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

Abstract

The present application relates to a secondary battery, a manufacturing method for an electrode assembly, and an electronic device. The secondary battery comprises an electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet and a separator, wherein the separator is arranged between the first electrode sheet and the second electrode sheet, and the first electrode sheet, the second electrode sheet and the separator are stacked and wound to form a wound structure; the first electrode sheet comprises a first current collector and a first active material layer, the first active material layer being disposed on at least one surface of the first current collector; the first current collector comprises a first surface and a second surface, which are arranged opposite each other in the direction of the thickness of the first current collector; and in the winding direction of the electrode assembly, the first current collector comprises a first empty foil region on the first surface that is not provided with a first active material layer, a first coated region on the first surface that is provided with a first active material layer, and a second coated region on the first surface that is provided with a first active material layer, the first empty foil region being located between the first coated region and the second coated region.

Description

Secondary battery, manufacturing method of electrode assembly, and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, and in particular to a secondary battery, a manufacturing method of an electrode assembly, and an electronic device. BACKGROUND

[0002] The winding structure is the most widely used structure in lithium ion batteries at present, and is usually formed by stacking and winding a first tab, a separator and a second tab. During the production process of the tab, weak areas exist on the tab due to various factors. During repeated charging and discharging of the bare battery cell, the weak areas on the tab have a risk of breaking.

[0003] SUMMARY

[0004] Therefore, the present application provides a secondary battery, a manufacturing method of an electrode assembly, and an electronic device, which can improve the problem of tab breaking at weak areas.

[0005] In a first aspect, an embodiment of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a first tab, a second tab and a separator, the separator being arranged between the first tab and the second tab, the first tab, the second tab and the separator being stacked and wound to form a winding structure; the first tab comprising a first current collector and a first active material layer, the first active material layer being arranged on at least one surface of the first current collector; the first current collector comprising a first surface and a second surface arranged oppositely along a thickness direction of the first current collector, along a winding direction of the electrode assembly, the first current collector comprising a first empty foil area without the first active material layer arranged on the first surface, a first coated area with the first active material layer arranged on the first surface, and a second coated area with the first active material layer, the first empty foil area being located between the first coated area and the second coated area; the first tab being partially folded in a first direction at the position of the first empty foil area and forming a first stacking part, the first direction being a stacking direction of the second tab and the separator adjacent to the first stacking part.

[0006] In the aforementioned secondary battery, the first empty foil area without the first active material layer, the first coated area with the first active material layer, and the second coated area with the first active material layer are located on the first surface of the first current collector, and the first empty foil area is located between the first coated area and the second coated area, thereby forming a groove on the first electrode. This groove will cause a weak area on the electrode at the groove. Since the first electrode is partially folded at the position of the first empty foil area to form a first stacked portion, the projected portions of the first electrode in the first stacked portion overlap along the first direction. 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 portion in the first stacked portion to gradually unfold, which helps to reduce the tensile force at the groove, thereby providing a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in the weak area.

[0007] In one of the above embodiments, a first active material layer is provided on the second surface of the first coating area and the second coating area, while the second surface of the first empty foil area is not provided with a first active material layer.

[0008] In the aforementioned secondary battery, when the first electrode is partially folded at the location of the first empty foil area, the projected portions of the first electrode in the first stacked portion overlap, and the second surface of the first empty foil area is not provided with the first active material layer, thereby reducing the loss of the first active material layer. Furthermore, neither the first nor the second surface of the first electrode at the location of the first empty foil area is provided with the first active material layer, so that when the first electrode is partially folded at the location of the first empty foil area, the influence of the first active material layer on the formation of the first stacked portion can be reduced, which helps to reduce the risk of the first active material layer peeling off and improves the structural stability of the first stacked portion.

[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, the first, second, and third segments are stacked along the first direction, with the first and third segments overlapping. During repeated charging and discharging, the electrode assembly heats up and expands, with the first segment being stretched first. This causes the overlapping portion of the first, second, and third segments to gradually unfold, which helps to reduce the tension at the slot and provides a margin for the expansion of the electrode assembly, thus improving the problem of electrode breakage in weak areas.

[0011] 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 away from the second coating area, 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.

[0012] 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, ensuring sufficient space between the first stacked portion and the first coating area. This provides space for the formation of the first stacked portion and improves its forming 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 10 mm, allowing the first stacked portion to be close to the first coating area. This helps the first stacked portion protect the weak area between the first empty foil area and the first coating area, reducing the tensile force at the slot and providing allowance for electrode assembly expansion, thus mitigating the problem of electrode breakage in weak areas.

[0013] In one or more of the above embodiments, 2mm≤A≤4mm is satisfied.

[0014] 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 2 mm. This ensures 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 4 mm. This allows the first stacked portion to be close to the first coating area, protecting the weak area 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 in weak areas.

[0015] In one or more of the above embodiments, the secondary battery further includes a first tab, which is disposed in a first empty foil area along the winding direction of the electrode assembly, and a first stacked portion is located on the side of the first tab near the winding center of the electrode assembly.

[0016] In the aforementioned secondary battery, the first tab is disposed in the first empty foil area, thus forming a centrally located tab structure. The connection between the first tab and the first empty foil area is also a weak area of ​​the first electrode. Along the winding direction of the electrode assembly, the first stacked portion is located on the side of the first tab closer to the winding center of the electrode assembly. When the electrode assembly heats up and expands, the first stacked portion is first stretched, causing the overlapping parts in the first stacked portion to gradually unfold. This helps to reduce the tensile force at the connection between the first tab and the first empty foil area, thereby providing a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in weak areas.

[0017] In one or more of the above embodiments, along the winding direction of the electrode assembly, the minimum distance between the bend of the second segment relative to the first segment and the first tab is L, satisfying 0.2mm≤L≤3mm.

[0018] In the aforementioned secondary battery, the minimum distance between the bend of the second segment relative to the first segment and the first tab is greater than or equal to 0.2 mm. This ensures sufficient space between the first stacked portion and the first tab, 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 minimum distance between the bend of the second segment relative to the first segment and the first tab is less than or equal to 3 mm. This allows the first stacked portion to be close to the first tab, protecting the weak area at the connection between the first tab and the first empty foil area. This reduces the tensile force at the connection, providing room for expansion of the electrode assembly and mitigating the problem of electrode breakage in weak areas.

[0019] In one or more of the above embodiments, the first electrode sheet further includes a partially folded second stacked portion at the location of the first empty foil area, and the projected portions of the first electrode sheet of the second stacked portion overlap along the first direction;

[0020] Along the winding direction of the electrode assembly, the second stacked portion is located on the side of the first stacked portion away from the winding center of the electrode assembly.

[0021] In the aforementioned secondary battery, along the winding direction of the electrode assembly, the second stacked portion is located on the side of the first stacked portion away from the winding center of the electrode assembly, and the projected portions of the first electrode sheets of the second stacked portion overlap, thereby increasing the expansion margin of the electrode assembly and further improving the problem of electrode sheet breakage in weak areas.

[0022] In one or more of the above embodiments, the secondary battery further includes a first tab, which is connected to a first empty foil area and located between a first stacked portion and a second stacked portion along the winding direction of the electrode assembly.

[0023] In the aforementioned secondary battery, the connection between the first electrode tab and the first empty foil area, the boundary between the first empty foil area and the first coated area, and the boundary between the first empty foil area and the second coated area are all weak areas of the first electrode tab. The first electrode tab is connected to the first empty foil area and located between the first stacked portion and the second stacked portion, such that the first stacked portion is located between the connection between the first electrode tab and the first empty foil area and the boundary between the first empty foil area and the first coated area, and the second stacked portion is located between the connection between the first electrode tab and the first empty foil area and the boundary between the first empty foil area and the second coated area. This facilitates the protection of the weak areas on both sides of the first stacked portion (the connection between the first electrode tab and the first empty foil area and the boundary between the first empty foil area and the first coated area) by the first stacked portion, and at the same time, it facilitates the protection of the weak areas on both sides of the second stacked portion (the connection between the first electrode tab and the first empty foil area and the boundary between the first empty foil area and the second coated area) by the second stacked portion, thereby providing a margin for electrode assembly expansion and improving the problem of electrode breakage in weak areas.

[0024] In one or more of the above embodiments, 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 fourth segment and the sixth segment overlap, and the fourth segment, the fifth segment, and the sixth segment are stacked along a first direction. Along the first direction, the projections of the fourth segment, the fifth segment, and the sixth segment overlap.

[0025] 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 connects with 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 tensile force at the slot, thereby increasing the expansion margin of the electrode assembly and further improving the problem of electrode breakage in weak areas.

[0026] In one or more of the above embodiments, the minimum 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 minimum 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.

[0027] In one or more of the above embodiments, L1+L2≤3mm is satisfied.

[0028] In one or more of the above embodiments, L1≥0.1mm and / or L2≥0.1mm is satisfied.

[0029] In one or more of the above embodiments, along the winding direction of the electrode assembly, the first electrode further includes a seventh segment and an eighth segment, the seventh segment being connected to the first segment and the eighth segment being 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 bonded to the first stacked portion.

[0030] 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.

[0031] In one or more of the above embodiments, the first electrode sheet is further provided with a second stacked portion at the position of the first empty foil area, the first empty foil area is provided with a first electrode tab, and the first adhesive is further adhered to the first electrode tab and the second stacked portion.

[0032] In the aforementioned secondary battery, the first adhesive is also bonded to the first tab and the second stacked portion to enhance the fixing effect of the first adhesive and further reduce the risk of the first stacked portion coming apart or partially coming apart during the winding process.

[0033] In one or more of the above embodiments, along the width direction of the first electrode, the first electrode tab is connected to the first electrode and extends out of the first electrode;

[0034] Along the direction in which the first electrode tab extends, the first adhesive element extends beyond the first electrode plate.

[0035] In the aforementioned secondary battery, the first adhesive extends beyond the first electrode sheet along the direction in which the first tab extends. This helps to reduce the risk of the separator being punctured at the first stacked portion position, thus preventing electrode short circuits and improving the safety of the secondary battery.

[0036] In one or more of the above embodiments, the secondary battery further includes a housing, an electrode assembly disposed inside the housing, a portion of the first electrode tab extending out of the housing, and an electrolyte disposed inside the housing;

[0037] The peel strength between the first adhesive component and the seventh segment is F1, the peel strength between the first adhesive component and the first overlapping portion is F2, and the peel strength between the first adhesive component and the eighth segment is F3, satisfying at least one of the following conditions:

[0038] (1) 0 N / mm ≤ F1 ≤ 0.08 N / mm;

[0039] (2) 0 N / mm ≤ F2 ≤ 0.08 N / mm;

[0040] (3) 0 N / mm ≤ F3 ≤ 0.08 N / mm.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] When F3 satisfies the condition 0 N / mm < F2 ≤ 0.08 N / 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 under the condition that the electrode assembly is subjected to impact, which is conducive to improving the reliability of the first stacked part.

[0045] 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.

[0046] 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, and 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, the area of ​​the first adhesive component is not too large, which helps to allow the first adhesive component to peel smoothly 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.

[0047] In one or more of the above embodiments, 6mm≤S1≤13mm is satisfied.

[0048] In the aforementioned secondary battery, 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, 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, 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, and further reduces the risk that the first adhesive component will affect the effect of the first stacked portion when the electrode assembly expands.

[0049] In one or more of the above embodiments, the material of the first adhesive includes at least one of acrylic resin, polypropylene, or rubber.

[0050] In one or more of the above embodiments, a first electrode tab is provided in the first empty foil area, and the first electrode tab is welded to the first electrode sheet.

[0051] In one or more of the above embodiments, the electrode assembly is a cylindrical structure and the housing is a metal housing.

[0052] 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.

[0053] Secondly, embodiments of this application provide a method for manufacturing an electrode assembly, used to manufacture the electrode assembly in one or more of the above embodiments, comprising the following steps:

[0054] The first electrode sheet in its unfolded state is stamped using a round bar to form an arc-shaped protrusion;

[0055] The arc-shaped protrusion on the first electrode is flattened to form the first stacked portion;

[0056] The first stacked portion is fixed in place using adhesive adhesive;

[0057] The first electrode, the second electrode, and the diaphragm are stacked and wound together in their unfolded state to form a wound structure.

[0058] The secondary battery obtained by the above manufacturing method has an electrode assembly that heats up and expands 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 a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in weak areas.

[0059] Thirdly, embodiments of this application provide an electronic device including the secondary battery described in one or more of the above embodiments. Attached Figure Description

[0060] Figure 1 is a schematic diagram of the structure of a secondary battery in one embodiment of this application.

[0061] Figure 2 is a schematic diagram of the cross-sectional structure along II-II in Figure 1.

[0062] Figure 3 is a schematic diagram of another type of secondary battery in one embodiment of this application.

[0063] Figure 4 is a schematic diagram of the cross-sectional structure along IV-IV in Figure 3.

[0064] Figure 5 is a schematic cross-sectional view of a secondary battery in one embodiment of this application.

[0065] Figure 6 is a schematic cross-sectional view of the secondary battery in another embodiment of this application.

[0066] Figure 7 is a schematic cross-sectional view of the secondary battery in another embodiment of this application.

[0067] Figure 8 is a schematic diagram of a structure of the first stacked portion in one embodiment of this application.

[0068] Figure 9 is a schematic diagram of a structure of the first stacked portion in another embodiment of this application.

[0069] Figure 10 is a schematic diagram of another structure of the first stacked portion in one embodiment of this application.

[0070] Figure 11 is a schematic diagram of another structure of the first stacked portion in another embodiment of this application.

[0071] Figure 12 is a schematic diagram of the structure of the first and second overlapping portions in one embodiment of this application.

[0072] Figure 13 is a schematic diagram of the structure of the first and second overlapping portions in another embodiment of this application.

[0073] Figure 14 is a schematic diagram of another structure of the first and second overlapping portions in one embodiment of this application.

[0074] Figure 15 is a schematic diagram of another structure of the first and second overlapping portions in another embodiment of this application.

[0075] Figure 16 is a top view of a portion of the first electrode and the first electrode tab in an embodiment of this application.

[0076] Figure 17 is a top view of a portion of the first electrode and the first electrode tab in another embodiment of this application.

[0077] Figure 18 is a bottom view of a portion of the first electrode plate and the first electrode tab in another embodiment of this application.

[0078] Figure 19 is a bottom view of a portion of the first electrode plate and the first electrode tab in another embodiment of this application.

[0079] Figure 20 is a side view of the first adhesive member after it has been unfolded according to an embodiment of this application.

[0080] Figure 21 is a side view of the second adhesive member after it has been unfolded according to an embodiment of this application.

[0081] Figure 22 is a schematic diagram of an electronic device according to an embodiment of this application.

[0082] Key Component Symbol Explanation: 001 Secondary Battery; 10 Electrode Assembly; 11 First Electrode; 111 First Current Collector; 1111 First Surface; 1112 Second Surface; 1113 First Coating Area; 1114 First Empty Foil Area; 1115 Second Coating Area; 1116 Third Coating Area; 1117 Second Empty Foil Area; 1118 Fourth Coating 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; 11436th paragraph 115, 7th paragraph 117, 8th paragraph 12, 2nd electrode 121, 2nd current collector 122, 2nd active material layer 13, diaphragm 20, 1st tab 30, 2nd tab 40, housing 50, 1st adhesive component 60, 2nd adhesive component X, winding direction of electrode assembly Y, 1st direction Z, width direction of 1st electrode 002, electronic device 020, device body Detailed Implementation

[0083] 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.

[0084] It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" 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. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intervening component present. When a component is considered to be "located" to another component, it can be directly mounted on the other component or there may be an intervening component present.

[0085] Unless otherwise stated, the term "multiple" as used herein refers to two or more.

[0086] The terms “first”, “second”, etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implying the quantity, specific order, or primary and secondary relationship of the indicated technical features.

[0087] The term "perpendicular" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately perpendicular. For example, in numerical terms, perpendicularity can refer to the angle between two straight lines within the range of 90° ± 10°, the dihedral angle between two planes within the range of 90° ± 10°, or the angle between a straight line and a plane within the range of 90° ± 10°.

[0088] The term "parallel" is used to describe an ideal state between two components. In actual production or use, two components can exist in a state that is approximately parallel. For example, in numerical terms, parallel can refer to the angle between two straight lines within the range of 180° ± 10°, the dihedral angle between two planes within the range of 180° ± 10°, or the angle between a straight line and a plane within the range of 180° ± 10°.

[0089] It should be noted that when a parameter is greater than, equal to or less than a certain endpoint value, it should be understood that the endpoint value is allowed to have a tolerance of ±5%.

[0090] It should be understood that the dimensions of the structures shown in the accompanying drawings are provided for better understanding and easier description, and this application is not limited to the dimensions shown in the drawings. For the sake of clarity, elements unrelated to the description have been omitted from the details of this specification.

[0091] 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 is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0092] In related technologies, during battery cycling, the delithiation and lithium insertion of the electrode cause repeated expansion of the electrode thickness, resulting in repeated contraction and expansion of the bare cell. During the manufacturing process, various factors can lead to weak areas on the electrode, and these weak areas have a higher risk of breakage compared to other parts of the electrode.

[0093] This application discloses a secondary battery, including an electrode assembly. The electrode assembly includes a first electrode, a second electrode, and a separator. The separator is disposed between the first electrode and the second electrode. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The first electrode includes a first current collector and a first active material layer. The first active material layer is disposed on at least one surface of the first current collector. The first current collector includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first current collector. Along the winding direction of the electrode assembly, the first current collector includes a first empty foil area on the first surface where the first active material layer is not disposed, a first coated area on the first surface where the first active material layer is disposed, and a second coated area where the first active material layer is disposed. The first empty foil area is located between the first coated area and the second coated area. The first electrode is partially folded at the position of the first empty foil area along a first direction to form a first stacked portion. The first direction is the stacking direction of the second electrode and the separator adjacent to the first stacked portion.

[0094] In the aforementioned secondary battery, the first empty foil area without the first active material layer, the first coated area with the first active material layer, and the second coated area with the first active material layer are located on the first surface of the first current collector, and the first empty foil area is located between the first coated area and the second coated area, thereby forming a groove on the first electrode. This groove will cause a weak area on the electrode at the groove. Since the first electrode is partially folded at the position of the first empty foil area to form a first stacked portion, the projected portions of the first electrode in the first stacked portion overlap along the first direction. 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 portion in the first stacked portion to gradually unfold, which helps to reduce the tensile force at the groove, thereby providing a margin for the expansion of the electrode assembly and improving the problem of electrode breakage in the weak area.

[0095] 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.

[0096] Please refer to Figures 1 to 3. 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.

[0097] In some embodiments, the secondary battery 001 further includes a second tab 30, which is connected to the electrode assembly 10, and the first tab 20 and the second tab 30 have different polarities.

[0098] In some embodiments, the secondary battery 001 can be a cylindrical battery, a square hard-shell battery, or a pouch battery; no specific limitations are made here.

[0099] In some embodiments, the secondary battery 001 further includes a housing 40, an electrode assembly 10 is housed within the housing 40, and an electrolyte is provided within the housing 40, which wets the electrode assembly 10.

[0100] 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.

[0101] 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.

[0102] 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 cylindrical battery or a square hard-shell battery, the housing 40 includes a steel housing or a resin housing; when the secondary battery 001 is a soft-pack battery, the housing 40 includes an aluminum-plastic film.

[0103] Referring to Figures 3 and 4, in some embodiments, one end of the housing 40 is open, and the secondary battery 001 also includes an end cap, which is disposed in the opening of the housing 40 and forms a receiving cavity. The electrode assembly 10 is electrically connected to the housing 40 and the end cap, respectively, and the end cap is insulated from the housing 40.

[0104] The housing 40 includes a bottom wall and a side wall, the side wall being enclosed and sealed to the bottom wall, and an end cap being sealed to the side of the side wall away from the bottom wall to form a receiving cavity.

[0105] In some embodiments, the bottom wall and side wall are integrally formed by stamping, so that the bottom wall and side wall have the same thickness.

[0106] In other embodiments, the bottom wall and the side wall are separately provided and welded together. The thickness of the bottom wall and the side wall can be the same, or the thickness of the bottom wall can be greater than the thickness of the side wall according to the structural design requirements of the cylindrical battery.

[0107] Please refer to Figures 5 and 8. In some embodiments, the electrode assembly 10 includes a first electrode 11, a second electrode 12, and a diaphragm 13. The diaphragm 13 is disposed between the first electrode 11 and the second electrode 12. The first electrode 11, the second electrode 12, and the diaphragm 13 are stacked and wound to form a wound structure.

[0108] In some embodiments, referring to Figures 5 and 6, the electrode assembly 10 can be cylindrical or flat with arc-shaped portions at both ends.

[0109] 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.

[0110] In some embodiments, the first current collector 111 is a cathode current collector, the second current collector 121 is an anode current collector, the first active material layer 112 is a cathode active material layer, and the second active material layer 122 is an anode active material layer.

[0111] In other embodiments, the first current collector 111 is an anode current collector, the second current collector 121 is a cathode current collector, the first active material layer 112 is an anode active material layer, and the second active material layer 122 is a cathode active material layer.

[0112] The cathode current collector can be a metal layer comprising at least one of aluminum, nickel, tantalum, and titanium, such as aluminum foil. The anode current collector can be a metal layer comprising at least one of copper, nickel, tantalum, and titanium, such as copper foil. The cathode active material layer comprises a cathode active material, which can include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide. The anode active material layer comprises an anode active material, which can include at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials.

[0113] 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.

[0114] In some embodiments, the first electrode tab 20 is connected to the first electrode plate 11, and the second electrode tab 30 is connected to the second electrode plate 12. The polarity of the first electrode tab 20 is the same as that of the first electrode plate 11, and the polarity of the second electrode tab 30 is the same as that of the second electrode plate 12.

[0115] In some embodiments, the first tab 20 is welded to the first current collector 111, and the second tab 30 is welded to the second current collector 121.

[0116] In some embodiments, the material of the first tab 20 is the same as the material of the first current collector 111, and the material of the second tab 30 is the same as the material of the second current collector 121.

[0117] Please refer to Figures 5 and 8. The first active material layer 112 can be disposed on one side of the first current collector 111, or it can be disposed on both sides of the first current collector 111. That is, the first current collector 111 includes a first surface 1111 and a second surface 1112 disposed opposite to each other along the thickness direction of the first current collector 111. The first active material layer 112 can be disposed on the first surface 1111, or it can be disposed on both the first surface 1111 and the second surface 1112.

[0118] In some embodiments, along the winding direction X of the electrode assembly 10, the first surface 1111 of the first current collector 111 includes a first empty foil area 1114 without the first active material layer 112, a first coating area 1113 with the first active material layer 112, and a second coating area 1115 with the first active material layer 112. The first empty foil area 1114 is located between the first coating area 1113 and the second coating area 1115, thereby forming a groove on the first electrode 11.

[0119] 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.

[0120] Referring to Figures 5 and 8, the first electrode 11 is partially folded at the position of the first empty foil area 1114 to form a first stacked portion 113. Along the first direction Y, the projected portions of the first electrode 11 in the first stacked portion 113 overlap. The second surface 1112 of the first current collector 111 is provided with a first active material layer 112. The first stacked portion 113 is formed by folding together the first empty foil area 1114 and a portion of the first active material layer 112 coated on the second surface 1112. The first direction Y is the stacking direction of the second electrode 12 and the separator 13 adjacent to the first stacked portion 113.

[0121] Referring to Figures 5 and 10, in some embodiments, the second surface 1112 of the first current collector 111 is partially provided with a first active material layer 112. The second surfaces 1112 of the first coating area 1113 and the second coating area 1115 are provided with the first active material layer 112, while the second surface 1112 of the first empty foil area 1114 is not provided with the first active material layer 112. That is, the second surface 1112 of the first current collector 111 includes a second empty foil area 1117 without the first active material layer 112, a third coating area 1116 with the first active material layer 112, and a fourth coating area 1118 with the first active material layer 112. The second empty foil area 1117 is located between the third coating area 1116 and the fourth coating area 1118, thereby forming another groove on the first electrode 11. Along the first direction Y, the projections of the second empty foil area 1117 and the first empty foil area 1114 at least partially overlap.

[0122] When the first electrode 11 is partially folded at the position of the first empty foil area 1114 along the first direction Y, the projection portions of the second empty foil area 1117 and the first empty foil area 1114 coincide, and the second empty foil area 1117 is not provided with the first active material layer 112, thereby reducing the loss of the first active material layer 112. Furthermore, the first electrode 11 is not provided with the first active material layer 112 on either of the two surfaces (the first empty foil area 1114 and the second empty foil area 1117) at the position of the first empty foil area 1114, so that when the first electrode 11 is partially folded at the position of the first empty foil area 1114, the influence of the first active material layer 112 on the forming of the first stacked portion 113 can be reduced, which helps to reduce the risk of the first active material layer 112 peeling off and improve the structural stability of the first stacked portion 113.

[0123] In some embodiments, along the first direction Y, the second empty foil region 1117 is directly opposite the first empty foil region 1114.

[0124] The slots on the first electrode 11 can create weak areas at these slots. During repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. Due to the tensile force generated by this expansion, the weak areas of the first electrode 11 are at risk of tearing or even breaking. Because the first electrode 11 is partially folded at the position of the first empty foil area 1114 to form a first stacked portion 113, the projected portions of the first electrode 11 in the first stacked portion 113 overlap along the first direction Y. During repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. The first stacked portion 113 is initially stretched, causing the overlapping portion to gradually unfold. This helps reduce the tensile force at the slots, thereby providing a margin for expansion of the electrode assembly 10 and improving the problem of electrode breakage in weak areas.

[0125] Referring to Figures 5 and 10, in some embodiments, along the winding direction X of the electrode assembly 10, the first stacked portion 113 includes a first segment 1131, a second segment 1132, and a third segment 1133 connected in sequence, with the first segment 1131 overlapping the third segment 1133, and the second segment 1132 located between the first segment 1131 and the third segment 1133. Along the first direction Y, the projections of the first segment 1131, the second segment 1132, and the third segment 1133 overlap.

[0126] 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 in a direction parallel to the first direction Y. During repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. The first segment 1131 is stretched first, causing the overlapping parts of the first segment 1131, the second segment 1132, and the third segment 1133 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 breakage in weak areas.

[0127] In some embodiments, along the winding direction X of the electrode assembly 10, the first coating area 1113 is located on the side of the first empty foil area 1114 away from the second coating area 1115, and the distance between the second segment 1132 and the end face of the first coating area 1113 near the first empty foil area 1114 is A, which satisfies 1mm≤A≤10mm. On the one hand, this ensures that there is sufficient space between the first stacked portion 113 and the first coating area 1113, which is beneficial for providing space for the forming of the first stacked portion 113 and improving the forming convenience of the first stacked portion 113. On the other hand, during repeated charging and discharging of the secondary battery 001, the electrode assembly 10 heats up and expands. The distance between the second segment 1132 and the end face of the first coating area 1113 near the first empty foil area 1114 is less than or equal to 10 mm, so that the first stacked portion 113 can be close to the first coating area 1113. This is beneficial for the first stacked portion 113 to protect the weak area between the first empty foil area 1114 and the first coating area 1113, reduce the tensile force at the slot, and thus provide the electrode assembly 10 with expansion margin, improving the problem of electrode breakage in the weak area.

[0128] Preferably, A satisfies 2mm≤A≤4mm.

[0129] As an example, the value of A can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0130] In some embodiments, along the first direction, 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.

[0131] Referring to Figure 6, in some other embodiments, along the first direction, 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.

[0132] Referring to Figures 5 and 10, in some embodiments, the secondary battery 001 further includes a first tab 20, which is welded to a first empty foil area 1114 to form a centrally located tab structure. The connection between the first tab 20 and the first empty foil area 1114 is a weak area of ​​the first electrode 11. Along the winding direction X of the electrode assembly 10, the first stacked portion 113 is located on the side of the first tab 20 near the winding center of the electrode assembly 10. When the electrode assembly 10 heats up and expands, the first stacked portion 113 is first stretched, causing the overlapping parts in the first stacked portion 113 to gradually unfold. This helps to reduce the tensile force at the connection between the first tab 20 and the first empty foil area 1114, thereby providing a margin for the expansion of the electrode assembly 10 and improving the problem of electrode breakage in weak areas.

[0133] In some embodiments, along the winding direction X of the electrode assembly 10, the minimum distance between the bend of the second segment 1132 relative to the first segment 1131 and the first tab 20 is L, satisfying 1mm≤L≤10mm. On one hand, this provides sufficient space between the first stacked portion 113 and the first tab 20, facilitating the forming of the first stacked portion 113 and improving its forming convenience. On the other hand, it allows the first stacked portion 113 to be close to the first tab 20, which helps protect the weak area at the connection between the first tab 20 and the first empty foil area 1114, reducing the tensile force at the connection and providing room for expansion of the electrode assembly 10, thus mitigating the problem of electrode breakage in weak areas.

[0134] As an example, the value of L can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0135] Referring to Figures 5 and 12, in some embodiments, the first electrode 11 further includes a partially folded second stacked portion 114 at the location of the first empty foil area 1114. Along the first direction Y, the projected portions of the first electrode 11 of the second stacked portion 114 overlap. Along the winding direction X of the electrode assembly 10, the second stacked portion 114 is located on the side of the first stacked portion 113 away from the winding center of the electrode assembly 10, thereby increasing the expansion margin of the electrode assembly 10 and further improving the problem of electrode breakage in weak areas.

[0136] Referring to Figures 5 and 12, in some embodiments, along the winding direction X of the electrode assembly 10, the second stacked portion 114 includes a fourth segment 1141, a fifth segment 1142, and a sixth segment 1143 connected in sequence. The fourth segment 1141 and the sixth segment 1143 overlap, and the fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 are stacked along the first direction Y. The fourth segment 1141 is connected to the third segment 1133. Along the first direction Y, the projections of the fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 overlap.

[0137] The fifth segment 1142 is bent relative to the fourth segment 1141, and the sixth segment 1143 is bent relative to the fourth segment 1141. The fourth segment 1141, the fifth segment 1142, and the sixth segment 1143 are stacked sequentially in a direction parallel to the first direction Y. The fourth segment 1141 overlaps with the sixth segment 1143. 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 weak areas.

[0138] In some embodiments, along the winding direction X of the electrode assembly 10, the distance B between the fifth segment 1142 and the end face of the second coating area 1115 near the first empty foil area 1114 satisfies 1mm≤B≤10mm.

[0139] Preferably, B satisfies 2mm≤B≤4mm.

[0140] As an example, the value of B can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0141] In some embodiments, along the first direction, 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.

[0142] Referring to Figure 6, in some other embodiments, along the first direction, 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.

[0143] Referring to Figures 7 and 8, in some embodiments, the outermost electrode of the electrode assembly 10 is a first electrode 11, the first tab 20 is welded to the empty foil area at the outermost end of the first electrode 11, and the first current collector 111 includes the first empty foil area 1114 at a position near the center, and the first stacked portion 113 is located in the first empty foil area 1114, thereby protecting the weak area around the first empty foil area 1114 at the position near the center of the first electrode 11.

[0144] Please refer to Figures 5 and 12. In some embodiments, the secondary battery 001 further includes a first tab 20 connected to the first empty foil region 1114.

[0145] The junction between the first electrode tab 20 and the first empty foil area 1114, the junction between the first empty foil area 1114 and the first coated area 1113, and the junction between the first empty foil area 1114 and the second coated area 1115 are all weak areas of the first electrode tab 20.

[0146] The first stacked portion 113 is located on the side of the second stacked portion 114 away from the first tab 20, thereby increasing the expansion margin of the electrode assembly 10 and further improving the problem of electrode breakage in weak areas.

[0147] In some embodiments, along the winding direction X of the electrode assembly 10, the minimum distance between the bend of the fifth segment 1142 relative to the fourth segment 1141 and the first tab 20 is M, satisfying 1mm ≤ M ≤ 10mm. On one hand, this provides sufficient space between the first stacked portion 113 and the first tab 20, facilitating the forming of the first stacked portion 113 and improving its forming convenience. On the other hand, it allows the first stacked portion 113 to be close to the first tab 20, which helps protect the weak area at the connection between the first tab 20 and the first empty foil area 1114, reducing the tensile force at the connection and providing room for expansion of the electrode assembly 10, thus mitigating the problem of electrode breakage in weak areas.

[0148] As an example, the value of M can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0149] Referring to Figures 5 and 14, in some other embodiments, along the winding direction X of the electrode assembly 10, the first tab 20 is located between the first stack 113 and the second stack 114, such that the first stack 113 is located between the connection between the first tab 20 and the first empty foil area 1114 and the boundary between the first empty foil area 1114 and the first coating area 1113, and the second stack 114 is located between the connection between the first tab 20 and the first empty foil area 1114 and the boundary between the first empty foil area 1114 and the second coating area 1115. This design facilitates the protection of weak areas on both sides of the first stacked portion 113 (the connection between the first electrode tab 20 and the first empty foil area 1114, and the boundary between the first empty foil area 1114 and the first coating area 1113) by the first stacked portion 113, and also facilitates the protection of weak areas on both sides of the second stacked portion 114 (the connection between the first electrode tab 20 and the first empty foil area 1114, and the boundary between the first empty foil area 1114 and the second coating area 1115) by the second stacked portion 114, thereby providing a margin for expansion of the electrode assembly 10 and improving the problem of electrode breakage in weak areas.

[0150] In some embodiments, along the winding direction X of the electrode assembly 10, the minimum distance N between the bend of the fifth segment 1142 relative to the fourth segment 1141 and the first tab 20 satisfies 1mm ≤ N ≤ 10mm. On one hand, this provides sufficient space between the first stacked portion 113 and the first tab 20, facilitating the forming of the first stacked portion 113 and improving its forming convenience. On the other hand, it allows the first stacked portion 113 to be close to the first tab 20, which helps protect the weak area at the connection between the first tab 20 and the first empty foil area 1114, reducing the tensile force at the connection and providing room for expansion of the electrode assembly 10, thus mitigating the problem of electrode breakage in weak areas.

[0151] As an example, the value of N can be any one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0152] In some embodiments, the maximum outer diameter that the electrode assembly 10 can expand to is D1, the minimum outer diameter of the electrode assembly 10 is D2, and along the winding direction X of the electrode assembly 10, the minimum 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 minimum 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(D1-D2).

[0153] When L1+L2 satisfies the condition L≥π(D1-D2) / 2, it is beneficial to increase the expansion margin of the electrode assembly 10, and to further reduce the tensile force on the weak area on the first electrode 11 when the electrode assembly 10 expands, thereby further reducing the risk of damage to the first electrode 11.

[0154] It should be noted that the maximum outer diameter D1 that the electrode assembly 10 can expand to can be detected in the charge and discharge test of the electrode assembly 10, and the minimum outer diameter D2 of the electrode assembly 10 is the outer diameter before charge and discharge.

[0155] The following example, using a cylindrical hard-shell secondary battery 100, illustrates the method for measuring the maximum outer diameter D1 and the minimum outer diameter D2:

[0156] Maximum outer diameter D1: When the secondary battery 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 inner diameter of the housing 40 is measured with an optical microscope at an ambient temperature of 25°C. This is the maximum outer diameter D1 that the electrode assembly 10 can expand to.

[0157] Minimum outer diameter D2: The minimum outer diameter D2 is obtained by measuring the outer diameter of the wound electrode assembly 10 with an optical microscope at an ambient temperature of 25°C.

[0158] When the electrode assembly 10 of the secondary battery 100 has other shapes, the detection method for the electrode assembly 10 described above can be used for detection, and will not be repeated here.

[0159] In some embodiments, L1 ≥ 0.1 mm is satisfied.

[0160] When L1 satisfies the condition 0.2mm≤L1, it helps to reduce the stress on the weak area of ​​the first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11.

[0161] As an example, L1 can be one of 0.2mm, 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.

[0162] In some embodiments, L1 ≥ 0.1 mm is satisfied.

[0163] When L2 satisfies the condition 0.2mm≤L2, it helps to reduce the stress on the weak area of ​​the first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11.

[0164] As an example, L2 can be one of 0.2mm, 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.

[0165] In some embodiments, the condition 0.2mm≤L1+L2≤3mm is satisfied. When L1+L2 satisfies the condition 0.2mm≤L1+L2≤3mm, on the one hand, it helps to reduce the stress on the weak area of ​​the first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11. On the other hand, it prevents the portion of the first electrode 11 reserved for the electrode assembly 10 to be stretched during expansion from being too long, which helps to reduce the space occupied by the first stacked portion 113 and also facilitates the processing and forming of the first stacked portion 113.

[0166] Referring to Figures 5 and 8, in some embodiments, along the winding direction X of the electrode assembly 10, the electrode assembly 10 further includes a seventh segment 115 and an eighth segment 117. The seventh segment 115 is connected to the first segment 1131, and the eighth segment 117 is connected to the sixth segment 1143. 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.

[0167] The first adhesive 50 is bonded to the seventh segment 115, the eighth segment 117, and the first stacked portion 113, which helps maintain the shape of the first stacked portion 113. When manufacturing the secondary battery 001, the first electrode 11 can be folded first to form the first stacked portion 113, 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, which helps reduce the risk of the first stacked portion 113 spreading out or partially spreading out during the winding process. In addition, in the event of an accident such as an impact to the electrode assembly 10, the first stacked portion 113 may be squeezed or impacted. The first adhesive 50 helps maintain the shape of the first stacked portion 113, which helps reduce the risk of the first stacked portion 113 spreading out or partially spreading out before the electrode assembly 10 expands.

[0168] Referring to Figures 5 and 8, in some embodiments, the secondary battery 001 further includes a second adhesive member 60. Along the first direction, the first adhesive member 50 is adhered to one side of the first electrode 11, and the second adhesive member 60 is adhered to a portion of the first active material layer 112 on the second surface 1112. 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. The second adhesive helps maintain the morphology of the first stacked portion 113, reduces the risk of the first stacked portion 113 unraveling or partially unraveling during winding, and also reduces the risk of the first stacked portion 113 unraveling or partially unraveling before the electrode assembly 10 expands.

[0169] Referring to Figures 5 and 8, 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 and the first stacked portion 113 helps to save on adhesive processes.

[0170] Referring to Figures 5 and 8, 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 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. Furthermore, bonding the first adhesive 50 together with the first tab 20 and the first stacked portion 113 saves on adhesive application processes.

[0171] Referring to Figures 5 and 9, in some embodiments, the first adhesive 50 is bonded to the seventh segment 115 and to the second segment 1132 of the first stacked portion 113, but not to the first tab 20. The second adhesive 60 is bonded to the seventh segment 115, the eighth segment 117, and the first active material layer 112 on the back side of the first empty foil area 1114.

[0172] Referring to Figures 5 and 10, in some embodiments, the first adhesive member 50 is bonded to the seventh segment 115, the eighth segment 117, and the first tab 20, and is also bonded to the second segment 1132 of the first stacked portion 113. The second adhesive member 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117.

[0173] Referring to Figures 5 and 11, in some embodiments, the first adhesive 50 is bonded to the seventh segment 115 and to the second segment 1132 of the first stacked portion 113, but not to the first tab 20. The second adhesive 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117.

[0174] Referring to Figures 5 and 12, in some embodiments, the first adhesive member 50 is bonded to the seventh segment 115, the eighth segment 117, and the first tab 20, and is also bonded to the second segment 1132 of the first stacked portion 113 and the fifth segment 1142 of the second stacked portion 114. The second adhesive member 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117.

[0175] Referring to Figures 5 and 13, in some embodiments, the first adhesive 50 is bonded to the seventh segment 115 and to the second segment 1132 of the first stack 113 and the fifth segment 1142 of the second stack 114. The second adhesive 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117.

[0176] Referring to Figures 5 and 14, in some embodiments, the first adhesive member 50 is bonded to the seventh segment 115, the eighth segment 117, and the first tab 20, and is also bonded to the second segment 1132 of the first stacked portion 113 and the fifth segment 1142 of the second stacked portion 114, wherein the first tab 20 is located between the first stacked portion 113 and the second stacked portion 114. The second adhesive member 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117.

[0177] Referring to Figures 5 and 15, in some embodiments, the first adhesive member 50 is divided into two independent segments. One segment is bonded to the seventh segment 115 and to the second segment 1132 of the first stacked portion 113, while the other segment is bonded to the eighth segment 117 and to the fifth segment 1142 of the second stacked portion 114. The second adhesive member 60 is bonded to the seventh segment 115 and the eighth segment 117, but not to the second empty foil area 1117. Referring to Figure 16, in some embodiments, along the width direction Z of the first electrode 11, the first tab 20 is connected to 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.

[0178] In extreme cases, the first stacked portion 113 may crack 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 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 helps improve the safety of the secondary battery 001.

[0179] 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.

[0180] Please refer to Figure 17. 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 being punctured and short-circuited, and helps to improve the safety of the secondary battery 001.

[0181] Referring to Figure 18, 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 being punctured and short-circuited, thus improving the safety of the secondary battery 001.

[0182] 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.

[0183] Please refer to Figure 19. 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 being punctured and short-circuited, and helps to improve the safety of the secondary battery 001.

[0184] 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.

[0185] F1 is the peel strength between the first adhesive 50 and the seventh segment 115 after being soaked in the electrolyte.

[0186] When F1 = 0, the peel strength between the first adhesive 50 and the seventh segment 115 before being soaked in the electrolyte is greater than 0, which helps to reduce the risk of the first stacked portion 113 unraveling or partially unraveling during the winding process.

[0187] 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 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 will fall apart or partially fall apart when the electrode assembly 10 is subjected to impact, which is conducive to improving the reliability of the first stacked portion 113.

[0188] 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.

[0189] 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 / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". The test procedure is as follows:

[0190] The secondary battery was discharged to 3.0V, and then disassembled. The first electrode 11 and the first adhesive component 50 bonded to it were removed as a whole, and the electrolyte on the surface was wiped off with lint-free paper. Then, the first adhesive component 50 and the seventh segment 115 were cut into strip-shaped samples. Along the length of the sample, the side of the sample with the first electrode 11 was adhered to the steel plate with double-sided adhesive (Nitto 5000NS), with an adhesion length of not less than 10mm. The steel plate was fixed in the corresponding position of the high-speed rail tensile testing machine, and one end of the seventh segment 115 on the other side of the sample was pulled up. The sample was placed in the clamp and clamped, with the angle between the pulled sample and the steel plate in space being 180°. The clamp pulled the sample at a speed of 5±0.2mm / s. The average tensile force in the stable area was finally measured and recorded as the peel strength between the first adhesive component 50 and the seventh segment 115, denoted as F1, in N / m.

[0191] In some embodiments, the housing 40 is further provided with an electrolyte. The peel strength between the first adhesive 50 and the first overlapping portion 113 is F2, which satisfies 0 N / mm ≤ F2 ≤ 0.08 N / mm.

[0192] F2 is the peel strength between the second adhesive 60 and the first stacked portion 113 after being soaked in electrolyte.

[0193] When F2 = 0, the peel strength between the second adhesive 60 and the first stacked portion 113 before being soaked in the electrolyte is greater than 0, which helps to reduce the risk of the first stacked portion 113 unraveling or partially unraveling during the winding process.

[0194] 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 is not too large, which helps the second adhesive 60 to peel smoothly from the first stacked portion 113 when the electrode assembly 10 expands, reducing the risk that the second adhesive 60 will affect the effect of the first stacked portion 113 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 is not too small, which helps reduce the risk that the first stacked portion 113 will fall apart or partially fall apart when the electrode assembly 10 is subjected to impact, which helps improve the reliability of the first stacked portion 113.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] F3 is the peel strength between the second adhesive 60 and the eighth segment 117 after being soaked in electrolyte.

[0199] 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 unraveling or partially unraveling during the winding process.

[0200] 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 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 will fall apart or partially fall apart when the electrode assembly 10 is subjected to impact, etc., which is conducive to improving the reliability of the first stacked portion 113.

[0201] 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.

[0202] 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.

[0203] Please refer to Figure 20. 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.

[0204] When the length S1 of the first adhesive 50 satisfies the condition 2mm≤S1≤20mm, on the one hand, the area of ​​the first adhesive 50 is not too small, which helps to improve the peel strength between the first adhesive 50 and the seventh segment 115, the first stacked portion 113 and the eighth segment 117, and reduces the risk of the first stacked portion 113 falling apart during the winding process or when it is impacted, which helps to improve the reliability of the first stacked portion 113; on the other hand, the area of ​​the first adhesive 50 is not too large, which helps to allow the first adhesive 50 to peel smoothly from the seventh segment 115, the first stacked portion 113 and the eighth segment 117 when the electrode assembly 10 expands, reducing the risk that the first adhesive 50 will affect the effect of the first stacked portion 113 when the electrode assembly 10 expands.

[0205] 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.

[0206] Referring to Figure 21, 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 peel strength between the second adhesive 60 and the seventh segment 115, the eighth segment 117 and the first stacked portion 113, reducing the risk of the first stacked portion 113 scattering during the winding process or when subjected to impact, thus improving the reliability of the first stacked portion 113. 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 and the first stacked portion 113 when the electrode assembly 10 expands, reducing the risk that the second adhesive 60 will affect the effect of the first stacked portion 113 when the electrode assembly 10 expands.

[0207] 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.

[0208] In some embodiments, satisfying 6mm≤S1≤13mm serves two purposes: firstly, it prevents the area of ​​the first adhesive 50 from being too small, which helps to improve the peel strength between the first adhesive 50 and the seventh segment 115, the first stacked portion 113, and the eighth segment 117, further reducing the risk of the first stacked portion 113 scattering during the winding process or when subjected to impact, and improving the reliability of the first stacked portion 113; secondly, it prevents the area of ​​the first adhesive 50 from being too large, which helps to facilitate the smooth peeling of the first adhesive 50 from the seventh segment 115, the first stacked portion 113, and the eighth segment 117 when the electrode assembly 10 expands, further reducing the risk that the first adhesive 50 will affect the effect of the first stacked portion 113 when the electrode assembly 10 expands.

[0209] In some embodiments, satisfying 6mm≤S2≤13mm serves two purposes: firstly, it prevents the area of ​​the second adhesive 60 from being too small, which helps to improve the peel strength between the second adhesive 60 and the seventh segment 115, the eighth segment 117, and the first stacked portion 113, further reducing the risk of the first stacked portion 113 scattering during the winding process or when subjected to impact, and improving the reliability of the first stacked portion 113; secondly, 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, and the first stacked portion 113 when the electrode assembly 10 expands, further reducing the risk that the second adhesive 60 may affect the effect of the first stacked portion 113 when the electrode assembly 10 expands.

[0210] In some embodiments, the first adhesive 50 includes a substrate layer (not shown) and an adhesive (not shown) disposed on the substrate layer. The substrate layer may be selected from polyethylene terephthalate, co-extruded polypropylene, oriented polystyrene, thermoplastic polyurethane, polylactic acid, and polyolefin. The adhesive is selected from one or a combination of acrylic resin, polypropylene, or rubber. By selecting different material types and / or qualities to adjust the adhesive strength, the peel strength between the first adhesive 50 and the fourth segment 114, as well as the peel strength between the first adhesive 50 and the third segment 1133, can be adjusted.

[0211] It should be noted that the peel strength between the first adhesive component 50 and the fourth segment 114 before immersion in the electrolyte affects the peel strength F1 between the first adhesive component 50 and the fourth segment 114 after immersion in the electrolyte. Therefore, by selecting different types and / or qualities of materials to adjust the adhesive strength, F1 can be adjusted. The principle and method for adjusting F2 can refer to the adjustment of F1, and will not be repeated here.

[0212] To verify the effect of the first stacked portion 113 and the first adhesive 50 on whether the first electrode 11 is damaged, the following test was conducted:

[0213] A battery cycle test was conducted on the secondary battery 001: The secondary battery 001 was placed in a 55°C environment and left to stand for 30 minutes, then 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, and left to stand for 5 minutes. This constitutes one cycle. The above cycle steps were repeated 300 times. The secondary battery 001 was then disassembled, and the edges of the first empty foil area 1114 and / or the connection between the first empty foil area 1114 and the first electrode 11 were observed to be undamaged.

[0214] 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.

[0215] In the two tests described above, 100 secondary batteries 001 were tested for each embodiment or comparative example. Each secondary battery 001 was 35mm long, 33mm wide, and 6.0mm thick. If the connection between the first electrode 11 and the first tab 20 was damaged, the test failed; if the connection between the first electrode 11 and the first tab 20 was undamaged, the test passed. Pass rate = (Number of passes / 100) × 100%.

[0216] The specific implementation of the secondary battery 001 in the embodiments and comparative examples will be described below.

[0217] Example 1:

[0218] The assembly process of a secondary battery 001 is as follows:

[0219] (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. An empty foil area was reserved in the middle section of the copper foil to form the first empty foil area 1114. Along the length of the copper foil, the two ends of the first empty foil area 1114 were the first coating area 1113 and the second coating area 1115, respectively. The electrode was dried at 110°C to obtain an anode electrode with a coating thickness of 150 μm, partially coated on one side with an anode active material layer. Repeat the above steps on another surface of the anode sheet to form a second empty foil area 1117. Along the length of the copper foil, the two ends of the second empty foil area 1117 are the third coating area 1116 and the fourth coating area 1118, respectively. The projections of the second empty foil area 1117 and the first empty foil area 1114 at least partially overlap, resulting in an anode sheet with coating areas and empty foil areas. Anode tabs are welded to the empty foil area at one end of the anode sheet.

[0220] (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. An empty foil area was reserved in the middle section of the aluminum foil to form a third empty foil area (not shown in the figure). Along the length of the aluminum foil, the two ends of the third empty foil area were the fifth coating area and the sixth coating area, respectively. The mixture was then dried at 90 °C to obtain a cathode electrode with a cathode active material layer thickness of 100 μm. Repeat the above coating steps on another surface of the aluminum foil to form a fourth empty foil area (not shown). Along the length of the aluminum foil, the two ends of the fourth empty foil area are the seventh coating area and the eighth coating area, respectively. The projections of the fourth empty foil area and the third empty foil area at least partially overlap to obtain a cathode electrode. Cathode tabs are welded to the empty foil area of ​​the cathode electrode.

[0221] (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.

[0222] (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.

[0223] (5) Manufacturing the first stacked portion 113: The anode electrode sheet in the unfolded state is stamped with a round bar 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 electrode tab near the winding center. The arc-shaped protrusion on the anode electrode sheet is flattened to form the first stacked portion 113. The first adhesive 50 and the second adhesive 60 are respectively bonded to both sides of the first stacked portion 113 along the thickness direction of the first electrode sheet 11. The substrate layer of the first adhesive and the second adhesive is polyethylene terephthalate with a thickness of 12 μm, and the adhesive is acrylic resin with a thickness of 4 μm.

[0224] (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, and the anode tab is connected to the first empty foil area 1114 of the anode electrode.

[0225] (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.

[0226] (8) Electrolyte injection and encapsulation: Electrolyte is injected into the assembled electrode assembly 10, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, the secondary battery 001 is obtained.

[0227] 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.

[0228] Comparative Example 2: The difference from Example 1 is that, in Comparative Example 2, along the winding direction X of the electrode assembly 10, the first stacked portion 113 is 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 Example 5.

[0229] In Example 19, the first overlapping portion 113 and the second overlapping portion 114 are not attached with the first adhesive 50 and the second adhesive 60.

[0230] The main parameter controls and test results for each embodiment and comparative example are shown in Table 1:

[0231] Table 1

[0232] As can be seen from Table 1 above, compared with Comparative Examples 1-2, Embodiments 1-18 are provided with a first stacking portion 113, and along the winding direction X of the electrode assembly 10, the first stacking portion 113 is located on the side of the first tab 20 close to the winding center of the electrode assembly 10, which helps to reduce the force at the connection between the first electrode 11 and the first tab 20, thereby providing a margin for the expansion of the electrode assembly 10 and helping to reduce the risk of damage to the first electrode 11.

[0233] As shown in Table 1 above, compared with Examples 1 and 9, Examples 2-8 satisfy 0.2mm≤L1+L2≤3mm, which is beneficial to reduce the force on the connection position of the first electrode 11 when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11. In Example 9, L1+L2>3mm, although the battery cycle test pass rate and drop test pass rate of the secondary battery 001 are both better, the stacked part is too long, resulting in a loss of energy density.

[0234] As shown in Table 1 above, compared to Example 18, the peel strength between the first adhesive 50 and the seventh segment 115 after being soaked in the electrolyte in Examples 10-17 satisfies 0 N / mm ≤ F1 ≤ 0.08 N / mm, and the peel strength between the second adhesive 60 and the eighth segment 117 after being soaked in the electrolyte satisfies 0 N / mm ≤ F2 ≤ 0.08 N / mm. This facilitates the smooth peeling of the first adhesive 50 and the second adhesive 60 when the electrode assembly 10 expands, reducing the risk that the first adhesive 50 and the second adhesive 60 will affect the effect of the folded portion when the electrode assembly 10 expands, thereby reducing the risk of damage to the first electrode 11. On the other hand, it helps to reduce the risk of the folded portion spreading out or partially spreading out when the electrode assembly 10 is subjected to impacts, which improves the reliability of the folded portion and thus helps to reduce the risk of damage to the first electrode 11.

[0235] As shown in Table 1 above, compared to Embodiment 7, in Embodiment 19, the first stacked portion 113 and the second stacked portion 114 are not bonded with the first adhesive 50 and the second adhesive 60. Therefore, the battery cycle test pass rate and drop test pass rate of the secondary battery 001 are both lower than those of Embodiment 7. 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, which helps reduce the risk of the first stacked portion 113 unraveling or partially unraveling before the electrode assembly 10 expands.

[0236] This application also provides a method for manufacturing the electrode assembly 10 in any of the above embodiments, comprising the following steps:

[0237] The first pole piece 11 in its unfolded state is stamped with a round bar to form an arc-shaped protrusion;

[0238] The arc-shaped protrusion on the first electrode 11 is flattened to form the first stacked portion 113;

[0239] The first stacked part 113 is fixed in place by adhesive;

[0240] 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.

[0241] The secondary battery 001 obtained by the above manufacturing method has an electrode assembly 10 that heats up and expands during repeated charging and discharging. 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 the electrode assembly 10 with room for expansion and improving the problem of electrode breakage in weak areas.

[0242] Please refer to Figure 22. An embodiment of this application also provides an electronic device 002, which includes the secondary battery 001 from any of the above embodiments. Since this electronic device 002 adopts the technical solution of the secondary battery 001 from any of the above embodiments, it at least possesses the beneficial effects brought about by the technical solution of the secondary battery 001 from any of the above embodiments, which will not be elaborated further here.

[0243] Referring to Figure 22, in some embodiments, the electronic device 002 further includes a device body 020, and a secondary battery 001 is mounted on the device body 020.

[0244] 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.

[0245] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the substantive scope of this application fall within the scope 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, wherein the diaphragm is disposed between the first electrode and the second electrode, and the first electrode, the second electrode, and the diaphragm are stacked and wound to form a wound structure. The first electrode includes a first current collector and a first active material layer, wherein the first active material layer is disposed on at least one surface of the first current collector; The first current collector includes a first surface and a second surface disposed opposite to each other along the thickness direction of the first current collector. Along the winding direction of the electrode assembly, the first current collector includes a first empty foil area on the first surface where the first active material layer is not disposed, a first coated area on the first surface where the first active material layer is disposed, and a second coated area where the first active material layer is disposed. The first empty foil area is located between the first coated area and the second coated area. The first electrode is partially folded along a first direction at the position of the first empty foil area 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.

2. The secondary battery as described in claim 1, characterized in that, The first active material layer is provided on the second surface of the first coating area and the second coating area, while the first active material layer is not provided on the second surface of the first empty foil area.

3. The secondary battery as described in claim 1 or 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, Along the winding direction of the electrode assembly, the first coating area is located on the side of the first empty foil area away from the second coating area, 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.

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

6. The secondary battery as described in claim 3, characterized in that, The secondary battery further includes a first tab, which is disposed in the first empty foil area along the winding direction of the electrode assembly, and the first stacked portion is located on the side of the first tab near the winding center of the electrode assembly.

7. The secondary battery as described in claim 6, characterized in that, Along the winding direction of the electrode assembly, the minimum distance between the bend of the second segment relative to the first segment and the first tab is L, satisfying 1mm≤L≤10mm.

8. The secondary battery as described in claim 3, characterized in that, The first electrode sheet at the position of the first empty foil area also includes a partially folded second stacked portion, and along the first direction, the projected portions of the first electrode sheet of the second stacked portion overlap; Along the winding direction of the electrode assembly, the second stacked portion is located on the side of the first stacked portion away from the winding center of the electrode assembly.

9. The secondary battery as described in claim 8, characterized in that, 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 fourth segment overlaps with the sixth segment. The fourth segment, the fifth segment, and the sixth segment are stacked along the first direction, and the projections of the fourth segment, the fifth segment, and the sixth segment overlap along the first direction.

10. The secondary battery as described in claim 9, characterized in that, The minimum 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 minimum 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.

11. The secondary battery as described in claim 8, characterized in that, The condition L1+L2≤3mm must be met.

12. The secondary battery as described in claim 9, characterized in that, The condition L1 ≥ 0.1 mm and / or L2 ≥ 0.1 mm must be satisfied.

13. The secondary battery as described in claim 9, 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.

14. The secondary battery as described in claim 13, characterized in that, The first electrode sheet is further provided with a second stacked portion at the position of the first empty foil area, the first empty foil area is provided with a first electrode tab, and the first adhesive is also adhered to the first electrode tab and the second stacked portion.

15. The secondary battery as described in claim 14, characterized in that, Along the width direction of the first electrode, the first electrode tab is connected to the first electrode and extends out of the first electrode; Along the direction in which the first electrode tab extends, the first adhesive member extends beyond the first electrode sheet.

16. The secondary battery as described in claim 14, 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... A peel strength of F3 is achieved if at least one of the following conditions is met: (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.

17. The secondary battery according to any one of claims 13 to 16, characterized in that, Along the winding direction of the electrode assembly, the length of the first adhesive is S1, which satisfies 2mm≤S1≤20mm.

18. The secondary battery as described in claim 17, characterized in that, The requirement is 6mm≤S1≤13mm.

19. The secondary battery according to any one of claims 13 to 18, characterized in that, The material of the first adhesive includes at least one of acrylic resin, polypropylene, or rubber.

20. The secondary battery according to any one of claims 1 to 18, characterized in that, The first empty foil area is provided with a first electrode tab, which is welded to the first electrode sheet.

21. The secondary battery according to any one of claims 1 to 20, characterized in that, The electrode assembly has a cylindrical structure, and the secondary battery also includes a housing. The electrode assembly is disposed inside the housing, and the housing is a metal housing.

22. 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 21, characterized in that, Includes the following steps: The first electrode sheet in its unfolded state is stamped with a round bar to form an arc-shaped protrusion; The arc-shaped protrusion on the first electrode is flattened to form the first stacked 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.

23. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 21.

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