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

Pressure control system and pressure control method

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

[0002] A lithium-ion secondary battery is known that includes an electrode assembly including 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 assembly in a predetermined direction (see, for example, Patent Document 1). The surface pressure control unit of this lithium-ion secondary battery controls the fluctuation of the surface pressure that varies with charge and discharge to 3.8 MPa or less. Specifically, this fluctuation is the difference between the maximum and minimum surface pressure values ​​observed when charging and discharging from 0% to 100% SOC, and is determined from the resistance increase ratio before and after charge and discharge cycles of the lithium-ion secondary battery (see, for example, Patent Document 1 (paragraphs

[0014] and

[0108] to

[0114] )).

[0003] JP 2019-61749 A

[0004] In conventional technology, the amplitude of the surface pressure fluctuation is determined by the resistance increase ratio between the resistance before the start of a charge / discharge cycle and the resistance after the end of the cycle. However, this technology does not take into account the deterioration of a secondary battery when it is left stationary and not being charged or discharged, which is thought to have a large impact on an in-vehicle secondary battery, nor does it take into account deterioration that does not appear in the resistance value of the secondary battery.

[0005] Generally, vehicle stop times are longer than vehicle operation times, so vehicle-mounted secondary batteries are left in a pressurized state for long periods without charging or discharging. In this case, negative electrodes containing Li are particularly prone to creep because of their relatively low rigidity. Although the amount of creep per unit time is minimal, if this creep accumulates over a long period of time, it can have a negative effect on the secondary battery.

[0006] The problem to be solved by the present invention 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.

[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, stopping the battery control system after reducing the pressure applied to the battery module to a predetermined pressure.

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

[0009] FIG. 1 is a block diagram showing a battery control system according to an embodiment of the present invention. FIG. 2 is a flowchart showing the procedure of a pressure control method when shutting down the battery control system according to an embodiment of the present invention. FIG. 3 is a graph showing the relationship between the pressure applied to the battery cell, the amount of creep in the negative electrode, and the resistance value of the battery cell. FIG. 4 is an explanatory diagram of creep that occurs in the negative electrode. FIG. 5 is a diagram showing the procedure of the pressure control method when shutting down the battery control system according to an embodiment of the present invention. ｅｘ >T ｔｈ 6 is a graph showing the change in pressure and resistance value over time in the pressure control method when it is determined that T ｅｘ ≦T ｔｈ 10 is a graph showing the change over time in pressure and resistance value in the pressure control method when it is determined that:

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing a battery control system 1 according to 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 DC-DC converter 14 , a pressure application mechanism 16 , and a pressure sensor 17 .

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

[0013] 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.

[0014] The controller 10 also controls a pressure application mechanism 16 that constitutes a pressure control system 15. The controller 10 controls the pressure application mechanism 16 to adjust the value of the pressure to be applied to the battery module 2.

[0015] The controller 10 also calculates the expected downtime T ｅｘ ) is estimated.

[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 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 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 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.

[0018] 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 transmitter 164, a fixed end plate 165, a movable end plate 166, and multiple 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. The motor driver circuit 161 controls the driving of the motor 162 based on a control signal from the controller 10.

[0020] 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 .

[0021] 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.

[0022] 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.

[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 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.

[0024] 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.

[0025] The battery module 2 is electrically connected to a charging device. The charging device connected to the battery cells 21 is, for example, a device for charging the battery module 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, 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 so that the state of charge of the battery module 2 reaches a target state of charge.

[0026] 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.

[0027] 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 power stored in the battery module 2 to a power grid (load) via the power grid.

[0028] The battery cells 21 included in the battery module 2 have at least a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode contains at least a positive electrode active material capable of absorbing and releasing an alkali metal such as lithium (Li), sodium (Na), or potassium (K), and preferably contains a positive electrode active material containing sulfur, although this is not particularly limited. As the solid electrolyte, for example, a sulfide solid electrolyte or an oxide solid electrolyte can be used, but it is preferable to use a sulfide solid electrolyte. The negative electrode may contain lithium, and preferably contains, for example, lithium metal.

[0029] The following describes a pressure control method for the battery module 2 using the pressure control system 15 included in the battery control system 1. Fig. 2 is a flowchart showing the procedure of the pressure control method when the battery control system of this embodiment is stopped. The pressure control method shown in Fig. 2 is repeatedly executed at predetermined intervals before the battery control system 1 is stopped, i.e., 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 ignition switch of the vehicle, an instruction to start the stop process 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.

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

[0032] If the controller 10 determines in step S1 that the vehicle is not currently in the process of stopping, the current pressure control is terminated, and pressure control is restarted from step S1 after a predetermined period.

[0033] In step S3, the controller 10 determines whether or not the stop processing (excluding the control processing performed by the controller 10 after step S3) that requires charging and discharging in the vehicle has been completed.

[0034] In step S3, if the controller 10 determines that the process requiring charging / discharging in the vehicle has been completed, in step S4, the controller 10 calculates the expected stop time T by using the vehicle's past behavior history, map information, SOC, etc. individually or in combination. ｅｘ If the controller 10 determines in step S3 that the process requiring charging / discharging has not been completed in the vehicle, the controller 10 ends the current pressure control and restarts the pressure control from step S1 after a predetermined period.

[0035] The past behavior history is, for example, a history of the time period during which the vehicle has been stopped and left unattended for each time period. The controller 10 calculates an expected stopping time T ｅｘ Furthermore, the controller 10 can predict the expected stopping time T at the current position from the position information on the map and the history of the stopping and leaving time at a specific position on the map in the past. ｅｘ For example, when it is determined that the current location is a company, a home, or the like, or when it is determined that the current time falls within a time period when an occupant is staying at a company, a home, or the like, the controller 10 predicts that the stopped and left-alive time will be relatively long. On the other hand, when it is determined that the current location is a convenience store, or the like, the controller 10 predicts that the stopped and left-alive time will be relatively short. Alternatively, the controller 10 may calculate the expected stopped time T at the current SOC from the history of the stopped and left-alive time for each SOC of the battery module 2 in the past. ｅｘThe SOC can be estimated by a general method using the open circuit voltage of each battery cell 21 or the integrated value of the charge and discharge charge.

[0036] Next, in step S5, the controller 10 determines the stop time threshold T ＴＨ Determine the stop time threshold T ＴＨ As will be described later, the pressure of the battery module 2 is set to the performance required pressure P １ This is the threshold value that serves as a criterion for determining whether to reduce the expected stop time T ｅｘ is the stopping time threshold T ＴＨ If the pressure exceeds the performance required pressure P １ In this embodiment, the stop time threshold T ＴＨ corresponds to an example of the "predetermined time" in the present invention.

[0037] Stop time threshold T ｔｈ The time (for example, about 5 to 10 minutes) is determined based on the energy balance between the amount of power consumed by the pressure application mechanism 16 due to the operation to reduce the pressure on the battery module 2 and the amount of power discharged due to 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, if the time of leaving the battery 2 stopped is short, the power consumed by operating the motor of the pressure application mechanism 16 may be greater than the amount of power that can be saved by suppressing self-discharge. Also, if the time of leaving the battery 2 stopped is short, it is considered that creep hardly occurs. For this reason, the stop time threshold T ｔｈ For example, the better the energy balance is (the greater the amount of discharge power due to self-discharge is the power consumption of the pressure application mechanism 16), the shorter the stop time threshold T is set, and the greater the amount of deformation of the negative electrode is. The energy balance and the amount of deformation of the negative electrode can be calculated in advance by experiment, and the time at which the benefits of suppressing self-discharge and suppressing creep are sufficiently obtained with respect to the power consumption of the pressure application mechanism 16 is set as the stop time threshold T ＴＨ Set to.

[0038] Furthermore, since the creep amount increases as the temperature increases, the deformation amount of the negative electrode increases as the temperature of the battery module 2 increases. Therefore, the controller 10 in this embodiment adjusts the stop time threshold T ｔｈ This shortens the time required for the negative electrode to deform. Even if the temperature of the battery module 2 is high and the deformation of the negative electrode due to creep is likely to 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 therefore the creep effect on the negative electrode becomes greater. Therefore, the higher the SOC of the battery module 2, the larger the deformation amount D of the negative electrode becomes. In contrast, the controller 10 in this embodiment, based on the temperature of the battery module 2, determines the stop time threshold T ｔｈ As a result, even if the SOC of the battery module 2 is high and the deformation of the negative electrode due to creep is likely to be large, the pressure applied to the battery module 2 in the post-processing can be reduced to suppress deformation of the negative electrode.

[0040] In step S6, the controller 10 calculates the expected stop time T ｅｘ is the stopping time threshold T ＴＨ Determine whether it is longer.

[0041] In step S6, the controller 10 calculates the expected stop time T ｅｘ is the stopping time threshold T ＴＨ If it is determined that the battery cell 21 is longer than the predetermined pressure, the controller 10 moves the movable end plate 166 of the pressure application mechanism 16 upward in step S7, thereby reducing the pressure applied to the battery module 2 to a predetermined pressure.

[0042] 3 is a graph showing the relationship between the pressure applied to the battery cell 21 and the resistance value and the amount of creep of the negative electrode of the battery cell 21. In Fig. 3, curve a shows the amount of creep. As shown by curve a in Fig. 3, the greater the pressure applied to the battery module 2, the greater the amount of creep in the negative electrode of the battery cell 21.

[0043] Fig. 4 is an explanatory diagram of creep that occurs in the negative electrode. The left diagram in Fig. 4 shows a battery cell 21B that was left stopped without reducing the pressure applied to the battery module 2, and the right diagram in Fig. 4 shows a battery cell 21 that was 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 pressure compresses the negative electrode 21Bc in the thickness direction and stretches it in the width direction. This results in an outwardly extending extension 22B on the side of the negative electrode 21Bc. Because this extension 22B does not face the positive electrode 21Ba, it does not contribute to charging and discharging, thereby deteriorating battery performance. Furthermore, the pressure also creates a protrusion 23B that protrudes toward the positive electrode 21Ba and solid electrolyte 21Bb. This protrusion 23B is closer to the positive electrode 21Ba and is prone to current concentration, increasing the possibility of short-circuiting the positive electrode 21Ba and the negative electrode 21Bc.

[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, and therefore, as shown in the right diagram of Figure 4, the negative electrode 21c is less likely to develop an extension 22B or a protrusion 23B that protrudes toward the positive electrode 21a and the solid electrolyte 21b, making it possible to suppress deterioration of battery performance and the occurrence of short circuits.

[0046] 2, in step S8, the controller 10 determines whether the pressure applied to the battery module 2 has reached a predetermined pressure based on the detected value of the pressure sensor 17. The predetermined pressure in this embodiment is the performance required pressure P １ Smaller seismic demand pressure P ０ The predetermined pressure is greater than the performance required pressure P １ Higher pressures are also possible.

[0047] As shown in FIG. 3, the earthquake resistance required pressure P ０ 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 required to prevent the battery module 2 from falling out from between the fixed end plate 165 and the movable end plate 166 even if an external force such as an impact or vibration is applied to the battery module 2. ０ By making it larger, it is possible to prevent the battery module 2 from falling off.

[0048] As shown in FIG. 3, the pressure applied to the battery module 2 is the performance required pressure P １ If the pressure is smaller than the performance required pressure P １ If the resistance is larger, a certain contact area or more can be obtained between the negative electrode 21c and the solid electrolyte 21b, and the resistance value can be maintained at a substantially constant low value.

[0049] Performance required pressure P １ is the 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 input and output the charge and discharge power required to operate the vehicle control system. １ is the earthquake resistance required pressure P ０ is greater than.

[0050] In this way, in step S7, the pressure is set to the performance required pressure P １ By setting the resistance value to less than 100 kJ / s, the resistance value is kept high, so that even if the battery module 2 is left stopped and left for a long period of time, the amount of self-discharge of the battery module 2 while it is stopped and left can be reduced.

[0051] Such a performance requirement pressure P １can be experimentally determined as follows: The higher the resistance of the battery cell, the less power the battery cell will charge and discharge. Therefore, pressure is applied to the battery cell to reduce its resistance until it can output at least the power required to operate the vehicle's control system. In this case, the minimum pressure at which the power required to operate the control system can be output can be experimentally determined from the relationship between pressure and power, and the performance required pressure P １ can be obtained.

[0052] In addition, in this embodiment, the pressure applied to the battery module 2 (the pressure applied to the battery cells 21) is detected by the pressure sensor 17, but this is not limiting. The pressure may be estimated without using the pressure sensor 17.

[0053] Specifically, for example, when the negative electrode is a Li metal negative electrode, the thickness of the battery cell changes approximately in proportion to the SOC. Therefore, the thickness of the battery module changes approximately in proportion to the charge / 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, screw pitch, etc., within the pressure application mechanism and the amount of motor operation. Therefore, if the relationship between the difference between the amount of change in the thickness of the battery module due to the charge / discharge amount and the amount of 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 the SOC based on this relationship.

[0054] 2 , if it is determined in step S8 that the pressure applied to the battery module 2 has reached the predetermined pressure, the controller 10 turns off the power to the pressure application mechanism 16 in step S9. That is, the pressure control by the pressure control system 15 is terminated. Note that even if the power to the pressure application mechanism 16 is turned off, the pressure is maintained at the predetermined pressure. In this way, in step S9, the controller 10 completes the pressure control and then stops the battery control system 1.

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

[0056] FIG. 5 shows the T ｅｘ >T ｔｈ 5 is a graph showing the change in pressure and resistance over time in the pressure control method when it is determined that the pressure is too high. The upper graph in Fig. 5 is a graph showing the change in pressure over time, and the lower graph in Fig. 5 is a graph showing the change in resistance over time.

[0057] As shown in the upper diagram of FIG. 5, from the start to step S6 of the flowchart shown in FIG. 2, the pressure is the performance required pressure P １ At this time, although charging and discharging are performed during the shutdown process, the resistance value of the battery cell 21 is maintained at a substantially constant value, as shown in the lower diagram of FIG.

[0058] Next, in step S6, the controller 10 ｅｘ >T ｔｈ After determining that the pressure is equal to or greater than the predetermined pressure P, the controller 10 starts reducing the pressure in step S7. As the pressure is reduced, the resistance of the battery cell 21 increases, as shown in the lower diagram of FIG. 5. This pressure reduction operation is performed until the pressure reaches a predetermined pressure P ２ This continues until it reaches

[0059] Next, in step S9, the power supply 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 drops to the performance required pressure P １ A predetermined pressure P ２ is maintained.

[0060] In this way, when the battery control system 1 is stopped, the pressure applied to the battery module 2 is set to at least the performance required pressure P １ This makes it possible to prevent a shortage of power required to operate the battery control system 1.

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

[0062] Next, in step S11, the controller 10 determines whether the pressure is equal to or greater than the performance requirement pressure P １ It is determined whether or not

[0063] The controller 10 determines that the pressure is the performance required pressure P １ If it is determined that the pressure has reached the performance required pressure P, the controller 10 turns off the power to the pressure application mechanism 16 in step S9. That is, the pressure control by the pressure control system 15 is terminated. Note that even if the power to the pressure application mechanism 16 is turned off, the pressure will not exceed the performance required pressure P １ In this way, in step S9, the controller 10 completes the pressure control and then 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 pressure is maintained at the performance required pressure P １ By not lowering the power consumption to below this value, an increase in power consumption can be suppressed.

[0064] In step S11, the pressure is the performance required pressure P １ If it is determined that the pressure has not reached the predetermined value, the process returns to step S10, and the pressure application mechanism 16 is again controlled to reduce the pressure.

[0065] FIG. 6 shows the T ｅｘ ≦T ｔｈ 6 is a graph showing the change in pressure and resistance over time in the pressure control method when it is determined that the pressure is too high. The upper graph in Fig. 6 is a graph showing the change in pressure over time, and the lower graph in Fig. 6 is a graph showing the change in resistance over time.

[0066] As shown in the upper diagram of FIG. 6, from the start to step S6 of the flowchart shown in FIG. 2, the pressure is the performance required pressure P １As shown in the lower diagram of Figure 6, at this time, although charging and discharging are performed during the shutdown process, the resistance value of the battery cell 21 is maintained at a substantially constant value.

[0067] Next, in step S6, the controller 10 ｅｘ ≦T ｔｈ After determining that the pressure is the performance required pressure P １ Since the resistance is within the above range, the resistance value of the battery cell 21 is maintained substantially constant, as shown in the lower diagram of FIG.

[0068] Next, in step S11, the pressure is set to the performance required pressure P １ After it is determined that the pressure has reached the predetermined pressure P, the motor 162 of the pressure application mechanism 16 is turned off in step S9. This completes the decompression operation, and the pressure reaches the predetermined pressure P as shown in the upper diagram of FIG. ２ Higher performance required pressure P １ The resistance value is maintained at a substantially constant value, as shown in the lower diagram of FIG.

[0069] In this way, when it is determined that the standstill time is short, the merit of suppressing self-discharge and suppressing deformation of the negative electrode due to creep is small. In other words, there is a possibility that the power consumption due to the operation of the pressure application mechanism 16 will be greater than the power saving amount due to the suppression of self-discharge. １ Therefore, it is possible to suppress an increase in power consumption due to the operation of the pressure application mechanism 16.

[0070] In this embodiment, in step S10, the controller 10 determines the performance required pressure P １ In step S10, the controller 10 reduces the pressure to the performance required pressure P １ 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 prevents power consumption due to the operation of the pressure application mechanism 16. However, if the actual stop time is shorter than the expected stop time Tｅｘ In case of such a case, the pressure is set to the performance required pressure P １ If the temperature is reduced to the above range, the effect of suppressing the occurrence of creep can be obtained.

[0071] In the past, when a vehicle was stopped and left standing, a pressure higher than the performance required pressure was applied to the battery module, which made it easy for creep to occur in the negative electrodes of the battery cells, which caused deterioration of battery performance and increased the probability of short circuits. In contrast, in this embodiment, when a vehicle was stopped and left standing, the pressure was applied at a pressure higher than the performance required pressure P １ Since the temperature is reduced to less than 100°C, the occurrence of creep can be suppressed, and the deterioration of battery performance and the increase in the probability of short circuiting can be suppressed.

[0072] In addition, in the past, when a vehicle was stopped and left standing, a pressure higher than the performance required pressure was applied to the battery module, which kept the resistance value of the battery module low and increased the self-discharge amount. In contrast, in the present embodiment, when a vehicle is stopped and left standing, the pressure is kept at the performance required pressure P １ Since the resistance value is increased by reducing the capacitance to less than 100 kJ / cm 2 , the amount of self-discharge can be reduced.

[0073] DESCRIPTION OF SYMBOLS 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...Gear box 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 pressure applied to a battery module in which a plurality of battery cells each having a solid electrolyte and a negative electrode containing lithium are stacked, The pressure control system includes: 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 for controlling the pressure applying means to adjust the value of the pressure; a stop time estimation means for estimating a stop time from when the battery control system is stopped until when the battery control system is restarted, when stopping a battery control system that controls charging and discharging of the battery module, if the stop time estimated by the stop time estimation means is longer than a predetermined time, the control means reduces the pressure to a predetermined pressure, and then the battery control system is stopped; A pressure control system in which, when the battery control system is stopped, if the stop time estimated by the stop time estimation means is equal to or shorter than a predetermined time, the control means maintains the pressure or reduces it to a pressure greater than the predetermined pressure, and then the battery control system is stopped.

2. 2. The pressure control system according to claim 1, The predetermined pressure is greater than the required earthquake resistance pressure, A pressure control system in which the earthquake resistance required pressure is the minimum pressure required to maintain contact between the pressure application means and the battery module.

3. (delete)

4. 2. The pressure control system according to claim 1, the pressure control system further includes a temperature acquisition means for measuring or estimating a temperature of the battery module; The stop time estimation means sets the predetermined time to be shorter as the temperature of the battery module increases.

5. 2. The pressure control system according to claim 1, the pressure control system further includes an SOC estimation means for estimating an SOC of the battery cell; The stop time estimation means sets the predetermined time to be shorter as the SOC of the battery cell is higher.

6. 2. The pressure control system according to claim 1, The predetermined pressure is lower than the performance required pressure, the performance requirement pressure is a pressure at which the electrical resistance of the battery cell becomes equal to a threshold value, A pressure control system in which the threshold value is the maximum value of the electrical resistance within the range of electrical resistance of the battery cell that allows the battery cell to input and output the charging and discharging power necessary to operate a vehicle control system.

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

8. A pressure control method for controlling pressure applied to a battery module in which a plurality of battery cells each having a solid electrolyte and a negative electrode containing lithium are stacked, the method comprising: When stopping a battery control system that controls charging and discharging of the battery module, a stop time estimation means estimates a stop time from when the battery control system is stopped until when the battery control system is restarted; 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 for stopping the battery control system after maintaining the pressure or reducing it to a pressure greater than the predetermined pressure when the stop time estimated by the stop time estimation means is equal to or less than a predetermined time.