Cylindrical battery cells, battery packs and electrical devices

Abstract

This application provides a cylindrical battery cell, a battery device, and an electrical device. It includes a housing, an end cap, and an electrode assembly. The housing has an opening at at least one end along its axial direction, and the housing is made of steel. The housing includes a sidewall extending circumferentially along the opening. The end cap covers the opening, and the end cap and housing together define a receiving space. The end cap is also made of steel, and is welded to the sidewall to form a first solder joint. The electrode assembly is housed within the receiving space. The effective penetration depth of the first solder joint is L, the maximum thickness of the sidewall is D, 0.5 ≤ L / D ≤ ​​1.5, and the average grain size of the first solder joint is 30 μm–150 μm. This cylindrical battery cell reduces the risk of fatigue cracking of the first solder joint and improves the service life of the cylindrical battery cell.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a cylindrical battery cell, a battery device, and an electrical device. Background Technology

[0002] Energy conservation and emission reduction are key to the sustainable development of the automotive industry, and electric vehicles, due to their energy-saving and environmentally friendly advantages, have become an important component of this sustainable development. For electric vehicles, battery technology is a crucial factor in their development.

[0003] In battery technology, the lifespan of individual battery cells is a crucial issue. Therefore, improving the lifespan of individual battery cells is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application provides a cylindrical battery cell, a battery device, and an electrical device, which can effectively extend the service life of the cylindrical battery cell.

[0005] In a first aspect, embodiments of this application provide a cylindrical battery cell, including a housing, an end cap, and an electrode assembly; the housing has an opening at at least one end along its axial direction, the housing is made of steel, and the housing includes a sidewall extending circumferentially along the opening; the end cap is disposed on the opening, the end cap and the housing together define a receiving space, the end cap is made of steel, and the end cap is welded to the sidewall to form a first solder mark; the electrode assembly is accommodated within the receiving space; wherein, the effective penetration depth of the first solder mark is L, the maximum thickness of the sidewall is D, 0.5≤L / D≤1.5, and the average grain size of the first solder mark is 30μm-150μm.

[0006] In the above technical solution, the ratio of the effective penetration depth L of the first solder joint to the maximum thickness D of the sidewall of the casing is 0.5-1.5, and the average grain size of the first solder joint is 30μm-150μm. This ensures that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall is not too small, and the average grain size of the first solder joint is not too large, thereby enhancing the strength of the first solder joint, reducing the risk of fatigue cracking, and extending the service life of the cylindrical battery cell. On the other hand, it also ensures that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall is not too large, and the average grain size of the first solder joint is not too small, reducing the welding difficulty between the end cap and the casing, lowering production costs, and achieving better economic efficiency. In this cylindrical battery cell, the influence of average grain size and effective penetration depth on the first solder joint is considered, and the ratio of the effective penetration depth L to the maximum thickness D of the sidewall of the casing, as well as the average grain size of the first solder joint, are controlled within a reasonable range, balancing the service life and economic requirements of the cylindrical battery cell.

[0007] In some embodiments, 2 / 3 ≤ L / D ≤ ​​1, and the average grain size of the first solder joint is 40 μm-100 μm. When L / D ≥ 2 / 3 and the average grain size of the first solder joint is less than or equal to 100 μm, the L / D ratio is not too small, and the average grain size of the first solder joint is not too large, thus enhancing the strength of the first solder joint, reducing the risk of fatigue cracking, and extending the service life of the cylindrical battery cell. When L / D ≤ ​​1 and the average grain size of the first solder joint is greater than or equal to 40 μm, the welding difficulty between the end cap and the casing is reduced, lowering production costs. Therefore, 2 / 3 ≤ L / D ≤ ​​1 and the average grain size of the first solder joint being 40 μm-100 μm further balances the service life and economic requirements of the cylindrical battery cell.

[0008] In some embodiments, 200μm≤L≤600μm. L≥200μm can improve the strength of the first solder mark and reduce the risk of welding failure between the end cap and the housing; L≤600μm can reduce the welding difficulty between the end cap and the housing and improve the welding efficiency. Therefore, 200μm≤L≤600μm can balance improving the strength of the first solder mark and reducing the welding difficulty between the end cap and the housing, thus reducing the risk of welding failure and improving the welding efficiency.

[0009] In some embodiments, 300μm ≤ L ≤ 400μm. L ≥ 300μm can further improve the strength of the first solder mark and reduce the risk of welding failure between the end cap and the housing; L ≤ 400μm can further reduce the welding difficulty between the end cap and the housing and improve the welding efficiency. Therefore, 300μm ≤ L ≤ 400μm can further improve the strength of the first solder mark and reduce the welding difficulty between the end cap and the housing, reduce the risk of welding failure between the end cap and the housing, and improve the welding efficiency between the end cap and the housing.

[0010] In some embodiments, 200μm ≤ D ≤ 600μm. D ≥ 200μm ensures sufficient wall thickness for the sidewalls of the casing, increasing their strength and reducing the risk of damage during internal pressure changes in the cylindrical battery cell. D ≤ 600μm prevents excessively thick sidewalls, reducing material usage and weight, thereby increasing the gravimetric energy density of the cylindrical battery cell. Therefore, 200μm ≤ D ≤ 600μm balances increasing sidewall strength and reducing weight, minimizing the risk of casing damage, and maximizing the gravimetric energy density of the cylindrical battery cell.

[0011] In some embodiments, 200μm ≤ D ≤ 450μm. D ≥ 200μm can improve the strength of the sidewalls of the casing and reduce the risk of casing damage; D ≤ 450μm can further reduce the weight of the casing, thereby increasing the gravimetric energy density of the cylindrical battery cell. Therefore, 200μm ≤ D ≤ 450μm can further improve the strength of the sidewalls of the casing and reduce the weight of the casing, reducing the risk of casing damage and increasing the gravimetric energy density of the cylindrical battery cell.

[0012] In some embodiments, along the axial direction of the housing, the end cap has a first outer surface facing away from the electrode assembly. The surface of the first solder joint includes a second outer surface, which connects the first outer surface and the outer peripheral surface of the sidewall. The sidewall has a first interface that contacts the end cap. The first interface is connected to the surface of the first solder joint at a first position, and the minimum distance between the first position and the second outer surface is the effective penetration depth of the first solder joint. On the one hand, during the cycling process of a cylindrical battery cell, the end cap is easily subjected to an expansion force along the axial direction of the housing. By connecting the second outer surface of the first solder joint to the first outer surface of the edge portion, the axial dimension of the first solder joint along the housing can be increased, thereby improving the connection strength between the end cap and the housing. On the other hand, the second outer surface connecting the first outer surface and the outer peripheral surface of the sidewall allows the first solder joint to eliminate sharp corners in the edge region of the end cap, reducing the risk of the cylindrical battery cell damaging other components.

[0013] In some embodiments, the first solder joint includes a first region and a second region. The average grain size of the first region is smaller than that of the second region. Along the radial direction of the housing, the first region is located outside the second region, and the outer surface of the first region is at least a portion of the second outer surface. By setting the average grain size of the outer first region to be smaller than that of the inner second region, the grain size of the outer region of the first solder joint is refined, thereby improving the strength of the first solder joint and effectively reducing the risk of fatigue cracking of the first solder joint.

[0014] In some embodiments, the end cap includes an edge portion and a body portion. The edge portion is connected to the body portion and is disposed around the outside of the body portion. A portion of the body portion extends into a sidewall along the axial direction of the housing. At least a portion of the edge portion is located on one side of the sidewall. A first solder joint connects the sidewall and the edge portion. The edge portion forms at least a portion of a first outer surface axially away from the surface of the electrode assembly. The sidewall acts as a limiter for the edge portion, reducing the risk of the end cap moving towards the electrode assembly during welding with the sidewall. This effectively improves the welding quality of the end cap and the housing and reduces the welding difficulty between the end cap and the housing.

[0015] In some embodiments, the first solder mark does not protrude from the outer peripheral surface of the sidewall along the radial direction of the housing. This reduces the risk of interference between the first solder mark and other components, and also reduces the risk of damage to the first solder mark due to external forces.

[0016] In some embodiments, the first solder mark partially protrudes from the outer peripheral surface of the sidewall along the radial direction of the housing. This increases the radial dimension of the first solder mark, improves its welding strength, and reduces the risk of cracking.

[0017] In some embodiments, the maximum dimension of the portion of the first solder mark protruding from the outer peripheral surface of the sidewall is K, where 0 μm < K ≤ 10 μm. K > 0 μm increases the radial dimension of the first solder mark, thereby improving its strength; K ≤ 10 μm reduces the risk of interference between the first solder mark and other components, thus reducing the risk of damage to the first solder mark. Therefore, 0 μm < K ≤ 10 μm balances improving the strength of the first solder mark with reducing the risk of damage, extending the lifespan of the cylindrical battery cell.

[0018] In some embodiments, the sidewall includes a third region and a fourth region arranged axially along the housing. The thickness of the third region is less than that of the fourth region. The third region is located between the fourth region and the first solder joint, and is connected to the first solder joint. When the internal pressure change of the cylindrical battery cell causes the end cap to be subjected to an axial external force away from the housing space, the third region can act as a buffer between the first solder joint and the fourth region, which can alleviate the rigid tension between the first solder joint and the fourth region and reduce the risk of cracking of the first solder joint.

[0019] In some embodiments, at least a portion of the hardness of the third region is less than that of the fourth region. When the internal pressure change of the cylindrical battery cell causes the end cap to be subjected to an axial external force away from the housing space, the region in the third region with lower hardness than the fourth region can reduce the impact of the axial external force on the area near the first solder joint, thereby reducing the risk of fatigue cracking of the first solder joint.

[0020] In some embodiments, the third region has a first inner circumferential surface and the fourth region has a second inner circumferential surface. Along the radial direction of the housing, the first inner circumferential surface is further away from the central axis of the housing than the second inner circumferential surface. The first inner circumferential surface of the third region can have a larger size, which helps to reduce the difficulty of installing the electrode assembly into the housing and reduces the assembly cost of the cylindrical battery cell.

[0021] In some embodiments, the sidewall further includes a transition region located between and connecting the third and fourth regions. The transition region has a transition surface connecting the first inner circumferential surface and the second inner circumferential surface. The transition surface guides the electrode assembly into the housing, further reducing the difficulty of installing the electrode assembly into the housing and reducing the assembly cost of the cylindrical battery cell.

[0022] In some embodiments, the third region has a second interface connected to the first solder mark, and the second interface is connected to the first inner peripheral surface. This allows the first solder mark to extend to the first inner peripheral surface, resulting in a larger radial dimension for the first solder mark, which is beneficial for increasing the effective penetration depth and strength of the first solder mark.

[0023] In some embodiments, the radial distance between the first inner circumferential surface and the second interface in the housing gradually increases along the direction from the third region to the fourth region. This gradual increase in the thickness of the third region along the direction from the third region to the fourth region helps to improve the strength of the third region, reduce the risk of cracking in the third region, and extend the service life of the cylindrical battery cell.

[0024] In some embodiments, at least a portion of the end cap extends into the sidewall and abuts against the first inner circumferential surface, with the portion of the end cap extending into the sidewall forming an interference fit with the third region. On one hand, the end cap and the housing can form a positioning fit, reducing welding difficulty and improving welding quality; on the other hand, during the welding process of the end cap and the housing, the interference fit between the end cap and the third region can block high-temperature substances generated during welding, reducing the risk of high-temperature substances entering the containment space and damaging the electrode assembly.

[0025] In some embodiments, the end cap extends at least partially into the sidewall and forms an interference fit with the sidewall. On the one hand, the end cap and the housing can form a positioning fit, reducing welding difficulty and improving welding quality; on the other hand, during the welding process of the end cap and the housing, the interference fit between the end cap and the sidewall can block the high-temperature substances generated during welding, reducing the risk of high-temperature substances entering the containment space and damaging the electrode assembly.

[0026] In some embodiments, the end cap includes a body portion and an edge portion. The edge portion is connected to the body portion and is disposed around the outside of the body portion. A portion of the body portion extends into the sidewall and forms an interference fit with the sidewall. Along the axial direction of the housing, at least a portion of the edge portion is located on one side of the sidewall. A first solder joint connects the edge portion and the sidewall. On the one hand, since at least a portion of the edge portion is located on one side of the sidewall along the axial direction, the edge portion and the sidewall can be welded radially along the housing, which can reduce welding difficulty and improve welding quality. On the other hand, when the end cap is assembled with the housing, the body portion extends into the sidewall, and the edge portion can play a limiting role, reducing the risk of axial movement between the end cap and the housing during welding and improving the welding quality between the end cap and the housing.

[0027] In some embodiments, along the axial direction of the housing, a groove is provided on the side of the end cap facing away from the electrode assembly, and a protrusion is formed in the area corresponding to the groove on the side of the end cap facing the electrode assembly, the protrusion being electrically connected to the electrode assembly; along the radial direction of the housing, at least a portion of the orthographic projection of the first solder mark is located within the groove. For cylindrical battery cells, since the end cap is located at the axial end of the cylindrical battery cell, the end cap is more susceptible to deformation under stress, and the high temperature during welding of the end cap and the housing can easily generate stress around the first solder mark. However, by providing a groove on the side of the end cap facing away from the electrode assembly, and ensuring that at least a portion of the orthographic projection of the first solder mark along the radial direction of the housing is located within the groove, the groove can absorb the stress on the end cap near the first solder mark, reducing the risk of end cap damage.

[0028] In some embodiments, the first weld mark is an annular structure arranged around the central axis of the housing. This improves the welding strength between the end cap and the housing, reducing the risk of welding failure; and enables a seal between the end cap and the housing through the first weld mark.

[0029] In some embodiments, the wall thickness of the end cap is 400μm-800μm. A thickness greater than or equal to 400μm ensures sufficient strength to meet the end cap's requirements; a thickness less than or equal to 800μm prevents excessive thickness, reducing material usage and manufacturing costs. Therefore, a wall thickness of 400μm-800μm balances end cap strength and manufacturing cost.

[0030] Secondly, embodiments of this application provide a battery device, including a cylindrical battery cell provided in any one of the embodiments of the first aspect.

[0031] Thirdly, embodiments of this application provide an electrical device, including a cylindrical battery cell provided in any embodiment of the first aspect or a battery device provided in any embodiment of the second aspect. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0034] Figure 2 Exploded views of battery devices provided in some embodiments of this application;

[0035] Figure 3 Exploded views of cylindrical battery cells provided in some embodiments of this application;

[0036] Figure 4 for Figure 3 The isometric view of the cylindrical battery cell shown.

[0037] Figure 5 Partial views of cylindrical battery cells provided for some embodiments of this application;

[0038] Figure 6 for Figure 5 A magnified view of a portion of region A in the middle;

[0039] Figure 7 for Figure 6 A magnified view of a portion of region B in the middle;

[0040] Figure 8 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application;

[0041] Figure 9 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application;

[0042] Figure 10 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application;

[0043] Figure 11 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application (showing a first sub-interface and a second sub-interface);

[0044] Figure 12 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application (showing that the first solder mark does not protrude from the outer peripheral surface of the sidewall);

[0045] Figure 13 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application (showing that the sidewalls include a transition region);

[0046] Figure 14 This is a schematic diagram of the end cap structure provided in some embodiments of this application;

[0047] Figure 15 for Figure 14 A magnified view of a portion of region C in the middle;

[0048] Figure 16 This application provides structural schematic diagrams of end caps for some embodiments;

[0049] Figure 17 This is a schematic diagram of the end cap structure provided in some embodiments of this application;

[0050] Figure 18 A partial structural schematic diagram of a cylindrical battery cell provided in some embodiments of this application (showing the second solder mark).

[0051] Icons: 1-Outer shell; 11-Shell; 111-Side wall; 1111-First interface; 11111-First sub-interface; 11112-Second sub-interface; 1112-Outer peripheral surface of side wall; 1113-Third region; 11131-First inner peripheral surface; 1114-Fourth region; 11141-Second inner peripheral surface; 1115-Transition region; 11151-Transition surface; 1116-Second interface; 12-End cap; 121-Edge portion; 1211-First outer surface; 122-Body portion; 1221-First surface; 1222-Second surface; 123-Groove; 1231-Protrusion; 124-Raised portion; 125-Pressure relief groove; 126-Weak portion; 127-Exhaust 13-Channel; 14-Receiving space; 15-First solder mark; 16-Second outer surface; 17-First zone; 18-Second zone; 19-Fourth interface; 10-Third interface; 11-First position; 12-Second position; 13-Electrode assembly; 24-First tab; 25-Second tab; 26-Electrode terminal; 27-First current collector; 28-Second current collector; 29-Central axis; 20-Second solder mark; 20-Cylindrical battery cell; 20-Casing; 201-First casing; 202-Second casing; 100-Battery device; 200-Controller; 300-Motor; 1000-Vehicle; U-First dividing interface; V-Second dividing interface; Z-Axial; X-Radial. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having," and any variations thereof, in the description, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy.

[0054] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0055] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0056] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0057] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0058] In this application, "multiple" means two or more (including two).

[0059] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0060] Battery cells include, but are not limited to, lithium-ion batteries, sodium-ion batteries, sodium-lithium-ion batteries, lithium metal batteries, sodium metal batteries, lithium-sulfur batteries, magnesium-ion batteries, nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid batteries, etc.

[0061] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, reduces the risk of short circuits while allowing active ions to pass through.

[0062] In some embodiments, the positive electrode can be a positive electrode sheet, which may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0063] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0064] As an example, the positive electrode current collector can be a foil or a composite current collector. For example, as a foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium, etc. Composite current collectors can include a polymer material base layer and a metal layer. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0065] As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials in battery cells may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM)622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds.

[0066] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloys, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, lithium source material, potassium metal, or sodium metal can also be filled and / or deposited within the foamed metal, where the lithium source material is lithium metal and / or a lithium-rich material.

[0067] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0068] As an example, the negative electrode current collector can be a foil, a foamed metal, or a composite current collector. For example, as a foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrodes, carbon, or titanium, etc. The foamed metal can be nickel foam, copper foam, aluminum foam, foam alloy, etc. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0069] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0070] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0071] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0072] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0073] In some embodiments, the separator is a separator membrane. The separator membrane can be any known porous structure separator membrane with good chemical and mechanical stability.

[0074] As an example, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. The separator may be a separate component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes.

[0075] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0076] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or solid. Liquid electrolytes include electrolyte salts and solvents.

[0077] In some embodiments, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0078] In some embodiments, the solvent may include at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0079] Among them, the gel electrolyte includes a polymer as the electrolyte backbone network, combined with an ionic liquid - lithium salt.

[0080] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0081] As an example, polymer solid electrolytes can be polyether (polyoxyethylene), polysiloxane, polycarbonate, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids-lithium salts, cellulose, etc.

[0082] As an example, inorganic solid electrolytes may include one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphate sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0083] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0084] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0085] In some implementations, the electrode assembly is a stacked structure.

[0086] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0087] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0088] As an example, the separator can be set continuously, either by folding or rolling between any adjacent positive or negative electrode plates.

[0089] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0090] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0091] In some embodiments, a battery cell may include a housing. The housing is used to encapsulate components such as electrode assemblies and electrolytes. The battery cell may be a cylindrical battery cell.

[0092] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0093] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module, which is formed by arranging multiple battery cells and fixing them together to form an independent module.

[0094] As an example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0095] In some embodiments, the battery device may be a battery pack, which may include a housing and one or more individual battery cell assemblies housed within the housing.

[0096] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0097] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0098] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0099] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0100] As an example, the housing can be part of the vehicle's chassis structure. For instance, the housing's roof can be at least part of the vehicle's floor, or the housing's frame can be at least part of the vehicle's crossbeams and longitudinal beams.

[0101] In some embodiments, the battery device refers to an energy storage device, which includes a housing with a door on at least one side. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0102] For a cylindrical battery cell, it generally includes a casing and an electrode assembly, with the electrode assembly housed within the casing. The casing may include a housing and end caps. The housing has an opening. After the electrode assembly is installed inside the housing, the opening of the housing can be closed by the end caps, and the end caps are welded to the housing to form a receiving space inside the casing to accommodate the electrode assembly.

[0103] In typical battery cells, the outer casing is usually made of aluminum, which has relatively low hardness and strength. However, to meet strength requirements, the aluminum casing needs to be made thicker, which affects the volumetric energy density of the battery cell. Therefore, to improve the volumetric energy density of the battery cell, a steel casing can be used, meaning both the outer casing and end caps are made of steel. This allows for a thinner outer casing while still meeting strength requirements.

[0104] In cylindrical battery cells, for steel-cased cells, since both the casing and end caps are made of steel, their strength is relatively high. The first weld joint formed by welding the casing and end caps has relatively low strength. Furthermore, due to the cylindrical structure of the battery cell, the casing has strong radial strength. During the cycling process of the cylindrical battery cell, the internal pressure changes make the end cap susceptible to axial expansion forces along the casing. The end cap pulls on the first weld joint along the axial direction, increasing the risk of fatigue cracking of the first weld joint, leading to welding failure between the end cap and the casing, and affecting the service life of the cylindrical battery cell.

[0105] Based on the above considerations, to alleviate the problem of easy welding failure between the end cap and the housing, this application provides a cylindrical battery cell, which includes a housing, an end cap, and an electrode assembly. The housing has an opening at at least one end along its axial direction, and the housing is made of steel. The housing includes a sidewall extending circumferentially along the opening. The end cap covers the opening, and the end cap and housing together define a receiving space. The end cap is also made of steel, and is welded to the sidewall to form a first solder joint. The electrode assembly is housed within the receiving space. The effective penetration depth of the first solder joint is L, the maximum thickness of the sidewall is D, 0.5 ≤ L / D ≤ ​​1.5, and the average grain size of the first solder joint is 30 μm-150 μm.

[0106] In such a cylindrical battery cell, the ratio of the effective penetration depth L of the first solder joint to the maximum thickness D of the sidewall of the casing is 0.5-1.5, and the average grain size of the first solder joint is 30μm-150μm. This ensures that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall of the casing is not too small, and the average grain size of the first solder joint is not too large. This enhances the strength of the first solder joint, reduces the risk of fatigue cracking of the first solder joint, and extends the service life of the cylindrical battery cell.

[0107] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use cylindrical battery cells and battery devices, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships and spacecraft, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft.

[0108] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0109] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. A battery device 100 is disposed inside the vehicle 1000, and the battery device 100 may be located at the bottom, front, or rear of the vehicle 1000. The battery device 100 can be used to power the vehicle 1000; for example, the battery device 100 can serve as the operating power source for the vehicle 1000.

[0110] The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery device 100 to supply power to the motor 300, for example, for the power needs of the vehicle 1000 during startup, navigation and driving.

[0111] In some embodiments of this application, the battery device 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0112] Please refer to Figure 2 , Figure 2 This is an exploded view of a battery device 100 provided in some embodiments of this application. The battery device 100 may include a cylindrical battery cell 10 and a housing 20 for accommodating the cylindrical battery cell 10.

[0113] The housing 20 has an enclosed space inside for accommodating the cylindrical battery cells 10. The housing 20 can have various structures. In some embodiments, the housing 20 may include a first housing 201 and a second housing 202, which are interlocked. The first housing 201 and the second housing 202 can have various shapes, such as cuboids or cylinders. The first housing 201 can be a hollow structure open on one side, and the second housing 202 can also be a hollow structure open on one side. The open side of the second housing 202 interlocks with the open side of the first housing 201, thus forming a housing 20 with an enclosed space. Alternatively, the first housing 201 can be a hollow structure open on one side, and the second housing 202 can be a plate-like structure, with the second housing 202 interlocked with the open side of the first housing 201, thus forming a housing 20 with a accommodating space.

[0114] In the battery device 100, there can be one or more cylindrical battery cells 10. If there are multiple cylindrical battery cells 10, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that the multiple cylindrical battery cells 10 are connected in both series and parallel. Alternatively, multiple cylindrical battery cells 10 can be first connected in series, parallel, or in a mixed configuration to form a battery module, and then the multiple battery modules can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing 20. Another option is that all the cylindrical battery cells 10 can be directly connected in series, parallel, or in a mixed configuration, and then the whole composed of all the cylindrical battery cells 10 is housed within the housing 20.

[0115] In some embodiments, the battery device 100 may further include a busbar component, through which multiple cylindrical battery cells 10 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple cylindrical battery cells 10. The busbar component may be a metallic conductor, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc.

[0116] Please refer to Figure 3 and Figure 4 , Figure 3 Exploded views of cylindrical battery cell 10 provided in some embodiments of this application; Figure 4 for Figure 3 The diagram shows an isometric view of a cylindrical battery cell 10. The cylindrical battery cell 10 may include a housing 1 and an electrode assembly 2, which is housed within the housing 1.

[0117] In some embodiments, the housing 1 may include a housing 11 and an end cap 12, the housing 11 having an opening, and the end cap 12 closing the opening of the housing 11. Here, "closed" means covered or shut, and can be either sealed or unsealed.

[0118] The housing 11 is a component used to house the electrode assembly 2. The housing 11 is cylindrical and can be a hollow structure with an opening at one end or a hollow structure with openings at both opposite ends. The electrode assembly 2 can be partially or completely located within the housing 11.

[0119] End cap 12 and housing 11 together define a receiving space 13 for accommodating electrode assembly 2 and other components. Figure 3 and Figure 4 (Not shown in the image). The end cap 12 can be welded to the housing 11 to close the opening of the housing 11. The shape of the end cap 12 can be adapted to the shape of the housing 11, and the end cap 12 can be a circular plate structure adapted to the housing 11.

[0120] In an embodiment where the housing 11 has an opening at one end, one end cap 12 may be provided accordingly. In an embodiment where the housing 11 has openings at both opposite ends, two end caps 12 may be provided accordingly. The two end caps 12 respectively close the two openings of the housing 11, and the two end caps 12 and the housing 11 together define the receiving space 13.

[0121] In some embodiments, the cylindrical battery cell 10 may further include electrode terminals 3, which are disposed on the housing 1 and are used for electrical connection with the tabs of the electrode assembly 2 to input or output electrical energy of the cylindrical battery cell 10. The electrode terminals 3 may be disposed on the housing 11 of the housing 1 or on the end cap 12 of the housing 1. The electrode terminals 3 and the tabs may be directly connected, for example, by welding the electrode terminals 3 to the tabs. Alternatively, the electrode terminals 3 and the tabs may be indirectly connected, for example, by a current collector. The current collector may be a metallic conductor, such as copper, iron, aluminum, steel, or aluminum alloy.

[0122] As an example, such as Figure 3 and Figure 4 As shown, one end of the housing 11 forms an opening, and there is one end cap 12 in the housing 1, which closes one opening of the housing 11. An electrode terminal 3 is provided at the end of the housing 11 opposite to the end cap 12. A first electrode tab 21 and a second electrode tab 22 are respectively formed at opposite ends of the electrode assembly 2. The first electrode tab 21 is electrically connected to the end cap 12 through a first current collector 4, and the second electrode tab 22 is electrically connected to the electrode terminal 3 through a second current collector 5. One of the first electrode tab 21 and the second electrode tab 22 is a positive electrode tab, and the other is a negative electrode tab.

[0123] Please refer to Figure 5 , Figure 6 and Figure 7 , Figure 5 A partial view of a cylindrical battery cell 10 provided in some embodiments of this application; Figure 6 for Figure 5 A magnified view of a portion of region A in the middle; Figure 7 for Figure 6 A partial enlarged view of region B. This application provides a cylindrical battery cell 10, including a housing 11, an end cap 12, and an electrode assembly 2. The housing 11 has an opening at at least one end along its axial direction Z. The housing 11 is made of steel and includes a sidewall 111 extending circumferentially along the opening. The end cap 12 covers the opening, and together with the housing 11, defines a receiving space 13. The end cap 12 is also made of steel and is welded to the sidewall 111 to form a first solder joint 14. The electrode assembly 2 is housed within the receiving space 13. The effective penetration depth of the first solder joint 14 is L, the maximum thickness of the sidewall 111 is D (0.5 ≤ L / D ≤ ​​1.5), and the average grain size of the first solder joint 14 is 30 μm-150 μm.

[0124] Along the axial direction Z of the cylindrical battery cell 10, the housing 11 may have an opening at only one end, and a corresponding end cap 12 may be provided; alternatively, the housing 11 may have openings at both opposite ends, and two corresponding end caps 12 may be provided. The opening of the housing 11 is circular, and the sidewall 111 extends circumferentially along the opening, making the sidewall 111 cylindrical.

[0125] The housing 11 includes a sidewall 111 surrounding the outer side of the electrode assembly 2. The sidewall 111 has an annular cross-section perpendicular to the axial direction Z of the cylindrical battery cell 10. In embodiments where the housing 11 has an opening at only one end, the housing 11 may further include a bottom wall located at the end of the sidewall 111 away from the end cap 12. The bottom wall and the sidewall 111 may be integrally formed. In embodiments where openings are formed at both opposite ends of the housing 11, the sidewall 111 constitutes the housing 11.

[0126] The shell 11 is made of steel. The shell 11 can be entirely made of steel, or only a portion of the shell 11 can be made of steel. For example, the shell 11 may include a first substrate and a first protective layer disposed on the surface of the first substrate, where the first substrate is made of steel and the first protective layer is not made of steel. The first protective layer may be an anti-oxidation layer, for example, a nickel layer plated on the surface of the first substrate.

[0127] The end cap 12 is made of steel. The end cap 12 can be entirely made of steel, or only a portion of it can be made of steel. For example, the end cap 12 may include a second substrate and a second protective layer disposed on the surface of the second substrate, where the second substrate is made of steel and the second protective layer is not made of steel. The second protective layer can be an anti-oxidation layer, for example, a nickel layer plated on the surface of the second substrate. The steel can include carbon steel, stainless steel, etc.

[0128] The axial direction Z of the housing 11 is the extension direction of the central axis 6 of the housing 11, and the axial direction Z of the housing 11 is the same as the axial direction Z of the cylindrical battery cell 10.

[0129] The electrode assembly 2 can be a wound structure or a stacked structure. There can be one or more electrode assemblies 2 housed within the housing 1. As an example, in... Figure 5 In the middle, only one electrode assembly 2 is set inside the outer shell 1. The electrode assembly 2 is roughly cylindrical and has a wound structure.

[0130] The first weld mark 14 is the portion of the weld mark formed after the end cap 12 and the housing 11 are welded together. The first weld mark 14 serves to connect the end cap 12 and the housing 11. Welding the end cap 12 and the housing 11 can form one first weld mark 14. For example, the first weld mark 14 can be an annular structure, extending circumferentially along the opening of the housing 11, thus achieving a sealed connection between the end cap 12 and the housing 11. Welding the end cap 12 and the housing 11 can also form multiple first weld marks 14, spaced apart circumferentially along the opening of the housing 11.

[0131] The thickness at the thickest point of sidewall 111 is the maximum thickness of sidewall 111.

[0132] L / D can take any one of the following point values: 0.5, 0.6, 2 / 3, 0.75, 0.8, 5 / 6, 6 / 7, 0.9, 1, 7 / 6, 1.2, 1.25, 4 / 3, 1.4, 1.5, or any value between two of them.

[0133] The grains of the first solder mark 14 may include equiaxed grains and / or columnar grains. The average grain size of the first solder mark 14 may be a point value or a range between any two of the following: 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, and 150μm.

[0134] The average grain size of the first solder mark 14 can be measured by electron backscatter diffraction or by the intercept method in GB / T-6394-2017 "Method for Determination of Average Grain Size of Metals".

[0135] In this embodiment, L / D ≥ 0.5 and the average grain size of the first solder mark 14 is less than or equal to 150 μm, ensuring that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall 111 of the casing 11 is not too small and that the average grain size of the first solder mark 14 is not too large. This enhances the strength of the first solder mark 14, reduces the risk of fatigue cracking of the first solder mark 14, and extends the service life of the cylindrical battery cell 10. L / D ≤ ​​1.5 and the average grain size of the first solder mark 14 is greater than or equal to 30 μm, ensuring that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall 111 of the casing 11 is not too large and that the average grain size of the first solder mark 14 is not too small. This reduces the welding difficulty between the end cap 12 and the casing 11, lowers production costs, and has better economic efficiency. In such a cylindrical battery cell 10, the influence of average grain size and effective melting depth on the first solder joint 14 is considered. The ratio of effective melting depth L to the maximum thickness D of the side wall 111 of the casing 11 and the average grain size of the first solder joint 14 are controlled within a reasonable range, taking into account both the service life and economic requirements of the cylindrical battery cell 10.

[0136] In some embodiments, 2 / 3 ≤ L / D ≤ ​​1, and the average grain size of the first solder mark 14 is 40 μm-100 μm.

[0137] L / D can take any one of the following point values: 2 / 3, 0.7, 0.75, 0.8, 5 / 6, 6 / 7, 0.9, 1, or any value between two of them.

[0138] The average grain size of the first solder mark 14 can be a point value or a range between any two of 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, and 100μm.

[0139] In this embodiment, L / D ≥ 2 / 3 and the average grain size of the first solder portion 14 is less than or equal to 100 μm, which further ensures that the L / D ratio is not too small and the average grain size of the first solder portion 14 is not too large. This enhances the strength of the first solder portion 14, reduces the risk of fatigue cracking, and extends the service life of the cylindrical battery cell 10. L / D ≤ ​​1 and the average grain size of the first solder portion 14 is greater than or equal to 40 μm, which further reduces the welding difficulty between the end cap 12 and the casing 11 and lowers production costs. Therefore, 2 / 3 ≤ L / D ≤ ​​1 and the average grain size of the first solder portion 14 is 40 μm-100 μm, which further balances the service life and economic requirements of the cylindrical battery cell 10.

[0140] In some embodiments, 200μm≤L≤600μm.

[0141] L can be 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300 μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 410μm The point value is any one of the following values: m, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm, 540μm, 550μm, 560μm, 570μm, 580μm, 590μm, and 600μm, or any value between two of them.

[0142] In this embodiment, L≥200μm can improve the strength of the first solder mark 14 and reduce the risk of welding failure between the end cap 12 and the housing 11; L≤600μm can reduce the welding difficulty between the end cap 12 and the housing 11 and improve the welding efficiency between the end cap 12 and the housing 11; therefore, 200μm≤L≤600μm can balance improving the strength of the first solder mark 14 and reducing the welding difficulty between the end cap 12 and the housing 11, reducing the risk of welding failure between the end cap 12 and the housing 11 and improving the welding efficiency between the end cap 12 and the housing 11.

[0143] In some embodiments, 300μm≤L≤400μm.

[0144] L can be any value from 300μm, 305μm, 310μm, 315μm, 320μm, 325μm, 330μm, 335μm, 340μm, 345μm, 350μm, 355μm, 360μm, 365μm, 370μm, 375μm, 380μm, 385μm, 390μm, 395μm, 400μm, or any value between two of them.

[0145] In this embodiment, L≥300μm can further improve the strength of the first solder mark 14 and reduce the risk of welding failure between the end cap 12 and the housing 11; L≤400μm can further reduce the welding difficulty between the end cap 12 and the housing 11 and improve the welding efficiency between the end cap 12 and the housing 11; therefore, 300μm≤L≤400μm can further improve the strength of the first solder mark 14 and reduce the welding difficulty between the end cap 12 and the housing 11, reduce the risk of welding failure between the end cap 12 and the housing 11 and improve the welding efficiency between the end cap 12 and the housing 11.

[0146] In some embodiments, 200μm≤D≤600μm.

[0147] D can be 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300 μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 410μm The point value is any one of the following values: m, 420μm, 430μm, 440μm, 450μm, 460μm, 470μm, 480μm, 490μm, 500μm, 510μm, 520μm, 530μm, 540μm, 550μm, 560μm, 570μm, 580μm, 590μm, and 600μm, or any value between two of them.

[0148] In this embodiment, D ≥ 200 μm ensures that the sidewall 111 has sufficient thickness, which improves its strength and reduces the risk of damage to the sidewall 111 of the casing 11 when the internal pressure of the cylindrical battery cell 10 changes. D ≤ 600 μm prevents the sidewall 111 from becoming too thick, reducing the material used in the casing 11 and its weight, thereby increasing the gravimetric energy density of the cylindrical battery cell 10. Therefore, 200 μm ≤ D ≤ 600 μm balances improving the strength of the sidewall 111 of the casing 11 with reducing the weight of the casing 11, reducing the risk of damage to the casing 11, and increasing the gravimetric energy density of the cylindrical battery cell 10.

[0149] In some embodiments, 200μm≤D≤450μm.

[0150] D can be any one of the following values: 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, 260μm, 270μm, 280μm, 290μm, 300μm, 310μm, 320μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, 410μm, 420μm, 430μm, 440μm, 450μm, or any value between two of them.

[0151] In this embodiment, D ≥ 200 μm can improve the strength of the sidewall 111 of the casing 11 and reduce the risk of damage to the sidewall 111 of the casing 11; D ≤ 450 μm can further reduce the weight of the casing 11, thereby increasing the gravimetric energy density of the cylindrical battery cell 10. Therefore, 200 μm ≤ D ≤ 450 μm can further improve the strength of the sidewall 111 of the casing 11 and reduce the weight of the casing 11, reducing the risk of damage to the casing 11 and increasing the gravimetric energy density of the cylindrical battery cell 10.

[0152] In some embodiments, please continue to refer to Figure 7 and further refer to Figure 8 and Figure 9 , Figure 8 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application; Figure 9 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application. Along the axial direction Z of the housing 11, the end cap 12 has a first outer surface 1211 facing away from the electrode assembly 2. The surface of the first solder joint 14 includes a second outer surface 141, which connects the first outer surface 1211 and the outer peripheral surface 1112 of the sidewall. The sidewall 111 has a first interface 1111 that contacts the end cap 12. The first interface 1111 is connected to the surface of the first solder joint 14 at a first position 15. The minimum distance between the first position 15 and the second outer surface 141 is the effective penetration depth of the first solder joint 14.

[0153] Along the axial direction Z, the first outer surface 1211 can be the surface of the end cap 12 furthest from the electrode assembly 2, or the first outer surface 1211 can be closer to the electrode assembly 2 than the surface of the end cap 12 furthest from the electrode assembly 2. The first outer surface 1211 can be a plane perpendicular to the axial direction Z.

[0154] In the entire surface of the first solder mark 14, a portion of the surface is covered by the sidewall 111, a portion of the surface is covered by the end cap 12, and the surface not covered by the sidewall 111 and the end cap 12 and located on the outside is the second outer surface 141 of the first solder mark 14. As an example, the surface of the first solder mark 14 also includes a third interface 145 and a fourth interface 144. The third interface 145 is connected to the end cap 12 and is the portion of the surface of the first solder mark 14 covered by the end cap 12. The fourth interface 144 is connected to the sidewall 111 and is the portion of the surface of the first solder mark 14 covered by the sidewall 111. The radial X-section of the cylindrical battery cell 10 is the first section, and the central axis 6 of the cylindrical battery cell 10 is located within the first section. The intersection lines of the first interface 1111 and the first section, the intersection lines of the fourth interface 144 and the first section, and the intersection lines of the third interface 145 and the first section are connected end to end in sequence.

[0155] The first interface 1111 is the surface where the sidewall 111 contacts the end cap 12. In some embodiments, such as Figure 7 As shown, the inner circumferential surface of the sidewall 111 contacts the end cap 12, and the portion of the inner circumferential surface of the sidewall 111 that contacts the end cap 12 forms the first interface 1111. In some embodiments, such as Figure 8 As shown, along the Z-axis, the end face of the sidewall 111 near the end cap 12 contacts the end cap 12, and the portion of this end face in contact with the end cap 12 is the first interface 1111. In some embodiments, such as Figure 9 As shown, the inner circumferential surface of the sidewall 111 and the end face of the sidewall 111 along the axial direction Z are in contact with the end cap 12. The portion of the inner circumferential surface of the sidewall 111 in contact with the end cap 12 and the portion of the end face of the sidewall 111 in contact with the end cap 12 constitute the first interface 1111.

[0156] The first interface 1111 is connected to the surface of the first solder mark 14 at the first position 15. As an example, the first interface 1111 is connected to the fourth interface 144 of the first solder mark 14 at the first position 15.

[0157] The first interface 1111 is connected to the surface of the first solder mark 14 to form a first intersection line. The location of the first intersection line is the first position 15, and the minimum distance between the first position 15 and the second outer surface 141 is the minimum distance between the first intersection line and the second outer surface 141. In an embodiment where the first solder mark 14 has an annular structure, the first intersection line is a circular line. In an embodiment where there are multiple first solder marks 14, and the multiple first solder marks 14 are circumferentially spaced along the opening of the housing 11, the first intersection line is an arc.

[0158] The outer peripheral surface 1112 of the sidewall can be a cylindrical surface arranged around the central axis 6 of the cylindrical battery cell 10.

[0159] In some embodiments, on the one hand, during the cycling process of the cylindrical battery cell 10, the end cap 12 is easily subjected to an expansion force along the axial direction Z of the housing 11. By providing the second outer surface 141 of the first solder portion 14 to connect the first outer surface 1211 of the edge portion 121, the size of the first solder portion 14 along the axial direction Z of the housing 11 can be increased, thereby improving the connection strength between the end cap 12 and the housing 11. On the other hand, the second outer surface 141 connects the first outer surface 1211 and the outer peripheral surface 1112 of the sidewall. The first outer surface 1211 and the outer peripheral surface 1112 of the sidewall can be smoothly transitioned through the second outer surface 141, so that the first solder portion 14 can eliminate the sharp corners of the edge region of the end cap 12, reducing the risk of the cylindrical battery cell 10 damaging other components.

[0160] In some embodiments, please refer to Figure 10 , Figure 10 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application. The first solder area 14 includes a first region 142 and a second region 143. The average grain size of the first region 142 is smaller than the average grain size of the second region 143. Along the radial direction X of the housing 11, the first region 142 is located outside the second region 143, and the outer surface of the first region 142 is at least a part of the second outer surface 141.

[0161] As an example, the grains in region 142 and region 143 are columnar crystals. The average grain size of region 142 is 40μm-60μm, and the average grain size of region 143 is 80μm-100μm.

[0162] The outer surface of the first region 142 can be the same as the second outer surface 141, or the outer surface of the first region 142 can be a part of the second outer surface 141. Figure 10 In the illustrated embodiment, a portion of the second outer surface 141 is the outer surface of the first region 142, and the other portion is the outer surface of the second region 143.

[0163] As an example, such as Figure 10 As shown, the first region 142 and the second region 143 can be arranged adjacently, with the first region 142 directly connected to the second region 143. As an example, the first region 142 and the second region 143 can be arranged alternately, with a connecting region between the first region 142 and the second region 143. The connecting region connects the first region 142 and the second region 143, and the grain size of the connecting region gradually increases from the first region 142 to the second region 143.

[0164] After the welding end cap 12 and side wall 111 form the first weld mark 14, the average grain size of the outer side of the first weld mark 14 can be adjusted by pressing the outer peripheral surface of the first weld mark 14 with external force such as roller pressing, so as to achieve that the average grain size of the first region 142 is smaller than the average grain size of the second region 143.

[0165] In this embodiment, by setting the average grain size of the first region 142 located on the outer side to be smaller than the average grain size of the second region 143 located on the inner side, the grain size of the outer region of the first solder part 14 is refined, thereby improving the strength of the first solder part 14 and effectively reducing the risk of fatigue cracking of the first solder part 14.

[0166] In some embodiments, please continue to refer to Figure 9 and Figure 10 The end cap 12 includes an edge portion 121 and a body portion 122. The edge portion 121 is connected to the body portion 122 and is disposed around the outside of the body portion 122. A portion of the body portion 122 extends into the side wall 111 along the axial direction Z of the housing 11. At least a portion of the edge portion 121 is located on one side of the side wall 111. A first solder mark portion 14 connects the side wall 111 and the edge portion 121 along the axial direction Z. The edge portion 121 forms at least a portion of the first outer surface 1211 opposite to the surface of the electrode assembly 2.

[0167] As an example, the body portion 122 has an outer peripheral surface, and the edge portion 121 is an annular structure protruding from the outer peripheral surface of the body portion 122; the body portion 122 and the edge portion 121 are integrally formed. Figure 9 and Figure 10 In the middle, the edge portion 121 and the body portion 122 are separated at the first dividing interface U (virtual surface), and the first dividing interface U is coplanar with the outer peripheral surface of the body portion 122.

[0168] The portion of the body portion 122 extending into the side wall 111 can form a clearance fit with the side wall 111. In this case, the portion of the body portion 122 extending into the side wall 111 may not contact the inner circumferential surface of the side wall 111. Alternatively, the portion of the body portion 122 extending into the side wall 111 may also have an interference fit with the side wall 111. In this case, the portion of the body portion 122 extending into the side wall 111 may be in contact with the inner circumferential surface of the side wall 111.

[0169] Along the axial direction Z of the housing 11, at least a portion of the edge portion 121 is located on one side of the sidewall 111, such that in a projection plane perpendicular to the axial direction Z, the projection of the edge portion 121 overlaps with the projection of the sidewall 111. Alternatively, the entire edge may be located on one side of the sidewall 111, such that in a projection plane perpendicular to the axial direction Z, the projection of the edge portion 121 lies within the projection of the sidewall 111; or only a portion of the edge portion 121 may be located on one side of the sidewall 111, such that in a projection plane perpendicular to the axial direction Z, a portion of the projection of the edge portion 121 lies within the projection of the sidewall 111.

[0170] The first outer surface 1211 can be a surface where the edge portion 121 faces away from the electrode assembly 2, or a portion of the first outer surface 1211 can be a surface where the edge portion 121 faces away from the electrode assembly 2. Figure 9 and Figure 10 In the illustrated embodiment, the surface of the edge portion 121 facing away from the electrode assembly 2 is part of the first outer surface 1211.

[0171] In this embodiment, by setting at least a portion of the edge portion 121 to be located on one side of the sidewall 111 along the axial direction Z, the sidewall 111 limits the edge portion 121, reducing the risk of the end cap 12 moving towards the electrode assembly 2 when it is welded to the sidewall 111, which can effectively improve the welding quality of the end cap 12 and the housing 11 and reduce the welding difficulty of the end cap 12 and the housing 11.

[0172] In some embodiments, please refer to Figure 11 , Figure 11 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application (showing a first sub-interface 11111 and a second sub-interface 11112). The sidewall 111 has a first interface 1111 that contacts the end cap 12. The surface of the first solder portion 14 is connected to the first interface 1111 at a first position 15 and a second position 16. The minimum distance between the first position 15 and the second position 16 is the effective penetration depth of the first solder portion 14.

[0173] Exemplarily, the first interface 1111 includes a first sub-interface 11111 and a second sub-interface 11112. The inner circumferential surface of the sidewall 111 that contacts the end cap 12 is the first sub-interface 11111, and the end face of the sidewall 111 that is closer to the end cap 12 along the axial direction Z is the second sub-interface 11112. The surface of the first solder mark 14 is connected to the first sub-interface 11111 to form a first intersection line, and the location of the first intersection line is the first position 15. The surface of the first solder mark 14 is connected to the second sub-interface 11112 to form a second intersection line, and the location of the second intersection line is the second position 16. In an embodiment where the first solder mark 14 has a ring structure, both the first intersection line and the second intersection line are ring lines. In an embodiment where there are multiple first solder marks 14 and the first solder marks 14 are spaced apart circumferentially along the housing 11, the first intersection line and the second intersection line are arc lines. The minimum distance between the first intersection line and the second intersection line is the minimum distance between the first position 15 and the second position 16.

[0174] In some embodiments, please refer to Figure 12 , Figure 12 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application (showing that the first solder mark 14 does not protrude from the outer peripheral surface 1112 of the sidewall). Along the radial direction X of the housing 11, the first solder mark 14 does not protrude from the outer peripheral surface 1112 of the sidewall.

[0175] In an embodiment where the second outer surface 141 of the first solder mark 14 connects the outer peripheral surface 1112 of the sidewall and the first outer surface 1211 of the end cap 12, the maximum distance from the second outer surface 141 to the center line of the cylindrical battery cell 10 may be less than or equal to the diameter of the outer peripheral surface.

[0176] For example, such as Figure 12 As shown, the second outer surface 141 includes a first conical surface, which is connected to the outer peripheral surface 1112 of the sidewall. Along the direction from the first outer surface 1211 to the outer peripheral surface 1112 of the sidewall, the distance between the first conical surface and the central axis 6 of the shell 11 gradually increases.

[0177] In this embodiment, the first solder mark 14 does not protrude from the outer peripheral surface 1112 of the sidewall, which reduces the risk of interference between the first solder mark 14 and other components, and also reduces the risk of damage to the first solder mark 14 due to external forces. In the battery device 100, multiple cylindrical battery cells 10 are spaced apart. The fact that the first solder mark 14 does not protrude from the outer peripheral surface 1112 of the sidewall reduces the risk of interference caused by contact between two adjacent cylindrical battery cells 10. Furthermore, the fact that the first solder mark 14 does not protrude from the outer peripheral surface 1112 of the sidewall allows the multiple cylindrical battery cells 10 of the battery device 100 to be arranged more closely, thereby enabling the battery device 100 to accommodate more cylindrical battery cells 10 and increasing the volumetric energy density of the battery device 100.

[0178] In some embodiments, please refer to Figure 13 , Figure 13 This is a schematic diagram of the structure of a cylindrical battery cell 10 provided in some embodiments of this application (showing that the sidewall 111 includes a transition region 1115). Along the radial direction X of the housing 11, a first solder mark 14 partially protrudes from the outer peripheral surface 1112 of the sidewall.

[0179] Along the radial direction X, a portion of the first solder mark 14 is located outside the outer peripheral surface 1112 of the sidewall, and another portion of the first solder mark 14 is located inside the outer peripheral surface 1112 of the sidewall.

[0180] In an embodiment where the second outer surface 141 of the first solder mark 14 connects the outer peripheral surface 1112 of the sidewall and the first outer surface 1211 of the end cap 12, the outer peripheral surface 1112 of the sidewall may be a cylindrical surface, and the maximum distance from a portion of the second outer surface 141 to the center line of the cylindrical battery cell 10 is greater than the radius of the outer peripheral surface of the sidewall 111.

[0181] In this embodiment, by setting the first solder mark 14 to partially protrude from the outer peripheral surface 1112 of the sidewall, on the one hand, the size of the first solder mark 14 along the radial X can be increased, the welding strength of the first solder mark 14 can be improved, and the risk of cracking of the first solder mark 14 can be reduced; on the other hand, the first solder mark 14 protruding from the outer peripheral surface 1112 of the sidewall is conducive to the welding of the first solder mark 14 and reduces the welding difficulty of the end cap 12 and the shell 11.

[0182] In some embodiments, please continue to refer to Figure 13 Along the radial direction X of the housing 11, the maximum dimension of the portion of the first solder mark 14 protruding from the outer peripheral surface 1112 of the sidewall is K, where 0 μm < K ≤ 10 μm.

[0183] exist Figure 12 In the middle, along the radial X of the housing 11, the portion of the first solder mark 14 located on the outer side of the outer peripheral surface 1112 of the sidewall and the portion of the first solder mark 14 located on the inner side of the outer peripheral surface 1112 of the sidewall are separated by a second dividing interface V (virtual surface), and the second dividing interface V is coplanar with the outer peripheral surface 1112 of the sidewall.

[0184] K can be any one of the following values: 0.01μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or any value between two of them.

[0185] In this embodiment, K > 0 μm increases the radial dimension of the first solder mark 14, thereby improving its strength; K ≤ 10 μm reduces the risk of interference between the first solder mark 14 and other components, thus reducing the risk of damage to the first solder mark 14; therefore, 0 μm < K ≤ 10 μm balances both improving the strength of the first solder mark 14 and reducing the risk of damage, extending the lifespan of the cylindrical battery cell 10. In some embodiments, the end cap 12 extends partially into the opening to form an interference fit with the sidewall 111. The end cap 12 presses against the inner circumferential surface of the sidewall 111, causing the end of the sidewall 111 with the opening to expand outward, increasing the outer diameter of the sidewall 111. Based on this, the first solder mark 14 extends beyond the outer circumferential surface 1112 of the sidewall, further increasing the maximum outer diameter of the cylindrical battery cell 10, which is detrimental to the arrangement of the cylindrical battery cell 10.

[0186] In some embodiments, please continue to refer to Figure 13 The sidewall 111 includes a third region 1113 and a fourth region 1114 arranged along the axial direction Z of the housing 11. The thickness of the third region 1113 is less than the thickness of the fourth region 1114. The third region 1113 is located between the fourth region 1114 and the first solder mark 14. The third region 1113 is connected to the first solder mark 14.

[0187] The third zone 1113 and the fourth zone 1114 can be arranged adjacently, with the third zone 1113 directly connected to the fourth zone 1114. Alternatively, the third zone 1113 and the fourth zone 1114 can be arranged alternately, with a transition zone 1115 connecting them. Both the third zone 1113 and the fourth zone 1114 are annular structures. The maximum thickness of the third zone 1113 is less than the maximum thickness of the fourth zone 1114, ensuring that the thickness of the third zone 1113 is less than the thickness of the fourth zone 1114. The maximum thickness of the fourth zone 1114 is the maximum thickness of the sidewall 111. As an example, the fourth zone 1114 has a uniform thickness structure.

[0188] Alternatively, the outer peripheral surfaces of the third region 1113 and the fourth region 1114 can be coplanar, with the inner peripheral surface of the third region 1113 being further away from the central axis 6 of the shell 11 than the inner peripheral surface of the fourth region 1114, resulting in a thickness of the third region 1113 being less than the thickness of the fourth region 1114. Or, the inner peripheral surfaces of the third region 1113 and the fourth region 1114 can be coplanar, with the outer peripheral surface of the third region 1113 being closer to the central axis 6 of the shell 11 than the outer peripheral surface of the fourth region 1114, resulting in a thickness of the third region 1113 being less than the thickness of the fourth region 1114. Alternatively, the inner peripheral surface of the third region 1113 can be further away from the central axis 6 of the shell 11 than the inner peripheral surface of the fourth region 1114, and the outer peripheral surface of the third region 1113 is closer to the central axis 6 of the shell 11 than the outer peripheral surface of the fourth region 1114, resulting in a thickness of the third region 1113 being less than the thickness of the fourth region 1114.

[0189] The third zone 1113 is connected to the first solder mark 14, such that the third zone 1113 covers the fourth interface 144 of the first solder mark 14.

[0190] In this embodiment, when the internal pressure change of the cylindrical battery cell 10 causes the end cap 12 to be subjected to an axial Z external force away from the receiving space 13, the third region 1113 can play a buffering role between the first solder part 14 and the fourth region 1114, which can alleviate the rigid tension between the first solder part 14 and the fourth region 1114 and reduce the risk of solder cracking.

[0191] In some embodiments, the first solder mark 14 protrudes partially from the outer peripheral surface of the third region 1113, such that the first solder mark 14 protrudes partially from the outer peripheral surface 1112 of the sidewall.

[0192] In some embodiments, the second boundary interface V is coplanar with the outer peripheral surface of the third region 1113, such that the portion of the first solder mark 14 located on the outer side of the second boundary interface V along the radial X protrudes from the outer peripheral surface 1112 of the sidewall.

[0193] In some embodiments, at least a portion of the hardness of the third region 1113 is less than the hardness of the fourth region 1114.

[0194] It is possible that the hardness of the entire third zone 1113 is less than the hardness of the fourth zone 1114; or it is possible that only a part of the third zone 1113 is less than the hardness of the fourth zone 1114. For example, the hardness of a part of the third zone 1113 within a first distance range from the fourth interface 144 is less than the hardness of the fourth zone 1114, while the hardness of the other parts is equal to the hardness of the fourth zone 1114. The first distance can be 1mm-2mm.

[0195] In this embodiment, when the internal pressure change of the cylindrical battery cell 10 causes the end cap 12 to be subjected to an axial Z external force away from the receiving space 13, the area in the third region 1113 with lower hardness than the fourth region 1114 can reduce the impact of the axial Z external force on the area near the first solder mark 14, thereby reducing the risk of fatigue cracking of the first solder mark 14.

[0196] In some embodiments, please continue to refer to Figure 13 The third region 1113 has a first inner circumferential surface 11131, and the fourth region 1114 has a second inner circumferential surface 11141. Along the radial direction X of the shell 11, the first inner circumferential surface 11131 is further away from the central axis 6 of the shell 11 than the second inner circumferential surface 11141.

[0197] Both the first inner circumferential surface 11131 and the second inner circumferential surface 11141 can be cylindrical surfaces, with the diameter of the first inner circumferential surface 11131 being larger than the diameter of the second inner circumferential surface 11141. Alternatively, one of the first inner circumferential surface 11131 and the second inner circumferential surface 11141 can be a conical surface, and the other a cylindrical surface. Taking the first inner circumferential surface 11131 as a conical surface and the second inner circumferential surface 11141 as a cylindrical surface as an example, the maximum diameter of the first inner circumferential surface 11131 is smaller than the diameter of the second inner circumferential surface 11141. Alternatively, both the first inner circumferential surface 11131 and the second inner circumferential surface 11141 can be conical surfaces, with the maximum diameter of the first inner circumferential surface 11131 being smaller than the minimum diameter of the second inner circumferential surface 11141.

[0198] The distance from the outer peripheral surface of the third zone 1113 to the first inner peripheral surface 11131 is equal to the thickness of the third zone 1113. The distance from the outer peripheral surface of the fourth zone 1114 to the second inner peripheral surface 11141 is equal to the thickness of the fourth zone 1114. The outer peripheral surface of the third zone 1113 can be coplanar with the outer peripheral surface of the fourth zone 1114, or they can be offset.

[0199] In this embodiment, the first inner circumferential surface 11131 of the third region 1113 can have a larger size, which helps to reduce the difficulty of installing the electrode assembly 2 into the housing 11 and reduces the assembly cost of the cylindrical battery cell 10.

[0200] In some embodiments, please continue to refer to Figure 13 The sidewall 111 also includes a transition region 1115, which is located between the third region 1113 and the fourth region 1114 and connects the third region 1113 and the fourth region 1114. The transition region 1115 has a transition surface 11151, which connects the first inner circumferential surface 11131 and the second inner circumferential surface 11141.

[0201] As an example, the thickness of the transition region 1115 gradually increases along the direction from the end cap 12 to the electrode assembly 2. The transition surface 11151 is the surface of the transition region 1115 facing the central axis 6. The transition surface 11151 is the inner circumferential surface of the transition region 1115. The transition surface 11151 connects the first inner circumferential surface 11131 and the second inner circumferential surface 11141, such that the first inner circumferential surface 11131 and the second inner circumferential surface 11141 are spaced apart along the axial direction Z.

[0202] It is understandable that the first inner circumferential surface 11131, the transition surface 11151, and the second inner circumferential surface 11141 are all inner circumferential surfaces of the sidewall 111.

[0203] In this embodiment, the transition surface 11151 guides the electrode assembly 2 into the housing 11, further reducing the difficulty of installing the electrode assembly 2 into the housing 11 and reducing the assembly cost of the cylindrical battery cell 10.

[0204] In some embodiments, please continue to refer to Figure 13 The third zone 1113 has a second interface 1116 connected to the first soldering part 14, and the second interface 1116 is connected to the first inner peripheral surface 11131.

[0205] The second interface 1116 is connected to the fourth interface 144, and the position where the second interface 1116 intersects with the first inner circumferential surface 11131 is the first position 15.

[0206] like Figure 12 As shown, the second interface 1116 is formed between the first solder pad 14 and the third region 1113, and connects the second outer surface 141 and the first inner peripheral surface 11131. In some embodiments, the second interface 1116 is connected to the first inner peripheral surface 11131 at a first position 15.

[0207] In this embodiment, the first solder mark 14 extends to the first inner peripheral surface 11131, so that the second interface 1116 is connected to the first inner peripheral surface 11131, so that the first solder mark 14 has a larger size along the radial X, which is beneficial to improve the effective penetration depth of the first solder mark 14 and improve the strength of the first solder mark 14.

[0208] In some embodiments, please continue to refer to Figure 13 The distance between the first inner circumferential surface 11131 and the second interface 1116 in the radial direction X of the shell 11 gradually increases along the direction from the third region 1113 to the fourth region 1114.

[0209] The first inner circumferential surface 11131 intersects the second interface 1116 at a first position 15. The second interface 1116 extends from the first position 15 toward the outside of the cylindrical battery cell 10 and extends in the direction from the third region 1113 to the fourth region 1114. The distance between a point on the first inner circumferential surface 11131 and the central axis 6 may be equal or unequal. For example, along the radial direction X of the housing 11, the distance between a point on the first inner circumferential surface 11131 and the central axis 6 gradually decreases in the direction from the third region 1113 to the fourth region 1114. Thus, the distance between the first inner circumferential surface 11131 and the second interface 1116 in the radial direction X of the housing 11 gradually increases in the direction from the third region 1113 to the fourth region 1114.

[0210] In this embodiment, the thickness of the third region 1113 gradually increases along the direction from the third region 1113 to the fourth region 1114, which is beneficial to improve the strength of the third region 1113, reduce the risk of cracking of the third region 1113, and extend the service life of the cylindrical battery cell 10.

[0211] In some embodiments, please continue to refer to Figure 13 The end cap 12 extends partially into the side wall 111 and abuts against the first inner circumferential surface 11131. The portion of the end cap 12 extending into the side wall 111 forms an interference fit with the third region 1113.

[0212] The end cap 12 includes a body portion 122 and an edge portion 121, at least a portion of the edge portion 121 being arranged axially Z-orientedly with the sidewall 111. A portion of the edge portion 121 may extend into the sidewall 111. Alternatively, at least a portion of the body portion 122 may extend into the sidewall 111; or the entire body portion 122 may extend into the sidewall 111. The portion of the end cap 12 extending into the sidewall 111 presses against the first inner circumferential surface 11131 of the third region 1113, such that the portion of the end cap 12 extending into the sidewall 111 forms an interference fit with the third region 1113.

[0213] In this embodiment, on the one hand, the end cap 12 and the housing 11 can form a positioning fit, reducing the welding difficulty and improving the welding quality; on the other hand, during the welding process of the end cap 12 and the housing 11, the interference fit between the end cap 12 and the third region 1113 can block the high-temperature material generated during welding, reducing the risk of the high-temperature material entering the containment space 13 and damaging the electrode assembly 2.

[0214] In some embodiments, the body portion 122 of the end cap 12 partially extends into the sidewall 111, and the body portion 122 partially compresses the third region 1113, causing the first inner peripheral surface 11131 of the third region 1113 to be recessed in a direction away from the central axis 6 of the housing 11, thereby reducing the thickness of the third region 1113. The outer peripheral surface of the third region 1113 expands outward to increase the maximum diameter of the cylindrical battery cell 10. In embodiments where the first solder mark 14 protrudes from the outer peripheral surface 1112 of the sidewall, the first solder mark 14 further increases the maximum diameter of the cylindrical battery cell 10, thereby increasing the volume of the cylindrical battery cell 10. When multiple cylindrical battery cells 10 are disposed in the battery device 100, the risk of interference between adjacent cylindrical battery cells 10 increases, and the volumetric energy density of the battery device 100 decreases.

[0215] In some embodiments, please continue to refer to Figure 13 The end cap 12 extends at least partially into the side wall 111 and forms an interference fit with the side wall 111.

[0216] The end cap 12 may extend entirely into the side wall 111; or a portion of the end cap 12 may extend into the side wall 111. The portion of the end cap 12 extending into the side wall 111 forms an interference fit with the side wall 111.

[0217] In this embodiment, on the one hand, the end cap 12 and the housing 11 can form a positioning fit, reducing the welding difficulty and improving the welding quality; on the other hand, during the welding process of the end cap 12 and the housing 11, the interference fit between the end cap 12 and the side wall 111 can block the high-temperature material generated during welding, reducing the risk of the high-temperature material entering the containment space 13 and damaging the electrode assembly 2.

[0218] In some embodiments, please continue to refer to Figure 13 The end cap 12 includes a body portion 122 and an edge portion 121. The edge portion 121 is connected to the body portion 122 and is disposed around the outside of the body portion 122. A portion of the body portion 122 extends into the side wall 111 and forms an interference fit with the side wall 111. Along the axial direction Z of the housing 11, at least a portion of the edge portion 121 is located on one side of the side wall 111. A first solder mark portion 14 connects the edge portion 121 and the side wall 111.

[0219] It is possible that only a portion of the edge portion 121 is located on one side of the sidewall 111 along the axial direction Z of the housing 11, or the entire edge portion 121 is located on one side of the sidewall 111 along the axial direction Z of the housing 11. A portion of the body portion 122 extends into the sidewall 111 such that the portion of the sidewall 111 connected to the first solder mark portion 14 forms an interference fit with the body portion 122.

[0220] In this embodiment, on the one hand, at least a portion of the edge portion 121 is located on one side of the sidewall 111 along the axial direction Z, and the edge portion 121 and the sidewall 111 can be welded along the radial direction X of the housing 11, which can reduce the welding difficulty and improve the welding quality; on the other hand, when the end cap 12 is assembled with the housing 11, the body portion 122 extends into the sidewall 111, and the edge portion 121 can play a limiting role, reducing the risk of axial movement of the end cap 12 and the housing 11 during welding, and improving the welding quality of the end cap 12 and the housing 11.

[0221] In some embodiments, please continue to refer to Figure 6 and further refer to Figures 14-17 , Figure 14 This is a schematic diagram of the structure of the end cap 12 provided in some embodiments of this application; Figure 15 for Figure 14 A magnified view of a portion of region C in the middle; Figure 16 Schematic diagram of the structure of the end cap 12 provided in some embodiments of this application; Figure 17 This is a schematic diagram of the structure of the end cap 12 provided in some embodiments of this application. Along the axial direction Z of the housing 11, a groove 123 is provided on the side of the end cap 12 away from the electrode assembly 2, and a protrusion 124 is formed in the area corresponding to the groove 123 on the side of the end cap 12 facing the electrode assembly 2. The protrusion 124 is electrically connected to the electrode assembly 2. Along the radial direction X of the housing 11, at least a portion of the orthographic projection of the first solder mark 14 is located in the groove 123.

[0222] As an example, along the axial direction Z of the housing 11, the surface of the end cap 12 furthest from the electrode assembly 2 is the first surface 1221. The first surface 1221 is further away from the electrode assembly 2 than the first outer surface 1211. The groove wall of the recess 123 connects the first outer surface 1211 and the first surface 1221.

[0223] The protrusion 124 is inserted into the housing 11 such that at least a portion of the orthographic projection of the first solder mark 14 along the radial direction X of the housing 11 is located within the groove 123. Along the radial direction X of the housing 11, the orthographic projection of the first solder mark 14 may be entirely located within the groove 123; or only a portion of the orthographic projection of the first solder mark 14 may be located within the groove 123.

[0224] The portion of the protrusion 124 inserted into the housing 11 can form a positioning fit with the housing 11. For example, the outer peripheral surface of the protrusion 124 is in contact with the first inner peripheral surface 11131 of the side wall 111 of the housing 11, so that the protrusion 124 and the housing 11 form a positioning fit.

[0225] The protrusion 124 can be electrically connected to the electrode assembly 2. The protrusion 124 can directly abut against the electrode assembly 2, for example, the protrusion 124 can be directly connected to the tab of the electrode assembly 2; the protrusion 124 can also indirectly abut against the electrode assembly 2, for example, the protrusion 124 can be connected to the tab of the electrode assembly 2 through an intermediate component, which can be a current collector.

[0226] In some embodiments, please continue to refer to Figure 6 and Figures 14-17 The cylindrical battery cell 10 also includes a first current collector 4, which is housed in the receiving space 13. Along the axial direction Z of the cylindrical battery cell 10, the first current collector 4 is disposed between the end cap 12 and the electrode assembly 2. The electrode assembly 2 has a first tab 21, and the first current collector 4 connects the first tab 21 and the protrusion 124. The first current collector 4 can be a metal conductor and can be disk-shaped; it can also be called a current collector disk. The first tab 21 can be a positive or negative tab. The first current collector 4 connects the first tab 21 and the protrusion 124, achieving electrical connection between the electrode assembly 2 and the end cap 12. The first current collector 4 and the first tab 21 can be connected by welding, bonding, or other methods; the first current collector 4 and the protrusion 124 can also be connected by welding, bonding, or other methods.

[0227] In this embodiment, for the cylindrical battery cell 10, since the end cap 12 is located at the end of the cylindrical battery cell 10 along the Z-axis, the end cap 12 is more prone to deformation under stress. The high temperature of welding when the end cap 12 and the housing 11 are welded can easily generate stress around the first solder mark 14. However, a groove 123 is provided on the side of the end cap 12 away from the electrode assembly 2, and at least a portion of the orthogonal projection of the first solder mark 14 along the radial X of the housing 11 is located in the groove 123. This allows the groove 123 to absorb the stress on the end cap 12 near the first solder mark 14, reducing the risk of damage to the end cap 12.

[0228] In some embodiments, the first solder mark 14 is an annular structure arranged around the central axis 6 of the housing 11. In this embodiment, on the one hand, it can improve the welding strength between the end cap 12 and the housing 11 and reduce the risk of welding failure between the end cap 12 and the housing 11; on the other hand, the first solder mark 14 can achieve a seal between the end cap 12 and the housing 11.

[0229] In some embodiments, the wall thickness of the end cap 12 is 400μm-800μm.

[0230] As an example, the thickness of the body portion 122 is the wall thickness of the end cap 12, and the body portion 122, the protrusion 124, and the edge portion 121 are integrally formed. The body portion 122 has a first surface 1221 facing away from the electrode assembly 2 along the axial direction Z of the cylindrical battery cell 10 and a second surface 1222 facing the electrode assembly 2. The first surface 1221 and the second surface 1222 are disposed opposite to each other, and the protrusion 124 is disposed around the outer periphery of the second surface 1222. The distance between the second surface 1222 and the first surface 1221 is equal to the thickness of the body portion 122.

[0231] The wall thickness of the end cap 12 is H, and H can be 400 μm, 410 μm, 420 μm, 430 μm, 440 μm, 450 μm, 460 μm, 470 μm, 480 μm, 4 90μm, 500μm, 510μm, 520μm, 530μm, 540μm, 550μm, 560μm, 570μm, 580μm, 590μm, 600μm The point value or the range between any two of the following values: 610μm, 620μm, 630μm, 640μm, 650μm, 660μm, 670μm, 680μm, 690μm, 700μm, 710μm, 720μm, 730μm, 740μm, 750μm, 760μm, 770μm, 780μm, 790μm, and 800μm.

[0232] In this embodiment, the thickness of the end cap 12 is greater than or equal to 400 μm, so that the end cap 12 has sufficient thickness to meet the strength requirements of the end cap 12; the thickness of the end cap 12 is less than or equal to 800 μm, so that the thickness of the end cap 12 is not too large, reducing the material used in the end cap 12 and reducing the manufacturing cost of the end cap 12; therefore, the wall thickness of the end cap 12 is 400 μm-800 μm, which can balance the strength and manufacturing cost of the end cap 12.

[0233] In some embodiments, please refer to Figures 14-17 The end cap 12 is provided with a pressure relief groove 125, and the end cap 12 is configured to split along at least a portion of the pressure relief groove 125 when the cylindrical battery cell 10 is depressurized.

[0234] The pressure relief groove 125 can be a groove extending along a closed trajectory, which can be a circular trajectory, a rectangular trajectory, etc.; the pressure relief groove 125 can also be a groove extending along a non-closed trajectory, which can be a C-shaped trajectory, a Y-shaped trajectory, a V-shaped trajectory, a U-shaped trajectory, etc. The pressure relief groove 125 can be formed on the end cap 12 by stamping, milling, laser etching, etc.

[0235] The end cap 12 forms a weak portion 126 at the location where the pressure relief groove 125 is provided. The weak portion 126 can be the bottom wall of the pressure relief groove 125. The weak portion 126 can be a structure of uniform thickness or a structure of non-uniform thickness. As an example, in Figure 14 In the illustrated embodiment, the weak portion 126 is a non-uniform thickness structure, and the thickness of the weak portion 126 gradually decreases from both ends to the middle along the width direction of the pressure relief groove 125. The thickness direction of the weak portion 126 is parallel to the axial direction Z of the cylindrical battery cell 10. When the end cap 12 cracks along at least a portion of the pressure relief groove 125, the end cap 12 cracks from the weak portion 126.

[0236] It is understandable that the weak part 126 is the area remaining after the pressure relief groove 125 is opened in the end cover 12, and the thickness of the area where the weak part 126 is located is less than the thickness of the end cover 12.

[0237] The end cap 12 is provided with a pressure relief groove 125, so that the end cap 12 forms an integrated pressure relief mechanism, which enables the end cap 12 to have a pressure relief function. When the internal pressure of the cylindrical battery cell 10 reaches the burst pressure of the end cap 12, the end cap 12 can crack along at least a part of the pressure relief groove 125, so that the local area of ​​the end cap 12 opens to release the internal pressure of the cylindrical battery cell 10, thereby reducing the risk of fire and explosion of the cylindrical battery cell 10 and effectively improving the reliability of the cylindrical battery cell 10.

[0238] In some embodiments, please continue to refer to Figures 14-17 The bottom surface of the groove 123 is provided with multiple protrusions 1231, which are spaced apart circumferentially along the end cover 12. A protrusion 124 is recessed at a position corresponding to the protrusion 1231, forming an exhaust channel 127 along the axial direction (Z) of the housing 11 away from the electrode assembly 2. The exhaust channel 127 connects to the pressure relief groove 125.

[0239] In some embodiments, please continue to refer to Figure 16 and Figure 17 and further refer to Figure 18 , Figure 18 This is a partial structural schematic diagram of a cylindrical battery cell 10 provided in some embodiments of this application (showing the second solder mark 7). Along the circumference of the end cap 12, the bottom wall of the groove 123 located between two adjacent protrusions 1231 is provided with a second solder mark 7, which connects the protrusion 124 and the first current collector 4.

[0240] Please continue to refer to Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 13This application provides a battery cell including a housing 11, an end cap 12, an electrode assembly 2, a first current collector 4, and a second current collector 5. The housing 11 is made of steel and has an opening at one end along its axial direction Z. The housing 11 includes a sidewall 111 extending circumferentially along the opening. The end cap 12 covers the opening and, together with the housing 11, defines a receiving space 13. The end cap 12 includes a body portion 122 and an edge portion 121. The edge portion 121 is disposed around the outer periphery of the body portion 122, and the body portion 122 partially extends into the opening. At least a portion of the edge portion 121 is arranged along the axial direction Z with the sidewall 111. The edge portion 121 is made of steel and is welded to the sidewall 111 to form a first weld mark portion 14. The effective penetration depth L of the first solder mark 14 is given by the maximum thickness D of the sidewall 111, where 2 / 3 ≤ L / D ≤ ​​1, and the average grain size of the first solder mark 14 is 40 μm-100 μm; 300 μm ≤ L ≤ 400 μm, 200 μm ≤ D ≤ 450 μm. The first solder mark 14 includes a first region 142 and a second region 143, with the first region 142 located outside the second region 143. The average grain size of the first region 142 is smaller than the average grain size of the second region 143. Along the radial direction X of the housing 11, the portion of the first region 142 protruding from the outer peripheral surface has a dimension K, where 0 μm < K ≤ 10 μm. A groove 123 is provided on the surface of the body portion 122 facing away from the electrode assembly 2, and the projection of the first solder mark 14 along the radial direction X of the housing 11 is located within the groove 123. A protrusion 124 is formed on the surface of the main body 122 facing the electrode assembly 2 at a position corresponding to the groove 123. At least a portion of the protrusion 124 is inserted into the housing 11, and the outer peripheral surface of the protrusion 124 abuts against the inner peripheral surface of the side wall 111. The protrusion 124 and the side wall 111 are interference-fitted.

[0241] In such a cylindrical battery cell 10, the ratio of the effective penetration depth L of the first solder joint 14 to the maximum thickness D of the sidewall 111 of the casing 11 is 2 / 3-1, and the average grain size of the first solder joint 14 is 30μm-150μm. On the one hand, this ensures that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall 111 of the casing 11 is not too small, and the average grain size of the first solder joint 14 is not too large, thereby enhancing the strength of the first solder joint 14, reducing the risk of fatigue cracking of the first solder joint 14, and extending the service life of the cylindrical battery cell 10. On the other hand, this ensures that the ratio of the effective penetration depth L to the maximum thickness D of the sidewall 111 of the casing 11 is not too large, and the average grain size of the first solder joint 14 is not too small, reducing the welding difficulty between the end cap 12 and the casing 11, reducing production costs, and having better economic efficiency. In this cylindrical battery cell 10, the influence of average grain size and effective penetration depth on the first solder joint 14 is considered. The ratio of effective penetration depth L to the maximum thickness D of the sidewall 111 of the housing 11 and the average grain size of the first solder joint 14 are controlled within a reasonable range, balancing the service life and economic requirements of the cylindrical battery cell 10. The protrusion 124 of the body portion 122 is at least partially inserted into the housing 11, which enables rapid positioning of the end cap 12 and the housing 11 and reduces the space for the electrode assembly 2 to move along the axial Z direction inside the cylindrical battery cell 10. The edge portion 121 of the body portion 122 abuts against the end of the housing 11 with an opening, which restricts the movement of the end cap 12 relative to the housing 11 in the direction close to the electrode assembly 2, facilitating the welding of the edge portion 121 to the housing 11. Furthermore, during the welding process between the edge portion 121 and the housing 11, whether the edge portion 121 is welded to the housing 11 along the axial direction Z of the cylindrical battery cell 10 or along the radial direction X of the cylindrical battery cell 10, the protrusion 124 can block the high-temperature substances generated during the welding process, reducing the risk of high-temperature substances entering the containment space 13 and damaging the electrode assembly 2. This cylindrical battery cell 10 balances improving the strength of the first solder mark 14 and its high-temperature creep resistance, thereby balancing the structural stability and high-temperature resistance of the first solder mark 14, reducing the risk of welding failure between the end cap 12 and the housing 11, and improving the service life of the cylindrical battery cell 10.

[0242] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0243] Example 1

[0244] The experiment was conducted using a cylindrical battery cell 10 based on the LFP system. The battery cell includes a housing 11, an end cap 12, and an electrode assembly 2. The housing 11 has an opening at one end along its axial direction Z. The housing 11 is made of steel and includes a sidewall 111 extending circumferentially along the opening. The end cap 12 covers the opening, and together with the housing 11, defines a receiving space 13. The end cap 12 is also made of steel and is welded to the sidewall 111 to form a first solder joint 14. The electrode assembly 2 is housed within the receiving space 13. The second outer surface 141 of the first solder joint 14 connects the outer peripheral surface 1112 of the sidewall and the first outer surface 1211 of the end cap 12. The sidewall 111 includes a third region 1113 and a fourth region 1114. The inner circumferential surface of the third region 1113 is connected to the second interface 1116 of the first solder mark 14 at a first position 15. The minimum distance between the first position 15 and the second outer surface 141 is the effective penetration depth L of the first solder mark 14. The maximum thickness of the fourth region 1114 is the maximum thickness D of the sidewall 111.

[0245] The effective penetration depth L of the first solder mark 14 is 200 μm, the maximum thickness D of the sidewall 111 is 400 μm, L / D = 0.5, and the average grain size of the first solder mark 14 is 30 μm.

[0246] Example 2

[0247] The process is basically the same as in Example 1, except that the effective penetration depth L of the first solder mark 14 is 300 μm, the maximum thickness D of the sidewall 111 is 450 μm, and L / D = 2 / 3.

[0248] Example 3

[0249] The process is basically the same as in Example 1, except that the effective penetration depth L of the first solder mark 14 is 200 μm, the maximum thickness D of the sidewall 111 is 200 μm, and L / D = 1.

[0250] Example 4

[0251] It is basically the same as Example 1, except that the effective penetration depth L of the first solder mark 14 is 600 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 1.5.

[0252] Example 5

[0253] It is basically the same as Example 1, except that the average grain size of the first solder mark 14 is 40 μm.

[0254] Example 6

[0255] The example is basically the same as Example 5, except that the effective penetration depth L of the first solder mark 14 is 300 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 2 / 3.

[0256] Example 7

[0257] The example is basically the same as Example 5, except that the effective penetration depth L of the first solder mark 14 is 300 μm, the maximum thickness D of the sidewall 111 is 300 μm, and L / D = 1.

[0258] Example 8

[0259] It is basically the same as Example 5, except that the effective penetration depth L of the first solder mark 14 is 600 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 1.5.

[0260] Example 9

[0261] It is basically the same as Example 1, except that the average grain size of the first solder mark 14 is 100 μm.

[0262] Example 10

[0263] The invention is basically the same as in Example 9, except that the effective penetration depth L of the first solder mark 14 is 400 μm, the maximum thickness D of the sidewall 111 is 600 μm, and L / D = 2 / 3.

[0264] Example 11

[0265] The example is basically the same as Example 9, except that the effective penetration depth L of the first solder mark 14 is 300 μm, the maximum thickness D of the sidewall 111 is 300 μm, and L / D = 1.

[0266] Example 12

[0267] It is basically the same as Example 9, except that the effective penetration depth L of the first solder mark 14 is 600 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 1.5.

[0268] Example 13

[0269] It is basically the same as Example 1, except that the average grain size of the first solder mark 14 is 150 μm.

[0270] Example 14

[0271] The example is basically the same as Example 13, except that the effective penetration depth L of the first solder mark 14 is 400 μm, the maximum thickness D of the sidewall 111 is 600 μm, and L / D = 2 / 3.

[0272] Example 15

[0273] The example is basically the same as Example 13, except that the effective penetration depth L of the first solder mark 14 is 400 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 1.

[0274] Example 16

[0275] It is basically the same as Example 13, except that the effective penetration depth L of the first solder mark 14 is 600 μm, the maximum thickness D of the sidewall 111 is 400 μm, and L / D = 1.5.

[0276] Comparative Example 1

[0277] It is basically the same as Example 1, except that the effective penetration depth L of the first solder mark 14 is 150 μm, the maximum thickness D of the sidewall 111 is 400 μm, L / D = 0.375, and the average grain size of the first solder mark 14 is 160 μm.

[0278] The cylindrical battery cell 10 in each embodiment and comparative example was tested according to the following steps:

[0279] The method for testing the number of cycles of the cylindrical battery cell 10 is as follows:

[0280] 1) Place the cylindrical battery cell 10 in a constant temperature environment of 25±2℃ and start the test after the cylindrical battery cell 10 reaches temperature equilibrium.

[0281] 2) The test procedure shall be performed in accordance with the "Standard Cycle Life" section 6.4 of "GBT31484-2015 Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles", and the test cycle cutoff condition shall be changed to "Cracking of the first solder mark 14".

[0282] Specifically, test according to the following steps:

[0283] a) Discharge to 2.8V with a current of 1I1(A);

[0284] b) Let it rest for no less than 30 minutes;

[0285] c) Charge according to method 6.1.1.3 of GB / T 31484-2015 "Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles";

[0286] d) Let it rest for no less than 30 minutes;

[0287] e) Discharge to 2.8V with a current of 1I1(A);

[0288] f) Repeat steps b) to e) until a crack occurs at the first solder mark 14 of the cylindrical battery cell 10, at which point the test is stopped.

[0289] The testing process involves continuously observing the first solder mark 14 area of ​​the cylindrical battery cell 10 until cracks appear in that area. The number of cycles is recorded as the cyclic fatigue count of the cylindrical battery cell 10. The more cyclic fatigue counts the cylindrical battery cell 10 has, the lower the probability of fatigue cracking of the first solder mark 14 during long-term use, and the longer its service life.

[0290] The effective melt depth L, the maximum thickness D of the sidewall 111, and the average grain size of the first solder joint 14 in each embodiment and comparative example were obtained by testing using the following method:

[0291] The cylindrical battery cell 10 is cut radially X along the casing 11. After fixing, the section along the central axis 6 from the outer casing 1 to the casing 11 is ground. This section is then polished. The polished sample is fixed on a sample stage tilted at 70°, and an appropriate magnification is selected. EBSD scanning is performed using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) attachment. Based on the scanning results, the average grain size of the first solder mark 14 is calculated. The polished section is photographed using a metallographic microscope, and the effective penetration depth L of the first solder mark 14 and the maximum thickness D of the sidewall 111 are measured. The value of L / D is then calculated.

[0292] Table 1

[0293]

[0294] A comparison between Comparative Example 1 and Examples 1-16 shows that, compared to cylindrical battery cells 10 with an effective penetration depth L of 150 μm in the first solder mark 14, a maximum thickness D of 400 μm in the sidewall 111, L / D = 0.375, and an average grain size of 160 μm in the first solder mark 14, cylindrical battery cells 10 with L / D ranging from 0.5 to 1.5 and an average grain size of 30 μm to 150 μm in the first solder mark 14 can achieve a cycle fatigue count exceeding 500 cycles, thus improving the service life of cylindrical battery cells 10.

[0295] As can be seen from Examples 1-4, when the average grain size of the first solder portion 14 of the cylindrical battery cell 10 reaches a certain requirement, the larger the ratio of the effective penetration depth L of the first solder portion 14 of the cylindrical battery cell 10 to the maximum thickness D of the sidewall 111, the more cyclic fatigue cycles the cylindrical battery cell 10 has and the longer its service life.

[0296] As can be seen from Examples 1, 5, 9 and 13, when the L / D value of the cylindrical battery cell 10 reaches a certain requirement, the smaller the average grain size of the first solder mark 14 of the cylindrical battery cell 10, the more cycle fatigue cycles the cylindrical battery cell 10 has, and the longer its service life.

[0297] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0298] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit this application. For those skilled in the art, this application can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A cylindrical battery cell, characterized by, include: A housing having an opening at at least one end along its axial direction, the housing being made of steel, the housing including sidewalls extending circumferentially along the opening; An end cap is provided over the opening, and the end cap and the housing together define a receiving space. The end cap is made of steel, and the end cap is welded to the side wall to form a first weld mark. Electrode assembly, housed within the receiving space; Wherein, the effective penetration depth of the first solder mark is L, the maximum thickness of the sidewall is D, 0.5≤L / D≤1.5, and the average grain size of the first solder mark is 30μm-150μm.

2. The cylindrical battery cell of claim 1, wherein, 2 / 3≤L / D≤1, and the average grain size of the first solder mark is 40μm-100μm.

3. The cylindrical battery cell of claim 1, wherein, 200μm≤L≤600μm; optionally, 300μm≤L≤400μm.

4. The cylindrical battery cell of claim 1, wherein, 200μm≤D≤600μm; optionally, 200μm≤D≤450μm.

5. The cylindrical battery cell of claim 1, wherein, Along the axial direction of the housing, the end cap has a first outer surface facing away from the electrode assembly, and the surface of the first solder mark includes a second outer surface, the second outer surface connecting the first outer surface and the outer peripheral surface of the sidewall; The sidewall has a first interface that contacts the end cap. The first interface is connected to the surface of the first solder mark at a first position. The minimum distance between the first position and the second outer surface is the effective penetration depth of the first solder mark.

6. The cylindrical battery cell of claim 5, wherein, The first solder mark includes a first region and a second region. The average grain size of the first region is smaller than the average grain size of the second region. Along the radial direction of the housing, the first region is located outside the second region, and the outer surface of the first region is at least a portion of the second outer surface.

7. The cylindrical battery cell as described in claim 5, characterized in that, The end cap includes an edge portion and a body portion. The edge portion is connected to the body portion and is disposed around the outside of the body portion. A portion of the body portion extends into the sidewall along the axial direction of the housing. At least a portion of the edge portion is located on one side of the sidewall. A first solder mark connects the sidewall and the edge portion. The edge portion forms at least a portion of the first outer surface away from the surface of the electrode assembly along the axial direction.

8. The cylindrical battery cell of any one of claims 1-7, wherein, Along the radial direction of the housing, the first solder mark does not protrude beyond the outer peripheral surface of the sidewall.

9. The cylindrical battery cell of any one of claims 1-7, wherein, Along the radial direction of the housing, the first solder mark portion partially protrudes from the outer peripheral surface of the sidewall.

10. The cylindrical battery cell of claim 9, wherein, Along the radial direction of the housing, the maximum dimension of the portion of the first solder mark protruding from the outer peripheral surface of the sidewall is K, where 0 μm < K ≤ 10 μm.

11. The cylindrical battery cell of any one of claims 1-7, wherein, The sidewall includes a third region and a fourth region arranged along the axial direction of the housing. The thickness of the third region is less than the thickness of the fourth region. The third region is located between the fourth region and the first solder mark and is connected to the first solder mark.

12. The cylindrical battery cell of claim 11, wherein, At least a portion of the third region has a lower hardness than the fourth region.

13. The cylindrical battery cell of claim 11, wherein, The third region has a first inner circumferential surface, and the fourth region has a second inner circumferential surface. Along the radial direction of the housing, the first inner circumferential surface is further away from the central axis of the housing than the second inner circumferential surface.

14. The cylindrical battery cell of claim 13, wherein, The sidewall also includes a transition zone located between and connecting the third and fourth zones. The transition zone has a transition surface that connects the first inner circumferential surface and the second inner circumferential surface.

15. The cylindrical battery cell as described in claim 13, characterized in that, The third region has a second interface connected to the first solder mark portion, and the second interface is connected to the first inner circumferential surface.

16. The cylindrical battery cell as described in claim 15, characterized in that, The radial distance between the first inner circumferential surface and the second interface in the housing gradually increases along the direction from the third region to the fourth region.

17. The cylindrical battery cell of claim 13, wherein, At least a portion of the end cap extends into the sidewall and abuts against the first inner circumferential surface, and the portion of the end cap extending into the sidewall forms an interference fit with the third region.

18. The cylindrical battery cell of any one of claims 1-7, wherein, The end cap extends at least partially into the sidewall and forms an interference fit with the sidewall.

19. The cylindrical battery cell of claim 18, wherein, The end cap includes a body portion and an edge portion. The edge portion is connected to the body portion and is disposed around the outside of the body portion. A portion of the body portion extends into the side wall and forms an interference fit with the side wall. Along the axial direction of the housing, at least a portion of the edge portion is located on one side of the side wall. The first solder mark connects the edge portion and the side wall.

20. The cylindrical battery cell according to any one of claims 1-7, characterized in that, Along the axial direction of the housing, a groove is provided on the side of the end cap away from the electrode assembly, and a protrusion is formed on the side of the end cap facing the electrode assembly in the area corresponding to the groove, and the protrusion is electrically connected to the electrode assembly. Along the radial direction of the housing, at least a portion of the orthographic projection of the first solder mark is located within the groove.

21. The cylindrical battery cell of any one of claims 1-7, wherein, The first solder mark is an annular structure arranged around the central axis of the housing.

22. The cylindrical battery cell of any one of claims 1-7, wherein, The end cap has a wall thickness of 400μm-800μm.

23. A battery device, characterized by Includes cylindrical battery cells as described in any one of claims 1-22.

24. An electrical device, comprising: Includes a cylindrical battery cell as described in any one of claims 1-22 or a battery device as described in claim 23.

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