JP6760241B2 - Rechargeable battery system - Google Patents

Description

The present disclosure relates to a secondary battery system, and more specifically to a secondary battery system including a lithium ion secondary battery containing a silicon oxide in the negative electrode.

In recent years, electric vehicles (hybrid vehicles, electric vehicles, etc.) equipped with a lithium-ion secondary battery assembly battery have become widespread. In general, the lithium ion secondary battery deteriorates due to charging / discharging or the passage of time, and the full charge capacity (hereinafter, may be abbreviated as "capacity") of the lithium ion secondary battery decreases. Then, the distance that the electric vehicle can travel (so-called EV travel distance) using the electric power stored in the assembled battery becomes short. Therefore, a technique for recovering the reduced capacity or alleviating the reduced capacity has been proposed.

Many assembled batteries are configured by restricting a plurality of stacked cells from the outside by a restraining member. It is known that the magnitude of the restraining pressure due to the restraining member affects the degree of deterioration of the assembled battery (more specifically, the amount of decrease in the capacity of the assembled battery). For example, Japanese Patent Application Laid-Open No. 2013-161543 (Patent Document 1) discloses a control device and a control method for controlling the magnitude of the restraint pressure by the restraint member. By appropriately controlling the magnitude of the confining pressure, the capacity of the assembled battery can be recovered (see, for example, FIGS. 4 and 5 of Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-161543

Conventionally, the typical negative electrode active material of a lithium ion secondary battery has been graphite. However, in recent years, adoption of silicon oxide (SiOx) as a negative electrode active material has been studied. This is because the full charge capacity of the assembled battery can be increased by adopting the silicon oxide.

In a lithium ion secondary battery containing a silicon oxide as a negative electrode active material, the capacity may not be properly restored only by increasing the restraining pressure. More specifically, the present inventors have found that when the negative electrode potential of the lithium ion secondary battery is outside the appropriate potential range, the negative electrode potential is within the potential range, based on the results of the evaluation test described later. It was found that the negative electrode material deteriorated or the capacity recovery amount decreased, and the capacity could not be recovered appropriately.

In the control method disclosed in Patent Document 1, it is not particularly described whether or not the negative electrode contains a silicon oxide, and therefore, there is room for improvement in that the negative electrode potential is not taken into consideration.

The present disclosure has been made in order to solve the above problems, and an object of the present invention is the capacity of an assembled battery in a secondary battery system including an assembled battery of a lithium ion secondary battery containing a silicon oxide in the negative electrode. Is to provide a technology that can properly recover the battery.

A secondary battery system according to a certain aspect of the present disclosure includes an assembled battery, a restraining member, a driving device, and a control device. The assembled battery includes a plurality of cells. Each of the plurality of cells is a lithium ion secondary battery containing a silicon oxide in the negative electrode. The restraint member is configured to apply a restraining pressure to the assembled battery by restraining the assembled battery. The drive device is configured to adjust the restraint pressure of the restraint member. The control device controls the drive device. In the control device, when the capacity of the assembled battery is lower than the reference value, when the potential of the negative electrode is within a predetermined potential range, the confining pressure increases as compared with the case where the capacity of the assembled battery is higher than the reference value. The drive unit is controlled so as to do so. The predetermined potential range is a range in which the potential of the negative electrode based on the metallic lithium potential is 0.3 V or more and 0.9 V or less.

According to the above configuration, by limiting the negative electrode potential to a specific potential range of 0.3 V or more and 0.9 V or less, the amount of capacity recovery of the assembled battery due to the increase in the confining pressure can be increased (details are described). See below). Further, deterioration of the negative electrode material (decomposition of the protective layer) that occurs when the negative electrode potential is higher than the upper limit value of the potential range can be suppressed. Therefore, the capacity of the assembled battery can be appropriately restored.

According to the present disclosure, in a secondary battery system including an assembled battery of a lithium ion secondary battery containing a silicon oxide in the negative electrode, the capacity of the assembled battery can be appropriately recovered.

It is a figure which shows schematic the whole structure of the vehicle which mounted the secondary battery system which concerns on this Embodiment. It is a figure which shows the structure of the assembled battery and the restraint member in more detail. It is a figure for demonstrating the structure of each cell in more detail. It is a figure for demonstrating the result of the evaluation test of capacity recovery control. It is a figure which summarized the condition and result of the evaluation test shown in FIG. It is a flowchart for demonstrating capacity recovery control in this embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

Hereinafter, a configuration in which the secondary battery system according to the present embodiment is mounted on an electric vehicle will be described as an example. However, the secondary battery system according to the present embodiment is applicable not only to electric vehicles but also to all vehicles (hybrid vehicles, fuel cell vehicles, etc.) equipped with assembled batteries. Further, the use of the secondary battery system according to the present embodiment is not limited to that for vehicles, and may be for stationary use.

[Embodiment]
<Overall configuration of electric vehicle>
FIG. 1 is a diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to the present embodiment. With reference to FIG. 1, the vehicle 1 is an electric vehicle, which includes an inlet 10, a power conversion device 20, a charging relay (CHR: Charge Relay) 30, an assembled battery 40, and a system main relay (SMR: System). It includes a main relay (50), a power control unit (PCU: Power Control Unit) 60, a motor generator (indicated by MG) 70, a drive wheel 80, and an electronic control unit (ECU: Electronic Control Unit) 100.

FIG. 1 shows a configuration in which the assembled battery 40 mounted on the vehicle 1 is charged (so-called external charging) by the electric power supplied from the charging device 9 outside the vehicle. The charging device 9 and the power conversion device 20 are electrically connected to each other via the charging cable 8 and the inlet 10.

The power conversion device 20 includes, for example, an AC / DC converter (not shown), converts AC power supplied from the system power supply 91 of the charging device 9 into DC power, and outputs the AC power to the charging relay 30.

The charging relay 30 is electrically connected to a power line connecting the power conversion device 20 and the assembled battery 40. The charging relay 30 is opened / closed in response to a control signal from the ECU 100. As a result, the supply and interruption of power between the power conversion device 20 and the assembled battery 40 can be switched.

The assembled battery 40 includes a plurality of cells 41 (see FIGS. 2 and 3), each of which is a lithium ion secondary battery. The assembled battery 40 stores electric power for driving the motor generator 70, and supplies electric power to the motor generator 70 through the PCU 60. Further, the assembled battery 40 is charged by the electric power supplied through the power conversion device 20 at the time of external charging. Further, the assembled battery 40 receives the generated power through the PCU 60 and is charged even when the motor generator 70 generates power.

A monitoring unit 401 is provided in the assembled battery 40. The monitoring unit 401 includes a voltage sensor, a current sensor, and a temperature sensor (none of which are shown). The voltage sensor detects the voltage VB of the assembled battery 40. The current sensor detects the current IB input / output to / from the assembled battery 40. The temperature sensor detects the temperature TB of the assembled battery 40. Each sensor outputs a signal indicating the detection result to the ECU 100.

Actually, the voltage of each cell 41 included in the assembled battery 40 or the voltage of each block (not shown) in which a plurality of cells 41 are connected in parallel is monitored by the voltage sensor. Similarly, the temperature sensor is provided for each of a plurality of cells or blocks. However, in the present embodiment, the number of cells included in the assembled battery 40 or the connection relationship between the cells does not matter. Therefore, for the sake of simplification of the description, the assembled battery 40 will be described below as the voltage and temperature monitoring unit instead of the cell or block.

Further, the assembled battery 40 is provided with a restraining member B for applying the restraining pressure P to the assembled battery 40. The restraint member B will be described in detail with reference to FIG.

The SMR 50 is electrically connected to a power line connecting the assembled battery 40 and the PCU 60. The SMR 50 is opened / closed in response to a control signal from the ECU 100. As a result, the continuity and disconnection between the assembled battery 40 and the PCU 60 are switched.

The PCU 60 executes bidirectional power conversion between the assembled battery 40 and the motor generator 70 according to the control signal from the ECU 100. The PCU 60 includes an inverter and a converter (none of which is shown) that boosts the DC voltage supplied to the inverter to a voltage higher than the output voltage of the assembled battery 40.

The motor generator 70 is, for example, a three-phase AC rotary electric machine in which a permanent magnet is embedded in a rotor (not shown). The motor generator 70 rotates the drive shaft using the power supplied from the assembled battery 40. The motor generator 70 can also generate electricity by regenerative braking. The AC power generated by the motor generator 70 is converted into DC power by the PCU 60 and charged into the assembled battery 40.

The ECU 100 includes a CPU (Central Processing Unit) 101, a memory 102, and an input / output port (not shown) for inputting / outputting various signals. The ECU 100 outputs a control signal based on the input of the signal from each sensor and the map and the program stored in the memory, and controls each device so that the vehicle 1 is in a desired state. More specifically, the ECU 100 controls the charging / discharging of the assembled battery 40 by controlling the power conversion device 20 and the PCU 60. Further, the ECU 100 calculates the capacity (fully charged capacity) of the assembled battery 40 based on the voltage VB, the current IB, and the temperature TB. Further, as a main control executed by the ECU 100 in the present embodiment, there is a capacity recovery control for recovering the capacity of the assembled battery 40. This control will be described in detail later.

<Structure of assembled battery and restraint member>
FIG. 2 is a diagram showing the configurations of the assembled battery 40 and the restraint member B in more detail. With reference to FIG. 2, the assembled battery 40 includes a plurality of cells 41, a pair of end plates 42, a restraint band 43, a plurality of bolts 44, an actuator 45, and a plurality of bus bars 46.

In FIG. 2, one end of the stacking direction (x-axis direction) of the laminated body formed by stacking the plurality of cells 41 is partially shown. A pair of end plates 42 are arranged so as to face one end of the laminated body and the other end in the stacking direction. The pair of end plates 42 are restrained by the restraint band 43 with all the cells 41 sandwiched therein.

Further, the pair of end plates 42 are fastened to each other by bolts 44 and nuts (not shown). A restraint pressure P [unit: MPa] is applied to each cell 41 by the end plate 42, the restraint band 43, the bolt 44, and the nut.

The actuator (driving device) 45 is configured to be able to adjust the restraint pressure P by controlling the tightening amount of the bolt 44 according to the control signal from the ECU 100. More specifically, the restraint pressure P can be measured by installing a pressure sensor (not shown) between the cells 41. Therefore, by obtaining the correlation between the tightening amount of the bolt 44 and the restraining pressure P in advance, the tightening amount for generating the desired restraining pressure P can be calculated.

In the present embodiment, the end plate 42, the restraint band 43, the bolt 44, and the nut correspond to the “restraint member” (shown by B in FIG. 2) according to the present disclosure. Further, the assembled battery 40, the restraint member B, the actuator 45, and the ECU 100 correspond to the "secondary battery system" (shown by A in FIG. 1) according to the present disclosure.

Each cell 41 has a positive electrode terminal 413 and a negative electrode terminal 414 (see FIG. 3). The positive electrode terminal 413 of a certain cell and the negative electrode terminal 414 of an adjacent cell are fastened by a bus bar 46 and electrically connected to each other. As a result, a plurality of cells 41 are connected in series. However, a configuration in which a plurality of cells 41 are connected in series is not essential. For example, a plurality of cells 41 may be connected in parallel to form a block, and the blocks may be connected in series to form an assembled battery 40.

<Cell configuration>
FIG. 3 is a diagram for explaining the configuration of each cell 41 in more detail. In FIG. 3, the cell 41 is shown through the inside thereof.

The cell 41 has a battery case 411 having a substantially rectangular parallelepiped shape. The upper surface of the battery case 411 is sealed by the lid 412. One end of each of the positive electrode terminal 413 and the negative electrode terminal 414 projects outward from the lid 412. The other ends of the positive electrode terminal 413 and the negative electrode terminal 414 are connected to the internal positive electrode terminal and the internal negative electrode terminal (neither of them is shown) inside the battery case 411, respectively.

The electrode body 415 is housed inside the battery case 411. The electrode body 415 is formed by laminating a positive electrode 416 and a negative electrode 417 via a separator 418 and winding the laminated body. The electrolytic solution (not shown) is held in the positive electrode 416, the negative electrode 417, the separator 418, and the like. It is also possible to use a laminated body as the electrode body 415 instead of the wound body.

<Battery capacity recovery control>
In the vehicle 1 configured as described above, the assembled battery 40 deteriorates with the repetition of charging and discharging or the passage of time, and the capacity of the assembled battery 40 decreases. In such a case, it is conceivable to increase the restraining pressure P in order to recover the reduced capacity or to alleviate the reduced capacity (see, for example, Patent Document 1). This control is also referred to as "capacity recovery control" in the present specification. The reason why the capacity is recovered by the capacity recovery control is that the restraining pressure P is increased and the distance between the silicon oxide and the carbon material (graphite) in the negative electrode is shortened so that the positive electrode 416 and the negative electrode 417 are separated. It is considered that this is because a sufficient electronic path is secured between them.

Here, the present inventors have focused on the fact that in a lithium ion secondary battery containing a silicon oxide in the negative electrode active material, the capacity may not be appropriately restored only by increasing the restraining pressure. .. More specifically, the present inventors consider that the negative electrode potential V2 of the assembled battery 40 (more specifically, each cell 41) is appropriate from the results of the capacity recovery control evaluation tests shown in FIGS. 4 and 5 below. It was found that when the negative electrode potential V2 is outside the potential range R, the capacity recovery amount is reduced or the negative electrode material is deteriorated as compared with the case where the negative electrode potential V2 is within the potential range R, and the capacity cannot be recovered appropriately. It was.

Therefore, in the present embodiment, the negative electrode potential V2 is taken into consideration, and a configuration is adopted in which the confining pressure P is increased when the negative electrode potential V2 is within the potential range R. Hereinafter, the evaluation test results (measurement results of the capacity retention rate of the assembled battery 40) under various conditions will be described. The capacity retention rate means the ratio of the capacity after deterioration based on the capacity before deterioration (initial capacity).

<Evaluation test>
The configurations of the positive electrode 416, the negative electrode 417, the separator 418, and the electrolytic solution used in the evaluation test will be described in detail.

As the positive electrode active material of the positive electrode 416, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an average particle diameter of 10 μm was used. A slurry adjusted so that the ratio of the positive electrode active material, acetylene black, and PVdF (polyvinylidene fluoride) was 87:10: 3 was prepared. Then, the prepared slurry was applied to the aluminum foil. Further, by applying a slurry to the back surface of the aluminum foil, a positive electrode plate having electrodes coated on both sides was produced.

As the negative electrode active material of the negative electrode 417, a mixture of natural graphite having an average particle diameter of 20 μm and silicon oxide (SiO) having an average particle diameter of 5 μm was used. A styrene-butadiene copolymer (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was used as the thickener. Then, graphite: SiO: SBR: CMC = 76: 20: 2: 2 was mixed to prepare a slurry. Water was used as the dispersion medium. Similar to the positive electrode plate, the negative electrode plate was produced by applying the slurry to both sides of the copper foil.

Twenty positive electrode plates and 21 negative electrode plates produced as described above were laminated with a separator in between to form an electrode body. Further, this electrode body was electrically connected to the internal positive electrode terminal and the internal negative electrode terminal, and was sealed in a rectangular laminated bag having three sides heat-welded and viewed from above. Then, the electrolytic solution was poured into this laminated bag. As the electrolytic solution, 1 lithium salt (LiPF ₆ ) is used for a solvent having a volume percent ratio s of ethylene carbonate (EC): diethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 3: 4: 3. A mixture was used so as to have a ratio of 0.0 M. After injecting the electrolytic solution, the laminated bag was sealed by heat-welding the remaining one of the four sides of the laminated bag. As a result, a cell was obtained. The cell was sandwiched between metal plates (not shown in FIG. 3, but corresponding to the end plate shown in FIG. 2), and the restraining pressure P was applied to the cell by maintaining the state.

Before applying the restraint pressure P or before changing the restraint pressure P, the negative electrode potential V2 was set to various values (0.1 V to 1.2 V as described later). The negative electrode potential V2 can be set to a desired value by adjusting the voltage VB based on the correspondence between the voltage VB measured in advance and the negative electrode potential V2. The adjustment of the voltage VB was carried out by performing constant current charging at 1 / 5C and then performing constant voltage charging until the current value decreased to 1 / 20C.

The first charge was a constant current / constant voltage method. Specifically, constant current charging was performed until the voltage VB reached 4.2 V at a current value of 1 / C of the capacity estimated from the amount of positive electrode active material. After that, the cell was fully charged by performing constant voltage charging until the current value reached 1 / 20C. Then, the cell was discharged with a constant current of 1 / 5C until the voltage VB dropped to 2.5V. Then, the initial capacity was calculated from the amount of electric charge discharged from the fully charged state.

The cell was placed in a constant temperature bath (not shown) in a 25 ° C. environment, and a cycle test was performed. In this cycle test, the cell is discharged until the voltage VB drops from 4.2V to 2.5V at the current value of 1C of the initial capacitance, and then until the voltage VB rises from 2.5V to 4.2V. The cell was charged. Further, every 50 cycles, charging / discharging was performed at a constant current of 1 / 5C between 4.2V and 2.5V, and the cell capacity was calculated.

As one specific example, the ratio of SiO / (SiO + C (graphite)) in the negative electrode is in the range of 3% or more and 40% or less, and the electrode density of the negative electrode is 1.3 (g / cc) or more and 1. When it is 7 (g / cc) or less, an appropriate potential range R is a potential range of 0.3 V or more and 0.9 V or less (vs. Li ^/ Li ⁺ ).

FIG. 4 is a diagram for explaining the result of the evaluation test of the capacity recovery control. FIG. 5 is a diagram summarizing the conditions and results of the evaluation test shown in FIG.

FIG. 4 shows curves L1 to L6 representing the evaluation results performed under six different conditions, respectively. In FIG. 4, the horizontal axis represents the number of charge / discharge cycles (0 to 350 cycles), and the vertical axis represents the capacity retention rate of the cell. FIG. 5 shows the conditions and results corresponding to the curves L1 to L6.

With reference to FIG. 5, the curve L1 shows the capacitance when the confining pressure P is increased in the order of 0.5 MPa (megapascal), 0.6 MPa, and 0.7 MPa when the negative electrode potential V2 is 1.2 V. Shows the change in maintenance rate. As shown in FIG. 4, the period of the first 100 cycles is described as T1, the period of the next 150 cycles is described as T2, and the period of the subsequent 100 cycles is described as T3.

The curve L2 shows the capacitance when the confining pressure P is increased to 0.5 MPa, 0.6 MPa, 0.7 MPa as the period elapses from T1, T2, T3 when the negative electrode potential V2 is 0.9V. Shows the change in maintenance rate.

The curve L3 shows the capacitance when the restraining pressure P is increased to 0.5 MPa, 0.6 MPa, 0.7 MPa as the period elapses from T1, T2, T3 when the negative electrode potential V2 is 0.6 V. Shows the change in maintenance rate.

The curve L4 shows the capacitance when the restraint pressure P is increased to 0.5 MPa, 0.6 MPa, and 0.7 MPa as the period elapses from T1, T2, and T3 when the negative electrode potential V2 is 0.3V. Shows the change in maintenance rate.

The curve L5 shows the capacitance when the restraint pressure P is increased to 0.5 MPa, 0.6 MPa, and 0.7 MPa as the period elapses from T1, T2, and T3 when the negative electrode potential V2 is 0.1 V. Shows the change in maintenance rate.

As a comparative example, the curve L6 shows the change in the capacity retention rate when the negative electrode potential V2 is not particularly set and the confining pressure P is maintained constant at 0.5 MPa.

As shown in FIGS. 4 and 5, the capacity retention rate of the assembled battery 40 decreases as the number of charge / discharge cycles increases in each of the curves L1 to L6. However, the curves L2 to L4 have a higher capacity retention rate than the curves L6. That is, when the negative electrode potential V2 is within the potential range R (see curves L2 to L4), the amount of decrease in the capacity retention rate is smaller than that in the comparative example (see curves L6), and the decrease in the capacity retention rate is alleviated. Has been done.

On the other hand, on the curves L1 and L5, the capacity retention rate is lower than that on the curve L6. That is, when the negative electrode potential V2 is lower than the lower limit value (0.3 V) of the potential range R (see curve L5) or when the negative electrode potential V2 is higher than the upper limit value (0.9 V) of the potential range R (see curve L1). ), The capacity retention rate is lower than that of the comparative example.

In this way, an appropriate potential range R can be set by setting the negative electrode potential V2 to various values and performing the evaluation test. The mechanism that should be considered when setting the upper limit value and the lower limit value of the potential range R will be described below.

The volume change of silicon oxide due to the insertion or desorption of lithium is larger than the volume change of graphite. Therefore, when silicon oxide is used as the negative electrode active material, it is between the silicon oxide and graphite due to charging and discharging (hereinafter, also abbreviated as "negative electrode active material") as compared with the case where graphite is used. The amount of change in the voids of is large.

When the negative electrode potential V2 is lower than the lower limit value (0.3V) of the potential range R, that is, when the cell voltage is relatively high, the cell is charged to some extent and the amount of lithium inserted in the negative electrode active material is large. .. Therefore, the negative electrode plate is expanded and the voids between the negative electrode active materials are narrow. Therefore, a certain amount of current path is formed between the electrodes before the restraint pressure P increases. Therefore, even if the restraining pressure P is increased, the effect of capacity recovery (amount of relaxation of capacity decrease) is considered to be small.

Further, in general, silicon (Si) and lithium-containing silicon oxide (LiSiO) are generated from the silicon oxide when the lithium ion secondary battery containing the silicon oxide (SiOx) as the negative electrode active material is charged for the first time. Then, a protective layer made of LiSiO is formed so as to surround the silicon. When the negative electrode potential V2 is higher than the upper limit value (0.9V) of the potential range R, LiSiO, which is a protective layer, is easily decomposed. Therefore, the deterioration of the negative electrode material (negative electrode active material) progresses, and the life of the assembled battery 40 is shortened.

As described above, the potential range R is experimentally determined so that the voids between the negative electrode active materials are appropriately secured and the LiSiO generated in the negative electrode active material is not easily decomposed. Is desirable.

<Capacity recovery control flow>
Based on the evaluation test results described above, in the capacity recovery control in the present embodiment, when the negative electrode potential V2 is within the potential range R, the restraining pressure P is increased as compared with before the capacity of the assembled battery 40 is reduced. On the other hand, when the negative electrode potential V2 is outside the potential range R, the assembled battery 40 is charged and discharged so that the negative electrode potential V2 is within the potential range R, and then the restraining pressure P is increased.

FIG. 6 is a flowchart for explaining the capacity recovery control in the present embodiment. The process shown in this flowchart is called and executed from the main routine every time a predetermined condition is satisfied or a predetermined cycle elapses. Further, each step (hereinafter abbreviated as "S") included in this flowchart is basically realized by software processing by the ECU 100, but is realized by dedicated hardware (electric circuit) manufactured in the ECU 100. You may.

In S10, the ECU 100 calculates the full charge capacity C of the assembled battery 40. As a method for calculating the full charge capacity C, various known methods can be adopted. For example, the SOC is estimated twice before and after the charging / discharging of the assembled battery 40, and the full charge capacity C is calculated according to the following equation (1) by using the estimation results S1 and S2 and the charging / discharging electric energy ΔAh. can do.

C = ΔAh / (S1-S2) × 100 ... (1)
In S20, the ECU 100 determines whether or not the full charge capacity C calculated in S20 is less than the threshold capacity TH. The threshold capacity TH is a capacity in which it is desirable to recover the full charge capacity C because the full charge capacity C has decreased to some extent. The threshold capacity TH may be a fixed value predetermined based on the results of prior experiments, or may be a variable value appropriately determined according to the usage mode of the vehicle 1. When the full charge capacity C is equal to or greater than the threshold capacity TH (NO in S20), the ECU 100 considers that recovery of the full charge capacity C is not particularly necessary, skips the following processing, and proceeds to the main routine. return.

When the full charge capacity C is less than the threshold capacity TH (YES in S20), the ECU 100 advances the process to S30 and calculates the negative electrode potential V2 of the assembled battery 40 (or any one of the representative cells 41). To do. As described above, the negative electrode potential V2 stores a map (not shown) showing the correspondence between the voltage VB and the negative electrode potential V2 in the memory 102, so that the voltage VB (voltage sensor in the monitoring unit 401) is stored. It can be calculated from the detected value).

In S40, the ECU 100 determines whether or not the negative electrode potential V2 calculated in S30 is within the potential range R. The potential range R is a potential range of 0.3 V or more and 0.9 V or less with reference to the potential of metallic lithium.

When the negative electrode potential V2 is outside the potential range R (NO in S40), the ECU 100 controls charging / discharging of the assembled battery 40 so that the negative electrode potential V2 is within the potential range R (S50).

More specifically, when the negative electrode potential V2 is higher than the upper limit value (0.9 V) of the potential range R, the ECU 100 sets the assembled battery 40 so that the negative electrode potential V2 is equal to or less than the upper limit value of the potential range R. Charge. For example, the ECU 100 can charge the assembled battery 40 by using the electric power supplied from the charging device 9 by controlling the power conversion device 20.

On the other hand, when the negative electrode potential V2 is less than the lower limit value (0.3 V) of the potential range R, the ECU 100 is stored in the assembled battery 40 so that the negative electrode potential V2 is equal to or higher than the lower limit value of the potential range R. Discharge power. For example, the ECU 100 may control the electric power conversion device 20 to discharge the electric power stored in the assembled battery 40 to a load (not shown) outside the vehicle via the charging cable 8. Alternatively, the ECU 100 can discharge the assembled battery 40 by controlling the PCU 60 when the vehicle 1 is running. After the processing of S50 is completed, the processing is returned to S30, so that the assembled battery 40 is appropriately charged and discharged until the negative electrode potential V2 is within the potential range R.

When the negative electrode potential V2 is within the potential range R (YES in S40), the ECU 100 advances the process to S60 and increases the restraining pressure P. The restraint pressure P after the increase is determined based on a preliminary experiment. If the restraining pressure P after the increase is small, the capacity recovery amount of the assembled battery 40 cannot be sufficiently increased. On the other hand, if the amount of increase in the restraint pressure P is set to be excessively large, there is a possibility that a short circuit may occur between the positive electrode 416 and the negative electrode 417 although the separator 418 is interposed. Therefore, the restraint pressure P after the increase can prevent a short circuit between the positive electrode 416 and the negative electrode 417, and the capacity recovery amount of the assembled battery 40 reaches a required amount (0.6 MPa or 0. In the above example. It is preferable to set it to 7 MPa). As a result, a series of processing is completed, and the processing is returned to the main routine.

As described above, according to the present embodiment, the negative electrode potential V2 is set within the specific potential range R in the capacity recovery control of the assembled battery 40 of the lithium ion secondary battery. As a result, it is possible to suppress the deterioration of the negative electrode material due to the decomposition of LiSiO while obtaining the capacity recovery effect of the assembled battery 40. Therefore, the capacity of the assembled battery 40 can be appropriately restored.

The embodiments disclosed this time should be considered as exemplary in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

A secondary battery system, B restraint member, 1 vehicle, 8 charging cable, 9 charging device, 10 inlet, 20 power converter, 30 charging relay, 40 sets of batteries, 41 cells, 42 end plate, 43 restraint band, 44 volts , 45 actuators, 46 bus bars, 50 SMRs, 60 PCUs, 70 motor generators, 80 drive wheels, 100 ECUs, 101 CPUs, 102 memories, 401 monitoring units, 411 battery cases, 412 lids, 413 positive terminals, 414 negative terminals, 415 electrode body, 416 positive electrode, 417 negative electrode, 418 separator.

Claims (1)

An assembled battery containing multiple cells and
A restraining member configured to apply a restraining pressure to the assembled battery by restraining the assembled battery,
A drive device configured to adjust the restraint pressure of the restraint member, and
A control device for controlling the drive device is provided.
Each of the plurality of cells is a lithium ion secondary battery containing a silicon oxide in the negative electrode.
When the capacity of the assembled battery is lower than the reference value and the potential of the negative electrode is within a predetermined potential range, the control device is compared with the case where the capacity of the assembled battery is higher than the reference value. , The driving device is controlled so that the restraining pressure is increased.
The predetermined potential range is a secondary battery system in which the potential of the negative electrode is 0.3 V or more and 0.9 V or less based on the metallic lithium potential.

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