Control system of secondary battery, and control method of secondary battery using the same

Abstract

To provide a control system of secondary battery capable of allowing reverse current flow considering charge and discharge conditions.SOLUTION: A control system 500 includes an execution unit 401 that executes a charge / discharge mode in which at least one of charging or discharging is performed with a given first amount of electricity to a secondary battery 100, and a convergence mode to accelerate the convergence of the open circuit voltage of the secondary battery after the charge / discharge mode. The convergence mode includes a first power supply mode in which the current flows in the opposite direction to the current flow in the charge / discharge mode at the first current value with a second amount of electricity smaller than the first amount of electricity to a secondary battery 100.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Lithium ion secondary batteries are a type of non-aqueous electrolyte secondary battery that has a high energy density and is therefore used as a battery for portable devices and, in recent years, as a battery for trains, aircraft, ships, electric vehicles, etc. However, it is known that lithium ion secondary batteries deteriorate with use, causing an increase in internal resistance and a decrease in charge / discharge capacity.

[0002] In lithium ion secondary batteries, lithium metal oxide is used as the positive electrode active material, and carbon materials such as graphite, silicon materials, lithium metal oxide, etc. are used as the negative electrode active material. The positive and negative electrodes constituting the lithium ion secondary battery can be formed, for example, by applying a slurry containing a binder, a conductive agent, etc. to a metal foil in a group of minute active material particles.

[0003] In a lithium-ion secondary battery, during charging, lithium ions released from the positive electrode active material are absorbed into the negative electrode active material. On the other hand, during discharging, the lithium ions absorbed into the negative electrode active material are released, and the released lithium ions are absorbed into the positive electrode active material. In this way, the lithium ions move between the electrodes, causing a current to flow between the electrodes of an external circuit. In a lithium-ion secondary battery, the battery capacity is reduced due to (1) electrical isolation of the positive electrode active material, (2) electrical isolation of the negative electrode active material, and (3) immobilization of the lithium ions moving between the electrodes.

[0004] The abstract of Patent Document 1 states that "The voltage measurement unit measures the cell voltage. The control unit controls the charging and discharging of the cell. After charging and discharging of the cell is completed, the control unit controls the flow of a reverse current to the cell to cancel out the polarization voltage of the cell. For example, the control unit sets a current command value in the power conversion device that instructs the power conversion device to flow a reverse current of a preset value for a preset period of time after charging and discharging of the cell is completed." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 003582 Summary of the Invention [Problem to be solved by the invention]

[0006] In the invention described in Patent Document 1, the value of the reverse current and the time of current flow are determined in advance by experiments or the like, for example, according to the measured voltage of the cell after charging is completed. However, the conditions of charging and discharging performed before the current flowing in the reverse current are various, and depending on the charging and discharging conditions, the effect of the current flowing in the reverse current is insufficient. The problem to be solved by the present disclosure is to provide a control system for a secondary battery capable of passing a reverse current taking into account charge and discharge conditions, and a control method for a secondary battery using the same. [Means for solving the problem]

[0007] The control system for a secondary battery disclosed herein includes an execution unit that executes a charge / discharge mode in which at least one of charging and discharging is performed with a predetermined first electric quantity with respect to the secondary battery, and a convergence mode that promotes convergence of an open circuit voltage of the secondary battery after the charge / discharge mode, and the convergence mode includes a first current flow mode in which a current of a first current value flows in a direction opposite to the current flow direction in the charge / discharge mode with a second electric quantity smaller than the first electric quantity to the secondary battery. Other solutions will be described later in the description of the embodiment of the invention. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a control system for a secondary battery capable of passing a reverse current taking into account charge and discharge conditions, and a control method for a secondary battery using the same. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram showing a control system for a secondary battery according to the present disclosure. [Diagram 2] FIG. 2 is a block diagram showing a hardware configuration of the control system. [Diagram 3] 11 is a graph showing an example of a result of a regression calculation process. [Figure 4] 4 is a flowchart showing a control method for a secondary battery according to the present disclosure. [Diagram 5] 10 is a flowchart showing a method of controlling a secondary battery in a case where a sleep mode is included. [Figure 6] 1 is a graph showing the relaxation behavior of OCV in Example 1 and Comparative Example 1. [Figure 7] FIG. 2 is an example of a cross-sectional view conceptually illustrating a cell. [Figure 8] FIG. 8 is an example of a cross-sectional view conceptually illustrating an electrode plate assembly of the cell shown in FIG. [Figure 9] FIG. 2 is an example of a configuration diagram conceptually illustrating a battery module. [Figure 10] FIG. 2 is an example of a configuration diagram clearly showing a load used for discharging a battery module. [Figure 11] FIG. 1 is a diagram conceptually illustrating an example of a configuration of a battery pack in which battery modules are connected in parallel. [Figure 12] FIG. 11 is an example of a configuration diagram conceptually illustrating a battery pack in which battery modules are connected in parallel according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a form for carrying out the present disclosure (referred to as an embodiment) will be described with reference to the drawings. In the following description of one embodiment, other embodiments applicable to the one embodiment will also be described as appropriate. The present disclosure is not limited to the following one embodiment, and different embodiments can be combined with each other or modified as desired without significantly impairing the effects of the present disclosure. In addition, the same symbols will be used for the same members, and duplicate descriptions will be omitted. Furthermore, the same names will be used for members having the same functions. The contents shown are merely schematic, and for the sake of illustration, changes may be made from the actual configuration within a range that does not significantly impair the effects of the present disclosure, and some members may be omitted or modified between drawings. In addition, the same embodiment does not necessarily need to have all the configurations.

[0011] 1 is a block diagram showing a control system 500 for a secondary battery according to the present disclosure. The control system 500 controls charging and discharging of a secondary battery 100 and is capable of diagnosing, for example, the degree of deterioration of the secondary battery 100 (FIG. 7, etc.). The degree of deterioration can be diagnosed, for example, by calculating a curve (OCV curve) relating to the open circuit voltage (hereinafter, appropriately referred to as OCV) of the secondary battery 100. First, the control system 500 for the secondary battery 100 and a control method for the secondary battery 100 using the same will be described, and then the control system 500 and the secondary battery 100 to which the control method can be applied will be described.

[0012] 2 is a block diagram showing a hardware configuration of the control system 500. The control system 500 is configured to include, for example, a central processing unit (CPU) 1001, a random access memory (RAM) 1002, a read only memory (ROM) 1003, an interface (I / F) 1004, and a bus 1005. The CPU 1001, the RAM 1002, the ROM 1003, and the interface 1004 are connected via, for example, the bus 1005. The control system 500 is realized by developing a predetermined control program (for example, a control method for the secondary battery 100 of the present disclosure) stored in the ROM 1003 into the RAM 1002 and executing the program by the CPU 1001. Signals and information are exchanged between the control system 500 and various devices (such as servers), an external network, and the like, in terms of hardware, through the interface 1004.

[0013] Returning to Fig. 1, the control system 500 includes an acquisition unit 400, an execution unit 401, a storage unit 402, a determination unit 403, a calculation unit 404, a timer unit 405, and a diagnosis unit 406. The execution unit 401 includes a first execution unit 407, a second execution unit 408, and a third execution unit 409. Information determined (including acquisition, calculation, etc.) by the control system 500 is appropriately stored in the storage unit 402.

[0014] The acquiring unit 400 receives measurement signals from the ammeter 101 and the voltmeter 102 (FIG. 9, etc.). The measurement signals are signals that indicate the state of the secondary battery 100, and are, for example, a current value flowing through the secondary battery 100 and an applied voltage value. The acquiring unit 400 outputs the acquired measurement signals to the executing unit 401. The acquiring unit 400 also associates the measurement signals with the times at which they were measured, and stores them in the memory unit 402 as time-series data of, for example, current values ​​and voltage values.

[0015] The execution unit 401 executes the charge / discharge mode and the convergence mode. The charge / discharge mode is a mode in which at least one of charging and discharging is performed with a predetermined first electric quantity on the secondary battery 100, and is executed by, for example, the first execution unit 407. In the present disclosure, only one of charging and discharging is described as an example, but both charging and discharging may be performed in the charge / discharge mode depending on, for example, the user's desire, the use of the secondary battery 100, and the like.

[0016] The convergence mode is a mode for promoting the convergence of the OCV of the secondary battery 100 after the charge / discharge mode, and is executed by, for example, the second execution unit 408. After the secondary battery 100 is charged or discharged, the OCV naturally converges by maintaining the open circuit state of the secondary battery 100. However, since the time until the convergence may be long, in the present disclosure, the convergence is promoted by executing the convergence mode. Each piece of information determined by the execution unit 401 is stored in the memory unit 402. The amount of electricity can be calculated, for example, by multiplying the current value by the time.

[0017] When the secondary battery 100 is discharged, for example, by connecting it to a load 104 (FIG. 10), the open circuit voltage of the secondary battery 100 increases gradually and converges to a constant voltage value after the discharge is completed. On the other hand, when the secondary battery 100 is charged, for example, by connecting it to a power source (not shown), the open circuit voltage of the secondary battery 100 decreases gradually and also converges to a constant voltage value after the charge is completed. Therefore, the OCV of the secondary battery 100 converges to a constant voltage value after the charge / discharge mode.

[0018] As described above, the deterioration state of the secondary battery 100 can be diagnosed by calculating (determining, acquiring) the OCV curve. However, the OCV curve is calculated using the convergence value of the OCV. Therefore, the time until the OCV curve is calculated can be shortened by shortening the time until the convergence. For this reason, in the present disclosure, after the charge / discharge mode, a convergence mode that promotes the convergence of the OCV is executed.

[0019] The convergence mode includes a first current flow mode in which a current (i.e., a reverse current) is passed through the secondary battery 100 at a second electric quantity smaller than the first electric quantity in the charge / discharge mode and at a first current value in a direction opposite to the current flow direction in the charge / discharge mode. For example, when the secondary battery 100 is charged in the charge / discharge mode, the OCV gradually drops as described above after charging. Therefore, in the convergence mode, the secondary battery 100 is "forced to discharge" by passing a reverse current in a direction opposite to the direction of the current during charging. This allows, for example, lithium ions in the secondary battery 100 to be forced to move in a direction opposite to the movement direction in the charge / discharge mode. This allows the drop in the OCV to be accelerated and the time until convergence to be shortened. These points can also be achieved by "forced charging" in the convergence mode when the secondary battery 100 is discharged in the charge / discharge mode.

[0020] In the charge / discharge mode, the secondary battery 100 is charged or discharged with a first amount of electricity as described above. On the other hand, in the convergence mode, the secondary battery 100 is charged or discharged with a second amount of electricity smaller than the first amount of electricity as described above. Therefore, a part of the first amount of electricity charged in the charge / discharge mode is discharged in the convergence mode. Similarly, a part of the first amount of electricity discharged in the charge / discharge mode is charged in the convergence mode. The amount of electricity discharged or charged in the convergence mode is the second amount of electricity smaller than the first amount of electricity as described above. Therefore, even after the convergence mode, the effect (capacity) of charging or discharging in the charge / discharge mode can remain. That is, if the second amount of electricity is larger than the first amount of electricity, the convergence mode is performed so as to "overwrite" the capacity of the secondary battery 100 that has changed in the charge / discharge mode, so that there is no need to perform the charge / discharge mode. However, as in the present disclosure, by making the second amount of electricity smaller than the first amount of electricity, the effect of the charge / discharge mode can be retained, and the promotion effect of OCV in the subsequent convergence mode can be achieved.

[0021] The duration of current flow in the first current flow mode is not particularly limited, but is preferably short in order to reduce the time required for OCV to converge, and more specifically, is preferably several seconds (e.g., 1 to 5 seconds). The current flowing in the first current flow mode may be, for example, a pulse current.

[0022] In the convergence mode, as described above, a current is passed so that the second amount of electricity becomes smaller than the first amount of electricity, which is the amount of electricity charged and discharged in the charge / discharge mode. This makes it possible to prevent, for example, excessive discharging if the current is applied to a charged secondary battery 100, and excessive charging if the current is applied to a discharged secondary battery 100, and to prevent a significant decrease in the effect of charging and discharging in the charge / discharge mode.

[0023] The second electrical quantity is not particularly limited as long as it is smaller than the first electrical quantity, but is, for example, greater than 0% and not greater than 20%, preferably greater than 0% and not greater than 15%, more preferably greater than 0% and not greater than 10%, and particularly preferably greater than 0% and not greater than 5% of the first electrical quantity.

[0024] The first electric quantity may be, for example, a value determined in advance for diagnosing the secondary battery 100, or may be any value (which may be a fixed value or a variable value) determined according to the desire of the user, the use of the secondary battery 100, etc. Therefore, the second electric quantity may also be determined according to the set first electric quantity.

[0025] The convergence mode includes a pause mode. In the pause mode, the execution unit 401 measures the time change of the OCV for the secondary battery 100 in an open circuit state. The pause mode can be executed, for example, after the first current application mode. By measuring the time change, time series data of the OCV can be obtained, and the convergence direction (relaxation direction) of the OCV can be detected.

[0026] That is, for example, if the secondary battery 100 is charged in the charge / discharge mode and the OCV drops in the pause mode, the convergence of the OCV can be further promoted by applying a reverse current in the first current conduction mode performed after the pause mode. On the other hand, if the secondary battery 100 is charged in the charge / discharge mode, the OCV should drop in the pause mode, but if the OCV rises, the flow of the reverse current may have caused the OCV to overshoot the value at which it should converge. In this case, the convergence of the OCV can be promoted by carrying out the second current conduction mode described below to carry a forward current.

[0027] Although it is preferable that the OCV overshoot does not occur, it cannot be said that it will never occur. For this reason, in the present disclosure, the charge and discharge of the secondary battery 100 is controlled assuming that an overshoot occurs. This makes it possible to prevent the time until the OCV converges from becoming significantly longer even if an unintended overshoot occurs.

[0028] As described above, in convergence mode, the voltage value rises or falls to converge (approach) a certain voltage value (the value to which it should converge). Convergence proceeds by a gradual rise or fall as it approaches the certain value. In other words, when a graph is drawn with time on the horizontal axis and OCV on the vertical axis, the graph is drawn such that the slope of the tangent line to the graph gradually decreases over time. Therefore, by measuring the change in OCV over time in sleep mode, the timing of convergence can be ascertained.

[0029] The pause mode can be performed after the first current conduction mode, but may also be performed between the charge / discharge mode and the first current conduction mode (i.e., before the first current conduction mode). In this manner, the change over time of the OCV immediately after the charge / discharge mode can be grasped, and the current value of the reverse current to be applied in the first current conduction mode can be determined based on the change over time, as will be described in detail later.

[0030] The execution unit 401 executes the first current-carrying mode after the sleep mode. The first current-carrying mode is usually executed following the sleep mode. At the same time, the execution unit 401 determines, based on the above-mentioned time change in the sleep mode, a current value in the first current-carrying mode executed after the sleep mode in which the above-mentioned time change was measured.

[0031] As described above, the timing of convergence can be grasped from the change in the OCV over time. Therefore, if it is considered that the convergence will take more time from the end of the pause mode, the current value can be increased in the first current-flow mode after the pause mode to greatly promote the convergence. On the other hand, if it is considered that the convergence will occur immediately after the end of the pause mode, the current value can be decreased (may be 0) to hardly promote the convergence. In such a case, for example, the time change rate of the OCV calculated from the time change in the pause mode is less than the predetermined threshold value. Therefore, the time until the convergence can be further shortened by determining the current value in the first current-flow mode based on the time change of the OCV. In addition, if the change rate is relatively small, the current value can also be decreased, so that the overshoot of the OCV can be suppressed.

[0032] The method for determining the first current value is not particularly limited, but for example, the first current value can be determined based on the slope of the tangent to a graph with the horizontal axis representing time and the vertical axis representing OCV (synonymous with the time rate of change of OCV). The time rate of change of OCV is the rate of change of OCV per any unit time, for example, from 1 second to 1 minute, and can be calculated from the time change in the pause mode.

[0033] For example, a reference value (initial value) of the reference current value is determined in advance, and the reference value is stored in the storage unit 402. Then, the value obtained by multiplying the reference value by the slope of the graph (which may be an absolute value or may include a sign (plus or minus)) can be used as the first current value. The greater the time rate of change of the OCV, the greater the slope, and therefore the greater the value obtained by multiplying the reference value. Therefore, by using such a method, the first current value can be easily determined. Also, by basing it on the time change in "second units" within one minute, for example, the behavior of the time change of the OCV can be quickly grasped, and the time until convergence is detected can be shortened.

[0034] As an even simpler method for determining the first current value, a relatively large third current value may be set when the time rate of change of the OCV is equal to or greater than a predetermined threshold, and a relatively small fourth current value (smaller than the third current value) may be set when the time rate of change of the OCV is less than the predetermined threshold. This makes it even easier to determine the current value, since it is only necessary to compare the magnitude with respect to the predetermined threshold.

[0035] When it is determined that the OCV has not yet converged in the pause mode, the execution unit 401 executes the first current-flow mode after the pause mode in which the time change was measured. In this way, the convergence can be promoted and the time until the convergence can be shortened. The first current-flow mode is usually executed following the pause mode.

[0036] The determination as to whether or not convergence has occurred can be performed, for example, by the later-described determination unit 403. A specific determination method performed by the determination unit 403 will be described later.

[0037] The convergence mode includes a second current conduction mode in which a current (forward current) with a second current value flows in the same direction (forward direction) as the current conduction direction in the charge / discharge mode to the secondary battery 100. Then, the execution unit 401 executes either the first current conduction mode or the second current conduction mode after the sleep mode based on the time change of the OCV in the sleep mode. Either the first current conduction mode or the second current conduction mode is usually executed following the sleep mode.

[0038] For example, after discharging in the charge / discharge mode, a current in the reverse direction (reverse current) is applied to the secondary battery 100 in the first current application mode included in the convergence mode. In this case, if the second electric quantity is appropriate, the OCV rises within a range that does not exceed a certain voltage value to be converged. At this time, the time rate of change of the OCV becomes positive.

[0039] However, if the second electric quantity is smaller than the first electric quantity but exceeds the certain voltage value to which the voltage should converge, the OCV "overshoots," so to speak. In the overshoot state, the first current flow mode ends and the pause mode is entered. In the pause mode, the OCV drops toward the certain voltage value to which the voltage should converge. Therefore, the time rate of change of the OCV becomes negative. In this case, the second current flow mode included in the convergence mode causes a current to flow in the same direction as the current flow in the charge / discharge mode, accelerating the drop. This shortens the time until convergence.

[0040] In this way, by selecting either the first current supply mode or the second current supply mode after the pause mode based on the change over time in the pause mode, the time until convergence can be shortened.

[0041] The method of determining the second current value is not particularly limited, but the second current value can be determined, for example, in the same manner as the method of determining the first current value. The second current value is usually smaller than the first current value. The reason for this is that, for example, when an overshoot or the like occurs in the first current conduction mode, the current is conducted at the second current conduction mode, and the fluctuation range of the OCV is smaller in the second current conduction mode than in the first current conduction mode. However, the second current value does not need to be smaller than the first current value, and may be the same as or larger than the first current value depending on the user's desire, the application of the secondary battery 100, and the like.

[0042] As another method of selecting the first or second current conduction mode, the execution unit 401 executes the second current conduction mode when a predetermined condition is satisfied, and executes the first current conduction mode when the predetermined condition is not satisfied. The predetermined condition here includes at least one of the first condition and the second condition. The first condition is a condition in which the secondary battery 100 is discharged in the charge / discharge mode, and the time rate of change of the OCV determined from the above-mentioned time change is a negative value. The second condition is a condition in which the secondary battery 100 is charged in the charge / discharge mode, and the time rate of change determined from the time change of the OCV is a positive value. In this way, an overshoot of the OCV due to the first current conduction mode in the convergence mode can be detected, and control can be performed to eliminate the overshoot.

[0043] The duration of current flow in the second current flow mode is not particularly limited, but is preferably short in order to reduce the time required for OCV to converge, and more specifically, is preferably several seconds (e.g., 1 to 5 seconds). The current flowing in the second current flow mode may be, for example, a pulse current.

[0044] The storage unit 402 stores each piece of information determined by the execution unit 401, the determination unit 403, the calculation unit 404, the timer unit 405, and the diagnosis unit 406. Furthermore, the storage unit 402 outputs the information stored in the storage unit 402 to the execution unit 401, the determination unit 403, the calculation unit 404, and the diagnosis unit 406 as appropriate.

[0045] The storage unit 402 also stores in advance information about the secondary battery 100, such as the correspondence (e.g., a table, function, etc.) between the battery voltage and the battery charging rate (SOC) of the secondary battery 100, the initial capacity of the secondary battery 100, the upper and lower limit voltages of the secondary battery 100, and maximum charge and discharge current values. The storage unit 402 also stores in advance electrode information, such as reference masses of the positive electrode 7 and negative electrode 8 (both shown in FIG. 8, etc.) constituting the secondary battery 100, and initial charge and discharge curves per reference mass or reference area of ​​each of the positive electrode 7 and negative electrode 8. The storage unit 402 also stores in advance a correction parameter m used for diagnosis by a diagnosis unit 406, which will be described later. p , m n , C p , C n The initial value of the correction parameter m p , m n , C p , C n Details will be provided later.

[0046] As described above, when the absolute value of the time rate of change determined from the time change in the sleep mode becomes less than the predetermined threshold, the determination unit 403 determines that the OCV has converged. At the same time, the determination unit 403 stores the OCV value (preferably the latest OCV value) when the absolute value of the time rate of change becomes less than the predetermined threshold in the storage unit 402 as the convergence value of the OCV. In this way, the OCV value when the OCV has converged, that is, the convergence value of the OCV, can be obtained. Then, the charge / discharge curve of the OCV of the secondary battery 100 can be calculated using the convergence value of the OCV. The information determined by the determination unit 403 is stored in the storage unit 402.

[0047] The predetermined threshold value here can be determined, for example, by experiments, simulations, etc. Specifically, for example, it can be set to 5%, preferably 3%, more preferably 1% of the maximum voltage of the secondary battery 100 (usually 4.2 V when the secondary battery 100 is a lithium ion secondary battery cell 10 (FIG. 7)).

[0048] The determination unit 403 records the amount of electricity (capacity) obtained by subtracting the amount of electricity (capacity) due to the current flow of the first current value in the convergence mode from the integrated amount of electricity (total amount of electricity; integrated capacity) charged and discharged in the charge / discharge mode in the storage unit 402 in association with the OCV value. Note that there is a correlation between the amount of electricity and the capacity of the secondary battery 100. This is because, for example, the amount of electricity provided to the secondary battery 100 during charging can be said to be the capacity of the secondary battery 100 increased by charging. Therefore, the amount of electricity can be said to be capacity.

[0049] In the first current-carrying mode of the convergence mode, as described above, a current flows in the opposite direction to the current flow direction in the charge / discharge mode. Therefore, in the convergence mode, when the charge / discharge mode is, for example, charging, discharging is performed, and when the charge / discharge mode is, for example, discharging, charging is performed. Therefore, by subtracting the amount of electricity in the convergence mode from the amount of electricity accumulated in the charge / discharge mode, the net accumulated amount of electricity contributed to the OCV of the secondary battery 100 can be calculated. And, since the net accumulated amount of electricity can be associated with the convergence value of the OCV, the accuracy of the charge / discharge curve of the OCV can be improved.

[0050] In addition, by executing the second current-carrying mode, a current (forward current) in the same direction as in the charge / discharge mode may be applied. In this case, the amount of electricity calculated from the current value flowing in the second current-carrying mode may be added to the integrated amount of electricity. This allows the net integrated amount of electricity to be calculated.

[0051] Then, by performing the charge / discharge mode and the convergence mode in this order as one loop and adding up the amount of electricity each time the loop is repeated, a collection of plots of the convergence value of the OCV versus the integrated amount of electricity (for example, a collection of plots of open circles shown in FIG. 3 described later) is obtained. This collection corresponds to the charge / discharge curve of the secondary battery 100. When the sweep direction of the SOC is charging, the obtained curve is called a charge curve, and when the sweep direction of the battery SOC is discharging, the obtained curve is called a discharge curve.

[0052] The calculation unit 404 calculates a charge / discharge curve, which is data of a convergence value for the charge / discharge capacity of the secondary battery 100. The charge / discharge curve here is, for example, a curve (SOC-OCV curve) drawn as a graph with the horizontal axis representing the charge / discharge capacity (amount of electricity, SOC) of the secondary battery 100 and the vertical axis representing the voltage (OCV). However, the charge / discharge curve does not have to be a graph itself, and may be a function representing a graph or the like. Each piece of information determined by the calculation unit 404 is stored in the storage unit 402.

[0053] The charge / discharge curve can be calculated, for example, by the following method. The SOC on the horizontal axis correlates with the battery voltage of the secondary battery 100. Therefore, as described above, the correspondence between the battery voltage of the secondary battery 100 and the battery charging rate (SOC) is stored in advance in the storage unit 402. Then, the SOC can be calculated from the battery voltage of the secondary battery 100. Then, the charge / discharge curve can be calculated, for example, by plotting a graph with the calculated SOC on the horizontal axis and the convergence value of the OCV on the vertical axis.

[0054] The charge / discharge curve may be calculated as follows. As described above, the amount of electricity correlates with the charge / discharge capacity (SOC) of the secondary battery 100. For example, the greater the amount of electricity supplied to the secondary battery 100 during charging, the greater the charge capacity. Therefore, the charge / discharge capacity can be determined from the integrated amount of electricity (not including the amount of electricity that increases or decreases in the first current-flow mode and the second current-flow mode) stored by the determination unit 403. Then, the charge / discharge curve can be calculated by plotting the OCV for each determined charge / discharge capacity.

[0055] The calculation unit 404 calculates a charge / discharge curve (e.g., a potential curve) of at least one electrode (preferably both electrodes) of the positive electrode 7 or the negative electrode 8 (both of which are shown in FIG. 8, etc.) constituting the secondary battery 100 from data of convergence values ​​for the charge / discharge capacity of the secondary battery 100 (e.g., the above-mentioned SOC-OCV curve). This makes it possible to evaluate for each electrode how much it has deviated from the charge / discharge curve of an undegraded electrode, and therefore to diagnose the degradation of each electrode.

[0056] The timer unit 405 counts the time in, for example, the charge / discharge mode and the convergence mode (including the first current supply mode, the pause mode, and the second current supply mode). In this way, the timer unit 405 generates time information. The time information is input to the storage unit 402 as appropriate.

[0057] The diagnosis unit 406 diagnoses the state (battery state) of the secondary battery 100 based on the relationship between the amount of electricity flowing and the convergence value of the OCV. The diagnosis can be performed by any method, but for example, it can be performed as follows.

[0058] First, the calculation unit 404 performs a regression calculation process (reproduction calculation process) using charge / discharge curves of, for example, undegraded positive electrode 7 and negative electrode 8 (both shown in FIG. 8, etc.) that have been measured in advance so as to reproduce the charge / discharge curve calculated by the calculation unit 404. The regression calculation process is carried out, for example, by using the correction parameter m p , m n , C p , C n This can be done using:

[0059] Correction parameter m p and m n are parameters that represent the capacity that the positive electrode 7 and the negative electrode 8 can charge and discharge independently. p and m n reflect the deterioration rate of the positive electrode 7 and the negative electrode 8, respectively, and are both 1 if they are not deteriorated, and gradually decrease as they deteriorate. In addition, the correction parameter C p and C n are parameters that represent the amount of side reactions at the positive electrode 7 and the negative electrode 8, respectively. p and C n reflect the amount of lithium ions that have become unavailable for charging and discharging in the positive electrode 7 and the negative electrode 8, respectively, and are both 0 if the battery is not yet deteriorated, and gradually increase as the battery deteriorates.

[0060] The diagnosis unit 406 calculates a correction parameter m for each charge / discharge capacity of the initial charge / discharge curves per reference mass or reference area of ​​the positive electrode 7 and the negative electrode 8 recorded in the memory unit 402.p , m n After multiplying by the initial value of the correction parameter C p , C n The calculated values ​​of the charge / discharge curves of the positive electrode 7 and the negative electrode 8 are obtained by adding and correcting the correction parameter m so that the calculated values ​​of the charge / discharge curves of the positive electrode 7 and the negative electrode 8 obtained in this manner are compared to obtain the difference between the potential of the positive electrode 7 and the potential of the negative electrode 8 corresponding to the same charge / discharge capacity, thereby obtaining the calculated value of the charge / discharge curve of the secondary battery 100. The diagnosis unit 406 adjusts the correction parameter m so that the calculated value of the charge / discharge curve of the secondary battery 100 coincides with the measured value. p , m n , C p , C n Adjust.

[0061] 3 is a graph showing an example of the result of the regression calculation process. The horizontal axis represents the capacity, and the vertical axis represents the open circuit voltage (in the case of the secondary battery 100) and Li / Li + The dashed line is the charge / discharge curve of the positive electrode 7, and the dotted line is the charge / discharge curve of the negative electrode 8. The solid line is the calculated value of the charge / discharge curve of the secondary battery 100, and the plot of white circles is the measured value of the charge / discharge curve of the secondary battery 100.

[0062] As shown in FIG. 3, the plots of the white circles (measured values, actual measured values) overlap with the calculated values ​​(solid line) of the charge / discharge curve of the secondary battery 100. Therefore, the calculated values ​​of the charge / discharge curve of the secondary battery 100 are in good agreement with the measured values. The correction parameter m p , m n , C p , C n The state of the secondary battery 100 can be diagnosed from the value of the correction parameter m p , m n , C p , C n By organizing each of these as time series data and fitting them to an appropriate function, the future correction parameter m p , m n , C p , C nThe applicable function here is, for example, a power function, an exponential function, a function used in machine learning, etc. By such prediction, a future charge and discharge curve of the secondary battery 100 can be constructed, and the life of the secondary battery 100 can be predicted.

[0063] If the diagnosis unit 406 determines that diagnosis is not necessary, the third execution unit 409 uses the secondary battery 100 in a normal manner. Specifically, for example, the third execution unit 409 charges and discharges the secondary battery 100 according to a user request, the use of the secondary battery 100, and the like, without entering the sleep mode, similar to the first execution unit 407.

[0064] The timing of diagnosing the battery state (e.g., a criterion for determining that it is necessary) is arbitrary. For example, when the battery state has not been diagnosed for a certain period of time, when it is known in advance that the operation of the battery-equipped device will be stopped for a certain period of time due to maintenance or the like, when a diagnostic process is requested by the user, etc. From the viewpoint of user convenience, the user of the battery-equipped device may ultimately decide whether or not to execute the diagnostic operation. In this case, for example, the control system 500 may be provided with a display (not shown) that provides information to the user and accepts input from the user, and may be provided with a mobile communication terminal (not shown) such as a smartphone that the user can use. In addition, when the control system 500 has, for example, a communication function, input to the control system 500 may be accepted from the user terminal.

[0065] As described above, in the example of the present disclosure, the control system 500 charges and discharges the secondary battery 100 while changing the SOC in the charge / discharge mode, and then applies a current flowing in the opposite direction to that in the charge / discharge mode in the convergence mode. The control system 500 then repeats this series of processes. This allows the OCV curve to be obtained, and the secondary battery 100 to be diagnosed.

[0066] The time and number of times the charge / discharge mode and the convergence mode are performed, i.e., the conditions for determining the end of the above-mentioned operation using the control system 500, are not particularly limited, but examples include when the number of charge / discharge repetitions reaches a specified value, when the battery voltage reaches a target voltage, when the charge / discharge capacity reaches a target value, etc.

[0067] 1 above, and may be configured to control charging and discharging of the secondary battery 100, and preferably to determine the state of the secondary battery 100. Furthermore, the functional units shown in the control system 500 do not all need to be integrated, and at least some of the functions may be processed by a separate server (not shown) that is spatially separated by a communication function. Furthermore, the control system 500 may be added to an existing control system that controls charging and discharging of the secondary battery 100, or may be obtained by constructing a new control system that controls charging and discharging of the secondary battery 100.

[0068] Furthermore, during control by the control system 500, the use conditions of the secondary battery 100, such as the maximum charge / discharge current, the voltage range, and the temperature, are controlled so as to fall within appropriate ranges.

[0069] 4 is a flowchart showing a control method for the secondary battery 100 of the present disclosure. Hereinafter, the control method for the secondary battery 100 of the present disclosure will be simply referred to as the "control method of the present disclosure" as appropriate. The control method of the present disclosure can be executed, for example, using the control system 500 shown in FIG. 1 above.

[0070] The control method of the present disclosure includes an execution step S1. The execution step S1 is a step of executing a charge / discharge mode (step S11) and a convergence mode (step S12) using the control system 500 of the secondary battery 100. The execution step S1 includes steps S11 and S12.

[0071] Step S11 is a step of at least one of charging and discharging the secondary battery 100 with a predetermined first electric quantity. Step S11 can be executed by, for example, the first execution unit 407. Step S12 is a step of promoting convergence of the OCV of the secondary battery 100 after step S11. Step S12 includes a first current flow mode in which a current of a first current value flows in the secondary battery 100 with a second electric quantity smaller than the first electric quantity in a direction opposite to the current flow direction in step S11. Step S12 can be executed by, for example, the second execution unit 408.

[0072] Following step S11, step S12 is performed. In step S12, the first current application mode is executed as described above. After step S12, an end determination is made (step S2). Step S2 can be performed, for example, by the determination unit 403. The end determination can be performed, for example, by the matters described in the control system 500. If the end is to be determined (Yes), the charge / discharge control of the secondary battery 100 is ended. At the same time, a charge / discharge curve of the secondary battery 100 is calculated, for example, by the diagnosis unit 406. On the other hand, if the end is not to be determined (No), step S11 and subsequent steps are repeated again.

[0073] In FIG. 4, for the sake of simplicity, only the first current supply mode is executed in step S12. However, the above-mentioned pause mode, second current supply mode, etc. may be executed as appropriate in step S12.

[0074] Fig. 5 is a flowchart showing a method of controlling a secondary battery in a case where the sleep mode is included. The flow shown in Fig. 5 partially overlaps with the flow shown in Fig. 4. Therefore, the following mainly describes the differences.

[0075] In step S12 (convergence mode), first, a reverse current is passed in the opposite direction to that in the charge / discharge mode (execution step S1) (step S13). Next, the sleep mode is started (step S14). In step S15, the absolute value of the time rate of change of the OCV in the sleep mode is determined. If the absolute value is less than a predetermined threshold, the time rate of change is sufficiently small and the OCV is considered to have converged, so an end determination is made in step S2. The predetermined threshold here is the same as that described in the control system 500 above, and is a value at which the OCV is considered to have converged (can be regarded as having converged). On the other hand, if the absolute value is equal to or greater than the predetermined threshold, the time rate of change is still large and the OCV is considered not to have converged. Therefore, step S16 is performed.

[0076] In step S16, the sign of the time rate of change of the OCV in the sleep mode is determined. The sign is either positive (OCV increases) or negative (OCV decreases). When the secondary battery 100 is charged in the charge / discharge mode, the OCV converges to decrease. If the sign is negative, it is considered that it will take time to converge even though there is no overshoot, so a reverse current is further passed (step S17, first current passing mode). On the other hand, if the sign is positive, it is considered that the OCV has overshot because the OCV has increased even though it should have decreased. Therefore, in order to eliminate the overshoot and bring the OCV closer to a predetermined threshold, a forward current is passed (step S18, second current passing mode). After steps S17 and S18, the sleep mode is executed again (step S19), and steps S15 and after are executed again.

[0077] Next, the present disclosure will be described more specifically with reference to examples.

[0078] FIG. 6 is a graph showing the relaxation behavior of the OCV in Example 1 and Comparative Example 1. The horizontal axis is time, and the vertical axis is OCV. In Example 1, the OCV relaxation behavior was measured after discharging a cylindrical cell 10 (FIG. 7, an example of a secondary battery 100) at a rate of 1C. The rate of 1C means a current value at which the capacity of the cell 10 can be charged or discharged in one hour. Comparative Example 1 represents a case where the cell 10 is in an open circuit state immediately after discharging, and Example 1 represents a case where the cell 10 is in an open circuit state in a pause mode after applying a reverse current of 1C for 1 second (i.e., executing the first current-carrying mode) immediately after discharging (i.e., immediately after the charge / discharge mode). Comparative Example 1 does not include the convergence mode, and Example 1 includes the convergence mode.

[0079] 6, it took 10 minutes for the OCV to converge in Example 1, and 20 minutes for the OCV to converge in Comparative Example 1. It is therefore clear that the OCV convergence was completed in a shorter time in Example 1 than in Comparative Example 1. As a result, the time required for the OCV to converge was reduced by about half.

[0080] Next, in Example 2, a cylindrical cell 10 was fully charged, and then discharged at a discharge rate of 1C by 2% as SOC to obtain a convergence value of OCV. Comparative Example 2 does not include the above convergence mode, while Example 2 includes the above convergence mode. In Example 2, a reverse current is applied in the convergence mode, so that an amount of electricity equivalent to a predetermined charge amount of reverse current is discharged more than in Comparative Example 2, thereby making the SOC at which the convergence value of OCV is obtained uniform between Comparative Example 2 and Example 2. Table 1 below shows the total time (measurement time) required to obtain the charge / discharge curve of cell 10.

[0081] [Table 1]

[0082] As shown in Table 1, in Example 2, the charge / discharge curve of the cell 10 could be obtained in half the time required in Comparative Example 2.

[0083] Finally, in Example 3, a cylindrical cell 10 was fully charged, and then discharged little by little at a discharge rate of 1C to obtain a convergence value of the OCV. Comparative Example 3 is similar to Comparative Example 2. In Example 3, the time rate of change of the OCV in the pause mode in the convergence mode was referenced, and the value of the reverse current was changed to cause the OCV to converge. Therefore, in Example 3, the SOC at which the convergence value of the OCV is obtained does not completely match that of Comparative Example 3, but a charge / discharge curve of the cell that can be used for diagnosis could be obtained. Table 2 below shows the total time (measurement time) required to obtain the charge / discharge curve of the cell 10.

[0084] [Table 2]

[0085] As shown in Table 2, in Example 3, the charge / discharge curve of the cell 10 could be obtained in one-third or less of the time required in Comparative Example 3.

[0086] Further, a secondary battery 100 to which the control system 500 and the control method of the present disclosure can be applied will be described.

[0087] FIG. 7 is an example of a cross-sectional view conceptually showing a cell 10. In the example of FIG. 7, the secondary battery 100 is the cell 10. The cell 10 includes an electrode plate group 1, a positive electrode terminal 2, a negative electrode terminal 3, a separator 5, and an exterior material 6. The positive electrode terminal 2 is connected to a positive electrode 7 described later, and the negative electrode terminal 3 is connected to a negative electrode 8 described later. The exterior material 6 is a laminate film or the like. The shape of the cell 10 is not limited to that shown in this figure, and may be rectangular as in FIG. 7, or may be cylindrical (not shown).

[0088] Fig. 8 is an example of a cross-sectional view conceptually illustrating the electrode plate group 1 of the cell 10 shown in Fig. 7. The electrode plate group 1 has a configuration in which positive electrodes 7 and negative electrodes 8 are alternately arranged to face each other with a separator 5 therebetween. The structure of the electrode plate group 1 is not limited to that shown in Fig. 8, and may be a laminated type as shown in Fig. 8, or may be a wound type (not shown) produced by stacking positive electrodes 7 and negative electrodes 8 to face each other with a separator 5 therebetween and then winding the stack.

[0089] The material of the separator 5 is not particularly limited, but for example, polypropylene is used. As the separator 5, a microporous film, nonwoven fabric, etc. made of polyolefin such as polyethylene can be used in addition to polypropylene.

[0090] The positive electrode 7 and the negative electrode 8 are each prepared by applying a mixture of an appropriate electrode active material, a conductive agent, a binder, and the like to a current collector foil made of an appropriate metal.

[0091] For the current collector foil of the positive electrode 7, aluminum foil having a thickness of 1 μm to 100 μm, aluminum perforated foil having a thickness of 1 μm to 100 μm and a pore size of 0.1 mm to 10 mm, expanded metal, foam metal plate, etc. are used, and in addition to aluminum, stainless steel, titanium, etc. can also be used. In the present disclosure, there are no limitations on the material, shape, manufacturing method, etc., and any current collector can be used.

[0092] The electrode active material of the positive electrode 7 is preferably one that contains a reactive species therein. The reactive species of a lithium ion secondary battery is lithium ions. In this case, the lithium-containing compound capable of reversibly inserting and detaching lithium ions is included. The type of electrode active material of the positive electrode 7 is not particularly limited, but examples thereof include lithium transition metal phosphates such as lithium cobalt oxide, lithium manganese-substituted cobalt oxide, lithium manganate, lithium nickel oxide, and olivine-type lithium iron phosphate; Li w Ni x Co y Mn z O2 (wherein w, x, y, and z are 0 or positive values). The electrode active material of the positive electrode 7 may include one or more of the above materials.

[0093] The current collector foil of the negative electrode 8 may be a copper foil having a thickness of 1 μm to 100 μm, a perforated copper foil having a thickness of 1 μm to 100 μm and a pore size of 0.1 mm to 10 mm, an expanded metal, a foamed metal plate, or the like, and may be made of other materials than copper, such as stainless steel or titanium. In the present disclosure, there are no limitations on the material, shape, manufacturing method, or the like, and any current collector may be used.

[0094] The electrode active material of the negative electrode 8 includes a material capable of reversibly inserting and detaching lithium ions. The type of electrode active material of the negative electrode 8 is not particularly limited, and may be, for example, natural graphite, a composite carbonaceous material in which a coating is formed on natural graphite by a dry CVD method or a wet spray method, artificial graphite produced by firing a resin material such as epoxy or phenol, or a pitch-based material obtained from petroleum or coal, silicon (Si), silicon oxide, graphite mixed with silicon or silicon oxide, a non-graphitizable carbon material, lithium titanate Li4Ti5O 12 , niobium titanium oxide TiNb2O7, etc. can be used. The negative electrode active material may contain one or more of the above materials.

[0095] An electrolyte is impregnated into the electrode plate group 1. The electrolyte is not particularly limited, but in the case of a lithium ion secondary battery, examples of the electrolyte include an electrolyte in which a lithium salt such as lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium iodide, lithium chloride, lithium bromide, LiB[OCOCF3]4, LiB[OCOCF2CF3]4, LiPF4(CF3)2, LiN(SO2CF3)2, LiN(SO2CF2CF3)2, or a mixed lithium salt of two or more of these is dissolved in an aprotic organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC), or a mixed organic compound solvent of two or more of these, is dissolved. A solid electrolyte may be used instead of the electrolytic solution. The solid electrolyte is not particularly limited, but examples thereof include ion-conductive polymers such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, polyhexafluoropropylene, and polyethylene oxide. When such a solid polymer electrolyte is used, the separator 5 can be omitted.

[0096] Metal tabs are connected to the current collecting foils of the positive electrode 7 and the negative electrode 8. The exterior material 6 is sealed so that only the tab portions are exposed to the outside of the exterior material 6. As a result, the tabs become the positive electrode terminal 2 and the negative electrode terminal 3 in FIG.

[0097] FIG. 9 is an example of a configuration diagram conceptually illustrating a battery module 110. In FIG. 9, the secondary battery 100 is the battery module 110. The battery module 110 includes three cells 10 connected in series. Each cell 10 includes a voltmeter 102 for measuring the voltage of the cell 10. The ammeter 101 and the voltmeter 102 respectively output the input / output current to / from the battery module 110 and the voltage of the cell 10 to a control system 500, and the control system 500 controls the charging and discharging of the battery module 110. The ammeter 101 may be installed outside the control system 500 as shown in this figure, or may be included in the control system 500 (not shown).

[0098] Any power may be used to charge the battery module 110. Examples of the power include power from a power grid, power generated by a diesel generator or the like, power generated by renewable energy sources such as solar power generation and wind power generation, regenerated power, and power supplied from a power storage system different from the battery module 110. The load 104 (FIG. 10) used to discharge the battery module 110 is also any load. Examples of the load include a load built into the control system 500, a load included in a device equipped with the battery module 110, and a load added externally.

[0099] Fig. 10 is an example of a configuration diagram clearly showing the load 104 used for discharging the battery module 110. In Fig. 10, a switch 103 and a load 104 are connected in parallel to the battery module 110. When charging or discharging the battery module 110, a control system 500 outputs a signal to the switch 103 to operate the switch 103. By closing the switch 103, the battery module 110 is connected to the load 104. On the other hand, by opening the switch 103, the connection between the battery mall 110 and the load 104 is released.

[0100] 10 and the above-mentioned Fig. 9 show the case where there are three cells 10, the number of cells 10 constituting the battery module 110 is not particularly limited and may be one, two, or four or more. In addition, the configuration of the battery module 110 is not limited to the above and may be any configuration as long as it is possible to measure the current flowing through each cell 10 and the voltage of each cell 10.

[0101] 11 is an example of a configuration diagram conceptually showing a battery pack 510 in which battery modules 110 are connected in parallel. The secondary battery 100 is the battery pack 510 and the battery modules 110. Here, a case in which three battery modules 110 are illustrated is shown, but the number of battery modules 110 constituting the battery pack 510 is not particularly limited, and the battery pack 510 may be composed of only one, two, or four or more battery modules 110.

[0102] An ammeter 101 that measures a current value is connected in series to each battery module 110. Each battery module 110 outputs information such as the voltage of each cell 10 to the control system 500, and each ammeter 101 outputs the input / output current to each battery module 110 to the control system 500. The control system 500 controls charging and discharging of the battery pack 510.

[0103] Any power may be used to charge the battery pack 510. Examples of such power include power from a power grid, power generated by a diesel generator or the like, power generated by renewable energy sources such as solar power generation and wind power generation, regenerated power, and power supplied from a power storage system different from the battery pack 510. The load 104 (FIG. 10) used to discharge the battery pack 510 is also any load. Examples of such load include a load built into the control system 500, a load included in a device equipped with the battery pack 510, and a load added externally.

[0104] 12 is an example of a configuration diagram conceptually illustrating a battery pack 510 in which battery modules 110 are connected in parallel according to another embodiment. A circuit connected to each battery module 110 may include a switch 111 capable of cutting off current to the battery module 110. When charging or discharging the battery pack 510, the control system 500 outputs a signal to the switch 111 to operate the switch 111. By closing the switch 111, the battery module 110 connected in series to the switch 111 is charged or discharged. This allows selective charging or discharging of a specific battery module 110, thereby reducing the number of ammeters 101 required.

[0105] 12 shows a case where one ammeter 101 is provided, but multiple ammeters may be provided. Also, the ammeter 101 may be provided outside the battery pack 510 and the control system 500 as shown in FIG 12, or may be provided inside the control system 500 and the battery pack 510, although not shown.

[0106] The configuration of the battery pack 510 is not limited to the above, and any configuration may be used as long as the current flowing through each battery module 110 and the voltage of each battery module 110 can be measured.

[0107] The present disclosure is not limited to the above-described embodiments, and other forms that are conceivable within the scope of the technical idea of ​​the present disclosure are also included in the scope of the present disclosure as long as they do not impair the characteristics of the present disclosure. [Explanation of symbols]

[0108] 100 Secondary battery 101 Ammeter 102 Voltmeter 400 Acquisition Department 401 Executive Department 402 Storage section 403 Judgment section 404 Arithmetic section 405 Timer section 406 Diagnostics Department 407 First Executive Division 408 2nd Executive Division 409 3rd Executive Division 500 Control System S1 Execution step

Claims

1. A control system for a secondary battery, comprising: The control system includes: an execution unit that executes a charge / discharge mode in which at least one of charging and discharging is performed with respect to the secondary battery with a predetermined first electric quantity, and a convergence mode in which, after the charge / discharge mode, a convergence of an open circuit voltage of the secondary battery is promoted; The convergence mode includes a first current flow mode in which a current of a first current value flows through the secondary battery in a direction opposite to a current flow direction in the charge / discharge mode, the current flow being a second electric quantity smaller than the first electric quantity. A control system for a secondary battery.

2. the convergence mode includes a dormant mode; In the sleep mode, the execution unit measures a time change in an open circuit voltage of the secondary battery in an open circuit state.

2. The control system for a secondary battery according to claim 1.

3. The execution unit is The first current application mode is executed after the pause mode, Based on the change over time in the pause mode, a current value in the first energization mode executed after the pause mode in which the change over time was measured is determined.

3. The control system for a secondary battery according to claim 2.

4. The execution unit executes the first current application mode after the pause mode in which the time change is measured when it is determined that the open circuit voltage has not yet converged in the pause mode.

3. The control system for a secondary battery according to claim 2.

5. the convergence mode includes a second current flow mode in which a current of a second current value flows through the secondary battery in the same direction as a current flow direction in the charge / discharge mode; The execution unit executes either the first current conduction mode or the second current conduction mode after the pause mode based on the time change in the pause mode.

3. The control system for a secondary battery according to claim 2.

6. the execution unit executes the second current conduction mode when a predetermined condition is satisfied, and executes the first current conduction mode when the predetermined condition is not satisfied, The predetermined condition is: A first condition in which the secondary battery is discharged in the charge / discharge mode, and the time change rate determined from the time change is a negative value; or a second condition in which the secondary battery is charged in the charge / discharge mode, and a time rate of change determined from the time change is a positive value; Contains at least one of the following conditions:

6. The control system for a secondary battery according to claim 5.

7. The control system includes a determination unit, The determination unit determines that the open circuit voltage has converged when an absolute value of a time rate of change determined from the time change in the pause mode becomes less than a predetermined threshold, and stores the value of the open circuit voltage when the absolute value of the time rate of change becomes less than the predetermined threshold in a storage unit as a convergence value.

3. The control system for a secondary battery according to claim 2.

8. the determination unit records in the storage unit an amount of electricity obtained by subtracting an amount of electricity caused by the current supply of the first current value in the convergence mode from an integrated amount of electricity charged and discharged in the charge / discharge mode in association with the value of the open circuit voltage; The control system includes a calculation unit, The calculation unit calculates a charge / discharge curve which is data of the convergence value with respect to the charge / discharge capacity of the secondary battery.

8. The control system for a secondary battery according to claim 7.

9. The calculation unit calculates a charge / discharge curve of at least one of a positive electrode and a negative electrode constituting the secondary battery from the data of the convergence value for the charge / discharge capacity of the secondary battery.

9. The control system for a secondary battery according to claim 8.

10. a charge / discharge mode for charging or discharging a secondary battery with a predetermined first electric quantity, and a convergence mode for promoting convergence of an open circuit voltage of the secondary battery after the charge / discharge mode, using a control system of the secondary battery; The convergence mode includes a first current flow mode in which a current of a first current value flows through the secondary battery in a direction opposite to a current flow direction in the charge / discharge mode, the current flow being a second electric quantity smaller than the first electric quantity. A method for controlling a secondary battery.

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