Abstract:
A battery module with microencapsulated phase change materials as an automotive thermal management system. In one form, the microencapsulated phase change material is in the form of a foam made of a core encased in a generally polymer-based shell. In a more particular form, the foamed material may be tailored to go through isothermal phase change at more than one temperature, such as a relatively cold temperature and a relatively high temperature. A thermal management system based on the use of such microencapsulated phase change material includes heating and cooling capabilities for conditions expected to be encountered under both high-temperature and low-temperature vehicular operating conditions. Methods of controlling the temperature in battery modules are also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/472,701, filed Apr. 7, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to passive thermal management of batteries and portions thereof, and more particularly to the use of microencapsulated phase change materials in conjunction with automotive battery packs, battery modules or individual battery cells as a way to improve thermal management of such battery components. 
         [0003]    Lithium-ion batteries are being used in automotive applications as a way to supplement, in the case of hybrid electric vehicles (HEVs), or supplant, in the case of purely electric vehicles (EVs), conventional internal combustion engines (ICEs). In either variant, HEVs or PEVs belong to a larger class of vehicles known as electric vehicles (EVs). The high volumetric heat generation rate and generally passive construction of lithium-ion batteries provides both the durability and functionality needed to serve as a propulsion system for cars, trucks, buses, motorcycles and related automotive or vehicular platforms. 
         [0004]    Temperature is one of the most significant factors impacting both the performance and life of a battery. Extremes (such as those encountered during protracted periods of inactivity in cold or hot environments, or due to extended periods of operation and concomitant heat generation on hot days) can negatively impact the ability of the battery to operate correctly, and in severe cases can destroy the battery entirely. Side effects of prolonged exposure to high temperature may include premature aging and accelerated capacity fade, both of which are undesirable. Conventional heat dissipation methods such as forced air and liquid cooling may prove to be effective at avoiding such side effects, but they add to overall vehicular system weight, complexity and parasitic power requirements. 
       SUMMARY OF THE INVENTION 
       [0005]    A battery thermal management system based on a phase change material (PCM) has the potential to limit battery temperature extremes, thus acting to increase temperature uniformity, as well as to reduce heating and cooling requirements. This helps to prolong the life of heat-sensitive components, such as the charge-carrying battery cells that form the building blocks of battery modules and battery packs. PCMs can absorb and release a large amount of latent heat (in some instances up to fifty times higher than sensible heat) during isothermal (i.e., constant temperature) changes of phase, such as from solid-to-liquid or liquid-to-solid. As such, the use of PCMs can help to reduce or eliminate the need for active cooling components such as a fan, blower or pump in forced-air or forced-liquid cooling systems. This is beneficial in that the PCM can provide the ability to maintain the cell temperature in a desired temperature range without drawing power from the battery or another energy source. An example of a PCM-based approach to battery thermal management may be found in a co-pending U.S. patent application Ser. No. ______ entitled BATTERIES WITH PHASE CHANGE MATERIALS which was filed on the same day as the present application, owned by the Assignee of the present invention and hereby incorporated in its entirety by reference. 
         [0006]    According to one aspect of the invention, a battery pack employing one or more battery modules which in turn employ one or more battery cells is disclosed. More particularly, a microencapsulated version of a PCM-based thermal management system is used to provide at least one of augmented heating or cooling to a configuration of such battery components. This version, known as a microPCM, is made up of very small bi-component particles or capsules that include a core material that exhibits latent heat changes tailored to a temperature range typically countered in an automobile battery pack, along with an outer shell or capsule made from a polymer or related material such that together, the core and shell define a generally spherical foam-like material. MicroPCM capsules range from less than one micron to several hundred microns in diameter, where all three states of matter (solids, liquids and gases) may be used to form the microencapsulatable core. Advantages compared to non-microencapsulated PCM includes increased protection of the core material, ease of incorporation into other materials, and decreased likelihood of leakage during melting. MicroPCMs may also be mixed in different mass percentages as a way to tailor their thermal response, for example, adjusting the phase change latent heat and phase change temperature. They can also be made to have more than one material be formed in the core such that each microPCM exhibits a thermal composite structure. Additional advantages include low material costs, where microencapsulation can include between about 50 and 90 percent active material. 
         [0007]    In a particular form, the battery pack is made up of numerous battery modules each of which is in turn made up of one or more battery cells that may deliver electric current for motive power for an automobile. In the present context, the term “motive power” describes a battery pack capable of providing more than mere starting power for another power source (such as an internal combustion engine); it includes battery packs capable of providing sustained power sufficient to propel a vehicle in a manner consistent with that for which it was designed. In one form, the current generated by the battery pack may be used to run one or more electric motors that in turn may be used to turn one or more wheels. Other members (for example, structural members) are placed in thermal communication with the battery cell to enable heat exchange between them. The member includes a microPCM such that upon exposure of the microPCM to a temperature change, the microPCM&#39;s ability to absorb (in situations involving high ambient temperatures) or release (in situations involving low ambient temperatures) significant amounts of latent heat allows significant quantities of heat to be exchanged with the battery cell without (or at least a significant reduction in) the need for supplemental cooling, such as forced-air or forced-liquid convective cooling. 
         [0008]    In one preferred form, the microPCM is made up of a two-layer structure of an outer shell containing an inner core of phase change material. In this way, a material of high latent heat absorption is protectively encased within the shell. For automotive applications, where much of the ambient temperature is between approximately −10° C. and 40° C., the material of high latent heat absorption may be made to exist in any of a sold, liquid or gaseous state some typical temperature at or within these limits. As such, in the present context, when a microPCM is mentioned as having a particular phase-change temperature (such as about −10° C. to about 40° C. generally, or a more particular value within that range, such as 37° C. (in the case of eicosane, discussed below) or a broader range, such as below about 0° C.), it will be appreciated by those skilled in the art that minor variations near these temperatures are also within the scope of the present invention so long as such variations correspond to the thermal environment in which the automobile is operating, and such environment is one that the automobile is designed for and reasonably expected to be encountered during such operation. 
         [0009]    One particularly promising material for the core material of microPCMs is eicosane, a paraffin-based mixture of alkanes that exhibit a high latent heat of fusion (for example, about 240 kJ/kg). The melting point of eicosane, 37° C., makes it ideal for electric vehicle applications, where a typical battery cell maximum excursion temperature of between about 40° C. and 50° C. may occur. Likewise, because automotive applications (such as those with HEV or PEV configurations) may operate within the above temperature ranges, it would be desirable to have at least the high-temperature phase change temperatures take place between about 28° C. and 40° C. Such paraffin-based PCMs are an excellent electrical insulator, with an electrical resistivity of between 10 13  and 10 17  ohm meter. Furthermore, such a microPCM has been shown to be durable under various battery charge and discharge cycles, with particular emphasis on avoidance of microcapsule damage due to the foam compression force deflection under different battery operating temperatures. Other materials may be used, such as non-paraffin organic PCM fatty acids; however, additional tailoring may be required to have the melting or related phase change occur in temperature ranges commensurate with HEV or PEV battery pack operating temperatures. Other paraffin wax-based materials that may be suitable include octadecan, subject to the needs of the particular automotive environment. While it is additionally possible to augment the thermal conductivity of materials such as paraffin wax through the use of certain high thermal conductivity materials (for example, graphite) in the wax matrix, care must be taken, at least for automotive and related transportation applications, as graphite tends to be brittle (and therefore exhibits negative crash-related damage properties), difficult to machine, electrically conductive and expensive. Other factors (for example, leakage behavior) militate against its use as a matrix for PCM, especially for HEV or PEV applications. 
         [0010]    In one particular configuration, the microPCM (which may embody a generally spherical shape) is approximately 20 microns in diameter Likewise, the material of high latent heat absorption used as the core may be in any of a solid, liquid or gaseous state at room temperature, so long as it retains the ability to absorb or release a significant amount of latent heat upon exposure to the respective high or low temperature from the battery pack that corresponds to at least one of an endothermic reaction absorption of heat and an exothermic reaction release of heat. In a more particular form, the member (which is preferably a part of, or provides structural support to, a heat-exchange mechanism) comprises at least one of a cooling fin, cooling plate or compressible foam isolator sheet, any or all of which can be used to provide support to the microPCM, such as by coating or otherwise placing a layer of the microPCM on an external surface. The microPCM may, in another form, be a composite, such that it is made up of a low-temperature phase change material (for example, one that is designed to go through a phase change from liquid to solid at a temperature in the range of about −10° C. to about 0° C.) and a high-temperature phase change material (for example, one that is designed to go through a phase change from solid to liquid at a temperature of about 40° C., or (in cases where higher temperature latent heat of vaporization is needed) between about 40° C. and 50° C.). Such a composite configuration is particularly valuable in automotive applications where time histories may reveal significantly different thermal environments. Various microPCMs can be mixed in the capsule in different mass percentages to get different phase change temperatures. For example, n-tetradecane (with melting point of 6° C.) and n-eicosane (with melting point of 37° C.) can be mixed in the capsule to limit the temperature swing between around 0° C. to around 40° C. In a variation on such composite, mixtures containing both high-temperature and low-temperature shell-and-core combinations may be used. 
         [0011]    The thermal management system of the present invention that employs microPCM is desirably applied to a battery to reduce repeated exposure to high temperatures that could otherwise lead to premature battery aging. More particularly, microPCMs in close contact with battery cells can act as a thermal buffer that in turn may result in reduced power fade, reduced capacity fade, improved battery life and durability, reduced warranty costs, improved vehicle range and prevention of thermal runaway. Furthermore, microPCMs with different (i.e., lower) melting points can be mixed in with the high-temperature microPCM, thereby providing protection against both high and low temperatures. For example, both a low-temperature phase change material and a high-temperature phase change material may be placed within a common capsule to result in one form of a composite microPCM. Likewise, a composite microPCM may include both low-temperature core-and-shell combinations mixed in with high-temperature core-and-shell combinations. In one form, the microPCM can be formed as part of a lithium-ion or related battery cell, or be part of a structural member or related component (such as foam isolator sheet, cooling plate or cooling fin) that can be placed in thermal communication with the battery cell. 
         [0012]    Preferably, the bulk volume of the microPCM is in the wet-cake form (i.e., a mixture of solids and water). In the present context, the wet-cake form refers to the bulk volume of the whole bi-component particles; in one preferred form, it contains about 70% solids and about 30% water. Compared to its dry-cake form, microPCM in the wet-cake form reacts fast when blended with other materials and proves to be more stable by being less susceptible to separation. The microPCM can be uniformly coated on or melt-blended with polyurethane material to form a new thermal foam isolator sheet, or formed into channels that are part of a cooling plate or cooling fin. In one advantageous form, the microencapsulation of the PCM is such that it has a high degree of temperature stability, where leakage is kept to a minimum. The high heat capacity of the microPCM, coupled with the juxtaposition of the sheet, plate or fin to which it is attached, forms the basis of a passive thermal management system that acts independently of, or as part of active or other forms of cooling as part of an integrated cooling system. Thus, even in situations where active cooling may be warranted, the use of microPCM as part of an integrated cooling scheme offers the possibility of a simplified cooling system. Moreover, the microPCM of the present invention can be used whether the cooling medium is air-based or liquid-based. 
         [0013]    According to another aspect of the invention, an automobile includes a portion for conveying at least one of a passenger, operator or cargo, a portion for engaging a surface upon which the automobile travels and a propulsion portion for providing motive power to the surface-engaging portion. In one form, the conveying portion may be the cabin or passenger compartment of a car, truck, bus or the like, as well as a seat for a motorcycle. Similarly, the surface-engaging portion may be made up of one or more wheels used to facilitate rolling motion of the automobile over a road, track, path or related surface. Relatedly, the propulsion portion provides motive force to the wheels, and may include a battery pack that in turn includes one or more battery modules that may be made of one or more individual battery cells. As stated above, temperature management is a significant issue for batteries and their components; the present invention includes a heat exchange mechanism made up of microPCM is placed in thermal communication with the one or more battery cells. Upon exposure of the microPCM to a temperature change in the battery cell or cells, the microPCM can be made (at the appropriate temperature) to go through a phase change as a way to absorb (upon heating) or release (upon cooling) heat with the one or more cells that make up the battery pack. 
         [0014]    Optionally, the microPCM is made up of an outer shell with an inner core of material of high latent heat absorption encased within the shell. In one form, the microPCM may include a low-temperature phase change material and a high-temperature phase change material such that the low-temperature phase change material is configured to experience a phase change from liquid to solid at a relatively low temperature, and further such that the high-temperature phase change material is configured to experience a phase change from solid to liquid at a relatively high temperature. Such relative temperatures preferably coincide with low and high temperatures that the automobile in general and the battery pack in particular may be exposed to. As discussed above, in one form, both the low-temperature and high-temperature core materials may be mixed together within a single shell, while in another, each may be retained autonomously within their own respective shells. This latter configuration permits the judicious placement of tailored-temperature microPCMs based on the expected local thermal environment. 
         [0015]    According to yet another aspect of the invention, a method of controlling temperature in a battery pack is disclosed. The method includes arranging a microPCM to be in thermal communication with a battery cell such that upon change to the cell&#39;s temperature, an exchange of heat takes place between the cell and the microPCM, where at least a portion of the heat exchange between them takes place during the phase change within the core of the microPCM. In a particular form of the exchange, the phase change comprises having the microPCM convert from substantially liquid form to substantially solid form at a temperature of less than about 0° C. Likewise, phase change comprises having the microPCM convert from substantially solid form to substantially liquid form at a temperature of greater than about 40° C. In other forms, the phase change temperature may be tailored to occur at other temperature regimes deemed important to the operation of the battery cells, depending on the configuration, use environment or related operating condition for the battery; it will be appreciated that such other temperature ranges are within the scope of the present invention. In another option, the microPCM may be made from numerous phase change materials; in this way, a first microPCM may be used in situations where the battery pack (or relevant portions thereof) is exposed to a low-temperature, while a second microPCM may be used in situations where it is exposed to a high-temperature. As previously mentioned, such a configuration (i.e., with both low-temperature and high-temperature capabilities) may be thought of as a composite PCM system. As discussed in conjunction with the previous embodiment, the microPCM is made up of an outer shell with an inner core of material of high latent heat absorption encased within the shell, where the core may contain one or both the low-temperature and high-temperature phase change materials as part of one form of the aforementioned composite structure. In yet another option, the microPCM is placed in compressible contact with a surface of the battery cell, such as through the aforementioned foam isolator sheet, where the combination of microPCM with a polyurethane or related substrate exhibits elastic, foam-like properties. This (and other direct) contact ensures ample opportunity for thermal communication between the microPCM and the heat present in the heat-generating portions of the battery. As also previously discussed, the microPCM may form part of a surface of a cooling plate (more particularly, being placed within one or more channels formed in the surface of the plate) or a cooling fin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a vehicular propulsion system in the form of a battery pack; 
           [0017]      FIG. 2  is an exploded view of one embodiment of a portion of a battery module that makes up the battery pack of  FIG. 1 , where the module includes liquid cooling; 
           [0018]      FIG. 3  is a Differential Scanning calorimetry (DSC) chart showing the phase change properties of a bulk laboratory grade microPCM that uses eicosane as the high latent heat material; 
           [0019]      FIG. 4  is a chart showing thermal testing in an environmental chamber of a microPCM that uses eicosane as the high latent heat material; 
           [0020]      FIG. 5  shows battery cell temperature distribution when the battery section was under charge and discharge operation for both a baseline foam isolator as well as one from a foam isolator according to an aspect of the present invention; 
           [0021]      FIG. 6A  shows an exploded view of a portion of a potential HEV battery module with a cooling plate with corrugated channels for air cooling; and 
           [0022]      FIG. 6B  shows an assembled battery module made up of multiple battery portions of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring first to  FIG. 1 , a vehicular propulsion system in the form of a battery pack  1  employing numerous battery modules  10  is shown in a partially-exploded view. Depending on the power output desired, numerous battery modules  10  may be combined as a group or section  100 ; such may be aligned to be supported by a common tray  200  that can also act as support for coolant hoses  300  that can be used in configurations where supplemental cooling may be desired. A bulkhead  400  may define a primary support structure that can function as an interface for the coolant hoses  300 , as well as house a battery disconnect unit in the event battery service is required. In addition to providing support for the numerous battery modules  10 , tray  200  and bulkhead  400  may support other modules, such as a voltage, current and temperature measuring module  500 . Placement of individual battery cells  35  (to be discussed in more detail below) within one of battery modules  10  is shown, as is the covering thereof by a voltage and temperature sub-module  600 . In one typical example, battery pack  1  may about two hundred individual battery cells  35 . Other features, such as manual service disconnect  700 , insulation  800  and a cover  900  complete the battery pack  1 . 
         [0024]    In addition to the aforementioned battery disconnect unit, other power electronic components may be used for section  100 , including a battery management system or related controllers. In conventional form involving liquid-cooled battery packs, such electronic components are not cooled, despite being located very close to the numerous battery modules  10 . As a result, they may heat up nearby modules  10 , thereby creating non-uniform degradation of the cells  35  and a concomitant imbalance between them. Since most of these power electronic components are located on the top and end of the battery module  10 , microPCM of the present invention placed on cooling plates between such components and the cells  35  of the battery modules  10  can act as heat sinks to absorb and subsequently dissipate the heat generated convectively through air-based or liquid-based means. 
         [0025]    Referring next to  FIG. 2 , one embodiment of a portion of a battery module  10  for use in conjunction with a liquid cooling-based system is shown in an exploded view. In order to form the module  10 , at least some of the components discussed below may be arranged in a repeating stack-like manner. End frame  15  and repeating frame  20  form the basis for the structure of the battery module  10 , where the end frame  15  can have an edge portion  25  surrounding a cooling plate  30  that may include ribs for added stability, while each repeating frame  20  may serve to both provide a secure mounting position for a corresponding cell  35 . As such, both the cooling plate  30  (where the microPCM may be formed into channels that are part of a cooling plate) and a foam isolator sheet  45  (where the microPCM can be uniformly coated on or melt-blended with polyurethane material to form the foam) may be used as a way to provide passive heat transfer to or from the battery cells  35 . Furthermore, liquid-bearing cooling fins  40  may be placed in thermal communication with the battery cells  35  as a way to further augment heat capacity and subsequent heat transfer; their proximity to a corresponding one of repeating frames  20  allows for a convenient securing location in a manner generally similar to that of cells  35 . In a particular embodiment of the present invention, any or all of cooling plate  30 , cooling fins  40  and foam isolator sheet  45  may have the microPCM applied, adhered or otherwise affixed to a surface thereof in order to provide the desired thermal interfaces with beneficial enhanced heat exchange capabilities. With particular regard to the cooling fins  40 , liquid coolant can be made to flow through one or more generally serpentine fluid-conveying channels or flowpaths, while the microPCM may be disposed on a surface placed against these flowpaths in order to maximize surface area contact and concomitant heat transfer Likewise, the cooling plates  30  (which may be mounted to end frame  15 ) may include channels formed in the generally planar surface thereof to allow the placement of microPCM therein; as with the cooling fins  40 , the cooling plates  30  present a relatively large area as a contact surface to augment heat transfer to or from the battery cells  35 . The end frames  15  and repeating frames  20  are typically made of a light-weight, non-conductive material, such as plastics (for example, polypropylene, nylon  6 - 6 ) and other low-cost materials. The frames  15 ,  20  can be fiber-reinforced for structural strength, if desired. With particular regard to the foam isolator sheet  45 , the microPCM may be disposed on a substrate (such as the aforementioned polyurethane) that makes up the foam isolator sheet  45 . With particular regard to the cooling plate  30 , the microPCM may be formed as part of a wet cake or other semi-solid form such that it can be deposited in the between-rib recesses formed in the surface of the plate. In addition, an insulative sheet  50  is placed between the battery cell  35  and the cooling plate  30  to protect the battery cell  35 . In a preferred form, insulative sheet  50  is made of a plastic or related material, and is affixed to cooling plate  30 . One or more thermistors (not shown) are situated between the insulative sheet  50  and the cooling plate  30  to monitor battery cell  35  temperature. In a battery module  10 , there may be numerous thermistors, for example, one for each insulative sheet  50 /cooling plate  30 /battery cell  35  interface. Additional components, such as pack plates, voltage inner connect boards or the like (many of which are shown in conjunction with an alternate embodiment discussed below in conjunction with  FIGS. 6A and 6B ) are used to help form the assembled battery module  10 . 
         [0026]    The use of microPCMs in a liquid coolant is discussed in more detail in co-pending U.S. patent application Ser. No. ______ entitled LIQUID COOLANT WITH MICROENCAPSULATED PHASE CHANGE MATERIALS FOR AUTOMOTIVE BATTERIES, which was filed on the same day as the present application, owned by the Assignee of the present invention and hereby incorporated in its entirety by reference. 
         [0027]    The nature of the microPCM is that it has high latent heat of absorption and reversible thermal regulation properties. In this way, when used as part of foam isolator sheet  45 , cooling plate  30 , cooling fin  40  or other structural member within battery module  10  that is in need of augmented heat transfer properties, the microPCM can act as a thermal capacitor which can passively buffer temperature extremes in battery module  10 . This promotes a reduction in battery module  10  parasitic losses, thereby allowing optimization of battery module  10  energy usages, as well as reduction of active cooling system use and complexity. In situations where more than one member or component, operating at more than one temperature regime, may require the use of the microPCM of the present invention, it will be appreciated by those skilled in the art that the makeup of both the core and shell may be tailored to such particular temperature regimes. In such circumstance, the cooling fin  40  may be configured to include a layer of material (such as foam, or a related substance) that can contain a microPCM that operates in a different temperature regime than that of a microPCM that may be placed in or on the foam isolator sheet  45  or cooling plate  30 . In such tailoring circumstances, blending of various pure materials (such as alkanes) may be performed to have the phase change temperature coincide with the thermal environment of the particular automotive application. One material useful for such tailoring is n-heptadecane, which can be added to eiconsane, octadecane or related phase change material. Similar blending may be used to adjust the phase change latent heat. 
         [0028]    One advantage of coupling the microPCM to the foam isolator sheet  45  stems from the proximity of the foam isolator sheet  45  to the heat-generating cells  35 . In this way, the microPCM absorbs heat generated by the cells  35  of the battery module  10  during discharge and regenerative charging, and then dissipates the heat during vehicle rest periods or by convection heat transfer (such as air cooling) during vehicle operation. Its enhanced heat capacity and reversible thermal properties can limit battery module  10  extreme temperature swings and improve temperature uniformity, thereby promoting battery module  10  life, performance and efficient use of energy. In addition, the foam isolator sheet  45  can be easily adopted by different battery packaging designs due to its simple and flexible structure. 
         [0029]    Referring next to  FIG. 3 , results from DSC testing are used to determine the phase change properties of bulk laboratory-grade microPCM eicosane. The scan rate used in this test was 5° C. per minute, and the temperature range was controlled from −50° C. to 80° C. The peaks indicate phase change upon heating (top) and cooling (bottom). The peak on the top curve shows the behavior of the solid-to-liquid phase change transition, while the area under the peak is the latent heat for the solid-to-liquid transition (i.e., the latent heat of fusion); in the present example, the latent heat was found to be 185.6 J/kg. This curve also indicates that liquid starts to appear at 32.28° C. and that eicosane is completely liquid at 36.35° C. Likewise, the peaks on the bottom together show the behavior of the liquid-to-solid phase change transition, where the left peak shows the liquid-to-liquid phase change transition associated with eicosane, while the right peak shows the liquid-to-solid phase change transition. The area under these peaks is the latent heat for the solid-to-liquid transition; in the present example, the latent heat was found to be 190.7 J/kg. This curve also indicates that solid eicosane starts to appear at 35.07° C. and that it is completely solid at 31.67° C. 
         [0030]    Referring next to  FIGS. 4 and 5 , the results of microPCM eicosane thermal testing conducted by the present inventor is shown. In particular, the test was conducted in an environmental chamber test setup with the temperature running from 23° C. to 48° C. Referring with particularity to  FIG. 4 , the lower curve (which corresponds to the microPCM temperature) shows that a 12.1 gram sample of eicosane managed to stay at approximately 37° C. for about 1 hour while being heated. Referring with particularity to  FIG. 5 , results are shown for a battery cell temperature distribution when the tested battery section of the test setup was under charge and discharge operation. The chart on the top shows the baseline testing results with foam isolator sheets that do not have the microPCM added to them, while the chart on the bottom shows the testing results with a simulated foam isolator sheet (such as foam isolator sheets  45  of  FIG. 2 ) incorporated with eicosane as the microPCM. Two thermocouple recordings are shown; the upper curve is the readings from the thermocouple at the location close to the positive tab of the battery cell (such as battery cell  35  of  FIG. 2 ) and the lower one is the readings from the thermocouple at the location close to the negative tab of the battery cell  35 . Test results show that the battery cell temperature was regulated between 37° C. to 38° C. with the foam isolator sheet  45  prototype of the present invention, and the temperature uniformity on the battery cell  35  was improved compared to the baseline test results. 
         [0031]    Referring next to  FIGS. 6A and 6B , a notional design is shown of an air-cooled HEV battery module  110  with the microPCM being encapsulated in the cooling fin  140  or cooling plate  130  (not presently shown, but which is contained within cell frame  115 ) channels, according to an aspect of the present invention. The stacking construction, as well as the structural members and battery cells  135 , are generally similar to that of the liquid-cooled variant depicted in  FIG. 2 . Referring with particularity to  FIG. 6A , pack plates  175  are used to act as edgewise outer support members for the module  110 . Intermittently-spaced cell frames  120  are used to securely hold and space various battery cells  135  as well as the cooling fins  140  in a manner generally comparable to that of frames  20  discussed above in conjunction with  FIG. 2 . As such, the frames  115 , the cell frames  120  and the pack plates  175  together cooperate to form a rigid, boxlike structure for each of the battery modules  110  Likewise, larger support structures, such as the tray  200  or bulkhead  400  mentioned above in conjunction with  FIG. 1 , may serve as support or mounting structure for the larger repeatable units of battery group or section  100  or battery pack  1 . In one form, the cooling fins  140  are of a construction generally similar to that of cooling fins  40  shown in  FIG. 2 , where both may exhibit corrugated cardboard-like features with numerous parallel channels can be formed between the opposing sheets such that edge-to-edge flowpaths are defined thereby. Referring with particularity to  FIG. 6B , the various components of  FIG. 6A , when placed in cooperative arrangement with one another, form the assembly that defines battery module  110 , where a voltage interconnect board  127  functions to hold and support the positive and negative tabs and a circuit board of the assembled battery module  110 . Combined with the high heat capacity of the microPCM, high thermal conductivity of the cooling plate material such as aluminum, and heat convection by air cooling, such a design may form the basis for an effective thermal management solution for HEV battery modules. Unlike the liquid-cooled system depicted in  FIG. 2  (where a liquid coolant flows through channels or flowpaths formed in cooling fin  40 ), the cooling fin in  FIG. 6  employs forced air passage. Regardless of whether an air-cooled or liquid-cooled approach is used, the addition of microPCM as part of an integrated cooling scheme offers the possibility of a simplified cooling system even in situations where active cooling may be warranted. 
         [0032]    Referring again to  FIG. 2  (and equally applicable to a comparable construction that may be present in  FIGS. 6A and 6B ), the construction of the microPCM-based foam isolator sheet  45  is such that it may form a thermal composite where, as alluded to above, the microPCM exhibits its phase-changing thermal properties (whether from solid to liquid or liquid to solid, for example) at two different temperatures. Also as discussed above, this can be achieved by using various microPCMs, each with latent heat properties tailored to particular temperature regimes. In one form, one microPCM may be made to have its phase change at a low temperature limit (e.g., about −10° C. to 0° C.), and another microPCM to have a phase change at a high temperature limit (e.g., about 40° C. to 45° C.). Such dual-temperature activation helps to maintain battery cell  35  temperature for longer periods of time and over extreme temperature conditions. In situations where higher temperatures may be experienced, the PCM-based thermal management system may be coupled with an active-based system (such as that involving the circulation of a liquid coolant discussed above in conjunction with the coolant hoses  300  of  FIG. 1 ) to augment overall system performance and reduced likelihood of catastrophic battery module  10  or section  100  failure. In one preferred form, the phase change temperatures can be tailored to coincide with the desired temperatures and large heat capacity values associated with an automotive battery module  10  that may coincide with the temperature ranges discussed above. 
         [0033]    As mentioned above, other supplemental devices may be used. For example, cooling fins  40  can be made of any conventional cooling material, including, but not limited to, light-weight thermal conductors such as aluminum or sandwich structures of two light-weight thermal conductors separated by a layer of compressible foam or other expansion compensator to allow for expansion and contraction of the battery cells  35  on either side of the cooling fin  40  caused by the charge state, heating and cooling of the cells  35 . There can be a film for electrical isolation on the cooling fin  40 , if desired, such as Mylar® polyester film with electrical insulation resistance of over 100,000 MΩ-μF. In addition to the aforementioned fin  40 , sheet  45  and plate  30 , other heat exchange mechanisms may be employed, such as heat pipe technology. 
         [0034]    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. Likewise, terms such as “substantially” are utilized to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. It is also utilized 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. 
         [0035]    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. Furthermore, variations on the terms “automobile”, “automotive”, “vehicular” or the like are meant to be construed generically unless the context dictates otherwise. As such, reference to an automobile will be understood to cover cars, trucks, buses, motorcycles and other similar modes of transportation unless more particularly recited in context. 
         [0036]    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.