Patent Publication Number: US-2023155206-A1

Title: Mitigation of thermal runaway in a battery module

Description:
INTRODUCTION 
     The present disclosure relates to heat removal and thermal runaway event mitigation in a battery module. 
     A battery module or array may include a plurality of battery cells in relatively close proximity to one another. Batteries may be broadly classified into primary and secondary batteries. Primary batteries, also referred to as disposable batteries, are intended to be used until depleted, after which they are simply replaced with new batteries. Secondary batteries, more commonly referred to as rechargeable batteries, employ specific chemistries permitting such batteries to be repeatedly recharged and reused, therefore offering economic, environmental and ease-of-use benefits compared to disposable batteries. 
     Rechargeable batteries may be used to power such diverse items as toys, consumer electronics, and motor vehicles. Particular chemistries of rechargeable batteries, such as lithium-ion cells, as well as external factors, may cause internal reaction rates generating significant amounts of thermal energy. Such chemical reactions may cause more heat to be generated by the batteries than is effectively withdrawn. Exposure of a battery cell to elevated temperatures over prolonged periods may cause the cell to experience a thermal runaway event. Accordingly, a thermal runaway event starting within an individual cell may lead to the heat spreading to adjacent cells in the module and cause the thermal runaway event to affect the entire battery array. 
     SUMMARY 
     A battery module includes a first battery cell and a neighboring second battery cell. The battery module also includes heat sink in contact with and configured to absorb thermal energy from each of the first battery cell and the second battery cell. The battery module additionally includes a battery module enclosure surrounded by ambient environment and configured to house each of the first battery cell, the second battery cell, and the heat sink. The battery module further includes a heat transfer mechanism having a first switch configured to detect temperature of the first battery cell exceeding a predetermined value indicative of a thermal runaway event. The heat transfer mechanism is also configured to transfer thermal energy from the first battery cell to the battery module enclosure to thereby control propagation of the thermal runaway event to the second battery cell. 
     An air gap may be arranged between the battery module enclosure and the heat sink and be configured to insulate the battery module enclosure from the heat sink. The first switch may be configured to bridge the air gap and establish a direct contact between the battery module enclosure and the heat sink to conduct thermal energy from the first battery cell to the battery module enclosure. 
     The first switch may be configured as a shape-memory alloy element mounted to the heat sink and configured to change shape and thereby bridge the air gap when the temperature of the first battery cell exceeds the predetermined value. 
     The first switch may be a bimetal strip configured to change shape when the temperature of the first battery cell exceeds the predetermined value. 
     The bimetal strip may be either welded or brazed to the heat sink. 
     The first switch may include at least one rotatable blade configured to bridge the air gap and a shape-memory alloy actuator configured to rotate the at least one rotatable blade when the temperature of the first battery cell exceeds the predetermined value. 
     The shape-memory alloy actuator may be a coiled member configured to change shape when the temperature of the first battery cell exceeds the predetermined value. 
     The at least one rotatable blade may include multiple rotatable blades linked via a connecting rod operated by the shape-memory alloy actuator. 
     The heat sink may be a coolant plate having a first coolant channel arranged proximate the first battery cell. In such an embodiment, the first switch may be mounted adjacent the first coolant channel. 
     The battery system may additionally include an insulating member arranged between the first battery cell and the second battery cell. 
     A motor vehicle having a power-source and the above-disclosed battery module configured to supply electric energy to the power-source is also disclosed. 
     The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described disclosure when taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic top view of an embodiment of a motor vehicle employing multiple power-sources and a battery system having battery cells configured to generate and store electrical energy, according to the disclosure. 
         FIG.  2    is a schematic close-up cross-sectional plan view of the battery system shown in  FIG.  1   , having a heat sink, a battery module enclosure, and a general representation of a heat transfer mechanism having a switch configured to mitigate thermal runaway in one of the battery cells, according to the disclosure. 
         FIG.  3    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  2    and one embodiment of a heat transfer mechanism, wherein the heat transfer mechanism is depicted in an open state, according to the disclosure. 
         FIG.  4    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  3   , with the switch of the heat transfer mechanism depicted in a closed state. 
         FIG.  5    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  2   , and another embodiment of the heat transfer mechanism having a switch configured to mitigate thermal runaway in one of the battery cells, wherein the heat transfer mechanism is depicted in an open state, according to the disclosure. 
         FIG.  6    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  5   , with the switch of the heat transfer mechanism depicted in a closed state. 
         FIG.  7    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  2    and another embodiment of a heat transfer mechanism, wherein the heat transfer mechanism is depicted in an open state, according to the disclosure. 
         FIG.  8    is a schematic close-up cross-sectional partial plan view of the battery system shown in  FIG.  7   , with the switch of the heat transfer mechanism depicted in a closed state. 
         FIG.  9    is a schematic view of a shape-memory alloy actuator configured to rotate respective blade(s) of the heat transfer mechanism shown in  FIGS.  7  and  8    to mitigate thermal runaway in the battery cell(s), according to the disclosure. 
         FIG.  10    is a schematic close-up cross-sectional perspective view of the heat sink, shown in  FIG.  2   , configured as a coolant plate and having a plurality of heat transfer mechanism switches mounted thereto, according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,”, “left”, “right”, etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. Furthermore, the teachings may be described herein in terms of functional and/or logical block components and/or various processing steps. It should be realized that such block components may be comprised of a number of hardware, software, and/or firmware components configured to perform the specified functions. 
     Referring to  FIG.  1   , a motor vehicle  10  having a powertrain  12  is depicted. The vehicle  10  may include, but not be limited to, a commercial vehicle, industrial vehicle, passenger vehicle, aircraft, watercraft, train or the like. It is also contemplated that the vehicle  10  may be a mobile platform, such as an airplane, all-terrain vehicle (ATV), boat, personal movement apparatus, robot and the like to accomplish the purposes of this disclosure. The powertrain  12  includes a power-source  14  configured to generate a power-source torque T (shown in  FIG.  1   ) for propulsion of the vehicle  10  via driven wheels  16  relative to a road surface  18 . The power-source  14  is depicted as an electric motor-generator. 
     As shown in  FIG.  1   , the powertrain  12  may also include an additional power-source  20 , such as an internal combustion engine. The power-sources  14  and  20  may act in concert to power the vehicle  10 . The vehicle  10  additionally includes an electronic controller  22  and a battery system  24  configured to generate and store electrical energy through heat-producing electro-chemical reactions for supplying the electrical energy to the power-sources  14  and  20 . The electronic controller  22  may be a central processing unit (CPU) that regulates various functions on the vehicle  10 , or as a powertrain control module (PCM) configured to control the powertrain  12  to generate a predetermined amount of power-source torque T. 
     The battery system  24  may be connected to the power-sources  14  and  20 , the electronic controller  22 , as well as other vehicle systems via a high-voltage BUS  25 . As shown in  FIGS.  2 - 5   , the battery system  24  may include one or more sections, such as a battery array or module  26 . As shown in  FIG.  2   , the battery module  26  includes a plurality of battery cells, such as a first battery cell  28 - 1  and a neighboring, directly adjacent, second battery cell  28 - 2 . Although one module  26  and two battery cells  28 - 1 ,  28 - 2  are shown, nothing precludes the battery system  24  from having a greater number of such modules and battery cells. The battery module  26  also includes an insulating member or pad  30  arranged between the first battery cell  28 - 1  and the second battery cell  28 - 2 . The insulating member  30  may be constructed from a high-temperature polymer foam configured to limit the amount of thermal energy transfer between the neighboring battery cells  28 - 1 ,  28 - 2 . The insulating member  30  is also configured to maintain consistent and uniform contact with the first cell  28 - 1  and the second cell  28 - 2  during alternate expansion of the subject cells when charging and contraction of the cells when discharging. 
     As shown in  FIGS.  2 - 10   , the battery module  26  also includes a heat sink  32 . The heat sink  32  is in direct contact with each of the first battery cell  28 - 1  and the second battery cell  28 - 2  and thereby configured to absorb thermal energy from the first and second battery cells. As shown, the heat sink  32  may be in direct physical contact with the first and second battery cells  28 - 1 ,  28 - 2 . The heat sink  32  may be configured as a coolant plate having a plurality of coolant channels, shown as respective first and second coolant channels  34 - 1  and  34 - 2  in  FIGS.  3 - 8   . The coolant channels  34 - 1 ,  34 - 2  are specifically configured to circulate a coolant  36  and thereby remove thermal energy from the first and second battery cells  28 - 1 ,  28 - 2  while the battery module  26  generates/stores electrical energy. As shown in  FIG.  2   , the first coolant channel  34 - 1  may be arranged proximate (generally, either above or below) the first battery cell  28 - 1  and the second coolant channel  34 - 2  may be arranged proximate the second battery cell  28 - 2 . 
     Generally, during normal operation of the module  26 , the insulating member  30  is effective in absorbing thermal energy released by the first and second cells  28 - 1 ,  28 - 2  and facilitating transfer of the thermal energy to the heat sink  32 . However, during extreme conditions, such as during a thermal runaway event (identified via numeral  37  in  FIG.  2   ), the amount of thermal energy released by the cell undergoing the event will typically saturate the insulating member  30  and exceed its capacity to absorb and efficiently transfer heat to the heat sink  32 . As a result, excess thermal energy will typically be transferred between the neighboring cells  28 - 1 ,  28 - 2 , leading to propagation of the thermal runaway through the module  26 . The term “thermal runaway event” generally refers to an uncontrolled increase in temperature in a battery system. During a thermal runaway event, the generation of heat within a battery system or a battery cell exceeds the dissipation of heat, thus leading to a further increase in temperature. A thermal runaway event may be triggered by various conditions, including a short circuit within the cell, improper cell use, physical abuse, manufacturing defects, or exposure of the cell to extreme external temperatures. 
     The battery module  26  also includes a battery module enclosure  38  surrounded by ambient environment  40  and configured to house each of the first battery cell  28 - 1 , the second battery cell  28 - 1 , and the heat sink  32 . With continued reference to  FIG.  2   , the battery module  26  also includes a heat transfer mechanism  42 . The heat transfer mechanism  42  includes a first switch  44 - 1  configured to detect temperature of the first battery cell  28 - 1  and a second switch  44 - 2  configured to detect temperature of the second battery cell  28 - 2 . Specifically, each of the first switch  44 - 1  and the second switch  44 - 2  is configured to detect when the temperature of the corresponding first and second battery cell  28 - 1 ,  28 - 2  exceeds a predetermined or critical temperature value tc. Such predetermined temperature value is intended to be indicative of the thermal runaway event occurring in the respective battery cells  28 - 1 ,  28 - 2 . 
     Each of the first switch  44 - 1  and the second switch  44 - 2  is further configured to transfer thermal energy from the corresponding first battery cell  28 - 1  and second battery cell  28 - 2  to the battery module enclosure  38  to thereby control propagation of the thermal runaway event to the neighboring cell. The first switch  44 - 1  may be arranged and mounted adjacent the first coolant channel  34 - 1 , while the second switch  44 - 2  may be arranged and mounted adjacent the second coolant channel  34 - 2 . The first and second switches  44 - 1 ,  44 - 2  may be normally open and then close upon detection of the critical temperature value tc. For example, upon detection of a thermal runaway event in the first battery cell  28 - 1 , the first switch  44 - 1  will close to transfer thermal energy from the first battery cell  28 - 1  directly to the battery module enclosure  38 . The transfer of excess thermal energy from the first battery cell  28 - 1  directly into the battery module enclosure  38  instead of through the insulating member  30  will thereby limit propagation of the thermal runaway to the neighboring cell. 
     As may be seen in  FIG.  2   , the battery module  26  includes an air gap  46  arranged between the battery module enclosure  38  and the heat sink  32 . During normal battery module  26  operation, the air gap  46  is generally configured to insulate the battery module enclosure  38  from the heat sink  32 . Furthermore, during normal battery module  26  operation, each of the first switch  44 - 1  and the second switch  44 - 2  is configured to remain open, such that the air gap  46  is maintained unbridged in the vicinity of the first and second battery cells  28 - 1 ,  28 - 2 . Under adverse conditions of the thermal runaway event  37 , for example, in the first battery cell  28 - 1 , the first switch  44 - 1  is configured to bridge the air gap  46  and establish a direct physical contact  48  (shown in  FIG.  4   ) between the battery module enclosure  38  and the heat sink  32 . Such contact  48  will conduct thermal energy  49  from under the first battery cell  28 - 1  to the battery module enclosure  38  and generate a direct heat transfer path from the first battery cell to the ambient environment  40 . 
     Each of the first and second switches  44 - 1 ,  44 - 2  may be configured as a shape-memory alloy (SMA) element mounted to the heat sink  32 . An exemplary first switch  44 - 1  configured as the SMA element is shown in  FIGS.  3  and  4   . The shape-memory alloy element switches  44 - 1 ,  44 - 2  may thus be configured to change shape and bridge the air gap  46  when the temperature of the respective first and second battery cells  28 - 1 ,  28 - 2  exceeds the predetermined value tc. The SMA element switch  44 - 1  or  44 - 2  may be either welded or brazed to the heat sink  32  at one end via a weld/braze  50  shown in  FIGS.  3 - 4   . Generally, the SMA switch  44 - 1  or  44 - 2  exhibits a shape memory effect. That is, the SMA element switches  44 - 1 ,  44 - 2  may undergo a solid state, crystallographic phase change via a shift between a martensite phase, i.e., “martensite”, and an austenite phase, i.e., “austenite.” The martensite phase is a relatively soft and easily deformable phase of the shape memory alloys, which generally exists at lower temperatures. The austenite phase, the stronger phase of shape memory alloys, occurs at higher temperatures. 
     The temperature at which a shape memory alloy remembers its high temperature form, referred to as the phase transformation temperature, can be adjusted by applying stress and other methods. Accordingly, a temperature difference between the austenite phase and the martensite phase may be the phase transformation delta T. Alternatively stated, the SMA element may undergo a displacive transformation rather than a diffusional transformation to shift between martensite and austenite. A displacive transformation is a structural change that occurs by the coordinated movement of atoms (or groups of atoms) relative to their neighbors. In general, the martensite phase refers to the comparatively lower-temperature phase and is often more deformable—i.e., Young&#39;s modulus is approximately 2.5 times lower—than the comparatively higher-temperature austenite phase. 
     The temperature at which the SMA element begins to change from the austenite phase to the martensite phase is known as the martensite start temperature, Ms. The temperature at which the SMA element completes the change from the austenite phase to the martensite phase is known as the martensite finish temperature, MF. Similarly, as the SMA element is heated, the temperature at which the SMA element begins to change from the martensite phase to the austenite phase is known as the austenite start temperature, A S . The temperature at which the SMA element completes the change from the martensite phase to the austenite phase is known as the austenite finish temperature, A F . Therefore, the SMA element may be characterized by a cold state, i.e., when a temperature of the SMA element is below the martensite finish temperature MF of the subject SMA element. Likewise, the SMA element may also be characterized by a hot state, i.e., when the temperature of the SMA element is above the austenite finish temperature A F  of the SMA element. 
     Alternatively, each of the first and second switches  44 - 1 ,  44 - 2  may be a bimetal strip configured to change shape, such as bow or curl, when the temperature of the first battery cell  28 - 1  exceeds the predetermined value tc. The subject bimetal strip may be constructed from a joined together first strip  52 - 1  and second strip  52 - 2 . An exemplary first switch  44 - 1  configured as the bimetal strip is shown in  FIGS.  5  and  6   . The bimetal strip  52  may be constructed as a strip of copper  52 - 1  and a strip of steel  52 - 2  joined together and either welded or brazed to the heat sink  32  at one end via the weld/braze  50  shown in  FIGS.  5 - 6   . The bimetal strip  52  embodiment of the switch  44 - 1  or  44 - 2  may also include a pad  53  arranged for contact with the battery module enclosure  38  and constructed from a thermal interface material, such as a thermally conductive pad made from silicone. 
     In another alternative, as shown in  FIGS.  7  and  8   , each of the first and second switches  44 - 1 ,  44 - 2  may include rotatable blade(s)  54  configured to shift into a conducting position (shown in  FIG.  8   ) to bridge the air gap  46 . Each of the first and second switches  44 - 1 ,  44 - 2  shown in  FIGS.  7  and  8    also includes an SMA actuator  56  configured to rotate the respective blade(s)  54  about a respective axle (not shown) when the temperature of the corresponding first and second battery cells  28 - 1 ,  28 - 2  exceeds the predetermined value tc. Specifically, as shown in  FIG.  9   , the shape-memory alloy actuator  56  may be a coiled member mounted to the heat sink  32  and configured to change shape and exert a force Fa when the predetermined temperature value tc is exceeded. The force Fa imparted to shift the blade(s)  54  by a distance L into a conducting position via the SMA actuator  56  through the connecting rod  58  is illustrated in  FIG.  9   . In the embodiment of  FIGS.  7  and  8   , the blades  54  may be linked via a connecting rod  58  operated by the SMA actuator  56 . As shown in  FIG.  9   , the action of the SMA actuator  56  may be countered by a bias spring  60  configured to assist the return of blade(s)  54  to their non-conducting position (shown in  FIG.  7   ). Specifically, the bias spring  60  generates a force F b  to retract the blade(s)  54  below the predetermined temperature value t c . 
     In an additional embodiment shown in  FIG.  10   , the battery module  26  may include multiple switches associated with each battery cell  28 - 1  and  28 - 2  and mounted to the heat sink  32 . Specifically, switches  44 - 1 A and  44 - 1 B are shown for the battery cell  28 - 1 , and switches  44 - 2 A and  44 - 2 B are shown for the battery cell  28 - 2 . Each of the switches  44 - 1 A and  44 - 1 B (as well as the switches  44 - 2 A and  44 - 2 B) may be configured to detect a distinct temperature range and transfer thermal energy from the corresponding first and second battery cell  28 - 1 ,  28 - 2  to the battery module enclosure  38  within the corresponding temperature range. Accordingly, in such an embodiment, the subject switches may operate in distinct temperature ranges, such that at an elevated, but lower temperature a single switch,  44 - 1 A or  44 - 2 A, may be activated, while at an even higher temperature, both switches  44 - 1 A and  44 - 1 B or  44 - 2 A and  44 - 2 B may operate together to transfer thermal energy to the battery module enclosure  38  quicker. 
     Overall, the heat transfer mechanism  42  is configured to detect and automatically respond to a battery cell in a battery module having reached a predetermined temperature by transferring excess thermal energy directly to the ambient. Thus, the heat transfer mechanism  42  is particularly effective in mitigating propagation of a thermal runaway within the battery module between individual battery cells, without requiring additional external hardware or controls. 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment may be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.