Pressure control system and pressure control method

Abstract

A pressure control system (15) for controlling the pressure applied to a battery module (2) in which a plurality of battery cells (21) having a solid electrolyte and a negative electrode containing lithium are stacked, the pressure control system (15) being provided with: a movable end plate (166) for applying pressure to the battery module (2) by pressing the battery module (2) in the stacking direction of the battery cells (21); and a controller (10) that adjusts the value of the pressure by controlling the movable end plate (166), in which, when a battery control system (1) that controls charging and discharging of the battery module (2) is to be stopped, the controller (10) stops the battery control system (1) after reducing the pressure to a predetermined pressure.

Description

Technical Field

[0001] The present invention relates to a pressure control system and a pressure control method. Background Art

[0002] There is known a lithium-ion secondary battery including an electrode body and a surface pressure control unit. In the electrode body, a positive electrode and a negative electrode containing a Si-containing negative electrode active material are provided. The surface pressure control unit controls the surface pressure applied to the electrode body in a specified direction (for example, refer to Patent Document 1). The surface pressure control unit of this lithium-ion secondary battery controls the amplitude of the surface pressure that varies during charge and discharge to 3.8 MPa or less. Specifically, this amplitude is the difference between the maximum value and the minimum value of the surface pressure observed during charge and discharge from SOC 0% to 100%, and is determined based on the resistance increase ratio before and after the charge and discharge cycle of the lithium-ion secondary battery (for example, refer to Patent Document 1 (

[0014] and

[0108] to

[0114] )).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-61749 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the prior art, the amplitude of the surface pressure is determined based on the resistance increase ratio of the resistance before the start of the charge and discharge cycle and the resistance after the end, but the deterioration of the secondary battery during the stopped storage without charge and discharge, which is considered to have a greater impact on the in-vehicle secondary battery, is not taken into account, and the deterioration that is not manifested in the resistance value of the secondary battery is also not considered.

[0008] Generally, the stop time of a vehicle is longer than the operation time, so the in-vehicle secondary battery is placed under pressure for a long time without charge and discharge. At this time, especially the negative electrode containing Li has a relatively low rigidity, so the negative electrode is prone to creep. Although the amount of creep per unit time is small, there is a problem that if this creep accumulates over a long time, it may sometimes have an adverse effect on the secondary battery.

[0009] The problem to be solved by the present invention is to provide a pressure control system and a pressure control method capable of reducing the amount of creep generated in the negative electrode.

[0010] Means for Solving the Problems

[0011] The present invention solves the above problems by stopping the battery control system that controls the charge and discharge of the battery module after reducing the pressure applied to the battery module to a specified pressure when the battery control system is to be stopped.

[0012] Effect of the Invention

[0013] According to the present invention, the amount of creep generated at the negative electrode can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a block diagram showing a battery control system according to an embodiment of the present invention.

[0015] Figure 2 is a flowchart showing a process of a pressure control method when the battery control system according to the embodiment of the present invention is stopped.

[0016] Figure 3 is a graph showing the relationship between the pressure applied to the battery cell, the amount of creep at the negative electrode, and the resistance value of the battery cell.

[0017] Figure 4 is an explanatory diagram of creep generated at the negative electrode.

[0018] Figure 5 is a diagram showing Figure 2 in step S6 where it is determined that T ex >T th a chart showing the time-dependent changes in pressure and resistance value in the pressure control method in this case.

[0019] Figure 6 is a diagram showing Figure 2 in step S6 where it is determined that T ex ≤T th a chart showing the time-dependent changes in pressure and resistance value in the pressure control method in this case. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a block diagram showing a battery control system 1 of this embodiment.

[0021] As Figure 1 shown, the battery control system 1 includes a controller 10, a voltage sensor 11, a current sensor 12, a temperature sensor 13, a DCDC converter 14, a pressure applying mechanism 16, and a pressure sensor 17.

[0022] In this embodiment, the controller 10, the pressure applying mechanism 16, and the pressure sensor 17 are elements constituting the pressure control system 15. Therefore, the controller 10 in this embodiment corresponds to an example of the "control unit", "stop time estimation unit", and "SOC estimation unit" in the present invention. In addition, the temperature sensor 13 in this embodiment corresponds to an example of the "temperature acquisition unit" in the present invention.

[0023] The controller 10 is a battery control unit (BCU). The controller 10 is composed of 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 the voltage sensor 11, the detected current detected by the current sensor 12, the detected temperature detected by the temperature sensor 13, etc., and determines the SOC usage range of the battery module 2 according to the state of the battery module 2.

[0024] In addition, the controller 10 controls the pressure applying mechanism 16 that constitutes the pressure control system 15. The controller 10 adjusts the value of the pressure applied to the battery module 2 by controlling the pressure applying mechanism 16.

[0025] In addition, the controller 10 estimates the stop time (expected stop time T ex ) from when the battery control system 1 stops until it starts again.

[0026] 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 wirings connected to the positive electrode and the negative electrode 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 wirings connected to the positive electrode and the negative electrode of the battery module 2. 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.

[0027] The DCDC converter 14 is a power conversion device that converts the voltage input from the battery module 2 into a specified voltage and outputs power to a load such as a motor. In addition, the DCDC converter 14 is also a power conversion device that converts the voltage input from a load such as a motor or a charging device into a specified voltage and outputs power to the battery module 2. The DCDC converter 14 is controlled by the controller 10. The battery module 2 is connected to the input side of the DCDC converter 14, and a load is connected to the output side of the DCDC converter 14. The load is a power grid including an electric motor inverter, etc. That is, the battery module 2 is connected to the load via the DCDC converter 14.

[0028] The pressure applying 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 applying mechanism 16 in the present embodiment has a motor drive circuit 161, a motor 162, a gearbox 163, a pressure transmission body 164, a fixed end plate 165, a movable end plate 166, and a plurality of shafts 167. The movable end plate 166 in the present embodiment is an example of the "pressure applying unit" in the present invention.

[0029] The motor drive circuit 161 operates the motor 162. The motor drive circuit 161 controls the drive of the operation of the motor 162 based on a control signal from the controller 10.

[0030] The motor 162 has a first drive shaft 162a. The motor 162 rotationally drives the first drive shaft 162a according to the output from the motor drive circuit 161.

[0031] The gearbox 163 is connected to the first drive shaft 162a and converts the rotational drive of the first drive shaft 162a into the drive of the pressure transmission body 164 in the stacking direction described above.

[0032] The pressure transmission body 164 moves in the vertical direction by the driving force transmitted via the gearbox 163. The 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 gearbox 163, and the rotational drive of the first drive shaft 162a of the motor 162 is transmitted through the gearbox 163. The pressure transmission plate 164b is a plate that moves in the stacking direction along with the rotation of the second drive shaft 164a. In the present embodiment, by moving the pressure transmission plate 164b downward in the figure, the pressure applied to the battery module 2 can be controlled in the increasing direction, and by moving the pressure transmission plate 164b upward in the figure, the pressure applied to the battery module 2 can be controlled in the decreasing direction.

[0033] The fixed end plate 165 and the movable end plate 166 are a pair of plate-like members and are 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 module 2. On the other hand, the movable end plate 166 is not fixed to the shaft 167 and can move along the extending direction of the shaft 167. The movable end plate 166 presses the battery module 2 from above according to the force transmitted from the pressure transmission body 164. In addition, the movable end plate 166 can move in the stacking direction corresponding to the expansion and contraction of the battery module 2 generated during charge and discharge and the expansion and contraction of the battery module 2 generated due to the change in the pressure applied to the battery module 2 by the movable end plate 166.

[0034] The pressure sensor 17 is a sensor that can measure the pressure applied to the battery module 2. The pressure sensor 17 can output the detected pressure to the controller 10.

[0035] The battery module 2 is electrically connected to the charging device. The charging device connected to the battery cell 21 is, for example, a device for charging the battery module 2 mounted on an electric vehicle or a hybrid vehicle. After removing the charging cable of the charging device and installing the charging gun at the front end of the charging cable on the connector of the vehicle's charging port, charging of the in-vehicle battery module 2 is performed by operating the charging start switch. The controller 10 controls the DCDC converter 14 and the charging device respectively to manage the charging state (SOC) of the battery cells 21 included in the battery module 2 and make the charging state of the battery module 2 the target charging state.

[0036] As described above, the battery module 2 is electrically connected to loads such as a motor. The load is a device that operates using the power of the battery module 2, and is an auxiliary device such as a motor, an air conditioner, and a lamp that are driving sources of the vehicle. Discharge of the battery module 2 is performed under the control of the controller 10 according to a system request or an external power request. The system request is equivalent to an instruction from an in-vehicle computer such as an ECU during vehicle travel. Regarding the external power request, for example, when the air conditioner is operated before vehicle travel by timer setting according to an instruction from an external device such as a portable terminal so that the interior of the vehicle becomes a suitable temperature when the vehicle starts to travel, the instruction from the external device is equivalent to the external power request.

[0037] In addition, the battery module 2 mounted on an electric vehicle or a hybrid vehicle can also be used for Vehicle Grid Integration (VGI). VGI is a technology for system-connecting an electric vehicle or a hybrid vehicle equipped with the battery module 2 to supply the electric power stored in the battery module 2 to the system (load) via the power grid.

[0038] The battery cell 21 included in the battery module 2 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 releasing and absorbing alkali metals such as lithium (Li), sodium (Na), or potassium (K), and preferably contains a sulfur-containing positive electrode active material, but is not particularly limited. As the solid electrolyte, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but a sulfide solid electrolyte is preferably used. The negative electrode only needs to contain lithium, and preferably contains lithium metal, for example.

[0039] Next, a pressure control method for the battery module 2 using the pressure control system 15 included in the battery control system 1 will be described. Figure 2 It is a flowchart showing the process of the pressure control method when the battery control system of the present embodiment is stopped. Before stopping the battery control system 1, that is, when the vehicle is stopped, the Figure 2 shown pressure control method is repeatedly executed at regular intervals.

[0040] In this control method, first, in step S1, the controller 10 determines whether the vehicle is in the process of stop processing. Generally, during the vehicle stop processing, when the occupant cuts off the ignition switch of the vehicle, an instruction to start the stop processing of each control system provided in the vehicle (specifically, the battery control system 1, the drive motor control system, the steering control system, etc.) is sent.

[0041] When the controller 10 determines that each control system provided in the vehicle is in the process of stop processing, in step S2, the controller 10 controls the battery module 2 and the DCDC converter 14 to perform the power supply for actuator operation included in the vehicle stop processing, the self-diagnosis of the battery module 2 performed by the battery control system 1, etc. In addition, as an example of actuator operation, the actuator operation used by the drive motor control system to return the stepping motor (drive motor) to the initial position can be cited. In this step S2, the stop processing of the vehicle that consumes power except for the control processing performed by the controller 10 of the battery control system 1 after step S3 is completed.

[0042] In addition, in step S1, when the controller 10 determines that the vehicle is not in the process of stop processing, in the case of determining no, the current pressure control is ended, and the pressure control is restarted from step S1 after a specified period.

[0043] In step S3, the controller 10 determines whether the stop processing (except for the control processing performed by the controller 10 after step S3) that requires charge and discharge in the vehicle is completed.

[0044] When the controller 10 determines in step S3 that the processing that requires charge and discharge in the vehicle is completed, in step S4, the controller 10 determines the expected stop time value T by using alone or in combination the past action history record of the vehicle, map information, SOC, etc. ex In addition, in step S3, when the controller 10 determines that the processing that requires charge and discharge in the vehicle is not completed, the current pressure control is ended, and the pressure control is restarted from step S1 after a specified period.

[0045] The past action history record is, for example, the history record of the vehicle's stop and parking time for each time period. The controller 10 can predict the expected stop time value T at the current moment based on the history record of the vehicle's stop and parking time for each past time period. ex In addition, the controller 10 can predict the expected stop time value T at the current position based on the position information on the map and the history record of the stop and parking time at a specific position on the past map. exFor example, when it is determined that the current position is a company, one's own home, etc., or when it is determined that the current time belongs to the time period when the occupant stays at the company, one's own home, etc., the controller 10 predicts that the stop placement time is relatively long. On the other hand, for example, when it is determined that the current position is a convenience store, etc., the controller 10 predicts that the stop placement time is relatively short. Alternatively, the controller 10 can also predict the expected stop time T at the current SOC based on the historical record of the stop placement time at each SOC of the battery module 2 in the past. ex In addition, the SOC can be estimated by a general method using the open-circuit voltage of each battery cell 21 and the cumulative value of the charge and discharge charge.

[0046] Next, in step S5, the controller 10 determines the stop time threshold T. TH As described later, the stop time threshold T TH is a threshold that serves as a reference for determining whether to reduce the pressure of the battery module 2 to less than the performance requirement pressure P. 1 When the expected stop time T ex exceeds the stop time threshold T TH , in the subsequent process, the controller 10 reduces the pressure of the battery module 2 to less than the performance requirement pressure P. 1 In addition, the stop time threshold T in the present embodiment TH corresponds to an example of the "specified time" in the present invention.

[0047] The stop time threshold T th (for example, about 5 minutes to 10 minutes) is determined based on the energy balance between the power consumption of the pressure application mechanism 16 caused by the operation of reducing the pressure on the battery module 2 and the discharge power caused by the self-discharge of the battery module 2 per unit time at the current pressure, and the amount of deformation of the negative electrode caused by creep per unit time at the current pressure. For example, when the stop placement time is short, the power consumption caused by the motor operation of the pressure application mechanism 16 is greater than the power that can be saved by suppressing self-discharge. In addition, when the stop placement time is short, it is considered that almost no creep will occur. Therefore, regarding the stop time threshold T th , for example, the better the energy balance (the greater the discharge power based on self-discharge compared to the power consumption of the pressure application mechanism 16), the shorter the stop time threshold T th is set, and the greater the amount of deformation of the negative electrode, the shorter the stop time threshold T th is set. The above energy balance and the amount of deformation of the negative electrode can be calculated in advance through experiments, and the time when the advantages of self-discharge suppression and creep suppression can be fully obtained with respect to the power consumption of the pressure application mechanism 16 is set as the stop time threshold T. TH。

[0048] In addition, the higher the temperature, the greater the creep amount. Therefore, the higher the temperature of the battery module 2, the greater the deformation amount of the negative electrode. Thus, the higher the temperature of the battery module 2 detected by the temperature sensor 13, the shorter the stop time threshold T in the present embodiment is made by the controller 10. Thereby, even when the temperature of the battery module 2 is high and the deformation of the negative electrode caused by creep may become large, the pressure applied to the battery module 2 can be reduced in the subsequent process to suppress the deformation of the negative electrode. th Moreover, the higher the SOC, the thicker the thickness of the negative electrode. Therefore, the influence of creep in the negative electrode becomes greater. Thus, the higher the SOC of the battery module 2, the greater the deformation amount D of the negative electrode. On the other hand, the higher the SOC estimated by the controller 10 based on the temperature of the battery module 2, the shorter the stop time threshold T is made by the controller 10. Thereby, even when the SOC of the battery module 2 is high and the deformation of the negative electrode caused by creep may become large, the pressure applied to the battery module 2 can be reduced in the subsequent process to suppress the deformation of the negative electrode.

[0049] In step S6, the controller 10 determines whether the stop time expected value T th is longer than the stop time threshold T

[0050] In the case where the controller 10 determines in step S6 that the stop time expected value T ex is longer than the stop time threshold T TH in step S7, the controller 10 moves the movable end plate 166 of the pressure applying mechanism 16 upward to reduce the pressure applied to the battery module 2 to a specified pressure. In addition, the pressure applied to the battery cell 21 becomes a value substantially equal to the pressure applied to the battery module 2.

[0051] is a graph showing the relationship between the pressure applied to the battery cell 21, the resistance value of the battery cell 21, and the creep amount of the negative electrode. In ex is longer than the stop time threshold T TH In the case where the controller 10 determines in step S6 that the stop time expected value T

[0052] Figure 3 is a graph showing the relationship between the pressure applied to the battery cell 21, the resistance value of the battery cell 21, and the creep amount of the negative electrode. In Figure 3 the curve a represents the creep amount. As shown by the curve a in Figure 3 the creep amount in the negative electrode of the battery cell 21 increases as the pressure applied to the battery module 2 increases.

[0053] Figure 4 is an explanatory diagram of the creep generated in the negative electrode. Figure 4 The left diagram of Figure 4 shows the battery cell 21B that is stopped and placed without reducing the pressure applied to the battery module, and the right diagram of

[0054] As Figure 4 shown in the left figure of Figure 4 , without reducing the pressure applied to the battery module, the negative electrode 21Bc is compressed in the thickness direction by the pressure and extends in the width direction. As a result, an extension portion 22B extending outward is generated at the side portion of the negative electrode 21Bc. Since this extension portion 22B does not face the positive electrode 21Ba, it is difficult to contribute to charge and discharge, so the battery performance deteriorates. In addition, a protrusion 23B protruding toward the positive electrode 21Ba and the solid electrolyte 21Bb is generated by the pressure. This protrusion 23B not only gets closer to the positive electrode 21Ba, but also current is likely to concentrate, so the possibility of short circuit between the positive electrode 21Ba and the negative electrode 21Bc becomes high.

[0055] On the other hand, according to the present embodiment, by reducing the pressure applied to the battery module, deformation of the negative electrode 21c caused by creep is suppressed. Therefore, as Figure 4 shown in the right figure of Figure 4 , in the negative electrode 21c, it is not easy to generate the extension portion 22B and the protrusion 23B protruding toward the positive electrode 21a and the solid electrolyte 21b. Therefore, deterioration of battery performance and occurrence of short circuit can be suppressed.

[0056] Return Figure 2 , in step S8, the controller 10 determines whether the pressure applied to the battery module 2 has reached a specified pressure according to the detection value of the pressure sensor 17. The specified pressure in the present embodiment is smaller than the performance requirement pressure P 1 and larger than the earthquake resistance requirement pressure P 0 . In addition, the specified pressure may also be a pressure larger than the performance requirement pressure P 1 .

[0057] As Figure 3 shown, the earthquake resistance requirement pressure P 0 in the present embodiment is the minimum value of the pressure required to maintain the contact between the movable end plate 166 and the battery module 2. In the present embodiment, it is the minimum value of the pressure that does not cause the battery module 2 to fall off between the fixed end plate 165 and the movable end plate 166 even when an external force based on impact, vibration, etc. is applied to the battery module 2. By making the pressure larger than the earthquake resistance requirement pressure P 0 , the battery module 2 can be prevented from falling off.

[0058] As Figure 3 shown, when the pressure applied to the battery module 2 is smaller than the performance requirement pressure P 1 , the resistance value of the battery cell 21 increases. It can be considered that this is because, as Figure 4 shown in the right figure of Figure 4 , the pressure of the negative electrode 21c on the solid electrolyte 21b decreases and the contact area between the two becomes smaller. On the other hand, when the pressure is larger than the performance requirement pressure P 1When it is large, a contact area of the negative electrode 21c and the solid electrolyte 21b above a certain level can be obtained, and thus the resistance value is maintained at a substantially constant low resistance value.

[0059] Performance requirement pressure P 1 is the pressure that makes the resistance of the battery cell 21 the same as a specified threshold value, which is the maximum value of the resistance within the range of the resistance at which the battery cell 21 can input and output the charge and discharge power required for the vehicle's control system to operate. Performance requirement pressure P 1 is larger than the earthquake resistance requirement pressure P 0 .

[0060] In this way, in step S7, by making the pressure less than the performance requirement pressure P 1 to set it to a state with a high resistance value, even if the battery module 2 is left stopped for a long time, the self-discharge amount of the battery module 2 during the stop period can be reduced.

[0061] Regarding such a performance requirement pressure P 1 , it can be obtained through experiments as follows. The larger the resistance of the battery cell, the less the charge and discharge power of the battery cell. Therefore, at least apply pressure to the battery cell to reduce the resistance of the battery cell until it can output the power required for the vehicle's control system to operate. Through experiments, find the minimum value of the pressure at which the power required for the control system to operate can be output in this case based on the relationship between pressure and power, and thus the performance requirement pressure P 1 can be obtained.

[0062] In addition, in the present embodiment, the pressure applied to the battery module 2 (the pressure applied to the battery cell 21) is detected by the pressure sensor 17, but it is not limited thereto. The pressure can also be estimated without using the pressure sensor 17.

[0063] Specifically, for example, when the negative electrode is a Li metal negative electrode, the thickness of the battery cell changes substantially in proportion to the SOC. Therefore, the thickness of the battery module changes substantially in proportion to the charge and discharge amount of the battery module. In addition, the amount of change in the thickness of the battery module generated by operating the motor is determined by the gear ratio, pitch, etc. in the pressure application mechanism and the operation amount of the motor. Therefore, as long as the relationship between the difference between the amount of change in the thickness of the battery module based on the charge and discharge amount and the amount of change in the thickness of the battery module based on the motor operation and the pressure is obtained through experiments, the pressure can be estimated based on this relationship according to the time series changes of the motor command value and the SOC.

[0064] Return Figure 2, in step S8, when it is determined that the pressure applied to the battery module 2 has reached the specified pressure, in step S9, the controller 10 cuts off the power supply of the pressure application mechanism 16. That is, the pressure control by the pressure control system 15 is ended. In addition, even if the power supply of the pressure application mechanism 16 is cut off, the pressure is maintained at the specified pressure. In this way, in step S9, after completing the pressure control, the controller 10 stops the battery control system 1.

[0065] In addition, in step S8, when it is determined that the pressure applied to the battery module 2 has not reached the specified pressure, the process returns to step S7, and the control to decrease the pressure by the pressure application mechanism 16 is executed again.

[0066] Figure 5 is a diagram showing Figure 2 in step S6 of ex >T th the temporal changes in pressure and resistance value in the pressure control method in the case of. Figure 5 The upper diagram of Figure 5 is a diagram showing the temporal change in pressure,

[0067] As Figure 5 shown in the upper diagram of Figure 2 during the period from the start to step S6 of the flowchart shown in 1 , the pressure is maintained at a pressure higher than the performance required pressure P Figure 5 . At this time, although charge and discharge are performed during the stop process, as

[0068] shown in the lower diagram of ex >T th the resistance value of the battery cell 21 is maintained at approximately constant. Figure 5 After that, in step S6, the controller 10 determines that T 2 >T

[0069] and then, in step S7, the controller 10 starts to reduce the pressure. Along with this pressure reduction, as 1 shown in the lower diagram of 2 , the resistance value of the battery cell 21 increases. This pressure reduction operation is continuously performed until the pressure reaches the specified pressure P

[0070] After that, in step S9, after cutting off the power supply of the motor 162 of the pressure application mechanism 16, the battery control system 1 is stopped. Thus, the pressure reduction operation is completed, and the pressure is maintained at a specified pressure P 1Thus, it is possible to prevent a shortage of power required for the operation of the battery control system 1.

[0071] Return Figure 2 , when it is determined in step S6 that T ex ≤T th , in step S10, the controller 10 of the present embodiment reduces the pressure to the performance required pressure P which is greater than the specified pressure 1 . That is, in this step S10, since it is determined that the stop placement time is short, the pressure is decreased within the range where the resistance value at which the battery control system 1 and the like can operate can be maintained. Thus, when the stop placement time is short, it is possible to suppress the power consumption generated by the operation of the pressure applying mechanism 16 and to suppress the occurrence of creep.

[0072] Next, in step S11, the controller 10 determines whether the pressure has reached the performance required pressure P 1 .

[0073] When the controller 10 determines that the pressure has reached the performance required pressure P 1 , in step S9, the controller 10 cuts off the power supply of the pressure applying mechanism 16. That is, the pressure control by the pressure control system 15 is ended. Further, even if the power supply of the pressure applying mechanism 16 is cut off, the pressure is maintained at the performance required pressure P 1 . In this way, in step S9, the controller 10 stops the battery control system 1 after completing the pressure control. In this way, when the occupant repeatedly operates the start and stop of the vehicle in a short period of time, by preventing the pressure from dropping below the performance required pressure P 1 , it is possible to suppress an increase in power consumption.

[0074] In addition, in step S11, when it is determined that the pressure has not reached the performance required pressure P 1 , the process returns to step S10, and the control to decrease the pressure by the pressure applying mechanism 16 is executed again.

[0075] Figure 6 is a diagram showing the temporal changes in the pressure and the resistance value in the pressure control method when it is determined in step S6 of Figure 2 that T ex ≤T th . Figure 6 The upper diagram of Figure 6 is a diagram showing the temporal change in the pressure,

[0076] As Figure 6 shown in the upper diagram of Figure 2During the period from the start to step S6 of the flowchart shown, the pressure is maintained at a pressure higher than the performance requirement pressure P. 1 As shown in the lower figure of Figure 6 , although charge and discharge are performed during the stop process at this time, the resistance value of the battery cell 21 is maintained at approximately constant.

[0077] Next, in step S6, the controller 10 determines that T ex ≤T th After that, in step S10, the controller 10 starts to reduce the pressure. Here, since the pressure is within the range of the performance requirement pressure P 1 or higher, as shown in the lower figure of Figure 6 , the resistance value of the battery cell 21 is maintained at approximately constant.

[0078] Next, when it is determined in step S11 that the pressure has reached the performance requirement pressure P 1 After that, in step S9, the motor 162 of the pressure application mechanism 16 is cut off. As a result, the pressure reduction operation is completed, and as shown in the upper figure of Figure 6 , the pressure is maintained at the performance requirement pressure P 2 greater than the specified pressure P 1 . In addition, as shown in the lower figure of Figure 6 , the resistance value is maintained at approximately constant.

[0079] In this way, when it is determined that the stop placement time is short, the advantages of suppressing self-discharge and suppressing the deformation of the negative electrode caused by creep are small. That is, the power consumption generated by operating the pressure application mechanism 16 may be greater than the power savings generated by suppressing self-discharge. Therefore, there is no need to reduce the pressure to less than the performance requirement pressure P 1 . Thus, an increase in power consumption generated by operating the pressure application mechanism 16 can be suppressed.

[0080] In addition, in the present embodiment, in step S10, the controller 10 reduces the pressure to the performance requirement pressure P 1 , but in step S10, the controller 10 may also reduce the pressure to a pressure greater than the performance requirement pressure P 1 . In addition, in the present embodiment, in step S10, the controller 10 reduces the pressure, but in step S10, the controller 10 may also maintain the pressure without reducing the pressure. As a result, no power consumption is generated due to operating the pressure application mechanism 16. However, since the actual stop time is sometimes longer than the stop time expected value T ex predicted by the controller 10, if the pressure is reduced to a range above the performance requirement pressure P 1 in order to prevent such a situation, the effect of suppressing creep generation can be obtained.

[0081] In the past, when the vehicle was parked, a pressure above the performance requirement pressure was applied to the battery module. As a result, creep was likely to occur at the negative electrode of the battery cell, and due to this creep, the battery performance deteriorated or the probability of short circuit increased. In contrast, according to the present embodiment, when the vehicle is parked, the pressure is reduced to less than the performance requirement pressure P 1 , so that the generation of creep can be suppressed, and thus the deterioration of battery performance and the increase in the probability of short circuit can be suppressed.

[0082] In addition, in the past, when the vehicle was parked, a pressure above the performance requirement pressure was applied to the battery module, so that the resistance value of the battery module was maintained low, resulting in an increase in the self-discharge amount. In contrast, according to the embodiment, when the vehicle is parked, the pressure is decreased to less than the performance requirement pressure P 1 to increase the resistance value, so that the self-discharge amount can be reduced.

[0083] Description of Reference Numerals

[0084] 1: Battery control system; 10: Controller; 11: Voltage sensor; 12: Current sensor; 13: Temperature sensor; 14: DCDC converter; 15: Discharge unit; 16: Pressure applying mechanism; 161: Motor drive circuit; 162: Motor; 162a: First drive shaft; 163: Gearbox; 164: Pressure transmission body; 164a: Second drive shaft; 164b: Pressure transmission plate; 165: Fixed end plate; 166: Movable end plate; 167: Shaft; 17: Pressure sensor; 2: Battery module; 21: Battery cell; 21a: Positive electrode; 21b: Solid electrolyte; 21c: Negative electrode.

Claims

1. A pressure control system controls the pressure applied to a battery module formed by stacking a plurality of battery cells. The battery cell has a solid electrolyte and a negative electrode containing lithium. The pressure control system includes: a pressure application unit that applies pressure to the battery module by pressing the battery module in the stacking direction of the battery cells; and a control unit that adjusts the value of the pressure by controlling the pressure application unit. Wherein, when the battery control system for controlling charging and discharging of the battery module is to be stopped, after the control unit reduces the pressure to a specified pressure, the battery control system is stopped.

2. The pressure control system according to claim 1, wherein, the specified pressure is greater than the earthquake resistance required pressure, and the earthquake resistance required pressure is the minimum value of the pressure required to maintain the contact between the pressure application unit and the battery module.

3. The pressure control system according to claim 1, wherein, the pressure control system further includes a stop time estimation unit that estimates the stop time from when the battery control system is stopped until it is restarted. When the stop time estimated by the stop time estimation unit is longer than a specified time, the control unit reduces the pressure to the specified pressure. When the stop time estimated by the stop time estimation unit is equal to or less than the specified time, the control unit maintains the pressure or reduces the pressure to a pressure greater than the specified pressure.

4. The pressure control system according to claim 3, wherein, the pressure control system further includes a temperature acquisition unit that measures or estimates the temperature of the battery module. The higher the temperature of the battery module, the shorter the specified time set by the stop time estimation unit.

5. The pressure control system according to claim 3, wherein, the pressure control system further includes a charge state estimation unit that estimates the charge state of the battery cell. The greater the charge state of the battery cell, the shorter the specified time set by the stop time estimation unit.

6. The pressure control system according to claim 1, wherein, the specified pressure is less than the performance required pressure, and the performance required pressure is the pressure at which the resistance of the battery cell becomes the same value as the threshold. The threshold is the maximum value of the resistance within the range of the resistance of the battery cell that can input and output the charge and discharge power required for the vehicle control system to operate.

7. The pressure control system according to claim 6, wherein, when the battery control system is restarted after being stopped, the control unit increases the pressure to at least the performance required pressure.

8. A pressure control method for controlling the pressure applied to a battery module formed by stacking a plurality of battery cells. The battery cell has a solid electrolyte and a negative electrode containing lithium. In the pressure control method, In the case where it is necessary to stop the battery control system that controls the charge and discharge of the battery module, the battery control is stopped after the pressure is decreased to a specified pressure.

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