Abstract:
A battery module is described. The battery module includes a plurality of battery cells; a plurality of cooling fin assemblies, each cooling fin assembly positioned between two battery cells, the cooling fin assemblies comprising at least one cooling fin and a foot on at least one side of the cooling fin assemblies, the foot having a bottom and interlocking profiles on each end, the interlocking profiles on adjacent feet of the cooling fin assemblies interlocking the feet and forming a surface; and a heat sink contacting the surface of the interlocked feet. A method of cooling a battery module is also described.

Description:
STATEMENT OF RELATED CASES 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/407,251, filed Oct. 27, 2010, entitled “Battery Thermal System with Interlocking Structure Components,” which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to batteries, and more particularly to a battery thermal system with interlocking structural components. 
     BACKGROUND OF THE INVENTION 
     Current battery internal heat exchangers require numerous components and sealing connections, and complicated manufacturing processes. One known method for cooling battery cells is to bring two cells into face contact with a cooling fin through which coolant flows. The cooling fins are connected by integrating an inlet and outlet header hole on both sides of the fin. The inlet and outlet headers are then formed by stacking two or more fins together, and connecting the inlet and outlet header holes. An o-ring seal (or similar seal) may be used to form the seal between two fins. The seals for both inlet and outlet are typically integrated into a frame, which holds the cells and fins in place in the stack. 
     An example of this type of system is shown in  FIG. 1 . An expanded view of the battery pack  10  is shown. The battery cells  15  are separated by cooling fins  20 . There is a cooling inlet  25  on one side of the cooling fin  20  and a cooling outlet  30  on the other side of the cooling fin  20 . Coolant flows through channels  35  in the cooling fin  15 . Heat from the battery cells  15  is conducted into the cooling fins  20 . Two battery cells  15  and a cooling fin  20  can be contained in a frame  40 . There are seals  45  on both sides of the cooling fin  15  for the cooling inlet  25  and cooling outlet  30 . The seals  45  can be integrated into the frame  40 . This arrangement requires multiple components and seals and a complicated assembly process. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a battery module. In one embodiment, the battery module includes a plurality of battery cells; a plurality of cooling fin assemblies, each cooling fin assembly positioned between two battery cells, the cooling fin assemblies comprising at least one cooling fin and a foot on at least one side of the cooling fin assemblies, the foot having a bottom and interlocking profiles on each end, the interlocking profiles on adjacent feet of the cooling fin assemblies interlocking the feet and forming a surface; and a heat sink contacting the surface of the interlocked feet. 
     Another aspect of the invention is a method of cooling a battery module. The method includes providing a battery module comprising: a plurality of battery cells; a plurality of cooling fin assemblies positioned between two battery cells, the cooling fin assemblies comprising at least one cooling fin and a foot on at least one side of the cooling fin assemblies, the foot having a bottom and interlocking profiles on each end, the interlocking profiles on adjacent feet of the cooling fin assemblies interlocking the feet and forming a surface; and a heat sink contacting the surface of the interlocked feet; and circulating cooling fluid through the heat sink, the feet transferring the heat generated in the plurality of battery cells to the heat sink over a contact area between the heat sink and the surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a prior art method of cooling battery cells. 
         FIG. 2  is an illustration of one embodiment of a module heat exchanger. 
         FIGS. 3A-B  are illustrations of the module base of  FIG. 2  in more detail. 
         FIG. 4  is an illustration of a portion of the module base of  FIG. 2  in more detail. 
         FIG. 5  is an illustration of one embodiment of the solid fin assembly. 
         FIG. 6A  is an illustration of the heat transfer for a system without a foot. 
         FIG. 6B  is a graph illustrating the heat flux through the TIM for the system of  FIG. 6A . 
         FIG. 6C  is an illustration of the heat transfer for a cooling fin assembly with a foot. 
         FIG. 6D  is a graph illustrating the heat flux through the TIM for the system of  FIG. 6C . 
     
    
    
     DETAILED DESCRIPTION 
     The new design provides a simple, more robust battery internal heat exchanger which reduces cost, improves reliability, and simplifies manufacturing. 
     The design allows simplification of the battery internal heat exchanger. There are fewer seals with the present solid fin design because the coolant flow is only at the sides of the module, instead of between every battery cell or every other battery cell. By “solid fin,” we mean that there are no cooling channels (and thus no coolant circulating) in the cooling fins between the cells. 
     In addition, the heat sink design is simple. There are also fewer components in the module because plastic frames are not required. Manufacturing is easier because the stacking procedure is simple. In addition, only normal cleanliness standards are required because no seals are made during stacking. 
     The thermal connection between a solid fin assembly and a heat sink is optimized because the interlocking foot design ensures that the fin feet align to each other and create a flat interface surface. 
     Thus, the design provides lower material, manufacturing, and warranty costs. 
       FIGS. 2 ,  3 A, and  3 B show one embodiment of the battery internal components for building the module  50 . The module  50  has a module base  55  and a heat sink  60 . The module base  55  contains the battery cells  65  and solid fin assemblies  70 , which are stacked between the battery cells  65 . The solid fin assemblies  70  conduct heat generated in the battery cells  65  to the heat sinks  60 , which are mounted on at least one side of the module base  55  (typically both sides). The module base  55  can be held together by end plates  75  and brackets  80 , if desired. 
     The solid fin assemblies  70  are stacked between the battery cells. In one embodiment, there can be solid fin assemblies between all of the battery cells (i.e., solid fin assembly, battery cell, solid fin assembly, battery cell, etc). However, other arrangements are possible, for example, arrangements in which there are solid fin assemblies between every two battery cells (i.e., solid fin assembly, 2 battery cells, solid fin assembly, 2 battery cells, etc.), or every three battery cells (i.e., solid fin assembly, 3 battery cells, solid fin assembly, 3 battery cells, etc.), etc. 
     The heat sinks  60  have a channel through which the coolant is pumped. The heat sinks can be formed by stamping two metal sheets (e.g., of aluminum) and brazing or welding them together, forming the channels. Because the heat sinks  60  are located on the sides of the module base  55 , only one coolant inlet and outlet are needed for each heat sink. This eliminates the need for multiple seals for each cooling fin, and reduces the cost and complexity of the system. 
       FIGS. 4-5  show details of one embodiment of the solid fin assemblies  70 . The solid fin assemblies  70  are placed between the battery cells  65 . In one embodiment, a pair of solid fins  85  surround an expansion unit  90 , and are inserted into a foot  95 . The design of the solid fin assembly  70  allows deformation and therefore cell tolerance and expansion management. 
     The feet  95  are in contact with the heat sink  60 . The contact can be direct such that the feet  95  touch the heat sink  60 , or indirect in which there is a layer of material between the feet  95  and the heat sink  60 , as discussed below. 
     The feet  95  have a top  107 , a bottom  105  opposite the top  107 , and interlocking profiles  110 ,  115  on opposite ends. The profile on one foot interlocks with the opposing profile on the next foot. As the battery cells  65  and solid fin assemblies  70  are stacked, the interlocking profiles  110 ,  115  on the feet  95  interlock with each other, forming a surface  100  onto which the heat sink  60  can be easily attached. 
     In one embodiment as shown, the bottom  105  of the feet is flat and consequently, the surface  100  is flat. However, other surface shapes are possible, such as a ribbed surface. The surface provides contact, and thus, heat transfer, with the heat sink. The surface shape should promote good contact and heat transfer. 
     One example of interlocking profiles  110 ,  115  is a tongue-and-groove arrangement as shown in  FIG. 5 , in which the feet  95  have a tongue profile  110  on one end and a groove profile  115  on an opposite end. As shown in  FIG. 4 , the tongue profile  110  projects from one end of the foot  95  and is received by and interlocks into a groove profile  111  of one adjacent foot  96 . Likewise, the groove profile  115  on the opposite end of the foot  95  receives and interlocks with a tongue profile  116  projecting from another adjacent foot  97 . However, other types interlocking profiles, such as lap joints, could be used, as is known to those of skill in the art. 
     The feet can be made of any material capable of transferring heat. Suitable materials include, but are not limited to, aluminum. Suitable processes for producing the feet include, but are not limited to, extrusion, which allows high volume manufacture. 
     The solid fins  85  can be placed in slots  120  on the top of the feet  95 . The solid fins  85  can be separated by the expansion unit  90 , which can be for example, a sheet of foam or a metal leaf spring. The expansion unit  90  compensates for the cell tolerance and expansion variation in the cell thickness direction. Alternatively, the solids fins could be spaced apart with nothing between them. In order for the cells to vary in thickness, the solid fins  85  move, and the free length of the solid fin  85  between the end of the cell and the start of the foot  95  allows the solid fin  85  to deform and accept different cell thicknesses. 
     In one embodiment, the feet are a separate piece from the solid fin assembly and are attached to the solid fin assemblies, as shown above. In another embodiment, the feet can be an integral part of the solid fins. 
     A layer  125  of thermal interface material (TIM) can optionally be applied between the inner surface of the heat sink  60  and the surface  100  formed by the feet  95 , which helps to provide good thermal contact. The use of TIM material to make thermal contact between the foot and the heat sink allows easy disassembly of the battery module (as opposed to adhesive, for example, which would not permit easy disassembly). The heat generated in the cell is conducted along the solid fin, through the foot, across the TIM, and into the coolant flowing through the heat sink. 
     The shape and material of the feet are selected so that the heat flow from the battery cells to the heat sink is evenly distributed over the whole contact area between the feet and the heat sink (or feet, TIM, and heat sink) and without a large temperature drop in the feet themselves. As a result, there is no heat flow concentration, and the entire contact area between the feet and heat sink (or feet, TIM, and heat sink) is available for heat transfer.  FIGS. 6A-B  illustrate the effect of an assembly without feet. There is a cooling fin assembly  150  between two battery cells  155 . The heat is forced through a very small area  160  of the TIM  165 . As shown in  FIGS. 6C-D , the cooling fin assembly includes interlocking feet  170 . This transfers the heat evenly over a larger area  175  of TIM  165 . 
     It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention. 
     For the purposes of describing and defining the present invention it is noted that the term “device” is utilized herein to represent a combination of components and individual components, regardless of whether the components are combined with other components. For example, a “device” according to the present invention may comprise an electrochemical conversion assembly or fuel cell, a vehicle incorporating an electrochemical conversion assembly according to the present invention, etc. 
     For the purposes of describing and defining the present invention it is noted that the term “substantially” is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term “substantially” is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.