Abnormality determination system and abnormality determination method

Abstract

This abnormality determination system comprises: a battery module 20 in which a plurality of battery cells 21 each having a positive electrode, a solid electrolyte, and a lithium-containing negative electrode are laminated; and a controller for determining whether there is an abnormality in the battery module 20. The battery module 20 includes: a pressurization mechanism for applying pressure to the battery cells 21; and a measurement unit for measuring pressure or the position of a pressure plate included in the pressurization mechanism. The controller detects a pressure reduction speed or a displacement speed from the measurement value of the measurement unit, and determines whether there is an abnormality in the battery cells 21 on the basis of the reduction speed or the displacement speed.

Description

Abnormality determination system and abnormality determination method

[0001] The present invention relates to an abnormality determination system and an abnormality determination method.

[0002] There are known methods for providing advance warning of thermal runaway in power batteries. For example, the warning method described in Patent Document 1 identifies the thermal runaway level based on three factors: battery voltage, battery temperature, and battery expansion force, and if the change in the battery expansion force exceeds a threshold value, issues an advance warning of the corresponding thermal runaway based on the level.

[0003] JP 2022-108252 A

[0004] However, in the case of a solid-state battery having a solid electrolyte, the expansion force does not increase significantly when an abnormality due to high temperature occurs, and therefore the above-mentioned conventional warning method has the problem that it is not possible to determine whether a high temperature abnormality has occurred in the solid-state battery.

[0005] The problem to be solved by the present invention is to provide an abnormality determination system and an abnormality determination method that can determine high temperature abnormalities in solid-state batteries.

[0006] The present invention solves the above problem by applying pressure to a battery cell having a positive electrode, a solid electrolyte, and a negative electrode containing lithium using a pressure mechanism, detecting the rate at which the pressure decreases or the rate at which the pressure plate is displaced, and determining whether there is an abnormality in the battery cell based on the rate at which the pressure decreases or the rate at which the pressure plate is displaced.

[0007] According to the present invention, it is possible to determine whether a solid-state battery is abnormally high in temperature.

[0008] Fig. 1 is a block diagram showing an abnormality determination system according to an embodiment of the present invention. Fig. 2 is a graph showing the characteristics of surface pressure versus charge / discharge time of a battery cell. Fig. 3 is a graph showing the characteristics of pressure on a battery cell. Fig. 4 is a graph showing the characteristics of the position of a pressure plate. Fig. 5 is a schematic diagram of a battery module. Fig. 6 is a schematic diagram of a battery pack that houses multiple battery modules. Fig. 7 is a schematic diagram of a battery module according to a modified example of this embodiment.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1, the abnormality determination system 1 includes a battery controller 10, a battery module 20, and a sensor 30. The abnormality determination system 1 is installed in, for example, a vehicle. The battery controller 10 in this embodiment corresponds to an example of the "controller" in this embodiment, and the sensor 30 corresponds to an example of the "measurement unit" in the present invention.

[0011] The battery controller 10 is a battery control unit (BCU). The battery controller 10 is configured with a memory such as a ROM or a RAM, and a processor such as a CPU. The battery controller 10 has a pressure control unit 11 and an abnormality determination unit 12 as functional blocks. The battery controller 10 stores programs for realizing various functions in the memory and executes the programs to perform each function in the functional blocks. Note that the battery controller 10 is not limited to the functions executed by the pressure control unit 11 and the abnormality determination unit 12, and may also have a function such as controlling the charging and discharging of the battery cells 21.

[0012] The pressure control unit 11 of the battery controller 10 outputs a control command to apply pressure to a pressure mechanism that applies pressure to the battery cells 21. The battery controller 10 controls the charging and discharging of the battery cells 21 while pressure is being applied to the battery cells 21. During charging and discharging of the battery cells 21, the battery controller 10 manages the state of charge (SOC) of the battery cells 21 based on measurements from a voltage sensor or a current sensor connected to the battery cells 21, and controls the charging and discharging current of the battery cells 21 to prevent the battery cells 21 from being overcharged or overdischarged. Furthermore, during charging or discharging of the battery cells 21, the abnormality determination unit 12 of the battery controller 10 detects the rate of decrease in pressure applied to the battery cells 21 or the rate of displacement of the pressure plate 23 from measurements from the sensor 30, and determines an abnormality in the battery cells 21 based on the rate of decrease in pressure or the rate of displacement.

[0013] The battery module 20 includes a plurality of battery cells 21 and a pressure mechanism. The battery module 20 is mounted, for example, on an electric vehicle or a hybrid vehicle. The battery module 20 can be electrically connected to a charging device. The charging device connected to the battery cells 21 is, for example, a device for charging the battery module 20 mounted on the electric vehicle or hybrid vehicle. The battery module 20 mounted on the vehicle is charged by removing the charging cable from the charging device, attaching the charging gun at the end of the charging cable to the connector of the vehicle's charging port, and then operating the charging start switch.

[0014] The battery module 20 is electrically connected to a load such as a motor. The load is a device that operates using the power of the battery module 20, such as a motor that serves as a drive source for the vehicle, or auxiliary devices such as an air conditioner or lights. Charging and discharging of the battery module 20 is performed under the control of the battery controller 10 in response to a system request. The system request corresponds to a command from an on-board computer such as an ECU while the vehicle is running.

[0015] The battery cell 21 is a solid-state battery (secondary battery). The battery cell 21 has at least a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode contains at least a positive electrode active material capable of absorbing and releasing an alkali metal such as lithium (Li), sodium (Na), or potassium (K), and may contain a positive electrode active material containing sulfur, although this is not particularly limited. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte. The negative electrode may contain lithium, for example, lithium metal or a lithium alloy. The battery cell 21 is sealed in an exterior member with tabs connected to a stacked body including the positive electrode, solid electrolyte, and negative electrode. The battery cell 21 is formed in a flat shape. The stacked battery cells 21 are connected to each other by bus bars.

[0016] The fixing plates 22, pressure plates 23, and elastic bodies 24 and 25 are mechanisms that apply pressure (load) to the battery cells 21 in response to displacement of the battery cells 21. The fixing plates 22 are end plates that maintain the position of the stack of battery cells 21 and are provided at the top and bottom of the stack. The pressure plates 23 are multiple cell pressure plates that apply pressure to the battery modules 20 by pressing the battery modules 20 in the stacking direction of the battery cells 21 included in the battery modules 20 based on control commands transmitted from the battery controller 10. The pressure plates 23 are provided above the stack of battery cells 21. The pressure plates 23 are connected to a motor (not shown) and can move up and down using power from the motor. The elastic bodies 24 are provided between the multiple pressure plates 23 and are capable of absorbing displacement due to charging and discharging of the battery modules 20. The elastic bodies 24 transmit pressure received from the pressure plates 23 to the stack of battery cells 21. The elastic bodies 24 are made of springs, rubber, or the like. The elastic bodies 25 are disposed between the plurality of battery cells 21 and are members capable of absorbing displacement caused by charging and discharging the battery module 20. It is not necessary to provide the elastic bodies 25 on each of the main surfaces of all the battery cells 21.

[0017] When pressure is applied to the battery cells 21, the position of the upper pressure plate 23 of the pair of pressure plates 23 is lowered so that it approaches the multiple battery cells 21. As the upper pressure plate 23 moves, pressure from the pressure plate 23 is transmitted to the stack of multiple battery cells 21 via the elastic body 24 and the lower pressure plate 23. When the surface pressure of the battery cells 21 is reduced, the position of the upper pressure plate 23 is raised so that it moves away from the multiple battery cells 21. The battery cells 21 expand when charged and contract when discharged. The battery module 20 includes the elastic body 24, and the elastic force of the elastic body 24 can absorb displacement of the battery cells 21 caused by expansion and contraction of the battery cells 21. The battery module 20 can also adjust the surface pressure applied to the battery cells 21 based on a control command from the battery controller 10. The fixing plate 22, pressure plate 23, and elastic body 24 correspond to the "pressure mechanism" in this invention. The number of fixing plates 22 and elastic bodies 25 is not limited to the number shown in Fig. 1 and may be any number. The mechanism for applying a load to the plurality of battery cells 21 is not limited to the mechanism shown in Fig. 1 and may be another mechanism.

[0018] The sensor 30 measures the pressure (surface pressure) applied to the battery cell 21 or the position of the pressure plate 23. A pressure sensor, a displacement sensor, or the like is used as the sensor 30. The sensor 30 transmits the measured value to the battery controller 10. Note that in addition to the sensor 30, a voltage sensor, a current sensor, a temperature sensor, or the like may also be provided on the battery cell 21. Note that the figure shows an example in which the sensor 30 is a pressure sensor. If the sensor 30 is a displacement sensor or other sensor that measures the position of the pressure plate 23, the sensor 30 may be provided in a position where it can directly detect the position of the pressure plate 23.

[0019] Next, the state of the battery cell 21 when a high-temperature abnormality occurs in the battery cell 21 will be described. In a battery cell 21 (battery module 20) that contains lithium in the negative electrode, when a high-temperature abnormality (thermal runaway) occurs, the thickness of the battery cell 21 decreases due to lithium melting and electrode ejection. The battery module 20 applies pressure to the stacking surfaces of the battery cells 21. Therefore, when a high-temperature abnormality occurs, the lithium inside the battery cell 21 melts and is pushed outward (spreading along the stacking surfaces of the battery cells 21), causing a rapid decrease in thickness. The decrease in thickness then reduces the pressure applied to the battery cell 21, and the high-temperature abnormality can be determined by detecting this pressure decrease.

[0020] In an all-solid-state battery such as the battery module 20 in this embodiment, a pressure drop occurs in the battery cells 21 when the temperature is abnormally high, but such a pressure drop does not occur in a secondary battery containing an electrolyte, which differs from this embodiment. That is, in a secondary battery containing an electrolyte, the electrolyte reacts at high temperatures, causing the cells to expand, and therefore no pressure drop occurs.

[0021] Next, a method for determining an abnormality (high temperature abnormality) in a battery cell 21 by the battery controller 10 will be described. The pressure control unit 11 of the battery controller 10 outputs a control command to the pressure mechanism to apply a predetermined pressure to the battery cell 21. A motor connected to the pressure plate 23 moves the pressure plate 23 in response to the control command, applying the predetermined pressure to the battery cell 21. The predetermined pressure is a surface pressure that makes the internal resistance of the battery cell 21 suitable for battery use, and is set in advance. The predetermined pressure may be specified as a range of surface pressure that can be used by the battery cell 21. During charging and discharging of the battery cell 21, the pressure control unit 11 detects the pressure of the battery cell 21 from the measurement value of the sensor 30, and outputs a control command to the pressure mechanism to adjust the pressure of the battery cell 21 to the predetermined pressure.

[0022] The abnormality determination unit 12 of the battery controller 10 detects the pressure decrease rate or the displacement rate of the pressure plate 23 from the measurement value of the sensor 30. A decrease rate threshold or a maximum displacement rate for determining a high temperature abnormality of the battery cell 21 is preset in the abnormality determination unit 12. The abnormality determination unit 12 compares the detected decrease rate with the decrease rate threshold, and if the decrease rate is equal to or greater than the decrease rate range, determines that a high temperature abnormality has occurred in the battery cell 21. Alternatively, the abnormality determination unit 12 compares the detected displacement rate with the maximum displacement rate, and if the detected displacement rate is equal to or greater than the maximum rate, determines that a high temperature abnormality has occurred in the battery cell 21. On the other hand, if the detected decrease rate is less than the decrease rate threshold, the abnormality determination unit 12 determines that the battery cell 21 is normal. Alternatively, if the detected displacement rate is less than the maximum displacement rate, the abnormality determination unit 12 determines that the battery cell 21 is normal.

[0023] 2 is a graph showing the characteristics of the surface pressure with respect to the charging or discharging time of the battery cell 21. Note that the pressure shown on the vertical axis of FIG. 2 may be the load applied to the battery cell 21. In the example of FIG. 2, the high temperature abnormality occurs from time t １ When a high temperature abnormality occurs, the thickness of the abnormal battery cell 21 decreases, and the pressure applied to the battery cell 21 decreases. As shown in FIG. 2, the measurement value of the pressure sensor decreases at an abnormal rate. The abnormality determination unit 12 detects the decrease in pressure corresponding to the area surrounded by the dotted line in FIG. 2 from the rate of pressure decrease. If the pressure of the battery cell 21 (measurement value of the sensor 30) is F, the abnormality determination unit 12 determines that a high temperature abnormality has occurred if the rate of pressure decrease (dF / dt) is equal to or greater than the decrease rate threshold.

[0024] In this embodiment, the decrease rate threshold may be the maximum decrease rate of the pressure that changes due to normal discharge of the battery cells 21. When the battery cells 21 discharge, the thickness of the battery cells 21 decreases, and therefore the pressure of the battery cells 21 also decreases. When the discharge amount is maximum, the normal (normal) pressure decrease of the battery cells 21 is greatest. For example, if the battery module 20 is provided as a power source for driving a motor, the discharge amount of the battery module 20 is greatest when the torque required of the motor to accelerate the vehicle is greatest. When the discharge amount is maximum, the pressure decrease rate of the battery cells 21 is also greatest. The maximum value of the pressure decrease rate can be calculated from the discharge amount of the battery cells 21 in normal conditions. The discharge amount corresponds to the discharge amount of the battery cells 21 when the output from the battery module 20 is greatest with respect to a load (e.g., a motor) connected to the battery module 20.

[0025] FIG. 3 is a graph showing the pressure decrease rate when the discharge amount is maximum (corresponding to the dotted line graph) and the pressure decrease rate of the battery cell 21 when a high temperature abnormality occurs (corresponding to the solid line graph). As shown in FIG. 3, when a high temperature abnormality occurs, the pressure decrease rate is greater than the pressure decrease rate when the discharge amount is maximum. The abnormality determination unit 12 then sets the pressure decrease rate when the discharge amount is maximum, or a value that is larger than the pressure decrease rate by a predetermined value, as the decrease rate threshold. When the abnormality determination unit 12 determines that a high temperature abnormality has occurred, it notifies the user of the abnormality. The abnormality notification is performed by turning on a lamp, emitting a warning sound, or the like.

[0026] FIG. 4 is a graph showing the characteristics of the displacement speed versus the charge or discharge time of the battery cell 21. The vertical axis represents the position of the pressure plate 23, and the slope of the graph represents the displacement speed. The graph shows the displacement speed when the discharge amount is maximum (corresponding to the dotted line graph) and the displacement speed of the battery cell 21 when a high temperature abnormality occurs (corresponding to the solid line graph). As shown in FIG. 4, when a high temperature abnormality occurs, the displacement speed is greater than the displacement speed when the discharge amount is maximum. The abnormality determination unit 12 then sets the displacement speed when the discharge amount is maximum as the maximum speed (speed threshold). When the abnormality determination unit 12 determines that a high temperature abnormality has occurred, it notifies the user of the abnormality.

[0027] If it is determined that a high-temperature abnormality has occurred, the pressure control unit 11 outputs a control command to the pressurizing mechanism to reduce the pressure. Figure 5 is a schematic diagram showing the state of the battery module 20 before and after the pressure is reduced. Figure 5(a) shows the state before the pressure is reduced, and Figure 5(b) shows the state after the pressure is reduced. Note that P is a battery cell 21 in which a high-temperature abnormality has occurred. As shown in Figure 5(b), reducing the pressure increases the spacing between the multiple battery cells 21, creating a gap (D) between the battery cell 21 (P) in which a high-temperature abnormality has occurred and an adjacent battery cell 21, reducing the thermal conductivity between these battery cells 21. This suppresses thermal chain reaction to the adjacent battery cell 21.

[0028] In this embodiment, a plurality of battery modules 20 may be housed in the battery pack 2. Fig. 6 is a schematic diagram of the battery pack 2 housing a plurality of battery modules 20, with Fig. 6(a) showing the state of the battery pack 2 before the pressure is reduced, and Fig. 6(b) showing the state of the battery pack 2 after the pressure is reduced. Each of the plurality of battery modules 20 included in the battery pack 2 has a pressure mechanism and a sensor 30. The pressure mechanism and the sensor 30 are not shown in Fig. 6.

[0029] The battery controller 10 adjusts the pressure by controlling the pressure mechanisms of each of the multiple battery modules 20, and detects the rate of pressure reduction in the battery cells 21 in the battery module 20 or the rate of displacement of the pressure plates 23 based on the measurements of each sensor 30. When the battery controller 10 determines that an abnormality has occurred in a battery cell 21 included in one of the multiple battery modules 20, it outputs a control command to the pressure mechanism to reduce the pressure applied to that battery module 20. The battery controller 10 also outputs control commands to the pressure mechanisms to reduce the pressure applied to battery cells 21 included in the other battery modules 20.

[0030] In the example of FIG. 6 , the battery pack 2 includes four battery modules 20, and a high-temperature abnormality occurs in a battery cell 21(P) included in one of the battery modules 20. In this case, the abnormality determination unit 12 of the battery controller 10 detects the rate of pressure decrease or the rate of displacement of the pressure plate 23 from measurements by the sensor 30 of the battery module 20 including the battery cell 21(P), and determines that an abnormality has occurred in the battery cell 21 based on the rate of decrease or displacement. The pressure control unit 11 outputs a control command to the pressure mechanism of each battery module 20 to reduce the pressure applied to the battery cell 21 not only for the battery module 20 including the battery cell 21(P) but also for other battery modules 20 not including the battery cell 21(P) (i.e., modules in which no high-temperature abnormality has occurred in any of the battery cells 21 included in the battery module 20). When the pressure in all battery modules 20 included in the battery pack 2 decreases, the spacing between the multiple battery cells 21 increases, as shown in FIG. 6( b). By reducing the pressure in battery modules 20 other than the battery module including the battery cell 21 where the high temperature abnormality occurred, thermal chain reaction is less likely to occur.

[0031] As described above, the abnormality determination system and method according to this embodiment apply pressure to a battery cell having a positive electrode, a solid electrolyte, and a negative electrode containing lithium using a pressure mechanism, detect the rate at which the pressure is reduced or the rate at which the pressure plate 23 is displaced, and determine an abnormality in the battery cell 21 based on the rate at which the pressure is reduced or the rate at which the pressure plate 23 is displaced. This makes it possible to determine a high temperature abnormality in the solid-state battery.

[0032] In this embodiment, the battery controller 10 determines that an abnormality has occurred in the battery cell 21 when the pressure decrease rate is equal to or greater than the decrease rate threshold or when the displacement rate is equal to or greater than the maximum rate. This improves the accuracy of determining high temperature abnormalities.

[0033] In this embodiment, the battery controller 10 reduces the pressure when it determines that an abnormality has occurred in the battery cell 21. This makes it possible to prevent a heat chain reaction from occurring in the battery cell 21 where the high-temperature abnormality has occurred to the adjacent battery cells 21.

[0034] Furthermore, in this embodiment, when the battery controller 10 determines that an abnormality has occurred in a battery cell 21 included in one of the plurality of battery modules 20, it reduces the pressure applied to the battery cells 21 included in the other battery modules 20. This makes it possible to prevent a thermal chain reaction from one battery module 20 to the other battery modules 20.

[0035] In this embodiment, the pressure mechanism of the battery module 20 may have an absorption mechanism that absorbs pressure generated by the expansion of the battery cells 21. For example, in the example of FIG. 1 , the elastic bodies 24 and 25 correspond to the absorption function. Then, to measure the pressure applied to the battery cells 21, the sensor 30 may measure the pressure absorbed by the elastic bodies 24 and 25. Furthermore, to measure the pressure applied to the battery cells 21, the pressure may be measured from the control amount of the motor that moves the pressure plate 23.

[0036] As a modification of this embodiment, the pressure mechanism included in the battery module 20 is not limited to an active mechanism (a mechanism that generates pressure mechanically or electrically using a motor or the like) as shown in FIG. 1 , but may be a passive mechanism (a mechanism that compresses using the properties of a material such as an elastic body). FIG. 7 is a schematic diagram of a battery module 20 according to a modification. FIG. 7(a) shows the state of the battery module 20 before the pressure is reduced, and FIG. 7(b) shows the state of the battery module 20 after the pressure is reduced. Note that P is a battery cell 21 in which a high temperature abnormality has occurred.

[0037] The battery module 20 according to the modified example includes pressure plates 26 and rubber bands 27. The pressure plates 26 are provided at the top and bottom of the stack of multiple battery cells 21. The rubber bands 27 restrain the stack of multiple battery cells 21 and the pair of pressure plates 26 from the periphery. Contraction of the rubber bands 27 applies pressure to the battery cells 21 (pressurized state). The abnormality determination unit 12 of the battery controller 10 detects the rate of pressure reduction or the rate of displacement of the pressure plates 23 from the measurements of the sensor 30 and determines an abnormality in the battery cells 21 based on the rate of pressure reduction or displacement. The methods for detecting the rate of pressure reduction or displacement and for determining an abnormality are the same as those described above. If an abnormality is determined in the battery cells 21, the pressure control unit 11 of the battery controller 10 releases the pressure applied by the rubber bands 27. For example, the pressure mechanism including the rubber bands 27 may have a cutter for cutting the rubber bands 27, and the pressure control unit 11 outputs a command to the pressure function to cut the rubber bands 27 with the cutter. 7(b), when the pressurized state is released, the spacing between the multiple battery cells 21 increases, creating a gap (D) between the battery cell 21 (P) where the high temperature abnormality is occurring and the adjacent battery cell 21, reducing the thermal conductivity between these battery cells 21. This makes it possible to suppress a heat chain reaction to the adjacent battery cell 21.

[0038] In this embodiment, the pressure mechanism of the battery module 20 may be a combination of an active mechanism and a passive mechanism.

[0039] REFERENCE SIGNS LIST 1 Abnormality determination system 10 Battery controller 11 Pressure control unit 12 Abnormality determination unit 20 Battery module 21 Battery cell 22 Fixing plate 23 Pressure plate 24 Elastic body 25 Elastic body 26 Pressure plate 27 Rubber band 30 Sensor

Claims

a battery module including a plurality of stacked battery cells each having a positive electrode, a solid electrolyte, and a negative electrode containing lithium; A controller for determining an abnormality in the battery module, The battery module includes: A pressure mechanism for applying pressure to the battery cell; a measuring unit for measuring the pressure or a position of a pressure plate included in the pressure mechanism; The controller detects the rate at which the pressure is reduced or the rate at which the pressure plate is displaced from the measurement value of the measurement unit, and determines whether or not there is an abnormality in the battery cell based on the rate at which the pressure is reduced or the rate at which the pressure plate is displaced.

2. The abnormality determination system according to claim 1, The controller determines that an abnormality has occurred in the battery cell when the decrease rate is equal to or greater than a decrease rate threshold or when the displacement rate is equal to or greater than a maximum rate; The decrease rate threshold is a maximum decrease rate of the pressure that changes due to normal discharging of the battery cell.

3. The abnormality determination system according to claim 1, The abnormality determination system reduces the pressure when the controller determines that an abnormality has occurred in the battery cell. 　 The abnormality determination system according to any one of claims 1 to 3, a battery pack including a plurality of the battery modules; An abnormality determination system in which, when the controller determines that an abnormality has occurred in the battery cell included in one of the plurality of battery modules, the controller reduces the pressure applied to the battery cells included in the other battery modules. 　 The abnormality determination system according to any one of claims 1 to 4, The controller is an abnormality determination system that determines the number of the battery cells in which an abnormality has occurred based on the amount of displacement of the pressure plate.

3. The abnormality determination system according to claim 1, the pressure mechanism has an elastic body that applies pressure to the battery cell, The abnormality determination system, wherein the controller releases the pressurized state applied by the elastic body when it determines that an abnormality has occurred in the battery cell.

3. The abnormality determination system according to claim 1, the pressurizing mechanism has an absorption mechanism that absorbs pressure generated by expansion of the battery cell, The measurement unit measures at least one of the value of the pressure absorbed by the absorption mechanism, the position of the pressure plate, and the control amount of a motor that moves the pressure plate as the measurement value.

1. A method for determining an abnormality in a battery module in which a plurality of battery cells each having a positive electrode, a solid electrolyte, and a negative electrode containing lithium are stacked, comprising the steps of: applying pressure to the battery cell using a pressure mechanism; a measuring unit measures the pressure or a position of a pressure plate included in the pressure mechanism; Detecting a rate of decrease in the pressure or a rate of displacement of the pressure plate from a measurement value of the measurement unit; An abnormality determination method for determining an abnormality in the battery cell based on the decrease rate or the displacement rate.

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