Abstract:
A secondary battery and a battery pack using the same are provided. In the secondary battery, an electrode terminal extending from an electrode assembly is structurally and electrically connected to a lead tab to turn on a circuit, and if swelling arises, the lead tab coupled to a pouch case is spaced apart from the electrode terminal due to expansion of the pouch case to break the structural connection between the electrode terminal and the lead tab, thereby turning off the circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Application No. 61/257,417 filed Nov. 2, 2009, the entire content of which is incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments relate to a secondary battery and a battery pack using the same. 
         [0004]    2. Description of Related Art 
         [0005]    Unlike primary batteries that are not designed to be rechargeable, secondary batteries are rechargeable and are widely used in various electronic devices such as cellular phones, laptop computers, and camcorders. 
         [0006]    Among various kinds of secondary batteries, lithium secondary batteries are widely used because of their high operational voltages and high energy density per unit weight. Lithium secondary batteries are manufactured into various shapes such as prismatic shapes, cylindrical shapes, and pouch shapes. 
         [0007]    An internal gas pressure of a secondary battery can be excessively increased due to overcharging, over-discharging, an internal short circuit, or overheating. When the internal gas pressure is too high, the secondary battery may not be normally charged/discharged but behave abnormally. In addition, a case of the secondary battery may swell due to its internal gas pressure. 
       SUMMARY 
       [0008]    Embodiments are directed to a secondary battery capable of generating an open circuit to stop charging/discharging by using a swelling phenomenon in a way different from that used in the related art, and a battery pack using the secondary battery. 
         [0009]    Other embodiments are directed to a secondary battery capable of generating an open circuit to stop charging/discharging when swelling arises by structurally breaking the electrical connection between an electrode assembly and a lead tab, and a battery pack using the secondary battery. 
         [0010]    According to the embodiments, the secondary battery and the battery pack using the same are configured so that the electrode terminal and the lead tab can be separated by the deformation of the pouch case that swells due to an increase in the internal gas pressure. 
         [0011]    Therefore, when swelling of the case occurs, the electrical connection between the electrode assembly and the lead tab can be structurally broken. This way, the secondary battery and the battery pack can be used more reliably. 
         [0012]    In an embodiment according to the present invention, a secondary battery includes: an electrode assembly including a first electrode, a second electrode, and a separator between the first and second electrodes; a case containing the electrode assembly; a terminal electrically coupled to the first electrode; and a lead tab electrically coupled to the first electrode via the terminal inside the case, extending to outside of the case, and configured to be separated from at least a portion of the terminal to be electrically decoupled from the first electrode if the case is deformed while the lead tab remains attached to the case. 
         [0013]    The secondary battery may further include an adhesive attaching the lead tab to the terminal, the adhesive having an opening therethrough, wherein the lead tab is electrically coupled to the terminal through the opening. 
         [0014]    The secondary battery may further include a coupling member attaching a portion of the lead tab to the case, wherein the coupling member is closer to an attachment position between the lead tab and the terminal than an attachment position of another portion of the lead tab to the case. 
         [0015]    The terminal and the lead tab may be electrically coupled to each other via spot welding. The terminal and the lead tab may be electrically coupled to each other at least one contact. 
         [0016]    The secondary battery may further include an adhesive attaching the lead tab to the terminal, wherein the lead tab is electrically coupled to the terminal via at least one contact on a first side of the adhesive and at least one other contact on a second side of the adhesive opposite the first side. 
         [0017]    The case may include a deformable portion, wherein the lead tab is attached to the deformable portion, such that the lead tab is configured to be electrically decoupled from the first electrode as the deformable portion is deformed. The deformable portion may have a sloped surface between two parallel walls of the case. 
         [0018]    The terminal may have a groove thereon that at least partially surrounds a contact region on which a conductive contact between the terminal and the lead tab is located. 
         [0019]    The case may include a deformable portion, the lead tab is attached to the deformable portion, and the contact region is configured to be separated from the rest of the terminal when the deformable portion is deformed. The groove may completely surround the contact region. The groove may partially surround the contact region at an edge of the terminal. 
         [0020]    The terminal may include a material for providing a resistance of about 10 mΩ or lower. 
         [0021]    The secondary battery may further include a coupling member for attaching the lead tab to an inner surface of the case. The secondary battery may further include a supporting member for attaching the terminal to an inner surface of the case. An attachment strength between the terminal and the lead tab may be lower than an attachment strength of the coupling member to the case and the lead tab. 
         [0022]    The terminal may include a first plate and a second plate stacked together, a strength of the first plate is lower than that of the second plate and the electrical conductivity of the first plate is higher than that of the second plate, and the first plate is electrically coupled to the lead tab via a conductive contact. 
         [0023]    In another embodiment according to the present invention, a battery pack includes: a plurality of secondary batteries; and a circuit board for controlling the secondary batteries. At least one of the secondary batteries includes: an electrode assembly including a first electrode, a second electrode, and a separator between the first and second electrodes; a case containing the electrode assembly; a terminal electrically coupled to the first electrode; and a lead tab electrically coupled to the first electrode via the terminal inside the case, extending to outside of the case, and configured to be separated from at least a portion of the terminal to be electrically decoupled from the first electrode if the case is deformed while the lead tab remains attached to the case, wherein the lead tab is electrically coupled to a lead tab of at least another one of the secondary batteries. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view illustrating a battery pack in an assembled state, according to an embodiment. 
           [0025]      FIG. 2  is a perspective view illustrating one of a plurality of secondary batteries of the battery pack of  FIG. 1 . 
           [0026]      FIG. 3  is a sectional view taken along the line III-III of  FIG. 2 . 
           [0027]      FIG. 4  is an exploded perspective view illustrating a connection part of  FIG. 3 . 
           [0028]      FIG. 5  is a sectional view that illustrates changes to the secondary battery of  FIG. 3  when the secondary battery swells. 
           [0029]      FIG. 6  is a simplified process diagram that illustrates the process by which the swelling and open circuit depicted in  FIG. 5  is generated. 
           [0030]      FIG. 7  is a perspective view that illustrates a welding method between a positive terminal and a first lead tab according to another embodiment. 
           [0031]      FIG. 8  is a sectional view illustrating a coupling structure between a positive terminal and a first lead tab according to another embodiment. 
           [0032]      FIG. 9  is a perspective view illustrating the positive terminal of  FIG. 8 . 
           [0033]      FIG. 10  is a perspective view illustrating a positive terminal according to another embodiment. 
           [0034]      FIG. 11  is a sectional view illustrating a coupling structure between a positive terminal and a first lead tab according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    A secondary battery and a battery pack using the same will now be described with reference to the accompanying drawings according to example embodiments. 
         [0036]      FIG. 1  is a perspective view illustrating a battery pack  100  in an assembled state, according to an embodiment. 
         [0037]    Referring to  FIG. 1 , the battery pack  100  includes a plurality of secondary batteries  110 , a connection part  200 , a circuit board  300 , and a detecting device  400 . 
         [0038]    The secondary batteries  110  are stacked in a manner such that main surfaces of the secondary batteries  110  face each other. In other words, the side surfaces of the secondary batteries  110  are parallel to each other. The charge/discharge capacity of the battery pack  100  increases in proportion to the number of the secondary batteries  110 . The battery pack  100  may be used for a large apparatus such as a hybrid electric vehicle (HEV) or an electric vehicle (EV) requiring a high battery capacity, rather than a small apparatus such as a cellular phone to which power can be sufficiently supplied by using only one secondary battery  110 . However, the present invention is not limited thereto. The secondary batteries  110  include exposed lead tabs  140 . 
         [0039]    The connection part  200  electrically connects together the lead tabs  140  having the same polarity. In other words, the lead tabs  140  having positive polarity are electrically connected to each other by the connection part  200 , and the lead tabs  140  having negative polarity are electrically connected to each other by the connection part  200 . The connection part  200  includes connection plates  210  located between the neighboring secondary batteries  110 , and a connection bar  220  electrically connected to the outermost one of the connection plates  210 . The connection part  200  may be formed of a conductive metal such as copper, nickel, or aluminum that has good electrical conductivity. 
         [0040]    The circuit board  300  is used to control the charging and discharging operations of the secondary batteries  110 , and only one circuit board  300  may be provided for the plurality of secondary batteries  110 . The circuit board  300  may be electrically connected to the secondary batteries  110  through the connection bars  220 . Since the secondary batteries  110  are controlled by the single circuit board  300 , the battery pack  100  can have a simple structure as compared with the case where the circuits are provided for the respective secondary batteries  110 . 
         [0041]    The circuit board  300  is electrically connected to the detecting device  400 , which is inserted in the respective lead tabs  140  or coupled to the outsides of the lead tabs  140 . For example, the detecting device  400  may be a wire through which voltage variations of the secondary batteries  110  can be detected by the circuit board  300 . The circuit board  300  includes an additional display  310  in the embodiment of  FIG. 1 . The display  310  may output information measured through the detecting device  400 . Information output on the display  310  may be primarily referred to when the battery pack  100  is tested. 
         [0042]      FIG. 2  is a perspective view illustrating one of the secondary batteries  110  of the battery pack  100  illustrated in  FIG. 1 . 
         [0043]    Referring to  FIG. 2 , the secondary battery  110  includes a pouch case  120 , an electrode assembly  130  (shown  FIG. 3 ), and lead tabs  140 . 
         [0044]    The pouch case  120  may have an approximately rectangular parallelepiped shape. The pouch case  120  is formed of a thin plate made of a metal such as aluminum. By coating opposing surfaces of the thin plate with a resin, the pouch case  120  may be electrically insulated from objects making contact with the coated surfaces. 
         [0045]    One side of the pouch case  120  may be sloped to form a sloped surface  121 . An end region or sealing part  122  extends from the sloped surface  121  to cover or clamp the lead tabs  140 . 
         [0046]    The electrode assembly  130  is contained together with electrolyte in an inner space (S) (refer to  FIG. 3 ) formed by the pouch case  120 . An end of each of the lead tabs  140  is connected (e.g., electrically connected) to the electrode assembly  130 , and the other end of the lead tab  140  is exposed to the outside of the pouch case  120 . 
         [0047]    The lead tabs  140  include a first lead tab  141  and a second lead tab  142  that are spaced apart from each other in the width direction of the sealing part  122 . The first lead tab  141  may be electrically connected to a positive or negative electrode plate and may be positive or negative electrically. The second lead tab  142  may be electrically connected to a negative or positive electrode plate and may have a polarity electrically opposite to that of the first lead tab  141 . 
         [0048]      FIG. 3  is a sectional view taken along the line III-III of  FIG. 2 . 
         [0049]    Referring to  FIG. 3 , the electrode assembly  130  includes a positive electrode plate  131 , a negative electrode plate  132 , and a separator  133  located between the positive electrode plate  131  and the negative electrode plate  132 . 
         [0050]    The positive electrode plate  131  is formed by coating a positive electrode collector with a positive electrode coating, and the negative electrode plate  132  is formed by coating a negative electrode collector with a negative electrode coating. 
         [0051]    The positive electrode collector of the positive electrode plate  131  is formed of a conductive metal so that electrons can be collected from the positive electrode coating to the positive electrode collector and then transferred to an external circuit when the secondary battery  110  is charged. The positive electrode coating in one embodiment is prepared by mixing a positive electrode active material, a conductive material and a binder, and is coated on the positive electrode collector (e.g., coated to a predetermined thickness). 
         [0052]    The negative electrode collector of the negative electrode plate  132  is formed of a conductive metal so that electrons can be collected from the negative electrode coating to the negative electrode collector and then transferred to an external circuit when the secondary battery  110  is discharged. The negative electrode coating is prepared by mixing a negative electrode active material, a conductive material and a binder, and is coated on the negative electrode collector (e.g., coated to a predetermined thickness). 
         [0053]    The separator  133  is formed of an insulating material so that the positive electrode plate  131  and the negative electrode plate  132  can be electrically insulated from each other. 
         [0054]    The positive electrode plate  131 , the separator  133 , and the negative electrode plate  132  are located in the inner space (S) (e.g., accommodation space) of the electrode assembly  130  in a state where the positive electrode plate  131 , the separator  133 , and the negative electrode plate  132  are sequentially stacked, or they are sequentially stacked and wound in a jelly role shape. Then, electrolyte is injected into the inner space (S) to impregnate the electrode assembly  130  with the electrolyte. 
         [0055]    A conductive positive terminal  135  extends form the positive electrode plate  131  of the electrode assembly  130 . The positive terminal  135  is formed of a material for providing a resistance of about 10 mΩ or lower so that a current level required by a middle-capacity or large-capacity battery can flow through the positive terminal  135 . The positive terminal  135  is connected to the conductive first lead tab  141 . The positive terminal  135  and the first lead tab  141  are electrically connected through a conductive connection part  145 . 
         [0056]    As two parts of the pouch case  120  forming the sealing part  122 , that is, a case lower part  123  and a case upper part  124 , are sealed, the first lead tab  141  is covered by the parts  123  and  124 . By sealing the two parts  123  and  124 , the inner space (S) can be sealed in a state where the electrode assembly  130  and the electrolyte are contained in the inner space (S). 
         [0057]    The first lead tab  141  is located higher than the positive terminal  135  such that the case lower part  123  of the sealing part  122  can be elevated in a stepped shape to a level higher than the lowermost outer surface of the pouch case  120 . 
         [0058]    A supporting member  161  is located between the positive terminal  135  and the pouch case  120  to support and fix the positive terminal  135  with respect to the pouch case  120 . For example, the supporting member  161  may be formed of an insulating tape. 
         [0059]    A coupling member  162  is located between the first lead tab  141  and the pouch case  120  so as to couple the first lead tab  141  to the inner surface of the pouch case  120 . The coupling member  162  may be formed of a material having a high coupling strength such as polypropylene film or polyethylene film. 
         [0060]    Although both the supporting member  161  and the coupling member  162  are described, only the coupling member  162  may be used or required if the positive terminal  135  is firmly coupled to the electrode assembly  130 . If the positive terminal  135  is firmly coupled to the electrode assembly  130 , when the secondary battery  110  swells, although the coupling member  162  causes the first lead tab  141  to be deformed together with the pouch case  120  in a manner such that the first lead tab  141  is spaced apart from the positive terminal  135 , the supporting member  161  functions relatively less so that the supporting member  161  may be omitted. 
         [0061]    An adhesive member  150  such as an insulating tape may be additionally located between the positive terminal  135  and the first lead tab  141 . Both sides of the adhesive member  150  are respectively bonded to the surfaces of the positive terminal  135  and the lead tab  140  that face each other. The surfaces (main surfaces) of the positive terminal  135  and the first lead tab  141  that face each other may be spaced (e.g., at a predetermined distance) from each other by the adhesive member  150 . 
         [0062]    Because of the adhesive member  150 , structurally firm coupling (bonding) can be made between the positive terminal  135  and the first lead tab  141 . Therefore, even if the secondary battery  110  receives impacts or external forces during a normal operation, the possibility of disconnection of the conductive connection part  145  can be reduced because of the adhesive member  150 . Therefore, during a normal operation of the electrode assembly  130 , stable electrical connection can be ensured between the electrode assembly  130  and an external circuit. 
         [0063]    Insulating tapes  171  and  172  may be located between the opposite sides of the first lead tab  141  and the sealing part  122  of the pouch case  120 . The insulating tapes  171  and  172  provide insulation between the first lead tab  141  and the sealing part  122 . 
         [0064]    Although only the connection structure between the positive terminal  135  and the first lead tab  141  is discussed, a negative terminal, which is connected to the negative electrode plate  132  and extends in a manner corresponding to the second lead tab  142 , may be connected to the second lead tab  142  in substantially the same structure. 
         [0065]      FIG. 4  is an exploded perspective view illustrating the connection part  45  of  FIG. 3 . 
         [0066]    Referring to  FIG. 4 , a penetration hole  151  is formed through the adhesive member  150  which is located between the positive terminal  135  and the first lead tab  141 . Except for a region of the adhesive member  150  where the penetration hole  151  is formed, the adhesive member  150  is bonded to the mutually facing surfaces of the positive terminal  135  and the first lead tab  141 . 
         [0067]    For spot welding, electrodes W 1  and W 2  may be located at regions of the positive terminal  135  and the first lead tab  141  corresponding to the penetration hole  151 , that is, regions  135 ′ and  141 ′. In detail, the first electrode W 1  of which an end makes contact with the region  135 ′ is aligned in a row with the second electrode W 2  of which an end makes contact with the region  141 ′, and the first and second electrodes W 1  and W 2  are pushed against the regions  135 ′ and  141 ′. For a short time, a current is allowed to flow through the first and second electrodes W 1  and W 2  across the positive terminal  135  and the first lead tab  141 , which generates Joule heat. Owing to this Joule heat, the mutually facing surfaces of the regions  135 ′ and  141 ′ of the positive terminal  135  and the first lead tab  141  may be fused together and adhere to each other. Then, as the adhered portions cool and harden to form the conductive connection part  145 . 
         [0068]    A plurality of conductive connection parts  145  can be formed (at different positions) by repeating spot welding. The coupling (welding) strength between the positive terminal  135  and the first lead tab  141  can be increased by increasing the number of spot welding processes (e.g., spot welding locations). 
         [0069]      FIG. 5  is a sectional view for that illustrates changes to the secondary battery  110  illustrated in  FIG. 3  when the secondary battery  110  swells, and  FIG. 6  is a simplified process diagram that illustrates the process by which the swelling and open circuit depicted in  FIG. 5  is generated. 
         [0070]    Referring to  FIGS. 5 and 6 , if the inside temperature (e.g., inner temperature) of the secondary battery  110  increases and the inside gas pressure of the secondary battery  110  increases to a certain level due to extreme conditions such as overcharging and over-discharging, the pouch case  120  can swell, which is called a “swelling phenomenon.” Both ends of the pouch case  120  in the length direction may be inflated primarily, and particularly, the sloped surface  121  may expand the most. 
         [0071]    If the sloped surface  121  expands outward, an end part of the first lead tab  141 , which is connected to the sloped surface  121  by the coupling member  162  and is located in the inner space (S), is also bent outward. Due to this deformation, the end of the first lead tab  141  is pulled away from the positive terminal  135 . Thus, if the internal gas pressure exceeds a certain level, the first lead tab  141  may be separated from the positive terminal  135 . Due to this separation, mainly, the connection part  145  may be split into two parts  145   a  and  146   b.    
         [0072]    As the two parts  145   a  and  145   b  are separated, the electrical connection between the positive terminal  135  and the first lead tab  141  is structurally destroyed. That is, the electrode assembly  130  is electrically disconnected from an external circuit. 
         [0073]    The fracture of the connection part  145  can occur according to the above-described mechanism when the fracture occurs before the coupling member  162  is separated from the pouch case  120  or the first lead tab  141 . For this, the welding strength between the positive terminal  135  and the first lead tab  141  (the strength of the connection part  145 ) is lower than the bonding strength of the coupling member  162  to the pouch case  120  and the first lead tab  141 . For example, if the former strength is 2.5 kgf or lower, the latter strength may be 3.0 kgf or higher. If the latter strength has the above-mentioned value, the coupling member  162  is not stripped even if the coupling member  162  is pulled away from the pouch case  120  or the first lead tab  141  at a speed of 50 mm/min. 
         [0074]    If any one of the plurality of secondary batteries  110  is disconnected from an external circuit, this will be detected through the detecting device  400  (shown in  FIG. 1 ). Then, the circuit board  300  connected to the detecting device  400  may control the other secondary batteries  110  or report the malfunctioning of one of the secondary batteries  110 . For this end, the circuit board  300  may include the display  310  shown in  FIG. 1 ) or a light emitting unit. In the example shown in  FIG. 1 , the display  310  indicates that No. 2 secondary battery  110  is malfunctioning. 
         [0075]    In the case where the adhesive member  150  is used, the function of the adhesive member  150  related to fracture of the connection part  145  will now be described. When the temperature of the secondary battery  110  increases, heat is concentrated at the positive terminal  135  and the first lead tab  141 . If heat is transferred to the adhesive member  150  from a part such as the positive terminal  135 , the temperature of the adhesive member  150  increases and the bonding ability of the adhesive member  150  decreases. Thus, after a period of time (e.g., predetermined time) from the start of malfunction of the secondary battery  110 , the positive terminal  135  and the first lead tab  141  are not firmly coupled by the adhesive member  150 . Unlike the case where the secondary battery  110  operates normally, when the secondary battery  110  operates abnormally, the adhesive member  150  cannot prevent separation of the positive terminal  135  from the first lead tab  141 . 
         [0076]      FIG. 7  is a perspective view that illustrates a welding method between the positive terminal  135  and the first lead tab  141  according to another embodiment. 
         [0077]    Referring to  FIG. 7 , unlike the embodiment of  FIG. 4 , a penetration hole is not formed through an adhesive member  150 ′. Instead, the adhesive member  150 ′ is smaller than that illustrated in the previous embodiment and is bonded to the mutually facing surfaces of the positive terminal  135  and the first lead tab  141 . 
         [0078]    The adhesive member  150 ′ is located at the center between the mutually facing parts of the positive terminal  135  and the first lead tab  141 , such that both sides of the mutually facing parts can be used as welding regions  135 ″ and  141 ″. In the current embodiment, the welding regions  135 ″ and  141 ″ are located close to both sides of the adhesive member  150 ′. 
         [0079]    In this structure, spot welding may be performed two times by using two electrodes W 1  and W 2 . Then, the positive terminal  135  and the first lead tab  141  may be coupled to each other through two connection parts (refer to the connection part  145  of  FIG. 3 ). 
         [0080]      FIG. 8  is a sectional view illustrating a coupling structure between a positive terminal  135   a  and a first lead tab  141  according to another embodiment, and  FIG. 9  is a perspective view illustrating the positive terminal  135   a  of  FIG. 8 . 
         [0081]    Referring to  FIGS. 8 and 9 , similar to the previous embodiment, the positive terminal  135   a  and the first lead tab  141  are coupled to each other through conductive connection parts  145  formed by welding. Further, similar to the previous embodiment, an adhesive member  150  may be additionally provided between the positive terminal  135   a  and the first lead tab  141 . 
         [0082]    Referring again to  FIGS. 8 and 9 , a groove  1351  is formed in the positive terminal  135 . The groove  1351  may have a closed loop shape such as a circular shape as shown in  FIG. 9 . The conductive connection parts  145  are located in a region  1352  defined by the groove  1351 . 
         [0083]    Even if the conductive connection parts  145  do not fracture during a swelling phenomenon, the positive terminal  135   a  and the first lead tab  141  can be separated from each other if the region  1352  of the positive terminal  135   a  defined by the groove  1351  is separated from the other region of the positive terminal  135   a.    
         [0084]      FIG. 10  is a perspective view illustrating a positive terminal  135   b  according to another embodiment. 
         [0085]    Referring to  FIG. 10 , a groove  1353  has a non-closed-loop shape, and opened end parts of the groove  1353  extend to an end of a positive terminal  135   b . A connection part may be located in a region  1354  defined by the groove  1353  and the end of the positive terminal  135   b.    
         [0086]    In this structure, the region  1354  may be separated from the other region of the positive terminal  135   b  more easily as compared with the case of the region  1352  of the previous embodiment. 
         [0087]      FIG. 11  is a sectional view illustrating a coupling structure between a positive terminal  135   c  and a first lead tab  141  according to another embodiment. 
         [0088]    Referring to  FIG. 11 , the positive terminal  135   c  may have a cladding structure in which a first plate  1356  and a second plate  1357  are coupled to each other. The strength of the first plate  1356  is lower than that of the second plate  1357  but the electrical conductivity of the first plate  1356  is higher than that of the second plate  1357 . The first lead tab  141  is connected to the first plate  1356  having higher electrical conductivity through a connection part  145 . The second plate  1357  enhances the overall rigidity of the positive terminal  135   c.    
         [0089]    The second plate  1357  has an opened region  1358  at the center of an end part. The connection part  145  is located in the region  1358 . 
         [0090]    Because of this structure, the strength of the positive terminal  135   c  can be increased while maintaining the electrical conductivity of the positive terminal  135   c . Therefore, when the first lead tab  141  is deformed, the positive terminal  135   c  may not be pulled by the first lead tab  141  but the positive terminal  135   c  may maintain its position. Thus, the first lead tab  141  can be separated from the positive terminal  135   c  more easily. 
         [0091]    Furthermore, during a swelling phenomenon, a part of the positive terminal  135   c  corresponding to the first lead tab  141 , the connection part  145 , and the region  1358  may be separated from the other part of the positive terminal  135   c  more easily. 
         [0092]    Exemplary embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims and their equivalents.