Abstract:
A lithium ion battery pack battery pack is disclosed. The battery pack comprises a housing, the housing having a sidewall and a sidewall opening extending there through, a plurality of lithium ion battery cells disposed within the housing, the battery cells having an anode terminal and a cathode terminal, first and second current collectors disposed in the housing, the first and second current collectors electrically engaging respective ones of the anode and the cathode terminals, a metal plate disposed in the sidewall opening adjacent one of the current collectors, and an electrically non-conductive barrier disposed between the adjacent one of the current collectors and the metal plate, wherein the metal plate draws heat from the adjacent one of the current collectors outwardly into the ambient environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/184,389, filed on Jun. 5, 2009, the entirety of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This patent relates to high energy density batteries, and more particularly to a lithium ion battery pack having a metal plate, such as aluminum, to draw heat away from internal battery cells and into the ambient environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
         FIG. 1  is a perspective view of a battery pack according to an embodiment of the invention; 
         FIG. 2  is an exploded view of the battery pack of  FIG. 1 ; 
         FIG. 3  is an exploded view of an alternative embodiment of a battery pack according to the present invention; 
         FIG. 3   a  is a perspective view of an underside of a top portion to a battery pack according to an embodiment of the invention 
         FIG. 4  is an exploded view of a current collector for the battery pack of  FIG. 1 ; 
         FIG. 5  is a partial cross-sectional view of the battery pack of  FIG. 1 ; and 
         FIG. 6  is an exploded view of a further alternative embodiment of a battery pack according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention of the present disclosure is susceptible to various modifications and alternative forms, an embodiment is shown by way of example in the drawings and this embodiment will be described in detail herein. It will be understood, however, that this disclosure is not intended to limit the invention to the particular forms described, but to the contrary, the invention is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claim. 
     A battery pack  100  according to the present invention is illustrated in  FIG. 1 . The battery pack  100  may be a LiFePO4 battery pack suitable for inclusion in various types of electric vehicles (EVs). Such EVs include automobiles, boats, aerospace vehicles, aviation vehicles, wheelchairs, motobikes, scooters, and the like. The battery pack  100  can also be used in hybrid vehicles (HVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like. 
     The battery pack  100  may have a height of about 8.2 inches, a width of about 3.2 inches, and a length of about 4.8 inches, though other dimensions are also contemplated. The total weight of the battery pack  100  may be about 3.0 kilograms, though other weights are also contemplated. The battery pack  100  includes an enclosure  101  with two external terminals  108 ,  110 . 
     Now referring to  FIG. 2 , the battery pack  100  includes twenty-eight cells  112 , arranged in parallel and contained in the enclosure  101 . Each of the cells  112  may be for example, an EV high energy rechargeable LiFePO4 cell with 3.2 volts and 3200 mAh, model LFP26650EV, as sold by K2 Energy Solutions, Inc, of Henderson, Nev. The battery pack  100  has high energy density, fast recharge times, long cycle life, a flat discharge profile, and is considered to be relatively environmentally friendly. The cells  112  are formed in a cylindrical shape and include a conductive cathode cover  140  and a conductive anode cover  142 . It will be understood that other shapes or configurations may be used depending on the application in which the battery pack  100  will be used. 
     The enclosure  101  includes a housing  102  and a top  104 . The top  104  includes two through holes  136   a ,  136   b  for receiving the external terminals  108 ,  110 . The through holes  136   a ,  136   b  may be formed by a number of methods, including drilling through the top  104 . The top  104 , which corresponds to an open end  106  of the housing  102 , is fixedly attached to the housing  102  in the final assembly after the rest of the components are placed in the housing  102 . The top  104  is made of a material such as plastic, though other materials are possible. The top  104  includes tapered tabs  104   a  which engage the upper row of the cells  112 , thereby helping to stabilize the cells  112  within the housing  101 . 
     The housing  102  is generally in the shape of a rectangle, is made of a material similar to that of the top  104  and may be formed by such as a molding process. However, it will be understood that other shapes or configurations are possible. The external terminal  108  is an anode terminal, and the other external terminal  110  is a cathode terminal. The anode and cathode  108 ,  110  may be electrically coupled to external components (not shown) of an EV. Each of the external terminals  108 ,  110  includes, for example, a base  120  having a pin  120   a , a hex nut  122 , a split washer  124 , and a hex head cap screw  126 . 
     The battery pack  100  further includes an insulating paper  114  and connecting members  116 ,  118 . The insulating paper  114 , which corresponds generally to the shape of the open end  106  of the housing  102 , is located below the top  104 . 
     The battery pack  100  includes two current collectors  128 . One of the current collectors  128  is an anode current collector and the other current collector  128  is a cathode current collector. 
     Each of the current collectors  128  includes two collector plate tabs  132 , preferably formed of nickel, welded to a collector plate  131 . The collector plates  131  may be formed of copper. If copper, the collector plates  131  are ultrasonically welded to the respective collector plate tabs  132 . Alternatively the collector plates  131  may be formed of another metal, such as brass. Brass provides a significant cost savings without a significant loss of electrical conductivity. Additionally if the collector plates  131  are formed of brass, they may be resistance welded to the nickel collector plate tabs  132 , which may provide further cost savings. 
     Although one or more of the collector plate tabs  132  could be used, in the present embodiment two are used as they are of a dimension which is commercially readily available. 
     The collector plate tabs  132  are resistance welded to the cathode and anode covers  140 ,  142  of the cells  112 . Copper and brass provides high electrical and thermal conductivity, and nickel provides corrosion and heat resistance. The use of the collector plate tabs  132  facilitates resistive welding to the cells  112 . Also, the use of the collector plate  131  and the collector plate tabs  132  increases the current capacity to the cells  112  without sacrificing the voltage drop over the cells  112 . More details about the construction of the current collectors  128  will be described with reference to  FIG. 3 . 
     An alternative embodiment of the present invention is illustrated in  FIG. 3 . In accordance with this embodiment, a housing  102 ′ is formed from an extrusion. This permits greater flexibility in the size of the housing  102 ′, and thus greater flexibility in the number of cells  112  which can be contained within the housing. Rather than having a base integrally molded into the housing, in this embodiment, a discrete base  133  is utilized. Of course, the size of the current collectors  128  will be appropriately determined based upon the number of the cells  112 . 
     One of the current collectors  128  for the battery pack  100  of  FIG. 1  is illustrated in  FIG. 4 . The current collector  128  includes the collector plate  131  and two collector plate tabs  132 . The collector plate  131  is typically fabricated from a flat stock material such as a thin strip of metal, a metal grid or a perforated metal. The use of the collector plate  131  provides high electrical and thermal conductivity to the cells  112 . The collector plate  131  includes a body portion  144  and a tab  146 . The tab  146  with an approximately 90 degree bend is formed during a bending operation. As shown, the tab  146  is bent toward the body portion  144  of the collector plate  131 . The body portion  144  is generally rectangular in shape and corresponds to the housing  102  of the battery pack  100 , however other known shapes or dimensions are possible. The body portion  144  of the collector plate  131  includes twenty-eight holes  152 , corresponding to the number of cells  112  used in the battery pack  100  ( FIG. 2 ). The holes  152  are also aligned with and mated with the cathode and anode covers  140 ,  142  of the cells  112 . The holes  152  may be generally circular in shape, though other shapes or configurations are contemplated. Each of the holes  152  may have a dimension of about 0.50 inches, though other dimensions are also contemplated. Holes  150  which have a dimension smaller than the dimension of the holes  152  are introduced on the tab  146  of the collector plate  131  for receiving the connecting members  114 ,  116  ( FIG. 2 ). The holes  150 ,  152  may be formed by a number of methods, including drilling through the collector plate  131 . 
     Additionally if the collector plate  131  is formed of brass, the external terminals  108 ,  110  may be resistance welded to the tab  146 , thereby eliminating the need for hardware to secure the external terminals  108 ,  110  to the tab  146 . Further as illustrated in  FIG. 3 , the underside of the top  104  is ribbed which keys the base  120  of the external terminals, restricting rotation thereof when connecting to external terminals  108 ,  110  to external components. 
     The housings  102 ′ is shaped to provide longitudinal recesses  102 ′ a . These recesses provide structural integrity as well as provide passages between adjacent ones of the battery packs  100  to permit passage of cooling air as well as straps (not shown). 
     As discussed above, the current collector  128  includes two collector plate tabs  132 . The collector plate tabs  132  are typically fabricated from a flat stock material such as a thin strip of metal. The use of the collector plate tabs  132  provides corrosion and heat resistances effect to the cells  112 . Each of the collector plate tabs  132  includes fourteen holes  156 . The holes  156  are aligned with and mated with the holes  152  of the collector plate  131 . The holes  156  of the collector plate tabs  132  may be generally round, with opposing slots to help align the current collectors  128  with the cathode and anode covers  140 ,  142 , of the cells  112 , during manufacture. Each of the holes  156  has a dimension smaller than the dimension of the holes  152  of the collector plate  131 , though other dimensions are also contemplated. The holes  156  may be formed by a number of methods, including drilling through the collector plate tabs  132 . 
     The collector plate tabs  132  are ultrasonically welded to the collector plate  131 . The use of the collector plate tabs  132  permits resistive welding of the collector plate  131  via the collector plate tabs  132  to the cathode and anode covers  140 ,  142  of the cells  112 . Also, the current collector  128  having the collector plate  131  and the collector plate tabs  132  increases the current capacity to the cells  112  and from an external generator (not shown) of the EV without sacrificing the voltage drop over the cells  112 . 
       FIG. 5  depicts a partial cross-sectional view of the battery pack  100 . Only the current collectors  128  and a row of four cells  112  are illustrated. Two collector plate tabs  132  are ultrasonically welded to the collector plate  131  and in turn the collector plate tabs  132  are resistance welded to the cathode and anode covers  140 ,  142  of the cells  112 . The through holes  152  of the collector plates  131  are aligned with and mated with the through holes  156  of the collector plate tabs  132  and the cathode and anode covers  140 ,  142  of the cells  112 . 
     The method of constructing the battery pack  100  of the present invention is as follows. First, the cells  112  are arranged in parallel. To hold the cells  112  in place, an adhesive such as glue (not shown) is applied to the body of the cells  112  to join the cells  112  together. The collector plate tabs  132  are placed side by side and are ultrasonically welded to respective ones of the body portion  144  of the collector plates  131  such that the holes  156  of the collector plate tabs  132  are aligned with and mated with the holes  152  of the collector plate  131 . Next, the tabs  146  of the collector plates  131  are fixedly attached to the pins  120  of the terminals  108 ,  110  via the connecting members  116 ,  118 . There are a number of ways to secure the tabs  146  in place, including fastening the tabs  146  to the pins  120  of the terminals  108 ,  110  using for example split washer  118  and screw  116 . The insulating paper  114  is placed over the first row of the cells  112 . Next, the collector plate tabs  132  are resistance welded to the cathode and anode covers  140 ,  142  of the cells  112 . The cells  112  attached to the current collectors  128  are placed inside the housing  102 . The top  104  is joined to the housing  102  to seal the open end  106  of the housing  102 . The hex nuts  122 , the split washers  124 , and the cap screws  126  of the terminal  108 ,  110  are fixed attached to the current collectors  128 . In this position, the battery pack  100  is formed and is in electrical connection with the external components (not shown) of the EV via the terminals  108 ,  110 . 
     The individual cells  112  are electrically isolated from each other by a cardboard sleeve  160  (see  FIG. 2 ). Although the cells  112  are connected in parallel, the cardboard sleeve  160  provides some mechanical compliance to the battery assembly that lets the assembly accommodate thermal expansion as well as isolates adjacent ones of the cells  112  from one another during vibration. 
     A further embodiment of the invention is illustrated in  FIG. 6 . According to this embodiment, an opening is provided through opposing sidewalls of the housing  102 ′, and heat conducting metal plates  170 , such as of aluminum, are placed therein to draw heat away from the cells  112 . Electrically non-conductive barriers electrically isolate the cells  112  from the plate  170 . The barriers may be a polyester film  172 , such as a Mylar film, disposed on the outer surface of the collector plates  131 . Resistance welding the collector plates  131  to the collector plate tabs  132  results in a smoother outer surface of the collector plates  131 . Smoother outer surfaces of the collector plates  131  may better protect the integrity of the polyester film  172  adjacent thereto. Alternatively the barriers may be a surface treatment  174 , formed such as by anodizing or powder coating the plates  170  on the side facing the cells  112 . 
     It will be appreciated that numerous variations to the above-mentioned approach are possible. Variations to the above approach may, for example, include performing the above steps in a different order. 
     Preferred embodiments of this invention are is described herein. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.