JP2022060891A - Power storage module - Google Patents

Abstract

[Problem] To suppress leakage of electrolyte. [Solution] An electricity storage module includes a cell stack 30 in which a plurality of lithium ion electricity storage cells 31 are stacked, and a control device. Each of the lithium ion electricity storage cells 31 includes a positive electrode 32, a negative electrode 33, an electrolyte 36, and a sealing material 35. The negative electrode 33 includes a copper negative electrode current collector 33a, and a negative electrode active material layer 33b provided on the negative electrode current collector 33a. The plurality of lithium ion electricity storage cells 31 include a first electricity storage cell 31a including a negative electrode current collector 33a located in the outermost layer of the cell stack 30, and a second electricity storage cell 31b other than the first electricity storage cell 31a. A first overdischarge threshold set for the first electricity storage cell 31a is higher than a second overdischarge threshold set for the second electricity storage cell 31b. [Selected Figure] FIG. 2

Description

The present invention relates to a power storage module.

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

Japanese Unexamined Patent Publication No. 2020-27694

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 the charge carriers stored in the negative electrode active material layer. In particular, when a copper negative electrode current collector is used, when the lithium ion storage cell is discharged in a state where the charge carriers of the negative electrode active material layer are deficient, that is, in an over-discharged state, the copper in the negative electrode current collector is ionized. Elute in the electrolyte. When the negative electrode current collector located in the outermost layer of the cell stack elutes, the electrolytic solution may leak to the outside of the power storage module.

The power storage module that solves the above problems is a cell stack in which a plurality of lithium ion power storage cells are stacked, and the lithium ion power storage cell is overdischarged when the voltage of the lithium ion power storage cell is lower than a predetermined overdischarge threshold. Over-discharge control configured to prohibit discharge of the cell stack when the determination unit determines that any one of the determination unit configured to determine and the lithium ion storage cell is over-discharged. A storage module including a unit, wherein the lithium ion storage cell has a positive electrode, a negative electrode, an electrolytic solution, and a sealing material for sealing the electrolytic solution between the positive electrode and the negative electrode, respectively. The negative electrode comprises a copper negative electrode current collector and a negative electrode active material layer provided in the negative electrode current collector, and the plurality of lithium ion storage cells are located in the outermost layer of the cell stack. The over-discharge threshold includes a first storage cell including the negative electrode current collector and a second storage cell other than the first storage cell, and the over-discharge threshold is a first over-discharge threshold set in the first storage cell. And the second over-discharge threshold set in the second storage cell, the first over-discharge threshold is higher than the second over-discharge threshold.

According to this, since the over-discharge threshold value of the first storage cell is higher than the over-discharge threshold value of the second storage cell, the first storage cell is regarded as over-discharged before the determination unit determines that the second storage cell is over-discharged. Easy to judge. When the first storage cell is determined to be over-discharged, the over-discharge control unit prohibits the discharge of the cell stack. By prohibiting the discharge of the cell stack, the discharge of the first storage cell in the state determined to be over-discharge is suppressed. Therefore, the elution of the negative electrode current collector located in the outermost layer of the cell stack is suppressed. Therefore, it is possible to suppress leakage of the electrolytic solution.

The power storage module includes a limit control unit configured to limit the discharge of the cell stack when the voltage of any one of the lithium ion power storage cells is lower than a predetermined limit threshold, and the limit threshold is the limit. The first limiting threshold includes a first limiting threshold set in the first storage cell and a second limiting threshold set in the second storage cell, and the first limiting threshold is higher than the first overdischarge threshold. Moreover, the second limiting threshold value may be higher than the second overdischarge threshold value, and the first limiting threshold value may be higher than the second limiting threshold value.

Regarding the storage module, the over-discharge control unit includes a second storage cell control unit that prohibits charging and discharging of the cell stack when the determination unit determines that the second storage cell is over-discharged. When the determination unit determines that the first storage cell is over-discharged, the cell stack may be provided with a first storage cell control unit that prohibits the discharge of the cell stack and allows the cell stack to be charged.

The power storage module may be provided with an inter-cell sealing material that seals between the plurality of lithium ion storage cells.

According to the present invention, it is possible to suppress leakage of the electrolytic solution.

A circuit diagram as an example to which a power storage module is applied. Cross-sectional view of the assembled battery. A flowchart showing the control performed by the control device.

Hereinafter, an embodiment of the power storage module will be described with reference to FIGS. 1 to 3. The power storage module of the present embodiment is used in a vehicle such as an electric vehicle or a hybrid vehicle, for example.
As shown in FIG. 1, the 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 a power source for supplying power to the motor 110 in the vehicle. The inverter 100 includes a switching element 101. The inverter 100 converts the DC power from the power storage module 10 into AC power by switching the switching element 101 at a predetermined duty ratio. The motor 110 drives the vehicle Ve using the electric power output from the inverter 100. The vehicle ECU 120 controls the discharge of the power storage module 10 and the like. The vehicle ECU 120 controls the input power to the inverter 100, that is, the discharge of the power storage module 10 by controlling the duty ratio of the inverter 100.

Hereinafter, the details of the power storage module 10 will be described.
As shown in FIGS. 1 and 2, the power storage module 10 includes an assembled battery 20, a positive electrode energizing plate 40, a negative electrode energizing plate 50, a relay switch 70, a cell balance circuit 80, a voltage sensor 85, and a control device. 90 and. The power storage module 10 discharges to the inverter 100.

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

Each lithium ion storage cell 31 includes a positive electrode 32, a negative electrode 33, a separator 34, a sealing material 35, and an electrolytic solution 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 inert conduction band. The positive electrode current collector 32a is, for example, an 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.

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

The positive electrode active material layer 32b contains a positive electrode active material that can occlude and release charge carriers such as lithium ions. As the positive electrode active material, a material that can be used as a positive electrode active material for a lithium ion secondary battery, such as a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, and a polyanionic compound, may be adopted. Further, two or more kinds of positive electrode active materials may be used in combination.

The negative electrode 33 includes a copper negative electrode current collector 33a 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 in the central portion of the first surface 33c of the negative electrode current collector 33a in a plan view. The peripheral edge of the first surface 33c of the negative electrode current collector 33a in a plan view is a negative electrode uncoated portion 33e in which the negative electrode active material layer 33b is not provided. The negative electrode uncoated portion 33e is arranged so as to surround the periphery of the negative electrode active material layer 33b in a 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 simple substance, an alloy, or a compound capable of occluding and releasing a charge carrier such as lithium ion. For example, examples of the negative electrode active material include lithium, carbon, a metal compound, and an element or a compound thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easy 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 so as 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 so as to face the positive electrode active material layer 32b. In a plan view, the entire forming region of the positive electrode active material layer 32b is located in the forming region of the negative electrode active material layer 33b.

The separator 34 is a member through which lithium ions pass. The separator 34 is arranged between the positive electrode active material layer 32b and the negative electrode active material layer 33b. As a result, 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 a non-woven fabric containing a polymer that absorbs and retains a liquid electrolyte. Examples of the material constituting the separator 34 include polypropylene, polyethylene, polyolefin, polyester and the like. The separator 34 may have a single-layer structure or a multi-layer structure. The multilayer structure may have, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

The sealing material 35 maintains a 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 arranged 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 closed space S surrounded by a frame-shaped sealing material 35, a positive electrode 32, and a negative electrode 33 is formed between the positive electrode 32 and the negative electrode 33.
The separator 34 and the electrolytic solution 36 are housed in the closed space S. 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. Examples of the electrolytic solution 36 include a liquid electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The peripheral portion of the separator 34 is in a state of being buried in the sealing material 35.

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

In the cell stack 30, a plurality of lithium ion storage cells 31 have a second surface 32d of a positive electrode current collector 32a of one adjacent lithium ion storage cell 31 and a negative electrode current collector of the other adjacent lithium ion storage cell 31. It has a structure in which the second surface 33d of 33a is overlapped so as to be in contact with the second surface 33d. As a result, a plurality of lithium ion storage cells 31 constituting the cell stack 30 are connected in series.

The cell stack 30 includes a bipolar electrode 38. Here, in the cell stack 30, by stacking two lithium ion storage cells 31 adjacent to each other in the stacking direction, the positive electrode current collector 32a and the negative electrode current collector 33a in contact with each other are regarded as one current collector. 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 superposed, a positive electrode active material layer 32b formed on one surface of the current collector, and the positive electrode active material layer 32b. It includes a negative electrode active material layer 33b formed on the other side surface. The bipolar electrode 38 may be formed by 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 cell-to-cell sealing material 37 is provided so as to surround the entire circumference of the cell stack 30 from a direction perpendicular to the stacking direction. As a result, the inter-cell sealing material 37 covers the outer periphery of the current collector. By covering the outer periphery of the current collector with the cell-to-cell encapsulant 37, the positive electrode of the adjacent lithium ion storage cell 31 is the second surface 32d of the current collector 32a, and the negative electrode of the other adjacent lithium ion storage cell 31. The space between the current collector 33a and the second surface 33d is sealed by the cell-to-cell sealing material 37. Therefore, the cell-to-cell sealing material 37 seals between the plurality of lithium ion storage cells 31.

In the cell stack 30 stacked in this way, the positive electrode current collector 32a is arranged at the first end of the cell stack 30 in the stacking direction. The positive electrode current collector 32a is located on the outermost layer of the cell stack 30 in the stacking direction. Further, the 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 on 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 in the outermost layer of the cell stack 30. The positive electrode current-carrying plate 40 is made of a metal conductor, for example, is made of a metal of the same material as the positive electrode current collector 32a, and is formed smaller than the positive electrode current collector 32a in a plan view. The positive electrode energizing 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 on the outermost layer of the cell stack 30 is a power extraction surface 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 in the outermost layer of the cell stack 30. The negative electrode current-carrying plate 50 is made of a metal conductor, for example, is made of a metal of the same material as the negative electrode current collector 33a, and is formed smaller than the negative electrode current collector 33a in a plan view. The negative electrode energizing 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 on the outermost layer of the cell stack 30 is a power extraction surface to the outside of the cell stack 30.

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

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

In the present embodiment, the sealing material 35 seals the electrolytic solution 36 between the positive electrode 32 and the negative electrode 33 of each lithium ion storage cell 31, and the housing for sealing the electrolytic solution 36 is a cell stack. Since it is not separately provided outside the cell stack 30, the elution of the negative electrode current collector 33a located in the outermost layer of the cell stack 30 may cause the electrolytic solution 36 to leak to the outside of the power storage module 10.

On the other hand, the negative electrode current collector 33a of the second storage cell 31b is laminated on another adjacent lithium ion storage cell 31. As a result, the negative electrode current collector 33a of the second storage cell 31b is covered with the positive electrode current collector 32a of another adjacent lithium ion storage cell 31. Therefore, even when the negative electrode current collector 33a of the second storage cell 31b elutes, leakage of the electrolytic solution to the outside of the storage module 10 is unlikely to occur.

The negative electrode current collector 33a located in the outermost layer of the cell stack 30 is in contact with and covered with the negative electrode current collecting plate 50, but when the negative electrode current collector 33a located in the outermost layer is eluted, the negative electrode is energized. The electrolytic solution 36 tends to leak to the outside of the power storage module 10 through the plate 50. In particular, when the negative electrode current collector plate 50 is made of copper like the negative electrode current collector 33a, when the negative electrode current collector 33a located in the outermost layer elutes, the negative electrode current collector plate 50 may also elute, and the power storage module 10 Leakage of the electrolytic solution 36 to the outside is more likely to occur. Further, when the negative electrode current collector plate 50 is formed smaller than the negative electrode current collector 33a in a plan view, the negative electrode current collector 33a located in the outermost layer may not be covered by the negative electrode current collector plate 50. Leakage of the electrolytic solution 36 to the outside of 10 is more likely to occur.

As shown in FIG. 1, the relay switch 70 is a switch for prohibiting charging or discharging of the power storage module 10. The relay switch 70 is connected in series with the assembled battery 20.

The cell balance circuit 80 includes a plurality of series connectors in which the cell balance resistor 81 and the switch 82 are connected in series. The series connection body is connected in parallel to each lithium ion storage cell 31. When the switch 82 is on, the lithium ion storage cell 31 and the cell balance resistor 81 are connected, and a current flows from the lithium ion storage cell 31 to the cell balance resistor 81. As a result, the lithium ion storage cell 31 is discharged. Then, the cell balance circuit 80 performs cell balance to equalize the remaining amount of the lithium ion storage cell 31 to be discharged to the remaining amount of the target lithium ion storage cell 31. The target remaining amount can be set to, for example, the lowest remaining amount among the remaining amount of each of the plurality of lithium ion storage cells 31. The cell balance circuit 80 of the present embodiment performs passive cell balance.

The voltage sensor 85 is a sensor for detecting the voltage of each lithium ion storage cell 31. The voltage sensor 85 is connected in parallel to each lithium ion storage cell 31.
The control device 90 includes a processor and a storage unit. As the processor, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor) is used. The storage unit includes RAM (Random access memory) and ROM (Read Only Memory). The storage unit stores a program code or a command configured to cause a processor to execute a process. The storage unit, i.e., a computer-readable medium, includes any available medium accessible by a general purpose or dedicated 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 operating according to a computer program, one or more hardware circuits such as ASICs and FPGAs, or a combination thereof.

The control device 90 controls the relay switch 70 and the switch 82. The control device 90 prohibits charging or discharging of the cell stack 30 by controlling the relay switch 70. Further, the control device 90 controls the switch 82 to perform cell balance for each lithium ion storage cell 31. The control device 90 can acquire the detection result of the voltage sensor 85. Further, the control device 90 sends a limit command to the vehicle ECU 120 so as to limit the duty ratio of the inverter 100 according to the remaining amount of the cell stack 30. Upon receiving the restriction command, the vehicle ECU 120 controls the switching element 101 to lower the duty ratio of the inverter 100 so that the input power of the inverter 100 is larger than 0 and smaller than the current input power. As a result, the control device 90 limits the input power of the inverter 100, that is, the output power of the cell stack 30. Therefore, it is possible to prevent the cell stack 30 from becoming over-discharged.

In the following description, the voltage of each lithium ion storage cell 31 may be collectively referred to as "voltage Vi". Among the voltages Vi, in particular, when the voltage of the first storage cell 31a is represented, it may be referred to as "voltage V1", and when the voltage of each second storage cell 31b is collectively referred to, it may be referred to as "voltage V2".

The control device 90 stores the first over-discharge threshold value Va, the second over-discharge threshold value Vb, the first limit threshold value Vc, and the second limit limit threshold value Vd in the storage unit. The first over-discharge threshold value Va is a value used when determining whether or not the first storage cell 31a is over-discharged. The second over-discharge threshold value Vb is a value used when determining whether or not the second storage cell 31b is over-discharged. The first over-discharge threshold value Va set in the first storage cell 31a is higher than the second over-discharge threshold value Vb set in the second storage cell 31b. The difference between the first over-discharge threshold value Va and the second over-discharge threshold value Vb is arbitrary, but is higher than, for example, the measurement error of the voltage sensor 85. As the second overdischarge threshold value Vb, for example, a voltage value higher than that in the overdischarge state in which the lithium ion storage cell 31 actually causes elution of the negative electrode current collector 33a is set.

When the voltage Vi of any of the lithium ion storage cells 31 falls below the set over-discharge threshold, the control device 90 determines that the lithium-ion storage cell 31 is over-discharged, and turns off the relay switch 70. Discharge of the cell stack 30 is prohibited. However, when the lithium ion storage cell 31 determined to be over-discharged continues to be discharged due to natural discharge or the like, the lithium ion storage cell 31 is in an over-discharged state in which elution of the negative electrode current collector 33a occurs.

On the other hand, the first over-discharge threshold value Va is set higher than the second over-discharge threshold value Vb. Therefore, when the voltage V1 of the first storage cell is the first over-discharge threshold value Va, the remaining amount of the first storage cell 31a is larger than the remaining amount when the over-discharged state is reached. Therefore, when the control device 90 determines that the first storage cell 31a is over-discharged and prohibits the discharge of the cell stack 30, the first storage cell 31a is over-discharged so that the negative electrode current collector 33a actually elutes. It is possible to extend the period until the condition is reached.

The first limit threshold value Vc and the second limit threshold value Vd are values used when determining whether or not to limit the discharge of the cell stack 30. The first limit threshold value Vc is set for the first storage cell 31a. The second limit threshold value Vd is set for the second storage cell 31b. Both the first limiting threshold value Vc and the second limiting threshold value Vd are higher than the second overdischarge threshold value Vb. The first limiting threshold value Vc is higher than the second limiting threshold value Vd and the first overdischarge threshold value Va. Therefore, the first limit threshold Vc is higher than the first overdischarge threshold Va, and the second limit threshold Vd is higher than the second overdischarge threshold Vb. The difference between the first limit threshold value Vc and the second limit threshold value Vd is, for example, larger than the measurement error of the voltage sensor 85.

Hereinafter, the control performed by the control device 90 will be described with reference to FIGS. 1 and 3. As shown in FIGS. 1 and 3, in step S10, the control device 90 acquires information indicating the detection result detected by the voltage sensor 85.

Next, in step S11, the control device 90 calculates the minimum voltage Vmin among the voltages V2 of all the second storage cells 31b. In the following description, the minimum voltage Vmin among the voltages V2 of all the second storage cells 31b may be simply referred to as "minimum voltage Vmin".

Next, in step S12, the control device 90 determines whether or not the minimum voltage Vmin is lower than the second overdischarge threshold value Vb set in the second storage cell. When the minimum voltage Vmin is lower than the second over-discharge threshold value Vb, the control device 90 determines that the second storage cell 31b is over-discharged. When the minimum voltage Vmin is equal to or higher than the second overdischarge threshold value Vb, the control device 90 determines that the second storage cell 31b is not overdischarged.

When the control device 90 determines that the second storage cell 31b is over-discharged, the control device 90 proceeds to step S13 and turns off the relay switch 70 to prohibit charging and discharging of the cell stack 30.

When the control device 90 determines that the second storage cell 31b is not over-discharged, the control device 90 proceeds to step S14, and the voltage V1 of the first storage cell 31a is set to the first storage cell 31a. It is determined whether or not the discharge threshold value is lower than Va. When the voltage V1 of the first storage cell 31a is lower than the first over-discharge threshold value Va, the control device 90 determines that the first storage cell 31a is over-discharged. When the voltage V1 of the first storage cell 31a is equal to or higher than the first overdischarge threshold value Va, the control device 90 determines that the first storage cell 31a is not overdischarged. Therefore, the control device 90 determines that the lithium ion storage cell 31 is overdischarged when the voltage Vi for each lithium ion storage cell 31 is lower than the overdischarge thresholds Va and Vb set for each lithium ion storage cell 31. A determination unit 91 configured to do so is included. Further, the over-discharge threshold value includes a first over-discharge threshold value Va set in the first storage cell 31a and a second over-discharge threshold value Vb set in the second storage cell 31b. Further, the control device 90 includes a second storage cell control unit 93 that prohibits charging and discharging of the cell stack 30 when the determination unit 91 determines that the second storage cell 31b is over-discharged.

When the control device 90 determines that the first storage cell 31a is over-discharged, the control device 90 proceeds to step S15 and turns off the relay switch 70 to prohibit the discharge of the cell stack 30 and the cell stack. Charging of the cell stack 30 is allowed by turning on the relay switch 70 when the 30 is connected to the charging device. Therefore, the control device 90 prohibits the discharge of the cell stack 30 and allows the cell stack 30 to be charged when the determination unit 91 determines that the first storage cell 31a is over-discharged. including.

Further, as a result, the control device 90 prohibits the discharge of the cell stack 30 when it is determined that any one of the first storage cell 31a and the second storage cell 31b is over-discharged. Therefore, the control device 90 includes an over-discharge control unit 94 configured to prohibit the discharge of the cell stack 30 when the determination unit 91 determines that any one of the lithium ion storage cells 31 is over-discharged. ..

When the control device 90 determines that the first storage cell 31a is not over-discharged, the control device 90 proceeds to step S16, and whether or not the voltage V1 of the first storage cell 31a is lower than the first limit threshold value Vc, and It is determined whether or not the minimum voltage Vmin is lower than the second limit threshold value Vd.

When the voltage V1 of the first storage cell 31a is lower than the first limit threshold value Vc or the minimum voltage Vmin is lower than the second limit threshold value Vd, the control device 90 proceeds to step S17 and limits the discharge of the cell stack 30. .. Therefore, the control device 90 includes a limiting control unit 95 configured to limit the discharge of the cell stack 30 when the voltage Vi of any one of the lithium ion storage cells 31 is lower than the predetermined limiting thresholds Vc and Vd. The limiting thresholds Vc and Vd include a first limiting threshold Vc set in the first storage cell 31a and a second limiting threshold Vd set in the second storage cell 31b.

When the voltage V1 of the first storage cell 31a is equal to or higher than the first limiting threshold value Vc and the minimum voltage Vmin is equal to or higher than the second limiting threshold value Vd, the control device 90 proceeds to step S18 to discharge the cell stack 30. Do not limit.

The operation of this embodiment will be described.
As the cell stack 30 is discharged, the voltage Vi of the lithium ion storage cell 31 decreases. The decrease in the voltage Vi of each lithium ion storage cell 31 depends on the degree of deterioration of each lithium ion storage cell 31. However, when the control device 90 controls the switch 82, the cell balance circuit 80 performs cell balance for each lithium ion storage cell 31. As a result, the voltages Vi of each lithium ion storage cell 31 match each other within an error range.

When the voltage V1 of the first storage cell 31a is lower than the first over-discharge threshold Va, or when the minimum voltage Vmin of the second storage cell 31b is lower than the second over-discharge threshold Vb, the control device 90 performs lithium ion storage. It is determined that the cell 31 is over-discharged, and the cell stack 30 is prohibited from being discharged.

If the voltage of the first storage cell 31a is the lowest and the first over-discharge threshold Va is equal to the second over-discharge threshold Vb, the discharge of the cell stack 30 (first storage cell 31a) is the first storage cell. It is prohibited when the voltage V1 of 31a becomes lower than the first overdischarge threshold Va, which is equal to the second overdischarge threshold Vb. In this case, if the first storage cell 31a continues to be discharged due to natural discharge or the like, the first storage cell 31a tends to be in an over-discharged state in which elution of the negative electrode current collector 33a occurs. Since the negative electrode current collector 33a of the first storage cell 31a is located in the outermost layer of the cell stack 30, the elution of the negative electrode current collector 33a may cause the electrolytic solution 36 to leak.

On the other hand, in the present embodiment, the first over-discharge threshold value Va is higher than the second over-discharge threshold value Vb. Therefore, before the first storage cell 31a reaches an over-discharged state in which the negative electrode current collector 33a actually elutes, the cell stack 30 (first storage cell 31a) is prohibited from being discharged with a margin. Therefore, it is possible to prevent the first storage cell 31a from reaching an over-discharged state. Therefore, the elution of the negative electrode current collector 33a of the first storage cell 31a is suppressed. Along with this, leakage of the electrolytic solution 36 due to elution of the negative electrode current collector 33a is suppressed.

Hereinafter, the effects of this embodiment will be described.
(1) When the voltage V1 of the first storage cell 31a is lower than the second overdischarge threshold value Vb, the first storage cell 31a is determined to be overdischarged. However, in the present embodiment, the over-discharge threshold value Va set in the first storage cell 31a is higher than the over-discharge threshold value Vb set in the second storage cell 31b. As a result, it is easy to determine that the first storage cell 31a is over-discharged before the control device 90 determines that the second storage cell 31b is over-discharged. When the first storage cell 31a is determined to be over-discharged, the control device 90 prohibits the discharge of the cell stack 30. By prohibiting the discharge of the cell stack 30, the discharge of the first storage cell 31a in the state determined to be over-discharge is suppressed. Therefore, the elution of the negative electrode current collector 33a located in the outermost layer of the cell stack 30 is suppressed. Therefore, it is possible to suppress the leakage of the electrolytic solution 36.

In particular, when the storage module 10 does not have a housing for accommodating the electrolytic solution 36 as in the storage module 10 of the present embodiment, if the electrolytic solution 36 leaks, the electrolytic solution 36 becomes the storage module 10. There is a risk of leakage to the outside of the module. Therefore, when the power storage module 10 does not have a housing for accommodating the electrolytic solution 36, the negative electrode collection located in the outermost layer of the cell stack 30 is compared with the case where the power storage module 10 includes the electrolytic solution 36. It is required to suppress the elution of the electric body 33a. By suppressing the elution of the negative electrode current collector 33a located in the outermost layer of the cell stack 30 and the leakage of the electrolytic solution 36 due to this, even if the power storage module 10 does not have a housing for accommodating the electrolytic solution 36, It is possible to prevent the electrolytic solution 36 from leaking to the outside of the power storage module 10.

(2) The first limiting threshold value Vc set in the first storage cell 31a is higher than the second limiting threshold value Vd set in the second storage cell 31b. As a result, the control device 90 determines that the voltage V2 of the second storage cell 31b is lower than the second limiting threshold value Vd, and the voltage V1 of the first storage cell 31a is lower than the first limiting threshold value Vc. Is determined. When the control device 90 determines that the voltage V1 of the first storage cell 31a is lower than the first limiting threshold value Vc, the control device 90 limits the discharge of the cell stack 30. Therefore, when the voltage sensor 85 measures the voltage V1 of the first storage cell 31a, the voltage drop due to the internal resistance of the first storage cell 31a is reduced. Then, when the voltage V1 of the first storage cell 31a approaches the first over-discharge threshold value Va, the voltage sensor 85 can measure the voltage V1 of the first storage cell 31a with higher accuracy. Therefore, the control device 90 can determine with higher accuracy whether or not the first storage cell 31a is over-discharged. Therefore, the elution of the negative electrode current collector 33a located in the outermost layer of the cell stack 30 is suppressed. Therefore, the leakage of the electrolytic solution 36 can be further suppressed.

(3) The control device 90 prohibits charging and discharging of the cell stack 30 when it is determined that the second storage cell 31b is over-discharged. As a result, it is possible to prevent the second storage cell 31b from being over-discharged due to the discharge and causing the negative electrode current collector 33a of the second storage cell 31b to elute. Further, it is possible to prevent the charging of the second storage cell 31b in the over-discharged state from causing the reprecipitation of the negative electrode current collector 33a of the second storage cell 31b. Therefore, deterioration of the cell stack 30 can be suppressed.

(4) When the control device 90 determines that the first storage cell 31a is over-discharged, the control device 90 prohibits the discharge of the cell stack 30 and allows the cell stack 30 to be charged. Since the first over-discharge threshold value Va is higher than the second over-discharge threshold value Vb, the first storage cell 31a and the second storage cell 31a and the second storage cell 31a even when the control device 90 determines that the first storage cell 31a is over-discharged. The storage cell 31b is unlikely to be in an over-discharged state, and the negative electrode current collector 33a is unlikely to reprecipitate. Therefore, even when the cell stack 30 is charged from the state determined to be over-discharged, the power storage module 10 is charged and recharged without accelerating the deterioration of the first power storage cell 31a and the second power storage cell 31b. Can be used.

(5) The power storage module 10 includes an inter-cell sealing material 37 that seals between a plurality of lithium ion storage cells 31. The cell-to-cell sealing material 37 seals between the second surface 32d of the positive electrode current collector 32a and the second surface 33d of the negative electrode current collector 33a interposed between the lithium ion storage cells 31. ing. Therefore, even when the negative electrode current collector 33a of the second storage cell 31b is eluted due to the over-discharge of each lithium ion storage cell 31, the cell-to-cell sealing material 37 is retained from the elution point of the negative electrode current collector 33a. It suppresses the leakage of the electrolytic solution 36 to the outside of the cell stack 30. Therefore, it is possible to more preferably suppress the leakage of the electrolytic solution 36.

The above embodiment can be modified and implemented as follows. Each of the above embodiments and the following modifications can be implemented in combination with each other to the extent that there is no technical contradiction.

○ The inter-cell sealing material 37 may be integrated with the sealing material 35 or may be a separate body.
○ The control performed by the control device 90 is not limited to that of the present embodiment, and is arbitrary. For example, control may be performed based on the remaining amount of the lithium ion storage cell 31 instead of the voltage Vi of the lithium ion storage cell 31.

○ The control performed by the control device 90 may be performed by a single control device 90, or may be performed by a separate control device for each of the sequences S10 to S18.
○ The control device 90 as the determination unit 91 does not have to use the minimum voltage Vmin to determine whether or not the second storage cell 31b is over-discharged. For example, the control device 90 determines whether or not the second storage cell 31b is over-discharged by determining whether or not the voltage V2 is lower than the second over-discharge threshold value Vb for each second storage cell 31b. It may be determined for each storage cell 31b.

○ The relay switch 70 may be replaced with various switches such as MOSFETs and IGBTs.
○ The control device 90 as the over-discharge control unit 94 does not have to realize the prohibition of charging / discharging of the cell stack 30 by turning off the relay switch 70. For example, the control device 90 may control the output of the inverter 100 to prohibit charging / discharging of the cell stack 30.

○ The cell balance circuit 80 is not limited to the one that performs passive cell balance as in the present embodiment. For example, the cell balance circuit 80 may perform an active cell balance in which the electric power released by the cell stack 30 is reduced to each lithium ion storage cell 31, or both a passive cell balance and an active cell balance. It may be what you do. The specific configuration of the active cell balance circuit is arbitrary, and examples thereof include a flyback converter type.

○ The power storage module 10 does not have to include the inter-cell sealing material 37.
○ The control device 90 may not allow charging when the first storage cell 31a is determined to be over-discharged, and may prohibit charging and discharging. Further, when the second storage cell 31b is determined to be over-discharged, charging may be permitted, and only discharging may be permitted. That is, the control device 90 does not have a function as the first storage cell control unit 92 and the second storage cell control unit 93, and at least the cell stack 30 is determined when the lithium ion storage cell 31 is determined to be over-discharged. It suffices to have a storage cell control unit that prohibits the discharge of.

○ The first limit threshold value Vc may be equal to or less than the second limit threshold value Vd. Further, the first limiting threshold value Vc and the second limiting threshold value Vd may not be set in the control device 90. That is, the control device 90 does not have to have a function as the restriction control unit 95.

○ The number of the first storage cell 31a is not limited to one. For example, when the assembled battery 20 in which two cell stacks 30 are stacked so that the positive electrodes 32 of the outermost layers face each other, the power storage module 10 has two first power storage cells 31a.

10 ... Energy storage module, 30 ... Cell stack, 31 ... Lithium ion energy storage cell, 31a ... First energy storage cell, 31b ... Second energy storage cell, 32 ... Positive electrode, 33 ... Negative electrode, 33a ... Negative electrode current collector, 33b ... Negative electrode activity Material layer, 35 ... Encapsulant, 36 ... Electrolyte, 37 ... Cell-to-cell encapsulant, 91 ... Judgment unit, 92 ... First storage cell control unit, 93 ... Second storage cell control unit, 94 ... Overdischarge control Unit, 95 ... Restriction control unit, Va ... First overdischarge threshold, Vb ... Second overdischarge threshold, Vc ... First limit threshold, Vd ... Second limit threshold.

Claims (4)

A cell stack in which multiple lithium-ion storage cells are stacked, and
A determination unit configured to determine that the lithium ion storage cell is overdischarged when the voltage of the lithium ion storage cell is lower than a predetermined overdischarge threshold.
A power storage module including an over-discharge control unit configured to prohibit discharge of the cell stack when the determination unit determines that any one of the lithium ion storage cells is over-discharged. ,
The lithium ion storage cell comprises a positive electrode, a negative electrode, an electrolytic solution, and a sealing material for sealing the electrolytic solution between the positive electrode and the negative electrode, respectively.
The negative electrode includes a copper negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.
The plurality of lithium ion storage cells include a first storage cell including the negative electrode current collector located in the outermost layer of the cell stack, and a second storage cell other than the first storage cell.
The over-discharge threshold includes a first over-discharge threshold set in the first storage cell and a second over-discharge threshold set in the second storage cell.
The first over-discharge threshold is a power storage module higher than the second over-discharge threshold. A limiting control unit configured to limit the discharge of the cell stack when the voltage of any one of the lithium ion storage cells is lower than a predetermined limiting threshold value is provided.
The limiting threshold includes a first limiting threshold set in the first storage cell and a second limiting threshold set in the second storage cell.
The first limiting threshold is higher than the first overdischarge threshold, and the second limiting threshold is higher than the second overdischarge threshold.
The power storage module according to claim 1, wherein the first limiting threshold is higher than the second limiting threshold. The over-discharge control unit is
A second storage cell control unit that prohibits charging and discharging of the cell stack when the determination unit determines that the second storage cell is over-discharged.
1. The power storage module according to claim 2. The power storage module according to any one of claims 1 to 3, further comprising an inter-cell sealing material for sealing between the plurality of lithium ion storage cells.

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