Patent Publication Number: US-9837647-B2

Title: Battery pack with air-type cooling

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a battery module having a number of electrically interconnected battery cells, wherein the individual battery cells are temperature-controlled by means of a temperature control fluid. 
     WO 2013/023847 A1 relates to a battery module with air-type cooling, and to a motor vehicle. The document discloses a battery module having a battery cell stack composed of at least two battery cells, wherein each battery cell is in contact with at least one air duct. The at least one air duct is integrated into the battery cell stack. In this way, despite a poor heat transfer coefficient, adequate cooling by means of an air stream of the battery cells is possible. 
     US 2012/00150003 A1 relates to a battery module. Said battery module comprises a number of rechargeable battery cells, and a housing which accommodates the rechargeable battery cells. First heat dissipation fins project from the housing and have a polygonal shape or a closed geometry. Furthermore, second heat dissipation fins project from the housing, which second heat dissipation fins are designed such that they couple the first heat dissipation fins to one another. 
     U.S. Pat. No. 6,689,510 B1 relates to a monoblock battery arrangement with a countercurrent cooling configuration. A multi-cell monoblock battery comprises a number of electrochemical cells which are arranged in a battery housing. The battery housing comprises one or more cell partitions which divide the interior of the housing into a number of cell-accommodating compartments in which the electrochemical cells are accommodated. It is preferable for one or more cooling ducts to be situated in the at least one cell partition implemented in the interior of the housing. 
     KR 2006 011 8797 relates to a battery module. The battery module according to said solution exhibits high heat dissipation capability and is very well insulated; furthermore, it has a reduced weight in relation to conventional battery modules. The battery module comprises a number of battery cells which are arranged at regular intervals. Walls are situated between the individual battery cells. A line for a heat-transporting medium is provided, said line being manufactured from a magnesium alloy. The walls are manufactured from a magnesium alloy with aluminum, zinc and zirconium and a small fraction of rare earths. The zirconium fraction within the magnesium alloy is between 2.0 wt % and 10 wt %. 
     Lithium-ion or lithium-polymer batteries warm up in particular when outputting energy. An optimum operating temperature of such battery systems lies in the region of approximately 25° C. Above an operating temperature of approximately 40° C., the service life of such battery systems is reduced considerably. Temperature changes and charging and discharging cycles lead to a decrease in capacity, and to an increase in the self-discharge of such batteries. The service life demands of 10 years and longer that are placed on such battery systems can thus be satisfied only with adequate thermal conditioning. 
     If more heat is generated in a battery cell than can be discharged to the surroundings, this can result in “thermal runaway”, with undesired consequences. This means that there is a need for an active, high-performance thermal management system for lithium-ion and lithium-polymer batteries, which thermal management system heats the battery cells at low temperatures and cools the battery cells at higher temperatures. 
     It must also be mentioned that, in the presence of a high pressure in a lithium-ion or lithium-polymer battery cell, a burst valve opens. Emerging undesired gases, which are at temperatures of greater than 600° C., should not pass into the vehicle interior of an electric or hybrid vehicle. 
     SUMMARY OF THE INVENTION 
     According to the invention, a battery module is proposed which comprises a number of electrically interconnected battery cells. The individual battery cells are temperature-controlled by means of an air flow which flows through ducts which extend substantially along the battery cells. The battery cells are thermally coupled by means of the ducts, wherein the ducts have a flow cross section which is bounded by a duct wall which has a variable wall width profile. 
     In an extremely advantageous refinement with regard to the strength of the air ducts, which are preferably manufactured from an aluminum material or an aluminum alloy, the variable wall thickness of the ducts through which temperature-control air flows follows a hyperbolic profile, in particular a hyperbolic cosine (cos h) profile. Aluminum profiles from which the ducts are manufactured can be produced most effectively and most inexpensively in terms of manufacture by extrusion processes. The variable flow cross section, through which the temperature-control fluid, that is to say the cooling air, flows, of the ducts is—with respect to the height of the ducts accommodated between the individual battery cells—designed to be variable in relation to the duct height. For this purpose, the ducts through which the cooling air flows are narrower in their upper and lower regions than, for example, in the center, where the ducts have their maximum width. 
     The ducts, which are manufactured from an aluminum material or an aluminum alloy, are electrically insulated, for which purpose use may be made in particular of an electrically insulating lacquer or an electrically insulating film. 
     Furthermore, the ducts are sealed off with respect to the battery cells, in particular the side walls of the batteries in the battery module, by means of a sealing compound or adhesive beads or the like, such that any hazardous gases escaping from the battery cells do not pass into the ducts that are connected to the passenger compartment in which the vehicle occupants are situated. The temperature-control air used for the temperature control of the battery cells in the proposed air-type temperature-control system originates from said passenger compartment. In a refinement of the concept on which the invention is based, an average wall thickness of the duct wall of the ducts—in relation to the vertical direction of the flow cross section—is substantially in the region of 3 mm. The ducts through which the temperature-control fluid, for example cooling air, flows extend along the side surfaces of the battery cell casing. The battery cells have burst valves which constitute a predetermined breaking point of the battery casing for degassing purposes, which burst valves issue directly into a degassing duct which extends through the housing of the battery module. 
     In an advantageous possible embodiment of the concept on which the invention is based, the ducts through which the temperature-control fluid flows can be formed into side walls of a battery cell holder. The battery cell holder comprises not only the side walls but also a rear wall and a front wall, wherein the side walls run through the battery cell holder such that a number of battery cell compartments is realized, which battery cell compartments accommodate individual battery cells. The side walls of the battery cell holder are in this case designed so as to have projecting lengths at each of their ends, which projecting lengths protrude beyond the front walls and rear walls arranged perpendicular to the side walls. The projecting lengths firstly greatly simplify the production of the battery cell holder, and secondly, reliable separation of temperature-control ducts and degassing ducts is possible. The production of adhesive beads or weld seams, and embossment of the rear wall and front wall with the respective side walls, can, with the formation of the projecting lengths, be realized in a significantly more reliable manner in process terms, such that reliable joining of the rear wall, front wall and side wall, and thus reliable sealing of degassing ducts and temperature-control flow ducts, can be realized. 
     The battery cell compartments, on their surface pointing in each case toward a battery cell, have an electrically insulating surface which may be implemented as a film or lacquer. 
     The battery module proposed according to the invention comprises at least one air duct which is connected to the passenger compartment of a hybrid or electric vehicle. By means of a fan, air is conveyed out of the passenger compartment into the ducts which extend between the individual battery cells of a battery module or which extend through side walls of a battery cell holder. A fan may be provided in a passenger compartment in order to blow or draw the temperature-control air through the ducts. The flow resistance in the air ducts is dependent on their width. In the case of an average gap width in the region of 3 mm, an optimum air flow with minimal pressure losses is realized. The fan may also be arranged downstream of the battery pack as viewed in the flow direction. A filter may be installed upstream of the battery pack; it is also possible for the temperature-control air, for example cooling air from the outside, to be drawn in. 
     The solution proposed according to the invention is distinguished by the advantage that the temperature-control fluid, in the present case cooling air, for the temperature control of the at least one battery module or multiple battery modules can be extracted from the air-conditioned vehicle interior of a hybrid, electric or fuel cell vehicle, yielding the possibility of considerable cost savings. By means of the solution proposed according to the invention, it is ensured that, in the event of degassing, no battery cell becomes connected to the vehicle interior compartment. With the solution proposed according to the invention, a considerable increase in the effectiveness of temperature control can be attained, because the temperature-control fluid is conducted laterally past the battery cells and not just under the battery cells. This means that flow passes around the side surfaces of the individual battery cells, which are generally considerably larger, in particular more than four times larger, than the base surfaces of the battery cells. For this reason, in the concept proposed according to the invention, with a flow of cooling air laterally around battery cells, significant removal of heat is possible. In the case of the cooling air concept, it must be taken into consideration that the specific heat capacity Cwater is more than four times greater than the specific heat capacity C air  (at room temperature, C water  is equal to 4.182 kJ/(kg·K), and C air =1.005 kJ/(kg·K)). 
     By means of the solution proposed according to the invention, the individual battery cells are thermally coupled to one another by the ducts. In this way, reliable detection of the temperature of the battery cells is possible. Furthermore, by means of the solution proposed according to the invention, the need to attach temperature sensors to each one of the battery cells can be circumvented. Thermal coupling between the individual battery cells can be realized by means of the air ducts, which are preferably manufactured from a material with good heat-conducting properties, such as aluminum. 
     The ducts have a profile which preferably corresponds to a hyperbolic cosine (cos h) function. In this way, it is possible to realize very small wall thicknesses of the duct which is preferably manufactured as an extruded profile, said wall thicknesses being substantially in the region of 3 mm. Owing to the selected hyperbolic cosine function, it is possible to mechanically realize high strength with respect to lateral pressure, such that the profiles that have the ducts, when braced together, exhibit very high strength and can be braced against one another by means of tension straps. In the case of an average air gap width of approximately 3 mm, optimum flow conditions are retained with regard to the design of a fan which conveys the cooling air flow. The individual battery cells may also be accommodated in and held by a battery cell holder which serves, in effect, as a grid composed of air ducts. The ducts are sealed off with respect to the battery cell casings by means of a thermally stable dispenser seal. In the case of the design variant proposed according to the invention, in which the ducts run through side walls of a battery cell holder composed of aluminum, projecting lengths of the side surfaces protrude beyond the front and rear walls. It is ensured in this way that, at their passages through the front and rear walls, and also through the respective module front wall and module rear wall, reliable sealing at passage points can be realized with an electrically conductive sealing and adhesive compound. A self-contained temperature-control system is realized in this way. 
     By means of the solution proposed according to the invention, the space or the duct in which degassing of a battery cell can be realized is separated from the space or the duct from which the battery cells or the battery modules can be temperature-controlled, in particular cooled, by means of air of the vehicle originating from the passenger compartment. The sealing between said spaces or said ducts, for example at the battery cell holder, can be implemented in a reliable manner in process terms through formation of projecting lengths on the side walls formed on those walls of the battery cell holder which are to be joined together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in more detail below on the basis of the drawing, in which: 
         FIG. 1  shows a perspective plan view of a battery cell holder which has multiple battery compartments for battery cells, 
         FIG. 2  shows a plan view of the battery cell holder, with battery cells accommodated therein, from the top side, 
         FIG. 3  shows the illustration of a duct composed of an aluminum or aluminum alloy extruded profile in an enlarged illustration, 
         FIG. 4  shows the profile of air ducts between individual battery cells of a battery module, 
         FIG. 5  shows the p/d characteristic curve with regard to the design of a delivery apparatus for an air-type temperature control concept, and 
         FIG. 6  is an illustration of a battery module with individual battery cells separated from one another by air gaps. 
     
    
    
     DETAILED DESCRIPTION 
     The illustration in  FIG. 1  shows, in a perspective plan view, a battery cell holder which comprises individual battery cell compartments in which the battery cells of a battery module are accommodated. 
       FIG. 1  shows a battery module  19  which comprises a number of battery cells  10 . The individual battery cells  10  each have cell terminals  12  which are arranged on a top side  14  of the battery cells  10 . On the battery cell top side  14 , there is situated a burst valve  16  which constitutes a predetermined breaking point of the battery cell housing, via which undesired degassing of the battery cell  10  can take place. The individual battery cells  10  are accommodated in an upright position in a battery cell holder  18  which is manufactured from aluminum or an aluminum alloy or from some other material which has good heat conduction characteristics. 
     The battery cell holder  18  has a base  20 ; individual battery cell compartments  28  for accommodating the battery cells  10  are separated from one another by a rear wall  22  and a front wall  24  and side walls  26 . Ducts  30  extend in each case through the side walls  26 , through which ducts a temperature control fluid, which in the proposed solution is air, flows. The ducts  30  each have a flow cross section  32 . 
     In  FIG. 1 , the reference  34  denotes projecting lengths by which the individual side walls  26  protrude in each case beyond the front wall  24  and the rear wall  22  of the individual battery cell compartments  28 . By means of the projecting lengths  34 , the production of a seal  40 , for example as an adhesive bead or weld seams  42  between the front and side walls  24 ,  26  or rear walls and side walls  22 ,  26 , is improved considerably in process terms. 
     In the perspective view as per  FIG. 1 , it can be seen that the flow cross sections  32 , which are in a substantially vertical orientation, extend through the side walls  26 . The flow cross section  32  of the ducts  30  has a maximum width in the center and has a narrowest width in each case at the top end and at the bottom end, as will be described in more detail below. 
     The illustration in  FIG. 2  shows a plan view of the battery cell holder as per the illustration in  FIG. 1 , with battery cells accommodated in individual battery cell compartments. 
     In  FIG. 2  it is possible to see the projecting lengths  34  by which the side walls  26 , through which the ducts  30  (not illustrated in  FIG. 2  as they run in the side walls  26 ) extend, protrude beyond the rear wall  22  and the front wall  24  of each battery cell compartment  28 . A battery cell  10  is situated in each of the battery cell compartments  28 . The air required for the temperature control of the battery cells  10  flows in from the passenger compartment of the vehicle through the ducts  30  that run in the side walls  26 . Degassing ducts  54 , which are only partially illustrated in the illustration of  FIG. 2 , are separated from the side walls  26  by seals  42  and  40 . Said degassing ducts run above the top side  14  of the individual battery cells  10 , above the drawing plane illustrated in the plan view in  FIG. 2 . Owing to the projecting lengths  34  at the ends of the respective side walls  26 , it is possible for the degassing ducts  54 , which are formed by the module rear wall  36  and the rear wall  22  at one side and by the module front wall  38  and the front wall  24  at the other side, to be sealed off with respect to the outlet ducts  30 . 
     From the plan view in  FIG. 2 , it can be seen that each of the battery cells  10  accommodated in the battery cell compartments  28  has, on its top side  14 , two cell terminals  12 , that is to say a positive terminal and a negative terminal, for electrical interconnection. For completeness, it is mentioned here that those surfaces of the battery cell compartments  28  of the battery cell holder  18  which face toward the battery cells  10  to be accommodated are, in  FIGS. 1 and 2 , provided with an electrically insulating surface, for example a lacquer. It is also possible for the battery cells  10  themselves to be provided with an electrically insulating surface, which may likewise be in the form of a lacquer or film. 
     The battery cells  10  of lithium-ion or lithium-polymer battery modules  19 , for example of a boost recuperation system (BRS), are held securely by the battery cell holder  18 , and are located in position in the downward direction by the base and on all four sides by the rear walls  22 , the front walls  24  and the side walls  26 . Furthermore, the battery cell holder  18  as per  FIGS. 1 and 2  also provides protection against mechanical deformation or damage, for example in the event of an accident. 
       FIG. 3  shows, on an enlarged scale, a section through a duct through which cooling air flows. 
     From the illustration of  FIG. 3 , it can be seen that the individual side walls  26  of the battery cell holder  18  each have ducts  30 . The ducts  30  comprise a flow cross section  32  which substantially follows a hyperbolic function, for example a hyperbolic cosine profile  44 . This yields a shape of the flow cross section  32  which, on the one hand, is characterized at the top of the duct  30  and at the base of the duct  30  by a first, relatively narrow duct width  46  in the region of 2 mm, and which, approximately centrally, has a maximum duct width  48  which is in the region of approximately 4 mm. All in all, the result is an average air gap width  50  in the region of 3 mm. The average duct width of 3 mm is advantageous, cf. the p/d diagram in  FIG. 5 , because that value yields an adequately low pressure loss for which a fan for delivering temperature-control air can be designed. 
     The contour, that is to say that which follows a hyperbolic cosine profile  44 , offers extremely high mechanical strength with regard to a laterally acting pressure for a given average wall thickness of approximately 1 mm of duct walls  45  which delimit the flow cross section  32 , wherein an average air gap width  50  is in the region of 3 mm, whereas an average wall thickness  52  remains in the region of 1 mm. By means of the cross section-delimiting inner contour of the side wall  26 , one attains, even with small wall thicknesses—on average approximately 1 mm—of the aluminum or of an aluminum alloy, the mechanically highest strength with regard to laterally acting lateral pressure  53 , such that the individual battery cells  10  can be braced together, for prevention of winding expansion, by means of tension straps. It is also possible for a multiplicity of ducts  30  to be formed in the side walls  26 , for example so as to be arranged one above the other, said ducts likewise having a cos h profile  44  with regard to the duct wall contour. This not only increases the rigidity with respect to lateral pressure  53 , but also the surface area available for heat transfer. 
       FIG. 4  shows a view of a battery module which has multiple battery cells, the burst valves of which issue into a common degassing duct. 
       FIG. 4  shows a battery module  19  which comprises a number of battery cells  10  which are configured so as to be situated adjacent to one another in an upended position. The ducts  30 , through which the temperature-control fluid, in the present case air-conditioned cooling air from the passenger compartment of a vehicle, flows run between the mutually opposite side walls of the individual battery cells  10 . In the upper region, that is to say on the top side  14  of the battery cells  10 , said battery cells have burst valves  16 , all of which issue into a common degassing duct  54  which extends through the housing for the battery module  19 . Position  58  denotes an electrically insulated module base which forms the set-down surface for the battery cells  10 , which are oriented substantially in a vertical installation position. Air-conditioned cooling air which is delivered from the passenger compartment of the hybrid, electric or fuel cell vehicle by means of a fan (not illustrated in any more detail) flows, perpendicular to the plane of the drawing, through the individual ducts  30  and passes over the relatively long side walls  26 , likewise extending into the plane of the drawing, of the individual battery cells  10 . Removal of heat from the battery cells  10  by means of an air flow which passes along the side walls thereof is significantly more effective, because the surface area passed over by the cooling medium is significantly larger than the base surface or the top surface of the battery cells  10 , which are of rectangular configuration.  FIG. 4  shows that, during a degassing process of a battery cell  10 , the respective burst valve  16  opens out directly into the common degassing duct  54 , which runs within the housing of the battery module  19  above the battery cells  10 . The individual ducts  30 , which run between the battery cells  10  in a substantially vertical arrangement and through which the temperature-control fluid flows, are separated from the common degassing duct  54  by the seals  40 , thus ensuring separation of the common degassing duct  54 , via which discharging  68  to the outside is realized, from the ducts  30  illustrated in  FIG. 6  and from the air duct  62  from the passenger compartment of the vehicle. 
     The illustration in  FIG. 5  shows the dependency of the pressure p and air gap width d. A fan is required for blowing temperature-controlled air through or for drawing temperature-controlled air in, said air being for example conditioned air which may be extracted from the interior of the passenger compartment. The resistance to the air flow through the ducts  30  is dependent on the average air gap width  50 . The behavior qualitatively illustrated in  FIG. 5  applies for the p/d dependency. Based on the diagram in  FIG. 5 , it is possible to arrive at an optimum configuration with regard to costs and the power of the required fan. 
     The plan view in  FIG. 6  shows a battery module  19  in which individual battery cells separated from one another by ducts  30  are arranged. 
     As can be seen from  FIG. 6 , temperature-controlled air, which in the present case is used as cooling medium, flows into an air duct  62  under a delivery action imparted by means of a fan arranged for example in the passenger compartment or at some other location. The air duct  62  opens out in the interior of the battery module  19 , in which the number of battery cells  10  is accommodated. The cooling air flows from the air duct  62  into the individual ducts  30 , which are each delimited by side walls of the battery cells  10 . In this case, the cooling air passes over the side walls of the battery cells  10 , the extent of which is greater, by at least a factor of 4, than the surface made up of the top side  14  of the battery cells  10  and the bottom side thereof. Heat is removed from the battery cells  10  by the air flow  70  passing the ducts  30 , wherein battery cell casings  64  are sealed off with respect to the ducts  30  by means of a seal  40 , for example adhesive beads or weld seams  42  or the like. The air flow  70  emerges from the ducts  30  and flows into an exhaust air discharge line  68  leading out of the battery module  19 . In the illustration of  FIG. 6 , the battery cells  10  are situated within a grid  66  which is formed from the air ducts  62 ,  30  and  68 . 
     From the plan view as per  FIG. 6 , it can be seen that burst valves  16  are situated on the top side  14  of the battery cells  10 . In the event of degassing, one of the battery cells  10  is degassed by virtue of the burst valve  16  opening into a common degassing duct  54  (compare the illustration as per  FIG. 3 ) which runs in a plane of the drawing which lies above the plane of the drawing illustrated in  FIG. 6 . The battery casings  64  of the battery cells  10  are sealed off with respect to the ducts  30  which conduct the temperature-control medium by means of the seals  40  and  42 , which in the illustration of  FIG. 6  are illustrated as having been turned into the plane of the drawing. The seal  40  is realized in particular by means of adhesive beads  42  or by means of weld seams  42 . In this way, it is possible to realize a separation between the guidance of the temperature-control fluid and the guidance of the degassing air, such that, in the event of degassing of a battery cell  10 , the common degassing duct  54  is reliably separated from the passenger compartment of a hybrid, electric or fuel cell vehicle. 
     From the plan view of  FIG. 6 , it can also be seen that a burst valve  16  is situated on the top side  14  of each battery cell  10 . Degassing of individual battery cells  10  takes place via the burst valves  16  into a common degassing duct  54  situated above the plane of the drawing in  FIG. 6 . Said degassing duct is illustrated in  FIG. 4  as being situated above the battery cells  10 . As can also be seen from  FIG. 6 , the seal  40  is implemented as an adhesive bead  42 ; it is also possible for the seal  40  to be implemented by means of an electrically conductive, thermally stable sealing compound which can be applied for example in a dispensing process. It is likewise possible for an electrically insulating coating to be applied to the inner sides, which point toward the battery cell  10 , of the battery cell compartments  28  during the course of the dispensing process. 
     By means of the solution proposed according to the invention, it is possible to avoid the need to assign temperature sensors to each of the battery cells  10 , which temperature sensors would then in turn have to be connected, with considerable signal processing outlay. In the case of the solution proposed according to the invention, it is possible, in the case of a sealingly encapsulated air-type temperature control system and correctly functioning degassing systems with at least one common degassing duct  54 , for burst windows of all of the battery cells  10  to be separated by means of seals  40  of the ducts  30  in a battery pack with multiple battery modules  19 , such that a passenger compartment from which temperature-control fluid is extracted is fully decoupled from the output system for undesired degassing. The encapsulated temperature-control system, equipped with a functioning degassing system fluidically separated therefrom, as discussed above, may also be accommodated below a driver&#39;s seat, below the rear seat or in the luggage compartment of a vehicle. 
     It can be seen from  FIG. 6  that the air duct  62  from the passenger compartment is delimited by the module front wall  38  of the housing of the battery module  19 , whereas the discharge line  68  is delimited by the module rear wall  36  of the housing of the battery module  19 . 
     The performance and service life targets of a battery pack composed of the battery modules  19  configured according to the invention can be attained only by way of cooling with air-conditioned vehicle interior air, wherein an outside air temperature of for example +50° C. may prevail, or an outside temperature may be −30° C. By means of the solution proposed according to the invention, it is possible to easily realize an efficient air-type cooling concept using the air-conditioned air present in the passenger compartment. 
     The invention is not restricted to the exemplary embodiments described here and the aspects highlighted therein. Rather, within the scope defined by the claims, numerous modifications are possible which fall within the capabilities of a person skilled in the art.