Current collector, electrode tab and method for manufacturing the same, electrode assembly, and secondary battery

Abstract

The application relates to a current collector, a pole piece and a preparation method thereof, an electrode assembly and a secondary battery. A through hole penetrating through the current collector body is arranged in at least one corner area, so that the electrode assembly formed by winding the pole piece with the current collector has the through hole feature in the inner part of at least one layer of the pole piece in the bending part. At this time, during the cyclic charging process, lithium ions on the convex side and the concave side of the pole piece can communicate through the through hole, so that the lithium intercalation concentrations on both sides of the pole piece are balanced, the risk of lithium precipitation between the negative pole piece and the positive pole piece in the bending part is reduced, and the service life of the secondary battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to current collectors, electrodes and their preparation methods, electrode assemblies and secondary batteries. Background Technology

[0002] Electrode assemblies are the components in secondary batteries where electrochemical reactions occur. They are mainly formed by winding or stacking positive and negative electrode plates, and a separator is usually provided between the negative and positive electrode plates. During winding, the electrode assembly can form a straight section and two bent sections located on both sides of the straight section.

[0003] Within the bending region, the negative and positive electrodes are stacked alternately. However, due to structural design flaws in the electrode assembly, lithium plating can easily occur between the negative and positive electrodes during cyclic charging and discharging, severely impacting the lifespan of the secondary battery. Summary of the Invention

[0004] Therefore, it is necessary to provide a current collector, an electrode and its preparation method, an electrode assembly and a secondary battery to reduce the risk of lithium plating and improve the service life of the secondary battery.

[0005] In a first aspect, this application provides a current collector for winding in a first direction. The current collector includes a current collector body having a plurality of corner regions spaced apart along the first direction, the corner regions being opposite to the bent portion of the electrode assembly; wherein at least one corner region has a through hole extending through it along the thickness direction of the current collector.

[0006] The aforementioned current collector has a perforation penetrating the current collector body in at least one corner region. This ensures that the electrode assembly formed by winding the electrode sheet with this current collector will have a perforation feature within at least one layer of the electrode sheet in the bend. During cyclic charging, lithium ions on the convex and concave sides of the electrode sheet can communicate through the perforation, ensuring a balance in lithium intercalation concentration on both sides of the electrode sheet. This reduces the risk of lithium plating between the negative and positive electrodes in the bend, thus improving the lifespan of the secondary battery.

[0007] In some embodiments, there are multiple perforations in the corner region, and all perforations are spaced apart within the corner region. This arrangement of multiple perforations in the corner region helps to accelerate the flow rate of lithium ions across the electrode, promoting a dynamic equilibrium of lithium ion concentrations on both sides of the electrode.

[0008] In some embodiments, within the corner region with perforations, the perforations are arranged in rows at intervals along the second direction. The sum of the opening areas of any row of perforations is denoted as S0. The sum of the opening areas S0 of each row decreases as it approaches any end of the corner region along the second direction. The first direction is perpendicular to the second direction. This helps to reduce the number of openings near one end of the corner region, avoiding stress concentration caused by excessive openings, thereby effectively preventing the risk of electrode breakage during cold pressing.

[0009] In some embodiments, within a perforated corner region, the number of openings in each row of perforations gradually decreases from the middle of the corner region to any end of the corner region along the second direction. This design reduces the number of openings closer to one end of the corner region, ensuring structural strength at the edge of the current collector body and preventing breakage during the cold pressing process.

[0010] In some embodiments, the current collector has a coating area for coating an active material layer. The coating area extends along a first direction and sequentially passes through each corner area. The perforations in the corner areas are all located within the coating area in a second direction, with the first direction perpendicular to the second direction. In this way, the location of the perforations is confined to the coating area, enabling effective flow of lithium ions on both sides of the electrode. At the same time, it avoids opening perforations in the tab portion, which would weaken its structural strength.

[0011] In some embodiments, at least one stress zone is provided within the coating area, extending along one edge of the coating area in a second direction. The perforations in the corner area are all located in the region of the coating area where the stress zone is removed in the second direction. Thus, by leaving a stress zone near one edge of the coating area without perforations, the mechanical strength of at least one side of the current collector is ensured, preventing breakage or tearing during processing and improving production efficiency.

[0012] In some embodiments, the width of each stress zone in the second direction is denoted as D, where D ≥ 3 mm. This reasonably limits the minimum threshold of the stress zone width, ensuring that a region at one edge of the coating area along the second direction is free of openings, thus guaranteeing the mechanical strength of the current collector on at least one side.

[0013] In some embodiments, two stress zones are spaced apart along the second direction within the coating area, with each stress zone corresponding to one of the two opposite edges of the coating area along the second direction. This arrangement of stress zones near the opposite edges of the coating area without perforations ensures the mechanical strength of both sides of the current collector, preventing breakage or tearing during processing and improving production efficiency.

[0014] In some embodiments, the current collector body also has a blank area located on at least one side of the coating area along the second direction. Thus, reserving a blank area on at least one side of the current collector body to facilitate the fabrication of the tab portion required for the electrode assembly improves manufacturing efficiency.

[0015] In some embodiments, within the perforated corner region, the sum of the opening areas of all the perforations is denoted as S1, and the area of ​​the corner region on the current collector body is denoted as S2, wherein 0.1% ≤ S1 / S2 ≤ 50%. Thus, by reasonably controlling the range of the S1 / S2 ratio, it is possible to ensure smooth flow of lithium ions on both sides of the electrode while also ensuring that the current collector body has sufficient structural strength, avoiding the risk of band breakage.

[0016] In some embodiments, perforations are provided in the first n corner regions starting from the beginning of the current collector winding, where n≤6. Thus, perforations in the first n corner regions can specifically address locations where lithium plating is prone to occur in the electrode assembly, reducing the need for perforation operations and improving the mechanical strength of the current collector while minimizing lithium plating.

[0017] Secondly, this application provides an electrode sheet comprising: a current collector as described above; and an active material layer disposed on at least one surface of the current collector body.

[0018] Thirdly, this application provides a method for preparing an electrode sheet, which includes the following steps: providing a current collector body; making perforations in the corner area of ​​the current collector body to form a current collector; coating an active material layer on the surface of the current collector; and rolling the coated current collector.

[0019] In some embodiments, the step of rolling the coated current collector includes: pressing the tension roller surface of the pressure roller and the extension roller surface located on both sides of the tension roller surface onto the active material layer and the blank areas on both sides of the current collector, respectively, and controlling a gap between the side of the extension roller surface facing the tension roller surface and the area where the perforation is located. In this way, when cold pressing the active material, controlling the gap between one side of the extension roller surface and the area where the perforation is located avoids stress concentration caused by the perforation opening position being too close to the extension roller surface, thereby preventing the electrode sheet from easily breaking during rolling.

[0020] Fourthly, this application provides an electrode assembly configured as a wound structure, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the wound structure includes a bending portion; wherein the positive electrode and / or the negative electrode are the above-mentioned electrode sheets, and the position of the bending portion is opposite to the corner area after winding.

[0021] Fifthly, this application provides a secondary battery including the electrode assembly described above.

[0022] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0024] Figure 1 This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0025] Figure 2 This is a schematic diagram of the electrode assembly structure provided in some embodiments of this application;

[0026] Figure 3 Schematic diagrams of current collector structures provided for some embodiments of this application;

[0027] Figure 4 Flowchart of the electrode preparation method provided in some embodiments of this application Figure 1 ;

[0028] Figure 5 Flowchart of the electrode preparation method provided in some embodiments of this application Figure 2 ;

[0029] Figure 6 This is a schematic diagram of the pressure roller structure provided for some embodiments of this application.

[0030] 100. Secondary battery; 10. Electrode assembly; 20. End cap; 30. Electrode terminal; 40. Housing; 1. Electrode; 1a. Current collector; 11. Current collector body; 12. Perforation; 13. Corner area; 14. Coated area; 15. Stress area; 16. Blank area; 17. Opening area; 18. Straight area; 2. Positive electrode; 3. Negative electrode; 4. Separator; 5. Straight part; 6. Bending part; 200. Pressure roller; 210. Extension roller surface; 220. Tension roller surface; X, First direction; Y, Second direction. Detailed Implementation

[0031] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0033] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0034] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0036] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0037] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0038] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0039] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0040] The applicant notes that when the electrode assembly is constructed as a wound structure, it includes a straight portion and bent portions on both sides of the straight portion. In the bent portions, there are alternating layers of positive and negative electrode sheets with different radii of curvature, and both the positive and negative electrode sheets form concave and convex surfaces when bent. Taking one layer of negative electrode sheet as an example (of course, it can also be explained using one layer of positive electrode sheet as an example), its concave side and convex side correspond to the inner and outer positive electrode sheets respectively; that is, the concave side of the negative electrode sheet faces the convex surface of the inner positive electrode sheet, and its convex side faces the concave surface of the outer positive electrode sheet.

[0041] Because the radius of curvature of the concave surface of the negative electrode is greater than that of the convex surface of the inner positive electrode, the active material capacity of the concave surface of the negative electrode is greater than that of the convex surface of the positive electrode. The corresponding NP value is greater than 1, which can be simply understood as the lithium vacancy concentration being greater than the lithium-ion concentration, indicating a surplus of lithium vacancies. Conversely, because the radius of curvature of the concave surface of the negative electrode is smaller than that of the convex surface of the outer positive electrode, the active material capacity of the concave surface of the negative electrode is less than that of the convex surface of the positive electrode. The corresponding NP value is less than 1, which can also be simply understood as the lithium vacancy concentration being insufficient for lithium-ion intercalation, leading to a risk of lithium plating during charging.

[0042] Based on this, in order to solve the problem that lithium plating easily occurs between the positive and negative electrode plates at the bending part of the electrode assembly, which affects the service life of the secondary battery, the applicant has conducted in-depth research and designed a current collector with a through hole in at least one corner area along the thickness direction of the current collector so that lithium ions on both sides of the current collector can flow to each other.

[0043] The aforementioned current collector has a perforation penetrating the current collector body in at least one corner area. In this way, when the electrode prepared using the current collector is made into a positive electrode or a negative electrode, lithium ions on both sides of the electrode can pass through the perforation, ensuring that the lithium ion concentration on both sides of the electrode reaches a balance. For example, the side with a high lithium ion concentration can flow into the side with a low lithium ion concentration through the perforation.

[0044] After the electrode assembly is formed by winding the electrode sheet prepared using this current collector, the electrode assembly will have perforations in at least one layer of the electrode sheet in the bending section. At this time, during the cyclic charging process, lithium ions on the convex and concave sides of the electrode sheet will be interconnected through the perforations, ensuring that the lithium intercalation concentration on both sides of the electrode sheet is balanced. For example, lithium ions on the convex side of the negative electrode sheet can flow to the concave side of the negative electrode sheet through the perforations, thereby reducing the lithium intercalation concentration on the convex side, ensuring that the local NP is greater than or equal to 1, reducing the risk of lithium plating between the negative and positive electrodes in the bending section, and improving the service life of the secondary battery.

[0045] The secondary batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system comprising such an electrical device can be constructed using the secondary batteries disclosed in this application.

[0046] In a battery system, there can be multiple secondary batteries, which can be connected in series, parallel, or a combination thereof. A combination connection means that multiple secondary batteries are connected in both series and parallel configurations. Multiple secondary batteries can be directly connected in series, parallel, or a combination thereof, and then the entire assembly is housed within a casing. Alternatively, the battery can consist of multiple secondary batteries first connected in series, parallel, or a combination thereof to form battery modules, which are then connected in series, parallel, or a combination thereof to form a single unit housed within a casing. The battery may also include other structures; for example, it may include a busbar component for electrical connection between the multiple secondary batteries. The secondary batteries can be cylindrical, flat, cuboid, or other shapes.

[0047] Please refer to Figure 1 , Figure 1 This is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. The secondary battery 100 refers to the smallest unit comprising a battery. For example... Figure 1 The secondary battery 100 includes an end cap 20, a housing 40, an electrode assembly 10, and other functional components.

[0048] End cap 20 refers to a component that covers the opening of housing 40 to isolate the internal environment of secondary battery 100 from the external environment. The shape of end cap 20 can be adapted to the shape of housing 40 to fit it. Optionally, end cap 20 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 20 is not easily deformed under pressure and impact, giving secondary battery 100 higher structural strength and improved safety performance. Functional components such as electrode terminals 30 can be provided on end cap 20. Electrode terminals 30 can be used for electrical connection with electrode assembly 10 for outputting or inputting electrical energy to secondary battery 100. In some embodiments, end cap 20 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of secondary battery 100 reaches a threshold. The material of end cap 20 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 20. The insulating element can be used to isolate the electrical connection components within the housing 40 from the end cap 20 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0049] The housing 40 is a component used to cooperate with the end cap 20 to form the internal environment of the secondary battery 100, wherein the formed internal environment can accommodate the electrode assembly 10, electrolyte, and other components. The housing 40 and the end cap 20 can be independent components. An opening can be provided on the housing 40, and the end cap 20 closes the opening to form the internal environment of the secondary battery 100. Alternatively, the end cap 20 and the housing 40 can be integrated. Specifically, the end cap 20 and the housing 40 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 40, the end cap 20 closes the housing 40. The housing 40 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 40 can be determined according to the specific shape and size of the electrode assembly 10. The material of the housing 40 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this embodiment does not impose any special limitations on this.

[0050] Please refer to Figure 2The electrode assembly 10 is the component in the secondary battery 100 where the electrochemical reaction occurs. The casing 40 may contain one or more electrode assemblies 10. The electrode assembly 10 is mainly formed by winding or stacking positive electrode plates 2 and negative electrode plates 3, and a separator 4 is typically provided between the positive electrode plates 2 and negative electrode plates 3. The portions of the positive electrode plates 2 and negative electrode plates 3 containing active material constitute the main body of the electrode assembly 10, while the portions of the positive electrode plates 2 and negative electrode plates 3 without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals 30 to form a current circuit.

[0051] According to some embodiments of this application, please refer to Figure 2 and Figure 3 This application provides a current collector 1a for winding in a first direction X. The current collector 1a includes a current collector body 11. The current collector body 11 has a plurality of corner regions 13 spaced apart along the first direction X. The corner regions 13 are used to face the bent portion 6 of the electrode assembly 10. Wherein, at least one corner region 13 is provided with a through hole 12 extending along the thickness direction of the current collector 1a.

[0052] The current collector 11 refers to the core structure that mainly comprises the current collector 1a; it can also be understood as any component on the current collector 1a other than features such as the perforation 12. The current collector 11 not only carries the active material but also collects and outputs the current generated by the electrode active material. The material of the current collector 11 can be selected differently depending on the polarity of the electrode 1. For example, in the positive electrode 2, the material of the current collector 11 can be, but is not limited to, metals such as aluminum and nickel, or composite materials such as conductive resin, titanium-nickel shape memory alloy, and carbon-coated aluminum foil. In the positive electrode 2, the material of the current collector 11 can be, but is not limited to, metals such as copper, or composite materials such as conductive resin and titanium-nickel shape memory alloy.

[0053] Corner region 13 refers to the area where, during the fabrication of the electrode assembly 10, the current collector 11 forms a bend in several segments when wound along the first direction X. This bend corresponds to the area of ​​the current collector 11 in the corner region 13. Please also refer to... Figure 2 The electrode assembly 10 formed by winding will form a bend 6, which includes a current collection body 11 of multiple stacked corner areas 13. That is, the corner areas 13 are used to be opposite to the bend 6 of the electrode assembly 10. This can be understood as: the corner areas 13 after winding are at the same position or overlap with the bend 6 of the electrode assembly 10.

[0054] Several corner regions 13 are arranged at intervals along the first direction X on the current collector body 11, with a straight region 18 between two adjacent corner regions 13, opposite to the straight portion 5 of the electrode assembly 10. Simultaneously, after winding, two adjacent corner regions 13 are located on different bends 6 of the electrode assembly 10. For ease of understanding, the two bends 6 of the electrode assembly 10 can be defined as the left bend 6 and the right bend 6, respectively. During winding, the first corner region 13 is wound on the left bend 6, the second corner region 13 is wound on the right bend 6; then, the third corner region 13 is wound on the left bend 6, the fourth corner region 13 is wound on the right bend 6, and so on. Following this logic, the remaining corner regions 13 are wound on different bends 6 respectively.

[0055] In all the corner areas 13 on the current collection body 11, only some corner areas 13 may be provided with perforations 12, or all corner areas 13 may be provided with perforations 12, etc.

[0056] The perforation 12 must be installed throughout the corner region 13 along the thickness direction of the current collector 1a to ensure that the formed electrode 1 has a channel for lithium ions to pass through. The number and shape of the perforation 12 can be designed in various ways. For example, the number of perforations 12 in the corner region 13 can be one or more; the shape of the perforation 12 in the corner region 13 can be, but is not limited to, regular shapes such as circles, triangles, squares, pentagons, and ellipses; of course, it can also be designed as an irregular shape.

[0057] A through-hole 12 is provided in at least one corner region 13, penetrating the current collector body 11. Thus, the electrode assembly 10 formed by winding the electrode sheet 1 with the current collector 1a will have the through-hole 12 feature within at least one layer of the electrode sheet 1 in the bending portion 6. During cyclic charging, lithium ions on the convex and concave sides of the electrode sheet 1 can communicate through the through-hole 12, ensuring a balance in lithium intercalation concentration on both sides of the electrode sheet 1. This reduces the risk of lithium plating between the negative electrode sheet 3 and the positive electrode sheet 2 in the bending portion 6, and helps to improve the service life of the secondary battery 100.

[0058] According to some embodiments of this application, please refer to Figure 3 In the corner area 13 with perforations 12, there are multiple perforations 12, and all perforations 12 are distributed at intervals in the corner area 13.

[0059] Within the same corner area 13, multiple perforations 12 are distributed at intervals. There are various ways to distribute them at intervals, such as: multiple perforations 12 can be arranged in a matrix, arranged in concentric rings, etc., or they can be arranged in an irregular dense arrangement, etc.

[0060] Multiple perforations 12 are opened at intervals in the corner area 13, which helps to accelerate the passage rate of lithium ion concentration on both sides of the electrode 1 and promotes the dynamic balance of lithium ion concentration on both sides of the electrode 1.

[0061] According to some embodiments of this application, please refer to Figure 3 In the corner area 13 with perforations 12, the perforations 12 are arranged in rows at intervals along the second direction Y. The sum of the opening areas of any row of perforations 12 is denoted as S0. The sum of the opening areas S0 of each row is smaller as it gets closer to any end of the corner area 13 along the second direction Y. The first direction X is perpendicular to the second direction Y.

[0062] The arrangement of perforations 12 in rows within the corner area 13 should be understood as several perforations 12 arranged linearly in rows along the first direction X, with each row spaced apart along the second direction Y. Within the same row, the opening area of ​​each perforation 12 may or may not be the same.

[0063] The sum of the opening areas S0 is related to the number of perforations 12 in each row and the opening area of ​​each individual perforation 12. The opening area of ​​each individual perforation 12 in each row may be the same or different; at the same time, the number of perforations 12 in each row may also be the same or different, but it should be noted that these two parameters cannot be the same at the same time.

[0064] The closer an end of the corner area 13 is to any end along the second direction Y, the smaller the sum of the opening areas of the perforations 12 along the second direction Y. This design results in the perforations 12 within the corner area 13 being smaller at both ends and larger in the middle. In some embodiments, the sum of the opening areas S0 of each row of perforations 12 gradually decreases from the middle of the corner area 13 to any end of the corner area 13 along the second direction Y. Meanwhile, the first direction X can be the length direction of the current collecting body 11, and the second direction Y can be the width direction of the current collecting body 11.

[0065] This design helps to reduce the number of openings near the corner area 13, avoiding stress concentration caused by too many openings, and thus effectively avoiding the risk of electrode 1 breaking during cold pressing.

[0066] According to some embodiments of this application, please refer to Figure 3 In the corner area 13 with perforations 12, the number of openings in each row of perforations 12 gradually decreases from the middle of the corner area 13 to any end of the corner area 13 along the second direction Y.

[0067] During the hole-making process, the number of perforations 12 at one end of the corner area 13 along the second direction Y can be designed to be zero, that is, no hole is made at one end of the corner area 13. At this time, there is a no-hole area between the perforation 12 closest to one end of the corner area 13 and one end of the corner area 13.

[0068] The opening area of ​​individual perforations 12 in each row can be consistent or inconsistent. When the opening area of ​​individual perforations 12 in each row is inconsistent, the sum of the opening areas S0 of each row should be designed to be smaller as it approaches the corner area 13.

[0069] The middle part of the corner area 13 should be understood as: the corner area 13 is located in the middle position in the second direction Y, or it can be understood as the middle position of the current collection body 11 along its own width direction.

[0070] This design reduces the number of openings closer to the corner area 13, ensuring the structural strength of the current collection body 11 at its edge and preventing breakage during the cold pressing process.

[0071] According to some embodiments of this application, please refer to Figure 3 The current collector 11 has a coating area 14 for coating an active material layer. The coating area 14 extends along the first direction X and passes through each corner area 13 in sequence. The perforations 12 in the corner areas 13 are all located in the coating area 14 in the second direction Y. The first direction X is perpendicular to the second direction Y.

[0072] The coating area 14 refers to the area on the current collector body 11 where active material can be coated. The distribution of the coating area 14 on the current collector body 11 may overlap with each corner area 13, or it may directly cover each corner area 13. When the coating area 14 covers each corner area 13, it means that the width of the coating area 14 along the second direction Y is the same as the width of the current collector body 11, that is, the entire surface of the current collector body 11 is coated with active material. At this time, the processing of the tab part can be carried out by cutting the current collector 1a in the previous process to obtain strip-shaped tabs; or, strip-shaped tabs can be welded onto the current collector 1a, etc.

[0073] The perforations 12 within the corner region 13 are all located within the coating region 14 in the second direction Y. This should be understood as meaning that the perforations 12 within the corner region 13 will not extend beyond the edge of the coating region 14 in the second direction Y. It should be noted that if the perforations extend beyond the coating region 14, it means that there are also perforations 12 in the part of the area where the active material layer is not coated. This part of the area is usually used as the tab part in the electrode assembly 10. Therefore, opening a hole in this part of the area not only prevents the effective flow of lithium ions, but also weakens the structural strength of the tab part.

[0074] By limiting the location of the perforation 12 to the coating area 14, lithium ions can flow effectively on both sides of the electrode 1; at the same time, it avoids opening the perforation 12 in the tab part, which would weaken its structural strength.

[0075] According to some embodiments of this application, please refer to Figure 3The coating area 14 is provided with at least one stress area 15, which extends along one edge of the coating area 14 in the second direction Y. The perforations 12 in the corner area 13 are all located in the area of ​​the coating area 14 excluding the stress area 15 in the second direction Y.

[0076] All perforations 12 within the corner area 13 are located in the area of ​​the coating area 14 where the stress zone 15 is removed. That is, in the second direction Y, there is an unopened area between the perforation 12 and one edge of the coating area 14. Because stress concentration occurs at the edge of the coating area 14 during the cold pressing of the electrode 1, opening a hole near one edge of the coating area 14 would create a weak point, leading to breakage of the current collector 1a or the electrode 1, resulting in the scrapping of the electrode 1, reducing production efficiency, and increasing costs. Therefore, the opening area 17 on the current collector 1a avoids the stress zone 15, ensuring the mechanical strength of at least one side of the current collector 1a, preventing breakage or tearing during processing, and improving production efficiency.

[0077] The opening area 17 can be understood as the area enclosed by all the perforations 12 within the corner area 13.

[0078] A stress zone 15 is left near the edge of the coating area 14 without perforations 12 to ensure the mechanical strength of at least one side of the current collector 1a, avoid breakage or tearing during processing, and improve production efficiency.

[0079] According to some embodiments of this application, please refer to Figure 3 The width of each stress zone 15 in the second direction Y is denoted as D, where D≥3mm.

[0080] The width D of the stress zone 15 can be greater than 3 mm. Of course, the specific value of the width D of the stress zone 15 can also be determined according to the overall width of the current collector 1a.

[0081] Reasonably limit the minimum threshold of the width of the stress zone 15 so that there is a section without openings at one edge of the coating zone 14 along the second direction Y, ensuring the mechanical strength of at least one side of the current collector 1a.

[0082] According to some embodiments of this application, please refer to Figure 3 Two stress zones 15 are provided at intervals along the second direction Y within the coating area 14. The two stress zones 15 are respectively adjacent to the two opposite edges of the coating area 14 along the second direction Y.

[0083] In the second direction Y, the coating area 14 has two stress areas 15 spaced apart, and the perforation 12 in the corner area 13 should be located between the two stress areas 15.

[0084] Stress zones 15 are left at the two opposite edges of the coating area 14 without perforations 12 to ensure the mechanical strength of both sides of the current collector 1a, avoid breakage or tearing during processing, and improve production efficiency.

[0085] According to some embodiments of this application, the current collection body 11 also has a blank area 16. The blank area 16 is located on at least one side of the coating area 14 along the second direction Y.

[0086] Blank area 16 refers to the area of ​​current collector 11 other than coating area 14, that is, the area without active material layer coating and without opening. In the fabrication of electrode assembly 10, this part can be used as electrode tab, for example, blank area 16 is wound to form a full electrode tab structure, etc.

[0087] There can be one or two blank areas 16. When there are two blank areas 16, the two blank areas 16 are located on opposite sides of the coating area 14 along the second direction Y. In some embodiments, the location of the perforation 12 in the same corner area 13 constitutes an opening area 17, and there is a stress area 15 between the opening area 17 and the blank area 16. To facilitate understanding of the width relationship between the respective areas, the width of the opening area 17 along the second direction Y is denoted as C, the width of the coating area 14 is denoted as B, the width of the blank area 16 is denoted as A, and the width of the current collecting body 11 is denoted as L. At this time, the width of the opening area 17 satisfies the condition: C≤B=Ln×A, where n can be 0, 1, or 2. It should be noted that the width of the opening area 17 can be reversed in the later confirmation of rights using the following method: take the two outermost perforations 12 located in the corner area 13 on the second direction Y, draw tangents to the two perforations 12 with a line parallel to the first direction X, and obtain the maximum distance between the two tangents as the width C of the opening area 17.

[0088] A blank area 16 is reserved on at least one side of the current collector body 11 to facilitate the fabrication of the tab portion required for the electrode assembly 10, which helps to improve manufacturing efficiency.

[0089] According to some embodiments of this application, in the corner area 13 with perforations 12, the sum of the opening areas of all perforations 12 is denoted as S1, and the area of ​​the corner area 13 on the current collection body 11 is denoted as S2, wherein 0.1%≤S1 / S2≤50%.

[0090] The corner area 13 with the perforation 12 should be understood as one of the corner areas 13 with the perforation 12, rather than all the corner areas 13 with the perforation 12.

[0091] The ratio S1 / S2 can be selected from 0.1% to 50%, for example, S1 / S2 can be, but is not limited to, 0.1% and 50%. It should be noted that the ratio of S1 / S2 should not be too large. If the ratio is greater than 50%, it is easy to weaken the structural strength at the corner area 13, which may lead to the risk of strip breakage during the cold pressing process.

[0092] By reasonably controlling the range of the S1 / S2 ratio, it is possible to ensure that lithium ions flow smoothly on both sides of the electrode 1, and also to ensure that the current collector 11 has a certain structural strength, thus avoiding the risk of strip breakage.

[0093] According to some embodiments of this application, starting from the beginning of the current collection body 11 winding, the first n corner areas 13 are provided with perforations 12, where n≤6.

[0094] The starting end of the current collector body 11 winding refers to the end that first begins to wind when the current collector body 11 is wound along the first direction X.

[0095] The first n corner areas 13 refer to the first to the nth corner areas 13 counted from the starting end of the main body 11. Here, n is a positive integer, such as 1, 2, 3, 4, 5, 6.

[0096] Through in-depth research, the applicant found that the lithium plating problem in the secondary battery 100 during cyclic charging and discharging is most likely to occur in the innermost to third rings of the electrode assembly 10, corresponding to the first six corner areas 13 on the current collector body 11. Therefore, this application incorporates openings in the first n corner areas 13 to effectively solve the lithium plating problem in the electrode assembly 10.

[0097] Making openings in the first n corner areas 13 can specifically improve the locations where lithium plating problems are prone to occur in the electrode assembly 10. While ensuring that the lithium plating problem is reduced, the opening operation is reduced and the mechanical strength of the current collector 1a is improved.

[0098] According to some embodiments of this application, an electrode 1 is provided. The electrode 1 includes an active material layer and a current collector 1a as described in any of the above embodiments. The active material layer is disposed on at least one surface of the current collector body 11.

[0099] The active material layer refers to the active material coated on the current collector 1a, and its material can be selected according to the polarity of the electrode 1. For example, in the positive electrode 2, the material of the active material layer can be, but is not limited to, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, ternary materials, etc. In the negative electrode 3, the material of the active material layer can be, but is not limited to, graphite, silicon oxide, etc. The active material layer can be coated only on one side of the current collector 1a, or it can be coated on both opposite sides of the current collector 1a.

[0100] The electrode 1 described above uses the current collector 1a. During the cyclic charging process, the lithium ions on the convex side and concave side of the electrode 1 can communicate with each other through the perforation 12, ensuring that the lithium intercalation concentration on both sides of the electrode 1 reaches a balance, reducing the risk of lithium plating between the negative electrode 3 and the positive electrode 2 in the bending part 6, and helping to improve the service life of the secondary battery 100.

[0101] According to some embodiments of this application, please refer to Figure 3 and Figure 4 This application provides a method for preparing electrode 1, which includes the following steps:

[0102] S100, provides the collection body 11;

[0103] S200, A perforation 12 is made in the corner area 13 on the current collection body 11 to form a current collection fluid 1a;

[0104] S300, Apply an active material layer to the surface of current collector 1a;

[0105] S400, Roll the coated current collector 1a.

[0106] The current collection body 11 in step S100 refers to the current collection fluid 1a without perforation, such as aluminum foil, copper foil, etc.

[0107] In step S200, there are various ways to open holes in the corner area 13, such as laser drilling, mechanical cutting, etc.

[0108] In step S300, coating is a process in which a suspension slurry containing positive and negative electrode active materials is uniformly coated onto an aluminum or copper foil sheet using relevant equipment, and then dried to form a film. The specific coating process includes at least shear coating, wetting and leveling, and drying. The specific operations of these processes are not detailed here, but can be directly referred to in existing literature.

[0109] In step S300, the rolling process is usually arranged after the coating and drying process. It is a process in which the coated powder electrode material on the positive and negative electrode metal current collector 1a is compacted by the rolling press, which is used for the rearrangement and densification of the powder.

[0110] The above-mentioned method for preparing electrode 1 involves opening a perforation 12 on the current collector body 11, allowing lithium ions on both sides of electrode 1 to flow between each other through the perforation 12. In this way, during the cyclic charging process, lithium ions on the convex side and the concave side of electrode 1 can communicate with each other through the perforation 12, ensuring that the lithium intercalation concentration on both sides of electrode 1 reaches a balance, reducing the risk of lithium plating between negative electrode 3 and positive electrode 2 in the bending part 6, and helping to improve the service life of secondary battery 100.

[0111] According to some embodiments of this application, please refer to Figure 5 and Figure 6 S400, the step of rolling the coated current collector 1a includes:

[0112] S410, the tension roller surface 220 of the pressure roller 200 and the extension roller surface 210 located on both sides of the tension roller surface 220 are pressed onto the active material layer and the blank area 16 located on both sides of the current collector 1a, respectively, and the extension roller surface 210 facing the tension roller surface 220 is kept at a distance from the area where the perforation 12 is located.

[0113] Please refer to Figure 6 The pressure roller 200 is a component that presses against the coated current collector 1a to compact the active material. The surface of the pressure roller 200 has a tension roller surface 220 and extension roller surfaces 210 located on both sides of the tension roller surface 220. The extension roller surface 210 presses against the blank area 16 of the current collector 1a, while the tension roller surface 220 presses against the active material layer of the current collector 1a. Both the extension roller surface 210 and the tension roller surface 220 extend circumferentially on the pressure roller 200, and the diameter of the extension roller surface 210 is larger than the diameter of the tension roller surface 220.

[0114] When cold pressing the active material, a gap is maintained between one side of the stretching roller surface 210 and the area where the perforation 12 is located, so as to avoid stress concentration caused by the perforation 12 being too close to the stretching roller surface 210, thereby preventing the electrode sheet 1 from easily breaking during rolling.

[0115] According to some embodiments of this application, please refer to Figure 2 This application provides an electrode assembly 10 configured as a wound structure. The electrode assembly 10 includes a positive electrode 2, a negative electrode 3, and a separator 4 disposed between the positive electrode 2 and the negative electrode 3, and the wound structure includes a bending portion 6. The positive electrode 2 and / or the negative electrode 3 are the aforementioned electrode 1, and the bending portion 6 is located opposite to the corner area 13 after winding.

[0116] According to some embodiments of this application, please refer to Figure 1 This application provides a secondary battery 100, including the electrode assembly 10 mentioned above.

[0117] According to some embodiments of this application, please refer to Figures 1 to 6This application provides a current collector 1a. Based on the winding dimensions of the electrode assembly 10, the location of the corner region 13 on the current collector 1a is determined, and then perforations 12 are drilled in the corner region 13. The shape and arrangement of the perforations 12 are not limited. The ratio of the total area of ​​all perforations 12 to the area of ​​the corner region 13 is 0.1% to 50%. The width of the area containing the perforations 12 along the second direction Y is limited within the coating region 14, and the sum of the areas of each row of perforations gradually decreases from the middle to both sides. Outside the edge of the coating region 14 is a blank region 16, and no perforations are drilled in the blank region 16 (the area without active material coating).

[0118] To make the objectives, technical solutions, and advantages of this application clearer and more concise, the following specific embodiments are used for illustration, but this application is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of this application and can be used to describe this application, but should not be construed as limiting the scope of this application. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

[0119] To better illustrate this application, the following description, in conjunction with specific embodiments, further explains its content. The following are specific embodiments.

[0120] Comparative Example 1

[0121] Positive electrode 2:

[0122] The positive electrode active material ternary material nickel cobalt manganese (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed evenly at a mass ratio of 97:2:1 and added to the solvent NMP to prepare a positive electrode slurry. The positive electrode slurry is evenly coated on aluminum foil, dried at 85°C, cold pressed, and then die-cut and slit to produce lithium-ion battery positive electrode sheet 2.

[0123] The coating weight of the active material in positive electrode 2 is 17.6 mg / cm². 2 The thickness of the current collector 1a of the positive electrode 2 is 13 micrometers (µm).

[0124] Negative electrode 3:

[0125] The negative electrode active material graphite, conductive agent acetylene black, thickener sodium hydroxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are added to the solvent water at a mass ratio of 96:2:1:1 and mixed evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on copper foil, dried at 85°C, and then cold-pressed to form a negative electrode sheet 3.

[0126] The coating weight of negative electrode 3 is 10 mg / cm³. 2The current collector 1a of the negative electrode 3 has a thickness of 8µm and a width of 170 mm. The active material coating area 14 of the negative electrode 3 has a width of 100 mm. In addition, no perforations 12 are made in the corner area 13 of the current collector 1a of the negative electrode 3.

[0127] Diaphragm 4:

[0128] Using polyethylene microporous film as the porous separator film substrate, inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent are mixed evenly in a weight ratio of 3:1.5:5.5 to form a slurry, which is then coated on one side of the substrate and dried to obtain the separator film.

[0129] Electrolyte:

[0130] Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was 1:2:1) to obtain a lithium-ion battery electrolyte.

[0131] Preparation of secondary battery 100:

[0132] The above-mentioned positive electrode 2, negative electrode 3 and separator are wound together to obtain a bare cell. After encapsulation, liquid injection, formation and degassing processes, a lithium-ion battery is obtained. The battery is designed to charge N / P=1.03 and the cell design capacity is 160Ah.

[0133] Comparative Example 2

[0134] It is basically the same as Comparative Example 1, except that: holes are made in the first 6 corner areas 13 of the current collector 1a of the negative electrode 3, and the ratio of the area of ​​the hole to the area of ​​the corner area 13 is 10%, and the width of the hole area 17 is 120mm.

[0135] Example 1

[0136] It is basically the same as Comparative Example 1, except that: holes are made in the first 6 corner areas 13 of the current collector 1a of the negative electrode 3, and the ratio of the area of ​​the hole to the area of ​​the corner area 13 is 1%, and the width of the hole area 17 is 100mm.

[0137] Example 2

[0138] It is basically the same as Comparative Example 1, except that: holes are made in the first 6 corner areas 13 of the current collector 1a of the negative electrode 3, and the ratio of the area of ​​the hole to the area of ​​the corner area 13 is 10%, and the width of the hole area 17 is 100mm.

[0139] Example 3

[0140] It is basically the same as Comparative Example 1, except that: holes are made in the first 6 corner areas 13 of the current collector 1a of the negative electrode 3, and the ratio of the area of ​​the hole to the area of ​​the corner area 13 is 10%, and the width of the hole area 17 is 80mm.

[0141] Example 4

[0142] It is basically the same as Comparative Example 1, except that: holes are made in the first 6 corner areas 13 of the current collector 1a of the negative electrode 3, and the ratio of the area of ​​the hole to the area of ​​the corner area 13 is 20%, and the width of the hole area 17 is 60mm.

[0143] Using the secondary battery 100 prepared in the above comparative examples and embodiments, the fracture frequency during the cold pressing process was recorded. Simultaneously, after the secondary battery 100 was fabricated, it was charged to 4.25V at a constant current and constant voltage of 0.5C. The battery cell was then disassembled to observe whether lithium plating occurred at the bending portion 6 of the electrode assembly 10. Specific results can be found in Table 1.

[0144] Table 1

[0145]

[0146] As can be seen from Table 1, compared with Comparative Example 1, Examples 2 to 4 show that drilling a hole 12 in the corner area 13 of the current collector 1a can effectively reduce the lithium plating problem at the bend 6.

[0147] Meanwhile, comparing Examples 1 and 2 with Comparative Example 1, it can be seen that if the width of the opening area 17 is the same as the width of the active material coating area 14, the mechanical strength of the electrode 1 will be weakened, making the electrode 1 prone to breakage during cold pressing.

[0148] Comparing Examples 2, 3, and 4 with Comparative Example 2, it can be seen that if the width of the opening area 17 is smaller than the width of the active material coating area 14, a stress area 15 without openings is left between the edge of the opening area 17 and the edge of the coating area 14, which can effectively reduce the number of times the electrode 1 breaks.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A current collector (1a), characterized in that, For winding in a first direction (X), the current collector (1a) comprises: The current collector body (11) has a plurality of corner areas (13) along the first direction (X), the corner areas (13) being opposite to the bends (6) of the electrode assembly (10); In one of the corner areas (13), a through hole (12) is provided along the thickness direction of the current collector (1a); In the corner area (13) with the perforations (12), there are multiple perforations (12), and all the perforations (12) are distributed at intervals in the corner area (13); in the corner area (13) with the perforations (12), a number of perforations (12) are arranged in rows linearly at intervals along the first direction (X), and each row is distributed at intervals along the second direction (Y). The sum of the opening areas of any row of perforations (12) is denoted as S0. The sum of the opening areas S0 of each row gradually decreases from the middle of the corner area (13) to both ends of the corner area (13) along the second direction (Y). No perforations (12) are provided at either end of the corner area (13) along the second direction (Y). The first direction (X) is perpendicular to the second direction (Y).

2. The current collector (1a) according to claim 1, characterized in that, Within the corner area (13) with the perforations (12), the number of openings in each row of perforations (12) gradually decreases from the middle of the corner area (13) toward both ends of the corner area (13) along the second direction (Y).

3. The current collector (1a) according to claim 1, characterized in that, The current collection body (11) has a coating area (14) for coating an active material layer. The coating area (14) extends along the first direction (X) and passes through each of the corner areas (13) in sequence. The perforations (12) in the corner areas (13) are all located in the coating area (14).

4. The current collector (1a) according to claim 3, characterized in that, The coating area (14) is provided with at least one stress area (15) without openings. The stress area (15) extends along an edge of the coating area (14) in the second direction (Y). The perforations (12) in the corner area (13) are all located in the area of ​​the coating area (14) excluding the stress area (15). The first direction (X) is perpendicular to the second direction (Y).

5. The current collector (1a) according to claim 4, characterized in that, The two opposite edges of each stress zone (15) along the second direction (Y) are kept spaced apart in the second direction (Y).

6. The current collector (1a) according to claim 5, characterized in that, The width of each stress zone (15) in the second direction (Y) is denoted as D, where D ≥ 3 mm.

7. The current collector (1a) according to claim 4, characterized in that, Two stress zones (15) are provided at intervals along the second direction (Y) within the coating area (14), and the two stress zones (15) are respectively adjacent to the two opposite edges of the coating area (14) along the second direction (Y).

8. The current collector (1a) according to any one of claims 3-7, characterized in that, The current collection body (11) also has a blank area (16), which is located on at least one side of the coating area (14) along the second direction (Y), and the first direction (X) is perpendicular to the second direction (Y).

9. The current collector (1a) according to any one of claims 1-7, characterized in that, In the corner area (13) with the perforations (12), the sum of the opening areas of all the perforations (12) is denoted as S1, and the area of ​​the corner area (13) on the current collection body (11) is denoted as S2, characterized in that 0.1%≤S1 / S2≤50%.

10. The current collector (1a) according to any one of claims 1-7, characterized in that, Starting from the beginning of the current collection body (11) winding, the first n corner areas (13) are provided with the perforation (12), where n≤6.

11. An electrode (1), characterized in that, include: The current collector (1a) as described in any one of claims 1-10; An active material layer is disposed on at least one surface of the current collection body (11).

12. The electrode (1) according to claim 11, characterized in that, The active material layer comprises two layers, which are respectively disposed on the two surfaces of the current collection body (11).

13. A method for preparing an electrode sheet, characterized in that, The preparation of the electrode (1) according to claim 11 or 12 includes the following steps: Provide the stream collection body (11); A perforation (12) is made in the corner area (13) of the current collection body (11) to form a current collection fluid (1a); An active material layer is coated on the surface of the current collector (1a); The coated current collector (1a) is rolled.

14. The method for preparing the electrode according to claim 13, characterized in that, The step of rolling the coated current collector (1a) includes: The tension roller surface (220) of the pressure roller (200) and the extension roller surface (210) located on both sides of the tension roller surface (220) are respectively pressed onto the active material layer and the blank area (16) located on both sides of the current collector (1a), and the extension roller surface (210) facing the tension roller surface (220) is controlled to leave a gap between the area where the perforation (12) is located.

15. An electrode assembly (10) configured as a wound structure, characterized in that, It includes a positive electrode (2), a negative electrode (3) and a separator (4) disposed between the positive electrode (2) and the negative electrode (3), and the winding structure includes a bending portion (6); Wherein, the positive electrode (2) and / or the negative electrode (3) are the electrode (1) as described in claim 11 or 12, and the position of the bent portion (6) is opposite to the corner area (13) after winding.

16. A secondary battery (100), characterized in that, Includes the electrode assembly (10) as described in claim 15.

17. An electrical device, characterized in that, Includes the secondary battery (100) as described in claim 16.

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