Battery pack management device, energy storage system, battery pack management method, and battery pack management program

Abstract

To provide a management device capable of appropriately correcting a deviation of SOC among a plurality of aqueous battery cells electrically connected in series in a battery pack, while realizing simplification of a system configuration.SOLUTION: A management device for managing a battery pack in which a plurality of aqueous battery cells are electrically connected in series is provided according to the embodiment. A control part in the management device charges the battery pack in constant current until a voltage of the battery pack becomes a reference voltage value, by at least corresponding to the fact that a SOC difference value between a maximum SOC cell whose SOC is highest and a minimum SOC cell whose SOC is lowest becomes a reference difference value or more, according to the plurality of aqueous battery cells constituting the battery pack. The control part charges the battery pack in constant voltage at the reference voltage value, by corresponding to the fact that the voltage of the battery pack reaches the reference voltage value via charging at the constant current.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] Embodiments of the present invention relate to a battery pack management device, a power storage system, a battery pack management method, and a battery pack management program.

Background Art

[0002] As a battery pack mounted on battery-powered devices such as smartphones, vehicles, stationary power supply devices, robots, and drones, a battery pack in which a plurality of aqueous battery cells are electrically connected in series may be used. In a battery pack in which a plurality of aqueous battery cells are electrically connected in series, each of the plurality of aqueous battery cells includes a positive electrode, a negative electrode, and an aqueous electrolyte. As the aqueous electrolyte, for example, an aqueous electrolyte solution obtained by dissolving an electrolyte salt in an aqueous solvent is used.

[0003] Further, when charging and discharging of the battery pack are repeated, an SOC deviation occurs between the plurality of aqueous battery cells constituting the battery pack. When the SOC deviation between the plurality of aqueous battery cells becomes large, the SOC deviation affects the deterioration of the battery pack itself. In fact, when the SOC deviation becomes large, the battery pack tends to deteriorate easily. Therefore, in the battery pack, it is required to correct the SOC deviation between the plurality of aqueous battery cells that are electrically connected in series.

[0004] In a battery pack, it is possible to correct SOC (State of Charge) differences among multiple aqueous battery cells by charging only some of the aqueous battery cells with relatively low SOCs, or discharging only some of the aqueous battery cells with relatively high SOCs. However, in energy storage systems equipped with battery packs, there is a need to simplify the system configuration from the standpoint of suppressing system size increases. Therefore, there is a need to be able to correct SOC differences among multiple aqueous battery cells without providing drive circuits that charge or discharge only some of the aqueous battery cells constituting the battery pack. In other words, there is a need to be able to correct SOC differences among multiple aqueous battery cells in a battery pack while achieving a simplified system configuration. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-124041 [Patent Document 2] Japanese Patent Publication No. 2014-39435 [Overview of the project] [Problems that the invention aims to solve]

[0006] The problem that this invention aims to solve is to provide a battery pack management device, an energy storage system, a battery pack management method, and a battery pack management program that enable the correction of SOC differences between multiple aqueous battery cells electrically connected in series in a battery pack, while simplifying the system configuration. [Means for solving the problem]

[0007] In one embodiment, a management device is provided for managing a battery pack in which a plurality of aqueous battery cells are electrically connected in series, and each of the plurality of aqueous battery cells comprises an aqueous electrolyte, a positive electrode, and a negative electrode. The management device includes a control unit. The control unit, in the operation of the battery pack, charges the battery pack at a constant voltage value.The control unit, in at least in response to the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell in the multiple aqueous battery cells constituting the battery pack becomes greater than or equal to a reference difference value, the voltage of the battery pack Higher than the pack charging voltage value The battery pack is charged with a constant current until it reaches the reference voltage value. The control unit, in response to the battery pack's voltage reaching the reference voltage value through constant current charging, charges the battery pack at a constant voltage at the reference voltage value. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an example of an energy storage system according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of an aqueous battery cell forming a battery pack according to the first embodiment. [Figure 3] Figure 3 is a schematic flowchart illustrating an example of the process performed by the control unit in the first embodiment to adjust the State of Operation (SOC) of multiple aqueous battery cells in the battery pack. [Figure 4] Figure 4 is a flowchart illustrating an example of the process performed by the control unit to adjust the State of Operation (SOC) of multiple aqueous battery cells in the battery pack in the first modified example. [Figure 5] Figure 5 is a schematic diagram showing an example of a system equipped with a stationary power supply device related to an application example. [Figure 6] Figure 6 is a schematic diagram showing the voltage changes of two aqueous battery cells during the correction process for SOC deviation in a series-connected cell structure in a verification related to the embodiment. [Figure 7] Figure 7 is a schematic diagram showing the discharge curves of two aqueous battery cells, measured during discharge from the series-connected cell structure after SOC deviation correction processing in a verification related to the embodiment. [Modes for carrying out the invention]

[0009] The embodiments and other details will be described below with reference to the drawings. Unless otherwise specified, the measurements of physical quantities such as voltage and SOC were performed in an environment of 25°C.

[0010] (First embodiment) First, as an example of an embodiment, a first embodiment will be described. Figure 1 shows an example of a power storage system 1 according to the first embodiment. As shown in Figure 1, the power storage system 1 includes a battery pack 2 and a management device 4. In the example in Figure 1, only one battery pack 2 is provided in the power storage system 1. The battery pack 2 includes a plurality of aqueous battery cells 3, and in the battery pack 2, the plurality of aqueous battery cells 3 are electrically connected in series. That is, in the battery pack 2, a cell series connection structure is formed in which the plurality of aqueous battery cells 3 are electrically connected in series.

[0011] In the battery pack 2, multiple aqueous battery cells 3 are arranged, for example, inside a housing (not shown). In the example shown in Figure 1, the battery pack 2 is mounted on a battery-powered device 5. Examples of battery-powered devices 5 on which the battery pack 2 is mounted include smartphones, vehicles, stationary power supply units, robots, and drones. Examples of vehicles that can be battery-powered devices 5 include electric vehicles, plug-in hybrid vehicles, and electric motorcycles. Examples of robots on which the battery pack 2 is mounted include transport robots such as automated guided vehicles (AGVs) used in factories.

[0012] Each of the aqueous battery cells 3 is a single cell (single battery), and is, for example, a battery cell that constitutes a lithium-ion secondary battery that uses an aqueous electrolyte as its electrolyte. Each of the aqueous battery cells 3 is equipped with an electrode group, and the electrode group is equipped with a positive electrode and a negative electrode. In the electrode group, a separator is interposed between the positive electrode and the negative electrode.

[0013] The separator is formed from an electrically insulating material and electrically insulates the positive electrode from the negative electrode. The separator is formed to a thickness of, for example, 1 μm or more and 30 μm or less. The separator is not limited to these, but porous films and nonwoven fabrics made of synthetic resins can be used. Examples of synthetic resins used to form the porous films and nonwoven fabrics that serve as separators include polyethylene (PE), polypropylene (PP), cellulose, and polyvinylidene fluoride (PVdF). In addition, a layer of nonconductive particles may be formed on at least one side of the porous film or nonwoven fabric of the separator. Examples of nonconductive particles are not limited to these, but include alumina, silica, zirconium, and solid electrolyte particles.

[0014] The positive electrode comprises a positive electrode current collector, such as a positive electrode current collector foil, and a positive electrode active material-containing layer supported on the surface of the positive electrode current collector. The positive electrode current collector is formed from a conductive metal. The positive electrode current collector is not limited to these, but for example, it is formed from any of aluminum, aluminum alloy, stainless steel, and titanium, and has a thickness of about 10 μm to 30 μm. The positive electrode active material-containing layer comprises a positive electrode active material and may optionally contain a binder and a conductive agent. Examples of positive electrode active materials are oxides, sulfides, and polymers that can intercept and deintercept lithium ions, but are not limited to these. The positive electrode active material includes, for example, at least one selected from the group consisting of lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, spinel-type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium iron oxide, lithium fluorinated iron sulfate, lithium iron composite phosphate compound, and lithium manganese composite phosphate compound.

[0015] As the conductive agent, for example, one or more types of carbonaceous substances are used. Examples of the carbonaceous substances serving as the conductive agent include acetylene black, ketjen black, graphite, and coke. Further, as the binder, for example, a polymer resin is used. The binder includes, for example, at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, ethylene-butadiene rubber, polypropylene (PP), polyethylene (PE), carboxymethyl cellulose (CMC), polyimide (PI), and polyacrylimide (PAI).

[0016] In the positive electrode active material-containing layer, the mixing ratio of the positive electrode active material, the conductive agent, and the binder is preferably such that the positive electrode active material is 70% by mass or more and 95% by mass or less, the conductive agent is 3% by mass or more and 20% by mass or less, and the binder is 2% by mass or more and 10% by mass or less. In the formation of the positive electrode, a slurry is prepared by suspending the positive electrode active material, the conductive agent, and the binder in an organic solvent, and the prepared slurry is applied to one or both sides of the positive electrode current collector. Then, after drying the applied slurry, the slurry is rolled by a roll press or the like, whereby a positive electrode active material-containing layer supported on one or both sides of the positive electrode current collector is formed. Further, the positive electrode current collector includes a positive electrode current collecting tab as a portion where the positive electrode active material-containing layer is not supported.

[0017] The negative electrode includes a negative electrode current collector such as a negative electrode current collector foil, and a negative electrode active material-containing layer supported on the surface of the negative electrode current collector. The negative electrode current collector is formed of a conductive metal. The negative electrode current collector is not limited to these, but for example, it is formed of any one of zinc, aluminum, an aluminum alloy, copper, etc., and has a thickness of about 10 μm to 30 μm. The negative electrode active material-containing layer includes a negative electrode active material and may optionally contain a binder and a conductive agent. The negative electrode active material is not particularly limited, and examples thereof include metal oxides, metal sulfides, metal nitrides, and carbonaceous materials that can occlude and release lithium ions. Examples of the metal oxide serving as the negative electrode active material include titanium-containing oxides. And the titanium-containing oxides serving as the negative electrode active material include, for example, titanium oxides, lithium titanium-containing composite oxides, niobium titanium-containing composite oxides, and sodium niobium titanium-containing composite oxides. Examples of the conductive agent and binder of the negative electrode active material-containing layer include the same materials as the conductive agent and binder of the positive electrode active material-containing layer.

[0018] In the negative electrode active material-containing layer, the mixing ratio of the negative electrode active material, the conductive agent, and the binder is preferably such that the negative electrode active material is 70% by mass or more and 95% by mass or less, the conductive agent is 3% by mass or more and 20% by mass or less, and the binder is 2% by mass or more and 10% by mass or less. In the formation of the negative electrode, in the same manner as in the formation of the positive electrode, a negative electrode active material-containing layer supported on one side or both sides of the negative electrode current collector is formed. Further, the negative electrode current collector includes a negative electrode current collecting tab as a portion where the negative electrode active material-containing layer is not supported.

[0019] In one example, in the electrode group, the positive electrode, the negative electrode, and the separator are wound around a winding axis in a state where the separator is sandwiched between the positive electrode active material-containing layer and the negative electrode active material-containing layer, and the electrode group has a wound structure. In another example, the electrode group has a stacked structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked, and a separator is provided between the positive electrode and the negative electrode.

[0020] Furthermore, in each of the aqueous battery cells 3, an aqueous electrolyte is held (impregnated) in the electrode group. As the aqueous electrolyte, for example, an aqueous electrolyte solution obtained by dissolving an electrolyte salt in an aqueous solvent is used. As the electrolyte salt dissolved in the aqueous solvent, for example, at least one of a lithium salt and a sodium salt is used. Examples of lithium salts dissolved in the aqueous solvent include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate (CH3COOLi), lithium oxalate (Li2C2O4), lithium carbonate (Li2CO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SO2F)2), and lithium bisoxalate borate (LiBOB; LiB[(OCO)2]2).

[0021] Furthermore, examples of sodium salts that dissolve in aqueous solvents include sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium hydroxide (NaOH), sodium nitrate (NaNO3), and sodium trifluoromethanesulfonylamide (NaTFSA). The molar concentration of lithium ions in the aqueous electrolyte is, for example, 3 mol / L or higher. Preferably, the molar concentration of lithium ions in the aqueous electrolyte is 6 mol / L or higher, and more preferably 12 mol / L or higher.

[0022] A water-containing solution is used as the aqueous solvent for dissolving the electrolyte salt. The aqueous solvent may be pure water or a mixed solvent of water and an organic solvent. An example of an organic solvent that can be mixed with water is N-methyl-2-pyrrolidone (NMP). In addition, a small amount of zinc chloride (ZnCl2) or the like may be added to the aqueous electrolyte.

[0023] Alternatively, instead of an aqueous electrolyte, an aqueous gel-like electrolyte formed by compounding an aqueous electrolyte with a polymer material may be used as the aqueous electrolyte. Examples of polymer materials compounded with the aqueous electrolyte include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0024] Furthermore, in each of the aqueous battery cells 3, the electrode group is housed inside the outer casing. As the outer casing, either a bag-shaped container made of laminate film or a metal container can be used. As the laminate film, for example, a multilayer film is used, and the multilayer film includes a plurality of resin layers and metal layers arranged between the resin layers. The thickness of the laminate film is preferably 0.5 mm or less, and more preferably 0.2 mm or less. The metal container is preferably made of at least one metal selected from the group consisting of aluminum, zinc, titanium, and iron, or an alloy of these metals. The wall thickness of the metal container is preferably 0.5 mm or less, and more preferably 0.2 mm or less.

[0025] Furthermore, each of the aqueous battery cells 3 is provided with a pair of electrode terminals. One electrode terminal is a positive electrode terminal electrically connected to a positive electrode current collector tab, and the other electrode terminal is a negative electrode terminal electrically connected to a negative electrode current collector tab. The electrode terminals may be internal terminals formed inside the exterior member, or external terminals formed on the outer surface of the exterior member. The electrode terminals are formed from a conductive material, preferably at least one metal selected from the group consisting of aluminum, zinc, titanium, and iron, or an alloy of these metals.

[0026] Figure 2 shows an example of an aqueous battery cell 3. In the example in Figure 2, the aqueous battery cell 3 has defined dimensions: a length direction (direction indicated by arrow X), a width direction (direction perpendicular or approximately perpendicular to the plane of Figure 2) intersecting (orthogonal or approximately perpendicular to) the length direction, and a thickness direction (direction indicated by arrow Y) intersecting (orthogonal or approximately perpendicular to) both the length and width directions. The aqueous battery cell 3 comprises an outer casing member 21 and an electrode group 22. The outer casing member 21 is the laminate film described above. The electrode group 22 is housed inside the outer casing member 21, and the electrode group 22 is impregnated with an aqueous electrolyte.

[0027] The electrode group 22 has a stack structure in which multiple positive electrodes 23 and multiple negative electrodes 25 are alternately stacked, with a separator 26 provided between the positive electrodes 23 and the negative electrodes 25. The stacking direction of the positive electrodes 23 and negative electrodes 25 in the electrode group 22 coincides with or approximately coincides with the thickness direction of the aqueous battery cell 3. In each positive electrode 23, a positive electrode active material-containing layer 23B is supported on both sides of the positive electrode current collector 23A, and in each negative electrode 25, a negative electrode active material-containing layer 25B is supported on both sides of the negative electrode current collector 25A. In the electrode group 22, a positive electrode current collector tab 23C is formed in the positive electrode current collector 23A, which is the portion that does not support the positive electrode active material-containing layer 23B, and the positive electrode current collector tab 23C protrudes toward one side in the longitudinal direction of the aqueous battery cell 3 relative to the negative electrodes 25 and the separator 26. Furthermore, in the electrode group 22, a negative electrode current collector tab 25C is formed in the negative electrode current collector 25A, which is the portion that does not support the negative electrode active material-containing layer 25B. The negative electrode current collector tab 25C protrudes from the positive electrode 23 and the separator 26 in the longitudinal direction of the aqueous battery cell 3, on the side opposite to the side from which the positive electrode current collector tab 23C protrudes.

[0028] Furthermore, the exterior member 21 has two openings, and each of these openings is closed by heat-sealing the resin layers of the laminate film together. The positive electrode current collector tab 23C is connected to the positive electrode terminal 27, which extends to the outside of the exterior member 21 from one of the two openings in the exterior member 21. The negative electrode current collector tab 25C is connected to the negative electrode terminal 28, which extends to the outside of the exterior member 21 from the other opening of the exterior member 21 from which the positive electrode terminal 27 extends.

[0029] As shown in Figure 1, the energy storage system 1 is equipped with a power source 6 and a load 7. Power source 6 can supply power to the battery pack 2, and the battery pack 2 is charged by the power supplied from power source 6, etc. Power can be supplied to the load 7 from the battery pack 2, and the battery pack 2 discharges by supplying power to the load 7, etc. Examples of power source 6 include a separate storage battery from the battery pack 2 and a generator, etc. Examples of load 7 include an electric motor and a light, etc.

[0030] In one example, the energy storage system 1 may be equipped with a motor-generator. In this case, power can be supplied from the battery pack 2 to the motor-generator, and power can be supplied from the motor-generator to the battery pack 2. That is, the motor-generator functions as both a power source and a load. Also, in the example shown in Figure 1, the battery-equipped device 5 on which the battery pack 2 is mounted is equipped with a power source 6 and a load 7. However, in one example, at least one of the power source 6 and the load 7 may be provided outside the battery-equipped device 5.

[0031] The management device 4 manages the battery pack 2 by controlling its charging and discharging, and manages the entire energy storage system 1. The management device 4 includes a control unit 10 that acts as a controller. In the example shown in Figure 1, the management device 4 is mounted on the battery-equipped device 5, and the battery-equipped device 5 constitutes a processing unit (computer). The control unit 10 of the management device 4 includes a processor and a storage medium. The processor includes any of the following: CPU (Central Processing Unit), GPU (Graphics Processing Unit), ASIC (Application Specific Integrated Circuit), microcontroller, FPGA (Field Programmable Gate Array), and DSP (Digital Signal Processor). The storage medium may include a main memory such as memory, as well as an auxiliary storage device. Examples of storage media include magnetic disks, optical disks (CD-ROM, CD-R, DVD, etc.), magneto-optical disks (MO, etc.), and semiconductor memory.

[0032] In the control unit 10, there may be one processor and one storage medium. In the control unit 10, the processor performs processing by executing programs stored in the storage medium, etc. The programs executed by the processor of the control unit 10 may be stored on a computer (server) connected via a network such as the Internet, or on a server in a cloud environment. In this case, the processor downloads the programs via the network. The control unit 10 manages the battery pack 2 by executing a management program. The control unit 10 also adjusts the State of Charge (SOC) of each of the multiple aqueous battery cells 3 that make up the battery pack 2, as will be described later, by executing an SOC adjustment program included in the management program.

[0033] Furthermore, the management device 4 may be located outside the battery-powered device 5. In this case, the management device 4 is, for example, an external server of the battery-powered device 5 and can communicate with the processing unit (computer) installed in the battery-powered device 5 via a network. In this case as well, the control unit 10 of the management device 4 includes a processor and a storage medium. In addition, the processing of the control unit 10 of the management device 4 may be performed collaboratively by the processing unit installed in the battery-powered device 5 and an external server (processing unit) of the battery-powered device 5. In this case, for example, the external server of the battery-powered device 5 becomes the master control unit, and the processing unit installed in the battery-powered device 5 becomes the slave control unit.

[0034] In another example, the processing of the control unit 10 of the management device 4 may be performed by a cloud server configured in a cloud environment. Here, the infrastructure of the cloud environment consists of virtual processors such as virtual CPUs and cloud memory. Therefore, when the cloud server functions as the control unit 10, processing is performed by the virtual processor, and the data necessary for processing is stored in the cloud memory. Alternatively, the processing of the control unit 10 may be performed collaboratively by the processing unit installed in the battery-powered device 5 and the cloud server. In this case, the processing unit (computer) installed in the battery-powered device 5 can communicate with the cloud server.

[0035] The energy storage system 1 is provided with a drive circuit 11. The control unit 10 controls the power supply from the battery pack 2 to the load 7 and the power supply from the power source 6 to the battery pack 2 by controlling the drive of the drive circuit 11. In other words, the control unit 10 controls the charging and discharging of the battery pack 2 by controlling the drive of the drive circuit 11. The drive circuit 11 includes a relay circuit that switches between the output of power from the battery pack 2 and the input of power to the battery pack 2. The drive circuit 11 also includes a conversion circuit, which converts power from the power source 6 into DC power supplied to the battery pack 2. The conversion circuit also converts DC power from the battery pack 2 into power supplied to the load 7. The conversion circuit can include a voltage transformer circuit, a DC / AC converter circuit, and an AC / DC voltage transformer circuit. In the example shown in Figure 1, the drive circuit 11 is provided in the battery-equipped device 5, but it may also be formed outside the battery-equipped device 5.

[0036] Furthermore, the energy storage system 1 is provided with a current detection circuit 12 and a plurality of voltage detection circuits 13. The current detection circuit 12 detects the current flowing through the battery pack 2, that is, the current flowing through the series connection structure of the plurality of aqueous battery cells 3. In addition, one voltage detection circuit 13 is provided corresponding to each of the plurality of aqueous battery cells 3 that make up the battery pack 2, so that the energy storage system 1 is provided with the same number of voltage detection circuits 13 as the plurality of aqueous battery cells 3 in the battery pack 2. Each voltage detection circuit 13 detects the voltage applied to the corresponding one of the plurality of aqueous battery cells 3. As a result, the voltage of each of the plurality of aqueous battery cells 3 that make up the battery pack 2 can be detected by the corresponding one of the voltage detection circuits 13.

[0037] In addition to the current detection circuit 12 and the voltage detection circuit 13, the energy storage system 1 may also be equipped with a temperature sensor. In this case, the temperature sensor detects the temperature of the battery pack 2. In one example, the temperature sensor detects the temperature at only one location in the environment in which the battery pack 2 is placed. The temperature detected at that one location is then taken as the temperature of the battery pack 2. In another example, the temperature sensor detects the temperature at multiple locations in the environment in which the battery pack 2 is placed. The average or median value of the temperatures detected at the multiple locations is then taken as the temperature of the battery pack 2.

[0038] The control unit 10 of the management device 4 acquires the detection results from the current detection circuit 12 and the voltage detection circuit 13. Based on the current detection result from the current detection circuit 12 and the voltage detection result from the voltage detection circuit 13, the control unit 10 controls the charging and discharging of the battery pack 2 and manages the battery pack 2. Furthermore, if a temperature sensor is provided, the control unit 10 manages the battery pack 2 based on the detection results from the temperature sensor in addition to the detection results from the current detection circuit 12 and the voltage detection circuit 13.

[0039] Furthermore, in the example of the energy storage system 1 shown in Figure 1, the user interface 15 is mounted on the battery-equipped device 5. The user interface 15 functions as an operating device into which operations and other information are input by the user of the energy storage system 1, and also functions as an information device that informs the user of the energy storage system 1 of information. The user interface 15 is equipped with input means such as buttons, dials, and touch panels as an operating device, and the control unit 10 processes the operation commands and other information input through the user interface 15. The control unit 10 also informs information through the user interface 15. Information is informed through either a screen display or an output means such as sound. The user interface 15 may be provided outside the battery-equipped device 5.

[0040] For battery pack 2, SOC (state of charge) is defined as a parameter indicating the charge state. For battery pack 2, a lower voltage limit and an upper voltage limit are defined. In battery pack 2, the state in which the voltage during discharge or charge under specified conditions reaches the lower voltage limit is defined as the SOC state of 0%, and the state in which the voltage during discharge or charge under specified conditions reaches the upper voltage limit is defined as the SOC state of 100%. Furthermore, in battery pack 2, the battery capacity is defined as the charging capacity (amount of charge) until the SOC value goes from 0% to 100% during charging under specified conditions, or the discharge capacity (amount of charge) until the SOC value goes from 100% to 0% during discharging under specified conditions. In battery pack 2, the SOC is the ratio of the remaining charge amount (remaining capacity) up to the SOC state of 0% to the battery capacity.

[0041] For each of the multiple aqueous battery cells 3 that make up the battery pack 2, a State of Charge (SOC) is defined as a parameter indicating the charge state. For each aqueous battery cell 3, similar to the battery pack 2, a lower voltage limit and an upper voltage limit are defined. Then, for each aqueous battery cell 3, the SOC is defined based on the lower voltage limit and upper voltage limit, similar to the SOC of the battery pack 2.

[0042] The control unit 10 calculates the State of Charge (SOC) in real time for each of the multiple water-based battery cells 3. The control unit 10 stores data showing the relationship between the SOC and the open-circuit voltage (OCV) for each individual water-based battery cell 3 in its storage medium. When calculating the SOC in real time for an individual water-based battery cell 3, the control unit 10 acquires the open-circuit voltage for that individual water-based battery cell 3 in real time. The open-circuit voltage of each water-based battery cell 3 can be detected by the corresponding one of the voltage detection circuits 13. The control unit 10 calculates the SOC in real time for each of the multiple water-based battery cells 3 using the open-circuit voltage detected in real time and the relationship between the SOC and the open-circuit voltage stored in the storage medium.

[0043] Furthermore, the control unit 10 may calculate the State of Charge (SOC) of the battery pack 2 in real time. In this case, data showing the relationship between the SOC and the open-circuit voltage for the battery pack 2 is stored in the storage medium of the control unit 10. The control unit 10 then acquires the real-time open-circuit voltage of the battery pack 2, that is, the real-time open-circuit voltage of the entire series-connected cell structure of the multiple aqueous battery cells 3. At this time, for example, each of the multiple voltage detection circuits 13 detects the open-circuit voltage of one of the corresponding aqueous battery cells 3, and the sum of the open-circuit voltages detected by the multiple voltage detection circuits 13 is calculated as the open-circuit voltage of the battery pack 2. The control unit 10 calculates the real-time SOC for the battery pack 2 using the real-time open-circuit voltage and the relationship between the SOC and the open-circuit voltage stored in the storage medium.

[0044] In the example described above, the real-time SOC of the battery pack 2 and the real-time SOC of each aqueous battery cell 3 are calculated based on the open-circuit voltage, but this is not the only way. The real-time SOC of the battery pack 2 and the real-time SOC of each aqueous battery cell 3 can be calculated as appropriate using well-known methods. In one example, the real-time charge amount of the battery pack 2 is calculated based on the charge amount at a predetermined point in time and the time change of the current flowing through the battery pack 2 from a predetermined point in time. For example, the real-time charge amount of the battery pack 2 is calculated by adding the time integrated value of the current flowing through the battery pack 2 from a predetermined point in time to the charge amount at a predetermined point in time. The time change of the current flowing through the battery pack 2 can be detected by the current detection circuit 12. In this example, the control unit 10 calculates the real-time SOC of the battery pack 2 based on the real-time charge amount.

[0045] In the energy storage system 1, repeated charging and discharging of the battery pack 2 causes a state of charge (SOC) deviation among multiple water-based battery cells 3 that are electrically connected in series within the battery pack 2. The control unit 10 of the management device 4 corrects the SOC deviation among the multiple water-based battery cells 3 in the battery pack 2 when it becomes sufficiently large. As a result, the control unit 10 manages the battery pack 2 so that the SOC deviation among the multiple water-based battery cells 3 in the battery pack 2 does not exceed a reference level. In other words, the SOC of each water-based battery cell 3 is adjusted so that the SOC deviation among the multiple water-based battery cells 3 does not exceed a reference level.

[0046] Figure 3 shows an example of the process performed by the control unit 10 to adjust the State of Charge (SOC) of multiple aqueous battery cells 3 in the battery pack 2. The process shown in the example in Figure 3 is performed periodically after the start of use of the energy storage system 1. The process shown in the example in Figure 3 is performed by executing the SOC adjustment program included in the management program. When the process shown in Figure 3 is started, the control unit 10 acquires the SOC in real time for each of the multiple aqueous battery cells 3 that make up the battery pack 2 (S101). At this time, for example, the open-circuit voltage is acquired in real time for each of the multiple aqueous battery cells 3, and the SOC is calculated in real time for each aqueous battery cell 3 based on the open-circuit voltage in real time and the relationship between the open-circuit voltage and the SOC.

[0047] The control unit 10 then calculates the SOC difference value η between the highest SOC cell and the lowest SOC cell among the multiple aqueous battery cells 3 (S102). The SOC difference value η is calculated by subtracting the SOC of the lowest SOC cell from the SOC of the highest SOC cell. The control unit 10 then determines whether the calculated SOC difference value η is greater than or equal to the reference difference value ηref (S103). It is preferable that the reference difference value ηref be set to a value that is either 10% or more and 20% or less.

[0048] If the SOC difference value η is greater than or equal to the reference difference value ηref (S103-Yes), the control unit 10 performs SOC deviation correction processing to correct the SOC deviation among the plurality of aqueous battery cells 3 that constitute the battery pack 2 (S104). The SOC deviation correction processing is performed by executing the SOC deviation correction program included in the SOC adjustment program. In the SOC deviation correction processing (S104), the control unit 10 controls the drive of the drive circuit 11 to charge the battery pack 2 (the entire cell series connection structure of the plurality of aqueous battery cells 3) with a constant current (S111). Therefore, the battery pack 2 is charged with a constant current at least in correspondence with the fact that the SOC difference value η between the highest SOC cell and the lowest SOC cell has become greater than or equal to the reference difference value ηref. The charge rate in constant current charging is preferably 0.2C or more and 1C or less.

[0049] Then, in the SOC deviation correction process (S104), while the battery pack 2 is being charged with a constant current, the control unit 10 determines whether the voltage V of the battery pack 2 is equal to or greater than the reference voltage value Vref (S112). The voltage V of the battery pack 2 corresponds to the voltage applied to the entire series connection structure of the multiple aqueous battery cells 3. If the voltage V of the battery pack 2 is lower than the reference voltage value Vref (S112-No), the process returns to S111, and the control unit 10 sequentially performs the processes from S111 onwards. For this reason, the battery pack 2 is charged with a constant current until the voltage V of the battery pack 2 reaches the reference voltage value Vref.

[0050] Furthermore, in the SOC deviation correction process (S104), if the voltage V of the battery pack 2 is equal to or greater than the reference voltage value Vref (S112-Yes), the control unit 10 controls the drive of the drive circuit 11 to charge the battery pack 2 (the entire cell series connection structure of multiple aqueous battery cells 3) at a constant voltage of the reference voltage value Vref (S113). Therefore, in response to the voltage V of the battery pack 2 reaching the reference voltage value Vref through constant current charging, the battery pack 2 is charged at a constant voltage of the reference voltage value Vref. In constant voltage charging, the current I input to the battery pack 2 is adjusted so that the voltage V of the battery pack 2 is maintained at the reference voltage value Vref.

[0051] Here, for each of the multiple aqueous battery cells 3 that make up the battery pack 2, a charging voltage value is set during manufacturing or other times as the voltage value for constant voltage charging. In the specifications for each aqueous battery cell 3, the charging voltage value is defined as the voltage value when charging at a constant voltage. The specifications also define the total value Vα of the charging voltage values ​​of the multiple aqueous battery cells 3 that make up the battery pack 2. In one example, the reference voltage value Vref is set to a value higher than the total value Vα of the charging voltage values ​​of the multiple aqueous battery cells 3. In this case, it is preferable that the reference voltage value Vref is set to 1.1 times or less the total value Vα, and more preferably to 1.05 times or less the total value Vα.

[0052] Furthermore, the open-circuit voltage Vβ1 of battery pack 2 when the SOC is 90% and the open-circuit voltage Vβ2 of battery pack 2 when the SOC is 100% are defined. Open-circuit voltage Vβ2 is higher than open-circuit voltage Vβ1. In one example, the reference voltage value Vref is set to a value higher than the open-circuit voltage Vβ1 when the SOC is 90%. In this case, it is preferable that the reference voltage value Vref is set to a value higher than the open-circuit voltage Vβ2 when the SOC is 100%. It is also preferable that the reference voltage value Vref is set to 1.1 times or less the open-circuit voltage Vβ2 when the SOC is 100%, and more preferably to 1.05 times or less the open-circuit voltage Vβ2.

[0053] Furthermore, the sum of the open-circuit voltages Vγ1 of multiple aqueous battery cells 3 when the SOC is 90%, and the sum of the open-circuit voltages Vγ2 of multiple aqueous battery cells 3 when the SOC is 100%, are defined. The sum Vγ2 is higher than the sum Vγ1. In one example, the reference voltage value Vref is set to a value higher than the sum of the open-circuit voltages Vγ1 when the SOC is 90%. In this case, it is preferable that the reference voltage value Vref is set to a value higher than the sum of the open-circuit voltages Vγ2 when the SOC is 100%. It is also preferable that the reference voltage value Vref is set to 1.1 times or less the sum of the open-circuit voltages Vγ2 when the SOC is 100%, and more preferably to 1.05 times or less the sum of the open-circuit voltages Vγ2.

[0054] In the SOC deviation correction process (S104), while the battery pack 2 is being charged at a constant voltage at the reference voltage value Vref, the control unit 10 determines whether the current I input to the battery pack 2 is less than or equal to the termination current value Iter (S114). If the current I of the battery pack 2 is greater than the termination current value Iter (S114-No), the process returns to S113, and the control unit 10 sequentially performs the processes from S113 onwards. As a result, the battery pack 2 is charged at a constant voltage until the current I of the battery pack 2 drops to the termination current value Iter.

[0055] If the current I of the battery pack 2 is less than or equal to the termination current value Iter (S114-Yes), the control unit 10 stops charging the battery pack 2 by controlling the drive of the drive circuit 11 (S115). This completes the SOC deviation correction process (S104), and the process of the example in Figure 3 is completed. Here, the termination current value Iter is set to, for example, any value less than or equal to 0.1C. Also, if the SOC difference value η is smaller than the reference difference value ηref in S103 (S103-No), the control unit 10 does not perform the SOC deviation correction process (S104). Therefore, the process of the example in Figure 3 is completed without performing the SOC deviation correction process (S104). This process of the example in Figure 3 is repeated as appropriate to correct the SOC deviation of the battery pack 2.

[0056] In one example, instead of processing in S114, the control unit 10 determines whether the elapsed time ε from the start of constant-voltage charging of the battery pack 2 at the reference voltage value Vref is equal to or greater than the termination time εter. If the elapsed time ε from the start of constant-voltage charging is less than the termination time εter, the process returns to S113, and the control unit 10 continues constant-voltage charging of the battery pack 2 at the reference voltage value Vref. On the other hand, if the elapsed time ε from the start of constant-voltage charging is equal to or greater than the termination time εter, the control unit 10 stops charging the battery pack 2.

[0057] In another example, while the battery pack 2 is being charged at a constant voltage at a reference voltage value Vref, the control unit 10 calculates the SOC difference value η between the highest SOC cell and the lowest SOC cell among the multiple aqueous battery cells 3. In this case, the SOC difference value η is calculated in the same manner as in the process of S102. The control unit 10 then determines whether the calculated SOC difference value η is less than or equal to the termination difference value ηter. If the SOC difference value η is greater than the termination difference value ηter, the process returns to S113, and the control unit 10 continues the constant voltage charging of the battery pack 2 at the reference voltage value Vref. On the other hand, if the SOC difference value η is less than or equal to the termination difference value ηter, the control unit 10 stops charging the battery pack 2. Here, the termination difference value ηter is set to a value smaller than the reference difference value ηref used in the determination in S103, for example, to a value between 0% and 5%.

[0058] As described above, in this embodiment, the battery pack 2 is charged with a constant current until the voltage V of the battery pack 2 reaches the reference voltage value Vref, at least in correspondence with the fact that the SOC difference value η between the highest SOC cell and the lowest SOC cell becomes equal to or greater than the reference difference value ηref. Then, in correspondence with the fact that the voltage V of the battery pack 2 has reached the reference voltage value Vref through constant current charging, the battery pack 2 is charged with a constant voltage at the reference voltage value Vref. Therefore, by performing constant voltage charging at the reference voltage value Vref after constant current charging, the SOC difference between the multiple aqueous battery cells 3 is corrected.

[0059] As mentioned above, since the SOC deviation is corrected, when the SOC of battery pack 2 becomes large enough, that is, when the overall voltage of battery pack 2 becomes large enough, the aqueous battery cells 3 with relatively high SOCs among the multiple aqueous battery cells 3 are more likely to undergo electrolysis of water even if charging continues. For this reason, when the overall voltage of battery pack 2 becomes large enough, the voltage increase is suppressed and the increase in SOC is suppressed even if charging continues in the aqueous battery cells 3 with relatively high SOCs.

[0060] On the other hand, even if the overall voltage of the battery pack 2 rises to a certain level, the battery reaction is more likely to proceed in the water-based battery cells 3 with relatively low SOCs among the multiple water-based battery cells 3 if charging continues. Therefore, even if the overall voltage of the battery pack 2 rises to a certain level, the voltage of the water-based battery cells 3 with relatively low SOCs will rise and the SOC will increase if charging continues. Consequently, in a battery pack 2 in which multiple water-based battery cells 3 are electrically connected in series, the SOC difference among the multiple water-based battery cells 3 is appropriately corrected by charging the battery pack 2 with a constant current and then charging it with a constant voltage at a reference voltage value Vref.

[0061] Furthermore, in this embodiment, since the SOC difference among the multiple aqueous battery cells 3 is corrected as described above, in the correction of the SOC difference, charging of only some aqueous battery cells 3 with relatively low SOCs and discharging of only some aqueous battery cells with relatively high SOCs are not performed. For this reason, it becomes possible to correct the SOC difference among the multiple aqueous battery cells 3 without providing a drive circuit or the like that charges or discharges only some of the multiple aqueous battery cells 3 that make up the battery pack 2. Thus, it becomes possible to correct the SOC difference among the multiple aqueous battery cells 3 in the battery pack 2 while simplifying the system configuration of the energy storage system 1. In addition, by simplifying the system configuration of the energy storage system 1, the system size of the energy storage system 1 is suppressed.

[0062] Furthermore, in this embodiment, constant current charging is initiated and correction processing for SOC deviations among the multiple aqueous battery cells 3 is started at least in response to the SOC difference value η between the highest SOC cell and the lowest SOC cell becoming equal to or greater than the reference difference value ηref. Therefore, by setting the reference difference value ηrer to an appropriate value, it is effectively prevented that the SOC deviation among the multiple aqueous battery cells 3 in the battery pack 2 will exceed the reference level. For example, by setting the reference difference value ηref to any value of 20% or less, it is effectively prevented that the SOC deviation among the multiple aqueous battery cells 3 will become large enough to affect the degradation of the battery pack 2 itself.

[0063] Furthermore, in this embodiment, by setting the reference difference value ηrer to an appropriate value, it is effectively prevented that the SOC deviation correction process is performed at a frequency that would interfere with the operation of the battery pack 2. For example, by setting the reference difference value ηref to any value of 10% or more, the SOC deviation correction process between the multiple aqueous battery cells 3 is performed appropriately without interfering with the operation of the battery pack 2. As described above, in this embodiment, for example, by setting the reference difference value ηref to any value between 10% and 20%, it is effectively prevented that the SOC deviation between the multiple aqueous battery cells 3 exceeds the reference level, and the SOC deviation between the multiple aqueous battery cells 3 is corrected without interfering with the operation of the battery pack 2.

[0064] Furthermore, in this embodiment, in one example, the reference voltage value Vref is set to a value higher than the sum of the charging voltage values ​​Vα of the multiple aqueous battery cells 3; in another example, the reference voltage value Vref is set to a value higher than the open-circuit voltage Vβ1 of the battery pack 2 when the SOC is 90%; and in yet another example, the reference voltage value Vref is set to a value higher than the sum of the open-circuit voltages Vγ1 of the multiple aqueous battery cells 3 when the SOC is 90%. By setting the reference voltage value Vref as in these examples, the SOC deviation among the multiple aqueous battery cells 3 is appropriately corrected by the SOC deviation correction process described above.

[0065] Furthermore, if the reference voltage value Vref is set to a value higher than the open-circuit voltage Vβ1 of battery pack 2 when the SOC is at 90%, setting the reference voltage value Vref to a value higher than the open-circuit voltage Vβ2 of battery pack 2 when the SOC is at 100% allows the aforementioned SOC deviation correction process to further appropriately correct the SOC deviation among multiple aqueous battery cells 3. And if the reference voltage value Vref is set to a value higher than the sum of the open-circuit voltages Vγ1 of multiple aqueous battery cells 3 when the SOC is at 90%, setting the reference voltage value Vref to a value higher than the sum of the open-circuit voltages Vγ2 of multiple aqueous battery cells 3 when the SOC is at 100% allows the aforementioned SOC deviation correction process to further appropriately correct the SOC deviation among multiple aqueous battery cells 3.

[0066] Furthermore, in this embodiment, in one example, the reference voltage value Vref is set to 1.1 times or less the sum of the charging voltage values ​​Vα of the multiple water-based battery cells 3; in another example, the reference voltage value Vref is set to 1.1 times or less the open-circuit voltage Vβ2 when the SOC is 100%; and in yet another example, it is set to 1.1 times or less the sum of the open-circuit voltages Vγ2 when the SOC is 100%. By setting the reference voltage value Vref as in these examples, overcharging of the water-based battery cells 3 is effectively prevented during charging of the battery pack 2 in the aforementioned SOC deviation correction process, and the amount of gas generated by the electrolysis of water in the water-based battery cells 3 is reduced.

[0067] Furthermore, if the reference voltage value Vref is set to be 1.1 times or less of the total value Vα, setting the reference voltage value Vref to be 1.05 times or less of the total value Vα will further effectively prevent overcharging of the water-based battery cell 3 and further reduce the generation of gas due to the electrolysis of water. Similarly, if the reference voltage value Vref is set to be 1.1 times or less of the open-circuit voltage Vβ2, setting the reference voltage value Vref to be 1.05 times or less of the open-circuit voltage Vβ2 will further effectively prevent overcharging of the water-based battery cell 3 and further reduce the generation of gas due to the electrolysis of water. And if the reference voltage value Vref is set to be 1.1 times or less of the total value Vγ2, setting the reference voltage value Vref to be 1.05 times or less of the total value Vγ2 will further effectively prevent overcharging of the water-based battery cell 3 and further reduce the generation of gas due to the electrolysis of water.

[0068] (modified version) Figure 4 shows an example of the process performed by the control unit 10 to adjust the State of Charge (SOC) of multiple aqueous battery cells 3 in the battery pack 2 in the first modified example. The process in the example in Figure 4, like the process in the example in Figure 3, is performed periodically after the start of use of the energy storage system 1, and is carried out by executing the SOC adjustment program included in the management program. In the process in the example in Figure 4, as in the process in the example in Figure 3, processes S101 to S103 are performed.

[0069] However, in this modified example, if the SOC difference value η between the highest SOC cell and the lowest SOC cell is greater than or equal to the reference difference value ηref in S103 (S103-Yes), the control unit 10 determines whether the SOC of the highest SOC cell is 90% or less (S121). If the SOC of the highest SOC cell is higher than 90% (S121-No), the processing of the example in Figure 4 ends without performing the SOC deviation correction processing (S104). On the other hand, if the SOC of the highest SOC cell is 90% or less (S121-Yes), the control unit 10 determines whether the battery pack 2 is in operation (S122). In this case, the determination of whether the battery pack 2 is in operation is made based, for example, on whether charging or discharging of the battery pack 2 is being performed.

[0070] If the battery pack 2 is in operation (S122-Yes), that is, if the battery pack 2 is being charged or discharged, the processing of the example shown in Figure 4 is completed without performing the SOC deviation correction process (S104). On the other hand, if the battery pack 2 is not in operation (S122-No), that is, if charging and discharging of the battery pack 2 is stopped, the control unit 10 performs an SOC deviation correction process to correct the SOC deviation among the multiple aqueous battery cells 3 (S104). The SOC deviation correction process is performed in the same manner as in the embodiments described above. Therefore, in the SOC deviation correction process, the battery pack 2 is charged with a constant current until the voltage V of the battery pack 2 reaches the reference voltage value Vref, and in correspondence with the fact that the voltage V of the battery pack 2 has reached the reference voltage value Vref due to constant current charging, the battery pack 2 is charged with a constant voltage at the reference voltage value Vref.

[0071] This modified example also produces the same functions and effects as the embodiments described above. Therefore, this modified example also simplifies the system configuration of the energy storage system 1 while making it possible to correct the difference in SOC among the multiple aqueous battery cells 3 in the battery pack 2.

[0072] Furthermore, in this modified example, in addition to the SOC difference value η between the highest SOC cell and the lowest SOC cell being greater than or equal to the reference difference value ηref, the SOC of the highest SOC cell is 90% or less, and the SOC correction process is performed accordingly. Therefore, the SOC deviation correction process is started and constant current charging is initiated when there are no aqueous battery cells 3 with an SOC higher than 90%. Since the SOC deviation correction is started when there are no aqueous battery cells 3 with an SOC higher than 90%, the SOC deviation among the multiple aqueous battery cells 3 is corrected even more appropriately by the aforementioned SOC deviation correction process.

[0073] Furthermore, in this modified version, the SOC deviation correction process is not initiated while the battery pack 2 is in operation, that is, while the battery pack 2 is being charged or discharged. Therefore, interference with the operation of the battery pack 2 due to the SOC deviation correction process is more effectively prevented.

[0074] In one modified example, in the processing of the example shown in Figure 4, only one of the determinations in S121 and S122 may be performed. In this case as well, the correction process for the SOC difference between the multiple aqueous battery cells 3 is performed, similar to the embodiments described above. This makes it possible to correct the SOC difference between the multiple aqueous battery cells 3 in the battery pack 2 while simplifying the system configuration of the energy storage system 1.

[0075] In one example, the energy storage system 1 is provided with multiple battery packs 2. In this case, the energy storage system 1 is configured with at least one of the following: a series connection structure in which multiple battery packs 2 are electrically connected in series, and a parallel connection structure in which multiple battery packs 2 are electrically connected in parallel. In this modified example, each of the multiple battery packs 2 comprises multiple aqueous battery cells 3. In each of the multiple battery packs 2, the multiple aqueous battery cells 3 are electrically connected in series, forming a series connection structure in which multiple aqueous battery cells 3 are electrically connected in series.

[0076] In this modified example, the State of Charge (SOC) of each of the multiple aqueous battery cells 3 is adjusted in each of the multiple battery packs 2 in the same manner as in the embodiments described above. Therefore, in each of the multiple battery packs 2, the SOC difference between the multiple aqueous battery cells 3 is corrected in the same manner as in the embodiments described above. This modified example also produces the same functions and effects as the embodiments described above.

[0077] (Examples of application) The following describes an example of how the aforementioned battery pack 2 is mounted on a battery-powered device 5, specifically an application example where the battery pack 2 is mounted on a stationary power supply unit. Figure 5 shows an example of a system equipped with a stationary power supply unit according to the application example. In the example in Figure 5, battery pack 2A is mounted on the stationary power supply unit 32, and battery pack 2B is mounted on the stationary power supply unit 43. The stationary power supply units 32 and 43 are used in system 30. System 30 comprises a power plant 31, stationary power supply units 32, a consumer-side power grid 33, and an energy management system (EMS) 35. System 30 also has a power grid 36 and a communication network 37, and the power plant 31, stationary power supply units 32, consumer-side power grid 33, and EMS 35 are connected via the power grid 36 and the communication network 37. The EMS 35 utilizes the power grid 36 and the communication network 37 to perform control to stabilize the entire system 30.

[0078] The power plant 31 generates a large amount of electricity using fuel sources such as thermal and nuclear power. Electricity is supplied from the power plant 31 through the power grid 36, etc. The battery pack 2A of the stationary power supply unit 32 can store electricity supplied from the power plant 31, etc. The stationary power supply unit 32 can also supply the electricity stored in the battery pack 2A through the power grid 36, etc. The system 30 is equipped with a power converter 38. The power converter 38 includes a converter, inverter, and transformer, etc. Therefore, the power converter 38 is capable of converting between DC and AC, converting between ACs with different frequencies relative to each other, and transforming (boosting and stepping down) voltage, etc. For this reason, the power converter 38 can convert the electricity from the power plant 31 into electricity that can be stored in the battery pack 2A. In the example in Figure 5, the power converter 38 functions in the same way as the drive circuit 11 described above during charging and discharging of the battery pack 2A.

[0079] The consumer-side power system 33 includes power systems for factories, buildings, and households. The consumer-side power system 33 is equipped with a consumer-side EMS 41, a power converter 42, and a stationary power supply unit 43. The consumer-side EMS 41 performs control to stabilize the consumer-side power system 33.

[0080] The consumer-side power grid 33 is supplied with power from the power plant 31 and power from the battery pack 2A through the power grid 36. The battery pack 2B of the stationary power supply unit 43 can store the power supplied to the consumer-side power grid 33. The power converter 42, like the power converter 38, includes a converter, inverter, and transformer. Therefore, the power converter 42 is capable of converting between DC and AC, converting between ACs with different frequencies, and transforming (boosting and stepping down). Thus, the power converter 42 can convert the power supplied to the consumer-side power grid 33 into power that can be stored in the battery pack 2B. In the example shown in Figure 5, the power converter 42 functions similarly to the drive circuit 11 described above during charging and discharging of the battery pack 2B.

[0081] The electricity stored in the battery pack 2B can be used, for example, to charge vehicles such as electric vehicles. Furthermore, the system 30 may be equipped with a renewable energy source. In this case, the renewable energy source generates electricity using natural energy sources such as wind and solar power. Electricity is then supplied from both the power plant 31 and the renewable energy source through the power grid 36.

[0082] In the example shown in Figure 5, for example, the current detection circuit 12 and voltage detection circuit 13 described above are mounted on each of the stationary power supply units 32 and 43. As a result, the currents of the battery packs 2A and 2B are detected, and the voltages of the multiple aqueous battery cells 3 in each of the battery packs 2A and 2B are detected. Alternatively, a temperature sensor may be mounted on each of the stationary power supply units 32 and 43. In this case, the temperatures of the battery packs 2A and 2B are detected.

[0083] Furthermore, one or more of the EMS35, a computer separate from the EMS35, and a cloud server, etc., function as the aforementioned management device 4 for managing the battery pack 2A. Then, in the battery pack 2A, adjustment processing of the SOC of each of the multiple aqueous battery cells 3 is performed, and correction processing of SOC differences between the multiple aqueous battery cells 3 is performed, in the same manner as in the embodiments described above. Furthermore, one or more of the EMS35, the customer-side EMS41, a computer separate from the EMS35 and the customer-side EMS41, and a cloud server, etc., function as the aforementioned management device 4 for managing the battery pack 2B. Then, in the battery pack 2B, adjustment processing of the SOC of each of the multiple aqueous battery cells 3 is performed, and correction processing of SOC differences between the multiple aqueous battery cells 3 is performed, in the same manner as in the embodiments described above.

[0084] (Verification related to the embodiment) Furthermore, verifications related to the aforementioned embodiments were conducted. The verifications performed are described below. In the verifications, an aqueous battery cell (single cell) was formed in which a stacked electrode group was housed inside a laminate film, similar to the aqueous battery cell 3 example in Figure 2. In the aqueous battery cell, the positive electrode and negative electrode were formed as follows.

[0085] For the positive electrode, a titanium sheet was used as the positive electrode current collector. As the positive electrode active material, particles of LiNiCoMnO2 (Ni:Co:Mn=5:2:3), a type of lithium nickel cobalt manganese composite oxide, were prepared. Acetylene black (AB), a carbonaceous material, was used as the conductive agent, and polyvinylidene fluoride (PVdF), a type of polymer resin, was used as the binder. Furthermore, a slurry was prepared by suspending 90% by mass of lithium nickel cobalt manganese composite oxide, 5% by mass of acetylene black, and 5% by mass of polyvinylidene fluoride in N-methylpyrrolidone (NMP), a type of organic solvent. The prepared slurry was then applied to both sides of the titanium sheet, which served as the positive electrode current collector. In this process, the slurry was applied to the positive electrode current collector, excluding the portion that would become the positive electrode current collector tab.

[0086] Then, after drying the applied slurry, the slurry was rolled using a roll press or the like to form positive electrode active material-containing layers on both sides of the titanium sheet. Finally, the positive electrode was formed by drying the positive electrode current collector and the positive electrode active material-containing layers formed on both sides of the positive electrode current collector.

[0087] In the negative electrode, a zinc sheet was used as the negative electrode current collector. Furthermore, Li4Ti5O, a type of lithium titanium-containing composite oxide, was used as the negative electrode active material. 12 Particles were prepared. Acetylene black (AB), a carbonaceous material, was used as a conductive agent, and polyvinylidene fluoride (PVdF), a type of polymer resin, was used as a binder. A slurry was prepared by suspending 90% by mass of lithium titanium-containing composite oxide, 5% by mass of acetylene black, and 5% by mass of polyvinylidene fluoride in N-methylpyrrolidone (NMP), a type of organic solvent. The prepared slurry was then applied to both sides of a zinc sheet, which served as the negative electrode current collector. At this time, the slurry was applied to the negative electrode current collector, excluding the portion that would become the negative electrode current collector tab.

[0088] Then, after drying the applied slurry, the slurry was rolled using a roll press or the like to form a negative electrode active material-containing layer on both sides of the zinc sheet. Finally, the negative electrode was formed by drying the negative electrode current collector and the negative electrode active material-containing layer formed on both sides of the negative electrode current collector.

[0089] The electrode group was formed in a stacked structure by alternately stacking four negative electrodes and three positive electrodes. A separator was interposed between the positive and negative electrodes. A porous polyethylene film, a type of synthetic resin film, was used as the separator. The thickness of the porous film was 15 μm. Furthermore, layers of alumina particles were formed on both sides of the porous film as layers of non-conductive particles. The thickness of the alumina particle layer was 3 μm. The formed electrode group was then housed inside an exterior component made of laminate film. The metal layer of the laminate film was made of aluminum.

[0090] Furthermore, the electrode group was impregnated with an aqueous electrolyte. The aqueous electrolyte used consisted of aqueous solutions in which lithium chloride (LiCl) and lithium hydroxide (LiOH) were dissolved as lithium salts. In the electrolyte, the concentration of lithium chloride was 12 mol / L, and the concentration of lithium hydroxide was 1 mol / L. In addition, to the aqueous solution in which the lithium salts were dissolved as described above, 10% by mass of N-methyl-2-pyrrolidone (NMP), an organic solvent, and 1% by mass of zinc chloride (ZnCl2) were added. Then, the aqueous electrolyte prepared as described above was injected into the interior of the outer casing through the injection port, and the outer casing was sealed liquid-tight by closing the injection port.

[0091] In the verification, two aqueous battery cells were formed as described above, creating two aqueous battery cells C1 and C2. The charging voltage for each of the aqueous battery cells C1 and C2 was set to 2.5V. In the verification, the state of charge (SOC) of the two aqueous battery cells C1 and C2 was adjusted so that their SOCs differed by 20%. Specifically, the SOC of aqueous battery cell C2 was set to be 20% higher than that of aqueous battery cell C1, and the voltage of aqueous battery cell C2 was set to be higher than that of aqueous battery cell C1. Then, with the SOCs of aqueous battery cells C1 and C2 differing by 20%, they were electrically connected in series to form a series cell connection structure.

[0092] Then, a correction process for the state of charge (SOC) deviation was performed on the series-connected cell structure using aqueous battery cells C1 and C2, in the same manner as in the embodiments described above. At this time, a voltage value corresponding to the reference voltage value Vref was set to 5.08V, and the series-connected cell structure was charged with a constant current of 0.5C until the voltage of the series-connected cell structure reached 5.08V. Then, corresponding to the fact that the voltage of the series-connected cell structure reached 5.08V through constant current charging, the series-connected cell structure was charged with a constant voltage of 5.08V.

[0093] Furthermore, the voltage corresponding to the reference voltage value Vref, 5.08V, was set to a value higher than the sum of the charging voltages of the aqueous battery cells C1 and C2, which is 5.0V. In addition, 5.08V was set to be 1.05 times or less of the sum of the charging voltages of the aqueous battery cells C1 and C2, i.e., 5.25V or less. In the verification, constant voltage charging of the series cell structure at 5.08V was carried out until the current input to the series cell structure dropped to 0.1C. That is, the charging of the series cell structure was stopped in accordance with the drop in the current input to the series cell structure to 0.1C, and the SOC deviation correction process was terminated.

[0094] Figure 6 shows the voltage changes of two aqueous battery cells C1 and C2 during the verification process, specifically during the correction of SOC deviation in a series-connected cell structure. In Figure 6, the horizontal axis represents the amount of charge relative to the start of the SOC deviation correction process, and the vertical axis represents the voltage. In Figure 6, the voltage change of aqueous battery cell C1 is shown by a solid line, and the voltage change of aqueous battery cell C2 is shown by a dashed line.

[0095] As shown in Figure 6, during the SOC deviation correction process, when the series-connected cell structure was charged to a certain extent, the aqueous battery cell C2, which was on the side with a higher SOC, showed suppressed voltage increases and suppressed SOC increases even with continued charging. On the other hand, during the SOC deviation correction process, even when the series-connected cell structure was charged to a certain extent, the aqueous battery cell C1, which was on the side with a lower SOC, showed increased voltage and SOC as charging continued. Thus, the SOC deviation of aqueous battery cells C1 and C2 was corrected by the SOC deviation correction process.

[0096] Furthermore, in the verification, after correcting the SOC difference between aqueous battery cells C1 and C2 as described above, discharge was performed from the series-connected structure of aqueous battery cells C1 and C2. During this discharge, the discharge was performed from the series-connected structure at a discharge rate of 1C. Then, while constant current discharge was being performed, the voltage of each aqueous battery cell C1 and C2 was detected, and the time change of the voltage of each aqueous battery cell C1 and C2 was measured. As a result, a discharge curve showing the voltage change during discharge after the SOC difference correction process was measured for each aqueous battery cell C1 and C2.

[0097] Figure 7 shows the discharge curves of two aqueous battery cells C1 and C2, measured during the verification process while discharging from a series-connected cell structure after the SOC deviation correction process. In Figure 7, the horizontal axis shows the discharge charge amount relative to the start of discharge, and the vertical axis shows the voltage. In Figure 7, the voltage change of aqueous battery cell C1 is shown by a solid line, and the voltage change of aqueous battery cell C2 is shown by a dashed line. As shown in Figure 7, when discharging from a series-connected cell structure after the SOC deviation correction process, the voltages shown in the discharge curves of aqueous battery cells C1 and C2 showed almost no deviation.

[0098] The above verification demonstrates that by correcting the SOC difference between multiple aqueous battery cells that are electrically connected in series in the same manner as in the embodiments described above, the voltage difference between multiple aqueous battery cells is appropriately corrected, and the SOC difference between multiple aqueous battery cells is appropriately corrected.

[0099] In the above-described embodiment or example, a plurality of aqueous battery cells are electrically connected in series in the battery pack, and the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value, at least in response to the SOC difference value between the highest SOC cell and the lowest SOC cell in the plurality of aqueous battery cells becoming equal to or greater than a reference difference value. Then, in response to the battery pack voltage reaching the reference voltage value through constant current charging, the battery pack is charged with a constant voltage at the reference voltage value. This makes it possible to provide a battery pack management device, energy storage system, battery pack management method, and battery pack management program that can correct SOC differences among a plurality of aqueous battery cells electrically connected in series in the battery pack while simplifying the system configuration.

[0100] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0101] The following are additional notes. [1] A management device for managing a battery pack in which a plurality of aqueous battery cells are electrically connected in series, and each of the plurality of aqueous battery cells is equipped with an aqueous electrolyte, a positive electrode and a negative electrode, In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value, at least in correspondence with the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell becomes equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. A control device equipped with a control unit. [2] The control device of [1] is set such that the reference difference value is set to a value that is either 10% or more and 20% or less. [3] For each of the plurality of aqueous battery cells constituting the battery pack, a charging voltage value is defined as the voltage value in constant voltage charging, The reference voltage value for the battery pack is set to a value higher than the sum of the charging voltage values ​​of the plurality of aqueous battery cells. A control device for [1] or [2]. [4] The control device of [1] or [2], wherein the reference voltage value for the battery pack is set to a value higher than the open-circuit voltage of the battery pack when the SOC is 90%. [5] The control device of [1] or [2] wherein the reference voltage value for the battery pack is set to a value higher than the sum of the open-circuit voltages of the plurality of aqueous battery cells when the SOC is 90%. [6] The control unit is a control device, which, in addition to the SOC difference value being equal to or greater than the reference difference value, also corresponds to the SOC of the highest SOC cell being 90% or less, and causes the battery pack to be charged with a constant current until the voltage of the battery pack reaches the reference voltage value. [7], one of the management devices from [1] through [6], A battery pack comprising a plurality of aqueous battery cells electrically connected in series, and managed by the management device, A power storage system equipped with the following features. [8] A battery-powered device further comprising the battery pack, [7] Energy storage system. [9] A management method for managing a battery pack in which a plurality of aqueous battery cells are electrically connected in series, and each of the plurality of aqueous battery cells is equipped with an aqueous electrolyte, a positive electrode and a negative electrode, In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value, at least in response to the SOC difference value between the highest SOC cell and the lowest SOC cell becoming equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. A management method that includes the following.

[10] A management program for managing a battery pack in which a plurality of aqueous battery cells are electrically connected in series, and each of the plurality of aqueous battery cells is equipped with an aqueous electrolyte, a positive electrode and a negative electrode, wherein the computer In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value, at least in correspondence with the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell becomes equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. Management program. [Explanation of symbols]

[0102] 1...Energy storage system, 2...Battery pack, 3...Water-based battery cell, 4...Management device, 5...Battery-equipped equipment, 10...Control unit, 32,43...Stationary power supply unit, η...SOC difference value, ηref...Reference difference value, V...Voltage, Vref...Reference voltage value.

Claims

1. A management device for managing a battery pack in which multiple aqueous battery cells are electrically connected in series, and each of the multiple aqueous battery cells is equipped with an aqueous electrolyte, a positive electrode, and a negative electrode, In the operation of the aforementioned battery pack, the battery pack is charged at a constant voltage value, In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value higher than the pack charging voltage value, at least in correspondence with the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell becomes equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. A control device equipped with a control unit.

2. The control device according to claim 1, wherein the aforementioned standard difference value is set to a value that is either 10% or more and 20% or less.

3. For each of the plurality of aqueous battery cells constituting the battery pack, a charging voltage value is defined as the voltage value in constant voltage charging. The reference voltage value for the battery pack is set to a value higher than the sum of the charging voltage values ​​of the plurality of aqueous battery cells. The control device according to claim 1.

4. The control device according to claim 1, wherein the reference voltage value for the battery pack is set to a value higher than the open-circuit voltage of the battery pack when the SOC is 90%.

5. The control device according to claim 1, wherein the reference voltage value for the battery pack is set to a value higher than the sum of the open-circuit voltages of the plurality of aqueous battery cells when the SOC is 90%.

6. The control device according to claim 1, wherein the control unit charges the battery pack with a constant current until the voltage of the battery pack reaches the reference voltage value, in accordance with the fact that the SOC difference value is greater than or equal to the reference difference value, and that the SOC of the highest SOC cell is 90% or less.

7. A control device according to any one of claims 1 to 6, A battery pack comprising a plurality of aqueous battery cells electrically connected in series, and managed by the management device, A power storage system equipped with the following features.

8. The aforementioned battery pack is further equipped in a battery-powered device, The energy storage system according to claim 7.

9. A management method for a battery pack in which multiple aqueous battery cells are electrically connected in series, and each of the multiple aqueous battery cells is equipped with an aqueous electrolyte, a positive electrode, and a negative electrode, In the operation of the aforementioned battery pack, the battery pack is charged at a constant voltage value, In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value higher than the pack charging voltage value, at least in correspondence with the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell becomes equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. A management method that includes the following.

10. A management program for managing a battery pack in which multiple aqueous battery cells are electrically connected in series, and each of the multiple aqueous battery cells comprises an aqueous electrolyte, a positive electrode, and a negative electrode, wherein the program is controlled by a computer. In the operation of the aforementioned battery pack, the battery pack is charged at a constant voltage value, In the plurality of aqueous battery cells constituting the battery pack, the battery pack is charged with a constant current until the voltage of the battery pack reaches a reference voltage value higher than the pack charging voltage value, at least in correspondence with the fact that the SOC difference value between the highest SOC cell and the lowest SOC cell becomes equal to or greater than a reference difference value. In response to the fact that the voltage of the battery pack has reached the reference voltage value due to the constant current charging, the battery pack is charged at a constant voltage at the reference voltage value. Management program.

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