Energy storage device, method for controlling a plurality of cells and method for controlling an energy storage device

Abstract

An energy storage device 50 includes: a plurality of cells 62 connected in series; a balancer 65 that adjusts a variation in discharge capacity for the plurality of cells; and a control unit 130. The control unit 130 calculates a discharge capacity DC of each of the cells 62 based on a full charge capacity X2 of each of the cells after a lapse of a predetermined time since the time of cell manufacture and on a remaining capacity Y2 of each of the cells 62 after the predetermined time since the time of cell manufacture, and adjusts, by means of a balancer 62, a variation in discharge capacity DC of each of the cells 62 after the predetermined time since the time of cell manufacture.

Description

Power storage device, control method for multiple cells, and control method for power storage device

[0001] One embodiment of the present invention relates to a power storage device including a plurality of storage batteries (secondary batteries), particularly lithium-ion batteries, connected in series, which has a function of eliminating variations in discharge capacity (difference between the fully charged capacity and the remaining capacity) between the storage batteries and maintaining a balance between the storage batteries.

[0002] Storage batteries are installed in vehicles such as automobiles, trains, ships, and aircraft, and are used as a power source for passenger cabin lighting, air conditioning, communication means, instruments and control devices required for operation, and for power equipment. Because storage batteries can store electricity from power generation facilities and generators and supply power when needed, they are also used as a buffer for industrial power supply and demand.

[0003] 2. Description of the Related Art Power storage devices each comprising a combination of a plurality of storage batteries (hereinafter also referred to as cells) are used for mobile or industrial purposes.

[0004] It is known that the capacity (fully charged capacity and / or remaining capacity) of each cell included in an electricity storage device varies due to individual internal resistance and other factors.

[0005] If a battery is charged when the capacities of the cells are uneven, one of the cells may be overcharged. To address this issue, the battery management unit is equipped with a function / circuit called a balancer. For example, the balancer can discharge a cell with a high voltage to eliminate the variation among the cells. Patent Document 1 discloses a related technology.

[0006] Japanese Patent Application Laid-Open No. 2006-353010

[0007] As mentioned above, conventional balancers discharge cells with higher voltages to eliminate variations among multiple cells.

[0008] Conventional balancers can sometimes have difficulty eliminating capacity variations. For example, in the case of a power storage device that combines multiple lithium-ion batteries (hereinafter also referred to as LFP cells) that use an iron phosphate (LiFePO4) active material in the positive electrode and a carbon-based active material in the negative electrode, there is a wide range of voltage values ​​(plateau region) where the voltage value of each cell remains almost constant even when the state of charge (SOC) of each cell changes. In the plateau region, it is impossible to detect capacity variations among multiple cells from the voltage values ​​of each cell.

[0009] By charging a power storage device that combines multiple LFP cells to a region near full charge (constant voltage charging region), it is possible to detect capacity variations among the multiple cells. However, such charging requires time and cost. One aspect of the present invention provides a technology for suppressing capacity variations among the multiple cells.

[0010] The power storage device includes a plurality of cells connected in series, a balancer that adjusts the variation in discharge capacity among the plurality of cells, and a control unit. The control unit calculates the discharge capacity of each cell based on the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, and adjusts the variation in discharge capacity among the cells after the predetermined time has elapsed since the time of cell manufacture using the balancer.

[0011] The power storage device includes a plurality of cells connected in series, a voltage measurement unit that measures the voltage of each of the cells, a balancer that adjusts variations in the state of charge of the plurality of cells, and a control unit. The control unit calculates a full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture, calculates the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture based on the cell voltage measured by the voltage measurement unit, calculates a difference in the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture from the state of charge of each cell, and adjusts the variation in the state of charge of the plurality of cells using the balancer based on the difference between the full charge capacity of each cell and the state of charge of each cell.

[0012] The control method for multiple cells connected in series calculates the discharge capacity of each cell based on the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, and adjusts the variation in the discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture using the balancer.

[0013] A control method for a power storage device having a plurality of cells connected in series calculates the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture, obtains the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture from the cell voltage, calculates the discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture from the full charge capacity and remaining capacity of each cell, and equalizes the variation in discharge capacity between each cell.

[0014] This technology eliminates variations in discharge capacity and state of charge between cells that occur over time from the time of cell manufacture, thereby preventing cells from becoming overcharged or overdischarged, allowing the cells to fully demonstrate their inherent performance.

[0015] Side view of the vehicle Exploded perspective view of the energy storage device Cross-sectional view of the cell Plan view of the cell Block diagram showing the electrical configuration of the energy storage device Circuit diagram of the balancer Graph showing the correlation between the SOC and OCV of the cell Diagram showing the manufacturing process of the energy storage device Flowchart of the discharge capacity equalization process Diagram showing the relationship between the full charge capacity at the time of cell manufacturing, the initial full charge capacity value of the cell when the energy storage device is assembled, and the initial remaining capacity value Diagram showing the change in discharge capacity Diagram showing the change in capacity after charging Diagram showing the CPU in functional blocks (diagram showing input / output of data processing)

[0016] (1) An embodiment of the present invention provides a power storage device including a plurality of cells connected in series, a balancer for adjusting the variation in discharge capacity of the plurality of cells, and a control unit, wherein the control unit calculates the discharge capacity of each cell based on the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, and adjusts the variation in discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture using the balancer.

[0017] According to an embodiment of the present invention, the energy storage device can eliminate variations in discharge capacity between cells that occur over time from the time of cell manufacture. Eliminating variations in discharge capacity between cells can prevent cells from becoming overcharged or overdischarged, and by minimizing excessive safety control to prevent overcharge or overdischarge, the performance of the cells can be fully demonstrated.

[0018] (2) A power storage device includes a plurality of cells connected in series, a voltage measurement unit that measures the voltage of each of the cells, a balancer that adjusts variations in the state of charge of the plurality of cells, and a control unit, wherein the control unit calculates a full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture, calculates the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture based on a cell voltage measurement value by the voltage measurement unit, calculates a difference in the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture from the state of charge of each cell, and adjusts the variation in the state of charge of the plurality of cells using the balancer based on the difference between the full charge capacity of each cell and the state of charge of each cell.

[0019] According to the energy storage device described in (2) above, it is possible to eliminate variations in the state of charge between cells that occur over time from the time of cell manufacture. By eliminating variations in the state of charge between cells, it is possible to prevent the cells from becoming overcharged or overdischarged, and by minimizing excessive safety control that prevents overcharge or overdischarge, it is possible to fully utilize the performance of the cells.

[0020] (3) In the energy storage device described in (1) or (2) above, the control unit may calculate the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture, based on the full charge capacity of the cell at the time of cell manufacture and the amount of decrease in full charge capacity over time since the time of cell manufacture.

[0021] According to the energy storage device described in (3) above, the full charge capacity and discharge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture can be accurately determined, and therefore, the difference in discharge capacity between cells after the predetermined time has elapsed since the time of cell manufacture can be estimated with high accuracy, and the variation in discharge capacity among cells can be accurately equalized.

[0022] (4) In the power storage device described in (3) above, the amount of decrease in full charge capacity due to the elapsed time after cell production may be calculated based on information about the elapsed time after cell production and temperature history.

[0023] According to the energy storage device described in (4) above, the full charge capacity and discharge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture can be accurately determined, and therefore, the difference in discharge capacity between cells after the predetermined time has elapsed since the time of cell manufacture can be estimated with high accuracy, and the variation in discharge capacity among cells can be accurately equalized.

[0024] (5) A method for controlling multiple cells according to one embodiment of the present invention calculates the discharge capacity of each cell based on the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, and adjusts the variation in the discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture using a balancer.

[0025] The method for controlling multiple cells described in (5) above can eliminate variations in discharge capacity between cells that occur over time from the time of cell manufacture. Eliminating variations in discharge capacity between cells can prevent cells from becoming overcharged or overdischarged, and by minimizing excessive safety control to prevent overcharge or overdischarge, the performance of the cells can be fully demonstrated.

[0026] (6) A control method for a storage device according to one embodiment of the present invention calculates, for each cell, the full charge capacity after a predetermined time has elapsed since the time of cell manufacture, obtains for each cell the remaining capacity after the predetermined time has elapsed since the time of cell manufacture from the cell voltage, calculates the discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture from the full charge capacity and remaining capacity of each cell, and equalizes the calculated variations in discharge capacity between each cell.

[0027] According to the control method for a power storage device described in (6) above, it is possible to eliminate variations in discharge capacity between cells that occur over time from the time of cell manufacture. By eliminating variations in discharge capacity between cells, it is possible to prevent cells from becoming overcharged or overdischarged, and by minimizing excessive safety control that prevents overcharge or overdischarge, it is possible to fully utilize the performance of the cells.

[0028] 1, a vehicle 10 is equipped with an engine 20 and a power storage device 50 used for starting the engine 20. In addition to or instead of the engine 20 (internal combustion engine), the vehicle 10 may be equipped with a motor, and a power storage device may be equipped as a power source for the motor.

[0029] As shown in Fig. 2, the power storage device 50 includes a battery pack 60, a circuit board unit 105, and a housing 71. The housing 71 includes a main body 73 and a lid 74 made of a synthetic resin material. The main body 73 is cylindrical and has a bottom 75 and four side surfaces 76. The four side surfaces 76 form an opening 77 at the top of the main body 73.

[0030] The housing 71 houses the battery pack 60 and a circuit board unit 105. The circuit board unit 105 is a board unit having various components (such as a current interruption device, a current detection unit, a balancer, and a management device, which will be described later, in FIG. 5 ) mounted on a circuit board 100, and is disposed adjacent to, for example, above, the battery pack 60 as shown in FIG. 2 . Alternatively, the circuit board unit 105 may be disposed adjacent to, and to the side of, the battery pack 60.

[0031] The lid 74 closes the opening 77 of the main body 73. An outer peripheral wall 78 is provided around the lid 74. The lid 74 has a protruding portion 79 that is generally T-shaped in plan view. The positive external terminal 51 is fixed to one corner of the front of the lid 74, and the negative external terminal 52 is fixed to the other corner. The circuit board unit 105 may be housed within the lid 74 (for example, within the protruding portion 79) instead of the main body 73 of the housing 71.

[0032] The battery pack 60 is composed of a plurality of cells 62. As shown in Fig. 3, each cell 62 has an electrode assembly 83 housed in a rectangular parallelepiped case 82 together with a non-aqueous electrolyte. The cells 62 are, for example, lithium-ion secondary battery cells. The case 82 has a case body 84 and a lid 85 that closes the upper opening.

[0033] Although not shown in detail, the electrode assembly 83 comprises a negative electrode plate made of a copper foil substrate coated with an active material, a positive electrode plate made of an aluminum foil substrate coated with an active material, and a separator made of a porous resin film disposed between them. Both of these are strip-shaped, and the negative electrode plate and the positive electrode plate are wound flat with their positions offset in the short direction relative to the separator. The electrode assembly 83 may be a laminated type instead of a wound type.

[0034] A positive electrode terminal 87 is connected to the positive electrode plate via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode plate via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 each have a flat base portion 90 and legs extending from the base portion 90. A through hole is formed in the base portion 90.

[0035] The positive electrode terminal 87 and the negative electrode terminal 89 each comprise a terminal body 92 and a shaft 93 that protrudes downward from the center of the underside of the terminal body 92. The terminal body 92 and shaft 93 of the positive electrode terminal 87 are integrally molded from aluminum (a single material). In the negative electrode terminal 89, the terminal body 92 is made of aluminum, and the shaft 93 is made of copper, and these are assembled together. The terminal bodies 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are disposed on both ends of the lid 85 via gaskets 94 made of an insulating material, and are exposed to the outside from the gaskets 94, as shown in FIG. 4 .

[0036] The lid 85 has a pressure relief valve (safety valve) 95. The pressure relief valve 95 is located, for example, between the positive electrode terminal 87 and the negative electrode terminal 89. The pressure relief valve 95 opens to reduce the internal pressure of the case 82 when the internal pressure of the case 82 exceeds a limit.

[0037] 5 is a block diagram showing the electrical configuration of the power storage device 50. The power storage device 50 includes a battery pack 60, a current detection unit 54, a current interruption device 53, a balancer 65, a voltage measurement unit 110, a temperature sensor 58, and a management device 130.

[0038] The battery pack 60 has, for example, 12 cells 62 (see FIG. 2), with three connected in parallel and four connected in series. In FIG. 5, three cells 62 connected in parallel are represented by one battery symbol. The cells may be cylindrical cells or pouch cells with a laminated film case.

[0039] The battery pack 60, the current interruption device 53, and the current detection unit 54 are connected in series via power lines 55P and 55N. The power lines 55P and 55N can be bus bars BSB (see FIG. 2), which are plate-shaped conductors made of a metal material such as copper.

[0040] 5 , power line 55P connects positive external terminal 51 to the positive electrode of battery pack 60. Power line 55N connects negative external terminal 52 to the negative electrode of battery pack 60. External terminals 51 and 52 are terminals for connection to electrical loads provided in vehicle 10.

[0041] The current interruption device 53 is provided on the positive power line 55P. The current interruption device 53 may be a semiconductor switch such as an FET or a relay with mechanical contacts. The current interruption device 53 is preferably a self-holding switch such as a latching relay. The current interruption device 53 is of a normally closed type and is normally controlled to a closed state. If an abnormality occurs in the power storage device 50, the current I of the battery pack 60 can be interrupted by switching the current interruption device 53 from a closed state to an open state.

[0042] The current detection unit 54 is provided on the negative power line 55N. The current detection unit 54 may be a shunt resistor. The resistive current detection unit 54 can measure the current I of the battery pack 60 based on the voltage Vr across the current detection unit 54. The resistive current detection unit 54 can distinguish between discharging and charging based on the polarity (positive or negative) of the voltage Vr. Alternatively, the current detection unit 54 may be a magnetic sensor.

[0043] The voltage measurement unit 110 can measure the voltage Vs of each of the cells 62A to 62D and the total voltage Vab of the battery pack 60. The temperature sensor 58 is attached to the battery pack 60 and detects the temperature of the battery pack 60.

[0044] The balancer 65 is used to equalize the voltages Vs of the cells 62, and in this embodiment, as shown in FIG. 6, is made up of four cell discharge circuits 66A to 66D.

[0045] Each of the cell discharge circuits 66A to 66D is connected in parallel to each of the cells 62A to 62D. Each of the cell discharge circuits 66A to 66D is composed of a discharge resistor 67 and a switch 68. By turning on the switch 68, the corresponding cell 62 can be discharged.

[0046] The management device 130 is mounted on the circuit board 100 (see FIG. 2 ), and as shown in FIG. 5 , includes a CPU 131, a memory 132, and a communication unit 133. The communication unit 133 is connected to the vehicle ECU via a communication port 134.

[0047] The management device 130 monitors the state of the power storage device 50 based on the outputs of the voltage measurement unit 110, the current detection unit 54, and the temperature sensor 58. That is, the management device 130 monitors the cell voltage Vs of each cell 62, the temperature of the battery pack 60, the current I, and the total voltage Vab. The management device 130 corresponds to a "control unit."

[0048] An execution program for an equalization process that adjusts the discharge capacity DC of the cells 62A to 62D, as well as data necessary for executing this program, are stored in the memory 132. The data stored in the memory 132 includes, for example, data on the SOC-OCV characteristics of the cells 62, which will be described next, and test data (described later) on the full charge capacity of each cell 62 during cell manufacture.

[0049] The program may be distributed using telecommunications lines.

[0050] 2. SOC-OCV Characteristics of Cell 62 Figure 7 is a graph showing the SOC-OCV characteristics of an LFP cell 62, which uses an iron phosphate (LiFePO4) active material in the positive electrode and a carbon-based active material in the negative electrode, with the horizontal axis representing SOC [%] and the vertical axis representing OCV [V]. The OCV (Open Circuit Voltage) may be the cell voltage when there is no current, which is not affected by polarization, or the cell voltage Vs when there is no current. A case where there is no current is when the current is below a predetermined value (for example, when dark current flows).

[0051] The SOC is the ratio of the remaining capacity [Ah] to the fully charged capacity [Ah], and is expressed by the following equation (1).

[0052] SOC=(Y / X)×100 (1) Here, X is the fully charged capacity of the cell, and Y is the remaining capacity of the cell (the amount of electricity stored in the cell).

[0053] In the SOC-OCV characteristics, cell 62 has a plateau region F0, a first rapid change region F1, and a second rapid change region F2. In the plateau region F0, the SOC ranges from SOC2 (30%) to SOC1 (95%). In the plateau region F0, the change in OCV relative to the change in SOC is equal to or less than a predetermined value, and the graph is substantially flat.

[0054] The first rapid change region F1 is a region where the SOC is equal to or greater than SOC 1, and the second rapid change region F2 is a region where the SOC is equal to or less than SOC 2. In both the first rapid change region F1 and the second rapid change region F2, the slope of the graph is greater than in the plateau region F0, and the OCV changes rapidly with changes in the SOC.

[0055] Because cell 62 has the first rapid change region F1, the cell voltage Vs rises rapidly near full charge at the end of charging (part A in FIG. 7 ). Also, because cell 62 has the second rapid change region F2, the cell voltage Vs drops rapidly at the end of discharging (part B in FIG. 7 ).

[0056] The cell 62 having such characteristics is not limited to an LFP cell.

[0057] 3. Method for Equalizing Discharge Capacity in the Manufacturing Process The manufacturing process of the energy storage device 50 includes, for example, a cell manufacturing process S1, a storage process S2, and an energy storage device assembly process S3, as shown in Fig. 8. In some cases, the storage process S2 may be skipped and the process may proceed directly to the energy storage device assembly process S3.

[0058] S1 is a process for manufacturing the cells 62, and S2 is a process for moving the manufactured cells 62 to a predetermined temperature-controlled warehouse or the like for storage. S3 is a process for assembling the parts (such as the battery case 20, the cover member 50, the cells 62A to 62D, and the circuit board unit 105) to produce the electricity storage device 50.

[0059] The causes of variations in discharge capacity among multiple cells in an energy storage device include the following: (1) Variations in full charge capacity among cells during cell manufacturing (due to individual differences between cells) (2) Variations in full charge capacity degradation among cells due to storage and transportation during the manufacturing of the energy storage device (3) Variations in cell self-discharge among cells after cell manufacturing (due to individual differences between cells)

[0060] Hereinafter, a method for eliminating variations in discharge capacity among cells that occur during the manufacturing process of an electricity storage device (from cell manufacturing to electricity storage device assembly) will be disclosed.

[0061] 9 is a flowchart of the discharge capacity equalization method, which is composed of eight steps S10 to S80 for equalizing the discharge capacities DC of the series-connected cells 62A to 62D.

[0062] As shown in FIG. 8, the discharge capacity equalization (S20 to S80) is a process that is carried out after the assembly of the power storage device 50 and before shipping.

[0063] During cell manufacturing, the full charge capacity X1 [Ah] of each of the cells 62A to 62D is measured (see FIG. 10). In S10, after the energy storage device is assembled, the measurement results of the full charge capacity X1 of each of the cells 62 during cell manufacturing are input to the memory 132 of the management device 130 built into the energy storage device 50. This will be explained in detail below.

[0064] The process from S20 onwards is a flow after the completion of assembly of the power storage device 50. In S20, the management device 130 estimates the initial full charge capacity X2 [Ah] of each of the cells 62A to 62D at the completion of assembly of the power storage device 50 (see FIG. 10). The initial full charge capacity X2 is the full charge capacity at the time of startup of the management device 130 (at the start of data processing) after assembly of the power storage device 50. The same applies to the initial remaining capacity Y2, which will be described later.

[0065] The initial full charge capacity X2 can be estimated by subtracting the decrease ΔX that occurs over time (a predetermined time or any time) after cell manufacture from the full charge capacity X1 at the time of cell manufacture, as shown in equation (2).

[0066] X2=X1-ΔX...(2)

[0067] Cells naturally deteriorate even when left unused (this is also called "deterioration due to storage" or "deterioration over time"), and the full charge capacity decreases by an amount ΔX. This is an unintended, irreversible reaction, and is one of the causes of the decrease in full charge capacity.

[0068] This step of calculating the decrease ΔX is an important step for equalizing the variation in discharge capacity.

[0069] In this embodiment, the decrease ΔX in the full charge capacity X1 is determined by taking into account the time elapsed since the time of cell manufacture as well as the temperature history of the cell (environmental temperature during storage and transportation). By taking into account the temperature history of the cell in addition to the elapsed time, the decrease ΔX in the full charge capacity X1 can be calculated with high accuracy. The amount of storage deterioration, i.e., the decrease ΔX, depends on time (for example, the root or n-th root of time) and is proportional to a constant that depends on temperature.

[0070] The reaction rate of the above-mentioned unintended reaction also depends on the temperature.

[0071] Therefore, temperature is also an important factor that affects the decrease amount ΔX. Strictly speaking, each cell undergoes its own unique degradation phenomenon, but if the materials (related substances) and configuration are the same, ΔX will often be roughly the same.

[0072] Regarding the variation in deterioration of each cell described above in (2), it can be considered that there is no variation if the materials (related substances) and configuration are the same.

[0073] Hereinafter, it is assumed that the temperature of each cell changes in the same manner from the time of cell manufacture to the time of completion of assembly of the power storage device 50.

[0074] Furthermore, if the temperature history of each cell and the time elapsed from the time of cell manufacture to the time of completion of assembly of the energy storage device 50 are the same (if the cells are stored under the same conditions), the amount of deterioration due to neglect, i.e., the decrease ΔX, can be considered to be the same.

[0075] In S30, the management device 130 determines the initial remaining capacity Y2 [Ah] of each cell 62 at the time of completion of assembly of the energy storage device 50 (see FIG. 10 ). The time elapsed from the time of cell manufacture to the time of completion of assembly of the energy storage device 50 can be determined through some form of time management, such as process time management using a server or the like. A code (barcode or two-dimensional code) may be printed on the cell in advance to store the time of cell manufacture. That is, the code information can be read with a reader or the like during assembly of the energy storage device 50, and the time elapsed from the time of cell manufacture to the time of completion of assembly of the energy storage device 50 can be calculated from the time from the time of cell manufacture to the time of completion of assembly of the energy storage device 50, which is stored in the code. This allows the amount of decrease ΔX, which is also the amount of neglected deterioration, to be determined.

[0076] The decrease amount ΔX can be calculated more accurately by taking into account the temperature change from the time of cell manufacture to the time of completion of assembly of the power storage device 50. As described above, when a temperature change occurs, the interval neglected deterioration amount at a certain temperature can be calculated by multiplying a constant by a time-dependent amount (the time the temperature remains in a state near that temperature) near a certain temperature, and the interval neglected deterioration amounts can be added together to calculate the overall neglected deterioration amount, i.e., the decrease amount ΔX.

[0077] A specific example is described below, but it is merely an example and other methods are also acceptable. First, after aging and lid attachment are completed, the capacities of cells 62A to 62D are measured. The cell voltage and current are measured, and the cell capacity is obtained from the relationship between the integrated current value and the SOC-OCV characteristics. This makes it possible to obtain the full charge capacity X1 of each cell 62A to 62D.

[0078] After the measurement, each of the cells 62A to 62D is discharged. At this point, the voltage of each of the cells 62A to 62D is measured, and the initial remaining capacity Y1 can be obtained from the relationship between the SOC and OCV characteristics. As described above, time information is obtained at this point. This information may be stored in the manufacturing / process control server, or may be recorded in a barcode, two-dimensional code, or the like. The subsequent control steps may be performed by the manufacturing / process control server or the management device 130. Alternatively, they may be performed by a work tool (a dedicated terminal such as a PC or tablet) used by an operator during manufacturing.

[0079] Next, the process moves to an assembly process of the power storage device 50. A worker or a manufacturing machine assembles the battery pack 62, and then attaches other components such as the management device 130, thereby completing the assembly of the power storage device 50.

[0080] Then, as described above, the time at which the cell was manufactured is obtained from the server or a barcode or two-dimensional code attached to the cell, and compared with the current time to determine the time elapsed from the time the cell was manufactured to the time the assembly of the energy storage device 50 was completed.

[0081] From this elapsed time, it is possible to determine the amount of deterioration of each of the cells 62A to 62D from the time of cell manufacture to the time of completion of assembly of the power storage device 50, that is, the decrease amount ΔX, which is also the amount of neglected deterioration. Next, the cell voltage Vs of each of the cells 62A to 62D is measured using the voltage measurement unit 110. From the measured value of the cell voltage Vs, the SOC [%] of each of the cells 62A to 62D is determined by referring to the SOC-OCV characteristics shown in FIG.

[0082] In this embodiment, for example, when the assembly of the power storage device 50 is completed, the SOC of each of the cells 62A to 62D is calculated using the characteristics (SOC-OCV) in the second rapid change region F2 shown in Fig. 7. Therefore, the SOC of each of the cells 62A to 62D can be estimated with high accuracy.

[0083] Here, the cell capacity at the time of cell manufacture is determined, and then the cells are discharged to determine the SOC of each of the cells 62A to 62D using the characteristics (SOC-OCV) in the second rapid change region F2. By setting the cells to a low SOC, it is possible to assemble the cells safely and to suppress the progression of battery degradation.

[0084] Then, the management device 130 calculates, from the determined SOC, an initial remaining capacity Y2 [Ah] of each of the cells 62A to 62D at the time of completion of assembly of the power storage device 50. The initial remaining capacity Y2 can be calculated by multiplying the SOC by the full charge capacity X2. In this embodiment, the initial remaining capacity Y2 is calculated using the SOC-OCV characteristic, but it may also be calculated using the remaining capacity Y-OCV characteristic.

[0085] 10 is the difference between the initial remaining capacity values ​​Y1 and Y2 at the time of cell manufacture and at the time of completion of assembly of the power storage device. ΔY is due to self-discharge of cells 62A to 62D.

[0086] In S40, the management device 130 determines the discharge capacity DC [Ah] of each cell 62A to 62D at the time of assembling the storage device by subtracting the initial remaining capacity value Y2 calculated in S30 from the initial full charge capacity value X2 calculated in S20 (see Figure 10).

[0087] DC=X2-Y2...(3)

[0088] In S50, the management device 130 compares the discharge capacities DC of the cells 62A to 62D calculated in S40, and determines the cell with the maximum discharge capacity DCmax.

[0089] Thereafter, in S60, the management device 130 subtracts the discharge capacity DC from the maximum discharge capacity DCmax as shown in equation (4) to determine the balancer discharge capacity S (amount of electricity to be discharged by the balancer 65) of each of the cells 62A to 62D.

[0090] S=DCmax-DC...(4)

[0091] In S70, the management device 130 determines the discharge time T of each of the cells 62A to 62D from the balancer discharge capacity S calculated in S60.

[0092] In S80, the management device 130 operates the balancer 65 to discharge each of the cells 62A to 62D for the discharge time T calculated in S70. As a result, the discharge capacities DC of the cells 62A to 62D can be equalized. The processes of S20 to S80 are performed, for example, after the assembly of the power storage device 50 is completed.

[0093] FIG. 11 shows the change in discharge capacity DC of each cell 62A to 62D, where (1) shows the time of cell manufacture, (2) and (3) show the time points at which the discharge capacity DC is compared, and (4) shows the discharge capacity DC after equalization.

[0094] In the example of Figure 11, cell 62D is the cell with the maximum discharge capacity DCmax, and by discharging the balancer discharge capacity S calculated in S60 in cells 62A to 62C, the discharge capacity DC of each cell 62A to 62C can be equalized to the maximum discharge capacity DCmax.

[0095] By equalizing the discharge capacities DC of the cells 62A to 62D, the cells 62A to 62D are charged equally after shipping, as shown in Figure 12, so that it is possible to prevent the voltage Vs of some of the cells 62A to 62D from rising toward the end of charging and becoming overcharged. The same applies when discharging, which helps prevent overdischarge (when discharging, the SOC is made uniform, not the discharge capacities DC).

[0096] Furthermore, if some of the cells 62A to 62D are abnormal (for example, have an internal short circuit), differences will occur in the cell voltages Vs over time after the electricity storage device is manufactured, and the cell voltages Vs of the abnormal cells will become lower.

[0097] Therefore, by leaving the cells 62A to 62D for a predetermined time and comparing the cell voltages Vs, it is possible to detect abnormalities in the cells 62A to 62D before shipping. Also, it is possible to detect cells that have a lower full charge capacity than normal cells, such as abnormally deteriorated cells.

[0098] 13 shows data processing related to eliminating variations in discharge capacity DC using calculation blocks. This example illustrates a case where the management device 130 performs a series of processes. In the calculation blocks of FIG. 13, the CPU 131 has a first calculation block 131A, a second calculation block 131B, a third calculation block 131C, a fourth calculation block 131D, and a fifth calculation block 131E.

[0099] The first calculation block 131A calculates the decrease ΔX in the full charge capacity X1 of each of the cells 62A to 62D based on information on the elapsed time since cell manufacture and temperature history. The second calculation block 131B calculates the initial full charge capacity X2 of each of the cells 62A to 62D at the time of completion of assembly of the power storage device based on the inspection data of the full charge capacity X1 at the time of cell manufacture and the decrease ΔX in the full charge capacity X1 calculated by the first calculation block 131A.

[0100] The third calculation block 131C calculates the initial remaining capacity Y2 of each of the cells 62A to 62D based on the measured cell voltage Vs at the time of completion of assembly of the power storage device. The fourth calculation block 131D calculates the discharge capacity DC of each of the cells 62A to 62D from the initial full charge capacity X2 calculated by the second calculation block 131B and the initial remaining capacity Y2 calculated by the third calculation block 131C.

[0101] The fifth calculation block 131E compares the discharge capacities DC of the cells 62A to 62D calculated by the fourth calculation block 131D to determine the maximum discharge capacity DCmax, and calculates the balancer discharge capacity S of the cells 62A to 62C.

[0102] The functional blocks in Figure 13 show the data processing required to calculate the maximum discharge capacity DC and the balancer discharge capacity S of each cell 62, and the CPU 131 may execute these processes using a dedicated arithmetic circuit or a program.

[0103] 4. Effects According to the present disclosure, by eliminating the variation in discharge capacity DC between cells that occurs from the time of cell manufacturing, it is possible to prevent overcharging and overdischarging, and the performance of the cells 62 can be fully demonstrated.

[0104] Furthermore, after manufacturing the power storage device, the discharge capacities DC of the cells 62A to 62D can be equalized without fully charging the cells 62A to 62D, eliminating the need for constant voltage charging (CV charging) using a dedicated charging device and preventing the work time (takt time) from becoming longer. This has the advantage of enabling early delivery of the power storage device 50.

[0105] According to the present disclosure, by taking into account temperature history information in addition to the time elapsed since cell manufacture, it is possible to accurately estimate the decrease ΔX in the full charge capacity X1 after cell manufacture. In particular, the manufacturing process of the energy storage device 50 (from cell manufacture to energy storage device assembly) is often temperature-controlled, and a highly accurate temperature history can be obtained. Therefore, the estimation error of the decrease ΔX in the full charge capacity X1 is small, and the discharge capacity DC and discharge capacity variation of the cell 62 can be accurately estimated.

[0106] According to the present disclosure, in S30, the SOC is estimated using the low SOC rapid change region F2 (part B of Figure 7), so the SOC of each cell 62A to 62D can be estimated with high accuracy without charging cell 62 to the high SOC rapid change region F1.

[0107] According to the present disclosure, it is possible to estimate the initial full charge capacity X2 of the cell 62 with high accuracy, which is expected to improve the accuracy of predicting the life of the cell 62. <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0108] (1) The cell (repeatedly chargeable and dischargeable storage cell) 62 is not limited to a lithium-ion secondary battery cell, but may be another non-aqueous electrolyte secondary battery cell. A capacitor may be used instead of the secondary battery cell 62. In addition, the SOC-OCV characteristics of the cell are not limited to those having a plateau region as shown in FIG. 7, but may be those without a plateau region.

[0109] (2) In the above embodiment, the power storage device 50 is mounted on the vehicle (automobile) 10. However, the power storage device 50 may be mounted on a moving body other than a vehicle, such as a ship or an aircraft. Furthermore, the power storage device may be used for stationary purposes, such as a power storage device for absorbing fluctuations in a distributed power generation system or an uninterruptible power supply (UPS).

[0110] (3) In the above embodiment, the balancer 65 is the discharge circuit 66 using resistors. However, the balancer may be any circuit that can individually discharge the cells 62. The cells 62 may be discharged using circuit elements other than resistors.

[0111] (4) In the above embodiment, equalization of the discharge capacities DC (discharge of the balancer discharge capacity S by the balancer) was performed during the period from the completion of assembly of the energy storage device 50 to its shipment. By storing necessary data in the memory 132, it is possible to calculate the full charge capacity X2 of each cell 62 after a predetermined time has elapsed since the time of cell manufacture. Therefore, it is also possible to calculate the discharge capacity DC of each cell 62 based on the full charge capacity X2 of each cell 62 after the predetermined time has elapsed since the time of cell manufacture and the remaining capacity Y2 of each cell 62 after the predetermined time has elapsed since the time of cell manufacture, and to equalize the discharge capacities DC among the cells after a predetermined time has elapsed since the time of cell manufacture (after shipment or installation in a vehicle). The necessary data includes information such as inspection data for the full charge capacity X1 at the time of cell manufacture, the time elapsed since cell manufacture, and temperature history.

[0112] (5) In the above embodiment, the decrease ΔX in the full charge capacity X1 of the cell 62 is calculated based on the elapsed time since cell manufacture and the temperature history. For example, if there is almost no temperature change after cell manufacture, the decrease ΔX in the full charge capacity X1 of the cell 62 may be calculated based only on the elapsed time since cell manufacture.

[0113] (6) In the above embodiment, the cells 62 are discharged based on the cell 62 with the maximum discharge capacity, thereby equalizing the discharge capacities DC of the cells 62. However, the discharge capacities DC of the cells 62 may be equalized by a method other than that described in the above embodiment, as long as the method discharges the cells 62 with shallow discharge capacities DC.

[0114] (7) In the above embodiment, a technique for eliminating variations in the discharge capacity of the cells 62 using the discharge capacity DC has been described. However, the problem of the present invention can also be solved by using the SOC (state of charge). For example, the cell voltage Vs of each cell 62 after a predetermined time has elapsed since the time of cell manufacture can be measured by the voltage measurement unit 110, and the SOC of each cell 62 after a predetermined time has elapsed since the time of cell manufacture can be calculated by referring to the SOC-OCV characteristics from the measured cell voltage Vs. By comparing the calculated SOCs of each cell 62, the SOC difference between the cells can be calculated, and by adjusting the calculated SOC difference using the balancer 65, the SOC of each cell 62 can be equalized.

[0115] Because the SOC is a relative value (the ratio of the full charge capacity X2 to the remaining capacity Y2), even if the SOC difference is zero, a difference in the remaining capacity Y2 may occur due to a difference in the full charge capacity X2. Therefore, when equalizing the SOC, the full charge capacity X2 at the time when a predetermined time has elapsed since the cell manufacture may be taken into consideration in addition to the SOC of each cell 62 at the time when a predetermined time has elapsed since the cell manufacture.

[0116] In other words, the variation in the SOC (state of charge) of the multiple cells 62 may be adjusted based on the full charge capacity X2 of each cell 62 at a predetermined time after the cell manufacture, in addition to the SOC difference between each cell 62.

[0117] For example, the discharge time of each cell 62 calculated from the SOC difference is corrected using the full charge capacity X2. The discharge time T for a cell 62 with a higher full charge capacity X2 is set longer than that for a cell 62 with a lower full charge capacity X2. Then, the balancer 65 discharges each cell 62 for the corrected discharge time. In this manner, the remaining capacity and SOC differences between cells can be accurately equalized while taking into account the differences in full charge capacity X2. Of course, other methods may be used to consider the full charge capacity, rather than simply correcting (adjusting) the discharge time. As described in the first embodiment, the full charge capacity X2 at a predetermined time after cell manufacture can be calculated based on the full charge capacity X1 at the time of cell manufacture and the decrease ΔX in the full charge capacity X1 over time since cell manufacture. In this way, the balancer can be controlled in a similar manner by replacing the discharge capacity DC with the SOC (state of charge). Furthermore, while the SOC is defined as the state of charge, this is merely a matter of definition; the state of charge can also be considered as a voltage or an amount of electricity. Therefore, the discharge capacity DC can be replaced with a variable such as voltage or quantity of electricity, and similar control can be performed.

[0118] REFERENCE SIGNS LIST 10 Vehicle 50 Power storage device 60 Assembled battery 62 Cell 65 Balancer 66 Cell discharge circuit 110 Voltage measurement unit 130 Management device (control unit)

Claims

1. A power storage device comprising: a plurality of cells connected in series; a balancer that adjusts variations in discharge capacity among the plurality of cells; and a control unit, wherein the control unit calculates the discharge capacity of each cell based on the fully charged capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, and adjusts variations in discharge capacity among the cells after the predetermined time has elapsed since the time of cell manufacture using the balancer.

2. A power storage device comprising: a plurality of cells connected in series; a voltage measurement unit that measures the voltage of each of the cells; a balancer that adjusts variations in the state of charge of the plurality of cells; and a control unit, wherein the control unit calculates the full charge capacity of each cell after a predetermined time has elapsed since the time of cell manufacture; calculates the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture based on the cell voltage measurement value by the voltage measurement unit; calculates the difference in the state of charge of each cell after the predetermined time has elapsed since the time of cell manufacture from the state of charge of each cell; and adjusts the variation in the state of charge of the plurality of cells using the balancer based on the difference between the full charge capacity of each cell and the state of charge of each cell.

3. A power storage device according to claim 1 or 2, wherein the control unit calculates the full charge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture, based on the full charge capacity of the cell at the time of cell manufacture and the amount of decrease in full charge capacity over time since the time of cell manufacture.

4. The energy storage device according to claim 3, wherein the control unit calculates the amount of decrease in full charge capacity over time since cell manufacture based on information on the time elapsed since cell manufacture and temperature history.

5. A method for controlling multiple cells that uses a balancer to adjust variations in discharge capacity among multiple cells connected in series, the method comprising: calculating the discharge capacity of each cell based on the fully charged capacity of each cell after a predetermined time has elapsed since the time of cell manufacture and the remaining capacity of each cell after said predetermined time has elapsed since the time of cell manufacture; and equalizing the discharge capacity of each cell by adjusting the variations in discharge capacity of each cell after said predetermined time has elapsed since the time of cell manufacture using the balancer.

6. A control method for an energy storage device having a plurality of cells connected in series, the control method comprising: calculating, for each cell, a full charge capacity after a predetermined time has elapsed since the time of cell manufacture; obtaining, for each cell, a remaining capacity after the predetermined time has elapsed since the time of cell manufacture from the cell voltage; calculating, from the full charge capacity and remaining capacity of each cell, a discharge capacity of each cell after the predetermined time has elapsed since the time of cell manufacture; and adjusting for variations in the discharge capacity of each cell.

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