Patent Publication Number: US-2022231381-A1

Title: Structural busbar for battery

Description:
TECHNICAL FIELD 
     The invention relates to busbars. In particular, the invention relates to busbars for batteries, busbar assemblies for batteries and batteries made with the busbars. 
     BACKGROUND 
     Advances in technology and an increasing desire to reduce damage to the environment have led to the more widespread adoption of electric vehicles. Electric cells for electric vehicles are usually grouped together in battery packs. The battery packs need to have sufficient strength to safely contain the cells while allowing electrical connections to them for drawing power and recharging. Due to the number of cells required, electrical vehicles can be considerably heavier than comparable gasoline powered vehicles. 
     This background is not intended, nor should be construed, to constitute prior art against the present invention. 
     SUMMARY 
     A busbar provides electrical connection to a plurality of cells in a battery. The busbar also provides mechanical strength to the structure of the battery pack. The mechanical strength provided to the battery pack is sufficient so that the remainder of the battery pack does not need to be as mechanically strong or as heavy as it would need to be if the busbar were a mere electrical connection. By using the busbar as a structural element, there may also be a reduction in the number of components required, such as fasteners, and a corresponding reduction in complexity. 
     The busbar&#39;s mechanical strength is provided by blisters or other equivalent structures projecting from a plate-like body of the busbar. The outermost ends of the blisters are welded to the terminals of the cells. The configuration of the busbar provides a convenient arrangement for the welding process, and contributes to a robust battery pack. The busbar may be used in a battery pack for a vehicle such as a motorcycle, for example. 
     Disclosed herein is a structural busbar for a battery comprising a metal plate and a plurality of blisters projecting from the metal plate. 
     Also disclosed is a structural busbar assembly for a battery comprising: a first structural busbar comprising a first metal plate and a plurality of first blisters projecting from the first metal plate; a second structural busbar comprising a second metal plate and a plurality of second blisters projecting from the second metal plate; and an insulating spacer between the first and second structural busbars; wherein each of the first and second blisters is spot-weldable to a different electrical terminal of a cell of the battery. 
     Further disclosed is a battery comprising: multiple cells; a battery case holding the cells in an array; a cooling plate to which the cells are glued; a battery case cap defining holes that are located to expose each cell&#39;s electrical terminals; an insulating layer positioned over and spaced apart from the battery case cap, the insulating layer defining holes that provide access to the electrical terminals; a first structural busbar comprising a first metal plate and a plurality of first blisters projecting perpendicularly from one side of the first metal plate, wherein the first structural busbar is positioned over the insulating layer, the first blisters project through the insulating layer and are welded to the electrical terminals having a first polarity, and the first metal plate defines holes that expose the electrical terminals having a second polarity; an insulating spacer positioned over the first structural busbar and defining holes that expose the electrical terminals of a second polarity and a recess behind each first blister; a second structural busbar comprising a second metal plate and a plurality of second blisters projecting perpendicularly from one side of the second metal plate, wherein the second structural busbar is positioned over the insulating spacer, the second blisters project through the insulating spacer, the first metal plate and the insulating layer, and are welded to the electrical terminals of the second polarity, and the second metal plate defines holes that expose a recess behind each first blister; and a collector cap with vent holes positioned over the second structural busbar; wherein the battery case, the battery case cap, the insulating layer, the first structural busbar, the insulating spacer, the second structural busbar, and the collector cap are fastened to the cooling plate. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cut-away perspective view of two structural busbars connected to a battery, according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the two structural busbars connected to a battery, according to an embodiment of the present invention. 
         FIG. 3  is a perspective view of a structural busbar showing the blisters, according to an embodiment of the present invention. 
         FIG. 4  is a perspective view of a structural busbar showing the recesses that are on the reverse side of the blisters, according to an embodiment of the present invention. 
         FIG. 5  is an exploded view of a battery pack with structural busbars, according to an embodiment of the present invention. 
         FIG. 6  is another exploded view of a battery pack with structural busbars, according to an embodiment of the present invention. 
         FIG. 7  is a portion of a circuit diagram showing connections of the structural busbar portions, according to an embodiment of the present invention. 
         FIG. 8  is schematic exploded view of a battery pack with structural busbars, according to an embodiment of the present invention. 
         FIG. 9  is another exploded view of a battery pack with structural busbars, according to an embodiment of the present invention. 
         FIG. 10  is a side cut-away view showing the connections between the structural busbars and the cells, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A. Glossary 
     Busbar—this refers to a metallic strip, spider, plate or other structure, which is used as an electrical conductor for multiple components. Usually, a busbar is a single piece of metal. 
     Structural busbar—this refers to a busbar that provides mechanical rigidity or strength to an assembly of which it is part. This is achieved by using, for example, thicker materials than are necessary for achieving a suitable electrical connection. It may also be achieved by incorporating structural features in the busbar. 
     Cell or electrical cell—this refers to a device capable of generating electricity from a chemical reaction. A cell typically has one positive terminal and one negative terminal. Cells may be rechargeable. 
     Collector—a form of busbar that connects to the terminals of one or more cells. 
     B. Exemplary Embodiments 
     Referring to  FIGS. 1 and 2 , where  FIG. 1  is a cut-away of  FIG. 2 , exemplary structural busbars  10  and  20  are shown. The structural busbar  10  has blisters  12  projecting outwards from plate  14  of the structural busbar  10 . The blisters  12  are beam-like elements with ends  30 . The blisters  12  are connected via their ends  30  to the positive terminals  16  of the cells  18 . Connections of the blisters  12  to the positive terminals  16  are spot-welds or laser spot-welds, for example. Structural busbar  20  has blisters  22  projecting outwards from plate  24  of the structural busbar  20 . The blisters  22  are connected via their ends  31  to the negative terminals  26  of the cells  18 . Connections of the blisters  12  to the negative terminals  18  are spot-welds or laser spot-welds, for example. The structural busbars  10 ,  20  are held apart from each other by an insulating spacer  28  or structural busbar holder that has a portion  33  that lies between the structural busbars. 
     The blisters  12 ,  22  may project perpendicularly from the plates  14 ,  24  of the structural busbars  10 ,  20 . That is, the axes of the beam-like portions of the blisters  12 ,  22  are perpendicular to the plates  14 ,  24 . However, the wall  32  or walls of the blisters may or may not be perpendicular to the bodies. In this example, the walls  32  are inclined or tapered, to form a frustum of a cone, and the blisters  12 ,  22  are therefore cup-shaped. The beam-like structure of the blisters  12 ,  22  provides strength to the structural busbars  10 ,  20 . In particular, the strength or stiffness is at least in part due to the blister  12 ,  22  having at least two non-parallel walls, or two portions  34 ,  36  of the wall  32  that are non-coplanar or non-parallel. As at least two portions  34 ,  36  of the wall  32  are non-parallel, the blisters  12 ,  22  act as structural beams, cantilevered from the plates  14 ,  24  of the structural busbars  10 ,  20 . 
     The formation of ends  30 ,  31  on the blisters  12 ,  22  at the extremities of the non-coplanar walls or wall portions  34 ,  36  add stiffness to the structural busbars  10 ,  20  in particular at the area of the weld. The weld is between the ends  30 ,  31  and the cells  18 . In the example shown, the geometry of the structural busbars  10 ,  20  presents a weld area at the base of the recess  29  that is not occluded or otherwise interfered with. Having stiffness in the structural busbar  10 ,  20  near the weld area allows for a fixturing force near the weld area, while allowing for the structural busbar plate  14 ,  24 , which is in a plane offset from the ends  30 ,  31 , to deflect and compensate for any gaps at the weld sites between the blisters  12 ,  22  and the cells  18 . This applies at the positive terminal  16  at the cap location and the negative terminal  26  at the perimeter crimp location. 
     The reverse sides of the structural busbars  10 ,  20  to the blisters  12 ,  22  have recesses  29  corresponding to the hollow interiors of the blisters as a result of their manufacture. The structural busbars  10 ,  20  are made by forming, for example. Blisters  12 ,  22  may be hydraulically or mechanically formed in metal plates. As there is usually a limit to the depth of offset features such as the blisters  12 ,  22 , they may need to be drawn in multiple steps, taking into consideration the plate thickness, the wall thickness and the properties of the plate material. After drawing, the metal plates are then blanked into individual structural busbars  10 ,  20  by laser or water jet cutting. As one of skill in the art would appreciate, other techniques may be employed to manufacture the structural busbars  10 ,  20 . 
     The structural busbars  10 ,  20  may be made from copper, for example, for its electrical and thermal conductivity. The structural busbars  10 ,  20  may also be made from any other suitable metal such as aluminum, aluminum alloys, copper alloys, silver, etc. The cans and positive terminals of the cells may be steel, for example. The thicknesses of the ends  30 ,  31  of the blisters  12 ,  22  may be, for example, 0.3 mm or less, which tends to be more suitable for laser spot welding. In other embodiments, thicker ends  30 ,  31  may be employed. In these cases, central regions of the ends  30 ,  31  may be thinned by a coining process prior to laser spot welding. The plates  14 ,  24  of the structural busbars  10 ,  20  may be the same thickness or a greater thickness than the ends  30 ,  31  of the blisters  12 ,  22 . 
     In this example, three cells  18  are connected in parallel to the structural busbars  10 ,  20 . However, in other embodiments, any number of two or more cells may be connected. Series, parallel and combinations of series and parallel connections may be used. For example, there may be 36 cells connected with the busbars in series-parallel, or over 120 cells connected in parallel. 
     As it can be seen, the structural busbars  10 ,  20  provide structural elements for securing one end (the top end) of an array of cells  18 . The blisters  12 ,  22  (or other equivalent connecting elements) also provide clearance between the plates  14 ,  24 , which are the main conducting portions of the structural busbars  10 ,  20 , and the tops of the cells  18 . 
     It is evident that other shapes of the structural busbars  10 ,  20  are possible in other embodiments, and also that other shapes of the insulating spacer  28  are possible. 
     Referring to  FIG. 3 , a structural busbar  40  (or collector) is shown. Structural busbar  40  has a plate  41 , which may be considered to be the body of the structural busbar. The side of the structural busbar  40  that connects to the cells is facing upwards, showing the blisters  42 . Also defined in the plate  41  of the structural busbar are holes  44 , which allow blisters of a similar structural busbar to project through and connect to different terminals of the cells than the blisters  42 . The plate  41  also defines fixing holes  46 , which permit the passage of screws, for example, to fasten two structural busbars and an intervening insulating spacer together onto a battery holder or case. 
     The shapes of the blisters may be circular, square with rounded corners, or rectangular with rounded corners, and different shapes may be used in the same busbar. For example, circular blisters may be used for connection to the positive terminals of the cells and rectangular blisters may be used for connection to the negative terminals of the busbars. 
       FIG. 4  shows the reverse side of busbar  40 , showing the holes  44  for accommodating other blisters, fixing holes  46  and recesses  48  inside the blisters. 
     Referring to  FIGS. 5 and 6 , exploded views of a battery pack are shown. The cells  18  are housed in a battery case  50 . An electrically insulating battery case cap  52  is placed over the cells  18  and case  50 , and may be attached thereto by one or more screws in holes  54 , for example. The battery case cap  52  has keyhole-shaped cap holes  53  in it that provide access to the positive terminals  16 A,  16 B and negative terminals  26 A,  26 B of the cells  18 . 
     An insulating layer  56  is placed over the battery case cap  52 , but is spaced apart from it by standoffs, for example, or stepped standoffs that locate the insulating layer  56  as well as maintaining its distance from the battery case cap  52 . Ensuring alignment in X&amp;Y and also height can be critical to weld success, as the welding process requires a high degree of positioning accuracy due to the fact that the target zone on the rim of the cell is small. The geometry of the standoff may be different on other embodiments, but the essential nature of its purpose is the same. 
     There are holes  57  defined in the insulating layer  56  to allow blisters  61 ,  81  on busbars  60 ,  80  to pass through for connection to the cells  18 . There are holes  58  defined in the insulating layer  56  to allow blisters  66 ,  82  on busbars  65 ,  80  to pass through for connection to the cells  18 . Fixing holes  59  are present in the insulating layer  56 , which align with the holes  54  in the battery case cap  52 . 
     Above the insulating layer  56  are two structural busbars  60 ,  65  (or collectors). Structural busbar  60  has blisters  61  projecting downwards through holes  57  for connection to the negative terminals  26 A of some of the cells  18 . Blisters  61  and holes  57  are therefore aligned with regions on the negative terminals  26 A of the cells  18 . Recesses  64  correspond to the insides of the blisters  61 . Also present in structural busbar  60  are holes  62  that allow blisters  82  to pass through from a structural busbar  80  above. Fixing holes  63  are present in the structural busbar  60 , which align with fixing holes  59 ,  54  in the insulating layer  56  and battery case cap  52  respectively. 
     Structural busbar  65  has blisters  66  projecting downwards through holes  58  for connection to the positive terminals  16 A of some of the cells  18 . Blisters  66  and holes  58  are therefore aligned with the positive terminals  16 A of the cells  18 . Blisters  66  extend from plate  79  of the structural busbar  65  less than blisters  61  extend from plate  77  of structural busbar  60 , due to the difference in height between the positive terminals  16 A and negative terminals  26 A. Recesses  69  correspond to the insides of the blisters  66 . Also present in structural busbar  65  are holes  67  that allow blisters  81  to pass through from a structural busbar  80  above. Fixing holes (not visible) are also present in the structural busbar  65 , which align with other fixing holes in the insulating layer  56  and battery case cap  52  respectively. Structural busbars  60 ,  65  may be considered to form the bottom layer of structural busbars. 
     Above the bottom layer of structural busbars  60 ,  65  is an insulating spacer  70 . There are holes  72  in the insulating spacer  70  that allow blisters  82  from structural busbar  80  to pass through for connection to the positive terminals  16 B of some of the cells  18 . There are also holes  73  in the insulating spacer  70  that allow blisters  81  from structural busbar  80  to pass through for connection to the negative terminals  26 B of some of the cells  18 . Also present in the insulating spacer  70  are further holes  74 , which allow access to the recesses  64  for welding the blisters  61  to the negative terminals  26 A. Likewise, holes  76  in the insulating spacer  70 , which align with holes in the structural busbar  80 , allow access to the recesses  69  for welding the blisters  66  to the positive terminals  16 A. Fixing holes  78  are aligned with fixing holes  63 ,  59 ,  54  in the structural busbar  60 , the insulating layer  56  and the battery case cap  52  respectively. 
     Structural busbar  80  is placed above the upper insulating spacer  70 . Blisters  81  pass through holes  73  in the intervening insulating spacer  70 , holes  67  in the structural busbar  65  and holes  57  in the lower insulating layer  56  to connect to the negative terminals  26 B of some of the cells  18 . Blisters  82  pass through holes  72  in the intervening insulating spacer  70 , holes  62  in the structural busbar  60  and holes  58  in the insulating layer  56  to connect to the positive terminals  16 B of some of the cells  18 . The blisters  81 ,  82  extend further from the plate  84  of structural busbar  80  than the blisters  61 ,  66  from the plates  77 ,  79  of the structural busbars  60 ,  65 . The blisters  81 ,  82  extend further because they need to pass through more layers (insulating spacer  70  and structural busbar  60  or  65 ) in order to reach the terminals of the cells  18 . Blisters  61 ,  81  pass through the battery case cap  52  to reach the negative terminals  26 A,  26 B. Depending on the relative thickness of the battery case cap  52  to the height of the positive terminals  16 B,  16 A, the blisters  66 ,  82  may or may not pass through the battery case cap to reach the positive terminals. 
       FIG. 6  is an alternate view of the battery pack shown in  FIG. 5 . Structural busbars  60 ,  65 , which form the lower structural busbar layer, are shown on the same level. The different shapes of the blisters  81 ,  82  in structural busbar  80  are more clearly discernable. Also, the different shapes of the various holes are more clearly visible. 
     Referring to  FIG. 7 , a circuit diagram of the structural busbars  60 ,  65 ,  80  is shown. Structural busbar  60  is connected to the negative terminals  26 A of cells  18 A. Structural busbar  80  is connected to the positive terminals  16 A of cells  18 A. The group of cells  18 A are therefore connected in parallel. Structural busbar  80  is also connected to the negative terminals  26 B of cells  18 B. Structural busbar  65  is connected to the positive terminals  16 B of cells  18 B. The group of cells  18 B are therefore also connected in parallel, and the two parallel groups of cells  18 A,  18 B are connected in series. 
       FIG. 8  is a view of the separate components of a battery pack that incorporates structural busbars. At the bottom, there is a cold plate  90 . The cells  18  are glued, for example with epoxy, to the cold plate  90 . The cold plate  90  therefore secures, at least in part, the bottom ends of the cells  18 , i.e. the ends opposite to the ends that are welded to the structural busbars. The cold plate  90  serves to draw heat from the cells  18  during charging or discharging so that they remain at a safe operating temperature. 
     The battery case  50  (or fixturing platen) is placed around the cells  18 , and serves to locate the cells in a uniform array while they are being glued to the cold plate  90 . The array may be a honeycomb array, for example. The battery case  50  also serves to protect the sides of the cells against possible damaging exposure to the environment. The battery case  50  may be made from plastic, for example, so that its weight is low. The honeycomb structure (or other array structure) of the battery case  50  provides it with structural rigidity, which contributes to the overall structural strength of the battery pack. 
     Above the battery case  50 , the battery case cap  52  is shown, with the keyhole-shaped cap holes  53  that provide access to the electrical terminals of the cells  18 . 
     Above the battery case cap  52  is the insulating layer  56  with its holes  57 ,  58  for providing access to the negative and positive terminals respectively of the cells  18 . Spacers  91  (e.g. bushes or standoffs) are shown that maintain the insulating layer  56  apart from the upper surface of the battery case cap  52 . The insulating layer  56  is held adjacent to the lower surface of the structural busbar(s) above it. 
     Above the insulating layer  56  is the lower layer of structural busbars  94 , which may include, for example, structural busbars  60 ,  65  ( FIG. 5 ). As it will be appreciated, the number of structural busbars in layer  94  may be one or more depending on the embodiment. In this embodiment, there are three structural busbars that are electrically isolated from each other. Each detail  95 ,  96  in the structural busbar layer  94  corresponds to either a recess of a blister or a hole, depending on the embodiment. 
     The upper insulating spacer  70  is shown above the lower layer of structural busbars  94 . The upper insulating spacer  70  has holes  74 ,  76  for providing access to the negative and positive terminals respectively of the cells  18 , or to corresponding recesses in the lower layer of structural busbars  94 , depending on the embodiment. 
     An upper layer of structural busbars  96  is shown. In this embodiment, there are two structural busbars that are electrically isolated from each other. Each detail  97 ,  98  in the structural busbar layer  96  corresponds to either a recess of a blister or a hole, depending on the embodiment. 
     On top is a collector cap  99 , which insulates the upper structural busbar layer  96  and provides touch protection. The collector cap  99  may have hanging sidewalls that include venting pathways to allow hot gases that may escape through the tops of the cells  18  to disperse. The gases exit the cells and pass between the battery case cap  52  and the insulating layer  56 . 
     Fixing holes  54  in all the various components allow the components to be fastened together to form the battery pack. Other fixing means are possible on other embodiments. For example, the battery case cap  52  may have press-studs that project downwards from its lower surface, and that can be pressed into receiving holes in the top of the battery case  50 , which are located between the larger holes for the cells. 
     A potential benefit with using the structural busbars may occur during assembly, particularly if the case  50  has through-holes that loosely accommodate the cells. If the cells are picked and placed into the case  50 , the battery case cap  52  is pressed into place and the lower layer of structural busbars  94  welded, then the busbars now secure all of the cells so that when the assembly is lifted by the case  50  to be moved to the next process, the cells do not fall out of the bottom of the case. This may be important in situations where the cells are not press-fitted into the case  50 , as may occur using a pick-and-place robot needs some clearance to place the cells rapidly. 
     The insulating layer  56  that is immediately below the first current collector layer (structural busbars  94 ) may represent the bottom of a thermally sealed assembly that includes a stack of three insulating layers ( 56 ,  70 ,  99 ) and two intervening copper layers ( 94 ,  96 ). 
     Referring to  FIG. 9 , another view is shown of the various components making up the battery pack. The battery case  50  is shown mounted on the cold plate  90 . The battery case  50  may be split into a bottom part  50 A and a top part  50 B. Above the battery case  50  is the battery case cap  52 , followed by the lower insulating layer  56 , the lower layer of structural busbars  94 , the upper insulating spacer  70  and the upper layer of structural busbars  96 . On top is the collector cap  99 , showing bosses  102  that extend downwards from a lower surface thereof. The bosses hold the planar portion  104  of the collector cap apart from the upper surface of the upper layer of structural busbars  96 . This allows gases, which may be generated by the cells  18  and pass upwards through gaps in the layers of the assembly, to readily escape from the battery pack. The sidewalls  106  of the collector cap  99  project downwards over the edges of one or more of the lower layers. For example, the sidewalls  106  may project downwards to cover the edges of the lower insulating layer  56 , or further downwards to overlap the upper region  108  of the battery case  50 . The sidewalls  106  have vent holes  110  that allow the hot gases that may be generated by the cells  18  to escape from the battery pack. 
       FIG. 10  is a side view showing the relative positioning of the layers in the battery pack. The battery case cap  52  is placed directly above the cells  18  and battery case  50 . Between the battery case cap  52  and the lower insulating layer  56  there is a gap  120 . The insulating layer  56 , the plate  122  of the lower structural busbar layer  94 , the insulating spacer  70  and the plate  124  of the upper structural busbar layer  96  form a sandwich arrangement  126 . That is, these layers  56 ,  122 ,  70 ,  124  are stacked, with adjacent members of the stack being in contact with each other. 
     C. Variations 
     Where the connecting elements between the busbars  10 ,  12  and the cells  18  have been described as blisters  12 ,  22 , it is recognized that other shapes are possible in other embodiments. For example, the connecting elements may be tabs that are offset from the plates  14 ,  24  of the structural busbars  10 ,  20 . The formation of the tabs may leave holes in the structural busbar plates  14 ,  24 . The main requirement is that the tabs have a beam-like structure that provides structural rigidity to the tabs in relation to the plates  14 ,  24  of the structural busbar  10 ,  20 . The beam-like structure may be provided by, for example, non-coplanar panels in each tab. 
     Individual holes shown in the components may be combined into larger holes in some embodiments. In other embodiments, holes may be subdivided into smaller holes. Additional holes may be present in the various layers of the structural busbar assembly in order to increase the venting capability of the battery pack. Some components in some embodiments may be omitted to provide other embodiments of the structural busbar, the structural busbar assembly and a battery pack incorporating the structural busbars. 
     In general, unless otherwise indicated, singular elements in one embodiment may be in the plural in other embodiments, and vice versa with no loss of generality. 
     Throughout the description, specific details have been set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail and repetitions of steps and features have been omitted to avoid unnecessarily obscuring the invention. Accordingly, the specification is to be regarded in an illustrative, rather than a restrictive, sense. 
     It will be clear to one having skill in the art that further variations to the specific details disclosed herein can be made, resulting in other embodiments that are within the scope of the invention disclosed. All parameters, dimensions, materials, proportions and configurations described herein are examples only and actual values of such depend on the specific embodiment. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.