JP2011154925A - Charging system and charging method for lithium ion battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly charge each lithium ion secondary battery without preparing a balancing circuit. <P>SOLUTION: When a whole lithium ion battery pack 20 is charged by a power supply system 3 and voltage of the whole lithium ion battery pack 20 reaches to a designated total voltage, or when voltage of either of lithium ion cells 2 reaches the designated voltage, charging on the basis of the power supply system 3 is stopped, and each lithium ion cell 2 is sequentially charged with a battery charger 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a charging system and a charging method for a lithium ion assembled battery that charges an assembled battery in which a plurality of lithium ion secondary batteries are connected in series.

  Lithium ion secondary batteries have advantages such as high energy density and low self-discharge, and are widely used as storage batteries for automobiles, storage batteries for electric / electronic devices, and the like. In addition, in order to obtain a voltage and capacity according to the purpose of use, a battery pack may be configured and used by connecting a plurality of single-cell lithium ion cells. Thus, when using as an assembled battery, the charge state of each lithium ion cell may vary at the time of charge. That is, the charge voltage of some lithium ion cells is high and the battery is overcharged, and the charge voltages of some other lithium ion cells are low and may be in a subcharged state (a state that does not reach full charge). On the other hand, in lithium ion secondary batteries, abnormal heat generation occurs due to continuation / progress of an overcharged state, and further, there is a risk of ignition accidents because the electrolyte is an organic solvent.

  For this reason, when using a lithium ion secondary battery as an assembled battery, in order to charge each lithium ion cell appropriately without a variation, the technique which provided the balance circuit is known (for example, patent document 1). reference.). In this technique, a plurality of lithium ion cells are connected in series, and each lithium ion cell is provided with a balance circuit. When the voltage of a certain lithium ion cell is equal to or higher than a predetermined voltage at the time of charging, the lithium ion cell is discharged by a balance circuit corresponding to this cell and the charging voltage is lowered to prevent overcharging of the lithium ion cell. That's it.

Japanese Patent Application Laid-Open No. 2002-064947

  By the way, when the lithium ion cell is discharged by the balance circuit while charging of the entire assembled battery is in progress, the balance circuit includes a charging current flowing through the entire assembled battery and a discharge current due to discharging from the lithium ion cell. Will flow. In other words, in order to reduce the voltage of a high-voltage (overcharged) lithium ion cell, a balance circuit having a current capacity capable of flowing a charging current flowing through the entire assembled battery and a discharging current from the lithium ion cell is required. It is. For this reason, it is necessary to enlarge the balance circuit in terms of capacity, heat dissipation, and the like, and it is necessary to provide a balance circuit in every lithium ion cell, resulting in an increase in equipment size and cost.

  Therefore, an object of the present invention is to provide a charging system and a charging method for a lithium ion assembled battery that can appropriately charge each lithium ion secondary battery without providing a balance circuit.

  In order to achieve the above object, the invention described in claim 1 is a charging system for a lithium ion assembled battery that charges a lithium ion assembled battery in which a plurality of lithium ion secondary batteries are connected in series. A power supply system connected to the battery so as to be able to supply power; monitoring means for monitoring the voltage of each lithium ion secondary battery and the voltage of the entire lithium ion assembled battery; and charging for charging each lithium ion secondary battery Switching means for switching the lithium ion secondary battery to be charged by the charging means, and control means for controlling the power supply by the power supply system and the switching means based on the monitoring result by the monitoring means. And the control means supplies power to the lithium ion assembled battery from the power supply system to supply the lithium ion assembled battery. When the total voltage reaches a predetermined total voltage, or when the voltage of any of the lithium ion secondary batteries reaches a predetermined voltage, power is supplied from the power supply system to the lithium ion assembled battery. And the switching means is controlled to sequentially charge the lithium ion secondary batteries by the charging means.

  According to the present invention, first, when the entire lithium ion assembled battery is charged by the power supply system and the voltage of the entire lithium ion assembled battery reaches a predetermined total voltage, for example, a target total voltage value that can be regarded as charging completion. When the voltage reaches a slightly low voltage, charging of the entire lithium ion assembled battery is stopped. In addition, when the voltage of any lithium ion secondary battery reaches a predetermined voltage, for example, when the target voltage that can be regarded as completion of charging is reached, charging of the entire lithium ion assembled battery is stopped. Then, each lithium ion secondary battery is sequentially charged by the charging means until it reaches a target voltage that can be regarded as completion of charging.

  According to a second aspect of the present invention, in the charging system according to the first aspect, the control unit controls the switching unit so that the charging unit sequentially charges from a lithium ion secondary battery having a low charging voltage. It is characterized by that.

  According to this invention, first, when the entire lithium ion assembled battery is charged by the power supply system and the voltage of the entire lithium ion assembled battery reaches a predetermined total voltage, or the voltage of any lithium ion secondary battery When the voltage reaches a predetermined voltage, charging of the entire lithium ion assembled battery is stopped. And it charges with a charging means in an order from the lithium ion secondary battery with a low voltage.

  According to a third aspect of the present invention, in the charging system according to the first or second aspect, the control means controls the switching means so that the lithium ion secondary batteries maintain a predetermined voltage. It is characterized by that. Here, the “predetermined voltage” may or may not be the same as the “predetermined voltage” in claim 1.

  According to the present invention, when the voltage of a certain lithium ion secondary battery drops below a predetermined voltage, the switching means charges the lithium ion secondary battery by the charging means, and the lithium ion secondary battery A predetermined voltage is maintained.

  The invention according to claim 4 is a charging method of a lithium ion assembled battery in which a plurality of lithium ion secondary batteries are connected in series, and the lithium ion assembled battery is charged by a power supply system. When the voltage of the entire lithium ion assembled battery reaches a predetermined total voltage, or when the voltage of any one of the lithium ion secondary batteries reaches a predetermined voltage, charging by the power supply system is performed. It stops, and each said lithium ion secondary battery is charged sequentially by a charging means.

  According to invention of Claim 1 and 4, the whole lithium ion assembled battery is charged with an electric power supply system to a certain charging state, and each lithium ion secondary battery is charged separately after that. For this reason, variations in the voltage of each lithium ion secondary battery caused by charging the entire assembled battery to the target voltage that can be regarded as being completed by the battery charger (power supply system), and some of the voltage variation It becomes possible to avoid an overcharged state of the lithium ion secondary battery. As a result, each lithium ion secondary battery can be appropriately charged without providing a balance circuit.

  In addition, since each lithium ion secondary battery is sequentially charged by the charging means, it is not necessary to provide each lithium ion secondary battery with a charging means. Moreover, since the entire assembled battery is charged by the power supply system until a certain charging state, the capacity of the charging means required thereafter can be reduced. Furthermore, as described above, it is not necessary to provide a balance circuit in each lithium ion secondary battery. For this reason, it becomes possible to simplify and miniaturize the configuration and reduce the equipment cost.

  According to the second aspect of the present invention, since the entire assembled battery is charged to a certain charged state and then charged in order from the lithium ion secondary battery having a lower charging voltage, the capacity of the entire assembled battery can be increased at an early stage. It becomes. That is, when discharging the entire assembled battery, in general, from the viewpoint of preventing overdischarge, the capacity of the entire assembled battery is generally terminated because the discharge is terminated when a certain lithium ion secondary battery reaches a predetermined voltage (discharge end voltage). Depends on the capacity of the lithium ion secondary battery having the lowest capacity (voltage) before discharging. For this reason, it becomes possible to raise the capacity | capacitance of the whole assembled battery at an early stage by charging in order from a lithium ion secondary battery with a low charging voltage.

  According to invention of Claim 3, each lithium ion secondary battery is charged sequentially by a charging means so that each lithium ion secondary battery maintains a predetermined voltage. In other words, even in the maintenance charge (float charge) state, each lithium ion secondary battery is individually charged by the charging means, so there is no need to provide a balance circuit, and each lithium ion has a simplified and miniaturized configuration. The secondary battery can be properly maintained and charged.

It is a schematic block diagram which shows the state which applied the charging system of the lithium ion assembled battery which concerns on embodiment of this invention to the rectifier. It is a figure which shows the charge condition by the charging system of FIG. It is a figure which shows the other charge state by the charging system of FIG. It is a schematic block diagram which shows the other application example of the charging system which concerns on this invention. It is a schematic block diagram which shows the state which applied the charging system which concerns on this invention to the electric vehicle.

  The present invention will be described below based on the illustrated embodiments.

  FIG. 1 is a schematic configuration diagram showing an application example in which a charging system 1 for a lithium ion assembled battery according to an embodiment of the present invention is used by being connected in parallel to a rectifier and a load. In this embodiment, 12 lithium ion cells 2 are configured as one set of lithium ion battery pack 20 and operated by float charging by a rectifier. This charging system 1 is a system for charging a lithium ion assembled battery 20 in which a plurality of lithium ion cells (lithium ion secondary batteries) 2 which are single cells are connected in series, and mainly a power supply system (battery charging means) ) 3, a charger (charging means) 4, a switching device (switching means) 5, and a monitoring control device (monitoring means, control means) 6. Hereinafter, the case where the lithium ion assembled battery 20 is operated by the above-described float charging will be described as an example.

  The power supply system 3 is connected so as to supply power to the load facility 100 and to supply power to the lithium ion assembled battery 20. Specifically, the power source 31 is composed of a commercial power source 31 and a rectifier (AC / DC converter) 32, and the power from the commercial power source 31 is rectified (DC conversion) by the rectifier 32, so It comes to be supplied. Further, power is supplied to the lithium ion assembled battery 20 via a charging switch 71, and this charging switch 71 is controlled to be opened and closed by a monitoring control device 6 as described later.

  Further, a bypass diode 72 is connected in parallel with the charge switch 71. The bypass diode 72 has a function of allowing only the flow of the discharge current from the lithium ion assembled battery 20 and prevents the discharge current from flowing to the lithium ion assembled battery 20. As a result, discharge from the lithium ion assembled battery 20 to the load facility 100 is always possible via the bypass diode 72 so that backup power is supplied in the event of a power failure of the AC input to the rectifier 32 or a failure of the rectifier 32. It has become.

  The charger 4 is a device that receives power from the commercial power supply 31 and individually charges each lithium ion cell 2. In this embodiment, one charger is used for one lithium ion battery pack 20. A vessel 4 is provided. The charger 4 is connected to each lithium ion cell 2 via a switch 5 so as to be switchable. That is, the switch 5 is a switch for switching the lithium ion cell 2 to be charged by the charger 4, and is charged with the designated lithium ion cell 2 based on a switching command from the monitoring controller 6 as will be described later. The device 4 is connected.

  The monitoring control device 6 is a device that monitors the voltage of each lithium ion cell 2 and the voltage of the entire lithium ion assembled battery 20 and controls the power supply by the power supply system 3 and the switch 5 based on the monitoring result. is there. Specifically, a cell voltmeter connected to each lithium ion cell 2 for measuring and monitoring the voltage of each lithium ion cell 2 and connected to both terminals of the lithium ion assembled battery 20, the entire lithium ion assembled battery 20 is And a total voltmeter that measures and monitors the voltage. The power supply by the power supply system 3 and the switch 5 are controlled as follows.

  That is, at the time of initial charging (at the start of system operation) and at the time of charging after discharging (at the time of recovery charging), first, power is supplied from the power supply system 3 to the entire lithium ion assembled battery 20, and the entire lithium ion assembled battery 20. Power supply from the power supply system 3 to the entire lithium ion assembled battery 20 is stopped when the voltage of the battery reaches the predetermined total voltage or when the voltage of any lithium ion cell 2 reaches the predetermined voltage To do. Next, the power supply by the power supply system 3 and the switching device 5 are controlled so that the lithium ion cells 2 are sequentially charged by the charger 4.

  Specifically, the target voltage (optimum value of the float charging voltage) that can be regarded as the completion of charging of each lithium ion cell 2 is 4.1 V, and the target voltage that can be regarded as the completion of charging of the lithium ion assembled battery 20 is 49.2 V (4.1 V). X12 cells), for example, the “predetermined total voltage” is 48V (4.0V × 12 cells), and the “predetermined voltage” is 4.1V. First, the charging switch 71 is turned on (closed) to supply power from the power supply system 3 to the entire lithium ion assembled battery 20 to charge the entire lithium ion assembled battery 20. At this time, the switch 5 is controlled to disconnect the charger 4 from all the lithium ion cells 2.

  As a result of this charging, as shown in FIG. 2, the voltage VT of the lithium ion battery pack 20 reaches 48 V (VT1) before the voltage of any lithium ion cell 2 reaches 4.1 V (VC1). (At time T1), the charging switch 71 is turned off (opened). Thereby, the charging of the entire lithium ion assembled battery 20 by the power supply system 3 is completed. Next, the switch 5 is controlled so as to be charged by the charger 4 in order from the lithium ion cell 2 having the lowest charging voltage. That is, in the state of FIG. 2, a switching command for connecting the lithium ion cell 2 (C1) having the lowest charging voltage to the charger 4 at T1 is transmitted to the switch 5. In response to this switching command, the lithium ion cell 2 of C1 is charged by the charger 4, and when the voltage of the lithium ion cell 2 of C1 reaches 4.1 V (at T2), the charging voltage is the second charging voltage at T1. Is sent to the switch 5 to connect the lithium ion cell 2 (C2) with a low charge to the charger 4.

  In response to this switching command, the lithium ion cell 2 of C2 is charged by the charger 4, and when the voltage of the lithium ion cell 2 of C2 reaches 4.1 V (at T3), the charging voltage is the third at T1. Is sent to the switch 5 to connect the lithium ion cell 2 (C3) with a low charge to the charger 4. Thereby, the lithium ion cell 2 of C3 is charged by the charger 4, and when the voltage reaches 4.1V (at time T4), the same individual charging is sequentially performed. Here, since the lithium ion cell 2 has a small amount of self-discharge, its voltage is substantially maintained as shown (between T1 and T3 of the C3 lithium ion cell 2) when not charged. When such individual charging is completed for all the lithium ion cells 2, the total voltage of the entire lithium ion assembled battery 20 reaches 49.2V (VT2). In such charging, as shown in FIG. 2, until the voltage VT of the entire lithium ion assembled battery 20 reaches 48 V (VT1) (until T1), the charging current to the entire assembled battery 20 is a constant current value. It becomes IT, and at the time of individual charging of each lithium ion cell 2, the charging current becomes a constant current value IC1, IC2, IC3, etc.

  On the other hand, as shown in FIG. 3, before the voltage of the entire lithium ion battery pack 20 reaches 48V (VT3 <VT1), the voltage of any lithium ion cell 2 (C3 in FIG. 3) is 4.1V (VC1). ) Is reached (at time T11), the charging switch 71 is turned off (opened). Thereby, the charging of the entire lithium ion assembled battery 20 by the power supply system 3 is completed. Next, the switch 5 is controlled so as to be charged by the charger 4 in order from the lithium ion cell 2 having the lowest charging voltage. That is, in the state of FIG. 3, a switching command for connecting the lithium ion cell 2 (C1) having the lowest charging voltage to the charger 4 at T11 is transmitted to the switch 5. In response to this switching command, the lithium ion cell 2 of C1 is charged by the charger 4, and when the voltage of the lithium ion cell 2 of C1 reaches 4.1V (T12 time), it is charged second at T11 time. A switching command to connect the lithium ion cell 2 (C2) having a low voltage to the charger 4 is transmitted to the switching device 5.

  In response to this switching command, the lithium ion cell 2 of C2 is charged by the charger 4, and when the voltage of the lithium ion cell 2 of C2 reaches 4.1 V (at T13), the same individual charging is sequentially performed. . When such individual charging is completed for all the lithium ion cells 2 (excluding C3), the voltage of the entire lithium ion assembled battery 20 reaches 49.2 V (VT2). Even in such charging, as shown in FIG. 3, until the voltage of any lithium ion cell 2 reaches 4.1 V (until T11), the charging current to the entire assembled battery 20 is a constant current value IT. Thus, when each lithium ion cell 2 is individually charged, the charging current becomes a constant current value IC1, IC2, or the like.

  Moreover, the monitoring control apparatus 6 controls the switch 5 so that each lithium ion cell 2 maintains a predetermined voltage at the time of maintenance charging. That is, when the voltage of any lithium ion cell 2 drops below a predetermined voltage (for example, 4.0 V) after the initial charge or recovery charge as described above, the lithium ion cell 2 is connected to the charger 4. A switching command for connection is transmitted to the switch 5. In response to this switching command, the lithium ion cell 2 is charged by the charger 4, and when the voltage of the lithium ion cell 2 reaches 4.1 V, the switching command for disconnecting the lithium ion cell 2 from the charger 4. Is transmitted to the switch 5. In this way, all the lithium ion cells 2 are maintained at a predetermined voltage.

  Next, an operation of the charging system 1 having such a configuration, a charging method by the charging system 1 and the like will be described.

  First, at the time of initial charging, the charging switch 71 is turned on, power is supplied from the power supply system 3 to the load equipment 100 and the entire lithium ion assembled battery 20, and the entire lithium ion assembled battery 20 is charged. In this charged state, the charger 4 is not connected to any lithium ion cell 2 (the charger 4 is in a non-operating state), and the voltage and lithium ion set of each lithium ion cell 2 is monitored by the monitoring controller 6. The voltage across the battery 20 is monitored in real time. Next, when the voltage of the entire lithium ion assembled battery 20 reaches 48 V (VT1) or when the voltage of any lithium ion cell 2 reaches 4.1 V (VC1), the monitoring control device 6 performs the charging switch 71. Is switched off and the switch 5 is controlled as described above. Thereby, the power supply from the power supply system 3 to the entire lithium ion assembled battery 20 is stopped, and the battery 4 is charged in order from the lithium ion cell 2 having a low voltage.

  In this way, all the lithium ion cells 2 are charged to 4.1 V (VC1), and the initial charging is completed. Even during the maintenance charge, the monitoring control device 6 monitors the voltage of each lithium ion cell 2 and the voltage of the entire lithium ion assembled battery 20 in real time. When the voltage of any lithium ion cell 2 drops below 4.0 V due to self-discharge, the lithium ion cell 2 is charged to 4.1 V by the charger 4 as described above. Such intermittent charging is performed sequentially and appropriately, and the maintenance charge is performed so that all the lithium ion cells 2 maintain a predetermined voltage (4.0 to 4.1 V).

  On the other hand, when the power supply from the commercial power supply 31 is stopped (power failure), the lithium ion assembled battery 20 starts to discharge instantaneously (without instantaneous interruption) via the bypass diode 71, and the power from the lithium ion assembled battery 20 is Supplied to the load facility 100. In this discharged state, the charger 4 is disconnected from all the lithium ion cells 2 by the switch 5. Subsequently, when power supply from the commercial power supply 31 is resumed (recovered), recovery charging is performed. That is, the charging switch 71 is turned on, and the entire lithium ion assembled battery 20 is charged to a predetermined voltage (charged state) by the power supply system 3 as in the case of initial charging, and then each lithium ion cell is charged by the charger 4. 2 are charged sequentially. In this way, the sustain charge, discharge, recovery charge, and sustain charge are performed, and the float charge operation is performed.

  As described above, according to the charging system 1 and the charging method, the entire lithium ion assembled battery 20 is charged to a certain charged state by the power supply system 3, and then each lithium ion cell 2 is individually charged. For this reason, it is possible to avoid variations in the voltage of each lithium ion cell 2 due to charging of the entire assembled battery 20 to 49.2 V by the power supply system 3, and an overcharged state of some lithium ion cells 2 due to this variation. It becomes possible. That is, since each lithium ion cell 2 is individually charged to 4.1 V, an overcharged state does not occur. As a result, each lithium ion cell 2 can be appropriately charged without providing a balance circuit.

  In addition, since charging is performed in order from the low voltage (low capacity) lithium ion cell 2 that affects the capacity of the entire assembled battery 20, the capacity of the entire assembled battery 20 can be increased at an early stage. Further, even during the maintenance charge, each lithium ion cell 2 is sequentially charged by the charger 4 so that each lithium ion cell 2 maintains a predetermined voltage, so that there is no need to provide a balance circuit.

  In addition, since each lithium ion cell 2 is sequentially charged by the charger 4, it is not necessary to provide the charger 4 in each lithium ion cell 2. Moreover, since the entire assembled battery 20 is charged by the power supply system 3 and charged by the charger 4 until a certain charging state, the capacity of the charger 4 can be reduced. For example, when the discharged lithium ion cell 2 is charged only by the charger 4, if a charging current of about 20A is required, according to the charging system 1, the charging current required by the charger 4 may be about 2A. Furthermore, as described above, it is not necessary to provide a balance circuit in each lithium ion cell 2. For this reason, the system configuration can be simplified and miniaturized, and the equipment cost can be reduced.

  Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there is a design change or the like without departing from the gist of the present invention, Included in the invention. For example, in the above embodiment, the “predetermined charging voltage” is set to 4.1 V, and when the voltage of any lithium ion cell 2 reaches 4.1 V, the total charging by the power supply system 3 is terminated. However, the total charging by the power supply system 3 may be terminated when a voltage lower than the target charging voltage of 4.1 V (for example, 4.0 V) is reached. Further, when the voltage of the entire lithium ion assembled battery 20 reaches 48V and when the voltage of any lithium ion cell 2 reaches 4.1V, the total charging by the power supply system 3 is finished. However, only one of them may be the end condition. Furthermore, although one charger 4 is sequentially charged, a plurality of lithium ion cells 2 may be charged simultaneously with a plurality of chargers 4 in accordance with the number of cells or capacity of the lithium ion cells 2. Good.

  Moreover, although the system which has one set of lithium ion assembled batteries 20 was demonstrated, it is applicable also to the system which connected multiple lithium ion assembled batteries 20 in parallel. In this case, the charger 4 and the switch 5 as described above are provided for each assembled battery 20. Furthermore, although the monitoring means and the control means are integrated into the monitoring control device 6, the monitoring means and the control means may be provided separately.

  By the way, although the case where the lithium ion assembled battery system 1 was applied to the rectifier was described, it can also be applied to an uninterruptible power supply (UPS), an automobile storage battery, and the like. For example, as shown in FIG. 4, the power supply system 3 and the lithium ion assembled battery 20 may be directly connected without including the load facility 100. Further, the lithium ion assembled battery 20 may be detachable from the power supply system 3 or the charger 4, and the lithium ion assembled battery 20 is removed from the device (drill, personal computer, illuminator, etc.) and charged. Alternatively, charging may be performed within the device. When applied to an electric vehicle, for example, as shown in FIG. 5, the charging facility side includes a rectifier 32, a charger 4, and a control device (control means) 62, and the assembled battery 20 and the switch 5 are provided on the electric vehicle side. And a monitoring device (monitoring means) 61. Then, the rectifier 32, the charger 4 and the assembled battery 20 are connected so as to be able to transmit power, and the control device 62, the switch 5 and the monitoring device 61 are connected so as to be communicable. As a result, the entire assembled battery 20 is charged via the rectifier 32, controlled by the control device 62 based on voltage monitoring by the monitoring device 61, and each lithium ion cell 2 is individually charged via the charger 4 and the switch 5. To do.

1 Lithium ion battery charging system 2 Lithium ion cell (lithium ion secondary battery)
20 Lithium-ion battery 3 Power supply system 31 Commercial power supply 32 Rectifier 4 Charger (charging means)
5 switcher (switching means)
6. Monitoring control device (monitoring means, control means)
71 Charging switch 72 Bypass diode 100 Load equipment

Claims (4)

A charging system for a lithium ion assembled battery for charging a plurality of lithium ion secondary batteries connected in series,
A power supply system connected to the lithium ion battery so as to be able to supply power;
Monitoring means for monitoring the voltage of each lithium ion secondary battery and the voltage of the entire lithium ion assembled battery;
Charging means for charging each lithium ion secondary battery;
Switching means for switching a lithium ion secondary battery to be charged by the charging means;
Control means for controlling the power supply by the power supply system and the switching means based on the monitoring result by the monitoring means,
The control means supplies power to the lithium ion assembled battery from the power supply system and the voltage of the entire lithium ion assembled battery reaches a predetermined total voltage, or any of the lithium ion secondary batteries When the voltage reaches a predetermined voltage, the switching means is configured to stop power supply from the power supply system to the lithium ion assembled battery and sequentially charge the lithium ion secondary batteries by the charging means. A charging system for a lithium-ion battery pack.   The said control means controls the said switching means to charge with the said charging means in an order from a lithium ion secondary battery with a low charging voltage, The charging system of the lithium ion assembled battery of Claim 1 characterized by the above-mentioned.   3. The lithium ion according to claim 1, wherein the control unit controls the switching unit so that each of the lithium ion secondary batteries maintains a predetermined voltage. 4. Battery charging system. A charging method of a lithium ion assembled battery for charging a lithium ion assembled battery in which a plurality of lithium ion secondary batteries are connected in series,
Charging the lithium-ion assembled battery by a power supply system,
When the voltage of the entire lithium ion assembled battery reaches a predetermined total voltage, or when the voltage of any of the lithium ion secondary batteries reaches a predetermined voltage, charging by the power supply system is stopped. ,
A method for charging a lithium ion battery pack, wherein the lithium ion secondary batteries are sequentially charged by a charging means.

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