrode tabs  112   c  may be formed (e.g., aligned) at a preset or predetermined position through the winding process in the course of fabricating the electrode assembly  110 , thereby forming a multi-tab structure. Each of the second electrode tabs  112   c  is electrically connected to the bottom plate  123  of the case  120 , thereby establishing a path for the flow of current between the second electrode plate  112  and the case  120 . 
         [0034]    The separator  113 , which is interposed between the first and second electrode plates  111  and  112 , may prevent short circuits between the first and second electrode plates  111  and  112 , and may allow fluid ions, such as lithium ions, to freely move. The separator  113  may be formed to have a greater width than the first electrode plate  111  and the second electrode plate  112 , so that it protrudes more than the first electrode plate  111  and the second electrode plate  112  in upward and downward directions. Therefore, the separator  113  may prevent the first electrode plate  111  and the second electrode plate  112  from directly contacting the internal surface of the case  120  (in both the upward and downward directions with respect to the first electrode plate  111  and the second electrode plate  112 ). 
         [0035]    As described above, the first electrode plate  111  may function as a negative electrode and the second electrode plate  112  may function as a positive electrode, or vice versa. 
         [0036]    The case  120  may be made of a conductive metal, such as aluminum, an aluminum alloy, or nickel plated steel, and may have a substantially hexahedral shape. 
         [0037]    The case  120  may include a body  121 , a cap plate  122 , and a bottom plate  123 . 
         [0038]    The body  121  may be shaped as a rectangular bar (container) having open top and bottom ends and may form a receiving space of the electrode assembly  110 . 
         [0039]    The cap plate  122  may be coupled to the top end of the body  121  to seal the top-end opening. A first terminal hole  122   a  may be formed at one side of the cap plate  122 . A terminal pin  131   b  of the first electrode terminal  131  may be inserted into and penetrate the first terminal hole  122   a.    
         [0040]    The bottom plate  123  may be coupled to the bottom end of the body  121  to seal the bottom-end opening. A coupling groove  124  may be formed on an outer surface of the bottom plate  123 . A connection plate  125  electrically connected to the second electrode tab  112   c  may be formed on a bottom surface of the coupling groove  124 . 
         [0041]    The connection plate  125  forms a preset or predetermined region of the coupling groove  124 , and a peripheral portion (e.g., circumferential portion) of the preset or predetermined region may be stamped, so that the connection plate  125  may be bent from the bottom plate  123 . 
         [0042]    For example, as illustrated in  FIG. 4 , the connection plate  125  may form the preset or predetermined region having a rectangular shape in the coupling groove  124 . 
         [0043]    In addition, the periphery (e.g., the circumference) of the connection plate  125  may be formed of a connecting part  125   a  and a stamping part  125   b.    
         [0044]    The connecting part  125   a  is connected to the bottom plate  123  and may be a portion bent from the bottom plate  123  when the second electrode tab  112   c  and the connection plate  125  are welded to each other. 
         [0045]    The stamping part  125   b,  which is a portion processed by stamping, may form a single line along the periphery (e.g., circumference) of the connection plate  125 , excluding the connecting part  125   a,  and may separate the peripheral portion (e.g., circumferential portion) of the connection plate  125  from the bottom plate  123 . 
         [0046]    In a state in which the connection plate  125  is outwardly bent from the bottom plate  123 , as illustrated in  FIG. 5 , it is welded to the second electrode tab  112   c  and then bent again to be parallel with the bottom plate  123 , so that it may restore its original position. The original position may refer to the original position of the connection plate  125 , suggesting that the connection plate  125  is positioned on the same line with the bottom plate  123 . Here, as the connection plate  125  restores to its original position, the second electrode tab  112   c  may be bent. For example, the second electrode tab  112   c  may downwardly extend from the electrode assembly  110  to the bottom plate  123  and may then be bent to be parallel with the connection plate  125  in a space A between the bottom plate  123  and the bottom insulation member  140 . 
         [0047]    The cover plate  126  may be placed in the coupling groove  124  to then be fastened therewith to seal the connection plate  125 . For example, the cover plate  126  is inserted into the coupling groove  124  and an outer peripheral portion (e.g., an outer circumferential portion) of the cover plate  126  and an inner peripheral portion (e.g., an inner circumferential portion) of the coupling groove  124  are then welded to each other, thereby achieving coupling of the cover plate  126  and the coupling groove  124 . 
         [0048]    Because an electrolyte may leak through the stamping part  125   b,  the case  120  may be coupled to the bottom plate  123  to allow the cover plate  126  to hermetically seal gaps created by the stamping part  125   b.  In addition, the cover plate  126  is coupled to the coupling groove  124  such that it is mounted in the coupling groove  124 , thereby increasing a coupling force between the bottom plate  123  and the cover plate  126  and reducing (e.g., minimizing) the increase in thickness of the bottom plate  123  due to the cover plate  126 . 
         [0049]      FIGS. 6 to 9  are diagrams illustrating an assembling sequence of a second electrode tab and a bottom plate according to an embodiment of the present invention. 
         [0050]    First, as illustrated in  FIG. 6 , in a state in which the bottom plate  123  is coupled to the body  121 , the connection plate  125  is outwardly bent from the bottom plate  123 , so that the bottom plate  123  may have an opening  123   b.    
         [0051]    Next, as illustrated in  FIG. 7 , the second electrode tab  112   c  may be drawn out from the case  120  through the opening  123   b  of the bottom plate  123 . The second electrode tab  112   c  drawn out from the case  120  may be disposed to be substantially parallel with the connection plate  125 . In such a state, the second electrode tab  112   c  and the connection plate  125  may be connected to each other by ultrasonic welding or laser welding. 
         [0052]    Next, as illustrated in  FIG. 8 , the connection plate  125  is bent again so as to be parallel with the bottom plate  123 , thereby closing the opening  123   b  of the bottom plate  123 . 
         [0053]    Finally, as illustrated in  FIG. 9 , the cover plate  126  is placed in the coupling groove  124  to then be coupled to the bottom plate  123  by welding. 
         [0054]    The electrode terminal portion  130  may include a first electrode terminal  131  and a second electrode terminal  132 . 
         [0055]    As illustrated in  FIG. 2 , the first electrode terminal  131  may be coupled to the cap plate  122  to then be electrically connected to the first electrode tabs  111   c.  The first electrode terminal  131  may include a bottom terminal plate  131   a,  a terminal pin  131   b  and a top terminal plate  131   c.    
         [0056]    A bottom surface of the bottom terminal plate  131   a  may be electrically connected to the first electrode tab  111   c  and a top surface thereof may be coupled to the terminal pin  131   b.  In addition, the bottom terminal plate  131   a  may be electrically insulated from the internal surface of the case  120  by a lower insulation member  133 . 
         [0057]    A bottom portion of the terminal pin  131   b  may be coupled to the bottom terminal plate  131   a.  A top portion of the terminal pin  131   b  may protrude to the outside of the case  120  while passing through the first terminal hole  122   a  formed in the cap plate  122 , may be inserted into a second terminal hole  131   ca  of the top terminal plate  131   c  to then be riveted, thereby achieving coupling of the terminal pin  131   b  and the top terminal plate  131   c.    
         [0058]    A seal gasket  135  may be assembled with the first terminal hole  122   a  together with the terminal pin  131   b.  The seal gasket  135  may insulate the terminal pin  131   b  from the cap plate  122  while sealing the first terminal hole  122   a.    
         [0059]    The top terminal plate  131   c  may be disposed on the cap plate  122  and may be electrically insulate from the cap plate  122  by an upper insulation member  134 . Stepped portions may be formed at top edges of the upper insulation member  134 . The stepped portions may protrude to an upper portion of the cap plate  122  so as to surround portions of lower side surfaces of the top terminal plate  131   c,  and may fix the top terminal plate  131   c  so as not to be rotated. 
         [0060]    The second electrode terminal  132  may be coupled to the cap plate  122  and may be electrically connected to the second electrode tab  112   c  through the case  120 . The second electrode terminal  132  may have the same configuration with the top terminal plate  131   c.    
         [0061]    The bottom insulation member  140  may be disposed between the electrode assembly  110  and the bottom plate  123  and may prevent the electrode assembly  110  and the bottom plate  123  from electrically contacting each other. 
         [0062]    A throughhole (or an opening)  141  through which the second electrode tab  112   c  passes may be formed in a portion of the bottom insulation member  140  corresponding to the connection plate  125 . The throughhole  141  may be sized to allow the second electrode tab  112   c  to pass therethrough. 
         [0063]    A spacer  123   a  for separating the bottom insulation member  140  from the bottom plate  123  may be formed on a top surface of the bottom plate  123 . The spacer  123   a  may be formed to protrude to a top portion of the bottom plate  123 . 
         [0064]    In the illustrated embodiment, the spacer  123   a  is formed at an edge portion of the top surface of the bottom plate  123  that is brought into contact with the body  121 , which is illustrated only by way of example. Rather, the spacer  123   a  may be formed at any portion of the top surface of the bottom plate  123 , so long as it does not interfere with the connection plate  125 . In addition, the spacer  123   a  may be formed to have various suitable shapes. 
         [0065]    An end  112   c′  bent from the second electrode tab  112   c  to be parallel with the connection plate  125  may be positioned in the space A between the bottom plate  123  and the bottom insulation member  140 , which is formed by the spacer  123   a.    
         [0066]    According to an embodiment of the present invention, a bent surface is formed by stamping a bottom surface of a case, and an electrode tab extending from an electrode assembly is directly connected to the bent surface without an auxiliary tab in a state in which a bottom plate of the case is coupled to a body, thereby reducing (e.g., minimizing) a welded and bent portion of the electrode tab. Accordingly, the welded and bent portion of the electrode tab may be reduced (e.g., minimized), thereby improving the durability against stress, such as vibrations or electrical or mechanical shocks. 
         [0067]    While the secondary battery of the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various suitable changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims, and equivalents thereof.