Control device and secondary battery system

Abstract

To provide a control device capable of appropriately recovering the capacity of a secondary battery.SOLUTION: A control device comprises: an operation mode selection unit 408 for selecting either a first operation mode Mn or a second operation mode Mr as an operation mode MD; a first discharge control unit 410, when the operation mode selection unit 408 selects the first operation mode Mn, for stopping the discharge of a secondary battery and suppressing the discharge current of the secondary battery to a first current or lower, when the battery voltage of the secondary battery becomes a first voltage or lower; and a second discharge control unit 412, when the operation mode selection unit 408 selects the second operation mode Mr, for stopping the discharge of the secondary battery and suppressing the discharge current of the secondary battery to a second current or lower, when the battery voltage of the secondary battery becomes a second voltage or lower.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a control device and a secondary battery system. [Background technology]

[0002] As background art in this technical field, the abstract of the following Patent Document 1 states, "[Problem] To provide a battery system and a capacity recovery method capable of effectively recovering the capacity of a lithium-ion secondary battery in a short period of time. [Solution] An ECU 960 controls a PCU 920 to execute capacity recovery control to recover the capacity of a battery pack 10. The capacity recovery control includes a discharge mode and a capacity recovery mode. In the discharge mode, the ECU 960 discharges the battery pack 10 to a predetermined over-discharge region. In the capacity recovery mode, the ECU 960 repeatedly executes, in the over-discharge region, a voltage increase of the lithium-ion secondary battery by stopping discharge, and a pulse discharge that discharges the lithium-ion secondary battery while oscillating the discharge current." The disclosure of this document is incorporated herein by reference. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-106333 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned technology, there are cases where the capacity of the secondary battery cannot be properly restored. The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a control device and a secondary battery system that can appropriately restore the capacity of a secondary battery. [Means for solving the problem]

[0005] In order to solve the above problems, a control device of the present invention includes an operation mode selection unit that selects either a first operation mode or a second operation mode as an operation mode, and when the operation mode selection unit selects the first operation mode, stops discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a first voltage. Functions and , When the operation mode selection unit selects the first operation mode, The discharge current of the secondary battery is suppressed to a first current or less. Function and having a first discharge control unit that, when the operation mode selection unit selects the second operation mode, stops discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a second voltage; Functions and , When the operation mode selection unit selects the second operation mode, The discharge current of the secondary battery is suppressed to a second current or less. Function and having and a second discharge control unit, wherein the second discharge control unit performs a capacity recovery process for the secondary battery by executing one or more cycles, each cycle consisting of a discharge period in which a discharge current of 1C or more and less than the second current is discharged between the positive and negative terminals of the secondary battery for a discharge time of 1 second or more and 60 seconds or less, when a current value at which the battery capacity of the secondary battery is completely charged or discharged in one hour is 1C, and a rest period in which the positive and negative terminals are opened for a period of 30 seconds or more, or the discharge current is made smaller than that in the discharge period, and wherein at least one of the following conditions is satisfied: the second voltage is lower than the first voltage, or the second current is greater than the first current. Effect of the Invention

[0006] According to the present invention, the capacity of a secondary battery can be appropriately restored. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic cross-sectional view of a bipolar battery cell. [Diagram 2] FIG. 2 is a schematic side view of the electricity storage element. [Diagram 3] 1 is a block diagram of a secondary battery system according to an embodiment. [Figure 4] FIG. 2 is a block diagram of a control unit. [Diagram 5] 4 is a flowchart showing the overall operation of the embodiment. [Figure 6] FIG. 11 is a diagram showing the recovered capacity obtained and the time required for the capacity recovery process in the first embodiment and a comparative example. [Figure 7] FIG. 11 is a diagram showing power loss due to capacity recovery and SOC after recovery processing in the first embodiment and the comparative example. [Figure 8] FIG. 11 is a diagram showing recovery capacity versus time of a pause step in the second embodiment and other comparative examples. [Figure 9] FIG. 13 is a graph showing recovery capacity versus discharge rate in the third embodiment and other comparative examples. [Figure 10] FIG. 13 is a graph showing recovery capacity versus discharge pulse application time in the fourth embodiment and other comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Outline of the embodiment] Lithium ion batteries are a type of non-aqueous electrolyte secondary battery, and because of their high energy density, they are used as batteries for portable devices and, in recent years, electric vehicles. However, it is known that lithium ion batteries deteriorate with use, resulting in a decrease in battery capacity. In lithium-ion batteries, lithium metal oxide is generally used as the active material for the positive electrode, and carbon materials such as graphite are generally used for the negative electrode. The positive and negative electrodes of lithium-ion batteries are formed by adding binders and conductive agents to tiny particles of the active material to form a slurry (mixture), which is then applied to metal foil.

[0009] During charging, lithium ions released from the positive electrode active material are absorbed into the negative electrode active material, and during discharging, the lithium ions absorbed into the negative electrode active material are released and absorbed into the positive electrode active material. In this way, a current flows between the electrodes as the lithium ions move between the electrodes. In these lithium-ion batteries, (1) Electrical isolation of the positive electrode active material, (2) Electrical isolation of the negative electrode active material, and (3) Fixation of lithium ions moving between the electrodes. This reduces the capacity.

[0010] The above factor (3) occurs when lithium ions are solidified as a film on the surface of the negative electrode due to the decomposition of the electrolyte, or when lithium ions are bound within the negative electrode. Of these, the capacity loss caused by lithium ions being bound within the negative electrode can be restored by electrochemical treatment. For example, by raising the potential of the negative electrode above the normal operating range, the lithium ions bound to the negative electrode are released, and the capacity is restored. This is equivalent to over-discharging the battery, and means that the state of charge (SOC) of the battery, which is determined by the operating voltage range of the battery, is reduced below 0%.

[0011] It is believed that the capacity of a lithium-ion secondary battery can be effectively restored in a short time by applying the technology of the above-mentioned Patent Document 1. In other words, it is believed that the time required for capacity recovery can be shortened by repeatedly discharging a lithium-ion secondary battery to the overdischarge region, and then stopping the discharge to increase the voltage, and then performing a pulse discharge in which the discharge current is oscillated while discharging.

[0012] However, there is room for improvement in the method of recovering the capacity of a battery by pulse discharge in the overdischarge region as described above. For example, overdischarging a battery results in a loss of power because all the power stored in the battery is discarded, but there is also a loss of time due to the overdischarge. In addition, when a battery is overdischarged, there is a problem that the device equipped with the battery cannot be used because it cannot supply power when it is suddenly needed. Therefore, the embodiment described below realizes a capacity recovery method for a secondary battery that reduces the loss of power and time while retaining the storage capacity of the battery.

[0013] [Battery cell structure] First, with reference to Figs. 1 and 2, a structural example of a bipolar battery cell applicable to the embodiment will be described. FIG. 1 is a schematic cross-sectional view of a bipolar battery cell 100. In Fig. 1, a battery cell 100 (secondary battery) is a lithium ion battery cell, and includes an electricity storage element 1, a positive electrode terminal 2, a negative electrode terminal 3, and an exterior material 6. A separator 5 is included in the electricity storage element 1. The exterior material 6 is made of a laminate film or a similar material. The shape of the battery cell 100 is not limited to a rectangular shape as shown in Fig. 1, and may be a cylindrical shape (not shown).

[0014] FIG. 2 is a schematic side view of the electricity storage element 1. As shown in FIG. As shown in FIG. 2, in the electric storage element 1, a plurality of positive electrodes 12 and a plurality of negative electrodes 13 are alternately stacked with a separator 5 interposed therebetween. The electric storage element 1 shown in FIG. 1 corresponds to the area where the positive electrodes 12 and the negative electrodes 13 appear to overlap. The structure of the electric storage element 1 is not limited to the stacked type as shown in FIG. 2. That is, although not shown, the electric storage element 1 may be a wound type fabricated by stacking the positive electrodes 12 and the negative electrodes 13 so as to face each other with the separator 5 therebetween and then winding the stack. The electric storage element 1 further contains an electrolyte (not shown), and the electrolyte is impregnated into the micropores of the positive electrodes 12, the negative electrodes 13, the separator 5, and the like. For example, polypropylene can be used as the separator 5. However, in addition to polypropylene, a microporous film or nonwoven fabric made of polyolefin such as polyethylene can also be used as the separator 5.

[0015] The positive electrode 12 and the negative electrode 13 are each made by applying a mixture of an appropriate electrode active material, a conductive agent, a binder, etc., to a current collector foil of an appropriate metal. Metal tabs are connected to the current collector foils of the positive electrode 12 and the negative electrode 13. The exterior material 6 is sealed so that only the tabs 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. 1. Hereinafter, the potentials of the positive electrode 12 and the negative electrode 13 are referred to as the positive electrode potential Ep and the negative electrode potential En. The difference between the two, i.e., "Ep-En", is the voltage between the positive electrode terminal 2 and the negative electrode terminal 3, and this is referred to as the battery voltage Epn.

[0016] The current collector foil of the positive electrode 12 may be made of aluminum foil having a thickness of 10 to 100 μm, aluminum perforated foil having a thickness of 10 to 100 μm and a pore size of 0.1 to 10 mm, expanded metal, foam metal plate, or the like. In addition to aluminum, stainless steel, titanium, or the like may also be used as the material of the current collector foil. In this embodiment, any current collector can be used without being limited by the material, shape, manufacturing method, or the like.

[0017] The electrode active material of the positive electrode 12 preferably contains a reactive species therein. The reactive species of a lithium ion battery is lithium ions. In this case, the electrode active material contains a lithium-containing compound capable of reversibly inserting and detaching lithium ions. The type of electrode active material of the positive electrode 12 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 O 2 (wherein w, x, y, and z are 0 or positive values). The electrode active material of the positive electrode 12 may contain one or more of the above materials.

[0018] The current collector foil of the negative electrode 13 may be a copper foil having a thickness of 10 to 100 μm, a perforated copper foil having a thickness of 10 to 100 μm and a pore size of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like. The material of the current collector foil may be, other than copper, stainless steel, titanium, or the like. In this embodiment, any current collector may be used without being limited by the material, shape, manufacturing method, or the like.

[0019] The electrode active material of the negative electrode 13 includes a material capable of reversibly inserting and detaching lithium ions. The type of electrode active material of the negative electrode 13 is not particularly limited, but 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), graphite mixed with silicon, a non-graphitizable carbon material, lithium titanate Li 4 Ti 5 O 12 , niobium titanium oxide TiNb 2 O 7 The negative electrode active material may contain one or more of the above materials.

[0020] An electrolyte is impregnated in the electricity storage element 1. The electrolyte is not particularly limited, but in the case of a lithium ion battery, for example, 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) can be used.

[0021] The electrolyte is a mixture of two or more of these organic compounds in a solvent, and is made by adding lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium iodide, lithium chloride, lithium bromide, LiB[OCOCF 3 ] 4 , LiB[OCOCF 2 CF 3 ] 4 , LiPF 4 (CF 3 ) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 CF 2 CF 3 ) 2or a mixture of two or more of these lithium salts may be dissolved in the lithium salt.

[0022] 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.

[0023] [Secondary battery system] FIG. 3 is a block diagram of a secondary battery system 500 according to an embodiment. The secondary battery system 500 includes a battery pack 510 (secondary battery) and a control device 550. The battery pack 510 may be one battery cell 100 (see FIG. 1) or a plurality of battery cells 100 connected in series and / or parallel. In this specification, the term "secondary battery" is a concept including a lithium ion battery cell, a battery module, or a battery pack. The battery pack 510 includes a positive terminal 502 and a negative terminal 503. The battery pack 510 may include a voltmeter for measuring the voltage of each cell or module, and may include a thermometer for measuring the internal temperature.

[0024] The control device 550 includes an ammeter 551, a voltmeter 552, a variable resistor 553, a power supply 554, switches 560, 562, and 564, a control unit 570, and an input / output control unit 580. The power supply 554 is mainly for charging, and the variable resistor 553 is for discharging. The control device 550 also serves as a measuring instrument for grasping the state of the battery pack 510.

[0025] The ammeter 551 measures the current flowing through the positive terminal 502 and the negative terminal 503 of the battery pack 510, and outputs the result to the control unit 570. The voltmeter 552 measures the battery voltage Ev between the positive and negative electrodes, and outputs the result to the control unit 570. The control unit 570 controls the switching of the switches 560, 562, and 564 based on information from the ammeter 551 and the voltmeter 552. As a result, the control unit 570 sets the positive terminal 502 and the negative terminal 503 of the battery pack 510 to an open state, a state in which the variable resistor 553 is connected, or a state in which the power source 554 is connected.

[0026] Moreover, the control unit 570 controls the discharge current by controlling the resistance value of the variable resistor 553. For example, the battery voltage Ev decreases over time during discharge, but the control unit 570 can keep the discharge current constant by decreasing the resistance value of the variable resistor 553 over time. The input / output control unit 580 inputs and outputs power between the battery pack 510 and the power system 600. However, various load devices (not shown) may be connected to the input / output control unit 580 instead of the power system 600. The configuration of the control device 550 is not limited to that shown in FIG. 3, and may be any circuit configuration that can connect the positive terminal 502 and the negative terminal 503 of the battery pack 510 to the input / output control unit 580, the variable resistor 553, or the power source 554 as necessary.

[0027] FIG. 4 is a block diagram of control unit 570. The control unit 570 includes hardware such as a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory), which are typical of a computer, and the ROM stores control programs executed by the CPU, various data, etc. In Fig. 4, the inside of the control unit 570 is shown as blocks, with functions realized by the control programs, etc.

[0028] That is, the control unit 570 includes a battery state acquisition unit 400, a battery state determination unit 401, a control output unit 402, a memory unit 403, a battery state calculation unit 404, a timer unit 405, an operation mode selection unit 408, a normal operation control unit 410 (first discharge control unit), and a capacity recovery control unit 412 (second discharge control unit).

[0029] The battery state acquisition unit 400 receives the current, battery voltage Ev, and other measurement signals input to and output from the battery pack 510 from the ammeter 551, voltmeter 552, and input / output control unit 580, and supplies the results to the battery state determination unit 401. The timer unit 405 measures the current time, the charging time for the battery pack 510, the discharging time from the battery pack 510, and other various times.

[0030] The memory unit 403 stores the following various parameters. Note that the illustrations of these parameters are all omitted. · The upper limit voltage Vn_max, lower limit voltage Vn_min (first voltage), maximum charging current Inc_max, and maximum discharging current Ind_max (first current) of the battery voltage Ev in the normal operation mode Mn (first operation mode). · The upper limit voltage Vr_max, lower limit voltage Vr_min (second voltage), maximum charging current Irc_max, and maximum discharging current Ird_max (second current) of the battery voltage Ev in the capacity recovery mode Mr (second operation mode).

[0031] Here, the normal operation mode Mn is an operation mode in which power is input to and output from between the battery pack 510 and the power system 600 via the input / output control unit 580. On the other hand, the capacity recovery mode Mr is an operation mode for performing the capacity recovery process of the battery pack 510. The lower limit voltage Vr_min and the maximum discharging current Ird_max in the capacity recovery mode Mr are set so as to satisfy at least one of Vn_min > Vr_min or Ind_max < Ird_max. It is more preferable to satisfy both Vn_min > Vr_min and Ind_max < Ird_max.

[0032] First, in the capacity recovery mode Mr, the discharge current of the battery pack 510 is an intermittent pulse current, so that even if the peak value of the discharge current is relatively large, the battery pack 510 is unlikely to be in an overheated state. For this reason, it is preferable to set the maximum discharge current Ird_max in the capacity recovery mode Mr larger than the maximum discharge current Ind_max in the normal operation mode Mn.

[0033] Furthermore, when high-rate discharge is performed in the capacity recovery mode Mr, the battery voltage Ev may reach Vn_min due to electrochemical polarization inside the battery pack 510 even if some storage capacity remains. For this reason, it is preferable to make Vn_min>Vr_min. Here, when Vn_min>Vr_min, Vr_min is preferably set to 0V or higher. This is to suppress side reactions such as dissolution of the current collecting foil caused by an extreme drop in the battery voltage.

[0034] The battery state determination unit 401 calculates the amount of electricity relating to charging and discharging based on the current value measured by the battery state acquisition unit 400 and the time measurement result by the timer unit 405, and stores the calculated amount of electricity in the memory unit 403. The battery state determination unit 401 also outputs the battery voltage Ev input from the battery state acquisition unit 400 as the latest value together with the current time to the memory unit 403 for storage.

[0035] The battery state calculation unit 404 reads parameters such as the amount of electricity related to charging and discharging and the battery voltage Ev from the storage unit 403, and calculates the SOC of the battery pack 510 and the battery capacity Q of the battery pack 510 based on the read parameters. Here, the SOC of the battery pack 510 is a value that is 100% in a state corresponding to the upper limit voltage Vn_max in the normal operation mode Mn and 0% in a state corresponding to the lower limit voltage Vn_min.

[0036] The battery state calculation unit 404 appropriately corrects various measurement values ​​and initial values ​​other than those described above, calculates physical quantities for determining the battery state, and outputs the calculated physical quantities to the battery state determination unit 401. Specifically, the battery state calculation unit 404 calculates the SOC from a correspondence table between the battery voltage and SOC of the battery pack 510 stored in the storage unit 403 and the battery voltage input from the battery state determination unit 401, and outputs the calculated SOC to the battery state determination unit 401. The battery state calculation unit 404 also calculates the current value of the discharge pulse from the initial capacity of the battery stored in the storage unit 403, and outputs the calculated SOC to the battery state determination unit 401. The battery state calculation unit 404 also calculates the application time of the discharge current and the retention time of the rest state (for example, an open circuit state), and outputs the calculated SOC to the battery state determination unit 401. Note that the calculation method of the SOC of the battery pack 510 is not limited to the method shown here, and the SOC can be calculated by any method.

[0037] The battery state determination unit 401 compares the calculation results of the SOC and battery capacity Q input from the battery state calculation unit 404 with the threshold SOCth and capacity threshold Qth stored in the storage unit 403. Then, the battery state determination unit 401 calculates the state of the battery pack 510 based on these comparison results and the usage history of the battery pack 510, and determines whether or not a capacity recovery process is required.

[0038] For example, the battery state determination unit 401 can determine that "capacity recovery processing is necessary" if either of the following is true: "capacity recovery processing has not been performed on the battery pack 510 within the past week" or "battery capacity Q has decreased by 1% or more from the battery capacity Q after the previous capacity recovery processing" is true and the SOC of the battery pack 510 is less than the threshold SOCth.

[0039] The reason why the usage history of the battery pack 510 is used to determine whether or not the capacity recovery process is required is that if lithium ions are not bound to the negative electrode, sufficient capacity recovery effect cannot be obtained. In addition, the threshold value SOCth used to determine whether or not the capacity recovery process is required can be set arbitrarily between 0 and 100%, which is the range of SOC normally used. However, it is preferable to set the threshold value SOCth to a value of 20% or less, and more preferably to a value of 10% or less. This is because the effect of the capacity recovery process decreases as the SOC increases.

[0040] The operation mode selection unit 408 selects one of the normal operation mode Mn and the capacity recovery mode Mr as the operation mode MD of the control device 550 based on a manual operation by the user or the result of the determination by the battery state determination unit 401 .

[0041] The configuration of the control unit 570 is not limited to that shown in FIG. 4, and may be any configuration that can determine the state of the battery pack 510, apply a specific discharge current to the battery pack 510 for a specific time, and keep the battery in a resting state (e.g., open circuit state). Although the application of this embodiment is not particularly limited, it is particularly effective in applications in which it is difficult to over-discharge the battery pack 510 during use. For example, in a secondary battery system 500 used for frequency adjustment or peak shifting in a power system, charging or discharging is performed constantly, so that it is very difficult to over-discharge the battery. In such applications, when the SOC of the battery decreases during operation, the technology of this embodiment can restore the capacity.

[0042] [Operation of the embodiment] <Normal operation mode> Next, the operation of this embodiment will be described. As described above, parameters of the normal operation mode Mn, i.e., the upper limit voltage Vn_max, the lower limit voltage Vn_min, the maximum charging current Inc_max, and the maximum discharging current Ind_max, are stored in the memory unit 403. When the battery pack 510 is applied to normal charging and discharging, that is, when the operation mode selection unit 408 selects the normal operation mode Mn as the operation mode MD, the normal operation control unit 410 sets these parameters of the normal operation mode Mn in the input / output control unit 580.

[0043] When the battery voltage Ev becomes equal to or higher than the upper limit voltage Vn_max, the input / output control unit 580 stops charging the battery pack 510 from the power system 600, and when the battery voltage Ev becomes equal to or lower than the lower limit voltage Vn_min, the input / output control unit 580 stops discharging from the battery pack 510 to the power system 600. The input / output control unit 580 also suppresses the charging current from the power system 600 to the battery pack 510 to equal to or lower than the maximum charging current Inc_max, and suppresses the discharging current from the battery pack 510 to the power system 600 to equal to or lower than the maximum discharging current Ind_max. When the battery voltage Ev becomes an extremely high or low value, there is a risk of deterioration, ignition, or the like of the battery pack 510. The input / output control unit 580 suppresses deterioration, ignition, or the like of the battery pack 510 by the above-mentioned control.

[0044] <Capacity recovery mode> In the capacity recovery mode Mr, the capacity recovery control unit 412 stops the operation of the input / output control unit 580. As a result, power is no longer input / output between the battery pack 510 and the power system 600. In addition, in the capacity recovery mode Mr, the capacity recovery control unit 412 performs a capacity recovery process. Here, the capacity recovery process refers to repeating one or more cycles, with a discharge pulse application process and a pause process being one cycle.

[0045] In the discharge pulse application step, the capacity recovery control unit 412 passes a discharge current of 1C or more and a maximum discharge current Ird_max or less at a C rate through the battery pack 510 for a discharge time of 1 second to 60 seconds. Here, the C rate is a method of specifying a charge / discharge current based on the battery capacity, and the current value at which the battery capacity is fully charged or discharged in one hour is expressed as 1C. The reason why the discharge rate is set to 1C or more is that a sufficient recovery effect cannot be obtained at a rate lower than that.

[0046] The discharge rate is set to the maximum discharge current Ird_max or less because an extremely high rate would increase the battery temperature due to Joule heat, which could lead to deterioration or even fire. The application time of the discharge pulse is set to 1 second or more because a short application time would not be sufficient to restore capacity, and the application time is set to 60 seconds or less because a long application time could lead to side reactions such as dissolution of the current collecting foil.

[0047] The capacity recovery control unit 412 executes a pause step immediately after the discharge pulse application step. The pause step is a period in which the discharge rate is lowered below the discharge rate in the above-mentioned discharge pulse application step. More preferably, the pause step is a step in which the battery pack 510 is put into an open circuit state and the current flowing through the battery pack 510 is set to "0". The length of the pause step is preferably 30 seconds or more and 6 hours or less per cycle. The reason why 30 seconds or more is preferable is that if the pause step is short, sufficient capacity recovery effect cannot be obtained. Also, the reason why 6 hours or less is preferable is that it is possible to prevent the pause time of the device (not shown) equipped with the battery pack 510 from becoming extremely long.

[0048] When the discharge pulse application process and the pause process are repeatedly executed over multiple cycles, the battery state determination unit 401 determines whether or not the end condition of the capacity recovery process is satisfied. If the end condition is satisfied, the operation mode selection unit 408 is notified of this fact. Upon receiving the notification, the operation mode selection unit 408 ends the capacity recovery process by the capacity recovery control unit 412, and returns the operation mode MD to the normal operation mode Mn.

[0049] The content of the end condition of the capacity recovery process is not particularly limited, but it is possible to determine that the process is ended when the number of cycles of the discharge pulse application process and the pause process reaches a predetermined number, for example. The predetermined number of cycles is not particularly limited, but is preferably between 1 and 10 times. The reason for this is that repeating the capacity recovery process even though it does not provide the effect of capacity recovery may promote battery deterioration. In other words, by setting the predetermined number of cycles to 10 or less, battery deterioration can be suppressed.

[0050] <Overall movement> FIG. 5 is a flowchart showing the overall operation of this embodiment. 5, when the process proceeds to step S2, the operation mode selection unit 408 (see FIG. 4) selects the normal operation mode Mn as the operation mode MD. As a result, the normal operation control unit 410 controls the input / output control unit 580 to charge and discharge the battery pack 510. That is, power is input / output between the battery pack 510 and the power system 600.

[0051] Next, when the process proceeds to step S4, the battery state determination unit 401 determines whether or not the capacity recovery process of the battery pack 510 is necessary based on the calculation results of the SOC and battery capacity Q input from the battery state calculation unit 404, the threshold value SOCth and the capacity threshold value Qth stored in the storage unit 403, and the usage history of the battery pack 510. If the determination is "No" here, the process returns to step S2, and the control of the normal operation mode Mn continues.

[0052] On the other hand, if the result of step S4 is "Yes", the process proceeds to step S6, where the operation mode selection unit 408 selects the capacity recovery mode Mr as the operation mode MD. Next, the process proceeds to step S8, where the capacity recovery control unit 412 executes the discharge pulse application process described above. Next, the process proceeds to step S10, where the capacity recovery control unit 412 executes the pause process described above. Next, the process proceeds to step S12, where the battery state determination unit 401 determines whether or not the end condition for the capacity recovery process is satisfied. If the result of this determination is "Yes", the process returns to step S2, where the operation mode selection unit 408 returns the operation mode MD to the normal operation mode Mn.

[0053] [Example] First Example In the following, various examples and comparative examples will be described in order to clarify the effects of this embodiment. In the first example, a discharge pulse was applied to a battery with an SOC of 10% for 5 seconds at a discharge rate of 10 C in the discharge pulse application step, and the open circuit voltage was then held for 15 minutes in the rest step. In the comparative example, the battery was overdischarged at a discharge rate of 0.1 C, and then a discharge pulse was applied for 5 seconds at a discharge rate of 10 C, and the open circuit voltage was then held for 15 minutes.

[0054] 6 is a diagram showing the recovered capacity and the time required for the capacity recovery process in the first embodiment and the comparative example. As shown in FIG. 6, according to this embodiment, the recovery effect was obtained to the same extent in a shorter time than in the comparative example. 7 is a diagram showing the power loss during the capacity recovery process and the SOC after the recovery process in the first embodiment and the comparative example. As shown in FIG. 7, in this embodiment, the power loss can be suppressed compared to the comparative example, and the SOC after the recovery process can be kept at 0% or more. As a result, according to this embodiment, it is possible to ensure discharge margin even immediately after the capacity recovery process.

[0055] Second Example In the second example, a battery with SOC 10% was subjected to a discharge pulse application process at a discharge rate of 10C for 5 seconds, and then the recovery capacity was measured by changing the open circuit voltage retention time in the rest process. As a comparative example, the recovery capacity was measured when only a discharge pulse was applied for 5 seconds at a discharge rate of 10C.

[0056] FIG. 8 is a diagram showing the recovery capacity versus the time of the pause step in the second embodiment and the comparative example. In the comparative example without the resting step, the capacity recovery effect was limited, whereas in the examples with the resting step of 30 seconds or more, the capacity recovery effect was improved. Also, the longer the open circuit voltage holding time, the higher the recovery capacity was obtained.

[0057] Third Example In the third example, a battery with SOC 10% was subjected to 5-second discharge pulses at various discharge rates in the discharge pulse application step, and then the open circuit state was maintained for 15 minutes in the rest step. As a comparative example, a discharge pulse was applied for 5 seconds at a discharge rate of 0.5C in the discharge pulse application step, and the recovery capacity was measured by changing the time for which the open circuit state was maintained in the rest step.

[0058] 9 is a diagram showing the recovery capacity versus discharge rate in the third embodiment and the comparative example. In the comparative example using a discharge rate of 0.5C, the capacity recovery effect was limited, whereas in this embodiment using a discharge rate of 1C or more, the capacity recovery effect was improved. Also, the higher the discharge rate, the higher the recovery capacity obtained.

[0059] Fourth embodiment In the fourth example, a battery with SOC 10% was subjected to various discharge pulses at a discharge rate of 10C in the discharge pulse application step, and then the open circuit state was maintained for 15 minutes in the rest step.In the comparative example, a discharge pulse was applied for 0.1 seconds at a discharge rate of 10C in the discharge pulse application step, and then the open circuit state was maintained for 15 minutes in the rest step.

[0060] FIG. 10 is a diagram showing the recovery capacity versus the discharge pulse application time in the fourth embodiment and the comparative example. In the comparative example in which a discharge pulse of 0.1 seconds was applied, the capacity recovery effect was limited, whereas in this example in which a discharge pulse of 1 second or more was applied, the capacity recovery effect was improved.

[0061] [Effects of the embodiment] According to the preferred embodiment as described above, the control device 550 includes an operation mode selection unit 408 which selects either the first operation mode (Mn) or the second operation mode (Mr) as the operation mode MD, a first discharge control unit (410) which, when the operation mode selection unit 408 selects the first operation mode (Mn), stops discharging the secondary battery (510) when the battery voltage Ev of the secondary battery (510) becomes equal to or lower than a first voltage (Vn_min) and suppresses the discharge current of the secondary battery (510) to equal to or lower than a first current (Ind_max), and a second discharge control unit (412) which, when the operation mode selection unit 408 selects the second operation mode (Mr), stops discharging the secondary battery (510) when the battery voltage Ev of the secondary battery (510) becomes equal to or lower than a second voltage (Vr_min) and suppresses the discharge current of the secondary battery (510) to equal to or lower than a second current (Ird_max). a second discharge control unit (412) for performing a capacity recovery process for the secondary battery (510) by executing one or more cycles, the cycle being defined as a discharge period in which a discharge current of 1 C or more and a second current (Ird_max) or less is discharged between a positive electrode terminal 502 and a negative electrode terminal 503 of the secondary battery (510) for a discharge time of 1 second or more and 60 seconds or less, and a pause period in which the positive electrode terminal 502 and the negative electrode terminal 503 are opened for a time of 30 seconds or more or the discharge current is made smaller than that during the discharge period, when a current value for completely charging or discharging the battery capacity of the secondary battery (510) in one hour is 1 C, and the second discharge control unit (412) performs a capacity recovery process for the secondary battery (510) by executing one or more cycles, the cycle being defined as a discharge period in which a discharge current of 1 C or more and a second current (Ird_max) or less is discharged between a positive electrode terminal 502 and a negative electrode terminal 503 for a discharge time of 1 second or more and 60 seconds or less, and a pause period in which the positive electrode terminal 502 and the negative electrode terminal 503 are opened for a time of 30 seconds or more, or the discharge current is made smaller than that during the discharge period, and at least one of the following conditions is satisfied: the second voltage (Vr_min) is lower than the first voltage (Vn_min) or the second current (Ird_max) is greater than the first current (Ind_max).

[0062] As a result, according to this embodiment, it is possible to appropriately recover the capacity of the secondary battery (510). In particular, even in applications in which it is difficult to over-discharge the secondary battery (510) during use, it is possible to appropriately recover the capacity of the secondary battery (510) while ensuring a discharge margin.

[0063] Moreover, it is more preferable that the operation mode selection unit 408 determines whether or not the capacity recovery process is necessary based on the usage history of the secondary battery (510) and the current SOC of the secondary battery (510), and selects the second operation mode (Mr) on the condition that the determination result is positive. This makes it possible to execute the capacity recovery process at an appropriate timing based on the usage history of the secondary battery (510) and the SOC of the secondary battery (510).

[0064] It is more preferable that the operation mode selection unit 408 determines that the capacity recovery process is necessary when either one of the following conditions is met: the capacity recovery process has not been performed for 7 days or more, or the current battery capacity has decreased by 1% or more from the battery capacity after the previous capacity recovery process was completed, and the SOC of the secondary battery (510) is less than a predetermined threshold SOCth between 0% and 20%. This makes it possible to execute the capacity recovery process at a more appropriate timing based on the contents of the past capacity recovery process.

[0065] Moreover, it is more preferable that the control device 550 further includes an input / output control unit 580 that inputs and outputs electric power between the secondary battery (510) and the power system 600. This makes it possible to apply the secondary battery system 500 to frequency adjustment and peak shifting in the power system 600.

[0066] [Variations] The present invention is not limited to the above-mentioned embodiment, and various modifications are possible. The above-mentioned embodiment is exemplified to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the configurations described. In addition, other configurations may be added to the configuration of the above-mentioned embodiment, and it is also possible to replace a part of the configuration with another configuration. In addition, the control lines and information lines shown in the figure show those that are considered necessary for explanation, and do not necessarily show all the control lines and information lines necessary on the product. In reality, it may be considered that almost all the configurations are connected to each other. Possible modifications of the above-mentioned embodiment are, for example, as follows.

[0067] (1) Since the hardware of control unit 570 in the above embodiment can be realized by a general-purpose computer, the flowchart shown in FIG. 5 and other programs for executing the various processes described above may be stored on a storage medium or distributed via a transmission path.

[0068] (2) In the above embodiment, the process shown in FIG. 5 and the other processes described above are described as software-based processes using a program. However, some or all of the processes may be replaced with hardware-based processes using an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), etc.

[0069] (3) The various processes executed in the above-described embodiments may be executed by a server computer via a network (not shown), and the various data stored in the above-described embodiments may also be stored in the server computer. [Explanation of symbols]

[0070] 100 Battery cells (secondary batteries) 408 Operation mode selection section 410 Normal operation control unit (first discharge control unit) 412 Capacity recovery control section (second discharge control section) 502 Positive terminal 503 Negative terminal 500 Secondary Battery System 510 Battery pack (secondary battery) 550 Control device 580 Input / Output Control Unit 600 Power system Ev Battery voltage MD Operation Mode Mn Normal operation mode (first operation mode) Mr Capacity Recovery Mode (Second Operation Mode) SOCth threshold Vn_min Lower limit voltage of normal operation mode Mn (first voltage) Vr_min Lower limit voltage of capacity recovery mode Mr (second voltage) Ind_max Maximum discharge current in normal operation mode Mn (first current) Ird_max Maximum discharge current in capacity recovery mode Mr (second current)

Claims

1. an operation mode selection unit that selects either a first operation mode or a second operation mode as an operation mode; a first discharge control unit having a function of stopping discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a first voltage when the operation mode selection unit selects the first operation mode, and a function of suppressing a discharge current of the secondary battery to equal to or lower than a first current when the operation mode selection unit selects the first operation mode; a second discharge control unit having a function of stopping discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a second voltage when the operation mode selection unit selects the second operation mode, and a function of suppressing a discharge current of the secondary battery to equal to or lower than a second current when the operation mode selection unit selects the second operation mode, The second discharge control unit performs a capacity recovery process for the secondary battery by executing one or more cycles, the cycle being defined as a discharge period in which a discharge current of 1C or more and the second current or less is discharged between a positive electrode terminal and a negative electrode terminal of the secondary battery for a discharge time of 1 second or more and 60 seconds or less, and a rest period in which the positive electrode terminal and the negative electrode terminal are opened for a time of 30 seconds or more, or the discharge current is made smaller than that in the discharge period, when a current value for completely charging or discharging the battery capacity of the secondary battery in one hour is 1C, and the second discharge control unit satisfies at least one of the conditions that the second voltage is lower than the first voltage or the second current is larger than the first current. A control device comprising:

2. The operation mode selection unit determines whether or not the capacity recovery process is necessary based on a usage history of the secondary battery and a current SOC of the secondary battery, and selects the second operation mode on condition that the determination result is positive. The control device according to claim 1 .

3. The operation mode selection unit determines that the capacity recovery process is necessary when any one of the following conditions is met: the capacity recovery process has not been performed for seven days or more; or the current battery capacity has decreased by 1% or more from the battery capacity after the previous capacity recovery process was completed; and the SOC of the secondary battery is less than a predetermined threshold value that is equal to or greater than 0% and equal to or less than 20%.

3. The control device according to claim 2.

4. An input / output control unit that inputs and outputs power between the secondary battery and a power grid.

4. The control device according to claim 1, wherein the control device is a control unit.

5. The present invention includes a secondary battery and a control device, the control device comprising: an operation mode selection unit that selects either a first operation mode or a second operation mode as an operation mode; a first discharge control unit having a function of stopping discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a first voltage when the operation mode selection unit selects the first operation mode, and a function of suppressing a discharge current of the secondary battery to equal to or lower than a first current when the operation mode selection unit selects the first operation mode; a second discharge control unit having a function of stopping discharging the secondary battery when the battery voltage of the secondary battery becomes equal to or lower than a second voltage when the operation mode selection unit selects the second operation mode, and a function of suppressing a discharge current of the secondary battery to equal to or lower than a second current when the operation mode selection unit selects the second operation mode, The second discharge control unit performs a capacity recovery process for the secondary battery by executing one or more cycles, the cycle being defined as a discharge period in which a discharge current of 1C or more and the second current or less is discharged between a positive electrode terminal and a negative electrode terminal of the secondary battery for a discharge time of 1 second or more and 60 seconds or less, and a rest period in which the positive electrode terminal and the negative electrode terminal are opened for a time of 30 seconds or more, or the discharge current is made smaller than that in the discharge period, when a current value for completely charging or discharging the battery capacity of the secondary battery in one hour is 1C, and the second discharge control unit satisfies at least one of the conditions that the second voltage is lower than the first voltage or the second current is larger than the first current. A secondary battery system comprising:

Images