JP2007325451A - Voltage balance adjusting method for battery pack in which a plurality of lithium-ion secondary batteries are connected in series - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently adjust a voltage balance between respective cells of a battery pack in which a plurality of lithium-ion secondary batteries are connected in series. <P>SOLUTION: A voltage V3 near a voltage saturation region where a voltage rise becomes slow due to charging characteristics of the lithium-ion secondary batteries 1a-1n is set to a full-charge voltage. An overcharge protection voltage is set between the full-charge voltage and a limit voltage at which chemical changes and a thermorunaway reaction start to occur. Charging is executed until when any one of a plurality of the lithium-ion secondary batteries 1a-1n reaches the overcharge protection voltage or when a voltage of the battery pack 1 reaches a sum voltage of the full-charge voltages of a plurality of the lithium-ion secondary batteries 1a-1n. Consequently, it is possible to adjust voltage variations in a plurality of the lithium-ion secondary batteries 1a-1n. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for adjusting a voltage balance of an assembled battery in which a plurality of lithium ion secondary batteries are connected in series to adjust voltage variation between battery cells of the assembled battery by charging.

  Lithium-ion batteries have higher energy density, smaller size, and lighter weight than other secondary batteries. Therefore, lithium-ion batteries can replace conventional nickel-metal hydride batteries as power sources for mobile devices such as mobile phones, laptop computers, and handy cameras. Instead, it is now mainstream. Lithium ion batteries include manganese and cobalt. Some manganese-based lithium ion batteries use a single cell with a nominal rated voltage (full charge voltage) of 4.2 V, for example, 4.3 V is used as the overcharge protection voltage, and 5.0 V is the chemical change. And the threshold voltage at which thermal runaway reaction begins to occur. Further, between the overcharge protection voltage and the limit voltage, 4.3 V to 5.0 V is set as a deterioration region.

  In the power supply for portable equipment, it is used as an assembled battery in which cells of a plurality of lithium ion batteries are connected in series. In the assembled battery having such a configuration, various variations occur between the cells, so that the terminal voltages cannot be made uniform during charging, resulting in an imbalance. Even if the battery packs connected in series are charged to the rated voltage, if an imbalance occurs, some cells will be overcharged and some cells will not be charged until full charge. Deteriorates and efficiency decreases.

Therefore, in order to eliminate such voltage imbalance during charging, a bypass circuit is provided in each cell that is connected in series to form the assembled battery to bypass the charging current of the cell exceeding the set voltage, or the set voltage It is configured so that cells exceeding the threshold voltage are discharged until the set voltage drops, or when any cell becomes fully charged, other cells are charged sequentially until the fully charged state is reached for each cell. Battery packs and charging methods for charging have been proposed (see, for example, Patent Documents 1 to 3).
JP 2003-157908 A JP 2003-217675 A JP 2005-176520 A

  However, the above-described conventional battery pack in which a bypass circuit is provided in each cell constituting an assembled battery connected in series has a problem such that a charging current and a discharging current flow in the bypass circuit, thereby consuming unnecessary power and generating heat. is doing. In addition, when one of the cells constituting the assembled battery connected in series is fully charged, the conventional battery pack that sequentially charges the other cells until it reaches a fully charged state for each cell. However, it is necessary to switch from individual charging to individual charging for each cell, and to repeatedly perform individual charging in accordance with the number of cells, resulting in problems such as a long charging time and complicated control.

  The present invention solves the above-mentioned problem, and makes it possible to efficiently adjust the voltage balance between cells of a battery pack in which a plurality of lithium ion secondary batteries are connected in series.

  To this end, the present invention provides a voltage balance adjustment method for an assembled battery in which a plurality of lithium ion secondary batteries are connected in series to adjust the voltage variation between the battery cells of the assembled battery by charging, the lithium ion secondary battery Set the voltage near the voltage saturation region where the voltage rise is slow due to the charging characteristics of the full charge voltage, and set the overcharge protection voltage between the full charge voltage and the limit voltage at which chemical change or thermal runaway reaction starts. Charging until either one of the plurality of lithium ion secondary batteries reaches the overcharge protection voltage or the assembled battery voltage reaches a total voltage of the full charge voltages of the plurality of lithium ion secondary batteries. By performing the adjustment, voltage variations of the plurality of lithium ion secondary batteries are adjusted.

  Further, an overcharge protection voltage is set between the full charge voltage and a limit voltage at which a chemical change or thermal runaway reaction starts to occur, and a release voltage lower than the full charge voltage is set to perform charging, and the plurality of lithium Charging is stopped on the condition that any of the ion secondary batteries has reached the overcharge protection voltage, and charging is repeated until the overcharge protection voltage is reached on the condition that the battery has been reduced to the release voltage. Adjusting the voltage variation of the plurality of lithium ion secondary batteries by terminating charging on condition that the battery voltage has reached a voltage obtained by summing up the full charge voltages of the plurality of lithium ion secondary batteries. In addition, the current that is charged until any one of the plurality of lithium ion secondary batteries reaches the overcharge protection voltage is decreased to the release voltage. It and performs the overcharge protection voltage course determines the abnormality when the charging is not completed even if a predetermined time from the stop of the charging reaches the on condition.

  According to the present invention, the voltage in the vicinity of the voltage saturation region where the voltage rise becomes dull due to the charging characteristics is set to the full charge voltage, and overcharge protection is performed between the full charge voltage and the limit voltage at which a chemical change or thermal runaway reaction starts. Since the voltage is set and one of the multiple lithium ion secondary batteries is charged to reach the overcharge protection voltage, the voltage variation between the low voltage secondary battery and the high voltage secondary battery should be reduced in this state. Therefore, efficient voltage balance adjustment can be realized. In addition, by repeatedly charging (pulse charging) with the release voltage in the region below the overcharge protection voltage, the low voltage can be raised while holding down the high voltage, and the voltage balance can be adjusted efficiently. it can. Furthermore, by setting the voltage slightly lower than the overcharge protection voltage as the full charge voltage, it is possible to make each of the plurality of lithium ion secondary batteries substantially equal to the full charge voltage.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an embodiment of a voltage balance adjustment method for an assembled battery in which a plurality of lithium ion secondary batteries according to the present invention are connected in series, and FIG. 2 is a diagram illustrating charging characteristics of the lithium ion secondary battery. . In the figure, 1 is an assembled battery, 1a, 1b, ..., 1n is a lithium ion secondary battery, 2a, 2b, ..., 2n is a voltage monitor, 3 is a charge control switch, 4 is a charge control unit, 5 Indicates a charging power source.

  In FIG. 1, lithium ion secondary batteries 1a, 1b,..., 1n each have the charge characteristics shown in FIG. The voltage monitors 2a, 2b,..., 2n monitor (detect, monitor) the cell voltages of the lithium ion secondary batteries 1a, 1b,. The charging control switch 3 turns on / off the charging current for charging the assembled battery 1 from the charging power source 5, and the charging control unit 4 is lithium monitored through the voltage monitors 2a, 2b,. ON / OFF of the charge control switch 3 according to the cell voltage of each of the ion secondary batteries 1a, 1b,..., 1n, the output side of the charge control switch 3, and the assembled battery voltage detected at the output terminal of the assembled battery 1 The voltage and current of the charging power source 5 are controlled.

  For example, in the case of a manganese-based standard product having a nominal rated voltage (full charge voltage) of 4.2 V, a nominal overcharge protection voltage of 4.3 V, a release voltage of 4.05 V, and a limit voltage of 5.0 V, FIG. In the charging characteristics shown in FIG. 1, the rated voltage and the overcharge protection voltage are in a region with a large slope in the vicinity of V1 (t1) and V2 (t2). Therefore, when a plurality of lithium ion secondary batteries 1a, 1b,..., 1n are connected in series as the assembled battery 1 and charging is performed from the charging power source 5, a relatively large voltage imbalance appears. In this embodiment, with respect to such lithium ion secondary batteries 1a, 1b,..., 1n, a phenomenon in which the voltage rise becomes dull due to charging characteristics is close to the voltage saturation region near V3 (t3). A voltage slightly higher than the nominal overcharge protection voltage, for example, 4.35 V is set as the full charge voltage, and a voltage lower than the limit voltage at which a chemical change or thermal runaway reaction starts, for example, 4.40 V is set as the overcharge protection voltage. Set to. And in the charging performed from the charging power source 5, the assembled battery voltage is detected and it is determined that the voltage becomes n times the full charge voltage (the total charge voltage of a plurality of lithium ion secondary batteries), It is determined that any cell voltage of the lithium ion secondary batteries 1a, 1b,..., 1n becomes an overcharge protection voltage, and charging is stopped according to any of the determination results.

  When charging is performed as described above, when charging is terminated based on the determination result of the assembled battery voltage, the voltage variation is small, but there is an imbalance from the start of charging as shown by the charging characteristics va and vb in FIG. When charging is terminated based on the determination result of the overcharge protection voltage, if a full charge voltage and an overcharge protection voltage are set in the vicinity of V1 and V2 in a region with a large slope, any lithium ion secondary battery ( When the overcharge protection voltage of the cell is determined and charging is terminated, a large voltage imbalance at the end of charging remains. However, when the full charge voltage and the overcharge protection voltage are set near V3 close to the voltage saturation region as in this embodiment, the voltage variation in the assembled battery 1 at the end of charging is adjusted.

  FIG. 3 is a diagram for explaining another embodiment of a voltage balance adjusting method in which a plurality of lithium ion secondary batteries according to the present invention are connected in series. In the above embodiment, the charging is terminated by determining the assembled battery voltage or by determining the overcharge protection voltage of any cell. However, if the overcharge protection voltage is determined by any cell, charging is temporarily stopped. Determine that the cell voltage drops to a release voltage lower than the full charge voltage due to self-discharge, charge again, and repeatedly charge between the overcharge protection voltage and the release voltage (hysteresis region) The charging may be finally terminated by determining the assembled battery voltage.

  FIG. 3 shows an example of processing by the charge control unit. First, when the charge control switch is turned on by starting charging (step S11), the voltage of each cell is taken in through the voltage monitor (step S11). S12), it is determined whether or not the voltage of each cell is an overvoltage (step S13).

  If an overvoltage is detected from the voltage of any cell by the determination process in step S13, the charge control switch is turned off (step S14), the voltage of the cell in which the overvoltage is detected is captured (step S15), and the release voltage is reached. It is determined whether or not it has decreased (step S16). If it is determined that the voltage has dropped to the release voltage, the process returns to step S11 to turn on the charge control switch, and thereafter the same processing is repeated.

  If no overvoltage is detected from the voltage of any cell in the determination process of step S13, the terminal voltage of the assembled battery 1 is taken in (step S17), and whether or not the terminal voltage of the assembled battery 1 has reached the fully charged voltage. Is determined (step S18). If the full charge voltage has not yet been reached, the process returns to step S12 to capture the voltage of each cell through the voltage monitor, and the same processing is repeated thereafter. If the full charge voltage has been reached, the charge control switch Is turned off (step S19), a fully charged state signal or a charging end signal is output (step S20), and the charging is terminated.

  FIG. 4 is a diagram for explaining another embodiment in which a bypass circuit is used in combination with a voltage balance adjustment method for an assembled battery in which a plurality of lithium ion secondary batteries according to the present invention are connected in series. Show. In contrast to the above embodiment, when the bypass circuit 1a-b is used in combination with each of the lithium ion secondary batteries 1a, 1b,..., 1n as shown in FIG. .

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the method for adjusting the voltage balance of a battery pack in which a plurality of manganese-based lithium ion secondary batteries having a nominal rated voltage of 4.2 V are connected in series has been described. Needless to say, the present invention can be similarly applied to a method of adjusting the voltage balance of a battery pack using a secondary battery or other secondary battery. Moreover, you may comprise the structure of the voltage monitors 2a, 2b, ..., 2n, and the charge control part 4 shown in FIG. 1 with the circuit which combined conventionally well-known protection IC. Further, a bypass circuit may be provided in each cell so that the charging current is bypassed at a predetermined voltage difference, for example, 0.05 V or more, or any one of the lithium ion secondary batteries has reached a full charge voltage, Alternatively, a timer may be started on the condition that the overcharge protection voltage has been reached, and abnormality determination may be performed when charging does not end even after a predetermined time (for example, 8 hours) has elapsed.

It is a figure explaining embodiment of the voltage balance adjustment method of the assembled battery which connected the some lithium ion secondary battery which concerns on this invention in series. It is a figure which shows the charge characteristic of a lithium ion secondary battery. It is a figure explaining other embodiment of the voltage balance adjustment method which connected the some lithium ion secondary battery which concerns on this invention in series. It is a figure explaining other embodiment which used the bypass circuit together in the voltage balance adjustment method of the assembled battery which connected the some lithium ion secondary battery which concerns on this invention in series.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Assembly battery, 1a, 1b, ..., 1n ... Lithium ion secondary battery, 2a, 2b, ..., 2n ... Voltage monitor, 3 ... Charge control switch, 4 ... Charge control part, 5 ... Charge power supply

Claims (3)

A voltage balance adjustment method for an assembled battery in which a plurality of lithium ion secondary batteries are connected in series to adjust voltage variation between battery cells of the assembled battery by charging,
A voltage in the vicinity of a voltage saturation region where the voltage rise becomes dull due to the charging characteristics of the lithium ion secondary battery is set to a full charge voltage, and an excess voltage is exceeded between the full charge voltage and a limit voltage at which a chemical change or thermal runaway reaction starts. A charge protection voltage is set, and any one of the plurality of lithium ion secondary batteries reaches the overcharge protection voltage, or the assembled battery voltage is a sum of the full charge voltages of the plurality of lithium ion secondary batteries. A voltage balance adjustment method for a battery pack in which a plurality of lithium ion secondary batteries are connected in series, wherein voltage variations of the plurality of lithium ion secondary batteries are adjusted by charging until reaching a voltage. A voltage balance adjustment method for an assembled battery in which a plurality of lithium ion secondary batteries are connected in series to adjust voltage variation between battery cells of the assembled battery by charging,
A voltage in the vicinity of a voltage saturation region where the voltage rise becomes dull due to the charging characteristics of the lithium ion secondary battery is set to a full charge voltage, and an excess voltage is exceeded between the full charge voltage and a limit voltage at which a chemical change or thermal runaway reaction starts. Set the charge protection voltage and set the release voltage lower than the full charge voltage to perform charging, and stop charging if any of the plurality of lithium ion secondary batteries has reached the overcharge protection voltage Then, charging is repeated until the overcharge protection voltage is reached on condition that the release voltage has been lowered, and the assembled battery voltage reaches the sum of the full charge voltages of the plurality of lithium ion secondary batteries. A plurality of lithium ion secondary batteries are connected in series by adjusting the voltage variation of the plurality of lithium ion secondary batteries by terminating charging on the condition Voltage balance adjustment method of the battery pack was. First, the overcharge protection voltage is reached and the charging is stopped on the condition that the current is charged until any of the plurality of lithium ion secondary batteries reaches the overcharge protection voltage and the release voltage is lowered. 3. The method for adjusting a voltage balance of a battery pack in which a plurality of lithium ion secondary batteries are connected in series according to claim 2, wherein the abnormality is determined when the charging is not completed even after a predetermined time has elapsed.

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