Abstract:
A modular battery includes: a first battery cell having a first electrode surface; a second battery cell having a second electrode surface; a compressible interconnector connecting the first battery cell and the second battery cell; and a polymeric material holding the first battery cell against the second battery cell with the interconnector in a compressed state. A method is also provided.

Description:
BACKGROUND 
       [0001]    Modular batteries are batteries which comprise two or more battery cells or cell modules or cells. A common example of a device using a modular battery is a hand held flashlight which may use for example two C cells. 
         [0002]    Recently, modular batteries have become important in many applications, including hybrid electric vehicles (“HEV”), plug-in hybrid electric vehicles (“PHEV”), and other applications. When used in HEV, PHEV, and other applications, in addition to being durable, safe and cost effective, modular batteries are required to deliver a great deal of power. 
         [0003]    Applications of modular batteries, like the hand-held flashlight, require the use of multiple battery cells connected in series. However, the modular batteries for HEVs and PHEVs, for example, may differ from the modular C cells used in a common flashlight. 
         [0004]    U.S. Patent Publication No. 2009-0239130 A1 discloses a modular battery with interconnectors, and is hereby incorporated by reference herein. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a modular battery comprising a first battery cell having a first electrode surface, a second battery cell having a second electrode surface, a compressible interconnector connecting the first battery cell and the second battery cell, and a polymeric material holding the first battery cell against the second battery cell with the interconnector in a compressed state. 
         [0006]    The present invention also provides a method for forming a modular battery comprising: placing a compressible interconnector between a first battery cell having a first electrode surface and a second battery cell having a second electrode surface, placing a polymeric material at the peripheries of the first and second battery cells, compressing the compressible interconnector, and curing the polymeric material to hold the first battery cell with respect to the second battery cell so that the compressible interconnector remains in a compressed state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will be described with respect to a preferred embodiment, in which: 
           [0008]      FIG. 1  schematically illustrates a step in manufacturing a modular battery according to one embodiment the present invention; 
           [0009]      FIG. 2  schematically shows a completed modular battery following the  FIG. 1  step; and 
           [0010]      FIG. 3  shows an alternate embodiment of the present invention. 
       
    
    
       [0011]    The drawings are schematic in nature and not to scale. For clarity and ease of understanding, some elements have been exaggerated in size. 
       DETAILED DESCRIPTION 
       [0012]    In order to be powerful enough for HEVs, PHEVs, and other applications, it is desirable to use modular batteries containing cells with a high surface to volume ratio, for example using a planar design for each cell of the battery. These cells may be, for example, about the size of a large book wherein the “front” of the book contains, for example, a positive terminal (also known as an electrode) and the “back” of the book contains, for example, a negative terminal. Unlike their cylindrical counterparts (e.g., C cell batteries) which use a raised dimple at one end of a cell to make electrical contact with the next cylindrical cell, substantially planar cells need not have such raised dimple(s). 
         [0013]    For many applications requiring high electrical power including HEVs and PHEVs, it is desirable that the battery delivers electrical power at a high voltage in order to reduce the required current needed to supply the electrical power which in turn will beneficially reduce the need for high-current carrying materials to the devices using the electrical power. Electrical power is the multiple of voltage and current and high voltage delivery of electrical power to a device, for example an electric motor, will require thinner or less conductive current carriers (for example copper wire) to the device which will reduce their cost. Electric vehicles for example may require a battery to provide electrical power at 300 to 600 volts. This high voltage is typically achieved by externally connecting multiple lower voltage battery modules electrically in series. This is in part due to safety considerations in assembling and operating a series connected “stack” of typical “pouch” cells within a battery module, since at higher voltages and especially above approximately 60 Volts, there is a significant risk of electrical arcing and a severe shock hazard since the edge peripheries of “flat” cells such as typical “pouch” cells have their cell terminals exposed. For safety these cell terminals are connected electrically in series within a low voltage battery module, for example, having less than 60 volts. 
         [0014]    An object of the present invention is to provide sufficient pressure to ensure that battery modules retain good electrical contact. Another alternate or additional object of the present invention is to reduce the weight and/or cost and/or complexity of manufacturing of a modular battery. Yet a further alternate or additional object is provide for ease of disassembly for example for service or recycling. 
         [0015]    The present invention may be used with the modular battery disclosed in incorporated-by-reference U.S. Patent Publication No. 2009-0239130 A1. 
         [0016]      FIG. 1  shows six cell modules  23  stacked one on another electrically in series and separated by compressible interconnectors  24  which serve to electrically connect in series one cell module to the next cell module. Each module  23  may have a port  20  for an electrolyte, electrical feedthroughs  21  and burst disc  22  for pressure relief in the module  23 . Further details of the cell modules are found in U.S. Patent Publication No. 2009-0239130 A1, although it is noted that other modules may be used in accordance with the present invention. Several compressible interconnectors  24  can be present between two cell modules, for example 8 layers, each 10 mils in thickness. Thus the space between cell modules for example can be 80 mils, and compressible to 60 mils when in use. 
         [0017]    For the lowest electrical resistance between cell modules  23  in the battery stack, pressure should be applied to the interconnectors  24  between the cell modules  23 . However, using the enclosure and springs described in U.S. Patent Publication No. 2009-0239130 A1 may not be advantageous from a cost and or manufacturing perspective. 
         [0018]    According to one embodiment of the present invention, shrink wrapping can be used to provide and maintain the compression desired. 
         [0019]    As shown in  FIG. 1 , a shrink wrap material  50 , such as polyolefin or PVC, is provided, preferably as a rectangular cross-section tubular material around the periphery of the cell stack. 
         [0020]    During manufacture, a compression device, such as a clamp, then can be used to compress the entire stack in  FIG. 1 , with a positive end plate  51  and a negative end plate  52 , for example be placed at the ends of the stack. Either together with the compression device or afterward, a positive electrical terminal  26  can be placed over the one end cell module  23  or interconnector  24  and a negative power terminal  27  can connected over the other end cell module  23 . 
         [0021]    Once compressed, the shrink wrap can be shrunk, for example via a heat gun, so that the shrink wrap material shrinks in the direction of the axial center of the stack, to a new position as wrap  50   a . The shrink wrap  50   a  overlaps the end plates  51 ,  52 , and thus retains compression of the interconnectors  24 . Spacing or connections for electrical feedthroughs  21  may also be provided prior to shrinking or post-shrinking, if desired. 
         [0022]    The wrap  50   a  preferably is spaced from the peripheries of the interconnectors, but contacts the peripheries of the cell modules  23 . 
         [0023]    The shrink wrap material  50  should have electrically insulating properties if the shrink wrap material makes or becomes in contact with the interconnector  24  if the interconnector  24  is not itself electrically insulated at its periphery. The shrink wrap material  50  would beneficially be thermally conductive. 
         [0024]    More than 50 cell modules may be wrapped, and preferably at least 20. 
         [0025]    The embodiment of  FIG. 1  provides a cost effective and simple manner for compression of the stack of cell modules, as well as hermetically sealing their enclosure. The shrink wrap also may reduce the weight of the cell stack and can be used efficiently in mass manufacturing. Instead of a heat gun, the cell stack also could pass with the wrap  50  through a heating device. 
         [0026]      FIG. 3  shows an alternative embodiment of the present invention in which a sealant  53  is placed at the peripheries of the cell modules  23  and if present the end plates  51 ,  52 . The sealant  53  can be spaced from a periphery of the interconnectors  24 . The sealant  53  is located around the entire stack, so that the stack is completely sealed. 
         [0027]    The sealant  53  can be applied in a liquid or viscous form, before or after the stack is compressed by a compression device. Strips or a ring of sealant  53  could also be placed as the stack is formed prior to compression. Once the stack is compressed and the sealant applied, the sealant  53  may be cured. Different sealants can be used depending on the adherence and sealing properties required, although preferred materials may include polyurethane or acrylic sealants. Heat, UV or other curing may be used depending on the sealant used. The adherence properties should ensure that a desired compression of the interconnectors remains after curing. 
         [0028]    In both examples shown in  FIGS. 2 and 3  the interconnector  24  and cell modules  23  are easily accessible and removable for individual cell module replacement by cutting through the sealant  53  in  FIG. 3  or the shrunken wrapping  50   a  in  FIG. 2 . This provides for easy recycling or service. Re-assembly after individual cell module replacement can by accomplished by resealing by application of additional heat shrinkable wrapping and then heat shrinking as shown in  FIG. 2  or in the arrangement illustrated in  FIG. 3 , applying additional sealant  53  to the upper and lower perimeters of the replacement cell module with the adjacent interconnectors under compression. 
         [0029]    In addition, the compressed stacks from both embodiments in  FIGS. 2 and 3  may be further housed in an insulating case, for example, an electrically insulating coating, bag or housing around the stacks shown in  FIGS. 2 and 3 . 
         [0030]    It will be appreciated by those ordinarily skilled in the art that obvious variations and changes can be made to the examples and embodiments described in the foregoing description without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular examples and embodiments disclosed, but is intended to cover all obvious modifications thereof which are within the scope and the spirit of the disclosure as defined by the appended claims.