Patent Publication Number: US-2023155209-A1

Title: Battery module with heat pipes

Description:
TECHNICAL FIELD 
     The application relates generally to energy storage such as batteries, and more particularly to energy storage such as batteries for use in aircraft, including more-electric, hybrid-electric, and full-electric aircraft. 
     BACKGROUND 
     Heat transfer is used in battery applications to transmit heat and reduce cell-to-cell temperature differences. Some devices used to transfer heat in battery applications are electrically insulated from the cells. Since electrical insulators may also insulate heat, the use of electrically-insulating devices may reduce their effectiveness in transferring heat, and may require electrical conductors to be added to connect the cells together, which may increase the weight of the battery. 
     SUMMARY 
     There is disclosed a battery module, comprising: at least one cell having a positive terminal, a negative terminal, and a voltage and a current rating; a first electrically conductive heat pipe thermally and electrically connected to the positive terminal; and a second electrically conductive heat pipe thermally and electrically connected to the negative terminal; and the first and second heat pipes having the voltage and the current rating. 
     There is disclosed a battery module, comprising: a case having walls defining an interior; at least one cell in the interior having a positive terminal, a negative terminal, and a voltage and a current rating; a first electrically conductive heat pipe in the interior mounted to one of the walls and thermally and electrically connected to the positive terminal; and a second electrically conductive heat pipe in the interior mounted to another of the walls and thermally and electrically connected to the negative terminal; and the first and second heat pipes having the voltage and the current rating. 
     There is disclosed a method of cooling a battery module, the method comprising: operating at least one cell of the battery module to generate an electrical current flowing through heat pipes of the battery module that are thermally and electrically connected to opposite ends of the at least one cell, operation of the at least one cell transferring heat to the heat pipes; and cooling the heat pipes at a heat sink of the battery module. 
     There is disclosed a method of transferring heat within a battery module having at least one cell and heat pipes connected to the at least one cell, the method comprising conducting heat between a terminal of the at least one cell and one of the heat pipes. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG.  1    is a perspective view of a battery module; 
         FIG.  2 A  is a perspective view of heat pipes and cells of the battery module of  FIG.  1   ; 
         FIG.  2 B  is an enlarged cross-sectional view of region IIB of  FIG.  2 A ; 
         FIG.  2 C  is an enlarged cross-sectional view of region IIC of  FIG.  2 A ; 
         FIG.  3    is an end view of the heat pipes and cells of  FIG.  2   ; 
         FIG.  4    is another end view of heat pipes and cells of a battery module as shown in  FIG.  1   ; 
         FIG.  5    is a perspective view of multiple battery modules of  FIG.  1    arranged in series; 
         FIG.  6    is a perspective view of multiple battery modules of  FIG.  1    arranged in parallel; 
         FIG.  7    is a flow chart of an example method; 
         FIG.  8 A  is another perspective view of heat pipes and cells of the battery module of  FIG.  1   ; 
         FIG.  8 B  is an end view of a heat pipe and cells of a battery module; 
         FIG.  8 C  is another end view of a heat pipe and cells of a battery module; 
         FIG.  8 D  is another end view of a heat pipe and cells of a battery module; 
         FIG.  9 A  is another perspective view of heat pipes and cells of the battery module of  FIG.  1   ; 
         FIG.  9 B  is an exploded view of  FIG.  9 A ; and 
         FIG.  10    is an illustration of an example method. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates a battery module  10  or battery module used to provide electrical power. The battery module  10  is an assembly of components some of which function to generate an electrical current and voltage which can be provided to a given load. The battery module  10  includes a case  12  or housing. The case  12  includes walls  12 W. The walls  12 W are interconnected to provide any desired shape to the case  12 . The walls  12 W collectively define an interior  121  of the case  12 . The interior  121  of the case  12  may be sealed by the walls  12 W so that other components of the battery module  10  within the interior  121 , such as one or more cell(s)  14  of the battery module  10 , are sheltered from the environment outside of the battery module  10 . Referring to  FIG.  1   , the walls  12 W are interconnected to shape the battery module  10  like a box. Other shapes for the battery module  10  are possible. 
     The one or more cell(s)  14  are positioned in the interior  121  and function to generate electrical power. Referring to  FIG.  2 A , the cell(s)  14  may include a single electrical-power generating cell, or may be a cell unit/assembly of multiple electrical-power generating cells stacked one against the other. In  FIG.  2 A , the cell(s)  14  have a cylindrical shape. The cylinder shape of the cell(s)  14  may facilitate cooling of the cell(s)  14 . Other shapes for the cell(s)  14  are possible. In  FIG.  2 A , the cell(s)  14  are spaced apart from each other in directions parallel to both a vertical axis  11 V of the battery module  10 , and a horizontal axis  11 H of the battery module  10 . The horizontal and vertical axes  11 H,  11 V are perpendicular to one another. The cell(s)  14  may include cooling fins, metal foams or other surface projections extending from the outer perimeter of the cell(s)  14  to improve heat transfer to and from the cell(s)  14 . Referring to  FIG.  2 A , the cell(s)  14  each having a positive terminal  14 P and a negative terminal  14 N. The positive terminal  14 P is located at one end of the cell(s)  14  and the negative terminal  14 N is located at the opposite, other end of the cell(s)  14 . In the cylindrical-shaped configuration of the cell(s)  14  of  FIG.  2 A , the cell(s)  14  define a longitudinal cell axis  14 A. The positive and negative terminals  14 P, 14 N of each cell  14  are spaced apart from each other an axial distance measured along the cell axis  14 A. The cell(s)  14  may be arranged as desired within the interior  121 . For example, and referring to  FIG.  2 A , the cells  14  are arranged in rows of cells  14 , where each row has two cells  14 . The cells  14  in each row are parallel to the cells  14  in the other rows. In an alternative possible arrangement of the cells  14  in the interior  121 , an example of which is described below, the cells  14  are staggered in the direction of the vertical axis  11 V such that each cell  14  occupies a different vertical position, and some of the cells  14  may have the same position along the horizontal axis  11 H. The cell(s)  14  may thus have any suitable arrangement within the interior  121 . The cell(s)  14  have a voltage rating and a current rating. The cell(s)  14  are configured to, during operation, output a given voltage value in Volts and a given current value in Amps. The voltage rating and the current rating of the cell(s)  14  may correspond to the voltage rating and the current rating of the battery module  10 . In an embodiment, one or more of the battery module(s)  10  are used in an aircraft to provide electrical power to one or more components of the aircraft. 
     When the cell(s)  14  are operating at their voltage and current ratings, they generate heat which may need to be evacuated away from the cell(s)  14 . The heat may also need to be evacuated after the cell(s)  14  have stopped operating. In some instances, the cell(s)  14  may themselves need to be heated prior to operating to ensure optimal operation of the cell(s)  14 , for example so that they can output their voltage and current ratings. The battery module  10  therefore includes one or more devices by which heat can be transferred to and from the cell(s)  14 . 
     One of these devices is now described in greater detail with reference to  FIG.  2 A . The battery module  10  includes heat pipes  20 . The heat pipes  20  are thermally and electrically conductive. The heat pipes  20  are electrically conductive so that the electrical current generated by the cell(s)  14  flows through the heat pipes  20 . The heat pipes  20  are also thermally conductive bodies which allow heat to be transferred to and from the cell(s)  14 . The heat pipes  20  have the same voltage rating and current rating as the cell(s)  14 . Since the heat pipes  20  are electrically conductive, having the same voltage rating and current rating as when the cell(s)  14  are operating allows the heat pipes  20  to form an electrical circuit with the cell(s)  14  so that the heat pipes  20  contribute to the voltage and current outputted by the cell(s)  14  to a load. In an embodiment, the heat pipes  20  have at least at the same rating as the overall voltage and current rating of the cell(s)  14 , meaning that the voltage and current rating of the heat pipes  20  may be larger than they are for the cell(s)  14 . 
     Referring to  FIG.  2 A , the heat pipes  20  are in the shape or form of plates. Thus, the expression “heat pipe plates  20 ” may be used herein, it being understood that the heat pipes  20  may have other shapes including, but not limited, cylinders, tubular, and other three-dimensional polygons. Referring to  FIG.  2 A , the heat pipe plates  20  are flat and planar bodies having a width, a height and a length. The heat pipe plates  20  have inner walls  221  which face the cell(s)  14  and opposite outer walls  220 . The heat pipe plates  20  also have a peripheral edge  22 E extending between and interconnecting the inner and outer walls  221 , 220 . The peripheral edge  22 E or the distance between the inner and outer walls  221 , 220  defines the thickness of the heat pipe plate  20 . The heat pipe plates  20  are shaped and sized to have at least at the same rating as the overall voltage and current rating of the cell(s)  14 . Although shown in  FIG.  2 A  as being flat, the heat pipe plates  20  may be curved, bent or have other shapes, or parts of the heat pipe plates  20  may be curved or bent. Referring to  FIG.  2 A , the heat pipe plates  20  have an upright orientation. The heat pipe plates  20  have an upper end  20 U, and a lower end  20 L positioned beneath the upper end  20 U. Referring to  FIG.  2 A , the heat pipe plates  20  have an orientation that is substantially parallel to the vertical axis  11 V of the battery module  10 . By “substantially parallel”, it will be understood that the magnitude of the vertical orientation vector of the heat pipe plates  20  is larger than the magnitude of the horizontal orientation vector. The heat pipe plates  20  may have an orientation forming a non-zero angle with a vertical plane, such that the heat pipe plates  20  are slanted relative to the vertical plane provided that they are still upright. It will thus be appreciated that the heat pipe plates  20  have vertical variation between the ends of the heat pipe plates  20 . The inner and outer walls  221 , 220  of the heat pipe plates  20  may be made of light metal, such as aluminum or copper. The heat pipe plate  20  may include cooling fins, metal foams or other surface projections extending from their surfaces to improve heat transfer with the fluid within the heat pipe plates  20 . 
     Referring to  FIG.  2 A , the heat pipe plates  20  have one or more contact plate portions  24 C. The contact plate portions  24 C are portions of the inner wall  221  of the heat pipe plates  20  which are in contact with, or face, the cell(s)  14 . In the configuration of the battery module  10  shown in  FIG.  2 A , the heat pipe plates  20  have multiple contact plate portions  24 C each of which is in contact with, or facing, one of the cells  14 . Referring to  FIG.  2 A , the heat pipe plates  20  also have one or more upper plate portions  24 U. The upper plate portions  24 U are portions or segments of the heat pipe plates  20  that are positioned vertically above the contact plate portions  24 C. This arrangement of the upper plate portion  24 U and the contact plate portions  24 C can take different forms. For example, and referring to  FIG.  2 A , the upper plate portion  24 U is at the upper end  20 U of the heat pipe plates  20  and the contact plate portions  24 C are located vertically between the upper and lower ends  20 U, 20 L. For example, in an alternate shape for the heat pipe plate  20  which is slanted with respect to a vertical plane, the contact plate portions  24 C may be located at the upper and lower ends  20 U, 20 L and the upper plate portion  24 U may be located between the upper and lower ends  20 U, 20 L in the middle of the heat pipe plates  20  at a position that is vertically higher than the contact plate portions  24 C. 
       FIGS.  2 B and  2 C  show the interior of the heat pipe plates  20  at the contact plate portions  24 C and at the upper plate portions  24 U, respectively. Referring to  FIGS.  2 B and  2 C , the heat pipe plates  20  have an internal passage  26 . The internal passage  26  is an inner volume of the heat pipe plate  20  that is sealed off from the environment outside of the heat pipe plate  20 . The internal passage  26  is delimited by the inner and outer walls  221 , 220  and the peripheral edge  22 E of the heat pipe plates  20 . The internal passage  26  is present along a length of some or all of the heat pipe plate  20 . The internal passage  26  extends through the heat pipe plate  20  from at least the contact plate portion  24 C to the upper plate portion  24 U. Referring to  FIGS.  2 B and  2 C , the heat pipe plates  20  also have a heat pipe thermal transfer fluid  20 F that is present in the internal passage  26 . The heat pipe thermal transfer fluid  20 F is a phase-change fluid which can undergo phase change (i.e. gas to liquid, or liquid to gas, or change in density) when heat is transferred to and from the heat transfer plate  20 . For example, and referring to  FIG.  2 B , when the cell(s)  14  are operating and heat is being transferred to the contact plate portions  24 C from the cell(s)  14 , the heat pipe thermal transfer fluid  20 F in the internal passage  26  along the contact plate portions  24 C may be vaporized by the heat and rise upwardly through the internal passage  26  to the upper plate portion  24 U. As explained in greater detail below, and referring to  FIG.  2 C , the heat pipe thermal transfer fluid  20 F may be cooled with a heat sink  30  at the upper plate portion  24 U, which causes the heat pipe thermal transfer fluid  20 F to condense in the internal passage  26  along the upper plate portion  24 U. The condensed heat pipe thermal transfer fluid  20 F may accumulate into a liquid and flow back down under gravity through the internal passage  26  to the contact plate portions  24 C below the upper plate portions  24 U. One possible and non-limiting example of the heat pipe thermal transfer fluid  20 F is glycol. Another possible and non-limiting example of the heat pipe thermal transfer fluid  20 F is water at low pressure. Thus, the internal passage  26  and the heat pipe thermal transfer fluid  20 F contained therein help to transfer heat from the cell(s)  14  to a heat sink  30 . The internal passage  26  and the heat pipe thermal transfer fluid  20 F contained therein may also help to transfer heat from a heat source  31  to the cell(s)  14  to heat the cell(s)  14 . The heat pipe plates  20  thus have an internal heat-transfer and phase-changing fluid (i.e. the heat pipe thermal transfer fluid  20 F) flowing therethrough which allows for heat transfer using gravity and/or wicking effects and thermal differences. The heat pipe plates  20  thus provide a conduit or medium along which heat can travel to/from/among the cell(s)  14 . 
     The presence of the heat pipe thermal transfer fluid  20 F within the heat pipe plates  20  may allow for equalizing or minimising hot spots in the heat pipe plates  20 . When the cell(s)  14  heat up during their operation, the heat may be transferred along the cell(s)  14  toward its positive and negative terminals  14 P, 14 N by conduction, and then by conduction to the heat pipe plates  20 . The heat is then transferred by convection to the heat pipe thermal transfer fluid  20 F in the internal passage  26 . If a particular cell(s)  14  is getting too hot, it will be able to shed its heat to the heat pipe thermal transfer fluid  20 F. The heat pipe thermal transfer fluid  20 F within the heat pipe plates  20  thus allows for concentrated and localised cooling of an individual cell  14 . In this way, the heat pipe plates  20  help equalize temperatures for the cell(s)  14  by applying more cooling to the cell(s)  14  that are running hotter, and less cooling effect to the cooler cell(s)  14 . In an embodiment, the heat pipe plates  20  are not solid plates used for direct thermal conduction, but instead have an internal thermal fluid (e.g. the plate heat transfer fluid  20 F) that can undergo a phase change and transfer heat, via convection and conduction, with the heat source  31  or the heat sink  30 . 
     The heat pipe plates  20  are electrically conductive, in addition to being thermally conductive. Referring to  FIG.  2 A , the heat pipe plates  20  include a first heat pipe plate  20 A and a second heat pipe plate  20 B within the interior  121  of the case  12  of the battery module  10 . More or fewer heat pipe plates  20  may be present in the battery module  10 . The first heat pipe plate  20 A is mounted to the positive terminal(s)  14 P of the cell(s)  14 . The second heat pipe plate  20 B is mounted to the negative terminal(s)  14 N of the cell(s)  14 . An electrical circuit is thus formed by the first and second heat pipe plates  20 A,  20 B and the cell(s)  14 , such that an electrical current can flow through the first and second heat pipe plates  20 A, 20 B and be provided to a load. When such a circuit is formed and the cell(s)  14  are operational, an electrical current will flow from the “positive” pipe or plate  20 A mounted to the positive terminal(s)  14 P to the “negative” pipe or plate  20 B mounted to the negative terminal(s)  14 N. The first and second heat pipes  20 A, 20 B are spaced apart from each other in direction that is parallel to the cell axes  14 A. The first and second heat pipes  20 A, 20 B are spaced apart from each other on opposite longitudinal ends of the cell(s)  14 . Referring to  FIG.  2 A , the first and second heat pipes  20 A, 20 B are spaced apart from each other by the cell(s)  14 . Referring to  FIG.  2 A , there is no direct contact between the first and second heat pipe plates  20 A, 20 B. Referring to  FIG.  2 A , the first and second heat pipe plates  20 A, 20 B are indirectly connected to each other via the cell(s)  14 . In the electrical circuit formed by the first and second heat pipe plates  20 A, 20 B and the cell(s)  14 , the electrical current and heat flows between the first and second heat pipe plates  20 A, 20 B only via the cell(s)  14 . The electrical conductivity of the heat pipe plates  20  allows them to be treated like electrodes of the battery module  10 . 
     Referring to  FIG.  1   , the first and second heat pipe plates  20 A, 20 B within the interior  121  are mounted to and supported by the case  12 . In an embodiment, the first heat pipe plate  20 A is mounted to one of the walls  12 W, and the second heat pipe plate  20 B is mounted to the same wall  12 W or a different wall  12 W. The cell(s)  14  are thus mounted to, and supported by, the case  12  via the first and second heat pipe plates  20 A, 20 B. When mounted to the walls  12 W, the first and second heat pipes  20  are load-bearing, and structurally support a weight of the cell(s)  14 . The mechanical link between the walls  12 W and the first and second heat pipe plates  20 A, 20 B may be, or may include, adequate electrical insulation so that electrical current is not conveyed from the first and second heat pipe plates  20 A, 20 B to the walls  12 W of the case  12 . In an embodiment, one or more of the walls  12 W are electrically non-conductive. In an embodiment, the walls  12 W are electrically insulating so that electricity generated by the cell(s)  14  in the interior  121  of the battery module  10  is not conducted through or via the walls  12 W. In an embodiment, the walls  12 W are thermally insulated or insulating to reduce or prevent the transfer of heat through or via the walls  12 W. In an embodiment, the walls  12 W are both electrically and thermally insulating. 
     The mounting of the cell(s)  14  to the first and second heat pipe plates  20 A, 20 B allows for the thermal and electrical conduction described above. The cell(s)  14  are secured to the first and second heat pipe plates  20 A, 20 B. Referring to  FIGS.  2 A and  2 B , at least the positive terminal(s)  14 P of the cell(s)  14  have a conductor  14 W which extends from the positive terminal(s)  14 P and is secured to the first heat pipe plate  20 A. In an embodiment, the conductor  14 W is welded or soldered to the contact plate portion  24 C of the first heat pipe plate  20 A. In an alternate embodiment, the conductor  14 W is secured in wiring holes in the contact plate portion  24 C of the first heat pipe plate  20 A. In an embodiment, the negative terminal(s)  14 N of the cell(s)  14  also have q conductor  14 W which extends from the negative terminal(s)  14 P and is secured to the second heat pipe plate  20 B. The conductor  14 W is thermally and electrically conductive. The conductor  14 W thus allows for forming an indirect mechanical, thermal and electrical connection between the heat pipe plates  20  and the cell(s)  14 . The heat pipe plates  20  may thus be welded or soldered to the cell(s)  14  for good thermal conductivity, and for minimum cost and complexity of manufacture. The conductor  14 W may include one or more wires  14 WS. The wires  14 WS may have round or rectangular cross-sectional shapes. The wire(s)  14 WS extend between and interconnect the contact plate portions  24 C and the terminal(s)  14 P, 14 N of the cell(s)  14 . The wire(s)  14 WS may be rigid or malleable. The wire(s)  14 WS may be flexible. The conductor  14 W may also include, or be compose of, other objects. For example, the conductor  14 W may include one or more tab(s). Using the conductor  14 W to join the cell(s)  14  to the heat pipe plates  20  may help to increase the heat transfer area between the cell(s)  14  and the heat pipe plates  20  and thus may help to improve heat transfer. The wire(s)  14 WS may form multiple flexible and thin connections for connecting the positive terminal(s)  14 P to the first heat pipe plate  20 A while allowing the positive terminal(s)  14 P to move due to thermal expansion, and to accommodate movement needed to enable venting of gasses from the positive terminal(s)  14 P, as described in greater detail below. The wire(s)  14 WS may form multiple flexible and thin connections for connecting the positive terminal(s)  14 P to the first heat pipe plate  20 A and enable the use of automatic disconnect mechanisms inside the cell(s)  14 . 
     Other configurations are possible for mounting the cell(s)  14  to the first and second heat pipe plates  20 A, 20 B in order to form the thermal and electrical conduction described above. For example, in an alternate embodiment, the positive and negative terminal(s)  14 P, 14 N of the cell(s)  14  are in flush contact and abutted directly against the contact plate portions  24 C, and may be pressed against the contact plate portions  24 C with a spring. For example, in another alternate embodiment, the conductor  14 W includes or is a rigid metal link extending between the positive and negative terminal(s)  14 P, 14 N and the contact plate portions  24 C. 
     In the configuration of  FIG.  2 A , where the multiple cells  14  are arranged in rows of cells  14 , the rows of cells  14  are secured in parallel to the first and second heat pipe plates  20 A, 20 B. In the configuration of the cells  14  of  FIG.  2 A , the cells  14  are electrically interconnected by the first and second heat pipe plates  20 A, 20 Bs via respective ones of the positive and negative terminals  14 P, 14 N of the cells  14  in a parallel arrangement to provide the voltage and the current rating. In an alternate embodiment, the cells  14  are electrically interconnected by the first and second heat pipe plates  20 A, 20 Bs via respective ones of the positive and negative terminals  14 P, 14 N of the cells  14  in a series arrangement to provide the voltage and the current rating. In the configuration of the battery module  10  which has one cell  14 , the voltage and the current rating is the voltage and the current rating of the single cell  14 . In the configuration of the battery module  10  which has multiple cells  14  in a parallel electrical arrangement, for example the configuration of  FIG.  2 A , the voltage and the current rating is the voltage and the current rating of each of the cells  14 . In the configuration of the battery module  10  which has multiple cells  14  in a series electrical arrangement, for example the configuration of  FIG.  2 A , the voltage and the current rating may be the collective voltage and the current rating of some or all of the cells  14 . Thus, the overall voltage and the current rating of the cell(s)  14  may be a function of characteristics of each cell  14  and/or on how the cell(s)  14  are interconnected (e.g. in parallel, series, or series-parallel). 
     Referring to  FIG.  2 A , the battery module  10  has a heat sink  30 . The heat sink  30  is in heat-exchange relationship with, and/or thermally connected to, an upper half or the upper plate portions  24 U of the heat pipe plates  20 . This heat exchange relationship allows heat to transfer between these components. For example, heat can be shed from the heat pipe plates  20  to the heat sink  30  to cool the cell(s)  14 . The heat sink  30  is thus in heat exchange relationship with the heat pipe thermal transfer fluid  20 F in the internal passage  26  along the upper plate portions  24 U to condense the heat pipe thermal transfer fluid  20 F. The heat sink  30  may be in heat-exchange relationship with other portions of the heat pipe plates  20  as well, such as the contact plate portions  24 C. Some or all of the heat sink  30  may be positioned within the interior  121  of the case  12 , and enclosed by part of the walls  12 W. 
     Referring to  FIG.  2 A , the battery module  10  has a heat source  31 . The heat source  31  is in heat-exchange relationship with, and/or thermally connected to, a lower portion, a lower half or the lower end  20 L of the heat pipe plates  20 . This heat exchange relationship allows heat to be transferred to the heat pipe plates  20 , and ultimately, to the cell(s)  14 . For example, heat can be transferred to the heat pipe plates  20  from the heat source  31  to then travel upward via the heat pipe thermal transfer fluid  20 F to heat the cell(s)  14 . The heat source  31  is thus in heat exchange relationship with the heat pipe thermal transfer fluid  20 F in the internal passage  26  along the lower end  20 L to vaporize the heat pipe thermal transfer fluid  20 F. The heat source  31  may be in heat-exchange relationship with other portions of the heat pipe plates  20  as well, such as the contact plate portions  24 C. The heat source  31  may be electric or a thermal engine. Some or all of the heat source  31  may be positioned within the interior  121  of the case  12 , and enclosed by part of the walls  12 W. In the configuration of the battery module  10  of  FIG.  2 A , the heat sink  30  is at a top portion or upper half of the heat pipes  20  where the vaporized heat pipe thermal transfer fluid  20 F will be to be condensed by the heat sink  30 , and the heat source  31  is at the bottom or lower half of the heat pipes  20  where the cooler thermal transfer fluid  20 F will be. In an embodiment, the battery module  10  has only a heat source  31  and no heat sink  30 . In an embodiment, the battery module  10  has only a heat sink  30  and no heat source  31 . In an embodiment, the battery module  10  has both a heat source  31  and a heat sink  30  which are selectively operated to heat or cool. Referring to  FIG.  2 A , the battery module  10  has a mounted orientation that it assumes when it is used in an aircraft, for example. In  FIG.  2 A , the mounted orientation of the battery module  10  is vertical. The battery module  10  may have this orientation while the aircraft is stationary on flat horizontal terrain. 
     The heat source  31  and the heat sink  30  may have different configurations to achieve this function. For example, and referring to  FIG.  2 A , a second thermal transfer fluid  32  flows through or along the heat source  31  and the heat sink  30  to absorb heat from the heat pipe plates  20  (the heat sink  30  configuration), or to convey heat to the heat pipe plates  20  (the heat source  31  configuration). In the configuration shown in  FIG.  2 A , the second thermal transfer fluid  32  is a liquid, for example glycol, water, or a mixture of water and glycol, that flows through the heat source  31  or the heat sink  30 . Referring to  FIG.  2 A , the second thermal transfer fluid  32  may be pumped into the heat sink  30  or into the heat source  31  via a fluid circuit  35 A which has a pump  35 B to pressurize and circulate the second thermal transfer fluid  32  through the fluid circuit  35 A. The fluid circuit  35 A may have a heat exchanger  35 C through which the second thermal transfer fluid  32  is circulated to shed heat, or to receive heat. The second thermal transfer fluid  32  may be other types of liquid, or any type of gas (e.g. air). The second thermal transfer fluid  32  may circulate between, and be used in, both the heat source  31  and the heat sink  30 . Thus, in the configuration of the heat source  31  and heat sink  30  shown in  FIG.  2 A , heat is transferred to/from the heat source  31 /heat sink  30  via convection. In another possible configuration of the heat source  31 /heat sink  30 , heat transfer is achieved by conduction between the inner walls  221  of the heat pipe plates  20  and the heat source  31 /heat sink  30 , in addition to, or to the exclusion of, convective heat transfer via the second thermal transfer fluid  32 . 
     Referring to  FIG.  2 A , the heat sink  30  includes a heat-exchange passage  34 . The heat-exchange passage  34  is a volume that extends along some or all of the width of the heat sink  30 , where the width is defined along the horizontal axis  11 H. Referring to  FIG.  2 A , the heat-exchange passage  34  is located at the upper ends  20 U of the heat pipe plates  20  and extends between the heat pipe plates  20 . Referring to  FIG.  2 A , the heat-exchange passage  34  is defined between, and delimited by, the first and second heat pipe plates  20 A, 20 B (more particularly their upper ends  20 U) and by a flow guide  36  of the heat sink  30 . The heat-exchange passage  34  may be delimited at its upper extremity by one of the walls  12 W of the case  12  (see  FIG.  1   ). The heat-exchange passage  34  is thus located in the interior  121  of the case  12  of the battery module  10 . The walls  12 W of the case  12  may have one or more inlet port(s) to admit the second thermal transfer fluid  32  into the heat-exchange passage  34 , and one or more outlet port(s) to allow the second thermal transfer fluid  32  to exit the heat-exchange passage  34 . 
     In the configuration of the heat-exchange passage  34  of  FIG.  2 A , the heat-exchange passage  34  is delimited by the following bodies: on its sides by the upper ends  20 U and the upper extremity of the peripheral edges  22 E of the first and second heat pipe plates  20 A, 20 B, at the bottom by the flow guide  36 , and on the top by one of the walls  12 W of the case  12 . Referring to  FIG.  2 A , the flow guide  36  extends between, and is attached to, the first and second heat pipe plates  20 A, 20 B. The flow guide  36  is positioned above the cell(s)  14 . The flow guide  36  is thermally conductive and electrically insulating. Therefore, heat can be conducted along the flow guide  36  between the first and second heat pipe plates  20 A, 20 B. An electrical current is prevented from being conducted between the first and second heat pipe plates  20 A, 20 B by the flow guide  36 . The flow guide  36  may be a planar or non-planar body. The flow guide  36  may define a smooth surface along which the second thermal transfer fluid  32  travels. Alternatively, the flow guide  36  may have one or more turbulence generators to disrupt the flow of the second thermal transfer fluid  32  in order to improve heat transfer. Alternatively, the flow guide  36  may have one or more channels therein to increase a heat transfer area and improve heat transfer. The second thermal transfer fluid  32  may be a gas or a liquid, or any other type of fluid. The second thermal transfer fluid  32  may be a liquid refrigerant and the flow guide  36  forms part of a liquid cooling plate. In an embodiment where the second thermal transfer fluid  32  is a liquid, the flow guide  36  may be sealingly attached to the first and second heat pipe plates  20 A, 20 B and thus forms a seal between the heat-exchange passage  34  and the interior  121  of the battery module  10  where the cell(s)  14  are located. In this embodiment, the flow guide  36  prevents the liquid from entering the portion of the interior  121  where the cell(s)  14  are located. In an alternate embodiment where the second thermal transfer fluid  32  is a gas or a dielectric liquid or vapor, the flow guide  36  may be absent or alternatively the flow guide  36  may not be sealingly attached to the first and second heat pipe plates  20 A, 20 B such that the gas may enter the portion of the interior  121  where the cell(s)  14  are located. 
     Other configurations or arrangements of the heat-exchange passage  34  and of the heat sink  30  are possible. For example, in one possible configuration, the heat-exchange passage  34  may be defined by a self-contained conduit through which the second thermal transfer fluid  32  flows. In such a configuration, the upper ends  20 U of the heat pipes  20  protrude into the conduit to allow heat transfer on all exposed surfaces of the heat pipes  20 . In another possible configuration, one or more of the heat pipes  20  has a portion which is in thermal contact with the second thermal transfer fluid  32  (e.g. liquid or air), which may flow over or around the portion of the heat pipe(s)  20 . In another possible configuration of the heat sink  30 , a portion of the heat pipe(s)  20 , such as the lower end  20 L, is immersed in the second thermal transfer fluid  32 . In this configuration, the second thermal transfer fluid  32  is a dielectric cooling fluid that boils at a temperature that is selected to be below the temperature of the cell(s)  14  at which there is risk of cell damage or thermal runaway. The boiled second thermal transfer fluid  32  may either be vented or condensed at a suitable cooler and returned to the lower end  20 L of the heat pipe(s)  20 . 
     One possible configuration of the heat sink  30  is now described with reference to  FIG.  2 A . The second thermal transfer fluid  32  enters the heat-exchange passage  34  and flows along the flow guide  36  and/or along the lower sections of the upper plate portions  24 U of the first and second heat pipe plates  20 A, 20 B. The second thermal transfer fluid  32  may be a liquid refrigerant. The temperature of the liquid second thermal transfer fluid  32  when it enters the heat-exchange passage  34  is lower than the temperature of the vaporized heat pipe thermal transfer fluid  20 F that is present in the internal passage  26  along the upper plate portions  24 U. The heat pipe thermal transfer fluid  20 F therefore sheds some of its heat to the second thermal transfer fluid  32  in the heat-exchange passage  34 , which causes the second thermal transfer fluid  32  to increase in temperature, and also causes the heat pipe thermal transfer fluid  20 F to decrease in temperature to condense and flow down via gravity through the internal passage  26  to the contact plate portions  24 C. The heat-exchange passage  34  therefore allows for the heat pipe plates  20  to transfer heat to/from the cell(s)  14  via the second thermal transfer fluid  32  flowing along an upper portion of the heat pipe plates  20 . 
     The arrangement of the heat sink  30  with the heat pipe plates  20  allows for the heat pipe plates  20  to be in direct cooling contact with the heat sink  30 . The heat pipe plates  20  allow for direct thermal conduction for cylindrical cell(s)  14  without sacrificing or compromising electrical conductivity. Since the heat pipe plates  20  are electrical and thermal conductors connected to the cell(s)  14 , there is less or no need for multiple layers of thermally conductive or electrically isolating materials between the cell(s)  14  and the heat pipe plates  20  which would inhibit heat or electricity conduction compared to the direct welded conductors that are the heat pipe plates  20 . Using the heat pipe plates  20  as electrical and thermal conductors may help to increase the life of the cell(s)  14 , and thus the life of the battery module  10 , by helping to keep the temperature of the cell(s)  14  more uniform, by reducing differences in temperatures between the cell(s)  14 , and by extracting heat from the cell(s)  14 . This can help reduce the probability of thermal runaway and of cell-to-cell propagation in the event of thermal runaway of a cell  14 . 
     Referring to  FIGS.  2 A and  2 B , one or both of the positive and negative terminals  14 P, 14 N of a cell  14  has a terminal surface  14 S. The terminal surface  14 S is a surface of one or both of the terminal(s)  14 P, 14 N that faces toward one of the heat pipe plates  20 . Referring to  FIG.  2 B , the terminal surface  14 S is spaced apart from the contact plate portion  24 C of the inner wall  221  of the heat pipe plate  20  in a direction parallel to the cell axis  14 A. Referring to  FIG.  2 B , a gap is formed between the terminal surface  14 S and the facing heat pipe plate  20 , and a width of the gap is defined in a direction parallel to the cell axis  14 A. The wires  14 WS of the conductor  14 W bridge the gap, or extend across the space, between the terminal surface  14 S and the inner wall  221 , and mechanically, thermally, and electrically connect the terminal surface  14 S to the inner wall  221 . In an alternative configuration, the gap is perpendicular to the cell axis  14 A of the cell(s)  14 , which may allow for flexing of the wires  14 WS of the conductor  14 A and thus allow for thermal expansion and movement of the positive terminal  14 P. In an alternate embodiment, the terminal surface  14 S of the negative terminal  14 N is directly abutted against, or in direct contact with, the inner wall  221  of the heat pipe plate  20 . 
     The terminal surface(s)  14 S of the cell(s)  14  may be misaligned with the heat pipe plate  20 , such that the inner wall  221  does not overlap or overlie all of the area defined by the terminal surface  14 S. Referring to  FIG.  2 A , the terminal surface  14 S has an exposed area  14 SA that does not face the inner wall  221  across the gap. The exposed area  14 SA is thus not covered by the heat pipe plate  20 . Referring to  FIG.  2 A , the terminal surfaces  14 S of both the positive and negative terminals  14 P, 14 N of the cells  14  have an exposed area  14 SA that extends past the peripheral edge  22 E of the first and second heat pipe plates  20 A, 20 B in a direction parallel to the horizontal axis  11 H. In an embodiment, only the terminal surface  14 S of the positive terminal  14 P of the cell(s)  14  has the exposed area  14 SA which is not overlapped by the inner wall  221 . 
     Exposing some or all of the terminal surface  14 S of one or both of the positive and negative terminal(s)  14 P, 14 N allows for gases, which may build up within the cell  14  when the cell  14  heats up, to be vented out of the cell  14  via the exposed portions of the terminal surfaces  14 S without the heat pipe plates  20  obstructing the venting of the gases. Exposing some or all of the terminal surface  14 S of one or both of the positive and negative terminal(s)  14 P, 14 N allows for the terminal surface  14 S itself (e.g. the end cap of the cell  14 ) to expand thermally in a direction parallel to the cell axis  14 A without such thermal expansion impacting the adjacent heat pipe plate  20 . In situations where the terminal surface  14 S experiences thermal expansion, the deformable conductor  14 W helps to accommodate the movement of the terminal surface  14 S while still allowing the cell  14  to remain mounted to the heat pipe plate  20 . Exposing some or all of the terminal surface  14 S of one or both of the positive and negative terminal(s)  14 P, 14 N helps to control the direction of gas that may vent from within the cell  14  in the event of damage or failure of the cell  14 . 
     Different configurations for achieving the exposed area  14 SA of one or both of the positive and negative terminal(s)  14 P, 14 N are possible. For example, and referring to  FIG.  2 A , the heat pipe plates  20  are free of cutouts or holes. The cells  14  of  FIG.  2 A  are positioned with respect to the first and second heat pipe plates  20 A, 20 B such that part of both the positive and negative terminals  14 P, 14 N—i.e. the exposed areas  14 SA—extend past the peripheral edge  22 E of the first and second heat pipe plates  20 A, 20 B in the direction of the horizontal axis  11 H. A remainder of the exposed areas  14 SA faces, and is aligned with, the inner wall  221 . The wires  14 WS of the conductor  14 W are welded around the peripheral edge  22 E of the first and second heat pipe plates  20 A, 20 B. In one possible configuration, the terminal face  14 S of the negative terminal  14 N is abutted against the second heat pipe plate  20 B such that no portion of the terminal face  14 S is exposed, and the terminal face  14 S of the positive terminal  14 P is wired with the wires  14 WS to the first heat pipe plate  20 A across the gap such that part of the terminal face  14 S (i.e. the exposed area  14 SA) of the positive terminal  14 P is exposed. 
     Another possible configuration for achieving the exposed area  14 SA of one or both of the positive and negative terminal(s)  14 P, 14 N is described with reference to  FIG.  3   . The first heat pipe plate  20 A is shown in  FIG.  3    as well as the positive terminals  14 P of the cells  14 . The surface area of the circle formed by the positive terminals  14 P in  FIG.  3    is less than the surface area of a circle whose diameter is defined by the outer walls of the cells  14 . The peripheral edge  22 E of the first heat pipe plate  20 A includes edge cut-outs  22 EC or grooves along the vertical segments of the peripheral edge  22 . The edge cut-outs  22 EC extend inwardly into the body of the first heat pipe plate  20 A in a direction that is parallel to the horizontal axis  11 H. The edge cut-outs  22 EC have semi-circular shapes. The edge cut-outs  22 EC may have other shapes. The edge cut-outs  22 EC extend inwardly into the body from a remainder of the peripheral edge  22 E, and may thus be considered recessed portions of the peripheral edge  22 E. All of the exposed area  14 SA of the terminal surfaces  14 S of the positive terminals  14 P is free of overlap by the inner wall  221  (not visible in  FIG.  3   ) of the first heat pipe plate  20 A. The cell axes  14 A of the cells  14  do not intersect the inner wall  221 . The cell axes  14 A of the cells  14  extend through the edge cut-outs  22 EC. The wires  14 WS of the conductor  14 W extend from the positive terminals  14 P and are welded to portions of the first heat pipe plate  20 A that are adjacent to the edge cut-outs  22 EC. The ends of the wires  14 WS closest to the positive terminal  14 P are welded to different portions of the terminal surface  14 S. 
     Another possible configuration for achieving the exposed area  14 SA of one or both of the positive and negative terminal(s)  14 P, 14 N is described with reference to  FIG.  4   . The first heat pipe plate  20 A is shown in  FIG.  4    as well as the positive terminals  14 P of the cells  14 . The surface area of the circle formed by the positive terminals  14 P in  FIG.  4    is less than the surface area of a circle whose diameter is defined by the outer walls of the cells  14 . The portion of the body of the first heat pipe plate  20 A spaced inwardly from the peripheral edge  22 E includes plate cut-outs  22 PC or plate holes which extend through the inner and outer walls  221 , 220 . The area of the plate cut-outs  22 PC may be less than the surface area of a circle whose diameter is defined by the outer walls of the cells  14 . The area of the plate cut-outs  22 PC may be greater than the surface area of the circle formed by the positive terminals  14 P. The plate cut-outs  22 PC extend through the first heat pipe plate  20 A in a direction that is parallel to the cell axes  14 A. The plate cut-outs  22 PC have circular shapes. The terminal surfaces  14 S of the positive terminals  14 P are aligned with the plate cut-outs  22 PC. All of the exposed area  14 SA of the terminal surfaces  14 S of the positive terminals  14 P is free of overlap by the inner wall  221  because of the plate cut-outs  22 PC of the first heat pipe plate  20 A. The cell axes  14 A of the cells  14  do not intersect the inner wall  221 . The cell axes  14 A of the cells  14  extend through the plate cut-outs  22 PC. The cell axes  14 A of the cells  14  are aligned with the center axes of the circular plate cut-outs  22 PC. The wires  14 WS of the conductor  14 W extend from the positive terminals  14 P and are welded to portions of the first heat pipe plate  20 A that are adjacent to the plate cut-outs  22 PC. The ends of the wires  14 WS closest to the positive terminal  14 P are welded to different portions of the terminal surface  14 S. 
     Referring to  FIG.  8 A , the cells  14  are arranged in the interior  121  of the battery module  10  to be staggered in the direction of the vertical axis  11 V such that each cell  14  occupies a different vertical position defined along the vertical axis  11 V. The cells  14  are also offset from each other along the horizontal axis  11 H, such that some of the cells  14  may have the same position along the horizontal axis  11 H. The cells  14  thus form a “zig-zag” pattern from one end  20 L, 20 U of the heat pipe plates  20 A, 20 B to the other end  20 U, 20 L. Referring to  FIG.  8 B , the cells  14  are staggered vertically and connected to the edge cut-outs  22 EC, similarly to the configuration in  FIG.  3    whose description and features apply mutatis mutandis to  FIG.  8 B . Referring to  FIG.  8 C , a heat pipe  20  with a “zig-zag” configuration is shown. The heat pipe  20  has heat pipe segments  20 S which are interconnected to each other at angles to form a serpentine or repeating shape from the upper end  20 U to the lower end  20 L of the heat pipe  20 . The terminal surfaces  14 S of the positive terminals  14 P of the cells  14  are connected, via the wiring  14 WS, to the ends of the heat pipe segments  20 S, so as to form the exposed areas  14 SA of the terminal surfaces  14 S. Referring to  FIG.  8 D , the portion of the body of the first heat pipe plate  20 A spaced inwardly from the peripheral edge  22 E includes the plate cut-outs  22 PC or plate holes which extend through the inner and outer walls  221 , 220 , similarly to the configuration in  FIG.  4    whose description and features apply mutatis mutandis to  FIG.  8 D . The first heat pipe plate  20 A also has circulation holes  22 PH which extend through the inner and outer walls  221 , 220  and interspersed among the plate cut-outs  22 PC. The circulation holes  22 PH are located between the cells  14 . The circulation holes  22 PH allow for circulation of air or fluid around and among the cells  14  and heat pipes  20 . 
     In the configurations of  FIGS.  3  and  4   , the cut-outs  22 EC, 22 PC and the flexible, thin connections provided by the wires  14 WS are used to connect the cap of the positive terminal  14 P to the heat pipe plate  20  while also allowing the cap to move due to thermal expansion and to accommodate movement needed to enable venting of gasses. The first and second heat pipe plates  20 A, 20 B may have different configurations to achieve the exposed area  14 SA, or may have the same configurations. For example, in an embodiment, the exposed area  14 SA of the terminal surfaces  14 S of the negative terminals  14 N may be completely overlapped by one of the heat pipe plates  20  because there may be a low risk of gas build-up within the cell(s)  14  venting out of the cell(s)  14  via the negative terminal  14 N. In an alternate embodiment, all of the terminal surface  14 S of one or both of the positive and negative terminal(s)  14 P, 14 N is overlapped by the inner wall  221 . This configuration may be used where the risk of cell blowout is minimal. 
     Referring to  FIGS.  9 A and  9 B , there is shown a configuration of the battery module  10  in which the cells  14  are pouch cells  14 PC. The description above regarding the battery module  10  and its components applies mutatis mutandis to the configuration of the battery module  10  shown in  FIGS.  9 A and  9 B  with the pouch cells  14 PC. The pouch cells  14 PC are substantially planar bodies. Each pouch cell  14 PC may include an electrically-insulating skin, which allows the pouch cell  14 PC to be applied or mounted directly against the heat pipes  20  without conducting electricity to the heat pipes  20  via the skin of the pouch cells  14 PC. Each pouch cell  14 PC has a positive terminal tab  114 P and a negative terminal tab  114 N. The positive terminal tabs  114 P are welded or otherwise attached to the heat pipes  20  (shown in this configuration as heat pipe plates) making these heat pipes  20  the “positive heat pipes”  20  or electrodes, and the negative terminal tabs  114 N are welded or otherwise attached to the heat pipes  20  making these heat pipes  20  the “negative heat pipes”  20  or electrodes. The positive and negative terminal tabs  114 P, 114 N are thermally and electrically conductive, such that both heat and electricity can be conducted through the positive and negative terminal tabs  114 P, 114 N and through the heat pipes  20 . The pouch cells  14 PC are therefore electrically and thermally directly connected to the heat pipes  20 , via their positive and negative terminal tabs  114 P, 114 N. During operation of the battery module  10  of  FIGS.  9 A and  9 B , some heat from the pouch cells  14 PC may pass to the heat pipes  20  through the skin of the pouch cells  14 PC via conduction, and substantially more heat from the pouch cells  14 PC may pass to the heat pipes  20  through the positive and negative terminal tabs  114 P, 114 N via conduction. 
     The heat pipe plates  20  may allow for cooling both the positive terminal(s)  14 P (where heat is conveyed to the positive terminal  14 P by being extracted from the central core of the cell(s)  14  via conduction) and the negative terminal(s)  14 N (where heat is conveyed to the negative terminal  14 N by being extracted from the walls and bottom of the cell(s)  14 ). Thus, the heat pipe plates  20  may operate so that the cell(s)  14  transfer heat from the core of the cell(s)  14  to one of the heat pipe plates  20  via the positive terminal  14 P, and transfer heat from a wall or bottom of the cell(s)  14  to the other of the heat pipe plates  20  via the negative terminal  14 N. 
     In an embodiment, the volume of the interior  121  of the case  12 , where the volume is defined outside of the cell(s)  14 , outside of the heat pipe plates  20  and outside of the heat source  31 /heat sink  30 , is filled only with air or another gas. In an embodiment, the volume of the interior  121  of the case  12 , where the volume is defined outside of the cell(s)  14 , outside of the heat pipe plates  20  and outside of the heat source  31 /heat sink  30 , is free of liquid. 
       FIGS.  5  and  6    show different arrangements of multiple battery modules  10 , such as the one disclosed herein and in the enclosed figures. Referring to  FIG.  5   , each battery module  10  of the plurality of battery modules  10  is connected in series to another one of the battery modules  10 . The series connection of battery modules  10  in  FIG.  5    may allow for increasing the collective voltage applied to a load by all the battery modules  10 . Referring to  FIG.  6   , each battery module  10  of the plurality of battery modules  10  is connected in parallel with another one of the battery modules  10 . In an embodiment, the cell(s)  14  are arranged in parallel connection within each of the battery modules  10  in the parallel or series arrangement of battery modules  10 . The number of battery modules  10  in series or parallel arrangement may vary. The multiple battery modules  10  connected together may be referred to collectively as a “battery pack”, in that a battery pack is made up of multiple battery modules  10 , where each battery module  10  includes the cell(s)  14  and the heat pipes  20 . 
     Referring to  FIG.  7   , there is disclosed a method  100  of cooling the battery module  10 . At  102 , the method  100  includes operating the cell(s)  14 ,  14 PC to generate an electrical current flowing through the heat pipes  20 . Operation of the cell(s)  14 ,  14 PC transfers heat to the heat pipes  20 . The transfer of heat may vaporize the heat pipe thermal transfer fluid  20 F within the heat pipes  20 . At  104 , the method  100  includes cooling the heat pipes  20  at the heat sink  30 . Cooling the heat pipes  20  may include cooling the vaporized, vapour-fluid, or heated plate thermal transfer  20 F fluid at the heat sink  30  of the battery module  10  to condense or cool the heat pipe thermal transfer fluid  20 F. The condensed heat pipe thermal transfer fluid  20 F may then flow downward via gravity through the internal passage  26  toward the lowed end  20 L of the heat pipes  20 . At  104 , cooling the heat pipes  20  may include cooling the vaporized heat pipe thermal transfer fluid  20 F at an upper extremity of the heat pipes  20 , such as at their upper plate portions  24 U. At  104 , cooling the heat pipes  20  may include cooling the vaporized heat pipe thermal transfer fluid  20 F with the second thermal-transfer liquid  32  flowing between the spaced-apart heat pipes  20  and through the battery module  10 . 
     Referring to  FIG.  10   , there is disclosed a method  200  of transferring heat within the battery module  10 . The method includes conducting heat between a terminal  14 P,  14 N,  114 P,  114 N of the cell(s)  14 ,  14 PC and one of the heat pipes  20 . The heat may be transferred when the cell(s)  14 ,  14 PC are operating to generate electricity. The heat may be transferred when the cell(s)  14 ,  14 PC have ceased to generate electricity, for example in order to cool down the cell(s)  14 ,  14 PC after they have ceased to operate. The heat may be transferred to warm the cell(s)  14 ,  14 PC before they being to operate to generate electricity. 
     There is disclosed a method of heating the battery module  10 . The method  100  includes heating the heat pipes  20  with the heat source  31 , such as with the second thermal transfer liquid  32 . This will also heat the cell(s)  14 . The method includes operating the cell(s)  14  to generate an electrical current flowing through the heat pipes  20 . 
     In an embodiment, the rate of cooling/heating of the second thermal transfer fluid  32  that is in contact with the heat pipes  20  may be varied by a control system that measures the temperature of the cell(s)  14  and the temperature of the second thermal transfer fluid  32 , and modifies the flow rate (e.g. by increasing or decreasing power to an electric pump or by using a variable displacement pump, or by using a thermostat or other actuator that responds to temperature) to increase the rate of cooling or heating when needed. For example, if a cell(s)  14  or string of battery modules  10  is suspected to be at risk of thermal runaway, the cooling rate of the second thermal transfer fluid  32  can be increased aggressively to reduce the probability of thermal runaway or the probability of cell-to-cell propagation in the event that a cell(s)  14  enters thermal runaway. The rate of circulation can also be increased when the heat pipe  20  is being used to warm up the battery module  10 , for example at the beginning of a mission when there is a need to warm-up the battery module  10  quickly. Reference is made to U.S. patent application 63/084,330 naming the assignee Pratt &amp; Whitney and to any patent application claiming priority to US patent application 63/084,33, the entirety of each application being incorporated by reference herein. 
     The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.