Battery module

Abstract

A battery module of the present invention may comprise: a first battery cell stack in which a plurality of first battery cells are stacked; a second battery cell stack in which a plurality of second battery cells are stacked and which is arranged in one direction with the first battery cell stack; a lower frame which accommodates the first battery cell stack and the second battery cell stack and has an open upper portion; and an upper frame which covers the first battery cell stack and the second battery cell stack and is connected to the lower frame. A plurality of slits passing through the upper and lower surfaces of the upper frame are formed in the upper frame, and an upper frame portion adjacent to the plurality of slits may be broken when thermal energy is concentrated at a predetermined value or more.

Description

battery module

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0190559 filed on December 18, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a battery module, wherein the area through which thermal energy is transferred is reduced by forming a plurality of slits in an upper frame, and the thermal energy is concentrated in the plurality of slits to break the upper frame portion adjacent to the plurality of slits.

[0005] Recently, with rising energy prices due to the depletion of fossil fuels and growing concern over environmental pollution, the demand for eco-friendly alternative energy sources has become an indispensable factor for future life. Accordingly, research on various power generation technologies, such as solar, wind, and tidal power, is ongoing, and there is also significant interest in power storage devices, such as batteries, to utilize this generated electrical energy more efficiently.

[0006] Rechargeable batteries are attracting significant attention as an energy source in various product categories, including mobile devices and electric vehicles. As an excellent energy resource capable of replacing existing products that use fossil fuels, these batteries are gaining prominence as an eco-friendly energy source because they do not generate byproducts associated with energy consumption.

[0007] Due to their high energy density, rechargeable batteries can generate heat during the charging and discharging processes. High temperatures can accelerate the degradation of active materials or the decomposition of electrolytes, thereby shortening battery life and reducing efficiency. Furthermore, exceeding a certain temperature poses a risk of lateral runaway, and if the resulting heat propagates to adjacent battery cells, it can lead to large-scale fires or explosions. To address these issues, technologies are being developed to effectively manage heat generated by rechargeable batteries.

[0008] The present invention has been devised to solve the above-mentioned problems, and the objective of the present invention is to provide a battery module that reduces the area through which thermal energy is transferred by forming a plurality of slits in an upper frame, and ruptures the upper frame portion adjacent to the plurality of slits by concentrating thermal energy in the plurality of slits.

[0009] A battery module according to one embodiment of the present invention may include a first battery cell stack in which a plurality of first battery cells are stacked, a second battery cell stack in which a plurality of second battery cells are stacked and arranged along one direction with respect to the first battery cell stack, a lower frame having an open top that accommodates the first battery cell stack and the second battery cell stack, and an upper frame that covers the first battery cell stack and the second battery cell stack and is connected to the lower frame. A plurality of slits penetrating the upper and lower surfaces are formed in the upper frame, and the portion of the upper frame adjacent to the plurality of slits may break when thermal energy is concentrated above a predetermined value.

[0010] The above battery module is accommodated inside the lower frame and further includes a central wall disposed between the first battery cell stack and the second battery cell stack, and the central wall can overlap with the plurality of slits.

[0011] Each of the plurality of slits extends in a first direction which is the spacing direction between the first battery cell stack and the second battery cell stack, and the plurality of slits may be spaced apart in a second direction that intersects the first direction.

[0012] Each of the above plurality of slits may be square in shape.

[0013] The plurality of slits each include first slits and second slits arranged spaced apart in the second direction, and the first slits and the second slits may be arranged intersectingly along the second direction.

[0014] Each of the first slits and the second slits has a trapezoidal shape including first and second bases parallel to each other and first and second hypotenuses connecting the first and second bases, and the first base may be shorter than the second base.

[0015] The length of the first base may be 1 / 3 or more and 2 / 3 or less of the length of the second base.

[0016] When the second base of the first slit is spaced apart from the first base in the first direction, the first hypotenuse of the first slit is extended from the first base in a direction opposite to the first direction and the second direction and connected to the second base, and the second hypotenuse of the first slit can be extended from the first base in a direction opposite to the first direction and the second direction and connected to the second base.

[0017] When the first base of the second slit is spaced apart from the second base in the first direction, the first hypotenuse of the second slit is extended from the second base in a direction opposite to the first direction and the second direction and connected to the first base, and the second hypotenuse of the second slit can be extended from the second base in a direction opposite to the first direction and the second direction and connected to the first base.

[0018] The first hypotenuse of the first slit is adjacent to the first hypotenuse of the second slit adjacent to the first hypotenuse of the first slit, and the second hypotenuse of the first slit may be adjacent to the second hypotenuse of the second slit adjacent to the second hypotenuse of the first slit.

[0019] The first base of the first slit overlaps with the second slit in the second direction, and the first base of the second slit can overlap with the first slit in the second direction.

[0020] The upper frame portion adjacent to the plurality of slits and fractured when thermal energy is concentrated is defined as a fracture portion, and the thickness of the fracture portion adjacent to the second base of the first slit may be thicker than the thickness of the fracture portion adjacent to the first base of the first slit.

[0021] The thickness of the fracture portion adjacent to the second base of the first slit may be 1.5 to 3 times the thickness of the fracture portion adjacent to the first base of the first slit.

[0022] The thickness of the above fractured portion may vary with a step difference.

[0023] The thickness of the above-mentioned fracture portion may gradually decrease as it approaches the first base of the first slit from the second base of the first slit.

[0024] A venting hole penetrating the upper and lower surfaces is further formed in the upper frame, and the venting hole can overlap with the first battery cell stack and the second battery cell stack.

[0025] As described above, by forming a plurality of slits in the upper frame, the area over which thermal energy is transferred can be reduced, and thermal energy can be induced to be concentrated in the plurality of slits. When thermal energy exceeding a certain level is generated in the first battery cell stack or the second battery cell stack, thermal energy may be concentrated in the upper frame portion adjacent to the plurality of slits, and the upper frame portion adjacent to the plurality of slits may be fractured. As a result, the phenomenon of thermal energy from the first battery cell stack or the second battery cell stack being transferred to the second battery cell stack or the first battery cell stack can be blocked.

[0026] FIG. 1 is an exploded perspective view of a battery module according to one embodiment of the present invention.

[0027] FIG. 2 is a plan view of an upper frame according to one embodiment of the present invention.

[0028] Figure 3 is an enlarged schematic diagram of the area corresponding to the AA' area of ​​Figure 2.

[0029] Figure 4 is an enlarged schematic diagram of the area corresponding to the AA' area of ​​Figure 2.

[0030] Figure 5 is a cross-sectional view taken along the II' cutting line of Figure 4.

[0031] Figure 6 is a cross-sectional view taken along the II' cutting line of Figure 4.

[0032] Hereinafter, preferred embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited or restricted by the following embodiments.

[0033] In order to clearly explain the present invention, detailed descriptions of related prior art that are irrelevant to the explanation or that may unnecessarily obscure the essence of the invention have been omitted. Furthermore, when assigning reference numerals to the components of each drawing in this specification, identical or similar reference numerals are assigned to identical or similar components throughout the entire specification.

[0034] Furthermore, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0035]

[0036] FIG. 1 is an exploded perspective view of a battery module (1) according to one embodiment of the present invention. FIG. 2 is a plan view of an upper frame (13) according to one embodiment of the present invention.

[0037] Referring to FIGS. 1 and 2, the battery module (1) may include a first battery cell stack (10), a second battery cell stack (11), a lower frame (12), a central wall (14), and an upper frame (13).

[0038] A first battery cell stack (10) may have a plurality of first battery cells stacked thereon, and a second battery cell stack (11) may have a plurality of second battery cells stacked thereon. The second battery cell stack (11) may be arranged spaced apart from the first battery cell stack (10) along one direction. The first and second battery cell stacks (10, 11) may further include a busbar assembly, an insulating cover, etc., in addition to the plurality of battery cells.

[0039] The lower frame (12) has an open top, and the open top can be connected to the upper frame (13). The lower frame (12) can accommodate the first battery cell stack (10) and the second battery cell stack (11). A central wall (14) can be further accommodated inside the lower frame (12). The central wall (14) can be positioned between the first battery cell stack (10) and the second battery cell stack (11). That is, the first battery cell stack (10) and the second battery cell stack (11) can be spatially separated by the central wall (14). In the event of a fire in the first battery cell stack (10) or the second battery cell stack (11), the transfer of thermal energy to the adjacent second battery cell stack (11) or first battery cell stack (10) can be delayed or blocked.

[0040] The upper frame (13) may be placed on the lower frame (12) and connected to the lower frame (12). The upper frame (13) may cover the first battery cell stack (10) and the second battery cell stack (11), and may cover the central wall (14). A plurality of slits (131) penetrating the upper and lower surfaces may be formed in the upper frame (13).

[0041] Multiple slits (131) may overlap with the central wall (14) in a plane. For example, multiple slits (131) and the central wall (14) may overlap in a third direction (DR3). The third direction (DR3) may be defined as the normal direction of the plane formed by the first direction (DR1) and the second direction (DR2). In this specification, the first direction (DR1), the second direction (DR2), and the third direction (DR3) are exemplary, and the first to third directions (DR1, DR2, DR3) may be relative directions.

[0042] A portion adjacent to a plurality of slits (131) in the upper frame (13) that breaks when thermal energy is concentrated above a predetermined value can be defined as a fracture portion (130). Since the upper frame (13) simultaneously covers the first battery cell stack (10) and the second battery cell stack (11), if a plurality of slits (131) are not formed in the upper frame (13), heat generated in the first battery cell stack (10) or the second battery cell stack (11) can be rapidly transferred through the upper frame (13) to the second battery cell stack (11) or the first battery cell stack (10). By forming a plurality of slits (131) in the upper frame (13), the present invention can reduce the area over which thermal energy is transferred and induce thermal energy to be concentrated in the plurality of slits (131). Accordingly, when thermal energy exceeding a certain amount is generated in the first battery cell stack (10) or the second battery cell stack (11), the thermal energy may be concentrated in the upper frame portion (130, or fracture portion) adjacent to the plurality of slits (131), and the upper frame portion (130, or fracture portion) adjacent to the plurality of slits (131) may be fractured. As a result, the phenomenon in which thermal energy from the first battery cell stack (10) or the second battery cell stack (11) is transferred to the second battery cell stack (11) or the first battery cell stack (10) may be blocked.

[0043] A venting hole (132) penetrating the upper and lower surfaces may be further formed in the upper frame (13). The venting hole (132) may overlap with the first battery cell stack (10) and the second battery cell stack (11) in a planar manner. That is, the venting hole (132) may overlap with the first battery cell stack (10) and the second battery cell stack (11) in a third direction (DR3). The venting hole (132) may be a passage for expelling gas generated when the first battery cell stack (10) or the second battery cell stack (11) ignites to the outside.

[0044] Figure 3 is an enlarged schematic diagram of the area corresponding to the AA' area of ​​Figure 2.

[0045] Referring to FIG. 3, the shape of the plurality of slits (131) and the fracture portion (130) of the upper frame (13) adjacent to the plurality of slits (131) may have a shape that facilitates fracture when thermal energy is concentrated above a predetermined value. Each of the plurality of slits (131) extends in a first direction (DR1), which is the direction of separation between the first battery cell stack (10) and the second battery cell stack (11), and the plurality of slits may be spaced apart from each other in a second direction (DR2). Each of the plurality of slits (131) may have a rectangular shape.

[0046] When heat is generated on one side of the upper frame (13) (the upper part of the first battery cell stack (10) or the second battery cell stack (11)), thermal energy is concentrated in the upper frame portion (130) between the plurality of slits (131), causing the temperature to rise locally, and the upper frame portion (130) adjacent to the plurality of slits (131) is cut off by itself, thereby blocking the transfer of thermal energy to the other side of the upper frame (13) (the upper part of the second battery cell stack (11) or the first battery cell stack (10)).

[0047] Figure 4 is an enlarged schematic diagram of the area corresponding to the AA' area of ​​Figure 2.

[0048] Referring to FIGS. 2 and 4, the shape of the plurality of slits (131-1) and the fracture portion (130-1) of the upper frame (13) adjacent to the plurality of slits (131-1) may have a shape that facilitates fracture when thermal energy is concentrated above a predetermined value. Each of the plurality of slits (131-1) extends in a first direction (DR1), which is the direction of separation between the first battery cell stack (10) and the second battery cell stack (11), and the plurality of slits may be spaced apart from each other in a second direction (DR2). The plurality of slits (131-1) may include first slits (1310) and second slits (1311). Each of the first slits (1310) and second slits (1311) may be arranged spaced apart in the second direction (DR2).

[0049] When heat is generated on one side of the upper frame (13) (the upper part of the first battery cell stack (10) or the second battery cell stack (11)), thermal energy is concentrated in the upper frame portion (130-1) between the plurality of slits (131-1), causing the temperature to rise locally, and the upper frame portion (130-1) adjacent to the plurality of slits (131-1) cuts itself, thereby blocking the transfer of thermal energy to the other side of the upper frame (13) (the upper part of the second battery cell stack (11) or the first battery cell stack (10)).

[0050] Each of the first slits (1310) may have a trapezoidal shape including first and second bases (1310a, 1310b) parallel to each other and first and second hypotenuses (1310c, 1310d) connecting the first and second bases (1310a, 1310b). Each of the second slits (1311) may have a trapezoidal shape including first and second bases (1311a, 1311b) parallel to each other and first and second hypotenuses (1311c, 1311d) connecting the first and second bases (1311a, 1311b).

[0051] When the second base (1310b) of the first slit (1310) is spaced apart from the first base (1310a) in the first direction (DR1), the first hypotenuse (1310c) of the first slit (1310) can be connected to the second base (1310b) by extending from the first base (1310a) in the direction where the first direction (DR1) and the second direction (DR2) intersect. The second hypotenuse (1310d) of the first slit (1310) can be connected to the second base (1310b) by extending from the first base (1310a) in the direction where the first direction (DR1) and the second direction (DR2) intersect.

[0052] When the first base (1311a) of the second slit (1311) is spaced apart from the second base (1311b) in the first direction (DR1), the first hypotenuse (1311c) of the second slit (1311) can be connected to the first base (1311a) by extending from the second base (1311b) in the direction where the opposite direction of the first direction (DR1) and the second direction (DR2) intersect. The second hypotenuse (1311d) of the second slit (1311) can be connected to the first base (1311a) by extending from the second base in the direction where the first direction (DR1) and the second direction (DR2) intersect.

[0053] The shape of the first slit (1310) and the shape of the second slit (1311) may be substantially the same. The shape of the first slits (1310) may be a shape that is line-symmetric to the shape of the second slits (1311) with respect to an axis parallel to the second direction (DR2).

[0054] The first base (1310a) of the first slit (1310) may be shorter than the second base (1310b) of the first slit (1310). The first base (1311a) of the second slit (1311) may be shorter than the second base (1311b) of the second slit (1311). In one embodiment, the length of each of the first bases (1310a, 1311a) may be between 1 / 3 and 2 / 3 of the length of each of the second bases (1310b, 1311b). For example, the length of each of the first bases (1310a, 1311a) may be half the length of each of the second bases (1310b, 1311b).

[0055] The first slits (1310) and the second slits (1311) may be arranged to intersect each other along the second direction (DR2). For example, they may be arranged repeatedly in the order of one first slit (1310), one second slit (1311), another first slit (1310), and another second slit (1311). That is, the first hypotenuse (1310c) of the first slit (1310) is adjacent to the first hypotenuse (1311c) of the second slit (1311) adjacent to the first hypotenuse (1310c) of the first slit (1310), and the second hypotenuse (1310d) of the first slit (1310) is adjacent to the second hypotenuse (1311d) of the second slit (1311) adjacent to the second hypotenuse (1310d) of the first slit (1310).

[0056] The first slits (1310) and the second slits (1311) may partially overlap. For example, the first base (1310a) of the first slit (1310) may overlap with the second slit (1311) in the second direction (DR2), and the first base (1311a) of the second slit (1311) may overlap with the first slit (1310) in the second direction (DR2).

[0057] Figure 5 is a cross-sectional view taken along the II' cutting line of Figure 4.

[0058] Referring to FIGS. 4 and 5, the thickness (L2) of the fracture portion (130-1) adjacent to the second base (1310b) of the first slit (1310) may be thicker than the thickness (L1) of the fracture portion (1310-1) adjacent to the first base (1310a) of the first slit (1310). In one embodiment, the thickness (L2) of the fracture portion (130-1) adjacent to the second base (1310b) of the first slit (1310) may be 1.5 to 3 times the thickness (L1) of the fracture portion (130-1) adjacent to the first base (1310a) of the first slit (1310). For example, the thickness (L2) of the fracture portion (130-1) adjacent to the second base (1310b) of the first slit (1310) may be twice the thickness (L1) of the fracture portion (130-1) adjacent to the first base (1310a) of the first slit (1310). The thickness of the fracture portion (130-1) may gradually decrease as it approaches the first base (1310a) of the first slit (1310) from the second base (1310b) of the first slit (1310).

[0059] The description of the thickness of the second slit (1311) may be substantially the same as the description of the thickness of the first slit (1310). The thickness of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be thicker than the thickness of the fracture portion (130-1) adjacent to the first base (1311a) of the second slit (1311). In one embodiment, the thickness (L2) of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be 1.5 to 3 times the thickness (L1) of the fracture portion (130-1) adjacent to the first base (1311) of the second slit (1311). For example, the thickness (L2) of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be twice the thickness (L1) of the fracture portion (130-1) adjacent to the first base (1311) of the second slit (1311). The thickness of the fracture portion (130-1) may gradually decrease from the second base (1311b) of the second slit (1311) to the first base (1311a) of the second slit (1311).

[0060] Figure 6 is a cross-sectional view taken along the II' cutting line of Figure 4.

[0061] Referring to FIGS. 4 and 6, the thickness (L2a) of the fracture portion (130-1) adjacent to the second base (1310b) of the first slit (1310) may be thicker than the thickness (L1a) of the fracture portion (1310) adjacent to the first base (1310a) of the first slit (1310). In one embodiment, the thickness (L2a) of the fracture portion (130-1) adjacent to the second base (1310b) of the first slit (1310) may be 1.5 to 3 times the thickness (L1a) of the fracture portion (130-1) adjacent to the first base (1310a) of the first slit (1310). For example, the thickness (L2a) of the fracture (130-1) adjacent to the second base (1310b) of the first slit (1310) may be twice the thickness (L1a) of the fracture (130-1) adjacent to the first base (1310a) of the first slit (1310). The thickness of the fracture (130-1) may vary with a step.

[0062] The description of the thickness of the second slit (1311) may be substantially the same as the description of the thickness of the first slit (1310). The thickness of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be thicker than the thickness of the fracture portion (130-1) adjacent to the first base (1311a) of the second slit (1311). In one embodiment, the thickness of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be 1.5 to 3 times the thickness of the fracture portion (130-1) adjacent to the first base (1311a) of the second slit (1311). For example, the thickness of the fracture portion (130-1) adjacent to the second base (1311b) of the second slit (1311) may be twice the thickness of the fracture portion (130-1) adjacent to the first base (1311a) of the second slit (1311). The thickness of the fracture portion (130-1) may vary with a step. The region (140) where the thin thickness is maintained constant may be the region where the first slit (1310) and the second slit (1311) overlap in the second direction (DR2).

[0063] Although the present invention has been described above by limited embodiments and drawings, the present invention is not limited thereto, and various implementations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

[0064] [Explanation of the symbol]

[0065] 1: Battery module

[0066] 10: First battery cell laminate

[0067] 11: Second battery cell laminate

[0068] 12: Lower frame

[0069] 13: Upper frame

[0070] 130, 130-1: Fracture section

[0071] 131, 131-1: Multiple slits

[0072] 1310: 1st slit

[0073] 1310a: First base of the first slit

[0074] 1310b: Second base of the first slit

[0075] 1310c: The first hypotenuse of the first slit

[0076] 1310d: Second hypotenuse of the first slit

[0077] 1311: Second slit

[0078] 1311a: First base of the second slit

[0079] 1311b: Second base of the second slit

[0080] 1311c: The first hypotenuse of the second slit

[0081] 1311d: Second hypotenuse of the second slit

[0082] 132: Benting Hall

[0083] 14: Central wall

Claims

1. A first battery cell stack in which a plurality of first battery cells are stacked; A plurality of second battery cells are stacked, and a second battery cell stack is arranged along one direction with the first battery cell stack; A lower frame having an open top that accommodates the first battery cell stack and the second battery cell stack; and It includes an upper frame that covers the first battery cell stack and the second battery cell stack and is connected to the lower frame, A battery module in which a plurality of slits penetrating the upper and lower surfaces are formed in the upper frame, and the upper frame portion adjacent to the plurality of slits breaks when thermal energy is concentrated above a predetermined value.

2. In Paragraph 1, It further includes a central wall that is accommodated inside the lower frame and disposed between the first battery cell stack and the second battery cell stack, The central wall above is a battery module that overlaps with the plurality of slits.

3. In Paragraph 1, Each of the plurality of slits extends in a first direction which is the spacing direction between the first battery cell stack and the second battery cell stack, and the plurality of slits are spaced apart in a second direction intersecting the first direction, forming a battery module.

4. In Paragraph 3, Each of the above plurality of slits is a battery module having a square shape.

5. In Paragraph 3, A battery module wherein the plurality of slits each include first slits and second slits arranged spaced apart in the second direction, and the first slits and the second slits are arranged intersectingly along the second direction.

6. In Paragraph 5, Each of the first slits and the second slits has a trapezoidal shape including first and second bases parallel to each other and first and second hypotenuses connecting the first and second bases, wherein the first base is shorter than the second base.

7. In Paragraph 6, A battery module in which the length of the first base is 1 / 3 or more and 2 / 3 or less of the length of the second base.

8. In Paragraph 6, A battery module in which, when the second base of the first slit is spaced apart from the first base in the first direction, the first hypotenuse of the first slit extends from the first base in a direction opposite to the first direction and the second direction and is connected to the second base, and the second hypotenuse of the first slit extends from the first base in a direction opposite to the first direction and the second direction and is connected to the second base.

9. In Paragraph 6, A battery module in which, when the first base of the second slit is spaced apart from the second base in the first direction, the first hypotenuse of the second slit extends from the second base in a direction opposite to the first direction and the second direction and is connected to the first base, and the second hypotenuse of the second slit extends from the second base in a direction opposite to the first direction and the second direction and is connected to the first base.

10. In Paragraph 6, A battery module in which the first hypotenuse of the first slit is adjacent to the first hypotenuse of the second slit adjacent to the first hypotenuse of the first slit, and the second hypotenuse of the first slit is adjacent to the second hypotenuse of the second slit adjacent to the second hypotenuse of the first slit.

11. In Paragraph 6, A battery module in which the first base of the first slit overlaps with the second slit in the second direction, and the first base of the second slit overlaps with the first slit in the second direction.

12. In Paragraph 6, The upper frame portion adjacent to the aforementioned plurality of slits and which fractures when thermal energy is concentrated is defined as a fracture portion, and A battery module in which the thickness of the fracture portion adjacent to the second base of the first slit is thicker than the thickness of the fracture portion adjacent to the first base of the first slit.

13. In Paragraph 12, A battery module in which the thickness of the fracture portion adjacent to the second base of the first slit is 1.5 to 3 times the thickness of the fracture portion adjacent to the first base of the first slit.

14. In Paragraph 12, A battery module in which the thickness of the above-mentioned fracture section changes with a step.

15. In Paragraph 12, A battery module in which the thickness of the above-mentioned fracture portion gradually decreases as it approaches the first base of the first slit from the second base of the first slit.

16. In Paragraph 1, A venting hole penetrating the upper and lower surfaces is further formed in the upper frame, and the venting hole is a battery module that overlaps with the first battery cell stack and the second battery cell stack.

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