Abstract:
A method of manufacturing a battery including: supplying a busbar having a U-shaped portion defining a channel and characterized by a bend corner at one end of the U-shaped portion, wherein the busbar has a reduced-reflectivity treatment at least in the vicinity of the bend corner; positioning a single battery terminal in the channel formed by the U-shaped portion so that the top end of the terminal is proximate to the bend corner; directing a laser beam at the bend corner of the U-shaped portion; and with the laser beam, melting the busbar at the bend corner and forming a metallurgical bond between the busbar and the top end of the single terminal.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/143,976, filed Jan. 12, 2009 and entitled “Prismatic Battery Module With Scalable Architecture,” the entire contents of which are incorporated herein by reference. 
         [0002]    This application is also related to the following applications, filed concurrently herewith, the entire contents of which are incorporated herein by reference: 
         [0003]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Prismatic Battery Module with Scalable Architecture,” 
         [0004]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Structure of Prismatic Battery Modules with Scalable Architecture,” 
         [0005]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Safety Venting Mechanism For Batteries,” 
         [0006]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Bi-metallic Busbar Jumpers for Battery Systems,” 
         [0007]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Fuse For Battery Cells,” and 
         [0008]    U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled “Busbar Supports And Methods Of Their Use for Battery Systems,” 
     
    
     TECHNICAL FIELD 
       [0009]    The present invention relates to battery modules and scalable architectures for manufacturing battery modules. 
       BACKGROUND OF THE INVENTION 
       [0010]    A ‘battery module’ is a subassembly that is typically installed inside a ‘battery pack’, which is an assembly that is installed in a terrain, marine, or aeronautic vehicle. These vehicles typically have a variety of high power electric loads, such as a computer-controlled power inverter driving an electric motor that is used for vehicle propulsion or some form of mechanical actuation. 
         [0011]    A large group of battery modules can also be used by an electric utility company to help equalize a local power distribution network&#39;s worst-case supply fluctuation episodes. The modules are installed inside a ‘battery station’, which is a large rigid stationary weather-proof climate-controlled enclosure that is secured to a concrete foundation. The modules are mounted and electrically connected via racks with docks so that any module can be rapidly connected or disconnected. 
         [0012]    Battery packs and battery stations typically have other subassemblies and components installed inside them in order to deliver complete end-item battery packs to vehicle manufacturers or complete end-item battery stations to electric utility companies. These subassemblies and components include electronic sensor modules, electronic control modules, electrical charging modules, electrical interface connectors, electrical fuses, electrical wiring harnesses, and thermal management means. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    In general, in one aspect, a method of manufacturing a battery includes: supplying a busbar having a U-shaped portion defining a channel and characterized by a bend corner at one end of the U-shaped portion, wherein the busbar has a reduced-reflectivity treatment at least in the vicinity of the bend corner; positioning a single battery terminal in the channel formed by the U-shaped portion so that the top end of the terminal is proximate to the bend corner; directing a laser beam at the bend corner of the U-shaped portion; and with the laser beam, melting the busbar at the bend corner and forming a metallurgical bond between the busbar and the top end of the single terminal. 
         [0014]    In certain embodiments, the busbar is attached to the battery cell terminal using laser welding where the laser beam is directed primarily at the area of reduced reflectivity. In certain of these embodiments, the laser beam is directed at an angle substantially head-on to the end of the battery cell terminal. In certain of these embodiments, the laser beam may move in a direction of travel parallel to the channel, where in some embodiments, the laser beam may be directed at an angle slightly less than perpendicular to the direction of travel. 
         [0015]    In some embodiments, the reduced-reflectivity treatment comprises a coating of one or more of nickel and tin. 
         [0016]    Other embodiments further comprise forming the busbar by joining a first busbar segment to a second busbar segment, wherein the first segment is made of a first metal and the second segment is made of a second metal that is different from the first metal. In certain of these embodiments, the first busbar segment is ultrasonically welded to the second busbar segment prior to attaching the busbar to the terminal. In some of these certain embodiments, the first segment is stamped and the second segment is extruded. In other of these certain embodiments, the first segment is made primarily of copper and the second segment is made primarily of aluminum, and these embodiments include those wherein at least one of the first segment and second segment is extruded. In still other of these certain embodiments, positioning the battery terminal in the channel comprises the steps of attaching the battery cell to a heatsink; attaching a busbar support to the heatsink; and mounting the busbar to the busbar support. 
         [0017]    In some embodiments, the battery cell is a prismatic battery cell. 
         [0018]    Certain embodiments further comprise securing a wiring clip to the busbar prior to attaching the busbar to the battery cell terminal. In certain of these embodiments, the wiring clip, the busbar and the battery cell terminal are attached together at the same time using laser welding, and may further comprise attaching a wire to the wiring clip prior to securing the wiring clip to the busbar. In certain embodiments comprising securing a wiring clip to the busbar prior to attaching the busbar to the battery cell terminal, the embodiments may further comprise attaching a wire to the wiring clip prior to securing the wiring clip to the busbar, and in addition, the wire may be attached to the wiring clip using ultrasonic welding. 
         [0019]    Additional embodiments include wherein positioning the battery terminal in the channel comprises the steps of attaching the battery cell to a heatsink; attaching a busbar support to the heatsink; and mounting the busbar to the busbar support. 
         [0020]    Also in general, in one aspect, a battery comprises: a battery cell having a voltage terminal; a busbar having a U-shaped portion defining a channel and characterized by a bend corner at one end of the U-shaped portion, the busbar also having a reduced reflectivity treatment at least in the vicinity of the bend corner, wherein the voltage terminal extends into the channel formed by the U-shaped portion and has a top end that is proximate to the bend corner; and a metallurgical junction formed between the top end of the terminal and the busbar inside the channel at the bend corner. The battery has various embodiments, including each of the following. 
         [0021]    In certain embodiments, the metallurgical junction is formed by a laser weld where a laser beam has been directed primarily at the area of reduced reflectivity. In certain of these embodiments, the laser beam has been directed at an angle substantially head-on to the end of the battery cell terminal. In certain of these embodiments, the metallurgical junction is formed by a laser beam moved in a direction of travel parallel to the channel, where in some embodiments, the laser beam may have been directed at an angle slightly less than perpendicular to the direction of travel. 
         [0022]    In some embodiments, the reduced-reflectivity treatment comprises a coating of one or more of nickel and tin. 
         [0023]    In still other embodiments, the busbar comprises a first busbar segment joined to a second busbar segment, wherein the first segment is made of a first metal and the second segment is made of a second metal that is different from the first metal. In certain of these embodiments, the first busbar segment is ultrasonically welded to the second busbar segment. In some of these certain embodiments, the first segment is stamped and the second segment is extruded. In other of these certain embodiments, the first segment is made primarily of copper and the second segment is made primarily of aluminum, and these embodiments include those wherein at least one of the first segment and second segment is extruded. Still other of these certain embodiments further comprise a busbar support attached to the heatsink wherein the busbar is mounted to the busbar support. 
         [0024]    In some embodiments, the battery cell is a prismatic battery cell. 
         [0025]    Certain embodiments further comprise a wiring clip secured to the bus. In certain of these embodiments, the wiring clip, the busbar and the battery cell terminal are attached together at the same metallurgical junction, and some such embodiments may further comprise a wire attached to the wiring clip. In certain embodiments, the wire may be attached to the wiring clip by an ultrasonic weld. 
         [0026]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0027]    For a fuller understanding of the nature and objects of the present invention, reference should be made to the following detailed description taken in connection with the accompanying drawings in which the same reference numerals are used to indicate the same or similar parts wherein: 
           [0028]      FIG. 1  shows a battery module. 
           [0029]      FIG. 2  shows a battery module with busbar covers and busbars removed and with cell subassemblies exposed. 
           [0030]      FIG. 3  shows a prismatic battery cell. 
           [0031]      FIG. 4  shows a zipper fuse of a prismatic battery cell. 
           [0032]      FIG. 5  shows a more detailed view of a cell subassembly. 
           [0033]      FIG. 6  shows another view of a cell subassembly. 
           [0034]      FIG. 7  shows an alternative heatsink and cell subassembly. 
           [0035]      FIG. 8  shows another alternative heatsink and cell subassembly. 
           [0036]      FIG. 9  shows a heatsink with attached pressure relief teeth. 
           [0037]      FIG. 10  shows a view of a battery module pressure plate. 
           [0038]      FIG. 11  shows a portion of a band component of a battery module. 
           [0039]      FIG. 12  shows several busbar supports, attached to cell subassemblies in a battery module, including a reduced-height cell subassembly. 
           [0040]      FIG. 13A  shows a busbar support attached to a heatsink. 
           [0041]      FIG. 13B  shows an alternative busbar support to support one battery cell. 
           [0042]      FIG. 14  shows several busbar supports attached to cell subassemblies in a battery module, each retaining at least a portion of a busbar jumper. 
           [0043]      FIG. 15  shows a side profile of a busbar jumper. 
           [0044]      FIG. 16  shows a busbar terminal in relation to pressure plate and cell subassemblies. 
           [0045]      FIG. 17  shows a busbar terminal attached to a pressure plate and a busbar bridge. 
           [0046]      FIG. 18  shows a busbar terminal with two variations of clips for attachment of wiring. 
           [0047]      FIG. 19  shows a side view of a wiring attachment clip. 
           [0048]      FIG. 20  shows a support clip for attachment of a thermistor. 
           [0049]      FIG. 21  shows a cutaway view of a busbar cover. 
           [0050]      FIG. 22  shows a family of battery modules incorporating a scalable architecture. 
           [0051]      FIG. 23  shows pressure relief teeth. 
           [0052]      FIG. 24  shows several arrangements of busbar components that may be used to achieve various configurations of battery modules. 
           [0053]      FIG. 25  shows views of a configuration of a welding laser with respect to a busbar component. 
           [0054]      FIG. 26  shows before and after views of the attachment of a busbar component to a battery cell terminal. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    A battery module consists of an assembly of cell subassemblies, each containing prismatic battery cells, where the cells are electrically connected to the other cells in the module to form the battery module. The term ‘prismatic’ refers to the shape of the battery cell that is described herein and it differentiates this module from other modules with cylindrical battery cells. 
         [0056]      FIG. 1  shows a battery module  10  with a negative terminal  20  and a positive terminal  21 . The battery module  10  contains one or more cell subassemblies  30 . As described in more detail below, the cell subassemblies are a basic building block from which battery modules of arbitrary scales may be constructed. The cell subassemblies contain prismatic battery cells (not shown), each of which provides a portion of the battery&#39;s electrical power and storage capacity. The cell subassemblies  30  are held together by pressure plates  50  and bands  51 . Pressure plates  50  act as a mounting mechanism for the battery module, and contain one or more mounting passages  52  to allow the module to accept hardware (not shown) to mount the battery module  10  within, for example, a battery pack enclosure or on a battery station&#39;s rack in various mounting orientations. The individual battery cells are electrically connected in parallel and/or series by busbars (described below) which connect the cells to one another and to the terminals of the battery, all of which are on one side of the battery module. That side of battery module  10  is covered with one or more busbar covers  40 . 
         [0057]      FIG. 2  shows a battery module  10  with busbars and busbar covers removed to reveal a view of the inside of cell subassemblies  30 . Each subassembly contains one or two prismatic battery cells  300 , each cell having a positive terminal  301  and negative terminal  302 . Terminals  301  and  302  are connected electrically in series and/or parallel by busbar jumpers (not shown). Busbar terminals (also not shown) connect some of the battery terminals to either the battery module&#39;s negative terminal  20  or positive terminal  21 . 
         [0058]    The prismatic battery module described herein has a group of identical cells. The quantity of cells per module and the module&#39;s electrical connection configuration (parallel count versus series count) defines the module&#39;s electrical characteristics and performance ratings. For example, a module with a ‘23S3P’ configuration has sixty-nine (69) cells, twenty-three (23) subgroups that are electrically connected in series, and three (3) cells in each subgroup that are electrically connected in parallel. Depending on the configuration, battery modules may contain either an even or an odd number of battery cells. 
       Prismatic Battery Cell 
       [0059]      FIG. 3  shows a prismatic battery cell  300 . A prismatic cell has two large flat surfaces, top surface  306  and bottom surface  307  (not visible), that are basically parallel to each other and which are used for mechanical retention and thermal management inside the module. The cell&#39;s enclosure may be referred to as a ‘pouch’ because it is a non-rigid flexible sheet that is folded and bonded to create a cost-effective environmentally-sealed housing. The pouch&#39;s material is a thin aluminum foil with a polymer coating applied to both surfaces. The pouch is folded at the bottom edge which provides a seal boundary  303 . The polymer coated pouch is formed into a thermally-bonded flange at the two sides, which creates two more seal boundaries  304  and  305 . This arrangement decreases the module&#39;s physical volume without a decrease in net performance. The side flange&#39;s size is selected so as to ensure long-term robustness. The cell&#39;s side flanges are folded to create a compact width. 
         [0060]    The cell&#39;s two flat electrical terminals, positive terminal  301  and negative terminal  302 , protrude from one of the pouch&#39;s edges and the terminals are environmentally-sealed using electrically-isolative polymeric perimeter seals. The remaining portion of the pouch&#39;s terminal edge is thermally-bonded to create a fourth environmentally-sealed boundary, which completes the cell&#39;s perimeter seal. The terminals are positioned symmetrically with respect to the center axis  315 , and preferably the terminals are in the center plane of the battery cell. Accordingly, battery cell  300  may be “flipped” 180 degrees around center axis  315  with the result that each terminal is in the same position that the opposite terminal held prior to “flipping” the cell (relative to viewing the cell along axis  315  facing the edge containing the cell terminals). This symmetry allows one to stack up a series of cells without regard to whether the negative terminal is on the left or right side (as viewed along center axis  315 ), and in either orientation the resulting rows of terminals will each be aligned in a straight row, and thus may be easily interconnected to one another. Specifically, battery modules can be built with different combinations of series and parallel connections by (1) selectively orienting the battery cells so that the terminals on the same left/right side of adjacent battery cells have either the same or opposite polarities; and (2) electrically connecting groups of these adjacent terminals using busbar components (described below) with connections between terminals of opposite polarities forming series configurations and connections between same-polarity terminals forming parallel configurations. The negative terminal&#39;s material is copper and the positive terminal&#39;s material is aluminum to compliment the cell&#39;s chemistry and internal construction. The terminal length is small compared to other commercially-available designs. The opportunity to use compact terminals is clarified in the subsection entitled ‘Busbar Components’. For the purpose of explanation, ancillary negative and positive symbols have been added to the cell of  FIG. 3 . 
         [0061]    The battery cell&#39;s non-rigid flexible pouch will physically expand if a worst case electrical overload incident occurs. Pressure relief (also known as out-gassing) during an electrical overload incident may be provided through the use of a “tooth” mounted externally to the cell, either as alternative to or in combination with pressure relief vent feature  309 . The tooth will puncture the cell in a controllable manner if the cell were to expand into contact with it. This tooth is described further below. 
         [0062]      FIG. 4  shows zipper fuse  308  integrated into an electrical terminal  302  of battery cell  300 . Zipper fuse  308  includes two rows, each row made up of a slot-shaped hole  310  at one end of the row and circular-shaped holes  311  between the slot-shaped hole  310  and the other end of the row. This fuse is referred to as a ‘zipper’ fuse because looks like a zipper. The zipper fuse is incorporated in the cell&#39;s negative terminal. The geometry, number and position of the zipper fuse slot holes  310  and circular holes  311  are selected so that the fuse actuates within a specified time period that prevents a cascading failure mode with the adjacent cells or potentially all of the cells in a module. Specifically, the fuse slot holes help to ensure a consistent pattern of fuse activation by concentrating current “hot spots” near the region around the holes, to promote fuse activation to start in those areas. The use of circular holes in addition to the slots helps, among other things, to maintain the structural integrity of the terminal prior to fuse activation. The positioning of the two parallel rows of slot holes and circular holes creates a region  312  between the rows that is partially thermally isolated from the remainder of the terminal, which concentrates the heat developed during fuse activation to help make the activation more complete and consistent. 
       Battery Subassembly 
       [0063]      FIG. 5  shows a group of cell subassemblies, including subassemblies  30   a  and  30   b . Subassembly  30   a  includes a heatsink  400   a  having two large, flat surfaces, as well as a battery cell  300   a  which also has two large, flat surfaces. Battery cell  300   a  is adjacently mounted to heatsink  400   a  such that the second large, flat surface of battery cell  300   a  abuts the first large, flat surface of heatsink  400   a . Subassembly  30   a  also includes a compliant pad  401   a  having two large, flat surfaces and a second battery cell  310   a  having two large, flat surfaces. Compliant pad  401   a  is adjacently mounted to battery cell  300   a  such that the first large, flat surface of battery cell  300   a  abuts the second large, flat surface of compliant pad  401   a . Compliant pad  401   a  is also adjacently mounted to battery cell  310   a  such that the first large, flat surface of compliant pad  401   a  abuts the second large, flat surface of a second battery cell  310   a . This arrangement forms a repeating “cassette” configuration of a battery cell, a heatsink, another battery cell, and a compliant pad, followed by another grouping of a battery cell, a heatsink, another battery cell, and a compliant pad, and so on. Compliant pad  401   a  helps to distribute pressure between the subassemblies when they are banded together between the pressure plates, as well as allowing expansion/contraction of cells during use. Similarly, subassembly  30   b  is mounted adjacently to subassembly  30   a . Subassembly  30   b  includes a heatsink  400   b  having two large, flat surfaces, as well as a battery cell  300   b  which also has two large, flat surfaces. Heatsink  400   b  is adjacently mounted to battery cell  310   a  such that the first large, flat surface of battery cell  310   a  abuts the second large, flat surface of heatsink  400   b . Battery cell  300   b  is adjacently mounted to heatsink  400   b  such that the second large, flat surface of battery cell  300   b  abuts the first large, flat surface of heatsink  400   b . Subassembly  30   b  also includes a compliant pad  401   b  having two large, flat surfaces and a second battery cell  310   b  having two large, flat surfaces. Compliant pad  401   b  is adjacently mounted to battery cell  300   b  such that the first large, flat surface of battery cell  300   b  abuts the second large, flat surface of compliant pad  401   b.    
         [0064]    As shown in both  FIG. 5  and  FIG. 2 , all of the heatsinks are bonded to the adjacent cells during the module&#39;s assembly process via a dispensed cure-after-assembly adhesive that is also used to bond the compliant pads to the adjacent cells. The group of cells, pads, and heatsinks creates the main stack subassembly for every module, which fosters a scalable architecture. In other words, one can readily change the size of the module by simply adding or subtracting identical subassemblies. The subassemblies may or may not be pre-assembled as such and then later assembled together as sub-units into the battery module&#39;s main stack. The assembly of the main stack may be accomplished as a one-step process where all of the battery cells, heatsinks and compliant pads are assembled together in one process. The concept of a ‘subassembly’ is used as a convenient label for a logical group of components when describing the overall structure of the battery module. 
         [0065]    Also as shown in  FIG. 5 , each of the battery cells (e.g.,  300   a ,  310   a ,  300   b  and  310   b ) are mounted on respective heatsinks (e.g.,  400   a  and  400   b ) with their positive terminals oriented on the left or right as viewed end on at the terminals. For example, in  FIG. 5 , battery cells  300   a ,  310   a , and  300   b  are each oriented with their negative terminals to the right from the perspective of  FIG. 5 , while battery cell  310   b  is mounted with its positive terminal to the right. Other orientations of groups of battery cells (e.g., flipping battery cell  310   b  180 degrees so that its positive and negative terminals exchange positions) allow different combinations of series or parallel connections between the terminals depending on which groups of adjacent terminals are electrically connected by the busbar jumpers and terminals described below. 
         [0066]      FIG. 6  shows a view of a cell subassembly  30  from which battery module  10  is built.  FIG. 6  shows a heatsink  400  joined to a battery cell  300 , which in turn is joined to a compliant pad  401 .  FIG. 6  does not show the adjacent cell that would be joined to compliant pad  401  as described above and in  FIG. 5 . Referring still to  FIG. 6 , when subassembly  30  is stacked adjacent to another subassembly, the metallic heatsink  400  contacts two cells  300  and  310 . Each cell contacts the heatsink via one of the cell&#39;s two flat surfaces to facilitate thermal management via conduction or forced convection heat transfer. This results in requiring only about half the number of heatsinks per module as compared to using a heatsink for each cell. The benefit is a compact module which has an improved power output/physical volume ratio compared to other commercially available modules some of which have larger and more elaborate heatsinks. 
         [0067]    The heatsink is made from an aluminum sheet that is stamped and formed using standard tooling practices. The heatsink has an electrically-isolative coating to ensure that a worst-case electrical overload incident does not allow an electrical short circuit path to any or all of the heatsinks. The coating thickness is preferably chosen so as to not substantially impede heat transfer. Protective coatings and application processes may be selected to simultaneously provide the electrical short circuit protection during an electrical overload incident, permit effective heat transfer, and reduce cost. 
         [0068]    Another function of the heatsink is to protect the cells from foreign objects during a severe vehicle crash. As discussed previously, the heatsink&#39;s formed wings  403  nest with an adjacent heatsink&#39;s profile to provide a satisfactory level of cell protection with respect to complexity, cost, and the module&#39;s physical volume. These wings are formed by folding three of the heatsink&#39;s edges at approximately a right angle to the large flat surfaces of the heatsink. 
         [0069]    Referring now to  FIG. 5 , an indentation ( 404   a ,  404   b ) is formed from the heatsink by using additional bends near the area of the wing that meets the large flat surfaces of the heatsink to receive a portion of an adjacent heatsink&#39;s wings. For example, indentation  404   b  is formed to receive a portion of wing  403   a . This makes the heatsinks with their internal components easier to stack on top of one another. The battery pack&#39;s enclosure may be the major protection barrier during a crash, so the heatsinks are another barrier to further improve the battery module&#39;s safety capability. 
         [0070]    A second type of heatsink with short formed wings that envelop only one battery cell (as opposed to the “full-height” heatsinks that envelop two cells) is used if a module has an odd cell count, where the second type of heatsink is located at one end of the stack of subassemblies. In these odd cell count configurations, no battery cell is attached to the bottom of the bottom-most heatsink, as is shown in  FIG. 5 . 
         [0071]      FIG. 7  shows this second type of heatsink  420  that nests into an adjacent cell subassembly  421 . Heatsink  420  is joined to battery cell  320  in the same manner as the full-height heatsinks are attached to adjacent cells.  FIG. 7  also shows the use of two compliant pads,  422   a  and  422   b , which are used at both ends of a module&#39;s main stack in order to distribute and equalize the clamp force imparted to the stack by the pressure plates. This second type of heatsink is also used if a module has an even cell count, but even cell count modules also use a third type of heatsink. 
         [0072]    A third type of heatsink with medium-height formed wings that envelop only one battery cell may also be used if a module has an even cell count, where the third type of heatsink is located at one end of the stack of subassemblies opposite the end with the second type of heatsink. In these even-cell-count configurations, this third type of heatsink is nested adjacent to a heatsink that would otherwise have an exposed battery cell. For example, referring to  FIG. 8 , this third type of heatsink  430  rests beneath the lower-most heatsink  429  to help protect a single battery cell  321  located between heatsinks  429  and  430 . Two compliant pads (not shown) are adjacently mounted to each other, and one side of one of the compliant pads is adjacently mounted to heatsink  430  at the end of the module&#39;s main stack of subassemblies. 
         [0073]    While these additional types of heatsinks cause additional components to be released and produced in the manufacturing process, they fully respect the principle that a heatsink contact every cell via one of the cell&#39;s two large flat surfaces, and that every cell be protected from foreign objects during a severe vehicle crash. 
         [0074]      FIG. 9  shows a heatsink  400  with pressure release teeth  410  and  411  mounted through holes in the heatsink. One tooth  410  is oriented so that its sharp end points toward one of the heatsink&#39;s attached battery cells, and if a second cell is joined to the heatsink, the other tooth  411  is pointed toward that cell. An additional pair of teeth may be positioned elsewhere on the heatsink  400  or on the busbar support connected to the heatsink. The tooth&#39;s material is molded plastic and it is either heat-staked or ultrasonically-welded to a plain hole in the stamped aluminum heatsink. If an electrical overload incident occurs, the cell&#39;s non-rigid flexible pouch will physically expand due to rapid internal gas generation. As it expands, the force of the internal pressure will press the pouch against the tooth, puncturing the cell and providing a controlled relief of the internal pressure. The battery cell has a port that helps define a specific region in which the pouch can expand, and within which the sharp point or edge of the tooth is at least partially situated to puncture the pouch when it expands. Although the battery cell can expand along multiple expansion paths, the port helps to define and promote expansion along at least one such path. The expansion of the pouch may be also be partially controlled by creating a region of the pouch of increased expandability relative to the rest of the battery cell. In some embodiments the port may expose a region of increased expandability. In any of these embodiments, the sharp point of the tooth is situated along at least one of the expansion paths of the pouch. 
         [0075]      FIG. 23  shows two additional alternative embodiments of pressure release teeth. Tooth  450  includes a point  451  and two channels  452 . Tooth  455  includes two points  456  and two channels  457  extending away from the region of the point. The structure of tooth  455  (along with other embodiments that use a sharp edge instead of a point) may help promote the formation of a ‘tear’ or rip in the pouch to promote gas escape. In each of these types of teeth, the channels help to provide a path for the gases to escape from the battery cell and to ensure the pouch does not inadvertently re-seal itself closed (despite the puncture) against the tooth. Other orientations and combinations of sharp points and channels may also be used, as may other combinations of sharp edges and/or channels. 
         [0076]    The tooth is produced from a non-conductive material to help prevent a short between the interior of the battery cell and the heatsink. 
         [0077]    As indicated in  FIGS. 5 and 6 , a compliant pad  401  contacts every cell via one of the cell&#39;s two large flat surfaces to provide the following functions: (a) Provide uniform pressure distribution for cell life and performance, (b) provide constant pressure on the cell&#39;s active area throughout the life of the cell, (c) compensate for the cell&#39;s thickness changes due to the inherent nature during charge and discharge cycles, and (d) compensate for the module&#39;s length changes due to the thermal expansion and contraction of the cell and other module components such as the heatsinks, pressure plate, and clamping bands. 
       Pressure Plate Component 
       [0078]      FIG. 10  shows a pressure plate  50 . Pressure plate  50  is a rigid structure imparts a static clamp force to the module&#39;s main stack of cells, compliant pads, and heatsinks. The structure also provides means by which the module can be attached inside a battery pack&#39;s enclosure. This component may be referred to as a ‘pressure plate’ to accentuate the primary function. The plate&#39;s material is a molded plastic polymer with defined temperature exposure and flammability ratings. The plate has a prominent flat surface to mate with one end of the module&#39;s main stack, which has two compliant pads at both ends to help distribute and equalize the clamp force. 
         [0079]    The side of pressure plate  50  that faces away from the subassemblies has a matrix of reinforcing ribs  520  to enhance its structural rigidity and complement the molded part design practice of targeting a uniform wall thickness. The matrix has a non-uniform pattern because the ribs also form pockets which accommodate large electronic components that are soldered to the module&#39;s active control printed-circuit board (PCB) subassembly (not shown). The PCB subassembly includes a circuit board and components, where the majority of the components are on one side of the board. The PCB subassembly is mounted component-side down on pressure plate  50 . The nesting of the electronic components preserves valuable space and contributes to a compact module length at the plate, which helps achieve an excellent power output to physical volume ratio. The plate&#39;s pockets are also valuable because they can be used as receptacles for vibration dampening elements (not shown) to grip the upper surfaces of the large electronic components that are soldered to the module&#39;s active control PCB subassembly. The elements prevent excess stress and fatigue at the solder joints on the PCB. The preferred vibration dampening element is a die-cut pad with an elastomeric closed-cell non-hydroscopic polyurethane foam material and pressure-sensitive adhesive material on one side, which both have defined temperature exposure and flammability ratings. 
         [0080]    The PCB assembly may be either passive or active. Passive PCB assemblies may be sufficient for smaller battery modules, while larger modules use one or two active PCB assemblies, with one assembly mounted on each of the pressure plates at each end of the module. The active PCB control subassembly has three right-angle PCB electrical connector headers that are selectively-soldered to industry-standard plated through holes in the PCB. All other electronic components are SMT (Surface Mount Technology) devices which are reflow-soldered to industry-standard pads on both sides of the PCB. Precautions are taken to ensure a proper electrical isolation between the module&#39;s steel bands and the PCB because the bands are routed nearby. PCB trace, via, and component keep-in and keep-out zones are carefully defined for both sides of the PCB to avoid electrical interference. The module&#39;s life capability may be improved by applying a silicone-based or polyurethane-based conformal coating to both sides of the PCB, which will reduce the growth of dendrites between adjacent low-current high-impedance copper traces. 
         [0081]    Side  510  of pressure plate  50  is opposite the side with the matrix of reinforcing ribs  520 , and faces the stack of subassemblies. Side  510  may be flat, or may form a non-flat shallow convex or concave domed profile to further optimize the force distribution within the module&#39;s main stack. 
         [0082]    Pressure plate  50  has two shallow tracks  501  to receive thin steel retention bands which impart the static clamp force to the module&#39;s main stack. The tracks have a domed profile to help distribute and equalize the clamp force. Appropriate dome profiles may be determined by measurements taken using existing sensing products specifically developed and marketed for this type of instrumentation application. 
         [0083]    Pressure plate  50  also has four passages with recessed sockets  503 ,  504 ,  505 , and  506  (also known as counter-bores) to receive steel fastener components such as cylindrical sleeves, washers, bushings, and retention bolts to foster a flexible attachment strategy. The present configuration permits a module to be mounted inside a battery pack&#39;s enclosure or on a battery station&#39;s rack via one of three mounting orientations, which is adequate for the majority of existing and predicted applications and customer requirements. 
         [0084]    The pressure plate may be formed from two separate portions which are vibration-welded together. Each portion would have half of the attachment hole and recessed socket profiles. After welding, complete circular holes and sockets would be formed. The benefit of this approach would be that the two portions could be molded without long active slides in the molding tool that are perpendicular to the tool&#39;s principle die draw direction. 
         [0085]    Pressure plate  50  has two recessed areas  508  to receive a steel busbar nut or nuts (not shown). The nut&#39;s design is intentionally simple to be a cost-effective solution. The nut has three threaded holes for attachment. The center hole grips a steel fastener (not shown) that retains the busbar nut to the pressure plate. The two other holes grip steel fasteners that attach an external power lug and wiring harness to the module&#39;s negative or positive busbar, which are explained in subsequent sections. 
       Band Component 
       [0086]      FIG. 11  shows steel band  530 , which is one of two steel bands used to envelop the module&#39;s main stack of cells, compliant pads, heatsinks, and pressure plates. Each steel band  530  sits in one of the shallow tracks  501  of pressure plate  50 . Two bands are sufficient and three bands are not necessary, if the module has seventy-six (76) cells or less. More bands can be used if desirable. The length of steel band  530  is defined by the required clamp force to properly compress all of the compliant pads in the main stack, and it is retained via an existing released and qualified steel buckle  531  that is permanently crimped onto the band. A hand-held pneumatic applicator with a pneumatic actuator may be used to tension the band and crimp buckle  531 , and the applicator may also have a mechanism to trim the band&#39;s extra tail after buckle  531  is crimped. Compared to an alternative approach that uses very long steel tie rods and retention nuts at both ends, using the bands and buckles is a more compact approach. The use of the same band and buckle and installation process for every module fosters a scalable architecture. Another approach is to tension and weld the band, instead of using the crimped buckle. The pressure plate  50  may incorporate flat or indented areas within the shallow tracks  501  to accommodate the clamping band buckles and to more evenly distribute the pressure in the region of the buckles. Pressure plate  50  may also have four corner rounds along each track  501  to ensure that the tensile forces are equalized in the straight portions of the two bands. 
         [0087]    An existing released and qualified hand-held computer-controlled electric applicator with a closed-loop servo control may be used instead of the standard pneumatic actuator. This may increase applied static clamp force precision and reduce band installation and buckle crimping process cycle times. While the pressure plates and bands help hold the battery module together physically, the module&#39;s busbars (described next) connect the system electrically. 
       Busbar Support Component 
       [0088]    The electrical interconnection between the module&#39;s adjacent cells is an important feature, which includes the registration of the flexible and fragile cell terminals relative to each other, and includes preventing an accidental contact between adjacent terminals that will not be electrically connected for the intended application.  FIG. 2  shows how all of the cells are securely retained and registered relative to each other in the module&#39;s main stack, except for the cell terminals, e.g.,  101  and  102 . 
         [0089]      FIG. 12  shows a robust, compact, and cost-effective solution using a molded plastic component. The component may be referred to as a ‘busbar support’ to accentuate its primary function. The standard busbar support  600   a  mates with the upper edge of one heatsink  600   a  and also envelops the two cells  300   a  and  310   a . Cells  300   a  and  310  are each affixed to respective a side of the heatsink, and each has two electrical terminals (the negative terminals of each battery cell  300   a  and  310   a  are shown in  FIG. 12 ) which extend through ports in the busbar support. A busbar support is used for every subassembly and fosters a scalable architecture. For example, busbar support  600   b  mates with the edge of the second type of heatsink, heatsink  400   b.    
         [0090]      FIG. 13A  shows another view of a busbar support  600  mounted to heatsink  400 . The standard busbar support has nine features/functions:
       1. Seven flex tabs  608  (four shown) as well as two wedge-shaped latches  609  to grip two slots (component  406  in  FIG. 5 ) in a heatsink.   2. Rectangular central port  604  to interface with a thermistor  605  that has an over-molded elastomeric grip.   3. Four tapered ports  601  to permit the simultaneous insertion and registration of four cell terminals.   4. Main body  610  that supports a busbar during a cell zipper fuse actuation incident. By maintaining a separation between any remainder of the terminal and the busbar, the busbar support prevents an accidental reconnection of the faulty cell to the busbar, which could cause a cascading failure mode with the adjacent cells.   5. Two fixed latches  602  and two flex latches  603  to grip two separate busbar components (not shown) during the laser welding of the busbars to the cell terminals. This feature helps eliminate the need for a special laser welding fixture. As described below, it functions as an assembly jig that secures the busbar components in registration with the cell terminals prior and during welding. These latches retain each busbar component in a substantially fixed position relative to the heatsink and the attached battery cells. The tapered ports and main body retain the terminals of each of the battery cells in a substantially fixed position relative to the heatsink and to the busbar component.   6. Eighteen reliefs  607  to ensure adequate clearance to any busbar electrical connection rivet.   7. Central channel  606  to permit the routing of the module&#39;s voltage sense wiring harness and thermistor wiring harness.   8. Four flex fingers ( 611 ) to retain the two wiring harnesses (not shown) before the busbar covers are installed.   9. Two screw bosses  612  at the ends for the attachment of the busbar covers.         
         [0100]    In addition,  FIGS. 13B and 16  show a second busbar support  650  that has been developed to envelop only one cell if a module has an odd cell count. While this decision causes another component to be released and produced, it fully respects the principle that every cell terminal be registered and protected from an accidental contact with an adjacent terminal. The module&#39;s vibration endurance robustness may be improved by adding two or more additional slots in the heatsink near the center and/or adding two more wedge-shaped latches in the busbar support. 
       Busbar Components 
       [0101]    Busbar components consist of busbar jumpers, which electrically connect the module&#39;s adjacent cells, and busbar terminals, which electrically connect one or more battery cell terminals to each of the external terminals of the battery module.  FIG. 14  shows a robust, compact, and cost-effective interconnection approach using these busbar components to enhance the module&#39;s life capability. This approach avoids using threaded fasteners for any of the electrical connections inside the module and to instead use precision welds that are produced with adaptive automatic computer-controlled processes. 
         [0102]      FIG. 14  shows several busbar jumpers  700  each held by busbar supports  600 . For each of the busbar supports through which a battery cell&#39;s terminal extends, the busbar jumper connected to that terminal is gripped between the support&#39;s fixed latch and its opposing flexible latch. The latches retain the busbar jumper against the terminal and prevent its movement. 
         [0103]      FIG. 15  shows a bimetallic busbar jumper  700 . The battery module uses a group of busbar jumpers  700 , each including a copper portion  701  that is laser welded to a group of cell negative terminals which are made of a copper material, and an aluminum portion  702  that is laser welded to a group of cell positive terminals made of an aluminum material. The busbar jumper&#39;s 180-degree bends  703  define an inside surface  704  in which the cell terminals are nested during assembly. The portions of the busbar that have the bends are continuous pieces of metal. Precision laser welding is used to partially melt and metallurgically connect the busbar jumpers to the terminals in order to avoid ultrasonic welding that could inflict too much energy into a cell terminal and in turn damage a cell&#39;s internal electrical connections. A liquid welding treatment is applied to the outer surface (opposite inner surface  704 ) of the busbar jumper&#39;s bends  703 . During welding, laser energy will be aimed at this surface. This treatment creates a finish that decreases the reflectivity of the laser beam during laser welding of the highly reflective surfaces of both aluminum and copper. This treatment may be a Nickel or Tin coating that provides for better absorption of the Nd-YAG laser beam wavelength. This allows one to minimize the energy required to weld and allows for the welding of cell terminals to be conducted without exceeding a maximum temperature limit of the cell terminal&#39;s seal. The laser beam&#39;s energy penetrates the busbar&#39;s 180-degree bend  703  and creates a molten bead inside the busbar&#39;s bend  704  and at the tip of the cell&#39;s terminal (not shown). The welding laser is aimed at the busbar&#39;s bend  703  at an angle substantially head-on to the end of the battery terminal and toward the outer surface of the bend as shown by angle of attack  708 . 
         [0104]      FIG. 25  shows an additional view  735  of the configuration of a welding laser  730  and a bimetallic busbar jumper  700 , with the laser beam  733  directed at the busbar&#39;s bend at an angle of attack  708  that is substantially head-on to the end of the battery terminal. A second view  740  shows the configuration of view  735  as seen along line of reference  736  (i.e., view  735  rotated 90 degrees around the vertical z axis). View  740  shows laser  730  moving from the right side end of the busbar&#39;s bend  742  to the left, where the laser beam  733  moves in a direction of travel parallel to the channel, with the laser beam  733  directed at a slight angle  741  with respect the bend  742 , with angle  741  opposing the direction of travel of the laser  730  to prevent the laser beam from backreflecting into the laser optics and causing damage. This results in laser beam  733  directed at an angle slightly less than perpendicular to the direction of travel of the laser beam. During welding, the laser  730  may move relative to the busbar and battery terminal being welded, the busbar and battery terminal assembly may move relative to the laser, or both may be moved relative to each other. The result in any case is that the busbar and battery terminal are attached to each other along the length of the channel in which the battery terminal resides. 
         [0105]      FIG. 26  shows side views of the attachment of a busbar component to battery cell terminal both before and after attachment. View  770  shows a bend  704  in a busbar  700  forming a channel in which battery terminal  771  is positioned. View  775  shows these components after welding in which the battery terminal  776  is attached to an inside corner of a bend in a busbar  777  by a resolidified pool of metal  778 . 
         [0106]    Welding processes such as laser welding or other conventional welding processes may not be practical to use to join a bimetallic jumper busbar&#39;s two portions together due to the dissimilar materials and known metallurgical constraints. Instead, busbar jumper  700  employs an ultrasonic roller seam welding process to create a linear weld  705 . The ultrasonic welding of the jumper busbar&#39;s two portions is performed separately from the module so that ultrasonic energy is not introduced into a cell terminal, in turn risking damage to a cell&#39;s internal electrical connections. As noted above, the busbar supports act as welding jigs. The busbar supports hold the busbar components in place with the cell terminals nested in the slots defined by the bends in the busbars until the busbars are laser welded to the terminals as discussed above. 
         [0107]    To further balance and optimize the electrical current characteristics of the bimetallic jumpers, the cross-sections, widths and/or thicknesses of the jumper busbar&#39;s two portions—whose materials are aluminum and copper—may be independently tailored to achieve similar resistances through each portion. In manufacturing the busbar jumpers, extruded cut-to-length profiles for one or both of the bimetallic jumper busbar&#39;s two portions may be used instead of sheet stamping and forming processes in order to reduce cost. In one configuration, the copper portion of the busbar jumper is stamped and the aluminum portion is extruded. 
         [0108]      FIG. 16  shows a busbar terminal  750  secured in part by busbar supports  600  and  650 . Busbar supports retain the busbar terminals in the same manner as the supports retain the busbar jumpers. Busbar terminal  750  is laser welded to a corresponding terminal of battery cells  300   a ,  310   a , and  320 . Battery modules use a monometallic negative busbar terminal with a copper material at one end of the module&#39;s main stack and a monometallic positive busbar terminal with an aluminum material at the other end of the module&#39;s main stack. The busbar terminals are secured by steel busbar nuts  760  that are attached to the sockets  508  of the pressure plate  50 . The busbar terminal  750  has a tapered central portion  751  that acts as a module fuse if a worst-case electrical overload incident occurs. The fuse will have a tendency to melt at the narrow portion where the current density if the highest. The module&#39;s safety capability may be improved by adjusting the actuation response time of the two module fuses by adding zipper fuse holes and slots to the busbar terminals in a similar manner to the way zipper fuses are integrated into the battery cell terminals. 
         [0109]      FIG. 17  shows the installation of busbar terminal  750  to pressure plate  50 . Busbar terminal  750  is attached to a steel busbar nut (not visible under busbar terminal in  FIG. 17 ). The busbar nut is attached to one of the pressure plate&#39;s sockets  508   a . Busbar terminal  750  is connected to an external power lug and wiring harness (not shown) as described earlier. In addition, a stamped copper busbar nut bridge  780  may be connected to busbar terminal  750  and also connected to pressure plate socket  508   b  through busbar nut  760   b . Busbar nut  760   b  is secured to pressure plate  50  through a center hole that grips a steel fastener disposed in pressure plate socket  508   b . The bridge is an accessory that permits an optional attachment site for the module-to-module high-power wiring harness. 
       Wiring Attachments 
       [0110]      FIG. 18  shows a busbar terminal  750  with two variations of clips used to attach wiring, such as voltage sense wiring harnesses, to busbar terminals and busbar jumpers. From one side, clip  791  is u-shaped and substantially convex, while clip  790  is w-shaped. Either or both of clips  790  and  791  may be used to connect wiring. Voltage sense wires are ultrasonically welded to the clips prior to attaching the clips to the busbar components. The clips have one or more teeth  793  that bite into the busbar jumpers or terminals so that the clips can be positioned and retained in place until a laser welding operation fastens the clips to the busbar. The clips may be of stamped copper or aluminum corresponding to and compatible with the type of busbar to which they will be attached. Clips have notching  792  for one metal type to indicate the type of clip for manufacturing using automatic vision systems. These clips are laser welded to the busbar components at the same time the busbar components are welded to the battery cell terminals and share a common weld. Using the same welding technique described above for attaching busbar components to battery terminals, a laser is directed through the clip and the underlying busbar component and pointed at the end of the terminal that rests in the u-shaped bend of the busbar component. In so doing, a single welding operation welds all three components (the clip, the busbar component, and the battery terminal) at the same time. The u-shaped clips may also be laser welded to the busbar component without sharing a common weld. 
         [0111]      FIG. 19  shows a side-view of w-shaped clip  790  with the clip&#39;s teeth  793  bent slightly inward for installation on a busbar. Teeth may or may not be required to secure the clip to the busbar until it is welded if the clip is designed with an interference fit such that the interference would provide the retaining function. 
         [0112]      FIG. 20  shows a busbar terminal  750  with a clip  794  for attaching a thermistor  795  to the busbar terminal. The thermistor&#39;s head is bonded inside the clip&#39;s retainer with a dispensed cure-after-assembly epoxy adhesive. The neck of the thermistor&#39;s head contacts the adjacent tab  796  so that the head has a defined repeatable location. Coined chamfers  797  to the retainer&#39;s upper edges help prevent damage to the thermistor&#39;s head when it is installed. 
       Busbar Covers 
       [0113]      FIG. 1  shows three busbar covers  40 . Battery modules use a group of molded plastic covers to protect the module&#39;s busbars and other internal components, such as the voltage sense wiring harness and thermistor wiring harness, from any accidental contact by external foreign objects, especially if they are metallic. 
         [0114]      FIG. 21  shows a busbar cover  40   a  without the cover&#39;s main flat skin so that the relative fits may be witnessed. Busbar cover  40   b  is also shown, including the cover&#39;s main flat skin. Each of the covers has a matrix of reinforcing ribs, including  801 ,  802  and  803 , to enhance its structural rigidity and to also redirect and distribute any adverse external forces to the module&#39;s busbar supports and heatsinks instead of the busbar terminals  750 , busbar jumpers  700  and/or cell terminals. Busbar covers envelop the module&#39;s busbars to help prevent adjacent busbars from contacting each other and causing electrical short circuit paths during a worst-case electrical overload incident or severe vehicle crash. Certain ribs, e.g., rib  802 , extend deeper into the battery module than other ribs and in between the busbar jumpers, e.g.,  803 , to help prevent contact between adjacent busbars, while ribs such as  803  are less deep to avoid distributing forces to the busbar terminals, busbar jumpers or cell terminals. Alternatively, the battery module may use lower-cost, simpler covers which have an overlap joint and fewer vertical contact tabs. The disadvantage with this latter approach is that the module&#39;s robustness to withstand vertical external forces may be diminished. 
       Scalable Architecture 
       [0115]    The above described features yield a scalable architecture. The term ‘scalable architecture’ refers to a flexible configuration which facilitates the rapid engineering, development, qualification, and production of battery modules that have different quantities of battery cells, subgroups with cells that are electrically connected in parallel, and subgroups that are electrically connected in series. This flexibility enables a battery supplier to tailor the electrical characteristics of many different modules and to satisfy diverse customer performance specifications. For example, the present A123Systems prismatic battery module family with the ‘3P’ configuration is shown in  FIG. 22 . The seven members of this family are the 23S3P, 22S3P, 16S3P, 13S3P, 11S3P, 6S3P, and 1S3P modules, identified respectively in  FIG. 22  as  907 ,  906 ,  905 ,  904 ,  903 ,  902 , and  901 . 
         [0116]      FIG. 24  shows various busbar component configurations for the following members of the A123Systems prismatic battery module family, 13S3P, 23S2P, 4S2P, and 4S6P identified respectively in  FIG. 23  as  950 ,  951 ,  952 , and  953 .