Power storage device, method for controlling plurality of battery cells, and method for controlling

Abstract

A power storage device (50) is provided with a plurality of battery cells (62) connected in series, a balancer (65) that adjusts the variation in discharge capacity for the plurality of battery cells, and a control unit (130). The control unit (130) calculates the discharge capacity (DC) of each battery cell (62) on the basis of the full charge capacity (X2) of each battery cell (62) after a prescribed time elapses from the battery cell manufacturing time point and the remaining capacity (Y2) of each battery cell (62) after the prescribed time elapses from the battery cell manufacturing time point. The balancer (62) adjusts the deviation in the discharge capacity (DC) of each battery cell (62) after the elapse of the predetermined time from the battery cell manufacturing time.

Description

Technical Field

[0001] One aspect of the present invention relates to a storage battery (secondary battery), and more particularly to a power storage device formed by connecting a plurality of lithium ion batteries in series. One aspect of the present invention relates to a power storage device having a function of eliminating a deviation in discharge capacity (difference between the full charge capacity and the remaining capacity of the storage battery) between storage batteries and maintaining balance between the storage batteries. Background Art

[0002] Storage batteries are mounted on transportation means such as automobiles, railways, ships, and aircraft, and are used as power sources for in-cabin lighting, air conditioners, communication means, measuring instruments required for operation, and control equipment. In addition, they are used as power sources for power equipment. Since storage batteries can store electricity from power generation facilities and generators in advance and supply electricity when needed, they are also used as industrial power supply buffers.

[0003] For mobile or industrial use, a power storage device that combines a plurality of storage batteries (hereinafter also referred to as battery cells) is used.

[0004] It is known that the capacities (full charge capacity and / or remaining capacity) of the respective battery cells included in the power storage device deviate due to their internal resistances and other reasons.

[0005] When charging is performed in a state where there is a deviation in capacity, it is possible for a certain battery cell among the plurality of battery cells to be overcharged. As a countermeasure, the battery management device has a function and a circuit called a balancer. For example, the balancer discharges a battery cell with a high voltage to eliminate the deviation between the plurality of battery cells. Patent Document 1 discloses related techniques.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-353010 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] As described above, the conventional balancer discharges a battery cell with a high voltage to eliminate the deviation between the plurality of battery cells.

[0011] In conventional balancers, it has been difficult to eliminate capacity deviations. For example, in the case of a power storage device formed by combining multiple lithium-ion batteries (hereinafter also referred to as LFP battery cells) in which the positive electrode uses an active material of the iron phosphate system (LiFePO4) and the negative electrode uses an active material of the carbon system, even when the state of charge (SOC) of each battery cell changes, a region where the voltage value is almost constant (plateau region) extends over a wide range. In the plateau region, it is impossible to detect the capacity deviation between multiple battery cells based on the voltage values of the individual battery cells.

[0012] By charging a power storage device formed by combining multiple LFP battery cells to a region close to full charge (constant voltage charging region), it is possible to detect the capacity deviation between multiple battery cells. However, such charging requires time and cost. One aspect of the present invention provides a technique for suppressing the capacity deviation between multiple battery cells.

[0013] Means for Solving the Problem

[0014] The power storage device includes: a plurality of battery cells connected in series; a balancer that adjusts the deviation of the discharge capacity for the plurality of battery cells; and a control unit. The control unit calculates the full charge capacity of each battery cell after a predetermined time has elapsed since the battery cell manufacturing time point and the remaining capacity of each battery cell after the predetermined time has elapsed since the battery cell manufacturing time point, calculates the discharge capacity of each battery cell, and adjusts the deviation of the discharge capacity of each battery cell after the predetermined time has elapsed since the battery cell manufacturing time point through the balancer.

[0015] The power storage device includes: a plurality of battery cells connected in series; a voltage measurement unit that measures the voltage of each of the battery cells; a balancer that adjusts the deviation of the state of charge for the plurality of battery cells; and a control unit. The control unit calculates the full charge capacity of each battery cell after a predetermined time has elapsed since the battery cell manufacturing time point, calculates the state of charge of each battery cell after the predetermined time has elapsed since the battery cell manufacturing time point based on the measured value of the battery cell voltage by the voltage measurement unit, calculates the difference in the state of charge of each battery cell after the predetermined time has elapsed since the battery cell manufacturing time point, and adjusts the deviation of the state of charge of the plurality of battery cells through the balancer based on the full charge capacity of each battery cell and the difference in the state of charge of each battery cell.

[0016] In the control method of a plurality of battery cells connected in series, based on the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point and the remaining capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point, the discharge capacity of each battery cell is calculated, and the balancer is used to adjust the deviation of the discharge capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point.

[0017] In the control method of an energy storage device having a plurality of battery cells connected in series, for each battery cell, the full charge capacity after a specified elapsed time since the battery cell manufacturing time point is calculated. For each battery cell, the remaining capacity after the specified elapsed time since the battery cell manufacturing time point is obtained based on the battery cell voltage. Based on the full charge capacity and the remaining capacity of each battery cell, the discharge capacity of each battery cell after the specified elapsed time since the battery cell manufacturing time point is calculated, and the deviation of the discharge capacity between the battery cells is equalized.

[0018] Advantages of the Invention

[0019] According to the present technology, by eliminating the deviation in the discharge capacity and charge state between battery cells generated during the passage of time since the battery cell manufacturing time point, it is possible to suppress overcharging and over-discharging of the battery cells and to fully exhibit the performance of the battery cells. Description of the Drawings

[0020] Figure 1 is a side view of a vehicle.

[0021] Figure 2 is an exploded perspective view of the energy storage device.

[0022] Figure 3 is a cross-sectional view of a battery cell.

[0023] Figure 4 is a top view of a battery cell.

[0024] Figure 5 is a block diagram showing the electrical structure of the energy storage device.

[0025] Figure 6 is a circuit diagram of a balancer.

[0026] Figure 7 is a graph showing the correlation between the SOC and OCV of a battery cell.

[0027] Figure 8 is a diagram showing the manufacturing process of the energy storage device.

[0028] Figure 9 is a flowchart of the discharge capacity equalization process.

[0029] Figure 10 It is a diagram showing the relationship between the full charge capacity at the time of manufacturing a battery cell, the initial value of the full charge capacity of the battery cell when the energy storage device assembly is completed, and the initial value of the remaining capacity.

[0030] Figure 11 It is a diagram showing the change in discharge capacity.

[0031] Figure 12 It is a diagram showing the change in capacity after charging.

[0032] Figure 13 It is a diagram showing the CPU in functional blocks (a diagram showing the input / output of data processing). Detailed implementation mode

[0033] (1) The energy storage device according to an embodiment of the present invention includes: a plurality of battery cells connected in series; a balancer that adjusts the deviation of the discharge capacity for the plurality of battery cells; and a control unit. The control unit calculates the discharge capacity of each battery cell after a predetermined time has elapsed from the time point of manufacturing the battery cell, and adjusts the deviation of the discharge capacity of each battery cell after the predetermined time has elapsed from the time point of manufacturing the battery cell through the balancer, based on the full charge capacity of each battery cell after the predetermined time has elapsed from the time point of manufacturing the battery cell and the remaining capacity of each battery cell after the predetermined time has elapsed from the time point of manufacturing the battery cell.

[0034] According to the energy storage device according to an embodiment of the present invention, it is possible to eliminate the deviation of the discharge capacity between battery cells generated during the passage of time from the time point of manufacturing the battery cell. By eliminating the deviation of the discharge capacity between battery cells, it is possible to suppress overcharging and over-discharging of the battery cells. In addition, it is possible to minimize excessive safety control that does not cause overcharging and over-discharging, and thus the performance of the battery cells can be fully exhibited.

[0035] (2) The energy storage device includes: a plurality of battery cells connected in series; a voltage measurement unit that measures the voltage of each of the battery cells; a balancer that adjusts the deviation of the charge state for the plurality of battery cells; and a control unit. The control unit calculates the full charge capacity of each battery cell after a predetermined time has elapsed from the time point of manufacturing the battery cell, calculates the charge state of each battery cell after the predetermined time has elapsed from the time point of manufacturing the battery cell based on the measured value of the battery cell voltage by the voltage measurement unit, calculates the difference in the charge state of each battery cell after the predetermined time has elapsed from the time point of manufacturing the battery cell according to the charge state of each battery cell, and adjusts the deviation of the charge state of the plurality of battery cells through the balancer based on the full charge capacity of each battery cell and the difference in the charge state of each battery cell.

[0036] The electricity storage device described in (2) above can eliminate the charging state deviation between battery cells generated during the passage of time since the battery cell manufacturing time point. By eliminating the charging state deviation between battery cells, it is possible to suppress overcharging and over-discharging of the battery cells. In addition, it is possible to minimize excessive safety control that does not cause overcharging and over-discharging. Thus, the performance of the battery cells can be fully exerted.

[0037] (3) In the electricity storage device described in (1) or (2) above, it may also be that the control unit calculates the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point based on the full charge capacity of the battery cell at the battery cell manufacturing time point and the reduction amount of the full charge capacity accompanying the passage of time since the battery cell manufacturing time point.

[0038] According to the electricity storage device described in (3) above, it is possible to accurately obtain the full charge capacity and discharge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point. Therefore, the estimation accuracy of the discharge capacity difference between battery cells after the specified time has elapsed since the battery cell manufacturing time point is high, and it is possible to equalize the discharge capacity deviation of the battery cells with high accuracy.

[0039] (4) In the electricity storage device described in (3) above, it may also be that based on the information of the elapsed time and temperature history after the battery cell is manufactured, the reduction amount of the full charge capacity accompanying the passage of time after the battery cell is manufactured is calculated.

[0040] According to the electricity storage device described in (4) above, it is possible to accurately obtain the full charge capacity and discharge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point. Therefore, the estimation accuracy of the discharge capacity difference between battery cells after the specified time has elapsed since the battery cell manufacturing time point is high, and it is possible to equalize the discharge capacity deviation of the battery cells with high accuracy.

[0041] (5) In the control method of multiple battery cells according to an embodiment of the present invention, the discharge capacity of each battery cell is calculated based on the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point and the remaining capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point, and the deviation of the discharge capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point is adjusted by a balancer.

[0042] According to the control method of multiple battery cells described in (5) above, it is possible to eliminate the discharge capacity deviation between battery cells generated during the passage of time from the battery cell manufacturing time point. By eliminating the discharge capacity deviation between battery cells, it is possible to suppress the battery cells from reaching overcharge and overdischarge. In addition, it is possible to minimize the excessive safety control that does not cause overcharge and overdischarge, and thus the performance of the battery cells can be fully exerted.

[0043] (6) In the control method of the power storage device according to an embodiment of the present invention, for each battery cell, the full charge capacity after a specified elapsed time from the battery cell manufacturing time point is calculated. For each battery cell, the remaining capacity after the specified elapsed time from the battery cell manufacturing time point is obtained based on the battery cell voltage. Based on the full charge capacity and the remaining capacity of each battery cell, the discharge capacity of each battery cell after the specified elapsed time from the battery cell manufacturing time point is calculated, and the deviation of the discharge capacity between the calculated battery cells is equalized.

[0044] According to the control method of the power storage device described in (6) above, it is possible to eliminate the discharge capacity deviation between battery cells generated during the passage of time from the battery cell manufacturing time point. By eliminating the discharge capacity deviation between battery cells, it is possible to suppress the battery cells from reaching overcharge and overdischarge. In addition, it is possible to minimize the excessive safety control that does not cause overcharge and overdischarge, and thus the performance of the battery cells can be fully exerted.

[0045] <Embodiment>

[0046] 1. Description of the power storage device 50

[0047] As Figure 1 shown, an engine 20 and a power storage device 50 for starting the engine 20 and the like are mounted on the vehicle 10. In the vehicle 10, in addition to the engine 20 (internal combustion engine), or instead of the engine 20, an electric motor may be mounted on the vehicle, and a power storage device may be mounted as a power source for the electric motor.

[0048] As Figure 2 shown, 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 made of a synthetic resin material and a lid 74. The main body 73 is a bottomed cylindrical shape, and includes a bottom surface portion 75 and four side surface portions 76. An opening 77 is formed at the upper end of the main body 73 by the four side surface portions 76.

[0049] The housing 71 houses the battery pack 60 and the circuit board unit 105. The circuit board unit 105 is a board unit on which various components (such as the current cut-off device, current detection unit, balancer, management device, etc. described later) are mounted on the circuit board 100, and as shown in Figure 5 , it is arranged adjacent to, for example, the upper side of the battery pack 60. Alternatively, the circuit board unit 105 may be arranged adjacent to the side of the battery pack 60. Figure 5 The current cut-off device, current detection unit, balancer, management device, etc. Figure 2 As shown, it is arranged adjacent to, for example, the upper side of the battery pack 60. Alternatively, the circuit board unit 105 may be arranged adjacent to the side of the battery pack 60.

[0050] The cover 74 closes the opening 77 of the main body 73. An outer peripheral wall 78 is provided around the cover 74. The cover 74 has a protruding portion 79 that is substantially T-shaped in a plan view. In the front portion of the cover 74, the external terminal 51 of the positive electrode is fixed at one corner, and the external terminal 52 of the negative electrode is fixed at the other corner. Instead of the main body 73 of the housing 71, the circuit board unit 105 may be housed in the cover 74 (for example, inside the protruding portion 79).

[0051] The battery pack 60 is composed of a plurality of battery cells 62. As shown in Figure 3 , for the battery cell 62, an electrode body 83 and a non-aqueous electrolyte are housed in a rectangular parallelepiped-shaped housing 82. The battery cell 62 is, for example, a lithium-ion secondary battery cell. The housing 82 has a housing main body 84 and a cover 85 that closes the opening above it. Figure 3 As shown, for the battery cell 62, an electrode body 83 and a non-aqueous electrolyte are housed in a rectangular parallelepiped-shaped housing 82. The battery cell 62 is, for example, a lithium-ion secondary battery cell. The housing 82 has a housing main body 84 and a cover 85 that closes the opening above it.

[0052] The electrode body 83 is not shown in detail. A separator made of a porous resin film is arranged between a negative electrode plate obtained by coating an active material on a base material made of copper foil and a positive electrode plate obtained by coating an active material on a base material made of aluminum foil. They are all in strip shape and are wound into a flat shape in a state where the negative electrode plate and the positive electrode plate are respectively offset in the short side direction with respect to the separator. The electrode body 83 may also be of a stacked type instead of a wound type.

[0053] Respectively, the positive electrode terminal 87 is connected to the positive electrode plate via the positive electrode current collector 86, and the negative electrode terminal 89 is connected to the negative electrode plate via the negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 have a flat base portion 90 and legs extending from the base portion 90. Through holes are formed in the base portion 90.

[0054] The positive electrode terminal 87 and the negative electrode terminal 89 are composed of a terminal main body portion 92 and a shaft portion 93 that protrudes downward from the central portion of its lower surface. The terminal main body portion 92 and the shaft portion 93 of the positive electrode terminal 87 are integrally formed of aluminum (a single material). In the negative electrode terminal 89, the terminal main body portion 92 is made of aluminum and the shaft portion 93 is made of copper, and they are combined. The terminal main body portions 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are arranged at both ends of the cover 85 via a gasket 94 made of an insulating material, as shown inFigure 4 As shown, it protrudes outward from the gasket 94.

[0055] The lid 85 has a pressure release valve (safety valve) 95. The pressure release valve 95 is located, for example, between the positive terminal 87 and the negative terminal 89. The pressure release valve 95 releases when the internal pressure of the housing 82 exceeds the limit, thereby reducing the internal pressure of the housing 82.

[0056] Figure 5 It is a block diagram showing the electrical structure of the power storage device 50. The power storage device 50 includes a battery pack 60, a current detection unit 54, a current cut-off device 53, a balancer 65, a voltage measurement unit 110, a temperature sensor 58, and a management device 130.

[0057] The battery cells 62 of the battery pack 60 are, for example, 12 (refer to Figure 2 ), and are connected in 3 parallel and 4 series. Figure 5 In the figure, 3 battery cells 62 connected in parallel are represented by 1 battery label. The battery cell can be a cylindrical battery cell or a pouch-shaped battery cell having a laminated film housing.

[0058] The battery pack 60, the current cut-off device 53, and the current detection unit 54 are connected in series via the power line 55P and the power line 55N. The power lines 55P and 55N can use a bus bar BSB (refer to Figure 2 ) which is a plate-shaped conductor made of a metal material such as copper.

[0059] As Figure 5 shown, the power line 55P connects the external terminal 51 of the positive electrode and the positive electrode of the battery pack 60. The power line 55N connects the external terminal 52 of the negative electrode and the negative electrode of the battery pack 60. The external terminals 51 and 52 are connection terminals for an electrical load provided in the vehicle 10.

[0060] The current cut-off device 53 is provided on the power line 55P of the positive electrode. The current cut-off device 53 can be a semiconductor switch such as an FET or a relay having a mechanical contact. The current cut-off device 53 is preferably a self-holding type switch such as a latch relay. The current cut-off device 53 is of the normally closed type and is controlled to be in the closed state during normal times. In the case of an abnormality in the power storage device 50, the current I of the battery pack 60 can be cut off by switching the current cut-off device 53 from the closed state to the open state.

[0061] The current detection unit 54 is provided on the power line 55N of the negative electrode. The current detection unit 54 may also 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 discriminate between discharge and charge according to the polarity (positive or negative) of the voltage Vr. Alternatively, the current detection unit 54 may also be a magnetic sensor.

[0062] The voltage measurement unit 110 can measure the voltage Vs of each battery cell 62A to 62D and the total voltage Vab of the battery pack 60. The temperature sensor 58 is mounted on the battery pack 60 to detect the temperature of the battery pack 60.

[0063] The balancer 65 is used for equalizing the voltages Vs of the battery cells 62, and as Figure 6 shown, in this embodiment, it is composed of four battery cell discharge circuits 66A to 66D.

[0064] Each of the battery cell discharge circuits 66A to 66D is connected in parallel with each of the battery cells 62A to 62D. Each of the battery 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 battery cell 62 can be discharged.

[0065] The management device 130 is mounted on the circuit board 100 (refer to Figure 2 ), and as Figure 5 shown, it 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.

[0066] 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 battery cell voltage Vs of each battery cell 62, the temperature of the battery pack 60, the current I, and the total voltage Vab. The management device 130 corresponds to the "control unit".

[0067] An execution program for equalizing the discharge capacity DC of the battery cells 62A to 62D and data required for the execution of these programs are stored in the memory 132. The data stored in the memory 132 includes, for example, data on the SOC-OCV characteristics of the battery cells 62 described below, inspection data on the full charge capacity of each battery cell 62 at the time of battery cell manufacturing (described later), etc.

[0068] The program can also be distributed using an electrical communication line.

[0069] 2. SOC-OCV Characteristics of Battery Cell 62

[0070] As an example, Figure 7It is a graph showing the SOC-OCV characteristics of the LFP battery cell 62 that uses an active material of the iron phosphate system (LiFePO4) for the positive electrode and an active material of the carbon system for the negative electrode, with the horizontal axis representing SOC [%] and the vertical axis representing OCV [V]. The OCV (Open Circuit Voltage) can also be the battery cell voltage when there is no current without the influence of polarization, or the battery cell voltage Vs that can be regarded as when there is no current. The situation where it can be regarded as no current means that the current is below a specified value (for example, the case where dark current flows).

[0071] The SOC is the ratio of the remaining capacity [Ah] to the full charge capacity [Ah], and is represented by Equation (1).

[0072] SOC = (Y / X) × 100 ·········· (1)

[0073] Here, X is the full charge capacity of the battery cell, and Y is the remaining capacity of the battery cell (the amount of electricity stored in the battery cell).

[0074] In the SOC-OCV characteristics, the battery cell 62 has a plateau region F0, a first rapid change region F1, and a second rapid change region F2. The plateau region F0 is in the range where the SOC is from SOC2 (30%) to SOC1 (95%). The plateau region F0 is a region where the change in OCV with respect to the change in SOC is below a specified value and the graph is approximately flat.

[0075] The first rapid change region F1 is the region where the SOC is above SOC1, and the second rapid change region F2 is the region where the SOC is below SOC2. Compared with the plateau region F0, the slopes of the graphs in the first rapid change region F1 and the second rapid change region F2 are both larger, and the OCV changes sharply with respect to the change in SOC.

[0076] Since the battery cell 62 has the first rapid change region F1, near full charge at the end of charging ( Figure 7 at part A), the battery cell voltage Vs rises sharply. In addition, since the battery cell 62 has the second rapid change region F2, at the end of discharge ( Figure 7 at part B), the battery cell voltage Vs drops sharply.

[0077] The battery cell 62 having such characteristics is not limited to the LFP battery cell.

[0078] 3. Method for Equalizing Discharge Capacity in the Manufacturing Process

[0079] As Figure 8As shown, the manufacturing process of the power storage device 50 includes, for example, a manufacturing process S1 of battery cells, a storage process S2, and a power storage device assembly process S3. There are also cases where the storage process S2 is skipped and the process directly proceeds to the power storage device assembly process S3.

[0080] S1 is a process of manufacturing battery cells 62, and S2 is a process of moving the manufactured battery cells 62 to a specified warehouse or the like where temperature management is performed for storage. S3 is a process of assembling components (such as the electrolytic cell 20, the cover member 50, battery cells 62A to 62D, and the circuit board unit 105, etc.) to produce the power storage device 50.

[0081] The main reasons for the discharge capacity deviation between multiple battery cells in the power storage device are as follows.

[0082] (1) The full charge capacity deviation between battery cells during battery cell manufacturing (due to individual differences of battery cells)

[0083] (2) The deterioration deviation of the full charge capacity between battery cells during storage and transportation during power storage device manufacturing

[0084] (3) The self-discharge deviation of battery cells between battery cells after battery cell manufacturing (due to individual differences of battery cells)

[0085] Hereinafter, a method for eliminating the discharge capacity deviation between each battery cell generated in the power storage device manufacturing process (from battery cell manufacturing to power storage device assembly) will be disclosed.

[0086] Figure 9 is a flowchart of the discharge capacity equalization method. Regarding the discharge capacity equalization method, it is composed of eight steps S10 to S80 in order to equalize the discharge capacities DC of the serially connected battery cells 62A to 62D.

[0087] As Figure 8 shown, the equalization of the discharge capacity (S20 to S80) is a process implemented after the assembly of the power storage device 50 and before shipment.

[0088] During battery cell manufacturing, the full charge capacity X1 [Ah] of each battery cell 62A to 62D is measured (refer to Figure 10 ). In S10, after the power storage device is assembled, the measurement results of the full charge capacity X1 of each battery cell 62 during battery cell manufacturing are input into the memory 132 of the management device 130 built in the power storage device 50. Hereinafter, a detailed description will be given.

[0089] After S20 is the process after the completion time point of assembling the power storage device 50. In S20, the management device 130 estimates the initial full charge capacity X2 [Ah] of each battery cell 62A to 62D at the completion time point of assembling the power storage device 50 (refer to Figure 10 ). The initial full charge capacity X2 is the full charge capacity at the start time point (when data processing starts) of the management device 130 after the power storage device 50 is assembled. The same applies to the initial remaining capacity Y2 described later.

[0090] As shown in equation (2), the initial full charge capacity X2 can be estimated by subtracting the reduction amount ΔX due to the passage of time (referring to a specified time passage or an arbitrary time passage) after the battery cell is manufactured from the full charge capacity X1 at the time of battery cell manufacturing.

[0091] X2 = X1 - ΔX ···· (2)

[0092] Even if the battery cell is left unattended, it will naturally deteriorate (also known as storage deterioration or deterioration over time), so the full charge capacity has decreased by the reduction amount ΔX. This is an unexpected irreversible reaction and is one of the reasons for the decrease in the full charge capacity.

[0093] The step of calculating this reduction amount ΔX is an important step for equalizing the deviation of the discharge capacity.

[0094] In the present embodiment, in addition to considering the passage of time from the battery cell manufacturing time point, the temperature history of the battery cell (ambient temperature during storage and transportation) is also considered to determine the reduction amount ΔX of the full charge capacity X1. By considering the temperature history of the battery cell in addition to the elapsed time, the reduction amount ΔX of the full charge capacity X1 can be calculated with high accuracy. The storage deterioration amount, that is, the reduction amount ΔX, depends on time (for example, the square root or nth root of time) and is in a proportional relationship with a constant depending on temperature.

[0095] The reaction rate of the above-mentioned unexpected reaction also depends on temperature.

[0096] Therefore, temperature is also an important factor affecting the reduction amount ΔX. In addition, strictly speaking, specific deterioration phenomena occur in each battery cell, but if the materials (related substances) and structures are the same, ΔX is mostly approximately the same.

[0097] For each battery cell, regarding the deviation of the deterioration in (2) above, if the materials (related substances) and structures are the same, it can be considered that there is no deviation.

[0098] Hereafter, it is assumed that the temperature of each battery cell changes in the same way from the battery cell manufacturing time point to the completion time point of assembling the power storage device 50.

[0099] Furthermore, if the temperature history of each battery cell is the same as the time elapsed from the battery cell manufacturing time point to the time point when the battery energy storage device 50 is assembled (if stored under the same conditions), the amount of degradation due to storage, i.e., the reduction amount ΔX, can be regarded as the same.

[0100] In S30, the management device 130 determines the initial value Y2 [Ah] of the remaining capacity of each battery cell 62 at the time point when the battery energy storage device 50 is assembled (refer to Figure 10 ). In addition, the time elapsed from the battery cell manufacturing time point to the time point when the battery energy storage device 50 is assembled can be obtained by some time management such as time management of the process using a server or the like. A code (barcode, QR code) can also be pre-printed on the battery cell to store the time of the battery cell manufacturing time point. That is, at the time of assembling the battery energy storage device 50, the information of the code is read by a reader or the like, and based on the time from the time of the battery cell manufacturing time point stored in the code to the time point when the battery energy storage device 50 is assembled, the time elapsed from the battery cell manufacturing time point to the time point when the battery energy storage device 50 is assembled can be calculated. Thereby, the reduction amount ΔX, which is also the amount of degradation due to storage, can be obtained.

[0101] If the temperature change from the battery cell manufacturing time point to the time point when the battery energy storage device 50 is assembled is considered, the reduction amount ΔX can be obtained with higher accuracy. As described above, in the case of a temperature change, by multiplying a constant by a time-dependent quantity (the time in the state near that temperature) near a certain temperature, the amount of degradation due to storage in the interval at that temperature can be obtained, and by adding up the amounts of degradation due to storage in these intervals, the overall amount of degradation due to storage, i.e., the reduction amount ΔX, can be obtained.

[0102] Hereinafter, a specific example will be described, but it is just an example, and it can also be a method other than this method. First, after aging and lid installation are completed, the capacities of the battery cells 62A to 62D are measured. The voltage and current of the battery cell are measured, and the capacity of the battery cell is obtained based on the relationship between the current cumulative value and the SOC-OCV characteristics. Thereby, the full charge capacity X1 of each of the battery cells 62A to 62D can be obtained.

[0103] After the measurement, each of the battery cells 62A to 62D is discharged. At this time point, the voltage of each of the battery cells 62A to 62D can be measured, and the initial value Y1 of the remaining capacity can be obtained based on the relationship between the SOC-OCV characteristics. As described above, time information is obtained at this time point. This information can be saved in the manufacturing and process management server, or the information can be recorded in a barcode, QR code, etc. Regarding the subsequent control steps, they can be performed by the manufacturing and process management server or by the management device 130. In addition, it can also be a dedicated terminal (personal computer, tablet computer, etc.) used by an operator during manufacturing.

[0104] Next, transfer to the assembly process of the power storage device 50. An operator or a manufacturing machine assembles the battery pack 62 and installs other components such as the management device 130, and the power storage device 50 is assembled.

[0105] After that, as described above, obtain the time at the battery cell manufacturing time point from the barcodes, QR codes, etc. attached to the server and the battery cells, and compare it with the current time to calculate the time elapsed from the battery cell manufacturing time point to the time point when the power storage device 50 is assembled.

[0106] Based on this elapsed time, it is possible to calculate the amount of deterioration of each battery cell 62A to 62D from the battery cell manufacturing time point to the time point when the power storage device 50 is assembled, that is, the reduction amount ΔX of the standing deterioration amount. Next, use the voltmeter measurement unit 110 to measure the battery cell voltages Vs of each battery cell 62A to 62D. Based on the measured values of the battery cell voltages Vs, refer to Figure 7 the SOC-OCV characteristics shown, and calculate the SOC [%] of each battery cell 62A to 62D.

[0107] In this embodiment, for example, when the assembly of the power storage device 50 is completed, use Figure 7 the characteristics (SOC-OCV) of the second rapid change region F2 shown to calculate the SOC of each battery cell 62A to 62D. Therefore, the SOC of each battery cell 62A to 62D can be estimated with high accuracy.

[0108] Here, after calculating the battery cell capacity at the battery cell manufacturing time point and discharging, use the characteristics (SOC-OCV) of the second rapid change region F2 to calculate the SOC of each battery cell 62A to 62D. By setting the battery cell to a low SOC, it is possible to perform assembly safely or suppress the progress of battery deterioration.

[0109] Then, the management device 130 calculates the initial values Y2 [Ah] of the remaining capacities of each battery cell 62A to 62D at the time point when the assembly of the power storage device 50 is completed according to the calculated SOC. The initial value Y2 of the remaining capacity can be obtained by multiplying the SOC by the full charge capacity X2. In this embodiment, the initial value Y2 of the remaining capacity is calculated using the SOC-OCV characteristics, but the initial value Y2 of the remaining capacity can also be calculated using the remaining capacity Y-OCV characteristics.

[0110] Figure 10 The ΔY shown is the difference between the initial values Y1 and Y2 of the remaining capacities at the battery cell manufacturing time point and the time point when the power storage device is assembled. ΔY is caused by the self-discharge of the battery cells 62A to 62D.

[0111] In S40, the management device 130 determines the discharge capacity DC [Ah] of each battery cell 62A to 62D at the time point of assembling the power storage device by subtracting the remaining capacity initial value Y2 calculated in S30 from the full charge capacity initial value X2 calculated in S20 (refer to Figure 10 ).

[0112] DC = X2 - Y2 ····· (3)

[0113] In S50, the management device 130 compares the discharge capacities DC of each battery cell 62A to 62D calculated in S40 and determines the battery cell with the maximum discharge capacity DCmax.

[0114] After that, in S60, as shown in equation (4), the management device 130 subtracts the discharge capacity DC from the maximum discharge capacity DCmax to determine the balancer discharge capacity (the amount of electricity to be discharged through the balancer 65) S of each battery cell 62A to 62D.

[0115] S = DCmax - DC ··· (4)

[0116] In S70, the management device 130 determines the discharge time T of each battery cell 62A to 62D based on the balancer discharge capacity S calculated in S60.

[0117] In S80, the management device 130 operates the balancer 65 to discharge each battery cell 62A to 62D for the discharge time T calculated in S70. Through the above, it is possible to equalize the discharge capacities DC of each battery cell 62A to 62D. The processing of S20 to S80 is performed, for example, after the completion of assembling the power storage device 50.

[0118] Figure 11 is a graph showing the change in the discharge capacity DC of each battery cell 62A to 62D. (1) represents the time point of manufacturing the battery cell, (2) and (3) represent the time points for comparing the discharge capacity DC, and (4) represents the discharge capacity DC after equalization.

[0119] In Figure 11 's example, the battery cell 62D is the battery cell with the maximum discharge capacity DCmax. Among the battery cells 62A to 62C, by discharging the balancer discharge capacity S calculated in S60, it is possible to equalize the discharge capacities DC of each battery cell 62A to 62C to the maximum discharge capacity DCmax.

[0120] By equalizing the discharge capacities DC of each battery cell 62A to 62D, as Figure 12As shown, after leaving the factory, each battery cell 62A to 62D is equally charged, so it is possible to suppress the voltage Vs of a part of the battery cells 62A to 62D from rising during the final stage of charging and becoming overcharged. The same applies during discharge, which helps prevent over-discharge (in the case of discharge, it is not the discharge capacity DC but the SOC that is made consistent).

[0121] In addition, in the case where there is an abnormality (such as an internal short circuit, etc.) in a part of the battery cells 62A to 62D, after the power storage device is manufactured, as time passes, a difference occurs in the battery cell voltage Vs, and the battery cell voltage Vs of the abnormal battery cell becomes lower.

[0122] Therefore, it is also possible to detect abnormalities in the battery cells 62A to 62D before leaving the factory by leaving the battery cells 62A to 62D for a specified time and comparing the battery cell voltages Vs. In addition, it is possible to detect battery cells such as abnormally deteriorated battery cells with a full charge capacity smaller than that of normal battery cells.

[0123] Figure 13 Data processing related to deviation elimination of the discharge capacity DC is shown by the arithmetic blocks. In addition, in this example, the case where the management device 130 performs a series of processes is described. In Figure 13 the arithmetic blocks, the CPU 131 has a first arithmetic block 131A, a second arithmetic block 131B, a third arithmetic block 131C, a fourth arithmetic block 131D, and a fifth arithmetic block 131E.

[0124] The first arithmetic block 131A calculates the reduction amount ΔX of the full charge capacity X1 of each battery cell 62A to 62D based on information on the elapsed time and temperature history after the battery cell is manufactured. The second arithmetic block 131B calculates the initial value X2 of the full charge capacity of each battery cell 62A to 62D at the time when the power storage device assembly is completed based on the inspection data of the full charge capacity X1 at the time of manufacturing the battery cell and the reduction amount ΔX of the full charge capacity X1 calculated by the first arithmetic block 131A.

[0125] The third arithmetic block 131C calculates the initial value Y2 of the remaining capacity of each battery cell 62A to 62D based on the measured value of the battery cell voltage Vs at the time when the power storage device assembly is completed. The fourth arithmetic block 131D calculates the discharge capacity DC of each battery cell 62A to 62D based on the initial value X2 of the full charge capacity calculated by the second arithmetic block 131B and the initial value Y2 of the remaining capacity calculated by the third arithmetic block 131C.

[0126] Then, the fifth arithmetic block 131E compares the discharge capacity DC of each battery cell 62A to 62D calculated by the fourth arithmetic block 131D, determines the maximum discharge capacity DCmax, and calculates the balancer discharge capacity S of each battery cell 62A to 62C.

[0127] Figure 13 The functional blocks for calculating the maximum discharge capacity DC and the balancer discharge capacity S of each battery cell 62 represent data processing. The CPU 131 can perform these processes through a dedicated arithmetic circuit or through a program.

[0128] 4. Effects

[0129] According to the present disclosure, by eliminating the deviation of the discharge capacity DC between battery cells generated from the battery cell manufacturing time point, overcharging and over-discharging can be suppressed, and the performance of the battery cell 62 can be fully exerted.

[0130] In addition, after the manufacturing of the power storage device, even if the battery cells 62A to 62D are not charged to full charge, the discharge capacities DC of the battery cells 62A to 62D can be equalized. Therefore, constant voltage charging (CV charging) using a dedicated charging device is not required, and the operation time (takt time) does not become long. Therefore, there is an advantage in that early delivery of the power storage device 50 can be achieved.

[0131] According to the present disclosure, in addition to considering the elapsed time after the manufacturing of the battery cell, information on the temperature history is also considered. Therefore, the decrease amount ΔX of the full charge capacity X1 after the manufacturing of the battery cell can be estimated with high accuracy. In particular, in many cases, temperature management is performed in the manufacturing process of the power storage device 50 (from the manufacturing of the battery cell to the assembly of the power storage device), and a highly accurate temperature history can be obtained. Therefore, the estimation error of the decrease amount ΔX of the full charge capacity X1 is small, and the discharge capacity DC and the discharge capacity deviation of the battery cell 62 can be estimated with high accuracy.

[0132] According to the present disclosure, in S30, the low SOC rapid change region F2 ( Figure 7 part B) is used to estimate the SOC. Therefore, even if the battery cell 62 is not charged to the high SOC rapid change region F1, the SOC of each battery cell 62A to 62D can be estimated with high accuracy.

[0133] According to the present disclosure, the initial value X2 of the full charge capacity of the battery cell 62 can be estimated with high accuracy. Therefore, an improvement in the accuracy of predicting the life of the battery cell 62 can also be expected.

[0134] <Other Embodiments>

[0135] The present invention is not limited to the embodiments described above and illustrated in the drawings. For example, embodiments such as the following are also included in the technical scope of the present invention.

[0136] (1) The battery cell (a rechargeable battery cell capable of repeated charge and discharge) 62 is not limited to a lithium-ion secondary battery cell, and may also be other non-aqueous electrolyte secondary battery cells. A capacitor can also be used instead of the secondary battery cell 62. In addition, the SOC-OCV characteristics of the battery cell are not limited to Figure 7 the characteristics having a plateau region as shown, and may also be characteristics without a plateau region.

[0137] (2) In the above-described embodiment, the power storage device 50 is mounted on a vehicle (automobile) 10, but it may also be mounted on a moving body other than a vehicle such as a ship or an aircraft. In addition, not limited to a moving body, it can also be used for a power storage device for absorbing fluctuations in a distributed power generation system, a fixed installation use such as a UPS (uninterruptible power supply device), etc.

[0138] (3) In the above-described embodiment, the balancer 65 is configured as a discharge circuit 66 using a resistor, but as long as the battery cell 62 can be discharged individually, the balancer can be any circuit. Circuit elements other than a resistor can be used to discharge the battery cell 62.

[0139] (4) In the above-described embodiment, equalization of the discharge capacity DC (discharge based on the balancer discharge capacity S of the balancer) is performed during the period from the completion of the assembly of the power storage device 50 to the factory shipment. If the required data is stored in the memory 132, the full charge capacity X2 of each battery cell 62 after a specified time has elapsed from the battery cell manufacturing time point can be obtained. Therefore, it is also possible to calculate the discharge capacity DC of each battery cell 62 based on the full charge capacity X2 of each battery cell 62 after the specified time has elapsed from the battery cell manufacturing time point and the remaining capacity Y2 of each battery cell 62 after the specified time has elapsed from the battery cell manufacturing time point, and perform equalization of the discharge capacity DC between the battery cells at the time point when a specified time has elapsed since the battery cells were manufactured (after factory shipment, after being mounted on a vehicle). The required data is inspection data of the full charge capacity X1 at the time of battery cell manufacturing, the elapsed time after battery cell manufacturing, temperature history, and other information.

[0140] (5) In the above-described embodiment, the decrease amount ΔX of the full charge capacity X1 of the battery cell 62 is calculated based on the elapsed time after battery cell manufacturing and the temperature history. For example, when there is almost no temperature change after battery cell manufacturing, the decrease amount ΔX of the full charge capacity X1 of the battery cell 62 can be calculated only based on the elapsed time after battery cell manufacturing.

[0141] (6)In the above-described embodiment, each battery cell 62 is discharged with the battery cell 62 having the maximum discharge capacity as a reference, thereby equalizing the discharge capacity DC of each battery cell 62. As long as it is a method of discharging the battery cell 62 with a shallow discharge capacity DC, the discharge capacity DC of each battery cell 62 can also be equalized by a method other than the embodiment.

[0142] (7)In addition, in the above-described embodiment, a technique of using the discharge capacity DC to eliminate the discharge capacity deviation of the battery cell 62 is described, but the problem of the present invention can also be solved by using the SOC (state of charge). For example, the battery cell voltage Vs of each battery cell 62 after a predetermined time has elapsed since the battery cell manufacturing time point is measured by the voltage measurement unit 110, and the SOC of each battery cell 62 after a predetermined time has elapsed since the battery cell manufacturing time point can be calculated by referring to the SOC-OCV characteristics based on the measured value of the battery cell voltage Vs. By comparing the calculated SOCs of the respective battery cells 62, the SOC difference between the battery cells can be obtained, and the obtained SOC difference is adjusted by the balancer 65, whereby the SOCs of the respective battery cells 62 can be equalized.

[0143] Since 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, there may be a difference in the remaining capacity Y2 due to the difference in the full charge capacity X2. Therefore, when equalizing the SOC, in addition to considering the SOC of each battery cell 62 at the time point when a predetermined time has elapsed since the battery cell manufacturing time, the full charge capacity X2 at the time point when a predetermined time has elapsed since the battery cell manufacturing time can also be considered.

[0144] That is, it may also be that, in addition to based on the SOC difference of each battery cell 62, the deviation of the SOC (state of charge) of the plurality of battery cells 62 is adjusted based on the full charge capacity X2 of each battery cell 62 at the time point when a predetermined time has elapsed since the battery cell manufacturing time.

[0145] For example, the full charge capacity X2 is used to correct the discharge time of each battery cell 62 calculated based on the SOC difference. The battery cell 62 with a larger full charge capacity X2 has a longer discharge time T compared to the battery cell 62 with a smaller full charge capacity X2. Then, the balancer 65 corrects the discharge time of each battery cell 62 after the discharge correction. Thus, the difference in the full charge capacity X2 can be considered, and the remaining capacity difference and SOC difference between the battery cells can be equalized with high precision. Not limited to the correction (adjustment) of the discharge time, of course, the full charge capacity can also be considered by other methods. The full charge capacity X2 at the time point when the specified time has elapsed since the manufacture of the battery cell can be calculated based on the full charge capacity X1 at the time of battery cell manufacture and the decrease amount ΔX of the full charge capacity X1 accompanying the passage of time from the battery cell manufacture time point, as described in Embodiment 1. In this way, the discharge capacity DC can be replaced with the SOC (state of charge), and the balancer can be controlled in the same manner. Furthermore, although the SOC is defined as the state of charge, this is a matter of definition, and it is also possible to consider replacing the state of charge with voltage or charge amount. Therefore, the discharge capacity DC can be replaced with variables such as voltage and charge amount, and the control can be performed in the same manner.

[0146] Description of Reference Numerals

[0147] 10 Vehicle; 50 Power storage device; 60 Battery pack; 62 Battery cell; 65 Balancer; 66 Battery cell discharge circuit; 110 Voltage measurement unit; 130 Management device (control unit).

Claims

1. A power storage device, comprising: A plurality of battery cells connected in series; A balancer for adjusting the deviation of the discharge capacity for the plurality of battery cells; and A control unit, The control unit Calculates the discharge capacity of each battery cell based on the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point and the remaining capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point; and Adjusts the deviation of the discharge capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point through the balancer.

2. A power storage device, comprising: A plurality of battery cells connected in series; A voltage measurement unit for measuring the voltage of each of the battery cells; A balancer for adjusting the deviation of the charge state for the plurality of battery cells ； And A control unit, The control unit Calculates the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point; Calculates the charge state of each battery cell after the specified time has elapsed since the battery cell manufacturing time point based on the measured value of the battery cell voltage of the voltage measurement unit; Calculates the difference in the charge state of each battery cell after the specified time has elapsed since the battery cell manufacturing time point according to the charge state of each battery cell; And Based on the full charge capacity of each battery cell and the difference in the charge state of each battery cell, adjusts the deviation of the charge state of the plurality of battery cells through the balancer.

3. The power storage device according to claim 1 or claim 2, Wherein, The control unit calculates the full charge capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point based on the full charge capacity of the battery cell at the battery cell manufacturing time point and the decrease amount of the full charge capacity accompanying the passage of time since the battery cell manufacturing time point.

4. The power storage device according to claim 3, Wherein, The control unit calculates the decrease amount of the full charge capacity accompanying the passage of time after the battery cell manufacturing based on the information of the elapsed time and temperature history after the battery cell manufacturing.

5. A control method for a plurality of battery cells, which adjusts the deviation of the discharge capacity for a plurality of battery cells connected in series through a balancer. In this control method, Calculates the discharge capacity of each battery cell based on the full charge capacity of each battery cell after a specified time has elapsed since the battery cell manufacturing time point and the remaining capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point; and Adjusts the deviation of the discharge capacity of each battery cell after the specified time has elapsed since the battery cell manufacturing time point through the balancer, thereby equalizing the discharge capacity of each battery cell.

6. A control method for a power storage device, the power storage device having a plurality of battery cells connected in series. In this control method, Calculates the full charge capacity after a specified elapsed time since the battery cell manufacturing for each battery cell; Obtains the remaining capacity after the specified elapsed time since the battery cell manufacturing for each battery cell based on the battery cell voltage; And Based on the full charge capacity and the remaining capacity of each battery cell, calculate the discharge capacity of each battery cell after the specified elapsed time since the manufacture of the battery cell, and adjust the deviation of the discharge capacity of each battery cell.

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