Patent Publication Number: US-2021184195-A1

Title: Passive thermal suppression material systems for battery packs

Description:
TECHNICAL FIELD 
     This disclosure relates generally to battery packs, and more particularly to battery packs that include thermal suppression material systems for preventing or delaying thermal runaway during battery thermal events. 
     BACKGROUND 
     The desire to reduce automotive fuel consumption and emissions has been well documented. Therefore, electrified vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. In general, electrified vehicles differ from conventional motor vehicles because they are selectively driven by battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to propel the vehicle. 
     A high voltage battery pack typically powers the electric machines and other electrical loads of the electrified vehicle. The battery pack includes a plurality of battery cells and various other battery internal components that support electric propulsion of electrified vehicles. The battery cells and battery internal components can experience thermal runaway during certain battery thermal events (e.g., overcharging, overheating, etc.). 
     SUMMARY 
     A battery pack according to an exemplary aspect of the present disclosure includes, among other things, a battery system and a passive thermal suppression material system positioned about at least a portion of the battery system. The passive thermal suppression material system includes a thermal suppression sheet comprised of a first polymer film, a second polymer film, and a suppression material between the first and second polymer films. 
     In a further non-limiting embodiment of the foregoing battery pack, the first and second polymer films are made of a low melting point polymer. 
     In a further non-limiting embodiment of either of the foregoing battery packs, the low melting point polymer includes polyethylene, polypropylene, nylon, or polyethylene terephthalate. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes sodium chloride-based salts. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes copper-based powders. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes graphite-based powders. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the thermal suppression sheet covers a top surface of a battery array of the battery system. 
     In a further non-limiting embodiment of any of the foregoing battery packs, a second thermal suppression sheet covers a first side surface of the battery array, a third thermal suppression sheet covers a second side surface of the battery array, a fourth thermal suppression sheet covers a first end surface of the battery array, and a fifth thermal suppression sheet covers a second end surface of the battery array. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the thermal suppression sheet is disposed across multiple battery arrays of the battery system. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material is sandwiched between the first and second polymer films inside the thermal suppression sheet. 
     A battery pack according to another exemplary aspect of the present disclosure includes, among other things, a battery system and a passive thermal suppression material system positioned about at least a portion of the battery system. The passive thermal suppression material system includes a slip cover including a polymer film and a suppression material encapsulated inside the polymer film. 
     In a further non-limiting embodiment of the foregoing battery pack, the polymer film is made of a low melting point polymer. 
     In a further non-limiting embodiment of either of the foregoing battery packs, the low melting point polymer includes polyethylene, polypropylene, nylon, or polyethylene terephthalate. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes sodium chloride-based salts. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes copper-based powders. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the suppression material includes graphite-based powders. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the slip cover is received over a battery array of the battery system. 
     In a further non-limiting embodiment of any of the foregoing battery packs, a second slip cover is received over a second battery array of the battery system. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the slip cover is received over multiple battery arrays of the battery system. 
     In a further non-limiting embodiment of any of the foregoing battery packs, the slip cover is receiver over a bus bar module, an ICB cover, or a battery cell holding frame of the battery system. 
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
     The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
         FIG. 2  illustrates a battery pack of an electrified vehicle. 
         FIGS. 3 and 4  illustrate select portions of a battery system of the battery pack of  FIG. 2 . An enclosure of the battery pack is removed in  FIGS. 3-4  to better illustrate the components of the battery system. 
         FIG. 5  schematically illustrates an exemplary passive thermal suppression material system positioned relative to a battery system. 
         FIG. 6  schematically illustrates another exemplary passive thermal suppression material system. 
         FIG. 7  schematically illustrates yet another exemplary passive thermal suppression material system. 
         FIG. 8  illustrates a thermal suppression sheet of a passive thermal suppression material system. 
         FIG. 9  schematically illustrates a method of manufacturing the thermal suppression sheet of  FIG. 8 . 
         FIG. 10  schematically illustrates the functionality of a passive thermal suppression material system during a battery thermal event. 
         FIG. 11  illustrates another exemplary passive thermal suppression material system. 
         FIG. 12  illustrates another exemplary passive thermal suppression material system. 
         FIG. 13  illustrates yet another exemplary passive thermal suppression material system. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure details exemplary battery pack designs for use in electrified vehicles. An exemplary battery pack may include a battery system and a passive thermal suppression material system positioned about at least a portion of the battery system. The passive thermal suppression material system is configured to release a thermal suppression material during certain battery thermal events. The thermal suppression material prevents or delays thermal runaway inside the battery pack. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
       FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 . Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEVs and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEVs), fuel cell vehicles, etc. 
     In an embodiment, the powertrain  10  is a power-split powertrain system that employs first and second drive systems. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery pack  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems are each capable of generating torque to drive one or more sets of vehicle drive wheels  28  of the electrified vehicle  12 . Although a power-split configuration is depicted in  FIG. 1 , this disclosure extends to any hybrid or electric vehicle including full hybrids, parallel hybrids, series hybrids, mild hybrids, or micro hybrids. 
     The engine  14 , which may be an internal combustion engine, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In a non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
     The generator  18  can be driven by the engine  14  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
     The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In a non-limiting embodiment, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
     The motor  22  can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In a non-limiting embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to the battery pack  24 . 
     The battery pack  24  is an exemplary electrified vehicle battery. The battery pack  24  may be a high voltage traction battery that includes a plurality of battery arrays  25  (i.e., battery assemblies or groupings of battery cells) capable of outputting electrical power to operate the motor  22 , the generator  18 , and/or other electrical loads of the electrified vehicle  12  for providing power to propel the wheels  28 . Other types of energy storage devices and/or output devices could also be used to electrically power the electrified vehicle  12 . 
     In an embodiment, the electrified vehicle  12  has two basic operating modes. The electrified vehicle  12  may operate in an Electric Vehicle (EV) mode where the motor  22  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery pack  24  state of charge up to its maximum allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a charge depleting mode of operation for the electrified vehicle  12 . During EV mode, the state of charge of the battery pack  24  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally OFF under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
     The electrified vehicle  12  may additionally operate in a Hybrid (HEV) mode in which the engine  14  and the motor  22  are both used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle  12 . During the HEV mode, the electrified vehicle  12  may reduce the motor  22  propulsion usage in order to maintain the state of charge of the battery pack  24  at a constant or approximately constant level by increasing the engine  14  propulsion. The electrified vehicle  12  may be operated in other operating modes in addition to the EV and HEV modes within the scope of this disclosure. 
       FIG. 2  schematically illustrates a battery pack  24  that can be employed within an electrified vehicle. For example, the battery pack  24  could be incorporated as part of the powertrain  10  of the electrified vehicle  12  of  FIG. 1 .  FIG. 2  is an assembled, perspective view of the battery pack  24 . 
     The battery pack  24  may include a battery system  54  and an enclosure assembly  58 . The battery system  54  may be housed inside the enclosure assembly  58 . The enclosure assembly  58  may be a sealed enclosure that includes a tray  59  and a cover  61  and may embody any size, shape, and configuration within the scope of this disclosure. For example, the enclosure assembly  58  could be rectangular, triangular, round, irregular, etc. The enclosure assembly  58  may be constructed of metallic materials, polymer-based materials, textile materials, or any combination of these materials. 
     The battery system  54  is shown removed from the enclosure assembly  58  in  FIG. 3 , which will now be described with continued reference to  FIGS. 1 and 2 . The battery system  54  of the battery pack  24  includes a plurality of battery cells  56  that store energy for powering various electrical loads of the electrified vehicle  12 . The battery system  54  could include any number of battery cells within the scope of this disclosure. Therefore, this disclosure is not limited to the exact battery system configuration shown in  FIG. 3 . 
     The battery cells  56  may be stacked side-by-side to construct a grouping of battery cells  56 , sometimes referred to as a battery array. In an embodiment, the battery cells  56  are prismatic, lithium-ion cells. However, battery cells having other geometries (cylindrical, pouch, etc.), other chemistries (nickel-metal hydride, lead-acid, etc.), or both could alternatively be utilized within the scope of this disclosure. 
     The battery system  54  depicted in  FIG. 3  includes a first battery array  25 A, a second battery array  25 B, a third battery array  25 C, a fourth battery array  25 D, a fifth battery array  25 E, and a sixth battery array  25 F. Although the battery system  54  is depicted as including six battery arrays, the battery pack  24  could include a greater or fewer number of battery arrays and still fall within the scope of this disclosure. Unless stated otherwise herein, when used without any alphabetic identifier immediately following the reference numeral, reference numeral “ 25 ” may refer to any of the battery arrays  25 A- 25 F. 
     The battery cells  56  of the first battery array  25 A are distributed along a first longitudinal axis A 1 , the battery cells  56  of the second battery array  25 B are distributed along a second longitudinal axis A 2 , the battery cells  56  of the third battery array  25 C are distributed along a third longitudinal axis A 3 , the battery cells  56  of the fourth battery array  25 D are distributed along a fourth longitudinal axis A 4 , the battery cells  56  of the fifth battery array  25 E are distributed along a fifth longitudinal axis A 5 , and the battery cells  56  of the sixth battery array  25 F are distributed along a sixth longitudinal axis A 6 . In an embodiment, the longitudinal axes A 1  through A 6  are laterally spaced from and parallel to one another once the battery arrays  25  are positioned within the enclosure assembly  58 . 
     Each battery array  25  of the battery system  54  may be positioned relative to one or more heat exchanger plates (see features  60 A,  60 B), sometimes referred to as cold plates or cold plate assemblies, such that the battery cells  56  are either in direct contact with or in close proximity to at least one heat exchanger plate. In an embodiment, the battery arrays  25  are positioned on top of at least one heat exchanger plate. Therefore, the heat exchanger plate at least partially supports the battery cells  56  of each battery array  25  in the Z-axis direction. 
     In an embodiment, the battery arrays  25 A,  25 B,  25 C share a first heat exchanger plate  60 A, and the battery arrays  25 D,  25 E, and  25 F share a second heat exchanger plate  60 B. Alternatively, each battery array  25  could be positioned relative to its own heat exchanger plate, or all battery arrays may share a single heat exchanger plate. 
     A thermal interface material (TIM)  62  (see  FIG. 4 ) may optionally be positioned between the battery arrays  25  and the heat exchanger plates  60 A,  60 B such that exposed surfaces of the battery cells  56  are in direct contact with the TIM  62 . The TIM  62  maintains thermal contact between the battery cells  56  and the heat exchanger plates  60 A,  60 B, thereby increasing the thermal conductivity between these neighboring components during heat transfer events. 
     The TIM  62  may be made of any known thermally conductive material. In an embodiment, the TIM  62  includes an epoxy resin. In another embodiment, the TIM  62  includes a silicone based material. Other materials, including thermal greases, may alternatively or additionally make up the TIM  62 . 
     The heat exchanger plates  60 A,  60 B may be part of a liquid cooling system that is associated with the battery system  54  and is configured for thermally managing the battery cells  56  of each battery array  25 . For example, heat may be generated and released by the battery cells  56  during charging operations, discharging operations, extreme ambient conditions, or other conditions. It may be desirable to remove the heat from the battery system  54  to improve capacity, life, and performance of the battery cells  56 . The heat exchanger plates  60 A,  60 B are configured to conduct the heat out of the battery cells  56 . In other words, the heat exchanger plates  60 A,  60 B may operate as heat sinks for removing heat from the heat sources (i.e., the battery cells  56 ). The heat exchanger plates  60 A,  60 B could alternatively be employed to heat the battery cells  56 , such as during extremely cold ambient conditions. 
     The battery system  54  may additionally include a plurality of electrical components (not shown) that establish an electrical assembly of the battery system  54 . The electrical components may include a bussed electrical center (BEC), a battery electric control module (BECM), an electrical distribution system, wiring, a plurality of input/output (I/O) connectors, etc. 
     The battery arrays  25  or the other battery internal components of the battery system  54  of the battery pack  24  may be susceptible to thermal runaway (i.e., thermal propagation). For example, during certain battery thermal events (e.g., overcharging, overheating, defective cell, damaged cell, etc.), the temperature of the battery cells  56  may increase until one or more of the battery cells  56  vent high temperature, pressurized gases. Flames and smoke may also be produced when battery cell temperatures exceed a threshold level, thereby rending nearby battery components, such as adjacent battery cells, susceptible to damage. This disclosure therefore proposes thermal suppression material systems that are configured to release a chemical suppressant in order to prevent or delay thermal runaway within the battery pack  24 . 
       FIG. 5 , with continued reference to  FIGS. 1-4 , illustrates an exemplary passive thermal suppression material system  64  for preventing or delaying thermal runaway during battery thermal events of the battery pack  24 . The system  64  is considered “passive” in that the thermal suppression capabilities (i.e., via the release of chemical suppressants) of the system  64  are automatically activated in response to excessive temperature conditions (e.g., greater than about 120 degrees C./148 degrees F.) and without requiring any action by the vehicle operator. 
     The passive thermal suppression material system  64  may include one or more thermal suppression sheets  66  that are positioned about portions of the battery system  54 . In a first embodiment, shown in  FIG. 5 , the thermal suppression sheets  66  are arranged to cover the tops  68 , sides  70 , and ends  72  of the battery arrays  25  of the battery system  54 . In the illustrated embodiment, five thermal suppression sheets  66  are arranged relative to one another to cover the tops  68 , sides  70 , and ends  72  of the first, second, and third battery arrays  25 A,  25 B,  25 C, and five additional thermal suppression sheets  66  are arranged relative to one another to cover the tops  68 , sides  70 , and ends  72  of the fourth, fifth, and sixth battery arrays  25 D,  25 E,  25 F of the battery system  54 . Other configurations are also contemplated within the scope of this disclosure. 
     The thermal suppression sheets  66  may be held in place with respect to the battery arrays  25  in a variety of manners. For example, the thermal suppression sheets  66  may be affixed relative to the battery arrays  25  using adhesives, adhesive tape, mechanical joints, welding, spring force, trapped in place, etc. 
     Although each thermal suppression sheet  66  is shown as spanning multiple battery arrays  25  in  FIG. 5 , the thermal suppression sheets  66  could alternatively be arranged about five sides of each battery array  25  (see  FIG. 6 ). In yet another embodiment, the thermal suppression sheets  66  are disposed only over the tops  68  of the battery arrays  25  of the battery system  54  (see  FIG. 7 ). 
       FIG. 8  illustrates exemplary features of a thermal suppression sheet  66  of the passive thermal suppression material system  64 . It should be understood that the various features of the thermal suppression sheet  66  of  FIG. 8  are not drawn to scale and that some features may be minimized or exaggerated in order to better illustrate certain characteristics. 
     Each thermal suppression sheet  66  may include a first or upper polymer film  74 , a second or lower polymer film  76 , and a suppression material  78  disposed between the first and second polymer films  74 ,  76 . The suppression material  78  may be sandwiched between the first and second polymer films  74 ,  76  such that the suppression material  78  is either partially exposed or completely enclosed inside the thermal suppression sheet  66 . 
     The first and second polymer films  74 ,  76  may be made from any suitable polymer having a relatively low melting point. Example low melting point polymers for constructing the first and second polymer films  74 ,  76  include but are not limited to polyethylene, polypropylene, nylon, and polyethylene terephthalate. 
     The suppression material  78  may include any Class D fire suppressant chemical or combination of chemicals. In an first embodiment, the suppression material  78  includes sodium chloride-based salts (with or without thermoplastic polymer fillers such as nylon). In a second embodiment, the suppression material  78  includes copper-based powders. In a third embodiment, the suppression material  78  includes graphite-based powders. 
     The thickness of each thermal suppression sheet  66  can vary depending on the application, the type of battery cell, the amount of suppression material required to prevent propagation of a thermal event, etc. The first and second polymer films  74 ,  76  may be thinner compared to the thickness of the suppression material  78 . In an embodiment, the thickness of each of the first and second polymer films  74 ,  76  is in the range of about 0.25 mm (0.010 inches) to about 1 mm (0.039 inches). In this disclosure, the term “about” means that the expressed quantities or ranges need not be exact but may be approximated and/or larger or smaller, reflecting acceptable tolerances, conversion factors, measurement error, etc. 
       FIG. 9 , with continued reference to  FIGS. 1-8 , schematically illustrate an exemplary method for manufacturing the thermal suppression sheet  66  discussed above. The first polymer film  74  may be held between a first roller  80  and a second roller  82 , and the second polymer film  76  may be held between the second roller  82  and a third roller  84 . The suppression material  78  may be held within a hopper  86 . As the rollers  80 ,  82 ,  84  rotate, the suppression material  78  may be released from the hopper  86 , thereby inserting a layer of the suppression material  78  between the first and second polymer films  74 ,  76 . The multi-layered construct may then be cut into individual sheets of any size or shape in order to form the thermal suppression sheets  66 . Once cut into sheets, the thermal suppression sheets  66  may be positioned as desired inside the battery pack  24  for establishing the passive thermal suppression material system  64 . 
     Referring to  FIG. 10 , the first polymer film  74  and/or the second polymer film  76  of the thermal suppression sheet  66  may melt in response to a battery thermal event in which a high heat source  88  (e.g., a damaged battery cell) is located proximate to one or more battery cells  56  of the battery arrays  25 . As the first polymer film  74  and/or the second polymer film  76  melts, the suppression material  78  is released about the surrounding battery cells  56  of the battery arrays  25 . The suppression material  78  may form an oxygen-excluding crust  90  over and/or around the battery cells  56 , thereby blocking the battery cells  56  from the high heat source  88  and preventing or delaying the onset of thermal runaway. 
       FIG. 11  illustrates another exemplary passive thermal suppression material system  164  for preventing or delaying thermal runaway during battery thermal events of the battery pack  24 . The passive thermal suppression material system  164  may include one or more suppression material slip covers  92  that are positioned about portions of the battery system  54 . In an embodiment, each slip cover  92  may be disposed about a plurality of battery arrays  25  (see  FIG. 11 ). In another embodiment, one slip cover  92  may be disposed about each battery array  25  of a battery system  54 . In yet another embodiment, the slip cover  92  may be disposed about a battery internal component  94  (e.g., a bus bar module, an ICB cover, a battery cell holding frame, etc.) to provide thermal suppression at more directed and discrete locations inside the battery pack  24 . 
     Each slip cover  92  of the passive thermal suppression material system  164  may include one or more polymer films  174  and a suppression material  178  encapsulated inside the polymer film  174 . The slip cover  92  may be heat or vacuum shrunk to more tightly conform to the battery arrays  25 /battery internal components  94 . As the polymer film  174  melts during battery thermal events that exceed a threshold temperature, the suppression material  178  may be released about the battery arrays  25 /battery internal components  94 , thereby preventing or delaying the onset of thermal runaway inside the battery pack  24 . 
     The suppression material  178  may be packaged at specific locations inside the polymer film  174  in order to provide a directed thermal suppression relative to the components that are covered by the slip cover  92 . In an embodiment, the suppression material  178  may be disposed within an upper plane  96  of the slip cover  92 . Other configurations are also contemplated within the scope of this disclosure. 
     The exemplary battery packs of this disclosure incorporate passive thermal suppression material systems that can automatically respond to excessive temperature conditions without any required user input. The thermal suppression material systems utilize chemical suppressants, rather than only thermal barriers, for preventing or delaying thermal runaway. The thermal suppression material systems provide reliable, relatively inexpensive, and easy to package thermal suppression designs. 
     Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
     The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.