Short circuit sign detection system and short circuit sign detection method

Abstract

This short circuit sign detection system (1) comprises: a battery cell (21); a temperature sensor (13) for measuring the temperature of a battery; a resistance measurement unit (101) for measuring the electrolyte resistance of a solid electrolyte of the battery cell (21); and a determination unit (104) for determining whether there is a sign that a short circuit will occur between the positive and negative electrodes, wherein the determination unit (104) determines that there is a sign when the decrement of the electrolyte resistance measured by the resistance measurement unit (101) during charging is greater, by a prescribed value, than the decrement of the electrolyte resistance due to a change in the battery temperature.

Description

Short circuit prediction detection system and short circuit prediction detection method

[0001] The present invention relates to a short circuit sign detection system and a short circuit sign detection method.

[0002] A method for detecting the state of a lithium secondary battery is known, which includes a discharging step of discharging the battery to an SOC of 10% or less, a measuring step of measuring the impedance of the battery discharged in the discharging step, and a state detecting step of detecting the state of the battery based on the measured impedance value obtained in the measuring step (see, for example, Patent Document 1). In the state detecting step of this method, a reaction resistance value is calculated based on the impedance in the measuring step, and the calculated reaction resistance value is compared with a predetermined threshold value to determine whether or not deterioration of the battery due to lithium deposition at the negative electrode has occurred.

[0003] Japanese Patent Application Laid-Open No. 2012-212513

[0004] However, in the above-mentioned conventional technology, the determination method described in Patent Document 1 determines whether or not deterioration of the battery due to lithium precipitation at the negative electrode has occurred by comparing the reaction resistance value with a threshold value, and therefore has the problem that it is difficult to detect the occurrence of a short circuit due to lithium precipitation at an early stage.

[0005] The problem to be solved by the present invention is to provide a short circuit sign detection system and a short circuit sign detection method that can detect the occurrence of a short circuit at an early stage.

[0006] The present invention solves the above problem by using a short circuit prediction determination means to determine that there are signs of a short circuit occurring between the positive electrode and the negative electrode when the decrease in electrolyte resistance measured by the resistance measurement means during charging is greater than a predetermined value by the decrease in electrolyte resistance caused by changes in battery temperature.

[0007] According to the present invention, the occurrence of a short circuit can be detected at an early stage.

[0008] Fig. 1(a) is a graph showing the current and voltage values ​​measured in Experimental Example 1, in which charging and discharging were performed under conditions that make it difficult for a battery to short-circuit, and Fig. 1(b) is a graph showing the current and voltage values ​​measured in Experimental Example 2, in which charging and discharging were performed under conditions that make it easy for a battery to short-circuit. Fig. 2(a) is a Cole-Cole plot showing the impedance measured during the first discharge cycle, indicated by II-a in Fig. 1(a), and Fig. 2(b) is a Cole-Cole plot showing the impedance measured during the first charge cycle, indicated by II-b in Fig. 1(a). Fig. 3(a) is a Cole-Cole plot showing the impedance measured during the first discharge cycle, indicated by III-a in Fig. 2(b). Fig. 3(b) is a Cole-Cole plot showing the impedance measured during the first charge cycle, indicated by III-b in Fig. 2(b). Fig. 3(c) is a Cole-Cole plot showing the impedance measured during the second discharge cycle, indicated by III-c in Fig. 2(b). Fig. 4 is a graph showing the imaginary part of the impedance of the Cole-Cole plot shown in Fig. 3(b) on the vertical axis and frequency on the horizontal axis. Fig. 5 is a block diagram showing a short circuit sign detection system according to an embodiment of the present invention. Fig. 6 is a flowchart showing a short circuit sign detection method according to an embodiment of the present invention. Fig. 7 is a graph showing an example of the relationship between battery temperature and resistance coefficient. Fig. 8(a) is a graph showing an example of measured and predicted values ​​of electrolyte resistance during charging, and Fig. 8(b) is a graph showing an example of a change in battery temperature during charging.

[0009] [Regarding Interfacial Resistance of Solid Electrolyte] The present inventors have studied methods for detecting signs of a short circuit caused by dendrites that precipitate at the interface between the solid electrolyte and the negative electrode during charging of an all-solid-state battery, and as a result, have found through the following experiment that the resistance of the solid electrolyte during charging (interfacial resistance of the solid electrolyte), calculated based on high-frequency impedance, tends to decrease before a short circuit occurs.

[0010] Fig. 1(a) is a graph showing the current and voltage values ​​measured in Experimental Example 1, in which charging and discharging were performed under conditions that made it difficult for a battery to short-circuit. Fig. 2(a) is a Cole-Cole plot (Nyquist plot) showing the impedance measured during the first discharge cycle, indicated by II-a in Fig. 1(a), and Fig. 2(b) is a Cole-Cole plot showing the impedance measured during the first charge cycle, indicated by II-b in Fig. 1(a).

[0011] In this Experimental Example 1, an experimental battery 1 was fabricated in which a Li metal layer was provided as a negative electrode on one side of a solid electrolyte, and a Li—In layer was provided as a positive electrode on the other side. Next, experimental battery 1 was charged and discharged multiple times while measuring the current, voltage, and impedance under conditions that make it difficult for a short circuit to occur between the negative electrode and the positive electrode (conditions that make it difficult for dendrites to precipitate at the contact interface between the negative electrode and the solid electrolyte during charging). Specifically, the current density was set to 0.32 mA / cm ２ The experimental battery 1 was subjected to multiple cycles of charge and discharge under the above conditions. Furthermore, the impedance was measured multiple times during discharge and charge by EIS measurement (electrochemical impedance measurement).

[0012] As shown in Fig. 1(a), the voltage of the experimental battery 1 was normal and no short circuit occurred during the charge-discharge cycles of Experimental Example 1. At this time, there was almost no difference between the impedance during discharge in the first cycle shown in Fig. 2(a) and the impedance during charge in the first cycle shown in Fig. 2(b).

[0013] In the Cole-Cole plot, the vertical axis represents the imaginary part of the impedance, and the horizontal axis represents the real part of the impedance. It is estimated that the diameter of the leftmost semicircle in the plot represents the resistance value of the solid-state electrolyte (SE) (hereinafter, also referred to as electrolyte resistance), the diameter of the rightmost semicircle represents the reaction resistance of the Li—In layer, and the diameter of the semicircle between them represents the reaction resistance of the Li layer. Therefore, for example, the electrolyte resistance can be calculated from the semicircles that appear in the Cole-Cole plot by fitting using an equivalent circuit.

[0014] Fig. 1(b) is a graph showing the current and voltage values ​​measured in Experimental Example 2, in which charging and discharging were performed under conditions that make the battery prone to short-circuiting. Fig. 3(a) is a Cole-Cole plot showing the impedance measured during the first cycle of discharging, indicated by III-a in Fig. 2(b), Fig. 3(b) is a Cole-Cole plot showing the impedance measured during the first cycle of charging, indicated by III-b in Fig. 2(b), and Fig. 3(c) is a Cole-Cole plot showing the impedance measured during the second cycle of discharging, indicated by III-c in Fig. 2(b).

[0015] In Fig. 3(a), impedance measurements were performed in the order of C1, C5, C10, C15, C20, and C25 during the first discharge cycle. In Fig. 3(b), impedance measurements were performed in the order of D1, D5, D10, D15, D20, and D25 during the first charge cycle. In Fig. 3(c), impedance measurements were performed in the order of 2C1, 2C5, 2C10, 2C15, 2C20, and 2C25 during the second discharge cycle.

[0016] In Experimental Example 2, an experimental battery 2 was fabricated in the same manner as in Experimental Example 1, in which a Li metal layer was provided as the negative electrode on one side of the solid electrolyte and a Li—In layer was provided as the positive electrode on the other side. Thereafter, experimental battery 2 was subjected to multiple cycles of charge and discharge while measuring the current, voltage, and impedance under conditions that tend to cause a short circuit between the negative and positive electrodes. Specifically, the current density was set to 0.64 mA / cm ２ The experimental battery 2 was subjected to multiple charge and discharge cycles.

[0017] In Experimental Example 2, as shown in FIG. 1(b), the voltage of Experimental Battery 2 began to rise during charging in the sixth cycle, and then gradually approached 0 V (short circuit) with each charge / discharge cycle. Comparing the impedance during discharge in the first cycle (shown in FIG. 2(a)) with the impedance during charge in the first cycle (shown in FIG. 2(b)), it was found that the electrolyte resistance based on the impedance during charging decreased during charging. As shown in FIG. 2(c), the electrolyte resistance returned to its original value during discharge in the second cycle. Although not specifically shown, the electrolyte resistance also decreased during charging from the second cycle onward, similar to the impedance shown in FIG. 2(b).

[0018] Figure 4 is a graph showing the imaginary part of the impedance of the Cole-Cole plot shown in Figure 3(b) on the vertical axis and frequency on the horizontal axis. As shown in Figure 4, the electrolyte resistance can be calculated based on the impedance of the experimental battery 2 to an AC signal having a frequency of 10 kHz or higher, although this is not particularly limited. In Experimental Example 2, the imaginary part of the electrolyte resistance calculated based on the impedance at 10 kHz or higher decreases over time during charging. In other words, the electrolyte resistance decreases over time during charging. On the other hand, the resistance of the Li metal layer and the resistance of the Li-In layer calculated based on the impedance below 10 kHz hardly changes during charging.

[0019] This decrease in electrolyte resistance during charging was detected in a charging cycle before a change in battery voltage was detected. Therefore, the inventors discovered that by detecting the decrease in electrolyte resistance during a charging cycle, it is possible to determine whether there is a sign of a short circuit occurring.

[0020] [Regarding the Influence of Temperature Changes] Furthermore, the inventors have considered the possibility that a decrease in electrolyte resistance due to dendrite growth during charging and a decrease in electrolyte resistance due to a rise in battery temperature during charging may occur simultaneously. As will be described in detail below, the inventors have conceived the short circuit sign detection system and short circuit sign detection method of this embodiment to experimentally obtain the characteristics of change in electrolyte resistance with temperature change, and to evaluate the decrease in electrolyte resistance due to dendrite growth during charging by comparing a predicted value of resistance change due to temperature change with a measured value of actual electrolyte resistance.

[0021] [Short Circuit Sign Detection System] Hereinafter, a short circuit sign detection system according to this embodiment will be described with reference to the drawings. FIG. 5 is a block diagram showing a short circuit sign detection system 1 according to this embodiment. The short circuit sign detection system 1 according to this embodiment is provided in a vehicle such as an automobile, although this is not particularly limited. The vehicle is not particularly limited as long as it is equipped with a battery module. Examples of automobiles include an EV (Electric Vehicle), a PHV (Plug-in Hybrid Vehicle), and an HV (Hybrid Vehicle).

[0022] The short circuit warning detection system 1 controls the charging and discharging of a battery module 2. The battery module 2 includes a plurality of battery cells 21 stacked on top of each other. The battery cells 21 are all-solid-state batteries and have at least a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode is not particularly limited as long as it contains at least a positive electrode material capable of absorbing and releasing lithium (Li), and materials such as NCM and NCA can be used as the positive electrode material. The solid electrolyte is not particularly limited, and examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte. The negative electrode is only required to contain lithium, and may contain, for example, lithium metal.

[0023] As shown in Figure 1, this short circuit precursor detection system 1 includes a controller 10, a voltage sensor 11, a current sensor 12, a temperature sensor 13, a DC-DC converter 14 connected to a load (power grid), a pressure application mechanism 16, and a pressure sensor 17.

[0024] The controller 10 in this embodiment corresponds to an example of the "resistance measuring means" and the "short circuit sign determining means" in the present invention. The temperature sensor 13 in this embodiment corresponds to an example of the "temperature measuring means" in the present invention. The pressure application mechanism 16 in this embodiment corresponds to an example of the "pressure applying means" in the present invention. The pressure sensor 17 in this embodiment corresponds to an example of the "pressure measuring means" in the present invention.

[0025] The controller 10 is a battery control unit (BCU) that includes a memory such as a ROM or a RAM, and a processor such as a CPU. The controller 10 manages the state of the battery module 2 based on the detected voltage detected by a voltage sensor 11, the detected current detected by a current sensor 12, the detected temperature detected by a temperature sensor 13, and the like, and determines the SOC usage range of the battery module 2 according to the state of the battery module 2.

[0026] The controller 10 in this embodiment can also determine whether there is a sign of a short circuit occurring in the battery cells 21 included in the battery module 2. The controller 10 includes a resistance measurement unit 101, a memory unit 102, a prediction unit 103, a determination unit 104, a current control unit 105, and a pressure control unit 106.

[0027] The resistance measurement unit 101 measures the impedance of the battery cells 21 included in the battery module 2 and calculates the electrolyte resistance of the battery cells 21 from the measured impedance. The resistance measurement unit 101 can measure the impedance of the battery cells 21, for example, by EIS measurement or the like. The resistance measurement unit 101 can calculate the electrolyte resistance based on the impedance of the battery 21 with respect to an AC signal having a high frequency of, for example, 10 kHz or higher. More specifically, the diameter of the impedance circle at 10 kHz or higher in the Cole-Cole plot described above can be used as the electrolyte resistance. This makes it possible to calculate the electrolyte resistance without being affected by electrode reaction resistance or the like that appears in the impedance in the low-frequency band.

[0028] Furthermore, the resistance measuring unit 101 can output the calculated electrolyte resistance to the storage unit 102 and the comparison unit 104 .

[0029] In this embodiment, the controller 10 includes a resistance measurement unit that measures impedance, but this is not limited to this. The short circuit sign detection system 1 may also include an impedance measurement device separate from the controller 10. Alternatively, a signal including high-frequency components may be generated by switching the DCDC converter 14 and input to the battery cell 21.

[0030] The memory unit 102 stores the measured temperature value input from the temperature sensor 13 and the electrolyte resistance input from the resistance measurement unit 101. In this embodiment, the memory unit 102 stores a pre-charge battery temperature, which is the battery temperature measured by the temperature sensor 13 before charging the battery module 2, and a pre-charge electrolyte resistance, which is the electrolyte resistance measured by the resistance measurement unit 101 before charging the battery module 2. The memory unit 102 also outputs the pre-charge battery temperature and the pre-charge electrolyte resistance to the prediction unit 103.

[0031] The prediction unit 103 calculates a predicted value of the electrolyte resistance corresponding to the battery temperature during charging based on the pre-charge battery temperature and pre-charge electrolyte resistance. This predicted value is calculated based on experimentally determined characteristics of changes in electrolyte resistance relative to temperature changes. A more specific method for calculating the predicted value will be described later.

[0032] The determination unit 104 determines whether there is a sign of a short circuit occurring between the positive and negative electrodes of the battery cell 21. The determination unit 104 determines that there is a sign of a short circuit when the decrease in electrolyte resistance measured by the resistance measurement unit 101 during charging is greater than the decrease in electrolyte resistance caused by a change in battery temperature by a predetermined value or more.

[0033] The judgment unit 104, for example, compares the predicted value calculated by the prediction unit 103 with the measured value of the electrolyte resistance measured by the resistance measurement unit 101 during charging, and if the result of the comparison shows that the measured value is smaller than the predicted value by a predetermined value or more, it can determine that there is a sign of a short circuit.

[0034] The current control unit 105 controls the discharge current from the battery module 2 to the load (power grid) and the charge current from the charging device 3 to the battery module 2. For example, when the determination unit 104 determines that there is a sign of a short circuit occurring, the current control unit 105 in this embodiment can either not increase the charge current from the charging device 3, or reduce the charge current, or discharge the battery.

[0035] The pressure control unit 106 controls the pressure application mechanism 16 to control the pressure applied to the battery module 2. The pressure applied to the battery module 2 is not particularly limited, but is set to a pressure equal to or higher than the performance required pressure when charging or discharging the battery module 2. This performance required pressure is a pressure at which the electrical resistance of the battery cell 21 becomes equal to a predetermined threshold value, and this threshold value is the maximum value of the electrical resistance within the range of electrical resistance at which the battery cell 21 can output and input the charging and discharging power required to operate the vehicle control system, etc.

[0036] In addition, the pressure control unit 106 in this embodiment can control the pressure application mechanism 16 to reduce the pressure applied to the battery, for example, when the judgment unit 104 determines that there are signs of a short circuit occurring.

[0037] The voltage sensor 11 is a sensor for detecting the voltage between the terminals of the battery module 2. The voltage sensor 11 is connected between the wiring connected to the positive and negative electrodes of the battery module 2. The current sensor 12 is a sensor for detecting the input / output current of the battery module 2. The current sensor 12 is connected to the wiring connected to the positive or negative electrode of the battery module 2. The measured values ​​of the voltage sensor 11 and the current sensor 12 are output to the current control unit 105 of the controller 10.

[0038] The temperature sensor 13 is provided in the battery module 2. The temperature sensor 13 is a sensor for detecting the temperature of the battery module 2. Although not particularly limited, the temperature of the battery module 2 can be considered as the temperature of the battery cell 21. The measurement value of this temperature sensor 13 is output to the memory unit 102 and the prediction unit 103.

[0039] The DC-DC converter 14 is a power conversion device that converts the voltage input from the battery module 2 to a predetermined voltage and outputs power to a load such as a motor. The DC-DC converter 14 is also a power conversion device that converts the voltage input from a load such as a motor or a charging device to a predetermined voltage and outputs power to the battery module 2. The DC-DC converter 14 is controlled by the controller 10. The battery module 2 is connected to the input side of the DC-DC converter 14, and a load is connected to the output side of the DC-DC converter 14. The load is a power grid or the like that includes a motor inverter or the like. In other words, the battery module 2 is connected to the load via the DC-DC converter 14.

[0040] The pressure application mechanism 16 applies pressure to the battery module 2 by pressing the battery module 2 along the stacking direction of the battery cells 21 in the battery module 2. The pressure application mechanism 16 in this embodiment has a motor driver circuit 161, a motor 162, a gear box 163, a pressure transmission body 164, a fixed end plate 165, a movable end plate 166, and multiple shafts 167.

[0041] The motor driver circuit 161 operates the motor 162. The motor driver circuit 161 controls the driving of the motor 162 based on a control signal from the controller 10.

[0042] The motor 162 has a first drive shaft 162 a. The motor 162 drives and rotates the first drive shaft 162 a in response to an output from the motor driver circuit 161 .

[0043] The gear box 163 is connected to the first drive shaft 162a and converts the rotational drive of the first drive shaft 162a into drive of the pressure transmission body 164 in the stacking direction.

[0044] The pressure transmission body 164 moves up and down by the driving force transmitted via the gear box 163. This pressure transmission body 164 includes a second drive shaft 164a and a pressure transmission plate 164b. The second drive shaft 164a is connected to the gear box 163, and the gear box 163 transmits the rotational drive of the first drive shaft 162a of the motor 162 to the pressure transmission body 164a. The pressure transmission plate 164b is a plate that moves in the stacking direction as the second drive shaft 164a rotates. In this embodiment, the pressure applied to the battery modules 2 can be controlled to increase by moving the pressure transmission plate 164b downward in the figure, and the pressure applied to the battery modules 2 can be controlled to decrease by moving the pressure transmission plate 164b upward in the figure.

[0045] The fixed end plate 165 and the movable end plate 166 are a pair of plate-like members connected to each other by a plurality of shafts 167. The fixed end plate 165 is fixed to the shaft 167 and supports the battery modules 2. On the other hand, the movable end plate 166 is not fixed to the shaft 167 and is movable along the extension direction of the shaft 167, applying pressure to the battery modules 2 from above in response to the force transmitted from the pressure transmitter 164. Furthermore, the movable end plate 166 can move along the stacking direction in response to the expansion and contraction of the battery modules 2 due to charging and discharging, and the expansion and contraction of the battery modules 2 in response to changes in the pressure applied to the battery modules 2 by the movable end plate 166.

[0046] The pressure sensor 17 is a sensor capable of measuring the pressure applied to the battery module 2. The pressure sensor 17 is capable of outputting the detected pressure to the pressure control unit 106 of the controller 10.

[0047] The battery module 2 is electrically connected to a charging device 3. The charging device 3 connected to the battery cells 21 may be, for example, a device for charging the battery module 2 mounted on an electric vehicle or a hybrid vehicle. Charging the mounted battery module 2 is performed by removing the charging cable from the charging device 3, 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. The controller 10 manages the state of charge (SOC) of the battery cells 21 included in the battery module 2 and controls the DCDC converter 14 and the charging device 3 so that the state of charge of the battery module 2 reaches a target state of charge. The charging device 3 may be mounted on the vehicle. Specifically, for example, the charging device 3 may be a device capable of generating electricity using the engine of an HV and charging the battery module 2.

[0048] As described above, the battery module 2 is electrically connected to a load such as a motor. The load is a device that operates using the power of the battery module 2, such as a motor that serves as a drive source for the vehicle, or auxiliary devices such as an air conditioner or lights. Discharge of the battery module 2 is executed under the control of the controller 10 in response to a system request or an external power request. The system request corresponds to a command from an on-board computer such as an ECU while the vehicle is running. With regard to an external power request, for example, when an external device such as a mobile terminal is used to operate an air conditioner by timer setting before the vehicle starts running so that the interior temperature of the vehicle is appropriate when the vehicle starts running, the command from the external device corresponds to an external power request.

[0049] The battery module 2 mounted on an electric vehicle or a hybrid vehicle may also be used for Vehicle Grid Integration (VGI), which is a technology for connecting an electric vehicle or a hybrid vehicle equipped with a battery module 2 to a power grid and supplying the power stored in the battery module 2 to the power grid (load) via the power grid.

[0050] [Method for detecting a sign of a short circuit] A method for detecting a sign of a short circuit for a battery module 2 using the short circuit sign detection system 1 will now be described. Fig. 6 is a flowchart showing the method for detecting a sign of a short circuit according to this embodiment. The method for detecting a sign of a short circuit shown in Fig. 6 is repeatedly executed at predetermined intervals.

[0051] In this short circuit sign detection method, first, in step S1, the resistance measurement unit 101 of the controller 10 measures the impedance of the battery cell 21. Then, based on the measured impedance, the current electrolyte resistance R of the battery cell 21 is calculated. ＳＥ＿ｍｅａ Calculate.

[0052] Next, in step S2, the current control unit 105 of the controller 10 determines whether the battery module 2 is being charged.

[0053] If the battery module 2 is not being charged, in step S3, it is determined whether the measured value of the pressure (surface pressure) applied to the battery 21 measured by the pressure sensor 17 is equal to or greater than a predetermined value. This determination may be made by the pressure control unit 106 of the controller 10.

[0054] Furthermore, the predetermined pressure value is not particularly limited, and may be the performance required pressure described above. The resistance of the battery cell 21 changes depending on the surface pressure applied to the battery cell 21. In particular, when the surface pressure is less than the performance required pressure, the resistance of the battery cell 21 tends to increase rapidly as the surface pressure decreases. In other words, when the pressure applied to the battery is lower than the predetermined pressure, the pressure sensitivity of the electrolyte resistance increases, and therefore, by not using the electrolyte resistance in such cases, the accuracy of short-circuit detection can be improved.

[0055] On the other hand, when the surface pressure is equal to or greater than the required performance pressure, the change in resistance according to the surface pressure is small enough to be negligible. Therefore, in this embodiment, when the surface pressure applied to the battery cell 21 is equal to or greater than a predetermined value, the electrolyte resistance R ＳＥ By storing the above in the storage unit 102 in step S4 described later, the accuracy of short circuit sign detection can be improved.

[0056] If the measured value of the pressure (surface pressure) applied to the battery 21 is equal to or greater than the predetermined value, in step S4, the storage unit 102 stores the current electrolyte resistance R calculated in step S1. ＳＥ＿ｍｅａ is the electrolyte resistance before charging R ＳＥ＿ｉｎｉ and stores (stores) the current temperature T ＣＥＬＬ Temperature T before charging ＣＥＬＬ＿ｉｎｉ Save (store) it as.

[0057] Next, in step S5, the current control unit 105 of the controller 10 determines whether or not there is a request to charge the battery module 2. Note that, in step S3, if the measured value of the pressure (surface pressure) is less than the predetermined value, step S4 is skipped and step S5 is executed.

[0058] If there is a request to charge the battery module 2, charging of the battery module 2 is started in step S6, and the short circuit sign detection is ended. If there is no request to charge the battery module 2, the short circuit sign detection is ended.

[0059] If it is determined in step S2 that the battery module 2 is being charged, it is determined in step S7 whether the pressure applied to the battery 21 measured by the pressure sensor 17 is equal to or greater than a predetermined value. This predetermined pressure value is not particularly limited, but may be the performance required pressure, as in step S3.

[0060] A case in which it is determined that the battery module 2 is being charged is when, in the short circuit prediction detection shown in the flowchart of Figure 6, steps S1 to S5 are executed, charging is started in step S6, and then this short circuit prediction detection is executed again.

[0061] If it is determined in step S7 that the measured pressure value is equal to or greater than the predetermined value, the current (charging) battery temperature T ＣＥＬＬ Electrolyte resistance R according to ＳＥ The predicted value R ＳＥ＿ｅｓｔ Calculate.

[0062] Since each battery cell 21 generates heat during charging, the battery temperature T ＣＥＬＬ is the pre-charge temperature T of the battery cell 21 before charging ＣＥＬＬ＿ｉｎｉ Higher than predicted value R ＳＥ＿ｅｓｔ is the temperature T of the battery cell 21 ＣＥＬＬ The higher the electrolyte resistance R ＳＥ In this embodiment, the resistance coefficient K Ｔ Using the predicted value R ＳＥ＿ｅｓｔ This resistance coefficient K Ｔ is the temperature T of the battery cell 21 ＣＥＬＬ Electrolyte resistance R according to ＳＥ The change rate is not particularly limited, but can be set in advance by experimentally confirming the change in electrolyte resistance due to the battery temperature.

[0063] FIG. 7 shows the battery temperature T ＣＥＬＬ and the resistance coefficient K Ｔ 7 is a graph showing an example of the relationship between the resistance coefficient K Ｔ 7, the horizontal axis represents the temperature of the battery cell 21. ＣＥＬＬ Electrolyte resistance R at 25°C ＳＥ＿２５ Based on the reference temperature, ＣＥＬＬ Electrolyte resistance R ＳＥ Electrolyte resistance R ＳＥ＿２５ The rate of change in the resistance coefficient K Ｔ ) is plotted (K Ｔ =R ＳＥ / R ＳＥ＿２５ ). The battery temperature T ＣＥＬＬ and the resistance coefficient K Ｔ If the relationship between the resistance coefficient K and the resistance coefficient K differs for each battery cell 21, Ｔ It is preferable to set

[0064] Such a resistance coefficient K Ｔ Using the predicted value R ＳＥ＿ｅｓｔ can be calculated as follows: First, the current temperature T ＣＥＬＬ＿ｎｏｗ The corresponding resistance coefficient K Ｔ＿ｎｏｗ and calculates the pre-charge battery temperature T ｃｅｌｌ＿ｉｎｉ Based on the resistance coefficient K before charging Ｔ＿ｉｎｉ Then, the predicted value R is calculated based on the following formula (1): ＳＥ＿ｅｓｔ Calculate R ＳＥ＿ｅｓｔ =R ＳＥ＿ｉｎｉ × (K Ｔ＿ｎｏｗ / K Ｔ＿ｉｎｉ ) ... (1)

[0065] If it is determined in step S7 that the measured pressure value is less than the predetermined value, the short circuit sign detection is terminated.

[0066] After step S8 is executed, in step S9, the determination unit 104 determines the electrolyte resistance R measured by the resistance measurement unit 101 during charging. ＳＥ Decrease D ＿ｍｅａ is the electrolyte resistance R due to changes in battery temperature. ＳＥ Decrease D ＿ｅｓｔ Specifically, in this embodiment, when the following formula (2) is satisfied, the decrease width D ＿ｍｅａ The power drop width D ＿ｅｓｔ It is determined that the difference is greater than the predetermined value C or more. ＳＥ＿ｅｓｔ ≧R ＳＥ＿ｍｅａ +C ... (2)

[0067] The predetermined value C in the above formula (2) is a margin for preventing erroneous determination. This margin is a numerical value set to prevent erroneous determination of the presence or absence of signs of a short circuit due to impedance measurement noise or individual variations in the battery cell 21. This margin can be determined experimentally by charging and discharging the battery under conditions where a short circuit may occur. In other words, a preliminary experiment is carried out to determine |R ＳＥ＿ｅｓｔ -R ＳＥ＿ｍｅａ It is only necessary to check in advance how large the value of | must be to indicate the possibility of a short circuit.ＳＥ＿ｍｅａ can be 3% to 50% of R ＳＥ＿ｍｅａ It is preferable that the ratio is 5% to 20% of R ＳＥ＿ｍｅａ It is more preferable to set it to 5% to 15% of the above.

[0068] FIG. 8(a) shows the measured value of the electrolyte resistance during charging, R ＳＥ＿ｍｅａ and predicted value R ＳＥ＿ｅｓｔ 8(b) is a graph showing an example of the temperature T ＣＥＬＬ 8 is a graph showing an example of a change in the voltage Vcc of the battery cell 21. Note that Fig. 8 illustrates a case where a short circuit occurs between the positive and negative electrodes of the battery cell 21.

[0069] As shown in FIG. 8B, when charging of the battery cell 21 starts, the temperature T ＣＥＬＬ As shown in FIG. 8(a), the measured value R of the electrolyte resistance actually measured after the start of charging ＳＥ＿ｍｅａ is the predicted value R of the electrolyte resistance due to the temperature rise ＳＥ＿ｅｓｔ In this example, the battery temperature T ＣＥＬＬ＿ｎｏｗ The electrolyte resistance R measured at ＳＥ＿ｍｅａ Electrolyte resistance before charging R ＳＥ＿ｉｎｉ Decrease from D ＿ｍｅａ is the battery temperature T ＣＥＬＬ＿ｎｏｗ Predicted value R ＳＥ＿ｅｓｔ Electrolyte resistance before charging R ＳＥ＿ｉｎｉ Decrease from D ＿ｅｓｔ is greater than the predetermined value C (D ＿ｍｅａ -D ＿ｅｓｔ ≧C).

[0070] In addition, the battery cell 21 deteriorates as the number of charge / discharge cycles increases, and the electrolyte resistance R ＳＥ On the other hand, as shown in the above formula (1), the pre-charge electrolyte resistance R ＳＥ＿ｉｎｉ The predicted value R ＳＥ＿ｅｓｔ The electrolyte resistance before and during charging in the same charge / discharge cycle is compared (the difference is taken). This makes it possible to determine signs of short circuiting after offsetting the effects of degradation, thereby improving the accuracy of detecting signs of short circuiting.

[0071] In step S9, the decrease width D ＿ｍｅａ is the decline D ＿ｅｓｔ If the predicted value R is greater than the predetermined value C or more, the determination unit 104 determines in step S10 that there is a sign of a short circuit between the positive and negative electrodes of the battery cell 21. ＳＥ＿ｅｓｔ and the measured value R of the electrolyte resistance actually measured during charging. ＳＥ＿ｍｅａ and the measured value R ＳＥ＿ｍｅａ is the predicted value R ＳＥ＿ｅｓｔ If the difference is smaller than the predetermined value C or more, it is determined that there is a sign of a short circuit.

[0072] Next, in step S11, the judgment unit 104 outputs a signal including information that there are signs of a short circuit to the current control unit 105 and the pressure control unit 106, and the current control unit 105 and the pressure control unit 106 perform processing to suppress the occurrence of a short circuit in the battery cell 21.

[0073] In this case, the current control unit 105, which has received a signal from the determination unit 104, does not increase the charging current to the battery cell 21, decreases the charging current, or discharges the battery cell 21. Alternatively, these processes may be used in combination. This makes it possible to suppress dendrite growth, thereby suppressing the occurrence of short circuits in the battery cell 21.

[0074] As an example of a combination of these processes, the charging current is controlled not to increase (keep constant) in the current short circuit sign detection, and if it is determined that there is again a short circuit sign in the next short circuit sign detection, the charging current is controlled to decrease, and if it is determined that there is still a short circuit sign in the next short circuit sign detection, the battery cell 21 is discharged. Note that when reducing the charging current, it is preferable to set the charging current to the minimum current value that the vehicle control system can tolerate.

[0075] Furthermore, although not limited to this, as a process for suppressing the occurrence of a short circuit, the pressure control unit 106 can reduce the pressure applied to the battery cell 21. This can suppress dendrite growth, thereby suppressing the occurrence of a short circuit in the battery cell 21.

[0076] In step S9, the decrease width D ＿ｍｅａ is the decline D ＿ｅｓｔ If it is determined that the difference is not greater than the predetermined value C, the short circuit sign detection is terminated.

[0077] The above-described short circuit sign detection system and short circuit sign detection method can detect signs of a short circuit by using electrolyte resistance without being affected by changes in electrode reaction resistance, etc. Furthermore, since signs of a short circuit can be detected at a stage before dendrite growth leads to a short circuit, the occurrence of a short circuit can be detected early.

[0078] DESCRIPTION OF SYMBOLS 1... Short circuit sign detection system 10... Controller 11... Voltage sensor 12... Current sensor 13... Temperature sensor 14... DCDC converter 16... Pressure application mechanism 17... Pressure sensor 2... Battery module 21... Battery cell

Claims

1. A short circuit sign detection system comprising: a battery including a positive electrode, a negative electrode containing lithium, and a solid electrolyte; a temperature measuring means for measuring a battery temperature, which is the temperature of the battery; a resistance measuring means for measuring the electrolyte resistance of the solid electrolyte; and a short circuit sign determination means for determining whether or not there is a sign of a short circuit occurring between the positive electrode and the negative electrode, wherein the short circuit sign determination means determines that there is a sign when a decrease in electrolyte resistance measured by the resistance measuring means during charging is greater than a predetermined value by which the decrease in electrolyte resistance caused by a change in the battery temperature.

2. A short circuit prediction system as claimed in claim 1, wherein the short circuit prediction determination means includes: a memory unit which stores a pre-charge battery temperature, which is the battery temperature measured by the temperature measurement means before charging, and a pre-charge electrolyte resistance, which is the electrolyte resistance measured by the resistance measurement means before charging; a prediction unit which calculates a predicted value of the electrolyte resistance corresponding to the battery temperature during charging based on the pre-charge battery temperature and the pre-charge electrolyte resistance; and a determination unit which compares the predicted value with a measured value of the electrolyte resistance measured by the resistance measurement means during charging, and determines that the prediction exists if the measured value is smaller than the predicted value by a predetermined value or more.

3. A short circuit indication detection system as claimed in claim 1, wherein the resistance measuring means calculates the electrolyte resistance based on the impedance of the battery in response to an AC signal having a frequency of 10 kHz or more.

4. A short circuit prediction detection system as described in claim 1, wherein, when the short circuit prediction determination means determines that the prediction exists, the charging / discharging means for charging / discharging the battery does not increase the charging current to the battery, reduces the charging current, or discharges the battery.

5. A short circuit sign detection system as claimed in any one of claims 1 to 4, further comprising a pressure application means for applying pressure to the battery, and a pressure measurement means for measuring the pressure applied to the battery, and the short circuit sign determination means determines whether or not the sign is present when the pressure measured by the pressure measurement means is equal to or greater than a predetermined value.

6. A short circuit indication detection system as described in claim 5, wherein the pressure application means reduces the pressure applied to the battery when the short circuit indication determination means determines that the indication exists.

7. A short circuit sign detection method for determining whether or not there is a sign of a short circuit occurring between a positive electrode and a negative electrode in a battery including a positive electrode, a negative electrode containing lithium, and a solid electrolyte, the method comprising: measuring a battery temperature, which is the temperature of the battery; measuring the electrolyte resistance of the solid electrolyte; and determining that the sign exists when a decrease in the electrolyte resistance during charging is greater than a predetermined value by a decrease in the electrolyte resistance caused by a change in temperature of the battery.

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