Battery shell, secondary battery and battery pack

Abstract

The utility model provides a battery shell, a secondary battery and a battery pack. The battery shell comprises a shell part and a folding part, the shell part comprises a surrounding side wall and an opening positioned at the end part of the side wall, the folding part is formed by extending and folding at least part of the side wall positioned at the opening, and the folding part and the corresponding side wall are stacked to form a thickened part. According to the battery shell, the folding parts are arranged at the openings in the end parts of the side walls, so that the shell wall thickness and the strength of at least part of the openings are increased on the premise that the shell part meets the strength requirement, the shell wall thickness at the openings meets the welding requirement with an end cover assembly, and the lightweight treatment of the battery shell is further realized. Meanwhile, the material cost is reduced, and the material utilization rate is increased. And under the condition that the volume of the battery shell is limited, the space utilization rate of the battery shell is further improved, so that the energy density of the battery is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to battery shell lightweight design technical field, concretely relates to a battery shell, secondary battery and battery pack. BACKGROUND

[0002] With the development of new energy technology, the progress of battery technology and the lightweight of battery shell have become an important development direction of the industry. The lightweight processing of the battery shell not only can reduce the overall weight of the battery pack, but also can indirectly improve the energy density of the battery pack. The battery with high energy density can store more electric energy under the same volume or weight, thereby prolonging the endurance mileage or use time of the equipment. However, in the existing battery shell, under the premise of meeting the strength requirement of the shell, the welding requirement of the shell and the end cover connection is also met. The battery shell is usually designed with equal wall thickness, which is difficult to achieve the ultimate wall thickness, and further realize the lightweight of the battery shell. SUMMARY

[0003] In view of the problems existing in the prior art, the utility model provides a battery shell, a secondary battery and a battery pack to improve the technical problem that the existing battery shell is usually designed with equal wall thickness and is difficult to further lightweight the battery shell.

[0004] To solve the above technical problems, the utility model provides a battery shell in the first aspect, the battery shell includes a shell part and a folded part. The shell part includes a surrounding side wall and an opening at the end of the side wall. The folded part is formed by at least part of the side wall at the opening being folded and extended, and the folded part is stacked with the corresponding side wall to form a thickened part.

[0005] In an embodiment of the battery shell of the utility model, the folded part includes at least one folded stacking layer.

[0006] In an embodiment of the battery shell of the utility model, the thickness of the thickened part is T1, and the thickness of the side wall corresponding to the folded part is T2, wherein T2+0.1mm≤T1≤3T2.

[0007] In an embodiment of the battery shell of the utility model, the material of the side wall is an aluminum plate or an aluminum alloy plate, and the thickness of the side wall ranges from 0.25mm to 1mm.

[0008] In an embodiment of the battery shell of the utility model, the material of the side wall is a steel plate or an alloy steel plate, and the thickness of the side wall ranges from 0.1mm to 1mm.

[0009] In an embodiment of the battery shell of the utility model, the length of the folded part is H, wherein 0.3mm≤H≤15mm.

[0010] In the battery shell embodiment of the utility model, the length of the folding part is 2mm≤H≤8mm.

[0011] In the battery shell embodiment of the utility model, the folding part is arranged around the inner side of the shell part.

[0012] The utility model discloses a secondary battery, which comprises the battery shell of any one of the above.

[0013] The utility model discloses a battery pack, which comprises the secondary battery of any one of the above.

[0014] The utility model provides a kind of battery shell, secondary battery and battery pack, the battery shell is by being provided with folding part at the opening of shell part, under the premise that shell part meets strength requirement, increase the shell wall thickness and strength of opening, make the shell wall thickness of opening meet the welding requirement with end cover assembly, further realize the lightweight processing of battery shell.Meanwhile, the raw material for making battery shell is the plate material of equal wall thickness satisfying shell strength requirement, not the equal wall thickness plate material of relatively larger thickness satisfying shell welding requirement, reduce material cost, improve the utilization of material.And, under the condition that the volume of battery shell is limited, further improve the space utilization of battery shell, thereby improve the energy density of battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical scheme in the embodiments of the utility model or prior art, the drawings needed to be used in the embodiment or prior art description will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the utility model, and those skilled in the art can obtain other embodiments according to these drawings without creating labor.

[0016] Figure 1 It is a three-dimensional schematic diagram in the battery shell embodiment of the utility model;

[0017] Figure 2 It is a part of three-dimensional state schematic diagram in the battery shell embodiment of the utility model;

[0018] Figure 3 It is the assembly connection schematic diagram of battery shell and end cover assembly in an embodiment of the utility model;

[0019] Figure 4 It is the structure section view of the assembly connection part of battery shell and end cover assembly in an embodiment of the utility model;

[0020] Figure 5 It is the thickening part forming schematic diagram in the battery shell embodiment of the utility model;

[0021] Figure 6 Figure 2 is a schematic view of a plurality of folded and stacked layers in an embodiment of the battery case of the present application.

[0022] Element number explanation:

[0023] 100, battery case; 101, first main wall surface; 102, second main wall surface; 103, first side wall surface; 104, second side wall surface; 105, first weld; 110, case portion; 111, side wall; 112, opening; 120, folded portion; 121, folded and stacked layer; 130, thickened portion; 200, end cover assembly. DETAILED DESCRIPTION

[0024] The above embodiments and the features thereof can be combined with each other on the premise of not conflicting with each other, and can be combined with the features in the embodiments. It should be understood that the terms used in the embodiments of the present application are used for describing specific embodiments, but are not intended to limit the protection scope of the present application. The test methods not specified in the following embodiments are usually performed according to the conventional conditions or the conditions recommended by the manufacturers.

[0025] When the embodiments give a numerical range, it should be understood that, unless otherwise specified by the present application, both ends of each numerical range and any number between the two ends can be selected. Unless otherwise defined, all technical and scientific terms used in the present application are used by those skilled in the art of the present technology and the description of the present application, and any method, device and material of the prior art similar or equivalent to the method, device and material of the embodiments of the present application can be used to realize the present application.

[0026] It should be understood that the terms such as "up", "down", "left", "right", "middle" and "one" in the specification are only for the convenience of clear description, and are not intended to limit the scope of the present application. The change or adjustment of the relative relationship without substantial change of the technical content is also regarded as the scope of the present application.

[0027] To address the technical challenge of achieving further weight reduction in battery casings, which are typically designed with uniform wall thickness, this invention provides a battery casing, a secondary battery, and a battery pack. This battery casing, while meeting strength requirements at the casing level, increases the wall thickness and strength at the opening, ensuring that the wall thickness at the opening meets the welding requirements with the end cap assembly. This further achieves weight reduction of the battery casing while maintaining welding quality.

[0028] Please see Figures 1 to 6 The first aspect of this utility model provides a battery housing 100, which includes a housing portion 110 and a folded portion 120. The housing portion 110 includes a surrounding sidewall 111 and an opening 112 located at the end of the sidewall 111. The sidewall 111 can be a cylindrical structure formed by bending and surrounding a metal sheet. The manner in which the sidewall 111 is formed into a cylindrical structure is not limited; it can be any type of surrounding structure that allows the housing portion 110 to form a closed loop contour. For example, it can be cylindrical, rectangular, or prismatic, or it can be surrounded along any other contour structure that can form a closed loop contour. The connecting ends of the sidewall 111 that are closed around the perimeter are connected by welding. The welding method is not limited; for example, it can be friction stir welding, gas metal arc welding (MIG), cold metal transfer welding (CMT), resistance spot welding, laser welding, etc., but is not limited thereto. The housing portion 110 can also be a cylindrical structure integrally stamped or integrally cast. Specifically, in this embodiment, the housing portion 110 adopts a rectangular cylindrical housing formed by bending a metal sheet. For details, please refer to... Figure 1 Based on the area of ​​the casing walls of the battery casing 100, the two opposite walls with larger areas are designated as the first main wall 101 and the second main wall 102, and the two opposite walls with smaller areas are designated as the first side wall 103 and the second side wall 104. The first side wall 103 is a welded wall that surrounds and closes the battery casing 100. The first side wall 103 is closed by welding, forming a first weld 105. Part of the first side wall 103, the first main wall 101, the second side wall 104, the second main wall 102, and another part of the first side wall 103 sequentially surround and form the casing portion 110 of the battery casing 100, forming a receiving cavity for accommodating the electrode assembly. Meanwhile, in order to ensure the welding quality of the first weld 105, the wall area at the first weld 105 can be thickened. The method of thickening is not limited. For example, a metal plate of the same material as the battery casing 100 can be set at the weld connection on the side of the first side wall 103 facing the cavity to ensure the connection reliability at the first weld 105. Alternatively, the thickness of the first side wall 103 at the first weld 105 can be increased.

[0029] The end of the side wall 111 is provided with an opening 112, the number of which can be one or two, depending on the forming method of the battery case 100, for example, when the case portion 110 is punch-formed or injection-molded, the number of the opening 112 at the end of the side wall 111 is one, when the side wall 111 is a closed structure, the number of the opening 112 of the case portion 110 is two. Specifically, in the present embodiment, the number of the opening 112 is two, which are respectively located at the two ends of the side wall 111, the structure of the opening 112 is rectangular, and the inside of the side wall 111 between the two openings 112 is a containing cavity for containing the electrode assembly and electrolyte of the battery. The end cover assembly 200 covers the opening 112 of the case portion 110 to seal the secondary battery. The end cover assembly 200 and the battery case 100 are connected and fixed by laser welding.

[0030] Please refer to Figures 1 to 6 The folding portion 120 is provided on the case portion 110 at the opening 112, and the folding portion 120 is formed by folding at least part of the side wall 111 at the opening 112. Specifically, the direction of folding to form the folding portion 120 is not limited, the side wall 111 at the opening 112 can be folded inward, so that the folding portion 120 is formed inside the containing cavity of the case portion 110. The side wall 111 at the opening 112 can also be folded outward, so that the folding portion 120 is formed to adhere to the side wall 111 outside the opening 112. The folding portion 120 can be a partial folding structure or a surrounding folding structure, for example, one, two or three end wall surfaces of the first main wall surface 101, the second main wall surface 102, the first side wall surface 103 and the second side wall surface 104 at the opening 112 can be folded, to form a partial folding portion 120 at the opening 112. All the wall surfaces of the first main wall surface 101, the second main wall surface 102, the first side wall surface 103 and the second side wall surface 104 at the opening 112 can also be folded to form a surrounding folding structure, as long as the welding effect between the battery case 100 and the end cover assembly 200 at the opening 112 can be strengthened. The formed folding portion 120 after folding needs to be flattened, that is, along the wall thickness direction of the side wall 111, the folding portion 120 adheres to the inner wall surface or the outer wall surface of the side wall 111.

[0031] The folding part 120 and the corresponding side wall 111 are stacked to form a thickened part 130. The thickened part 130 at least partially overlaps with the end cover assembly 200 of the cover opening 112, wherein the overlapping area of the thickened part 130 and the end cover assembly 200 is the welding area of the end cover assembly 200 and the battery shell 100. The thickened part 130 formed by the folding part 120 and the corresponding side wall 111 increases the material thickness of the welding area, thereby providing a solid base for welding and helping to improve the strength and durability of the welding joint, reducing the risk of structural failure caused by welding defects. Further, the structure of the thickened part 130 can make the heat distribution more uniform during welding, avoiding local overheating or overcooling, thereby reducing welding distortion and stress concentration, further improving welding quality. The design of the thickened part 130 also improves the local strength of the shell part 110 of the battery shell 100 near the opening 112.

[0032] The battery shell 100 increases the shell wall thickness and strength at the opening 112 of the shell part 110 by providing a folding part 120 at the opening 112, thereby meeting the welding requirements of the end cover assembly 200 while meeting the strength requirements of the shell part 110, further realizing the lightweight processing of the battery shell 100. At the same time, the raw material for manufacturing the battery shell 100 is an equal-thickness plate that meets the shell strength requirements, rather than an equal-thickness plate that meets the shell welding requirements, thereby reducing material costs and improving material utilization. In addition, in the case of limited volume of the battery shell 100, the space utilization of the battery shell 100 is further improved, thereby improving the energy density of the secondary battery. Further, since the folding part 120 is a structure formed by folding the side wall 111, the folding connection between the folding part 120 and the side wall 111 is a circular arc structure, which can facilitate the embedded installation of the battery shell 100 and the end cover assembly 200, thereby reducing the installation difficulty.

[0033] Please refer to Figures 5 to 6 In an embodiment of the battery shell of the utility model, the folding part 120 includes at least one folding stack layer 121 formed by folding the side wall 111. Specifically, according to the strength requirements of the welding between the battery shell 100 and the end cover assembly 200, when the wall thickness of the side wall 111 is relatively thick, the side wall 111 at the opening 112 can be folded once, i.e. to form one folding stack layer 121. When the wall thickness of the side wall 111 is relatively thin, the side wall 111 at the opening 112 can be folded multiple times, for example, it can be folded twice in succession to form two folding stack layers 121, or it can be folded three times in succession to form three folding stack layers 121, until the thickened part 130 formed by the folding part 120 and the side wall 111 can meet the welding thickening requirements of the battery shell 100 and the end cover assembly 200.

[0034] Please refer toFigures 4 to 6 In the battery shell embodiment, the thickness of the thickened portion 130 is T1 in the wall thickness direction of the side wall 111, and the thickness of the side wall 111 is T2, wherein T2+0.1mm≤T1≤3T2. The thickness value of the thickened portion 130 can be adjusted according to different application scenarios and performance requirements. For example, when the thickness T2 of the side wall 111 is 0.1mm, the side wall 111 of the opening 112 is folded once, that is, the number of folded stacking layers 121 is one, thereby forming the thickness T1 of the thickened portion 130 as 0.2mm, that is, T1=T2+0.1mm. Please refer to Figure 6 When in a scenario with higher strength requirements, the side wall 111 of the opening 112 is folded twice, that is, the number of folded stacking layers 121 is two, thereby forming the thickness T1 of the thickened portion 130 as T1=3T2.

[0035] In the battery shell embodiment, the material of the side wall 111 is an aluminum plate or an aluminum alloy plate. Compared with a steel plate, the aluminum plate or the aluminum alloy plate has a lower density. Using the aluminum plate or the aluminum alloy plate as the manufacturing material of the battery shell 100 can significantly reduce the weight of the battery shell 100 while ensuring the structural strength. At the same time, the aluminum plate or the aluminum alloy plate has good heat conduction performance, which can effectively help the battery to dissipate heat and reduce the damage of the battery due to overheating during charging and discharging. At the same time, the battery shell 100 made of aluminum plate or aluminum alloy plate has better bending performance. When the side wall 111 is formed by surrounding bending or the folded portion 120 is formed by folding, the manufacturing and forming difficulty of the battery shell 100 is reduced. The thickness of the side wall 111 is in the range of 0.25mm≤T2≤1mm. By selecting the thickness range of 0.25mm to 1mm, the battery shell 100 can balance between light weight and strength. For example, for small batteries, a thinner material (such as 0.25mm, 0.4mm) can be selected for the side wall 111 to reduce the weight, and for large batteries that require higher strength, a thicker material (such as 0.8mm, 1mm) can be selected to manufacture the battery shell 100.

[0036] In the battery shell embodiment of the utility model, the material of the side wall 111 is steel plate or alloy steel plate, the steel plate or alloy steel plate is selected as the material of the side wall 111, that is, the manufacturing material of the battery shell 100, the steel plate and alloy steel plate have higher mechanical strength, good processing performance and corrosion resistance, can effectively resist external impact and mechanical stress, can guarantee the structural strength of the battery shell 100, and meet the use demand of battery under complex working condition. For example, the battery shell 100, that is, the side wall 111, can adopt low-carbon steel, stainless steel, pre-plated nickel steel strip, cold-rolled steel, high-strength steel and other metal plate materials, but not limited to. In order to realize the balance of light weight and strength of the battery shell 100, preferably, when the material of the side wall 111 is steel plate or alloy steel plate, the thickness of the side wall 111 is 0.1mm≤T2≤1mm. For example, the thickness of the side wall 111 can be 0.1mm, 0.3mm, 0.5mm, 0.8mm or 1mm, but not limited to. The thickness of the battery shell 100 can be determined comprehensively according to the size of the secondary battery and the use scene and other factors, for example, the thinner thickness of the side wall 111 (such as 0.1mm) can still provide sufficient structural strength while reducing the weight of the battery, and meet the mechanical requirements of the battery in the use process. And the side wall 111 formed by the thicker material (such as 1mm) is suitable for the scene with higher strength requirement, such as used in high-vibration or high-impact environment.

[0037] Please refer to Figure 5 In the battery shell embodiment of the utility model, along the axis direction of the shell part 110 away from the opening 112, the length of the folding part 120 is H. Wherein 0.3mm≤H≤15mm. That is, in the embodiment, along the connecting direction of the two end openings 112 of the side wall 111 of the rectangular cylindrical structure, the length of the folding part 120 from the folding end of the folding part 120 and the side wall 111 to the folding end away from the folding end is H, the minimum folding length of the folding part 120 is Hmin, Hmin≥0.3mm, to ensure that the thickening part 130 and the end cover assembly 200 have at least a certain lap area, that is, the area where the lap area is the welding area between the thickening part 130 and the end cover assembly 200, on the basis of the lightest weight of the battery shell 100, the welding strength between the end cover assembly 200 and the battery shell 100 can be improved to a certain extent. The maximum folding length of the folding part 120 is Hmax, Hmax≤15mm. When the folding length of the folding part 120 increases, there is enough lap area between the folding part 120 and the end cover assembly 200, the thickening part 130 has enough strength, the welding effect between the folding part 120 and the shell part 110 is effectively improved, the folding difficulty of the folding part 120 is reduced, and the production efficiency of the battery shell 100 is improved.

[0038] Further, on the basis of considering factors such as material cost, production efficiency, welding strength, folding difficulty and the like, the length dimension of the folding part 120 is further optimized, in an embodiment of the battery shell of the utility model, the length range of the folding part 120 is 2mm≤H≤8mm, that is, when the folding forms the folding part 120, the folding length of the folding part 120 is not less than 2mm, the lap area between the folding part 120 and the end cover assembly 200 can be increased, the welding area between the thickening part 130 and the end cover assembly 200 is increased, the welding effect of welding the end cover assembly 200 and the battery shell 100 is guaranteed, the sealing property of the containing cavity of the battery shell 100 is improved, liquid or gas leakage and external substances entering are prevented.The folding length of the folding part 120 does not exceed 8mm, on the basis of guaranteeing that the folding part 120 and the end cover assembly 200 have sufficient lap area, the folding difficulty of the folding part 120 is further reduced, and the material cost of the battery shell 100 is reduced.At the same time, when the folding part 120 is an inward turning structure, the folding part 120 is prevented from excessively penetrating into the containing cavity of the battery shell 100, the installation of the electrode assembly in the containing cavity is affected or the electrode assembly is damaged, and the safety performance of the battery is guaranteed.When the folding part 120 is an outward turning structure, the conspicuousness of the folding part 120 outside the side wall 111 is reduced.The length of the folding part 120 can be any folding length of 2mm to 8mm, for example, can be 2mm, 3.5mm, 5mm, 7mm or 8mm, but is not limited thereto.

[0039] Since the end cover assembly 200 covers the opening 112 of the battery shell 100, and the end cover assembly 200 and the opening end of the battery shell 100 are circumferentially sealed and welded, in order to guarantee that the welding position of the battery shell 100 has sufficient strength and thickness, please refer to Figure 2 and Figure 4 In an embodiment of the battery shell of the utility model, the folding part 120 and the contour of the opening 112 are matched, the folding part 120 is a circumferential structure, and the folding part 120 is circumferentially arranged on the side wall 111 at the opening 112.That is, along the thickness direction of the side wall 111, the thickening part 130 is basically an equal-thickness structure, compared with forming a partial thickening structure at the opening 112 of the side wall 111, the equal-thickness structure of the thickening part 130 ensures uniform heat distribution during welding, reduces welding defects (such as virtual welding, cracks and the like), and further improves the welding quality after the battery shell 100 and the end cover assembly 200 are welded.At the same time, the circumferential structure of the folding part 120 and the contour of the opening 112 are matched, the structural damage caused by weak welding points is reduced, stress can be better dispersed, and the overall stability of the battery shell 100 is enhanced.

[0040] Further, please refer to Figure 2In the embodiment, the folding part 120 is an inward folding structure, and the folding part 120 is arranged around the inner side of the shell part 110. That is, the folding part 120 is located on the inner wall surface of the side wall 111 facing the accommodation cavity. The folding part 120 in the inward folding structure is at least partially attached to the end cover assembly 200, so as to ensure the sealing of the accommodation cavity after the end cover assembly 200 is installed on the battery shell 100, and prevent liquid leakage, gas leakage or external substances from entering. Compared with the outward folding structure of the folding part 120, the folding part 120 in the inward folding structure does not increase the external size of the battery shell 100, so that the mounting surface on the outer side of the battery shell 100 is more flat, and the assembly with other components is facilitated. Further, the folding part 120 is hidden in the accommodation cavity of the battery shell 100, and the end of the folding part 120 extending in the direction away from the opening 112 does not need to be processed again, that is, there is no need to worry about the edge lifting of the folding part 120 or the gap between the folding part 120 and the wall surface of the battery shell 100, thereby reducing the dependence on the complex welding process and reducing the process difficulty and cost in the production process.

[0041] The second aspect of the utility model further provides a secondary battery, the secondary battery includes the battery shell 100, the end cover assembly 200 and the electrode assembly (not shown in the figure) arranged in the battery shell 100 of any one of the above. The end of the battery shell 100 has an opening 112, and the electrode assembly is accommodated in the interior of the battery shell 100 through the opening 112. It should be noted that the end cover assembly 200 of the utility model includes a cover plate, a lower plastic, a pole, a tab welding piece and other conventional components and conventional layout structures, which will not be described here. Since the battery shell 100 of the embodiment adopts the technical solutions in the above embodiments, it at least has the beneficial effects brought by the technical solutions in the above embodiments, which will not be described here.

[0042] The third aspect of the utility model further provides a battery pack, and the battery pack at least includes a plurality of secondary batteries, a battery pack box and a box cover matched with the box. The plurality of secondary batteries are placed in the box, and are connected in series or parallel with each other or a combination of series and parallel connection. The box cover is sealed on the box to protect the plurality of secondary batteries. Since the battery pack of the embodiment adopts the technical solutions in the above embodiments, it at least has the beneficial effects brought by the technical solutions in the above embodiments, which will not be described here. It should be noted that the battery pack can include a battery pack thermal management system, a circuit board and other parts in addition to the secondary battery of the utility model. The battery pack can be a battery module or a battery pack, an energy storage cabinet, etc. The details will not be described here.

[0043] The utility model provides a kind of battery shell, secondary battery and battery pack, the battery shell is set to turn over and fold part at the opening of shell part, increase the shell wall thickness and strength of opening under the premise that shell part meets strength requirement, make the shell wall thickness of opening meet the welding requirement with end cover assembly, further realize the lightweight processing of battery shell.Meanwhile, the raw material for making battery shell is the plate material of equal wall thickness satisfying shell strength requirement, not the equal wall thickness plate material of relatively large thickness satisfying shell welding requirement, reduce material cost, improve the utilization of material.And, under the condition that the volume of battery shell is limited, further improve the space utilization of battery shell, so as to improve the energy density of battery.

[0044] The utility model discloses a kind of battery shell, secondary battery and battery pack, the battery shell is set to turn over and fold part at the opening of shell part, increase the shell wall thickness and strength of opening under the premise that shell part meets strength requirement, make the shell wall thickness of opening meet the welding requirement with end cover assembly, further realize the lightweight processing of battery shell.Meanwhile, the raw material for making battery shell is the plate material of equal wall thickness satisfying shell strength requirement, not the equal wall thickness plate material of relatively large thickness satisfying shell welding requirement, reduce material cost, improve the utilization of material.And, under the condition that the volume of battery shell is limited, further improve the space utilization of battery shell, so as to improve the energy density of battery. To improve the technical problem that existing battery shell is difficult to be further lightweighted under the condition of equal wall thickness design. Therefore, the utility model effectively overcomes some practical problems in prior art and has high utilization value and use significance.

[0045] The above embodiment is only illustrative of the principle and effect of the utility model, and is not used to limit the utility model. Any person skilled in the art can modify or change the above embodiment without departing from the spirit and scope of the utility model. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical idea disclosed by the utility model should be covered by the claims of the utility model.

Claims

1. A battery case characterized by comprising: The battery case comprises: a case portion comprising a surrounding side wall and an opening at an end of the side wall; a folded portion formed by folding at least a part of the side wall at the opening, the folded portion and the corresponding side wall being stacked to form a thickened portion.

2. The battery case according to claim 1, characterized by The folded portion comprises at least one folded stack layer.

3. The battery case according to claim 1 or 2, characterized by The thickened portion has a thickness T1, and the side wall corresponding to the folded portion has a thickness T2, wherein T2+0.1mm≤T1≤3T2.

4. The battery case according to claim 3, characterized by The material of the side wall is aluminum plate or aluminum alloy plate, and the thickness of the side wall ranges from 0.25mm≤T2≤1mm.

5. The battery case of claim 3, wherein, The material of the side wall is steel plate or alloy steel plate, and the thickness of the side wall ranges from 0.1mm≤T2≤1mm.

6. The battery case of claim 1, wherein, The length of the folded portion is H, wherein 0.3mm≤H≤15mm.

7. The battery case of claim 6, wherein, The length of the folded portion ranges from 2mm≤H≤8mm.

8. The battery case of claim 1, wherein, The folded portion is arranged on the inner side of the case portion.

9. A secondary battery characterized by comprising: The battery case according to any one of claims 1 to 8.

10. A battery pack characterized by comprising: The secondary battery according to claim 9.

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