THERMAL MITIGATION SYSTEMS FOR TRACTION BATTERY PACKS

Thermal mitigation systems are provided for traction battery packs. An exemplary thermal mitigation system may include a cartridge containing a nitrogen releasing material, and a heating element. The heating element may be activated to cause the nitrogen releasing material to release a nitrogen gas for actively mitigating battery thermal events. Another exemplary thermal mitigation system may include one or more passive release devices that are mounted to a battery array. A nitrogen releasing material may be activated via heat generated within the battery array to release a nitrogen gas from a polymeric encapsulating material of the passive release device to passively mitigate battery thermal events.

TECHNICAL FIELD

This disclosure relates generally to traction battery packs, and more particularly to thermal mitigation systems for mitigating battery thermal events within traction battery packs.

BACKGROUND

Electrified vehicles include a traction battery pack for powering electric machines and other electrical loads of the vehicle. The traction battery pack includes a plurality of battery cells and various other battery internal components that support electric vehicle propulsion.

SUMMARY

A thermal mitigation system for a traction battery pack according to an exemplary aspect of the present disclosure includes, among other things, a cartridge containing a nitrogen releasing material, a heating element housed within the cartridge, and a controller configured to control the heating element for causing the nitrogen releasing material to release a nitrogen gas when a temperature within the traction battery pack exceeds a predefined temperature threshold.

In a further non-limiting embodiment of the foregoing thermal mitigation system, the nitrogen releasing material includes guanidine nitrate (C(NH2)3NO3).

In a further non-limiting embodiment of either of the foregoing thermal mitigation systems, the nitrogen releasing material includes sodium azide (NaN3).

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the cartridge includes a vent patch that is configured to open to release the nitrogen gas when a pressure inside the cartridge exceeds a predefined pressure threshold.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the vent patch is comprised of a different material than the cartridge.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the vent patch includes polytetrafluoroethylene (PTFE), and the cartridge includes a polycarbonate.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, a desiccant is housed within the cartridge.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the controller is a 12V controller circuit that is independent or part of a battery management system of the traction battery pack.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the cartridge is comprised of a polycarbonate.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the nitrogen releasing material is configured to decompose to release the nitrogen gas.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, a thermal sensing device is mounted to a battery array of the traction battery pack and is configured to detect the temperature within the battery array.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the thermal sensing device is a thermistor or a thermocouple.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, a passive release device is mounted to a battery array of the traction battery pack.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the passive release device includes a polymeric encapsulating material and a nitrogen releasing material encapsulated within the polymeric encapsulating material.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the nitrogen releasing material is configured to release a nitrogen gas when the temperature within the traction battery pack exceeds the predefined temperature threshold.

A thermal mitigation system for a traction battery pack according to another exemplary aspect of the present disclosure includes, among other things, a battery array, and a passive release device mounted to the battery array. The passive release device includes a polymeric encapsulating material and a nitrogen releasing material encapsulated within the polymeric encapsulating material. The nitrogen releasing material is configured to release a nitrogen gas when a temperature within the traction battery pack exceeds a predefined temperature threshold.

In a further non-limiting embodiment of the foregoing thermal mitigation system, the nitrogen releasing material includes guanidine nitrate (C(NH2)3NO3).

In a further non-limiting embodiment of either of the foregoing thermal mitigation systems, the polymeric encapsulating material is configured as a polyethylene laminated pouch.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the polymeric encapsulating material is configured to break open to release the nitrogen gas when a pressure inside the polymeric encapsulating structure exceeds a predefined pressure threshold.

In a further non-limiting embodiment of any of the foregoing thermal mitigation systems, the passive release device is mounted to a battery cell or an array support structure of the battery array.

DETAILED DESCRIPTION

This disclosure details thermal mitigation systems for traction battery packs. An exemplary thermal mitigation system may include a cartridge containing a nitrogen releasing material and a heating element. The heating element may be activated to cause the nitrogen releasing material to release a nitrogen gas for actively mitigating battery thermal events. Another exemplary thermal mitigation system may include one or more passive release devices that are mounted to a battery array. A nitrogen releasing material may be activated via heat generated within the battery array to release a nitrogen gas from a polymeric encapsulating material of the passive release device to mitigate battery thermal events. These and other features are discussed in greater detail in the following paragraphs of this detailed description.

FIG.1schematically illustrates an electrified vehicle10. The electrified vehicle10may include any type of electrified powertrain. In an embodiment, the electrified vehicle10is a battery electric vehicle (BEV). However, the concepts described herein are not limited to BEVs and could extend to other electrified vehicles, including, but not limited to, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEV's), fuel cell vehicles, etc. Therefore, although not specifically shown in the exemplary embodiment, the powertrain of the electrified vehicle10could be equipped with an internal combustion engine that can be employed either alone or in combination with other power sources to propel the electrified vehicle10.

In the illustrated embodiment, the electrified vehicle10is depicted as a car. However, the electrified vehicle10could alternatively be a sport utility vehicle (SUV), a van, a pickup truck, or any other vehicle configuration. Although a specific component relationship is illustrated in the figures of this disclosure, the illustrations are not intended to limit this disclosure. The placement and orientation of the various components of the electrified vehicle10are shown schematically and could vary within the scope of this disclosure. In addition, the various figures accompanying this disclosure are not necessarily drawn to scale, and some features may be exaggerated or minimized to emphasize certain details of a particular component or system.

In an embodiment, the electrified vehicle10is a full electric vehicle propelled solely through electric power, such as by one or more electric machines12, without any assistance from an internal combustion engine. The electric machine12may operate as an electric motor, an electric generator, or both. The electric machine12receives electrical power and can convert the electrical power to torque for driving one or more wheels14of the electrified vehicle10.

A voltage bus16may electrically couple the electric machine12to a traction battery pack18. The traction battery pack18is an exemplary electrified vehicle battery. The traction battery pack18may be a high voltage traction battery pack assembly that includes a plurality of battery cells capable of outputting electrical power to power the electric machine12and/or other electrical loads of the electrified vehicle10. Other types of energy storage devices and/or output devices could alternatively or additionally be used to electrically power the electrified vehicle10.

The traction battery pack18may be secured to an underbody20of the electrified vehicle10. However, the traction battery pack18could be located elsewhere on the electrified vehicle10within the scope of this disclosure.

Referring now toFIG.2, the traction battery pack18may include a battery system22housed within an interior area30of an enclosure assembly24. The enclosure assembly24of the traction battery pack18may include an enclosure cover26(shown in phantom) and an enclosure tray28. The enclosure cover26may be secured (e.g., bolted, welded, adhered, etc.) to the enclosure tray28to provide the interior area30for housing the battery system22.

The battery system22may include one or more battery arrays32(e.g., groupings of battery cells34) arranged within the interior arear30. Once electrically coupled, the battery cells34of the battery arrays32may supply electrical power for powering various components of the electrified vehicle10. Although two battery arrays32are shown, the battery system22could include one or more battery arrays32within the scope of this disclosure. Thus, the total number of battery cells34included as part of the battery system22is not intended to limit this disclosure.

In an embodiment, the battery cells34are prismatic, lithium-ion cells. However, battery cells having other geometries (cylindrical, pouch, etc.) and/or chemistries (nickel-metal hydride, lead-acid, etc.) could alternatively be utilized within the scope of this disclosure.

From time to time, one or more battery cells34of the traction battery pack18can experience a battery thermal event in which pressure and thermal energy of the one or more battery cells34increases. The pressure and thermal energy increase can be due to an overcharge condition, an overdischarging condition, or a short circuit event, for example. The pressure and thermal energy increase can cause the battery cell34experiencing the thermal event to release gas and/or effluents. The gases may be released as a result of an applied force or a thermal event, and can either cause or exacerbate an existing battery thermal event. A relatively significant amount of heat can be generated during battery thermal events, and this heat can sometimes cascade from array-to-array and/or cell-to-cell within the traction battery pack18/array. The traction battery pack18may therefore be equipped with a thermal mitigation system36for mitigating the effects of battery thermal events.

An exemplary thermal mitigation system36for use within the traction battery pack18is further illustrated with reference toFIGS.3and4(with continued reference toFIG.2). As discussed in greater detail below, the thermal mitigation system36may actively respond to a battery thermal event (e.g., by releasing nitrogen (N2) gas) when a temperature within the traction battery pack 18 exceeds a predefined temperature threshold.

The thermal mitigation system36may include one or more cartridges38that house a nitrogen releasing material40. The cartridge38may be mounted at any location inside the enclosure assembly24of the traction battery pack18. In an embodiment, the cartridge38includes a box-like or cuboid shape. However, the size and the shape of the cartridge38are not intended to limit this disclosure.

The cartridge38may be made of a plastic material. In an embodiment, the plastic material includes polycarbonate. However, other plastic materials may also be suitable for constructing the cartridge38.

The nitrogen releasing material40may be contained inside the cartridge38during normal operation of the traction battery pack18(seeFIG.3). The nitrogen releasing material40may be a sheet or a film or could take any other form or geometry. The nitrogen releasing material40may be selectively activated to release a nitrogen (N2) gas42from the cartridge38(seeFIG.4). The nitrogen releasing material40may be activated by being heated to a temperature that exceeds its decomposition temperature (e.g., about 240 degrees C.). 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. The released N2 gas42reduces the oxygen content inside the traction battery pack18, thereby hindering combustion and actively mitigating battery thermal events when the temperature within the traction battery pack18exceeds the predefined temperature threshold.

In an embodiment, the nitrogen releasing material40includes guanidine nitrate (C(NH2)3NO3), which is a colorless, water-soluble salt. In another embodiment, the nitrogen releasing material40includes sodium azide (NaN3), which is another colorless, water-soluble salt. Other nitrogen releasing materials may also be suitable within the scope of this disclosure.

The N2 gas42may be released from the cartridge38through a vent patch44. The vent patch44may open when a pressure inside the cartridge38exceeds a predefined pressure threshold. In an embodiment, the vent patch44is made of a non-permeable polymer film that is configured to rupture when the pressure inside the cartridge38exceeds the predefined pressure threshold. An exemplary non-permeable polymer film may include polytetrafluoroethylene (PTFE). However, other materials may also be utilized as part of the construction of the vent patch44within the scope of this disclosure.

The release of the N2 gas42from the cartridge38may be controlled by a heating element46and a controller48. The heating element46may be packaged inside the cartridge38and is operably connected to the controller48. In an embodiment, the heating element46includes a metallic wire (e.g., nichrome) that is encapsulated in a polyamide film (e.g., Kapton®). However, other heating elements are also contemplated.

One or more thermal sensing devices50may also be operably connected to the controller48. In an embodiment, one thermal sensing device50is mounted on or in the direct vicinity of one of the battery arrays32(seeFIG.2) of the traction battery pack18and is configured to monitor a temperature of the respective battery array32, or a temperature of the air near the respective battery array32. In an embodiment, the thermal sensing devices50are thermistors. In another embodiment, the thermal sensing devices50are linear heat detection devices that are designed to short in the presence of heat. In yet another embodiment, the thermal sensing devices50are flex film thermocouples.

The thermal sensing devices50may be designed to communicate a signal52to the controller48when the temperature within the traction battery pack18exceeds the predefined temperature threshold. Temperatures that exceed the predefined temperature threshold may be indicative of battery thermal events. The controller48may thus be configured to detect overtemperature conditions of the traction battery pack18based on the signals52received from the thermal sensing devices50. When the detected temperature of one or more battery arrays32or the air near the arrays exceeds the predefined temperature threshold, the controller48may command that a current be sent to the heating element46that causes the heating element46to begin generating heat. The heat induces the nitrogen releasing material40to generate the N2 gas42, which thereby causes the pressure inside the cartridge38to rapidly increase. When the pressure increases beyond the predefined pressure threshold of the vent patch44, the vent patch44may break open and release the N2 gas into the interior area30of the traction battery pack18(or an interior area of battery array32) for mitigating the battery thermal event. For example, the N2 gas may reduce the oxygen content inside the traction battery pack18, and in so doing, reduce temperatures and/or reduce the array-to-array transfer of heat within the traction battery pack18.

The nitrogen releasing material40may be a moisture sensitive material. Therefore, a desiccant56may additionally be housed within the cartridge38. The desiccant56may be configured to absorb water molecules from surrounding air and thus decrease the overall moisture level inside the cartridge38. The desiccant56may include silicone dioxide or any other suitable absorption or adsorption material.

In some implementations, the controller48may be a 12V controller circuit of a battery management system (BMS)54(seeFIG.2) of the traction battery pack18. In other implementations, the controller48may be a stand alone control unit operable to communicate with the BMS54as part of a control system of the traction battery pack18. The controller48may therefore be programmed with instructions for controlling certain aspects of the thermal mitigation system36.

FIG.5illustrates another exemplary thermal mitigation system60for a traction battery pack118. In this implementation, the thermal mitigation system60may be passive system that does not require the use of a controller for mitigating the effects of battery thermal events. As discussed in greater detail below, the thermal mitigation system60may actively mitigate battery thermal events by releasing N2 gas when a temperature within the traction battery pack118exceeds a predefined temperature threshold.

The thermal mitigation system60may include one or more passive release devices62. One or more of the passive release device62may be mounted directly to each battery array132of the traction battery pack118. The one or more passive release devices62may be mounted directly to an array support structure64(e.g., a top plate, side plate, end plate, etc.) of each battery array132(seeFIG.5), or the one or more passive release devices62could be mounted directly to one or more battery cells134of each battery array132(seeFIG.6). The battery arrays132may be positioned within an interior area130established by an enclosure assembly124of the traction battery pack118.

An exemplary passive release device62of the thermal mitigation system60is further illustrated with reference toFIGS.7and8(with continued reference toFIGS.5-6). The passive release device62may include a polymeric encapsulating material66and a nitrogen releasing material68encapsulated within the polymeric encapsulating material66.

In an embodiment, the polymeric encapsulating material66is configured as a polyethylene laminated pouch. However, other geometries and materials are contemplated within the scope of this disclosure, and therefore the size, shape, and material make-up of the polymeric encapsulating material66is not intended to limit this disclosure.

The nitrogen releasing material68may be contained inside the polymeric encapsulating material66during normal operation of the traction battery pack118(seeFIG.7). The nitrogen releasing material68may be a sheet or a film or could take any other form or geometry. The nitrogen releasing material68may be selectively activated to release a nitrogen (N2) gas70from the polymeric encapsulating material66(seeFIG.8). For example, when a predefined temperature threshold inside the traction battery pack118is reached, the nitrogen releasing material68may decompose to release the N2 gas70. The release of the N2 gas70causes a pressure build-up within the polymeric encapsulating material66. When the pressure exceeds a predefined pressure threshold of the polymeric encapsulating material66, the polymeric encapsulating material66may break open and allow the N2 gas70to escape into the traction battery pack118. The released N2 gas70reduces the oxygen content inside the traction battery pack118, thereby hindering combustion and mitigating the effects of battery thermal events.

In an embodiment, the nitrogen releasing material68includes guanidine nitrate (C(NH2)3NO3). In another embodiment, the nitrogen releasing material68includes sodium azide (NaN3). Other nitrogen releasing materials may also be suitable within the scope of this disclosure.

FIG.9illustrates another exemplary thermal mitigation system72for a traction battery pack218. In this embodiment, the thermal mitigation system72may include a combination of the cartridges38that house the nitrogen releasing material40and the passive release devices62. The passive release devices62may be mounted in physical contact with battery arrays232of the traction battery pack218, and the cartridges38may be mounted remote from the battery arrays232, such as to an interior wall74of an enclosure assembly224of the traction battery pack218, for example.

The exemplary thermal mitigation systems of this disclosure are capable of rapidly releasing nitrogen gas in order to hinder combustion during battery thermal events. The proposed systems are simple to install yet effective at limiting the effects of battery thermal events.