Thermal chain determination system and thermal chain determination method

Abstract

A thermal chain determination system 100 comprises: voltage sensors 3 for detecting cell voltages of a plurality of cells 2 in a battery pack 1; a temperature sensor 4 for detecting a temperature in the battery pack 1; and a controller 10 for determining a thermal chain in the battery pack 1, wherein the controller 10 determines a voltage abnormality of the cell voltages on the basis of the detected voltages detected by the voltage sensors 3, determines a high-temperature abnormality in the battery pack 1 on the basis of the detected temperature detected by the temperature sensor 4, and determines that a thermal chain has occurred in the battery pack 1 when it is determined that both the high-temperature abnormality and the voltage abnormality have occurred.

Description

Heat chain determination system and heat chain determination method

[0001] The present invention relates to a thermal linkage determination system and a thermal linkage determination method.

[0002] An active thermal runaway mitigation system that prevents the propagation of a thermal runaway event to adjacent cells in a battery pack has been known (Patent Document 1). The active thermal runaway mitigation system described in Patent Document 1 includes at least one fluid-containing conduit adjacent to cells in the battery pack. The conduit includes multiple fracture points adjacent to a subset of the cells, each fracture point configured to form a fracture at a preset temperature lower than the melting temperature of the conduit. Once the fracture forms, the fluid contained within the conduit is discharged through the fracture.

[0003] JP 2011-60755 A

[0004] The active thermal runaway mitigation system is designed to cause cracks in the conduit due to cell heat generation, and is based on the assumption that thermal runaway depends solely on the temperature inside the battery pack. However, cells also generate heat during charging and discharging. If an attempt is made to determine thermal chain reaction based on the assumption that thermal runaway can be determined solely from the temperature inside the battery pack, as with the active thermal runaway mitigation system, temperature increases due to factors other than thermal runaway may be mistakenly determined to be thermal runaway, resulting in low accuracy.

[0005] The problem to be solved by the present invention is to provide a heat linkage determination system and a heat linkage determination method with high determination accuracy.

[0006] The present invention solves the above problem by determining whether a cell voltage is abnormal based on the detected voltage detected by a voltage sensor, determining whether a high temperature is abnormal within the battery pack based on the detected temperature detected by a temperature sensor, and determining that a thermal chain reaction has occurred in the battery pack if it is determined that both a high temperature abnormality and a voltage abnormality have occurred.

[0007] According to the present invention, it is possible to improve the accuracy of determining thermal chain reactions.

[0008] Figure 1 is a block diagram of a thermal linkage determination system according to an embodiment of the present invention. Figure 2 is a graph illustrating the voltage characteristics, temperature characteristics, and determination logic of a cell when a thermal linkage occurs. Figure 3 is a block diagram of a thermal linkage determination system according to a modified embodiment of the present invention. Figure 4 is a graph illustrating the voltage characteristics, temperature characteristics, and determination logic of a cell when a thermal linkage occurs.

[0009] A heat chain determination system and a heat chain determination method according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a block diagram of a heat chain determination system. The heat chain determination system 100 includes a battery pack 1 and a controller 10.

[0010] The battery pack 1 includes multiple cells 2, a voltage sensor 3, and a temperature sensor 4. The battery pack 1 includes a battery group in which multiple battery cells (battery group) 2 are connected in series or parallel, a voltage sensor 3, and a temperature sensor 4. The battery pack 1 includes multiple battery modules in which multiple cells (battery cells) 2 are modularized, and the battery modules are housed in a case. The cells 2 are, for example, lithium-ion secondary batteries. As an example of the cells 2, a flat-type laminate film lithium-ion secondary battery includes a power generating element formed by stacking electrode layers (positive and negative electrode layers) and separators and filling them with an electrolyte, a positive electrode tab connected to the positive electrode layer, a negative electrode tab connected to the negative electrode layer, and an exterior member that houses and seals these. Note that although a detailed description of the materials contained in the lithium-ion secondary battery and the battery structure will be omitted, well-known battery materials and structures can be applied to lithium-ion secondary batteries. The cells 2 are not limited to secondary batteries containing an electrolyte, and may also be lithium-ion batteries containing a solid electrolyte layer (so-called all-solid-state lithium-ion batteries).

[0011] The voltage sensor 3 is a sensor that detects the cell voltages of the multiple cells 2. The voltage sensor 3 detects the voltage between the terminals of the cells 2 and is connected between the wiring connected to the positive and negative electrodes of the cells 2. As shown in FIG. 1 , the multiple voltage sensors 3 are connected to the multiple cells 2, respectively. That is, the voltage sensors 3 detect the cell voltages of the correspondingly connected cells 2. The multiple voltage sensors 3 output the detected cell 2 voltages to the controller 10. Note that in the example of FIG. 1 , the multiple voltage sensors 3 are provided inside the battery pack 1, but the multiple voltage sensors 3 may also be provided outside the battery pack 1. For example, the multiple cells 2 have voltage detection tabs, and lead-out wiring is connected to the detection tabs. The voltage sensor 3 may then be electrically connected to the cells 2 and detect the voltages of the cells 2 by connecting the voltage sensors 3 to lead-out wiring from outside the pack.

[0012] The temperature sensor 4 detects the temperature inside the cell 2 and outputs the detected temperature to the controller 10. One or more temperature sensors 4 may be provided in the battery pack 1.

[0013] The controller 10 determines whether a thermal chain reaction has occurred within the battery pack based on the voltage detected by the voltage sensor 3 and the temperature detected by the temperature sensor 4. The controller 10 is configured as a computer equipped with hardware and software, and includes a memory that stores programs and a CPU that executes the programs stored in the memory. The controller 10 has functions such as determining high temperature abnormalities within the battery pack 1, determining voltage abnormalities in cell voltages, and determining thermal chain reaction within the pack, and has functional blocks corresponding to each function: a voltage abnormality determination unit 11, a high temperature abnormality determination unit 12, and a thermal chain reaction determination unit 13.

[0014] The voltage abnormality determination unit 11 determines a voltage abnormality in the cell voltage based on the detected voltage of the voltage sensor 3. The voltage abnormality determination unit 11 acquires the detected voltages of the cells 2 from the multiple voltage sensors 3. The voltage abnormality determination unit 11 compares the detected voltages of the multiple cells 2 with a cell voltage threshold. The cell voltage threshold is a determination threshold for determining a drop in cell voltage and is set in advance depending on the battery material contained in the cells 2, the battery structure of the cells 2, etc. Note that the cell voltage threshold may be a value experimentally determined depending on the voltage drop that occurs when thermal runaway occurs in the cells 2. Note that the cell 2 has a predetermined voltage range and temperature range for normal use. For example, when the battery pack 1 is mounted on a vehicle, the operating voltage range is determined to include the range of voltage changes that occur during charging and discharging of the battery pack 1 while the vehicle is running, while the vehicle is stopped, or while the battery is being charged by a charging device external to the vehicle. Similarly, the operating temperature range is determined to include the range of temperature changes that occur during charging and discharging of the battery pack 1. The cell voltage threshold is preferably set to a voltage lower than the lower limit of the operating voltage range.

[0015] If the cell voltage of cell 2 is equal to or less than the cell voltage threshold, the voltage abnormality determination unit 11 determines that a voltage abnormality has occurred in the cell voltage. On the other hand, if the cell voltage of cell 2 is higher than the cell voltage threshold, the voltage abnormality determination unit 11 determines that a voltage abnormality has not occurred in the cell voltage.

[0016] The high temperature abnormality determination unit 12 determines a high temperature abnormality in the battery pack 1 based on the temperature detected by the temperature sensor 4. Specifically, the voltage abnormality determination unit 11 acquires the detected temperature of the cell 2 from the temperature sensor 4. The voltage abnormality determination unit 11 determines a high temperature abnormality when the temperature detected by the temperature sensor 4 increases by a predetermined temperature or more per predetermined time. The predetermined time and the predetermined temperature are determination thresholds for determining a temperature increase during thermal runaway, and are set in advance depending on the battery material contained in the cell 2, the battery structure of the cell 2, etc. Note that the predetermined time and the predetermined temperature may be values ​​experimentally determined depending on the temperature increase that occurs when thermal runaway occurs in the cell 2. If the temperature detected by the temperature sensor 4 increases by a predetermined temperature or more per predetermined time, the high temperature abnormality determination unit 12 determines that a high temperature abnormality has occurred in the battery pack 1. On the other hand, if the temperature detected by the temperature sensor 4 does not increase by a predetermined temperature or more per predetermined time, the high temperature abnormality determination unit 12 determines that a high temperature abnormality has not occurred in the battery pack 1. The high temperature abnormality determination unit 12 may determine that a high temperature abnormality has occurred when the temperature detected by the temperature sensor 4 is equal to or higher than a predetermined temperature threshold.

[0017] When it is determined that both a high temperature abnormality and a voltage abnormality have occurred, the thermal chain determination unit 13 determines that a thermal chain has occurred in the battery pack 1. On the other hand, when it is determined that only one of a high temperature abnormality and a voltage abnormality has occurred, or when it is determined that neither a high temperature abnormality nor a voltage abnormality has occurred, the thermal chain determination unit 13 determines that a thermal chain has not occurred in the battery pack 1.

[0018] When thermal runaway occurs, abnormal heat generation occurs in cell 2, causing the cell 2 to reach a high temperature. However, heat generation in cell 2 also occurs during normal charging and discharging, so the cell temperature may rise sharply during rapid charging or high-load driving. Unlike the present embodiment, a determination method that determines thermal runaway or thermal chain reaction based solely on the temperature rise in cell 2 cannot determine whether the high temperature abnormality in cell 2 is due to thermal runaway or a factor other than thermal runaway, and there is a risk of false detection.

[0019] In this embodiment, a thermal chain reaction is determined based on both a high temperature abnormality and a voltage abnormality in the cell 2. This improves the accuracy of determining a thermal chain reaction.

[0020] Referring to Figure 2, the voltage characteristics, temperature characteristics, judgment logic, and thermal chain judgment method of the cells when a thermal chain occurs will be described. In the graph of Figure 2, the judgment flag of the judgment result indicates normal at a low level and "abnormal" at a high level. The voltage sensor 3 and the temperature sensor 4 detect the cell voltages of the multiple cells 2 and the temperature inside the battery pack 1 at a predetermined cycle. The controller 10 obtains the detected voltage from the voltage sensor 3 and the detected temperature from the temperature sensor 4. At time t １ At time t, the temperature of cell 2 rises due to thermal runaway. The cell voltage drops due to thermal runaway of cell 2. ２ When the cell voltage becomes equal to or less than the cell voltage threshold value at time t, the voltage abnormality determination unit 11 determines that a voltage abnormality has occurred in the cell voltage. ３ When the temperature inside the battery pack 1 rises by a predetermined temperature (Tp) or more per predetermined time (tp), the high temperature abnormality determination unit 12 determines that a high temperature abnormality has occurred inside the battery pack 1. ３ If the voltage abnormality judgment flag and the high temperature abnormality judgment flag both become "abnormal," that is, if it is determined that both high temperature abnormality and voltage abnormality have occurred, the thermal chain judgment unit 13 determines that a thermal chain has occurred.

[0021] As described above, in the thermal chain determination system or thermal chain determination method according to this embodiment, the controller 10 determines whether there is a voltage abnormality in the cell voltage based on the detected voltage detected by the voltage sensor 3, determines whether there is a high temperature abnormality in the battery pack 1 based on the detected temperature detected by the temperature sensor 4, and determines that there is a thermal chain occurrence in the battery pack 1 if it is determined that both a high temperature abnormality and a voltage abnormality have occurred. This improves the accuracy of determining whether there is a thermal chain occurrence.

[0022] In this embodiment, the controller 10 determines that a high temperature abnormality has occurred when the temperature detected by the temperature sensor 4 increases by a predetermined temperature or more per predetermined time period, thereby improving the accuracy of determining a thermal chain reaction.

[0023] As a first modification of this embodiment, the thermal linkage determination system 100 may include a gas duct 5, and the temperature sensor 4 may detect the surface temperature of the gas duct 5. A high temperature abnormality may be determined based on the surface temperature detected by the temperature sensor 4. FIG. 3 is a block diagram of the thermal linkage determination system according to the first modification. As shown in FIG. 3, the battery pack 1 includes the gas duct 5. The gas duct 5 is a pipe that collects gas generated from the cells 2 and releases it outside the vehicle cabin. The cells 2 release gas during thermal runaway. The inlet of the gas duct 5 is located inside the battery pack 1, and the outlet of the gas duct 5 faces the outside of the vehicle cabin. This allows gas generated during thermal runaway of the cells 2 to be released outside the vehicle cabin. The temperature sensor 4 detects the surface temperature of the gas duct 5. The high temperature abnormality determination unit 12 compares the surface temperature of the gas duct 5 detected by the temperature sensor 4 with a surface temperature threshold. The surface temperature threshold is a preset determination threshold, and is set, for example, to a temperature threshold higher than the upper limit of the surface temperature of the gas duct 5 during normal use of the cells 2. The surface temperature threshold may be set according to the environmental temperature of the battery pack 1, etc. When the surface temperature of the gas duct 5 is equal to or higher than the surface temperature threshold, the high temperature abnormality determination unit 12 determines that a high temperature abnormality has occurred in the battery pack 1. On the other hand, when the surface temperature of the gas duct 5 is lower than the surface temperature threshold, the high temperature abnormality determination unit 12 determines that a high temperature abnormality has not occurred in the battery pack 1. This allows the number of temperature sensors 4 to be installed in the battery pack 1 to be reduced, resulting in cost savings. The high temperature abnormality determination unit 12 may also determine that a high temperature abnormality has occurred when the surface temperature of the gas duct 5 increases by a predetermined temperature or more per predetermined time.

[0024] In a second modification of this embodiment, a temperature sensor 4 may be provided for each of the plurality of cells 2, and the controller 10 may determine a high temperature abnormality based on the detected values ​​of the plurality of temperature sensors 4. If at least one of the detected values ​​(detected temperature) detected by the plurality of temperature sensors 4 increases by a predetermined temperature or more per predetermined time, the high temperature abnormality determination unit 12 determines that a high temperature abnormality has occurred in the battery pack 1. The temperature inside the battery pack 1 may vary due to the structure of the pack, etc. In the second modification, multiple temperature sensors 4 are provided, thereby improving the accuracy of detecting the temperature of the cells 2.

[0025] In a third modification of this embodiment, the temperature sensor 4 may detect the temperature of gas generated from the cell 2, and the controller 10 may determine a high temperature abnormality based on the gas temperature detected by the temperature sensor 4. For example, the temperature sensor 4 may be provided in the battery pack 1 in a path through which gas generated during thermal runaway passes. The temperature sensor 4 may also be provided inside the gas duct 5 of the second modification or at the outlet of the gas duct 5. The method of determining a high temperature abnormality by the high temperature abnormality determination unit 12 is the same as in the above embodiment, and the temperature threshold may be set appropriately depending on the temperature reached at the detection location during thermal runaway of the cell 1. This improves the accuracy of detecting the temperature of the cell 2.

[0026] In a fourth modification of this embodiment, the temperature sensor 4 may detect the temperatures of components other than the plurality of cells 2, and the controller 10 may determine a high temperature abnormality based on the component temperatures detected by the temperature sensor 4. For example, the temperature sensor 4 may be provided on a component constituting the battery pack other than the cells 2. The component other than the cells 2 may be, for example, a bus bar or a case. The temperature sensor 4 may also be provided on a component constituting the battery pack to which heat from the cells 2 is easily transferred when the temperature is high. The method of determining a high temperature abnormality by the high temperature abnormality determination unit 12 is the same as in the above embodiment, and the temperature threshold may be set appropriately depending on the temperature reached at the detection location when the cell 1 experiences thermal runaway. This improves the accuracy of detecting the temperature of the cell 2.

[0027] Furthermore, as a fifth modification of this embodiment, at least two types of sensors may be provided among the temperature sensors 4 of modifications 1, 3, and 4. In the thermal linkage determination system 100 according to this modification, the temperature sensors 4 may include at least two temperature sensors: a sensor for detecting the surface temperature of the gas duct 5, a sensor for detecting the gas temperature of the gas generated from the cell 2, and a sensor for detecting the temperatures of components other than the plurality of cells 2. The controller 10 may determine a high temperature abnormality based on the detected values ​​of the at least two temperature sensors 4. The method of determining a high temperature abnormality by the high temperature abnormality determination unit 12 is the same as in the above embodiment, and the temperature threshold may be set appropriately depending on the temperature of the detection location reached during thermal runaway of the cell 1. This improves the accuracy of detecting the temperature of the cell 2.

[0028] In a sixth variation of this embodiment, the controller 10 may distinguish between instantaneous voltage drops, which are cell voltage drops that occur instantaneously, short-term voltage drops, which are cell voltage drops that occur over a short period of time, and long-term voltage drops, which are cell voltage drops that occur over a long period of time, based on the voltage detected by the voltage sensor 3. If a short-term voltage drop occurs, the controller 10 may determine that the voltage abnormality is due to cell thermal runaway. The instantaneous voltage drop, short-term voltage drop, and long-term voltage drop are distinguished by the length of time it takes for the cell voltage to drop by a predetermined amount, with the instantaneous voltage drop having the shortest duration and the long-term voltage drop having the longest duration. In other words, the instantaneous voltage drop, short-term voltage drop, and long-term voltage drop are distinguished by the rate of voltage drop, with the instantaneous voltage drop corresponding to the largest rate of voltage drop and the long-term voltage drop corresponding to the smallest rate of voltage drop. For example, if a disconnection occurs, the cell voltage drops instantaneously. If an external short circuit occurs, the cell voltage drops over a long period of time. If thermal runaway occurs, the cell voltage drops quickly. In other words, the voltage transition during an abnormality varies depending on the cause of the abnormality. Therefore, in the sixth modification, the voltage drop is identified depending on the cause of the cell voltage drop.

[0029] Specifically, the voltage abnormality determination unit 11 acquires the detected temperature periodically detected by the voltage sensor 3 and compares the previous and current detected temperature values ​​to determine whether the cell voltage is dropping. If the cell voltage is dropping, it measures the elapsed time until the cell voltage drops by a predetermined amount. If the measured elapsed time is instantaneous, the voltage abnormality determination unit 11 determines that an instantaneous voltage drop has occurred. If the elapsed time is short, the voltage abnormality determination unit 11 determines that a short-term voltage drop has occurred. If the elapsed time is long, the voltage abnormality determination unit 11 determines that a long-term voltage drop has occurred. If a short-term voltage drop has occurred, the voltage abnormality determination unit 11 determines that the voltage abnormality is due to thermal runaway of the cell 2. This improves the accuracy of determining thermal chain reactions.

[0030] Furthermore, in the seventh modification, the controller 10 may determine that the voltage abnormality is due to thermal runaway of the cell 2 if the detected voltage is maintained for a certain period of time after a short-term voltage drop. For example, if the cell voltage drops for a short period of time due to electromagnetic noise or the like, the cell voltage will return to its original voltage after the drop. Therefore, in order to distinguish between a voltage drop due to electromagnetic noise and a voltage drop due to thermal runaway, the voltage abnormality determination unit 11 determines that the voltage abnormality is due to thermal runaway of the cell 2 if the detected voltage is maintained for a certain period of time after a short-term voltage drop. In other words, the criterion for determining a voltage abnormality due to thermal runaway may be the duration of the voltage drop in addition to the time (or speed) of the voltage drop.

[0031] 4, the voltage characteristics, temperature characteristics, and decision logic of the cell when a thermal chain reaction occurs will be described. １ The temperature of cell 2 rises due to thermal runaway. The cell voltage drops due to thermal runaway of cell 2 (time t ２ The voltage abnormality determination unit 11 measures the elapsed time of the cell voltage drop. ３ The cell voltage drop ends at time t, and the voltage abnormality determination unit 11 determines that a short-term voltage drop has occurred based on the elapsed time (tx) of the cell voltage drop. The voltage abnormality determination unit 11 also measures the elapsed time (ty) when the detected voltage remains at a certain time after the cell voltage drop. ４When the temperature inside the battery pack 1 rises by a predetermined temperature (Tp) or more per predetermined time (tp), the high temperature abnormality determination unit 12 determines that a high temperature abnormality has occurred inside the battery pack 1. When the elapsed time (ty) is equal to or greater than a predetermined time, the voltage abnormality determination unit 11 determines that a voltage abnormality has occurred due to thermal runaway (time t ５ ). And at time t ５ When both the voltage abnormality determination flag and the high temperature abnormality determination flag are set to "abnormal," the heat chain determination unit 13 determines that a heat chain has occurred. This improves the accuracy of heat chain determination.

[0032] REFERENCE SIGNS LIST 1 Battery pack 2 Cell 3 Voltage sensor 4 Temperature sensor 5 Gas duct 10 Controller 11 Voltage abnormality determination unit 12 High temperature abnormality determination unit 13 Heat chain determination unit 100 Heat chain determination system

Claims

1. A thermal chain reaction determination system comprising: a voltage sensor that detects the cell voltages of multiple cells in a battery pack; a temperature sensor that detects the temperature inside the battery pack; and a controller that determines whether a thermal chain reaction has occurred within the battery pack, wherein the controller determines whether the cell voltage is abnormal based on the detected voltage detected by the voltage sensor; determines whether a high temperature abnormality is occurring within the battery pack based on the detected temperature detected by the temperature sensor; and determines whether a thermal chain reaction has occurred in the battery pack if it is determined that both the high temperature abnormality and the voltage abnormality have occurred.

2. A thermal chain determination system according to claim 1, further comprising a gas duct for discharging gas generated from the cell to the outside of the vehicle cabin, wherein the temperature sensor detects the surface temperature of the gas duct, and the controller determines the high temperature abnormality based on the surface temperature detected by the temperature sensor.

3. A thermal chain determination system according to claim 1 or 2, wherein the temperature sensor is provided for each of the plurality of cells, and the controller determines the high temperature abnormality based on the detected values ​​of the plurality of temperature sensors.

4. A thermal chain determination system according to claim 1, wherein the temperature sensor detects the gas temperature of the gas generated from the cell, and the controller determines the high temperature abnormality based on the gas temperature detected by the temperature sensor.

5. A thermal chain determination system according to claim 1, wherein the temperature sensor detects temperatures of components other than the plurality of cells, and the controller determines the high temperature abnormality based on the component temperatures detected by the temperature sensor.

6. A thermal chain determination system according to claim 1, wherein the temperature sensors include at least two temperature sensors selected from the group consisting of a sensor for detecting the surface temperature of a gas duct that discharges gas generated from the cell outside the vehicle cabin, a sensor for detecting the gas temperature of the gas, and a sensor for detecting the component temperatures of components other than the plurality of cells, and the controller determines the high temperature abnormality based on the detection values ​​of the at least two temperature sensors.

7. A thermal chain reaction determination system according to any one of claims 1 to 6, wherein the controller distinguishes between an instantaneous voltage drop, in which the cell voltage drops instantaneously, a short-term voltage drop, in which the cell voltage drops over a short period of time, and a long-term voltage drop, in which the cell voltage drops over a long period of time, based on the detected voltage, and determines that the voltage abnormality is due to thermal runaway of the cell when a short-term voltage drop occurs.

8. A thermal chain determination system as described in claim 7, wherein the controller determines that the voltage abnormality is due to thermal runaway of the cell if the detected voltage is maintained for a certain period of time after the short-term voltage drop occurs.

9. A thermal linkage judgment system according to any one of claims 1 to 8, wherein the controller judges that the high temperature is abnormal when the detected temperature rises by a predetermined temperature or more per predetermined time.

10. A thermal chain determination method executed by a controller, wherein the controller: acquires a detected temperature from a temperature sensor that detects the temperature inside a battery pack; acquires detected voltages from a voltage sensor that detects the cell voltages of multiple cells inside the battery pack; determines whether the cell voltages are abnormal based on the detected voltages; determines whether a high temperature abnormality is present inside the battery pack based on the detected temperatures; and determines that a thermal chain has occurred in the battery pack if it is determined that both the high temperature abnormality and the voltage abnormality have occurred.

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