Patent Publication Number: US-2011052969-A1

Title: Cell tab joining for battery modules

Description:
TECHNICAL FIELD 
     The present invention generally relates to a battery module, and more specifically, to a prismatic stack-type battery module for a battery pack. 
     BACKGROUND OF THE INVENTION 
     Batteries are useful for converting chemical energy into electrical energy, and may be described as primary or secondary. Primary batteries are generally non-rechargeable; secondary batteries are readily rechargeable. That is, secondary batteries may be restored to a full charge after use. As such, secondary batteries may be useful for a wide range of applications, such as powering electronic devices, tools, machinery, and vehicles. For example, secondary batteries for vehicle applications may be recharged external to the vehicle via a conventional plug-in electrical outlet, or onboard the vehicle via a regenerative event. 
     Although primary alkaline, voltaic pile, and lead-acid batteries have been used in numerous household and industrial applications, nickel cadmium (NiCd), nickel-metal hydride (Ni-MH), lithium ion, and lithium ion polymer secondary batteries may be particularly useful for emerging electric and hybrid gas/electric vehicle applications. That is, such secondary batteries often exhibit superior energy densities as compared to conventional primary batteries. Further, secondary batteries may be constructed without a rigid and heavy outer metal battery casing, and may therefore be useful for applications requiring reduced battery size and weight. 
     A battery, which also may be known as a battery pack, may include one or more battery modules. Similarly, a battery module may include one or more electrochemical battery cells positioned adjacent to each other, e.g., stacked. Further, each electrochemical battery cell may include foil cell tabs that function as conductive terminals. The cell tabs of the electrochemical battery cells may be joined together in a manner suitable for completing an electrical circuit of the battery module. For example, the cell tabs may be joined to a conductive interconnecting member. Therefore, quality and cost advantages may be obtained by optimizing the integrity of the connections, i.e., joints, between the cell tabs. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention, a battery module includes a plurality of electrochemical battery cells positioned adjacent one another and each having a positive cell tab and a negative cell tab. The positive cell tab of a first of the plurality of electrochemical battery cells is overlappingly joined to the negative cell tab of a second of the plurality of electrochemical battery cells. Further, each of the positive cell tabs and the negative cell tabs is not joined to a conductive interconnecting member. Also, at least one of the positive cell tabs or the negative cell tabs defines a flexure configured for reducing stress applied to the electrochemical battery cells during overlappingly joining the positive cell tabs and the negative cell tabs. 
     In one aspect, the flexure extends along substantially an entire length of at least one of the positive cell tabs and the negative cell tabs. In another aspect, at least one of the positive cell tabs and the negative cell tabs define a plurality of flexures. 
     In accordance with another aspect, the positive cell tab of the first electrochemical battery cell is bent at a substantially 90 degree angle so as to extend over and contact the negative cell tab of the second electrochemical battery cell. Alternatively, in another aspect, the negative cell tab of the second electrochemical battery cell is bent at a substantially 90 degree angle so as to extend over and contact the positive cell tab of the first electrochemical battery cell. 
     As part of another aspect of this embodiment, a positive cell tab is positioned adjacent to and in contact with two other positive cell tabs to form a first tab group. In one facet of this aspect, a negative cell tab is positioned adjacent to and in contact with two other negative cell tabs to form a second tab group that is bent at a substantially 90 degree angle so as to extend over and contact the first tab group. In another facet, the second tab group and two positive cell tabs of the first tab group each define a void therethrough that is configured to at least partially overlap with every other void. In an additional facet, one positive cell tab of the first tab group and one negative cell tab of the second tab group each extend beyond the other positive cell tabs of the first tab group and the other negative cell tabs of the second tab group, respectively, and are configured for overlappingly contacting each other. 
     Alternatively, a negative cell tab is positioned adjacent to and in contact with two other negative cell tabs to form a second tab group that is bent at a substantially 90 degree angle so that the first tab group extends over and contacts the second tab group. In another facet, the first tab group and two negative cell tabs of the second tab group each define a void therethrough that is configured to at least partially overlap with every other void. In yet another facet, one positive cell tab of the first tab group and one negative cell tab of the second tab group each extend beyond the other positive cell tabs of the first tab group and the other negative cell tabs of the second tab group, respectively, and are configured for overlappingly contacting each other. 
     In another aspect of this embodiment, at least two of the plurality of positive cell tabs and negative cell tabs each define a void therethrough so that at least two voids at least partially overlap. 
     In yet another aspect, the battery module is a lithium-ion polymer secondary battery module. 
     In another embodiment, a battery module includes a plurality of electrochemical battery cells each having a positive cell tab and a negative cell tab. The positive cell tabs are stacked adjacent to one another and the negative cell tabs are stacked adjacent to one another. Further, each of the positive cell tabs and the negative cell tabs is not joined to a conductive interconnecting member. The positive cell tabs and the negative cell tabs are joined to one another to thereby form a plurality of joints each having a thickness that is equivalent to one cell tab joined to another cell tab. 
     In one aspect, at least one of the positive cell tabs and at least one of the negative cell tabs each define a hole that is configured to at least partially overlap with an adjacent positive cell tab or negative cell tab, respectively, at one of the plurality of joints. 
     In another aspect, at least one of the positive cell tabs and the negative cell tabs define a flexure configured for reducing stress applied to the electrochemical battery cells during joining of the positive cell tabs and the negative cell tabs. 
     In yet another embodiment, a battery module includes a plurality of electrochemical battery cells and a conductive interconnecting member. The plurality of electrochemical battery cells each has a positive cell tab and a negative cell tab. The positive cell tabs are stacked adjacent to one another and the negative cell tabs are stacked adjacent to one another. Further, the positive cell tabs and the negative cell tabs are joined to the conductive interconnecting member to thereby form a respective first joint and a second joint. Additionally, at least one of the positive cell tabs or the negative cell tabs defines a flexure configured for reducing stress applied to the electrochemical battery cells during joining. The positive cell tabs and the negative cell tabs are each configured for intermeshing at the first joint and the second joint, respectively, so that the first joint and the second joint each has a thickness that is equivalent to one positive cell tab or one negative cell tab joined to the conductive interconnecting member. 
     In one aspect of this embodiment, each of the positive cell tabs and the negative cell tabs defines one or more holes that are configured to at least partially overlap and intermesh with an adjacent positive cell tab at the first joint and an adjacent negative cell tab at the second joint, respectively. 
     In another aspect, the positive cell tabs and the negative cell tabs are welded to the conductive interconnecting member. 
     The battery modules of the present invention are cost-effective to manufacture and optimize the integrity of the connections between the cell tabs of the electrochemical battery cells. As such, the battery modules optimize cell tab joint quality, allow for a variety of cell tab joining processes, experience reduced stresses during cell tab joining, and minimize energy input during cell tab joining. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a portion of a prior art battery module including a conductive interconnecting member; 
         FIG. 2  is a schematic perspective view of a battery pack and components thereof, including a plurality of electrochemical battery cells and a plurality of battery modules; 
         FIG. 3  is a schematic plan view of an exemplary electrochemical battery cell having a positive cell tab and a negative cell tab; 
         FIG. 4A  is a schematic perspective partial view of a plurality of positive cell tabs extended over and contacting a plurality of negative cell tabs of one embodiment of the battery module of  FIG. 2 ; 
         FIG. 4B  is a schematic perspective partial view of the plurality of negative cell tabs extended over and contacting the plurality of positive cell tabs of  FIG. 4A ; 
         FIG. 5A  is a schematic perspective view of a portion of the positive cell tabs and the negative cell tabs of another embodiment of the battery module of  FIG. 2 , wherein the positive cell tabs and the negative cell tabs are not yet joined to one another; 
         FIG. 5B  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of  FIG. 5A , wherein the positive cell tabs and the negative cell tabs are joined to one another to thereby form a plurality of joints each having a thickness that is equivalent to one cell tab joined to another cell tab; 
         FIG. 6  is a schematic top view of a portion of another embodiment of the battery module of  FIG. 2 ; 
         FIG. 7A  is a schematic perspective exploded view of a portion of a plurality of positive cell tabs of the battery module of  FIG. 6 ; 
         FIG. 7B  is a schematic exploded sectional view of a joint and the portion of the plurality of positive cell tabs of  FIG. 7A ; 
         FIG. 8A  is a schematic perspective partial view of a second tab group and two positive cell tabs of a first tab group of the battery module of  FIG. 2 , each overlappingly contacting and defining a void therethrough; 
         FIG. 8B  is a schematic perspective partial view of the first tab group of  FIG. 8A  and two negative cell tabs of the second tab group of  FIG. 8A , each overlappingly contacting and defining a void therethrough; 
         FIG. 9A  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of the battery module of  FIG. 2 , wherein one positive cell tab and one negative cell tab each extend beyond the other positive cell tabs and the other negative cell tabs to overlappingly contact each other for joining at point C, and wherein two of the positive cell tabs and two of the negative cell tabs each define a void therethrough so that the voids at least partially overlap for joining at points A and B; 
         FIG. 9B  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of the battery module of  FIG. 2 , wherein at least two of the plurality of positive cell tabs and negative cell tabs each define a void therethrough so that the at least two voids at least partially overlap; 
         FIG. 9C  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of the battery module of  FIG. 2 , wherein one positive cell tab and one negative cell tab each extend beyond the other positive cell tabs and the other negative cell tabs to overlappingly contact each other for joining at point X, and wherein two of the positive cell tabs and two of the negative cell tabs each define a void therethrough so that the voids at least partially overlap for joining at points V, Y, and Z; 
         FIG. 10A  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of the battery module of  FIG. 2 , wherein one positive cell tab and one negative cell tab each extend beyond the other positive cell tabs and the other negative cell tabs to overlappingly contact each other for joining at point C; 
         FIG. 10B  is a schematic partial sectional view of a portion of the positive cell tabs and the negative cell tabs of the battery module of  FIG. 2 , wherein one positive cell tab and one negative cell tab each extend beyond the other positive cell tabs and the other negative cell tabs to overlappingly contact each other for joining at points P, Q, R, and S; and 
         FIG. 11  is a schematic perspective view of a positive or negative cell tab of the battery modules of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the Figures, wherein like reference numerals refer to like components, a battery module is shown generally at  10 ,  110 ,  210  in  FIG. 2 . The battery module  10 ,  110 ,  210  may be useful for automotive applications, such as for a plug-in hybrid electric vehicle (PHEV). For example, the battery module  10 ,  110 ,  210  may be a lithium-ion polymer secondary battery module. Referring to  FIG. 2 , a plurality of battery modules  10 ,  110 ,  210  may be combined to form a battery pack  12 . By way of example, the battery pack  12  may be sufficiently sized to provide a necessary voltage for powering a hybrid electric vehicle (HEV), an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV), and the like, e.g., approximately 300 to 400 volts or more, depending on the required application. However, it is to be appreciated that the battery module  10 ,  110 ,  210  may also be useful for non-automotive applications, such as, but not limited to, household or industrial tools, recreational vehicles, and electronic devices. 
     Referring to  FIGS. 2 and 3 , the battery module  10 ,  110 ,  210  includes a plurality of electrochemical battery cells  14  positioned adjacent one another. The electrochemical battery cell  14  may be any suitable electrochemical battery cell known in the art. For example, the electrochemical battery cell  14  may be lithium ion, lithium ion polymer, lithium iron phosphate, lithium vanadium pentoxide, lithium copper chloride, lithium manganese dioxide, lithium sulfur, lithium titanate, nickel metal hydride, nickel cadmium, nickel hydrogen, nickel iron, sodium sulfur, vanadium redox, lead acid, or combinations thereof. 
     Referring to  FIG. 3 , each electrochemical battery cell  14  has a positive cell tab  16  and a negative cell tab  18 . The electrochemical battery cell  14  may be suitable for stacking. That is, the electrochemical battery cell  14  may be formed from a heat-sealable, flexible foil that is sealed to enclose a cathode, an anode, and a separator (not shown). Therefore, any number of electrochemical battery cells  14  may be stacked or otherwise placed adjacent to each other to form a cell stack, i.e., the battery module  10 ,  110 ,  210  ( FIG. 2 ). Further, although not shown in  FIG. 2 , additional layers, such as, but not limited to, frames and/or cooling layers may also be positioned between individual electrochemical battery cells  14 . Consequently, referring generally to embodiments shown in  FIGS. 4A-10B , the battery module  10 ,  110 ,  210  may include a plurality of positive cell tabs  16  and a plurality of negative cell tabs  18 . The actual number of electrochemical battery cells  14  may be expected to vary with the required voltage output of each battery module  10 ,  110 ,  210 . Likewise, the number of interconnected battery modules  10 ,  110 ,  210  may vary to produce the necessary total output voltage for a specific application. 
     Referring again to  FIG. 3 , the positive cell tab  16  and the negative cell tab  18  are electrode extensions that are internally welded to various cathodes and anodes (not shown) of the electrochemical battery cell  14 , as is understood by one of ordinary skill in the art. The positive cell tab  16  and the negative cell tab  18  may be constructed of a conductive metal. For example, the positive cell tab  16  may be constructed substantially of aluminum, and the negative cell tab  18  may be constructed substantially of copper. 
     Referring to  FIGS. 4A and 4B , the positive cell tab  16  of a first electrochemical battery cell  14 A is overlappingly joined to the negative cell tab  18  of a second electrochemical battery cell  14 B. For example, referring to  FIG. 4A , the positive cell tab  16  of the first electrochemical battery cell  14 A may be bent at a substantially 90 degree angle so as to extend over and contact the negative cell tab  18  of the second electrochemical battery cell  14 B. Stated differently, the positive cell tab  16  may overlap, i.e., fold over, and contact the negative cell tab  18 . Similarly, referring to  FIG. 4B , the negative cell tab  18  of the second electrochemical battery cell  14 B may be bent at a substantially 90 degree angle so as to extend over and contact the positive cell tab  16  of the first electrochemical battery cell  14 A. That is, the negative cell tab  18  may overlap, i.e., fold over, and contact the positive cell tab  16 . Therefore, in contrast to the prior art battery module shown in  FIG. 1 , each of the positive cell tabs  16  and the negative cell tabs  18  is not joined to a conductive interconnecting member  20 . Rather, the overlappingly connected positive cell tab  16  and the negative cell tab  18  are connected at one end of the respective first electrochemical battery cell  14 A and the second electrochemical battery cell  14 B so as to provide electrical conductivity for the battery module  10  without any conductive interconnecting member  20  ( FIG. 1 ). Thus, the battery module  10  is lighter, more compact, and includes fewer components as compared to existing battery modules that may include, for example, the conductive interconnecting member  20  ( FIG. 1 ). Further, because each of the positive cell tabs  16  and the negative cell tabs  18  is not joined to a conductive interconnecting member, manufacturing processes for the battery module  10  are simplified. Consequently, manufacturing costs for the battery module  10  are minimized. 
     Referring to  FIGS. 4A and 4B , in one example, three positive cell tabs  16  may be placed adjacent to each other, i.e., stacked, in the battery module  10  and three negative cell tabs  18  may be placed adjacent to each other, i.e., stacked, in the battery module  10 . For example, referring to  FIG. 4A , a positive cell tab  16  may be positioned adjacent to and in contact with two other positive cell tabs  16  to form a first tab group  22 . That is, one positive cell tab  16  may be positioned between two other positive cell tabs  16  to form the first tab group  22 . Therefore, in this example, the first tab group  22  includes three positive cell tabs  16 . Likewise, a negative cell tab  18  may be positioned adjacent to and in contact with two other negative cell tabs  18  to form a second tab group  24 . That is, one negative cell tab  18  may be positioned between two other negative cell tabs  18  to form the second tab group  24 . Therefore, in this example, the second tab group  24  also includes three negative cell tabs  18 . 
     Referring again to  FIG. 4A , the first tab group  22  may be bent at a substantially 90 degree angle so as to extend over and contact the second tab group  24 . Stated differently, the first tab group  22  may overlap, i.e., fold over, and contact the second tab group  24 . Likewise, referring to  FIG. 4B , the second tab group  24  may be bent at a substantially 90 degree angle so that the second tab group  24  extends over and contacts the first tab group  22 . That is, the second tab group  24  may overlap, i.e., fold over, and contact the first tab group  22 . 
     In another embodiment described with respect to  FIGS. 5A and 5B , the battery module  110  includes a plurality of electrochemical battery cells  14  ( FIG. 3 ), each having the positive cell tab  16  ( FIG. 3 ) and the negative cell tab  18  ( FIG. 3 ). That is, in one example, the battery module  110  may include two electrochemical battery cells  14 . In another example, referring to  FIGS. 5A and 5B , the battery module  110  may include at least six electrochemical battery cells  14 . That is, as shown in  FIG. 5A , the battery module  110  may include at least three positive cell tabs  16 D, E, F and at least three negative cell tabs  18 D, E, F. Further, although not shown in  FIGS. 5A and 5B , the battery module  110  may include more than six electrochemical battery cells  14 . 
     Additionally, as shown in  FIG. 5B , one positive cell tab  16 D and one negative cell tab  18 F may each extend beyond the other positive cell tabs  16 E, F and the other negative cell tabs  18 D, E, respectively. It is to be appreciated that any one of the positive cell tabs  16 D, E, F may extend beyond the other positive cell tabs  16 D, E, F. Likewise, any one of the negative cell tabs  18 D, E, F may extend beyond the other negative cell tabs  18 D, E, F. 
     Referring to  FIG. 5A , in preparation for joining, the positive cell tabs  16 D, E, F are positioned with respect to one another and the negative cell tabs  18 D, E, F are positioned with respect to one another. Referring to  FIG. 5B , after joining, the positive cell tabs  16 D, E, F are stacked adjacent to one another and the negative cell tabs  18 D, E, F are stacked adjacent to one another. 
     Referring again to  FIGS. 5A and 5B , each of the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F is not joined to a conductive interconnecting member  20  ( FIG. 1 ). Rather, as shown in  FIG. 5B , the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F are joined to one another to thereby form a plurality of joints, designated by phantom line circles V, W, X, Y, and Z. For example, the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may be joined to one another by welding to thereby form five joints. It is also to be appreciated that the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may be joined to one another to thereby form more or fewer than five joints, depending upon the configuration of the positive cell tabs  16  and the negative cell tabs  18 . For example, the battery module  110  may include only three joints, if at least one of the joints is a 3-layer joint. 
     Referring again to  FIGS. 5A and 5B , at least one of the positive cell tabs  16 D, E, F and at least one of the negative cell tabs  18 D, E, F may each define a hole  26  that is configured to at least partially overlap with an adjacent positive cell tab  16 D, E, F or negative cell tab  18 D, E, F, respectively, at one of the plurality of joints designated by phantom line circles V, W, X, Y, Z ( FIG. 5B ). That is, referring to  FIG. 5A , the hole  26  may be a cut-out portion of the positive cell tab  16 D, E, F and/or the negative cell tab  18 D, E, F. The hole  26  may have any size and/or shape. For example, the hole  26  may be three adjacent slots, one rectangular slot, two adjacent slots, or a combination thereof Additionally, one or more positive cell tabs  16 D, E, F and/or one or more negative cell tab  18 D, E, F may each define a plurality of holes  26 . 
     Prior to joining ( FIG. 5A ), the plurality of positive cell tabs  16 D, E, F of the electrochemical battery cells  14  ( FIG. 3 ) may be stacked adjacent to each other to at least partially overlap the holes  26  at the desired locations for the plurality of joints designated by phantom line circles V, W, X,Y, Z ( FIG. 5B ). Likewise, the plurality of negative cell tabs  18 D, E, F may be stacked adjacent to each other to at least partially overlap the holes  26 . 
     Referring to  FIG. 5B , upon joining, the plurality of joints designated by phantom line circles V, W, X, Y, Z each has a thickness, t, that is equivalent to one cell tab  16 D, E, F,  18 D, E, F joined to another cell tab  16 D, E, F,  18 D, E, F. That is, the positive cell tabs  16 D, E, F at least partially overlap with the negative cell tabs  18 D, E, F via the holes  26  to form the plurality of joints designated by phantom line circles V, W, X, Y, Z. Stated differently, referring to  FIG. 5B , the thickness, t, of each of the entire joints designated by phantom line circles V, W, X, Y, Z may be equivalent in thickness to a joint between, for example, only one positive cell tab  16 F and one negative cell tab  18 F, one positive cell tab  16 D and another positive cell tab  16 E, or one negative cell tab  18 D and another negative cell tab  18 E. That is, the thickness, t, is equivalent to the thickness of two joined cell tabs  16 D, E, F,  18 D, E, F and forms a 2-layer joint. 
     Further, it is to be appreciated that the at least one hole  26 , the positive cell tabs  16 D, E, F, and/or the negative cell tabs  18 D, E, F may be arranged in any other suitable configuration to provide some or all of the plurality of joints designated by phantom line circles V, W, X, Y, Z each having the thickness, t, equivalent to the thickness of two joined cell tabs  16 D, E, F,  18 D, E, F. That is, for example, although not shown in  FIGS. 5A and 5B , the positive cell tabs  16 D, E, F may be stacked alternatingly with the negative cell tabs  18 D, E, F. 
     The resulting 2-layer joints designated by phantom line circles V, W, X, Y, Z have a reduced number of layers as compared to, for example, a 4-layer joint, and therefore optimize the ease of joining the cell tabs  16 D, E, F,  18 D, E, F of the electrochemical battery cells  14 . Consequently, the resulting 2-layer joints may also have a reduced thickness, t. A minimization of the number of layers and/or thickness of the joints is desirable, since a 2-layer joint is easier to join than, for example, a 4- or more-layer joint. As such, the battery module  110  has excellent weldability and weld quality. More specifically, the battery module  110  optimizes cell tab joint quality, allows for a variety of cell tab joining processes, experiences reduced stresses during cell tab joining, and minimizes energy input during cell tab joining as compared to a 4- or more-layer joint. 
     Moreover, it is to be appreciated that the exemplary configurations shown in  FIGS. 5A and 5B  may be combined with the exemplary configurations shown in  FIGS. 4A and 4B . That is, the first tab group  22  and/or the second tab group  24  may define one or more holes  26 . Further, the first tab group  22  and/or the second tab group  24  may be bent at a substantially 90 degree angle for overlappingly joining the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F. 
     In another embodiment, described generally with respect to  FIG. 6 , a battery module  210  includes a plurality of electrochemical battery cells  14  ( FIG. 3 ) each having the positive cell tab  16  ( FIG. 3 ) and the negative cell tab  18  ( FIG. 3 ). In one example, the battery module  210  may include two electrochemical battery cells  14 . In another example, referring to  FIG. 6 , which is not drawn to scale, the battery module  210  may include at least six electrochemical battery cells  14 . That is, referring to  FIG. 6 , the battery module  210  may include a plurality of positive cell tabs  16 D, E, F and/or a plurality of negative cell tabs  18 D, E, F. Further, in this embodiment, the positive cell tabs  16 D, E, F are stacked adjacent to one another and the negative cell tabs  18 D, E, F are stacked adjacent to one another. 
     The battery module  210  also includes a conductive interconnecting member, shown generally at  20  in  FIG. 6 . Referring to  FIGS. 1 and 6 , the conductive interconnecting member  20 , may be shaped, sized, or otherwise configured to form an elongated rail or bus bar. For example, referring to  FIG. 1 , an exemplary conductive interconnecting member  20  may include a pair of side walls  28  that are each operatively connected to or formed integrally with a base  30  to define a generally U-shaped profile. Further, the conductive interconnecting member  20  may be constructed of any suitable conductive material, e.g., pure or elemental copper, or at least approximately 90% copper if an alloy of elemental copper is used. Additionally, the battery module  210  may also include more than one conductive interconnecting member  20 . 
     Referring to  FIG. 6 , the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F are joined to the conductive interconnecting member  20  to thereby form a respective first joint  32  and a second joint  34 . For illustration, the first joint  32  and the second joint  34  are shown in exploded, i.e., non-joined, view in  FIGS. 6 ,  7 A, and  7 B. The positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may be joined by any suitable joining technique or method known in the art. For example, the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may be welded to the conductive interconnecting member  20 . As known in the art, welding may utilize oscillations or vibrations in a particular range of frequency to bond adjacent plastic or metallic work pieces, e.g., the positive cell tab  16  and the conductive interconnecting member  20 . More specifically, the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may be welded to the conductive interconnecting member  20 , e.g., using a horn, i.e., sonotrode, and anvil style ultrasonic welding apparatus (not shown). The first joint  32  and the second joint  34  should be of sufficient quality to ensure electrical conduction between the positive cell tabs  16 D, E, F, the conductive interconnecting member  20 , and the negative cell tabs  18 D, E, F, thereby ensuring electrical conductivity of the battery module  210 . 
     As shown in  FIG. 6 , the first joint  32  may be formed between the positive cell tabs  16  and one of the side walls  28  of the conductive interconnecting member  20 . Likewise, the second joint  34  may be formed between the negative cell tabs  18  and one of the side walls  28  of the conductive interconnecting member  20 . Further, the first joint  32  and the second joint  34  may be formed at opposite ends of the conductive interconnecting member  20 . 
     Referring to  FIGS. 6 ,  7 A, and  7 B, the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F are each configured for intermeshing at the first joint  32  and the second joint  34 , respectively, so that the first joint  32  and the second joint  34  each has a thickness, t 2 , ( FIG. 6 ) that is equivalent to one positive cell tab  16  or one negative cell tab  18  joined to the conductive interconnecting member  20 . Stated differently, referring to  FIG. 6  and described with respect to the positive cell tabs  16 D, E, F and the first joint  32 , after joining, the thickness, t 2 , of the entire first joint  32  may be equivalent in thickness to a joint between only one positive cell tab  16  and the conductive interconnecting member  20 . Similarly, as shown in  FIG. 6 , the thickness, t 2 , of the second joint  34  after joining may also be equivalent in thickness to a joint between only one negative cell tab  18  and the conductive interconnecting member  20 . The resulting 2-layer joint  32 ,  34  has a reduced number of layers as compared to, for example, a 4-layer joint, and therefore provides the associated advantages of excellent weldability as set forth above. 
     Referring to  FIG. 7A , in this embodiment, each of the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may define one or more holes  26  that are configured to at least partially overlap and intermesh with an adjacent positive cell tab  16 D, E, F at the first joint  32  and an adjacent negative cell tab  18 D, E, F at the second joint  34 , respectively. For example, referring to  FIGS. 7A and 7B  and described with respect to the positive cell tabs  16 D, E, F, the plurality of positive cell tabs  16 D, E, F of the plurality of electrochemical battery cells  14  ( FIG. 3 ) may be stacked adjacent to each other. Each of the positive cell tabs  16 D, E, F may define one or more holes  26  that are configured to at least partially overlap and intermesh with an adjacent positive cell tab  16 D, E, F at the first joint  32 . 
     That is, in one example, four layers, i.e., a first, second, and third positive cell tab  16 F, E, D and the conductive interconnecting member  20  may be stacked adjacent to each other in preparation for joining ( FIG. 7A ). Referring to  FIG. 7A , the second layer (the first positive cell tab  16 F) may define one hole  26 , i.e., cutout, configured to intermesh with the third layer (the second positive cell tab  16 E) during joining, e.g., welding. Likewise, referring to  FIG. 7A , the third layer (the second positive cell tab  16 E) may define two holes  26  configured to intermesh with both the second layer (the first positive cell tab  16 F) and the fourth layer (the third positive cell tab  16 D), respectively. Similarly, referring to  FIG. 7A , the fourth layer (the third positive cell tab  16 D) may define one hole  26  configured to intermesh with the third layer (the second positive cell tab  16 E). Therefore, when the four layers are joined, the first joint  32  may be two layers thick throughout the first joint  32 . Stated differently, the thickness, t 2 , ( FIG. 6 ) of the first joint  32  is at most equal to the thickness of one positive cell tab  16  joined to the conductive interconnecting member  20  at any position of the first joint  32 . 
     The resulting 2-layer joint, e.g., the first joint  32 , has a reduced number of layers as compared to, for example, a 4-layer joint, and therefore optimizes the ease of joining the cell tabs  16 D, E, F,  18 D, E, F of the electrochemical battery cells  14 . Consequently, the resulting 2-layer joint  32 ,  34  may also have a reduced thickness, t. As set forth above, a minimization of the number of layers and/or thickness of the joints  32 ,  34  is desirable. As such, the battery module  210  has excellent weldability and weld quality. That is, the battery module  210  optimizes cell tab joint quality, allows for a variety of cell tab joining processes, experiences reduced stresses during cell tab joining, and minimizes energy input during cell tab joining as compared to a 4- or more-layer joint. 
     Referring now to  FIG. 8A , the second tab group  24  and two positive cell tabs  16 D, E of the first tab group  22  may each define a void  36  therethrough that is configured to at least partially overlap with every other void  36 . That is, each negative cell tab  18 D, E, F of the second tab group  24 , and the topmost two positive cell tabs  16 D, E of the first tab group  22  may each define the void  36  so that each void  36  at least partially overlaps every other void  36  as the first tab group  22  and the second tab group  24  are overlappingly joined, i.e., as the second tab group  24  overlaps and contacts the first tab group  22 . In this example, the second tab group  24  and two positive cell tabs  16 D, E of the first tab group  22  may define a 1-layer joint that may be joined, for example, by soldering. 
     Similarly, referring to  FIG. 8B , the first tab group  22  and two negative cell tabs  18 D, E of the second tab group  24  may each define the void  36  therethrough that is configured to at least partially overlap with every other void  36 . That is, each positive cell tab  16 D, E, F of the first tab group  22 , and the topmost two negative cell tabs  18 D, E of the second tab group  24  may each define the void  36  so that each void  36  at least partially overlaps every other void  36  as the second tab group  24  and the first tab group  22  are overlappingly joined, i.e., as the first tab group  22  overlaps and contacts the second tab group  24 . In this example, the first tab group  22  and two negative cell tabs  18 D, E of the second tab group  24  may define a 1-layer joint that may also be joined, for example, by soldering. 
     In another example, referring to  FIGS. 9A ,  9 B, and  9 C, at least two of the plurality of positive cell tabs  16 D, E, F and negative cell tabs  18 D, E, F may each define the void  36  therethrough so that the at least two voids  36  at least partially overlap. For example, referring to  FIGS. 9A-9C , two of the positive cell tabs  16 D, E and two of the negative cell tabs  18 D, E may each define the void  36  therethrough. The two voids  36  of the positive cell tabs  16 D, E may each at least partially overlap and the two voids  36  of the negative cell tabs  18 D, E may each at least partially overlap. Similarly, referring to  FIG. 9B , two of the positive cell tabs  16 D, E may each define two voids  36 , and one of the negative cell tabs  18 E may define two voids  36 . In this example, each set of voids  36  of the positive cell tabs  16 D, E may at least partially overlap and the voids  36  of the negative cell tabs  18 D, E may at least partially overlap. And, one or more voids  36  of the positive cell tab  16 D may at least partially overlap with one or more of the negative cell tabs  18 E. Likewise, referring to  FIG. 9C , two of the negative cell tabs  18 D, F may each define two voids  36  therethrough so that the at least one set of voids  36  of the negative cell tabs  18 D, E (or  18  D, F) may at least partially overlap. 
     The void  36  may have any suitable shape, such as, but not limited to, elongated, circular, rectangular, and/or oval. In addition, the first tab group  22  and/or the second tab group  24  may each define a plurality of voids  36  to form, for example, a screen or mesh. Further, each void  36  may have the same or different size and/or shape, as long as each void  36  at least partially overlaps with every other void  36  when the first tab group  22  and the second tab group  24  are overlappingly joined. 
     The void  36  may be suitable for receiving, for example, molten or paste solder so that the first tab group  22  and the second tab group  24  may be soldered. It is also to be appreciated that the soldering may be reversible so that the first tab group  22  and/or the second tab group  24  may be disassembled. The resulting soldered joint, shown generally at points A and B in  FIG. 9A , points P, Q, R, and S in  FIG. 9B , and points V, W, X, Y, and Z in  FIG. 9C , for example, has a thickness equivalent to a thickness of only one positive or negative cell tab  16 ,  18 . That is, the resulting joint is a 1-layer joint that may be joined by soldering. Therefore, the one or more voids  36  allow for a reduction in the number of layers and/or the thickness of each joint of the battery module  10 . 
     Additionally, referring to  FIGS. 9A and 10A , one positive cell tab  16 F of the first tab group  22  and one negative cell tab  18 F of the second tab group  24  may each extend beyond the other positive cell tabs  16 D, E of the first tab group  22  and the other negative cell tabs  18 D, E of the second tab group  24 , respectively, and may be configured for overlappingly contacting each other. That is, for example, one bottommost positive cell tab  16 F of the first tab group  22  and one bottommost negative cell tab  18 F of the second tab group  24  may be longer than the other adjacent positive cell tabs  16 D, E and negative cell tabs  18 D, E, respectively. Therefore, referring to  FIGS. 9A and 10A , one bottommost positive cell tab  16 F and one bottommost negative cell tab  18 F may be configured for overlapping and contacting each other. It is to be appreciated that, in this example, the one negative cell tab  18 F may overlap and contact the positive cell tab  16 F (as shown in  FIG. 9A ), or that the one positive cell tab  16 F may overlap and contact the negative cell tab  18 F. 
     It is also to be appreciated that multiple variations of cell tab arrangements are possible and contemplated. For example, referring to  FIGS. 9B and 10B , more than one positive cell tab, e.g.,  16 D, E, of the first tab group  22  and/or more than one negative cell tab, e.g.,  18 F, E of the second tab group  24  may each extend beyond the other positive cell tab  16 F of the first tab group  22  and the other negative cell tab  18 D of the second tab group  24 , respectively, and may be configured for overlappingly contacting each other. And, any of the positive cell tabs  16 D, E, F and the negative cell tabs  18 D, E, F may extend beyond the other positive cell tabs  16  and negative cell tabs  18 . For example, a topmost positive cell tab  16 D ( FIG. 5B ,  9 B,  9 C, and  10 B) and a bottommost negative cell tab  18 F may each extend beyond the other positive cell tabs  16 E, F and negative cell tabs  18 D, E, respectively, and may be configured for overlappingly contacting each other. 
     In the aforementioned examples, the first tab group  22  and the second tab group  24  may be overlapping joined by any suitable method. For example, the first tab group  22  and the second tab group  24  may be vibration welded, ultrasonically welded, resistance spot welded, soldered, glued, and/or riveted. More specifically, in one example, the first tab group  22  and the second tab group  24  may be ultrasonically welded via a controlled application of pressure and high-frequency mechanical vibration to form a solid bond or joint. 
     Referring to  FIG. 10A , in one example, the first tab group  22  and the second tab group  24  may be welded at three points, designated by phantom line circles A, B, and C. In another example, the first tab group  22  and the second tab group  24  may be welded at four points, designated by phantom line circles P, Q, R, and S in  FIG. 10B . In yet another example, the first tab group  22  and the second tab group  24  may be welded at five points, designated by phantom line circles V, W, X, Y, and Z in  FIG. 5B . Although not shown, the first tab group  22  and the second tab group  24  may also be joined at fewer than three joints. 
     More specifically, referring to phantom line circles A ( FIG. 10A ) and P ( FIG. 10B ), the positive cell tabs  16 D, E, F of the first tab group  22  may be welded to each other to form a 3-layer joint. Similarly, referring to phantom line circles B ( FIG. 10A ) and S ( FIG. 10B ), the negative cell tabs  18 D, E, F of the second tab group  24  may be welded to each other to form a 3-layer joint. Additionally, referring to phantom line circle Q ( FIG. 10B ), the one bottommost negative cell tab  18 F may be welded to two positive cell tabs  16 D, E to form a 3-layer joint. Likewise, referring to phantom line circle R ( FIG. 10B ), the one topmost positive cell tab  16 D may be welded to two negative cell tabs  18 E, F. 
     And, referring to phantom line circles C ( FIG. 10A ) and X ( FIG. 5B ), the one bottommost negative cell tab  18 F and the one bottommost positive cell tab  16 F may be welded to each other to form a 2-layer joint. Similarly, referring to phantom line circle V ( FIG. 5B ), two positive cell tabs  16 E, F may be welded to each other. Referring to phantom line circle Z ( FIG. 5B ), two negative cell tabs  18  may also be welded to each other. 
     Referring to  FIGS. 5B ,  10 A, and  10 B as examples, the resulting 3-layer joints of phantom line circles A, B, P, Q, R, and S, and the 2-layer joints of phantom line circles C, V, W, X, Y, and Z are easily joined. That is, 2-layer and 3-layer joints are easier to join than, for example, a 4-layer joint. As such, the battery module  10 ,  110  exhibits excellent weldability as compared to existing battery modules. 
     Referring now to  FIG. 11 , at least one of the positive cell tabs  16  or the negative cell tabs  18  of the battery module  10 ,  210  defines a flexure  38 . In general, the flexure  38  may reduce stress applied to the electrochemical battery cell  14  during joining and/or during vehicle operation. Any or all of each of the positive cell tabs  16  and the negative cell tabs  18  may define the flexure  38 . For applications including the battery module  10 , the flexure  38  is configured for reducing stress applied to the electrochemical battery cell  14  ( FIG. 3 ) during overlappingly joining the positive cell tabs  16  and the negative cell tabs  18 . Likewise, for applications including the battery module  210 , the flexure  38  is configured for reducing stress applied to the electrochemical cells  14  during joining. 
     For applications including the battery module  110 , at least one of the positive cell tabs  16  and the negative cell tabs  18  may each define the flexure  38  configured for reducing stress applied to the electrochemical battery cells  14  ( FIG. 3 ) during joining of the positive cell tabs  16  and the negative cell tabs  18 . 
     In particular, the electrochemical battery cell  14 , and more specifically, joints at points A, B, and C ( FIG. 10A ); P, Q, R, and S ( FIG. 10B ); V, W, X, Y, and Z ( FIG. 5B ); the first joint  32  ( FIG. 6 ); the second joint  34  ( FIG. 6 ); and/or internal joints of the various cathodes and anodes (not shown) of the electrochemical battery cell  14 , may be subjected to shear stress during joining, particularly during welding, and/or during vehicle operation. For example, during manufacturing of the battery module  10 ,  110 ,  210  and/or during vehicle operation, vibrations may be transmitted to internal joints (not shown) of the electrochemical battery cell  14  and may cause undesirable deformation and stress unless dissipated. That is, during manufacturing of the battery module  110  for example, the second joint  34  may be formed after the first joint  32 . Therefore, as a horn of a welding apparatus (not shown) vibrates at a high frequency to form the second joint  34 , vibrations may be transmitted to the first joint  32  and any internal joints (not shown). Depending on the amplitude of the vibrations, the first joint  32  may experience shear stress and undesirable deformation and stress, thereby affecting the joint quality of the battery module  110 . Similarly, during vehicle operation, vibrations may be transmitted to internal joints (not shown) of the electrochemical battery cell  14  and may cause undesirable deformation unless dissipated. That is, without intending to be limited by theory, the flexure  38  may allow the positive cell tab  16  and/or the negative cell tab  18  to flex, bend, accordion, and/or compress to thereby minimize deformation and stress of the battery module  10 ,  110 ,  210 . 
     Referring to  FIG. 11 , the flexure  38  may extend along substantially an entire length, L, of at least one of the positive cell tabs  16  and the negative cell tabs  18 . As used herein, the terminology “substantially” is used to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terminology also represents the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. Therefore, it is contemplated that the flexure  38  may extend along slightly less than the entire length, L, of at least one of the positive cell tabs  16  and the negative cell tabs  18 . 
     Further, referring to  FIG. 11 , the flexure  38  may have any suitable shape, such as, but not limited to, a box-like-shape or S-shape. In one example, the flexure  38  may be substantially C-shaped. In another example, the flexure  38  may be a bend in the positive cell tab  16  or negative cell tab  18 . Further, referring to  FIG. 11 , at least one of the positive cell tabs  16  and the negative cell tabs  18  may define a plurality of flexures  38 . For example, at least one of the positive cell tabs  16  and the negative cell tabs  18  may define two or more flexures  38 . Also, the positive cell tabs  16  may define the same number of, fewer, or more flexures  38  than the negative cell tabs  18 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.