Cylindrical busbar assembly and battery cell unit including the same

Abstract

A cylindrical busbar assembly is provided, including a busbar frame including a bottom plate, a sidewall including a slit, and a fixing pin, a busbar including an upper end portion having an upper hole and a lower end portion having a lower hole connected to the upper hole, and a fastener, wherein the fixing pin is inserted into the lower hole, and the fastener is inserted into the upper hole and bonded to the fixing pin.

Description

Technical Field

[0001] This disclosure relates to a cylindrical busbar assembly and a battery cell unit including the same.

[0002] This application claims the benefit of Korean Patent Application No. 10-2025-0013356, filed on February 3, 2025, the disclosure of which is incorporated herein by reference. Background Technology

[0003] Rechargeable batteries can be reused for extended periods through recharging. They are used in various fields, such as mobility, portable electronic devices, and energy storage systems (ESS). In particular, the demand for rechargeable batteries for mobility applications is further increasing in order to reduce dependence on fossil fuels and reduce carbon emissions.

[0004] A battery pack is the final unit in a secondary battery system used for storing energy in mobility applications, and it is installed in a mobility vehicle. A battery pack comprises multiple battery cell assemblies, and each battery cell assembly comprises multiple battery cells. A battery cell is the smallest unit used to store energy in a secondary battery system for mobility applications.

[0005] To meet the current and voltage requirements of the battery cell assembly, the battery cells are connected in parallel and series with each other via busbar assemblies. Conventional busbar assemblies are designed to match the number of battery cells included in the battery cell assembly. Therefore, in related technologies, it is difficult to add battery cells to the battery cell assembly. Summary of the Invention

[0006] Technical issues

[0007] The purpose of this disclosure is to provide a cylindrical busbar assembly with a novel structure that allows battery cells to be easily added to a battery cell assembly.

[0008] Technical solution

[0009] An exemplary embodiment of this disclosure for solving the above problems is as follows.

[0010] The cylindrical busbar assembly according to an exemplary embodiment includes: A busbar frame, comprising a base plate, sidewalls containing slots, and retaining pins; A manifold, comprising an upper end having an upper hole and a lower end having a lower hole connected to the upper hole; and Fasteners, among which The retaining pin is inserted into the lower hole, and The fastener is inserted into the upper hole and engaged with the retaining pin.

[0011] In an exemplary embodiment, the retaining pin can be connected to the base plate.

[0012] In an exemplary embodiment, the fixing pin may include a straight portion and a tapered portion.

[0013] In an exemplary embodiment, the axial direction of the cylindrical busbar assembly is a first direction, and the area of ​​the cross-section of the tapered portion perpendicular to the first direction can increase as the cross-section gets closer to the base plate.

[0014] In an exemplary embodiment, the tapered portion may be located between the straight portion and the base plate.

[0015] In an exemplary embodiment, the axial direction of the cylindrical busbar assembly is a first direction, the area of ​​the cross-section at the upper end that is perpendicular to the first direction can decrease as the cross-section gets closer to the bottom plate, and the area of ​​the cross-section at the lower end that is perpendicular to the first direction can increase as the cross-section gets closer to the bottom plate.

[0016] In an exemplary embodiment, the busbar may include: an upper gap configured to expand when a fastener is inserted into an upper hole; and a lower gap configured to expand when a retaining pin is inserted into a lower hole.

[0017] In an exemplary embodiment, the radial direction of the cylindrical busbar assembly is the second direction, the size of the upper end in the second direction can increase as the upper gap expands, and the size of the lower end in the second direction can increase as the lower gap expands.

[0018] In an exemplary embodiment, the axial direction of the cylindrical busbar assembly is a first direction, the fastener includes a head and a shank, and the area of ​​the cross-section of the head perpendicular to the first direction can decrease as the cross-section gets closer to the base plate.

[0019] In an exemplary embodiment, the axial direction of the cylindrical busbar assembly is a first direction, and the slit may extend in the first direction.

[0020] According to an exemplary embodiment, the battery cell unit includes: The first battery cell includes a first electrode lead; The second battery cell includes a second electrode lead; and A cylindrical busbar assembly connects a first electrode lead and a second electrode lead to each other. The cylindrical busbar assembly includes a busbar frame, a busbar, and fasteners. The busbar frame includes a base plate, sidewalls including slits, and fixing pins. The manifold includes an upper end having an upper hole and a lower end having a lower hole connected to the upper hole, wherein, The first electrode lead and the second electrode lead are inserted into the slit. The retaining pin is inserted into the lower hole, and Fasteners can be inserted into the upper hole and can be attached to the retaining pin.

[0021] In an exemplary embodiment, the circumferential direction of the cylindrical busbar assembly is a third direction, and the first electrode lead and the second electrode lead can be wound in the third direction within the busbar frame.

[0022] In an exemplary embodiment, the first electrode lead and the second electrode lead can be inserted and fixed between the upper end and the sidewall and between the lower end and the sidewall.

[0023] In an exemplary embodiment, the first electrode lead and the second electrode lead can be inserted between the upper end and the sidewall and between the lower end and the sidewall and connected to each other.

[0024] Beneficial effects

[0025] The cylindrical busbar assembly according to an exemplary embodiment of the present disclosure allows for easy addition of battery cells to a battery cell assembly, occupies less space, and provides simple assembly with the battery cells.

[0026] The effects of the exemplary embodiments of this disclosure are not limited to those described above, and other effects not mentioned will be clearly derived and understood by those skilled in the art to which this disclosure pertains from the following description. In other words, those skilled in the art to which this disclosure pertains can also clearly derive and understand unintended effects arising from implementing the exemplary embodiments of this disclosure. Attached Figure Description

[0027] Figure 1 This is an exploded perspective view of a cylindrical busbar assembly according to an exemplary embodiment.

[0028] Figure 2 This is a perspective view of a busbar frame included in a cylindrical busbar assembly according to an exemplary embodiment.

[0029] Figure 3 This is a cross-sectional view of a busbar frame included in a cylindrical busbar assembly according to an exemplary embodiment.

[0030] Figure 4 yes Figure 3 A magnified view of a portion of it.

[0031] Figure 5 This is a perspective view of a busbar included in a cylindrical busbar assembly according to an exemplary embodiment.

[0032] Figure 6 This is a side view of a busbar included in a cylindrical busbar assembly according to an exemplary embodiment.

[0033] Figure 7 This is a perspective view of a fastener included in a cylindrical busbar assembly according to an exemplary embodiment.

[0034] Figure 8 This is a longitudinal sectional view of a cylindrical busbar assembly according to an exemplary embodiment.

[0035] Figure 9 This is an exploded perspective view of a battery cell according to an exemplary embodiment.

[0036] Figure 10 This is a diagram showing the state in which the first electrode lead and the second electrode lead are fixed and connected in a battery cell according to an exemplary embodiment. Detailed Implementation

[0037] The terms or words used in this disclosure should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as having a meaning consistent with the technical concept of this disclosure, based on the inventor's ability to appropriately define the meaning of the terms or words in order to best describe the principles of his or her invention.

[0038] In this disclosure, terms such as “comprising” or “having” are intended to specify the presence of features, quantities, steps, operations, components, parts, or combinations thereof described in this disclosure, and should be understood as not precluding the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts, or combinations thereof. Furthermore, when a portion of a layer, film, region, plate, etc., is referred to as being “on” another portion, this includes not only the case where it is “directly” on the other portion, but also the case where the other portion is inserted therein. Conversely, when a portion of a layer, film, region, plate, etc., is referred to as being “under” another portion, this includes not only the case where it is “directly” under the other portion, but also the case where the other portion is inserted therein.

[0039] Since the embodiments and drawings are merely examples of this disclosure and do not represent all the technical concepts of this disclosure, it should be understood that various equivalents and modifications may exist that can replace them.

[0040] In describing this disclosure, detailed descriptions of known configurations or functions will be omitted where it is determined that such detailed descriptions may obscure the main points of this disclosure.

[0041] Because the accompanying drawings are intended to describe this disclosure more fully to those skilled in the art, the shapes, dimensions, quantities, etc., of the components in the drawings may be exaggerated, omitted, or shown schematically for clarity. The shapes, dimensions, proportions, and quantities of the components in the drawings do not fully reflect the actual shapes, dimensions, proportions, and quantities of the components.

[0042] In the following, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0043] (First embodiment)

[0044] Figure 1 This is an exploded perspective view of a cylindrical busbar assembly according to an exemplary embodiment.

[0045] Reference Figure 1 The cylindrical busbar assembly 100 may include a busbar frame 10, a busbar 20, and fasteners 30. The structure of the cylindrical busbar assembly 100 according to the exemplary embodiment is completely different from that of a conventional busbar assembly. The structure of the cylindrical busbar assembly 100 according to the exemplary embodiment allows for easy addition of battery cells to a battery cell assembly. The structure of the cylindrical busbar assembly 100 according to the exemplary embodiment allows for easy addition of battery cells to a battery cell assembly included in a cell-to-pack (CTP) battery pack. The cylindrical busbar assembly 100 according to the exemplary embodiment occupies less space than a conventional busbar assembly and is easy to assemble with battery cells.

[0046] In this disclosure, the axial direction of the cylindrical busbar assembly 100 is defined as "axial direction". In this disclosure, the radial direction of the cylindrical busbar assembly 100 is defined as "radial direction". In this disclosure, the circumferential direction of the cylindrical busbar assembly 100 is defined as "circumferential direction".

[0047] Figure 2 This is a perspective view of a busbar frame included in a cylindrical busbar assembly according to an exemplary embodiment.

[0048] Figure 3 This is a cross-sectional view of a busbar frame included in a cylindrical busbar assembly according to an exemplary embodiment.

[0049] Reference Figure 2 and Figure 3 The busbar frame 10 may include a base plate 11, side walls 12, and fixing pins 13. The busbar frame 10 may include a hollow portion 10HP. The hollow portion 10HP may be a space defined by the base plate 11 and side walls 12. The hollow portion 10HP may be open at its upper part and closed at its lower part. The busbar 20 and fasteners 30 may be located within the hollow portion 10HP (see [link to documentation]). Figure 8 ).

[0050] The base plate 11 may be substantially perpendicular to the axial direction. The shape of the cross-section of the base plate 11 perpendicular to the axial direction may be approximately circular. The material of the base plate 11 may be a material with high electrical insulation properties, such as plastic.

[0051] The shape of the cross-section of the sidewall 12 perpendicular to the axial direction can be approximately a hollow circle. The material of the sidewall 12 can be a material with high electrical insulation properties, such as plastic. The sidewall 12 may include a slit 12SL. The slit 12SL can extend in the axial direction. The dimensions of the slit 12SL in the axial direction and the circumferential direction can be determined based on the width of the electrode leads, the thickness of the electrode leads, and the number of electrode leads to be inserted into the slit 12SL.

[0052] The retaining pin 13 can be located in the hollow portion 10HP. The retaining pin 13 can be connected to the base plate 11. The retaining pin 13 can extend from the base plate 11 in the axial direction. The material of the retaining pin 13 can be a material with high electrical insulation properties, such as plastic.

[0053] Figure 4 yes Figure 3 A magnified view of a portion of it.

[0054] Reference Figure 4 The retaining pin 13 may include a straight portion 13SP and a tapered portion 13TP. The tapered portion 13TP may be located between the straight portion 13SP and the base plate 11. The area of ​​the cross-section of the straight portion 13SP perpendicular to the axial direction may be substantially constant. The dimension of the straight portion 13SP in the radial direction may be substantially constant. The dimension of the straight portion 13SP in the radial direction may be equal to or less than the diameter of the lower hole 20BH of the manifold 20, which will be described later. The area of ​​the cross-section of the tapered portion 13TP perpendicular to the axial direction may increase as the cross-section becomes closer to the base plate 11. The dimension of the tapered portion 13TP in the radial direction may increase as this dimension becomes closer to the base plate 11. The dimension of the tapered portion 13TP in the radial direction may be equal to or greater than the diameter of the lower hole 20BH of the manifold 20, which will be described later.

[0055] Figure 5 This is a perspective view of a busbar included in a cylindrical busbar assembly according to an exemplary embodiment.

[0056] Figure 6 This is a side view of a busbar included in a cylindrical busbar assembly according to an exemplary embodiment.

[0057] Reference Figure 5 and Figure 6The busbar 20 may include an upper end 20TP, a middle portion 20MP, and a lower end 20BP. With the middle portion 20MP inserted therein, the upper end 20TP and the lower end 20BP may be spaced apart from each other in the axial direction. The upper end 20TP may be connected to the upper end of the middle portion 20MP, and the lower end 20BP may be connected to the lower end of the middle portion 20MP. The busbar 20 may be made of a highly conductive material, such as copper or aluminum.

[0058] The busbar 20 can have a generally biconical structure. The area of ​​the cross-section perpendicular to the axial direction of the upper end 20TP can decrease as the cross-section gets closer to the base plate 11. The radial dimension of the upper end 20TP can decrease as this dimension gets closer to the base plate 11. When no force is applied in the outward radial direction, the area of ​​the cross-section perpendicular to the axial direction of the middle portion 20MP can be substantially constant. When no force is applied in the outward radial direction, the radial dimension of the middle portion 20MP can be substantially constant. The radial dimension of the lower end 20BP can increase as this dimension gets closer to the base plate 11. The area of ​​the cross-section perpendicular to the axial direction of the lower end 20BP can increase as the cross-section gets closer to the base plate 11.

[0059] The upper end portion 20TP can be configured such that its radial dimension increases when a force is applied to the upper end portion 20TP in the outward radial direction. A portion of the middle portion 20MP can be configured such that its radial dimension increases when a force is applied to the middle portion 20MP in the outward radial direction. The lower end portion 20BP can be configured such that its radial dimension increases when a force is applied to the lower end portion 20BP in the outward radial direction.

[0060] The upper portion 20TP may include an upper hole 20TH. The upper hole 20TH may extend in the axial direction. The middle portion 20MP may include a middle hole. The middle hole may extend in the axial direction. The lower portion 20BP may include a lower hole 20BH. The lower hole 20BH may extend in the axial direction.

[0061] The upper hole 20TH, the middle hole, and the lower hole 20BH can be connected to each other. That is, the upper hole 20TH, the middle hole, and the lower hole 20BH can be considered as a single hole located at the center of the busbar 20 and extending in the first direction.

[0062] The busbar 20 may include an upper gap 20TG and a lower gap 20BG.

[0063] The upper clearance 20TG can be located in the upper part of the intermediate portion 20MP and the upper end 20TP. The upper clearance 20TG can be configured to expand when a force is applied to it in the outward radial direction. The upper clearance 20TG can be connected to the upper hole 20TH. The upper clearance 20TG can be configured to expand when the fastener 30, described later, is inserted into the upper hole 20TH.

[0064] When the fastener 30, described later, is inserted into the upper hole 20TH and the upper gap 20TG expands, the upper end 20TP can increase in the radial direction. When the fastener 30, described later, is inserted into the upper hole 20TH and the upper gap 20TG expands, the upper part of the middle portion 20MP can increase in the radial direction.

[0065] The lower gap 20BG can be located in the lower part of the intermediate portion 20MP and the lower end 20BP. The lower gap 20BG can be configured to expand when a force is applied to it in the outward radial direction. The lower gap 20BG can be connected to the lower hole 20BH. The lower gap 20BG can be configured to expand when the retaining pin 13 is inserted into the lower hole 20BH.

[0066] When the retaining pin 13 is inserted into the lower hole 20BH and the lower gap 20BG expands, the radial dimension of the lower end 20BP can increase. When the retaining pin 13 is inserted into the lower hole 20BH and the lower gap 20BG expands, the radial dimension of the lower part of the middle portion 20MP can increase.

[0067] Figure 7 This is a perspective view of a fastener included in a cylindrical busbar assembly according to an exemplary embodiment.

[0068] Reference Figure 7 The fastener 30 may include a head 30HE and a shank 30SH. The area of ​​the cross-section of the head 30HE perpendicular to the axial direction may decrease as the cross-section gets closer to the base plate 11. The radial dimension of the head 30HE may be equal to or greater than the diameter of the upper hole 20TH of the manifold 20. The radial dimension of the shank 30SH may be equal to or less than the diameter of the upper hole 20TH of the manifold 20. A thread 30TH may be formed on the shank 30SH.

[0069] Figure 8 This is a longitudinal sectional view of a cylindrical busbar assembly according to an exemplary embodiment.

[0070] Reference Figure 8The busbar 20 can be secured by a fastener 30 inserted into the upper hole 20TH and a retaining pin 13 inserted into the lower hole 20BH. When the fastener 30 is inserted into the upper hole 20TH, the upper gap 20TG expands, allowing the upper end 20TP to increase in the radial direction (see...). Figure 8 (See arrow in the image). When the fastener 30 is inserted into the upper hole 20TH and the retaining pin 13 is inserted into the lower hole 20BH, the upper gap 20TG and the lower gap 20BG expand, allowing a portion of the intermediate portion 20MP to increase in the radial direction (see...). Figure 8 (See the arrow in the image). When the retaining pin 13 is inserted into the lower hole 20BH, the lower gap 20BG expands, allowing the lower end 20BP to increase in the radial direction (see [reference]). Figure 8 (The arrow in the image).

[0071] (Second Embodiment)

[0072] Figure 9 This is an exploded perspective view of a battery cell according to an exemplary embodiment.

[0073] Reference Figure 9 The battery cell unit 1000 may include a cylindrical busbar assembly 100, a first battery cell 210, and a second battery cell 220. Although this disclosure describes only embodiments with two battery cells, the number of battery cells is not particularly limited. Based on this disclosure, those skilled in the art can readily derive embodiments in which the number of battery cells is three or more.

[0074] The cylindrical busbar assembly 100 is substantially the same as that described in the first embodiment.

[0075] The first battery cell 210 can be a lithium secondary battery. The first battery cell 210 can include an electrode assembly, an electrolyte, and a battery cell casing. The electrode assembly can include a positive electrode, a negative electrode, and a separator. The positive electrode can include a positive electrode active material layer, a positive electrode current collector, and a positive electrode terminal block. The negative electrode can include a negative electrode active material layer, a negative electrode current collector, and a negative electrode terminal block. The electrode assembly can be wound or stacked. The wound type can have a structure with the positive electrode, negative electrode, and separator wound together. The stacked type can have a structure including a first electrode unit comprising a first positive electrode, a first negative electrode, and a first separator, and a second electrode unit comprising a second positive electrode, a second negative electrode, and a second separator stacked therein, with a third separator inserted therebetween. The electrolyte can be liquid or gel type. The battery cell casing can be pouch type. The first battery cell 210 can include a first electrode lead 210EL. The first electrode lead 210EL can be a positive electrode lead or a negative electrode lead. The first electrode lead 210EL can protrude to one side of the pouch type battery cell casing. The positive lead can be electrically connected to one or more positive terminals, and the negative lead can be electrically connected to one or more negative terminals.

[0076] The second battery cell 220 is basically the same as the first battery cell 210. The second electrode lead 220EL of the second battery cell is basically the same as the first electrode lead 210EL of the first battery cell 210.

[0077] The first electrode lead 210EL and the second electrode lead 220EL can have the same or opposite polarities. Both the first electrode lead 210EL and the second electrode lead 220EL can be positive leads. Both the first electrode lead 210EL and the second electrode lead 220EL can be negative leads. The first electrode lead 210EL can be a positive lead, and the second electrode lead 220EL can be a negative lead. The first electrode lead 210EL can be a negative lead, and the second electrode lead 220EL can be a positive lead.

[0078] Figure 10 This is a diagram showing the state in which the first electrode lead and the second electrode lead are fixed and connected in a battery cell according to an exemplary embodiment.

[0079] Reference Figure 9 and Figure 10The first electrode lead 210EL and the second electrode lead 220EL can be inserted into the slit 12SL. The first electrode lead 210EL and the second electrode lead 220EL can be wound circumferentially inside the busbar frame 10. The first electrode lead 210EL and the second electrode lead 220EL can be inserted and fixed between the upper end 20TP and the side wall 12. The first electrode lead 210EL and the second electrode lead 220EL can be inserted and connected to each other between the upper end 20TP and the side wall 12. The first electrode lead 210EL and the second electrode lead 220EL can be inserted and fixed between the lower end 20BP and the side wall 12. The first electrode lead 210EL and the second electrode lead 220EL can be inserted between the lower end 20BP and the side wall 12 and connected to each other.

[0080] The above description is intended to illustrate this disclosure by way of example only. The scope of this disclosure should be interpreted as the appended claims, and all technical concepts within the scope of their equivalents should be interpreted as being included within the scope of this disclosure.

[0081] [Explanation of reference numerals in the attached figures]

[0082] 100: Cylindrical busbar assembly

[0083] 10: Busbar Framework

[0084] 10HP: Hollow section

[0085] 11: Base Plate

[0086] 12: Sidewall

[0087] 12SL: Slit

[0088] 13: Fixing pin

[0089] 13SP: Straight section

[0090] 13TP: Conical section

[0091] 20: Busbar

[0092] 20TP: Upper end

[0093] 20MP: Middle section

[0094] 20BP: Lower end

[0095] 20TH: Top Hole

[0096] 20BH: Bottom hole

[0097] 20TG: Upper gap

[0098] 20BG: Lower Gap

[0099] 30: Fasteners

[0100] 30HE: Head

[0101] 30SH: Handle

[0102] 30TH: Thread

[0103] 210: First battery cell

[0104] 210EL: First electrode lead

[0105] 220: Second battery cell

[0106] 220EL: Second electrode lead

Claims

1. A cylindrical busbar assembly, comprising: A busbar frame, the busbar frame including a base plate, a sidewall including a slit, and a fixing pin; A manifold, the manifold including an upper end having an upper hole and a lower end having a lower hole connected to the upper hole; as well as Fasteners, among which, The retaining pin is inserted into the lower hole, and The fastener is inserted into the upper hole and engaged with the retaining pin.

2. The cylindrical busbar assembly according to claim 1, wherein, The fixing pin is connected to the base plate.

3. The cylindrical busbar assembly according to claim 1, wherein, The fixing pin includes a straight portion and a tapered portion.

4. The cylindrical busbar assembly according to claim 3, wherein, The axial direction of the cylindrical busbar assembly is the first direction, and The area of ​​the section perpendicular to the first direction of the tapered portion increases as the section gets closer to the base plate.

5. The cylindrical busbar assembly according to claim 3, wherein, The tapered portion is located between the straight portion and the base plate.

6. The cylindrical busbar assembly according to claim 1, wherein, The axial direction of the cylindrical busbar assembly is the first direction. The area of ​​the cross-section perpendicular to the first direction at the upper end decreases as the cross-section gets closer to the bottom plate, and The area of ​​the cross section perpendicular to the first direction at the lower end increases as the cross section gets closer to the bottom plate.

7. The cylindrical busbar assembly according to claim 1, wherein, The busbar includes: Upper gap, the upper gap being configured to expand when the fastener is inserted into the upper hole; and The lower gap is configured to expand when the retaining pin is inserted into the lower hole.

8. The cylindrical busbar assembly according to claim 7, wherein, The radial direction of the cylindrical busbar assembly is the second direction. The dimension of the upper end in the second direction increases as the upper gap expands, and The dimension of the lower end in the second direction increases as the lower gap expands.

9. The cylindrical busbar assembly according to claim 1, wherein, The axial direction of the cylindrical busbar assembly is the first direction. The fastener includes a head and a shank, and The area of ​​the cross-section of the head perpendicular to the first direction decreases as the cross-section gets closer to the base plate.

10. The cylindrical busbar assembly according to claim 1, wherein, The axial direction of the cylindrical busbar assembly is the first direction, and The slit extends in the first direction.

11. A battery cell unit, comprising: The first battery cell includes a first electrode lead; The second battery cell includes a second electrode lead. as well as A cylindrical busbar assembly connects the first electrode lead and the second electrode lead to each other. The cylindrical busbar assembly includes a busbar frame, a busbar, and fasteners. The busbar frame includes a base plate, sidewalls including slits, and fixing pins. The busbar includes an upper end having an upper hole and a lower end having a lower hole connected to the upper hole, wherein, The first electrode lead and the second electrode lead are inserted into the slit. The retaining pin is inserted into the lower hole, and The fastener is inserted into the upper hole and engaged with the retaining pin.

12. The battery cell according to claim 11, wherein, The circumferential direction of the cylindrical busbar assembly is the third direction, and The first electrode lead and the second electrode lead are wound in the third direction within the busbar frame.

13. The battery cell according to claim 11, wherein, The first electrode lead and the second electrode lead are inserted and fixed between the upper end and the side wall and between the lower end and the side wall.

14. The battery cell according to claim 11, wherein, The first electrode lead and the second electrode lead are inserted between the upper end and the sidewall and between the lower end and the sidewall and are connected to each other.

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