Abstract:
A prismatic-cell battery pack is provided with integral coolant passages and a distributed array of coolant channels coupled between an intake plenum and a pair of exhaust plenums. Coolant medium forced into the intake plenum draws heat away from the battery cells, and then exits via the exhaust plenum for expulsion of heat into the atmosphere. The battery pack is configured as a set of stackable interlocking battery cell modules including at least one battery cell in thermal proximity to an array of coolant channels distributed over the profile of the battery cell, and a pair of peripheral chambers joined to opposite ends of the coolant channels to form the intake and exhaust plenums when the modules are arranged and interlocked in a lineal stack. The entry end of each channel is closer to a centerline of the battery cell than the exit end of the channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part application and claims the benefit of U.S. patent application Ser. No. 12/611,168, filed on Nov. 3, 2009, the entire disclosure of which is hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD OF INVENTION 
       [0002]    The present invention relates to a high-voltage battery pack containing prismatic battery cells arranged in a lineal stack, and more particularly to a prismatic-cell battery pack with integral coolant passages for forced convection cooling of the battery cells. 
       BACKGROUND OF INVENTION 
       [0003]    High voltage battery packs can be configured for efficient space utilization by stacking and co-packaging battery cells of a prismatic (i.e., rectangular) form factor. The prismatic cells are typically arranged so that their terminals are all accessible from the top of the pack, and the terminals of adjacent cells lie in close proximity for convenient interconnection due to the thin profile of the cells. Lithium-ion batteries are well-suited to such applications because of their low weight, high power density and relatively high cell voltage, and because they can be produced at relatively low cost in prismatic form, particularly when encapsulated by a soft package of metalized plastic film instead of a rigid plastic or metal case. When soft-package cells are used, they can be conveniently mounted in stackable rigid plastic frames, as shown for example, in the U.S. Patent Publication No. 2006/01232119. Also, foam pads can be used for cell-to-cell isolation and to compressively support the cells. 
         [0004]    A serious challenge involved in the design of a battery pack is the provision of adequate cooling for the individual cells. This is particularly true in hybrid vehicle and other applications that require the battery pack to supply large amounts of energy at a high rate. The usual approach is to attach one or more liquid-cooled or air-cooled heat sinks to the bottom and/or sides of the battery pack, and to use metal heat runners to transfer heat from the battery cells to the heat sinks by conduction. While this approach can be effective if sufficient space is available to accommodate the heat sinks, space and weight considerations often take precedence, forcing sub-optimal sizing and placement of the heat sinks. Moreover, the effectiveness of this approach is hampered for two additional reasons: first, the heat produced in a battery cell causes the greatest temperature rise near the terminals, which may be separated from the heat sinks by a substantial distance; and second, the cooling medium rises in temperature as it travels through the heatsink, which degrades heat rejection capability at the downstream end of the heatsink. Since over-heating can permanently damage a battery cell, the power output of the battery pack is often limited to extend battery pack life expectancy. Accordingly, what is needed is a way to more effectively and uniformly cool a prismatic-cell battery pack so that reliability and performance can be improved. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is directed to an improved prismatic-cell battery pack having integral coolant passages including an intake plenum, an exhaust plenum, and a distributed array of coolant channels coupled between the intake plenum and the exhaust plenum. A coolant medium such as air is forced into the intake plenum, enters the various coolant channels in parallel, draws heat away from the battery cells, and then enters the exhaust plenum and so removes heat from the battery cell. 
         [0006]    The improved battery pack is conveniently configured as a set of stackable interlocking battery cell modules, where each module supports at least one prismatic battery cell in thermal proximity to an array of coolant channels distributed over the profile of the battery cell. Each battery cell module also includes peripheral chambers joined to opposite ends of the coolant channels to form the intake and exhaust plenums when the modules are arranged and interlocked in a lineal stack. In a preferred mechanization, the intake and exhaust plenums are disposed below the battery cells, and the coolant channels are in the shape of an inverted-U, conducting coolant from the intake plenum, upward across the central portion of the battery cell toward the battery cell terminals, outward away from the vertical centerline of the battery cell, and then back downward to enter the exhaust plenums. 
         [0007]    In accordance with one embodiment of this invention, a prismatic-cell battery pack is provided. The prismatic-cell battery pack includes a set of battery cell modules arranged and interlocked in a lineal stack. Each battery cell module includes at least one prismatic battery cell supported in thermal contact with one or more coolant channels distributed over a profile surface of the battery cell. Each battery cell also includes a plurality of peripheral chambers joined to opposite ends of the coolant channels that are configured to form an intake plenum and a pair of exhaust plenums that are, respectively, upstream and downstream of the coolant channels when the modules are lineally arranged and interlocked. Each coolant channel defines an entry end coupled to the intake plenum and one or more exit ends coupled to one or both of exhaust plenums. Coolant supplied to the intake plenum enters the entry end of a channel and is returned to one or more exhaust plenums via one or more exit ends for expulsion of heat from the battery pack and thereby cools the respective battery cells. The one or more coolant channels are configured such that the entry end is closer to a centerline of the battery cell than the exit end. 
         [0008]    Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  is an perspective view of a prismatic-cell battery pack according to this invention; 
           [0011]      FIG. 2  is an perspective view of a battery cell module of the battery pack of  FIG. 1 ; 
           [0012]      FIG. 3  is a partially sectioned perspective view of the battery pack of  FIG. 1 , illustrating coolant flow through a representative battery cell module; 
           [0013]      FIG. 4  is an abbreviated coolant flow diagram for the battery pack of  FIG. 1 ; 
           [0014]      FIG. 5  is a partial cross-sectional view illustrating inlet and outlet end caps for the battery pack of  FIG. 1 ; and 
           [0015]      FIG. 6  is an exploded perspective view of the battery cell module of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]    Referring to the drawings, and particularly to  FIGS. 1-3 , the reference numeral  10  generally designates prismatic-cell battery pack according to this invention. In general, the battery pack  10  includes a lineal stack  12  of battery cell modules  14  longitudinally bounded by first and second end pieces  16  and  18 , an inlet end cap  20 , and an outlet end cap  22 . Referring particularly to  FIG. 2 , each of the battery cell modules  14  includes a set of interlocking frames  24  for supporting and retaining a pair of prismatic battery cells  26  (only one of which is shown in  FIG. 2 ), and for channeling coolant in proximity to the battery cells  26 . The battery cells  26  are preferably soft-package cells, and a pad of resilient material such as open-cell foam (not shown) is inserted between each of the battery cell modules  14  of the stack  12  to support and compressively load the non-marginal portions of the battery cells  26 . The battery pack elements may be held in place, for example, by a set of fasteners routed through suitable openings (not shown) in the modules  14  and end pieces  16 ,  18 . 
         [0017]    Referring to  FIG. 2 , each of the battery cell modules  14  includes a set of coolant passages, including an intake chamber  28 , an exhaust chambers  30 A and  30 B, and several U-shaped coolant channels  32   a,    32   b,    32   c,    32   d  (as represented by phantom flow lines) that couple an entry end  54  ( FIG. 6 ) of each coolant channel to the intake chamber  28 , and couple an exit end  56  ( FIG. 6 ) of each coolant channel to the exhaust chambers  30 A or  30 B. When the battery cell modules  14  are arranged and interlocked in a lineal stack as shown in  FIGS. 1 and 3 , the various intake chambers  28  axially align to form an intake plenum  34  that extends the length of the stack  12 , and the various exhaust chambers  30 A and  30 B similarly align to form a pair of exhaust plenums  36 A and  36 B that also extends the length of the stack  12 . As illustrated in  FIG. 5 , the coolant inlet cap  20  blocks the exhaust plenums  36 A and  36 B, and establishes a pathway  38  between intake plenum  34  and an inlet port  20   a  formed in the coolant inlet cap  20 . Conversely, the coolant outlet cap  22  blocks the intake plenum  34  but establishes a pathway  39  between exhaust plenums  36 A and  36 B and an outlet port  22   a  formed in the coolant outlet cap  22 . Accordingly, and as illustrated in the coolant flow diagram of  FIG. 4 , coolant (forced air, or fluid for example) entering inlet port  20   a  is directed into the intake plenum  34 , through the U-shaped coolant channels  32   a - 32   d  in each of the stacked battery cell modules  14 , into the exhaust plenums  36 A and  36 B, and is expelled from the outlet port  22   a.    
         [0018]    The temperature of the coolant entering each of the battery cell modules  14  is essentially the same because each module  14  receives coolant from the intake plenum  34 , as opposed to coolant that has already passed through another module  14  of the pack  10 . As a result, the cooling performance is substantially equivalent for each battery cell module  14  of the pack  10 . Additionally, the U-shaped coolant channels  32   a - 32   d  traverse substantially the entire surface area of the respective battery cells  26  to prevent any battery cell hot-spots, particularly in the region of the battery terminals where much of the battery cell heat is generated. Furthermore, by routing coolant first toward a central portion of the battery cell, that is nearby or along a centerline  50  of the battery cell, where the greatest temperature rise has been observed with other coolant channel configurations, the range of temperature variation across the battery cell may be reduced. While the temperature of the coolant flowing into the entry end  54  of each coolant channels  32   a - 32   d  will obviously rise as it traverses up the U-shaped coolant channels  32   a - 32   d,  the coolant flow can be controlled to provide sufficient cooling to the battery cell portions adjacent the exit ends  56  of the coolant channels  32   a - 32   d.  Also, the coolant channels  32   a,    32   b,    32   c,    32   d  in a given battery call module  14  can vary in width to achieve a desired coolant flow distribution for optimal cooling performance. 
         [0019]    Referring to  FIG. 6 , each of the battery cell modules  14  is constructed as an assembly of two prismatic battery cells  26   a,    26   b  and a set of four interlocking frame members  24   a - 24   d.  In this non-limiting example, the two inner frame members  24   a  and  24   b  are identical, as are the two outer frame members  24   c  and  24   d.  Although not shown in  FIG. 6 , the modules  14  may include a provision for suitably interconnecting the battery cell terminals  48   a,    48   b,    48   c,    48   d,  and the battery cells  26   a,    26   b  may be placed in an orientation that facilitates the desired series or parallel battery terminal interconnection. 
         [0020]    The two inner frame members  24   a  and  24   b  each have a planar outboard face  40   a  and sculpted inboard face  40   b.  When they are arranged as shown in  FIG. 6  and mutually joined, the outboard faces  40   a  provide smooth support surfaces for the battery cells  26   a  and  26   b,  and the sculpted inboard faces  40   b  form the U-shaped coolant channels  32   a - 32   d.  Specifically, the coolant channels  32   a,    32   b,    32   c,    32   d  indicated in FIG.  2  are formed by an arrangement of nested pairs U-shaped recesses  42   a,    42   b,    42   c,    42   d  on the inboard face  40   b  of each inner frame member  24   a,    24   b.  The opposed recesses  42   a - 42   d  on the inboard faces  40   b  of frame members  24   a  and  24   b  abut when the frame members  24   a  and  24   b  are joined, thereby defining the U-shaped coolant channels  32   a - 32   d,  including the respective entry end  54  and exit end  56  of each coolant channels  32   a - 32   d.  The inner frame members  24   a,    24   b  also include lower openings or apertures  44  that align as indicated to form the intake chamber  28  and exhaust chambers  30 A and  30 B mentioned above in reference to  FIG. 2 . The recesses  42   a - 42   d  open at one end into the openings  44  that form the intake chamber  28 , and at the other end into the openings  44  that form the exhaust chambers  30 A and  30 B to produce the coolant flow illustrated in  FIG. 4  when coolant is supplied to the inlet port  20   a.  A tongue-in-groove seal  46  near the periphery of the inner frame members  24   a,    24   b  prevents coolant leaks to atmosphere; and tongue-in-groove seals  52  helps prevent short-cut coolant leakages between intake plenum  34  and exhaust plenums  36 A and  36 B. It is expected that some coolant leakage between adjacent coolant channels  32   a  and  32   b,  or between adjacent coolant channels  32   c  and  32   d  may occur, but any such leakage is expected to be both minor and inconsequential. 
         [0021]    The battery cells  26   a,    26   b  are maintained in contact with the smooth and planar outboard faces  40  of the inner frame members  24   a,    24   b,  and the coolant in coolant channels  32   a - 32   d  is only separated from the battery cells  26   a,    26   b  by the local thickness of the respective inner frame member  24   a  or  24   b,  which may be on the order of 1 mm or less. Accordingly, heat produced by the battery cells  26   a,    26   b  is quickly and efficiently transferred to the coolant flowing in coolant channels  32   a - 32   d,  even if the inner frame members  24   a,    24   b  are constructed of a material such as plastic. Of course, the inner frame members  24   a,    24   b  could be constructed of a material exhibiting high thermal conductivity if desired. Also, it is possible to utilize an insulating material such as plastic for the marginal portions of inner frame members  24   a,    24   b,  and a conductive material such as aluminum for the non-marginal portions of inner frame members  24   a,    24   b.    
         [0022]    The two outer frame members  24   c  and  24   d  fasten to the inner frame members  24   a  and  24   b,  respectively, to retain the prismatic battery cells  26   a  and  26   b  in the module  14 . In effect, the terminal and marginal portions of each battery cell  26   a,    26   b  are sandwiched between an inner frame member  24   a,    24   b  and an outer frame member  24   c ,  24   d.  And the inter-module foam pads, mentioned above in respect to  FIG. 1 , press against the exposed non-marginal portions of the battery cells  26   a  and  26   b  to maintain them in abutment with the exterior surfaces  40  of the inner frame members  24   a  and  24   b.    
         [0023]    In summary, present invention provides an effective and low-cost packaging arrangement for efficiently and uniformly cooling a prismatic-cell battery pack with a flow-through coolant. Integrating the coolant channels  32   a - 32   d  and plenums  34 ,  36  into the frames  24   a,    24   b  that support the cells  26  of the battery pack  10  contributes to low overall cost, and ensures that the coolant will uniformly cool each of the cells  26 . The use of identical parts in reverse orientation (for example, the inlet and outlet end caps  20 ,  22 , the inner frame members  24   a,    24   b,  and the outer frame members  24   c,    24   d ) also contributes to low overall cost of the battery pack  10 . The ‘up-the-middle, down-the-outside’ configuration of the flow channels  32   a - 32   d  helps to deliver lower temperature coolant to the central area of the battery cells where the highest temperatures have been observed, and as such provide for more uniform operating temperatures across the battery cells. 
         [0024]    While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the number of coolant channels  32   a - 32   d  in a battery cell module  14  may be different than shown, as may the number of battery cells  26  in a battery cell module  14 , or the entry end  54  of coolant channels  32   a  and  32   d  may be joined to form a common inlet end overlying the center line  50  to form a ‘T’ shaped coolant channel, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.