Capacity recovery device, secondary battery system, and capacity recovery method

Abstract

To appropriately recover the capacity of a secondary battery in a capacity recovery device.SOLUTION: A capacity recovery device 550 includes a capacity recovery processing unit 576 that sets, as one cycle, a discharge period in which a discharge current flows between a positive electrode terminal 502 and a negative electrode terminal 503 of a secondary battery 510, and a rest period in which the space between the positive electrode terminal 502 and the negative electrode terminal 503 is opened or the discharge current is made smaller than in the discharge period, and performs capacity recovery processing of a secondary battery 510 by the discharge period and the rest period of one cycle or more, and a capacity recovery stop unit 578 that stops the capacity recovery processing according to the change in a battery voltage Ev of the secondary battery 510 in the capacity recovery processing.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a capacity recovery device, a secondary battery system, and a capacity recovery method. [Background technology]

[0002] As background art in this technical field, the abstract of the following Patent Document 1 states, "[Problem] An object of the present invention is to provide a method for restoring the performance of a deteriorated lithium-ion battery, and a power supply system equipped with a means for restoring battery performance. [Solution] A method for regenerating a battery which carries out at least one cycle of a step of increasing the potential of the negative electrode of a deteriorated lithium-ion battery above the potential of the positive electrode and then decreasing the potential of the negative electrode below the potential of the positive electrode. Also, a power supply system equipped with a means for increasing the potential of the negative electrode of a lithium-ion battery above the potential of the positive electrode and then decreasing the potential of the negative electrode below the potential of the positive electrode."

[0003] Furthermore, the abstract of Patent Document 2 listed below 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 the 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 disclosures of these documents are incorporated herein by reference. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-169094 A [Patent Document 2] JP 2019-106333 A Summary of the Invention [Problem to be solved by the invention]

[0005] 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 view of the above circumstances, and has an object to provide a capacity recovery device, a secondary battery system, and a capacity recovery method that can appropriately recover the capacity of a secondary battery. [Means for solving the problem]

[0006] In order to solve the above problems, the capacity recovery device of the present invention includes a capacity recovery processing unit that performs capacity recovery processing of the secondary battery by one or more cycles of a discharge period in which a discharge current is caused to flow between a positive electrode terminal and a negative electrode terminal of a secondary battery, and a pause period in which the positive electrode terminal and the negative electrode terminal are opened or the discharge current is made smaller than that during the discharge period, and a capacity recovery stopping unit that stops the capacity recovery processing in accordance with a change in the battery voltage of the secondary battery during the capacity recovery processing. The capacity recovery stopping unit stops the capacity recovery process when a discharge time, which is a time until the battery voltage reaches a predetermined reference voltage after the discharge period starts, is equal to or shorter than a predetermined first time. It is characterized by: Effect of the Invention

[0007] According to the present invention, the capacity of a secondary battery can be appropriately restored. [Brief description of the drawings]

[0008] [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] FIG. 1 is a schematic diagram of a presumed mechanism for capacity recovery by overdischarge treatment. [Figure 4] FIG. 1 is a block diagram of a secondary battery system according to a preferred embodiment. [Diagram 5] 4 is a flowchart showing the operation of a control unit. [Figure 6] FIG. 4 is a diagram showing the change in battery voltage during a discharging period. [Figure 7] 13 is an example showing measurement results of discharge time, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Overview of the embodiment] Lithium-ion batteries are a type of non-aqueous electrolyte secondary battery that have a high energy density and 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.

[0010] 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.

[0011] Regarding (3), it is thought that this occurs when lithium ions are absorbed into the coating component (SEI; Solid Electrolyte Interphase) formed at the interface between the negative electrode and the electrolyte, causing a loss of mobility. In addition, if lithium ions are absorbed into the negative electrode active material present on the negative electrode surface (non-opposing surface) that does not face the positive electrode during charging, the lithium ions cannot be used in the battery reaction during discharge, which may result in a decrease in capacity.

[0012] Of these factors, the capacity loss due to (3) above can be recovered by electrochemically oxidizing and decomposing the SEI, thereby restoring the capacity or battery output. In addition, the negative electrode potential can be reduced to a level that forces the lithium ions captured on the non-facing surface to be released during the discharge reaction, and the released lithium ions can be reused as battery capacity to recover the capacity.

[0013] The battery capacity is restored by releasing the lithium ions captured in the non-negative electrode facing portion by overdischarge treatment of a deteriorated secondary battery. On the other hand, the deterioration of the positive electrode and negative electrode is accelerated by the extreme drop in the positive electrode potential and the extreme rise in the negative electrode potential due to overdischarge treatment. When lithium ions remain in the non-negative electrode facing portion, the overdischarge energy is consumed by the movement of these lithium ions, but when lithium ions do not remain, the overdischarge energy is consumed to increase the positive electrode and negative electrode potential and promote the deterioration phenomenon of the positive electrode and negative electrode associated therewith. Therefore, it is desirable to perform recovery by overdischarge treatment only when lithium ions remain in the non-negative electrode facing portion. However, the above-mentioned Patent Documents 1 and 2 do not show a method for determining whether or not lithium ions remain in the non-negative electrode facing portion. For this reason, even if the battery capacity is not restored by overdischarge treatment, there is a possibility that the deterioration of the positive electrode and negative electrode will progress.

[0014] In the embodiment described later, the deterioration caused by the overdischarge process is suppressed in a secondary battery system using a lithium-ion battery in which the lithium ions fixed in the negative electrode are released and the capacity is restored by executing a cycle of overdischarge (discharge period) and rest (rest period) multiple times between the positive electrode and the negative electrode. Therefore, in the embodiment described later, the cycle of overdischarge and rest is repeated multiple times, the change in voltage over time during the overvoltage is detected, and based on the result, it is determined whether or not to continue the overdischarge process.

[0015] [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. As shown in FIG. 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.

[0016] FIG. 2 is a schematic side view of the electricity storage element 1. As shown in FIG. As shown in FIG. 2, in the electricity storage element 1, a plurality of positive electrodes 12 and a plurality of negative electrodes 13 are alternately stacked with separators 5 interposed therebetween. The electricity storage element 1 shown in FIG. 1 corresponds to a region where the positive electrodes 12 and the negative electrodes 13 appear to overlap. The electricity storage element 1 further contains an electrolyte (not shown), and the electrolyte is impregnated into micropores in 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, other than polypropylene, a microporous film or nonwoven fabric made of polyolefin such as polyethylene can also be used as the separator 5.

[0017] The positive electrode 12 includes a positive electrode current collector foil 122 and a positive electrode mixture layer 121 applied thereto. The negative electrode 13 includes a negative electrode current collector foil 132 and a negative electrode mixture layer 131 applied thereto. The positive electrode current collector foil 122 and the negative electrode current collector foil 132 are current collector foils made of appropriate metals. The positive electrode mixture layer 121 and the negative electrode mixture layer 131 are mixtures of appropriate electrode active materials, conductive agents, binders, and the like. Metal tabs are connected to the positive electrode current collector foil 122 and the negative electrode current collector foil 132 as terminals, respectively. These tabs become the positive electrode terminal 2 and the negative electrode terminal 3 shown in FIG. 1. In FIG. 1, the exterior material 6 is sealed with the positive electrode terminal 2 and the negative electrode terminal 3 exposed to the outside of the exterior material 6. This allows the battery cell 100 to be connected to the outside via the positive electrode terminal 2 and the negative electrode terminal 3. Hereinafter, the potentials of the positive electrode 12 and the negative electrode 13 will be 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 will be referred to as the battery voltage Epn.

[0018] Examples of materials and the like for each part of the battery cell 100 will be described below, but these are merely examples, and the battery cell 100 of the lithium-ion battery of this embodiment is not limited to a material, shape, manufacturing method, etc., and any material, shape, manufacturing method, etc. can be applied.

[0019] (positive electrode 12) The positive electrode current collector foil 122 (see FIG. 2) may be made of an aluminum foil having a thickness of 10 to 100 μm, a perforated aluminum 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 positive electrode current collector foil 122 may be stainless steel, titanium, or the like, in addition to aluminum. The electrode active material of the positive electrode mixture layer 121 preferably contains 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.

[0020] The type of electrode active material of the positive electrode 12 may be, for example, lithium cobalt oxide, lithium manganese-substituted cobalt oxide, lithium manganate, lithium nickel oxide, lithium iron phosphate, or other transition metal lithium phosphate, or 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 12 may contain one or more of the above-mentioned materials.

[0021] (Negative electrode 13) The negative electrode current collector foil 132 may be made of copper foil having a thickness of 10 to 100 μm, perforated copper foil having a thickness of 10 to 100 μm and a pore size of 0.1 to 10 mm, expanded metal, or foamed metal plate. The material of the negative electrode current collector foil 132 may be stainless steel or titanium in addition to copper. The electrode active material in the negative electrode 13 contains a material capable of reversibly inserting and releasing lithium ions.

[0022] The types of electrode active materials applied to the negative electrode mixture layer 131 include, for example, natural graphite, composite carbonaceous materials formed by forming a coating on natural graphite by a dry CVD method or a wet spray method, artificial graphite produced by firing resin materials such as epoxy and phenol, or pitch-based materials obtained from petroleum or coal, silicon (Si), graphite mixed with silicon, non-graphitizable carbon materials, and lithium titanate Li4Ti5O 12 The electrode active material applied to the negative electrode mixture layer 131 may contain one or more of the above-mentioned materials.

[0023] (electrolyte) In the case of a lithium ion battery, the electrolyte may be, 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).

[0024] Alternatively, an electrolyte solution in which lithium salts 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, and LiN(SO2CF2CF3)2 are dissolved in a solvent of the above-mentioned mixed organic compounds of two or more kinds can be mentioned. Alternatively, an electrolyte solution in which a mixed lithium salt of two or more of the above-mentioned types is dissolved can be used.

[0025] [Estimated mechanism of battery capacity recovery due to overdischarge] FIG. 3 is a schematic diagram of a presumed mechanism for capacity recovery by overdischarge treatment. 3, state STA shown on the upper side is a state in which the battery cell 100 with reduced capacity is overdischarged. State STB shown on the lower side is a state in which the positive electrode 12 and the negative electrode 13 of the battery cell 100 are open. The portion of the negative electrode 13 of the battery cell 100 that faces the positive electrode 12 is called the facing portion 13A, and the other portion is called the non-facing portion 13B.

[0026] In a lithium ion secondary battery such as the battery cell 100, charging and discharging proceeds by the exchange of lithium ions 22 between the positive electrode 12 and the opposing portion 13A of the negative electrode 13. However, during the charging and discharging process, if lithium ions 22 are taken into the non-opposing portion 13B that does not face the positive electrode, they become metallic lithium 24 (hatched in the figure) that does not contribute to charging and discharging, which causes a decrease in capacity.

[0027] Usually, the positive electrode potential Ep is set sufficiently higher than the negative electrode potential En. For example, w Ni x Co y Mn zIn a bipolar battery cell using graphite for the negative electrode, the value of the positive electrode potential Ep relative to the negative electrode potential En, i.e., the battery voltage Epn, is in the range of 2.5 to 4.5 V, and from the viewpoint of lifespan and safety, it is often in the range of, for example, 2.5 to 4.2 V. In this example, a battery voltage Epn of less than 2.5 V is called an "overdischarge state."

[0028] When performing the capacity recovery process, for example, as shown in state STA, the DC power supply 30 is connected in reverse polarity to the battery cell 100. That is, when the positive electrode of the DC power supply 30 is connected to the negative electrode 13 and the negative electrode of the DC power supply 30 is connected to the positive electrode 12, the battery cell 100 enters an overdischarge state. However, as long as the battery voltage Epn=Ep-En is set to less than 2.5V, the DC power supply 30 does not necessarily have to be in reverse polarity.

[0029] In this way, when the battery cell 100 is in an overdischarge state, the negative electrode potential En increases, the discharge reaction in the facing portion 13A progresses, and the lithium ions 22 are almost completely released from the facing portion 13A. This causes a difference in the concentration of lithium ions between the facing portion 13A and the non-facing portion 13B, resulting in a potential difference between the two.

[0030] Thereafter, when the battery cell 100 is put into a state STB in which the supply of voltage and current from the outside is stopped, electrons 26 move from the metallic lithium 24 adsorbed to the non-facing portion 13B to the facing portion 13A. This causes lithium ions 22 to leave the non-facing portion 13B, and at the same time, lithium ions 22 are inserted into the facing portion 13A. It is believed that this mechanism is how the capacity of the battery cell 100 is restored.

[0031] In the figure, the facing portion 13A and the non-facing portion 13B are arranged to sandwich the current collecting foil (no reference number), but the arrangement of the facing portion and the non-facing portion is not limited to this. That is, when the negative electrode 13 is wider than the positive electrode 12, the portion of the surface of the negative electrode 13 facing the positive electrode 12, which is a projection of the positive electrode 12, becomes the facing portion. And, the portion of the surface of the negative electrode 13 facing the positive electrode 12, which is located outside the projected portion, becomes the non-facing portion. In this case, the lithium ions taken in the non-facing portion located outside also contribute to capacity recovery.

[0032] When the battery cell 100 is subsequently charged, the DC power supply 30 is connected to the battery cell 100 in the direction opposite to the state STA. As a result, when the negative electrode potential En decreases, lithium ions 22 are again taken into the non-facing portion 13B, which may cause a decrease in the capacity of the battery cell 100.

[0033] [Secondary battery system] FIG. 4 is a block diagram of a secondary battery system 500 according to a preferred embodiment. The secondary battery system 500 includes a battery pack 510 (secondary battery) and a current control device 550 (capacity recovery device). The battery pack 510 includes a battery cell module 512 and a battery heating unit 514. The battery cell module 512 may be one battery cell 100 (see FIG. 1) or may be a battery cell 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 heating unit 514 heats the battery cell module 512 based on a command from the current control device 550. However, the battery heating unit 514 is not essential and may be omitted.

[0034] The battery pack 510 includes a positive terminal 502 and a negative terminal 503. When the battery cell module 512 includes only one battery cell 100, the positive terminal 502 and the negative terminal 503 correspond to the positive terminal 2 and the negative terminal 3 (see FIG. 1) of the battery cell 100, respectively. On the other hand, when a plurality of battery cells 100 are connected in series in the battery cell module 512, the positive terminal 502 corresponds to the positive terminal 2 of the battery cell 100 having the highest voltage, and the negative terminal 503 corresponds to the negative terminal 3 of the battery cell 100 having the lowest voltage. In FIG. 4, the positive terminal 502 and the negative terminal 503 of the battery pack 510 are each connected to a current control device 550.

[0035] Current control device 550 includes ammeter 551, voltmeter 552, variable resistor 553, power supply 554, switches 560, 562, and 564, and control unit 570 (computer). Power supply 554 is mainly for charging, and variable resistor 553 is for discharging. Current control device 550 also serves as a measuring instrument for grasping the state of battery pack 510.

[0036] 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 the information of 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. The control unit 570 also controls the resistance value of the variable resistor 553 to control the discharge current. 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.

[0037] The control unit 570 includes hardware such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), which are typical computer hardware. The ROM stores control programs executed by the CPU, various data, and the like. In Fig. 4, the inside of the control unit 570 shows functions realized by the control programs and the like as blocks. That is, the control unit 570 includes a mode setting unit 572, a charge / discharge processing unit 574, a capacity recovery processing unit 576 (capacity recovery processing process), and a capacity recovery stopping unit 578 (capacity recovery stopping process).

[0038] (Mode setting unit 572) The mode setting unit 572 switches the operation mode of the current control device 550 between a charge / discharge mode or a capacity recovery mode in response to a user operation or the state of the battery pack 510 .

[0039] (Charge / discharge processing unit 574) When the operation mode is set to the charge / discharge mode, the charge / discharge processing unit 574 performs charge / discharge operation of the battery pack 510 according to a normal application based on predetermined control parameters. For example, when the battery pack 510 is applied to drive a vehicle, the charge / discharge processing unit 574 performs charge / discharge operation for running the vehicle. The above-mentioned control parameters include a "discharge stop voltage Evs (not shown)". When the battery pack 510 is being discharged, if the battery voltage Ev becomes equal to or lower than the discharge stop voltage Evs, the charge / discharge processing unit 574 stops discharging the battery pack 510. Here, the discharge stop voltage Evs is a voltage at which the terminal voltage per battery cell 100 becomes equal to or lower than 2.5 V, for example.

[0040] (Capacity recovery processing unit 576) The capacity recovery processing unit 576 executes a capacity recovery process when the operation mode is set to the capacity recovery mode. Here, the capacity recovery process is a process in which a "discharge period" and a "rest period" are alternately repeated. The discharge period is a period during which the battery pack 510 is discharged so that the battery voltage Ev becomes equal to or lower than the discharge stop voltage Evs, and may include, for example, a period during which the terminal voltage per battery cell 100 becomes equal to or lower than 2.0 V.

[0041] The rest period is a period during which the discharge current flowing between the positive electrode terminal 502 and the negative electrode terminal 503 is made smaller than the discharge current flowing during the above-mentioned discharge period. Or, more preferably, the rest period is a period during which the positive electrode terminal 502 and the negative electrode terminal 503 are opened to make the discharge current "0". The length of the rest period may be determined arbitrarily, but is preferably 1 minute or longer. In this way, by repeating the discharge period and the components, the lithium ions deactivated inside the negative electrode 13 can be reactivated by the mechanism shown in FIG. 3, and the capacity of the battery pack 510 can be restored.

[0042] During the discharge period, the overdischarge current can be passed in a pulsed manner. The time for passing the current is not particularly limited, but can be, for example, 0.1 to 60 seconds. If it is shorter than 0.1 seconds, the effect is weak, and if it is longer than 60 seconds, the active material structure of the positive and negative electrodes is easily destroyed, which may shorten the lifespan.

[0043] The current value during the discharge period may be set arbitrarily, but if the current value is too large, battery deterioration due to heat generation or overvoltage cannot be ignored, and if the current value is too small, the recovery effect is small. If the current for discharging the capacity of a fully charged battery in 1 hour is 1 CA, and the current for discharging in 2 hours is 0.5 CA, it is preferable to set the current value in the range of 1 to 20 CA. The end condition for one discharge period may be "when the battery voltage reaches a predetermined lower limit discharge voltage Evd (not shown)", "when discharging continues for a predetermined discharge time td (not shown)", "when a predetermined capacity is discharged", or the like. Alternatively, any combination of these conditions may be set as the end condition for one discharge period.

[0044] (Capacity recovery stop part 578) The capacity recovery stopping unit 578 stops the capacity recovery process by the capacity recovery processing unit 576 based on the state of the battery pack 510 during the above-mentioned discharge period. For example, the capacity recovery stopping unit 578 measures the discharge time tk (not shown) until the battery voltage Ev reaches a predetermined reference voltage Evk (not shown) after the start of discharge. Then, when the discharge time tk satisfies a predetermined capacity recovery end condition, the capacity recovery stopping unit 578 may stop the operation of the capacity recovery processing unit 576. Note that the reference voltage Evk may be the same as the above-mentioned lower limit discharge voltage Evd, or may be a different voltage.

[0045] The above-mentioned capacity recovery ending conditions include, for example, the following conditions #1 to #3: That is, it is preferable to end the capacity recovery process when any one of these conditions #1 to #3 is satisfied. Condition #1: The discharge time tk in the most recent discharge period has become equal to or less than a predetermined time tkm (a first time, not shown). Here, the predetermined time tkm may be any value, but is preferably about 1 to 10 seconds. Condition #2: When the discharge time tk in the first discharge period in the capacity recovery process is defined as an initial discharge time tk1 (not shown), the ratio of the discharge time tk in the most recent discharge period to the initial discharge time tk1 is equal to or less than a predetermined ratio Rtk (first ratio, not shown). Here, the value of the ratio Rtk may be any value, but is preferably in the range of 0.05 to 0.5.

[0046] Condition #3: When the discharge time tk in the immediately preceding discharge period is defined as the previous discharge time tkp (not shown), the ratio of the discharge time tk in the most recent discharge period to the previous discharge time tkp becomes equal to or greater than a predetermined ratio Rtp (second ratio, not shown). Here, the value of the ratio Rtp may be any value, but is preferably 0.7 or more.

[0047] (Overall operation) FIG. 5 is a flowchart showing the operation of control unit 570. 5, when the process proceeds to step S2, the capacity recovery processing unit 576 executes a process for a discharging period. That is, a predetermined discharge current is caused to flow between the positive electrode terminal 502 and the negative electrode terminal 503. Next, when the process proceeds to step S4, the capacity recovery processing unit 576 executes a process for a pause period. For example, the positive electrode terminal 502 and the negative electrode terminal 503 are opened.

[0048] Next, when the process proceeds to step S6, the capacity recovery stopping unit 578 measures the discharge time tk from the start of discharge until the battery voltage Ev reaches the reference voltage Evk. Next, when the process proceeds to step S8, the capacity recovery stopping unit 578 determines whether or not the discharge time tk satisfies a predetermined capacity recovery end condition (for example, any one of the above conditions #1 to #3). If the determination here is "No", the process returns to step S2, and the processes of steps S2 to S8 are repeated. On the other hand, if the determination in step S8 is "Yes", the process proceeds to step S10, and the capacity recovery stopping unit 578 stops the capacity recovery process.

[0049] [Example] Next, examples that are preferable specific examples of the above-described embodiment will be described. (Configuration of battery pack 510) In this embodiment, a lithium ion battery was prototyped as the battery pack 510 with the cell configuration shown in FIG. 1 and FIG. 2. In the prototype lithium ion battery, an organic electrolyte was used that was applied to a carbonate solvent with a volatilization temperature of 20° C. Specifically, a 1M (=mol / dm 3 The solvent composition was ethyl carbonate (EC): dimethyl carbonate (DMC) = 1:2. The positive electrode was LiNi 1 / 3 Co 1 / 3 Mn 1 / 3A laminate cell was produced using O2 for the positive electrode and graphite for the negative electrode. The positive electrode material was applied to both sides of the Al current collector foil, and the negative electrode material was applied to both sides of the Cu current collector foil, so that the opposing negative / positive electrode capacity ratio was 1.3. After punching out the positive and negative electrodes to a specified shape, a porous substrate made of polyolefin material was laminated with the positive and negative electrodes. The capacity of the positive electrode was designed to be approximately 80 mAh on one side, and the capacity of the negative electrode was designed to be approximately 90 mAh on one side. The capacity of the battery pack 510 after initialization was approximately 280 mAh.

[0050] (Degradation test and capacity recovery process) As a deterioration test of the above-mentioned battery pack 510, 500 charge / discharge cycles were repeated in a 50°C environment, and it was confirmed that the battery capacity decreased to about 80% of the initial capacity. Next, the battery pack 510 was discharged to adjust the battery voltage Ev to 3.0V, and then a capacity recovery process was performed. In the capacity recovery process, a discharge period and a rest period were defined as one cycle, and this cycle was repeated multiple times. First, in the discharge period, a discharge pulse of 10 CA was passed for 5 seconds or until the battery voltage Ev reached the lower limit discharge voltage Evd=0V. That is, if the battery voltage Ev did not reach the lower limit discharge voltage Evd=0V, the discharge period was 5 seconds, and if the battery voltage Ev reached the lower limit discharge voltage Evd, the discharge period ended at that point. In addition, the rest period was set to 15 minutes, and the battery pack 510 was in an open state for that time.

[0051] Fig. 6 is a diagram showing the change in battery voltage Ev during the discharging period, in which characteristics P1 to P4 show the change characteristics of battery voltage Ev during the discharging periods of the first to fourth cycles, respectively. Each time the cycle is repeated, the number of lithium ions remaining in the non-facing portion decreases, and as shown in the figure, the rate at which the voltage decreases increases.

[0052] FIG. 7 is an example showing the measurement results of the discharge time tk, etc. In FIG. 7, 1.5V is used as the above-mentioned reference voltage Evk. In this embodiment, when the discharge time tk becomes less than 0.2 times the initial discharge time tk1 (4 seconds in the illustrated example), the capacity recovery process is terminated. As a result, the capacity recovery process is terminated after four cycles. FIG. 7 also shows the capacity recovery amount in each cycle. According to this embodiment, 3% of the capacity can be recovered by repeating four cycles. Also, referring to the capacity recovery amounts for the first to third cycles, it can be seen that the recovery efficiency reaches a plateau each time the cycle is repeated.

[0053] [Comparative Example] Next, in order to clarify the effect of this embodiment, a comparative example will be described. The configuration of the battery pack 510 in this comparative example is the same as that in the above-mentioned embodiment. The processing contents per cycle of the discharge period and the rest period in the capacity recovery process are also the same as those in the above-mentioned embodiment. However, in the capacity recovery process of this comparative example, the cycle of the discharge period and the rest period was repeated 10 times. The capacity recovery amount after the capacity recovery process was completed was 3% of the initial capacity, which was the same as in the above-mentioned embodiment. However, in this comparative example, the internal resistance of the battery pack 510 after the capacity recovery process was higher than that in the embodiment, and a side effect of battery degradation occurred.

[0054] [Effects of the embodiment] According to the preferred embodiment as described above, the capacity recovery device (550) includes a capacity recovery processing unit (576) that performs a capacity recovery process for the secondary battery (510) by one or more cycles of discharge periods and pause periods, each cycle being defined as a discharge period during which a discharge current is passed between the positive electrode terminal (502) and the negative electrode terminal (503) of the secondary battery (510) and a pause period during which the positive electrode terminal (502) and the negative electrode terminal (503) are opened or the discharge current is made smaller than that during the discharge period, and a capacity recovery stopping unit (578) that stops the capacity recovery process according to a change in the battery voltage (Ev) of the secondary battery (510) during the capacity recovery process. Since the capacity recovery process can be stopped according to a change in the battery voltage (Ev), deterioration of the secondary battery (510) can be suppressed and the capacity of the secondary battery can be appropriately restored.

[0055] More preferably, the discharge period is from 0.1 to 60 seconds, and the capacity recovery processor (576) applies a pulsed current to the secondary battery (510) during the discharge period and the rest period, thereby enabling the capacity of the secondary battery to be more appropriately recovered.

[0056] More preferably, the capacity recovery processor 576 performs the capacity recovery process for the secondary battery 510 by repeating one cycle multiple times, so that the capacity recovery process can be continued until a sufficient capacity recovery effect is obtained.

[0057] It is more preferable that the capacity recovery stop unit (578) stops the capacity recovery process when the discharge time (tk), which is the time it takes for the battery voltage (Ev) to reach a predetermined reference voltage (Evk) after the start of the discharge period, is equal to or shorter than a predetermined first time (tkm). This allows the capacity recovery stop unit (578) to stop the capacity recovery process when the recovery efficiency reaches a plateau, based on the relationship between the discharge time (tk) and the first time (tkm).

[0058] More preferably, the capacity recovery stopping unit (578) sets the discharge time (tk) in the first cycle as the initial discharge time (tk1) and stops the capacity recovery process when the ratio of the discharge time (tk) in the second or subsequent cycles to the initial discharge time (tk1) becomes equal to or less than a predetermined first ratio (Rtk). In this way, the capacity recovery stopping unit (578) can stop the capacity recovery process when the recovery efficiency reaches a plateau, based on the relationship between the initial discharge time (tk1) and the discharge time (tk) in the second or subsequent cycles.

[0059] More preferably, the capacity recovery stopping unit (578) sets the discharge time (tk) in the immediately preceding cycle as the immediately preceding discharge time (tkp) and stops the capacity recovery process when the ratio of the discharge time (tk) in the immediately preceding cycle to the immediately preceding discharge time (tkp) becomes equal to or greater than a predetermined second ratio (Rtp). In this way, the capacity recovery stopping unit (578) can stop the capacity recovery process when the recovery efficiency reaches a plateau, based on the relationship between the immediately preceding discharge time (tkp) and the discharge time (tk) in the immediately preceding cycle.

[0060] [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.

[0061] (1) The hardware of current control device 550 in the above embodiment can be realized by a general computer. Therefore, a program for executing the various processes described above may be stored on a storage medium or distributed via a transmission line.

[0062] (2) In the above embodiment, each of the above-mentioned processes has been 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.

[0063] (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]

[0064] 100 Battery cells (secondary batteries) 500 Secondary Battery System 502 Positive terminal 503 Negative terminal 510 Battery pack (secondary battery) 550 Current control device (capacity recovery device) 576 Capacity recovery processing unit (capacity recovery processing process) 578 Capacity recovery stop section (capacity recovery stop process) Ev Battery voltage tk discharge time Evk Reference Voltage Rtk ratio (first ratio) RTP ratio (second ratio) tk1 First discharge time tkm Predetermined time (first time) tkp Last discharge time

Claims

1. a capacity recovery processing unit that performs a capacity recovery process on the secondary battery by one or more cycles of a discharge period in which a discharge current is passed between a positive electrode terminal and a negative electrode terminal of the secondary battery, and a pause period in which the positive electrode terminal and the negative electrode terminal are opened or the discharge current is made smaller than that in the discharge period; a capacity recovery stopping unit that stops the capacity recovery process in response to a change in a battery voltage of the secondary battery during the capacity recovery process, The capacity recovery stopping unit stops the capacity recovery process when a discharge time, which is a time until the battery voltage reaches a predetermined reference voltage after the discharge period starts, is equal to or shorter than a predetermined first time. A capacity recovery device.

2. The discharge period is from 0.1 seconds to 60 seconds, The capacity recovery processing unit causes a pulsed current to flow through the secondary battery during the discharge period and the pause period.

2. The capacity recovery device according to claim 1 .

3. The capacity recovery processing unit performs a capacity recovery process for the secondary battery by repeating the one cycle a plurality of times.

3. The capacity recovery device according to claim 1 or 2.

4. The capacity recovery stopping unit determines a time until the battery voltage reaches a predetermined reference voltage after the start of the discharge period as a discharge time, determines the discharge time in a first cycle as an initial discharge time, and stops the capacity recovery process when a ratio of the discharge time in a second or subsequent cycle to the initial discharge time becomes equal to or less than a predetermined first ratio.

4. The capacity recovery device according to claim 3.

5. The capacity recovery stopping unit determines a time until the battery voltage reaches a predetermined reference voltage after the start of the discharge period as a discharge time, determines the discharge time in the immediately preceding cycle as a previous discharge time, and stops the capacity recovery process when a ratio of the discharge time in the most recent cycle to the previous discharge time becomes equal to or greater than a second predetermined ratio.

4. The capacity recovery device according to claim 3.

6. A secondary battery; a capacity recovery processing unit that performs a capacity recovery process on the secondary battery by one or more cycles of a discharge period in which a discharge current is passed between a positive electrode terminal and a negative electrode terminal of the secondary battery, and a pause period in which the positive electrode terminal and the negative electrode terminal are opened or the discharge current is made smaller than that in the discharge period; a capacity recovery stopping unit that stops the capacity recovery process in response to a change in a battery voltage of the secondary battery during the capacity recovery process, The capacity recovery stopping unit stops the capacity recovery process when a discharge time, which is a time until the battery voltage reaches a predetermined reference voltage after the discharge period starts, is equal to or shorter than a predetermined first time. A secondary battery system comprising:

7. The capacity recovery processing unit performs a capacity recovery process for the secondary battery by repeating the one cycle a plurality of times.

7. The secondary battery system according to claim 6.

8. The capacity recovery stopping unit determines a time until the battery voltage reaches a predetermined reference voltage after the start of the discharge period as a discharge time, determines the discharge time in a first cycle as an initial discharge time, and stops the capacity recovery process when a ratio of the discharge time in a second or subsequent cycle to the initial discharge time becomes equal to or less than a predetermined first ratio.

8. The secondary battery system according to claim 7.

9. The capacity recovery stopping unit determines a time until the battery voltage reaches a predetermined reference voltage after the start of the discharge period as a discharge time, determines the discharge time in the immediately preceding cycle as a previous discharge time, and stops the capacity recovery process when a ratio of the discharge time in the most recent cycle to the previous discharge time becomes equal to or greater than a second predetermined ratio.

8. The secondary battery system according to claim 7.

10. a capacity recovery process in which one cycle is defined as a discharge period during which a discharge current is passed between a positive electrode terminal and a negative electrode terminal of a secondary battery, and a rest period during which the positive electrode terminal and the negative electrode terminal are opened or the discharge current is made smaller than that during the discharge period, and a capacity recovery process is performed on the secondary battery through one or more cycles of the discharge period and the rest period; a capacity recovery stopping step of stopping the capacity recovery process in response to a change in the battery voltage of the secondary battery during the capacity recovery process, The capacity recovery stopping step is a step of stopping the capacity recovery process when a discharge time, which is a time until the battery voltage reaches a predetermined reference voltage after the discharge period starts, is equal to or shorter than a predetermined first time. A capacity recovery method comprising:

11. The capacity recovery process performs the capacity recovery process on the secondary battery by repeating the one cycle a number of times. The capacity recovery method according to claim 10 .

12. The capacity recovery stopping step is a step of setting a time from when the discharge period starts until the battery voltage reaches a predetermined reference voltage as a discharge time, setting the discharge time in a first cycle as an initial discharge time, and stopping the capacity recovery process when a ratio of the discharge time in a second or subsequent cycle to the initial discharge time becomes equal to or less than a first ratio. The capacity recovery method according to claim 11 .

13. The capacity recovery stopping step is a step of setting a time from when the discharge period starts until the battery voltage reaches a predetermined reference voltage as a discharge time, setting the discharge time in the immediately preceding cycle as a previous discharge time, and stopping the capacity recovery process when a ratio of the discharge time in the most recent cycle to the previous discharge time becomes equal to or greater than a second predetermined ratio. The capacity recovery method according to claim 11 .

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