JP2017037734A - Secondary battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To timely determine whether overcharge processing of a battery should be executed or not in a secondary battery system having a battery containing a lithium ion secondary battery and an electrical load.SOLUTION: An ECU 300 carries out a IV measurement for measuring a variation amount ΔV of a battery voltage VB when charging/discharging is performed with predetermined input/output current IB between after stop of the operation of PCU 200 and before start of the operation. Results of at least three IV measurements which are performed under the condition that the battery temperature TB is different and the charging time or discharging time is different among the IV measurements are plotted on a graph in which 1/TB is set on the abscissa axis and |ΔV| is set on the ordinate axis, the ECU 300 calculates the gradient of a straight line obtained by linearly approximating at least three plotted points as a current value E of the activation energy of a side reaction. When the rate R of the current value E to the initial value E0 of the activation energy exceeds 1.05, the ECU 300 performs overdischarge processing.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a secondary battery system, and more particularly to a secondary battery system including a lithium ion secondary battery.

  It is known that a lithium ion secondary battery can be deteriorated depending on the mode of storage or charge / discharge. A factor causing such deterioration is a side reaction of the lithium ion secondary battery. By the side reaction, the electrolyte or the solvent in the electrolytic solution is decomposed to form a film on the negative electrode surface. Thereby, the capacity maintenance rate of a lithium ion secondary battery falls.

  The ease with which a side reaction occurs in a lithium ion secondary battery is expressed by the activation energy of the side reaction. Therefore, it has been proposed to control charging / discharging of the lithium ion secondary battery according to the activation energy of the side reaction. For example, Japanese Patent Laying-Open No. 2005-149793 (Patent Document 1) discloses a method for calculating a charge / discharge upper limit temperature of a lithium ion secondary battery. In this calculation method, the activation energy of the side reaction is obtained from the use temperature of the lithium ion secondary battery and the amount of decrease in capacity at that temperature. And the charging / discharging temperature when activation energy changes is set as charging / discharging upper limit temperature.

JP 2005-149793 A

  When the capacity retention rate of the battery decreases due to a side reaction of the lithium ion secondary battery, it is desirable to overdischarge the battery. Thereby, since the film formed on the negative electrode surface is removed, the capacity retention rate can be recovered. This process is also referred to as “overdischarge process” in this specification.

  Here, according to the calculation method disclosed in Patent Document 1, the activation energy of the side reaction is represented by a logarithmic display indicating the deterioration rate per charge / discharge cycle of a battery including a lithium ion secondary battery. It is calculated based on a graph (see FIG. 3 of Patent Document 1) with the horizontal axis representing the reciprocal of the discharge temperature. In order to create this graph, the battery is repeatedly charged and discharged within a predetermined temperature range.

  More specifically, the battery is charged by, for example, a constant current / constant voltage method. That is, charging at a constant current is performed until the battery voltage reaches the upper limit charging voltage, and after the battery voltage reaches the upper charging limit, charging is performed for a predetermined time while maintaining the voltage. On the other hand, the battery is discharged by, for example, a constant current method. That is, discharging at a constant current is performed until the battery voltage reaches the discharge lower limit voltage (see paragraphs [0031] and [0032] of Patent Document 1).

  In general, such charge / discharge control requires a relatively long time. Therefore, for example, when a battery is mounted on an electric vehicle and configured to be able to supply electric power to an electric load (such as a drive inverter of a motor of the electric vehicle), the time for executing the above-described charge / discharge control is set. It may be difficult to secure. That is, with the calculation method disclosed in Patent Document 1, it may be difficult to create the graph under the actual usage conditions of the battery. If it does so, it may become difficult to determine timely about whether to perform the overdischarge process of a battery.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a side reaction of a lithium ion secondary battery in a secondary battery system including a battery including a lithium ion secondary battery and an electric load. It is to provide a technique capable of determining in a timely manner whether or not to perform battery overdischarge processing according to activation energy.

  A secondary battery system according to an aspect of the present invention includes a power storage device including a lithium ion secondary battery, an electric load that operates using power supplied from the power storage device, and an overdischarge of the power storage device, thereby And a control device that performs an overdischarge process for recovering the capacity of the battery. The control device measures the amount of change in the voltage of the power storage device when the power storage device is charged or discharged at a predetermined current value after the operation of the electric load is stopped and before the operation of the electric load is started. To implement. Further, in the graph in which the horizontal axis represents the reciprocal of the temperature of the power storage device and the vertical axis represents the absolute value of the voltage change amount, the control device has different power storage device temperatures, and the charge time or discharge time of the power storage device. When the results of at least three current-voltage measurements performed under different conditions are plotted, the slope of the straight line obtained by linearly approximating at least three plotted points is expressed as the side reaction of the power storage device. Calculated as activation energy. When the ratio of the calculated activation energy to the activation energy in the initial state of the power storage device exceeds 1.05, the control device performs an overdischarge process.

  According to the above configuration, the activation energy is calculated based on the amount of change in the voltage of the power storage device when the power storage device is charged or discharged at a predetermined current value. Since this current / voltage measurement requires only a short time, it can be performed after the operation of the electric load is stopped and before the operation of the electric load is started. Therefore, it is possible to determine in a timely manner whether or not to perform the overdischarge process of the power storage device, according to the calculation result of the activation energy by the current voltage measurement.

  According to the present invention, in a secondary battery system including a battery including a lithium ion secondary battery and an electric load, the battery is overdischarged according to the activation energy of the side reaction of the lithium ion secondary battery. Whether or not to do so can be determined in a timely manner.

It is a block diagram which shows roughly the whole structure of the vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a figure which shows the structure of a battery in detail. It is a figure which shows the structure of a cell in detail. It is a figure for demonstrating the method of a current-voltage measurement. It is a figure for demonstrating the calculation method of the activation energy of the side reaction of the battery in this Embodiment. It is a figure for demonstrating the change of the activation energy of a side reaction. It is a figure which shows the relationship between the ratio of the activation energy of a side reaction, the film quantity formed in the negative electrode, and the capacity maintenance rate of a battery. It is a flowchart for demonstrating the battery overdischarge process performed in this Embodiment.

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

  In the embodiments described below, a configuration in which the secondary battery system according to the present invention is mounted on a hybrid vehicle will be described as an example. However, the vehicle on which the secondary battery system according to the present invention can be mounted is not limited to a hybrid vehicle as long as a battery is mounted, and may be an electric vehicle or a fuel vehicle. Furthermore, the use of the secondary battery system according to the present invention is not limited to vehicles.

<Vehicle configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to the present embodiment. Referring to FIG. 1, vehicle 1 is a hybrid vehicle, and includes secondary battery system 2, first motor generator (MG) 10, second MG 20, power split mechanism 30, and drive wheels 40. The engine 50 is provided. The secondary battery system 2 includes a battery 100, a voltage sensor 102, a current sensor 104, a temperature sensor 106, a system main relay 150, a power control unit (PCU) 200, and an electronic control unit (ECU). : Electronic Control Unit) 300.

  The engine 50 is an internal combustion engine such as a gasoline engine or a diesel engine. Engine 50 generates a driving force for vehicle 1 to travel in response to a control signal from ECU 300.

  Each of first MG 10 and second MG 20 is a three-phase AC rotating electric machine. First MG 10 is coupled to the crankshaft of engine 50 via power split mechanism 30. When starting engine 50, first MG 10 uses the power of battery 100 to rotate the crankshaft of engine 50. The first MG 10 can also generate power using the power of the engine 50. The AC power generated by the first MG 10 is converted into DC power by the PCU 200 and charged to the battery 100. Further, the AC power generated by the first MG 10 may be supplied to the second MG 20.

  Second MG 20 rotates the drive shaft using at least one of the electric power from battery 100 and the electric power generated by first MG 10. The second MG 20 can also generate power by regenerative braking. The AC power generated by the second MG 20 is converted into DC power by the PCU 200 and charged to the battery 100.

  Power split device 30 mechanically connects the three elements of the crankshaft of engine 50, the rotation shaft of first MG 10 and the drive shaft.

  Although not shown, PCU 200 includes two inverters and a converter. Each of the two inverters is a general three-phase inverter. During the boosting operation, the converter boosts the voltage supplied from the battery 100 and supplies the boosted voltage to the inverter. During the step-down operation, the converter steps down the voltage supplied from the inverter and charges battery 100. The PCU 200 corresponds to an “electric load” according to the present invention.

  SMR 150 is connected to a current path connecting battery 100 and PCU 200. The closing / opening of the SMR 150 is controlled according to a control signal from the ECU 300. When SMR 150 is closed, power can be exchanged between battery 100 and PCU 200.

  The battery 100 is a power storage device configured to be rechargeable. In the present embodiment, a lithium ion secondary battery is employed as the battery 100. The configuration of the battery 100 will be described with reference to FIGS.

  The voltage sensor 102 detects the voltage (battery voltage) VB of the battery 100. The current sensor 104 detects a current (input / output current) IB input / output to / from the battery 100. The temperature sensor 106 detects the temperature (battery temperature) TB of the battery 100. Each sensor outputs a signal indicating the detection result to ECU 300.

  ECU 300 includes a CPU (Central Processing Unit) (not shown), a memory 302, an input / output buffer, and the like. ECU 300 controls each device so that vehicle 1 is in a desired state based on a signal received from each sensor and a map and a program stored in memory 302. More specifically, ECU 300 controls charging / discharging of battery 100 based on battery voltage VB, input / output current IB, and battery temperature TB. The ECU 300 corresponds to a “control device” according to the present invention.

  FIG. 2 is a diagram showing the configuration of the battery 100 in more detail. Referring to FIG. 2, battery 100 includes a plurality of cells 110, a pair of end plates 120, a restraining band 130, and a plurality of bus bars 140.

  A stacked body is formed by stacking a plurality of cells 110. In FIG. 2, one end in the stacking direction of the stacked body is partially shown. A pair of end plates 120 are arranged so as to face the one end and the other end in the stacking direction. The pair of end plates 120 are restrained by the restraining band 130 in a state where all the cells 110 are sandwiched. Each cell 110 has a positive terminal 113 and a negative terminal 114 (see FIG. 3). A positive electrode terminal 113 of a certain cell and a negative electrode terminal 114 of an adjacent cell are electrically connected by being fastened by a bus bar 140. Thereby, a plurality of cells 110 are connected in series.

  FIG. 3 is a diagram for explaining the configuration of the cell 110 in more detail. In FIG. 3, the cell 110 is shown through the inside.

  Referring to FIG. 3, cell 110 has a battery case 111 having a substantially rectangular parallelepiped shape. The upper surface of the battery case 111 is sealed with a lid 112. One end of each of the positive terminal 113 and the negative terminal 114 protrudes from the lid 112 to the outside. The other ends of the positive electrode terminal 113 and the negative electrode terminal 114 are respectively connected to an internal positive electrode terminal and an internal negative electrode terminal (both not shown) inside the battery case 111. An electrode body 115 is accommodated in the battery case 111. The electrode body 115 is formed by laminating a positive electrode 116 and a negative electrode 117 via a separator 118 and winding the laminated body. The electrolytic solution is held by the positive electrode 116, the negative electrode 117, the separator 118, and the like.

As the positive electrode 116, the negative electrode 117, the separator 118, and the electrolytic solution, conventionally known configurations and materials can be used as the positive electrode, the negative electrode, the separator, and the electrolytic solution of the lithium ion secondary battery, respectively. As an example, the electrolyte includes an organic solvent (for example, a mixed solvent of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate)), a lithium salt (for example, LiPF ₆ ), and an additive (for example, LiBOB). (Lithium bis (oxalate) borate) or Li [PF ₂ (C ₂ O ₄ ) ₂ ]).

<Activation energy of side reaction and overdischarge treatment>
The battery 100 having the above configuration can be deteriorated depending on the mode of storage or charge / discharge. As a factor that causes deterioration of the battery 100, a side reaction of the lithium ion secondary battery can be cited. By the side reaction, the electrolyte or the solvent in the electrolytic solution is decomposed to form a film on the negative electrode surface. Thereby, the capacity maintenance rate of the battery 100 decreases.

  The ease with which a side reaction occurs in a lithium ion secondary battery is expressed by the activation energy of the side reaction. In general, the side reaction is less likely to occur as the deposition amount (the coating amount) of the coating formed on the negative electrode surface increases. That is, as the coating amount increases, the side reaction activation energy increases. Conversely, the activation energy of the side reaction can be used as an index value indicating the coating amount.

  When deterioration of the battery 100 progresses and the activation energy of the side reaction becomes larger than a predetermined value, an excessive film may be formed on the negative electrode surface, so it is desirable to remove the film. . Therefore, it is conceivable that an overdischarge process for recovering the capacity of the battery 100 is performed by overdischarging the battery 100 until the battery voltage VB falls below the reference value. As an example, constant current discharge at 1 C can be performed until the voltage of each cell 110 becomes 2.5 V or less. Thereby, since a film is removed, the capacity maintenance rate of the battery 100 can be recovered.

  For example, as disclosed in Patent Document 1, the activation energy of the side reaction is calculated by repeatedly charging and discharging the battery within a predetermined temperature range. For example, charging at a constant current is performed until the battery voltage reaches the charging upper limit voltage, and after the battery voltage reaches the charging upper limit voltage, charging is performed for a predetermined time while maintaining the voltage. Alternatively, discharging at a constant current is performed until the battery voltage reaches the discharge lower limit voltage. Such charge / discharge control often takes a long time. Therefore, when the battery 100 is mounted on the hybrid vehicle as in the present embodiment, it may be difficult to secure time for executing the above-described charge / discharge control.

  Therefore, according to the present embodiment, the current and voltage of battery 100 are measured in a stopped state of PCU 200 that is the electrical load of vehicle 1 (that is, after the operation of PCU 200 is stopped and before the operation of PCU 200 is started). And the structure which determines whether the overdischarge process of the battery 100 is implemented according to the measurement result is employ | adopted. Hereinafter, this current-voltage measurement is also referred to as “IV measurement”.

<IV measurement>
FIG. 4 is a diagram for explaining a method of IV measurement. In FIG. 4, the horizontal axis represents elapsed time. The vertical axis represents the input / output current IB and the battery voltage VB in order from the top. The input / output current IB is expressed with a discharge current from the battery 100 as a positive value and a charge current to the battery 100 as a negative value.

  Referring to FIG. 4, battery 100 is not charged / discharged during the period up to time t. The input / output current IB is substantially 0, and the battery voltage VB is Vo.

  During the period from time t to time (t + Δt), a discharge current flows in a pulse shape. The period Δt during which the discharge current flows is desirably 1 ms or more and 0.1 s or less, for example. When the reciprocal of the period Δt is expressed as a frequency f (f = 1 / Δt), the frequency f is preferably 10 Hz or more and 1000 Hz or less. Further, the peak value Io of the discharge current is desirably 1 C or less, for example. As the discharge current flows, the battery voltage VB decreases from Vo by ΔV. This change amount ΔV is detected by the voltage sensor 102.

  Thus, the IV measurement of the battery 100 can be performed in a short time because it is only necessary to flow the pulsed input / output current IB through the battery 100. Therefore, the IV measurement can be performed after the vehicle 1 finishes running and after the PCU 200 stops operating and before the PCU 200 starts operating.

  Although the example in which the battery 100 is discharged has been described here, the change amount ΔV of the battery voltage VB may be measured when the battery 100 is charged. Further, the number of pulses is not limited to one. An average value of the change amount Vo of the battery voltage VB may be calculated for a plurality of pulsed charging currents or discharging currents.

<Calculation of activation energy>
By performing the IV measurement and obtaining the change amount ΔV of the battery voltage VB, the activation energy of the side reaction of the lithium ion secondary battery can be calculated as described below. Whether or not to perform the overdischarge process of the battery 100 is determined according to the calculated activation energy of the side reaction.

  FIG. 5 is a diagram for explaining a method for calculating the activation energy of the battery 100 in the present embodiment. In FIG. 5 and FIG. 6 described later, the horizontal axis represents the reciprocal number (1 / TB) of the battery temperature TB. The vertical axis represents the absolute value | ΔV | of the variation ΔV of the battery voltage VB.

  Referring to FIG. 5, each of P <b> 1 to P <b> 3 is a measurement point indicating a result of performing three IV measurements. These IV measurements are performed under conditions where the battery temperatures TB are different from each other and the frequencies f (that is, the period Δt during which the battery 100 is charged or discharged) are different from each other. The measurement point P1 indicates a change amount ΔV of the battery voltage VB when the IV measurement is performed at the frequency f1 in an environment where the battery temperature TB is T1. The measurement point P2 indicates a change amount ΔV of the battery voltage VB when IV measurement is performed at the frequency f2 in an environment where the battery temperature TB is T2. The measurement point P3 indicates a change amount ΔV of the battery voltage VB when the IV measurement is performed at the frequency f3 in an environment where the battery temperature TB is T3.

  As an example, the battery temperature TB and the frequency f can be set as follows. For measurement point P1, T1 = 40 ° C. and f1 = 1000 Hz. For measurement point P2, T2 = 25 ° C. and f2 = 100 Hz. For measurement point P3, T3 = 10 ° C. and f3 = 10 Hz.

  Of the three IV measurements, the measurement under a relatively low temperature condition is performed when the amount of heat generated from the battery 100 is relatively small, for example, after the vehicle 1 has traveled for a short time, or the vehicle 1 This can be done when the vehicle is parked indoors or in the shade, or during periods of low outside temperature. Alternatively, when the battery 100 is provided with a cooling mechanism such as a fan, the IV measurement may be performed after the battery 100 is cooled by the cooling mechanism.

  On the other hand, the IV measurement under a relatively high temperature condition is performed when the amount of heat generated from the battery 100 is relatively large, for example, after the vehicle 1 travels for a long time, or when the vehicle 1 stops outdoors or in the sun. It can be carried out during the day or during a time when the outside temperature is high. Alternatively, when the battery 100 is provided with a heating mechanism such as a heater, the IV measurement may be performed after the battery 100 is heated by the heating mechanism.

  Since the number of measurements may be at least 3 or more, it may be 4 or more. It is desirable to perform these measurements in a short period of time. For example, three measurements can be performed on the same day. This is because if the IV measurement result carried out over a long period (for example, several months) is used, the deterioration state of the battery 100 changes during that time, and the calculation accuracy of the activation energy may be lowered.

  The measurement points P1 to P3 can be linearly approximated. The slope of the straight line L obtained by the linear approximation corresponds to the activation energy of the side reaction in the current battery 100.

  FIG. 6 is a diagram for explaining a change in the activation energy of the side reaction. With reference to FIG. 6, straight line La indicates a straight line obtained in the initial state of battery 100. The straight line Lb indicates a straight line acquired when the battery 100 has been deteriorated to some extent. The straight line Lc indicates a straight line acquired when the deterioration of the battery 100 further proceeds than when the straight line Lb is acquired.

  The inclination of the straight line Lb is larger than the inclination of the straight line La, and the inclination of the straight line Lc is further larger than the inclination of the straight line Lb. Thereby, it is shown that the activation energy of the side reaction of the battery 100 increases as the deterioration of the battery 100 progresses.

  Hereinafter, the ratio of the current value E of activation energy based on the initial value E0 of activation energy (activation energy corresponding to the slope of the straight line La) is referred to as “ratio R” (R = E / E0). . That is, the straight line La corresponds to a state where the ratio R = 1.000. The straight line Lb corresponds to a state where the ratio R = 1.050. The straight line Lc corresponds to a state where the ratio R = 1.100.

  FIG. 7 is a diagram showing the relationship between the activation energy ratio R of the side reaction, the amount of coating formed on the negative electrode 117, and the capacity retention rate of the battery 100. In FIG. 7, the horizontal axis represents the ratio R. The left vertical axis represents the coating amount. The vertical axis on the right represents the capacity maintenance rate of the battery 100. The capacity maintenance rate is a value indicating how much the current capacity has decreased with respect to the initial capacity (reference capacity) of the battery 100.

  Referring to FIG. 7, when the ratio R = 1.000 is compared with the ratio R = 1.005, the coating amount is hardly changed. On the other hand, it can be seen that when the ratio R is 1.050 or more, the coating amount is significantly increased as compared with the case where the ratio R is less than 1.050. Furthermore, it turns out that the capacity | capacitance maintenance factor of the battery 100 falls with the increase in the amount of films. From FIG. 7, when the ratio R is 1.050 or more, the amount of decrease in the capacity retention rate from the initial state of the battery 100 increases. Therefore, when the ratio R is 1.050 or more, it is desirable to perform the overdischarge process of the battery 100.

  FIG. 8 is a flowchart for explaining overdischarge processing of battery 100 executed in the present embodiment. Each step (hereinafter abbreviated as S) shown in this flowchart is called from the main routine and executed every predetermined time or when a predetermined condition is satisfied.

  Referring to FIGS. 1 to 3 and 8, in S10, ECU 300 determines whether or not the operation of PCU 200 is stopped, that is, whether or not the power supply from battery 100 to PCU 200 is stopped. judge. If the operation of PCU 200 is not stopped (NO in S10), ECU 300 skips the subsequent processing and returns the processing to the main routine.

  On the other hand, when operation of PCU 200 is stopped (YES in S10), ECU 300 performs IV measurement of battery 100. Since the method for performing the IV measurement has been described in detail with reference to FIG. 4, the description will not be repeated. ECU 300 stores in memory 302 a count value indicating the number of times of IV measurement. The initial value of the count value is 0. ECU 300 increments the count value after performing the IV measurement.

  In S30, the ECU 300 determines whether or not the number of IV measurements is 3 or more based on the count value. In this determination, when the number of IV measurements is one or two (NO in S30), ECU 300 skips the subsequent processing and returns the processing to the main routine.

  If the number of IV measurements is three or more (YES in S30), ECU 300 advances the process to S40 and calculates current value E of activation energy. Since this calculation method has been described in detail with reference to FIGS. 4 and 5, the description thereof will not be repeated here.

  In S50, the ECU 300 reads the initial value E0 of the activation energy of the side reaction of the battery 100 from the memory 302 (S50). As the initial value E0 of the activation energy, for example, IV measurement of the battery 100 can be executed before shipment of the vehicle 1, and a value calculated from the measurement result can be stored in the memory 302. Alternatively, instead of such measurement, a representative value obtained from the specifications of the battery 100 may be stored in the memory 302. Note that the order of the process of S40 and the process of S50 may be switched.

  In S60, ECU 300 calculates a ratio R of current value E to initial value E0 of activation energy (R = E / E0). Then, ECU 300 determines whether or not ratio R is 1.05 or more (S70). When ratio R is 1.05 or more (YES in S70), ECU 300 may have an excessive film formed on the negative electrode surface of battery 100 due to a side reaction, and the capacity maintenance rate of battery 100 may be reduced. The battery 100 is overdischarged as high. Thereby, the capacity maintenance rate of the battery 100 can be recovered.

  On the other hand, when ratio R is less than 1.05 (NO in S70), ECU 300 determines that the amount of the coating formed on the negative electrode surface of battery 100 is relatively small and performs the process without performing the overdischarge process of battery 100. Return to the main routine.

  As described above, according to the present embodiment, the activation energy of the side reaction of the lithium ion secondary battery is the change in the battery voltage VB when the battery 100 is charged or discharged at the predetermined current value (Io). It is calculated based on the quantity ΔV. Since this IV measurement requires only a short time, it can be performed after the PCU 200 stops operating and before the PCU 200 starts operating. Therefore, it is possible to determine in a timely manner whether or not to perform the overdischarge process of the battery 100 according to the calculation result of the activation energy based on the IV measurement.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 10 1st motor generator, 20 2nd motor generator, 30 Power split mechanism, 40 Driving wheel, 50 Engine, 100 Battery, 102 Voltage sensor, 104 Current sensor, 106 Temperature sensor, 110 cell, 111 Battery case, 112 Cover body, 113 positive electrode terminal, 114 negative electrode terminal, 115 electrode body, 116 positive electrode, 117 negative electrode, 118 separator, 120 end plate, 140 restraint band, 160 bus bar, 300 ECU, 302 memory.

Claims (1)

A power storage device including a lithium ion secondary battery;
An electrical load that operates using electric power supplied from the power storage device;
A controller for performing an overdischarge process for recovering the capacity of the power storage device by overdischarging the power storage device;
The controller is
Current voltage measurement for measuring the amount of change in the voltage of the power storage device when the power storage device is charged or discharged at a predetermined current value after the operation of the electric load is stopped and before the operation of the electric load is started Carried out
In a graph in which the horizontal axis represents the reciprocal of the temperature of the power storage device and the vertical axis represents the absolute value of the change amount of the voltage, the temperatures of the power storage devices are different from each other, and the charging time or discharging time of the power storage device is mutually different. When the results of at least three current-voltage measurements performed under different conditions are plotted, the slope of a straight line obtained by linearly approximating at least three plotted points is expressed as a side reaction of the power storage device. Calculated as activation energy,
The secondary battery system which performs the said overdischarge process, when the ratio of the calculated activation energy with respect to the activation energy in the initial state of the said electrical storage apparatus exceeds 1.05.