Abstract:
A battery pack comprises: a plurality of secondary batteries, wherein each battery comprises a terminal; and a tab coupling a terminal of a first secondary battery to a terminal of a second secondary battery; wherein a first end of the tab comprises a first region having a first welding portion and a second region having a second welding portion, and wherein the first and second regions of the first end of the tab are separated by a first space.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/334,089, filed on May 12, 2010, the disclosure of which is incorporated herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    One or more embodiments of the present invention relate to a battery pack, and more particularly, to a battery pack including a tab coupling a terminal of a first secondary battery to a terminal of a second secondary battery. 
         [0004]    2. Description of the Related Technology 
         [0005]    Secondary batteries typically include lithium-based oxides as positive electrode active materials and carbonaceous materials as negative electrode active materials. In general, according to the type of electrolyte used, secondary batteries can be categorized into liquid electrolyte batteries and polymer electrolyte batteries. Batteries using a liquid electrolyte are called lithium ion batteries, and batteries using a polymer electrolyte are called lithium polymer batteries. In secondary batteries, a bare cell formed by sealing a can housing an electrode assembly and an electrolytic solution is typically electrically connected to a protection circuit substrate. The bare cell is typically electrically charged or discharged by a chemical reaction, and the protection circuit substrate typically protects the bare cell by preventing overcharge and over-discharge while controlling charge and discharge of the bare cell. The battery pack typically includes a plurality of secondary batteries arranged in series or parallel. In this regard, the secondary batteries may be electrically connected by a coupling tab or the like. 
       SUMMARY 
       [0006]    One or more embodiments of the present invention relate to a battery pack, and more particularly, to a structure of a battery pack including a coupling tab. 
         [0007]    According to an embodiment of the present invention, the battery pack comprises a plurality of secondary batteries, wherein each battery comprises a terminal; and a tab coupling a terminal of a first secondary battery to a terminal of a second secondary battery; wherein a first end of the tab comprises a first region having a first welding portion and a second region having a second welding portion, and wherein the first and second regions of the first end of the tab are separated by a first space. 
         [0008]    According to another embodiment, a method of forming a battery pack comprises: providing a plurality of secondary batteries, wherein each battery comprises a terminal; and coupling a tab between a terminal of a first secondary battery and a terminal of a second secondary battery; wherein a first end of the tab comprises a first region having a first welding portion and a second region having a second welding portion, and wherein the first and second regions of the first end of the tab are separated by a first space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic perspective view of a battery pack according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a partially exploded and enlarged perspective view of  FIG. 1 . 
           [0011]      FIG. 3  is a plan view of a coupling tab according to an embodiment of the present invention. 
           [0012]      FIG. 4A  is a schematic sectional view taken along a line  4   a - 4   a ′ of  FIG. 3 . 
           [0013]      FIG. 4B  is a schematic sectional view taken along a line  4   b - 4   b ′ of  FIG. 3 . 
           [0014]      FIG. 5  is a schematic perspective view illustrating a relation between a coupling tab and welding rods. 
           [0015]      FIG. 6  is a schematic sectional view illustrating a welding process in which a coupling tab is welded by welding rods. 
           [0016]      FIG. 7A  is a first modified example of an embodiment as illustrated in  FIG. 4A . 
           [0017]      FIG. 7B  is a second modified example of an embodiment as illustrated in  FIG. 4B . 
           [0018]      FIG. 8  is a first modified example of an embodiment as illustrated in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. 
         [0020]      FIG. 1  is a schematic perspective view of a battery pack  1  according to an embodiment of the present invention.  FIG. 2  is a partially exploded and enlarged perspective view of  FIG. 1 . 
         [0021]    According to an embodiment, the battery pack  1  includes a plurality of secondary batteries  10  and a case  100 . The secondary batteries  10  may form a rechargeable battery assembly. In this regard, each secondary battery  10  may be, for example, a nickel-cadmium (Ni—Cd) battery, a nickel-hydrogen (Ni—MH) battery, or a lithium (Li) secondary battery. Lithium ion secondary batteries typically have operation voltages about three times higher than those of nickel-cadmium batteries, which are generally used as power sources for portable electronic devices, and those of nickel-hydrogen batteries. Lithion ion secondary batteries generally have high energy density per unit weight and can therefore be widely used. An output current and an output voltage of a single secondary battery  10  may be increased by connecting a plurality of secondary batteries in series or parallel. In this regard, the shape of the secondary batteries  10  may be rectangular or cylindrical. 
         [0022]    Referring to  FIG. 2 , although the shape of the embodiment of the present invention is described as cylindrical secondary batteries, the shape of the secondary batteries  10  is not limited thereto. Each of secondary batteries  10  may include terminals  10   a  and  10   b  at both ends for electrical contacts to the external device. However, the location of the terminals  10   a  and  10   b  on the secondary battery may not be limited to the embodiments illustrated in  FIG. 1  or  2 . For example, the cylindrical or rectangular secondary batteries  10  may include the terminals  10   a  and  10   b  on an end or a side surface thereof for an electric contact with the external device. 
         [0023]    The disposition direction of the secondary battery  10  may vary. Referring to  FIG. 1 , every four secondary batteries  10  are disposed in the same direction according to an embodiment. However, the disposition direction is not limited thereto. For example, the secondary batteries  10  may be disposed in alternative directions in every two or six secondary batteries. 
         [0024]    The case  100  may include an upper case  100 A and a lower case  100 B. In this regard, the case  100  may accommodate the secondary batteries  10  therein or pull the secondary batteries  10  therefrom by coupling or separating of the upper case  100 A and the lower case  100 B as illustrated in  FIG. 2 . The case  100  may include a material that does not conduct electricity, such as plastic. Alternatively, the case  100  may have a frame including metal such as aluminum, and a surface of the frame may be coated with a material that insulates electricity. In this regard, the upper case  100 A and the lower case  100 B may include plates  100 A 1  and  100 B 1 , side walls  100 A 2  and  100 B 2 , and guide rails  100 A 3  and  100 B 3 , respectively. In this regard, the plates  100 A 1  and  100 B 1 , the side walls  100 A 2  and  100 B 2 , and the guide rails  100 A 3  and  100 B 3  may be coupled together by a separable component or may be integrated to form one body. In this regard, the upper case  100 A and the lower case  100 B may be symmetrical to each other. 
         [0025]    Referring to  FIG. 2 , the plates  100 A 1  and  100 B 1  each have holes h according to an embodiment. In this regard, the hole h may be formed to corresponding with the ends of the secondary batteries  10 . Accordingly, the terminals  10   a  and  10   b  of each secondary battery  10  may be electrically connected through the holes h of the plates  100 A 1  and  100 B 1  with the external device. In addition, the secondary batteries  10  may be connected in series or parallel through the hole h. 
         [0026]    As described above, the cases  100 A and  100 B respectively including the plates  100 A 1  and  100 B 1 , side walls  100 A 2  and  100 B 2 , and guide rails  100 A 3  and  100 B 3  may be coupled to the secondary batteries  10 . In addition, the coupled secondary batteries  10  may be connected to each other in series or parallel by connecting the coupling tab  200  to the terminals  10   a  and  10   b  of the secondary battery  10 . In this regard, the coupling tab  200  may be coupled to the terminals  10   a  and  10   b  of the secondary battery  10  by welding. For example, the coupling tab  200  may be coupled to the terminals  10   a  and  10   b  of the secondary battery  10  by resistance welding. The resistance welding may be performed by using, for example, a projection melding method. The projection welding may be, for example, performed in a way that the current passage is restricted by the shape of a structure of the parts being welded, such as an embossed shape. 
         [0027]      FIG. 3  is a plan view of the coupling tab  200  according to an embodiment of the present invention.  FIG. 4A  is a schematic sectional view taken along a line  4   a - 4   a ′ of  FIG. 3 .  FIG. 4B  is a schematic sectional view taken along a line  4   b - 4   b ′ of  FIG. 3 .  FIG. 5  is a schematic perspective view illustrating a relation between the coupling tab  200  and welding rods  300  and  310 .  FIG. 6  is a schematic sectional view illustrating a welding process in which the coupling tab  200  is welded to the terminal  10   a  of the secondary battery  10  using welding rods. 
         [0028]    With respect to the welding process, a side surface of an embossing portion could be easily destroyed after the welding. When the side surface of the embossed portion is destroyed after welding, tension may be reduced although a nugget is formed. To solve this problem, according to an embodiment of the present invention, the coupling tab  200  can have a structure such that the strength of adherence between the coupling tab  200  and the terminals  10   a  and  10   b  may increase and destruction of the side surface of the embossed portion after welding may decrease. Referring to  FIG. 3 , illustrating a plan view of the coupling tab  200  according to an embodiment of the present invention, the coupling tab  200  may have welding portions  210  that have an oval shape. One welding portion  210  and another welding portion  210  may be separated by a slit S. According to an embodiment of the present invention, the coupling tab  200  may have, for example, a letter ‘H’ shape as illustrated in  FIG. 3 . Referring to  FIG. 3 , the coupling tab  200  may include four welding portions  210  and a slit S may be formed between neighboring welding portions  210 . 
         [0029]    The welding portion  210  may include a first plane  210   a  and an inclined plane  210   b.  A circumference of the welding portion  210  may have an oval shape in a plan view thereof, and the first plane  210   a  inside the oval structure may be rectangular and may be formed inside the welding portion  210 . In this regard, ends of the welding rods  300  and  310  may contact the first plane  210   a  of the coupling tab  200 , and the inclined plane  210   b  can safely guide the welding rods  300  and  310  to the first plane  210   a.    
         [0030]    The rectangular first plane  210   a  can have a length of a first direction x and a length of a second direction y, respectively referred to as a and b. In this regard, the first plane  210   a  can extend along the first direction x and thus have a degree of freedom so that the welding rods  300  and  310  contacting the first plane  210   a  are moveable. If the first plane  210   a  is quadrilateral or circular, the degree of freedom for movement of the welding rods  300  and  310  would be limited and thus automatic or manual movement of the welding rods  300  and  310  would require a higher level of control. If the welding rods  300  and  310  and the coupling tab  200  are misaligned or have contact errors with respect to each other, a side surface of an embossed portion could be destroyed. Accordingly, the extension of the first plane  210   a  in the first direction x can allow for a higher degree of freedom of the welding rods  300  and  310 , and thus stability can be improved. For example, referring to  FIG. 5 , the welding rods  300  and  310  can have a degree of freedom such that when the welding rod  300  contacts the coupling tab  200 , the welding rod  300  can move along the first direction x. Thus, even when the welding rods  300  and  310  are misaligned within the margins of error, structurally, the position error of the welding rods  300  and  310  may be controlled. In this regard, for example, a ratio of a, the length of the first plane  210   a  in the first direction x to b, the length of the first plane  210   a  in the second direction y may be in the range of about 1.5:1 to 3:1. For example, the ratio of a to b may be about 1.7:1. 
         [0031]    In this regard, having the extension direction of the first plane  210   a  in the first direction x may be advantageous compared to having the direction in the second direction y. This is because the distance t between the welding portion  210  and an edge of the coupling tab  200  should ensure a predetermined length or more for safety reasons. If the first plane  210   a  extends in a direction of the second direction y, it may be difficult to retain t, the distance between the welding portion  210  and the edge of the coupling tab  200 , to be a predetermined value or more. Accordingly, the first plane  210   a  may extend in the first direction x. 
         [0032]    In addition, the first plane  210   a  may be a plane having a straight line. When the first plane  210   a  is a plane having a straight line, the ends of the welding rods  300  and  310  may properly contact the first plane  210   a.  If the first plane  210   a  is curved, the first plane  210   a  and the welding rods  300  and  310  may have a contact error and thus a side surface of an embossed portion may be easily destroyed after welding. In this regard, a second surface  210   c  of the coupling tab  200  disposed in an opposition direction (−z) to a third direction may also be a flat plane. Due to the flat plane surface of the second surface  210   c,  it can be ensured that the coupling tab  200  contacts the terminals  10   a  and  10   b  of the secondary battery  10 . That is, the coupling tab  200  can contact the surface of the terminals  10   a  and  10   b  such that the coupling tab  200  does not slide with respect to the terminals  10   a  and  10   b.    
         [0033]    Hereinafter, a slit S formed between the welding portions  210  according to embodiments will be described in detail. Referring to  FIG. 6 , the coupling tab  200  may contact the terminal  10   a,  and electricity having a predetermined current and voltage is provided to the coupling tab  200  from the first welding rod  300  and the second welding rod  310 , thereby flowing a current from a first spot A 1  to second spot A 2  of the coupling tab  200 , that is, along passage A as shown in  FIG. 6 . In this regard, heat may occur by resistance generated between the coupling tab  200  and the terminal  10   a,  and thus welding can be performed. If the slit S is not formed, a current can flow from the first spot A 1  to the second spot A 2 , that is, an opposition direction (−y) of the second direction, and the flowing current may be a wattless current that does not affect welding. Since a space may be formed between the first spot A 1  and the second spot A 2  by the slit S and thus a current can flow along passage A, a wattless current may be decreased due to the slit S. In addition, referring to  FIG. 3 , the slit S may be formed to extend in the first direction x, and thus, passage B may be formed to be longer than passage A, thereby inducing a current to flow along passage A, not passage B. That is, since a current is likely to flow along a shorter passage and the B passage extends in the first direction x by the slit S, a current at the first spot A 1  may be induced to flow through passage A, not passage B. In this regard, in  FIG. 3 , a ratio of a width c of the slit S to a distance d between a center of the welding portion  210  and a split point of the slit S may be in the range of about 1:3 to 1:10, for example, about 1:6.5. However, the ratio of c:d may not be limited thereto. 
         [0034]    Accordingly, wattless currents flowing in other directions can be reduced and thus more current can flow along the passage A. Since a large amount of current flows along passage A, an electric resistance between the welding portion  210  and the terminal  10   a  can be increased and more heat can be generated. In this regard, a welding clump formed by fusing the welding portion  210  with the terminal  10   a  by heat dissipation, that is, a large welding nugget can be formed. In this regard, the amount of heat of the welding portion  210  may be proportional to a square of the current flowing from the welding rods  300  and  310 . Accordingly, since the coupling tab  200  may be welded to the terminal  10   a  by a large welding nugget with a high welding strength, the coupling tab  200  may be more strongly welded to the terminal  10   a.    
         [0035]    In this regard, the coupling tab  200  may be formed of, for example, a conductive metal including any one kind of metal or a plurality of metals selected from the group consisting of nickel, nickel alloy, iron, iron alloy, stainless, zinc, zinc alloy, copper, copper alloy, silver, silver alloy, gold, gold alloy, platinum, platinum alloy, aluminum, aluminum alloy, molybdenum, molybdenum alloy, tungsten, tungsten alloy, titanium, titanium alloy, beryllium, berylium alloy, rhodium, and rhodium alloy. 
         [0036]    With reference to  FIG. 7A  or  7 B, modified examples of an embodiment of the present invention will be described in detail.  FIG. 7A  is a first modified example of the embodiment illustrated in  FIG. 4A , and  FIG. 7B  is a second modified example of the embodiment illustrated in  FIG. 4B . Referring to  FIG. 7A  or  7 B, the welding portion  210  may include the first plane  210   a  and the inclined surface  210   b,  and the third surface  210   d  disposed in an opposition direction (−z) to the third direction of the coupling tab  200 . The third surface  210   d  may be curved. In this regard, when the curved third surface  210   d  is welded to the terminal  10   a  by a resistance, the third surface  210   d  may have a planar shape corresponding to the shape of the terminal  10   a.    
         [0037]    Although the coupling tab  200  having a letter ‘H’ shape is illustrated in  FIG. 3 , the shape of the coupling tab  200  is not limited thereto. For example, two coupling tabs  200  may be connected to each other by a connection portion C.  FIG. 8  is a first modified example of the embodiment illustrated in  FIG. 2 . In this regard, the coupling tab  200  may have various shapes according to the number and arrangement of the secondary batteries  10  included in a battery pack ( 1 ), and the coupling tab  200  may be welded to the secondary battery  10  through various numbers of the welding portions  210 , and the location of the welding portions of the coupling tab  200  may vary. 
         [0038]    During welding, the welding current amount, current flowing time, and a pressure between the welding rods  300  and  310  and the coupling tab  200  may be variously controlled. 
         [0039]    It should be understood that certain embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.