JP2010118265A - Secondary battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery system which can decrease an internal resistance increased during an idle period in each lithium ion secondary battery included in the secondary battery system. <P>SOLUTION: The secondary battery system 6 includes a plurality of lithium ion secondary batteries 100, wherein the secondary battery system 6 includes a charge-transfer control means (battery control apparatus 70) that transfers an electric charge accumulated in the lithium ion secondary batteries 100 between the plurality of lithium ion secondary batteries 100 to perform SOC 0% control for making each of the plurality of lithium ion secondary batteries 100 undergo a state of SOC 0%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery system including a plurality of lithium ion secondary batteries.

  Secondary batteries such as lithium ion secondary batteries and nickel metal hydride secondary batteries are attracting attention as power sources for portable devices and as power sources for vehicles such as electric vehicles and hybrid vehicles. Currently, various secondary battery systems including a plurality of secondary batteries have been proposed (see, for example, Patent Document 1).

JP 2004-327385 A

  Patent Document 1 discloses a secondary battery system that performs refresh charge / discharge when the temperature difference between the single cells constituting the battery pack exceeds a certain value during charge / discharge of the battery pack. It is described that by performing refresh charging / discharging, inactivation of the nickel-metal hydride storage battery can be eliminated and the battery capacity can be made uniform, so that the battery can be used effectively.

  By the way, in the lithium ion secondary battery, when the charge is stored and the resting state (the state where charging / discharging is not performed) continues for a long time (for example, 6 hours or more), the internal resistance greatly increases. Sometimes. In a lithium ion secondary battery whose internal resistance has greatly increased, sufficient output characteristics may not be obtained. In particular, when used as a power source for driving a vehicle such as a hybrid vehicle or an electric vehicle that requires a large output, there is a possibility that an output necessary for traveling (particularly at the time of starting) cannot be obtained.

However, with the technique disclosed in Patent Document 1, it is difficult to reduce the internal resistance of the lithium ion secondary battery that has risen during the suspension period, and there is a possibility that sufficient output characteristics may not be obtained.
The present invention has been made in view of the current situation, and for each lithium ion secondary battery included in the secondary battery system, a secondary battery system capable of reducing the internal resistance that has increased during the suspension period. The purpose is to provide.

  The solution is a secondary battery system including a plurality of lithium ion secondary batteries, wherein electric charges stored in the lithium ion secondary batteries are moved between the plurality of lithium ion secondary batteries. The secondary battery system includes charge transfer control means for performing SOC 0% control that allows each of the plurality of lithium ion secondary batteries to experience a state of SOC 0%.

In the secondary battery system of the present invention, the charge stored in the lithium ion secondary battery is moved between the plurality of lithium ion secondary batteries, and each of the plurality of lithium ion secondary batteries has an SOC of 0%. Control to experience the state (this control is called SOC 0% control) is performed.
By setting each lithium ion secondary battery included in the secondary battery system to SOC 0% once, the internal resistance increased during the suspension period can be reduced for each lithium ion secondary battery. .

  By the way, as a method for setting each lithium ion secondary battery to a state of SOC 0%, each lithium ion secondary battery is simply discharged, and the charge stored in each lithium ion secondary battery is secondary. A method of releasing the battery system outside is conceivable. However, in this method, each lithium ion secondary battery must be charged after discharging each lithium ion secondary battery, and the energy efficiency is very poor.

  On the other hand, in the secondary battery system of the present invention, the charge stored in the lithium ion secondary battery is moved between the plurality of lithium ion secondary batteries, so that the lithium ion secondary battery is in the SOC 0% state. I will do it. For example, in the case of a secondary battery system having two lithium ion secondary batteries, one battery is discharged until the SOC reaches 0%, and all the discharged charges are supplied to the other battery. Thereafter, the other battery is discharged until the SOC reaches 0%, and all the discharged charges are supplied to the one battery.

Thereby, each lithium ion secondary battery can be once brought into a SOC 0% state without reducing the amount of electricity stored in the entire lithium ion secondary battery included in the secondary battery system. Therefore, in the secondary battery system of the present invention, it is possible to reduce the internal resistance increased during the suspension period for each lithium ion secondary battery with good energy efficiency.
Note that SOC is an abbreviation for “State Of Charge”.

  Furthermore, in the above secondary battery system, the charge transfer control means stores the lithium ion secondary battery among the plurality of lithium ion secondary batteries after performing the SOC 0% control. The secondary battery system may be configured to perform SOC equalization control by moving the electric charge to equalize the SOC of each of the plurality of lithium ion secondary batteries.

In the secondary battery system of the present invention, after the SOC 0% control is performed, the electric charge stored in the lithium ion secondary battery is moved between the plurality of lithium ion secondary batteries, so that the plurality of lithium ion secondary batteries are transferred. The SOC of each battery is made equal.
Thus, for example, when all the lithium ion secondary batteries constituting the secondary battery system are electrically connected in series, all the lithium ion secondary batteries constituting the secondary battery system are appropriately used. can do. Specifically, for example, it is possible to prevent a decrease in discharge capacity (discharge characteristics) in the entire secondary battery system. Specifically, a battery with a smaller amount of electricity than other batteries (a battery with a low SOC) reaches a lower discharge limit earlier than other batteries, and discharges other batteries that have not yet reached the lower discharge limit. It can be prevented that it cannot be made to occur. In addition, some batteries that have a smaller amount of electricity (smaller SOC) than other batteries are overcharged or overdischarged, and it is possible to prevent problems that lead to early life.

  Furthermore, in any one of the above secondary battery systems, the plurality of lithium ion secondary batteries are mounted on the vehicle as a power source for driving the vehicle, and the charge transfer control means includes the lithium ion secondary battery. Only when the internal resistance value of the battery rises, it is preferable that the secondary battery system performs the SOC 0% control.

  In this secondary battery system, SOC 0% control is performed only when the internal resistance of the lithium ion secondary battery increases, so unnecessary SOC 0% control is not performed (that is, the inside of the battery). SOC 0% control is not performed until the resistance has not increased). Thereby, about each lithium ion secondary battery, the internal resistance which raised during the idle period can be reduced efficiently.

  Furthermore, in any one of the above secondary battery systems, the plurality of lithium ion secondary batteries are mounted on the vehicle as a power source for driving the vehicle, and the charge transfer control unit is configured to A secondary battery system that performs the SOC 0% control only when the internal resistance value R1 of the lithium ion secondary battery is larger than the internal resistance value R0 of the lithium ion secondary battery at the time of the previous vehicle start; Good.

  The secondary battery system of the present invention (lithium ion secondary battery constituting the system) is mounted on a vehicle as a power source for driving the vehicle. Examples of the vehicle include a hybrid vehicle, an electric vehicle, and a train. In such a vehicle, a particularly large output is required. Therefore, when the internal resistance of the lithium ion secondary battery constituting the secondary battery system is increased, the running performance may be greatly deteriorated.

  On the other hand, in the secondary battery system of the present invention, the internal resistance value R1 of the lithium ion secondary battery at the time of starting the vehicle is larger than the internal resistance value R0 of the lithium ion secondary battery at the time of starting the previous vehicle. In addition, SOC 0% control is performed. As a result, when the internal resistance of the lithium ion secondary battery increases during the suspension period from when the vehicle is stopped to when the vehicle starts, for each lithium ion secondary battery, the internal increased during the suspension period appropriately. Resistance can be reduced.

In addition, since the SOC 0% control is performed only when the internal resistance value R1 is larger than the internal resistance value R0, unnecessary SOC 0% control is not performed (that is, the internal resistance of the battery is reduced). SOC 0% control will not be performed until it has not risen). Thereby, about each lithium ion secondary battery, the internal resistance which raised during the idle period can be reduced efficiently.
Note that when the vehicle is started, it means when the vehicle power switch (main switch) is turned on. The vehicle stop means turning off a vehicle power switch (main switch).

  Further, in the above secondary battery system, the secondary battery system includes a voltage change amount detecting means for detecting a voltage change amount of the lithium ion secondary battery at the moment of starting the vehicle, and the voltage change amount. The voltage change amount ΔV1 of the lithium ion secondary battery detected by the detection means is compared with the voltage change amount ΔV0 of the lithium ion secondary battery detected by the voltage change amount detection means at the previous vehicle start. Voltage change amount determining means for determining whether or not the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, the charge transfer control means in the voltage change amount determining means, Only when it is determined that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, the secondary battery system that performs the SOC 0% control may be used.

  When the internal resistance of the lithium ion secondary battery constituting the secondary battery system is increased, the lithium ion secondary battery at the moment of starting the vehicle (that is, the moment of turning on the vehicle power switch (main switch)) There is a feature that the amount of voltage change of becomes large. Therefore, if the voltage change amount ΔV1 of the lithium ion secondary battery at the time of starting the vehicle is larger than the voltage change amount ΔV0 of the lithium ion secondary battery at the previous time of starting the vehicle, the inside of the lithium ion secondary battery It can be determined that the resistance is rising.

According to a test conducted by the inventors of the present application, when a lithium ion secondary battery with a SOC of 60% is continuously suspended for 6 hours or more in a temperature environment of 60 ° C., the internal resistance increases by about 9%. In the battery in which the internal resistance is greatly increased, the voltage change amount at the moment of discharging (the instant at which the vehicle is started) is increased by about 12% (about 1.12) as compared with that before the suspension (before the internal resistance is increased). Doubled). From this test result, when the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, it can be determined that the internal resistance of the battery is greatly increased.
Therefore, in the secondary battery system of the present invention, SOC 0% control is performed only when it is determined that the voltage change amount ΔV1 is 1.1 times or more the voltage change amount ΔV0. Thereby, about the lithium ion secondary battery which comprises a secondary battery system, the internal resistance which raised significantly during the idle period can be reduced appropriately.

  Further, in any one of the above secondary battery systems, it is determined whether or not the amount of electricity stored in the plurality of lithium ion secondary batteries is an amount of electricity capable of performing the SOC 0% control. The charge transfer control means is an electric quantity determining means for controlling the SOC 0% of the quantity of electricity stored in the plurality of lithium ion secondary batteries. Only when it is determined that the amount is the amount, it is preferable that the secondary battery system performs the SOC 0% control.

  When the amount of electricity stored in the lithium ion secondary battery constituting the secondary battery system is large, the SOC 0% control may not be performed. For example, in the case of a secondary battery system having two lithium ion secondary batteries, if the SOC of each battery is greater than 50%, the amount of discharged electricity when one battery is discharged to SOC 0% is Since the SOC of the battery is greater than the amount of electricity that increases by 50%, it is not possible to charge the other battery with all of the discharged electricity. In such a case, even if the SOC 0% control is performed, the internal resistance that has risen during the suspension period cannot be reduced appropriately, and therefore the control becomes useless.

  On the other hand, in the secondary battery system of the present invention, the amount of electricity stored in the lithium ion secondary battery constituting the secondary battery system can be controlled by SOC 0% by the electricity amount determination means. Determine if it is a quantity. For example, in the case of a secondary battery system having two lithium ion secondary batteries, it is determined whether the SOC of each battery is 50% or less.

  Furthermore, in the secondary battery system of the present invention, the amount of electricity stored in the lithium ion secondary battery that constitutes the secondary battery system is the amount of electricity that can perform SOC 0% control in the electricity amount determination means. Only when it is determined that there is a SOC 0% control. In the above example, when the SOC of each battery is 50% or less, it is determined that the amount of electricity is capable of performing SOC 0% control. Therefore, SOC 0% control is performed only in this case. Thereby, it is possible to appropriately reduce the internal resistance increased during the suspension period for each lithium ion secondary battery without performing useless control.

Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the hybrid vehicle 1 includes a vehicle body 2, an engine 3, a front motor 4, a rear motor 5, a secondary battery system 6, and a cable 7, and the engine 3, the front motor 4, and the rear motor 5 are used together. It is a hybrid car driven by. Specifically, the hybrid vehicle 1 is configured to be able to travel using the engine 3, the front motor 4, and the rear motor 5 using the secondary battery system 6 as a driving power source for the front motor 4 and the rear motor 5. .

  Among these, the secondary battery system 6 is attached to the vehicle body 2 of the hybrid vehicle 1 and is connected to the front motor 4 and the rear motor 5 by a cable 7. As shown in FIG. 2, the secondary battery system 6 includes an assembled battery 30 having a first battery unit 10 and a second battery unit 20, a battery control device 70, and a voltage detection means 50. The first battery unit 10 and the second battery unit 20 have a plurality (for example, 50) of lithium ion secondary batteries 100 electrically connected in series. The first battery unit 10 and the second battery unit 20 are usually electrically connected in series. Further, the SOCs of all the lithium ion secondary batteries 100 constituting the assembled battery 30 are usually equal.

  The voltage detection means 50 detects the battery voltage (inter-terminal voltage) of each lithium ion secondary battery 100 that constitutes the assembled battery 30 (the first battery unit 10 and the second battery unit 20). In this embodiment, the battery voltage (inter-terminal voltage) of each lithium ion secondary battery 100 is detected every 0.1 second.

The battery control device 70 includes a ROM, a CPU, a RAM, and the like (not shown), and controls charging / discharging of the assembled battery 30 (the first battery unit 10 and the second battery unit 20). The battery control device 70 normally includes an assembled battery 30 in which a plurality of lithium ion secondary batteries 100 are electrically connected in series with the switches 41 and 42 turned off and the switch 43 turned on, and an inverter (motor). Controls the exchange of electricity with the.
Further, the battery control device 70 estimates the SOC of each lithium ion secondary battery 100 based on the battery voltage detected by the voltage detection means 50. The battery control device 70 is connected to the control unit 60 that controls the hybrid vehicle 1, and transmits and receives electrical signals to and from the control unit 60.

  Furthermore, the battery control device 70 detects the voltage change amount of the lithium ion secondary battery 100 at the moment when the hybrid vehicle 1 is started. Specifically, when a signal to the effect that the vehicle power switch 45 is turned on is received from the control unit 60, the battery voltage value V11 detected by the voltage detection unit 50 immediately after that is received immediately before (0 in this embodiment). 1 second before and immediately before the vehicle power switch 45 is turned on), the battery voltage value V10 detected by the voltage detecting means 50 is subtracted, and this difference value is used as the lithium at the moment when the hybrid vehicle 1 is started. The voltage change amount ΔV of the ion secondary battery 100 is detected.

By the way, when the internal resistance of the lithium ion secondary battery 100 is increasing, the voltage change amount of the lithium ion secondary battery 100 at the moment when the hybrid vehicle 1 is started (that is, when the vehicle power switch 45 is turned on). There is a feature that becomes larger. Therefore, if the voltage change amount ΔV1 of the lithium ion secondary battery 100 at the time of starting the vehicle is larger than the voltage change amount ΔV0 at the time of starting the previous vehicle, the vehicle is stopped (the lithium ion secondary battery 100 It can be determined that the internal resistance of the lithium ion secondary battery 100 has increased during the rest period. That is, it can be determined that the internal resistance value R1 of the lithium ion secondary battery 100 at the start of the vehicle is greater than the internal resistance value R0 of the lithium ion secondary battery 100 at the previous start of the vehicle.
From the result of the storage test described later, when the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, it can be determined that the internal resistance of the battery is greatly increased.

Therefore, the battery control device 70 compares the voltage change amount ΔV1 detected at the start of the hybrid vehicle 1 with the voltage change amount ΔV0 detected at the previous vehicle start, and the voltage change amount ΔV1 is the voltage change amount. It is determined whether it is 1.1 times or more of ΔV0. When the battery control device 70 determines that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, the lithium ion secondary battery 100 between the lithium ion secondary batteries 100 constituting the assembled battery 30 is used. The charge stored in the battery 100 is moved so that each of the lithium ion secondary batteries 100 is controlled to experience a SOC 0% state (this control is referred to as SOC 0% control). Thereby, about the lithium ion secondary battery 100 which comprises the assembled battery 30, the internal resistance which raised during the idle period can be reduced. The effect of reducing internal resistance will be described in detail in the storage test described later.
In the present embodiment, the battery control device 70 corresponds to a voltage change amount detection unit and a voltage change amount determination unit.

  As shown in FIG. 3, the lithium ion secondary battery 100 is a rectangular sealed lithium ion secondary battery including a rectangular parallelepiped battery case 110, a positive electrode terminal 120, and a negative electrode terminal 130. Among these, the battery case 110 is made of metal, and includes a rectangular housing portion 111 that forms a rectangular parallelepiped housing space, and a metal lid portion 112. An electrode body 150, a positive current collecting member 122, a negative current collecting member 132, and the like are accommodated in the battery case 110 (rectangular accommodation portion 111).

  The electrode body 150 is an oblong cross section, and is a flat wound body formed by winding a sheet-like positive electrode 155, a negative electrode 156, and a separator 157 (see FIGS. 4 and 5). The positive electrode 155 has a positive electrode current collecting member 151 made of an aluminum foil and a positive electrode mixture 152 coated on the surface thereof. The negative electrode 156 has a negative electrode current collecting member 158 made of copper foil and a negative electrode mixture 159 coated on the surface thereof.

  The electrode body 150 is positioned at one end portion (right end portion in FIG. 3) in the axial direction (left and right direction in FIG. 3), and a positive electrode winding portion 155b in which only a part of the positive electrode current collecting member 151 overlaps in a spiral shape. The negative electrode winding portion 156b is located at the other end portion (left end portion in FIG. 3) and only a part of the negative electrode current collecting member 158 is spirally overlapped.

  The positive electrode 155 is coated with a positive electrode mixture 152 including a positive electrode active material 153 at a portion other than the positive electrode winding portion 155b (see FIG. 5). Further, the negative electrode 156 is coated with a negative electrode mixture 159 including a negative electrode active material 154 at a portion excluding the negative electrode winding portion 156b (see FIG. 5). The positive electrode winding part 155 b is electrically connected to the positive electrode terminal 120 through the positive electrode current collecting member 122. The negative electrode winding part 156 b is electrically connected to the negative electrode terminal 130 through the negative electrode current collecting member 132.

In this embodiment, lithium nickelate is used as the positive electrode active material 153. Further, graphite (specifically, amorphous coated graphite) is used as the negative electrode active material 154. Further, as the separator 157, a porous sheet made of polyethylene is used. As the non-aqueous electrolyte, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a solution obtained by mixing EC (ethylene carbonate) and DEC (diethyl carbonate) is used.

  Here, the SOC 0% control will be specifically described with reference to FIG. When the battery control device 70 determines that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, the SOC0 is displayed during the stop period of the hybrid vehicle 1 (while the vehicle power switch 45 is OFF). % Control.

  Specifically, after the vehicle power switch 45 is turned off, the battery control device 70 switches the switch 43 off and switches 41 and 42 on. Thereafter, the lithium ion secondary battery 100 constituting the first battery unit 10 is discharged until the SOC reaches 0%, and all the charges discharged from the lithium ion secondary battery 100 constituting the first battery unit 10 are discharged. Is supplied to the lithium ion secondary battery 100 constituting the second battery unit 20. Thereby, all the lithium ion secondary batteries constituting the first battery unit 10 can be discharged without releasing the charge stored in the entire lithium ion secondary battery 100 constituting the first battery unit 10 to the outside of the assembled battery 30. The secondary battery 100 can be brought into a SOC 0% state.

Next, on the contrary, the lithium ion secondary battery 100 constituting the second battery unit 20 is discharged until the SOC reaches 0% and discharged from the lithium ion secondary battery 100 constituting the second battery unit 20. All of the generated charges are supplied to the lithium ion secondary battery 100 constituting the first battery unit 10. As a result, all the lithium ion secondary batteries constituting the second battery unit 20 can be discharged without releasing the charge stored in the entire lithium ion secondary battery 100 constituting the second battery unit 20 to the outside of the assembled battery 30. The secondary battery 100 can be brought into a SOC 0% state.
In this way, with respect to all the lithium ion secondary batteries 100 constituting the assembled battery 30 without reducing the amount of electricity stored in the entire lithium ion secondary battery 100 constituting the assembled battery 30, SOC 0% You can experience the condition.
In the present embodiment, the battery control device 70 corresponds to charge transfer control means.

  By the way, when the amount of electricity stored in the lithium ion secondary battery 100 constituting the assembled battery 30 is large, the SOC 0% control may not be performed. Specifically, when the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is greater than 50%, the lithium ion secondary battery 100 constituting the first battery unit 10 is discharged to SOC 0%. Is larger than the amount of electricity that increases the SOC of the lithium ion secondary battery 100 constituting the second battery unit 20 by 50%. For this reason, at this time, all the amount of electricity discharged from the lithium ion secondary battery 100 constituting the first battery unit 10 is supplied to all the lithium ion secondary batteries 100 constituting the second battery unit 20. I can't do that.

On the other hand, in the secondary battery system 6 of the present embodiment, is the amount of electricity stored in the lithium ion secondary battery 100 constituting the assembled battery 30 an amount of electricity that can perform SOC 0% control? The battery control device 70 determines whether or not. Specifically, the battery control device 70 determines whether or not the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is 50% or less. When the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is 50% or less, it can be determined that the amount of electricity is capable of performing SOC 0% control. Therefore, the battery control device 70 performs SOC 0% control only when it is determined that the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is 50% or less.
In the present embodiment, the battery control device 70 corresponds to an electric quantity determination unit.

  In addition, when the battery control device 70 determines that the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is greater than 50%, the battery control device 70 waits for the SOC of the lithium ion secondary battery 100 to be 50% or less. Then, SOC 0% control is performed. Specifically, each time the hybrid vehicle 1 stops (the vehicle power switch 45 is turned OFF), it is determined whether or not the SOC of the lithium ion secondary battery 100 is 50% or less. If it is determined that the SOC of the secondary battery 100 is 50% or less, SOC 0% control is performed.

In the present embodiment, when the battery voltage of the lithium ion secondary battery 100 is 3.0 V, the SOC of the lithium ion secondary battery 100 is 0%. As described above, the battery control device 70 estimates the SOC of each lithium ion secondary battery 100 based on the battery voltage of the lithium ion secondary battery 100 detected by the voltage detection means 50. Accordingly, the battery control device 70 estimates that the SOC of the lithium ion secondary battery 100 is 0% when the voltage detection unit 50 detects a battery voltage of 3.0V.
In the lithium ion secondary battery 100 of the present embodiment, when the battery voltage is 3.0V, the positive electrode potential (vs. Li) is 3.0V. Therefore, the positive electrode potential (vs. Li) of each lithium ion secondary battery 100 can be set to 3.0 V by setting the lithium ion secondary battery 100 constituting the assembled battery 30 to the SOC 0% state.

  Further, the battery control device 70 performs the SOC 0% control, and then uses the charge stored in the lithium ion secondary battery 100 constituting the first battery unit 10 as the lithium ion secondary constituting the second battery unit 20. It moves to the battery 100, and the SOC of the lithium ion secondary battery 100 which comprises the assembled battery 30 is equalized. That is, the lithium ion secondary battery 100 constituting the first battery unit 10 is discharged, and the discharged electric charge is supplied to the lithium ion secondary battery 100 constituting the second battery unit 20, so that the assembled battery 30 is The SOC of the lithium ion secondary battery 100 to be configured is made equal.

  Thereby, all the lithium ion secondary batteries 100 which comprise the assembled battery 30 can be used appropriately. Specifically, for example, it is possible to prevent the discharge capacity (discharge characteristics) of the assembled battery 30 from being lowered. Specifically, when the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is not uniform, the lithium ion secondary battery has a smaller amount of electricity (smaller SOC value) than the other lithium ion secondary batteries 100. When 100 reaches the discharge lower limit earlier than other lithium ion secondary batteries 100, it becomes impossible to discharge other lithium ion secondary batteries 100 that have not yet reached the discharge lower limit. However, such a problem can be prevented by making the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 uniform. In addition, some lithium ion secondary batteries 100 that have a smaller amount of electricity (smaller SOC value) than other lithium ion secondary batteries 100 are overcharged or overdischarged, preventing problems that lead to early life. You can also

(Preservation test)
Next, a storage test was performed on the lithium ion secondary battery 100, and the internal resistance before and after the storage test was measured. Furthermore, SOC 0% control was performed on the lithium ion secondary battery 100 after the storage test, and the internal resistance of the subsequent lithium ion secondary battery 100 was measured.

  Specifically, first, the lithium ion secondary battery 100 adjusted to SOC 60% was discharged at a constant current of 100 A for 10 seconds in a temperature environment of 25 ° C. During this discharge period, the battery voltage (inter-terminal voltage) of the lithium ion secondary battery 100 was measured every 0.1 seconds. The measurement results are shown by a solid line (before the storage test) in FIG. Based on the measurement results, the internal resistance (IV resistance) of the lithium ion secondary battery 100 before the storage test was calculated.

  Specifically, in the graph in which the current value is set on the horizontal axis and the battery voltage is set on the vertical axis, the battery voltage value and current value (0 A) at the discharge time of 0 seconds and the battery voltage after 10 seconds from the discharge are shown. The slope of the straight line connecting these two points was calculated as the internal resistance (IV resistance) of the lithium ion secondary battery 100 before the storage test. The internal resistance of the lithium ion secondary battery 100 before the storage test was calculated to be 3.32 mΩ.

  Next, after adjusting the lithium ion secondary battery 100 to SOC 60%, the lithium ion secondary battery 100 was stored in a thermostatic bath whose internal temperature was adjusted to 60 ° C. for 6 hours. That is, the lithium ion secondary battery 100 was allowed to stand continuously for 6 hours in a temperature environment of 60 ° C. in a resting state. Thereafter, in the same manner as before the storage test, the lithium ion secondary battery 100 was discharged at a constant current of 100 A for 10 seconds in a temperature environment of 25 ° C., and the battery voltage (terminal voltage) was changed every 0.1 seconds. Measured. The measurement result is shown by a broken line (after the storage test) in FIG. Based on this measurement result, the internal resistance of the lithium ion secondary battery 100 after the storage test (6 hr) was calculated in the same manner as before the storage test, and it was 3.62 mΩ. From this result, when the lithium ion secondary battery 100 of SOC 60% is suspended for 6 hours in a temperature environment of 60 ° C., the internal resistance is about 9% (= (3.62-3.32) compared to before the suspension. ) /3.32) also increases.

  Furthermore, after the lithium ion secondary battery 100 after the storage test (6 hours) was adjusted to SOC 60%, it was again stored for 37 hours in a thermostat whose internal temperature was adjusted to 60 ° C. Thereafter, in the same manner as before the storage test, the lithium ion secondary battery 100 was discharged at a constant current of 100 A for 10 seconds in a temperature environment of 25 ° C., and the battery voltage (terminal voltage) was changed every 0.1 seconds. Measured. Based on this measurement result, the internal resistance of the lithium ion secondary battery 100 after the storage test (37 hr) was calculated in the same manner as before the storage test, and it was 3.62 mΩ as in the case after the storage test (6 hr). It was. From the above results, it can be seen that the internal resistance increases by about 9% when the lithium ion secondary battery 100 of SOC 60% is suspended for 6 hours or more in a temperature environment of 60 ° C.

  Thereafter, SOC 0% control was performed on the lithium ion secondary battery 100 after the storage test (37 hr). Specifically, discharging was performed until the battery voltage (inter-terminal voltage) of the lithium ion secondary battery 100 dropped to 3.0V. As described above, in the lithium ion secondary battery 100, the SOC is 0% when the battery voltage is 3.0V.

  Next, after adjusting the lithium ion secondary battery 100 to SOC 60%, as in the case before the storage test, the battery was discharged at a constant current of 100 A for 10 seconds in a temperature environment of 25 ° C. Was measured every 0.1 seconds. Thereafter, in the same manner as before the storage test, the internal resistance of the lithium ion secondary battery 100 after SOC 0% control was calculated to be 3.43 mΩ, and the internal resistance value was smaller than after the storage test. Specifically, the internal resistance value of the lithium ion secondary battery 100 after SOC 0% control is about 5% (= (3.62-3.43) /3.3) compared to the internal resistance value after the storage test. 62) also became smaller. From this result, the internal resistance increased during the rest period of the lithium ion secondary battery 100 by temporarily setting the lithium ion secondary battery 100 to the SOC 0% state (that is, by performing SOC 0% control). It can be said that this can be greatly reduced.

  In addition, about the lithium ion secondary battery, the reason why the internal resistance greatly increases due to the prolonged resting state (the state where charging / discharging is not performed) is continued for a long time in a state where electric charges are stored. I am thinking. When a lithium ion secondary battery is in a state where electric charge is stored and is in a resting state (a state in which charging / discharging is not performed) continues for a long time, the surface of the positive electrode active material is caused by a reaction between the positive electrode active material and the electrolytic solution. A film is formed on the surface. It is presumed that the internal resistance of the lithium ion secondary battery increases due to the effect of this coating.

  On the other hand, when the lithium ion secondary battery is once in the SOC 0% state (that is, by performing SOC 0% control), the coating produced on the surface of the positive electrode active material can be removed. thinking. In the present embodiment, SOC 0% control is performed on the lithium ion secondary battery 100 using lithium nickelate as the positive electrode active material 153 to reduce the battery voltage to 3.0V. At this time, the positive electrode potential (vs. Li) is 3.0V. From the above, for the lithium ion secondary battery using lithium nickelate, the positive electrode potential (vs.Li) is reduced to 3.0 V or less (battery voltage at which the positive electrode potential (vs.Li) becomes 3.0 V or less). It is presumed that the internal resistance that has increased during the resting period can be reduced by removing the coating formed on the surface of the positive electrode active material.

Next, the voltage change amount ΔV at the moment of discharging the lithium ion secondary battery 100 (0 to 0.1 seconds in FIG. 7) will be examined.
In the lithium ion secondary battery 100 before the storage test, the voltage change ΔVA at the moment of discharge (0 to 0.1 seconds in FIG. 7) was 0.1966V. On the other hand, in the lithium ion secondary battery 100 after the storage test (6 hours), the voltage change ΔVB at the moment of discharge (0 to 0.1 seconds in FIG. 7) was 0.2205V. In addition, also about the lithium ion secondary battery 100 after a preservation | save test (37 hours), it became the same result as the lithium ion secondary battery 100 after a preservation | save test (6 hours). From the above results, when the lithium ion secondary battery 100 with 60% SOC is paused for 6 hours or more in a temperature environment of 60 ° C., the voltage change ΔV at the moment when the lithium ion secondary battery 100 is discharged is It can be seen that it is about 1.12 times (= 0.2205 / 0.1966) (up about 12%).

  As described above, the lithium ion secondary battery 100 is characterized in that the voltage change amount ΔV at the moment of discharge increases when the internal resistance increases due to a long pause. Therefore, when the hybrid vehicle 1 is started (that is, when the vehicle power switch 45 is turned on), the lithium ion secondary battery 100 is discharged. Similarly, the internal resistance of the lithium ion secondary battery 100 is Can be said that the voltage change amount ΔV of the lithium ion secondary battery 100 increases. Therefore, if the voltage change amount ΔV1 of the lithium ion secondary battery 100 at the time of starting the vehicle is larger than the voltage change amount ΔV0 of the lithium ion secondary battery 100 at the previous time of starting the vehicle, the lithium ion secondary battery It can be determined that the internal resistance of 100 has increased.

  From the above test results, when the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, it can be determined that the internal resistance of the lithium ion secondary battery 100 is greatly increased. Therefore, in the secondary battery system 6 of the present embodiment, as described above, when the battery control device 70 determines that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0, the SOC 0% control is performed. I did it. Thereby, about the lithium ion secondary battery 100 which comprises the assembled battery 30, the internal resistance which raised significantly during the idle period can be reduced appropriately.

  Next, SOC control of the lithium ion secondary battery 100 (the assembled battery 30) according to the present embodiment will be described. 8 and 9 are flowcharts showing the flow of SOC control according to the present embodiment.

  As shown in FIG. 8, first, in step S1, the battery control device 70 obtains the voltage change amount ΔV1 detected at the start of the current hybrid vehicle 1 and the voltage change amount ΔV0 detected at the previous start of the vehicle. In comparison, it is determined whether or not the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0. If it is determined that the voltage change amount ΔV1 is not 1.1 times or more of the voltage change amount ΔV0 (No), the SOC control is terminated. This is because the internal resistance of the lithium ion secondary battery 100 constituting the assembled battery 30 has not increased so much.

  On the other hand, when the battery control device 70 determines in step S1 that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0 (Yes), the process proceeds to step S2 and the vehicle power switch 45 is OFF. It is determined whether or not there is. That is, it is determined whether the hybrid vehicle 1 is in a stopped state. If it is determined that the vehicle power switch 45 is not OFF (No), the process of step S2 is repeated until it is determined that the vehicle power switch 45 is OFF.

  If it is determined in step S2 that the vehicle power switch 45 is OFF (Yes), the process proceeds to step S3, in which the battery control device 70 determines that the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is 50%. It is determined whether or not: That is, it is determined whether or not the amount of electricity stored in the lithium ion secondary battery 100 constituting the assembled battery 30 is an amount of electricity that can be subjected to SOC 0% control.

  In step S3, when the battery control device 70 determines that the SOC of the lithium ion secondary battery 100 is 50% or less (Yes), the process proceeds to step S4 and performs SOC 0% control. Specifically, as shown in FIG. 9, first, in step S <b> 41, the charge stored in the lithium ion secondary battery 100 constituting the first battery unit 10 is converted into the lithium ion constituting the second battery unit 20. Move to the secondary battery 100. Specifically, after the battery control device 70 switches the switch 43 to OFF and the switches 41 and 42 to ON, the lithium ion secondary battery 100 constituting the first battery unit 10 is discharged and discharged. The charge is supplied to the lithium ion secondary battery 100 constituting the second battery unit 20.

  Next, the process proceeds to step S42, and the battery control device 70 determines whether or not the SOC of the lithium ion secondary battery 100 constituting the first battery unit 10 has reached 0%. If it is determined that the SOC has not reached 0% (No), the process of step S42 is repeated until it is determined that the SOC has reached 0% (Yes).

  In Step S42, when it is determined that the SOC of the lithium ion secondary battery 100 constituting the first battery unit 10 has reached 0% (Yes), the process proceeds to Step S43, and the battery control device 70 determines that the first battery unit The discharge of the lithium ion secondary battery 100 constituting the battery 10 is stopped. As a result, all the charges constituting the first battery unit 10 can be obtained without discharging (discharging) the charge stored in the entire lithium ion secondary battery 100 constituting the first battery unit 10 to the outside of the assembled battery 30. The lithium ion secondary battery 100 can be brought into a SOC 0% state.

  Next, the process proceeds to step S44, and on the contrary, the charge stored in the lithium ion secondary battery 100 constituting the second battery unit 20 is moved to the lithium ion secondary battery 100 constituting the first battery unit 10 on the contrary. To do. Specifically, the lithium ion secondary battery 100 constituting the first battery unit 20 is discharged, and the discharged charge is supplied to the lithium ion secondary battery 100 constituting the first battery unit 10.

  Next, in step S45, the battery control device 70 determines whether or not the SOC of the lithium ion secondary battery 100 constituting the second battery unit 20 has reached 0%. If it is determined that the SOC has not reached 0% (No), the process of step S45 is repeated until it is determined that the SOC has reached 0% (Yes).

If it is determined in step S45 that the SOC of the lithium ion secondary battery 100 constituting the second battery unit 20 has reached 0% (Yes), the process proceeds to step S46, and the battery control device 70 The discharge of the lithium ion secondary battery 100 constituting 20 is stopped. As a result, all the charges constituting the second battery unit 20 can be formed without discharging (discharging) the charge stored in the entire lithium ion secondary battery 100 constituting the second battery unit 20 to the outside of the assembled battery 30. The lithium ion secondary battery 100 can be brought into a SOC 0% state.
In this way, with respect to all the lithium ion secondary batteries 100 constituting the assembled battery 30 without reducing the amount of electricity stored in the entire lithium ion secondary battery 100 constituting the assembled battery 30, SOC 0% You can experience the condition.

  Thereafter, returning to the main routine shown in FIG. 8, the process proceeds to step S <b> 5, and the battery control device 70 converts the charge stored in the lithium ion secondary battery 100 constituting the first battery unit 10 to the second battery unit 20. It moves to the lithium ion secondary battery 100 which comprises, and makes SOC of the lithium ion secondary battery 100 which comprises the assembled battery 30 equalize. That is, the lithium ion secondary battery 100 constituting the first battery unit 10 is discharged, and the discharged electric charge is supplied to the lithium ion secondary battery 100 constituting the second battery unit 20, so that the assembled battery 30 is The SOC of the lithium ion secondary battery 100 to be configured is made equal. When the process of step S5 is completed, a series of processes ends.

  Thus, in the secondary battery system 6 of the present embodiment, all the lithium ion secondary batteries 100 constituting the assembled battery 30 during the stop period of the hybrid vehicle 1 (during the period when the vehicle power switch 45 is OFF). Can experience a state of SOC 0%. Furthermore, the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 can be equalized during the stop period of the hybrid vehicle 1 (during the period when the vehicle power switch 45 is OFF).

  In step S3, when the battery control device 70 determines that the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is not 50% or less (No), the process proceeds to step S6, and the vehicle power switch 45 is turned on. It is determined whether or not it is turned on. If it is determined that the vehicle power switch 45 is not ON (No), this process is repeated until it is determined that the vehicle power switch 45 is ON. If it is determined that the vehicle power switch 45 is turned on (Yes), the process returns to step S2 to determine again whether or not the vehicle power switch 45 is turned off. That is, it is determined whether or not a next vehicle stop state (a state in which the vehicle power switch 45 is turned off) has been reached.

  If it is determined that the vehicle power switch 45 is OFF (Yes), the process proceeds to step S3, and it is again determined whether or not the SOC of the lithium ion secondary battery 100 constituting the assembled battery 30 is 50% or less. judge. When it is determined that the SOC is 50% or less (Yes), the processes of steps S4 and S5 are performed as described above. On the other hand, when it is determined that the SOC is not 50% or less (Yes), the processes of steps S6, S2, and S3 are performed again. In this way, the process of step S3 is performed every time the hybrid vehicle 1 stops (the vehicle power switch 45 is turned OFF) until it is determined in step S3 that the SOC is 50% or less (Yes). Thereafter, when it is determined that the SOC is 50% or less (Yes), the processes of steps S4 and S5 are performed as described above, and the series of processes is terminated.

  In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.

1 is a schematic view of a hybrid vehicle. It is the schematic of the secondary battery system concerning embodiment. It is sectional drawing of the lithium ion secondary battery concerning embodiment. It is sectional drawing of an electrode body. It is a partial expanded sectional view of an electrode body, and is equivalent to the B section enlarged view of FIG. It is a figure which shows the internal resistance change of a lithium ion secondary battery. It is a figure which shows the battery voltage fluctuation | variation at the time of discharge of a lithium ion secondary battery. It is a main routine of SOC control concerning an embodiment. It is a subroutine of SOC control concerning an embodiment.

Explanation of symbols

1 Hybrid vehicle (vehicle)
6 secondary battery system 10 first battery unit 20 second battery unit 30 assembled battery 45 vehicle power switch 70 battery control device (charge transfer control means, voltage change amount detection means, voltage change amount determination means, electric quantity determination means)
100 Lithium ion secondary battery

Claims (5)

A secondary battery system comprising a plurality of lithium ion secondary batteries,
The SOC 0% that causes the charge stored in the lithium ion secondary battery to move between the plurality of lithium ion secondary batteries to experience the state of SOC 0% for each of the plurality of lithium ion secondary batteries. A secondary battery system comprising charge transfer control means for performing control. The secondary battery system according to claim 1,
The charge transfer control means includes
After performing the SOC 0% control, the electric charge stored in the lithium ion secondary battery is moved between the plurality of lithium ion secondary batteries, and each SOC of the plurality of lithium ion secondary batteries is transferred. A secondary battery system that performs SOC equalization control to equalize. The secondary battery system according to claim 1 or 2,
The plurality of lithium ion secondary batteries are mounted on the vehicle as a power source for driving the vehicle,
The charge transfer control means includes
The SOC 0% control is performed only when the internal resistance value R1 of the lithium ion secondary battery at the time of starting the vehicle becomes larger than the internal resistance value R0 of the lithium ion secondary battery at the time of starting the previous vehicle. Secondary battery system. The secondary battery system according to claim 3,
The secondary battery system includes:
Voltage change amount detecting means for detecting a voltage change amount of the lithium ion secondary battery at the moment of starting the vehicle;
The voltage change amount ΔV1 of the lithium ion secondary battery detected by the voltage change amount detection means, and the voltage change amount ΔV0 of the lithium ion secondary battery detected by the voltage change amount detection means when the vehicle was started before that time. And a voltage change amount determination means for determining whether or not the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0,
The charge transfer control means includes
The secondary battery system that performs the SOC 0% control only when the voltage change amount determining means determines that the voltage change amount ΔV1 is 1.1 times or more of the voltage change amount ΔV0. The secondary battery system according to any one of claims 1 to 4,
An electric quantity determining means for determining whether or not the electric quantity stored in the plurality of lithium ion secondary batteries is an electric quantity capable of performing the SOC 0% control;
The charge transfer control means includes
The SOC 0% control is performed only when the amount of electricity stored in the plurality of lithium ion secondary batteries is determined to be an amount of electricity capable of performing the SOC 0% control in the electricity amount determination means. Do secondary battery system.

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