Abnormality detection method for power storage device and assembled battery

Abstract

To detect abnormal cell deterioration.SOLUTION: A power storage device 50 includes a plurality of cells 62A to 62D connected in series, a balancer 65 that equalizes the cell voltages of the plurality of cells by discharging, and a controller 130, and the control device 130 accumulates, for each of the cells 62A to 62D, the balance discharge amount of the balancer 65 executed to eliminate the voltage difference between the cells that occurs during charging, and determines a cell 62 in which the cumulative discharge amount, which is the cumulative value of the balance discharge amount for a predetermined period, is greater than the other cells 62 by a predetermined value or more to be abnormal deterioration.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a technique for detecting abnormal deterioration of a cell. [Background technology]

[0002] In energy storage devices installed in automobiles, etc., abnormal cell degradation due to factors such as metal deposition during charging can cause a decline in battery performance, such as a decrease in input / output characteristics and charging capacity. Therefore, it is necessary to detect abnormally deteriorated cells.

[0003] Patent Document 1 focuses on the fact that shorted battery cells undergo continuous discharge due to an internal short circuit, preventing cell balancing, and determines that cells with small cell balancing discharge capacity are shorted battery cells. Specifically, the following conditions are determined for each battery cell, and if the conditions are met, the cell is determined to be a shorted battery cell (paragraphs 49 to 52).

[0004] CB_max-CB_n>REF CB_max is the maximum value of the cell balancing discharge capacity, CB_n is the cell balancing discharge capacity of each cell, and REF is the reference value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-155825 Summary of the Invention [Problem to be solved by the invention]

[0006] During charging, cell voltage may rise in the low state of charge (SOC) region due to cell degradation. An object of one embodiment of the present invention is to detect abnormal deterioration of a cell. [Means for solving the problem]

[0007] The power storage device includes a plurality of cells connected in series, a balancer that equalizes the cell voltages of the plurality of cells by discharging, and a control device. The control device accumulates the balance discharge amount of the balancer executed for each cell to eliminate the voltage difference between cells that occurs during charging, and determines that a cell whose cumulative discharge amount, which is the cumulative value of the balance discharge amount over a predetermined period of time, is greater than that of other cells by a predetermined value or more is abnormally deteriorated.

[0008] This technology can also be applied to a method for detecting an abnormality in a battery pack and a program for detecting an abnormality in a battery pack. [Effects of the Invention]

[0009] This technology can suppress the use of an electricity storage device whose battery performance has deteriorated due to abnormal cell deterioration. [Brief explanation of the drawings]

[0010] [Figure 1] Side view of the vehicle [Figure 2] Exploded perspective view of the battery [Figure 3] Cell plan view [Figure 4] Cross section of line AA in Figure 3 [Figure 5] Block diagram showing the electrical configuration of the battery [Figure 6] Balancer circuit diagram [Figure 7] Graph showing the correlation between cell capacity and OCV [Figure 8] Graph showing the correlation between cell capacity and OCV before and after degradation [Figure 9] Graph showing changes in cell voltage during charging in a battery containing deteriorated cells [Figure 10] Graph showing changes in cell voltage during charging in a battery containing deteriorated cells [Figure 11] Graph showing changes in cell voltage during charging [Figure 12] Graph showing the cumulative discharge amount of each cell [Figure 13]Detection flow for abnormally degraded cells DETAILED DESCRIPTION OF THE INVENTION

[0011] An overview of the power storage device will be described. The power storage device includes a plurality of cells connected in series, a balancer that equalizes the cell voltages of the plurality of cells by discharging, and a control device. The control device accumulates the balance discharge amount of the balancer executed for each cell to eliminate the voltage difference between cells that occurs during charging, and determines that a cell whose cumulative discharge amount, which is the cumulative value of the balance discharge amount over a predetermined period of time, is greater than that of other cells by a predetermined value or more is abnormally deteriorated.

[0012] When a cell voltage rises at a low capacity due to degradation during charging, if a degraded cell is included in the multiple cells, the balancer operates more frequently for the degraded cell than for the other cells. Therefore, by comparing the cumulative discharge amount over a specified period (the cumulative value of the balanced discharge amount by the balancer) with that of the other cells, cells that are greater than a specified value can be determined to be abnormally degraded. Abnormal cell degradation can be detected without requiring additional hardware.

[0013] In this configuration, abnormal cell deterioration can be notified to the outside, and the use of a power storage device with deteriorated battery performance can be suppressed.

[0014] The control device may calculate the difference between the average cumulative discharge amount and the maximum cumulative discharge amount for a cell that exhibits the maximum cumulative discharge amount over a predetermined period, and if the difference in cumulative discharge amount is greater than a threshold, determine that the cell exhibiting the maximum cumulative discharge amount is abnormally degraded. If the difference in cumulative discharge amount is greater than the threshold, the cell exhibiting the maximum cumulative discharge amount is outside the average range of cumulative discharge amounts, and is therefore likely to be abnormally degraded. This configuration allows for accurate detection of abnormally degraded cells.

[0015] The power storage device may be for on-board use (for example, for automobiles or industrial vehicles such as railway vehicles). On-board power storage devices are frequently charged while the vehicle is traveling. Therefore, if a degraded cell is included in the multiple cells, the balancer in the degraded cell operates more frequently, which is likely to result in differences in the cumulative discharge amount. This makes it possible to accurately detect abnormally degraded cells. Furthermore, because the charging frequency is high, it is possible to set a short predetermined period for judgment, which is expected to enable early detection of abnormally degraded cells.

[0016] <Embodiment> 1. Battery 50 Description As shown in Fig. 1, vehicle 10 is equipped with engine 20 and battery 50 used for starting engine 20, etc. Battery 50 is an example of an "electricity storage device." Vehicle 10 may be equipped with an electricity storage device for driving the vehicle or a fuel cell instead of engine 20 (internal combustion engine).

[0017] As shown in Fig. 2, the battery 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.

[0018] 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 the current interruption device 53, the current detection unit 54 shown in FIG. 5, and the management device 130) 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.

[0019] The lid 74 closes the opening 77 of the main body 73. An outer peripheral wall 78 is provided around the periphery of the lid 74. The lid 74 has a protruding portion 79 that is generally T-shaped in plan view. A positive external terminal 51 is fixed to one corner of the front of the lid 74, and a negative external terminal 52 is fixed to the other corner. The circuit board unit 105 may be housed inside the lid 74 (for example, inside the protruding portion 79) instead of inside the main body 73 of the housing 71.

[0020] The battery pack 60 is composed of a plurality of cells 62. As shown in Fig. 4, each cell 62 has an electrode assembly 83 housed in a rectangular (prismatic) case 82 together with a non-aqueous electrolyte. The cell 62 is, for example, a lithium ion secondary battery cell. The case 82 has a case body 84 and a lid 85 that closes the upper opening.

[0021] 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 offset from each other on opposite sides in the width direction relative to the separator, and are wound in a flat shape so that they can be housed in the case body 84. The electrode assembly 83 may be a laminated type instead of a wound type.

[0022] 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 91 extending from the base portion 90. A through hole is formed in the base portion 90. The legs 91 are connected to the positive electrode plate or the negative electrode plate.

[0023] 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 lower surface 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. 3 .

[0024] The lid 85 has a pressure relief valve 95. The pressure relief valve 95 is located between the positive terminal 87 and the negative terminal 89. The pressure relief valve 95 is a safety valve. 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.

[0025] 5 is a block diagram showing the electrical configuration of the battery 50. The battery 50 includes a battery pack 60, a current detection unit 54, a current interruption device 53, a balancer 65, a voltage detection unit 110, a temperature sensor 58, and a management device 130.

[0026] The battery 50 is electrically connected to a vehicle ECU (Electronic Control Unit) 140, an alternator 150 which is a generator that generates electricity using the power of the engine 20, and an electrical load 160 mounted on the vehicle. The vehicle ECU 140 is a vehicle control unit that controls the vehicle 10. The vehicle ECU 140 controls the alternator 150 and the electrical load 160. The vehicle ECU 140 may also control a drive system such as an engine. The number of vehicle ECUs 140 is not limited to one, and multiple vehicle ECUs 140 may be used.

[0027] When the engine 20 is running, if the amount of power generated by the alternator 150 is greater than the amount of power consumed by the electrical load 160, the battery 50 is charged by the alternator 150. If the amount of power generated by the alternator 150 is less than the amount of power consumed by the electrical load 160, the battery 50 discharges to make up for the shortfall.

[0028] While the engine 20 is stopped, the alternator 150 stops generating power. While power generation is stopped, the battery 50 is not charged, and only discharges power to the vehicle ECU 140 and the electrical load 160.

[0029] The battery pack 60 has, for example, 12 cells 62 (see FIG. 2), three connected in parallel and four in series. In FIG. 5, three cells 62 connected in parallel are represented by one battery symbol. The cells are not limited to prismatic cells, and may be cylindrical cells or pouch cells with a laminated film case.

[0030] 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.

[0031] 5, a power line 55P connects the positive external terminal 51 to the positive electrode of the battery pack 60. A power line 55N connects the negative external terminal 52 to the negative electrode of the battery pack 60. The external terminals 51 and 52 are terminals for connecting the battery 50 to the vehicle 10 (electrical load 160). The battery 50 can be electrically connected to the alternator 150 and the electrical load 160 via the external terminals 51 and 52.

[0032] 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 any abnormality occurs in the battery 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.

[0033] 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.

[0034] The voltage detection unit 110 can detect 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 or its surroundings.

[0035] The balancer 65 is used to equalize the cell voltages Vs, and as shown in FIG. 6, is made up of four cell discharge circuits 66A to 66D.

[0036] Each cell discharge circuit 66A-66D is connected in parallel to each cell 62A-62D. Each cell discharge circuit 66A-66D is composed of a discharge resistor 67 and a switch 68. By turning on the switch 68 and discharging the cell 62 with the highest cell voltage Vs, the cell voltages Vs can be equalized (hereinafter referred to as a balancing operation). The balancing operation may be to equalize the cell capacities [Ah], i.e., the amount of electricity charged.

[0037] 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 management device 130 is an example of a "control device."

[0038] The communication unit 133 is connected to the vehicle ECU 140 via a signal line and communicates with the vehicle ECU 140. The management device 130 can receive signals related to the operating state of the vehicle 10 (driving, stopped, parked, etc.) from the vehicle ECU 140 via communication.

[0039] The management device 130 monitors the state of the battery 50 based on the outputs of the voltage detection 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.

[0040] The memory 132 stores an execution program for equalization processing to equalize the cell voltages Vs, an execution program for the flow of detecting abnormally deteriorated cells shown in FIG. 13, and data required for executing these programs.

[0041] The program may be stored on a recording medium such as a CD-ROM and used, transferred, loaned, etc. The program may be distributed via an electric communication line.

[0042] 2. Capacity-OCV characteristics of cell 62 7 is a graph showing the capacity-OCV characteristics of cell 62, with the horizontal axis representing capacity [Ah] and the vertical axis representing OCV [V]. The OCV (Open Circuit Voltage) may be the cell voltage Vs when there is no current or when it can be considered as no current, and there is no influence of polarization. A case where it can be considered as no current is when the current is below a predetermined value.

[0043] In the capacity-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 capacity is in the range of Y2 (30%) to Y1 (95%). In the plateau region F0, the change in OCV relative to the change in capacity is equal to or less than a predetermined value, and the graph is substantially flat.

[0044] The first rapid change region F1 is the region where the capacity is Y1 or more, and the second rapid change region F2 is the region where the capacity is Y2 or less. 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 in response to a change in capacity.

[0045] 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).

[0046] An example of a cell 62 having such characteristics is an LFP / Gr-based (so-called iron-based) lithium ion secondary battery in which the positive electrode active material contains LiFePO4 (lithium iron phosphate) and the negative electrode active material contains Gr (graphite).

[0047] FIG. 8 is a graph showing the capacity-OCV characteristics of the cell 62 before and after degradation, where "L1" shows the characteristics of the normal cell (cell before degradation) 62 and "L2" shows the characteristics of the deteriorated cell 62.

[0048] When the degraded cell 62 is near full charge at the end of charging, the OCV rises rapidly at a lower capacity than the normal cell 62. Therefore, if the battery pack 60 includes a degraded cell 62, the cell voltage Vs of the degraded cell 62 rises before the other cells 62 do, causing a voltage difference between the degraded cell 62 and the other cells 62 while the battery pack 60 is being charged.

[0049] The management device 130 constantly monitors the cell voltage Vs of each cell 62 based on the detection results of the voltage detection unit 110, and when a difference in cell voltage Vs occurs among the cells 62, the cell 62 with the higher voltage is discharged using the balancer 65 to reduce the voltage difference ΔVs.

[0050] In this embodiment, the cell 62 with the lowest cell voltage Vs among the four cells 62 is used as the reference cell, and the voltage difference ΔVs between the other cells 62 is calculated.

[0051] If the voltage difference ΔVs exceeds the threshold, the management device 130 operates the cell discharge circuit 66 to discharge the cell 62. By discharging the cell 62, the voltage difference with the reference cell 62 can be reduced to below the threshold.

[0052] The discharge time of the cell 62 may be a fixed time that does not depend on the voltage difference ΔVs, or may be a time that depends on the voltage difference ΔVs.

[0053] 9 and 10 are graphs showing the change in cell voltage Vs during charging in a battery 50 including a degraded cell 62, with Fig. 9 showing the change in cell voltage from t0 to t1. t0 is the time when charging begins. C0 is the capacity [Ah] of cell 62 at the start of charging (time t0), C1 is the fully charged capacity [Ah] of the degraded cell, and C2 is the fully charged capacity [Ah] of a normal cell.

[0054] t1 is the time when the deteriorated cell 62 reaches the full charge capacity C1, and a voltage difference (V1-V0) occurs between it and the normal cell 62 that has not yet reached the full charge capacity C2.

[0055] Figure 10 shows the change in cell voltage Vs from t1 to t2. Between t1 and t2, charging continues and balancer 65 discharges degraded cell 62. As degraded cell 62 discharges, the capacity difference (C2 - C1) is balanced, and at time t2 when normal cell 62 reaches full charge capacity C2, the cell voltages Vs of normal cell 62 and degraded cell 62 become equal to V1 (see Figure 11).

[0056] Compared to other cells 62, the cell voltage Vs of a deteriorated cell 62 tends to rise more easily during charging at a lower capacity, and the cell discharge circuit 66 tends to operate more frequently within a predetermined period of time.

[0057] Therefore, a cell 62 whose cumulative discharge amount Q for a predetermined period (for example, one month) is greater than that of other cells 62 by a predetermined value or more can be determined to be abnormally deteriorated.

[0058] The cumulative discharge amount Q [Ah] is the cumulative value of the balanced discharge amount [Ah] by the cell discharge circuit 66. The balanced discharge amount can be calculated by multiplying the discharge current by the discharge time. The discharge current can be calculated from the cell voltage Vs and the discharge resistance 67.

[0059] Fig. 12 is a graph comparing the cumulative discharge amount Q of cells 62. In the example of Fig. 12, cell 62A has a cumulative discharge amount Q that is greater than or equal to a predetermined value compared to the other cells 62B to 62D, and is therefore likely to be abnormally deteriorated.

[0060] 3. Detection of abnormally degraded cells The process of detecting abnormally degraded cells will be described in detail below with reference to FIG.

[0061] The flow for detecting abnormally degraded cells consists of steps S100 to S170, and is executed periodically, with one cycle being a predetermined period. The predetermined period is a period during which at least several full charges are expected to be performed, and in this embodiment, it is one month. The predetermined period is not limited to one month, and may be about one week for vehicles that are driven frequently, such as taxis.

[0062] When the flow for detecting abnormally deteriorated cells starts, the management device 130 accumulates the balance discharge amount [Ah] of the balancer 65 executed to eliminate the voltage difference between cells that occurs during charging for each cell 62, and saves the data in memory 132 (S100).

[0063] In parallel with accumulating the balanced discharge amount, the management device 130 estimates the maximum capacity difference Σq [Ah] that occurs between normal cells in a predetermined period (S110). The maximum capacity difference Σq is an example of a "threshold value."

[0064] The maximum capacitance difference Σq can be calculated from the total value of (a) to (c). Σq=q1+q2+q3

[0065] (a) Initial capacity difference q1 between cells (b) The difference in capacity between cells per given period due to degradation variation, q2 (c) The difference in capacity between cells per given period due to variations in self-discharge amount, q3

[0066] For example, q1 = 500mAh, q2 = 700mAh, and q3 = 300mAh, and in this case, Σq = 1500mAh. Experimental or empirical values ​​can be used for q1, q2, and q3.

[0067] When a predetermined period has elapsed since the start of the flow, the management device 130 calculates the cumulative discharge amount Q [Ah] from the balanced discharge amount of each cell 62 during the predetermined period, and then compares the cumulative discharge amounts Q of the cells 62 to identify the cell 62 with the maximum cumulative discharge amount Qmax [Ah] (S120).

[0068] 12, the cumulative discharge amount Q of each cell 62 is 1600 mAh for cell 62A, 5 mAh for cell 62B, 15 mAh for cell 62C, and 13 mAh for cell 62D. Therefore, the management device 130 identifies cell 62A as the cell with the maximum cumulative discharge amount Qmax.

[0069] The management device 130 excludes the cell 62 with the maximum cumulative discharge amount Qmax characterized in S120, and calculates the average cumulative discharge amount Qav [Ah] for the other cells 62 (S130).

[0070] In this example, the cell 62A is excluded and the average cumulative discharge amount Qav is calculated for the cells 62B to 62D. The average cumulative discharge amount Qav is (5mAh+15mAh+13mAh) / 3, or "11mAh."

[0071] The management device 130 subtracts the average cumulative discharge amount Qav calculated in S130 from the maximum cumulative discharge amount Qmax calculated in S120 to calculate the difference ΔQ [Ah] (S140). ΔQ=Qmax-Qav

[0072] In the above example, Qmax=1600mAh, Qav=11mAh, and therefore ΔQ=1589mAh.

[0073] Next, the management device 130 compares the difference ΔQ calculated in S140 with the maximum capacity difference Σq calculated in S110, and determines whether the difference ΔQ is greater than the maximum capacity difference Σq (S150).

[0074] If ΔQ>Σq, the management device 130 determines that the cell 62 identified in S120 is abnormally degraded (S160). On the other hand, if ΔQ≦Σq, the management device 130 determines that the cell 62 identified in S120 is normal (S170).

[0075] In the above example, ΔQ=1589 mAh, Σq=1500 mAh, and since ΔQ>Σq, the management device 130 determines that the cell 62A is abnormally deteriorated.

[0076] When the management device 130 detects an abnormally deteriorated cell 62, it notifies the vehicle ECU 140 of the abnormality in the battery 50.

[0077] As a result, the vehicle ECU 140 issues a warning requesting battery replacement, thereby encouraging early replacement of the battery 50 whose battery performance has deteriorated due to abnormal deterioration of the cells 62.

[0078] 4.Effectiveness In this configuration, it is possible to suppress the use of the battery 50 whose battery performance has deteriorated due to abnormal deterioration of the cells 62.

[0079] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0080] (1) The cell (repeatedly chargeable and dischargeable storage cell) 62 is not limited to a lithium-ion secondary battery cell, and may be another non-aqueous electrolyte secondary battery cell. A capacitor may also be used instead of the secondary battery cell 62. The type of cell is not important as long as it has a characteristic that the voltage during charging tends to rise due to degradation at a lower capacity than before degradation. Furthermore, the point at which a voltage difference occurs between a deteriorated cell and a normal cell may be other than near full charge.

[0081] (2) In the above embodiment, the battery 50 is mounted on the vehicle 10, but it may also be mounted on a moving body other than a vehicle, such as a ship or an aircraft. Furthermore, the method for detecting an abnormality in the battery 50 or a battery pack may be used not only in moving bodies but also in stationary applications such as a power storage device for absorbing fluctuations in a distributed power generation system or an uninterruptible power supply (UPS).

[0082] (3) In the above embodiment, the balancer 65 is a resistive discharge type cell discharge circuit 66. However, any circuit may be used as long as it can individually discharge the cells 62. The cells 62 may be discharged using circuit elements other than resistors.

[0083] (4) In the above embodiment, the maximum capacity difference between cells is estimated using the initial capacity difference, the variation in deterioration, the variation in self-discharge amount, etc. (S110). The maximum capacity difference between cells may be the maximum capacity difference allowable in the energy storage device. The maximum allowable capacity difference is "the capacity difference between cells at which the input / output characteristics or charge capacity of the battery deteriorates and the battery is no longer able to perform satisfactorily," and is determined by factors such as the ambient temperature and the number of cycles used.

[0084] (5) In the above embodiment, abnormal degradation of cell 62 was detected based on the difference ΔQ between the maximum cumulative discharge amount Qmax and the average cumulative discharge amount Qav. Abnormal degradation may be detected using other methods. For example, the cells with the largest cumulative discharge amounts may be compared with the cells with the second largest cumulative discharge amounts, and if the cumulative discharge amount of the first cell is greater than that of the second cell by a predetermined value or more, the first cell may be determined to be abnormally degraded.

[0085] (6) In the above embodiment, when an abnormally deteriorated cell is detected, the management device 130 notifies the vehicle ECU 140 of the abnormality and prompts the replacement of the battery 50. In addition, the detection result of the abnormally deteriorated cell may be reflected in the charging control or output control of the battery 50. In other words, when the control device 130 detects an abnormally deteriorated cell, it may perform control to lower the charging voltage of the battery 50 or control to limit the output current (discharge current). [Explanation of symbols]

[0086] 10 vehicles 50 Battery (energy storage device) 60 battery packs 62 cells 65 Balancer 66 Cell discharge circuit 130 Management device (control device)

Claims

1. An electricity storage device, A plurality of cells connected in series; a balancer that equalizes the cell voltages of the plurality of cells by discharging; a control device; The control device accumulating, for each cell, the amount of balance discharge of the balancer executed to eliminate the voltage difference between the cells that occurs during charging; The power storage device determines that a cell whose cumulative discharge amount, which is the cumulative value of the balanced discharge amount over a predetermined period, is greater than that of other cells by at least a predetermined value is abnormally deteriorated.

2. The power storage device according to claim 1, The control device calculates the difference between the average cumulative discharge amount and the maximum cumulative discharge amount for a cell that exhibits the maximum cumulative discharge amount over a predetermined period, and if the difference in cumulative discharge amount is greater than a threshold value, determines that the cell that exhibits the maximum cumulative discharge amount is abnormally deteriorated.

3. The power storage device according to claim 1 or 2, The cell has a characteristic that the cell voltage during charging rises due to degradation at a capacity lower than that before degradation.

4. The on-vehicle power storage device according to any one of claims 1 to 3.

5. A method for detecting an abnormality in a battery pack, comprising: The battery pack includes a plurality of cells connected in series, The amount of balance discharge performed by the balancer to eliminate the voltage difference between the cells that occurs during charging is stored for each cell, A method for detecting abnormalities in a battery pack, in which a cell whose cumulative discharge amount, which is the cumulative value of the balanced discharge amount over a predetermined period, is greater than that of other cells by a predetermined value or more, is determined to be abnormally deteriorated.

Images