Patent Publication Number: US-11664522-B2

Title: Bus bars for battery packs

Description:
BACKGROUND 
     A bus bar is a metal strip or bar that conducts electricity and is used for electrical power distribution. Battery cells can be connected with bus bars to make battery packs. Some battery packs using cylindrical cells make electrical connections to the tops and the bottoms of the cells. When connecting cells in series, bus bars and high current interconnects link the positive terminal of one cell, or a parallel group of cells, to the negative terminal of the next cell or the next parallel group of cells. However, connections to the bottoms of the cells obstruct airflow or liquid flow from cooling mechanisms utilized to remove heat generated by the cells. In addition, the high current interconnect from the bottoms of the cells to the bus bars, which may be in the form of a wire somewhat longer than the length of a cell, introduces a small amount of resistance which gives rise to a voltage drop at high current levels. Assembly of this wire to the bus bars or to the bottom of the battery adds costs to a battery pack and may introduce reliability issues. 
     It is within this context that the embodiments arise. 
     SUMMARY 
     One embodiment of a battery pack has a plurality of battery cells and a plurality of bus bars. The battery cells have first terminals of the battery cells at first ends of the battery cells. The battery cells have portions of second terminals of the battery cells at the first ends of the battery cells. The first ends of the battery cells are in a coplanar arrangement. The plurality of bus bars is disposed proximate to the first ends of the battery cells. The plurality of bus bars is coupled to the first terminals and the portions of the second terminals of the battery cells at the first ends of the battery cells to place the battery cells in one of a series connection, a parallel connection or a series and parallel connection. 
     Another embodiment of a battery pack has a cell holder, a plurality of bus bars and a plurality of battery cells. The plurality of bus bars is positioned at a first end of the cell holder. The plurality of battery cells is arranged in the cell holder. Each of the battery cells has a first terminal proximate to the plurality of bus bars. Each of the battery cells has a portion of a second terminal proximate to the plurality of bus bars. The first terminal and the portion of the second terminal are electrically coupled to the plurality of bus bars at a first end of the battery cell. The battery cells are in one of a parallel connection, a series connection, or a parallel and series connection. 
     A method of assembling a battery pack is provided. The method includes arranging a plurality of battery cells so that first ends of the battery cells are coplanar. Each of the battery cells has a first terminal of a first polarity at the first end of the battery cell and a portion of a second terminal of a second polarity at the first end of the battery cell. The method includes arranging a plurality of bus bars proximate to the coplanar first ends of the battery cells. Coupling the plurality of bus bars to the first terminals and the second terminals of the battery cells is included in the method. The coupling is at the first ends of the battery cells thereby leaving the opposing end available for heat removal. The battery cells may be coupled in one of a series connection, a parallel connection, or a series and parallel connection. 
     Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no Way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIG.  1    is a schematic diagram of a battery pack with bus bars above and below the battery cells. 
         FIG.  2 A  is a schematic diagram of a battery pack with bus bars adjacent to the positive terminals of the battery cells, in accordance with one embodiment. 
         FIG.  2 B  is a cross-section view of bus bars in a layer stack, in an embodiment of the battery pack of  FIG.  2 A . 
         FIG.  3    is a perspective view of a cell holder in accordance with one embodiment. 
         FIG.  4    is a perspective view of a battery pack with a bus bar layer at one end of the battery pack, in accordance with one embodiment. 
         FIG.  5    is a perspective view of the battery pack of  FIG.  4    with an insulator layer on top of the bus bar layer. 
         FIG.  6    is a perspective view of the battery pack of  FIG.  5    with another bus bar layer on top of the insulator layer. 
         FIG.  7    illustrates bus bars with interleaved fingers in accordance with one embodiment. 
         FIG.  8    is a perspective view of bond wires coupling a bus bar to a terminal of a battery cell at one end of the battery cell in accordance with one embodiment. 
         FIG.  9    is a flow diagram of a method for making a battery pack having the bus bars at a single end of the battery cells in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed illustrative embodiments of a battery pack where the bus bars are located proximate to one end of the battery terminals to leave the opposing end accessible to a heat sink are provided herein. However, specific functional details disclosed herein are merely representative for purposes of describing embodiments. Embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, and, similarly, a second step could be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     One type of battery pack, as shown in schematic form in  FIG.  1   , uses bus bars above and below the battery cells to connect the battery cells in a parallel, series or series-parallel manner, which limits the ability to remove heat generated by the cells of the battery pack. By contrast, embodiments of the battery pack of  FIGS.  2 A and  4 - 7    have bus bars only at one end of the battery cells or the cell holder, in various arrangements as will be further discussed below. The battery packs described herein may be used with lithium-ion battery cells or other types of rechargeable battery cells, and may be used in electric vehicles, hybrid vehicles and other applications. Electric vehicles and hybrid vehicles include land based motor vehicles as well as air based vehicles, such as airplanes, helicopters, rockets, spaceships, etc., and water based vehicles, such as boats, submarines, etc. It should be appreciated that the embodiments may also be integrated with non-rechargeable battery cells. 
       FIG.  1    shows a battery pack  100  with a first group of battery cells  102 ,  104  in a parallel connection, a second group of battery cells  106 ,  108  in a parallel connection, and a third group of battery cells  110 ,  112  in a parallel connection. The first group, the second group and the third group are coupled in a series connection. Bus bars  114 ,  116 ,  118 ,  120 ,  122 ,  124  are used to connect the battery cells in this parallel and series coupling. Each of the bus bars is coupled to the respective battery cells with one or more wires. A relatively thick wire couples the second bus bar  114  to the third bus bar  122 , making a series connection for the first group and the second group of battery cells. Another relatively thick wire couples the fourth bus bar  116  to the fifth bus bar  124 , making a series connection for the second group and the third group of battery cells, so that the sixth bus bar is the positive terminal for the battery pack  100 . 
       FIG.  2 A  shows a battery pack  200  with a bus bar arrangement enabling efficient heat removal from one end of the battery pack as all the bus bars are proximate to the other end of the battery pack. In this embodiment, the bus bars  214 ,  216 ,  222 ,  218  are assembled proximate to one end of the battery cells, enabling the use of fewer bus bars than in the battery pack of  FIG.  1   . The relatively thick wires from upper bus bars to lower bus bars are eliminated in the embodiment of  FIG.  2 A . The battery pack  200  makes use of the access to both positive and negative terminals at one end of the cells, e.g., a top end of the cells, by coupling the bus bars to the positive and negative terminals through wires proximate to the top end of the cells. It should be appreciated that the embodiment of  FIG.  2 A  enables the use of wires that are shorter in length than any of the battery cells. As shown in  FIG.  2 A , the first group of battery cells  102 ,  104  is in a parallel connection, the second group of battery cells  106 ,  108  is in a parallel connection, and the third group of battery cells  110 ,  112  is in a parallel connection. The first group, the second group and the third group are in a series connection with each other. Bus bars  214 ,  216 ,  218 ,  222  are used to couple the battery cells in this parallel and series coupling, as follows. Starting with the negative terminal of the battery pack  200 , a first bus bar  214  is connected to the negative terminals of the first group of battery cells  102 ,  104  at a top end  138  of each of the battery cells. The second bus bar  222  is connected to the positive terminals of the first group of battery cells  102 ,  104  at the top end  138  of each of the battery cells. The first and second bus bars  214 ,  222  couple the first group of battery cells  102 ,  104  in parallel. The second bus bar  222  and the third bus bar  216  couple the second group of battery cells  106 ,  108  in parallel. The third bus bar  216  and the fourth bus bar  218  couple the third group of battery cells  110 ,  112  in parallel. Series connections are formed by the bus bars. The second bus bar  222  connects the positive terminals of the first group of battery cells  102 ,  104  to the negative terminals of the second group of battery cells  106 ,  108 . The third bus bar  216  connects the positive terminals of the second group of battery cells  106 ,  108  to the negative terminals of the third group of battery cells  110 ,  112 . The fourth bus bar  218  is the positive terminal of the battery pack  200 . Other arrangements of bus bars and parallel connections, serial connections, or parallel and series connections are readily devised as variations. Battery cells of other polarities may be used in these variations. It should be appreciate that the connections between the battery cells and the bus bars may be made through wires extending through apertures defined through the layer stack as described below with reference to  FIG.  2 B . 
     The bus bars can be arranged in a layer stack  250 , or in other arrangements as will be later discussed. In the layer stack  250 , the first bus bar  214  and the third bus bar  216  are placed in a first layer  230 , and are separated by a gap so as not to short-circuit. The gap may be filled with an insulator in some embodiments, however this is optional. An insulator is disposed as the second layer  232 . The second bus bar  222  and the fourth bus bar  218  are placed in a third layer  234 , and are separated by a gap or insulator so as not to short-circuit. The third layer  234  is separated from the first layer  230  by the second layer  232 , namely the insulator, so that the bus bars on differing layers do not short-circuit. It should be appreciated that alternate configurations of the layer stack are possible as  FIG.  2 A  is one example and not meant to be limiting. For example, the layer stack may have more than three layers and each bus bar layer may have a single bus bar or two or more bus bars disposed within a single co-planar layer. 
     Battery cells  102 - 112  have a projecting nub as a positive terminal at the top end of the cell. Battery cells  102 - 112  have a can or casing as a negative terminal of the cell. The casing has a relatively flat surface at the bottom end of the cell, cylindrical sides, and a portion of the negative terminal at the top end of the cell. In some types of battery cells, the casing has a crimp at the top end of the cell, which is formed as the casing is sealed around the contents of the battery cell. This crimp or other portion of the negative terminal at the top end of the cell provides physical and electrical access at the top end to the negative terminal of the battery cell. The crimp is spaced apart from the peripheral sides of the projecting nub through a gap that may, or may not be filled with an insulator. 
     It should be appreciated that having bus bars at both ends, i.e., the top and the bottom, of the battery cells does not leave an area where a heat sink can be affixed to be in thermal communication with the top or bottom surfaces of the battery cells for efficient heat removal. In addition soldering or otherwise connecting the relatively thick wire from an upper bus bar to a lower bus bar involves an assembly operation which adds to costs of the production of battery packs. This relatively thick wire is longer than the length of any one of the battery cells and can introduce parasitic resistance into the current path, which in turn can introduce a voltage drop under high current drain conditions. The relatively thick wire can also be subject to breakage and contact to one or more of the cells and attendant short-circuit, open circuit or other reliability problems. 
     In one embodiment, the layer stack is formed using layers of a circuit hoard. For example, the bus bars can be made of (or on) copper layers or another suitable conductive metal and the insulator can be made of resin impregnated fiberglass or other suitable insulator materials. In variations, the bus bars can be made of aluminum or other metals, and various materials may be applied as an insulator. In one embodiment, a heat sink  252  is assembled to the bottom ends  140  of the battery cells  102 ,  104 ,  106 ,  108 ,  110 ,  112  and is thermally coupled to the bottom ends  140 . The heat sink may have finning or passages for air or liquid cooling. A fan may supply air flow across a surface of the heat sink  252  in some embodiments. In a variation, the heat sink is attached or affixed to the bottom of a battery cell holder, such as the battery cell holder of  FIG.  3   . The co-planar arrangement of the battery cells provides a relatively flat surface to attach a heat sink and in some embodiments the battery cells are designed to cool efficiently through the bottom of the cells, e.g., 18650 Lithium ion batteries. 
     One way of routing wires connecting the bus bars to the battery cell terminals is shown in  FIG.  2 B . These wires, as shown in  FIGS.  2 A and  2 B , can be shorter than the length of a battery cell, and are thus shorter than and less resistive than wires connecting from overhead bus bars to the bottoms of the battery cells as shown in  FIG.  1   . In  FIG.  2 B , each of the materials in the layer stack has an aperture, and the sizes of the apertures are arranged so that a bond wire  236  or other wire is less likely to short out to one of the bus bars. In the example shown, a bus bar on the first layer  230  of the layer stack has an aperture  238 , through which the bond wire  236  can pass. An insulator on the second layer  232  of the layer stack has a smaller aperture  240 , through which the bond wire  236  can pass. A bus bar on the third layer  234  of the layer stack has a larger aperture  242 , through which the bond wire  236  can pass. The smaller aperture  240  of the insulator, i.e., the second layer  232 , constrains motion of the bond wire  236  so that the bond wire  236  is less likely to contact edges of the larger aperture  242  or aperture  238 . In other words, the bond wire  236  is less likely to contact the bus bar on the third layer  234  or the first layer as a result of the staggered sizes of the apertures. Bond wire  236  couples the bus bar on the first layer  230  to a surface  134  of a battery cell, e.g., a positive nub terminal or a negative terminal at the top of the battery cell. The apertures of the lower bus bar, closer to the first ends of the battery cells, are larger than the apertures of the insulator. In some embodiments the apertures are circular and the diameter of aperture  240  is less than the diameter of the apertures through the bus bars above and below the insulator layer. In addition, it should be appreciated that the apertures of one layer are aligned with apertures of another layer so that access is provided through the layer stack. It should be further appreciated that the apertures may be any geometric configuration and are not limited to circular shapes. Other arrangements of apertures are readily devised, for example to accommodate wires bonded or attached to another surface of a bus bar or attached in another manner. The embodiments of the stacked bus bars may be encased within a housing for use in a particular application, such as a hybrid or electric vehicle. 
       FIG.  3    shows a battery cell holder  300 . In the embodiment shown, the battery cell holder  300  is made of a plastic material. Variations of the battery cell holder  300  may be made of other materials, and may be molded, cast or even produced using a 3-D printer. Battery cells  308  are inserted into a housing  302 , and a lid  304  is attached to the housing  302 , for example by one or more fasteners  306  or other means. The battery cell holder  300  retains the battery cells in a close-pack or dense-pack, staggered row or hexagonal arrangement. Other arrangements are readily devised as the embodiments are not limited to the hexagonal arrangement. As shown, the battery cell holder  300  is only partially populated, and can readily be filled with battery cells. These can be commercially available battery cells, such as lithium ion cells or cells of another chargeable or non-chargeable technology. In other embodiments, the battery cells may be proprietary battery cells made especially for a specific battery pack. The battery cell holder  300  is shown without the bus bars, which are readily added as shown in  FIGS.  4 - 6   . 
       FIG.  4    shows a battery pack  400 , such as the battery cell holder  FIG.  3    or a variation thereof fully populated with battery cells. At one end of the housing  402 , for example the top end of the housing  402 , a bus bar layer is added. The bus bar layer has a first bus bar  404  and a second bus bar  406 . The first bus bar  404  couples a first group of battery cells to a second group of battery cells in series, and the second bus bar  406  connects a third group of battery cells to a fourth group of battery cells in series. A gap separates the first bus bar  404  and the second bus bar  406  (similarly to the arrangement shown in  FIG.  2 A ) so that these bus bars do not short. The first bus bar  404  and the second bus bar  406  extend over an entirety of the top surface of the housing  402  in this embodiment. The first bus bar  404  and the second bus bar  406  have apertures through which bond wires or other wires can pass to form electrical connections with the battery cells and corresponding bus bar. 
       FIG.  5    shows the battery pack  400 , with an insulator layer  502  added on top of the bus bar layer. The insulator layer  502  covers the top surface of first bus bar  404  and the second bus bar  406  of  FIG.  4   , and may have apertures through which bond wires or other wires can pass to form electrical connections with the battery cells. As illustrated, the apertures of the insulator layer  502  are aligned with corresponding apertures of the bus bar layer of  FIG.  4   .  FIG.  6    shows the battery pack  400 , with a bus bar layer on top of the insulator layer  502  of  FIG.  5   . In  FIG.  6   , the added bus bar layer includes a third bus bar  602 , a fourth bus bar  604 , and a fifth bus bar  606 . The third bus bar  602  connects the first group of battery cells to another block or group of battery cells, e.g., in a neighboring battery pack. The fourth bus bar  604  connects the second group of battery cells to the third group of battery cells. The fifth bus bar  606  connects the fourth group of battery cells to another block or group of battery cells, e.g., in a second neighboring battery pack. Bus bars  602 - 604  include apertures defined through the surface and these apertures are aligned with the apertures of the insulator layer of  FIG.  5    and the apertures of the first bus bar layer of  FIG.  6   . Thus with the corresponding apertures of each layer substantially aligned, access is provided for wires or leads from the battery cells to each bus bar layer as illustrated with reference to  FIG.  2 B . 
     Referring to  FIGS.  4 - 6   , the first group of battery cells is thus connected in parallel by the first bus bar  404  and the third bus bar  602 . The second group of battery cells is connected in parallel by the first bus bar  404  and the fourth bus bar  604 . The third group of battery cells is connected in parallel by the fourth bus bar  604  and the second bus bar  406 . The fourth group of battery cells is connected in parallel by the fifth bus bar  606  and the second bus bar  406 . Other groupings of parallel and series connections can be formed by other arrangements and connections of bus bars as readily devised in variations. In addition, more stacks of bus bars and insulator layer may be integrated into the embodiments discussed herein. 
       FIG.  7    shows an alternative technique for arranging bus bars at a single end of a battery pack, i.e., at one end of each of the battery cells. Two bus bars  702 ,  704  are in coplanar arrangement, and have interleaved fingers  706 ,  710 , projecting from a respective bus body  711  to their respective distal ends  714 , in an interleaved bus bar arrangement  700 . That is, the lingers  706  of a first bus bar  702  are interleaved and co-planar with the fingers  710  of a second bus bar  704 . The fingers  706  of the first bus bar are coupled to the negative terminals  706  of a first group  720  of the battery cells. The fingers  710  of the second bus bar  704  are coupled to the positive terminals  712  of the first group  720  of the battery cells. In this example, the coupling from the bus bars to the positive and negative terminals of the battery cells is via bond wires attached at the top ends of the battery cells. The first bus bar  702  and the second bus bar  704  connect the first group  720  of the battery cells in parallel. Additional fingers of the second bus bar  704  are connected to the negative terminals of a second group  722  of battery cells. Fingers of a third bus bar  724  are connected to the positive terminals of the second group  722  of battery cells. The second bus bar  704  and the third bus bar  724  connect the second group  722  of the battery cells in parallel. Thus, the second bus bar  704  connects the first group  720  and the second group  722  of battery cells in series. Additional groups of battery cells can be connected in series by additional bus bars with interleaved fingers, in related arrangements. 
       FIG.  8    shows bond wires  810  coupling or electrically connecting a bus bar  808  to the negative terminal  806  of a battery cell  802 , in a bus to cell wiring arrangement  800 . The battery cell  802  has a nub  804  as a positive terminal, which will be later connected to another one of the bus bars. The bond wires  810  are, in one example, ultrasonically welded to the bus bar  808  at a proximate end of the bond wire, and ultrasonically welded to the negative terminal  806  of the battery cell at distal end of the bond wire. The bond wires may be aluminum, copper, silver or other conductive metals or combinations thereof. Other types of electrical connections between bus bars and battery terminals may be devised, such as spot welding, soldering, spring contacts, etc. It should be appreciated that the positive and negative electrical connections can be made utilizing the same machine or tool in these embodiments to further enhance manufacturing efficiencies. 
       FIG.  9    shows a flow diagram of a method  900  for assembling a battery pack. Variations of the method  900  are readily devised, using fewer operations, additional operations, changing the order of the operations and so on. In an operation  902 , battery cells are inserted into a cell holder or some suitable support structure for the battery cells. For example, the cell holder  300  and battery cells shown in  FIG.  3    may be used. The battery cells are arranged with the first ends coplanar, in an operation  904 . Bus bars are arranged proximate to the first ends of the battery cells, in operation  906 . The bus bars are arranged over one end of the battery cells in a stacked arrangement in order for efficient heat removal from the opposing end. In operation  908 , in one embodiment, a first bus bar and a second bus bar are placed on a first layer of a layer stack. An insulator is placed as the second layer over the first layer of the layer stack, in an operation  910 . A third bus bar is placed on a third layer of the layer stack, in an operation  912 . For example, the layer stack shown in  FIGS.  2 A and  2 B  may be used with apertures as shown in  FIG.  2 B . Thus, all the bus bars are assembled along a single plane along the top of the cells to free up the area at the bottom of the cells for thermal management. In addition, both the positive and negative electrical connection discussed below can be made from a single end of the assembly thereby enabling completion of the high current connections without having to reposition the bus bars. 
     In one embodiment, bond wires are passed through apertures of the layer stack, in an operation  916 . The bus bars are coupled to the first terminals and the second terminals of the battery cells, at first ends of the battery cells, in an operation  918 . For example, in operation  920 , the first bus bar is coupled to the second terminals of a first group of battery cells. In operation  922 , the third bus bar is coupled to the first terminals of the first group of battery cells. In operation  924 , the third bus bar is coupled to the second terminals of a second group of battery cells. The second bus bar is coupled to the first terminals of the second group of battery cells, in an operation  926 . The operations  920 ,  922 ,  924 ,  926  of coupling the first second and third bus bars to the terminals of the first and second groups of battery cells results in a parallel-connected first group of battery cells and a parallel-connected second group of battery cells, with the first and second groups in series connection. Other arrangements of battery cells are provided by variations of the method  900 . In an operation  928 , in one embodiment, a heat sink is attached to the bottom of the cell holder. The heat sink may have air flow or liquid flow directed over a surface of the heat sink by a further cooling mechanism, e.g., a fan or a liquid pump. Duct work or plumbing for the airflow or the liquid flow, mourning of a fan or a liquid pump, and electrical wiring for the fan or the liquid pump are readily devised. 
     With the above embodiments in mind, it should be understood that the embodiments might employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. Further, the manipulations performed are often referred to in terms, such as producing, identifying, determining, or comparing. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to a device or an apparatus for performing these operations. The apparatus can be specially constructed for the required purpose, or the apparatus can be a general-purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general-purpose machines can be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations. 
     Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing. 
     The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.