Abstract:
A battery assembly including: a plurality of prismatic battery cells; first and second fluid manifolds; and a plurality of corrugated flow plates interleaved with the plurality of battery cells, each the flow plates extending from the first manifold to the second manifold and providing an array of flow channels for carrying fluid from the first manifold to the second manifold, wherein each plate of the plurality of corrugated flow plates is an extruded plastic structure comprising first and second fluid impermeable sheets and a plurality of parallel ribs between and connecting the first and second sheets, said plurality of ribs forming the array of flow channels.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of Provisional Application Ser. No. 61/552,739, filed Oct. 28, 2011, entitled A Multi-Cell Battery Assembly, the entire contents of which are incorporated by reference here. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to cooling systems for a multi-cell battery assembly. 
       BACKGROUND OF THE INVENTION 
       [0003]    Rechargeable high performance batteries, such as Li-ion batteries, are widely used today to power electric vehicles. In such environments, the batteries can experience exceptionally high loads as a result of, for example, rapid acceleration or rapid breaking. Such high loads can generate large electrical currents which in turn may result in a significant warming of the Li-ion cells due to their internal resistance. This generation of waste heat and resulting warming cannot be ignored. 
         [0004]    In the case of Li-ion batteries, for example, achieving efficient operation requires that they must be operated within a specific temperature range. At operating temperatures greater than about 40° C., the life span of the battery can be significantly reduced. In addition, the temperature gradient among cells in a multi-cell battery must be kept within 5-10 degrees centigrade. 
         [0005]    As a consequence, it is essential to have an effective cooling system for such batteries. The cooling system should provide a way to dispose of the waste heat while at the same time assuring that excessive thermal gradients do not occur within the multi-cell battery. It is also desirable that the cooling system be inexpensive and lightweight. 
       SUMMARY OF THE INVENTION 
       [0006]    In general, in one aspect, the invention features a battery assembly including: a plurality of battery cells; a plurality of corrugated flow plates; and first and second fluid manifolds. Each plate of the plurality of corrugated flow plates includes first and second fluid impermeable sheets and a corrugated structure between the first and second sheets. The corrugated structure forms an array of parallel channels extending from one end of that plate to an opposite end of that plate. The plurality of corrugated plates and the plurality of battery cells are interleaved with each other, and each plate of the plurality of corrugated plates extends from the first manifold to the second manifold and is oriented so that the plurality of channels within that plate forms a plurality of fluid flow paths connecting the first and second manifolds. 
         [0007]    Other embodiments include one or more of the following features. The battery cells within the plurality of battery cells are lithium-ion batteries. The battery cells within the plurality of battery cells are flat battery cells, e.g. prismatic battery cells. In each corrugated flow plate of the plurality of corrugated flow plates the first and second sheets are made of a plastic material, e.g. a polypropylene polymer. Each corrugated flow plate of the plurality of corrugated flow plates is an extruded structure. In each corrugated flow plate, the corrugated structure is a plurality of ribs between and connecting the first and second sheets. The interleaved arrangement forms a battery cell stack and the assembly also includes a clamping system applying compressive force to the battery cells within the battery cell stack. The battery assembly further includes first and second end plates, the first end plate on one end of the battery cell stack and the second end plate on an opposite end of the battery cell stack. The clamping system includes a plurality of springs exerting forces on at least one of the first and second end plates. Each of the first and second manifolds has an internal cavity and a back wall including a plurality of slots extending into the internal cavity and into each of which is inserted a corresponding one of the plurality of flow plates. Each battery cell among the plurality of battery cells is within direct contact with and between a corresponding two flow plates of the plurality of flow plates. 
         [0008]    In general, in another aspect, the invention features a battery assembly including: a plurality of prismatic battery cells; first and second fluid manifolds; and a plurality of corrugated flow plates interleaved with the plurality of battery cells. Each the flow plates extends from the first manifold to the second manifold and provides an array of flow channels for carrying fluid from the first manifold to the second manifold. Each plate of the plurality of corrugated flow plates is an extruded plastic structure having first and second fluid impermeable sheets and a plurality of parallel ribs between and connecting the first and second sheets, wherein the plurality of ribs forms the array of flow channels. 
         [0009]    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 DRAWINGS 
         [0010]      FIG. 1  presents an auxiliary view of a liquid-cooled multi-cell battery pack assembly. 
           [0011]      FIG. 2  is a cross-sectional view of the battery pack assembly shown in  FIG. 1 . 
           [0012]      FIG. 3  illustrates the flat or prismatic battery cell used in the battery pack of  FIG. 1 . 
           [0013]      FIG. 4  shows a side view of a portion of the corrugated flow plate used in the battery pack of  FIG. 1 . 
           [0014]      FIGS. 5   a - b  show front and back views, respectively, of the cover plate and back plate which make up the manifold from the battery pack of  FIG. 1 . 
           [0015]      FIG. 6  shows the end plate from the battery pack of  FIG. 1 . 
           [0016]      FIGS. 7   a - b  show bottom and top views, respectively, of the wedge bus bar plate from the battery pack of  FIG. 1 . 
           [0017]      FIG. 8  shows the bus bar terminal clamp from the battery pack of  FIG. 1 . 
           [0018]      FIG. 9  shows a cross-sectional view of the portion of the wedge bus bar plate with terminals extending through the terminal slots. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring to  FIGS. 1 and 2 , the described embodiment is a liquid-cooled multi-cell battery pack assembly  100 . It includes a stack of  16  rechargeable lithium-ion battery cells  102  (see  FIG. 2 ) clamped together by two rectangular-shaped end plates  104   a  and  104   b  that are under compressive forces supplied by four springs  106 . End plates  104   a  and  104   b,  which have holes in each of their four corners, are mounted on four rods  128 , with each rod  128  passing through a corresponding hole in each of the two end plates  104   a  and  104   b.  On one end of each rod  128  there is a retaining ring  130  (see  FIG. 2 ) that prevents that rod from sliding out of the hole in the end plate. On the other end of each rod, there is an adjustment mechanism  132  affixed onto the rod, with one of the springs mounted on rod  128  between end plate  104   a/b  and adjustment mechanism  132 . The position of adjustment mechanism  132  can be varied by turning it in one direction to compress spring  106  or the other to allow spring  106  to relax. On each rod  128 , there is also a thrust needle roller bearing assembly  134  between the spring and the end plate. Springs  106 , which are held in a compressed state by the adjustment mechanism  132 , apply a force on end plate  104   a  thereby causing the end plate to press against and apply pressure on the stack of battery cells. By adjusting the position of adjustment mechanism  132 , one can adjust the compressive force that is applied to the battery cells. Bearing assembly  134  helps achieve a smoother and more accurate adjustment of the compression force. 
         [0020]    Battery cells  102  are contained within the assembly shown in  FIG. 1 . Note that in this figure only their positive and negative terminals  108   a  and  108   b  which extend through a wedge bus bar plate  110  are visible. Bus bar plate  110  holds the bus bar clamps (to be described later) which make up the bus that electrically interconnects the terminals of the cells. The coolant system for the assembly includes two manifolds  112   a  and  112   b  located on opposite sides of the stack of battery cells  102 . Each manifold  112   a  and  112   b  includes a cover plate  114  and a back plate  116  secured together by two rows of bolts  118 . Coolant introduced into manifold  112   a  through an input port  120   a  flows between and cools the battery cells in the assembly and is collected on the other side by manifold  112   b  which has a corresponding exit port  120   b  (not shown). Battery pack assembly  100  also includes a circuit board  124  mounted on bus bar plate  110  that includes sensing and control circuitry that such as is commonly used to manage the charging, discharging, and balancing of the lithium ion cells during use. 
         [0021]      FIG. 3  shows one of the battery cells that is contained within the battery pack assembly. It is also commonly referred to as a prismatic cell. It is a laminated polymer pouch with a flat, thin geometry. Two terminals  108   a  (the positive terminal) and  108   b  (the negative terminal) extend out of the edge of one end the pouch. Prismatic cells are commercially available from multiple sources. The cell described herein is available from A123. It has an output voltage of nominally 3.3 volts, a capacity of 14-20 Ah, and for operation requires an applied compressive pressure of about 5-7 PSI. 
         [0022]    Referring to  FIG. 2 , the internal structure of battery pack assembly is shown in cross-section. In manifolds  112   a  and  112   b,  cover plate  116  and back plate  114  define an internal chamber  117  for receiving the coolant that flows through the battery pack. Referring to  FIGS. 5   a - b , the inside surface of cover plate  116  is recessed with the surface tapering at a constant gradient from an outer location in toward the inlet/exit port  120   a/b . Back plate  114  also includes a recessed region  126  on the side that faces cover plate  116  when manifold  112   a  is assembled. On the wall within recessed region  126  there is an array of equally-spaced slots  128  through back plate  114 . Extending between the two manifolds  112  is an array of corrugated flow plates  160  for carrying coolant between the battery cells from one manifold  112   a  to the other manifold  112   b.    
         [0023]    Referring to  FIG. 4 , corrugated flow plate  160  has two liquid impermeable side sheets  162  separated from each other by an array of equally spaced, parallel ribs  164  connecting one sheet to the other sheet. The array of ribs forms an array of parallel channels  166  extending in one direction inside of the flow plate and through which coolant is flowed. In addition, ribs  164  provide significant strength preventing the flow sheet from collapsing when put under compressive forces. In the described embodiment, the corrugated flow plates are commercially available Coroplast™ sheets that are made of an extruded polypropylene polymer having a thickness of about 2 mm. Other thicknesses are commercially available, e.g. 2-10 mm. 
         [0024]    Referring to  FIGS. 2 ,  5   a  and  5   b , flow plates  160  fit into slots  128  in back plates  114  of the two manifolds  112 , with a flow plate  160  arranged in each slot  128 . Slots  128  are sized so that the flow plates fit snuggly into them. Flow plates  160  are oriented so that channels  126  within flow plates  160  extend from one manifold to the other. Flow plates  160  pass through the slots  128  in the back plates  114  and extend into cavity  117  defined within manifold  112 . On the inside of manifold  112 , there is an epoxy seal  168  along slot  128  between flow plate  130  and back plate  114  that prevents coolant from leaking into the regions inside of the battery assembly where it would contact the cells. Each slot  128  has a tapered entrance on the side that is within the manifold and another smaller tapered entrance (not visible in the figures) on the opposite side. The smaller taper makes insertion of flow plate  160  into slots  128  during assembly easier. The larger taper on the inside facilitates a better seal between flow plate  160  and back plate  114  when epoxy is applied by drawing the epoxy into the tapered area and providing a larger surface area for forming the seal. 
         [0025]    The sloped upper wall of internal chamber  117  that is formed by the inside surface of cover plate  116  serves to reduce or prevent the Coanda Effect, which could result in some of the many flow channels within the flow plates not supporting a flow and containing stagnant fluid/coolant. 
         [0026]    The separations between the flow plates provide spaces into which the battery cells are inserted during assembly. The distances between the flow plates are selected so as to provide a snug fit for the battery cells. This is important so that the compressive forces provide by the end plates will be effectively distributed throughout the stack of battery cells and all battery cells cells will be under sufficient pressure when the battery pack is fully assembled and the springs are adjusted appropriately. 
         [0027]    On the inside of back plate  116  there is a channel  142  formed around the perimeter of back plate  116 . This channel  142  receives a flexible o-ring (not shown) which forms a seal when cover plate  114  is bolted onto back plate  116 . 
         [0028]    As indicated in  FIGS. 1 and 6 , end plates  104   a  and  104   b  have ribbed structures. This is to reduce the weight of the end plates while still giving them sufficient rigidity. It is generally desirable to keep the weight of the overall assembly as low as possible and the ribbed end plates provide one way of achieving that objective. As can be observed from  FIG. 1 , manifolds  112  are designed with a similar objective in mind. Material has been milled out to form an array of recesses in cover plate  114 . 
         [0029]    Wedge bus bar plate  110 , which is shown more clearly in  FIGS. 7   a - b , has two columns of equally spaced terminal slots  146 . Each terminal slot  146  is for a corresponding terminal of a battery cell  102  within the stack of battery cells. When bus bar plate  110  is assembled onto the array of battery cells  102 , the terminals pass through their corresponding terminal slots  146  in bus bar plate  110  and extend above bus plate  110  where electrical connections can be made to them. On the front side of bus plate  110  (see  FIG. 7   b ), there is a recessed region  144  surrounding each pair of terminal slots in each column of terminal slots. In the described embodiment which has 16 battery cells, there is one column of eight recessed regions  144  and a second column of nine recessed regions  144 . These recessed regions  144  are shaped to receive bus bar terminal clamps  148 , an example of which is depicted in  FIG. 8 . As is more apparent in  FIG. 9 , the side walls of the recessed regions  144  are slightly tapered inward so the recess becomes narrower as one goes deeper into the recessed region. On the backside of bus bar plate  110  (see  FIG. 7   a ), there are threaded inserts  150  located within holes arranged on each end of a terminal slot  146 . 
         [0030]    Referring to  FIG. 8 , bus bar terminal clamps  148  are made up of two identical L-shaped metal (e.g. copper) parts  154 . In each part there are three holes  156   a - c . When the parts are assembled onto each other as indicated, holes  156   a  and  156  align with each other. The assembled bus bar terminal clamp  148  has four holes which align with threaded inserts  150  when bus bar terminal clamp  148  is placed into a recessed region  144 . The assembled clamps are then secured within the recessed regions by bolts (not shown) which screw into the threaded inserts. through the four holes 
         [0031]    Battery cells  102  are arranged within the assembly in an alternating orientations, i.e., back-to-back, front-to-front. By alternating the cells, if the first cell will has its positive terminal on the right, then second cell (i.e., the second cell in the stack) will have its negative terminal on the right, the third cell will have its positive terminal on the right, etc. 
         [0032]    Thus, when a bus bar terminal clamp  148  is placed into a corresponding recessed region  144  in bus bar plate  110 , it electrically connects a negative terminal of one battery cell with a positive terminal of a neighboring battery cell. In this way, the set of seventeen bus bar terminal clamps electrically connect the cells in series so that the total output voltage of a battery assembly with N cells is N times the voltage of an individual cell (e.g. 3.3·N volts). 
         [0033]    When bus bar terminal clamp  148  is inserted into its recessed region  144  with the two terminals present, the terminals  108   a  and  108   b  are pinched between an outer wall of the recessed region  144  and the bus bar terminal clamp. The bus bar terminal clamp, when tightened into its recessed region by the four bolts, pinches the battery terminal against the bus bar plate thereby establishing a solid electrical contact with the two battery terminals. Cables (not shown) are connected to the bus bar terminal clamps at either end of the array o bus bar terminal clamps to provide power to an external load. 
         [0034]    Note that the end plates  104   a  and  104   b  have a flange  152  on either end with a thicker central region. The thicker central region is the portion that applies pressure to the stack of cells when under the compressive force of springs  106 . The width of the manifolds  112   a  and  112   b  is sufficiently narrow so that when the pack is assembled, flanges  152  on the end plates do not contact manifolds  112   a  and  112   b.  There is room available for pressing the two end plates  104   a ,  104   b  toward each other with the aid of springs  106  thereby increasing the pressure that is applied to the stack of cells. 
         [0035]    In the described embodiment, end plates  104   a  and  104   b  are made of aluminum, manifolds  112   a  and  112   b,  wedge bus bar plate  110 , and the bottom cover are made of ABS (acrylonitrile butadiene styrene) or polypropylene, and the epoxy adhesive: is DP100 Plus from 3M. The coolant could be water or Fluorinert™, which is an electrically insulating coolant sold commercially by 3M. Of course, there are many other commercially available acceptable alternatives to these materials that could be used. In addition, the battery pack assembly can have any number of battery cells depending on the output voltage requirements of the application. Furthermore, clamping mechanisms other than the spring arrangement described herein can be used to accomplish basically the same thing. 
         [0036]    In addition, other corrugated structures are possible. The Coroplast is particularly convenient because it commercially available, inexpensive, and has properties that are appropriate for this particular application. However, there are other ways to design and fabricate the corrugated flow plates. Another, though less efficient, approach to making a corrugated plate is to bond a “wavy” sheet of material between two flat sheets of impermeable material. The resulting structure would look more like the corrugated cardboard with which everybody is familiar. 
         [0037]    Other embodiments are within the following claims.