JP7489001B2 - Energy Storage Module - Google Patents

Description

The present invention relates to an energy storage module.

An example of a storage module is described in Patent Document 1. The storage module described in Patent Document 1 includes a cell stack in which multiple storage cells are stacked, and a current-carrying plate adjacent to the cell stack. Each storage cell includes a positive electrode, a negative electrode, an electrolyte, and a sealant that seals the electrolyte 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 multiple storage cells include a first storage cell that includes 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 disposed at one end of the cell stack in the stacking direction and is in contact with the current-carrying plate.

JP 2020-27694 A

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 collector is used, if the lithium-ion storage cell is discharged in a state where the negative electrode active material layer is deficient in charge carriers, i.e., in an overdischarged state, the copper of the negative electrode collector is ionized and dissolved into the electrolyte. If the negative electrode collector located in the outermost layer of the cell stack dissolves, there is a risk that the electrolyte will leak outside the storage module.

The storage module that solves the above problem is a storage module that includes a cell stack in which multiple lithium ion storage cells are stacked, a judgment unit configured to judge whether the lithium ion storage cell is over-discharged, and an over-discharge control unit configured to prohibit discharging of the cell stack when the judgment unit judges that the lithium ion storage cell is over-discharged. Each of the lithium ion storage cells includes a positive electrode, a negative electrode, an electrolyte, and a sealant that seals the electrolyte between the positive electrode and the negative electrode. The positive electrode includes a positive electrode collector and a positive electrode active material provided on the positive electrode collector. The negative electrode includes a copper negative electrode collector and a negative electrode active material provided on the negative electrode collector. The multiple lithium ion storage cells include a first storage cell that includes the negative electrode collector located in the outermost layer of the cell stack, and a second storage cell other than the first storage cell. The battery capacity of the first storage cell is greater than the battery capacity of any of the second storage cells.

According to this, since the battery capacity of the first storage cell is larger than the battery capacity of the second storage cell, the second storage cell is likely to be in an over-discharged state before the first storage cell is in an over-discharged state. Therefore, the judgment unit is likely to judge the second storage cell as over-discharged before the first storage cell is in an over-discharged state. When the second storage cell is judged to be over-discharged, the over-discharge control unit prohibits discharging the cell stack. By prohibiting discharging the cell stack, discharging of the first storage cell is suppressed before the first storage cell is in an over-discharged state. Therefore, elution of the negative electrode collector located in the outermost layer of the cell stack is suppressed. Therefore, leakage of the electrolyte can be suppressed.

The power storage module may include a plurality of the second power storage cells, and the battery capacities of the plurality of second power storage cells may be equal to one another.
In the above-mentioned storage module, a material of the positive electrode active material used in the first storage cell may be the same as a material of the positive electrode active material used in the second storage cell, a material of the negative electrode active material used in the first storage cell may be the same as a material of the negative electrode active material used in the second storage cell, a mass of the positive electrode active material of the first storage cell may be greater than a mass of the positive electrode active material of the second storage cell, and a mass of the negative electrode active material of the first storage cell may be greater than a mass of the negative electrode active material of the second storage cell.

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

The present invention makes it possible to prevent leakage of electrolyte.

FIG. 1 is a circuit diagram showing an example of an application of a power storage module. FIG. 4 is a flowchart showing control performed by a control device.

Hereinafter, one embodiment of the electricity storage module will be described with reference to FIGS.
The power storage module 10 shown in FIG. 1 is used in batteries for various vehicles, such as forklifts, hybrid cars, and electric cars.

As shown in Figs. 1 and 2, the energy storage module 10 includes a battery pack 20, a positive electrode conductive plate 40, a negative electrode conductive plate 50, a relay switch 70, a cell balance circuit 80, a voltage sensor 85, and a control device 90. The energy storage module 10 discharges to a device 100. The device 100 is, for example, an inverter.

As shown in FIG. 2 , the battery pack 20 includes a cell stack 30 and an inter-cell sealing material 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 direction in which the lithium ion storage cells 31 are stacked may be referred to as the stacking direction. In the following description, a planar view of the cell stack 30 seen from the stacking direction may be simply referred to as the planar 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 electrolyte 36 .
The positive electrode 32 includes a positive electrode collector 32a and a positive electrode active material layer 32b. The positive electrode collector 32a is a chemically inactive electrical conduction band. The positive electrode collector 32a is, for example, an aluminum foil. The positive electrode 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 collector 32a.

In a plan view of the cell stack 30 viewed from the stacking direction, the positive electrode active material layer 32b is formed in the center of the first surface 32c of the positive electrode current collector 32a. The peripheral portion 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 to surround the periphery of the positive electrode active material layer 32b in plan view.

The positive electrode active material layer 32b includes a positive electrode active material 32g that can absorb and release charge carriers such as lithium ions. Therefore, the positive electrode active material 32g is provided on the positive electrode current collector 32a. As the positive electrode active material 32g, any 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, or a polyanion-based compound, may be used. Two or more types of positive electrode active materials may also be used in combination.

The negative electrode 33 includes a copper negative electrode collector 33a and a negative electrode active material layer 33b. The negative electrode collector 33a is a copper foil. The negative electrode 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 collector 33a.

The negative electrode active material layer 33b is formed in the center of the first surface 33c of the negative electrode current collector 33a in a plan view. The peripheral portion of the first surface 33c of the negative electrode current collector 33a in a 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 to surround the periphery of the negative electrode active material layer 33b in a plan view.

The negative electrode active material layer 33b includes a negative electrode active material 33g. Therefore, the negative electrode active material 33g is provided on the negative electrode current collector 33a. There is no particular limitation on the negative electrode active material 33g, so long as it is a simple substance, an alloy, or a compound that can absorb and release charge carriers such as lithium ions. For example, the negative electrode active material 33g may be lithium, carbon, a metal compound, or an element or compound thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, hard carbon (hardly 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 disposed 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 disposed so as to face the positive electrode active material layer 32b. In a plan view, the entire formation area of the positive electrode active material layer 32b is located within the formation area of the negative electrode active material layer 33b.

The separator 34 is a member that allows lithium ions to pass through. The separator 34 is disposed 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 caused by 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 a liquid electrolyte. Examples of materials that constitute the separator 34 include polypropylene, polyethylene, polyolefin, and polyester. The separator 34 may have a single-layer structure or a multi-layer structure. The multi-layer structure may have, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, etc.

The sealant 35 maintains the distance between the positive electrode collector 32a and the negative electrode collector 33a and prevents short-circuiting between the positive electrode collector 32a and the negative electrode collector 33a. In a plan view, the sealant 35 is provided along the peripheral portions of the positive electrode collector 32a and the negative electrode collector 33a, and is formed in a frame shape surrounding the periphery of the positive electrode active material layer 32b and the negative electrode active material layer 33b. The sealant 35 is disposed between the positive electrode uncoated portion 32e of the first surface 32c of the positive electrode collector 32a and the negative electrode uncoated portion 33e of the first surface 33c of the negative electrode collector 33a.

Between the positive electrode 32 and the negative electrode 33 , a sealed space S surrounded by a frame-shaped sealing material 35 , the positive electrode 32 , and the negative electrode 33 is formed.
The sealed space S contains a separator 34 and an electrolyte 36. Therefore, it can be said that the sealant 35 seals the electrolyte 36 between the positive electrode 32 and the negative electrode 33. The electrolyte 36 may be, for example, 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 embedded in the sealant 35.

The sealing material 35 can prevent the electrolyte 36 contained in the sealed space S from leaking out by sealing the sealed space S between the positive electrode 32 and the negative electrode 33. The sealing material 35 can also prevent moisture from entering the sealed space S from outside the cell stack 30. Furthermore, the sealing material 35 can prevent gas generated from the positive electrode 32 or the negative electrode 33 due to, for example, a charge/discharge reaction, from leaking out of the sealed space S.

The cell stack 30 has a structure in which multiple lithium ion storage cells 31 are stacked so that the second surface 32d of the positive electrode collector 32a of one adjacent lithium ion storage cell 31 contacts the second surface 33d of the negative electrode collector 33a of the other adjacent lithium ion storage cell 31. This allows the multiple lithium ion storage cells 31 that make up the cell stack 30 to be connected in series.

The cell stack 30 includes a bipolar electrode 38. Here, in the cell stack 30, by stacking two adjacent lithium ion storage cells 31 in the stacking direction, a pseudo bipolar electrode 38 is formed in which the positive electrode collector 32a and the negative electrode collector 33a that are in contact with each other are regarded as one current collector. The pseudo bipolar electrode 38 includes a current collector having a structure in which the positive electrode collector 32a and the negative electrode collector 33a are stacked, a positive electrode active material layer 32b formed on one side of the current collector, and a negative electrode active material layer 33b formed on the other side. The bipolar electrode 38 may be formed using a current collector having a structure in which the positive electrode collector 32a and the negative electrode 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. 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 inter-cell sealing material 37, the gap between the second surface 32d of the positive electrode current collector 32a of one adjacent lithium ion storage cell 31 and the second surface 33d of the negative electrode current collector 33a of the other adjacent lithium ion storage cell 31 is sealed by the inter-cell sealing material 37. Therefore, the inter-cell sealing material 37 seals the gap between the multiple lithium ion storage cells 31.

In the cell stack 30 stacked in this manner, a positive electrode current collector 32a is disposed at a first end of the cell stack 30 in the stacking direction. The positive electrode current collector 32a is located in the outermost layer of the cell stack 30 in the stacking direction. In addition, a negative electrode current collector 33a is disposed at a second end of the cell stack 30 in the stacking direction. The negative electrode current collector 33a is also located in 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, made of the same metal 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 current-carrying plate 40 is used to extract power from the cell stack 30 to the outside of the energy storage module 10. Therefore, the second surface 32d of the positive electrode current collector 32a located in the outermost layer of the cell stack 30 is the 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, made of the same metal 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 current-carrying plate 50 is used to extract power from the cell stack 30 to the outside of the energy storage module 10. Therefore, the second surface 33d of the negative electrode current collector 33a located in the outermost layer of the cell stack 30 is the 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 has a negative electrode current collector 33a located in the outermost layer of the cell stack 30. The second storage cell 31b is one of the lithium ion storage cells 31 constituting the cell stack 30 other than the first storage cell 31a.

The plurality of lithium ion storage cells 31 therefore includes a first storage cell 31a having 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.

The material of the positive electrode active material 32g used in the first storage cell 31a is the same as the material of the positive electrode active material 32g used in the second storage cell 31b. The density of the positive electrode active material 32g used in the first storage cell 31a is equal to the density of the positive electrode active material 32g used in the second storage cell 31b. In this description, "same" and "equal" mean the same or equal within the range of uncertainty, and are not necessarily limited to the case where they are strictly the same or equal. The volume of the positive electrode active material 32g used in the first storage cell 31a is larger than the volume of the positive electrode active material 32g used in the second storage cell 31b. Therefore, it can be said that the mass of the positive electrode active material 32g of the first storage cell 31a is larger than the mass of the positive electrode active material 32g of the second storage cell 31b.

The material of the negative electrode active material 33g used in the first storage cell 31a is the same as the material of the negative electrode active material 33g used in the second storage cell 31b. The density of the negative electrode active material 33g of the first storage cell 31a is equal to the density of the negative electrode active material 33g of the second storage cell 31b. The volume of the negative electrode active material 33g of the first storage cell 31a is larger than the volume of the negative electrode active material 33g of the second storage cell 31b. Therefore, it can be said that the mass of the negative electrode active material 33g of the first storage cell 31a is larger than the mass of the negative electrode active material 33g of the second storage cell 31b.

Here, the battery capacity of the lithium ion storage cell 31 increases with an increase in the amount of material of the positive electrode active material 32g and the negative electrode active material 33g. As described above, since the material of each active material 32g, 33g is the same, in this embodiment, the battery capacity of the lithium ion storage cell 31 increases with an increase in the mass of each active material 32g, 33g. Therefore, it can be said that the battery capacity of the first storage cell 31a is larger than the battery capacity of any of the second storage cells 31b.

In this embodiment, the volumes of the positive electrode active material 32g of the second storage cells 31b are equal to each other. The volumes of the negative electrode active material 33g of the second storage cells 31b are equal to each other. Therefore, the battery capacities of the second storage cells 31b are equal to each other.

In this embodiment, the sealing material 35 seals the electrolyte 36 between the positive electrode 32 and the negative electrode 33 of each lithium ion storage cell 31, and since no separate housing for sealing the electrolyte 36 is provided outside the cell stack 30, dissolution of the negative electrode collector 33a located in the outermost layer of the cell stack 30 may cause leakage of the electrolyte 36 to the outside of the storage module 10.

On the other hand, the negative electrode collector 33a of the second storage cell 31b is stacked on the other adjacent lithium ion storage cell 31. As a result, the negative electrode collector 33a of the second storage cell 31b is covered by the positive electrode collector 32a of the other adjacent lithium ion storage cell 31. Therefore, even if the negative electrode collector 33a of the second storage cell 31b dissolves, leakage of the electrolyte to the outside of the storage module 10 is unlikely to occur.

The negative electrode collector 33a located in the outermost layer of the cell stack 30 is in contact with and covered by the negative electrode current-carrying plate 50. However, if the negative electrode collector 33a located in the outermost layer dissolves, the electrolyte 36 is likely to leak along the negative electrode current-carrying plate 50 to the outside of the storage module 10. In particular, if the negative electrode current-carrying plate 50 is made of copper like the negative electrode collector 33a, when the negative electrode collector 33a located in the outermost layer dissolves, the negative electrode current-carrying plate 50 may also dissolve, making it more likely that the electrolyte 36 will leak to the outside of the storage module 10. Furthermore, if the negative electrode current-carrying plate 50 is formed smaller than the negative electrode collector 33a in a plan view, there will be a position where the negative electrode collector 33a located in the outermost layer is not covered by the negative electrode current-carrying plate 50, making it more likely that the electrolyte 36 will leak to the outside of the storage module 10.

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

The cell balance circuit 80 includes a plurality of series-connected bodies in which a cell balance resistor 81 and a switch 82 are connected in series. The series-connected bodies are connected in parallel to each lithium ion storage cell 31. When the switch 82 is in an on state, 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. This causes the lithium ion storage cell 31 to be discharged. Then, the cell balance circuit 80 performs cell balancing to equalize the remaining capacity of the lithium ion storage cell 31 to be discharged to the target remaining capacity of the lithium ion storage cell 31. The target remaining capacity can be set to, for example, the lowest remaining capacity among the remaining capacities of the plurality of lithium ion storage cells 31. The cell balance circuit 80 of this embodiment performs passive cell balancing.

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. The processor may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores program code or instructions configured to cause the processor to execute a process. The storage unit, i.e., the 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 application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). 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 an ASIC or an FPGA, 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. The control device 90 also performs cell balancing for each lithium ion storage cell 31 by controlling the switch 82. The control device 90 can obtain the detection results of the voltage sensor 85.

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

The control device 90 stores an overdischarge threshold value Va in a memory unit. The overdischarge threshold value Va is set to, for example, a voltage value higher than the voltage value at which the lithium ion storage cell 31 actually goes into an overdischarge state where elution of the negative electrode collector 33a occurs.

When the voltage 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 to prohibit discharging of the cell stack 30. However, if the lithium ion storage cell 31 determined to be over-discharged continues to discharge due to natural discharge or the like, the lithium ion storage cell 31 will enter an over-discharged state in which elution of the negative electrode current collector 33a occurs.

The control performed by the control device 90 will be described below with reference to FIG. 3. As shown in FIG. 3, in step S10, the control device 90 acquires information indicating the detection result detected by the voltage sensor 85, specifically, the voltage Vi of each lithium ion storage cell 31.

Next, in step S11, the control device 90 calculates the minimum voltage Vmin among the voltages Vi of each lithium ion storage cell 31. In the following description, the minimum voltage Vmin among the voltages Vi of each lithium ion storage cell 31 may be simply referred to as the "minimum voltage Vmin."

Next, in step S12, the control device 90 determines whether the minimum voltage Vmin is lower than the over-discharge threshold value Va.
If the minimum voltage Vmin is lower than the over-discharge threshold value Va, the control device 90 proceeds to step S13 and determines that the lithium ion storage cell 31 is over-discharged. Therefore, the control device 90 includes a determination unit 91 configured to determine whether or not the lithium ion storage cell 31 is over-discharged. In addition, the control device 90 prohibits charging and discharging of the cell stack 30 by turning off the relay switch 70. Therefore, the control device 90 includes an over-discharge control unit 92 configured to prohibit charging and discharging of the cell stack 30 when the determination unit 91 determines that the lithium ion storage cell 31 is over-discharged. At this time, at least one lithium ion storage cell 31 having the minimum voltage Vmin is determined to be over-discharged. Therefore, it can be said that the determination unit 91 is configured to determine whether or not at least one of the multiple lithium ion storage cells 31 is over-discharged. In addition, when the control device 90 prohibits charging and discharging of the cell stack 30, the control device 90 notifies the user that the lithium ion storage cell 31 has been determined to be over-discharged. The method of notifying the user is arbitrary, but possible methods include notifying the user by light or sound, for example.

If the minimum voltage Vmin is equal to or greater than the over-discharge threshold value Va, the control device 90 proceeds to step S 14 and does not limit the discharge of the cell stack 30 .
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, the control device 90 controls the switch 82, so that the cell balance circuit 80 performs cell balancing for each lithium ion storage cell 31. As a result, the voltage Vi of each lithium ion storage cell 31 matches within the error range.

If the minimum voltage Vmin is lower than the overdischarge threshold Va, the control device 90 determines that one of the lithium ion storage cells 31 is overdischarged and prohibits discharging the cell stack 30. When the cell stack 30 discharges, the discharge amount of the first storage cell 31a and the discharge amount of the second storage cell 31b are both equal to the discharge amount of the cell stack 30. Therefore, when the battery capacity of the first storage cell 31a and the second storage cell 31b is equal, when the second storage cell 31b is determined to be overdischarged due to the discharge of the cell stack 30, the first storage cell 31a is also likely to be determined to be overdischarged. Discharging the cell stack 30 is prohibited by determining that the lithium ion storage cell 31 is overdischarged. In this case, if the first storage cell 31a continues to discharge due to natural discharge or the like, it is likely to enter an overdischarge state in which the elution of the negative electrode collector 33a occurs. In particular, since the negative electrode collector 33a of the first storage cell 31a is located in the outermost layer of the cell stack 30, dissolution of the negative electrode collector 33a may cause leakage of the electrolyte 36.

On the other hand, in this embodiment, the battery capacity of the first storage cell 31a is larger than the battery capacity of the second storage cell 31b. Therefore, even if the second storage cell 31b is in an overdischarged state, the first storage cell 31a has a remaining capacity corresponding to the difference between the battery capacity of the first storage cell 31a and the battery capacity of the second storage cell 31b. Therefore, before the first storage cell 31a and the second storage cell 31b reach an overdischarged state in which the elution of the negative electrode collector 33a occurs, the discharge of the cell stack 30 (the first storage cell 31a) is prohibited in advance. Therefore, the first storage cell 31a is prevented from reaching an overdischarged state. Therefore, the elution of the negative electrode collector 33a of the first storage cell 31a is suppressed. In addition, along with this, leakage of the electrolyte 36 due to the elution of the negative electrode collector 33a is suppressed.

The effects of this embodiment will be described below.
(1) In this embodiment, the battery capacity of the first storage cell 31a is larger than the battery capacity of any of the second storage cells 31b. Therefore, even if the second storage cell 31b is determined to be over-discharged due to discharging of the cell stack 30, the first storage cell 31a has a remaining capacity corresponding to the difference between the battery capacity of the first storage cell 31a and the battery capacity of the second storage cell 31b. Therefore, the first storage cell 31a is prevented from reaching an over-discharge state. Thus, it is possible to prevent the elution of the negative electrode collector 33a of the first storage cell 31a. In addition, it is possible to prevent leakage of the electrolyte 36 due to the elution of the negative electrode collector 33a.

In particular, when the storage module 10 does not have a housing for containing the electrolyte 36, as in the case of the storage module 10 of this embodiment, leakage of the electrolyte 36 may cause the electrolyte 36 to leak to the outside of the storage module 10. Therefore, when the storage module 10 does not have a housing for containing the electrolyte 36, it is necessary to suppress the elution of the negative electrode collector 33a located in the outermost layer of the cell stack 30, compared to when the storage module 10 has the electrolyte 36. By suppressing the elution of the negative electrode collector 33a located in the outermost layer of the cell stack 30 and the resulting leakage of the electrolyte 36, even in a storage module 10 that does not have a housing for containing the electrolyte 36, it is possible to suppress the electrolyte 36 from leaking to the outside of the storage module 10.

(2) Even if some of the lithium ion storage cells 31 have a large battery capacity, the battery capacity of the cell stack 30 is dominated by the lithium ion storage cells 31 with the smallest battery capacity. Therefore, in this embodiment, only the battery capacity of the first storage cell 31a is made larger than that of the second storage cell 31b, and the battery capacities of the multiple second storage cells 31b are equal to each other. This makes it possible to discharge the cell stack 30 with the remaining amount of the second storage cells 31b uniform, while suppressing the elution of the negative electrode collector 33a of the first storage cell 31a, compared to the case where there is a difference in battery capacity between the second storage cells 31b. Therefore, it is possible to reduce the battery capacity wasted in the second storage cells 31b having a battery capacity other than the smallest battery capacity while suppressing the leakage of the electrolyte 36.

(3) The charge and discharge characteristics of the lithium ion storage cell 31 depend on the materials used for the positive electrode active material 32g and the negative electrode active material 33g. Therefore, in this embodiment, the same material is used for the active materials 32g, 33g of each lithium ion storage cell 31, and the masses of the active materials 32g, 33g of the first storage cell 31a are set so that the masses of the active materials 32g, 33g of the second storage cell 31b are larger. As a result, the battery capacity of the first storage cell 31a is made larger than the battery capacity of the second storage cell 31b, while the first storage cell 31a exhibits charge and discharge characteristics similar to those of the second storage cell 31b. Therefore, the difference between the control of the first storage cell 31a and the control of the second storage cell 31b can be reduced. Therefore, the storage module 10 can be controlled with a simpler configuration.

(4) The storage module 10 includes an inter-cell sealant 37 that seals between the multiple lithium ion storage cells 31. The inter-cell sealant 37 seals between the second surface 32d of the positive electrode collector 32a and the second surface 33d of the negative electrode collector 33a, which are interposed between the lithium ion storage cells 31. Therefore, even if the negative electrode collector 33a of the second storage cell 31b dissolves due to over-discharging of each lithium ion storage cell 31, the inter-cell sealant 37 prevents the electrolyte 36 from leaking out of the cell stack 30 from the dissolution site of the negative electrode collector 33a. Therefore, leakage of the electrolyte 36 can be more effectively prevented.

The above embodiment can be modified as follows. The above embodiments and the following modified examples can be combined together to the extent that no technical contradiction exists.

The inter-cell sealing material 37 may be integrated with the sealing material 35 or may be separate from the sealing material 35 .
The control performed by the control device 90 is not limited to that in the present embodiment and may be any control. For example, the control may be performed based on the state of charge of the lithium ion storage cell 31, instead of the voltage Vi of the lithium ion storage cell 31.

The control device 90 as the determination unit 91 may not use the minimum voltage Vmin to determine whether the lithium ion storage cell 31, particularly the second storage cell 31b, is over-discharged. For example, the control device 90 may determine whether the second storage cell 31b is over-discharged for each second storage cell 31b by determining whether the voltage V2 for each second storage cell 31b is lower than the over-discharge threshold Va.

The relay switch 70 may be replaced with various switches such as a MOSFET or an IGBT.
The control device 90 as the overdischarge control unit 92 does not have to turn off the relay switch 70 to prohibit charging and discharging of the cell stack 30. For example, the control device 90 may directly control the output of the device 100 to prohibit charging and discharging of the cell stack 30.

The cell balance circuit 80 is not limited to a passive cell balance circuit as in this embodiment. For example, the cell balance circuit 80 may be an active cell balance circuit that returns the power discharged from the cell stack 30 to each lithium ion storage cell 31, or may be a circuit that performs both passive and active cell balancing. The specific configuration of the active cell balance circuit is arbitrary, but examples include a flyback converter type.

The control performed by the control device 90 may be performed by a single control device 90, or may be performed by separate control devices for the sequences S10 to S14.
The energy storage module 10 does not necessarily have to include the inter-cell sealing material 37 .

○ The volumes of the active materials 32g, 33g of the first storage cell 31a do not have to be larger than the volumes of the active materials 32g, 33g of the second storage cell 31b. For example, the volumes of the active materials 32g, 33g of the first storage cell 31a may be equal to the volumes of the active materials 32g, 33g of the second storage cell 31b, and the densities of the active materials 32g, 33g of the first storage cell 31a may be larger than the densities of the active materials 32g, 33g of the second storage cell 31b. In short, as long as the battery capacity of the first storage cell 31a is larger than the battery capacity of the second storage cell 31b, the materials, densities, and volumes of the active materials 32g, 33g of the first storage cell 31a and the active materials 32g, 33g of the second storage cell 31b are arbitrary.

As long as the battery capacity of the first storage cell 31a is larger than the battery capacity of any one of the second storage cells 31b, the battery capacities of the second storage cells 31b do not need to be equal to each other.
It is sufficient that only one second storage cell 31b is provided, and it is not necessary to provide a plurality of second storage cells 31b.

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

10...storage module, 30...cell stack, 31...lithium ion storage cell, 31a...first storage cell, 31b...second storage cell, 32...positive electrode, 32a...positive electrode collector, 32g...positive electrode active material, 33...negative electrode, 33a...negative electrode collector, 33g...negative electrode active material, 35...sealing material, 36...electrolyte, 37...inter-cell sealing material, 91...determination unit, 92...overdischarge control unit.

Claims (4)

A cell stack in which a plurality of lithium-ion storage cells are stacked;
A determination unit configured to determine whether the lithium ion storage cell is over-discharged;
an overdischarge control unit configured to prohibit discharging of the cell stack when the determination unit determines that the lithium ion storage cell is overdischarged,
Each of the lithium ion storage cells includes a positive electrode, a negative electrode, an electrolyte, and a sealant that seals the electrolyte between the positive electrode and the negative electrode;
The positive electrode includes a positive electrode current collector and a positive electrode active material provided on the positive electrode current collector,
The negative electrode includes a copper negative electrode current collector and a negative electrode active material 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 an outermost layer of the cell stack, and a second storage cell other than the first storage cell,
A storage module in which the battery capacity of the first storage cell is larger than the battery capacity of any of the second storage cells. The second storage cell is provided in plurality,
The energy storage module according to claim 1 , wherein the battery capacities of the second energy storage cells are equal to each other. a material used for the positive electrode active material of the first storage cell is the same as a material used for the positive electrode active material of the second storage cell;
a material used for the negative electrode active material of the first storage cell is the same as a material used for the negative electrode active material of the second storage cell;
a mass of the positive electrode active material of the first storage cell is greater than a mass of the positive electrode active material of the second storage cell;
The energy storage module according to claim 1 or 2, wherein a mass of the negative electrode active material of the first energy storage cell is greater than a mass of the negative electrode active material of the second energy storage cell. The storage module according to any one of claims 1 to 3, further comprising an inter-cell sealing material that seals between the plurality of lithium ion storage cells.