Abstract:
A battery pack is disclosed. The battery pack includes at least two battery cells to provide a high capacity battery pack. The battery pack includes a single PCM assembly controlling at least two battery cells to decrease inferiority due to overcharge and overdischarge. Since a connector tab electrically connecting at least two battery cells to a single PCM assembly is provided, contacts are not separated during the swelling of the battery cells to prevent contact inferiority. A top case and a bottom case are provided to be coupled with at least two battery cells to maintain a secure coupling between the at least two battery cells.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/074,549, filed Jun. 20, 2008, entitled BATTERY PACK, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery pack, and more particularly, to a battery pack having at least two battery cells in order to satisfy consumers demanding a high capacity battery pack. 
     2. Description of the Related Art 
     Recently, industries related to electronics, communications, computers, and the like are developing rapidly and due to the rapid development, there is an impatient demand for development of a reliable and high capacity small sized secondary battery. 
     Especially, the secondary battery must satisfy a demand from a mobile communication market for a small sized battery, a light weight battery, a long life battery, etc. For this reason, consumer demand for an extended capacity secondary battery is increasing. 
     To achieve the high capacity of the battery, there are possibly several proposals such as increasing the size of cells and connecting a plurality of cells to each other within a single battery pack. The proposal of increasing the size of cells is retrogressive in that it represents a less efficient solution. Therefore, there is a need for using a plurality of cells within a single battery pack and improving the performance of the battery pack. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems, and the present invention provides a battery pack including at least two battery cells. 
     The present invention also provides a battery pack including a protection circuit module (PCM) assembly capable of controlling charge and discharge of at least two battery cells. 
     The present invention also provides a battery pack including a connection tab connecting at least two battery cells to a protection circuit module assembly. 
     The present invention also provides a battery pack including a top case and a bottom case that are coupled with at least two battery cells. 
     The battery pack may include at least two battery cells to provide a high capacity battery pack. 
     The battery pack may include a single PCM assembly controlling at least two battery cells to decrease inferior performance due to overcharge and overdischarge. 
     Since a connector tab electrically connecting at least two battery cells to a single PCM assembly may be provided, the connector tab may be configured so as not to be separated during the swelling of the battery cells to prevent inferior contact. 
     A top case and a bottom case may be provided to be coupled with at least two battery cells to maintain a secure coupling between the at least two battery cells. 
     One aspect of the invention comprises a battery assembly comprising a first battery cell, a second battery cell wherein the first and second battery cells are mounted adjacent each other, a protection circuit module that is electrically coupled to the first and second battery cells, and at least one connector tab that includes a protection circuit mounting portion and a first and second battery cell mounting portions wherein the protection circuit module is coupled to the protection circuit mounting portion and the first and second battery cells are coupled to the first and second battery cell mounting portions and wherein the protection circuit mounting portion is displaced in a first direction from the first and second battery cell mounting portions. 
     Another aspect of the invention comprises a method of assembling a battery pack, the method comprising positioning a first and a second battery cell adjacent each other; and electrically coupling the first and second battery cells together and to a protection circuit with at least one connector tab, wherein the at least one connector tab includes a protection circuit mounting portion and a first and second battery cell mounting portions wherein the first and second battery cells and the protection circuit are mounted to the at least one connector tab so that the protection circuit is offset from the first and second battery cells in a first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating an external appearance of a battery pack according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view illustrating the battery pack in  FIG. 1 ; 
         FIG. 3  is a sectional view of the battery pack taken along the line III-III in  FIG. 1 ; 
         FIG. 4  is a perspective view illustrating a connector tab employed in the battery pack according to the embodiment of the present invention; 
         FIGS. 5A to 5H  are perspective views illustrating an assembling process of the battery pack according to the embodiment of the present invention; 
         FIG. 6A  is a sectional view illustrating main parts of the battery pack according to the embodiment of the present invention; 
         FIG. 6B  is a sectional view illustrating a swelling occurring in the battery pack in  FIG. 6A ; 
         FIG. 7  is a sectional view illustrating main parts of a battery pack according to another embodiment of the present invention; and 
         FIG. 8  is a sectional view illustrating main parts of a battery pack according to still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Referring to  FIGS. 1 to 4 , a battery pack  100  according to an embodiment of the present invention includes a first battery cell  110 , a second battery cell  120  electrically connected to the first battery cell  110 , a protection circuit module (PCM) assembly  130  electrically connected to the first battery cell  110  and the second battery cell  120 , a top case  150  accommodating the PCM assembly  130  and coupled to tops of the first and second battery cells  110  and  120 , a bottom case  160  coupled to the lower sides of the first and second battery cells  110  and  120 , and a label  170  wrapping lateral sides of the first and second battery cells  110  and  120 . 
     The battery pack  100  further includes connector tabs  140  and  140 ′ electrically connecting the PCM assembly  130  to the first battery cell  110  and the second battery cell  120 . 
     Each of the first battery cell  110  and the second battery cell  120  has an approximate hexahedron. However, the shapes of the first and second battery cells  110  and  120  are not limited to the hexahedron. From tops  110   a  and  120   a  of the first and second battery cells  110  and  120 , negative terminals  111  and  121  respectively protrude outwardly. The lateral sides of the first and second battery cells  110  and  120  include two wide lateral sides  110   b  and  120   b  and two narrow lateral sides  110   c  and  120   c  that face each other. Bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120  are integrally formed with the wide lateral sides  110   b  and  120   b  and the narrow lateral sides  110   c  and  120   c.    
     The first battery cell  110  and the second battery cell  120  are bonded to each other in a way that one of the wide lateral sides  110   b  and one of the wide lateral sides  120   b  are facing and are bonded to each other. In this case, a spacer such as an insulator tape  180  is interposed between the wide lateral side  110   b  of the first battery cell  110  and the wide lateral side  120   b  of the second battery cell  120 . Preferably, the insulator tape  180  is a double-sided adhesive tape. 
     The insulator tape  180  has a through-hole  181  formed in the middle thereof. Preferably, the through-hole  181  has a rectangular shape, but its shape is not limited thereto. A space defined by the through-hole  181  acts as an escaping or release space that is preferably sized so as to accommodate the increased thicknesses of the first and second battery cells  110  and  120  occurring as a result of swelling of the battery cells  110 ,  120 . 
     The PCM assembly  130  includes a circuit board  131 , an electric device  132  installed on the circuit board  131 , and an external terminal  133  conducting current from the battery cells to the outside. 
     The circuit board  131  has a rectangular shape with a width corresponding to the tops  110   a  and  120   a  of the two battery cells  110  and  120 . The circuit board  131  has electrode through-holes  131   a  and  131   b  such that the negative terminal  111  of the first battery cell  110  and the negative terminal  121  of the second battery cell  120  are electrically connected to a negative terminal (not shown) of the circuit board  131 . The circuit board  131  has cutaway portions  131   c  formed at four corners. Each of the cutaway portions  131   c  has an arc shape but the shape is not limited thereto. The cutaway portions  131   c  are formed to enable laser welding of the connector tabs  140  and  140 ′ to the tops of the battery cells  110  and  120 . Any shape enabling the laser welding may be employed in the cutaway portions  131   c . Further, the overall configuration of the circuit board  131  may be selected to permit access to perform the laser welding of the connector tabs  140 ,  140 ′. 
     The connector tabs  140  and  140 ′ include board connection portions  141  and  141 ′ installed on the circuit board  131 , first cell connection portions  144  and  144 ′ connected to the first battery cell  110 , second cell connection portions  145  and  145 ′ connected to the second battery cell  120 , first connectors  142  and  142 ′ connecting the board connection portions  141  and  141 ′ to the first cell connection portions  144  and  144 ′, and second connectors  143  and  143 ′ connecting the board connection portions  141  and  141 ′ to the second cell connection portions  145  and  145 ′. 
     Thus, the circuit board  131  is supported by the first connector tab  140  and the second connector tab  140 ′ to be placed on the tops  110   a  and  120   a  of the first battery cell  110  and the second battery cell  120 . 
     Since the structure of the first connector tab  140  is identical to that of the second connector tab  140 ′, hereinafter the first connector tab  140  only will be described in detail. The board connection portion  141  is parallel to the circuit board  131 . The first connector  142  and the second connector  143  are integrally formed with the lower sides of the lateral edges of the board connection portion  141 . The first cell connection portion  144  is integrally formed with an edge of the first connector  142  and the second connection portion  145  is integrally formed with an edge of the second connector  143 . The first and second connection portions  144  and  145  are formed at the edges of the first and second connectors  142 , 143  to face each other by interposing the board connection portion  141  therebetween. 
     Thus, the circuit board  131  is electrically connected to the two battery cells  110  and  120  at once by the connector tabs  140  and  140 ′. In this configuration, the first battery cell  110  is connected in parallel to the second battery cell  120 . 
     The first connector tab  140  and the second connector tab  140 ′ electrically connect positive terminals of the first and second battery cells  110  and  120  (surfaces of the battery cells) to a positive terminal (not shown) of the circuit board  131 . In this case, at least one of the first and second connector tabs  140  and  140 ′ connects the first and second battery cells  110  and  120  to the circuit board  131 . Preferably, the first and second connector tabs  140  and  140 ′ are made of nickel or nickel alloy with good electrical conductivity, but are not limited thereto. Thus, any one of the first and second connector tabs  140  and  140 ′, which electrically connects the battery cells  110  and  120  to the circuit board  131 , may be made of the nickel with good electrical conductivity and the other may not be made of an electrical conductor. 
     The top case  150  includes a case body  151  and right and left frames  152  and  153 . The case body  151  has a hexahedron shape with an internal space accommodating the PCM assembly  130 , and the right and left frames  152  and  153  are integrally formed with right and left ends of the case body  151 . The case body  151  includes a single planar surface  151   a  and four lateral sides  151   b  extending from the planar surface  151   a . The planar surface  151   a  has external terminal through-holes  151   c  formed at a side and a water-sensitive label attachment  151   d  formed at the other side. Guide ribs  151   e  to which the label  170  is attached extend downwardly from the four lateral sides  151   b . The right and left frames  152  and  153  are formed at the case body  151  in the vertical direction. The right and left frames  152  and  153  have protrusions  152   a  and  153   a  formed at inner middle portions thereof respectively. The protrusions  152   a  and  153   a  are formed in the longitudinal directions of the right and left frames  152  and  153 . The protrusions  152   a  and  153   a  are inserted into gaps G defined by the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120  that are adhered to each other. 
     The bottom case  160  includes a case body  161  and right and left frames  162  and  163 . The case body  161  has a rectangular shape with a size sufficient to accommodate the bottoms of the first and second battery cells  110  and  120 , and the right and left frames  162  and  163  are integrally formed with right and left edges of the case body  161 . The case body  161  includes a single planar surface  161   a  and both lateral sides  161   b  extending from an edge of the planar surface  161   a . Guide ribs  161   e  to which the label  170  is attached extend from the lateral sides  161   b . The right and left frames  162  and  163  are formed at the case body  161  in the vertical direction. The right and left frames  162  and  163  have protrusions  162   a  and  163   a  formed at inner middle portions thereof respectively. The protrusions  162   a  and  163   a  may be formed in the longitudinal directions of the right and left frames  162  and  163 . The protrusions  162   a  and  163   a  are inserted into gaps G defined by the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120  that are adhered to each other. 
     Grooves  152   b  and  153   b  are formed at ends of the right and left frames  152  and  153  of the top case  150  respectively. Protrusions  162   b  and  163   b  are formed at ends of the right and left frames  162  and  163  of the bottom case  160  to be inserted into the grooves  152   b  and  153   b  respectively. The grooves  152   b  and  153   b  and the protrusions  162   b  and  163   b  may have any shapes enabling male-female coupling. 
     The label  170  is attached to wrap a circumference of an assembly of the first and second battery cells  110  and  120 , the top case  150 , and the bottom case  160  at least one turn. Thus, the first and second battery cells  110  and  120  are securely assembled such that the wide lateral sides  110   b  and  120   b  are bonded to each other with the insulation tape  180  and are wrapped by the label  170 . The label  170  is made of insulator and insulates the first and second battery cells  110  and  120  from the external device. 
     An upper end of the label  170  wraps the guide ribs  151   e  of the top case  150  and a lower end of the label  170  wraps the guide ribs  161   c  of the bottom case  160 . Thus, the top case  150  and the bottom case  160  are coupled with the first and second battery cells  110  and  120  by the label  170 . 
     The tops  110   a  and  120   a  of the first and second battery cells  110  and  120  are adhered with a second insulator tape  190 . Due to the second insulator tape  190 , the first and second battery cells  110  and  120  are insulated from the PCM assembly  130 . 
     The bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120  are adhered with an adhesive tape  195 . The adhesive tape  195  securely adheres to the first battery cell  110  and the second battery cell  120 . Moreover, the adhesive tape employs a double-sided tape. Thus, due to the adhesive tape  195 , the bottom case  160  can be securely adhered to the bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120 . 
     An assembling process of the battery pack according to the embodiment of the present invention will be described. 
     1. Attach the First Battery Cell and the Second Battery Cell with the Insulator Tape. 
     Referring to  FIG. 5A , when one wide lateral side  110   b  of the first battery cell  110  faces one wide lateral side  120   b  of the second battery cell  120 , the insulator tape  180  is interposed therebetween and the first and second battery cells  110  and  120  are closely adhered to each other. Thus, the first and second battery cells  110  and  120  are adhered to each other while maintaining a space between the battery cells corresponding to the thickness of the insulator tape  180 . The insulator tape  180  has the through-hole  181 . The through-hole  181  corresponds to an approximate middle portion where the battery cells swell during the charge of the battery cells. In general, when a battery cell is charged approximately 500 times, a thickness increases by about 10% of the initial thickness. Even a battery cell repeatedly charged several times can escape through the through-hole of the insulator tape  180  as much as the increased thickness. Thus, the first battery cell  110  and the second battery cell  120  are less likely to push each other while maintaining the assembled state. 
     2. Adhere the Second Insulator Tape to the Tops of the First and Second Battery Cells. 
     Referring to  FIG. 5B , the second insulator tape  190  is adhered to the tops  110   a  and  120   a  of the first and second battery cells  110  and  120  to cover the tops  110   a  and  120   a.    
     The tops  110   a  and  120   a  of the first and second battery cells  110  and  120  function as positive electrodes. Thus, the second insulator tape  190  inhibits shorting with other elements. 
     3. Place the PCM Assembly on the Tops of the First and Second Battery Cells to be Welded. 
     Referring to  FIG. 5C , the PCM assembly  130  is welded to the first connector tab  140  and the second connector tab  140 ′. Firstly, the board connection portions  141  and  141 ′ of the connector tabs  140  and  140 ′ are welded to the bottom of the circuit board  131 . And, the first and second cell connection portions  144 ,  145 ,  144 ′, and  145 ′ of the connector tabs  140  and  140 ′ are placed on the tops  110   a  and  120   a  of the first and second battery cells  110  and  120  respectively. 
     The PCM assembly  130  is welded to the battery cells such that the first and second cell connection portions  144  and  145  of the first connector tab  140  and the first and second cell connection portions  144 ′ and  145 ′ of the second connector tab  140 ′ are welded to the tops  110   a  and  120   a  of the first and second battery cells  110  and  120  by means of a laser. In this case, the first and second cell connection portions  144  and  145  of the first connector tab  140  and the first and second cell connection portions  144 ′ and  145 ′ of the second connector tab  140 ′ are exposed through the cutaway portions  131   c  formed at the four corners of the circuit board  131  so that the laser welding can be carried out. 
     Cases of the first and second battery cells  110  and  120  may be made of aluminum (Al) and the first and second connector tabs  140  and  140 ′ may be made of nickel (Ni). Aluminum and nickel allow excellent laser welding. 
     4. Adhere the Adhesive Tape to the Bottoms of the First and Second Battery Cells. 
     Referring to  FIG. 5D , a single adhesive tape  195  is adhered to the bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120 . Thus, the first and second battery cells  110  and  120  maintain a securely bonded state. 
     5. Couple the Bottom Case. 
     Referring to  FIG. 5E , the bottom case  160  is coupled with the lower sides of the first and second battery cells  110  and  120 . The case body  161  of the bottom case  160  supports the bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120 . The right and left frames  162  and  163  of the bottom case  160  support the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120 . The protrusions  162   a  and  163   a  of the right and left frames  162  and  163  are inserted into the gaps G defined between the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120 . The protrusions  162   a  and  163   a  closely contact the first and second battery cells  110  and  120  to prevent movement of the case body  161 . 
     The bottom case  160  maintains adhesion to the first and second battery cells  110  and  120  by means of the double-sided tape, which is the adhesive tape  195  adhered to the bottoms  110   d  and  120   d  of the first and second battery cells  110  and  120 . 
     6. Couple the Top Case. 
     Referring to  FIG. 5F , the top case  150  is coupled with the tops of the first and second battery cells  110  and  120  on which the PCM assembly  130  is placed. 
     The case body  151  of the top case  150  is placed on the top of the PCM assembly  130 . The right and left frames  152  and  153  of the top case  150  support the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120 . Protrusions  152   a  and  153   a  of the right and left frames  152  and  153  are inserted into the gaps G defined between the narrow lateral sides  110   c  and  120   c  of the first and second battery cells  110  and  120  to inhibit movement of the case body  151 . 
     The top case  150  is coupled with the bottom case  160 . The protrusions  162   b  and  163   b  formed at the ends of the right and left frames  162  and  163  of the bottom case  160  are inserted into the grooves  152   b  and  153   b  formed at the ends of the right and left frames  152  and  153  of the top case  150 , so that male-female coupling is established. 
     7. Attach the Label. 
     Referring to  FIG. 5G , the label  170  fully wraps the circumference of the first and second battery cells  110  and  120  at least one turn. The right and left frames  152 ,  153 ,  162 , and  163  of the top case  150  and the bottom case  160  fill up the gaps G between the first and second battery cells  110  and  120 . When the label  170  is wrapped, the right and left frames  152 ,  153 ,  162 , and  163  of the top case  150  and the bottom case  160  support the label  170 . 
     An upper end of the label  170  is attached to the guide ribs  151   e  of the top case  150  to fix the top case  150  to the first and second battery cells  110 . A lower end of the label  170  is attached to the guide ribs  161   c  of the bottom case  160  to fix the bottom case  160  to the first and second battery cells  110  and  120 . 
     8. Attach the Water-Sensitive Label. 
     Referring to  FIG. 5H , the water-sensitive label  175  is attached to the water-sensitive label attachment  151   d  formed on the top of the top case  150 . In this implementation, the label  175  is a water sensitive label that turns color when the battery is exposed to water. In this way, the cause of failure of the device using the battery can be determined, e.g., the label can tell if an electronic device, such as a mobile phone, has been immersed in water. 
     As described above, in the assembled battery pack according to the embodiment of the present invention, the two battery cells are controlled by the single PCM assembly during the charge and discharge so that inferior performance caused by overcharge and overdischarge is reduced. 
     The first and second battery cells  110  and  120  are electrically connected to the PCM assembly  130  such that the negative terminals  111  and  121  of the battery cells  110  and  120  are electrically connected to negative terminals (not shown) of the circuit board  131 . The first and second battery cells  110  and  120  are electrically connected to positive terminals (not shown) of the circuit board  131  by the first and second connector tabs  140  and  140 ′. 
     On the tops of the first and second battery cells  110  and  120 , the connector tabs  140  and  140 ′ support the PCM assembly  130 . The connector tabs  140  and  140 ′ respectively have a bridge shape in which the board connection portions  141  and  141 ′, the first and second connection portions  142 ,  142 ′,  143 , and  143 ′, the first cell connection portions  144  and  144 ′, and the second cell connection portions  145  and  145 ′ are integrally formed with each other. 
     Although the connector tabs  140  and  140 ′ of the battery pack  100  according to the embodiment of the present invention respectively are configured such that vertical relationships between the board connection portions  141  and  141 ′, and the first and second connection portions  142 ,  142 ′,  143 , and  143 ′ and the first and second cell connection portions  144 ,  144 ′,  145 , and  145 ′ are established, another relationship may be possible. 
     A battery pack according to another embodiment of the present invention will be described. 
       FIGS. 6A and 6B , a battery pack  200  according to another embodiment of the present invention includes a first battery cell  110  and a second battery cell  120  electrically connected to the first battery cell  110 , a protection circuit module (PCM) assembly  130  electrically connected to the first and second battery cells  110  and  120 , a top case  150  accommodating the PCM assembly  130  and coupled to tops of the first and second battery cells  110  and  120 , a bottom case  160  coupled to the lower sides of the first and second battery cells  110  and  120 , and a label  170  wrapping lateral sides of the first and second battery cells  110  and  120 . This configuration is substantially the same to that of the battery pack  100  according to the embodiment of the present invention. The same reference numerals are assigned to the same elements and their description will be omitted. 
     The battery pack  200  according to another embodiment of the present invention includes a connector tab, different from that of the battery pack  100  according to the previous embodiment of the present invention, electrically connecting the first and second battery cells  110  and  120  to the PCM assembly  130 . The connector tab includes first and second connector tabs supporting both ends of the PCM assembly  130 . Since the first and second connector tabs are identical to each other, a single connector tab  240  only will be described. 
     The connector tab  240  in another embodiment of the present invention includes a board connection portion  241  installed in the PCM assembly  130 , a first cell connection portion  244  connected to the first battery cell  110 , a second cell connection portion  245  connected to the second battery cell  120 , a first connection portion  242  connecting the board connection portion  241  to the first cell connection portion  244 , and a second connection portion  243  connecting the board connection portion  241  to the second cell connection portion  245 . 
     The board connection portion  241  is parallel to the PCM assembly  130 . The first and second connection portions  242 ,  243  are downwardly formed at edges of the board connection portion  241  in the vertical direction to the board connection portion  241 . 
     The first cell connection portion  244  is integrally formed with an edge of the first connection portion  242  or a slope portion  246  as described below, and the second cell connection portion  245  is integrally formed with an edge of the second connection portion  243  or a slope portion  247  as described below. The first and second cell connection portions  244  and  245  oppositely run from the edges of the first and second connection portions  242  and  243  with respect to the board connection portion  241 . 
     In another embodiment of the present invention, a slope portion  246  is formed between the first connection portion  242  and the first cell connection portion  244  and a slope portion  247  is formed between the second connection portion  243  and the second cell connection portion  245 . The slope portions  246  and  247  extend from the lower sides of the first and second connection portions  242  and  243  to the first and second cell connection portions  244  and  245  at a preset angle Θ. Preferably, the angle Θ is approximately 20 degrees to 70 degrees. 
     Operation of the battery pack according to another embodiment of the present invention will be described. 
     In the battery pack  200  according to another embodiment of the present invention, when the first and second battery cells  110  and  120  swell, the first and second battery cells  110  and  120 , as illustrated in  FIG. 6B , are spaced away from each other with respect to the insulator tape  180 . 
     In this case, the connector tab  240  is deformed such that the first and second connection portions  242  and  243  are moved apart from the edges of the board connection portion  241  by the slopes  246  and  247 . 
     The connection portions  242  and  243  of the connector tab  240  moved away from each other as the gap, between the battery cells, increases due to the swelling of the first and second battery cells  110  and  120 . Thus, the first and second cell connection portions  244  and  245  of the connector tab  240  are less likely to be separated from the tops  110   a  and the  120   a  of the first and second battery cells  110  and  120 , so that the welded state can be maintained and the inferior welds do not occur. 
     When the angle Θ of the slopes  246  and  247  is less than 20 degrees, since an angle between each of the connection portions  242  and  243  and each of the slopes  246  and  247  is small and the connection portions  242  and  243  do not substantially spread, the first and second cell connection portions  244  and  245  are more likely to be separated from the tops  110   a  and  120   a  of the first and second battery cells  110  and  120 . Moreover, when the angle Θ of the slopes  246  and  247  is greater than 70 degrees, since an angle between each of the first and second cell connection portions  244  and  245  and each of the slopes  246  and  247  is small and the connection portions  242  and  243  do not spread, the first and second cell connection portions  244  and  245  are more likely to be separated from the tops  110   a  and  120   a  of the first and second battery cells  110  and  120 . 
     A battery pack  300  according to still another embodiment of the present invention will described as follows. 
     Referring to  FIG. 7 , since the battery pack  300  according to still another embodiment of the present invention is established by a connector tab, the battery pack  300  will be described by concentrating on the connector tab. 
     A connector tab  340  in the battery pack  300  according to still another embodiment of the present invention includes a board connection portion  341  installed in the PCM assembly  130 , a first cell connection portion  344  electrically connected to the first battery cell  110 , a second cell connection portion  345  electrically connected to the second battery cell  120 , a first connection portion  342  electrically connecting the board connection portion  341  to the first cell connection portion  344 , and a second connection portion  343  electrically connecting the board connection portion  341  to the second cell connection portion  345 . 
     The board connection portion  341  is parallel to the PCM assembly  130 . The first and second connection portions  342  and  343  are obliquely connected to edges of the board connection portion  341 . 
     The first cell connection portion  344  is integrally formed with an edge of the first connection portion  342 , and the second cell connection portion  345  is integrally formed with an edge of the second connection portion  343 . The first and second cell connection portions  344  and  345  oppositely run from the edges of the first and second connection portions  342  and  343  with respect to the board connection portion  341 , respectively. 
     In the connector tab  340  of the battery pack  300  according to still another embodiment of the present invention, the first and second connection portions  342  and  343  extend from the edges of the board connection portion  341  outwardly oblique to the vertical direction. In other words, the connector tab  240  of the battery pack  200  according to another embodiment of the present invention is configured such that the slopes  246  and  247  are formed at some portions of the first and second connection portions  242  and  243 , and in still another embodiment, the first and second connection portions  342  and  343  wholly form the slopes. 
     The first and second connection portions  342  and  343  extend from the edges of the board connection portion  341  toward the first and second cell connection portions  344  and  345  at a preset angle Θ, respectively. Preferably, the preset angle Θ ranges approximately from 20 degrees to 70 degrees. When the angle Θ is less than 20 degrees or greater than 70 degrees, a gap between the connection portions  342  and  343  does not increase in a case that an external force is exerted, so that the contact inferiority occurs. 
     Operation of the battery pack  300  according to still another embodiment of the present invention will be described. 
     In this embodiment, when the first and second battery cells  110  and  120  swell, the connector tab  340  spreads laterally with respect to the board connection portion  341 . 
     Thus, the first and second connection portions  342  and  343  of the connector tab  340  are moved away from each other as the gap increases due to the swelling of the first and second battery cells  110  and  120 . Consequently, the first and second cell connection portions  344  and  345  of the connector tab  340  are less likely to be separated from the tops  110   a  and  120   a  of the first and second battery cells  110  and  120  while maintaining the welded state, so that the contact inferiority does not occur. 
     A battery pack  400  according to still another embodiment of the present invention will be described. 
     Referring to  FIG. 8 , since the battery pack  400  according to still another embodiment of the present invention is established by a connector tab, the battery pack  400  will be described by concentrating on the connector tab. 
     A connector tab  440  in the battery pack  400  according to still another embodiment of the present invention includes a board connection portion  441  installed in the PCM assembly  130 , a first cell connection portion  444  electrically connected to the first battery cell  110 , a second cell connection portion  445  electrically connected to the second battery cell  120 , a first connection portion  442  electrically connecting the board connection portion  441  to the first cell connection portion  444 , and a second connection portion  443  electrically connecting the board connection portion  441  to the second cell connection portion  445 . 
     The board connection portion  441  is parallel to the PCM assembly  130 . The first and second connection portions  442  and  443  are rounded at edges of the board connection portion  441 . 
     The first cell connection portion  444  is integrally formed with an edge of the first connection portion  442 , and the second cell connection portion  445  is integrally formed with an edge of the second connection portion  443 . The first and second cell connection portions  444  and  445  oppositely run from the edges of the first and second connection portions  442  and  443  with respect to the board connection portion  441 , respectively. 
     The first and second connection portions  442  and  443  of the connector tab  440  are rounded. 
     The first and second connection portions  442  and  443  are respectively bent at the edges of the board connection portion  441  opposite to the positions where the first and second cell connection portions  444  and  445  and bent again from their middle portions toward the positions of the first and second cell connection portions  444  and  445 . 
     Even in the battery pack  400  employing the connector tab  400 , when the first and second battery cells  110  and  120  swell, the first and second connection portions  442  and  443  of the connector tab  400  spread in the lateral direction. 
     Thus, the first and second connection portions  442  and  443  of the connector tab  440  are moved apart from each other as the gap increase due to the swelling of the first and second battery cells  110  and  120 . Consequently, the first and second cell connection portions  444  and  445  of the connector tab  440  are less likely to be separated from the tops  110   a  and  120   a  of the first and second battery cells  110  and  120  while maintaining the welded state, so that the contact inferiority is prevented. 
     Although the embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and modifications of the basic inventive concept herein described will still fall within the spirit and scope of the present invention as defined in the appended claims.