Cylindrical secondary battery to which laser welding is applied, manufacturing method thereof, battery pack including such secondary battery, and automobile

Abstract

To provide a cylindrical secondary battery having an improved electrode terminal structure.SOLUTION: There are provided a cylindrical secondary battery having an improved electrode terminal structure and a manufacturing method thereof. The cylindrical secondary battery according to the present invention has an improved electrode terminal structure, in which a first current collector plate and the electrode terminal are joined by a laser welding method. A laser welding portion formed on a contact surface between the first current collector plate and the electrode terminal is located within an overlapping portion of the first current collector plate and the electrode terminal within a winding center hole of an electrode assembly.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a cylindrical secondary battery and a method for manufacturing the same, and also to a battery pack and a vehicle including such a cylindrical secondary battery.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0136997 filed on October 14, 2021, and Korean Patent Application No. 10-2022-0021589 filed on February 18, 2022, and the contents disclosed in the specifications and drawings of those applications are incorporated herein in their entirety. [Background technology]

[0003] Secondary batteries, which are easily applicable to various products and have electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs), hybrid electric vehicles (HEVs), etc. These secondary batteries are attracting attention as a new energy source because they not only have the primary advantage of dramatically reducing the use of fossil fuels, but also because they are environmentally friendly and improve energy efficiency by not producing any by-products associated with energy use.

[0004] Known types of secondary batteries include cylindrical, prismatic, and pouch-type secondary batteries. In cylindrical secondary batteries, a separator, which is an insulator, is interposed between a positive electrode and a negative electrode, and the separator is wound up to form a jelly-roll-shaped electrode assembly. This jelly-roll-shaped electrode assembly is then inserted into a battery can together with an electrolyte to form a battery. Strip-shaped electrode tabs may be connected to the uncoated portions of the positive and negative electrodes, and the electrode tabs connect the electrode assembly to electrode terminals exposed to the outside. However, conventional cylindrical secondary batteries with this structure have problems such as high resistance, excessive heat generation, and poor current collection efficiency due to current concentration in the strip-shaped electrode tabs connected to the uncoated portions of the positive and / or negative electrodes.

[0005] Small cylindrical secondary batteries with 18650 or 21700 form factors do not pose significant resistance or heat generation issues. However, when the form factor of cylindrical secondary batteries is increased for use in electric vehicles, a large amount of heat is generated around the current collecting tab during fast charging, which can lead to the cylindrical secondary battery catching fire. Here, the term "form factor" refers to a value that indicates the diameter and height of a battery. In the form factor number, the first two digits indicate the cell diameter, the next two digits indicate the cell height, and the final digit "0" indicates that the cell cross section is circular. If the cell height exceeds 100 mm, a three-digit number is required to indicate the cell height, so the final digit "0" can be omitted.

[0006] In order to solve the problems of resistance and heat generation in cylindrical secondary batteries with increased form factors, cylindrical secondary batteries (so-called tab-less cylindrical secondary batteries) have been proposed that have a structure that improves current collection efficiency by using current collector plates with a larger area than strip-shaped electrode tabs.

[0007] Figures 1 to 3 are diagrams showing the manufacturing process of a conventional tabless cylindrical secondary battery. Figure 1 shows the structure of the electrode plate, Figure 2 shows the electrode plate winding process, and Figure 3 shows the process of welding a current collector plate to the bent surface of the uncoated portion. Figure 4 is a cross-sectional view of a conventional tabless cylindrical secondary battery cut in the longitudinal direction (Y direction).

[0008] 1, positive electrode plate 10 and negative electrode plate 11 have a structure in which active material 21 is coated on sheet-shaped current collector 20, and include an uncoated portion 22 on one long side along the winding direction (X direction) where the active material is not coated. In the direction along the long side of current collector 20 (X direction), one side becomes the core and the other side becomes the periphery.

[0009] The electrode assembly A is fabricated by stacking the positive electrode plate 10 and the negative electrode plate 11 together with two separators 12 in order as shown in Figure 2, and then winding them in one direction (X direction) from the core. In this case, the uncoated portions of the positive electrode plate 10 and the negative electrode plate 11 are arranged in opposite directions in the direction (Y direction) along the short side of the current collector 20.

[0010] Referring to Figure 3, a winding center hole 13 is formed in the inner core of the electrode assembly A manufactured by the method of Figure 2. After the winding process, the uncoated portion 10a of the positive electrode plate 10 and the uncoated portion 11a of the negative electrode plate 11 are bent toward the core. Then, current collector plates 30 and 31 are connected to the uncoated portions 10a and 11a.

[0011] Since no separate electrode tabs are attached to the non-coated portions 10a, 11a and current collector plates 30, 31 are connected to external electrode terminals, and the current path is formed with a large cross-sectional area along the winding axis direction of electrode assembly A (see arrow), this has the advantage of lowering the resistance of the secondary battery, since resistance is inversely proportional to the cross-sectional area of the path through which current flows.

[0012] However, as the form factor of cylindrical secondary batteries increases and the magnitude of the charging current increases during fast charging, heat generation problems also occur in tableless cylindrical secondary batteries.

[0013] Specifically, as shown in Figure 4, a conventional tabless cylindrical secondary battery 40 includes a battery can 41 and a sealing body 42. The sealing body 42 includes a cap plate 42a, a sealing gasket 42b, and a connection plate 42c. The sealing gasket 42b surrounds the periphery of the cap plate 42a and is fixed by a crimping portion 43. In addition, an electrode assembly A is fixed inside the battery can 41 by a beading portion 44 to prevent vertical movement.

[0014] Typically, the positive electrode terminal is the cap plate 42a of the sealed body 42, and the negative electrode terminal is the battery can 41. Thus, the current collector 30 attached to the uncoated portion 10a of the positive electrode plate 10 is connected to a connection plate 42c attached to the cap plate 42a via a strip-shaped lead 45. Also, the current collector 31 attached to the uncoated portion 11a of the negative electrode plate 11 is connected to the bottom of the battery can 51. An insulator 46 covers the current collector 30 to prevent the battery can 51 and the uncoated portion 10a of the positive electrode plate 10, which have opposite polarities, from coming into contact with each other and causing a short circuit.

[0015] In the cylindrical secondary battery 40, a strip-shaped lead 45 is used when the current collector 30 is connected to the connection plate 42c. The lead 45 is either attached separately to the current collector 30 or is manufactured integrally with the current collector 30. However, because the lead 45 is in the form of a thin strip, its cross-sectional area is small, and a large amount of heat is generated when a fast charging current flows. In addition, the excessive heat generated in the lead 45 is transferred to the electrode assembly A and causes the separator (12 in FIG. 2) to contract, which can cause an internal short circuit, a major cause of thermal runaway.

[0016] Furthermore, the leads 45 occupy a considerable amount of installation space within the battery can 41. As a result, the cylindrical secondary battery 40 including the leads 45 has low space efficiency and is limited in increasing its energy density. Therefore, there is a need in the art to solve the heat generation problem of cylindrical secondary batteries and improve the structure of the electrode terminals to increase space efficiency within the battery can.

[0017] Meanwhile, the cylindrical secondary battery 40 includes current collector plates 30 and 31, and connection portions between the current collector plates 30 and 31 and other components are present in the upper and lower portions of the cylindrical secondary battery 40. Various welding processes can be used to connect the current collector plates 30 and 31 to other components at these positions. In this case, it is important to achieve appropriate joint strength with high efficiency and to perform welding without damaging the welded body or surrounding components.

[0018] When resistance welding is used in a welding process, if the workpiece is made of aluminum, an oxide film forms on the welding rod, making continuous welding impossible. Furthermore, if such an oxide film forms, the welding rod generates heat before the workpiece generates heat. If either of the current collector plates 30 and 31 is made of aluminum, resistance welding inevitably reduces the efficiency of the welding process. Furthermore, if either of the current collector plates 30 and 31 is made of copper, the low resistance of copper makes it difficult to generate resistance heat, resulting in poor welding, such as reduced joint strength. Furthermore, resistance welding equipment sandwiches the workpiece between the upper and lower welding rods, applies pressure to bring them into close contact, and then applies current to weld them using resistance heat. Therefore, pressure is essential. Insufficient pressure can result in partial welding, leading to quality variations and the risk of part deformation due to the pressure.

[0019] Additionally, when ultrasonic welding is used in a welding process, a horn must vibrate while in contact with the contact points. However, if the horn vibrates in a linear or zigzag pattern, the horn may break. For example, when ultrasonically welding the current collector plate 31 to the bottom of the battery can 41 of a cylindrical secondary battery 40, the horn must be inserted through the winding center hole 13 of the electrode assembly A to perform the welding. Therefore, the ultrasonic welding horn must be longer than the length from one end of the winding center hole 13 to the other. Therefore, if strong vibrations occur in a linear or zigzag pattern, the horn may break. To address this issue, a method using a rotating horn may be used, but this method still creates problems such as the generation of numerous burrs and makes it difficult to check for unbonded areas. Furthermore, ultrasonic welding can also cause problems due to the generation of foreign matter (slag) during welding. Ultrasonic welding also suffers from the problem of lower joint strength compared to resistance welding.

[0020] Therefore, in a manufacturing method for a tabless-less cylindrical secondary battery in which there are connection points between the current collector plate and other components and the connection is to be made by welding, it is necessary to apply a welding technique that is different from the conventional welding method described above. Summary of the Invention [Problem to be solved by the invention]

[0021] The present invention has been devised against the background of the prior art described above, and a problem to be solved by the present invention is to provide a cylindrical secondary battery having an improved electrode terminal structure.

[0022] Another object of the present invention is to provide a method for manufacturing a cylindrical secondary battery having an improved electrode terminal structure using a laser welding method.

[0023] Yet another problem to be solved by the present invention is to provide a battery pack manufactured using a cylindrical secondary battery having an improved structure, and a vehicle including the battery pack.

[0024] It should be noted that the technical problems that the present invention aims to solve are not limited to the problems described above, and other problems not mentioned above will be clearly understood by those skilled in the art from the following description of the invention. [Means for solving the problem]

[0025] To achieve the above object, a cylindrical secondary battery according to the present invention provides a jelly-roll-type electrode assembly having a structure in which sheet-like first and second electrode plates and a separator interposed therebetween are wound in one direction, the first electrode plate having an uncoated portion at a long side end thereof exposed to the outside of the separator, the second electrode plate having an uncoated portion at a long side end thereof exposed to the outside of the separator in a direction opposite to the uncoated portion of the first electrode plate, the electrode assembly having a winding center hole in an inner core, and a front electrode assembly having an opening formed on one side thereof, the front electrode assembly being received in the opening formed on the front side thereof, the front electrode assembly being wound ... the battery includes a cylindrical battery can connected to the uncoated portion of the second electrode plate; a sealing body that seals an open portion of the battery can so as to be insulated from the battery can; a first current collector plate connected to the uncoated portion of the first electrode plate; an electrode terminal that is riveted through a through-hole formed in a bottom of the battery can located on the opposite side of the open portion of the battery can and connected to the first current collector plate; and a laser weld formed on a contact surface between the first current collector plate and the electrode terminal, the laser weld being located at an overlapping portion of the first current collector plate and the electrode terminal within the winding center hole.

[0026] Preferably, the equivalent diameter of the laser welded portion exposed on the surface of the first current collector plate is 0.15D to 0.90D (D: diameter of the winding center hole).

[0027] Preferably, the electrode terminal may include a main body portion inserted into the through hole, an outer flange portion extending from a periphery of one side of the main body portion exposed on an outer surface of the bottom of the battery can along the outer surface, an inner flange portion extending from a periphery of the other side of the main body portion exposed on an inner surface of the bottom of the battery can toward the inner surface, and a flat portion provided on the inside of the inner flange portion.

[0028] Preferably, the electrode terminal and the first current collecting plate are joined at the flat portion by the laser weld.

[0029] In one embodiment, the laser welded portion is formed at a joining portion between the first current collector plate and the electrode terminal from one surface of the first current collector plate facing the inside of the winding center hole to the electrode terminal side.

[0030] The outer surface of the electrode terminal may be smooth.

[0031] In another embodiment, the laser weld may be an overlapping overlay type weld bead on the center of the winding center hole.

[0032] In yet another embodiment, the laser weld may be configured in a linear shape.

[0033] In this case, the laser weld may form a continuous closed line or a closed curve. For example, the laser weld may be either a ring-shaped circle type centered on the center of the winding center hole or a wobble circle type centered on the center of the winding center hole. The laser weld may also form an open curve. For example, the laser weld may have a structure in which one quarter of the quarter is open. For example, the laser weld may be C-shaped.

[0034] In yet another embodiment, the laser welds may be multi-spot type welds formed at radially symmetrical positions with respect to the center of the winding center hole.

[0035] In still another embodiment, the laser weld may be any one of an X-type in which two lines intersect at the center of the winding center hole, a square frame type centered at the center of the winding center hole, an L-type in which two lines meet at one point, and an 8-type in which two circles are circumscribed.

[0036] In yet another embodiment, the laser weld may have a center at the center of the winding center hole, an outer periphery having a regular or negative polygonal shape, and a weld bead formed in a weaving manner to fill the outer periphery.

[0037] Preferably, the tensile strength of the laser welded portion between the first current collector plate and the electrode terminal may be 3 kgf or more and 15 kgf or less.

[0038] In one embodiment, the first current collector plate and the electrode terminal may be made of a material containing aluminum as a main component.

[0039] In another embodiment, the diameter of the winding center hole may be 2 mm or more and 8 mm or less.

[0040] In this case, the laser welded portion exposed on the surface of the first current collector plate may have a converted diameter of 2 mm or more.

[0041] Here, the diameter of the flat portion of the electrode terminal may be 3 mm to 14 mm.

[0042] In this case, the ratio of the area of the laser welded portion exposed on the surface of the first current collector plate to the area of the flat portion of the electrode terminal may be 2.04% to 44.4%.

[0043] In yet another embodiment, the inner surfaces of the flat portion and the bottom portion may be parallel to each other.

[0044] In yet another embodiment, the angle formed between the inner flange portion and the inner surface of the bottom portion may be 0° to 60°.

[0045] Preferably, a recess may be provided between the inner flange portion and the flat portion.

[0046] In one embodiment, the recessed portion may have an asymmetric groove cross-sectional configuration.

[0047] In another aspect, the asymmetric groove may include a sidewall of the flat portion and a sloped surface of the inner flange portion connected to an end of the sidewall.

[0048] In yet another embodiment, the sidewalls may be perpendicular to the inner surface of the base.

[0049] In yet another embodiment, the sidewall may be sloped toward the flat portion.

[0050] Preferably, the thickness of the inner flange portion decreases with increasing distance from the body portion.

[0051] Preferably, the cylindrical secondary battery further includes a rivet gasket interposed between the electrode terminal and the through-hole, the rivet gasket including an outer gasket interposed between the outer flange portion and an outer surface of the bottom, and an inner gasket interposed between the inner flange portion and an inner surface of the bottom, and the inner gasket may have a thickness that varies depending on the position.

[0052] In one embodiment, in the region of the internal gasket, the thickness of the region interposed between the inner edge of the through hole connected to the inner surface of the bottom and the internal flange portion may be relatively smaller than that of other regions.

[0053] In another embodiment, the thickness of the region of the internal gasket interposed between the through hole and the body portion may decrease with increasing distance from the external flange portion.

[0054] In yet another embodiment, the thickness of the inner gasket may be thinnest in the region interposed between the inner surface of the base and the end of the inner flange.

[0055] In yet another aspect, the inner edge of the through hole may include a facing surface that faces the inner flange portion.

[0056] In yet another embodiment, the internal gasket may extend beyond the internal flange portion, leaving an exposed end.

[0057] In yet another embodiment, the height of the flat portion relative to the inner surface of the bottom portion may be equal to or greater than the height of the end portion of the internal gasket.

[0058] In yet another embodiment, the height of the flat portion relative to the inner surface of the bottom portion may be the same as or greater than the height of the inner flange portion.

[0059] In still another embodiment, the height of the inner flange portion may be 0.5 mm to 3.0 mm based on the inner surface of the bottom of the battery can.

[0060] Preferably, the height of the electrode terminal from the lower surface of the outer flange portion to the surface of the flat portion may be 1.5 mm to 7 mm.

[0061] Preferably, the height of the outer flange portion based on the outer surface of the bottom of the battery can may be 0.8 mm or more.

[0062] Preferably, at least a portion of the outer gasket is exposed to the outside of the outer flange portion, and the exposed width of the outer gasket measured in a direction parallel to the outer surface of the bottom of the battery can may be 0.1 mm to 1 mm.

[0063] Preferably, the radius from the center of the body to the periphery of the outer flange may be 10% to 70% of the radius of the bottom of the battery can.

[0064] Preferably, the radius from the center of the main body to the periphery of the flat portion may be 4% to 30% of the radius of the bottom portion.

[0065] Preferably, when the compression ratio is defined as the ratio of the thickness change at the maximum compression point to the thickness of the gasket before compression, the compression ratio of the inner gasket may be 30% to 90%.

[0066] More preferably, the inner gasket includes polybutylene terephthalate, polyfluoroethylene, or polypropylene, and the compressibility of the inner gasket may be 50% to 90%.

[0067] In one embodiment, the first current collecting plate includes an edge portion, a first electrode plate coupling portion extending inward from the edge portion and coupling with an uncoated portion of the first electrode plate, and a terminal coupling portion spaced apart from the first electrode plate coupling portion, and the electrode terminal may be coupled to the terminal coupling portion.

[0068] Preferably, the cylindrical secondary battery further includes an insulator interposed between the battery can and the first current collector plate, and the electrode terminal may penetrate the insulator and be coupled to the terminal coupling part.

[0069] More preferably, the cylindrical secondary battery further includes insulators interposed between the first current collector plate and an inner circumferential surface of the bottom of the battery can and between an inner circumferential surface of the sidewall of the battery can and the electrode assembly.

[0070] The insulator may include a welding hole that exposes a flat portion of the electrode terminal toward the first current collector plate, and may cover a surface of the first current collector plate and a periphery of one side of the electrode assembly.

[0071] Preferably, the height from the inner surface of the bottom of the battery can to the flat portion of the electrode terminal may be equal to or smaller than the thickness of the insulator.

[0072] Preferably, the cylindrical secondary battery further includes a rivet gasket interposed between the electrode terminal and the through hole, and the rivet gasket may include an outer gasket interposed between the outer flange portion and an outer surface of the bottom, and an inner gasket interposed between the inner flange portion and an inner surface of the bottom.

[0073] Preferably, an end of the inner gasket may be exposed to the outside of the inner flange portion.

[0074] In yet another embodiment, the weld hole may expose a flat portion and an inner flange portion of the electrode terminal.

[0075] In yet another embodiment, the weld hole may expose a flat portion and an inner flange portion of the electrode terminal and the inner gasket.

[0076] In yet another embodiment, the form factor ratio of the diameter divided by the height of the cylindrical secondary battery may be greater than 0.4.

[0077] In one form, the edge may have a rim configuration with at least a portion of the inner region being open.

[0078] Preferably, the first electrode plate coupling portion and the terminal coupling portion may be connected by the edge portion.

[0079] The terminal coupling portion may be located at the center of the inner space of the edge portion.

[0080] Preferably, the first electrode plate coupling portion may include a plurality of first electrode plate coupling portions.

[0081] In this case, the first electrode plate coupling portions may be arranged at equal intervals along the circumferential direction.

[0082] Additionally, the extension lengths of the first electrode plate coupling portions may be the same as each other.

[0083] Furthermore, the terminal coupling portion may be arranged so as to be surrounded by a plurality of the first electrode plate coupling portions.

[0084] Preferably, the terminal coupling portion may be disposed at a position corresponding to the winding center hole.

[0085] Preferably, at least a portion of the uncoated portion of the first electrode plate is divided into a plurality of segments, and the plurality of segments may be bent along a radial direction of the electrode assembly.

[0086] Preferably, the plurality of segment pieces may be overlapped in multiple layers along the radial direction of the electrode assembly.

[0087] In one embodiment, the first current collecting plate includes an edge portion, a first electrode plate coupling portion extending inward from the edge portion and coupling with an uncoated portion of the first electrode plate, and a terminal coupling portion positioned spaced apart from the first electrode plate coupling portion, and the first electrode plate coupling portion may be coupled to a region where the plurality of segment pieces are overlapped in multiple layers.

[0088] In another embodiment, the battery can may include a beading portion formed at an end adjacent to the opening and pressed inward, and the sealing body may include a non-polar cap plate and a sealing gasket interposed between a periphery of the cap plate and the opening of the battery can.

[0089] The battery can may further include a crimping portion that extends and is bent toward the inside of the battery can and surrounds and fixes the periphery of the cap plate together with the sealing gasket.

[0090] The cap plate may include a vent notch that ruptures when the pressure inside the battery can exceeds a critical value.

[0091] The vent notch is formed so that the pressure inside the battery can is 15 to 35 kgf / cm 2 If it does, it may burst.

[0092] In yet another embodiment, the second current collector plate may further include a second current collector plate coupled to the uncoated portion of the second electrode plate, and at least a portion of the edge of the second current collector plate that does not contact the uncoated portion of the second electrode plate may be interposed between the beading portion and the sealing gasket and fixed by the crimping portion.

[0093] At least a portion of an edge of the second current collector plate may be fixed to an inner circumferential surface of the beading portion adjacent to the crimping portion by welding.

[0094] In yet another embodiment, at least a portion of the uncoated portion of the second electrode plate may be divided into a plurality of segmented pieces, and the plurality of segmented pieces may be bent in the radial direction of the electrode assembly.

[0095] In this case, the plurality of segments may be overlapped in multiple layers along the radial direction of the electrode assembly.

[0096] In such a case, the second current collector plate may include a second electrode plate connecting portion that connects to the uncoated portion of the second electrode plate and a can connecting portion that electrically connects to the beading portion, and the second electrode plate connecting portion may be connected to an area where the plurality of segment pieces are overlapped in multiple layers.

[0097] The second electrode plate coupling portion and the can coupling portion may be indirectly coupled to each other through the center of the second current collector plate, and may not be directly coupled to each other.

[0098] The second electrode plate coupling portion may include at least one liquid inlet.

[0099] The second current collector plate may include a circular current collector hole at a center of the second current collector plate.

[0100] The diameter of the current collecting plate hole may be the same as or larger than the diameter of the winding center hole.

[0101] The present invention also provides a method for manufacturing a cylindrical secondary battery, the method comprising the steps of providing a jelly-roll-type electrode assembly having a structure in which sheet-like first and second electrode plates and a separator interposed therebetween are wound in one direction, the first electrode plate including an uncoated portion at a long side end exposed to the outside of the separator, the second electrode plate including an uncoated portion at a long side end exposed to the outside of the separator in a direction opposite to the uncoated portion of the first electrode plate, and the electrode assembly having a winding center hole in an inner core; and connecting a first current collector to the uncoated portion of the first electrode plate. providing a cylindrical battery can having an opening formed on one side, the battery can including an electrode terminal riveted through a through hole formed in a bottom of the battery can located on the opposite side of the opening of the battery can; inserting the electrode assembly into the battery can such that the first current collecting plate faces the bottom of the battery can; and forming a laser weld at a contact surface between the first current collecting plate and the electrode terminal using a laser welding device, wherein a laser beam of the laser welding device is irradiated into the winding center hole along a longitudinal direction of the winding center hole.

[0102] In one embodiment, the laser welding device may weld the first current collector plate to the electrode terminal in a pulse mode or a continuous mode.

[0103] The laser welding device may irradiate a laser beam with a pulse width of 100 ns to 2,000 ns.

[0104] The laser welding device may emit a laser beam with an output of 50 W to 4 kW.

[0105] The laser welding device may irradiate a laser beam at a processing speed of 40 mm / s to 1,000 mm / s.

[0106] The spot diameter of the laser beam of the laser welding device may be 10 μm to 200 μm.

[0107] Preferably, a pulse dot type laser beam is irradiated onto the center of the winding center hole in an overlapping manner to form an overlapping overlay type laser weld.

[0108] Preferably, the step of forming the laser welded portion may include the steps of inserting a hollow tube into the winding center hole, exposing at least a portion of the first current collecting plate in the hollow tube, and illuminating a laser beam emitted from the laser welding device through the hollow tube to weld the first current collecting plate to the electrode terminal.

[0109] At this time, the first current collector plate may be pressed against the electrode terminal by the hollow tube.

[0110] The method may further include supplying an inert gas to remove oxygen from a space between the hollow tube and the inner circumferential surface of the winding center hole while the laser welding is performed.

[0111] The length of the hollow tube is greater than the height of the electrode assembly, and the hollow tube may be a metallic hollow tube.

[0112] The method may also include removing welding fumes from one end of the winding center hole while the laser welding is performed.

[0113] The method for manufacturing a cylindrical secondary battery according to the present invention is a method for manufacturing a cylindrical secondary battery according to the present invention, characterized in that the step of forming the laser welded portion is a step of welding by irradiating a laser beam using the winding center hole inside the battery can.

[0114] Here, the laser beam can heat the first current collector plate.

[0115] A temperature difference can be created between the area where the laser beam is concentrated and the surrounding area.

[0116] After preheating by the laser beam, full melting can occur.

[0117] The laser beam is preferably single-mode.

[0118] The present invention also provides a battery pack including at least one such cylindrical secondary battery, and a vehicle including at least one such battery pack. [Effects of the Invention]

[0119] According to one aspect of the present invention, the electrode terminal structure of a cylindrical secondary battery is improved to increase the space efficiency within the battery can, thereby reducing the internal resistance of the cylindrical secondary battery and increasing the energy density.

[0120] According to another aspect of the present invention, the problem of internal heat generation occurring during rapid charging can be alleviated by improving the electrode terminal structure of a cylindrical secondary battery to increase the cross-sectional area of the current path.

[0121] According to yet another aspect of the present invention, electrical wiring for connecting cylindrical secondary batteries in series and / or parallel can be performed on one side of the cylindrical secondary batteries, which improves space efficiency and electrical wiring efficiency, thereby significantly improving the assembly process of electric vehicles and battery pack maintenance.

[0122] According to another aspect of the present invention, there is provided a cylindrical secondary battery including a first current collector plate and / or a second current collector plate having a structure that prevents stress from concentrating on the joint between components even when subjected to external impact and / or vibration during use, and that can improve the bonding strength of the joint with the battery can, thereby improving the energy density of the cylindrical secondary battery. The first current collector plate and the second current collector plate have a structure that facilitates laser welding of the first current collector plate to the electrode terminal. This improves the mechanical and electrical performance of the cylindrical secondary battery, and makes it easy to manufacture such a secondary battery by welding.

[0123] The manufacturing method according to the present invention is highly suitable for large-sized batteries with increased form factors. The jelly-roll-type electrode assemblies included in large-sized batteries are taller than conventional ones, and therefore the length of the winding center hole is also longer than conventional ones. When welding the first current collector to the electrode terminal at the bottom of the battery can, damage to the electrode assembly must be prevented during the welding process. In the manufacturing method according to the present invention, a laser beam can be applied to the portion of the first current collector placed in the long winding center hole while preventing damage to the electrode assembly. The present invention can eliminate defects that can occur during laser welding and can weld the first current collector to the electrode terminal, thereby meeting the demand for high-power, low-resistance batteries in the technical field to which the present invention pertains.

[0124] According to the manufacturing method of the present invention, problems such as damage to the workpiece and surrounding components and reduced joint strength that may occur when welding an electrode terminal to a first current collecting plate using conventional welding methods can be solved, thereby improving the processability and efficiency of welding.

[0125] According to the manufacturing method of the present invention, it is possible to connect and join the current collector plate to other components without causing problems due to the material of the current collector plate and without the risk of breaking the welding horn. Furthermore, since no welds are formed on the outer surface of the cylindrical secondary battery, it is possible to more effectively ensure the connection between the cylindrical secondary battery and the bus bar component during electrical wiring work for series and / or parallel connection of the cylindrical secondary batteries.

[0126] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention, so the present invention should not be interpreted as being limited to the matters described in the drawings. [Brief explanation of the drawings]

[0127] [Figure 1] FIG. 1 is a plan view showing the structure of an electrode plate used in a conventional tabless cylindrical secondary battery. [Figure 2] 10A and 10B are diagrams illustrating a winding process of an electrode assembly included in a conventional tabless cylindrical secondary battery. [Figure 3] 3 is a view showing a process of welding a current collecting plate to a bent surface of an uncoated portion in the electrode assembly of FIG. 2. FIG. [Figure 4] FIG. 1 is a cross-sectional view of a conventional tablets cylindrical secondary battery cut in the longitudinal direction (Y direction). [Figure 5] 1 is a cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention taken along the longitudinal direction (Y direction). [Figure 6] 1 is a cross-sectional view showing a riveting structure of an electrode terminal according to an embodiment of the present invention; [Figure 7] FIG. 7 is an enlarged cross-sectional view of part B in FIG. 6. [Figure 8] 10 is a partially enlarged cross-sectional view showing a riveting structure for an electrode terminal according to another embodiment of the present invention; [Figure 9] 4 is a cross-sectional view of a cylindrical secondary battery according to another embodiment of the present invention taken along the longitudinal direction (Y direction). [Figure 10] 1 is a plan view showing an electrode plate structure according to a preferred embodiment of the present invention; [Figure 11] 1 is a cross-sectional view taken along the longitudinal direction (Y direction) of an electrode assembly in which a segmented structure of an uncoated portion of an electrode plate according to an embodiment of the present invention is applied to a first electrode plate and a second electrode plate. [Figure 12] 3 is a cross-sectional view of an electrode assembly in which a non-coated portion is bent in accordance with an embodiment of the present invention, taken along the longitudinal direction (Y direction). [Figure 13] 1 is a perspective view of an electrode assembly in which a non-coated portion is bent according to an embodiment of the present invention; [Figure 14] 3A to 3C are views showing a process of joining an electrode terminal and a first current collecting plate of a cylindrical secondary battery by laser welding according to an embodiment of the present invention. [Figure 15] FIG. 10 is a cross-sectional view of a laser-welded electrode terminal and a first current collector plate. [Figure 16]1A to 1C are diagrams illustrating various surface forms of a laser weld according to an embodiment of the present invention. [Figure 17] 1A to 1C are diagrams illustrating various surface forms of a laser weld according to an embodiment of the present invention. [Figure 18] FIG. 10 is a diagram for explaining a method for calculating the converted diameter of a laser weld in the case of three-spot welding. [Figure 19] 10A and 10B are diagrams illustrating the appearance and equivalent diameter of a laser welded portion according to an experimental example, in comparison with the diameter of a winding center hole of an electrode assembly. [Figure 20] 10 is a diagram showing the appearance and equivalent diameter of a laser welded portion according to an experimental example, in comparison with the diameter of a hollow tube inserted into the winding center hole of an electrode assembly. FIG. [Figure 21] 10A to 10C are diagrams showing various embodiments of a first current collecting plate. [Figure 22] 10A to 10C are diagrams showing various embodiments of a first current collecting plate. [Figure 23] 10A to 10C are diagrams showing various embodiments of a first current collecting plate. [Figure 24] 10A to 10C are diagrams showing various embodiments of a first current collecting plate. [Figure 25] 10A to 10C are diagrams showing various embodiments of the second current collecting plate. [Figure 26] 10A to 10C are diagrams showing various embodiments of the second current collecting plate. [Figure 27] 10A to 10C are diagrams showing various embodiments of the second current collecting plate. [Figure 28] 10A to 10C are diagrams showing various embodiments of the second current collecting plate. [Figure 29] 1 is a schematic diagram illustrating a battery pack according to an embodiment of the present invention. [Figure 30] 1 shows a vehicle according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0128] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best explain the invention.

[0129] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of the present invention, and that there may be various equivalents and modifications that can be substituted for them at the time of this application.

[0130] In order to facilitate understanding of the invention, the accompanying drawings may be drawn not to scale but with some components exaggerated. The same reference numerals may be used to refer to the same components in different embodiments.

[0131] FIG. 5 is a cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention taken along the longitudinal direction (Y direction).

[0132] 5, a cylindrical secondary battery 70 according to an embodiment of the present invention includes a jelly-roll-type electrode assembly 71. The electrode assembly 71 has a structure in which first and second electrode sheets and a separator interposed therebetween are wound in one direction. In illustrating the electrode assembly 71 in FIG. 5, only the uncoated portions 72 and 73 that are exposed and extended to the outside of the separator are shown in detail, and the winding structure of the first and second electrode sheets and separator is not shown.

[0133] A winding center hole 80 is formed in the inner core of the electrode assembly 71. The winding center hole 80 is the location where the winding core, which becomes the winding shaft when the electrode plate and separator are wound, is removed. If there is no deformation of the electrode assembly 71 after the winding core is removed, it can be said that the diameter of the winding center hole 80 is the same as the diameter of the winding core.

[0134] The method for winding the electrode assembly 71 is substantially the same as the method for winding an electrode assembly used in manufacturing a conventional table-less cylindrical secondary battery described with reference to FIG.

[0135] The first and second electrode plates each have a structure in which an active material layer is coated on one or both sides of a sheet-shaped current collector having long and short sides. The first and second electrode plates each include an uncoated portion 72, 73 at one long side along the winding direction X. The uncoated portions 72, 73 may be continuously formed along one side of the current collector. The first electrode plate includes an uncoated portion 73 at the long side end that is exposed to the outside of the separator, and the second electrode plate includes an uncoated portion 72 at the long side end that is exposed to the outside of the separator in the opposite direction to the uncoated portion 73 of the first electrode plate. That is, the uncoated portion 72 of the second electrode plate is exposed at the bottom of the electrode assembly 71, and the uncoated portion 73 of the first electrode plate is exposed at the top. In this embodiment, the first electrode plate may be a positive electrode plate and the second electrode plate may be a negative electrode plate. The reverse is also possible.

[0136] In one embodiment of the present invention, the current collector may be appropriately selected depending on the polarity of the electrode plate, and its material may be aluminum, copper, nickel, or stainless steel, but is not limited to these, and may be any metal or metal alloy commonly used as a current collector material. For example, the current collector for the positive electrode plate may be aluminum or an aluminum alloy, and the current collector for the negative electrode plate may be copper or a copper alloy.

[0137] In one embodiment of the present invention, the active material coated on the current collector may be any active material known in the art without limitation.

[0138] In one example, the positive electrode active material has the general chemical formula A[A x M y ]O 2+z(A includes at least one element selected from Li, Na, and K; M includes at least one element selected from Ni, Co, Mn, Ca, Mg, Al, Ti, Si, Fe, Mo, V, Zr, Zn, Cu, Mo, Sc, Zr, Ru, and Cr; x≧0, 1≦x+y≦2, −0.1≦z≦2; and the stoichiometric coefficients x, y, and z are selected to maintain electroneutrality of the compound.)

[0139] Preferably, the positive electrode active material includes a lithium transition metal oxide, such as a nickel-cobalt-manganese-based lithium oxide, or a high-concentration nickel-cobalt-manganese-based lithium oxide having a high content of nickel among the transition metals.

[0140] In another example, the positive electrode active material is an alkali metal compound xLiM disclosed in US Pat. No. 6,677,082, US Pat. No. 6,680,143, etc. 1 O2‐(1‐x)Li2M 2 O3(M 1 contains at least one element having an average oxidation state of 3; M 2 may contain at least one element having an average oxidation state of 4; 0≦x≦1).

[0141] In yet another example, the positive electrode active material has the general chemical formula Li a M 1 x Fe 1‐x M 2 y P 1‐y M 3 z O 4‐z (M 1 contains at least one element selected from Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Mg, and Al; M 2 contains at least one element selected from Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Mg, Al, As, Sb, Si, Ge, V, and S; M 3contains a halogen group element selectively containing F; 0 < a ≤ 2, 0 ≤ x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1; the stoichiometric coefficients a, x, y and z are selected so that the compound maintains electrical neutrality.), or can be a lithium metal phosphate represented by Li3M2(PO4)3 [M contains at least one element selected from Ti, Si, Mn, Fe, Co, V, Cr, Mo, Ni, Mg and Al.].

[0142] Desirably, the positive electrode active material may include primary particles and / or secondary particles aggregated from primary particles.

[0143] In one example, the negative electrode active material can use a carbon material, a lithium metal or a lithium metal compound, silicon or a silicon compound, tin or a tin compound, etc. Metal oxides such as TiO2 and SnO2 with a potential less than 2V can also be used as the negative electrode active material. As the carbon material, both low-crystalline carbon and high-crystalline carbon can be used.

[0144] The separation membrane can be used alone or laminated with a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. In another example, the separation membrane can use a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0145] At least one surface of the separation membrane may include a coating layer of inorganic particles. Also, the separation membrane itself can be composed of a coating layer of inorganic particles. The particles constituting the coating layer can have a structure bonded to a binder so that an interstitial volume exists between adjacent particles.

[0146] The inorganic particles can be made of an inorganic substance with a dielectric constant of 5 or more. As this non-limiting example, the inorganic particles are Pb(Zr,Ti)O3 (PZT), Pb1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT), BaTiO3, HfO2, SrTiO3, TiO2, Al2O3, ZrO2, SnO2, CeO2, MgO, CaO, ZnO, and Y2O3.

[0147] As shown in the figure, the uncoated portions 72 and 73 of the electrode assembly 71 are arranged in opposite directions. The uncoated portions 72 and 73 are exposed to the outside of the separator. In this electrode assembly 71, at least a portion of the uncoated portions 72 and 73 can be used as an electrode tab. For example, the uncoated portion 72 of the second electrode plate can be used as a negative electrode tab, and the uncoated portion 73 of the first electrode plate can be used as a positive electrode tab.

[0148] The cylindrical secondary battery 70 also includes a cylindrical battery can 51 that houses the electrode assembly 71 and is connected to the uncoated portion 72 of the second electrode plate. The battery can 51 is made of a conductive metal material. For example, the battery can 51 may be made of iron, nickel-plated iron, or stainless steel (SUS), but the present invention is not limited thereto.

[0149] Preferably, one side (the bottom in this embodiment) of the battery can 51 is open to form an open portion. The opposite side of the open portion of the battery can 51 is a closed portion. In this embodiment, the closed portion is the bottom 52 of the battery can 51. The bottom 52 of the battery can 51 is circular. The side (outer surface) and the bottom 52 of the battery can 51 may be formed integrally. The bottom 52 of the battery can 51 has a generally flat shape. The battery can 51 houses the electrode assembly 71 through the open portion, and also houses the electrolyte. The side of the battery can 51 extends a certain length from the bottom 52.

[0150] The electrolyte plays a role in enabling the mobility of lithium ions generated by electrochemical reactions on the electrode plates inside the secondary battery during charging and discharging.+ B - The salt may have the structure: + Li + , Na + , K. + or a combination thereof. - is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN- and (CF3CF2SO2)2N - The anion comprises one or more anions selected from the group consisting of:

[0151] Alternatively, the electrolyte may be dissolved in an organic solvent, such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or a mixture thereof.

[0152] The bottom 52 of the battery can 51 has a structure in which the electrode terminal 50 is riveted to the through-hole 53 by a caulking process. The cylindrical secondary battery 70 may also include a rivet gasket 54 interposed between the electrode terminal 50 and the through-hole 53.

[0153] The electrode terminal 50 is made of a conductive metal material. For example, the electrode terminal 50 may be made of a material primarily composed of aluminum, but the present invention is not limited to this. The electrode terminal 50 may be made of a 10-series aluminum alloy that is easy to rive and has low resistance. A portion of the electrode terminal 50 is inserted inside the battery can 51, and another portion is exposed to the outside of the battery can 51.

[0154] The rivet gasket 54 may be made of a polymer resin having insulating and elastic properties. For example, the rivet gasket 54 may be made of polypropylene, polybutylene terephthalate, polyfluoroethylene, or the like, but the present invention is not limited thereto.

[0155] The cylindrical secondary battery 70 includes a first current collector 79 connected to the uncoated portion 73 of the first electrode plate. The uncoated portion 73 of the first electrode plate and the first current collector 79 may be connected by welding. The first current collector 79 is also connected to the electrode terminal 50. The first current collector 79 and the electrode terminal 50 are connected by laser welding. The first current collector 79 may be made of the same metal as the current collector of the first electrode plate and / or the electrode terminal 50, or a material that is easy to weld to them. For example, the first current collector 79 may be made of a material primarily composed of aluminum, such as iron, nickel-plated iron, or stainless steel. The electrode terminal 50 is connected to the uncoated portion 73 of the first electrode plate via the first current collector 79.

[0156] A laser weld (not shown) is formed by laser welding on the contact surface between the first current collector plate 79 and the electrode terminal 50. This laser weld is characterized by being located at the overlapping portion of the first current collector plate 79 and the electrode terminal 50 inside the winding center hole 80. The laser welding between the first current collector plate 79 and the electrode terminal 50, the configuration of the laser weld and a related manufacturing method, and specific embodiments of the first current collector plate 79 will be described in detail with reference to FIGS. 14 to 24 .

[0157] The cylindrical secondary battery 70 may include a sealing body 74 that seals the open portion of the battery can 51 to be insulated from the battery can 51. Preferably, the sealing body 74 may include a non-polar cap plate 74a and a sealing gasket 74b interposed between the periphery of the cap plate 74a and the open portion of the battery can 51.

[0158] The cap plate 74a may be made of a conductive metal material such as aluminum, iron, nickel-plated iron, or stainless steel. The sealing gasket 74b may be made of an insulating and elastic material such as polypropylene, polybutylene terephthalate, or polyfluoroethylene. However, the present invention is not limited by the materials of the cap plate 74a and the sealing gasket 74b. The cap plate 74a may cover the opening of the battery can 51. Even if the cap plate 74a is made of a conductive metal material, it may not have polarity. Having no polarity may mean that the cap plate 74a is not connected to the electrode assembly 71. It may also mean that the cap plate 74a is electrically insulated from the battery can 51 and the electrode terminal 50. Because it has no polarity, the cap plate 74a does not function as an electrode terminal. The cap plate 74a does not need to be connected to the electrode assembly 71 and the battery can 51, and its material does not necessarily need to be a conductive metal.

[0159] The cap plate 74a may include a vent notch 77 that ruptures when the pressure inside the battery can 51 exceeds a critical value. The vent notch 77 may be formed on one or both surfaces of the cap plate 74a. The vent notch 77 may form a continuous or discontinuous circular pattern, a linear pattern, or other pattern on the surface of the cap plate 74a. For example, the vent notch 77 may be formed in a substantially annular shape with a constant width. Such an annular vent notch 77 may have the same center as the center of the cap plate 74a and a radius smaller than the radius of the cap plate 74a.

[0160] The rupture pressure of the battery can 51 can be controlled by controlling the depth and width of the vent notch 77. For example, the vent notch 77 can be formed when the internal pressure of the battery can 51 is 15 to 35 kgf / cm. 2The vent notch 77 may be configured to burst when the pressure inside the battery can 51 reaches a certain level. The vent notch 77 may be formed by notching to partially reduce the thickness of the battery can 51. The vent notch 77 may have a thickness gradient. The thickness gradient means that when the cross section of the vent notch 77 is examined, it is formed at a certain angle with respect to a predetermined horizontal plane. Such a vent notch 77 determines that the pressure inside the battery can 51 is abnormally increasing and releases all of the gas inside to the outside.

[0161] The battery can 51 may include a crimping part 75 that extends and bends inward to secure the sealing body 74 and surrounds and secures the periphery of the cap plate 74a together with the sealing gasket 74b. Preferably, the lower surface of the cap plate 74a may be located higher than the lower end of the crimping part 75. In this case, a vent space is formed below the cap plate 74a, allowing gas to be easily discharged when the vent notch 77 ruptures.

[0162] The battery can 51 may further include a beading part 76 that is press-fitted into the inside of the battery can 51 in a region adjacent to the opening. The beading part 76 is recessed into the inside of the battery can 51. When the sealing body 74 is fixed by the crimping part 75, the beading part 76 supports the periphery of the sealing body 74, in particular the outer peripheral surface of the sealing gasket 74b.

[0163] The cylindrical secondary battery 70 may further include a second current collector 78 connected to the uncoated portion 72 of the second electrode plate. The uncoated portion 72 of the second electrode plate and the second current collector 78 may be connected by welding. The second current collector 78 may be made of the same metal as the current collector of the second electrode plate or a material that is easily welded thereto. For example, the second current collector 78 may be made of copper or a copper alloy, nickel or a nickel alloy, iron, stainless steel, or a composite material thereof. Preferably, at least a portion 78a of the edge of the second current collector 78 that does not contact the uncoated portion 72 of the second electrode plate may be interposed between the beading portion 76 and the sealing gasket 74b and secured by the crimping portion 75. Optionally, at least a portion 78a of the edge of the second current collector 78 may be secured to the inner circumferential surface 76a of the beading portion 76 adjacent to the crimping portion 75 by welding. As a result, the second current collector plate 78 is also connected to the battery can 51, and the battery can 51 is connected to the uncoated portion 72 of the second electrode plate via the second current collector plate 78. The second current collector plate 78 may also have a current collector hole (not shown) in its center. The current collector hole does not block the winding center hole 80. The second current collector plate 78 includes the current collector hole so that a laser beam can pass through and reach the first current collector plate 79 when welding the first current collector plate 79 to the electrode terminal 50.

[0164] Each current collecting plate 78, 79 guides the current generated in each electrode plate of the electrode assembly 71 to the electrode terminal 50 and the battery can 51. Each current collecting plate 78, 79 is a component connected to lead out current from the uncoated portions 72, 73, which are the ends of each electrode plate. Because the current collecting plates 78, 79 are directly connected to the uncoated portions 72, 73 by welding or other methods, a separate current collecting tab is not required. This eliminates the need for a current collecting tab attachment process, improving productivity. Furthermore, the space required to accommodate the current collecting tabs can be reduced, resulting in a more compact battery structure and improved space utilization.

[0165] Furthermore, the cylindrical secondary battery 70 has a structure in which the electrode terminal 50 and the remaining areas on the outer surface of the battery can 51, excluding the area occupied by the electrode terminal 50, can be used as the positive and negative terminals, respectively. That is, the structure allows most of the surface opposite the open part of the battery can 51 to be used as the negative terminal. This has the advantage of ensuring a sufficient area for welding connection components such as bus bars for electrical wiring.

[0166] Fig. 6 is a cross-sectional view showing a riveting structure for an electrode terminal according to an embodiment of the present invention. Fig. 7 is an enlarged cross-sectional view of part B in Fig. 6. Figs. 6 and 7 show a state in which the bottom 52 of the battery can 51 is positioned downward.

[0167] 6 and 7, the electrode terminal 50 may preferably include a main body portion 50a inserted into the through-hole 53, an external flange portion 50b extending from the periphery of one side of the main body portion 50a exposed on the outer surface 52a of the bottom 52 of the battery can 51 along the outer surface 52a, an internal flange portion 50c extending from the periphery of the other side of the main body portion 50a exposed on the inner surface 52b of the bottom 52 of the battery can 51 toward the inner surface 52b, and a flat portion 50d provided on the inside of the internal flange portion 50c.

[0168] Desirably, at least a portion of the first current collector plate 79, for example, the central portion (79a in FIG. 5), can be laser welded to the flat portion 50d of the electrode terminal 50. This allows the electrode terminal 50 and the first current collector plate 79 to be joined at the flat portion 50d by a laser weld.

[0169] Desirably, the flat portion 50d and the inner surface 52b of the bottom portion 52 of the battery can 51 can be parallel to each other. Here, "parallel" means that they are substantially parallel when observed visually.

[0170] The flat portion 50d is the surface facing the first current collector plate 79. In the electrode terminal 50, the surface opposite to this surface, which is exposed to the outside of the battery can 51, may be a flat surface. Furthermore, it may be a smooth surface. "Flat" means flat. "Smooth" means both flat and smooth.

[0171] According to one aspect, the angle θ formed between the inner flange portion 50c and the inner surface 52b of the bottom 52 of the battery can 51 may be between 0° and 60°. The size of the angle is determined by the caulking strength when the electrode terminal 50 is installed in the through-hole 53 of the battery can 51 by a caulking method. For example, as the caulking strength increases, the angle θ may decrease to 0°. If the angle exceeds 60°, the sealing effect of the rivet gasket 54 may be reduced.

[0172] Alternatively, a recess 55 may be provided between the inner flange portion 50c and the flat portion 50d. The recess 55 may have an asymmetrical groove cross-sectional structure. For example, the asymmetrical groove may be substantially V-shaped. The asymmetrical groove may include a sidewall 55a of the flat portion 50d and an inclined surface 55b of the inner flange portion 50c connected to an end of the sidewall 55a. The sidewall 55a may be substantially perpendicular to the inner surface 52b of the bottom 52 of the battery can 51. "Perpendicular" means substantially perpendicular when observed visually. As will be described later, the sidewall 55a may be inclined toward the flat portion 50d. The recess 55 is formed by the shape of a caulking jig when the electrode terminal 50 is installed in the through-hole 53 of the battery can 51 by a caulking method.

[0173] Preferably, the thickness of the inner flange portion 50c may decrease as it becomes farther from the main body portion 50a of the electrode terminal 50.

[0174] In another aspect, the rivet gasket 54 may include an outer gasket 54a interposed between the outer flange portion 50b and the outer surface 52a of the bottom 52 of the battery can 51, and an inner gasket 54b interposed between the inner flange portion 50c and the inner surface 52b of the bottom 52 of the battery can 51. Preferably, the outer gasket 54a and the inner gasket 54b are separated based on the outer surface 52a of the bottom of the battery can 51.

[0175] The thickness of the outer gasket 54a and the inner gasket 54b may vary depending on the position. Preferably, the thickness of the inner gasket 54b may be relatively small in a region between the inner edge 56 of the through hole 53 connected to the inner surface 52b of the bottom 52 of the battery can 51 and the inner flange portion 50c. Preferably, a minimum thickness point may be present in the gasket region between the inner edge 56 of the through hole 53 and the inner flange portion 50c. In addition, the inner edge 56 of the through hole 53 may include an opposing surface 57 facing the inner flange portion 50c.

[0176] Meanwhile, the upper and lower ends of the inner wall of the through hole 53 perpendicular to the bottom 52 of the battery can 51 are chamfered (corner cut) to form a surface tapered toward the electrode terminal 50. However, the upper and / or lower ends of the inner wall of the through hole 53 may be deformed into a soft curved surface having a curvature. In this case, the stress applied to the rivet gasket 54 near the upper and / or lower ends of the inner wall of the through hole 53 can be further alleviated.

[0177] Preferably, the inner gasket 54b forms an angle of 0° to 60° with the inner surface 52b of the bottom 52 of the battery can 51 and can extend longer than the inner flange portion 50c.

[0178] Furthermore, the height H1 of the flat portion 50d, measured from the inner surface 52b of the bottom 52 of the battery can 51, may be equal to or greater than the height H2 of the end of the internal gasket 54b. Furthermore, the height H1 of the flat portion 50d, measured from the inner surface 52b of the bottom 52 of the battery can 51, may be equal to or greater than the height H3 of the end of the internal flange portion 50c. Here, the height H2 is the maximum height of the end of the internal gasket 54b measured from the inner surface 52b. Furthermore, the height H3 is the maximum height of the end of the internal flange portion 50c measured from the inner surface 52b.

[0179] When the height parameters H1, H2, and H3 satisfy the above conditions, the inner flange portion 50c and the inner gasket 54b can be prevented from interfering with other components.

[0180] Preferably, the height H3 of the inner flange portion 50c is 0.5 mm to 3.0 mm. If the height H3 of the inner flange portion 50c is less than 0.5 mm, it is difficult to ensure sufficient sealing. Also, if the height H3 of the inner flange portion 50c exceeds 3 mm, the internal space of the battery can 51 occupied by the electrode assembly 71 will be reduced.

[0181] Preferably, the height H4 of the electrode terminal 50 is 1.5 mm to 7 mm. The height H4 of the electrode terminal 50 is the distance from the lower surface of the outer flange portion 50b to the flat portion 50d. If the height H4 of the electrode terminal 50 is less than 1.5 mm, it is difficult to increase the height of the inner flange portion 50c to a level that ensures sealing due to the thickness of the bottom portion 52 of the battery can 51. For reference, the thickness of the bottom portion 52 of the battery can 51 is approximately 0.5 mm to 1 mm. Also, if the height H4 of the electrode terminal 50 exceeds 7 mm, the internal space of the battery can 51 occupied by the electrode assembly 71 is reduced, and the cell height increases, resulting in a corresponding decrease in energy density per unit volume. When H3 and H4 are within the above numerical ranges, the sealing of the electrode terminal 50 can be sufficiently ensured without reducing the internal space of the battery can 51. Most preferably, the height H4 of the electrode terminal 50 is 4 mm to 7 mm.

[0182] On the other hand, the height H5 of the external flange portion 50b, measured from the outer surface 52a of the bottom 52 of the battery can 51, may be 0.8 mm or more. If the height H5 of the external flange portion 50b is less than 0.8 mm, the external flange portion 50b may be deformed when the electrode terminal 50 is riveted. The thickness of the external gasket 54a is 0.3 mm or more, taking into consideration insulation and sealing properties. Considering the thickness of the external gasket 54a, if the height of the external flange portion 50b is less than 0.8 mm, the thickness of the external flange portion 50b becomes too thin to ensure sufficient mechanical rigidity. This is especially true when the electrode terminal 50 is made of aluminum. The height of the external flange portion 50b may be appropriately set taking into consideration the space margin at the top of the cell. For example, the height of the external flange portion 50b may be set to 2 mm or less, 3 mm or less, or 4 mm or less, but the present invention is not limited thereto.

[0183] Furthermore, at least a portion of the external gasket 54a may be exposed outside the external flange portion 50b of the electrode terminal 50. The purpose of exposing the external gasket 54a is to insulate the electrode terminal 50 from the outer surface 52a, which has the opposite polarity to the electrode terminal 50. To electrically insulate the electrode terminal 50 from the outer surface 52a, the exposed width G of the external gasket 54a may be 0.1 mm to 1 mm. If the exposed width G is less than 0.1 mm, electrical insulation between the electrode terminal 50 and the outer surface 52a may be broken down on a flat surface during high-rate charging and discharging of 300 A or more. Furthermore, if the exposed width G is greater than 1 mm, the electrical insulation effect is not improved, and instead the area of the outer surface 52a used as the negative electrode region is reduced, thereby reducing the contact area of components (e.g., bus bars) used for connection.

[0184] On the other hand, the radius R1 from the center of the main body 50a to the periphery of the outer flange 50b may be 10% to 70% of the radius R2 of the bottom 52 of the battery can 51.

[0185] If R1 is small, there is insufficient welding space when welding a component (bus bar) used to connect the electrode terminal 50. On the other hand, if R1 is large, there is less welding space when welding a connection component (bus bar) to the outer surface 52a of the bottom 52 of the battery can 51 excluding the electrode terminal 50.

[0186] When the ratio R1 / R2 is adjusted to be between 10% and 70%, an appropriate welding space between the electrode terminal 50 and the outer surface 52a of the bottom 52 of the battery can 51 can be ensured.

[0187] Furthermore, a radius R3 from the center of the main body 50a of the electrode terminal 50 to the periphery of the flat portion 50d can be 4% to 30% of the radius R2 of the bottom 52 of the battery can 51 as the reference.

[0188] If R3 is small, there may be insufficient welding space when laser welding the first current collecting plate 79 to the flat portion 50d of the electrode terminal 50, reducing the welding area of the electrode terminal 50 and increasing contact resistance. In addition, R3 must be smaller than R1, and if R3 is large, the thickness of the inner flange portion 50c may become thin, weakening the force with which the inner flange portion 50c crimps the rivet gasket 54, which may reduce the sealing force of the rivet gasket 54.

[0189] When R3 / R2 is adjusted between 4% and 30%, the welding area between the flat portion 50d of the electrode terminal 50 and the first current collecting plate 79 is sufficiently secured, which not only facilitates the welding process but also reduces the contact resistance in the welding area and prevents a decrease in the sealing force of the rivet gasket 54.

[0190] According to an embodiment of the present invention, the riveting structure of the electrode terminal 50 can be formed using a caulking jig that moves up and down. First, a preform (not shown) of the electrode terminal 50 is inserted into a through-hole 53 formed in the bottom 52 of a battery can 51 with a rivet gasket 54 interposed therebetween. The preform refers to the electrode terminal before being riveted.

[0191] Next, a caulking jig is inserted into the inner space of the battery can 51. The caulking jig has grooves and protrusions corresponding to the final shape of the electrode terminal 50 on the surface facing the preform in order to rivet the preform to form the electrode terminal 50.

[0192] The caulking jig is then moved downward to press the top of the preform to transform it into a riveted electrode terminal 50 .

[0193] While the preform is pressurized by the caulking jig, the outer gasket 54a interposed between the outer flange portion 50b and the outer surface 52a of the bottom 52 of the battery can 51 is elastically compressed, thereby reducing its thickness. Furthermore, the portion of the inner gasket 54b interposed between the inner edge 56 of the through-hole 53 and the preform is elastically compressed by the inner flange portion 50c, thereby reducing its thickness more than other regions. In particular, the region where the thickness of the inner gasket 54b is reduced intensively is the portion indicated by the dotted circle in FIG. 7. This significantly improves the sealing and airtightness between the riveted electrode terminal 50 and the battery can 51.

[0194] Desirably, the rivet gasket 54 is compressed sufficiently to ensure the desired sealing strength without being physically damaged during the preform riveting process.

[0195] Preferably, the compression ratio of the rivet gasket 54 may be 30% to 90%. The minimum compression ratio is the minimum level of compression ratio required to ensure the sealing (hermeticity) of the electrode terminal 50. The maximum compression ratio is the maximum level of compression ratio that can be achieved without physically damaging the rivet gasket 54.

[0196] In one example, when the rivet gasket 54 is made of polybutylene terephthalate, it is desirable that the rivet gasket 54 have a compressibility of 50% or more at the point where it is compressed to its minimum thickness. The compressibility is the ratio of the change in thickness before and after compression to the thickness before compression.

[0197] Preferably, the compression ratio is determined for the inner gasket 54b. That is, the compression ratio can be defined as the ratio of the thickness change at the maximum compression point to the thickness of the inner gasket 54b before compression. The same applies below. The thickness of the inner gasket 54b before compression is uniform, and the maximum compression point may be located near the inner edge 56.

[0198] In another example, if the rivet gasket 54 is made of polyfluoroethylene, the rivet gasket 54 preferably has a compressibility of 60% or more at the point where it is compressed to its minimum thickness. Preferably, the compressibility is determined for the inner gasket 54b.

[0199] In yet another example, if the rivet gasket 54 is made of polypropylene, the rivet gasket 54 preferably has a compressibility of 60% or more at the point where it is compressed to its minimum thickness. Preferably, the compressibility is determined for the inner gasket 54b.

[0200] Preferably, the caulking jig can be moved up and down at least two times to compress the upper part of the preform in stages. That is, the preform can be compressed in stages and deformed several times. At this time, the pressure applied to the caulking jig can be increased in stages. This distributes the stress applied to the preform over several steps, thereby preventing damage to the rivet gasket 54 during the caulking process. In particular, damage to the rivet gasket 54 is minimized when the portion of the inner gasket 54b interposed between the inner edge 56 of the through hole 53 and the preform is compressed intensively by the inner flange portion 50c.

[0201] After the pressure molding of the preform using the caulking jig is completed, the caulking jig is separated from the battery can 51 to obtain the riveting structure of the electrode terminal 50 according to the embodiment of the present invention as shown in Figures 6 and 7.

[0202] According to the above-described embodiment, the caulking jig presses the top of the preform by moving up and down inside the battery can 51. In some cases, a rotary jig used in the prior art can be used to press the preform.

[0203] However, the rotary rotation jig rotates at a predetermined angle relative to the central axis of the battery can 51. Therefore, a rotary rotation jig with a large rotation radius may interfere with the inner wall of the battery can 51. Furthermore, if the battery can 51 is deep, the length of the rotary rotation jig must also be long. In this case, the rotation radius of the end of the rotary rotation jig becomes large, which may prevent proper pressure molding of the preform. Therefore, pressure molding using a caulking jig is more effective than a method using a rotary rotation jig.

[0204] Meanwhile, the electrode terminal 50 may have various structures depending on the design of the preform and / or the caulking jig and / or the rivet gasket 54 and the amount of pressure applied to the preform during the caulking process.

[0205] FIG. 8 is a partially enlarged cross-sectional view showing the structure of an electrode terminal 50' according to another embodiment of the present invention.

[0206] 8, an electrode terminal 50' according to another embodiment has a structure in which an internal flange portion 50c is riveted substantially parallel to an inner surface 52b of a bottom 52 of a battery can 51. Therefore, the angle formed by the surface of the internal flange portion 50c facing the inner surface 52b of the bottom 52 of the battery can 51 and the inner surface 52b is substantially close to 0, and a height H3 of the internal flange portion 53c is greater than a height H2 of an internal gasket 54b. Furthermore, an inner edge 56 of the through-hole 53 is arc-shaped with a predetermined curvature (arc: a portion defined by two points on a circumference or other curve). Furthermore, a sidewall 55a of the flat portion 50d is inclined toward the flat portion 50d.

[0207] Preferably, the thickness of the inner gasket 54b gradually decreases upward, then decreases to a minimum thickness near the end of the inner flange portion 53c, and then increases slightly toward the top end. This compressible structure of the inner gasket 54b further improves the sealing of the electrode terminal 50'. The compressibility of the inner gasket 54b can be calculated at the point of minimum thickness near the end of the inner flange portion 53c.

[0208] In the cylindrical secondary battery 70 shown in FIG. 5, the electrode terminal 50 may be replaced with the electrode terminal 50' structure shown in FIG. 8. The electrode terminals 50, 50' described above can increase the space efficiency within the battery can 51. This can reduce the internal resistance of the cylindrical secondary battery 70 including them and increase the energy density. The electrode terminals 50, 50' are improved to increase the cross-sectional area of the current path. This can alleviate the problem of internal heat generation that occurs during fast charging in the cylindrical secondary battery 70 including them.

[0209] Furthermore, a cylindrical secondary battery 70 employing a riveting structure for the electrode terminals 50, 50′ can perform electrical wiring in one direction. As described with reference to FIG. 5 , in a cylindrical secondary battery 70 according to an embodiment of the present invention, the cap plate 74a of the encapsulant 74 does not have a polarity. Instead, because the second current collector plate 78 is connected to the battery can 51, the outer surface 52a of the bottom 52 of the battery can 51 has the opposite polarity to the electrode terminal 50. This allows for unidirectional connection of the positive and negative electrodes when connecting multiple cylindrical secondary batteries 70, simplifying the connection structure. Therefore, when connecting multiple cylindrical secondary batteries 70 in series and / or parallel to manufacture a battery pack, wiring such as bus bar connections can be performed at the top of the cylindrical secondary batteries 70 using the outer surface 52a of the bottom 52 of the battery can 51 and the electrode terminal 50. This increases the number of secondary batteries that can be installed in the same space, improving energy density, and facilitating electrical wiring work. Therefore, the space efficiency is good and the efficiency of electrical wiring is high, which brings about a significant improvement in the work process during the assembly of electric vehicles and the assembly and maintenance of battery packs.

[0210] Furthermore, electrical wiring is performed on the outer surface 52a of the bottom 52 of the battery can 51 and the side where the electrode terminal 50 is located, and electrical wiring is not required on the opposite cap plate 74a, thereby maximizing the effect of the vent notch 77 formed in the cap plate 74a. Furthermore, by providing a heat sink, cooling plate, tray, etc. on the cap plate 74a side, assembly and cooling purposes can be effectively achieved regardless of the electrical wiring connection location. Furthermore, assembling the secondary battery so that the vent notch 77 is located downward allows gas emitted from inside the secondary battery to be discharged downward. Since secondary batteries are typically mounted lower than the passengers in vehicles such as EVs, gas discharged upward from the secondary battery could pose a risk of injury to the passengers. However, the cylindrical secondary battery 70 according to one embodiment of the present invention is not only capable of effectively venting high-pressure gas inside the secondary battery, but is also safe regardless of the electrical wiring connection portion at the top. Furthermore, when gas is released due to the rupture of the vent notch 77, the gas is released downward, so that no harm is done to passengers, and safety is greatly improved.

[0211] Preferably, the riveting structure of the electrode terminals 50, 50′ according to the above-described embodiment of the present invention can be applied to cylindrical secondary batteries having a form factor larger than 21700. Recently, as cylindrical secondary batteries are being applied to electric vehicles, the form factor of cylindrical secondary batteries is increasing beyond the conventional 18650, 21700, etc. The increase in form factor brings about an increase in energy density, an increase in safety against thermal runaway, and an improvement in cooling efficiency.

[0212] Preferably, the cylindrical secondary battery 70 may be a cylindrical secondary battery having a form factor ratio (defined as the value obtained by dividing the diameter of a cylindrical secondary battery by its height, i.e., the ratio of the diameter Φ to the height H) of greater than about 0.4. Such a secondary battery is suitable, for example, as a high-output, large-capacity secondary battery for HEVs.

[0213] The cylindrical secondary battery according to an embodiment of the present invention may be, for example, a 46110 cell, a 48750 cell, a 48110 cell, a 48800 cell, or a 46800 cell.

[0214] A secondary battery according to one embodiment of the present invention may be a cylindrical secondary battery that is an approximately cylindrical cell, with a diameter of about 46 mm, a height of about 110 mm, and a form factor ratio of 0.418.

[0215] A secondary battery according to another embodiment may be a cylindrical secondary battery, which is a substantially cylindrical cell having a diameter of about 48 mm, a height of about 75 mm, and a form factor ratio of 0.640.

[0216] A secondary battery according to yet another embodiment may be a cylindrical secondary battery, which is a substantially cylindrical cell having a diameter of about 48 mm, a height of about 110 mm, and a form factor ratio of 0.436.

[0217] A secondary battery according to yet another embodiment may be a cylindrical secondary battery that is an approximately cylindrical cell with a diameter of about 48 mm, a height of about 80 mm, and a form factor ratio of 0.600.

[0218] A secondary battery according to yet another embodiment may be a cylindrical secondary battery, which is a substantially cylindrical cell having a diameter of about 46 mm, a height of about 80 mm, and a form factor ratio of 0.575.

[0219] Conventionally, secondary batteries with a form factor ratio of approximately 0.4 or less have been used. For example, 18650 cells and 21700 cells have been used. 18650 cells have a diameter of approximately 18 mm, a height of approximately 65 mm, and a form factor ratio of 0.277. 21700 cells have a diameter of approximately 21 mm, a height of approximately 70 mm, and a form factor ratio of 0.300.

[0220] The cylindrical secondary battery 70 according to one embodiment of the present invention includes the improved electrode terminal structure (riveting) and current collection structure (connection between the uncoated portion and the current collector plate) as described above, and as described below, specific means that not only embody these structures but also provide improved functionality (such as a current collector segment structure for bending the uncoated portion, an insulator designed to enable laser welding of the first current collector plate and electrode terminal when combined with the electrode assembly, and components such as a second current collector plate), making it possible to manufacture cylindrical secondary batteries with form factors larger than 21700.

[0221] 5 , the cylindrical secondary battery 70 may further include an insulator 85 interposed between the closure of the battery can 51 and the first current collector 79. The insulator 85 may be interposed between the first current collector 79 and the inner surface 52b of the bottom 52 of the battery can 51, and between the inner circumferential surface 51a of the side wall of the battery can 51 and the electrode assembly 71.

[0222] Preferably, the insulator 85 may include a welding hole 85a that exposes the flat portion 50d of the electrode terminal 50 toward the first current collecting plate 79. The welding hole 85a may also expose the inner flange portion 50c and the inner gasket 54b, along with the flat portion 50d of the electrode terminal. Preferably, the welding hole 85a does not block the winding center hole 80. This prevents gas from moving toward the cap plate 74a through the winding center hole 80 when a large amount of gas is generated due to an abnormality in the secondary battery. This facilitates the vent notch 77's ability to control the internal pressure of the battery when a large amount of gas is generated. Furthermore, the cap plate 74a includes the welding hole 85a, allowing a laser beam to pass through and reach the first current collecting plate 79 during the welding process of the first current collecting plate 79 to the electrode terminal 50.

[0223] Preferably, the insulator 85 covers at least the surface of the first current collector 79 and the periphery of one side (top) of the electrode assembly 71. This prevents the first current collector 79, which has a polarity different from that of the battery can 51, and the uncoated portion 73 of the first electrode plate from coming into contact with each other.

[0224] Preferably, the insulator 85 is made of insulating resin and may include an upper plate 85b and a side sleeve 85c. In one example, the upper plate 85b and the side sleeve 85c may be an integral injection-molded product. Alternatively, the side sleeve 85c may be replaced with insulating tape. The insulating tape may cover the outer periphery of the first current collector plate 79 as well as the uncoated portion 73 of the first electrode plate exposed on the outer periphery of the electrode assembly 71.

[0225] Preferably, the insulator 85 and the inner surface 52b of the bottom 52 of the battery can 51 may be in close contact with each other as shown in Fig. 9. Fig. 9 is a cross-sectional view of a cylindrical secondary battery according to another embodiment of the present invention taken along the longitudinal direction (Y direction).

[0226] Here, "close contact" means that there is no space (gap) that can be visually confirmed. To eliminate the space (gap), the distance from the inner surface 52b of the bottom 52 of the battery can 51 to the flat portion 50d of the electrode terminal 50 may be the same as or slightly smaller than the thickness of the insulator 85.

[0227] Referring further to FIG. 5 , preferably, the uncoated portions 72, 73 of the first and / or second electrode plates may be bent in the radial direction of the electrode assembly 71, for example, from the outer periphery toward the core, to form bent surfaces at the top and bottom of the electrode assembly 71. The second current collector 78 may be welded to the bent surface formed by bending the uncoated portion 72 of the second electrode plate, and the first current collector 79 may be welded to the bent surface formed by bending the uncoated portion 73 of the first electrode plate. By bending the uncoated portions 72, 73, their space is reduced, thereby improving energy density. Furthermore, the increased bonding area between the uncoated portions 72, 73 and the current collectors 78, 79 may improve bonding strength and reduce resistance. This structure is particularly suitable for high-power secondary batteries.

[0228] In addition, in order to reduce stress generated when the non-coated portions 72 and 73 are bent, the first electrode plate and / or the second electrode plate may have an improved structure different from that of a conventional electrode plate (see FIG. 1).

[0229] FIG. 10 is a plan view showing the structure of an electrode plate 90 according to a preferred embodiment of the present invention.

[0230] Referring to FIG. 10, the electrode plate 90 includes a sheet-like current collector 91 made of a foil of a conductive material, an active material layer 92 formed on at least one surface of the current collector 91, and an uncoated portion 93 on the long side end of the current collector 91 where the active material is not coated.

[0231] Preferably, the non-coated portion 93 may include a plurality of segment pieces 93a formed by notching. At least a portion of the non-coated portion 93 is divided into a plurality of segment pieces 93a. The segment pieces 93a form a plurality of groups, and the segment pieces 93a belonging to each group may have the same height (length in the Y direction) and / or width (length in the X direction) and / or spacing pitch. The number of segment pieces 93a belonging to each group may be greater or less than that shown. The segment pieces 93a have a geometric shape formed by combining at least one straight line and / or at least one curved line. Preferably, the segment pieces 93a may be trapezoidal, but may be any shape, such as a rectangle, parallelogram, semicircle, or inverse ellipse.

[0232] Desirably, the height of the segment pieces 93a may increase stepwise along a direction parallel to the winding direction of the electrode assembly, for example, from the core side to the outer periphery side. Also, the core-side uncoated portion 93' adjacent to the core side may not include segment pieces 93a, and the height of the core-side uncoated portion 93' may be smaller than the other uncoated portion regions. Also, the outer-periphery-side uncoated portion 93" adjacent to the outer periphery side may not include segment pieces 93a, and the height of the outer-periphery-side uncoated portion 93" may be smaller than the other uncoated portion regions.

[0233] Optionally, the electrode plate 90 may include an insulating coating layer 94 covering the boundary between the active material layer 92 and the uncoated portion 93. The insulating coating layer 94 includes an insulating polymer resin and may optionally further include an inorganic filler. The insulating coating layer 94 prevents the end of the active material layer 92 from contacting the active material layer of the opposite polarity that faces the separator, and serves to structurally support the folding of the segment piece 93a. For this reason, it is preferable that at least a portion of the insulating coating layer 94 be exposed to the outside through the separator when the electrode plate 90 is wound into an electrode assembly.

[0234] FIG. 11 is a cross-sectional view taken along the longitudinal direction (Y direction) of an electrode assembly 100 in which the segmented structure of the non-coated portion of the electrode plate 90 according to an embodiment of the present invention is applied to the first and second electrode plates.

[0235] 11, the electrode assembly 100 may be manufactured using the winding method described in FIG. 2. For ease of explanation, the protruding structure of the uncoated portions 72 and 73 extending outward from the separator is shown in detail, and the winding structure of the first electrode plate, the second electrode plate, and the separator is not shown. The uncoated portion 72 protruding downward extends from the second electrode plate, and the uncoated portion 73 protruding upward extends from the first electrode plate.

[0236] The varying heights of the uncoated portions 72, 73 are shown only schematically. That is, the heights of the uncoated portions 72, 73 may vary irregularly depending on where the cross section is cut. For example, if the side portions of a trapezoidal segment (93a in FIG. 10) are cut, the height of the uncoated portions in the cross section will be lower than the height of segment 93a. Therefore, it should be understood that the heights of the uncoated portions 72, 73 shown in the cross-sectional views of the electrode assembly 100 correspond to the average height of the uncoated portions included in each winding turn.

[0237] The uncoated portions 72, 73 can be folded. In Fig. 11, the folded portion 101 is indicated by a dotted box. For example, the uncoated portions 72, 73 can be folded from the outer periphery toward the core along the direction of the arrow in Fig. 11. Figs. 12 and 13 show the electrode assembly 100 in which the uncoated portions 72, 73 are folded in this manner from the outer periphery toward the core along the radial direction of the electrode assembly 100.

[0238] 11 and 12, when the uncoated portions 72 and 73 are bent, adjacent segments (93a in FIG. 10) overlap each other in multiple radial directions, forming bent surfaces 101a at the top and bottom of the electrode assembly 100. The core-side uncoated portion (93' in FIG. 10) is not bent due to its low height, and the height h of the innermost bent segment is equal to or smaller than the radial length r of the winding region formed by the core-side uncoated portion 93' without a segment structure. This prevents the bent segments from blocking the winding center hole 80 of the electrode assembly 100. If the winding center hole 80 is not blocked, the electrolyte injection process becomes easier and the electrolyte injection efficiency improves. Furthermore, when laser welding is performed using the winding center hole 80, the path of the laser beam is not blocked, facilitating welding of the electrode terminal 50 and the first current collecting plate 79.

[0239] Next, a method for manufacturing a cylindrical secondary battery 70 will be described in detail with reference to both Fig. 5 and Fig. 14. Fig. 14 illustrates a process for joining an electrode terminal and a first current collector plate of a cylindrical secondary battery by laser welding according to one embodiment of the present invention. Fig. 15 is an enlarged view of the dotted box area in Fig. 14, and is also a cross-sectional view of the laser-welded electrode terminal and first current collector plate.

[0240] First, an electrode assembly 71 is provided according to the method and structure described above with reference to Fig. 5, etc. The electrode assembly 71 may be the electrode assembly 100 described with reference to Fig. 13, etc.

[0241] Next, the first current collecting plate 79 is connected to the uncoated portion 73 of the first electrode plate of the electrode assembly 71. For example, this can be done by welding. Methods for welding the first current collecting plate 79 to the uncoated portion 73 of the first electrode plate include laser welding, resistance welding, and ultrasonic welding. When the first current collecting plate 79 is made of aluminum, laser welding or ultrasonic welding is preferred. An insulator 85 can be attached to the top of the first current collecting plate 79 connected to the uncoated portion 73 of the first electrode plate.

[0242] The second current collecting plate 78 is connected to the uncoated portion 72 of the second electrode plate of the electrode assembly 71. For example, this connection can be made by welding. Methods for welding the second current collecting plate 78 to the uncoated portion 72 of the second electrode plate include laser welding, resistance welding, ultrasonic welding, etc.

[0243] Next, the electrode terminal 50 is formed and prepared in the battery can 51 using the method and structure described above. The electrode assembly 71 is inserted into the battery can 51 from the open portion of the battery can 51 so that the first current collector plate 79 connected to the uncoated portion 73 of the first electrode plate of the electrode assembly 71 faces the bottom 52 of the battery can 51.

[0244] Next, as shown in Fig. 14, the first current collecting plate 79 is laser-welded to the electrode terminal 50 using a laser welding device 102. In Fig. 14, for convenience of illustration, the shape of the electrode terminal 50 is shown schematically, and other parts surrounding the electrode terminal 50, such as the rivet gasket 54 and the insulator 85, are not shown. The laser welding device 102 is also shown schematically.

[0245] Preferably, the first current collecting plate 79 is connected to the uncoated portion 73 of the first electrode plate, and then inserted downward into a battery can 51 with its bottom 52 placed downward and having an open top, and connected to the inner surface of the electrode terminal 50 formed on the bottom 52 of the battery can 51 by laser welding, in which a laser beam 103 is irradiated from above. The laser beam 103 is irradiated into the winding center hole 80 along the longitudinal direction of the winding center hole 80.

[0246] As described above, one embodiment of the present invention is characterized in that laser welding is performed while the opening of the battery can 51 is open and the electrode assembly 71 is inserted through the opening. Laser welding is used to connect the first current collector 79 and the electrode terminal 50. During laser welding, the laser beam 103 can reach the welding area of the first current collector 79 through the winding center hole 80 of the electrode assembly 71. When the first current collector 79 is welded to the flat portion 50d of the electrode terminal 50, the electrode terminal 50 can support the welding area of the first current collector 79. Furthermore, since the flat portion 50d of the electrode terminal 50 has a large area, a large welding area can be secured. This reduces the contact resistance of the welding area, thereby reducing the internal resistance of the cylindrical secondary battery 70. The face-to-face welding structure of the riveted electrode terminal 50 and the first current collector 79 is very useful for rapid charging. This is because the current density per unit area can be reduced in the cross section in the direction of current flow, and the amount of heat generated in the current path can be reduced compared to conventional methods.

[0247] The laser beam 103 passes through the central winding hole 80 of the electrode assembly 71 above the electrode assembly 71 and the battery can 51 and then passes downward to directly reach the surface of the first current collector plate 79, which is the workpiece. The laser welding device 102 may include a laser light source (laser beam source), an optical system that may include optical components such as a collimator, lens, and mirror for converging the laser from the laser source to form a laser beam 103 with a predetermined spot diameter and irradiating it onto the workpiece, and a system for supplying welding atmosphere gas and discharging by-products. The spot diameter refers to the diameter at the focal point. Although welding can be performed in air, it is preferable to partially supply an inert gas such as nitrogen gas (N) or argon gas (Ar). Therefore, a welding atmosphere gas supply system including an inert gas supply unit is preferably included. Furthermore, a by-product discharge system including a dust collector for removing welding fumes is preferably included.

[0248] 15 , a laser beam 103 is used to form a laser weld 104 in a welding area including the contact surface between the first current collecting plate 79 and the electrode terminal 50, thereby welding the first current collecting plate 79 to the electrode terminal 50. Of course, the battery can 51 may be turned over so that the bottom 52 faces upward, and the laser beam 103 may be irradiated upward from the open portion of the battery can 51. In this case, the key is to irradiate the laser beam 103 so that it passes through the winding center hole 80. Because the laser beam 103 does not pass through the outer surfaces of the battery can 51 or the electrode terminal 50 formed on the battery can 51, no weld beads or weld spots are formed on the outer surface of the cylindrical secondary battery 70, and the outer surface is smooth. This is advantageous in ensuring a good connection between the cylindrical secondary battery 70 and the busbar component during electrical wiring work for connecting the cylindrical secondary batteries 70 in series and / or parallel.

[0249] Since the laser beam 103 is incident on the surface of the first current collecting plate 79 exposed inside the winding center hole 80 toward the electrode terminal 50 below it, the laser weld 104 is formed from one surface of the first current collecting plate 79 facing the inside of the winding center hole 80 toward the electrode terminal 50 at the joint between the first current collecting plate 79 and the electrode terminal 50, as shown in Figure 15. The width WS of the part of the laser weld 104 that is exposed on the surface of the first current collecting plate 79, the depth WD of the laser weld 104, and the aspect ratio, which is the ratio between these, can be managed as design factors.

[0250] In a manufacturing method according to an embodiment of the present invention, it is preferable that the laser beam 103 does not deviate from the winding center hole 80. As a result, the laser weld 104 can be located at the overlapping portion of the first current collecting plate 79 and the electrode terminal 50 within the winding center hole 80. If the laser beam 103 does not deviate from the winding center hole 80, damage to peripheral components of the workpiece, such as the separator located near the winding center hole 80 of the electrode assembly 71, can be prevented. However, even if the laser beam 103 does not deviate from the winding center hole 80, damage to the separator can occur if heat transferred to the workpiece spreads to the periphery and is transferred to the separator. Furthermore, damage to the separator can occur if by-products or metal fragments generated by laser welding are scattered onto the separator. Therefore, the welding process is controlled to prevent such damage to the separator.

[0251] A laser weld 104 is formed in the welding region of the first current collecting plate 79, and by adjusting the depth WD of the laser weld 104, the laser weld 104 can be prevented from penetrating the electrode terminal 50 and being exposed to the outside. As a result, the outer surface of the welding region of the electrode terminal 50, i.e., the surface to which a component such as a bus bar is further connected, such as the top end of the part of the electrode terminal 50 exposed to the outside of the battery can 51, can be made smooth, and good contact with the bus bar can be maintained when connected to the bus bar, thereby ensuring connection effect and energy transmission efficiency.

[0252] In a secondary battery 70 manufactured by a manufacturing method according to an embodiment of the present invention, a first current collecting plate 79 is welded to an electrode terminal 50 by laser welding, and a laser weld 104 is formed on the contact surface between the first current collecting plate 79 and the electrode terminal 50. The laser weld 104 is located within the winding center hole 80 and the overlapping portion where the first current collecting plate 79 and the electrode terminal 50 overlap each other, and the outer surface of the welded area of the electrode terminal 50 may be smooth. The fact that the outer surface of the welded area is smooth indicates that the laser weld 104 is formed only on the inner surface of the bottom 52 of the battery can 51 when the first current collecting plate 79 and the electrode terminal 50 are welded together with a laser beam 103. In other words, the laser weld 104 is only visible inside the battery can 51, i.e., only inside the cylindrical secondary battery 70, and does not penetrate the inner surface of the bottom 52 of the battery can 51 to be exposed to the outer surface of the electrode terminal 50. The outer surface of the electrode terminal 50 can still maintain the same state as before the first current collecting plate 79 is welded, that is, the smooth surface state.

[0253] The diameter D of the winding center hole 80 can be 2 mm or more and 8 mm or less. A smaller diameter D of the winding center hole 80 is more advantageous for utilizing the internal space of the battery can 51; however, because a winding core is used, the diameter D of the winding center hole 80 cannot be zero. Furthermore, since the winding center hole 80 serves as a passageway for the electrolyte during electrolyte injection, it must be at least a certain size to ensure smooth impregnation with the electrolyte. Therefore, it is desirable to set the diameter D of the winding center hole 80 to 2 mm or more as much as possible within the allowable winding process level. If the diameter D of the winding center hole 80 exceeds 8 mm, the internal space of the battery can 51 is utilized inefficiently, which is undesirable from the perspective of energy density.

[0254] The optical system of the laser welding device 102 is configured so that the laser beam 103 does not deviate from the winding center hole 80. The winding center hole is also longer for jelly-roll-type electrode assemblies included in large batteries. For example, if a cylindrical secondary battery 70 is manufactured larger than the 21700 form factor, the height of the cylindrical secondary battery 70 will be 70 mm or more, approximately 75 mm or more. In such a case, the length of the winding center hole 80 will be 60 mm or more, which is longer than that of conventional small cylindrical secondary batteries. To weld the first current collecting plate 79 to the electrode terminal 50 on the bottom 52 side of the battery can 51, easy focusing on the first current collecting plate 79 is required, and damage to the electrode assembly 71 during the welding process must be prevented. The laser beam 103 has advantages such as monochromaticity, linearity, high brightness, focusability, and high energy intensity. However, a process margin is required to align the laser beam 103 with the winding center hole 80. Furthermore, even after alignment, the position of the winding center hole 80 may change due to minute vibrations, etc. Furthermore, the diameter of the laser beam 103 at one end of the winding center hole 80, where the laser beam 103 reaches first, differs from the diameter of the laser beam at the other end of the winding center hole 80, which is near where the laser beam 103 is incident on the first current collecting plate 79. Therefore, it is necessary to irradiate the laser beam 103 with a predetermined interference margin secured between the laser beam 103 and the winding center hole 80 so that the laser beam 103 does not deviate from the winding center hole 80 while passing through the winding center hole 80.

[0255] Furthermore, when the laser beam 103 is emitted and irradiated using a focusing lens that focuses the laser beam 103 onto the first current collector plate 79, the focal depth of the focusing lens must be greater than the length of the winding center hole 80. The laser beam focused by the focusing lens has a minimum diameter at the focal position and the diameter increases with increasing distance from the focal point. The focal depth refers to the length of the area in front of and behind the focal plane (first current collector plate 79) where the diameter of the laser beam does not significantly deviate from the focal diameter. Preferably, the focal depth of the focusing lens should be greater than the height of the electrode assembly 71. More preferably, the focal depth of the focusing lens should be greater than the height of the battery can 51.

[0256] If the focal depth is smaller than the height of the electrode assembly 71, the diameter of the laser beam may expand before reaching the welding position, causing it to irradiate the electrode assembly 71 away from the winding center hole 80, resulting in interference and damage to the electrode assembly 71. Because the height of the cylindrical secondary battery 70 can be approximately 75 mm, 80 mm, 110 mm, or more, the focal depth of the focusing lens is preferably approximately 60 mm or more. The focal depth varies depending on the focal length (the distance from the focusing lens to the welding position), the wavelength of the laser beam, the diameter of the laser beam incident on the focusing lens, the optical quality factor, etc. Since the laser beam 103 must be irradiated as far away from the top of the battery can 51 as possible to ensure sufficient working space, the longer the focal depth of the focusing lens, the better. For example, the focal depth of the focusing lens may be two to three times the height of the electrode assembly 71. Therefore, the laser welding device 102 may include a focusing lens with a long focal depth. Most desirably, the focal depth is set to a value greater than the height of the battery can 51, so that the diameter of the laser beam does not expand before it reaches the first current collector plate 79, thereby preventing irradiation of and interference with components surrounding the winding center hole 80.

[0257] In one embodiment of the present invention, by using a laser welding device 102 with an improved optical system, it is possible to irradiate a laser beam 103 onto a portion of the first current collecting plate 79 placed at the lower end of the winding center hole 80, which is longer than conventional, that is exposed inside the winding center hole 80, while preventing damage to the electrode assembly 71. According to one embodiment of the present invention, it is possible to weld the first current collecting plate 79 to the electrode terminal 50 while eliminating defects that may occur during laser welding, thereby satisfying the demand for high-power, low-resistance batteries in the technical field to which the present invention pertains.

[0258] The laser welding used in one embodiment of the present invention can weld the first current collecting plate 79 to the electrode terminal 50 by simply irradiating the first current collecting plate 79 with a laser beam 103 emitted from the laser welding device 102 without directly contacting the first current collecting plate 79. This prevents deformation of components that may occur due to contact pressure welding, and is advantageous not only for ensuring the quality and performance of the cylindrical secondary battery 70 but also for improving product yield.

[0259] When the first current collecting plate 79 and the electrode terminal 50 are made of aluminum, welding using a welding rod reduces efficiency. Rapid welding wear requires frequent replacement of the welding rod and adjustments to the welding equipment, which not only impacts production efficiency but also increases the cost of the welding rod. The use of a welding rod requires pressure, which can cause deformation of the battery can 51 and the workpiece, affecting quality and performance and product yield. Ultrasonic welding of the first current collecting plate 79 and the electrode terminal 50 is also undesirable. This requires a long horn that can be inserted into the winding center hole 80, which is prone to breaking and resulting in burrs, and makes it difficult to check for unbonded areas. Problems also arise from foreign matter generated during welding.

[0260] In one embodiment of the present invention, laser welding is used to prevent deformation caused by contact pressure welding, such as resistance welding, thereby ensuring quality and performance as well as improving product yield. Since the laser weld 104 is formed inside the secondary battery 70 and not on the exterior, the exterior of the electrode terminal 50, which connects to a bus bar, is smooth, which is advantageous for ensuring connection with other components and energy transmission efficiency. Furthermore, since there is no need to change welding rods or horns, this is advantageous for improving production efficiency, reducing production costs, and shortening manufacturing process time. It also provides higher joint strength than ultrasonic welding and ensures more consistent welding performance and quality than resistance welding.

[0261] The laser weld 104 may include one or more weld beads. A weld bead refers to the deposited metal formed by one weld (one pass of the laser beam 103) and may also be called a weld spot. The size, shape, position, and overlap of the weld beads may vary depending on the welding conditions. The laser weld 104 includes not only weld beads that are formed separately and therefore distinct from each other, but also weld beads that are partially overlapped to form a single mass. Welding methods using the laser beam 103 include wobble welding, spot welding, weaving (hatching) welding, and scan welding, and can be selected and applied as needed by a person skilled in the art to which the present invention pertains.

[0262] 16 and 17 are diagrams illustrating various surface configurations of a laser weld 104 according to an embodiment of the present invention. The shape of the laser weld 104 is not particularly limited as long as it maintains sufficient joint strength. However, because the laser weld 104 must be formed inside the winding center hole 80, which has a diameter D of 2 mm to 8 mm, it is desirable to select a shape that can be formed in a position and size that does not deviate from the winding center hole 80 and that is advantageous for achieving the desired joint strength. The winding center hole 80 and its diameter D are also shown in FIGS. 16 and 17 for reference. D may be the diameter of the winding core.

[0263] First, referring to FIG. 16 , the laser weld 104 may be an overlapping overlay type weld bead formed at the center of the winding center hole 80. For example, the weld bead may be circular, formed by spot welding. The overlapping overlay type is formed by forming multiple such weld beads at the same point and overlapping them. The circular weld beads may have the same or different diameters. That is, they may have the shape of multiple concentric circles with the same or different diameters overlapping each other. The overlapping overlay type can be achieved by irradiating the laser beam 103 at the same position in a low-power pulse mode. Irradiating a high-power laser beam at a single time can result in over-welding. For example, the workpiece may be perforated or a back bead may occur. Here, a back bead refers to a phenomenon in which a color change or a weld bead occurs on the surface opposite to the laser welded surface. The use of a safe, low-power laser beam 103 can prevent such problems. Another advantage is that the bonding strength can be adjusted by adjusting the number of times the laser beam 103 is irradiated. Because the laser beam 103 does not need to be moved, there is little risk that the laser beam 103 will deviate from the narrow winding center hole 80, and the laser weld 104 can be stably formed in the center of the winding center hole 80. This allows the weld to be formed with ideal precision and high reliability, minimizing welding defects.

[0264] A plurality of circular weld beads formed by spot welding may overlap to form a continuous line. For example, when a laser beam 103 emitted from a laser welding device 102 is irradiated onto the first current collecting plate 79 in the winding center hole 80 while moving along a linear path, the laser weld 104 may be configured as a line. The line may be a straight line, a curved line, a bent line, or a spiral (e.g., a spiral, a helical, a vortex, etc.). The movement of the laser beam 103 may be implemented by moving the laser beam 103 while the first current collecting plate 79 is fixed. Alternatively, the laser beam 103 may be fixed and a work table carrying the battery can 51 with the first current collecting plate 79 mounted thereon may be set on, for example, an NC-controlled XY table, and the battery can 51 may be moved to relatively move the laser beam 103.

[0265] The laser weld 104 may be a continuous closed line or curve, with the start and end points of the irradiation of the laser beam 103 coinciding. Alternatively, the start and end points of the irradiation of the laser beam 103 may not necessarily coincide. Alternatively, the laser weld 104 may be an open curve. For example, the laser weld 104 may have a structure in which one quarter face is open, such as a C-shape.

[0266] 17(a), the laser weld 104 may be a ring-shaped circle centered on the center of the winding center hole 80. This is desirable because the circular shape allows for uniform distribution of force even when applied from multiple directions.

[0267] 17(b), the laser weld 104 may be a wobble circle type centered on the center of the winding center hole 80. This type is also desirable because it can distribute force evenly even when force is applied from multiple directions.

[0268] Referring to FIG. 17(c), the laser weld 104 may be an 8-type in which two circles are circumscribed.

[0269] 17(a) and (c) are examples of closed curves, and FIG. 17(b) is an example that includes a closed curve but where the starting point and ending point of the irradiation of the laser beam 103 do not coincide.

[0270] Referring to Fig. 17(d), the laser weld 104 may be a square frame type centered on the center of the winding central hole 80. Fig. 17(d) is an example of a closed line.

[0271] In addition to square frames, polygonal frame types such as triangular and pentagonal frames are also possible. When forming a circular or polygonal laser weld, if the starting point and ending point of the laser beam irradiation coincide, a weld bead that is slightly deeper than the surrounding area may be formed. In this case, the starting point and ending point may not coincide perfectly, resulting in an incomplete circular or polygonal shape.

[0272] The laser welds 104 may be arc-shaped, as shown in FIG. 17(e). The arcs may be formed radially and symmetrically with respect to the center of the winding center hole 80. Symmetrical formation is desirable because it allows for even distribution of force even when applied from multiple directions. The number of arcs is not particularly limited, and may be preferably 2 to 4. For example, three arcs may be arranged at equal intervals, forming arc shapes with lengths corresponding to an angle range of 50° to 80° with respect to the center of the winding center hole 80.

[0273] The laser weld 104 may be an X-type, in which two lines intersect at the center of the winding center hole 80, as shown in Figure 17(f), or an L-type, in which two lines meet at one point, as shown in Figure 17(g).

[0274] Circular spot weld beads may be formed in multiple, separate locations without overlapping other weld beads. In such cases, the laser welds 104 may be multi-spot welds formed at radially symmetrical positions relative to the center of the winding center hole 80, as shown in FIG. 17(h). Symmetrical formation is desirable because it allows for uniform force distribution even when force is applied from multiple directions. The number of circular spot weld beads may be two or more. For example, the number may be two, three, four, five, six, or eight, or any number not less than two depending on actual needs. In the illustrated example, the number is three. They may be arranged at equal intervals. For example, each weld bead may be arranged every 120° relative to the center of the winding center hole 80.

[0275] The laser beam 103 may pass over a point more than once, moving in a weaving manner. In this case, the laser weld 104 may have a center at the center of the winding central hole 80, a polygonal or irregular periphery, and a weld bead filling the periphery, as shown in (i) and (j) of Figure 17.

[0276] As described above, the shape of the laser weld 104 is not particularly limited as long as the joining strength is maintained, and it may include various shapes that can be realized by the laser beam 103 within the winding center hole 80.

[0277] Regarding the joint strength, the tensile force at the joint between the first current collecting plate 79 and the electrode terminal 50 by the laser weld 104 is 2 kgf or more, preferably 3 kgf to 15 kgf, and more preferably 5 kgf to 15 kgf. The tensile force is a force applied perpendicular to the joint surface. It can be converted to tensile strength by multiplying the force by the size of the surface on which the force acts. If the tensile force is 2 kgf or more, preferably 3 kgf or more, the performance of the cylindrical secondary battery 70 is not affected when using the secondary battery, and the first current collecting plate 79 does not become detached from the electrode terminal 50 due to vibration or pressure of the equipment generated during the process. The tensile force at the joint between the first current collecting plate 79 and the electrode terminal 50 may be at least 2 kgf or more, or 3 kgf or more, or 5 kgf or more, or 6 kgf or more, or 7 kgf or more, or 8 kgf or more, or 9 kgf or more, or 10 kgf or more. It is desirable to maximize the tensile force within the allowable range by optimally selecting the welding method.

[0278] The tensile strength of the joint is also related to the area and depth (WD in FIG. 15 ) of the laser weld 104, so the area and depth WD of the laser weld 104 can be adjusted to control the joint strength. As shown in the cross section of FIG. 15 , the weld bead does not exist only on the surface, but is a three-dimensional shape with thickness formed at the contact surface of two components joined by welding. The depth WD of the laser weld 104 includes the thickness of the weld bead. The depth WD of the laser weld 104 can be adjusted by the power and irradiation time of the laser beam 103. The depth WD increases as the power of the laser beam 103 increases, and decreases as the irradiation time increases. The power and irradiation time of the laser beam 103 can be adjusted to ensure that the weld bead does not extend too deep and reach the outer surface of the electrode terminal 50 while maintaining an appropriate joint strength. In an actual process, the thickness range of the first current collecting plate 79 and the electrode terminal 50 is limited, so the depth WD of the laser beam 103 that can be adjusted to a level that prevents over-welding is somewhat limited. The process window can be further widened by adjusting the area of the laser weld 104. The area of the laser weld 104 is related to the width WS of the laser weld 104, but as proposed in the present invention, it can be controlled using a design factor called the equivalent diameter D' of the laser weld 104.

[0279] The converted diameter D' of the laser weld 104 is the diameter of an imaginary circle circumscribing the laser weld 104 at the portion exposed on the surface of the workpiece, i.e., the laser weld 104 exposed on the surface of the first current collector plate 79. Therefore, the converted diameter D' can indicate the distance between a pair of laser weld points located at the farthest distance from each other among the laser weld points forming the weld bead included in the laser weld 104. The converted diameter D' proposed in the present invention is calculated by multiplying the area SA of the weld shown on the surface of the workpiece by the area πr of the circle. 2 When converted to the diameter of the circle (D=2×(SA / π) 0.5) is different from the equivalent diameter D'. The latter relates to the size of the weld or indicates information about the area the weld occupies on a plane, and is a control factor that indicates the percentage of the area the weld occupies compared to the total area of a given region. On the other hand, the equivalent diameter D' relates to the size of the weld but also includes information about the shape of the weld. Therefore, it is a control factor that takes into account the distance between welding points in a weld even for welds of the same area, i.e., it can indicate how far the weld spreads within a given region. In accordance with one embodiment of the present invention, the laser weld 104 is formed within the winding center hole 80, and control must be exercised to prevent the laser weld 104 from departing from the winding center hole 80. Therefore, even if the weld has a small area, it must not spread too far. Therefore, it is preferable to control the equivalent diameter D'.

[0280] FIG. 18 is a diagram for explaining a method for calculating the converted diameter of the laser welded portion in the case of three-spot welding.

[0281] When the laser welding forms a multi-spot type laser weld 104 such as (h) among the various forms shown in FIG. 17, for example, a three-spot type, the converted diameter D' of the laser weld 104 is the diameter of an imaginary circle 104b circumscribing the three welding points 104a.

[0282] To facilitate understanding of the converted diameter D', the converted diameter D' of the laser welded portion 104 is also shown in FIGS. 16 and 17(a), (b), (d), and (g).

[0283] In one embodiment of the present invention, the equivalent diameter D' of the laser weld 104 may be 0.15D to 0.90D. That is, the equivalent diameter of the laser weld 104 may be formed in a range of about 15% to 90% of the diameter D of the winding center hole 80. Using conventional laser welding methods, it is very difficult to achieve an equivalent diameter D' of 0.4D or more. This is because it is very difficult to focus a laser beam on the bottom side of the winding center hole 80, which is longer than conventional methods, without affecting the surrounding area of the winding center hole 80. That is, in the manufacture of large batteries, an improved optical system or other implementation means is required to ensure that the laser beam does not deviate from the winding center hole 80, which has a diameter D of 2 mm to 8 mm, while passing through the winding center hole 80, which is 60 mm or longer. The laser welding apparatus 102 according to one embodiment of the present invention includes an improved optical system that takes into consideration the narrow and long winding center hole 80, thereby enabling the equivalent diameter D' to be 0.4D or more. A larger equivalent diameter D' is advantageous in terms of joint strength, but if the equivalent diameter D' is 0.9D or more, there is a risk of damage to components surrounding the winding center hole 80 due to minute vibrations, movements, or other accidents during the process. Therefore, while a larger equivalent diameter D' is possible, it is preferable that the equivalent diameter D' be 0.9D or less. If the equivalent diameter D' is too small, sufficient joint strength cannot be obtained. Therefore, it is preferable that the equivalent diameter D' be a minimum of 0.15D.

[0284] As described above, the diameter D of the winding center hole 80 may be 2 mm or more and 8 mm or less. The converted diameter D' of the laser weld 104 exposed on the surface of the first current collector plate 79 may be 2 mm or more. The area SA of the laser weld 104 exposed on the surface of the first current collector plate 79 is the area (π(D' / 2)) of a circle having the converted diameter D'. 2 ) is considered.

[0285] The diameter of the flat portion 50d of the electrode terminal 50 can be determined in consideration of the bonding strength between the first current collector plate 79 and the electrode terminal 50. The diameter of the flat portion 50d of the electrode terminal 50 is twice the radius R3 from the center of the main body 50a of the electrode terminal 50 to the periphery of the flat portion 50d, which was described with reference to FIG. 8, and can be 3 mm to 14 mm.

[0286] The flat portion 50d of the electrode terminal 50 is the weldable region. Therefore, the diameter of the weldable region of the electrode terminal 50 can be 3 mm to 14 mm. If the diameter of the weldable region is smaller than 3 mm, it is difficult to secure a laser welded joint with a converted diameter D' of 2 mm or more. If the diameter of the weldable region exceeds 14 mm, the diameter of the outer flange portion 50b of the electrode terminal 50 becomes excessively large, making it difficult to secure a sufficient area for the outer surface 52a of the bottom 52 of the battery can used as the negative terminal.

[0287] Considering the converted diameter D' of the laser welded portion 104 and the diameter of the weldable region of the electrode terminal 50, the ratio of the area of the laser welded portion 104 exposed on the surface of the first current collector plate 79 to the area of the flat portion 50d of the electrode terminal 50 required to ensure a tensile strength of at least 2 kgf, preferably 3 kgf or more, is 2.04% (π1 2 / π7 2 )~44.4%(π1 2 / π1.5 2 ) is desirable.

[0288] 14, the step of forming the laser weld 104 may include inserting a hollow tube 105 into the winding center hole 80 and exposing at least a portion of the first current collector plate 79 in the inner hollow portion of the hollow tube 105.

[0289] At this time, the hollow tube 105 can press the first current collecting plate 79 against the electrode terminal 50. A laser beam 103 emitted from the laser welding device 102 can pass through the inner hollow portion of the hollow tube 105 and weld the first current collecting plate 79 to the electrode terminal 50.

[0290] The laser beam 103 is focused onto the first current collecting plate 79 through an optical system that expands, reflects, and focuses the beam, and the laser beam 103 irradiated onto the first current collecting plate 79 can heat the first current collecting plate 79, which is the workpiece to be welded. Heat from the surface is diffused inward by thermal conduction, and the pulse width, energy, peak power, and repetition frequency (pulse cycle) of the laser beam 103 are precisely controlled as set in advance. The irradiation of the laser beam 103 melts, vaporizes, and evaporates material at the irradiated area, and the molten area solidifies after the laser beam 103 has passed, forming a weld bead. The laser beam 103 can be controlled to move along a predetermined trajectory or position.

[0291] Improved joining quality can be achieved by preventing poor joining, such as cracks and backbeads, and by suppressing thermal deformation and spatter at the joining area. These defects can occur due to excessive heat input. In one embodiment of the present invention, when heating the first current collecting plate 79 with the laser beam 103, the mode of the laser beam 103 or the output of the laser beam 103 can be adjusted over time to vary the heating area and heating temperature. This can prevent spatter by creating a temperature difference between the area where the laser beam 103 is concentrated and its surrounding area, or by allowing full melting to occur after preheating. If a deep weld bead is initially formed in the area where the laser beam 103 is concentrated with high energy, the high welding heat can cause pores to form in the first current collecting plate 79 or spatter-like debris to form. Therefore, the generation of spatter can be prevented by controlling the welding heat, such as by using a preheating process. In addition, even if spatter or other debris occurs on the surface, the temperature difference can be applied to melt it, maintain it in a molten state, and then solidify it to form a part of the weld bead on the first current collector plate 79.

[0292] On the other hand, when the hollow tube 105 is used to press the first current collecting plate 79 against the electrode terminal 50, it prevents welding defects due to insufficient adhesion between the first current collecting plate 79 and the electrode terminal 50, thereby improving the quality and performance of the cylindrical secondary battery 70. On the other hand, it not only prevents the laser beam 103 from damaging the electrode assembly 71 by isolating the laser beam 103 from the electrode assembly 71 and guiding the laser beam 103, but also serves as a mask that prevents the laser beam 103 from being irradiated at positions other than the welding area. In this way, when the hollow tube 105 is used to press the first current collecting plate 79, stronger pressure is applied to the welding area, thereby improving welding quality.

[0293] The hollow tube 105 is an optional element. Optionally, the length of the hollow tube 105 may be greater than the height of the electrode assembly 71, thereby ensuring separation between the electrode assembly 71 and the laser beam 103. For example, the length of the hollow tube 105 is greater than 60 mm. The outer diameter of the hollow tube 105 is smaller than the diameter D of the winding center hole 80. For example, the diameter D of the winding center hole 80 may be 80 mm, and the outer diameter of the hollow tube 105 may be 60 mm. The inner diameter DI of the hollow tube 105 has a value obtained by subtracting twice the wall thickness of the hollow tube 105 from the outer diameter. The wall thickness of the hollow tube 105 may be, for example, 0.1 mm to 1 mm.

[0294] The hollow tube 105 is, for example, a metallic hollow tube. For example, the hollow tube 105 may be made of iron, nickel-plated iron, stainless steel, or an aluminum alloy. Alternatively, the hollow tube 105 may be made of a high-temperature resistant non-metallic material, such as ceramic. In addition, the hollow tube 105 can effectively prevent problems such as molten material, i.e., spatter, generated during the laser welding process from flowing into the electrode assembly 71 and causing a short circuit.

[0295] While welding is being performed with the laser beam 103, an inert gas such as nitrogen gas or argon gas may be supplied to the space between the hollow tube 105 and the inner surface of the winding center hole 80 to remove the oxygen atmosphere. To more smoothly guide the inert gas onto the first current collecting plate 79, the bottom of the hollow tube 105 may be spaced apart so as to be positioned higher than the top surface of the first current collecting plate 79. As another example, at least one hole for gas inlet and outlet may be formed in the wall of the hollow tube 105 adjacent to the first current collecting plate 79.

[0296] When the inert gas is supplied, the internal space of the hollow portion of the hollow tube 105 can be converted to an inert gas atmosphere. This prevents the aluminum melted by the laser irradiation from reacting with oxygen to form welding smoke in the form of fine dust, if the first current collecting plate 79 and the electrode terminal 50 are made of aluminum.

[0297] Additionally, while welding is being performed using the laser beam 103, a step of removing welding fume may be performed at one end of the winding center hole 80, which is opposite the portion being welded. The hollow tube 105 can temporarily prevent welding fume from entering the electrode assembly 71. Furthermore, if an inert gas atmosphere is formed when welding is performed using an inert gas supply, welding fume generation can be prevented. However, even if welding fume is generated despite this configuration, product defects can be more reliably prevented by suctioning and removing the fume. This further improves welding quality.

[0298] The laser welding apparatus 102 may weld the first current collecting plate 79 to the electrode terminal 50 in a pulsed mode or a continuous mode. In the continuous mode, the laser medium of the laser source is continuously excited to generate a continuous laser beam. In the pulsed mode, the laser medium is excited in pulses rather than continuously. In this mode, a laser beam that is interrupted at intervals (a pulsed beam) is generated. The duration, energy, and pulse cycle of the laser pulse may be adjusted. A specific operating mode may be predetermined during the design of the laser welding apparatus 102. For example, the laser welding apparatus 102 may irradiate the laser beam 103 with a pulse width of 100 ns to 2000 ns. When the first current collecting plate 79 and the electrode terminal 50 are made of aluminum or an aluminum alloy, it is desirable to irradiate the welding area with a high-power beam due to its high thermal conductivity. Therefore, welding with a pulsed beam is desirable. When welding with a pulsed beam, conditions such as the pulse width and pulse cycle may be appropriately determined taking into account the type of material, penetration depth, etc. Other welding conditions, such as the spot diameter and processing speed, can also be appropriately determined depending on the materials of the first current collector plate 79 and electrode terminal 50 to be joined, and the welding design, such as the width WS, depth WD, and aspect ratio of the laser weld 104.

[0299] Known laser light sources include carbon dioxide lasers, argon lasers, ruby lasers (a type of solid-state laser), YAG lasers, and fiber lasers, and an appropriate laser source can be selected depending on the material and thickness of the workpiece. The output power can also be determined appropriately depending on these factors. For example, a YAG laser is desirable because it has high bonding efficiency with metals and excellent processing performance. The laser beam 103 is selected to minimize thermal deformation and deterioration of the material properties of the workpiece.

[0300] The wavelength of the laser beam 103 is not particularly limited as long as efficient welding is possible. A green laser light source (515 nm) is preferred because it has a high output range for welding. When using a green laser light source, the optical system can be configured by changing lenses, etc., to reduce the beam size (spot diameter). A larger beam size can increase the impact on corrosion and reduce the aspect ratio of the laser weld 104, resulting in poor welding efficiency. An IR laser light source (1070 nm) may also be used. Even if the output range for welding is smaller than that of a green laser light source, a low-output laser beam can be used to form an overlapping overlay type weld bead. Preferably, a pulsed dot laser beam can be superimposed and irradiated onto the center of the winding center hole 80 to form an overlapping overlay type laser weld 104, as shown in FIG. 6.

[0301] The wavelength of the laser beam 103 may be 1,000 to 1,500 nm, preferably 900 to 1,350 nm, and more preferably 1,060 to 1,080 nm, taking into consideration the materials of the metal terminal 50 and the first current collecting plate 79 to be welded. If the wavelength of the laser beam 103 is below this range, the output range that can be welded may be widened, but there is a problem in that it is difficult to reduce the size of the laser beam 103. Also, if the wavelength of the laser beam 103 exceeds this range, the output range that can be welded is narrowed, and there is a high possibility of welding defects. Therefore, it is preferable that the wavelength of the laser beam 103 be within this range. In addition, a laser beam 103 with a wavelength of 400 nm to 600 nm may be used.

[0302] The laser welding device 102 may irradiate the laser beam 103 at a processing speed of 40 mm / s to 1,000 mm / s. The processing speed refers to the moving speed of the laser beam 103 on the first current collecting plate 79. The processing speed of the laser beam 103 is important because the shape of the weld bead changes depending on the processing speed. In the laser welding step according to one embodiment of the present invention, the processing speed of the laser beam 103 may be 40 mm / s to 1,000 mm / s, preferably 100 mm / s to 500 mm / s, and more preferably 200 mm / s to 300 mm / s. If the processing speed of the laser beam 103 is less than this range, a back bead may occur, and if it exceeds this range, a problem of reduced joint strength may occur. Therefore, it is preferable that the processing speed of the laser beam 103 be within this range.

[0303] The laser welding device 102 may emit a laser beam 103 with an output of 50W to 4kW. The output of the laser beam 103 may be converted into "line energy," which is the output value of the laser beam 103 relative to the processing speed of the laser beam 103, and managed as a design factor. If the output of the laser beam 103 is below this range, a problem of reduced joining strength may occur, and if it exceeds this range, backbead may occur. Therefore, it is desirable that the output of the laser beam 103 be within this range. The output of the laser beam 103 may be 300W to 500W.

[0304] The spot diameter of the laser beam 103 may be 10 μm to 200 μm. If the spot diameter of the laser beam 103 exceeds 200 μm, there are disadvantages such as increased susceptibility to corrosion and a reduced aspect ratio of the laser weld 104, which may reduce welding efficiency. Furthermore, if the size of the laser beam 103 is less than 10 μm, there is a disadvantage that the welding area is small and sufficient joint strength cannot be ensured with a single welding. Therefore, it is preferable that the spot diameter of the laser beam 103 be within this range. Preferably, the spot diameter of the laser beam 103 may be approximately 50 μm.

[0305] When a laser beam 103 having a spot diameter within this range is irradiated in a pulse dot manner, a single weld bead can be formed in a circular shape by spot welding, as shown in (h) of Figure 17. The width of the circular spot weld bead (WS in Figure 15) is not less than 50 μm, for example, 50 μm, 60 μm, 70 μm, 80 μm, or 100 μm, or can be set to any value not less than 50 μm depending on actual needs. By setting the width to not less than 50 μm, the welding effect between the first current collecting plate 79 and the electrode terminal 50 can be well guaranteed and the welding effect between the first current collecting plate 79 and the electrode terminal 50 can be prevented from being affected by an excessively small width of the circular spot weld bead.

[0306] The laser beam 103 may be single-mode or multi-mode. The energy distribution within the cross section of the laser beam is called the laser beam mode, and the laser welding device 102 may be predetermined to have a specific mode during design. The laser beam mode varies in output energy and application field, and the mode used can be identified from the shape of the weld bead. The spot diameter of the single-mode laser beam 103 may be 50 μm or less. The spot diameter of the multi-mode laser beam 103 may be 50 μm or more.

[0307] A single-mode laser beam has a Gaussian energy distribution with one energy peak. Achieving a single-mode laser beam may result in a loss of laser power, but is advantageous for high-precision processing. In one embodiment of the present invention, when it is necessary to form a fine laser weld 104, a single-mode laser beam may be used.

[0308] Multimode has two or more energy peaks in its energy distribution. Many high-power lasers have multimode beams. To convert such a multimode beam into a single-mode beam, the output energy is reduced by about half. Multimode has a larger spot diameter when connected than single-mode. Furthermore, the part of the multimode that comes into contact with and heats the workpiece is different from single-mode. These characteristics can be used to further improve welding quality and work efficiency.

[0309] The laser welding device 102 may use a fiber laser. The wavelength of the laser beam 103 may be 1,070 nm, allowing for scanning welding. A commercially available laser device may be used, which has a maximum output of approximately 200 W in pulse mode and a maximum output of approximately 700 W in continuous mode. The commercially available laser device has a beam size of approximately 30 μm, making it easy to form welds with small areas. A laser welding device 102 may be configured with a larger maximum output and a smaller or larger beam size, and may be used to perform a manufacturing method according to an embodiment of the present invention.

[0310] Laser welding, which can process smaller areas than resistance welding, is advantageous for increasing the capacity of a secondary battery by further reducing the diameter D of the winding center hole 80 and increasing the height of the electrode assembly 71. Furthermore, laser welding is not limited by the material of the workpiece compared to resistance welding. The present invention does not arbitrarily select and apply laser welding among the well-known techniques of resistance welding, ultrasonic welding, and laser welding. The present invention provides an improved positive terminal 50. The technical problem of connecting the first current collecting plate 79, which may be primarily made of aluminum, to the positive terminal 50 inside the battery can 51 for an electrode assembly 71 having a long winding center hole 80 was previously unknown. This makes it difficult for even those with ordinary skill to connect the first current collecting plate 79 and the positive terminal 50 using laser welding. Even if laser welding is used, it is not possible to laser weld the first current collecting plate 79 and the positive terminal 50 within the area overlapping the winding center hole 80 in a manner that prevents damage to the components surrounding the long winding center hole 80, prevents the generation of spatter, and ensures appropriate joint strength.

[0311] Hereinafter, an experimental example of the welding step in the manufacturing method according to an embodiment of the present invention will be described.

[0312] Fig. 19 is a diagram showing the appearance of the laser weld and a comparison of the equivalent diameter D' with the diameter of the winding center hole 80 of the electrode assembly 71. Fig. 20 is a diagram showing the appearance of the laser weld and a comparison of the equivalent diameter D' with the diameter of the hollow tube 105 inserted into the winding center hole 80 of the electrode assembly 71.

[0313] The diameter D of the winding center hole 80 was 8 mm. The surface appearance of the laser weld 104 formed on the first current collecting plate 79 inside the winding center hole 80 using a manufacturing method according to an embodiment of the present invention is the same as that shown in FIG. 19. The laser weld 104 was successfully formed using a manufacturing method according to an embodiment of the present invention. Experimental examples #1, #2, #4, and #5 are the same circle type as the example shown in FIG. 17(a), and #3 is an overlapping overlay type. In each experimental example, the laser weld 104 was not exposed on the outer surface of the electrode terminal below the first current collecting plate 79, and it was confirmed that the first current collecting plate 79 and the electrode terminal were firmly welded. In #1 to #5, the converted diameter D' of the laser weld 104 was 3.8 mm, 4.1 mm, 2.6 mm, 3.5 mm, and 3.6 mm, respectively, so the converted diameter D' was 0.325 D to 0.5125 D, satisfying the condition that D' should be 0.15 D to 0.90 D. It was also confirmed that the manufacturing method according to one embodiment of the present invention can successfully form laser welds 104 with a converted diameter D' of 2 mm or more.

[0314] The diameter D of the winding center hole 80 may vary. The outer and inner diameters of the hollow tube 105 may also vary to accommodate the winding center hole 80 with various diameters D. The results of laser welding using various hollow tubes 105 are shown in FIG.

[0315] Referring to FIG. 20, the laser weld 104 was successfully formed in the inner hollow portion of the hollow tube 105, with a size smaller than the inner diameter DI of the hollow tube 105. The equivalent diameter D' of the laser weld 104 was arranged in ascending order from 2.6 mm for #6 to 4.9 mm for #13. The inner diameter DI of the hollow tube 105 was different for each experimental example. The equivalent diameter D' / inner diameter DI of the hollow tube 105 for each experimental example was also arranged in ascending order from 27% to 96%. The inner diameter DI of the hollow tube 105 for #6 was 9.6 mm. The inner diameter DI of the hollow tube 105 for #13 was 5.1 mm.

[0316] Because the inner diameter DI of the hollow tube 105 is smaller than the diameter D of the winding center hole 80, in Experimental Examples #6 to #13 where D' / DI is in the range of 27% to 96%, the upper and lower limits of D' / D are changed to smaller values. For example, D' / D may be in the range of 30% to 94%. In this way, by forming laser welds 104 with various equivalent diameters D' using various hollow tubes 105, it was possible to satisfy the condition that D' is 0.15D to 0.90D.

[0317] In particular, when D' / DI is 96%, as in #13, it is noted that the laser weld 104 was formed very close to the wall of the hollow tube 105, and even in such a case, the laser weld was able to be formed without damaging the electrode assembly portion around the winding center hole 80. In this way, even when using the hollow tube 105, the condition of D' being 0.15D to 0.90D, i.e., the condition of D' / D being in the range of 15% to 90%, was fully achieved.

[0318] After the laser welding step is completed, further steps such as assembling the sealing body 74, beading, crimping, electrolyte injection, sizing, etc. The order of the steps may be changed as needed. For example, depending on the structure of the second current collector plate 78, a step of welding the second current collector plate 78 to the battery can 51 may also be performed.

[0319] A cylindrical secondary battery 70 according to an embodiment of the present invention includes a first current collecting plate 79 and a second current collecting plate 78. The first current collecting plate 79 may have a structure that prevents stress from concentrating on the joint between components even when external impact and / or vibration is applied during use. The second current collecting plate 78 not only has a structure that improves the joint strength with the battery can 51 but also improves the energy density of the cylindrical secondary battery 70. The first current collecting plate 79 and the second current collecting plate 78 also have a structure that makes it easy to laser-weld the first current collecting plate 79 to the electrode terminal 50.

[0320] Various embodiments of the first current collecting plate 79 and the second current collecting plate 78 will be described below.

[0321] 21 to 24 are diagrams showing various surface forms of the first current collector plate.

[0322] 21 to 24, the first current collecting plate 120 includes an edge portion 121, a first electrode tab coupling portion 122, and a terminal coupling portion 123. The edge portion 121, the first electrode tab coupling portion 122, and the terminal coupling portion 123 may all be on the same plane. That is, the first current collecting plate 120 is a substantially plate-shaped member whose thickness is smaller than the width or length of its large area portion. When the large area portion of the first current collecting plate 120 is placed on the upper or lower end of the electrode assembly 71, the entire first current collecting plate 120 extends parallel to the upper or lower end surface of the electrode assembly 71. There is no difference in height between the edge portion 121, the first electrode tab coupling portion 122, and the terminal coupling portion 123 of the first current collecting plate 120. This planar structure does not occupy much volume within the battery can 51, resulting in good space utilization.

[0323] The edge 121 may have a substantially rim shape with a space S formed in at least a portion of the inner region. Although the drawings show only the case where the edge 121 has a substantially circular rim shape, the present invention is not limited thereto. The edge 121 may have a substantially square rim shape or other shapes different from those shown in the drawings.

[0324] The first electrode tab coupling portion 122 may extend inward from the edge portion 121 and be coupled to the uncoated portion 73 of the first electrode plate by welding. The terminal coupling portion 123 may be located inside the edge portion 121 and spaced apart from the first electrode tab coupling portion 122. As described above, the terminal coupling portion 123 may be coupled to the positive electrode terminal 50 by laser welding. The terminal coupling portion 123 may be located, for example, in the center of the inner space of the edge portion 121. The terminal coupling portion 123 may be disposed at a position corresponding to the winding center hole 80 of the electrode assembly 71. The size of the terminal coupling portion 123 may be larger than the diameter of the winding center hole 80. The laser weld 104 may be formed at the terminal coupling portion 123 as described above.

[0325] The first electrode tab coupling portion 122 and the terminal coupling portion 123 are not directly connected, but are spaced apart and connected by an edge 121. As such, the first current collecting plate 120 has a structure in which the first electrode tab coupling portion 122 and the terminal coupling portion 123 are not directly connected to each other but are connected via the edge 121. This allows the cylindrical secondary battery 70 to disperse impacts and / or vibrations applied to the coupling portion between the first electrode tab coupling portion 122 and the uncoated portion 73 of the first electrode plate and the coupling portion between the terminal coupling portion 123 and the positive terminal 50. As a result, the first current collecting plate 120 also has the effect of minimizing or preventing damage to welded portions due to external impacts. The first current collecting plate 120 has a structure in which stress may be concentrated at the connection portion between the edge portion 121 and the terminal coupling portion 123 when an external impact is applied, and because this connection portion is not a portion where a weld for connecting components is formed, it is possible to prevent product defects due to damage to the weld due to external impact. As such, the first current collecting plate 120 has a structure in which force is not concentrated at the connection portion between components even when external impact and / or vibration is applied during use, thereby improving the performance of the cylindrical secondary battery 70 including it.

[0326] The first current collecting plate 120 may further include a connecting portion 124 extending inward from the edge 121 and connected to the terminal connecting portion 123. At least a portion of the connecting portion 124 may be formed with a width smaller than that of the first electrode tab connecting portion 122. In this case, electrical resistance increases in the connecting portion 124, and when current flows through the connecting portion 124, greater resistance occurs than in other portions. As a result, when an overcurrent occurs, a portion of the connecting portion 124 breaks, thereby interrupting the overcurrent. The width of the connecting portion 124 may be adjusted to an appropriate level in consideration of this overcurrent interruption function. At least a portion of the connecting portion 124 may have a relatively narrow width to enhance its current interruption function. For example, both sides of the connecting portion 124 may be formed with notches cut inward to partially reduce the width of the connecting portion 124. When the notches are formed, electrical resistance in the notched areas increases further, and the notched areas melt and break due to resistance heating, preventing current flow. This allows for rapid current interruption when an overcurrent occurs.

[0327] The connecting portion 124 may include a tapered portion 124a whose width gradually narrows in a direction from the inner end of the edge portion 121 toward the terminal coupling portion 123. When the tapered portion 124a is included, the rigidity of the part may be improved at the connection portion between the connecting portion 124 and the edge portion 121. When the notch portion is included, the notch portion may be located closer to the tapered portion 124a than the terminal coupling portion 123. In this case, the structure of the edge portion 124a whose width gradually narrows allows the notch portion to be located in an area adjacent to an area where heat is generated more quickly, thereby enabling more rapid overcurrent interruption.

[0328] The first current collecting plate 120 may include a plurality of first electrode tab coupling portions 122. The plurality of first electrode tab coupling portions 122 may be arranged at equal intervals along the circumferential direction. The extension lengths of the plurality of first electrode tab coupling portions 122 may be the same. The terminal coupling portion 123 may be arranged to be surrounded by the plurality of first electrode tab coupling portions 122. The connecting portion 124 may be located between a pair of adjacent first electrode tab coupling portions 122. In this case, the distance from the connecting portion 124 to one of the pair of first electrode tab coupling portions 122 in the direction along the edge 121 may be the same as the distance from the connecting portion 124 to the remaining one of the pair of first electrode tab coupling portions 122 in the direction along the edge 121.

[0329] There may be a plurality of connecting portions 124. Each of the connecting portions 124 may be disposed between a pair of adjacent first electrode tab coupling portions 122. The connecting portions 124 may be disposed at equal intervals from one another along the circumferential direction.

[0330] As described above, in the case where a plurality of first electrode tab coupling portions 122 and / or connecting portions 124 are included, if the distance between the first electrode tab coupling portions 122 and / or the distance between the connecting portions 124 and / or the distance between the first electrode tab coupling portions 122 and the connecting portions 124 are uniform, a current can smoothly flow from the first electrode tab coupling portions 122 to the connecting portions 124 or from the connecting portions 124 to the first electrode tab coupling portions 122.

[0331] The first electrode tab coupling portion 122 may be welded to a certain region while being placed on the bent surface of the uncoated portion 73 of the first electrode plate in the electrode assembly 71. That is, the first electrode tab coupling portion 122 may be coupled to a region where a plurality of segment pieces (93a in FIG. 12) overlap each other. A weld may be formed for each first electrode tab coupling portion 122. The weld may be formed to extend along the extension direction of the first electrode tab coupling portion 122.

[0332] When a cylindrical secondary battery is used in a device such as an automobile, it may be subjected to frequent external shocks and vibrations during use, which can cause damage to the joints connecting components. Such damage to the joints can result in product defects. Even if the joints are damaged and the connection is not completely cut off, partial damage to the welded parts can reduce the joint area between components, resulting in excessive heat generation due to increased resistance or internal short circuits due to deformation of the components. The cylindrical secondary battery 70 according to one embodiment of the present invention can solve these problems by including the first current collector 120 described above.

[0333] 25 to 28 are diagrams showing various surface forms of the second current collector plate.

[0334] 25, the second current collecting plate 140 includes at least one second electrode tab coupling portion 142 that couples with the uncoated portion 72 of the second electrode plate and at least one can coupling portion 143 that electrically couples with the beading portion 76 on the inner surface of the battery can 51. The second electrode tab coupling portion 142 and the can coupling portion 143 do not have to be on the same plane. That is, the second current collecting plate 140 is a substantially plate-shaped member that is thinner than the width or length of the portion having a large area, and when the portion having a large area of the second current collecting plate 140 is placed at the lower end of the electrode assembly 71, there is a height difference between the second electrode tab coupling portion 142 and the can coupling portion 143 of the second current collecting plate 140. This three-dimensional structure ensures a sufficient contact area between the second electrode tab coupling portion 142 and the non-coated portion 72 of the second electrode plate, while lowering the can coupling portion 143 to be fixed to the beading portion 76 of the battery can 51, thereby improving the bonding strength of the bonding portion with the battery can 51.

[0335] The center portion 141 of the second current collector plate 140 may be a substantially circular plate. The center portion 141 may be selectively coupled to the uncoated portion 72 of the second electrode plate. The center portion 141 may be a ring-shaped plate having a current collector hole 145 at its center.

[0336] The current collecting plate hole 145 may be circular and may be formed at a position corresponding to the winding center hole 80 of the electrode assembly 71. The winding center hole 80 and the current collecting plate hole 145, which are connected to each other, may function as a passage for irradiating the laser beam 103 for welding the electrode terminal 50 and the positive current collecting plate 120. In addition, the current collecting plate hole 145 may also serve to allow gas to quickly move downward through the winding center hole 80 if a large amount of gas is generated due to an abnormality in the secondary battery.

[0337] The diameter of the current collecting plate hole 145 may be 0.5D or more, preferably 0.7D or more, and more preferably 1.0D or more, based on the diameter D of the winding center hole 80 of the electrode assembly 71. If the diameter of the current collecting plate hole 145 is 0.5D or more but less than 1.0D, it is possible to prevent the separator or electrode plate from being pushed out of the winding center hole 80 when the cell is vented. Preferably, if the diameter of the current collecting plate hole 145 is set larger than the diameter D of the winding center hole 80 of the electrode assembly 71, it becomes easier to secure a space for inserting the hollow tube 105 when irradiating the laser beam 103 to weld the electrode terminal 50 and the positive current collecting plate 120 together.

[0338] The second current collecting plate 140 may include a plurality of second electrode tab coupling portions 142 and a plurality of can coupling portions 143. In this case, although not shown, the plurality of can coupling portions 143 may be connected to each other to be integrally formed.

[0339] The second electrode tab coupling portions 142 may extend radially from the center portion 141 of the second current collector plate 140 toward the sidewall of the battery can 51. The plurality of second electrode tab coupling portions 142 may be spaced apart from one another around the center portion 141. By providing the plurality of second electrode tab coupling portions 142, the coupling area with the uncoated portion 72 of the second electrode plate may be increased. This may ensure a strong coupling force between the uncoated portion 72 of the second electrode plate and the second electrode tab coupling portions 142, thereby reducing electrical resistance.

[0340] The second electrode tab coupling portion 142 may be welded to the uncoated portion 72 of the second electrode plate. The second electrode tab coupling portion 142 may be welded to a certain region while placed on the bent surface of the uncoated portion 72 of the second electrode plate in the electrode assembly 71. That is, the second electrode tab coupling portion 142 may be coupled to a region where a plurality of segment pieces (93a in FIG. 12) are overlapped. A weld may be formed for each second electrode tab coupling portion 142. The weld may be formed to extend along the extension direction of the second electrode tab coupling portion 142.

[0341] The plurality of can coupling portions 143 may be spaced apart from one another around the center portion 141. The can coupling portions 143 may be coupled to the beading portion 76 on the inner surface of the battery can 51. As such, the second current collector 140 is coupled to the beading portion 76 of the battery can 51 rather than to the inner surface of the cylindrical portion of the battery can 51, which may reduce the distance between the second current collector 140 and the beading portion 76. This minimizes dead space inside the battery can 51, thereby improving the energy density of the cylindrical secondary battery 70.

[0342] The can coupling portion 143 may be crimped and fixed by the crimping portion 114 of the battery can 51. The can coupling portion 143 may include a contact portion 143a that couples to the beading portion 76 on the inner surface of the battery can 51, and a coupling portion 143b that connects the second electrode tab coupling portion 142 and the contact portion 143a.

[0343] The contact portion 143a is bonded to the inner surface of the battery can 51. If a beading portion 76 is formed on the battery can 51, the contact portion 143a may be bonded to the beading portion 76. In this case, as described above, for stable contact and bonding, the beading portion 76 and the contact portion 143a may all have a shape extending in a direction substantially parallel to the bottom surface of the battery can 51, i.e., in a direction substantially perpendicular to the sidewall of the battery can 51. In other words, the contact portion 143a includes at least a portion of a flat portion substantially parallel to the bottom surface of the battery can 51.

[0344] As shown in FIG. 25 , the connecting portion 143b may have at least one bent portion BD, where the extension direction thereof is reversed at least once between the center portion 141 and the contact portion 143a. That is, the connecting portion 143b may have, for example, a spring-like or bellows-like structure that can contract and expand within a certain range. Meanwhile, the connecting portion 143b may be elastically biased upward by the bent portion BD. This structure of the connecting portion 143b allows the contact portion 143a to closely contact the beading portion 76 when the electrode assembly 71, having the second current collecting plate 140 attached thereto, is placed in the battery can 51, even if there is a certain range of variation in the height of the electrode assembly 71. In addition, this structure of the connecting portion 143b allows for a more stable shape to be achieved during the sizing process. The sizing process is a compression process for reducing the height occupied by the beading portion 76 of the battery can 51 in order to reduce the total height of the cylindrical secondary battery 70 during the manufacture of the cylindrical secondary battery 70. In addition, due to the contractible and expandable structure of the connecting portion 143b, even if vibrations and / or impacts occur during use of the cylindrical secondary battery 70 and cause the electrode assembly 71 to move up and down, the impact caused by the movement of the electrode assembly 71 can be mitigated within a certain range.

[0345] The shapes of the contact portion 143a and the connecting portion 143b may be variously changed. The second current collecting plate 140 of Fig. 25 and the second current collecting plate 140 of Fig. 26 differ only in the shape of the contact portion 143a, and otherwise the structure of the second current collecting plate 140 described above may be substantially the same.

[0346] 26, the contact portion 143a may have a shape in which at least a portion thereof extends along the inner circumferential surface of the battery can 51. For example, the contact portion 143a may have an arc shape extending along the beading portion of the battery can 51. Also, although not shown, in order to maximize the contact area, the second current collector 140 may be configured such that the sum of the extension lengths of the contact portions 143a of at least one can coupling portion 143 is substantially the same as the inner periphery of the battery can 51. In this embodiment, the maximization of the coupling area may result in improved coupling strength and reduced electrical resistance.

[0347] The contact portion 143a may be interposed and fixed between the beading portion 76 of the battery can 51 and the sealing gasket 180. That is, the contact portion 143a may be fixed by the crimping force of the crimping portion 114 while being interposed between the beading portion 76 of the battery can 51 and the sealing gasket 180.

[0348] Referring to FIG. 27, the second current collecting plate 140 of FIG. 27 differs from the second current collecting plate 140 described with reference to FIG. 25 in that it further includes an additional can coupling portion 144, but apart from that, the structure of the second current collecting plate 140 of FIGS. 25 and 26 described above can be applied in substantially the same manner.

[0349] The additional can coupling portion 144 extends from an end of the second electrode tab coupling portion 142 and is coupled to the inner surface of the battery can 51. At least one end of the plurality of second electrode tab coupling portions 142 is provided with the additional can coupling portion 144. The additional can coupling portion 144 includes an additional contact portion 144a that is coupled to the inner surface of the battery can 51, and an additional connection portion 144b that connects the end of the second electrode tab coupling portion 142 and the additional contact portion 144a.

[0350] The additional contact portion 144a is bonded to the inner surface of the battery can 51. In the case where a beading portion 76 is formed on the battery can 51, the additional contact portion 144a can be bonded to the beading portion 76 in the same manner as the contact portion 143a. Furthermore, like the shape of the contact portion 143a shown in FIG. 26 , the additional contact portion 144a can also have a shape in which at least a portion thereof extends along the inner circumferential surface of the battery can 51.

[0351] The additional connecting portion 144b may have at least one bent portion where its extension direction is changed at least once between the second electrode tab coupling portion 142 and the additional contact portion 144a, similar to the connecting portion 143b described with reference to Fig. 25. The formation of the bent portion allows the additional connecting portion 144b to have a contractible and expandable structure, which provides advantages and cushioning effects in the assembly process of the cylindrical secondary battery 70, as described above.

[0352] 28 , the second current collecting plate 140 may have at least one liquid inlet 146. The liquid inlet 146 may be provided, for example, in the second electrode tab coupling portion 142. When a plurality of second electrode tab coupling portions 142 are provided, the liquid inlet 146 may be provided in at least one of the second electrode tab coupling portions 142. The liquid inlet 146 may be provided, for example, on one side or both sides of the welded portion W formed in the second electrode tab coupling portion 142. When manufacturing the cylindrical secondary battery 70, an electrolyte may be injected after the assembly including the electrode assembly 71 and the second current collecting plate 140 is placed in the battery can 51. In this case, the liquid inlet 146 allows the electrolyte to quickly flow into the electrode assembly 71, improving the efficiency of the liquid inlet.

[0353] A plurality of liquid inlet holes 146 may be provided. The plurality of liquid inlet holes 146 may be arranged substantially symmetrically with respect to the center of the second electrode tab coupling portion 142 in the width direction. A welded portion W for coupling the second electrode tab coupling portion 142 and the uncoated portion 72 of the second current collecting plate may be formed between the liquid inlet holes 146 arranged substantially symmetrically in this manner.

[0354] The second electrode tab coupling portion 142 may be formed so that its width at a position spaced a predetermined distance from the coupling portion toward a longitudinal end of the tab coupling portion is greater than its width at a coupling portion between the second electrode tab coupling portion 142 and the center portion 141. At least a portion of the region where the liquid inlet hole 146 is formed may be included in this increased region, which is formed by increasing the width at a position spaced a predetermined distance from the coupling portion toward the end of the second electrode tab coupling portion 142 compared to the width at the coupling portion between the second electrode tab coupling portion 142 and the center portion 141. Meanwhile, the longitudinal end of the second electrode tab coupling portion 142 may be substantially arc-shaped to correspond to the inner circumferential surface of the battery can 51. In addition, the description of the structure of the second current collecting plate 140 in FIG. 28 may be substituted for the description of the second current collecting plate 140 described with reference to FIGS. 25 to 27.

[0355] As described above, the current collector plates 120 and 140 have a structure suitable for the electrode assembly 71 having a low resistance structure, thereby improving the mechanical and electrical performance of the cylindrical secondary battery 70 including the current collector plates 120 and 140. In addition, the cylindrical secondary battery 70 can be easily manufactured by welding.

[0356] The cylindrical secondary battery 70 according to the above-described embodiment can be used to manufacture a battery pack.

[0357] FIG. 29 is a diagram schematically illustrating the configuration of a battery pack according to an embodiment of the present invention.

[0358] 29, a battery pack 200 according to an embodiment of the present invention includes an assembly of connected cylindrical secondary batteries 201 and a pack housing 202 that accommodates the assembly. The cylindrical secondary batteries 201 may be the secondary batteries 70 according to the above-described embodiment. For ease of illustration, components such as bus bars for connecting the cylindrical secondary batteries 201, a cooling unit, and external terminals are omitted from the drawings.

[0359] The battery pack 200 may be installed in a vehicle. The vehicle may be, for example, an EV, an HEV, or a plug-in hybrid vehicle (PHEV). The vehicle may be a four-wheeled vehicle or a two-wheeled vehicle.

[0360] FIG. 30 is a diagram illustrating a vehicle including the battery pack 200 of FIG.

[0361] 30, an automobile 300 according to an embodiment of the present invention includes a battery pack 200 according to an embodiment of the present invention. The automobile 300 operates by receiving power from the battery pack 200 according to an embodiment of the present invention.

[0362] In the substrate of the present invention, unless otherwise clearly specified or limited, the terms "installed," "connected," "connected," "coupled," etc. should be understood in a broad sense. For example, they may refer to a fixed connection, a detachable connection, or an integral connection, a mechanical connection, an electrical connection, a direct connection or an indirect connection via an intermediary, or an internal communication between two components. A person skilled in the art to which the present invention pertains will be able to understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0363] In describing the present invention, the terms "first" and "second" are merely used to distinguish between similar structures and are not intended to describe a particular order or sequence. Such numerals may be interchanged with one another or with other numerals in appropriate circumstances.

[0364] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is of course possible for a person having ordinary skill in the art to which the present invention pertains to make various modifications and variations within the scope of the technical concept of the present invention and the scope of the claims. [Explanation of symbols]

[0365] 10 Positive electrode plate 10a Uncoated part 11 Negative electrode plate 11a Uncoated part 12 Separation membrane 13 Winding center hole 20 Current collector 21 Active material 22 Uncoated part 30 Current collector plate 31 Current collector plate 40 Cylindrical secondary battery 41 Battery can 42 Sealed body 42a Cap Plate 42b Sealing gasket 42c connecting plate 43 Crimping section 44 Beading section 45 Lead 46 Insulator 50 electrode terminal 50' electrode terminal 50a Main body 50b External flange 50c Internal flange 50d flat part 51 Battery can 52 Bottom 53 Through hole 54 Rivet Gasket 54a External gasket 54b Internal gasket 55 Recessed part 56 Inner Edge 70 Secondary battery 71 Electrode assembly 72 Uncoated part 73 Uncoated part 74 Sealed body 74a Cap Plate 74b Sealing gasket 75 Crimping section 76 Beading section 77 Vent Notch 78 Second current collector plate 79 First current collector plate 80 Winding center hole 85 insulator 85a Welding hole 85b Upper plate 85c side sleeve 90 Electrode plate 91 Current collector 92 Active material layer 93 Uncoated part 93' Uncoated section 93a segmental piece 94 Insulation coating layer 100 electrode assembly 102 Laser welding equipment 103 Laser Beam 104 Laser welded section 114 Crimping section 120 First current collector plate 122 first electrode tab connection part 123 Terminal connection part 124 Connection section 140 Second current collector plate 142 second electrode tab connection part 143 Can joint 144 Additional can joint 145 Current collector plate hole 146 Liquid injection hole 180 Sealing Gasket 200 battery pack 201 Cylindrical secondary battery 202 Pack Housing 300 cars

Claims

1. a jelly-roll type electrode assembly having a structure in which sheet-like first and second electrode plates and a separator interposed therebetween are wound in one direction, wherein the first electrode plate includes an uncoated portion at a long side end that is exposed to the outside of the separator, and the second electrode plate includes an uncoated portion at a long side end that is exposed to the outside of the separator in a direction opposite to the uncoated portion of the first electrode plate, and the electrode assembly has a winding center hole in an inner core; a battery can that accommodates the electrode assembly and is connected to the uncoated portion of the second electrode plate; a first current collector plate connected to the uncoated portion of the first electrode plate; an electrode terminal formed on the bottom of the battery can and connected to the first current collector plate; a laser weld formed on a contact surface between the first current collector plate and the electrode terminal, the laser welded portion is located at an overlapping portion of the first current collector plate and the electrode terminal within the winding center hole.

2. The secondary battery according to claim 1, wherein the equivalent diameter of the laser welded portion exposed on the surface of the first current collector plate is 0.15D to 0.90D (D: diameter of the winding center hole).

3. The electrode terminal is a main body portion inserted into the through hole; an external flange portion extending from a peripheral edge of one side of the body portion exposed on an outer surface of the bottom of the battery can along the outer surface; an inner flange portion extending from the other peripheral edge of the main body portion exposed on the inner surface of the bottom of the battery can toward the inner surface; The secondary battery according to claim 1 or 2, further comprising a flat portion provided inside the inner flange portion.

4. The secondary battery according to claim 3 , wherein the electrode terminal and the first current collector plate are joined at the flat portion by the laser welding portion.

5. 3. The secondary battery according to claim 1, wherein the laser weld is formed on one surface of the first current collector plate facing the inside of the winding center hole toward the electrode terminal at a joining portion between the first current collector plate and the electrode terminal.

6. 3. The secondary battery according to claim 1, wherein the laser welded portion is an overlay type in which a weld bead is overlapped on the center of the winding center hole.

7. The first current collector plate is An edge portion; a first electrode plate coupling portion extending inward from the edge portion and coupled to the uncoated portion of the first electrode plate; a terminal coupling portion spaced apart from the first electrode plate coupling portion, The secondary battery according to claim 1 or 2, wherein the electrode terminal is coupled to the terminal coupling portion.

8. providing a jelly-roll type electrode assembly having a structure in which sheet-like first and second electrode plates and a separator interposed therebetween are wound in one direction, the first electrode plate including a first uncoated portion exposed to the outside of the separator at a long side end, the second electrode plate including a first uncoated portion exposed to the outside of the separator at a long side end in a direction opposite to the uncoated portion of the first electrode plate, and the electrode assembly having a winding center hole in an inner core; connecting a first current collecting plate to the uncoated portion of the first electrode plate; providing a battery can including an electrode terminal at its bottom; inserting the electrode assembly into the battery can so that the first current collector plate faces a bottom of the battery can; forming a laser weld on a contact surface between the first current collecting plate and the electrode terminal using a laser welding device; The method for manufacturing a secondary battery, wherein the laser beam of the laser welding device is irradiated into the winding center hole along the longitudinal direction of the winding center hole.

9. The method for manufacturing a secondary battery according to claim 8 , wherein the laser welded portion is located at an overlapping portion of the first current collector plate and the electrode terminal within the winding center hole.

10. 10. The method for manufacturing a secondary battery according to claim 8, wherein the converted diameter of the laser welded portion exposed on the surface of the first current collector plate is 0.15D to 0.90D (D: diameter of the winding center hole).

11. The step of forming the laser weld includes: a hollow tube is inserted into the winding center hole, and at least a portion of the first current collector plate is exposed in an inner hollow portion of the hollow tube; 10. The method of claim 8, further comprising: welding the first current collector plate to the electrode terminal by passing a laser beam emitted from the laser welding device through an inner hollow portion of the hollow tube.

12. The method for manufacturing a secondary battery according to claim 11, wherein the first current collector plate is pressed against the electrode terminal by the hollow tube.

13. 12. The method of claim 11, further comprising: supplying an inert gas to remove an oxygen atmosphere using a space between the hollow tube and an inner circumferential surface of the winding center hole while the laser beam welding is performed.

14. The method of manufacturing a secondary battery according to claim 11, wherein the length of the hollow tube is greater than the height of the electrode assembly, and the hollow tube is a metal hollow tube.

15. The method of claim 11, further comprising removing welding fumes from the one end of the winding center hole while the welding is performed by the laser beam.

16. 3. A method for manufacturing the secondary battery according to claim 1, wherein the step of forming the laser welded portion is a step of welding by irradiating a laser beam using the winding center hole inside the battery can.

17. The method for manufacturing a secondary battery according to claim 16, wherein the laser beam heats the first current collector plate.

18. 18. The method for manufacturing a secondary battery according to claim 17, wherein a temperature difference is created between the area where the laser beam is intensively irradiated and a surrounding area.

19. The method for manufacturing a secondary battery according to claim 17, wherein the melting occurs completely after the preheating by the laser beam.

20. A battery pack comprising the secondary battery according to claim 1 or 2.

21. The battery can accommodates the electrode assembly through an opening formed on one side thereof, the secondary battery further includes a sealing body that seals an open portion of the battery can so as to be insulated from the battery can, The secondary battery according to claim 1 or 2, wherein the bottom of the battery can is located on the opposite side of the open part of the battery can.

22. The battery can includes an opening formed on one side thereof, 10. The method of claim 8, wherein the electrode terminal is riveted through a through-hole formed in a bottom of the battery can opposite the opening of the battery can.

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