WO2025221504A1

WO2025221504A1 - Batteries and systems for testing batteries

Info

Publication number: WO2025221504A1
Application number: PCT/US2025/023581
Authority: WO
Inventors: John Paul Vance; Phillip Partin; Noah S. Podolefsky; LINNA, Jr
Original assignee: Viridi Parente Inc
Current assignee: Viridi Parente Inc
Priority date: 2024-04-19
Filing date: 2025-04-08
Publication date: 2025-10-23
Anticipated expiration: 2026-10-19

Abstract

Systems and methods are provided for testing and/or validating anti-propagation systems designed to mitigate a thermal runaway condition in lithium-ion batteries. A system comprises a first temperature sensor for detecting a temperature of a trigger battery cell within the battery module and a heater removably couplable to a substantially central portion of the trigger cell and configured to heat the trigger cell to a threshold temperature. The system further comprises a second temperature sensor for detecting a temperature of a test battery cell adjacent to the trigger cell within the battery module. The trigger cell undergoes a thermal runaway condition upon reaching the threshold temperature. The system may further comprise a controller for controlling the rate of heating of the trigger cell. The system ensures that the trigger cell will breach via the pressure release valve or cell vent after reaching the threshold temperature.

Description

BATTERIES AND SYSTEMS FOR TESTING BATTERIES

TECHNICAL FIELD

[0001] This description generally relates to batteries and battery testing and more particularly to systems and methods for testing and/or validating anti-propagation systems designed to mitigate a thermal runaway condition in lithium-ion batteries.

BACKGROUND

[0002] Lithium-ion batteries (LIBs) are considered to be one of the most promising energy sources for many applications, such as energy storage and electric vehicles, owing to their high efficiency, high energy density, and long-life cycle. However, with the increase in cell capacity packaged within a given volume, there is an increased risk associated with thermal runaway in such batteries. Thermal runaway is an uncontrollable exothermic reaction that can occur within lithium-ion batteries when damaged or short circuited, resulting in a rapid release of heat. Thermal runaway occurs when an individual battery cell has reached a temperature at which the temperature will continue to increase on its own and thus becomes self-sustaining as the battery cell creates oxygen to feed the fire.

[0003] Thermal runaway reactions occurring in LIB cells often lead to gas-phase reactions involving volatile des like hydrocarbons and generate additional heat resulting in the propagation of thermal failure. If the temperature of a LIB cell reaches the onset temperature for thermal runaway, usually around 160°C, exothermic reactions such as SEI layer decomposition, reduction of metal-oxide electrode material, and electrolyte decomposition occur. This results in abrupt increase of cell temperature, generation of internal volatile gases and pressure build-up within the cell. When the temperature of the released gas reaches its autoignition temperature, exothermal reactions happen

[0004] During thermal runaway, the battery can rapidly reach temperatures greater than 700°C. This heating breaks down the materials in the battery into a mixture of toxic and flammable gases. These gases could ignite and result in flames or explosion. Moreover, the heat released by the battery can propagate to adjacent batteries, resulting in a chain reaction. Systems including large stacks of batteries can suffer from a catastrophic cascade, resulting in considerable damage, pollution and potentially loss of life. [0005] With the proliferation of lithium-ion batteries, various anti-propagation systems are in development to safeguard against thermal runaway. Such systems must be tested in a controlled environment with a methodology conforming to specific regulatory standards to ensure their efficacy and reliability before a battery product can be released to the public. One of the common tests within the industry to trigger thermal runaway is using an external heater. In this test, a single battery cell is heated until the cell safety separator fails creating a short circuit between the anode and cathode that induces a thermal runaway event in the cell. By inducing the abnormal heating of the battery, the effect of a thermal runaway event on the battery system can be assessed. The thermal propagation process is verified by measuring each cell’s voltage and temperature as heat from the thermal runaway event propagates to nearby cells. Another method to induce thermal runaway is nail penetration which involves puncturing the cell with a conductive object such as a sharp nail. Once the outer cell casing is punctured the conductive nail will create a short circuit between one or more layers of the cathode and anode.

[0006] Since thermal propagation testing of batteries is a destructive test, it is difficult to perform repeatedly from a cost standpoint. This necessitates the use of a data logger that can reliably acquire all necessary data during a single test. In addition, current testing imposes risks associated with contingencies such as the heating and possible combustion of the battery, making it necessary to take steps to ensure the safety of the test personnel. Moreover, it is unusual for an event like nail penetration to occur in normal operation as it is much more likely that thermal runaway will initiate due to overheating or overcharging of the battery cell. Therefore, nail penetration tests may not adequately simulate real-life thermal runaway conditions to properly validate anti-propagation systems.

[0007] It would therefore be desirable to provide improved testing systems and methods for anti-propagation systems in lithium-ion batteries. It would be particularly desirable to provide systems and methods for testing batteries that simulate realistic thermal runaway conditions within these batteries to help ensure the safety and reliability of lithium- ion battery modules.

SUMMARY

[0008] Systems and methods are provided for testing and/or validating antipropagation systems designed to mitigate a thermal runaway condition in lithium-ion batteries. Lithium-ion batteries are also provided that include such anti-propagation systems. [0009] In one aspect, a system for testing a battery module comprising a plurality of battery cells is provided. The system comprises a heater configured for coupling to a substantially central portion of a trigger battery cell within the battery module to heat the trigger battery cell to a threshold temperature, and a first temperature sensor configured for monitoring the temperature of the trigger battery cell. The system further comprises a second temperature sensor for detecting a temperature of a test battery cell adjacent to the trigger battery cell. The trigger battery cell undergoes a thermal runaway condition upon reaching the threshold temperature, which is at least about 100°C, or at least about 125°C, or at least about 150°C, or at least about 250°C.

[0010] In various embodiments, the trigger battery cell has a main body with first and second ends and the heater is configured to be spaced from the first and second ends such that heat is applied primarily to the central portion of the trigger battery cell, which provides a more uniform, consistent heating of the interior of the trigger cell. The heater preferably has a sufficiently low profile to allow the heater to fit within the battery module without forcing changes in the overall design of the module.

[0011] In an exemplary embodiment, the battery module comprises battery cells each having a pressure release valve or cell vent for allowing gases to vent from the cells. Positioning the heater within the center of the trigger cell increases the likelihood that the cell will eventually breach and vent hot ejecta from the cell vent through the positive end of the cell after reaching the threshold temperature. This represents a realistic case scenario of thermal runaway (TR) from the trigger cell due to overheating or overcharging of the battery cell. In addition, it reduces the likelihood that the cell will experience an uncontrolled sidewall breach which would result in hot ejecta venting in an uncontrolled direction.

[0012] In various embodiments, the heater comprises a flexible polyimide film configured to at least partially surround a central portion of the main body of the trigger battery cell. In one such embodiment, the film comprises an electrical resistance film configured to form a substantially circular arc around the trigger battery cell of at least about 45 degrees, or at least about 90 degrees or at least about 270 degrees. In an exemplary embodiment, the heater substantially surrounds the trigger cell to ensure that the interior of the cell is uniformly heated by the heater. The film heater may have a thickness of about 0.004 to about 0.020 inches, a width of about 10 to about 40 mm, or about 25 mm, and a length of about 30 to about 75 mm, or about 50 mm. [0013] In various embodiments, the system comprises a computing device coupled to the second temperature sensor and configured to determine whether the test battery cell reaches a second threshold temperature. The second threshold temperature is the temperature at which the test battery cell undergoes a thermal runaway condition and may be at least about 100°C, or at least about 125°C, or at least about 150°C, or at least about 250°C.

[0014] The computing device may comprise any general -purpose computing article of manufacture capable of executing computer program instructions installed thereon. The computing device may include one or more processors (e.g., microprocessor, microchip, or application-specific integrated circuit), one or more memory devices (e.g., random-access memory and/or read-only memory), an I/O processor, and/or a communication interface. In an exemplary embodiment, the computing device comprises a data acquisition component (DAQ) which functions to monitor all of the thermocouples in the system.

[0015] In various embodiments, the battery module comprises a top row of batteries and a bottom row of batteries. The trigger battery cell is disposed in the bottom row and the test battery cell is disposed in the top row adjacent to the trigger battery cell.

[0016] In various embodiments, the battery module comprises one or more pouches containing a liquid and disposed adjacent to the trigger battery cell and the test battery cell. The pouches comprise a material configured to melt at a temperature at, or greater than, the threshold temperature. The pouches are positioned within the battery module to allow the liquid to exit the pouches and cool the battery cells adjacent to the trigger batter cell, thereby mitigating or preventing the thermal runaway condition from spreading to these cells.

[0017] In another aspect, the system further comprises a second heater configured for coupling to a second trigger cell to heat the second trigger cell to the threshold temperature. The computing device is configured to detect whether the second trigger cell reaches the threshold temperature. In an exemplary embodiment, the system further comprises additional temperature sensors positioned on battery cells adjacent to the second trigger cell for determining whether thermal runaway from the second trigger cell propagates to other battery cells within the module. The system may be configured, for example, to test whether the second trigger cell initiates thermal runaway in the event that thermal runaway from the first trigger cell has been substantially contained. [0018] In another aspect, a system for testing a battery module comprising a plurality of battery cells is provided. The system comprises a heater configured for coupling to a trigger battery cell within the battery module to heat the trigger battery cell to a threshold temperature, and a first temperature sensor configured for monitoring the temperature of the trigger battery cell. The system further comprises a controller coupled to the heater and configured to detect a rate of temperature change of the trigger battery cell and a second temperature sensor coupled to a test battery cell adjacent to the trigger battery cell within the battery module for detecting a temperature of the test battery cell.

[0019] In various embodiments, the controller controls the rate of temperature change of the trigger battery cell. Applicant has discovered through extensive testing that controlling the heating rate of the trigger cell ensures that the cell will eventually breach via a cell vent after reaching the threshold temperature (and reducing the likelihood that the cell will experience an uncontrolled sidewall breach). This ensures that the cell has undergone a thermal runaway due to overheating or overcharging of the battery cell, thereby providing an effective and realistic simulation of a thermal runaway of the cell.

[0020] In various embodiments, the system further comprises a power supply coupled to the controller and the heater and configured to activate the heater. The power supply may comprise any suitable source of power for operating the heater to increase the temperature of the trigger cell to the threshold temperature. In one embodiment, the power supply comprises a DC power supply that provides a direct current (DC) voltage to the heater.

[0021] In various embodiments, the controller is coupled to the first temperature sensor and configured to adjust a parameter of the power supply to control a rate of temperature change of the trigger battery cell. In one embodiment, the controller adjusts the duty cycle of the power supply to adjust the rate of work applied by the power supply to the heater, thereby controlling the rate of heat applied to trigger cell. The rate of temperature change of the trigger battery cell is preferably about 2°C to about 10°C per minute, or about 4°C to about 8°C per minute, or about 4°C to about 7°C per minute.

[0022] In various embodiments, the controller is configured to deactivate the heater when the trigger battery cell reaches the threshold temperature. In other embodiments, the controller is configured to reduce the rate of temperature change when the trigger battery cell reaches the threshold temperature. In yet another embodiment, the controller reduces the rate of temperature change to zero when the trigger battery cell reaches the threshold temperature.

[0023] In various embodiments, the system further comprises a computing device coupled to the second temperature sensor and configured to determine whether the test battery cell reaches the threshold temperature.

[0024] In another aspect, a method is provided for testing a battery module comprising a plurality of battery cells. The method comprises coupling a temperature sensor to a trigger battery cell within the battery module and heating a substantially central portion of the trigger battery cell to a threshold temperature. The method further comprises coupling a temperature sensor to a test battery cell adjacent to the trigger batter cell within the battery module and detecting a temperature of the test battery cell after the trigger battery cell reaches the threshold temperature.

[0025] In various embodiments, the heating comprises coupling a heater to the substantially central portion of the trigger battery cell. The heater preferably comprises a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

[0026] In various embodiments, the method further comprises controlling a rate of temperature change of the trigger battery cell. The rate of temperature change may be controlled by adjusting a parameter, such as the duty cycle, of a power supply coupled to the heater. The rate of temperature change is selected such that the trigger battery cell breaches through the pressure release valve at the threshold temperature. The rate of temperature change of the trigger battery cell is preferably about 2°C to about 10°C per minute, or about 4°C to about 8°C per minute, or about 4°C to about 7°C per minute.

[0027] In another aspect, the method further comprises heating a second trigger cell to the threshold temperature after the first trigger battery cell has reached the threshold temperature. In the event that the first trigger battery cell does not initiate a thermal runaway event, a temperature sensor may be coupled to one or more battery cell(s) adjacent to the second trigger battery cell within the battery module. The temperature of the battery cell(s) adjacent to the second test battery cell are monitored after the second trigger battery cell reaches the threshold temperature to determine if thermal runaway induced in the second trigger cell spreads to adjacent cells within the module.

[0028] In another aspect, a battery assembly comprises a housing comprising plurality of lithium-ion battery cells including a trigger battery cell and a test battery cell positioned adjacent to the trigger battery cell. The assembly further comprises a heater within the housing and in contact with the trigger battery cell, a first temperature sensor within the housing and in contact with the trigger battery cell and a second temperature sensor within the housing and in contact with the test battery cell.

[0029] In various embodiments, the battery assembly comprises an antipropagation system configured to mitigate thermal runaway from the trigger battery cell. In one such embodiment, the anti-propagation system comprises one or more pouches disposed within the housing adjacent to the trigger battery cell and one or more adjacent battery cells. The pouches containing a liquid and comprise a material configured to melt at a temperature at or above the threshold temperature. The trigger battery cell reaches a thermal runaway condition at the threshold temperature and the liquid prevents the neighboring battery cells from reaching the thermal runaway condition.

[0030] In various embodiments, the trigger battery cell comprises a pressure release valve for venting gases. The heater is configured to cause the trigger battery cell to breach through the pressure release valve at the threshold temperature.

[0031] In various embodiments, the trigger battery cell has a main body with first and second ends, and the heater is spaced from the first and second ends. The heater may comprise a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate several embodiments of the disclosure and together with the description, explain the principles of the disclosure.

[0033] FIG. l is a perspective view of a representative battery pack;

[0034] FIG. 2 is a partially exploded view of the battery pack of FIG. 1; [0035] FIG. 3 is an enlarged further exploded view of the battery pack of FIG. 1;

[0036] FIG. 4 is an enlarged partially exploded view of one portion of the battery pack of FIG. 1;

[0037] FIG. 5A is an end view of one of the battery modules in the battery pack of FIG. 1;

[0038] FIG. 5B is a side sectional view of the battery module of FIG. 5 A;

[0039] FIG. 6 illustrates a battery assembly comprising two battery modules stacked on top of each other;

[0040] FIGS. 7A, 7B, and 7C are side, sectional and detail views of the battery assembly of FIG. 6;

[0041] FIGS. 8 A and 8B are perspective views respectively showing the front and back of a stacking frame for the battery assembly of FIG. 6;

[0042] FIGS. 9 A and 9B are rear and detail views of the stacking frame design illustrating a peripheral groove;

[0043] FIG. 10 is a schematic illustration of a system for testing a battery module;

[0044] FIG. 11 is a schematic illustration of the system testing a single battery cell;

[0045] FIG. 12 is a schematic illustration of another embodiment of a system for testing a battery module

[0046] FIG. 13 illustrates a heater positioned on a battery cell;

[0047] FIG. 14 is a schematic view of a test setup for the system of FIG. 10;

[0048] FIG. 15 is a schematic view of a test control container for the system of

FIG. 10;

[0049] FIG. 16 is a flow chart depicting steps in a battery testing method;

[0050] FIG. 17 is a flow chart depicting steps in an optimized heater control testing method; [0051] FIG. 18 is a flow chart depicting steps in an optimized heater testing method;

[0052] FIG. 19 is a flow chart depicting steps in an optimized heater geometry, orientation, and location testing method; and

[0053] FIG. 20 is a flow chart depicting steps in a method to evaluate an antipropagation system and to monitor test setup stability.

DESCRIPTION OF THE EMBODIMENTS

[0054] This description and the accompanying drawings illustrate exemplary embodiments and should not be taken as limiting, with the claims defining the scope of the present disclosure, including equivalents. Various mechanical, compositional, structural, and operational changes may be made without departing from the scope of this description and the claims, including equivalents. In some instances, well-known structures and techniques have not been shown or described in detail so as not to obscure the disclosure. Like numbers in two or more figures represent the same or similar elements. Furthermore, elements and their associated aspects that are described in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment. Moreover, the depictions herein are for illustrative purposes only and do not necessarily reflect the actual shape, size, or dimensions of the system or illustrated components.

[0055] It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

[0056] FIGS. 1-9 depict exemplary embodiments of a representative battery pack 10 that may be tested according to the systems, devices and methods described herein. Battery pack 10 includes a plurality of battery modules 12 assembled into an array and retained inside a housing or enclosure 30 (as discussed in detail below). In the preferred embodiment, the battery modules 12 are composed of a plurality of lithium-ion battery cells and are of the same design and configuration as the battery modules disclosed in commonly assigned, co-pending U.S. Application No. 17/933,966, the complete disclosure of which is incorporated herein by reference for all purposes.

[0057] While the following testing systems and methods described herein and illustrated in FIGS. 10-20 are presented with respect to the representative battery modules shown in FIGS. 1-9, it should be understood that these systems and methods may be readily adapted for testing a variety of different types of batteries, battery modules and battery packs, including mobile and large scale energy storage systems, drive systems for equipment and machines, emergency power backup systems, computing devices, such as computers, mobile electronic devices and the like, portable power packs, electric vehicles and others. In addition, the features of the presently described systems and methods may be readily adapted for testing a variety of different types of batteries, such as lithium-ion batteries, including lithium iron phosphate (LFP), lithium nickel manganese cobalt (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium-ion manganese oxide (LMO), lithium-ion cobalt oxide (LCO), lithium titanate oxide (LTO) and the like.

[0058] As shown in FIG. 1, battery pack 10 comprises a sealed enclosure 30 for retaining the plurality of battery modules 12. The enclosure 30 includes a front plate 30a, side plates 30b, a back plate 30c, a top plate 30d, and a bottom plate 30e, thereby enclosing the array of battery modules 12. As shown in FIG. 2, cover strips 32a are mounted in horizontal rows along the interior surface of the front plate 30a and back plate 30c. Side strips 32b are mounted in vertical rows along the interior surface of the side plates 30b. Sides 34a, 34b are retained on the interiors of the front plate 30a, side plates 30b, and back plate 30c. Spacers 36a, 36b are retained on the top and bottom of the array of modules 12. The cover strips 32a and side strips 32b are preferably foam strips that cooperate together with the sides 34a, 34b which are plastic sheets to keep the module stacks under compression.

[0059] As shown in FIG. 3, battery pack 10 comprises electrical conductors including bus bars 40 with bus bar covers 42 and a copper braid (not shown) for cooperating with the electrical connections (not shown) in a conventional manner to enable the exchange of electrical power for alternately charging and discharging each module 12 in the array. The copper bus bars 40 are used to retain five modules 12 in a parallel orientation and provide a series electrical connection to the next row of five modules above or below. The copper braid is used to connect the modules 12 in series from the modules 12 from the one side to the other side. The top plate 30d encloses the electronics components of the battery pack system 10. These conventional components include a battery harness 46a, battery management system 46b, cell tap harness 46c, contactor 46d, fuse 46e and disconnect switch 46f. The outer edge of the top plate 30d includes a positive receptacle 48a, HVDC (High Voltage Direct Current) connection 48b, and a socket flange 48c. The HVDC connection 48a connects to the positive side of the battery pack. Next to it is an HVDC connection for the negative side. Dust caps are used during transportation only to keep the connectors sealed from dust and moisture. The socket flange 48c connects the battery pack to 24 VDC to power the BMS. The socket flange 48c also provides an external CANBUS 20 communication connection 80 from the battery pack to an external PMS (Power Management System) which controls the battery pack and an external power converter (inverter), connected via a MODBUS. In some embodiments, configurations are employed where multiple battery packs can be connected in series so that the same connector provides communications link to the remote battery pack BMS (not shown).

[0060] An electronic cover plate 50 is provided to enclose the top plate 30d with the electronics components. An electronics lid gasket 52 seals the volume enclosing the aforementioned electronics components. A disconnect handle 54 is used to attach and remove the cover plate 50. A plastic vent cap is provided for venting the interior of the enclosure 30 in the event of an increase in internal pressure resulting from a thermal runaway event. The vent pipe with mounting flange 56b and seal 56a are connected to flame arrestor backer plate 58 with associated mesh 58a and gauze 58b. In this manner, the vent cap 56 and related structures provide a vent for subsequently relieving the increase in air pressure within the sealed enclosure associated with the thermal runaway event.

[0061] In certain embodiments, the enclosure 30 includes one or more pressure monitoring switches (not shown) for detecting an increase in air pressure within the sealed enclosure associated with gas released from the thermal runaway event in one or more of the 10 battery cells 14 in one or more of the battery modules 12. The pressure monitoring sensors may be connected to a port (not shown) on the lid of enclosure 30 exterior to the battery pack to allow for calibration and service of the sensors, if needed, the port (not shown) may be in fluid communication with the interior of the enclosure 30 and fluidly connected to the pressure monitoring sensor for transmitting a pressure spike from an increase in internal pressure resulting from a thermal runaway event in one of the modules 12. In the preferred embodiment, the pressure switches can be the Dwyer Series 1950, explosion-proof 15 differential pressure switches sold by Dwyer Instruments, Inc. of Michigan City, Indiana, preferably a Dwyer 1950P-2-2F or an-OmegaPSW-152 sold by Omega Engineering Inc. ofNorwalk, Connecticut. Both pressure switches have LOW- and HIGH- pressure ports. The HIGH- pressure port is connected to the battery pack lid via copper tubing and the LOW- pressure port is left open to atmospheric pressure. A more complete description of a suitable pressure monitoring mechanism can be found in commonly assigned, co-pending U.S. Application No. 17/933,976, the complete disclosure of which is incorporated herein by reference for all purposes.

[0062] With particular reference to FIGS. 4, 5 A and 5B, battery pack 10 may comprise a thermal runaway or anti-propagation system. Thermal runaway is defined herein as an increase in temperature that changes the conditions of an individual battery cell in a way that causes a further increase in temperature (or the point wherein the heat generated within the battery cell exceeds the amount of heat that is dissipated to its surroundings). Generally, if the cause of heat is not remedied, the internal battery temperature will continue to rise until it begins to affect adjacent batteries cells within module 12 causing a chain reaction.

[0063] As shown in FIGS. 4, 5A and 5B, the anti-propagation system preferably comprises one or more liquid pouches 20a, 20b (or thermal runaway shield (TRS) pouches) associated with each of the plurality of battery modules 12. The liquid pouches 20a, 20b comprise a material that has a melting temperature low enough to melt at a threshold temperature. Liquid pouches 20a, 20b each include a thermal cooling fluid that ruptures into the associated respective battery module 12 from heat produced in a thermal runaway event in the battery module 12. A side pouch 20a can be provided over the horizontal top and/or bottom surfaces of a module 12, and an end pouch 20b can be provided over one or both of the vertical side surfaces of the module 12. The TRS pouches 20a, 20b are preferably multilayer metallized sealed plastic pouches that include a thermally cooling fluid that ruptures into the battery module from heat produced in a thermal runaway event in the battery module 12. In one exemplary embodiment of the invention, the TRS pouches are of a type manufactured by KULR Technology Group, Inc., as also disclosed in the aforementioned commonly assigned patent application, although it will be recognized that other liquid pouches may be used with system 10. Upon rupturing, the pouches 20a, 20b release the thermally cooling fluid composed of a water-based coolant having known properties that safely extinguish flame and absorb heat in a lithium-ion battery. In this manner, the present passive cooling system is an antipropagation system that extinguishes thermal runaway in a single battery module 12 and thereby protects any nearby battery modules 12 from thermal runaway thus preventing a dangerous cascade situation.

[0064] The individual battery cells within battery module 12 and the TRS pouches 20a, 20b are separated by one or more plates or sheets 22a, 22b, 22c inserted therebetween, so that the sheets 22a, 22b, 22c divide and separate the TRS pouches 20a, 20b. A top/bottom sheet 22a is horizontally provided between each of the vertically stacked modules 12. A mid sheet 22b is vertically provided in between the back ends of the modules 12 stacked within the array. An end sheet 22c is vertically provided along the sides of the modules 12 stacked within the array. In this manner, the sheets 22a, 22b, 22c provide physical and thermal barriers between the TRS pouches 20a, 20b during the thermal runaway event in battery module 12. The sheets 22a, 22b, 22c are formed of a suitably heat resistant material such as phenolic having known properties that contain the heat. The sheets 22a, 22b, 22c can allow one of the TRS pouches 20a, 20b to rupture and quench the battery module 12 but can protect another of the TRS pouches 20 20a, 20b from prematurely rupturing unless the heat in the battery module 12 is sufficiently high that a second pouch is required to extinguish the flame. Thus, sheets 22a, 22b, 22c only allow a sufficient amount of cooling fluid to be released without wasting.

[0065] As depicted in FIG. 5B each of the battery modules 12 also include additional sheets or spacers 26a, 26b, 26c that provide additional separation and protection between each of the battery cells 14. A short vertical member 26a alternates with long vertical members 26b and are perpendicularly oriented with respect to horizonal members 26c, to provide an additional measure of thermal protection around each individual battery cell 14. The spacers 26a, 26b are phenolic sheets used as part of the anti-propagation system as a thermal barrier and ablative material (which absorbs heat via combustion and decomposes into carbon as discussed in further detail below). Each of the 10 modules 12 include electrical connections 28 that enable an exchange of electrical power for alternately charging and discharging each module 12. These electrical connections 28 enable individual control over each module 12 by a battery manager (discussed below) and connect to a bus for supplying power, using commonly available mating electrical connections as understood by those having skill in the art. [0066] Referring now to FIGS. 6-10B, one embodiment of a battery module assembly 100 will now be described. As shown in FIG. 6, each battery module assembly 100 comprises two or more battery modules 110 stacked on top of each other. Each battery module assembly 100 may further comprise one or more stacking frames 124, each formed of the same basic stacking frame design. Thus, the stacking frames 124 are substantially identical and interchangeable with each other, both having features of the same stacking frame 24 that are interoperable and interconnectable. The stacking frames 124 each include a peripheral frame portion that is configured to sit atop a perimeter of the surface of each battery module 110. As shown, the peripheral frame portion is generally rectangular and is defined by a solid frame having frame members parallel, opposite, and identical to each other, where the peripheral frame portion is generally open or void in a central area within the periphery of the frame structure.

[0067] As shown in FIGS. 7A-7C, one or more TRS side pouches 120 are enclosed between the first and second stacking frames 124. One or more TRS end pouches 144 are positioned at the end of each battery module 110. The TRS side and end pouches 120, 144 are preferably composed of water-based coolant and a carbon fiber wick enclosed in a multilayer metallized sealed plastic pouch. The pouches 120, 144 will rupture from the heat produced in a thermal runaway event in the battery module 110 when temperatures are greater than 160 degrees C. Upon rupturing, the pouches 120, 144 release a thermally cooling fluid composed of a water-based coolant having known properties that safely extinguish flame and reduce heat in a lithium-ion battery. Thus, the TRS pouches 120, 144 are the primary protection as the cell in thermal runaway will vent into the pouch 120, 144 bursting and it will burst first. In this manner, the passive cooling system is an anti-propagation system that extinguishes thermal runaway in a single battery module and thereby protects any nearby battery modules from thermal runaway thus preventing a dangerous cascade situation.

[0068] As shown in FIG. 7C, the first and second TRS side pouches 120 are separated by a spacer plate 122 inserted therebetween, so that the spacer plate 122 divides and separates the TRS side pouches 120. In this manner, the spacer plate 122 provides both a physical and a thermal barrier between the first and second TRS side pouches 120 during the thermal runaway event in the battery module 120. The spacer plate 122 is formed of a suitably heat resistant material such as phenolic having known properties that contain the heat. In this manner, the spacer plate 122 allows the first TRS side pouch 120 to rupture and quench the battery module 120 but protects the second TRS side pouch 120 from prematurely rupturing unless the heat in the battery module 14 is sufficiently high that the second pouch is required to extinguish the flame. Thus, spacer plate 122 prevents transfer of heat from cell thermal runaway from one battery module 110 to the battery module(s) immediately above or below the compromised battery module.

[0069] As shown in FIGS. 8A and 8B, stacking frames 124 each include a peripheral frame portion 130 that is configured to sit atop a perimeter of the surface of the battery module 120. As shown, the peripheral frame portion 130 is generally rectangular and is defined by a solid frame having a first frame member 130 parallel and opposite to an identical second frame member 130, both of which are perpendicular to third and fourth frame members 130, 130 which respectively parallel and identical to each other. The peripheral frame portion 130 is generally open or void in a central area within the periphery of the frame structure.

[0070] The peripheral frame portion 130 includes mating structures in the form or projections 134 and alignment recesses 136 formed thereon. Optionally, the shape of the projections 134 and alignment recesses 136 can be configured to allow ultrasonically welding the two halves together to make a subassembly. When each of the stacking frames 124 are connected together, the projections 134 on each of the respective stacking frames 124 are received within the alignment recesses 136 of the respective other of the stacking frames 124. That is to say, the projections 134 of the first stacking frame 124 are received within the alignment recesses 136 of the second stacking frame 124. Conversely, the projections 134 of the second stacking frame 124 are received within the alignment recesses 136 of the first stacking frame 124. Frame portion 130 may further include predefined cut outs 141 in the sides of the stacking spacer to allow hot ejecta or effluent to flow out and up the “chimneys” created by the stacking spacer in the event of a sidewall breach.

[0071] The projections 134 and alignment recesses 136 are formed alternately along each of the first and second frame members 124 and staggered so that the projections 134 are pre-aligned to mate with the alignment recesses 136. Thus, the projections 134 and the alignment recesses 136 are formed on the same surface of each of the stacking frames 124, which is to say, the same respective surfaces of each of the first and second frame members 124. [0072] The stacking frames 124 include spacing features or notches 139 formed along an opposite side of each of the frame members 130 to direct hot effluent from a thermal event in a cell toward the ends of the cells. As also shown in FIG. 6, the hot effluent can then escape via “chimneys” 138 (shown in phantom) which are vertical channels defined by voids between protruding notches 139 formed along an outer perimeter of the stacking frames 130. A retention feature can optionally be added to the end of the spacing features that would help guide and retain the TRS end pouches 144. The retention feature also operates as a lead in feature to make it easier to insert the TRS end pouches 144 in the middle of the stacks. The chimneys 138 direct the hot effluent and heated water vapor up toward a vent located on the top of the assembled battery pack. The chimneys 138 allow pressure to be released and enables hot gasses to escape to ensure that surrounding battery cells remain cool after a thermal runaway condition is quenched. As depicted, there are 8 chimneys per module, 2 on each side of the module. However, the present design can be adapted to include any desired number of chimneys without departing from the invention. It is to be appreciated that the chimneys 138 are features formed from the stacking frames 124 that are most particularly embodied in the assembled battery pack system composed of a stack of modules 120.

[0073] Peripheral frame portion 130 of each stacking frame 124 includes a plurality of transverse locating pins 132 extending inwardly toward a center of the peripheral frame portion 130. The plurality of transverse locating pins 132 engages and retains the TRS pouch(es) 120 between the first and second stacking frames 124 and serve as pouch holders when assembled. Transverse locating pins 132 are formed on each of the first and second frame members 130 so that opposite pins 132 generally face each other and are aligned with each other. As shown, the peripheral frame portion 130 includes six pins, three pairs of opposing pins. However, it is to be appreciated that any suitable number and orientation of transverse locating pins 132 could be contemplated without departing from the present innovative concept.

[0074] Referring now to FIGS. 9A and 9B, stacking frames 124 each include a peripheral groove 140 for substantially surrounding and enclosing the perimeter of the surface of the battery module 120. The peripheral groove 140 is essentially a continuous notch encompassing the inner periphery of the stacking frame 124, and thereby mates with the peripheral edge of the top or bottom surface of the battery module 120 so that the stacking frame 124 can alternately support the battery module 120 or be supported by the battery module 120.

[0075] Referring now to FIGS. 10-16 a system 200 for testing one or more of the battery modules in a battery pack will now be described. As shown in FIG. 10, a battery module 210 may include a container 212 housing a plurality of battery cells, such as 2 to 100 cells, or 4 to 64 cells, or 8 to 32 cells, or about sixteen cells. In an exemplary embodiment, the battery cells being tested are lithium-ion batteries, such as lithium iron phosphate (LFP), lithium nickel manganese cobalt (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium-ion manganese oxide (LMO), lithium-ion cobalt oxide (LCO), lithium titanate oxide (LTO) and the like. Battery module 210 may have a similar construction as described above in FIGS. 1-9, or may have any suitable configuration known to those of skill in the art. In one embodiment, battery module 210 comprises a lower row of batteries and an upper row of batteries, with each of the batteries generally facing into the page (i.e., a positive terminal at one end of the module facing the page and a negative terminal at the other end of the battery facing away from the page).

[0076] Module 210 may comprise voltage output 222 for monitoring the voltage of module 210. Module 210 may further include a thermal runaway prevention mechanism, such as, for example, first and second liquid pouches 225 positioned between the inner surfaces of container 212 and the battery cells that retain a water-based fire extinguishing fluid. Module 210 may also include pouches 225 above and below module (not shown). Pouches 225 comprise a material designed to melt at a threshold temperature, as described above. During a thermal runaway condition, heat and/or flame from the affected battery cell(s) cause liquid pouches 225 to rupture, releasing the extinguishing fluid into the battery module 210 to absorb the heat energy and mitigate thermal runaway. Battery module 210 may further comprising one or more spacer plates 228, preferably made of phenolic material, placed on the top and bottom of the battery module 210 to provide an additional level of thermal isolation for the battery module 210, as described above. In one aspect, spacer plates 228 are also arranged between adjacent batteries within the module, as described above.

[0077] System 200 comprises one or more heaters for increasing a temperature of certain battery cells within module 210 and a plurality of sensors for detecting temperature in various locations of battery module 210, as described below. The sensors may comprise any suitable temperature detection device. In an exemplary embodiment, the sensors comprise thermocouples. In one embodiment, system 200 comprises a thermocouple 214 coupled to a trigger cell 216 and configured to detect a temperature of a trigger cell 216. Trigger cell 216 may be located at any position within module 210. In an exemplary embodiment, trigger cell 216 is located in the interior of the module 210, such as, for example, the fourth position away from the terminals 222 on the bottom row of module 210. Trigger cell 216 will be the battery that is heated to a temperature sufficient to cause the battery to undergo a thermal runaway, as described below. Thermal runaway is defined herein as an increase in temperature that changes the conditions of the battery in a way that causes a further increase in temperature or the point wherein the heat generated within the battery exceeds the amount of heat that is dissipated to its surroundings. Generally, if the cause of heat is not remedied, the internal battery temperature will continue to rise until it begins to affect adjacent batteries within module 210 causing a chain reaction.

[0078] In an exemplary embodiment, system 100 comprises a heater 240 positioned in contact with trigger cell 216 and a thermocouple 220 positioned on heater 240 and configured to detect a temperature of heater 240. Heater 240 may comprise any suitable heating device for increasing the temperature of trigger cell 216 to a threshold temperature that is sufficient to cause cell 216 to undergo a thermal runaway. The threshold temperature will vary depending on the type of lithium battery that is being tested. In an exemplary embodiment, the threshold temperature is at least about 100°C, or at least about 125°C, or at least about 150°C, or at least about 250°C.

[0079] In certain embodiments, heater 240 comprises a heater configured for attachment to a battery cell within module 210 and having a sufficiently low profile to allow heater 240 to fit within module 210 without forcing changes in the overall design of module 210. In this manner, heater 240 may be permanently attached to the battery cell such that after the module 210 has been tested as described below, it may be retested if a destructive thermal runaway was not achieved in the first test.

[0080] As shown most clearly in FIG. 13, heater 240 is configured for coupling to a substantially central portion of trigger cell 216. Thus, heater 240 is spaced from each of the ends 274, 276 of cell 216. In certain embodiments, heater 240 is spaced away from each end 374, 276 by at least about 10%, or at least about 20%, or at least about 25% of the total length of cell 216. In an exemplary embodiment, heater 240 forms a circular arc around trigger cell 216 of at least about 45 degrees, or at least about 90 degrees or at least about 270 degrees. In an exemplary embodiment, heater 240 substantially surrounds trigger cell 216 (i.e., 360 degrees or almost 360 degrees) to ensure that the cell is uniformly heated by heater 240. Heater 240 is preferably positioned between trigger cell 216 and container 212 (opposite test cell 224, as discussed below).

[0081] In an exemplary embodiment (shown more clearly in FIGS. 11 and 13), heater 240 comprises a thin flexible film heater that may be heated through electrical resistance (i.e., passing a DC current through resistive elements within heater 240). In one such embodiment, heater 240 preferably comprises a polyamide film heater having a thickness of about 0.004 to about 0.020 inches, a width of about 10 to about 40 mm, or about 25 mm, and a length of about 30 to about 75 mm, or about 50 mm.

[0082] Referring again to FIG. 10, system 200 further comprises a power supply 250 coupled to heater 240 for supplying power to heater 240. Power supply 250 may comprise any suitable source of power for operating heater 240 to increase the temperature of trigger cell 216 to the threshold temperature. In one embodiment, power supply 250 comprises a DC power supply that provides a direct current (DC) voltage to heater 240. Power supply 250 may have certain parameters that control the rate of heating of heater 240, such as duty cycle, current, voltage and power. In one embodiment, adjusting the duty cycle of power supply 250 will adjust the rate of work applied by the power supply 250 to heater 240, thereby adjusting the rate of heat applied to trigger cell 216 (discussed below).

[0083] System 200 further comprises a controller 260 coupled between power supply 250 and thermocouple 214. Controller 260 may comprise any suitable computing device, electrical circuit, proportional, integral, or derivative controller or the like, that is configured to receive an input signal (i.e., temperature detected by the thermocouple 214) compare that input signal with a predetermined control point value or set point and determine the appropriate amount of output by the power supply 250 to provide correction action with a control loop. In an exemplary embodiment, controller 260 comprises a proportional integral derivative controller (PID Controller).

[0084] Controller 260 is configured to receive temperature data from thermocouple 214 and to adjust one of the parameters of power supply 250 based on this temperature data. In one embodiment, controller 260 adjusts the duty cycle of power supply 150 such that the rate of heating of trigger cell 216 remains within a threshold range, such as about 2°C to about 10°C per minute, or about 4°C to about 8°C per minute or about 4°C to about 7°C per minute. Applicant has discovered through extensive testing (see below in Examples) that controlling the heating rate of trigger cell 216 within this range ensures that cell 216 will eventually breach via a cell vent after reaching the threshold temperature. This ensures that the cell 216 has undergone a thermal runaway through overheating or overcharging of the cell. Therefore, ensuring that the temperature of trigger cell 216 increases at a rate within this range provides a realistic simulation of thermal runaway of the cell.

[0085] System 200 may also comprise an electrical shunt 246 positioned between heater 240 and controller 260. Shunt 246 functions to provide a low-resistance path for an electrical current to monitor the series current to the heater by measuring the voltage across the shunt resistor and calculating the current based on the known ohmic resistance of the shunt resistor.

[0086] System 200 further comprises a computer device 270 coupled to heater thermocouple 220, and voltage input 222 of battery module 210. Computing device 270 may also be coupled to an ambient thermocouple 290 configured to detect the temperature of the ambient environment immediately surrounding battery module 210. Computing device 270 can comprise any general-purpose computing article of manufacture capable of executing computer program instructions installed thereon. However, the computing device 270 is only representative of various possible computing devices that can perform the processes described herein. To this extent, in embodiments, the functionality provided by the computing device 270 can be any combination of general and/or specific purpose hardware and/or computer program instructions. In each embodiment, the program instructions and hardware can be created using standard programming and engineering techniques. For example, computing device 270 can include one or more processors (e.g., microprocessor, microchip, or application-specific integrated circuit), one or more memory devices (e.g., random-access memory and/or read-only memory), an I/O processor, and/or a communication interface. The memory devices can include a local memory (e.g., a random-access memory and a cache memory) employed during execution of program instructions. Additionally, the computing device 270 can include at least one communication channel (e.g., a data bus) by which it communicates with the storage system, VO processor, and the communication interface. In an exemplary embodiment, computing device 270 comprises a data acquisition component (DAQ) which functions to monitor all the thermocouples, the battery voltage, heater voltage and the current in system 200 and controller 260 to control heater 240. Computing device 270 may be wirelessly, or directly, coupled to a remote source 280, such as a mobile device, remote processor or the like.

[0087] System 200 further comprises a thermocouple 230 positioned on test cell 224. Test cell 224 may also function as a “second trigger” cell as discussed below. Test cell 224 is located adjacent to trigger cell 216 and may be used to determine if any thermal runaway from trigger cell 216 produces a thermal runaway in test cell 224. In other words, the system 200 will monitor whether test cell 224 reaches the threshold temperature after trigger cell 216 has been brought to the threshold temperature. In the exemplary embodiment, test cell 224 is located on the fourth position away from the terminal on the top row of battery module immediately above trigger cell 216.

[0088] In certain embodiments, third and fourth thermocouples 240, 250 are attached to the battery cells 242, 252 on either side of trigger cell 216. In certain embodiments, an additional thermocouple (not shown) may be attached to other battery cells, such as a battery cell above cells 242, 252, or batteries spaced further away from trigger cell 216. System 200 may further comprise one or more thermocouples 260 positioned to monitor the temperature of liquid pouches 225.

[0089] In another aspect, the present method can include a test for testing an individual battery cell of the battery module 210 (see FIG. 11), in order to develop a cell heating method in accordance with the UL9540A standard in order to induce thermal runaway on the lithium-ion cell (such as a LG MH1 lithium-ion cell in a Volta 180 lithium-ion battery module). In certain embodiments, the following test configurations can be used to develop the test parameters: three lithium-ion cells around a fourth lithium-ion trigger cell with an external heater, four lithium-ion modules without phenolic insulator spacer plates 228, and four lithium- ion modules including TRS pouches 225 and phenolic insulator spacer plates 228. A data acquisition (DAQ) routine is pre-programmed. Three thermocouples are provided for temperature measurement labeled TCtrigger #1, TCheater, and TCambient. Voltages are provided for the various components as Vcell/module, Vheater (40V), and Vheater (shunt, mV). A PID Temperature Controller, and a TC trigger #2 are also provided. A DC power supply (such as BK Precision Model 1687) is used to provide electrical energy source for the trigger cell heater. A laboratory computer is used to control the DAQ (Data Acquisition unit such as an NI Model) and collect data. The lithium-ion cell is held in place by a plastic housing which is permanently mounted on a ceramic tile.

[0090] In certain embodiments (see FIG. 12), system 100 further comprises a second heater 270 positioned around second test cell 224. In this embodiment, the user may test whether a thermal runaway in the test cell 224 (or second trigger cell) is controlled by the anti-propagation system, or whether this thermal runaway will extend to other cells. System 100 may further comprise additional thermocouples 264, 268 on the cells 262, 266 adjacent to second test cell 224.

[0091] Similar to the first heater 240, second heater 270 preferably comprises a thin flexible film heater that may be heated through electrical resistance (i.e., passing a DC current through resistive elements within heater 240. In one such embodiment, heater 240 preferably comprises a polyamide film heater having a thickness of about 0.004 to about 0.020 inches, a width of about 10 to about 40 mm, or about 25 mm, and a length of about 30 to about 75 mm, or about 50 mm. The back side of first and second heaters 240, 270 may be covered with a high temperature insulating material (not shown), such as UNIFRAX LLC. FyreWrap LiB FX70 Paper 1.6mm, to prevent trigger cell heat being absorbed by liquid pouches 225 and premature melting/rupturing of liquid pouches 225.

[0092] FIG. 13 illustrates an exemplary embodiment of one of the heaters 240, 270. As shown, first heater 240 is preferably wrapped around a central portion of trigger cell 216. As shown, trigger batter cell 216 comprises a main body 272 with first and second ends 274, 276. Heater 240 is preferably spaced from first and second ends 274, 276. Applicant has discovered that this configuration provides a more uniform, consistent heating of trigger cell 216. In addition, positioning the heater within the center of the trigger cell ensures that the cell will eventually breach via a cell vent after reaching the threshold temperature, which represents a “worse case” scenario of thermal runaway (TR) from the trigger cell 216.

[0093] The system further includes positive and negative terminals 280, 282, such as nickel tabs 3 (0.25 x 1-inch x 5mil) that may be, for example, resistance welded to each of the battery cell terminals. A full charge is applied to each cell on a commercial battery charger (such as a Maccor battery tester) using a constant current charge rate consistent with industry standards for the particular battery to be tested until the cell voltage reaches a full charge and then the current is reduced until a suitable cutoff current is reached indicating the cell is fully charged. First heater 240 comprises one or more leads 284 that are connected to a suitable power supply, such as a DC power supply 250 (see FIG. 11). In one embodiment, one or more additional thermocouples 290, 292 may be coupled to the negative end of cell 216 and voltage leads are attached to the nickel tab cell terminals 280, 282.

[0094] System 200 is configured to validate if the heating rate within the battery module 210 is impacted by using the anti -propagation system described above. In addition, system 200 may be configured to determine if the second cell heater 270 can initiate a second thermal runaway condition if the rupturing of liquid pouches 200 stop propagation in the test cell 224 after the thermal runaway condition is extinguished in trigger cell 216, in accordance with the CSA and UL requirements. In one exemplary scenario, the propagation is stopped within the first trigger cell 216. In another embodiment, the propagation is stopped within two cells. If the first trigger cell 216 goes into TR by external heating and it results in a second adjacent cell going into TR and then if propagation stops, it is considered to be a valid test. It is also acceptable if the first trigger cell goes into TR by external heating, then the TRS system stops propagation. If after forcing a second trigger cell into TR by external heating, there is no propagation to other battery cells within module 110, then it is also considered to be a successful test.

[0095] According to an exemplary embodiment, a test sequence is implemented as follows to validate an anti-propagation feature of a battery module. The temperature is monitored in battery module 210 having a plurality of battery cells including a top row of battery cells and a bottom row of battery cells. The cell heater 240 monitored by thermocouple 220 is activated in connection with the first trigger cell 216 monitored by thermocouple 214 in the bottom row of battery cells. Cell heater 240 is deactivated when cell self-heating has been detected which will lead to a thermal runaway condition in the first trigger cell 216. Extinguishing fluid is released into the battery module 210 from one or more of the TRS pouches 225 upon obtaining the thermal runaway condition. An observing step is performed to determine whether the thermal runaway condition in the first trigger cell 216 is either mitigated by the extinguishing fluid from the pouch(es) 225 or produces the thermal runaway condition in one or more of the other battery cells in the battery module 210 (e.g., test cell 224). Temperature in the battery module 210 is monitored to measure a decrease in temperature upon mitigation of the thermal runaway condition in the first trigger cell 216. Temperature in the battery module 120 is monitored until a temperature of 60 degrees C is reached indicating completion of the test.

[0096] FIG. 14 illustrates a test chamber 320 and a test control container 300. Test chamber 320 comprises a battery module 210, computing device 270 and a webcam 350 for observing the test. Test control container 300 includes a computing device 360 coupled to webcam 350, shunt 246, controller 260 and power supply 250, as discussed in detail above. Test control container 300 may further comprise an additional 100 W power supply 330 for driving current and voltage through battery module 210 to charge module 210, and a computing device 280, such as remote computer, processor, or mobile device.

[0097] In use, computing device 280 is set up to monitor the following components with a 1Hz sampling rate: Vmodule (voltage to the module 210), Vshunt (voltage across current shunt 246 to heater 240 in mV), Vheater (voltage to heater240), TCcell (temperature of trigger cell 216), TCheater (temperature of heater 240), TCambient (ambient temperature inside the test chamber 330). Controller 260 monitors the temperature of trigger cell 216 to change the duty cycle of power supply 250 to control the heating rate. Heater thermocouple 220 is monitored every minute to confirm a heating rate of between about 4 to 7 degrees C per minute until reaching a maximum (Tmax) of 210 deg C. The trigger cell 216 should go into thermal runaway within 30 minutes.

[0098] Computing device 270 controls the trigger cell heater 240 monitoring trigger cell thermocouple 214 on the primary trigger cell 216 and thermocouple 230 on the test cell 224. Heating is performed at the same rate as a battery module such as a Volta 180 that does not include a thermal runaway prevention mechanism, such as liquid pouches 225 or phenolic spacers 228. A full charge is applied to the module 210 on a battery charger such as Maccor battery cycler, where the charge is preferably 24.5A (-0.5C) CCCV until 4.1V, 2.5A cutoff is reached.

[0099] FIG. 15 depicts another test setup in accordance with an alternative embodiment. As shown, a test container 310 includes the battery module 210, computing device 270, controller 260 and a space heater 370. Container 310 may also include a webcam 350 for observing the test. The webcam 350 and the computing device 270 may be suitably coupled to a remote processor or computer outside of container 310. The objective of this test is to determine the correct PID settings for a Volta 180 module to allow for a consistent 4 to 7 degrees C per minute rise in temperature. Another objective is to validate that the cell heating rate is not impacted by the addition of anti -propagation features. Another objective is to determine if a second cell heater can initiate a second thermal runaway condition if antipropagation features stop propagation after a first thermal runaway condition, in accordance with (CSA and UL requirement). A die cast aluminum enclosure was used as it closely mimics a full pack by replicating the oxygen limited environment and keeping the anti-propagation material contained near the battery cells instead of immediately venting to open air.

[00100] Preliminaries to the testing procedure include testing the ambient container temperature from the outside temperature to the UL required test temperature (25+7-5 degree C). The battery module 210 inside the container 310 is maintained at the UL required test temperature until the test sample has reached thermal equilibrium. The module 210 is tested with and without the die cast aluminum enclosure to observe how it affects the battery module 210. The module 210 is placed on top of a steel table 365, and equipment is placed underneath to ensure it is not damaged. Weights 375 are placed behind a negative side of the module 210 to prevent module 210 from shifting backwards due to the force of the ejecta. Heater 370 is turned on and the container 310 is closed until ambient thermocouple reads the UL required test temperature. Afterwards, the heater 370 is turned down, not off, to maintain the UL required test temperature. The module leads and thermocouples are connected to computing device 270 and PID temperature controller 260 and ensure that the setup is in view of a camera 350.

[00101] In the testing procedure, recording begins at computing device 270 according to specifications given in a “Module Callout Diagram.” The camera 350 is started simultaneously. The container 310 is quickly opened to turn on PID controller 270 and then closed to check temperature to ensure there is not too much heat loss. Temperature data is observed throughout the test to keep track of cell temperature, venting and thermal runaway. The PID controller 260 is quickly turned off after the onset of thermal runaway. The module 210 is allowed to either propagate or not, based on the test requirements, and then allowed to cool down. Data collection and video stream is then stopped, and the collected data is exported to the correct folder for subsequent analysis. In the test, the positive ends of the battery cells are ensured to be facing away from table 365. The setup is ensured to be a minimum of 10 feet away from space heater 370 within container 310. The cables are ensured to be taut when crossed to the control area. EXAMPLES

[00102] Applicant conducted a number of tests of different systems to optimize the testing system. With reference to FIG 16, this figure depicts the original method including steps used to drive cells into TR and to evaluate various anti-propagation materials (mainly high temperature insulators). The original method included the following steps: 1) upon starting, applying a new anti-propagation material; 2) wrapping nichrome wire around a cell to serve as the cell heater; 3) attaching the nichrome wire heater to a DC power supply; 4) turning on the power supply; 5) determining whether the cell heated at a rate of 5 degrees C per minute; if YES, 6) determining if the cell achieved TR; if NO, adjusting the length and placement of the nichrome wire heater and adjusting DC power supply settings and returning to step 2); if YES at 6) determining if the material stopped propagation, and if YES, ending, or if NO, returning to step 1) and repeating the entire method, and reiterating until a material is determined to stop propagation. No positive results were obtained, and Applicant noted inconsistency in how cells were failing which made the task more difficult, including cell breaches in the sidewalls and the negative ends of the cells. In some cases, cell crimp failure resulted in the cap being forcibly ejected.

[00103] With reference to FIG 17, this figure depicts a method including steps used to evaluate alternative methods to control the heater power and heat rate using a more precise method (PID controller 260). The method included the following steps: 1) upon starting, conducting a TR test with a PI film heater connected to the heater’s DC power supply manual control method; 2) Post testing DPA (Destructive Physical Analysis) of the TR cell to determine a cell breach pathway; 3) determining whether the cell was breached via a cell vent; if YES, the method ends, but if NO, the heater DC power control method is changed (for example, manual adjustment vs. electronic PID controller supporting automatic adjustment) and the method returns to step 1), repeating the entire method, and reiterating until the cell is breached.

[00104] With reference to FIG 18, this figure depicts a method including steps used to evaluate alternative heater options. The original heater included nichrome wire that was cut to length and wrapped around the cell a fixed number of times. Applicant discovered that this heater did not cause the cell to breach via a cell vent and that using the thin film heaters described above improved the consistency of the heating and the location where the heat was applied. The method included the following steps: 1) upon starting, conducting a TR test with a selected heater connected to the heater DC power supply; 2) post-test DPA of the TR cell to determine the cell breach pathway; 3) ) determining whether the cell was breached via a cell vent; if YES, the method ends, but if NO, the heater type and quality is changed and the method returns to step 1), repeating the entire method, and reiterating until the cell is breached via its integrated vent.

[00105] With reference to FIG 19, this figure depicts a method including steps used to optimize the size, shape, and placement of the cell heater. The key findings included enabling a smaller heater to be located around the center of the cell. The method includes the following steps: 1) upon starting, conduct a TR test with a selected PI film heater and heater DC power supply controlled by PID controller; 2) posttest DPA of the TR cell to determine the cell breach pathway; 3) determining whether the cell was breached via its integrated cell vent; if YES, the method ends, but if NO, the PI film heater size, shape, or location on cell is changed and the method returns to step 1), repeating the entire method, and reiterating until the cell is breached.

[00106] With reference to FIG 20, the figure depicts a test process optimized for the method used to evaluate, test, and refine an anti-propagation technology. The method includes the following steps: 1) upon starting, preparing a test sample and test setup; 2) determining whether the environment around the cell is changed, if NO, 3) conducting a TR test with a selected PI film heater and heater DC power supply controlled by the PID controller, but if YES, retune the PID Controller and proceed to 3); determine whether there is no cell to cell propagation, if YES, the method ends, but if NO, 4) conduct a posttest DPA to determine whether there is test setup error, if YES, 5) update the test setup to correct the setup error and return to step 1), or 6) update anti-propagation device(s) and return to step 1), repeating the entire method, and reiterating until there is no cell to cell propagation. During this testing, the volume of coolant within the liquid pouches was adjusted to optimize the anti-propagation characteristics of these pouches.

[00107] Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiment disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the embodiment being indicated by the following claims. [00108] For example, in a first aspect, a first embodiment is a system for testing a battery module comprising a plurality of battery cells. The system comprises a first temperature sensor configured for coupling to a trigger battery cell within the battery module for detecting a temperature of the trigger battery cell, a heater configured for coupling to a substantially central portion of the trigger battery cell and configured to heat the trigger battery cell to a threshold temperature and a second temperature sensor configured for coupling to a test battery cell adjacent to the trigger battery cell within the battery module for detecting a temperature of the test battery cell.

[00109] A second embodiment is the first embodiment, wherein the trigger battery cell comprises a pressure release valve for venting gases, and the heater is configured to cause the trigger battery cell to breach through the pressure release valve at the threshold temperature.

[00110] A third embodiment is any combination of the first two embodiments, wherein the trigger battery cell has a main body with first and second ends, and the heater is configured to be spaced from the first and second ends.

[00111] A 4^th embodiment is any combination of the first 3 embodiments, wherein the heater comprises a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

[00112] A 5^th embodiment is any combination of the first 4 embodiments, wherein the film is configured to form a substantially circular arc of about 180 degrees to about 360 degrees around the trigger battery cell.

[00113] A 6^th embodiment is any combination of the first 5 embodiments, wherein the film has a length of about 40 mm to about 60 mm and a width of about 20 mm to about 30 mm.

[00114] A 7^th embodiment is any combination of the first 6 embodiments, wherein the film is an electrical resistance film.

[00115] An 8^th embodiment is any combination of the first 7 embodiments, further comprising a computing device coupled to the second temperature sensor and configured to detect whether the test battery cell reaches a second threshold temperature. [00116] A 9^th embodiment is any combination of the first 8 embodiments, wherein the second threshold temperature is at least about 150°C or greater.

[00117] A 10^th embodiment is any combination of the first 9 embodiments, wherein the battery module comprises a top row of batteries and a bottom row of batteries, wherein the trigger battery cell is disposed in the bottom row and the test battery cell is disposed in the top row adjacent to the trigger battery cell.

[00118] An 11^th embodiment is any combination of the first 10 embodiments, further comprising a second heater configured for coupling to the test battery cell and configured to heat the test battery cell to the threshold temperature.

[00119] A 12^th embodiment is any combination of the first 11 embodiments, further comprising a third temperature sensor configured for coupling to a second test battery cell adjacent to the test battery cell.

[00120] A 13^th embodiment is any combination of the first 12 embodiments, wherein the computing device is configured to detect whether the second test battery cell reaches the threshold temperature.

[00121] A 14^th embodiment is any combination of the first 13 embodiments, further comprising a fourth temperature sensor configured to detect a temperature of the heater.

[00122] A 15^th embodiment is any combination of the first 14 embodiments, wherein the trigger battery cell undergoes a thermal runaway condition upon reaching the threshold temperature.

[00123] A 16^th embodiment is any combination of the first 15 embodiments, wherein the battery module comprises one or more pouches containing a liquid and disposed adjacent to the trigger battery cell and the test battery cell.

[00124] A 17^th embodiment is any combination of the first 16 embodiments, wherein the pouches comprise a material configured to melt at a temperature at or above the threshold temperature, the pouches being positioned within the battery module to allow the liquid to exit the pouches and cool the test battery cell. [00125] An 18^th embodiment is any combination of the first 17 embodiments, further comprising one or more insulators positioned between the heater and the one or more pouches.

[00126] A 19^th embodiment is any combination of the first 18 embodiments, wherein the battery cells comprise lithium-ion.

[00127] In another aspect, a first embodiment is a system for testing a battery module comprising a plurality of battery cells. The system comprises a first temperature sensor configured for coupling to a trigger battery cell within the battery module for detecting a temperature of the trigger battery cell, a heater configured for coupling to the trigger battery cell to heat the trigger battery cell to a threshold temperature, a controller coupled to the heater and configured to detect a rate of temperature change of the trigger battery cell and a second temperature sensor coupled to a test battery cell adjacent to the trigger battery cell within the battery module for detecting a temperature of the test battery cell.

[00128] A second embodiment is the first embodiment, wherein the controller controls the rate of temperature change of the trigger battery cell.

[00129] A third embodiment is any combination of the first two embodiments, wherein the trigger battery cell comprises a pressure release valve for venting gases and the rate of temperature change is selected such that the trigger battery cell breaches through the pressure release valve at the threshold temperature.

[00130] A 4^th embodiment is any combination of the first 3 embodiments, further comprising a power supply coupled to the controller and the heater and configured to activate the heater.

[00131] A 5^th embodiment is any combination of the first 4 embodiments, wherein the controller is coupled to the first temperature sensor and configured to adjust a parameter of the power supply to control a rate of temperature change of the trigger battery cell.

[00132] A 6^th embodiment is any combination of the first 5 embodiments, wherein the rate of temperature change is about 4°C to about 7°C per minute.

[00133] A 7^th embodiment is any combination of the first 6 embodiments, wherein the parameter is a duty cycle of the power supply. [00134] An 8^th embodiment is any combination of the first 7 embodiments, wherein the controller is configured to deactivate the heater when the trigger battery cell reaches the threshold temperature.

[00135] A 9^th embodiment is any combination of the first 8 embodiments, wherein the controller is configured to reduce the rate of temperature change when the trigger battery cell reaches the threshold temperature.

[00136] A 10^th embodiment is any combination of the first 9 embodiments, wherein the controller reduces the rate of temperature change to zero when the trigger battery cell reaches the threshold temperature.

[00137] An 11^th embodiment is any combination of the first 10 embodiments, further comprising a computing device coupled to the second temperature sensor and configured to detect whether the test battery cell reaches a second threshold temperature.

[00138] A 12^th embodiment is any combination of the first 11 embodiments, wherein the second threshold temperature is at least about 150°C or greater.

[00139] A 13^th embodiment is any combination of the first 12 embodiments, wherein the trigger battery cell undergoes a thermal runaway condition upon reaching the threshold temperature.

[00140] A 14^th embodiment is any combination of the first 13 embodiments, wherein the battery module comprises one or more pouches containing a liquid and disposed adjacent to the trigger battery cell and the test battery cell.

[00141] A 15^th embodiment is any combination of the first 14 embodiments, wherein the pouches comprise a material configured to melt at a temperature at or above the threshold temperature, the pouches being positioned within the battery module to allow the liquid to exit the pouches and cool the test battery cell.

[00142] In another aspect, a first embodiment is a method for testing a battery module comprising a plurality of battery cells. The method comprises coupling a temperature sensor to a trigger battery cell within the battery module, heating a substantially central portion of the trigger battery cell to a threshold temperature, coupling a temperature sensor to a test battery cell adjacent to the trigger batter cell within the battery module and detecting a temperature of the test battery cell after the trigger battery cell reaches the threshold temperature.

[00143] A second embodiment is the first embodiment, wherein the trigger battery cell comprises a pressure release valve for venting gases from the cell, the method further comprising causing the trigger battery cell to breach through the pressure release valve at the threshold temperature.

[00144] A 3^rd embodiment is any combination of the first 2 embodiments, wherein the heating comprising coupling a heater to the substantially central portion of the trigger battery cell.

[00145] A 4^th embodiment is any combination of the first 3 embodiments, wherein the heater comprises a flexible polyimide film.

[00146] A 5^th embodiment is any combination of the first 4 embodiments, wherein the film has a length of about 40 mm to about 60 mm and a width of about 20 mm to about 30 mm.

[00147] A 6^th embodiment is any combination of the first 5 embodiments, further comprising controlling a rate of temperature change of the trigger battery cell.

[00148] A 7^th embodiment is any combination of the first 6 embodiments, wherein the rate of temperature change is about 4°C to about 7°C per minute.

[00149] An 8^th embodiment is any combination of the first 7 embodiments, wherein the controlling comprises adjusting a duty cycle of a power supply coupled to the heater.

[00150] A 9^th embodiment is any combination of the first 8 embodiments, further comprising heating the test battery cell to the threshold temperature after the trigger battery cell has reached the threshold temperature.

[00151] A 10^th embodiment is any combination of the first 9 embodiments, further comprising: coupling a temperature sensor to a second test battery cell adjacent to the first test battery cell within the battery module and detecting a temperature of the second test battery cell after the first test battery cell reaches the threshold temperature. [00152] In another aspect, a first embodiment is a battery assembly comprising a housing comprising plurality of lithium ion battery cells including a trigger battery cell and a test battery cell positioned adjacent to the trigger battery cell, a heater within the housing and in contact with the trigger battery cell, a first temperature sensor within the housing and in contact with the trigger battery cell and a second temperature sensor within the housing and in contact with the test battery cell.

[00153] A second embodiment is the first embodiment, further comprising one or more pouches disposed within the housing adjacent to the trigger battery cell and the test battery cell, wherein the pouches containing a liquid and comprise a material configured to melt at a temperature at or above the threshold temperature.

[00154] A third embodiment is any combination of the first two embodiments, wherein the trigger battery cell reaches a thermal runaway condition at the threshold temperature and the liquid prevents the test battery cell from reaching the thermal runaway condition.

[00155] A 4^th embodiment is any combination of the first 3 embodiments, wherein the trigger battery cell comprises a pressure release valve for venting gases, and the heater is configured to cause the trigger battery cell to breach through the pressure release valve at the threshold temperature.

[00156] A 5^th embodiment is any combination of the first 4 embodiments, wherein the trigger battery cell has a main body with first and second ends, and the heater is spaced from the first and second ends.

[00157] A 6^th embodiment is any combination of the first 5 embodiments, wherein the heater comprises a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

[00158] A 7^th embodiment is any combination of the first 6 embodiments, further comprising a controller coupled to the heater and configured to detect a rate of temperature change of the trigger battery cell.

[00159] An 8^th embodiment is any combination of the first 7 embodiments, further comprising a power supply coupled to the controller and the heater and configured to activate the heater, wherein the controller is coupled to the first temperature sensor and configured to adjust a parameter of the power supply to control a rate of temperature change of the trigger battery cell.

[00160] A 9^th embodiment is any combination of the first 8 embodiments, wherein the rate of temperature change is about 4°C to about 7°C per minute.

[00161] A 10^th embodiment is any combination of the first 9 embodiments, wherein the parameter is a duty cycle of the power supply.

Claims

1. A system for testing a battery module comprising a plurality of battery cells, the system comprising: a first temperature sensor configured for coupling to a trigger battery cell within the battery module for detecting a temperature of the trigger battery cell; a heater configured for coupling to a substantially central portion of the trigger battery cell and configured to heat the trigger battery cell to a threshold temperature; and a second temperature sensor configured for coupling to a test battery cell adjacent to the trigger battery cell within the battery module for detecting a temperature of the test battery cell.

2. The system of claim 1, wherein the trigger battery cell comprises a pressure release valve for venting gases, and the heater is configured to cause the trigger battery cell to breach through the pressure release valve at the threshold temperature.

3. The system of any one of claims 1 to 2, wherein the trigger battery cell has a main body with first and second ends, and the heater is configured to be spaced from the first and second ends.

4. The system of claim 3, wherein the heater comprises a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

5. The system of claim 4, wherein the film is configured to form a circular arc of about 180 degrees to about 360 degrees around the trigger battery cell.

6. The system of claim 4, wherein the film has a length of about 40 mm to about 60 mm and a width of about 20 mm to about 30 mm.

7. The system of any one of claims 4 to 6, wherein the film is an electrical resistance film heater.

8. The system of any one of claims 1 to 7, further comprising a computing device coupled to the second temperature sensor and configured to detect whether the test battery cell reaches a second threshold temperature.

9. The system of claim 8, wherein the second threshold temperature is at least about 150°C or greater.

10. The system of any one of claims 1 to 9, wherein the battery module comprises a top row of batteries and a bottom row of batteries, wherein the trigger battery cell is disposed in the bottom row and the test battery cell is disposed in the top row adjacent to the trigger battery cell.

11. The system of any one of claims 1 to 10, further comprising a second heater configured for coupling to the test battery cell and configured to heat the test battery cell to the threshold temperature.

12. The system of claim 11, further comprising a third temperature sensor configured for coupling to a second test battery cell adjacent to the test battery cell.

13. The system of claim 12, wherein the computing device is configured to detect whether the second test battery cell reaches the threshold temperature.

14. The system of any one of claims 1 to 13, further comprising a fourth temperature sensor configured to detect a temperature of the heater.

15. The system of any one of claims 1 to 14, wherein the trigger battery cell undergoes a thermal runaway condition upon reaching the threshold temperature.

16. The system of any one of claims 1 to 15, wherein the battery module comprises one or more pouches containing a liquid and disposed adjacent to the trigger battery cell and the test battery cell.

17. The system of claim 16, wherein the pouches comprise a material configured to melt at a temperature at or above the threshold temperature, the pouches being positioned within the battery module to allow the liquid to exit the pouches and cool the test battery cell.

18. The system of claim 16, further comprising one or more insulators positioned between the heater and the one or more pouches.

19. The system of any one of claims 1 to 18, wherein the battery cells comprise lithium-ion.

20. A system for testing a battery module comprising a plurality of battery cells, the system comprising: a first temperature sensor configured for coupling to a trigger battery cell within the battery module for detecting a temperature of the trigger battery cell; a heater configured for coupling to the trigger battery cell to heat the trigger battery cell to a threshold temperature; a controller coupled to the heater and configured to detect a rate of temperature change of the trigger battery cell; and a second temperature sensor coupled to a test battery cell adjacent to the trigger battery cell within the battery module for detecting a temperature of the test battery cell.

21. The system of claim 20, wherein the controller controls the rate of temperature change of the trigger battery cell.

22. The system of claim 21, wherein the trigger battery cell comprises a pressure release valve for venting gases and the rate of temperature change is selected such that the trigger battery cell breaches through the pressure release valve at the threshold temperature.

23. The system of any one of claims 20 to 22, further comprising a power supply coupled to the controller and the heater and configured to activate the heater.

24. The system of claim 23, wherein the controller is coupled to the first temperature sensor and configured to adjust a parameter of the power supply to control a rate of temperature change of the trigger battery cell.

25. The system of claim 24, wherein the rate of temperature change is about 4°C to about 7°C per minute.

26. The system of any one of claims 23 to 25, wherein the parameter is a duty cycle of the power supply.

27. The system of any one of claims 20 to 26, wherein the controller is configured to deactivate the heater when the trigger battery cell reaches the threshold temperature.

28. The system of any one of claims 20 to 27, wherein the controller is configured to reduce the rate of temperature change when the trigger battery cell reaches the threshold temperature.

29. The system of any one of claims 20 to 28, wherein the controller reduces the rate of temperature change to zero when the trigger battery cell reaches the threshold temperature.

30. The system of any one of claims 20 to 29, further comprising a computing device coupled to the second temperature sensor and configured to detect whether the test battery cell reaches a second threshold temperature.

31. The system of claim 30, wherein the second threshold temperature is at least about 150°C or greater.

32. The system of claim 31 , wherein the trigger battery cell undergoes a thermal runaway condition upon reaching the threshold temperature.

33. The system of any one of claims 20 to 32, wherein the battery module comprises one or more pouches containing a liquid and disposed adjacent to the trigger battery cell and the test battery cell.

34. The system of claim 33, wherein the pouches comprise a material configured to melt at a temperature at or above the threshold temperature, the pouches being positioned within the battery module to allow the liquid to exit the pouches and cool the test battery cell.

35. A method for testing a battery module comprising a plurality of battery cells, the method comprising: coupling a temperature sensor to a trigger battery cell within the battery module; heating a substantially central portion of the trigger battery cell to a threshold temperature; coupling a temperature sensor to a test battery cell adjacent to the trigger batter cell within the battery module; and detecting a temperature of the test battery cell after the trigger battery cell reaches the threshold temperature.

36. The method of claim 35, wherein the trigger battery cell comprises a pressure release valve for venting gases from the cell, the method further comprising causing the trigger battery cell to breach through the pressure release valve at the threshold temperature.

37. The method of claim 35, wherein the heating comprising coupling a heater to the substantially central portion of the trigger battery cell.

38. The method of claim 37, wherein the heater comprises a flexible polyimide film.

39. The method of claim 38, wherein the film has a length of about 40 mm to about 60 mm and a width of about 20 mm to about 30 mm.

40. The method of any one of claims 35 to 39, further comprising controlling a rate of temperature change of the trigger battery cell.

41. The method of claim 40, wherein the rate of temperature change is about 4°C to about 7°C per minute.

42. The method of claim 40, wherein the controlling comprises adjusting a duty cycle of a power supply coupled to the heater.

43. The method of any one of claims 35 to 42, further comprising heating the test battery cell to the threshold temperature after the trigger battery cell has reached the threshold temperature.

44. The method of claim 43, further comprising: coupling a temperature sensor to a second test battery cell adjacent to the first test battery cell within the battery module; and detecting a temperature of the second test battery cell after the first test battery cell reaches the threshold temperature.

45. A battery assembly comprising: a housing comprising plurality of lithium-ion battery cells including a trigger battery cell and a test battery cell positioned adjacent to the trigger battery cell; a heater within the housing and in contact with the trigger battery cell; a first temperature sensor within the housing and in contact with the trigger battery cell; and a second temperature sensor within the housing and in contact with the test battery cell.

46. The battery assembly of claim 45, further comprising one or more pouches disposed within the housing adjacent to the trigger battery cell and the test battery cell, wherein the pouches containing a liquid and comprise a material configured to melt at a temperature at or above the threshold temperature.

47. The battery assembly of claim 46, wherein the trigger battery cell reaches a thermal runaway condition at the threshold temperature and the liquid prevents the test battery cell from reaching the thermal runaway condition.

48. The battery assembly of any one of claims 45 to 47, wherein the trigger battery cell comprises a pressure release valve for venting gases, and the heater is configured to cause the trigger battery cell to breach through the pressure release valve at the threshold temperature.

49. The battery assembly of any one of claims 45 to 48, wherein the trigger battery cell has a main body with first and second ends, and the heater is spaced from the first and second ends.

50. The battery assembly of any one of claims 45 to 49, wherein the heater comprises a flexible polyimide film configured to at least partially surround the main body of the trigger battery cell.

51. The battery assembly of any one of claims 45 to 50, further comprising a controller coupled to the heater and configured to detect a rate of temperature change of the trigger battery cell.

52. The battery assembly of any one of claims 45 to 51, further comprising a power supply coupled to the controller and the heater and configured to activate the heater, wherein the controller is coupled to the first temperature sensor and configured to adjust a parameter of the power supply to control a rate of temperature change of the trigger battery cell.

53. The battery assembly of claim 52, wherein the rate of temperature change is about 4°C to about 7°C per minute.

54. The battery assembly of claim 53, wherein the parameter is a duty cycle of the power supply.

55. The battery assembly of any one of claims 51 to 54, wherein the controller controls the rate of temperature change of the trigger battery cell.

56. The battery assembly of claim 55, wherein the trigger battery cell comprises a pressure release valve for venting gases and the rate of temperature change is selected such that the trigger battery cell breaches through the pressure release valve at the threshold temperature.

57. The battery assembly of any one of claims 51 to 56, wherein the controller is configured to deactivate the heater when the trigger battery cell reaches the threshold temperature.

58. The battery assembly of any one of claims 51 to 57, wherein the controller is configured to reduce the rate of temperature change when the trigger battery cell reaches the threshold temperature.

59. The battery assembly of any one of claims 51 to 58, wherein the controller reduces the rate of temperature change to zero when the trigger battery cell reaches the threshold temperature.

60. The battery assembly of any one of claims 51 to 59, further comprising a computing device coupled to the second temperature sensor and configured to detect whether the test battery cell reaches a second threshold temperature.