Battery Immersion Cooling with Controllable Dielectric Boiling Point and Passive Thermal Runaway Protection

Abstract

The present invention relates to battery immersion cooling of a battery cell by vaporization of a dielectric liquid due to nucleate boiling or the like. The boiling point of the liquid can be adjusted by controlling the pressure to which the dielectric liquid is exposed. The amount of the liquid dielectric material is selected to absorb the complete reaction energy of the electrically parallel cells in the case of thermal runaway, thereby not causing propagation, flame or explosion.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 334,848, filed Apr. 26, 2022, which is hereby incorporated by reference in its entirety.

[0002] The present invention relates to battery immersion cooling of lithium - ion battery cells. More particularly, aspects of the present invention relate to battery immersion cooling systems and methods for battery module thermal control and passive prevention of thermal runaway.

Background Art

[0003] The demand for alternative environmentally friendly power sources for power machinery and equipment has been increasing rapidly. In particular, in contrast to more conventional power generation means such as the combustion of fossil fuels, there is a growing demand for machines that rely on battery systems to supply power for operation. The increasing popularity of electric vehicles and other machines that were conventionally powered by internal combustion engines is evident, but many other types of vehicles that already use electric propulsion systems still rely on fossil fuel generators to supply the electricity required for their propulsion systems and other operating systems. These vehicles include cargo ships, ferries, aircraft, mining equipment, airport ground service equipment, hyperloop pods, and locomotives. In addition to transportation applications, battery - driven electric systems can currently be used in many off - grid applications that rely on fossil fuel power generation or inconsistent clean energy sources such as sunlight and wind.

[0004] Lithium-ion battery cells are currently preferred for many power storage applications. However, the safety concerns associated with the use of these cells are well known, and steps must be taken to ensure the safe operation of large-scale battery systems that use lithium-ion battery cells. One particular operational safety concern associated with the use of lithium-ion battery cells is thermal energy management. Lithium-ion cells tend to release a significant amount of heat during normal cell operation. This heat generation needs to be managed, and system design needs to consider appropriate cooling and / or heat dissipation so that the battery cells can operate efficiently and safely.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Currently, air cooling systems are used to transfer heat from battery cells. However, there is a limit to the amount of heat that can be transferred from the battery cells in this way. Therefore, the heat transfer capacity is often a limiting feature in the construction of battery modules. Furthermore, due to the limitations of using air cooling, battery modules often have to employ other structures and systems, including the use of heat barriers, to avoid the propagation of adverse heat events associated with battery cells. Therefore, there is a need for an efficient battery module cooling system that has a high heat transfer capacity and also provides mitigation of heat event propagation without the need for additional heat barriers.

Means for Solving the Problems

[0006] Broadly speaking, the present invention relates to a battery immersion / liquid cooling system and method for removing heat from battery cells using a boiling liquid dielectric material.

[0007] More specifically, in some embodiments, the battery module includes a battery module housing that houses a plurality of battery cells immersed in a liquid dielectric material contained in a liquid reservoir, the liquid dielectric material having a boiling point of less than 75°C at 1 atmosphere, and during operation, the plurality of battery cells generate thermal energy transferred to the liquid dielectric material, thereby vaporizing at least a portion of the liquid dielectric material, and the battery module includes one or more heat exchange devices configured to condense the dielectric material by removing heat from the vaporized dielectric material and return it to the liquid reservoir. In certain embodiments, the battery module includes a perforated screen, and the screen is horizontally positioned within the upper half of the battery module housing so as to form a headspace above the liquid reservoir. In a preferred embodiment, the one or more heat exchange devices include a heat sink and / or are passive.

[0008] In other embodiments, the battery module includes a battery module housing that houses a plurality of battery cells immersed in a liquid dielectric material contained in a liquid reservoir, the liquid dielectric material having a boiling point of less than 75°C at 1 atmosphere, and during operation, the plurality of battery cells generate thermal energy transferred to the liquid dielectric material, thereby vaporizing at least a portion of the liquid dielectric material, and the battery module includes a pressure control device operable to control the pressure within the battery module housing to which the liquid dielectric material is exposed, the pressure control device including a compressor configured to increase or decrease the pressure within the housing, the compressor being connected to the housing via a conduit circuit including at least one control valve, the at least one control valve being switchable between a first mode in which the compressor decreases the pressure within the housing and a second mode in which the compressor increases the pressure within the housing, and the operation of the compressor and the at least one control valve being controlled by a battery management system.

[0009] In another embodiment, a method for preventing propagation, flame, or explosion within a battery module is provided. The method includes selecting the amount of liquid dielectric material to be present within the battery module housing based on the latent heat of vaporization of the liquid dielectric material such that during thermal runaway, the amount of liquid dielectric material can absorb the complete reaction energy of the battery cell.

Brief Description of the Drawings

[0010]

Figure 1A

Figure 1B

Figure 1C

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5A

Figure 5B

Modes for Carrying Out the Invention

[0011] The present invention relates to a battery immersion cooling system and method for thermal control of a battery module. The battery immersion cooling system and method generally use a liquid dielectric material to transfer heat from a plurality of battery cells, also generally referred to as a battery module. In a preferred embodiment, the battery cells are immersed in the liquid dielectric material, and the liquid dielectric material extracts heat from the battery cells by surrounding the battery cells and utilizing the latent heat of the vaporization characteristics of the liquid dielectric material.

[0012] This can be more easily understood with reference to the drawings. FIG. 1 is a schematic diagram of a battery immersion cooling system according to three different embodiments of the present invention. Referring first to FIG. 1A, the battery immersion cooling system 10 is configured as a tank nucleate boiling system 20. The tank nucleate boiling system 20 generally includes a battery module housing 22 and a heat sink and / or heat exchanger 24 that can be located on the upper surface of the battery module housing 22. The battery module housing 22 generally surrounds one or more battery cells 26 and a liquid dielectric material 28. The portion of the housing 22 that houses the cells 26 and the liquid dielectric material 28 is also referred to as a liquid reservoir 29. The one or more battery cells 26 may be oriented within the battery module housing 22 in any manner suitable for a particular form of the battery cell. In a preferred embodiment, the battery cells 26 are immersed in the liquid dielectric material 28 (i.e., completely surrounded by the liquid dielectric material).

[0013] In other embodiments, the battery module housing 22 includes one or more current collectors 32 and a perforated screen 34. One or more current collectors 32 attached to the electrodes on each battery cell 26 collect the current generated at the electrodes and connect to an external circuit, such as a terminal, not shown in this embodiment. In a preferred embodiment, the perforated screen 34 is positioned above the upper half of the battery module housing 22 and may form a headspace 36. As will be appreciated by those skilled in the art, the perforated screen 34 allows the gas 30 generated by the heat of one or more battery modules 26 to enter the headspace while stopping the ejecta, which is a common problem in the art, and damping the tilting phenomenon during normal operation. Due to the generation of this gas 30, in a preferred embodiment, the battery module housing 22 has a large expansion volume (i.e., the headspace 36) and can withstand the high pressure resulting from the generation of vapor from the liquid dielectric material 28.

[0014] To cool the battery cells 26, the tank nucleate boiling system 20 facilitates a cryogenic evaporation process that uses the latent heat of the liquid dielectric material 28 to transfer heat away from the cells 26. As described above, the battery cells 26 are initially directly immersed in the liquid dielectric material 28, which is at room temperature. When the battery cells 26 generate heat at a temperature sufficient to raise the temperature of the liquid dielectric material 28 to its boiling point (latent heat) or near it and convert the liquid dielectric material 28 into vapor 30 (sensible heat), the material evaporates and extracts heat from the battery cells 26. When a perforated screen 34 is used, the generated gas 30 passes through the screen 34 and enters the headspace 36 above the cells 26 before reaching the heat sink 24. The gas 30 is cooled by the heat sink 24, which provides a surface for the condensation of the vapor to be generated. After the gas 30 is cooled, the condensate 30 falls to the portion of the battery module housing 22 that houses the cells 26. Thereby, a cooling cycle is established.

[0015] The liquid dielectric material may be any non-conductive fluid that can remove heat from a battery cell or battery module having a high dielectric strength, such as a fluorinated fluid. As will be appreciated by those skilled in the art, a non-conductive fluid having a high dielectric strength reduces the need for electrical insulation and allows the fluid to contact the battery cell, printed circuit board, etc. These properties help prevent clearance (i.e., the shortest distance in air between two conductive components) / creepage distance (i.e., the shortest distance along the surface of an insulating material to another conductive component) problems such as arc discharge due to densely packed conductive components. In a preferred embodiment, the liquid dielectric material is non-corrosive (supporting stable and reliable battery performance and reducing maintenance costs), chemically and thermally stable (functioning consistently over the life of the system (from about -40°C to about 85°C)), non-flammable and incombustible (helping to increase the safety margin), and / or may have other desirable properties such as low viscosity (reducing the required pump power and increasing the formation of turbulent flow). The liquid dielectric material has a boiling point range of about 0°C to about 60°C, preferably about 30°C to about 50°C. In a preferred embodiment, the liquid dielectric material has a boiling point that matches or is close to the desired maximum operating temperature of the battery cell. The liquid dielectric material also has a 100-year time horizon global warming potential (GWP) of less than about 500, less than 250, less than 100, less than 50, less than 25, less than 10, or less than 1. In some preferred embodiments, the liquid dielectric material is 3M NOVEC 7000 Engineered Fluid (known as methyl perfluoropropyl ether or 1-methoxyheptafluoropropane). In other preferred embodiments, the liquid dielectric material is 3M NOVEC 649 Engineered Fluid (known as 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone).

[0016] As will be appreciated by those skilled in the art, embodiments of the tank nucleate boiling system are self - contained systems, i.e., systems that do not include piping or pumps and do not use forced convection to enhance heat transfer. Further, since the system does not use pumps, embodiments of the tank nucleate boiling system are passive systems that do not require an input of energy from an external source for recirculation operations.

[0017] In one or more embodiments, in the case of thermal runaway of a battery cell, the reaction energy of a complete battery cell (or cell) can be absorbed by the latent heat of vaporization of the liquid dielectric material, resulting in the complete attenuation of propagation and of flames and flame formation. As used herein, the term "thermal runaway" refers to an event in which the temperature within a battery cell suddenly rises, causing a chain reaction within the cell that releases more heat and triggers further chemical reactions. The gas generated by the vaporization of the dielectric fluid is then vented from the battery module housing, preferably at the location of the burst disk 102 (Figure 3). In a preferred embodiment, when the battery module has a number of battery cells (n p ) electrically connected in parallel, the selection of the amount of liquid dielectric material is made according to Equation 1: M>np*(E / he)*S (1) (where M = mass of the liquid dielectric material (kg); h e = latent heat of vaporization of the liquid dielectric material (J / kg); E = cell reaction energy (J); n p = number of electrically parallel battery cells; S = 2 = safety factor at 200% cell overcharge).

[0018] Referring to FIG. 1B, the battery immersion cooling system 10 is configured as a thermosiphon circuit 40 which is also a passive system. The thermosiphon circuit 40 generally includes a battery module housing 42, a heat sink and / or heat exchanger 44, a pressure control device (not shown), and at least two conduits 46, 50 interconnecting the heat sink 44 with the battery module housing 42. The battery module housing 42 of the thermosiphon circuit 40 can be configured similarly to the battery module housing 22 of the tank nucleate boiling system 20 of FIG. 1A (i.e., a plurality of battery cells 43, a liquid dielectric material 54, a gas 56, a current collector 57, a perforated screen 58, and a head space 59). In a preferred embodiment, the battery module housing 42 further includes a perforated screen. However, the conduits 46, 50 interconnect the housing 42 with the heat sink 44.

[0019] To cool the battery cells 53 like the tank nucleate boiling system 20, the thermosiphon circuit 40 facilitates a cryogenic evaporation process that uses the latent heat of the liquid dielectric material 54 to transfer heat from the cells 53 through the generation of vapor from the liquid dielectric material 54. However, in the thermosiphon system 40, the vapor 56 is drawn towards the heat sink and / or heat exchanger 44 where the gas 56 condenses and is reintroduced into the battery module housing 42, creating a siphon-like effect. In the illustrated embodiment, the vapor 56 travels through one pipe 46, contacts the heat sink 44 and condenses, and returns under gravity through a second conduit 50 to the battery module housing 42.

[0020] The circuit 40 is sensitive to changes in the orientation of the battery module such as tilting and rotation, but as will be appreciated by those skilled in the art, the thermosiphon circuit 40 does not include a pump and does not require an additional expansion tank. Further, the thermosiphon circuit 40 utilizes low forced convection to facilitate fluid circulation and heat transfer.

[0021] Referring to FIG. 1C, the battery immersion cooling system 10 is configured as a forced flow circuit 60 that is much less dependent on the use of latent heat (due to the limitation of expansion) compared to the embodiments of FIGS. 1A and 1B. The forced flow circuit 60 generally includes a battery module housing 62, a heat sink and / or heat exchanger 64, a pressure control device (not shown), conduits 66, 70, and a pump 74. The battery module housing 62 generally encloses one or more battery cells 78 and a liquid dielectric material 80. In a preferred embodiment, the battery cells 78 are immersed in the liquid dielectric material 80. In other embodiments, the battery module housing 62 further includes one or more current collectors 84 or a perforated screen, preferably a perforated screen. In a preferred embodiment, the circuit may also include an accumulator tank 76 that smooths the fluid flow and reduces the on / off cycle of the pump 74 by reducing pressure and flow fluctuations between the pump 74 and the housing 62 within the forced flow circuit system 60.

[0022] To cool the battery cells 78, the forced flow circuit 60 uses a pump to circulate the liquid dielectric material 80, thereby transferring heat from the cells 78. Evaporation 82 of the liquid dielectric material 80 generally occurs only in the case of local overheating of a particular cell 78 (i.e., subcooled nucleate boiling). In these embodiments, the vapor 82 is conducted by circulating the liquid dielectric material 80 using the pump 74. The gas 82 contacts the heat sink and / or heat exchanger 64 and recondenses.

[0023] The circuit 60 utilizes a pump and pipes, but as will be appreciated by those skilled in the art, the forced flow circuit system 60 can utilize high forced convection as a method of promoting heat transfer. This embodiment shows an active system since it uses a pump. Further, there is a significant increase in the local heat transfer coefficient (HTC) due to boiling, which results in a more uniform temperature due to "selective" cooling.

[0024] Figures 2 and 3 show the tank nucleate boiling system 20 in more detail. Specifically, FIG. 2A shows a schematic side cross-sectional view of a tank nucleate boiling system 20 according to an embodiment of the present invention. In the illustrated embodiment, the battery module housing 22 further encloses a module control board (MCB) 86, one or more compression pads 88, and one or more current collectors 90. As shown, the battery cells 26 are directly immersed in the liquid dielectric material 28. The module control board 86 may be located anywhere within the battery module housing 22, preferably near one of the ends of the battery module housing 22. As shown, one or more compression pads 88 that help hold the battery cells in place are located between the battery modules having four battery cells, although this is not necessarily the case.

[0025] FIG. 2B is a schematic top cross-sectional view of a tank nucleate boiling system 20 according to an embodiment of the present invention. In the illustrated embodiment, the battery module housing further encloses a plurality of fins 92 disposed preferably on the top surface of the battery module housing 22. These fins 92 increase the amount of surface area on the top surface of the housing 22 and allow for greater heat transfer between the vapor and the heat sink.

[0026] Figure 3 is a schematic side cross-sectional view of a tank nucleate boiling system 20 according to an embodiment of the present invention. In the illustrated embodiment, the battery module housing 22 may also include a module pan 94 and a module cover 96, which may be bolted 97 to each other to form a tightly sealed housing. For easy access to the terminals 98, 100, the module pan 94 may include two or more holes as shown. For safety, a burst disk 102 may be disposed within the module pan 94 of the battery module housing 22, and a pressure relief valve 104 may be disposed within the module cover 96 of the battery module housing 22. The battery module housing 22 may also further surround one or more compression plates 106 and one or more rods 108 positioned to hold the battery cells 26 in place. When rods are used, the rods 108 may be positioned on the upper surface of one or more battery modules 26 to prevent the cells 26 from shifting within the battery module housing 22. When a second rod 108 is used, that rod may be positioned on the bottom surface of one or more battery modules 26.

[0027] Figure 4 is a schematic side cross-sectional view of a tank nucleate boiling system according to an embodiment of the present invention. In the illustrated embodiment, the tank nucleate boiling system 20 further includes conduits 110, 112, shut-off valves 114, 116, a filter 118, a pressure control device (not shown), an electric compressor 120, and a tank / gas reservoir 122. The battery module housing 22 generally encloses one or more battery cells 26 and a liquid dielectric material 28 having a preferably low GWP and / or a boiling point range of about 40°C to 50°C (e.g., 3M NOVEC 649, Solvay Galden PFPE, or Opteon SF10).

[0028] To cool the battery cell 26, the illustrated embodiment of the tank core system 20 controls the pressure within the headspace 36 to adjust the boiling point of the liquid dielectric material 28. By controlling the temperature at which the liquid dielectric material 28 vaporizes, the rate of heat transfer from the cell 26 can be controlled. For example, in a preferred embodiment, a pressure control device may be used to control the pressure within the battery module housing 22. In other preferred embodiments, the pressure control device may comprise an electric compressor 120, and this electric compressor 120 may be used to reduce (i.e., evacuate) the pressure within the battery module housing 22. This reduction in pressure causes the liquid dielectric material to boil at a lower temperature. Thus, the heat transfer from the cell 26 (through latent heat transfer) may be affected at a lower temperature. Alternatively, the compressor 120 may be used to increase the pressure within the headspace 36, thereby causing the dielectric material 28 to vaporize at a higher temperature. A battery management system (not shown) can be used to control the operation of the compressor 120 and the valves 114, 116 according to the specific requirements of the system 20.

[0029] FIG. 5 shows a battery immersion cooling system according to a complete rack embodiment of the present invention. Referring to FIGS. 5A and 5B, the complete rack system 124 includes a cabinet 126 and a tightly sealed door 128 that prevents the liquid dielectric material 130 from leaking out of the system 124. Referring to FIG. 5B, the cabinet 126 preferably includes one or more racks 132 that can house one or more battery modules 134, and optionally a module control board 136 and / or a string control board (SCB) 138. In the illustrated embodiment, the battery modules 134 may be housed in each rack 132, but this is not necessarily the case. Similar to the single module embodiment, the battery cells 134 are immersed in the liquid dielectric material 130. The cabinet 126 may further include a fill valve 140, a burst disk 142, and a bleed valve 144. A heat sink and / or heat exchanger 146 can be positioned on the upper surface of the cabinet 126.

[0030] To cool the battery cell 134, the complete rack system 124 facilitates a cryogenic evaporation process, such as in a single module embodiment.

[0031] Further advantages of various embodiments of the present invention will be apparent to those skilled in the art upon consideration of the disclosure herein and the following examples. It is to be understood that the various embodiments described herein are not necessarily mutually exclusive unless otherwise indicated herein. For example, features described or depicted in one embodiment may be included in other embodiments, but not necessarily included. Thus, the present invention encompasses various combinations and / or integrations of the specific embodiments described herein.

[0032] As used herein, the phrase "and / or" when used in a list of two or more items means that any one of the listed items can be used alone or any combination of two or more of the listed items can be used. For example, if a composition is described as containing or excluding components A, B, and / or C, the composition can contain or exclude A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C.

[0033] As used herein, the term "battery module" refers to an assembly of two or more battery cells. The battery cells within a battery module may be connected in series, in parallel, or there may be cells connected in series and cells connected in parallel within the same module.

[0034] As used herein, the term "battery cell" refers to an electrochemical cell capable of generating electrical energy from a chemical reaction. The battery cell may be an electrolytic cell in which a cathode and an anode are separated by an electrolyte. An exemplary battery cell for use with the present invention is a lithium-ion battery cell. There are many types of electrolytes that can be used in lithium-ion battery cells, including, but not limited to, mixtures of organic carbonates such as ethylene carbonate or diethyl carbonate containing lithium-ion complexes. These non-aqueous electrolytes generally use non-coordinating anion salts such as lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate monohydrate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), and lithium triflate (LiCF 3 SO 3 ). Note that many of the concepts of the present invention described herein may also be applicable to other electrochemical devices and energy storage devices other than those based on battery cells, including lithium-ion capacitors and supercapacitors. For convenience, all such non-battery devices are included within the term "battery cell" as used herein.

[0035] This specification also uses numerical ranges to quantify certain parameters relating to various embodiments of the present invention. When a numerical range is provided, it should be understood that such a range is to be interpreted as providing literal support for claims that limit only the lower limit of the range and claims that limit only the upper limit of the range. For example, the disclosed numerical range of about 10 to about 100 literally supports claims that recite "greater than about 10" (no upper limit) and claims that recite "less than about 100" (no lower limit).

Claims

1. A battery module housing having a plurality of battery cells housed therein that are immersed in a liquid dielectric material contained in a liquid reservoir.

1. A battery module comprising: the liquid dielectric material having a boiling point of less than 75° C. at 1 atmosphere; During operation, the plurality of battery cells generate thermal energy that is transferred to the liquid dielectric material, thereby vaporizing at least a portion of the liquid dielectric material; The battery module includes one or more heat exchange devices configured to remove heat from the vaporized dielectric material to cause the dielectric material to condense and return to the liquid reservoir.

2. 10. The battery module of claim 1, wherein the one or more heat exchange devices comprise a heat sink having a plurality of fins configured to contact the vaporized dielectric material.

3. 10. The battery module of claim 1, wherein the battery module comprises a perforated screen, the screen positioned horizontally within an upper half of the battery module housing, thereby forming a headspace above the liquid reservoir.

4. 10. The battery module of claim 1, wherein the liquid dielectric material is an inert, non-conductive fluid having a dielectric constant of 25 or less.

5. The battery module of claim 1 , wherein the liquid dielectric material comprises a fluorinated alkyl ether.

6. The battery module according to claim 5 , wherein the fluorinated alkyl ether is methyl perfluoropropyl ether.

7. 10. The battery module of claim 1, wherein the liquid dielectric material is provided in an amount capable of absorbing the complete reaction energy of the battery cells during a thermal runaway.

8. The battery module of claim 1 , wherein the one or more heat exchange devices are passive cooling devices.

9. The battery module of claim 1 , wherein the one or more heat exchange devices comprise a pump configured to circulate the liquid dielectric material within the liquid reservoir.

10. The battery module of claim 1 , wherein the battery module housing further comprises a cabinet having one or more racks configured to receive the plurality of battery cells.

11. 2. The battery module of claim 1, wherein the battery module comprises at least one conduit interconnecting the housing with the one or more heat exchange devices, through which vaporized dielectric material released from the liquid reservoir is conducted, and wherein the battery module comprises at least one other conduit configured to conduct condensed dielectric material from the one or more heat exchange devices to the liquid reservoir.

12. The battery module of claim 1 , further comprising a pressure control device operable to control a pressure within the battery module housing to which the liquid dielectric material is exposed.

13. 13. The battery module of claim 12, wherein the pressure control device comprises a compressor configured to increase or decrease the pressure in the housing, the compressor connected to the housing via a conduit circuit including at least one control valve, the at least one control valve being switchable between a first configuration in which the compressor decreases the pressure in the housing and a second configuration in which the compressor increases the pressure in the housing.

14. The battery module of claim 13 , wherein operation of the compressor and the at least one control valve is controlled by a battery management system.

15. A battery module housing having a plurality of battery cells housed therein that are immersed in a liquid dielectric material contained in a liquid reservoir. The liquid dielectric material has a boiling point of less than 75° C. at one atmosphere; During operation, the plurality of battery cells generate thermal energy that is transferred to the liquid dielectric material, thereby vaporizing at least a portion of the liquid dielectric material; the battery module comprises a pressure control device operable to control a pressure within the battery module housing to which the liquid dielectric material is exposed, the pressure control device comprising a compressor configured to increase or decrease a pressure within the housing, the compressor being connected to the housing via a conduit circuit comprising at least one control valve; the at least one control valve is switchable between a first configuration in which the compressor reduces pressure in the housing and a second configuration in which the compressor increases pressure in the housing; The battery module, wherein operation of the compressor and the at least one control valve is controlled by a battery management system.

16. 20. A method for preventing spread, fire, or explosion in a battery module as described in claim 1 or 15, comprising selecting an amount of liquid dielectric material to be present in the battery module housing based on the latent heat of vaporization of the liquid dielectric material such that the amount of liquid dielectric material can absorb the complete reaction energy of the battery cells during thermal runaway.

17. The method of claim 16 , wherein the plurality of battery cells are electrically connected in parallel.

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