Detecting thermal events in a battery pack

Abstract

This invention relates to the detection of thermal events in a battery pack. A battery module for use in a battery pack is disclosed. The battery module (12, 12') includes a plurality of battery cells and a sensing circuit (62) extending across the battery cells. A monitoring unit (46) is connected to the sensing circuit. The monitoring unit includes a continuity detector (66) configured to detect interruptions in the continuity of the sensing circuit (62). This allows for the detection of thermal events occurring in one of the plurality of battery cells.

Description

Technical Field

[0001] This invention relates to techniques for detecting uncontrolled thermal events in battery packs. The invention has specific but non-exclusive applications in battery packs used in traction applications (such as electric or hybrid vehicles), construction equipment, etc., as well as applications with stationary batteries. Background Technology

[0002] Electric and hybrid vehicles (such as cars, buses, vans, and trucks) use battery packs designed with high ampere-hour capacities to provide power over extended periods. Battery packs typically consist of a large number of individual electrochemical cells connected in series and parallel to meet total energy, voltage, and current requirements. To facilitate manufacturing, assembly, and maintenance, the cells within a battery pack can be modularized. These modules may include support structures and battery management units for managing the charging and discharging of the cells.

[0003] To improve packaging efficiency, battery modules typically use flat battery cells, such as prismatic cells or pouch cells. Prismatic cells are electrochemical cells (usually lithium-ion cells) contained in rectangular canisters, while pouch cells are contained in flexible material pouches. Multiple such cells are typically stacked together within a support structure to form a battery module. The cells within the module are connected in series and parallel to achieve the target voltage. Other types of battery packs use multiple cylindrical battery cells connected in a suitable configuration. Especially for traction applications, modules and their internal cells can be configured to fit the battery pack into space-constrained environments, particularly where space is extremely limited.

[0004] Battery packs used in traction applications typically contain a large number of adjacent cells to provide energy-intensive electrical storage. However, if a cell short-circuits or is exposed to high temperatures, an exothermic reaction can be triggered, potentially leading to cell overheating or fire. The proximity of individual cells means that if one cell catches fire, the flame can easily cascade and spread through the module. Moreover, due to the proximity of modules within the battery pack, the flame can spread to other modules. This cascading of thermal events is known as battery pack thermal runaway.

[0005] In automotive applications, it may be necessary to detect thermal runaway events quickly and reliably so that drivers and passengers have time to safely exit the vehicle before a dangerous situation occurs.

[0006] It is known to provide temperature sensors to battery packs that can detect temperature rises caused by thermal runaway events. For example, a battery module may include one or more temperature sensors that a battery management unit can use to detect temperature rises in the battery module that could potentially lead to a thermal runaway event.

[0007] However, a drawback of detecting temperature changes throughout the battery module is that the initially failing cell can be isolated by both thermal mass and distance from the temperature sensor. Consequently, a thermal runaway event may already be underway before a corresponding temperature rise is detected, leading to a delay in issuing an alert. On the other hand, equipping each individual cell with a temperature sensor would increase the size, cost, and complexity of the battery pack, a significant consideration in the automotive industry. Summary of the Invention

[0008] Therefore, there is a need to provide technologies that can enable the early detection of thermal events in a cost-effective and space-efficient manner.

[0009] According to one aspect of the present invention, a battery module is provided, the battery module comprising:

[0010] Multiple battery cells;

[0011] Sensing circuitry extending across the plurality of battery cells; and

[0012] A monitoring unit, which is connected to the sensing circuit,

[0013] The monitoring unit is configured to detect changes in the state of the sensing circuit.

[0014] The present invention offers the following advantages: by providing a sensing circuit extending across the plurality of battery cells and a monitoring unit configured to detect changes in the state of the sensing circuit, a thermal event occurring in one of the plurality of battery cells can be detected by monitoring a single parameter or a reduced number of parameters of all the battery cells. Therefore, the present invention offers the advantage of enabling early detection of impending or likely thermal runaway events without significantly increasing the size, cost, or complexity of the battery module.

[0015] In one embodiment, the monitoring unit includes a continuity detector configured to detect interruptions in the continuity of the sensing circuitry. This allows for the detection of thermal events occurring in one of the plurality of cells by monitoring a single parameter, i.e., the continuity of the sensing circuitry.

[0016] Preferably, the monitoring unit is configured to generate an alarm signal when an interruption in the continuity of the sensing circuit is detected. This allows for the provision of warnings of impending thermal runaway events.

[0017] This alarm signal can be used to provide local alerts. For example, it can warn vehicle users. Alternatively, upon detecting a change in the state of the sensing circuitry, the notification system can notify a central system, such as a dispatch center, fleet owner, fleet operator, or emergency responder, of the event along with its location / GPS coordinates. This allows the fleet owner to dispatch replacement vehicles and / or emergency personnel to rectify the situation (if necessary).

[0018] The sensing circuit may include a severable component. Preferably, the severable component extends across the venting paths of each of the plurality of battery cells. The severable component may be configured to cut off, for example, when a battery cell heats up or vents due to a thermal event. The severable component may be configured to cut off based on the venting action of a cell experiencing a thermal event. In this case, the severable component may be configured to cut off based on the venting action caused by the temperature of the vented component, the momentum and subsequent force exerted on the severable component by the vented component, the chemical properties of the severable component and the vented component, or all or some combination of these.

[0019] A continuously interruptible component can be, for example, an electrical conductor. This allows for the detection of interruptions in the sensing circuitry by monitoring the continuity of the electrical signal passing through the conductor. For example, the monitoring unit can be configured to apply an electrical signal to the conductor and detect an open circuit in it. This can be accomplished, for example, by applying a voltage and detecting the presence of current.

[0020] In one implementation, the continuously cuttable component includes traces on a circuit board. Typically, for example, a circuit board is already provided as part of a battery module design to provide voltage measurements to the battery management unit. Therefore, this implementation allows for the implementation of sensing circuitry with minimal or no increase in the size and cost of the battery module.

[0021] Preferably, the circuit board includes multiple vents, each associated with a battery cell, and a continuous trace spans the multiple vents. This allows the trace to be supported by the circuit board while exposing the battery cell to venting at locations where a thermal event is likely to occur. This can help cut off the trace when the battery cell vents due to a thermal event.

[0022] Traces on a circuit board may include stress concentration features where the trace crosses a vent hole. These stress concentration features may, for example, include regions on the trace with reduced cross-sections. This can be formed, for example, by providing notches or holes in the trace. When the cell is vented, the stress concentration features make it easier to break the trace.

[0023] A battery module may include a laminated bus. For example, a laminated bus can be used to make electrical connections between two or more battery cells to provide appropriate series and / or parallel connections for the battery cells in the battery module. In this case, a circuit board may be part of the laminated bus. This allows the circuit board to be supplied as part of existing components, thereby reducing cost and complexity.

[0024] Alternatively, the circuit board can be configured to allow electrical signals to travel from the battery cells to the battery management unit. This circuit board may already be provided as part of the battery module. Therefore, this allows for the use of few or no additional components to provide the sensing circuitry.

[0025] The monitoring unit may be part of the battery management unit, and it may be provided to monitor and manage cell charging and / or other aspects of cell operation. Therefore, the monitoring unit may at least partially utilize some existing components.

[0026] In any of the above arrangements, the monitoring unit can be configured to receive input from at least one of the following additional sensors: such as a temperature sensor, pressure sensor, strain sensor, chemical sensor, opacity sensor, voltage sensor, current sensor, or any other suitable type of sensor. This allows more than one factor to be considered when generating an alarm signal, and thus allows for increased redundancy and / or reduced false alarms.

[0027] The battery cells are preferably stackable, which helps to improve packaging efficiency. For example, the battery cells can be prismatic cells or pouch cells. Preferably, the plurality of battery cells are stacked, and each cell is oriented such that the exhaust path is in the direction of the sensing circuit. However, the principles of the invention can also be applied to other types of cells, such as cylindrical cells.

[0028] The sensing circuitry can extend across some or all of the battery cells in the battery module. If desired, two or more sensing circuits can be provided, each with a monitoring unit. Each of these sensing circuits can extend across some or all of the battery cells. This may help provide redundancy and / or help reduce false alarms.

[0029] In alternative arrangements, the sensing circuit may include different types of continuously cuttable components, such as conductive wires or optical fibers. In the case of optical fibers, a continuity detector can detect whether light is being transmitted through the fiber. In either case, stress concentration characteristics can be provided even when the sensing circuit is in an exhaust path.

[0030] In other arrangements, the cut-off assembly may include a plurality of cut-off assemblies connected in series. In this case, each of the plurality of cut-off assemblies may be associated with at least one battery cell. Each of the cut-off assemblies may be configured to cut off when the battery cell heats up or vents.

[0031] In another embodiment, the sensing circuit includes a plurality of sensing elements connected in series. In this case, each of the plurality of sensing elements can be associated with at least one battery cell. This can help detect thermal events in an individual battery cell while monitoring the entire sensing circuit.

[0032] Preferably, the state change of the sensing circuit is caused by a state change in one or more of the sensing elements. The state change of the sensing element can be, for example, a change in the resistance of the sensing element or the switching off of the sensing element. This provides a convenient way to detect state changes using a suitable monitoring unit.

[0033] The sensing elements are preferably connected in series along a single conductive path. Therefore, the monitoring unit can monitor the series connection of multiple sensing elements, which allows for the detection of thermal events occurring in one of the multiple cells by monitoring a single parameter or a reduced number of parameters (compared to the number of cells).

[0034] Alternatively, at least some of the sensing elements can be connected in parallel. Therefore, the sensing circuit may include multiple sensing elements connected in parallel.

[0035] The monitoring unit can be configured to detect changes in a single parameter of the sensing circuit. For example, the monitoring unit can be configured to detect changes in the resistance and / or continuity of the sensing circuit in order to detect thermal events occurring in one (or more) of the plurality of cells. This can facilitate a simple and inexpensive design.

[0036] The monitoring unit can be configured to detect changes in the electrical parameters of the sensing circuit. For example, the monitoring unit can be configured to detect changes in the resistance, current, and / or voltage of the sensing circuit. For example, in one embodiment, the monitoring unit is configured to detect when the resistance of the sensing circuit exceeds a threshold. However, other parameters can be used, or alternatively.

[0037] In any of the above arrangements, the monitoring unit can be configured to monitor the rate of change of a parameter of the sensing circuit or any other time derivative of that parameter. For example, the monitoring unit can be configured to monitor the rate of change of the resistance of the sensing circuit and detect when the rate of change exceeds a threshold. This can help avoid false alarms, for example, due to changes in overall environmental conditions (such as ambient temperature).

[0038] The sensing circuit can be supported by a board for connecting the battery cells. For example, the sensing circuit can be supported by a laminated bus that is used to connect the cells in a suitable series and / or parallel configuration. This allows the sensing circuit to extend across the multiple battery cells using existing components.

[0039] The sensing circuitry can be mounted on a circuit board. The circuit board can be, for example, a flexible printed circuit board, and can be part of or attached to a laminated bus. For instance, the circuit board can be used to transmit voltage and / or other signals to a battery management unit. This allows the sensing circuitry to be implemented, at least partially, using existing components.

[0040] The sensing circuit can extend across the venting paths of each of the plurality of battery cells. For example, the sensing circuit includes a plurality of sensing elements, each of which can be located within the venting path of a battery cell. The venting path of the cell is preferably a path that allows gas to escape from the cell in the event of thermal runaway. For battery cells with vents (such as prismatic cells), the sensing element can be positioned adjacent to the vent. For pouch cells, the sensing element can be positioned at the top where the electrodes of the cell are located. This allows for easy detection of gas emissions during thermal runaway.

[0041] Conveniently, each sensing element can be placed at the vent on the circuit board, and each vent is associated with a battery cell.

[0042] In one embodiment, the sensing element is a sensor. The sensor is preferably a component configured to sense changes in environmental parameters such as temperature or pressure. Therefore, the sensing circuit may include multiple sensors connected in series. The sensors are preferably connected in series along a single conductive path. A monitoring unit can be configured to detect when the resistance of the series-connected sensors exceeds a threshold.

[0043] Changes in the state of the sensor circuit may be caused by temperature variations in one or more sensors connected in series. Therefore, the sensors can be temperature sensors. In this case, each temperature sensor is preferably capable of thermal sensing of the battery cell or its emissions (e.g., gases emitted from the cell during a thermal runaway event). This allows a temperature rise in one of the cells that could lead to a thermal runaway event to be detected before the event inevitably spreads to other cells. Moreover, this can be achieved by monitoring the entire sensing circuit rather than individual cells. Therefore, this arrangement can help provide early indication of an impending thermal runaway event in a cost-effective and space-efficient manner.

[0044] For example, each temperature sensor in the aforementioned temperature sensor system can make thermal contact with the battery cell. It should be understood that "thermal contact" does not necessarily mean physical contact between the sensor and the battery cell, but rather that contact can be established through an intermediary or through advection, convection, conduction and / or radiation, and / or alternatively, conduction.

[0045] Preferably, the sensors are nonlinear, meaning they can have a nonlinear response to the parameter being measured. In this case, the sensors can become nonlinear above the normal operating range of the system. For example, the sensors can have a nonlinear resistance response to temperature, meaning the rate of change of resistance with temperature can increase as the temperature exceeds a threshold. Preferably, the sensors become nonlinear above the normal temperature range of the battery module. As an example, the sensors can be nonlinear above 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or any other value. This can help provide rapid detection of impending thermal runaway events while helping to avoid false alarms caused by an increase in the overall temperature of the battery module.

[0046] In a preferred embodiment, the sensor is a thermistor. This allows temperature changes in one of the battery cells to be detected by monitoring the total resistance of a series of thermistors connected in series. Therefore, this embodiment provides a simple, convenient, cost-effective, and space-efficient way to detect thermal events in one (or more) of the battery cells.

[0047] Preferably, the sensor is a positive temperature coefficient (PTC) thermistor. Therefore, the sensing circuit may include a series of PTC thermistors connected in series. In this case, the monitoring unit can be configured to detect when the resistance of the series of PTC thermistors exceeds a threshold. Typically, the resistance of a PTC thermistor increases rapidly with temperature. Therefore, this implementation offers the advantage that the state change of the sensing circuit corresponding to a temperature rise in one (or more) of the battery cells can be easily detected. Moreover, in the event that one of the thermistors fails or becomes disconnected (e.g., due to cell venting), the resistance of the sensing circuit will also increase to an open-circuit state. Therefore, detecting whether the resistance of a series of PTC thermistors exceeds a threshold also allows for the detection of the disconnection or failure of one (or more) of the thermistors.

[0048] Alternatively, the sensor can be other types of temperature sensors, such as negative temperature coefficient (NTC) thermistors, thermocouples, or infrared (IR) sensors. For example, the sensing circuit may include multiple thermocouples connected in series. In this case, the sensing circuit may include alternating types of thermocouple wires connected in series, and the sensing element may be a thermocouple junction. In such an arrangement, the monitoring unit can detect temperature differences within the battery module. This difference can be compared to the nominal temperature within the battery pack to make a decision. Since thermal runaway events are likely to initiate in individual cells, this arrangement can help provide an early indication of impending thermal runaway events.

[0049] In other alternatives, instead of using a temperature sensor, any other type of sensor may be used, such as a pressure sensor, strain sensor, chemical sensor, opacity sensor, or any other suitable type of sensor.

[0050] In cases where the monitoring unit is configured to detect when parameters of the sensing circuit exceed a threshold, the monitoring unit can adjust the threshold based on input received from at least one other sensor. For example, the monitoring unit could receive input from a temperature sensor configured to monitor ambient temperature or the average temperature of the battery pack. In this case, the threshold can be adjusted based on the ambient or average temperature. For instance, if the ambient or average temperature increases, the threshold can be increased. This can help avoid false alarms and allow for early detection of impending or likely thermal runaway events. If desired, other parameters (such as pressure and / or the current drawn from or supplied to the battery cells) can also be used to adjust the threshold.

[0051] According to another aspect of the present invention, a battery pack comprising a plurality of battery modules according to any one of the preceding claims is provided. The battery pack may include a battery management unit. The battery management unit may be configured to receive alarm signals from each of the battery modules and to generate external alarm signals based on the alarm signals.

[0052] The principle of measuring a single parameter of multiple series-connected components that become nonlinear above the normal operating range of a system can be extended to any system requiring such monitoring. For example, this principle can be used to detect overheating in a system of multiple high-current power connectors, or in a system of multiple high-current power bolted joints, or in any other system with multiple components that may have experienced overheating, where it may be desirable to detect overheating in one or more of the multiple components.

[0053] Therefore, according to another aspect of the present invention, a system for monitoring changes in environmental parameters of multiple components is provided, the system comprising:

[0054] A plurality of sensor elements connected in series, each of the sensor elements being associated with at least one of the components; and

[0055] A monitoring unit is connected to the plurality of sensor elements connected in series.

[0056] The monitoring unit is configured to detect state changes of the plurality of series-connected sensor elements.

[0057] Environmental parameters may include, for example, temperature or pressure. Changes in the state of the multiple series-connected sensor elements may include, for example, changes in resistance.

[0058] The sensor element preferably has a nonlinear response to environmental parameters. For example, the sensor element may have a nonlinear resistance response to temperature. In one example, the sensor element is a (nonlinear) PTC thermistor.

[0059] Preferably, the sensor elements become nonlinear above the system's normal operating range (e.g., above the normal temperature range). In this case, the nonlinear response of the individual sensors outside (above or below) their normal operating range can help detect individual unwanted system events using a single measurement of the series-connected sensing elements.

[0060] The monitoring unit can be configured to detect when the series connection parameters of the sensor elements exceed a threshold. For example, the monitoring unit can be configured to detect when the resistance of the plurality of sensor elements exceeds a threshold.

[0061] A corresponding method can also be provided. Therefore, according to another aspect of the present invention, a method for detecting thermal events in a battery module comprising multiple battery cells is provided, the method comprising the following steps:

[0062] Monitoring is performed on a sensing circuit that extends across the plurality of battery cells; and

[0063] Changes in the state of the sensing circuit are detected.

[0064] The method further includes the following step: generating an alarm signal when a change in the state of the sensing circuit is detected.

[0065] A feature of one aspect of the invention can be used in conjunction with any other aspect. Any of the device features can be provided as a method feature, and vice versa. Attached Figure Description

[0066] The preferred features of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein:

[0067] Figure 1 An example of a battery pack is shown;

[0068] Figure 2 An example of a battery module is shown;

[0069] Figure 3 yes Figure 2 Exploded view of the battery module;

[0070] Figure 4 This demonstrates how to connect the battery cells in a battery module using laminated busbars;

[0071] Figure 5 An alternative battery module comprising multiple prismatic cells is shown;

[0072] Figure 6A and Figure 6B A portion of the prismatic battery cell is shown;

[0073] Figure 7 A portion of the laminated busbar in an embodiment of the present invention is shown;

[0074] Figure 8 A portion of the monitoring system in an embodiment of the present invention is shown;

[0075] Figure 9 A portion of the laminated busbar in another embodiment of the invention is shown;

[0076] Figure 10 Showing more details Figure 9 Part of the laminated busbar;

[0077] Figure 11 This is a circuit diagram of a monitoring system in one implementation method;

[0078] Figure 12 It shows the result of Figure 11 An example of the voltage seen by a voltage monitor;

[0079] Figure 13 A portion of the monitoring system in another embodiment is shown;

[0080] Figure 14 This illustrates how multiple discrete thermistors can be connected to a battery cell;

[0081] Figure 15 The resistance of an example PTC device versus temperature is shown;

[0082] Figure 16 This is a circuit diagram of a monitoring system using two thermistor circuits; and

[0083] Figure 17 It shows that it will be by Figure 16 An example of the voltage seen by a voltage monitor. Detailed Implementation

[0084] Figure 1 An example of a battery pack is shown. Figure 1 The battery packs are designed for use with electric and hybrid vehicles, especially high-horsepower applications such as buses, trucks, vans, construction equipment, etc.

[0085] Reference Figure 1 The battery pack 10 includes: multiple battery modules 12, multiple cooling plates 14, a battery management system 16, a surrounding frame 18, a top plate 20, and a bottom plate 22. In this example, the fifteen battery modules 12 are provided in five rows of three modules each. Each row of three battery modules 12 is positioned on a corresponding cooling plate 14. The cooling plate 14 is hollow to allow coolant flow. The battery management system 16 is located at one end of the battery pack. In the assembled state, the top plate 20 and the bottom plate 22 are attached to the top and bottom of the frame 18, respectively. The battery modules 12, cooling plates 14, and battery management system 16 are housed within the frame 18, the top plate 20, and the bottom plate 22.

[0086] Figure 2An example of a battery module 12 is shown. In this example, the battery module 12 includes twenty-four battery cell units 24 stacked side by side. The battery cell units 24 are electrically connected in series and / or parallel to achieve a target group voltage. End plates 26 are provided on each side of the module. The battery cell units 24 and the end plates 26 are held together by steel straps 28. A removable cover 30 is provided at one end of the module. A battery management unit is integrated with the module 12 inside the removable cover 30 to monitor and manage cell charging and other aspects of cell operation.

[0087] Figure 3 yes Figure 2 An exploded view of the battery module. (Refer to...) Figure 3 The battery module 12 is formed by stacking multiple battery cell units 24 together. Each battery cell in the battery cell unit 24 is in the form of a pouch cell 32 held within a cell tray 34. In this example, the cell tray 34 is made of a plastic polymer material such as thermoplastic. Each battery cell in the battery cell unit 24 includes a terminal block 36 for electrical connection to the pouch cell 32. Each battery cell in the battery cell unit 24 also has a cooling fin 38 for conducting heat away from the pouch cell 32. Compressed foam expansion pads 40 are placed between adjacent battery cells.

[0088] exist Figure 3 In this arrangement, a laminated busbar 42 is used for electrical connections to the individual battery cell units 24. The laminated busbar 42 is connected to the battery cell units 24 via conductive pins 44. The pins 44 pass through holes in the laminated busbar 42 and into corresponding holes in the terminal plate 36 of the battery cell to provide both electrical and mechanical connections between the busbar and the battery cell. The laminated busbar 42 includes electrical conductors that connect the battery cell units 24 in desired series and / or parallel connections to achieve a target voltage. The laminated busbar 42 is also connected to positive and negative terminals 45, which provide electrical connections to and from the battery module.

[0089] Figure 3 A battery management unit 46 is also shown. The battery management unit 46 includes a processor with appropriate software, as well as memory and other components used for monitoring and managing other aspects of cell charging and cell operation. The battery management unit 46 is mounted on a circuit board, which is mounted on a laminated busbar 42 via an electrically insulating barrier 48. The battery management unit 46 is protected by a removable cover 30. The removable cover 30 is made of a plastic polymer material such as thermoplastic.

[0090] Figure 4This illustrates how to connect battery cells in a battery module using laminated busbars. (Refer to...) Figure 4 The laminated busbar 42 comprises multiple metal strips 50 held between plastic sheets. The laminated busbar 42 is connected to the cell unit 24 by means of conductive pins 52. The pins pass through holes in the metal strips 50 and enter corresponding holes in the terminal plate of the cell unit 24. The ends of the pins 52 are threaded and engage with threads in holes in the terminal plate. The metal strips 50 are configured to connect adjacent battery cells in appropriate series and parallel configurations. A connector 54 is provided for connecting the laminated busbar 42 to the battery management unit 46.

[0091] Figure 5 An alternative battery module comprising multiple prismatic cells is shown. (Refer to...) Figure 5 In this example, battery module 12' includes eighteen prismatic cells 25 stacked side-by-side. A laminated bus 56 is used to connect the battery cells in series and / or in parallel to achieve a target group voltage. A battery management unit (BMU) is also included. Figure 5 (Not shown) is connected to the laminated bus and is used to monitor and manage cell charging and other aspects of cell operation.

[0092] Figure 6A and Figure 6B A portion of one of the prismatic battery cells is shown in more detail. Figure 6A A top view of the battery cell is shown. Figure 6B A perspective view is shown. The battery cell includes a metal casing 70 and a terminal block 72. A pressure relief vent 74 is located on the top of the battery cell. The vent 74 is designed to open when the pressure inside the battery cell exceeds a certain level in order to release gases generated during thermal runaway.

[0093] In the above arrangement, the battery cells are typically lithium-ion cells housed in pouches or metal casings. Compared to other types of rechargeable battery cells, lithium-ion cells offer high specific capacity, energy density, and power density. These advantages make lithium-ion cells suitable for long-term operation and high-current use in applications such as electric vehicles. However, if a lithium-ion cell short-circuits or is exposed to high temperatures, an exothermic reaction can be triggered. This can lead to cell overheating or fire. The close proximity of individual cells means that if one cell catches fire, the flame can easily spread through the module. Moreover, due to the close proximity of the modules in the battery pack, the flame can spread to other modules, potentially causing a thermal runaway event in the entire battery pack. If the battery pack is being used in a vehicle, this could pose a safety hazard to the vehicle occupants.

[0094] Therefore, it is desirable to provide a monitoring system that can provide early warnings of thermal runaway events.

[0095] Previous attempts to detect thermal runaway events involved providing the battery management unit with one or more temperature sensors capable of detecting temperature rises. However, in such an arrangement, the cell initially failing might be located some distance from the temperature sensors. Therefore, a thermal runaway event could already be underway before the corresponding temperature rise is detected. On the other hand, equipping each cell with a temperature sensor would increase the size, cost, and complexity of the battery pack, a significant consideration in automotive space management.

[0096] In an embodiment of the invention, a single sensing circuit is used to sense multiple cells in a battery module in order to provide an indication of an impending thermal runaway event.

[0097] Figure 7 A portion of the laminated busbar in an embodiment of the present invention is shown. (Refer to...) Figure 7 The laminated busbar 56 includes a plurality of metal strips 58 held between plastic sheets. In this embodiment, the metal strips 58 are configured to connect eighteen prismatic cells in series.

[0098] exist Figure 7 In this arrangement, the laminated busbar 56 includes multiple vent holes 60. Each vent hole 60 is located above a corresponding battery cell. The holes are positioned such that they are directly above the vent holes 74 of the battery cells. This provides a path for the gas to escape.

[0099] Figure 7 A trace circuit 62 is also shown. The trace circuit 62 is a thin metal strip (such as copper) on a flexible printed circuit board, and is one of the layers of the laminated bus 56 (or attached to the laminated bus). The trace circuit 62 extends from one end of the laminated bus 56 to the other end, then loops and extends back to the first end. The trace circuit 62 traverses a hole 60 in the laminated bus via both outward and return paths. The hole 60 also passes through the printed circuit board on which the trace is formed. Thus, where the trace 62 traverses the hole 60, the trace is exposed to the vent 74 corresponding to the top of the battery cell. The two ends of the trace circuit 62 are connected to the battery management unit.

[0100] Figure 8 The monitoring system is shown to include Figure 7 The laminated busbar section. (Refer to...) Figure 8The monitoring system includes a laminated bus 56 and a battery management unit (BMU) 46. The laminated bus 56 includes the via 60 and trace circuit 62 as described above. The battery management unit 46 includes a continuity detector 66 and an alarm signal generator 68. The two ends of the trace circuit 62 are connected to the continuity detector 66. The output of the continuity detector 66 is connected to the alarm signal generator 68. The output of the alarm signal generator is an alarm signal that can be sent to the battery management system 16.

[0101] During operation, for example, if the cell has defects that could cause a short circuit, if the cell overheats, if the cell is subjected to excessive power consumption, or if the cell is punctured, thermal runaway of the battery cell may be triggered. During thermal runaway, the electrolyte reacts with the electrodes and releases flammable hydrocarbon gases. In pouch cells, the release of gas will force the bag to open at its weakest point, which is usually the top of the cell where the electrodes are located. In prismatic cells, a vent is usually provided at the top of the cell to release gas in the event of thermal runaway. Therefore, during thermal runaway, hot flammable gases are typically released from the top of the cell.

[0102] exist Figure 7 and Figure 8 In the arrangement, the trace circuit 62 is configured such that it passes directly within the projected path of the gas vented from the cell in the event of thermal runaway. The thickness of the trace 62 is selected such that the metal is cut off by the venting action when a single cell vents. This can occur due to the temperature of the vented component, or the momentum and subsequent force exerted on the trace by the vented component, or the chemical properties of the trace and the vented component, or a combination of these. A suitable thickness of the trace 62 can be between 0.0005 inches and 0.1 inches (0.0127 mm to 2.54 mm), but other values ​​may be used alternatively.

[0103] Reference Figure 8 A continuity detector 66 is used to sense the continuity of the trace circuit 62. This can be done, for example, by applying a voltage to the trace circuit (via a series resistor) and detecting whether any current flows. If the trace 62 has been interrupted by the venting action of one or more of the battery cells, the continuity detector 66 will detect a lack of continuity in the trace circuit. In this case, the continuity detector outputs a signal to an alarm signal generator 68 indicating that the trace has been interrupted. The alarm signal generator generates an alarm signal when the signal from the continuity detector 66 indicates that the trace 62 has been interrupted. The output of the alarm signal generator 68 is sent to the battery management system 16. In response, the battery management system can trigger an alarm that warns vehicle occupants (e.g., the driver and / or passengers) of a thermal runaway event and allows for the safe evacuation of the vehicle.

[0104] Optionally, the alarm signal generator 68 can also receive outputs from one or more other sensors, such as pressure and / or temperature sensors. This allows the alarm signal generator to generate alarm signals based on multiple different sensing parameters, which can help improve the speed and reliability of thermal runaway event detection.

[0105] Figure 9 A portion of a laminated busbar according to another embodiment of the invention is shown. (Refer to...) Figure 9 The laminated busbar 56' includes: a plurality of metal strips 58', a plurality of vent holes 60', and trace circuits 62'. The metal strips 58', vent holes 60', and trace circuits 62' are as described above. Figure 7 The corresponding part of the description works in a similar way. However, in Figure 9 In the arrangement, the trace circuit 62' includes a plurality of notches 64. The notches 64 are located in the region where the trace circuit traverses the via 60'. The notches 64 are gaps in the trace circuit that reduce the cross-sectional area of ​​the trace circuit and thus reduce its strength. The notches 64 act as stress concentration features to help interrupt the trace circuit when the cell vents.

[0106] Figure 10 Showing more details Figure 9 One of the vent holes 60' in the arrangement. (Refer to...) Figure 10 As can be seen, the notch 64 in the trace circuit 62' takes the form of a notch on both sides of the trace. The notch can be formed by etching the copper trace during manufacturing. The size of the notch is adjusted to increase the likelihood of the trace circuit being cut off when the cell is venting, while minimizing the risk of accidental disconnection (e.g., due to mechanical shock).

[0107] Can replace Figure 9 and Figure 10 The notch shown or the one shown Figure 9 and Figure 10 The notch shown provides other types of stress concentration features. For example, holes can be provided in the trace, or the trace can be made to taper inward at appropriate locations.

[0108] If desired, two or more can be provided on the laminated bus 56. Figures 7 to 9 The type of trace circuit shown. In this case, each trace circuit can cross some or all of the vent holes 60 in the laminated busbar. The continuity of each trace circuit can be monitored.

[0109] Figure 11 This is a circuit diagram of a monitoring system using two trace circuits. (Refer to...) Figure 11The monitoring system in this example includes a first trace circuit 62A and a second trace circuit 62B. Each trace circuit 62A, 62B is a continuous loop extending from one end of the laminating bus 56 to the other and back to the first end. One branch of trace circuit 62A crosses the vent 60 in the laminating bus at locations indicated by A1-A18. Similarly, one branch of trace circuit 62B crosses the vent 60 at locations indicated by B1-B18. The two trace circuits 62A, 62B are connected to the corresponding monitoring circuit.

[0110] In this example, the monitoring circuits include voltage sources VSA and VSB, first resistors RA1 and RB1, second resistors RA2 and RB2, and voltage monitors VMA and VMB. Resistor RA1, trace circuit 62A, and resistor RA2 are connected in series. Similarly, resistor RB1, trace circuit 62B, and resistor RB2 are connected in series.

[0111] During operation, voltage source VSA applies a predetermined voltage (5 V in this example) to resistors RA1, 62A, and RA2 connected in series. Voltage monitor VMA monitors the voltage across 62A and RA2. Similarly, voltage source VSB applies a predetermined voltage to resistors RB1, 62B, and RB2 connected in series, and voltage monitor VMB monitors the voltage across 62B and RB2.

[0112] Figure 12 An example of the voltages observed by voltage monitors VMA and VMB is shown when venting occurs in one of the battery cells, causing one of the traces to be cut off. In this example, it is assumed that one of the cells disconnects trace 62A at time 75s and trace 62B at time 80s. In this case, voltage monitor VMA will see the voltage increase to 5V (the voltage applied by voltage source VSA) at 75s, and voltage monitor VMB will see the voltage increase to 5V at 80s. By comparing the measured voltages to thresholds, the outputs of voltage monitors VMA and VMB can be used to provide an indication of a thermal runaway event.

[0113] In the example above, by detecting when the first of the two trace circuits has been disconnected, both trace circuits can be used to provide an indication of a thermal runaway event as early as possible. Alternatively, detecting when both trace circuits have been disconnected can provide some form of protection against false alarms.

[0114] In the above embodiments, the trace circuit can be provided as part of a flexible circuit board attached to or as part of a laminated bus. Typically, such a flexible circuit board already exists as part of a laminated bus, for example, to transmit voltage measurements to the battery management unit. Therefore, the trace circuit can be provided with minimal additional cost and without increasing the size of the battery module. Moreover, the battery management unit only needs to monitor the state of one component (i.e., the trace circuit). Thus, these embodiments allow for the provision of indications of impending thermal runaway events without significantly increasing the size, cost, and complexity of the battery module.

[0115] In an alternative arrangement, instead of using trace circuitry as part of a circuit board, a separate conductive line can pass through the top of the battery cell at a location where venting is likely in the event of thermal runaway. In this case, the continuity of the conductive line can be monitored. In another alternative example, optical fiber can be used instead, and the presence of light transmitted through the optical fiber can be detected.

[0116] In a further alternative arrangement, instead of determining whether current is flowing through the trace circuit, the system can be configured to determine the amount of current flowing through the trace circuit and / or the resistance of the trace circuit.

[0117] When hot gas is expelled from one of the battery cells, the portion of the trace circuit located in the gas path heats up. Since the trace is made of metal, its resistance increases with temperature. Therefore, the resistance of the metal trace increases as hot gas is expelled. Furthermore, during thermal runaway, the battery cell typically heats up before any gas is expelled. This can also cause the temperature of the metal trace to increase, thereby increasing its resistance. Therefore, by detecting a decrease in current through the trace circuit or an increase in the resistance of the trace circuit, an impending thermal runaway event can be detected before the metal trace has been severed.

[0118] A potential drawback of the above-described implementations is that they may rely on battery cell venting or reaching high temperatures before a thermal runaway event can be detected. However, in some situations, it may be desirable to provide an early indication of an impending thermal runaway event before the battery cells have begun venting. For example, this could provide additional time to evacuate the vehicle before the thermal runaway event spreads throughout the battery pack.

[0119] Figure 13 A portion of the monitoring system according to another embodiment is shown. (Refer to...) Figure 13The monitoring system includes: multiple thermistors 76, a resistance measurement unit 78, a comparator 80, a threshold generator 82, and an alarm signal generator 68. Each thermistor 76 is in thermal contact with or near one of the battery cells in the battery cell unit 24 of the battery module. The battery cell can be any type of battery cell, such as a prismatic cell, a pouch cell, or a cylindrical cell. The thermistors 76 are connected in series to form a string of thermistors. Each end of the string of thermistors is connected to the resistance measurement unit 78. The output of the resistance measurement unit 78 is connected to the input of the comparator 80. The comparator also receives input from the threshold generator 82. The output of the comparator 80 is connected to the alarm signal generator 68.

[0120] The resistance measurement unit 78, comparator 80, threshold generator 82, and alarm signal generator 68 can be comprised of discrete hardware. Alternatively, some or all of these components can be implemented using an analog-to-digital converter within a microprocessor, which incorporates associated software logic performing the functions shown in the figure. If desired, some or all of these components can be integrated into a battery management unit.

[0121] In this embodiment, the thermistor 76 is a positive temperature coefficient (PTC) thermistor. This type of device has a resistance that increases with temperature. Since the thermistors are connected in series, the total resistance of the series of thermistors is the sum of the resistances of the individual thermistors.

[0122] During operation, if a battery cell has a defect that could lead to a thermal runaway event, that cell will be the first to heat up. This typically occurs before the cell begins to vent. The heat from the cell will then be transferred to the associated PTC thermistor in the string of thermistors. As the thermistor heats up, its resistance increases. This will cause the total resistance of the string of resistors to increase.

[0123] exist Figure 13 In this arrangement, the total resistance of the string of thermistors is measured by the resistance measuring unit 78. This can be achieved, for example, by passing a constant current through the string of thermistors and measuring the voltage across them. Alternatively, a constant voltage can be applied and the resulting current measured. In either case, Ohm's law can be used to determine the resistance. It should be appreciated that other techniques for measuring resistance can be used alternatively.

[0124] The total resistance of the string of thermistors, measured by the resistance measurement unit 78, is fed to one input of comparator 80. Comparator 80 also receives a threshold from threshold generator 82. When the total resistance of the string of thermistors exceeds the threshold, comparator 80 outputs a signal to alarm signal generator 68. Alarm signal generator 68 generates an alarm signal in response to the signal. As in the previous embodiments, alarm signal generator 68 may also receive outputs from one or more other sensors. The output of alarm signal generator is sent to battery management system 16, which can trigger an appropriate alarm.

[0125] The threshold set by threshold generator 82 is selected to be higher than the normal operating temperature of the battery pack, but low enough to provide an indication of an impending thermal runaway event as quickly as possible. The threshold can be fixed or variable. For example, the threshold generator can receive other inputs (such as signals indicating ambient temperature and / or the amount of current being supplied to or from the battery pack) and adjust the threshold accordingly.

[0126] Alternatively, instead of detecting when the resistance of the thermistor string exceeds a threshold, the rate of change of resistance, or some other time derivative of the resistance, can be monitored. In this case, alarm signal generator 68 can generate an alarm signal when the time derivative of the resistance exceeds a threshold. Since cell heating due to thermal runaway often occurs faster than other temperature changes (e.g., due to changes in ambient temperature), this can help avoid false alarms.

[0127] In one embodiment, the PTC thermistor is a surface-mount device mounted on a flexible circuit board. The flexible circuit board can be positioned below the laminate bus 56 (i.e., the side facing the battery cell). Electrically insulating / thermally conductive spacer material can be provided between the individual thermistors and their associated battery cells to increase thermal contact between them.

[0128] In another embodiment, the PTC thermistor is a discrete component mounted on a flexible circuit board. In this case, the thermistor can be in direct contact with the battery cell or connected to the battery cell via a thermally conductive (and electrically insulating) material.

[0129] Figure 14 This illustrates how multiple discrete thermistors can be connected to a battery cell. (Refer to...) Figure 14Each thermistor 76 is mounted on the underside of a circuit board 84. The circuit board is a flexible circuit board located below the laminated busbar 56. Leads of the thermistors 76 pass through holes in the circuit board 84. The thermistors 76 are connected in series using metal traces 86 on the upper side of the circuit board 84. In this example, each thermistor 76 is in direct contact with its associated battery cell unit 24. Therefore, if one of the battery cells begins to heat up, this will increase the resistance of the corresponding thermistor, and thus increase the total resistance of the series of thermistors.

[0130] In the above arrangement, the temperature rise of the battery cell can be detected before it begins to release gas, which can help provide a more predictive indication of thermal runaway events. On the other hand, if the battery cell does release gas, this will rapidly increase the temperature of the associated thermistor and / or disconnect or damage the thermistor. In either case, this will be considered an increase in the total resistance of the thermistor string, potentially considered an open circuit. Therefore, if the battery cell begins to release gas, the monitoring system will also generate an alarm signal.

[0131] The PTC thermistor used in the above embodiments is preferably a nonlinear device whose resistance increases nonlinearly with temperature. Figure 15 The resistance versus temperature relationship of an example PTC device is shown. In this example, the cell thermal runaway threshold is set to 70°C, but other values ​​can be used instead.

[0132] Reference Figure 15 As can be seen, the device in this example exhibits the temperature dependence shown in the table below.

[0133]

[0134] Therefore, if there are 18 battery cells, each with an associated PTC thermistor, the total resistance of this string of thermistors will be 18 × 100 Ω = 1.8 kΩ between 25°C and 55°C. However, if the temperature of one of the thermistors increases to 70°C, the total resistance will increase to 1.9 kΩ. At 80°C, the total resistance is 2.2 kΩ, at 90°C it is 9.7 kΩ, and at 100°C it is 82 kΩ. This rapid change in resistance with temperature can be easily detected, allowing the detection of temperature increases in one battery cell without having to monitor all cells individually. For example, in this case, the threshold could be set at around 1.9 kΩ, corresponding to a temperature of 70°C.

[0135] Figure 16 This is a circuit diagram of a monitoring system using two thermistor circuits. (Refer to...) Figure 16In this example, the monitoring system includes a first string of PTC thermistors PTCA1 to PTCA17 and a second string of PTC thermistors PTCB1 to PTCB17. The thermistors from each string are located above one of the vent holes 60 in the laminated busbar. Both strings of thermistors are connected to corresponding monitoring circuits. Each monitoring circuit includes: voltage sources VSA and VSB, resistors RA1 and RB1, and voltage monitors VMA and VMB. Resistors RA1 and thermistors PTCA1 to PTCA17 are connected in series. Similarly, resistors RB1 and thermistors PTCB1 to PTCB17 are connected in series.

[0136] During operation, voltage source VSA applies a predetermined voltage (5V in this example) to resistors RA1 and thermistors PTCA1 to PTCA17 connected in series. Voltage monitor VMA monitors the voltage across the thermistors PTCA1 to PTCA17. Similarly, voltage source VSB applies a predetermined voltage to resistors RB1 and thermistors PTCB1 to PTCB17 connected in series, and voltage monitor VMB monitors the voltage across the thermistors PTCB1 to PTCB17.

[0137] Figure 17 An example is shown of the voltages at various temperatures for one of the thermistors in the series, as seen by the voltage monitors VMA and VMB. In this example, it is assumed that the cell thermal runaway detection threshold is set to 3V, corresponding to a temperature of approximately 70°C. It is assumed that one of the thermistors begins to heat up due to a thermal runaway event, while the other thermistors in the series remain at a temperature of 25°C. (Refer to...) Figure 15 As can be seen, the voltage observed by voltage monitors VMA and VMB increases rapidly above the threshold as the temperature of the thermistor increases. Therefore, by comparing the measured voltage with the threshold, the outputs of voltage monitors VMA and VMB can be used to provide an indication of a thermal runaway event.

[0138] In the example above, by detecting when the resistance of one of the two circuits crosses a threshold, the two thermistor circuits can be used to provide an indication of a thermal runaway event as early as possible. Alternatively, some form of prevention against false alarms can be provided by detecting when the resistance of both circuits crosses a threshold. If desired, different thresholds can be set depending on whether the first or second circuit crosses the threshold.

[0139] By using a string of thermistors as described above, it is possible to detect when a battery cell begins to heat up above its normal operating temperature before thermal runaway begins. Because PTC thermistors are non-linear, this can be done with greater accuracy compared to using trace circuits. Moreover, this can be achieved by monitoring a single parameter—the total resistance of the string of thermistors. The thermistors can be placed on existing circuit boards without significantly increasing size or cost. Therefore, early indication of impending thermal runaway events can be provided without significantly increasing the size, cost, or complexity of the battery module.

[0140] Instead of associating thermistors with individual battery cells, thermistors can be associated with two or more battery cells. For example, a thermistor can be positioned between two adjacent battery cells. There can also be some cells without associated thermistors. On the other hand, two or more thermistors can be associated with individual battery cells for redundancy or to monitor different parts of the cell. For example, since thermistors are connected in series, they can be positioned on both the outgoing and return branches, where each cell or a pair of cells has two thermistors. Generally, any number of thermistors can be used with any number of battery cells.

[0141] If desired, a coordinated arrangement of battery cells and sensors with cell vents pointing to a common location can be provided. For example, thermistors and cell vents can be configured such that multiple cell vents point to a single location. In this case, one thermistor can monitor multiple cells.

[0142] As an alternative to nonlinear positive temperature coefficient (PTC) thermistors, devices with a fundamentally linear response or a nonlinear response different from that of PTC thermistors can be used. For example, sensing circuitry that has a linear response or at least some responses in all operating modes can be used to train machine learning algorithms. Such algorithms can also receive various types of inputs from the entire battery pack. This can allow the detection of various temperature anomalies within the pack, which can indicate impending or likely thermal runaway events.

[0143] For example, as an alternative to PTC thermistors, a series of negative temperature coefficient (NTC) thermistors connected in series can also be used, where each thermistor is associated with a battery cell. In this case, comparator 80 would be configured to determine when the resistance drops below a threshold. However, such an arrangement may be less accurate and does not by itself indicate whether the series of thermistors is disconnected.

[0144] In another embodiment, instead of using sensors connected in series, at least some of the sensors can be connected in parallel. For example, a typical NTC thermistor has a resistance of about 10 kΩ at 25°C and about 1 kΩ at 100°C. For such devices, it is preferable to arrange them at least partially in parallel.

[0145] In another embodiment, instead of using a single string of thermistors, multiple thermocouples connected in series can be used instead. In this case, the string will consist of alternating types of thermocouple wires, with the wire type switching from one type to another. Each thermocouple junction can be associated with one or more battery cells, for example, at each vent. For a four-junction configuration, the approximate voltage output of the string of thermocouples can be given by the following expression:

[0146]

[0147] in, and These are the Seebeck coefficients of the first and second materials, respectively. to This is the temperature at the thermocouple junction. Therefore, by monitoring the voltage of this string of thermocouples, it is possible to determine if there are any significant temperature differences inside the battery module. Since thermal runaway events typically begin with the failure of a single cell, this arrangement can also be used to provide an early indication of an impending thermal runaway event.

[0148] For example, if a BMS receiving input from a series of thermocouples senses that the battery pack appears to be largely stationary at 25°C, then a rapid increase in temperature somewhere within the thermocouple indicating circuitry (say, 40°C) could itself be a warning sign. In this case, the rapid nature of the temperature change rules out the possibility that it is related to a large-scale temperature change.

[0149] Typically, in any of the embodiments disclosed herein, the rate of change of the parameter being monitored, or any other time derivative of that parameter, can be used to detect an impending or potential thermal runaway event. For example, if a string of NTC thermistors is connected in series, then due to the characteristics of the devices, it may be necessary to monitor the time derivative. This may also help mitigate the effects of a broken string. For example, if the resistance drops rapidly before the string breaks, this may indicate thermal runaway.

[0150] In other embodiments, other temperature sensing devices can be used, either directly or in place of any of the devices described above. For example, a series of resistance temperature detectors (RTDs) or a series of infrared thermometers can be used instead of the thermistors or thermocouples described above.

[0151] The various embodiments described above can also be used in combination. For example, a temperature sensing device (such as a PTC thermistor) can be connected across a vent hole on a circuit board in such a way that the temperature sensing device responds to an increase in the temperature of the associated battery cell, and is disconnected from the circuit board if the battery cell needs to vent. For example, the device can be connected to a cuttable metal trace. In this way, the system can respond to both an increase in the temperature of the battery cell and venting of the battery cell. Similarly, any other combination of the embodiments described above can be used, or alternatively.

[0152] It should be understood that the embodiments of the invention have been described above by way of example only, and specific modifications will be apparent to those skilled in the art within the scope of the appended claims.

Claims

1. A battery pack, the battery pack comprising: Multiple battery cells (25); Sensing circuit (62) extending across the plurality of battery cells; as well as Monitoring unit (46), which is connected to the sensing circuit, The monitoring unit includes a continuity detector (66) configured to detect interruptions in the continuity of the sensing circuit. The sensing circuit includes a continuously cut-off component, and The continuously cut-off assembly extends across the venting paths of each of the plurality of battery cells.

2. The battery pack according to claim 1, wherein, The monitoring unit is configured to generate an alarm signal when an interruption in the continuity of the continuously disconnectable component is detected.

3. The battery pack according to claim 1 or 2, wherein, The continuously cut-off component is configured to be cut off by the venting action of the cell that has experienced a thermal event.

4. The battery pack according to claim 1 or 2, wherein, The continuously cuttable component is an electrical conductor.

5. The battery pack according to claim 4, wherein, The monitoring unit is configured to apply an electrical signal to the electrical conductor and detect open circuits in the electrical conductor.

6. The battery pack according to claim 1 or 2, wherein, The continuously cuttable component includes traces on a circuit board.

7. The battery pack according to claim 6, wherein, The circuit board includes multiple vent holes, each of which is associated with a battery cell, and the trace is a continuous trace spanning multiple vent holes.

8. The battery pack according to claim 7, wherein, The trace includes a stress concentration feature at which the trace crosses the exhaust port.

9. The battery pack according to claim 8, wherein, The stress concentration feature includes at least one notch in the trace.

10. The battery pack according to claim 6, wherein the battery pack further comprises a laminated bus, wherein, The circuit board is part of the laminated bus.

11. The battery pack according to claim 6, wherein, The circuit board is configured to transmit electrical signals from the battery cell to the battery management unit.

12. The battery pack according to claim 1 or 2, wherein, The monitoring unit is part of the battery management unit.

13. The battery pack according to claim 1 or 2, wherein, The monitoring unit is configured to receive input from at least one other sensor.

14. The battery pack according to claim 1 or 2, wherein the battery pack includes a plurality of sensing circuits.

15. The battery pack according to claim 1 or 2, wherein, The plurality of battery cells are stacked, and each cell is oriented such that the exhaust path is in the direction of the sensing circuit.

16. The battery pack according to claim 1 or 2, wherein the battery pack comprises a plurality of battery modules, and each battery module comprises a plurality of battery cells.

17. A method for detecting thermal events in a battery pack comprising multiple battery cells, the method comprising the following steps: The sensing circuit is monitored, the sensing circuit including a continuously cut-off component extending across the venting paths of each of the plurality of battery cells; Detect interruptions in the continuity of the continuously cut-off component; as well as An alarm signal is generated when an interruption in the continuity of the continuously cut-off component is detected.

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