Thermal event identification

Abstract

A thermal event identification device for detecting a thermal event in a battery pack having at least one battery cell. The thermal identification device includes a heat-sensitive component, a conductive substrate, and an enclosure containing an electrolyte. When the temperature is lower than the lower threshold temperature, the substrate has a first resistance value. When the heat sensitive component is heated above a threshold temperature, the electrolyte is released from the enclosure and the substrate is immersed in the electrolyte. This changes the resistance of the substrate to different resistance values. By measuring the resistance of the conductive substrate, the controller may determine whether a thermal event has occurred. The heat sensitive component is positioned adjacent to the battery cell to identify a thermal event associated with the battery cell.

Description

Technical Field

[0001] The present invention relates to the field of identifying thermal events. Specifically, the present invention relates to the identification of thermal events in battery cells of a battery pack. Background Art

[0002] It is known that a battery pack includes more than one battery cell, which are arranged in parallel or in series, or in a combination of parallel and series. It is known that batteries are sensitive to temperature. Specifically, it is generally preferred to operate the batteries at temperatures below the maximum operating temperature. Above the maximum operating temperature for a particular battery, the performance of the battery may deteriorate, potential failures may occur in the battery cell, or the safety risk may increase. This may be especially the case for lithium batteries or other rechargeable batteries, in which there is a risk of thermal runaway at high temperatures. Thermal runaway is a phenomenon in which the battery enters a self-heating state, and may be a problem if a rechargeable battery is not handled properly or if there are defects or errors in the battery. As an example, certain lithium batteries can operate safely at temperatures up to between 60 °C and 75 °C. Thermal runaway may occur in these batteries at temperatures in the region of 85 °C to 110 °C. However, these temperatures vary depending on the battery chemistry. It may be beneficial to identify whether the temperature of the battery has risen above a certain temperature.

[0003] As a safety feature, many rechargeable batteries have a separator that is configured to disable the battery cell when the temperature of the battery cell exceeds a threshold. The separator may allow ion exchange between the cathode and the anode via the separator at temperatures below the threshold temperature, and may prevent ion exchange through the separator at temperatures above the threshold temperature, thereby preventing thermal runaway in most cases. For example, the separator may melt at the threshold temperature, thereby permanently disabling the cell. An example of such a separator is a three-layer battery separator including a layer of polyethylene between two layers of polypropylene. In the case where a battery cell experiences such a failure, it is beneficial to be able to identify the battery cell.

[0004] It is known to identify a disabled battery cell by measuring the impedance of the battery cell. However, for battery cells arranged in a parallel configuration, it is not possible to measure the impedance of each individual battery cell. Although it is possible to measure the impedance of each individual battery cell arranged in a series configuration, this may be time-consuming.

[0005] As an alternative to directly measuring whether a battery cell has been disabled, it is known to monitor the temperature of the battery cell to determine whether the separator melting temperature has been exceeded. This can be achieved by having a thermistor in each cell, although this can be expensive. Alternatively, thermochromic stickers are available which change color at a certain temperature. The stickers can be adhered to each battery cell, providing a visual indication of whether a specific temperature has been exceeded. However, battery cells are typically contained within a sealed housing. The stickers may only be visible by opening the housing. Generally, the housing is opened during use or by a technician, so a visual indication of the temperature change is not available. Summary of the Invention

[0006] In view of the above background art and according to a first aspect of the present invention, there is provided a thermal event identification device for a battery pack including at least one battery cell. The thermal identification device includes a thermosensitive component, which includes a substrate and a casing containing an electrolyte, wherein the substrate is conductive. Below a first temperature, the resistance of the substrate has a first resistance value. When the thermosensitive component is heated to above the first temperature, the electrolyte is released from the casing, such that the substrate is immersed in the electrolyte and the resistance of the substrate becomes a second resistance value. The thermal identification device further includes a first electrical connection and a second electrical connection, wherein the thermosensitive component is electrically connected to the first electrical connection and the second electrical connection such that the resistance of the substrate of the thermosensitive component can be measured. The thermal identification device further includes a controller configured to determine whether a thermal event has occurred based on the resistance of the thermosensitive component. In use, the thermosensitive component is configured to be adjacent to the battery cell.

[0007] In this way, a battery cell in the battery pack that has exceeded a threshold temperature can be identified and located. The thermal event identification device can be used to determine whether a battery cell has exceeded the temperature at which the separator is configured to disable the battery cell, such that any disabled battery cells can be removed and replaced. The thermal event identification device can be used to determine whether a battery has exceeded a temperature at which there is a known risk of problems such as thermal runaway occurring. This can allow the battery cell to be replaced before it fails or is disabled.

[0008] According to a second aspect of the present invention, there is provided a battery pack including two or more battery cells and a thermal event identification device according to the first aspect of the present invention, wherein each thermosensitive component is adjacent to a battery cell.

[0009] According to a third invention of the present invention, there is provided a method for identifying whether a thermal event has occurred in a battery cell of a battery pack, the method including measuring the resistance of a thermosensitive component adjacent to the battery cell. The thermosensitive component includes a substrate and a casing containing an electrolyte. The thermosensitive component is conductive. Below a first temperature, the substrate has a first resistance value. In the case where the thermosensitive component is heated to above the first temperature, the electrolyte is released from the casing, such that the substrate is immersed in the electrolyte and the resistance of the substrate becomes a second resistance value. The thermosensitive component is electrically connected to a first electrical connection and a second electrical connection such that the resistance of the substrate of the thermosensitive component can be measured, wherein in the case where the measured resistance is lower than a threshold resistance, a thermal event has occurred in the battery cell adjacent to the thermosensitive component. The method further includes comparing the measured resistance with the threshold resistance. Description of the Drawings

[0010] Specific embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0011] Figure 1 A schematic diagram showing a first thermosensitive component and a second thermosensitive component of a thermal identification device according to an embodiment of the present invention is shown.

[0012] Figure 2 A schematic diagram showing an array of thermosensitive components of a thermal identification device according to an embodiment of the present invention is shown.

[0013] Figure 3 A schematic cross-sectional view showing a substrate of a thermosensitive component of a thermal identification device according to an embodiment of the present invention is shown.

[0014] Figure 4 A flowchart showing a method for identifying whether a thermal event has occurred in a battery cell according to an embodiment of the present invention is shown. Detailed Description

[0015] According to an embodiment of the present invention, there is provided a thermal event identification device for a battery pack including at least one battery cell. The thermal event identification device includes a thermosensitive component. The thermosensitive component includes a substrate and a casing containing an electrolyte. The substrate is conductive. Below a first temperature, the resistance of the substrate has a first resistance value. In the case where the thermosensitive component is heated to above the first temperature, the electrolyte is released from the casing, such that the substrate is immersed in the electrolyte and the resistance of the substrate becomes a second resistance value. The thermal identification device further includes a first electrical connection and a second electrical connection. The thermosensitive component is electrically connected to the first electrical connection and the second electrical connection such that the resistance of the substrate of the thermosensitive component can be measured. The thermal identification device further includes a controller configured to determine whether a thermal event has occurred based on the resistance of the thermosensitive component. In use, the thermosensitive component is configured to be adjacent to the battery cell.

[0016] In some embodiments, the second resistance value is lower than the first resistance value.

[0017] The first electrical connection and the second electrical connection are connected to the thermosensitive component such that current can flow through the thermosensitive component from the first electrical connection to the second electrical connection, or from the second electrical connection to the first electrical connection. In other words, the current path can be along the first electrical connection, through the thermosensitive component, and along the second electrical connection (or vice versa, where the current path is along the second electrical connection, through the thermosensitive component, and along the first electrical connection). In this context, the first electrical connection and the second electrical connection are wires or other conductive elements that can be used to connect the thermosensitive component to a device, circuit, or component for measuring resistance.

[0018] In use, the controller can be used to monitor the resistance of the substrate. Since the thermosensitive component is configured to be adjacent to the battery cell during use, the temperature of the thermosensitive component is affected by the temperature of the battery cell. If the temperature of the battery cell increases, the temperature of the thermosensitive component also increases, and if the temperature of the battery cell decreases, the temperature of the thermosensitive component also decreases. The temperature of the thermosensitive component can be similar to the temperature of the battery cell, or can deviate from the temperature of the battery cell. In the case where the resistance of the substrate is equal to or close to the first resistance value, this indicates that the enclosure is intact and thus the temperature of the thermosensitive component has not yet risen above the first temperature. This in turn indicates that the temperature of the battery has not yet risen above the threshold temperature. In the case where the resistance of the substrate is equal to or close to the second resistance value, this indicates that the electrolyte has been released from the enclosure and thus the temperature of the thermosensitive component has risen above the first temperature. This in turn indicates that the temperature of the battery has risen above the threshold temperature.

[0019] In some embodiments, the thermal identification device includes two or more thermosensitive components and at least one additional electrical connection. Each thermosensitive component is electrically connected to two electrical connections such that the resistance of the substrate of each thermosensitive component can be measured individually. The controller is configured to determine whether a thermal event has occurred at each thermosensitive component based on the resistance of each thermosensitive component. In use, each thermosensitive component is configured to be adjacent to a battery cell.

[0020] In some embodiments where the thermal identification device includes two or more thermosensitive components, a given electrical connection can be connected to more than one thermosensitive component. Each thermosensitive component can be connected to a unique combination of electrical connections such that the resistance of each thermosensitive component can be measured individually. In a simple example, refer to Figure 1, the thermal identification device 100 may include a first thermosensitive component 110 and a second thermosensitive component 120. The first thermosensitive component 110 is connected to a first electrical connection 130 at 131 and to a second electrical connection 150 at 151. The second thermosensitive component 120 is connected to a third electrical connection 140 at 141 and to the second electrical connection 150 at 153. When the resistance measurement is performed between point 132 and point 152, current flows through the first thermosensitive component between 131 and 151, and the resistance measurement of the first thermosensitive component can be performed. No current flows through the second thermosensitive component. When the resistance measurement is performed between point 142 and point 152, current flows through the second thermosensitive component between 141 and 153, and the resistance measurement of the second thermosensitive component can be performed. The positions of the points at which the electrical connections are connected to the thermosensitive components are for illustrative purposes only. The electrical connections can be connected to each thermosensitive component such that the resistance measurement is performed in the plane of the thermosensitive component, or such that the resistance measurement is performed through the thermosensitive component, or the resistance measurement is performed in some other configuration.

[0021] In some embodiments, the thermal identification device includes more than two thermosensitive components. Each thermosensitive component is electrically connected to two electrical connections such that the resistance of the substrate of each thermosensitive component can be measured individually. The controller is configured to determine whether a thermal event has occurred at each thermosensitive component based on the resistance of each thermosensitive component. In use, each thermosensitive component is configured to be adjacent to a battery cell. In some embodiments where the thermal identification device includes more than two thermosensitive components, a given electrical connection can be connected to more than one thermosensitive component. Each thermosensitive component can be connected to a unique combination of electrical connections such that the resistance of each thermosensitive component can be measured individually.

[0022] Reference Figure 2, the thermal identification device 200 is shown as having an array of thermal components 211, 212, 213, 221, 222, 223, 231, 232, 233, 241, 242, and 243. The first (top) row of thermal components 211, 212, 213 are all connected to a first electrical connection 251. The second row of thermal components 221, 222, 223 are all connected to a second electrical connection 252. The third row of thermal components 231, 232, 233 are all connected to a third electrical connection 253. The fourth row of thermal components 241, 242, 243 are all connected to a fourth electrical connection 254. The first (left - hand) column of thermal components 211, 221, 231, 241 are all connected to a fifth electrical connection 261. The second column of thermal components 212, 222, 232, 242 are all connected to a sixth electrical connection 262. The third column of thermal components 213, 223, 233, 243 are all connected to a seventh electrical connection 263. The points at which the thermal components are connected to their respective electrical connections are shown as dots. In this way, each thermal component can be individually addressed to measure its resistance. For example, using the second electrical connection 252 and the sixth electrical connection 262 allows the resistance of the thermal component 222 to be measured and does not cause current to flow through any other thermal component. The electrical connections can be made to each thermal component such that the resistance measurement is made in the plane of the thermal component, or such that the resistance measurement is made through the thermal component, or in some other configuration.

[0023] Figure 2 The example shown in shows twelve thermal components and seven electrical connections. This is only an example. The thermal identification device can include any number of thermal components and any number of electrical connections. Figure 2 Thermal components are shown arranged in an array of rows and columns, thereby allowing each thermal component to be addressed by row - column. The thermal components and electrical connections can be arranged in a configuration different from that Figure 2 shown. Any electrical connection arrangement that allows the resistance of each thermal component to be measured individually is possible.

[0024] Each thermal component includes a housing containing an electrolyte. In some embodiments, the thermal component can include more than one housing containing an electrolyte. In some embodiments, the thermal component can include more than one micro - housing containing an electrolyte. The micro - housing can include a small sphere (typically, with a diameter of 1000 microns or less), where a substantially uniform wall surrounds a core. The core includes the electrolyte. The micro - housing can also take other forms. For example, the wall may be non - uniform, the micro - housing can have multiple walls, or the micro - housing can be any other housing that can contain an electrolyte.

[0025] (One or more) casings containing electrolyte can be configured to rupture at a certain threshold temperature. When the casing ruptures, the electrolyte is released into the substrate. The substrate is soaked with the electrolyte. Soaking the substrate with the electrolyte in this context means that the electrolyte enters the substrate such that the electrical properties of the substrate change where the electrolyte is present.

[0026] In some embodiments, (one or more) casings can be embedded in the substrate. Specifically, a micro-casing can be embedded in the substrate.

[0027] Reference Figure 3 , in some embodiments, the thermosensitive component 300 can include a substrate 310, wherein the micro-casing is embedded in the substrate 310. The substrate 310 is positioned between a first layer of aluminum foil 320 and a second layer of aluminum foil 330. A first insulator 340 and a second insulator 350 are positioned adjacent to the first layer of aluminum foil 320 and the second layer of aluminum foil 330, respectively. When the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the casing such that the substrate is soaked in the electrolyte and the resistance of the substrate becomes a second resistance value. The resistance of the thermosensitive component can be measured through the thermosensitive component such that a first electrical connection is connected to the first layer of aluminum foil 320 and a second electrical connection is connected to the second layer of aluminum foil 330 (or vice versa). The first layer of aluminum foil and the second layer of aluminum foil can be replaced with other conductive layers. The first electrical connection can be connected to the first conductive layer and the second electrical connection can be connected to the second conductive layer, wherein the substrate is positioned between the first conductive layer and the second conductive layer such that the first conductive layer and the second conductive layer are electrically connected via the substrate.

[0028] Figure 3 The arrangement in is only an example. Other arrangements are also possible.

[0029] When the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the casing such that the substrate is soaked in the electrolyte. In some embodiments, the electrolyte can then dry out on the substrate over time. The resistance of the substrate can remain at the second resistance value until the electrolyte dries out. Once the electrolyte dries out, the resistance value of the substrate can return to the first resistance value. In other embodiments, once the electrolyte dries out, the resistance of the substrate can remain at the second resistance value or can become a third resistance value.

[0030] The substrate and (one or more) casings can be wrapped such that when the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the casing such that the substrate is soaked in the electrolyte, the substrate does not dry out and the resistance of the substrate remains at the second resistance value.

[0031] In some embodiments, the thermosensitive component can be an adhesive such that the thermosensitive component can adhere to the battery cell.

[0032] In use, the one or more thermosensitive components may be placed adjacent to or adhered to an area of the battery cell that is visible when the battery pack is open. For example, the one or more thermosensitive components may be placed adjacent to or adhered to the top edge of the battery cell.

[0033] In some embodiments, the controller may be configured to determine at fixed intervals whether a thermal event has occurred based on the resistance of the thermosensitive component. In some embodiments, the interval may be shorter than the time it takes for the electrolyte to dry on the substrate. In cases where the thermal identification device includes more than one thermosensitive component, the controller may be configured to sequentially determine the resistance of each thermosensitive component. The controller may be configured to repeat the sequential determination of the resistance of each thermosensitive component at fixed intervals.

[0034] In some embodiments, the thermosensitive component may include more than one type of enclosure containing an electrolyte, where each type of enclosure is configured to release the electrolyte at a different temperature. In some embodiments, the resistance of the substrate may have different values depending on the released electrolyte. In this way, different temperatures reached by the thermosensitive component can be detected by measuring the resistance of the substrate.

[0035] An example of a suitable electrolyte is lithium hexafluorophosphate. However, other electrolytes may also be used.

[0036] In use, the thermosensitive component is adjacent to the battery cell, and thus the temperature of the thermosensitive component is related to the temperature of the battery cell. The temperature of the thermosensitive component relative to the temperature inside the battery cell depends on the position of the thermosensitive component relative to the battery cell and on how the temperature outside the battery cell is related to the temperature inside the battery cell. The temperature of the thermosensitive component may follow the temperature change of the battery cell such that when the temperature of the battery cell increases, the temperature of the thermosensitive component also increases. Similarly, when the temperature of the battery cell decreases, the temperature of the thermosensitive component also decreases. The magnitude of the temperature of the thermosensitive component may deviate from the temperature of the battery cell. The temperature at which the enclosure releases the electrolyte may be calibrated based on the relationship between the temperature of the battery cell and the temperature of the thermosensitive component.

[0037] The first resistance value may vary slightly depending on the ambient temperature and the operating temperature of the battery cell. However, the variation of the first resistance value is less than the difference between the first resistance value and the second resistance value. In some embodiments, the first resistance value may be a numerical range higher than a threshold resistance value, and the second resistance value may be a numerical range lower than the threshold resistance value. Below the first temperature, the resistance of the substrate is within the first resistance value range. When the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the enclosure, such that the substrate is immersed in the electrolyte, and the resistance of the substrate becomes a resistance within the second resistance value range. In some examples, below the first temperature, the resistance of the substrate is higher than the threshold resistance. When the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the enclosure, such that the substrate is immersed in the electrolyte, and the resistance of the substrate becomes lower than the threshold resistance.

[0038] As discussed, releasing the electrolyte changes the resistance of the substrate. In some embodiments, the enclosure may also contain a dye such that when the thermosensitive component is heated to a temperature higher than the first temperature, the dye is released from the enclosure, causing the substrate to change color. In other embodiments, the thermal identification device may include an additional enclosure containing a dye such that when the thermosensitive component is heated to a temperature higher than the first temperature, the dye is released from the enclosure, causing the thermosensitive component to change color. The color change may be irreversible.

[0039] A method for identifying whether a thermal event has occurred in a battery cell of a battery pack is also provided. The method includes measuring the resistance of a thermosensitive component adjacent to the battery cell. The thermosensitive component includes a substrate and an enclosure containing an electrolyte, wherein the thermosensitive component is conductive. Below the first temperature, the substrate has a first resistance value. When the thermosensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the enclosure, such that the substrate is immersed in the electrolyte, and the resistance of the substrate becomes a second resistance value. The thermosensitive component is electrically connected to a first electrical connection and a second electrical connection such that the resistance of the substrate of the thermosensitive component can be measured. If the measured resistance is lower than the threshold resistance, a thermal event has occurred in the battery cell adjacent to the thermosensitive component.

[0040] Reference Figure 4 , the method may include measuring the resistance of a thermosensitive component adjacent to the battery cell at step 410. The method may also include comparing the measured resistance with a threshold resistance 421 at step 420. If the measured resistance is lower than the threshold resistance, a thermal event has occurred in the battery cell adjacent to the thermosensitive component.

[0041] In the case where the thermal identification device includes more than one thermosensitive component, the method includes sequentially measuring the resistance of each thermosensitive component and comparing the measured resistance with the threshold resistance.

[0042] The method can be repeated at fixed intervals.

[0043] In the case where it is determined that a thermal event has occurred, a notification can be provided. The notification can include: sending a signal to a controller or processor, sending an electronic or wireless message, turning on a light or buzzer, or other notifications. The notification can be visible, audible, electronic, wireless, or in other ways.

Claims

1. A thermal event recognition device for identifying a thermal event in a battery pack including at least one battery cell, the thermal recognition device comprising: A heat-sensitive component, the heat-sensitive component comprising a substrate and a capsule containing an electrolyte, wherein: The substrate is conductive; Below a first temperature, the resistance of the substrate has a first resistance value; and When the heat-sensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the package so that the substrate is immersed in the electrolyte and the resistance of the substrate becomes a second resistance value; a first electrical connection and a second electrical connection, wherein the temperature sensitive component is electrically connected to the first electrical connection and the second electrical connection so that the resistance of the substrate of the temperature sensitive component can be measured; and A controller is configured to determine whether a thermal event has occurred based on the resistance of the thermally sensitive component, wherein, in use, the thermally sensitive component is configured adjacent a battery cell.

2. The thermal recognition device according to claim 1, wherein: The second resistance value is lower than the first resistance value.

3. The thermal event identification device according to claim 1, further comprising: Two or more heat-sensitive components and at least one additional electrical connection, wherein: each heat-sensitive component being electrically connected to two electrical connections so that the resistance of said substrate of each heat-sensitive component can be measured individually; The controller is configured to determine whether a thermal event has occurred at each temperature-sensitive component based on the resistance of each temperature-sensitive component; and In use, each heat-sensitive component is arranged adjacent to a battery cell.

4. The thermal recognition device according to claim 3, wherein: At least one electrical connection is common to more than one temperature-sensitive component, enabling the resistance of the substrate to be measured individually for each temperature-sensitive component.

5. The thermal recognition device according to claim 1, further comprising: An array of temperature-sensitive components arranged in an array of more than one row and more than one column, wherein: each heat-sensitive component being electrically connected to two electrical connections so that the resistance of said substrate of each heat-sensitive component can be measured individually; The controller is configured to determine whether a thermal event has occurred at each temperature-sensitive component based on the resistance of each temperature-sensitive component; and In use, each heat-sensitive component is arranged adjacent to a battery cell.

6. The thermal recognition device according to claim 5, wherein: Each temperature sensitive component in a row of temperature sensitive components is connected to a common electrical connection, and each temperature sensitive component in a column of temperature sensitive components is connected to a common electrical connection.

7. The thermal recognition device according to claim 1, wherein: The capsule is embedded in the substrate.

8. The thermal recognition device according to claim 7, wherein: The heat-sensitive component includes a plurality of capsules embedded in the substrate, the capsules containing an electrolyte.

9. The thermal recognition device according to claim 8, wherein: The capsule is a micro capsule.

10. The thermal identification device according to claim 1, further comprising a first conductive layer and a second conductive layer, and wherein: the first electrical connection being connected to the first conductive layer; the second electrical connection is connected to the second conductive layer; and The substrate is positioned between the first conductive layer and the second conductive layer such that the first conductive layer and the second conductive layer are electrically connected via the substrate.

11. The thermal recognition device according to claim 1, wherein: The temperature-sensitive component further comprises one or more capsules containing a first dye, and wherein the dye is released from the one or more capsules when the temperature-sensitive component is heated above the first temperature.

12. The thermal recognition device according to claim 11, wherein: The temperature-sensitive component further comprises one or more capsules containing a second dye, and wherein the dye is released from the one or more capsules when the temperature-sensitive component is heated above a second temperature.

13. A battery pack comprising: two or more battery cells; as well as The thermal event identification device according to claim 3, wherein each heat-sensitive component is adjacent to the battery cell.

14. A method for identifying whether a thermal event has occurred in a battery cell of a battery pack, the method comprising: measuring the resistance of a heat-sensitive component adjacent to the battery cell, wherein: The heat-sensitive component includes a substrate and a capsule containing an electrolyte; The heat-sensitive component is conductive; When the temperature is lower than the first temperature, the substrate has a first resistance value; When the heat-sensitive component is heated to a temperature higher than the first temperature, the electrolyte is released from the package so that the substrate is immersed in the electrolyte and the resistance of the substrate becomes a second resistance value; the temperature sensitive component being electrically connected to a first electrical connection and a second electrical connection so that the resistance of the substrate of the temperature sensitive component can be measured; and In the event that the measured resistance is below a threshold resistance, a thermal event has occurred in the battery cell adjacent to the thermally sensitive component; and The measured resistance is compared to the threshold resistance.

15. The method according to claim 14, wherein: The second resistance value is lower than the first resistance value.

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