JP2017091817A - Secondary battery system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery system for a vehicle that can increase the temperature of plural secondary batteries A and B at an early stage and improve the output while suppressing precipitation of lithium under an extremely low temperature environment below -30°C.SOLUTION: When the temperatures of plural secondary batteries A and B detected based on temperature information acquired by temperature sensors A1 and B1 are lower than a predetermined temperature of not more than -30°C, a control device D sets a charging current value when the other secondary batteries are charged by a charging/discharging device C. Then, charging and discharging are performed between the plural secondary batteries by a charging/discharging device. Here, the charging current value is set on the basis of a map M in which the relationship of the temperature, the voltage or the SOC, and the maximum current value at which lithium does not deposit under charging is predetermined.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a vehicle secondary battery system.

  Japanese Patent Application Laid-Open No. 2013-149471 discloses a method of heating a secondary battery by repeatedly charging and discharging each other between a plurality of secondary batteries. In this method, the secondary battery is heated while suppressing power loss.

JP 2013-149471 A

  By the way, secondary batteries are also widely used in vehicles. Examples of the vehicle application include a hybrid vehicle, a plug-in hybrid vehicle, an electric vehicle, and a fuel cell vehicle. In such vehicle applications, the secondary battery is used as a power source that electrically stores energy, outputs the energy to a drive motor, and applies driving force to the wheels. In such an application, since it is mainly used outdoors, it can be used in a cryogenic environment such as a temperature lower than −30 ° C. in a cold district. Under an extremely low temperature environment below −30 ° C., the viscosity of the electrolyte solution of the secondary battery tends to increase, and the output of the secondary battery tends to rapidly decrease as the temperature decreases. Furthermore, in an extremely low temperature environment below −30 ° C., the secondary battery is likely to deteriorate with respect to charging and discharging at a high rate. Moreover, in the said vehicle use, especially big output is calculated | required at the time of start for the secondary battery used as a power supply output to a drive motor.

  In view of such a specific problem in vehicle applications, the present inventor is beneficial if the temperature can be raised quickly while suppressing power loss when it can be used in a cryogenic environment below -30 ° C. I think there is. When using a method in which the temperature of the secondary battery is increased by repeatedly charging and discharging between multiple secondary batteries, the higher the charge current value and the discharge current value, the faster the secondary battery heats up. To do. For this reason, it is desirable to repeatedly charge and discharge with as large a current value as possible. On the other hand, in an extremely low temperature environment where the temperature is lower than −30 ° C., if charging and discharging at a high rate with a large charging current value and discharging current value are repeated, the secondary battery is likely to deteriorate. For this reason, when adopting a method of repeatedly charging and discharging between a plurality of secondary batteries to raise the temperature of the secondary battery, in particular, quickly raising the temperature from an extremely low temperature environment such as −30 ° C. There is a trade-off relationship between minimizing the deterioration of the secondary battery.

  The proposed secondary battery system for a vehicle includes a plurality of secondary batteries to be controlled, a temperature sensor, a voltmeter or an SOC detector, a charge / discharge device, and a control device. Here, the temperature sensor is a sensor that acquires temperature information regarding a plurality of secondary batteries. The voltmeter is a device that detects a voltage for each of a plurality of secondary batteries. The SOC detection unit is a device that detects the SOC of each of the plurality of secondary batteries. Here, SOC is an abbreviation for State of Charge, and means remaining capacity. The charging / discharging device is a device that is electrically connected to a plurality of secondary batteries, and charges other secondary batteries with electric power discharged from some of the secondary batteries. When the temperature of the plurality of secondary batteries detected based on the temperature information acquired by the temperature sensor is lower than a predetermined temperature of −30 ° C. or lower, the control device is connected to the other two charging / discharging devices. A process S1 for setting a charging current value for charging the secondary battery and a process S2 for charging and discharging between the secondary batteries by the charge / discharge device are performed. Here, in the process S1, the temperature sensor obtains the relationship between the temperature, the voltage or the SOC, and the maximum current value at which lithium does not precipitate with charging, for a plurality of secondary batteries. Obtaining the maximum current value according to the temperature of the plurality of secondary batteries detected based on the obtained temperature information and the voltage obtained by the voltmeter or the SOC obtained by the SOC detector, and the maximum current value Is the charging current value.

  By such control, the charging current value at the time of charging can be appropriately controlled, and while the deterioration of the secondary battery is suppressed to be small, the temperature is quickly raised from an extremely low temperature environment such as −30 ° C., and a plurality of secondary objects to be controlled The output of the battery can be improved.

FIG. 1 is a schematic diagram schematically showing the vehicular secondary battery system proposed here. FIG. 2 is a schematic diagram illustrating a configuration example of the map M. FIG. 3 is a flowchart illustrating an example of a control flow of the control device. FIG. 4 is a graph schematically showing changes in temperature, voltage, and charge / discharge operation of the secondary batteries A and B. FIG. 5 is a graph schematically showing the transition of the temperature, voltage, and charge / discharge operation of the secondary batteries A and B.

  Hereinafter, an embodiment of the secondary battery system for vehicles proposed here will be described. The embodiments described herein are, of course, not intended to limit the present invention. Each drawing is schematically drawn. For example, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship.

  FIG. 1 is a schematic diagram schematically showing the vehicular secondary battery system proposed here. The proposed vehicle secondary battery system 100 includes a plurality of secondary batteries A and B to be controlled, temperature sensors A1 and B1, voltmeters A2 and B2, a charge / discharge device C, and a control device. D. In the following description, FIG. 1 is appropriately referred to for each member of the vehicular secondary battery system 100, and the reference numerals in FIG.

  The plurality of secondary batteries A and B to be controlled are, for example, non-aqueous electrolyte secondary batteries, and typically lithium ion secondary batteries. Each of the plurality of secondary batteries A and B may be a single battery or an assembled battery in which a plurality of cells are combined into one set. Further, the plurality of secondary batteries A and B may be a battery group (not limited to an assembled battery) composed of a plurality of single cells, or an assembled battery group composed of a plurality of assembled batteries.

  In such a non-aqueous electrolyte secondary battery, the viscosity of the electrolyte of the secondary battery becomes high and the output of the secondary battery is difficult to increase in an extremely low temperature environment below -30 ° C. Furthermore, the secondary battery is likely to be deteriorated by charging and discharging at a high rate. For example, in a lithium ion secondary battery, in an extremely low temperature environment below −30 ° C., an event in which lithium in the electrolyte solution is likely to deposit during high-rate charging or discharging. When lithium is deposited and a part thereof is immobilized, lithium ions contributing to the battery reaction are reduced, and the battery capacity is reduced. For this reason, the phenomenon in which lithium is deposited is one of the causes of battery capacity deterioration. Here, according to the knowledge of the present inventor, lithium is likely to be deposited on the surface of the negative electrode, particularly when charged at a high rate, in a cryogenic environment lower than −30 ° C.

  In the vehicle application, the plurality of secondary batteries A and B are used as a power source that electrically stores energy generated in the vehicle and outputs it to a drive motor that applies driving force to the wheels. As shown in FIG. 1, in a vehicle application, a plurality of secondary batteries A and B are connected to a generator and an electric motor (not shown) via a power supply control device E. Although not shown, the generator and the electric motor are further connected to the drive wheels through a power distribution mechanism and a speed reducer.

  The temperature sensors A1 and B1 are sensors that acquire temperature information regarding the plurality of secondary batteries A and B. Here, the temperature sensors A1 and B1 may be attached to predetermined positions of the plurality of secondary batteries A and B (for example, predetermined positions on the side surfaces of the batteries) or the plurality of secondary batteries A. , B may be arranged at the position where they are arranged. The temperature sensors A1 and B1 are connected to the control device D by signal lines A1a and B1a, respectively.

  The voltmeters A2 and B2 are devices that detect voltages for the plurality of secondary batteries A and B, respectively. For example, the voltage may be detected based on a voltmeter electrically connected to the secondary batteries A and B in parallel. Voltmeters A2 and B2 are connected to the control device D by signal lines A2a and B2a, respectively. Here, the secondary batteries A and B have a correlation between the voltage (open circuit voltage: OCV) and the SOC (remaining capacity).

  In the example shown in FIG. 1, voltmeters A2 and B2 are employed, but the processing units that detect voltages based on voltmeters A2 and B2 and voltmeters A2 and B2 are secondary batteries A in control device D, respectively. , B can be replaced with SOC detectors A3 and B3 that detect the SOC of B. Here, the SOC detection units A3 and B3 may employ various methods that can infer the SOC of the plurality of secondary batteries A and B. For example, the SOC may be inferred from a map prepared in advance based on the voltage, temperature, capacity deterioration rate, and the like detected based on the voltmeters A2 and B2. Alternatively, the secondary battery may be adjusted to a predetermined SOC, and the remaining capacity may be calculated based on the difference between the amount of current input and the amount of current output with reference to the SOC. Good. When an appropriate correlation is not recognized between the open circuit voltage and the SOC in the usage range of the plurality of secondary batteries A and B (in other words, when it is difficult to infer the SOC from the open circuit voltage) ) May be an SOC detected by the SOC detectors A3 and B3.

  The charging / discharging device C is electrically connected to the plurality of secondary batteries A and B, respectively, and other secondary batteries are used by the electric power discharged from some of the secondary batteries A and B. Charge. For example, when the secondary battery A is discharged from the secondary batteries A and B, the charging / discharging device C charges the secondary battery B with the electric power. In addition, when the secondary battery B is discharged, the charging / discharging device C charges the secondary battery A with its power. Such a structural example of the charging / discharging device C is disclosed, for example, as “charging / discharging means 12” in paragraphs 0015 and 0016 of FIG. For this reason, the structure of the charge / discharge device C is not disclosed in detail. As described above, the charging / discharging device C is electrically connected to the plurality of secondary batteries A and B, respectively, and discharged from some of the secondary batteries A and B. It is only necessary to realize a function of charging another secondary battery with electric power, and the structure disclosed in Patent Document 1 is not necessarily limited.

  The control device D is a computer that includes an arithmetic device and a storage device, and performs electrical processing according to a predetermined program. Each process executed by the control device D can be realized by such a computer. Here, the control device D is illustrated separately from the power supply control device E, but may not necessarily be separate from the power supply control device E. For example, the control device D may be incorporated in the power supply control device E so that the process embodied by the control device D is embodied as one function of the power supply control device E. In addition to the power supply control device E, the control device D may be incorporated in another control unit mounted on the vehicle.

  Here, the control device D detects the temperatures of the plurality of secondary batteries A and B based on the temperature information acquired by the temperature sensors A1 and B1. Then, the detected temperatures T1 of the plurality of secondary batteries A and B are stored in the control device D together with the time when the temperature information is detected. Further, the voltages of the plurality of secondary batteries A and B are detected based on voltage information obtained by the voltmeters A2 and B2. And the detected voltage V1 of the secondary batteries A and B is memorize | stored in the control apparatus D with the time when voltage information was detected.

  The control device D determines whether or not the detected temperatures T1 of the secondary batteries A and B are lower than a predetermined temperature Xt of −30 ° C. or less (T1 ≧ Xt). Then, when the temperatures T1 of the secondary batteries A and B are lower than a predetermined temperature Xt of −30 ° C. or less, the following processes S1 and S2 are performed.

  Here, the process S1 is a process of setting a charging current value when the charging / discharging device C charges another secondary battery. The process S2 is a process in which charging and discharging are performed between the secondary batteries A and B by the charge / discharge device C. Here, the process S2 is appropriately referred to as “temperature increase process”.

  The control device D includes a map M in which the relationship between the temperature, the voltage or the SOC, and the maximum current value at which lithium does not precipitate with charging is predetermined for the plurality of secondary batteries A and B. And based on the said map M, based on the temperature information obtained by temperature sensor A1, B1, the maximum according to the temperature of several secondary battery A, B and the voltage obtained by voltmeter A2, B2 The current value is acquired, and the maximum current value is set as the charging current value.

  FIG. 2 is a schematic diagram illustrating a configuration example of the map M. In the map M illustrated in FIG. 2, SOC and voltage are set on the vertical axis, and temperature is set on the horizontal axis. A predetermined maximum current value is stored in each square of the map M defined by the voltage (or SOC) and the temperature. Here, the maximum current value is based on the temperature specified by the grid and the voltage or SOC. A current value may be stored. For example, in consideration of the safety factor (for example, 80%), a current value slightly lower than the maximum current value at which lithium deposition was not recognized in a test performed in advance is set as the “maximum current value” in the map M. It may be memorized. By setting the “maximum current value” in this way, it is possible to set a current value at which lithium does not deposit more reliably with charging. Note that FIG. 2 schematically shows a configuration example of the map M. In practice, it is preferable that the grids of the SOC, voltage, and temperature are set more finely. The vertical axis may be defined by either the SOC or the voltage.

  The above-described processes S1 and S2 are performed in an extremely low temperature environment where the output of the secondary batteries A and B can fall below −30 ° C. by such control of the control device D. At this time, in the process S1, a current value corresponding to the temperature and the voltage is set so that lithium is not reliably deposited with the charging. And in process S2, when charge and discharge are performed between the secondary batteries A and B by the charging / discharging device C, charging is performed with the charging current value set in process S1. As described above, the secondary batteries A and B are repeatedly charged and discharged between the plurality of secondary batteries A and B with the maximum current value to the extent that lithium is not deposited. As a result, a plurality of secondary batteries A and B can be quickly removed from an extremely low temperature state where the output can fall below −30 ° C. while suppressing lithium deposition.

  FIG. 3 is a flowchart illustrating an example of a control flow of the control device. As shown in FIG. 3, the control device D detects the temperatures and voltages of the plurality of secondary batteries A and B (S101). Here, the temperature is detected based on the temperature information obtained by the temperature sensors A1 and B1. The voltage is detected based on voltage information obtained by the voltmeters A2 and B2.

  In the flowchart of FIG. 3, it is determined whether or not the detected voltage V1 (OCV) of the plurality of secondary batteries A and B is higher than a predetermined voltage Xv (S102). In this determination process, when the open circuit voltages of the plurality of secondary batteries A and B are not higher (lower) than the predetermined voltage Xv (No), the plurality of secondary batteries A and B are charged together. Due to the power loss due to the discharge, the output of the secondary battery is eventually limited even if the temperature is raised. In addition, when the detected voltage V1 differs in the some secondary batteries A and B, it is good to employ | adopt the highest voltage among the detected voltages as "voltage V1" in determination process S102. That is, of the plurality of secondary batteries A and B, the capacity of one secondary battery has no margin, but when the other secondary battery has a margin, the battery having the capacity has a margin. It is good to start the control which repeats charge and discharge between several secondary batteries mutually so that it may discharge and a battery with a margin may be charged.

  When the highest voltage V1 among the detected voltages is not higher than the predetermined voltage Xv (No), charging and discharging are repeated between the secondary batteries A and B. Even if the temperature of the secondary battery is raised, the outputs of the secondary batteries A and B are limited. For this reason, this control may be terminated as shown by the solid arrow in FIG. In addition, in FIG. 3, the process may be returned to the process S101 again as indicated by the dashed arrow. When returning to the process S101, the voltages of the secondary batteries A and B are detected (S101), and it is determined whether or not the detected voltage V1 is higher than a predetermined voltage Xv (S102). As described above, the secondary batteries A and B may be charged to wait for the capacity of the secondary batteries A and B to recover.

  When the detected voltage V1 is higher than the predetermined voltage Xv (Yes), it is determined whether or not the detected temperature T1 is lower than the predetermined temperature Xt (S103). The threshold value Xt can be arbitrarily set at a temperature of −30 ° C. or lower. For example, the temperature Xt (threshold) may be set to a temperature at which a rapid decrease in output is recognized due to the temperature in the plurality of secondary batteries A and B to be controlled. In addition, when the temperature detected in process S101 varies between the some secondary batteries A and B, it is good to use the lowest temperature among the detected temperatures as the temperature T1 used by a determination process. Thus, it is determined whether or not the temperature raising process (S2) is performed based on the temperature of the secondary battery having the lowest temperature among the plurality of secondary batteries A and B. For example, when there is a secondary battery at a very low temperature of about −30 ° C. and the output is difficult to increase among the plurality of secondary batteries A and B, a process (S2) for raising the temperature of the secondary battery is executed. Can be controlled.

  When the detected temperature T1 is lower than the predetermined temperature Xt, if it is determined in the process S103 (Yes), as described above, the process for setting the charging current value C1 (S1) and the temperature increasing process ( S2) are performed in order. If it is determined in step S103 that the detected temperature T1 is not lower than the predetermined temperature Xt (No), it is determined whether or not to end this control (S104). And when it determines with not complete | finishing control (No), it is good to return to process S101 which detects temperature and a voltage. When it is determined that the control is to be ended (Yes), this control may be ended. Here, as a determination condition for determining whether or not to end the present control, it is preferable to arbitrarily set an appropriate condition for ending the present control.

  FIG. 4 is a graph schematically showing changes in temperature, voltage, and charge / discharge operation of the secondary batteries A and B. In FIG. 4, the secondary batteries A and B are left in an extremely low temperature environment below −30 ° C. with a required remaining capacity. In this case, the temperature of the secondary batteries A and B gradually decreases with time. Then, at the timing P1 when it is determined that the detected temperature T1 is lower than the predetermined temperature Xt, the maximum charging current value C1 is set in a range where lithium is not deposited by charging (S1). And the temperature increase process (S2) which repeats charge and discharge mutually between the secondary batteries A and B by the charging / discharging device C to raise the temperature of the secondary battery is performed. In the charging in the temperature raising process (S2), the battery is charged with the charging current value C1 set in the process S1. As a result, even when left in an extremely low temperature environment below −30 ° C., the secondary batteries A and B are heated up early and the output is reduced while suppressing lithium deposition. It can be improved.

  FIG. 5 is a graph schematically showing the transition of temperature and voltage and charge / discharge operations of the secondary batteries A and B. In FIG. 5, the plurality of secondary batteries A and B are initially left in a cryogenic environment below −30 ° C. without the required remaining capacity. For this reason, the temperature T1 detected in the secondary batteries A and B gradually decreases. Thereafter, charging is started at the timing of Q1. Here, the state connected to the power supply for charge like a plug-in hybrid vehicle is estimated. By this charging, the capacity of the secondary batteries A and B is gradually recovered. Then, at timing Q2 when the capacities of the plurality of secondary batteries A and B exceed a certain voltage Xv (threshold), the maximum charging current value C1 is set in a range where lithium is not deposited by charging (S1). And the temperature increase process (S2) which repeats charge and discharge mutually between the secondary batteries A and B by the charging / discharging device C to raise the temperature of the secondary battery is performed. In the charging in the temperature raising process (S2), the battery is charged with the charging current value C1 set in the process S1. As a result, even when left in an extremely low temperature environment below −30 ° C., the secondary batteries A and B are heated up early and the output is reduced while suppressing lithium deposition. It can be improved.

According to the tests conducted by the present inventors, the following results were confirmed by employing the proposed vehicle secondary battery system.
Test: A plurality of secondary batteries are mutually charged with an appropriate charging current value C1 set in the process S1 for setting a charging current value from a state where the battery temperature is -32 ° C at an environmental temperature of -33 ° C. The discharge was repeated, and the temperature raising process S2 for raising the temperature of the secondary battery was performed.
Result: At an ambient temperature of -33 ° C, the battery temperature was -27 ° C. Here, the battery temperature increased by about 5 ° C. in a relatively short time of about 1000 seconds. At this time, the output of the secondary battery when the battery temperature was −32 ° C. was about 96 W, but the output of the secondary battery was improved to about 116 W when the battery temperature was −27 ° C. Thus, the output improvement was confirmed by performing temperature rising process S2 by appropriate charging current value C1. In this control, the charging current value C1 is appropriately managed so that the deposition of lithium is suppressed in the temperature raising process (S2). For this reason, the capacity maintenance rates of the secondary batteries A and B hardly deteriorate before and after the temperature raising process (S2).

  As mentioned above, although one embodiment was described about the secondary battery system for vehicles proposed here, the secondary battery system for vehicles proposed here is not limited to the embodiment mentioned above unless it mentions especially.

100 Secondary Battery System A, B Secondary Battery A1, B1 Temperature Sensor A2, B2 Voltmeter A3, B3 Detector C Charging / Discharging Device D Control Device E Power Supply Control Device

Claims (1)

A plurality of secondary batteries to be controlled;
A temperature sensor for acquiring temperature information regarding the plurality of secondary batteries;
A voltmeter for detecting a voltage for each of the plurality of secondary batteries, or an SOC detection unit for detecting an SOC for each of the plurality of secondary batteries;
A charge / discharge device that is electrically connected to each of the plurality of secondary batteries and charges another secondary battery with electric power discharged from some of the plurality of secondary batteries;
A control device,
The controller is
When the temperature of the plurality of secondary batteries is detected based on the temperature information acquired by the temperature sensor, and the detected temperature is lower than a predetermined temperature of −30 ° C. or less,
A process S1 for setting a charging current value when the charge / discharge device charges the other secondary battery;
The charging / discharging device performs processing S2 for charging and discharging between the plurality of secondary batteries.
Here, in the process S1,
For the plurality of secondary batteries, based on a map in which the relationship between temperature, voltage or SOC, and the maximum current value at which lithium does not precipitate with charging is predetermined,
The maximum current value according to the temperature of the plurality of secondary batteries detected based on the temperature information obtained by the temperature sensor and the voltage obtained by the voltmeter or the SOC obtained by the SOC detector. Acquired,
The maximum current value is the charging current value.
Secondary battery system for vehicles.

Images