Electrode assembly, secondary battery, battery pack including the same, and automobile

Abstract

The longitudinal current path is minimized, thereby providing a cylindrical secondary battery with a low resistance electrode assembly that exhibits excellent quality in terms of heat generation while having high capacity and / or high output. [Solution] An electrode assembly in which a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes are wound around a winding shaft, wherein the electrode (160) includes a sheet-like current collector (141) having long and short sides and including an uncoated portion (143) at an end of the long side, the uncoated portion including an electrode tab-defined section used as an electrode tab and at least one or more undefined electrode tab sections not used as an electrode tab, the maximum current path for the at least one undefined electrode tab section includes a current path in the width direction along the short side of the current collector and a current path in the length direction along the long side of the current collector, and when the length of the current path in the width direction and the length of the current path in the length direction are L1 and L2, respectively, the current path ratio L2 / L1 is 11 or less.

Description

[Technical Field]

[0001] The present invention relates to an electrode assembly, a secondary battery, a battery pack including the same, and an automobile, and more particularly to a jelly-roll-shaped electrode assembly that can realize low resistance, a cylindrical secondary battery including the same, and a battery pack and an automobile including the same.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0103378 filed on August 5, 2021, and Korean Patent Application No. 10-2022-0089230 filed on July 19, 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) and hybrid electric vehicles (HEVs) that are driven by electrical sources. 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 the case of 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, which is then inserted into a battery can to form a battery. Strip-shaped electrode tabs may be connected to the uncoated portions of each of the positive and negative electrodes, and the electrode tabs electrically connect the electrode assembly to electrode terminals exposed to the outside.

[0005] Cylindrical secondary batteries can increase capacity by increasing cell size. This requires a low-resistance cell design that can exhibit excellent quality in terms of energy loss and heat generation even at high current densities. The key to designing such low-resistance cells is ultimately minimizing the current path.

[0006] FIG. 1 is a diagram showing a state in which a positive electrode and a negative electrode applied to a conventional cylindrical secondary battery are spread out.

[0007] Referring to FIG. 1, a positive electrode 1 and a negative electrode 2 are shown as electrodes used in a conventional cylindrical secondary battery. A strip-shaped positive electrode tab 1b is connected to an uncoated portion 1a formed in the longitudinal middle of the positive electrode 1 so as to protrude upward along the width direction, and a strip-shaped negative electrode tab 2b is connected to an uncoated portion 2a formed at both longitudinal ends of the negative electrode 2 so as to protrude downward along the width direction. FIG. 1(a) shows a case where there is one positive electrode tab 1b and one negative electrode tab 2b, and FIG. 1(b) shows a case where there is one positive electrode tab 1b and two negative electrode tabs 2b.

[0008] Fig. 2 is a diagram schematically illustrating the flow of current or electrons outside a conventional cylindrical secondary battery, and Fig. 3 is a diagram schematically illustrating the flow of current or electrons in a positive electrode and a negative electrode that constitute an electrode assembly in a conventional cylindrical secondary battery.

[0009] Referring to Figures 2 and 3, the current path can be broadly divided into two paths: a path from the module busbar welding position to the electrode tabs 1b and 2b of each electrode 1 and 2 (hereinafter referred to as the "first path"), and a path from the electrode tabs 1b and 2b of each electrode 1 and 2 to the end points of the electrodes.

[0010] Figure 2 shows the first path, and the current starting points (indicated by ●) in Figure 2 are located at the positive electrode terminal 1c and the negative electrode terminal 2c. The positive electrode terminal 1c is a sealing cap that seals the open end of the battery can 3, and the negative electrode terminal 2c is the battery can 3. This example shows a case where the welding position of the module bus bar is located at the top end of a cylindrical secondary battery. A current path is formed starting from the positive electrode terminal 1c and connecting to the positive electrode tab 1b, and a current path is formed starting from the negative electrode terminal 2c and connecting to the negative electrode tab 2b (the connecting position is indicated by ▲). In this way, the first path is determined by the appearance of the cell.

[0011] When an electrochemical oxidation reaction occurs in the active material layer of the electrode, metal atoms (Li) are converted to metal cations (Li+) throughout the active material layer, generating electrons. The electrons travel through the current collector (foil) that makes up the electrode to the electrode tab, then flow to the outside through the first path. At this time, current flows in the opposite direction to the electron flow. Meanwhile, when an electrochemical reduction reaction occurs in the electrode, electrons flow from the first path through the electrode tab to the current collector (foil) that makes up the electrode, travel throughout the active material layer of the electrode, combine with cations (e.g., Li+), and convert the metal cations to metal. At this time, current flows in the opposite direction to the electron flow.

[0012] Meanwhile, when an oxidation or reduction reaction occurs at an electrode, the path through which electrons move corresponds to the current path. The maximum current path of an electrode is determined depending on the geometric structure of the current collector (foil) that constitutes the electrode and the position and number of electrode tabs. The maximum current path of an electrode can be defined as the longest distance between the electrode point farthest from the electrode tab. When an electrochemical oxidation or reduction reaction occurs at the electrode point farthest from the electrode tab, electrons move through multiple paths connecting the electrode point and the electrode tab, and some of the electrons also move through the maximum current path. Therefore, as the maximum current path of an electrode becomes longer, the average movement distance of electrons increases from the perspective of the entire electrode, and the resistance of the electrode also increases.

[0013] For ease of explanation, the maximum current path that is uniquely determined by the geometric structure of the electrode and the number and positions of the electrode tabs will be referred to as the second path of the electrode. Figure 3 shows the second path, which is the maximum current path of the electrode, and indicates that the length of the second path varies depending on the formation positions and number of electrode tabs 1b and 2b.

[0014] 3(a), the second path (maximum current path) of the positive electrode 1 includes a widthwise current path that runs from the positive electrode terminal 1c in FIG. 2 along the positive electrode tab 1b inside the cylindrical secondary battery, and a longitudinal current path that runs across the positive electrode 1 in the longitudinal direction and ends at the lower right end of the positive electrode 1 (the electrode point farthest from the electrode tab is indicated by a square). The second path (maximum current path) of the negative electrode 2 includes a widthwise current path that runs from the negative electrode terminal 2c in FIG. 2 along the negative electrode tab 2b inside the cylindrical secondary battery, and a longitudinal current path that runs across the negative electrode 2 in the longitudinal direction and ends at the upper left end of the negative electrode 2.

[0015] Referring to Figure 3(b), the second path of the positive electrode 1 is the same as that shown in Figure 3(a). In the case of the negative electrode 2, since it includes two negative electrode tabs 2b, the second path (maximum current path) of the negative electrode 2 is shorter than that shown in Figure 3(a) because the longitudinal current path is reduced by half. As such, as the number of electrode tabs increases, the second path is reduced accordingly due to the reduction in the longitudinal current path.

[0016] Currently used small cylindrical secondary batteries with form factors of 1865 (18 mm diameter, 65 mm height) and / or 2170 (21 mm diameter, 70 mm height) exhibit very large resistance due to the second path. Here, form factor refers to values ​​indicating the diameter and height of a cylindrical secondary battery. In the numerical value indicating the form factor, the first two digits indicate the diameter of the cell, and the remaining digits indicate the height of the cell.

[0017] As shown in Figure 3, in conventional cylindrical secondary batteries, the longitudinal current path is much longer than the width current path. The longer the current path, the higher the battery resistance. Increasing the number of negative electrode tabs 2b in Figure 3(b) rather than Figure 3(a) is also intended to reduce the longitudinal current path of the negative electrode and lower the resistance.

[0018] The resistance of a cylindrical secondary battery is affected by the resistance of the first path outside the cell and the resistance of the second path inside the cell, with the second path being the dominant factor. This is related to the length of the current (or electron) flow path due to the electrode assembly structure. Therefore, considering the main causes of increased resistance, a method is needed to achieve low resistance in cylindrical secondary batteries. The lower the resistance, the less heat is generated in actual usage environments and the more advantageous it is for fast charging and high-rate discharging.

[0019] Meanwhile, conventional cylindrical secondary batteries suffer from poor current collection efficiency due to current concentration at the strip-shaped electrode tabs 1b and 2b connected to the uncoated portions 1a and 2a, resulting in high resistance and heat generation. For compact cylindrical secondary batteries, resistance and heat generation are not a major issue. However, when the form factor of cylindrical secondary batteries is increased for application in electric vehicles, resistance and heat generation become a major issue, potentially leading to fires. To address these issues, cylindrical secondary batteries (e.g., tabless cylindrical secondary batteries) have been proposed, which have a structure in which positive and negative uncoated portions are located at the top and bottom of a jelly-roll-type electrode assembly, respectively, and current collector plates are welded to these uncoated portions, thereby improving current collection efficiency.

[0020] 4 to 6 are diagrams showing the manufacturing process of a tabless cylindrical secondary battery: Fig. 4 shows the structure of the electrode, Fig. 5 shows the electrode winding process, and Fig. 6 shows the process of welding a current collector plate to the folded surface area of ​​the non-coated portion.

[0021] 4 to 6, the positive electrode 10 and the negative electrode 11 have a structure in which an active material 21 is coated on a sheet-shaped current collector 20, and include an uncoated portion 22 on one long side along the winding direction X. The long side refers to the side that is parallel to the X-axis direction and has a relatively long length.

[0022] The electrode assembly A is fabricated by sequentially stacking a positive electrode 10 and a negative electrode 11 together with two separators 12, as shown in Figure 5, and then winding them in one direction (X direction). At this time, the uncoated portions of the positive electrode 10 and the negative electrode 11 are arranged in opposite directions. The upper portion of the electrode assembly A is entirely formed with a positive electrode uncoated portion 10a, and the lower portion of the electrode assembly A is entirely formed with a negative electrode uncoated portion 11a.

[0023] After the winding process, the uncoated portion 10a of the positive electrode 10 and the uncoated portion 11a of the negative electrode 11 are bent toward the core side, and then the current collector plates 30 and 31 are welded and joined to the uncoated portions 10a and 11a, respectively.

[0024] Since separate electrode tabs are not attached to the positive electrode uncoated portion 10a and the negative electrode uncoated portion 11a, and current collector plates 30 and 31 are connected to external electrode terminals, the current path is formed with a large cross-sectional area along the winding axis direction of electrode assembly A (see arrow), which has the advantage of lowering the resistance of the secondary battery. This is because resistance is inversely proportional to the cross-sectional area of ​​the path through which current flows.

[0025] In a tableless cylindrical secondary battery, to improve the welding characteristics between the non-coated portions 10a, 11a and the current collector plates 30, 31, it is necessary to apply strong pressure to the welding areas of the non-coated portions 10a, 11a to maximally flatten them. However, when bending the welding areas of the non-coated portions 10a, 11a, the patterns of the non-coated portions 10a, 11a may become irregularly distorted and deformed. In this case, the deformed areas may come into contact with the electrode of the opposite polarity, causing an internal short circuit or microcracks in the non-coated portions 10a, 11a. Furthermore, as the non-coated portion 32 adjacent to the core 33 of the electrode assembly A is bent, it may block all or a significant portion of the cavity in the core of the electrode assembly A. This causes problems during the electrolyte injection process. That is, the cavity in the core 33 of the electrode assembly A serves as a passage for injecting the electrolyte. However, if this passage is blocked, it is difficult to inject the electrolyte. Furthermore, when the electrolyte injector is inserted into the cavity in the core 33, it may interfere with the non-coated portion 32 near the core 33, causing the non-coated portion 32 to break.

[0026] In addition, the bent portions of the non-coated portions 10a, 11a where the current collector plates 30, 31 are welded must be overlapped in multiple places without any gaps. This is because sufficient welding strength can be obtained and even when using the latest technology such as laser welding, it is possible to prevent the laser from penetrating into the electrode assembly A and ablating the separator 12 or the active material 21.

[0027] Furthermore, in conventional tabless cylindrical secondary batteries, the positive electrode non-coated portion 10a is formed entirely on the top of the electrode assembly A. Therefore, when the outer periphery of the top of the battery can is pressed into the interior to form a beading portion, the peripheral region 34 of the top of the electrode assembly A is compressed by the battery can. This compression can cause partial deformation of the electrode assembly A, which can rupture the separator 12 and cause an internal short circuit. A short circuit inside the secondary battery can result in heat generation or explosion.

[0028] Considering these points, the uncoated portions 10a, 11a should not be formed entirely on the upper and lower portions of the electrode assembly A, but should be omitted in some sections. If the uncoated portions 10a, 11a are omitted in some sections, resistance due to the longitudinal current path inside the electrode assembly increases. Therefore, a low-resistance cell design that minimizes the current path should also be considered for tableless cylindrical secondary batteries. In particular, when the form factor of cylindrical secondary batteries is increased for application to electric vehicles, a large amount of heat may be generated during fast charging, which could lead to the cylindrical secondary battery catching fire. Therefore, a low-resistance cell design that minimizes the current path becomes even more important. Summary of the Invention [Problem to be solved by the invention]

[0029] The present invention has been made in light of the background of the prior art as described above, and aims to provide an electrode assembly in a cylindrical secondary battery that minimizes current paths, particularly longitudinal current paths, to implement low resistance, thereby enabling the cylindrical secondary battery to have high capacity and / or high output while also exhibiting excellent quality in terms of the degree of heat generation due to the resulting high current density.

[0030] Another object of the present invention is to provide a secondary battery including an electrode assembly with an improved structure that minimizes current paths, a battery pack including the secondary battery, and a vehicle including the battery pack.

[0031] 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]

[0032] To achieve the above object, an electrode assembly according to the present invention is an electrode assembly in which a core and an outer circumferential surface are defined by winding a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode around a winding shaft, wherein the positive electrode or the negative electrode comprises a sheet-shaped current collector having long and short sides and an uncoated portion at an end of the long side, the uncoated portion including an electrode tab-defined section used as an electrode tab and at least one undefined electrode tab section not used as an electrode tab, wherein a maximum current path for the at least one undefined electrode tab section includes a widthwise current path along the short side of the current collector and a lengthwise current path along the long side of the current collector, and wherein, when the length of the widthwise current path and the lengthwise current path are defined as L1 and L2, respectively, a current path ratio L2 / L1 is 11 or less.

[0033] Preferably, the ratio L2 / L1 of the current paths may be 10.15 or less.

[0034] The ratio L2 / L1 of the current paths may be 8.5 or less, or may be 2-5.

[0035] The electrode tab undefined section may have a height of an uncoated portion smaller than that of the electrode tab defined section.

[0036] The maximum length of the electrode tab undefined section may be 4% to 23% of the length of the positive electrode and the negative electrode.

[0037] The maximum length of the electrode tab undefined section may be 2.5 to 11 times the width of the positive electrode and the negative electrode.

[0038] According to one aspect of the present invention, the non-coated portion may include a first portion adjacent to the core, a second portion adjacent to the outer circumferential surface, and a third portion between the first portion and the second portion, and the first portion may have a smaller height in the winding axis direction than the third portion.

[0039] The third portion may be defined as an electrode tab when bent along the radial direction of the electrode assembly.

[0040] The second portion may have a height in the winding axis direction that is the same as or smaller than the third portion.

[0041] In this case, the second and third portions may be defined as electrode tabs when bent along the radial direction of the electrode assembly.

[0042] The length of the short side of the current collector may be 60 mm to 85 mm, and the length of the long side of the current collector may be 3 m to 5 m.

[0043] Here, the maximum length of the first portion along the long side of the current collector may be 4% to 23% of the length of the long side of the current collector.

[0044] The length of the first portion along the long side of the current collector may be 660 mm or less.

[0045] The first portion may correspond to the electrode tab undefined section.

[0046] The first portion may not be bent along the radial direction of the electrode assembly.

[0047] The second portion may not be bent along the radial direction of the electrode assembly.

[0048] The third portion may have a length greater than the first portion and the second portion in a winding direction of the electrode assembly.

[0049] The first portion may start from the short side of the current collector on the core side, the height of the first portion may be constant along the winding direction, and the first portion may not be bent along the radial direction of the electrode assembly.

[0050] According to another aspect of the present invention, at least a partial region of the third portion may be divided into a plurality of segmented pieces that can be bent independently.

[0051] The segment pieces are folded and stacked in the direction of the winding axis.

[0052] Preferably, the length of the short side of the current collector is 60 mm to 85 mm, the length of the long side of the current collector is 3 m to 5 m, the thickness of the current collector is 5 μm to 25 μm, the width of the segment pieces is 10 mm or less, and the height of the segment pieces is 10 mm or less.

[0053] Here, the length of the first portion along the long side of the current collector is 660 mm or less.

[0054] The electrode assembly includes, sequentially along the radial direction based on a cross section taken along the winding axis direction, segment-free sections where no segment pieces exist and uniform-height sections where the segment pieces have a uniform height, and the plurality of segment pieces are arranged in the uniform-height sections and are bent along the radial direction of the electrode assembly to form a bent surface region.

[0055] In another example, the electrode assembly may further include a height-variable section between the segment-free section and the uniform-height section, in which the height of the segment pieces is variable, and the plurality of segment pieces may be arranged in the height-variable section and the uniform-height section and bent along the radial direction of the electrode assembly to form a bent surface region.

[0056] The segment-omitted section may correspond to the electrode tab undefined section.

[0057] The second portion may not be divided into segments, and the height of the first portion and the height of the second portion may be the same.

[0058] The third portion may include one or more segment-free sections in which no segment exists along the winding direction of the electrode assembly.

[0059] Here, the height of the non-coated portion in the segment-omitted section may be the same as the height of the first portion.

[0060] The segment pieces may be located in two or more sector-shaped or polygonal regions that are circumferentially arranged relative to the core.

[0061] The segment-omitted section may correspond to the electrode tab undefined section.

[0062] The core may have a cavity, and the third portion may be defined as an electrode tab when bent along the radial direction of the electrode assembly, and the third portion may be divided into a plurality of segments that can be bent independently, and the bent segments may not obstruct the cavity.

[0063] In such a case, the maximum length of the first portion along the long side of the current collector may be 4% to 23% of the length of the long side of the current collector.

[0064] In order to achieve the other object, a secondary battery according to the present invention includes the electrode assembly according to the present invention; a cylindrical battery housing that receives the electrode assembly through an opening formed on one side and is connected to an uncoated portion of a negative electrode; a seal that seals the opening of the cylindrical battery housing so as to be insulated from the cylindrical battery housing; and a positive electrode terminal that is riveted through a through-hole formed in a bottom of the cylindrical battery housing opposite the opening of the cylindrical battery housing and is connected to the uncoated portion of a positive electrode.

[0065] Preferably, the secondary battery of the present invention further includes a positive electrode current collector electrically connected to the uncoated portion of the positive electrode, a negative electrode current collector electrically connected to the uncoated portion of the negative electrode, and a positive electrode current collector electrically connected to the uncoated portion of the negative electrode, wherein the uncoated portion of the positive electrode is exposed to the outside of the separator and the uncoated portion of the negative electrode is exposed to the outside of the separator in a direction opposite to the uncoated portion of the positive electrode.

[0066] The secondary battery may have a DC resistance of 4 mΩ or less and an AC resistance of 3 mΩ or less.

[0067] Preferably, the AC resistance of the secondary battery may be 2 mΩ or less.

[0068] The secondary battery may have a diameter to height ratio of greater than 0.4.

[0069] The seal may include a non-polar cap plate and a sealing gasket interposed between a peripheral edge of the cap plate and the open end of the cylindrical battery housing.

[0070] The positive terminal may include a main body portion inserted into the through hole, an external flange portion extending from the periphery of one side of the main body portion exposed on the outer surface of the bottom of the cylindrical battery housing along the outer surface, an internal flange portion extending from the periphery of the other side of the main body portion exposed on the inner surface of the bottom of the cylindrical battery housing toward the inner surface, and a flat portion provided on the inside of the internal flange portion.

[0071] The secondary battery may further include a positive electrode current collector electrically connected to the uncoated portion of the positive electrode and a negative electrode current collector electrically connected to the uncoated portion of the negative electrode, and the positive electrode terminal may be connected to the positive electrode current collector at the flat portion by laser welding.

[0072] The electrode tab undefined section may be a portion where no current path is formed by not connecting with the negative electrode current collector plate and the positive electrode current collector plate.

[0073] Another object of the present invention can be achieved by a battery pack including a plurality of the above-described secondary batteries.

[0074] Preferably, the plurality of secondary batteries are arranged in a predetermined number of rows, with the positive terminal of each secondary battery and the outer surface of the bottom of the battery housing facing upward.

[0075] Another object of the present invention can also be achieved by a vehicle including at least one of the above battery packs. [Effects of the Invention]

[0076] According to one aspect of the present invention, an upper limit of the current path ratio L2 / L1 in the maximum current path is proposed. This range of the current path ratio L2 / L1 allows the electrode assembly to have high capacity while minimizing internal resistance. Therefore, a secondary battery including such an electrode assembly has high capacity and / or high power, and exhibits excellent quality in terms of the degree of heat generation due to the resulting high current density.

[0077] According to another aspect of the present invention, the non-coated portions protruding upward and downward from the electrode assembly are used as electrode tabs, thereby reducing the internal resistance of the secondary battery and increasing the energy density.

[0078] According to another aspect of the present invention, the structure of the non-coated portion of the electrode assembly is improved to prevent the non-coated portion from breaking when the non-coated portion is bent, and the number of overlaps of the non-coated portion is sufficiently increased to improve the welding strength of the current collector plate.

[0079] According to yet another aspect of the present invention, a segmented piece structure is applied to the uncoated portion of the electrode, and the dimensions (width, height, and spacing pitch) of the segmented pieces are optimized to sufficiently increase the number of segmented pieces stacked in the area used as the welding target area, thereby improving the physical properties of the area where the current collector plate is welded.

[0080] According to yet another aspect of the present invention, an electrode assembly is provided in which a current collector plate is welded over a large area to a bent surface area formed by bending a segment piece, thereby improving energy density and reducing resistance.

[0081] According to yet another aspect of the present invention, a cylindrical secondary battery can be provided that has an improved design in which electrical wiring is performed at the top.

[0082] According to yet another aspect of the present invention, the problem of internal heat generation occurring during rapid charging can be alleviated by improving the positive electrode terminal structure of a cylindrical secondary battery to increase the cross-sectional area of ​​the current path.

[0083] According to another aspect of the present invention, the structure of the uncoated portion adjacent to the core of the electrode assembly is improved to prevent the cavity in the core of the electrode assembly from being blocked when the uncoated portion is bent, thereby facilitating the process of injecting the electrolyte and the process of welding the battery housing (or the positive electrode terminal) to the current collector plate.

[0084] According to yet another aspect of the present invention, there is provided a cylindrical secondary battery having a structure in which internal resistance is low, internal short circuits are prevented, and welding strength between a current collector plate and an uncoated portion is improved, as well as a battery pack and a vehicle including the same.

[0085] In particular, the present invention provides a cylindrical secondary battery having a DC resistance of 4 mΩ or less, an AC resistance of 3 mΩ or less, and a diameter to height ratio of 0.4 or more, as well as a battery pack and a vehicle including the same.

[0086] The present invention also provides various other effects, which will be explained in each embodiment, and explanations of effects that can be easily inferred by ordinary skilled artisans will be omitted.

[0087] 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]

[0088] [Figure 1] FIG. 1 is a diagram showing a state in which a positive electrode and a negative electrode applied to a conventional cylindrical secondary battery are spread out. [Figure 2]1 is a diagram schematically showing the flow of current or electrons outside a conventional cylindrical secondary battery. FIG. [Figure 3] 1 is a diagram schematically illustrating the flow of current or electrons in a positive electrode and a negative electrode that constitute an electrode assembly in a conventional cylindrical secondary battery. [Figure 4] FIG. 1 is a plan view showing the structure of an electrode used in manufacturing a conventional tabless cylindrical secondary battery. [Figure 5] 1A and 1B are diagrams showing a winding process of electrodes for a conventional tabless cylindrical secondary battery. [Figure 6] 1 shows a process in which a current collector plate is welded to the curved surface of the uncoated portion in a conventional tabless cylindrical secondary battery. [Figure 7] 1A and 1B are views illustrating an electrode assembly according to an embodiment of the present invention; [Figure 8] FIG. 8 is a diagram for explaining the background behind the setting of the ratio of the current path to the maximum current path in the electrodes included in the electrode assembly of FIG. 7 within a certain range, and is a diagram that schematically shows the flow of current or electrons in the positive and negative electrodes that make up a virtual electrode assembly. [Figure 9] 8 is a plan view showing an electrode structure of a first embodiment included in the electrode assembly of FIG. 7. FIG. [Figure 10] FIG. 1 is a schematic diagram of an electrode including an undefined section of an electrode tab used in a simulation. [Figure 11] 10 is a graph showing resistance as a function of the number of welding points confirmed by simulation. [Figure 12] 10 is a plan view showing a second embodiment of an electrode structure included in an electrode assembly according to another embodiment of the present invention. FIG. [Figure 13] 10 is a plan view showing an electrode structure of a third embodiment included in an electrode assembly according to another embodiment of the present invention. FIG. [Figure 14] FIG. 10 is a plan view showing an electrode structure of a fourth embodiment included in an electrode assembly according to another embodiment of the present invention. [Figure 15] FIG. 10 is a plan view showing an electrode structure of a fifth embodiment included in an electrode assembly according to another embodiment of the present invention. [Figure 16]10 is a diagram showing the definition of the width, height and spacing pitch of segment pieces according to an embodiment of the present invention. FIG. [Figure 17] FIG. 10 is a plan view showing a modified structure of an electrode according to a fifth embodiment of the present invention. [Figure 18] 10 is a top view showing independent areas where multiple segment pieces can be located when an electrode according to a modified example of the present invention is wound into an electrode assembly. FIG. [Figure 19] FIG. 10 is a plan view showing the structure of an electrode according to a sixth embodiment of the present invention. [Figure 20] FIG. 10 is a diagram showing the definition of the width, height, and spacing pitch of segments included in an electrode according to a sixth embodiment of the present invention. [Figure 21] 1 is a top perspective view schematically illustrating an electrode assembly having a folded surface region formed thereon; FIG. [Figure 22] FIG. 10 is a cross-sectional view of a jelly roll-type electrode assembly in which one of the electrodes of the fifth and sixth embodiments (modifications thereof) is applied to the positive and negative electrodes, taken along the Y-axis direction (winding axis direction). [Figure 23] FIG. 10 is a plan view showing a modified structure of an electrode according to a fifth embodiment of the present invention. [Figure 24] 1 is a cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention. [Figure 25] 1 is a diagram illustrating a schematic configuration of a battery pack according to an embodiment of the present invention; [Figure 26] FIG. 26 is a diagram for explaining a vehicle including the battery pack of FIG. 25. DETAILED DESCRIPTION OF THE INVENTION

[0089] 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 this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical concept of the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of terms in order to best explain the invention. 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 concept of the present invention, and therefore, various equivalents and modifications that can be substituted therefor may exist at the time of filing this application.

[0090] 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.

[0091] When two comparison objects are "identical," it means that they are "substantially identical." Therefore, "substantially identical" may include deviations that are considered low in the art, for example, deviations within 5%. Furthermore, uniformity of any parameter in a given region may mean uniformity on average.

[0092] Throughout the specification, unless otherwise specified, each element may be singular or plural.

[0093] When any structure is placed "on top (or bottom)" of a component or "above (or below)" a component, it can mean that the structure is placed directly on the top (or bottom) surface of the component, but also that other structures may be interposed between the component and any structure placed above (or below) the component.

[0094] Furthermore, when a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the components may be directly coupled or connected to each other, but there may also be other components "intervening" between the components, or each component may be "coupled," "coupled," or "connected" by other components. Furthermore, "coupled" may include electrical or physical connections.

[0095] For ease of explanation, in this specification, the direction along the longitudinal direction of the winding shaft of the electrode assembly wound into a jelly roll is referred to as the winding axis direction (Y-axis direction), the direction surrounding the winding shaft is referred to as the circumferential direction or circumferential direction (X-axis direction), and the direction toward or away from the winding shaft is referred to as the radial direction.

[0096] One feature of the present invention is to set a maximum current path in the positive and / or negative electrodes constituting a jelly-roll-type electrode assembly in order to minimize resistance in a cylindrical secondary battery. In particular, the present invention provides an upper limit for the current path ratio L2 / L1, where L1 is the length of the current path in the width direction along the short side of the current collector and L2 is the length of the current path in the length direction along the long side of the current collector. This range of current path ratio allows the electrode assembly to have high capacity while minimizing internal resistance. Exceeding the upper limit of the current path ratio L2 / L1 will result in the secondary battery failing to meet its minimum resistance requirements (e.g., DC resistance of 4 mΩ or less and AC resistance of 3 mΩ or less).

[0097] First, an electrode assembly according to an embodiment of the present invention will be described. Figure 7 is a view illustrating an electrode assembly according to an embodiment of the present invention.

[0098] Referring to FIG. 7, the electrode assembly 100 includes a positive electrode 40, a negative electrode 50, and a separator 60 interposed therebetween. The electrode assembly 100 may be a jelly-roll type electrode assembly having a structure in which the positive electrode 40, the negative electrode 50, and the separator 60 are wound in one direction. The electrode assembly 100 may be manufactured by winding a stack formed by stacking the positive electrode 40, the separator 60, the negative electrode 50, and the separator 60 in this order at least once around a winding axis B in one direction (the X-axis direction in the drawing). The innermost part of the electrode assembly 100 is defined as the core, and the outermost part is defined as the outer periphery. The X-axis direction is the winding direction.

[0099] The core may have a cavity. The diameter of the cavity may be, for example, 2 mm to 8 mm. The cavity may be the area where the winding core, which serves as the winding shaft, has been removed. A smaller diameter of the cavity is advantageous for utilizing the internal space of the battery housing including the electrode assembly 100. However, since the electrode assembly 100 cannot be manufactured without using a winding core, the diameter of the cavity cannot be zero. Furthermore, since the cavity serves as a passageway for the electrolyte during electrolyte injection, it must be at least a certain size to ensure smooth impregnation of the electrolyte. Therefore, it is preferable that the diameter of the cavity be at least 2 mm to allow for a sufficient winding process. A diameter of the cavity exceeding 8 mm is undesirable from the viewpoint of energy density due to inefficient utilization of the internal space.

[0100] The positive electrode 40 has a structure in which a positive electrode active material layer 40b is coated on one or both sides of a sheet-shaped positive electrode current collector having long and short sides, and includes a positive electrode uncoated portion 40a at the end of one long side along the winding direction where the active material is not coated. Here, the long side refers to a side that is parallel to the X-axis direction and has a relatively long length. The X-axis direction may also be referred to as the longitudinal direction. The short side refers to a side that is parallel to the Y-axis direction in the drawing and is shorter than the long side. The Y-axis direction may also be referred to as the width direction.

[0101] The positive electrode uncoated portion 40a is defined as an electrode tab, which distinguishes it from conventional techniques in which a strip-shaped electrode tab is separately attached. Here, being defined as an electrode tab means that it will be a portion that will be connected to a current collector plate to form a current path during secondary battery manufacturing. Furthermore, only a portion of the positive electrode uncoated portion 40a is defined as an electrode tab. This means that a portion of the positive electrode uncoated portion 40a will not be used as an electrode tab. The portion not used as an electrode tab may be a portion that is not connected to a current collector plate and therefore will not form a current path, such as having a smaller height in the winding axis direction (Y-axis) than the other portions of the positive electrode uncoated portion 40a or being omitted in some sections. This distinguishes it from conventional techniques in that only a portion of the positive electrode uncoated portion 40a is defined as an electrode tab. The positive electrode uncoated portion 40a may include an electrode tab-defined section that is used as an electrode tab and at least one electrode tab-undefined section that is not used as an electrode tab.

[0102] The negative electrode 50 also has a structure in which a negative electrode active material layer 50b is coated on one or both sides of a sheet-shaped negative electrode current collector having long and short sides, and includes a negative electrode uncoated portion 50a at the end of one long side along the winding direction where the active material is not coated. The negative electrode uncoated portion 50a is also defined as an electrode tab. In addition, only a portion of the negative electrode uncoated portion 50a is defined as an electrode tab. In this way, the negative electrode uncoated portion 50a may also include an electrode tab-defined section used as an electrode tab and at least one electrode tab-undefined section not used as an electrode tab.

[0103] The positive electrode uncoated portion 40a and the negative electrode uncoated portion 50a are arranged in opposite directions, and the electrode assembly 100 has a substantially cylindrical shape after winding. The positive electrode uncoated portion 40a is located at the upper end of the electrode assembly 100, and the negative electrode uncoated portion 50a is located at the lower end of the electrode assembly 100. In this electrode assembly 100, the upwardly protruding portion of the positive electrode uncoated portion 40a and the downwardly protruding portion of the negative electrode uncoated portion 50a are used as electrode tabs, and by welding and connecting the respective current collector plates to these electrode tabs, a tabless cylindrical secondary battery with improved current collection efficiency can be manufactured. Using the upwardly and downwardly protruding uncoated portions 40a and 50a of the electrode assembly 100 as electrode tabs reduces the internal resistance of the secondary battery and increases its energy density.

[0104] The electrode assembly 100 according to one embodiment of the present invention is further distinguished from the prior art in that, in the positive electrode 40 or negative electrode 50 included in the electrode assembly 100, the ratio L2 / L1 ("current path ratio") of the length L2 of the longitudinal current path along the long side of the current collector that constitutes the second path of the electrode to the length L1 of the widthwise current path along the short side of the current collector that constitutes the second path (maximum current path) of the electrode is 11 or less.

[0105] The short and long sides of the electrode current collector correspond to the width and length of the electrode, respectively. Therefore, in the maximum current path of the positive electrode 40 or the negative electrode 50, the ratio L2 / L1 of the length L2 of the longitudinal current path to the length L1 of the widthwise current path is 11 or less.

[0106] The reason why the ratio of the current paths in the maximum current paths in the electrodes included in the electrode assembly is set within a certain range as described above in the present invention will be explained with reference to Figure 8. Figure 8 shows a schematic diagram of the flow of current or electrons in the positive and negative electrodes that make up a virtual electrode assembly (the connection position between the first and second paths is indicated by a triangle, and the end points of the electrodes are indicated by a square).

[0107] The positive electrode 10′ and negative electrode 11′ shown in FIG. 8 have a structure in which, for example, in the conventional technology described with reference to FIGS. 4 to 6, the non-coated portion 10a of the positive electrode 10 and the non-coated portion 11a of the negative electrode 11 are notched in the width direction to form multiple positive electrode tabs 10c and multiple negative electrode tabs 11c.

[0108] If an electrode assembly including positive electrode 10' and negative electrode 11' shown in Figure 8 is manufactured into a cylindrical secondary battery and the module bus bar welding position is the same as that of the secondary battery described with reference to Figure 2, the first path, which is the path leading to electrode tabs 10c and 11c of each electrode 10' and 11', will also be the same as that of the secondary battery described with reference to Figure 2. However, the second path (maximum current path) of electrodes 10' and 11' is clearly different from that of Figure 3, as shown in Figure 8.

[0109] In Figure 8, the widthwise current path length of both the positive electrode 10' and the negative electrode 11' is short, and the longitudinal movement is shorter than the conventional second path shown in Figure 3 due to the nearly continuous uncoated portions 10a and 11a. In particular, if the positive electrode tab 10c of the positive electrode 10' and the negative electrode tab 11c of the negative electrode 11' are positioned corresponding to each other at the top and bottom of the electrode assembly, the longitudinal movement is almost nonexistent or very short, as shown. As a result, the maximum current path of the electrodes 10' and 11' is substantially the same as the widthwise current path of the electrodes.

[0110] That is, if the positive electrode 10' and the negative electrode 11' have the electrode structure shown in Figure 8, the length of the maximum current path in the width direction is short, practically equal to the distance in the width direction of the electrode, and the current path in the longitudinal direction of the electrode is very short, so the ratio of the current path is close to 0.

[0111] However, the length of the longitudinal current path of the maximum current path of the electrode may vary depending on the structure of the electrode tabs (uncoated areas), as described with reference to Figure 3. Figure 8 shows a structure in which electrode tabs 10c, 11c are formed almost continuously along the longitudinal direction of electrodes 10', 11', but preferably there may be areas where the electrode tabs are removed.

[0112] For example, an electrode assembly according to an embodiment of the present invention may have an uncoated portion bent toward the core. In this case, to prevent the bent uncoated portion from blocking a cavity in the core, the uncoated portion close to the core may not be bent, may have a reduced height in the winding direction, or may be removed to form the aforementioned undefined electrode tab section. The undefined electrode tab section may be formed near the core side of the electrode assembly after the electrode is wound. The undefined electrode tab section may be formed at multiple locations between one end and the other end in the longitudinal direction of the electrode before winding. The length of the undefined electrode tab section in the winding direction may be varied depending on the position and length of the undefined electrode tab section. When an electrode includes multiple undefined electrode tab sections, the maximum current path of the electrode may be defined by the undefined electrode tab section with the longest length in the winding direction. Because electrons should move toward the undefined electrode tab sections in the undefined electrode tab sections, the maximum current path is defined by the longest undefined electrode tab section. Therefore, as the length of the electrode tab undefined section in the winding direction increases, the proportion of the current path becomes longer than that shown in Fig. 8. In addition, the proportion of the current path may vary depending on the position of the electrode tab defined section.

[0113] The maximum current path varies depending on how the electrode tab-defined section is positioned, and the smaller the maximum current path, the lower the electrode resistance. However, when designing an electrode assembly, it is necessary to include an electrode tab-undefined section in a portion of the non-coated portion, which can increase resistance. Therefore, in the present invention, an upper limit is set for the current path ratio L2 / L1 of the maximum current path relative to the electrode tab-undefined section to satisfy the low resistance condition. That is, the range of the current path ratio L2 / L1 can be limited so that the resistance of the secondary battery does not increase beyond a predetermined range.

[0114] In this way, the present invention is characterized in that at least a portion of the non-coated portion includes an electrode tab undefined section, and the upper limit of the current path ratio L2 / L1 of the maximum current path to the electrode tab undefined section is limited to a predetermined range. In other words, the present invention provides a guide for determining the length of the electrode tab undefined section while minimizing the increase in resistance of the secondary battery.

[0115] FIG. 9 is a plan view showing the electrode structure of the first embodiment included in the electrode assembly of FIG.

[0116] 9, an electrode 140, which is the positive electrode 40 or the negative electrode 50 shown in FIG. 7, includes an electrode current collector 141 made of a metal foil and an active material layer 142. The metal foil may be a conductive metal, such as aluminum or copper, and is appropriately selected depending on the polarity of the electrode 140. The thickness of the positive electrode current collector (foil) may be 10 μm to 20 μm, and the thickness of the negative electrode current collector (foil) may be 5 μm to 15 μm.

[0117] The length of the short side of the current collector 141 may be 60 mm to 85 mm, and the length of the long side of the current collector 141 may be 3 m to 5 m. In this case, the ratio of the short side to the long side of the current collector 141 may be 1.2% to 2.8%, which is significantly smaller than the 6% to 11% level in cylindrical secondary batteries having an 1865 or 2170 form factor. In other words, the current collector 141 is very long in the longitudinal direction and has a very large number of turns when wound up. The number of turns may be counted based on the core-side end of the electrode assembly 100.

[0118] An active material layer 142 is formed on at least one surface of the current collector 141. The active material layer 142 is formed along the winding direction (X-axis direction). The electrode 140 includes an uncoated portion 143 at the end of a long side in the winding direction. The uncoated portion 143 is a partial area of ​​the current collector 141 that is not coated with active material. A part of the uncoated portion 143 in the winding direction is set as an electrode tab undefined section, and the rest is set as an electrode tab defined section.

[0119] The electrode 140 is manufactured by forming an active material layer 142 on a current collector 141 and then compressing the resultant. Preferably, an insulating coating layer 144 may be formed at the boundary between the active material layer 142 and the non-coated portion 143. The insulating coating layer 144 is formed so that at least a portion of the insulating coating layer 144 overlaps the boundary between the active material layer 142 and the non-coated portion 143. The insulating coating layer 144 prevents short-circuiting between two electrodes 140 of opposite polarity that face each other across a separator (see 60 in FIG. 7 ), i.e., the positive electrode 40 and the negative electrode 50. The insulating coating layer 144 may have a width of 0.3 mm to 5 mm and cover the boundary between the active material layer 142 and the non-coated portion 143. The width of the insulating coating layer 144 may vary along the winding direction of the electrode 140. The insulating coating layer 144 includes a polymer resin and may also include an inorganic filler such as Al2O3. The portion of the current collector 141 covered with the insulating coating layer 144 is not an area coated with an active material layer, and can therefore be considered an uncoated portion.

[0120] The non-coated portion 143 includes a first portion B1 (core-side non-coated portion) adjacent to the core of the electrode assembly 100, a second portion B3 (outer-side non-coated portion) adjacent to the outer peripheral surface of the electrode assembly 100, and a third portion B2 (middle non-coated portion) between the first portion B1 and the second portion B3.

[0121] The B1 / B2 boundary may be appropriately defined as a point where the height (or change pattern) of the uncoated portion substantially changes as one moves from the core side to the outer periphery of the electrode assembly, or as a predetermined percentage point based on the radius of the electrode assembly (e.g., 5%, 10%, 15% of the radius, etc.). The B2 / B3 boundary may also be defined as a point where the height (or change pattern) of the uncoated portion substantially changes as one moves from the outer periphery to the core side of the electrode assembly, or as a predetermined percentage point based on the radius of the electrode assembly (e.g., 85%, 90%, 95% of the radius, etc.). Once the B1 / B2 boundary and the B2 / B3 boundary are identified, the third portion B2 may be automatically identified.

[0122] It is not excluded that another structure is interposed between the first portion B1 and the third portion B2, and it is also not excluded that another structure is interposed between the third portion B2 and the second portion B3.

[0123] In this embodiment, the height of the uncoated portion 143 is not uniform, but varies relative to the winding direction. That is, the first portion B1 has a smaller height in the winding axial direction than the third portion B2. After forming the uncoated portion 143 to have a uniform height, the uncoated portion of the first portion B1 can be cut further than the uncoated portion of the third portion B2 to create a height difference. Here, the height of each portion may be an average height or a maximum height, and the same applies hereinafter.

[0124] The height of the first portion B1 and the second portion B3 in the winding axis direction is equal to or greater than 0, and the heights of the first portion B1 and the second portion B3 may be the same or different. In this embodiment, the heights of the first portion B1 and the second portion B3 are different from each other, and the height of the second portion B3 is the same as the height of the third portion B2.

[0125] In this embodiment, the first portion B1 is an electrode tab undefined section, and the third portion B2 is an electrode tab defined section. The second portion B3 may also be set as an electrode tab defined section. The third portion B2 may be defined as an electrode tab when bent along the radial direction of the electrode assembly 100. Similarly, the second portion B3 may also be defined as an electrode tab when bent along the radial direction. Because the first portion B1 is not bent along the radial direction and does not make electrical contact with the current collector plate (described later), when an oxidation-reduction reaction occurs in the first portion B1, current (electrons) bypasses and flows through the adjacent third portion B2.

[0126] In the electrode 140 having such a structure, the second portion B3 can be bent to become a welding area. B2 is the length d of the first part B1 B1 The length d of the third portion B2 may be longer than B2 is the length d of the second part B3 B3 The length d of the third portion B2 may be longer thanB2 By increasing the length d of the third portion B2, the folded portions can be overlapped in multiple places when folded. B2 By making the length longer, a sufficient welding area can be secured.

[0127] Preferably, the first portion B1, which is the electrode tab undefined section, is close to the core. The first portion B1 is wound first, followed by the third portion B2. Because the third portion B2 is positioned farther from the core by the first portion B1, the third portion B2 is not deformed when it is bent.

[0128] The first portion B1 has a small height and cannot be bent, so it does not block the cavity in the core of the electrode assembly 100. If the cavity in the core is not blocked, the electrolyte injection process becomes easier and the efficiency of electrolyte injection improves. In addition, a welding jig can be inserted through the core to easily perform the welding process between the negative (or positive) electrode side current collector plate and the battery housing (or electrode terminal).

[0129] After forming the uncoated portion 143 with a uniform height, the uncoated portion of the first portion B1 is cut further than the uncoated portion of the third portion B2 to create a height difference, so that the first portion B1 is not used as an electrode tab. When the uncoated portion 143 includes an undefined section for an electrode tab, the resistance increases as the maximum current path increases compared to when the entire uncoated portion is designed as an electrode tab defined section.

[0130] Preferably, the first portion B1 is necessary to prevent the electrode tab-defining section from being folded over and blocking the cavity of the core. The length d of the first portion B1 B1 Even if the length of the third part B2 is increased, the length d B2 and the length of the second part B3, d B3 If the length d of the first part B1 is relatively long or the welding area secured by the third part B2 is sufficient, the resistance (AC resistance and DC resistance) of the whole cell may not change much, but the resistance in the first part B1 will increase. Therefore, taking into account the increase in the resistance in the first part B1, B1needs to be limited.

[0131] In the ratio L2 / L1 of the current path to the maximum current path, the denominator is constant as the width of the electrode. B1 is a factor that determines the ratio L2 / L1 of the current path of the maximum current path. B1 By adjusting the ratio L2 / L1 of the current path of the maximum current path to 11 or less, the closure of the cavity in the core is prevented while minimizing an increase in resistance. Preferably, the ratio L2 / L1 of the current path of the maximum current path is 10.15 or less. More preferably, the ratio L2 / L1 of the current path of the maximum current path is 8.5 or less. More preferably, the ratio L2 / L1 of the current path of the maximum current path is 2 to 5. Each value is determined based on the electrical, physical, and chemical properties of the current collector 141 and the active material layer 142, the resistance conditions of the secondary battery, and the length d of the first portion B1 required to avoid blocking the cavity in the core. B1 , the length d of the second portion B3 necessary to have an appropriate overlap number and to ensure an effective welding area B3 , and the length of the third part B2 is d B2 In this way, the present invention adjusts the number and length of the electrode tab undefined sections while limiting the current path ratio L2 / L1 of the maximum current path to a predetermined range, and designs the remaining sections as electrode tab defined sections.

[0132] Figure 9 shows the maximum current path according to one embodiment (the connection point between the first and second paths is indicated by a triangle, and the end points of the electrodes are indicated by a square). The maximum current path is included in the first part B1, which is an undefined section of the electrode tab. The maximum current path is the path along which the length of the current (electrons) flows is the longest when an electrochemical redox reaction occurs in the first part B1.

[0133] The length L1 of the current path in the width direction of the maximum current path is short on the same level as the length of the short sides of the current collector 141 and the electrode 140. Specifically, the length L1 of the current path in the width direction is the minimum length from one end of the long side of the uncoated portion 143 to the other end of the long side of the current collector 141. Because the heights of the second portion B3 and the third portion B2 are the same, the length of the current path in the width direction of the electrode 140 is the same as the length (width) of the short side of the electrode 140, and because the uncoated portion of the second portion B3 is not cut, it is also the same as the length of the short side of the current collector 141.

[0134] In this embodiment, the current path ratio of the maximum current path is L2 / L1, where L1 corresponds to the width of the electrode 140. Therefore, the current path ratio is calculated by dividing the length d of the first portion B1 by the length d of the first portion B1. B1 can be adjusted using

[0135] The upper limit of the current path ratio L2 / L1 may be a value that makes the DC resistance of a secondary battery including the electrode assembly 100 4 mΩ or less and the AC resistance of a secondary battery including the electrode assembly 100 3 mΩ or less. More preferably, the upper limit of the current path ratio L2 / L1 may be a value that makes the AC resistance of a secondary battery including the electrode assembly 100 2 mΩ or less.

[0136] The resistance of the secondary battery varies depending on the electrical, physical, and chemical properties of the current collector 141 and the active material layer 142. For example, when the length of the short side of the current collector 141 is 60 mm to 85 mm, the length of the long side of the current collector 141 is 3 m to 5 m, and the thickness of the current collector 141 is 5 μm to 20 μm, the length d B1 In such a case, the length d of the first portion B1 may be 660 mm or less. B1 The maximum value of the length d of the first portion B1 is 660 mm, and considering the length of the long side of the current collector 141, B1 The maximum value of may be 13.2% to 22% of the length of the long side of the current collector 141. When the length or thickness of the long side of the current collector 141 changes, the length d B1The maximum value of the length of the portion of the electrode 140 that is not defined as an electrode tab, i.e., the maximum value of the length of the electrode tab undefined section, is 660 mm. Considering that the length of the long side of the current collector 141 is the same as the length of the long side of the electrode 140, this can be said to be 4% to 23% of the length of the electrode 140. Also, if the length of the short side of the current collector 141 is the same as the length of the short side of the electrode 140, it can be seen that the maximum length of the portion of the electrode 140 that is not defined as an electrode tab, 660 mm, is 9.4 to 11 times the width of the electrode 140. When the length or thickness of the short side of the current collector 141 changes, the length d of the first portion B1 B1 The maximum value can be 2.5 to 11 times.

[0137] Also, the length d of the first portion B1 B1 When the length d of the first portion B1 is 660 mm, if the length of the long side of the current collector 141 is 4 mm, the ratio L2 / L1 of the current paths can be 10.15. B1 The ratio L2 / L1 of the current paths can be further reduced by making the length of the wire shorter than 660 mm.

[0138] The upper limit of the current path ratio L2 / L1 may satisfy the minimum resistance requirement of the secondary battery. That is, it may be determined to indicate a resistance of the secondary battery that is smaller than the maximum resistance of the secondary battery. The values ​​of 4 mΩ, which is the maximum DC resistance, and 3 mΩ, which is the maximum AC resistance, used in this embodiment may vary depending on the specifications of the secondary battery.

[0139] The inventors confirmed through simulation that the resistance of a secondary battery increases as the length of the undefined electrode tab section increases, as in the first portion B1. However, they also confirmed that once the length of the undefined electrode tab section exceeds a certain level, the resistance does not increase any further and converges. By examining the correlation between the length of the undefined electrode tab section and the resistance of a secondary battery, they were able to determine the length of the undefined electrode tab section that satisfies the minimum resistance requirement of the secondary battery.

[0140] FIG. 10 is a schematic diagram of an electrode including an undefined section of the electrode tab used in the simulation, and FIG. 11 is a graph of resistance according to the number of welding points confirmed by the simulation.

[0141] 10 shows a case where the electrode tabs 143a1 are evenly spaced, with the connection positions of the first and second paths indicated by ▲ and the end points of the electrodes indicated by ■. For example, if the number of electrode tabs 143a1 is six, the number of electrode tab undefined sections 143a2 is seven, and if the number of electrode tabs 143a1 is seven, the number of electrode tab undefined sections 143a2 is eight. An even spacing condition was assumed where the number of electrode tabs 143a1 is Q and the number of electrode tab undefined sections 143a2 is Q+1. Because each electrode tab 143a1 is welded to a current collecting plate, the number of welding points is the same as the number of electrode tabs 143a1.

[0142] In the simulation, it was assumed that the length of the short side of the current collector 141' included in the electrode 140' was 60 mm to 85 mm, the length of the long side of the current collector 141' was 3 m to 5 m, and the thickness of the current collector 141' was 5 μm to 20 μm.

[0143] The AC resistance of a secondary battery including an electrode assembly in which such electrodes 140' are included in the positive and negative electrodes was simulated while increasing the number of electrode tabs 143a1 from 1 to 50. Referring to the results shown in Figure 11, it was found that the resistance converges as the number of electrode tabs 143a1 increases, and it was found that the number of electrode tabs 143a1 that would keep the AC resistance of the secondary battery below 2 mΩ under the simulation conditions was 6.

[0144] The number of electrode tabs 143a1 can be converted into the length of the electrode tab undefined section 143a2. When the width of the electrode tab 143a1 is 10 mm and there are six electrode tabs 143a1 evenly spaced on the current collector 141' whose long side is 3 to 5 m long, the length of one electrode tab undefined section 143a2 is 660 mm. When there are seven electrode tabs 143a1, the length of one electrode tab undefined section 143a2 is 564 mm. When there are seven electrode tabs 143a1, the AC resistance of the secondary battery was simulated to be 1.7 mΩ.

[0145] From these simulations, it was found that the length of the electrode tab undefined section 143a2 is preferably 660 mm or less. Considering that the short side of the current collector 141' has a length of 60 mm to 85 mm, the ratio of the length of the electrode tab undefined section 143a2, which is the longitudinal current path, to the length of the short side of the current collector 141', which is the widthwise current path, is 11 or less. As a result, it was found that when an electrode tab undefined section is included, if the current path ratio L2 / L1 is 11 or less, the low resistance condition of 2 mΩ or less AC resistance of the secondary battery can be met.

[0146] Based on the results of such simulations, the length d of the first portion B1 is set as proposed in this embodiment. B1 In other words, the length of the electrode tab undefined section 143a2 is controlled so as not to exceed 660 mm, so that the cell resistance satisfies the minimum resistance requirement of the secondary battery.

[0147] Length d of the first portion B1 B1 If the length of the first portion B1 is longer, the ratio L2 / L1 of the current path becomes larger. B1 If the length d of the first portion B1 is shorter, the ratio L2 / L1 of the current path becomes smaller. B1 can be designed under the condition that when the uncoated portion of the third part B2 is bent toward the core, the cavity provided in the core of the electrode assembly 100 is not blocked, and the condition of the current path ratio L2 / L1 is satisfied.

[0148] That is, the length d of the first portion B1 B1 The length d of the first part B1 is 660 mm or less and may be determined by requirements. B1 When the length of the short side of the current collector 141 is 65 mm, the ratio L2 / L1 of the current paths is 10.15. Therefore, the length d B1 In other words, if the electrode 140 is designed to include the first portion B1, the current path ratio increases compared to when the first portion B1 does not exist and the entire electrode includes an uncoated portion such as the third portion B2. However, as a guide to satisfy the minimum resistance, the length d of the first portion B1 must be increased until the current path ratio L2 / L1 becomes 10.15 or less. B1 Since the thickness of the non-coated portion of the third portion B2 can be increased, when the non-coated portion of the third portion B2 is bent toward the core, the cavity provided in the core of the electrode assembly 100 can be prevented from being blocked.

[0149] FIG. 12 is a plan view showing a second embodiment of an electrode structure included in an electrode assembly according to another embodiment of the present invention.

[0150] The electrode 145a shown in FIG. 12 differs from the first embodiment only in that the height of the second portion B3 gradually decreases toward the outer periphery, and the remaining configuration is substantially the same. In one modification, the second portion B3 can be deformed in a stepped manner (see dotted lines) in which the height decreases stepwise. Here, the second portion B3 has a height smaller than the third portion B2. By making the second portion B3 smaller in height than the third portion B2, deformation of the third portion B2 can be further suppressed when the second portion B3 is bent over the bent third portion B2.

[0151] FIG. 13 is a plan view showing an electrode structure of a third embodiment included in an electrode assembly according to another embodiment of the present invention.

[0152] In the third embodiment, the electrode 145b has a first portion B1 and a second portion B3 whose heights are greater than or equal to 0 and are relatively smaller than the third portion B2. The first portion B1 and the second portion B3 have the same height. Similar to the first portion B1, the second portion B3 corresponds to an undefined electrode tab section, and the uncoated portion of the second portion B3 is not defined as an electrode tab, while the third portion B2 is defined as an electrode tab. In the winding direction, the length of the second portion B3 is d B1 The second portion B3 may be an uncoated portion of the electrode region including the outermost winding turn. The third portion B2 may be defined as an electrode tab when folded along the radial direction of the electrode assembly 100. The first portion B1 and the second portion B3 are not folded along the radial direction. According to this embodiment, when the electrode assembly is inserted into the battery housing and the outer circumferential surface of the battery housing is pressed inward to form a beading portion, the beading portion and the second portion B3 may come into contact with each other during the process of pressurizing the beading portion around the second portion B3, thereby preventing an internal short circuit.

[0153] FIG. 14 is a plan view showing a fourth embodiment of an electrode structure included in an electrode assembly according to another embodiment of the present invention.

[0154] In the fourth embodiment, the heights of the first and second portions B1 and B3 of the electrode 150 are equal to or greater than 0, but are relatively smaller than the height of the third portion B2. The heights of the first and second portions B1 and B3 may be the same or different.

[0155] Preferably, the height of the third portion B2 may be stepped, increasing stepwise from the core side toward the outer periphery.

[0156] Patterns 1 to 7 divide the third portion B2 around the positions where the height of the non-coated portion 143 changes. Preferably, the number of patterns and the height (length in the Y-axis direction) and width (length in the X-axis direction) of each pattern can be adjusted to maximize stress dispersion during the bending process of the non-coated portion 143. The stress dispersion is intended to prevent the non-coated portion 143 from breaking when it is bent toward the core of the electrode assembly.

[0157] Length d of the first portion B1 B1 is designed so that the cavity provided in the core is not blocked when the pattern of the third portion B2 is bent toward the core side. B1 can increase in proportion to the fold length of pattern 1. The fold length is the height of the pattern relative to the fold point of the pattern.

[0158] Preferably, the length d of the first portion B1 B1 The length d of the first portion B1 may be set so that the radial width of the wound turn formed by the first portion B1 is equal to or greater than the bending length of the pattern 1. B1 may be set so that the value obtained by subtracting the radial width of the wound turn formed by the first portion B1 from the bent length of pattern 1 is less than 0 or 10% or less of the core radius.

[0159] In a specific example, when the electrode 150 is used to manufacture an electrode assembly for a cylindrical secondary battery having a form factor of 4680, the length d of the first portion B1 is B1 The length d of the first portion B1 can be set to 180 mm to 350 mm depending on the diameter of the core and the bending length of the pattern 1. In this case, the ratio L2 / L1 of the current paths can be 2.57 to 5.83. B1 Further adjustment can be made so that the ratio of current paths L2 / L1 is 2-5.

[0160] In one embodiment, the width of each pattern can be designed to accommodate one or more winding turns of the electrode assembly.

[0161] In one modification, the height of the third portion B2 may be stepped, increasing and then decreasing from the core side toward the outer periphery.

[0162] In another variation, the second portion B3 can be modified to have the same structure as in the second embodiment.

[0163] Also, in another variant, the pattern structure applied to the third portion B2 may extend to the second portion B3 (see dotted line).

[0164] FIG. 15 is a plan view showing a fifth embodiment of an electrode structure included in an electrode assembly according to another embodiment of the present invention.

[0165] Preferably, in the electrode 160, the third portion B2 may include a plurality of segment pieces 161. In other words, at least a portion of the third portion B2 may be divided into a plurality of segment pieces 161 that can be bent independently.

[0166] The height of the plurality of segment pieces 161 may increase stepwise from the core side to the outer periphery side. The plurality of segment pieces 161 may have a geometric shape in which the width decreases from the bottom to the top. Preferably, the geometric shape may be a trapezoid. As will be described later, the shape of the geometric shape may be variously modified.

[0167] The segments 161 may be laser notched. The segments 161 may be formed by known metal foil cutting processes such as ultrasonic cutting or punching. The segments 161 are folded and overlapped in the direction of the winding axis.

[0168] The segment pieces 161 are preferably bendable independently, which further reduces deformation of the non-coated portion 143 when the segment pieces 161 are bent. Another advantage is that the segment pieces 161 can be folded and overlapped in multiple layers to prevent gaps (gaps). The structure of the segment pieces 161 prevents the non-coated portion 143 from tearing when bent.

[0169] The first portion B1 starts from the short side of the current collector 141 on the core side, and the height of the first portion B1 is constant along the winding direction and is not bent along the radial direction. Only the segment 161 of the third portion B2 is defined as an electrode tab. Therefore, in the electrode 160, in order to ensure that the current path ratio L2 / L1, which is the ratio of the length L2 of the longitudinal current path along the long side of the current collector 141 to the length L1 of the width direction of the current path along the short side of the current collector 141, is 11 or less, the length from the core side end of the electrode 160 to the bottom end of the segment 161 located first in the longitudinal direction, here, the length d of the first portion B1, is B1 The length of the same can be adjusted.

[0170] Preferably, the thickness of the current collector 141 is 5 μm to 25 μm, the width of the segment 161 (see D in FIG. 16) is 3 mm to 10 mm, and the height of the segment (see H in FIG. 16) is 10 mm or less.

[0171] On the other hand, the plurality of segment pieces 161 may be divided into a plurality of segment piece groups from the core side toward the outer periphery side. At least one of width, height, and spacing pitch of segment pieces belonging to the same segment piece group may be substantially the same. Preferably, width, height, and spacing pitch of segment pieces belonging to the same segment piece group may be the same.

[0172] The dimensions (width, height, spacing pitch) of the segment pieces 161 can be adjusted taking into consideration resistance, ease of processing (e.g., whether laser notching can be applied without cracking), ease of bending, and the degree of overlap between multiple segment pieces 161.

[0173] Preferably, the width and height of segments belonging to the same segment group may be substantially the same.

[0174] FIG. 16 shows the definition of the width D, height H and spacing pitch P of the trapezoidal segment pieces 161.

[0175] Referring to FIG. 16, the width D, height H, and spacing pitch P of the segment pieces 161 are designed to prevent the non-coated portion 143 from breaking near the bending point when the non-coated portion 143 is bent, and to ensure sufficient welding strength by sufficiently increasing the number of overlaps of the non-coated portion 143 to prevent abnormal deformation of the non-coated portion 143.

[0176] The segment pieces 161 are bent along or above a line G that passes through the lower end of the cutting groove 163. The cutting groove 163 allows the segment pieces 161 to be smoothly and easily bent in the radial direction of the electrode assembly.

[0177] The width D of the segment piece 161 is defined as the length between two points where two straight lines extending from both side edges 163b of the segment piece 161 intersect with a straight line extending from the bottom 163a of the cutting groove 163. The height H of the segment piece 161 is defined as the shortest distance between the top edge of the segment piece 161 and a straight line extending from the bottom 163a of the cutting groove 163. The separation pitch P of the segment pieces 161 is defined as the length between two points where a straight line extending from the bottom 163a of the cutting groove 163 intersects with a straight line extending from the two side edges 163b connected to the bottom 163a. ​​When the side edges 163b and / or the bottom edge 163a are curved, the straight lines may replace tangents extending from the side edges 163b and / or the bottom edge 163a at the intersections where the side edges 163b and the bottom edge 163a intersect.

[0178] Preferably, the width D of the segment pieces 161 is 1 mm or more. If D is less than 1 mm, when the segment pieces 161 are bent toward the core, regions or spaces (gaps) may occur where the segment pieces 161 do not overlap to an extent that sufficient welding strength can be ensured.

[0179] Preferably, the width D of the segment piece 161 can be adaptively adjusted depending on the radius of the winding turn in which the segment piece 161 is located so that the overlap of the segment piece 161 is well performed in the radial direction when the segment piece 161 is bent toward the core side.

[0180] The height H of the segment pieces 161 may be 2 mm or more. If the height H of the segment pieces 161 is less than 2 mm, when the segment pieces 161 are bent toward the core, an area or space (gap) may be generated where the segment pieces 161 do not overlap to an extent that sufficient welding strength can be ensured.

[0181] The height H of the segment piece 161 can be determined by applying the condition that the cavity of the core is not blocked when the segment piece 161 is bent toward the core side. Preferably, the height H of the segment piece 161 can be adjusted so that 90% or more of the diameter of the core is open to the outside.

[0182] Preferably, the height H of the segment 161 may gradually increase from the core side to the outer periphery side depending on the radius of the winding turn where the segment 161 is located and the radius of the core.

[0183] In one embodiment, the height H of the segment 161 increases from h1 to h as the radius of the winding turn increases. N The amount of saturation can be increased stepwise over N steps up to

[0184] In one example, the radius of the entire winding turn of electrode 160 is 22 mm, and the height of segment 161 starts at 3 mm, but as the radius of the winding turn including segment 161 increases by 1 mm, the height of segment 161 increases sequentially to 3 mm, 4 mm, 5 mm, and 6 mm, and the height of the remaining winding turns can be maintained substantially constant at 6 mm. In other words, the radial width of the height-variable section of segment 161 within the radius of the entire winding turn is 3 mm, and the remaining radius sections are uniform height sections.

[0185] In another example, the core radius r cWhen the length of the core C is 3 mm, the starting radii r1, r2, r3, and r4 of the winding turn including segment pieces 161 with heights of 3 mm (h1), 4 mm (h2), 5 mm (h3), and 6 mm (h4) are 6 mm, 7 mm, 8 mm, and 9 mm, respectively, and the height of the segment pieces 161 can be maintained at 6 mm from the radius of 9 mm to the last winding turn. Also, the winding turn having a radius smaller than 6 mm (r1) may not include the segment pieces 161. In this example, since the segment piece 161 with a height of 3 mm (h1) closest to the core C is located from the winding turn with a radius of 6 mm, even if the segment piece 161 is bent toward the core C, it only covers the radius section from 3 mm to 6 mm and does not substantially shield the core cavity.

[0186] The height H of the segment 161 in the height-variable section may be 10 mm or less. For electrical insulation, the end of the separator 60 may extend further outward from the end of the electrode 160 by a length corresponding to the insulation gap. In addition, considering that the end of the separator 60 may meander when the electrode 160 and the separator 60 are wound, a section with a minimum meandering margin of the separator 60 must be allocated to the uncoated portion 143. In addition, in order to cut the segment 161, a minimum cutting scrap margin must be allocated to the end of the current collector foil.

[0187] Preferably, the insulating gap may be 0.2 mm to 6 mm when the electrode 160 is a positive electrode. Furthermore, the insulating gap may be 0.1 mm to 2 mm when the electrode 160 is a negative electrode. Preferably, the minimum meandering margin of the separator 60 may be 0 to 1 mm. Preferably, the cutting scrap margin may be 1.5 mm to 8 mm. The cutting scrap margin may not be determined depending on the process of forming the segment pieces 161. For example, the cutting grooves 163 may be formed so that the upper edges of the segment pieces 161 and the upper edges of the current collector foil coincide with each other, in which case the cutting scrap margin may be zero.

[0188] Considering the above conditions, the maximum height of the segment 161 in the height variable section of the segment 161 may be set to 10 mm. Thus, the height of the segment 161 in the height variable section of the segment 161 may increase stepwise or gradually in the radial direction of the electrode assembly in the range of 2 mm to 10 mm.

[0189] 16, the spacing pitch P of the segment pieces 161 can be adjusted in the range of 0.05 mm to 1 mm. If the spacing pitch P is less than 0.05 mm, cracks may occur in the uncoated portion 143 near the bottom of the cut groove 163 due to stress when the electrode 160 is transported during a winding process, etc. On the other hand, if the spacing pitch P exceeds 1 mm, when the segment pieces 161 are bent, regions or spaces (gaps) may be generated where the segment pieces 161 do not overlap each other to an extent that sufficient welding strength can be ensured.

[0190] On the other hand, when the current collector 141 of the electrode 160 is made of aluminum, it is more preferable to set the separation pitch P to 0.5 mm or more. When the separation pitch P is 0.5 mm or more, even if the electrode 160 travels at a speed of 100 mm / sec or more under a tension of 300 gf or more during a winding process, etc., it is possible to prevent cracks from occurring below the cutting grooves 163.

[0191] As shown in FIG. 16 , a cut groove 163 is interposed between two adjacent segments 161 in the winding direction. The cut groove 163 is a space created by removing the non-coated portion 143. Preferably, both corners of the lower end of the cut groove 163 are rounded. That is, the cut groove 163 includes a substantially flat bottom portion 163a and a rounded portion 163c. The rounded portion 163c connects the bottom portion 163a to the side edge 163b of the segment 161. In a modified example, the bottom portion 163a of the cut groove 163 may be arc-shaped. In this case, the side edge 163b of the segment 161 can be smoothly connected by the arc-shaped bottom portion 163a.

[0192] The lower interior angle θ of the plurality of segment pieces 161 may increase from the core side toward the outer periphery. In one example, the lower interior angle θ of the plurality of segment pieces 161 may increase gradually or stepwise from the core side toward the outer periphery. The lower interior angle θ is the angle formed by a line extending from the bottom 163a of the cutting groove 163 and a line extending from the side edge 163b of the segment piece 161. When the segment piece 161 is symmetrical, the lower interior angle θ on the left and right sides is substantially the same.

[0193] As the radius of the electrode assembly increases, the radius of curvature also increases. If the lower interior angle θ of the segment 161 increases as the radius of the electrode assembly increases, stresses occurring in the radial and circumferential directions when the segment 161 is bent can be alleviated. Furthermore, as the lower interior angle θ increases, the overlap area and number of overlaps with the inner segment 161 also increase when the segment 161 is bent, thereby ensuring uniform welding strength in the radial and circumferential directions and forming a flat bent surface area.

[0194] Preferably, the lower interior angle θ may be determined by the radius of the winding turn in which the segment 161 is located and the width D of the segment 161. In one example, if the electrode 160 forms a winding structure with a diameter of 22 mm and a core radius of 4 mm, the lower interior angle of the segment 161 may increase gradually or stepwise in the 60° to 85° range of the height variable section.

[0195] Further referring to FIG. 15, the length d of the first portion B1 B1 The length d of the first portion B1 is designed so that when the segment piece 161 of the third portion B2 is bent toward the core side, 90% or more of the core is exposed to the outside based on its diameter. B1 may increase in proportion to the bending length of the first group of segment pieces 161. The bending length is the length from the bending point to the top edge of the segment piece 161.

[0196] The bending points of the segments 161 may be set on a line passing through the lower end of the cutting groove 163 or at a point spaced a predetermined distance above that line. When the segments 161 are bent toward the core at a point spaced a predetermined distance from the lower end of the cutting groove 163, the segments can be more easily folded radially. When the segments 161 are folded, the outer segments press the inner segments relative to the center of the core. In this case, when the bending points are spaced a predetermined distance from the lower end of the cutting groove 163, the inner segments are pressed toward the winding axis by the outer segments, making it easier to fold the segments. The distance between the bending points is preferably 1 mm or less. Since the minimum height of the segments is 2 mm, the ratio of the distance between the bending points to the minimum height may be 50% or less.

[0197] In one embodiment, the width of each segment group can be designed to constitute the same winding turn of the electrode assembly, where the winding turns can be counted relative to the end of the first portion B1 when the electrode 160 is in a wound state.

[0198] In another variation, the width of each segment group can be designed to form at least one or more winding turns of the electrode assembly.

[0199] The first to eighth groups are merely examples of segment groups included in the third portion B2. The number of groups, the number of segment pieces 161 included in each group, and the width of the group may be adjusted to allow the segment pieces 161 to overlap in multiple layers so as to maximize stress distribution during the bending process of the non-coated portion 143 and ensure sufficient welding strength with the current collector.

[0200] In the third portion B2, the sections (groups 1 to 7) in which the height of the segment pieces 161 increases stepwise based on the winding direction of the electrode 160 are defined as segment piece height variable sections, and the final segment piece group (group 8) can be defined as a uniform height section in which the height of the segment pieces is maintained uniform.

[0201] That is, in the third portion B2, the height of the segment piece 161 is h1 to h N When the value increases stepwise from h1 to h N-1 A section in which a segment piece 161 having a height of (N is a height index and is a natural number of 2 or more) is arranged becomes a height variable section, and h N The section in which the segment pieces 161 having the height are arranged becomes a uniform height section.

[0202] The width of the first group may be 35 to 40% of the width of the first portion B1. The width of the second group may be 130 to 150% of the width of the first group. The width of the third group may be 120 to 135% of the width of the second group. The width of the fourth group may be 85 to 90% of the width of the third group. The width of the fifth group may be 120 to 130% of the width of the fourth group. The width of the sixth group may be 100 to 120% of the width of the fifth group. The width of the seventh group may be 90 to 120% of the width of the sixth group. The width of the eighth group may be 115 to 130% of the width of the seventh group. Length d of the second portion B3 B3 The width of the first portion B1 may be 180 mm to 350 mm, similar to the width of the first portion B1.

[0203] The reason why the widths of the first to eighth groups do not show a uniform increase or decrease pattern is that although the width of the segments gradually increases from group 1 to group 8, the number of segments included in each group is limited to an integer, and the thickness of the electrode varies slightly in the winding direction. As a result, the number of segments may decrease in a particular segment group. As a result, the width of the groups may show an irregular change pattern as shown in the example above as they move from the core side to the outer periphery side.

[0204] According to the above-described embodiment, the welding strength of the current collecting plate can be improved by sufficiently increasing the number of overlapping segments 161. By optimizing the dimensions (width, height, and spacing pitch) of the segments 161 and sufficiently increasing the number of overlapping segments 161 in the area used as the welding target area, the physical properties of the area where the current collecting plate is welded can be improved.

[0205] Figure 15 also shows representative current paths. The connection point between the first and second paths is indicated by a triangle, and the end points of the electrodes are indicated by a square. The connection points between the first and second paths can be any position in the second part B3 or the third part B2, but for convenience of illustration, they are shown at one position in the first group and one position in the eighth group. The end points of the electrodes can also be any position, but are shown at one position to indicate the length L1 of the current path in the width direction and at one position located on the maximum current path.

[0206] Here, L2, which determines the upper limit of the ratio L2 / L1 of the current path, is the distance to the end point of the electrode in the third portion B2 defined as the electrode tab, and is the length d of the first portion B1. B1 The length d of the first part B1 B1 The ratio L2 / L1 of the current paths can be adjusted by adjusting the length d of the third portion B2. Although the ratio L2 / L1 of the current paths may increase the resistance somewhat, it satisfies the minimum resistance requirement of the secondary battery. Therefore, when further consideration is given to the overlapping degree of the segment pieces 161 and the securing of welding strength, the ratio L2 / L1 may be set to 11 or less, 10.15 or less, 8.5 or less, or in the range of 2 to 5. For example, when the length d of the third portion B2 is B2 If it is necessary to increase the overlap of the segment pieces 161 by making the segments 161 larger or by forming more segments 161, the current path ratio L2 / L1 may be set to 8.5 or less, or may be set to a range of 2 to 5. The significance of the present invention is that the upper limit of the current path ratio L2 / L1 is determined from the viewpoint of designing a low-resistance cell that minimizes the current path. If the upper limit of the current path ratio L2 / L1 is exceeded, the minimum resistance requirement of the secondary battery cannot be met.

[0207] In the electrode 160 having such a structure, the third portion B2 can be bent to form a welding area. B2 is the length d of the first part B1 B1 The length d of the third portion B2 may be longer than B2 is the length d of the second part B3 B3 The length d of the third portion B2 may be longer thanB2 By increasing the length d of the third portion B2, the folded portions can be overlapped in multiple places when folded. B2 By making the length longer, a sufficient welding area can be secured.

[0208] According to another modification, when the non-coated portion 143 of the electrode 160 has a segmented structure, the electrode 160 may include segment-omitted sections 164 in which some of the segments are omitted regularly or irregularly, as shown in Fig. 17. Fig. 17 is a plan view showing a modified structure of an electrode according to a fifth embodiment of the present invention.

[0209] 17, preferably, there may be a plurality of segment-omitted sections 164. In one example, the width of the segment-omitted sections 164 may be constant as one progresses from the core side to the outer periphery side. In another example, the width of the segment-omitted sections 164 may increase or decrease regularly or irregularly as one progresses from the core side to the outer periphery side. Preferably, the height of the uncoated portion present in the segment-omitted sections 164 may correspond to the height of the first portion B1 and / or the second portion B3.

[0210] The number of segments 161 present between the segment-free sections 164 may be at least one. The electrode 160 may include non-coated sections in which the number of segments 161 present between the segment-free sections 164 increases as it moves from the core toward the outer periphery, as shown in FIG.

[0211] Even when the segment piece-omitted section 164 is placed in the middle of the non-coated portion 143 in this manner, the segment piece-omitted section 164 corresponds to the electrode tab undefined section, so the length of the segment piece-omitted section 164 can be determined taking into account the condition that the ratio L2 / L1 of the current path in the electrode tab undefined section is 11 or less.

[0212] FIG. 18 is a top plan view showing independent areas where multiple segment pieces may be located when an electrode according to a modified embodiment of the present invention is wound into an electrode assembly.

[0213] Preferably, the width of the segment omission section 164 can be set so that when the electrode 160 is wound, the segment located on each winding turn is located within a predetermined independent region 166 based on the core C of the electrode assembly 200, as shown in FIG.

[0214] That is, when the electrode assembly 200 is viewed from the winding axis direction, the plurality of segment pieces 161 may be located within a plurality of independent regions 166 based on the core C. The number of independent regions 166 may be varied to two, three, four, five, etc.

[0215] Preferably, the independent regions 166 may be sector-shaped. In this case, the angles between the independent regions 166 may be substantially uniform. Also, the circumferential angle δ of the independent regions 166 may be 20° or greater, optionally 25° or greater, optionally 30° or greater, optionally 35° or greater, or optionally 40° or greater.

[0216] In variations, the independent regions 166 may have the form of geometric shapes such as squares, rectangles, balanced quadrilaterals, trapezoids, and the like.

[0217] In this case, the welded portion with the current collecting plate can be formed only in the independent region 166, and the current collecting plate can be designed to have a leg structure corresponding to the independent region 166, which is advantageous in terms of current collection efficiency.

[0218] FIG. 19 is a plan view showing the structure of an electrode according to a sixth embodiment of the present invention.

[0219] 19, the electrode 170 of the sixth embodiment has substantially the same configuration as the previous embodiments except for the shape of the segment 161'. Therefore, unless otherwise specified, the configuration of the fifth embodiment is equally applicable to the sixth embodiment.

[0220] The segment piece 161' has a geometric shape in which the widths of the top and bottom are substantially the same. Preferably, the segment piece 161' may have a rectangular shape.

[0221] FIG. 20 is a diagram illustrating the definition of the width, height, and spacing pitch of segments included in an electrode according to a sixth embodiment of the present invention.

[0222] 20, the width D, height H, and spacing pitch P of the segment pieces 161' may be set to prevent tearing of the uncoated portions 143 during bending, to increase the number of overlaps of the uncoated portions 143 to improve the welding strength with the current collector, and to prevent abnormal deformation of the uncoated portions 143. Abnormal deformation refers to the uncoated portions below the bending points collapsing and becoming irregularly deformed, instead of maintaining a straight state.

[0223] The width D of the segment piece 161' is defined as the length between two points where two straight lines extending from both side edges of the segment piece 161' intersect with a straight line extending from the bottom 163a of the cutting groove 163. The height H of the segment piece 161' is defined as the shortest distance between the top edge of the segment piece 161' and a straight line extending from the bottom 163a of the cutting groove 163. The separation pitch P of the segment pieces 161' is defined as the length between two points where a straight line extending from the bottom 163a of the cutting groove 163 intersects with a straight line extending from the two side edges 163b connected to the bottom 163a. ​​If the side edges 163b and / or the bottom edge 163a are curved, the straight lines may replace tangents extending from the side edges 163b and / or the bottom edge 163a at the intersections where the side edges 163b and the bottom edge 163a intersect.

[0224] Preferably, the conditions regarding the width D, height H, and spacing pitch P of the segment pieces 161' are substantially the same as those in the fifth embodiment described above, and therefore, repeated description will be omitted. However, since the segment pieces 161' have a rectangular shape, the lower interior angle of the segment pieces 161' may be constant at 90°.

[0225] Similar to the electrode 160 of the fifth embodiment, the electrode 170 of the sixth embodiment may also include segment-omitted sections 164 in which some of the segments are omitted regularly or irregularly.

[0226] When the third portion B2 includes a plurality of segment pieces 161, 161' as in the fifth and sixth embodiments, the shape of each segment piece 161, 161' can be modified in various ways.

[0227] According to yet another aspect of the present invention, after the electrodes 160, 170 are wound into an electrode assembly, the segment pieces exposed at the top and bottom of the electrode assembly may be overlapped in multiple layers along the radial direction of the electrode assembly to form a folded surface region.

[0228] The folded surface regions F formed by bending the segment pieces 161 toward the core C of the electrode assembly 200 may be formed on both the upper and lower parts of the electrode assembly 200. Figure 21 is a top perspective view schematically showing an electrode assembly having folded surface regions formed thereon.

[0229] 21, the folded surface region F has a structure in which segment pieces 161 are stacked in a plurality of layers in the winding axis direction. The stacking direction is the winding axis direction.

[0230] The height, width and spacing pitch of the segment pieces 161 can be adjusted according to the radius of the winding turn containing the segment pieces 161, so that the number of stacked segment pieces 161 at each position of the folded surface area F can be optimized according to the required welding strength of the current collector plate.

[0231] The electrode structures of the above-described embodiments (variations) are applicable to positive and negative electrodes included in a jelly roll type or other types of electrode assemblies known in the art.

[0232] In the present invention, the positive electrode active material coated on the positive electrode and the negative electrode active material coated on the negative electrode may be any active material known in the art without any limitation.

[0233] In one example, the positive electrode active material has the general chemical formula A[A x M y ]O 2+z(A contains at least one element of Li, Na, and K; M contains 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; the stoichiometric coefficients x, y, and z are selected so that the compound maintains electrical neutrality.) It may contain an alkali metal compound represented by.

[0234] In other examples, the positive electrode active material is an alkali metal compound xLiM disclosed in US6,677,082, US6,680,143, etc. 1 O2-(1-x)Li2M 2 O3(M 1 (M contains at least one element having an average oxidation state of 3; M 2 (M contains at least one element having an average oxidation state of 4; 0≦x≦1).

[0235] In still other examples, 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 (M contains at least one element selected from Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Al, and Mg; M 2 (M contains at least one element selected from Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Al, Mg, As, Sb, Si, Ge, V, and S; M 3 (M contains a halogen group element selectively containing F;

[0236] Preferably, the positive electrode active material may include primary particles and / or secondary particles formed by aggregation of primary particles.

[0237] For example, the negative electrode active material may be a carbon material, lithium metal or a lithium metal compound, silicon or a silicon compound, or tin or a tin compound. Metal oxides with a potential of less than 2 V, such as TiO2 and SnO2, may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon.

[0238] The separator may be a porous polymer film, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc., either alone or in a laminate. In another example, the separator may be a conventional porous nonwoven fabric, for example, a nonwoven fabric made from high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0239] At least one surface of the separator may include a coating layer of inorganic particles. Alternatively, the separator itself may be made of a coating layer of inorganic particles. The particles constituting the coating layer may have a structure in which they are bound with a binder so that interstitial volume exists between adjacent particles.

[0240] The inorganic particles may be made of an inorganic material having a dielectric constant of 5 or more. Non-limiting examples of the inorganic particles include Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), PB(Mg3Nb 2 / 3)O3-PbTiO3 (PMN-PT), BaTiO3, hafnia (HfO2), SrTiO3, TiO2, Al2O3, ZrO2, SnO2, CeO2, MgO, CaO, ZnO, and Y2O3.

[0241] FIG. 22 is a cross-sectional view of a jelly roll-type electrode assembly in which one of the electrodes of the fifth and sixth embodiments (or their modified examples) is applied to the positive and negative electrodes, taken along the Y-axis direction (winding axis direction).

[0242] Referring to FIG. 22, the positive electrode uncoated portion 143a includes a first portion B1 adjacent to the core of the electrode assembly 200, a second portion B3 adjacent to the outer peripheral surface of the electrode assembly 200, and a third portion B2 interposed between the first portion B1 and the second portion B3.

[0243] The height of the first portion B1 is relatively smaller than the height of the third portion B2. The bending length of the innermost positive electrode uncoated portion 143a in the third portion B2 is equal to or smaller than the radial length R of the first portion B1. The bending length H' is the distance from the point where the positive electrode uncoated portion 143a is bent to the upper end of the positive electrode uncoated portion 143a. In a modified example, the bending length H' may be smaller than the sum of the radial length R of the first portion B1 and 10% of the radius of the core C.

[0244] Therefore, even if the third portion B2 is bent, 90% or more of the diameter of the core C of the electrode assembly 200 is open to the outside. The core C is located at the center of the electrode assembly 200 and has a cavity. If the cavity of the core C is not blocked, the electrolyte injection process is easy and the efficiency of the electrolyte injection is improved. In addition, a welding jig can be inserted through the core C to easily perform the welding process between the negative (or positive) electrode side current collector plate and the battery housing (or electrode terminal).

[0245] The height of the second portion B3 is relatively smaller than the height of the third portion B2, which prevents the beading portion and the second portion B3 from coming into contact with each other and causing an internal short circuit when the beading portion of the battery housing is pressed near the second portion B3.

[0246] The negative electrode uncoated portion 143b has the same structure as the positive electrode uncoated portion 143a. In one variation, the negative electrode uncoated portion 143b may have a conventional electrode structure or an electrode structure of another embodiment (variation).

[0247] In one variation, the height of the second portion B3 may decrease gradually or in steps, unlike that shown in Fig. 22. Also, in Fig. 22, the height of the third portion B2 is uniform along a portion of the outer periphery, but the height of the third portion B2 may increase gradually or in steps from the boundary between the first portion B1 and the third portion B2 to the boundary between the third portion B2 and the second portion B3. When the third portion B2 is divided into multiple segments, the section where the height of the positive electrode uncoated portion 143a changes becomes the segment height variable section E2.

[0248] More specifically, the electrode assembly 200 includes, in sequence along the radial direction based on a cross section along the winding axis, a segment-free section E1 where no segments exist, a height-variable section E2 where the height of the segments varies, and a height-uniform section E3 where the height of the segments is uniform.

[0249] The ends 201 of the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b may be bent in the radial direction of the electrode assembly 200, for example, from the outer periphery toward the core side. At this time, the first portion B1 and the second portion B3 are not bent.

[0250] The plurality of segment pieces 161, 161' are arranged in the height-variable section E2 and the height-uniform section E3, and are bent along the radial direction of the electrode assembly 200 to form a bent surface region (F in FIG. 21). A structure in which a current collector plate is welded over a wide area can be applied to the bent surface region F formed by bending the segment pieces 161, 161', thereby improving the energy density of the electrode assembly 200 including the bent surface region F and reducing the resistance.

[0251] When the third portion B2 includes multiple segments, bending stress is alleviated, thereby preventing tearing or abnormal deformation of the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b near the bending points. Furthermore, when the width and / or height and / or spacing pitch of the segments 161, 161' are adjusted within the ranges of the values ​​in the above-described embodiment, the segments 161, 161' are bent toward the core C and overlapped to an extent that sufficient welding strength can be ensured, and no holes (gaps) are formed in the bent surface areas.

[0252] In this embodiment, the segment-omitted section E1 corresponds to the first part B1.

[0253] Meanwhile, a modified example in which the height variable section E2 is omitted from the electrode assembly 200 is also possible.

[0254] FIG. 23 is a plan view showing a modified structure of an electrode according to a fifth embodiment of the present invention.

[0255] 23, the electrode 180 of the modified example has segments 161 of uniform height, and when manufactured into the electrode assembly 200 shown in FIG. 22, it includes only segment-free section E1 and uniform-height section E3 without height-variable section E2, but the remaining configuration is substantially the same. Therefore, unless otherwise noted, the configuration of the fifth embodiment is equally applicable to this modified example. In addition, the second portion B3 is not divided into segments, and the height of the first portion B1 and the height of the second portion B3 are the same.

[0256] FIG. 23 shows the maximum current paths L1 and L2 (the connection point between the first and second paths is indicated by ▲, and the end points of the electrodes are indicated by ■).

[0257] In the electrode 180 having the structure shown in FIG. 23, the length d of the first portion B1 B1 Secondary batteries of the examples and comparative examples were fabricated by varying the temperature, and then AC resistance, DC resistance, low-temperature cycling, and rapid charging cycling were tested. The number of segment pieces 161 was 115, and the width of each segment piece 161 was 8 mm at its widest point and 6 mm in height. The negative electrode current collector was made of copper and had a thickness of 10 μm, and the positive electrode current collector was made of aluminum and had a thickness of 15 μm. Each current collector had a short side length approximately equal to L1 of 65 mm and a long side length of 4 m. The positive electrode active material contained a lithium composite transition metal oxide, and the negative electrode active material contained graphite. A polyolefin separator was used. The electrolyte was a 1.4 M LiPF6 solution dissolved in a solvent consisting of a 20:70:10 volume mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0258] For example, AC resistance evaluation can be performed by applying an AC current of 1 kHz using a commonly used AC impedance meter. In this experiment, formation was performed at 200 mA (0.1 C), followed by CC / CV charging at 4.2 V, 666 mA (0.3 C, 0.05 C cutoff), and CC discharging at 2.5 V, 666 mA (0.3 C) three times. Then, AC resistance was measured in the range of 10 mHz to 100 kHz using a multi-impedance analyzer (Biologic, Model VMP3) at 25°C and a state of charge (SOC) of 50%.

[0259] For example, DC resistance can be measured using a commonly used DC resistance meter by placing a probe on the surface of the electrode so that current flows only through the electrode surface. In this experiment, a fully charged secondary battery was discharged to 50% SOC at room temperature and discharged at a current of 0.5 C for 10 seconds. The voltage drop that occurred when the battery was discharged was recorded, and the DC resistance (DC-IR) value calculated using Ohm's law (R = V / I) was measured. [Discharge pulse (0.5 C pulse applied for 10 seconds): DC-IR = (V0 - V1) / I, where V0 is the voltage before the discharge pulse and V1 is the voltage after the discharge pulse.]

[0260] Low-temperature cycle performance (low-temperature life characteristic evaluation) was performed by forming the battery at 200 mA (0.1 C), followed by CC / CV charging at 4.2 V, 666 mA (0.3 C, 0.05 C cutoff), and CC discharging at 2.5 V, 666 mA (0.3 C) for 300 cycles at 10°C. The first discharge capacity was taken as the initial capacity, and the 300th discharge capacity was compared to the initial capacity to calculate the capacity retention rate (%). Discharge capacity measurements can be performed using a device such as the PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5 V, 6 A).

[0261] The rapid cycle performance was evaluated by repeating the process of rapid charging from 10% SOC to 80% SOC for 25 minutes and then discharging to 10% SOC 500 times. All charging and discharging was performed in CC mode. The percentage change in charge capacity after 500 cycles was calculated.

[0262] The secondary battery of Example 1 has a length d of the first portion B1 that determines L2. B1 The length d of the first portion B1 of the secondary battery of Comparative Example 1 is 556 mm. B1 The length d of the first portion B1 of the secondary battery of Comparative Example 2 is 680 mm. B1 In Example 1, the length d of the first portion B1 was 920 mm. B1 Since the length d of the first portion B1 is 556 mm, it satisfies the length of the electrode tab undefined section 143a2 confirmed by simulation, which is 660 mm or less. B1is larger than the length of the electrode tab undefined section 143a2, which is 660 mm, confirmed by simulation.

[0263] Table 1 summarizes the conditions and experimental results for Example 1, Comparative Example 1, and Comparative Example 2.

[0264] [Table 1]

[0265] Referring to Table 1, in Example 1, the AC resistance was measured to be 1.5 mΩ and the DC resistance was measured to be 3.6 mΩ. As shown in the simulation results, the AC resistance was 2 mΩ or less, and the DC resistance also met the minimum resistance requirement for a secondary battery (DC resistance of 4 mΩ or less and AC resistance of 3 mΩ or less).

[0266] The measured DC resistance of Comparative Example 1 was 3.9 mΩ and the AC resistance was 1.7 mΩ, which satisfied the minimum resistance requirement of the secondary battery. However, the low temperature cycle was 76% and the fast charge cycle was 83%, which was inferior to Example 1, which had a low temperature cycle of 82% and a fast charge cycle of 87%. In particular, in terms of the fast charge cycle, the length d of the first portion B1 as in Example 1 was 1.5 mΩ. B1 It can be seen that it is advantageous when the distance is 660 mm or less.

[0267] The DC resistance measured in Comparative Example 2 was 4.3 mΩ, which did not meet the minimum resistance requirements for a secondary battery. The low-temperature cycle was 58% and the fast charge cycle was 64%, which indicated that the performance was inferior to that of Comparative Example 1. That is, the length d of the first portion B1 B1 As the thickness increases beyond 660 mm (680 mm → 920 mm), the resistance increases, and the low-temperature cycle and fast charging cycle performance deteriorates.

[0268] Thus, according to this embodiment of the present invention, the length d of the first portion B1 B1When the ratio of current paths L2 / L1 is set to a predetermined range and is 11 or less, it is possible to design a low-resistance cell that satisfies the minimum resistance requirements of a secondary battery, and it can also have excellent performance in terms of low-temperature cycles and fast charging cycles, so it can be confirmed that it is suitable for manufacturing cylindrical secondary batteries with an increased form factor for application in electric vehicles.

[0269] Various electrode assembly structures according to embodiments of the present invention can be applied to cylindrical secondary batteries.

[0270] Desirably, the cylindrical secondary battery may be, for example, 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.

[0271] Preferably, the cylindrical secondary battery may have a diameter of 40 mm to 50 mm and a height of 60 mm to 130 mm. The form factor of the cylindrical secondary battery according to one embodiment may be, for example, 46110, 4875, 48110, 4880, or 4680. In the numerical value indicating the form factor, the first two digits indicate the diameter of the secondary battery, and the remaining digits indicate the height of the secondary battery.

[0272] When a tabless-type electrode assembly is applied to a cylindrical secondary battery with a form factor ratio exceeding 0.4, bending the uncoated portion can easily cause the uncoated portion to break due to the large radial stress. Furthermore, to ensure sufficient welding strength and reduce resistance when welding a current collector to the bent surface area of ​​the uncoated portion, the number of layers of the uncoated portion in the bent surface area must be increased. These requirements can be achieved by the electrode and electrode assembly according to an embodiment (variant) of the present invention. In particular, these requirements can be achieved by ensuring a current path ratio (L2 / L1) of 11 or less, thereby enabling a low-resistance design.

[0273] The secondary battery according to one embodiment of the present invention may be a cylindrical secondary battery having a diameter of approximately 46 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0274] The secondary battery according to another embodiment may be a substantially cylindrical secondary battery having a diameter of about 48 mm, a height of about 75 mm, and a form factor ratio of 0.640.

[0275] Furthermore, the secondary battery according to another embodiment may be a substantially cylindrical secondary battery having a diameter of about 48 mm, a height of about 110 mm, and a form factor ratio of 0.436.

[0276] Furthermore, the secondary battery according to another embodiment may be a substantially cylindrical secondary battery having a diameter of about 48 mm, a height of about 80 mm, and a form factor ratio of 0.600.

[0277] A secondary battery according to yet another embodiment may be a substantially cylindrical secondary battery having a diameter of about 46 mm, a height of about 80 mm, and a form factor ratio of 0.575.

[0278] Conventionally, secondary batteries with a form factor ratio of approximately 0.4 or less have been used. For example, 18650 secondary batteries and 21700 secondary batteries have been used. The 18650 secondary battery has a diameter of approximately 18 mm, a height of approximately 65 mm, and a form factor ratio of 0.277. The 21700 secondary battery has a diameter of approximately 21 mm, a height of approximately 70 mm, and a form factor ratio of 0.300.

[0279] Hereinafter, a cylindrical secondary battery according to an embodiment of the present invention will be described in detail.

[0280] Figure 24 is a cross-sectional view of a cylindrical secondary battery according to one embodiment of the present invention. The secondary battery 300 of Figure 24 includes an electrode assembly 200, which is a jelly roll-type electrode assembly in which one of the electrodes of the fifth embodiment or the sixth embodiment (or their modifications) is applied to the positive and negative electrodes. Figure 24 is a cross-sectional view of the secondary battery 300 taken along the winding axis direction.

[0281] 24, the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b are arranged in opposite directions in the electrode assembly 200. The positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b are exposed to the outside of the separator (see 60 in FIG. 7). In this electrode assembly 200, only a portion of the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b may be defined and used as an electrode tab. For example, only a portion of the positive electrode uncoated portion 143a may be used as a positive electrode tab, and only a portion of the negative electrode uncoated portion 143b may be used as an electrode tab.

[0282] The secondary battery 300 also includes a cylindrical battery housing 305 that houses the electrode assembly 200 and is connected to the negative electrode uncoated portion 143b. The battery housing 305 is made of a conductive metal material. In one example, the battery housing 305 may be a battery can made of iron, nickel-plated iron, or stainless steel (SUS), but the present invention is not limited thereto.

[0283] Preferably, one side of the battery housing 305 (the bottom in this embodiment) is open to form an open portion. The opposite side of the open portion of the battery housing 305 is a closed portion. In this embodiment, the closed portion is the bottom 310 of the battery housing 305. The bottom 310 of the battery housing 305 is circular. The side (outer periphery) and the bottom 310 of the battery housing 305 may be integrally formed. The bottom 310 of the battery housing 305 has a substantially flat shape. The battery housing 305 receives the electrode assembly 200 through the open portion and also receives an electrolyte. The side of the battery housing 305 extends a certain length from the bottom 310.

[0284] The bottom 310 of the battery housing 305 has a structure in which the positive terminal 315 is riveted to the through-hole 320 by a crimping process. The secondary battery 300 may also include a rivet gasket 325 interposed between the positive terminal 315 and the through-hole 320.

[0285] The positive terminal 315 is made of a conductive metal material. In one example, the positive terminal 315 may be made of a material primarily composed of aluminum, but the present invention is not limited to this. The positive terminal 315 may be made of a 10-series aluminum alloy, which is easy to rive and has low resistance. A portion of the positive terminal 315 is inserted inside the battery housing 305, and another portion is exposed to the outside of the battery housing 305.

[0286] The rivet gasket 325 may be made of a polymer resin having insulating and elastic properties. For example, the rivet gasket 325 may be made of polypropylene, polybutylene terephthalate, polyfluoroethylene, etc., but the present invention is not limited thereto.

[0287] The secondary battery 300 includes a positive current collector 330 connected to the positive electrode uncoated portion 143a. The positive current collector 330 may be connected to the positive electrode uncoated portion 143a by welding. The positive current collector 330 is connected to the electrode tab-defined section of the positive electrode uncoated portion 143a. The positive current collector 330 is also connected to the positive electrode terminal 315. The positive current collector 330 and the positive electrode terminal 315 are connected by laser welding. The positive current collector 330 may be made of the same metal as the positive electrode current collector and / or the positive electrode terminal 315, or may be made of a material that is easily welded to them. For example, the positive current collector 330 may be made of a material primarily containing aluminum, such as iron, nickel-plated iron, or stainless steel. The positive electrode terminal 315 is connected to the positive electrode uncoated portion 143a via the positive current collector 330.

[0288] The secondary battery 300 may also include a seal 335 that seals the open portion of the battery housing 305 so as to be insulated from the battery housing 305. Preferably, the seal 335 may include a non-polar cap plate 340 and a sealing gasket 345 interposed between the peripheral edge of the cap plate 340 and the open portion of the battery housing 305.

[0289] The cap plate 340 may be made of a conductive metal material such as aluminum, iron, nickel-plated iron, or stainless steel. The sealing gasket 345 may be made of insulating and elastic materials such as polypropylene, polybutylene terephthalate, or polyfluoroethylene. However, the present invention is not limited by the materials of the cap plate 340 and the sealing gasket 345. The cap plate 340 may cover the opening of the battery housing 305. Even if the cap plate 340 is made of a conductive metal material, it may not have polarity. Having no polarity may mean that the cap plate 340 is not connected to the electrode assembly 200. It may also mean that the cap plate 340 is electrically insulated from the battery housing 305 and the positive terminal 315. Because it has no polarity, the cap plate 340 does not function as an electrode terminal. The cap plate 340 does not need to be connected to the electrode assembly 200 and the battery housing 305, and its material does not necessarily need to be a conductive metal.

[0290] The cap plate 340 may include a vent notch 350 that ruptures when the pressure inside the battery housing 305 exceeds a critical value. The vent notch 350 may be formed on one or both surfaces of the cap plate 340. The vent notch 350 may form a continuous or discontinuous circular pattern, a linear pattern, or other pattern on the surface of the cap plate 340. For example, the vent notch 350 may be formed in a substantially circular ring shape having a constant width. Such a circular ring-shaped vent notch 350 may be coaxial with the center of the cap plate 340 and have a radius smaller than the radius of the cap plate 340.

[0291] The burst pressure of the battery housing 305 can be controlled by controlling the depth and width of the vent notch 350. For example, the vent notch 350 can be formed when the internal pressure of the battery housing 305 is 15 to 35 kgf / cm. 2 The vent notch 350 may be configured to burst when the internal pressure of the battery housing 305 reaches a certain level. The vent notch 350 may be formed by partially reducing the thickness of the battery housing 305 through notching. The vent notch 350 may have a thickness gradient. The thickness gradient means that the cross section of the vent notch 350 is formed at a certain angle with respect to a predetermined horizontal plane. The vent notch 350 ruptures when the internal pressure of the battery housing 305 increases abnormally, thereby releasing all of the internal gas to the outside.

[0292] The battery housing 305 may include a crimping part 355 that extends and bends inward to secure the seal 335 and surrounds and secures the periphery of the cap plate 340 together with the sealing gasket 345. Preferably, the lower surface of the cap plate 340 may be positioned higher than the lower end of the crimping part 355. In this case, a vent space is formed below the cap plate 340, allowing gas to be released smoothly when the vent notch 350 ruptures.

[0293] The battery housing 305 may further include a beading part 360 press-fitted into the area adjacent to the opening toward the inside of the battery housing 305. The beading part 360 is recessed toward the inside of the battery housing 305. The beading part 360 supports the peripheral edge of the sealing body 335, particularly the outer peripheral surface of the sealing gasket 345, when the sealing body 335 is fixed by the crimping part 355.

[0294] The secondary battery 300 may further include a negative current collector 365 connected to the negative electrode uncoated portion 143b. The connection between the negative electrode uncoated portion 143b and the negative current collector 365 may be performed by welding. The negative current collector 365 is connected to the electrode tab-defined section of the negative electrode uncoated portion 143b. The negative current collector 365 may be made of the same metal as the negative current collector or a material that is easily welded thereto. For example, the negative current collector 365 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 365a of the edge of the negative current collector 365 that does not contact the negative electrode uncoated portion 143b may be interposed between the beading portion 360 and the sealing gasket 345 and secured by the crimping portion 355. Optionally, at least a portion 365a of the edge of the negative current collector 365 may be fixed to the inner circumferential surface 360a of the beading portion 360 adjacent to the crimping portion 355 by welding. As a result, the negative current collector 365 is also connected to the battery housing 305, and the battery housing 305 is connected to the negative electrode uncoated portion 143b via the negative current collector 365. The negative current collector 365 may also have a current collector hole (not shown) in its center. The current collector hole does not obstruct the cavity of the core C. The negative current collector 365 includes the current collector hole, allowing a laser beam to pass through and reach the positive current collector 330 during the step of welding the positive current collector 330 to the positive terminal 315.

[0295] Each current collecting plate 330, 365 guides current generated at each electrode of the electrode assembly 200 to the positive terminal 315 and the battery housing 305. Each current collecting plate 330, 365 is a component connected to lead current from the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b, which are the ends of each electrode. Because current is introduced and led out by directly connecting the current collecting plates 330, 365 to the positive electrode uncoated portion 143a and the negative electrode uncoated portion 143b via welding or other methods, separate current collecting tabs are not required. This eliminates the need for a current collecting tab attachment process, thereby 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.

[0296] In addition, the secondary battery 300 has a structure in which the positive terminal 315 and the remaining area of ​​the outer surface 310a of the battery housing 305, excluding the area occupied by the positive terminal 315, can be used as the positive terminal and the negative terminal, respectively. That is, most of the surface opposite the open portion of the battery housing 305 can be used as the negative terminal. This has the advantage of ensuring a sufficient area for welding connecting components such as bus bars for electrical wiring.

[0297] The positive terminal 315 can increase the space efficiency within the battery housing 305. As a result, the internal resistance of the secondary battery 300 including the positive terminal 315 can be reduced and the energy density can be increased. The positive terminal 315 can be improved to increase the cross-sectional area of ​​the current path. As a result, the secondary battery 300 including the positive terminal 315 can be improved to alleviate the problem of internal heat generation that occurs during fast charging.

[0298] The positive terminal 315 may include a main body portion 315a inserted into the through hole 320, an external flange portion 315b extending from the periphery of one side of the main body portion 315a exposed on the outer surface 310a of the bottom 310 of the battery housing 305 along the outer surface 310a, an internal flange portion 315c extending from the periphery of the other side of the main body portion 315a exposed on the inner surface 310b of the bottom 310 of the battery housing 305 toward the inner surface 310b, and a flat portion 315d provided on the inside of the internal flange portion 315c.

[0299] Preferably, at least a portion of the positive current collector plate 330 may be laser-welded to the flat portion 315d of the positive terminal 315. Preferably, the flat portion 315d and the inner surface 310b of the bottom portion 310 of the battery housing 305 may be parallel to each other. Here, "parallel" means that they are substantially parallel when observed visually.

[0300] The diameter of the flat portion 315d can be 3 mm to 14 mm. The flat portion 315d can determine the size of the weldable area. If the diameter of the weldable area is smaller than 3 mm, it may be difficult to ensure adequate welding strength. If the diameter of the weldable area exceeds 14 mm, the diameter of the external flange portion 315b of the positive terminal 315 is too large, making it difficult to ensure a sufficient area of ​​the outer surface 310a of the bottom portion 310 of the battery housing 305 to be used as the negative terminal.

[0301] Laser welding is used to connect the flat portion 315d to the positive current collector plate 330. Laser welding can be performed with the electrode assembly 200 inserted through the opening of the battery housing 305 and the opening of the battery housing 305 open. During laser welding, a laser beam can reach the welding area of ​​the positive current collector plate 330 through a cavity in the core C of the electrode assembly 200. When the positive current collector plate 330 is welded to the flat portion 315d of the positive terminal 315, the positive terminal 315 can support the welding area of ​​the positive current collector plate 330. Furthermore, because the flat portion 315d of the positive terminal 315 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 secondary battery 300. The face-to-face welding structure of the riveted positive terminal 315 and positive current collector plate 330 is very useful for fast charging. This is because the current density per unit area in the cross section in the direction of current flow can be reduced, and the amount of heat generated in the current path can be reduced compared to conventional methods.

[0302] Furthermore, the secondary battery 300 employing the riveting structure of the positive terminal 315 can perform electrical wiring in one direction. In the secondary battery 300, the cap plate 340 of the encapsulant 335 does not have a polarity. Instead, because the negative current collector 365 is connected to the battery housing 305, the outer surface 310a of the bottom 310 of the battery housing 305 has the opposite polarity to the positive terminal 315. This simplifies the connection structure because the positive and negative electrodes can be connected in one direction when connecting multiple secondary batteries 300. Therefore, when connecting multiple secondary batteries 300 in series and / or parallel to manufacture a battery pack, wiring such as bus bar connection can be performed at the top of the secondary battery 300 using the outer surface 310a of the bottom 310 of the battery housing 305 and the positive terminal 315. 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.

[0303] Furthermore, electrical wiring is performed on the outer surface 310a of the bottom 310 of the battery housing 305 and the side where the positive terminal 315 is located, and electrical wiring is not required on the opposite side of the cap plate 340, thereby maximizing the effect of the vent notch 350 formed in the cap plate 340. Furthermore, by providing a heat sink, cooling plate, tray, etc. on the cap plate 340 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 350 is located downward allows gas emitted from inside the secondary battery to be discharged downward. Since secondary batteries are typically installed 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 secondary battery 300 of the present invention is not only capable of effectively discharging 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 discharged due to the rupture of the vent notch 350, the gas is discharged downward, so that no harm is done to passengers and safety is significantly improved.

[0304] The secondary battery 300 may further include an insulator 370 interposed between the closing portion of the battery housing 305 and the positive current collector 330. The insulator 370 may be interposed between the positive current collector 330 and the inner surface 310b of the bottom 310 of the battery housing 305, and between the inner circumferential surface 305a of the side wall of the battery housing 305 and the electrode assembly 200.

[0305] Preferably, the insulator 370 may include a welding hole 370a that exposes the flat portion 315d of the positive terminal 315 to the positive current collector plate 330. The welding hole 370a may also expose the inner flange portion 315c and the inner gasket 325b, along with the flat portion 315d of the electrode terminal. Preferably, the welding hole 370a does not block the cavity of the core C. This prevents gas from moving through the cavity of the core C toward the cap plate 340 in the event of a large amount of gas generation due to an abnormality in the secondary battery. This facilitates the vent notch 350's ability to control the internal pressure of the battery when a large amount of gas is generated. The cap plate 340 also includes the welding hole 370a, allowing a laser beam to pass through and reach the positive current collector plate 330 during the process of welding the positive terminal 315.

[0306] Preferably, the insulator 370 may cover at least the surface of the positive current collector 330 and one (upper) end of the electrode assembly 200. This may prevent the positive current collector 330 and the positive uncoated portion 143a, which have a polarity different from that of the battery housing 305, from coming into contact with each other.

[0307] Preferably, the insulator 370 is made of insulating resin and may include an upper plate 370b and a side sleeve 370c. In one example, the upper plate 370b and the side sleeve 370c may be an integral injection-molded product. Alternatively, the side sleeve 370c may be replaced with insulating tape. The insulating tape may cover the outer edge of the positive current collector plate 330 as well as the positive electrode uncoated portion 143a exposed on the outer periphery of the electrode assembly 200.

[0308] Preferably, the insulator 370 and the inner surface 310b of the bottom 310 of the battery housing 305 may be in close contact with each other. Here, "close contact" means that there is no space (gap) visible to the naked eye. To eliminate the space (gap), the distance from the inner surface 310b of the bottom 310 of the battery housing 305 to the flat portion 315d of the positive terminal 315 may be the same as or slightly smaller than the thickness of the insulator 370.

[0309] Meanwhile, Figure 24 shows a path (first path) from the welding position of the module bus bar to the positive electrode uncoated portion 143a and negative electrode uncoated portion 143b, which are the electrode tabs of each electrode 140 (the current starting point is indicated by a ●, and the connecting position is indicated by a ▲). The current starting points are located at the positive electrode terminal 315 and the negative electrode terminal. The negative electrode terminal is the battery housing 305. The module bus bar welding position is located at the upper end of the secondary battery 300. A current path is formed that starts from the positive electrode terminal 315 and connects to the positive electrode uncoated portion 143a, and a current path is formed that starts from the negative electrode terminal and connects to the negative electrode uncoated portion 143b.

[0310] Although the first paths are similar to each other in comparison with the conventional cylindrical secondary battery shown in FIG. 2, the second path in the electrode 140 constituting the electrode assembly 200 has a significant difference from the conventional second path described with reference to FIG. 3 and the virtual second path described with reference to FIG. 8, as also shown in FIG. 15, and the ratio L2 / L1 of the current paths is set to 11 or less. Therefore, the length of the undefined section of the electrode tab, for example, the length d of the first portion B1, B1 The present invention is characterized in that the range is set as follows.

[0311] Unlike the conventional electrode structure described with reference to FIGS. 1 to 3, the present invention forms electrode tabs consisting of uncoated portions on the long sides of the electrode when viewed in an unrolled state before winding. This minimizes current flow along the electrode's length and forces it to flow along its width, thereby minimizing the current path and reducing resistance. Furthermore, a portion of the uncoated portion is designated as an electrode tab undefined section, preventing deformation when bending the welding area of ​​the uncoated portion and preventing closure of cavities present in the core of the electrode assembly. When manufacturing a jelly-roll-type electrode assembly and a cylindrical secondary battery including the same using an electrode with this structure, the length of the electrode tab undefined section or the spacing between adjacent segments is adjusted to ensure that the current path ratio L2 / L1 in the maximum current path is 11 or less, as described above.

[0312] The cylindrical secondary battery according to the above-described embodiment (variation) can be used to manufacture a battery pack.

[0313] FIG. 25 is a diagram schematically illustrating the configuration of a battery pack according to an embodiment of the present invention.

[0314] 25, a battery pack 400 according to an embodiment of the present invention includes an assembly of electrically connected secondary batteries 401 and a pack housing 402 that accommodates the assembly. The secondary batteries 401 may be any one of the secondary batteries according to the above-described embodiments (variations). For ease of illustration, components such as a bus bar for electrically connecting the secondary batteries 401, a cooling unit, and external terminals are omitted from the drawing.

[0315] The battery pack 400 may be installed in a vehicle. For example, the vehicle may be an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle may include a four-wheeled vehicle or a two-wheeled vehicle.

[0316] FIG. 26 is a diagram illustrating a vehicle including the battery pack 400 of FIG.

[0317] 26, a vehicle V according to an embodiment of the present invention includes a battery pack 400 according to an embodiment of the present invention. The vehicle V operates by receiving power from the battery pack 400 according to an embodiment of the present invention.

[0318] Although the present invention has been described above using limited examples and drawings, it goes without saying that the present invention is not limited thereto, and various modifications and variations can be made by a person having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the scope of the claims. [Explanation of symbols]

[0319] 100, 200 electrode assembly 140, 150, 160, 170, 180 electrodes 141 Current collector 142 Active material layer 143 Uncoated part 143a Positive electrode uncoated part 143b Negative electrode uncoated part 161, 161' segmental piece 164 Segment fragment omission section 166 Independent Area 300, 401 Secondary battery 305 Battery Housing 315 Positive terminal 330 Positive current collector plate 335 Sealing body 340 Cap Plate 345 Sealing Gasket 365 Negative current collector plate 400 battery pack

Claims

1. An electrode assembly in which a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode are wound around a winding shaft to define a core and an outer surface, The electrode which is the positive electrode or the negative electrode is a sheet-like current collector having a long side and a short side, and includes a current collector with an uncoated portion at the end of the long side. The uncoated portion includes an electrode tab defined section used as an electrode tab and at least one electrode tab undefined section that is not used as an electrode tab. The maximum current path for at least one undefined electrode tab section includes a current path in the width direction along the short side of the current collector and a current path in the longitudinal direction along the long side of the current collector, and when the lengths of the current path in the width direction and the current path in the longitudinal direction are L1 and L2, respectively, the ratio of the current paths L2 / L1 is greater than 0 and less than or equal to 11. An electrode assembly characterized in that the electrode tab definition section includes a bent surface region formed by bending along the radial direction of the electrode assembly.

2. The electrode assembly according to claim 1, characterized in that the height of the undefined section of the electrode tab is 0 or more.

3. The uncoated portion includes a first portion adjacent to the core, a second portion adjacent to the outer peripheral surface, and a third portion between the first portion and the second portion. The electrode assembly according to claim 1, characterized in that the length of the second portion is shorter than the length of the first portion.

4. The electrode assembly according to claim 1, characterized in that the ratio of the short side to the long side of the current collector is 1.2% to 2.8%.

5. The electrode assembly according to claim 1, characterized in that an active material layer is formed on at least one surface of the current collector, and an insulating coating layer is formed at the boundary between the active material layer and the uncoated portion.

6. The electrode assembly according to claim 5, characterized in that the insulating coating layer contains a polymer resin and an inorganic filler.

7. The electrode assembly according to claim 1, characterized in that the undefined electrode tab section has a smaller height than the defined electrode tab section.

8. The uncoated portion includes a first portion adjacent to the core, a second portion adjacent to the outer circumferential surface, and a third portion between the first and second portions. The electrode assembly according to claim 1, characterized in that the first portion has a smaller height than the third portion in the winding axis direction.

9. The electrode assembly according to claim 1, characterized in that the maximum length of the undefined section of the electrode tab is 4% to 23% of the lengths of the positive electrode and the negative electrode.

10. The electrode assembly according to claim 8, characterized in that the third portion forms the bent surface region.

11. The electrode assembly according to claim 8, characterized in that the second portion is the same height as or smaller than the third portion in the winding axis direction.

12. The electrode assembly according to claim 8, characterized in that the first portion corresponds to the undefined section of the electrode tab.

13. The electrode assembly according to claim 8, characterized in that the first portion is not bent along the radial direction of the electrode assembly.

14. The electrode assembly according to claim 8, characterized in that the second portion is not bent along the radial direction of the electrode assembly.

15. The electrode assembly according to claim 8, characterized in that, in the winding direction of the electrode assembly, the length of the third portion is longer than the length of the first portion and the length of the second portion.

16. The electrode assembly according to claim 8, characterized in that the first portion starts from the short side on the core side of the current collector, the height of the first portion is constant along the winding direction, and the first portion is not bent along the radial direction of the electrode assembly.

17. The electrode assembly according to claim 8, characterized in that at least a portion of the third portion is divided into a plurality of independently foldable segmented pieces.

18. The electrode assembly according to claim 17, characterized in that the segmented pieces are bent and overlapped in the direction of the winding axis.

19. The electrode assembly according to claim 17, characterized in that, with respect to the cross-section in the winding axis direction, the electrode assembly sequentially includes, along the radial direction, sections where no segmented segments are present and sections where the height of the segmented segments is uniform, and the plurality of segmented segments are arranged in the sections where the height of the segmented segments is uniform, forming the bent surface region.

20. The electrode assembly according to claim 19, characterized in that the segmented section omitted corresponds to the electrode tab undefined section.

21. The electrode assembly according to claim 19, characterized in that the second portion is not divided into segmented pieces, and the height of the first portion and the height of the second portion are the same.

22. The electrode assembly according to claim 17, characterized in that the third portion includes one or more segments without segments along the winding direction of the electrode assembly.

23. The electrode assembly according to claim 22, characterized in that the height of the uncoated portion in the segmented portion omitted section is the same as the height of the first portion.

24. The electrode assembly according to claim 8, characterized in that the core is provided with a cavity, and the bent surface region does not obstruct the cavity.

25. An electrode assembly according to any one of claims 1 to 24, A cylindrical battery housing, which houses the electrode assembly through an open portion formed on one side and is connected to the uncoated portion of the negative electrode, A sealing body that seals the opening of the cylindrical battery housing, A positive electrode terminal is riveted through a through hole formed in the bottom of the cylindrical battery housing, located on the opposite side of the opening of the cylindrical battery housing, and connected to the uncoated portion of the positive electrode. A secondary battery characterized by containing [something].

26. The uncoated portion of the positive electrode is exposed to the outside of the separation membrane, and the uncoated portion of the negative electrode is exposed to the outside of the separation membrane in the opposite direction to the uncoated portion of the positive electrode. The secondary battery according to claim 25, further comprising a positive electrode current collector plate electrically connected to the uncoated portion of the positive electrode.

27. The secondary battery according to claim 26, characterized in that the uncoated portion of the positive electrode includes a bent surface region, and the positive electrode current collector plate is welded to the bent surface region.

28. The aforementioned positive terminal is, The main body portion inserted into the aforementioned through hole, An external flange portion extending along the outer surface from one peripheral edge of the main body portion exposed on the outer surface of the bottom of the cylindrical battery housing, An internal flange portion extending toward the inner surface from the other peripheral edge of the main body portion exposed on the inner surface of the bottom of the cylindrical battery housing, A flat portion provided on the inside of the aforementioned internal flange portion, The secondary battery according to claim 25, characterized by including the following:

29. The secondary battery further includes a positive electrode current collector plate electrically connected to the uncoated portion of the positive electrode, The secondary battery according to claim 28, characterized in that the positive electrode terminal is joined to the positive electrode current collector plate by laser welding in the flat portion.

30. The secondary battery according to claim 26, characterized in that the undefined electrode tab section is a portion where no current path is formed because it is not connected to the positive electrode current collector plate.

31. The secondary battery according to claim 25, characterized in that the sealing body includes a vent notch that ruptures when the pressure inside the cylindrical battery housing exceeds a critical value.

32. A battery pack characterized by comprising a plurality of secondary batteries as described in claim 25.

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