Pressure control system and pressure control method

Abstract

This pressure control system (15) controls 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 laminated. The pressure control system (15) comprises a movable end plate (166) for applying pressure to the battery module (2) by pressing the battery module (2) along the lamination direction of the battery cells (21), and a controller (10) for adjusting the pressure value by controlling the movable end plate (166), and in a case in which a battery control system (1) controlling charging / discharging of the battery module (2) is to be stopped, the controller (10) first reduces the pressure to a prescribed pressure, then the battery control system (1) is stopped.

Description

[Technical Field]

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

[0002] A lithium-ion secondary battery is known that comprises an electrode body having a positive electrode and a negative electrode containing a Si-containing negative electrode active material, and a surface pressure control unit that controls the surface pressure applied to the electrode body in a predetermined direction (see, for example, Patent Document 1). The surface pressure control unit of this lithium-ion secondary battery controls the amplitude of the surface pressure that fluctuates with charging and discharging to 3.8 MPa or less. Specifically, this amplitude is the difference between the maximum and minimum values ​​of the surface pressure observed when charging and discharging from SOC 0% to 100%, and is determined from the resistance increase ratio before and after the charge-discharge cycle of the lithium-ion secondary battery (see, for example, Patent Document 1 (paragraphs

[0014] and

[0108] to

[0114] )). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-61749 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Conventional technology determines the amplitude of surface pressure fluctuations based on the ratio of resistance increase between the resistance before the start of a charge-discharge cycle and the resistance after its completion. However, it does not take into account the degradation of secondary batteries during periods of inactivity when they are not being charged or discharged, which is considered to have a significant impact on automotive secondary batteries. Furthermore, it does not consider degradation that does not manifest in the resistance value of the secondary battery.

[0005] Generally, since vehicle downtime is longer than operating time, onboard secondary batteries are left under pressure for extended periods without charging or discharging. In this situation, the negative electrode, in particular, which contains lithium, has relatively low rigidity, making it prone to creep. Although the amount of creep per unit time is minute, the problem is that if this creep accumulates over a long period, it can adversely affect the secondary battery.

[0006] The problem that this invention aims to solve is to provide a pressure control system and a pressure control method that can reduce the amount of creep that occurs in the negative electrode. [Means for solving the problem]

[0007] The present invention solves the above problem by, when stopping a battery control system that controls the charging and discharging of a battery module, if the stop time of the battery control system estimated by the stop time estimation means is longer than a predetermined time, the pressure applied to the battery module is reduced to a predetermined pressure before stopping the battery control system; and if the stop time is less than or equal to the predetermined time, the pressure is maintained or reduced to a pressure greater than the predetermined pressure before stopping the battery control system. [Effects of the Invention]

[0008] According to the present invention, the amount of creep that occurs in the negative electrode can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a block diagram showing a battery control system according to an embodiment of the present invention. [Figure 2] Figure 2 is a flowchart showing the procedure for a pressure control method when stopping a battery control system according to an embodiment of the present invention. [Figure 3] 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. [Figure 4] Figure 4 is an explanatory diagram of creep that occurs at the negative electrode. [Figure 5]FIG. 5 is a graph showing changes over time in pressure and resistance values in the pressure control method when it is determined that Tex > Tth in step S6 of FIG. 2. [Figure 6] FIG. 6 is a graph showing changes over time in pressure and resistance values in the pressure control method when it is determined that Tex ≤ Tth in step S6 of FIG. 2.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a battery control system 1 of the present embodiment.

[0011] As shown in FIG. 1, 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 application mechanism 16, and a pressure sensor 17.

[0012] The controller 10, the pressure application mechanism 16, and the pressure sensor 17 in the present embodiment are elements that constitute the pressure control system 15. Therefore, the controller 10 in the present embodiment corresponds to an example of the "control means", "stop time estimation means", and "SOC estimation means" in the present invention. Further, the temperature sensor 13 in the present embodiment corresponds to an example of the "temperature acquisition means" in the present invention.

[0013] The controller 10 is a battery control unit (BCU). The controller 10 is composed of a memory such as a ROM or RAM, and a processor such as a CPU. 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., while managing the state of the battery module 2, the SOC usage range of the battery module 2 is determined according to the state of the battery module 2.

[0014] Furthermore, the controller 10 controls the pressure application mechanism 16 that constitutes the pressure control system 15. By controlling the pressure application mechanism 16, the controller 10 adjusts the value of the pressure applied to the battery module 2.

[0015] Furthermore, this controller 10 controls the downtime (expected downtime T) between the time the battery control system 1 is stopped and when it is restarted. ex We estimate ).

[0016] 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 terminals of the battery module 2. The current sensor 12 is a sensor for detecting the input and output current of the battery module 2. The current sensor 12 is connected to the wiring connected to either the positive or negative terminal 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.

[0017] The DC-DC converter 14 is a power conversion device that converts the voltage input from the battery module 2 into a predetermined voltage and outputs power to a load such as a motor. The DC-DC converter 14 also converts the voltage input from a load such as a motor or a charging device into a predetermined voltage and outputs power to the battery module 2. This 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 the load is connected to the output side of the DC-DC converter 14. The load is a power grid including a motor inverter, etc. In other words, the battery module 2 is connected to the load via the DC-DC converter 14.

[0018] The pressure application mechanism 16 applies pressure to the battery module 2 by pressing it along the stacking direction of the battery cells 21 in the battery module 2. The pressure application mechanism 16 in this embodiment includes a motor driver 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 this embodiment corresponds to an example of the "pressure application means" in the present invention.

[0019] The motor driver circuit 161 operates the motor 162. Based on the control signals from the controller 10, the motor driver circuit 161 controls the operation of the motor 162.

[0020] The motor 162 has a first drive shaft 162a. The motor 162 rotates the first drive shaft 162a in response to the output from the motor driver circuit 161.

[0021] The gearbox 163 is connected to the first drive shaft 162a and converts the rotational drive of the first drive shaft 162a into a drive of the pressure transmission body 164 in the aforementioned stacking direction.

[0022] The pressure transmission body 164 moves up and down due to the driving force transmitted via the gearbox 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 gearbox 163, which transmits the rotational drive of the first drive shaft 162a of the motor 162. The pressure transmission plate 164b is a plate that moves along the stacking direction as the second drive shaft 164a rotates. In this embodiment, the pressure applied to the battery module 2 can be controlled to increase by the downward movement of the pressure transmission plate 164b in the figure, and the pressure applied to the battery module 2 can be controlled to decrease by the upward movement of the pressure transmission plate 164b in the figure.

[0023] 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 shafts 167 and supports the battery module 2. On the other hand, the movable end plate 166 is not fixed to the shafts 167 and is movable along the extending direction of the shafts 167, and pressurizes the battery module 2 from above in accordance with the force transmitted from the pressure transmission body 164. Furthermore, this movable end plate 166 can move along the stacking direction in response to the expansion and contraction of the battery module 2 due to charging and discharging, and the expansion and contraction of the battery module 2 due to changes in the pressure applied to the battery module 2 by the movable end plate 166.

[0024] The pressure sensor 17 is a sensor capable of measuring the pressure applied to the battery module 2. This pressure sensor 17 can output the detected pressure to the controller 10.

[0025] The battery module 2 is electrically connected to a charging device. The charging device connected to the battery cell 21 is, for example, a device for charging the battery module 2 installed in an electric vehicle or a hybrid vehicle. Charging the vehicle-mounted battery module 2 is performed by taking out 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. The controller 10 manages the state of charge (SOC) of the battery cell 21 contained in the battery module 2, and controls the DC-DC converter 14 and the charging device respectively so that the charge state of the battery module 2 reaches the target charge state.

[0026] As described above, battery module 2 is electrically connected to loads such as motors. The loads are devices that operate using the power of battery module 2, and include motors that are the driving source of the vehicle, as well as auxiliary equipment such as air conditioners and lights. Discharging of battery module 2 is performed under the control of controller 10 in response to system requests or external power requests. System requests correspond to commands from an on-board computer such as an ECU while the vehicle is running. Regarding external power requests, for example, when an external device such as a mobile terminal commands the air conditioner to be operated before the vehicle starts running via a timer setting, so that the interior of the vehicle reaches an appropriate temperature when the vehicle starts running, the command from the external device corresponds to an external power request.

[0027] Furthermore, battery modules 2 installed in electric vehicles and hybrid vehicles may be used for Vehicle Grid Integration (VGI). VGI is a technology that connects electric vehicles and hybrid vehicles equipped with battery modules 2 to the grid and supplies the power stored in the battery modules 2 to the grid (load) via the power network.

[0028] The battery cell 21 contained in the battery module 2 comprises 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 is not particularly limited, but preferably contains a positive electrode active material containing sulfur. As the solid electrolyte, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but the use of a sulfide solid electrolyte is preferred. The negative electrode may contain lithium, and for example, it is preferable that it contains lithium metal.

[0029] The following describes a method for controlling the pressure of a battery module 2 using a pressure control system 15 included in such a battery control system 1. Figure 2 is a flowchart showing the procedure for the pressure control method when stopping the battery control system of this embodiment. The pressure control method shown in Figure 2 is repeatedly executed at predetermined intervals before the battery control system 1 is stopped, that is, when the vehicle is stopped.

[0030] In this control method, first, in step S1, the controller 10 determines whether the vehicle is in the process of stopping. Generally, when an occupant turns off the vehicle's ignition switch, an instruction is sent to each control system installed in the vehicle (specifically, the battery control system 1, the drive motor control system, the steering control system, etc.) to start the stopping process for each system.

[0031] If the controller 10 determines that each control system installed in the vehicle is in the process of stopping, in step S2, the controller 10 controls the battery module 2 and the DC-DC converter 14 to supply power to actuator operations included in the vehicle stopping process, and to perform self-diagnosis of the battery module 2, which is performed by the battery control system 1. An example of actuator operation is the actuator operation by the drive motor control system to return the stepping motor (drive motor) to its initial position. In this step S2, the vehicle stopping process that consumes power is completed, except for the control processing performed by the controller 10 of the battery control system 1 in step S3 and beyond.

[0032] If, in step S1, the controller 10 determines that the vehicle is not in the process of stopping, ,now After completing one cycle of pressure control, the pressure control is restarted from step S1 after a predetermined period.

[0033] In step S3, the controller 10 determines whether the vehicle has completed the stop process that requires charging and discharging (excluding the control process performed by the controller 10 from step S3 onward).

[0034] In step S3, if the controller 10 determines that the charging and discharging processes required in the vehicle have been completed, in step S4, the controller 10 uses the vehicle's past activity history, map information, SOC, etc. individually or in combination to determine the expected stopping time T ex This is determined. If, in step S3, the controller 10 determines that the charging and discharging process required in the vehicle has not been completed, the current pressure control is terminated, and after a predetermined cycle, the pressure control is restarted from step S1.

[0035] Past behavioral history includes, for example, the history of vehicle stopping time for each time period. Controller 10 calculates the expected stopping time T at the current time from the past history of vehicle stopping time for each time period. ex It can predict this. In addition, the controller 10 can determine the expected stopping time T at the current location from the location information on the map and the history of stopping time at specific locations on the map in the past. ex It can predict the following. For example, if the current location is determined to be a company or home, or if the current time is determined to be within the time frame when the occupant is at a company or home, the controller 10 predicts that the idle time will be relatively long. On the other hand, if the current location is determined to be a convenience store, for example, the controller 10 predicts that the idle time will be relatively short. Alternatively, the controller 10 can use the history of idle time for each SOC of the battery module 2 to determine the expected idle time T for the current SOC. ex It is also possible to predict this. The State of Charge (SOC) can be estimated using a general method that utilizes the open-circuit voltage and the integrated charge / discharge charge of each battery cell 21.

[0036] Next, in step S5, the controller 10 sets the stop time threshold T th Determine the stop time threshold T. th As will be described later, this is a threshold value that serves as a criterion for determining whether or not to reduce the pressure of battery module 2 to below the performance requirement pressure P1. Expected stop time T ex The stop time threshold Tth If it exceeds, in the subsequent process, the controller 10 reduces the pressure of the battery module 2 to less than the performance required pressure P1. Note that the stop time threshold T th in this embodiment corresponds to an example of the "predetermined time" in the present invention.

[0037] The stop time threshold T th (for example, about 5 to 10 minutes) is determined based on the energy balance between the power consumption of the pressure application mechanism 16 by the operation of reducing the pressure on the battery module 2 and the discharge power due to the self-discharge of the battery module 2 per unit time under the current pressure, and the amount of deformation of the negative electrode due to creep per unit time under the current pressure. For example, when the stop time is short, the power consumption by the motor operation of the pressure application mechanism 16 may be larger than the power that can be saved by suppressing self-discharge. Also, when the stop time is short, creep is considered to hardly occur. Therefore, the stop time threshold T th is set shorter, for example, the better the energy balance (the larger the discharge power due to self-discharge is than the power consumption of the pressure application mechanism 16), and the larger the deformation amount of the negative electrode. The above energy balance and the deformation amount of the negative electrode can be calculated in advance by experiments, and for the power consumption of the pressure application mechanism 16, the time when the merits of self-discharge suppression and creep suppression can be sufficiently obtained is set as the stop time threshold T th .

[0038] Also, since the amount of creep increases as the temperature gets higher, the deformation amount of the negative electrode increases as the temperature of the battery module 2 gets higher. Therefore, in this embodiment, the controller 10 shortens the stop time threshold T th as the temperature of the battery module 2 detected by the temperature sensor 13 gets higher. Thereby, even when the temperature of the battery module 2 is high and the deformation of the negative electrode due to creep can be large, the pressure applied to the battery module 2 in the subsequent process can be reduced to suppress the deformation of the negative electrode.

[0039] Furthermore, the higher the SOC, the thicker the negative electrode becomes, and the greater the effect of creep in the negative electrode. Therefore, the deformation amount D of the negative electrode increases as the SOC of the battery module 2 increases. In contrast, the controller 10 in this embodiment sets the stop time threshold T as the SOC estimated by the controller 10 increases based on the temperature of the battery module 2. th This shortens the distance. As a result, even if the State of Charge (SOC) of the battery module 2 is high and deformation of the negative electrode due to creep may be significant, the pressure applied to the battery module 2 in the subsequent process can be reduced to suppress deformation of the negative electrode.

[0040] In step S6, the controller 10 determines the expected stop time T. ex The stop time threshold T th Determine whether it is longer or not.

[0041] In step S6, the controller 10 has an expected stop time T. ex The stop time threshold T th If it is determined that the length is longer, in step S7, the controller 10 moves the movable end plate 166 of the pressure application mechanism 16 upward to reduce the pressure applied to the battery module 2 to a predetermined pressure. The pressure applied to the battery cell 21 will be approximately the same as the pressure applied to the battery module 2.

[0042] 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 amount of creep at the negative electrode. In Figure 3, curve a represents the amount of creep. As shown by curve a in Figure 3, the amount of creep at the negative electrode of the battery cell 21 increases as the pressure applied to the battery module 2 increases.

[0043] Figure 4 is an explanatory diagram of creep occurring at the negative electrode. The left side of Figure 4 shows battery cell 21B that has been left stopped without reducing the pressure applied to the battery module, and the right side of Figure 4 shows battery cell 21 that has been left stopped after reducing the pressure applied to the battery module 2.

[0044] As shown in the left diagram of Figure 4, if the pressure applied to the battery module is not reduced, the negative electrode 21Bc is compressed in the thickness direction and stretched in the width direction due to the pressure. As a result, an outwardly extending portion 22B is created on the side of the negative electrode 21Bc. Since this extended portion 22B does not face the positive electrode 21Ba, it does not contribute much to charging and discharging, thus degrading battery performance. In addition, a protrusion 23B is created that protrudes toward the positive electrode 21Ba and the solid electrolyte 21Bb due to the pressure. Since this protrusion 23B is closer to the positive electrode 21Ba and current tends to concentrate there, the possibility of short-circuiting the positive electrode 21Ba and the negative electrode 21Bc increases.

[0045] On the other hand, in this embodiment, by reducing the pressure applied to the battery module, deformation due to creep of the negative electrode 21c is suppressed. As shown in the right diagram of Figure 4, the stretched portion 22B and the protrusion 23B that extends toward the positive electrode 21a and solid electrolyte 21b are less likely to occur in the negative electrode 21c. Therefore, deterioration of battery performance and the occurrence of short circuits can be suppressed.

[0046] Returning to Figure 2, in step S8, the controller 10 determines from the value detected by the pressure sensor 17 whether the pressure applied to the battery module 2 has reached a predetermined pressure. In this embodiment, the predetermined pressure is less than the performance requirement pressure P1 and greater than the seismic resistance requirement pressure P0. Note that the predetermined pressure may also be greater than the performance requirement pressure P1.

[0047] As shown in Figure 3, the seismic resistance requirement pressure P0 in this embodiment is the minimum pressure required to maintain contact between the movable end plate 166 and the battery module 2. In this embodiment, it is the minimum pressure at which the battery module 2 will not fall out from between the fixed end plate 165 and the movable end plate 166, even if external forces such as shock or vibration are applied to the battery module 2. By making the pressure greater than the seismic resistance requirement pressure P0, the battery module 2 can be prevented from falling out.

[0048] As shown in Figure 3, when the pressure applied to the battery module 2 falls below the performance requirement pressure P1, the resistance of the battery cell 21 increases. This is thought to be because, as shown in the right-hand diagram of Figure 4, the pressure of the negative electrode 21c against the solid electrolyte 21b decreases, and the contact area between the two decreases. On the other hand, when the pressure exceeds the performance requirement pressure P1, a certain level of contact area is obtained between the negative electrode 21c and the solid electrolyte 21b, so the resistance is maintained at a nearly constant low resistance value.

[0049] The performance requirement pressure P1 is the pressure at which the electrical resistance of the battery cell 21 equals a predetermined threshold value. This threshold is the maximum electrical resistance within the range of electrical resistance at which the battery cell 21 can input and output the charge and discharge power necessary to operate the vehicle's control system. The performance requirement pressure P1 is greater than the seismic resistance requirement pressure P0.

[0050] Thus, by setting the pressure to less than the performance requirement pressure P1 in step S7, the resistance value is increased, and even if the battery module 2 is left stopped for a long period of time, the amount of self-discharge of the battery module 2 during the stopped state can be reduced.

[0051] Such a performance requirement pressure P1 can be determined experimentally as follows: Since the greater the resistance of a battery cell, the less power it can charge and discharge, pressure is applied to the battery cell to reduce its resistance until it can output at least the power necessary to operate the vehicle's control system. The minimum pressure at which the power necessary to operate the control system can be output is determined experimentally from the relationship between pressure and power, thereby determining the performance requirement pressure P1.

[0052] Furthermore, in this 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 this is not limited to this. The pressure may be estimated without using the pressure sensor 17.

[0053] Specifically, for example, if the negative electrode is a lithium metal negative electrode, the thickness of the battery cell changes approximately in proportion to the State of Charge (SOC). Therefore, the thickness of the battery module changes approximately in proportion to the charge and discharge amount of the battery module. Furthermore, the amount of change in the thickness of the battery module due to motor operation is determined by the gear ratio and screw pitch in the pressure application mechanism, as well as the amount of motor operation. Therefore, if the relationship between the difference between the change in the thickness of the battery module due to charge and discharge amount and the change in the thickness of the battery module due to motor operation, and the pressure is experimentally obtained, the pressure can be estimated from the time-series changes in the motor command value and SOC based on this relationship.

[0054] Returning to Figure 2, if in step S8 it is determined that the pressure applied to the battery module 2 has reached a predetermined pressure, in step S9 the controller 10 turns off the power to the pressure application mechanism 16. In other words, the pressure control by the pressure control system 15 is terminated. Even if the power to the pressure application mechanism 16 is turned off, the pressure is maintained at the predetermined pressure. Thus, in step S9, after completing the pressure control, the controller 10 stops the battery control system 1.

[0055] If, in step S8, it is determined that the pressure applied to the battery module 2 has not reached a predetermined pressure, the process returns to step S7, and the control to reduce the pressure by the pressure application mechanism 16 is executed again.

[0056] Figure 5 shows that in step S6 of Figure 2, T ex >T th This graph shows the changes in pressure and resistance over time in the pressure control method when a certain condition is determined. The upper graph in Figure 5 shows the change in pressure over time, and the lower graph in Figure 5 shows the change in resistance over time.

[0057] As shown in the upper part of Figure 5, from the start to step S6 of the flowchart shown in Figure 2, the pressure is maintained at a level higher than the performance requirement pressure P1. During this time, although charging and discharging occur during the stop process, the resistance value of the battery cell 21 is maintained at approximately a constant level, as shown in the lower part of Figure 5.

[0058] Next, in step S6, the controller 10 T ex >T th After determining that this is the case, in step S7, the controller 10 starts to reduce the pressure. As a result of this pressure reduction, the resistance value of the battery cell 21 increases, as shown in the lower part of Figure 5. This pressure reduction operation is continued until the pressure reaches a predetermined pressure P2.

[0059] Next, in step S9, the power to the motor 162 of the pressure application mechanism 16 is turned OFF, and then the battery control system 1 is stopped. This completes the pressure reduction operation, and the pressure is maintained at a predetermined pressure P2 that is lower than the performance requirement pressure P1.

[0060] Thus, when the battery control system 1 is stopped, the pressure applied to the battery module 2 is increased to at least the performance requirement pressure P1 when the battery control system 1 is restarted. This prevents a shortage of power necessary to operate the battery control system 1.

[0061] Returning to Figure 2, in step S6, T ex ≦T th If it is determined that the above is the case, in step S10, the controller 10 of this embodiment lowers the pressure to a performance-required pressure P1 that is greater than the predetermined pressure. In other words, in step S10, since it is determined that the idle time is short, the pressure is reduced within a range in which the battery control system 1, etc., can maintain an operable resistance value. This makes it possible to suppress the occurrence of creep while suppressing the power consumption due to the operation of the pressure application mechanism 16 when the idle time is short.

[0062] Next, in step S11, the controller 10 determines whether the pressure has reached the performance requirement pressure P1.

[0063] If the controller 10 determines that the pressure has reached the performance requirement pressure P1, in step S9, the controller 10 turns off the power to the pressure application mechanism 16. In other words, it terminates the pressure control by the pressure control system 15. Even if the power to the pressure application mechanism 16 is turned off, the pressure is maintained at the performance requirement pressure P1. In this way, in step S9, after completing the pressure control, the controller 10 stops the battery control system 1. In this way, when the occupant repeatedly starts and stops the vehicle in a short period of time, the increase in power consumption can be suppressed by not letting the pressure drop below the performance requirement pressure P1.

[0064] If it is determined in step S11 that the pressure has not reached the performance requirement pressure P1, the process returns to step S10, and the control to reduce the pressure by the pressure application mechanism 16 is executed again.

[0065] Figure 6 shows that in step S6 of Figure 2, T ex ≦T th This graph shows the changes in pressure and resistance over time in the pressure control method when a certain condition is determined. The upper graph in Figure 6 shows the change in pressure over time, and the lower graph in Figure 6 shows the change in resistance over time.

[0066] As shown in the upper part of Figure 6, from the start to step S6 of the flowchart shown in Figure 2, the pressure is maintained at a level higher than the performance requirement pressure P1. As shown in the lower part of Figure 6, although charging and discharging occur during the shutdown process, the resistance value of the battery cell 21 is maintained at approximately a constant level.

[0067] Next, in step S6, the controller 10 T ex ≦T th After determining that this is the case, in step S10, the controller 10 starts to reduce the pressure. Here, the pressure is within the range of the performance requirement pressure P1 or higher, so the resistance value of the battery cell 21 is maintained at approximately a constant value, as shown in the lower part of Figure 6.

[0068] Next, after it is determined in step S11 that the pressure has reached the performance requirement pressure P1, in step S9 the motor 162 of the pressure application mechanism 16 is turned OFF. This completes the pressure reduction operation, and as shown in the upper part of Figure 6, the pressure is maintained at the performance requirement pressure P1, which is greater than the predetermined pressure P2. Also, as shown in the lower part of Figure 6, the resistance value is maintained at approximately a constant level.

[0069] Thus, when the idle time is determined to be short, the benefits of suppressing self-discharge and deformation of the negative electrode due to creep are small. In other words, the power consumption due to the operation of the pressure application mechanism 16 may be greater than the amount of power saved by suppressing self-discharge, so it is not necessary to lower the pressure to below the performance requirement pressure P1. Therefore, the increase in power consumption due to the operation of the pressure application mechanism 16 can be suppressed.

[0070] In this embodiment, the controller 10 reduces the pressure to the performance-required pressure P1 in step S10, but the controller 10 may reduce the pressure to a pressure greater than the performance-required pressure P1 in step S10. Also, in this embodiment, the controller 10 reduces the pressure in step S10, but the controller 10 may maintain the pressure without reducing it in step S10. This eliminates power consumption due to the operation of the pressure application mechanism 16. However, the actual stop time is the expected stop time T predicted by the controller 10. ex Since this can sometimes be longer, reducing the pressure to a range above the performance requirement pressure P1 in preparation for such cases can help suppress creep.

[0071] Conventionally, when a vehicle was left stationary, a pressure exceeding the performance requirement pressure was applied to the battery module, which made it easy for creep to occur in the negative electrode of the battery cell. This creep caused deterioration of battery performance and increased the probability of short circuits. In contrast, with this embodiment, when the vehicle is left stationary, the pressure is reduced to below the performance requirement pressure P1, thereby suppressing the occurrence of creep and preventing deterioration of battery performance and an increase in the probability of short circuits.

[0072] Furthermore, conventionally, when a vehicle was stopped and left idle, a pressure exceeding the performance requirement pressure was applied to the battery module, resulting in a low resistance value for the battery module and an increased self-discharge rate. In contrast, with this embodiment, when a vehicle is stopped and left idle, the pressure is reduced to below the performance requirement pressure P1, increasing the resistance value and thus reducing the self-discharge rate. [Explanation of Symbols]

[0073] 1…Battery control system 10…Controller 11…Voltage sensor 12...Current sensor 13…Temperature sensor 14…DC-DC converter 15...Discharge means 16…Pressure application mechanism 161…Motor driver 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 for controlling the pressure applied to a battery module comprising a plurality of stacked battery cells, each having a solid electrolyte and a lithium-containing negative electrode, The pressure control system is A pressure applying means for applying pressure to the battery module by pressing the battery module along the stacking direction of the battery cells, A control means that adjusts the value of the pressure by controlling the pressure application means, The system includes a stop time estimation means for estimating the stop time between the time the battery control system, which controls the charging and discharging of the battery module, is stopped and the time it is restarted, When stopping the battery control system, if the stop time estimated by the stop time estimation means is longer than a predetermined time, the control means will reduce the pressure to a predetermined pressure before stopping the battery control system. A pressure control system in which, when stopping the battery control system, if the stop time estimated by the stop time estimation means is less than or equal to a predetermined time, the control means maintains the pressure or reduces it to a pressure greater than the predetermined pressure before stopping the battery control system.

2. In the pressure control system according to claim 1, The aforementioned predetermined pressure is greater than the seismic resistance requirement pressure. The seismic resistance requirement pressure is the minimum pressure necessary to maintain contact between the pressure application means and the battery module in a pressure control system.

3. In the pressure control system according to claim 1, The pressure control system further comprises temperature acquisition means for measuring or estimating the temperature of the battery module. The stop time estimation means is a pressure control system that sets the predetermined time shorter as the temperature of the battery module increases.

4. In the pressure control system according to claim 1, The pressure control system further comprises SOC estimation means for estimating the SOC of the battery cell, The stop time estimation means is a pressure control system that sets the predetermined time shorter the larger the SOC of the battery cell.

5. In the pressure control system according to claim 1, The aforementioned predetermined pressure is smaller than the performance requirement pressure. The performance requirement pressure is the pressure at which the electrical resistance of the battery cell equals the threshold value. The threshold is the maximum value of the electrical resistance within the range of electrical resistance of the battery cell at which the battery cell can input and output the charge and discharge power necessary to operate the vehicle's control system.

6. In the pressure control system according to claim 5, The control means is a pressure control system that increases the pressure to at least the performance requirement pressure when the battery control system is restarted after being stopped.

7. A pressure control method for controlling the pressure applied to a battery module comprising a plurality of stacked battery cells, each having a solid electrolyte and a lithium-containing negative electrode, When stopping the battery control system that controls the charging and discharging of the battery module, the stop time estimation means estimates the stop time from when the battery control system is stopped until it is started again. If the stop time estimated by the stop time estimation means is longer than a predetermined time, the pressure is reduced to a predetermined pressure and then the battery control system is stopped. A pressure control method which, if the stop time estimated by the stop time estimation means is less than or equal to a predetermined time, maintains the pressure or reduces it to a pressure greater than the predetermined pressure, and then stops the battery control system.

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