Battery having selective phase change function

Abstract

To provide a battery submodule that absorbs excessive heat capable of being released within a battery cell and / or the battery submodule.SOLUTION: A battery submodule comprises: a container; a cell stack that is formed from one or more battery cells provided within the container; a phase change material that is constituted to absorb heat released from the cell stack; and one or more heat insulation layers that are stacked with the one or more battery cells. The phase change material includes one or more phase change material solid layers that are stacked with the one or more battery cells. The one or more phase change material solid layers are provided among the one or more battery cells.SELECTED DRAWING: Figure 4

Description

Background Art

[0001] A battery is an electrochemical device that can convert stored chemical energy into electrical energy. Many examples of battery technologies are known in the art, including lithium-ion batteries, nickel-metal hydride batteries, lead-acid batteries, nickel-cadmium batteries, alkaline batteries, and the like. Batteries can be made in many sizes and with various operating characteristics (e.g., voltage (or potential), maximum current, charge capacity, etc.). To provide a high voltage or high charge capacity, a battery pack can be made by electrically connecting multiple battery cells in series and / or in parallel. Depending on the technology, there are also types of batteries that can be charged by connecting to a charging current source.

[0002] Batteries (especially lithium-ion batteries) are used in various applications, such as a portable power source for driving the motors of vehicles such as automobiles, airplanes, and ships. In some cases, a battery or battery pack may be the sole power source of a vehicle. A vehicle that depends solely on a battery for propulsion may suddenly lose its power if a malfunction occurs in the battery. Depending on the state of the vehicle when a battery failure occurs, the consequences can range from inconvenient to tragic.

[0003] In many cases, multiple cells are required to reach a higher voltage and store sufficient energy to be effective for the intended use of the battery. Multiple battery cells can be packaged together to form a battery sub-module. One or more cells within a battery sub-module may fail in the form of a heat generation process called thermal runaway. The thermal runaway process within a cell can be caused by manufacturing defects in the cell, incorrect handling or abuse, or factors that increase the temperature of the cell or expose the cell to high temperatures from an external source. High temperature often causes an increase in the reaction rate within the cell, thereby further increasing the temperature of the cell and thus the reaction rate. As a result of this runaway process, the cells within the battery sub-module release a large amount of heat into the area surrounding the cells.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the cells of the battery sub-module are often very densely packed, if one cell in a part of the cell assembly experiences thermal runaway, the high temperature of the failed cell may cause thermal runaway (e.g., propagation of thermal runaway) of nearby cells. Such a process may cause nearby cells to release heat, and the thermal runaway process may spread to all the remaining cells in the battery, resulting in cascade failures of the battery and the release of a large amount of energy. Therefore, it may be desirable to manufacture a battery that reduces the risk of thermal runaway.

Means for Solving the Problems

[0005] This specification describes examples (or embodiments) of battery sub-modules that include a phase change material (PCM) for absorbing excess heat that may be released within a battery cell and / or a battery sub-module. In the case of a battery cell failure or other situations involving an undesired rise in local temperature, the phase change material can limit the temperature rise and provide an emergency cooling effect to prevent a thermal runaway event.

[0006] According to various embodiments, a battery sub-module includes a container, a battery stack formed from one or more battery cells provided within the container, and a phase change material provided within the container. The phase change material is configured to absorb heat released from the battery stack. The battery sub-module can also include one or more thermal insulation layers stacked together with one or more battery cells within the battery stack. The container can be configured to compress the battery stack and the phase change material provided therein.

[0007] In some embodiments, the phase change material includes one or more solid phase change material layers stacked with one or more battery cells. The one or more solid phase change material layers are provided between the one or more battery cells. The one or more solid phase change material layers can be provided on the upper or lower surface of the battery stack. The one or more solid phase change material layers can be provided on one or more side surfaces of the battery stack. According to some embodiments, the phase change material can enclose the battery stack within a container.

[0008] According to various embodiments, at least one layer within the battery stack can be impregnated with a phase change material. The phase change material includes an expandable coating.

[0009] In some embodiments, the phase change material includes a predetermined amount of liquid phase change material provided within a container. The battery stack is at least partially immersed in the liquid phase change material. The predetermined amount can be from about 1 milliliter to about 30 milliliters.

[0010] Some embodiments are directed to a method of manufacturing a battery sub-module that includes a container, a battery stack formed from one or more battery cells provided within the container, and a phase change material layer provided within the container. The phase change material is configured to absorb heat released from the battery stack. The battery sub-module can also include one or more insulating layers stacked with one or more battery cells within the battery stack. The method can also include calculating the energy released from the battery stack in the event of a failure, and determining the thickness of the phase change material layer based on the latent heat of fusion of the phase change material and the energy released from the battery stack.

[0011] Some embodiments are directed to a method of manufacturing a battery sub-module that includes inserting a battery stack formed from one or more battery cells into a container and adding a liquid phase change material to the container such that at least a portion of the battery stack is immersed in the liquid phase change material. The liquid phase change material is configured to absorb heat released from the battery stack. The method can further include testing the performance of the battery sub-module, comparing the performance of the battery sub-module to a predetermined threshold, and adjusting the amount of the liquid phase change material based on the comparison. The adjusting step can further include adding a predetermined amount of the liquid phase change material to the container or removing a predetermined amount of the liquid phase change material from the container.

[0012] Various embodiments of the present invention are disclosed in the following detailed description and the accompanying drawings.

Brief Description of the Drawings

[0013]

Figure 1A

Figure 1B

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Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention can be implemented in many ways, such as a process, an apparatus, a system, and / or a composition. In this specification, these implementations, or other forms that the present invention can take, can be referred to as techniques. Generally, the order of the steps of the disclosed process can be changed within the scope of the present invention. Unless otherwise specified, the components can be general components temporarily configured to perform tasks at a given time, or specific components manufactured to perform the tasks.

[0015] Embodiments provide a battery cell and / or battery sub-module that includes a phase change material (PCM) for absorbing excess heat that may be released within the battery cell and / or battery sub-module. According to various embodiments, the PCM may be provided in the form of a layer within the battery cell, in addition to a thermal insulation layer. Alternatively, the PCM layer can replace the thermal insulation layer. In some embodiments, the PCM can be provided on one or more surfaces (e.g., bottom, top, front, back) of the battery sub-module within a container that houses the battery sub-module. The PCM may be a solid PCM provided in the form of a layer and / or one or more strips. In yet other embodiments, the PCM material is a liquid PCM provided within a container that houses the battery sub-module. The various implementations of the PCM within the battery cell / sub-module discussed herein (e.g., solid PCM layer, one or more solid PCM strips, liquid PCM) can be provided by themselves or in any reasonable combination thereof.

[0016] Exemplary battery sub-module First, it may be helpful to describe the components of the battery cell and battery sub-module. FIG. 1A shows a top view of the stacked (e.g., layered) contents of an exemplary battery sub-module 150 that includes a battery cell, a thermal insulation layer, and a thermal conduction layer. FIG. 1B shows the battery sub-module 150 provided within a container 120 (e.g., a metal can) that surrounds and compresses the stacked contents of the battery sub-module 150.

[0017] The battery sub-module 150 can be used, for example, to supply power to vehicles such as aircraft, ships, railway vehicles, passenger cars, trucks, off-road vehicles, personal transportation vehicles (e.g., skateboards or scooters), and electric bicycles. The battery sub-module 150 can be any type of battery including lithium-ion batteries, lead-acid batteries, nickel-metal hydride batteries, etc. The battery sub-module 150 can be implemented as a single battery cell or as a battery pack including a plurality of battery cells connected together in series and / or in parallel as desired. As used herein, the term "battery cell" or "cell" can be understood to include a stand-alone battery or, in the case of a battery sub-module, one of several independently replaceable battery units within the battery sub-module.

[0018] As shown in FIG. 1A, the stacked contents of an exemplary battery sub-module 150 can include a repeating pattern including a thermal conduction layer 100, battery cells 102, and an insulating layer 104. In some embodiments, the thermal conduction layer 100 can include fins on one or both sides. In some embodiments, each battery sub-module 150 includes twelve battery cells and a corresponding number of insulating layers and thermal conduction layers. The specific start and end of the stacking pattern are not shown here and any suitable start and end layers can be used. In some embodiments, the stacked layers can start with two insulating layers and end with two insulating layers. As will be described in more detail below, additional PCM layers can be provided on one or both sides of the insulating layer (e.g., to sandwich the battery sub-module 150).

[0019] In some embodiments, the thermal conduction layer 100 can function as a heat sink for the battery cell 102 that contacts the thermal conduction layer. By distributing the heat generated by the battery cell (e.g., during normal operation and / or catastrophic failure) from the inside to the outside of the stacked layers, the thermal conduction layer 100 prevents nearby battery cells from overheating and, in some cases, failing. In some embodiments, the thermal conduction layer 100 can be made from a metal (e.g., Al of the 1235 series) due to the good thermal conduction properties of the metal.

[0020] According to various embodiments, the battery cell 102 may be a pouch cell. The pouch cell has improved performance when pressure (e.g., about 3 - 5 PSI) is applied. More specifically, by applying pressure to the pouch cell, the cycle life of the pouch cell can be extended. Thus, the stacked layers shown in FIG. 1A can be compressed using a metal container 120 as shown in FIG. 1B.

[0021] FIG. 1B is a perspective view of the stacked contents of the battery sub-module 150, including a container 120 that compresses the contents of the container. As shown in FIG. 1A, each battery cell 102 of the battery sub-module 150 can include a positive tab 106 and a negative tab 108. Each positive tab 106 can be electrically connected, and each negative tab 108 can be electrically connected. As a result, when the contents of the container 120 are sealed with a lid 130 (as shown in FIG. 1B), the lid 130 exposes a single positive connection 116 or port and a single negative connection 118 or port.

[0022] Referring back to FIG. 1A, the thermal insulation layer 104 can prevent (or at least slow down and / or mitigate) heat from spreading from one cell to another. For example, if one cell fails catastrophically, a large amount of heat is released from the failed cell. Without thermal insulation, all of that heat would propagate to nearby cells, causing those cells to also fail catastrophically. Eventually, all of the cells would fail catastrophically in a domino-like effect. This domino-like effect is sometimes referred to as thermal runaway propagation. Thermal runaway can occur when a single battery cell undergoes an uncontrollable temperature increase due to an exothermic chemical reaction. When thermal runaway in one cell causes another cell to enter a thermal runaway state, the effect is sometimes referred to as a thermal runaway propagation event (or simply thermal runaway propagation). The thermal insulation layer 104 can prevent (or at least slow down and / or mitigate) the occurrence of thermal runaway.

[0023] The thermal insulation layer 104 can be made of a material that can withstand (e.g., without collapsing) the expected pressure from the metal container 120. For example, using the spring constant of the material as a measurement criterion for the object, the spring constant of the thermal insulation layer 104 should not be negligible. In some embodiments, the thermal insulation layer 104 may be made of an aerogel that is a good thermal insulator and has a non-negligible spring constant. FIGS. 2A-2B show a battery sub-module having an aerogel 200 used as a thermal insulation layer.

[0024] The heat insulation layer has a low thermal conductivity, thereby confining excessive heat within the overheated battery cell. Although the excessive heat is still transmitted to other areas of the battery sub-module, the transmission speed is slowed down. Also, by using the heat insulation layer to increase the thermal resistance between the overheated battery cell and other nearby battery cells, heat can be directed away from the nearby battery cells to other areas of the battery sub-module (e.g., other components and non-adjacent battery cells). As a result, even if a battery cell overheats, a large amount of heat will not immediately transfer to other nearby battery cells. Instead, the heat is not only slowly released to nearby areas but may also be directed to more distant areas, and then the nearby areas continue to dissipate the heat to more distant areas of the battery sub-module. By slowly releasing the heat, extra time is available for the excess heat to be more evenly and effectively distributed around the battery sub-module instead of accumulating in local areas. Thereby, the heat insulation layer can prevent a specific local area of the sub-module outside the failed battery cell from reaching the critical temperature (e.g., 200 °C). The heat insulation layer can achieve this goal by (1) extending the time until the sub-module reaches the critical temperature and (2) favoring heat transfer to the outside of the highly conductive sub-module over heat transfer to adjacent battery cells, thus improving the temperature uniformity of the entire sub-module and preventing any part from approaching the critical temperature. Therefore, the heat insulation layer effectively distributes heat more evenly and reduces the temperature within the battery sub-module.

[0025] However, in some cases, even when the temperature is evenly distributed among all cells of the battery sub-module, the temperature may still exceed the critical temperature.

[0026] Battery sub-module with a PCM The embodiments described herein provide a phase change material (PCM) within a battery sub-module to prevent the battery sub-module from reaching a critical temperature. The PCM may be used in connection with the thermal insulation layer described above, although in some embodiments, the PCM may be used by itself (e.g., the thermal insulation material may be formed of or replaced by the PCM). Instead of dissipating heat through the battery sub-module (e.g., dissipating heat generated from one battery cell to one or more adjacent cells, or other cells within the battery sub-module), the PCM absorbs the excess heat and reconfigures the bonds between the molecules of the PCM. That is, the PCM absorbs heat and transfers from one phase (e.g., solid, gel) to another phase (e.g., liquid).

[0027] During the phase change process of the PCM, the absorbed thermal energy that causes the phase change does not cause a temperature increase within the PCM. As a result, the PCM can absorb the heat within the battery sub-module without experiencing a temperature increase. Due to this effect, the PCM can provide a temperature upper limit within the battery sub-module. The temperature upper limit (also referred to as an isothermal boundary condition) can be the temperature at or near which the PCM undergoes the phase change process. The temperature upper limit can prevent an uncontrollable temperature increase within the battery sub-module. For example, if a failure occurs in one battery cell, the PCM can absorb the excess heat from that battery cell so that the heat does not increase the temperature of the rest of the battery sub-module or affect other battery cells. As a result, the PCM can provide an emergency cooling effect when the local temperature rises without being controlled. The emergency cooling effect provided by the PCM is sufficient to contain the heat generated by the failure of the battery cell, thereby preventing catastrophic events such as thermal runaway.

[0028] The amount of heat that the PCM can absorb without experiencing a temperature increase during its phase change is a function of the latent heat of the material and the amount of the material. These factors (e.g., the type and size of the PCM material) can be configured so that the PCM can absorb and hold enough heat to prevent thermal runaway (or other overheating concerns).

[0029] Also, based on the temperature at which the PCM undergoes a phase change, the type of PCM can be selected. To prevent damage to one or more battery cells, it may be desirable to limit the temperature within the battery sub-module to below a specific predetermined temperature. To establish a temperature upper limit below the specific predetermined temperature, a PCM that undergoes a phase change below that specific predetermined temperature can be used. For example, the critical temperature can be the temperature at which the battery cell is prone to failure, or the temperature at which overheating increases without control. A PCM that undergoes a phase change at a specific temperature below the critical temperature can be selected.

[0030] Figure 8 shows an example of a thermal runaway event. The first curve 850 represents the temperature of a failed battery cell in a conventional battery system that does not include a PCM layer. As the fault occurs, the temperature of the first faulty battery cell rises rapidly, and the temperature rises rapidly to the first peak temperature 870. Due to the temperature spike of the first battery cell, a large amount of heat is dissipated to the battery sub-module and other battery cells. The second curve 851 and the third curve 852 represent the temperatures of two other battery cells in a battery sub-module that may be adjacent to or near the first battery cell. When the first failed battery cell leaks heat, it causes the temperatures of the second and third battery cells to rise. When the second and third battery cells reach a specific critical temperature 860, these battery cells also suffer a fault and experience an uncontrolled temperature spike. As shown by the second curve 851, the temperature of the second failed battery cell rises rapidly as the second fault occurs, and the temperature rises rapidly to the second peak temperature 871. As shown by the third curve 852, the temperature of the third failed battery cell rises rapidly as the third fault occurs, and the temperature rises rapidly to the third peak temperature 872. Due to the time required for heat to dissipate from the first battery cell to the second and third battery cells, there is a time lag between the failure of the first battery cell (indicated by the temperature peak 870) and the failures of the second and third battery cells (indicated by the temperature peaks 871 and 872). This propagation of uncontrolled temperature rise across multiple battery cells is a thermal runaway event. The critical temperature 860 varies depending on the type of battery cell. In this example, the critical temperature 860 is approximately 175 degrees Celsius.

[0031] FIG. 9 shows an example of a thermal runaway event prevented by the PCM in a battery sub-module according to various embodiments. The first curve 950 represents the temperature of the failed battery cell. The temperature of the first failed battery cell rapidly increases as the fault occurs, and the temperature rapidly rises to the first peak temperature 970. As a result of the temperature spike of the first battery cell, a large amount of heat is generated. The excess heat is absorbed by the PCM, thereby preventing the temperature from rising in other battery cells and other areas of the battery sub-module. The PCM can undergo a phase change at a specific phase change temperature 965. As a result, the temperature within the battery sub-module and the temperature of other battery cells outside the failed battery cell may not rise above the phase change temperature 965 (e.g., as long as at least a portion of the PCM has not yet changed phase). Since the phase change temperature 965 is lower than the critical temperature 960 at which other battery cells may fail, the PCM prevents other battery cells from reaching the critical temperature 960 and failing. This is shown by the second curve 951 and the third curve 952 representing the temperatures of two other battery cells within the battery sub-module. The temperatures of these other battery cells may reach the phase change temperature 965, but do not reach the critical temperature 960. As a result, an uncontrolled temperature increase in the second and third battery cells is prevented, and a thermal runaway event is prevented. The critical temperature 960 depends on the type of battery cell, and the phase change temperature 965 depends on the type of PCM. In this example, the critical temperature 960 is approximately 175 degrees Celsius, and the phase change temperature 965 is approximately 130 degrees Celsius.

[0032] As shown in FIG. 3A, the PCM layer 300 can be provided as a heat absorption layer within the battery sub-module 350. In some embodiments, the PCM layer 300 may be provided on top of the container 305 immediately below the lid. For example, the PCM layer 300 can be formed in the form of one or more strips disposed on top of the stack of battery cells and below the cell tabs and interconnections 304. The upper part of the cell has been shown to be a major heat transfer path leading to the propagation of thermal runaway, particularly when a fire is observed. Thus, disposing the PCM layer 300 at the upper part of the battery sub-module 350 prevents ignition that limits the total energy release (e.g., prevents the electrolyte within the battery sub-module from igniting). Also, disposing the PCM layer 300 at the upper part of the battery sub-module 350 suppresses the combustion at the upper part of the battery sub-module 350, which is a secondary heat energy source within the battery sub-module 350.

[0033] When thermal runaway propagation occurs within the battery sub-module, one or more battery cells may break and open at the upper part where the tabs 304 are provided. This location is also the weakest point where the adhesive maintaining the seal of the battery cell is. When the pouch of the battery cell opens, a cloud of electrolyte vaporized at high pressure is released into the battery sub-module. The vaporized electrolyte tends to ignite when the local temperature is too high. Thus, by disposing the PCM layer 300 on top of the battery cells, it becomes possible to maintain a constant temperature at the upper part (and the rest) of the battery sub-module. In the case of thermal runaway propagation or an undesired temperature rise, the PCM layer 300 absorbs heat and locally reduces the temperature. By reducing the temperature at the upper part of the battery sub-module where the exhaust gas accumulates, the PCM layer 300 prevents the exhaust gas from igniting (e.g., the PCM layer 300 prevents combustion).

[0034] In some embodiments, an exemplary battery sub-module can include multiple layers of the PCM 300, such as a bottom layer and a top layer provided within the container 305. A stack of battery cells can be sandwiched between the bottommost PCM layer and the uppermost PCM layer. In some embodiments, the PCM layer can also be formed as a front (and / or back) layer 306 with respect to the stack of battery cells. Alternatively, a stack of battery cells can be wrapped in a pouch of the PCM layer and then inserted into the container 305. In all of these exemplary embodiments, in addition to the heat insulating layer 302 such as an aerogel, the PCM layer 300 can be provided.

[0035] As shown in FIG. 3A, the PCM layer 300 can be formed from a plurality of PCM pieces (e.g., strips). According to various embodiments, the PCM layer 310 can be a continuous layer (e.g., a film-like layer) disposed at a desired position within the container 305 and / or over or around a stack of battery cells, as shown in FIG. 3B. An exemplary PCM layer 310 can include one or more openings 303 (e.g., slots) for receiving the cell tabs and interconnections 304. The PCM layer (300 or 310) can be coupled to the stack of battery cells via any suitable coupling means such as using an adhesive. In some embodiments, the PCM layer(s) can be held in place by the compression provided by the container 305 (and lid).

[0036] If the PCM layer 300 or 310 is in gel form, the PCM layer 300 or 310 can be injected into a desired position within the container 305.

[0037] Figure 4 shows another exemplary embodiment in which the PCM layer 400 is formed as a stacked layer between battery cells. The exemplary battery sub-module 450 shown in Figure 4 includes a plurality of layers stacked in an exemplary order of a PCM layer 400, a battery cell 402, a heat spreader 404, another PCM layer 400, and a thermal insulation layer 406. These layers may be repeated to form the exemplary battery sub-module 450. In this exemplary embodiment, the PCM layer 400 is provided between each pair of battery cells. The PCM layer(s) 400 are provided in addition to the thermal insulation layer(s) 406.

[0038] As described above, the PCM layer 400 functions independently and in a different manner from the thermal insulation layer 406. The thermal insulation layer 406 prevents rapid heat leakage from overheating battery cells, thereby allowing excess heat to dissipate slowly around the entire battery sub-module instead of accumulating in a local area. In contrast, the PCM layer 400 absorbs excess heat. According to various embodiments, the thickness of the PCM layer 400 can be determined based on the latent heat of fusion of the PCM and the amount of energy released from the battery cell(s). The embodiments allow the PCM layer 400 to be thick enough to absorb the energy released during normal operation, overheating, and / or failure of one or more battery cells.

[0039] The heat spreader 404 can receive heat from any contact point with the battery cell 402 and can conduct heat rapidly throughout the heat spreader 404. Since the heat spreader 404 can transfer heat to the PCM layer 400 at an equal transfer rate at each contact point of the PCM spreader, this can functionally increase the contact surface area for transferring heat to the PCM layer 400. As a result, the heat spreader 404 can assist in the rapid transfer of heat from the battery cell 402 to the PCM layer 400. The thermal insulation material 406 can prevent the transfer of heat from one battery cell region to another.

[0040] Embodiments enable the battery sub-module 450 layer to have other configurations. For example, in some embodiments, each battery cell 402 may be in contact with two heat spreaders 404, one on each side of the battery cell 402. Further, a PCM layer 400 can follow each heat spreader 404, and a thermal insulation layer 406 can follow each PCM layer 400, so that each battery cell 402 is sandwiched between two heat spreaders 404, two PCM layers 400, and two thermal insulation layers 406. The layers surrounding the first and last battery cells may be different. For example, there may be no thermal insulation layer 406 at the top or bottom of the battery cell stack.

[0041] In some embodiments, a PCM layer 400 can be used instead of the thermal insulation layer(s) 406. It is also possible to place a PCM layer 400 after a set (e.g., two or more) of battery cells without the need to use a PCM layer 400 between each pair of battery cells. This layering may be made possible by the efficient heat absorption characteristics of the PCM layer 400. This exemplary structure can provide further volume and / or weight savings for a given battery sub-module.

[0042] The PCM layers shown in the exemplary embodiments shown in FIGS. 3A - 4 may be formed from a PCM material or, for example, from a substrate impregnated with an expandable coating.

[0043] For example, exemplary materials for the PCM layer 300 shown in FIGS. 3A - 3B and the PCM layer 400 shown in FIG. 4 can include a phase change ceramic separator. The ceramic separator has an integral hydrate PCM. While the ceramic separator functions as a heat spreader, the PCM may turn into the gas phase.

[0044] In the case of the expandable coating, exemplary materials for the PCM layer 300 may include ceramic paper insulation materials with expandable coatings (e.g., Superwool® EST with IC100 coating). The expandable coating can be applied, for example, to layers of the battery sub-module (e.g., battery cells, insulation layers, etc.). Thus, the layers of the battery sub-module can be impregnated with the expandable coating (PCM). In the case of excessive heat (or fire), the expandable coating changes phase while absorbing heat (e.g., turns into ash). The latent heat of the expandable coating can absorb the initial temperature spike of potential thermal runaway related to the battery cell, while the insulation material prevents the remaining heat from spreading to adjacent cells.

[0045] FIG. 5 shows another exemplary battery sub-module 550 including a liquid PCM layer 500. The stacked cells (e.g., a stack of a repeating pattern of battery cells 502, heat spreaders 504, and insulation layers 506) can be at least partially immersed in the volume of the liquid PCM 500 (e.g., PCM reservoir) within the container 510 that includes the battery sub-module 550. The volume of the liquid PCM should be minimized and only be sufficient to mitigate the impact of a single cell's thermal runaway. In some embodiments, any suitable volume of liquid PCM may be present. For example, the volume of the liquid PCM can be from about 10 milliliters to about 100 milliliters depending on the configuration and size of the battery sub-module 550. The embodiment shown in FIG. 5 can be adjusted based on the performance of the battery sub-module 550 (e.g., the liquid PCM can be added to or removed from the container 510). Since the liquid PCM can contact multiple battery cells and remove heat from multiple battery cells, the same liquid PCM can be useful for multiple scenarios where different battery cells may overheat. The same liquid PCM can be essentially shared among multiple battery cells. As a result, separate portions of the PCM are not required for each battery cell, reducing the total amount of PCM and thereby reducing the weight of the battery sub-module.

[0046] According to an exemplary embodiment, the excess heat released by the intermediate battery cell 512 of the battery sub-module 550 can be dissipated as shown by the heat vector 530 in FIG. 5. While a large amount of heat may be absorbed by the liquid PCM 500, the heat insulating layer 506 also absorbs some of the heat. The heat spreader 504 directs (e.g., dissipates) the excess heat towards the liquid PCM 500 as shown by the heat vector. As shown by the heat vector, a minimal amount of excess heat may still be transferred to the adjacent cell 522.

[0047] In an exemplary battery sub-module 550, PCM can be used to enforce isothermal boundary conditions across the section of the sub-module immersed in the PCM reservoir. When distributed across the sub-module, the PCM can create a fin effect that prioritizes all heat transfer to the PCM. In the case of a solid PCM (such as the exemplary embodiments shown in FIGS. 3A - 4), the PCM layer needs to be continuous (e.g., the strip shown in FIG. 3A may not be ideal), and the material of the PCM layer may need to be highly conductive to achieve a fin effect similar to the PCM reservoir solution (as in the exemplary embodiment shown in FIG. 5).

[0048] According to various embodiments, the container 510 can be hermetically sealed. In embodiments where one or more vent holes are formed in the container 510, the vent hole(s) can be sealed using, for example, weather stripping or airtight tape. When thermal runaway propagation occurs within the sub-module, heat breaks (e.g., melts) the seal of the vent hole, thereby opening the vent hole and releasing the hot gas to the external environment of the external battery sub-module. If the battery sub-module includes a liquid PCM layer as shown in FIG. 5, the seal of the vent hole may last longer because the liquid PCM layer absorbs excess heat. In some embodiments, when the temperature of the sub-module rises above a level that can be accommodated by the liquid PCM layer, the seal may melt and release the hot gas. At that time, the liquid PCM may change to a gas, but it does not cause concern about leakage. For example, the seal material can be selected to have a melting temperature higher than the temperature at which the PCM undergoes a phase change (e.g., vaporization). As long as a part of the PCM undergoes a phase change, the PCM can absorb excess heat from the battery cell without causing a temperature rise or a rise in the temperature of the battery sub-module. When all of the PCM undergoes a phase change (such as vaporization), the PCM temperature and the battery sub-module temperature may rise above the PCM phase change temperature. Then, if the temperature rises until the seal melts, the seal may melt and the hot gas may escape from the battery sub-module.

[0049] Exemplary liquid PCMs can include phase change dielectric liquid materials (e.g., 3M™ Novec™ 7000) that boil at low temperatures, allow for the addition of thermal mass, have low surface tension (good wicking ability), and good compatibility with engineering materials. Exemplary liquid PCMs may also be electrically insulating. In certain embodiments, the liquid PCM can have a low thermal conductivity. Also, according to various embodiments, the gas is intended to be discharged from the battery sub-module, allowing for the disposal of thermal energy. Thus, the material of the liquid PCM should not exhibit a heat of condensation phase. In certain embodiments, the container 510 can include one or more openings for adding additional liquid PCM and / or replacing the discharged PCM. The opening for adding the PCM can have a removable cap and / or can be configured to allow insertion without leaking or venting fluid and gas.

[0050] In some embodiments, a combination of liquid PCM and solid PCM can be utilized within the same battery sub-module.

[0051] In some embodiments, two or more types of PCMs having different phase change temperatures can be included within the same battery sub-module. This can create two different artificial temperature limits within the battery sub-module (a first temperature limit provided by a first type of PCM having a first phase change temperature and a second temperature limit provided by a second type of PCM having a second phase change temperature higher than the first phase change temperature). The two different temperature limits can help to determine the amount of heat released from one or more battery cells and can improve the battery diagnostic and warning system. For example, if a temperature sensor indicates that it has reached and then exceeded the first temperature limit, it can indicate that the first type of PCM has been fully utilized (e.g., all of the first type of PCM has experienced a phase change). This can indicate how much heat has been released and absorbed (e.g., the amount of heat required to cause a complete phase change of the first type of PCM) and can indicate that only one line of defense remains (e.g., the second type of PCM), which can trigger an advanced warning system. Further, using multiple types of PCMs can be a way to control the temperature such that the temperature is within a particular preferred temperature band (e.g., higher than the first temperature limit and lower than the second temperature limit). This can be advantageous since the battery cells may operate more efficiently at slightly higher temperatures. Thus, the temperature limits created by the PCMs can be configured such that the temperature of the sub-module is at or near the temperature optimal for the performance of the battery cells.

[0052] FIG. 6 shows an exemplary flowchart of steps for manufacturing an exemplary battery sub-module having a PCM reservoir, according to various embodiments. In step 602, a battery stack formed from one or more battery cells is inserted into a container, thereby forming a battery sub-module. In some embodiments, the battery sub-module may also include one or more layers of a thermal insulation layer between the battery cells.

[0053] In step S604, an initial amount of the liquid phase change material is added to the container, thereby forming a PCM reservoir within the container. The battery stack can be at least partially immersed within the PCM reservoir. The initial amount of the liquid phase change material can be from about 10 milliliters to about 100 milliliters. The initial amount can be selected such that there is sufficient liquid PCM to provide sufficient emergency cooling in the event of a battery cell failure or other undesirable temperature rise. The initial amount can be determined based on the latent heat of vaporization of the PCM and a predetermined expected voltage output of the battery sub-module.

[0054] In step S606, one or more test methods can be used to test the performance of the battery sub-module in order to evaluate the voltage output of the battery sub-module.

[0055] In step S608, the performance (e.g., voltage output) of the battery sub-module can be compared to a predetermined threshold value.

[0056] In step S608, based on the comparison result, the amount of the liquid phase change material can be adjusted by adding liquid phase change material to the container or removing liquid phase change material from the container. For example, if the tested / measured voltage output is greater than a predetermined threshold value, the battery sub-module may be able to generate more heat. In this case, additional liquid PCM can be added to the container so that the total PCM has an increased heat absorption capacity. If the tested / measured voltage output is less than the predetermined threshold value, the battery sub-module may have a reduced heat generation capacity. In this case, since a reduced heat absorption capacity may be sufficient and it may be advantageous to reduce the weight of the battery sub-module, some liquid PCM can be removed from the container. Once the liquid phase change material reaches the desired level, the container can be hermetically sealed.

[0057] In some embodiments, in step S608, a predetermined amount of the liquid phase change material can be removed or added. Any suitable predetermined amount such as 1 milliliter, 5 milliliters, 10 milliliters, 15 milliliters, 20 milliliters, 25 milliliters, or 30 milliliters can be used. In other embodiments, the amount of the liquid phase change material to be removed or added can be calculated based on the difference between the tested performance and a predetermined threshold.

[0058] Figure 7 shows an exemplary flowchart of steps for manufacturing an exemplary battery sub-module having one or more PCM layers, according to various embodiments. In step S702, a battery stack is formed by stacking one or more battery cells. In some embodiments, the battery stack may also include one or more layers of a thermal insulation layer between the battery cells.

[0059] In step S704, the energy level released from one or more battery cells in the event of a battery failure is calculated. The calculation can be performed for the failure of one battery cell, two battery cells, all battery cells, or any other suitable number of battery cells. The calculation can be based on certain characteristics and configurations of the one or more battery cells, such as the total amount of energy stored in the one or more battery cells and the maximum voltage output of the one or more battery cells. In some embodiments, the calculation can include measuring the energy released during a battery failure test.

[0060] In step S706, the thickness of the one or more phase change material layers is determined based on the calculated energy level released from the battery stack in case of a failure and one or more properties of the phase change material. For example, the latent heat of fusion of the phase change material, which represents how much thermal energy is absorbed during the melting process of the phase change material, can be used to determine the thickness of the one or more phase change materials. The thickness can be configured such that a sufficient amount of the phase change material is included. In some embodiments, it may be desirable to include an amount of phase change material sufficient to absorb the amount of energy released when one battery cell fails, when two battery cells fail, when all battery cells fail, or when any other appropriate number of battery cells fail. In some embodiments, the amount of the phase change material can be set to sufficiently absorb the energy released during battery failure so as to prevent thermal runaway. This may be less than the total amount of energy released during battery cell failure because some thermal energy may dissipate and some temperature rise within the battery sub-module may be tolerated.

[0061] In step S708, the one or more phase change material layers are inserted into the battery stack. The thickness of the one or more phase change material layers can be the amount determined in step S706. For example, the one or more phase change material layers can be inserted between one or more battery cells. The one or more phase change material layers may also be added to the bottom, top, or side of the battery stack. In some embodiments, the battery stack can be encapsulated (e.g., thereby encapsulated) in the one or more phase change material layers. In some embodiments, steps S702 and S708 may be performed simultaneously such that the phase change material layer is added during the process of stacking one or more battery cells.

[0062] In step S710, the battery stack and the phase material layer can be inserted into a container, thereby forming a battery sub-module.

[0063] Embodiments provide a PCM layer that absorbs excess heat within a battery sub-module while occupying a minimal volume, especially when compared to conventional thermal insulation materials. This property is particularly important for batteries used in aircraft (e.g., electric aircraft). Electric aircraft can be subject to strict volume and weight constraints. By using a PCM layer instead of conventional thermal insulation materials, the volume and weight constraints can be efficiently met.

[0064] The present invention has been described with reference to specific embodiments, but those skilled in the art who have access to this disclosure will understand that variations and modifications are possible. The battery sub-modules described herein can include any number of battery cells, and the systems and processes can be adapted to cells implemented using various battery technologies.

[0065] It should be understood that all numerical values used herein are for illustrative purposes and can be changed. In some cases, ranges are specified to give a sense of scale, but numerical values outside the disclosed ranges are not necessarily excluded.

[0066] Also, it should be understood that all the figures in this specification are intended to be schematic. Unless otherwise specified, the drawings do not mean a specific physical arrangement of the elements shown therein, or that all the elements shown are necessary. Those skilled in the art who have access to this disclosure will understand that the elements shown in the drawings, or the elements described in this disclosure, can be changed or omitted, and other elements not illustrated or described can be added.

[0067] The above description is illustrative and not restrictive. Many variations of the present invention will be apparent to those skilled in the art upon considering this disclosure. Accordingly, the scope of patent protection should not be determined with reference to the above description, but instead should be determined with reference to the following claims, along with their full scope or equivalents.

Claims

1. A container; a battery stack formed from one or more battery cells disposed within the container; a phase change material provided within the container, the phase change material configured to absorb heat dissipated from the battery stack; and one or more thermal insulation layers stacked with the one or more battery cells; Equipped with A battery sub-module, wherein the phase change material includes one or more solid layers of phase change material stacked with the one or more battery cells, the one or more solid layers of phase change material being provided between the one or more battery cells.

2. The battery submodule of claim 1 , wherein the one or more thermal insulation layers comprise aerogel.

3. The battery sub-module further includes a plurality of heat spreaders provided within the container; each of the one or more battery cells is positioned adjacent a respective first heat spreader from a plurality of heat spreaders on a first side of the battery cell and adjacent a respective second heat spreader from a plurality of heat spreaders on a second side of the battery cell; The battery sub-module of claim 1 , wherein the plurality of heat spreaders are positioned adjacent to respective layers of solid phase change material from the one or more layers of solid phase change material.

4. The battery sub-module of claim 3 , wherein the one or more solid phase change material layers are located adjacent to a respective insulation layer from the one or more insulation layers.

6. The battery sub-module of claim 1 , wherein the phase change material comprises a quantity of a liquid phase change material provided within the container, the battery stack being at least partially immersed in the liquid phase change material.

7. The battery sub-module of claim 6 , wherein the predetermined amount of the liquid phase change material is between about 1 milliliter and about 30 milliliters.

8. 7. The battery submodule of claim 6, wherein the solid layer of phase change material has a first phase change temperature and the liquid phase change material has a second phase change temperature, the first phase change temperature being different from the second phase change temperature.

9. The battery sub-module of claim 1 , wherein the battery stack is impregnated with the phase change material.

10. The battery sub-module of claim 1 , wherein the phase change material comprises an expandable coating.

11. The battery sub-module of claim 1 , wherein the container is configured to compress the battery stack and the phase change material within the container.

12. 2. The battery submodule of claim 1, wherein a first characteristic of the phase change material is a phase change temperature and a second characteristic of the battery submodule is a critical temperature at which the battery submodule experiences thermal runaway, the phase change temperature being lower than the critical temperature.

13. The phase change material is a first continuous layer disposed on an outer top surface of the battery stack and in contact with each of the one or more battery cells; a second continuous layer disposed on an outer bottom surface of the battery stack and contacting each of the one or more battery cells; a third continuous layer disposed on a first outer side of the cell stack; and a fourth continuous layer disposed on a second outer side of the cell stack; and 2. The battery sub-module of claim 1, wherein each of the one or more battery cells is located between the third successive layer and the fourth successive layer.

14. The phase change material is a fifth layer disposed on a third side of the battery stack; and a sixth layer disposed on a fourth side of the battery stack; The battery sub-module of claim 13 , comprising:

15. the first layer completely covers an outer top surface of the battery stack; the second layer completely covers a bottom exterior surface of the battery stack; The battery sub-module of claim 13 , wherein the battery stack is encapsulated by the solid phase change material layer.

16. the first layer being a first thin film layer located between a first wall of the container and an outer top surface of the battery stack; 14. The battery submodule of claim 13, wherein the second layer is a second thin film layer located between a second wall of the container and an outer bottom surface of the battery stack.

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