JP7444016B2 - Energy storage module - Google Patents

Description

The present disclosure relates to a power storage module.

The power storage module is described in Patent Document 1, for example. The power storage module described in Patent Document 1 includes a cell stack in which a plurality of power storage cells are stacked, and a current-carrying plate adjacent to the cell stack. Each of the power storage cells includes a positive electrode, a negative electrode, an electrolytic solution, and a sealing material that seals the electrolytic solution between the positive electrode and the negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The plurality of power storage cells include a first power storage cell including a negative electrode current collector located in the outermost layer of the cell stack, and a second power storage cell other than the first power storage cell. The negative electrode current collector located at the outermost layer is disposed at one end of the cell stack in the stacking direction and is in contact with the current-carrying plate.

JP2020-27694A

By the way, when a lithium ion storage cell made of a lithium ion battery is used as the storage cell, the lithium ion storage cell functions as a battery by releasing charge carriers stored in the negative electrode active material layer. In particular, when a copper negative electrode current collector is used, when a lithium ion storage cell is discharged in a state where the negative electrode active material layer is deficient in charge carriers, that is, in an overdischarge state, the copper in the negative electrode current collector becomes ionized. Dissolves in electrolyte. If the negative electrode current collector located at the outermost layer of the cell stack elutes, there is a possibility that the electrolyte solution may leak from the cell stack to the outside of the electricity storage module.

A power storage module that solves the above problem includes a cell stack in which a plurality of lithium ion power storage cells are stacked, a determination unit configured to determine whether or not the lithium ion power storage cell is overdischarged, and the lithium ion power storage cell an overdischarge control section configured to prohibit discharging of the cell stack when the determination section determines that any one of the lithium ion storage cells is overdischarged, the lithium ion storage module comprising: Each cell includes a positive electrode, a negative electrode, an electrolytic solution, and a sealing material that seals the electrolytic solution between the positive electrode and the negative electrode, and the negative electrode includes a negative electrode current collector made of copper, and a negative electrode current collector made of copper; a negative electrode active material layer provided on a negative electrode current collector, and the lithium ion storage cell includes a first storage cell provided with the negative electrode current collector located at the outermost layer of the cell stack, and the first storage cell. The electricity storage module includes a discharge circuit that discharges the second electricity storage cell, and a discharge circuit that discharges at least one of the second electricity storage cells. and a voltage control section configured to make the voltage of the second storage cell lower than the voltage of the first storage cell.

The voltage control unit discharges the second power storage cell using the discharge circuit so that the voltage of the second power storage cell becomes lower than the voltage of the first power storage cell. The determination unit can easily determine that the second power storage cell is over-discharged before the first power storage cell becomes over-discharged. When it is determined that the second storage cell is over-discharged, the over-discharge control section prohibits discharging of the cell stack. By prohibiting the discharge of the cell stack, the discharge of the first power storage cell is suppressed before overdischarge occurs. Therefore, elution of the negative electrode current collector located at the outermost layer of the cell stack is suppressed. Therefore, leakage of the electrolytic solution can be suppressed.

Regarding the electricity storage module, the voltage control unit lowers the voltage of the second electricity storage cell below the voltage of the first electricity storage cell when the determination unit judges that the lithium ion electricity storage cell is not over-discharged. Good too.

Regarding the electricity storage module, the determination unit determines that the lithium ion storage cell is overdischarged when the voltage of the lithium ion storage cell is equal to or lower than a predetermined overdischarge threshold, and the voltage control unit determines that the lithium ion storage cell is overdischarged. When the voltage of the lithium ion storage cell is higher than the overdischarge threshold and lower than a predetermined threshold larger than the overdischarge threshold, the voltage of the second storage cell is lowered than the voltage of the first storage cell. Good too.

Regarding the electricity storage module, the predetermined threshold value may be a limiting threshold value at which discharging of the cell stack is limited.
Regarding the power storage module, the voltage control unit may set the voltage of the second power storage cell to be lower than the voltage of the first power storage cell when power from the cell stack is not being supplied to a device.

The power storage module may include a charging circuit provided in the first power storage cell, and the charging circuit may charge the first power storage cell with power discharged from the second power storage cell.

Regarding the electricity storage module, the charging circuit may be provided only in the first electricity storage cell.
Regarding the above-described power storage module, the discharge circuit may be a cell balance circuit that performs cell balance of the lithium ion power storage cell.

Regarding the electricity storage module, the voltage control unit sets a target voltage to the lithium ion electricity storage cell, performs cell balancing of the lithium ion electricity storage cell so that the lithium ion electricity storage cell reaches the target voltage, and controls the second The target voltage set to the power storage cell may be lower by a predetermined value than the target voltage set to the first power storage cell.

The electricity storage module may include an inter-cell sealing material that seals between the lithium ion storage cells.

According to the present disclosure, leakage of electrolyte solution can be suppressed.

FIG. 1 is a schematic configuration diagram of a power storage module in a first embodiment. Cross-sectional view of a cell stack. 5 is a flowchart showing control performed by the control device. 5 is a flowchart showing discharge control performed by a control device. FIG. 3 is a schematic configuration diagram of a power storage module in a second embodiment. The figure which shows the modification of the process which a control apparatus performs.

(First embodiment)
A first embodiment of the power storage module will be described below. The power storage module of this embodiment is used, for example, in a vehicle such as an electric vehicle or a hybrid vehicle.

As shown in FIG. 1, vehicle Ve includes a power storage module 10, an inverter 100, a motor 110, and a vehicle ECU 120. The vehicle Ve may be an industrial vehicle such as a forklift or a towing tractor, or may be a passenger car.

The power storage module 10 is, for example, a power source for supplying power to the motor 110. Inverter 100 includes switching element 101 . Inverter 100 converts DC power from power storage module 10 into AC power by switching switching element 101 at a predetermined duty ratio. Motor 110 drives vehicle Ve using the electric power output by inverter 100. Motor 110 is a device driven by power supplied from power storage module 10. Vehicle ECU 120 controls the discharge of power storage module 10 and the like. Vehicle ECU 120 controls the input power to inverter 100, that is, the discharge of power storage module 10, by controlling the duty ratio of inverter 100.

As shown in FIGS. 1 and 2, the power storage module 10 includes a battery pack 20, a positive current-carrying plate 40, a negative current-carrying plate 50, a relay switch 70, a cell balance circuit 80, a voltage sensor 85, and a control device. 90.

As shown in FIG. 2, the assembled battery 20 includes a cell stack 30 and an inter-cell sealant 37.
The cell stack 30 includes a plurality of lithium ion storage cells 31. The cell stack 30 is a laminate in which a plurality of lithium ion storage cells 31 are stacked. In the following description, the lithium ion storage cell 31 may be referred to as the storage cell 31, and the direction in which the lithium ion storage cells 31 are stacked may be referred to as a stacking direction. In the following description, a plan view of the cell stack 30 from the stacking direction may be simply referred to as a plan view.

Each power storage cell 31 includes a positive electrode 32, a negative electrode 33, a separator 34, a sealing material 35, and an electrolyte 36.
The positive electrode 32 includes a positive electrode current collector 32a and a positive electrode active material layer 32b. The positive electrode current collector 32a is a chemically inactive electrically conductive band. The positive electrode current collector 32a is, for example, aluminum foil. The positive electrode current collector 32a has a first surface 32c perpendicular to the stacking direction, and a second surface 32d located on the opposite side of the first surface 32c in the stacking direction. The positive electrode active material layer 32b is provided on the first surface 32c of the positive electrode current collector 32a.

In a plan view of the cell stack 30 from the stacking direction, the positive electrode active material layer 32b is formed at the center of the first surface 32c of the positive electrode current collector 32a. The peripheral edge of the first surface 32c of the positive electrode current collector 32a in plan view is a positive electrode uncoated portion 32e where the positive electrode active material layer 32b is not provided. The positive electrode uncoated portion 32e is arranged so as to surround the positive electrode active material layer 32b in plan view.

The positive electrode active material layer 32b includes a positive electrode active material that can insert and release charge carriers such as lithium ions. As the positive electrode active material, materials that can be used as positive electrode active materials for lithium ion secondary batteries may be used, such as lithium composite metal oxides having a layered rock salt structure, metal oxides having a spinel structure, and polyanionic compounds. Furthermore, two or more types of positive electrode active materials may be used in combination.

The negative electrode 33 includes a negative electrode current collector 33a made of copper and a negative electrode active material layer 33b. The negative electrode current collector 33a is a copper foil. The negative electrode current collector 33a has a first surface 33c perpendicular to the stacking direction, and a second surface 33d located on the opposite side of the first surface 33c in the stacking direction. The negative electrode active material layer 33b is provided on the first surface 33c of the negative electrode current collector 33a.

The negative electrode active material layer 33b is formed at the center of the first surface 33c of the negative electrode current collector 33a in plan view. The peripheral edge of the first surface 33c of the negative electrode current collector 33a in plan view is a negative electrode uncoated portion 33e where the negative electrode active material layer 33b is not provided. The negative electrode uncoated portion 33e is arranged so as to surround the negative electrode active material layer 33b in plan view.

The negative electrode active material layer 33b contains a negative electrode active material. The negative electrode active material is not particularly limited as long as it is a single substance, alloy, or compound that can insert and release charge carriers such as lithium ions. For example, examples of the negative electrode active material include lithium, carbon, metal compounds, and elements that can be alloyed with lithium or compounds thereof. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin.

The first surface 33c of the negative electrode 33 is arranged to face the first surface 32c of the positive electrode 32 in the stacking direction. Therefore, the negative electrode active material layer 33b is arranged to face the positive electrode active material layer 32b. In plan view, the entire formation region of the positive electrode active material layer 32b is located within the formation region of the negative electrode active material layer 33b.

The separator 34 is a member that allows lithium ions to pass through. Separator 34 is arranged between positive electrode active material layer 32b and negative electrode active material layer 33b. Thereby, the separator 34 prevents a short circuit due to contact between the positive electrode 32 and the negative electrode 33. The separator 34 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains liquid electrolyte. Examples of the material constituting the separator 34 include polypropylene, polyethylene, polyolefin, and polyester. The separator 34 may have a single layer structure or a multilayer structure. The multilayer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

The sealing material 35 maintains the distance between the positive electrode current collector 32a and the negative electrode current collector 33a, and prevents a short circuit between the positive electrode current collector 32a and the negative electrode current collector 33a. The sealing material 35 is provided along the peripheral edges of the positive electrode current collector 32a and the negative electrode current collector 33a in a plan view, and is formed in a frame shape surrounding the positive electrode active material layer 32b and the negative electrode active material layer 33b. has been done. The sealing material 35 is disposed between the positive electrode uncoated portion 32e on the first surface 32c of the positive electrode current collector 32a and the negative electrode uncoated portion 33e on the first surface 33c of the negative electrode current collector 33a. .

A sealed space S surrounded by a frame-shaped sealing material 35, the positive electrode 32, and the negative electrode 33 is formed between the positive electrode 32 and the negative electrode 33.
The sealed space S accommodates a separator 34 and an electrolytic solution 36. Therefore, it can be said that the sealing material 35 seals the electrolytic solution 36 between the positive electrode 32 and the negative electrode 33. The electrolytic solution 36 includes, for example, a liquid electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Note that the peripheral edge portion of the separator 34 is buried in the sealing material 35.

The sealing material 35 can suppress leakage of the electrolytic solution 36 accommodated in the sealed space S to the outside by sealing the sealed space S between the positive electrode 32 and the negative electrode 33. Further, the sealing material 35 can suppress moisture from entering the sealed space S from the outside of the cell stack 30. Further, the sealing material 35 can suppress leakage of gas generated from the positive electrode 32 or the negative electrode 33 to the outside of the closed space S due to, for example, a charge/discharge reaction.

In the cell stack 30, a plurality of storage cells 31 have a second surface 32d of a positive electrode current collector 32a of one adjacent storage cell 31 and a second surface 33d of a negative electrode current collector 33a of the other adjacent storage cell 31. It has a structure in which the two are overlapped so that they are in contact with each other. Thereby, the plurality of power storage cells 31 configuring the cell stack 30 are connected in series.

Cell stack 30 includes bipolar electrodes 38. Here, in the cell stack 30, by stacking two adjacent electricity storage cells 31 in the stacking direction, a pseudo current collector 32a and a negative electrode current collector 33a which are in contact with each other are considered as one current collector. A bipolar electrode 38 is formed. The pseudo bipolar electrode 38 includes a current collector having a structure in which a positive electrode current collector 32a and a negative electrode current collector 33a are stacked, a positive electrode active material layer 32b formed on one surface of the current collector, and a negative electrode active material layer 33b formed on the other surface. Note that the bipolar electrode 38 may be formed using a current collector having a structure in which the positive electrode current collector 32a and the negative electrode current collector 33a are integrated or joined to each other.

The inter-cell sealing material 37 is provided so as to surround the entire circumference of the cell stack 30 in a direction perpendicular to the stacking direction. Thereby, the inter-cell sealing material 37 covers the outer peripheral edge of the current collector. By covering the outer periphery of the current collector with the inter-cell sealing material 37, the second surface 32d of the positive electrode current collector 32a of one adjacent power storage cell 31 and the negative electrode current collector of the other adjacent power storage cell 31 are separated. 33a and the second surface 33d are sealed with an inter-cell sealing material 37. Therefore, the inter-cell sealing material 37 seals between the plurality of power storage cells 31.

In the cell stack 30 stacked in this manner, the positive electrode current collector 32a is disposed at the first end of the cell stack 30 in the stacking direction. The positive electrode current collector 32a is located at the outermost layer of the cell stack 30 in the stacking direction. Further, a negative electrode current collector 33a is arranged at the second end of the cell stack 30 in the stacking direction. The negative electrode current collector 33a is also located at the outermost layer of the cell stack 30.

The positive electrode current-carrying plate 40 is in contact with the second surface 32d of the positive electrode current collector 32a located at the outermost layer of the cell stack 30. The positive electrode current-carrying plate 40 is made of a metal conductor, for example, made of the same metal as the positive electrode current collector 32a. The positive electrode current-carrying plate 40 is formed smaller than the positive electrode current collector 32a in plan view. The positive electrode current-carrying plate 40 is used to take out the electric power of the cell stack 30 to the outside of the power storage module 10. Therefore, the second surface 32d of the positive electrode current collector 32a located at the outermost layer of the cell stack 30 is a surface for extracting power to the outside of the cell stack 30.

The negative electrode current-carrying plate 50 is in contact with the second surface 33d of the negative electrode current collector 33a located at the outermost layer of the cell stack 30. The negative electrode current-carrying plate 50 is made of a metal conductor, for example, made of the same metal as the negative electrode current collector 33a. The negative electrode current-carrying plate 50 is formed smaller than the negative electrode current collector 33a in plan view. The negative electrode current-carrying plate 50 is used to take out the electric power of the cell stack 30 to the outside of the power storage module 10. Therefore, the second surface 33d of the negative electrode current collector 33a located at the outermost layer of the cell stack 30 is a surface for extracting power to the outside of the cell stack 30.

The plurality of power storage cells 31 include a first power storage cell 31a and a second power storage cell 31b. The first power storage cell 31a includes a negative electrode current collector 33a located at the outermost layer of the cell stack 30. The second power storage cell 31b is one of the power storage cells 31 constituting the cell stack 30 other than the first power storage cell 31a.

Therefore, the plurality of power storage cells 31 include a first power storage cell 31a provided with a negative electrode current collector 33a located in the outermost layer of the cell stack 30, and a second power storage cell 31b other than the first power storage cell 31a.

In this embodiment, the sealing material 35 seals the electrolytic solution 36 between the positive electrode 32 and the negative electrode 33 of each power storage cell 31, and the casing for sealing the electrolytic solution 36 is used as the casing of the cell stack 30. Since it is not separately provided outside, there is a possibility that elution of the negative electrode current collector 33a located at the outermost layer of the cell stack 30 may cause leakage of the electrolytic solution 36 to the outside of the power storage module 10.

On the other hand, the negative electrode current collector 33a of the second power storage cell 31b is stacked on another adjacent power storage cell 31. Thereby, the negative electrode current collector 33a of the second power storage cell 31b is covered by the positive electrode current collector 32a of the other adjacent power storage cell 31. Therefore, even if the negative electrode current collector 33a of the second power storage cell 31b is eluted, leakage of the electrolytic solution 36 to the outside of the power storage module 10 is unlikely to occur.

Note that although the negative electrode current collector 33a located at the outermost layer of the cell stack 30 is in contact with the negative electrode current-carrying plate 50 and is covered by the negative electrode current-carrying plate 50, the negative electrode current collector 33a located at the outermost layer is eluted. In this case, the electrolytic solution 36 is likely to leak to the outside of the power storage module 10 along the negative electrode current-carrying plate 50. In particular, when the negative electrode current-carrying plate 50 is made of copper like the negative electrode current collector 33a, when the negative electrode current collector 33a located at the outermost layer elutes, the negative electrode current-carrying plate 50 may also be eluted. Leakage of the electrolytic solution 36 to the outside is more likely to occur. Furthermore, if the negative electrode current-carrying plate 50 is formed smaller than the negative electrode current collector 33a in plan view, there will be a position where the negative electrode current collector 33a located at the outermost layer is not covered by the negative electrode current-carrying plate 50. The electrolytic solution 36 is more likely to leak to the outside of the electrolyte 10.

As shown in FIG. 1, relay switch 70 is a switch for prohibiting charging or discharging of power storage module 10. Relay switch 70 is connected in series to battery pack 20.

Voltage sensor 85 is connected in parallel to power storage cell 31 . Voltage sensor 85 detects the voltage of power storage cell 31 . Voltage sensor 85 is provided individually for each power storage cell 31.
The cell balance circuit 80 is a passive type cell balance circuit. The cell balance circuit 80 includes a plurality of resistance elements 81 and a plurality of switches 82. The number of resistance elements 81 and the number of switches 82 are, for example, the same as the number of storage cells 31. A unit in which one resistance element 81 and one switch 82 are connected in series is referred to as a series connection body. One series connection body is connected in parallel to each power storage cell 31 . By turning the switch 82 on and off, connection to and disconnection from the resistance element 81 can be switched individually for each power storage cell 31.

The control device 90 includes a processor 91 and a storage section 92 as hardware. As the processor 91, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor) is used. The storage unit 92 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 92 stores program codes or instructions configured to cause the processor 91 to execute processes. Storage 92, or computer readable media, includes any available media that can be accessed by a general purpose or special purpose computer. The control device 90 may be configured by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control device 90, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as ASIC or FPGA, or a combination thereof.

The control device 90 includes an acquisition section 93 , a cell balance control section 94 , a determination section 95 , and an overdischarge control section 96 as functional elements that function when the processor 91 executes a program stored in the storage section 92 . A voltage control section 97 is provided.

The control device 90 acquires the detection results of the voltage sensor 85 at predetermined time intervals. Thereby, the control device 90 can acquire information indicating the voltage of each power storage cell 31. It can be said that the control device 90 includes an acquisition unit 93 that acquires the detection result of the voltage sensor 85.

The control device 90 performs cell balancing by controlling the switch 82. Cell balance is performed to equalize the voltages of all storage cells 31. Note that "uniform" here means that an error is allowed. Cell balance is performed, for example, when a predetermined period of time has elapsed during which the storage cells 31 are not being charged or discharged. The predetermined time is, for example, a time during which it is assumed that polarization occurring in the storage cell 31 due to charging and discharging can be eliminated.

Control device 90 performs cell balancing so that the voltage of each power storage cell 31 becomes the target voltage. The target voltage set in cell balance is the same for all power storage cells 31. As the target voltage, for example, among the voltages of each power storage cell 31, the voltage of the power storage cell 31 having the lowest voltage at the time before cell balancing is started is used. By controlling the switch 82, the control device 90 connects the storage cell 31 whose voltage is higher than the target voltage and the resistance element 81, and causes the storage cell 31 whose voltage is higher than the target voltage to discharge. Control device 90 finishes cell balancing when the voltages of all power storage cells 31 reach the target voltage. Note that "the voltage of the electricity storage cell 31 becomes the target voltage" does not only mean that the voltage of the electricity storage cell 31 and the target voltage match, but also that there is an error between the voltage of the electricity storage cell 31 and the target voltage. including aspects. By controlling the switch 82 so that cell balancing is performed in this manner, the control device 90 can be said to include a cell balance control unit 94 that performs cell balancing of the power storage cells 31.

The control device 90 repeatedly performs the following control at a predetermined control cycle. The following control is performed regardless of whether the cell stack 30 is being charged or discharged.
As shown in FIG. 3, in step S1, control device 90 determines whether the voltage of power storage cell 31 is higher than a predetermined overdischarge threshold. In this embodiment, the control device 90 determines whether the voltage of the electrical storage cell 31 with the lowest voltage among the plurality of electrical storage cells 31 is greater than the overdischarge threshold. There is a correlation between the remaining capacity of the electricity storage cell 31 and the voltage of the electricity storage cell 31, and the voltage of the electricity storage cell 31 becomes higher as the remaining capacity of the electricity storage cell 31 increases. Therefore, it can be determined from the voltage of the power storage cell 31 whether or not the power storage cell 31 is over-discharged. The overdischarge threshold is a threshold for determining whether or not the storage cell 31 is overdischarged. The overdischarge threshold is a preset fixed value. The overdischarge threshold may be the voltage at which the storage cell 31 is overdischarged, or may be a value obtained by adding a margin to the voltage at which the storage cell 31 is overdischarged. When the voltage of the power storage cell 31 is less than or equal to the overdischarge threshold, the power storage cell 31 is determined to be overdischarged. When the voltage of the power storage cell 31 is greater than the overdischarge threshold, it is determined that the power storage cell 31 is not overdischarged. If the determination result in step S1 is negative, the control device 90 performs the process in step S2. If the determination result in step S1 is affirmative, the control device 90 performs the process in step S3. By performing the process of step S1, it can be said that the control device 90 includes the determination section 95.

In step S2, the control device 90 prohibits the cell stack 30 from discharging. Control device 90 cuts off the connection between cell stack 30 and motor 110 by turning off relay switch 70 . If the power storage module 10 is mounted on the vehicle Ve as in this embodiment, it can be said that the control device 90 puts the vehicle Ve in a non-drivable state. By performing the process of step S2, it can be said that the control device 90 includes the overdischarge control section 96. By performing the processing in step S1 and step S2, when at least one of the plurality of power storage cells 31 becomes over-discharged, discharging of the cell stack 30 is prohibited.

When the control device 90 prohibits discharge of the cell stack 30, the control device 90 may notify the user to that effect. The user can be notified by any method. When it is assumed that a notification is to be sent to a user aboard the vehicle Ve, it is necessary to display a message on a display section installed in a position visible to the user, or to turn on or blink a lamp installed in a position visible to the user. You may report by doing so. The notification may be made using sound, such as a buzzer sound or a voice notification. In addition, when it is assumed that the user is to be notified even when the user is not on board the vehicle Ve, the control device 90 performs wireless communication using the communication device to detect information registered in the vehicle Ve. The notification may also be sent to a mobile communication terminal. For example, the control device 90 causes a device that performs control regarding telematics to perform wireless communication by sending a command.

In step S3, control device 90 determines whether the voltage of power storage cell 31 is smaller than the limit threshold. In this embodiment, the control device 90 determines whether the voltage of the electricity storage cell 31 with the lowest voltage is lower than the limit threshold. The limiting threshold is a threshold for limiting the discharge of the cell stack 30. In the power storage module 10, the discharge of the cell stack 30 is restricted when the voltage of the power storage cell 31 becomes less than the limit threshold so that the power storage cell 31 is not over-discharged when the power storage cell 31 is discharged. The limit threshold is a predetermined threshold that is larger than the overdischarge threshold. If the determination result in step S3 is affirmative, the control device 90 performs the process in step S4. If the determination result in step S3 is negative, the control device 90 ends the control.

In step S4, the control device 90 limits discharge. The discharge is limited so that the voltage of the storage cell 31 does not become over-discharged due to a voltage drop during discharge. Control device 90 limits the output power command value to a value smaller than the current value and larger than 0 according to the remaining capacity of power storage cell 31 . The output power command value is a command sent to vehicle ECU 120. Vehicle ECU 120 sets the duty ratio of inverter 100 so that power storage cell 31 is discharged according to the output power command value. Therefore, when the control device 90 sets the output power command value to a value smaller than the current value, the power supplied from the power storage cell 31 to the inverter 100 is limited. This suppresses the storage cell 31 from becoming over-discharged.

The control device 90 repeatedly performs the following discharge control at a predetermined control cycle. Discharge control will be explained in detail below.
As shown in FIG. 4, in step S11, the control device 90 determines whether power from the cell stack 30 is being supplied to the motor 110 as a device. If the power storage module 10 is mounted on the vehicle Ve as in this embodiment, it is sufficient to determine whether the vehicle Ve is in the key-off state or the key-on state in step S11. The key-off state is a state in which the vehicle Ve cannot travel, and the key-on state is a state in which the vehicle Ve is able to travel. When the vehicle Ve is in the key-off state, it can be said that the electric power of the cell stack 30 is not supplied to the motor 110. When the vehicle Ve is in the key-on state, it can be said that the electric power of the cell stack 30 is supplied to the motor 110. The key-off state and the key-on state can be switched by an operation by a passenger of the vehicle Ve. If the determination result in step S11 is affirmative, the control device 90 ends the discharge control. If the determination result in step S11 is negative, the control device 90 performs the process in step S12.

In step S12, control device 90 determines whether the voltage of power storage cell 31 is higher than a predetermined overdischarge threshold. That is, it is determined whether or not the storage cell 31 is not over-discharged. The determination in step S12 is the same process as the determination in step S1. If the determination result in step S12 is affirmative, the control device 90 performs the process in step S13. If the determination result in step S12 is negative, the control device 90 ends the discharge control.

In step S13, control device 90 determines whether the voltage of power storage cell 31 is smaller than the limit threshold. The determination in step S13 is the same process as the determination in step S3. If the determination result in step S13 is affirmative, the control device 90 performs the process in step S14. If the determination result in step S13 is negative, the control device 90 ends the discharge control.

In step S14, the control device 90 determines whether the electricity storage cell 31 with the lowest voltage is the first electricity storage cell 31a. If the determination result in step S14 is negative, the control device 90 performs the process in step S15. If the determination result in step S14 is affirmative, the control device 90 performs the process in step S16.

In step S15, the control device 90 determines whether the voltage difference between the first power storage cell 31a and the second power storage cell 31b having the lowest voltage is greater than or equal to a predetermined value. Since the determination in step S15 is performed when the electricity storage cell 31 with the lowest voltage is the second electricity storage cell 31b, in step S15, the voltage of the second electricity storage cell 31b with the lowest voltage is a predetermined value higher than the voltage of the first electricity storage cell 31a. It can be said that it is determined whether or not the value is lower than the value. If the determination result in step S15 is affirmative, the control device 90 ends the discharge control. If the determination result in step S15 is negative, the control device 90 performs the process in step S16.

In step S16, the control device 90 discharges the second power storage cell 31b, thereby lowering the voltage of the second power storage cell 31b to be discharged by a predetermined value than that of the first power storage cell 31a. In this embodiment, the second electricity storage cell 31b having the lowest voltage among the plurality of second electricity storage cells 31b is discharged.

The control device 90 controls the switch 82 to connect the second storage cell 31b to be discharged and the resistance element 81 to cause discharge to occur. The control device 90 performs discharging so that the voltage of the second power storage cell 31b to be discharged is lower than the voltage of the first power storage cell 31a by a predetermined value. Thereby, the voltage of one of the second power storage cells 31b becomes lower than the voltage of the first power storage cell 31a by a predetermined value. As the predetermined value, for example, when the voltage of the electricity storage cell 31 drops due to natural discharge after performing the process of step S16, the voltage of the second electricity storage cell 31b that has discharged becomes the voltage of the first electricity storage cell 31a. The overdischarge threshold is set to a value that reaches the overdischarge threshold earlier than the overdischarge threshold. The predetermined value may be, for example, 0.1 [V]. Note that this predetermined value and the predetermined value used for the determination in step S15 are the same value. By performing the process of step S16, it can be said that the control device 90 includes the voltage control section 97. By making the determinations in steps S11 to S13, it is determined that the power of the cell stack 30 is not being supplied to the motor 110 and the voltage of any of the storage cells 31 is higher than the overdischarge threshold and lower than the limit threshold. If it is smaller, the second storage cell 31b is discharged.

The operation of the first embodiment will be explained.
When the cell stack 30 is maintained in a non-charged/discharged state, the voltage of each storage cell 31 gradually decreases. In the case of the cell stack 30 mounted on the vehicle Ve, when the vehicle Ve is maintained in a key-off state or an uncharged state, the voltage of each power storage cell 31 gradually decreases. In the power storage module 10, by discharging the second power storage cell 31b, the voltage of the second power storage cell 31b can be made lower than the voltage of the first power storage cell 31a.

In this embodiment, when the voltage of any of the power storage cells 31 falls below the limiting threshold, it is determined whether or not to discharge the second power storage cell 31b. If there is a second electricity storage cell 31b whose voltage is lower than the voltage of the first electricity storage cell 31a by a predetermined value or more, the second electricity storage cell 31b is not discharged. If there is no second electricity storage cell 31b whose voltage is lower than the voltage of the first electricity storage cell 31a by a predetermined value or more, by discharging the second electricity storage cell 31b, the voltage of the second electricity storage cell 31b is changed to the first electricity storage cell 31b. The voltage is set to be a predetermined value lower than the voltage of the cell 31a. When the voltage of any of the electricity storage cells 31 falls below the limit threshold, the voltage of the second electricity storage cell 31b falls below the limit threshold, regardless of whether the electricity storage cell 31 that has fallen below the limit threshold is the first electricity storage cell 31a or the second electricity storage cell 31b. The voltage of the first storage cell 31a is set to be lower than the voltage of the first storage cell 31a by a predetermined value or more. In this state, as the voltage of each power storage cell 31 further decreases, the voltage of any of the power storage cells 31 becomes equal to or less than the overdischarge threshold, and discharging of the cell stack 30 is prohibited. Further, when discharging the cell stack 30 is prohibited, a notification can be given to the user. Assuming that the voltage of each storage cell 31 decreases in the same way by discharging the second storage cell 31b to make it lower than the voltage of the first storage cell 31a, the voltage of the second storage cell 31b that has been discharged is lower than that of the second storage cell 31b. reaches the overdischarge threshold before the first storage cell 31a.

The effects of the first embodiment will be explained.
(1-1) The control device 90 can discharge the second power storage cell 31b by controlling the cell balance circuit 80. The control device 90 discharges the second power storage cell 31b to make the voltage of the second power storage cell 31b lower than the voltage of the first power storage cell 31a. If the voltage of the first power storage cell 31a and the voltage of the second power storage cell 31b decrease in the same way, the voltage of the second power storage cell 31b reaches the overdischarge threshold earlier than the voltage of the first power storage cell 31a. Therefore, it is easy to determine that the second storage cell 31b is overdischarged before the first storage cell 31a becomes overdischarged, and discharging of the cell stack 30 is prohibited before the first storage cell 31a becomes overdischarged. be able to. Since the first electricity storage cell 31a is less likely to be overdischarged, elution of the negative electrode current collector 33a located at the outermost layer of the cell stack 30 is suppressed. Since the negative electrode current collector 33a of the second power storage cell 31b is provided overlapping the positive electrode current collector 32a of the adjacent power storage cell 31, the negative electrode current collector 33a of the second power storage cell 31b is eluted. Also, the electrolyte 36 is less likely to leak. On the other hand, since the positive electrode current collector 32a is not stacked on the negative electrode current collector 33a located at the outermost layer of the cell stack 30, the negative electrode current collector 33a is larger than the negative electrode current collector 33a of the second storage cell 31b. When body 33a is eluted, electrolytic solution 36 tends to leak to the outside of power storage module 10. Therefore, by suppressing elution of the negative electrode current collector 33a located at the outermost layer of the cell stack 30, leakage of the electrolytic solution 36 can be suppressed.

In particular, when the power storage module 10 is not provided with a housing for accommodating the electrolytic solution 36 like the power storage module 10 of this embodiment, if the electrolytic solution 36 leaks, the electrolytic solution 36 will be transferred to the power storage module 10. It is easy to reach the outside. Therefore, when the power storage module 10 is not provided with a casing for accommodating the electrolyte 36, compared to a case where the power storage module 10 is provided with a casing for accommodating the electrolyte 36, the cell stack 30 is It is required to suppress elution of the negative electrode current collector 33a located in the outer layer. As in the present embodiment, by suppressing the elution of the negative electrode current collector 33a located at the outermost layer of the cell stack 30 and suppressing the leakage of the electrolytic solution 36, there is no need for a casing for accommodating the electrolytic solution 36. Even in the case of the power storage module 10, it is possible to suppress the electrolytic solution 36 from reaching the outside of the power storage module 10.

Further, by notifying the user when discharging the cell stack 30 is prohibited, the user can be prompted to take measures such as replacing the power storage module 10. By notifying the user before the first storage cell 31a becomes over-discharged due to natural discharge, the user can be prompted to take measures before the electrolytic solution 36 leaks.

(1-2) When the voltage of the electricity storage cell 31 is smaller than the limit threshold, the control device 90 controls the second electricity storage cell so that the voltage of the second electricity storage cell 31b is lower than the voltage of the first electricity storage cell 31a. 31b is discharged. When the voltage of the second power storage cell 31b is lower than the voltage of the first power storage cell 31a, an imbalance occurs in the voltage between the power storage cells 31. By discharging the second electricity storage cell 31b when the voltage of the electricity storage cell 31 is lower than the limit threshold, the frequency of discharging is increased so that the voltage of the second electricity storage cell 31b becomes lower than the voltage of the first electricity storage cell 31a. can be lowered. For example, suppose that each time the cell balance of the power storage cell 31 is performed, discharge is performed so that the voltage of the second power storage cell 31b becomes lower than the voltage of the first power storage cell 31a. The frequency with which the voltage of the power storage cell 31 becomes lower than the limiting threshold tends to be lower than the frequency with which cell balancing is performed. For this reason, if discharge is performed so that the voltage of the second power storage cell 31b becomes lower than the voltage of the first power storage cell 31a every time cell balancing is performed, imbalance in the voltage between the power storage cells 31 will occur more frequently. . By discharging the second power storage cell 31b when the voltage of the power storage cell 31 is lower than the limit threshold, the voltage of the second power storage cell 31b becomes lower than the voltage of the first power storage cell 31a every time cell balancing is performed. Compared to the case where discharge is performed in this manner, it is possible to reduce the frequency at which imbalance occurs in the voltage between the electricity storage cells 31. In addition, since the limit threshold is a value higher than the overdischarge threshold, the voltage of the second storage cell 31b is made lower than the voltage of the first storage cell 31a before any of the storage cells 31 reaches overdischarge. be able to. Therefore, it is possible to suppress overdischarge of the first electricity storage cell 31a while suppressing the electricity storage cell 31 from becoming unbalanced.

(1-3) The storage cells 31 are sealed by the intercell sealing material 37. For this reason, leakage of the electrolytic solution 36 when the negative electrode current collector 33a included in the second power storage cell 31b is eluted is further suppressed. The inter-cell sealing material 37 suppresses leakage of the electrolytic solution 36 when the negative electrode current collector 33a of the second storage cell 31b is eluted, and the voltage of the second storage cell 31b is adjusted to the voltage of the first storage cell 31a. By making it lower, it is possible to suppress the elution of the outermost layer negative electrode current collector 33a. Thereby, even if any of the storage cells 31 becomes over-discharged, the electrolytic solution 36 is unlikely to leak.

(1-4) The cell balance circuit 80 is used as a discharge circuit for discharging the second storage cell 31b. Since the cell balance circuit 80 for performing cell balance of each power storage cell 31 can also be used as a discharge circuit, the number of parts can be reduced compared to the case where the cell balance circuit 80 and the discharge circuit are provided separately.

(Second embodiment)
A power storage module according to a second embodiment will be described. In the following description, description of members similar to those in the first embodiment will be omitted.

As shown in FIG. 5, the power storage module 10 of the second embodiment includes a charging circuit 60. In this embodiment, the charging circuit 60 is a discharging circuit.
The charging circuit 60 charges the first power storage cell 31a with the power discharged from the second power storage cell 31b. The charging circuit 60 of this embodiment is a chopper type DC/DC converter. Charging circuit 60 includes a transformer 61, a switching element 64, and a rectifying element 65. The transformer 61 includes a primary winding 62 and a secondary winding 63.

The primary winding 62 is connected to the cell stack 30 in parallel. Specifically, one end of the primary winding 62 is connected to the positive electrode of the power storage cell 31 having the outermost positive electrode current collector 32a, and the other end of the primary winding 62 is connected to the negative electrode of the first power storage cell 31a. connected.

The secondary winding 63 is connected in parallel to the first power storage cell 31a. Specifically, one end of the secondary winding 63 is electrically connected to the positive electrode of the first power storage cell 31a, and the other end of the secondary winding 63 is electrically connected to the negative electrode of the first power storage cell 31a.

The switching element 64 is connected in series to the primary winding 62. The switching element 64 is chopper-controlled by the control device 90. As the switching element 64, for example, a transistor can be used.

A diode can be used as the rectifying element 65. The anode of the diode is connected to the secondary winding 63, and the cathode of the diode is connected to the positive electrode of the first power storage cell 31a.

By subjecting the switching element 64 to chopper control, power is transmitted from the primary winding 62 to the secondary winding 63. The power transmitted to the secondary winding 63 is rectified by the rectifying element 65. Note that the charging circuit 60 may include a smoothing capacitor connected to both ends of the secondary winding 63.

The voltage generated across the secondary winding 63 is applied to the first power storage cell 31a. As a result, the second power storage cell 31b is discharged, and the first power storage cell 31a is charged by the power discharged from the second power storage cell 31b. Since the charging circuit 60 can charge only the first power storage cell 31a, it can be considered that the charging circuit 60 is provided only in the first power storage cell 31a.

In the second embodiment, when discharging the second power storage cell 31b in step S16, the charging circuit 60 is used to perform the discharge. The control device 90 controls the charging circuit 60 so that the voltage of one of the second power storage cells 31b is lower than the voltage of the first power storage cell 31a by a predetermined value.

The effects of the second embodiment will be explained. In the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment.
(2-1) The charging circuit 60 allows the second storage cell 31b to be discharged. Since the first power storage cell 31a can be charged using the power discharged by the second power storage cell 31b, the power of the second power storage cell 31b can be effectively utilized.

(2-2) The charging circuit 60 is provided only in the first storage cell 31a. Compared to the case where charging circuit 60 is provided so that all storage cells 31 can be charged, manufacturing cost can be reduced.

Each embodiment can be modified and implemented as follows. Each embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
In each embodiment, the cell balance circuit 80 may be an active type cell balance circuit. The circuit configuration of the active type cell balance circuit is arbitrary as long as some of the power storage cells 31 among the plurality of power storage cells 31 can be charged using the power of some of the power storage cells 31. An example of an active type cell balance circuit is one in which a selection circuit is added to the charging circuit 60 shown in FIG. 5. The selection circuit includes a plurality of switches, and the switches enable selection of the storage cell 31 to which both ends of the secondary winding 63 are connected. Thereby, any power storage cell 31 can be charged. Note that the active type cell balance circuit also functions as a charging circuit. Therefore, by using an active type cell balance circuit, it can be said that a charging circuit is provided for each power storage cell 31. The charging circuit 60 only needs to be provided at least in the first power storage cell 31a, and may or may not be provided in the second power storage cell 31b.

In the second embodiment, the power storage module 10 does not need to include the cell balance circuit 80.
In the second embodiment, the cell balance circuit 80 and the charging circuit 60 may be used together when discharging the second power storage cell 31b so that the voltage becomes lower than the voltage of the first power storage cell 31a. For example, after the charging circuit 60 charges the first power storage cell 31a using the power of the second power storage cell 31b, the cell balance circuit 80 performs cell balancing of the second power storage cell 31b, thereby further increasing the power of the second power storage cell 31b. Electric discharge may also be performed. In this case, the discharge circuit includes a charging circuit 60 and a cell balance circuit 80.

In each embodiment, the discharge circuit may have any circuit configuration as long as it can discharge the second power storage cell 31b. For example, of the resistive element 81 and switch 82, the resistive element 81 and switch 82 connected in parallel to the first electrical storage cell 31a may be omitted, and the discharge circuit may be configured such that the first electrical storage cell 31a cannot be discharged.

In each embodiment, the control device 90 only needs to be able to determine in step S1 whether or not there is an over-discharged storage cell 31 among the plurality of storage cells 31, and the control device 90 only needs to be able to determine whether or not an over-discharged storage cell 31 exists among the plurality of storage cells 31. It may also be determined whether or not there is overdischarge. For example, the control device 90 may determine whether or not all the storage cells 31 are over-discharged. In this case, the control device 90 performs the process of step S2 when at least one storage cell 31 is over-discharged, and performs the process of step S3 when there is no over-discharged storage cell 31. Similarly, the control device 90 only needs to be able to determine whether or not there is an over-discharged power storage cell 31 among the plurality of power storage cells 31 in step S12.

In each embodiment, the control device 90 may determine whether or not the storage cell 31 is over-discharged based on the SOC (State of Charge) of the storage cell 31 in at least one of step S1 and step S12. Examples of the SOC include charging rate [%] and remaining capacity [Ah]. In this case, the overdischarge threshold is set for SOC. The SOC of the power storage cell 31 can be derived from the correlation with the voltage of the power storage cell 31.

In each embodiment, the control device 90 may determine whether the SOC of the power storage cell 31 is smaller than the limit threshold in at least one of step S3 and step S13.
In the first embodiment, in step S16, a target voltage is set for each power storage cell 31, and the cell balance of each power storage cell 31 is performed so that each power storage cell 31 reaches the target voltage, thereby increasing the voltage of the second power storage cell 31b. Electric discharge may also be performed. The process performed in step S16 will be described in detail below.

As shown in FIG. 6, in step S21, the control device 90 sets a target voltage for each of the first power storage cell 31a and the second power storage cell 31b. If the target voltage set to the first electricity storage cell 31a is the first target voltage, and the target voltage set to the second electricity storage cell 31b is the second target voltage, the second target voltage is lower by a predetermined value than the first target voltage. . Note that the second target voltage is set for all second storage cells 31b. By performing the process of step S21, it can be said that the voltage control unit 97 includes a setting unit that sets the target voltage of the second power storage cell 31b to be lower by a predetermined value than the target voltage of the first power storage cell 31a.

Next, in step S22, control device 90 controls switch 82 so that the voltage of each storage cell 31 becomes the target voltage. Cell balancing is performed so that the voltage of all the second power storage cells 31b becomes the second target voltage and the voltage of the first power storage cell 31a becomes the first target voltage. Thereby, the second power storage cell 31b is discharged such that the voltage of the second power storage cell 31b becomes lower than the voltage of the first power storage cell 31a. By performing the process of step S22, it can be said that the voltage control unit 97 includes a target voltage control unit that controls the voltage of the storage cell 31 to reach the target voltage.

By discharging the second electricity storage cell 31b as described above, while discharging the second electricity storage cell 31b so that the voltage of the second electricity storage cell 31b becomes lower than the voltage of the first electricity storage cell 31a, Cell balance between 31 and 31 cells can be performed. Although a predetermined difference occurs between the voltage of the first power storage cell 31a and the voltage of the second power storage cell 31b, the voltage difference between the second power storage cells 31b can be made smaller than in the case where the above cell balancing is not performed. I can do it. It can be said that the control device 90 performs two types of cell balancing: a cell balance performed by the cell balance control unit 94, and a cell balance for making the voltage of the second power storage cell 31b lower than the voltage of the first power storage cell 31a.

Further, when the cell balance by the cell balance control unit 94 is replaced with the cell balance described above and the cell balance by the cell balance control unit 94 is performed, the first target voltage is applied to the first power storage cell 31a, and the first target voltage is applied to the second power storage cell. A second target voltage may be set in each of the voltages 31b.

In the first embodiment, in step S16, it is sufficient that the voltage of at least one second power storage cell 31b can be made lower than the voltage of the first power storage cell 31a, and the second power storage cell 31b to be discharged is arbitrary. For example, by discharging the second electricity storage cell 31b with the highest voltage among the second electricity storage cells 31b, the voltage of the second electricity storage cell 31b may be lowered by a predetermined value than the voltage of the first electricity storage cell 31a.

In the first embodiment, the plurality of second storage cells 31b may be discharged in step S16. For example, the second power storage cells 31b may be discharged such that the voltage of the two second power storage cells 31b is lower than the voltage of the first power storage cell 31a by a predetermined value, or the voltage of all the second power storage cells 31b may be lowered by a predetermined value. The second power storage cell 31b may be discharged so that the voltage becomes a predetermined value lower than the voltage of the first power storage cell 31a.

In each embodiment, the timing of discharging the second power storage cell 31b is arbitrary so that the voltage of the second power storage cell 31b is lower than the voltage of the first power storage cell 31a. For example, the second storage cell 31b may be discharged when the cell stack 30 is not charged or discharged for a predetermined period of time or more, or the second storage cell 31b may be discharged when the key of the vehicle Ve is turned off. Two storage cells 31b may be discharged. In these cases, it can be said that the second power storage cell 31b is discharged when power from the cell stack 30 is not being supplied to the device. Further, a predetermined threshold value that is larger than the limit threshold value and smaller than the full charge voltage, or a predetermined threshold value that is larger than the overdischarge threshold value and smaller than the control threshold value is set, and the voltage of any of the storage cells 31 is set to this predetermined threshold value. The second storage cell 31b may be discharged when the voltage falls below a threshold value. The full charge voltage is the voltage when the storage cell 31 is fully charged. By setting the predetermined threshold to a value larger than the overdischarge threshold, the voltage of the second storage cell 31b can be made lower than the voltage of the first storage cell 31a before any of the storage cells 31 reaches overdischarge. can. Moreover, the smaller the predetermined threshold value is set, the lower the frequency at which imbalance occurs in the voltage between the storage cells 31 can be reduced.

- In each embodiment, the number of first power storage cells 31a is not limited to one. For example, two or more first power storage cells 31a may be provided, such as a cell stack 30 in which two cell stacks 30 are stacked such that the outermost layer positive electrodes 32 face each other.

In each embodiment, the power storage module 10 does not need to include the inter-cell sealing material 37.
In each embodiment, the inter-cell sealing material 37 may be integrated with the sealing material 35 or may be separate.

In each embodiment, the acquisition section 93, the cell balance control section 94, the determination section 95, the overdischarge control section 96, and the voltage control section 97 may each be configured as separate devices.
In each embodiment, the device supplied with power from the power storage module 10 may be any device as long as it is driven by electric power. As long as it is a vehicle Ve, it may be an electrical component such as an auxiliary machine.

In each embodiment, the power storage module 10 may be mounted on a device other than the vehicle Ve.

DESCRIPTION OF SYMBOLS 10... Electricity storage module, 30... Cell stack, 31... Lithium ion electricity storage cell, 31a... First electricity storage cell, 31b... Second electricity storage cell, 32... Positive electrode, 33... Negative electrode, 33a... Negative electrode current collector, 33b... Negative electrode active Substance layer, 35... Sealing material, 36... Electrolyte, 37... Inter-cell sealing material, 60... Charging circuit as a discharge circuit, 80... Cell balance circuit as a discharge circuit, 95... Judgment unit, 96... Overdischarge Control unit, 97... Voltage control unit, 110... Motor as a device.

Claims (10)

A cell stack consisting of multiple lithium ion storage cells,
a determination unit configured to determine whether the lithium ion storage cell is over-discharged;
an overdischarge control section configured to prohibit discharging of the cell stack when the determination section determines that any one of the lithium ion storage cells is overdischarged; ,
Each of the lithium ion storage cells includes a positive electrode, a negative electrode, an electrolytic solution, and a sealing material that seals the electrolytic solution between the positive electrode and the negative electrode,
The negative electrode includes a negative electrode current collector made of copper, and a negative electrode active material layer provided on the negative electrode current collector,
The lithium ion storage cell includes a first storage cell including the negative electrode current collector located at the outermost layer of the cell stack, and a second storage cell other than the first storage cell,
The electricity storage module is
a discharge circuit that discharges the second storage cell;
a voltage control unit configured to make the voltage of the second storage cell lower than the voltage of the first storage cell by causing the discharge circuit to discharge at least one of the second storage cells; Equipped with an electricity storage module. The voltage control unit lowers the voltage of the second storage cell than the first storage cell when the determination unit determines that the lithium ion storage cell is not over-discharged. Energy storage module. The determination unit determines that the lithium ion storage cell is overdischarged when the voltage of the lithium ion storage cell is equal to or lower than a predetermined overdischarge threshold;
The voltage control unit is configured to control the voltage of the second storage cell when the voltage of any of the lithium ion storage cells is higher than the overdischarge threshold and lower than a predetermined threshold larger than the overdischarge threshold. The electricity storage module according to claim 1 or 2, wherein the voltage is lower than that of one electricity storage cell. The electricity storage module according to claim 3, wherein the predetermined threshold is a limiting threshold at which discharge of the cell stack is limited. Any one of claims 1 to 4, wherein the voltage control unit makes the voltage of the second storage cell lower than the voltage of the first storage cell when power from the cell stack is not being supplied to a device. The energy storage module described in section. The power storage module includes a charging circuit provided in the first power storage cell,
The power storage module according to any one of claims 1 to 5, wherein the charging circuit charges the first power storage cell with the power discharged from the second power storage cell. The power storage module according to claim 6, wherein the charging circuit is provided only in the first power storage cell. The power storage module according to any one of claims 1 to 7, wherein the discharge circuit is a cell balance circuit that performs cell balance of the lithium ion power storage cell. The voltage control unit sets a target voltage for the lithium ion storage cell, and performs cell balancing of the lithium ion storage cell so that the lithium ion storage cell reaches the target voltage,
The power storage module according to claim 8, wherein the target voltage set to the second power storage cell is lower by a predetermined value than the target voltage set to the first power storage cell. The power storage module according to any one of claims 1 to 9, further comprising an inter-cell sealing material that seals between the lithium ion power storage cells.