JP2022178037A - Capacity recovery device, secondary battery system, and capacity recovery method - Google Patents

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

The present invention relates to a capacity recovery device, a secondary battery system and a capacity recovery method.

As a background art of this technical field, the abstract of Patent Document 1 below states, "[Problem] An object of the present invention is to provide a method for recovering the performance of a deteriorated lithium-ion battery and a power supply system provided with means for recovering the battery performance. [Solution] A battery in which a step of increasing the potential of a negative electrode of a deteriorated lithium-ion battery to a level higher than that of a positive electrode and then lowering the potential of the negative electrode to a level lower than that of the positive electrode is performed for at least one cycle. and a power supply system comprising means for increasing the potential of the negative electrode of a lithium-ion battery above the potential of the positive electrode and then lowering the potential of the negative electrode below the potential of the positive electrode.” ing.

In addition, the summary of Patent Document 2 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 time. The ECU 960 executes capacity recovery control to recover the capacity of the assembled battery 10. The capacity recovery control includes a discharge mode and a capacity recovery mode.In the discharge mode, the ECU 960 controls the assembled battery 10 to a predetermined In the capacity recovery mode, in the overdischarge region, the ECU 960 controls the voltage rise of the lithium ion secondary battery by stopping discharge and pulse discharge to discharge the lithium ion secondary battery while oscillating the discharge current. is repeatedly executed.”
The descriptions of these documents are incorporated as part of the present specification.

JP 2012-169094 A JP 2019-106333 A

By the way, in the above-described technique, there were cases where the capacity of the secondary battery could not be appropriately recovered.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a capacity recovery device, a secondary battery system, and a capacity recovery method capable of appropriately recovering the capacity of a secondary battery.

In order to solve the above problems, the capacity recovery device of the present invention provides a discharge period in which a discharge current flows between a positive electrode terminal and a negative electrode terminal of a secondary battery, and a space between the positive electrode terminal and the negative electrode terminal is opened. or a rest period in which the discharge current is smaller than that of the discharge period is set as one cycle, and a capacity recovery processing unit that performs capacity restoration processing of the secondary battery in one or more cycles of the discharge period and the rest period; and a capacity recovery stopping unit that stops the capacity recovery process according to a change in the battery voltage of the secondary battery during the capacity recovery process.

ADVANTAGE OF THE INVENTION According to this invention, the capacity|capacitance of a secondary battery can be recovered appropriately.

1 is a schematic cross-sectional view of a bipolar battery cell; FIG. FIG. 4 is a schematic side view of a power storage element; FIG. 4 is a schematic diagram of a presumed mechanism regarding capacity recovery by overdischarge treatment. 1 is a block diagram of a secondary battery system according to a preferred embodiment; FIG. 4 is a flow chart showing the operation of a control unit; FIG. 4 is a diagram showing changes in battery voltage during a discharge period; It is an example which shows the measurement results, such as discharge time.

[Overview of embodiment]
Lithium ion batteries are one type of non-aqueous electrolyte secondary batteries, and because of their high energy density, they are also used as batteries for mobile devices and, in recent years, as batteries for electric vehicles. However, lithium ion batteries are known to deteriorate with use and decrease in battery capacity.
Lithium ion batteries generally use a lithium metal oxide as a positive electrode active material and a carbon material such as graphite as a negative electrode active material. A positive electrode and a negative electrode of a lithium ion battery are formed by adding a binder (binder), a conductive agent, etc. to minute active material particles to form a slurry (mixture), and then applying the slurry (mixture) to a metal foil.

During charging, the lithium ions released from the positive electrode active material are absorbed by the negative electrode active material, and during discharging, the lithium ions absorbed by the negative electrode active material are released and absorbed by the positive electrode active material. Thus, current flows between the electrodes as lithium ions move between the electrodes.
In such lithium-ion batteries,
(1) electrical isolation of the positive electrode active material,
(2) electrical isolation of the negative electrode active material, and (3) immobilization of lithium ions traveling between the electrodes,
capacity is reduced by

Regarding (3), it is considered that lithium ions are taken into a film component (SEI: Solid Electrolyte Interphase) formed at the interface between the negative electrode and the electrolyte, resulting in loss of mobility. In addition, if lithium ions are taken into the negative electrode active material present on the negative electrode surface (non-facing surface) that does not face the positive electrode during charging, the lithium ions cannot be used for the battery reaction during discharging, resulting in a decrease in capacity. It is also possible that it will decrease.

Of these factors, the decrease in capacity due to the above (3) can be recovered by electrochemically oxidizing and decomposing and removing the above SEI to restore the capacity or battery output. In addition, during the discharge reaction, the negative electrode potential is reduced enough to forcibly release the lithium ions taken into the non-facing surface, and the released lithium ions are used again as battery capacity, thereby recovering the capacity.

The battery capacity is restored by releasing the lithium ions taken into the negative electrode non-facing portion by the overdischarge treatment of the deteriorated secondary battery. On the other hand, the overdischarge treatment causes the positive electrode potential to extremely decrease and the negative electrode potential to extremely increase, thereby accelerating the deterioration of the positive electrode and the negative electrode. When lithium ions remain in the portion not facing the negative electrode, the movement of the lithium ions consumes the energy of overdischarge. The energy of overdischarge is consumed to accelerate the degradation phenomenon of the positive and negative electrodes that accompanies this. Therefore, it is desirable to perform recovery by overdischarge treatment only when lithium ions remain in the portion not facing the negative electrode. However, the aforementioned Patent Documents 1 and 2 do not disclose a method for determining whether or not lithium ions remain in the portion not facing the negative electrode. For this reason, there is a possibility that the deterioration of the positive and negative electrodes progresses while the battery capacity does not recover even after the overdischarge treatment.

Therefore, in the embodiment described later, the cycle of overdischarge (discharge period) and rest (rest period) is executed multiple times between the positive electrode and the negative electrode to release the lithium ions immobilized in the negative electrode and increase the capacity. An object is to suppress deterioration due to overdischarge treatment in a secondary battery system using a recoverable lithium ion battery. Therefore, in the embodiment described later, the cycle of overdischarge and rest is repeated multiple times, the time change of the voltage during the overvoltage is detected, and based on the result, it is determined whether or not to continue the overdischarge process.

[Battery cell structure]
First, a structural example of a bipolar battery cell applicable to the embodiment will be described with reference to FIGS. 1 and 2. FIG.
FIG. 1 is a schematic cross-sectional view of a bipolar battery cell 100. FIG.
In FIG. 1 , a battery cell 100 (secondary battery) is a cell of a lithium ion battery, and includes a power 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 storage element 1 . The exterior material 6 is constructed using a laminate film or a similar material.

FIG. 2 is a schematic side view of the storage element 1. FIG.
As shown in FIG. 2 , in the 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 storage element 1 shown in FIG. 1 corresponds to the region where the positive electrode 12 and the negative electrode 13 appear to overlap. The storage element 1 further contains an electrolytic solution (not shown), and the electrolytic solution impregnates micropores of the positive electrode 12, the negative electrode 13, the separator 5, and the like. As the separator 5, for example, polypropylene can be applied. However, as the separator 5, a microporous film made of polyolefin such as polyethylene or a non-woven fabric can be applied in addition to polypropylene.

The positive electrode 12 includes a positive current collector foil 122 and a positive electrode mixture layer 121 applied thereto. Further, the negative electrode 13 includes a negative electrode 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 suitable metal current collector foils. Also, the positive electrode mixture layer 121 and the negative electrode mixture layer 131 are mixtures of suitable electrode active materials, conductive agents, binders, and the like. Metal tabs serving as terminals are connected to the positive current collector foil 122 and the negative current collector foil 132, respectively. These tabs become the positive terminal 2 and the negative terminal 3 shown in FIG. 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 . Thereby, the battery cell 100 can be connected to the outside through the positive terminal 2 and the negative terminal 3 . The potentials of the positive electrode 12 and the negative electrode 13 are hereinafter referred to as a positive electrode potential Ep and a negative electrode potential En. The difference between the two, ie, "Ep-En", is the voltage between the positive terminal 2 and the negative terminal 3, and is called the battery voltage Epn.

Examples of materials and the like of each part of the battery cell 100 will be described below, but these are only examples, and the battery cell 100 of the lithium ion battery of the present embodiment is not limited to materials, shapes, manufacturing methods, and the like. , any material, shape, manufacturing method, etc. can be applied.

(Positive electrode 12)
The positive current collector foil 122 (see FIG. 2) is made of an aluminum foil with a thickness of 10 to 100 μm, a perforated aluminum foil with a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like. can be applied. In addition to aluminum, stainless steel, titanium, and the like can also be used for the material of the positive electrode current collector foil 122 . The electrode active material of the positive electrode mixture layer 121 preferably contains reactive species therein. The reactive species in lithium ion batteries is lithium ions. In this case, the electrode active material contains a lithium-containing compound capable of reversibly intercalating and deintercalating lithium ions.

Examples of the electrode active material of the positive electrode 12 include lithium cobaltate, manganese-substituted lithium cobaltate, lithium manganate, lithium nickelate, lithium transition metal phosphate such as olivine-type lithium iron phosphate, or Li _w Ni _x . Co _y Mn _z O ₂ (here, w, x, y, and z are 0 or positive values). Further, as the electrode active material of the positive electrode 12, the materials described above may be contained singly or in combination of two or more.

(Negative electrode 13)
As the negative electrode current collector foil 132, a copper foil with a thickness of 10 to 100 μm, a perforated copper foil with a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like can be applied. Further, as the material of the negative electrode current collector foil 132, other than copper, stainless steel, titanium, or the like can be applied. The electrode active material in the negative electrode 13 contains a material capable of reversibly intercalating and deintercalating lithium ions.

Examples of the type of electrode active material applied to the negative electrode mixture layer 131 include natural graphite, a composite carbonaceous material obtained by forming a film on natural graphite by a dry CVD method or a wet spray method, and a resin such as epoxy or phenol. Synthetic graphite manufactured by firing materials or pitch-based materials obtained from petroleum or coal as raw materials, silicon (Si), graphite mixed with silicon, non-graphitizable carbon materials, and lithium titanate Li ₄ Ti ₅ O ₁₂ . be done. As the electrode active material applied to the negative electrode mixture layer 131, the materials described above may be contained singly or in combination of two or more.

(Electrolyte)
In the case of lithium-ion batteries, the electrolyte is, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl Aprotic organic solvents such as propyl carbonate (MPC) and ethyl propyl carbonate (EPC) can be applied.

Alternatively, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium iodide, lithium chloride, lithium bromide, LiB[OCOCF ₃ ] is added to the solvent of the mixed organic compound of two or more kinds described above. ₄ , LiB[ _OCOCF2CF3 ] ₄ , _{LiPF4 ( CF3} ) _{2 ,} LiN _{( SO2CF3} ) ₂ , LiN( _SO2CF2CF3 ) ₂ and other lithium salt _- dissolved electrolytes. .
Alternatively, an electrolytic solution in which two or more kinds of mixed lithium salts described above are dissolved can be used.

[Presumed mechanism of battery capacity recovery due to overdischarge]
FIG. 3 is a schematic diagram of a presumed mechanism regarding capacity recovery by overdischarge treatment.
In FIG. 3, the state STA illustrated on the upper side is a state in which the battery cell 100 whose capacity has decreased is over-discharged. A state STB illustrated on the lower side is a state in which the positive electrode 12 and the negative electrode 13 of the battery cell 100 are opened. A portion of the negative electrode 13 of the battery cell 100 that faces the positive electrode 12 is called a facing portion 13A, and the other portion is called a non-facing portion 13B.

In a lithium-ion secondary battery such as the battery cell 100 , charge/discharge proceeds as lithium ions 22 are exchanged between the positive electrode 12 and the opposing portion 13A of the negative electrode 13 . However, when the lithium ions 22 are taken into the non-facing portion 13B that does not face the positive electrode in the charging/discharging process, they become metal lithium 24 (hatched in the figure) that does not contribute to the charging/discharging, which is a factor in the decrease in capacity. becomes.

Normally, the positive electrode potential Ep is set sufficiently higher than the negative electrode potential En. For example, in a bipolar battery cell using Li _w Ni _x Co _y Mn _z O ₂ as the positive electrode and graphite as the negative electrode, the value of the positive electrode potential Ep with respect to the negative electrode potential En, that is, the battery voltage Epn is 2.5 to 4. 5V, and from the viewpoint of life and safety, it is often in the range of, for example, 2.5 to 4.2V. In this example, the state where the battery voltage Epn becomes less than 2.5V is called an "overdischarge state."

When the capacity recovery process is performed, the DC power supply 30 is connected to the battery cell 100 in reverse polarity, as shown in state STA, for example. That is, when the positive electrode of the DC power source 30 is connected to the negative electrode 13 and the negative electrode of the DC power source 30 is connected to the positive electrode 12, the battery cell 100 is over-discharged. However, if the battery voltage Epn=Ep-En is less than 2.5V, the DC power supply 30 does not necessarily have the reverse polarity.

Thus, when the battery cell 100 is over-discharged, the negative electrode potential En increases, the discharge reaction in the opposing portion 13A proceeds, and the lithium ions 22 are almost completely released from the opposing portion 13A. As a result, a difference in lithium ion concentration occurs between the facing portion 13A and the non-facing portion 13B, and a potential difference occurs between the two.

After that, when the battery cell 100 is put into the state STB in which the voltage/current supply from the outside is stopped, the electrons 26 move from the metallic lithium 24 adsorbed to the non-facing portion 13B to the facing portion 13A. As a result, the lithium ions 22 are released from the non-facing portion 13B, and at the same time the lithium ions 22 are inserted into the opposing portion 13A. It is considered that the capacity of the battery cell 100 is recovered by such a mechanism.

Note that the facing portion 13A and the non-facing portion 13B in the drawing are arranged so as to sandwich the collector foil (no reference numeral), but the arrangement of the facing portion and the non-facing portion is not limited to this. In other words, 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 where the positive electrode 12 is projected becomes the facing portion. Of the surface of the negative electrode 13 facing the positive electrode 12, the portion located outside the projected portion is the non-facing portion. In this case, the lithium ions taken into the non-opposing portion located on the outer side also become a factor for capacity recovery.

When charging the battery cell 100 after that, the DC power supply 30 is connected to the battery cell 100 in the opposite direction to the state STA. As a result, when the negative electrode potential En drops, the lithium ions 22 are taken into the non-facing portion 13B again, and there is concern that the capacity of the battery cell 100 may drop.

[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 section 514 . The battery cell module 512 may be a single battery cell 100 (see FIG. 1), or multiple battery cells 100 connected in series and/or in parallel. As used herein, the term "secondary battery" is a concept that includes lithium-ion battery cells, battery modules, and battery packs. Battery heating unit 514 heats battery cell module 512 based on a command from current control device 550 . However, the battery heating unit 514 is not essential and may be omitted.

The battery pack 510 has a positive terminal 502 and a negative terminal 503 . If the battery cell module 512 comprises 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 of the battery cell 100 (see FIG. 1), 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 with the highest voltage, and the negative terminal 503 has the lowest voltage. It corresponds to the negative electrode terminal 3 of the battery cell 100 . In FIG. 4, positive terminal 502 and negative terminal 503 of battery pack 510 are each connected to current control device 550 .

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

Ammeter 551 measures the current flowing through positive terminal 502 and negative terminal 503 of battery pack 510 and outputs the result to control section 570 . Voltmeter 552 measures battery voltage Ev between the positive electrode and the negative electrode, and outputs the result to control unit 570 . Control unit 570 switches and controls switches 560 , 562 and 564 based on information from ammeter 551 and voltmeter 552 . As a result, control unit 570 sets positive terminal 502 and negative terminal 503 of battery pack 510 to an open state, a state in which variable resistor 553 is connected, or a state in which power source 554 is connected. Also, 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 with the lapse of time during discharging, but the control unit 570 reduces the resistance value of the variable resistor 553 with the lapse of time, so that the discharge current can be kept constant.

The control unit 570 includes general computer hardware such as a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). Programs, various data, etc. are stored. In FIG. 4, the inside of the control unit 570 shows functions implemented by 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). .

(Mode setting unit 572)
Mode setting unit 572 switches the operation mode of current control device 550 between the charge/discharge mode and the capacity recovery mode according to the user's operation or the state of battery pack 510 .

(Charge/discharge processing unit 574)
When the operation mode is set to the charge/discharge mode, charge/discharge processing unit 574 performs charge/discharge operation of battery pack 510 in accordance with a normal application based on predetermined control parameters. For example, when the battery pack 510 is used for driving a vehicle, the charging/discharging processing unit 574 performs charging/discharging operation for driving the vehicle. The above control parameters include "discharge stop voltage Evs (not shown)". When the battery voltage Ev becomes equal to or lower than the discharge stop voltage Evs while the battery pack 510 is being discharged, 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 is 2.5 V or less, for example.

(Capacity recovery processing unit 576)
The capacity recovery processing unit 576 executes capacity recovery processing when the operation mode is set to the capacity recovery mode. Here, the capacity recovery process is a process that alternately repeats the "discharge period" and the "idle period". The discharge period is a period during which the battery pack 510 is discharged so that the battery voltage Ev becomes equal to or less than the discharge stop voltage Evs. Good.

The pause period is a period in 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 discharge period described above. Alternatively, more preferably, the pause period is a period in which the positive terminal 502 and the negative terminal 503 are opened to set the discharge current to "0". Although the length of the rest period may be determined arbitrarily, it is preferably one minute or longer. By repeating the discharge period and the components in this way, the deactivated lithium ions inside the negative electrode 13 can be reactivated by the mechanism shown in FIG. can be made

During the discharge period, the overdischarge current can be passed in pulses. The flow time is not particularly limited, but can be 0.1 to 60 seconds, for example. 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 electrode and the negative electrode is likely to be destroyed, and the life may rather be shortened.

The current value during the discharge period may be determined 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. Assuming that the current for discharging the capacity of a fully charged battery in one hour is 1 CA and the current for discharging in two hours is 0.5 CA, it is preferable to set the current value in the range of 1 to 20 CA. Conditions for ending one discharge period are "when the battery voltage reaches a predetermined lower discharge voltage Evd (not shown)" and "when discharge continues for a predetermined discharge time td (not shown)". , "when a predetermined capacity is discharged", etc. may be used. Alternatively, an arbitrary combination of these conditions may be used as the termination condition for one discharge period.

(Capacity Recovery Stop Unit 578)
Capacity recovery stopping unit 578 stops the capacity recovery processing by capacity recovery processing unit 576 based on the state of battery pack 510 during the discharge period described above. 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 discharging. Then, it is preferable to stop the operation of the capacity recovery processing section 576 when the discharge time tk satisfies a predetermined capacity recovery termination condition. Note that the reference voltage Evk may be the same as or different from the above-described lower limit discharge voltage Evd.

Conditions #1 to #3 below, for example, are examples of the above-described capacity recovery termination conditions. In other words, 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 (first time, not shown).
Here, the predetermined time tkm may be arbitrary, 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 set to the initial discharge time tk1 (not shown), the ratio between the discharge time tk and the initial discharge time tk1 in the most recent discharge period is a predetermined value. It has become equal to or less than the ratio Rtk (first ratio, not shown).
Here, the value of the ratio Rtk may also be arbitrary, but is preferably in the range of 0.05 to 0.5.

・Condition #3: When the discharge time tk in the discharge period immediately before the most recent discharge period is defined as the immediately preceding discharge time tkp (not shown), the ratio between the discharge time tk in the most recent discharge period and the immediately preceding discharge time tkp is a predetermined value. A ratio Rtp (second ratio, not shown) or higher.
Here, the value of the ratio Rtp may also be arbitrary, but is preferably 0.7 or more.

(Overall operation)
FIG. 5 is a flow chart showing the operation of the control unit 570. As shown in FIG.
When the process proceeds to step S2 in FIG. 5, the capacity recovery processing section 576 executes the discharge period process. That is, a predetermined discharge current is caused to flow between the positive terminal 502 and the negative terminal 503 . Next, when the process proceeds to step S4, the capacity recovery processing unit 576 executes processing for the idle period. For example, the space between the positive terminal 502 and the negative terminal 503 is opened.

Next, when the process proceeds to step S6, the capacity recovery stopping unit 578 measures the discharge time tk until the battery voltage Ev reaches the reference voltage Evk after the start of discharge. 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). do. If "No" is determined here, the process returns to step S2, and the processes of steps S2 to S8 are repeated. On the other hand, if it is determined "Yes" in step S8, the process proceeds to step S10, and the capacity recovery stopping unit 578 stops the capacity recovery process.

[Example]
Next, an example, which is a preferred specific example of the above-described embodiment, will be described.
(Configuration of battery pack 510)
In this example, a lithium-ion battery was prototyped as the battery pack 510 with the cell configuration shown in FIGS. 1 and 2 . In the prototype lithium ion battery, an organic electrolyte with a carbonate solvent having a volatilization temperature of 20° C. was used. Specifically, LiPF6 was dissolved in a carbonate-based solvent at a concentration of 1M (=mol/dm ³ ). The solvent composition was ethyl carbonate (EC):dimethyl carbonate (DMC)=1:2. A laminate cell was fabricated using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode and graphite as the negative electrode. Both sides of the Al current collector foil were coated with the positive electrode material, and both sides of the Cu current collector foil were coated with the negative electrode material, so that the facing negative electrode/positive electrode capacity ratio was 1.3. After punching out the positive electrode and the negative electrode into a predetermined shape, the porous base material of polyolefin material, the positive electrode, and the negative electrode were laminated. The capacity of the positive electrode was designed to be about 80 mAh on one side, and the capacity of the negative electrode was designed to be about 90 mAh on one side. The capacity of battery pack 510 after initialization was about 280 mAh.

(Deterioration test and capacity recovery treatment)
As a deterioration test of the battery pack 510 described above, when the charge/discharge cycle was repeated 500 times in a 50° C. environment, it was confirmed that the battery capacity decreased to about 80% of the initial capacity. Next, after discharging the battery pack 510 and adjusting the battery voltage Ev to 3.0 V, capacity recovery processing was performed. In the capacity recovery treatment, one cycle was defined as a discharge period and a rest period, and this cycle was repeated multiple times. First, in the discharge period, a discharge pulse of 10 CA was applied 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. The rest period was set to 15 minutes, and the battery pack 510 was left open for that period of time.

FIG. 6 is a diagram showing changes in the battery voltage Ev during the discharge period. In FIG. 6, characteristics P1 to P4 respectively show the change characteristics of the battery voltage Ev during the discharge period of the first to fourth cycles.
Since the number of lithium ions remaining in the non-facing portion decreases each time the cycle is repeated, the voltage drop rate increases as shown.

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

[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 similar to that of the above-described embodiment. Further, the contents of processing per cycle of the discharge period and rest period in the capacity recovery process are also the same as those of the above-described embodiment. However, in the capacity recovery treatment of this comparative example, the cycle of the discharge period and 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-described example. However, in this comparative example, the internal resistance of the battery pack 510 after the capacity recovery process became higher than that of the example, and the battery deteriorated as a side effect.

[Effects of Embodiment]
As described above, according to the preferred embodiment, the capacity recovery device (550) has a discharge period that causes a discharge current to flow between the positive terminal (502) and the negative terminal (503) of the secondary battery (510). and a rest period in which the connection between the positive terminal (502) and the negative terminal (503) is opened or the discharge current is made smaller than the discharge period. A capacity recovery processing unit (576) that performs capacity recovery processing for the secondary battery (510), and a capacity that stops the capacity recovery processing according to the change in the battery voltage (Ev) of the secondary battery (510) during the capacity recovery processing. a recovery stop (578). As a result, the capacity recovery process can be stopped in accordance with the state of change in the battery voltage (Ev), so the deterioration of the secondary battery (510) can be suppressed and the capacity of the secondary battery can be appropriately recovered.

Further, the discharge period is 0.1 seconds or more and 60 seconds or less, and the capacity recovery processing section (576) causes the secondary battery (510) to pass a pulse-like current through the discharge period and the rest period. preferable. Thereby, the capacity of the secondary battery can be recovered more appropriately.

Further, it is more preferable that the capacity recovery processing unit (576) performs capacity recovery processing of the secondary battery (510) by repeating one cycle multiple times. Thereby, the capacity recovery process can be continued until a sufficient capacity recovery effect is obtained.

In addition, the capacity recovery stopping unit (578) sets the discharge time (tk), which is the time until the battery voltage (Ev) reaches a predetermined reference voltage (Evk) after the discharge period is started, to a predetermined first time. It is more preferable to stop the capacity recovery process when the time (tkm) is less than or equal to . Thereby, the capacity recovery stopping unit (578) can stop the capacity recovery process when the recovery efficiency hits a ceiling based on the relationship between the discharge time (tk) and the first time (tkm).

In addition, the capacity recovery stopping unit (578) sets the discharge time (tk) in the first cycle as the initial discharge time (tk1), and the ratio of the discharge time (tk) in the second and subsequent cycles to the initial discharge time (tk1) becomes equal to or less than a predetermined first ratio (Rtk), it is more preferable to stop the capacity recovery process. As a result, the capacity recovery stopping unit (578) starts the capacity recovery process when the recovery efficiency peaks out based on the relationship between the initial discharge time (tk1) and the discharge time (tk) in the second and subsequent cycles. can be stopped.

In addition, the capacity recovery stopping unit (578) sets the discharge time (tk) in the cycle immediately before the most recent cycle to the immediately preceding discharge time (tkp), and sets the discharge time (tk) in the most recent cycle to the immediately preceding discharge time (tkp). It is more preferable to stop the capacity recovery process when the ratio becomes equal to or higher than a second predetermined ratio (Rtp). As a result, the capacity recovery stopping unit (578) stops the capacity recovery process when the recovery efficiency hits a ceiling based on the relationship between the immediately preceding discharge time (tkp) and the discharge time (tk) in the most recent cycle. can be done.

[Modification]
The present invention is not limited to the embodiments described above, and various modifications are possible. The above-described embodiments are illustrated for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations. Further, other configurations may be added to the configurations of the above embodiments, and part of the configurations may be replaced with other configurations. Also, the control lines and information lines shown in the drawings are those considered to be necessary for explanation, and do not necessarily show all the control lines and information lines necessary on the product. In practice, it may be considered that almost all configurations are interconnected. Possible modifications to the above embodiment are, for example, the following.

(1) Since the hardware of the current control device 550 in the above embodiment can be realized by a general computer, the programs and the like for executing the various processes described above can be stored in a storage medium or distributed via a transmission line. good.

(2) Each of the processes described above has been described as a software process using a program in the above embodiment, but part or all of it may be an ASIC (Application Specific Integrated Circuit) or an FPGA (Field It may be replaced with hardware processing using a Programmable Gate Array) or the like.

(3) Various processes executed in the above embodiments may be executed by a server computer via a network (not shown), and various data stored in the above embodiments may also be stored in the server computer. .

100 battery cell (secondary battery)
500 secondary battery system 502 positive electrode terminal 503 negative electrode terminal 510 battery pack (secondary battery)
550 current controller (capacity recovery device)
576 capacity recovery processing unit (capacity recovery processing process)
578 capacity recovery stop part (capacity recovery stop process)
Ev battery voltage tk discharge time Evk reference voltage Rtk ratio (first ratio)
Rtp ratio (second ratio)
tk1 Initial discharge time tkm Predetermined time (first time)
tkp last discharge time

Claims (16)

A discharge period in which a discharge current flows between the positive terminal and the negative terminal of the secondary battery, and a pause in which the gap between the positive terminal and the negative terminal is opened or the discharge current is made smaller than the discharge period. a capacity recovery processing unit that performs capacity recovery processing of the secondary battery in one cycle or more of the discharge period and the rest period, and
a capacity recovery stopping unit that stops the capacity recovery process according to a change in the battery voltage of the secondary battery during the capacity recovery process. The discharge period is 0.1 seconds or more and 60 seconds or less,
The capacity recovery device according to claim 1, wherein the capacity recovery processing section causes a pulsed current to flow through the secondary battery during the discharge period and the rest period. The capacity recovery device according to claim 1 or 2, wherein the capacity recovery processing unit performs capacity recovery processing of the secondary battery by repeating the one cycle a plurality of times. The capacity recovery stopping unit performs the capacity recovery processing when the discharge time, which is the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started, is equal to or less than a predetermined first time. 4. The capacity recovery device according to any one of claims 1 to 3, which stops the 2. The capacity recovery stopping unit sets the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started as the discharge time, sets the discharge time in the first cycle as the initial discharge time, and 2 4. The capacity recovery device according to claim 3, wherein the capacity recovery process is stopped when the ratio of the discharge time to the initial discharge time in the cycles after the first cycle becomes equal to or less than a predetermined first ratio. The capacity recovery stopping unit sets the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started as the discharge time, and the discharge time in the most recent previous cycle is the immediately preceding discharge time. 4. The capacity recovery device according to claim 3, wherein the capacity recovery process is stopped when the ratio of the discharge time in the most recent cycle to the immediately preceding discharge time reaches or exceeds a predetermined second ratio. a secondary battery;
A discharge period in which a discharge current flows between the positive electrode terminal and the negative electrode terminal of the secondary battery, and a space between the positive electrode terminal and the negative electrode terminal is opened, or the discharge current is made smaller than the discharge period. a capacity recovery processing unit that performs capacity recovery processing of the secondary battery in one cycle or more of the discharge period and the rest period, wherein a rest period is defined as one cycle;
A secondary battery system, comprising: a capacity recovery stopping unit that stops the capacity recovery process according to a change in the battery voltage of the secondary battery during the capacity recovery process. The secondary battery system according to claim 7, wherein the capacity recovery processing unit performs capacity recovery processing of the secondary battery by repeating the one cycle a plurality of times. The capacity recovery stopping unit performs the capacity recovery processing when the discharge time, which is the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started, is equal to or less than a predetermined first time. The secondary battery system according to claim 7 or 8, characterized by stopping the 2. The capacity recovery stopping unit sets the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started as the discharge time, sets the discharge time in the first cycle as the initial discharge time, and 2 9. The secondary battery system according to claim 8, wherein the capacity recovery process is stopped when the ratio of the discharge time to the initial discharge time in the cycles after the first cycle becomes equal to or less than a predetermined first ratio. The capacity recovery stopping unit sets the time until the battery voltage reaches a predetermined reference voltage after the discharge period is started as the discharge time, and the discharge time in the most recent previous cycle is the immediately preceding discharge time. 9. The secondary battery system according to claim 8, wherein the capacity recovery process is stopped when the ratio of the discharge time in the most recent cycle to the immediately preceding discharge time reaches or exceeds a predetermined second ratio. A discharge period in which a discharge current flows between the positive terminal and the negative terminal of the secondary battery, and a pause in which the gap between the positive terminal and the negative terminal is opened or the discharge current is made smaller than the discharge period. a capacity recovery processing step of performing capacity recovery processing of the secondary battery with the discharge period and the rest period of one cycle or more, wherein the period is one cycle;
and a capacity recovery stopping step of stopping the capacity recovery process according to a change in the battery voltage of the secondary battery in the capacity recovery process. 13. The capacity recovery method according to claim 12, wherein in the capacity recovery process, the capacity recovery process of the secondary battery is performed by repeating the one cycle a plurality of times. In the capacity recovery stop process, the capacity recovery process is performed when the discharge time, which is the time required for the battery voltage to reach a predetermined reference voltage after the discharge period is started, is equal to or less than a predetermined first time. 14. The capacity recovery method according to claim 12 or 13, characterized by stopping. In the capacity recovery stop process, after the discharge period is started, the time until the battery voltage reaches a predetermined reference voltage is set as the discharge time, the discharge time in the first cycle is set as the initial discharge time, and the second cycle is set to the discharge time. 14. The capacity recovery method according to claim 13, wherein the capacity recovery process is stopped when the ratio of the discharge time to the initial discharge time in subsequent cycles becomes equal to or less than a predetermined first ratio. In the capacity recovery stop process, after the discharge period is started, the time until the battery voltage reaches a predetermined reference voltage is set as the discharge time, and the discharge time in the most recent previous cycle is set as the previous discharge time. 14. The capacity recovery method according to claim 13, wherein the capacity recovery process is stopped when the ratio of the discharge time in the most recent cycle to the immediately preceding discharge time reaches or exceeds a predetermined second ratio.

Images