Secondary battery, manufacturing method for electrode assembly, and electronic device

Abstract

Disclosed in the present application are a secondary battery, a manufacturing method for an electrode assembly, and an electronic device. The secondary battery comprises an electrode assembly and a first tab, wherein the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a separator arranged between the first electrode sheet and the second electrode sheet. The first tab is connected to the outermost ring of the first electrode sheet, and the relative position between the first tab and the electrode assembly is fixed. In the winding direction of the electrode assembly, the electrode sheet at the outermost ring of the electrode assembly is the first electrode sheet, and the outermost ring of the first electrode sheet is partially laminated in a first direction to form a first laminated portion, the first direction being the lamination direction of the second electrode sheet and the separator that are adjacent to the first laminated portion; and in the winding direction of the electrode assembly, the shortest distance between a first junction position and a second junction position on the first electrode sheet is P, a first portion is formed therefrom, and P satisfies 0 mm≤P≤6 mm; and the first laminated portion is disposed between the first tab and the first portion.

Description

Manufacturing methods for secondary batteries, electrode assemblies, and electronic devices Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery, a method for manufacturing electrode components, and an electronic device. Background Technology

[0002] The square winding structure is currently the most widely used structure in lithium-ion batteries. During battery cycling, the delithiation and lithium insertion of the electrode sheets cause repeated expansion of the electrode sheet thickness, resulting in repeated contraction and expansion of the bare cell. The winding structure with the first tab welded to the outer ring is often used in narrow cells and hard-shell wound cells. For this type of wound cell with the first tab welded to the outside, the first tab is located on the outer ring of the bare cell. Because the first tab is fixed to the external components of the bare cell (such as packaging aluminum-plastic film, shell cap, or terminal posts), it cannot move along the winding direction. When the cell expands, the electrode sheets near the outer ring are stretched and are prone to breakage at weak points.

[0003] Summary of the Invention

[0004] In view of this, this application provides a method for manufacturing a secondary battery, an electrode assembly, and an electronic device that can improve the problem of outer electrode breakage.

[0005] In a first aspect, embodiments of this application provide a secondary battery, including an electrode assembly and a first tab. The electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first tab is connected to the outermost ring of the first electrode, and the relative position of the first tab and the electrode assembly is fixed. Along the winding direction of the electrode assembly, the outermost electrode of the electrode assembly is the first electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first coated area with the first active material layer and a first empty foil area without the first active material layer. At the outermost ring of the first electrode, at the junction of the first coated area and the first empty foil area... The first boundary position is defined as follows: along the winding direction of the electrode assembly, the outermost ring of the first electrode includes a second curved segment, a second straight segment, a first curved segment, and a first straight segment connected in sequence, with both ends of the first curved segment and the second curved segment being the second boundary positions; the outermost ring of the first electrode is partially stacked along a first direction to form a first stacked portion, the first direction being the stacking direction of the second electrode and the diaphragm adjacent to the first stacked portion; along the winding direction of the electrode assembly, the shortest distance between the first boundary position and the second boundary position is P, forming a first part, satisfying 0mm≤P≤6mm; along the winding direction of the electrode assembly, the first part is closer to the winding center of the electrode assembly than the first tab, and the first stacked portion is disposed between the first tab and the first part.

[0006] In the aforementioned secondary battery, along the winding direction of the electrode assembly, the outermost ring of the first electrode includes a second curved section, a second straight section, a first curved section, and a first straight section connected in sequence. After the secondary battery is wound and compressed, uneven stress exists between the first straight section and the first curved section, between the first curved section and the second straight section, between the second straight section and the second curved section, and between the second curved section and the straight section of the second outer ring due to the compression force of the secondary battery, resulting in a type of weak point on the first electrode. Simultaneously, the first current collector includes a first coated area with a first active material layer and a first empty foil area without a first active material layer. Between the first coated area and the first empty foil area on the outermost ring of the first electrode, another type of weak point exists at the boundary between the first coated area and the first empty foil area due to the compression force of the secondary battery. When the two types of weak points are sufficiently close, i.e., the shortest distance between the first and second boundary positions is P, forming a first part, satisfying 0mm≤P≤6mm, the cell is prone to damage or even breakage in the first part after expansion. By placing the first stacked portion between the first tab and the first part, the outermost ring of the first electrode is partially stacked along the first direction to form the first stacked portion. During repeated charging and discharging of the secondary battery, the electrode assembly heats up and expands. The first stacked portion is first stretched, causing the overlapping part in the first stacked portion to gradually unfold. This helps to reduce the tensile force at the slot, thereby providing a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in the first part.

[0007] In one of the above embodiments, the first boundary position is located in the second straight section.

[0008] In the aforementioned secondary battery, the second curved section, the second straight section, the first curved section, and the first straight section are arranged along the winding direction of the electrode assembly, and the first junction position is located in the second straight section, so that the first empty foil area is located in the first curved section, the first straight section, and part of the second straight section, which is beneficial to improving the structural stability of the electrode assembly.

[0009] In one or more of the above embodiments, along the winding direction of the electrode assembly, the first stacked portion includes a first segment, a second segment, and a third segment connected in sequence, the first segment and the third segment overlap, the first segment, the second segment, and the third segment are stacked along a first direction, and the projections of the first segment, the second segment, and the third segment overlap along the first direction.

[0010] In the aforementioned secondary battery, when the electrode assembly expands, the first electrode sheet between the bend of the second segment relative to the first segment and the bend of the third segment relative to the second segment is first stretched, causing the first stacked portion to gradually unfold. This helps to reduce the force at the connection between the first electrode sheet and the first tab, thereby providing a margin for the expansion of the electrode assembly and helping to reduce the risk of damage to the outermost ring of the first electrode sheet.

[0011] In one or more of the above embodiments, the first electrode further includes a second stacked portion, which is located between the first stacked portion and the first electrode tab along the winding direction of the electrode assembly; the second stacked portion includes a fourth segment, a fifth segment and a sixth segment connected in sequence, the fifth segment is bent relative to the fourth segment, the sixth segment is bent relative to the fifth segment, the fourth segment, the fifth segment and the sixth segment are stacked in sequence along the first direction, and the projections of the fourth segment, the fifth segment and the sixth segment overlap along the first direction.

[0012] In the aforementioned secondary battery, the fourth, fifth, and sixth segments are stacked along the first direction, with the fourth and sixth segments overlapping. During repeated charging and discharging, the electrode assembly heats up and expands. The fourth segment is connected to the third segment. After the first stacked portion is fully expanded, the third segment first pulls the fourth segment, causing the overlapping portion of the fourth, fifth, and sixth segments to gradually expand. This helps to reduce the tension at the slot, thereby increasing the expansion margin of the electrode assembly and further improving the problem of electrode breakage in the first part.

[0013] In one or more of the above embodiments, the stacking direction of the first segment, the second segment, and the third segment is the same as the stacking direction of the fourth segment, the fifth segment, and the sixth segment, the first electrode tab is located in the sixth segment, and the fourth segment is connected to the third segment.

[0014] In the aforementioned secondary battery, the sixth segment is connected to the first tab, and the fourth segment is connected to the third segment, so that the folding directions of the first stacked portion and the second stacked portion are opposite. The first stacked portion and the second stacked portion with this shape can be formed by pressing out the first electrode sheet and then flattening the protrusion, which is beneficial to the forming of the first stacked portion and the second stacked portion.

[0015] In one or more of the above embodiments, along the winding direction of the electrode assembly, the distance between the bend of the second segment relative to the first segment and the bend of the third segment relative to the second segment is L1, and the distance between the bend of the fifth segment relative to the fourth segment and the bend of the fifth segment relative to the sixth segment is L2, satisfying L1+L2≥0.2mm.

[0016] When the aforementioned secondary battery is subjected to impacts or drops, if L1+L2≥0.2mm, it helps to reduce the stress on the connection position of the outermost first electrode plate during the expansion of the electrode assembly, thereby reducing the risk of damage to the first electrode plate.

[0017] In one or more of the above embodiments, any of the following conditions are met:

[0018] a. L2 > L1;

[0019] b. L1+L2≤3mm.

[0020] When the aforementioned secondary battery is subjected to impact, drop, or other conditions, the electrode assembly is subjected to instantaneous force impact. When the condition L2 > L1 is met, it helps to pull apart the second stacked part to disperse the stress at the connection between the first electrode and the first electrode tab.

[0021] When L1+L2≤3mm is satisfied, reducing the length of the portion reserved for the first electrode sheet that can be stretched when the electrode assembly expands helps to reduce the space occupied by the first and second stacked portions. At the same time, it is beneficial to the processing and forming of the first and second stacked portions.

[0022] In one or more of the above embodiments, along the winding direction of the electrode assembly, the first coating area is located on the side of the first empty foil area near the winding center of the electrode assembly, and the distance between the second segment and the end face of the first coating area near the first empty foil area is A, satisfying 1mm≤A≤10mm.

[0023] In the aforementioned secondary battery, the distance between the second segment and the end face of the first coating area near the first empty foil area is greater than or equal to 1 mm. This ensures sufficient space between the first stacked portion and the first coating area, facilitating the formation of the first stacked portion and improving its ease of formation. During repeated charging and discharging, the electrode assembly heats up and expands. The distance between the second segment and the end face of the first coating area near the first empty foil area is less than or equal to 10 mm. This allows the first stacked portion to be close to the first coating area, protecting the first part between the first empty foil area and the first coating area. This reduces the tensile force at the slot, providing room for electrode assembly expansion and mitigating the problem of electrode breakage at the first part.

[0024] In one or more of the above embodiments, 2mm≤A≤4mm is satisfied.

[0025] In the aforementioned secondary battery, the distance between the second segment and the end face of the first coating area near the first empty foil area is greater than or equal to 2mm. This provides sufficient space between the first stacked portion and the first coating area, facilitating the formation of the first stacked portion and further improving its molding convenience. During repeated charging and discharging, the electrode assembly heats up and expands. The distance between the second segment and the end face of the first coating area near the first empty foil area is less than or equal to 4mm. This allows the first stacked portion to be close to the first coating area, protecting the first part between the first empty foil area and the first coating area, reducing the tensile force at the slot, and providing room for electrode assembly expansion, further mitigating the problem of electrode breakage at the first part.

[0026] In one or more of the above embodiments, the first electrode further includes a seventh segment and an eighth segment. Along the winding direction of the electrode assembly, the seventh segment is connected to the first segment, and the eighth segment is connected to the sixth segment. The secondary battery further includes a first adhesive member, which is simultaneously bonded to the seventh segment and the eighth segment, and is also bonded to the first stacked portion.

[0027] In the aforementioned secondary battery, the first adhesive component helps to fix the shape of the first stacked portion, which helps to reduce the risk of the first stacked portion unraveling or partially unraveling during the winding process. Furthermore, in the event of an accident such as an impact on the electrode assembly, the first stacked portion may be subjected to compression or impact; the first adhesive component helps to maintain the shape of the first stacked portion, further reducing the risk of the first stacked portion unraveling or partially unraveling before the electrode assembly expands.

[0028] In one or more of the above embodiments, the first adhesive member is also adhered to the first tab and the second stacked portion.

[0029] In the aforementioned secondary battery, the first adhesive component secures the first tab, which helps reduce the risk of the first tab detaching from or partially detaching from the first electrode, reduces the risk of damage to the first electrode, and also reduces the possibility of the first tab piercing the separator and coming into contact with an electrode of different polarity. Furthermore, bonding the first adhesive component together with the first tab and the first stacked portion saves on adhesive processing.

[0030] In one or more of the above embodiments, along the width direction of the first electrode, the first tab is connected to the first electrode and extends out of the first electrode; along the direction in which the first tab extends, the first adhesive member extends beyond the first electrode.

[0031] In the aforementioned secondary battery, the first adhesive extends beyond the first electrode sheet along the direction in which the first tab extends, which helps to reduce the possibility of the separator being punctured and short-circuited at the first stacked portion, and thus helps to improve the safety of the secondary battery.

[0032] In one or more of the above embodiments, the secondary battery further includes a housing, an electrode assembly disposed within the housing, a portion of the first tab extending out of the housing, and an electrolyte disposed within the housing; the peel strength between the first adhesive and the seventh segment is F1, the peel strength between the first adhesive and the first overlapping portion is F2, and the peel strength between the first adhesive and the eighth segment is F3, satisfying at least one of the following conditions:

[0033] (1) 0 N / mm ≤ F1 ≤ 0.08 N / mm;

[0034] (2) 0 N / mm ≤ F2 ≤ 0.08 N / mm;

[0035] (3) 0 N / mm ≤ F3 ≤ 0.08 N / mm.

[0036] In the aforementioned secondary battery, when F1 = 0, the peel strength between the first adhesive and the seventh segment before immersion in electrolyte is greater than 0, which helps to reduce the risk of the first stacked portion unraveling or partially unraveling during the winding process.

[0037] When F1 satisfies the condition 0N / mm < F1 ≤ 0.08N / mm, on the one hand, the peel strength F1 between the first adhesive and the seventh segment is not too large, which is conducive to the smooth peeling of the first adhesive and the seventh segment when the electrode assembly expands, reducing the risk that the first adhesive will affect the effect of the first stacked part when the electrode assembly expands; on the other hand, the peel strength F1 between the first adhesive and the seventh segment is not too small, which is conducive to reducing the risk that the first stacked part will fall apart or partially fall apart under the condition that the electrode assembly is subjected to impact, which is conducive to improving the reliability of the first stacked part.

[0038] When F2 satisfies the condition 0N / mm < F2 ≤ 0.08N / mm, on the one hand, the peel strength F2 between the first adhesive and the first stacked part is not too large, which is conducive to the smooth peeling of the first adhesive and the first stacked part when the electrode assembly expands, reducing the risk that the first adhesive will affect the effect of the first stacked part when the electrode assembly expands; on the other hand, the peel strength F2 between the first adhesive and the first stacked part is not too small, which is conducive to reducing the risk that the first stacked part will fall apart or partially fall apart when the electrode assembly is subjected to impact, which is conducive to improving the reliability of the first stacked part.

[0039] When F3 satisfies the condition 0N / mm < F3 ≤ 0.08N / mm, on the one hand, the peel strength F3 between the first adhesive and the eighth segment is not too large, which is conducive to the smooth peeling of the first adhesive and the eighth segment when the electrode assembly expands, reducing the risk that the first adhesive will affect the effect of the first stacked part when the electrode assembly expands; on the other hand, the peel strength F3 between the first adhesive and the eighth segment is not too small, which is conducive to reducing the risk that the first stacked part will fall apart or partially fall apart when the electrode assembly is subjected to impact, which is conducive to improving the reliability of the first stacked part.

[0040] In one or more of the above embodiments, the length of the first adhesive member along the winding direction of the electrode assembly is S1, which satisfies 2mm≤S1≤20mm.

[0041] In the aforementioned secondary battery, when the length S1 of the first adhesive component satisfies the condition 2mm≤S1≤20mm, on the one hand, the area of ​​the first adhesive component is not too small, which helps to improve the peel strength between the first adhesive component and the seventh segment, the first stacked portion, and the eighth segment, reducing the risk of the first stacked portion coming apart during the winding process or when subjected to impact, and thus improving the reliability of the first stacked portion; on the other hand, the area of ​​the first adhesive component is not too large, which helps to facilitate the smooth peeling of the first adhesive component from the seventh segment, the first stacked portion, and the eighth segment when the electrode assembly expands, reducing the risk that the first adhesive component will affect the effect of the first stacked portion when the electrode assembly expands.

[0042] In one or more of the above embodiments, 6mm≤S1≤13mm is satisfied.

[0043] The aforementioned secondary battery, on the one hand, prevents the area of ​​the first adhesive member from being too small, which helps to improve the peel strength between the first adhesive member and the seventh segment, the first stacked portion, and the eighth segment, and further reduces the risk of the first stacked portion coming apart during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion; on the other hand, it prevents the area of ​​the first adhesive member from being too large, which helps to facilitate the smooth peeling of the first adhesive member from the seventh segment, the first stacked portion, and the eighth segment when the electrode assembly expands, and further reduces the risk that the first adhesive member will affect the effect of the first stacked portion when the electrode assembly expands.

[0044] In one or more of the above embodiments, the material of the first adhesive includes at least one of acrylic resin, polypropylene, or rubber.

[0045] In one or more of the above embodiments, the first electrode tab is welded to the second segment.

[0046] In one or more of the above embodiments, the electrode assembly is a cylindrical structure and the housing is a metal housing.

[0047] In the aforementioned secondary battery, the cylindrical electrode assembly may rotate relative to the first tab when it expands. The folded portion helps to suppress the stress on the first electrode and the first tab when the electrode assembly rotates, and helps to reduce the risk of damage to the outermost first electrode.

[0048] Secondly, embodiments of this application provide a method for manufacturing an electrode assembly for manufacturing the electrode assembly of the secondary battery in one or more of the above embodiments, characterized by comprising the following steps:

[0049] The first electrode sheet, formed by stamping and unfolding a round bar, creates an arc-shaped protrusion.

[0050] Flatten the arc-shaped protrusion to form the first overlapping part;

[0051] The first stacked portion is fixed in place using adhesive adhesive;

[0052] The first electrode, the second electrode, and the diaphragm are stacked and wound together in their unfolded state to form a wound structure.

[0053] The electrode assembly obtained by the above manufacturing method causes the secondary battery to heat up and expand during repeated charging and discharging. The first stacked part is first stretched, causing the overlapping part in the first stacked part to gradually unfold. This helps to reduce the tensile force at the slot, thereby providing the electrode assembly with expansion margin and improving the problem of electrode sheet breakage in the first part.

[0054] Thirdly, embodiments of this application provide an electronic device including the secondary battery described in the above embodiments. Attached Figure Description

[0055] Figure 1 is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application.

[0056] Figure 2 is an exploded view of the secondary battery in Figure 1.

[0057] Figure 3 is a schematic diagram of the wound electrode assembly and the first and second electrodes in one embodiment of this application.

[0058] Figure 4 is a partial side view of the first electrode and the first electrode tab provided in an embodiment of this application.

[0059] Figure 5 is a schematic diagram of the wound electrode assembly and the first and second tabs in another embodiment of this application.

[0060] Figure 6 is a schematic diagram of the wound electrode assembly and the first and second electrodes in another embodiment of this application.

[0061] Figure 7 is a schematic diagram of the wound electrode assembly and the first and second electrodes in another embodiment of this application.

[0062] Figure 8 is a schematic diagram of the wound electrode assembly and the first and second electrodes in another embodiment of this application.

[0063] Figure 9 is a partial view of the first electrode plate and a side view of the first electrode ear provided in another embodiment of this application.

[0064] Figure 10 is a top view of a portion of the first electrode and the first electrode tab provided in an embodiment of this application.

[0065] Figure 11 is a top view of a portion of the first electrode and the first electrode tab provided in another embodiment of this application.

[0066] Figure 12 is a bottom view of a portion of the first electrode and the first electrode tab provided in another embodiment of this application.

[0067] Figure 13 is a bottom view of a portion of the first electrode and the first electrode tab provided in another embodiment of this application.

[0068] Figure 14 is a side view of the first adhesive member after it has been unfolded according to an embodiment of this application.

[0069] Figure 15 is a side view of the second adhesive member after it has been unfolded according to an embodiment of this application.

[0070] Figure 16 is a schematic diagram of an electronic device provided in an embodiment of this application.

[0071] Key Component Symbols Explanation: 001 Secondary Battery; 10 Electrode Assembly; 11 First Electrode; 111 First Current Collector; 1111 First Coating Area; 1112 First Empty Foil Area; 112 First Active Material Layer; 113 First Stacked Section; 1131 First Segment; 1132 Second Segment; 1133 Third Segment; 114 Second Stacked Section; 1141 Fourth Segment; 1142 Fifth Segment; 1143 Sixth Segment; 115 Seventh Segment; 117 Eighth Segment; 11a First Straight Segment; 11b First Curved Segment; 11c Second Straight Segment; 11d Second Curved Segment; 11e First Junction Position; 11f Second Junction Position; 12 Second Electrode; 121 Second Current Collector; 122Second active material layer 13, diaphragm 20, first electrode tab 30, second electrode tab 40, housing 50, first adhesive component 60, second adhesive component X, winding direction of electrode assembly Y, first direction Z, width direction of first electrode sheet 002, electronic device 020, device body Detailed Implementation

[0072] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0073] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intervening element present. When an element is considered to be "set" on another element, it can be directly set on the other element or there may be an intervening element present. In this application, unless otherwise expressly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a 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 between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances. The term "and / or" as used herein includes any and all combinations of one or more of the related listed items.

[0074] 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 belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms "comprising" and "equivalent to," and any variations thereof, in the specification, claims, and foregoing description of the drawings, are intended to cover non-exclusive inclusion.

[0075] 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.

[0076] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Where there is no conflict, the various embodiments in this application can be combined with each other. In the method steps, S1, S2, etc., only indicate the name of the step and do not limit the order of the steps.

[0077] It should be noted that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative examples and should not constitute any limitation on this application.

[0078] One embodiment of this application provides a secondary battery, including an electrode assembly and a first tab. The electrode assembly includes a first electrode, a second electrode, and a separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first tab is connected to the outermost ring of the first electrode, and the relative position of the first tab and the electrode assembly is fixed. Along the winding direction of the electrode assembly, the outermost electrode of the electrode assembly is the first electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first coated area with the first active material layer and a first empty foil area without the first active material layer. At the outermost ring of the first electrode, the junction of the first coated area and the first empty foil area is the first electrode. A first junction position; along the winding direction of the electrode assembly, the outermost ring of the first electrode includes a second curved segment, a second straight segment, a first curved segment, and a first straight segment connected in sequence, with both ends of the first curved segment and the second curved segment being second junction positions; the outermost ring of the first electrode is partially stacked along a first direction to form a first stacked portion, the first direction being the stacking direction of the second electrode and the diaphragm adjacent to the first stacked portion; along the winding direction of the electrode assembly, the shortest distance between the first junction position and the second junction position is P, forming a first part, satisfying 0mm≤P≤6mm; along the winding direction of the electrode assembly, the first part is closer to the winding center of the electrode assembly than the first tab, and the first stacked portion is disposed between the first tab and the first part.

[0079] In the aforementioned secondary battery, along the winding direction of the electrode assembly, the outermost ring of the first electrode includes a second curved section, a second straight section, a first curved section, and a first straight section connected in sequence. After the secondary battery is wound and compressed, uneven stress exists between the first straight section and the first curved section, between the first curved section and the second straight section, between the second straight section and the second curved section, and between the second curved section and the straight section of the second outer ring due to the compression force of the secondary battery, resulting in a type of weak point on the first electrode. Simultaneously, the first current collector includes a first coated area with a first active material layer and a first empty foil area without a first active material layer. Between the first coated area and the first empty foil area on the outermost ring of the first electrode, another type of weak point exists at the boundary between the first coated area and the first empty foil area due to the compression force of the secondary battery. When the two types of weak points are sufficiently close, i.e., the shortest distance between the first and second boundary positions is P, forming a first part, satisfying 0mm≤P≤6mm, the cell is prone to damage or even breakage in the first part after expansion. By placing the first stacked portion between the first tab and the first part, the outermost ring of the first electrode is partially stacked along the first direction to form the first stacked portion. During repeated charging and discharging of the secondary battery, the electrode assembly heats up and expands. The first stacked portion is first stretched, causing the overlapping part in the first stacked portion to gradually unfold. This helps to reduce the tensile force at the slot, thereby providing a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in the first part.

[0080] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0081] Please refer to Figures 1 and 2. This application embodiment provides a secondary battery 001, which includes an electrode assembly 10 and a first tab 20, with the first tab 20 connected to the electrode assembly 10.

[0082] In some embodiments, the secondary battery 001 may be a square hard-shell battery or a soft-pack battery; no specific limitation is made here.

[0083] Please refer to Figures 1 and 2. In some embodiments, the secondary battery 001 further includes a second tab 30, which is connected to the electrode assembly 10. The first tab 20 and the second tab 30 have different polarities.

[0084] In some embodiments, the secondary battery 001 further includes a housing 40, and the electrode assembly 10 is disposed within the housing 40.

[0085] In some embodiments, a portion of the first tab 20 extends out of the housing 40 and is used for electrical connection with an external structure, and a portion of the second tab 30 extends out of the housing 40 and is used for electrical connection with an external structure.

[0086] In other embodiments, the first tab 20 is connected to a conductive first adapter (not shown), which extends out of the housing 40 and is used for electrical connection with an external structure. The second tab 30 is connected to a conductive second adapter (not shown), which extends out of the housing 40 and is used for electrical connection with an external structure.

[0087] In some embodiments, the housing 40 includes at least one of a steel housing, a resin housing, or an aluminum-plastic film. For example, when the secondary battery 001 is a square hard-shell battery, the housing 40 includes a steel housing or a resin housing, and when the secondary battery 001 is a soft-pack battery, the housing 40 includes an aluminum-plastic film.

[0088] Please refer to Figures 3 and 4. In some embodiments, the electrode assembly 10 includes a first electrode 11, a second electrode 12, and an isolation film disposed between the first electrode 11 and the second electrode 12. The isolation film is used to isolate the first electrode 11 and the second electrode 12. The first electrode 11, the second electrode 12, and the isolation film are stacked and wound to form a wound structure.

[0089] In some embodiments, the first electrode 11 includes a first current collector 111 and a first active material layer 112 stacked together, and the second electrode 12 includes a second current collector 121 and a second active material layer 122 stacked together.

[0090] Along the winding direction X of the electrode assembly 10, the first current collector 111 includes a first coated area 1111 with a first active material layer 112 and a first empty foil area 1112 without the first active material layer 112.

[0091] Along the winding direction X of the electrode assembly 10, the second current collector 121 includes a second coated area with a second active material layer 122 and a second empty foil area without the second active material layer 122.

[0092] The winding direction X can be understood as the direction from the starting section of the winding of the electrode assembly 10 to the ending section of the winding of the electrode assembly 10.

[0093] Referring to Figure 3, in some embodiments, along the winding direction X of the electrode assembly 10, the outermost ring of the electrode assembly 10 includes a second electrode 12, the outermost ring of the second electrode 12 includes a second empty foil region, and the second tab 30 is connected to the second empty foil region of the outermost ring of the second electrode 12.

[0094] In some embodiments, the outermost electrode of the electrode assembly 10 is a first electrode 11. At the outermost edge of the first electrode 11, the junction of the first coating area 1111 and the first empty foil area 1112 is a first junction position 11e.

[0095] In some embodiments, the first coating area 1111 includes a first single-layer coating area (not shown) and a first double-layer coating area (not labeled). The first current collector 111 of the first single-layer coating area has a first active material layer 112 on one side in the thickness direction Y, and no first active material layer 112 on the other side. The first current collector 111 of the first double-layer coating area has a first active material layer 112 on both opposite sides in the thickness direction Y. The second coating area has the same structure as the first coating area 1111, and will not be described in detail here.

[0096] In some embodiments, the first current collector 111 is a cathode current collector, and the first active material layer 112 is a cathode active material layer; the second current collector 121 is an anode current collector, and the second active material layer 122 is an anode active material layer.

[0097] In other embodiments, the first current collector 111 is an anode current collector, and the first active material layer 112 is an anode active material layer; the second current collector 121 is a cathode current collector, and the second active material layer 122 is a cathode active material layer.

[0098] In some embodiments, the separator is an insulating film material such as a polyethylene film, a polypropylene film, a polyester film, or a polyimide film.

[0099] In some embodiments, the outermost ring of the first electrode 11 includes a second curved segment 11d, a second straight segment 11c, a first curved segment 11b, and a first straight segment 11a connected in sequence. Between the first straight segment 11a and the first curved segment 11b, the first curved segment 11b and the second straight segment 11c, the second straight segment 11c and the second curved segment 11d, and the second curved segment 11d and the straight segment of the next outer ring, that is, at both ends of the first curved segment 11b and the second curved segment 11d, there is a problem of uneven stress due to the clamping force of the secondary battery 001. These four positions are the second boundary positions 11f.

[0100] In some embodiments, when the first boundary position 11e and the second boundary position 11f are close to each other, that is, the shortest distance between the first boundary position 11e and the second boundary position 11f is P, which satisfies 0mm≤P≤6mm, a first part is formed on the outermost ring of the first electrode 11, which is the weak area of ​​the first electrode 11.

[0101] In some embodiments, P can be one of 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 1.4mm or 6mm.

[0102] It is worth noting that since there are four second boundary positions 11f, the shortest distance between the first boundary position 11e and the second boundary position 11f can be determined by measurement and comparison. For example, along the winding direction of the first electrode 11, the distances between the first boundary position 11e and each of the four second boundary positions 11f are measured, and the minimum value is the shortest distance between the first boundary position 11e and the second boundary position 11f. Alternatively, the four second boundary positions 11f can be marked, and then the first electrode 11 can be unrolled, and the distances between the two second boundary positions 11f adjacent to the first boundary position 11e can be measured, and the minimum value is the shortest distance between the first boundary position 11e and the second boundary position 11f.

[0103] The outermost ring of the first electrode 11 is partially stacked along the first direction Y to form a first stacked portion 113. Along the first direction Y, the projections of the first electrode 11 in the first stacked portion 113 at least partially overlap. The first stacked portion 113 is disposed between the first tab 20 and the first portion along the winding direction X of the electrode assembly 10. The first direction is the stacking direction of the second electrode and the diaphragm adjacent to the first stacked portion.

[0104] By placing the first stacked portion 113 between the first tab 20 and the first part, the projections of the first electrode 11 of the first stacked portion 113 overlap at least partially along the first direction Y. During repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands, and the first stacked portion 113 is first stretched, causing the overlapping part in the first stacked portion 113 to gradually unfold. This helps to reduce the tension at the slot, thereby providing a margin for the expansion of the electrode assembly 10 and improving the problem of electrode breakage in the first part.

[0105] It should be noted that the shortest distance between the first boundary position 11e and the second boundary position 11f is the distance between the first boundary position 11e and the second boundary position 11f that is closest to the first boundary position 11e among the four second boundary positions 11f along the winding direction X of the electrode assembly 10.

[0106] In some embodiments, the second curved segment 11d, the second straight segment 11c, the first curved segment 11b, and the first straight segment 11a are arranged along the winding direction X of the electrode assembly 10.

[0107] In some embodiments, the first boundary position 11e is located in the second straight section 11c, that is, the first boundary position 11e may be located on the side of the second straight section 11c near the first curved section 11b, or the first boundary position 11e' may be located on the side of the second straight section 11c near the second curved section 11d. The first stacking portion 113 is disposed in the first curved section 11b or the first straight section 11a, and along the winding direction X of the electrode assembly 10, the first stacking portion 113 is located on the side of the first boundary position 11e away from the winding center of the electrode assembly 10. The first boundary position 11e is located in the second straight section 11c, so that the first empty foil area 1112 is located in the first curved section 11b, the first straight section 11a, and part of the second straight section 11c, which is beneficial to improving the structural stability of the electrode assembly 10.

[0108] Referring to Figure 5, in some embodiments, the first boundary position 11e is located on the first curved section 11b, that is, the first boundary position 11e may be located on the side of the first curved section 11b closer to the first tab 20, or the first boundary position 11e' may be located on the side of the first curved section 11b closer to the second straight section 11c. The first stacking portion 113 is disposed on the first curved section 11b or the first straight section 11a, along the winding direction X of the electrode assembly 10, and the first stacking portion 113 is located on the side of the first boundary position 11e away from the winding center of the electrode assembly 10.

[0109] Referring to Figure 6, in some embodiments, the first boundary position 11e is located in the first straight section 11a and along the winding direction X of the electrode assembly 10, the first boundary position 11e is located on the side of the first tab 20 away from the winding center of the electrode assembly 10. The first stacking portion 113 is disposed in the first straight section 11a, and the first stacking portion 113 is located between the first boundary position 11e and the first tab 20.

[0110] Referring to Figure 7, in some embodiments, the first boundary position 11e is located on the second curved section 11d, that is, the first boundary position 11e can be located on the side of the second curved section 11d close to the second straight section 11c, or the first boundary position 11e' is located on the side of the second curved section 11d close to the outermost ring of the first electrode 11. The first stacked portion 113 is disposed on the second straight section 11c or the second curved section 11d. Along the winding direction X of the electrode assembly 10, the first stacked portion 113 is located on the side of the first boundary position 11e away from the winding center of the electrode assembly 10.

[0111] Referring to Figures 3 and 4, in some embodiments, the first tab 20 is connected to the first empty foil area 1112, and a portion of the first empty foil area 1112 is folded to form a first stacked portion 113. By providing the first stacked portion 113 in the first empty foil area 1112, the interference of the first active material layer 112 on the formation of the first stacked portion 113 and the second stacked portion 114 is reduced. Furthermore, compared to providing the first stacked portion 113 in the portion where the first active material layer 112 is provided, providing the first stacked portion 113 in the first empty foil area 1112 also helps to reduce the risk of the first active material layer 112 peeling off.

[0112] In some embodiments, the first stacked portion 113 includes a first segment 1131, a second segment 1132, and a third segment 1133 connected in sequence. The second segment 1132 is bent relative to the first segment 1131, and the third segment 1133 is bent relative to the second segment 1132. The first segment 1131, the second segment 1132, and the third segment 1133 are stacked sequentially along a first direction Y. Along the first direction Y, the projections of the first segment 1131, the second segment 1132, and the third segment 1133 overlap. When the electrode assembly 10 expands, the first electrode 11 between the bend of the second segment 1132 relative to the first segment 1131 and the bend of the third segment 1133 relative to the second segment 1132 is first stretched, causing the first stacked portion 113 to gradually unfold. This helps to reduce the force at the connection between the first electrode 11 and the first electrode tab 20, thereby providing a margin for the expansion of the electrode assembly 10 and reducing the risk of damage to the outermost ring of the first electrode 11.

[0113] Referring to Figures 3 and 4, in some embodiments, the first electrode 11 further includes a second stacked portion 114. Along the winding direction X of the electrode assembly 10, the second stacked portion 114 is located between the first stacked portion 113 and the first electrode tab 20. The second stacked portion 114 includes a fourth segment 1141, a fifth segment 1142, and a sixth segment 1143 connected in sequence. The fifth segment 1142 is bent relative to the fourth segment 1141, and the sixth segment 1143 is bent relative to the fifth segment 1142. The fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 are stacked sequentially along the first direction Y. Along the first direction Y, the projections of the fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 overlap.

[0114] The fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 are stacked along the first direction Y. The fourth segment 1141 and the sixth segment 1143 overlap. During repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. The fourth segment 1141 is connected to the third segment 1133. After the first stacked part 113 is fully unfolded, the third segment 1133 first pulls the fourth segment 1141, so that the overlapping part of the fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 gradually unfolds. This helps to reduce the tension at the slot, thereby increasing the expansion margin of the electrode assembly 10 and further improving the problem of electrode breakage in the first part.

[0115] When the electrode assembly 10 expands, the first stacked portion 113 and the second stacked portion 114 are subjected to lamination pressure along the stacking direction of the first electrode 11, the separator, and the second electrode 12. This may inhibit the extension of the first stacked portion 113 and the second stacked portion 114, posing a risk that the first stacked portion 113 and the second stacked portion 114 may be difficult to open or fully extend. In the embodiment described above with the first stacked portion 113 and the second stacked portion 114, only at least one of the first stacked portion 113 and the second stacked portion 114 needs to extend or partially open, which helps to reduce the risk of damage to the outermost ring of the first electrode 11 and improves the reliability of the first stacked portion 113 and the second stacked portion 114.

[0116] In some embodiments, along the first direction Y, the distance between the first segment 1131 and the winding center of the electrode assembly 10 is greater than the distance between the third segment 1133 and the winding center of the electrode assembly 10. In other embodiments, along the first direction Y, the distance between the fourth segment 1141 and the winding center of the electrode assembly 10 is greater than the distance between the sixth segment 1143 and the winding center of the electrode assembly 10.

[0117] Referring to Figure 8, in some embodiments, along the first direction Y, the distance between the first segment 1131 and the winding center of the electrode assembly 10 is less than the distance between the third segment 1133 and the winding center of the electrode assembly 10. In other embodiments, along the first direction Y, the distance between the fourth segment 1141 and the winding center of the electrode assembly 10 is less than the distance between the sixth segment 1143 and the winding center of the electrode assembly 10.

[0118] In some embodiments, the sixth segment 1143 is connected to the first tab 20, and the fourth segment 1141 is connected to the third segment 1133, so that the folding directions of the first stacked portion 113 and the second stacked portion 114 are opposite. The first stacked portion 113 and the second stacked portion 114 with this shape can be formed by pressing out the protrusion of the first electrode 11 and then flattening the protrusion, which is beneficial to the forming of the first stacked portion 113 and the second stacked portion 114.

[0119] Please refer to Figures 3 and 4. In some embodiments, along the winding direction X of the electrode assembly 10, the distance between the bend of the second segment 1132 relative to the first segment 1131 and the distance between the bend of the third segment 1133 relative to the second segment 1132 is L1, and the distance between the bend of the fifth segment 1142 relative to the fourth segment 1141 and the distance between the bend of the fifth segment 1142 relative to the sixth segment 1143 is L2, satisfying L2 > L1.

[0120] In cases such as the secondary battery 001 being dropped, the electrode assembly 10 is subjected to instantaneous impact. When the condition L2 > L1 is met, it helps to pull apart the second stacked portion 114 to disperse the stress at the connection between the first electrode 11 and the first electrode tab 20.

[0121] In some embodiments, L2 can be 1.1L1, 1.15L1, 1.2L1, 1.25L1, 1.3L1, 1.35L1, 1.4L1, 1.45L1, 1.5L1, 1.55L1, 1.6L1, 1.65L1, 1.7L1, 1.75L1, 1.8L1, 1.85L1, 1.9L1, 1.95L1, or 2L1.

[0122] In some embodiments, along the width direction Z of the electrode assembly 10, the maximum width that the electrode assembly 10 can expand to is W1, and the minimum width of the electrode assembly 10 is W2. Along the winding direction X of the electrode assembly 10, the distance between the bend of the second segment 1132 relative to the first segment 1131 and the bend of the third segment 1133 relative to the second segment 1132 is L1, and the distance between the bend of the fifth segment 1142 relative to the fourth segment 1141 and the bend of the fifth segment 1142 relative to the sixth segment 1143 is L2, satisfying 2(L1+L2)≥π(W1-W2).

[0123] When L1+L2 satisfies the condition L≥π(W1-W2) / 2, it is beneficial to increase the expansion margin of the electrode assembly 10, and to further reduce the force on the connection position of the outermost first electrode 11 when the electrode assembly 10 expands, thereby further reducing the risk of damage to the first electrode 11.

[0124] The following example, using a secondary battery 001 as a square hard-shell battery, illustrates the method for measuring the maximum width W1 and the minimum width W2:

[0125] Maximum width W1: When the secondary battery 001 is fully discharged, that is, when the terminal device is disassembled at 0% SOC (State of Charge, the usable state of the remaining charge in the battery), the electrode assembly 10 is obtained and the housing 40 is obtained. The width of the housing 40 is measured with an optical microscope along the width direction Z of the housing 40 at an ambient temperature of 25°C. This is the maximum width W1 that the electrode assembly 10 can expand to.

[0126] Minimum width W2: The minimum width W2 is obtained by measuring the width of the wound electrode assembly 10 along the width direction Z of the electrode assembly 10 at an ambient temperature of 25°C using an optical microscope.

[0127] It should be noted that when the shell 40 is a rigid shell 40, the maximum width W1 is equal to the maximum width of the inner wall of the shell 40.

[0128] In some embodiments, L1 ≥ 0.2 mm is satisfied.

[0129] When L1 satisfies the condition L1≥0.2mm, it helps to reduce the stress on the connection position of the outermost first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11.

[0130] As an example, L1 can be one of 0.25mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, or 5mm.

[0131] In some embodiments, L2 ≥ 0.2 mm is satisfied.

[0132] When L2 satisfies the condition L2≥0.2mm, it helps to reduce the stress on the connection position of the outermost first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11.

[0133] As an example, L2 can be one of 0.25mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, or 5mm.

[0134] In some embodiments, L1+L2≥0.2mm is satisfied. When L1+L2 satisfies the condition L1+L2≥0.2mm, it helps to reduce the stress on the connection position of the outermost first electrode 11 when the electrode assembly 10 expands, thereby helping to reduce the risk of damage to the first electrode 11.

[0135] In some embodiments, L1+L2≤3mm is satisfied. When L1+L2 satisfies the condition L1+L2≤3mm, the length of the portion reserved in the first electrode 11 for the electrode assembly 10 to be stretched during expansion is reduced, which is beneficial to reducing the space occupied by the first stacked portion 113 and the second stacked portion 114, and at the same time, it is beneficial to the processing and forming of the first stacked portion 113 and the second stacked portion 114.

[0136] Referring to Figures 3 and 4, in some embodiments, along the winding direction X of the electrode assembly 10, the outermost ring of the electrode assembly 10 includes a second electrode 12, the outermost ring of the second electrode 12 includes a second empty foil region b, and the second tab 30 is connected to the second empty foil region b of the outermost ring of the second electrode 12. Along the winding direction X of the electrode assembly 10, the projections of the first stacked portion 113 and the second stacked portion 114 are located between the projection of the first tab 20 and the projection of the second tab 30. The projection directions of the first stacked portion 113 and the second stacked portion 114, the projection direction of the first tab 20, and the projection direction of the second tab 30 are the stacking directions of the first electrode 11, the separator, and the second electrode 12.

[0137] In the winding structure of the electrode assembly 10, the diameters of the first tab 20 and the second tab 30 are relatively large. During the expansion of the electrode assembly 10, the interlayer compressive force at the first tab 20 and the second tab 30 is relatively large. When the projections of the first stacked portion 113 and the second stacked portion 114 are located between the projections of the first tab 20 and the second tab 30, it is beneficial to reduce the risk that the first stacked portion 113 and the second stacked portion 114 will be squeezed and difficult to disperse or unfold. At the same time, it is also beneficial to reduce the influence of the interface between the first electrode 11 and the second electrode 12 and the electrolyte wetting, and reduce the possibility of deterioration of the cycle performance of the secondary battery 001.

[0138] In some embodiments, along the winding direction X of the electrode assembly 10, the minimum distance between the first stacked portion 113 and the second stacked portion 114 and the first tab 20 is between 1 and 10 mm. This ensures that the distance between the connection point of the first electrode 11 and the first tab 20 and the first stacked portion 113 and the second stacked portion 114 is not too far, which helps to reduce the stress at the connection point of the first electrode 11 and the first tab 20, thereby further reducing the risk of damage to the outermost ring of the first electrode 11. It also ensures that the distance between the connection point of the first electrode 11 and the first tab 20 and the first stacked portion 113 and the second stacked portion 114 is not too close, which helps to provide space for the forming of the first stacked portion 113 and the second stacked portion 114, and helps to reduce the risk of interference between the first stacked portion 113 and the second stacked portion 114 and the tab.

[0139] As an example, the minimum distance between the first stacked portion 113 and the second stacked portion 114 and the first electrode tab 20 can be one of 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm or 10mm.

[0140] Please refer to Figure 9. In some embodiments, the first electrode 11 further includes a seventh segment 115 and an eighth segment 117. Along the winding direction X of the electrode assembly 10, the seventh segment 115 is connected to the first segment 1131, and the eighth segment 117 is connected to the sixth segment 1143.

[0141] The seventh segment 115, the first stacked portion 113, the second stacked portion 114, and the eighth segment 117 are connected in sequence. The secondary battery 001 also includes a first adhesive member 50, which is bonded to both the seventh segment 115 and the eighth segment 117, and is also bonded to the first stacked portion 113 and the second stacked portion 114.

[0142] The first adhesive 50 is bonded to the seventh segment 115, the eighth segment 117, the first stacked portion 113, and the second stacked portion 114, which helps maintain the shape of the first stacked portion 113 and the second stacked portion 114. When manufacturing the secondary battery 001, the first electrode 11 can be folded first to form the first stacked portion 113 and the second stacked portion 114, and then the first electrode 11, the separator, and the second electrode 12 can be wound to form a wound structure. The first adhesive 50 plays a role in fixing the shape of the first stacked portion 113 and the second stacked portion 114, which helps reduce the risk of the first stacked portion 113 and the second stacked portion 114 unraveling or partially unraveling during the winding process.

[0143] Referring to Figures 3 and 9, in some embodiments, the secondary battery 001 further includes a second adhesive member 60. Along the first direction Y, the first adhesive member 50 is adhered to one side of the first electrode 11, and the second adhesive member 60 is adhered to the other side of the first electrode 11. The second adhesive member 60 is adhered to both the seventh segment 115 and the eighth segment 117, and also to the first stacked portion 113 and the second stacked portion 114. The second adhesive helps maintain the morphology of the first stacked portion 113 and the second stacked portion 114, reduces the risk of the first stacked portion 113 and the second stacked portion 114 unraveling or partially unraveling during winding, and also reduces the risk of the first stacked portion 113 and the second stacked portion 114 unraveling or partially unraveling before the electrode assembly 10 expands.

[0144] In some embodiments, the first adhesive member 50 is also bonded to the first tab 20. The first adhesive member 50 serves to fix the first tab 20, which helps to reduce the risk of the first tab 20 detaching from or partially detaching from the first electrode 11, reduces the risk of damage to the first electrode 11, and also reduces the possibility of the first tab 20 piercing the diaphragm 13 and coming into contact with an electrode of different polarity. In addition, bonding the first adhesive member 50 together with the first tab 20, the first stacked portion 113, and the second stacked portion 114 helps to save on adhesive processes.

[0145] In some embodiments, the second adhesive 60 is also bonded to the first tab 20. The second adhesive 60 serves to fix the first tab 20, which helps to reduce the risk of the first tab 20 detaching from or partially detaching from the first electrode 11, reduces the risk of damage to the first electrode 11, and also reduces the possibility of the first tab 20 piercing the diaphragm 13 and coming into contact with an electrode of different polarity. In addition, bonding the first adhesive 50 together with the first tab 20, the first stacked portion 113, and the second stacked portion 114 helps to save on adhesive processes.

[0146] Referring to Figure 10, in some embodiments, along the width direction Z of the first electrode 11, the first tab 20 is connected to the first electrode 11 and extends beyond the first electrode 11. Along the direction in which the first tab 20 extends, the first adhesive member 50 extends beyond the first electrode 11.

[0147] In extreme cases, the first stacked portion 113 and the second stacked portion 114 may develop cracks or break. Sharp cracks and burrs at the cracks can easily puncture the separator 13, causing contact between electrodes of different polarities and resulting in a short circuit. Along the direction in which the first tab 20 extends, the first adhesive member 50 extends beyond the first electrode 11, which helps reduce the possibility of the separator 13 being punctured and short-circuited at the first stacked portion 113 and the second stacked portion 114, and helps improve the safety of the secondary battery 001.

[0148] In an embodiment where the first adhesive 50 is also bonded to the first tab 20, the first adhesive 50 extends beyond the first electrode 11 along the direction in which the first tab 20 extends. This helps to reduce the possibility of short circuits caused by burrs on the first tab 20 puncturing the separator 13, thereby improving the safety of the secondary battery 001.

[0149] Please refer to Figure 11. In some embodiments, the first adhesive 50 extends beyond the first electrode 11 in the direction opposite to the direction in which the first tab 20 extends. This helps to reduce the possibility of the separator 13 at the first stacked portion 113 and the second stacked portion 114 being punctured and short-circuited, and helps to improve the safety of the secondary battery 001.

[0150] Referring to Figure 12, in some embodiments, along the width direction Z of the first electrode 11, the first tab 20 is connected to the first electrode 11 and extends beyond the first electrode 11. Along the direction in which the first tab 20 extends, the second adhesive member 60 extends beyond the first electrode 11, which helps reduce the possibility of the separator 13 corresponding to the first stacked portion 113 and the second stacked portion 114 being punctured and short-circuited, thus improving the safety of the secondary battery 001.

[0151] In an embodiment where the second adhesive 60 is also bonded to the first tab 20, the second adhesive 60 extends beyond the first electrode 11 along the direction in which the first tab 20 extends. This helps to reduce the possibility of short circuits caused by burrs on the first tab 20 puncturing the separator 13, thereby improving the safety of the secondary battery 001.

[0152] Please refer to Figure 13. In some embodiments, the second adhesive 60 extends beyond the first electrode 11 in the direction opposite to the direction in which the first tab 20 extends. This helps to reduce the possibility of the separator 13 corresponding to the first stacked portion 113 and the second stacked portion 114 being punctured and short-circuited, thereby improving the safety of the secondary battery 001.

[0153] In some embodiments, the peel strength between the first adhesive 50 and the seventh segment 115 is F1, which satisfies 0 N / mm ≤ F1 ≤ 0.08 N / mm.

[0154] F1 is the peel strength between the first adhesive 50 and the seventh segment 115 after being soaked in electrolyte.

[0155] When F1 = 0, the peel strength between the first adhesive 50 and the seventh segment 115 before immersion in electrolyte is greater than 0, which helps to reduce the risk of the first stacked portion 113 and the second stacked portion 114 coming apart or partially coming apart during the winding process.

[0156] When F1 satisfies the condition 0 N / mm < F1 ≤ 0.08 N / mm, on the one hand, the peel strength F1 between the first adhesive 50 and the seventh segment 115 is not too large, which is conducive to the smooth peeling of the first adhesive 50 and the seventh segment 115 when the electrode assembly 10 expands, reducing the risk that the first adhesive 50 will affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands; on the other hand, the peel strength F1 between the first adhesive 50 and the seventh segment 115 is not too small, which is conducive to reducing the risk that the first stacked portion 113 and the second stacked portion 114 will separate or partially separate under the condition that the electrode assembly 10 is subjected to impact, which is conducive to improving the reliability of the first stacked portion 113 and the second stacked portion 114.

[0157] As an example, F1 can be any one of 0 N / mm, 0.01 N / mm, 0.02 N / mm, 0.03 N / mm, 0.04 N / mm, 0.05 N / mm, 0.06 N / mm, 0.07 N / mm or 0.08 N / mm.

[0158] This application uses a high-speed rail tensile testing machine to test the peel strength between the first bond 50 and the seventh bond 115, according to GB / T2792-2014 "Test Method for Peel Strength of Adhesive Tapes". The test procedure is as follows:

[0159] Discharge the secondary battery 001 to 3.0V, then disassemble it. Remove the first electrode 11 and the first adhesive component 50 bonded to it as a whole, and wipe the electrolyte off the surface with a lint-free paper. Then cut the first adhesive component 50 and the seventh segment 115 into strip-shaped samples. Along the length of the sample, adhere the side of the sample with the first electrode 11 to the steel plate using double-sided adhesive (Nitto 5000NS), with an adhesion length of not less than 10mm. Fix the steel plate in the corresponding position on the high-speed rail tensile testing machine, pull up one end of the seventh segment 115 on the other side of the sample, and clamp the sample in the clamp. The angle between the pulled sample and the steel plate in space is 180°. The clamp pulls the sample at a speed of 5±0.2mm / s. The average tensile force in the stable area is recorded as the peel strength between the first adhesive component 50 and the seventh segment 115, denoted as F1, in N / m.

[0160] In some embodiments, the housing 40 is further provided with an electrolyte. The peel strength between the first adhesive 50 and the first stacked portion 113 and the second stacked portion 114 is F2, which satisfies 0 N / mm ≤ F2 ≤ 0.08 N / mm.

[0161] Wherein, F2 is the peel strength between the second adhesive 60 and the first stacked portion 113 and the second stacked portion 114 after being soaked in the electrolyte.

[0162] When F2 = 0, the peel strength between the second adhesive 60 and the first stacked portion 113 and the second stacked portion 114 is greater than 0 before being soaked in the electrolyte, which helps to reduce the risk of the first stacked portion 113 and the second stacked portion 114 coming apart or partially coming apart during the winding process.

[0163] When F2 satisfies the condition 0N / mm < F2 ≤ 0.08N / mm, on the one hand, the peel strength F2 between the second adhesive 60 and the first stacked portion 113 and the second stacked portion 114 is not too large, which is beneficial for the second adhesive 60 to peel smoothly from the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands, reducing the risk that the second adhesive 60 will affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands; on the other hand, the peel strength F2 between the second adhesive 60 and the first stacked portion 113 and the second stacked portion 114 is not too small, which is beneficial for reducing the risk that the first stacked portion 113 and the second stacked portion 114 will separate or partially separate under the condition that the electrode assembly 10 is subjected to impact, which is beneficial for improving the reliability of the first stacked portion 113 and the second stacked portion 114.

[0164] As an example, F2 can be any one of 0 N / mm, 0.01 N / mm, 0.02 N / mm, 0.03 N / mm, 0.04 N / mm, 0.05 N / mm, 0.06 N / mm, 0.07 N / mm or 0.08 N / mm.

[0165] The F2 test can be referenced from the peel strength F1 between the first adhesive 50 and the seventh segment 115 after being soaked in electrolyte, and will not be repeated here.

[0166] In some embodiments, the housing 40 is further provided with an electrolyte. The peel strength between the first adhesive 50 and the eighth segment 117 is F3.

[0167] F3 is the peel strength between the second adhesive 60 and the eighth segment 117 after being soaked in electrolyte.

[0168] When F3 = 0, the peel strength between the second adhesive 60 and the eighth segment 117 before immersion in electrolyte is greater than 0, which helps to reduce the risk of the first stacked portion 113 and the second stacked portion 114 coming apart or partially coming apart during the winding process.

[0169] When F3 satisfies the condition 0 N / mm < F2 ≤ 0.08 N / mm, on the one hand, the peel strength F3 between the second adhesive 60 and the eighth segment 117 is not too large, which is conducive to the smooth peeling of the second adhesive 60 and the eighth segment 117 when the electrode assembly 10 expands, reducing the risk that the second adhesive 60 will affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands; on the other hand, the peel strength F3 between the second adhesive 60 and the eighth segment 117 is not too small, which is conducive to reducing the risk that the first stacked portion 113 and the second stacked portion 114 will separate or partially separate under the condition that the electrode assembly 10 is subjected to impact, which is conducive to improving the reliability of the first stacked portion 113 and the second stacked portion 114.

[0170] As an example, F3 can be any one of 0 N / mm, 0.01 N / mm, 0.02 N / mm, 0.03 N / mm, 0.04 N / mm, 0.05 N / mm, 0.06 N / mm, 0.07 N / mm or 0.08 N / mm.

[0171] The F3 test can be referenced from the peel strength F1 between the first adhesive 50 and the seventh segment 115 after being soaked in electrolyte, and will not be repeated here.

[0172] Please refer to Figure 14. In some embodiments, the length of the first adhesive 50 along the winding direction X of the electrode assembly 10 is S1, which satisfies 2mm≤S1≤20mm.

[0173] When the length S1 of the first adhesive member 50 satisfies the condition 2mm≤S1≤20mm, on the one hand, the area of ​​the first adhesive member 50 is not too small, which helps to improve the bonding strength between the first adhesive member 50 and the seventh segment 115, the first stacked portion 113, the second stacked portion 114, and the eighth segment 117, reducing the risk of the first stacked portion 113 and the second stacked portion 114 coming apart during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion 113 and the second stacked portion 114; on the other hand, the area of ​​the first adhesive member 50 is not too large, which helps to allow the first adhesive member 50 to be easily separated from the seventh segment 115, the first stacked portion 113, the second stacked portion 114, and the eighth segment 117 when the electrode assembly 10 expands, reducing the risk that the first adhesive member 50 will affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands.

[0174] As an example, S1 can be one of 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm or 20mm.

[0175] Referring to Figure 15, in some embodiments, the length of the second adhesive 60 along the winding direction X of the electrode assembly 10 is S2, satisfying 2mm≤S2≤20mm. On the one hand, this prevents the area of ​​the second adhesive 60 from being too small, which helps to improve the bonding strength between the second adhesive 60 and the seventh segment 115, the eighth segment 117, the first stacked portion 113, and the second stacked portion 114, reducing the risk of the first stacked portion 113 and the second stacked portion 114 coming apart during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion 113 and the second stacked portion 114. On the other hand, this prevents the area of ​​the second adhesive 60 from being too large, which helps to facilitate the smooth peeling of the second adhesive 60 from the seventh segment 115, the eighth segment 117, the first stacked portion 113, and the second stacked portion 114 when the electrode assembly 10 expands, reducing the risk that the second adhesive 60 will affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands.

[0176] As an example, S2 can be one of 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm or 20mm.

[0177] In some embodiments, satisfying 6mm≤S1≤13mm serves two purposes. First, it prevents the area of ​​the first adhesive member 50 from being too small, which helps to improve the bonding strength between the first adhesive member 50 and the seventh segment 115, the first stacked portion 113, the second stacked portion 114, and the eighth segment 117. This further reduces the risk of the first stacked portion 113 and the second stacked portion 114 coming apart during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion 113 and the second stacked portion 114. Second, it prevents the area of ​​the first adhesive member 50 from being too large, which helps to facilitate the smooth separation of the first adhesive member 50 from the seventh segment 115, the first stacked portion 113, the second stacked portion 114, and the eighth segment 117 when the electrode assembly 10 expands. This further reduces the risk that the first adhesive member 50 may affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands.

[0178] In some embodiments, satisfying 6mm≤S2≤13mm serves two purposes. First, it prevents the area of ​​the second adhesive 60 from being too small, which helps to improve the bonding strength between the second adhesive 60 and the seventh segment 115, the eighth segment 117, the first stacked portion 113, and the second stacked portion 114. This further reduces the risk of the first stacked portion 113 and the second stacked portion 114 coming apart during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion 113 and the second stacked portion 114. Second, it prevents the area of ​​the second adhesive 60 from being too large, which helps to facilitate the smooth peeling of the second adhesive 60 from the seventh segment 115, the eighth segment 117, the first stacked portion 113, and the second stacked portion 114 when the electrode assembly 10 expands. This further reduces the risk that the second adhesive 60 might affect the effect of the first stacked portion 113 and the second stacked portion 114 when the electrode assembly 10 expands.

[0179] In some embodiments, the material of the first adhesive 50 includes at least one of acrylic resin, polypropylene, or rubber.

[0180] In some embodiments, the material of the second adhesive 60 includes at least one of acrylic resin, polypropylene, or rubber.

[0181] To verify the impact of the first stacked portion 113, the second stacked portion 114, and the first adhesive member 50 on whether the first electrode 11 is damaged, the following experiment was conducted:

[0182] A battery cycle test was conducted on secondary battery 001: Secondary battery 001 was placed in a 55°C environment and left to stand for 30 minutes. Then, it was charged and discharged according to the following steps: Charged at a constant current of 2.5C to 4.2V, then charged at a constant voltage to 0.5C; then charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage to 0.02C; left to stand for 5 minutes; then discharged at a constant current of 1C to 3V; left to stand for 5 minutes. This constitutes one cycle. The above cycle was repeated 300 times. Secondary battery 001 was then disassembled, and the connection between the first electrode 11 and the first tab 20 was observed to be undamaged.

[0183] Battery drop test: Secondary battery 001 was pretreated at 25℃ and left to stand at room temperature for 60 minutes. The voltage of secondary battery 001 before the drop test was then measured. Secondary battery 001 was placed in a fixture and dropped freely from a height of 2m above the ground using a drop tester in the following sequence: head-tail-right head corner-right tail corner-left head corner-left tail corner (angle: 45±15°), repeated 10 times. After the drop test, secondary battery 001 was disassembled, and the connection between the first electrode plate 11 and the first tab 20 was observed for damage.

[0184] In the two tests described above, 100 secondary batteries 001 were tested in each embodiment or comparative example. Each secondary battery 001 had a length of 29 mm, a width of 27 mm, and a thickness of 4.8 mm. The minimum distance between the first boundary position 11e and the second boundary position 11f along the winding direction X of the electrode assembly 10, i.e., the width P of the first part, was 0.5 mm. If the connection point between the first electrode 11 and the first tab 20, or the first part, was damaged, the test failed. If the connection point between the first electrode 11 and the first tab 20 was undamaged, the test passed. Pass rate = (number of passes / 100) × 100%.

[0185] The specific implementation of the secondary battery 001 in the embodiments and comparative examples will be described below.

[0186] Example 1:

[0187] The assembly process of a secondary battery 001 is as follows:

[0188] (1) Preparation of the anode electrode: Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5, and deionized water was added as a solvent to prepare a slurry with a weight percentage of 70 wt%, which was then stirred evenly. The slurry was uniformly coated on one surface of a copper foil with a thickness of 10 μm for the anode current collector, leaving an empty foil area at the edge of the copper foil. The foil was dried at 110 °C to obtain an anode electrode with a coating thickness of 150 μm on one side, partially coated with an anode active material layer. The above steps were repeated on the other surface of the anode electrode to obtain an anode electrode with a coated area and an empty foil area. An anode tab was welded to the empty foil area at one end of the anode electrode.

[0189] (2) Preparation of cathode electrode: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The slurry was uniformly coated on one surface of a 12 μm thick aluminum foil cathode current collector, leaving an empty foil area. The foil was then dried at 90 °C to obtain a cathode electrode with a cathode active material layer thickness of 100 μm. The above coating steps were repeated on the other surface of the aluminum foil to obtain a cathode electrode. Cathode tabs were welded to the empty foil area of ​​the cathode electrode.

[0190] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0191] (4) Preparation of the separator: A three-layer separator is adopted, which includes a first adhesive layer, a first substrate layer and a first adhesive layer stacked together. The first substrate layer is made of polyethylene (PE), the first adhesive layer contains a first adhesive, and the first adhesive layer also contains boehmite.

[0192] (5) Manufacturing the first stacked portion 113 and the second stacked portion 114: A round bar is used to press the anode electrode sheet in its unfolded state to form an arc-shaped protrusion. Along the winding direction X of the electrode assembly 10, the arc-shaped protrusion is located on the side of the anode tab near the winding center. The arc-shaped protrusion on the anode electrode sheet is flattened to form the first stacked portion 113 and the second stacked portion 114. The first adhesive 50 is used to bond the seventh segment 115 and the eighth segment 117 of the first electrode sheet 11.

[0193] (6) Electrode assembly 10 preparation: The cathode electrode, the separator and the anode electrode are stacked, the structure obtained after stacking is wound, and the outermost electrode of the wound structure is the anode electrode located on the electrode, and the anode tab is connected to the outermost anode electrode.

[0194] (7) Assembly of electrode assembly 10: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing up, place the electrode assembly 10 in the punch, and apply external force to press it. Then cover the electrode assembly 10 with another punched aluminum-plastic film with the punched surface facing down, and heat seal the two aluminum-plastic films around their perimeter by hot pressing to obtain the assembled electrode assembly 10.

[0195] (8) Electrolyte injection and encapsulation: Electrolyte is injected into the cylindrical shell 40 through the injection hole. After encapsulation, standing and formation processes, secondary battery 001 is obtained. The secondary battery 001 has a length of 29mm, a width of 27mm and a thickness of 4.8mm. The minimum distance between the first junction position 11e and the second junction position 11f along the winding direction X of the electrode assembly 10 is the width P of the first part, which is 0.5mm.

[0196] Comparative Example 1: The difference from the embodiment is that Comparative Example 1 does not perform step (5) of the embodiment, and the remaining steps are the same as those of Embodiment 1.

[0197] Comparative Example 2: The difference from the embodiment is that, in Comparative Example 2, along the winding direction X of the electrode assembly 10, the first stacked portion 113 and the second stacked portion 114 are located on the side of the first tab 20 away from the winding center of the electrode assembly 10, and the remaining steps are the same as in Embodiment 5.

[0198] In Example 26, the first overlapping portion 113 and the second overlapping portion 114 are not attached with the first adhesive 50 and the second adhesive 60.

[0199] The main parameter controls and test results for each embodiment and comparative example are shown in Table 1:

[0200] Table 1

[0201] In the first electrode 11, the first boundary position 11e is located at the junction of the first coating area 1111 and the first empty foil area 1112. There are four second boundary positions 11f between the first straight segment 11a and the first curved segment 11b, between the first curved segment 11b and the second straight segment 11c, between the second straight segment 11c and the second curved segment 11d, and between the second curved segment 11d and the straight segment of the second outer ring. Therefore, in the aforementioned Comparative Examples 1 to 2 and Examples 1 to 26, the first boundary position 11e is located in the second straight segment 11c, and the first boundary position 11e is located on the side of the second straight segment 11c closer to the first curved segment 11b. The shortest distance between the first boundary position 11e and the second boundary position 11f is P, which satisfies 0mm ≤ P ≤ 6mm.

[0202] As shown in Table 1 above, compared to Comparative Examples 1 and 2, Examples 1 to 26 are provided with a first stacking portion 113 and a second stacking portion 114. Along the winding direction X of the electrode assembly 10, the first stacking portion 113 and the second stacking portion 114 are located on the side of the first tab 20 near the winding center of the electrode assembly 10. This helps reduce the stress at the connection between the first electrode 11 and the first tab 20, thereby providing a margin for expansion of the electrode assembly 10 and reducing the risk of damage to the outermost ring of the first electrode 11. Furthermore, the first stacking portion 113 and the second stacking portion 114 also act as a buffer at the connection between the first electrode 11 and the first tab 20 in the event of a drop of the secondary battery 001, further reducing the risk of damage to the outermost ring of the first electrode 11.

[0203] As shown in Table 1 above, compared with Example 1, Examples 2 to 9 satisfy L1+L2≥0.2mm, which helps to reduce the force on the connection position of the outermost first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11.

[0204] Example 10 also satisfies L1+L2≥0.2mm, but since L1+L2>3mm, the first stacked portion 113 and the second stacked portion 114 are too large. Although they can pass the battery cycle test and the battery drop test, the space occupied by the first stacked portion 113 and the second stacked portion 114 is too large, which leads to a decrease in the energy density of the secondary battery 001.

[0205] As shown in Table 1 above, compared with Example 18, the peel strength between the first adhesive 50 and the seventh segment 115 after being soaked in the electrolyte in Examples 10 to 17 satisfies 0 N / mm ≤ F1 ≤ 0.08 N / mm, the peel strength between the first adhesive 50 and the first empty foil area 1112 after being soaked in the electrolyte satisfies 0 N / mm ≤ F2 ≤ 0.08 N / mm, and the peel strength between the first adhesive 50 and the eighth segment 117 after being soaked in the electrolyte satisfies 0 N / mm ≤ F3 ≤ 0.08 N / mm. This is beneficial for the first adhesive 50 to peel off smoothly when the electrode assembly 10 expands, reducing the risk that the first adhesive 50 will affect the effect of the folded part when the electrode assembly 10 expands, thereby reducing the risk of damage to the outermost first electrode sheet 11. In Example 18, because the adhesive force of the first adhesive 50 is greater than 0.08 N / mm, the adhesive force is too large. During the battery cycle test and battery drop test, the first stacked portion 113 and the second stacked portion 114 of some secondary batteries 001 were not pulled apart, resulting in the outermost first electrode 11 being damaged to varying degrees.

[0206] As can be seen from Table 1 above, compared with Examples 1 to 8, L2 > L1 in Examples 19 to 26, which is beneficial to pull apart the second stacked portion 114 in the event of a drop of the secondary battery 001, so as to disperse the stress at the connection between the first electrode 11 and the first tab 20, thereby reducing the risk of damage to the first electrode 11 in the event of a drop.

[0207] As shown in Table 1 above, compared to Example 7, in Example 26, neither the first adhesive 50 nor the second adhesive 60 are attached to the first stacked portion 113 or the second stacked portion 114. Therefore, the battery cycle test pass rate and drop test pass rate of the secondary battery 001 are lower than those of Example 7. This indicates that the first adhesive 50 plays a role in fixing the shape of the first stacked portion 113, which helps reduce the risk of the first stacked portion 113 unraveling or partially unraveling during winding. Furthermore, in the event of an accident such as an impact to the electrode assembly 10, the first stacked portion 113 may be subjected to compression or impact. The first adhesive 50 helps maintain the shape of the first stacked portion 113, further reducing the risk of the first stacked portion 113 unraveling or partially unraveling before the electrode assembly 10 expands.

[0208] This application also provides a method for manufacturing the electrode assembly 10 in any of the above embodiments, comprising the following steps:

[0209] The first electrode 11, formed by stamping and unfolding a round bar, forms an arc-shaped protrusion;

[0210] Flatten the arc-shaped protrusion to form the first overlapping part 113;

[0211] The first stacked part 113 is fixed in place by adhesive;

[0212] The first electrode 11, the second electrode 12, and the diaphragm 13 are stacked and wound together in their unfolded state to form a wound structure.

[0213] The electrode assembly 10 obtained by the above manufacturing method, during repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. The first stacked portion 113 is first stretched, causing the overlapping part in the first stacked portion 113 to gradually unfold. This helps to reduce the tensile force at the slot, thereby providing the electrode assembly 10 with expansion margin and improving the problem of electrode sheet breakage in the first part.

[0214] Please refer to the embodiments in this application, which also provide an electronic device 002, which includes the secondary battery 001 in any of the above embodiments. Since this electronic device 002 adopts the technical solution of the secondary battery 001 in any of the above embodiments, it has at least the beneficial effects brought by the technical solution of the secondary battery 001 in any of the above embodiments, which will not be described in detail here.

[0215] Please refer to 16. In some embodiments, the electronic device 002 also includes a device body 020, on which a secondary battery 001 is mounted.

[0216] In some embodiments, the electronic device 002 may be a mobile phone, tablet computer, e-reader, AR glasses or VR glasses, etc., which will not be listed here.

[0217] Furthermore, those skilled in the art can make various other corresponding changes and modifications based on the technical concept of this application, and all such changes and modifications should fall within the protection scope of the claims of this application.

Claims

1. A secondary battery, characterized in that, include: An electrode assembly, comprising a first electrode, a second electrode, and a diaphragm disposed between the first electrode and the second electrode, wherein the first electrode, the second electrode, and the diaphragm are stacked and wound to form a wound structure; The first electrode tab is connected to the outermost ring of the first electrode plate, and the relative position of the first electrode tab and the electrode assembly is fixed. Along the winding direction of the electrode assembly, the outermost electrode of the electrode assembly is the first electrode. The first electrode includes a first current collector and a first active material layer. The first current collector includes a first coated area with the first active material layer and a first empty foil area without the first active material layer. At the outermost edge of the first electrode, the junction of the first coated area and the first empty foil area is the first junction position. Along the winding direction of the electrode assembly, the outermost ring of the first electrode includes a second curved section, a second straight section, a first curved section, and a first straight section connected in sequence, with the two ends of the first curved section and the second curved section being second boundary positions; The outermost ring of the first electrode is partially stacked along a first direction to form a first stacked portion, where the first direction is the stacking direction of the second electrode and the diaphragm adjacent to the first stacked portion; Along the winding direction of the electrode assembly, the shortest distance between the first junction position and the second junction position is P, forming a first part, satisfying 0mm≤P≤6mm; along the winding direction of the electrode assembly, the first part is closer to the winding center of the electrode assembly than the first tab, and the first overlapping part is disposed between the first tab and the first part.

2. The secondary battery as described in claim 1, characterized in that, The first boundary position is located in the second straight section.

3. The secondary battery as described in any one of claims 1 to 2, characterized in that, Along the winding direction of the electrode assembly, the first stacked portion includes a first segment, a second segment, and a third segment connected in sequence. The first segment overlaps with the third segment. The first segment, the second segment, and the third segment are stacked along the first direction. Along the first direction, the projections of the first segment, the second segment, and the third segment overlap.

4. The secondary battery as described in claim 3, characterized in that, The first electrode further includes a second stacked portion, which is located between the first stacked portion and the first electrode tab along the winding direction of the electrode assembly. The second stacked portion includes a fourth segment, a fifth segment, and a sixth segment connected in sequence. The fifth segment is bent relative to the fourth segment, and the sixth segment is bent relative to the fifth segment. The fourth segment, the fifth segment, and the sixth segment are stacked in sequence along the first direction, and the projections of the fourth segment, the fifth segment, and the sixth segment overlap along the first direction.

5. The secondary battery as described in claim 4, characterized in that, The stacking direction of the first segment, the second segment, and the third segment is the same as that of the fourth segment, the fifth segment, and the sixth segment, and the fourth segment is connected to the third segment.

6. The secondary battery as described in claim 4, characterized in that, Along the winding direction of the electrode assembly, the distance between the bend of the second segment relative to the first segment and the bend of the third segment relative to the second segment is L1, and the distance between the bend of the fifth segment relative to the fourth segment and the bend of the fifth segment relative to the sixth segment is L2, satisfying L1+L2≥0.2mm.

7. The secondary battery as described in claim 6, characterized in that, If any of the following conditions are met: a. L2 > L1; b. L1+L2≤3mm.

8. The secondary battery as described in claim 4, characterized in that, Along the winding direction of the electrode assembly, the first coating area is located on the side of the first empty foil area near the winding center of the electrode assembly, and the distance between the second segment and the end face of the first coating area near the first empty foil area is A, satisfying 1mm≤A≤10mm.

9. The secondary battery as described in claim 8, characterized in that, It satisfies 2mm≤A≤4mm.

10. The secondary battery as described in claim 4, characterized in that, The first electrode further includes a seventh segment and an eighth segment, along the winding direction of the electrode assembly, wherein the seventh segment is connected to the first segment and the eighth segment is connected to the sixth segment; The secondary battery also includes a first adhesive component, which is simultaneously bonded to the seventh segment and the eighth segment, and is also bonded to the first stacked portion.

11. The secondary battery as described in claim 10, characterized in that, The first adhesive is also bonded to the first electrode tab and the second stacked portion.

12. The secondary battery as described in claim 11, characterized in that, Along the width direction of the first electrode sheet, the first tab is connected to the first electrode sheet and extends beyond the first electrode sheet; along the direction in which the first tab extends, the first adhesive member extends beyond the first electrode sheet.

13. The secondary battery as described in claim 11, characterized in that, The secondary battery also includes a housing, the electrode assembly is disposed inside the housing, a portion of the first electrode tab extends out of the housing, and an electrolyte is also disposed inside the housing; The peel strength between the first adhesive and the seventh segment is F1, the peel strength between the first adhesive and the first overlapping portion is F2, and the peel strength between the first adhesive and the eighth segment is F3, satisfying at least one of the following conditions: (1) 0 N / mm ≤ F1 ≤ 0.08 N / mm; (2) 0 N / mm ≤ F2 ≤ 0.08 N / mm; (3) 0 N / mm ≤ F3 ≤ 0.08 N / mm.

14. The secondary battery according to any one of claims 11 to 13, characterized in that, Along the winding direction of the electrode assembly, the length of the first adhesive is S1, which satisfies 2mm≤S1≤20mm.

15. The secondary battery as described in claim 14, characterized in that, The requirement is 6mm≤S1≤13mm.

16. The secondary battery according to any one of claims 11 to 15, characterized in that, The material of the first adhesive includes at least one of acrylic resin, polypropylene, or rubber.

17. The secondary battery according to any one of claims 3 to 8, characterized in that, The first electrode tab is welded to the second section.

18. The secondary battery according to claim 13, characterized in that, The electrode assembly has a cylindrical structure, and the housing is a metal housing.

19. A method for manufacturing an electrode assembly, used to manufacture an electrode assembly for a secondary battery as described in any one of claims 1 to 18, characterized in that, Includes the following steps: The first electrode sheet, in its unfolded state after being stamped from a round bar, forms an arc-shaped protrusion; Flatten the arc-shaped protrusion to form the first overlapping portion; The first stacked portion is fixed in place using adhesive adhesive; The first electrode, the second electrode, and the diaphragm are stacked and wound together in their unfolded state to form a wound structure.

20. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 18.

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