Abstract:
A prismatic-cell battery pack is provided with 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. Coolant medium forced into the intake plenum enters the coolant channels in parallel, draws heat away from the battery cells, and then enters the exhaust plenum for expulsion 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.

Description:
TECHNICAL FIELD 
     The present invention relates to a high-voltage battery pack containing prismatic battery cells arranged a lineal stack, and more particularly to prismatic-cell battery pack with integral coolant passages for forced-air cooling of the battery cells. 
     BACKGROUND OF THE INVENTION 
     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. 
     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 heatsinks 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 heatsinks by conduction. While this approach can be effective if sufficient space is available to accommodate the heatsinks, space and weight considerations often take precedence, forcing sub-optimal sizing and placement of the heatsinks. Moreover, the effectiveness of this approach is hampered for two additional reasons: first, the heat produced in a battery cell is greatest near its terminals, which may be separated from the heatsinks 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. And since over-heating can permanently damage a battery cell, the power output of the battery pack often has to be limited to preserve battery pack life expectancy. Accordingly, what is needed is a way of more effectively and uniformly cooling a prismatic-cell battery pack so that its life and performance will not be heat-limited. 
     SUMMARY OF THE INVENTION 
     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 is expelled into the atmosphere. 
     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 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. 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 toward the battery cell terminals and then back downward to enter the exhaust plenum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a prismatic-cell battery pack according to this invention. 
         FIG. 2  is an isometric view of a battery cell module of the battery pack of  FIG. 1 . 
         FIG. 3  is a partially sectioned isometric view of the battery pack of  FIG. 1 , illustrating coolant flow through a representative battery cell module. 
         FIG. 4  is an abbreviated coolant flow diagram for the battery pack of  FIG. 1 . 
         FIG. 5  is a partial cross-sectional view illustrating inlet and outlet end caps for the battery pack of  FIG. 1 . 
         FIG. 6  is an exploded isometric view of the battery cell module of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 . 
     Referring to  FIG. 2 , each of the battery cell modules  14  includes a set of coolant passages, including an intake chamber  28 , an exhaust chamber  30 , and several U-shaped coolant channels  32   a ,  32   b ,  32   c ,  32   d  (as represented by phantom flow lines) that couple the intake chamber  28  to the exhaust chamber  30 . 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  similarly align to form an exhaust plenum  36  that also extends the length of the stack  12 . As illustrated in  FIG. 5 , the coolant inlet cap  20  blocks the exhaust plenum  36  but establishes an airway  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 an airway  39  between exhaust plenum  36  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, 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 plenum  36 , and is expelled from the outlet port  22   a.    
     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. While the temperature of the coolant will obviously rise as it traverses 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 downstream ends 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. 
     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 . 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  also 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. 
     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  are formed by a set of nested 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 forming the U-shaped 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 and exhaust chambers  28  and  30  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 chamber  30 , 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 a tongue-in-groove seal  48  in a central portion of the inner frame members  24   a ,  24   b  prevents coolant leakage between intake and exhaust plenums  34 ,  36 . It is expected that some coolant leakage between adjacent coolant channels  32   a - 32   d  may occur, but any such leakage will be both minor and inconsequential. 
     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 insulative 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.    
     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.    
     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 . 
     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 , 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.