JP2019193348A - Charging method - Google Patents

Abstract

To provide a charging method which can reduce a dispersion of capacity among cells with a simple configuration, when charging a power storage module which includes a plurality of cells.SOLUTION: The charging method of a power storage module 1, which includes a plurality of cells 11 connected in series, includes: a first step which performs the constant current charging of the power storage module 1 with a charge current set to a first current value, until a charge voltage reaches a first voltage value; a second step which, after the first step, decreases a charge current gradually so that the charge voltage is maintained to the first voltage value until a preset termination condition is satisfied, to perform a constant voltage charging of the power storage module 1; and a third step which, after the second step, further charges the power storage module 1 with a charge current smaller than the first current value.SELECTED DRAWING: Figure 2

Description

  One aspect of the present invention relates to a charging method.

  Conventionally, a technique for equalizing the capacity (voltage) of each cell when charging a power storage module including a plurality of batteries (cells) connected in series is known. For example, Patent Documents 1 and 2 disclose a technique for performing the above-described equalization by providing an equalization circuit connected in parallel for each cell. The equalization circuit includes a switching element and a resistance element connected in series.

Japanese Patent Laying-Open No. 2006-5288 JP 2011-1115016 A

  In the method of equalizing the capacity of each cell by the above-described equalization circuit, man-hours and costs for providing the equalization circuit for each cell are generated. In addition, for example, when the power storage module is a bipolar battery including a very large number of cells (for example, 100 cells), it may be difficult to provide an equalization circuit for each cell and it may not be practical.

  In view of the above, an object of one aspect of the present invention is to provide a charging method capable of reducing variation in capacity between cells with a simpler configuration in charging of a power storage module including a plurality of cells.

  A charging method according to one aspect of the present invention is a charging method of an energy storage module including a plurality of cells connected in series, and charging is performed at a first current value until the charging voltage reaches the first voltage value. First step of performing constant current charging of the power storage module with current, and after the first step, gradually reduce the charging current so that the charging voltage is maintained at the first voltage value until a predetermined termination condition is satisfied. Thus, a second step of performing constant voltage charging of the power storage module and a third step of further charging the power storage module with a charging current smaller than the first current value after the second step are included.

  In the above charging method, after completion of charging in the first step and the second step (that is, CCCV charging), charging with a charging current smaller than the first current value (low rate charging) is performed. At the time of completion of the second step, there may be a variation in charge capacity (that is, open circuit voltage (OCV)) among a plurality of cells included in the power storage module. When such a variation occurs, a cell having a large capacity (high capacity cell) has a larger internal resistance than a cell having a small capacity (low capacity cell), and thus the amount of energy consumed by heat generation is large. For this reason, the low-capacity cell is charged more efficiently than the high-capacity cell by further performing low-rate charging after CCCV charging. As a result, the capacity difference between the low-capacity cell and the high-capacity cell can be reduced, and the variation in capacity between the cells can be reduced. Moreover, in the said charging method, it is not necessary to provide the equalization circuit connected in parallel for every cell like a prior art. Therefore, according to the above charging method, variation in capacity between cells can be reduced with a simpler configuration in charging of a power storage module including a plurality of cells.

  The termination condition may be that the charging current decreases to a second current value that is smaller than the first current value. In the third step, the charging current is changed so that the charging voltage is maintained at the first voltage value. The power storage module may be charged at a constant voltage by gradually narrowing down to a third current value smaller than the two current values. In this case, after the normal CCCV charge (first step and second step) is completed, the constant voltage charge is continued with a low-rate current smaller than the end current value (second current value), so that Capacitance variation can be reduced. Further, for example, when the power storage module is a lithium ion secondary battery, charging is performed with a current at a low rate smaller than the normal CCCV charging end current value (second current value), so that the lithium metal in the negative electrode is charged. Precipitation can be effectively suppressed.

  The termination condition may be that the charging current decreases to a second current value smaller than the first current value, and the third step reaches a second voltage value where the charging voltage is higher than the first voltage value. Until the constant current charging of the power storage module with the charging current set to the fourth current value smaller than the first current value and larger than the second current value, and after the constant current charging by the fourth current value, A step of performing constant voltage charging of the power storage module by gradually reducing the charging current so that the charging voltage is maintained at the second voltage value until a predetermined additional termination condition is satisfied. In this case, after completion of normal CCCV charging (first step and second step), by performing additional CCCV charging with the second voltage value as a constant voltage value and the fourth current value as a constant current value , Variation in capacitance between cells can be reduced.

  The additional end condition may be that the charging current decreases to the second current value. In this case, the charge control can be simplified by using the normal CCCV charge (first step and second step) termination condition (second current value) as it is as the additional CCCV charge termination condition.

  The additional end condition may be that the charging current decreases to a fifth current value smaller than the second current value. In this case, since the IR drop generated in the power storage module after completion of charging can be reduced as compared with the case where the second current value is set as the termination condition, the charging rate of the power storage module can be further increased.

  The termination condition may be that the charging current decreases to a second current value smaller than the first current value, and the third step reaches a third voltage value where the charging voltage is higher than the first voltage value. Up to the step of performing constant current charging of the power storage module with the charging current set to the second current value may be included. In this case, after completion of normal CCCV charging (first step and second step), by further performing constant current charging with the end current (second current value) of the CCCV charging as a new constant current, Simple current control can reduce the variation in capacitance between cells.

  The third step further includes the step of performing constant voltage charging of the power storage module by gradually reducing the charging current so that the charging voltage is maintained at the third voltage value after the constant current charging with the second current value. But you can. In this case, since the IR drop can be reduced by further performing constant voltage charging as compared with the case where the constant voltage charging is not performed, the charging rate of the power storage module can be further increased.

  The charging method may further include a determination step of determining whether or not there is a variation in capacity among a plurality of cells included in the power storage module based on the voltage value of the power storage module after the second step. The third step is executed when it is determined that variation occurs in the determination step, and is not executed when it is not determined that variation occurs in the determination step. In this case, unnecessary overcharge (that is, the third step is executed when there is no variation in capacity between cells) can be prevented appropriately.

  The charging method may be executed for a plurality of power storage modules connected in series. In the determination step, the voltage value of each of the plurality of power storage modules is acquired after the second step, and the voltage value between the power storage modules is obtained. Based on the comparison result, it may be determined whether or not there is a power storage module having a variation among the plurality of power storage modules. The third step is executed when it is determined in the determination step that there is a power storage module with variation, and is not performed when it is not determined in the determination step that there is a power storage module with variation. In this case, based on the comparison result of the voltage values between the power storage modules, it can be easily determined whether or not there is a power storage module in which the capacity variation between the cells is present. As a result, it is possible to appropriately prevent unnecessary overcharging (that is, executing the third step when there is no power storage module in which there is a variation in capacity between cells).

  The charging method may further include a step of providing a period in which the current value of the charging current is 0 between the second step and the determination step. In this case, by setting the current value of the charging current to 0 before the determination step (that is, preventing the current from flowing through the power storage module), voltage fluctuations that occur when current flows through the power storage module are eliminated. Can do. As a result, in the determination step, it can be determined with higher accuracy whether there is a variation in capacity between cells.

  The power storage module to be charged by the above charging method may be a lithium ion secondary battery using lithium titanate as a negative electrode material. Charging in the third step is overcharged for cells that are fully charged at the time of completion of the second step. Therefore, by targeting lithium ion secondary batteries using lithium titanate with high overcharge resistance as a negative electrode material, while suppressing adverse effects due to overcharge on already fully charged cells, Capacitance variation can be reduced.

  According to one aspect of the present invention, in charging of a power storage module including a plurality of cells, variation in capacity between cells can be reduced with a simpler configuration.

It is a schematic block diagram of the charging system which implements the charging method of one Embodiment. It is a figure for demonstrating the outline | summary of the charging method of this embodiment. It is a figure which shows the relationship between the voltage and resistance of a high capacity | capacitance cell and a low capacity | capacitance cell. It is a figure which shows the 1st example of the charging method of this embodiment. It is a figure which shows the 2nd example of the charging method of this embodiment. It is a figure which shows the 3rd example of the charging method of this embodiment. It is a figure which shows the 4th example of the charging method of this embodiment. It is a flowchart which shows the charging method which concerns on a modification. It is a schematic block diagram which shows the charging system which concerns on a modification.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are used for the same or corresponding elements, and duplicate descriptions are omitted.

  FIG. 1 is a schematic configuration diagram of a charging system in which the charging method of the present embodiment is implemented. The charging system 100 shown in the figure includes a power storage module 1 to be charged, a control device 2 that controls charging of the power storage module 1, and charging of the power storage module 1 based on an instruction (control signal) from the control device 2. And a charging device 3 that performs the above.

  The power storage module 1 includes a plurality of cells 11 connected in series. The power storage module 1 is, for example, a bipolar battery in which a plurality of electrodes (positive electrode and negative electrode) are stacked via a separator. The power storage module 1 is a secondary battery such as a nickel metal hydride secondary battery or a lithium ion secondary battery. In the present embodiment, the power storage module 1 is a lithium ion secondary battery using lithium titanate (LTO) as a negative electrode material.

  The control device 2 is a device that controls the charging current flowing through the power storage module 1 by controlling the operation of the charging device 3. The control device 2 is physically a processor such as a CPU (Central Processing Unit), a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), an HDD (Hard Disk Drive) or an SSD (Solid State Drive). It can be configured as a computer device provided with an auxiliary storage device or the like. Further, when the power storage module 1 is mounted on a vehicle, the control device 2 may be an ECU (Electronic Control Unit) that comprehensively manages the system of the vehicle. The control device 2 is configured to perform charge control for reducing variation in capacity (that is, open circuit voltage (hereinafter referred to as “OCV (Open Circuit Voltage))) between the plurality of cells 11 included in the power storage module 1. Yes. Specifically, in the control device 2, a control for instructing a charging method from the control device 2 to the charging device 3 by a predetermined charging control program read into the memory or the like being executed by the processor or the like. A signal is output.

  The charging device 3 is a device that is connected to the power storage module 1 and charges the power storage module 1 by flowing a charging current having a predetermined current value through the power storage module 1 in accordance with an instruction from the control device 2. is there.

  The voltage sensor 4 is a sensor that measures the voltage applied between the terminals of the power storage module 1. The control device 2 is connected to the voltage sensor 4 so that the measured value of the voltage sensor 4 can be referred to. The control device 2 can appropriately grasp the voltage value of the power storage module 1 by referring to the measurement value of the voltage sensor 4.

  First, the outline of the charging method of the present embodiment will be described with reference to FIG. FIG. 2 shows a case where a cell 11 having a high capacity (hereinafter “high capacity cell”) and a cell 11 having a low capacity (hereinafter “low capacity cell”) are charged when there is a variation in capacity among a plurality of cells 11. 2 is a diagram schematically showing an example of a closed circuit voltage (hereinafter referred to as “CCV (Closed Circuit Voltage)”) and an OCV in FIG. In FIG. 2, CCV1 and OCV1 are CCV and OCV of a high capacity cell. CCV2 and OCV2 are CCV and OCV of a low capacity cell.

  The period P1 from time t1 to time t2 is charged by the charging current set to a constant current value C1 until the charging voltage (voltage applied across the terminals of the power storage module 1) reaches a predetermined voltage value V1. This is a period during which constant current charging (CC (Constant Current) charging) of the module 1 is performed. Here, the voltage value V1 is a voltage threshold set based on, for example, the OCV when the power storage module 1 is fully charged (the sum of the OCVs of all the cells 11) and the safety factor. Specifically, the voltage value V1 may be a full charge voltage of the power storage module 1 (that is, a voltage corresponding to a charge state (SOC) of 100 [%]), or a full charge in consideration of a safety factor. The voltage may be set lower than the voltage.

  During a period P2 from time t2 to time t3, the charging current is gradually reduced so that the charging voltage is maintained at V1 until a predetermined termination condition is satisfied, whereby constant voltage charging (CV ( This is the period during which constant voltage is charged. The termination condition here is that the current value of the charging current decreases to the current value C2 (<C1). Charging that combines the period P1 and the period P2 is a conventional general charging method called constant current constant voltage charging (CCCV charging).

  As shown in FIG. 2, when the CCCV charging is completed (time t3), the difference (OCV1-OCV2) between the capacity (OCV1) of the high capacity cell and the capacity (OCV2) of the low capacity cell is relatively large. Therefore, in the charging method of the present embodiment, after the completion of CCCV charging, lower rate charging (charging in the period P3 from time t3 to time t4) is executed. Low-rate charging is charging using a charging current smaller than the current value C1. By carrying out such low rate charging, the capacity difference (OCV1-OCV2) between the high capacity cell and the low capacity cell can be reduced. This will be described in detail with reference to FIG.

  FIG. 3 is a diagram showing the relationship between the voltage and resistance of the high capacity cell and the low capacity cell. In FIG. 3, three solid lines indicate the voltage or resistance of a cell (that is, the above-described high-capacity cell) that is almost ideally charged. On the other hand, one broken line indicates the voltage or resistance of the cell in which the capacity deviation occurs (that is, the above-described low capacity cell). FIG. 3A shows the voltage with respect to the charging time. FIG. 3B shows the resistance value with respect to the charging time. As shown in FIG. 3, at time t, a high capacity cell (three solid lines) with a high voltage and a high state of charge (SOC) is a low capacity cell (one broken line) with a low voltage and a low state of charge (SOC). Have a greater resistance. In addition, since the cells are connected in series, the same current flows in the high capacity cell and the low capacity cell. For this reason, the amount of energy consumed by heat generation in the high-capacity cell (the product of the square of the current and the resistance) is greater than the amount of energy consumed by heat generation in the low-capacity cell. Therefore, by performing the above-described low rate charging in a state where high capacity cells and low capacity cells are mixed (that is, in a state where there is a variation in capacity between cells), the low capacity cell is more preferable than the high capacity cell. It will be charged efficiently. As a result, as shown in FIG. 2, the difference between the high-capacity cell voltage (OCV1, CCV1) and the low-capacity cell voltage (OCV2, CCV2) is reduced by performing the above-described low rate charging. Can do. That is, as shown in FIG. 2, since the voltage gradient of the low capacity cell is larger than the voltage gradient of the high capacity cell, the voltage difference between the high capacity cell and the low capacity cell is reduced. As described above, the charging method according to the present embodiment is based on the knowledge that a difference in energy consumption due to heat generation occurs between the high-capacity cell and the low-capacity cell, and after normal charging (here, CCCV charging) is completed. Furthermore, the capacity difference (OCV1-OCV2) between the high capacity cell and the low capacity cell is reduced by performing low rate charging.

Then, with reference to FIGS. 4-7, several charge patterns (1st example-4th example) of the charge method (especially low-rate charge mentioned above) of this embodiment are demonstrated. In the first to fourth examples, the above-described period P1 and period P2 (CCCV charging) are common. That is, in any of the first to fourth examples, first, it is predetermined until the charging voltage reaches a predetermined voltage value V1 (first voltage value) in the period P1 (time t1 to t2). The power storage module 1 is charged with a constant current by the charging current set to the current value C1 (first current value) (first step). Subsequently, in the period P2 (time t2 to t3), the charging current is gradually reduced so that the charging voltage is maintained at the voltage value V1 until a predetermined termination condition is satisfied. Charging is performed (second step). In the present embodiment, the termination condition is that the current value of the charging current decreases to a current value C2 (second current value) smaller than the current value C1. The current value C2 is a current value determined in advance as the end current value.
(First example)

  As shown in FIG. 4, in the first example, after completion of the CCCV charging (periods P1, P2), the charging current is set to a current value C3 smaller than the current value C2 so that the charging voltage is maintained at the voltage value V1. This is a charging pattern in which constant voltage charging of the power storage module 1 is further performed by gradually narrowing down to (third current value). That is, in the first example, the low rate charging described above is performed in a period P3 from time t3 when CCCV charging is completed to time t4 when the charging current becomes the current value C3.

In the first example, after completion of normal CCCV charging (first step and second step), constant voltage charging is performed with a low-rate current (charging current of current value C3) smaller than the end current value (current value C2). By continuing the above, variation in capacity between the cells 11 can be reduced. Further, when the power storage module 1 is a lithium ion secondary battery as in the present embodiment, charging is performed with a current at a low rate smaller than the normal CCCV charging end current value (current value C2). Precipitation of metallic lithium in the negative electrode can also be effectively suppressed.
(Second example)

  As shown in FIG. 5, the second example is a pattern in which additional CCCV charging is performed after completion of the CCCV charging (periods P1, P2). Specifically, in the second example, the low rate charge (period P3) is greater than the current value C1 until time t31 when the charge voltage reaches a voltage value V2 (second voltage value) higher than the voltage value V1. Including a step of performing constant current charging (period P31) of the power storage module 1 with a charging current set to a current value C4 (fourth current value) that is smaller and larger than the current value C2. In addition, the low rate charging is performed after the constant current charging (period P31) with the current value C4 until the charging voltage is maintained at the voltage value V2 until a predetermined additional termination condition is satisfied. This includes a step of performing constant voltage charging (period P32) of the power storage module 1 by narrowing down. In the second example, the additional end condition is that the charging current decreases to the current value C2.

In the second example, after the normal CCCV charging (periods P1, P2) is completed, the cell 11 It is possible to reduce the variation in capacitance between the two. Further, by using the normal CCCV charge termination condition (that is, the current value C2 as the termination condition) as it is as the additional CCCV charge termination condition in the low-rate charging, it is possible to simplify the charge control.
(Third example)

  As shown in FIG. 6, the third example is different from the second example in that additional CCCV charging is performed using an additional end condition different from the second example. Other points of the third example are the same as those of the second example. Specifically, in the third example, the additional end condition is that the charging current decreases to a current value C5 (fifth current value) smaller than the current value C2. The current value C5 is a current value determined in advance as an additional end current value. Thus, in the third example, the charging period is longer than that in the second example only during a period P33 from time t32 when the charging current becomes the current value C2 to time t4 when the charging current becomes the current value C5.

In the third example, the IR drop generated in the power storage module 1 after completion of charging can be reduced as compared with the second example in which the current value C2 is the termination condition, so that the charging rate of the power storage module 1 can be further increased. it can. In the third example, since the charging period is longer than that in the second example, the influence of overcharge on the high-capacity cell is larger than that in the second example, but the capacity between the cells 11 is higher than that in the second example. The effect of reducing the variation (that is, the capacity difference between the high capacity cell and the low capacity cell) can be enhanced.
(4th example)

  As shown in FIG. 7, the fourth example is similar to the second and third examples in that additional CCCV charging is performed after completion of the CCCV charging (periods P1, P2). The second example is different from the third example in that the end current (current value C2) of the CCCV charging (periods P1, P2) is a new constant current. Specifically, in the fourth example, the low-rate charging (period P3) is set to the current value C2 until time t33 when the charging voltage reaches a voltage value V3 (third voltage value) higher than the voltage value V1. A step of performing constant current charging (period P34) of the power storage module 1 by the charged current. In the low rate charging, after the constant current charging with the current value C2 (period P34), the charging current is gradually reduced so that the charging voltage is maintained at the voltage value V3 until a predetermined termination condition is satisfied. Thus, a step of performing constant voltage charging (period P35) of the power storage module 1 is included. The termination condition here is, for example, that the charging current decreases to a current value C6 that is smaller than the current value C2. The current value C6 is a current value determined in advance as an additional end current value.

  In the fourth example, after completion of normal CCCV charging (periods P1, P2), by further performing constant current charging (period P34) with the end current (current value C2) of the CCCV charging as a new constant current, The variation in capacity between the cells 11 can be reduced by relatively simple current control. Further, in the fourth example, the IR drop can be reduced by further performing constant voltage charging (period P35) as compared with the case where the constant voltage charging is not performed, so that the charging rate of the power storage module 1 can be further increased. it can. In the fourth example, constant voltage charging (period P35) may be omitted. That is, only the additional CC charging (period P34) may be performed after the completion of the CCCV charging (period P1, P2).

  The second to fourth examples described above are patterns in which low-rate charging is performed using thresholds (voltage values V2, V3) larger than the voltage control thresholds (voltage values V1) in the CCCV charging (periods P1, P2). It is. By charging with a low-rate current (current smaller than the current value C1), IR drop can be suppressed and, as a result, voltage measurement error can be reduced. Can be high.

  In the charging method of the present embodiment described above, after completion of charging in the first step and the second step (CCCV charging in the periods P1 and P2), charging with a charging current smaller than the current value C1 (low rate in the period P3) Charging) is performed. As described above, at the time of completion of the second step (time t3), there may be a variation in the charge capacity (OCV) among the plurality of cells 11 included in the power storage module 1. When such a variation occurs, a cell having a large capacity (high capacity cell) has a larger internal resistance than a cell having a small capacity (low capacity cell), and thus the amount of energy consumed by heat generation is large. For this reason, the low-capacity cell is charged more efficiently than the high-capacity cell by further performing low-rate charging after CCCV charging. As a result, the variation in capacity between the cells 11 is reduced. That is, the above-described low rate charging functions as a charging mode for correcting variation in capacity between cells 11. Moreover, in the said charging method, it is not necessary to provide the equalization circuit connected in parallel for every cell 11 like the prior art. Therefore, according to the above charging method, variation in capacity between the cells 11 can be reduced with a simpler structure in charging the power storage module 1 including the plurality of cells 11. Thereby, the capacity | capacitance of a low capacity | capacitance cell can be approximated to the capacity | capacitance of a high capacity | capacitance cell, and the usable capacity | capacitance of the electrical storage module 1 whole can be increased.

In addition, although the low rate charge (3rd step) mentioned above becomes overcharge for the cell 11 fully charged at the time of 2nd step completion (time t3), in this embodiment, it has high overcharge tolerance. Lithium ion secondary batteries using LTO as a negative electrode material are charged. Thereby, the dispersion | variation in the capacity | capacitance between the cells 11 can be reduced, suppressing the bad influence by the overcharge with respect to the cell 11 already fully charged. That is, the charging method of this embodiment is a charging method suitable for a lithium ion secondary battery using LTO with high overcharge resistance as a negative electrode material.
[Modification]

  FIG. 8 is a flowchart showing the procedure of the charging method according to the modification. As shown in FIG. 8, the charging method according to the modification executes the first step (S1) for performing CC charging in the period P1 and the second step (S2) for performing CV charging in the period P2. After that, a determination step (S3) for determining whether or not to execute the third step (S4) for performing the low rate charging in the period P3 described above is included. In the present embodiment, a period in which the current value of the charging current is 0 is provided between the second step and the determination step. Specifically, in the determination step, based on the voltage value of the power storage module 1 after the second step (voltage value after the charging current is turned off (after the voltage drop)), a plurality of power storage modules 1 included in the power storage module 1 It is determined whether or not there is a variation in capacity between the cells 11. And the low rate charge mentioned above is performed when it determines with the variation having arisen in the determination step (S3: YES). On the other hand, when it is not determined that the variation occurs in the determination step (S3: NO), the low rate charging described above is not executed. In this case, only normal CCCV charging is performed as in the conventional charging method.

  The determination step is performed as follows, for example. As shown in FIG. 1, in the present embodiment, as an example, the control device 2 is connected to a voltage sensor 4 for measuring a voltage between terminals of the power storage module 1. Thereby, the control apparatus 2 can acquire the voltage value of the electrical storage module 1 after a 2nd step. Here, when there is a variation in capacity between the plurality of cells 11 (that is, when there is a low-capacity cell whose capacity is smaller than a certain level compared to other cells), the capacity is evenly distributed among the plurality of cells 11. The capacity (voltage) of the entire power storage module 1 is smaller than the case where it is charged so that The control device 2 may execute the above determination by using such characteristics, for example, as follows. For example, the control device 2 holds in advance the voltage value (ideal voltage value IV) of the power storage module 1 when there is no variation in capacity among the plurality of cells 11 (that is, when ideal charging is completed). Keep it. Then, the control device 2 compares the voltage value V of the power storage module 1 after the second step measured by the voltage sensor 4 with the ideal voltage value IV, thereby causing a variation in capacity among the plurality of cells 11. It can be determined whether or not. For example, when the difference between the ideal voltage value IV and the voltage value V (ideal voltage value IV−voltage value V) is equal to or larger than a predetermined threshold (or larger than the threshold), the control device 2 has a plurality of cells 11. It is determined that there is a variation in capacity between the cells, and when the difference is less than the threshold value (or less than the threshold value), it can be determined that there is no variation in capacity among the plurality of cells 11. As another example, the charging system 100 may include a voltage sensor for measuring the voltage of any one cell 11 in addition to the voltage sensor 4 for measuring the voltage between the terminals of the power storage module 1. Good. In this case, when the voltage value of one cell 11 is the cell full charge voltage (the voltage corresponding to SOC = 100 [%] of the cell 11), the voltage value V of the power storage module 1 is compared with the ideal voltage value IV. By doing so, it can be determined whether or not there is a variation in capacity among the plurality of cells 11. The subsequent determination procedure is the same as the determination procedure described above. As another example, when the voltage value V of the power storage module 1 is the ideal voltage value IV, the capacity value between the plurality of cells 11 is compared by comparing the voltage value of one cell 11 with the cell full charge voltage. It can be determined whether or not there is a variation. For example, when the difference between the voltage value of one cell 11 and the cell full charge voltage is equal to or greater than a predetermined threshold (or greater than the threshold), the control device 2 causes a variation in capacity among the plurality of cells 11. When it is determined that the difference occurs and the difference is less than the threshold value (or less than the threshold value), it can be determined that there is no variation in capacity among the plurality of cells 11.

  According to the charging method according to the modified example, unnecessary overcharging (that is, performing the above-described low rate charging when there is no variation in capacity between the cells 11) can be appropriately prevented. That is, the low rate charging described above can be appropriately executed only when the variation correction (capacity equalization) between the cells 11 is necessary. Further, as described above, when the current value of the charging current is flowing in the power storage module 1 by setting the current value of the charging current to 0 (that is, preventing the current from flowing through the power storage module 1) before the determination step. The voltage fluctuation that occurs can be eliminated. As a result, in the determination step, it can be determined with higher accuracy whether or not there is a variation in capacity between the cells 11.

  FIG. 9 is a schematic configuration diagram illustrating a charging system 100A according to a modification. In charging system 100 </ b> A, a plurality of power storage modules 1 are connected in series with charging device 3. Thereby, in the charging system 100 </ b> A, the plurality of power storage modules 1 are simultaneously charged by the charging current supplied from the charging device 3. In addition, a voltage sensor 4 for measuring a voltage between terminals of each power storage module 1 is provided for each power storage module 1. The control device 2 is connected to each voltage sensor 4. Thereby, the control apparatus 2 can acquire the voltage value of each electrical storage module 1.

  In charging system 100A, control device 2 can execute the determination process in the determination step (S3 in FIG. 8), for example, as follows. That is, the control device 2 acquires the voltage value of each of the plurality of power storage modules 1 after the second step, and the variation among the plurality of power storage modules 1 is based on the comparison result of the voltage values between the power storage modules 1. It is determined whether or not the generated power storage module 1 exists. And the low rate charge mentioned above is performed when it determines with the electrical storage module 1 in which the dispersion | variation has arisen in the determination step existing (S3: YES). On the other hand, when it is not determined that there is the power storage module 1 in which variation occurs in the determination step (S3: NO), the above-described low rate charging is not performed.

  For example, the control device 2 extracts the maximum voltage value Vmax and the minimum voltage value Vmin from the plurality of voltage values. Then, the control device 2 stores the variation in power when the difference (Vmax−Vmin) between the maximum voltage value Vmax and the minimum voltage value Vmin is greater than or equal to a predetermined threshold value (or greater than the threshold value). When it is determined that there is a module 1 (that is, the power storage module 1 having the minimum voltage value Vmin) and the difference is less than the threshold value (or less than or equal to the threshold value), there is no power storage module 1 in which variation occurs. It can be determined.

  As described above, in charging system 100 </ b> A in which a plurality of power storage modules 1 are connected in series with charging device 3, capacity variation between cells 11 occurs based on a comparison result of voltage values between power storage modules 1. It can be easily determined whether or not the power storage module 1 exists. As a result, it is possible to appropriately prevent unnecessary overcharging (that is, performing the above-described low rate charging when there is no power storage module 1 in which the capacity variation between the cells 11 occurs).

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above-described embodiment (modified example), whether or not to perform low-rate charging is determined based on the voltage value of the power storage module 1 after the second step. The determination criteria are not limited to the above. For example, whether or not to perform low rate charging may be determined based on the years of use or the number of times of charging of the power storage module 1. For example, when the number of years of use or the number of times of charging of the power storage module 1 increases, the deterioration of the power storage module 1 proceeds and the capacity variation between cells is likely to occur. In this case, low rate charging may be performed.

  Whether or not to perform low-rate charging may be selected by a manual operation such as an operator (for example, an input operation to the control device 2). In addition, the determination result as to whether or not the low rate charging is performed may be temporarily output to an output device (a monitor or the like) included in the control device 2 so that the operator can check it. In this case, low-rate charging may be started based on a subsequent input operation from the operator.

  Further, when charging is performed by connecting a plurality of power storage modules 1 in series as in the charging system 100A, the power storage modules 1 determined to have variations (for example, voltages compared to other power storage modules 1). The above-described low-rate charging may be performed after extracting the power storage module 1) that is lower than a certain standard and connecting only the extracted power storage module 1 in series with the charging device 3.

  DESCRIPTION OF SYMBOLS 1 ... Power storage module, 2 ... Control apparatus, 3 ... Charging apparatus, 4 ... Voltage sensor, 11 ... Cell, 100, 100A ... Charging system, C1 ... Current value (first current value), C2 ... Current value (second current) Value), C3 ... current value (third current value), C4 ... current value (fourth current value), C5 ... current value (fifth current value), V1 ... voltage value (first voltage value), V2 ... voltage Value (second voltage value), V3... Voltage value (third voltage value).

Claims (11)

A method for charging a power storage module including a plurality of cells connected in series,
A first step of performing constant current charging of the power storage module with the charging current set to the first current value until the charging voltage reaches the first voltage value;
After the first step, the charging current is gradually reduced so that the charging voltage is maintained at the first voltage value until a predetermined termination condition is satisfied, whereby constant voltage charging of the power storage module is performed. A second step to perform;
A third step of further charging the power storage module with the charging current smaller than the first current value after the second step;
Including a charging method. The termination condition is that the charging current decreases to a second current value smaller than the first current value,
In the third step, the charging current is gradually reduced to a third current value smaller than the second current value so that the charging voltage is maintained at the first voltage value. Charging,
The charging method according to claim 1. The termination condition is that the charging current decreases to a second current value smaller than the first current value,
The third step includes
Until the charging voltage reaches a second voltage value higher than the first voltage value, the charging current set to a fourth current value that is smaller than the first current value and larger than the second current value. Performing constant current charging of the power storage module;
After the constant current charging with the fourth current value, the charging current is gradually reduced so that the charging voltage is maintained at the second voltage value until a predetermined additional termination condition is satisfied. Performing constant voltage charging of the module,
The charging method according to claim 1. The additional termination condition is that the charging current is reduced to the second current value.
The charging method according to claim 3. The additional termination condition is that the charging current decreases to a fifth current value smaller than the second current value.
The charging method according to claim 3. The termination condition is that the charging current decreases to a second current value smaller than the first current value,
The third step includes a step of performing constant current charging of the power storage module with a charging current set to the second current value until the charging voltage reaches a third voltage value higher than the first voltage value. Including,
The charging method according to claim 1. In the third step, the constant voltage charging of the power storage module is performed by gradually reducing the charging current so that the charging voltage is maintained at the third voltage value after the constant current charging with the second current value. Further comprising the step of:
The charging method according to claim 6. Based on the voltage value of the power storage module after the second step, further including a determination step of determining whether or not there is a variation in capacity among the plurality of cells included in the power storage module;
The third step is performed when it is determined that the variation occurs in the determination step, and is not performed when it is not determined that the variation occurs in the determination step.
The charging method according to any one of claims 1 to 7. The charging method is executed for a plurality of power storage modules connected in series,
In the determination step, the voltage value of each of the plurality of power storage modules is acquired after the second step, and the variation among the plurality of power storage modules is determined based on a comparison result of the voltage values between the power storage modules. Determine whether there is a power storage module
The third step is executed when it is determined in the determination step that there is a power storage module in which the variation occurs, and in the case where it is not determined in the determination step that there is a power storage module in which the variation occurs. Will not run,
The charging method according to claim 8. The method further includes a step of providing a period during which the current value of the charging current is 0 between the second step and the determination step.
The charging method according to claim 8 or 9. The power storage module to be charged is a lithium ion secondary battery using lithium titanate as a negative electrode material.
The charging method according to claim 1.

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